Salts of boronium (+3) ions with unprecedented hydrolytic stability. Design, synthesis, single-crystal X-ray structures, electrochemistry, and thermophysical properties

Abstract

Boron cations (boronium ions) of any charge – 1+, 2+, or 3+ – are demonstrably among the least well-known and studied family of monoboron species. Those of 3+ charge are especially few in number, and scant information is available about them. This lack of information is likely rooted in the relatively poor stability – especially towards water – of known exemplars. Now, by utilizing strongly donating 4-N,N-dialkylaminopyridines as ligands to the boron center we have succeeded in preparing salts indefinitely stable in water at pH values from 1 to 14. Further, we have acquired multinuclear NMR spectra on each of the new species and for the first time evaluated their thermal characteristics (DSC and TGA), finding that they are quite robust. In addition, the electrochemical behaviour of the new salts was evaluated using cyclic voltammetry. The structures of several of the new materials have been determined by single-crystal X-ray crystallography, and detailed computational modelling has been undertaken to provide additional insight into the experimental data.