Modification of Catalytically Active and/or Switchable Complexes for Surface Attachment

Abstract

The overall aim of this project was to take robust complexes which exhibit reversible redox, catalytic activity, or spin crossover (SCO), and design, prepare and characterise suitably functionalised analogues of them, in order to immobilise them by covalent bonds onto a range of solid supports. These compounds represent new generations of cyclic and acyclic Schiff base ligands and complexes, following on from previously reported unfunctionalised diphenylamine-2,2’-dicarboxaldehyde (HU1), 3,6-diformylpyridazine (HU2) and pyridine-2-carboxaldehyde (HU3) based compounds.

In Chapter 1 an introduction to Schiff base chemistry and an overview of the recent work done by the Brooker group on HU1 and HU2 Schiff base macrocyclic complexes are provided. Then the SCO phenomenon is discussed, and specific iron(II) complexes of the ligand type relevant to this project, based on HU3, are reviewed. Then an overview of photo- and electrocatalysts for CO2 reduction and H2 evolution is given. Finally, some possible methods of immobilisation of complexes onto solid supports are discussed.

In Chapter 2 four dicopper(II) acetate complexes of unfunctionalised HU1 [2+2] macrocycles, previously synthesised in the Brooker group, were screened for photocatalytic CO2 reduction activity in DMF with a [Ru(bpy)3]2+ photosensitiser by PhD student Fola Akogun and the resulting data were worked up by the author. All four complexes are active catalysts, with the dicopper(II) complex of the butylene linked macrocycle being the most active for CO evolution.

In Chapter 3 the synthesis and characterisation of four new OR functionalised metal-free [2+2] Schiff base macrocycles, H2LIPr-OR [where R = alkene (allyl group), alkyne (propargyl group), C14 (tetradecane group) or quin (quinoline group)], obtained by condensation of HU1 and OR functionalised 1,3-diaminopropan-2-ol (DAPO-OR), is presented. One proof of principle attachment of H2LIPr-Oalkyne onto azide-functionalised monomer (AzThP) and azide-functionalised polymer (TG(4)-Az(1)ThP), by CuAAC, is described.

In Chapter 4 three dinuclear complexes of the macrocycle H2LIPr-Oquin, [ZnII2(LIPr-Oquin)](BF4)2·0.4toluene, [CuII2(LIPr-Oquin)](BF4)2·0.6toluene and [CoII2(H2LIPr-Oquin)(H2O)4](BF4)4, are reported. Crystallographic characterisation of [ZnII2(LIPr-Oquin)](BF4)2·toluene and electrochemical studies of all three complexes, are described.

In Chapter 5 the synthesis and characterisation of two OR functionalised pyridazinebased [2+2] macrocycles [PbII2(Lpdz’-OR)](ClO4)4·xH2O (where R = alkene or alkyne and x = 4 or 5) complexes, obtained by lead(II) template reaction of HU2 and functionalised DAPO-OR are discussed. Subsequent transmetallation of the dilead complexes by cobalt(II) results in two complexes, [CoII2(Lpdz-Oalkyne)(H2O)4](ClO4)4 and contaminated [CoII2(Lpdz-Oalkene)(H2O)4](ClO4)4·Pb(ClO4)2. One attempt at surface immobilisation, by CuAAC chemistry, of [CoII2(Lpdz-Oalkyne)(H2O)4](ClO4)4 onto an azide-functionalised polymer (EDOT-N3:EDOT 1:7) deposited on indium tin oxide (ITO) is reported. Electrochemical studies on the functionalised surface indicates successful immobilisation.

In Chapter 6 three new acyclic ligands HLBrH, HLHBr and HLHCl were synthesised by 2:1 condensation of the appropriately 5- or 6-halo-pyridine-2-carboxaldehyde (HU3) with DAPO. Reaction with one equivalent of cobalt(II) tetrafluoroborate resulted in the expected mononuclear complex [CoII(HLHBr)(MeOH)2](BF4)2 for 5-bromo-pyridine-2-carboxaldehyde (HU3) and two unexpected dinuclear complexes, [CoII2(LBrHOBF3)] 2(BF4)2 and [CoII2(LClH-OBF3)]2(BF4)2, for the sterically demanding 6-halo substituted versions of HU3, as confirmed by X-ray crystal structures. Electrochemistry is reported for all three complexes.

In Chapter 7 the synthesis of a new alkene functionalised tetradentate amine acyclic ligand, LA3HH-Oalkene from HLHH is discussed. The immobilisation of LA3HH-Oalkene by hydrosilylation onto a silicon-H surface, followed by complexation with [Fe(py)4(NCSe)2], resulted in a functionalised monolayer. This was characterised by Xray photoelectron spectroscopy at different temperatures, which showed a change in the population of the Fe 2p core level, indicative of some SCO behaviour.