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

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-dipheny l-3,6-diazaocta-1,3,5,7-tetraene (1). Using 1 as an N,N donor ligand, catio nic copper(I) complexes of the type [Cu(1)(2)]X . nH(2)O (X-=ClO4-, n=1.5; X-=PF6-, n=0) and [Cu(1)(PPh3)(2)]X (X-=ClO4- or PF6-) have been synthesize d. Compound 1 and its copper(I) complexes have been thoroughly characterise d by H-1 NMR (300 MHz). The Cu-II/I potential in [Cu(1)(2)]X . nH(2)O is ra ther high, 0.92 V vs. SCE in CH2Cl2 at a glassy carbon electrode. This indi cates that 1 is a potential pi 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 . nH(2)O.