Synthetic and computational studies of conjugated acetylenic systems

Abstract

Conjugated molecular materials offer a range of useful physical properties from highly efficient luminescent behaviour to wire like conduction. This thesis describes the synthesis, molecular and electronic structures of a range of unusually conjugated organic and organometallic compounds. A combination of synthetic and absorption spectroscopic studies, as well as calculations (DFT) were used to probe the electronic structure of the 1, 4-bis(phenylethynyl)benzene and 1,2,4,5-tetraethynyl benzene framework. These revealed that the ground state of l,4-bis(phenylethynyl)benzene type molecules can be described as thermally populated distributions of conformers, while the exited state is best described in terms of planar conformations with considerable acetylenic character. A novel synthesis of 1,1,2,2-tetraethynylethenes has been discovered involving cross-coupling reactions of tetrachloroethene with terminal acetylenes. Reactions of these tetraethynylethenes with [Co(_2)(CO)(_6)(L(_2))][L(_2)= (CO)(_2), dppm] give complexes with one or two (trans) cobalt fragment coordinated to the acetylenic moieties. A theoretical study of the electronic structure of [Ru(L)(_2)Cp] (n = 1-6; L = CO, PH(_3); R = CH(_3), H, C(_6)H(_4)NH(_2)-p, C(_6)H(_5), C(_6)H(_4)NO(_2)-P, CN) has been carried out. The redox potentials of these species may be tuned by the length of the polyynyl ligand, the nature of the supporting ligands, as well the electronic properties of the non-metal end-cap. Electrochemical and spectroelectrochemical analysis of [Ru(_4)(CO)(_11)](Ų4-(RC(_2)C≡CR)(_2)](^0/2-) have revealed an unusual reversible conversion of 62/64 CVE cluster frameworks. This switching behaviour has been modelled using [Ru(_4)(C0)(_11)(Ų4-HC(_2)H)(_2)](^0/2)- via DFT methods.