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

Two borane salts ((Me)₄N]B₃H₈] and CsB₃H₈]) 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(OCH₃) 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.