Indian Journal of Chemistry Vol. 41A, March 2002 , pp. S06-S12

Synthesis and characterization of azaphosphole complexes of ruthenium and rhodium

Virnal K lain*, Leena Hernrajani+ & Raj K Bansal+

*Novel Material s & Structural Chemislry Divi sion, Bhabha Atomic Research Centre, Trombay , Mumbai 400 08S, Indi a

Received 12 JUlie 2001 ; revised 1 October 2001

Reaction of azaphospholes (L) [2-phosphaindolizines (1) and I ,3-azaphospholo[S, I-a]isoquinolines (2)] with [1'( Cp*RhC1 2h (Cp* = pentamethylcyclopentadienyl) and [Ru(116-cy mene)CI2h in 2: I molar ratio in dichloromethane yields mononuclear complexes of the type [Cp*RhCli L)] .H20 and [Ru(cy mene)Cli L)] .H20. These complexes have been characterized by elemental analysis, FAB mass, IR and NMR (IH and 31p) spectral data. Stereochemistry of these complexes has been discussed based on NMR data. NMR studies reveal a dynamic equilibrium between covalent and ionic forms of the complexes derived from 1 in solution.

Wilkinson's discovery of phosphine-rhodium complexes I as extremely reactive and selective hydroformylation catalysts promoted the development of a variety of these catalysts. The studies indicated that the 7t-acceptor ligands might be expected to be more active and regioselective hydroformylation catalysts2.5. Following this approach, recently rhodium complexes of A?-phosphorin and 2-phosphaindolizine, the potential 7t-acceptor ligands, have been used as catalysts in the regioselective hydroformylation of styrene6.8 which shows that catalytic activity of 1.3 -phosphorin is influenced by substitution in the ring. Rhodium complexes have been used as catalysts In enantioselective hydrogenation als09.lo.

Recently facile synthetic methods have been developed for 2-phosphaindolizinesll .13. The complex chemistry of 2-phosphaindolizines is so far predominated by metal carbonyl complexes I4.15. The P-donor ability in their complexes can be compared to the pyridinic nitrogen as in [AuMe2CI(L)] (L = di­and tri-azaphospholes)t6, or with tertiary phosphine/phosphite ligands as in the complexes of Cr, Mo, W, Mn, ptI4.15.17.19. In view of these results,

we have now studied the reactions of 2-phosphaindo­lizines (1) and 1 ,3-azaphospholo[5, l-a]isoquinolines (2) with [T)5-Cp*RhCI2h and [Ru(T)6-cymene)Chh. The results of this work are reported in this paper.

;Department of Chemistry, University of Rajasthan, Jaipur 302 004, India

Materials and Methods The ligands 1 (La 13, Lb I2), 220 and complexes [T)5-

Cp*RhChh (Cp* = pentamethylcyciopentadienyl) and [Ru(T)6-cymene)Chh were prepared according to. published methods21.22. All the preparations were carried out under nitrogen atmosphere and subsequent crystallization and product handling were done under normal laboratory conditions. The elemental analyses were done in the Analytical Chemistry Division , BARe. The FAB mass spectra were recorded on a JEOL SX 102/DA-6000 Mass Spectrometer at CDRl , Lucknow. The infrared spectra were recorded as Nujol mulls between CsI plates on a Bomem MB-102 FT-IR spectrometer. The IH and 31p{ IH}NMR spectra were recorded in CDCh in 5 mm tube on a Bruker DPX-300 NMR spectrometer operating at 300 and 121.42 MHz, respectively . The chemical shifts are relative to internal solvent peak (CHCl3, 8 7.26 ppm for IH) and external 85% H3P04 for 31p.

Preparation of [r(Cp*RhClz( Lb)}.fhO To a dichloromethane solution (10 ml) ot

[Cp*RhCI2h (59 mg, 0.095 mmol), a benzene solution (5 ml) of Lb (42 mg, 0.19 mmol) was added under nitrogen atmosphere with stirring which continued for 24 h during which the colour darkened. The solvents were evaporated in vacuo and the residue was recrystallized from dichloromethane-hexane at -10°C (in freezer for 24 h) as brick-red crystalline solid (yield 98 mg, 96%) (m.p. 170-172" dec.). Analytical data are summarized in Table 2. Similarly, all other rhodium complexes were prepared.

\..

Compound

,~7~. I •

, Me Ld= ,N I

)=Pl MeOOC

[Rh(l{Cp*)C12(LJ1.H20

[Ru(Tt6 -cymene)CI2(L.)].H20

,~7~. I • Lb = ',N\ I Me

,!,=Il EtOOC 1

[Rh(llS -Cp*)CI2(Lb)] .H20

--

Table I_IH and 31p{ IH} NMR data for azaphospholes and thei r rhcxlium and rutheni um complexes in CDCI3.

31p NMR

I)(ppm)

165.1

A 127.3 (d) B 99.2 (d)

A 128.7 B 104.2

165.5

A 127.0 (d) B 98.4 (d)

Data 31p NMR IJ(I 03Rh_3Ip) Coordination

in Hz. Shift

160 156

159 156

-37 .8 -65.9

-36.4 -60.9

-38.5 -67.1

IHNMR I) (ppm), J (Hz).

2.62 (d, 3H, 31PIl = 12.1, I-Me); 3.90 (5, 3H. OMe); 6.88 (dt, IH, 5JI'1l = 1.2, 3JHH = 6.4, 6-H); 7.12 (dt. IH, sl PH = 0.7, 311111 = 8.9. 7-H); 7.46 (d, IH, 31"" = 8.8, 8-H); 9.85 (dd, IH, 4JI'I'I,III; = 0.9, 31HH = 7.2, 5-H).

A 1.66 (d, 15H, 4JpIl = 3.8, CsMes); 1.SJ (d, 3H, 31m = 11.6, I-Me), 3.87 (5 , 3H, OMe); 7.14 (d, tH, 3ho; = 4.6, 8-H) ; 7.55 (t, lH, 31lf1l = 8.8, 6-H); 8.13 (t, IH, 3hu; = 9.4, 7-H); 8.18 (d, tH, 31(111 = 6.1. 5-H).

B 1.66 (d, 3H, 31PH = 11.5, I-Me), 1.71 (d, 15H, 41PH = 4.0, CsMes); 3.90 (5, 3H, OMe); 7.68 (t, IH, 3JHJl = 7.7, 6-H); 7.80 (d, IH, 31HJl = 7.9, 8-H); 8.21-8.27 (m, 2H, 5-H, 7-H).

A 0.85 (td, 6H. 3JIlH = 6.6, CHMe2); 1.78 (dd, 3H, 311'1l = 15,1, sl HH = 6.7, I-Me) ; 2.13 (5, 3H, Me); 2.95 (proton resonance mcrged with B, CH<); 3.85 (5, 3H, OMe); 5.29 (d, 2H, 31m! = 5.5, C6~); 5,50 (d, 2H, 31HH = 6,2. CJl4); 5,63 (d, 2H, 3JHJl = 5.5, C6H4); 6.82 (d, IH, 31HJl = 4.0, 8-H); 7.49 (t, IH, 31m! = 6.5, 6-H); 8.07 (t, tH, 31HH = 7.4, 7-H); 8.13 (d, IH, 31HH = 5.6, 5-H),

B 1.24 (dd, 6H. 31H/; = 6.9, sJm! = 3.3. CHMe2); 1.65 (dd, 3H, 31pH = 15.6, slHJl = 7.5, 1-Me);2.15 (5, 3H, Me); 2.95 (scp, IH, 3JHH = 7.0, CH<); 3.98 (5, 3H, OMe); 5.38 (d, 2H, 3JHl-! = 5.5, C6~); 5.55 (d, 2H, 3JIlH = 6.3, C6~); 5.68 (d, 2H, 3JHH = 6.1, C6~); 7.63 (t, IH, 3JHII = 7.4, 6-H); 7.75 (d, lH, 3hlll = 8.0, 8-H); 8.21 (t, lH, 3hIH = 7.4, 7-H); 8.27 (d, I H, 31HJl = 5.7, 5-H).

1.39 (t, 3H. 3JIlH = 7.1, OCH2Me); 2.57 (d, 3H, 31pH = 12.0, I-Me) ; 4.36 (q, 2H, 3Jm; = 7.1, OCH2Me); 6.84 (ddt, IH, 5JpII = 1.0, 3JIlH = 6.6. 411lH = 1.5, 6-H); 7.09 (t, IH, 3JHJl = 8.9, 7-H); 7.44 (d, IH, 41pH = 1.0, 8-H); 9.83(dd, IH, 4JpH = 1.8, 3I1lH = 7.3, 5-H).

A 1.34 (t, 3H. 3h u-1 = 7.1. OCH2Me); Another triplet due to B merged in the base of Cp* protons, A 1.64 (d. 15H, 41PH = 3.8, CsMes); B 1.70 (d, 15H, 4IpH = 3.9. CsMes); 1.73 (d, 3H, 31PH = 9.9. I-Me), B 4.05-4.27 (m. 2H, OCHzMc); A 4.28-4.39 (m, 2H, OCH2Mc); 7.04 (small d, 1 = 4.3); 7.56 (t. I H, 3JIlH = 7.2, 6-H) , 7.67 (d, IH.3JIiIi = 8.2. 8-H); 8. 11 (t, I H, 3IB IJ = 7.7. 7-H); 8.22 (d, I H, 3JIIII = 5.9. 5-H).

COli/d.

'-» z ~

~ Ul -l C o -< o ."

» N » "0 :r: o Ul "0 :r: o r tTl n o 3:: "0 r tTl >< tTl Ul

o ." ;;0 C -l :r: tTl Z c 3:: pP ;;0 :r: o o 2 3::

1Il o -.....l

RU(Tl6-cymene)CI2(Lb)].H10

• ~ •• N ~'~'

Ie =. . r<XXM! P,

~1:fiX::

# [Rh(115-Cp*)Clz(Lc)].HzO

[Ru(116-cymene)Clz(Lc)].H10

ld =" .,'\\ I

nooc #

[Rh(115 -Cp*)CI2(Ld) J.H10

lRu(116-cymene)CI2(Ld).Hl0]

# Data from Ref. No. 22

)I'

Tab!e I_IH and IIp{ IH ) NMR data for azaphospholes and their rhodium and ruthenium complexes in CDCI3.--Contd.

101.8

173.2

98.9 (d) 165

99.8

174.5

98.0 (d) 164

9R.8

-63 .7

-74.3

-73.4

-76.5

-75 .7

1.25 (dd, 6H, 3JHH = 6.9, 5h(H = 2.5, CHMe2) ; 1.46 (t, 3H, JJHH = 7.1. OCH2Me); 1.66 (dd, 3H, 3JI'H = 11.9, 5J IIH = 7.5, I-Me) ; 2.16 (s, 3H. Me); 3.00 (sep, IH, 31H1! = 6.9, GI<);4.46 (m, 2H, OCHzMe); 5.40 (d, 2H, 3JHH = 5.6, C6H4 ); 5.57 (d, 2H, 3JHH = 6.2, C6H4 ); 5.67 (d, 2H, 3111H = 5.8, C6lL); 7.59 (t, I H, 3JHH = 6.8. 6-H); 7.76 (d, IB, 31HH = 8.4, 8-H) ; 8. 19 (t, IH. 31~IH = 7.4, 7-H); 8.20 (d, lH, 3JHli = 6.8, 5-H).

3.87.3.92 (s, each, 6B, 1- & 3-0Me); 7.12 (d, IH, 3JHH = 7.8, 6-H); 7.37-7.93 (m, 3H, 7-H. 8-H, 9-H); 9.17 (d. 1 B, 31HJi = 8.3, 10-H); 9.57 (d, IH, 3JHH = 7.8, 5-H) .

1.75 (d, 15H, 4JpH = 3.6, C5Me5); 3.75 (s, 3H, OMe); ); 3.90 (s, 3H, OMe); 5.77 (d, lH, 3JHH = 4.8. 6-H); 6.65 (d, IH, 3JHH = 3.2,1O-H); 7.90-8.06 (m, 3H, 7-H, 8-H, 9-H); 8.19 (d, IH, 311m = 8.3. 5-H).

1.26 (dd, 6H, 31HJi = 6.9, 5hrn = 2.8, CHMez); 2.2 1 (5, 3H. Me); 3.00 (sep, lH, 3JHH = 6.9, CH<); 3.78. 3.91 (5, each, 6H, 1-&3-0Me); 5.55-5.66 (m. 4H, C6H4) ; 5.98 (d, lH, 3JHH = 4.9, 6-H); 6.76 (d, lH, 31HH = 2.5, lO-H); 7.85-7.98 (m, 3H. 7-H, 8-H, 9-H); 8.16 (d, lH, 3JBli = 8.4, 5-H).

1.42, 1.45 (t. each. 6H, 3JHH = 7.1 , 1- & 3- OCH2Me); ); 4.40, 4.46 (q, each, 4H, 3JHH = 7.1, 1-& 3-0CHzMe); 7. 16 (d, lH, 31Hll = 7.7. 6-H) ; 7.57-7.70 (m, 3H, 7-H, 8-H, 9-H); 8.90 (ddd. IH. 31HH = 7.1, 4JH1i = 3.1, 511IH = 0.7, IO-H) ; 9.64 (d. IH, 3JHH = 7.7, 5-H).

1.17 (t, 3H, 3JHJi = 7.0, OCHzMe); 1.36 (t. 3H, 31HH = 7.0, OCB2Mc); 1.75 (d, 15H, 4JpH = 4.3, CSMe5); 4.13-4.29 (m. 2H, OCHzMe); 4.32-4.40 (m, 2H, OCHzMe); 5.79 (d, IH, 3JHII = 4.6. 6-H); 6.64 (d. IH, lJH1 ! = 3.0, IO-H); 7.87-8.05 (m, 3H, 7-H, 8-H, 9-H); 8.20 (d. IH, 3hrn = 8.4, 5-H).

1.21 (t. 3H, 3J IIII = 7.1. OCH2Mc); 1.26 (d, 6H, 3J HH = 6.9. CHMcz); 1.36 (t, 3H. 3J IlH = 7.1 , OCH2Me); 2.1 9 (s . 3H. CH1); 3.02 (sep, I H, 31H1i = 6.9, CH<); 4.27 (m, 2H, OCHzMe); 4.37 (m. 2H, OCHzMe); 5.55-5.68 (m, 4H. C6lL); 6.00 (d, IH, 3JHH = 4.8,6-H); 6.74 (br. 1 H, IO-H); 7.85-8.04 (m. 3H, 7-H, 8-H, 9-H); 8.17 (d. 1 H. 3hrn = 8.4, 5-H).

Vl o 00

z o :; z (") :r: tTl 3:: en tTl (')

? 3:: :> ;;0 (") :r: N o o N

JAIN el al.: STUDY OF AZAPHOSPHOLE COMPLEXES OF RUTHENIUM & RHODIUM 509

Preparation of [Ru{7{cYlllene)Cl2( Lc)].H20 To a dichloromethane solution (10 ml) of [Ru(116

-

cymene)Chh (51 mg, 0 .083 mmol) , a dichloromethane solution of Lc (50 mg, 0 . 166 mmol) was added with stirring which continued for 60 h. The brown solution was filtered in air through a filter paper and concentrated in vacuo to 5 m\. To this, 2 ml hexane was added which on cooling in freezer (­

lODC) gave brown crystals . They were washed with CH2Clr hexane mixture (l:4, v/v) and dried in vacuo (yie ld 49 mg, 49%). Similarly, all other ruthenium complexes were prepared.

Results and Discussion The reaction of 2-phosphaindolizines (1) and 1,3-

azaphospholo[5 , I-a]isoquinolines (2) with [11 5-

Cp*RhChh (Cp* = pentamethyIcyclopentadienyl)

and [Ru(rtcymene)Chh in 2: 1 molar ratio in dichloromethane resulted in the cleavage of the metal­chloride bridge with the formation of red to brown coloured mononuclear complexes .. The latter were isolated as mono-hydrate [11 5 -Cp*RhCh(L)] .H20 and

[Ru(116-cymene)Ch(L)].H20. The water molecule appears to be trapped in these complexes from atmospheric moisture either during the work-up of reaction or recrystallization of the product. These complexes can be recrystallised from dichloromethane-hexane mixture.

FAB mass spectra of [Cp*RhCh(La)] .H20, [Cp*RhCI2(Lc)] .H20 and [Ru(cymene)Ch(Lc)].H20 have been recorded. The spectra showed molecular ion peaks at mlz 534, 628 and 625, respectively. The appearance of peaks at [M-CI] (mlz = 498, 592, 589, respectively) indicate primary decomposition by the loss of chloride ligand. Absence of peaks either due to the free ligand or [Cp*RhCh]n/[Ru(cymene)Ch]n (n = 1 or 2) suggests that M-P linkage is sufficiently stable.

The IR spectra of ligands and the complexes were recorded in nujol mull. The spectra of the complexes exhibited a broad band in the region 3550-3360 cm- I ,

1

.Qy' I • , N Me

• \ I

F=P, ROOe Rooe

2

R= Me(Lc)

= El <41)

which was absent in the spectra of ligands and the chloro-bridged rhodiumlruthenium precursor. Thi s

band can be assigned to vOH of the water molecule. The spectra of 1 (La and L b) and 2 (Lc and Ld)

showed one and two carbonyl stretching frequenci es respectively in the region 1706-1683 cm-I. On complexation, this absorption moved to higher wavenumbers by 35±5 cm-I indicating dimini shed conjugation of the carbonyl group with the heterocyclic aromatic ring. The metal chloride stretchings could not be identified unambiguously due to the presence of several absorptions from organic groups in the region 400-200 cm-I.

The NMR spectra (IH and 31p{ IH}NMR) were recorded for freshly prepared CDCI3 solutions and the resulting data are given in Table 1. The 31p NMR spectra of 2-phosphaindolizines (1) and 1,3-azaphospholo[5 , I-a]isoquinolines (2) showed a single resonance which on complexation is shielded by - 35 and - 75 ppm, respectively. In the case of rhodium

B

II A

I I I

ppm 120 100 80

Fig. 1_3I p( IH} NMR spectra of [Cp*RhCI2(L,)].H20 in CDCI, . (A) after 30 mins.; (B) after 24 hrs.; (C) after 40 days.

U1

o

Table 2---Characterization data for azaphosphole complexes of rhodium and ruthenium

Complex Recrystallization M.pt. Found (Calcd.), % JR (Molecular fo rmula) solvent (0C) C H N (cm· l

) Z 0

% yield u-OH u-C=O » z

[Rh(Tjs -Cp *CI2(La)]. H2O CH2Cl2-Hexane 218-220 43.9 4.7 2.8 3390 (br) 1731 ()

(C2oH27PIN I0 3CI2Rh) (71 ) (dec.) (44.9) (5 .1) (2.6) ::c [11

[Ru(Tj6-cymene)CIi La)].H20 CH2CI 2-Hexane 43.9 5.1 2 .8 3360 1738 3: (C2oH26P IN :0 3ClzRu) (sticky) (45.2) (4.9) (2 .6) en [RhCp*Cli Lb)].H2O CH2CI2-Hexane 170-172 43 .4 5.3 2 .5 3447 (br) 1719 [11

()

(C21 H29P IN I0 3CI2Rh) (96) (dec.) (46.0) (5 .3) (2.5) » [Ru(cymene)Cli Lb)].H2O CH2CIr Hexane 155-158 43.7 5.2 2.3 3395 (br) 1724 -

3: (C21 H2SPIN I0 3CI2Ru) (45) (46.2) (5 .2) (2.6) » [RhCp*Clz(Lc)].H2O CH2CIz-Hexane 202 45.1 4.4 2.0 3350, 3396 (br) 1742, 1720 ::0

() (C2sH29PIN IOsCI2Rh) (83) (dec.) (47.8) (4.6) (2.2) ::c [Ru(cymene)CI2(Lc)] .H2O CH2CIz-Hexane 195 46.2 4.4 2.2 3515, 3437 (br) 1742, 1720 (sh) tv

0

(C2sH2SPIN IOsCI2Ru) (49) (dec. ) (48.0) (4.5) (2.2) 0 tv

[RhCp*CliLd)] .H2O CH2CI2-Hexane 140-142 49.9 4.9 3.0 3450 (br) 1733, 1720 (sh) (C27H33P IN IOsCI2Rh) (99) (49.4) (5 . 1 ) (2.1 ) [Ru(cymene)Clz(Ld)] .HzO CH2Cl2-Hexane 156-158 48.4 4.9 2.7 3364 (br) 1741,1718 (C 27 HJ2P IN IOsC[zRu) (99) (49.6) (4.9) (2.1 )

JAIN et al.: STUDY OF AZAPHOSPHOLE COMPLEXES OF RUTHENIUM & RHODIUM 511

complexes, resonances appeared as a doublet due to 1J( 103Rh}lp) couplings (- 160 Hz). The magnitude of IJe 03 Rh_3IP) coupling is in accord with the values

d f . hI' 1 ?3 24 reporte or tertiary p osp 11l1e comp exes-" . Shielding of 31p NMR chemical shift on complexation of 2-phosphaindolizines to metal carbonyls has been reported I4.ls . In general shielding increases with increasing mass of the central metal atom as in the case of [M(CO)sL] complexes (M = Cr, Mo, W)IS.

Although NMR spectra of [Cp*RhCb(La)].H20 , [Cp*RhCI(Lb)].H20 and [Ru(cymene)CIz(La)].H20 of freshly prepared solutions exhibited only one set of resonances attributable to 3, a new species began to form on leaving the solution at room temperature. The concentration of the latter increases with time with concomitant decrease in the parent resonances. Thus the 31p NMR spectrum of [Cp*RhCb(La)].H20 (Fig. I), was monitored at room temperature. An upfield doublet (8 99.2 ppm) begins to appear within a few minutes. After a few days, an equilibrium between the two species was established. Further increase in concentration was not observed even on keeping the solution for more than a month. This equilibrium can be attained if a few drops of methanol were added to the freshly prepared solution. The upfield doublet may be attributed to the ionic form 4 resulting from the backside attack of the carbonyl oxygen on the metal causing replacement of the chloride ion2s . The conjugation of the lone pair of electrons on the pyridinic nitrogen to the C=O group and positioning of the latter on the rear side of M-CI bond, as revealed by X-ray crystal structure investigation of the Cr(CO)s complex of l -methyl-3-pivaloy 1-2-phosphaindolizinel 4

, may help this conversion. A similar dynamic equilibrium between covalent and

ionic forms has been observed In some azaphospholes26.27. The presence of 3 and 4 in CDCl3 solution of these complexes is further confirmed by their IH NMR spectra (Table I). The 31p NMR spectra of the remaining complexes derived from 1,3-bis(alkoxycarbonyl)[ I ,3]azaphospholo[5, I-a]isoqui­lines 2 however did not show the formation of the ionic species which can be explained on the basis of -M effect of l-alkoxycarbonyl group which partly nullifies the +M effect of the pyridinic lone pair thus suppressing the nuc\eophilicity of the carbonyl oxygen in these complexes. The steric requirements of isoquinoline group may also inhibit coordination of carbonyl group to the metal centre. A similar difference in the behaviour of 3-alkoxycarbonyl- and 1,3-bis(alkoxycarbonyl)-2-phosphaindolizines has been observed in their reaction with tetrachloro-o­benzoquinone when the former forms zwitterionic 1:2 adducts while the latter gives covalent I: I addition products28.

The IH NMR spectra exhibited expected peak mutiplicities and integration for the ligands and complexes. The ester group proton resonances in the free ligand and their complexes are very similar. However, the methyl resonance of 1 on complexation showed considerable shielding which is more pronounced for rhodium complexes. Although various coupling constants for the ring protons are littl e affected on coordination with Rh/Ru , there is chemical shift difference between the ligands and their complexes reflecting variation in electron density on coordination with the metal atom. The methyl protons of the pentamethylcyclo­pentadienylrhodium appeared as a doublet due to 4JClp_IH) couplings (- 4 Hz). A COSY IH NMR spectrum of [Ru(T]6-cymene)Cb(Lc)].H20 showed expected proton-proton con·elation.

Acknowledgement We thank Dr. J P Mittal, Director, Chemistry Group

and Dr. P Raj, Head, NM&SC Division, BARC for their support and encouragement of thi s work. We are grateful to the Analytical Chemistry Division BARC and RSIC, Lucknow for microanalysis and mass spectra respectively . One of us, (LH) is thankful to DA E for a senior research fellowship under a BRNS project (No. 37/9/97-R&D II).

512 INDIAN J CHEM., SEC. A, MARCH 2002

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28 Bansal R K, Gupta N, Kabra V, Surana A & Karaghiosoff K

(Results to be published).