A family of oxygen evolving catalysts was investigated, which was based on the most desired first-row transition metal iron. Among them, the highest turnover number of 2380 was obtained in acetate buffer at pH 4.5 with [(TPA)2Fe2(μ-O)(μ-OAc)]3+.

N,N′-Bis(salicylidene)ethylenediaminecobalt(II) (1) has been investigated as a highly efficient water oxidation precatalyst with a TON of 854 at pH = 9.0, using [Ru(bpy)3](ClO4)2 as a photosensitizer and Na2S2O8 as a sacrificial electron acceptor.

A new class of cyclopropenes containing a chroman-4-one motif were synthesized using 3-diazochroman-4-one and phenylacetylene with rhodium(II) catalyst and followed by cycloisomerization to give 2-substituted or 3-substituted 4H-furo[3,2-c]chromene, respectively. Using BF3·Et2O as catalyst, 2-substituted 4H-furo[3,2-c]chromene was exclusively obtained in 70% yield. Using Cu(OTf)2 as catalyst, 3-substituted 4H-furo[3,2-c]chromene was obtained in 95% yield with 98:2 regioselectivity. A one-pot cascade addition–cycloisomerization process was also developed with no need to isolate cyclopropenes of chroman-4-one intermediates.

A new reaction-controlled phase-transfer catalyst based on silicotungstate of [(C18H37)2(CH3)2N]3[SiO4H(WO5)3] for oxidation of hydrocarbons is developed. The catalyst is a new heteropoly compound with silicon as heteroatom, which is different to the previously reported reaction-controlled phase transfer catalysts that were composed of quaternary ammonium heteropolyoxotungstates of [π-C5H5N(CH2)15CH3]3[PW4O16] and [π-C5H5N(CH2)15CH3]3[PW4O32] with phosphorus as heteroatom. The oxidation of various alkenes (such as linear terminal olefins, internal olefins, cyclic olefins and unactivated alkenes) to epoxides, sulfides to sulfoxides and sulfones, alcohols to carbonyl compounds, are successfully catalyzed by this recyclable and environmentally benign catalyst using H2O2 as oxidant and ethyl acetate as solvent. This catalyst is not only capable of catalyzing homogeneous oxidation of organic substrates with unique reaction-controlled phase-transfer character, but also avoids the use of toxic solvents. The catalyst could be easily recovered and reused after reaction, and the epoxidation of cyclohexene was performed twenty times without obvious loss in activity. The fresh catalyst and the used one were characterized by ICP, IR, UV-vis, 29Si MAS NMR and 183W NMR in detail.

A novel homogeneous vanadium-substituted polyoxometalate catalyst of [n-Bu4N]3H3[PW9V3O40] showed good catalytic activity for the activation of CH bonds of toluene and substituted toluene with TBHP (70% aq) under solvent-free conditions. Under the optimal conditions, a 65% yield of benzaldehyde and a TON of 5221 were obtained over this catalyst at 343 K. This catalyst also showed good conversion and selectivity for the oxidation of a series of substituted toluene. The vanadium-substituted Keggin-POM was not decomposed to some species upon the treatment of 530-fold of TBHP by IR characterization. A free radical mechanism was proposed based on the experimental results and the literature supports.Graphical abstractHighlights► A homogeneous vanadium-substituted polyoxometalate catalyst was prepared. ► This catalyst showed good activity for oxidation of toluene and substituted toluene. ► A free radical mechanism was proposed based on the experimental results.

A vanadium-substituted polyoxometalate, K6[PW9V3O40]·4H2O, was used as a recyclable and effective catalyst for the oxidation of pyridines. The reactions were successfully conducted in water under mild conditions. The catalyst could be easily recovered and reused.

The epoxidation of alkenes was successfully catalyzed by a recyclable and environmentally benign catalytic system: [π-C5H5N(CH2)15CH3]3[PW4O32]/H2O2/ethyl acetate/olefin

A dilacunary silicotungstate, K8[γ-SiW10O36]·13H2O, catalyzed the selective oxidation of alcohols with 30% aqueous hydrogen peroxide. The reaction was carried out in an aqueous/oil biphasic system, which allowed easy recovery of a catalyst under relative mild conditions. The high yields of ketones were obtained in oxidation of alcohols by the dilacunary silicotungstate and the catalyst was recycled five times without activity loss at room temperature.A dilacunary silicotungstate, K8[γ-SiW10O36]·13H2O, catalyzed the selective oxidation of alcohols with 30% aqueous hydrogen peroxide. The reaction was carried out in an aqueous/oil biphasic system, which allowed easy recovery of a catalyst under relative mild conditions.Download full-size image

A family of oxygen evolving catalysts was investigated, which was based on the most desired first-row transition metal iron. Among them, the highest turnover number of 2380 was obtained in acetate buffer at pH 4.5 with [(TPA)2Fe2(μ-O)(μ-OAc)]3+.

N,N′-Bis(salicylidene)ethylenediaminecobalt(II) (1) has been investigated as a highly efficient water oxidation precatalyst with a TON of 854 at pH = 9.0, using [Ru(bpy)3](ClO4)2 as a photosensitizer and Na2S2O8 as a sacrificial electron acceptor.