Synthesis and characterisation of novel hienylphosphines and their gold(I) complexes.

Abstract

This study comprises the preparation and characterisation of various novel tertiary monoand polyphosphines as well as their gold(I) complexes. The possible modes of coordination of mono-, bi- and tridentate phosphine ligands to gold(I) are summarised in Chapter One, thus serving as an introduction to coordination behaviour of the new ligands to gold(I). The synthesis and characterisation of twelve novel tertiary mono- and polyphosphines as well as the three previously known thienylphosphines, diphenyl(2-thienyl)phosphine (PS), phenyldi(2-thienyl)phosphine (PDS) and tris(2-thienyl)phosphine (PTS), are reported in Chapter Two. There are four phosphines derived from a monothiophene unit i.e., diphenyl(5-bromo-2-thienyl )phosphine (PSBr), 2,5-bis(diphenylphosphino)thiophene (PSP), phenylbis[(5-diphenylphosphino)-2-thienyl]phosphine (PDSP) and tris[(5-diphenylphosphino)- 2-thienyl]phosphine (PTSP); two from a 2,2'-bithiophene unit i.e.. diphenyl[5( 2,2'-bithienyl)]phosphine (PSS) and 5,5'-bis(diphenylphosphino )-2,2'-bithiophene (PSSP); h hi fr ') ')'. two P osp mes om a _,_ .)-,,_')"-terthiiophene um.t t..e., diipheny1[)--('_)._')'..)-,._')"-terthiieny1)]- phosphine (PSSS) and 5,5"-bis(diphenylphosphino)-2,2':5',2"-terthiophene (PSSSP); three phosphines from a 2-(2'-thienyl)pyridine unit i.e., diphenyl[5-(2'-pyridyl)-2-thienyl]phosphine (PSN), diphenyl[6-(2'-thienyl)-2-pyridyl]phosphine (PNS) and diphenyl[5-(2'{ 6'-diphenylphosphino}pyridyl)-2-thienyl]phosphine (PSNP); and one phosphine from a 2,6-bis(2'-thienyl)pyridine unit i.e., 2,6-bis[(5'-diphenylphosphino )-2'-thienyl]pyridine (PSNSP). A combination of IH, l3C and 31p NMR spectroscopy as well as mass spectrometry and microanalysis is employed to establish the structures for all the compounds, while in three cases (for the ligands PSSP. PSNP and PSNSP) the structural assignment is confirmed by X-ray crystallography. The synthetic strategies used for the preparation of the phosphine ligands vary widely from a traditional reaction between a metallated thiophene and a chlorophosphine on one hand, to a Ni-catalysed coupling reaction involving phosphine-substituted heterocycles on the other. the choice depending not only on the parent heterocyclic molecule. but also on the number of phosphorus atoms present. A new synthetic methodology leading to a potentially water-soluble diphosphine ligand is also explored. Although the target compound itself is not isolated, the preparation of its precursor, 5.5'-bis(phenylphosphino )- Xl 2,2'-bithiophene (HPSSPH), represents the first example of the synthesis of a secondary phosphine containing a thiophene moiety. In Chapter Three the reactions of the mono- and diphosphine ligands PS, PDS, PTS, PSBr, PSS, PSSS.- PSN.. PNS.- PSP.' PSSP.. PSNP.. PSSSP and PSNSP with the. gold(I) precursors (such as HAuCI4, reduced in situ with thiodiglycoL and [Au{MeCNh]SbF6) are studied. The structures of the products are elucidated by means of 'n and 31 p NMR and IR spectroscopy as well as X-ray crystallography in the case of [CIAuPSS], [CIAuPNS], [CIAu(PDS)2], [CIAu(PS)3] and [Au2(~-PSNh](SbF 6)2. Neutral complexes containing twocoordinate gold(I) are obtained for all the ligands, having general formulae [ClAuP] and [CIAu(~-PP)AuCI] , where P and PP represent a mono- and a diphosphine respectively. Isolation of neutral complexes with three-coordinate gold(I) proved more difficult and is only achieved for the complexes [CIAuP2] (P = PS, PDS, PTS and PSN) and [CIAu(~PP)] n (PP = PSP and PSSSP). A 31 p NMR study of the behaviour of complexes in solution shows the complexes with three-coordinate gold to be very labile with respect to dissociation of the third ligand. The complex [CIAu(PS)3], where gold(I) exhibits a coordination number intermediate between 3 and 4 in the solid state (as shown by the Xray crystallographic analysis), is serendipitously obtained from a reaction of [CIAu(PPh3)] and PS in a I :1 molar ratio. Both mono- and dinuclear complexes with two-coordinate gold(I) are formed when the monophosphines PSN and PNS are reacted with suitable precursors (viz. [CIAuPNS] and [Au{MeCNh]SbF6). The mononuclear complexes are of formula [Au(r{Ph]SbF6, as confirmed by IH and 3lp NMR and IR spectroscopy. In the case of the dinuclear complexes. [AU2(~-PhJX2 (P = PSN. X = SbF6: P = PNS. X = PF6), bridging is achieved via the phosphorus atom and nitrogen atom of the pyridine ring 1n both ligands. This coordination mode is consistent with the IH and 31 p NMR data for both complexes. and it is also confirmed by an X-ray structure determination of the former complex. The diphosphine ligands PSSP, PSNP and PSNSP tend to produce insoluble polymeric products when reacted with cationic gold(I) precursors. while the diphosphines PSP and PSSSP allow discrete species (e.g. [Au{r!'-PSSSP}z]PF6 and [Au2 {~-PSP hHPF6 }z ) to be isolated under similar conditions. None of the gold(I) complexes synthesised in this work displays any evidence of the thiophene ring being one way or the other coordinated to the metal, XII Chapter Three concludes with a short description of the luminescence properties of a selection of gold(I)-phosphine complexes both in solution and in the solid state. Our results confirm the previously established trend that complexes containing three-coordinate gold(I) tend to luminesce. They also show, for the first time, that a dinuclear complex with no metal-metal interaction, and where each gold atom is coordinated to one phosphorus and one nitrogen donor atom i.e., [Au2(Il-PSN)2](SbF6L exhibits luminescent properties. The results of the cytotoxic testing of a number of mono- and diphosphines (PS, PDS, PTS, PSS, PSSS, PSSP, PSSSP, PSNSP and dppe) as well as of some heterocyclic compounds and the gold(I ) complexes [CIAuPSS] and (CIAu(Il-PP)AuCI] (PP = PSSP and dppe) against two cell lines are presented in Chapter Four. The complex [CIAuPSS] shows great potency against the HepG2 (liver cancer) cell line, far exceeding that of the known cytotoxic agent, [Cl.Autu-dppej.Auf'l]. For the other cell line. A549 (lung cancer), the cytotoxicity measurements are compared for 'in the dark' and under DVA light conditions. The results show that application of DVA light generally increases the cytotoxic properties of the compounds tested. Although there appears to be a link between the phototoxic properties of a compound and its photosensitising ability (a photophysical property of thienylphosphine ligands and their gold(I ) complexes, reported at the beginning of Chapter Four) , it is not yet possible to establish a quantitative correlation between the two.