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

Abstract

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.