Dimesitylborane dimer has been shown to exist in equilibrium with dimesitylborane monomer in solution. This equilibrium has been investigated by variable concentration and variable temperature multinuclear NMR spectroscopy and values for the dissociation constant, enthalpy and entropy of dissociation were found to be Kdiss=(3.2±0.4)× 10− 3 M, ΔH= 70 kJ mol− 1, and ΔS= 212 JK− 1mol− 1, respectively. Ab initio methods have been ...