Cobalt 1,3-Diisopropyl-1<i>H</i>-imidazol-2-ylidene Complexes: Synthesis, Solid-State Structures, and Quantum Chemistry Calculations

The reaction of (η5-C5H5)Co(PPh3)2 (1) with 1,3-bis(isopropyl)imidazol-2-ylidene (ImiPr2, 17) leads to the formation of (η5-C5H5)Co(PPh3)(ImiPr2) (5) in 69% yield. N-Heterocyclic carbene 17 also undergoes reaction with (η5-C5H5)Co(CO)2 (9) to give (η5-C5H5)Co(ImiPr2)(CO) (6) in 30% yield. The barrier to rotation about the Co−Ccarbene bond in 6 has been determined by variable-temperature 1H NMR spectroscopy (13.6 kcal/mol) and by computation (13.3 kcal/mol). Complex 5 undergoes reaction with PhSSPh to give the paramagnetic thiolato complex (η5-C5H5)Co(ImiPr2)(SPh) (7), which is oxidized to the metallosulfone complex (η5-C5H5)Co(ImiPr2)(SO2Ph) (8). The solid-state structures of 5−8 were determined by X-ray crystallography. The structural and dynamic properties of 6, (η5-C5H5)Co(ImMe2)(CO) (ImMe2 = 1,3-dimethylimidazol-2-ylidene), and (η5-C5H5)Co(ImAr2)(CO) (ImAr2 = 1,3-dimesityl-2-ylidene) were examined by quantum chemistry calculations.