High Catalytic Efficiency of Nanostructured Molybdenum Trioxide in the Benzylation of Arenes and an Investigation of the Reaction Mechanism

Abstract

The synthesis and characterization of nanostructured MoO(3) with a thickness of about 30 nm and a width of about 450 nm are reported. The composition formula of the MP (precipitation method) precursor was estimated to be [(NH(4))(2)O](0.169) x MoO(3) x (H(2)O)(0.239). The calcination of the precursor in air afforded nanostructured pellets of the alpha-MoO(3) phase. The nanostructured MoO(3) catalyst exhibited high efficiency in catalyzing the benzylation of various arenes with substituted benzyl alcohols, which were strikingly different to common bulk MoO(3). Most reactions offered >99% conversion and >99% selectivity to monoalkylated compounds. MoO(3) is a typical acid catalyst. However, the benzylation reaction over nanostructured MoO(3) does not belong to the acid-catalyzed type or defect site-catalyzed type, since the catalyst has no acidity and defect site on surface. Characterization with thermal, spectroscopic, and electronic techniques reveal that the catalyst contains fully oxygen-coordinated MoO(6) octahedrons on the surface but partially reduced species (Mo(5+)) within the bulk phase. The terminal oxygen atoms of Mo=O bonds on the (010) basal plane resemble oxygen anion radicals and act as active sites for the adsorption and activation of benzyl alcohols by electrophilic attack. Such sites are indispensable for catalytic reactions since the blocking of these sites by electron acceptors, such as tetracyanoethylene (TCNE), can greatly decrease catalytic activity. This work represents a successful example of combining a heterogeneous catalysis study with nanomaterial synthesis.

Sublimation growth and vibrational microspectrometry of α-MoO3 single crystals

“…Presently four polymorph modifications are known for molybdenum trioxide, orthorhombic a-MoO 3 [6,7], monoclinic b-MoO 3 [8], high-pressure monoclinic MoO 3 -II [9] and hexagonal h-MoO 3 [10,11]. Phase composition, micromorphology and defect structure of molybdenum oxides in thin film, micro-and nanocrystalline forms are strongly dependent on the technological conditions used for synthesis [3][4][5]7,[12][13][14][15][16][17][18]. Orthorhombic a-MoO 3 , space group Pbmn, with unique layered structure is a stable polymorph modification at normal conditions [6,7].…”

“…Molybdenum trioxide possesses attractive catalytic, photochromic and electronic properties and has numerous potential applications [1][2][3][4][5]. Presently four polymorph modifications are known for molybdenum trioxide, orthorhombic a-MoO 3 [6,7], monoclinic b-MoO 3 [8], high-pressure monoclinic MoO 3 -II [9] and hexagonal h-MoO 3 [10,11].…”

BF<sub>3</sub>.OEt<sub>2</sub>-Mediated Benzylation of Arenes and Heteroarenes with Benzyl Ether Derivatives

“…1-Benzyl-4-methoxybenzene (3f) [36] and 1-benzyl-2methoxybenzene (4d) [15] (3f/4d = 5:1), liquid. 3f: 1 2-Benzylnaphthalene (3i) [37] and 1-benzylnaphthalene (4f) 14 (3i/4f =3:1), liquid. 3i: 1 di-p-Tolylmethane (3m) [40] and o-tolyl(p-tolyl)methane (4i) [19] (3m/4i = 5:3), liquid.…”

“…Among the various functionalization reactions of arenes, Friedel-Crafts alkylation (FCA) provides an efficient access to building a diarylmethane framwork via the electrophilic addition of cationic species to aromatic compounds. Previous work about FCA has mainly centred on using alcohols [11][12][13][14], benzyl halides [15][16][17][18], aldehyde [19][20][21], carboxylic acid ester [22,23] or alkenes [24][25][26] as the alkylating agents in the presence of kinds of Brønsted acids, Lewis acids and transition metal salts [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], but there have not been many trials for the development of FCA with ethers as electrophilics possibly due to the stable ether bond. Nevertheless, recently Peris and Shiina group, etc.…”

Synthesis of Methylene‐Bridge Polyarenes through Palladium‐Catalyzed Activation of Benzylic Carbon‐Hydrogen Bond

“…[8,9] The formation of fluorene by metal-catalyzed C À H bond activation can be classified as either the aryl or the benzylic type (Scheme 1). For example, the Pd-catalyzed cyclization of 1-halo-2-(arylmethyl)-benzene [10] and o-aryl-substituted benzyl chloride [11] via intermediates A and B, respectively, proceeds by aryl C À H bond activation (Type I). These approaches have been extensively investigated, and were found to be non-regiospecific.…”