Catalytic reductions of C=O and C=N bonds mediated by novel main-group frustrated Lewis pairs
File(s)
Author(s)
Sapsford, Joshua
Type
Thesis
Abstract
The formalisation of the concept of ‘frustrated Lewis pairs’ (FLPs), where bulky Lewis acids (LAs) and bases (LBs) are sterically precluded from forming classical adducts, has resulted in a surge of interest in small molecule activation using compounds featuring p-block reaction centres. Chief among the applications of FLPs is the activation of H2 to H+ and H− equivalents that can be delivered to a substrate to effect the reduction of an unsaturated bond. Hydrogenations using FLPs are now well-established for a broad range of substrates. Current research focuses overwhelmingly on designing triarylborane LAs, but their inherent oxophilicity usually renders them incompatible with hydroxylic species. This thesis concerns ‘softer’ stannylium LAs that catalyse the hydrogenation of unsaturated bonds in the presence of hydroxylic species.
Chapter 1 provides an introduction to FLPs within the context of H2 activation and hydrogenation catalysis, and discusses recent advances in developing moisture tolerant LAs.
Chapter 2 presents the direct reductive aminations of carbonyls catalysed by iPr3SnOTf, a LA that displays remarkable tolerance towards moisture.
Chapter 3 probes the mechanism of H2 activation using iPr3SnOTf to elucidate the role of the OTf− anion.
Chapter 4 describes how changing the iPr3Sn+ anion from OTf− to NTf2− increases the Lewis acidity of the stannylium core, and how this potent Lewis acid catalyses the hydrosilylation and hydrogenation of esters.
Chapter 5 describes efforts to tune the alkyl substituents of R3SnOTf to increase its Lewis acidity.
Chapter 6 provides experimental details of the novel research presented in this thesis.
Chapter 1 provides an introduction to FLPs within the context of H2 activation and hydrogenation catalysis, and discusses recent advances in developing moisture tolerant LAs.
Chapter 2 presents the direct reductive aminations of carbonyls catalysed by iPr3SnOTf, a LA that displays remarkable tolerance towards moisture.
Chapter 3 probes the mechanism of H2 activation using iPr3SnOTf to elucidate the role of the OTf− anion.
Chapter 4 describes how changing the iPr3Sn+ anion from OTf− to NTf2− increases the Lewis acidity of the stannylium core, and how this potent Lewis acid catalyses the hydrosilylation and hydrogenation of esters.
Chapter 5 describes efforts to tune the alkyl substituents of R3SnOTf to increase its Lewis acidity.
Chapter 6 provides experimental details of the novel research presented in this thesis.
Version
Open Access
Date Issued
2020-03
Date Awarded
2020-07
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Ashley, Andrew
Sponsor
Engineering and Physical Research Council
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)