Counterion Effect in Cobaltate-Catalyzed Alkene Hydrogenation |
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| Authors: | Martin Gawron Franziska Gilch Daniel Schmidhuber Dr John A Kelly Dr Thomas M Horsley Downie Prof Dr Axel Jacobi von Wangelin Prof Dr Julia Rehbein Prof Dr Robert Wolf |
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| Institution: | 1. Institute of Inorganic Chemistry, University of Regensburg, 93040 Regensburg, Germany;2. Institute of Organic Chemistry, University of Regensburg, 93040 Regensburg, Germany;3. Department of Chemistry, University of Hamburg, 20146 Hamburg, Germany |
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| 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(η4-cod)2] (Cat=K ( 1 ), Na ( 2 ), Li ( 3 ), (Depnacnac)Mg ( 4 ), and N(nBu)4 ( 5 ); cod=1,5-cyclooctadiene, Depnacnac={2,6-Et2C6H3NC(CH3)}2CH)]) 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. |
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| Keywords: | Alkenes Cobalt Homogenous Catalysis Hydrogenation Ion Pairing |
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