Application of empirical molecular mechanics to asymmetric oxidation of sulfides catalyzed by metal complexes

1. 复合催化剂的x射线结构分析。由于分子力学是一种经验方法，为了获得可靠的结果，设置合适的参数是必不可少的。为此，我们对光学活性希夫碱-锰（III）， -钴（II）和-钒氧(V)配合物进行了x射线结构分析。分子力学的构象分析。对上述配合物进行了分子力学计算（MMP2）。计算出的几何形状与在晶体结构中观察到的相当吻合。然而，为了进行更详细的讨论，似乎有必要对几个参数进行改进。硫化物的不对称氧化。采用含光学活性席夫碱配体的金属配合物催化有机氢过氧化物将前手性有机硫化物不对称氧化成光学活性亚砜；最高的对映体过量（ee）约为60%。苯基的取向在不对称催化反应中起重要作用。因此，我们制备了含有四个苯基的希夫碱配体的锰（III）配合物，并研究了其催化性能。出乎意料的是，催化氧化导致了低对映体选择性。人们认识到，对活性位点周围的几何结构进行微调对于获得高ee非常重要。

1. X-ray Structure Analyses of Complex Catalysts.Since molecular mechanics is an empirical method, the setting of suitable parameters is essential in order to obtain reliable results. For this purpose, we have carried out X-ray structure analyses of optically active Schiff base- manganese(III), -cobalt(II), and -oxovanadium(V) complexes.2. Conformational Analyses by Means of Molecular Mechanics.Molecular mechanics calculations (MMP2) were carried out on the above complexes. The computed geometries agree fairly well with those observed in the crystal structures. However, the refinement of several parameters seems to be necessary for more detailed discussion.3. Asymmetric Oxidation of Sulfides.Asymmetric oxidation of prochiral organic sulfides into optically active sulfoxides was carried out with organic hydroperoxides catalyzed by metal complexes containing an optically active Schiff base ligand;the highest enantiomeric excess (ee) was ca. 60%. The orientation of phenyl groups was suggested to play an important role in asymmetric catalytic reactions. Thus, we prepared a manganese(III) complex of a Schiff base ligand involving four phenyl groups, and the catalytic properties were studied. Unexpectedly, the catalytic oxidation induced low enantioselectivity. It was realized that fine tuning of the geometry around the active site is very important to get high ee's.