Visible
Light-Driven Hydrogen Evolution from Water
Catalyzed by A Molecular Cobalt Complex
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Abstract
An approximately planar tetradentate
polypyridine ligand, 8-(1″,10″-phenanthrol-2″-yl)-2-(pyrid-2′-yl)quinoline
(ppq), has been prepared by two sequential Friedländer condensations.
The ligand readily accommodates Co(II) bearing two axial chlorides,
and the resulting complex is reasonably soluble in water. In DMF the
complex shows three well-behaved redox waves in the window of 0 to
−1.4 V (vs SHE). However in pH 7 buffer the third wave is obscured
by a catalytic current at −0.95 V, indicating hydrogen production
that appears to involve a proton-coupled electron-transfer event.
The complex [Co(ppq)Cl<sub>2</sub>] (<b>6</b>) in pH 4 aqueous
solution, together with [Ru(bpy)<sub>3</sub>]Cl<sub>2</sub> and ascorbic
acid as a sacrificial electron donor, in the presence of blue light
(λ<sub>max</sub> = 469 nm) produces hydrogen with an initial
TOF = 586 h<sup>–1</sup>