title: NMR-spectroscopic and solid-state investigations of cometal-free asymmetric conjugate addition: a dinuclear paracyclophaneimine zinc methyl complex.
abstract: We present herein the first indications for dimeric structures in cometal-free asymmetric conjugate addition reactions of dialkylzinc reagents with aldehydes. These are revealed by nonlinear effect (NLE) studies. A monomer-dimer equilibrium can be assumed which explains the increase of the ee value in the product over time. Also, DOSY NMR spectroscopic measurements indicate the existence of the catalyst as [LZnEt](n) complexes in solution. Additionally, the first X-ray structure of a zinc complex with a [2.2]paracyclophane ligand was determined. The structures of the zinc complexes are supported by DFT calculations of monomeric and dimeric species.
authors.affiliation: Institute of Organic Chemistry, Karlsruhe Institute of Technology, Fritz-Haber-Weg 6, D-76131 Karlsruhe, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Ay
authors.forename: R E
authors.initials: RE
authors.lastname: Ziegert
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: M
authors.initials: M
authors.lastname: Nieger
authors.forename: K
authors.initials: K
authors.lastname: Rissanen
authors.forename: K
authors.initials: K
authors.lastname: Fink
authors.forename: A
authors.initials: A
authors.lastname: Kubas
authors.forename: R M
authors.initials: RM
authors.lastname: Gschwind
authors.forename: S
authors.initials: S
authors.lastname: Bräse