Cooperative Two-Electron Reagents of Lower Transition Metals of Group 10
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| Language: | English |
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University of Cincinnati / OhioLINK
2009
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250266435 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-ucin1250266435 |
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oai_dc |
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NDLTD |
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English |
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NDLTD |
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Chemistry redox electron transfer platinum palladium complexes |
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Chemistry redox electron transfer platinum palladium complexes Chatterjee, Sayandev Cooperative Two-Electron Reagents of Lower Transition Metals of Group 10 |
| author |
Chatterjee, Sayandev |
| author_facet |
Chatterjee, Sayandev |
| author_sort |
Chatterjee, Sayandev |
| title |
Cooperative Two-Electron Reagents of Lower Transition Metals of Group 10 |
| title_short |
Cooperative Two-Electron Reagents of Lower Transition Metals of Group 10 |
| title_full |
Cooperative Two-Electron Reagents of Lower Transition Metals of Group 10 |
| title_fullStr |
Cooperative Two-Electron Reagents of Lower Transition Metals of Group 10 |
| title_full_unstemmed |
Cooperative Two-Electron Reagents of Lower Transition Metals of Group 10 |
| title_sort |
cooperative two-electron reagents of lower transition metals of group 10 |
| publisher |
University of Cincinnati / OhioLINK |
| publishDate |
2009 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250266435 |
| work_keys_str_mv |
AT chatterjeesayandev cooperativetwoelectronreagentsoflowertransitionmetalsofgroup10 |
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1719433038666924032 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-ucin12502664352021-08-03T06:13:37Z Cooperative Two-Electron Reagents of Lower Transition Metals of Group 10 Chatterjee, Sayandev Chemistry redox electron transfer platinum palladium complexes Increase in worldwide fossil fuel consumption and environmental concerns aremotivating efforts to develop efficient multi-electron catalysts for energetically orkinetically unfavorable reactions. Examples include splitting water to make oxygen andhydrogen fuel and fixing carbon dioxide produced in combustion processes. Squareplanar d<sup>8</sup>- and octahedral d<sup>6</sup>- electron complexes of 2<sup>nd</sup> and 3<sup>rd</sup> row of Group 10 are attractive candidates for catalysis, as they undergo cooperative two electron changes in oxidation states. The cooperativity arises from the stability of the d<sup>6</sup>- and d<sup>8</sup>-electron configurations with respect to the intermediate d<sup>7</sup>, causing an inversion of the one-electron reduction potentials: E<sub>1</sub>°′(d<sup>6</sup>/d<sup>7</sup>)<E<sub>2</sub>°′(d<sup>7</sup>/d<sup>8</sup>). Fine control over these redox potentials and rates represents a powerful strategy for improving and designing new catalysts. However, attempts to implement this strategy are hampered by the fact that the redox reactions involve drastic changes in molecular geometry, making them irreversible. To address this problem, this work is focused on designing metal complexes with ligand architectures capable stabilizing four-coordinate geometry favored by the d<sup>8</sup>- electron configuration and six-coordinate geometry favored by the d<sup>6</sup>-electron configuration. In certain instances, these ligand scaffolds allow for facile two-electron transfer and measurement of the two-electron redox couple. This dissertation reports the synthesis of two new classes of palladium andplatinum complexes with ligand architectures capable of supporting outer-sphere two electron transfer. The first class includes complexes with a combination of monodentate, bidentate and pincer ligands. In these systems, the pincer ligand is capable of interconverting between a monodentate coordination mode and a meridional coordination mode, thus allowing for interconversion. Electrochemical studies demonstrate that these complexes are capable of undergoing two-electron transfer. The reactions show a wide variation in the redox potentials, chemical reversibility, and electron-transfer kinetics that can be rationalized in terms of the electronic, steric and conformational properties of the ligands, as also the electronic properties of the metal. One critical discovery is that the metal can act as both a Brønsted base and Lewis acid. Accumulated data suggest that the Lewis acid behavior causes preorganization of the d<sup>8</sup>-electron complex and is therefore a crucial element in the cooperative two-electron reactivity. The second category of complexes is composed of a bidentate ligand and apotentially facially coordinating tripodal ligand. In the presence of nucleophiles, thesesystems undergo remarkably reversible outer-sphere two-electron transfer. Mechanisticstudies indicate interconversion between four- and six-coordinate geometries, in whichthe nucleophile bonds at an open axial site. Varying the ligand, metal and exogenousnucleophile allows for tuning the redox potential over an astoundingly wide range,exceeding 1 V. The major findings from this work are significant because they establishfundamental guidelines for designing two-electron reagents and controlling their redoxpotentials. Furthermore, the compounds in the new class of two-electron reagents haveopen coordination sites that can potentially interact with substrate. Thus, these newcompounds afford the opportunity to couple two-electron reactivity with bond-makingand bond-breaking steps necessary for substrate activation. Knowledge derived from this dissertation work is expected to lead to the development of new multielectron catalysts, photocatalysts, and redox mediators for solar cells. 2009 English text University of Cincinnati / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250266435 http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250266435 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |