Activation of chlorobenzene with Ni(0) N,N-chelates -: A remarkably profound effect of a minuscule change in ligand structure

Activation of the C-Cl bond of chlorbenzene with [(COD)(2)Ni] and a bidentate N,N-ligand such as N,N,N',N'-tetramethylethylenediamine (tmeda) and 2,2'- bipyridyl (bipy) has been reported to produce sigma-phenyl complexes [(tmeda)Ni(Ph)Cl] (1) and [(bipy)Ni(Ph)Cl], respectively. However, in sharp contrast, we found that similar reactions involving almost the identical ligands N,N,N',N'-tetraethylethylenediamine (teeda) and 6,6'-dimethyl-2,2'-bipyridyl (6,6'-Me(2)bipy) resulted in homocoupling and the formation of non-organometallic dichlorocomplexes [(teeda)NiCl2] and [(6,6'-Me(2)bipy)NiCl2]. The latter two compounds and 1 were characterized by single-crystal X-ray diffraction data. The remarkable change in the reaction outcome points to its extremely high sensitivity to minor alterations in the structure of the stabilizing N,N-ligand. In contrast, analogous reactions of [Pd(dba)(2)] with PhI in the presence of teeda or 1,2-dipiperidinoethane (dpe) produced the expected sigma-phenyl complexes [(teeda)Pd(Ph)I] and [(dpe)Pd(Ph)I], much like the previously reported reaction with tmeda.