Electrospray mass spectrometry of borane salts: The electrospray needle as an electrochemical cell

Two borane salts ([(Me) 4N][B 3H 8] and Cs[B 3H 8]) were examined by electrospray mass spectrometry in the positive ion mode. Acetonitrile solutions provided the most informative spectra; the salts exhibited a remarkable degree of clustering under electrospray conditions, and virtually all signals corresponded to cationic cluster ions of the general formula [cation m+ ] x [anion n− ] y ( mx − ny)+ . In contrast, methanol solutions of these salts produced only B(OCH 3) 4 − cluster ions under otherwise identical conditions. 11B NMR analyses corroborate the identities of the methanol solution species that enter the electrospray source and the reaction product generated during the electrospray process.