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Experimental Observation of a Terminal Borylene-Dinitrogen Adduct via Cleavage of a 1,2,3,4,5-Diboratriazoline.
Angew Chem Int Ed Engl
November 2024
Institute for Inorganic Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
While azides do not react with simple alkenes except under harsh conditions, a diboron alkene analogue, the doubly cyclic alkyl(amino)carbene (CAAC)-stabilized dicyanodiborene 1, reacts spontaneously with organic azides (7-10 equiv.) at room temperature to yield two equivalents of stable CAAC-imino(cyano)boranes (2-R). NMR-spectroscopic monitoring of the reaction mixtures shows the initial formation of a 1 : 1 mixture of 2-R and a relatively long-lived intermediate (Int), which in the presence of excess azide is converted into a second equivalent of 2-R.
View Article and Find Full Text PDFSynthesis and reactivity of an N-heterocyclic carbene-stabilized diazoborane.
Science
July 2024
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Diazo compounds and organic azides are widely used as reagents for accessing valuable molecules in multiple areas of fundamental and applied chemistry. Their capacity to undergo versatile chemical transformations arises from the reactive nature of an incipient dinitrogen molecule at the terminal position. In this work, we report the synthesis and characterization of an N-heterocyclic carbene (NHC)-stabilized diazoborane-a boron-centered analog of organic azides and diazoalkanes.
View Article and Find Full Text PDFA hampered oxidative addition of pre-coordinated pincer ligands can favour alternative pathways of activation.
Chem Commun (Camb)
May 2023
Institute of Chemistry, Faculty of Natural Sciences II, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Str. 2, D-06120 Halle (Saale), Germany.
Pre-coordination to a transition metal by the terminal donor groups of a tri-dentate ligand is a common strategy to stabilise elusive groups, to achieve unprecedented bond activation and to develop novel modes of metal-ligand-cooperation for catalysis. In the current manuscript, we demonstrate that the oxidative addition of a central E-H-bond after pre-coordination to the metal centre is disfavoured for metals with d electron configuration. For exemplary pincer ligands and metals with d electron configuration, quantum chemical calculations suggest a second barrier, which is associated with the rearrangement of the saw-horse structure, obtained after oxidative addition, to the expected square planar geometry for the resulting d electron configuration.
View Article and Find Full Text PDFReactivity of cyano- and isothiocyanatoborylenes: metal coordination, one-electron oxidation and boron-centred Brønsted basicity.
Chem Sci
May 2021
Institute for Inorganic Chemistry, Julius-Maximilians-Universität Würzburg Am Hubland 97074 Würzburg Germany
Doubly base-stabilised cyano- and isothiocyanatoborylenes of the form LL'BY (L = CAAC = cyclic alkyl(amino)carbene; L' = NHC = N-heterocyclic carbene; Y = CN, NCS) coordinate to group 6 carbonyl complexes the terminal donor of the pseudohalide substituent and undergo facile and fully reversible one-electron oxidation to the corresponding boryl radical cations [LL'BY]˙. Furthermore, calculations show that the borylenes have very similar proton affinities, both to each other and to NHC superbases. However, while the protonation of LL'B(CN) with PhSH yielding [LL'BH(CN)][PhS] is fully reversible, that of LL'B(NCS) is rendered irreversible by a subsequent B-to-C hydrogen shift and nucleophilic attack of PhS at boron.
View Article and Find Full Text PDFIntermetallic transfer of unsymmetrical borylene fragments: isolation of the second early-transition-metal terminal borylene complex and other rare species.
Dalton Trans
December 2020
Institute for Inorganic Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
Transition metal borylene complexes of the type [(OC)5M[double bond, length as m-dash]BN(SiMe3)(tBu)] (M = Cr, Mo, W) have been synthesised by salt elimination of the corresponding dibromoborane and the dianionic metallates Na2[M(CO)5]. The borylene complexes have been characterised by multinuclear solution-state NMR spectroscopy and solid-state molecular structure determination. The group 6 borylene complexes can be used to effectively transfer the borylene ligand to other transition metal complexes by replacing one or two carbonyl ligands upon irradiation of the reaction mixture with UV light.
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