Mechanism and Regioselectivity of the Osmium-Catalyzed Aminohydroxylation of Olefins

The mechanism and regioselectivity of the osmium-catalyzed aminohydroxylation of olefins was investigated in detail by density functional theory (B3LYP/6-31G(d)) calculations in the gas phase and with the CPCM-solvent model. A systematic variation of the catalyst system (OsO4 and various nitrogen sources) and the substrate's electronic situation was conducted. Activation barriers could be correlated to Hammett values and linear Gibbs free energy relations could be determined. Experimental results, which indicated an electronic influence on the regioselectivity, could be confirmed and appear to be predictable. The reaction follows a [3+2] mechanism. We additionally report results on the experimentally observed competing dihydroxylation reaction and the ligand-induced reaction rate acceleration.