Synthesis and characterisation of two Cu(I) metalloligands based on tetradentate tripodal ligands

doi:10.1016/j.poly.2016.08.049

Polyhedron

Volume 125, 29 March 2017, Pages 44-49

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Abstract

Two new tetradentate tripodal ligands (L¹ and L²) have been synthesized via Schiff base condensation of tris(2-aminoethyl)amine (tren) with 4-(4-pyridinyl)benzaldehyde or 4-(3-pyridinyl)benzaldehyde in ethanol. Four Cu(I) complexes [CuL¹]PF₆, [CuL¹]I, [CuL²]PF₆ and [CuL²]I (1–4) have been prepared and characterised by NMR, HR-MS, SEM-EDS, FT-IR, Raman and UV–Vis measurements. X-ray structures for 1 and 4 are presented. In both structures, the four-coordinate copper(I) centres are bound within the cavity defined by the tren backbone. In such Cu(I) complexes, steric considerations dictate that the three uncoordinated pyridine nitrogen donors will have their coordination vectors oriented in a mutually divergent manner suitable for coordination to three different metal centres and thus are preorganized to act as new tripodal metalloligands.

Graphical abstract

Two new tetradentate tripodal ligands (L¹ and L²) have been successfully prepared through Schiff base condensation of tris(2-aminoethyl)amine (tren) with 4-(4-formylphenyl)pyridine or 4-(3-pyridinyl)benzaldehyde in ethanol, respectively. Four Cu(I) complexes, [CuL¹]PF₆, [CuL¹]I, [CuL²]PF₆ and [CuL²]I (1–4), have been prepared and characterised by NMR, HR-MS, SEM-EDS, FT-IR, Raman and UV–Vis. X-ray structures for 1 and 4 are presented.

Introduction

Recently, the design and synthesis of metalloligands for use as building blocks in supramolecular chemistry has been of increasing interest [1], [2], [3] due to their usefulness for precisely controlling the construction of larger homo or hetero metallo-supramolecular entities. Despite considerable effort devoted to the development of different metalloligand types, their synthesis for use in producing new supramolecular architectures with designed properties remains a significant challenge [4], [5], [6], [7], [8], [9], [10].

Mononuclear tripodal complexes incorporating uncoordinated secondary donor sites consisting of pyridine [4], [9], [11], [12] and imidazolate [4], [8] nitrogens are typical examples of metalloligands. In these, uncoordinated donor sites at the terminus of each arm of the tripodal complex are available for coordination to a second metal ion.

Tris(2-aminoethyl)amine (tren), incorporating a classic tripodal backbone, is well documented to form complexes with a wide range of transition, post-transition and rare earth metal ions. Condensation of 4-formylimidazole with tren in a 3:1 ratio yields the corresponding “extended” tripodal ligand which, for example, forms 1:1 complexes with Fe(III) or Ln(III) ions, leaving the three imidazole NH groups available (following deprotonation) for coordination to additional metal centres [4], [8]. Such an outcome was recently demonstrated for this system by our group [4], [8] using both the Fe(III) and the Dy(III) metalloligands; we were successful in preparing discrete heterometallic Fe(III)/Cu(II) or Dy(III)/Cu(II) polyhedral nanocages. As above, both symmetrical and unsymmetrical metalloligands have been reported by employing metal ions with different coordination number and geometries.

As an extension of our previous studies involving tripodal metalloligands incorporating Fe(III) and Dy(III), we now describe the design and preparation of two new Cu(I) metalloligands using the tetradentate ligands L¹ and L² (see below). A key feature of our design was to incorporate longer aromatic components that would give rise to larger void cavities as well as providing (potential) additional π–π interactions sites that could aid subsequent host–guest studies.

Section snippets

Results and discussion

The Schiff base C₃-symmetric tetradentate ligands L¹ and L² were prepared in 73% and 76% yield, respectively, from the reaction of tren with 4-(4-formylphenyl)pyridine or 4-(3-pyridinyl)benzaldehyde employing slight modifications of reported procedures [13], [14], [15]. ¹H and ¹³C NMR spectra (Figs. S1-4) and high resolution electrospray ionization (HR-ESI) mass spectrometry results were consistent with the proposed structures of L¹ and L², with the NMR spectra confirming the formation of

Conclusions

In summary, we report the efficient synthesis of two new tetradentate tripodal ligands (L¹ and L²) and their Cu(I) complexes, 1–4, incorporating PF₆⁻ or I⁻ counter ions and designed to act as metalloligands. The structures of both ligands and their Cu(I) complexes have been unambiguously characterised by NMR, X-ray crystallography, HR-ESI mass spectrometry, SEM-EDS, UV–Vis, FT-IR and Raman spectroscopy. Further studies employing these metalloligands for the construction of heteronuclear

Experimental

All reagents and solvents were purchased from commercial sources and used without further purification. ¹H NMR and ¹³C NMR spectra were recorded on a Bruker 300 MHz spectrometer. High resolution ESI-MS data were acquired using a Waters Xevo QToF mass spectrometer, operating in positive ion mode. FT-IR measurements were undertaken on a Bruker Vertex 70 with a diamond ATR stage. Data collection was via OPUS 7.2 software without any data processing required. The solid state UV–Vis spectra were

Acknowledgements

The research described herein was supported by the Western Sydney University. The authors acknowledge AMCF and Mass Spectrometry facilities at the Western Sydney University. The crystallographic data for 4 were collected on the MX1 beamline at the Australian Synchrotron, Victoria, Australia. L.L. also acknowledges an Australian Postgraduate Award and the Western Sydney University Top-up Award. In addition, D.J.F. acknowledges a Western Sydney University postgraduate award and the CSIRO Top-up

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Polyhedron

Abstract

Graphical abstract

Introduction

Section snippets

Results and discussion

Conclusions

Experimental

Acknowledgements

References (24)

Coord. Chem. Rev.

J. Incl. Phenom. Macro. Chem.

Chem. Soc. Rev.

Dalton Trans.

Nat. Commun.

Inorg. Chem.

Angew. Chem. Int. Ed.

Inorg. Chem.

J. Am. Chem. Soc.

Angew. Chem. Int. Ed.

Angew. Chem. Int. Ed.

Angew. Chem. Int. Ed.

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Unique spin crossover pathways differentiated by scan rate in a new dinuclear Fe(ii) triple helicate: mechanistic deductions enabled by synchrotron radiation studies

Investigating the Conformations of a Family of [M<inf>2</inf>L<inf>3</inf>]<sup>4+</sup> Helicates Using Single Crystal X-ray Diffraction

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