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

Abstract

Hydrogen sulfate salts of [Ru(1) 2 ] 2+ where 1 ¼ 4 0-(4-pyridyl)-2,2 0 :6 0 ,2 00-terpyridine and four N-alkylated derivatives [Ru(L) 2 ] 4+ were used as photosensitizers (l max $510 nm) for water oxidation in light driven reactions with peroxydisulfate as a sacrificial electron acceptor and Na 10 [Co 4 (H 2 O) 2 (a-PW 9 O 34) 2 ] (Co 4 POM) as the catalyst in sodium borate buffers at pH 8.0 and 9.0. The N-substituents investigated were benzyl (L + ¼ 2 +), ethyl (L + ¼ 3 +), allyl (L + ¼ 4 +) and 4-cyanobenzyl (L + ¼ 5 +). The O 2 yield in the presence of [Ru(L) 2 ] 4+ (L + ¼ 2 +-4 +) was comparable to that obtained in the presence [Ru(bpy) 3 ] 2+ (bpy ¼ 2,2 0bipyridine) using light sources with l max z 490 nm. The ruthenium(III) complexes [Ru(1) 2 ] 3+ and [Ru(L) 2 ] 5+ (L + ¼ 2 +-5 +) are rather unstable in acidic conditions and could not be isolated. The most efficient photosensitizers [Ru(L) 2 ] 5+ (L + ¼ 2 + and 4 +) were the least stable under weakly basic conditions (pH 9.0) with a half-life s 1/2 $ 10 ms. The stability of the complexes under photocatalytic turnover conditions is probably controlled by the rate at which ligand L + is oxidized by Co 4 POM in its highest oxidation state.

Photochemical and electrocatalytic water oxidation activity of cobalt carbodiimide

“…Buffer-dependent WOC performance was furthermore found to increase in the order carbonate z phosphate [ borate, despite the higher stability of [Ru(bpy) 3 ] 2+ in borate compared to phosphate media. 68,69 Recycling tests with CoNCN. Catalyst recycling experiments at pH 9 upon addition of fresh carbonate buffer solution and PS/ electron acceptor, respectively, resulted in a reactivation of WOC performance by ca.…”

Electrochemical and Photophysical Study of Homoleptic and Heteroleptic Methylated Ru(II) Bis‐terpyridine Complexes

“…Compounds similar to the methylated complexes 3 and 4 , i. e., N ‐alkylated 4’‐pyridyl substituted terpyridine ruthenium complexes, were previously studied as photosensitizers in photocatalytic water oxidation. These studies showed that the N‐alkylated bis‐terpyridine complexes can lead to a comparable oxygen evolution activity as the standard ruthenium tris‐bipyridine PS [5j] …”

Collecting meaningful early-time kinetic data in homogeneous catalytic water oxidation with a sacrificial oxidant

“…5.5, 34 0.02 and 0.05 s À1 in borate buffer at pH 8 and 9, respectively. 35,36 This is for a generic reaction (eqn (2)) where one or more of the bpy ligands are oxidized one or more times; some of the bpy ligand is fully oxidized to CO 2 , however, the products are largely [Ru(bpy) 3 ] 2+ with the yield up to 98% based on initial Ru 3+ . Sutin et al have identified at least eight separate products in previous work.…”