Intrinsic kinetics of 'frustrated Lewis pair' hydrogenation catalysis
File(s)
Author(s)
Allcock, Nathan James
Type
Thesis
Abstract
The past decade has seen the discovery and exploration of frustrated Lewis pair chemistry; these
novel main group systems have been investigated in the context of small molecule activation,
particularly their role in dihydrogen activation and hydrogenation catalysis. However, studies thus
far are often proof-of-concept and detailed intrinsic kinetic investigations into reaction mechanism
are limited. The focus of this thesis has been to address this gap with a detailed study of the
mechanistic pathway of frustrated Lewis pair catalysed hydrogenation reactions.
The initial part of this thesis was dedicated to the development of a method capable of
measurement of intrinsic kinetics of hydrogenation, followed by a study of hydrogen mass
transfer effects. Three methods for measurement of intrinsic kinetics in a Parr 5500 laboratory
scale reactor were compared and contrasted: hydrogen pressure monitoring, reaction sampling,
and analysis via an FT-IR transmission cell. Sampling reaction mixture for ex situ measurement via
1H NMR was selected as a robust and preferred method for monitoring hydrogenation of organic
substrates. A set of boundary conditions for measurement of intrinsic kinetics were then
established, through measurement of the rate of hydrogen absorption into 1,2-dichlorobenzene,
toluene and 1,4-dioxane solvents over a range of temperatures and pressures.
The second part of the thesis begins with an investigation of the robustness of several Lewis acid
catalysts under typical hydrogenation conditions described in the literature. The remainder of the
thesis is dedicated to a detailed mechanistic study of a particularly moisture tolerant tin
catalyst, triisopropyltin(IV)triflate, in particular the catalytic hydrogenation of imine and carbonyl
substrates; an investigation of potential rate determining factors concludes that dihydrogen
activation is the rate determining step of reaction. It is envisaged that successful catalyst designs
in the future must address both the efficiency of dihydrogen activation and catalyst inhibitory
effects; it is recommended that a study via in situ FT-IR analysis will aid development in this area.
novel main group systems have been investigated in the context of small molecule activation,
particularly their role in dihydrogen activation and hydrogenation catalysis. However, studies thus
far are often proof-of-concept and detailed intrinsic kinetic investigations into reaction mechanism
are limited. The focus of this thesis has been to address this gap with a detailed study of the
mechanistic pathway of frustrated Lewis pair catalysed hydrogenation reactions.
The initial part of this thesis was dedicated to the development of a method capable of
measurement of intrinsic kinetics of hydrogenation, followed by a study of hydrogen mass
transfer effects. Three methods for measurement of intrinsic kinetics in a Parr 5500 laboratory
scale reactor were compared and contrasted: hydrogen pressure monitoring, reaction sampling,
and analysis via an FT-IR transmission cell. Sampling reaction mixture for ex situ measurement via
1H NMR was selected as a robust and preferred method for monitoring hydrogenation of organic
substrates. A set of boundary conditions for measurement of intrinsic kinetics were then
established, through measurement of the rate of hydrogen absorption into 1,2-dichlorobenzene,
toluene and 1,4-dioxane solvents over a range of temperatures and pressures.
The second part of the thesis begins with an investigation of the robustness of several Lewis acid
catalysts under typical hydrogenation conditions described in the literature. The remainder of the
thesis is dedicated to a detailed mechanistic study of a particularly moisture tolerant tin
catalyst, triisopropyltin(IV)triflate, in particular the catalytic hydrogenation of imine and carbonyl
substrates; an investigation of potential rate determining factors concludes that dihydrogen
activation is the rate determining step of reaction. It is envisaged that successful catalyst designs
in the future must address both the efficiency of dihydrogen activation and catalyst inhibitory
effects; it is recommended that a study via in situ FT-IR analysis will aid development in this area.
Version
Open Access
Date Issued
2020-12
Date Awarded
2021-06
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Tighe, Christopher
Fuchter, Matthew
Ashley, Andrew
Sponsor
Engineering and Physical Research Council
GlaxoSmithKline
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)