Low coordinate late transition metal platforms for CO₂ and CO complexes
Omolo, Kevin Omondi
MetadataShow full item record
Transition metal complexes that enable catalytic reactions to selectively and efficiently yield different products remain as indispensable tools in the synthetic chemist’s toolbox. Ligands, through their electronic and/or steric properties, play a vital role in modulating reactivity at the metal center in a complex either as spectator molecules or via metal ligand cooperation, and as such their development continues to attract considerable interest. This thesis presents the synthesis, characterization and elaboration of acridone and acridine-based ligands, their complexes’ synthesis and application in CO and CO₂ coordination. A new synthetic route to substituted acridones that uses carbamate anion as a removable directing group for lithiation, avoiding the requirement of pre-functionalized substrates is described. Acridones of different steric hindrance are synthesized via transition metal-catalyzed coupling reactions. Also presented herein is a new method for the synthesis of acridine-based ligands starting from 4,5-dibromo-2,7-di-tert-butylacridin-9(10H)-one. This method uses simplified substrates, avoids high reaction temperatures, and uses ClPPh₂ instead of diphenylphosphide intermediates. The resulting 2,7-di-tert-butyl-9-chloro-4,5-bis(diphenylphosphino)acridine ligand scaffold possess an active C-9 position that makes it possible to modify the acridine structures, and thus tune the stability and reactivity of the transition metal center and allow for synthesis and reactivity studies of CO and CO₂ coordination complexes. A structure-property relationship is investigated by comparing the reactivity of nickel CO and CO₂ complexes of a wide bite angle chelating diphosphine ligand Cy-xantphos to those of acridine-based complexes.