In coordination chemistry and organometallic chemistry, transition metal imido complexes is a coordination compound containing an imido ligand. Imido ligands can be terminal or bridging ligands. The parent imido ligand has the formula NH, but most imido ligands have alkyl or aryl groups in place of H. The imido ligand is generally viewed as a dianion, akin to oxide.
In some terminal imido complexes, the M=N−C angle is 180° but often the angle is decidedly bent. Complexes of the type M=NH are assumed to be intermediates in nitrogen fixation by synthetic catalysts.[3]
Imido ligands are observed as doubly and, less often, triply bridging ligands.
Synthesis
From metal oxo complexes
Commonly metal-imido complexes are generated from metal oxo complexes. They arise by condensation of amines and metal oxides and metal halides:
LnMO + H2NR → LnMNR + H2O
This approach is illustrated by the conversion of MoO2Cl2 to the diimido derivative MoCl2(NAr)2(dimethoxyethane), precursors to the Schrock carbenes of the type Mo(OR)2(NAr)(CH-t-Bu).[4]
LnMCl2 + 3 H2NR → LnMNR + 2 RNH3Cl
Aryl isocyanates react with metal oxides concomitant with decarboxylation:
LnMO + O=C=NR → LnMNR + CO2
Structure of OsO3(N-t-Bu) (multiple bonds are not drawn explicitly). Selected distances: Os-N, 1.689; Os-O, 1.678 Å.[5]
Alternative routes
Some are generated from the reaction of low-valence metal complexes with azides:
^Brian S. McGilligan; John Arnold; Geoffrey Wilkinson; Bilquis Hussain-Bates; Michael B. Hursthouse (1990). "Reactions of Dimesityldioxo-Osmium(VI) with Donor Ligands; Reactions of MO2(2,4,6-Me3C6H2)2, M = Os or Re, with Nitrogen Oxides. X-Ray Crystal Structures of [2,4,6-Me3C6H2N2]+[OsO2(ONO2)2(2,4,6-Me3C6H2)]–, OsO(NBut)(2,4,6-Me3C6H2)2, OsO3(NBut), and ReO3[N(2,4,6-Me3C6H2)2]". J. Chem. Soc., Dalton Trans. (8): 2465–2475. doi:10.1039/DT9900002465.
