A novel approach for the design of dirhodium(II) tetracarboxylates derived from (S)- amino acid ligands is outlined. The new approach is founded on modifying the catalyst sterics through reducing the symmetry of the ligand’s N-heterocyclic tether. Investigations towards the new approach led to the preparation of Rh2(S-1, 2-NTTL)4 and analogues, Rh2(S-1-Ph-BPTTL)4, Rh2(S-tertPTTL)4, Rh2(S-BHTL)4, Rh2(SBOTL) 4 and Rh2(β-D-TAGA)4. The screening of the new complexes led to the uncovering of Rh2(S-tertPTTL)4 as a new member to the dirhodium(II) complexes family with an extraordinary selectivity. The stereoselectivity of Rh2(S-tertPTTL)4 was found to be comparable to Rh2(S-PTAD)4 (up to >99% ee), while being much more synthetically accessible catalyst. X-ray structure-based correlations justifying the observed enantioinduction enhancement are also discussed. The process of preparation and characterization of a Rh2(S-tertPTTL)4-catalyzed cyclopropanation capillary microreactor is also presented. The continuous flow Rh2(S-tertPTTL)4-catalyzed cyclopropanation microreaction is carried out to generate the cyclopropane product in moderate yield (44%) and excellent diastereoselectivity (>20:1 E:Z dr). The microreaction enantioselectivity, however, did not exceed 10% ee. Finally, the results are concluded and an outlook regarding the current field of research is outlined highlighting potential investigations that might be necessary for future development.
|Date of Award||2015|
|Supervisor||Ashraf Ghanem (Supervisor) & Bill Maher (Supervisor)|
Design and synthesis of novel chiral dirhodium(II) carboxylate complexes for asymmetric cyclopropanation reactions
Gouany, F. (Author). 2015
Student thesis: Doctoral Thesis