title: Metal-Free sp(2)-C-H Borylation as a Common Reactivity Pattern of Frustrated 2-Aminophenylboranes.
abstract: C-H borylation is a powerful and atom-efficient method for converting affordable and abundant chemicals into versatile organic reagents used in the production of fine chemicals and functional materials. Herein we report a facile C-H borylation of aromatic and olefinic C-H bonds with 2-aminophenylboranes. Computational and experimental studies reveal that the metal-free C-H insertion proceeds via a frustrated Lewis pair mechanism involving heterolytic splitting of the C-H bond by cooperative action of the amine and boryl groups. The adapted geometry of the reactive B and N centers results in an unprecedentently low kinetic barrier for both insertion into the sp(2)-C-H bond and intramolecular protonation of the sp(2)-C-B bond in 2-ammoniophenyl(aryl)- or -(alkenyl)borates. This common reactivity pattern serves as a platform for various catalytic reactions such as C-H borylation and hydrogenation of alkynes. In particular, we demonstrate that simple 2-aminopyridinium salts efficiently catalyze the C-H borylation of hetarenes with catecholborane. This reaction is presumably mediated by a borenium species isoelectronic to 2-aminophenylboranes.
authors.affiliation: Department of Chemistry, University of Helsinki , A. I. Virtasen aukio 1, P.O. Box 55, 00014 Helsinki, Finland.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Chernichenko
authors.affiliation: Department of Chemistry, University of Helsinki , A. I. Virtasen aukio 1, P.O. Box 55, 00014 Helsinki, Finland.
authors.forename: Markus
authors.initials: M
authors.lastname: Lindqvist
authors.affiliation: Research Centre for Natural Sciences, Hungarian Academy of Sciences , Magyar tudósok körútja 2, H-1117 Budapest, Hungary.
authors.forename: Bianka
authors.initials: B
authors.lastname: Kótai
authors.affiliation: Department of Chemistry, University of Helsinki , A. I. Virtasen aukio 1, P.O. Box 55, 00014 Helsinki, Finland.
authors.forename: Martin
authors.initials: M
authors.lastname: Nieger
authors.affiliation: Department of Chemistry, University of Helsinki , A. I. Virtasen aukio 1, P.O. Box 55, 00014 Helsinki, Finland.
authors.forename: Kristina
authors.initials: K
authors.lastname: Sorochkina
authors.affiliation: Research Centre for Natural Sciences, Hungarian Academy of Sciences , Magyar tudósok körútja 2, H-1117 Budapest, Hungary.
authors.forename: Imre
authors.initials: I
authors.lastname: Pápai
authors.affiliation: Department of Chemistry, University of Helsinki , A. I. Virtasen aukio 1, P.O. Box 55, 00014 Helsinki, Finland.
authors.forename: Timo
authors.initials: T
authors.lastname: Repo