Palladium(II) and Platinum(II) Compounds of 1,1′-Bis(phosphino)metallocene (M = Fe, Ru) Ligands with Metal–Metal Interactions

Abstract

The reaction of [Pd(dtbpf)Cl2] (dtbpf = 1,1′-bis(di-tert-butylphosphino)ferrocene) with a chemical oxidant led unexpectedly to the formation of [Pd(dtbpf)Cl]+. Further study found that a variety of reagents could be used to abstract a chloride ligand from [Pd(dtbpf)Cl2] to yield [Pd(dtbpf)Cl]+. The solid-state structure suggests the formation of an Fe–Pd interaction. The presence of the bulky tert-butyl groups is essential, as similar reactions with [Pd(PP)Cl2] (PP = other 1,1′-bis(phosphino)ferrocene ligands) results in the formation of [Pd(PP)(μ-Cl)]22+. The analogous platinum compounds have also been investigated and appear to behave in a similar manner. Similar compounds of the type [M′(PP)(PR3)]2+ (M′ = Pd, Pt, R = Ph, Me) have been prepared, and a metal–metal interaction has also been observed. Steric and electronic effects dictate the formation of these compounds. X-ray crystal structures were obtained for eight of these compounds and were used as the basis for a computational analysis of the metal–metal interaction. DFT analysis indicates the presence of a weak, noncovalent interaction between the two metal centers. The electrochemical properties of these compounds were examined by cyclic voltammetry and typically show one oxidative wave and either one two-electron or two one-electron reductive waves.