Lotz, Simon2017-09-012017-09-012017-10-062017Weststrate, N 2017, Structural and electronic features of tungsten(0) and platinum(II) complexes with Fischer carbene ligands, PhD thesis, University of Pretoria, Pretoriahttp://hdl.handle.net/2263/62162Thesis (PhD (Chemistry))--University of Pretoria, 2017Fischer carbene complexes of tungsten pentacarbonyl were synthesised on N,N-dimethylaniline and anisole coordinated in a η6-fashion to a Cr(CO)3 fragment. Single carbene complexes were isolated on all (o-, m-, and p-) positions of the π-coordinated N,N-dimethylaniline while only mono- (o-isomer) and biscarbene (o, o-isomer) complexes were isolated for the π-coordinated anisole. The o-isomers of N,N-dimethylaniline and anisole form five-membered chelate complexes. Cyclovoltammetry and IR spectroelectrochemistry revealed the site dependence of the ring substituents of the N,N-dimethylaniline complexes. For the tungsten pentacarbonyl carbene complexes of N,N-dimethylaniline, electron density from the heteroatom was donated into the ring. The delocalisation effect was greatest p-isomer. No delocalisation of electron density present on the oxygen towards the stabilisation of the carbene complexes present in the compound, was observed. The structural study of the complexes revealed ring distortion because of η6-coordination which also determined the orientation of the tricarbonylchromium tripod with respect to the arene carbons. Further, a series of ethoxy- and aminocarbene tungsten pentacarbonyl complexes were synthesised at the p-position on several aromatic tertiary amines. The aminolysis of the ethoxycarbene complexes was achieved through an economic and novel method developed for the generation of dimethylamine. The remote stabilisation of the Fischer carbene complexes were investigated using NMR spectroscopy, cyclovoltammetry, IR spectroelectrochemistry and X-Ray crystallography. The ethoxycarbene complexes were influenced more by the substituents of the remote nitrogen while the aminocarbene complexes remained unaffected. A series of multi-carbene complexes of Pt(II) was synthesised through a carbene transfer reaction from the previously synthesised tungsten carbene complexes with Pt(COD)Cl2. Neutral bisethoxycarbene complexes and positively charged Pt(II) trisaminocarbene complexes were isolated. The complexes were characterised through NMR spectroscopy, elemental analysis and mass spectrometry. Further, the photophysical properties of the mononuclear complexes were investigated using UV/Vis and emission spectroscopy. The compounds displayed blue fluorescence of low quantum yields, indicating that the photoexcited complexes return to the ground state through a dominant, non-emissive pathway. Multicarbene complexes of binuclear Pt(II) bithienylene bridged compounds were synthesised using the same transmetallation approach. The multicarbene complexes isolated, all of which contained at least five carbene ligands, were singly or doubly charged. The complexes displayed the same blue fluorescence as the mononuclear complexes upon excitation at 380 nm, although at similar or lower quantum yields. Using femtosecond transient absorption spectroscopy, a long-lived charge separated state was observed for all the binuclear Pt(II) carbene complexes. Finally, a comparison between analogous mono- and binuclear Pt(II) carbene complexes revealed that the blue fluorescence observed upon photoexcitation at 380 nm for both types of complexes is carbene ligand-based. Further, it was postulated that the charge separated state formed with the positive polaron found on the bithienylene bridge while the negative polaron is found on one of the carbene carbons at positively charged Pt(II) fragment. The study represents the first comprehensive investigation of the electronic features of the photoactivation of selected Pt(II) Fischer carbene complexes.enChemistryUCTDThesis