A Rhenium–Cyclohexane Complex with Preferential Binding of Axial C[BOND]H Bonds: A Probe into the Relative Ability of C[BOND]H, C[BOND]D, and C[BOND]C Bonds as Hyperconjugative Electron Donors?


  • We acknowledge Prof. W. Adcock (Flinders University) and Prof. M. Paddon-Row (UNSW) for early communication of results and helpful discussions, and the Australian Research Council for funding and an Australian Postgraduate Award to D.J.L. The work at Erlangen was supported by the Deutsche Forschungsgemeinschaft as part of SFB583 “Redox-active metal complexes: Control of reactivity via molecular architecture”.


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Which bonds bind better? According to NMR experiments with the alkane complex [CpRe(CO)2(cyclohexane)] at low temperatures, complexation with an axial proton is preferred over that through an equatorial one by about 1.5 kJ mol−1. Calculations support this order of binding energies. The preference is proposed to be due to stronger electron donation through hyperconjugation from a C[BOND]H bond than from a C[BOND]C bond.