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

Abstract

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 (H2salamo = 1,2‐bis(salicylideneaminooxy)ethane) with zinc(II) and cobalt(II) afforded trinuclear complexes [M3L2(OAc)2] (M = ZnII, CoII; L = salamo, 3‐MeOsalamo). The phenoxo groups of the two [ML] units coordinate to the third MII, which results in the trinuclear structure. Upon complexation with nickel(II) acetate, the parent H2salamo gave a trinuclear complex [Ni3(salamo)2(OAc)2(EtOH)2], whereas H2(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 (H2salbn), 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 [Zn3(3‐MeOsalamo)2(OAc)2] was formed cooperatively, whereas the imine analog [Zn3(3‐MeOsalbn)2(OAc)2] was not.

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

“…We employed salamo derivatives, the oxime analog of salen, as the constituent of the oligomers (H 2 salamo = 1,2-bis(salicylideneaminooxy)ethane) [47,48]. The salamo ligands show a high stability to suppress the C=N bond recombination to facilitate the synthesis of acyclic salamo oligomers, keeping the tetradentate coordination ability for various transition metals [49][50][51][52][53][54][55]. When each of the salamo units in an oligo(salamo) ligand accommodates a metal ion in a tetradentate fashion, its structure is fixed in a curved conformation due to the newly formed coordination bonds (Figure 5b).…”