2-Pyridyl pyrazoles

The polydentate ligands 2-(diphenylphosphino)-6-[3-(2 -pyridyl)pyrazol-l-yl)pyridine and 2-(diphenylphosphino)-6-(pyrazol-l-yl)pyridine react with [Ag(NCMe)4]C104 to give the dinuclear complexes where the ligands are P,N,N bonded as in (249).1 82 The reaction of two equivalents of AgBF4 with 6,6-bis(diphenylphosphine)-2,2 -bipyridyl (P2-bipy) gives the complex [Ag4(P2-bipy)2](BF4)4. Addition of Br or I leads to complexes [Ag4X2(P2-... 

Reaction of 3-(2-pyridyl)pyrazole and 6-(3-pyrazolyl)-2,2 -bipyridine with zinc salts results in mononuclear pseudo-octahedral complexes [ZnL3](PF6)2 and [ZnL2](PF6)2 respectively. The ligands coordinate as neutral mononucleating chelates in a similar fashion to the bidentate 2,2 -bipyridine or tridentate 2,2 6, 2"-terpyridine respectively.153... 

Yu WS, Cheng CC, Cheng YM et al (2003) Excited-state intramolecular proton transfer in five-membered hydrogen-bonding systems 2-pyridyl pyrazoles. J Am Chem Soc 125 10800-10801... 

Kijak M, Nosenko Y, Singh A et al (2007) Mode-selective excited-state proton transfer in 2-(2 -pyridyl)pyrazole isolated in a supersonic jet. J Am Chem Soc 129 2738-2739... 

Just as with nondoped red fluorescent dyes, nondoped phosphorescent iridium complexes consisting of two chelating phenyl-substituted quinazoline and one (2-pyridyl) pyrazolate or triazolate have recently been reported by Chen et al. (278-280) (Scheme 3.88) [308]. All of these complexes exhibited bright red phosphorescence with relatively short excited state lifetimes of 0.4-1.05 ps. PHOLEDs fabricated using the compounds A and B with relatively... 

The reaction of 2-pyridylhydrazine and EMME in diphenyl ether at 190°C for 30 min give ethyl 5-hydroxy-l-(2-pyridyl)pyrazole-4-carboxylate in 6% yield (89MI435). 

Armaroli, N. Balzani, V. Barigelletti, F. Ward, M. D. McCleverty, J. A. Luminescence properties of Eu3 +, Tb3+ and Gd3+ complexes of the hexadentate N-podand tris-[3-(2-pyridyl)pyrazol-lyl]hydroborate. Chem. Phys. Lett. 1997, 276, 435-440. 

Inspired by the good chelating properties of bipy (65) and phen (67), analytical chemists had already studied their derivatives 30 years ago160 (see also Chapter 10). Some examples are 2-(2-pyridyl)benzimidazole (83), 2-(2-pyridyl)imidazoline (84)160,161 and l-(2-pyridyl)pyrazoles... 

Heath and Rees corrected the earlier conclusions of Potts et al. (66JOC265) and Sai et al. [81IJC(B)10] who had reacted 1,2,4-triazolo[4,3-a]pyridine with dimethyl acetylenedicarboxylate in boiling toluene and benzene. The latter believed that 3-substituted triazolopyridines 209 and 210 were the products. Heath and Rees repeated the experiments in refluxing benzene and in refluxing toluene both in the presence and absence of 5% palladium-on-charcoal, and showed that under all sets of conditions 3-cyano-4-oxo-4f/-pyrido[l,2-a]pyrimidine-2-carboxylate 212, 5-(2-pyridyl)pyrazole-3,4-dicarboxylate 213, and an adduct 211 were isolated from the complex reaction mixtures in 20%, 20%, and 1% yields, respectively (82CC1280). When the reaction was carried out in methanol, only 3-cyano-4-oxo-4//-pyrido[ 1,2-a]pyrimidine-2-carboxylate 212 was obtained... 

This type of tetrahedron was first synthesised by M. D. Ward et al. in 1995. It is obtained from the reaction of [3-(2,-pyridyl)pyrazol-l-yl]hydroborate (L15) and Mn2+. Beside Mn2+, analogous tetrahedra could be made with Fe2+, Co2+, Ni2+ and Zn2+. The resulting cages are all nearly completely closed ones (Fig. 8) [87]. 

The structure of 4-substituted 3,5-bis(2-pyridyl)pyrazoles [245], seventeen C-nitropyrazoles affected ocular blood flow and retinal function recovery after ischemic insult [244], and a large series of nitroazoloanhydrosacchares [295] has been determined by II and 13C NMR method. 

Using hexadentate tris[3-(2-pyridyl)pyrazol-l-yl]hydroborate (34) or tetradentate bis[3-(2-pyridyl)pyrazol-l-yl]dihydroborate (35) as a ligand, Ward and coworkers reported the preparation, characterization, and photophysical properties of a series of binary or ternary complexes of lanthanide(III) complexes with dibenzoylmethane anions (dbm) or nitrate anion as a co-ligand [58-60]. Sizeable NIR emission was detected for these pyrazolylborate-derived complexes of Nd(III), Pr(III), Er(III), and Yb(III) ions. They gave longer lifetimes of lanthanide luminescence than those of aminocarboxylate complexes due to the lack of C-H oscillators in close proximity to the lanthanide(III) ions in the pyrazolylborate complexes compared with that in the aminocarboxylate species. 

The potassium salt of the podand ligand tris[3-(2-pyridyl)-pyrazol-l-yl]borate O Tp) reacts with thorium tetra(nitrate) to generate the complex (P Tp)Th(N03)3. The crystal structure of the complex reveals that the metal center is 12-coordinate, binding to the six nitrogen atoms of the podand ligand, and to two of the oxygen atoms of each nitrate. The molecule has three-fold symmetry, and the nitrates are located between the bidentate arms of the podand. 

Figure 45 Crystal structure of UO fpyTplfOEt) (pyTp=tris[3-(2-pyridyl)-pyrazol-l-yl]borate) (Amoroso,...

The potentially tetradentate bis(pyrazolyl)borate ligand BpPy with two bidentate arms (7), was prepared from reaction of 3-(2-pyridyl)pyrazole (Hpzpy) with KBH4 in a melt.76... 

Since an asymmetric pyrazole such as 3(5)-Mepz can exist in two tautomeric structures in solution the reaction of asymmetric pyrazole with alkylation agents under P.T.C. conditions yields the three isomers I, II, and III shown in Scheme 14. Generally, the relative amounts of isomeric RR C(pz)2 (I II III) correspond to (a + b)2. Reaction of 3-(2-pyridyl)pyrazole with CH2Br2 affords only two isomers I and II,218 whereas 3-(tertbutyl)pyrazole under analogous conditions gives only isomer I.219... 

Figure 4.4.11 Structure of mepirizole, of 3,5-dimethyl-l-(2 -pyridyl)pyrazole and of its R2SnCl2 adducts...

The IR and Raman spectra of SnX4(DMPP) and R2SnX2(DMPP), where X = Cl, Br or I R = Me, Et, Bu or Ph DMPP = 3,5-dimethyl-1-(2 -pyridyl)pyrazole, were all consistent with the presence of an N,N bidentate ligand.206... 

The 12-dentate compartmental ligand hexakis [3-(2-pyridyl)-pyrazol]-lyl diboran(IV)ate (BisTpPy) has two hexadentate tris (pyrazolyl)borate-based cavities, linked back-to-back by a B-B bond, which have been reported.238 [Ln(BisTpPy)(NC>3)2]2 (Ln = La or Gd) is dinuclear with each metal center being 10-coordinate from a tripodal hexadentate ligand cavity and two bidentate nitrates. 

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