在本文中,报道了一种具有可微调电子特性的双歧性N杂环卡宾的新例子,即Coumaraz-2-on-4-Yidene(1)。卡宾碳中心上的N-氨基甲酸和芳基同时向卡宾中心提供了极高的亲电子性和亲核性,其硒酮衍生物的77 Se NMR化学位移和羰基铑配合物的CO拉伸强度证明了这一点。由于前体1可从各种官能席夫碱在一个实际和可扩展的方式来合成的电子性质1可以进行微调以定量和可预测的方式,通过使用哈米特σ芳环上官能团的常数。简便的电子调谐能力1可能适用于在主族和过渡金属化学中引发新的特性。
在本文中,报道了一种具有可微调电子特性的双歧性N杂环卡宾的新例子,即Coumaraz-2-on-4-Yidene(1)。卡宾碳中心上的N-氨基甲酸和芳基同时向卡宾中心提供了极高的亲电子性和亲核性,其硒酮衍生物的77 Se NMR化学位移和羰基铑配合物的CO拉伸强度证明了这一点。由于前体1可从各种官能席夫碱在一个实际和可扩展的方式来合成的电子性质1可以进行微调以定量和可预测的方式,通过使用哈米特σ芳环上官能团的常数。简便的电子调谐能力1可能适用于在主族和过渡金属化学中引发新的特性。
Bis-Salicylaldiminato Complexes of Zinc. Examination of the Catalyzed Epoxide/CO<sub>2</sub> Copolymerization
作者:Donald J. Darensbourg、Patrick Rainey、Jason Yarbrough
DOI:10.1021/ic0006403
日期:2001.2.1
A series of salicylaldimine ligands of the general formula ((NRC7H5-x)-C-2(R-1)(x)OH) [x = 1 or 2; R-1 = Me, (BU)-B-t, Cl, OMe: R-2 = 2 6-(Pr2C6H3)-Pr-1, or 3,5-(CF3)(2)C6H3] have been synthesized and characterized via H-1 and C-13 NMR, elemental analysis, and X-ray crystallography. The concomitant series of zinc bis(salicylaldiminato) complexes of the general formula ((NRC7H5-x)-C-2(R-1)(x)O)(2)Zn have been synthesized and characterized in the solid state by X-ray crystallography. All complexes crystallized as four coordinate monomers with distorted tetrahedral geometry about the zinc center. The O-Zn-O angles range between 105 and 112.5 degrees, and the N-Zn-N bond angles were more obtuse spanning the range 122.9-128.9 degrees The only deviation from distorted tetrahedral geometry occurred when R-2 = 3,5-(CF3)(2)C6H3 which crystallized as a distorted trigonal bipyramidal dimeric species with O-ax-Zn-O-ax bond angles of 165.00(15)degrees. The equatorial angles approach 120 degrees except for the N-eq-Zn-N-eq angle of 110.54(16)degrees which is attributed to the strain of the bridging ligands. The zinc bis(salicylaldiminato) complexes showed varying activities as catalyst precursors for the copolymerization of CO2 and cyclohexene oxide. Activation is proposed to occur via CO, insertion in the phenolic Zn-O bond with simultaneous ring-opening resulting in a site for epoxide binding. The difference in activity has been ascribed to the different steric/electronic effects provided by the R-1 and R-2 substituents an the various steps of the copolymerization mechanism, The activity of the zinc bis(salicyaldiminato) catalyst precursors (< 16 gpoly/m/g . Zn/hr) were similar to the activities of the previously reported zinc phenoxide complexes for this reaction: however, unlike; the zinc phenoxide catalysts, the zinc bis(salicylaldiminato) complexes produced poly(cyclohexane carbonate) with greater than 99% carbonate linkages.