Département de chimie moléculaire

An efficient homogeneous system for visible-light driven H prodn. in H2O is reported. This comprises the [Co(CR)Cl2]+ Co(iii) tetraaza-macrocyclic complex (Cat1) as a noble metal-free catalyst, [Ru(bpy)3]Cl2 as a photosensitizer and ascorbate/ascorbic acid as a sacrificial electron donor and buffer. This system gives up to 1000 turnovers at pH 4.0 vs. the catalyst with a relatively low photosensitizer/catalyst ratio (10/1) and a high concn. of catalyst (1 × 10-4 M), thus producing a significant amt. of H2 (12.3 mL for 5 mL of soln.). It also exhibits long-term stability - more than 20 h. The efficiency of Cat1 was compared under the same exptl. conditions to those of 3 other H2-evolving catalysts, which are known to operate in H2O, [Co{\{}(DO)(DOH)pn{\}}Br2] (Cat2), [Co(dmbpy)3]Cl2 (Cat3) and [Rh(dmbpy)2Cl2]Cl (Cat4). These comparative studies show that Cat4, although based on a noble metal, is ∼4 times less active, while Cat2 and Cat3 produce more than one hundred times less H than Cat1. The low-valent CoI form of Cat1 was successfully electrogenerated in MeCN. Its high stability can be related to the high catalytic performance of the Cat1 system. Also in acidic aq. soln. (photocatalytic conditions) redn. at a slightly more neg. potential than the CoII/CoI couple is needed to ensure efficient catalysis; this redn. is performed by the photogenerated [RuII(bpy)2(bpy·-)]+ species. [on SciFinder(R)]