Structural Variation and Magneto-Structural Correlation in Two New Dinuclear Bis(μ2-Phenoxo)-Bridged CuII Schiff-Base Complexes: Catalytic Potential for the Peroxidative Oxidation of Cycloalkanes

Subhra Basak; Soma Sen; Partha Roy; Carlos J. Gómez-García; David L. Hughes; Ray J. Butcher; Eugenio Garribba; Samiran Mitra

doi:10.1071/CH09396

RESEARCH ARTICLE

Structural Variation and Magneto-Structural Correlation in Two New Dinuclear Bis(μ₂-Phenoxo)-Bridged Cu^II Schiff-Base Complexes: Catalytic Potential for the Peroxidative Oxidation of Cycloalkanes

Subhra Basak ^A , Soma Sen ^A ^B , Partha Roy ^A ^C , Carlos J. Gómez-García ^D , David L. Hughes ^E , Ray J. Butcher ^F , Eugenio Garribba ^G and Samiran Mitra ^A ^H

+ Author Affiliations

- Author Affiliations

^A Department of Chemistry, Jadavpur University, Kolkata 700032, West Bengal, India.

^B Current address: Rishi Bankim Chandra College, Kantalpara, Naihati 743165, West Bengal, India.

^C Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, West Bengal, India.

^D Instituto de Ciencia Molecular (ICMol), Parque Científico, Universidad de Valencia, 46980 Paterna (Valencia), Spain.

^E School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, NR4 7TJ, UK.

^F Department of Chemistry, Howard University, Washington, DC 20059, USA.

^G Dipartimento di Chimica e Centro Interdisciplinare per lo Sviluppo della Ricerca Biotecnologica e per lo Studio della Biodiversità della Sardegna, Università di Sassari, via Vienna 2, 1-07100 Sassari, Italy.

^H Corresponding author. Email: smitra_2002@yahoo.com

Australian Journal of Chemistry 63(3) 479-489 https://doi.org/10.1071/CH09396
Submitted: 21 July 2009 Accepted: 28 December 2009 Published: 26 March 2010

Abstract

Two new dinuclear bis(μ₂-phenoxo)-bridged copper(ii) complexes [Cu(NCS)L¹]₂ (1) and [Cu(NCS)L²]₂ (2) have been synthesized using two tridentate NNO-donor Schiff-base ligands, L¹H (Me₂N(CH₂)₃N=CHC₆H₃(OMe)(OH)) and L²H (Me₂N(CH₂)₃N=C(CH₃)C₆H₄(OH)), respectively. They have been characterized by elemental analyses, IR, UV-visible, and electron paramagnetic resonance (EPR) spectroscopy, cyclic voltammetry, and magnetic susceptibility measurements. X-Ray single-crystal structures reveal a central Cu₂O₂ core in each complex with an isothiocyanate ligand coordinated terminally to each metal centre. The coordination environments around the Cu^II ions in 1 and 2 are a distorted trigonal bipyramid and a quasi-regular square pyramid, respectively, with significant differences in the Cu–O–Cu bridging angles (100.22(5)° for 1 and 95.64(7)° for 2). Although both Cu^II dimers present intradimer antiferromagnetic exchange interactions, the magnitudes of the coupling constants in 1 and 2 (J = –119(1) and –0.361(3) cm^–1, respectively) are quite different as a result of the different coordination geometries and Cu–O–Cu bridging angles. Both complexes act as promising catalysts or catalyst precursors for the efficient peroxidative oxidation of cycloalkanes (cyclohexane and cycloheptane) to the corresponding cyclic alcohols and ketones, with maximum overall yields of 53% and 56% for 1 and 2, respectively.

Acknowledgements

S. Basak gratefully acknowledges the DRDO, New Delhi, India for financial assistance. The authors’ thanks are also extended to the All India Council for Technical Education (AICTE), New Delhi, India. The authors are thankful to Professor S. Bhattacharya and Dr S. Halder, Department of Chemistry, Jadavpur University, Kolkata, India for the electrochemical study and to Professor P. Banerjee, Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata, India for providing laboratory facilities. C. J. Gómez-García acknowledges the European Union for financial support (MAGMANet network of excellence), and the Spanish Ministerio de Educación y Ciencia (Projects MAT2007-61584 and Consolider-Ingenio 2010 CSD 2007-00010 in Molecular Nanoscience) and the Generalitat Valencia (Project PROMETEO/2009/095).

References

Structural Variation and Magneto-Structural Correlation in Two New Dinuclear Bis(μ2-Phenoxo)-Bridged CuII Schiff-Base Complexes: Catalytic Potential for the Peroxidative Oxidation of Cycloalkanes

Abstract

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Structural Variation and Magneto-Structural Correlation in Two New Dinuclear Bis(μ₂-Phenoxo)-Bridged Cu^II Schiff-Base Complexes: Catalytic Potential for the Peroxidative Oxidation of Cycloalkanes