title: A Highly Effective Ruthenium System for the Catalyzed Dehydrogenative Cyclization of Amine-Boranes to Cyclic Boranes under Mild Conditions.
abstract: We recently disclosed a new ruthenium-catalyzed dehydrogenative cyclization process (CDC) of diamine-monoboranes leading to cyclic diaminoboranes. In the present study, the CDC reaction has been successfully extended to a larger number of diamine-monoboranes (4-7) and to one amine-borane alcohol precursor (8). The corresponding NB(H)N- and NB(H)O-containing cyclic diaminoboranes (12-15) and oxazaborolidine (16) were obtained in good to high yields. Multiple substitution patterns on the starting amine-borane substrates were evaluated and the reaction was also performed with chiral substrates. Efforts have been spent to understand the mechanism of the ruthenium CDC process. In addition to a computational approach, a strategy enabling the kinetic discrimination on successive events of the catalytic process leading to the formation of the NB(H)N linkage was performed on the six-carbon chain diamine-monoborane 21 and completed with a (15) N NMR study. The long-life bis-σ-borane ruthenium intermediate 23 possessing a reactive NHMe ending was characterized in situ and proved to catalyze the dehydrogenative cyclization of 1, ascertaining that bis σ-borane ruthenium complexes are key intermediates in the CDC process.
authors.affiliation: CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP 44099, 31077 Toulouse Cedex 4 (France).|Université de Toulouse, UPS, INPT, 31077 Toulouse Cedex 4 (France).
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Wallis
authors.affiliation: CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP 44099, 31077 Toulouse Cedex 4 (France). gilles.alcaraz@lcc-toulouse.fr.|Université de Toulouse, UPS, INPT, 31077 Toulouse Cedex 4 (France). gilles.alcaraz@lcc-toulouse.fr.
authors.forename: Gilles
authors.initials: G
authors.lastname: Alcaraz
authors.affiliation: Institut Charles Gerhardt, Université de Montpellier, CNRS 5253, cc 1501, Place Eugène Bataillon, 34095 Montpellier Cedex 5 (France).
authors.forename: Alban S
authors.initials: AS
authors.lastname: Petit
authors.affiliation: Institut Charles Gerhardt, Université de Montpellier, CNRS 5253, cc 1501, Place Eugène Bataillon, 34095 Montpellier Cedex 5 (France).
authors.forename: Amalia I
authors.initials: AI
authors.lastname: Poblador-Bahamonde
authors.affiliation: Institut Charles Gerhardt, Université de Montpellier, CNRS 5253, cc 1501, Place Eugène Bataillon, 34095 Montpellier Cedex 5 (France).
authors.forename: Eric
authors.initials: E
authors.lastname: Clot
authors.affiliation: CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP 44099, 31077 Toulouse Cedex 4 (France).|Université de Toulouse, UPS, INPT, 31077 Toulouse Cedex 4 (France).
authors.forename: Christian
authors.initials: C
authors.lastname: Bijani
authors.affiliation: CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP 44099, 31077 Toulouse Cedex 4 (France).|Université de Toulouse, UPS, INPT, 31077 Toulouse Cedex 4 (France).
authors.forename: Laure
authors.initials: L
authors.lastname: Vendier
authors.affiliation: CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP 44099, 31077 Toulouse Cedex 4 (France).|Université de Toulouse, UPS, INPT, 31077 Toulouse Cedex 4 (France).
authors.forename: Sylviane
authors.initials: S
authors.lastname: Sabo-Etienne
keywords: boranes; cyclization; dehydrogenation; density functional calculations; ruthenium; synthetic methods