TY - JOUR
T1 - Synthesis and characterization of cyclometalated Ir(III) complexes with pyrazolyl ancillary ligands
AU - Li, Jian
AU - Djurovich, Peter I.
AU - Alleyne, Bert D.
AU - Tsyba, Irina
AU - Ho, Nam N.
AU - Bau, Robert
AU - Thompson, Mark E.
N1 - Funding Information:
The authors thank Universal Display Corporation and the Defense Advanced Research Projects Agency for financial support of this work.
PY - 2004/1/22
Y1 - 2004/1/22
N2 - 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.
AB - 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.
KW - Boat conformations
KW - Cyclometalated Ir(II) complexes
KW - Electroluminescence
KW - Iridium
KW - Luminescent
KW - Pyrazolyl ancillary ligands
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U2 - 10.1016/j.poly.2003.11.028
DO - 10.1016/j.poly.2003.11.028
M3 - Article
AN - SCOPUS:0842332882
SN - 0277-5387
VL - 23
SP - 419
EP - 428
JO - Polyhedron
JF - Polyhedron
IS - 2-3
ER -