University of Groningen

Structure - property relationships in early transition metal based olefin polumerisationcatalystsBeetstra, Dirk Johannes

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4 Synthesis and Reactivity of Cyclopentadienyl-

Amine Transition Metal 2,3-Dimethyl-1,3-

Butadiene Complexes‡ In chapter 3, a series of M(III) dichloride compounds were described that are

supported by the 2-dimethylaminoethyl cyclopentadienyl ligand [η5,η1-C5H4(CH2)2NMe2]

–. As a cyclopentadienyl-amine Ti(III) dichloride complex could not be isolated without PMe3 as an additional Lewis base ligand, a full comparison of the catalytic properties of isostructural Cp-amine dichloride complexes with d0 – d3 configuration was not possible.

In the same chapter, the 1,3-butadiene complex [η5,η1-C5H4(CH2)2NMe2]V(C6H10) (3) was introduced, where it was used as a precursor for a phosphine-free Cp-amine vanadium dichloride complex. Early transition-metal 1,3-butadiene complexes are known to react with activators, e.g. the Lewis acid B(C6F5)3, via electrophilic attack on one of the diene methylene groups to give zwitterionic metal allyl species that act as single-site ethene polymerisation catalysts (scheme 4.1).1,2 Provided that the corresponding butadiene complexes of the other trivalent metal centres in the series are accessible as well, this should enable a fair comparison of base-free Cp-amine olefin polymerization catalysts.

Unfortunately, earlier attempts by Döhring et al. to prepare Cp-amine chromium butadiene complexes had been unsuccessful, apparently due to decomposition of the initial product.3 Only use of additional PMe3 was found to lead to a stable complex, with a bound phosphine and an uncoordinating amine group.4 This preference for the soft Lewis base is likely to be the result of the soft Lewis acidic nature of the Cr(I) centre.5 Nevertheless, as 1,3-butadiene complexes of Sc and of paramagnetic Ti ions were still unknown, it was deemed sufficiently challenging to try to prepare these. If successful, at least a comparison of isostructural base-free d0–d2 metal complexes

‡ Part of this chapter has been published: Beetstra, D.J.; Meetsma, A.; Hessen, B.; Teuben, J.H. Organometallics, 2003, 22, 4372-4374.

LnMLnM

B(C6F5)3

B(C6F5)3

Scheme 4.1.

4

88

would be possible. In addition, the chemistry of novel Sc and Ti diene complexes could provide interesting new possibilities in terms of physical behaviour and reactivity of such organometallic species.

In this chapter, the syntheses and structures of the 2,3-dimethyl-1,3-butadiene compounds [η5,η1-C5H4(CH2)2NMe2]M(C6H10) (M = Sc, Ti and V) are described in section 4.1. Their conversion to zwitterionic allyl compounds by reaction with B(C6F5)3 is described in section 4.2, and the polymerisation activity of these zwitterionic compounds in section 4.3. The sections 4.4 and 4.5 respectively describe the thermolysis and the reactive properties of the novel scandium 1,3-diene species.

4.1 Synthesis and structure of cyclopentadienyl-amine M(III) 2,3-dimethyl-1,3-diene complexes

1,3-Diene compounds of early transition metals can be synthesised by means of several routes. For the synthesis of the target compounds the routes depicted in scheme 4.2 were been used. In the first route, the metal dichloride precursor is reduced, typically by magnesium6 or an alkali metal,7 in the presence of a 1,3-diene. In the second route the metal dichloride precursor is reacted with the appropriate (1,3-diene)magnesium compound.8 In this reagent, the 1,3-diene fragment is doubly reduced and reacts as a but-2-ene-1,3-diyl dianion.9,10

LnMCl2 (1)LnMMg, butadiene

- MgCl2

LnMCl2 (2)LnMMg(butadiene)

- MgCl2

Scheme 4.2.

Scandium

Reaction of {[η5,η1-C5H4(CH2)2NMe2]ScCl2}n with an excess of Mg(C6H10)(THF)211

in diethyl ether at 0°C resulted in a deep red solution. Evaporation of the solvents and extraction of the residue with pentane, followed by crystallisation from this solvent,

1/n ScN

1

Mg(C6H10)(THF)2

- MgCl2, THF

ScN

ClCln

Scheme 4.3.

Chapter 4

89

yielded [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) as deep red crystals in 48% yield.

Titanium

Reaction of a suspension of [η5,η1-C5H4(CH2)2NMe2]TiCl2(PMe3) in diethyl ether with Mg(C6H10)(THF)2 resulted in the formation of a deep purple solution. Removal of the solvents and extraction of the residue with pentane yielded [η5,η1-C5H4(CH2)2NMe2]Ti(C6H10) (2) as deep purple crystals in 75% yield.

TiN

2

Mg(C6H10)(THF)2

- MgCl2, THF- PMe3

TiN

ClCl

PMe3

Scheme 4.4.

Vanadium

The synthesis of the vanadium butadiene compound [η5,η1-C5H4(CH2)2NMe2]V(C6H10) (3) was described in chapter 3. This compound was prepared by reduction of [η5,η1-C5H4(CH2)2NMe2]VCl2(PMe3) by magnesium in the presence of 2,3-dimethyl-1,3-butadiene.

Chromium

As mentioned earlier, the chromium butadiene [η5,η1-C5H4(CH2)2NMe2]Cr(C6H10) appears to be inaccessible as, due to the soft character of the Cr(I) centre, the (hard) amine donor is not coordinated to the metal centre, resulting in decomposition of the compound.12

Structural comparison

The butadiene compounds are highly soluble in THF, diethyl ether, toluene and benzene. Their solubility in pentane and hexane is somewhat lower, which makes these the preferred solvents for crystallisation. The butadiene compounds 1 – 3 are isostructural (which is also reflected in the nearly identical IR spectra of these compounds). In the complexes the butadiene is coordinated in a prone orientation,13 as observed earlier for Cp(PMe3)M(III)(butadiene) (M = V, Cr) compounds.14 The effect of the metal on the bond lengths is summarised in table 4.1. As can be seen from this table, distances to the metal centre increase in the order V < Ti < Sc. This is in accordance with the order of the ionic radii of these 3d metals.15 Accordingly, the angles Cg-M-N (Cg is defined as the centroid of the C(1)-C(5) ring) increase upon going from Sc to V (table 4.2).

90

The crystal structure determination of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) showed that the butadiene fragment has considerable 2-ene-1,4-diyl character, as indicated by the relative short central C-C bond of 1.386(3) Å and relatively long C-CH2 bonds of 1.455(3) and 1.464(3) Å (a difference of 0.073 Å).16,17 In the titanium

Figure 4.1. Molecular structures of [η5,η1-C5H4(CH2)2NMe2]M(C6H10) (M = Sc, 1; M = Ti, 2; M = V, 3), showing 50% probability ellipsoids.

Table 4.1. Selected bond lengths (Å) of [η5,η1-C5H4(CH2)2NMe2]M(C6H10) (M = Sc, 1; M = Ti, 2 and M = V, 3).

1 2 3M – Cga 2.1596(11) 2.0444(9) 1.9567(8)M – N 2.3576(17) 2.3151(6) 2.3075(16)M – C(10) 2.249(3) 2.1993(18) 2.1880(17)M – C(11) 2.401(2) 2.2713(17) 2.2316(16)M – C(12 ) 2.400(2) 2.2995(18) 2.2305(16)M – C(13) 2.251(2) 2.209(2) 2.2185(18)C(10) – C(11) 1.455(3) 1.450(3) 1.430(2)C(11) – C(12) 1.386(3) 1.405(2) 1.412(2)C(12) – C(13) 1.464(3) 1.442(3) 1.435(2)a Cg is the centroid of the C(1) – C(5) ring.

Chapter 4

91

analogue 2 the 2-ene-1,4-diyl character is less pronounced; the central bond is 0.041 Å shorter than the two outer C-C bonds. For the vanadium analogue 318 the central C-C-bond is only 0.021 Å shorter than the outer bond.19 This expresses the reducing power of the metal centre; Sc(I) and Ti(I) are very rare oxidation states, and these are expected to strongly reduce the 1,3-diene fragment.

In the 1H and 13C NMR spectra of diamagnetic 1, the resonances for the diene methylene groups are observed at δ 1.76 and 2.58 ppm (d, 2JHH = 6.6 Hz) and δ 59.0 ppm (∆ν1/2 = 183 Hz, broadened by the quadrupolar 45Sc nucleus, I = 7/2), respectively. The 1H NMR spectrum of the titanium analogue 2 is less informative due to its d1 electronic configuration. The spectroscopic properties of the paramagnetic (d2) vanadium compound 3 were described in section 3.1.

4.2 Formation of zwitterionic/betaine compounds.

Reaction of early transition-metal diene compounds with strongly Lewis acidic boranes (scheme 4.1) proceeds via electrophilic attack of these acids on one of the diene methylene carbon atoms. This results in the formation of zwitterionic compounds,20 in which one of the diene methylene carbons is attached to the B/Al atom, the other three diene carbon atoms remain bonded to the metal centre in an η3-allylic fashion (scheme 4.1, reaction 1).21–23 This method has resulted in single component olefin polymerisation catalysts. For some of these zwitterionic compounds stoichiometric primary insertions have been observed.24,25

Table 4.2. Selected (torsion) angles (°) of [η5,η1-C5H4(CH2)2NMe2]M(C6H10) (M = Sc, 1, M = Ti, 2 and M = V, 3).

Angle (°) 1 2 3Cga – M – N 102.77(5) 104.38(5) 106.11(5)N – M – C(10) 96.39(8) 89.55(7) 89.43(6)N – M – C(11) 131.11(7) 126.74(6) 125.14(5)N – M – C(12) 138.02(6) 136.27(6) 129.36(6)N – M – C(13) 107.13(7) 105.81(7) 95.93(6)Cg – M – C(10) 134.21(7) 143.43(7) 137.88(5)Cg – M – C(11) 119.37(6) 122.95(5) 122.84(5)Cg – M – C(12) 117.41(6) 116.74(5) 121.50(5)Cg – M – C(13) 130.00(7) 125.69(5) 134.93(5)Torsion angle (°) C(10) – C(11) – C(12) – C(13) 1.3(3) -3.2(3) 0.3(2)a Cg is the centroid of the C(1) – C(5) ring.

92

For the zwitterionic compounds, obtained from reaction of a butadiene compound with tris(pentafluorophenyl)borane (B(C6F5)3), two main bonding modes for the anionic borate moiety are observed. Coordination of one of the fluorines of the perfluorinated phenyls to the metal centre is observed in sterically not too demanding environments, whereas agostic coordination of (one of) the BCH2 protons is observed for sterically more congested environments.22b,26

Titanium

Reaction of the titanium diene complex [η5,η1-C5H4(CH2)2NMe2]Ti(C6H10) (2) with B(C6F5)3 in toluene or benzene yielded a deep purple solution of the paramagnetic compound [η5,η1-C5H4(CH2)2NMe2]Ti[C6H10B(C6F5)3] (4, scheme 4.5). Due to the asymmetry of the compound in combination with its paramagnetic nature (d1 metal centre), no informative 1H NMR spectrum of 4 could be obtained; only overlapping broad signals were observed.

In the 19F NMR spectrum, three resonances for the aromatic fluorides are observed. The resonance of the ortho-fluorines is strongly broadened due to the paramagnetism of the compound (δ ≈ –122 ppm, ∆ν½ ≈ 2400 Hz). This broadening is less pronounced for the resonances of the (more remote) meta- and para-fluorines (resp. δ –160.5; ∆ν½ = 195 Hz and δ –164.1; ∆ν½ = 65 Hz). The proposed composition was confirmed by elemental analysis.27 The IR spectrum is very similar to that of metallocene-butadiene/B(C6F5)3 betaine systems reported in the literature.28 Typical absorptions for the perfluorophenylborate are observed at 1640, 1460 and 950 cm–1.29

On a preparative scale 4 was synthesised by mixing solutions of B(C6F5)3 and [η5,η1-C5H4(CH2)2NMe2]Ti(C6H10) (2) in toluene. Deep purple crystals of 4 were obtained in 62% yield by concentrating the solution until solid precipitates, redissolving the solid in the remaining toluene by warming, followed by slow cooling to –80°C. The crystallised compound is poorly soluble in cold toluene and other apolar solvents, but can be recrystallised from boiling toluene. The molecular structure of 4 is shown in figure 4.2, selected bond lengths and angles are presented in table 4.3 and table 4.4.

In 4 the distances between the titanium and the Cp-ligand are all slightly shorter than in 2, what can be attributed to the more electrophilic metal centre in 4. The structure is related to that of the (diamagnetic) Cp-amide complex

+ B(C6F5)3Ti

N

B(C6F5)3

TiN

42

Scheme 4.5.

Chapter 4

93

[C5Me4(SiMe2)NtBu]Ti[(CH{Me}CHCHCH2)B(C6F5)3] (5), reported by Cowley et al.30

The bond lengths C(10)-C(11) and C(11)-C(12), as well as the angle C(10)-C(11)-C(12) are very similar to those reported for 530 and those reported for zirconocene based zwitterionic compounds.31 The observed bond lengths and angles indicate that the C(10)-C(11)-C(12)-fragment is bound as an η3-allyl moiety. The interatomic distances between the titanium and the carbons in the allyl moiety in 4 are shorter than in 5, which may be attributed to the higher steric demand of the [C5Me4(SiMe2)N

tBu] ligand in 5. The short Ti-H(131) and Ti-H(132) distances in 4 strongly suggest agostic

interactions of the CH2 hydrogens of C(13). The interatomic distances Ti-H(131),

Figure 4.2. Molecular structure of [η5,η1-C5H4(CH2)2NMe2]Ti[C6H10B(C6F5)3] (4), showing 50% probability ellipsoids. Hydrogen atoms (except those

connected to C13) are omitted for clarity.

Table 4.3. Selected bond lengths in [η5,η1-C5H4(CH2)2NMe2]Ti[C6H10B(C6F5)3] (4).

Bond lengths (Å) Ti – Cga 1.997(2) C(10) – C(11) 1.427(6) Ti – N 2.305(3) C(11) – C(12) 1.404(5) Ti – C(10) 2.205(4) C(12) – C(13) 1.512(5) Ti – C(11) 2.290(4) C(13) – H(131) 0.99(4) Ti – C(12) 2.256(4) C(13) – H(132) 0.89(4) Ti – C(13) 2.350(4) B – C(16) 1.652(6) Ti – H(131) 2.36(3) B – C(22) 1.658(6) Ti – H(132) 2.23(4) B – C(28) 1.660(6) C(13) – B 1.697(5) Ti – nearest F (F15) 4.030(2) a Cg is the centroid of the C(1) – C(5) ring.

94

Ti-H(132), Ti-C(13) and C(13)-B are very similar to those in 5. Due to the paramagnetic nature of 4, it cannot be confirmed whether the solid state structure persists in solution.

Scandium

Upon reaction of the scandium diene complex [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) with B(C6F5)3 in benzene or toluene, a clear orange solution was obtained. NMR spectroscopy (1H, 13C and 19F) showed the quantitative formation of the zwitterionic compound [η5,η1-C5H4(CH2)2NMe2]Sc[C6H10B(C6F5)3] (6). In the 13C NMR spectrum the signal for the CH2-B is observed at δ 35.0 (br.q, 1JCB = 35 Hz), the corresponding 1H resonances are found at δ 2.33 and 1.55 ppm. In the 19F NMR spectrum three (broadened) resonances are observed at δ –132.4, –161.0 and –165.6 ppm (toluene-d8 solvent, RT). The broadening is indicative of dynamical behaviour in solution. Indeed, cooling of the toluene-d8 solution to –60°C results in the resolution of 6 resonances for the ortho-fluorines at δ –124.0, –125.4, –128.3, –129.1, –129.5 and –131.3 and 9 resonances for the meta- and para-F at δ –155.4, –156.1, –156.8, –158.5, –160.5, –160.6, –161.1, –161.3 and –162.3.32 Warming the toluene-d8 solution above ambient temperature leads to a broadening of the 1H NMR spectrum and a sharpening of the 19F spectrum. At 100°C the para and meta-F resonances appear as triplets at δ –156.8 and –161.2 ppm (1JCF = 19.8 Hz), respectively, the ortho-F resonance (δ –127.1 ppm) is still slightly broadened (∆ν½ = 50.5 Hz). The broadening of the signals in the 1H NMR spectrum at 100°C indicates fluxional behaviour at this temperature. Upon cooling the original 19F NMR spectrum is regained, but the 1H NMR spectrum is still broadened.

Table 4.4. Selected angles in [η5,η1-C5H4(CH2)2NMe2]Ti[C6H10B(C6F5)3] (4).

Angles (°) Cg – Ti – N 105.66(11) B – C(13) – C(12) 119.0(3) N – Ti – C(10) 89.53(14) H(131) – Ti – H(132) 38.1(15) N – Ti – C(11) 125.68(14) Ti – C(13) – B 173.4(3) N – Ti – C(12) 137.57(14) C(13) – B – C(16) 109.6(3) N – Ti – C(13) 105.74(13) C(13) – B – C(28) 115.8(3) N – Ti – H(131) 84.2(7) C(10) – C(11) – C(12) 121.7(4) N – Ti – H(132) 102.0(10) C(11) – C(12) – C(13) 121.3(4) Ti – H(131) – C(13) 77(2) C(13) – B – C(22) 101.2(3) Ti – H(132) – C(13) 87(2) Torsion angle (°) C(10) – C(11) – C(12) – C(13) 11.8(6) a Cg is the centroid of the C(1) – C(5) ring.

Chapter 4

95

On a preparative scale, 6 is conveniently obtained by mixing solutions of B(C6F5)3 and [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in hexane. The zwitterionic compound separates out as an orange microcrystalline solid and was obtained in 51% isolated yield. The IR-spectrum of the compound closely resembles that of 4, and elemental analysis confirms the proposed composition.27 The resulting solid is virtually insoluble in apolar solvents at room temperature, but can be recrystallised from hot toluene. Upon slow cooling of a concentrated solution, crystals of 6 suitable for X-ray diffraction were obtained.

Compound 6 crystallises in the monoclinic spacegroup C2 with two independent molecules per unit cell. The two molecules show substantial disorder, but were identified as the prone and supine isomers of 6. The packing of the crystals appears to be dominated by the butadiene-borane fragment, with disorder in the cyclopentadienyl-amine ligand fragments (probably by partial cocrystallisation of the opposite orientation). The disorder could not be satisfactory modelled, resulting in unrealistic atom displacement parameters. Nevertheless the connectivity of the non-H atoms could be established unequivocally. In both isomers the short Sc(1)-C(113)/Sc(2)-C(213) distance suggests agostic interaction with the hydrogens connected to this carbon. There

+ B(C6F5)3

prone-6

+

supine-61

ScN

B(C6F5)3

ScN

ScN B(C6F5)3

Scheme 4.6.

Figure 4.3. Molecular structures of prone (left) and supine (right) [η5,η1-C5H4(CH2)2NMe2]Sc[C6H10B(C6F5)3] (6) showing 30% probability ellipsoids. Hydrogen atoms (except those connected to C(113)/C(213)) are omitted for clarity.

96

is no interaction between the Sc-atoms and nearby fluorines (distance Sc – nearest F is approximately 4 Å in both the prone and supine isomers) in the solid state.

Vanadium

In the reaction of the vanadium diene complex [η5,η1-C5H4(CH2)2NMe2]V(C6H10) (3) with B(C6F5)3 in benzene or toluene a wine red microcrystalline material precipitates rapidly. This probably corresponds to “[η5,η1-C5H4(CH2)2NMe2]V[C6H10B(C6F5)3]” (7), and was isolated in 81% yield when calculated for this composition. The solid is virtually insoluble in common solvents (pentane, toluene, diethyl ether, THF). The insolubility of (asymmetric) 7 in combination with its paramagnetic nature (d2, S = 1 configuration) thwarts NMR spectroscopic analysis. Nevertheless, the strong similarity of the IR spectrum of compound 7 with that of 4 and 6 suggests that also for vanadium a related zwitterionic complex is formed. Elemental analysis also confirms the proposed formula.27

4.3 Olefin polymerisation experiments

The zwitterionic Cp-amine species 4, 6, and 7 are trivalent metal analogues of structurally related zwitterionic Cp-amide derivatives of tetravalent Ti that are active in olefin polymerisation.2 In ethene polymerisation, these zwitterionic species generally display activities comparable to those of the ionic [L2MR][R’B(C6F5)3] systems.

Given the low solubility of the isolated zwitterionic complexes 4, 6, and 7, the olefin polymerisation behaviour of these compounds was tested on in situ prepared zwitterionic species (by reaction of the butadiene precursors 1 – 3 with an excess of B(C6F5)3 in the reactor). The results of the ethene polymerisation experiments are presented in table 4.5.

In these experiments, catalytic activity could only be observed for the Sc system. There is considerable variance in the polymer yield due to the absence of impurity scavengers, and the overall activity is only modest. Nevertheless, polyethene is obtained with a reproducible Mw of around 160 × 103 and a polydispersity consistent with single-site catalyst behaviour.

The low activity of these zwitterionic species is in sharp contrast to the behaviour described for Ti(IV) and Zr(IV) zwitterionic species, which in general show activities comparable to their ionic analogues (e.g. comparing Cp2Zr[CH2C(Me)C(Me)CH2-B(C6F5)3] with [Cp2ZrMe][B(C6F5)4)]). To exclude the possibility of problems in the activation step, the pre-formed zwitterionic species 4, 6 and 7 were also injected into the autoclave under the conditions described in table 4.5, but in this case all species were inactive in polymerisation.

The apparent intrinsic low activity of the zwitterionic species might be attributed to the low valence electron count of the complexes, combined with a sterically not very

Chapter 4

97

demanding ancillary ligand system. This may lead to a prohibitively strong interaction of the metal centre with the borate moiety. To the best of our knowledge, the only reported first row transition metal zwitterionic species that is active in olefin polymerisation is the [C5Me4(SiMe2)N

tBu]Ti[(CH(Me)CHCHCH2B(C6F5)3] system (5) described by Cowley et al.33 Not only is the ancillary ligand system much more sterically demanding, but the experiments were also conducted in the presence of dihydrogen. It can not be excluded that in this case the dihydrogen initially activates the complex by hydrogenolysis of the anionic moiety. Comparable experiments in the presence of H2 have not been performed with the catalysts presented here.

4.4 Thermal decomposition of the scandium butadiene complex.

As compound 1 is the first example of a group 3 metal 1,3-butadiene complex, a closer look was taken at its properties. Although the compound can readily be isolated, it is thermally unstable at room temperature. In C6D6 solution, the compound decomposes over a period of 3 – 4 days. The 1H NMR spectrum after 3 days suggests the formation of a 1 : 2 mixture of a symmetric (8) and an asymmetric (9) compound (figure 4.4, upper spectrum). Both are converted into a third species (10). This process takes about 3 months at ambient temperature to go to completion (figure 4.4, lower spectrum). The colour of the solution changes from red to brown in the first few days and then finally to purple. The ratio of the two transient decomposition products does not notably change.

In the 1H NMR spectrum of the symmetric compound 8 two Cp signals are observed at 6.21 and 5.99 ppm, whereas the asymmetric compound 9 is characterised by 4 Cp signals (at 6.32, 5.89, 5.73, and 5.58 ppm). Besides the signals for several methyl groups, triplets (for the CH2-groups of the bridge of the symmetric compound) and

Table 4.5. Ethene polymerisation activity of 1, 2 and 3 with B(C6F5)3

(in situ generation of 4, 6, and 7).a

Entry catalyst Yield Activityb Mw

(× 10–3)Mn

(× 10–3)Mw/Mn

1 1 1.23 47 151 83 1.822 1 0.78 30 161 80 2.023 1 0.71 26 166 91 1.844 2 – – – – –5 3 – – – – –a Toluene solvent (250 mL), T = 50°C, [M] = 1.25 × 10–4 M, 1.5 eq. B(C6F5)3, 2 bar ethene, 30 min. runtime; b kg (PE) × mol cat–1 × bar–1 × h–1.

98

multiplets for the CH2-groups of the bridge of the asymmetric compound, two downfield singlets appear at 5.98 and 5.04 ppm, and two broadened doublets are observed at 1.59 and 0.49 ppm (2JHH ~ 3.5 Hz). In a 13C-1H HSQC NMR spectrum the upfield doublets in 1H NMR spectrum show a weak cross peak with the broad signal in the 13C NMR spectrum at δ 58.3 ppm (∆ν½ = 25.5 Hz). The broadness of the 13C NMR signal is indicative for a scandium bound carbon, in this case probably of a diastereotopic Sc-CH2 group or of an allylic moiety. The two downfield singlets in the 1H NMR spectrum give no observable cross-peak in 13C-1H gHSQC NMR spectra, suggesting that these are either bound to carbons that are directly bonded to scandium (these Sc-CH-groups give very weak cross-peaks) or bound to a non-carbon atom. At present, there is insufficient evidence for a precise structure assignment for the two products 8 and 9, but they are likely to result from intramolecular H-transfer processes.

The final product, compound 10, is apparently a species with at least Cs symmetry, characterised by 2 Cp signals (δ 6.27 and 6.13 ppm, 2 protons each), 3 different Me-signals in a 2:2:1 ratio (1H NMR signals at δ 2.27 (NMe2), 1.60 and 1.06 ppm.; 13C NMR signals at resp. δ 45.7, 25.3 and 20.4 ppm.), 2 triplets for the (CH2)2-bridge of the ligand (2.97 and 2.70 ppm, 2 protons each), and a singlet in the 1H NMR spectrum at δ 4.68 ppm (1 proton). For the latter the corresponding carbon is found at 145.4 ppm (∆ν½ ~ 75 Hz). From the assignment it is clear that the Cp-amine ligand system is intact at the end of the reaction. One possibility is that in this product the 2,3-dimethyl-1,3-butadiene fragment has rearranged into a =CH-C(Me)=C(Me2) fragment (assuming no C–C bonds have been broken). This could then lead to the formation of a scandium

ppm1234567

Figure 4.4. 1H NMR spectra in C6D6 after 3 days (upper spectrum, mixture of 8 and 9, some residual starting material (1) left), and after approximately

3 months (10, lower spectrum, some residual peaks of 8 and 9 left).

Chapter 4

99

µ-vinylalkylidene complex. The NMR spectral data are in reasonable agreement with this proposal (provided that the Cp-amine ligands adopt a cis configuration around the central Sc2C2 ring), with the exception that this would require the =CMe2 methyl resonances to be accidentally degenerate both in the 1H and in the 13C NMR spectra. Although scandium alkylidene species are as yet unknown, our findings on the thermolysis of Cp-amine scandium dialkyl complexes (reported in section 5.3) suggest that formation of scandium µ-alkylidene species is indeed feasible.

4.5 Reactivity of the scandium 1,3-butadiene complex

Conjugated dienes form a group of molecules that can be bound to and activated by transition metals in various ways.34 When all four olefinic carbons are involved in bonding to a single metal centre, a 1,3-butadiene ligand can adopt a structure in which either the η4-diene (s-cis- and s-trans-A)35 or the σ2,π-metallacyclopentene (B) resonance structure is prevalent (figure 4.5).36 These two structures are related by an oxidative addition operation in which the diene in structure B is effectively doubly reduced, and behaves as a but-2-ene-1,4-diyl dianion.

The relative importance of diene or metallacyclopentene character in s-cis 1,3-diene complexes depends on several factors, in particular the reducing power of the low-valent metal fragment.37 Reactivity corresponding to the η4-diene character (A) includes the ready displacement of the neutral diene ligand by a variety of reagents, which may then perform oxidative addition or oxidative coupling reactions on the resultant low-valent transition-metal species.21,38 Reactivity corresponding to the σ2,π-metallacyclopentene character (B) is expressed in the nucleophilic character of the

10

ScSc

N N

+8 9ScN

1

Scheme 4.7.

cis-A cis-B

M(n+2)+Mn+ Mn+

trans-A

Figure 4.5. η4-s-cis-1,3-diene (cis-A), (σ2,π-bonded)-η4-metallacyclo-3-pentene (cis-B), and 1,2-η2-s-trans-1,3-diene (trans-A).

100

diene methylene groups, that are readily attacked by electrophiles. This includes the insertion of various unsaturated substrates into the metal-methylene bond,39 and attack of Lewis acids on the diene methylene carbons.40 Many transition-metal diene complexes exhibit structures that are intermediate between these two extremes, and may show both insertion and 1,3-diene displacement chemistry, depending on the type of reagent used.

The scandium-1,3-diene complex 1 is the first scandium complex with a butadiene ligand. Scandium has a strong preference for the trivalent oxidation state, and a Cp-amine-Sc(I) fragment would be expected to be strongly reducing. Accordingly, in its structural features (figure 4.1, table 4.2) 1 shows pronounced σ2,π-metallacyclopentene character. Nevertheless, as many 1,3-diene compounds of transition metals show reactivity related to σ2,π-metallacyclopentene character (insertion into the M-C bond) as well as η4-diene character (elimination of the diene), we explored whether reactivity associated with the Sc(I)-η4-diene resonance structure could be observed.

Some inorganic compounds with scandium in the monovalent oxidation state are known, e.g. solid ScCl.41 Recently Roesky et al. reported the compound {[Et2N(CH2)2NC(Me)CHC(Me)N(CH2)2NEt2]MgBr}2ScBr,42 containing a Sc(I)Br-unit sandwiched between two (β-diketiminato)MgBr-fragments. A triple-decker structure [{η5-P3C2

tBu2)Sc}2(µ-η6:η6-P3C3tBu3)],

43 which formally contains two Sc(I) atoms, has been reported by Arnold et al.6

In line with its structural features, 1 reacts readily with polar unsaturated substrates to give products that derive from insertion into the Sc-methylene bonds. In an

Figure 4.6. Molecular structure of {[η5,η1-C5H4(CH2)2NMe2]Sc[µ-NC(Ph)C6H10]}2

(11) showing 50% probability ellipsoids. Hydrogen atoms are omitted for clarity

Chapter 4

101

NMR-tube experiment with 1 equivalent of benzonitrile, 1 reacts quantitatively to give the colourless µ-imido complex {[η5,η1-C5H4(CH2)2NMe2]Sc[µ-NC(Ph)C6H10]}2 (11). The dimer was isolated on preparative scale in 60% yield and was characterised by single-crystal X-ray diffraction (figure 4.6, selected bond lengths in table 4.6, angles in table 4.7) on crystals of its benzene solvate.The Cp-amine ligands adopt a trans geometry around the central Sc2N2 core, which is practically equilateral. Although common for many transition metals, M2(η2-NR)2 species of group 3 metals to our knowledge have not yet been reported and have only very recently been observed for lanthanide metals.44

Formation of this product can be explained by the sequence depicted in scheme 4.8, in which the nitrile initially inserts into one of the Sc-CH2 bonds, followed by an intramolecular nucleophilic attack of the other diene methylene group on the carbon atom of the imide intermediate. This yields an electronically unsaturated metal imido

Table 4.6. Selected bond lengths (Å) for 11.

Sc(1) – Cg(1)a 2.2233(15) C(10) – C(11) 1.551(4) Sc(1) – N(1) 2.375(3) C(10) – C(14) 1.565(4) Sc(1) – N(2) 2.017(2) C(11) – C(12) 1.510(3) Sc(1) – N(2a) 2.056(2) C(12) – C(13) 1.332(4) N(2) – C(10) 1.465(3) C(13) – C(14) 1.501(4) C(10) – C(17) 1.541(4) a Cg is the centroid of the C(1) – C(5) ring.

PhCN Sc

N N

Ph

Sc

N

Sc

N

N Ph N

Sc

NPh

Sc

NN

Ph

1

11

Scheme 4.8.

102

species that will dimerise.45 A similar reaction sequence was observed earlier in the reaction of Cp*Hf(2,3-dimethyl-1,3-butadiene)Cl with acetylene, in which case a µ-alkylidene complex was formed.46 Double insertion of nitriles has also been observed in lanthanide hydride clusters.47

Reaction of 1 with diphenylacetylene in C6D6 results in a mixture of compounds (as seen by 1H NMR spectroscopy, see figure 4.7). The 1H NMR spectrum shows the liberation of 2,3-dimethyl-1,3-butadiene (singlets at 5.03, 4.92 and 1.82 ppm) and the formation of a mixture of an asymmetric (12) and a symmetric compound (13) in approximately a 1:1 ratio.48

The asymmetric compound is likely to derive from insertion of the alkyne into one of the Sc-CH2 bonds to yield a 2,3-diphenyl-5,6-dimethyl-metallacyclohepta-2,5-diene (12, scheme 4.9). In the 1H NMR spectrum (figure 4.7) four resonances for the Cp-protons (6.55, 5.94, 5.87, and 5.77 ppm) of asymmetric 12 are found, and the two CH2-groups in the seven-membered ring, with diastereotopic protons, are observed at 3.77 + 3.14 ppm (2JHH = 17.7 Hz; C(Ph)-CH2), and 2.42 + 1.92 ppm (2JHH = 1.3 Hz, C(Me)CH2; the latter signal was located using a 1H-1H gCOSY experiment). The small

Table 4.7. Selected (torsion) angles for 11.

Angles (°) Cg – Sc(1) – N(1) 99.87(7) Sc(1) – N(2) – Sc(1a) 92.86(9) Cg – Sc(1) – N(2) 122.40(7) N(2) – Sc(1) – N(2a) 87.14(9) Cg – Sc(1) – N(2a) 133.22(7) Torsion angles (°) C(11) – C(12) – C(13) – C(14) 0.3(3) N(2) – Sc(1) – N(2a) – Sc(1a) 0.03(15) C(15) – C(12) – C(13) – C(16) -0.7(6) a Cg is the centroid of the C(1) – C(5) ring.

ppm1234567

+

* * **+ # #

* * *

#

Figure 4.7. 1H NMR spectrum of the reaction mixture of 1 with 2 equivalents of diphenylacetylene. * denotes 12, + denotes 13, # denotes 2,3-dimethyl-1,3-butadiene.

Chapter 4

103

2JHH coupling constant for the second methylene group indicates an η3 allylic bonding mode for that part of the ligand.

Integration of the 1H NMR spectrum reveals that the amount of 2,3-dimethyl-1,3-butadiene released is the same as the amount of the symmetric product in the reaction mixture, suggesting that this symmetrical compound is formed from 1 via elimination of the 2,3-dimethylbutadiene. When only 1 equivalent of diphenylacetylene per Sc is used in the reaction, some Sc diene complex remains unreacted. This suggests that more than one equivalent of diphenylacetylene is required to displace the 2,3-dimethyl-1,3-butadiene. It is then likely that this results in the formation of a scandacyclopenta-2,4-diene 13 through oxidative coupling of two alkyne molecules. Such reactivity has been observed with other 1,3-diene compounds,49 and other low valent metal centres.50 Although metallacyclopentadiene species in some cases are able to catalyse the cyclotrimerisation of alkynes, reaction of 1 with an excess (~ 25 eq.) of PhCCPh does not lead to an observable formation of 1,2,3,4,5,6-hexaphenylbenzene51 after 5 days at 50°C. Further heating to 80°C leads to decomposition into unidentified species.

Although the reaction with diphenylacetylene results in the formation of a mixture of compounds, the elimination of 2,3-dimethylbutadiene indicates that reactivity corresponding to Sc(I)-η4-diene character of 1 is possible. Therefore other substrates were sought that could displace the butadiene fragment, but are less prone to insertion.

Reaction of 1 with 2 equiv of 4,4’-dimethyl-2,2’-bipyridine (scheme 4.10) leads to liberation of free 2,3-dimethyl-1,3-butadiene (as seen by 1H NMR spectroscopy) and the formation of a paramagnetic compound. From a reaction in toluene, the resulting bis(4,4’-dimethyl-2,2’-bipyridine) adduct [η5,η1-C5H4(CH2)2NMe2]Sc(η2-N2C12H12)2

+ +2

1 12 13

Sc

N

Sc

N

Ph

Ph

ScN Ph

Ph

Ph

Ph2 PhCCPh

Scheme 4.9.

NN

2

1 14

Sc

N

ScN

NN

N

N

Scheme 4.10.

104

(14) was isolated as a black crystalline material, that nevertheless was persistently contaminated with free bipyridine (as e.g. seen by NMR spectroscopy and elemental analysis).

A crystal structure determination of the compound revealed that the metal centre is pseudo 6-coordinate, with one η5-cyclopentadienyl group, two η2-bipyridine ligands and the coordinated pendant amine (figure 4.8). The Sc-N(amine) distance of 2.564(4) Å is 0.2 Å longer than that in 1 or 11 in response to the high coordination number of the metal centre in 14. This bond length is anomalously long compared to calculated values based on covalent radii (2.205 Å).52

Figure 4.8. Molecular structure of [η5,η1-C5H4(CH2)2NMe2]Sc(η2-N2C12H12)2 (14) showing 50% probability ellipsoids. Hydrogen atoms are omitted for clarity.

Table 4.8. Selected bond lengths (Å) for [η5,η1-C5H4(CH2)2NMe2]Sc(η2-N2C12H12)2 (14).

Sc – Cga 2.248(2) N(4) – C(22) 1.349(6) C(17) – C(16) 1.405(6) Sc – N(1) 2.564(4) N(5) – C(28) 1.368(5) C(22) – C(23) 1.346(7) Sc – N(2) 2.272(3) N(5) – C(30) 1.360(6) C(23) – C(24) 1.388(6) Sc – N(3) 2.252(3) C(10) – C(11) 1.357(7) C(24) – C(25) 1.353(6) Sc – N(4) 2.219(3) C(11) – C(12) 1.411(6) C(25) – C(26) 1.399(6) Sc – N(5) 2.228(3) C(12) – C(13) 1.349(6) C(26) – C(28) 1.422(5) N(2) – C(10) 1.348(5) C(14) – C(16) 1.410(5) C(32) – C(31) 1.344(7) N(2) – C(14) 1.385(5) C(20) – C(19) 1.343(7) C(31) – C(30) 1.389(6) N(3) – C(20) 1.349(5) C(19) – C(18) 1.395(6) C(30) – C(29) 1.364(6) N(3) – C(16) 1.374(5) C(18) – C(17) 1.344(6) C(29) – C(28) 1.404(5) N(4) – C(26) 1.364(5) a Cg is the centroid of the C(1) – C(5) ring.

Chapter 4

105

Inspection of C-C and C-N distances within the 4,4’-dimethyl-2,2’-bipyridine ligands reveals that both appear to be reduced to their radical monoanions (e.g. as seen from the central bipyridine C-C bonds in 14 of 1.41 – 1.42 Å as compared to 1.48 Å in neutral bipyridine).53,54 This indicates that the effective oxidation state of the Sc metal centre in 14 is trivalent, a tribute to the reducing power of Sc(I), which here has performed two separate one-electron reductions.

1H NMR spectra of solutions of 14 in C6D6 only show resonances of some free 4,4’-dimethyl-2,2’-bipyridine (which always seems to be present in samples of 14), suggesting that the compound is paramagnetic. An Evans method determination55 of the magnetic moment of 14 on a benzene solution of 14 generated in situ from 1 and 2 equivalents of 4,4’-dimethyl-2,2’-bipyridine yielded µeff = 1.54 (expected spin-only for an S = 1 system: µeff = 2.83). This indicates either a degree of magnetic coupling between the bipyridyl radical anion ligands in 14, or partial decomposition of 14 (e.g. by partial loss of free ligand, a possible source of the persistent presence of 4,4’-dimethyl-2,2’-bipyridine in solid samples). Attempts to drive such a reaction by removal of 4,4’-dimethyl-2,2’-bipyridine from 14 by e.g. vacuum sublimation did not yield well-defined organometallic products.

Reagents that are known to give facile oxidative addition to low-valent metals are I2 and PhSSPh.56 NMR tube reactions in C6D6 monitored by 1H NMR spectroscopy showed that upon reaction of 1 with these substrates the diene ligand is readily eliminated. With diiodine, a white solid (15) precipitates from C6D6. After removal of the solvent, and the formed 2,3-dimethyl-1,3-butadiene, in vacuo the solid was

Table 4.9. Selected (torsion) angles in [η5,η1-C5H4(CH2)2NMe2]Sc(η2-N2C12H12)2 (14) .

Angles (°) Cga – Sc – N(1) 94.95(10) N(1) – Sc – N(5) 92.53(11) Cg – Sc – N(2) 105.29(10) N(2) – Sc – N(3) 71.49(11) Cg – Sc – N(3) 171.69(10) N(4) – Sc – N(5) 71.71(11) Cg – Sc – N(4) 108.29(10) N(2) – Sc – N(4) 85.58(12) Cg – Sc – N(5) 103.85(10) N(2) – Sc – N(5) 147.45(12) N(1) – Sc – N(2) 99.06(11) N(3) – Sc – N(4) 79.35(11) N(1) – Sc – N(3) 78.25(11) N(3) – Sc – N(5) 81.41(12) N(1) – Sc – N(4) 154.29(11) Torsion Angles (°) N(2) – C(14) – C(16) – N(3) 6.9(5) C(14) – C(16) – C(26) – C(28) 127.7(3) N(4) – C(26) – C(28) – N(5) 1.9(5) a Cg is the centroid of the C(1) – C(5) ring.

106

dissolved in THF-d8. The 1H NMR spectrum shows resonances corresponding to a Cs symmetric compound, suggesting that the monomeric THF adduct [η5,η1-C5H4(CH2)2NMe2]ScI2(THF)n is formed.

From the reaction of 1 with diphenyldisulphide (scheme 4.11) in C6D6 a colourless solution is obtained. 1H NMR spectrum shows resonances corresponding to a Cs symmetric compound, presumably [η5,η1-C5H4(CH2)2NMe2]Sc(SPh)2. On preparative scale 16 was isolated in 48% yield as colourless crystals by slow condensation of pentane onto the benzene solution. In the solid state 16 is a dimer with Ci symmetry, as revealed by X-ray crystallographic analysis. The molecular structure is depicted in figure 4.9, selected bond lengths and angles are presented in table 4.10. Formation of a dimeric structure is analogous to the behaviour of Ln(EPh)nLm (Ln = Y, lanthanides, E = S, Se, Te; n = 2,3; L = a Lewis base), which readily form dimeric to polymeric structures with bridging and terminal chalcogenide atoms.57

In its structural features, the Sc-S core is comparable to yttrium and lanthanide chalcogenolates.57 The rhomboid central Sc2S2 core shows unequal interatomic

Figure 4.9. Molecular structure of {[η5,η1-C5H4(CH2)2NMe2]Sc(SPh)(µ-SPh)}2 (16) showing 50% probability ellipsoids. Hydrogen atoms are omitted for clarity.

PhSSPh(x 2)

ScN

II

I2

n

1615

ScN S S

S

Ph

NScS

Ph

Ph

Ph

Sc

N

1

Scheme 4.11.

Chapter 4

107

distances Sc-S(2) and Sc-S(2a) (2.6519(5) and 2.5988(5) Å, respectively). The unequal interatomic distances suggest a small trans-like-influence (the longer Sc-S bond is trans to the dimethylamino group).58 Both bonds are significantly longer than the bond between the Sc and the terminal S (2.4980(6) Å).

Once obtained in crystalline form, 16 is difficult to (re)dissolve in benzene, but addition of a few drops of THF causes the material to dissolve gradually. The 1H NMR spectrum of this solution is indicative of a Cs symmetric species, suggesting that under these conditions 16 dissolves as the monomeric THF adduct [η5,η1-C5H4(CH2)2NMe2]Sc(SPh)2(THF)n.

4.6 Conclusions

A series of cyclopentadienyl-amine 2,3-dimethyl-1,3-butadiene complexes [η5,η1-C5H4(CH2)NMe2]M(C6H10) (M = Sc, Ti, V) was successfully synthesised and structurally characterised. The degree of σ2,π-metallacyclopentene character of the diene ligand in these complexes decreases upon going from Sc to Ti to V, in line with the expected reducing power of the transition metal in its low (univalent) valence state. By reaction with B(C6F5)3, these diene complexes were transformed into the corresponding zwitterionic species [η5,η1-C5H4(CH2)2NMe2]M[C6H10B(C6F5)3], which were structurally characterised for Sc and Ti. Nevertheless, only for the M = Sc system was ethene polymerisation activity observed, precluding a comparison of active d0–d2

Table 4.10. Selected bond lengths and angles in {[η5,η1-C5H4(CH2)2NMe2]Sc(SPh)(µ-SPh)}2 (16).

Bond Lengths (Å) Sc – Cga 2.1509(9) Sc – S(2) 2.6519(5) Sc – N 2.4143(14) Sc – S(2a) 2.5988(5) Sc – S(1) 2.4980(6) S(2) – C(16) 1.7804(16) Angles (°) Cg – Sc – N 100.73(4) N – Sc – S(1) 91.52(3) Cg – Sc – S(1) 109.53(3) N – Sc – S(2) 146.04(4) Cg – Sc – S(2) 111.32(3) N – Sc – S(2a) 88.33(4) Sc – S(2) – C(16) 116.15(5) S(2) – Sc – S(2a) 66.91(1) Sc(a) – S(2) – C(16) 127.13(5) Sc – S(2) – Sc(a) 113.09(2) Sc – S(1) – C(10) 110.52(6) Torsion angles (°) Sc – S(2) – Sc(a) – S(2a) -0.02(8) a Cg is the centroid of the C(1) – C(5) ring.

108

metal catalysts. Probably, the borate-metal interaction in these species is too strong to give facile initiation of ethene polymerisation.

The scandium compound [η5,η1-C5H4(CH2)NMe2]Sc(C6H10), the first scandium

1,3-diene complex to be reported, shows reactivity that reflects either (σ2,π-metallacyclopentene)Sc(III) or (η4-diene)Sc(I) character, depending on the type of reagent used. This complex can thus be used as a synthetic precursor of the rare Sc(I) oxidation state, that was found to be able to undergo 2 electron oxidative addition reactions, or to perform two separate one-electron reductions of suitable substrates.

4.7 Experimental section

For general considerations see chapter 2 (page 54) and chapter 3 (page 80). 4,4’-Dimethyl-2,2’-bipyridine and PhSSPh were used as purchased. PhCN was distilled and I2 was sublimed before use. Mg(C6H10)(THF)2 was synthesised according to literature procedures.59

Synthesis of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1). Solid Mg(C6H10)(THF)2 (295 mg, 1.17 mmol) was added to a cooled (0°C) suspension of 220 mg (0.87 mmol) of {[η5,η1-C5H4(CH2)2NMe2]ScCl2}n in 30 mL diethyl ether. The solution turned orange-red within seconds. The solution was stirred

for 1.5 h at 0ºC. The solvents were removed in vacuo and the red residue was freed of residual THF by stirring with 2 portions of 15 mL cold (0°C) pentane, which were subsequently pumped off. Extraction of the solid residue with 3 portions of 20 mL cold (0°C) pentane, followed by concentration of the resulting solution to 20 mL and cooling to –80°C yielded 1 as a red crystalline material (110 mg, 0.42 mmol, 48%). 1H NMR (C6D6, 300 MHz, 25°C) δ 6.20 (ps. t, J = 2.8 Hz, 2H, Cp), 6.01 (ps. t, J = 2.8 Hz, 2H, Cp), 2.58 (d, 2JHH = 6.6 Hz, 2H, syn Sc–CH2), 2.11 (t, 3JHH = 6.2, 2H, CH2N), 1.87 (t, 3JHH = 6.2, 2H, CH2Cp), 1.82 (s, 6H, NMe2), 1.76 (d, 2JHH = 7.0, 2H, anti Sc–CH2), 1.71 (s, 6H, CMe). 13C{1H} NMR (C6D6, 75 MHz, 25°C) δ 125.7 and 123.9 (Cp ipso-C and diene CMe), 111.6 (Cp CH), 110.5 (Cp CH), 64.4 (CH2N), 59.0 (Sc–CH2; broad, ∆ν½ = 183 Hz), 44.5 (NMe2), 25.9 (CH2Cp), 23.6 (CMe). IR (Nujol mull) 1461 (vs), 1376 (s), 1302 (mw), 1288 (w), 1181 (w), 1156 (w), 1096 (m, b), 1064 (mw, b), 1027 (m, b), 921 (w), 775 (ms), 745 (mw), 722 (mw), 603 (w), 539 (w), 468 (w) cm–1. Anal. calcd. for C15H24NSc: C, 68.66; H, 9.22; N, 5.34; Sc, 16.79. Found: C, 68.00; H, 9.27; N, 5.23; Sc, 16.68.

Sc

N

Chapter 4

109

Crystal structure analysis of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) Suitable red block-shaped crystals were obtained by cooling a saturated solution of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in pentane to –30°C. Bruker SMART APEX CCD diffractometer, Mo-Kα radiation (λ = 0.71073 Å), T = 125(1) K, unit formula: C15H24NSc, monoclinic, C2/c, a = 17.707(1) Å, b = 8.4651(6) Å, c = 19.903(1) Å, β = 105.984(1)°, V = 2868.0(3) Å3, Z = 8, Dx = 1.220 g × cm–3, F(000) = 1136, µ = 4.93 cm–1, 13775 reflections measured, GooF = 0.995, wR(F2) = 0.0975 for 3544 reflections and 250 parameters and R(F) = 0.0445 for 2418 reflections obeying Fo ≥ 4.0 σ(Fo) criterion of observability.

Synthesis of [η5,η1-C5H4(CH2)2NMe2]Ti(C6H10) (2). Solid Mg(C6H10)(THF)2 (390 mg, 1.56 mmol) was added to a suspension of 429 mg (1.30 mmol) of [η5,η1-C5H4(CH2)2NMe2]TiCl2(PMe3) in 20 mL of diethyl ether, resulting in a purple solution. After stirring for two hours the solvents

were removed in vacuo and the remaining solid freed of residual solvent by stirring with two portions of 5 mL pentane, which were subsequently pumped off. The residue was extracted with 40 mL of pentane. Upon cooling to –80°C, 203 mg (0.76 mmol, 60%) of black, crystalline 2 was obtained. Upon concentration of the mother liquor, another portion of 49 mg (0.18 mmol, 15%; total yield 75%) of 2 was isolated. 1H NMR (C6D6, RT, 300 MHz) δ 20.0 (∆ν½ = 5800 Hz, 10H), 16.5 (∆ν½ = 1360 Hz, 6H), –1.3 (∆ν½ = 250 Hz, 4H) ppm. IR (Nujol mull) 1401 (m), 1326 (m), 1301 (m), 1266 (mw), 1237 (mw), 1213 (ms), 1179 (mw), 1168 (mw), 1116 (mw), 1095 9 (mw), 1044 (m), 1025 (s), 1000 (ms), 957 (mw), 924 (ms), 878 (w), 853 (w), 840 (mw), 778 (vs, b), 717 (w), 681 (w), 637 (mw), 540 (m), 473 (w), 452 (w) cm–1. Anal. calcd. For C15H24NTi: C, 67.66; H, 9.08; N, 5.26; Ti, 17.99. Found: C, 67.34; H, 9.00; N, 5.32; Ti, 17.86.

Crystal structure analysis of [η5,η1-C5H4(CH2)2NMe2]Ti(C6H10) (2) Bruker SMART APEX CCD diffractometer, Mo-Kα radiation (λ = 0.71073 Å), unit formula: C15H24NTi, monoclinic, C2/c, a = 17.131(1) Å, b = 8.5677(7) Å, c = 19.550(2) Å, β = 104.018(2)°, V = 2784.0(4) Å3, Z = 8, Dx = 1.270 g × cm–3, F(000) = 1144, µ = 3960 cm–1, T = 110(1) K, 13347 reflections measured, GooF = 1.030, wR(F2) = 0.0953 for 3452 reflections and 250 parameters and R(F) = 0.0399 for 2775 reflections obeying Fo ≥ 4.0 σ(Fo) criterion of observability.

TiN

110

Crystal structure analysis of [η5,η1-C5H4(CH2)2NMe2]V(C6H10) (3) Crystals suitable for X-ray were obtained by slowly (1°C/min) cooling a solution of 375 mg of [η5,η1-C5H4(CH2)2NMe2]V(C6H10) (3) in 5 mL pentane to –40°C. Enraf-Nonius CAD-4F diffractometer, MoKα -radiation (λ = 0.71073 Å), T = 180 K, unit formula: C15H24NV, monoclinic, C2/c, a = 17.171(2) Å, b = 8.2450(10) Å, c = 20.383(3) Å, β = 105.150(10)°, V = 2785.4(6) Å3, Z = 8, Dx = 1.284 g × cm–3, µ = 6.9 cm–1, F(000) = 1152, GooF = 1.062, wR(F2) = 0.1242 for 3348 reflections and 251 parameters and R(F) = 0.0431 for 3078 reflections obeying Fo ≥ 4.0 σ(Fo) criterion of observability.

Synthesis of [η5,η1-C5H4(CH2)2NMe2]Ti[C6H10B(C6F5)3] (4) A solution of 125 mg (340 µmol) of B(C6F5)3 in 10 mL toluene was added to a solution of 65 mg (240 µmol) of [η5,η1-C5H4(CH2)2NMe2]Ti(C6H10) (2). The colour of the solution turned from purple to wine red. The volume of the solution was reduced to 0.5 mL (upon which solid precipitated). The mixture was

heated to reflux until the solid dissolved. Upon slow cooling to –80°C small crystals of 4 precipitate. The solvent was decanted off and the crystalline material washed with two portions of 2 mL pentane and dried in vacuo. Yield 117 mg (150 µmol, 62 %) of 4. 19F NMR (toluene-d8, RT, 188 MHz) δ ~ –122 ppm (∆ν½ ~ 2400 Hz, 2F, o-F), –160.5 (b, ∆ν½ = 65 Hz, 1F, p-F), –164.1 (b, ∆ν½ = 195 Hz, 2F, m-F). IR (Nujol mull) 1642 (ms), 1604 (w), 1513 (s), 1330 (w), 1276 (m), 1169 (mw), 1089 (s), 1041 (mw), 1029 (mw), 1017 (mw), 975 (s), 921 (mw), 882 (w), 818 (ms), 799 (ms), 774 (m) 763 (mw), 752 (mw), 737 (mw), 679 (mw), 485 (w), 467 (w), 450 (w) cm–1. Anal. calcd. for C33H24BF15NTi: C 50.93, H 3.11, N 1.80, Ti 6.15. Found: C 47.55; H 3.12; N 1.76; Ti 5.88.27

Crystal structure analysis of [η5,η1-C5H4(CH2)2NMe2]Ti[C6H10B(C6F5)3] (4) Bruker SMART APEX CCD diffractometer, Mo-Kα radiation (λ = 0.71073 Å), unit formula: C33H24BF15NTi , monoclinic, C2/c, a = 25.934(2) Å, b = 12.9022(8) Å, c = 20.517(1) Å, β = 115.958(1)°, V = 6172.5(7) Å3, Z = 8, Dx = 1.675 g × cm–3, F(000) = 3128, µ = 3960 cm–1, T = 100(1) K, 12668 reflections measured, GooF = 0.976, wR(F2) = 0.1431 for 6007 reflections and 526 parameters and R(F) = 0.0555 for 3703 reflections obeying Fo ≥ 4.0 σ(Fo) criterion of observability. The positional and anisotropic displacement parameters for the non-hydrogen atoms were refined. A subsequent difference Fourier synthesis resulted in the location of all the hydrogen atoms, which coordinates and isotropic displacement parameters were refined, except those belonging to C7, C8 and C9 which did not behave well, so they

TiN

B(C6F5)3

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were included in the final refinement riding on their carrier atoms with their positions calculated by sp3 hybridization at the C-atom as appropriate with Uiso = c × Uequiv of their parent atom, where c = 1.2 for the non-methyl hydrogen atoms and c = 1.5 for the methyl hydrogen atoms and where values Uequiv are related to the atoms to which the H atoms are bonded. The methyl-groups were refined as rigid groups, which were allowed to rotate free.

Synthesis of [η5,η1-C5H4(CH2)2NMe2]Sc[C6H10B(C6F5)3] (6) A solution of 128.4 mg (251 µmol) of B(C6F5)3 in 10 mL hexane was added to a solution of 68.8 mg (261 µmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in 10 mL hexane, resulting in an orange

suspension. The solid was isolated by filtration and washed with portions of 20 mL of hexane. Yield: 100 mg (129 µmol, 51%) of orange, microcrystalline 6. 1H NMR (toluene-d8, RT, 500 MHz) δ 5.90, 5.88, 5.78, 5.62 (4 × br s, 4 × 1H, Cp), 2.33 (br, ∆ν½ ~ 30 Hz, 1H, B–CHH–Sc), ~2.25 (m, 1H, CH2N, partially obscured by toluene-Me), ~2.25 (m, 1H, allyl–CH2, partially obscured by toluene-Me), ~1.85 (m, 1H, CH2N), ~1.80 (m, 1H, CH2), 1.74 (s, 3H, Me), 1.55 (br, overlapping, 1H, B–CHH–Sc), 1.46 (s, 3H, Me), 1.39 (s, 3H, Me), 1.28 (s, 3H, Me). The positions of overlapping signals were located with the aid of 13C–1H gHSQC NMR techniques. Due to overlapping 1H signals, several couplings could not be assigned. 13C NMR (toluene-d8, RT, 125 MHz) δ 148.9 (d, 1JCF = 232 Hz), ~139.4 (d, 1JCF ~ 240 Hz, obscured by neighbouring CF resonance and ipso-toluene), 137.5 (d, 1JCF = 243 Hz), ~124 ppm (broad, ipso-B-C6F5, partially overlapping with solvent peak), 116.2 (d, 1JCH = 172 Hz, Cp), 116.0 (d, 1JCH = 172 Hz, Cp), 115.6 (d, 1JCH = 172 Hz, 2 x Cp), 69.4 (t, 1JCH = 138 Hz, allyl–CH2), 65.8 (t, 1JCH = 138 Hz, CH2N), 45.3 (q, 1JCH = 138 Hz, NMe), 44.0 (q, 1JCH = 137 Hz, NMe), 35.0 (br. q, 1JCB ~ 35 Hz, B–CH2–Sc), 25.5 (t, 1JCH = 129 Hz, CH2Cp), 24.4 (q, 1JCH = 129 Hz, CMe), 18.7 (q, 1JCH = 127 Hz, CMe). 19F NMR (C6D6, RT, 470 MHz) δ –132.0 (broad, ∆ν½ = 540 Hz, 2F, o-F), –161.0 (t, 3JFF = 18.4 Hz, 1F, p-F), –165.6 (broad, ∆ν½ = 90 Hz, 2F, m-F). 1H NMR (C6D5CD3, -60°C, 500 MHz) δ 5.76 (br s, 2H, Cp), 5.66 (br s, 1H, Cp), 5.52 (br s, 1H, Cp), 1.00 – 2.55 (broad signals) ppm. 19F NMR (C6D5CD3, –60°C, 470 MHz) δ –124.0, –125.4, –128.3, –129.1, –129.5, –131.3 (1F each, o-F), –155.4, –156.1, –156.8, –158.5, –160.5, –160.6, –161.1, –161.3, –162.3 (1F each, m- or p-F) ppm. 1H and 13C assignments were aided by 1H–1H gCOSY and 1H–13C gHSQC experiments. IR (Nujol mull) 1641 (m), 1512 (s), 1396 (mw), 1273 (m), 1189 (w), 1168 (w), 1150 (w), 1083 (ms), 1053 (mw), 1029 (m), 1020 (m), 977 (s), 943 (w), 986 (w), 957 (w), 808 (ms), 800 (ms), 784 (m), 768 (m), 741 (w), 679 (w), 491 (w), 439

+Sc

N

B(C6F5)3

ScN B(C6F5)3

112

(w) cm–1 Anal. calcd. for C33H24BF15NSc: C 51.12; H 3.12; N 1.81 Sc 5.80; Found: C 48.18; H 3.09; N 1.83; Sc 5.60.

Crystal structure analysis of [η5,η1-C5H4(CH2)2NMe2]Sc[C6H10B(C6F5)3] (6) A solution of 180 mg (0.33 mmol) of B(C6F5)3 in 10 mL hexane was added to a solution of 86 mg (0.35 mmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in 10 mL hexane, resulting in an orange suspension. The solid was isolated by filtration and washed with two portions of 40 mL hexane. The resulting solid was dissolved in 10 mL toluene, and concentrated until 6 separated out. The suspension was refluxed shortly to dissolve the precipitate and subsequently slowly cooled to room temperature. Compound 6 was obtained as orange crystals. Yield: 50 mg (64 µmol, 20%). Crystals from this procedure were suitable for single crystal structure determination. Bruker SMART APEX CCD diffractometer, Mo-Kα radiation (λ = 0.71073 Å), unit formula: C33H24BF15NSc, monoclinic, C2, a = 26.707(1) Å, b = 12.8668(7) Å, c = 20.493(1) Å, β = 117.196(1)°, V = 6263.6(5) Å3, Z = 8, Dx = 1.644 g × cm–3, F(000) = 3120, µ = 3.52 cm–1, T = 100(1) K, 24621 reflections measured, GooF = 0.977, wR(F2) = 0.2247 for 12204 reflections and 928 parameters, 2 restraints and R(F) = 0.0975 for 7987 reflections obeying Fo ≥ 4.0 σ(Fo) criterion of observability. The positional and anisotropic displacement parameters for the non-hydrogen atoms were refined. Some atoms showed unrealistic displacement parameters when allowed to vary anisotropically, suggesting dynamic disorder (dynamic means that the smeared electron density is due to fluctuations of the atomic positions within each unit cell). The disorder in the molecules mainly results in unrealistic displacement parameters for some atoms in the {[η5,η1-C5H4(CH2)2NMe2]Sc}-fragment, whereas in the {C6H10-B(C6F5)3}-fragment such unrealistic displaced atoms are not observed. This suggests that the crystallisation is mainly governed by the C6H10-B(C6F5)3-fragment, whereas the positioning of the {[η5,η1-C5H4(CH2)2NMe2]Sc}-fragment is less selective. The hydrogen atoms were included in the final refinement riding on their carrier atoms with their positions calculated by using sp2 or sp3 hybridization at the C-atom as appropriate with Uiso = c × Uequiv of their parent atom, where c = 1.2 for the non-methyl hydrogen atoms and c = 1.5 for the methyl hydrogen atoms and where values Uequiv are related to the atoms to which the H atoms are bonded. The methyl-groups were refined as rigid groups, which were allowed to rotate free.

Reaction of [η5,η1-C5H4(CH2)2NMe2]V(C6H10) with B(C6F5)3; synthesis of “[η5,η1-C5H4(CH2)2NMe2]V[C6H10B(C6F5)3]” (7). A solution of 510 mg (1.00 mmol) of B(C6F5)3 in 4 mL of toluene was added to a solution of 259 mg (0.96 mmol) of [η5,η1-C5H4(CH2)2NMe2]V(C6H10) 3 in 3.5 mL of toluene and the mixture was briefly shaken, resulting in a wine-red solution. The

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solution was allowed to stand undisturbed at ambient temperature. After a few minutes, red crystals of 7 began to separate. After 30 minutes the solid was isolated by filtration and washed with 2 portions of 10 mL pentane. Yield 610 mg of 7 (0.71 mmol, 81%). NMR spectroscopy is hindered by the very poor solubility of the compound. IR (Nujol mull) 1643 (ms), 1517 (s), 1408 (mw), 1332 (w), 1276 (m), 1175 (mw), 1128 (m), 1084 (s), 1063 (mw), 1052 (mw), 1029 (mw), 1016 (mw), 977 (s), 922 (mw), 907 (mw), 877 (mw), 819 (ms), 797 (m), 779 (m), 754 (m), 738 (mw), 683 (mw), 655 (w), 486 (w), 450 (w), 407 (w) cm–1. Anal. Calcd. for C33H24BF15NV: C, 50.73; H, 3.10; N, 1.79; V, 6.52. Found: C, 53.35; H, 3.49; N, 1.71; V, 6.29.27

Polymerisation experiments Polymerisation experiments were carried out in a thermostated (electrical heating, water cooling) 500 mL stainless steel autoclave (Medimex), equipped with solvent and catalyst injection systems. The autoclave was pre-dried by heating in vacuo at 120°C for 1 h. After cooling to the desired reaction temperature toluene solvent (150 mL) was injected. Ethene (2 bar) was admitted and the mixture was allowed to equilibrate. For the in situ activated runs, the activator was injected as a toluene solution (5 – 10 mL) and the flask and injector were rinsed with two portions of 5 – 10 mL of toluene. Polymerisation was initiated by injection of a solution of the appropriate butadiene complex (1 – 3) in 10 mL of toluene followed by two rinsing portions of 5 – 10 mL toluene. For the runs with the preformed zwitterionic compounds (4, 6 and 7), the polymerisation was initiated by injection of suspensions of the compounds in 10 mL of toluene, followed by two rinsing portions of 5 – 10 mL toluene. The total amount of toluene in the reactor (including portions used to rinse the injector) was 200 mL. During the run the monomer pressure was kept constant within 0.1 bar by replenishing flow. After the run the reactor was opened to ambient, and the resulting suspension was filtered to isolate the polymer. The polymer was washed with dilute HCl/methanol mixture, rinsed with petroleum ether and dried in vacuo.

Decomposition of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in C6D6; formation of 8, 9 and 10. The decomposition of 5 mg (19 µmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) as a solution in 0.5 mL C6D6 at room temperature was monitored by NMR spectroscopy. After 3 days at RT (no starting material left, resonances of compounds 8 & 9; ratio ~ 1 : 2). 1H NMR (C6D6, 400 MHz, RT; integrations, where possible, relative to the singlet at δ 5.04 ppm, set at 1H) δ 6.33 (dt, 3JHH = 2.2, 3.2 Hz, 2H, Cp, 9), 6.20 (ps. t, J = 2.7 Hz, 2H, Cp, 8), 5.99 (ps. t, J = 2.7 Hz, 2H, Cp, 8), 5.97 (s, 1H), 5.89 (dt, 3JHH = 2.2, 3.2 Hz, 2H, Cp, 9), 5.73 (dt, 3JHH = 3.2, 2.2 Hz, 2H, Cp, 9), 5.58 (dt, 3JHH = 3.2, 2.2 Hz, 2H, Cp, 9), 5.04 (s, 1H), 3.11 (t, 3JHH = 8.0 Hz, 2H, CH2Cp, 8), 2.72 (t, 3JHH =

114

8.0 Hz, 2H, CH2N, 8) 2.60-2.42 (m), 2.30 (s), 2.16 (m), 2.06 (s), 1.92 (s), 1.83 (s), 1.75 (s), 1.67 (s), 1.59 (d, broad, overlapping, J = ~ 3.5 Hz, 2H), 0.49 (d, broad, J = ~3.5 Hz, 2H). 13C{1H} NMR (C6D6, 100 MHz, RT; for the following resonances, the 1H NMR resonances with which correlation is found are given in brackets, where found) δ 158.6, 150.8, 134.2, 132.7, 126.1, 125.5, 115.1 (assignment uncertain), 110.8 (Cp, 8), 109.9 (Cp, 8), 109.4 (Cp, 9), 109.1 (Cp, 9), 108.4 (Cp, 9), 106.8 (Cp, 9), 63.7 (δ 2.16), 62.6 (CH2N, 8), 58.3 (broad s, ∆ν½ = 25.5 Hz, δ 1.57 & 0.49), 47.6 (δ 2.06), 45.9 (δ 2.30), 29.8 (CH2Cp, 8), 27.7 (δ ~2.53), 26.7 (δ 1.92), 24.8 (δ 1.67), 24.1 (δ 1.75) ppm. After approximately 3 months at RT; nearly complete conversion to compound 10. 1H NMR (C6D6, 400 MHz, RT) δ 6.27 (ps. t, J = 2.7 Hz, 2H, Cp), 6.13 (ps. t, J = 2.7 Hz, 2H, Cp), 4.68 (s, 1H), 2.97 (t, 3JHH = 7.9 Hz, 2H, CH2Cp), 2.70 (t, 3JHH = 7.9 Hz, 2H, CH2N), 2.27 (s, 6H, NMe2), 1.60 (s, 6H, Me), 1.06 (s, 3H, Me). 13C NMR (C6D6, 100 MHz, RT) δ 145.4 (b, ∆ν½ ~ 75 Hz, Sc-CH), 130.2 (Cp, ipso-C), 112.2 (d, 1JCH = 163 Hz, Cp CH), 111.4 (d, 1JCH = 163 Hz, Cp CH), 62.0 (t, 1JCH = 132 Hz, CH2N) 45.7 (q, 1JCH = 133 Hz, NMe2), 29.6 (t, 1JCH = 126 Hz, CH2Cp), 25.3 (q, 1JCH =126 Hz, Me, correlates to the signal at 1.60 ppm in the 1H NMR), 20.4 (q, 1JCH = 127 Hz, Me, correlates to the signal at 1.06 ppm in the 1H NMR) ppm. Assignments were aided by 1H–13C gHSQC, 1H–1H gCOSY and CH-coupled 13C spectra.

Synthesis of {[η5,η1-C5H4(CH2)2NMe2]Sc-µ-N(C(Ph)C6H10)}2 (11). PhCN (13 µL, 13.1 mg, 127 µmol) was added to a solution of 33.2 mg (126 µmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in 1 mL benzene and the solution was homogenised by shaking. Onto the benzene solution 5 mL of pentane was layered at room temperature. Upon gradual diffusion of pentane into the benzene solution, colourless crystals of (11)2⋅C6H6 were deposited. The crystals were isolated by filtration, washed with three portions of 2 mL of pentane and dried in vacuo. Yield: 33.9 mg (76.3 µmol, 60%). 1H NMR (THF-d8, 500 MHz, 25°C) δ 7.64 (d, 3JHH = 7.5 Hz, 2H, Ph), 7.18 (ps. t, J = 7.5 Hz; 2H,

Ph), 6.98 (ps. t, J = 7.5; 1H, Ph), 6.36 (ps. t, J = 2.2 Hz, 2H, Cp), 5.67 (ps. t, J = 2.3 Hz, 2H, Cp), 3.14 (d, 2JHH = 15.2 Hz; 1H, C6H10–CHH), 2.81 (d, 2JHH = 14.3 Hz; 1H, C6H10–CHH, partially obscured by neighbouring resonances), 2.37 (t, 3JHH = 6.2 Hz, 2H, CH2N), 2.27 (s, 6H, NMe2), 2.10 (2H, 2 × C6H10–CHH), 2.04 (t, 3JHH = 6.2 Hz; 2H, CH2Cp), 1.65 (s, 3H, CMe), 1.41 (s, 3 H, CMe). 13C{1H} NMR (THF-d8, 125 MHz, 25°C) δ 158.1 (Ph C-ipso), 130.8 (Cp ipso-C), 130.1, 128.7, 126.0 (Ph CH), 125.4 (C=CMe), 111.4 and 110.5 (Cp CH), 77.0 (NCPh), 66.8 (C6H10 CH2), 63.0 (CH2N), 59.3 (C6H10, CH2) 48.7 (NMe2), 27.5 (CH2Cp), 15.0 and 14.9 (CMe). Assignments were aided by 1H–1H gCOSY, 13C{APT} and 1H–13C gHSQC experiments. IR (Nujol mull):

Sc

N

N Ph N

Sc

NPh

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1594 (b, vw), 1377 (ms), 1295 (w), 1275 (w), 1237 (mw), 1096 (ms), 1047 (m), 1027 (m), 1000 (mw), 921 (w), 827 (m), 795 (mw), 760 (s), 704 (mw), 681 (ms), 598 (ms), 564 (w), 512 (mw) cm–1 Anal. calcd. for (C22H29N2Sc)2⋅C6H6: C, 74.05; H, 7.95; N, 6.91. Found: C, 74.16; H, 8.18; N, 6.91.

Crystal structure analysis of {[η5,η1-C5H4(CH2)2NMe2]Sc-µ-N[C(Ph)C6H10]}2 (11) Bruker SMART APEX CCD diffractometer, Mo-Kα radiation (λ = 0.71073 Å), unit formula: (C22H29N2Sc)2⋅C6H6, triclinic, P-1, a = 8.7222(8) Å, b = 10.5565(9) Å, c = 12.580(1) Å, α = 70.455(2)°, β = 88.427(2)°, γ = 88.719(2)°, V = 1091.05(16) Å3, Z = 2, Dx = 1.234 g × cm–3, F(000) = 434, µ = 3500 cm–1, T = 110(2) K, 5899 reflections measured, GooF = 1.018, wR(F2) = 0.1232 for 4441 reflections and 381 parameters and R(F) = 0.0517 for 3279 reflections obeying Fo ≥ 4.0 σ(Fo) criterion of observability.

NMR tube reaction of 1 with PhCCPh, formation of 12 and 13. Diphenylacetylene (6 mg, 33.7 µmol) was added to a solution of 4.7 mg (17.8 µmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in 0.5 mL C6D6. The deep red colour of the solution turned to brown in approximately 10 minutes. 1H NMR (400 MHz, C6D6, RT) δ 7.53 – 7.48 (m, Ph), 7.21 – 6.81 (m, Ph), 6.72 – 6.65 (m, Ph), 6.55 (ps. t, J = 2.8 Hz, 2H, Cp, 12), 6.41 (dt, 3JHH = 2.2, 3.3 Hz, Cp, 13), 6.10 (dt, 3JHH = 3.3, 2.2 Hz, Cp, 13), 5.94 (dt, 3JHH = 3.3, 2.2 Hz, Cp, 13), 5.87 (dt, 3JHH = 2.2, 3.3 Hz, Cp, 13), 5.77 (ps. t, J = 2.75 Hz, 2H, Cp, 12), 3.77 (d, 2JHH = 17.7 Hz, C(Ph)–CHH–C(Me), 13), 3.14 (d, 2JHH = 17.7 Hz, C(Ph)-CHH-C(Me), 13), 2.42 (dd, 2JHH = 4.2, 1.3 Hz, allylic C(Me)–CHH, 13), ~ 2.03 (CH2N), ~ 2.00 (CH2Cp), 1.99 (s, CMe, 13), ~ 1.93 (allylic C(Me)–CHH, 13), ~ 1.92 (CH2Cp), ~ 1.85 (CH2N), 1.80 (s, CMe, 13), 1.78 (s, NMe), 1.77 (s, NMe), 1.70 (s, NMe) ppm. The positions of the overlapping signals (δ 2.03 – 1.70 ppm) were located with the aid of 1H–1H gCOSY and 1H–13C gHSQC NMR techniques. Due to overlapping 1H signals, several couplings could not be assigned. 13C NMR (100 MHz, C6D6, RT) δ 130.6, 128.3, 127.6, 127.1, 126.8, 126.4, 125.2, 124.9, 123.9, 122.4, 121.7 (Ph CH’s), 115.0 (Cp, 12), 114.1 (Cp, 13), 114.0 (Cp, 13), 113.3 (Cp, 12), 112.5 (Cp, 12), 108.8 (Cp, 12), 83.4 (allyl CH2, 13), 65.8 (CH2N), 64.5 (CH2N), 48.0 (C(Ph)–CH2–C(Me), 13), 46.8 (NMe), 45.9 (NMe), 43.5 (NMe), 25.8 (CH2Cp), 25.7 (CH2Cp), 21.2, 20.7 (2 × CMe) ppm. Quarternary carbons not observed. 1H NMR (signals of 2,3-dimethyl-1,3-butadiene, 400 MHz, C6D6, RT) δ 5.03 (s, 2H, =CHH), 4.92 (s, 2H, =CHH), 1.82 (s, 6H, Me) ppm.

116

Synthesis of [η5,η1-C5H4(CH2)2NMe2]Sc(η2-N2C12H12)2 (14) A solution of 93 mg (0.50 mmol) of 4,4'-dimethyl-2,2'-bipyridine in 10 mL toluene was added to a solution of 53 mg (0.20 mmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in 5 mL toluene. A red solution was obtained, which slowly turned brown. The solution was stirred for 2 h, the solvents were removed in vacuo and the residue was freed from toluene by stirring with 2 portions of 10 mL hexane, which were

subsequently pumped off. The residue was extracted with 2 portions of 25 mL hexane yielding a green-brown solution. Concentration of the solution to 15 mL and cooling to –80°C yielded 73 mg (0.132 mmol, 66%) of black, microcrystalline 14. According to elemental analysis approx. 0.7 equivalents of 4,4’-dimethyl-2,2’-bipyridine is present in this sample. Anal. calcd. for C33H26N5Sc: C, 72.11; H, 6.97; N, 12.74; Found: C, 73.55; H, 7.01; N, 13.01. Anal. Calcd. For C33H26N5Sc⋅(C12H12N2)0.7: C, 73.27; H, 6.89; N, 13.31. All subsequent purification attempts by recrystallisation were hindered by gradual decomposition of the compound resulting in the formation of more free 3,3’-dimethyl-2,2’-bipyridine (as observed by NMR) and an unknown side product. The isolated yield of 14⋅0.7(N2C12H12) material was calculated to be 53% (0.107 mmol) based on Sc. (NB: the synthesis procedure described here uses a 25% excess of 4,4’-dimethyl-2,2’-bipyridine, but this does not seem to be the cause of the contamination of the product with free ligand. Experiments using the exact stoichiometry Sc : bpy = 1:2 also produced material containing free 4,4’-dimethyl-2,2’-bipyridine). IR (Nujol mull): 1613 (w), 1592 (ms), 1578 (m), 1500 (ms), 1487 (ms), 1377 (s), 1315 (m), 1272 (m), 1174 (w), 1128 (w), 1103 (w), 1097 (w), 1040 (mw), 1016 (mw), 967 (m), 952 (m), 825 (m), 774 (m), 548 (w), 515 (w) cm–1.

Crystal structure analysis of [η5,η1-C5H4(CH2)2NMe2]Sc(η2-N2C12H12)2 (14) Slow evaporation of the solvents from a solution of 15 mg (57 µmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) and 23 mg (125 µmol) of 4,4-dimethyl-2,2’-bipyridine in a mixture of 2 mL toluene and 2 mL hexane afforded black crystals of 14, suitable for X-ray analysis. Bruker SMART APEX CCD diffractometer, Mo-Kα radiation (λ = 0.71073 Å), unit formula: C33H38N5Sc, monoclinic, P21/a, a = 9.277(2) Å, b = 17.315(3) Å, c = 17.786(3) Å, β = 100.951(3)°, V = 2805.0(9) Å3, Z = 4, Dx = 1.302 g × cm–3, F(000) = 1168, µ = 2.940 cm–1, T = 100(1) K, 16598 reflections measured, GooF = 1.002, wR(F2) = 0.1316 for 3885 reflections and 504 parameters and R(F) = 0.0519 for 2523 reflections obeying Fo ≥ 4.0 σ(Fo) criterion of observability.

ScN

NN

N

N

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Reaction of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) 1 with 2 equiv. 4,4’-dimethyl-2,2’-bipyridine, formation of [η5,η1-C5H4(CH2)2NMe2]Sc(η2-N2C12H12)2 (14), Evans susceptibility measurement A mixture of 22,2 mg (84.3 µmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) and 31.0 mg (168.2 µmol) of 4,4’-dimethyl-2,2’-bipyridine was dissolved in 1.00 mL of benzene. The solution was transferred to an NMR tube containing a sealed inner tube with neat benzene. 1H NMR spectroscopy (200 MHz, RT) revealed a chemical shift difference ∆f of 34.5 Hz. The mass susceptibility was calculated from the chemical shift difference ∆f of the benzene.55b Diamagnetic corrections of the molar susceptibilities χm were applied with the aid of the Pascal constants. The effective magnetic moment was calculated from µeff = 2.828(χm × T)½ = 1.54.

NMR-tube reaction of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) with I2, formation of {[η5,η1-C5H4(CH2)2NMe2]ScI2}n (15) I2 (10.7 mg, 42,2 µmol) was added to a solution of 11.1 mg (42.2 µmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in 0.5 mL C6D6. The deep red solution gradually turned into a pale orange suspension. The 1H NMR spectrum showed mainly free 2,3-dimethyl-1,3-butediene and some small, broad resonances attributed to the poorly soluble organometallic product. The volatiles were removed in vacuo and the residue was redissolved in THF-d8 to give a clear solution of [η5,η1-C5H4(CH2)2NMe2]ScI2(THF-d8)n.

1H NMR (300 MHz, THF-d8, 25°C) δ 6.81 (ps. t, J = 2.8 Hz, 2H, Cp), 6.19 (ps. t, J = 2.8 Hz, 2H, Cp), 3.08 (t, 3JHH = 6.3 Hz, 2H, CH2N), 2.83 (t, 3JHH = 6.3 Hz; CH2Cp), 2.70 (s, 6H, NMe2).

NMR-tube reaction of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) with PhSSPh, formation of [η5,η1-C5H4(CH2)2NMe2]Sc(SPh)2 (16) PhSSPh (5.0 mg, 22.9 µmol) was added to a solution of 5.9 mg (22.4 µmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in 0.5 mL C6D6. The colour of the solution turned from deep red to pale orange. 1H NMR spectroscopy revealed the formation of free 2,3-dimethyl-1,3-butadiene and [η5,η1-C5H4(CH2)2NMe2]Sc(SPh)2 (15). 1H NMR (300 MHz, C6D6, 25°C) of [η5,η1-C5H4(CH2)2NMe2]Sc(SPh)2: δ 7.80 (d, 3JHH = 7.7 Hz, 4H, PhS o-H), 7.15 (ps. t, J ~ 7.5 Hz, PhS p-H, partially overlapped by solvent resonance), 6.97 (ps. t, J ~ 7.3 Hz, 4H, PhS m-H), 6.27 (ps. t, J = 2.6 Hz, 2H, Cp), 6.12 (ps. t, J = 2.6 Hz, 2H, Cp), 2.24 (br. t, 3JHH = 6.0 Hz, 2H, CH2N), 2.02 (t, 3JHH = 6.0 Hz, 2H, CH2Cp), 1.93 (s, 6H, NMe2).

118

Synthesis of {[η5,η1-C5H4(CH2)2NMe2]Sc(SPh)(µ-SPh)}2 (16) PhSSPh (52.1 mg, 233 µmol) was added to a solution of 61.4 mg (238 µmol) of [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (1) in 4 mL C6D6. The colour turned from deep red to pale orange. The solution was stirred for 1 hour, after which pentane (20 mL) was allowed to condense slowly into the benzene solution. Colourless crystals of 16 were isolated by filtration and dried in vacuo. Yield 44.7 mg

(112 µmol, 48%). 1H NMR (300 MHz, C6D6 with a few drops of THF-d8, 25°C) δ 7.53 (d, 3JHH = 7.3 Hz, 4H, PhS o-H), 7.05 (ps. t, J = 7.3 H, 4H, PhS m-H), 6.89 (ps. t, J = 7.3 Hz, 2H, PhS p-H), 6.36 (ps. t, J = 2.6 Hz, 2H, Cp), 6.00 (ps. t, J = 2.6 Hz, 2H, Cp), 2.66 (t, 3JHH = 6.2 Hz, 2H, CH2Cp), 2.34 (t, 3JHH = 6.2 Hz, 2H, CH2N, partially overlapping with NMe2 peak), 2.32 (s, 6H, NMe2).

13C NMR (76.5 MHz, C6D6 with a few drops of THF-d8, 25°C) δ 133.2, 128.4, 123.3 (Ph CH), 115.3, 113.8 (Cp CH), 64.2 (CH2N); 48.4 (NMe2), 26.0 (CH2Cp). Ipso-C’s of SPh’s and Cp not observed. IR (Nujol mull): 1574 (m), 1211 (w), 1085 (m), 1067 (mw), 1039 (w), 1022 (ms), 1001 (m), 919 (mw), 906 (mw), 889 (w), 855 (m), 789 (s), 733 (s), 690 (s), 537 (w), 477 (m), 431 (m) cm–1 Anal. calcd. for C21H24NS2Sc: C, 63.14; H, 6.05; N, 3.51; Found: C, 63.0; H, 6.45; N, 3.5.

Crystal structure analysis of {[η5,η1-C5H4(CH2)2NMe2]Sc(SPh)(µ-SPh)}2 (16) Bruker SMART APEX CCD diffractometer, MoKα radiation (λ = 0.71073 Å), unit formula: (C21H24NS2Sc)2, triclinic, P-1, a = 8.7995(5) Å, b = 11.1912(6) Å, c = 11.4489(6) Å, α = 94.825(1)°, β = 106.665(1)°, γ = 112.864(1)°, V = 970.51(9) Å3, Z = 1, Dx = 1.367 gcm–3, F(000) = 420, µ = 5.98 cm–1, T = 100(1) K, 8946 reflections measured, GooF = 1.060, wR(F2) = 0.0848 for 4628 unique reflections and 322 parameters and R(F) = 0.0325 for 4034 reflections obeying Fo ≥ 4.0 σ(Fo) criterion of observability.

4.8 References

1 Erker, G. Acc. Chem. Res. 2001, 34, 309-317. 2 (a) Ruwwe, J.; Erker, G.; Fröhlich, R. Angew. Chem. Int. Ed. Engl. 1996, 35, 80-82; (b) Karl, J.; Erker,

G.; Fröhlich, R. J. Am. Chem. Soc. 1997, 119, 11165-11173; (c) Karl, J.; Erker, G.; Fröhlich, R.; Zippel, F.; Bickelhaupt, F.; Schreuder Goedheijt, M.; Akkerman, O.S.; Binger, P.; Stannek, J. Angew. Chem. Int. Ed. Engl. 1997, 36, 2771-2773; (d) Pindado, G.J.; Thormton-Pett, M.; Bouwkamp, M.; Meetsma, A.; Hessen, B.; Bochmann, M. Angew. Chem. Int. Ed. Engl. 1997, 36, 2358-2361; (e) Karl, J.; Erker, G. J. Mol. Catal. A: Chem. 1998, 128, 85-102; (f) Cowley, A.H.; Hair, G.S.; McBurnett, B.G.; Jones, R.A. Chem. Commun. 1999, 437-438; (g) Dahlmann, M.; Erker, G.; Fröhlich, R.; Meyer, O. Organometallics 2000, 19, 2956-2967; (h) Dahlmann, M.; Fröhlich, R.; Erker, G. Eur. J. Inorg.

ScN S S

S

Ph

NScS

Ph

Ph

Ph

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Chem. 2000, 1789-1793; (i) Kleigrewe, N.; Brackemeyer, T.; Kehr, G.; Fröhlich, R.; Erker, G. Organometallics 2001, 20, 1952-1955; (j) Strauch, J.W.; Erker, G.; Kehr, G.; Fröhlich, R. Angew. Chem. Int. Ed. 2002, 41, 2543-2546; (k) Strauch, J.W.; Fauré, J.-L.; Bredeau, S.; Wang, C.; Kehr, G.; Fröhlich, R.; Luftmann, H.; Erker, G. J. Am. Chem. Soc. 2004, 126, 2089-2104.

3 Döhring, A.; Göhre, J.; Jolly, P.W.; Kryger, B.; Rust, J.; Verhovnik, G.P.J. Organometallics 2000, 19, 388-402.

4 Betz, P.; Döhring, A.; Emrich, R.; Goddard, R.; Jolly, P.W.; Krüger, C.; Romão, C.C.; Schönfelder, K.U.; Tsay, Y.-H. Polyhedron 1993, 12, 2651-2662.

5 Döhring, A.; Göhre, J.; Jolly, P.W.; Kryger, B.; Rust, J.; Verhovnik, G.P.J. Organometallics 2000, 19, 388-402.

6 Hessen, B.; Meetsma, A.; Van Bolhuis, F.; Teuben, J.H.; Helgesson, G.; Jagner, S. Organometallics 1990, 9, 1925-1936.

7 Witte, P.T.; Meetsma, A.; Hessen, B. Organometallics 1999, 18, 2944-2946. 8 (a) Fujita, K.; Ohnuma, Y.; Yasuda, H.; Tani, H. J. Organomet. Chem. 1976, 113, 201-213; (b) Yasuda,

H.; Ohnuma, Y.; Yamauchi, M.; Tani, H.; Nakamura, A. Bull. Chem. Soc. Jpn. 1979, 52, 2036-2045; (c) Dzhemilev, U. M.; Ibragimov, A.G.; Tolstikov, G.A. J. Organomet. Chem. 1991, 406, 1-47.

9 See for example: Field, L.D.; Gardiner, M.G.; Kennard, C.H.L.; Messerle, B. A.; Raston, C.L. Organometallics 1991, 10, 3167-3172 and references cited.

10 Erker, G.; Wicher, J.; Engel, K.; Rosenfeldt, F.; Dietrich, W.; Krüger, C. J. Am. Chem. Soc. 1980, 102, 6344.

11 (a) Yasuda, H.; Kajihara, Y.; Mashima, K.; Nagasuna, K.; Lee, K.; Nakamura, A. Organometallics, 1982, 1, 388-396; (b) Blenkers, J.; Hessen, B.; Van Bolhuis, F.; Wagner, A.J.; Teuben, J.H. Organometallics, 1987, 6, 459-469.

12 (a) Döhring, A.; Göhre, J.; Jolly, P. W.; Kryger, B.; Rust, J.; Verhovnik, G.P. J. Organometallics 2000, 19, 388-402; (b) Betz, P.; Döhring, A.; Emrich, R.; Goddard, R.; Jolly, P.W.; Krüger, C.; Romão, C.C.; Schönfelder, K.U.; Tsay, Y.-H. Polyhedron 1993, 12, 2651-2662.

13 Nakamura, A.; Mashima, K. J. Organomet. Chem. 2001, 61, 224-230. 14 (a) Betz, P.; Döhring, A.; Emrich, R.; Goddard, R.; Jolly, P. W.; Krüger, C.; Romão, C.C.; Schönfelder,

K.U.; Tsay, Y.-H. Polyhedron 1993, 12, 2651-2662; (b) Hessen, B.; Meetsma, A.; Van Bolhuis, F.; Teuben, J.H.; Helgesson, G.; Jagner, S. Organometallics 1990, 9, 1925-1936.

15 The ionic radii as reported for the 6-coordinated metal cations: Sc3+: 0.75 Å; Ti3+: 0.67 Å; V3+: 0.64 Å; Handbook of Chemistry and Physics, 80th ed.; CRC Press: Boca Raton, Fl, 2000; table 12-14 to 16.

16 For comparison, C–C = 1.54 Å and C=C = 1.34 Å: Handbook of Chemistry and Physics, 67th ed.; CRC Press: Boca Raton, Fl, 1986; table F-158.

17 A larger difference was e.g. reported by Visser et al. in (C5Me5)Hf(C6H10)(CH(SiMe3)2: 1.477(16) and 1.468(15) for the outer bonds vs. 1.342(14) for the central bond: Visser, C.; Meetsma, A.; Hessen, B. Organometallics 2002, 21, 1912-1918.

18 For specific spectroscopic data see section 3.1. 19 In the limiting “M(I) butadiene” case the bond lenghts within the butadiene fragment would be equal,

as e.g. seen in CpCr(C4H6)(PMe3): 1.408(4) and 1.393(4) for the outer bonds vs. 1.402(5) for the the central bond; Betz, P.; Döhring, A.; Emrich, R.; Goddard, R.; Jolly, P.W.; Krüger, C.; Romão, C.C.; Schönfelder, K.U.; Tsay, Y.-H. Polyhedron 1993, 12, 2651-2662.

20 (a) Karl, J.; Erker, G.; Froehlich, R. J. Am. Chem. Soc. 1997, 119, 11165-11173; (b) Green, J.C.; Green, M.L.H.; Taylor, G.C.; Saunders, J. J. Chem. Soc., Dalton Trans. 2000, 317-327; (c) Chen,

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21 Temme, B.; Karl, J.; Erker, G. Chem. Eur. J. 1996, 2, 919-924; 22 (a) Cowlay, A.H.; Hair, G.S.; McBurnett, B.G.; Jones, R.A. Chem.Commun. 1999, 437-438; (b)

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23 Besides these, unexpected activations may occur: Horton, A.D. Organometallics 1992, 11, 3271-3275. 24 (a) Temme, B.; Karl, J.; Erker, G. Chem. Eur. J. 1996, 2, 919-924; (b) Karl, J.; Erker, G. J. Mol. Cat.

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26 (a) Dahlmann, M.; Erker, G.; Fröhlich, R.; Meyer, O. Organometallics 2000, 19, 2956-2967; (b) Hannig, F.; Fröhlich, R.; Bergander, K.; Erker, G.; Petersen, J. L. Organometallics 2004, 23, 4495-4502.

27 The zwitterionic compounds [C5H4(CH2)2NMe2]M[C6H10B(C6F5)3] (M = Sc, Ti, V; 5–7) give reasonable H, N and metal analyses, but carbon analysis is generally unsatisfactory.

28 (a) Karl, J.; Erker, G.; Fröhlich, R. J. Am. Chem. Soc. 1997, 119, 11165-11173; (b) Dahlmann, M.; Erker, G.; Fröhlich, R.; Meyer, O. Organometallics 2000, 19, 2956-2967.

29 Pohlmann, J. L.W.; Brinckmann, F.E. Z. Naturforschg. 1965, 20b, 5-11. 30 Cowley, A.H.; Hair, G.S.; McBurnett, B.G.; Jones, R.A. Chem. Commun. 1999, 437-438. 31 Karl, J.; Erker, G.; Fröhlich, R. J. Am. Chem. Soc. 1997, 119, 11165-11173. 32 Dahlmann, M.; Erker, G.; Fröhlich, R.; Meyer, O. Organometallics 2000, 19, 2956-2967. 33 Devore, D.D.; Timmers, F.J.; Hasha, D.L.; Rosen, R.K.; Marks, T.J.; Deck, P.A.; Stern, C.L.

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37 Dahlmann, M.; Erker, G.; Fröhlich, R.; Meyer, O. Organometallics 2000, 19, 2956-2967. 38 (a) Atwood, J.L.; Hunter, W.E.; Alt, H.; Rausch, M.D. J. Am. Chem. Soc. 1976, 98, 2454-2459; (b)

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