Gas-phase positive-ion chemistry of trimethylboron and

Organometallics 1982,1, 1303-1307

1303

Gas-Phase Positive-Ion Chemistry of Trimethylboron and Trimethylaluminum Manfred M. Kappes, Jack S. Uppal, and Ralph H. Staley’’ Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02 739

Received January 27, 7982

Me2B+and Me2Al+are the principal ions produced by electron impact on Me3Band Me& respectively. Study of halide transfer to these species leads to determination of the halide affinities: D(MezB+-F-) = 238.5 f 3 kcal/mol, D(MezB+-C1-) = 192.5 f 3 kcal/mol, D(Me2A1+-F) = 228 f 8 kcal/mol, and D(Me2A1+-Cl-) = 185 f 5 kcal/mol. These show about 9 kcal mol greater stability for Me2A1+compared to Me2B+. Me3B reacts by methyl anion transfer with CF3 and CF2C1+but not with CC13+,C3H7+,or CHC&+,establishing a value for the methyl anion affinity of Me2B+of D(Me2B+4H