Observing and modelling energetically close α- and β-carbon–hydrogen agostic interactions in an isopropyl tris(pyrazolyl)boratoniobium complex

An equilibrium between α- and β-agostic interactions has been observed in Tp*Nb(Cl)(CHMe2)(PhC≡CMe) 1 [Tp* = hydridotris(3,5-dimethylpyrazolyl)borate] while only α-agostic interactions have been observed for the analogous ethyl complex; calculations using the hybrid QM/MM method IMOMM (B3LYP:mm3) methodology properly account for the experimental results, and suggest that steric effects are responsible for the presence of distinct minima in the isopropyl complex.

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