Sila- and germacyclopentenes in fundamental and applied organometallic chemistry

Abstract

We have been interested by sila and germacyclopentenes (I) for a long time. Such rings formally result from 1,4- cycloaddition of silylenes and germylenes with 1,3- dienes. We summarize the principal methods we have developed to obtain several series of heterocyclic compounds (I) with various substituents on metal M and or on the 3 or 4 sp2 carbons of the metallacyclopent-3-enes. Compounds (I) have a chemistry mainly governed by the electro deficient M center and by the electron rich C3-C4 double bond which is in a β- position to the metal center. Grignard derivatives give substitution reactions on M, and, on an other hand, organolithium compounds induce ring opening polymerisation. A catalytic amount of n-butyllithium, in presence of HMPA, transforms (I) into poly(1-germa and 1-sila-cis-pent-3-enes). Chemical, physical and mechanical properties of such polymers have been explored. 6-Oxa-3-sila (and germa) bicyclo[3.1.0] hexanes (IV) are directly obtained from (I) by epoxidation of the C3-C4 double bond. Such compounds (IV) have been included in this survey because of their typical chemical, thermal and biological properties.