Interfacial N-Site Electronic Structure for Efficient β–C(sp3)–H Activation in Lignin Model Compounds

Abstract

Engineering the local bonding environment and microscopic electronic structure of interfacial sites in metal-free carbon catalysts provides a powerful strategy for constructing active centers with tailored electronic states for selective bond activation. Herein, an N-doped carbon catalyst with tailored sp2-N configurations (NUC-c-950) is developed, in which coupled pyridinic N (Py-N) and graphitic N (Gr-N) sites create a bifunctional interfacial center for β–O–4 bond cleavage in lignin model compounds. Through the complementary electronic functions of the localized lone pair in the sp2 orbital of Py-N and the delocalized pz electron associated with Gr-N, β–C(sp3)–H deprotonation and O2 activation are coupled to generate an enolate intermediate and reactive oxygen species, respectively. The resulting N–C interfacial electronic configuration enables efficient oxidative cleavage of the lignin model compound 2-phenoxy-1-phenylethanone (PP-one) in methanol (MeOH), affording phenol and methyl benzoate (MB) in yields of 96.83 and 53.23%, respectively. More broadly, the coupled Py-N/Gr-N motif provides an effective metal-free platform for selectively cleaving lignin model compounds beyond β–O–4 ketones, including β–O–4 alcohols and β–1 model compounds, and offers a strategy for tailoring N-site electronic structures in metal-free carbon catalysts for selective lignin valorization.