Universidad de Castilla-La Mancha, Departamento de Química Inorgánica, Orgánica y Bioquímica, Centro de Innovación en Química Avanzada (ORFEO-CINQA) Campus Universitario, 13071-Ciudad Real, Spain.
Dalton Trans. 2017 Nov 7;46(43):15107-15117. doi: 10.1039/c7dt03045b.
The preparation of new chiral bis(pyrazol-1-yl)methane-based N,N,O-donor scorpionate ligands in the form of the alcohol compounds bpzampeH (1) {2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[4-(dimethylamino)phenyl]ethanol}, bpzaepeH (2) {2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[4-(diethylamino)phenyl]ethanol}, and bpzimeH (3) {2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[1-methyl-1H-imidazol-2-yl]ethanol} has been carried out by the 1,2-addition reactions of a series of aldehydes. These new chiral heteroscorpionate ligands reacted with [ZnR] (R = Me, Et, CHSiMe) in a 1 : 1 molar ratio in toluene to give the mononuclear monoalkyl zinc complexes [Zn(R)(κ-NNO)] (4-12). When these reactions were carried out in a 1 : 2 molar ratio the binuclear trisalkyls [Zn(R)(κ-NNμ-O)Zn(R)] (13-18) were obtained. The structures of these complexes were elucidated by H and C{H} NMR spectroscopy and the X-ray crystal structures of 4 and 5 were also established. Interestingly, alkyl-containing zinc complexes 4-13, 15 and 17 act as efficient single-component initiators for the ring-opening polymerization of rac-lactide at 20 °C to afford PLA materials with low molecular weights in a few hours. The dinuclear trisalkyls showed higher activity in comparison with the mononuclear zinc counterparts, suggesting a cooperative effect of the two remote metals. The narrow dispersity ranges (M/M = 1.05) of the isolated polymers in conjunction with the linear nature of the number average molecular weight versus conversion plot provided evidence for living behavior. Inspection of the kinetic parameters showed that the propagations have the usual pseudo-first-order dependence on rac-lactide and catalyst concentration. End-group analysis and MALDI-TOF mass spectrometry confirmed that the initiation occurs through nucleophilic attack of the alkyl on the lactide monomer. Microstructural analysis of poly(rac-lactide)s revealed that the most sterically hindered ligand on the alkoxide fragment exerts a moderate influence on the degree of stereoselectivity, with heteroenriched-PLAs (P = 0.68) produced at room temperature.
已通过一系列醛的 1,2-加成反应制备了新的手性双（吡唑-1-基）甲烷基 N,N,O-供体异硫氰酸酯配体的醇化合物 bpzampeH（1）{2,2-双（3,5-二甲基吡唑-1-基）-1-[4-（二甲氨基）苯基]乙醇}、bpzaepeH（2）{2,2-双（3,5-二甲基吡唑-1-基）-1-[4-（二乙氨基）苯基]乙醇}和 bpzimeH（3）{2,2-双（3,5-二甲基吡唑-1-基）-1-[1-甲基-1H-咪唑-2-基]乙醇}。这些新的手性异硫氰酸酯配体与[ZnR]（R = Me、Et、CHSiMe）在甲苯中以 1：1 摩尔比反应，得到单核单烷基锌配合物[Zn（R）（κ-NNO）]（4-12）。当这些反应以 1：2 摩尔比进行时，得到双核三烷基[Zn（R）（κ-NNμ-O）Zn（R）]（13-18）。这些配合物的结构通过 H 和 C{H} NMR 光谱阐明，并且还确定了 4 和 5 的 X 射线晶体结构。有趣的是，含烷基的锌配合物 4-13、15 和 17 在 20°C 下作为 rac-丙交酯开环聚合的有效单组分引发剂，在数小时内提供低分子量的 PLA 材料。双核三烷基与单核锌对应物相比表现出更高的活性，表明两个远程金属之间存在协同作用。分离聚合物的窄分散度范围（M/M = 1.05）以及数均分子量与转化率关系图的线性表明存在活性聚合行为。对动力学参数的检查表明，聚合反应通常对 rac-丙交酯和催化剂浓度具有准一级依赖性。端基分析和 MALDI-TOF 质谱证实引发是通过烷氧基片段上的烷基对丙交酯单体的亲核攻击进行的。聚（rac-丙交酯）的微结构分析表明，在烷氧基片段上最具空间位阻的配体对立体选择性有适度影响，在室温下产生杂原子富集-PLA（P = 0.68）。
