High-yield synthesis and catalytic response of chainlike hybrid materials of the [(MoO3)m(2,2′-bipyridine)n] family

Abstract

The one-dimensional organic–inorganic hybrid material [MoO₃(2,2′-bipy)] (1) (2,2′-bipy = 2,2′-bipyridine) has been used as a starting material to prepare the bipy-deficient phases [Mo₂O₆(2,2′-bipy)] (2) and [Mo₃O₉(2,2′-bipy)₂] (3) in excellent yields. The hybrid 2 was obtained by a solid-state thermal treatment of 1 (300 °C, 10 min) while 3 was obtained by a hydrothermal treatment of 1 (160 °C, 6 d). A study was performed to compare the catalytic properties of 1–3 in the epoxidation of cis-cyclooctene at 55 °C with tert-butylhydroperoxide (TBHP) or aqueous H₂O₂ as oxidant. In all cases Cy was converted to cyclooctene oxide (CyO) with 100% selectivity, and Cy conversions increased in the order 1 < 3 < 2, which parallels an increase in the Mo/2,2′-bipy molar ratio of the hybrid (1 < 1.5 < 2). With compound 2, CyO yields at 24 h were 96% for TBHP (cosolvent α,α,α-trifluorotoluene) and 53% for H₂O₂ (cosolvent CH₃CN). The catalytic reactions occurred in homogeneous phase with active species formed in situ from 1–3. All three hybrids react with aqueous H₂O₂ to give the catalytically active oxodiperoxo complex [MoO(O₂)₂(2,2′-bipy)]. The 2 : 1 hybrid 2 was further examined for the epoxidation of other cyclic and linear non-functionalised olefins with TBHP, namely cyclododecene, 1-octene and trans-2-octene, and the biomass-derived olefins DL-limonene, α-pinene and methyl oleate.