Selective Hydration of Nitriles to Amides Promoted by an Os–NHC Catalyst: Formation and X‑ray Characterization of κ²‑Amidate Intermediates

The complex [Os­(η⁶-<i>p</i>-cymene)­(OH)­IPr]­OTf (<b>1</b>; IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazolylidene; OTf = CF₃SO₃) reacts with benzonitrile and acetonitrile to afford the κ²-amidate derivatives [Os­(η⁶-<i>p</i>-cymene)­{κ²<i>O</i>,<i>N</i>-NHC­(O)­R}­IPr]­OTf (R = Ph (<b>2</b>), CH₃ (<b>3</b>)). Their formation has been investigated by DFT calculations (B3PWP1), starting from the model intermediate [Os­(η⁶-benzene)­(OH)­(CH₃CN)­IMe]⁺ (IMe = 1,3-bis­(2,6-dimethylphenyl)­imidazolylidene). Complex <b>2</b> has been characterized by X-ray diffraction analysis. In the presence of water, the κ²-amidate species release the corresponding amides and regenerate <b>1</b>. In agreement with this, complex <b>1</b> has been found to be an efficient catalyst for the selective hydration of a wide range of aromatic and aliphatic nitriles to amides, including substituted benzonitriles, cyanopyridines, acetonitrile, and 2-(4-isobutylphenyl)­propionitrile among others. The mechanism of the catalysis is also discussed