First Schiff base of vinylamine and an α-diketone: a novel N,N donor ligand with extensive conjugation. Synthesis, properties and its copper(I) complexes

Abstract

Exhaustive methylation of 8,8a-diphenyl-1,2,3,5,6,8a-hexahydroimidazo[1,2-a]pyrazine by NaH and CH₃I in dehydrated tetrahydrofuran yielded 4,5-diphenyl-3,6-diazaocta-1,3,5,7-tetraene (1). Using 1 as an N,N donor ligand, cationic copper(I) complexes of the type [Cu(1)₂]X·nH₂O (X⁻ = ClO₄⁻, n = 1.5; X⁻ = PF₆⁻, n = 0) and [Cu(1)(PPh₃)₂]X (X⁻ = ClO₄⁻ or PF₆⁻) have been synthesized. Compound 1 and its copper(I) complexes have been thoroughly characterised by ¹H NMR (300 MHz). The Cu^II/I potential in [Cu(1)₂]X·nH₂O is rather high, 0.92 V vs. SCE in CH₂Cl₂ at a glassy carbon electrode. This indicates that 1 is a potential π acid which preferentially stabilises copper(I) much more than copper(II). It is photoluminescent in fluid solution, its emission being somewhat quenched in [Cu(1)₂]X·nH₂O.