Spectroscopic and thermal properties of stannadithiane compounds bearing endocyclic ether and lactone groups

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 210 (2019) 222–229

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Spectroscopic and thermal properties of stannadithiane compounds bearing endocyclic ether and lactone groups Zuly Y. Delgado Espinosa a, Ileana Daniela Lick b, Aamer Saeed c, Carlos O. Della Védova a, Mauricio F. Erben a,⁎ a b c

CEQUINOR (UNLP, CONICET-CCT La Plata), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Boulevard 120 e/60 y 64 N°1465, La Plata 1900, Argentina CINDECA (UNLP, CONICET-CCT La Plata), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Calle 47, N° 257, La Plata B1900BJW, Argentina Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan

a r t i c l e

i n f o

Article history: Received 2 August 2018 Received in revised form 9 October 2018 Accepted 12 November 2018 Available online 13 November 2018 Keywords: Tin compounds Stannadithiane Raman Infrared Conformation Pseudopotential

a b s t r a c t Four related stannadithiane compounds containing different endocyclic functional groups -including ether (1), diether (2), lactone (3), and spirolactone (4)- were prepared. The conformational landscape has been fully determined for the 8-membered representative (compound 1) resulting in a distorted crown form with the butyl chains adopting an extended conformation. The infrared and Raman spectra of stannadithiane species have been measured and interpreted, aided by quantum chemical calculations and potential energy surface analysis. Special attention has been devoted to the analysis of the vibrational features of the heterocyclic moieties. The characteristic νas(Sn\\S) and νs(Sn\\S) stretching modes of the SnS2 endo-cyclic group were clearly observed in the Raman spectra at around 340 and 315 cm−1, respectively. The exo-cyclic ν(Sn\\C) stretching modes were found near 590 and 565 cm−1 for the antisymmetric and symmetric motions, respectively. Thermal behavior for compounds 2–4 has been determined by thermogravimetric methods. © 2018 Elsevier B.V. All rights reserved.

1. Introduction Stannadithianes are cyclic organotin sulfides that have been known since the early 1960s [1] and were useful chemical intermediates in synthetic organic chemistry [2]. The chemistry of stannadithianes received renewed attention after the work by Shanzer and Libman [3] where they serve as activated dithiol intermediates to prepare macrocyclic poly-thiolactone compounds via ring-opening condensation. On the other hand, Kricheldorf and coworkers demonstrated that polymeric materials, i.e. aliphatic poly-thioesters, can be also obtained by ringopening poly-condensation of 2 stanna 1,3 dithiacycloalkanes with aliphatic dicarbonylic acid chlorides [4,5]. Vibrational infrared spectra for some stannatetrathio spiro compounds were early reported and interpreted assuming planar geometry of the heterocyclic system [6]. Kolb and Dräger reported the IR and Raman spectra region below 600 cm−1 for a series of tin-compounds in the solid phase allowing for a correlation between stretching vibrations (force constants) and bond distances around the hypervalent tin atom as a tool for structure determination [7]. The analysis of the Raman [8] and NMR [9] spectra of tetracoordinate SnS4 compounds shows to be dependent on the local geometry. Moreover, the structure of 1,3,2 dithiastannolanes in the solid state depends also on the 2,2 di alkyl substitution. Thus, 2,2 di-butyl 1,3,2 dithiastannolanes ⁎ Corresponding author. E-mail address: [email protected] (M.F. Erben).

https://doi.org/10.1016/j.saa.2018.11.018 1386-1425/© 2018 Elsevier B.V. All rights reserved.

show a six-coordination environment around the tin atoms since two neighboring molecules interact to form two relatively long Sn\\S coordinate bonds [10]. In contrast, the 2,2 di methyl analogue forms only one short coordinate bond to give a 5-coordinate geometry around the tin atom [11]. The formation of cyclic tetramer and polymers are also common in 1,3,2 oxa [12] and thiolate [13] stannane compounds. The structural and conformational properties of stannadithiane containing five-membered SnS2C2 rings [R1R2Sn(SCH2CHR3S), with R1, R2_CH3 or C6H5 and R3_H or CH3] were studied by X-ray diffraction [14] and dynamic nuclear magnetic resonance spectroscopy [15]. The most stable form corresponds to the highly puckered half-chair conformation, with the\\CH2CHR3\\adopting a chiral fully staggered configuration. The ΔG‡ values for the interconversion between the two halfchair forms are in the range of 30–32 kJ/mol and were found to be independent on the alkyl substituents at the Sn atom. Conformational and structural studies for organotin compounds have also been performed on computational basis. Boyd and Grindley [16,17] have reported that the combination of the LANL2 and LANL2DZdp effective core potentials for tin with extended basis sets gives good prediction of the molecular structure of organotin compounds. Tarassoli and Kord [18] reported the synthesis of [O(CH2CH2S) 2SnR2](R_Me, But and Ph) compounds by using the di-(alkyl/phenyl) tin dichloride and 2,2 oxydiethanethiol [19] dissolved in benzene in the presence of sodium ethoxide. Spectroscopic features were interpreted in terms of trans-annular O⋯Sn secondary bonding. In particular, eight-membered rings of the type X(CH2CH2Y)2SnRR′, with X

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Scheme 1. The 2 stanna 1,3 dithianes prepared in this work.

2. Experimental

LANL2DZdp basis set augmented with polarization and diffuse functions was used for the tin atom, with the core orbitals replaced by Effective Core Potentials (ECP) [16]. The calculated vibrational properties corresponded in all cases to potential energy minima for which no imaginary frequency was found. The Potential Energy Distribution PED analysis are determined from the VEDA4 program [24,25] using the calculated vibrational frequencies at the B3LYP method with 6-311++G (d,p) and LANL2DZdp/ECP for the tin atom. The magnetic isotropic shielding tensors were calculated within the gauge independent atomic orbital (GIAO) method [26] and B3LYP with 6-311++G(d,p) and LANL2DZdp/ECP for the tin atom, using the lowest energy structures calculated at the same level of approximation. Chemical shifts were derived with respect to the NMR isotropic magnetic shielding tensors (in ppm) from the corresponding standard tensor of TMS.

2.1. Instruments and Materials

3. Results and Discussion

The studied compounds 1–4 were synthesized according to the method reported recently [21]. The identification of the compounds was carried out by using a high-resolution mass spectrometer (Xevo G2-S QTof model), equipped with an electrospray ionization probe. Dibutyltin oxide, 2 mercaptoethyl ether, 2,2′ (ethylenedioxy) diethanethiol, ethylene glycol bisthioglycolate, pentaerythritoltetrakis (3 mercaptopropionate), were used as obtained from commercial sources. Unless stated otherwise, reagent grade solvents were used. Melting points were recorded using a Gallenkamp (SANYO) model MPD.BM 3.5 apparatus and are uncorrected. Thin layer chromatography (TLC) was conducted on 0.25 mm silica gel plates (60 F254, Merck) and the plates were visualized by brief exposure to iodine vapor or to UV light. Solid-phase (in KBr pellets) infrared spectra were recorded with a resolution of 2 cm−1 in the 4000–400 cm−1 range on a Bruker EQUINOX 55 FTIR spectrometer. Raman spectra were recorded using a Horiba Jobin Yvon T64000 Raman spectrometer equipped with a liquid N2-cooled back-thinned CCD detector. Spectra were recorded as the coaddition of up to 16 individual spectra with CCD exposure times of 10–20s each. 1H, 13C, 119Sn and HSQC NMR spectra were obtained using Bruker Avance II series 500 MHz spectrometer in CDCl3. Chemical shifts are given in δ-scale (ppm). Abbreviations s, d, t and m have been used for singlet, doublet, triplet and multiplet respectively. The thermal decomposition of samples is analyzed with the thermogravimetric analysis (TGA) and the first derivative of the TGA, or DTG curves. The apparatus used in the thermogravimetric studies was a Shimadzu TA-50. The temperature of the furnace was programmed to rise at constant heating rate of 10 °C/min, from ambient temperature to 500 °C. The tests were performed under an oxidant atmosphere (air flow of 40 mL min−1 + He flow 40 mL min−1). The amount of the substance used in each case was ca. 5 mg.

3.1. Conformational Study

and Y being oxygen and/or sulfur donors, have been long studied in order to understand the hypervalency around the tin atom, as reviewed by Cea-Olivares and coworkers [20]. Very recently, a series of cyclic 2 stanna 1,3 dithiane compounds containing endocyclic ether and lactone groups (see compounds 1–4 in Scheme 1) were prepared in our laboratory [21]. These compounds show to be effective intermediates to prepare macrocyclic polythiolactone compounds. Here, we present an experimental study on the vibrational properties (infrared and Raman) and on the Nuclear Magnetic Resonance (1H, 13C and 119Sn) spectra of compounds 1–4, complemented by a computational analysis of the conformational space, together with the determination of thermal properties.

2.2. Computational Details Molecular quantum chemical calculations have been performed with the GAUSSIAN 03 program package [22] by using the B3LYP DFT hybrid methods employing Pople-type basis set [23]. The valence triple-zeta basis set augmented with diffuse and polarization functions in both the hydrogen and weighty atoms [6–311++G(d,p)] has been used for geometry optimization and frequency calculations. The

Anet [27] and Hendrickson [28] studied the conformation of cyclooctane and its simple derivatives. The conformational space for saturated 8-membered heterocycles was early mapped in terms of puckering parameters by Boeyens [29]. The most stable forms correspond to the crown (Cr), boat-boat (BB), chair-chair (CC), boat-chair (BC) conformations, with D4d, D2d, C2v and CS symmetry, respectively. Both cyclooctane 1,5 diol/dione compounds prefer the thermodynamically most stable BC conformation. The same is observed in bis (1,5 dithioacyclooctane)nickel(II) chloride, with the dithiacyclooctane ring adopts a BC conformation, whereas in 1,5 dithiacyclooctane 3,7 dione the intermediate twist-chair conformation is observed. To the best of our knowledge, there are no studies available describing the conformational preference of 8-membered heterocycles containing the 2 stanna 1,3 dithia group. Thus, in a first approximation for investigating compound 1, we performed a computational study on the model molecule 2,2 dimethyl 2 stanna 1,3 dithia 6 oxocyclooctane, i.e. the butyl groups were replaced by methyl groups for avoiding the conformational complexity arising by the rather flexible alkyl chain. As shown in Fig. 1, eight structures are found to be stable conformers for which no imaginary frequencies were computed at the B3LYP/6-311 ++G(d,p) level of approximation and the LANL2DZdp/ECP for the tin atom. These forms correspond approximately to the canonical structures described for the octa-cycloalkane “parent” compound [29]. The most stable conformation relates to a distorted crown conformation, while the boat-chair form is the second stable conformer, slightly higher in energy by 1.55 kcal/mol (relative electronic energy including zero point correction). The computed molecular structure is similar to that experimentally found in the related 1,3,6 trithia 2 stannocane, with a monocapped tetrahedron environment around the Sn and boat-chair conformation for the eight-membered ring [30]. In the present case, short O⋯Sn distances are found, 2.833 and 2.863 Å, suggesting the importance of trans-annular interactions in the conformational preference of the studied compounds. The boat-boat conformation is higher in energy by 4.49 kcal/mol and the twist-chair-chair structure is located at 8.81 kcal/mol. Taken into consideration the previous results, a series of structures for compound 1 was subject to geometry optimization and frequency

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Fig. 1. Molecular structures optimized [B3LYP/6-311++G(d,p) and LANL2DZdp pseudopotential for the tin atom] for the model molecule 2,2 dimethyl 2 stanna 1,3 dithia 6 oxocyclooctane (for simplicity hydrogen atoms are not shown). Relative electronic energies values including zero point correction (ΔE°, in kcal/mol) are given (E° = −1112.054985 Hartrees for the most stable pseudo-crown form).

calculations. Based on the most stable ring forms, the conformation of the butyl chain was also analyzed by allowing the dihedral angles of the alkyl group to adopt different values. Thus, six different structures have been optimized by using quantum chemical calculations at the B3LYP/6-311++G(d,p) level of approximation and the LANL2DZdp/ ECP for the tin atom. These conformers, without imaginary frequencies, are shown in Fig. 2, together with the computed electronic energy values (including zero point correction). The results show that the distorted crown form persists as the most stable conformer for compound 1 and an extended (all trans) conformation for the alkyl chain is preferred, as expected [10,11]. However, the relative orientation of both chains gives rise to different conformers (Fig. 2). In the most stable form, one butyl chain bisects the S\\Sn\\S angle while the second butyl group adopts a syn orientation around the C\\Sn bond reducing the steric interaction with the heteroatoms in the bulky 8-membered ring. For the most stable conformer, the local symmetry around the Sn is intermediate between a tetrahedron and a trigonal bipyramid, a form that corresponds to a monocapped tetrahedron, with a short 1,5 trans-

annular distance O⋯Sn of 2.916 Å, indicating a strong interaction through the Lewis acidic tin acceptor and the donor ether group [31]. The second stable form is only 0.12 kcal/mol higher in energy (ΔE°, including zero point correction) and shows a less extended arrangement of the butyl chains than the most stable structure, with a similar conformation of the heterocycle. 3.2. Vibrational Analysis The FTIR (3200–400 cm−1) and FT-Raman (3200–100 cm−1) spectra for compounds 1–4 are shown in Figs. 3–6, respectively. The observed wavenumbers and those calculated for the most stable conformation of the isolated molecule are reported in Tables S1–S4 (given as Supplementary Information), together with a tentative assignment of the bands. The B3LYP method has been applied in this calculation in conjunction with the 6-311++G(d,p) basis set and the LANL2DZdp/ECP for the tin atom. The assignment of the bands was determined from the normal coordinate analysis aided by visualization of

Fig. 2. Molecular structures optimized [B3LYP/6-311++G(d,p), LANL2DZdp pseudopotential for the tin atom] for compound 1 (for simplicity hydrogen atoms are not shown). Relative electronic energies values including zero point correction (ΔE°, in kcal/mol) are given (E° = −1347.823739 Hartrees for the most stable form).

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Fig. 5. FT-Raman and FTIR spectra for compound 3 in the solid phase. Fig. 3. FT-Raman and FTIR spectra for compound 1 in the liquid phase.

the animations for displacement vectors of localized vibrational modes and complemented by comparison with spectra of related molecules [32,33]. Selected infrared absorptions and Raman signals are shown in Table 1 for the characteristic functional groups. 3.2.1. Vibrations of the Butyl Groups The 2,2 di butyl substitution in compounds 1–4 gives rise to a group of absorptions in the range 2960–2900 that can be readily correlated with the frequencies of the n-butyl group in Bu2SnCl2 [34] suggesting that in these molecules the butyl chains are principally in the extended conformation. In particular, the C\\H stretching modes of methylene groups are higher in energy than that of endocyclic\\CH2CH2\\groups. The region between 1300 and 1100 cm−1 in the infrared spectra shown strong contribution of absorptions due to the C\\H deformation modes of the 2,2 di butyl arms. The calculations indicate that the set of bands

Fig. 4. FT-Raman and FTIR spectra for compound 2 in the solid phase.

near 1000 cm−1 arises from almost pure C\\C stretching modes in the butyl chain. The butyl chains originate the exocyclic C\\Sn\\C antisymmetric and symmetric motions, usually found in the 600–500 cm−1 region for related compounds [33]. In our case, medium intensity bands in both infrared and Raman spectra of compounds 1–4 are assigned to these stretching modes at around 600 cm−1 and 560 cm−1, respectively (see Table 1). For example, well-defined absorptions appearing in the spectra of compound 1 at 593 (589 Raman) and 565 cm−1 can be assigned with confidence to these modes, respectively. 3.2.2. Vibrations of the Heterocycle Moiety The interpretation of the infrared and Raman spectra for compound 1 has been done on the assumption of CS symmetry for the ring, as computed for the most stable conformation. To a good approximation the skeletal modes may be considered independently of the CH modes and thus, the skeletal vibrations for the SnS2C4O cycle have the group representation 10A′ + 8A″. The eight stretching modes fall into the

Fig. 6. FT-Raman and FTIR spectra for compound 4 in the solid phase.

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Table 1 FTIR and Raman experimental and calculated [B3LYP/6-311++G(d,p), LANL2DZdp pseudopotential for the tin atom] data for compounds 1–4, together with computed values and tentative mode assignment. 1

2

3

4

Assignment

FTIR cm−1

Raman cm−1

Calc.

FTIR cm−1

Raman cm−1

Calc.

FTIR cm−1

Raman cm−1

Calc.

FTIR cm−1

Raman cm−1

2953-2919vs 2852vs

2920s 2857s

3022 2977

2957-2915vs 2875-2850vs

2922vs 2857s

3020 2961

2964-2929m 2855m

1121s 1099s 1011m 690m 665s 593s 565m

1144m 1180

1125 1096 1006 685 660 596 580 328 309

1130vs 1099 1006m 698w 666m 597m 568w

1146m 1108 1009vw

1140 1080 1010 682 670 590 584 341 326

2960-2920vs 2870-2855s 1736vs 1182s 1153w 1027m 705m 676m 601m 569m

3082 3009 1796 1142 1126 1053 699 686 598 581 317 315

2953-2919vs 2869-2851s 1733vs 1184s 1140m 1022m 700w 675m 618w 600 sh

2932-2908s 2872-2858m 1740w 1173m 1149w 997vw 741vw 665w 595m

663m 589m 335vs 311 sh

663m 588m 339vs 298 sh

1179m 1552w 994vw 702vw 664vw 599m 563sh 376vs 345 sh

337vs 319 sh

νas C\ \H νs C\ \H ν C_O νas C\ \O νs C\ \O ν C\ \C (n-Bu) νas C\ \S νs C\ \S νas C\ \Sn νs C\ \Sn νas Sn\ \S νs Sn\ \S

a Band intensities and shape: vs = very strong; s = strong; m = medium; w = weak; vw = very weak, sh: shoulder, br: broad. bν: stretching (subscripts “s” and “as” refer to symmetric and antisymmetric modes, respectively).

classification 4A′ + 4A″ for the symmetric and antisymmetric motions, respectively. The characteristic tin-sulfur stretching modes, νas(Sn\\S) and νs(Sn\\S), are observed in the Raman spectra as very strong intensity signals and shoulder at 335 and 311 cm−1, respectively. The calculated values of the antisymmetric and symmetric endocyclic C\\S stretches are at 685 and 660 cm−1, respectively, and, on the basis of the infrared and Raman intensities, are readily correlated with the IR bands at 690 and 665 (663 Raman) cm−1, respectively, in perfect agreement with the band assignment proposed for related compounds [7]. The endocyclic ether groups are characterized by the presence of intense absorptions in the infrared spectrum at around 1121 and 1099 cm−1. They are originated by the antisymmetric and symmetric stretching motions of the C\\O\\C group, respectively. The remaining CH2, CCH and SCH angle deformations of the ring system can be identified with bands at ca. 1493 cm−1, 1249 and 960 cm−1 respectively. Based on this description, the assignment of similar features observed in the spectra of compound 2 is straightforward. The vibrations of the characteristic Sn\\S2 group appear at 339 and 298 cm−1 in the Raman spectrum, for the νas(Sn\\S) and νs(Sn\\S) modes, respectively, in good agreement with the Raman spectra reported for similar species [8]. The Sn\\C stretching modes are observed at 597 (588 in Raman) and 568 cm−1 for the antisymmetric and symmetric motions, respectively. The ether groups present in compound 2 give rise to strong and broad absorptions at 1130 (1146 in Raman) and 1099 (1108 in Raman) cm−1 for the νas(C\\O) and νs(C\\O), respectively. The νas (C\\S) and νs(C\\S) stretching modes appear at 698 and 666 (663 in Raman) cm−1, respectively. The calculated values of the antisymmetric and symmetric C\\S stretching modes are at 682 and 670 cm−1, respectively. For the 2 stanna 1,3 dithianes 3 and 4, the spectra are more complex, as observed in Figs. 5 and 6. The broad signals at 376 and 337 cm−1 in the Raman spectra can be assigned to the ν(Sn\\S) stretchings. The endocyclic lactone groups present in compounds 3 and 4, originate strong absorptions at ca. 1740 cm−1 in the infrared spectra, which are characteristic for the ν(C_O) stretching mode. These are accompanied by strong and broad absorptions at 1182 (Raman: 1179) and 1184 (Raman: 1173) cm−1 for the νas(C\\O), respectively. The potential energy analysis suggest that the C\\O stretching motion of both lactone groups are coupled with the symmetric motion appearing at slightly lower frequencies, at 1153 (Raman: 1152) and 1140 (Raman: 1149) cm−1 for the νs(C\\O), for compounds 3 and 4, respectively. These relatively high values for the C\\O stretching are representative for partial double bond in the lactone moiety, as already reported for lactone species [35].

3.3. NMR Analysis The 1H NMR spectra of all four derivatives are displayed in Fig. 7 whereas Table 2 lists the 1 H, 13 C and 119Sn NMR data for the compounds in solution. Di-alkyl-dithiastannolanes are monomeric species in diluted solution [36] and the ring conformations are rapidly fluxional on the NMR time scale [37]. These hypotheses are further supported by the high-resolution mass analysis for which the monomeric species were determined. For compound 2 the experimental mass spectra yields m/z = 437.0596/415.0776 [M + Na] +/[M + H] + (calc. for C14 H30O 2 S2 SnNa/C 14H31 O2 S 2Sn = 437.0606/415.0787), while for compound 4 m/z = 975.1116/ 953.1298 [M + Na] +/[M + H] + (calc. for C33 H60O 8 S4 Sn2 Na/ C33H61O8S4Sn2 = 975.1118/953.1298). Thus, the NMR results refer to unassociated four-coordinate tin species with a single set of signals for the two butyl groups and equivalent signals for the methylene groups in the dithiastannolane ring. All the protons of the butyl chain can be readily assigned to signals at around δ = 1.3, 1.4, 1.6 and 0.9 ppm for α, β, γ methylene, and methyl groups, respectively. The CH2S and CH2O groups in compounds 1 and 2 appear as triplet signals at δ values ca. 2.9 and 3.7 ppm, respectively. The CH2\\O methylenes bonded to the lactone group are observed at δ = 4.39 and 4.23 ppm and the 13C signal for the C_O group are observed at δ = 170.7 and 171.5, in compounds 3 and 4, respectively. For compound 4, the characteristic quaternary carbon appears at δ = 41.4 ppm. Both, chemical shift and coupling constants (see Table 2) are in good agreement with previous reports for similar compounds [18,36]. Furthermore, the proposed assignment is smartly supported by the 2-dimensional–heteronuclear-single-quantum-coherence (2DHSQC) NMR spectra for the accurate and simultaneous assignment of the 1H and 13C chemical shifts. In particular, the 1H and 13C signals for the butyl groups are easily identified in these correlation spectra. Moreover, the assignment of the signals observed in the 1H and 13C NMR at δ = 2.88/2.95 and 27.4/27.2 ppm to the CH2-S group, is corroborated by the correlation observed in the HSQC NMR spectra of compounds 1/2, respectively, in good agreement with previously reported 13CNMR spectra for related compounds [9]. The introduction of the endocyclic lactone group produced a shift of these signals to δ = 3.47/2.99 and 28.1/ 22.6 ppm for compounds 3/4, respectively (see Figs. S3–S6 in the Supporting Information). It is worthy to mention the outstanding correlation between experimental and computed 1H and 13C chemical shift observed for compounds 1–3 (see Figs. S7–S9 in the Supporting Information). These results reinforce the proposed assignment and suggest that the GIAO method at the B3LYP/6-311++G(d,p) level of approximation together

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Fig. 7. 1H NMR spectra for compounds 1–4.

with the LANL2DZdp pseudopotential for the tin atom, is good alternative for complement the assignment of NMR spectra of dithiastannolane compounds. The 119Sn NMR spectra show a unique signal for all the species here studied, as expected [38]. Depending on the ring size and local geometry around the tin atom, the observed values span over a broad range of chemical shift [39], as previously observed for related compounds [36,40,41]. Holeček and Lyčka [42] early proposed the equation |1J(119Sn\\C)| = (9.99 ± 0.73)ϕ − (746 ± 100) correlating spin-spin coupling and the C\\Sn\\C bond angle (ϕ) in dibutyltin (IV) cyclic compounds. The observed 1J(119Sn\\C) values (see

Table 2) suggest very similar angles ϕ of 112°, 111°, and 111° for 1, 2 and 4 dissolved in CHCl3 , respectively. These values agree with the computed C\\Sn\\C bond angles of 113.8° and 113.5° for 1 and 2, respectively. 3.4. Thermal Analysis Thermal behavior of the three solid stannadithianes 2–4 has been studied by means of thermogravimetric analysis (TGA), as shown in Fig. 8. The analysis of the differential thermogravimetric curves (Fig. S10 in the Supporting Information) reveals that compound 2

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Table 2 Experimental and calculated [B3LYP/6-311++G(d,p), LANL2DZdp pseudopotential for the tin atom] 1H, 13C, 119Sn NMR data for compounds 1–4, chemical shift (ppm), together with integration, multiplicity and multinuclear coupling constant values (Hz). N°

Fragment

δ 1H (ppm)

δ 13C (ppm)

δ 119

1

2

3

4

1 2 3 4 5 6 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8

CH3 CH2 γ CH2 β CH2 α CH2-S CH2-O CH3 CH2 γ CH2 β CH2 α CH2-S CH2-O O-CH2 CH3 CH2 γ CH2 β CH2 α CH2-S C_O O-CH2 CH3 CH2 γ CH2 β CH2 α CH2-S CH2-C(O) C_O CH2-O

Exp.

Calc.

Integration

Multiplicity

0.90 1.61 1.37 1.33 2.88 3.66 0.93 1.65 1.48 1.38 2.95 3.67 3.72 0.94 1.64 1.45 1.40 3.47

0.98 1.29 1.38 1.02 2.78 3.49 1.01 1.33

6 4

t m

4.39 0.94 1.66 1.55 1.40 2.99 2.71

4.22

4.23

8

m

4 4 6 4

t t t m

1.61

8

m

2.70 3.77 3.67 1.01 1.34 1.44 1.55 2.93

4 4 4 6 4

t m t t m

8

1,3

J (H\ \H) Hz 7.5

J (H\ \Sn) Hz 5

J 124 J 74

4

4.9 5.0 7.4

5.9 6.0 7.3

3

J 40 4 J 144 5 J 125

3

5

J 49

J 125

m

4

s

4 12 8 8 8 8 8

t t m m t t t

8

s

6.5 7.2

5

J 125

6.3 6.3

Exp.

Calc.

13.7 28.4 26.8 19.6 27.4 71.9 13.6 28.2 26.8 18.6 27.2 71.7 73.8 13.7 27.6 26.6 22.7 28.1 170.7 63.0 13.6 28.1 26.8 17.6 22.6 38.3 171.5 62.6

16.8 33.9 33.2 20.0 36.8 77.1 16.9 34.3 33.4 22.2 33.4 76.2 74.2 16.8 33.9 32.6 20.1 35.0 178.1 66.4

J (C\ \119Sn) Hz

J (C\ \117Sn) Hz

Sn (ppm) 95

3

J 24 J 74 1 J 377 2

1

J 395

3

J 11 131

1

J 362

1

J 378

−45 2

J 84

2

J 99

2

J 42

127 3

J 25 2 J 73 1 J 367

1

J 383

3

J 33

41.4

9

is stable up to ca. 315 °C, while compound 3 decomposes in a twostep process at lower temperature (290 °C). For 3, the observed mass loss of 68.0% is compatible with the formation of SnO2 as the final decomposition product (calculated 65.9%). The presence of SnO2 in the solid residue was further corroborated by infrared spectroscopy. For the spiro compound 4, decomposition occurs in the temperature range of 280–350 °C, with a maximum in the differential curve at 324 °C. For compounds 2 and 4, the experimental mass loss at the higher temperature here used (500 °C) are 85.3% and 68.0%, respectively.

4. Conclusions In summary, close related stannadithiane compounds containing ether and lactone endocyclic functional groups were investigated, including a highly symmetric spiro organotin species (bis 2 stanna 1,3 dithia) bearing lactone groups. The conformational landscape has been fully determined for the 8membered representative containing the endocyclic ether group (compound 1) resulting in a distorted crown form with the butyl chains adopting an extended conformation. Calculations using the effective

Fig. 8. TGA diagrams of the solid stannadithianes a) compound 2, b) compound 3 and c) compound 4.

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core potential approximation and extended basis set for the tin atom are adequate complementary tool for better understands the conformational properties and molecular structure, as well as for determining the vibrational and NMR properties of the organotin compounds here studied. The detailed analysis of the vibrational spectra of 2,2 di butyl 2 stanna 1,3 dithianes allow determining the occurrence of the characteristic νas(Sn\\S) and νs(Sn\\S) stretching modes of the SnS2 endo-cyclic group at around 340 and 315 cm−1, respectively. The exo-cyclic ν(Sn\\C) stretching modes appear near 590 and 565 cm−1 for the antisymmetric and symmetric motions, respectively. Acknowledgement ZYDE is a postdoctoral fellow and IDL, CODV, and MFE are members of the Carrera del Investigador of CONICET (Argentina). The Argentinean authors thank the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), the Agencia Nacional de Promoción Científica y Tecnológica (ANPCYT, PICT-2130), and the Facultad de Ciencias Exactas, Universidad Nacional de La Plata (11/X794) for financial support. MFE thanks Prof. Dr. R. M. Romano (CEQUINOR) for her help during the recording of Raman spectra. Appendix A. Supplementary Data Vibrational data with normal mode assignment are given in Tables S1–4 for compounds 1–4, respectively. Multinuclear and 2DHSQC NMR spectra for studied compounds are shown in Figs. S1–S6. Comparisons between experimental and computed (GIAO) NMR data are graphically shown in Figs. S7–S9 for compounds 1–3, respectively. Fig. S10 displays the differential thermogravimetric curves. Supplementary data to this article can be found online at doi:https://doi.org/10. 1016/j.saa.2018.11.018. References [1] E.W. Abel, D.B. Brady, 210. The preparation and properties of some alkylthiocompounds of tin, J. Chem. Soc. (1965) 1192–1197. [2] K. Abersfelder, T.-l. Nguyen, D. Scheschkewitz, Stannyl-substituted disilenes and a disilastannirane, Z. Anorg. Allg. Chem. 635 (2009) 2093–2098. [3] A. Shanzer, J. Libman, F. Frolow, A novel series of macrocyclic lactones, J. Am. Chem. Soc. 103 (1981) 7339–7340. [4] H.R. Kricheldorf, N. Probst, G. Schwarz, G. Schulz, R.-P. Krüger, New polymer syntheses. 107. Aliphatic poly(thio ester)s by ring-opening polycondensation of 2-stanna1,3-dithiacycloalkanes, J. Polym. Sci. A Polym. Chem. 38 (2000) 3656–3664. [5] M. Al-Masri, G. Schwarz, H.R. Kricheldorf, New polymer syntheses. 105. Syntheses of aliphatic poly(thioesters) by ring-opening polycondensation of 2,2-dibutyl-2stanna-1,3-dithiolane, J. Macromol. Sci. A 38 (2001) 1007–1017. [6] A. Finch, R.C. Poller, D. Steele, Vibrational spectra of some heterocyclic tin compounds, Trans. Faraday Soc. 61 (1965) 2628–2634. [7] U. Kolb, M. Dräger, Hypervalent tin-organic compounds: vibrational spectroscopy in the solid as a tool for structure determination, Spectrochim. Acta 53A (1997) 517–529. [8] J. Shamir, P. Starostin, V. Peruzzo, Low-frequency vibrational spectra of spirocyclic bis(ethane-1,2-dithiolato[2-]-S,S′-tin(IV)) and its pyridine and related complexes, J. Raman Spectrosc. 25 (1994) 251–254. [9] G. Domazetis, R.J. Magee, B.D. James, J.D. Cashion, Synthesis and spectroscopic studies of organotin compounds containing the Sn-S bond, J. Inorg. Nucl. Chem. 43 (1981) 1351–1359. [10] P.A. Bates, M.B. Hursthouse, A.G. Davies, S.D. Slater, The structure of 2,2-di-t-butyl1,3,2-dioxa-, -oxathia-, and -dithia-stannolanes: a study by solution and solid state NMR and single crystal X-ray diffraction, J. Organomet. Chem. 363 (1989) 45–60. [11] A.G. Davies, S.D. Slater, D.C. Povey, G.W. Smith, The structures of 2,2-dialkyl-1,3,2dithiastannolanes, J. Organomet. Chem. 352 (1988) 283–294. [12] T.B. Grindley, R. Thangarasa, Oligomerization equilibria and dynamics of 2,2-di-nbutyl-1,3,2-dioxastannolanes, J. Am. Chem. Soc. 112 (1990) 1364–1373. [13] N.M. Comerlato, G.B. Ferreira, R.A. Howie, C.X.A. Silva, J.L. Wardell, Synthesis of bis (tert-butyl)(2-thioxo-1,3-dithiole-4,5-dithiolato)stannane, But2Sn(dmit), and bis (tert-butyl)(2-oxo-1,3-dithiole-4,5-dithiolato)stannane, But2Sn(dmio): crystal structures, at 120K, of polymeric But2Sn(dmit), and two polymorphs of But2Sn (dmio), a polymer and a cyclic tetramer, J. Organomet. Chem. 693 (2008) 2424–2430. [14] M. Dräuger, Über Zinn-haltige Heterocyclen. III. 2,2-Dimethyl-1,3,2-dithiastannolan, eine linear vernetzte Molekülstruktur mit trigonal-bipyramidal-koordiniertem Zinn, Z. Anorg. Allg. Chem. 477 (1981) 154–160.

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