Polyoxometalate‐based Inorganic‐Organic Hybrids as Heterogeneous Catalysts for Asymmetric and Tandem Reactions

Abstract

Chiral and bi/multifunctional catalysts have contributed to the sustainability of organic transformations. Polyoxometalates (POMs) with diverse structures, good redox properties and oxidation abilities offer excellent opportunities in the area of asymmetric and one-pot tandem reactions. However, the potential applications of POM catalysts are limited due to their solubility in many solvents. One approach to cope with this problem is to combine them with organic units and generate POM-based inorganic-organic hybrid materials with unique structural characteristics. This review presents the targeted design of POM-based hybrids as heterogeneous catalysts for asymmetric and one-pot tandem reactions. Chirality induction from chiral POMs and/or organic linkers to the whole hybrid material as well as the possibility of self-assembly of building units via non-covalent interactions are described. It also discusses the catalytic sites ranging from POM salts to 3D POMbased frameworks with the focus on organic transformations such as oxidation, esterification and CÀ C bond formation.

Magnetic Thiaminum Octamolybdate Nanocatalyst for Oxygenation of Styrenes to Benzaldehydes and Tandem Synthesis of Benzimidazoles

“…63 Many previously reported oxygenation catalysts based on polyoxomolybdates contained low valent elements in addition to Mo VI but not necessarily Mo in lower oxidation states than Mo-(VI). [24][25][26]28,29,56,63,64 In our system, thiaminium might partially reduce Mo VI to Mo V and Mo IV as confirmed by our XPS results and in line with similar observations for the compound (VB) 2 [HPMo 12 O 40 ]•6DMF. 31 For the previously reported system Fe 3 O 4 @SiO 2 /(NH 4 ) 6 Mo 7 O 24 , no such "reductive activation" seemed to be necessary.…”

“…Polyoxometallates (POMs) have turned out to be versatile platforms for oxidation/oxygenation catalysis in solution or in supported heterogeneous systems. − Among them, polyoxomolybdates are frequent owing to the redox-active Mo­(VI) which is also important in molybdenum-dependent redox enzymes in biology . In many of the reported polyoxomolybdate catalysts for oxygenation reactions, the POM catalysts contain other atoms with inherently lower oxidation states such as P­(V) , or Zr­(IV) were garnished with transition metal complexes.…”

“…In many of the reported polyoxomolybdate catalysts for oxygenation reactions, the POM catalysts contain other atoms with inherently lower oxidation states such as P­(V) , or Zr­(IV) were garnished with transition metal complexes. Multicomponent (hybrid) heterogeneous structures and composites are frequent. − …”

Epoxidation of Cis‐cyclooctene with Hydrogen Peroxide Catalyzed by Lindqvist Type Polyoxometalates

“…Polyoxometalates (POMs) are significant class of transition metal-oxygen clusters which got attention in catalys chemistry, [1][2][3][4][5][6][7][8] photochemistry, [9][10][11][12] electrochemistry, [13][14][15] medicine chemistry, [16][17][18] materials science. [19] POMs-supported organometallic compounds have attracted attention thanks to the organometallic fragment, which can provide a different reactivity compared to inorganic POMs.…”

“…Heterometallic/Homo Lindqvist type POMs [M'(L)M 5 O 18 ] nÀ (M=W, Mo; M'=Nb, V, Mo, W, Ta) can be obtained by replacing the MO t unit (O t , the terminal oxygen) with the organometallic type M'L (L = ligand, e. g. O 2À , RO À , Cp*, etc.). [20] In recent years, η 5 -pentamethylcyclopentadienyl (Cp*, η 5 -C 5 Me 5 ) involving Lindqvist type POMs such as [Cp* 2 W 6 O 17 ], [21] [n-Bu 4 N][Mo 6 Cp*O 18 ] synthesis and electrochemical properties, [22] Cp* 2 Mo 6 O 17 , [23] Cp* 2 Mo x W 6À x O 17 (x = 0, 2, 4, 6) [24] and [Cp*Mo x W 6À x O 18 ] À (x = 0, 1, 5, 6), [25] [Cp 2 *M 5 VO 17 ] À (M=Mo, W) [26] synthesis and antimicrobial properties have been reported.…”