Metal complexes of a new bis(salicylidene) bicycle diamine ligand

The rigidity of cis-endo-2,3-diaminobicyclo[2.2.2]oct-5-ene (1) locks the nitrogens into spatial positions that are favorable to metal binding and should result in thermodynamically and kinetically more stable metal ligand complexes. Condensation of 1 and salicylaldehyde affords the N,N{prime}-bis(salicyclidene)-cis-endo-2,3-diamino-bicyclo[2.2.2]oct-5-ene (2) in high yield. X-ray diffraction of 2 shows that the nitrogens are cis and endo and that the phenolic hydrogens are hydrogen bonded to the nitrogens. The ligand 2 was found to form neutral complexes with divalent metals such as cobalt, nickel, and copper. X-ray crystal studies of the nickel complex (which contains one CHCl{sub 3} per Ni) showed a square planar arrangement of the coordinating groups around the metal. The nickel and the salicyclidene moieties roughly lie in the plane defined by carbons 2 and 3 and the two nitrogens.