Synthesis and crystal structure of 2,4-dihydro-4-[(5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)imino]-5-methyl-2-phenyl-3H-pyrazol-3-one and its copper(II) complex

2-Diazo-3-methyl-1-phenyl-5-pyrazolone (2) and 2,4-dihydro-4-[(5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)imino]-5-methyl-2-phenyl-3H-pyrazol-3-one (3) were obtained in a one-pot reaction from 3-methyl-1-phenylpyrazol-5-one (1), mesyl azide, and K2CO3 in MeOH or CH2Cl2 solution. NMR, IR and ESI mass spectra as well as the crystal structure are reported for red colored 3. The crystal structure determined at 150 K reveals that the corresponding bonds in the two phenylpyrazol-5-one moieties in each of the two independent “U” shaped molecules have essentially the same lengths, with an extensive delocalization in the central O–C–C–N–C–C–O fragment of the molecule. In particular, the hydrogen atom, formally a part of a hydroxyl group, is found near-midway [O1–HY and O11–HY = 1.24(4) and 1.19(4) Å, in molecule 1, and O21–HX and O31–HY = 1.203(4) and 1.19(4) Å, in molecule 2] between the two oxygen atoms (formally in a carbonyl and a hydroxy group), with near linear O–H–O bond angles of 173.8(4)° and 172.7(4)° in the two independent molecules. All C–O bond lengths are in the narrow range of 1.271(3)–1.288(3) Å. Further, since this compound shows different coordinating groups, its binding ability towards copper(II) ions was investigated. A dark red complex 4, obtained by reaction of 3 with copper(II) ions at stoichiometric ratio, was characterized as a neutral 1:1 species, [3:CuCl2], involving tautomeric forms, by ESI-MS, ESI-MS/MS, IR, UV/Vis and EPR spectra. Interestingly, copper coordination to ligand 3 occurs solely by oxygen atoms, in spite of the presence of nitrogen donor centers. The deprotonation of 4 was monitored by UV/Vis, and a corresponding pKa value was determined as (5.6 ± 0.2).

A new method for preparing 2,4-dihydro-4-[(5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)imino]-5-methyl-2-phenyl-3H-pyrazol-3-one (3), in an one-step diazo-transfer process, and its corresponding crystal structure are reported. Reaction of 3 with copper(II) ions at stoichiometric ratio gave complex 4 involving tautomeric forms.Figure optionsDownload as PowerPoint slide