Complexes of dimethylsulfoxonium methylide (1) and organoboranes are crystalline for ylide(.)BH(3) (2), ylide(.)BPh(3) (3), ylide(.)B(C6F5)(3) (4), and ylide(.)BF(3) (5). These complexes undergo exothermic rearrangement by 1,2-migration upon heating to produce homologated organoboranes and dimethylsulfoxide. Non-isothermal kinetic analysis of the differential scanning calorimetry (DSC) data for ylide(.)BPh(3) (3) and ylide(.)B(C6F5)(3) (4) complexes was applied using the Flynn-Wall-Ozawa and Kissinger methods. The calculated apparent activation energy for the reaction of ylide(.)BPh(3) (3) yielded consistent results between the A(1.5) model (E-a = 120 kJ mol(-1), A = 4.79 x 10(13) min(-1)) and Kissinger method (E-a = 129 kJ mol(-1), A = 1.73 x 10(17) min(-1)). The analysis for the reaction of ylide(.)B(C6F5)(3) (4) gave consistent results between R-2, R-3, and F-1 models with the average parameters, E-a = 262 kJ mol(-1), A = 3.33 x 10(33) min(-1). The Kissinger analysis for the reaction of ylide(.)B(C6F5)(3) (4) gave Arrhenius activation parameters (E-a = 171 kJ mol(-1), A = 7.80 x 10(19) min(-1)) that were higher than for the reaction of ylide(.)BPh(3) (3). The kinetic data revealed that the C6F5 electron-deficient group has a higher activation energy for 1,2-migration and a higher entropy of activation for 1,2-migration than the C6H5 group. HF/6-31G(d) ab initio calculations agree with the kinetic data. (C) 2004 Elsevier B.V. All rights reserved.