Towards the photoreduction of CO{sub 2} with Ni(bpy){sub n}{sup 2+} complexes

When an acetonitrile solution containing Ni(bpy){sub 3}{sup 2+}, trithylamine and CO{sub 2} is irradiated at 313 nm, CO is produced with a quantum yield {approximately} 0.1% (defined as CO produced/photons absorbed). Flash photolysis, electrochemistry, and pulse radiolysis experiments provide evidence for the formation of Ni{sup I}(bpy){sub 2+}, as an intermediate, in the photochemical Ni(bpy){sub 3}{sup 2+}/TEA/CO{sub 2} system. Although Ni{sup 0}(bpy){sub 2} does react with CO{sub 2}, Ni{sup I}(bpy){sub 2+} seems unreactive toward CO{sub 2} addition. The x-ray structure of [Ni{sub 3}(bpy){sub 6}](ClO{sub 4}), which crystallize as blue-violet needles, reveals the existence of a dimer in the solid. UV-vis spectra also indicate that reduced Ni(bpy){sub 3}{sup 2+} solutions contain Ni{sup I}(bpy){sub 2+}, Ni{sup 0}(bpy){sub 2} and [Ni(bpy){sub 2}]{sub 2} complexes in equilibrium