Synthesis and Reactivity Studies of a [Cp*Rh] Complex Supported by a Methylene-Bridged Hybrid Phosphine-Imine Ligand.

[CpRh] complexes (Cp = -pentamethylcyclopentadienyl) supported by bidentate chelating ligands are useful in studies of redox chemistry and catalysis, but little information is available for derivatives bearing "hybrid" [] chelates. Here, the preparation, structural characterization, and chemical and electrochemical properties of a [CpRh] complex bearing the κ-[,]-2-[(diphenylphosphino)methyl]pyridine ligand (PN) are reported. Cyclic voltammetry data reveal that [CpRh(PN)Cl]PF () undergoes a chemically reversible, net two-electron reduction at -1.28 V vs. ferrocenium/ferrocene, resulting in generation of a rhodium(I) complex () that is stable on the timescale of the voltammetry. However, H and P{H} NMR studies reveal that chemical reduction of generates a mixture of products over a 1 h timescale; this mixture forms as a result of deprotonation of the methylene group of by followed by further reactivity. The analogous complex [Cp*Rh(PQN)Cl]PF (; PQN = κ-[,]-8-(diphenylphosphino)quinoline) does not undergo self-deprotonation or further reactivity upon two-electron reduction, confirming the reactivity of the acidic backbone methylene C-H bonds in the PN complexes. Comparison of the electrochemical properties and also shows that the extended conjugated system of PQN contributes to an additional ligand-centered redox event for that is absent for .