A Co^II-Hydroxide Complex That Converts Directly to a Co^II-Acetamide during Catalytic Nitrile Hydration

Abstract

In exploring structural and functional mimics of nitrile hydratases, we report the synthesis of the pseudo-trigonal bipyramidal Co II complexes (K)[Co II (DMF)(L Ph )] (1(DMF)), (NMe 4 ) 2 [Co II (OAc)(L Ph )] (1(OAc)), and (NMe 4 ) 2 [Co II (OH)-(L Ph )] (1(OH)) (L Ph = 2,2′,2''-nitrilo-tris-(N-phenylacetamide; DMF = N,N-dimethylformamide; − OAc = acetate)). The complexes were characterized using NMR, FT-IR, ESI-MS, electronic absorption spectroscopy, and X-ray crystallography, showing the L Ph ligand to bind in a tetradentate tripodal fashion alongside the respective ancillary donor. One of the complexes, 1(OH), is an unusual structural and functional mimic of the Co active site in Co nitrile hydratases. 1(OH) reacted with acetonitrile to yield the Co II -acetamide complex (NMe 4 ) 2 [Co II (NHC-(O)CH 3 )(L Ph )], 2, which was also thoroughly characterized. In the presence of excess hydroxide, 1(OH) was found to catalyze quantitative conversion of the added hydroxide into acetamide. Despite the differences in Co oxidation state in nitrile hydratases and 1(OH) (Co III versus Co II , respectively), 1(OH) was nonetheless an effective nitrile hydration catalyst, selectively producing acetamide over multiple turnovers.