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Pyrazole-Based PCN Pincer Complexes of Palladium(II): Mono- and Dinuclear Hydroxide Complexes and Ligand Rollover C–H Activation

  • Wilson Bailey
    ,
  • Lapo Luconi
    ,
  • Andrea Rossin
    ,
  • Dmitry Yakhvarov
    ,
  • Sarah E. Flowers
    ,
  • Werner Kaminsky
  • Chemistry & Biochemistry
    ,
  • Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali
    ,
  • Institute of Chemistry of Organometallic Compounds
    ,
  • Kazan Federal University
    ,
  • University of Washington
    ,
  • University of New Mexico
Research Output: Contribution to journal Article Peer-review

Abstract

Palladium complexes of the novel unsymmetrical phosphine pyrazole-containing pincer ligands PCNH (PCNH = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole) and PCNMe (PCNMe = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-5-methyl-1H-pyrazole) have been prepared and characterized through single-crystal X-ray diffraction and multinuclear 1H, 13C{1H}, and 31P{1H} NMR spectroscopy. In preparations of the monomeric hydroxide species (PCNH)Pd(OH), an unexpected N detachment followed by C–H activation on the heterocycle 5-position took place resulting in conversion of the monoanionic {P,C–,N} framework into a dianionic {P,C–,C–} ligand set. The dinuclear hydroxide-bridged species (PCNH)Pd(μ-OH)Pd(PCC) was the final product obtained under ambient conditions. The “rollover” activation was followed via 31P{1H} NMR spectroscopy, and dinuclear cationic μ-OH and monomeric PdII hydroxide intermediates were identified. DFT computational analysis of the process (M06//6-31G*, THF) showed that the energy barriers for the pyrazolyl rollover and for C–H activation through a σ-bond metathesis reaction are low enough to be overcome under ambient-temperature conditions, in line with the experimental findings. In contrast to the PCNH system, no “rollover” reactivity was observed in the PCNMe system, and the terminal hydroxide complex (PCNMe)Pd(OH) could be readily isolated and fully characterized.

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Bibliographic Information

Output type

Research Output: Contribution to journal Article Peer-review

Original language

American English

Pages from-to (Number of pages)

Pages 3998-4010 (13 pages)

Journal (Volume, Issue Number)

Organometallics (Volume 34, Issue 16)

Publication milestones

  • Published - 31/07/2015

Publication status

Published - 31/07/2015

ISSN

0276-7333

Publication IDs

  • Scopus: 84940213856