Epoxidation of cyclohexene catalyzed by new derivatives of cis-dioxomolybdenum(VI) complexes with bis-bidentate Schiff-base Supported on Single Wall Nanotubes (SWNTs)

Epoxides are useful compounds that have found applications in diverse areas. Many different methods for the preparation of epoxides have been developed, but the most extensive industrial method is the oxidation of alkenes to the corresponding epoxide in liquid phase with organic hydroperoxides in the presence of a catalyst. Indeed, hydrocarbon-soluble transition metal complexes can be employed as homogeneous catalysts. Epoxide selectivity depends on the Lewis acidity and the oxidation state of the metals [1,2]. High surface area carbons have been the supports of choice for many noble metals and Lewis acids to convert a homogeneous into a heterogeneous process [3]. A special type of carbon that has attracted much current interest is carbon nanotubes [4] and in particular single-walled carbon nanotubes (SWNTs) [5]. Besides chemical composition (SWNTs are considered a new allotropic form of elemental carbon, while active carbons contain H as well as significant percentages of O, N, and S depending on the source [6]), the major difference between carbon nanotubes and active carbons is the well-defined structure of the former that contains exclusively fibers or bundles of fibers of several micrometers in length. In particular, the sample of SWNTs used in the present work is formed exclusively by nanotubes of 1–2 nm in diameter and bundles of them with lengths of 5–30 μm, having a specific surface area of 400 m2 g–1 While this area is far from the maximum specific area achievable in activated carbons, the special structured topology of the SWNT surface introducing a characteristic periodicity and regularity may play a positive role when these materials are used as supports in heterogeneous catalysis. However, to our knowledge, there is lack of report on epoxidation by using SWNTs supported homogeneous catalyst. Both the effect of SWNTs as support on the oxidative activity and selectivity of homogeneous catalyst and the stability of SWNTs as carbon materials at mild oxidation conditions are still uncertain. In this paper, we reported three kinds of easily prepared dioxomolybdenum(VI) complexes; [MoO2L1]2, [MoO2L2]2, [MoO2L3]2; and their catalytic applications in the epoxidation of cyclohexene with tert-butylhydroperoxide (TBHP). Also, we reported new advances in the epoxidation of cyclohexene catalyzed by new bis-bidentate Schiff-base Mo(VI) complexes with additive SWNTs under mild reaction conditions