Nickel‐Catalyzed Intramolecular 1,2‐Aryl Migration of Mesoionic Carbenes (iMICs)

Intramolecular 1,2‐Dipp migration of seven mesoionic carbenes (iMICAr) 2 a–g (iMICAr=ArC{N(Dipp)}2CHC; Ar=aryl; Dipp=2,6‐iPr2C6H3) under nickel catalysis to give 1,3‐imidazoles (IMDAr) 3 a–g (IMDAr=ArC{N(Dipp)CHC(Dipp)N}) has been reported. The formation of 3 indicates the cleavage of an N−CDipp bond and the subsequent formation of a C−CDipp bond in 2, which is unprecedented in NHC chemistry. The use of 3 in accessing super‐iMICs (5) (S‐iMIC=ArC{N(Dipp)N(Me)C(Dipp)}C) has been shown with selenium (6), gold (7), and palladium (8) compounds. The quantification of the stereoelectronic properties reveals the superior σ‐donor strength of 5 compared to that of classical NHCs. Remarkably, the percentage buried volume of 5 (%Vbur=45) is the largest known amongst thus far reported iMICs. Catalytic studies show a remarkable activity of 5, which is consistent with their auspicious stereoelectronic features. Super‐iMICs (5) with the largest buried volume (Vbur=45 %) known thus far for iMICs are accessible via unprecedented Ni‐catalyzed intramolecular 1,2‐aryl migration of C5‐protonated iMICs (2) to 3, subsequent N‐alkylation of 3 to 4, and the deprotonation of 4. S‐iMICs (5) are stronger σ‐donors and superior π‐acceptors than 2. A comparative catalytic study reveals superior activity of S‐iMICs (5) over iMICs (2) and NHC (IPr).