C-C bond coupling with sp C-H bond via active intermediates from CO hydrogenation.

Compared to the sluggish kinetics observed in methanol-mediated side-chain alkylation of methyl groups with sp C-H bonds, CO hydrogenation emerges as a sustainable alternative strategy, yet it remains a challenge. Here, as far as we know, it is first reported that using CO hydrogenation replacing methanol can conduct the side-chain alkylation of 4-methylpyridine (MEPY) over a binary metal oxide-zeolite ZnZrO/CsX tandem catalyst (ZZO/CsX). This ZZO/CsX catalyst can achieve 19.6% MEPY single-pass conversion and 82% 4-ethylpyridine (ETPY) selectivity by using CO hydrogenation, which is 6.5 times more active than methanol as an alkylation agent. The excellent catalytic performance is realized on the basis of the dual functions of the tandem catalyst: hydrogenation of CO on the ZZO and activation of sp C-H bond and C-C bond coupling on the CsX zeolite. The thermodynamic and kinetic coupling between the tandem reactions enables the highly efficient CO hydrogenation and C-C bond coupling. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations suggest that the CHO* (CHO*) species, rather than methanol produced from CO hydrogenation, is the key intermediate to achieve the C-C bond coupling.