Coordination Chemistry Pioneered by Bridging Si- and Ge-Ligands

Transition metal complexes, having the coordination bonds with strong covalent-bond characters, undergo various bond-forming reactions, similar to the organo-transition metal complexes with a metal-carbon s -bond. This article reviews recent studies by the author and his co-workers on the multinuclear complexes of group 10 transition metal complexes having bridging Si- and Ge-ligands. Triangular triplatinum(0) complexes having three bridging diarylsilylene ligands are newly prepared, and undergo skeletal rearrangement on addition of alkynes. The complex with SiPh 2 ligands catalyzes hydrosilylation of aromatic aldehydes and ketones with H 2 SiPh 2 . Detailed studies on the dipalladium and diplatinum complexes with bridging Si- and Ge-ligands revealed unique chemical properties, such as activation of the Si–H bond of the ligand as well as bond forming reactions of the bridging germylene with germyl ligands. Tetra-, penta-, hexa-, and octa-nuclear Pd and Pt complexes with the bridging silylene and germylene ligands are obtained from heating a mixture of the metal-phosphine complexes, precursor of the Si- and Ge-ligands, and scavenger of the auxiliary ligands. Thus formed complexes react with metal halides and with the Si- and Ge-compounds to produce new multinuclear transition metal complexes. The reactions occur reversibly because of kinetic lability of the multinuclear complexes with the bridging Si- and Ge-ligands.