Extending the Library of Boron Bases: A Contribution from Theory

In
recent years, the isolation of nucleophilic boron bases led
to a paradigm shift in boron chemistry which prompted us to perform
computational studies on a series of bis­(carbene) borylene complexes.
The structure and electronic properties of these complexes have been
studied, and all of them were found to possess strong donor ability
as evident from high values of calculated pKa and proton affinities (244–300 kcal mol–1). The ability to form strong donor–acceptor bond between
the boron and carbene center, together with the high thermodynamic
stability of the complexes, render them as a promising class of ligands
for use in transition metal based systems. The comparable bond dissociation
energies of hitherto unknown acyclic (3A–5A, 8A, 15A, 18A, 19A, and 21A) and
cyclic borylenes (2C–5C, 9C, 10C, and 15C) to that of the synthetically accessible
borylenes (2A, 7A, 9A, and 16A) indicate the likelihood
of isolation of these hitherto unknown borylenes.