PHOTOGENERATION, CHARACTERIZATION, AND KINETIC STUDY OF A NEW PHTHALOCYANINE SPECIES

In the search for green chemistry, the development of synthetic metal complexes that model enzyme function has been extensively studied. Phthalocyanine metal complexes, closely related to these heme-containing macrocycles, have gained continued interest due to their ease of direct synthesis, efficient redox, and optical properties. Despite the significant progress in phthalocyanine metal complexes, much more work needs to be done in the characterization and identification of their metal-oxo species, as well as mechanistic insights into their catalytic oxidations. To date, the reactivity of metal-oxo species on phthalocyanine platforms has not been probed. In this study, metal phthalocyanine complexes have been synthesized using a facile direct method. Importantly, a new phthalocyanine-manganese-oxo intermediate was generated by visible-light photolysis of chlorate or nitrite manganese (III) precursors and the metastable oxo species was characterized by UV-vis and ESI-MS. The photo-generated manganese-oxo species showed wide levels of reactivity towards alkenes, benzylic hydrocarbons, and alcohols. The second-order rate constants (kox) vary from 1.4 × 10-2 M-1s-1 for cyclohexene to 1.2 M-1s-1 for phenol. The oxidation kinetics has provided insights into the structure-function relationship of organic substrates and an understanding of their involvement in the catalytic oxidations. For comparison, the same oxo species was also produced by chemical oxidation of manganese (III) precursor using PhI(OAc)2 as the mild terminal oxidant.