Efficient Cobalt-Catalyzed Oxidative Conversion of Lignin Models to Benzoquinones
摘要:
Phenolic lignin model monomers and dimers representing the primary substructural units of lignin were successfully oxidized to benzoquinones in high yield with molecular oxygen using new Co-Schiff base catalysts bearing a bulky heterocyclic nitrogen base as a substituent. This is the first example of a catalytic system able to convert both S and G lignin model phenols in high yield, a process necessary for effective use of lignin as a chemical feedstock.
Unsymmetric salen ligands bearing a Lewis base: intramolecularly cooperative catalysis for cyanosilylation of aldehydes
作者:Ye-Qian Wen、Wei-Min Ren、Xiao-Bing Lu
DOI:10.1039/c1ob05695f
日期:——
A series of unsymmetric salen ligands derived from 1,2-diaminocyclohexane bearing an appended Lewis base on the three-position of one aromatic ring were synthesized by the reaction of various functional salicyaldehydes with the condensation product of 1,2-diaminocyclohexane mono(hydrogen chloride) and 3,5-di-tert-butylsalicylaldehyde. These ligands in conjunction with Ti(OiPr)4 exhibited excellent activity in catalyzing the cyanosilylation of aldehydes with trimethylsilyl cyanide (TMSCN) at mild conditions. The highest activity was observed in the catalyst system with regard to the salen ligand bearing a diethylamino group, which proved to be active even at a high [aldehyde]/[catalyst] ratio up to 50000. In a low catalyst loading of 0.05 mol%, the quantitative conversion of benzaldehyde to the corresponding cyanosilylation product was found within 10 min. at ambient temperature. An intramolecularly cooperative catalysis was proposed wherein the central metal Ti(IV) is suggested to play a role of Lewis acid to activate aldehydes while the appended Lewis base to activate TMSCN.
Mechanism and scope of salen bifunctional catalysts in asymmetric aldehyde and α-ketoester alkylation
作者:Michael W. Fennie、Erin F. DiMauro、Erin M. O'Brien、Venkatachalam Annamalai、Marisa C. Kozlowski
DOI:10.1016/j.tet.2005.03.117
日期:2005.6
complexes of C2-symmetric Lewisacid/Lewis base salen ligands provide bifunctional activation resulting in rapid rates in the enantioselective addition of diethylzinc to aldehydes (up to 92% ee). Further experiments probed the reactivity of the individual Lewisacid and Lewis base components of the catalyst and established that both moieties are essential for asymmetriccatalysis. These catalysts are also
C 2对称的路易斯酸/路易斯碱塞伦配体的金属配合物提供双功能激活,从而使二乙基锌对醛的对映选择性加成速率加快(最高ee为92%)。进一步的实验探查了催化剂中各个路易斯酸和路易斯碱组分的反应性,并确定这两个部分对于不对称催化都是必不可少的。这些催化剂在将二乙基锌不对称加成到α-酮酸酯中也是有效的。这一发现意义重大,因为单独的α-酮酸酯充当其自身的配体,以加速Et 2的外消旋1,2-羰基加成反应锌与外消旋羰基还原。后者通过金属茂途径进行,并且通常占主要产物。奇异的路易斯酸催化剂不能在这两个竞争路径上加速对映选择性的1,2-加成。然而,双官能氨基塞伦催化剂以优异的收率,完全的化学选择性和良好的对映选择性(高达88%ee)快速提供对映体富集的1,2-加成产物。合成了双功能氨基塞隆的文库,并在该反应中进行了评估。已经在鸦片拮抗剂的合成中证明了α-酮酸酯方法的实用性。
[EN] METHOD OF PREPARING POLY(ALKYLENE CARBONATE) VIA COPOLYMERIZATION OF CARBON DIOXIDE/EPOXIDE IN THE PRESENCE OF NOVEL COMPLEX<br/>[FR] PROCÉDÉ DE PRÉPARATION DE POLY(CARBONATE D'ALKYLÈNE) PAR COPOLYMÉRISATION DE DIOXYDE DE CARBONE ET D'ÉPOXYDE EN PRÉSENCE D'UN NOUVEAU COMPLEXE
申请人:SK INNOVATION CO LTD
公开号:WO2014148825A1
公开(公告)日:2014-09-25
Provided is a method of preparing poly(alkylene carbonate) using a molecular weight regulator in a process of preparing a copolymer of carbon dioxide/epoxide using a novel complex synthesized from salen-type ligand including a quaternary ammonium salt as a catalyst. According to the present invention, even though the molecular weight regulator is used, an activity of the catalyst may be stably maintained, whereby the low molecular weight of poly(alkylene carbonate) having a desirable level may be effectively provided. In addition, it is expected that since the novel complex as the catalyst of the present invention has a simple structure as compared to the existing copolymerization catalyst, due to the economical preparation cost thereof, the novel complex may be effectively applied to a large-scale commercial process.
Solvent extraction of metal sulfates by zwitterionic forms of ditopic ligands
作者:Robert A. Coxall、Leonard F. Lindoy、Hamish A. Miller、Andrew Parkin、Simon Parsons、Peter A. Tasker、David J. White
DOI:10.1039/b207015b
日期:2003.12.20
provision of a non-planar N2O22− donor-set. This is exemplified by its cis-octahedral nickel(II) sulfate complex in which the sulfate acts as a bidentate ligand. Competitive metal ion transport experiments show the selectivity of this ligand for copper(II) transport over a range of other metals including nickel(II) and zinc(II). The pH profiles for loading of Cu2+ (pH1/2 2.0, i.e. pH at 50 percent extraction)
Development of Bifunctional Salen Catalysts: Rapid, Chemoselective Alkylations of α-Ketoesters
作者:Erin F. DiMauro、Marisa C. Kozlowski
DOI:10.1021/ja026498h
日期:2002.10.1
which is a major coproduct with other catalysts, is not observed with these bifunctional salens. As a result, high yields of the additionproducts can be obtained (57−99%). Both the Lewisacid and Lewis base portions of the catalyst are critical to the reactivity and selectivity. The two separate portions of the catalyst have been shown to function in a cooperative manner.