Transferring photocatalytic CO₂ reduction mediated by Cu(N^N)(P^P)⁺ complexes from organic solvents into ionic liquid media

Abstract

Photocatalytic carbon dioxide reduction utilizing metal complexes based on the earth-abundant transition metals iron and copper was transferred from organic solvents into ionic liquids with high selectivity and moderate turn-over numbers.

Photoactive Copper Complexes: Properties and Applications

“…Therefore, ionic liquids have been tested as alternatives to conventional organic solvents because they offer some advantages such as low vapor pressure, high thermal stability, wide electrochemical stability window, tunable polarity, hydrophobicity, and solvent miscibility. In this context, the Beller group recently tested various ionic liquids (Figure ) in CO 2 photoreduction systems using two copper(I) photosensitizers ([Cu( NN 94 )( PP 12 )]PF 6 and [Cu( NN 94 )( PP 28 )]PF 6 ), which showed high selectivity for the photocatalytic CO 2 reduction to CO with comparable TON to previously reported systems using rhenium or ruthenium and cobalt. These results nicely illustrate the high versatility of copper(I) photosensitizers (entries 61–66 in Table ).…”

Homogeneous Systems Containing Earth‐Abundant Metal Complexes for Photoactivated CO2 Reduction: Recent Advances

“…The iron cyclopentadienone complex Fe2 was used in the investigation led by Beller and coworkers, combined with the in situ generated Cu(I) complex Cu1 [29] . In the first work, the catalytic components were dissolved in a mixture of N ‐methyl‐2‐pyrrolidone (NMP) and TEOA, [29a] while in the following paper, the photoactivated CO 2 ‐reduction was evaluated in different classes of ionic liquids (ILs) [29b] . In both cases, the sacrificial electron donor BIH was used, proving that the photosensitizer Cu1* excited state was reductively quenched.…”

“…In the case of the organic solvent mixtures, under white light irradiation for 5 hours, the turnover number of CO was 487, and the quantum efficiency of the reaction was 13.3 %, measured after 2 hours (Table 2, entry 10). The selectivity of CO versus molecular hydrogen was decreased to 93 %, when using Cu12 as photosensitizer (Table 2, entry12) [29b] . The use of ionic liquids as a solvent for the photoactivated CO 2 reduction has some advantages since they are not volatile (and therefore, more sustainable in respect to common organic solvents), and they can facilitate CO 2 capture.…”

Heteroleptic copper(i) complexes [Cu(dmp)(N^P)]BF4 for photoinduced atom-transfer radical addition reactions

“…[36][37][38][39] The pioneering work of Sauvage and coworkers published in 1987 demonstrated that bis-chelate homoleptic copper(I) complex [Cu(dap) 2 ]Cl {dap = bis[2,9-bis (4-anisyl)-1,10-phenanthroline]} could be used as a photoredox catalyst for the reductive dimerization of benzylic halides. 40 Subsequently, homoleptic and heteroleptic copper(I) complexes [Cu(N^N) 2 ] + , [Cu(N^N)(N^N)′] + and [Cu(N^N)(P^P)] + have been successfully applied to photocatalytic water splitting, [41][42][43] light-driven reduction of CO 2 , [44][45][46][47] and various other photocatalytic transformations [48][49][50] under visible light. The choice of chelating diimine and diphosphine ligands is crucial because these reactions depend on the visible-light absorption, excited-state lifetime, redox potential, and photo-stability of the resulting copper complexes.…”