Chiral Co(II) Metal-Organic Framework in the Heterogeneous Catalytic Oxidation of Alkenes under Aerobic and Anaerobic Conditions

The chiral Co(II) MOF [Co(L-RR)(H2O)center dot H2O](infinity) [1; L-RR = (R,R)-thiazolidine-2,4-dicarboxylate] has been exploited in the catalytic oxidation of different alkenes (cyclohexene, (Z)-cyclooctene, 1-octene) using either tert-butyl hydroperoxide ((BuOOH)-Bu-t) or molecular oxygen (O-2) as oxidants. Different chemoselectivities are observed, both substrate- and oxidant-dependent. A moderate enantioselectivity is also obtained in the case of prochiral precursors, revealing the chiral induction ability of the optically pure metal environment. The interaction of O-2 with the exposed metal sites in 1 (after material preactivation and consequent removal of the coordinated aquo ligand) has been studied through TPD-MS analysis combined with DFT calculations, with the aim of probing effective oxygen uptake by the heterogeneous catalyst and unraveling the nature of the active species in the catalytic oxidation process under aerobic conditions. Theoretical results indicate the presence of an eta(1)-superoxo species at the cobalt center, with concomitant Co(II) <-> Co(III) oxidation. Finally, the experimental estimation of the O-2 adsorption enthalpy is found to be in good agreement with the calculated binding energy.