Photocatalytic Carboxylation of Terminal Alkynes with CO2 over Metal–Porphyrin Framework Nanosheets

To develop an environmentally benign and efficient route for converting CO2 into value-added chemicals is of great importance. Here, we demonstrate the photocatalytic carboxylation of terminal alkynes with CO2 at room temperature and atmospheric pressure, by copper-based porphyrinic framework photocatalysts Cu2TCPP(M) (TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin; M = Fe, Co, Ni, Cu). The Cu2TCPP(Cu) nanosheets (with a small thickness of ∼5.1 nm) exhibit an extremely high performance for the reaction of 1-ethynylbenzene with CO2 to produce 3-phenylpropiolic acid. The turnover frequency is up to 3.33 mmol g–1 h–1 at 10 h, which is much higher than those of the photothermally and thermally driven routes that are usually adopted for the carboxylation reactions catalyzed by metal–organic frameworks. The mechanism for the superior activity of Cu2TCPP(Cu) nanosheets was investigated by a series of experiments and theoretical calculations. It is revealed that the Cu2TCPP(Cu) nanosheets not only possess good photoelectronic properties but have desired molecular structure for boosting CO2 activation, alkyne activation, and carboxylation reactions.