Synthesis of phthalocyanine compounds utilizing thymol and carvacrol azo dyes as catalysts in transfer hydrogenation of aromatic aldehydes and ketones with 2-propanol

Abstract

Hydrogen transfer reduction systems are attracting increasing interest from synthetic chemists because of their simplicity in functioning. In this work, eight new metallophthalocyanine (MPc) compounds ligated on phthalonitrile ligands, including thymol or carvacrol, have been structurally elucidated and used as precatalysts in the transfer hydrogenation (TH) of acetophenone. FT-IR and UV–vis spectroscopies, elemental analyses, and LC-MS spectrometry were used to establish the molecular structures of the new phthalocyanine complexes. The nickel compounds (1b and 2b) act as efficient catalysts, which bring about catalytic TH reactions of a broad array of ketones in propan-2-ol and inert conditions (99% conversion in 3.5 h for 1b and 97% conversion in 4 h for 2b, respectively). The electronic properties arising from the position of the groups on the ligand and the nature of the metals appear to regulate the catalytic performances of the complexes in transfer hydrogenation. Furthermore, the modular construction of these catalysts and their flexibility toward transfer hydrogenation (TH) make these systems to pursue.