Oxidative halogenation of Sn(II)heteroaryl alkenolates: Formation of unusual trans-dihalo Sn(IV) complexes

Inorganica Chimica Acta 455 (2017) 197–203

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Research paper

Oxidative halogenation of Sn(II)heteroaryl alkenolates: Formation of unusual trans-dihalo Sn(IV) complexes Lisa Czympiel, Jean-Marius Lekeu, Corinna Hegemann, Sanjay Mathur ⇑ Department of Chemistry, Institute of Inorganic Chemistry, University of Cologne, Greinstrasse 6, 50939 Cologne, Germany

a r t i c l e

i n f o

Article history: Received 16 June 2016 Received in revised form 7 October 2016 Accepted 19 October 2016 Available online 20 October 2016 Dedicated to Professor Walter Frank on the Occasion of His 60th Birthday Keywords: Oxidative halogenation Sn(IV) complexes X-ray crystal structures Multinuclear NMR spectroscopy

a b s t r a c t A series of novel tin(IV)-heteroaryl alkenolates of the general formula [Sn(DMOTFP)2X2] (3–6, X = F, Cl, Br, I) were prepared by direct oxidative halogenation of the corresponding tin(II) derivative [SnII(DMOTFP)2] (2) and by cleavage of the carbon-tin bonds in diphenyltin dichloride [Ph2SnCl2] by (4,5-dimethyloxazolyl)-1,1,1-trifluoropropen-2-ol, (H-DMOTFP, 1) with a subsequent halide exchange reaction. The molecular structures elucidated in solution (multi-nuclear NMR spectroscopy) and by single crystal X-ray diffraction confirmed the sixfold coordination of the tin(IV) center with a distorted octahedral arrangement of ligands. An unusual centrosymmetric octahedral trans-dihalo configuration was found for the compounds [SnIV(DMOTFP)2X2] (X = Cl, Br, I), while the compound [Sn(DMOTFP)2F2] adopted a cis-dihalide configuration. Ó 2016 Published by Elsevier B.V.

1. Introduction Organotin compounds have been widely used in various scientific fields such as organic synthesis and catalysis [1,2], materials synthesis [3,4], as well as biomedical applications [5,6]. They exhibit a vast structural diversity, ranging from monomers [7–9] to dimers [2,10–12], trimers [13–15] and oligomers [16], depending on the steric bulk of the ligands. In the field of coordination chemistry b-diketonato donors represent one of the most important classes of chelating ligands due to easy access and widely studied properties such as volatility. They can be readily synthesized in aqueous or anhydrous media and have been described for a wide range of elements [17]. Given the versatility of their applications, a large number of tin(II) and tin(IV) b-diketonates have been synthesized and structurally characterized in the past [18–24]. We have demonstrated the use of functionalized heteroarylalkenols as substituted equivalents of b-diketones for synthesizing stable and volatile metal complexes in various contributions [3,25–34]. Heteroaryl substituted alkenols allow to vary the (perfluoro)alkyl chain as well as modify the heteroaryl moiety. In 2011 Giebelhaus et al. reported on the application of a homoleptic bis(g2-N, O-2-[4,5-dimethyloxazolyl]-1,1,1-trifluoro-propen-2-olato)tin ([SnII(DMOTFP)2] 2) as precursor for the chemical vapor deposition

⇑ Corresponding author. E-mail address: [email protected] (S. Mathur). http://dx.doi.org/10.1016/j.ica.2016.10.023 0020-1693/Ó 2016 Published by Elsevier B.V.

of SnO2 nanowires. In continuation of our research concerning molecular approaches to nanomaterials we report here on the solution and structural chemistry of the first examples of dihalogenotin(IV) bis(heteroarylalkenolates).

2. Results and discussion The synthesis of dihalo-bis-(g2-N,O-2-[4,5-dimethyloxazolyl]1,1,1trifluoropropen2olato)-tin(IV) compounds (3–6) was selectively achieved by oxidative halogenation of [SnII(DMOTFP)2] (2). Alternatively, the very atom-economical reaction of diphenyltinIV dichloride with H-DMOTFP with a subsequent halide exchange reaction produced [Sn(DMOTFP)2X2] (3–6, X = F, Cl, Br, I) (Scheme 1) in average yields. Following a procedure described by Giebelhaus et al. [3] 2 was obtained via ligand exchange reaction between 1 and [Sn{N (SiMe3)2}2]. Through an oxidative halogenation of 2 compounds 3–6 were accessible as has already been shown for other Sn(II) compounds [35]. Fluorination of 2 was accomplished using XeF2 as a mild and easy-to-handle fluorinating agent [36]. In order to suppress any undesired side reactions, synthesis was performed in anhydrous EtCN at
196 °C and the reaction mixture was gently warmed up to room temperature over a period of approximately one hour, when 3 was obtained in 42% yield. Oxidative chlorination was achieved using the mild chlorinating agent hexachloroethane [37] at a temperature of 60–80 °C in CH2Cl2 to obtain 4 in 30%

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O

+II

+II

[Sn{N(SiMe3)2}2]

N HO

CF 3

1

O Sn N N O

F3C

- 2 HN(SiMe3)2

O

O

F3C

"X2"

CF 3

+IV

X

O

+IV

Sn

N

O

O

X

2

[Ph 2SnCl 2]

O

N

CF3

3-6

- 2 HPh F 3C

O

O N

Cl

+IV

Sn Cl

N

O

O

F3C

O

2 MX CF3

-2 MCl

O

X

Sn

N

O

N

+IV

O

X

CF 3

3, 6

4

Scheme 1. Synthetic pathways to [Sn(DMOTFP)2X2] (X = F (3), Cl (4), Br (5), I (6)).

yield. The bromo (5) and iodo (6) compounds were prepared by reacting 2 with stoichiometric amounts of elementary halogen at 0 °C following a modified procedure by Kao et al. [38] obtaining a yield of 71% and 12%, for 5 and 6 respectively. After removing the volatile by-products and excess solvents, all compounds were obtained as analytically pure solids. In addition to the oxidative halogenation 4 was readily accessible through direct reaction of neat ligand (1) with diphenyltin dichloride at 115–120 °C. Both reactants are liquid under reaction conditions and mix readily, which eliminates the need for a solvent. A highly unusual feature of this reaction is the exclusive twofold carbon-tin bond cleavage which led to the formation of 4 in almost quantitative (95%) yield. Unlike the tin-chlorine bond cleavage occurring in most ligand exchange and metathesis reactions [38,39], here the organic moieties act as volatile leaving groups. This type of dephenylation reaction is usually observed upon reacting diphenyltin dichloride (or triphenyltin monochloride) with strong tri- or tetradentate ligands such as thiosemicarbazones [40,41], or bidentate thiocarbamates [42]. Due to the easy accessibility and high yield of compound 4 it was further used as starting material for salt metatheses reactions leading to compounds 3 and 6, the driving force for the reaction being the precipitation of AgCl and NaCl, respectively. Attempted synthesis of 3 from 4 and excess AgF yielded a substantial amount of the side product tetrafluoro-(g2-N,O-2-[4,5-dimethyloxazolyl]1,1,1-trifluoropropen-2-olato)tin(IV) ([Sn(DMOTFP)X4]
, (7)), indicating further ligand exchange reactions with an elimination of the chelating group. The reaction could be pushed to form hexafluorostannate(IV) Ag2[SnF6], as described by Tyrra [43]. Using a stoichiometric amount of AgF compound 3 was accessible with a yield of 22%.

trans-isomers: X

X F 3C

O N

O

Sn X

N O

F3C

O

O

CF3

trans(x)-trans(O)-trans(N) (C 2h)

O N

O

Sn

CF 3

N

O

X

trans(x)-cis(O)-cis(N) (C2v)

cis-isomers: X

X F 3C O

O N

Sn O

O

X N O

F3C cis(x)-cis(O)-cis(N) (C 1)

F 3C

N O

Sn O

X F 3C

X N

O O

F 3C cis(x)-cis(O)-trans(N) (C2)

O N

X

Sn

O

N

CF3

O cis(x)-trans(O )-cis(N) (C 2)

Fig. 1. Possible isomers of octahedral [Sn(DMOTFP)2X2] compounds, with X = halide.

2.1. Structure elucidation Crystals of 3–6 suitable for X-ray diffraction analyses were obtained from a saturated solution in chloroform stored over several days at room temperature. Crystallographic data of the X-ray diffraction analysis of 3–6 are summarized in the Supporting Information Table S1. There are five possible diastereomeric forms for octahedral complexes with two unsymmetrical bidentate and two monodentate ligands (Fig. 1) [44,45]. Crystals suitable for X-ray structure elucidation for [Sn (DMOTFP)2F2] (3) were obtained from the product of the oxidative halogenation reaction. The molecular structure (Fig. 2) of the octahedral [Sn(DMOTFP)2F2] (3) compound reveals a cis(F)-cis(O)-trans (N) configuration, which is typical for hexacoordinate dihalotin(IV) complexes with bidentate ligands [5,6,8,38,42,46–53]. The Sn-O (2.011(5) and 2.069(6) Å), Sn-N (2.145(7) and 2.141(7) Å) as well as the Sn-F (1.924(5) and 1.915(5) Å) bond lengths are in

Fig. 2. Molecular structure of [Sn(DMOTFP)2F2] (3). Thermal ellipsoids are shown at 50% probability level. Protons are omitted for clarity. Selected bond lengths (Å) and angles (°): Sn1-O1 2.069(6), Sn1-O3 2.011(5), Sn1-N1 2.145(7), Sn1-N2 2.141(7), Sn1-F7 1.915(5), Sn1-F8 1.924(5); F8-Sn1-F7 89.8(2), F7-Sn1-O1 87.7(2), F7-Sn1-O3 179.8(3), F7-Sn1-N1 91.5(2), F7-Sn1-N2 94.4(2), F8-Sn1-O1 177.4(3), F8-Sn1-O3 90.3(2), F8-Sn1-N1 93.5(3), F8-Sn1-N2 93.1(3), O1-Sn1-O3 92.0(2), O1-Sn1-N1 85.6 (3), O1-Sn1-N2 88.0(3), O3-Sn1-N1 88.4(2), O3-Sn1-N2 85.7(2), N1-Sn1-N2 171.1(3).

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accordance with those found in comparable literature known structures [6,54]. The coordination octahedron around tin(IV) shows slight distortions with cis and trans angles ranging from 85.6–94.4° and 171.1–179.8°, respectively. This distortion is caused by the bite angle of the chelate ligands (85.6–85.7°). In contrast to the fluoride derivative [Sn(DMOTFP)2F2] (3), complexes [Sn(DMOTFP)2X2] (X = Cl (4), Br (5), I(6)) adopt in the solid state a trans regular octahedral geometry with an inversion center at Sn1 (Fig. 3) which is, at least for dihalo tin(IV) compounds, quite unusual. To the best of our knowledge no other dihalide tin(IV) complexes with N^O or O^O bidentate ligands and a trans(X)trans(O)-trans(N) configuration in the solid state have been reported so far. As observed for 3, crystallographically characterized dihalo tin(IV) complexes with N^O or O^O chelating ligands typically adopt a cis configuration of the halo ligands, whereas dialkyl tin(IV) compounds are more often reported with a trans alkyl configuration [18,22]. Trans dihalo tin(IV) complexes on the other hand are generally reported with four fold coordinated ligands that possess a fixed planar configuration, such as porphyrin derivatives [55,56], and force the halo ligands into a trans configuration. The unusual trans configuration of the halo ligands is possibly facilitated by the planarity of the chelating ligand and the fact that steric hindering of square planar coordination of the two bidentate N^O ligands is countered by a slight twist of the ligand backbone out of the N-O-Sn-N-O coordination plane (Fig. 4). Through this twist the two ligands fit perfectly in the square planar arrangement and the halide ligands saturate the coordination sphere of the Sn(IV) compound in axial positions. In compound 3 the high electronegativity of the fluoride ligands as well as the smaller size in comparison to chloride, bromide and iodide seem to counteract the square planar coordination of the chelating ligands. Crystals suitable for X-ray structure elucidation for [Sn (DMOTFP)2Cl2] (4) were obtained from the product of the melting

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reaction of (1) with [Ph2SnCl2]. Crystals of (5) and (6) were taken from the product of the oxidative halogenation approach. The two bidentate ligands in 4–6 coordinate the central Sn(IV) atom in an almost square planar fashion. The octahedral arrangement around the tin center is only very slightly distorted with bite angles O1-Sn1-N1 of 86.7–86.9°, which causes a widening of the angles O1-Sn1-N10 and O10 -Sn1-N1 to 93.1–93.3°, while all other angles coincide with the ideal value of 90°. All Sn-O and Sn-N distances are in accordance with expected values for six fold coordinated tin(IV) complexes. A comparison of the Sn-Cl and Sn-Br bond lengths of 2.380(1) and 2.534(5) Å respectively with literature known dihalotin(IV) complexes with cis standing halo ligands shows a good congruence [38,46,47,52,54]. The Sn-I bond length of 2.56 Å is notably shorter than the values observed for other SnIV iodide complexes listed in the Cambridge Structural Database (average of 2.830 Å), furthermore, the measured electron density only allowed a refinement of the iodide atoms with site occupancies of 50%. Compound 6 was further characterized in solution by multinuclear (1H, 13C, 19F and 119Sn) and correlated 2D NMR experiments thoroughly. These showed three partly overlapping (6A, 6B, 6C) sets of resonances with relative intensities of 20:15:9. The respective 119Sn NMR shifts of compounds 6A and 6B were observed at similar field (
867 and
869 ppm) as known diiodo tin(IV) complexes (between
900 and
1000 ppm) [6,38,47] and are attributed to the coexistence of two isomers of Sn(DMOTFP)2I2 in solution. The low field shifts point toward an easy dissociation of iodide ligands in solution. While the tin atom in compound 6C shows a signal at
504 ppm, which is closer to but still different to that of starting compound 2 [Sn(DMOTFP)2], indicating the presence of a tin(II) compound in solution. Moreover, the F,F NOESY NMR spectrum shows an interaction between 6A and 6C further supporting the indication of an equilibrium with an ionic intermediate.

Fig. 3. Molecular structures of (a) [Sn(DMOTFP)2Cl2] (4), (b) [Sn(DMOTFP)2Br2] (5), [Sn(DMOTFP)2I2] (6). Thermal ellipsoids are shown at 50% probability. Protons are omitted for clarity. Selected bond lengths (Å) and angles (°): a) Sn1-O1 2.050(3), Sn1-N1 2.181(3), Sn1-Cl1 2.380(2); O1-Sn1-N1 86.7(1), O1-Sn1-N10 93.3(1), O1-Sn1-Cl1 90.3(1), O1Sn1-Cl10 89.7(1), N1-Sn1-Cl1 90.8(1), N1-Sn1-Cl10 89.7(1). b) Sn1-O1 2.060(3), Sn1-N1 2.195(3), Sn1-Br1 2.534(5); O1-Sn1-N1 86.8(1), O1-Sn1-N10 93.2(1), O1-Sn1-Br1 89.8 (1), O1-Sn1-Br10 90.2(1), N1-Sn1-Br1 90.4(1), N1-Sn1-Br10 89.6(1). c) Sn1-O1 2.051(4), Sn1-N1 2.191(4), Sn1-I1 2.557(1); O1-Sn1-N1 86.9(2), O1-Sn1-N10 93.1(2), O1-Sn1-I1 90.7(1), O1-Sn1-I10 89.3(1), N1-Sn1-I1 89.8(1), N1-Sn1-I10 90.2(1).

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Fig. 4. a) Space filling and b) wire and stick model of [Sn(DMOTFP)2Cl2] (4) with coordination planes trough N-O-Sn-N-O that show the perfect fit of chelating ligands in square planar arrangement and twist of the ligand backbone out of plane.

A contamination of 6 with unreacted educt 2 ([Sn(DMOTFP)2]) can be ruled out due to differences in chemical shifts in NMR spectra and the clearly square planar arrangement of the chelating ligands around the central Sn atom in the solid state structure. We propose an equilibrium in solution with an ionic intermediate and a possible coexistence of a Sn(II) and a Sn(IV) derivative which ultimately led to the isolation of the discussed solid-state structure. Attempts to locate a counterion like {I}
in the solid state structure to prove an ionic intermediate were not successful. The NMR spectroscopic investigation of compounds 3–6 by multinuclear (1H, 13C, 19F and 119Sn) and correlated 2D NMR experiments confirmed the presence of mixtures of isomeric tin(IV) derivatives for 3 and 4 in solution. Due to the lack of symmetry, the chelating ligands of the cis(X)-cis(O)-cis(N) form are expected to be magnetically inequivalent and thus would show two distinct sets of signals with equal integrative ratio both in 1H and 19F NMR spectra. Since this was not observed for any of the compounds discussed here, the presence of this diastereomer can be excluded. All other isomers possess at least one rotation axis (C2, C2v, C2h), which makes the chelating ligands magnetically equivalent showing only one set of signals in the NMR spectra. The vinylic protons of compounds 3–6 showed 1H NMR signals between 6.16 and 6.08 ppm with a gradual downfield shift with increasing atomic number of the halide ligand. The methyl fragments appeared between 2.66 and 2.30 ppm and were often divided into quartetts due to spin-spin coupling between protons of neighboring methyl groups (5JH,H  0.9 Hz). The strong bonding interaction between the ligand and the tin atom was evident in the observation of 119Sn satellites in the 19F NMR spectra of the tin(IV) derivatives, in comparison with neat ligand and the parent tin(II) derivative. The long range spin-spin coupling constant 4JSn,F decreases with increasing atomic number of the halide ligands, a tendency which has been previously reported for bis(acetylacetonato)tin dihalides [57]. Further information was obtained from 119 Sn NMR experiments, whereby 119Sn chemical shifts are found at increasingly high field in the order Cl, F, Br/I [6]. The NMR spectroscopic studies of 3 revealed the presence of two isomeric compounds 3A and 3B in a ratio of approximately 5:1 in solution. The 19F NMR signal of the fluoro ligands of 3A at
147.1 ppm showed sets of tin satellites for 119Sn (1JSn,F = 2146 Hz) and 117Sn (1JSn,F = 2046 Hz), respectively in the ratio of their magnetic moments. The corresponding resonances of isomer 3B (
139.0 ppm) were too weak to allow assignment of Sn satellites. As expected, the 119Sn NMR signal of isomer 3A at
677 ppm was divided into a 1:2:1 triplet by spin-spin coupling with the directly bound fluoride ligands. The 119Sn NMR signal for the minor compound could not be detected. For the reaction of [Ph2SnCl2] with 2 equivalents of ligand two sets of NMR signals attributed to compounds 4A and 4B were observed with an initial relative intensity of 1:7, which slowly changes to a ratio of nearly 1:2 upon storage in solution. The presence of two stereoisomers in 4 is confirmed by the small difference between the respective 119Sn NMR shifts (
600 and
607 ppm), whereas for 5 compounds 5A

and 5B were not clearly identified as stereoisomers, which is mainly due to the much larger difference between the 119Sn NMR shifts (
801 ppm;
876 ppm) and might hint to an equilibrium of two related species in solution. Due to the coexistence of several structural isomers in solution in 3 and 4, a distinct assignment of those involved could not be made. Presumably, the cis(F)-cis(O)-trans(N) isomer, whose structure was also elucidated in the solid state, is the predominant compound. Structures in solution exhibiting magnetically inequivalent fluorine atoms can be excluded, due to the lack of splitting of the SnF resonances by F-F interactions[44]. The F,H HOESY NMR spectrum of 4 showed cross peaks attributed to a through-space interaction between the methyl protons and the CF3-groups of two ligands coordinating one Sn-atom (Fig. 5). This rules out the presence of the trans(X)-cis(O)-cis(N) diastereomer (in addition to the all-cis diastereomer), since the respective groups would be too far away from each other to interact, leaving three possible isomers (cis(X)-cis(O)-trans(N), cis(X)-trans(O)-trans(N), trans(X)-trans(O)trans(N)) which are not discernable by NMR spectroscopy. The 1H and 19F NMR spectroscopic studies of the salt metathesis reaction carried out with excess AgF and [Sn(DMOTFP)2Cl2] showed three distinct sets of signals, of which two correspond to the already discussed compounds 3A and 3B. The third set of signals was attributed to the anionic complex 7 [Sn(DMOTFP)F4]
(Fig. 6). The 19F NMR spectrum in CDCN3 showed signals for the trifluoromethyl group of 7 at
74.9 ppm, signals between
137.7 and
166.0 ppm were attributed to tin-bonded fluoro ligands. The signals of the fluoro ligands of 7 were divided into multiplets by F,F and Sn,F spin-spin coupling. An additional through-space F,H coupling is observed for F(e1) indicating the steric proximity of the fluoro ligand to the methyl group of the remaining chelate ligand. NMR studies of the reaction with stoichiometric AgF show exclusively signals for 3A and 3B. The IR-spectra (Supporting information Fig. 13) of complexes [Sn(DMOTFP)2X2] all show strong bands between 1634 to 1621 cm
1 and 1543 to 1531 cm
1 attributed to C@C and C@O/ C@N stretching vibrations. They reveal strong bands in the ranges of 1358–1314 as well as 1186–1065 cm
1 due to CH3 and C-F stretching vibrations of the ligand HDMOTFP. Furthermore outof-plane CH vibrations are observed around 887–884 cm
1. The formation of [Sn(DMOTFP)2X2] complexes 3–6 is further evidenced through-space F,H coupling F 3C O

X O Sn N X CH3

X

H3C N O

O

F3C O

CF3

O N

Sn X

O N

CF 3 O

no F,H coupling through-space F,H coupling

Fig. 5. Through-space F,H coupling interaction between methyl protons and trifluoromethyl-fluorine: of the two possible trans(X)-isomers only trans(X)-trans (O)-trans(N) adopts a suitable conformation for through-space coupling.

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F3 C

O

O N

F(a) Sn

F(a) CH 3

F(e2) F(e1) through space F,H coupling

Fig. 6. Presumed structure of the anionic complex [Sn(4,5-MeOxCHCOCF3)F4]
(7) with axial fluoro ligands F(a) and equatorial fluoro ligands F(e1) und F(e2).

by EI-MS measurements in which the molecular ion peaks are detected in varying intensities (Table 1). The measured isotopic pattern of the fragments fit perfectly the theoretical patterns. Mass spectrometric experiments conducted on trialkyltin halides by Gielen and Mayence [58] showed that the ease of cleavage of a Sn-X bond followed the sequence I > Br, Cl > F, which correlated with the respective bond strengths. Indeed, in the present study the intensity of the molecular ion decreases with increasing atomic number of X, as does the sum of the intensities of the respective halogen containing fragments. While the molecular ion of 3 constitutes the base peak of the spectrum, practically no molecular ion is detected for 6. Obviously the already in solution observed easy cleavage of especially the Sn-I bond is also apparent in the gas phase. 3. Conclusions Dihalogeno tin(IV) bis heteroaryl alkenolates were synthesized by a twofold strategy involving oxidative halogenation of the corresponding [SnII(DMOTFP)2] compound (2) and the solvent free dephenylation reaction of the heteroaryl alkenol (1) with [Ph2SnCl2]. NMR experiments show the coexistence of different isomeric forms which interconvert in solution. The solid-state structure data confirmed the presence of monomeric species with octahedrally coordinated tin(IV) centers and an unusual trans(X)trans(O)-trans(N) configuration (X = Cl, Br, I). Even though the synthesis of all four [Sn(DMOTFP)2X2] (X = F, Cl, Br, I) complexes was successful we could show a dependence of the preferred ligand arrangement (cis(X) or trans(X)) as well as stability in solution on the halide ligand. The ease of cleavage of a Sn-X bond, which correlates with the respective bond strengths, leads to stable compounds [Sn(DMOTFP)2F2] and [Sn(DMOTFP)2Cl2] whereas in compounds [Sn(DMOTFP)2Br2] and especially [Sn(DMOTFP)2I2] a very easy dissociation of the halide ligands is observed.

10
3 mbar). Due to its sensitivity to air and moisture it was manipulated under argon using standard Schlenck techniques. Ligand molecule 1 (HDMOTFP) as well as precursor compound 2 ([Sn (DMOTFP)2]) were synthesized following the previously reported procedure by Giebelhaus et al. [3]. Melting points were measured with a Stuart SMP10. Elemental analyses were performed with a Hekatech CHNS Euro NA 3000 Analyzer. EI Mass spectra were obtained with a Finigan MAT 95 mass spectrometer (E = 20 eV). Fourier transform infrared (FT-IR) measurements were recorded on a PerkinElmer Spectrum 400. 1 H, 13C, 19F and 119Sn NMR spectra were recorded on a Bruker Avance II 300 spectrometer with a BBFO z-Grad. probe-head operating at room temperature at a frequency of 300.13 MHz, or on a Bruker AV 400 MHz spectrometer with a H, F, X TBI z-Grad probe-head operating at room temperature with a frequency of 400.13 MHz. 1H and 13C chemical shifts are reported in ppm vs. SiMe4, 19F chemical shifts in ppm vs. CFCl3 whereas 119Sn chemical shifts in ppm vs. SnMe4, couplings J in Hz. The numbering for the ligands used throughout the experimental section is displayed in Fig. 7. Data collection for X-ray structure elucidation was performed on STOE IPDS I/II diffractometer using graphite-monochromated Mo Ka radiation (0.71073 Å). The data were corrected for Lorentz and polarization effects. A numerical absorption correction based on crystal-shape optimization was applied for all data. The programs used in this work are STOE’s X-Area, including X-RED [60] and X-Shape [61] for data reduction and absorption correction, SIR-92 [62] and SHELXL-97 [63] for structure solution and SHELXL [63] as well as ShelXle [64] for structure refinement. The hydrogen atoms were placed in idealized positions and constrained to ride on their parent atom. The last cycles of refinement included atomic positions for all atoms, anisotropic thermal parameters for all nonhydrogen atoms and isotropic thermal parameters for all hydrogen atoms. 4.2. [SnIV(DMOTFP)2F2] (3) 4.2.1. Synthesis from 2 and XeF2 Anhydrous propionitrile (5 mL) was added to XeF2 (0.31 g, 1.8 mmol) in a dry Schlenck tube upon cooling with liquid nitrogen. [Sn(DMOTFP)2] (0.93 g, 1.75 mmol) was slowly added. The reaction mixture was allowed to warm to room temperature and then left to stir for additional 3 hours. The volatile compounds were removed in vacuo to give a yellowish solid. The crude product appeared to be a mixture of two isomeric compounds according

4. Experimental section 6

4.1. General procedures 7

[Sn(N(SiMe3)2]2 was prepared according to a procedure published by Gynane et al. [59] and purified by distillation (80 °C,

5 O 4 3 8 N

2 HO

CF3 1

Fig. 7. Numbering for the ligands used throughout Section 4.

Table 1 EI-MS data for compounds 3–6. Compound

3

Temperature/°C Fragment [M]+ [Sn(C8H7O2NF3)2X]+ [Sn(C8H7O2NF3)X2]+ [Sn(C8H7O2NF3)X]+ [Sn(C8H7O2NF3)2]+ [Sn(C8H7O2NF3)]+ [C8H7O2NF3]+ [C8H7O2NF]+ [C7H7O2N]+

124 m/z 570 550 364 345 530 326 206 – –

4 I/% 100 38 4 91 10 7 87 – –

128 m/z 602 567 395 – – – 206 – 138

5 I/% 46 25 100 – – – 57 – 4

138 m/z 690 611 484 405 532 326 206 168 138

6 I/% 7 100 46 7 7 39 52 18 13

130 m/z 785 659 580 – 532 326 207 168 138

I/% <<1 100 12 – 5 64 6 16 4

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to NMR spectra. Yield 42 %. 1H NMR (300.1 MHz, CDCl3): d = 6.10 (1H, H3B, 4JSn,H = 5.7 Hz); 6.08 (1H, H3A, 4JSn,H = 6.6 Hz); 2.43 (3H, H7B); 2.39 (3H, H7A); 2.36 (3H, H6B); 2.35 (3H, H6A); 13C NMR (300.1 MHz, CDCl3): d = 164.5 (Cq, C4B); 162.4 (Cq, C4A, 3 JF,C = 1.7 Hz); 158.6 (Cq, C2A); 157.9 (Cq, C2B); 143.1 (Cq, C8B); 142.9 (Cq, C8A, 2JF,C = 1.7 Hz); 128.2 (Cq, C5B); 128.1 (Cq, C5A); 119.5 (CF3, C1B); 119.3 (CF3, C1A); 86.5 (C3B, 3JF,C = 4 Hz); 86.0 (C3A, 3JF,C = 4 Hz); 10.3 (C7B); 9.8 (C7A); 9.7 (C6A+B); 19F NMR (300.1 MHz, CDCl3): d =
147.1 (s, F1A, 1JSn,F = 2146 Hz),
139.0 (s, F1B, 1JSn,F = 2141 Hz),
73,8 (s, 6F, CF3B, 1JF,C = 278 Hz; 2 JF,C = 36 Hz; 4JSn,F = 6.6 Hz);
74.4 (s, 6F, CF3A, 1JF,C = 278 Hz; 2 JF,C = 36 Hz, 4JSn,F = 5.1 Hz); 119Sn NMR (300.1 MHz, CDCl3): d =
677 (SnA, 1JSn,F = 2146 Hz). 4.2.2. Synthesis from 4 and AgF 4.2.2.1. Synthesis with stoichiometric AgF Silver fluoride (0.13 g, 1.0 mmol) was added to a stirred solution of [Sn(DMOTFP)2Cl2] (0.30 g, 0.5 mmol) in anhydrous propionitrile (5 mL). The reaction mixture was stirred for 17 hours at room temperature and filtered through a filter paper. The filtrate was dried in vacuo to afford colorless crystals of 3. Yield 22%, 1H NMR (300.1 MHz, CD3CN): d = 6.25 (s, H3); 2.34(m, –CH3); 2.33(m, –CH3); 2.24(s); 19F NMR (300.1 MHz, CD3CN): d = 75.0 (s, CF3, 4 JSn,F = 4.9 Hz);
137.9 (s, F1B); 145.3 (s, F1A, 1JSn,F = 2049 Hz, 1 JSn,F = 2140 Hz). M.p.: 185 °C. Anal. Calc. for C16H14F8N2O4Sn: C, 33.76; H, 2.46; N, 4.92. Found: C, 33.51; H, 3.30; N, 4.51. IR (cm
1): m(C@C) 1624, m(C@O, C@N) 1539, m(CH3) 1358, 1315, m(CF) 1183–1071, m(C-O) 1032, c(=CH) 885. EI-MS: m/z (intensity) = 206 [DMOTFP]+ (87%), 326 [Sn(DMOTFP)]+ (7%), 345 [Sn (DMOTFP)F]+ (91%), 364 [Sn(DMOTFP)F2]+ (4%), 530 [Sn (DMOTFP)2]+ (10%), 550 [Sn(DMOTFP)2F]+ (38%), 570 [M]+ (100%). 4.2.2.2. Synthesis with excess AgF leading to a mixture of 3 and 7 Silver fluoride (0.11 g, 0.9 mmol) was added to a stirred solution of [Sn(DMOTFP)2Cl2] (0.18 g, 0.3 mmol) in anhydrous propionitrile (2.5 mL). The reaction mixture was stirred for 17 hours at room temperature and filtered through a filter paper. The filtrate was dried in vacuo to afford colorless crystals of 7. M.p.: 195 °C. 1H NMR (400.1 MHz, CD3CN): d = 6.26 (s, H3, compound 3); 5.97 (s, H3, compound 7); 2.34 (q, CH3, compound 3); 2.33 (q, CH3, compound 3); 2.29 (q, H7, compound 7); 2.27(q, H6, compound 7); 2.11 (s, acetone); 19F NMR (400.1 MHz, CD3CN): d =
74.93 (s, CF3, compound 7, 4JSn,F = 5.2 Hz);
74.96 (s, CF3, compound 3, 4 JSn,F  5.0 Hz);
137.78 (s, F1, compound 3, 1JSn,F = 2141 Hz);
145.20 (s, F1, compound 3, 1JSn,F = 2146 Hz);
146.20 (dd, F(a), compound 7, 1JSn,F(a) = 1845 Hz, 2JF(a),F(e1) = 50 Hz, 2JF(a),F(e2) = 42 Hz);
151.84 (tdq, F(e1), compound 7, 1JSn,F(e1) = 1926 Hz, 2 JF(e1),F(e2) = 42 Hz, 2JF(e1),F(a) = 50 Hz, 2JF(e1),H = 2.7 Hz);
166.0 (‘‘q”, F(e2), compound 7, 1JSn,F(e2) = 1861 Hz, 2JF(e1),F(e2) = 42 Hz, 2 JF(e2),F(a) = 42 Hz); 119Sn NMR (400.1 MHz, CDCl3): d =
676 (compound 3). 4.3. Synthesis of [SnIV(DMOTFP)2Cl2] (4) 4.3.1. Synthesis from 1 and Diphenyltin dichloride Diphenyltin dichloride (0.69 g, 2.0 mmol) and HDMOTFP (1.04 g, 5.0 mmol) were heated at 115 °C in a 50 mL round flask for 19 hours. The formed colorless crystalline solid was washed with chloroform and dried in vacuo. The product was recrystallized from chloroform to afford colorless crystals of 4. Yield 95 %. 4.3.2. Synthesis from 2 and hexachloroethane Hexachloroethane (0.12 g, 0.5 mmol) was added to a stirred solution of [Sn(DMOTFP)2] (0.32 g, 0.5 mmol) in dichloromethane (5 mL) in a round flask and refluxed for 3 h at 80 °C. The reaction mixture was washed with n-pentane (10 mL) and decanted to

afford a colorless solid that was dried at atmospheric pressure. Yield 30%. M.p.: 206 °C. Anal. Calc. for C16H14Cl2F6N2O4Sn: C, 31.96; H, 2.34; N, 4.65. Found: C, 31.85; H, 2.28; N, 4.29. 1H NMR: (400.1 MHz, CDCl3): d = 6.11 (2H, H3A+B); 2.46 (d, 3H, H6A); 2.44 (d, 3H, H6B); 2.32 (d, 6H, H7A+B); 13C NMR: (400.1 MHz, CDCl3): d = 162.1 (Cq, C4A, 4JSn,C = 15 Hz); 161.0 (Cq, C4B, 4JSn,C = 21 Hz); 157.8 (Cq, C2B, 2JSn,C = 33 Hz); 156.9 (Cq, C2A, 2 JSn,C = 40 Hz); 142.8 (Cq, C8B, 2JSn,C = 33.5 Hz); 142.6 (Cq, C8A, 2 JSn,C = 35 Hz); 127.9 (Cq, C5A, 3JSn,C = 12 Hz); 127.5 (Cq, C5B, 3JSn,C = 9,5 Hz); 119.4 (CF3, C1A, 3JSn,C = 61 Hz); 119.5 (CF3, C1B, 3 JSn,C = 65 Hz); 87.1 (C3A, 3JSn,C = 43 Hz); 87.0 (C3B, 3JSn,C = 40 Hz); 10.7 (C6A); 10.2 (C6B); 9.9 (C7A); 9.7 (C7B); 19F NMR: (400.1 MHz, CDCl3): d =
74.0 (s, 3F, CF3A; 1JF,C = 278 Hz; 2JF,C = 31 Hz; 3 JF,C = 4 Hz; JF,Sn = 4.3 Hz);
73.9 (s, 3F, CF3B; 1JF,C = 278 Hz; 2 JF,C = 36 Hz; 3JF,C = 4 Hz; JF,Sn = 4.6 Hz); 119Sn NMR: (400.1 MHz, CDCl3): d =
601 (SnA);
607 (SnB). IR (cm
1): m(C@C) 1634, m(C@O, C@N) 1534, m(CH3) 1356, 1317, m(CF) 1186–1065, m(C-O) 1088, c(=CH) 884. EI-MS: m/z (intensity) = 138 [DMOTFP –CF3]+ (4%), 206 [DMOTFP]+ (57%), 395 [Sn(DMOTFP)Cl2]+ (100%), 567 [Sn(DMOTFP)2Cl]+ (25%), 602 [M]+ (46%). 4.4. Synthesis of [SnIV(DMOTFP)2Br2] (5) 4.4.1. Synthesis from 2 and Br2 Bromine (0.13 g, 0.85 mmol) was added to a stirred solution of [Sn(DMOTFP)2] (0.54 g, 0.85 mmol) in dichloromethane (5 mL) at 0 °C. The reaction mixture was allowed to warm to room temperature and then left to stir for an additional 24 hours. The volatile compounds were removed in vacuo and the resulting solid was recrystallized from a saturated CHCl3 solution yielding light yellow crystals. Yield 71 %. M.p.: 220 °C. Anal. Calc. for C16H14Br2F6N2O4Sn: C, 27.81; H, 2.03; N, 4.06. Found: C, 27.35; H, 2.38; N, 4.05. 1H NMR: (300.1 MHz, CDCl3): d = 6.16 (s, H3A); 6.14 (s, H3B); 2.53 (m, H6B); 2.45 (m, H6A); 2.33 (m, H7A+B); 13C NMR: (300.1 MHz, CDCl3): d = 161.7 (Cq, C2B); 160.3 (Cq, C2A); 142.7 (Cq, C8A); 142.6 (Cq, C8B); 127.7 (Cq, C5A); 127.2 (Cq, C5B); 119.3 (CF3, C1A+B); 87.2 (C3B); 87.0 (C3A); 11.1 (C6B); 10.2 (C6A); 9.7 (C8A+B); 19F NMR: (300.1 MHz, CDCl3): d =
74.0 (CF3); 119Sn NMR: (300 MHz, CDCl3): d =
876;
801. IR (cm
1): m(C@C) 1621, m(C@O, C@N) 1543, m(CH3) 1356, 1313, m(CF) 1181–1066, m(C-O) 1051, c(=CH) 887. EI-MS: m/z (intensity) = 138 [DMOTFP
CF3]+ (13%), 168 [DMOTFP
F2]+ (18%), 206 [DMOTFP]+ (52%), 326 [Sn(DMOTFP)]+ (39%), 405 [Sn(DMOTFP) Br]+ (7%), 484 [Sn(DMOTFP)Br2]+ (46%), 532 [Sn(DMOTFP)2]+ (7%), 611 [Sn(DMOTFP)2Br]+ (100%), 690 [M]+ (7%). 4.5. Synthesis of SnIV(DMOTFP)2I2 (6) 4.5.1. Synthesis from 2 and I2 A solution of [Sn(DMOTFP)2] (0.70 g, 1.10 mmol) in diethyl ether (20 mL) was added dropwise to a stirred solution of I2 (0.28 g, 1.10 mmol) in diethyl ether (10 mL) at 0 °C. The reaction mixture was stirred for additional 3 days. Volatiles were removed in vacuo and the resulting solid was recrystallized from CHCl3/n-heptane at room temperature to afford yellow crystals. Yield 12%. 4.5.2. Synthesis from 4 and NaI Sodium iodide (0.16 g, 1.1 mmol) was added to a stirred solution of [Sn(DMOTFP)2Cl2] (0.31 g, 0.5 mmol) in anhydrous propionitrile (5 mL). The reaction mixture was stirred for 4 days at room temperature. Volatiles were removed in vacuo to afford a yellow-brown solid. Yield 30%. M.p.: 173 °C. Anal. Calc. for C16H14F6I2N2O4Sn: C, 24.47; H, 1.78; N, 3.57. Found: C, 24.29; H, 1.94; N, 4.24. 1H NMR: (300.1 MHz, CDCl3): d = 6.38 (s, H3C); 6.21 (s, H3A+B); 2.68 (m, H5A); 2.48 (m, H5B); 2.32 (m, H8A+B); 2.27 (m, H8C); 1.93 (m, H5C); 13C NMR: (300.1 MHz, CDCl3): d = 161.6 (Cq, C4C); 161.5 (Cq, C4A); 160.0 (Cq, C4B); 157.3 (Cq, C2C); 156.8 (Cq, C2A); 155.5 (Cq,

L. Czympiel et al. / Inorganica Chimica Acta 455 (2017) 197–203

C2B); 143.1 (Cq, C8C); 142.69 (Cq, C8A); 142.68 (Cq, C8B); 127.6 (Cq, C5A); 127.0 (Cq, C5C); 126.4 (Cq, C5B); 119.2 (CF3, C1A); 118.9 (CF3, C1B); 118.5 (CF3, C1C); 87.5 (C3C); 87.2 (C3A); 86.5 (C3B); 11.7 (C6A); 10.3 (C6B); 9.9 (C6C); 9.74 (C7C); 9.70 (C7B); 9.65 (C7A); 19F NMR: (300.1 MHz, CDCl3): d =
73.9 (CF3A; JSn,F = 2 Hz);
74.0 (CF3B; JSn,F = 2 Hz);
74.8 (CF3C); 119Sn NMR: (300.1 MHz, CDCl3): d =
504 (SnC);
867 (SnA);
869 (SnB). IR (cm
1): m(C@C) 1632, m(C@O, C@N) 1531, m(CH3) 1354, 1314, m(CF) 1186–1067, m(C-O) 1050, c(=CH) 884. EI-MS: m/z (intensity) = 168 [DMOTFP
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