Synthesis and oxidation of (benzimidazolylidene)Cr(CO)5 complexes

A series of (benzimidazolylidene)pentacarbonylchromium(0) complexes were synthesized by the addition of lithium 1,2-phenylenediamides to Cr(CO)6 in the presence of 12-crown-4, followed by the treatment of chlorotrimethylsilane. X-ray crystal structural analysis revealed a rather single-bond-like character between Cr and the carbene carbon. One reversible oxidation process was observed in the cyclic voltammograms of these complexes. Chemical oxidation using (4-BrC6H4)3NSbCl6 was studied by ESR to afford a hyperfine structure derived not from Cr but from N and H, indicating that the spin is delocalized on the benzimidazolidene moiety.