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Title: Studies on main group and transition metal compounds containing a sterically demanding, electron-withdrawing ligand
Author: Sequeira, L. J.
ISNI:       0000 0001 3394 0507
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 1996
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The studies described herein relate to the co-ordination chemistry of l,3,5-tris(trifluoromethyl)benzene, Ar(^F)H. The unique combination of steric bulk and a highly electron-withdrawing nature found in the a- bound Ar(^F) ligand has already been exploited to stabilise a variety of unusual main group compounds including the surprisingly air- and moisture-stable diphosphene Ar(^F)P=Par(^F). Other examples are discussed in the introductory chapter, as is the increasingly active area of diphosphene research. Chapter 2 describes the synthesis and structural characterisation of six early σ-Ar(^F) transition metal complexes, Mo(N(^t)Bu)(_2)(Ar(^F))2, Cr(NAd)(_2)(Ar(^F))(_2), [Mo(NAr)(_2)(Ar(^F))Cl-LiCl(dme)](_2), V(Ar(^F))(_2)Cl(thf), V(Ar(^F))(_3)-O -Li(thf)(_3) and Cr(Ar(^F))(_2)(PMe(_3))(_2). The first five of these compounds exhibit the rare phenomenon of weak metal-fluorine interactions, which is discussed in terms of several structural factors such as tilting of the aryl ring towards the direction of the M-F interaction The co-ordination chemistry of the diphosphenes Ar(^F)p=PArF, Ar*P=PAr* and Ar*P=PArF (Ar* = 2,4,6-(^t)BuC6H3) is reported in chapter 3. Ar(^F)p=Par(^F) is shown to displace olefins from a bis(imido)molybdenum centre to generate complexes such as Mo(NR)(_2)(PMe)(_3)(Ti2-ArFp=PArF) (R = tBu, 2,6-iPr2C6H3). The crystal structure of Mo(NtBu)2(PMe)3(Ti2- ArFp=PArF) has been elucidated. Related investigations have focused on the co-ordination mode of the diphosphenes Ar*P=PAr* and Ar*P=PArFwith [Pt(PEt3)Cl2]2/ and a variety of Til-complexes has been spectroscopically observed. The development of phosphorus based analogue of the industrially important olefin metathesis reaction is detailed in chapter 4. The reaction of ArPCl2, [Ar = Ar(^F), Ar* and 2,6-(CF3)2-C6H3 (Ar(^f1)] with the halide abstractor W(PMe3)6 leads to the generation of ArP=PAr via a postulated [W]=PAr phosphinidene intermediate. The unsymmetrical diphosphene ArFp=PAr* has been synthesised analogously from a mixture of ArFPCl2 and Ar*PCl2 with W(PMe3)6- When Ar is small (2,4,6-iPr3C6H2, 2,4,6- Me3C6H2), ArPCl2 reacts with W(PMe3)6 to give three-membered tricyclophosphanes, [ArP](_3) π-bound complexes of the Ar(^F)H ligand have been synthesised via metal vapour synthesis experiments, carried out in collaboration with Prof. F.G.N. Cloke at Sussex University. Chapter 5 describes the preparation of the bis-arene complexes M(T|6-ArFH)2 (M=Cr, V, Nb) and Ru(Ti6-ArFH)(Ti4-ArFH).Full experimental details and characterising data for chapters 2-5 are collected in chapter 6.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: 1,3,5-tris(trifluoromethyl)benzene; Diphosphenes