While mononuclear, polynuclear, and polymeric metal complexes are most often synthesized by the reaction of a metal precursor and a presynthesized organic ligand, it is also possible to generate the ligand in situ from an easily available organic compound. This approach allows the reactivity of the metal ion to activate a proligand, transforming it through an in situ reaction, sometimes providing coordination compounds with ligands not accessible by conventional organic synthesis. The intense interest in the reactivity of coordinated ligands is mainly due to the necessity of interpreting the mechanisms of homogeneous metal-catalyzed processes, in which a substrate is activated upon its coordination to one or more metal sites. A coordinated oxime group contains three active sites (C, N, O) for reactivity.
Researchers from Patras (Greece), Nicosia (Cyprus), Karlsruhe (Germany), Zaragoza (Spain), and the ALS at Berkeley Lab have studied metal-ion-mediated reactions of 2-pyridinealdoxime (the simplest 2-pyridyl oxime and the only aldoxime in this family) and observed novel transformations of the ligand. A cationic nitrato zinc(II) complex possessing both the 2-pyridinealdoxime and picolinic acid ligands have been prepared from the reaction of zinc nitrate and the oxime ligand in refluxing methanol. The formation of the complex is triggered by the zinc ion-assisted hydrolysis of an amount of 2-pyridinealdoxime to the corresponding aldehyde, followed by the atmospheric oxygen oxidation of the latter to picolinic acid. The authors believe that metal-mediated reactions of 2-pyridyl oximes are still in their infancy; ongoing studies in their groups reveal impressive transformations.
The preliminary results of this research are in press in the Royal Society of Chemistry journal Dalton Transactions (DOI: 10.1039/c1dt11881a) and the Communication has been selected as a Dalton Transactions Hot Article.
The zinc(II)-assisted transformation of 2-pyridinealdoxime to picolinic acid and structural features of the resulting cationic complex; this transformation illustrates the rich reactivity chemistry of the coordinated oxime group.
Work performed on ALS Beamline 11.3.1
Citation: K.F. Konidaris, C.D. Polyzou, G.E. Kostakis, A.J. Tasiopoulos, O. Roubeau, S.J. Teat, E. Manessi-Zoupa, A.K. Powell, and S.P. Perlepes, “Metal ion-assisted transformations of 2-pyridinealdoxime and hexafluorophosphate,” Dalton Transactions, (2012). DOI: 10.1039/c1dt11881a
This work was featured on the cover of Dalton Transactions: Metal Ion-Assisted Transformations of 2-Pyridinealdoxime and Hexafluorophosphate.