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

Journal article, 2010

The reactions of six diimine ligands with Cu(II) and Ni(II) halide salts have been investigated. The diimine ligands were Ph2C=N(CH2)(n)NC=Ph-2 (n = 2 (Bz(2)en, 1a), 3 (Bz(2)pn, 1b), 4 (Bz2bn, 1c)), N, N'-bis-(2-tert-butylthio- 1-ylmethylenebenzene)-2,2'diamino-biphenyl (2), N,N'-bis-(2-chloro-1-ylmethylenebenzene)-1,3diaminobenzene (3) and N,N'-bis-(2-chloro-1-ylmethylenebenzene)-1,2-ethanediamine (4). Reactions of 1a-c, 2-4 with CuCl2 center dot 2H(2)O 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 NiCl2 center dot 6H(2)O or [NiBr2(dme)] led to rapid hydrolysis of the imines and Ni complexes containing half-hydrolyzed 1a (Bzen; [trans-[Ni(Bzen)(2)Br-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.