IPr* and Its Analog for Arene-Induced Precatalyst Activation and Stabilization in Ni-Catalyzed Kumada–Tamao–Corriu Coupling of Unactivated Aryl Halides

Bulky NHCs, such as IPr, SIPr, IPent, and IPr*, were employed for a new series of heteroleptic Ni(II) halide complexes. The highly accumulated aromatic substituents of IPr* and its analog were found to be more effective for the nickel-catalyzed Kumada–Tamao–Corriu (KTC) coupling of unactivated aryl chlorides than for the other NHCs. Theoretical studies demonstrated that weak arene coordination of IPr* to the Ni(0) center can facilely induce precatalyst activation and stabilization of the IPr*–Ni complex. A new NHC ligand, IPr*Ani, was designed and synthesized by introducing p-methoxy groups to the eight phenyl substituents of IPr*. DFT calculations also suggested that the aryl group of IPr*Ani coordinates more strongly to the Ni(0) species than that of IPr*, and IPr*Ani shows high performance compared to IPr* in the KTC coupling.