Structural insights into phenoxide containing alkali metal magnesiates with extensions to the d-block

Student thesis: Doctoral Thesis

Abstract

The application of alkoxide and phenoxide ligands in the synthesis of alkali metal magnesiates is becoming more widespread with the resulting magnesiates finding applications in metal-halogen exchange. This project develops the structural chemistry of heterobimetallic sodium magnesiates containing the phenoxide ligand 5,5´,6,6´-tetramethyl 3,3´-di-tert-butyl-1,1´-biphenyl-2,2´-diol [(rac)-BIPHEN]. Nine sodium magnesiates, 2-10, have been prepared and characterised by X-ray crystallography and/or multinuclear NMR spectroscopy. Introduction of sodium as the alkali metal was found to have a detrimental impact on the stability of the resulting magnesiates in comparison to their lithium analogues, making them more prone to undergo disproportionation in the presence of ethereal solvents. This instability could be circumvented through judicial choice of Lewis donor ligand. The reactivities of sodium magnesiates, 3 and 5 which contain N, N, N´, N´- tetramethylethylenediamine (TMEDA) and N, N, N´, N´´, N´´ - pentamethyldiethylenetriamine (PMDETA) respectively, were examined in metal-halogen exchange with iodoarenes in an attempt to ascertain if sodium magnesiates containing the (rac)-BIPHEN phenoxide ligand were sufficiently reactive to carry out two-fold metal-halogen exchange. A difference was observed in the reactivity of the two magnesiates upon moving from bidentate TMEDA to tridentate PMDETA, with 3 generally possessing a higher reactivity than 5, indicating that sodium likely has a role to play in metal-halogen exchange. It is postulated that coordination of the iodoarene to a vacant coordination site on sodium could prime the substrate to undergo metal-halogen exchange. Utilising the chiral variant (S)-3 in metal-halogen exchange followed by electrophilic quenching of the metallated intermediate produced chiral alcohols 11, 12 and 13, thus demonstrating the synthetic utility of sodium magnesiates of this type by giving access to asymmetric synthesis. Finally, utilisation of the (rac)-BIPHEN phenoxide ligand for the synthesis of heterobimetallic complexes was extended to alkali metal zincates. Two novel inverse lithium zincates, 15 and 16, were prepared and characterised by X-ray crystallography and multinuclear NMR spectroscopy. Attempts to generate a conventional lithium zincate through the reaction of (rac)-BIPHEN with the tetra- and tris(alkyl) lithium zincates Li2ZnR4(TMEDA)2, Li2ZnR4((R,R)- TMCDA)2 and LiZnR3(PMDETA) revealed these complexes to react as monometallic lithium bases, leading to the isolation of the tetranuclear lithium phenoxides 17, 18 and 19. A surprising alkali metal effect was observed upon switching to the tris(alkyl) sodium zincates aZnR3(PMDETA) and NaZnR3(15-crown-5) which were found to react as bimetallic dialkyl bases to generate the sodium zincates 22 and 23. KZnR3(PMDETA) was also found to react with (rac)-BIPHEN as a dialkyl base; however, only the homoleptic potassium zincate 24 could be isolated as a result of disproportionation.
Date of Award28 Jun 2021
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorCharles O'Hara (Supervisor) & Robert Mulvey (Supervisor)

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