Pyridyl pyrazole

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... 

The same effect is observed for the substituted pyridyl-pyrazole and -imidazole systems. While 2-(pyrazol-l-yl)pyridine 24 gives a low spin iron(II) complex a continuous spin transition is observed centred just above room temperature in solid salts of [Fe (31)3]2+ and just below in solution [39]. Spin crossover occurs in the [Fe N6]2+ derivative of 2-(pyridin-2-yl)benzimidazole 32 (Dq(Ni2+)=1050 cm"1) but not in that of the 6-methyl-pyridyl system 33 (Dq(Ni2+)=1000 cm"1). Although the transition in salts of [Fe 323]2+ is strongly influenced by the nature of the anion and the extent of hydration, suggesting an influence of hydrogen-bonding, in all instances it is continuous [40]. 

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). 

Since nicotine is the major precursor to NNN in tobacco and tobacco smoke, the reaction of nicotine with sodium nitrite was studied to provide information on formation of other tobacco specific nitrosamines, especially NNK and NNA, which could arise by oxidative cleavage of the l -2 bonds or l -5 bond of nicotine followed by nitrosation (26). The reaction was investigated under a variety of conditions as summarized in Table I. All three nitrosamines were formed when the reaction was done under relatively mild conditions (17 hrs, 20 ). The yields are typical of the formation of nitrosamines from tertiary amines (27). At 90 , with a five fold excess of nitrite, only NNN and NNK were detected. Under these conditions, both NNK and NNA gave secondary products. NNK was nitrosated a to the carbonyl to yield 4-(N-methyl-N-nitrosamino)-2-oximino-l-(3-pyridyl)-1-butanone while NNA underwent cyclization followed by oxidation, decarboxylation and dehydration to give l-methyl-5-(3-pyridyl)pyrazole, as shown in Figure 4. Extensive fragmentation and oxidation of the pyrrolidine ring was also observed under these conditions. The products of the reaction of nicotine and nitrite at 90 are summarized in Table II. 

Figure 4. Formation of l-methyl-5-(3-pyridyl)pyrazole from NNA...

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. 

Thermolysis of the (Z)-acraldehyde 265 gives a mixture of the pyridyl-pyrazoles 266 and 267.258 From the (JS )-acraldehyde only compound 266 was obtained. In this reaction the diazoalkane is presumably trapped by the side-chain double bond, with subsequent formyl migration. 

Amino 5 pyridyl pyrazole or 3-Amino-5-pyridyl- l,2-diazolet CeHtN4, mw 160.18,... 

Ndls. Was prepd by treating an alkaline soln of 3,4-dinitro-5-pyridyl -pyrazole with HaS at 90°... 

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... 

Note No other nitrated derivs of 3-amino-5-pyridyl pyrazole were found in Beil or CA through 195 ... 

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... 

Steel et al.211 photolyzed a pyridyl-pyrazole chelate in acetonitrile to obtain [Ru(AB)2 (solv)2]2+, which was used in further syntheses. 

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 oxidation of nicotine by nitric acid gave a product that was initially assigned the structure of 4-nitro-3(5)-(3-pyridyl)pyrazole [568, 569], Later on, however, it was established that this substance was 3(5)-nitro-5(3)-(3-pyridyl)pyrazole [27-29], The mechanism of this reaction can be represented by the following Scheme [570] (Scheme 108). 

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. 

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