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 CuII/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.