Synthesis and Vibrational Circular Dichroism of Enantiopure Chiral Oxorhenium(V) Complexes Containing the Hydrotris(1-pyrazolyl)borate Ligand Peter R. Lassen, ²,‡ Laure Guy, § Iyad Karame, § Thierry Roisnel, | Nicolas Vanthuyne, ⊥ Christian Roussel, ⊥ Xiaolin Cao, ² Rosina Lombardi, ² Jeanne Crassous,* ,| Teresa B. Freedman,* ,² and Laurence A. Nafie ² Department of Chemistry, Syracuse UniVersity, Syracuse, New York 13244, Laboratoire de Chimie, E Ä cole Normale Supe ´ rieure de Lyon, UMR CNRS 5182, 46 Alle ´ e d’Italie, F-69364 Lyon 07, France, Sciences chimiques de Rennes, UMR CNRS 6226, UniVersite ´ de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France, and UMR Chirotechnologies: Catalyse et Biocatalyse, UniVersite ´ Paul Ce ´ zanne, 13397 Marseille Cedex 20, France Received July 28, 2006 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(η 2 -O(CH 3 )CH 2 CH 2 O-O,O)] (4a and 4b) diastereomers and [TpReO(η 2 - N(CH 3 )CH 2 CH 2 O-N,O)] (5) and [TpReO(η 2 -N(tBu)CH 2 CH 2 O-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(η 2 -N(CH 3 )CH(CH 3 )CH(Ph)O-N,O)] (2) and [TpReO(η 2 -N(CH 2 ) 3 CHCO 2 -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. Introduction Oxorhenium complexes have proven useful in catalysis 1 and in radiopharmaceutical chemistry. 2 Moreover, chiral oxorhenium complexes have been revealed to be good candidates for the observation of parity violation (PV) effects in chiral molecules. 3 Parity violation is a fundamental effect which breaks the space symmetry and which is due to weak interaction between elementary particles. 4 It has been ex- perimentally observed in atoms and in nuclear physics. 5 At the molecular level, PV is known to induce a very tiny energy difference (PVED) between the two enantiomers of a chiral molecule. However, observing such a tiny energy difference, ∆E PV (∆E PV ) ca. 10 -17 kT) is still a scientific challenge and requires very accurate spectroscopy methods together with a good chiral model molecule. 6 For example, PV may be observed by unpolarized infrared (IR) spectroscopy, i.e., by measuring slightly different absorption frequencies for opposite enantiomers. PVED measurements have already been searched on simple chiral heterohalogenomethanes such * To whom correspondence should be addressed. (J.C.) Phone: +33 02 23 23 63 70. Fax: +33 02 23 23 69 39. E-mail: jeanne.crassous@univ- rennes1.fr. (T.B.F.) Phone: (315) 443-1134. Fax: (315) 443-4070. E- mail: tbfreedm@syr.edu. ² Syracuse University. ‡ Visiting from the Quantum Protein Centre, Department of Physics, Technical University of Denmark, DK-2800 Lyngby, Denmark. § E Ä cole Normale Supe ´rieure de Lyon. | Universite ´ de Rennes 1. ⊥ Universite ´ Paul Ce ´zanne. (1) (a) Morris, L. J.; Downs, A. J.; Greene, T. M.; McGrady, G. S.; Herrmann, W. A.; Sirsch, P.; Scherer, W.; Gropen, O. Organometallics 2001, 20, 2344-2352 and references therein. (b) Kennedy-Smith, J. J.; Nolin, K. A.; Gunterman, H. P.; Toste, F. D. J. Am. Chem. Soc. 2003, 125, 4056-4057. (c) Morrill, C.; Grubbs, R. H. J. Am. Chem. Soc. 2005, 127, 2842-2843. (d) Rudolph, J.; Reddy, K. L.; Chiang, J. P.; Sharpless, K. B. J. Am. Chem. Soc. 1997, 119, 6189-6190. (e) Cai, Y.; Espenson, J. H. Inorg. Chem. 2005, 44, 2560-2565. (f) Ison, E. A.; Trivedi, E. R.; Corbin, R. A.; Abu-Omar, M. M. J. Am. Chem. Soc. 2005, 127, 15374-15375. Inorg. Chem. 2006, 45, 10230-10239 10230 Inorganic Chemistry, Vol. 45, No. 25, 2006 10.1021/ic061418m CCC: $33.50 © 2006 American Chemical Society Published on Web 11/08/2006