Preparation and structural characterization of chloro- and alkyl-isocyanidoniobocene compounds. Synthesis of the 1st dicyclopentadienylniobium species containing iminoacyl groups

Abstract

The reduction of the niobocene complexes Nb(η5-C5H3RR′)2Cl2 (R = H, R′ = SiMe3 (I); R = R′ = SiMe3 (II)) with one equivalent of (1%) sodium amalgam in the presence of an isocyanide ligand R″NC yields Nb(η5-5H3RR′)2Cl(CNR″) (R = H, R′ = SiMe3, R″ = Cy = cyclohexyl (III); tBu (IV); Ph (V); 2,6-Me2C6H3 (VI), and R = R′ = SiMe3, R″ = Cy (VII), tBu (VIII)). Reactions of III and V with LiMe and LiCH2SiMe3 give the thermally stable iminoacyl compounds [Nb(η5-C5H4SiMe3)2-(CRNR′)]n(R = Me, R′ = Cy (IX); R = CH2SiMe3, R′ = Cy (X) and R = Me, R′ = Ph (XII)), through spontaneous insertion of the isocyanide ligand into the alkyl-niobium bond. Insertion of t-BuNC into the metal-alkyl bond in IV was not observed, and only the alkyl isocyanide derivative Nb(η5-C5H4SiMe3)2(Me)(CNtBu) (XI) was isolated. The compounds were characterized by IR and NMR spectroscopy.