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Experimental and Theoretical Study of Photochemical Hydrogen Evolution Catalyzed by Paddlewheel‐Type Dirhodium Complexes with Electron Withdrawing Carboxylate Ligands
Author(s) -
Kataoka Yusuke,
Yano Natsumi,
Kohara Yoshihiro,
Tsuji Takeshi,
Inoue Satoshi,
Kawamoto Tatsuya
Publication year - 2019
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201901534
Subject(s) - chemistry , rhodium , carboxylate , catalysis , hydrogen , medicinal chemistry , stereochemistry , density functional theory , electron donor , photochemistry , computational chemistry , organic chemistry
The photochemical hydrogen evolution capabilities of paddlewheel‐type dirhodium complexes with electron withdrawing carboxylates, [Rh 2 (O 2 CR) 4 (H 2 O) 2 ] (R=CF 3 and CCl 3 for [2(H 2 O) 2 ] and [3(H 2 O) 2 ], respectively), were investigated and compared with that of [Rh 2 (O 2 CCH 3 ) 4 (H 2 O) 2 ], ([1(H 2 O) 2 ]), which is the most effective hydrogen evolution catalyst (HEC) among rhodium complexes developed to date. Artificial photosynthesis (AP) systems with [2(H 2 O) 2 ] or [3(H 2 O) 2 ], [Ir(ppy) 2 (bpy)](PF 6 ), and TEA showed highly efficient hydrogen evolution activities; the turnover numbers (TON) of hydrogen evolution per Rh by the AP systems with [2(H 2 O) 2 ] and [3(H 2 O) 2 ] after 12 h of photo‐irradiation were 3334 and 3138, respectively. Experimental analyses and density functional theory (DFT) calculations afforded valuable insight into the hydrogen evolution mechanism of paddlewheel‐type dirhodium complexes; (i) hydrogen evolution activities of the AP systems with [2(H 2 O) 2 ] and [3(H 2 O) 2 ] were slightly lower than that of the AP system with [1(H 2 O) 2 ] despite one‐electron reduction potentials of [2(H 2 O) 2 ] and [3(H 2 O) 2 ] lie on the anode side than that of [1(H 2 O) 2 ], and (ii) two different pathways exist during the early stages in the photochemical hydrogen evolution by [2(H 2 O) 2 ] and [3(H 2 O) 2 ]. Moreover, the relative free‐energy diagrams estimated by DFT calculations clarified the energy profiles of the mechanism including the rate‐determining steps of the hydrogen evolution by [1(H 2 O) 2 ]−[3(H 2 O) 2 ].