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

Abstract

The complex [Os(η 6 - p -cymene)(OH)IPr]OTf ( 1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene; OTf = CF 3 SO 3 ) reacts with benzonitrile and acetonitrile to afford the κ 2 -amidate derivatives [Os(η 6 - p -cymene){κ 2 O, N -NHC(O)R}IPr]OTf (R = Ph ( 2 ), CH 3 ( 3 )). Their formation has been investigated by DFT calculations (B3PWP1), starting from the model intermediate [Os(η 6 -benzene)(OH)(CH 3 CN)IMe] + (IMe = 1,3-bis(2,6-dimethylphenyl)imidazolylidene). Complex 2 has been characterized by X-ray diffraction analysis. In the presence of water, the κ 2 -amidate species release the corresponding amides and regenerate 1 . In agreement with this, complex 1 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.