The stereodynamics of 5,5'-disubstituted BIPHEPs

Frank Maier; Oliver Trapp

doi:10.1002/chir.22125

The stereodynamics of 5,5'-disubstituted BIPHEPs

Chirality. 2013 Feb;25(2):126-32. doi: 10.1002/chir.22125. Epub 2012 Dec 22.

Authors

Frank Maier¹, Oliver Trapp

Affiliation

¹ Ruprecht-Karls-Universität Heidelberg, Organisch-Chemisches Institut, Heidelberg, Germany.

PMID: 23280627
DOI: 10.1002/chir.22125

Abstract

We investigated the stereodynamics of 5,5'-substituted tropos BIPHEP ligands (2,2'-bis(diphenylphosphino)-biphenyls) by enantioselective dynamic high-performance liquid chromatography (DHPLC) to elucidate the influence of the substitution pattern and electronics of the substituents (methyl, methoxy, and hydroxyl groups). By temperature-dependent dynamic HPLC measurements the activation parameters ΔG(╪), ΔH(╪), and ΔS(╪) could be determined with high precision, revealing that the activation barrier of these 5,5'-substituted BIPHEP ligands ranges in a narrow band between 87.8 and 93.0 kJ mol(-1), making them highly attractive as deracemizable dynamic chiral ligands in asymmetric catalysis. Interestingly, the activation parameters are highly influenced by a hydroxyl or methoxy group in the 5,5'-position of the BIPHEP ligands.