Insertion of unsaturations into the 1,4,7-triazacyclononane skeleton. Photochemical reaction between benzil and diethylenetriamine: synthesis and properties of 2,3-diphenyl-1,4,7-triazacyclonona-1,3-diene

Abstract

Photochemical reaction between benzil and diethylenetriamine (dien) in anhydrous methanol in the presence of oxygen yields a novel triaza macrocycle 2,3-diphenyl-1,4,7-triazacyclonona-1,3-diene (L). It was characterised by FTIR, EI mass and NMR (¹H and ¹³C) spectra. A comparative study between the various physicochemical properties of L and the product (L₁; reported earlier by others) of the thermal reaction between benzil and dien is made in detail. L and L₁ can be regarded as isomers. While L₁ cannot be converted to L by UV radiation, L is transformed into L₁ upon refluxing in anhydrous methanol. The macrocycle L affords cationic copper(I) complexes of the type [CuL]X (X=ClO₄⁻ and PF₆⁻). Cyclic voltammetry and coulometry at platinum electrodes in dimethylformamide under an N₂ atmosphere show that the Cu^II/I potential in [CuL]X is 0.25 V s. SCE. This indicates that L is a weak π-acid. L is photoluminescent in methanol at room temperature (emission maxima λ_em=380 nm; quantum yield φ=1.96×10⁻²). Its emission when in the form of [CuL]X in methanol is quenched considerably (λ_em=370 nm; φ=6.2–6.7×10⁻³).