title: Room temperature ring expansion of N-heterocyclic carbenes and B-B bond cleavage of diboron(4) compounds.
abstract: We report the isolation and detailed structural characterization, by solid-state and solution NMR spectroscopy, of the neutral mono- and bis-NHC adducts of bis(catecholato)diboron (B2 cat2 ). The bis-NHC adduct undergoes thermally induced rearrangement, forming a six-membered -B-C=N-C=C-N-heterocyclic ring via C-N bond cleavage and ring expansion of the NHC, whereas the mono-NHC adduct is stable. Bis(neopentylglycolato)diboron (B2 neop2 ) is much more reactive than B2 cat2 giving a ring expanded product at room temperature, demonstrating that ring expansion of NHCs can be a very facile process with significant implications for their use in catalysis.
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg (Germany).
authors.forename: Sabrina
authors.initials: S
authors.lastname: Pietsch
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg (Germany).
authors.forename: Ursula
authors.initials: U
authors.lastname: Paul
authors.affiliation: School of Chemistry, The University of Manchester, Manchester M13 9PL (UK).
authors.forename: Ian A
authors.initials: IA
authors.lastname: Cade
authors.affiliation: School of Chemistry, The University of Manchester, Manchester M13 9PL (UK). michael.ingleson@manchester.ac.uk.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ingleson
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg (Germany). u.radius@uni-wuerzburg.de.
authors.forename: Udo
authors.initials: U
authors.lastname: Radius
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg (Germany). todd.marder@uni-wuerzburg.de.
authors.forename: Todd B
authors.initials: TB
authors.lastname: Marder
keywords: BB bond activation; CN bond cleavage; N-heterocyclic carbene; boron compounds; ring expansion reaction