Water oxidation with ruthenium catalysts

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Title: Water oxidation with ruthenium catalysts
Author: Kaveevivitchai, Nattawut
Abstract: CeIV -activated water oxidation : A family of 29 mononuclear RuII complexes have been prepared and characterized by 1H NMR , electronic absorption , and cyclic voltammetry . These complexes are studied as catalysts for water oxidation . The complexes may be divided into three basic types . The type -1 complexes involve a [RuII (NNN ) (NN ) (X )]n (NNN = tridentate ligand , NN = a bidentate ligand , and X = halogen and n = 1+ ; X = H2O and n = 2+ ) . The type -2 complexes contain a NNN , two molecules of 4 -methylpyridine (pic ) , and halogen or H2O to form a [RuII (NNN ) (pic )2 (X )]n complex . The type -3 complexes contain no water molecule and thus are constructed from a tetradentate ligand (NNNN ) and two molecules of pic to provide a [RuII (NNNN ) (pic )2]2+ complex . In general the type -2 catalysts are more reactive than the type -1 . The type -2 iodo -catalyst shows first -order behavior and , unlike the bromo - and chloro -catalysts , does not require water -halogen exchange to show good activity . The importance of steric strain and hindrance around the metal center is examined . The introduction of three t -butyl groups at the 4 , 4′ , and 4″ positions of tpy (ttbt ) sometimes improves catalyst activity , but the effect does not appear to be additive . Photo -activated water oxidation : Two mononuclear RuII complexes , [Ru (ttbt ) (pynap ) (I )]I and [Ru (tpy ) (pic )2 (I )]I (tpy = 2 ,2' ;6 ,2'' -terpyridine ; pynap = 2 - (pyrid -2' -yl ) -1 ,8 -naphthyridine ) , are effective catalysts for the oxidation of water . This oxidation can be driven by a blue LED light source using [Ru (bpy )3]Cl2 (bpy = 2 ,2' -bipyridine ) as the photosensitizer . Sodium persulfate acts as a sacrificial electron acceptor to oxidize the photosensitizer that in turn drives the catalysis . The presence of all four components : light , photosensitizer , sodium persulfate , and catalyst are required for water oxidation . A dyad assembly has been prepared using a pyrazine -based linker to join a photosensitizer and catalyst moiety . Irradiation of this intra -molecular system with blue light produces oxygen with a higher turnover number than the analogous intermolecular component system under the same conditions .
URI: http : / /hdl .handle .net /10657 /ETD -UH -2012 -08 -496
Date: 2012-09-28

Citation

Water oxidation with ruthenium catalysts. Doctoral dissertation, University of Houston. Available electronically from http : / /hdl .handle .net /10657 /ETD -UH -2012 -08 -496 .

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