Bimetallic silicon chemistry - New opportunities in coordination and organometallic chemistry

Bimetallic complexes containing silyl or siloxy ligands may display unique structures and reactivity patterns that are directly related to a subtle interplay between the metals and the ligands. Access to this class of compounds will be discussed. The recently discovered hemilabile behaviour of the bridging -Si(OR)(3) ligand in heterobimetallic complexes has led to a number of developments in our group and others that are reviewed here. This will include the chemistry of Ph2PCH2PPh2 (dppm)-stabilized Fe-Pd and Fe-Pt alkyl complexes which allow, under mild conditions, controlled insertion reactions of isonitriles, allkynes or CO/olefins into the metal-carbon bond. In some cases, silicon migration reactions leading to new mu-siloxycarbene complexes have been observed. Other reactions that will be presented are the alkyne insertion into metal-hydride bonds, fluorination of the Si(OR)(3) ligand and the catalytic dehydrogenative coupling of stannanes HSnR3. By altering the nature of the assembling ligand (mu-PR2 vs. mu-dppm) but keeping the metals and the silyl ligand unchanged, the first examples of intramolecular silyl migration from one metal to another were discovered. Finally, the use of aminosilyl in place of alkoxysilyl ligands led to the formation of new silylene complexes, to unprecedented examples of metal-mediated substituent exchange reactions between phosphorus and silicon, and to the characterization of the first complexes containing a bridging aminosilyl ligand. Many of these reactions involve steps that are directly relevant to the mechanisms of currently investigated catalytic systems. (C) 1998 Elsevier Science S.A. All rights reserved.