Issue 3, 2017

Exploring secondary-sphere interactions in Fe–NxHy complexes relevant to N2 fixation

Abstract

Hydrogen bonding and other types of secondary-sphere interactions are ubiquitous in metalloenzyme active sites and are critical to the transformations they mediate. Exploiting secondary sphere interactions in synthetic catalysts to study the role(s) they might play in biological systems, and to develop increasingly efficient catalysts, is an important challenge. Whereas model studies in this broad context are increasingly abundant, as yet there has been relatively little progress in the area of synthetic catalysts for nitrogen fixation that incorporate secondary sphere design elements. Herein we present our first study of Fe–NxHy complexes supported by new tris(phosphine)silyl ligands, abbreviated as [SiPNMe3] and [SiPiPr2PNMe], that incorporate remote tertiary amine hydrogen-bond acceptors within a tertiary phosphine/amine 6-membered ring. These remote amine sites facilitate hydrogen-bonding interactions via a boat conformation of the 6-membered ring when certain nitrogenous substrates (e.g., NH3 and N2H4) are coordinated to the apical site of a trigonal bipyramidal iron complex, and adopt a chair conformation when no H-bonding is possible (e.g., N2). Countercation binding at the cyclic amine is also observed for anionic {Fe–N2} complexes. Reactivity studies in the presence of proton/electron sources show that the incorporated amine functionality leads to rapid generation of catalytically inactive Fe–H species, thereby substantiating a hydride termination pathway that we have previously proposed deactivates catalysts of the type [EPR3]FeN2 (E = Si, C).

Graphical abstract: Exploring secondary-sphere interactions in Fe–NxHy complexes relevant to N2 fixation

Supplementary files

Article information

Article type
Edge Article
Submitted
31 Oct 2016
Accepted
07 Dec 2016
First published
08 Dec 2016
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2017,8, 2321-2328

Exploring secondary-sphere interactions in Fe–NxHy complexes relevant to N2 fixation

S. E. Creutz and J. C. Peters, Chem. Sci., 2017, 8, 2321 DOI: 10.1039/C6SC04805F

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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