The mechanism of the reaction between the complex [Re(OH)(CO)(3)(N2C2H4)] and azetidin-2-one or 3-formylamino-N-sulf onatoazetidin-2-one was investigated by using the B3LYP density functional theory methodology in conjunction with the PCM-UAHF model to take into account solvent effects. According to our calculations, the rate-determining energy barrier for the azetidin-2-one case of 38.8 kcal mol(-1), becomes 25.7 kcal mol(-1) in the case of the 3-formylamino-N-sulf onatoazetidin-2-one species. The presence of the sulfonato group is crucial for the cleavage of the P-lactam N1-C2 bond by the Re complex thanks to the interaction of the sulfonato group with the hydroxy and bidentate ligands of the complex. This could be of interest for the synthesis of beta-amino acids and their derivatives from beta-lactams under mild conditions and in solvents of low polarity promoted by organometallic complexes. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)