Completing the Triad: Synthesis and full Characterization of Homoleptic and Heteroleptic Carbonyl and Nitrosyl Complexes of the Group VI Metals

Oxidation of M(CO)6 (M = Cr, Mo, W) with the synergistic oxidative system Ag[WCA] / 0.5 I2 yields the fully characterized metalloradical salts [M(CO)6]+∙[WCA]– (weakly coordinating anion WCA = [F‑(Al(ORF)3}2]–, RF = C(CF3)3). The new metalloradical cations with M = Mo and W showcase a similar structural fluxionality as the previously reported [Cr(CO)6]+∙. Their reactivity increases from M = Cr < Mo < W and their syntheses allow for in-depth insights into the properties of the group 6 carbonyl triad. Furthermore, the reaction of NO+[WCA]– with neutral carbonyl complexes M(CO)6 gives access to the heteroleptic carbonyl/nitrosyl cations [M(CO)5(NO)]+ as salts of the WCA [Al(ORF)4]–, the first complete transition metal triad of their kind.