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

The reaction of 1,3‐diisopropylimidazolin‐2‐ylidene ( i Pr 2 Im) with diphenyldichlorosilane (Ph 2 SiCl 2 ) leads to the adduct ( i Pr 2 Im)SiCl 2 Ph 2 1 . Prolonged heating of isolated 1 at 66 °C in THF affords the backbone‐tethered bis(imidazolium) salt [( a H i Pr 2 Im) 2 SiPh 2 ] 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 i Pr 2 Im and Ph 2 SiCl 2 . 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 i Pr 2 Im) 2 SiPh 2 3 , in which two NHCs are backbone‐tethered with a SiPh 2 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 i Pr 2 Im)} 2 SiPh 2 ] 4 .