Pyrazole 3- -, crystal structure

X-Ray crystal structure determinations of l-(aminocarbonyl)-3-methyl-4-methoxy-l//-pyrazol-5(2H)-one 107 (R = H) and l-(phenylaminocar-bonyl)-3-methyl-4-methoxy-l//-pyrazol-5(2H)-one 107 (R = Ph) demonstrated that both molecules exist in the crystal exclusively as NH-CO tautomers (97T5617). The tautomeric form similar to 104b is realized in the crystal of 4,4-dichloro-substituted pyrazolone 108 (93BSB735). 

Byers, P.K, Carr, N. and Stone, F.G.A. (1990) Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 106. Synthesis and reactions of the alkylidyne complexes [M ( CR)(CO)2 (C6F5)AuC(pz)3 j (M = W or Mo, R — alkyl or aryl, pz — pyrazol-l-yl) crystal structure of pjC PtAu(C6F5)( l3-CMe)(CO)2(PMe2Ph)2 (C6F5)AuC(pz)3 ]. Journal of the Chemical Society, Dalton Transactions, (12), 3701—3708. 

Chelated species are less common. The substituted thiourea 7V-ethoxycarbonyl-/V-[3-(/>-anisyl) pyrazol-5-yl]thiourea (eatu) acts as a monoanionic 0,S-chelate to cobalt(II), forming Co(eatu)2.506 Whereas ethylenethiourea (etu) has been observed to act as a S-donor monodentate in Co (etu)2X2(H20)2 (X = C1, Br), it binds as an S,N-chelate in Co(etu)2(OOCCH3)2.507 Both violet octahedral and blue tetrahedral cobalt(II) compounds Co(pptu)2Cl2 and Cp(pptu)Cl2 respectively were prepared with bidentate A -2-(5-pico 1 y 1)- A"-pheny 11hiourea (pptu) chelated.508 Refluxing Co powder with thiourea in 4-methylpyridine provides a route to isothiocyanates, which form by decomposition of thiourea to ammonium thiocyanate509 with one product, Co(pic)4(NCS)2, characterized by a crystal structure. 

Kim s group in Seoul report the application of another of the E. coli ATs, the aromatic l-AAT encoded by the tyrB gene, to enrich the D-component of racemic preparations of alanine substituted at the /3-position with pyrazole, triazole, and imidazole. They also carried out an in silico investigation based on the crystal structure (PDB 3TAT) providing a reasonable rationalization (and therefore also potentially prediction) of substrate specificities. 

The potentially octadentate, pendant arm ligand l,4,7,10-tetrakis(pyrazol-l-ylmethyl)-l,4,7,10-tetraazacyclododecane (L (182)) gives [MnL][PF6]2 Me2CO with manganese(II)." The crystal structure of this complex shows that the central metal is coordinated by eight nitrogens of L. 

Bardwell, D. A. Jeffery, J. C. Jones, P. L. McCleverty, J. A. Psillakis, E. Reeves, Z. R. Ward, M. D. Lanthanide complexes of the tetradentate N-donor ligand dihydrobis[3-(2-pyridyl)pyrazolyl]borate and the terdentate N-donor ligand 2,6-bis(lH-pyrazol-3-yl)pyridine syntheses, crystal structures and solution structures based on luminescence lifetime studies. J. Chem. Soc., Dalton Trans. 1997, 2079-2086. 

C NMR studies, especially in the solid state (83H(20)1713), are of value in studies of tautomerism (83H(20)1713, 86ZC378). Solid state studies on imidazole (and pyrazole) show there are three distinct signals for the annular carbon atoms (imidazole C-2, 136.3 C-4, 126.8 C-5, 115.3 ppm). Proton exchange does not occur in the solid, hence the compounds resemble their crystal structures. Comparison with the corresponding chemical shifts for 1-methylimidazole (137.6, 129.3, 119.7 ppm) implies that the tautomerism has been frozen in the solid state (81CC1207). Solid-state examination of 2,2 -bis-lH-imidazole also reveals frozen tautomerism. 

Crystalline 2-methylimidazole exhibits different 13C (CPMAS) chemical shifts for C-4 and C-5 (125.0, 115.7 ppm). The average (120.3 ppm) is close to that reported for imidazole in deuterated DMSO (121.2 ppm). These results imply that solid state chemical shifts can be used instead of N-methyl models in tautomerism studies (87H(26)333). For imidazole the solid state l3C shifts are 137.6 (C-2), 129.3 (C-4), and 119.7 (C-5) (81JA6011). No proton exchange occurs in the solid, and the data support a structure resembling the crystal structure. Cooling imidazole solutions has not yet allowed the detection of individual tautomers, but by symmetry the compound exists in equal tautomeric forms, as does pyrazole (81CC1207). 

The crystal structure of tris(l-phenyl-3,5-dimethylpyrazole)silver(I) nitrate (3) has been determined.63 The Ag+ ion sat at the centre of a triangle of 3 Ns from the pyrazole rings and the Ag—N bond lengths were about 224 pm. The nitrate groups were situated between the silver ions in the crystal lattice but the separations were of the order of 550-700 pm—too far... 

The crystal structure of the cocrystal formed by celecoxib (4-[5-(4-methylphenyl)-3-(trifluoromethyl)-lH-pyrazol-l-yl]benzenesulfonamide) with nicotinamide has been solved from powder X-ray diffraction data [54], The dissolution and solubility of the cocrystal product were found to depend on the medium involved, and a number of the observed phenomena were shown to originate from differences in conversion of the cocrystal celecoxib polymorphic forms I and III. However, through the judicious use of choice excipients, a formulation was developed that took advantage of the crystalline conversion to be up to fourfold more bioavailable than the celecoxib Form-Ill marketed product. 

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