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CO_2 reduction by Fe(I): solvent control of C-O cleavage versus C-C coupling

Saouma, Caroline T. and Lu, Connie C. and Day, Michael W. and Peters, Jonas C. (2013) CO_2 reduction by Fe(I): solvent control of C-O cleavage versus C-C coupling. Chemical Science, 4 (10). pp. 4042-4051. ISSN 2041-6520 . http://resolver.caltech.edu/CaltechAUTHORS:20131007-093329618

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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, [PhBP^R_3]- ([PhBP^R_3]- =[PhB(CH_2PR_2)_3]-; R = CH_2Cy,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 CO_2 activation reaction. For instance, exposure of methylcyclohexane (MeCy) solutions of [PhBP^(CH_2Cy)_3 ]Fe(PR’_3) to CO_2 yields the partial decarbonylation product {[PhBP^(CH_2Cy)_3 ]Fe}_2(µ-O)(µ-CO). When the reaction is instead carried out in benzene or THF, reductive coupling of CO_2 occurs to give the bridging oxalate species {[PhBP^(CH_2Cy_3 ]Fe}_2(µ- κOO’: κOO’-oxalato). 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., [PhBP^(Ph)_3]- and [PhBP^(iPr)_3 ]-), complete decarbonylation is observed to afford structurally unusual diiron(II) products of the type {[PhBP^R_3]Fe}_2(µ-O). A mechanistic hypothesis that is consistent with the collection of results described is offered, and suggests that reductive coupling of CO_2 likely occurs from an electronically saturated “Fe^(II)–CO_2-” species.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1039/c3sc51262b DOIArticle
http://pubs.rsc.org/en/Content/ArticleLanding/2013/SC/c3sc51262b#!divAbstractPublisherArticle
Additional Information:© 2013 The Royal Society of Chemistry. Received 07 May 2013, Accepted 11 Jul 2013, First published online 12 Jul 2013. This work was generously supported by the NSF (CHE-0750234) and the Gordon and Betty Moore Foundation. C. T. S. is grateful for an NSF graduate fellowship. We are also grateful to the Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139, where some of the research described was conducted.
Funders:
Funding AgencyGrant Number
NSFCHE-0750234
Gordon and Betty Moore FoundationUNSPECIFIED
NSF Graduate FellowshipUNSPECIFIED
Record Number:CaltechAUTHORS:20131007-093329618
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20131007-093329618
Official Citation:Chem. Sci., 2013, 4, 4042
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41700
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:07 Oct 2013 17:21
Last Modified:07 Oct 2013 17:21

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