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

Intramolecular 1,2-Dipp migration of seven mesoionic carbenes (iMIC(Ar)) 2 a-g (iMIC(Ar)=ArC{N(Dipp)}(2)CHC; Ar=aryl; Dipp=2,6-iPr(2)C(6)H(3)) 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-C-Dipp bond and the subsequent formation of a C-C-Dipp 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 sigma-donor strength of 5 compared to that of classical NHCs. Remarkably, the percentage buried volume of 5 (%V-bur=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.