A Facile Route to Backbone-Tethered N-Heterocyclic Carbene (NHC) Ligands via NHC to aNHC Rearrangement in NHC Silicon Halide Adducts

摘要

The reaction of 1,3-diisopropylimidazolin-2-yl-idene (iPr(2)Im) with diphenyldichlorosilane (Ph2SiCl2) leads to the adduct (iPr(2)Im)SiCl2Ph2 1. Prolonged heating of isolated 1 at 668C in THF affords the backbone-tethered bis(imidazolium) salt [((a)HiPr(2)Im)(2)SiPh2](2+) 2Cl(-) 2 (("a") denotes "abnormal" coordination of the NHC), which can be synthesized in high yields in one step starting from two equivalents of iPr(2)Im and Ph2SiCl2. 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)iPr(2)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-iPr(2)Im)}(2)SiPh2] 4.