Syntheses and Stuctures of Alkyl Peroxo Adducts of β-Diketonate Cobalt(III) Complexes and Their Role in Oxidation of Hydrocarbons and Olefin Epoxidation

Abstract

To assess the oxidizing capacity of [Co( -diketonate) 2 (L)OOR] complexes, four such species, namely, [Co-(acac) 2 (L)(OO t Bu)] (acacH ) acetylacetone; L ) pyridine (py) (1), 4-methylpyridine (4-Mepy) (2), 1-methylimidazole (1-MeIm) (3)) and [Co(dbm) 2 (py)(OO t Bu)] (4, dbmH ) dibenzoylmethane), have been synthesized and the structures of 1, 3, and 4 have been determined by X-ray crystallography. Complex 1 crystallizes in the triclinic space group P1 h with a ) 9.149(2) Å, b ) 9.741(2) Å, c ) 13.067 (2) Å, R ) 84.22 (2)°, ) 77.89(2)°, γ ) 67.83(2)°, V ) 1054.1(4) Å 3 , and Z ) 2. Complex 3 crystallizes in the monoclinic space group P2 1 /n with a ) 11.341(2) Å, b ) 10.485(2) Å, c ) 18.863(2) Å, R ) 90°, ) 106.230(15)°, γ ) 90°, V ) 2153.6(8) Å 3 , and Z ) 4. Complex 4‚1.5C 6 H 6 crystallizes in the monoclinic space group P2 1 /c with a ) 14.907(5) Å, b ) 18.701-(5) Å, c ) 15.207(4) Å, R ) 90°, ) 103.52 (2)°, γ ) 90°, V ) 4122(2) Å 3 , and Z ) 4. The geometry around the Co(III) center in all four complexes is distorted octahedral, and the two -diketonate ligands are cis to each other. The Co-O and O-O bond distances in the Co-OO t Bu moiety fall in the narrow ranges of 1.860(3)-1.879 (2) and 1.451(3)-1.466(3) Å, respectively. Although stable in the solid state, these complexes decompose in benzene or halocarbon solutions to afford t BuOO • and t BuO • radicals. When alkanes like cyclohexane are present in the reaction mixture, these radicals initiate oxidation of the C-H bond. The oxidizing capacity follows the order 1 > 2 > 3 > 4. Decomposition of the complexes in the presence of cyclohexene and an aldehyde results in selective epoxidation in high yield.

Room Temperature Aerobic Peroxidation of Organic Substrates Catalyzed by Cobalt(III) Alkylperoxo Complexes

“…Analysis of the amount of t BuOH produced indicates the stoichiometry shown in eq . Similar methods have been reported for the preparation of other Co III OOR complexes. ,− …”

Cobalt(II) Complexes with N,N,N-Scorpionates and Bidentate Ligands: Comparison of Hydrotris(3,5-dimethylpyrazol-1-yl)borate Tp* vs. Phenyltris(4,4-dimethyloxazolin-2-yl)borate ToM to Control the Structural Properties and Reactivities of Cobalt Centers

“…To date, some cobalt compounds, including Tp R [ 27 , 28 ] and To M [ 10 ] complexes, have been employed as catalysts for hydrocarbon oxygenation with organic peroxides (ROOH) such as tert -butyl hydroperoxide (TBHP) [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ] and meta -chloroperbenzoic acid ( m CPBA) [ 10 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ]. Therefore, we explored catalysis of the entitled mixed ligand complexes toward alkene oxidation with TBHP and alkane oxidation with m CPBA as indicated below.…”

“…It is known that Co II (acac) 2 reacts with excess TBHP in the presence of N-donating L ligands such as pyridine or 1-methyimidazole to yield the corresponding cobalt(III)-OO t Bu complex [Co III (OO t Bu)(acac) 2 (L)] [ 29 , 30 ]. In contrast, relatively hindered Tp R ligand hydrotris(3-alkyl-5- iso propylpyrazol-1-yl)borates such as Tp i Pr2 (when 3-alkyl = iso propyl) and Tp t Bu, i Pr (when 3-alkyl = tert -butyl) stabilize the corresponding alkylperoxo complexes of cobalt(II), [Co II (OO t Bu)(Tp R )] [ 45 ].…”

Curing of Air-Drying Paints: A Critical Review

“…117 This approach has been utilized to elucidate the molecular structure of acetylacetonate derivatives. 118 Scheme 15. Mechanism of cobalt(II) catalyzed deperoxidation.…”