Photocatalytic Carboxylation of Terminal Alkynes with\nCO<sub>2</sub> over Metal–Porphyrin Framework Nanosheets

To\ndevelop an environmentally benign and efficient route for converting\nCO<sub>2</sub> into value-added chemicals is of great importance.\nHere, we demonstrate the photocatalytic carboxylation of terminal\nalkynes with CO<sub>2</sub> at room temperature and atmospheric pressure,\nby copper-based porphyrinic framework photocatalysts Cu<sub>2</sub>TCPP(<i>M</i>) (TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin; <i>M</i> = Fe, Co, Ni, Cu). The Cu<sub>2</sub>TCPP(Cu) nanosheets\n(with a small thickness of ∼5.1 nm) exhibit an extremely high\nperformance for the reaction of 1-ethynylbenzene with CO<sub>2</sub> to produce 3-phenylpropiolic acid. The turnover frequency is up\nto 3.33 mmol g<sup>–1</sup> h<sup>–1</sup> at 10 h,\nwhich is much higher than those of the photothermally and thermally\ndriven routes that are usually adopted for the carboxylation reactions\ncatalyzed by metal–organic frameworks. The mechanism for the\nsuperior activity of Cu<sub>2</sub>TCPP(Cu) nanosheets was investigated\nby a series of experiments and theoretical calculations. It is revealed\nthat the Cu<sub>2</sub>TCPP(Cu) nanosheets not only possess good photoelectronic\nproperties but have desired molecular structure for boosting CO<sub>2</sub> activation, alkyne activation, and carboxylation reactions.