Dissociation of the complexes [Rh(η6-arene)L2]ClO4 (arene = mesitylene (Ia), toluene (Ib) and benzene (Ic); L = P(OPh)3) with loss of the arene ligand in CD2Cl2/ acetone-d6 (95/5 mol/mol) has been studied by 31P NMR spectroscopy; for initial 0.025 M concentrations of degrees of dissociation were 0.23, 0.33 and 0.85, respectively. The dissociations were first-order, with half-lifes of 31 (Ia), 1.2 (Ib)