Enhancing the cooperative binding properties of1,1'-bis(1,2,3,4-tetrahydroisoquinolines)
The design of partially reduced 1,1'-bisisoquinoline derivatives was investigated with the aim of controlling the conformation about the C1-C1' axis. This would produce ligands with unusual but predictable ligand binding properties, particularly cooperativity. The introduction of ω-aminoalkyl, ω-azidoalkyl, ω-alkynyl and ω-alkenyl groups onto the nitrogens of the reduced bisisoquinoline core was conducted with the intention of broadening the scope of the ligand. Subsequent epoxidation, hydroboration and Huisgen 1,3-dipolar cycloaddition of terminal unsaturated groups and nucleophilic displacement of the chlorine of the corresponding known bischloroacetyl derivative afforded representative examples of new ligand types for future study. 1,1'-Bis(1,2,3,4-tetrahydro-6,7-dimethoxyisoquinoline) was found to readily condense with a wide range of aldehydes to give imidazolines and aspects of the rates of condensation were determined. Mono-alkyl bisisoquinolines were obtained efficiently by cleavage of the imidazolines through a newly defined treatment with sodium cyanoborohydride under acidic conditions. A procedure was developed whereby these two steps could be accomplished in a sequential one-pot process. The mono-alkyl compounds were further derivatized through acetylation, alkylation, sulfonylation and reductive alkylation. Synthetic strategies towards π-excessive N-arenealkyl derivatives were established with the goal to create scaffolds for the coordination of π-deficient systems, of which the X-ray crystal structures of three N-arenemethyl derivatives were elucidated. These are each closely related in conformation about the C1-C1' axis. Reaction of two examples of the N-arenealkyl compounds with copper(II) and palladium(II) chlorides, furnished the first known examples of this type of highly reduced 1,1'-bisisoquinoline-metal complex. Single crystal X-ray crystallography was used to analyse the structures of these complexes in the solid state. Preliminary physicochemical investigations were conducted with a view to determining the conformation of the molecules about the bisisoquinoline C1-C1' bond. The interaction of intermolecular N-aryl π-excessive compounds with π-deficient systems was found to result in minimal spectroscopic changes. Complementary intramolecular π-excessive/π-deficient systems were found through fluorometric analysis to readily form charge transfer complexes. Finally, it was determined that the conformation of 1,1'-bis[2-(methoxy-18- crown-6)ethanoyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline] could be controlled by the simultaneous coordination of the termini of the diperchlorate salt of 1,3-diaminopropane to the crown ether moieties of the ligand. A range of new N-substituted bisisoquinolines have been synthesised and methods developed for determining interactions between parts of these molecules that through these physicochemical characteristics could allow monitoring of conformational behaviour in future studies. Keywords: 1,1'-bisisoquinoline, conformational analysis, supramolecular chemistry, functional ligands, metal complexes.
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