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Dioxomolybdenum(VI) Complexes with Salicylamide Ligands: Synthesis, Structure, and Catalysis in the Epoxidation of Olefins under Eco‐Friendly Conditions
Author(s) -
Annese Cosimo,
Caputo Daniela,
D'Accolti Lucia,
Fusco Caterina,
Nacci Angelo,
Rossin Andrea,
Tuci Giulia,
Giambastiani Giuliano
Publication year - 2019
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201801096
Subject(s) - chemistry , cyclooctene , selectivity , catalysis , epoxide , aqueous solution , amide , medicinal chemistry , isoindoline , solvent , stereochemistry , organic chemistry
Five salicylamides [ R1 R2 SaAmH; R 1 , R 2 = N ‐substituents: n Bu, H ( 1a ); t Bu, H ( 1b ); n Oc, H ( 1c ); Bn, H ( 1d ); and n Bu, n Bu ( 1e )] were successfully coordinated to the dioxomolybdic fragment, resulting in MoO 2 ( R1 R2 SaAm) 2 complexes 2a‐e , which were characterized through elemental analysis, IR, 1 H‐ and 13 C NMR, ESI‐HRMS, and XRD (for 2a , b , e ). All complexes are active catalysts in the solvent‐free epoxidation of cis ‐cyclooctene with tert ‐butyl hydroperoxide in decane (TBHPdec), showing high turnover frequencies (TOF 1890 h –1 for 2b ) at 1 % loading. Using aqueous TBHP (TBHPaq) or H 2 O 2 , selectivity to cyclooctene oxide is always 100 %, although reactions are more sluggish. The 2c /TBHPaq system, which displays the best TOF (1070 h –1 ) at 0.25 % loading and 75 °C, allowed for the quantitative conversion of trans ‐2‐octene into its epoxide, while low epoxide selectivity was observed in the case of 1‐octene, styrene, and methyl oleate. In the latter case, 90 % epoxide selectivity at 92 % conversion was achieved with the 2b /TBHPdec system at 55 °C, under solvent‐free conditions. Compared to related MoO 2 X 2 ( O ‐amide)‐type complexes, 2a‐e exhibit increased catalytic performance under the greener conditions involving the use of aqueous oxidants.