Aerobic oxidation of benzylic alcohols catalysed by new (aryl‐BIAN)copper(I) complexes: Their synthesis and structural characterization

• Published in: Applied organometallic chemistry Vol. 37; no. 9
• Main Authors: Rosa, Vitor, Laronha, Helena, Gomes, Clara S. B., Cordas, Cristina M., Brinco, João, Freitas, Flávia, Gomes da Silva, Marco D. R., Avilés, Teresa
• Format: Journal Article
• Language: English
• Published: HOBOKEN Wiley 01.09.2023; Wiley Subscription Services, Inc
• Subjects: Acetonitrile; alcohol oxidation; Alcohols; Aldehydes; Argon; Aromatic compounds; Ar‐BIAN ligands; Catalytic activity; Chelates; Chemistry; Chemistry, Applied; Chemistry, Inorganic & Nuclear; Copper bromide; Copper chloride; Cu(I); Dimers; Electrochemical analysis; Halides; homogeneous catalysis; Ligands; Molecular structure; NMR spectroscopy; Oxidation; Physical Sciences; Refluxing; Science & Technology; Single crystals; Structural analysis; MECHANISM; Ar-BIAN ligands; CRYSTAL-STRUCTURES; ALDEHYDES; alcohol oxidation; COPPER(II) COMPLEXES; CYCLOADDITION; Cu(I); homogeneous catalysis; NITRILES; LIGANDS SYNTHESIS; ACTIVATED ALCOHOLS; EFFICIENT; WATER
• DOI: 10.1002/aoc.7193
• ISSN: 0268-2605

A new neutral dimeric Ar‐BIAN Cu(I) complex (where Ar‐BIAN = bis(aryl‐imino)acenaphthene) of formulation [CuBr(4‐iPrC6H4‐BIAN)]2 (2) was obtained by reacting CuBr and ligand 4‐iPrC6H4‐BIAN (L2) in refluxing acetonitrile under an argon atmosphere. When the ligand used was 2,4,6‐Me3C6H2‐BIAN (L1), we obtained 1 in which the expected dimer (1a) is present, but we could also observe, in solution, the presence of the bis‐chelate dimer [Cu(2,4,6‐Me3C6H2‐BIAN)2][CuBr2] (1b) bearing CuBr2− as counter‐ion; attempts to separate them failed. When the ligand used was 2‐iPrC6H4‐BIAN (L3), we obtained 3 in which the expected dimer (3a) is in equilibrium, in solution, with its bis‐chelate isomer [Cu(2‐iPrC6H4‐BIAN)2][CuBr2] (3b). The solid‐state molecular structures of compounds 2 and 3b were determined by single crystal X‐ray diffraction. The electrochemical behaviour of complexes: 1 (1a, and 1b), 2, and 3 (3a and 3b) and the known compound [Cu(2‐iPrC6H4‐BIAN)2][BF4] (7) were investigated by cyclic voltammetry. The new complexes 1 (1a, 1b), 2, and 3 (3a, 3b) were tested as catalysts for the aerobic oxidation of benzylic alcohols into aldehydes; they all catalyse the reaction, with good results; the catalytic studies were extended to the similar known complexes [CuBr(2,6‐iPr2C6H3‐BIAN)]2 (4), [CuI(2,6‐iPr2C6H3‐BIAN)]2 (5), [CuCl(2,6‐iPr2C6H3‐BIAN)]2 (6) and (7), in order to study the effect of different bridging halides or counter ions in the catalytic activity. We found that compound 4 exhibited a high catalytic activity comparable to the best results published so far. The oxidation products, benzaldehydes, were detected and further confirmed by NMR spectroscopy, and the conversion rate was determined after GC‐FID analysis.