Transition metal-free direct hydrogenation of esters via a frustrated Lewis pair
Author(s)
Type
Journal Article
Abstract
‘Frustrated Lewis pairs’ (FLPs) continue to exhibit unique reactivity for the reduction of organic substrates, yet to date the catalytic hydrogenation of an ester functionality has not been demonstrated. Here we report that iPr3SnNTf2 (1-NTf2; Tf = SO2CF3) is a more potent Lewis acid than the previously studied iPr3SnOTf; in an FLP with 2,4,6-collidine/2,6-lutidine (col/lut) this translates to faster H2 activation and the catalytic hydrogenolysis of an ester bond by a by a main-group compound, furnishing alcohol and ether (minor) products. The reaction outcome is sensitive to the steric and electronic properties of the substrate; CF3CO2Et and simple formates (HCO2Me, HCO2Et) are catalytically reduced, whereas related esters CF3CO2nBu and CH3CO2Et show only stoichiometric reactivity. A computational case study on the hydrogenation of CF3CO2Et and CH3CO2Et reveals that both share a common mechanistic pathway, however, key differences in the energies of a Sn-acetal intermediate and transition states emerge, favoring CF3CO2Et reduction. The alcohol products reversibly inhibit 1-NTf2/lut via formation of resting-state species 1-OR/[1·(1-OR)]+[NTf2]–, however the extra energy required to regenerate 1-NTf2/lut exacerbates the unfavorable reduction energy profile for CH3CO2Et, ultimately preventing turnover. These findings will assist the design of future main-group catalysts for ester hydrogenation, with improved performance.
Date Issued
2021-08-06
Date Acceptance
2021-06-16
Citation
ACS Catalysis, 2021, 11 (15), pp.9143-9150
ISSN
2155-5435
Publisher
American Chemical Society
Start Page
9143
End Page
9150
Journal / Book Title
ACS Catalysis
Volume
11
Issue
15
Copyright Statement
© 2021 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, after peer review and technical editing by the publisher. To access the final edited and published work see: https://pubs.acs.org/doi/10.1021/acscatal.1c01940
Sponsor
The Royal Society
The Royal Society
Engineering & Physical Science Research Council (EPSRC)
Engineering & Physical Science Research Council (EPSRC)
The Royal Society
The Royal Society
Grant Number
RG2010/R2
UF110061
EP/K030760/1
EP/N026004/1
UF160395
RGF\EA\180179
Subjects
0302 Inorganic Chemistry
0305 Organic Chemistry
0904 Chemical Engineering
Publication Status
Published
Date Publish Online
2021-07-09