Synthesis of multidentate PNE ligands and their late transition metal coordination chemistry

Abstract

This thesis describes the synthesis of a family of potentially tridentate PNE (E = NMe, О, S, СН(_2), NPh) ligands comprising a six-membered diheteroatomic saturated ring system bearing a pendent phosphine donor arm and studies on their coordination chemistry with a selection of late transition metals. Chapter 1 comprises an overview of the nature of the bonding of phosphine, amine, ether and thioether donors to metals and reviews the dynamic behaviour of saturated heteroatom-containing ring systems in solution. Selected examples of the coordination chemistry and catalytic applications of complexes of Pd, Pt and Rh are given. Chapter 2 details the concise synthesis of variously-substituted diphenylphosphine- bearing PNE ligands, Ph(_2)PCH(_2)CH(_2)N(CH(_2)CH(_2)) (_2)E (E = NMe, 2.4-1; E = о, 2.4-2; E = S, 2.4-3; E = СН(_2), 2.4-4; E = NPh, 2.4-5; E = NCH(_2)CH(_2)PPh(_2), 2.4-7), by reaction of diphenylvinylphosphine with a cyclic secondary amine. The synthesis of both hydrochloride and chalcogen derivatives are also reported. Attempts to synthesise a related family of PNE ligands with amino-substituents at P were unsuccessful. Similar reactions of allyldiphenylphosphine with N-methylpiperazine led to the formation of Ph(_2)PCH(_2)CH(Me)N(CH(_2)CH(_2)) (_2)NMe as a result of base-catalysed isomerisation of the allyl phosphine. The complexation of the PNE ligands with a variety of Pd(II) fragments is detailed in Chapter 3. Reaction with [PdCl(_2) (MeCN) (_2)] affords the [PdCl](^+) Сl(^-) salts when E = NMe, O, S and CH(_2), although when E = NPh and NCHzCHjPPha, the expected products were not obtained. A bidentate [PdCİ2] isomer of 3.1-1 was characterised crystallographically although this was indicated not to be representative of the bulk sample, which consisted mainly of the tridentate [PdCl] (^+0Cl(^-)isomer. Treatment of 3.1-l with MgSO(_4) affords the unusual [PdCl](^+)1/2[Mg(SO(_4))շ.41-1շՕ] complex which was characterised crystallographically. Reaction of 2.4-1 ֊ 2.4-4 with [PdCl(Me)(cod)] and [PdMe(_2)(tmeda)] affords the [PdCl(Me)] and [PdMe(^2)](^+)Cl(_1) complexes, respectively. Chapter 4 describes the coordination chemistry of the PNE ligands with Pt(II) metal fragments. The reaction of 2.4-1 - 2.4-3 with [PtCİ2(cod)] affords the doubly ligated [PtCl ]^ СГ complexes with both stoichiometric and half molar equivalents of the platinum precursor. Reaction of the PNE ligands with [рі(РЕїз)]2 gives [PtCl(PEt3)] complexes in all cases.The coordination of the PNE ligands with Rh(I) metal centres is detailed in Chapter 5. Reaction of 2.4-1 ― 2.4-4 with [Кіі22(00)4] affords the [RhCl(CO)] complexes in all cases, although when E = NMe and ร, dynamic interconversion between [RhCl(CO)] and [Rh(CO)]^ Сl(^-) complexes is observed by low temperature NMR spectroscopy. By contrast, no isomerisation is noted when E = О. When E = NPh and NCH2CH2PPh2, the expected products were not obtained. Abstraction of the metal-bound chloride from [RhCl(CO)] proved successful when E-= NMe and S but this reaction failed to afford the expected product when E = 0， even in MeCN solution. Full experimental data and methods of preparation for the compounds in this thesis are listed in Chapter 6 with supplementary crystallographic data available in the Appendices.