An investigation of redox-active isoindoline-based ligands and their coordination complexes

The structural and electronic properties of metal complexes with isoindoline-based redox-active ligands and the ability of these ligands to stabilize unusual oxidation states was investigated. Two types of redox-active ligands were examined: phthalocyanines (Pc) and bis(2-pyridylimino)isoindolines also known as lobsterates (Lb). In contrast to the ancillary or spectator ligands more commonly used in coordination chemistry, redox-active ligands can exist in a range of oxidation states. Additionally, the chemical inertness of the Pc ligand could be used to develop new catalysts where the Pc ligand can stabilize a highly reactive metal centre and also act as an electron reservoir in a catalytic cycle. With this in mind, the reduction of trichloro(phthalocyanato)niobium(V) was performed with various reducing agents in order to study the bond activating ability of the reduced species and to determine the crystal structure of the reduced products. C–O bond activation of ether-type solvents suggests that the Pc ligand is able to withstand bond activation from a highly reduced niobium centre while, at the same time, allowing the niobium centre to activate the C–O bonds of the solvent. NbPc complexes containing Pc(4–) ligands were structurally characterized. A reduced MgPc complex containing a Pc(3–) ligand was also structurally characterized. A report of gold(II) Pc and the ability of Pc to stabilize gold in an unusual, paramagnetic +2 oxidation state was re-investigated. Attempts to synthesize soluble versions of AuPc as well as the original AuPc did not produce the desired gold(II) products and only diamagnetic gold(III) Pcs were obtained. An unprecedented, ring- contracted gold(III) Pc analogue was discovered and structurally characterized in the process of these studies. A series of three new 5,6-substituted Lb ligands were synthesized and the redox properties of these ligands in copper(II) acetate complexes were evaluated using cyclic voltammetry. The reductions of the copper acetate Lb complexes were not chemically reversible. The 2,6-diisopropylphenoxy-substituted Lb copper acetate complexes formed acetate-bridged 1-D chains. Superconducting quantum interference device magnetometry suggests that the Cu centres are very weakly antiferromagnetically coupled.