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 I${}_2$ yields the fully characterized metalloradical salts [M(CO)${}_6$]+˙[WCA]− (weakly coordinating anion WCA = [F-{Al(OR${}^F$)${}_3$}${}_2$]${}^{-}$, R${}^F$ = C(CF${}_3$)${}_3$). 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.