Rhodium and iridium complexes of N-heterocyclic carbenes: Structural investigations and their catalytic properties in the borylation reaction

Guido D. Frey, Christoph F. Rentzsch, Denise von Preysing, Tobias Scherg, Michael Mühlhofer, Eberhardt Herdtweck, Wolfgang A. Herrmann

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Abstract

Bridged and unbridged N-heterocyclic carbene (NHC) ligands are metalated with [Ir/Rh(COD)2Cl]2 to give rhodium(I/III) and iridium(I) mono- and biscarbene substituted complexes. All complexes were characterized by spectroscopy, in addition [Ir(COD)(NHC)2][Cl,I] [COD = 1,5-cyclooctadiene, NHC = 1,3-dimethyl- or 1,3-dicyclohexylimidazolin-2-ylidene] (1, 4), and the biscarbene chelate complexes 12 [(η4-1,5-cyclooctadiene)(1,1′-di-n-butyl-3,3′-ethylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] and 14 [(η4-1,5-cyclooctadiene)(1,1′-dimethyl-3,3′-o-xylylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] were characterized by single crystal X-ray analysis. The relative σ-donor/π-acceptor qualities of various NHC ligands were examined and classified in monosubstituted NHC-Rh and NHC-Ir dicarbonyl complexes by means of IR spectroscopy. For the first time, bis(carbene) substituted iridium complexes were used as catalysts in the synthesis of arylboronic acids starting from pinacolborane and arene derivatives.

Original languageEnglish
Pages (from-to)5725-5738
Number of pages14
JournalJournal of Organometallic Chemistry
Volume691
Issue number26
DOIs
StatePublished - 15 Dec 2006

Keywords

  • Carbene complexes
  • Catalysis
  • Coupling
  • Hydroborations
  • Iridium
  • Rhodium

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