Models of molecular photocatalysts for water oxidation: Strategies for conjugating the Ru(bda) fragment (bda = 2,2′-bipyridine-6,6′-dicarboxylate) to porphyrin photosensitizers

Model dyads, in which the Ru(bda) water oxidation catalyst (WOC) is connected to a porphyrin, were prepared following two different modular strategies: i) the direct linkage approach, in which porphyrins bearing peripheral pyridyl rings are bound to the {Ru(bda)} fragment as axial ligands, and ii) the metal-containing ligand approach, in which symmetrical trans-[Ru(bda)(L)2] or unsymmetrical trans-[Ru(bda)(L)(pic)] compounds (L = bifunctional pyridyl linker), are axially bound to metalloporphyrins. Both synthetic strategies are modular and thus rather flexible in nature. As proofs of principle, the following Ru(bda) – porphyrin dyads are described: trans-[Ru(bda)(4′ -MPyP)2] (2, 4′ -MPyP = 5-(4′ -pyridyl)-10,15,20-phenylporphyrin), and the sandwich compounds [trans-Ru(bda)(4,4′ -bpy)2{Ru(CO)(TPP)}2] (5) and [trans-Ru(bda)(4,4′ -bpy)2(6Zn)]2 (7), where 6Zn is the porphyrin metallacycle [trans,cis,cis-RuCl2(CO)2(Zn⋅4′ -cisDPyP)]2 (4′ -cisDPyP = 5,10-(4′ -pyridyl)-15,20- (phenyl)-porphyrin.