This article describes three types of photoreactions of the complexes (CO)5MM'(CO)3(alpha-diimine) (M, M' = Mn, Re). First of all, halogen atom transfer reactions are discussed which take place in the presence of halocarbons. Reactions with CCl4 and CBr4 appeared to proceed by a radical chain mechanism. This catalytic behaviour was ascribed to the CX3 radicals, formed out of CX4 which can initiate secondary halogen atom transfer reactions. Quantum yields for the reactions with halocarbons were therefore determined for CH2Cl2 which did not show a catalytic behaviour because of its higher C-Cl bond dissociation energy. For all complexes high quantum yields were obtained (0.3-0.7) and variations of these values throughout the series of complexes were ascribed to changes in spin-orbit coupling and rates of non-radiative decay processes. The photoreactions were also studied in the presence of 9,10-phenanthrenequinone in order to confirm that these quantum yields were indeed a measure for the photolysis of the parent compounds. Quinones are known to react with the primary photoproducts of both the CO loss and M-M' bond homolysis reactions. From the agreement between the quantum yield data for the reactions with CH2Cl2 and 9,10-phenanthrenequinone, it was concluded that the CO loss products of the (CO)5MM'(CO)3(alpha-diimine) compounds, contrary to those of the Ph3SnMn(CO)3(alpha-diimine) complexes, also react with halocarbons. Finally, the complexes (CO)5MRe(CO)3(alpha-diimine) photodisproportionate in the presence of 2e-donors L (L = THF, PR3) into M(CO)5- and Re(CO)3(alpha-diimine)(L)+ ions. Irradiation of the complexes in toluene at 183 K gave rise to another electron transfer reaction, viz. the formation of a contact ion-pair (CIP). The CIPs [M(CO)5----Re(CO)3(alpha-diimine)+] showed a characteristic low frequency nu(CO) band of a bridging CO ligand that was not present in the spectra of solvent-separated ion-pairs.