University of Johannesburg
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Direct and indirect CO2 hydrogenation catalyzed by Ir (III), Rh (III), Ru (II), and Os (II) half-sandwich complexes to generate formates and N, N-diethylformamide Journal of CO2 Utilization, 2020 Item

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posted on 2020-05-05, 08:09 authored by Siphelele S.P Malaza, Banothile C. E. Makhubela
As a contribution to the valorization of carbon dioxide, new N,O-coordinated Ir(III), Rh(III), Ru(II), and Os(II)
half-sandwich complexes have been designed, synthesized, and applied as homogeneous pre-catalysts in the
experiments for direct and indirect CO2 hydrogenation under basic conditions. The complexes contain a N,Odonor
Schiff base ligand derived from N-(β-naphthyl)-2-oxy-1-naphthaldimine that assisted by partitioning the
catalysts to the organic layer in biphasic mixtures, enabling catalyst separation. In the presence of DBU, the Os
(II) half-sandwich complex N,O-Os(II) (C2) gave a TON of 889 for [DBUH][HCO2] formation under a partial
pressure of 60 bar CO2/H2 at 120 °C over 48 h, assisted by heterogeneous side reactions. Complexes N,O-Rh(III)
(C3) and N,O-Ir(III) (C4) exhibited great efficiency in the homogeneous hydrogenation of carbon dioxide to
afford formate and N,N-diethylformamide in the presence of DBU and diethylamine, respectively. Group 9 halfsandwich
complexes eminently qualify as useful in the direct and indirect hydrogenation of CO2 to afford reaction
intermediates that can be used to make carbon-neutral fuel.


SASOL SA, the National Research Foundation, South Africa, (Grant number 117989),

University of Johannesburg Centre for Synthesis and Catalysis