Frustrated Lewis pair chemistry of chiral (+)-camphor-based aminoboranes

Markus Lindqvist; Kirill Axenov; Martin Nieger; Minna Räisänen; Markku Leskelä; Timo Repo

doi:10.1002/chem.201300462

Frustrated Lewis pair chemistry of chiral (+)-camphor-based aminoboranes

Chemistry. 2013 Jul 29;19(31):10412-8. doi: 10.1002/chem.201300462. Epub 2013 Jun 20.

Authors

Markus Lindqvist¹, Kirill Axenov, Martin Nieger, Minna Räisänen, Markku Leskelä, Timo Repo

Affiliation

¹ Department of Chemistry, Laboratory of Inorganic Chemistry, University of Helsinki, P.O. Box 55, 00014, Finland.

PMID: 23788132
DOI: 10.1002/chem.201300462

Abstract

Dimethylamino-(+)-camphorenamine reacted with an equimolar amount of Piers' borane, HB(C6F5)2, to give the corresponding iminium-hydroborate zwitterionic salt. Being in equilibrium with the parent enamine-HB(C6F5)2 N-B pair, this salt was able to split hydrogen heterolytically, hydrogenating the iminium group in the molecule. Detailed studies revealed that the hydrogen splitting in this reaction proceeded through an intermolecular pathway leading to a bornylamine-HB(C6F5)2 adduct. When the starting enamine is present in excess over HB(C6F5)2, the produced bornylamine-HB(C6F5)2 adduct breaks up, eliminating free bornylamine and forming the initial camphorenamine-HB(C6F5)2 pair. This results in hydrogenation of the camphorenamine framework in a catalytic fashion.

Keywords: boron; frustrated Lewis pairs; hydrogenation; nitrogen; reaction mechanism.