Synthesis and characterization of cyclometalated Ir(III) complexes with pyrazolyl ancillary ligands

Jian Li, Peter I. Djurovich, Bert D. Alleyne, Irina Tsyba, Nam N. Ho, Robert Bau, Mark E. Thompson

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Abstract

The syntheses and structures of a series of (N,C2′-(2-para- tolylpyridine))2Ir(LX) [(tpy)2Ir(LX)] and (N,C2′-(4′,6′-difluorophenylpyridine))2Ir(LX) [(dfppy)2Ir(LX)] are reported, where LX are pyrazolyl and pyrazolyl-borate ligands. Reaction of the dichloro-bridged dimer [(tpy) 2Ir(μ-Cl)]2 with excess pyrazolyl-borate ligands forms a protonated-dipyrazolyl Ir complex, (tpy)2Ir(pz2H). The Ir bound chloride in [(tpy)2Ir(μ-Cl)]2 presumably facilitates the hydrolysis of pyrazolyl-borate. Thus, the syntheses of Ir complexes with bis(pyrazolyl)borates, e.g., (tpy)2Ir(pz 2Bpz2) and (tpy)2Ir(pz2BEt 2) require the chloride abstraction by CF3SO 3Ag before pyrazolyl-borate is added to the reaction solution. (tpy)2Ir(pz2H), (tpy)2Ir(pzH) 2(CF3SO3), (tpy)2Ir(pz 2Bpz2) and (tpy)2Ir(pz2BEt 2) have been structurally characterized by X-ray crystallography. The two pyrazolyl rings of (tpy)2Ir(pz2H) are nearly coplanar (dihedral angle, 12°), due to the presence of N-HN hydrogen bond (NN distance of 2.56 Å), while the two pyrazolyl rings of (tpy) 2Ir(pzH)2(CF3SO3) are not coplanar (pz-pz dihedral angle, 47°). Unlike other η2-pyrazolyl- borate complexes, the (tpy)2Ir(pz2BEt2) exhibits a rare quasi-chair conformation adopted by the ring, rather than the more common boat conformations which have been observed previously. Similarly, the cycle of (tpy)2Ir(pz2Bpz2) adopts a half-chair conformation, more flattened than the typical boat conformation. While the choice of pyrazolyl-borate ligand does not change the structural properties of the "(tpy)2Ir" fragment, it markedly affects the photophysical properties of both (tpy)2Ir(pz2BR 2) and (dfppy)2Ir(pz2BR2) complexes. The pyrazolyl-borate ancillary ligands affect the absorption and emission energies of these complexes by tuning the HOMO (highest occupied molecular orbital) energies. The electron-withdrawing ancillary ligands, e.g., pz 2Bpz2 -, decrease the electron density on the iridium, stabilizing the metal-centered HOMOs.

Original languageEnglish (US)
Pages (from-to)419-428
Number of pages10
JournalPolyhedron
Volume23
Issue number2-3
DOIs
Publication statusPublished - Jan 22 2004
Externally publishedYes

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Keywords

  • Boat conformations
  • Cyclometalated Ir(II) complexes
  • Electroluminescence
  • Iridium
  • Luminescent
  • Pyrazolyl ancillary ligands

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry
  • Physical and Theoretical Chemistry
  • Materials Chemistry

Cite this

Li, J., Djurovich, P. I., Alleyne, B. D., Tsyba, I., Ho, N. N., Bau, R., & Thompson, M. E. (2004). Synthesis and characterization of cyclometalated Ir(III) complexes with pyrazolyl ancillary ligands. Polyhedron, 23(2-3), 419-428. https://doi.org/10.1016/j.poly.2003.11.028