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Title: Studies of the reactions of perfluoroarylborane Lewis acids with transition metal compounds
Author: Graham, Andrew J.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1998
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This thesis describes the preparation of strongly electrophilic boranes and their reactivity with transition metal compounds. Chapter One presents an overview of the reactivity of boron-containing Lewis acids as found in the literature focusing primarily on reactions of electrophiles containing a boron-perfluoroaryl bond that are of synthetic rather than catalytic interest. Chapter Two presents studies into the reactivity of boranes of the general formula RB(C6F5)2 [R = (C6F5), Ph, H or Cl] with some metallocene hydrides. The previously synthesised adduct [(η5-C5H5)2Mo(H)(η1-HB(C6F5)3)] has been further investigated and the analogous adduct of HB(C6F5)2 is also reported. The zwitterionic compounds [(η5-C5H4B(C6F5)2R)(η5-C5H5)WH3] {R = (C6F5), Ph, H or Cl*} and [(η5-C5H4B(C6F5)3)(η5-C5H5)ReH2] are described and have been fully characterised (* indicates that an X-ray crystal structure was obtained). Investigations into the reactivity of these compounds towards competing Lewis bases have been undertaken and reveal that the rhenium zwitterion is considerably more stable than the tungsten analogues. Chapter Three presents reactions between B(C6F5)3 and transition metal nitrido complexes. B(C6F5)3 reacts directly with a number of nitrido compounds; [{(C66F5)3BN}Re(PR3)(S2CNR'2)2] (R3 = MePh2 and R' = Et*; R3 = Me2Ph and R' = Me*), [{(C6F5)3BN}ReCl(PMePh2)2(S2CNMe2)], [{(C6F5)3BN}Mo(S2CNR2)3] (R = Me or Et) and [{(C66F5)3BN}Os(1,2-S2C6H4)2][nBu4N] have all been prepared (* indicates that an X-ray crystal structure has been obtained). The reactivity of these adducts towards competing Lewis bases has been probed revealing a range of stabilities over the three metals considered. The adduct of an osmium nitrido compound has also been reacted with competing Lewis acids and the compound [{(C6F5)3BN}Os(1,2- (S)(SMe)C6H4)(1,2-S2C6H4)] has been made and characterised by NMR spectroscopy. Chapter Four describes the synthesis of Lewis acids containing a boronperfluoroaryl bond. Firstly, modified literature preparations of RB(C6F5)2 [R = (C6F5), Cl or H] are reviewed. Attempts to prepare the new Lewis acid BAr'3 [Ar' = (3,5- C6H3(CF3)2)] are described, including the synthesis and characterisation of the new tin reagent nBu3SnAr'. Additionally, the new electrophile B(C6H5)(C6F5)2 has been prepared using either nBu3Sn(C6F5) or [LiC6F5] as the source of (C6F5). Chapter Five contains experimental details for the thesis, characterising data for new compounds are presented in Chapter Six and details of the X-ray crystal structures may be found in the Appendices.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Organic chemistry