Three Types of Nickel(II) Complexes Derived from 2-Substituted Benzothiazoline; Formation of a Tetranuclear Complex by a Sterically Induced Orthometallation Reaction

The reaction of 2-(2,4-dichlorophenyl)benzothiazoline with nickel (II) acetate tetrahydrate in ethanol has afforded the monohelical bis[2-(2,4-dichlorophenylmethyleneamino)benzenethiolato]nickel(II) ([Ni(HL 1 ) 2 ] (1)). The X-ray structure of 1 has revealed that ortho-phenyl hydrogen atoms of pendant arms are oriented to the nickel center in a monohelical structure. The low-field resonance for their ortho-protons in the 1 H NMR spectrum indicates that the Ni...H-C interaction is maintained in solution. Heating 1 in toluene gave a square-planar nickel(II) complex with a non-innocent ligand ([Ni(L 2 )] (2)), and prolonged heating yielded a thiolato-bridged tetranuclear nickel(II) complex ([Ni 4 (L 1 ) 4 ] (3)). The tetranuclear complex 3 was formed from activation of the ortho C-H bond, not the C-Cl bond, through sterically controlled Ni...H-C contacts in 1. The molecular structures of 2 and 3 have also been determined by X-ray crystallographic methods.