Bis(diazadien)metall(O)-Komplexe, III. Nickel(O)-bis(chelate) mit aliphatischen N-Substituenten/ Bis(diazadien)metal(O) Complexes, III. Nickel(O)-bis(chelates) with Aliphatic N-Substituents

Diazadienes (DAD) (with R 1 , R 2 = H, CH 3 and R 3 , R 4 = alkyl) form nickel complexes 1-14 with composition (DAD) 2 Ni. They can be prepared by ligand substitution from other Ni(O) compounds or, preferably, by the reduction of Ni(II) salts in the presence of DAD. Spectroscopic differences (NMR, UV) indicate different structures (type 1 and 2) for diamagnetic (DAD) 2 Ni of same composition, depending on substituents R 1 -R 4 . The steric requirement of R 3 , R 4 is most important as the main differences show up when going from tertiary (type 1: R 2 CH-N = ) to secondary a-carbon (type 2: RCH2-N = ) . X-ray analysis of a type 1 complex (R 1 , R 2 = H, R 3 , R 4 = cyclo-hexyl) reveals two strictly orthogonal chelate rings (D 2d ) corresponding to (pseudo-)tetrahedrally coordinated Nickel(O). A D 2 -structure with smaller dihedral angle is discussed for type 2 complexes.