Titanocene and zirconocene complexes in phosphinine chemistry

The implication of titanocene and zirconocene complexes in phosphinine chemistry is reviewed. Two approaches to polyfunctional phosphinines using dimethyltitanocene as starting precursor have been developed so far. The first one involves the thermal rearrangement of 1-alkynyl-dihydrophosphetes. The second relies on the reactivity towards alkynes of 1,3,2-diazaphosphinines which are obtained by a metal transfer reaction from the corresponding diazatitanacycle. (2-Phosphininyl)-halogenozirconocene complexes, prepared by insertion of zirconocene into the carbon-halogen bond of 2-halogenophosphinines, have found interesting applications in the synthesis of alpha-functionalized compounds and 2,2'-biphosphinines upon reaction with electrophiles and nickel(0) complexes, respectively. Another important development of their chemistry is provided by the synthesis of monomeric and dimeric phosphabenzyne-zirconocene complexes. Preliminary investigations have shown that their reactivity closely mimics that of their carbon counterparts. Various molecules such as polar alkynes, aldehydes, ketones, nitriles, phosphine sulfides, insert into the carbon-zirconium bond of these complexes to give a wide range of annelated metallacycles which can be subsequently transformed into functional phosphinines upon acidic hydrolysis. (C) 1998 Elsevier Science S.A. Al rights reserved.