Why Is Cobalt the Best Transition Metal in Transition-Metal Hangman Corroles for O-O Bond Formation during Water Oxidation?
O-O bond formation catalyzed by a variety of β-octafluoro hangman corrole metal complexes was investigated using density functional theory methods. Five transition metal elements, Co, Fe, Mn, Ru, and Ir, that are known to lead to water oxidation were examined. Our calculations clearly show that the formal Co(V) catalyst has a Co(IV)-corrole(•+) character and is the most efficient water oxidant among all eight transition-metal complexes. The O-O bond formation barriers were found to change in the following order: Co(V) ≪ Fe(V) < Mn(V) < Ir(V) < Co(IV) < Ru(V) < Ir(IV) < Mn(IV). The efficiency of water oxidation is discussed by analysis of the O-O bond formation step. Thus, the global trend is determined by the ability of the ligand d-block to accept two electrons from the nascent OH(-), as well as by the OH(•) affinity of the TM(IV)═O species of the corresponding TM(V)═O·H2O complex. Exchange-enhanced reactivity (EER) is responsible for the high catalytic activity of the Co(V) species in its S = 1 state.
†Department of Chemistry, Renmin University of China, Beijing 100872, China.
Wenzhen
W
Lai
†Department of Chemistry, Renmin University of China, Beijing 100872, China.
Rui
R
Cao
†Department of Chemistry, Renmin University of China, Beijing 100872, China.
Geng
G
Dong
§Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, Givat Ram Campus, 91904 Jerusalem, Israel.
Sason
S
Shaik
‡Beijing National Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
Jiannian
J
Yao
‡Beijing National Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
Hui
H
Chen
O−O bond formation; density functional theory; hangman corrole; nucleophilic attack; transition metal; water oxidation