Synthesis and Crystal Structures of an Unexpected Tetranuclear Zinc(II) Complex and a Benzoquinone Compound Derived from Zn II ‐ and Cd II ‐Promoted Reactivity of Schiff Base Ligands

An unexpected polyhydroxyl‐bridged tetranuclear Zn II complex and a benzoquinone compound derived from metal‐ion promoted reactivity of Schiff base ligands were synthesized and characterized. The reaction of zinc(II) acetate dihydrate with oxime‐type Schiff base ligand HL 1 [HL 1 = 1‐(3‐((3,5‐dibromosalicylaldehyde)amino)phenyl)ethan‐1‐one O ‐benzyl oxime] in methanol, acetone, and acetonitrile resulted in the chemoselective cleavage of the C=N bond of the Schiff base HL 1 , and then the further addition of acetone to two salicylaldehyde molecules derived from cleavage of the C=N bond in situ α,α double aldol reaction promoted by Zn II ions. The newly formed ligands H 4 L 2 coordinate to four Zn II ions forming a defect‐dicubane core structure [Zn II 4 (H 2 L 2 ) 2 (μ 3 ‐OCH 3 ) 2 (μ‐OCH 3 ) 2 (CH 3 OH) 2 ] ( 1 ) bridged exclusively by oxygen‐based ligands. The similar ligand HL 3 [HL 3 = 1‐(3‐((3,5‐dichlorosalicylaldehyde)amino)phenyl)ethan‐1‐one O ‐benzyl oxime)] was employed to react with Cd II acetate dihydrate under the same reaction conditions. No aldol addition occurred but a unexpected benzoquinone compound 2,5‐bis(((3‐(1‐((benzyloxy)imino)ethyl)phenyl)imino)methyl)‐1,4‐benzoquinone ( 2 ) formed. The results provided interesting insights into one‐pot routes involving in situ reactions act as a strategy for obtaining a variety of polymeric/polynuclear complexes which are inconvenient to obtain from directly presynthesizing the ligands.