Electronic interactions in dinuclear platinum and palladium ethynylferrocene and ferrocenylvinylidene complexes

Abstract

The complex [Pd2(dppm)2(μ-η1: η1-H-C=C-Fc)Cl2] (2) and its vinylidene isomer [Pd2(dppm)2(μ-C=CH-Fc)Cl2] (3) [dppm = bis(diphenylphosphanyl)methane, Fc = ferrocenyl unit, CpFeC5H 4] have been synthesized and characterized by single-crystal X-ray diffraction. Both 2 and 3 are A-frame structures with long Pd-Pd distances of 3.2055(9) Å (2) and 3.1002(2) Å (3), respectively, and square-planar metal coordination. The cyclic voltammograms (CV) of the complexes are measured and compared with that of [Pt2(dppm)2(μ- η1:η1-H-C=C-Fc)Cl2] (1). The CV of 2 and 3 consist of a nearly reversible Fc-oxidation, an irreversible oxidation and a small reversible couple. The E1/2 values (vs. Cp 2Fe+/Cp2Fe) of the Fc-groups in complexes 1-3 follow the order 2 (-75±8 mV) > 1 (-108±10 mV) > 3 (-124±8 mV). The difference in the E1/2 values is explained by the orbital interactions between the acetylene and vinylidene groups with Pt2 and Pd2 cores. Our analysis shows that the metal-to-ligand π back-bonding and ligand-to-metal σ-donation have determining effects on the electronic interactions between the dimetallic centers and the bridgehead ligands. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.