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dc.contributor.advisorBetley, Theodore A
dc.contributor.authorPowers, Tamara Michelle
dc.date.accessioned2013-10-15T13:34:42Z
dash.embargo.terms2015-10-10en_US
dash.embargo.terms2015-10-10
dc.date.issued2013-10-15
dc.date.submitted2013
dc.identifier.citationPowers, Tamara Michelle. 2013. Multi-Electron Reduction of Small Molecules by Triiron Reaction Sites. Doctoral dissertation, Harvard University.en_US
dc.identifier.otherhttp://dissertations.umi.com/gsas.harvard:11071en
dc.identifier.urihttp://nrs.harvard.edu/urn-3:HUL.InstRepos:11169793
dc.description.abstractThe observation that multi-electron activation of small molecule substrates occurs at polynuclear reaction sites, common to both metalloenzymes and heterogeneous catalysts, has led to the articulation of the polynuclear hypothesis - the idea that the expanded redox reservoir afforded by M-M interactions in polynuclear systems stabilizes multiple oxidation states and facilitates multi-electron transformations. Currently, examples of synthetic clusters that test the viability of polynuclear reaction sites towards effecting multi-electron activation of small molecule substrates are lacking. To test the polynuclear hypothesis, we targeted a system that embodies design elements common to metaloenzyme cofactors: polynuclear reaction sites that feature high-spin, coordinatively unsaturated metal centers. Metallation of tbsLH6 [tbsLH6 = 1,3,5-C6H9(NHC6H4-o-NHSiMe2tBu)3] yields high-spin trinuclear Fe(II) complex (tbsL)Fe3(THF). The filled anti-bonding orbitals in high-spin cluster (tbsL)Fe3(THF) renders ligand reorganization facile, which allows for a range of metal-substrate binding modes. The polynuclear site within the (tbsL)Fe3(THF) cluster cooperatively binds anionic donors and allows 2e- reduction of substrates including inorganic azide and hydrazines, yielding μ3-nitrido and μ3-imido products, respectively. The 4e- reductive N=N bond cleavage of azobenzene is also achieved in the presence of (tbsL)Fe3(THF) to yield Fe3 bis-imido complex ((tbsL)Fe3(μ3-NPh)(μ2-NPh), which has been structurally characterized. Cyclic voltammograms of a series of selected triiron imido and nitrido clusters suggest that oxidation states up to [Fe(IV)][Fe(III)]2 are electrochemically accessible. Addition of neutral pi-acidic molecules including tert-butylisonitrile (tBuNC) and carbon monoxode (CO) to trinuclear cluster (tbsL)Fe3(THF) led to the formation of a new series of coordination compounds, where binding to a single metal center is favored over cooperative substrate binding. Coordinated substrates are activated toward further reactivity, highlighted by the reductive coupling of isonitriles by (tbsL)Fe3(μ1-CNtBu)3 in the presence of phenylsilane. Finally, efforts to synthesize of a family of mixed Fe-Mn clusters that differ by single metal-site substitutions are presented. Substitutionally homogeneous (tbsL)Fe2Mn(THF) cluster is accessed from binuclear complex (tbsLH2 )Fe2. Attempts to synthesize similar Mn2Fe clusters results in isolation of a mixture of heterotrinuclear species. In conjunction with NMR, EPR, Mössbauer, and X-ray fluorescence spectroscopies, anomalous scattering measurements were critical for the unambiguous assignment of the metal substitution products that were synthesized.en_US
dc.description.sponsorshipChemistry and Chemical Biologyen_US
dc.language.isoen_USen_US
dash.licenseLAA
dc.subjectChemistryen_US
dc.titleMulti-Electron Reduction of Small Molecules by Triiron Reaction Sitesen_US
dc.typeThesis or Dissertationen_US
dash.depositing.authorPowers, Tamara Michelle
dc.date.available2015-10-10T07:33:04Z
thesis.degree.date2013en_US
thesis.degree.disciplineChemistry and Chemical Biologyen_US
thesis.degree.grantorHarvard Universityen_US
thesis.degree.leveldoctoralen_US
thesis.degree.namePh.D.en_US
dc.contributor.committeeMemberHolm, Richarden_US
dc.contributor.committeeMemberGordon, Royen_US
dash.contributor.affiliatedPowers, Tamara Michelle


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