Abstract
We report the synthesis of a rigid phosphine-substituted, redox-active pincer ligand and its application to electrocatalytic CO2 reduction with first-row transition metal complexes. The tridentate ligand was prepared by Stille coupling of 2,8-dibromoquinoline and 2-(tributylstannyl)pyridine, followed by a palladium-catalyzed cross-coupling with HPPh2. Complexes were synthesized from a variety of metal precursors and characterized by NMR, high-resolution mass spectrometry, elemental analysis, and cyclic voltammetry. Formation of bis-chelated metal complexes, rather than mono-chelated complexes, was favored in all synthetic conditions explored. The complexes were assessed for their ability to mediate electrocatalytic CO2 reduction, where the cobalt complex was found to have the best activity for CO2-to-CO conversion in the presence of water as an added proton source.
Highlights
Carbon dioxide (CO2) is a greenhouse gas which is produced in large quantities from fossil fuel combustion
Earth-abundant first-row transition metals supported by well-designed pincer ligands have been successfully employed in a variety of catalytic applications
The Fe and Co complexes were initially purified by a Sephadex R column and obtained in high yields of ∼90%
Summary
Carbon dioxide (CO2) is a greenhouse gas which is produced in large quantities from fossil fuel combustion. From the Industrial Revolution forward, anthropogenic CO2 emissions have increased at an alarming rate, along with associated concerns including climate change, rising sea levels, and ocean acidification (Hansen et al, 2008; Jiang and Guan, 2016; Blunden and Arndt, 2017). These environmental issues can be mitigated by effective technologies capable of converting CO2 into sustainable fuels (Lim et al, 2014). Earth-abundant first-row transition metals supported by well-designed pincer ligands have been successfully employed in a variety of catalytic applications
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