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Attachment of a Hydrogen‐Bonding Carboxylate Side Chain to an [FeFe]‐Hydrogenase Model Complex: Influence on the Catalytic Mechanism
Author(s) -
Gao Weiming,
Sun Junliang,
Åkermark Torbjörn,
Li Mingrun,
Eriksson Lars,
Sun Licheng,
Åkermark Björn
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200902278
Subject(s) - protonation , triflic acid , chemistry , hydrogenase , hydrogen bond , catalysis , carboxylate , ascorbic acid , photochemistry , aqueous solution , inorganic chemistry , medicinal chemistry , stereochemistry , organic chemistry , molecule , ion , food science
Azapropanedithiolate (adt)‐bridged model complexes of [FeFe]‐hydrogenase bearing a carboxylic acid functionality have been designed with the aim of decreasing the potential for reduction of protons to hydrogen. Protonation of the bisphosphine complexes 4 – 6 has been studied by in situ IR and NMR spectroscopy, which revealed that protonation with triflic acid most likely takes place first at the N‐bridge for complex 4 but at the FeFe bond for complexes 5 and 6 . Using an excess of acid, the diprotonated species could also be observed, but none of the protonated species was sufficiently stable to be isolated in a pure state. Electrochemical studies have provided an insight into the catalytic mechanisms under strongly acidic conditions, and have also shown that complexes 3 and 6 are electro‐active in aqueous solution even in the absence of acid, presumably due to hydrogen bonding. Hydrogen evolution, driven by visible light, has been observed for three‐component systems consisting of [Ru(bpy) 3 ] 2+ , complex 1 , 2 , or 3 , and ascorbic acid in CH 3 CN/D 2 O solution by on‐line mass spectrometry.