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

The reactions of <i>N</i>-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 (<b>1a</b>), IMesNHC-Mo(CO)₅ (<b>2a</b>), IMesNHC-W(CO)₅ (<b>3a</b>), IPrNHC-Cr(CO)₅ (<b>1b</b>), IPrNHC-Mo(CO)₅ (<b>2b</b>), and IPrNHC-W(CO)₅ (<b>3b</b>). With the exception of <b>1b</b>, 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 <b>1a</b>, <b>2a</b>, <b>3a</b>, and <b>2b</b> 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.