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

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 (Mg²⁺) 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(BPh₄)]⁺ is observed. At 10 ms, [(HO)Mg(BPh₃)]⁺ and [(HO)₂Mg(BPh₂)]⁺ are observed. At 100 ms, the water adducts [(HO)₂Mg(BPh₂)(H₂O)]⁺ and [(HO)₂Mg(BPh₂)(H₂O)₂]⁺ appear, and these become the dominant ions at longer reaction times. DFT calculations provide a plausible explanation as to why only [(HO)Mg(BPh₃)]⁺ and [(HO)₂Mg(BPh₂)]⁺ but not [(HO)₃Mg(BPh)]⁺ are observed.