Systematic Metallaborane Chemistry

Abstract

Monocyclopentadienyl metal chlorides of transition metals of groups 5−9 react with monoboranes (LiBH4 or BH3THF) to give metallaboranes (and LiCl or BH2Cl). The composition of the metallaborane produced depends on the nuclearity of the metal complex, the number of chlorides (oxidation state of the metal), and the monoborane used. For both monoboranes, a monocyclopentadienyl metal polyborohydride is implicated as the key intermediate, which is competitively converted into either a metal hydride or a metallaborane. The comparative reaction chemistry of these metallaboranes exhibits a dependence on transition metal properties for borane addition, metal fragment addition, and dihydrogen elimination. In addition, base degradation and small molecule reactivity promise similar metal dependencies. These observations suggest that control of borane chemistry with transition metals, analogous to that achieved in organometallic chemistry, can be realized.