title: Ligand spheres in asymmetric hetero Diels-Alder reactions catalyzed by Cu(II) box complexes: experiment and modeling.
abstract: The stereoselective hetero Diels-Alder reaction between ethyl glyoxylate and cyclohexadiene catalyzed by [Cu(ii)t-Bu-(box)](OTf)2 was investigated. The reaction was performed step-by-step and the geometry of the Cu(ii) complexes formed in the course of the catalysis was analysed by EPR spectroscopy, advanced pulsed EPR methods (ENDOR, and HYSCORE) and DFT calculations. Our results show that one triflate counterion is directly coordinated to Cu(ii) during the catalytic process (axial position). This leads to penta-coordinated Cu(ii) complexes. Solvent molecules are able to alter the geometry of the Cu(ii) complexes although their coordination is weak. These findings provide an explanation for the solvent and counterion effects observed in many catalytic reactions.
authors.affiliation: Institute of Physical and Theoretical Chemistry, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria. g.gescheidt-demner@tugraz.at.
authors.forename: V
authors.initials: V
authors.lastname: Umamaheswari
authors.forename: Pawel
authors.initials: P
authors.lastname: Cias
authors.forename: Andreas
authors.initials: A
authors.lastname: Pöppl
authors.forename: Martin
authors.initials: M
authors.lastname: Kaupp
authors.forename: Georg
authors.initials: G
authors.lastname: Gescheidt