The Magnesium Dication and Water Synergistically Promote the Protonolysis of Two of the B–C Bonds in the Tetraphenylborate Anion

Abstract

Analytes are sampled from both solution phase and gas-phase environments during the ESI process, and thus, the mass spectrum that is measured can reflect both solution and gas-phase conditions. In the gas-phase regime, ion−molecule reactions can influence the types of ions that are observed. Herein, the synergistic effects of a Lewis acid (Mg 2+ ) and background water are shown to lead to protonolysis of two of the B−C bonds of the tetraphenylborate ion in the gas phase, giving rise to different ions at different reaction times in ESI-MS/MS experiments in a linear ion trap mass spectrometer. At short reaction times (1 ms), the expected adduct [Mg(BPh 4 )] + is observed. At 10 ms, [(HO)Mg(BPh 3 )] + and [(HO) 2 Mg(BPh 2 )] + are observed. At 100 ms, the water adducts [(HO) 2 Mg(BPh 2 )(H 2 O)] + and [(HO) 2 Mg(BPh 2 )(H 2 O) 2 ] + appear, and these become the dominant ions at longer reaction times. DFT calculations provide a plausible explanation as to why only [(HO)Mg(BPh 3 )] + and [(HO) 2 Mg(BPh 2 )] + but not [(HO) 3 Mg(BPh)] + are observed.