Enthalpy- vs Entropy-Driven Complexation of Homoallylic Alcohols by Rhodium(I) Complexes

The thermodynamics of binding between several homoallylic alcohols and simple olefinic Rh­(I) compounds was examined with 1H NMR spectroscopy and isothermal titration calorimetry (ITC). 1H NMR titrations revealed moderate binding of these alcohols with [Rh­(COD)2]+ (1) and [Rh­(COD)­(CH3CN)2]+ (3), but weaker binding with [Rh­(NBD)2]+ (2). ITC indicated that the complexation with [Rh­(COD)2]+ is mainly governed by enthalpy, whereas binding with [Rh­(COD)­(CH3CN)2]+ is entirely driven by entropy. The thermodynamic parameters for the homoallylic alcohol binding of Rh­(I) complexes 1–3 are consistent with crystallographic data.