Reaction of 3,6-bis(2-pyridyl)-diketopyrrolopyrrole (H2-BPDPP) with two equiv. of Ru(H)(CO)(Cl)(PPh3)3 in EtOH produced two sym. dinuclear isomers, (m-BPDPP)Ru(CO)H(PPh3)22, green 1 and blue 2, which could be sepd. chromatog. and characterized spectroscopically (1H and 31P NMR, IR, and UV-VIS). Isomeric forms of 1 and 2 were authenticated using their single crystal X-ray structures. In addn. to the essentially planar bis-chelating bridge BPDPP2- and the mutually trans positioned axial PPh3 ligands in both complexes, compd. 1 was established with the CO groups trans to the pyrrolate-N atoms, whereas 2 has the p acceptors CO and pyridine-N situated trans to each other. While the redn. of 1 and 2 proceeds irreversibly at neg. potentials, the reversible oxidns. at rather low potentials could be monitored by EPR and UV-VIS-NIR absorption measurements. Together with TD-DFT calcns., these results reveal that the primary electron transfers are largely confined to the BPDPP ligand. Despite the bridge centered processes, small differences between the isomers 10/+ and 20/+ were found, affecting e.g. the near IR absorption of the radical cation species. on SciFinder(R)
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