Godbole Meenal D, Hotze Anna C G, Hage Ronald, Mills Allison M, Kooijman Huub, Spek Anthony L, Bouwman Elisabeth
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
Inorg Chem. 2005 Dec 12;44(25):9253-66. doi: 10.1021/ic051223z.
Manganese complexes of the ligand HphoxCOOR (R=H or Me) have been synthesized and characterized by X-ray analysis, ESI-MS, ligand-field spectroscopy, electrochemistry, and paramagnetic 1H NMR. The ligands, chirally pure or racemic, influence the structures of the complexes formed. Manganese(III) complexes of the ligand HphoxCOOMe are square-pyramidal or octahedral with two ligands bound in a trans fashion in the solid state. The racemic ligand (RS-HphoxCOOMe) as well as the enantiopure ligand (R-HphoxCOOMe) forms manganese complexes with similar solid-state structures. Ligand-exchange reactions occur in solution giving rise to meso complexes as confirmed by ESI-MS and deuteration studies. The manganese(III) complex of R-HphoxCOOH is octahedral, with two dianionic ligands bound in a fac-cct fashion in a tridentate manner. The manganese(III) complex of RS-HphoxCOOH is also octahedral with two dianionic ligands now bound in a trans fashion in a didentate manner and with two water molecules occupying axial sites. The paramagnetic 1H NMR spectra of the complexes have been interpreted on the basis of the relaxation times with the help of the inversion-recovery pulse technique. The binding of imidazole with the metal center depends on the chirality of the ligands in the metal complexes of HphoxCOOMe. Imidazole coordination was found to occur with the metal complex that contains two ligands with the same chirality (R and R) (R-1), while no imidazole coordination was found upon reaction with the metal complex that contains two ligands with opposite chirality (R and S) (RS-1). Epoxidation reactions of various alkenes with H2O2 as the oxidant reveal that the complexes give turnover numbers in the range of 10-35, the epoxide being the major product. The catalytic activity depends on the additives used, and a clear base effect is observed. The turnover numbers have been found to be higher in the complexes where no binding of N-Meim is observed. The latter fact unambiguously shows that imidazole binding is not a prerequisite for higher turnover numbers, in contrast to the Mn-Schiff base catalysts.
已合成配体HphoxCOOR（R = H或Me）的锰配合物，并通过X射线分析、电喷雾电离质谱（ESI-MS）、配体场光谱、电化学和顺磁1H核磁共振进行了表征。手性纯或外消旋的配体会影响所形成配合物的结构。配体HphoxCOOMe的锰（III）配合物为四方锥或八面体结构，在固态下有两个配体以反式方式结合。外消旋配体（RS-HphoxCOOMe）以及对映体纯配体（R-HphoxCOOMe）形成具有相似固态结构的锰配合物。溶液中发生配体交换反应，生成内消旋配合物，这已通过ESI-MS和氘代研究得到证实。R-HphoxCOOH的锰（III）配合物为八面体结构，两个二价阴离子配体以面-面-边的方式以三齿形式结合。RS-HphoxCOOH的锰（III）配合物也是八面体结构，现在两个二价阴离子配体以反式方式以双齿形式结合，且有两个水分子占据轴向位置。借助反转恢复脉冲技术，根据弛豫时间对配合物的顺磁1H核磁共振谱进行了解释。咪唑与金属中心的结合取决于HphoxCOOMe金属配合物中配体的手性。发现咪唑与含有两个相同手性（R和R）配体的金属配合物（R-1）发生配位，而与含有两个相反手性（R和S）配体的金属配合物（RS-1）反应时未发现咪唑配位。以H2O2为氧化剂对各种烯烃进行环氧化反应表明，这些配合物的周转数在10 - 35范围内，环氧化物是主要产物。催化活性取决于所使用的添加剂，并且观察到明显的碱效应。已发现在所观察到没有N-甲基咪唑结合的配合物中周转数更高。后一事实明确表明，与锰-席夫碱催化剂相反，咪唑结合不是获得更高周转数的先决条件。
