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Chemical transformation of dithiolene ligands in heteroleptic and homoleptic complexes (M = Ti, Zn, Au)
Journal of Organometallic Chemistry 819 (2016) 182e188
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Chemical transformation of dithiolene ligands in heteroleptic and homoleptic complexes (M ¼ Ti, Zn, Au) Agathe Filatre-Furcate, Thierry Roisnel, Dominique Lorcy* ^t 10A, 35042 Rennes Cedex, France Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Universit e de Rennes 1, Campus de Beaulieu, Ba
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 May 2016 Received in revised form 24 June 2016 Accepted 29 June 2016 Available online 11 July 2016
Heteroleptic and homoleptic dithiolene metal complexes such as Cp2Ti(dithiolene), [Zn(dithiolene)2]2 and [Au(dithiolene)2]1 complexes have been synthesized from the 1-tertiobutyl-1,3-thiazoline-2thione-4,5-dithiolate (tBu-thiazdt) dithiolene ligand. The reactivity of these complexes towards iodomethane (MeI) has been examined. Both the titanocene and the gold complexes undergo a transformation of the tBu-1,3-thiazoline-2-thione core to a 2-methylthio-1,3-thiazole one with elimination of the tBu substituent. The reaction of MeI with the Zn complex leads to a tris(thiomethyl)-thiazole derivative due to the alkylation of the sulfur atoms and the decoordination together with the transformation into the thiazole core. Electrochemical, spectral and X-ray diffraction investigations carried out on these various complexes are also presented. © 2016 Elsevier B.V. All rights reserved.
Keywords: Dithiolene Titanocene Zinc Gold Methyl iodide
1. Introduction Numerous metal (1,2-dithiolene) complexes, either homoleptic or heteroleptic have been prepared for their highly unusual physical properties and their rich redox-chemistry but fewer studies were performed on the chemical reactivity of these complexes as quite often decomposition is observed [1,2]. For instance, alkylation reaction with alkyl halides might occur on the sulfur atoms of the metallacycle followed in some cases by the decoordination of the bis(alkylthio) derivative [3e5]. It has been shown also that the redox state of metal bis(1,2-dithiolene) complexes has an influence on the nucleophilicity of the sulfur atoms and thus on the reactivity. For example, the monoanion state of [M(mnt)2] is less reactive towards alkyl halides than the corresponding dianion [M(mnt)2]2 [6]. Recently we have also evidenced an unprecedented transformation of N-tert-butyl-1,3-thiazoline-2-thione heterocycles in 2-alkylthiothiazole derivatives in the presence of electrophile such methyliodide (Chart 1) [7]. Thus, we decided to explore the reactivity of homoleptic and heteroleptic dithiolene complexes bearing a N-tert-butyl-1,3thiazoline-2-thione-4,5-dithiolate ligand towards methyliodide. We choose methyliodide as it is more reactive than most of the other
* Corresponding author. E-mail address: [email protected] (D. Lorcy). http://dx.doi.org/10.1016/j.jorganchem.2016.06.033 0022-328X/© 2016 Elsevier B.V. All rights reserved.
alkyl iodides in order to test the robustness of the metal-sulfur bond towards this electrophile while at the same time we wanted to induce the transformation of N-tBu-1,3-thiazoline-2-thione into the 2-methylthio-1,3-thiazole. Concerning the heteroleptic complexes, we investigated the reactivity of the bis(cyclopentadienyl)/dithiolene Titanium complex formulated as Cp2Ti(tBu-thiazdt). For the homoleptic complexes, we focused on bis(dithiolene) complexes of d10 and d8 metal ions such as the tetrahedral dianionic zinc bis(dithiolene) complex [NEt4]2[Zn(tBu-thiazdt)2] and the square planar monanionic gold bis(dithiolene) complex, [PPh4][Au(tBu-thiazdt)2]. Both the titanocene and the Zn complexes can be considered as protected form of the dithiolene ligands and these complexes have been widely used as starting material for the synthesis of various heterocycles [8,9]. Moreover, the titanocene and the Zn dithiolene complexes are also known for their ability to transfer the dithiolene ligand to softer metals. Herein we report the synthesis of three novel metal dithiolene complexes: the Cp2Ti(tBu-thiazdt), the
Chart 1
R
R
N tBu
S
R
R
CH3I S
N
R=H R R
S
SMe
N-tBu-1,3-thiazoline-2-thione
2-MeS-1,3-thiazole
=
Chart 1. Reactivity of N-tBu substituted thiazole derivatives.
S O S
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[NEt4]2[Zn(tBu-thiazdt)2] and the [PPh4][Au(tBu-thiazdt)2] (Chart 2) together with their reactivity towards MeI. The transformation of the thiazoline-2-thione core into the 2-methylthio1,3-thiazole occurs with the Ti and Au complexes without destruction of the metal dithiolene complex. Contrariwise, for the Zn complex, a transformation of the heterocycle occurs concomitantly with the alkylation of the sulfur atoms of the metallacycle, followed by the decoordination of the bis(methylthio) derivative. The spectroscopic and redox properties of the various complexes obtained as well as their X-Ray crystal structures have been compared with those of their precursors and discussed.
S
N But
N tBu
Cp2Ti(tBu-thiazdt)
S
M S S
S
S
Ti S
S
S
S
tBu N
-n S
S
M = Zn [Zn(tBu-thiazdt)2]-2 Au [Au(tBu-thiazdt)2]-1
Chart 2. Investigated metal dithiolene complexes.
2. Results and discussion
183
Cp2Ti(tBu-thiazdt) 2 with MeI in refluxing CH2Cl2 afforded the corresponding 2-methylthio-1,3-thiazole derivative, Cp2Ti(MeStzdt) 3, in 90% yield. In this reaction of MeI with a 1,3-thiazoline-2thione derivative, the nucleophilic attack of the exocyclic sulfur atom on the electrophile generates the 2-methylthio-1,3thiazolium salt [10] which evolves rapidly, in the case of the NtBu-derivative, to the thiazole core through the loss of tBuI. It is worth mentioning that the formation of Cp2Ti(MeS-tzdt), 3, can also be realized in one step by adding in the medium where 2 was formed, after the addition of LDA, successively sulfur, Cp2TiCl2, and MeI. Using that strategy, the Cp2Ti(MeS-tzdt) 3 was formed at room temperature in 56% yield in one step from 1. Crystals of the complexes Cp2Ti(tBu-thiazdt) 2, and Cp2Ti(MeStzdt) 3 suitable for an X-ray diffraction study were obtained by slow concentration of a dichloromethane solution. They crystallize in the triclinic system, space group P-1 and the monoclinic system, space group C2/c for 2 and 3 respectively. The molecular structures are given in Fig. 1. These complexes adopt a distorted tetrahedral geometry around the titanium atom with fully planar thiazoline-2-thione and thiazole cores and a non-planar metallacycle folded along the S/S axis by a q angle (Chart 3). Selected bond lengths and folding angles are listed in Table 1 together with the N-methyl thiazole analogue, Cp2Ti(Me-thiazdt) [11], for comparison. The bond lengths, TieS and SeC, and bond angles, SeTieS and q, in the metallacycles for all these compounds are in the same range indicating that the nature of the heterocycle, 2-methylthio-1,3-thiazole or N-methyl-1,3-
2.1. Titanocene complexes The mixed cyclopentadienyl/dithiolene target complex 2 was prepared from N-tBu-1,3-thiazoline-2-thione 1 according to the chemical route described in Scheme 1. Sequential metalation of the thiazole core 1 followed by the addition of sulfur leads to the formation of the dithiolate which reacts in situ with Cp2TiCl2. The corresponding Cp2Ti(tBu-thiazdt) 2 was isolated as blue green crystals in 68% yield after purification (Scheme 1). Reaction of
S S
N tBu S 1
Ti
S
1) LDA, S8 2) Cp2TiCl2
Ti
S
CH3I N
S S 2
1) LDA, S8 2) Cp2TiCl2
S
3) CH3I Scheme 1.
tBu
Chart 3. Folding angle q along the S/S axis of the metallacycle.
Table 1 Significant bond lengths [Å] and angles [ ], of titanocenes 2, 3 and Cp2Ti(Methiazdt). Compound
S
TieS (Å)
N SMe 3
Cp2Ti(tBu-thiazdt) 2 Ti(1): 2.4225(14) 2.4244(16) Ti(2): 2.4226(15) 2.4306(16) 2.4157(6) Cp2Ti(MeS-tzdt) 3 2.4588(6) 2.4336(10) Cp2Ti(Me-thiazdt) [11] 2.4516(10)
Fig. 1. Molecular structure of Cp2Ti(tBu-thiazdt) 2 (left) Cp2Ti(MeS-tzdt) 3 (right).
SeC (Å) C]C Å) SeTieS ( )
q ( )
1.723(5) 1.718(5) 1.730(5) 1.716(5) 1.717(2) 1.740(2) 1.714(4) 1.722(3)
1.379(6) 83.67(5)
48.63 (2)
1.383(6) 83.24(5)
48.59(2)
1.383(3) 85.48(2)
47.78(5)
1.386(5) 85.30(4)
48.34(13)
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into one single signal at Tc (coalescence temperature), as shown in Fig. 2. This process is reversible as upon cooling down the temperature the two signals for the Cp reappeared. Contrariwise, the behavior observed for Cp2Ti(tBu-thiazdt) 2 is different as upon raising the temperature in CD3CN until 343 K no significant changes are observed on the 1H NMR spectra. In order to raise the temperature we repeated the experiments in DMSO and at 353 K novel signals are observed at 6.5 and 6.6 ppm indicating an evolution of the complex upon heating. This was confirmed by the analysis of the spectra upon cooling as the initial spectrum of the Cp2Ti(tButhiazdt) 2 was not recovered. Determination of Tc for 3 and the use of Eyring equation [12] allowed us to determine the activation energy DGs. The data (q, TC, DGs) for the complex 3 are collected in Table 2 together with those of Cp2Ti(Me-thiazdt) and Cp2Ti(dmit) for comparison. It can be noticed that the nature of the heterocycle ring, thiazoline-2-thione, thiazole or dithiole does not influence significantly the value of the activation energy for the inversion process. 2.2. Zinc and gold bis (1,2-dithiolene) complexes
Fig. 2. Variable temperature 1H NMR spectra of Cp2Ti(MeS-tzdt) 3 in CD3CN.
Table 2 Variable-temperature 1H NMR data for 3, Cp2Ti(Me-thiazdt) and Cp2Ti(dmit). Solvent TC (K) Dn (Hz)a DGs (kJ.mol1)
q ( )
47.78(5) CD3CN Cp2Ti(MeS-tzdt) 3 Cp2Ti(Me-thiazdt) [11] 48.34(13) CD3CN Cp2Ti(dmit) [9b] 47.45(39) CDCl3 a
318 326 308
245 302 84
61.4 60.6 60.0
Dn corresponds to the frequency difference between the Cp signals at RT.
thiazoline-2-thione has no significant influence on the geometry of these complexes. The non-planarity of the metallacycles with torsion angles q in the range 47e49 implies that the two cyclopentadienyl groups are in different surroundings. Thus a common feature on the 1H NMR spectra for all these titanocene complexes is that at room temperature the two cyclopentadienyl groups are not equivalent and two singlets are observed. It is possible to determine the activation energies for the ring inversion process through variable temperature 1 H NMR experiments. Upon raising the temperature, due to a rapid inversion process, for Cp2Ti(MeS-tzdt) 3 the two signals coalesce
O S
Ti
S N
S S 2
O=C(OCCl3)2 tBu
1) MeONa
S
S
S
N tBu S 4
We also investigated the possibility to observe this original transformation of the N-tBu thiazoline-2-thione core into the MeSthiazole one, when the dithiolate ligand is part of a homoleptic complex. For that purpose, we decided to investigate two bis(dithiolene) complexes, namely the dianionic Zn and the monoanionic gold complexes. In order to prepare the homoleptic bis(dithiolene) metal complexes, we first converted the titanocene 2 into a more convenient proligand precursor, the dithiocarbonate derivative 4 (Scheme 2). The reaction of 2 with triphosgene in refluxing THF afforded 4 in 94% yield. The use of this organic protected form of a dithiolene ligand presents the following advantages: no transmetallation or formation of undesired complexes is observed and an easier purification of the desired monanionic or dianionic metal complexes. Deprotection of 4 to the dithiolate ligand was realized by adding sodium methanolate in the medium (Scheme 2). The dithiolate ligand in the presence of ZnCl2 and NEt4Br leads to the corresponding Zn bis(dithiolene) complex 5 while in the presence of KAuCl4 and PPh4Cl, the Au bis(dithiolene) complex 6 was obtained. The gold complex 6 was isolated as dark greenish crystals suitable for an X-ray diffraction study. The molecular structure of the monanionic gold complex in [PPh4][Au(tBu-thiazdt)2] is represented in Fig. 3. The Au atom is surrounded by two dithiolene ligands in a square planar environment with a trans configuration of the two N-tBu moieties. In the solid state, only the trans configuration of the complex is observed even if the two configurations, cis and trans are susceptible to exist due to the dissymmetry of the dithiolene ligand. The metallacycles are nearly planar with a folding angle along the SS axis of 8 . The bond lengths of the metallacycles, AueS, SeC and C]C, as well as the bond length of the thiazoline-2-thione are in the range of those
2) ZnCl2
S NEt4
S N tBu
2
3) NEt4Br
1) MeONa 2) KAuCl4 3) PPh4Cl Scheme 2.
S S Zn S S
tBu N S
S
5 S PPh4
S N tBu
S S Au S S 6
tBu N S
S
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185
Table 3 Redox potentials in V vs SCE and UVevis absorption band and extinction coefficient of the titanocenes 2 and 3, the Zn and the gold complexes in CH2Cl2. Ered Cp2Ti(Methiazdt) [11] Cp2Ti(tButhiazdt) 2 CP2Ti(MeS-tzdt) 3 [Zn(tButhiazdt)2]2 5 [Au(tButhiazdt)2]1 6 [Au(MeStzdt)2]1 8
Fig. 3. Molecular structure of the monanionic gold complex [Au(tBu-thiazdt)2]e in 6.
found for other monanionic complexes bearing dithiolene ligands with different R groups on the thiazoline-2-thione core [13]. Thermal behavior of the Zn and Au complexes 5 and 6 were investigated. After 24 h in refluxing toluene, these complexes were entirely recovered. The reactivity of these homoleptic complexes towards MeI was also investigated at room temperature in dichloromethane (Scheme 3). The Zn complex 5 in these conditions evolves extremely rapidly in less than 2 min. This can be simply visualized by the change of color of the medium while the reaction proceeds. The compound isolated is an organic derivative, the tris(methylthio)thiazole 7, formed thanks to the alkylation of the dithiolate ligand and the transformation of the N-tBu-1,3thiazoline-2-thione core into the methylthio-1,3-thiazole. The gold complex 6 is soluble in CH2Cl2 and in the presence of MeI a precipitate appears into the medium. Analysis of this precipitate indicates that the complex obtained is the gold dithiolene complex 8 with two 2-methylthio-1,3-thiazole-4,5-dithiolate ligands that we recently prepared according to a different procedure [7]. Herein, no displacement of the dithiolene ligand is observed, only the transformation of the thiazoline moiety into the 2-methylthio-1,3thiazole core occurred leading to the complex [Au(MeS-tzdt)2]e 8. Thus the nucleophilicity of the sulfur atoms within dianionic Zn complex with a tetrahedral structure is higher than those within the monoanionic Au complex within a square planar geometry.
2.3. Spectral and electrochemical investigations The redox behavior of the different complexes has been studied by cyclic voltammetry in dichloromethane solution with 0.1 M nBu4NPF6 as supporting electrolyte and the data are collected in Table 3. All the titanocene complexes exhibit very similar cyclic voltammograms (Fig. 4). On the cathodic scan, a reversible reduction process is observed corresponding to the reduction of the
S PPh4
S N tBu
2
S S Zn S S 5
S PPh4
S N tBu
S S Au S S
S
S
S
S
lmax(nm) (ε [M1cm1])
0.92 þ0.78a
653(7600), 493(5010), 347 (21420)
0.99 þ0.73a
652(8200), 483(3450), 346(22550)
a
622(5518), 459(3842), 299(19690)
0.99 þ0.79
0.01a
404(25350), 274(29830)
1.08 þ0.46 þ0.57a 374(29280), 304(23280), 260(36000), 228(60600) 356(12840), 294(29360), 262(30940), 1.15a þ0.48 228(57860)
Fig. 4. Cyclic voltammogram of Cp2Ti(tBu-thiazdt) 2 in CH2Cl2, Bu4NPF6.
metal Ti(IV)/Ti(III). On the anodic scan, an irreversible oxidation peak attributed to the oxidation of the dithiolene. The irreversibility of this process is a consequence of the decoordination of the oxidized ligand from the complex [14]. No significant influence of the nature of the ligands can be noticed on the value of the oxidation or reduction potentials. For the Zn complex, [NEt4]2[Zn(tBu-thiazdt)2] 5, only an irreversible oxidation wave is observed at Epa ¼ 0.01 V vs SCE. This behavior is typical for Zn bis(dithiolene) complexes [15]. Contrariwise, for the gold complex [PPh4][Au(tBu-thiazdt)2] 6, three redox
CH3I CH2Cl2
tBu N
E2ox
a Irreversible process the value correspond to the anodic peak potential Epa or to the cathodic peak potential Epc.
MeS
tBu N
E1ox
CH3I CH2Cl2
S
SMe N SMe 7 S
PPh4 MeS
N
S S Au S S 8
6 Scheme 3.
N S
SMe
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processes can be observed on the cyclic voltammogram. On the anodic scan, the monoanionic complex can be reversibly oxidized to the neutral state and then to the monocation while, on the cathodic scan, the monanionic species can be reduced to the dianionic one. Concerning the gold complex 8, only two redox systems can be observed in the potential window. The oxidation of the monoanionic species into the neutral one and the reduction of the monanionic species into the dianionic one. UVevis absorption spectra of the different complexes were measured in dichloromethane. The absorption maxima and extinction coefficients are collected in Table 3. The titanocene complexes exhibit similar absorption spectra with absorption bands in the UVevis region. The low energy bands are assigned to ligand to metal charge transfer transitions (LMCT). It can be observed that, the nature of the dithiolene ligands, do not modify significantly the absorption spectra only a bathochromic shift of about 30 nm can be noticed for Cp2Ti(tBu-thiazds) when compared with Cp2Ti(MeS-tzdt). The gold complexes exhibit absorption bands in only the UVevis region. There again a 20 nm bathochromic shift can be observed between the [PPh4][Au(tButhiazdt)2] 6 and [PPh4][Au(MeS-tzdt)2] 8 (Fig. 5). In accordance with the redox properties of the complexes the tBu-thiazdt ligand exerts a slightly stronger electron releasing effect than the MeStzdt ligand.
3. Conclusions Heteroleptic and homoleptic dithiolene metal complexes such as Cp2Ti(dithiolene), [Zn(dithiolene)2]2 and [Au(dithiolene)2]1 complexes were prepared from the 1-tertiobutyl-1,3-thiazoline-2thione-4,5-dithiolate (tBu-thiazdt) dithiolene ligand. In the presence of MeI, the ligand within these complexes undergo a transformation into a 2-methylthio-1,3-thiazole one with elimination of the tBu substituent. In addition, for the Zn complex, alkylation of the sulfur atoms of the metallacycles is followed by decoordination of the formed tris(methylthio)thiazole derivative. The reactivity of the dithiolene ligand towards MeI without affecting the metalsulfur bonds observed here, within the titanocene and the gold complexes, will be explored in the near future for functionalizing these dithiolene complexes with different alkyl iodide derivatives in order to introduce either groups able to form hydrogen or halogen bonding.
Fig. 5. UVevis absorption spectra of [PPh4][Au(tBu-thiazdt)2] 6 and [PPh4][Au(MeStzdt)2] 8.
4. Experimental 4.1. General NMR spectra were recorded on a Bruker AV300III spectrometer at room temperature using CDCl3 unless indicated otherwise. Chemical shifts are reported in ppm and 1H NMR spectra were referenced to residual CHCl3 (7.26 ppm) and 13C NMR spectra were referenced to CHCl3 (77.2 ppm). Mass spectra were recorded with Bruker MicrOTOF-Q II instrument for complex 3 and compound 4, and with Thermo-fisher Q-Exactive instrument for complexes 2, 5 gional de Mesures Physiques de l’Ouest, and 6 by the Centre Re Rennes. CVs were carried out on a 103 M solution of complex in CH2Cl2-[NBu4][PF6] 0.1 M. CVs were recorded on a Model 362 scanning potentiostat from EG&G Instruments at 0.1 V1 on a platinum disk electrode. Potentials were measured versus KCl Saturated Calomel Electrode (SCE). Column chromatography was performed using silica gel Merck 60 (70e260 mesh). All other reagents and materials from commercial sources were used without further purification. The N-tBu-1,3-thiazoline-2-thione 1 was prepared according to literature procedure [16]. 4.2. Synthesis and characterization [Cp2Ti(tBu-1,3-thiazoline-2-thione-4,5-dithiolate)] 2. Under inert atmosphere at 10 C, LDA was prepared by adding BuLi (2.7 mL, 4.3 mmol, 1.6 M in hexanes) to a solution of diisopropylamine (0.4 mL, 4.3 mmol) in 15 mL of anhydrous THF. The LDA solution was then added to a solution of 1,3-thiazoline-2-thione 1 (0.50 g, 2.8 mmol) of 1,3- thiazoline -2-thione 1 dissolved in 40 mL of anhydrous THF. After stirring for 30 min at 10 C, sulfur (S8, 0.14 g, 4.3 mmol) was added and the solution was stirred for an additional 30 min. A solution of 5.7 mmol of LDA was added to the reaction medium and after 3 h of stirring sulfur (0.19 g, 5.7 mmol) was added. After 30 min of stirring Cp2TiCl2 (1.1 g, 4.3 mmol) was added and the reaction mixture was stirred for 15 h. The solvent was evaporated and the residue was extracted with dichloromethane. The organic phase was washed with water and then dried over MgSO4. The resulting solid was purified by column chromatography using dichloromethane as eluent. Cp2Ti(tBu-thiazdt) 2 was isolated as a blue powder (m ¼ 0.78 g). in 68% yield, mp ¼ 148 C. Rf ¼ 0.72, (SiO2, CH2Cl2). 1H NMR (300 MHz) d 1.91 (s, 9H, CH3), 5.57 (s, 5H, Cp), 6.09 (s, 5H, Cp); 13C NMR (75 MHz) d 30.5 (CeCH3), 68.4 (CeCH3), 107.5 (Cp), 111.6 (Cp), 135.8 (C]C), 147.8 (C]C), 193.5 (C]S); HRMS (ASAP) calcd for [MþH]þ C17H20NS4Ti: 413.99526 Found: 413.9953. Anal calcd for C17H19NS4Ti: C, 47.38; H, 4.63; N, 3.39. Found: C, 47.17; H, 4.47; N, 3.55. [Cp2Ti(2-MeS-1,3-thiazole-4,5-dithiolate)] 3. To a solution of [Cp2Ti(tBu-thiazdt)] 2 (0.66 g, 1.6 mmol) in 20 mL of dichloromethane, CH3I (2.24 gr, 16 mmol) was added. The reaction mixture was refluxed for 2 h. The solvent was removed under vacuum and the resulting solid was purified by column chromatography using dichloromethane as eluent. [Cp2Ti(-2-MeS-1,3-thiazdt)] 3 was obtained as a blue powder, yield ¼ 90%, mp ¼ 150 C; Rf ¼ 0.66, (SiO2, CH2Cl2). 1H NMR (300 MHz) d 2.72 (s, 3H, SCH3), 5.52 (s, 5H, Cp), 6.14 (s, 5H, Cp); 13C NMR (75 MHz) d 15.7 (SeCH3), 107.7 (Cp), 111.6 (Cp), 139.6 (C]C), 158.8 (C]C), 170.4 (C]N); HRMS (ESI) calcd for C14H13NS4Ti: 371.94886. Found. 371.9503. Anal calcd for C14H13NS4Ti: C, 45.28; H, 3.53; N, 3.77; S, 34.53. Found: C, 44.77; H, 3.49; N, 3.71; S, 34.59. [Cp2Ti(MeS-1,3-thiazole-4,5-dithiolate)] 3 from 1. Similar procedure as the one described for the synthesis of 2 until the addition of Cp2TiCl2. After the addition Cp2TiCl2, the reaction mixture was stirred for 30 min at 10 C, and then an excess of iodomethane for 3 was added to the medium. The reaction was
A. Filatre-Furcate et al. / Journal of Organometallic Chemistry 819 (2016) 182e188
stirred overnight. The solvent was evaporated under vacuum and the solid was extracted with dichloromethane. The organic phase was washed with water, dried over MgSO4. The resulting solid was purified by column chromatography using dichloromethane as eluent. (m ¼ 0.54 g). According to this procedure 3 was obtained in 56% yield. 6-(tBu)-5-thioxo-5,6-dihydro-[1,3]dithiolo[4,5-d] thiazole-2one 4. Under inert atmosphere, to a solution of 2 (0.73 mmol, 0.30 g for 2) in 20 mL of THF, triphosgene (0.43 g, 1.46 mmol) was added. The reaction mixture was refluxed under inert atmosphere for 25 mn. The medium was cooled to room temperature and 2.5 mL of water were added. The solvent was evaporated under vacuum and the solid residue was dissolved in CH2Cl2 (20 mL). The organic phase was washed with water (3 20 mL) and dried with MgSO4. The bicyclic derivative was purified by column chromatography using dichloromethane as eluent and 4 was isolated as yellow crystals in 94% yield, mp ¼ 110 C; Rf ¼ 0.90, (SiO2, CH2Cl2); 1 H NMR (300 MHz) d 1.98 (s, 9H, CH3); 13C NMR (75 MHz) d 28.4 (CH3), 67.2 (C(CH3)3)), 115.5 (¼C), 188.9 (C]O), 199.9 (C]S); IR ʋ (cm1): 1674(C]O); HRMS (ESI) calcd for C8H10NOS4 [MþH]: 263.96453 Found. 263.9646. Anal calcd for C8H9NOS4: C, 36.48; H, 3.44; N, 5.32. Found: C, 36.68; H, 3.49; N, 5.34. [NEt4]2[Zn(tBu-thiazdt)2] 5 Under an inert atmosphere and at room temperature, a solution of MeONa 1 M in MeOH (6 mL, 6 mmol) was added to 1,3-thiazoline-2-ones 19 (0.16 g, 0.61 mmol). After dissolution of the compound, zinc chloride (ZnCl2) (0.05 g, 0.37 mmol) dissolved in 5 mL of dry methanol was added to the reaction medium. After stirring 4 h, tetraethylammonium bromide (NEt4Br) (0.26 g, 1.22 mmol) dissolved in 5 mL of dry methanol was added to the medium. Then the reaction was stirred overnight at room temperature under argon atmosphere. The yellow was introduced to a flask containing diethylether to pre. The Zn complexes crystallize from acetonitrile (m ¼ 0.15 g), yield ¼ 95%, mp ¼ 150 C. 1H NMR (CD3CN, 300 MHz) d 1.21 (t, 24H, CH3), 2.11 (s, 18H, CH3), 3.16 (q, 16H, CH2); 13C NMR (DMSO-d6, 75 MHz) d 6.8 (CH3), 30.7 (CH3), 55.2 (CH2), 66.4 (C(CH3)3), 119.7 (C]C), 141.6 (C] C), 181.7 (C]S). HRMS (ESI) calcd for [A2] C14H18N2S8Zn: 266.92691 Found. 266.9268. [PPh4][Au(tBu-thiazdt)2] 6. Under an inert atmosphere and at room temperature, a solution of sodium methanolate 1 M in MeOH (6 mL, 6 mmol) was added to the bicyclic derivative 4 (0.15 g,
187
0.57 mmol). After dissolution of the compound, potassium tetrachloroaurate (III) hydrate, KAuCl4.H2O, (0.13 g, 0.34 mmol) dissolved in 5 mL of dry methanol were added to the reaction mixture. After stirring 4 h, tetraphenylphosphonium chloride (0.13 g, 0.34 mmol) dissolved in 5 mL of dry methanol were added to the medium. Then the reaction was stirred overnight at room temperature under argon atmosphere. The precipitate was filtered off and dissolved in acetonitrile. The gold complex crystallize in acetonitrile (m ¼ 0.15 g) and was isolated as green crystal. yield ¼ 54%, mp ¼ 210 C; 1H NMR (300 MHz) d 2.01 (s, 9H, CH3), 7.64 (m, 8H, CH,Ar), 7.76 (m, 8H, CHAr), 7.89 (m, 4H, CH, Ar); 13C NMR (75 MHz) d 30.4 (NeC(CH3)3), 67.6 (NeC(CH3)3), 116.6 (C, Ar), 117.2 (C]C), 117.8 (C, Ar), 130.5 (C, Ar), 133.6 (C]C), 134.1 (C, Ar), 135.6(C, Ar), 194.6 (C]S); HRMS (Q-Exactive) [2A, Cþ]þ for C52H56N4PS16Au2: Calcd: 1672.91108. Found: 1672.9113; Anal calcd for C34H38AuN2PS8: C, 45.32; H, 3.80; N, 2.78; S, 25.47. Found: C, 45.34; H, 3.71; N, 2.74; S, 24.83. 2,4,5-trimethylthio-thiazole 7. The dianionic Zn complex 5 (0.2 g, 0.25 mmol) was dissolved in 20 mL of dichloromethane. An excess of MeI was then added (0.25 mL, 4 mmol) and the reaction mixture was stirred at room temperature for 2 min. The solvent was removed in vacuum and the residue was purified by column chromatography using dichloromethane as eluent. 7 was obtained as a yellow oil in 73% yield. 1H NMR (300 MHz) d 2.36 (s, 3H, CH3), 2.61 (s, 3H, CH3), 2.66 (s, 3H, CH3); 13C NMR (75 MHz) d 28.4 (CH3), 34.7 (CH3), 41.9 (CH3), 105.5 (C]C), 154.2 (C]C), 168.2 (C]N); HRMS (ESI) calcd for C6H10NS4 [MþH]: 223.96906 Found. 223.969. [PPh4][Au(MeS-tzdt)2] The monoanionic gold dithiolene complex [PPh4][Au(tBu-thiazdt)2] (50 mg, 4.97 105 mol) was dissolved in 10 mL of CH2Cl2. An excess of MeI was added to the reaction medium and the solution was refluxed for 1 h. After cooling, a greenish precipitate was formed. The solid was filtered and washed with dichloromethane (m ¼ 20 mg). Complex 8 was obtained as green powder in 44% yield. mp ¼ 230 C; 1H NMR (300 MHz) d 2.59 (s, 6H, CH3), 7.63 (m, 8H, CH, Ar), 7.75 (m, 8H, CH, Ar), 7.85 (m, 4H, CH, Ar); 13C NMR (DMSO-d6, 75 MHz) d 17.3 (SeCH3), 118.1 (C, Ar), 122.7 (C]C), 130.8 (C, Ar), 134.9 (C, Ar), 135.7 (C, Ar), 148.3 (C]C), 169.7 (C]N); HRMS (ESI) Calcd. for [A] C8H6N2S8Au: 582.79678. Found: 582.7967. Anal. Calcd. for C32H26AuN2PS8: C, 41.64; H, 2.84; N, 3.03. Found: C, 41.74; H, 2.84; N, 2.99.
Table 4 Crystallographic data for [Cp2Ti(tBu-thiazdt)] 2, [Cp2Ti(MeS-tzdt)] 3 and [PPh4][Au(tBu-thiazdt)2] 6 complexes. Compound
Cp2Ti(tBu-thiazdt) 2
Cp2Ti(MeS-tzdt) 3
[PPh4][Au(tBu-thiazdt)2] 6
Formulae FW (g.mol1) System Space group a (Å) b (Å) c (Å) a (deg) b (deg) g (deg) V (Å3) T (K) Z Dcalc (g.cm1) m (mm1) Total refls Abs corr Uniq refls (Rint) Uniq refls (I > 2s(I)) R1, wR2 R1, wR2 (all data) GOF
2(C17H19NS4Ti) 826.94 triclinic P-1 11.5094(9) 12.0571(9) 13.4730(10) 93.252(3) 90.450(3) 103.308(2) 1816.1(2) 294 2 1.512 0.928 21450 multiscan 8154(0.0409) 6786 0.0833, 0.1942 0.0980, 0.2055 1.061
C14H13NS4Ti 371.39 monoclinic C2/c 12.1924(2) 10.4359(2) 23.4526(5) 90 93.3850(10) 90 2978.87(10) 150(2) 8 1.656 1.122 12933 multiscan 3425(0.0477) 3002 0.0297, 0.0803 0.0367, 0.0971 1.151
(C14H18AuN2S8, C24H20P) 1007.12 monoclinic C2/c 28.4935(16) 7.5674(4) 24.2516(13) 90 131.173(2) 90 3936.1(4) 150(2) 4 1.7 4.234 11632 multi-scan 4511(0.04) 3433 0.0381, 0.1026 0.0535, 0.1138 1.036
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4.3. Crystallography
References
Data were collected on an APEX II Brucker AXS diffractometer for 3 and 8 and on D8 VENTURE Bruker AXS diffractometer for 2, Mo-Ka radiation (l ¼ 0.71073 Å). The structures were solved by direct methods using the SIR97 program [17], and then refined with full-matrix least-square methods based on F2 (SHELXL-97) [18] with the aid of the WINGX program [19]. All non-hydrogen atoms were refined with anisotropic atomic displacement parameters. H atoms were finally included in their calculated positions. Details of the final refinements are given in Table 4 for all compounds.
[1] Special issue on, Dithiolenes and non-innocent redox-active ligands, Coord. Chem. Rev. 13e14 (2010) 1357e1588. [2] Dithiolene chemistry: synthesis, properties, and applications, in: K.D. Karlin, E.I. Stiefel (Eds.), Prog. Inorg. Chem, vol. 52, Wiley, New York, 2004. [3] R.Y.C. Shin, L.Y. Goh, Acc. Chem. Res. 39 (2006) 301e313. [4] (a) G.N. Schrauzer, H.N. Rabinowitz, J. Am. Chem. Soc. 90 (1968) 4297e4302; (b) G.N. Schrauzer, R.K.Y. Ho, R.P. Murillo, J. Am. Chem. Soc. 92 (1970) 3508e3509. [5] V.H. Nguyen, R.S.H. Khoo, J.H.K. Yip, Inorg. Chem. 54 (2015) 2264e2277. [6] A. Vl cek, Inorg. Chim. Acta 43 (1980) 35e42. , T. Roisnel, V. Dorcet, [7] A. Filatre-Furcate, P. Auban-Senzier, M. Fourmigue D. Lorcy, Dalton Trans. 44 (2015) 15683e15689. €pf, Angew. Chem. Int. Ed. Engl. 10 (1971) 134e135. [8] H. Ko , Coord. Chem. Rev. 178e180 (1998) 823e864; [9] (a) M. Fourmigue , J. Larsen, J. Amaudrut, Bull. Soc. Chim. Fr. (b) F. Guyon, C. Lenoir, M. Fourmigue 131 (1994) 217e226. [10] D.J. Fry, J.D. Kendall, J. Chem. Soc. (1951) 1716e1722. [11] S. Eid, T. Roisnel, D. Lorcy, J. Organomet. Chem. 693 (2008) 2755e2760. [12] H. Eyring, Chem. Rev. 17 (1935) 65e77. ~ iguez, [13] (a) N. Tenn, N. Bellec, O. Jeannin, L. Piekara-Sady, P. Auban-Senzier, J. In E. Canadell, D. Lorcy, J. Am. Chem. Soc. 131 (2009) 16961e16967; , (b) G. Yzambart, N. Bellec, G. Nasser, O. Jeannin, T. Roisnel, M. Fourmigue ~ iguez, E. Canadell, D. Lorcy, J. Am. Chem. Soc. 134 (2012) P. Auban-Senzier, J. In 17138e17148; (c) Y. Le Gal, T. Roisnel, P. Auban-Senzier, T. Guizouarn, D. Lorcy, Inorg. Chem. 53 (2014) 8755e8761. [14] H.A. Harris, D.R. Kanis, L.F. Dahl, J. Am. Chem. Soc. 113 (1991) 8602e8611. [15] S. Eid, M. Guerro, D. Lorcy, Tetrahedron Lett. 47 (2006) 8333e8336. [16] C.M. Roussel, R. Gallo, M. Chanon, J. Metzger, Bull. Soc. Chim. Fr. (1971) 1902e1907. [17] A. Altomare, M.C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagna, J. Appl. Cryst. 32 (1999) 115e119. [18] G.M. Sheldrick, Acta Cryst. A64 (2008) 112e122. [19] L.J. Farrugia, J. Appl. Cryst. 45 (2012) 849e854.
Supplementary material Crystallographic data for structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC 1479118-1479120 for complexes 2, 3, 6 respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union road, Cambridge CB2 1EZ, UK (Fax: þ44 1223 336033; e-mail: [email protected] or www: http://www. ccdc.cam.ac.uk).
Acknowledgements Financial support was obtained from ANR (Paris, France) under contract n 12-BS07-0032-01.
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem
Chemical transformation of dithiolene ligands in heteroleptic and homoleptic complexes (M ¼ Ti, Zn, Au) Agathe Filatre-Furcate, Thierry Roisnel, Dominique Lorcy* ^t 10A, 35042 Rennes Cedex, France Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Universit e de Rennes 1, Campus de Beaulieu, Ba
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 May 2016 Received in revised form 24 June 2016 Accepted 29 June 2016 Available online 11 July 2016
Heteroleptic and homoleptic dithiolene metal complexes such as Cp2Ti(dithiolene), [Zn(dithiolene)2]2 and [Au(dithiolene)2]1 complexes have been synthesized from the 1-tertiobutyl-1,3-thiazoline-2thione-4,5-dithiolate (tBu-thiazdt) dithiolene ligand. The reactivity of these complexes towards iodomethane (MeI) has been examined. Both the titanocene and the gold complexes undergo a transformation of the tBu-1,3-thiazoline-2-thione core to a 2-methylthio-1,3-thiazole one with elimination of the tBu substituent. The reaction of MeI with the Zn complex leads to a tris(thiomethyl)-thiazole derivative due to the alkylation of the sulfur atoms and the decoordination together with the transformation into the thiazole core. Electrochemical, spectral and X-ray diffraction investigations carried out on these various complexes are also presented. © 2016 Elsevier B.V. All rights reserved.
Keywords: Dithiolene Titanocene Zinc Gold Methyl iodide
1. Introduction Numerous metal (1,2-dithiolene) complexes, either homoleptic or heteroleptic have been prepared for their highly unusual physical properties and their rich redox-chemistry but fewer studies were performed on the chemical reactivity of these complexes as quite often decomposition is observed [1,2]. For instance, alkylation reaction with alkyl halides might occur on the sulfur atoms of the metallacycle followed in some cases by the decoordination of the bis(alkylthio) derivative [3e5]. It has been shown also that the redox state of metal bis(1,2-dithiolene) complexes has an influence on the nucleophilicity of the sulfur atoms and thus on the reactivity. For example, the monoanion state of [M(mnt)2] is less reactive towards alkyl halides than the corresponding dianion [M(mnt)2]2 [6]. Recently we have also evidenced an unprecedented transformation of N-tert-butyl-1,3-thiazoline-2-thione heterocycles in 2-alkylthiothiazole derivatives in the presence of electrophile such methyliodide (Chart 1) [7]. Thus, we decided to explore the reactivity of homoleptic and heteroleptic dithiolene complexes bearing a N-tert-butyl-1,3thiazoline-2-thione-4,5-dithiolate ligand towards methyliodide. We choose methyliodide as it is more reactive than most of the other
* Corresponding author. E-mail address: [email protected] (D. Lorcy). http://dx.doi.org/10.1016/j.jorganchem.2016.06.033 0022-328X/© 2016 Elsevier B.V. All rights reserved.
alkyl iodides in order to test the robustness of the metal-sulfur bond towards this electrophile while at the same time we wanted to induce the transformation of N-tBu-1,3-thiazoline-2-thione into the 2-methylthio-1,3-thiazole. Concerning the heteroleptic complexes, we investigated the reactivity of the bis(cyclopentadienyl)/dithiolene Titanium complex formulated as Cp2Ti(tBu-thiazdt). For the homoleptic complexes, we focused on bis(dithiolene) complexes of d10 and d8 metal ions such as the tetrahedral dianionic zinc bis(dithiolene) complex [NEt4]2[Zn(tBu-thiazdt)2] and the square planar monanionic gold bis(dithiolene) complex, [PPh4][Au(tBu-thiazdt)2]. Both the titanocene and the Zn complexes can be considered as protected form of the dithiolene ligands and these complexes have been widely used as starting material for the synthesis of various heterocycles [8,9]. Moreover, the titanocene and the Zn dithiolene complexes are also known for their ability to transfer the dithiolene ligand to softer metals. Herein we report the synthesis of three novel metal dithiolene complexes: the Cp2Ti(tBu-thiazdt), the
Chart 1
R
R
N tBu
S
R
R
CH3I S
N
R=H R R
S
SMe
N-tBu-1,3-thiazoline-2-thione
2-MeS-1,3-thiazole
=
Chart 1. Reactivity of N-tBu substituted thiazole derivatives.
S O S
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[NEt4]2[Zn(tBu-thiazdt)2] and the [PPh4][Au(tBu-thiazdt)2] (Chart 2) together with their reactivity towards MeI. The transformation of the thiazoline-2-thione core into the 2-methylthio1,3-thiazole occurs with the Ti and Au complexes without destruction of the metal dithiolene complex. Contrariwise, for the Zn complex, a transformation of the heterocycle occurs concomitantly with the alkylation of the sulfur atoms of the metallacycle, followed by the decoordination of the bis(methylthio) derivative. The spectroscopic and redox properties of the various complexes obtained as well as their X-Ray crystal structures have been compared with those of their precursors and discussed.
S
N But
N tBu
Cp2Ti(tBu-thiazdt)
S
M S S
S
S
Ti S
S
S
S
tBu N
-n S
S
M = Zn [Zn(tBu-thiazdt)2]-2 Au [Au(tBu-thiazdt)2]-1
Chart 2. Investigated metal dithiolene complexes.
2. Results and discussion
183
Cp2Ti(tBu-thiazdt) 2 with MeI in refluxing CH2Cl2 afforded the corresponding 2-methylthio-1,3-thiazole derivative, Cp2Ti(MeStzdt) 3, in 90% yield. In this reaction of MeI with a 1,3-thiazoline-2thione derivative, the nucleophilic attack of the exocyclic sulfur atom on the electrophile generates the 2-methylthio-1,3thiazolium salt [10] which evolves rapidly, in the case of the NtBu-derivative, to the thiazole core through the loss of tBuI. It is worth mentioning that the formation of Cp2Ti(MeS-tzdt), 3, can also be realized in one step by adding in the medium where 2 was formed, after the addition of LDA, successively sulfur, Cp2TiCl2, and MeI. Using that strategy, the Cp2Ti(MeS-tzdt) 3 was formed at room temperature in 56% yield in one step from 1. Crystals of the complexes Cp2Ti(tBu-thiazdt) 2, and Cp2Ti(MeStzdt) 3 suitable for an X-ray diffraction study were obtained by slow concentration of a dichloromethane solution. They crystallize in the triclinic system, space group P-1 and the monoclinic system, space group C2/c for 2 and 3 respectively. The molecular structures are given in Fig. 1. These complexes adopt a distorted tetrahedral geometry around the titanium atom with fully planar thiazoline-2-thione and thiazole cores and a non-planar metallacycle folded along the S/S axis by a q angle (Chart 3). Selected bond lengths and folding angles are listed in Table 1 together with the N-methyl thiazole analogue, Cp2Ti(Me-thiazdt) [11], for comparison. The bond lengths, TieS and SeC, and bond angles, SeTieS and q, in the metallacycles for all these compounds are in the same range indicating that the nature of the heterocycle, 2-methylthio-1,3-thiazole or N-methyl-1,3-
2.1. Titanocene complexes The mixed cyclopentadienyl/dithiolene target complex 2 was prepared from N-tBu-1,3-thiazoline-2-thione 1 according to the chemical route described in Scheme 1. Sequential metalation of the thiazole core 1 followed by the addition of sulfur leads to the formation of the dithiolate which reacts in situ with Cp2TiCl2. The corresponding Cp2Ti(tBu-thiazdt) 2 was isolated as blue green crystals in 68% yield after purification (Scheme 1). Reaction of
S S
N tBu S 1
Ti
S
1) LDA, S8 2) Cp2TiCl2
Ti
S
CH3I N
S S 2
1) LDA, S8 2) Cp2TiCl2
S
3) CH3I Scheme 1.
tBu
Chart 3. Folding angle q along the S/S axis of the metallacycle.
Table 1 Significant bond lengths [Å] and angles [ ], of titanocenes 2, 3 and Cp2Ti(Methiazdt). Compound
S
TieS (Å)
N SMe 3
Cp2Ti(tBu-thiazdt) 2 Ti(1): 2.4225(14) 2.4244(16) Ti(2): 2.4226(15) 2.4306(16) 2.4157(6) Cp2Ti(MeS-tzdt) 3 2.4588(6) 2.4336(10) Cp2Ti(Me-thiazdt) [11] 2.4516(10)
Fig. 1. Molecular structure of Cp2Ti(tBu-thiazdt) 2 (left) Cp2Ti(MeS-tzdt) 3 (right).
SeC (Å) C]C Å) SeTieS ( )
q ( )
1.723(5) 1.718(5) 1.730(5) 1.716(5) 1.717(2) 1.740(2) 1.714(4) 1.722(3)
1.379(6) 83.67(5)
48.63 (2)
1.383(6) 83.24(5)
48.59(2)
1.383(3) 85.48(2)
47.78(5)
1.386(5) 85.30(4)
48.34(13)
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into one single signal at Tc (coalescence temperature), as shown in Fig. 2. This process is reversible as upon cooling down the temperature the two signals for the Cp reappeared. Contrariwise, the behavior observed for Cp2Ti(tBu-thiazdt) 2 is different as upon raising the temperature in CD3CN until 343 K no significant changes are observed on the 1H NMR spectra. In order to raise the temperature we repeated the experiments in DMSO and at 353 K novel signals are observed at 6.5 and 6.6 ppm indicating an evolution of the complex upon heating. This was confirmed by the analysis of the spectra upon cooling as the initial spectrum of the Cp2Ti(tButhiazdt) 2 was not recovered. Determination of Tc for 3 and the use of Eyring equation [12] allowed us to determine the activation energy DGs. The data (q, TC, DGs) for the complex 3 are collected in Table 2 together with those of Cp2Ti(Me-thiazdt) and Cp2Ti(dmit) for comparison. It can be noticed that the nature of the heterocycle ring, thiazoline-2-thione, thiazole or dithiole does not influence significantly the value of the activation energy for the inversion process. 2.2. Zinc and gold bis (1,2-dithiolene) complexes
Fig. 2. Variable temperature 1H NMR spectra of Cp2Ti(MeS-tzdt) 3 in CD3CN.
Table 2 Variable-temperature 1H NMR data for 3, Cp2Ti(Me-thiazdt) and Cp2Ti(dmit). Solvent TC (K) Dn (Hz)a DGs (kJ.mol1)
q ( )
47.78(5) CD3CN Cp2Ti(MeS-tzdt) 3 Cp2Ti(Me-thiazdt) [11] 48.34(13) CD3CN Cp2Ti(dmit) [9b] 47.45(39) CDCl3 a
318 326 308
245 302 84
61.4 60.6 60.0
Dn corresponds to the frequency difference between the Cp signals at RT.
thiazoline-2-thione has no significant influence on the geometry of these complexes. The non-planarity of the metallacycles with torsion angles q in the range 47e49 implies that the two cyclopentadienyl groups are in different surroundings. Thus a common feature on the 1H NMR spectra for all these titanocene complexes is that at room temperature the two cyclopentadienyl groups are not equivalent and two singlets are observed. It is possible to determine the activation energies for the ring inversion process through variable temperature 1 H NMR experiments. Upon raising the temperature, due to a rapid inversion process, for Cp2Ti(MeS-tzdt) 3 the two signals coalesce
O S
Ti
S N
S S 2
O=C(OCCl3)2 tBu
1) MeONa
S
S
S
N tBu S 4
We also investigated the possibility to observe this original transformation of the N-tBu thiazoline-2-thione core into the MeSthiazole one, when the dithiolate ligand is part of a homoleptic complex. For that purpose, we decided to investigate two bis(dithiolene) complexes, namely the dianionic Zn and the monoanionic gold complexes. In order to prepare the homoleptic bis(dithiolene) metal complexes, we first converted the titanocene 2 into a more convenient proligand precursor, the dithiocarbonate derivative 4 (Scheme 2). The reaction of 2 with triphosgene in refluxing THF afforded 4 in 94% yield. The use of this organic protected form of a dithiolene ligand presents the following advantages: no transmetallation or formation of undesired complexes is observed and an easier purification of the desired monanionic or dianionic metal complexes. Deprotection of 4 to the dithiolate ligand was realized by adding sodium methanolate in the medium (Scheme 2). The dithiolate ligand in the presence of ZnCl2 and NEt4Br leads to the corresponding Zn bis(dithiolene) complex 5 while in the presence of KAuCl4 and PPh4Cl, the Au bis(dithiolene) complex 6 was obtained. The gold complex 6 was isolated as dark greenish crystals suitable for an X-ray diffraction study. The molecular structure of the monanionic gold complex in [PPh4][Au(tBu-thiazdt)2] is represented in Fig. 3. The Au atom is surrounded by two dithiolene ligands in a square planar environment with a trans configuration of the two N-tBu moieties. In the solid state, only the trans configuration of the complex is observed even if the two configurations, cis and trans are susceptible to exist due to the dissymmetry of the dithiolene ligand. The metallacycles are nearly planar with a folding angle along the SS axis of 8 . The bond lengths of the metallacycles, AueS, SeC and C]C, as well as the bond length of the thiazoline-2-thione are in the range of those
2) ZnCl2
S NEt4
S N tBu
2
3) NEt4Br
1) MeONa 2) KAuCl4 3) PPh4Cl Scheme 2.
S S Zn S S
tBu N S
S
5 S PPh4
S N tBu
S S Au S S 6
tBu N S
S
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185
Table 3 Redox potentials in V vs SCE and UVevis absorption band and extinction coefficient of the titanocenes 2 and 3, the Zn and the gold complexes in CH2Cl2. Ered Cp2Ti(Methiazdt) [11] Cp2Ti(tButhiazdt) 2 CP2Ti(MeS-tzdt) 3 [Zn(tButhiazdt)2]2 5 [Au(tButhiazdt)2]1 6 [Au(MeStzdt)2]1 8
Fig. 3. Molecular structure of the monanionic gold complex [Au(tBu-thiazdt)2]e in 6.
found for other monanionic complexes bearing dithiolene ligands with different R groups on the thiazoline-2-thione core [13]. Thermal behavior of the Zn and Au complexes 5 and 6 were investigated. After 24 h in refluxing toluene, these complexes were entirely recovered. The reactivity of these homoleptic complexes towards MeI was also investigated at room temperature in dichloromethane (Scheme 3). The Zn complex 5 in these conditions evolves extremely rapidly in less than 2 min. This can be simply visualized by the change of color of the medium while the reaction proceeds. The compound isolated is an organic derivative, the tris(methylthio)thiazole 7, formed thanks to the alkylation of the dithiolate ligand and the transformation of the N-tBu-1,3thiazoline-2-thione core into the methylthio-1,3-thiazole. The gold complex 6 is soluble in CH2Cl2 and in the presence of MeI a precipitate appears into the medium. Analysis of this precipitate indicates that the complex obtained is the gold dithiolene complex 8 with two 2-methylthio-1,3-thiazole-4,5-dithiolate ligands that we recently prepared according to a different procedure [7]. Herein, no displacement of the dithiolene ligand is observed, only the transformation of the thiazoline moiety into the 2-methylthio-1,3thiazole core occurred leading to the complex [Au(MeS-tzdt)2]e 8. Thus the nucleophilicity of the sulfur atoms within dianionic Zn complex with a tetrahedral structure is higher than those within the monoanionic Au complex within a square planar geometry.
2.3. Spectral and electrochemical investigations The redox behavior of the different complexes has been studied by cyclic voltammetry in dichloromethane solution with 0.1 M nBu4NPF6 as supporting electrolyte and the data are collected in Table 3. All the titanocene complexes exhibit very similar cyclic voltammograms (Fig. 4). On the cathodic scan, a reversible reduction process is observed corresponding to the reduction of the
S PPh4
S N tBu
2
S S Zn S S 5
S PPh4
S N tBu
S S Au S S
S
S
S
S
lmax(nm) (ε [M1cm1])
0.92 þ0.78a
653(7600), 493(5010), 347 (21420)
0.99 þ0.73a
652(8200), 483(3450), 346(22550)
a
622(5518), 459(3842), 299(19690)
0.99 þ0.79
0.01a
404(25350), 274(29830)
1.08 þ0.46 þ0.57a 374(29280), 304(23280), 260(36000), 228(60600) 356(12840), 294(29360), 262(30940), 1.15a þ0.48 228(57860)
Fig. 4. Cyclic voltammogram of Cp2Ti(tBu-thiazdt) 2 in CH2Cl2, Bu4NPF6.
metal Ti(IV)/Ti(III). On the anodic scan, an irreversible oxidation peak attributed to the oxidation of the dithiolene. The irreversibility of this process is a consequence of the decoordination of the oxidized ligand from the complex [14]. No significant influence of the nature of the ligands can be noticed on the value of the oxidation or reduction potentials. For the Zn complex, [NEt4]2[Zn(tBu-thiazdt)2] 5, only an irreversible oxidation wave is observed at Epa ¼ 0.01 V vs SCE. This behavior is typical for Zn bis(dithiolene) complexes [15]. Contrariwise, for the gold complex [PPh4][Au(tBu-thiazdt)2] 6, three redox
CH3I CH2Cl2
tBu N
E2ox
a Irreversible process the value correspond to the anodic peak potential Epa or to the cathodic peak potential Epc.
MeS
tBu N
E1ox
CH3I CH2Cl2
S
SMe N SMe 7 S
PPh4 MeS
N
S S Au S S 8
6 Scheme 3.
N S
SMe
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processes can be observed on the cyclic voltammogram. On the anodic scan, the monoanionic complex can be reversibly oxidized to the neutral state and then to the monocation while, on the cathodic scan, the monanionic species can be reduced to the dianionic one. Concerning the gold complex 8, only two redox systems can be observed in the potential window. The oxidation of the monoanionic species into the neutral one and the reduction of the monanionic species into the dianionic one. UVevis absorption spectra of the different complexes were measured in dichloromethane. The absorption maxima and extinction coefficients are collected in Table 3. The titanocene complexes exhibit similar absorption spectra with absorption bands in the UVevis region. The low energy bands are assigned to ligand to metal charge transfer transitions (LMCT). It can be observed that, the nature of the dithiolene ligands, do not modify significantly the absorption spectra only a bathochromic shift of about 30 nm can be noticed for Cp2Ti(tBu-thiazds) when compared with Cp2Ti(MeS-tzdt). The gold complexes exhibit absorption bands in only the UVevis region. There again a 20 nm bathochromic shift can be observed between the [PPh4][Au(tButhiazdt)2] 6 and [PPh4][Au(MeS-tzdt)2] 8 (Fig. 5). In accordance with the redox properties of the complexes the tBu-thiazdt ligand exerts a slightly stronger electron releasing effect than the MeStzdt ligand.
3. Conclusions Heteroleptic and homoleptic dithiolene metal complexes such as Cp2Ti(dithiolene), [Zn(dithiolene)2]2 and [Au(dithiolene)2]1 complexes were prepared from the 1-tertiobutyl-1,3-thiazoline-2thione-4,5-dithiolate (tBu-thiazdt) dithiolene ligand. In the presence of MeI, the ligand within these complexes undergo a transformation into a 2-methylthio-1,3-thiazole one with elimination of the tBu substituent. In addition, for the Zn complex, alkylation of the sulfur atoms of the metallacycles is followed by decoordination of the formed tris(methylthio)thiazole derivative. The reactivity of the dithiolene ligand towards MeI without affecting the metalsulfur bonds observed here, within the titanocene and the gold complexes, will be explored in the near future for functionalizing these dithiolene complexes with different alkyl iodide derivatives in order to introduce either groups able to form hydrogen or halogen bonding.
Fig. 5. UVevis absorption spectra of [PPh4][Au(tBu-thiazdt)2] 6 and [PPh4][Au(MeStzdt)2] 8.
4. Experimental 4.1. General NMR spectra were recorded on a Bruker AV300III spectrometer at room temperature using CDCl3 unless indicated otherwise. Chemical shifts are reported in ppm and 1H NMR spectra were referenced to residual CHCl3 (7.26 ppm) and 13C NMR spectra were referenced to CHCl3 (77.2 ppm). Mass spectra were recorded with Bruker MicrOTOF-Q II instrument for complex 3 and compound 4, and with Thermo-fisher Q-Exactive instrument for complexes 2, 5 gional de Mesures Physiques de l’Ouest, and 6 by the Centre Re Rennes. CVs were carried out on a 103 M solution of complex in CH2Cl2-[NBu4][PF6] 0.1 M. CVs were recorded on a Model 362 scanning potentiostat from EG&G Instruments at 0.1 V1 on a platinum disk electrode. Potentials were measured versus KCl Saturated Calomel Electrode (SCE). Column chromatography was performed using silica gel Merck 60 (70e260 mesh). All other reagents and materials from commercial sources were used without further purification. The N-tBu-1,3-thiazoline-2-thione 1 was prepared according to literature procedure [16]. 4.2. Synthesis and characterization [Cp2Ti(tBu-1,3-thiazoline-2-thione-4,5-dithiolate)] 2. Under inert atmosphere at 10 C, LDA was prepared by adding BuLi (2.7 mL, 4.3 mmol, 1.6 M in hexanes) to a solution of diisopropylamine (0.4 mL, 4.3 mmol) in 15 mL of anhydrous THF. The LDA solution was then added to a solution of 1,3-thiazoline-2-thione 1 (0.50 g, 2.8 mmol) of 1,3- thiazoline -2-thione 1 dissolved in 40 mL of anhydrous THF. After stirring for 30 min at 10 C, sulfur (S8, 0.14 g, 4.3 mmol) was added and the solution was stirred for an additional 30 min. A solution of 5.7 mmol of LDA was added to the reaction medium and after 3 h of stirring sulfur (0.19 g, 5.7 mmol) was added. After 30 min of stirring Cp2TiCl2 (1.1 g, 4.3 mmol) was added and the reaction mixture was stirred for 15 h. The solvent was evaporated and the residue was extracted with dichloromethane. The organic phase was washed with water and then dried over MgSO4. The resulting solid was purified by column chromatography using dichloromethane as eluent. Cp2Ti(tBu-thiazdt) 2 was isolated as a blue powder (m ¼ 0.78 g). in 68% yield, mp ¼ 148 C. Rf ¼ 0.72, (SiO2, CH2Cl2). 1H NMR (300 MHz) d 1.91 (s, 9H, CH3), 5.57 (s, 5H, Cp), 6.09 (s, 5H, Cp); 13C NMR (75 MHz) d 30.5 (CeCH3), 68.4 (CeCH3), 107.5 (Cp), 111.6 (Cp), 135.8 (C]C), 147.8 (C]C), 193.5 (C]S); HRMS (ASAP) calcd for [MþH]þ C17H20NS4Ti: 413.99526 Found: 413.9953. Anal calcd for C17H19NS4Ti: C, 47.38; H, 4.63; N, 3.39. Found: C, 47.17; H, 4.47; N, 3.55. [Cp2Ti(2-MeS-1,3-thiazole-4,5-dithiolate)] 3. To a solution of [Cp2Ti(tBu-thiazdt)] 2 (0.66 g, 1.6 mmol) in 20 mL of dichloromethane, CH3I (2.24 gr, 16 mmol) was added. The reaction mixture was refluxed for 2 h. The solvent was removed under vacuum and the resulting solid was purified by column chromatography using dichloromethane as eluent. [Cp2Ti(-2-MeS-1,3-thiazdt)] 3 was obtained as a blue powder, yield ¼ 90%, mp ¼ 150 C; Rf ¼ 0.66, (SiO2, CH2Cl2). 1H NMR (300 MHz) d 2.72 (s, 3H, SCH3), 5.52 (s, 5H, Cp), 6.14 (s, 5H, Cp); 13C NMR (75 MHz) d 15.7 (SeCH3), 107.7 (Cp), 111.6 (Cp), 139.6 (C]C), 158.8 (C]C), 170.4 (C]N); HRMS (ESI) calcd for C14H13NS4Ti: 371.94886. Found. 371.9503. Anal calcd for C14H13NS4Ti: C, 45.28; H, 3.53; N, 3.77; S, 34.53. Found: C, 44.77; H, 3.49; N, 3.71; S, 34.59. [Cp2Ti(MeS-1,3-thiazole-4,5-dithiolate)] 3 from 1. Similar procedure as the one described for the synthesis of 2 until the addition of Cp2TiCl2. After the addition Cp2TiCl2, the reaction mixture was stirred for 30 min at 10 C, and then an excess of iodomethane for 3 was added to the medium. The reaction was
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stirred overnight. The solvent was evaporated under vacuum and the solid was extracted with dichloromethane. The organic phase was washed with water, dried over MgSO4. The resulting solid was purified by column chromatography using dichloromethane as eluent. (m ¼ 0.54 g). According to this procedure 3 was obtained in 56% yield. 6-(tBu)-5-thioxo-5,6-dihydro-[1,3]dithiolo[4,5-d] thiazole-2one 4. Under inert atmosphere, to a solution of 2 (0.73 mmol, 0.30 g for 2) in 20 mL of THF, triphosgene (0.43 g, 1.46 mmol) was added. The reaction mixture was refluxed under inert atmosphere for 25 mn. The medium was cooled to room temperature and 2.5 mL of water were added. The solvent was evaporated under vacuum and the solid residue was dissolved in CH2Cl2 (20 mL). The organic phase was washed with water (3 20 mL) and dried with MgSO4. The bicyclic derivative was purified by column chromatography using dichloromethane as eluent and 4 was isolated as yellow crystals in 94% yield, mp ¼ 110 C; Rf ¼ 0.90, (SiO2, CH2Cl2); 1 H NMR (300 MHz) d 1.98 (s, 9H, CH3); 13C NMR (75 MHz) d 28.4 (CH3), 67.2 (C(CH3)3)), 115.5 (¼C), 188.9 (C]O), 199.9 (C]S); IR ʋ (cm1): 1674(C]O); HRMS (ESI) calcd for C8H10NOS4 [MþH]: 263.96453 Found. 263.9646. Anal calcd for C8H9NOS4: C, 36.48; H, 3.44; N, 5.32. Found: C, 36.68; H, 3.49; N, 5.34. [NEt4]2[Zn(tBu-thiazdt)2] 5 Under an inert atmosphere and at room temperature, a solution of MeONa 1 M in MeOH (6 mL, 6 mmol) was added to 1,3-thiazoline-2-ones 19 (0.16 g, 0.61 mmol). After dissolution of the compound, zinc chloride (ZnCl2) (0.05 g, 0.37 mmol) dissolved in 5 mL of dry methanol was added to the reaction medium. After stirring 4 h, tetraethylammonium bromide (NEt4Br) (0.26 g, 1.22 mmol) dissolved in 5 mL of dry methanol was added to the medium. Then the reaction was stirred overnight at room temperature under argon atmosphere. The yellow was introduced to a flask containing diethylether to pre. The Zn complexes crystallize from acetonitrile (m ¼ 0.15 g), yield ¼ 95%, mp ¼ 150 C. 1H NMR (CD3CN, 300 MHz) d 1.21 (t, 24H, CH3), 2.11 (s, 18H, CH3), 3.16 (q, 16H, CH2); 13C NMR (DMSO-d6, 75 MHz) d 6.8 (CH3), 30.7 (CH3), 55.2 (CH2), 66.4 (C(CH3)3), 119.7 (C]C), 141.6 (C] C), 181.7 (C]S). HRMS (ESI) calcd for [A2] C14H18N2S8Zn: 266.92691 Found. 266.9268. [PPh4][Au(tBu-thiazdt)2] 6. Under an inert atmosphere and at room temperature, a solution of sodium methanolate 1 M in MeOH (6 mL, 6 mmol) was added to the bicyclic derivative 4 (0.15 g,
187
0.57 mmol). After dissolution of the compound, potassium tetrachloroaurate (III) hydrate, KAuCl4.H2O, (0.13 g, 0.34 mmol) dissolved in 5 mL of dry methanol were added to the reaction mixture. After stirring 4 h, tetraphenylphosphonium chloride (0.13 g, 0.34 mmol) dissolved in 5 mL of dry methanol were added to the medium. Then the reaction was stirred overnight at room temperature under argon atmosphere. The precipitate was filtered off and dissolved in acetonitrile. The gold complex crystallize in acetonitrile (m ¼ 0.15 g) and was isolated as green crystal. yield ¼ 54%, mp ¼ 210 C; 1H NMR (300 MHz) d 2.01 (s, 9H, CH3), 7.64 (m, 8H, CH,Ar), 7.76 (m, 8H, CHAr), 7.89 (m, 4H, CH, Ar); 13C NMR (75 MHz) d 30.4 (NeC(CH3)3), 67.6 (NeC(CH3)3), 116.6 (C, Ar), 117.2 (C]C), 117.8 (C, Ar), 130.5 (C, Ar), 133.6 (C]C), 134.1 (C, Ar), 135.6(C, Ar), 194.6 (C]S); HRMS (Q-Exactive) [2A, Cþ]þ for C52H56N4PS16Au2: Calcd: 1672.91108. Found: 1672.9113; Anal calcd for C34H38AuN2PS8: C, 45.32; H, 3.80; N, 2.78; S, 25.47. Found: C, 45.34; H, 3.71; N, 2.74; S, 24.83. 2,4,5-trimethylthio-thiazole 7. The dianionic Zn complex 5 (0.2 g, 0.25 mmol) was dissolved in 20 mL of dichloromethane. An excess of MeI was then added (0.25 mL, 4 mmol) and the reaction mixture was stirred at room temperature for 2 min. The solvent was removed in vacuum and the residue was purified by column chromatography using dichloromethane as eluent. 7 was obtained as a yellow oil in 73% yield. 1H NMR (300 MHz) d 2.36 (s, 3H, CH3), 2.61 (s, 3H, CH3), 2.66 (s, 3H, CH3); 13C NMR (75 MHz) d 28.4 (CH3), 34.7 (CH3), 41.9 (CH3), 105.5 (C]C), 154.2 (C]C), 168.2 (C]N); HRMS (ESI) calcd for C6H10NS4 [MþH]: 223.96906 Found. 223.969. [PPh4][Au(MeS-tzdt)2] The monoanionic gold dithiolene complex [PPh4][Au(tBu-thiazdt)2] (50 mg, 4.97 105 mol) was dissolved in 10 mL of CH2Cl2. An excess of MeI was added to the reaction medium and the solution was refluxed for 1 h. After cooling, a greenish precipitate was formed. The solid was filtered and washed with dichloromethane (m ¼ 20 mg). Complex 8 was obtained as green powder in 44% yield. mp ¼ 230 C; 1H NMR (300 MHz) d 2.59 (s, 6H, CH3), 7.63 (m, 8H, CH, Ar), 7.75 (m, 8H, CH, Ar), 7.85 (m, 4H, CH, Ar); 13C NMR (DMSO-d6, 75 MHz) d 17.3 (SeCH3), 118.1 (C, Ar), 122.7 (C]C), 130.8 (C, Ar), 134.9 (C, Ar), 135.7 (C, Ar), 148.3 (C]C), 169.7 (C]N); HRMS (ESI) Calcd. for [A] C8H6N2S8Au: 582.79678. Found: 582.7967. Anal. Calcd. for C32H26AuN2PS8: C, 41.64; H, 2.84; N, 3.03. Found: C, 41.74; H, 2.84; N, 2.99.
Table 4 Crystallographic data for [Cp2Ti(tBu-thiazdt)] 2, [Cp2Ti(MeS-tzdt)] 3 and [PPh4][Au(tBu-thiazdt)2] 6 complexes. Compound
Cp2Ti(tBu-thiazdt) 2
Cp2Ti(MeS-tzdt) 3
[PPh4][Au(tBu-thiazdt)2] 6
Formulae FW (g.mol1) System Space group a (Å) b (Å) c (Å) a (deg) b (deg) g (deg) V (Å3) T (K) Z Dcalc (g.cm1) m (mm1) Total refls Abs corr Uniq refls (Rint) Uniq refls (I > 2s(I)) R1, wR2 R1, wR2 (all data) GOF
2(C17H19NS4Ti) 826.94 triclinic P-1 11.5094(9) 12.0571(9) 13.4730(10) 93.252(3) 90.450(3) 103.308(2) 1816.1(2) 294 2 1.512 0.928 21450 multiscan 8154(0.0409) 6786 0.0833, 0.1942 0.0980, 0.2055 1.061
C14H13NS4Ti 371.39 monoclinic C2/c 12.1924(2) 10.4359(2) 23.4526(5) 90 93.3850(10) 90 2978.87(10) 150(2) 8 1.656 1.122 12933 multiscan 3425(0.0477) 3002 0.0297, 0.0803 0.0367, 0.0971 1.151
(C14H18AuN2S8, C24H20P) 1007.12 monoclinic C2/c 28.4935(16) 7.5674(4) 24.2516(13) 90 131.173(2) 90 3936.1(4) 150(2) 4 1.7 4.234 11632 multi-scan 4511(0.04) 3433 0.0381, 0.1026 0.0535, 0.1138 1.036
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4.3. Crystallography
References
Data were collected on an APEX II Brucker AXS diffractometer for 3 and 8 and on D8 VENTURE Bruker AXS diffractometer for 2, Mo-Ka radiation (l ¼ 0.71073 Å). The structures were solved by direct methods using the SIR97 program [17], and then refined with full-matrix least-square methods based on F2 (SHELXL-97) [18] with the aid of the WINGX program [19]. All non-hydrogen atoms were refined with anisotropic atomic displacement parameters. H atoms were finally included in their calculated positions. Details of the final refinements are given in Table 4 for all compounds.
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Supplementary material Crystallographic data for structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC 1479118-1479120 for complexes 2, 3, 6 respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union road, Cambridge CB2 1EZ, UK (Fax: þ44 1223 336033; e-mail: [email protected] or www: http://www. ccdc.cam.ac.uk).
Acknowledgements Financial support was obtained from ANR (Paris, France) under contract n 12-BS07-0032-01.