Ligand-Bound CO 2 as a Nonclassical Route toward Efficient Photocatalytic CO 2 Reduction with a Ni N-Confused Porphyrin

Implementing the synergistic effects between the metal and the ligand has successfully streamlined the energetics for CO activation and gained high catalytic activities, establishing the important breakthroughs in photocatalytic CO reduction. Herein, we describe a Ni(II) N-confused porphyrin complex ( ) featuring an acidic N-H group. It is readily deprotonated and exists in an anion form during catalysis. Owing to this functional site, gave rise to an outstanding turnover number (TON) as high as 217,000 with a 98% selectivity for CO reduction to CO, while the parent Ni(II) porphyrin ( ) was found to be nearly inactive. Our mechanistic analysis revealed a nonclassical reaction pattern where CO was effectively activated via the attack of the Lewis-basic ligand. The resulting ligand-bound CO adduct could be further reduced to produce CO. This new metal-ligand synergistic effect is anticipated to inspire the design of highly active catalysts for small molecule activations.