Synthesis, crystal structure and fluorination effects in vinylidenebis(diphenylphosphine)gold(I) thiolate coordination compounds
Introduction
Fluorination is a valuable tool for the tuning of properties of compounds. Particularly, it has been successfully used in the design of drugs and therapeutic agents with all kind of purposes, [[1], [2], [3], [4]] but also there are examples of the use of this tool in the modulation of different properties of organic and inorganic materials, e.g. there is a recent increase in the use of fluorination in the design of optoelectronic materials. [[5], [6], [7]] While the effects of the fluorination in short ranges are well known, their long-range influence is less studied. [8,9] Additionally to the electronic effects that are associated with the inclusion of fluorine in the structure of compounds, the supramolecular interaction patterns associated with fluorinated moieties are another attractive source of modulation, in this case of the supramolecular packing and self-assembly behavior [6,10,11].
On the other hand, gold(I) coordination compounds have attracted attention in the last decades due to the increasing number of interesting properties of technological relevance such as their luminescent, [12,13] pharmacological [14] and catalytic behavior [15]. In many cases, these interesting properties are promoted or modified by the occurrence of aurophilic (Au···Au) interactions [16], whose formation is driven by a balance of electronic and supramolecular parameters [17]. The use of fluorinated and unfluorinated thiolate ligands in gold coordination compounds has attracted attention due to their electronic and structural versatility [[18], [19], [20], [21], [22], [23], [24]].
Being electronic modulation one of the pillars of the fluorine chemistry, herein we have studied the fluorination effects over the properties of gold(I) complexes with phosphines. To this end, we have synthesized and characterized a series of compounds based on 1,1-bis(diphenylphosphane)ethylene (vinylidenebis(diphenylphosphine), vdpp) with the general formula [Au2(SR)2(μ-vdpp)] in which SR = SC6F5, 1; SC6HF4, 2; SC6H3F2-2,4, 3; SC6H3F2-3,4, 4; SC6H3F2-3,5, 5; SC6H4F-2, 6; SC6H4F-3, 7; SC6H4F-4, 8 and SC6H5, 9. Our studies show, via the examination of the crystal structures of compounds 1, 2, 3 and 8, the important modulation which fluorinated moieties can produce over the Au···Au interactions. Moreover, in these compounds, the linear coordination geometry of the gold(I) centers permits the communication between the P and S atoms, allowing us to observe by the shifting of the 31P-NMR signals the electronic influence caused by the fluorinated groups. In fact, the 31P-NMR chemical shift variations are sensitive enough for allowing us to differentiate the long-range effects of fluorination in the diverse positions of the phenylthiolate. Through fitting these effects to an additive model, we separated the contribution of fluorination in the ortho, meta and para positions over the 31P-NMR chemical shift.
Section snippets
X-ray structures
By the slow diffusion of liquid hexane into a solution of the corresponding compound in CH2Cl2, we were able to obtain adequate samples of systems 1, 2, 3 and 8 to determine their structures by single-crystal X-ray diffraction. All the compounds display linear coordination geometry around gold atom. While the Au-S bond distances are practically equal in the studied systems, the Au-P distances increase slightly by decreasing the fluorination degree of the thiolate ligand (Table 1). This result
Conclusions
By the analysis of this family of compounds we have shown the relevance of fluorination to modulate the electronic properties of compounds, in particular, we pointed out the surprisingly long-range influence that fluorine has over distant atoms which are big enough to be followed and analyzed in terms of NMR. Additionally, we show the potential of fluorination as a useful tool to exert supramolecular modulation by promoting the rise of different interaction synthons that can act concomitantly
Experimental
Reagents. Tetrahydrothiophene (THT), H[AuCl4], vdpp and all the thiols were purchased from Sigma-Aldrich and used as received. [AuCl(THT)], [29] and lead thiolates [11] were prepared according to reported procedures. [Au2Cl2(μ-vdpp)] [30] was prepared by a modification of the reported method detailed in the SI [31].
General method for the preparation of [Au2(SR)2(μ-vdpp)]. In a round bottom flask, a solution of the precursor [Au2Cl2(μ-vdpp)] 100.0 mg (0.116 mmol) in 10 mL of CH2Cl2 was mixed
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We acknowledge the financial support from DGAPA-UNAM project IN210818 and CONACYT-Mexico CB-2012/177498 along with the postdoctoral grant 740732 for G.M.A. Besides, G.R.I. acknowledges the PhD scholarship from Fundación Carolina-SRE and the support of Prof. Laura Rodríguez. We also thank the Unit of Support Services for Research and Industry (USAII) of the Faculty of Chemistry – UNAM for the instrumental support.
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Present address: Departament de Química Inorgànica i Orgànica, Secció de Química Inorgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028, Barcelona, Spain.