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Issue 42, 2012
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A novel ruthenium(II)–cobaloxime supramolecular complex for photocatalytic H2 evolution: synthesis, characterisation and mechanistic studies

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Abstract

We report the synthesis and characterization of novel mixed-metal binuclear ruthenium(II)–cobalt(II) photocatalysts for hydrogen evolution in acidic acetonitrile. First, 2-(2′-pyridyl)benzothiazole (pbt), 1, was reacted with RuCl3·xH2O to produce [Ru(pbt)2Cl2]·0.25CH3COCH3, 2, which was then reacted with 1,10-phenanthroline-5,6-dione (phendione), 3, in order to produce [Ru(pbt)2(phendione)](PF6)2·4H2O, 4. Compound 4 was then reacted with 4-pyridinecarboxaldehyde in order to produce [Ru(pbt)2(L-pyr)](PF6)2·9.5H2O, 5 (where L-pyr = (4-pyridine)oxazolo[4,5-f]phenanthroline). Compound 5 was then reacted with [Co(dmgBF2)2(H2O)2] (where dmgBF2 = difluoroboryldimethylglyoximato) in order to produce the mixed-metal binuclear complex, [Ru(pbt)2(L-pyr)Co(dmgBF2)2(H2O)](PF6)2·11H2O·1.5CH3COCH3, 6. [Ru(Me2bpy)2(L-pyr)Co(dmgBF2)2(OH2)](PF6)2, 7 (where Me2bpy = 1,10-phenanthroline, 4,4′-dimethyl-2,2′-bipyridine) and [Ru(phen)2(L-pyr)Co(dmgBF2)2(OH2)](PF6)2, 8 were also synthesised. All complexes were characterized by elemental analysis, ESI MS, HRMS, UV-visible absorption, 11B, 19F, and 59Co NMR, ESR spectroscopy, and cyclic voltammetry, where appropriate. Photocatalytic studies carried out in acidified acetonitrile demonstrated constant hydrogen generation longer than a 42 hour period as detected by gas chromatography. Time resolved spectroscopic measurements were performed on compound 6, which proved an intramolecular electron transfer from an excited Ru(II) metal centre to the Co(II) metal centre via the bridging L-pyr ligand. This resulted in the formation of a cobalt(I)-containing species that is essential for the production of H2 gas in the presence of H+ ions. A proposed mechanism for the generation of hydrogen is presented.

Graphical abstract: A novel ruthenium(ii)–cobaloxime supramolecular complex for photocatalytic H2 evolution: synthesis, characterisation and mechanistic studies

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Publication details

The article was received on 10 Feb 2012, accepted on 02 Apr 2012 and first published on 11 Apr 2012


Article type: Paper
DOI: 10.1039/C2DT30309D
Citation: Dalton Trans., 2012,41, 13060-13073
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    A novel ruthenium(II)–cobaloxime supramolecular complex for photocatalytic H2 evolution: synthesis, characterisation and mechanistic studies

    D. M. Cropek, A. Metz, A. M. Müller, H. B. Gray, T. Horne, D. C. Horton, O. Poluektov, D. M. Tiede, R. T. Weber, W. L. Jarrett, J. D. Phillips and A. A. Holder, Dalton Trans., 2012, 41, 13060
    DOI: 10.1039/C2DT30309D

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