Structure diversity of silver(I) [1,1′-bis(diphenylphosphino)cobaltocenium] complexes: Effect of counteranions

Control over Anion Coordination on Pd(II), Cu(I), and Ag(I) with Regioisomeric Phosphine-Carboxylate Ligands

The coordination of anionic donors is involved at various stages of catalytic cycles in transition-metal catalysis, but control over the spatial positioning of anions around a metal center is a challenge in coordination chemistry. Here we show that regioisomeric phosphine-carboxylate ligands provide spatial anion control on palladium(II) centers by favoring either κ2, cis-κ1, or trans-κ1 coordination of the carboxylate donor. Additionally, the palladium(II) carboxylates, which contain a methyl donor, upon protonation, deliver metal-alkyl complexes that feature a coordinated carboxylic acid. Such complexes can be considered as models for the minima that follow the concerted metalation-deprotonation transition state for C-H activation. The predictability of the coordination modes is further demonstrated on silver(I) and copper(I) centers, for which less common structures of mononuclear and dinuclear complexes can be obtained by using spatial anion control. Our results demonstrate the potential for spatial control over carboxylate anions in coordination chemistry.

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.