Structural and thermal properties of three cyano-substituted azoderivatives of β-diketones

https://doi.org/10.1016/j.molstruc.2011.02.045Get rights and content

Abstract

3-(2-Cyanophenylhydrazo)pentane-2,4-dione (HL1), 3-(4-cyanophenylhydrazo)pentane-2,4-dione (HL2) and 1-ethoxy-2-(4-cyanophenylhydrazo)butane-1,3-dione (HL3), and the Pd(II) complex [Pd(L2)2] were synthesized and characterized by IR, 1H and 13C NMR spectroscopies, ESI-MS, elemental and X-ray diffraction analyses (for HL1). HL3 derived from the unsymmetric 1-ethoxybutane-1,3-dione exists in solution as a mixture of the enol-azo and hydrazo tautomeric forms and a decrease of the solvent polarity shifts the tautomeric balance to the hydrazo form, while for HL1 and HL2, derived from the symmetric pentane-2,4-dione, the hydrazo form is dominating under all the studied conditions. HL1–3 and [Pd(L2)2] show a high thermal stability with well-defined peaks of phase transition at 438 (HL1), 462 (HL2), 392 (HL3) and 404 K ([Pd(L2)2]).

Introduction

It is well known that many azocompounds and β-diketones, under certain conditions, tend to perform tautomeric transformations. Thus, diazocompounds can exist as a mixture of azo- and hydrazone tautomeric forms [1], while β-diketones easily switch to the enol form [2], [3]. These tautomeric equilibria are important from theoretical and practical aspects: about 92% of azo dyes published in Colour Index possess this tautomery [4] which affects their tone, photostability, etc. On the other hand, tautomeriс equilibria of β-diketones also influence their spectral properties, reactivity, coordination ability, etc. [5], [6]. However, there is a lack of experimental data on the tautomerism of the pigments combining both of the those functionalities, i.e. azoderivatives of β-diketones (ADB).

Moreover, this tautomeric balance can play an important role for the application of ADB as bistate molecular switches [8], [9], [10] or regulation of the ionophore selectivity in analytical chemistry [11], [12]. Within this view, special attention should be paid to the nature of the strong intramolecular O⋯Hsingle bondN hydrogen bond and its influence on the enol-azo  hydrazo transformation [7]. Additionally, the synthetic potential of ADB for coordination chemistry was underestimated, notwithstanding their potentially rich chelating ability [7], [13], [14], [15], [16], [17], [18].

On the other hand, the cyano group has a well-recognized chemical versatility [19]. In particular, in organic chemistry the addition of nucleophiles or electrophiles and the asymmetric dipolar cycloaddition to the Ctriple bondN triple bond offer attractive routes for the creation of Csingle bondC, Csingle bondN, Csingle bondO and Csingle bondS bonds. Therefore, cyano-substituted ADB are expected to be good candidates towards the development of a rich organic chemistry.

Thus, taking in mind all the above mentioned considerations, the main aims of the current work are as follows: (i) to synthesize new ADB with cyano substituents in the aromatic part of the molecule (Scheme 1) and prove their coordination ability by synthesizing a new Pd(II)-ADB complex; (ii) to study the influence of the introduced substituents on the tautomeric balance and thermal properties of the synthesized materials.

Section snippets

Materials and instrumentation

All the chemicals were obtained from commercial sources (Aldrich) and used as received. Infrared spectra (4000–400 cm−1) were recorded on a BIO-RAD FTS 3000MX instrument in KBr pellets. 1D (1H, 13C{1H}) and 2D (1H, 1H-COSY, 1H, 13C-HMQC, 1H, 13C-HSQC and 1H, 13C-HMBC) NMR spectra were recorded on Bruker Avance II + 300 and 400 MHz (UltraShield™ Magnet) spectrometers at ambient temperature. Chemical shifts (δ) are relative to internal TMS. Carbon, hydrogen, and nitrogen elemental analyses were

Spectroscopic and crystallographic investigation of HL1–3

The new cyano-substituted azoderivatives of β-diketones HL1–3 were synthesized via the Japp–Klingemann reaction [20], [21], [22] between the respective cyano-substituted aromatic diazonium salts and pentane-2,4-dione or 1-ethoxybutane-1,3-dione in water solution containing sodium hydroxide. IR spectra of the isolated compounds show ν(NH) vibrations at 3437–3448 cm−1, while ν(Cdouble bondO), ν(Cdouble bondO⋯H), ν(Cdouble bondN) and ν(Ctriple bondN) are observed at 1672–1690, 1637–1660, 1601–1608 and 2220 cm−1, correspondingly, what is

Conclusions

Three new cyano-substituted ADB, HL1–3, were synthesized and characterized by IR and multi-nuclear NMR spectroscopies, ESI-MS, elemental and X-ray diffraction analysis (for HL1). The derivative of the unsymmetric β-diketone, HL3, exists in solution as a mixture of the enol-azo and hydrazo tautomeric forms, and a decrease of the solvent polarity shifts the tautomeric balance to the hydrazo form. The formation of the heterodienic system, HNsingle bondNdouble bondCsingle bondCdouble bondO, and the fairly weak heteronuclear

Acknowledgements

This work has been partially supported by the Foundation for Science and Technology (FCT), Portugal, and its PPCDT (FEDER funded) and “Science 2007” programs. M.N.K., K.T.M. K.V.L. and A.M. express gratitude to the FCT for a post-doc fellowship and working contracts. The authors gratefully acknowledge Dr. Conceição Oliveira for the ESI-MS analysis, and the Portuguese NMR Network (IST-UTL Centre) for the NMR facility.

References (35)

  • K. Wojciechowski et al.

    Dyes Pigments

    (2007)
  • G. Aromi et al.

    Coord. Chem. Rev.

    (2008)
  • P.A. Vigato et al.

    Coord. Chem. Rev.

    (2009)
  • P. Gilli et al.

    J. Mol. Struct.

    (2006)
  • Z. Li et al.

    Inorg. Chim. Acta

    (2010)
  • F.X. Huang et al.

    Spectrochim. Acta Part A

    (2005)
  • Z. Chen et al.

    Dyes Pigments

    (2008)
  • R.S. Brown et al.

    J. Am. Chem. Soc.

    (1979)
  • Z. Rappoport

    The Chemistry of Enols

    (1990)
  • J. Kelememn

    Dyes Pigments

    (1981)
  • M.N. Kopylovich et al.

    Inorg. Chem.

    (2011)
  • P. Gilli et al.

    Acc. Chem. Res.

    (2009)
  • P. Gilli et al.

    J. Am. Chem. Soc.

    (2002)
  • K.T. Mahmudov et al.

    J. Hazard. Mater.

    (2011)
  • K.T. Mahmudov et al.

    Anal. Lett.

    (2010)
  • J. Marten et al.

    Z. Anorg. Allg. Chem.

    (2005)
  • E. Weber et al.

    J. Coord. Chem.

    (2009)
  • Cited by (8)

    • 2-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl)benzonitrile as novel inhibitor of receptor tyrosine kinase and PI3K/AKT/mTOR signaling pathway in glioblastoma

      2019, European Journal of Medicinal Chemistry
      Citation Excerpt :

      Synthesis scheme of know compound is give in the supplemental file 1 while novel compounds synthesis scheme is given below. The aryl hydrazones R212, R221, R156, R246, R40, R313 and R283 were synthesized via Japp−Klingemann reaction [61–74] between the substituted aryldiazonium chloride and active methylene compounds in water solution containing sodium hydroxide (Table 1). 0.025 mol of substituted aniline was dissolved in 50 mL of water and then 0.025 mol of crystalline NaOH was added.

    • Coordination chemistry of arylhydrazones of methylene active compounds

      2013, Coordination Chemistry Reviews
      Citation Excerpt :

      On the other hand, AHMACs constitute a promising type of ligand toward the formation of novel coordination compounds. For example, a particular representative of the AHMAC family – arylhydrazones of β-diketones (AHBD) – drastically differ in physico-chemical, analytical and coordination properties from β-diketones [14–23,29–50]; the possibility to include –OH, –AsO3H2, –SO3H, –COOH or –NO2 groups at the ortho-position of the aromatic ring (Scheme 2b and c) increases the stability of AHBD complexes in comparison with “simple” AHBD (Scheme 2a) and β-diketones [31,51–55]. Moreover, the coordination compounds of AHBD possess catalytic [51–55] and biological [14] activities, photoluminescence [56], can also be used in thin films as optical recording media [57], in high-density recordable optical storage and spin-coating films [58].

    • Hemilabile and luminescent palladium(II) azo-2-phenylindole complexes

      2013, Journal of Organometallic Chemistry
      Citation Excerpt :

      The chemistry of azobenzene derivatives has stimulated research efforts directed towards their use as materials for digital storage, as building blocks in supramolecular systems, switches in nanomolecular devices and polymer materials [1–3].

    View all citing articles on Scopus
    View full text