Synthesis of amino-phenolate manganese complexes and their catalytic activity in carbon dioxide activation and oxidation reactions

Two manganese(III) compounds were studied as catalysts for the reaction of carbon dioxide with propylene oxide, styrene oxide, and cyclohexene oxide, and formed cyclic carbonate products selectively under solvent free conditions in the presence of an ionic co-catalyst such as TBAB or PPNCl. Variable temperature kinetic studies allowed the activation energy for propylene carbonate formation to be determined (64 kJ [mol.sup.-1]). The catalysts showed good stability in these reactions and overall turnover numbers (TON) of up to 6000 were observed. The complexes showed low activity for the aerobic oxidation of 4-methyoxybenzylalcohol to the corresponding aldehyde, achieving up to 40% conversion in 72 h. However, near quantitative conversion of 1,2-diphenyl-2-methoxyethanol to provide up to 90% yield of benzaldehyde could be achieved over the course of 5 days. Both complexes showed similar reactivity in the two catalytic processes, and this is likely due to the weakly coordinating nature of the pendant donor within the tetradentate ligand. Key words: manganese, oxidation catalysis, NO ligand, carbon dioxide, C-C cleavage. Nous avons etudie deux composes de manganese(III) comme catalyseurs de la reaction entre le dioxyde de carbone et l'oxyde de propylene, l'oxyde de styrene ou l'oxyde de cyclohexene. Cette reaction a donne lieu a la formation selective de carbonates cycliques dans des conditions sans solvant, en presence d'un cocatalyseur ionique tel que le TBAB ou le PPNCl. Des etudes cinetiques a differentes temperatures ont permis de determiner l'energie d'activation pour la formation du carbonate de propylene (64 kJ mol[.sup.1]). Les catalyseurs ont montre une bonne stabilite dans ces conditions de reaction. En effet, nous avons observe jusqu'a 6 000 cycles catalytiques. Ces complexes ont montre une faible activite pour l'oxydation aerobie du 4methoxybenzylalcool en l'aldehyde correspondant, la conversion atteignant 40 % en 72 h. Cependant, ils ont montre une conversion presque quantitative du 1,2diphenyl-2-methoxyethanol, qui a permis d'obtenir le benzaldehyde correspondant dans un rendement atteignant 90 % en 5 jours. Les deux complexes ont montre une reactivite similaire dans les deux processus catalytiques, et cela s'explique probablement par la faible coordination du groupe donneur appendiculaire que porte le ligand tetradentate. [Traduit par la Redaction] Mots-cles: manganese, catalyse d'oxydation, ligand NO, dioxyde de carbone, clivage C-C.
Introduction Amino-phenolate ligands are easily tailored in terms of their electronic and steric properties, and with their combination of donors, they are readily suited for coordination with metals from across [...]