Tetracobalt Cluster Research Articles

A tetracobalt(II) cluster with a two vertex truncated dicubane topology endogenously supported by carboxylate-based (2-pyridyl)methylamine ligands: magneto-structural and DFT studies.

A reaction between CoCl2 and L3-(CO2-)2 (2 : 1 stoichiometry) in CH3OH affords a discrete complex [CoII4-{L3-(CO2-)2}2(μ3-OCH3)2(CH3OH)2(H2O)2Cl2] (1) [L3-(CO2-)2 = 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)]. The structure of 1 reveals two terminal mononuclear CoII{L3-(CO2-)2}Cl units connected by a dimeric CoII2(μ3-OCH3)2(CH3OH)2(H2O) unit present in the centre through two methoxo (μ3-OCH3)- and two carboxylate (μ-1,1-OCO-) bridges affording a tetranuclear coordination cluster of Co(II) with a defective dicubane topology. In 1, Co1 (terminal) has distorted octahedral CoIIN2O3Cl and the central Co2 has CoIIO6 coordination. Such coordination arrangements afford the observed topology. Variable-temperature magnetic studies reveal anti-ferromagnetic coupling in 1. Three magnetic exchange interactions (one anti-ferromagnetic and two ferromagnetic: J1 = +3.3 cm-1 (Co⋯Co 3.176 Å; μ-1,1-OCO- and μ3-OCH3 bridges), J2 = -2.5 cm-1 (Co⋯Co 3.228 Å; μ-1-OCO- and μ3-OCH3 bridges) and J3 = +10.6 cm-1 (Co⋯Co 3.084 Å; two μ3-OCH3 bridges)) have been identified, with the inclusion of the orbital reduction parameter (α = Aκ = 1.38), spin-orbit coupling (λ = -158 cm-1) and axial distortion (energy gap Δ = -975 cm-1 between singlet and doublet levels), rationalized by density functional theory (DFT) calculations.

New tetracobalt cluster compounds for electrocatalytic proton reduction: syntheses, structures, and reactivity.

Reaction of Co2(CO)8 and 1,3-propanedithiol in a 1:1 molar ratio in toluene affords a novel tetracobalt complex, [(μ2-pdt)2(μ3-S)Co4(CO)6] (pdt = -SCH2CH2CH2S-, 1), which possesses some of the structural features of the active site of [FeFe]-hydrogenase. Carbonyl displacement reaction of complex 1 in the presence of mono- or diphosphine ligands leads to the formation of [(μ2-pdt)2(μ3-S)Co4(CO)5(PCy3)] (2) and [(μ2-pdt)2(μ3-S)Co4(CO)4(L)] [L = Ph2PCH=CHPPh2, 3; Ph2PCH2N(Ph)CH2PPh2, 4; Ph2PCH2N(iPr)CH2PPh2, 5]. Complexes 1-5 have been fully characterized by spectroscopy and single-crystal X-ray diffraction studies. Cyclic voltammetry has revealed that complexes 1-5 show a reversible first reduction wave and are active for electrocatalytic proton reduction in the presence of CF3COOH. Protonation reactions have been monitored by (31)P and (1)H NMR and infrared spectroscopies, which revealed the formation of different protonated species. The mono-reduced species of 1-5 have been spectroscopically characterized by EPR and spectro-electro-infrared techniques.

One-dimensional hybrid polyoxometalate based on tetra-cobalt sandwiched phosphotungstate units

A one-dimensional polyoxotungstate, Na(H2O)2[Co(en)3]3H3[Co4(H2O)2(B-α-PW9O34)2]·10.5H2O(en=ethylenediamine), was hydrothermally synthesized and characterized by single crystal X-ray diffraction,infrared spectroscopy,thermogravimetric analysis,and powder X-ray diffraction, respectively.The structure was constructed from the[Co4(H2O)2(B-α-PW9O34)2]- units, in which a tetra-cobalt cluster core was sandwiched between two PW9O349- polyanions,that were further connected via Na+ cations forming a one-dimensional chain structure.

Hydrogen-Bonded Helical Array, Sodium-Ion-Mediated Head-to-Tail Chain, and Regular Ionic Bilayer: Structural Diversities of p-Sulfonatothiacalix[4]arene Tetranuclear Cluster Units

Exploration into the supramolecular chemistry of p-sulfonatothiacalix[4]arene (TCAS) tetranuclear clusters with methylviologen dihexafluorophosphate (MV(PF6)2) and 4,4′-diaminodiphenyl ether (4,4′-Dadpe) has resulted in three interesting structural motifs: {[MV][Co4(TCAS)(μ4-SO4)(H2O)8]·8H2O}n (1), {[Na(H2O)2][Co4(TCAS)(μ5-SO4)(H2O)7(4,4′-HDadpe)]·6H2O}n (2), and {[MV][Cu4(TCAS)(μ4-SO4)(H2O)4]·9H2O}n (3). In complex 1, the assembly of TCAS tetracobalt(II) clusters driven by multiple hydrogen bonding forms supramolecular helices along three crystallographic axes, while TCAS tetracobalt(II) clusters in complex 2 have assembled into a rare head-to-tail chain mediated by sodium ions in the presence of 4,4′-Dadpe. Complex 3 features a regular ionic bilayer structure, in which TCAS tetracopper(II) clusters and MV2+ cations form negative and positive layers, respectively.

Preparations of cobalt-containing phosphines and reactions toward dicobalt octacarbonyl

Treatments of bis(diphenylphosphino)methylene (dppm) bridged dicobalt complex, Co 2(CO) 6(μ-Ph 2PCH 2PPh 2), with alkynes, Ph 2PCCR ( 2: R=CMe 3; 3: R=SiMe 3), at 60 °C in THF for 6 h gave alkyne-bridged complexes [(μ-Ph 2PCH 2PPh 2)Co 2(CO) 4][(μ-Ph 2PCCR)] ( 4: R=CMe 3; 5: R=SiMe 3). Further reactions of 4 and 5 with Co 2(CO) 8 at 80 °C in toluene for 3 h resulted in the formations of unexpected tetra-cobalt clusters, [(μ-Ph 2PCH 2PPh 2)(μ-PPh 2)Co 4(CO) 7(μ 4,μ 2-CCR)] ( 6: R=CMe 3; 7: R=SiMe 3). All these compounds were characterized by spectroscopic means; 5, 6 and 7 were studied by X-ray diffraction methods as well. The structure of 6 (or 7) can be looked upon as a tetra-cobalt arachno cluster being coordinated with phosphine ligands and linked by organic moiety.

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

AbstractTreatment 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.

The reaction of Co 2(CO) 8 and Co 4(CO) 12 with the dipropargylamine [(HCCCMe 2) 2NMe]. : Synthesis and crystal structure of the complex Co 4(CO) 10(μ-CO)[H 2CCC(Me) 2N(Me)C(Me 2)C(μ 4-C)

The reaction of Co 4(CO) 12 with the dipropargylamine [(HCCCMe 2) 2NMe] (ligand A) leads to moderate yields of the title complex (complex 4). An X-ray analysis has shown that this tetranuclear complex is a ‘spiked’ (or metallo-ligated) triangular cluster containing one molecule of ligand A partially cyclized and coordinated to all four metal atoms. Complex 4 is the first tetracobalt cluster showing this type of structure which was previously found only for two M 2Ni 2 (M=Fe, Ru) isopropenylacetylene derivatives. Reaction pathways leading to the formation of complex 4 are discussed.

Electrochemical behaviour, IR spectroelectrochemistry and theoretical studies of tetracobalt carbonyl cluster complexes with a facial cyclooctatetraene ligand

The redox properties of some cluster complexes with a facial cyclooctatetraene (cot) ligand were investigated using electrochemical and IR spectroelectrochemical techniques. Reduction of [Co4(CO)3(μ3-CO)3(μ3-C8H8)L2] 1 (L2 = η4-C8H8), 2 (L2 = η4-C6H8), and 3 (L2 = η4-6,6-Ph2C6H4) occurs in CH2Cl2 or THF solution in two consecutive one-electron electrochemically reversible steps. Both one- and two-electron primary reduction products are unstable on a longer timescale; eventually degradation (decapitation) of the tetranuclear clusters takes place, to give the stable anion [Co3(CO)3(μ-CO)3(μ3-C8H8)]−5. The electronic structure of 1, 2, the octacarbonyl derivative [Co4(CO)5(μ3-CO)3(μ3-C8H8)] 4, their monoanions, dianions and 5 was investigated using ab initio DFT MO calculations. The calculations showed the monoanions to be relatively stable compared to the neutral parent clusters, the relative stability depending on the type of apical ligand and reflecting its bonding capabilities, namely the possibility of ring slippage for a cot ring. Hence, an η4 → η2 haptotropic shift of the apical C8H8 ring is calculated to occur during the reduction of 1 to give the dianion [1]2−. In marked contrast, in complex 4 the haptotropic shift involves the facial, η8-coordinated cot, which is pushed into an η6-coordination in the optimized structure of the two-electron reduction product [4]2−. In all the cases studied, the second reduction step is however not favored energetically and reinforces the structural and electronic effects caused by the first reduction. The observed decapitation of the anionic tetranuclear cluster complexes can be traced to an ubiquitous weakening of the Coapical–Cobasal bonds.

Redox Chemistry of [Co4(CO)3(μ3-CO)3(μ3-C7H7)(η5-C7H9)] – Reversible Carbon−Carbon Coupling versus Metal Cluster Degradation

Chemical reduction of the tetracobalt cluster complex [Co4(CO)3(μ3-CO)3(μ3-C7H7)(η5-C7H9)] (3), followed by addition of [PPh4]Br, gives the complex [{Co4(CO)3(μ3-CO)3(μ3-C7H7)}2{μ-η4:η4-(C7H9)2}]2− as a mixture of two diastereomers [4A]2− and [4B]2− in high yield. The crystal structure of [4A]2−[PPh4]2·1.5C7H8 has been determined and confirms the reductive coupling of two Co4 cluster coordinated apical cycloheptadienyl rings to form a bridging bicycloheptyl-3,5,3′,5′-tetraene ligand. Reduction of 3 with Li[HBEt3] and subsequent treatment with aqueous [NnBu4]Cl results in the formation of [Co4(CO)3(μ3-CO)3(μ3-C7H7)(C7H10)]− [5]−. Addition of [(η-C6H6)Ru(NCMe)3][BF4]2 after the borohydride reduction gives [Ru(η-C6H6)Co3(CO)3(μ3-CO)3(μ3-C7H7)] (6), a product derived from reductive Co4 cluster degradation. A detailed electrochemical and spectro-electrochemical study of the redox behaviour of 3 and [4]2− has been carried out. The complex potential current response of 3 is rationalized in terms of the formation of the radical anion [3]− as the primary intermediate, which may be reversibly reduced further to give the much more stable [3]2− and then [3]3−. Dimerization of [3]− to give [4]2− occurs by formation of a new carbon−carbon bond between the apical C7H9 ligands. The two redox-active moieties in [4]2− behave as independent, non-interacting redox centres. The oxidized form 4 is unstable and dissociates back to 3 almost quantitatively, thus completing a redox cycle characteristic of a “molecular battery”. The homogeneous rate constant for dimerization has been evaluated as kDIM (2 [3]− [4]2−) = 0.30 ± 0.05 mM−1 s−1.

Reductive Degradation of Tetracobalt Cluster Complexes with a Facial C8H8 Ligand – Synthesis of [Co3(CO)3(μ3-CO)3(μ3-C8H8)]– and [Ru(C5Me5)Co3(CO)3(μ3-CO)3(μ3-C8H8)

Chemical reduction of the cluster complexes [Co4(CO)3(μ3-CO)3(μ3-C8H8)L2] 3 (L2 = C8H8), 4 (L = CO), 5 (L2 = C6H8) and 6 (L2 = 6,6-Ph2C6H4) gives the trinuclear anion [Co3(CO)3(μ2-CO)3(μ3-C8H8)]– (7) in high yield. It is proposed that formation of 7 occurs via degradation of the radical anions [3]– – [6]–, which can be generated reversibly via cyclic voltammetry. The anion 7 is stabilised by the facial C8H8 ligand and does not degrade further. Reaction of 7 with [(C5Me5)Ru(NCMe)3][BF4] results in the formation of [Ru(C5Me5)Co3(CO)3(μ3-CO)3(μ3-C8H8)] (8). The crystal structures of [NEt4]+-7, [(C5H5)2Co]+-7, and 8 were determined. In 7 and 8, the cyclooctatetraene ligand is coordinated to the Co3 face of the cluster in the facial mode.

Reductive Degradation of Tetracobalt Cluster Complexes with a Facial C8H8 Ligand – Synthesis of [Co3(CO)3(μ3-CO)3(μ3-C8H8)] and [Ru(C5Me5)Co3(CO)3(μ3-CO)3(μ3-C8H8)

Reductive Degradation of Tetracobalt Cluster Complexes with a Facial C8H8 Ligand – Synthesis of [Co3(CO)3(μ3-CO)3(μ3-C8H8)] and [Ru(C5Me5)Co3(CO)3(μ3-CO)3(μ3-C8H8)

Tetracobalt Complexes with Co3 Face-Capping Cycloheptatrienyl and Cyclooctatetraene Ligands

The novel tetracobalt cluster complexes1 and 2, which contain facial CnHn ligands, have been synthesized and their crystal structures determined. The apical C8H8 ligand can be selectively substituted by a number of other ligands. In the solid state, the hydrogen atoms of the cycloheptatrienyl and cyclooctatetraene ligands take part in intra- and intermolecular hydrogen-bonding interactions of the C−H⋅⋅⋅O type.

PhPMe2 ligand substitution in the tetracobalt cluster Co4(CO)10(μ4-PPh)2: X-ray diffraction structure of Co4(CO)8(PPhMe2)2(μ4-PPh)2

The thermal substitution chemistry of the tetracobalt cluster Co4(CO)10(μ4-PPh)2 with the phosphine ligand PhPMe2 (2.5 equiv) has been explored and found to afford the bis(phosphine)-substituted cluster Co4(CO)8(PPhMe2)2(μ4-PPh)2 as the major reaction product. The regiochemistry and stereoselectivity exhibited by the two phosphine ligands in Co4(CO)8(PPhMe2)2(μ4-PPh)2 have been unambiguously established by X-diffraction analysis as having a 1,3-cis orientation. Co4(CO)8(PPhMe2)2(μ4-PPh)2 crystallizes in the monoclinic space group P21/n,a=10.314(1) A,b=18.051(3) A,c=21.313(2) A, β=90.10(1)°,V=3968.0(8) A3,Z=4,dcalc=1.590 g cm−3;R=0.051,Rw=0.042 for 4987 observed reflections withI>3σ(I). Generalizations concerning the stereochemical disposition of two P-ligands about the Co4(CO)8P2(μ4-PPh)2 (where P=phosphine or phosphite) polyhedron are discussed with respect to the cone angle of the P-ligand and its steric interactions with the capping phenylphosphinidene group.

Synthesis of tetracobalt clusters from dicobalt alkyne complexes

The room-temperature reactions of [Co2(µ-PhCCH)(CO)6] or [Co2(µ-MeCCMe)(CO)6] with Ph2PCCPh (L) afford [Co2(µ-PhCCH)(CO)5(η1-L)] or [Co2(µ-MeCCMe)(CO)5(η1-L)] and [Co2(µ-MeCCMe)(CO)4(η1-L)2], respectively, in which L is bound via the phosphine functionality. The structure of [Co2(µ-MeCCMe)(CO)4(η1-L)2] has been established by X-ray crystallography and comprises two Co(CO)2(η1-L) units bridged by a MeCCMe ligand. Reactions of [Co2(µ-R1CCR2)(CO)5(η1-L)] with [Co2(CO)8] afford [Co2(µ-R1CCR2)(CO)5(µ-η1:η2-L)Co2(CO)6](R1= Ph, R2= H; R1= R2= Me), in which L is bound to the Co2(CO)6 unit via the alkyne functionality. Pyrolysis of [Co2(µ-MeCCMe)(CO)5(µ-η1:η2-L)Co2(CO)6] results in phosphorus–carbon bond cleavage and cobalt–cobalt and carbon–carbon bond formation to afford a butterfly cluster [Co4{µ4-η3-PhCCC(Me)C(Me)C(O)}(µ-PPh2)(µ-CO)6], whose structure has been established by X-ray diffraction.

Reactions of di- and poly-nuclear complexes. 12 . Synthesis and thermal decomposition reactions of tetranuclear clusters [Co 4Cp 2(CO) 5- nL n(RC 2R′)] (L = PPh 2H; n = 0, 1 or 2) (R = R′ = CF 3, C 6F 5, C 6H 5 or Me; R = H, R′ = CF 3).

The dinuclear complexes [(CO) 3 Co(μ-RC 2R′)C o(CO) 3] (R = R′ = CF 3, C 6F 5, C 6H 5 or Me; R = H, R′ = CF 3) react with [CpCo(CO) 2] in refluxing octane to afford tetranuclear complexes [Co 4Cp 2(CO) 4(μ-CO)(μ-RC 2R′)] ( 2) in good yield; these tetracobalt clusters have been characterised by spectroscopic methods. Thermolysis of [Co 4 Cp 2(CO) 5(RC 2R′)] ( 2) and of the related substituted complexes [Co 4Cp 2(CO) 4- n (μ-CO)(PPh 2H) n (CF 3C 2CF 3)] results mainly in the loss of carbonyl and the formation of trinuclear clusters [Co 3Cp 3(μ 3-CO)(μ 3-η 2-RC 2R′)] ( 3) and [Co 3Cp 2(CO) 2(μ-PPh 2)(μ 3-η 2-CF 3C 2CF 3)] ( 7), respectively. The conversion of clusters 3 and 7 into dialkylidyne complexes has been examined. The spectroscopic data for the new complexes are discussed and mechanisms proposed to account for their formation.

Reactivity of tri- and tetra-nuclear ethylidyne cyclopentadienylcobalt clusters towards protonic acids

The bis(μ 3-ethylidyne) tricobalt cluster [(CpCo) 3(μ 3-CCH 3) 2] ( 1b) is protonated by trifluoroacetic acid to give the dicobalt edge-protonated cation [H(CpCo) 3(μ 3-CCH 3) 2] + [ lb + H] +. Protonation of the μ 3-ethylidyne tetracobalt cluster hydride [H(CpCo) 4(μ 3-CCH 3)] ( 3) takes place in two consecutive steps. At low temperature [H 2(CpCo) 4(μ 3-CCH 3)] + [ 3 + H] + is formed first, and is then slowly converted into [H 3(CpCo) 4(μ 3-CCH 3)] 2+ [ 3 + 2H] 2+ by an excess of acid. As judged by the 1H NMR data and the crystal structure of [ 3 + X] +[(CF 3COO) 2X] − (X  H or D) the endo hydrogens in [ 3 + H] + and [ 3 + 2H] 2+ occupy μ 3-(Co 3) face capping hydridic positions. The cations [ 1b + H] + and [ 3 + H] + show hydride fluxionality in solution, which in the case of [ 3 + H] + can be frozen out on the NMR timescale at low temperature (ΔG ≠ (203 K) = 40.8 kJ/mol). The structure of [ 3 + X] + [(CF 3COO) 2X] − (X  H or D) was determined by X-ray crystallography. One of the hydrides/deuterides is located on the crystallographic mirror plane, capping a tricobalt face of the cluster cation. The other endo hydrogen atom is believed to be disordered between the other two μ 3-(Co 3) sites, which are related by space group symmetry. Deuteronation of 3 shows a strong normal kinetic deuterium isotope effect. From the temperature independence of the 1H NMR spectrum of [ 3 + 2D] 2+ a non-fluxional solution structure can be inferred. In all the systems studied, hydridic (μ 2- or μ 3-) sites are thermodynamically preferred to possible isomeric agostic CoHC or Co 2HC sites for the endo hydrogens. Agostic interactions cannot, however, be ruled out in transient intermediates during the course of the protonations.

Site selectivity and competitive CO attack in Co4(CO)10(μ4-PPh)2 using methanolic [Et4N][OH

The reaction between the tetracobalt cluster Co4(CO)10(μ4-PPh)2 (1) and [Et4N][OH] (1.1 equivalents of a 1.3 M solution in MeOH) has been examined in THF at -78°C. Low-temperature IR analysis reveals the presence of both the hydroxycarbonyl cluster [Co4(CO)9(μ4-PPh)2(CO2H)-] [2-] and the methoxycarbonyl cluster [Co4(CO)9(μ4-PPh)2(CO2Me)-] [3-] as a result of hydroxide and methoxide attack, respectively, on a terminal carbonyl group in 1. IR band-shape analysis indicates that [2-] and [3-] exist in a 77:23 ratio at -72°C. Addition of excess [Li+] (as [CF3SO3][Li]) to solutions of [2-] and [3-] affords [3-] in quantitative yield at -72°C. The thermal stability and reactivity of these anionic clusters are discussed and comparisons made to the structural similar formyl and acetyl clusters derived from 1.

Reaction of Ph 2PH with the tetracobalt cluster Co 4(CO) 10(μ 4-PPh) 2. Kinetic studies of sequential CO replacement and X-ray crystal structure of Co 4(CO) 8(μ 4-PPh) 2(Ph 2PH) 2

The kinetics for the sequential substitution of CO on the tetracobalt cluster Co 4(CO) 10(μ 4-PPh) 2 have been investigated for the ligand Ph 2PH. Ligand substitution is observed under mild conditions to yield Co 4(CO) 10− n (μ 4-PPh) 2(Ph 2PH) n ( n = 1, 2). The kinetics for each substitution step reveal a two-term rate law: ( k 1 + k 2[Ph 2PH])[cluster]. The k 2 component corresponds to a Ph 2PH-dependent attack on Co 4(CO) 10(μ 4-PPh) 2 and Co 4(CO) 9(μ 4-PPh) 2(Ph 2PH). The k 1 contribution is inconsistent with a dissociative loss of CO, but rather a unimolecular closo → nido cluster rearrangement. The bis-substituted cluster Co 4(CO) 8(μ 4-PPh) 2(Ph 2PH) 2 is observed to crystallize in the triclinic space group P 1 with a 9.800(1) Å, b 14.849(2) Å, c 15.583(2) Å, α 83.89(1)°, β 81.69(1)°, γ 79.34(1)°, V 2197.7(5) å 3 and Z = 2. Block-cascade least-squares refinement yielded R = 0.0379 for 4860 reflections. The importances of thermodynamic product control in directing the phosphine regiochemistry and stereochemistry in Co 4(CO) 8(μ 4-PPh) 2(Ph 2PH) 2 and other reported clusters of this genre is discussed.

Carbon-13 relaxation and phenyl group rotation in a benzylidyne-capped tricobalt cluster

13C spin-lattice relaxation times of the protonated carbons in Co 3(CO) 9(μ 3-CPh) were measured as a function of temperature in the solvent chloroform. The T 1's were used to calculate the phenyl group's tumbling ( D ⊥) and spinning ( D s) rotational diffusion constants. It was observed that the ratio, D s D ⊥ > 1, revealing extremely facile internal rotation of the phenyl ring. This result is in direct contrast to earlier data on the bicapped tetracobalt cluster Co 4(CO) 10(μ 4-PPh) 2, and indicates a complete lack of steric or electronic interaction between the aromatic ring and the tricobalt nonacarbonyl skeleton. Theoretical diffusion constants calculated by the GiererWirtz Microviscosity model are in excellent agreement with experimental values of D ⊥.

Reaction of bis(dimethylphosphino)ethane with the tetracobalt cluster Co 4(CO) 10(μ 4-PPh) 2; synthesis, structure, and solution dynamics of Co 4(CO) 8(μ 4-PPh) 2(dmpe)

The reaction of the tetracobalt cluster Co 4(CO) 10(μ 4-PPh) 2 ( 1) with the bidentate ligand 1,2-bis(dimethylphosphino)ethane (dmpe) gives the disubstituted cluster Co 4(CO) 8(μ 4-PPh) 2(dmpe) ( 3) in high yield. The dmpe ligand is bound to a single cobalt atom in a chelating fashion as determined by FTIR and NMR ( 31P and 13C) spectroscopy and singlecrystal X-ray crystallography. Co 4(CO) 8(μ 4-PPh) 2(dmpe) · 1 2 toluene crystallizes in the triclinic space group P 1 with a 11.673(1), b 15.986(5), c 20.276(7) Å, α 94.40(3), β 106.28(2), γ 94.89(2)°, V 3599(2) Å 3 and Z  4. Blockcascade least squares refinement yielded R  0.0521 for 6830 reflections. The temperaturedependent 13C NMR spectra of 3 reveal two distinct fluxional processes which serve to equilibrate the carbonyl ligands about the cluster polyhedron. The stability of 3 under different conditions has been examined by Cylindrical Internal Reflectance (CIR) spectroscopy. In benzene solution 3 is stable under 250 psi of H 2 at 150°C; partial decomposition to Co(CO) − 4 is observed using CO and H 2/CO under analogous conditions.