Catalytic Photooxidation of Alcohols by an Unsymmetrical Tetra(pyridyl)pyrazine‐Bridged Dinuclear Ru Complex

Abstract

The dinuclear complexes [(tpy)Ru(tppz)Ru(bpy)(L)](n+) (where L is Cl(-) or H(2)O, tpy and bpy are the terminal ligands 2,2':6',2''-terpyridine and 2,2'-bipyridine, and tppz is the bridging backbone 2,3,5,6-tetrakis(2-pyridyl)pyrazine) were prepared and structurally and electronically characterized. The mononuclear complexes [(tpy)Ru(tppz)](2+) and [(tppz)Ru(bpy)(L)](m+) were also prepared and studied for comparison. The proton-coupled, multi-electron photooxidation reactivity of the aquo dinuclear species was shown through the photocatalytic dehydrogenation of a series of primary and secondary alcohols. Under simulated solar irradiation and in the presence of a sacrificial electron acceptor, the photoactivated chromophore-catalyst complex (in aqueous solutions at room temperature and ambient pressure conditions) can perform the visible-light-driven conversion of aliphatic and benzylic alcohols into the corresponding carbonyl products (i.e., aldehydes or ketones) with 100% product selectivity and several tens of turnover cycles, as probed by NMR spectroscopy and gas chromatography. Moreover, for aliphatic substrates, the activity of the photocatalyst was found to be highly selective toward secondary alcohols, with no significant product formed from primary alcohols. Comparison of the activity of this tppz-bridged complex with that of the analogue containing a back-to-back terpyridine bridge (tpy-tpy, i.e., 6',6''-bis(2-pyridyl)-2,2':4',4'':2'',2'''-quaterpyridine) demonstrated that the latter is a superior photocatalyst toward the oxidation of alcohols. The much stronger electronic coupling with significant delocalization across the strongly electron-accepting tppz bridge facilitates charge trapping between the chromophore and catalyst centers and therefore is presumably responsible for the decreased catalytic performance.

Targeting Human Telomeric G-Quadruplex DNA and Inhibition of Telomerase Activity With [(dmb)2Ru(obip)Ru(dmb)2]4+

“…The geometry about two Ru centers is a distorted octahedral, with angles in the 78.4–102.7 °and 169.7–173.6 ° ranges. The Ru-N pyridine distances vary in the 2.051–2.084 Å ranges, which are consistent with the typical values observed for related Ru II polypyridyl complexes [39,40]. However, the Ru–N imidazo distance (2.136 Å) is significantly larger than the Ru-N pyridine distances.…”

Towards A Solar Fuel Device: Light‐Driven Water Oxidation Catalyzed by a Supramolecular Assembly

“…Secondly, for comparison, [Ru(tpy) 2 ] 2+ (tpy = 2,2':6',2''-terpyridine) was used as a photosensitizer to couple to the catalyst (2, Figure 1) 2+ is an efficient metalto-ligand charge-transfer (MLCT) pump in an assembly including a photosensitizer catalyst and dyads for photocatalytic oxidation of alcohols involving a two-electron/twoproton coupled process. [18] The trinuclear ruthenium assembly 2, having a relatively rigid structure, was synthesized through a similar procedure as described for 1 with functionalization of pyridyl group at the 4'-position of the terpyridine ligand as a precursor.…”

“…Secondly, for comparison, [Ru(tpy) 2 ] 2+ (tpy = 2,2':6',2''-terpyridine) was used as a photosensitizer to couple to the catalyst (2, Figure 1) since a related report by Rocha et al has shown that [Ru(tpy) 2 ] 2+ is an efficient metalto-ligand charge-transfer (MLCT) pump in an assembly including a photosensitizer catalyst and dyads for photocatalytic oxidation of alcohols involving a two-electron/twoproton coupled process. [18] The trinuclear ruthenium assembly 2, having a relatively rigid structure, was synthesized through a similar procedure as described for 1 with functionalization of pyridyl group at the 4'-position of the terpyridine ligand as a precursor. Both assemblies were fully characterized by 1 H NMR spectroscopy, as well as ESI/MS and elemental analysis (see The electrochemistry of the two supramolecular assemblies was characterized in a phosphate buffer (pH 6.8) solution by cyclic voltammetry, which displays similar electrochemical behaviors.…”

H2 generation and sulfide to sulfoxide oxidation with H2O and sunlight with a model photoelectrosynthesis cell

“…(3), has been described in the literature using [Ru(bpy) 3 [17,18]. As before, dyad systems with catalytic and photosensitizer units in the same molecule have shown good turnover numbers (TN) for the oxidation of a large variety of substrates, such as alcohols, sulfides and alkenes [19][20][21][22][23][24][25][26].…”