Electronically distinctive cyclic phosphanes: synthesis and structural modifications toward the control of chemical and electronic properties

Pearce, Kyle (2021) Electronically distinctive cyclic phosphanes: synthesis and structural modifications toward the control of chemical and electronic properties. Doctoral thesis (PhD), University of Sussex.

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Abstract

This thesis describes the synthesis and development of novel cyclic phosphanes, with the intent to exploit their electronic character and subsequently explore their respective reactivities.

A family of diphosphametacyclophanes bearing the electronically distinctive diketophosphanyl functionality are prepared from reacting RP(SiMe3)2 (R = Me, Ph) with the respective diacyl chloride and were characterised spectroscopically and unequivocally by single-crystal X-Ray diffraction. The aromatic 5-R substituent can influence the displacement angle between π-systems, allowing control over the cavity size, which could hold promise for metal sequestration. Electronically, it was found that the LUMO was more stabilised for weaker donating substituents and overall exhibit no delocalisation/conjugation around the macrocyclic core; instead the two diketophosphanyl units are essentially discretely isolated. Attempts to enhance their electron acceptor character via oxidation was unsuccessful, yet these macrocycles coordinate to transition metals, facilitating the synthesis of [M(η4-C8H12)Cl{3-C(O)-C6H4-(C(O)PMe)}2] (M = Rh, Ir) and [{Pt(PEt3)Cl2}2{3-C(O)-C6H4-(C(O)PPh)}2].

e first examples of 6- and 7-membered saturated phosphorus heterocycles bearing the diketo-functionality, RP{C(O)}2CnH2n (n = 3, 4; R= aryl, alkyl) have been synthesised and fully characterised. The coordination chemistry of these species has been explored including a series of tungsten-pentacarbonyl complexes, which were prepared and elucidated spectroscopically and by X-Ray diffraction. Data suggest these heterocycles are relatively weak σ-donors, placing them between traditional phosphanes and phosphites in this regard.

In tangential studies, novel trifluorophosphalkenes (RP=C(OSiMe3)CF3) are pursued by reacting the respective bis-silylated phosphane, RP(SiMe3)2 (R = Ph, tBu, Mes, SiMe3) with one equivalent of trifluoroacetic anhydride, leading to the isolation of both the E- and Z-isomers. The reactivity of these phosphaalkenes has been explored, including [4+2] cyclicadditions to afford cyclic species such as Me3SiPCH2CHCHCH2C(OSiMe3)(CF3), which was tentatively identified. Similarly, reactions with LiN(SiMe3)2 afford a range of complex products at ambient temperature, but with evidence for trifluoromethylphosphaalkyne below −20 °C, respectively. Efforts to effect coordination are outlined, demonstrating an unexpected variability in coordination mode.

Finally, the first dianionic diphosphaboracycles ([C6P2BC6H5]2- 2[Li(THF)1.5]2+, [C6P2BC6H5]2- 2[Li(TMEDA)]2+) are synthesised from the reaction between 1,2-bis(phosphino)benzene and dichlorophenylborane. The reactivity and coordination chemistry of which has been extensively explored leading to a series of novel compounds, including a ɳ5, ɳ1, ɳ1-trimolybdenum complex, confirming that the diphosphaboracycle can act as a
π-ligand with metals other than lithium.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Chemistry
Subjects: Q Science > QD Chemistry > QD0241 Organic chemistry > QD0258 Operations in organic chemistry > QD0262 Organic synthesis
Depositing User: Library Cataloguing
Date Deposited: 12 Aug 2021 06:38
Last Modified: 12 Aug 2021 06:38
URI: http://sro.sussex.ac.uk/id/eprint/100994

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