University of Sussex
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Synthesis and chemistry of novel ambiphilic phosphorus based ligands and complexes

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posted on 2023-06-09, 05:09 authored by Victoria Greenacre
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 ?2–phosphaalkenic compounds of the type [Ru(CO){?3-N,C,P-P(PzR',R")CH(SiMe2R)}(PPh3)2], building on earlier work within the group.


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