Gas-Phase reactivity of Diastereomeric Acetate Ion/Tributylborate Complexes

The reactivity of (CH3COOY)nH+ (n = 1, 2) and (CH3COOY)CH3CO+ ions [Y = CH3, C2H5, sC3H7, (R)-sC4H9, (S)-sC4H9, and (rac)-sC4H9] toward chiral and achiral tributylborates has been measured by Fourier transform ion cyclotron resonance mass spectrometry. Proton transfer between monomeric ions (CH3COOY)H+ and (S,S,S)-tri-sec-butylborate competes with nucleophilic addn. of the borate to the CO center of the ion followed by elimination of either a butanol mol. or the mixed borate. A similar reaction network is obsd. for dimeric ions (CH3COOY)2H+, although the presence of a spectator CH3COOY mol. in the relevant encounter complexes modifies substantially the evolution kinetics as well as the product pattern. Acetyl group transfer from (CH3COOY)CH3CO+ to the borate preludes to an intracomplex CH3COOY-induced elimination reaction. Enantiodifferentiation between (R)-(CH3COOsBu)H+ and (S)-(CH3COOsBu)H+ is achieved by comparing their reactivity towards (S,S,S)-tri-sec-butylborate.