Zinc Ammonio-dodecaborates: Synthesis, Lewis Acid Strength, and Reactivity.

Two series of zinc salts, [EtZn][A] and Zn[A], with weakly coordinating anions [A] as counterions have been prepared, and their activities as catalysts for hydrosilylation reactions of 1-hexene, benzophenone, and acetophenone have been investigated. The counterions and per- and partially chlorinated 1-ammonio--dodecaborate anions [MeNBCl] [], [PrNBHCl] [], [BuNBHCl] [], and [HexNBHCl] [] were chosen as potential and more readily available alternatives to carborate anions such as [CHBCl] and [HexCBCl]. The basicity of anion [] was determined as being close to that of the triflimide anion [N(SOCF)], and the fluoride ion affinities (FIAs) of compounds [EtZn][] and Zn[] are lower than those of the Lewis acids B(CF) and Zn[HexCBCl]. The higher anion basicity and the resulting lower Lewis acidity of the zinc centers result in low activity in 1-hexene hydrosilylation catalysis and only moderate activity in the hydrosilylation catalysis of benzophenone and acetophenone.