Cycloalkyl niobium complexes, TpMe2NbX(R)(MeC≡CMe) (TpMe2= hydrotris(3,5-dimethylpyrazolyl)borate; X = Cl, R = c-C3H5(2a) X = Br, R = c-C3H5(2b), X = Cl, R = c-C5H9(3), X = Cl, R = c-C6H11(4),) have been prepared from TpMe2NbCl2(MeC≡CMe). The cyclopropyl complex 2a shows no sign of C–H agostic interactions either in the solid state (X-ray) or in solution. In contrast, the NMR spectra of 3 and 4 are temperature dependent as a consequence of an equilibrium between a major α-agostic species and a minor non-agostic one. Hybrid QM/MM calculations are used to rationalise the behaviour of these cycloalkyl species, and illustrate the subtle interplay of steric and electronic effects in these systems. © 2003 The Royal Society of Chemistry.
|Journal||Journal of the Chemical Society. Dalton Transactions|
|Publication status||Published - 22 Oct 2003|
- Agostic interactions
- Density functional calculations
- Molecular mechanics