Platinum(II) bis(diketonate) complexes as photocatalysts for organic reactions and mechanistic study.

摘要

As part of a program targeting new photochemical routes to preceramic polymers, our group has been studying the photoreactions of organic silanes with platinum complexes for many years. Platinum(II) β-diketonate complexes have proven to be efficient catalysts for photoactivated hydrosilylation reactions. In this dissertation, my work is aimed at understanding how these complexes initiate chemical processes that involve carbosilanes, particularly hydrosilylation processes. Our purpose is to identify the active species that form as one irradiates a Pt(II) β-diketonate/silane composition in the presence of certain reactant/acceptors. Many new products have also been isolated. Furthermore, applications of these complexes in other organic reactions involving hydrosilanes are reported.; Photochemical reactions of platinum(II) bis(acetylacetonate) [Pt(acac) ₂] in pyridine, piperidine, 2-picoline, 3-picoline and 4-picoline solutions were studied. In the pyridine case, two products were obtained: (2,4-pentanedionato-C 3)(2,4-pentanedionato-O,O′) pyridineplatinum(II), Pt(acac)(γ-acac)pyridine (1a) and bis(2,4-pentanedionato-C 3) bispyridineplatinum(II), Pt(γ-acac)₂pyridine ₂ (1b). Two corresponding complexes were also obtained in the piperidine case, while only the type a complexes could be separated when 2-, 3-, 4-picoline were used.; Platinum(II) bis(hexafluoroacetylacetonate) [Pt(hfac)₂] reacts with ethylene when irradiated at 350 nm to yield a single photoproduct which we were first to successfully isolate. X-ray diffraction reveals that it is a five-coordinated complex Pt(hfac)₂(η2-C ₂H₄), with two bidentate hfac ligands remaining in tact. The photoproducts formed from Pt(hfac)₂ and propene, Pt(acac) ₂ with ethylene and Pt(tfac)₂ with ethylene were also observed. Though attempts to isolate these complexes were not successful, similar structures may be proposed from spectral data.; Platinum (II) β-diketonate complexes have also been discovered to be efficient photocatalysts for the polymerization of epoxides in the presence hydrosilanes. Silanes with greater numbers of silicon-hydrogen bonds are better cocatalysts. A homogeneous, cationic polymerization mechanism is proposed.; Platinum (II) β-diketonate complexes, upon irradiation at 350 nm, were also found to be good catalysts for the hydrosilylation of alkynes, as well for the isomerization of linear alkenes in the presence of excess silane. The major product of the hydrosilylation of alkynes is the β- trans isomer formed by means of a cis addition reaction. In the isomerization reaction, more than 98% isomerization of the alkene occurs immediately after irradiation in the presence of triphenylsilane. There is no concomitant hydrosilylation. (Abstract shortened by UMI.)