Synthesis and Vibrational Circular Dichroism of Enantiopure Chiral Oxorhenium(V) Complexes Containing the Hydrotris(1-pyrazolyl)borate Ligand

The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complexes, bearing a
hydrotris(1-pyrazolyl)borate (Tp) ligand, have been investigated. These complexes are promising candidates for
observation of parity violation (symmetry breaking due to the weak nuclear force). New chiral oxorhenium complexes
have been synthesized, namely, [TpReO(η2-O(CH3)CH2CH2O-O,O)] (4a and 4b) diastereomers and [TpReO(η2-N(CH3)CH2CH2O-N,O)] (5) and [TpReO(η2-N(tBu)CH2CH2O-N,O)] (6) enantiomers. All compounds could be obtained
in enantiomerically pure form by using either column chromatography or HPLC over chiral columns. VCD spectroscopy
of these compounds and of [TpReO(η2-N(CH3)CH(CH3)CH(Ph)O-N,O)] (2) and [TpReO(η2-N(CH2)3CHCO2-N,O)]
(3) (with chiral bidentate ligands derived, respectively, from ephedrine and proline) were studied. This allowed the
absolute configuration determination of all compounds together with their conformational analysis, by comparing
calculated and experimental spectra. This is the first VCD study of rhenium complexes which further demonstrates
the applicability of VCD spectroscopy in determining the chirality of inorganic complexes.