New copper(I) and silver(I) triazolato-complexes: Synthesis, reactivity and catalytic activity in olefin cyclopropanation

A new class of azolate ligands, deriving from the equimolar condensation of 3,5-diamino-1,2,4-triazole with salicylaldehyde (H3L1) and o-anisaldehyde (H3L2) was prepared. In their anionic form, these species act as bridging moieties upon coordination to Cu(I) and Ag(I), giving rise to the formation of dinuclear complexes with the ligand in the typical N,N′-exobidentate conformation. The copper derivative [Cu(H2L1)(CH3CN)]2 (1) showed attractive reactivity in the replacement of the labile acetonitrile molecules. In particular, it was possible to isolate a dinuclear copper(I)-carbonyl complex [Cu(H2L1)(CO)]2 (4), by substitution of the nitrile with carbon monoxide. Moreover, the reaction of 1 with ethyl diazoacetate (EDA) in CH2Cl2 afforded a mono-carbene product, as established by 13C NMR data. Finally, the copper derivative 1 proved to be a highly diastereoselective catalyst in olefin cyclopropanation in the presence of ethyl diazoacetate. In the case of internal alkenes a trans:cis ratio of up to 97:3 was reached. The X-ray structure of a dinuclear Ag(I) complex, namely [Ag(H2L1)(PPh3)]2 (3), obtained by reacting the polymeric [Ag(H2L1)]n (2), with triphenylphosphine, is also reported.