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Issue 10, 2013
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CO2 reduction by Fe(I): solvent control of C–O cleavage versus C–C coupling

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Abstract

This manuscript explores the product distribution of the reaction of carbon dioxide with reactive iron(I) complexes supported by tris(phosphino)borate ligands, [PhBPR3] ([PhBPR3] = [PhB(CH2PR2)3]; R = CH2Cy, Ph, iPr, mter; mter = 3,5-meta-terphenyl). Our studies reveal an interesting and unexpected role for the solvent medium with respect to the course of the CO2 activation reaction. For instance, exposure of methylcyclohexane (MeCy) solutions of Image ID:c3sc51262b-t1.gif to CO2 yields the partial decarbonylation product Image ID:c3sc51262b-t2.gif. When the reaction is instead carried out in benzene or THF, reductive coupling of CO2 occurs to give the bridging oxalate species Image ID:c3sc51262b-t3.gif. Reaction studies aimed at understanding this solvent effect are presented, and suggest that the product profile is ultimately determined by the ability of the solvent to coordinate the iron center. When more sterically encumbering auxiliary ligands are employed to support the iron(I) center (i.e., [PhBPPh3] and [PhBPiPr3]), complete decarbonylation is observed to afford structurally unusual diiron(II) products of the type {[PhBPR3]Fe}2(μ-O). A mechanistic hypothesis that is consistent with the collection of results described is offered, and suggests that reductive coupling of CO2 likely occurs from an electronically saturated “FeII–CO2˙” species.

Graphical abstract: CO2 reduction by Fe(i): solvent control of C–O cleavage versus C–C coupling

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Publication details

The article was received on 07 May 2013, accepted on 11 Jul 2013 and first published on 12 Jul 2013


Article type: Edge Article
DOI: 10.1039/C3SC51262B
Citation: Chem. Sci., 2013,4, 4042-4051
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    CO2 reduction by Fe(I): solvent control of C–O cleavage versus C–C coupling

    C. T. Saouma, C. C. Lu, M. W. Day and J. C. Peters, Chem. Sci., 2013, 4, 4042
    DOI: 10.1039/C3SC51262B

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