Synthesis of catalytically active polymer-bound Schiff base manganese complexes for selective epoxidation of unfunctionalized olefins

A polymerizable unsymmetric tetradentate Schiff base with one vinyl group 3 was synthesized and copolymerized with styrene in toluene. Mn(III) ion was quantitatively incorporated into the copolymers by the functional moieties. The resulting linear polymer-bound manganese complexes ( 4a ′ and 4b ′) were used as catalyst under homogeneous condition for selective epoxidation of unfunctionalized olefins (i.e. styrene, α-methylstyrene and cyclohexene) at room temperature in the presence of iodosylbenzene (PhIO) as the terminal oxidant. The efficacy of epoxidation using the polymeric catalysts was comparable to that of the monomolecular analog. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3249–3254, 1997     

Synthesis of catalytically active polymer-bound schiff base manganese complexes for selective epoxidation of unfunctional olefins

An unsymmetric tetradentate Schiff base with one vinyl group was first synthesized and copolymerized with styrene in toluene. Metalation of the copolymer with Mn(OAc)₂ ·4H₂O and LiCl-H₂O was quantitatively incorporated by the functional moiety determined by ICP-AES technology The linear polymer-bound manganese complexes were used in homogeneous condition as catalysts in acetonitrile for selective epoxidation of unfunctional olefins(i.e. styrene, α -methylstyrene and cyclohexene) at room temperature in the presence of iodosylbenzene (PhIO) as the terminal oxidant. The efficacy of epoxidation using the polymeric catalysts was comparable to the monomolecular analogs. Polymer effect was discussed.     

Highly selective, recyclable epoxidation of allylic alcohols with hydrogen peroxide in water catalyzed by dinuclear peroxotungstate

The highly chemo-, regio-, and diastereoselective and stereospecific epoxidation of various allylic alcohols with only one equivalent of hydrogen peroxide in water can be efficiently catalyzed by the dinuclear peroxotungstate, K2[[W(=O)(O2)2(H2O)]2(mu-O)].2H2O (I). The catalyst is easily recycled while maintaining its catalytic performance. The catalytic reaction mechanism including the exchange of the water ligand to form the tungsten-alcoholate species followed by the insertion of oxygen to the carbon-carbon double bond, and the regeneration of the dinuclear peroxotungstate with hydrogen peroxide is proposed. The reaction rate shows first-order dependence on the concentrations of allylic alcohol and dinuclear peroxotungstate and zero-order dependence on the concentration of hydrogen peroxide. These results, the kinetic data, the comparison of the catalytic rates with those for the stoichiometric reactions, and kinetic isotope effects indicate that the oxygen transfer from a dinuclear peroxotungstate to the double bond is the rate-limiting step for terminal allylic alcohols such as 2-propen-1-ol (1a).     

Redox-associated eta(1) to eta(2) conversion of disulfide ligands in dinuclear ruthenium complexes

Disulfide-bridged dinuclear ruthenium complexes [[Ru(MeCN)(P(OMe)(3))(2)](2)(mu-X)(mu,eta(2)-S(2))][ZnX(3)(MeCN)] (X = Cl (2), Br (4)), [[Ru(MeCN)(P(OMe)(3))(2)](2)(mu-Cl)(2)(mu,eta(1)-S(2))](CF(3)SO(3)) (5), [[Ru(MeCN)(P(OMe)(3))(2)](2)(mu-Cl)(mu,eta(2)-S(2))](BF(4)) (6), and [[Ru(MeCN)(2)(P(OMe)(3))(2)](2)(mu-Cl)(mu,eta(1)-S(2))](CF(3)SO(3))(3) (7) were synthesized, and the crystal structures of 2 and 4 were determined. Crystal data: 2, triclinic, P1, a = 15.921(4) A, b = 17.484(4) A, c = 8.774(2) A, alpha = 103.14(2) degrees, beta = 102.30(2) degrees, gamma = 109.68(2) degrees, V = 2124(1) A(3), Z = 2, R (R(w)) = 0.055 (0.074); 4, triclinic, P1 a = 15.943(4) A, b = 17.703(4) A, c = 8.883(1) A, alpha = 102.96(2) degrees, beta = 102.02(2) degrees, gamma = 109.10(2) degrees, V = 2198.4(9) A(3), Z = 2, R (R(w)) = 0.048 (0.067). Complexes 2 and 4 were obtained by reduction of the disulfide-bridged ruthenium complexes [[RuX(P(OMe)(3))(2)](2)(mu-X)(2)(mu,eta(1)-S(2))] (X = Cl (1), Br (3)) with zinc, respectively. Complex 5 was synthesized by oxidation of 2 with AgCF(3)SO(3). Through these redox steps, the coordination mode of the disulfide ligand was converted from mu,eta(1) in 1 and 3 to mu,eta(2) in 2 and 4 and further reverted to mu,eta(1) in 5. Electrochemical studies of 6 indicated that similar conversion of the coordination mode occurs also in electrochemical redox reactions.     

Asymmetric epoxidation of conjugated olefins with dioxygen

A complex situation: Asymmetric epoxidation of conjugated olefins was achieved at room temperature using ruthenium complex 1 as the catalyst and air as the oxidant to give epoxides in up to 95?%?ee. When the product was acid sensitive, the reaction was carried out at 0?°C under oxygen.     

Toward the de novo design of a catalytically active helix bundle: a substrate-accessible carboxylate-bridged dinuclear metal center.

De novo design of proteins provides an attractive approach to uncover the essential features required for their functions. Previously, we described the design and crystal structure determination of a di-Zn(II) complex of "due-ferri-1" (DF1), a protein patterned after the diiron-dimanganese class of redox-active proteins [Lombardi, A.; Summa, C.; Geremia, S.; Randaccio, L.; Pavone, V.; DeGrado, W. F. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 6298-6305]. The overall structure of DF1, which contains a carboxylate-bridged dinuclear metal site, agrees well with the intended design. However, access to this dimetal site is blocked by a pair of hydrophobic leucine residues (L13 and L13'), which prevent facile entry of metal ions and small molecules. We have now taken the next step in the eventual construction of a catalytically active metalloenzyme by engineering an active site cavity into DF1 through the replacement of these two leucine residues with smaller residues. The crystal structure of the dimanganous form of L13A-DF1 indeed shows a substrate access channel to the dimetal center. In the crystal structure, water molecules and a ligating dimethyl sulfoxide molecule, which forms a monatomic bridge between the metal ions, occupy the cavity. Furthermore, the diferric form of a derivative of L13A-DF1, DF2, is shown to bind azide, acetate, and small aromatic molecules.     

m-CPBA/KOH: an efficient reagent for nucleophilic epoxidation of gem-deactivated olefins

The m-chloroperoxybenzoate anion (generated from m-CPBA and bases such as K(2)CO(3) or KOH) is a highly efficient nucleophilic epoxidating reagent for strongly deactivated olefins containing two electron-withdrawing groups at the same carbon, under mild conditions which affect neither other double bonds nor electrophilic oxidizable centers such as sulfoxides.     

Enantioselective epoxidation of terminal olefins by chiral dioxirane

[see reaction]. This paper describes an enantioselective epoxidation of terminal olefins using chiral ketone 3 as catalyst and Oxone as oxidant. Up to 85% ee has been obtained.     

The stereospecific epoxidation of olefins catalysed by ruthenium

Epoxidation of olefins by sodium periodate is effected by the catalysis of RuCl₃, (H₂O)_n associated with bipyridyl. The reaction is stereospecific for both cis and trans alkenes.     

A new reagent pair sodium percarbonateacetic anhydride for epoxidation of olefins

A new convenient method for epoxidation of olefins by sodium percarbonate — acetic anhydride is reported. It is found that the epoxides in 60–80% yields can be obtained in 18–24 h without ultrasonication. However, higher yields (some nearly quantitative) can be reached only within 1–3 h under ultrasonication. A comparison between the ultrasonicated epoxidations by use of sodium percarbonate and sodium perborate is also made. The experimental results have revealed that ultrasonication plays a main role in accelerating the interaction of both sodium percarbonate and sodium perborate with acetic anhydride, but it does not alter the mechanism of these two epoxidations.     

简单烯烃不对称环氧化的手性金属配合物催化剂

介绍了多类简单烯烃不对称环氧化反应的手性过渡金属配合物催化剂系统的催化效果。论述了配体结构与配合物作为环氧化反应催化剂的活性，稳定性，催化效率的关系。从配合物的电子和立体因素，几何构型与过渡态的构象和非对映异构体的能量差别探讨对不对称诱导效果的影响。同时陈述机理的研究情况。     

一例多钒酸盐杂化材料的制备及高效催化烯烃环氧化

以2-(2-吡啶基)咪唑(pIM)、Co²⁺和NaVO₃为原料,在水热条件下,制备了新的钒氧簇化合物[Co(pIM)V₂O₆] (1)。采用X射线单晶衍射、粉末X射线衍射、傅里叶变换红外光谱和元素分析等方法对化合物进行了表征。单晶解析表明,该化合物由VO₄四面体和CoO₃N₂四方锥通过氧原子共边、共角连接成二维结构。基于钒氧簇在催化氧化体系中的高效活性,1作为非均相反应的催化剂,在以H₂O₂为氧化剂的催化烯烃环氧化反应中表现出优秀的催化性能,催化剂能够多次重复使用且活性基本保持不变。此外,磁化率研究表明1中存在反铁磁相互作用。     

一例多钒酸盐杂化材料的制备及高效催化烯烃环氧化

以2-(2-吡啶基)咪唑(pIM)、Co²⁺和NaVO₃为原料,在水热条件下,制备了新的钒氧簇化合物[Co (pIM) V₂O₆](1)。采用X射线单晶衍射、粉末X射线衍射、傅里叶变换红外光谱和元素分析等方法对化合物进行了表征。单晶解析表明,该化合物由VO₄四面体和CoO₃N₂四方锥通过氧原子共边、共角连接成二维结构。基于钒氧簇在催化氧化体系中的高效活性,1作为非均相反应的催化剂,在以H₂O₂为氧化剂的催化烯烃环氧化反应中表现出优秀的催化性能,催化剂能够多次重复使用且活性基本保持不变。此外,磁化率研究表明1中存在反铁磁相互作用。     

Highly efficient epoxidation of electron-deficient olefins with tetrabutylammonium peroxydisulfate

The epoxidation of α,β-unsaturated carbonyl compounds such as enones and enals was efficiently achieved with tetrabutylammonium peroxydisulfate in the presence of equimolar amounts of hydrogen peroxide and NaOH in acetonitrile or methanol at 25 °C in excellent yields. Base-sensitive substrate such as cinnamaldehyde could be successfully epoxidized in short reaction time under mild reaction conditions.     

Practical synthesis of an L-fructose-derived ketone catalyst for asymmetric epoxidation of olefins

An L-fructose-derived ketone catalyst for asymmetric epoxidation of trans- and trisubstituted olefins was efficiently prepared from L-sorbose in five steps.