An investigation of Cu(II) and Ni(II)-catalysed hydrolysis of (di)imines

Abstract

The reactions of six diimine ligands with Cu(II) and Ni(II) halide salts have been investigated. The diimine ligands were Ph 2C N(CH 2) n NC Ph 2 ( n = 2 (Bz 2en, 1a), 3 (Bz 2pn, 1b), 4 (Bz 2bn, 1c)), N, N′-bis-(2- tert-butylthio-1-ylmethylenebenzene)-2,2′diamino-biphenyl ( 2), N, N′-bis-(2-chloro-1-ylmethylenebenzene)-1,3-diaminobenzene ( 3) and N, N′-bis-(2-chloro-1-ylmethylenebenzene)-1,2-ethanediamine ( 4). Reactions of 1a– c, 2– 4 with CuCl 2·2H 2O in dry ethanol at ambient temperature led to complete or partial hydrolysis of the diimine ligands to ultimately form copper diamine complexes. The non-hydrolyzed complexes of 1b and 1c, [Cu(L)Cl 2] (L = 1b, 1c), could be isolated when the reactions were carried out at low temperatures, and the half-hydrolyzed complex [Cu(Bzpn)Cl 2] could also be identified via X-ray crystallography. Similarly, reactions of 1a or 1b with NiCl 2·6H 2O or [NiBr 2(dme)] led to rapid hydrolysis of the imines and Ni complexes containing half-hydrolyzed 1a (Bzen; [ trans-[Ni(Bzen) 2Br 2]) and 1b (Bzpn; [Ni(Bzpn)Br 2] could be isolated and identified via single crystal X-ray analysis. Kinetic studies were made of the hydrolyses of 1a, 1b in THF and 2 in acetone, in the presence of Cu(II), and of 1a in acetonitrile, in the presence of Ni(II). Activation parameters were determined for the latter reaction and for the copper-catalyzed hydrolysis of 2; the relatively large negative activation entropies clearly indicate rate-determining steps of an associative nature.