A Terminally Bound Niobium Methylidyne

Complex (PNP)Nb(CH3)(2)(OAr) (PNP = N[2-(PPr2)-Pr-i-4-methylphenyl](2)(-), Ar = 2,6-(Pr2C6H3)-Pr-i), prepared from treatment of (PNP)NbCl3 with NaOAr followed by 2 equiv of H3CMgCl, can be oxidized with [FeCp2][OTf] to afford (PNP)Nb(CH3)(2)(OAr)(OTf). While photolysis of the latter resulted in formation of a rare example of a niobium methylidene, (PNP)Nb=CH2(OAr)(OTf), treatment of the dimethyl triflate precursor with the ylide H2CPPh3 produced the mononuclear group 5 methylidyne complex, (PNP)Nb CH(OAr). Adding a Bronsted base to (PNP)Nb=CH2(OAr)(OTf) also resulted in formation of the methylidyne. Solid-state structural analysis confirms both methylidene and methylidyne moieties to be terminal, having very short Nb-C distances of 1.963(2) angstrom and 1.820(2) angstrom, respectively. It is also shown that methylidyne for nitride cross-metathesis between (PNP)Nb CH(OAr) and NCR (R = tert-butyl or 1-adamantyl) results in formation of a neutral and mononuclear niobium nitride, (PNP)Nb N(OAr), along with the terminal alkyne HC CR.