Dicarbenes as bridges in mixed-metal systems

• Author / Creator

  Zamora, Matthew Thomas

• The study of heterobimetallic complexes (having two different metal atoms) involves combining the unique properties of each metal, which can give rise to interesting contrasts in reactivity compared to either metal alone. With two different metals incorporated into one complex, a more diverse array of reactivity patterns becomes available. In binuclear systems comprised of late, low-valent metals, the metals are most-often connected by diphosphines, ensuring metal-metal proximity during the reactions of interest. However, recently various carbene ligands (:CR2) have become established as phosphine mimics with interesting electronic and steric properties. As a result, dicarbenes are beginning to be probed as diphosphine substitutes.

  Chapter 2 of this thesis explores the synthesis of heterobimetallic complexes bridged by di-N-heterocyclic carbenes (di-NHCs) from diimidazolium salts. The use of an “internal base strategy” (using transition metal precursors containing basic ligands to afford deprotonation of imidazolium moieties in situ) prevents double- deprotonation, and avoids issues which normally result in chelation. Furthermore, we establish a “pendent” ligand strategy wherein one end of the diimidazolium salt is first deprotonated by one metal (giving a metal-bound carbene), followed by deprotonation of the pendent imidazolium group by the second metal, resulting in heterobimetallic complexes of Rh, Ir, and Pd.

  Chapter 3 describes our investigations into a series of new bidentate di-cyclic (alkyl)(amino)carbenes based on their monodentate counterparts. The synthesis of these species involved protocols similar to those employed for their monodentate analogues, and our efforts are described here.

  Chapter 4 recounts our success in developing several unsymmetrical, hybrid dicarbenes based on both N-heterocyclic and mesoionic carbenes (MICs). The dicationic NHC/MIC precursors can be deprotonated one ring at a time, resulting in NHC/MIC-bridged Pd/Rh complexes, comparable to the di-NHC analogues in Chapter 2. Similarly, Chapter 5 describes our development of new di-MIC frameworks, and their incorporation into mixed metal systems (again, employing internal base and “pendent” ligand strategies).

  Finally, Chapter 6 discusses our brief studies on these newly-developed complexes as “tandem catalysts”, wherein the heterobimetallic complex (as opposed to two monometallic catalysts) can effect the tandem transformation of a bifunctionalized substrate in one pot through Suzuki-Miyaura coupling and catalytic hydrogenation processes.

• Subjects / Keywords

  • Di-carbene
  • Catalysis
  • Bimetallic
  • X-ray crystallography
  • Palladium (Pd)
  • N-heterocyclic carbene (NHC)
  • Ligand design
  • Mesoionic carbene (MIC)
  • Iridium (Ir)
  • Hybrids
  • Inorganic
  • Organometallic
  • Rhodium (Rh)
  • Nuclear magnetic resonance (NMR)
  • Pendent
  • Cyclic (alkyl)(amino)(carbene) (CAAC)
  • Chemistry
  • Cooperativity
  • Bridging

• Graduation date

  Spring 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3WP9TJ1T

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.