A new synthetic method for annulating hydroquinones to Fe2S 2(CO)6 moieties is reported. Piperidine catalyzed a multistep reaction between Fe2(μ-SH)2(CO)6 and quinones to afford bridged adducts in 26-76% yields. The hydroquinone adducts undergo reversible two-electron reductions. In the presence of acetic acid, hydrogen is produced catalytically with these adducts at potentials more negative than that of the initial reversible reduction. Spectroscopic studies suggest the presence of intramolecular hydrogen bonding between the phenolic OH groups and the adjacent sulfur atoms. Computations, which are in good agreement with the electrochemical studies and spectroscopic data, indicate that the hydrogen bonding is most important in the reduced forms of the catalysts. This hydrogen bonding lowers the reduction potential for catalysis but also lowers the basicity and thereby the reactivity of the catalysts.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry