Mononuclear ReI complexes derived from pyrazolyl-piridazine : Structure and photophysical properties

Rhenium(I) diimine tricarbonyl complexes have attracted the researchers attention during the last deades because of their useful photophysical properties, well-behaved synthesis and stability. 1 This includes light capture for reactions, anion sensing, biolabeling and therapy, carbon dioxide photo-reduction, among others. Its complexes with chelating di-imines characteristically exhibit light absorption with moderate values of molar extinction coefficient in the visible to near UV region, which corresponds to metal to ligand charge transfer (MLCT) transition. Simple imines like pyrazolyl-pyridazine derivatives are appealing candidates to be explored, owing to their planarity and limited conformational flexibility; diminishes non-radiative deactivation paths. They are also relatively easy to be prepared and modified as request. Examples of complexes of pyrazolyl-piridazine coordinating to metals belonging to any of the transition series have been described. 2 Although this situation, coordination to ReI(CO)3X (X = Cl or Br) fragments are limited. In the present paper we present the present the synthesis and structure of a series of monometallic ReI complexes based on the pyrazol-pyridazine moiety with different substituents in order to explore the tuning of the photophysical properties and its potential use as ligands to a second metal site.