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

Research output: Contribution to journalArticlepeer-review

149 Scopus citations

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
StatePublished - Jan 22 2004
Externally publishedYes

Keywords

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

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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