Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor

Dr. Richard J. Puddephatt

Abstract

Abstract

This thesis describes the synthesis and characterization of monomeric and polymeric gold(I), silver(I) and platinum(II) complexes containing diphosphine dicarboxamide and pyridine carboxamide donor ligands. The major focus of the project was to characterize these complexes in the solid state using X-ray crystallography. Many of the complexes were also characterized in solution by NMR spectroscopy and electrospray ionization mass spectroscopy.

Chapter one serves as an overall introduction to the topic. Chapter two describes the preparation and characterization of gold(I) and silver(I) complexes with the chiral Trost ligand; R,R-trans-1,2-C6H10(NHCO-2-C6H4PPh2)2 [R,R-1]. R,R-1 gives the fluxional trans-chelate complexes [M(R,R-1)]X, M = Au or Ag, X = Cl-, BF4- or CF3CO2-. It is suggested that a similar trans-chelate conformation may be present in the catalytic intermediate [Pd(R,R-1)]. The prepared gold(I) and silver(I) complexes could be useful in the interpretation of the catalytic allylic alkylation reaction mechanism.

Chapter three describes the characterization of the self-assembled silver(I) polymers with the chiral diphosphine ligand R,R-1, of the empirical formula {Ag2X2(μ-R,R-1)}n. It is found that the diphosphine ligand bridges in different modes depending critically on the donor ability of the anion X- = Cl- > CF3CO2- > NO3- or BF4-.

Chapter 4 describes the synthesis and characterization of the new diphosphine ligand, N,N’-bis(2-diphenylphosphinoethyl)terephthalamide, dppeta, and its gold(I) and silver(I) complexes; [Au2Cl2(m-dppeta)].Me2SO, [Ag2(O2CCF3)2(m-dppeta)], and [Ag2(OTf)2(OH2)2(m-dppeta)]. The ligand dppeta undergoes self-association by NH...O=C hydrogen bonding in a classical way, but the complexes undergo self-association through a combination of hydrogen bonding and either aurophilic bonding (complex [Au2Cl2(m-dppeta)].Me2SO) or secondary coordination (silver(I) complexes). In all cases, sheet structures are formed by self-assembly, in which the bonding interactions occur in the interior, with the outer faces containing mostly phenyl groups. In contrast, the bis(phosphine oxide) derivative, dppetaO2, forms a ribbon polymer using the P=O groups as hydrogen bond acceptors.

Chapter 5 focuses on the preparation of the newly synthesized diphosphine ligand, N,N’-bis(2-diphenylphosphinoethyl)isophthalamide, dpipa, and its complexes with gold(I) and platinum(II). The ligand dpipa, contains two amide groups and can form cis or trans chelate complexes or cis,cis or trans,trans bridged complexes. The amide groups may be involved in intramolecular or intermolecular hydrogen bonding. This combination of properties of the ligand dpipa leads to very unusual structural properties of its complexes, which often exist as mixtures of monomers and dimers in solution. In the complex [Au2(m-dpipa)2]Cl2, the ligands adopt the trans,trans bridging mode, with linear gold(I) centers, and the amide groups hydrogen bond to the chloride anions. In [Pt2Cl4(m-dpipa)2], the ligands adopt the cis,cis bridging mode, with square planar platinum(II) centers, and the amide groups form intermolecular hydrogen bonds to the chloride ligands to form a supramolecular polymer. Both the monomeric and dimeric complexes [PtMe2(dpipa)] and [Pt2Me4(m-dpipa)2] have cis-PtMe2 units with cis chelating or cis,cis bridging dpipa ligands respectively; each forms a supramolecular dimer through hydrogen bonding between amide groups and each contains an unusual NH...Pt interaction. Attempted oxidative addition reactions with methyl iodide or bromine have given the complex [PtIMe(dpipa)], which contains trans chelating dpipa, and a disordered complex [Pt2MenBr8-n(m-dpipa)2], n ca. 2.92, which contains trans,trans bridging dpipa ligands.

Chapter 6 describes the double and quadruple cyclometalation of the ligands 1,3- or 1,4-C6H4(CONHCH2CH2PPh2)2 (dpipa or dppeta respectively) by either reagent [Pt2Me4(m-SMe2)2] or [Pt(O2CCF3)2(SMe2)2], to give complexes containing new PNC-pincer ligands. The major product formed depends primarily on the stoichiometry of the reaction, but also on the reaction conditions. Reaction of a 1:1 mixture of dppeta and[Pt2Me4(m-SMe2)2], which contains two platinum atoms, followed by crystallization from a solvent mixture containing dmso, gave quadruple metalation of dppeta in the product [Pt2(dmso)2(m-k6-(PNC)2-C6H2{(C=O)N(CH2)2PPh2}2)], which contains two PNC-pincer groups. Reaction of a 1:1 mixture of dpipa and [Pt(O2CCF3)2(SMe2)2], which contains only one platinum atom, gave double metalation of dpipa in the dimeric product [Pt2{m-k4-PPNC-C6H3(CONH(CH2)2PPh2)(CON(CH2)2PPh2)}2], which contains one PNC-pincer group for each dpipa ligand used. Related reactions were monitored by NMR spectroscopy and gave insight into the reaction sequences involved in the cyclometalation steps. It is argued that phosphine coordination directs a first N-H bond activation and then, in a faster step, that the amido group formed in this step directs an aryl C-H bond activation step, to give double cyclometalation of one arm of the dicarboxamide-diphosphine ligand and that, if stoichiometry allows, this can be followed by similar double cyclometalation of the second arm to give the quadruply cyclometalated ligand.

Chapter 7 focuses on the preparation of a new diphosphine ligand, N,N’-bis(2-diphenylphosphinoethyl)phthalamide, dpppa, and its complexes with gold(I) and silver(I). The ligand dpppa forms the binuclear gold(I) complex [Au2Cl2(m-dpppa)], and the polymeric complex [{Ag2(m-O2CCF3)2(m-dpppa)}n]. The ligand and both complexes undergo further association through hydrogen bonding to give supramolecular polymer or network structures.

Chapter 8 describes the chemistry of the ligand dpppa with platinum(II). The reaction of dpppa with [Pt2Me4(m-SMe2)2], in a 2:1 ratio gave a mixture of [PtMe2(dpppa)] and [Pt2Me4(m-dpppa)2], both of which contain Pt...H-N hydrogen bonds. However, reaction in a 1:1 ratio gave a remarkable tetraplatinum complex [Pt4Me6(m-dpppa-H)2], which is shown to contain two Pt-Pt donor-acceptor bonds, and in which one arm of the dpppa ligand has been cyclometalated. The reaction of [PtCl2(dpppa)] with silver trifluoroacetate, to abstract chloride, and triethylamine as base has given the bis(cyclometalated) complex [Pt(dpppa-2H)] and this has been crystallized in three different forms, in which one or both of the carbonyl groups act as donors to a proton or to silver(I). The complex [Pt(dpppa-2H)].AgO2CCF3.dmso forms a dimer and [Pt(dpppa-2H)].(AgO2CCF3)2 forms a coordination polymer in the solid state.

In chapter 9, the pyridine-carboxamide ligand PhNHC(=O)-2-C5H4N is shown to react with Na[AuCl4] either by cation exchange, to give [PhNHC(=O)-2-C5H4NH][AuCl4], or by ligand substitution to give [AuCl2(k2-N,N’-PhNC(=O)-2-C5H4N)]. Similar reactions with bis(pyridine-carboxamide) ligands gave complexes [AuCl2(k2-N,N’-RNC(=O)-2-C5H4N)], with R = (CH2)3NHC(=O)-2-C5H4N or 2-C6H4NHC(=O)-2-C5H4N, in which the ligands are bidentate, but no complexes with tetradentate ligands could be isolated. The complex [AuCl2(k2-N,N’-PhNC(=O)-2-C5H4N)] in methanol solution is an efficient catalyst for oxidative cyanation of PhNMe2 to give PhMeNCH2CN, and it is proposed that the catalysis involves gold(I), gold(II) and gold(III) intermediates.


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