Counterion Effect in Cobaltate‐Catalyzed Alkene Hydrogenation
Martin Gawron, Franziska Gilch, Daniel Schmidhuber, John A. Kelly, Thomas M. Horsley Downie, Axel Jacobi von Wangelin, Julia Rehbein, Robert Wolf
Abstract
Abstract We show that countercations exert a remarkable influence on the ability of anionic cobaltate salts to catalyze challenging alkene hydrogenations. An evaluation of the catalytic properties of [Cat][Co(η 4 ‐cod) 2 ] (Cat=K ( 1 ), Na ( 2 ), Li ( 3 ), ( Dep nacnac)Mg ( 4 ), and N( n Bu) 4 ( 5 ); cod=1,5‐cyclooctadiene, Dep nacnac={2,6‐Et 2 C 6 H 3 NC(CH 3 )} 2 CH)]) demonstrated that the lithium salt 3 and magnesium salt 4 drastically outperform the other catalysts. Complex 4 was the most active catalyst, which readily promotes the hydrogenation of highly congested alkenes under mild conditions. A plausible catalytic mechanism is proposed based on density functional theory (DFT) investigations. Furthermore, combined molecular dynamics (MD) simulation and DFT studies were used to examine the turnover‐limiting migratory insertion step. The results of these studies suggest an active co‐catalytic role of the counterion in the hydrogenation reaction through the coordination to cobalt hydride intermediates.