From Multifunctional Precursor to Novel Reaction Products: Oligimerization and Central Metal Ion Exchange Reaction of Ferrocenyl Carboxylate Complexes

A distinctive multifunctional precursor complex Zn(bafca)₂(phen)(H₂O), 1 (bafca⁻ = α-benzamido-β-ferrocenylacrylic carboxylate; phen = 1,10-phenantholine), is synthesized. As an acceptor, it takes part in the oligimerization to produce a novel decanuclear Zn(II) cluster, [Zn(OCH₃)(HOCH₃)(bafca)]₁₀·8H₂O, 1A; as a donor, it undergoes the unusual central metal ion exchange reaction, resulting in a new Cd(II) skeleton, [Cd(bafca)₂(phen)]₂·8H₂O, 1B. X-ray crystallographic analysis shows that the molecule of 1A consists of a centrosymmetric ring comprised of 10 Zn(II) ions held together by 10 μ₂-methoxide, 10 μ₂-methanol, 10 1,3-bridging bafca⁻ ligands. In the ring, the 10 zinc atoms are approximately coplanar and are coordinated in a distorted octahedral manner by six oxygen donor atoms. Compound 1A is the analogue of Lippard’s famous “ferric wheel” [Fe(OMe)₂(O₂CCH₂Cl)]₁₀ of bivalent metal ions (Lippard and coworkers J. Am. Chem. Soc. 1990, 112, 9629; 1994, 116, 823), and its synthesis proves that the bivalent metal ions can also form such wheel structures. Compound 1B has a dinuclear structure with the Cd ions, which are linked by two tridentate bafca⁻. In addition, we verify that the oligimerization of metal−carboxylate complexes with methanol under basic conditions is a relatively reliable synthetic route to produce wheel structures by the synthesis of a similar planar decanuclear Cd(II) wheel of formula [Cd(OCH₃)(HOCH₃)(bafca)]₁₀·8H₂O·6CH₃OH, 2A, which is obtained from the precursor [Cd(bafca)₂(H₂O)₂]₂, 2 or 1B, under the same reaction conditions as those used for the preparation of 1A. The strong electrochemical responses of precursors 1 and 2 to 1,1′-(1,4-butanediyl)bis-1H-benzotriazole (bbbt) verify further that N-containing ligands play an important role in the formation of 1A or 2A.