Half-sandwich iridium complexes for homogeneous water-oxidation catalysis.
Iridium half-sandwich complexes of the types Cp*Ir(N-C)X, [Cp*Ir(N-N)X]X, and [CpIr(N-N)X]X are catalyst precursors for the homogeneous oxidation of water to dioxygen. Kinetic studies with cerium(IV) ammonium nitrate as primary oxidant show that oxygen evolution is rapid and continues over many hours. In addition, [Cp*Ir(H(2)O)(3)]SO(4) and [(Cp*Ir)(2)(μ-OH)(3)]OH can show even higher turnover frequencies (up to 20 min(-1) at pH 0.89). Aqueous electrochemical studies on the cationic complexes having chelate ligands show catalytic oxidation at pH > 7; conversely, at low pH, there are no oxidation waves up to 1.5 V vs NHE for the complexes. H(2)(18)O isotope incorporation studies demonstrate that water is the source of oxygen atoms during cerium(IV)-driven catalysis. DFT calculations and kinetic experiments, including kinetic-isotope-effect studies, suggest a mechanism for homogeneous iridium-catalyzed water oxidation and contribute to the determination of the rate-determining step. The kinetic experiments also help distinguish the active homogeneous catalyst from heterogeneous nanoparticulate iridium dioxide.
Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States.
James D
JD
Blakemore
Nathan D
ND
Schley
David
D
Balcells
Jonathan F
JF
Hull
Gerard W
GW
Olack
Christopher D
CD
Incarvito
Odile
O
Eisenstein
Gary W
GW
Brudvig
Robert H
RH
Crabtree
D002384:Catalysis; D018360:Crystallography, X-Ray; D007495:Iridium / Q000737:chemistry*; D008024:Ligands; D010084:Oxidation-Reduction; D014867:Water / Q000737:chemistry*
D008024:Ligands; D014867:Water; D007495:Iridium