- Synthesis and electronic investigation of mono- and di-substituted 4-nitro- and 4-amino-pyrazol-1-yl bis(pyrazol-1-yl)pyridine-type ligands and luminescent Eu(III) derivatives
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Four new disubstituted and monosubstituted nitro- and amino- bis(pyrazol-1-yl)pyridine (bppy) ligands, substituted at the pyrazole 4-position (1, 2, 5, 6) have been synthesized, along with two luminescent Eu(iii) tris-β-diketonate derivatives of the amino
- Strohecker,Lynch,Holliday,Jones
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- Selective C-N bond-forming reaction of 2,6-dibromopyridine with amines
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A practical and efficient protocol for the syntheses of 6-substituted 2-bromopyridine compounds has been developed by using a selective copper-catalyzed C-N bond-forming reaction between 2,6-dibromopyridine and a range of amines. The major advantage of this protocol is the complete control of selectivity of the pyridine bromine atom for the C-N cross-coupling reaction. There are few reported syntheses of unsymmetrical 2,6-disubstituted pyridine-bridged compounds because of their complicated preparations. Although this is the case, a new series of these unsymmetrical compounds have been successfully prepared in two steps by using this copper-catalyzed coupling approach. A practical protocol for the syntheses of 6-substituted 2-bromopyridine compounds has been developed by using a selective copper-catalyzed coupling reaction of 2,6-dibromopyridine with a range of amines.
- Wang, Lei,Liu, Ning,Dai, Bin,Hu, Hengcai
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- Redox-Induced Single-Molecule Magnetism in Mixed-Valent [2 × 2] Co4 Grid Complexes
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Homovalent [2 × 2] Co4 grid complexes [CoII4LH4](BF4)4 (1) and [CoII4LMe4](BF4)4 (2) with two new bis(terdentate) pyrazolate-bridged ligands, HLH = 3,5-bis(6-(1H-pyrazol-1-yl)pyrid-2-yl)pyrazole and HLMe = 4-methyl-3,5-bis(6-(1H-pyrazol-1-yl)pyrid-2-yl)pyrazole, were synthesized and comprehensively characterized. X-ray crystallographic analyses of 1 and 2 showed a square arrangement of cobalt(II) ions, each metal ion in distorted octahedral {N6} coordination created by two terdentate compartments from orthogonal ligand strands. Magnetic measurements revealed the metal ions high-spin (S = 3/2) state and moderate antiferromagnetic interactions to give an overall diamagnetic ST = 0 ground state of 1 and 2. Twofold oxidation, electrochemically or chemically, led to the dimixed-valent [2 × 2] Co4 grids [CoII2CoIII2LH4](BF4)6 (3) and [CoII2CoIII2LMe4](BF4)6 (4). ESI mass spectrometry confirmed the ruggedness of all grids 1-4 and their integrity in solution, and analysis of the UV/vis/NIR spectra suggested moderate electronic coupling. Solution 1H and 13C NMR spectra of paramagnetic 1-4 were recorded and confirmed that the dimixed-valent CoII2CoIII2 grids are charge-localized on the NMR time scale. X-ray crystallography revealed significant structural grid distortion upon oxidation, with the low-spin CoIII at opposite corners and in almost octahedral {N6} environment but the remaining CoII ions coordination sphere approaching a trigonal prism. SQUID studies showed the high-spin CoII to be magnetically isolated in the dimixed-valent CoII2CoIII2 grids, and both 3 and 4 to display frequency-dependent peaks in the out-of-phase (X′) component of the alternating-current (ac) magnetic susceptibility data, characteristic for single molecule magnet (SMM) properties (with energy barriers Ueff/kB = 16 and 26 K, and relaxation times 0 = 6.7·10-6 and 5.0·10-6 s for 3 and 4, respectively). The results are discussed in terms of cooperative effects that originate from elastic coupling within the grids, mediated by the rigid bridging ligands. These effects synergistically lead to the preferred trans configuration of the dimixed-valent CoII2CoIII2 grids and to structural distortions that are beneficial for SMM properties.
- Tong, Jin,Demeshko, Serhiy,John, Michael,Dechert, Sebastian,Meyer, Franc
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- Ethylene polymerization by PN3-type pincer chromium(III) complexes
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Chromium (III) complexes, Cr1, [2,6-(tBu2PNH) 2C5H4N]CrCl3; Cr2, [2,6-(Ph 2PNH)2C5H4N]CrCl3; Cr3, [2-(tBu2PNH)C5H4N]CrCl3 THF; Cr4, [6-(tBu2PNH)C5H4N-2- CH2NEt2]CrCl3; Cr5, [6-(tBu 2PNH)C5H4N-2-C3H2N 2]CrCl3; Cr6, [6-(tBu2PNH)C 5H4N-2-(3,5-Me2)C3H 2N2]CrCl3; Cr7, [6-(tBu 2PNH)C5H4N-2-(3,5-iPr 2)C3H2N2]CrCl3; Cr8, [6-(tBu2PNH)C5H4N-2-(3,5-Ph 2)C3H2N2]CrCl3, bearing a family of neutral PN3-type pincer ligands have been prepared. The molecular structure of Cr2 was further elucidated by the X-ray crystallographic analysis, showing an octahedral geometry. Treatment of these complexes with MAO or alkylaluminum led to catalysts with moderate activities (about 105 g (PE)/Cr(mol) h) for ethylene polymerization, affording exclusively linear low molecular weight solid PE without any detectable oligomers. Among Cr1-Cr8, the highest activity was achieved for Cr1/MAO at room temperature with production of PE with highest molecular weight, indicating that replacement of both tBu groups in Cr1 with Ph groups, or one PtBu2 with the N (imine) arm, resulted in a lower catalytic activity and lower M w.
- Gong, Dirong,Liu, Wen,Chen, Tao,Chen, Zhong-Ren,Huang, Kuo-Wei
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- Palladium(II) pyrazolyl–pyridyl complexes containing a sterically hindered N-heterocyclic carbene moiety for the Suzuki-Miyaura cross-coupling reaction
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Cationic palladium complexes stabilized by a tridentate neutral {N,N,C} ligand containing a sterically hindered N-heterocyclic carbene (NHC) moiety have been prepared and characterized. The nature of the anionic counterion in the palladium complex has been varied to get crystals suitable for X-ray diffraction. The square planar structure of one of these complexes along with the axial contribution of the sterically hindered NHC fragment has been confirmed by X-ray analysis. In addition, all the isolated [{κ3-N,N,C}PdIICl]+X? [X? = Cl, PF6, BF4, B(C6H3Cl2)4] ion pairs have been scrutinized as catalysts in the cross-coupling Suzuki-Miyaura reaction between phenylboronic acid and variably substituted halo-aryl acceptors. Selected issues from this series have shown improved catalyst turn-over frequencies (TOFs) with respect to structurally related catalytic systems of the state-of-the-art.
- Luconi, Lapo,Gafurov, Zufar,Rossin, Andrea,Tuci, Giulia,Sinyashin, Oleg,Yakhvarov, Dmitry,Giambastiani, Giuliano
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- Highly efficient cuprous complexes with thermally activated delayed fluorescence and simplified solution process OLEDs using the ligand as host
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Two strongly luminescent complexes, [Cu(czpzpy)(PPh3)]BF4 (1) and [Cu(czpzpy)(POP)]BF4 (2), bearing a new carbazole-based diimine ligand (czpzpy = 2-(9H-carbazolyl)-6-(1H-pyrazolyl)pyridine, PPh3 = triphenylphosphine, and POP = bis[2-(diphenylphosphine)phenyl]ether) were synthesized and characterized. Complex 2 emits intense thermally activated delayed fluorescence (TADF) with high photoluminescence quantum yields (PLQYs) of up to 0.98 at room temperature in the solid state. A highly efficient solution-processed OLED, with an emissive layer was spin-coated using a mixture of the diimine ligand czpzpy and the starting material, [Cu(CH3CN)2)(POP)]BF4, was fabricated with peak efficiencies of 6.36% (external quantum efficiency, EQE) and 17.53 cd A-1 (current efficiency, CE) and a maximum brightness of 3251 cd m-2. These performances are nearly identical to those of the device whose emissive layer was comprised of complex 2 and czpzpy, indicating that this simplified process, which omits the preparation and purification of the emissive complex, is practicable in preparing efficient solution-processed OLEDs. In this approach, czpzpy, which bears a carbazole unit, was used both as a ligand to form the emissive cuprous complex and as a host matrix for the formed emitter. This journal is
- Chen, Xu-Lin,Lin, Chen-Sheng,Wu, Xiao-Yuan,Yu, Rongming,Teng, Teng,Zhang, Qi-Kai,Zhang, Qing,Yang, Wen-Bing,Lu, Can-Zhong
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- Metal-free site-selective C-N bond-forming reaction of polyhalogenated pyridines and pyrimidines
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This paper presents a metal-free method for highly site-selective C-N bond-forming reaction of polyhalogenated pyridines and pyrimidines. The preferred coupling site can be tuned from the fluorine group bearing the N-heterocyclic ring to the chlorine group when changing from the pyridine ring to the pyrimidine ring. A wide array of halogenated pyridines preferentially reacted with amines at the fluorine group of the pyridine ring to generate monosubstituted halogenated pyridines with high selectivities. Different halogen atoms at various positions were produced by the pyridine ring that performed well under mild conditions. Halogenated pyrimidines underwent highly selective coupling at the chloride group with a wide range of amines having broad substrate applicability and moderate to good yields. The selectivity of the polyfluoropyridines in the developed reaction system was also tested, and the result indicated that the reaction occurred site-selectively at the ortho-position of the nitrogen ring. This reaction accommodated a wide range of halogenated groups. Thus, a wide range of chloro-, bromo-, iodo-, and fluoropyridines were generated, which have a wide utility for organic synthesis.
- Wang, Lei,Liu, Ning,Dai, Bin
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p. 82097 - 82111
(2015/10/12)
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- Synergetic effect of CN∧N/C∧N∧N coordination and the arylacetylide ligands on the photophysical properties of cyclometalated platinum complexes
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Six coordinated Pt(II) complexes were prepared, in which the CN∧N or the C∧N∧N ligand were used to form the Pt(II) coordination center. For each coordination profile, three different arylacetylide ligands were used, i.e. naphthalenediimide (NDI), pyrenyl (Py) and naphthaleneimide (NI) acetylides. The electrochemical and the photophysical properties of the complexes were studied with steady-state and time-resolved absorption and emission spectroscopy, cyclic voltammetry and DFT calculations. The photostability and the photoluminescent properties of the complexes are finely tuned by the photoredox and photophysical properties of the arylacetylide ligands and the CN∧N/C∧N∧N Pt(II) coordination center. The triplet excited states of the complexes are an intraligand feature and the lifetime is long (90.1 μs). The photophysical properties of the complexes were rationalized with DFT calculations. The complexes were used as triplet photosensitizer for triplet-triplet annihilation upconversion. The upconversion quantum yield was up to 29.7%. The results are useful for future designing of Pt(II) complexes showing strong visible light-absorption, RT phosphorescence and long-lived triplet excited states.
- Wu, Wenting,Wu, Xueyan,Zhao, Jianzhang,Wu, Mingbo
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supporting information
p. 2291 - 2301
(2015/04/27)
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- Highly luminescent charge-neutral europium(III) and terbium(III) complexes with tridentate nitrogen ligands
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We report on the synthesis of tridentate-nitrogen pyrazole-pyridine-tetrazole (L1H) and pyrazole-pyridine-triazole (L2H) ligands and their complexation with lanthanides (Ln = Gd(iii), Eu(iii) and Tb(iii)) resulting in stable, charge-neutral complexes Ln(L1)3 and Ln(L2)3, respectively. X-ray crystallographic analysis of the complexes with L1 ligands revealed tricapped trigonal coordination geometry around the lanthanide ions. All complexes show bright photoluminescence (PL) in the solid state, indicating efficient sensitization of the lanthanide emission via the triplet states of the ligands. In particular, the terbium complexes show high PL quantum yields of 65 and 59% for L1 and L2, respectively. Lower PL efficiencies of the europium complexes (7.5 and 9%, respectively) are attributed to large energy gaps between the triplet states of the ligands and accepting levels of Eu(iii). The triplet state energy can be reduced by introducing an electron withdrawing (EW) group at the 4 position of the pyridine ring. Such substitution of L1H with a carboxylic ester (COOMe) EW group leads to a europium complex with increased PL quantum yield of 31%. A comparatively efficient PL of the complexes dissolved in ethanol indicates that the lanthanide ions are shielded against nonradiative deactivation via solvent molecules.
- Senthil Kumar, Kuppusamy,Sch?fer, Bernhard,Lebedkin, Sergei,Karmazin, Lydia,Kappes, Manfred M.,Ruben, Mario
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supporting information
p. 15611 - 15619
(2015/09/07)
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- Biphenyl bridged hexadentate N6-ligands-a rigid ligand backbone for Fe(ii) spin crossover complexes
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The novel hexadentate nitrogen based ligand N,N′-bis-(2-(1H-pyrazol- 1-yl)pyridine-6-ylmethyl)-2,2′-biphenylenediamine (3) was synthesized and used for the preparation of iron Spin Crossover (SCO) complexes [Fe(3)][BF 4]2 (4) and [Fe(3)][ClO4]2 (5), which differ only by the respective counter ion. These complex salts show different spin transition temperatures T1/2 (135 and 157 K, respectively). This effect was studied by the investigation of the solid state structure of different low- and high-spin isomers. All complexes of this series show closely related crystal packing regardless of the counter ion, metal (Zn/Fe) and spin state. The isomer exhibiting the lower transition temperature (4) was also investigated in respect to its photomagnetic behaviour. The LIESST process could be monitored for this complex, but no reverse-LIESST was observed. The relaxation of the photo-induced state occurs at ca. 80 K, showing a complex, three-state relaxation mechanism.
- Heider, Silvio,Petzold, Holm,Chastanet, Guillaume,Schlamp, Stephan,Rueffer, Tobias,Weber, Birgit,Letard, Jean-Francois
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p. 8575 - 8584
(2013/07/27)
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- Novel phosphorescent tetradentate bis-cyclometalated ?C *N?N-coordinated platinum complexes: Structure, photophysics, and a synthetic adventure
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A long but adventurous journal to the synthesis of tetradentate bis-cyclometalated ?C*N?N-coordinated platinum complexes is described, where ?C and N?N denote a five-membered chelation and C*N denotes a six-membered chelation. Initial ligand designs resulted in the selective cycloplatination to form a tridentate coordination complex. The structures of the tridentate coordination complexes were confirmed by the X-ray crystallographic studies. The selective formation of the tridentate coordination complexes was analyzed, which led us to an ultimate design of the ligand 15 and 16. Ligands 15 and 16 differ only in the N?N motif; a bipyridine-based N?N for 15 and a pyrazolylpyridine-based N?N for 16, respectively. In both cases, a forced consecutive double cycloplatination would be possible to form a ?C*N?N- coordinated platinum complex. As expected, the reaction of ligand 15 and 16 with K2PtCl4 in acetic acid at reflux produced 17 and 18, respectively. The coordination geometry was confirmed by the X-ray crystallography of the complex 17. The square planar geometry and dual intermolecular π-π and Pt-Pt interactions were revealed in the molecular packing. The photophysical properties of the complexes were studied. It was found that the complex 18 emitted intensely yellow phosphorescence at room temperature in deoxygenated solution, while complex 17 emitted red emission in a frozen glass matrix. Both compounds have the lifetime of the excited states in the scale of micro seconds. The DFT calculations were carried out to elucidate the frontier orbitals of the complexes, which are used in interpreting the electronic spectra of the complexes.
- Huo, Shouquan,Harris, Caleb F.,Vezzu, Dileep A.K.,Gagnier, Joshua P.,Smith, Meredith E.,Pike, Robert D.,Li, Yumin
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p. 1030 - 1040
(2013/06/05)
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- PHOSPHO-AMINO PINCER-TYPE LIGANDS AND CATALYTIC METAL COMPLEXES THEREOF
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The present invention provides phospho-amino pincer-type ligands, metal complexes thereof, and catalytic methods comprising such metal complexes.
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Page/Page column 13
(2013/02/27)
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- TRIDENTATE PLATINUM (II) COMPLEXES
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A platinum (II) complex of the general formula (I) or (II), in which Ar1, Ar2, and Ar3 are each independently aryl, heteroaryl, or heterocyclic. Ar1, Ar2, and Ar3 together form a tridentate ligand coordinated to the platinum through atoms X, Y, and Z, respectively, and X, Y, and Z are independently carbon or nitrogen. V is a bridging group or a covalent bond, and W is an anion. In general formula (I) in some cases, Ar1 is an anion and Ar2 and Ar3 are neutral; in other cases, Ar1 and Ar3 are neutral and Ar2 is an anion. In general formula (II), in some cases, Ar3 is an anion and Ar1 and Ar2 are neutral; in other cases, Ar1 and Ar3 are neutral and Ar2 is an anion. The complexes are asymmetric. The complexes emit in the UV to near IR range and are useful as emitters for organic light emitting devices.
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Page/Page column 26
(2009/10/22)
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- Unexpected product distributions in the synthesis of 2,6-bis-(indazolyl)pyridine and 2-(pyrazol-1-yl)-6-(indazolyl)pyridine
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Reaction of 2-bromopyridine with 2 equiv of sodium indazolide in diglyme at 140 °C affords 2,6-bis-(indazol-1-yl)pyridine and 2-(indazol-1-yl)-6-(indazol-2-yl)pyridine in purified yields of 24% and 68% respectively. A similar reaction, using 1 equiv of so
- Pritchard, Ruth,Kilner, Colin A.,Halcrow, Malcolm A.
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supporting information; experimental part
p. 2484 - 2486
(2009/08/17)
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- 2,6-Bis(N-pyrazolyl)pyridines: The Convenient Synthesis of a Family of Planar Tridentate N3 Ligands That Are Terpyridine Analogues
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A series of four symmetric 2,6-bis(N-pyrazolyl)pyridines were prepared in good yields by the reaction of an excess of potassium pyrazolate with 2,6-dihalopyridines in the solvent diglyme.Pyrazoles bearing bulky substituents react at the less sterically hi
- Jameson, Donald L.,Goldsby, Kenneth A.
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p. 4992 - 4994
(2007/10/02)
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