Homoleptic isocyanidemetalates of 4d- and 5d-transition metals: [Nb(CNXyl)(6)](-), [Ta(CNXyl)(6)](-), and derivatives thereof

Treatment of M(CO)(6)](-), M = Nb, Ta, with Ag(+), I(2) or NO(+) in the presence of CNXyl provided M(CNXyl)(7)](+), M(CNXyl)(6)I, or cis-M(CNXyl)(4)(NO)(2)](+), which are isocyanide analogues of the unknown carbonyl complexes M(CO)(7)](+), M(CO)(6)I, or cis-M(CO)(4)(NO)(2)](+), respectively. Reduction of M(CNXyl)(6)I by cesium graphite gave the respective CsM(CNXyl)(6)], which have been structurally characterized and represent the first isolable homoleptic isocyanidemetalates for second or third row transition metals. Nitrosylation of Ta(CNXyl)(6)](-) affords a rare example of a mononitrosyl tantalum complex, Ta(CNXyl)(5)NO, which is an isocyanide analogue of the unknown Ta(CO)(5)NO. This study emphasizes, inter alia, the remarkable versatility of the CNXyl ligand compared to CO in stabilizing various electronic environments at heavier group 5 metal centers.