Catalytic Generation of Hydrogen with Titanium Citrate and a Macrocyclic Cobalt Complex

✍ Scribed by Ewa Szajna-Fuller; Andreja Bakac

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 377 KB
• Volume: 2010
• Category: Article
• ISSN: 1434-1948
• DOI: 10.1002/ejic.200901176

✦ Synopsis

Abstract

Hydrogen evolution from acidic aqueous solutions of Ti^III^citrate is strongly catalyzed by Co(dmgBF~2~)~2~. The reaction generates an intermediate with maximum absorbance at 770 nm. The slow disappearance of this intermediate takes place simultaneously with the generation of H~2~ in a process that was most efficient at pH 1.6 (turnover number 53). The loss of the catalytic activity is caused by the loss of the macrocyclic ligand and formation of Co~aq~^2+^. Control experiments implicate Co^III^ as the most likely oxidation state responsible for catalyst destruction, and thus provide indirect evidence for the involvement of Co^III^ in the catalytic cycle. Taken together, the data suggest that hydrogen generation takes place at least in part by the H^+^/HCo^III^(dmgBF~2~)~2~ route. Incitrate‐containing solutions at 7 ≤ pH ≤ 8, the protonation of Co^I^(dmgBF~2~)~2~^–^ to yield HCo^III^(dmgBF~2~)~2~ has a rate constant k~H~ = 1.4 × 10^6^ M^–1^ s^–1^. This reaction is about ten times slower in the absence of citrate.