Dedicated to Professor Mingyuan He on the occasion of his 80th birthday Carbon dioxide is a green and sustainable one-carbon source, which could be utilized in the production of various fine chemicals. In recent studies, the light-mediated carboxylation employing CO 2 has received considerable attention. The photocarboxylation of substrates with CO 2 to build novel CÀ C bonds is introduced in this Minireview. The article is arranged based on the light-driven reactive intermediates, including CO 2 radical anion, substrate radical anions, carbanions, and MÀ C species. Most of the cases are under the topic of photoredox catalysis, with single electron transfer as the main driving force. Some non-catalytic examples are also discussed to provide more mechanistic insights.

Carboxylation of allylic alcohols with carbon dioxide is accomplished by photoredox/nickel dual catalysis, generating linear acids exclusively with good Z/E stereoselectivity. Hantzsch ester is employed as the reductant instead of stoichiometric metallic reductants, and the reaction can be conducted under room temperature with a blue LED light source. Mechanistic studies reveal that the presence of water in this catalytic system is critical to the success of the reaction, and the reaction is more likely to proceed in oxidative addition of the in situ formed allylic hydrogen carbonate.

Intermolecular carbon–carbon bond formation between acylsilanes and carbon dioxide (CO2) was achieved by photoirradiation under catalyst-free conditions. In this reaction, siloxycarbenes generated by photoisomerization of the acylsilanes added to the CO bond of CO2 to give α-ketocarboxylates, which underwent hydrolysis to afford α-ketocarboxylic derivatives in good yields. Control experiments suggest that the generated siloxycarbene is likely to be from the singlet state (S1) of the acylsilane and the addition to CO2 is not in a concerted manner.

Treating a scandium mixed alkyl/diaryloxide complex with phosphino-substituted alcohols resulted in the formation of scandium mixed alkoxyl/diaryloxide complexes Sc[OC(CH)CHPR][O-2,6- tBu-CH][THF] (6, R = Ph; 8, R = tBu). The reactivity of Sc-based Lewis pair complexes 6 and 8 toward a wide range of substrates was investigated. A ligand substitution reaction occurred when complex 6 was treated with benzophenone. The reaction of complex 6 with sulfur afforded a phosphane oxidative product. Complexes 6 and 8 also exhibited typical Sc/P frustrated Lewis pair (FLP) reactivity. They added to the carbonyl group of phenyl isocyanate to form seven-membered metallacycles. Complex 6 underwent selective Sc/P 1,4-addition reactions with α,β-unsaturated carbonyl compounds to give the corresponding nine-membered metallacyclic products. The reaction of 6 with 0.5 mol of dimethyl acetylenedicarboxylate led to the formation of bicyclo[7.7.0]cetane-derived metallacycle 16 in a distinctive double 1,4-addition pattern. With benzil complex 6 underwent a 1,4-addition reaction to afford a cis-enediolate which was coordinated to the Sc/P FLP through Sc-O and P-O bonds. Treatment of complex 6 with cyclopropyl phenyl ketone afforded the 10-membered metallaheterocycle 18, in which a scandium Lewis acid added to the oxygen atom and the phosphine Lewis base attacked the cyclopropyl group with ring opening. A ring-opening reaction also took place when epoxycyclohexane was employed as a substrate. Complex 6 successfully cleaved the C-Br bond of benzyl bromide to give zwitterionic complex 20 with newly formed Sc-Br and P-C bonds. Scandium phosphazine complex 21 was generated by a Sc/P 1,1-addition to the terminal nitrogen atom of (trimethylsilyl)diazomethane. Aided by the phosphorus Lewis base, scandium Lewis acid was able to abstract chloride from (PhP)AuCl to produce heterobimetallic Sc/Au complexes 22 and 23. Many complexes in this study were characterized by single-crystal X-ray diffraction.

A photoredox-catalyzed intermolecular dearomative trifluoromethycarboxylation of indoles as well as heteroanalogues with CO2 and fluorinated radical precursors has been achieved. A range of substrares can realize in sequential conversion to...