Formazanate Ligands as Structurally Versatile, Redox-Active Analogues of beta-Diketiminates in Zinc Chemistry

Mu-Chieh Chang, Peter Roewen, Raquel Travieso-Puente, Martin Lutz, Edwin Otten*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

53 Citations (Scopus)
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Abstract

A range of tetrahedral bis(formazanate)zinc complexes with different steric and electronic properties of the formazanate ligands were synthesized. The solid-state structures for several of these were determined by X-ray crystallography, which showed that complexes with symmetrical, unhindered ligands prefer coordination to the zinc center via the terminal N atoms of the NNCNN ligand backbone. Steric or electronic modifications can override this preference and give rise to solid-state structures in which the formazanate ligand forms a 5-membered chelate by binding to the metal center via an internal N atom. In solution, these compounds show dynamic equilibria that involve both 5- and 6-membered chelates. All compounds are intensely colored, and the effect of the ligand substitution pattern on the UV-vis absorption spectra was evaluated. In addition, their cyclic voltammetry is reported, which shows that all compounds may be electrochemically reduced to radical anionic (L2Zn-) and dianionic (L2Zn2-) forms. While unhindered NAr substituents lie in the plane of the ligand backbone (Ar = Ph), the introduction of sterically demanding substituents (Ar = Mes) favors a perpendicular orientation in which the NMes group is no longer in conjugation with the backbone, resulting in hypsochromic shifts in the absorption spectra. The redox potentials in the series of L2Zn compounds may be altered in a straightforward manner over a relatively wide range (similar to 700 mV) via the introduction of electron-donating or -withdrawing substituents on the formazanate framework.

Original languageEnglish
Pages (from-to)379-388
Number of pages10
JournalInorganic Chemistry
Volume54
Issue number1
DOIs
Publication statusPublished - 5-Jan-2015

Keywords

  • BORON DIFLUORIDE COMPLEXES
  • SUPRAMOLECULAR ARCHITECTURE
  • PENTADIENYL COMPLEXES
  • MOLECULAR-STRUCTURES
  • METAL-COMPLEXES
  • COPPER(I)
  • SALTS
  • 1-(2-HYDROXYPHENYL)-3,5-DIPHENYLFORMAZAN
  • BIS(PENTAFLUOROPHENYL)ZINC
  • 1,3,5-TRIAZAPENTADIENES

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