Mechanism of the formation of dihydrogen from the photoinduced reactions of poly(pyridine)ruthenium(II) and poly(pyridine)rhodium(III) complexes

Journal Article · Wed Jan 28 04:00:00 EST 1981 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00392a022· OSTI ID:6662450

Chan, S F; Chou, M; Creutz, C; Matsubara, T; Sutin, N

The irradiation of Ru(bpy)/sub 3//sup 2 +/, and triethanolamine (TEOA) solutions 10/sup 9/ 8, 25/sup 0/C) with 450 +- 20-nm light yields rhodium(I) phi = 0.13 +- 0.02) ( units for phi in mol einstein/sup -1/ throughout the paper) and dihydrogen (phi = 0.11 +- 0.02) in the absence and presence of platinum, respectively. A detailed mechanistic scheme has been deduced from the results of continuous- and flash-photolysis experiments: light absorption by Ru(bby)/sub 3//sup 2 +/ gives the excited state *Ru(bpy)/sub 3//sup 2 +/ which is oxidized by Rh(bpy)/sub 3//sup 3 +/ (k = 3.9 x 10/sup 8/M/sup -1/s/sup -1/) yielding Ru(bpy)/sub 3//sup 3 +/ and Rh(bpy)/sub 3//sup 2 +/ with a cage escape yield of 0.15 +- 0.03. Back-reaction of Ru(bpy)/sub 3//sup 3 +/ with Rh(bpy)/sub 3//sup 2 +/ (k = 3 x 10/sup 9/M/sup -1/s/sup -1/) is prevented by reduction of Ru(bpy)/sub 3//sup 3 +/ by TEOA (k = 0.2 x 10/sup 8/M/sup -1/s/sup -1/). The oxidized TEOA radical so generated undergoes a TEOA-promoted rearrangement (k = 0.3 x 10/sup 7/M/sup -1/s/sup -1/) to a reducing radical. The latter reduces Rh(bpy)/sub 3//sup 2 +/ so that the net yield for Rh(bpy)/sub 3//sup 2 +/ formation is 0.3 +- 0.1. Rate-determining loss of bpy from Rh(bpy)/sub 3//sup 2 +/ (k = 1.0 +- 0.5 s/sup -1/) is followed by rapid reduction of Rh(bpy)/sub 2//sup 2 +/ by Rh(bpy)/sub 3//sup 2 +/ (k = 0.3 x 10/sup 9/M/sup -1/s/sup -1/) giving Rh(bpy)/sub 3//sup 3 +/ and Rh(I). In the presence of platinum, H/sub 2/ is formed at the expense of Rh(I); catalyzed reaction of Rh(II) with water occurs before disproportionation to Rh(I) can take place. The H/sub 2/ quantum yield in this system is limited only by the cage escape of the primary products, the homogeneous and heterogeneous dark reactions being very efficient. In the course of this study the electrochemistry of Rh(bpy)/sub 3//sup 3 +/, Rh(phen)/sub 3//sup 3 +/, and Rh(bpy)/sub 2/(OH)/sub 2//sup +/ in aqueous solution was investigated, and the quenching of Ru(bpy)/sub 3//sup 2 +/ emission by these Rh(III) complexes was characterized.

• Research Organization: Brookhaven National Lab., Upton, NY
• OSTI ID: 6662450
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 103:2; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
080106* -- Hydrogen-- Production-- Biosynthesis & Photochemical Processes
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500 -- Photochemistry
AMINES
AQUEOUS SOLUTIONS
AZINES
BIPYRIDINES
CATALYTIC EFFECTS
CHEMICAL REACTIONS
COMPLEXES
DECOMPOSITION
DISPERSIONS
ELEMENTS
ENERGY LEVELS
EXCITED STATES
HETEROCYCLIC COMPOUNDS
HYDROGEN PRODUCTION
MEDIUM TEMPERATURE
METALS
MIXTURES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PLATINUM
PLATINUM METALS
PYRIDINES
QUENCHING
RHODIUM COMPLEXES
RUTHENIUM COMPLEXES
SOLUTIONS
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENTS