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

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journal contribution
posted on 18.01.2000, 00:00 authored by Stephen L. J. Conway, Linda H. Doerrer, Malcolm L. H. Green, Michael A. Leech
The new compounds [Nb{(η-C5H4)X(η-C5H4)}Cl2] (X = CEt2 1a, C(C5H10) 1b, C2Me4 1c), [Nb{(η-C5H3tBu)C2Me4(η-C5H3tBu)}Cl2] 1d, [Nb{(η-C5H4)X(η-C5H4)}(η2-BH4)] (X = CEt2 2a*, C(C5H10) 2b, C2Me4 2c*, SiMe2 2e*), [Nb{(η-C5H3tBu)C2Me4(η-C5H3tBu)}(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 2ae, 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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