This tutorial review covers the recent advances made in the study of gold complexes containing N-heterocyclic carbene ligands with biological properties.

Complex OsH 2 (CO)(P i Pr 3 ) 2 , generated from OsH 2 (CO)(η 2 -CH 2 CHEt)(P i Pr 3 ) 2 by dissociation of the olefin, promotes the release of 1 equiv of H 2 from ammonia-borane and the formation of polyaminoborane. The dehydrogenation rate law is of the form d[H 2 ]/dt = k[Os] with activation parameters of ΔH ‡ = 19.6 ± 2.5 kcal•mol −1 and ΔS ‡ = 6 ± 9 cal•mol −1 •K −1 . On the basis of kinetic results, spectroscopic NMR observations, and DFT calculations, the dihydride-dihydrogen derivative OsH 2 (η 2 -H 2 )(CO)(P i Pr 3 ) 2 is proposed as a key intermediate for the dehydrogenation. Its formation involves the concerted BH-and NH-hydrogen transfers from the amine-borane to the metal center and to a hydride ligand, respectively.

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Heterolytic B-H activation and H-H formation on an Os-SH bond give borylthiolate-dihydrogen derivatives. These species exchange borylthiol by borane to afford σ-borane derivatives or release H2 and undergo a hydride-boryl exchange to yield boryl-hydrogensulfide complexes depending on the boryl group bonded to the sulfur atom.