BRIDGED HALF-SANDWICH NIOBIOCENES BY INTRAMOLECULAR CH ACTIVATION

The reaction of [Nb(NMe2)(3)(=N-2,6-iPr(2)C(6)H(3))] 3 with the cyclop entadienes C5H5R (R = C3H5, C6H5, CH2C6H5) 2a-c gave the new half-sand wich niobium complexes [Nb(eta(5)-C5H4R)(NMe2)(2)(=N-2,6-iPr(2)C6(H3)) ] 4a-c in high yields. The new ansa-type half-sandwich complexes [Nb(N Me2)(=N(2,6)i-PrC6H3)(eta(5):eta(3)-{C5H4}] 5a, [Nb(NMe2)(=N(2,6)i-PrC 6H3)(eta(5):eta(1)- {C5K4}C(CH3)(2){C6H4}] 5b, [Nb(NMe2)(=N(2,6)i-PrC6 H3)(eta(5):eta(3)-{C5H4}] 5c were thus obtained at higher temperatures by an intramolecular C-H activation resulting in the coordination of the R group. (C) 1997 Elsevier Science S.A.