Photocatalytic Hydrogen Evolution by [FeFe] Hydrogenase Mimics in Homogeneous Solution

Abstract

To mimic [FeFe] hydrogenases (H(2)ases) in nature, molecular photocatalysts 1 a, 1 b, and 1 c anchoring rhenium(I) complex S to one of the iron cores of [FeFe]-H(2)ases model complex C, have been constructed for H(2) generation by visible light in homogeneous solution. The time-dependence of H(2) evolution and a spectroscopic study demonstrate that the orientation of S and the specific bridge in 1 a, 1 b, and 1 c are important both for the electron-transfer step from the excited S* to the catalytic C, and the formation of unprecedented long-lived charge separation for 1 a (780 micros), 1 b, and 1 c (>2 ms) in [FeFe]-H(2)ases mimics. The fast forward electron-transfer step from the excited S* to the catalytic C but the slow back electron-transfer step of the charge-recombination in the designed photocatalysts 1 a, 1 b, and 1 c are reminiscent of the behavior of [FeFe]-H(2)ases in nature.

Chitosan confinement enhances hydrogen photogeneration from a mimic of the diiron subsite of [FeFe]-hydrogenase

“…As compared with those reported in the literature [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] , the durability and activity of the present system are greatly increased; possibly as a result of the stabilization of the components by chitosan confinement leading to consecutive multi-step electron transfer in equilibrium. The importance of the stabilization was also analysed by exchanging chitosan for relatively small and loose aggregates, anionic SDS (0.166 mol l À 1 ) and cationic CTAB (0.055 mol l À 1 , cetyl trimethyl ammonium bromide) micelles 37 .…”

“…From a photochemical point of view, the electron transfer is triggered by the absorption of a photon by a photosensitizer [13][14][15][16][17][18][19][20][21][22][23][24][25] . Since the first attempt by Sun and Åkermark 34 to construct an artificial photocatalytic system for H 2 evolution in 2003, a large number of synthetic model complexes have been pursued to mimic the structure and functionality of the diiron subunit of the natural [FeFe]-H 2 ase H-cluster [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] . It is encouraging to see that the catalytic efficiency for H 2 evolution from artificial photocatalytic systems using mimics of the diiron subsite of [FeFe]-H 2 ase as catalysts has been increased from null to more than hundreds or thousands of turnover numbers (TON) under different irradiation conditions.…”

Hydrogen Production by Noble‐Metal‐Free Molecular Catalysts and Related Nanomaterials

“…Three molecular photocatalysts with a Re I -photosensitizer directly linked to one of the Fe centers of an [Fe 2 S 2 ] unit by linear and rigid bridges in two different linkage orientations were reported by Wu and co-workers. [10] It was found that such ReÀFeFe molecular devices displayed relatively long-lived charge-separated states, formed by oxidative quenching, and they proved to be active for photoinduced H 2 evolution with CH 3 OH as sacrificial electron donor and HOAc as proton source in CH 3 CN/ H 2 O. Although some reports have described electrochemical H 2 production by Ni-or NiFe-based molecular catalysts, [16] photocatalytic H 2 production by Ni complexes has not been described in the literature so far.…”

“…[5,7,10] It is surprising that a catalyst system comprising an all-carbonyl multinuclear iron complex, [Fe 3 (CO) 12 ], [Ir(bpy)(ppy) 2 ]PF 6 (Hppy = 2-phenylpyridine), and triethylamine (TEA) displayed a high efficiency for visiblelight-driven H 2 production, with turnovers of up to 400 vs. [Fe 3 (CO) 12 ] in THF/H 2 O over 3 h of irradiation, [7] which is the best result ever reported for an Fe-based catalyst system in the photochemical production of H 2 from water reduction. Three molecular photocatalysts with a Re I -photosensitizer directly linked to one of the Fe centers of an [Fe 2 S 2 ] unit by linear and rigid bridges in two different linkage orientations were reported by Wu and co-workers.…”

“…[1] In most cases, the photosensitizers and/or proton reduction catalysts in the systems are complexes that contain noble metals, such as Ru, [2][3][4][5] Ir, [6][7][8] Re, [8][9][10] Pt, [11,12] Pd, [13] Rh, [14] and others. From a point of view towards future practical application, light-harvesting photosensitizers or catalysts (preferably both) should rely on earth-abundant elements rather than unsustainable noble metals.…”