Four organic-inorganic compounds based on polyoxometalates: crystal structures and catalytic epoxidation of styrene

• Published in: Journal of coordination chemistry 2014-02, Vol.67 (3), p.506-521
• Main Authors: Wang, Chunling, Ren, Yuanhang, Feng, Sujiao, Kong, Zuping, Hu, Yichen, Yue, Bin, Deng, Mingli, He, Heyong
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; Covalent bonds; Crystal structure; Diffraction; Epoxidation; Heterogeneous catalyst; Hydrogen bonds; Organic-inorganic hybrid; Polyoxometalates; Polyoxometallates; Styrene; Styrene epoxidation; Styrenes; Three dimensional
• ISSN: 0095-8972; 1029-0389
• DOI: 10.1080/00958972.2014.892592

Four compounds based on polyoxometalates, [Cu(4-bpo)(H 2 O)][Cu 2 (μ 2 -Cl)(4-bpo) 2 (H 2 O)][SiW 12 O 40 ][N(CH 3 ) 4 ] 2 ·H 2 O (1), [Cu(4-bpo)] 4 [P 2 W 18 O 62 ][N(CH 3 ) 4 ] 2 ·6H 2 O (2), [Cu 2 (μ 2 -OH)(4-bpo) 2 (Hina)(H 2 O) 2 ] 2 [P 2 W 18 O 62 ]·4H 2 O (3), and [Cu 2 (Hina) 4 (H 2 O) 2 ][H 2 P 2 W 18 O 62 ](Hina)·11H 2 O (4) (4-bpo=2,5-bis(4-pyridyl)-1,3,4-oxadiazole, ina=isonicotinic acid), have been hydrothermally synthesized and characterized by elemental analysis, IR, and single-crystal X-ray diffraction. The 3-D framework of 1 is composed by Keggin-type polyoxoanions {SiW 12 } and two types of infinite chains, {Cu(4-bpo)(H 2 O)} n and {Cu 2 (μ 2 -Cl)(4-bpo) 2 (H 2 O)} n , through hydrogen bonds. Compound 2 has a 3-D rigid framework which is fabricated by Wells-Dawson type polyoxoanions {P 2 W 18 } and Cu-(4-bpo) chains through covalent bonds. Compound 3 contains an infinite {Cu 2 (μ 2 -OH)(4-bpo) 2 (Hina)(H 2 O) 2 } n double-chain and {P 2 W 18 } polyoxoanions immobilized in the voids between the chains. Compound 4 exhibits a 3-D supramolecular network directed by hydrogen bonds between {P 2 W 18 } polyoxoanions and the double paddle-wheel {Cu 2 (Hina) 4 (H 2 O) 2 }. Compounds 1-4 were tested as heterogeneous catalysts for the epoxidation of styrene using tert-butyl hydroperoxide (TBHP) as oxidant. The compounds show catalytic activity with 2 giving the highest yield of styrene oxide. Four organic-inorganic hybrid compounds were hydrothermally synthesized based on polyoxometalates, copper salts, and 2,5-bis(4-pyridyl)-1,3,4-oxadiazole or isonicotinic acid ligands. Among those four compounds, compound 2, [Cu(4-bpo)] 4 [P 2 W 18 O 62 ][N(CH 3 ) 4 ] 2 ·6H 2 O, showed the best catalytic activity for heterogeneous epoxidation of styrene to styrene oxide using tert-butyl hydroperoxide as oxidant.