LIGAND CONFIGURATION ON WEAKLY PARAMAGNETIC (BETA-IMINO CARBONYL ENOLATO)NICKEL COMPLEXES - A COMBINED SOLID-STATE C-13 NMR AND INFRARED STUDY

The two forms of the [Ni((MeCO)2CC(COPh)NH)2] complex resulting from the reaction of bis(acetylacetonato)-nickel(II) with benzoyl cyanide have been studied by C-13 CP/MAS NMR and FT-IR techniques. Despite their paramagnetism (mu = 0.61 (form I), 0.57 (form II) mu(B)), the C-13 signals in the solid state are narrow and well resolved, so that specific isotopic enrichment allows a safe signal attribution. In both cases the data indicate that the trifunctional (N,O,O) beta-imino carbonyl enolato ligand is bonded to the nickel center via the nitrogen and oxygen atoms. The same behavior and type of ligand coordination is observed in the two forms of the related cyanogen derivative [Ni((MeCO)2CC(CN)NH)2] (mu = 0.68 and 0.50 mu(B)). A correlation is found between the carbonyl chemical shift of the uncoordinated acetyl group and its torsion angle relative to the {NiNONO} plane, which indicates that, for both complexes, the two isolable forms are ligand conformation isomers.