Coordination of 12-Electron Organometallic Fragments to the AreneRing of Nonsymmetric Group 10 POCOP Pincer ComplexesNoel Angel Espinosa-Jalapa,† Simon Hernandez-Ortega,† Xavier-Frederic Le Goff,‡

David Morales-Morales,† Jean-Pierre Djukic,§ and Ronan Le Lagadec*,†

†Instituto de Quımica, Universidad Nacional Autonoma de Mexico, Circuito Exterior s/n, Ciudad Universitaria, 04510 Mexico D. F.,Mexico‡Laboratoire Hetero-element et Coordination, Ecole Polytechnique, Route de Saclay, 91128 Palaiseau Cedex, France§Institut de Chimie de Strasbourg, UMR CNRS 7177, Universite de Strasbourg, 4 rue Blaise Pascal, 67000 Strasbourg, France

*S Supporting Information

ABSTRACT: A series of heterobimetallic complexes have been prepared in good yields by η6 coordination of [Cp*Ru]+,[CpRu]+, [CpFe]+, and [Cr(CO)3] fragments to the aromatic ring of nonsymmetric Ni(II), Pd(II), and Pt(II)naphthoresorcinate POCOP compounds, and the molecular structures of the new compounds have been unequivocallydetermined by single-crystal X-ray diffraction crystallography. The reaction is regiospecific, and only coordination at thenoncyclometalated ring is observed. The coordination occurs in an orthogonal fashion, and as a consequence, theheterobimetallic species exhibit axial desymmetrization of the pincer fragment, generating molecules with planar chirality. Inaddition, the electronic properties of the metal center can be tuned by the effect of π coordination of the second metal, as shownby electrochemical studies. The observed specificity of the reaction is discussed and supported with theoretical studies.

■ INTRODUCTIONTransition-metal complexes with tridentate ECE pincer ligandshave been a center of attraction for more than a decade, mainlybecause of their stability and ease of modification, findingimportant applications in areas such as homogeneous catalysis.1

Complexes bearing POCOP phosphinite pincer ligands are ofspecial interest due to their relatively simpler preparation, basedon the initial deprotonation of resorcinols and the furtheraddition to chlorophosphines, in comparison to their analogousPCP phosphine ligands, maintaining the same characteristics ofthermal robustness and in some procedures increasedreactivity.2 However, interest in those species on occasion hasbeen limited due, for example, to the difficulty in preparingECE pincer complexes as efficient catalysts for asymmetricsynthesis. The methods that have led to chiral pincer complexesusually require multistep reaction procedures. For example,ECE arene-based ligands can possess elements of centralchirality at the benzylic positions3 or the chirality of the ligandresults from the presence of different substituents at the donoratom.4 In both cases the effects are remote from the catalytic

metallic center and are often reflected in moderate to poor ee’s.One exception is the work of Zhang, where ee values >70%have been obtained in aldol reactions of methyl isocyanoacetateand aldehydes.3d One way of solving this problem would be tobind a second metal to the aromatic backbone of anonsymmetric pincer complex, allowing the design of planar-chiral molecules.5 It has been shown in many instances6,7 thatthe direct binding of an electron-deficient organometallicfragment to a heterodisubstituted arene was possible, providedthat some minimal electronic requirements were met:7d−f (1)sufficient available electron density at the arene ligand and (2)no major steric bulk at the arene ligand that could preclude theapproach of the incoming metal center. This syntheticprocedure allows the preparation of neutral6 as well as cationic7

racemic planar chiral complexes, the resolution of which by theso-called Pasteur method seems reachable by use of chemicallyinert enantiopure anions.8 From the viewpoint of their use in

Received: February 21, 2013

Article

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catalysis, novel bimetallic pincer systems are very attractive. Forexample, the presence of a second metal atom could allow thetuning of the electron density on the catalytic center as well asthe steric constraints and stereochemistry. In this respect, theprevious strategies aimed at the synthesis of bimetalliccomplexes by π coordination of a second metal at the aromaticring of tridentate ECE ligands principally rely on substitutionby the electrophilic moieties [(C5R5)Fe]

+ to form metallocene-like pincer complexes9 or [(C5R5)Ru]

+ on arene-based PCP,NCN, and SCS pincer derivatives.10 However, one majordrawback lies in the difficulty in preparing nonsymmetric pincercomplexes.8b We have recently reported the synthesis in onestep of heterobimetallic POCOP pincer complexes of group 10metals by coordination of the [CpRu]+ fragment to thesymmetric aromatic backbone of the phosphinite ligand.11

Interestingly, the coordination of the second metal moietyinduced diastereotopicity in the PR2 substituents. In the presentstudy, a similar synthetic approach was used to introduce asecond organometallic fragment MLn (MLn = [Cp*Ru]+,[CpRu]+, [CpFe]+, [Cr(CO)3]) to nonsymmetric group 10POCOP pincer complexes based on a naphthoresorcinatebackbone, [M′{C10H5-2,10-(OP

iPr2)2}Cl] (M′ = Ni, Pd, Pt), inorder to generate compounds with planar chirality. The use ofthese pincer complexes represents a great advantage incomparison with other nonsymmetric pincer derivativespreviously reported, mainly because of the relatively straightfor-ward synthesis. In addition, the possibility that the πcoordination does not take place on the same ring thatsupports the η1 coordination of the metal in the pincerfragment could decrease the steric congestion around thecatalytic center, still allowing the tuning of the electronicproperties through the aromatic system.

■ RESULTS AND DISCUSSIONSynthesis and Characterization. Phosphinite ligand 1

and the corresponding pincer complexes 2a−c (M′ = Ni (a),Pd (b), Pt (c)) were prepared according to published methodsfor related compounds.2 In order to avoid the formation ofundesirable secondary products during the reaction with theelectrophilic precursors, isopropyl substituents on the phos-phorus atoms were preferred over the more commonly usedphenyl groups. Naphthoresorcinol was first deprotonated andthen reacted with iPr2PCl to afford 1 in quantitative yield.Reaction with the M′Cl2 salts in toluene gave complexes 2a−cin excellent yields (Scheme 1).Crystals suitable for X-ray diffraction studies were obtained

from CH2Cl2/hexane for 2a,b. The structure of the nickelcomplex 2a consists of two independent molecules in theasymmetric unit (only one cation is shown in Figure 1). Themolecular structures of the complexes show the metal center ina slightly distorted square planar environment, two of thecoordination sites being occupied by the phosphorus donoratoms in a mutually trans conformation. The P−M bonddistances between the two phosphorus atoms are slightlydifferent (ΔdP−M = 0.012 (2a), 0.011 Å (2b)), an inherenteffect of their nonsymmetric nature, in contrast with theanalogous symmetric pincer compound based on resorcinol inwhich the P−M bond distances between the phosphorus arepractically the same (ΔdP−M = 0.0021 (nickelated pincer),12

0.008 (palladated pincer),13 0.0052 Å (platinated pincer)14).The organometallic M′−C bond and the chloride ligand transto this connection complete the coordination sphere (Figure1).

The cationic complexes [Ru(Cp*)(CH3CN)3]PF6 and[Ru(Cp)(CH3CN)3]PF6 are readily available precursors tocyclopentadienylruthenium species due to the substitutionallability of the CH3CN ligands,15 and the high affinity of the[Cp*Ru]+ and [CpRu]+ fragments for arene rings has led totheir application in the synthesis of bimetallic complexes by πcoordination on aromatic substituents.16 Reaction of bothprecursors with compounds 2a−c in CH2Cl2 at roomtemperature for 20 h afforded the heterobimetallic derivatives3a−c (Cp*Ru) and 4a−c (CpRu) in ca. 70% yield (Scheme 2).Reaction times are notably shorter than for similar pincersystems based on a resorcinate backbone, for which a minimumof 3 days is required under the same conditions.11 This isprobably due to lower steric restrictions. As previouslyreported, steric factors are of special importance in such η6-coordination reactions of [Ru(C5R5)(MeCN)3]

+,17 and im-portant differences have been observed between the [Cp*Ru]+

and [CpRu]+ fragments. For instance, the use of Cp* instead ofCp allowed steric control of the reactions, increasing theregiospecificity.10d However, in the present case, the reaction isregiospecific and only compounds with coordination on thenoncyclometalated ring (exo ring) of the naphthyl skeleton areobtained and no difference in reactivity has been observedbetween Cp* and Cp.As mentioned earlier, most of the known cases of

coordination of the electrophilic moieties [(C5R5)Fe]+ to

ECE pincer complexes form metallocene-like derivatives,9 andvery few examples of coordination to arene-based pincerderivatives have been reported. Recently, one Fe/Ir bimetallicPOCOP complex has been prepared, starting from [Cp′Fe]I2and [Ir(POCOP)(C2H4)], where Cp′ = 1,2,4-C5H2(

tBu)3 andPOCOP = C6H3-2,6-(OP

tBu2)2.18 We were interested to find if

bimetallic complexes of iron and group 10 metals, analogues of3 and 4, could be prepared. Indeed, using the known activationof metallocenes by Lewis acids,19 complexes 5a−c wereobtained in good yields starting from ferrocene and 2a−c inthe presence of an excess of aluminum(III) chloride, inrefluxing 1,2-dichloroethane, followed by quenching byaqueous ammonium hexafluorophosphate. The same regiospe-cificity as for ruthenium compounds was observed.

Scheme 1. Synthesis of Phosphinite Ligand 1 and PincerComplexes 2a−c

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In order to evaluate if electronic rather than steric factorswere determining the regiospecificity of the reaction,coordination of a non-half-sandwich organometallic fragmentwas studied. Arene chromium complexes have been widelystudied and constitute a well-established class of organometalliccompounds, particularly for their applications in organicsynthesis.20 A general method to obtain arene chromiumcomplexes is through the substitution of the tricarbonylchromium fragment, the most common precursors being[Cr(CO)3(CH3CN)3] and [Cr(η6-C10H8)(CO)3] complexesdue to the substitutional lability of the CH3CN andnaphthalene ligands.21 As [Cr(η6-C10H8)(CO)3] is easy tohandle and can be stored in the solid state, it was favored in thepresent study. Starting from [Cr(η6-C10H8)(CO)3] and pincerprecursors 2a−c in THF at room temperature, complexes 6a−cwere obtained in slightly lower yields than for its rutheniumand iron analogues, but importantly the same regiospecificity asin the series 3−5 is observed.Single crystals suitable for X-ray diffraction were obtained for

most of the new heterobimetallic complexes (Figure 2 andFigures S6−S8 (Supporting Information)). The crystals of 4a−c and 5a−c were obtained by slow diffusion of diethyl etherinto a dichloromethane solution of the complex, those for 6a byslow diffusion of pentane into dichloromethane, and those forfor 6b,c by slow diffusion of hexane into dichloromethane. Thestructures of complexes 4a,c consist of two independentmolecules in the asymmetric unit (only one cation is shown in

Figure 2). Interestingly, the structures of complexes 6b,c areisomorphic, and these complexes crystallize in the ortho-rhombic crystal system within the noncentrosymmetric P212121space group. The absolute configurations of 6b,c were assignedon the basis of the crystal structures using the Schloglnotation22 for the absolute configuration descriptors of a 1,2-disubstituted arene complex. Both complexes have the pSabsolute configuration with Flack parameters (x) of 0.003(12)and −0.001(4), respectively. In all complexes the P−M−Pangles are smaller than 180°, which is typical for ECE-pincercomplexes. Important bond distances and angles aresummarized in Table 1 and Table S5 (Supporting Informa-tion). Scheme 3 shows the nomenclature used for thedescription of the structures.The crystal structures of the complexes with ruthenium and

iron are isostructural. However, the distances between the ironor the ruthenium atom and the cyclopentadienyl plane and thearene plane increase as a result of the enlargement of themetallic center (for instance, from 1.660 Å in 5a to 1.804/1.807Å in 4a for the cyclopentadienyl plane and from 1.556 Å in 5ato 1.719/1.716 Å in 4a for the arene plane). For all of thecompounds, the distance between the ruthenium or iron atomand the average plane of the cyclopentadienyl ring is marginallylonger than that between the ruthenium or iron atom and theaverage plane of the arene ring (for instance: 4a, 1.804/1.719and 1.807/1.716 Å; 4b, 1.795/1.711 Å; 4c, 1.809/1.723 and1.813/1.718 Å). The cyclopentadienyl and arene rings arealmost parallel for the bimetallic complexes with iron, forming adihedral angle between 2.22 and 1.25° for 5a−c, while for theruthenium derivatives, the dihedral angle is slightly higher(between 4.17 and 2.56° for 4a−c).The bond distances between the four ligands coordinated to

the metallic center in the pincer fragment for a group ofheterobimetallic complexes based on the same M′ metal aresimilar. For example, the Pd−C bond length is 1.950(9) Å in4b, 1.96(1) Å in 5b, and 1.982(2) Å in 6b. More interesting isthe fact that these bond distances are very close to the distancesin the monometallic pincer complex (Pd−C = 1.980(2) Å for2b). Even in the case of the chromium series 6a−c, the bonddistances between the four ligands and the M′ metal in thebimetallic derivatives are practically the same as in themonometallic pincer complex (Pd−C = 1.980(2) (2b),

Figure 1. ORTEP views of pincer complexes 2a,b. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity.

Scheme 2. Synthetic Routes Used for the Preparation ofHeterobimetallic Complexes

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1.982(2) Å (6b); Pd−P = 2.2696(8)/2.2580(8) (2b),2.2702(5)/2.2765(5) Å (6b); Pd−Cl = 2.3570(8) (2b),2.3535(4) Å for (6b)). We can thus consider than the effectof the coordination of the second metallic fragment on thebond distances around the pincer metallic center is notsignificant.The NMR spectra of the bimetallic derivatives clearly

indicate that, upon coordination of the new fragment, thetwo faces of the pincer complex have become nonequivalent.The 1H NMR spectrum of 2a at room temperature shows twomultiplets for the isopropyl groups, whereas the spectra of 3a−6a show four broad multiplets for the isopropyl groups (FigureS1, Supporting Information). As a consequence of the electron-withdrawing properties of the [Cp*Ru]+, [CpRu]+, [CpFe]+,and [Cr(CO)3] fragments, displacements of the chemical shiftfor the aromatic protons are more important on thenonmetalated ring. For example, the signals for the H3−H6protons (see Scheme 3 for nomenclature) for 3a−6a are shiftedupfield between 0.51 and 1.85 ppm in comparison with 2a,whereas the H8 proton in a position meta to the η1-coordinatednickelated ring only shows a difference of 0.01 ppm for 5a, 0.19ppm for 4a, 0.28 ppm for 6a, and 0.46 ppm for 3a. The high-field shift of the aromatic protons on the ring supporting the πcoordination of the second metal increase in the order [CpFe]+

< [CpRu]+ < [Cp*Ru]+ < [Cr(CO)3] and are in agreementwith the electron-withdrawing properties of these fragments, aspreviously described.23

Slightly broad signals are observed in all 1H NMR spectra ofiron compounds 5a−c. In order to study a potential dynamicbehavior, variable-temperature NMR experiments were per-formed in CD2Cl2 for 5a. However, no changes in the NMRspectra were noted, discarding a possible haptotropic rearrange-ment24 within the studied temperature range (from +25 to −60°C). Such broadening of the NMR signals for pincer complexesbearing the [CpFe]+ fragment has previously been observed.9

To confirm if the η6 coordination could take place on themetalated ring of the naphthyl backbone, the reaction between2a and [Ru(Cp)(CH3CN)3]PF6 was monitored by 1H NMR atroom temperature (Figure S2, Supporting Information). Onlythe formation of 4a is observed from the beginning, and nosignals arising from the coordination of the ruthenium moietyto the nickelated ring can be detected, confirming that thereaction is regioselective. Unfortunately, under the reactionconditions used for the chromium derivatives, monitoring thereactions by NMR was not possible, but we assume that thereactivity is similar to that of ruthenium. In order to evaluatethe thermal stability of the new compounds, 4a−6a wereheated in CD2Cl2 at 40 °C for 2 h and no changes were

Figure 2. ORTEP views of heterobimetallic complexes 4a, 5c, and 6b. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atomsand PF6

− anions are omitted for clarity.

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observed in the NMR spectra. When these complexes wereheated in DMF-d6 at 80 °C for 2 h, 4a showed some loss of theruthenium fragment (about 9% by 1H NMR), whereasdemetalation was 65% for 5a and complete for 6a, but noproof of a possible haptotropic rearrangement was detected.Finally, 4b and 5b were heated in DMF-d6 at 110 °C for 12 h.Loss of the ruthenium moiety was low for 4b (16%), while theloss of iron was complete in 5b, but again no signals due to ahaptotropic rearrangement were visible.

The 13C{1H} NMR spectrum of ligand 1 exhibits a doubletat 27.3 ppm (JPC = 27 Hz) for the methine carbons of the iPrsubstituent and four doublets at 16.9, 16.5, 16.1, and 17.5 ppm(JPC ≈ 2.5 Hz) for the methyl carbons. The spectrum ofcomplex 2a shows two triplets (JPC = 9 Hz) at 28.0 and 27.9ppm for the methine carbon and four signals, two triplets at17.6 and 17.5 ppm (JPC = 3.7 Hz) and two singlets at 16.9 and16.8 ppm, for the methyl carbons, indicating that the two pairsof the isopropyl groups are symmetry-related (mirror plane).The signals for the carbon atoms of the cyclometalated ring

Table 1. Selected Bond Distances (Å) and Angles (deg) for the Monometallic Pincer and the Bimetallic Complexes inExperimental Structures and in the Computed Modelsa in the Gas Phase (ZORA-PBE-D3/All Electron TZP)

2a IIa 4a exo-IVa 5a exo-Va 6a VIa

M−Cp(plane) 1.804 1.807 2.219 1.660 1.663M−arene(plane) 1.719 1.716 1.767 1.556 1.566Cp(centroid)−arene(centroid) 3.577 3.525 3.61 3.212 3.23Ni−Cipso 1.876(2) 1.881(2) 1.884 1.871(3) 1.883(3) 1.861 1.873(7) 1.859 1.872(3) 1.873Ni−Pb 2.1459(6) 2.1481(6) 2.147 2.159(1) 2.1570(8) 2.148 2.155(2) 2.146 2.160(1) 2.149Ni−Pa 2.1576(6) 2.1568(6) 2.148 2.1667(8) 2.1585(8) 2.151 2.173(3) 2.149 2.157(1) 2.148Ni−Cl 2.1850(6) 2.1834(7) 2.222 2.190(1) 2.2023(8) 2.196 2.182(2) 2.196 2.179(1) 2.216Pa−Ni−Pb 162.93(3) 164.88(3) 165.3 164.43(3) 164.74(3) 167.8 165.0(1) 168.0 164.42(4) 166.1Cipso−Ni−Cl 176.39(6) 178.65(7) 179.8 178.1(1) 177.6(1) 176.7 177.3(2) 179.1 174.6(1) 176.6Cp(centroid)−M−arene(centroid) 179.11 179.01 178.02 177.16 176.83

2b IIb 4b exo-IVb 5b exo-Vb 6b

M−Cp(plane) 1.795 1.842 1.642 1.662M−arene(plane) 1.711 1.767 1.535 1.565Cp(centroid)−arene(centroid) 3.507 3.60 3.178 3.22Pd−Cipso 1.980(2) 2.010 1.950(9) 1.993 1.96(1) 1.994 1.982(2)Pd−Pb 2.2580(9) 2.289 2.284(3) 2.291 2.274(3) 2.305 2.2765(5)Pd−Pa 2.2696(8) 2.286 2.272(4) 2.297 2.291(3) 2.285 2.2702(5)Pd−Cl 2.3570(8) 2.392 2.367(3) 2.364 2.367(3) 2.369 2.3535(4)Pa−Pd−Pb 160.78(3) 160.9 160.92(12) 162.7 161.0(1) 162.6 161.00(2)Cipso−Pd−Cl 179.15(8) 179.8 177.4(3) 177.3 176.70(3) 175.8 178.40(5)Cp(centroid)−M−arene(centroid) 178.56 178.13 178.39 176.86

4c exo-IVc 5c exo-Vc 6c

M−Cp(plane) 1.809 1.813 1.481 1.650 1.662M−arene(plane) 1.723 1.718 1.767 1.542 1.565Cp(centroid)−arene(centroid) 3.534 3.532 3.61 3.192 3.22Pt−Cipso 1.980(1) 1.98(1) 1.982 1.98(1) 1.979 1.825(5)Pt−Pb 2.270(3) 2.261(2) 2.280 2.256(3) 2.281 2.257(1)Pt−Pa 2.266(3) 2.268(3) 2.283 2.278(3) 2.284 2.265(1)Pt−Cl 2.376(3) 2.373(2) 2.383 2.363(3) 2.379 2.362(1)Pa−Pt−Pb 161.4(1) 161.7(1) 163.8 161.8(1) 164.0 161.68(4)Cipso−Pt−Cl 176.9(3) 177.2(3) 178.2 176.50(3) 178.3 178.2(1)Cp(centroid)−M−arene(centroid) 179.07 179.14 177.91 176.87 176.79

aRoman numbering used: IIa,b, IVa−c, Va−c, VIa.

Scheme 3. Nomenclature Used for the Discussion of Bond Distances and Angles of the Complexes (A) and Nomenclature Usedfor the Description of the Complexes in NMR (B)

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(with the exception of C7) also present such virtual couplingswith J values ranging from ca. 6.8 Hz (C2 and C8) and 9.8 Hz(C1 and C9) to ca. 21 Hz (C10) for 2a (virtual couplingconstants are slightly lower for 2b,c; Figure S3, SupportingInformation). These changes in multiplicity are characteristic ofvirtual couplings generally present in NMR spectra of PCPpincer compounds,12 and the changes in the number of signalsfor the methine carbon are consequences of the absence of axialsymmetry in the pincer complex. For the bimetallic complex 3a,the signals belonging to the isopropyl substituents are split intotwo different sets in comparison with 2a, showing a morecomplex pattern (Figure 3) as a consequence of the loss of axialand equatorial symmetry in the heterobimetallic species.

While the 1H and 13C NMR spectra confirm the axialdesymmetrization of the pincer fragment, in 31P{1H} NMR thenonsymmetric nature of the pincer fragment can be observed.For instance, for complex 2a the two phosphorus atoms are indifferent chemical and magnetic environments, as expected fora nonsymmetric pincer complex with both phosphorus nucleiin a mutually trans conformation, and two doublets areexpected. However, the external signals are difficult to observebecause the intensity of the signals are in accordance with anAB system in which the two doublets are very close,contributing to an increase in the intensity of the two centralsignals.25 Nevertheless, two doublets can be distinguished at185.97 and 185.50 ppm, with 2JPaPb = 331 Hz (Figure S4,Supporting Information). In contrast, when the π coordinationof the second metal has taken place, the two expected doubletsare better defined. Spectra of 4a and 5a show two signals at

194.32 and 193.65 ppm (2JPaPb = 331 Hz) and at 195.22 and

194.40 ppm (2JPaPb = 331 Hz), respectively, while complexes 3aand 6a exhibit well-defined doublets at 194.57 and 193.06 ppm(2JPaPb = 333 Hz) and at 192.40 and 190.19 ppm (2JPaPb = 330Hz), respectively. Apparently, [RuCp*]+ and [Cr(CO)3]contribute more in differentiating the two phosphorus atomsthan the [RuCp]+ and [FeCp]+ fragments and thus thenonsymmetric nature of the pincer complex is more evident.Similar features are observed for the NMR spectra of all

compounds, with additional satellites due to coupling with theplatinum center in complexes 2c−6c. The 31P{1H} NMRspectrum of 2c shows a singlet at 175.01 ppm with twosatellites (1JPPt = 3055 Hz). Despite the fact that thephosphorus atoms are not equivalent, the two expecteddoublets are not apparent. Once the coordination of thesecond metal has been carried out, the heterobimetalliccomplexes exhibit much more elaborate spectra. The 31P{1H}NMR spectra of the heterobimetallic complexes show twodoublets as a consequence of the nonequivalence of thephosphorus atoms (AB system), with the additional couplingdue to the three-spin ABX system (A, B = 31P, X = 195Pt),generating two satellites for each signal of the AB system(Figure S5, Supporting Information).

Electrochemical Studies. In order to study the influenceof the second metal on the electronic density of the metalliccenter in the pincer complex, cyclic voltammetry (CV)experiments in acetone of the pincer complexes 2a−c andthe heterobimetallic complexes 3a−c, 4a−c, and 5a−c wereperformed (under the experimental conditions in which theelectrochemical studies were performed, complexes 6a−cgenerate intricate CVs, probably due to CO loss). For thepurposes of comparison, CVs of [RuCp*(η6-naphthalene)]PF6,[RuCp(η6-naphthalene)]PF6, and [FeCp(η6-naphthalene)]PF6were also measured in acetone. All the potentials discussed arerelated to the reference electrode Ag/AgCl, and all thecomplexes undergo fully irreversible oxidation. Table 2

Figure 3. 13C{1H} NMR spectra of 1 (in CDCl3) and 2a and 3a (inCD2Cl2) at room temperature.

Table 2. Cyclic Voltammetry Dataa

complexEox(M′II/M′III)

(V)Eox(M′II/M′IV)

(V)Ered(M

II/MI)(V)

2a +1.252b +1.492c +1.42 +1.62[Ru(Cp*)(naphthalene)]PF6

−1.43

3a +1.39 +2.00 −1.51b

3b +1.66 +1.87 −1.44b

3c +1.62 +1.87 −1.48[Ru(Cp)(naphthalene)]PF6

−1.17

4a +1.40 +1.80 −1.234b +1.78 −1.25b

4c +1.71 −1.24[Fe(Cp)(naphthalene)]PF6

−0.87

5a +1.44 +1.90 −0.935b +1.68 −0.935c +1.66 −0.94

aAll of the oxidation potentials were observed as irreversible waves.bOnly reduction was observed. Reference electrode Ag/AgCl,[Complex] = 3 mM in acetone, (n-Bu)4NPF6 0.1 M, scan rate 100mVs−1.

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summarizes the observed cyclic voltammetric data. For complex2a an irreversible wave is observed at 1.25 V, probably due to aone-electron NiII/NiIII oxidation, while for 2b one two-electronirreversible wave is noted at 1.49 V for the possible PdII/PdIV

oxidation and 2c shows two waves at 1.42 and 1.62 V, whichmay be due to the one-electron oxidations PtII/PtIII and PtIII/PtIV. The oxidation waves due to the metallic center of thepincer complex in the binuclear derivatives are located at morepositive potentials in comparison with the monometalliccompounds. For instance in the 3a−c series (Figure 4), two

irreversible oxidation waves are observed at 1.39 and 2.00 V for3a, 1.66 and 1.87 V for 3b, and 1.62 and 1.87 V for 3c. Inreduction, the quasi-reversible waves observed around −1.50 V(3), −1.20 V (4), and −0.90 V (5) are attributed to RuII/RuI

and FeII/FeI, and are slightly more negative than thoseobserved for [RuCp*(η6-naphthalene)]PF6 (−1.43 V), [RuCp-(η6-naphthalene)]PF6 (−1.17 V) and [FeCp(η6-naphthalene)]-PF6 (−0.87 V). Although the oxidation potentials do notcorrespond to reversible processes and a full interpretation isbeyond the reach of the present work, those observationsreflect the interactions between the two metallic centers and arein agreement with the electron-withdrawing properties of[RuCp*]+, [RuCp]+, and [FeCp]+, resulting in a less electronrich POCOP-pincer metal center. No clear tendencies of theinfluence of the different π-bound groups within a given seriescan be deduced from the data, and more electrochemicalstudies are needed to clearly establish the metal−metalinteractions. Nonetheless, DFT investigations and particularlyNOCV-ETS analyses tend to suggest that the chelated metal

center contributes to the interaction between the exo ring andthe π-bonded metal center. However, this transfer of electrondensity to the π-bonded metal seems to be very limited.

Theoretical Investigation. The peculiar selectivity of the πmetalation of the naphthyl-based pincer complexes isreminiscent of previous reports by Oprunenko,26 Dotz,27 andDolg28 on the haptotropy of the [Cr(CO)3] moiety inheterosubstituted naphthyl ligands. Indeed it was shown that,under thermodynamic control, the [Cr(CO)3] moiety wouldnot necessarily bind the substituted benzo ring but rather theunsubstituted one.27a

To address the issue of endo−exo ring site selectivity of the π-bonding of the pincer complexes by the metal moiety, weperformed a systematic modeling of a series of structures in thegas phase, using a state of the art first-principles-baseddispersion-corrected DFT method (DFT-D3). All geometrieswere optimized at their singlet ground state at the (ZORA)PBE-D3 level with an all-electron Slater type triple-ζ basis setcontaining one polarization function. Table 1 shows goodagreement between the experimental and the computedinteratomic distances in the considered models that havebeen labeled using Roman numbers: i.e., exo-IVa−VIa, exo-IVb−VIb, and exo-IVc−VIc. The critical M′−Cipso (M′ = Ni,Pd, Pt) bond was reproduced within 0.005 Å accuracy, and themetal−π-arene bond distances were all realistically reproduced.Further investigations of the π-bonding selectivity were carriedout with the prototypical case of 5a by comparing twosituations where the metal moiety could be either π-bonded tothe metalated ring of the pincer ligand (the endo ring) orbonded at the outer ring (the exo ring), as in the experiments. Itmust first be stated that compound 2a does not display obviousfeatures that could explain the preference of the [CpRu]+, the[CpFe]+, or the [Cr(CO)3] moiety for binding the exo benzoring. Considerations of a possible kinetic orbital/charge controlare not conclusive here because no major imbalance in terms ofcharge density distribution or frontier orbital coefficients(HOMO) exists between the two benzo rings of IIa. Figure5 displays the computed map of electrostatic potentials and thehighest occupied molecular orbital of the singlet ground stateIIa.In the case of VIa, computation indicated a clear energetic

preference for the exo isomer, which was found to be morestable than the endo isomer by ca. 6 kcal/mol (zero-pointenergies considered) whatever the conformation of the[Cr(CO)3] tripod, i.e., syn or anti-eclipsed with respect to theNi atom.In the case of Va, theory indicated that the difference in

energy between the exo and endo structures (Figure 6) waswithin the generally accepted limit of accuracy of DFT, i.e. 1.1kcal/mol in favor of the exo isomer, indicating a possible equalthermodynamic stability of the two isomers. Of course, it isimportant to note that the correction for dispersion in the PBE-D3 functional is partially responsible for this relatively lowenergetic difference between the two isomers. Morokuma−Ziegler energy decomposition analysis (an example of thefragmentation scheme is given in Figure 7) confirmed this quiteclearly. The decomposition into orbital, electrostatic, Pauli, anddispersion terms was performed to compare the interactionenergy terms in the exo and endo configurations of Va byconsidering the interaction between prepared [CpFe]+ andprepared pincer derivative IIa.It appeared clear that the differences in the orbital and the

Pauli terms are very thin between exo- and endo-Va: within 1

Figure 4. Cyclic voltammograms of complexes 3a−c (see text forconditions).

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kcal/mol for each term (Table 3). The largest variation for Vaon going from the exo to the endo isomer was noticed for the

dispersion term, which increases in absolute value by ca. 3.3kcal/mol, and for the electrostatic attractive term, whichdecreases in absolute value by 4.8 kcal/mol. The latter resultsuggests that electrostatic attractive interactions are lessfavorable in the endo isomer in spite of a large compensatingdispersion term.In-depth analysis of the orbital interaction using the ETS-

NOCV (Figure 8) framework in the endo and exoconfigurations of Va provided convergent information as tothe indirect donation of electron density by the chelated metalcenter: i.e., the Ni atom. It is important to note that thisdonation from the metal does not much influence theinteraction between the [CpFe]+ moiety and the naphthylring. A comparison of the corresponding interaction energyΔEint in the Va−c series gives identical values, i.e. around −123kcal/mol, within ca. 1 kcal/mol, which is about the error (2%with a DFT-D3 functional) introduced by the basis setsuperposition error (BSSE) with a triple-ζ polarized basis set.In the nonmetalated fictitious complex Vd the value of ΔEint(−124.7 kcal/mol; Table 3) reveals a slightly more stabilizingπ-bonding interaction. At this stage, the origin of the exclusiveformation of exo-type isomers of Va is not clear, given the equalthermodynamic likeliness of formation of the endo form.The origin of this regioselectivity might reside in the

mechanism of π coordination itself and its sensitivity to stericcluttering in the early stages of the interaction between thecoordinatively unsaturated metal center bound for π coordina-tion. A kinetically favored addition of the metal moiety to theexo ring seems to be a reasonable assumption. Experimentssuggest that, even when they are heated to ca. 80 °C, thereported complexes do not isomerize into the endo form.Oprunenko26 and Dolg28 have stressed that inter-ringhaptotropy of the [Cr(CO)3] group may face barriers ofactivation of up to 25−30 kcal/mol. The situation is verysimilar in the case of VIa, for which a singlet transition state(Figure 9) very much similar to those proposed by the lattertwo authors was located 24 kcal above the singlet ground stateof exo-VIa in the gas phase. The models used here do notaccount for possible combined ion pair and solvation effects

Figure 5. Electronic structure of model cation IIa computed at the(ZORA) PBE-D3/all electron TZP level: (a) map of the electrostaticpotential (values span −0.168 to +0.326 hartree,; cf. color bar) drawnover an isosurface of the SCF electron density (isosurface density0.025 e/bohr3), wherein the red color represents areas of high chargedensity; (b) isosurface plot of the highest occupied molecular orbital.

Figure 6. Singlet ground state geometries of the exo and endo isomersof Va and VIa computed in the gas phase at the (ZORA) PBE-D3/all-electron TZP level.

Figure 7. Example of a fragment-decomposition scheme in a typicalenergy decomposition analysis. Here, the fictitious compound exo-Vdresults from the interaction between prepared [CpFe]+ and ligand 1.

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that may well affect the energetic gap between the exo and theendo isomers of the cationic bimetallic complexes of interest.

■ CONCLUSIONSThe facile synthesis of a series of planar chiral heterobimetallicpincer complexes by π coordination of the [RuCp*]+, [RuCp]+,[FeCp]+, and [Cr(CO)3] fragments to the aromatic ring ofnonsymmetric POCOP pincer derivatives of nickel, palladium,and platinum allowed the synthesis of a series of new planarchiral heterobimetallic complexes. The reaction is regiospecific,and only coordination on the noncyclometalated ring isobserved. The use of nonsymmetric pincer complexes togenerate chiral molecules represents a great advantage in

comparison with other methods previously reported, basicallybecause their synthesis is relatively straightforward. Theresolution of the enantiomers and a study of the catalyticproperties of the new compounds are currently under way; theresults will be published elsewhere.

■ EXPERIMENTAL SECTIONMaterials and Reagents. All reactions were carried out under an

inert atmosphere (dinitrogen or argon) using conventional Schlenkglassware; all solvents were dried using established procedures anddistilled under dinitrogen prior to use. All reagents were purchasedfrom Sigma Aldrich and were used as received, except foraluminum(III) chloride, which was sublimed under vacuum at 100°C prior to use. The precursors [Ru(Cp)(CH3CN)3]PF6,

15 [Ru-(Cp*)(CH3CN)3]PF6,

29 and [Cr(η6-C10H8)(CO)3]30 were synthe-

sized according to the reported procedures. Details of the synthesisand characterization of compounds 1 and 2a−c are given in theSupporting Information. The 1H (300.53 MHz), 31P{1H} (121.5MHz), and 13C{1H} (75.56 MHz) NMR spectra were recorded on aJEOL GX300 spectrometer in CD2Cl2 or CDCl3. Chemical shifts (δ)are in ppm downfield of TMS using the residual protons in the solventas the internal standard (1H and 13C) and 85% phosphoric acid as anexternal standard (31P). Two-dimensional shift-correlated experiments(COSY, HETCOR) were used to unambiguously assign the chemicalshifts. Mass spectra (FAB+) were obtained using a JEOL JMS-SX102Ainstrument with m-nitrobenzyl alcohol as a matrix. IR spectra wererecorded on a Bruker-Tensor 27 apparatus; signals are given in cm−1.Elemental analyses were carried out with an Exeter Analytical CE-440instrument analyzer. Electrochemical measurements were performedon a PC-interfaced AUTOLAB PGSTAT 12 potentiostat−galvanostat.A three-electrode setup was used with a BAS glassy-carbon workingelectrode, Ag/AgCl reference electrode, and auxiliary Pt electrode.Before each measurement, the working electrode was polished with adiamond paste and rinsed with acetone and distilled water. Allpotential scans were carried out at a scan rate of 100 mV s−1 in 3 mMacetone solutions and 0.1 M of tetra-n-butylammonium hexafluor-ophosphate as support analyte.

Synthesis of the Heterobimetallic Complexes with Ruthe-nium. Solutions of 0.25 mmol of the pincer complexes 2a−c and 0.23mmol of [Ru(Cp*)(CH3CN)3]PF6 (116 mg) or [Ru(Cp)-(CH3CN)3]PF6 (100 mg) in 15 mL of dichloromethane were stirredat room temperature for 20 h. The reaction mixture was poured over acolumn (180 mm high × 20 mm diameter) of silica gel (70−230).Small amounts of remaining uncoordinated pincer complexes werefirst eluted with dichloromethane, and the bimetallic complexes wereeluted with a dichloromethane/diethyl ether (80/20) mixture,affording a reddish fraction. This fraction was collected, concentratedto about 5 mL, and recrystallized by slow diffusion from CH2Cl2/diethyl ether, affording complexes 3a−c and 4a−c as yellow crystals.

Complex 3a. From 121 mg of 2a, compound 3a was obtained in74% yield (147 mg). 1H NMR (CD2Cl2): 6.33 (m, 1H, H3), 6.28 (s,1H, H8), 6.12 (s, 1H, H6), 5.69 (m, 2H, H5 and H4), 2.58−2.42 (m,4H, CH(CH3)2), 1.61 (s, 15H, Cp*), 1.56−1.21 (m, 24H,CH(CH3)2).

13C{1H} NMR (CD2Cl2): 168.6 (dd, vJCP = 11.3 Hz,vJCP = 9 Hz, C1), 162.5 (dd, vJCP = 12.8 Hz, vJCP = 9 Hz, C9), 131.7 (t,vJCP = 20.4 Hz, C10), 100.6 (s, C7), 93.8 (dd, vJCP = 9.8 Hz, vJCP = 3Hz, C8), 93.1 (s, Cp*), 86.6 (s, C6), 85.7 (s, C5), 84.4 (dd, vJCP = 9.8

Table 3. Interaction Energies ΔEinta for the Interaction between Prepared Structures of [CpFe]+ and the Corresponding

Metalated Pincer Ligand

exo-IVa exo-Va endo-Va exo-VIa exo-Vb exo-Vc exo-Vd

ΔEint −111.2 −124.3 −123.5 −70.4 −123.0 −123.6 −124.7ΔEorb −167.4 −169.4 −169.5 −117.1 −168.5 −168.9 −168.4ΔEel −125.5 −106.9 −102.08 −86.1 −106.8 −107.1 −108.9ΔEdisp −5.8 −7.1 −10.4 −5.3 −7.0 −7.1 −7.3ΔEPauli +187.4 +159.1 +158.5 +138.1 +159.3 +159.6 +159.9

aΔEint is further decomposed into orbital (ΔEorb), electrostatic (ΔEel), dispersion (ΔEdisp), and Pauli (ΔEPauli) terms; all values are given in kcal/mol.

Figure 8. Plots of the ETS-NOCV density deformations (isosurfacesdrawn at 0.05 e/bohr3) associated with the strongest orbital interactionenergetic contributions (in kcal/mol) for the interaction betweenprepared [CpFe]+ fragment and prepared complex IIa in isomer exo-Va. Red and blue lobes are associated with areas of electron densitydepletion and enrichment, respectively, upon interaction of theconsidered fragments. The contribution of the chelated metal center,here Ni, appears in the donation of electron density for theestablishment of the Fe−π bonds of σ symmetry.

Figure 9. Gas-phase structure (selected distances given in Å) of thesinglet transition state TS-VIa computed at the (ZORA) PBE-D3/all-electron TZP level. This transition state lies about 24 kcal/mol aboveexo-VIa and 19 kcal/mol above endo-VIa.

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Hz, vJCP = 2.2 Hz, C2), 82.4 (s, C4), 79.3 (s, C3), 28.6 (dd, vJCP = 12.8Hz, vJCP = 6.8 Hz, CH(CH3)2), 27.4 (m, CH(CH3)2), 26.7 (dd, vJCP =13.6 Hz, vJCP = 6.8 Hz, CH(CH3)2), 17.2 (d, vJCP = 3.7 Hz,CH(CH3)2), 16.7 (d,

vJCP = 4.5 Hz, CH(CH3)2), 16.6 (s, CH(CH3)2),16.4 (s, CH(CH3)2), 15.9 (s, CH(CH3)2), 15.7 (s, CH(CH3)2), 9.1 (s,Cp*). 31P{1H} NMR (CD2Cl2): 194.6 (d, 2JPaPb

= 333 Hz), 193.1 (d,2JPaPb

= 333 Hz), −144.4 (stp, 1JPF = 711 Hz, PF6). FAB+-MS: 721 [(M

+ H) − PF6]+ (100%), 449 [(M + H) − (Ru + Cp* + Cl + PF6)]

+

(5%), 391 [(M + H) − (Ru + Ni + Cp* + Cl + PF6)]+ (12%). Anal.

Calcd for C32H48ClF6NiO2P3Ru: C, 44.34; H, 5.58. Found: C, 44.31;H, 5.48.Complex 3b. From 133 mg of 2b, compound 3b was obtained in

71% yield (149 mg). 1H NMR (CD2Cl2): 6.58 (s, 1H, H8), 6.53 (m,1H, H3), 6.32 (s, 1H, H6), 5.86 (m, 2H, H5 and H4), 2.75−2.56 (m,4H, CH(CH3)2), 1.73 (s, 15H, Cp*), 1.62−1.24 (m, 24H,CH(CH3)2).

13C{1H} NMR (CD2Cl2): 168.2 (dd, vJCP = 8.3 Hz,vJCP = 5.3 Hz, C1), 160.7 (dd, vJCP = 9.8 Hz, vJCP = 5.3 Hz, C9), 134.7(t, vJCP = 2.3 Hz, C10), 100.9 (s, C7), 96.3 (dd, vJCP = 10.6 Hz, vJCP =2.3 Hz, C8), 94.3 (s, Cp*), 87.9 (s, C6), 86.9 (s, C5), 86.1 (dd, vJCP =11.3 Hz, vJCP = 3 Hz, C2), 83.5 (s, C4), 80.85 (s, C3), 30.3 (dd, vJCP =12.8 Hz, vJCP = 7.5 Hz,, CH(CH3)2), 29.62−29.02 (m, CH(CH3)2),17.8 (dd, vJCP = 4.5 Hz, vJCP = 1.5 Hz, CH(CH3)2), 17.5 (d, vJCP = 1.5Hz, CH(CH3)2), 17.4 (s, CH(CH3)2), 17.3 (dd, vJCP = 4.5 Hz, vJCP =1.5 Hz, CH(CH3)2), 17.1 (dd, vJCP = 5.3 Hz, vJCP = 1.5 Hz,CH(CH3)2), 16.9 (d,

vJCP = 0.75 Hz, CH(CH3)2), 16.7 (dd,vJCP = 3.8

Hz, vJCP = 0.75 Hz, CH(CH3)2), 10.03 (s, Cp*). 31P{1H} NMR(CD2Cl2): 196.4 (d, 2JPaPb = 420 Hz), 194.2 (d, 2JPaPb = 430 Hz),−144.4 (stp, 1JPF = 711 Hz, PF6). FAB

+-MS: 771 [(M + H) − PF6]+

(100%), 563 [(M + H) − (Ru + Cp* + PF6)]+ (3%), 497 [(M + H) −

(Ru + Cp* + Cl + PF6)]+ (15%), 391 [(M + H) − (Ru+Ni + Cp* +

Cl + PF6)]+ (8%). Anal. Calcd for C32H48ClF6O2P3PdRu: C, 42.03; H,

5.29. Found: C, 42.05; H, 5.20.Complex 3c. From 155 mg of 2c, compound 3c was obtained in

66% yield (152 mg). 1H NMR (CD2Cl2): 6.47 (s, Pt satellites 4JHPt =16.8 Hz, 1H, H8), 6.42 (m, 1H, H3), 6.18 (s, 1H, H6), 5.71 (m, 2H,H5 and H4), 2.76−2.62 (m, 4H, CH(CH3)2), 1.60 (s, 15H, Cp*),1.49−1.11 (m, 24H, CH(CH3)2).

13C{1H} NMR (CD2Cl2): 167.2 (t,vJCP = 5.3 Hz, C1), 158.5 (t, vJCP = 6 Hz, C9), 126.9 (t, vJCP = 4.5 Hz,C10), 100.0 (s, C7), 96.2 (dd, vJCP = 9 Hz, vJCP = 2.3 Hz, C8), 94.1 (s,Cp*), 87.4 (s, C6), 87.0 (s, C5), 86.7 (dd, vJCP = 9 Hz, vJCP = 3 Hz,C2), 83.7 (s, C4), 80.4 (s, Pt satellites JCPt = 12.8 Hz, C3), 31.1 (dd,vJCP = 21 Hz, vJCP = 12.1 Hz, CH(CH3)2), 30.0−29.4 (m, CH(CH3)2),17.5−16.5 (m, CH(CH3)2), 10.1 (s, Cp*). 31P{1H} NMR (CD2Cl2):AB system, 182.4 (d, 2JPaPb = 416 Hz), 180.5 (d, 2JPaPb = 416 Hz).FAB+-MS: 859 [(M + H) − PF6]

+ (100%), 586 [(M + H) − (Ru +Cp* + Cl + PF6)]

+ (10%), 391 [(M + H) − (Ru + Ni + Cp* + Cl +PF6)]

+ (40%). Anal. Calcd for C32H48ClF6O2P3PtRu: C, 38.31; H,4.82. Found: C, 38.25; H, 4.67.Complex 4a. From 121 mg of 2a, compound 4a was obtained in

71% yield (130 mg). 1H NMR (CD2Cl2): 6.97 (d, 3JHH = 6 Hz, 1H,H3), 6.88 (d, 3JHH = 6 Hz, 1H, H6), 6.55 (s, 1H, H8), 6.19 (t, 3JHH = 6Hz, 1H, H5), 6.14 (t, 3JHH = 6 Hz, 1H, H4), 4.95 (s, 5H, Cp), 2.79−2.61 (m, 4H, CH(CH3)2), 1.39−1.15 (m, 24H, CH(CH3)2).

13C{1H}NMR (CD2Cl2): 170.8 (t, vJCP = 9.8 Hz, C1), 165.3 (dd, vJCP = 12.1Hz, vJCP = 9.8 Hz, C9), 133.0 (t, vJCP = 20.5 Hz, C10), 102.8 (s, C7),96.7 (dd, vJCP = 6.8 Hz, vJCP = 3.8 Hz, C8), 85.3 (s, C6), 84.1 (s, C5),83.3 (dd, vJCP = 7.6 Hz, vJCP = 4.5 Hz, C2), 82.6 (s, C4), 79.5 (s, Cp),78.6 (s, C3), 28.8−28.2 (m, CH(CH3)2), 17.6−17.3 (m, CH(CH3)2),17.0 (s, CH(CH3)2), 16.8 (s, CH(CH3)2), 16.7 (s, CH(CH3)2).31P{1H} NMR (CD2Cl2): 194.3 (d, 2JPaPb

= 331 Hz), 193.7 (d, 2JPaPb=

331 Hz), −155.7 (stp 1JPF = 711 Hz, PF6). FAB+-MS: 653 [(M + H) −

PF6]+ (100%), 449 [(M + H) − (Ru + Cp + Cl + PF6)]

+ (8%). Anal.Calcd for C27H38ClF6NiO2P3Ru: C, 40.70; H, 4.81. Found: C, 40.56;H, 4.61.Complex 4b. From 133 mg of 2b, compound 4b was obtained in

64% yield (124 mg). 1H NMR (CD2Cl2): 7.05 (d, 3JHH = 6 Hz, 1H,H3), 6.93 (d, 3JHH = 6 Hz, 1H, H6), 6.73 (s, 1H, H8), 6.23 (t, 3JHH = 6Hz, 1H, H5), 6.18 (t, 3JHH = 6 Hz, 1H, H4), 4.97 (s, 5H, Cp), 2.82−

2.55 (m, 4H, CH(CH3)2), 1.49−1.31 (m, 24H, CH(CH3)2).13C{1H}

NMR (CD2Cl2): 168.5 (dd, vJCP = 7.6 Hz, vJCP = 5.3 Hz, C1), 162.5(dd, vJCP = 9.1 Hz, vJCP = 5.3 Hz, C9), 135.2 (t, vJCP = 2.3 Hz C10),102.1 (s, C7), 98.1 (dd, vJCP = 10.6 Hz, vJCP = 3 Hz, C8), 85.5 (s, C6),84.4 (s, C5), 84.1 (dd, vJCP = 10.6 Hz, vJCP = 3.8 Hz, C2), 82.7 (s, C4),79.7 (s, Cp), 79.2 (s, C3), 29.7−29.2 (m, CH(CH3)2), 17.3 (dd,

vJCP =5.3, vJCP = 1.5 Hz, CH(CH3)2), 17.1 (m, CH(CH3)2), 16.8 (s,CH(CH3)2), 16.7 (s, CH(CH3)2).

31P{1H} NMR (CD2Cl2): 196.5 (d,2JPaPb

= 420 Hz), 194.7 (d, 2JPaPb= 420 Hz), −157.8 (stp, 1JPF = 710 Hz,

PF6). FAB+-MS: 699 [(M + H) − PF6]

+ (78%), 497 [(M + H) − (Ru+ Cp + Cl + PF6)]

+ (24%). Anal. Calcd for C27H38ClF6O2P3PdRu: C,38.40; H, 4.54. Found: C, 38.40; H, 4.33.

Complex 4c. . From 155 mg of 2c, compound 4c was obtained in68% yield (146 mg). 1H NMR (CD2Cl2): 6.95 (d, 3JHH = 6 Hz, 1H,H3), 6.80 (d, 3JHH = 6 Hz, 1H, H6), 6.62 (s, Pt satellites 4JHPt = 16.5Hz, 1H, H8), 6.09 (td, 3JHH = 6 Hz, 4JHH = 1 Hz, 1H, H5), 6.04 (td,3JHH = 6 Hz, 4JHH = 1 Hz, 1H, H4), 4.82 (s, 5H, Cp), 2.82−2.61 (m,4H, CH(CH3)2), 1.39−1.24 (m, 24H, CH(CH3)2).

13C{1H} NMR(CD2Cl2): 167.4 (t,

vJCP = 6 Hz, C1), 160.3 (t, vJCP = 6 Hz, C9), 127.4(t, vJCP = 4.5 Hz, C10), 101.2 (s, C7), 98.0 (dd, vJCP = 7.6 Hz, vJCP =3.8 Hz, C8), 85.09 (s, C6), 84.9 (dd, vJCP = 8.3 Hz, vJCP = 3 Hz, C2),84.4 (s, C5), 82.9 (s, C4), 79.5 (s, Cp), 78.6 (s, Pt satellites JCPt = 12.8Hz, C3), 30.3−29.5 (m, CH(CH3)2), 17.0−16.6 (m, CH(CH3)2).31P{1H} NMR (CD2Cl2): AB system, 182.4 (d 2JPaPb

= 414 Hz), 181.1

(d 2JPaPb= 414 Hz). FAB+-MS: 788 [(M + H) − PF6]

+ (28%), 586[(M + H) − (Ru + Cp + Cl + PF6)]

+ (5%). Anal. Calcd forC27H38ClF6O2P3PtRu: C, 34.75; H, 4.10. Found: C, 34.70; H, 3.96.

Synthesis of the Heterobimetallic Complexes with Iron.Solutions of the pincer complexes 2a−c (0.4 mmol), aluminum(III)chloride (160 mg/1.2 mmol), and ferrocene (223 mg/1.2 mmol) in 15mL of 1,2-dichloroethane were heated at reflux for 2 h. After they werecooled to room temperature, the reaction mixtures were poured over15 mL of an aqueous solution of ammonium hexafluorophosphate (1.2mmol) with vigorous stirring during 25 min. The organic phase wasseparated and purified through a column (180 mm high × 20 mmdiameter) of silica gel (70−230). Unreacted ferrocene and pincercomplexes were first eluted with dichloromethane, and the desiredcompounds were eluted with a dichloromethane/diethyl ether (80/20), mixture affording a reddish fraction. This fraction was collected,concentrated to about 5 mL, and recrystallized by slow diffusion fromCH2Cl2/diethyl ether, affording complexes 5a−c as red crystals.

Complex 5a. From 194 mg of 2a, compound 5a was obtained in61% yield (183 mg). 1H NMR (CD2Cl2): 7.14 (d, 3JHH = 6 Hz, 1H,H3), 7.02 (d, 3JHH = 6 Hz, 1H, H6), 6.75 (s, 1H, H8), 6.29 (t, 3JHH = 6Hz, 1H, H5), 6.23 (t, 3JHH = 6 Hz, 1H, H4), 4.54 (s, 5H, Cp), 2.78−2.59 (m, 4H, CH(CH3)2), 1.62−1.45 (m, 24H, CH(CH3)2).

13C{1H}NMR (CD2Cl2): 171.5 (t, vJCP = 10 Hz, C1), 166.7 (t, vJCP = 11 Hz,C9), 133.9 (t, vJCP = 20 Hz, C10), 101.0 (s, C7), 98.2 (m, C8), 86.0 (s,C6), 84.3 (s, C5), 83.7 (s, C4), 81.1 (m, C2), 79.9 (s, C3), 76.3 (s,Cp), 28.9−28.2 (m, CH(CH3)2), 17.7 (t, vJCP = 2.3 Hz, CH(CH3)2),17.5 (m, CH(CH3)2), 17.1 (s, CH(CH3)2), 16.9 (d, vJCP = 3 Hz,CH(CH3)2), 16.8 (s, CH(CH3)2).

31P{1H} NMR (CD2Cl2): 195.2 (d,2JPaPb

= 331 Hz), 194.4 (d, 2JPaPb= 331 Hz), −155.7 (stp, 1JPF = 711 Hz,

PF6). FAB+-MS: 605 [(M + H) − PF6]

+ (55%), 485 [(M + H) − (Fe+ Cp + PF6)]

+ (32%), 449 [(M + H) − (Fe + Cp + Cl + PF6)]+

(100%). Anal. Calcd for C27H38ClF6FeNiO2P3: C, 43.15; H, 5.10.Found: C, 43.27; H, 5.11.

Complex 5b. From 213 mg of 2b, compound 5b was obtained in52% yield (166 mg). 1H NMR (CD2Cl2): 7.22 (d, 3JHH = 6 Hz 1H,H3), 7.08 (d, 3JHH = 6 Hz, 1H, H6), 6.93 (s, 1H, H8), 6.33 (t, 3JHH = 6Hz, 1H, H5), 6.27 (t, 3JHH = 6 Hz, 1H, H4), 4.57 (,s 5H, Cp), 2.82−2.66 (m, 4H, CH(CH3)2), 1.55−1.41 (m, 24H, CH(CH3)2).

13C{1H}NMR (CD2Cl2): 169.0 (dd, vJCP = 8.3 Hz, vJCP = 5.3 Hz, C1), 163.9(dd, vJCP = 9.1 Hz, vJCP = 5.3 Hz, C9), 135.8 (t, vJCP = 2.3 Hz, C10),101.4 (s, C7), 99.5 (dd, vJCP = 10.6 Hz, vJCP = 3 Hz, C8), 86.3 (s, C6),84.7 (s, C5), 83.8 (s, C4), 82.0 (dd, vJCP = 11.3 Hz, vJCP = 3 Hz, C2),80.4 (s, C3), 76.5 (s, Cp), 29.9−29.2 (m, CH(CH3)2), 17.3 (dd,

vJCP =5.3 Hz, vJCP = 1.5 Hz, CH(CH3)2), 17.2 (m, CH(CH3)2), 16.9 (s,

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CH(CH3)2), 16.8 (d, vJCP = 3 Hz, CH(CH3)2).31P{1H} NMR

(CD2Cl2): 197.4 (d, 2JPaPb = 418 Hz), 195.4 (d, 2JPaPb = 418 Hz),

−157.8 (stp, 1JPF = 710 Hz, PF6). FAB+-MS: 653 [(M + H) − PF6]

+

(36%), 534 [(M + H) − (Fe + Cp + PF6)]+ (12%), 497 [(M + H) −

(Fe + Cp + Cl + PF6)]+ (100%). Anal . Calcd for

C27H38ClF6FeO2P3Pd·1/2C4H10O: C, 41.65; H, 5.18. Found: C,

41.60; H, 4.85.Complex 5c. From 249 mg of 2c, compound 5c was obtained in

63% yield (224 mg). 1H NMR (CD2Cl2): 7.11 (d, 3JHH = 6 Hz, 1H,H3), 6.94 (d, 3JHH = 6 Hz, 1H, H6), 6.82 (s, Pt satellites 4JHPt = 15 Hz,1H, H8), 6.18 (t, 3JHH = 6 Hz, 1H, H5), 6.12 (t, 3JHH = 6 Hz, 1H, H4),4.42 (s 5H, Cp), 2.87−2.70 (m, 4H, CH(CH3)2), 1.41−1.27 (m, 24H,CH(CH3)2).

13C{1H} NMR (CD2Cl2): 168.1 (t, vJCP = 6 Hz, C1),161.7 (t, vJCP = 7 Hz, C9), 128.0 (m, C10), 99.5 (dd, vJCP = 7.6 Hz,vJCP = 3.8 Hz, C8), 99.3 (s, C7), 85.7 (s, C6), 84.6 (s, C5), 84.0 (s,C4), 82.7 (dd, vJCP = 8.3 Hz, vJCP = 3.8 Hz, C2), 79.8 (s, Pt satellitesJCPt = 12.8 Hz, C3), 76.3 (s, Cp), 30.6−29.5 (m, CH(CH3)2), 17.1 (s,CH(CH3)2), 16.9−16.6 (m, CH(CH3)2).

31P{1H} NMR (CD2Cl2):AB system, 183.0 (d, 2JPaPb = 415 Hz), 181.7 (d, 2JPaPb = 415 Hz).

FAB+-MS: 742 [(M + H) − PF6]+ (45%), 621 [(M + H) − (Fe + Cp

+ PF6)]+ (37%), 586 [(M + H) − (Fe + Cp + Cl + PF6)]

+ (100%).Anal. Calcd for C27H38ClF6FeO2P3Pt: C, 36.52; H, 4.31. Found: C,36.49; H, 4.23.Synthesis of the Heterobimetallic Complexes with Chro-

mium. Complex 6a. A solution of 2a (92 mg/0.19 mmol) and 0.38mmol (100 mg) of [Cr(η6-C10H8)(CO)3] in 10 mL of THF wasstirred for 24 h at room temperature. After evaporation under reducedpressure, 10 mL of a CH2Cl2/hexane 30/70 mixture was added, andthe suspension was poured over a silica column. Free naphthalene,unreacted 2a, and [Cr(η6-C10H8)(CO)3] were removed by elutionwith a CH2Cl2/hexane 30/70 mixture. The desired complex was elutedwith a CH2Cl2/hexane 60/40 mixture. Recrystallization from CH2Cl2/pentane afforded 6a as red crystals in 64% yield (76 mg). 1H NMR(CD2Cl2): 6.46 (s, 1H, H8), 6.46 (d,

3JHH = 6.5 Hz, 1H, H3), 6.07 (d,3JHH = 6.5 Hz, 1H, H6), 5.68 (t, 3JHH = 6.5 Hz, 1H, H5), 5.33 (t, 3JHH= 6.5 Hz, 1H, H4), 2.59−2.49 (m, 4H, CH(CH3)2), 1.51−1.43 (m,24H, CH(CH3)2).

13C{1H} NMR (CD2Cl2): 233.2 (CO) 169.6 (dd,vJCP = 12.1 Hz, vJCP = 8.3 Hz, C1), 165.8 (dd, vJCP = 9 Hz, vJCP = 9 Hz,C9), 127.6 (t, vJCP = 20.4 Hz, C10), 112.5 (s, C7), 97.4 (dd, vJCP = 9.8Hz, vJCP = 2.3 Hz, C8), 94.7 (s, C5), 89.7 (s, C4), 89.6 (s, C6), 89.5(d, vJCP = 2.3 Hz, C2), 88.7 (s, C3), 28.7−28.4 (m, CH(CH3)2), 28.1(dd, vJCP = 15.1 Hz, vJCP = 6.8 Hz, CH(CH3)2), 17.7−17.34 (m,CH(CH3)2), 17.0 (s, CH(CH3)2), 16.9 (s, CH(CH3)2), 16.7 (s,CH(CH3)2).

31P{1H} NMR (CD2Cl2): 192.40 (d, 2JPaPb = 330 Hz),

190.19 (d, 2JPaPb= 330 Hz). IR (FTIR, 3 mM in CH2Cl2): ν 1958 (CO,

sh), 1885 (CO, br). FAB+-MS: 620 [M + H]+ (12%), 536 [(M + H) −(3CO)]+ (85%), 484 [(M + H) − (3CO + Cr)]+ (72%), 449 [(M +H) − (3CO + Cr + Cl)]+ (100%). Anal. Calcd forC25H33ClCrNiO5P2: C, 48.30; H, 5.35. Found: C, 48.15; H, 5.40.Complexes 6b,c. A solution of 2b (101 mg/0.19 mmol) or 2c (118

mg/0.19 mmol) and 0.38 mmol (100 mg) of [Cr(η6-C10H8)(CO)3] in10 mL of THF was stirred for 24 h at room temperature. Afterevaporation under reduced pressure, 10 mL of a CH2Cl2/hexane 30/70 mixture was added, and the suspension was poured over a silicacolumn. Free naphthalene and unreacted [Cr(η6-C10H8)(CO)3] werefirst removed by elution with a CH2Cl2/hexane 30/70 mixture. Elutionwith CH2Cl2 led to a reddish fraction containing small amounts ofunreacted 2b or 2c and the heterobimetallic complex. Recrystallizationfrom CH2Cl2/hexane afforded 6b,c as red crystals in 32% (41 mg) and38% yields (55 mg), respectively.Data for 6b are as follows. 1H NMR (CD2Cl2): 6.50 (s, 1H, H8),

6.35 (d, 3JHH = 6.5 Hz, 1H, H3), 5.97 (d, 3JHH = 6.5 Hz, 1H, H6), 5.66(t, 3JHH = 6.5 Hz, 1H, H5), 5.23 (t, 3JHH = 6.5 Hz, 1H, H4), 2.50−2.42(m, 4H, CH(CH3)2), 1.28 (m, 24H, CH(CH3)2).

13C{1H} NMR(CD2Cl2): 233.5 (CO), 167.0 (dd, vJCP = 8.3 Hz, vJCP = 4.5 Hz, C1),162.9 (dd, vJCP = 9.8 Hz, vJCP = 4.5 Hz, C9), 131.0 (t, vJCP = 3.8 Hz,C10), 111.5 (s, C7), 98.7 (dd, vJCP = 11.3 Hz, vJCP = 2.3 Hz, C8), 94.7(s, C5), 90.4 (dd, vJCP = 12.1 Hz, vJCP = 3 Hz, C2), 89.9 (s, C4), 89.7

(s, C6),, 88.8 (s, C3), 29.7−29.0 (m, CH(CH3)2), 17.5−16.7 (m,CH(CH3)2).

31P{1H} NMR (CD2Cl2): 194.4 (d, 2JPaPb = 418 Hz),

191.8 (d, 2JPaPb= 418 Hz). IR (FTIR, 3 mM in CH2Cl2): ν 1959 (CO,

sh), 1886 (CO, br). FAB+-MS: 670 [M + H]+ (3%), 586 [(M + H) −(3CO)]+ (22%), 534 [(M + H) − (3CO + Cr)]+ (10%), 499 [(M +H) − (3CO + Cr + Cl)]+ (60%). Anal. Calcd for C25H33ClCrO5P2Pd:C, 44.86; H, 4.97. Found: C, 44.67; H, 5.00.

Data for 6c are as follows. 1H NMR (CD2Cl2): 6.56 (s, Pt satellites4JHPt = 17 Hz, 1H, H8), 6.51 (d, 3JHH = 7 Hz 1H, H3), 6.13 (d, 3JHH =7 Hz, 1H, H6), 5.67 (t, 3JHH = 7 Hz, 1H, H5), 5.38 (t, 3JHH = 7 Hz,1H, H4), 2.79−2.71 (m, 4H, CH(CH3)2), 1.37 (m, 24H, CH(CH3)2).13C{1H} NMR (CD2Cl2): 233.7 (CO), 165.9 (t, vJCP = 6 Hz, C1),160.9 (t, vJCP = 6 Hz, C9), 122.9 (t, vJCP = 4.5 Hz, C10), 110.6 (s, C7),98.6 (dd, vJCP = 9.1 Hz, vJCP = 3 Hz, C8), 94.1 (s, C6), 91.1 (dd, vJCP =9.1 Hz, vJCP = 3 Hz, C2), 90.3 (s, C5 and C4), 88.3 (s, Pt satellites JCPt= 12 Hz, C3), 30.4−29.4 (m, CH(CH3)2), 16.9−16.5 (m, CH(CH3)2).31P{1H} NMR (CD2Cl2): AB system, 180.4 (d 2JPaPb

= 416 Hz), 178.5

(d 2JPaPb= 415 Hz). IR (FTIR, 3 mM in CH2Cl2): ν 1958 (CO, sh),

1884 (CO, br). FAB+-MS: 758 [M + H]+ (10%), 674 [(M + H) −(3CO)]+ (58%), 622 [(M + H) − (3CO + Cr)]+ (14%), 586 [(M +H) − (3CO + Cr + Cl)]+ (100%). Anal. Calcd for C25H33ClCrO5P2Pt:C, 39.61; H, 4.39. Found: C, 39.30; H, 4.20.

Computational Details. Computations were performed by DFTmethods using the dispersion corrected31 Perdew−Burke−Ernzerhof32(PBE-D3) GGA functional implemented in the Amsterdam DensityFunctional package33 (ADF201234 version). Within the PBE schemeelectron correlation was treated within the local density approximation(LDA) in the PW92 parametrization.35 Scalar relativistic computationswith the Zeroth Order Regular Approximation36 were carried outusing ad hoc all-electron (AE) basis sets:37 polarized triple-ζ (TZP)Slater type orbitals were used in this study.38 NBO analyses werecarried out on geometries of models relaxed at the (ZORA) PBE-D3level. Ground-state and transition-state search optimizations werecarried out in all cases with an integration grid comprised between 4.5and 6.5, an energy gradient convergence criterion of 10−3 au, and atight SCF convergence criterion. All ground-state and transition-stategeometries were computed using a “zero-damped” PBE-D330 (ZORA)functional. Counterpoise correction for basis set superposition error(BSSE) was neglected throughout this study.36 ETS-NOCV38 analysesas well as calculations of vibrational modes (analytical secondderivative frequencies and two-point numerical integration forCOSMO geometries) were performed with optimized geometriesusing ADF2012 subroutines. Vibrational modes were computed in allcases to verify that the optimized geometries were related to energyminima: statistical thermodynamic data were computed at 298.15 K.Representations of molecular structures and orbitals were drawn usingADFview v12.

Crystallography. Crystalline prisms for compounds 2a,b, 4a−c,5a−c, and 6a−c were grown independently as described in thediscussion and mounted on glass fibers. The X-ray intensity data for2a,b, 4b, 5a−c, and 6c were measured at 298 K on a Bruker SMARTAPEX CCD-based X-ray diffractometer system equipped with a Mo-target X-ray tube (λ = 0.71073 Å). The detector was placed at adistance of 4.837 cm from the crystals in all cases. The frames wereintegrated with the Bruker SAINT software package using a narrow-frame integration algorithm.39 The X-ray intensity data for 4a,c and6a,b were measured at 150 K on a Nonius Kappa CCD X-raydiffractometer system equipped with a Mo-target X-ray tube (λ =0.71073 Å). The frames were integrated using the DENZO40 andCOLLECT41 program systems. The integrations of the data weredone using a monoclinic crystal system for 2a,b, 4a,c, and 6a andorthorhombic crystal system for 4b, 5a−c, and 6c. Analysis of the datashowed in all cases negligible decay during data collections. Thestructures for 2a,b, 4b, 5a−c, and 6c were solved by Pattersonmethods using the SHELXS-97 program,42 and those for 4a,c and 6a,bwere solved using SIR97.43 The remaining atoms were located via afew cycles of least-squares refinements and difference Fourier maps.Absorption corrections were applied for 4a,c and 6a,b using the

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DENZO/SCALEPACK program, for 2a,b, 4b, and 5a−c by theSHELXTL program, and for 6c by the SADABS program.44 All non-hydrogen atoms were refined anisotropically. The hydrogen atomswere input at calculated positions and allowed to ride on the atoms towhich they are attached. Thermal parameters were refined forhydrogen atoms on the phenyl groups using a Ueq value 1.2 timesthat of the precedent atom in all cases. For all complexes, the finalcycle of refinement was carried out on all non-zero data usingSHELXTL. The isopropyl groups in 2a,b, 4a,b, and 5a−c and the PF6anion in 5a−c were disordered and were modeled as two majorcontributors and refined anisotropically.

■ ASSOCIATED CONTENT*S Supporting InformationText, tables, figures, and CIF files giving experimentalprocedures for compounds 1 and 2a−c and NMR spectra,computational details, and crystallographic data for 2a,b, 4a−c,5a−c, and 6a−c. This material is available free of charge via theInternet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*E-mail for R.L.L.: ronan@unam.mx.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSWe acknowledge financial support from the DGAPA (PAPIITProjects IN205209, IN204812, and IN227008), CONACyT(Projects 153151, F58692 and scholarship to N.A.E-J.), and theANR (from project ANR 2010 blanc WEAKINTERMET-2DA).

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Organometallics Article

dx.doi.org/10.1021/om400147x | Organometallics XXXX, XXX, XXX−XXXM