Polyaromatic Fused Zn–Salen as a Photocatalyst for Carboxylation of Terminal Alkynes Using CO ₂ as a C1‐Source

Blue LED‐driven conversion of CO ₂ into value‐added products under mild conditions remains a primary challenge in sustainable synthetic methods. Herein, we report a B–N fused phenanthroimidazolyl Zn–salen complex catalysed protocol for carboxylation of terminal alkynes using CO ₂ at atmospheric pressure under blue LED irradiation. A wide range of aromatic and heteroaromatic alkynes were screened and efficiently converted to their corresponding propiolic acids with good to excellent yields using 1,8‐diazabicycloundec‐7‐ene (DBU) as a base and DMSO as a solvent. Subsequent alkylation of propiolic acids enables a wide array of structurally diverse propiolate esters, revealing its electrophile compatibility. Mechanistic studies indicate that continuous light irradiation is crucial for efficient conversion, and also reveal that DBU plays a dual role in C(sp)─H proton abstraction and CO ₂ activation. This work reflects the potential of Zn–salen complex as an efficient photocatalyst for mild, sustainable, and greener utilization of CO ₂ .