Bis(4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine)ruthenium(ii) complexes and their N-alkylated derivatives in catalytic light-driven water oxidation

Hongjin Lv,Petro F Zhuk,Catherine E Housecroft,Djamaladdin G Musaev,Yurii V Geletii,Jennifer A Rudd,Edwin C Constable,Ji Young Lee,Craig L Hill

doi:10.1039/c3ra44192j

Hongjin Lv, Petro F Zhuk + Show 7 more

Open Access

https://doi.org/10.1039/c3ra44192j

Copy DOI

Journal: RSC Advances	Publication Date: Jan 1, 2013
Citations: 17	License type: cc-by

Affiliation: Emory University, University of Basel

Abstract

Hydrogen sulfate salts of [Ru(1)2]2+ where 1 = 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine and four N-alkylated derivatives [Ru(L)2]4+ were used as photosensitizers (λmax ∼510 nm) for water oxidation in light driven reactions with peroxydisulfate as a sacrificial electron acceptor and Na10[Co4(H2O)2(α-PW9O34)2] (Co4POM) as the catalyst in sodium borate buffers at pH 8.0 and 9.0. The N-substituents investigated were benzyl (L+ = 2+), ethyl (L+ = 3+), allyl (L+ = 4+) and 4-cyanobenzyl (L+ = 5+). The O2 yield in the presence of [Ru(L)2]4+ (L+ = 2+–4+) was comparable to that obtained in the presence [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) using light sources with λmax ≈ 490 nm. The ruthenium(III) complexes [Ru(1)2]3+ and [Ru(L)2]5+ (L+ = 2+–5+) are rather unstable in acidic conditions and could not be isolated. The most efficient photosensitizers [Ru(L)2]5+ (L+ = 2+ and 4+) were the least stable under weakly basic conditions (pH 9.0) with a half-life τ1/2 ∼ 10 ms. The stability of the complexes under photocatalytic turnover conditions is probably controlled by the rate at which ligand L+ is oxidized by Co4POM in its highest oxidation state.

Highlights

The world's fossil energy resources are rapidly diminishing and the search for renewable and sustainable sources to replace these is becoming paramount
It has become clear that water splitting to dihydrogen and dioxygen by arti cial photosynthesis reactions would be an ideal way to convert solar energy into a renewable fuel.[1,2]. This reaction is thermodynamically unfavorable by 1.23 V and requires the input of four photons with l < 1000 nm.[3,4,5,6]
Stracke and Finke[22] showed that under electrocatalytic conditions and 0.5 mM Co4POM, a cobalt oxide lm forms on the electrode surface and is the dominant water oxidation catalyst (WOC) under these conditions. This group recently reported that at the Co4POM concentrations used in our original work,[7] soluble Co4POM could be a dominant catalyst,[23] as all our experiments and since have shown it to be.[24]

Summary

Introduction

The world's fossil energy resources are rapidly diminishing and the search for renewable and sustainable sources to replace these is becoming paramount. Hydrogen sulfate salts of [Ru(1)2]2+ where 1 1⁄4 40-(4-pyridyl)-2,20:60,200-terpyridine and four N-alkylated derivatives [Ru(L)2]4+ were used as photosensitizers (lmax $510 nm) for water oxidation in light driven reactions with peroxydisulfate as a sacrificial electron acceptor and Na10[Co4(H2O)2(a-PW9O34)2] (Co4POM) as the catalyst in sodium borate buffers at pH 8.0 and 9.0. The low stability and short life-time of [RuIII(L)2] excited states could be prohibitive for use of these complexes as photosensitizers in light driven water oxidation reaction, their higher oxidation potentials are advantageous.

Results

Conclusion