Oxidatively Resistant Ligands for Palladium-Catalyzed Aerobic Alcohol Oxidation

The complex [(neocuproine)Pd(OAc)]2[OTf]2 (1) catalyzes the aerobic oxidation of 2-heptanol at room temperature, but competitive ligand oxidation leads to low catalyst lifetimes. In an effort to mitigate the oxidative degradation of the ligand, a variety of Pd complexes ligated by fluorinated phenanthrolines (bis-2,9-(trifluoromethyl)-1,10-phenanthroline (btfm-phen), 4-methyl-2-(trifluoromethyl)-1,10-phenanthroline (tfmm-phen), and 2-(o-difluorophenyl)-1,10-phenanthroline (odfp-phen)) were prepared and tested. Active catalyst precursors were generated by in situ conproportionation of (N−N)Pd(OAc)2 and [(N−N)Pd(NCCH3)2[OTf]2. Pd complexes derived from tfmm-phen catalyzed the aerobic oxidation of 2-heptanol at room temperature with up to 22 turnovers, nearly double that of 1.