In this work, a series of novel rhenium and molybdenum carbonyl complexes carring 1,2-diimine ligands as strong [pi]-acceptor moieties with chromophoric metal to ligand charge transfer (MLCT) bands in the visible spectral region is reported. The first part of the work focuses on the synthesis and characterization of rhenium tricarbonyl chloride complexes carring substituted bis(arylimino)acenaphtene (BIAN) ligands by means of various spectroscopic methods. Among these derivatives, the remarkable example of a deeply coloured water soluble and stable organometallic compound is presented, which offers highly desirable features for biomedical applications. This water soluble rhenium carbonyl complex is introduced as a carrier for the controlled release of carbon monoxide (CORM) under physiological conditions. Further detailed studies on cellular uptake of the rhenium carbonyl derivative into human cells and cell morphology effects show a reasonable biocompatibility and a negligible dark cytotoxicity. Furthermore, the non-water soluble rhenium-BIAN derivatives are tested as potential catalysts for CO2 reduction. Cyclic voltammetry measurements and controlled potential electrolysis experiments are performed to determine the catalytic CO2 reduction capability of the complexes. Additionally, rhenium and molybdenum carbonyl complexes bearing pyridine based 1,2-diimine ligands are reported. The molecular structures of the derivatives are determined by X-ray diffraction. Finally, the photoreactivity and luminescent properties of the complexes are described.