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Article

Dialkyl Effect on Enantioselectivity: π-Stacking as a Structural Feature in P,N Complexes of Palladium(II)

Supporting Info

Pascal Dotta, Alessandra Magistrato,^† Ursula Rothlisberger, and Paul S. Pregosin*

Laboratory of Inorganic Chemistry, ETHZ, 8093 Zrich, Switzerland

Alberto Albinati*

Chemical Pharmacy, University of Milan, I-20131 Milan, Italy

Organometallics, 2002, 21 (14), pp 3033–3041

DOI: 10.1021/om020314q

Publication Date (Web): June 13, 2002

†

Present address: Chemistry Department, University of Pennsylvania, Philadelphia, PA, 19104-6323.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Abstract

A phosphino,oxazoline P,N-bidentate ligand, 4, containing 3,5-di-tert-butylphenyl groups has been prepared. In the Heck arylation of dihydrofuran, 4 is shown to afford higher ee's than either 2 or 3, the unsubstituted and m-dimethylphenyl analogues, respectively. Several Pd(0) complexes of 4 are reported. The exchange dynamics of Pd(4)(dba) are shown to involve an interconversion of diastereomers via an intramolecular process. The X-ray structure for PdCl₂(4), 8, was determined by X-ray diffraction methods. Comparison of data with PdCl₂(2), 9, and PdCl₂(3), 10, suggests that differing amounts of π−π stacking influence the structures of these relatively simple Pd complexes, with 9 and 10 revealing the strongest π−π interactions. An estimation of the van der Waals energies involved in the interaction supports a ca. 4 kcal/mol stabilization via π−π stacking.