The photochemistry of azaferrocene and its derivatives
Heenan, Davnat (2002) The photochemistry of azaferrocene and its derivatives. PhD thesis, Dublin City University.
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Chapter one contains a literature survey of the relevant organometallic chemistry and the current understanding of the bonding in these systems, along with a theoretical description of the electronic structure of ferrocene. A brief outline of the techniques used to characterise the photochemical intermediates in this research is presented. The main part of the chapter consists of a literature review of the photo and thermal chemistry o f half sandwich complexes, such as the rj6-arene-chromium tricarbonyl system.
Chapter two opens with a review of the photochemistry of ferrocene, (^-CsHs^Fe and goes on to detail the results of the investigation into the photochemistry of azaferrocene, (775-C5H5)(775-GiH4N)Fe. The photochemistry of azaferrocene is then described in alkane solvents at room temperature using both steady-state photolysis and laser flash photolysis. The matrix photochemistry monitored by ultraviolet-visible (UV-vis) and Fourier transform infrared (FT-IR) spectroscopy is also presented. Room temperature photolysis using broad band irradiation ( \ xc. > 500 nm) in carbon monoxide saturated cyclohexane produced cyclopentadienyliron dicarbonyl ij'-pyrrolyl, while monochromatic irradiation (\ xc. = 532 nm) also produced an allyl monocarbonyl complex, e*o-(ij5-C5H5)Fe(CO)(?73-C-C4H4N), as identified by FT-IR. In carbon monoxide doped argon matrixes at 12 K, both (^-CsHs^etCOMr/'-vV^I^N), and (rj5- C5H5)Fe(CO)(771-ALC4H4N) were observed following broad band irradiation (Kxc. > 495 nm) of azaferrocene in a ratio dependent on the concentration of carbon monoxide in the matrix. Initial photolysis with monochromatic irradiation (XeXC. = 538 nm) followed by broad band irradiation (XeXC. > 495 nm) in carbon monoxide doped matrixes formed an additional monocarbonyl complex, assigned to an azaallyl complex, (rj5-C5H5)Fe(CO)()?3-AA-C4H4N).
Chapter three reviews the photochemistry of (r/5-C5Hs)Fe(CO)2X, (X = Cl, Br, I or CH3, C3H5, C6H5 etc.). In addition, photochemical studies o f (7y5-C5H5)Fe(CO)2(ij1-Af-C4H4N) and (jj5-C5H5)Fe(CO)2(i?1-A^-C8H6N) are detailed. Steady-state photolysis, laser flash photolysis and in the case of (ij5-C5H5)Fe(CO)2(i71-iV-C4H4N), matrix isolation techniques were employed to detect and identify the photochemical intermediates. These results suggest that carbon monoxide loss is the dominant photoprocess. The activation parameters were also measured for the reaction o f the monocarbonyl, (r/5- C5H5)Fe(CO)(?71 -/V-C4H4N) with carbon monoxide to regenerate (i]5-C5H5)Fe(CO)2(r?'- N-C4H4N) in carbon monoxide saturated cyclohexane at \ xc. = 355 nm. No significant variation in the rate constant was observed for the reaction o f (?j5-C5H5)Fe(CO)(rj1-A^- C4H4N) with carbon monoxide to reform -(^-CsHs^eiCO^CV-N^HUN), irrespective of the solvent used.
The results of an investigation into the photochemistry of 2,5-dimethylazaferrocene, (r/5-C5H5)(i]5-2,5-C4(CH3)2H2N)Fe are presented in chapter four. High energy photolysis (Xexc. > 410 or = 355 nm) of 2,5-dimethylazaferrocene in carbon monoxide saturated solutions leads to predominantly to the formation of the (r/5-C5H5)Fe(CO)2(ij1- yV-2,5-C4(CH3)2H2N) and the iron dimer [(r/5-CsH5)Fe(CO)2]2- Low energy photolysis (^exc. > 500 or = 532 nm) on the other hand, leads to the formation of two more carbonyl containing complexes in addition to the dicarbonyl complex and the dimer described above. Matrix isolation studies in carbon monoxide doped argon matrixes revealed evidence o f intramolecular C-H activation occurring.
The final chapter contains the experimental details of the complexes synthesised, the method used for sample preparation for the flash photolysis experiments. Details of the equipment used for the laser flash photolysis and matrix isolation experiments is also outlined.
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