Complexes of chiral tridentate ligands for spin-crossover and catalysis

This thesis delves into the breadths of chemistry, comprising the exploration of the organic synthesis of the underexplored, sulfur analogue of the ligand, 2,6- bis(oxazoline) pyridine (PyBOX), namely 2,6-bis(thiazolinyl)pyridine (thioPyBOX). A series of coordination complexes of iron(II), copper(I), copper(II) and ruthenium(II) featuring the PyBOX and thioPyBOX ligands, have been synthesised for a manifold of applications. These include molecular electronics, catalysis and metal-based anti-cancer medicines. A continuous narrative throughout this work is the electronic and steric effects of swapping oxygen for sulfur in such coordination complexes and the impact of this on their chemistry in end applications. The exploration of chiral metal complexes, designed by the diastereomeric nature of substituted PyBOX and thioPyBOX ligands, forms a significant proportion of the work herein.

Substituted thioPyBOX ligands have been synthesised in two different enantiomeric forms, following which homochiral and heterochiral iron(II) thioPyBOX complexes were synthesised and studied. The concept of chiral discrimination of spin states was corroborated with a pair of enantiomers displaying a High Spin-Low Spin dichotomy at ambient conditions. Heteroleptic iron(II) (thio/)PyBOX complexes have also been synthesised of these ligands and with other classical N,N’,N’’-tridentate pincer ligands. The overall findings have demonstrated an increased stability of metal-thioPyBOX complexes compared to their PyBOX counterparts, this is attributed to the reduced electron-withdrawing nature of thiazoline compared to oxazoline.

Copper(I) and copper(II) (thio/)PyBOX complexes have been synthesised with a view to achieve an effective catalyst for the copper-catalysed azide-alkyne Click reaction and the copper-catalysed Ullman coupling reactions respectively. Furthering the catalysis aspect, ruthenium(II) (thio/)PyBOX complexes of mono- and bis- ligand coordination were synthesised for the catalysis of the asymmetric transfer hydrogenation reaction. Further afield, cell-line testing of one of these complexes was found to exhibit better cytotoxic activity than cisplatin against pancreatic cancer cells and human bone cancer cells which is also presented in this thesis.