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dc.contributor.advisorDaniel G. Nocera.en_US
dc.contributor.authorHeyduk, Alan F. (Alan Frank), 1974-en_US
dc.contributor.otherMassachusetts Institute of Technology. Dept. of Chemistry.en_US
dc.date.accessioned2005-08-23T18:38:26Z
dc.date.available2005-08-23T18:38:26Z
dc.date.copyright2001en_US
dc.date.issued2001en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/8251
dc.descriptionThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2001.en_US
dc.descriptionVita.en_US
dc.descriptionIncludes bibliographical references.en_US
dc.description.abstractTwo-electron mixed-valence complexes of rhodium may be supported by diphosphazane ligands (RN(PY2)2). Whereas diphosphazane ligands with strongly [pi]-acidic phosphine groups (Y = F, OCH2CF3) react with RhI starting materials to afford binuclear Rh20,II complexes, Rh20,II(MeN(PY)2)3X2(L) or Rh2"II(MeN(PY),)3X2 (X = Cl, Br), diphosphazane ligands with weaker [pi]-acid phosphines (Y = OMe, OPh) give only valence-symmetric Rh2I,I complexes, Rh2I,I(MeN(PY2)2X2(L)2. Moreover, the formation of Rh20,II(tfepma)3C12 and [ClRh'(tfepx)]2([mu]-tfepx) (tfepma = MeN[P(OCH2CF3)2]2; tfepx = (3,5-Me2C6H3)N[P(OCH2CF3)2] suggest that delocalization of the nitrogen lone pair into the [pi]-system of the aryl group defeats formation of the two-electron mixed-valence species. These results are interpreted in terms of a polarizable nitrogen lone pair mediating the [pi]-acid properties of the PY2 groups to induce disproportionation of valence-symmetric dirhodium cores. Application of this knowledge to iridium provided the first example of a two-electron mixed-valence complex for this metal, Ir20,II(tfepma)3C12. X-ray diffraction studies reveal a coordination environment with two bridging tfepma ligands and a third tfepma chelating the Ir0 center. Trigonal bipyramidal geometry at the Ir0 is completed by a metal-metal bond to a square pyramidal IrII containing cis-disposed chloride ligands. Ir20-II(tfepma)3C12 is Lewis-acidic, readily accepting donor ligands to form 36 e- complexes. Oxidative addition is also rapid: chlorine and hydrogen chloride react to afford Ir2I-III(tfepma)3C14 and Ir2I,III(tfepma)3HC13, respectively. Hydrogen adds reversibly to Ir20,II(tfepma)3C12, providing the first example of such an addition across a preserved metal-metal single bond.en_US
dc.description.abstract(cont.) Two electron oxidation and reduction reactions also are facile for Rh20,II(dfpma)X2(L), affording Rh2II-II(dfpma)X4 and Rh20,0(dfpma)(L)2 complexes, respectively. These three species form a homologous series of metal-metal bonded complexes with well characterized trigonal bipyramidal Rh0 and octahedral RhII centers. Preservation of the metal-metal bond across the series supports the multi-electron reactivity of the system, as evidenced by photo-induced halogen elimination. We obtained the mixed-valence complex, Rh20-II(dfpma)X2(L), quantitatively when solutions of Rh2(dfpma)3X4 containing excess L were photolyzed in the presence of a halogen-atom trap such as THF. Further irradiation of the Rh20,II(dfpma)X2(L) photoproduct resulted in a second 2e- elimination reaction to give Rh20,0(dfpma)(L)2 in quantitative yield. In the overall transformation, the two-electron mixed-valence LRh0--RhIIX2 compound sustains the multi-electron photoreactivity of the system by coupling the 2e- M-X chemistry of the individual Rh centers. M-X photoactivation from this two-electron mixed-valence platform provides the basis for the photocatalytic production of H2 from HX in homogeneous solution ...en_US
dc.description.statementofresponsibilityby Alan F. Heyduk.en_US
dc.format.extent188 leavesen_US
dc.format.extent14338494 bytes
dc.format.extent14338251 bytes
dc.format.mimetypeapplication/pdf
dc.format.mimetypeapplication/pdf
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582
dc.subjectChemistry.en_US
dc.titleTwo-electron mixed-valence complexes small molecule activation and photocatalytic hydrogen productionen_US
dc.title.alternative2-electron mixed-valence complexes small molecule activation and photocatalytic hydrogen productionen_US
dc.typeThesisen_US
dc.description.degreePh.D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Chemistry
dc.identifier.oclc50324049en_US


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