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

Two series of zinc salts, [EtZn][A] and Zn[A] 2 , 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- closo -dodecaborate anions [Me 3 NB 12 Cl 11 ] - [ 1 ] - , [Pr 3 NB 12 H 5 Cl 6 ] - [ 2 ] - , [Bu 3 NB 12 H 4 Cl 7 ] - [ 3 ] - , and [Hex 3 NB 12 H 5 Cl 6 ] - [ 4 ] - were chosen as potential and more readily available alternatives to carborate anions such as [CHB 11 Cl 11 ] - and [HexCB 11 Cl 11 ] - . The basicity of anion [ 4 ] - was determined as being close to that of the triflimide anion [N(SO 2 CF 3 ) 2 ] - , and the fluoride ion affinities (FIAs) of compounds [EtZn][ 2 ] and Zn[ 2 ] 2 are lower than those of the Lewis acids B(C 6 F 5 ) 3 and Zn[HexCB 11 Cl 11 ] 2 . 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.