Organically Functionalized Polyoxovanadium Clusters And Their Catalytic Oxidation Properties

Design and synthesis of function-oriented catalyst is a hot research field of catalysis. Polyoxometalates(POMs) are easy to be modified and designed to meet the needs of the catalytic reaction system due to their redox activity and the regulated structure size. Because of the wide application prospect of carbonyl and sulfone compounds in the organic chemistry and industrial production, the conversion of the cheap and readily available compounds in nature, such as hydrocarbons, alcohols, and sulfides, to these compounds by selective catalytic oxidation becomes a very valuable organic reaction.This paper mainly focus on the design and synthesis of organically functionalized polyoxovanadium clusters and their catalytic properties in the selective oxidation of benzyl hydrocarbons, alcohols, sulfides,and the oxidative desulfurization. The main work is as follows:(1) By regulating the initial reaction conditions, Palladium hybrid and methoxy functionalized Lindqvist type hexavanadate clusters [Pd(dpa)(acac)]2[VV6O13(OMe)6](1), [Pd(dpa)(acac)]2[VIV2VV4O11(OMe)8](2), [Pd(dpa)(acac)]2[VIV2VV4O11(OMe)8]·H2O(3), and [Pd(DMAP)2(acac)]2[VIV2VV4O11(OMe)8]·H2O(4) and a methoxy functionalized Lindqvist type hexavanadate cluster [NHEt3]2[V6O13(OMe)6](5)(dpa = 2, 2’-dipyridine amine; DMAP = 4-dimethylaminopyridine; acac = acetylacetone anion) have been synthesized by conventional method. Their catalytic performance in the selective oxidation of benzyl-alkanes is further investigated. The results show that they all have high activity in converting various benzyl-alkanes to corresponding benzyl ketones using t-butylhydroperoxide as the oxidant and remain stable. Specifically, as a heterogeneous catalyst, compound 1 exhibits more excellent catalytic performance than others and even some homogeneous catalyst under the same reaction conditions(the yield of corresponding ketones of xanthene, fluorene, substituted fluorine close to 100%) and it can be reused without obvious lose of its activity. The mechanism research show that the catalytic reaction may involve a radical process and it is further verified by EPR experiments.(2) Copper hybrid and 1-methylimidazole functionalized polyoxovanadium clusters α-[Cu(m IM)4]V2O6(6), β-[Cu(m IM)4]V2O6(7) and [Cu(m IM)2)](VO3)2(8)(m IM = 1-methylimidazole) have been synthesized by rationally controlling of the solvothermal conditions. It is worth noting that compounds 6 and 7 are isolated as geometric isomers by tuning the solvothermal reaction temperature. As heterogeneous catalysts, compounds 6-8 exhibit excellent catalytic performance in the oxidation of sulfides and alcohols with H2O2 as oxidant. The results show that 6 exhibits more excellent catalytic performance than others under the optimized conditions in the oxidation of sulfides(conv. up to 98.7 %, sele. up to 100 %) and alcohols(conv. up to 98.5 %, sele. up to 100 %) and it can be reused without obvious lose of its activity.(3) To avoid using of noble metal in the first part, copper hybrid and methoxy functionalized Lindqvist type hexavanadate cluster [Cu(dpa)(acac)(Me OH)]2[VIV2VV4O11-(OMe)8](dpa = 2, 2’-dipyridine amine)(9) has been synthesized by conventional method. Its catalytic performance in the oxidative desulfurization of model oil is investigated. The results show that when using hydrogen peroxide as oxidant, the dibenzothiophene and its derivatives can be completely oxidized to the corresponding sulfoxides or sulfones in model oil achieving the purpose of oxidative desulfurization of petroleum. The catalyst can be reused without obvious lose of its activity.(4) A novel Nickel hybrid and organic ligands functionalized polyoxovanadium cluster [Ni2(C2O4)(dpa)4][(C4H6O4)(VO2)]2·2[CH3OH](dpa = 2, 2’-dipyridine amine) was in situ synthesized by a facile procedure and further used as catalyst to oxidize sulfur-containing heterocyclic compounds to corresponding sulfones using molecular oxygen as the oxidant and isobutyl aldehyde as the sacrificial agent in model oil under mild conditions. The results show that under optimized conditions, the dibenzothiophene and its derivatives can be completely oxidized to the corresponding sulfones and can be further extracted with extracting agent, so as to achieve the purpose of the catalytic oxidative desulfurization of petroleum. The catalyst can be recycled while maintaining its activity.