New Ni(II) complexes based on NNN pincer ligands: syntheses, structures and B-F cleavage of BF4- promoted by a di-cationic Ni(II) center

A neutral complex [Ni(L1)Cl-2] (1) with trigonal bipyramidal geometry at Ni(II) was prepared by the reaction of NiCl2 with 2,6-bis(isopropylaminomethyl)pyridine (L1) in THF and then a mono-cationic complex [Ni(L1)Cl](BF4) (2) and di-cationic complex [Ni(L1)(CH3CN)(3)](BF4)(2) (3) could be obtained by extracting one or two Cl- ions from 1 with one or two equivalents of AgBF4 in THF or acetonitrile, respectively. Similarly, a neutral complex Ni(L2)Cl-2 (4) was formed by reaction of NiCl2 with 2,6-bis(diethylaminomethyl)pyridine (L2), and the experimental results indicate that Ni(II) of 4 adopts a slightly distorted square pyramidal geometry, which is different from that of 1. Although the reaction of 4 with one equivalent of AgBF4 resulted in a mono-cationic complex, [Ni(L2)Cl]BF4 (5), with Ni(II) in a slightly distorted square planar coordination geometry, an unexpected dinuclear Ni(II) complex [Ni(L2-H)(MeOH)F(-F)](2)(BF4)(2) (6) with two fluoride ligands bridging the two Ni(II) centers rather than a di-cationic Ni(II) complex was formed by extracting two Cl- anions from 4 through the reaction with two equivalents of AgBF4 in methanol. Complexes 1-6 were characterized by elemental analysis and IR, and structures of 1, 3, 4, 5, and 6 were confirmed by X-ray diffraction analysis.