Département de chimie moléculaire

Optical excitation in the visible region of trans-(Cl)-[Os(bpy)(CO)2Cl2] (bpy=2,2'-bipyridine; C1) and trans-(Cl)-[Os(dmbpy)(CO)2Cl2] (dmbpy=4,4'-dimethyl 2,2'-bipyridine; C2) is known to induce the common CO dissocn. reaction. However, the quantum yield of the reactions is less than 0.15, although C1 and C2 display pronounced photoluminescence in the visible region at room temp. with a lifetime of few tens of nanoseconds. Taking into account the characteristics of their emitting state, we have investigated the capability of C1 and C2 to act as a photosensitizer in redox reactions in different solvents (MeCN, PrCN and DMF). The efficient oxidn. and redn. of both complexes under continuous irradn. in the presence of a sacrificial electron acceptor or donor is reported here. The photo-induced transformations and the nature of the resulting compds. were analyzed by UV/Vis and IR spectroscopies and cyclic voltammetry. Photo-induced oxidn. of C1 and C2 leads to the corresponding monocarbonyl oxidized species, whereas photo-induced redn. under argon leads mainly to the formation of the corresponding Os-bonded mol. wires P1 and P2 after exchange of two electrons assocd. with the loss of two chloro ligands. The chem. yield of the latter reaction (around 65 {%}) becomes quant. by adding [Ru(bpy)3]2+ as an external redox photosensitizer. This behavior has been used to photocatalyze the two electron, two proton conversion of CO2 to CO. Turnover nos. (TON) of 11.5 and 19.5 have been obtained resp. for C1 and C2 after 4.5 h of irradn. under CO2 in DMF with triethanolamine as the electron donor. TON can be slightly increased by adding [Ru(bpy)3]2+ to the soln. [on SciFinder(R)]