Group 5 ansa-Metallocenes: Structural and Dynamic Properties of Tetrahydroborate Complexes

Conway, Stephen L. J.; Doerrer, Linda H.; Green, Malcolm L. H. and Leech, Michael A. (2000). Group 5 ansa-Metallocenes: Structural and Dynamic Properties of Tetrahydroborate Complexes. Organometallics, 19(4) pp. 630–637.

DOI: https://doi.org/10.1021/om990810n

Abstract

The new compounds [Nb{(η-C₅H₄)X(η-C₅H₄)}Cl₂] (X = CEt₂ 1a, C(C₅H₁₀) 1b, C₂Me₄ 1c), [Nb{(η-C₅H₃^tBu)C₂Me₄(η-C₅H₃^tBu)}Cl₂] 1d, [Nb{(η-C₅H₄)X(η-C₅H₄)}(η²-BH₄)] (X = CEt₂ 2a*, C(C₅H₁₀) 2b, C₂Me₄ 2c*, SiMe₂ 2e*), [Nb{(η-C₅H₃^tBu)C₂Me₄(η-C₅H₃^tBu)}(η²-BH₄)] (2d*), [Nb{(η-C₅H₄)X(η-C₅H₄)}(η²-BD₄)] (X = C₂Me₄ 3c, CMe₂ 4), and [V{(η-C₅H₄)C₂Me₄(η-C₅H₄)}(η²-BH₄)] (5*) have been prepared. The asterisk indicates the crystal structure has been determined. The hydrogen scrambling processes in the tetrahydroborate complexes 2a−e, 3c, 4, 5, and [Nb{(η-C₅H₄)CMe₂(η-C₅H₄)}(η²-BH₄)] have been studied. The free energy barrier ΔG^⧧ to bridge-terminal hydrogen exchange is considerably reduced when the bridging unit imposes significant structural changes in the metallocene.

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