Abstract
The catalytic oxidation of the phenyl-substituted cis alkenes 1a,b by the MnIII(salen)X complexes 3a−f with iodosyl benzene (PhIO) as oxygen source affords the corresponding epoxides 2a,b in cis/trans ratios of 79:21 to 26:74. The diastereoselectivity (cis/trans ratio) depends on the counterion of the MnIII(salen)X complexes 3a−f. Thus, for the complexes 3a−c (Cl−, Br− and AcO− as ligating counterions) extensive isomerization (cis/trans ratio ca. 30:70) takes place, while for the complexes 3d−f (BF4−, PF6− and SbF6− as nonligating counterions) only moderate isomerization (cis/trans ratio ca. 75:25) is observed. This counterion effect may be rationalized in terms of the two-state reactivity paradigm; specifically, the axial ligand in the radical intermediate alters the triplet-quintet energy gap.
Published Version
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