Supported bis(maltolato)oxovanadium complexes as catalysts for cyclopentane and cyclooctane oxidations with dioxygen

• DOI: 10.1016/j.molcata.2006.09.049
• Publication Date: 2006-10-10T07:25:09Z
• Authors: Gopal S. Mishra; João J.R. Fraústo...; Armando J.L. Pomb...
• Keywords: Cyclooctane; Cyclopentanes; Cyclopentanone; Cycloheptane; Cycloalkane; Isobutyraldehyde

Abstract Carbamated silica gel supported bis(maltolato)oxovanadium(IV or V) complexes, [VO(ma)2] (1), [VO(py)(ma)2] (2) (py = pyridine), cis-[VO(OCH3)(ma)2] (3) and cis-[VO(OC2H5)(ma)2] (4), were used as catalysts for the oxidation of cyclopentane and cyclooctane by molecular oxygen in a batch reactor, under moderate reaction conditions (typically p(O2) ca. 10–14 atm, at 150–160 °C). The corresponding ketones, i.e. cyclopentanone and cyclooctanone are the main products (up to 10 and 25% yields, respectively) of the cycloalkane oxidations, but cyclopentanol and cyclooctanol are also formed in smaller amounts. The supported complex 1 shows the best activity and selectivity. The reaction is further promoted by the use of some heteroaromatic acids as co-catalysts, namely 2-pyrazine-carboxylic acid. Experiments with radical traps suggest the involvement of a free-radical mechanism.