Synthesis and Study of bis(η5-Cyclopentadienyl) (Ene-1,2-Dithiolato)titanium(IV) Complexes. A Contribution to the Investigation of Metal-Sulphur Bond

• Main Author: De Lena, Jorge Carvalho
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1994
• Subjects: Organic chemistry
• ISBN: 0438687868; 9780438687868

The preparation of a series of substituted 2,3-quinoxaline-dithiol derivatives is described. These compounds and other ene-1,2-dithiols were used in the preparation of a series of bis(η5-cyclopentadienyl)(ene-1,2-dithiolato)titanium(IV) complexes. Thus, the syntheses of new complexes of general formula [Cp2Ti(R-qdt)] (where R = H, CH3, Br, CI or F) and [Cp2Ti(Me-sdt)] are described. These compounds together with [Cp2Ti(tdt)], [Cp2Ti(mnt)], [Cp2Ti(sdt)] and [Cp2Ti(bdt)] were used in a systematic study involving UV/VIS spectroscopy, electrochemistry and Optically Transparent Thin Layer Electrode. Their redox properties have been assessed and for the [Cp2Ti(R-qdt)] derivatives the study was carried out in neutral and acidic solution (with added acetic acid). [Cp2Ti(tdt)], [Cp2Ti(bdt)], [Cp2Ti(mnt)], [Cp2Ti(sdt)] and [Cp2Ti(Me-sdt)] undergo one-electron redox process while [Cp2Ti(R-qdt)] present two redox processes both in neutral and acidic solution. These redox properties are influenced by the nature the nature of the ligand. The redox potential is correlated with 1H N.M.R. chemical shifts. The UV/VIS spectra are studied and the OTTLE technique is used to assess the changes in the electronic spectra of these complexes upon reduction. The interpretation and assignments of the electronic transitions for this complexes are proposed on the basis of a molecular orbital scheme proposed in the literature for similar compounds with the general formula [Cp2TiX2] (where X = F, CI, Br or F). 1H N.M.R. spectroscopy identified some interesting features in solution for the [Cp2Ti(R-qdt)] derivatives showing one singlet corresponding to the Cp protons. Variable temperature N.M.R. suggests that the interconversion between the two conformers occurs at faster rates than [Cp2Ti(tdt)], [Cp2Ti(bdt)], [Cp2Ti(sdt)], [Cp2Ti(edt)].