Density Functional Study of Nickel N-Heterocyclic Carbene Catalyzed C–O Bond Hydrogenolysis of Methyl Phenyl Ether: The Concerted β-H Transfer Mechanism
The catalytic C–O bond activation of aryl ethers attracts substantial interest as it is significant for the lignin degradation process. A nickel complex with N-heterocyclic carbene (Ni-SIPr) has been shown to selectively catalyze C–O bond hydrogenolysis of aryl methyl ether to obtain arene and alcohol as the only products. Here, the reaction mechanism of Ni-SIPr catalyzed C–O bond hydrogenolysis of methyl phenyl ether (PhOMe) was studied using density functional theory. In the presence of H2, the catalytic cycle involves the following: (i) aromatic C–O bond oxidative addition of Ni(SIPr)(η2-PhOMe) to form Ni(SIPr)(OMe)(Ph), (ii) β-H transfer from the methoxy to phenyl group in Ni(SIPr)(OMe)(Ph) via σ-complex-assisted metathesis (σ-CAM), which eliminates benzene and forms Ni(SIPr)(η2-CH2O), (iii) H2 binding to form Ni(SIPr)(H2)(η2-CH2O) prior to H-transfer from H2 to the formaldehyde carbon via σ-CAM to generate Ni(SIPr)(H)(OMe), and (iv) reductive elimination to form methanol and the binding of methyl phe...