Synthesis 2017; 49(15): 3485-3494
DOI: 10.1055/s-0036-1588861
paper
© Georg Thieme Verlag Stuttgart · New York

Temperature-Controlled Bidirectional Enantioselectivity in Asymmetric Hydrogenation Reactions Utilizing Stereodynamic Iridium Complexes

Max Siebert
a   Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München, Germany
,
Golo Storch
a   Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München, Germany
,
Frank Rominger
b   Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany   Email: oliver.trapp@cup.uni-muenchen.de
,
a   Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München, Germany
› Author Affiliations
Generous financial support by the European Research Council (ERC) for a Starting Grant (No. 258740, AMPCAT) is gratefully acknowledged. G.S. acknowledges the Fonds der Chemischen Industrie for a Ph.D. fellowship
Further Information

Publication History

Received: 09.05.2017

Accepted: 11 May 2017

Publication Date:
20 June 2017 (online)


This contribution is dedicated to Prof. Dr. Herbert Mayr on the occasion of his 70th birthday.

Abstract

Stereochemically flexible 2,2(-bis(diphenylphosphino)biphenyl (BIPHEP) ligands were modified with chiral α-substituted carboxylic acid auxiliaries in the 3- and 3′-position. The resulting central-to-axial chirality transfer to the stereochemically flexible chiral axis of the BIPHEP­ core was investigated as well as complexation of these diastereomeric ligands to iridium(I). Solid-state structures of both ligand diastereomers and a diastereomerically pure iridium(I) BIPHEP complex were obtained. Thermal equilibration of the resulting iridium(I) complexes was studied to investigate the stereodynamic properties of the BIPHEP ligands. The iridium(I) complexes without and after pre-catalysis warming in solution — which induces a shift of the diastereomeric ratio — were applied for asymmetric hydrogenation of a prochiral α-substituted acrylic acid, resulting in temperature-controlled bidirectional enantioselectivity of iridium catalysts for the first time. In both cases, enantioenriched (R)-naproxen as well as (S)-naproxen — after re-equilibration of the catalyst at elevated temperatures — was obtained by using the same catalyst.

Supporting Information