Synthesis and Characterization of New N-Alkylamino-3,5-diphenylpyrazole Ligands and Reactivity Toward PdII and PtII. Study of the cis–trans Isomerization

Gemma Aragay; Josefina Pons; Vicenç Branchadell; Jordi García-Antón; Xavier Solans; Mercé Font-Bardía; Josep Ros

doi:10.1071/CH09371

RESEARCH ARTICLE

Synthesis and Characterization of New N-Alkylamino-3,5-diphenylpyrazole Ligands and Reactivity Toward Pd^II and Pt^II. Study of the cis–trans Isomerization

Gemma Aragay ^A , Josefina Pons ^A ^D , Vicenç Branchadell ^B , Jordi García-Antón ^A , Xavier Solans ^C ^E , Mercé Font-Bardía ^C and Josep Ros ^A

+ Author Affiliations

- Author Affiliations

^A Departament de Química, Unitat de Química Inorgànica, Universitat Autònoma de Barcelona, 08193-Bellaterra, Barcelona, Spain.

^B Departament de Química, Unitat de Química Física, Universitat Autònoma de Barcelona, 08193-Bellaterra, Barcelona, Spain.

^C Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, Martí i Franqués s/n, 08028-Barcelona, Spain.

^D Corresponding author. Email: josefina.pons@uab.es

^E Deceased 3 September 2007.

Australian Journal of Chemistry 63(2) 257-269 https://doi.org/10.1071/CH09371
Submitted: 1 July 2009 Accepted: 4 August 2009 Published: 26 February 2010

Abstract

In this paper, the synthesis and characterization of two new N-alkylaminopyrazole ligands, 1-[2-(ethylamino)ethyl]-3,5-diphenylpyrazole (dpea) and 1-[2-(octylamino)ethyl]-3,5-diphenylpyrazole (dpoa) are reported. The reaction of these ligands with [MCl₂(CH₃CN)₂] (M = Pd^II, Pt^II) affords the following square planar complexes: cis-[MCl₂(NN′)] (M = Pd^II: NN′ = dpea, 1; dpoa, 2; M = Pt^II: NN′ = dpea, 3; dpoa, 4). Reaction of [PdCl₂(CH₃CN)₂] and dpea or dpoa in 1:2 M:NN′ molar ratio, in the presence of NaBF₄, yields complexes [Pd(NN′)₂](BF₄)₂ (NN′ = dpea, [5](BF4)₂); dpoa, [6](BF4)₂). The solid-state structures of complexes 1, 3, and [5](BF₄)₂ have been determined by single-crystal X-ray diffraction methods. In complexes 1 and 3, the dpea ligand is coordinated through the N_pz and N_amino atoms to the metallic centre, which completes its coordination with two chlorine atoms in a cis disposition. For complex [5](BF₄)₂, the crystal structure consists of cations involving a [Pd(N_pz)₂(N_amino)₂]²⁺ core with a cis disposition of the two dpea ligands in a square-planar geometry and BF₄ ^– anions. Theoretical calculations were carried out to optimize the geometries of the cis and trans isomers of the [Pd(dpea)₂]²⁺ cation and of the [Pd(dpea)₂](BF₄)₂ complex. The results show that the trans isomer is the most stable for [Pd(dpea)₂]²⁺, in contrast with the cis stereochemistry observed in the crystal structure of [Pd(dpea)₂](BF₄)₂. The calculations also predict that in acetonitrile solution, the dissociation of this complex into the corresponding ions is thermodynamically favourable. The cis–trans isomerization process of [Pd(dpea)₂]²⁺ in acetonitrile solution has been studied by NMR spectroscopy at different temperatures. These experimental results confirm that the trans isomer is the thermodynamically most stable form of the complexes [5](BF₄)₂ and [6](BF₄)₂.

Acknowledgements

Support by the Spanish Ministerio de Ciencia e Innovación (projects CTQ2007–63913/BQU and CTQ2007–61704/BQU) and allowance of computer resources from the Centre de Supercomputació de Catalunya supercomputing centre are gratefully acknowledged.

References

Synthesis and Characterization of New N-Alkylamino-3,5-diphenylpyrazole Ligands and Reactivity Toward PdII and PtII. Study of the cis–trans Isomerization

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Synthesis and Characterization of New N-Alkylamino-3,5-diphenylpyrazole Ligands and Reactivity Toward Pd^II and Pt^II. Study of the cis–trans Isomerization