Auxiliary Ligand‐Coordinated Nanoconfined Hydrophobic Microenvironments in Nickel(II)–Acetylide Framework for Enhanced CO 2 Photoreduction

Abstract Metal–acetylide frameworks (MAFs), featuring metal‐bis(acetylide) linkages (─C≡C─M─C≡C─), are emerging as a new class of 2D nanomaterials with promise in catalysis. Here, we report a new 2D Ni II –acetylide framework, TPA‐Ni(PR 3 ) 2 ‐GYs, that incorporates the Ni II (PR 3 ) 2 moiety [R = CH 3 (Me), CH 2 CH 3 (Et), and CH 2 CH 2 CH 2 CH 3 (Bu)] into tris(4‐ethynylphenyl)amine‐based graphdiyne framework (TPA‐GDY). As a result, TPA‐Ni(PBu 3 ) 2 ‐GY exhibits an exceptional photocatalytic CO 2 reduction activity of 3807 µmol g −1  h −1 and a high selectivity of 99.4% for CO production upon visible light irradiation. Mechanistic investigations reveal a strong orbital matching effect between the d orbitals of Ni II and the p orbitals of the alkynyl C atoms in organic ligands, which not only accelerates the transfer and separation of photogenerated charge carriers but also reduces the reaction potential barrier for the formation of *COOH intermediates. Furthermore, the high hydrophobicity of the auxiliary coordinated ligands (trialkylphosphines) to Ni center, particularly tributylphosphine, creates a nanoconfined space that enhances both the accessibility of CO 2 and the utilization of Ni II catalytic active sites while inhibiting hydrogen evolution. This study highlights the benefit of modulating the microenvironment around the coordinated metal center to enhance the performance of catalysts with direct metal–acetylide bonding.