Increased Nuclearity of Salen-Type Transition Metal Complexes by Incorporation of O-Alkyloxime Functionality

The effect of incorporation of O-alkyloxime functionality in the salen-type tetradentate ligand was investigated from a viewpoint of complexation behavior with cobalt(II), nickel(II), and zinc(II). The complexation of salamo ligands (H(2)salamo = 1,2-bis(salicylideneaminooxy)ethane) with zinc(II) and cobalt(II) afforded trinuclear complexes [M3L2(OAc)(2)] (M = Zn-II, Co-II; L = salamo, 3-MeOsalamo). The phenoxo groups of the two [ML] units coordinate to the third M-II, which results in the trinuclear structure. Upon complexation with nickel(II) acetate, the parent H(2)salamo gave a trinuclear complex [Ni-3(salamo)(2)(OAc)(2)(EtOH)(2)], whereas H-2(3-MeOsalamo) produced a mononuclear complex [Ni(3-MeOsalamo)(H2O)(2)]. The salamo complexes described here are similar to the corresponding complexes with N,N-disalicylidene-1,4-diaminobutane (H(2)salbn), indicating that the difference between the -OCH2CH2O- and -(CH2)(4)- groups has a small influence on the structural features of the complexes. However, this difference affects the complexation process with zinc(II) acetate. The trinuclear complex [Zn-3(3-MeOsalamo)(2)(OAc)(2)] was formed cooperatively, whereas the imine analog [Zn-3(3-MeOsalbn)(2)(OAc)(2)] was not.