CaltechTHESIS
  A Caltech Library Service

C(sp³)–H Activation via Dehydrogenation of Cyclic and Heterocyclic Alkanes by Single-Site Iridium Pincer Ligated Complexes

Citation

Al-Saihati, Zainab Ahmed (2020) C(sp³)–H Activation via Dehydrogenation of Cyclic and Heterocyclic Alkanes by Single-Site Iridium Pincer Ligated Complexes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/tsge-5m91. https://resolver.caltech.edu/CaltechTHESIS:06012020-135910044

Abstract

The direct dehydroaromatization of C(sp³)–H alkanes may seem conceptually simple but in fact is a challenging transformation. Industrially practiced methods utilize energy intensive processes operating at high pressures and temperatures due to the requirement of such conditions to overcome the endergonic and unreactive nature of alkanes. Chapter 1 briefly discusses early and recent achievements in the field of alkanes dehydrogenation by Ir pincer ligated complexes. While there has been great advancement in the dehydrogenation transformation recently, the direct dehydroaromatization of heterocyclic substrates generating functionalized aromatics is significantly underdeveloped. In Chapter 2, we successfully extended the applicability of Ir catalyzed dehydrogenation systems using pincer ligated complexes on a diverse collection of heterocyclic alkanes with functionalities known to be strongly coordinating and poorly compatible with (PCP)–Ir type catalysts. Carbo- and heteroarenes containing oxygen and nitrogen can be synthesized in moderate to excellent yields up to 99%, and the reaction tolerates functional groups such as bromides and fluorides. In Chapter 3, we demonstrate the efficient disproportionation of cycloalkenes to the corresponding arenes and cycloalkanes with up to 100% conversion, which has been a long-standing challenge in the field of pincer-ligated Ir-catalyzed dehydrogenation studies. For example, 1-cyclohexene was disproportionated to benzene and cyclohexane and 1-4-vinyl-1-cyclohexene was disproportionated to ethylbenzene and ethylcyclohexane. We also demonstrate that a key mechanistic feature of our system is a lack of catalyst inhibition by arenes. In addition, our method is advantageous to previous reports as no sacrificial olefin is used, thereby circumventing the requirement for exogeneous hydrogen acceptors. Our studies presented in Chapter 2 and Chapter 3 provides a novel and a complementary pathway to access important aromatic building blocks and may help create alternative routes to complex molecules via late stage dehydrogenation without the need of stoichiometric oxidants.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:dehydrogenation, dehydroaromatization, pincer, iridium, catalysis
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Grubbs, Robert H. (co-advisor)
  • Stoltz, Brian M. (co-advisor)
Thesis Committee:
  • Agapie, Theodor (chair)
  • Tirrell, David A.
  • Grubbs, Robert H.
  • Stoltz, Brian M.
Defense Date:29 May 2020
Funders:
Funding AgencyGrant Number
Saudi AramcoUNSPECIFIED
Projects:C-H Activation: Dehydrogenation by Iridium Pincer Complexes
Record Number:CaltechTHESIS:06012020-135910044
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:06012020-135910044
DOI:10.7907/tsge-5m91
ORCID:
AuthorORCID
Al-Saihati, Zainab Ahmed0000-0002-3837-9736
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13760
Collection:CaltechTHESIS
Deposited By: Zainab Al Saihati
Deposited On:03 Jun 2020 21:58
Last Modified:04 Jan 2021 18:50

Thesis Files

[img]
Preview
PDF (Full thesis) - Final Version
See Usage Policy.

13MB

Repository Staff Only: item control page