N-heterocyclic carbene coordinated gallanes and chlorogallanes

The preparation of the N-heterocyclic carbene coordinated gallium complexes GaH₃(IXy)] (1), GaH₃(IDipp)] (2), GaClH₂(IMes)] (3) and GaCl₂H(IMes)] (4), where IXy = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene, IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene and IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, are reported. All four complexes have been characterised by ¹H, ¹³C NMR and IR spectroscopy and, for complexes 2, 3 and 4, single crystal X-ray structure determination. These compounds represent some of the most thermally stable molecular gallium hydrides known, with 4 being the most thermally stable gallium hydride reported (dec. 274 °C). These remarkable thermal stabilities translate to significant aerobic stability such that all four compounds may be handled in dry air without significant decomposition. Compounds 2, 3 and 4 exist as distorted tetrahedra in the solid state with gallium to carbene C-donor bonds that shorten with increasing Lewis acidity of the gallium centre. Compound 2 co-crystallizes with 1 equiv. of 2,6-diisopropylphenylaniline and exhibits several weak intermolecular bonding interactions in the solid-state.