Studies on the reactivity of Nb(η5-C5H4SiMe3)2(X)(L), X = H,Cl;: L = CNXylyl, CNCy, CO and Nb(η5-C5H4SiMe3)2(H)3 complexes toward the Lewis acids B(C6F5)3 and BF3

The reaction of the electron-rich, coordinatively saturated, :niobocene-hydride or -halide complexes Nb(eta(5)-C5H4SiMe3)(2)(X)(L), X = H or Cl, L = 2,6-dimethylphenylisocyanide (CNXylyl), cyclohexylisocyanide (CNCy) and carbonyl (CO), with the strong Lewis acid (B(C6F5)(3)) gives the zwitterionic compounds [(eta(5)-C5H4SiMe3)(2)(CNXylyl)Nb(mu-X)(B(C6F5)(3)] (1), [(eta(5)-C5H4SiMe3)(2)(CNCy)Nb(mu-X)(B(C6F5)(3)] (2), [(eta(5)-C5H4SiMe3)(2)(CO)Nb(mu-X) (B(C6F5)(3))] (3), respectively, where the complexes possess a bridging hydride or halide group. Similarly, the starting niobocene-hydride species react with BF3 to afford the corresponding zwitterionic complexes containing a bridging hydride ligand, namely [eta(5)-C5H4SiMe3)(2)(CNXylyl)Nb(mu-H)(BF3)] (4), [(eta(5)-C5H4SiMe3)(2)(CNCy)Nb(mu-H)(BF3)] (5), [(eta(5)-C5H4SiMe3)(2)(CO)Nb(mu-H)(BF3)] (6). The reaction of the hydride containing compounds 1-3 with the appropriate ligand L (1:1 molar ratio for 1 and 2) in toluene at room temperature leads to the ionic compounds [(eta(5)-C5H4SiMe3)(2)Nb(CNXylyl)(2)][(HB(C6F5)(3))] (7), [(eta(5)-C5H4SiMe3)(2)Nb(CNCy)(2)][(HB(C6F5)(3))] (8), and [(eta(5)-C5H4SiMe3)(2)Nb(CO)(2)][(HB(C6F5)(3))] (9), which contain two coordinated L ligands and a noncoordinated [(HB(C6F5)(3))](-) counteranion. Analogous complexes were not observed in the same reaction for 4-6. Finally, the compound [Nb(eta(5)-C5H4SiMe3)(2)(H)(3)] reacts in acetone with (B(C6F5)(3)) in a clean reaction to give the ionic compound [(eta(5)-C5H4SiMe3)(2)Nb][((CH3)(2)CHO)B(C6F5)(3))] (10), which contains the isopropoxide berate ion [((CH3)(2)CHO)B(C6F5)(3))](-) as the counteranion. (C) 2000 Elsevier Science S.A. All rights reserved.