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

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.