title: A facile route to backbone-tethered N-heterocyclic carbene (NHC) ligands via NHC to aNHC rearrangement in NHC silicon halide adducts.
abstract: The reaction of 1,3-diisopropylimidazolin-2-ylidene (iPr2 Im) with diphenyldichlorosilane (Ph2 SiCl2 ) leads to the adduct (iPr2 Im)SiCl2 Ph2 1. Prolonged heating of isolated 1 at 66 °C in THF affords the backbone-tethered bis(imidazolium) salt [((a) HiPr2 Im)2 SiPh2 ](2+)  2 Cl(-) 2 ("(a) " denotes "abnormal" coordination of the NHC), which can be synthesized in high yields in one step starting from two equivalents of iPr2 Im and Ph2 SiCl2 . Imidazolium salt 2 can be deprotonated in THF at room temperature using sodium hydride as a base and catalytic amounts of sodium tert-butoxide to give the stable N-heterocyclic dicarbene ((a) iPr2 Im)2 SiPh2 3, in which two NHCs are backbone-tethered with a SiPh2 group. This easy-to-synthesize dicarbene 3 can be used as a novel ligand type in transition metal chemistry for the preparation of dinuclear NHC complexes, as exemplified by the synthesis of the homodinuclear copper(I) complex [{(a) (ClCuiPr2 Im)}2 SiPh2 ] 4.
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg (Germany).
authors.forename: Heidi
authors.initials: H
authors.lastname: Schneider
authors.forename: David
authors.initials: D
authors.lastname: Schmidt
authors.forename: Udo
authors.initials: U
authors.lastname: Radius
keywords: N-heterocyclic carbenes; carbene ligands; copper; ring expansion; silanes