Synthesis and characterization of dendritic salicylaldimine complexes of copper and cobalt and their use as catalyst precursors in the aerobic hydroxylation of phenol

• Published in: Inorganica Chimica Acta 2013-01, Vol.394, p.649-655
• Main Authors: Mapolie, S.F., van Wyk, J.L.
• Format: Article
• Language: English
• Subjects: Dendritic complexes; Hydroxylation; Metallodendrimers; Phenol; Phenol oxidation; Salicylaldimine complexes
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2012.09.006

Novel metallodendrimers of Cu and Co were found to be active catalysts for the hydroxylation of phenol using H2O2 and molecular oxygen as oxidants. Catechol and hydroquinone were found to be the major products with catechol being produced in higher amounts at pH 6. The cobalt based catalysts showed a substantially higher selectivity for catechol than their copper analogues producing this isomer in amounts exceeding 80% of the product mix. [Display omitted] ► In this paper we report on the preparation of new diaminobutane cored metallodendrimers of copper and cobalt. ► These dendritic complexes are active catalysts for the hydroxylation of phenol when used in conjunction with H2O2 as oxidant. ► The copper catalysts are more active than the cobalt analogues. ► The cobalt catalyts exhibit high selectivity to catechol as product. A series of generation 1 (G1) and generation 2 (G2) salicylaldimine functionalized polypropylene imine dendrimers were used to prepare a range of new copper and cobalt metallodendrimers. These were found to be efficient catalysts in the aerobic hydroxylation of phenol using H2O2 and molecular oxygen as oxidants. The major products obtained were catechol and hydroquinone. The selectivity to these two products was greatly influenced by the nature of the metallodendrimer as well as by the pH of the reaction medium.