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" Studies of Isocyano Analogues to Manganese Carbonyls and the Development of Low-Valent Coordination Polymers using Multitopic m-Terphenyl Isocyanides "
Agnew, Douglas Walter
Figueroa, Joshua S
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Latin Dissertation
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English
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898858
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TL8w86900n
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Lee, Kah-Wee
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Studies of Isocyano Analogues to Manganese Carbonyls and the Development of Low-Valent Coordination Polymers using Multitopic m-Terphenyl Isocyanides\ Agnew, Douglas WalterFigueroa, Joshua S
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2017
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2017
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| Abstract
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The work presented in this dissertation is best apportioned into two distinct parts; the first part (Chapters 2-4) describes several investigations of low-valent manganese carbonyl/isocyanide complexes, while the second part (Chapters 5-7) details the generation of coordination polymers and other supramolecular complexes using the ditopic isocyanide [CNArMes2]2. With this division in mind, the attentive reader will hopefully observe that the interrogative method utilized in studies of discrete, molecular complexes can be translated efficiently and effectively to materials development. In the first part, the mixed carbonyl/isocyanide complex Mn(CO)3(CNArDipp2)2 was isolated in gram scale with the aid of the sterically encumbering isocyanide CNArDipp2. This green solid, which is electronically and structurally similar to the homoleptic carbonyl Mn(CO)5, displays the radical-based chemistry expected for an open-shelled, low-spin d7 organometallic species. However, the kinetic stabilization engendered by the m-terphenyl groups has allowed for a careful study of reaction products, with the notable isolation of several manganese η2-N,O-nitroxide radicals. The identification of these species raises doubts concerning earlier work regarding nitrosoarene spin-trapping of photolytically generated Mn(CO)5, and underscores the importance of the cis-labilizing effect in low-valent Mn chemistry. This latter fact has been elaborated upon with the generation of multiple Mn κ2-carboxylates (eg. (κ2-O,O’-RCO2)Mn(CO)2(CNArDipp2)2) via the cis-labilization of CO from the [Mn(CO)3(CNArDipp2)2] framework using a variety of metal carboxylate reagents. These Mn carboxylate species can serve as viable sources of the [Mn(CO)2(CNArDipp2)2]+ fragment under reductive conditions or with the use of Lewis acidic reagents. Finally, the stability of Mn(CO)3(CNArDipp2)2 permitted a thorough electrochemical study of the Mn(-1/0/1) redox couple, with particular attention paid to the reduction of CO2 by the manganate [Mn(CO)3(CNArDipp2)2]–. The results of this study are informative towards the design of improved Mn-based molecular catalysts for the catalytic reduction of CO2. In the second part of this dissertation, the development of isocyanide coordination polymers derived from the sterically encumbering diisocyanide [CNArMes2]2 is described. In particular, it was found that control over nodal geometry and ligand coordination number is accomplished for Cu(I) isocyanide coordination polymers in direct analogy to previously surveyed chemistry for molecular Cu(I) m-terphenyl isocyanide complexes. The ability to favor low isocyanide coordination was further utilized in the preparation of Ni-ISOCN-1, the first authenticated metal-organic material utilizing zerovalent metal sites as nodes. Similar to the aforementioned Cu(I) polymers, Ni-ISOCN-1 features low isocyanide coordination, which results in a formal 16 e– count at each Ni(0) site. An assessment of the physical properties of these and other polymers is presented, providing a first glimpse into the chemistry of crystalline transition metal-isocyanide coordination polymers.
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Agnew, Douglas Walter
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UC San Diego
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