INSERTION REACTIONS OF HETEROCUMULENES INTO THE NIOBIUM-HYDRIDE BOND OF ISOCYANIDE AND CARBONYL NIOBOCENE COMPLEXES

The reaction of the hydride niobocene complexes, Nb(eta(5)-C5H4SiMe3)( 2)(H) (CNR) (R = 2,6-dimethylphenyl (Xylyl) orcyclohexyl (Cy)) and Nb( eta(5)-C5H4SiMe3)(2)(H)(CO) with the heterocumulenes PhN = C = X (X = O or S) affords the new formamido and thioformamido complexes Nb(eta(5 )-C5H4SiMe3)(2)(CNR) (eta(1)-XC(H)NPh) (R = Xylyl, X = O (1); R=Xylyl, X = S (2); R = Cy, X = O (3); R = Cy, X = S (4)) and Nb(eta(5)-C5H4Si Me3)(2)(CO) (eta(1)-XC(H)NPh) (X = O (5); X = S (6)). The protonation of these derivatives using HCF3COO yields the trifluoroacetato complex es Nb(eta(5)-C5H4SiMe3)(2)(CNR) (eta(1)-OOCCF3) (R = Xylyl (7); R = Cy (8)) and Nb(eta(5)-C5H4SiMe3)(2)(CO) (eta(1). OOCCF3) (9) and the imi ne derivatives HOC(H) = NPh and HSC(H) = NPh. Thermal treatment of 5 g ives the eta(2)-formamido complex Nb(eta(5)-C5H4SiMe3)(2)(eta(2)-OC(H) NPh) (10). All these complexes have been characterised by spectroscopi c methods.