Enantioselective transition-metal-based catalysis is a well-developed field with numerous applications. However, efficient chiral catalysts based on cheap and abundant first-row metals like Fe are, so far, scarce. In our group we have characterized a family of octanuclear Fe3+-complexes of the general formula [Fe8(m4-O)4(m-4-R-pz)12X4], [Fe8], where pz = pyrazolato anion, for a variety of terminal X-ligands and 4-R-substituents on the bridging pyrazolates. These complexes contain a central Fe4(m4-O)4-cubane surrounded by four more Fe-centers, the X-ligands coordinated to the latter, forming all together a Fe8(m4-O)4X4-core with tetrahedral geometry. However, the twelve bridging pyrazolato ligands (each bridging one cubane-Fe to one outer-Fe) adopt a propeller-like rotation in order to adjust to the steric requirements of the iron oxide core, and in so doing violate the mirror symmetry of the Td point group. This reduces the symmetry of the complex to that of the chiral T point group resulting in its crystallization as a racemic mixture of M and P enantiomers. Here we demonstrate that substitution of the terminal Cl, in the case of [Fe8(m4-O)4(m-4-Cl-pz)12Cl4, by rac-4-sec-Bu-C6H4O, results in spontaneous resolution upon crystallization of the P/S and M/R enantiomers, as shown by single-crystal X-ray crystallography. Further proof of the selectivity of each complex enantiomer towards the R or S enantiomer of the phenol, is given by single-crystal Circular Dichroism experiments.

Resolution of the chiral octanuclear iron-oxo-pyrazolate to its P and M enantiomers

2019 Spring National Meeting

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