Anionic Cyclometalated Platinum(II) Tetrazolato Complexes as Viable Photoredox Catalysts

The synthesis, characterization, photophysical and photocatalytic studies of anionic platinum(II) tetrazolato complexes, with the general structure [TBA] [Pt(CNC)TzR], are reported, where CNC2- represents a doubly cyclometalated 2,4,6-triphenylpyridine, TzR(-) is an anionic 5-substituted tetrazolato ligand (with a variable R functional group), and TBA(+) is the tetrabutylammonium countercation. The complexes were prepared by substitution of the DMSO ligand in [Pt(CNC)(DMSO)] with the corresponding tetrazolato ligand. No emission from the platinum(II) complexes was detected at room temperature in solution, but the photophysical properties could be assessed in the solid state, where all the complexes display emission bands attributed to aggregates. The platinum(II) complexes were found to facilitate a range of fundamental classes of visible-light-mediated photoredox-catalyzed reactions, including alpha-amino C-H functionalization processes, such as Povarov-type reactions and the addition of a-amino C-H bonds across Michael acceptors, in addition to ATRA chemistry, and a hydrodeiodination. With the exception of the hydrodeiodination process, the best Pt(II) catalysts provided turnover numbers of 150-175 in each of these transformations.