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Carbon-hydrogen bond and carbon-carbon bond activation of alkanes with rhodium porphyrins. / CUHK electronic theses & dissertations collection

Base-promoted CHA of unstrained alkanes with 5,10,15,20-tetratolylporphyrinatorhodium complexes, Rh(ttp)X (X = Cl, H, Rh(ttp)), has been achieved. Rh(ttp)Cl, reacted with n-pentane, n-hexane, n-heptane, c-pentane and c-hexane in the presence of potassium carbonate at 120 °C in 6 to 24 h to give rhodium porphyrin alkyls, Rh(ttp)R, in 29--76% yields. Mechanistic investigations suggested that Rh 2(ttp)2 and Rh(ttp)H are key intermediates for the parallel CHA step. The roles of base are (i) to facilitate the formation of Rh(ttp)Y (Y- = OH-, KCO3 -), (ii) to enhance the CHA rate with alkane and generate Rh(ttp)H by a Rh(ttp)Y species which is more reactive than Rh(ttp)Cl, and (iii) to provide a parallel CHA pathway by Rh2(ttp)2. / c-Octane reacted with Rh(ttp)Cl at 120 °C in 7.5 h in the presence of K2CO3 to yield Rh(ttp)( n-octyl) and Rh(ttp)H in 33% and 58% yields, respectively. Mechanistic investigations indicate that the CCA product is generated from the Rh II(ttp)-catalyzed 1,2-addition of c-octane with Rh(ttp)H. Reaction of c-octane and Rh(ttp)H/Rh2(ttp) 2 (10:1) selectively yielded Rh(ttp)(n-octyl) in 73% at 120 °C in 15 h. The catalyst RhII(ttp) radical cleaves the C-C bond of c-octane to form to a Rh(ttp)-alkyl radical, which then abstracts a hydrogen atom from Rh(ttp)H to generate the Rh(ttp)( n-octyl), and subsequently leading to regeneration of the Rh II(ttp) radical. (Abstract shortened by UMI.) / K2CO3-promoted CHA of the ring-strained cycloheptane with Rh(ttp)Cl at 120 °C in 6 h gave the CHA product Rh(ttp)( c-heptyl) and together with, unexpectedly, the CCA product Rh(ttp)Bn, in 30% and 24% yields, respectively. Mechanistic studies revealed that Rh(ttp)( c-heptyl) undergoes beta-hydride elimination in neutral condition or beta-proton elimination in basic condition followed by reprotonation to give rhodium(III) porphyrin hydride, Rh(ttp)H, and c-heptene. Successive base-promoted CHA of c-heptene with Rh(ttp)H, followed by beta-proton elimination, generates cycloheptatriene. The CHA of cycloheptatriene with Rh(ttp)H formed Rh(ttp)(c-heptatrienyl), which underwent rearrangement with carbon-carbon cleavage at 120 °C in 16 d to yield Rh(ttp)Bn in 96% yield. / The objectives of this research focus on the investigation of carbon-hydrogen bond activation (CHA) and carbon-carbon bond activation (CCA) of alkanes by rhodium porphyrin complexes as well as the mechanistic understanding. / Chan, Yun Wai. / Adviser: Kin Shing Chan. / Source: Dissertation Abstracts International, Volume: 73-02, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Identiferoai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_344719
Date January 2010
ContributorsChan, Yun Wai., Chinese University of Hong Kong Graduate School. Division of Chemistry.
Source SetsThe Chinese University of Hong Kong
LanguageEnglish, Chinese
Detected LanguageEnglish
TypeText, theses
Formatelectronic resource, microform, microfiche, 1 online resource (x, 227 leaves : ill.)
RightsUse of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/)

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