Synthesis and chemistry of novel ambiphilic phosphorus based ligands and complexes

Greenacre, Victoria (2017) Synthesis and chemistry of novel ambiphilic phosphorus based ligands and complexes. Doctoral thesis (PhD), University of Sussex.

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Abstract

The chemistry of ambiphilic molecules, such as phosphine-boranes, has experienced a resurgence in interest, in part due to the emergence of Frustrated Lewis Pairs (FLPs).
With a 2-atom bridge to separate the phosphine and borane units, the unsaturated, 1-borata-4-phosphoniacyclobut-2-enes R2BC(R)=C(Ph)PPh2 have been investigated. Their solid state data has been complemented by DFT studies, with a view towards controlling the geometry around a metal centre in order to position the Lewis acid unit over the Lewis basic metal centre without forming an adduct.
The reactivity of the saturated and unsaturated phosphine-boranes has been also probed with a series of Lewis-basic metals. It was found that while the saturated systems readily coordinate to group 9 and 10 metals, the phosphorus-boron bond of the unsaturated systems remains too strong for coordination. Therefore, attempts to disrupt the strong P-B bond were made using pyridine.
Phosphaalkynes of the type RMe2SiC≡P have been prepared from RSiMe2CH2Cl, by converting the 'CH2Cl' unit into 'CH2PCl2', before dehydrochlorination. The ruthenaphosphaalkenyls [Ru{P=CH(SiMe2R)}Cl(CO)(PPh3)2] are then prepared in high yield from the corresponding phosphaalkynes (P≡CSiMe2R, R = Ph, tolyl, nBu, p-CF3-C6H4) through hydroruthenation with [RuHCl(CO)(PPh3)3]. The first solid-state structural data of these ruthenaphosphaalkenyls is described and complemented by DFT studies of the precedent [Ru(P=CHtBu)Cl(CO)(PPh3)2)] alongside silyl based systems, allowing the visualisation of molecular orbitals and calculated NMR data.
The silyl systems mimic the previously reported propensity toward electrophilic addition shown by Ru{P=CH(tBu)}Cl(CO)(PPh3)2]. However, the presence of the silyl group also appears to modify the reactivity compared to that previously published for [Ru{P=CH(tBu)}Cl(CO)(PPh3)2]; demonstrated by the addition of HCl to form the saturated P-C linkage shown in [RuCl2(CO)(PPh3)2{P(HCl)CH2SiMe2R}]. The ruthenaphosphaalkenes also exhibit reactivity with nucleophiles (pyrazolates) to form novel bridging pyrazolyl η2–phosphaalkenic compounds of the type [Ru(CO){κ3-N,C,P-P(PzR',R")CH(SiMe2R)}(PPh3)2], building on earlier work within the group.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Chemistry
Subjects: Q Science > QD Chemistry > QD0241 Organic chemistry
Depositing User: Library Cataloguing
Date Deposited: 13 Feb 2017 15:53
Last Modified: 13 Feb 2017 15:53
URI: http://sro.sussex.ac.uk/id/eprint/66736

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