Reductive Carbonylation of [NiCl2(dippf)] (dippf = 1,1′-Bis(diisopropylphosphino)ferrocene) with Fe(CO)5 and (Spectro)electrochemistry of the Resulting [Ni(CO)2(dippf)]

Metal-metal communication between 1,1'-bis(diphenylphosphino)cobaltocenium and an organonickel moiety

1,1'-Bis(diphenylphosphino)cobaltocenium (dppc)⁺, similar to 1,1'-bis(diphenylphosphino)ferrocene, can be coordinated by dicarbonylnickel(0) or cyclopentadienylnickel(II), respectively. The cyclic voltammogram of [Ni(CO)₂(dppc)]⁺ ([1]⁺) showed two reversible reductions, at potentails nearly identical to (dppc)⁺. The ligand-based reductions were confirmed by IR spectroelectrochemistry (SEC), although the Δν_CO was larger than might be expected if the ligand was electronically decoupled to the Ni(CO)₂ moiety. The larger Δν_CO was attibuted to changes in the donor/accpetor properties of the -PPh₂ moeities based on the occupation of the Co-Cp anti-bonding orbital, where the Cp ligand adopts an ylide-like structure. A similar analysis was performed on [CpNi(dppc)]²⁺ ([2]²⁺), where the two reductions were anodically shifted by ΔE = 292 and 520 mV from (dppc)⁺, indicating an increase in the M-M communication. The EPR SEC spectrum for [2]⁺ showed that the cobalt was reduced, while the UV-Vis-NIR SEC spectrum for [2]⁺ showed a NIR absportion at 1200 nm assinged as a MMCT Co^II → Ni^II band. The second reduction formed [2]⁰ which was EPR silent but the UV-Vis-NIR SEC spectrum showed an increase in the intensity of the MMCT Co^I → Ni^II.

(Electrochemical) Properties and Computational Investigations of Ferrocenyl-substituted Fe3(μ3-PFc)2(CO)9 and Co4(μ4-PFc)2(CO)9 Clusters and Their Reduced Species

The formation of ferrocenyl-functionalized iron and cobalt carbonyl clusters is reported, based on a reaction of FcPCl₂ (3) (Fc = Fe(η⁵-C₅H₅)(η⁵-C₅H₄)) with Fe₂(CO)₉ and Co₂(CO)₈, respectively. Therein, nido-Fe₃(CO)₉(μ₃-PFc)₂ (4) and nido-Co₄(CO)₁₀(μ₃-PFc)₂ (5) clusters were obtained as the first diferrocenyl-substituted carbonyl clusters with a symmetrical cluster core. Cluster 4 shows two reversible one-electron processes within the anodic region, based on Fc/Fc⁺ redox events, as well as two processes in the cathodic region. In situ IR and electron paramagnetic resonance (EPR) measurements of all electronic states confirmed an Fc-based oxidation and a core-based reduction. On the basis of the results of a single-crystal X-ray analysis of structures of 4 and 5, computational studies of the highest occupied molecular orbital-lowest unoccupied molecular orbital energies, the spin density, quantum theory of atom-in-molecule delocalization indices, and the atomic charges were performed to explain the experimental results. The latter revealed a reorganization of the cluster core upon reduction and the existence of weak P···P interactions in 4 and 5. Ferrocenyl-related redox processes, occurring reversibly in case of 4, were absent for 5, due to a different distribution of the HOMO energies. EPR measurements furthermore confirmed the core-based radical anion and the formation of a decomposition product at potentials lower than [M]^2- (M = Fe, Co).