Carbazole-based Schiff base Macrocycles and Complexes: Redox, Fluorescence and Catalysis
This thesis outlines the successful synthesis of the first families of pure samples of carbazole-based Schiff base macrocycles and complexes. These compounds represent a new generation of Schiff base macrocycles and complexes, following on from the previously reported pyrrole and diphenylamine based analogues. These new carbazole complexes have shown interesting structural, redox, fluorescent and catalytic behaviours.In Chapter 2 two routes to the key precursors, 1,8-diformyl-carbazole (1a) and 1,8-diformyl-3,6-ditert-butyl-carbazole (1b), are investigated. Discussion of the optimisation of the two routes to 1a and 1b, and of the potential for access to a wider range of R-groups is detailed.In Chapters 3 and 4 the synthesis of [1+1] Schiff base macrocyclic complexes from 1 is discussed. In Chapter 3 diethylene triamine was used to produce metal free macrocycles HLH and HLtBu in high yields, as well as in template reactions to give four [1+1] macrocyclic complexes [MLR]OAc featuring M = Cu or Ni and R = H or tBu. In Chapter 4 dipropylene triamine was used to produce metal free macrocycle HLtBu-2 in high yield. This macrocycle was then complexed with iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) to form a series of seven complexes. Crystallographic and electrochemical studies are presented and discussed in both chapters. The cobalt complex of HLtBu-2 is currently being tested by collaborators as a hydrogen evolution catalyst.In Chapter 5 the preparation of dinuclear [2+2], and one tetranuclear [4+4], Schiff base macrocyclic complexes is presented. Template reactions using 1, ethylene diamine and copper(II) acetate yielded a pair of dinuclear complexes, [Cu2LR-Et(OAc)2] where R = H or tBu. Synthesis of the metal free macrocycles, H2LH-Et and H2LtBu-Et, allowed for the synthesis of two zinc complexes, [Zn2LH-Et(OAc)2] and [Zn4LtBu-Et*(OAc)4]. [Zn2LH-Et(OAc)2] is currently being tested for both anhydride/epoxide and CO2/epoxide polymerisation by collaborators in Oxford University. Initial results show moderate activity (TOF = 2-13 h-1), with high selectivity for ester linked polymers.In Chapter 6 fluorescence testing of the [2+2] macrocycles, H2LH-Et and H2LtBu-Et, and the dizinc complex, [Zn2LH-Et(OAc)2], is presented. [Zn2LH-Et(OAc)2] displayed strong blue fluorescence in solution and was tested as a ‘turn-off’ fluorescence sensor for a wide range of anions. H2LH-Et and H2LtBu-Et were tested as ‘turn-on’ fluorescent sensors for zinc(II) ions, with H2LH-Et showing excellent selectivity and sensitivity at nanomolar concentrations.In Chapter 7 a series of new families of ligands and complexes that can be accessed from 1 is presented. An N5 donor [1+1] macrocyclic complex, [ZnLN5]OAc, has been synthesised by reaction of triethylene tetraamine, zinc acetate and 1b. A pair of acyclic complexes, [CoIII(LtBu-iBu)2]BF4 and [NiII(LH-iBu)2], have been prepared, by reaction of nickel(II) or cobalt(II) tetrafluoroborate with acyclic di-isobutyl armed ligands. Five new [2+2] Schiff base macrocycles have been prepared from 1b and longer diamine linkers. These are the first examples of the next wave of carbazole-based Schiff base compounds and highlight a few of the many options that are available.Finally, in Chapter 8 the key findings are summarised and a look towards future directions is provided.
Advisor: Brooker, Sally
Degree Name: Doctor of Philosophy
Degree Discipline: Chemistry
Publisher: University of Otago
Keywords: Carbazole; Macrocycle; Schiff Base; Inorganic Chemistry; Fluorescence; Electrochemistry; Catalysis
Research Type: Thesis