Iron Pentapyridyl Complexes as Molecular Water Oxidation Catalysts: Strong Influence of a Chloride Ligand and pH in Altering the Mechanism.
The development of molecular water oxidation catalysts based on earth-abundant, non-noble metals is essential for artificial photosynthesis research. Iron, which is the most abundant transition metal in the earth's crust, is a prospective candidate for this purpose. Herein, we report two iron complexes based on the polypyridyl ligand Py5OH (Py5OH=pyridine-2,6-diylbis [di(pyridin-2-yl)methanol]) that can catalyse water oxidation to produce O2 in Ru(III) -induced (at pH 8, highest turnover number (TON)=26.5; turnover frequency (TOF)=2.2 s(-1) ), Ce(IV) -induced (at pH≈1.5 highest TON=16; TOF=0.75 s(-1) ) and photo-induced (at pH 8, highest TON=43.5; TOF=0.6 s(-1) ) reactions. A chloride ligand in one of the iron complexes is shown to affect the activity strongly, improve stability and, thereby, the performance at pH 8 but it inhibits oxygen evolution at pH≈1.5. The observations are consistent with a change in mechanism for catalytic water oxidation with the Fe(Py5OH) complexes between acidic (Ce(IV) ) and near-neutral pH (Ru(III) ).
Department of Chemistry-Ångström Laboratory, Uppsala University, P.O.Box 523, 75120, Uppsala, Sweden.
Biswanath
B
Das
Department of Chemistry-Ångström Laboratory, Uppsala University, P.O.Box 523, 75120, Uppsala, Sweden.
Andreas
A
Orthaber
Department of Chemistry-Ångström Laboratory, Uppsala University, P.O.Box 523, 75120, Uppsala, Sweden.
Sascha
S
Ott
Department of Chemistry-Ångström Laboratory, Uppsala University, P.O.Box 523, 75120, Uppsala, Sweden. anders.thapper@kemi.uu.se.
Anders
A
Thapper
D002384:Catalysis; D002712:Chlorides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D014867:Water / Q000737:chemistry*
D002712:Chlorides; D008024:Ligands; D009942:Organometallic Compounds; D014867:Water; D007501:Iron
homogeneous catalysis; iron; oxidation; reaction mechanisms; water splitting