CATALYTIC DEHYDROCOUPLING - A GENERAL-METHOD FOR THE FORMATION OF ELEMENT-ELEMENT BONDS

The general status of catalytic dehydrocoupling as a method for the synthesis of element-element bonds is discussed and evaluated in the context of studies carried out in the authors' and other laboratories. Available thermodynamic data show that dehydrocoupling is favourable for the formation of homopolar bonds between a number of the heavier congeners of the p-groups, and heteropolar bonds between first members and lower members of the p-groups. Metallocene alkyls and hydrides of group 4 show a particularly high catalytic activity in a number of dehydrocoupling reactions, including Si-H/Si-H, Ge-H/Ge-H, Si-H/O-H, Si-H/N-H and B-H/N-H reactions. The role of some novel silyl intermediates in the dimethyltitanocene- and dimethylzirconocene-catalysed silane coupling reactions is discussed. Current views on the mechanism of these reactions are presented, particularly with respect to the intervention of cyclization reactions and their role in molecular weight limitation.