Different coordination modes for disulfoxides towards diorganotin(IV) dichlorides. X-ray crystal structures of 1,2-cis-bis-(phenylsulfinyl)ethene (rac-,cis-cbpse) and adducts [{Ph2SnCl2(meso-bpse)}n] and [{n-Bu2SnCl2(pdtd)}2]

ARTICLE

Different coordination modes for disulfoxides towards diorganotin(IV) dichlorides. X-ray crystal structures of 1,2-cis-bis-(phenylsulfinyl)ethene (rac-,cis-cbpse) and adducts [{Ph₂SnCl₂(meso-bpse)}_n] and [{n-Bu₂SnCl₂(pdtd)}₂]

Gerimário F. de Sousa^I,*; Javier Ellena^II; Valéria R. S. Malta^III; José D. Ardisson^IV

^IInstituto de Química, Universidade de Brasília, 70919-970 Brasília-DF, Brazil

^IIInstituto de Física de São Carlos, Universidade de São Paulo, 13560-970 São Carlos-SP, Brazil

^IIIDepartamento de Química e Biotecnologia, Universidade Federal de Alagoas, 57072-970 Alagoas-AL, Brazil

^IVLaboratório de Física Aplicada, Centro de Desenvolvimento de Tecnologia Nuclear, 30123-970 Belo Horizonte-MG, Brazil

ABSTRACT

The reactions of meso-1,2-bis(phenylsulfinyl)ethane (meso-bpse) with Ph₂SnCl₂, 2-phenyl-1,3-dithiane trans-1-trans-3-dioxide (pdtd) with n-Bu₂SnCl₂ and 1,2-cis-bis-(phenylsulfinyl)ethene (rac-,cis-cbpse) with Ph₂SnCl₂, in 1:1 molar ratio, yielded [{Ph₂SnCl₂(meso-bpse)}_n], [{n-Bu₂SnCl₂(pdtd)}₂] and [{Ph₂SnCl₂(rac,cis-cbpse)}_x] (x = 2 or n)_, respectively. All adducts were studied by IR, Mössbauer and ¹¹⁹Sn NMR spectroscopic methods, elemental analysis and single crystal X-ray diffractometry. The X-ray crystal structure of [{Ph₂SnCl₂(meso-bpse)}_n] revealed the occurrence of infinite chains in which the tin(IV) atoms appear in a distorted octahedral geometry with Cl atoms in cis and Ph groups in trans positions. The X-ray crystal structure of [{n-Bu₂SnCl₂(pdtd)}₂] revealed discrete centrosymmetric dimeric species in which the tin(IV) atoms possess a distorted octahedral geometry with bridging disulfoxides in cis and n-butyl moieties in trans positions. The spectroscopic data indicated that the adduct containing the rac,cis-cbpse ligand can be dimeric or polymeric. The X-ray structural analysis of the free rac-,cis-cbpse sulfoxide revealed that the crystals belong to the C2/c space group.

Keywords: Tin(IV) complexes, disulfoxide ligand, crystal structure

RESUMO

As reações de meso-1,2-bis(fenilsulfinil)etano (meso-bpse) com Ph₂SnCl₂, de 2-fenil-1,3-ditiona trans-1-trans-dióxido (pdtd) com n-Bu₂SnCl₂ e de 1,2-cis-bis-(phenylsulfinyl)ethene (rac-,cis-cbpse) com Ph₂SnCl₂, na proporção molar 1:1, levaram à formação de [{Ph₂SnCl₂(meso-bpse)}_n], [{n-Bu₂SnCl₂(pdtd)}₂] e [{Ph₂SnCl₂(rac,cis-cbpse)}_x] (x = 2 ou n)_, respectivamente. Na investigação das propriedades estruturais dos produtos foram empregadas as espectroscopias de absorção no infravermelho, Mössbauer e RMN de ¹¹⁹Sn, além de análise elementar e difratometria de raios X em monocristal. O estudo de [{Ph₂SnCl₂(meso-bpse)}_n] por difratometria de raios X revelou a ocorrência de um encadeamento infinito no qual os átomos de tin(IV) apresentam uma geometria octaédrica distorcida com os átomos de Cl em posições cis e os grupos Ph em trans. A estrutura cristalina de [{n-Bu₂SnCl₂(pdtd)}₂] revelou a presença de espécies diméricas centrossimétricas nas quais os átomos de tin(IV) possuem geometria octaédrica distorcida com dissulfóxidos em ponte ocupando posições cis e grupos n-butila ocupando posições trans. Os dados espectroscópicos indicaram que o produto contendo o ligante rac,cis-cbpse pode ser dimérico ou polimérico. O estudo por difratometria de raios X do sulfóxido rac-,cis-cbpse livre revelou que os cristais pertencem ao grupo espacial C2/c.

Introduction

Organotin(IV) compounds have been demonstrated to exhibit wide biological activity.^1,2 Insofar as many sulfoxides are also noteworthy for the same reasons,³ a combination of the two chemistries is an interesting line to pursue. The Lewis base rac-,cis-1,2-bis(phenylsulfinyl)ethene (rac-,cis-cbpse) is known to bond to different metal centres via either the O atoms, the S atoms or the olefinic (-HC=CH-) centre. An O,O-bonded chelate with this ligand has been described for a typically 'hard' Lewis acid, namely Ph₃SnCl,⁴ whereas the 'softer' platinum(II) species interacts exclusively with the S atoms to afford an S,S-bonded 5-membered ring.⁵ On the other hand, the very soft platinum(0) site, interestingly, yielded yet another ligating mode, namely an h²-alkene platinum(0) linkage.⁶ It is thus apparent that the two factors, inherent basicity and hardness/softness, play a part in complex formation.⁶

Filgueiras and collaborators⁴ have shown that the reactions of Ph₃SnCl with disulfoxides of the type meso-,rac-PhSO(CH₂CH₂)SOPh [1,2-bis-(phenylsulfinyl)ethane: meso-,rac-bpse] and rac-,cis-PhSO(HC=CH)SOPh [1,2-cis-bis(phenylsulfinyl)ethene: rac-,cis-cbpse], in 1:1 ratio (acid:base), afford adducts of stoichiometry [Ph₃SnCl(meso-,rac-bpse)] and [Ph₃SnCl(rac-,cis-cbpse)], respectively. On the other hand, Zhu et al.⁷ have reported the preparation and crystal structure of a bridged 2:1 (acid:base) bimetallic adduct of formula [(Ph₃SnCl)₂(meso-bpse)]. In contrast with these results, the X-ray structure of the adduct [{Me₂SnCl₂(meso-bpse)}_n] has been determined and revealed the occurrence of polymeric chains along the crystallographic a axis in which the ligand and organotin(IV) moiety alternate.⁸

Herein, we describe the preparation and X-ray crystal structure of rac-,cis-cbpse and of the adducts [{Ph₂SnCl₂(meso-bpse)}_n] and [{n-Bu₂SnCl₂(pdtd)}₂], where the second compound shows an uncommon coordination mode of a disulfoxide (pdtd) towards a diorganotin(IV) dihalide, namely n-Bu₂SnCl₂. The spectroscopic data has shown that the adduct [{Ph₂SnCl₂(rac-,cis-cbpse)}_x] (x = 2 or n) possesses either dimeric or polymeric molecules. In spite of being bifunctional, pdtd, meso-bpse and rac-,cis-cbpse act as bis-monodentate ligands, as a result of their peculiar stereochemistry.

Experimental

Materials and methods

Solvents and diorganotin(IV) dichorides were commercially available (Aldrich) and were used as supplied. The disulfoxides pdtd, meso-bpse and rac-,cis-cbpse were kindly provided by Prof. C. Celso, who had prepared them previously.⁴ The adducts [Ph₂SnCl₂(meso-cbpse)] (m.p. 138-141 ºC), [{n-Bu₂SnCl₂(pdtd)}₂] (m.p. 265-267 ºC) and [{Ph₂SnCl₂(rac-,cis-cbpse)}_x] (m.p. 85-87 ºC) were synthesized by the following procedure: equal amounts (0.50 mmol) of both the diorganotin(IV) dichloride and the appropriate sulfoxide were dissolved in EtOH. After refluxing for 1 h, the solution was filtered and a clear filtrate was obtained. Slow cooling and evaporation of the first two solutions afforded an abundant crop of colorless crystals (ca. 60% yield) appropriated for X-ray diffraction analysis. [{Ph₂SnCl₂(meso-bpse)}_n]: Found: C, 44.8; H, 3.4; S, 5.9. Calcd. for C₃₆H₃₄Cl₄O₂S₂Sn₂: C, 45.9, H, 3.6, S, 6.1%. [{n-Bu₂SnCl₂(pdtd)}₂]: Found: C, 40.3; H, 5.4; S, 12.2. Calcd. for C₃₆H₆₀Cl₄O₄S₄Sn₂: C, 40.6, H, 5.7, S, 12.0%. [{Ph₂SnCl₂(rac-,cis-cbpse)}_x] (x = 2 or n): Found: C, 49.5; H, 3.51; S, 9.8. Calcd. For C₅₂H₄₄Cl₄O₄S₄Sn₂: C, 50.3, H, 3.58, S, 10.3%.

Physical measurements

IR spectra were recorded on a Bomem MB100 FT-IR spectrophotometer in the 4000-400 cm^-1 range using KBr pellets. ¹¹⁹Sn, ¹H and ¹³C NMR spectra were run on a Bruker Advance DRX 400 MHz spectrophotometer using CDCl₃. Chemical shifts are related to tetramethylsilane (tms) and SnMe₄. ¹¹⁹Sn Mössbauer spectra were collected at 100 K in the transmission geometry on a constant-acceleration conventional spectrometer by using a CaSnO₃ source kept at room temperature. All isomer shift values reported in this work are given with respect to this source. All Mössbauer spectra were computer-fitted assuming Lorentzian line shapes and the resulting isomer shifts and quadrupole splittings are accurate to ca. ± 0.05 mm s^-1. The microanalyses for C, H, N and S were performed in a Fissons EA 1108 elemental analyzer.

X-ray crystallography studies

Crystallographic data for rac-,cis-cbpse and adducts [{Ph₂SnCl₂(meso-bpse)}_n] and [{n-Bu₂SnCl₂(pdtd)}₂] are listed in Table 2. Selected bond distances and angles are presented in Table 3. Crystal data for all compounds were collected at 293(2) K on a Enraf-Nonius Kappa-CCD area detector diffractometer with graphite-monochromated MoK_β radiation (λ = 0.71073 Å). Data collections employed the COLLECT program,⁹ integration and scaling of the reflections were performed with the HKL Denzo-Scalepack system¹⁰ and absorption corrections were carried out using the multi-scan method.¹¹

Results and Discussion

IR spectroscopy

Table 1 shows the selected infrared data. The IR spectra of the disulfoxides (meso-bpse, pdtd and rac-,cis-cbpse) show very strong ν(S=O) absorptions at 1037, 1044 and 1040 cm^-1, respectively, which appear at 998, 981 and 965 cm^-1 in the spectra of the corresponding adducts. This behavior is consistent with the fact that both S=O groups are bonded to the metal, causing the shift to lower frequency. The IR spectra of the adducts also show bands at 456 cm^-1 for [{Ph₂SnCl₂(meso-bpse)}_n], at 413 cm^-1 for [{ⁿBu₂SnCl₂(pdtd)}₂]_, and at 459 cm^-1 for [{Ph₂SnCl₂(rac-,cis-cbpse)}_x], which were assigned to the ν(Sn-O) vibration.⁴ The Δν(S=O) value of 75 cm^-1 calculated for rac-,cis-cbpse and its comparison with the 63 cm^-1 shift for meso-bpse indicates that the unsaturated ligand is much more basic than the saturated one.⁴

NMR spectroscopy

The ¹H and ¹³C NMR spectra for rac-,cis-cbpse in CDCl₃ show a singlet resonance at δ = 6.78 and δ = 144.0 ppm attributed, respectively, to the chemically and magnetically equivalent protons and carbons present in the ethylene (-HC=CH-) moiety. Regarding the ¹¹⁹Sn NMR, the chemical shifts, δ(¹¹⁹Sn), relative to SnMe₄ in six-coordinate organotin(IV) derivatives were found to lie between ca. -125 and -515 ppm,¹² whereas those from five-coordinate species from +25 to -319 ppm.¹³ A series of five-coordinate diphenyltin(IV) complexes were found to have shifts from -62 to -276 ppm.¹⁴ Therefore, the chemical shift values of +69 and -115 ppm found for [{n-Bu₂SnCl₂(pdtd)}₂] and [{Ph₂SnCl₂(rac-,cis-cbpse)}_x], respectively, are indicative of considerable shielding and five-coordination of the tin(IV) atoms. In view of this, in CDCl₃ solution both adducts are considerably dissociated, suggesting that the six-coordination pattern in the solid state has not remained in solution.

Mössbauer spectroscopy

¹¹⁹Sn Mössbauer spectral parameters of the disulfoxide derivatives are reported in Table 1, which includes parameters from literature for comparison. The similarity among the quadrupole splittings (Δ) observed for [{Ph₂SnCl₂(meso-bpse)}_n] (3.73 mm s^-1), [{Me₂SnCl₂(meso-bpse)}₂] (3.54 mm s^-1), [{n-Bu₂SnCl₂(pdtd)}₂] (3.59 mm s^-1) and [{Ph₂SnCl₂(rac-,cis-cbpse)}_x] (3.71 mm s^-1) compared to [Ph₂SnCl₂(pdtd)] (D = 2.85 mm s^-1) may be accounted for by a greater asymmetry in the electronic density distribution around the tin(IV) in the first three adducts. These results indicate that [Ph₂SnCl₂(pdtd)] is five-coordinate, while the others are six-coordinate in the solid state.

The isomer shift (δ) is very sensitive to the first coordination sphere and is dependent on the nature and number of organic groups bonded to the tin(IV) nucleus. This parameter is correlated to the change of s-electron density on the metal by means of the +I inductive effect imposed by the ligands, and a result of this is the inverse dependence of δ with electronegativity.¹⁵ Thus, d increases on replacing the Ph by the Me groups in the coordination sphere of tin(IV), as given by the adducts [{Ph₂SnCl₂(meso-bpse)}_n] (1.28 mm s^-1) and [{Me₂SnCl₂(meso-bpse)}₂] (1.35 mm s^-1) (Table 1). The similarity in isomer shifts observed in [{n-Bu₂SnCl₂(pdtd)}₂] (1.49 mm s^-1) and in [{Ph₂SnCl₂(rac-,cis-cbpse)}_x] (1.50 mm s^-1) is noteworthy. The d value of 1.50 mm s^-1 may be a consequence of the much more basic behavior of the unsaturated rac-,cis-cbpse ligand compared to the saturated meso-cbpse ligand. These results are corroborated by IR and ¹¹⁹Sn NMR spectroscopies. The lower value of δ found in the five-coordinate adduct [Ph₂SnCl₂(pdtd)] (δ = 1.32 mm s^-1)¹⁶ is a consequence of rehybridization (sp³d) of tin(IV), which may be thought of as a linear combination of sp² and p_zd_z² orbitals. Thus, the equatorial Sn-C bonds will have greater s-character and smaller p-character, thereby decreasing the δ value.¹⁷

Crystal structure of rac-,cis-cbpse

Figure 1 depicts the molecular structure of rac-,cis-cbpse obtained by oxidation of 1,2-cis-bis(phenylsulfide)ethene with 30% H₂O₂ in HOAc. Selected bond distances and angles with their estimated standard deviations are listed in Table 3. Crystals of the rac-,cis-cbpse isomer belong to the C2/c space group. The structure of this dissulfoxide shows that the S=O sulfinyl groups are trans to each other, and the same is observed for the Ph groups, as seen from the O1-S1-C7-C7#1 and C1-S1-C7-C7#1 torsion angles of 133.7(2)º and -117.3(2)º, respectively. The S=O groups are quasi-coplanar with the their bonded Ph rings, as shown by the O1-S1-C2-C6 torsion angle of 7.15(18)º, due to the conjugation between the sulfur lone pairs and the π-systems of the Ph rings. This observation was also previously reported for other phenylsulfinyl derivative.¹⁸

Crystal structure of [{Ph ₂ SnCl ₂ (meso-bpse)} _n ]

Figure 2 shows the molecular structure of the adduct [{Ph₂SnCl₂(meso-bpse)}_n]. Its structure determination revealed the occurrence of infinite chains along the crystallographic a axis; additionally, each meso-bpse molecule has an inversion centre at the -H₂C-CH₂- (ethane) group midpoint. The tin(IV) atom is octahedrally coordinated by Cl atoms at cis [Sn-Cl: 2.4591(9), 2.4648(7) Å], by Ph carbon atoms at trans [Sn-C: 2.130(3), 2.133(3) Å], and by the two O atoms from the S=O groups at cis positions [Sn-O: 2.3527(19), 2.3979(18) Å]. The ligand bonds through both O atoms and forms bridges between the tin(IV) atoms, generating chains along the n glide. This kind of chain, along with similar bond distances and angles, has also been observed when Me₂SnCl₂ replaces Ph₂SnCl₂. For example, bond distances Sn-C [2.101(4), 2.105(5 Å)], Sn-O [2.397(3), 2.404(3) Å], Sn-Cl [2.482(1), 2.486(1) Å] and bond angles Me-Sn-Me [165.2(2)º], O-Sn-O [86.03(1)º] and Cl-Sn-Cl [98.73(4)º] have been observed for [{Me₂SnCl₂(meso-bpse)}_n].¹⁹

Crystal structure of [{n-Bu ₂ SnCl ₂ (pdtd)} ₂ ]

Figure 3 presents the molecular structure of the dimer [{n-Bu₂SnCl₂(pdtd)}₂]. The X-ray crystal structure revealed a discrete centrosymmetric dimeric assembly in which the tin(IV) atoms possess a distorted octahedral geometry originated from the bis-monodentate disulfoxide bonded through the O atoms. One of the n-Bu group is disordered (C1a-C4a), while the other group (C5-C8) does not show any sign of disorder. The dimeric assembly occurs via a 12-membered ring (Sn₂C₂O₄S₄) formation and constitutes the first example of a diorganotin(IV) dichloride bonded to a disulfoxide ligand in a 1:1 molar ratio. Usually, most 1:1 adducts of diorganotin(IV) dihalides with disulfoxides form polymeric alternating chains^19-21 containing six-coordinate tin(IV), but 1:1 five-coordinate adducts are rare. In view of this, it is interesting to compare our results with literature data for the five-coordinate adduct [Ph₂SnCl₂(pdtd)].¹⁶ The trigonal bipyramidal structure of the monomer [Ph₂SnCl₂(pdtd)] shows two nearly identical equatorial bond distances Sn-C [2.11(5); 2.122(5) Å] and different axial Sn-Cl [2.455(1) Å] and equatorial Sn-Cl [2.346(2) Å] bond lengths, as expected. The Sn-O distance [2.367(3) Å] is significantly shorter than the similar Sn-O [2.482(3) and 2.755(3) Å] observed for our dimeric adduct, probably due to the more acidic nature of Ph₂SnCl₂ compared to n-Bu₂SnCl₂, whereas the two S=O distances of 1.533(4) and 1.450(6) Å are significantly different, as a consequence of the former being complexed to tin(IV) and the latter remaining uncoordinated. However, in our dimeric adduct the shorter S=O distances of 1.501(3) and 1.512(3) Å indicate that the acid-base interactions are not strong enough. Perhaps, the long Sn-O1# bond distance of 2.755(3) Å is the reason the dimer dissociates in solution to the monomeric form, as suggested by spectroscopic data (Table 1). The values of the 90.35(6)º angle subtended by the two Cl atoms and of the equatorial C-Sn-C bond angle [138.6(2)º] observed in [Ph₂SnCl₂(pdtd)] are smaller than the equivalent angles found in our octahedral adduct, as expected (Table 3).

Structure of [{Ph ₂ SnCl ₂ ∙(rac-,cis-cbpse)} _x ] (x = 2 or n)

The spectroscopic data shown in Table 1 indicate that [{Ph₂SnCl₂(rac-,cis-cbpse)}_x] do not show any evidence of a monomeric adduct in which the tin(IV) atoms exhibit trigonal bipyramidal geometry in the solid state. However, the same spectroscopic data are not sufficient to characterize the product as being a dimeric [{Ph₂SnCl₂(rac-,cis-cbpse)}₂], or a polymeric [{Ph₂SnCl₂(rac-,cis-cbpse)}_n] compound containing octahedral tin(IV) centres.

Conclusions

The reaction between Ph₂SnCl₂ and the disulfoxide pdtd in 1:1 molar ratio affords a monomeric¹⁶ adduct containing a five-coordinate tin(IV) centre, while a similar reaction with n-Bu₂SnCl₂ affords dimeric species in which the tin(IV) atoms are six-coordinate. Surprisingly, the characterization of the adduct [{Ph₂SnCl₂(rac-,cis-cbpse)}_x] as being a dimeric or a polymeric species was not possible using microanalysis and spectroscopic methods such as IR, NMR and ¹¹⁹Sn Mössbauer.

Acknowledgements

The authors are grateful to Prof. C. Celso for providing the sulfoxides used in this work and to Prof. G. M. Lima (UFMG) for the ¹¹⁹Sn NMR spectra. CNPq, FAPESP, FINEP (CT INFRA 0970/01) are thanked for financial support.

Supplementary Information

Crystallographic data for the compounds have been deposited at the Cambridge Crystallographic Data Center with the deposition numbers CCDC 694402 for rac-,cis-cbpse, CCDC 679894 for [{Ph₂SnCl₂(meso-bpse)}_n] and CCDC 693796 for [{n-Bu₂SnCl₂(pdtd)}₂]. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (Fax: [phone] or e-mail: [e-mail]).

Received: August 22, 2008

Web Release Date: August 14, 2009

FAPESP helped in meeting the publication costs of this article

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Publication Dates

• Publication in this collection
  30 Oct 2009
• Date of issue
  2009

History

• Received
  22 Aug 2008
• Accepted
  14 Aug 2009