Synthesis and properties of new mononuclear Ru(ii)-based photocatalysts containing 4, 4′-diphenyl-2, 2′-bipyridyl ligands. Issue 12 (18th February 2016)

• Record Type: Journal Article
• Authors: Coe, Benjamin J.; Sánchez, Sergio
• Is Part Of: Dalton transactions. Volume 45:Issue 12(2016)
• Page Start: 5210
• Page End: 5222
• Publication Date: 2016-02-18
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c6dt00039h
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Almost colourless trans -Ru II Cl2 (N^N)(CO)2 (N^N = a derivative of 4, 4′-diphenyl-2, 2′-bipyridyl) complexes are reasonably effective photocatalytic oxidants in combination with a photosensitizer and sacrificial oxidant. Abstract : The synthesis and characterisation of a series of eleven new 4, 4′-diphenyl-2, 2′-bipyridyl derivatives (N^N) with varying 4- or 3, 5-substituents on the phenyl rings are reported. The molecular structures of two of these compounds, 4, 4′-bis(3, 5-diheptyloxyphenyl)-2, 2′-bipyridyl and 4, 4′-bis(3, 5-di-4, 4, 5, 5, 5-pentafluoropentyloxyphenyl)-2, 2′-bipyridyl are confirmed by X-ray crystallography. Fourteen neutral complexes trans -Ru II Cl2 (N^N)(CO)2 are prepared by reacting the new proligands and three known ones with the polymeric precursor [Ru II Cl2 (CO)2 ] n, and their optical and electrochemical properties are studied. Density functional theory (DFT) and time-dependent DFT calculations have been carried out on selected complexes in order to rationalise their electronic structures and absorption properties. The low energy electronic absorption bands have metal-to-ligand charge-transfer and ligand-to-ligand charge-transfer (LLCT) character, but these dominate only in the 4-substituted species. In the 3, 5-disubstituted ones, intraligand charge-transfer (ILCT) within the bpy ligands becomes more important. The complexes show only irreversible reductive electrochemistry and no signs of polymerisation. The photocatalytic oxidation behaviour of selected trans -Ru II Cl2 (N^N)(CO)2 complexes and their mono-aquo derivatives [Ru II (H2 O)(CO)2 Cl(N^N)] + with 4-methoxybenzyl alcohol is studied. Turnover numbers of up to ca. 130 are achieved when using [Ru II (bpy)3 ] 2+ (bpy = 2, 2′-bipyridyl) as photosensitizer and [Co III (NH3 )5 Cl] 2+ as a sacrificial oxidant.