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Title: Activation of small molecules by solid-supported frustrated Lewis pairs
Author: Xing, Junyi
ISNI:       0000 0004 6495 7354
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
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The aims of this thesis have been to develop heterogeneous frustrated Lewis pairs for the catalytic activation of small molecules. Frustrated Lewis pairs capable of H2 activation and CO2 hydrogenation based on electron-deficient tri-aryl boranes and sterically encumbered phosphines have been immobilised on silica. The reactivity of these heterogeneous systems with small molecules has been tested and compared with a variety of soluble siloxane and silsesquioxane molecular models. The use of layered double hydroxides as a potential support for the immobilisation of FLPs has also been explored. Chapter One introduces the methanol economy and provides a background to recent advances in CO2 capture and hydrogenation. The development of frustrated Lewis pairs, their reactivity with small molecules, together with theoretical studies on the mechanism of H2 cleavage and CO2 fixation by FLPs are summarised. Recent developments on heterogeneous frustrated Lewis pairs is discussed, in addition to a brief account of surface organometallic chemistry grafting procedures on silica and layered double hydroxide (LDH) supports. Chapter Two reports H2 heterolytic cleavage by [B(C6Cl5)(C6F5)2/PtBu3] FLP and the H2 reduction of CO2 to give the methoxy borate [(C6Cl5)(C6F5)2BOCH3][HPtBu3]. These results are compared with formato- and methoxy borate derivatives prepared independently via reaction of formic acid and MeOH with [B(C6Cl5)(C6F5)2/PtBu3]. The products are characterised by FTIR and NMR spectroscopy, [(C6Cl5)(C6F5)2BOCHO][HPtBu3] is characterised by single crystal X-ray structure analysis. Chapter Three details the synthesis of a group of siloxane and silsesquioxane bound Lewis acids [(tBuO)3SiOB(C6F5)2], [(tBuO)3SiOB(Fxyl)2] (Fxyl = 3,5-bis-trifluoromethylphenyl), [T8(OB(C6F5)2)2] (T8 = (C4H9)8Si8O12), [T8(OB(Fxyl)2)2], and preparation of the corresponding FLPs with Lewis bases PtBu3 and PMes3 as soluble molecular models for silica-immobilised FLPs. Their ability to activate H2 is investigated. The side-product ((tBuO)3Si)2OBC6F5 is characterised by single-crystal X-ray structure analysis. Chapter Four describes the preparation of heterogeneous Lewis acids by immobilisation of -B(C6F5)2 and -B(Fxyl)2 on the surface of thermally pretreated silica, and the subsequent formation of the corresponding solid-supported FLPs (s-FLPs) by addition of PtBu3 to the Lewis acids. s-FLPs are shown to activate H2, D2 and CD3OD. The products are characterised by FTIR and solid state NMR (SSNMR) spectroscopy. Chapter Five investigates the immobilisation of B(C6F5)2 on a thermally pretreated aqueous miscible organic layered double hydroxide (AMO-LDH) support, and formation of LDH FLP by the addition of a Lewis base, PtBu3. The B(C6F5)2 modified LDH-FLP is shown to react with H2 and D2 and the products are characterised by SSNMR and FTIR spectroscopy. Chapter Six provides experimental procedures, characterisation techniques and data for those compounds described in the preceding chapters.
Supervisor: O'Hare, Dermot Michael Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available