Molybdenum(vi) catalysts obtained from η3-allyl dicarbonyl precursors: Synthesis, characterization and catalytic performance in cyclooctene epoxidation

Abstract

The oxidative decarbonylation of the η(3)-allyl dicarbonyl complexes [Mo(η(3)-C(3)H(5))Cl(CO)(2)(L)] (L = 2,2'-bipyridine (bipy) (1), 4,4'-di-tert-butyl-2,2'-bipyridine (di-tBu-bipy) (2)) by reaction with aqueous tert-butylhydroperoxide (TBHP) or H(2)O(2) gave the following compounds in good to excellent yields: the oxo-bridged dimers [MoO(2)Cl(L)](2)O (L = bipy (3), di-tBu-bipy (6)) using TBHP(10 equiv.)/CH(3)CN/r.t.; the molybdenum oxide/bipyridine hybrid material {[MoO(3)(bipy)][MoO(3)(H(2)O)]}(n) (4) and the octanuclear complex [Mo(8)O(24)(di-tBu-bipy)(4)] (7) using TBHP(50 equiv.)/H(2)O/70 °C; the oxodiperoxo complexes MoO(O(2))(2)(L) (L = bipy (5), di-tBu-bipy (8)) using H(2)O(2)(10 equiv.)/CH(3)CN/r.t. The structure of 7·x(solvent) (where solvent = CH(2)Cl(2) and/or diethyl ether) was determined by single crystal X-ray diffraction. Despite possessing the same windmill-type complex as that described previously for 7·10CH(2)Cl(2), the crystal structure of 7·x(solvent) is unique due to differences in the crystal packing. Compounds 1-8 were examined as catalysts or catalyst precursors for the epoxidation of cyclooctene using aqueous TBHP or H(2)O(2) as oxidant at 55 or 70 °C. Reactions were performed without co-solvent or with the addition of water, ethanol or acetonitrile. Cyclooctene oxide was always the only reaction product. Solids recovered after 24 h reaction at 70 °C were identified by FT-IR spectroscopy as the hybrid 4 from (1,3-5)/TBHP, complex 5 from (1,3-5)/H(2)O(2), and complex 8 from (2,6-8)/H(2)O(2). With TBHP as oxidant, the highest epoxide yields (for 24 h reaction at 70 °C) were obtained using excess H(2)O as solvent (28-38% for 1,3-5; 87-98% for 2,6-8), while with H(2)O(2) as oxidant, the highest epoxide yields were obtained using CH(3)CN as solvent (54-81% for 3-8).

Synthesis, structure and catalytic olefin epoxidation activity of a dinuclear oxo-bridged oxodiperoxomolybdenum(VI) complex containing coordinated 4,4′-bipyridinium

“…Oxoperoxo-molybdenum(VI) complexes are known to contain MoO(O 2 ) 2 , MoO(O 2 ) and MoO 2 (O 2 ) fragments, although the latter is rare [5]. These motifs are present in mononuclear complexes such as [MoO(O 2 ) 2 (L) n ] [6][7][8][9][10][11][12][13][14][15], [MoO(O 2 )Cl 2 (L) n ] acyclic alkenes. A limited number of studies have focussed on the epoxidation of olefins obtained from renewable resources such as citrus and turpentine oils, plant oils and fats [12,13,[24][25][26].…”

Excellent alkene epoxidation catalytic activity of macrocyclic‐based complex of dioxo‐Mo(VI) on supermagnetic separable nanocatalyst

“…After running the catalytic process for epoxidation of cyclooctene with TBHP and various solvents, it was found that chloroform was a suitable solvent among dichloromethane, toluene, acetonitrile, chloroform, methanol and 1,2-dichloroethane with highest conversion (98%) during 10 min. By considering of mechanism in Scheme 2, it seems that the competition between methanol and acetonitrile as a coordinator solvent and (CH 3 ) 3 COO − in coordination to Mo(VI) causes a marked decrease in the catalyst activity. [37] Apparently, the lower reflux reaction temperature is the reason for the lowest epoxidation conversion in CH 2 Cl 2 (37%).…”

“…[1][2][3] Molybdenum(VI) Schiff base complexes have significant advantages such as stability, economy, commercial availability and environmental friendliness in epoxidation of olefins compounds. [4][5][6][7] tert-Butyl hydroperoxide (TBHP)…”

Molybdenum(II) catalyst precursors in olefin oxidation reactions

“…A later work by another group using the 4,4'-di-tert-Bu-2,2'-bipyridine (bpy*) derivative of 4 (4a) led to the structural characterization of the products resulting from its oxidation with TBHP. [46] One of them (6c [47] in Figure 1) is very similar to our proposed species 6a and 6b. …”