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.