Efficient Photocatalytic CO₂ Reduction by a Ni(II) Complex Having Pyridine Pendants through Capturing a Mg²⁺ Ion as a Lewis-Acid Cocatalyst

Abstract

We have synthesized a new Ni­(II) complex having an S2N2-tetradentate ligand with two noncoordinating pyridine pendants as binding sites of Lewis-acidic metal ions in the vicinity of the Ni center, aiming at efficient CO production in photocatalytic CO2 reduction. In the presence of Mg2+ ions, enhancement of selective CO formation was observed in photocatalytic CO2 reduction by the Ni complex with the pyridine pendants through the formation of a Mg2+-bound species, as compared to the previously reported Ni complex without the Lewis-acid capturing sites. A higher quantum yield of CO evolution for the Mg2+-bound Ni complex was determined to be 11.1%. Even at lower CO2 concentration (5%), the Ni complex with the pendants exhibited comparable CO production to that at the CO2-saturated concentration (100%). The Mg2+-bound Ni complex was evidenced by mass spectrometry and 1H NMR measurements. The enhancement of CO2 reduction by the Mg2+-bound species should be derived from cooperativity between the Ni and Mg centers for the stabilization of a Ni–CO2 intermediate by a Lewis-acidic Mg2+ ion captured in the vicinity of the Ni center, as supported by DFT calculations. The detailed mechanism of photocatalytic CO2 reduction by the Ni complex with the pyridine pendants in the presence of Mg2+ ions is discussed based on spectroscopic detection of the intermediate and kinetic analysis.

Inside‐and‐Out Semiconductor Engineering for CO2 Photoreduction: From Recent Advances to New Trends

“…Homogeneous and heterogeneous catalysis are two main branches of the catalysis family, both of which are applied in photocatalytic CO 2 conversion to produce hydrocarbons. Several advantages of homogeneous photocatalysts are depending on their atomically dispersed active sites, [ 428–430 ] tunable light absorption, [ 431–433 ] as well as high activity and selectivity. [ 434–439 ] Heterogeneous photocatalysts with relatively low cost are easy to synthesize and facile to be extracted and recycled for long‐term run.…”

Visible‐Light‐Driven CO2 Reduction Catalyzed by a Dinuclear Nickel Complex

“…[ 8 ] More recent instances of nickel molecular catalysts for light‐driven CO 2 reduction include several nickel N‐heterocyclic carbene (NHC) complexes, [ 9 ] nickel‐polypyridine complexes [ 10 ] and nickel‐N2S2 complexes. [ 11 ] Albeit with the above progress, rare dinuclear nickel complex has been utilized in photocatalytic CO 2 reduction, while the development of dinuclear metal catalysts is valuable as they are capable to bind and activate CO 2 with a synergistic fashion between two metals, [ 12 ] which are relatively unapproachable for the mononuclear counterparts. To this end, we have synthesized a dinuclear nickel complex, [Ni 2 (bpbp)(CH 3 OH) 2 Cl 2 ]Cl · 2H 2 O {Hbpbp = 2,6‐bis((bis(pyridin‐2‐ylmethyl)amino)‐methyl)‐4‐( tert ‐butyl)phenol; denoted as Ni 2 ‐BPBP}, as the molecular catalyst for visible‐light‐driven CO 2 reduction to CO with a high selectivity of 99 %.…”

An NADH-Inspired Redox Mediator Strategy to Promote Second-Sphere Electron and Proton Transfer for Cooperative Electrochemical CO2 Reduction Catalyzed by Iron Porphyrin

“…[16][17][18][19][20][21][22][23][24] Beyond this platform and other privileged primary coordination sphere motifs, approaches to enhance CO 2 reduction catalysis with secondary coordination sphere pendants have largely focused on improving the delivery of protons using intramolecular proton relays and/or stabilization of metal-bound CO 2 intermediates via hydrogen bonding. [17][18][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Additionally, reduced CO 2 intermediates can be captured by inter/intra-molecular Lewis acid cations [40][41][42] or intramolecular charge-compensation moieties, such as ammonium 21,43 or imidazolium groups. [44][45][46] In addition to proton control, strategies for facilitating electron delivery from the secondary coordination sphere for CO 2 reduction have also been explored.…”