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(η5-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 [(η5-C5H4SiMe3)2(CNXylyl)Nb(μ-X)(B(C6F5)3)] (1), [(η5-C5H4SiMe3)2(CNCy)Nb(μ-X)(B(C6F5)3)] (2), [(η5-C5H4SiMe3)2(CO)Nb(μ-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 [(η5-C5H4SiMe3)2(CNXylyl)Nb(μ-H)(BF3)] (4), [(η5-C5H4SiMe3)2(CNCy)Nb(μ-H)(BF3)] (5), [(η5-C5H4SiMe3)2(CO)Nb(μ-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 [(η5-C5H4SiMe3)2Nb(CNXylyl)2][(HB(C6F5)3)] (7), [(η5-C5H4SiMe3)2Nb(CNCy)2][(HB(C6F5)3)] (8), and [(η5-C5H4SiMe3)2Nb(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(η5-C5H4SiMe3)2(H)3] reacts in acetone with (B(C6F5)3) in a clean reaction to give the ionic compound [(η5-C5H4SiMe3)2Nb][((CH3)2CHO)B(C6F5)3)] (10), which contains the isopropoxide borate ion [((CH3)2CHO)B(C6F5)3)]− as the counteranion.