Redox properties of (RC2R')Co2(CO)6-nLn and reactivity of (RC2R')Co2(CO)6-nLn towards PPh3[LPPh3, P(OEt)3]

Cyclic voltammetric studies of clusters (C₅H₅-C₂C₆ H₄-R-p)Co₂(CO)6-n L_n[n=0,2; L=PPh₃, P(OEt)₃] and (RCH₂C)₂Co₂(CO₄) (PPh₃)₂ on Pt electrode are described. The primary reduction (0 / ?1) and oxidation (+ 1 / 0) steps are considered as a mono-electron process for all clusters. For the clusters (C₅H₅C₂C₆H₄-R-p)Co₂(CO)₆, a good linear relation between reduction potential E_p^red and Hammett constant σ_p of R in the clusters is found. For the clusters (RC₂R')Co₂(CO)₄L₂, their radical anions are extremely unstable at room temperature and fragment into a series of mononuclear species, one of which is (RC₂R')Co(CO)₂PPh₃. The reaction of radical anions of (RC₂R')Co₂(CO)_6–n (PPh₃)_n(n=0,2) with PPh₃ also produces mononuclear species (RC₂R')Co(CO)₂PPh₃ which has been detected by means of cyclic voltammetry and ESR. The influence of R on redox properties of clusters is discussed.     

Mechanism of the photochemistry of Mn2(CO)10 in the presence of para- and ortho-quinones

The photochemical reaction of Mn₂(CO)₁₀ with para- and ortho-quinones has been studied by ESR spectroscopy in tetrahydrofuran, CH₃CN, and in 10⁻¹ M pyridine in toluene. The p-quinone (2,6-di-t-butyl-1,4-benzoquinone) has been found to undergo an electron transfer with photogenerated [Mn(CO)_{6 − n} (S)_n]^. radicals, n = 1–3, 19 e⁻ spcies producing [Mn^I(CO)_{6 − n}(S)⁺_n] · [p-semiquinone anion-radical] ion-pairs, which undergo further photolysis leading to the [Mn^I(CO)_{5 − m}(S)_m(p-semiquinone)] radical-adducts; m = 0–2. These reactions take place alongside the photodisproportionation of Mn₂(CO)₁₀. It has been confirmed that o-quinones, on the other hand, act as good radical-traps, adding oxidatively to the photogenerated Mn(CO)5₅ radicals directly. The overall pattern of photochemical reactions of Mn₂(CO)₁₀ in the presence of coordinating reducible substrates is briefly discussed.     

On the behaviour of Ru(I) and Ru(II) carbonyl acetates in the presence of H2 and/or acetic acid and their role in the catalytic hydrogenation of acetic acid

The reactivity of phosphine substituted ruthenium carbonyl carboxylates Ru(CO)₂(MeCOO)₂(PBu₃)₂, Ru₂(CO)₄(μ-MeCOO)₂(PBu₃)₂, Ru₄(CO)₈(μ-MeCOO)₄(PBu₃)₂ with H₂ and/or acetic acid was investigated by IR and NMR spectroscopy to clarify their role in the catalytic hydrogenation of acetic acid. Evidences were collected to suggest hydride ruthenium complexes as the catalytically active species. Equilibria among ruthenium hydrides and carboxylato complexes take place in the presence of hydrogen and acetic acid, that is in the conditions of the catalytic reaction. Nevertheless the presence of acetic acid reduces the rate of the formation of hydrides. Working at a very high temperature (180°C) polynuclear phosphido hydrides such as [Ru₆(μ-H)₆(CO)₁₀(μ-PHBu)(μ-PBu₂)₂(PBu₃)₂(μ₆-P)] were formed. These phosphido clusters are suggested as the resting state of the catalytic system.Furthermore the bi- or tetranuclear Ru(I) carboxylato complexes react with acetic acid giving a mononuclear ruthenium complex Ru(CO)₂(MeCOO)(μ-MeCOO)(PBu₃), containing a monodentate and a chelato acetato ligands. This complex was spectroscopically characterised. Its identity and structure were confirmed by its reactivity with stoichiometric amount of PPh₃ to give Ru(CO)₂(MeCOO)₂(PBu₃)(PPh₃), a new mononuclear ruthenium carbonyl carboxylate containing two different phosphines, that was fully characterised.     

Dehydrotropylium-Co2(CO)6 ion: generation, reactivity and evaluation of cation stability

The dehydrotropylium–Co₂(CO)₆ ion was generated by the action of HBF₄ or BF₃ ? OEt₂ on the corresponding cycloheptadienynol complex, which in turn has been prepared in four steps from a known diacetoxycycloheptenyne complex. The reaction of the cycloheptadienynol complex via the dehydrotropylium–Co₂(CO)₆ ion with several nucleophiles results in substitution reactions with reactive nucleophiles (N>1) under normal conditions, and a radical dimerisation reaction in the presence of less reactive nucleophiles. Competitive reactions of the cycloheptadienynol complex with an acyclic trienynol complex show no preference for generation of the dehydrotropylium–Co₂(CO)₆ ion over an acyclic cation. DFT studies on the dehydrotropylium–Co₂(CO)₆ ion, specifically evaluation of its harmonic oscillator model of aromaticity (HOMA) value (+0.95), its homodesmotic‐reaction‐based stabilisation energy (≈2.8 kcal mol^?1) and its NICS(1) value (?2.9), taken together with the experimental studies suggest that the dehydrotropylium–Co₂(CO)₆ ion is weakly aromatic.     

Cobalt Chalcogenide Clusters. Synthesis,Characterization and DFT Calculations of [Co4Se2(CO)10] and [Co4Te2(CO)11]. Crystal Structure of [Co8Se4(CO)16(μ‐dppa)2]

The reactions of [Co₂(CO)₈] with E(SiMe₃)₂ (E = Se, Te) in CH₂Cl₂ result in the formation of the compounds [Co₄Se₂(CO)₁₀]> ( 1 ) and [Co₄Te₂(CO)₁₁] ( 2 ), respectively. Both cluster complexes have similar molecular structures in which the cobalt atoms form four‐membered rings with μ₄‐bridging chalcogen atoms (Se and Te) above and below the plane of the metal atoms and the carbonyl ligands as either terminal or μ₂‐bridging ligands. DFT‐calculations for both compounds have been carried out in order to obtain some more information about their electronic distribution. In the presence of the phosphine Ph₂PC≡CPPh₂ (dppa), the reaction of [Co₂(CO)₈] with Se(SiMe₃)₂ leads to the formation of [Co₈Se₄(CO)₁₆(μ‐dppa)₂] ( 3 ). During the reaction two molecules of [Co₂(CO)₈] have been added to the acetylene groups of the dppa ligands, whilst the remaining cobalt atoms coordinate to the phosphorus atoms of the phosphine. In this compounds the selenium atoms act as μ₃‐ligands, bridging the metal atoms bonded to the phosphorus with those bonded to the acetylene groups.     

High Nuclearity Bimetallic Rhodium–Palladium Carbonyl Cluster Complexes. Synthesis and Characterization of Rh6(CO)16[Pd(PBu t 3)]3 and Rh6(CO)16[Pd(PBu t 3)]4

The reaction of Rh₄(CO)₁₂ with Pd(PBu ^t ₃)₂ yielded the high nuclearity bimetallic hexarhodium-tripalladium cluster complex Rh₆(CO)₁₆[Pd(PBu ^t ₃)]₃, 10, in 11% yield. Compound 10 was converted to the hexarhodium-tetrapalladium cluster Rh₆(CO)₁₆[Pd(PBu ^t ₃)]₄, 11, in 62% yield by reaction with an additional quantity of Pd(PBu ^t ₃)₂. Both compounds were characterized crystallographically. Structurally, both compounds consist of an octahedral cluster of six rhodium atoms with sixteen carbonyl ligands analogous to that of the known compound Rh₆(CO)₁₆. Compound 10 also contains three Pd(PBu ^t ₃) groups that bridge three Rh–Rh bonds along edges of the Rh₆ octahedron to give an overall D₃ symmetry to the Rh₆Pd₃ cluster. Compound 11 contains four edge bridging Pd(PBu ^t ₃) groups distributed across the Rh₆ octahedron to give an overall D_2d symmetry to the Rh₆Pd₄ cluster. Each Rh–Pd connection in both compounds contains a bridging carbonyl ligand that helps to stabilize the bond between the Pd(PBu ^t ₃) groups and the Rh atoms. Both compounds can be regarded as Pd(PBu ^t ₃) adducts of Rh₆(CO)₁₆.     

Electronic structure and reactivity of X2Co2(CO)6 (X2  RC2R′, P2, As2) and RxR′ 6-xC6Co2(CO)4 radical anions

Radical anions of the dinuclear species X₂Co₂(CO)₆ (X₂  P₂, As₂, RC₂R′) and R_x,R′_6-xC₆CO₂(CO)₄ have been characterized by electrochemical and ESR methods. The frozen solution spectra could be analysed in unusual detail to evaluate the g and hyperfine tensor components and these data allow definitive statements to be made about the directional nature and orbital character of the unpaired electron density. Most of the RC₂R′Co₂(CO)₆^? radical anions decay to monomeric paramagnetic species.     

Permetalloplumbanes: Preparation of [Pb{Co(CO)3(L)}4] and [Pb{Fe(CO)2(NO)(L)}4].: Complexes containing four transition metal to lead bonds (L = tertiary arsine,phosphine or phosphite).

The sole and unexpected products from the reactions of a variety of lead (II) and lead (IV) compounds with [Co₂(CO)₆(L)₂] complexes (L = tertiary arsine, phosphine, or phosphite) in refluxing benzene solution are the blue, air-stable percobaltoplumbanes [Pb{Co(CO)₃(L)}₄]. These have also been obtained from the reaction of Na[Co(CO)₃(L)] (L  PBu₃ⁿ) with lead (II) acetate which with Na[Fe(CO)₂(NO)(L)] forms the isoelectronic [Pb{Fe(CO)₂(NO)(L)}₄] [L  P(OPh)₃]. The IR spectra of the complexes in the v(CO) and v(NO) regions are consistent with tetrahedral PbCo₄ or PbFe₄ fragments, trigonal bipyramidal coordination about the cobalt or iron atoms and linear PbCoAs, PbCoP, or PbFeP systems. Unlike [Pb{Co(CO)₄}₄], our complexes do not dissociate to [Co(CO)₃(L)]^? or [Fe(CO)₂(NO)(L)]^? ions when dissolved in donor solvents.     

Polymorphism of the dinuclear CoIII–Schiff base complex [Co2(o‐van‐en)3]·4CH3CN (o‐van‐en is a salen‐type ligand)

Reactions of Co(OH)₂ with the Schiff base bis(2‐hydroxy‐3‐methoxybenzylidene)ethylenediamine, denoted H₂(o‐van‐en), under different conditions yielded the previously reported complex aqua[bis(3‐methoxy‐2‐oxidobenzylidene)ethylenediamine]cobalt(II), [Co(C₁₈H₁₈N₂O₄)(H₂O)], 1 , under anaerobic conditions and two polymorphs of [μ‐bis(3‐methoxy‐2‐oxidobenzylidene)ethylenediamine]bis{[bis(3‐methoxy‐2‐oxidobenzylidene)ethylenediamine]cobalt(III)} acetonitrile tetrasolvate, [Co₂(C₁₈H₁₈N₂O₄)₃]·4CH₃CN, i.e. monoclinic 2 and triclinic 3 , in the presence of air. Both novel polymorphs were chemically and spectroscopically characterized. Their crystal structures are built up of centrosymmetric dinuclear [Co₂(o‐van‐en)₃] complex molecules, in which each Co^III atom is coordinated by one tetradentate dianionic o‐van‐en ligand in an uncommon bent fashion. The pseudo‐octahedral coordination of the Co^III atom is completed by one phenolate O and one amidic N atom of the same arm of the bridging o‐van‐en ligand. In addition, the asymmetric units of both polymorphs contain two acetonitrile solvent molecules. The polymorphs differ in the packing orders of the dinuclear [Co₂(o‐van‐en)₃] complex molecules, i.e. alternating ABABAB in 2 and AAA in 3 . In addition, differences in the conformations, the positions of the acetonitrile solvent molecules and the pattern of intermolecular interactions were observed. Hirshfeld surface analysis permits a qualitative inspection of the differences in the intermolecular space in the two polymorphs. A knowledge‐based study employing Full Interaction Maps was used to elucidate possible reasons for the polymorphism.     

Synthesis of large palladium clusters. The preparation of Pd38(CO)28(PR3)12 (R = Et,Bun) and Pd34(CO)24(PEt3)12

Several methods for the synthesis of the Pd₃₈(CO)₂₈L₁₂ cluster (L = PEt₃) by treatment of Pd₁₀(CO)₁₂L₆ with CF₃COOH-Me₃NO, CF₃COOH-H₂O₂, Pd(OAc)₂-Me₃NO, and Pd₂(dba)₃ mixtures (dba is dibenzylideneacetone) were proposed. The tri-n-butylphosphine analog, Pd₃₈(CO)₂₈(PBu₃)₁₂, was synthesized by the reaction of Pd₁₀(CO)₁₄(PBu₃)₄ with Me₃NO. The reaction of Pd₄(CO)₅L₄ with Pd₂(dba)₃ yields clusters with an icosahedral packing of the metal atoms, Pd₃₄(CO)₂₄L₁₂ and Pd₁₆(CO)₁₃L₉.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 167–170, January, 1995.     

Synthesis and thermal transformations of molecular complexes of bis[tris(trifluoromethyl)germyl]mercury(ii witho-quinones

Stable molecular complexes of bis[tris(trifluoromethyl)germyl]mercury(II) Hg[(CF₃)₃Ge]₂ (1) witho-quinones (3,6-di-tert-butylbenzoquinone-1,2 (2), 3,6-di-tert-butyl-4,5-dimethoxybenzoquinone-1,2 (3), and 1,4,5,7-tetra-tert-butyldibenzo[1,4]dioxin-2,3-dione (4)) have been synthesized and characterized by elemental analysis and IR and electronic absorption spectroscopies. Depending on the ratio between the starting reactants, the reactions ofo-quinones with1 gave complexes of the composition R₂Hg · Q (5,7,9) or R₂Hg · Q₂ (6,8,10), where Q=2 (5,6),3 (7,8),4 (9,10); R=Ge(CF₃)₃. According to the spectral data, the molecule ofo-quinone in R₂Hg · Q acts as a neutral ligand, whereas the second molecule ofo-quinone in R₂Hg · Q₂ is not coordinated to1. It has been found by ESR that thermolysis of polycrystalline samples of complexes6 and10 involves intermediate formation of radical pairs and finally yields paramagnetico-semiquinone complexes, SQGe(CF₃)₃, which are typical products of one-electron oxidation of Organometallic compounds byo-quinones.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1568–1573, August, 1995.The authors wish to thank M. A. Lopatin for his help in recording the electronic absorption spectra.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No. 93-03-18369).     

Bisphosphoranylacetylene und der Cobaltkomplex Co2(CO)6{[(C2H5)2N]2PF2CCPF2[N(C2H5)2]2}

Bisphosphoranylacetylenes and the Cobalt Complex Co₂(CO)₆{[(C₂H₅)₂N]₂PF₂C?CPF₂[N(C₂H₅)₂]₂} Synthesis and properties of bis[difluorobis(diethylamino)phosphoranyl]acetylene, 2 , bis(difluorodimorpholinophosphoranyl)acetylene, 4 , and bis(trifluorodiethylaminophosphoranyl)-acetylene, 6 , are described. With Co₂(CO)₈ 2 forms the coordination compound hexacarbonyl-μ-η-bis-[difluorobis(diethylamino)phosphoranyl]acetylene-dicobalt(Co? Co), 7 . The results of the X-ray structural analysis of 2 and 7 are reported.     

Formation of Alkyne Bridged Multicobalt Carbonyl Complexes with Tris(2‐Thienyl)Phosphine or Bis(Trimethylsilylethynyl)Phenylphosphine Ligand

Treatment of Co₄(CO)₁₂ with an excess of trimethylsilylacetylene (TMSA) in the presence of tri(2‐thienyl)phosphine in THF at 25 °C for 2 hours yielded six compounds. Two pseudo‐octahedral, alkyne‐bridged tetracobalt clusters, [Co₄(μ₄‐η²‐HC≡CSiMe₃)(CO)₁₀(μ‐CO)₂] ( 4 ) and [Co₄(μ₄‐η²‐HC≡CSiMe³)‐(CO)₉(μ‐CO)₂{P(C₄H₄S)₃}] ( 6 ), along with an alkyne‐bridged dicobalt complex, [Co₂(CO)₅(μ‐HC≡CSiMe₃)‐{P(C₄H₄S)₃}] ( 5 ), were obtained as new compounds. The addition of the thienylphosphine ligand, in fact, facilitates the reaction rate. Reaction of an alkyne‐bridged dicobalt complex, [(η²‐H‐C≡C‐SiMe₃)Co₂(CO)₆] ( 3 ), with a bi‐functional ligand, PPh(‐C≡C‐SiMe₃)₂, yielded an unexpected six‐membered, cyclic compound, {(Ph)(Me₃Si‐C≡C)P‐[(η²‐C≡C‐SiMe₃)Co₂(CO)₅]}₂ ( 7 ). All of these new compounds were characterized by spectroscopic means; the solid‐state structures of ( 5 ), ( 6 ) and ( 7 ) have been established by X‐ray crystallography.     

Synthesis of poly-yne polymer containing platinum and silicon atoms in the main chain by oxidative coupling and its reactions with transition-metal carbonyl complexes

The platinum poly-yne polymer, [? C?C? SiMe₂? C?C? Pt(PBu₃)₂? C?C? SiMe₂? C?C? ]_n (2), was synthesized by the oxidative coupling of a silicon–platinum monomer, trans-(PBu₃)₂Pt(C?C? SiMe₂–C?CH)₂ (1). The reaction of platinum poly-yne polymer 2 with dicobaltoctacarbonyl gave μ-coordinated complexes, {[? C?C? SiMe₂? C?C? Pt(PBu₃)₂? C?C? SiMe₂? C?C? ] [Co₂(Co)₆]₂}_n (4). the electric conductivity of iodine adducts of the polymer complexes 4 was 3.0×10^?5 S cm^?1. As an aid to spectroscopic characterization of the polymer complex 4, a model complex, {trans-[(PBu₃)₂Pt? (C?C? SiMe₂? C?CH)₂]} {[Co₂(CO)₆]₂} (3), was also prepared by the reaction of 1 with dicobaltocatacarbonyl. Selective coordination of Co₂(CO)₆ groups to ? SiMe₂? C?C C?C? Si(Me)₂? Moieties and coordinative inertness of the Pt? C?C? moieties were confirmed by comparison of the NMR spectra of 3 with those of 4. All new compounds have been characterized by analytical and spectral analysis (IR, ¹H NMR).     

Elektronenreiche übergangsmetallkomplexe : IV. Dien-bis(phosphin)-molybdändicarbonyle

Dienes can replace the acetonitrile in (CH₃CN)₂Mo(PBu₃)₂,(CO)₂ or acetoni- trile and the one phosphine trans to the CO group in (CH₃CN)Mo(PBu₃)₃(CO)₂ under mild conditions. IR-, H NMR, ¹³C NMR and electronic spectra of the new (diene)Mo(PBu₃)₂(CO)₂ complexes are discussed and compared with similar compounds of other transition metals.     

Synthesen und Strukturen neuer amido- und imidoverbrückter Cobaltcluster: [Li(THF)2]3[Co3(μ2-NHMes)3Cl6] (1), [Li(DME)3]2[Co18(μ4-NPh)3(μ3-NPh)12Cl3] (2), [Li(DME)3]2[Co6(μ4-NPh)(μ2-NPh)6(PPh2Et)2] (3) und [Li(THF)4][Co8(μ3-NPh)6(μ2-NPh)3(PPh3)2] (4)

Syntheses and Crystal Structures of new Amido- und Imidobridged Cobalt Clusters: [Li(THF)₂]₃[Co₃(μ₂-NHMes)₃Cl₆] (1), [Li(DME)₃]₂[Co₁₈(μ₄-NPh)₃(μ₃-NPh)₁₂Cl₃] (2), [Li(DME)₃]₂[Co₆(μ₄-NPh)(μ₂-NPh)₆(PPh₂Et)₂] (3), and [Li(THF)₄][Co₈(μ₃-NPh)₆(μ₂-NPh)₃(PPh₃)₂] (4) The reactions of cobalt(II)-chloride with the lithium-amides LiNHMes and Li₂NPh leads to an amido-bridged multinuclear complex [Li(THF)₂]₃[Co₃(μ₂-NHMes)₃Cl₆] ( 1 ) as well as to the imido-bridged cobalt cluster [Li(DME)₃]₂[Co₁₈(μ₄-NPh)₃(μ₃-NPh)₁₂Cl₃] ( 2 ). In the presence of tertiary phosphines two imido-bridged cobalt clusters [Li(DME)₃]₂[Co₆(μ₄-NPh)(μ₂-NPh)₆(PPh₂Et)₂] ( 3 ) and [Li(THF)₄][Co₈(μ₃-NPh)₆(μ₂-NPh)₃(PPh₃)₂] ( 4 ) result. The structures of 1 – 4 were characterized by X-ray single crystal structure analysis.     

The Photochemistry of the (Cycloalkene)(hydro)(trispyrazolylborato)iridium Complexes [Ir(η4-cod)(TpMe2)] and [Ir(η2-coe)H2(TpMe2)]: the Formation of [IrH4(TpMe2)] and [Ir(CO)H2(TpMe2)]

Photolysis of [Ir(η²-coe)H₂(Tp^Me2)] ( 1 ; Tp^Me2=hydrotris(3,5-dimethylpyrazolyl)borato, coe=(Z)-cyclooctene) in CH₃OH gives a mixture of [IrH₄(Tp^Me2)] ( 4 ) and [Ir(CO)H₂(Tp^Me2)] ( 5 ) in a ca. 1 : 1 ratio. Mass-spectral analysis of the distillate of the reaction mixture at the end of the photolysis shows the presence of coe. When pure CD₃OD is used as solvent, the deuteride complexes [IrD₄(Tp^Me2)] ((D₄)- 4 ) and [Ir(CO)D₂(Tp^Me2)] ((D₂)- 5 ) are obtained. Also the photolysis of [Ir(η⁴-cod)(Tp^Me2)] ( 3 ) (cod=cycloocta-1,5-diene) gives 4 and 5 . A key feature of this photoreaction is the intramolecular dehydrogenation of cod with formation of cycloocta-1,3,5-triene, detected by mass spectroscopy at the end of the photolysis. Labeling experiments using CD₃OD show that the hydrides in 4 originate from MeOH. When ¹³CH₃OH is used as solvent, [Ir(¹³CO)H₂(Tp^Me2)] is formed demonstrating that CH₃OH is the source of the CO ligand. The observation that the photolysis of both 1 and 3 give the same product mixture is attributed to the formation of a common intermediate, i.e., the coordinatively unsaturated 16e⁻ species {IrH₂(Tp^Me2)}.     

Reaction of (η5‐C5H5)Fe(CO)2I with Anionic Bidentate Phosphine Ligands PPh2(o‐C6H4NHLi) or PPh2(o‐C6H4OLi)

The o‐substituted hybrid phenylphosphines, PPh₂(o‐C₆H₄NH₂) and PPh₂(o‐C₆H₄OH), could be deprotonated with LDA or n‐BuLi to yield PPh₂(o‐C₆H₄NHLi) and PPh₂(o‐C₆H₄OLi), respectively. When added to a solution of (η⁵‐C₅H₅)Fe(CO)₂I at room temperature, these two lithiated reagents produce a chelated neutral complex 1 (η⁵‐C₅H₅)Fe(CO)[C(O)NH(o‐C₆H₄)PPh₂‐C,P‐η²] for the former and mainly a zwitterionic complex 2 , (η⁵‐C₅H₅)Fe⁺(CO)₂[PPh₂(o‐C₆H₄O^?)] for the latter. Complex 1 could easily be protonated and then decarbonylated to give 4 [(η⁵‐C₅H₅)Fe(CO){NH₂(o‐C₆H₄)PPh₂‐N,P‐η²}⁺]. Complexes 1 and 4‐I have been crystallographically characterized with X‐ray diffraction.     

Synthesis of Co2Pt, Co2Pd and MoPd2 mixed-metal clusters with the P–N–P assembling ligands (Ph2P)2NH (dppa) and (Ph2P)2NMe (dppaMe). Crystal structure of [Co2Pt(μ3-CO)(CO)6(μ-dppa)]

Heterometallic triangular platinum–cobalt, palladium–cobalt and palladium–molybdenum clusters stabilized by one or two bridging diphosphine ligands such as Ph₂PNHPPh₂ (dppa) or (Ph₂P)₂NMe (dppaMe) or by mixed ligand sets Ph₂PCH₂PPh₂ (dppm)/dppa have been prepared with the objectives of comparing the stability and properties of the clusters as a function of the short-bite diphosphine ligand used and of the metal carbonyl fragment they contain. Ligand redistribution reactions were observed during the purification of [Co₂Pd(μ₃-CO)(CO)₄(μ-dppa)(μ-dppm)] (4) by column chromatography with the formation of [Co₂Pd(μ₃-CO)(CO)₄(μ-dppm)₂] and the dinuclear complex [(OC)₂ Cl] (5). The latter was independently prepared by reaction of [Pd(dppa-P,P′)₂](BF₄)₂ with Na[Co(CO)₄]. Attempts to directly incorporate the ligand (Ph₂P)₂N(CH₂)₃Si(OMe)₃ (dppaSi) into a cluster or to generate it by N-functionalization of coordinated dppa were unsuccessful, in contrast to results obtained recently with related clusters. The crystal structure of [Co₂Pt(μ₃-CO)(CO)₆(μ-dppa)] (1) has been determined by X-ray diffraction.     

Heterobimetallic complexes CpNiCo(CO)2(PPh3)(PhC2C6H4-R -p): their synthesis,electrochemistry and ESR

Three new heterobimetallic acetylene complexes CpNiCo (CO)₃ (PPh₃) (PhC₂C₄H₄-R-p) [R = H (2), Br (3), COCH₂ (4)] have been synthesized in suitable yield (31–47%) via the reaction of (PhC₂C₃H₄-R-p)CO₂(CO)₅ PPh₂ with nickelcene in n-octane. The complex CpNiCo(CO)₃ (Ph₂C₃) (1) has also been obtained in 12% by the reaction of (Ph₂C₂) Co₂ (CO)₄ with nickelcene. The complexes have been characterized by elemental analysis, IR and ¹H NMR. Electrochemical study of redox couples of these complexes was presented by using cyclic voltammetry on Pt electrodes in acetone. At room temperature, all complexes underwent electrochemically reversible or guasi-reversible oneelectron oxidation or reduction to the stable radicals. The radical anions of the complexes could be easily detected by ESR method in situ electrolysis in the THF solution. The isotropic parameters, <a>CO=2.20mT, <g> = 2.052 for the radical anion of complex 1, <a>CO= 2.20 mT, <a>P = 1.42 mT, <g>=2.057 for the radical anion of complex 2, might indicate that NiCoC₂ framework is a delocalized unit and the ligand obitals in the complex have more contribution to the LUMO of the complex.