A silicododecamolybdate/pyridinium-tetrazole hybrid molecular salt as a catalyst for the epoxidation of bio-derived olefins

authors	Nunes, MS; Neves, P; Gomes, AC; Cunha-Silva, L; Lopes, AD; Valente, AA; Pillinger, M; Goncalves, IS
nationality	International
journal	INORGANICA CHIMICA ACTA
author keywords	Polyoxometalate; Inorganic-organic hybrid; Pyridinium; Hydrogen bonds; Epoxidation; Bio-olefins
keywords	EPOXIDIZED METHYL OLEATE; CRYSTAL-STRUCTURE; POLYOXOMETALATE; HETEROPOLYMOLYBDATE
abstract	The hybrid polyoxometalate (POM) salt (Hptz)(4)[SiMo12O40].nH(2)O (1) (ptz = 5-(2-pyridyl)tetrazole) has been prepared, characterized by X-ray crystallography, and examined as a catalyst for the epoxidation of cis-cyclooctene (Cy) and bio-derived olefins, namely dl-limonene (Lim; a naturally occurring monoterpene found in the rinds of citrus fruits), methyl oleate and methyl linoleate (fatty acid methyl esters (FAMEs) obtained by transesterification of vegetable oils). The crystal structure of 1 consists of alpha-Keggin-type heteropolyanions, [SiMo12O40](4-), surrounded by space-filling and charge-balancing 2-(tetrazol-5-yl)pyridinium (Hptz(+)) cations, as well as by a large number of water molecules of crystallization (n = 9). The water molecules mediate an extensive three-dimensional (3D) hydrogen-bonding network involving the inorganic anions and organic cations. For the epoxidation of the model substrate Cy in a nonaqueous system (tert-butylhydroperoxide as oxidant), the catalytic performance of 1 (100% epoxide yield at 24 h, 70 degrees C) was superior to that of the tetrabutylammonium salt (Bu4N)(4) [SiMo12O40] (2) (63% epoxide yield at 24 h), illustrating the role of the counterion Hptz(+) in enhancing catalytic activity. The hybrid salt 1 was effective for the epoxidation of Lim (69%/85% conversion at 6 h/24 h) and the FAMEs (87-88%/100% conversion at 6 h/24 h), leading to useful bio-based products (epoxides, diepoxides and diol products).
publisher	ELSEVIER SCIENCE SA
issn	0020-1693
isbn	1873-3255
year published	2021
volume	516
digital object identifier (doi)	10.1016/j.ica.2020.120129
web of science category	7
subject category	Chemistry, Inorganic & Nuclear
unique article identifier	WOS:000605617900010