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New tunable metal phosphine complexes with polymerisation capabilities

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posted on 03.08.2022, 10:02 authored by Bo Cao

A new series of alkene based functionalised phosphorus ligands bearing PCN backbones were synthesised using a phosphorus Mannich condensation reaction. They were further studied by coordination to various transition metal centres. Following a procedure well established within our research group, two phosphorus ligands were obtained using [P(CH2OH)4]Cl (THPC). THPC was reacted with ortho and para anilines to give the phosphonium salts [P{CH2N(H)R}4]Cl [R = o–{C(Me)=CH2}C6H4, p–(CH=CH2)C6H4]. They were reacted with tBuOK to produce P{CH2N(H)R}3 phosphines [R = o–{C(Me)=CH2}C6H4, p–(CH=CH2)C6H4]. In addition, new phosphine ligands were synthesised by reacting alkene containing amines (2–isopropenylaniline, 4–vinylaniline, 2–aminoethyl methacrylate hydrochloride) with one or two equivalents of hydroxymethyldiphenylphosphine, Ph2PCH2OH. These ligands were coordinated with a number of transition metals [Pd(II), Pt(II), Rh(III), Rh(I), Ru(II), Au(I)]. Coordination chemistry of P{CH2N(H)R}3 (R = p–{CH=CH2}C6H4) was unsuccessful as the product changes colour and becomes insoluble in both sunlight and under a dark environment.

The family of alkyne based functionalised phosphorus ligands was extended by reacting alkyne containing amines (1–ethynylcyclohexylamine, 2–ethynylaniline, 3–ethynylaniline, 4–ethynylaniline) with Ph2PCH2OH. 1–Ethynylcyclohexylamine and 2–ethynylaniline were able to react with only one equivalent of Ph2PCH2OH while 3–ethynylaniline and 4–ethynylaniline reacted with two equivalents of Ph2PCH2OH. 2–ethynylaniline and 4–ethynylaniline were synthesised following literature procedures however they were purified using different procedures. These ligands were treated with transition metals [Pd(II), Pt(II), Rh(III), Rh(I), Ru(II)] to study their coordination properties. In all cases, the ligands bond through the P–donor ligands. 

Another five potentially polymerisable phosphorus ligands were synthesised to enlarge the family of polymerisable monomers. They were synthesised from various amines [dopamine, 3–amino–2–azepanone, 4–(4,4,5,5–tetramethyl–1,3,2–dioxaborolan–2–yl)phenylamine, 4–(2–aminoethyl)morpholine] and appropriate amounts of Ph2PCH2OH. 3–Amino–2–azepanone was synthesised following the literature procedure by reacting L–lysine methyl ester dihydrochloride with NaOH. The study of 4–(4,4,5,5–tetramethyl–1,3,2–dioxaborolan–2–yl)phenylamine and 4–(2–aminoethyl)morpholine) reacting with Ph2PCH2OH has been successful while their coordination chemistries were only studied briefly. These phosphine ligands were subsequently reacted with transition metals [Pd(II), Pt(II), Rh(III), Rh(I), Ru(II)]. All these phosphine ligands and their coordinated monomers were characterised by 31P{1H} NMR, IR spectroscopy and MS. Two of the compounds were further confirmed by single crystal X–ray crystallography.

A preliminary study of polymerisation work was conducted on four of the alkene based metal supported monomers [PdCl2L, L = Ph2PCH2N(R)CH2PPh2, R = 4–vinylaniline; RhCl2(Cp*)L, L = Ph2PCH2NH(R), R = o–{C(Me)=CH2}C6H4, [RhCl2(Cp*)]2L, L = Ph2PCH2N(R)CH2PPh2, R = p–(CH=CH2)C6H4, RhCl(cod)L, L= Ph2PCH2NH(R), R = o–{C(Me)=CH2}C6H4]. The products were insoluble in regular solvents such as MeOH, EtOH, and NMR solvents CDCl3, (CD3)2SO, D2O which is very much different from the literature and were characterised using IR spectroscopy, MS and elemental analysis. The disappearance of the C=C double bond indicated a possible reason for successfully preliminary study of polymerisation. 



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Loughborough University

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© Bo Cao

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A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.




Martin Smith

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