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Abstract
A series of C,O‐chelated organotin(IV) alkoxides, L2PhSnOtBu (4), L2PhSnOMe (6), L2Sn(OtBu)2 (11), and siloxides L2PhSnOSiPh3 (3), L2Sn(OSiPh3)2 (10) (L=[2‐(CH2O)2CH]C6H4), was prepared by salt elimination reactions. They were obtained from the organotin(IV) iodides L2PhSnI (1) or L2SnI2 (2) upon reactions with tBuOK, MeONa or Ph3SiONa, respectively, in dry THF or methanol. Under non‐inert conditions, compounds 4 and 6 undergo combined hydrolysis and condensation to give the hexaorganodistannoxane (L2PhSn)2O (5). The stannoxane 5 is easily hydrolysed to L2PhSnOH (7), which quickly converts back when heated. Basic hydrolysis of diiodide 2 produces the cyclic oxide (L2SnO)3 (8). Its reaction with an equimolar amount of Ph3SiONa gives only a mixture of the expected L2SnI(OSiPh3) (9), 10 and the precursor, 2. Yet, 8 shows a unique reactivity pattern when combine with m‐tolyl boronic acid, affording stannaboroxane (L2SnO)2OB(m‐tol) (12). All the isolated species were characterised in solution by NMR spectroscopy and mass spectrometry. The solid‐state molecular structures of 1–5, 10–12 were established by single‐crystal X‐ray diffraction (XRD). Additionally, thermogravimetric analysis of 3–5, 8, 10, and 12 was conducted.
Full text
Introduction
Metal alkoxides represent versatile species that are useful precursors for a wide variety of metal oxide materials,[1,2] or inorganic-organic hybrid materials.[3,4] Although Davis and coworkers reported two alternative methods to prepare organotin(IV) alkoxides (i. e. reaction of bis[trialkyltin(IV)] oxides with dialkyl carbonates or with alcohols) more than 50 years ago,[5] structurally characterised organotin(IV) alkoxides with general formula RnSn(OR’)4-n (R, R’=alkyl, aryl; n=1–3) are scarce.[6–10] An illustrative example of intramolecular arene C−H bond activation was observed in the reaction of SnCl4 with 2 equiv. of LiOAr (OAr=2,6-diphenylphenoxide) which gave a cyclometalated dimer (Figure 1a).[11] Deacon showed the ability of Me3SnOAr (OAr=2,6-di-tert-butyl-4-methylphenoxide) to transfer the aryloxide ligand to Sm or Yb via a redox transmetallation reaction in THF.[12] Several diaryltin(IV) di-iso-propoxides were screened for their catalytic activity in ring-opening polymerization of L–Lactide. The activity found was moderate.[13] A significant contribution was made by Růžička and co-workers who synthesised [2-(Me2NCH2)C6H4]-containing tin compounds (Figure 1b) and probed their reactivity towards CO2 or employed them in transesterification reactions.[14] Yet, none of the isolated organotin(IV) alkoxides was structurally authenticated by single-crystal XRD analysis.
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Metal triorganosiloxides (M–OSiR3) are also suitable precursors for MSiOx metal silica-based materials.[15–19] However, the lack of molecular organotin(IV) siloxides is even more pronounced compared to alkoxides. Thus, only a few studies have reported fully characterised organotin(IV) siloxides up to date, while their reactivity potential was neglected.[20–22] A recent paper describes the synthesis, photocatalytic properties and potential application of some diaryltin(IV) siloxanes as single-source precursors for tin-silicate materials. Nevertheless, only dibuthyltin(IV) bis(triphenylsiloxide) (Figure 1c) was validated by single-crystal XRD.[23]
Organotin(IV) oxides are also a significant class of tin compounds.[24–26] Their solid-state structure ranges from polymeric, when small substituents are present on the metal centre,[27] to trimeric[28–30] or even monomeric, as in hexaorganodistannoxanes (R3Sn)2O (R = Ph,[31] o-tol,[32] o-methoxyphenyl,[33] etc.). Moreover, it was shown that the polarity of the crystallisation solvent can constrain the oligomerization rate of various stannoxanes.[34]
In recent years, the seeking for metallaboroxines [M(O3B2R2), M = Au,[35] Sb,[36,37] Bi,[37–39] Sn,[36,39] Ga[40]] was extended. Thus, a variety of synthetic methods have been described, such as the reaction of organoboronic acids or boroxines[41] with either organopnictogen(III) oxides,[39] organotin(IV) carbonates,[36] or organogallium(III) amides,[40] or by arrested transmetallation reactions.[35] Some of these molecular compounds have shown promising features, including luminescence[35] or the utilisation as precursors for the deposition of thin film layers.[40] Yet, there are still aspects to clarify regarding the bond situation and reactivity of all these species.
We have successfully employed various C,O-chelating aromatic ligands in organotin(IV) chemistry as an alternative to the ubiquitous [2-(Me2NCH2)C6H4]. Their oxygen-containing pendant arms displayed more functionalisation possibilities, i. e. the aldehyde can be readily converted into a carboxylic acid or imine without affecting the C−Sn bond.[42–45] The resulting species show great potential as organometalloligands able to generate heterometallic species containing Sn/Pd,[43] Sn/Zn[44] or Sn/Cu[46] cores. We are currently exploring other potential applications for organotin(IV) species containing C,O-chelating aromatic substituents. Thus, herein we report on the synthesis, spectroscopic characterisation, thermogravimetric studies, and the crystal structures of novel aryltin(IV) oxides, alkoxides and siloxides.
Results and Discussion
Synthesis
The reaction in dichloromethane of L2SnPh2[47] (A) (L = [2-(CH2O)2CH]C6H4) with one or two molar equivalents of elemental iodine afforded in high yields the organotin(IV) iodides L2PhSnI (1) and L2SnI2 (2), respectively, as pale-yellow crystalline solids (Scheme 1). Treatment of 1 with a THF solution of NaOSiPh3[48] using Schlenk techniques gave the desired L2PhSnOSiPh3 (3), a rare occurrence of structurally characterised organotin(IV) siloxide, prepared through the salt metathesis reaction.[20,22] The siloxide 3 is an air and moisture stable solid which is inert towards reaction with CO2. The alkoxides L2PhSnOtBu (4) and L2PhSnOMe (6) were synthesised in a similar manner by reaction of 1 with a THF solution of tBuOK or a methanolic solution of freshly prepared sodium methoxide. The moisture-sensitive 4 forms in yields over 70 % in 30 minutes, when a commercially available 1 M THF solution of tBuOK is used. Yet, the utilisation of solid tBuOK only affords traces of 4, while the main product is (L2PhSn)2O (5) as authenticated by NMR and XRD analysis (Figure S43). Although 6 was isolated as a white crystalline solid, the decomposition product 5, was also detected in solution by 1H and 119Sn{1H} NMR spectroscopy. The amount of stannoxane 5 is about 14 %. On the other hand, 5 is quantitatively hydrolysed to give L2PhSnOH (7), which rapidly converts back upon heating. Basic hydrolysis of 1 in a biphasic CH2Cl2/water system is an alternative pathway to 7.
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The cyclotristannoxane (L2SnO)3 (8) was isolated almost quantitatively as colourless sharp melting solid upon reaction of 2 with aqueous KOH in THF.
Treatment of 2 with two equivalents of Ph3SiONa in dry THF under inert atmosphere effected its quantitative conversion to diaryltin(IV) bis(triphenylsiloxide) L2Sn(OSiPh3)2 (10) (Scheme 2). Compound 10 was isolated as an air stable colourless solid. A mixture of L2SnIOSiPh3 (9), 10 and 2 was detected in solution by NMR spectroscopy, when 2 reacted with only one equiv. of Ph3SiONa at −78 °C in THF. The same outcome was observed by the reaction of 2 with 10 in a 1 : 1 molar ratio, showing there is an equilibrium in solution between these 3 species. Compound 9 was only detected in solution by 1H and 119Sn{1H} NMR spectroscopy (δ119Sn=−297.9 ppm) (Figure S36).
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The diorganotin(IV) dialkoxide L2Sn(OtBu)2 (11) was prepared upon reacting 2 with two equivalents of tBuOK in THF, for 30 minutes. It shows good solubility in acetonitrile, THF, and in aromatic hydrocarbons and is less prone to hydrolysis compared to 6. When stannoxane 8 is heated at reflux in toluene with m-tolyl boronic acid in a 2 : 3 molar ratio, the stannaboroxane (L2SnO)2OB(m-tol) (12) is obtained as a single product.
The new species exhibit good solubility in THF and/or in chlorinated (CH2Cl2, CHCl3) solvents.
Spectroscopic Characterisation
All the isolated compounds were fully characterised in solution by 1H, 13C, 119Sn and 29Si NMR where appropriate, in CDCl3 and/or C6D6 at room temperature. Except for compound 9 being involved in an equilibrium with different species, the 1H and 13C{1H} NMR spectra each display one set of characteristic resonance signals for the organic substituents bound to the tin centre. The 1H NMR spectra of 1 and 2 exhibit similar features, with the most deshielded resonances corresponding to H-6 (for the numbering scheme, see Figure 11). The two iodide substituents attached to tin in 2 increase the 3JSn-H coupling constant of H-6 resonance, from 75 Hz, found for the iodide 1, to 111 Hz. The CH2 protons from the 1–3 dioxolane rings in 1 give rise to a multiplet centred at 3.6 ppm, whereas the same protons appear as a broad resonance (δ=3.7 ppm) for 2. The difference was also noticed in 13C{1H} NMR spectra, where only one resonance was observed for C8−C9 in 2 (δ=65.10 ppm), which contrasts with two distinct resonances (δ=64.65, 64.96 ppm) corresponding to the same carbon atoms in 1. This indicates a strong intramolecular O→Sn interaction in solution of 1, which alters the symmetry of the dioxolane rings. This feature is also consistent with different strength of Sn−O interactions observed in the solid-state structure of 1 (vide infra). The same behaviour perpetuates to derivatives 3–7 (Figures S7–S20). Besides, on the NMR time scale, there is a faster fluctional behaviour involving coordination/decoordination of both C,O-pendant-arm ligands of 2 in CDCl3, implied by the broad resonance in 1H NMR and only one resonance for C8-C9 in 13C{1H} NMR. The formation of the siloxide 3 was easily recognizable by 1H NMR, where the singlet resonance corresponding to H-7 shifted from 5.85 ppm (1) to 5.64 ppm. The 29Si NMR for 3 completed its characterisation in solution with a singlet at −22.3 ppm. Indeed, the resonance for H-7 in 1H NMR spectra is also indicative for the formation of the alkoxides 4 and 6 [δ1H=5.77 ppm (4); 5.69 ppm (6)], the oxide 5 (δ1H=5.75 ppm), or the hydroxide 7 (δ1H=5.77 ppm). Each of the 1H NMR spectrum of tert-butoxides 4 and 11 in C6D6 exhibits a singlet [δ1H=1.45 ppm (4), 1.52 ppm (11)] as expected, while the presence of the methoxy substituent in 6 is confirmed by a sharp resonance (δ1H=4.00 ppm), surrounded by tin satellites (3JSn-H=38 Hz). A sharp singlet was also detected in the 1H NMR spectrum of 7, where the -OH proton shows at δ1H=0.69 ppm (2JSn-H=24 Hz). This is consistent with solution NMR data found for similar organotin(IV) hydroxides reported in the literature.[14]
The 119Sn{1H} NMR spectroscopy was an indispensable tool that consolidated our findings in solution and helped in the monitoring of the reactions. Thus, 119Sn NMR spectra have been recorded in both C6D6 and/or CDCl3 and the resulted chemical shifts are summarized in Figure 2. The triorganotin(IV) compounds 1, 3–7 display typical 119Sn NMR chemical shifts (range between −154.3 to −191.0 ppm in C6D6) which are indicative for pentacoordinated triaryltin(IV) species in solution showing only one O→Sn intramolecular interaction. These findings fit well those from a series of compounds containing the L1 = [2-(Me2NCH2)C6H4] moiety, i. e.: L1Ph2SnX (δ119Sn (ppm)=−199.5, X = I;[49] −187.6, X = OH; −173.2, X = OSnPh2L1)[14] and with the phosphine-based derivative, [o-(Ph2P)C6H4]3SnI, δ119Sn=−177.2 ppm.[50] The 119Sn NMR resonance found for 3 is significantly upfield shifted compared to that reported for (Ph3SnO)Ph2SiOSiPh2(OSnPh3) (−106.5 ppm),[22] suggesting the presence of intramolecular O→Sn contacts in solution. The diorganotin diiodide 2 and the corresponding disiloxide derivative 10 exhibit 119Sn NMR resonances at −319.5 ppm and −335.6 ppm, substantially shifted related to that in 12 (−258.7 ppm), Ph2SnI2 (−243.8 ppm)[51] or (o-An)2SnI2 (−287.3 ppm)[52] and in the same region as those containing the C,N-pendant arm ligand, L1, e. g. L12SnI2 (−346.9 ppm)[49] and L1PhSnI2 (−337.4 ppm).[53]
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In the ESI+ or APCI+HRMS spectra of 1–3 and 5 the base peaks correspond to [M−X]+ fragments, where X = I (1, 2), OSiPh3 (3) and OSnPhL2 (5). Relevant fragments were also detected for 8 m/z=435.02344 [L2SnOH]+ and 10 m/z=693.10999 [L2SnOSiPh3]+ that validate the fragmentation pattern for the isolated species (see Figures S52–58, for details). The molecular ion [M+H]+ of the stannaboroxane 12 was also observed (m/z=985.10458).
Solid-State Structures
Despite the well-known di- and triaryltin chlorides, there are only several examples of XRD structurally authenticated aryltin(IV) iodides and diiodides that can be found in CCDC.
Suitable crystals for XRD analysis of the triorganotin iodide 1 and diorganotin diiodide 2 were grown by slow diffusion of pentane into concentrated CH2Cl2 solutions of the corresponding compound. Compound 1 crystallised in the monoclinic space group P21/c with two pairs of crystallographic independent molecules in the unit cell (Figure S37–S39).
The molecular structure of SC7-SC16-1 a isomer (Figure 3) features a hexacoordinated tin centre, in a distorted octahedral arrangement, with the O1−Sn1−I1 angle of 174.35(6)°, slightly smaller than the one found in SC31-SC40-1 b [O5−Sn2−I2 175.72(5)°]. In addition, the coordination geometry in 1 a displays a higher distortion from the ideal octahedral one, with O3−Sn1−C19 angle of 164.99(1)° substantially altered with respect to its correspondent angle in 1 b [O7−Sn2−C43 178.37(1)°]. The two O→Sn intramolecular contacts in 1 a [O1→Sn1 2.430(2) Å, O3→Sn1 3.120(3) Å] are also different than those observed in 1 b [O5→Sn2 2.492(2) Å, O7→Sn2 2.847(2) Å] (Table 1, Table S3). These magnitudes are commensurate with those found for other hexacoordinated triaryltin(IV) halides containing C,O-bidentate ligands, e. g. L3SnI [2.598(4)/2.849(5) Å],[54] and [2-(O=CH)C6H4]2PhSnCl [2.444(2)/2.931(2) Å][47] or O,C,O pincer-type ligands, e. g. [2,6-(ROCH2)2C6H3]SnPh2X [2.586(2)/2.891(2) Å; R = Me, X = I;[55] 2.567(2)/2.993(2) Å; R = Me X = Cl].[56]
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Table 1 Selected interatomic distances (Å) and bond angles (°) for compounds 1, 3, 4 and 10.
|
1 |
3 |
4 |
10 |
Sn1−C1 |
2.134(3) |
2.138(4) |
2.130(2) |
2.126(4) |
Sn1−C10 |
2.144(3) |
2.140(3) |
2.145(2) |
2.119(4) |
Sn1−X[a] |
2.817(3) |
2.005(2) |
1.9997(1) |
1.996(3) |
Sn1−Y[b] |
2.147(3) |
2.139(4) |
2.135(2) |
1.991(3) |
Sn1−O1 |
2.430(2) |
2.563(2) |
2.706(2) |
2.492(3) |
Sn1−O3 |
3.120(3) |
2.966(2) |
3.713(1) |
2.567(3) |
O1−Sn1−X |
174.35(6) |
168.27(7) |
163.89(5) |
171.97(11) |
O3−Sn1−C19 |
164.99(1) |
171.34(11) |
151.82(5) |
165.60(11) |
C1−Sn1−C10 |
132.36(13) |
126.48(14) |
121.86(6) |
148.11(18) |
C1−Sn1−C19 |
112.70(13) |
114.32(12) |
112.12(6) |
104.79(14) |
C1−Sn1−O1 |
74.21(10) |
71.66(11) |
70.07(5) |
73.21(14) |
C1−Sn1−O3 |
68.27(12) |
67.61(11) |
63.37(5) |
80.38(13) |
C1−Sn1−X |
92.50(9) |
96.74(14) |
93.83(6) |
99.25(15) |
Consequently, two five-membered SnC3O rings are formed in 1, and the methylene carbon atoms (C7, C16) become chiral centres, giving a racemate of two enantiomers for each different molecule in the crystal (see Figure S38 and S39 for details).
Compound 2 crystalises in the centrosymmetric monoclinic space group C2/c. Its molecular structure shows the tin(IV) atom to lie in a six-coordinate environment adopting a distorted octahedral geometry with a cis-arrangement of the two iodide substituents (Figure 4). Both aryl ligands act in a bidentate fashion, with O1 strongly coordinated to Sn [2.4903(13) Å]. This value matches those observed in related cis-configured diaryltin(IV) dihalides L2SnCl2 [2.500(5)/2.475(5) Å], [2-(O=CH)C6H4]2SnCl2 [2.431(7)/2.480(7) Å],[43] [2-(MeOCH2)C6H4]2SnBr2 [2.419(4)/ 2.499(4) Å],[57] and is smaller than the dative bonds found in [2,6-(tBuOCH2)2C6H3]PhSnI2 [2.843(3)/2.789(3) Å].[58] Yet, the O1→Sn1 contact in 2 is considerably weaker than those in the trans-configured P=O→Sn coordinated diorganotin(IV) dihalide (LP=O)PhSnCl2 [LP=O={C6H2[P(O)(OEt)2]2–2,6-tBu-4}−] [Sn1−O1 2.278(6) Å, Sn1−O2 2.203(5) Å].[59]
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The siloxide 3 crystalised upon slow diffusion of hexane into an Et2O solution of the compound. Crystal contains a racemic mixture of SC7-RC16-3 (Figure 5) and RC7-SC16-3 (Figure S41). The O→Sn intramolecular interactions in 3 lie between the sum of the covalent radii [Σrcov(Sn,O) 2.05 Å][60] and the sum of the vdW radii [ΣrvdW(Sn,O) 3.92 Å][61] of the elements, contributing to a distorted octahedral arrangement around tin with 3 bond angles close to 180° (Table 1). The Sn1−O5 bond [2.005(2) Å] is slightly longer compared to those in other reported organotin(IV) siloxides with a four-coordinate tin centre [1.87(1) Å in Ph3SnOSiPh3,[20] 1.93(2)/1.96(1) Å in (Ph3SnO)Ph2SiOSiPh2(OSnPh3)[22]], but commensurable with those in six-coordinate tin containing siloxides.[62,63]
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Compound 4 is a very rare example of non-solvated aryltin(IV) alkoxide authenticated by single-crystal XRD (Figure 6).[13,64] Its solid-state structure reveals a six-coordinate tin atom with a loose O3→Sn1 contact of 3.713 Å, [ΣrvdW(Sn,O) 3.92 Å]. Thus, the geometry about the tin centre in 4 could rather be described as a distorted capped trigonal bipyramid (τ5=0.70).[65] The angle between the axial atoms, O1−Sn1−O5 is 163.89(5)°, while the equatorial site angles range between 112.12(7)° and 121.86(6)°, close to the ideal value of 120°. The Sn1−O5 bond length in 4 [1.9997(1) Å] resembles those observed in the few reported triaryltin(IV) alkoxides, Ph3SnOCMe2-C(O)OEt [1.996(1) Å],[64] (p-Me2NC6H4)3SnOiPr [2.0007(15) Å],[13] and that from the siloxide 3 [2.005(2) Å]. The electronic density brought by the tert-butoxy fragment clearly decreases the Lewis acidity of the tin centre in 4. Accordingly, the coordination of O1 and O3 atoms to tin is weakened with respect to that in 1 or 3 (vide supra). The five-membered ring SnC3O1 in 4 is folded along the Sn⋅⋅⋅C7 axis [dihedral angle SnC3/SnCO of 31.32°] with O1 atom deviated −0.58 Å out of the best SnC3 plane. This particularity contrasts the data disclosed for the molecular structures of 1 and 3, where the chelating rings, generated by O1→Sn coordination, are almost planar [dihedral angles: 5.65° in 1; 3.74° in 3, with O1 out of the best SnC3 plane with 0.08 Å/−0.06 Å respectively].
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The asymmetric unit of the disiloxide, L2Sn(OSiPh3)2 (10) contains two independent molecules, with one depicted in Figure 7. Both pendant-arm aromatic ligands are strongly coordinated to tin through O1 and O3 respectively, [2.492(3)/2.567(3) Å] giving a distorted octahedral geometry about the metal centre. The cis arrangement of the bulky Ph3SiO− fragments on tin, alters substantially the Sn−O−Si angles. Accordingly, the Sn1−O5−Si1 and Sn1−O6−Si2 angles [168.41(2)/149.68(2)°] are wider relative to that found in 3 [144.7(2)°], but comparable with those observed in (tBu)2Sn(OSiPh3)2 163.84(1)°/149.75(1)°.[23] Additional crystallographic data (including those for the second independent molecule of 10) are listed in Table S5. On the whole, compound 10 is only the third representative of the family of diorganotin(IV) disiloxides,[23,66] and the sole example with aromatic ligands.
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Single crystals of 11 suitable for XRD were grown by cooling a concentrated acetonitrile solution to −24 °C. Compound 11 is a rare case of structurally characterised organotin(IV) dialkoxide[13,67] and the sole mononuclear one. Its molecular structure (Figure 8) shows the tin centre to rest in a six-coordinate environment featuring a distorted octahedral geometry. The Sn1−O3 distance in 11 [1.991(1) Å] match those in 10 [Sn1−O5 1.996(2) Å, Sn1−O6 1.991(3) Å]. Yet, the O3−Sn1−O3’ angle is wider [107.17(8)°] compared to O5−Sn1−O6 angle in 10 [97.67(1)°], showing a higher distortion of the octahedral core (Table S6).
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Single crystals of the stannaboroxane 12 grown by slow diffusion of hexane into a concentrated dichloromethane solution. Its unique molecular structure reveals two symmetric tin atoms, comprised in a non-planar six-membered heterocycle (Figure 9). The O9 atom is out −0.396 Å of the Sn2BO2 plane. Four strong intramolecular O→Sn interactions [O1−Sn1 2.781(2) Å, O3−Sn1 2.624(1) Å, O5−Sn2 2.604(2) Å, O7−Sn2 2.635(2) Å], that satisfy the electronic demands of the two tin atoms, prevent the addition of the intermediate, L2Sn(OH)2, to the six-membered ring, contrasting the structure reported by Molloy, where a tBu2Sn(OH)2 unit wraps up the molecular structure of the stannaboroxane.[68] As a result, both metal centres are hexacoordinated, displaying a distorted octahedral environment (for crystallographic data, see Table S7; details about the reaction pathway for the formation of 12 are given in Figure S50).
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Thermogravimetric Analysis (TG)
Thermal degradation of the alkoxide 4, oxides 5 and 8, siloxides 3, 10, and stannaboroxane 12 was monitored by thermogravimetry. The most interesting features were observed for the organotin(IV) siloxides.
Thus, thermal behaviour of 10 is presented in Figure 10, where the obtained TG and DTA curves are displayed. The curves present variations in thermal stability among the sample. Compound 10 exhibits a three-step decomposition during TG analysis (three exothermic peaks on DTA curve). The total weight loss of 78.63 % is close to the theoretically calculated weight loss due to organic moieties of the sample (78.22 %), resulting in 21.37 % SnO2.SiO2 ceramic.
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Compound 3 exhibits a thermal behaviour with a two-step decomposition visible on the TG/DTA curve. (Figure S59) The DTA curve shows two exothermic peaks at 310 °C and 474 °C resulting in an overall weight loss of 73.13 % (calculated 72.60 %). As previously, this total weight loss is close the theoretical value, thus resulting in 26.87 % residue, which could be attributed to SnO2.SiO2 ceramic (calculated 27.39 %).
The alkoxide 4 and the oxides 5 and 8 displayed similar two-step decomposition patterns (Figure S60–S62). However, the residual mass found for these species (Table S8) does not resemble with any kind of tin oxide material, thus, for the complete identification of their decomposition products, additional investigations are required. A peculiar thermal behaviour was also observed for the stannaboroxane 12. The TGA curve of 12 (Figure S63) displays a multistep decomposition pattern that progresses even at elevated temperatures (>1000 °C). This shows a complete decomposition of the material indicating sublimation of the title compound.
Conclusions
The synthesis and complete characterisation of some organotin(IV) alkoxides, siloxides, stannoxanes and a unique stannaboroxane were presented. Both triorganotin(IV) alkoxides 4 and 6 show moisture sensitivity, their hydrolysis giving organotin(IV) oxide (L2PhSn)2O (5). The diorganotin dialkoxide 11 is more stable when exposed to air, while the corresponding siloxides 3 and 10 are inert towards oxygen or CO2. The two intramolecular O→Sn interactions, which vary in strength depending on the substituents, are a defining feature shared by all these derivatives. A cis-arrangement of the substituents was observed in the solid-state structures of the diorganotin(IV) compounds 2, 10–12. Both organotin(IV) siloxides display typical decomposition patterns, producing a tin silicate material residue. Most importantly, we achieved the preparation of a unprecedented stannaboroxane (12) following a facile high-yield protocol that starts from the cyclic oxide (L2SnO)3 (8). An attempt at isolating a mono-substituted diorganotin(IV) siloxide, 9, failed under the experimental conditions employed but instead showed an equilibrium between the starting materials and the expected product. We are now further exploring the potential of different siloxides to be used as tin-silicate precursors and will report on these findings in a forthcoming report.
Experimental Section
Materials and Procedures
All air- and moisture-sensitive reactions were carried out under argon atmosphere, using standard Schlenk techniques or in a dry glovebox (Jacomex: O2 <1 ppm, H2O <1 ppm) for reagents loading. THF was distilled under argon from K prior to use. Starting materials: L2SnPh2[47] and Ph3SiONa[48] were prepared according to literature procedures. Commercially available products such as I2, Ph3SiOH, tBuOK, KOH and Na were purchased from Fluorochem or Sigma and used as received. Deuterated benzene (Deutero, Germany) was stored in sealed ampoule over activated 4 Å molecular sieves and degassed by a minimum of three freeze–thaw cycles.
NMR spectra were recorded at room temperature on Bruker Avance III 400 and 600 NMR spectrometers. All chemical shifts are reported in δ units (ppm) relative to the residual signal of the deuterated solvent. (ref. CDCl3: 1H 7.26 ppm, 13C 77.16 ppm; ref. C6D6: 1H 7.16 ppm, 13C 128.06 ppm). Assignment of the signals was conducted using 1D (1H, 13C{1H}) and 2D (COSY, HMBC, HSQC) NMR experiments. (for the numbering schemes, see Figure 11; for 1H, 13C, and 119Sn NMR spectra, see Figures S1–S36). The chemical shifts for the 119Sn NMR spectra are reported relative to SnMe4 as external standard. The NMR spectra were processed using MestReNova software.[69]
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Mass spectra were recorded on a Thermo Scientific LTQ Orbitrap XL mass spectrometer equipped with a standard ESI/APCI source. Data analysis and calculations of the theoretical isotopic patterns were carried out with the Xcalibur software package.[70] Melting points were measured with an Electrothermal 9200 apparatus and are not corrected. Elemental analyses were carried out on a Flash EA 1112 analyser. Infrared spectra were recorded on a JASCO FT/IR-615 instrument.
Thermal analyses were conducted on an SDT Q600 (USA) device from T.A. Instruments. Data on thermogravimetry (TG) and differential thermal analysis (DTA) curves, were simultaneously acquired under the following measurement conditions: heating from laboratory temperature to 1000 °C, at a heating rate of 10 °C/min, under normal air atmosphere, using alumina crucibles. For each measurement ~5 mg of material was used.
Crystal Structure Determination
The details of the crystal structure determination and refinement for compounds 1–5, 10–12 are given in Tables S1 and S2, respectively (see ESI†). The crystals were collected on a Bruker D8 VENTURE diffractometer using Mo−Kα radiation (λ=0.71073 Å) from a IμS 3.0 microfocus source with multilayer optics, at low temperature (100 K). The structures were refined with anisotropic thermal parameters for non-H atoms. Hydrogen atoms were placed in fixed, idealized positions and refined with a riding model and a mutual isotropic thermal parameter. For structure solving and refinement the Bruker APEX5 Software Package was used.[71] Visual representations were created with the Diamond program.[72] The C41 and C42 carbon atoms from one of the 1,3-dioxolan-2-yl rings of compound 1 are disordered over two positions and were modelled with site occupancies of 58 : 42. For compound 10 the measured crystal proved to be a two-component twin [twin ratio: 80 : 20], arising from a rotation of −179.97° around the vector normal to (−1 0 0). In a final difference Fourier map, highly disordered electron density was observed for compound 12. The residual electron density was difficult to model and therefore the SQUEEZE routine in PLATON[73] was used to eliminate this contribution of the electron density in the solvent region from the intensity data. The solvent-free model was employed for the final refinement. It was estimated that each cavity contains 42 electrons which correspond to a solvent molecule of dichloromethane (CH2Cl2).
Synthesis of L2PhSnI (1)
Elemental iodine (1.226 g, 4.83 mmol) was dissolved in CH2Cl2 (90 mL) and slowly added dropwise to a solution of [2-{(CH2O)2CH}C6H4]2SnPh2 (A) (2.759 g, 4.83 mmol) in CH2Cl2 (60 mL), at 0 °C. The reaction mixture was then left under vigorous stirring overnight. The crude was washed with a concentrated aqueous solution of Na2S2O3, then dried over Na2SO4 and separated by filtration. The organic solvent was removed in a rotary evaporator and pentane (50 mL) was added to the resulting oil to precipitate the title compound. The precipitate was filtered, washed with pentane (30 mL) and dried, resulting in 2.524 g (84 %) of a colourless crystalline solid, m.p. 107.8–108.2 °C. Elemental analysis calcd. for C24H23IO4Sn (621.06 g/mol): C, 46.41; H, 3.73; Found: C, 45.12; H, 3.62 %. 1H NMR (CDCl3, 400.13 MHz, 21 °C), δ (ppm): 3.63 (m, 8H, H-8, H-9), 5.85 (s, 2H, H-7), 7.37 (m, 3H, H-5, H-13), 7.45 (m, 4H, H-4, H-12), 7.52 (m, 2H, H-3), 7.81 (dd, 2H, 3JH-H =7.7 Hz, 4JH-H =1.5 Hz, 3JSn-H =61 Hz, H-11), 7.99 (m, 2H, 3JSn-H =75 Hz, H-6). 13C{1H} NMR (CDCl3, 100.62 MHz, 21 °C) δ (ppm): 64.65 (s, C-8/9), 64.96 (s, C-8/9), 103.16 (s, 3JSn-C=19 Hz, C-7), 127.09 (s, 3JSn-C=59 Hz, C-3), 128.45 (s, 3J117Sn-C=61 Hz, 3J119Sn-C=64 Hz, C-12), 129.12 (s, 4JSn-C=14 Hz, C-13), 129.40 (s, 3JSn-C=71 Hz, C-5), 129.55 (s, 4JSn-C=14 Hz, C-4), 136.75 (s, 2JSn-C=48 Hz, C-6), 136.87 (s, 2JSn-C=47 Hz, C-11), 137.94 (s, 1J117Sn-C=715 Hz, 1J119Sn-C=748 Hz, C-1), 141.04 (s, 2JSn-C=38 Hz, C-2), 142.25 (s, 1J117Sn-C=598 Hz, 1J119Sn-C=626 Hz, C-10). 119Sn{1H} NMR (CDCl3, 149.19 MHz, 21 °C) δ (ppm): −152.2. HRMS (ESI+, MeCN), m/z (relative intensity, %): [L2SnPh]+, calcd for C24H23O4Sn: 495.06128. Found 495.06185 (100). IR (ATR, υ, cm−1): ν(C−O−C) 948(s), 937(s).
Synthesis of L2SnI2 (2)
Elemental Iodine (1.912 g, 7.53 mmol) was added to a solution of A (2.151 g, 3.77 mmol) in CH2Cl2 (100 mL) and the mixture was stirred overnight. The crude was washed with a concentrated aqueous solution of Na2S2O3, then dried over Na2SO4 and separated by filtration. The organic solvent was removed in a rotary evaporator and the product was precipitated with pentane from the resulting oil. The compound was further washed with pentane and then dried to give 2.137 g (85 %) of a colourless crystalline solid, m.p. 206.4–206.6 °C. Elemental analysis: calcd. for: C18H18I2O4Sn (670.86 g/mol): C, 32.23; H, 2.70; Found: C, 33.08; H, 3.13. 1H NMR (CDCl3, 600.13 MHz, 21 °C), δ (ppm): 3.70 (m, 8H, H-8, H-9), 5.91 (s, 2H, H-7), 7.44 (dd, 2H, 3JH-H =7.7 Hz, 4JH-H =1.4 Hz, H-3), 7.49 (td, 2H, 3JH-H=7.5 Hz, 4JH-H=1.5 Hz, H-4), 7.61 (td, 2H, 3JH-H=7.4 Hz, 4JH-H=1.5 Hz, H-5), 8.22 (dd, 2H, 3JH-H=7.5 Hz, 4JH-H=1.2 Hz, 3JSn-H=111 Hz, H-6). 13C{1H} NMR (CDCl3, 150.92 MHz, 21 °C), δ (ppm): 65.10 (s, C-8, C-9), 102.04 (s, 3JSn-C=21 Hz, C-7), 127.10 (s, 3JSn-C=81 Hz, C-3), 129.86 (s, 3J117Sn-C=97 Hz, 3J119Sn-C=101 Hz, C-5), 130.41 (s, 4JSn-C=19 Hz, C-4), 134.68 (s, 2JSn-C=62 Hz, C-6), 136.82 (s, 1J117Sn-C=961 Hz, 1J119Sn-C=1004 Hz, C-1), 138.14 (s, 2JSn-C=54 Hz, C-2). 119Sn{1H} NMR (CDCl3, 223.76 MHz, 21 °C) δ (ppm): −319.5. HRMS (APCI+, MeCN), m/z (relative intensity, %): [L2SnI]+, calcd. for C18H18IO4Sn: 544.92663. Found 544.92749 (100); [L'LSnI]+, calcd. for C16H14IO3Sn: 500.90041. Found 500.90125 (67); [L’2SnI]+, calcd. for C14H10IO2Sn: 456.87420. Found: 456.87500 (37); L’=2-(O=CH)C6H4.
Synthesis of L2SnPhOSiPh3 (3)
A solution of Ph3SiONa (0.216 g, 0.72 mmol, 1.5 equiv.) in anhydrous THF (10 mL) was added dropwise to a solution of 1 (0.300 g, 0.48 mmol) in anhydrous THF (10 mL) and was left under stirring overnight. The solvent was removed in vacuo and anhydrous toluene (15 mL) was added to the mixture. The solution was filtered, and the solvent removed. The resulting solid was washed with small portions of Et2O and dried, resulting in 0.195 g (52 %) of a white solid, m.p. 119.5 °C. Elemental analysis: calcd. for C42H38O5SiSn (769.56 g/mol): C, 65.55; H, 4.98; Found: C, 65.73; H, 5.35.1H NMR (CDCl3, 400.13 MHz, 20 °C), δ (ppm): 3.34–3.60 (m, 8H, H-8, H-9), 5.64 (s, 2H, H-7), 7.17 (t, 6H, 3JH-H=7.3 Hz, H-16), 7.24 (m, 2H, H-12), 7.27 (m, 4H, H-17, H-13), 7.32 (m, 2H, H-5). 7.41 (td, 2H, 3JH-H=7.4 Hz, 4JH-H=1.4 Hz, H-4), 7.46 (m, 8H, H-3, H-15), 7.59 (m, 2H, H-11), 7.85 (dd, 2H, 3JH-H=7.4 Hz, 4JH-H=1.4 Hz, 3JSn,H=68 Hz, H-6). 13C{1H} NMR (CDCl3, 100.62 MHz, 20 °C), δ (ppm): 64.54 (s, C-9), 64.79 (s, C-8), 103.32 (s, 3JSn-C=20 Hz, C-7), 126.84 (s, 3JSn-C=61 Hz, C-3), 127.24 (s, C-16), 128.17 (s, 3JSn-C=62 Hz, C-12), 128.70 (s, C-17), 128.71 (s, C-13), 129.02 (s, 3JSn-C=66 Hz, C-5), 129.09 (s, 4JSn-C=13 Hz, C-4), 135.42 (s, C-15), 136.28 (s, 2JSn-C=41 Hz, C-6), 136.77 (s, 2JSn-C=45 Hz, C-11), 139.54 (s, 3JSn-C=79 Hz, C-14), 139.55 (s, 1J117Sn,C=792 Hz, 1J119Sn,C=825 Hz, C-1), 141.73 (s, 2JSn-C=41 Hz, C-2), 143.37 (s, 1J117Sn-C=665 Hz, 1J119Sn-C=695 Hz, C-10).119Sn{1H} NMR (CDCl3, 149.19 MHz, 19 °C), δ (ppm): −183.2. 29Si INEPT NMR (CDCl3, 79.49 MHz, 19 °C), δ (ppm): −22.3. HRMS (APCI+, MeCN), m/z (relative intensity, %): [LL'SnPh]+, calcd. for C22H19O3Sn: 451.03507. Found 451.03555 (100); [L2SnPh]+, calcd. for C24H23O4Sn: 495.06128. Found 495.06165 (62); [L’2SnPh]+, calcd. for C20H15O2Sn: 407.00885. Found 407.00940 (57); [Ph3Si]+, calcd. for C18H15Si: 259.09375. Found 259.09393 (67); L’=2-(O=CH)C6H4.
Synthesis of L2SnPhOtBu (4)
A solution of tBuOK (0.112 g, approx. 1 mL of 1 M solution in THF) was added dropwise to a solution of 1 (0.621 g, 1.00 mmol) in anhydrous THF (4 mL), and then stirred for 30 minutes. The resulting suspension was filtered through a cannula and the solvent was removed in vacuo, resulting in a colourless, viscous oil. The title compound was obtained as a white crystalline solid 0.400 g (71 %) upon crystallisation from acetonitrile at −24 °C, m.p.=106 °C. 1H NMR (C6D6, 400.13 MHz, 22 °C), δ (ppm): 1.45 (s, 9H, H-15), 3.00–3.23 (m, 8H, H-8, H-9), 5.77 (s, 4H, 4JSn-H=7 Hz, H-7), 7.15–7.23 (m, 3H, H-5, H-13), 7.25 (td, 2H, 3JH-H=7.4 Hz, 4JH-H=1.5 Hz, H-4), 7.30 (m, 2H, H-12), 7.60 (m, 2H, H-3), 8.15 (d, 2H, 3JH-H=8.0 Hz, 4JH-H=1.4 Hz, H-11), 8.39 (m, 4H, 3JSn-H=61 Hz, H-6). 13C{1H} NMR (C6D6, 100.62 MHz, 22 °C), δ (ppm): 34.32 (s, 3JSn-C=13 Hz, C-15), 64.57 (s, C-8/C-9), 64.70 (s, C-8/C-9), 71.85 (s, 2JSn-C=31 Hz, C-14), 104.04 (s, 3JSn-C=23 Hz, C-7), 127.18 (s, 3JSn-C=56 Hz, C-3), 128.52 (s, C-12), 128.97 (s, C-4/C-5/C-13), 129.10 (s, C-4/C-5/C-13), 137.06 (s, 2JSn-C=35 Hz, C-6), 137.41 (s, 2JSn-C=43 Hz, C-11), 141.82 (s, 1J117Sn-C=722 Hz, 1J119Sn-C=755 Hz, C-1), 143.40 (s, 2JSn-C=40 Hz, C-2), 144.82 (s, 1J117Sn-C=660 Hz, 1J119Sn-C=691 Hz, C-10). 119Sn{1H} NMR (C6D6, 149.19 MHz, 21 °C) δ (ppm): −191.0.
Synthesis of (L2SnPh)2O (5)
In a 100 mL Schlenk flask a solution of 1 (1.00 g, 1.06 mmol) in anhydrous THF (25 mL) was added dropwise to a suspension of tBuOK (0.208 g, 1.85 mmol, 1.15 equiv.) in anhydrous THF (25 mL), and the mixture was left under stirring overnight. The solvent was removed in vacuo and anhydrous Et2O (30 mL) was added to extract the product. The etheric solution was transferred into a new Schlenk flask, then the solvent was removed in vacuo and the resulting solid was dried. The product was obtained as a white solid, 0.699 g (76 %), m.p. 70.3–72.9 °C. Elemental analysis: calcd. for C48H46O9Sn2 (1004.31 g/mol): C, 57.71; H, 4.62; O, 14.34; Found: C, 57.70; H, 4.68. 1H NMR (C6D6, 600.13 MHz, 21 °C), δ (ppm): 3.04–3.30 (m, 16H, H-8, H-9), 5.75 (s, 4H, 4JSn-H=7 Hz, H-7), 7.16 (m, 12H, H-4, H-5, H-12), 7.20 (td, 2H, 3JH-H=7.5 Hz, 4JH-H=1.6 Hz, H-13), 7.58 (dd, 4H, 3JH-H=7.5 Hz, 4JH-H=1.5 Hz, 4JSn-H=31 Hz, H-3), 7.86 (m, 4H, H-11), 8.20 (dd, 4H, 3JH-H=7.2 Hz, 4JH-H=1.6 Hz, 3JSn-H=63 Hz, H-6). 13C{1H} NMR (C6D6, 150.92 MHz, 21 °C), δ (ppm): 64.46 (s, C-8/C-9), 64.71 (s, C-8/C-9), 103.99 (s, 3JSn-C=21 Hz, C-7), 126.84 (s, 3JSn-C=55 Hz, C-3), 128.35 (s, C-4/C-5/C-12/C-13), 128.38 (s, C-4/C-5/C-12/C-13), 128.51 (s, C-4/C-5/C-12/C-13), 128.56 (s, C-4/C-5/C-12/C-13), 137.16 (s, 2JSn-C=39 Hz, C-6), 137.53 (s, 2JSn-C=44 Hz, C-11), 142.98 (s, 1J117Sn-C=720 Hz, 1J119Sn-C=755 Hz, C-1), 143.43 (s, 2JSn-C=38 Hz, C-2), 145.86 (s, 1J117Sn-C=641 Hz, 1J119Sn-C=670 Hz, C-10). 119Sn{1H} NMR (C6D6, 223.76 MHz, 21 °C), δ (ppm): −155.9. HRMS (APCI+, MeCN), m/z (relative intensity, %): [L2SnPh]+, calcd. for C24H23O4Sn: 495.06128. Found 495.06193 (100); [L'LSnPh]+, calcd. for C22H19O3Sn: 451.03507. Found 451.03671 (33); [L’2SnPh]+, calcd. for C20H15O2Sn: 407.00885. Found 407.01052 (9); L’=2-(O=CH)C6H4.
Synthesis of L2SnPhOMe (6)
Clean sodium (0.100 g, 4.35 mmol) was washed with petroleum ether and added into MeOH (25 mL) in a 2-neck round-bottom flask equipped with a Liebig condenser and a vacuum adapter. The mixture was left with no stirring, under continuous argon flow until the sodium was consumed in the reaction. Compound 1 (1.00 g, 1.61 mmol) was added under stirring and the mixture was heated at reflux at 70 °C for 4 hours. The solvent was removed in vacuo and anhydrous toluene (20 mL) was added. The resulting suspension was filtered through a canula, and the solvent was evaporated. The compound was washed with anhydrous Et2O (20 mL) and dried in vacuum, to yield 0.671 g (79 %) of a white solid. The title compound was obtained as the major product (86 %) in a mixture with 5, one of its decomposition products. m.p.=71 °C. 1H NMR (C6D6, 600.13 MHz, 21 °C), δ (ppm): 3.05–3.30 (m, 8H, H-8, H-9), 4.00 (s, 3H, 3JSn-H=38 Hz, -OCH3), 5.69 (s, 2H, 4JSn-H=7 Hz, H-7), 7.19 (m, 4H, H-12, H-4), 7.23 (m, 1H, H-13), 7.31 (t, 2H, 3JH-H=7.6 Hz, H-5), 7.54 (dd, 2H, 3JH-H=7.1 Hz, 4JH-H=1.9 Hz, H-3), 8.07 (dd, 3JH-H=7.7 Hz, 4JH-H=1.2 Hz, 3JSn-H=54 Hz, H-11), 8.20 (dd, 3JH-H=7.0 Hz, 4JH-H=1.4 Hz, 3JSn-H=63 Hz, H-6) 119Sn{1H} NMR (C6D6, 223.76 MHz, 21 °C) δ (ppm): −154.2.
Synthesis of L2SnPhOH (7)
(Route 1) An aqueous solution of KOH (0.200 g, 3.56 mmol, 2 mL H2O) was added to a solution of 1 (0.225 g, 0.36 mmol) in CH2Cl2 (5 mL) and stirred vigorously for 20 minutes. The reaction mixture was then extracted with CH2Cl2 (2x10 mL) and the resulting organic phases were combined and dried over Na2SO4. The title compound was obtained quantitatively as a colourless oil after filtration and removal of the organic solvent.
(Route 2) Compound 5 (0.045 g, 0.04 mmol) was dissolved in CH2Cl2 (5 mL) and stirred overnight with distilled water (6 mL). The mixture was then extracted with CH2Cl2 (3x5 mL), and the combined organic layers were dried over Na2SO4. The solvent was removed using a rotary evaporator after filtration to produce a colourless oil, 0.027 g (60 %). 1H NMR (CDCl3, 400.13 MHz, 20 °C), δ (ppm): 0.69 (s, 1H, 2JSn-H=24 Hz, OH), 3.62 (m, 8H, H-8, H-9), 5.77 (s, 2H, 4JSn-H=7 Hz, H-7), 7.38 (m, 3H, H-5, H-13), 7.43 (m, 4H, H-4, H-12), 7.49 (m, 2H, H-3), 7.77 (m, 2H, H-11), 7.88 (m, 2H, H-6). 13C{1H} NMR (CDCl3, 100.62 MHz, 21 °C) δ (ppm): 64.81 (s, C-8), 64.83 (s, C-9), 103.75 (s, 3JSn-C=20 Hz, C-7), 127.43 (s, 3J117Sn-C=55 Hz, 3J119Sn-C=57 Hz, C-3), 128.44 (s, 3J117Sn-C=59 Hz, 3J119Sn-C=62 Hz, C-5), 129.03 (s, 4JSn,C=13 Hz, C-13), 129.23 (s, C-12), 129.29 (s, 4JSn,C=C-4), 136.45 (s, C-6), 136.65 (s, C-11), 138.99 (s, C-1), 141.88 (s, 2JSn-C=38 Hz, C-2), 142.62 (s, C-10). 119Sn{1H} NMR (C6D6, 223.8 MHz, 23 °C) δ (ppm): −155.0. 119Sn{1H} NMR (CDCl3, 149.19 MHz, 20 °C) δ (ppm): −155.4.
Synthesis of (L2Sn)3O3 (8)
An aqueous solution of KOH (0.209 g, 3.75 mmol, 5 equiv., 5 mL H2O) was added to a solution of 2 (0.250 g, 0.37 mmol) in THF (20 mL) and the resulting mixture was stirred overnight. After removal of the organic solvent, the title compound was extracted with 3×20 mL CH2Cl2. The combined organic phases were dried over anhydrous Na2SO4, filtered and the solvent was removed in a rotary evaporator. Pentane was added to the resulting oil and the resulting precipitate is dried, affording 0.157 g (98 %) isolated product, m.p.=165.7–167.4 °C. Elemental analysis: calcd. for: C54H54O15Sn3 (1299.14 g/mol): C, 49.92; H, 4.19; Found: C, 50.14; H, 4.45. 1H NMR (CDCl3, 600.13 MHz, 21 °C), δ (ppm): 3.48–3.73 (m, 24H, H-8, H-9), 5.65 (s, 6H, H-7), 7.14 (t, 6H, 3JH-H=7.2 Hz, H-4), 7.20–7.27 (m, 12H, H-3, H-5), 7.97 (d, 6H, 3JH-H=7.3 Hz, 3JSn-H=73 Hz, H-6). 13C{1H} NMR (CDCl3, 150.92 MHz, 21 °C), δ (ppm): 64.77 (s, C-8, C-9), 103.34 (s, 3JSn-C=24 Hz, C-7), 126.33 (s, 3JSn-C=72 Hz, C-3), 128.25 (s, 4JSn-C=14 Hz, C-4), 128.43 (s, 3JSn-C=73 Hz, C-5), 136.16 (s, 2JSn-C=35 Hz, C-6), 141.31 (s, 2JSn-C=50 Hz, C-2), 142.51 (s, 1J117Sn-C=974 Hz, 1J119Sn-C=1019 Hz, C-1). 119Sn{1H} NMR (CDCl3, 223.8 MHz, 21 °C) δ (ppm): −214.2. HRMS (APCI+, MeCN), m/z (relative intensity, %): [LL'SnOH]+, calcd. for C16H15O4Sn: 390.99868. Found 390.99754 (100); [L2SnOH]+ calcd. for C18H19O5Sn: 435.02490. Found: 435.02344 (53); [LL'SnH]+, calcd. for C16H15O3Sn: 375.00377. Found 375.00270 (49); [L’2SnOH]+, calcd. for C14H11O3Sn: 346.97247. Found 346.97148 (34); [L’2SnH]+, calcd. for C14H11O2Sn: 330.97755. Found 330.97664 (46); L’=2-(O=CH)C6H4.
Synthesis of L2Sn(OSiPh3)2 (10)
In a 50 mL Schlenk flask a solution of the compound Ph3SiONa (0.300 g, 1.0 mmol, 1.1 equiv.) in anhydrous THF (6 mL) was added dropwise to a solution of 2 (0.300 g, 0.48 mmol) in anhydrous THF (11 mL) and the mixture was stirred overnight. The solvent was removed in vacuum and anhydrous toluene (12 mL) was added to the mixture. The obtained suspension was filtered in another Schenk flask and toluene was then removed in vacuum, giving a colourless solid. The product was crystallised by layering hexane over a concentrated THF solution of 10 resulting in 0.317 g (73 %) colourless crystals. m.p.=207.5–209.8 °C. Elemental analysis: calcd. for: C54H48O6Si2Sn (967.85 g/mol): C, 67.01; H, 5.00; Found: C, 67.94; H, 5.17. 1H NMR (CDCl3, 600.13 MHz, 21 °C), δ ppm: 3.03–3.63 (m, 8H, H-8, H-9), 5.01 (s, 2H, 4JSn-H=10 Hz, H-7), 7.09 (t, 12H, 3JH-H=7.5 Hz, H-12), 7.24 (m, 8H, H-3, H-13), 7.35 (td, 2H, 3JH-H=7.4 Hz, 4JH-H=1.4 Hz, H-5), 7.39 (td, 2H, 3JH-H=7.4 Hz, 4JH-H=1.4 Hz, H-4), 7.45 (d, 12H, 3JH-H=7.0 Hz, H-11), 8.10 (d, 2H, 3JH-H=7.2 Hz, 3JSn-H=87 Hz, H-6). 13C{1H} NMR (CDCl3, 150.92 MHz, 21 °C), δ ppm: 64.53 (s, C-8, C-9), 102.03 (s, 3JSn-C=28 Hz, C-7),127.03 (s, C-3), 127.22 (s, C-12), 128.70 (s, C-13), 129.52 (s, C-4, C-5), 135.17 (s, C-6), 135.48 (s, C-11), 137.69 (s, C-1), 139.24 (s, C-10), 139.87 (s, C-2). 119Sn{1H} NMR (CDCl3, 223.76 MHz, 21 °C) δ (ppm): −335.6 HRMS (APCI+, MeCN), m/z (relative intensity, %): [LL'SnPh]+, calcd. for C22H19O3Sn: 451.03507. Found 451.03398 (100); [L2SnOSiPh3]+, calcd. for C36H33O5SiSn: 693.11137. Found 693.10999 (84); [Ph3Si]+, calcd. for C18H15Si: 259.09375. Found 259.09236 (56); L’=2-(O=CH)C6H4.
Synthesis of L2Sn(OtBu)2 (11)
A solution of tBuOK (0.167 g, approx. 1.5 mL of 1 M solution in THF) was added dropwise to a solution of 2 (0.500 g, 0.75 mmol) in anhydrous THF (20 mL), and the reaction mixture was stirred for 30 minutes. The resulting suspension was filtered through a cannula and the solvent removed in vacuum, resulting a colourless, viscous oil. Colourless crystals of the title compound, 0.344 g (82 %), were isolated after one day upon cooling a concentrated MeCN solution to −24 °C. m.p.=180–182 °C. 1H NMR (C6D6, 400.13 MHz, 21 °C), δ (ppm): 1.52 (s, 18H, H-11), 3.00 (m, 4H, H-8/H-9), 3.29 (m, 4H, H-8/H-9), 5.53 (s, 2H, 4JSn-H=8 Hz, H-7), 7.17 (td, 2H, 3JH-H=7.5 Hz, 4JH-H=1.4 Hz, H-3), 7.33 (td, 2H, 3JH-H=7.4 Hz, 4JH-H=1.4 Hz, H-4), 7.39 (m, 2H, H-5), 8.80 (dd, 2H, 3JH-H=7.5 Hz, 4JH-H=1.4 Hz, 3JSn-H=73 Hz, H-6). 13C{1H} NMR (C6D6, 100.62 MHz, 21 °C), δ (ppm): 34.28 (s, 3JSn-C=16 Hz, C-11), 64.57 (s, C-8, C-9), 72.06 (s, 2JSn-C=36 Hz, C-10), 103.09 (s, 3JSn-C=24 Hz, C-7), 127.57 (s, C-3), 129.01 (s, 4JSn-C=15 Hz, C-4), 129.18 (s, 3J117Sn-C=73 Hz, 3J119Sn-C=76 Hz, C-5), 136.69 (s, 2JSn-C=25 Hz, C-6), 141.00 (s, 2JSn-C=53 Hz, C-2), 142.48 (s, 1J117Sn-C=1053 Hz, 1J119Sn-C=1103 Hz, C-1). 119Sn{1H} NMR (C6D6, 149.19 MHz, 21 °C) δ (ppm): −307.5.
Synthesis of (L2SnO)2OB(m–tol) (12)
Compound 8 (0.440 g, 0.34 mmol) and 3-Me-C6H4B(OH)2 (0.069 g, 0.51 mmol) were dissolved in toluene (60 mL) and heated at reflux in a 100 mL round-bottom flask equipped with a Dean-Stark apparatus and an air condenser, for 22 h. Removal of the solvent using a rotary evaporator yielded a colourless oil. Pentane was added to the resulting oil affording the title compound as a white precipitate, 0.473 g (95 %). m.p.=191–194 °C. Elemental analysis: calcd. for: C43H43BO11Sn2 (984.04 g/mol): C, 52.49; H, 4.40; Found: C, 53.46; H, 4.78. 1H NMR (CDCl3, 400.13 MHz, 19 °C), δ (ppm): 2.32 (s, 3H, H-16), 3.75 (m, 8H, H-8/H-9), 3.92 (m, 8H, H-8/H-9), 5.87 (s, 4H, 4JSn-H=7 Hz, H-7,), 7.11 (m, 1H, H-13), 7.18 (t, 1H, 3JH-H=7.6 Hz, H-12), 7.24 (td, 4H, 3JH-H=7.2 Hz, 4JH,H=1.3 Hz, H-5), 7.34 (td, 4H, 3JH-H=7.4 Hz, 4JH-H=1.4 Hz, H-4), 7.39 (m, 4H, H-3), 7.72 (m, 2H, H-11, H-15), 7.97 (d, 4H, 3JH-H=7.1 Hz, 3JSn-H=78 Hz, H-6). 13C{1H} NMR (CDCl3, 100.62 MHz, 19 °C), δ (ppm): 21.80 (s, C-16), 64.96 (s, C-8/C-9), 65.03 (s, C-8/C-9), 103.01 (s, 3JSn-C=25 Hz, C-7), 126.80 (s, 3JSn-C=79 Hz, C-3), 127.04 (s, C-12), 129.09 (s, 3JSn-C=82 Hz, C-5), 129.11 (s, 4JSn-C=15 Hz, C-4), 129.32 (s, C-13), 131.88 (s, C-11), 135.61 (s, 2JSn-C=38 Hz, C-6), 135.70 (s, C-15), 136.01 (s, C-10), 139.54 (s, 1J117Sn-C=1047 Hz, 1J119Sn-C=1097 Hz, C-1), 141.02 (s, 2JSn-C=54 Hz, C-2). 119Sn{1H} NMR (CDCl3, 149.19 MHz, 21 °C) δ (ppm): −258.7. 11B{1H} NMR (CDCl3, 128.38 MHz, 21 °C) δ (ppm): 28.9 (br). HRMS (APCI+, MeCN), m/z (relative intensity, %): [M+H]+ calcd. for C43H44BO11Sn2: 985.10092. Found 985.10458 (100).
Acknowledgments
We are grateful for the financial support offered by the National Council for Scientific Research CNCS-UEFISCDI, project PN-III-P1-1.1-PD-2019-0976. The support provided by the National Centre for X-Ray Diffraction (Babeş-Bolyai University, Cluj-Napoca, Romania) for the solid-state structure determinations is highly appreciated. Open Access publishing facilitated by Anelis Plus (the official name of "Asociatia Universitatilor, a Institutelor de Cercetare – Dezvoltare si a Bibliotecilor Centrale Universitare din Romania”), as part of the Wiley - Anelis Plus agreement.
Conflict of Interests
The authors declare no conflict of interest.
Data Availability Statement
The data that support the findings of this study are available in the supplementary material of this article.
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Deposition Number(s) 2387283 (for 1), 2387279 (for 2), 2387280 (for 3), 2387282 (for 4), 2403846 (for 5), 2387281 (for 10), 2403845 (for 11), and 2389609 (for 12) contain(s) the supplementary crystallographic data for this paper. These data are provided free of charge by the joint Cambridge Crystallographic Data Centre and Fachinformationszentrum Karlsruhe Access Structures service.
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