Organometallic complexes featuring oligo-phenylene ethnylene ligands

Abstract

This thesis describes the synthesis and analysis of organometallic complexes that feature oligo-phenylene ethynylene based ligands. Chapter 1 introduces the general topic of molecular electronics and provides a general overview of the interest in phenylene ethynylene systems as foundation architectures for molecular wires. The role of metal complexes in molecular electronics and the application of the cluster - surface analogy to the study of model systems is also described. Chapter 2 describes the synthesis of oligo-phenylene ethynylene pro-ligands of the general form Мe(_3)SіС≡СС(_6)H(_4)C≡СС(_6)H(_4) (1-5), in which R is either an electron donor (Me, OMe) or acceptor (СО(_2)Ме, NO(_2), CN). The compounds were synthesised either via Sonogashira Pd/Cu cross-coupling reactions or via the nucleophilic attack of benzoquinones by lithiated acetylide anions and subsequent reduction. The desilylation of these compounds afforded the terminal alkynes НС≡СС(_6)Н(_4)С≡СС(_6)Н(_4)R (6-10). Furthermore, the extended "three-ring" 1,4- bis(phenyl ethynylbenzene) derivatives Мe(_3)SіС≡СС(_6)Н(_4)С≡СС(_6)Н(_4) ≡C(_6)H(_4)С≡СSiMe(_3), 11 and Мe(_3)SіС≡СС(_6)Н(_4)С≡СС(ОМе)(_2)(Н)(_2)С≡С(_6)Н(_4)С≡CSiMe(_3), 13 and the terminal alkyne НС≡СС(_6)Н(_4)С≡СС(OMe)(_2)(H)(_2)C≡ C(_6)(h)(_4)C≡CH (14) have also been prepared. These compounds were fully spectroscopically characterised and in the case of 14 the molecular structure analysis is discussed. Chapter 3 discusses the synthesis of the gold(I) oligo-phenylene ethynylene complexes The complexes were prepared by treating the ligands precursors 1-5 with АuСl(Рl(_3)) (L = Ph or Су) in the presence of NaOMe to afford complexes Аu(С≡СС(_6)Н(_4)С≡СС(_6)Н(_4)R)PPh(_3) [R = Me (15), OMe (16), СО(_2)Me (17), NO(_2) (18) and CN (19) and Аu(С≡СС(_6)Н(_4)С≡СС(_6)Н(_4)R)PCy(_3) [R = Me (20), OMe (21) and NO(_2) (22)]. The "three-ring" complexes 2(μ-С≡СС(_6)H(_4)С≡СС(_6)Н(_4)С=С(_6)Н(_4)С≡С), 23 and (_2)( μ-C≡CC(_6)H(_4)C≡CC(_6)(OMe)(_2)H(_2)C≡C(_6)H(_4)C≡C 24 were also prepared. These complexes were spectroscopically characterised and molecular structural analyses reveal intermolecular interactions between the phenylene ethynylene portion of the molecules in the solid state, but not aurophilic interactions. Chapter 4 examines the synthesis of half-sandwich Ru(L(_2))Cp' [L = РРh(_3), Cp' = Cp ; L(_2) = dppe, Cp' = Cp*) acetylide complexes derived from simple phenyl, tolan and oligo(phenylene ethynylene) based acetylenes. The electrochemical properties of these complexes have been explored, as have some of the molecular structural details. Chapter 5 describes the synthesis of some cluster complexes. The gold acetylide complexes Аu(С≡СС(_6)Н(_4)С≡СС(_6)Н(_4)R)(РРh(_3)) react readily with Ru(_3)(CO)(_10)(μ-dppm) to afford phenylene ethynylene derivatives Ru(_3)(μ-АuРРh(_3))(μ-С(_2)С(_6)Н(_4)С≡СС(_6)Н(_4)-R)(μ-dppm)(C0)(_7) (38-42) in which the conjugated organic moiety is "end-capped" by the cluster and an R group that is either electron donating or withdrawing (R = Me, OMe, СО(_2) Мe, NO(_2), CN). The clusters 38-42 are linked to the hydrido clusters Ru(_3)(μ-Н)(μ-С(_2)С(_6)Н(_4)С≡СС(_6)Н(_4)R)(СО)(_7) (36 and 37) through the well-known isolobal relationship between H and Аu(РR(_3)). In addition, the bis-cluster (_2)(_2)(μ-C(_2)C(_6)H(_4)C≡CC(_6)H(_4)C≡CC(_6)H(_4)C(_2)) (43) has also been prepared. All the clusters reported in this chapter were crystallographically determined. Structural, spectroscopic, photophysical and electrochemical studies were conducted and have revealed little electronic interaction between the remote substituent and the organometallic end-caps. Chapter 6 explores the novel, preparative scale stoichiometric transmetallation reactions involving the simple Аu(С≡СR)(РРh(_3)) (R = Ph or С(_6)Н(_4)Мe) complexes. These gold(I) complexes have been treated with several inorganic and organometallic compounds MXL(_n) [M = metal, L(_n) = supporting ligands, X = halide], to afforded the corresponding metal-acetylide complexes M(C≡CR)L(_n), with representative examples featuring metals from Groups 8-11. The acetylide products were fully characterised by usual spectroscopic methods including the molecular structural analysis. Chapter 7 concludes the general summary of the thesis and discusses briefly the findings achieved in each chapter and the vital role of oligo-phenyelene ethynylenes ligands in the construction of numerous organometallic complexes which show interesting and promising properties for the molecular wires development. In addition, further future work is also proposed on other systems that feature this ligands.