Investigation of selectivity in C-H bond activation by platinum

The synthesis, structure, and photophysical properties of a series of novel, highly luminescent tridentate platinum complexes with general coordination geometry of (C^N*N)-PtL are reported, where "C^N" denotes a coordination of C and N to the platinum to form a five-membered metallacycle and "N*N" denotes a coordination of two N atoms to the platinum to form a six-membered metallacycle; L is a mono anionic ligand such as halides or acetylides. Compared to the known (C^N^N)-PtL type of complexes that were reported to emit with low quantum yields, the structural modification leads to dramatic improvements in phosphorescence efficiency. For example, new complexes (C^N*N)-PtL with L = hexylacetylide and phenylacetylide emitted intensely with quantum yields of 47% and 56%, respectively, latter of which is among the highest quantum yields reported so far for cyclometalated platinum (II) complexes. Selectivity in C-H bond activation by platinum and the exact mechanism of cycloplatination are issues that still remain unclear. A series of ligands which include sp²/sp³, primary/secondary sp³ C-H bonds, and aromatic/vinylic sp² C-H bonds with a carbon linker between the bipyridine and the carbon groups have been prepared. All ligands have been attempted for cycloplatination in glacial acetic acid and acetonitrile. All ligands produced the same sp² C-H bond activated complex in both solvents, which suggests that the linker atom does play a role on selectivity.M.S