Isomerization reactions in anionic mesoionic carbene-borates and control of properties and reactivities in the resulting coII complexes through agostic interactions

Jessica Stubbe, Nicolás Neuman, Ross McLellan, Michael Sommer, Maite Nößler, Julia Beerhues, Robert Mulvey, Biprajit Sarkar Sarkar

Research output: Contribution to journalArticle

Abstract

We present here anionic borate based bi-mesoionic carbene compounds of the 1,2,3-triazol-4-ylidene type (with additional cyclohexyl or phenyl substituents on borate) that undergo C-N isomerization reactions. The isomerized compounds are excellent ligands for CoII centers. Strong agostic interactions with the „C-H“-groups of the cyclohexyl substituents result in an unusual low spin square planar CoII complex, which is unreactive towards external substrates. Such agostic interactions are absent in the complex with phenyl substituents on the borate backbone. That complex displays a high spin tetrahedral CoII center, which is reactive towards external substrates including dioxygen. A combined synthetic, crystallographic, spectroscopic and theoretical approach is used to investigate the compounds. To the best of our knowledge, this is also the first investigation of agostic interactions through single crystal EPR spectroscopy. We conclusively show here that the structure and properties of these CoII complexes can be strongly influenced through interactions in the secondary coordination sphere. Additionally, we unravel a unique ligand rearrangement for these classes of anionic mesoionic carbene based ligands.
Original languageEnglish
Number of pages17
JournalAngewandte Chemie International Edition
Early online date20 Oct 2020
DOIs
Publication statusE-pub ahead of print - 20 Oct 2020

Keywords

  • cobalt
  • mesoionic carbene
  • EPR spectroscopy
  • ligand rearrangement
  • spin state
  • reactivity

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