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 σ-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)NiCl 2 ] and [(6,6′-Me 2 bipy)NiCl 2 ]. 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 σ-phenyl complexes [(teeda)Pd(Ph)I] and [(dpe)Pd(Ph)I], much like the previously reported reaction with tmeda.