Isolation and crystal structures of both enol and keto tautomer intermediates in a hydration of an alkyne-carboxylic acid ester catalyzed by iridium complexes in water.
Isolation and crystal structures of both enol and keto tautomer intermediates in a hydration of an alkyne-carboxylic acid ester catalyzed by iridium complexes in water.
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DOI：
10.1021/ja807254d
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发表时间：
2008-12
影响因子：
15
通讯作者：
Hironobu Kanemitsu;Keiji Uehara;S. Fukuzumi;S. Ogo
中科院分区：
文献类型：
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作者：
Hironobu Kanemitsu;Keiji Uehara;S. Fukuzumi;S. Ogo
在Ir-水络合物[Ir（III）Cp*（bpy）（OH 2）]2+（1，Cp* = eta 5-C5 Me 5，bpy = 2，2 '-联吡啶）的催化下，作为炔-羧酸酯的四酸乙酯在水中水合，得到作为β-酮酸酯的乙酰乙酸乙酯。通过优化分离条件，如溶液pH值、反应时间和抗衡阴离子的选择，我们成功地分离了Ir-烯醇互变异构体中间体[Ir（III）Cp*（bpy）{CH 3C（O）CHC（O）OC 2 H5}]+（2）和Ir-酮互变异构体中间体[Ir（III）Cp*（bpy）{CH 3C（O）CHC（O）OC 2 H5}]+（3）。通过X射线衍射、红外光谱、电喷雾质谱（ESI-MS）、核磁共振（1H、13 C）、无畸变极化转移增强（DEPT）和相关谱（COSY）等实验，确定了具有特征Ir-（sp2碳）键和Ir-（sp3碳）键的烯醇和酮配合物的结构。结果表明，以2或3为起始催化剂时，四酸乙酯的水合反应生成乙酰乙酸乙酯。本文通过Ir-烯醇和Ir-酮互变异构体的同位素标记实验，探讨了四酸乙酯催化水合生成炔羧酸酯的机理。
Hydration of tetrolic acid ethyl ester as an alkyne-carboxylic acid ester catalyzed by an Ir-aqua complex [Ir(III)Cp*(bpy)(OH2)]2+ (1, Cp* = eta5-C5Me5, bpy = 2,2'-bipyridine) in water provides ethyl acetoacetate as a beta-keto acid ester. We report the successful isolation of both an Ir-enol tautomer intermediate [IrIIICp*(bpy){CH3C(OH)=CC(O)OC2H5}]+ (2) and an Ir-keto tautomer intermediate [Ir(III)Cp*(bpy){CH3C(O)CHC(O)OC2H5}]+ (3) in the catalytic hydration by optimizing the conditions of the isolation, such as pH of the solution, reaction time, and selection of counteranions. The structures of the enol and keto complexes with characteristic Ir-(sp2carbon) bond and Ir-(sp3 carbon) bond, respectively, were unequivocally determined by X-ray analysis, IR, electrospray ionization mass spectrometry (ESI-MS), and NMR studies including 1H, 13C, distortionless enhancement by polarization transfer (DEPT) and correlation spectroscopy (COSY) experiments. It was confirmed that the hydration of tetrolic acid ethyl ester catalyzed by 2 or 3 as initial catalysts provides ethyl acetoacetate. Mechanism of the catalytic hydration of tetrolic acid ethyl ester as an alkyne-carboxylic acid ester is discussed based on isotopic labeling experiments with the Ir-enol and Ir-keto tautomers.