The first chapter consists of a literature review of the known photochemistry of the compounds studied in this work along with relevant related systems. The second chapter describes the photochemistry of a number of (r|6- arene)Cr(CO)3 compounds. The rate constants for the reaction of photogenerated solvated dicarbonyl intermediate derived from these compounds with carbon monoxide were measured by UV/vis. monitored laser flash photolysis. These rate constants were found to depend on the nature and number of the substituents on the arene ligand. The associated activation parameters for these reactions were also determined. The difference in the rate constants were found to be the result of variations in the activation entropy term, which became less negative as the number of electron donating substituents on the ring increased. The activation enthalpy remained constant however. The displacement of various alkane solvents by CO was measured for the (r|6-benzene)Cr(CO)3 system. Rate constants increased on increasing the alkane chain length. This increase was also the result of an increase in the entropy of activation. The enthalpies of activation were similar for all aliphatic solvents. The photochemisty of (r|6- benzene)Cr(CO)3 was investigated in fluorinated solvents and this was found to differ significantly from the photochemistry in alkane solvents, Cr(CO)6 being formed on irradiating (r|6-benzene)Cr(CO)3 in fluorinated solvents under one atmosphere of CO. Flash photolysis studies were carried out on the analogous molybdenum system in hydrocarbon solvents. No significant variation in rate constants, entropy or enthalpy of activation values were observed for this system irrespective of the nature of the arene or the solvent used. The photochemistries of (ri6-allylbenzene)Cr(CO)3 and (r|6-tetrahydronaphthalene) Cr(CO)3 are reported in chapter three. (r|6-Allylbenzene)Cr(CO)3 behaves differently to any of the previous chromium tricarbonyl systems investigated. Mass-spectrometry of the photoproduct confirmed the presence of three carbonyl ligands. A process involving a change in ring hapticity is proposed to explain these observations. This chapter also outlines the photochemistry of(ri6-tetrahydronaphthalene)Cr(CO)3. This investigation included both UV/vis. monitored laser flash photolysis and Transient Infrared (TRIR) studies. The primary photoproduct was assigned to the carbonyl loss product but a second long-lived species was also observed, the identity of which remains unknown. In the fourth chapter the results of flash photolysis studies are reported for a number of polyaromatic chromium tricarbonyl compounds (namely naphthalene, phenanthrene and pyrene). The photolysis of these compounds in the presence of CO results in the formation of Cr(CO)6 and the liberation of the aromatic ligand. Extensive matrix isolation work was carried out on the (ri6-naphthalene)Cr(CO)3 compound which exhibited wavelength dependent photochemistry. On short wavelength irradiation the dicarbonyl photoproduct is observed while long wavelength irradiation a second species which is attributed to a (r|3- naphthalene)Cr(CO)3-type intermediate was detected. The fifth chapter discusses the photochemistries of both the cis and trans-isomers of (ri6-l,2-diphenylethene)Cr(CO)3. Visible irradiation of the czs-isomer results in a efficient conversion to the trans-isomer as confirmed by NMR and UV/vis. spectroscopy. The molecular structure of the /ram-isomer was also determined by single crystal X-ray diffraction. Within the sixth chapter the photochemistry of a number of pentadienyl manganese carbonyls compounds is reported along with the photochemistry of (r) 3-C3H4-C6H5)Mn(CO)4 and Mn(CO)4(r|3-C3H4-ri6-C6H5)Cr(CO)3. The photochemistry of the dinuclear compound was intially investigated using laser flash photolysis but as the results were not conclusive it was decided to investigate a number of manganese ligands namely (r\ l-pentadienyl)Mn(CO)5’ (r)3-pentadienyl)Mn(CO)4 and (rj5-pentadienyl)Mn(CO)3. The final chapter consists of the experimental procedures used for the preparation and analysis of the compounds synthesised in this work.