One-Pot Syntheses and Characterization of Group VI Carbonyl NHC Coordination Compounds

The reactions of N-heterocyclic carbenes (IMesNHC and IPrNHC) with transition metal carbonyls of group VI (Cr(CO)₆, Mo(CO)₆, and W(CO)₆) were carried out in acetonitrile in simple one-pot syntheses and led to the formation of the coordination compounds IMesNHC-Cr(CO)₅ (1a), IMesNHC-Mo(CO)₅ (2a), IMesNHC-W(CO)₅ (3a), IPrNHC-Cr(CO)₅ (1b), IPrNHC-Mo(CO)₅ (2b), and IPrNHC-W(CO)₅ (3b). With the exception of 1b, the coordination compounds were formed selectively and in high yields. The method represents an effective and easy-to-perform alternative to the previously described methods for NHC-M(CO)₅ (M = Cr, Mo, W). All prepared compounds were characterized by NMR and Raman spectroscopy. Compounds 1a, 2a, 3a, and 2b were also crystallized and structurally characterized by X-ray structure analysis. Finally, the structural features of all compounds were compared with DFT calculations of structurally optimized coordination compounds.