Single-Site Osmium Catalysts on MgO: Reactivity and Catalysis of CO Oxidation

MgO-supported osmium dioxo species, described as Os(=O)(2){-O-support}(1or2) (the brackets denote O atoms of the MgO surface), formed from Os-3(CO)(12) via supported Os(CO)(2), and characterized by spectroscopy, microscopy, and theory, react with ethylene at 298 K to form osmium glycol species or with CO to give osmium mono- and di-carbonyls. Os(=O)(2){-O-support}(1or2) is the precursor of a CO oxidation catalyst characterized by a turnover frequency of 4.0 x 10(-3) (molecules of CO)/(Os atom x s) at 473 K; the active species are inferred to be osmium mono-carbonyls. The structures and frequencies calculated at the level of density functional theory with the B3LYP functional bolster the experimental results and facilitate structural assignments. The lowest-energy structures have various osmium oxidation and spin states. The results demonstrate not only new chemistry of the supported single-site catalysts but also their complexity and the value of complementary techniques used in concert to unravel the chemistry.