Elsevier

Inorganica Chimica Acta

Volume 394, 1 January 2013, Pages 146-151
Inorganica Chimica Acta

Synthesis and characterization of new trimetallic complexes with {Pt2Au(μ-S)2}n+ (n = 2, 3) cores containing C, N and N, N donor ligands

https://doi.org/10.1016/j.ica.2012.07.002Get rights and content

Abstract

Reactions of the dinuclear platinum(II) sulfide complex [Pt2(μ-S)2(PPh3)4] with a range of gold(III) dichloride complexes [AuLCl2] containing C, N- or N, N-cycloaurated ligands L gives a new series of dicationic adducts [Pt2(μ-S)2(PPh3)4AuL]2+, isolated as their PF6 salts. The complexes investigated are [Au{C6–H4(CH2NMe2)-2}Cl2], [Au{C6H3(CH2NMe2)-2-(OMe)-5}Cl2], [Au{NC5H4(CH2C6H4)-2}Cl2], [Au{NC5H4(COC6H4)-2}Cl2] and [Au{NC5H4(CONH)-2}Cl2]. An X-ray structure determination on the picolinamide-derived complex [Pt2(μ-S)2(PPh3)4Au{NC5H4(CONH)-2}](PF6)2 was not of sufficiently high quality for detailed discussion, but confirmed the atom connectivity. Reactions of [Pt2(μ-S)2(PPh3)4] with [AuCl2(bipy)]PF6 (L = bipy = 2,2’-bipyridine) and [AuCl2(phen)]Cl (L = phen = 1,10-phenanthroline) gives the corresponding tricationic adducts [Pt2(μ-S)2(PPh3)4AuL]3+, also isolated as their PF6 salts. The complexes are characterised by NMR spectroscopy, electrospray mass spectrometry and microelemental analyses. Biological assay data of a selection of these new complexes towards the P388 murine leukemia cell line, as well as a range of antimicrobial tests, reveals overall low activity compared to other cycloaurated gold(III) complexes.

Graphical abstract

A series of new trimetallic complexes with {Pt2S2Au} cores were obtained by reaction of [Pt2(μ-S)2(PPh3)4] with a range of gold(III) dichloride complexes [AuLCl2] containing C, N- or N, N-cycloaurated ligands L, namely [Au{C6H3(CH2NMe2)-2}Cl2], [Au{C6H3(CH2NMe2)-2-(OMe)-5}Cl2], [Au{NC5H4(CH2C6H4)-2}Cl2], [Au{NC5H4(COC6H4)-2}Cl2] and [Au{NC5H4(CONH)-2}Cl2]. Reactions of [Pt2(μ-S)2(PPh3)4] with [AuCl2(bipy)]PF6 (L = bipy = 2,2′-bipyridine) and [AuCl2(phen)]Cl (L = phen = 1,10-phenanthroline) gave the corresponding tricationic adducts [Pt2(μ-S)2(PPh3)4AuL]3+.

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Highlights

► Series of new gold(III) adducts of the metalloligand [Pt2(μ-S)2(PPh3)4] synthesized. ► Picolinamide complex [Pt2(μ-S)2(PPh3)4Au{NC5H4(CONH)-2}](PF6)2 structurally characterised. ► Tricationic adducts [Pt2(μ-S)2(PPh3)4AuL]3+ (L = phen or bipy) prepared. ► Complexes display low biological activity, e.g. in P388 murine leukemia assay.

Introduction

Complexes with {Pt2(μ-S)2} cores, typified by [Pt2(μ-S)2(PPh3)4] 1, have been known for many years to contain very reactive sulfide centres. These complexes are renowned for their ability to act as a metalloligands, yielding sulfide-bridged polymetallic aggregates [1], [2]. We have been exploring the metalloligand chemistry of [Pt2(μ-S)2(PPh3)4] primarily using the technique of electrospray ionisation mass spectrometry (ESI MS) [3] as an efficient, convenient and informative tool [4]. Adducts of 1 with a diverse range of metal centres are known, but in the area of gold chemistry most adducts have involved gold(I), primarily phosphine [5], [6] and N-heterocyclic carbene [7] adducts. To date, only four gold(III) adducts 25 are known (Scheme 1) [8], [9], where the gold(III) centre is stabilised (towards reduction) by a chelating C, N-donor ligand, a common strategy in gold(III) chemistry [10]. We have now explored the chemistry of [Pt2(μ-S)2(PPh3)4] towards a range of other C, N- and N, N-cycloaurated complexes, together with the cationic complexes [AuCl2L]+ containing the neutral N, N-donor ligands 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen), and the results of these investigations are reported herein.

Section snippets

Results and discussion

The reactions of [Pt2(μ-S)2(PPh3)4] 1 with the gold(III) complexes [Au{C6H4(CH2NMe2)-2}Cl2], [Au{C6H3(CH2NMe2)-2-(OMe)-5}Cl2], [Au{NC5H4(CH2C6H4)-2}Cl2], [Au{NC5H4(COC6H4)-2}Cl2] and the picolinamide-derived N, N-donor complex [Au{NC5H4(CONH)-2}Cl2] proceeded readily in methanol suspension, from which solutions containing the adducts 610 respectively are obtained, Scheme 2. Progress of the reactions was readily monitored by ESI mass spectrometry, where the [1 + H]+ ion was replaced by the

Experimental

Methanol was distilled prior to use. Dichloromethane was dried and purified by distillation from calcium hydride under nitrogen. Diethyl ether and THF were dried and purified by distillation from sodium/benzophenone under nitrogen. Ammonium hexafluorophosphate (Aldrich) and 2-benzoylpyridine (Aldrich) were used as supplied. Reactions were carried out without regard for exclusion of air, light or moisture.

Low resolution ESI mass spectra were recorded on a VG Platform II instrument, and a Bruker

X-ray structure determination on [Pt2(μ-S)2Au{NC5H4(CONH)-2}] (PF6)2 10·(PF6)2

Crystals were grown by slow diffusion of benzene into a 1,2-dichloroethane solution of 10·(PF6)2 at 25 °C. A crystal of dimensions 0.48 × 0.14 × 0.10 mm was chosen for the study. Accurate cell parameters and intensity data were collected on a Siemens Smart CCD diffractometer at the University of Auckland. The data were corrected empirically for absorption using sadabs [23]. The structure was solved by Direct Methods and refined with shelx97 [24].

A combination of a small needle crystal, a large linear

Acknowledgements

We thank the University of Waikato for financial support of this work, Dr. Tania Groutso (University of Auckland) for collection of the X-ray data set, and Gill Ellis (University of Canterbury) for assay data. BCW thanks the Asia 2000 Foundation for provision of a travel grant to visit NUS. WH thanks Oguejiofo Ujam for collecting some of the NMR data.

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