Recent Advances of Anderson-Type Polyoxometalates as Catalysts Largely for Oxidative Transformations of Organic Molecules.

Anderson-type ([XM6O24]n-) polyoxometalates (POMs) are a class of polymetallic-oxygen cluster inorganic compounds with special structures and properties. They have been paid extensive attention by researchers now, due to their chemical modification and designability, which have been widely applied in the fields of materials, catalysis and medicine. In contemporary years, the application of Anderson-type POMs in catalytic organic oxidation reaction has gradually shown great significance for the research of green catalytic process. In this paper, we investigate the application of Anderson-type POMs in organic synthesis reaction, and these works are summarized according to the different structure of POMs. This will provide a new strategy for further investigation of the catalytic application of Anderson-type POMs and the study of green catalysis.

Additive-Mediated Selective Oxidation of Alcohols to Esters via Synergistic Effect Using Single Cation Cobalt Catalyst Stabilized with Inorganic Ligand.

The direct catalytic oxidation of alcohols to esters is very appealing, but the economical-friendly catalysis systems are not yet well established. Herein, we show that a pure inorganic ligand-supported single-atomic cobalt compound, (NH4)3[CoMo6O18(OH)6] (simplified as CoMo6), could be used as a heterogeneous catalyst and effectively promote this type of reaction in the presence of 30% H2O2 using KCl as an additive. The oxidative cross-esterification of various alcohols (aromatic and aliphatic) could be achieved under mild conditions in nearly all cases, affording the corresponding esters in high yields, including several drug molecules and natural products. Detailed studies have revealed that chloride ion is able to bind to the CoMo6 to form a supramolecular dimer 2(CoMo6∙Cl), which can effectively catalyze the reaction via a synergistic effect from chloride ion and CoMo6. Mechanism studies and control reactions demonstrate that the esterification proceeds via the key oxidative immediate of aldehydes.

Iron-catalyzed oxidative functionalization of C(sp3)-H bonds under bromide-synergized mild conditions.

An efficient oxidation and functionalization of C-H bonds with an inorganic-ligand supported iron catalyst and hydrogen peroxide to prepare the corresponding ketones was achieved using the bromide ion as a promoter. Preliminary mechanistic investigations indicated that the bromide ion can bind to FeMo6 to form a supramolecular species (FeMo6·2Br), which can effectively catalyze the reaction.

Synthesis and Crystallization Behavior of Surfactants with Hexamolybdate as the Polar Headgroup.

Alkyl chains with different lengths were covalently grafted onto the surface of hexamolybdate through the postfunctionalization protocol of polyoxometalates. The obtained compounds represent typical structures of the so-called giant surfactants. Unexpectedly, those surfactants with hexamolybdates as polar headgroups are able to crystallize, while single-crystal X-ray diffraction reveals that the crystallization behavior of the surfactants is highly dependent on the length of the alkyl chains. For surfactants with comparatively short alkyl chains (C6 and C10), the alkyl chains prefer to interact with tetrabutylammonium, the countercation of hexamolybdate. However, the alkyl chains tend to pack with each other to form a domain of alkyl chains in the surfactant with a longer alkyl chain (C18). The possible mechanism is that a long alkyl chain cannot be fully compatible with the short chain (C4) of tetrabutylammonium.