Iminopyridine ligand complexes of group 14 dihalides and ditriflates – neutral chelates and ion pair formation

2.2.1 NMR spectroscopy

The ¹¹⁹Sn NMR spectra of the tin complexes 3–5, 9, 10 and 12 clearly demonstrate the dependence of the ¹¹⁹Sn NMR shifts on the nature of the halides, which corroborates the absence of complete dissociation of the Sn–halide bonds upon dissolving the samples. The ¹¹⁹Sn signals of the SIMPY complexes 3–5 move to lower field upon descending group 17. [SIMPY·SnCl₂], 3, shows a resonance at −216 ppm in THF, the resonance of the respective bromide 4 is shifted to −80 ppm and the iodide resonates at +317 ppm. The shifts of 3 and 4 correlate well with literature data for tin dichloride (−236 ppm in THF) and tin dibromide (−72 ppm in dimethoxyethane) dissolved in strong donor solvents.

The tin-based ion pairs [DIMPY·SnX]⁺[SnX₃]⁻9 (X=Br), and 12 (X=Cl) exhibit two pairs of well distinguishable ¹¹⁹Sn NMR resonances in solution each, at +98 ppm [DIMPY·SnBr]⁺/−406 ppm [SnBr₃]⁻ and −452 [DIMPY·SnCl]⁺/−58 ppm [SnCl₃]⁻. The shifts of the chloride derivative 12 correlate well with those observed for the previously reported compounds [^Me2DIMPY SnCl]⁺[SnCl₃]⁻ (−435/−73 ppm) [36] and [^6-MeOSIMPY SnCl]⁺[SnCl₃]⁻ (−330/−73 ppm) [38] and related transition metal complexes reported by Jambor, Jurkschat and coworkers [40]. In comparison to the chlorides, the positions of the resonances of the bromides switch places. The signal for the cationic fraction is shifted downfield and is observed at −98 ppm, the [SnBr₃]⁻ ion resonates at −406 ppm, which correlates reasonably well with literature data [36]. Despite numerous attempts including variation of the concentration, solvent and sample temperature, no ¹¹⁹Sn NMR resonances for the iodide 10 were observed. Both tin(II) ditriflates 6 and 11 show only one ¹¹⁹Sn NMR signal in solution at −27 ppm (6) and −46 ppm (11). These values agree reasonably well with data for [^6-MeOSIMPYSnOTf₂] (δ=−78 ppm) [41]. Together with the significant line broadening effects observed in ¹H spectra and rather long Sn–O distances in the solid state, NMR spectroscopic evidence points towards rapid dissociation/association processes in solution. Although low-temperature NMR experiments were conducted, we were unable to resolve the exchange processes on the NMR timescale. As shown in our previous publication, the ¹H NMR shift of the imino proton and the resonances of the pyridine fragment are diagnostic for the formation of the group 14 element complexes [42]. In all complexes 1–6, the ¹H NMR shifts of these signals differ notably from those of the free ligand and therefore provide clear evidence for the existence of the complex species in solution. Dissociation of the complexes to yield free ligand and solvates of the tetrel dihalides can be ruled out even when strong donor solvents (e.g. THF, dimethoxyethane) are used in sample preparation. In all SIMPY complexes, the ¹H resonances of the imino proton ArN=CH is shifted downfield with respect to the free ligand (8.31 ppm). The most pronounced effect is observed for the tin ditriflate (9.43 ppm) and the germanium and tin dichlorides (8.65 ppm in 1 and 8.50 ppm in 3). The bromides 2 and 4 and the iodide 5 display less significant shift changes. Similar trends are observed in the DIMPY complexes 7–12, where once again the shift changes between free ligand and group 14 complexes decrease from chloride to bromide and iodide. The tin ditriflates, however, are different in this context as the SIMPY complex shows the most pronounced downfield shift, whereas the DIMPY complex exhibits a slightly upfield shifted ¹H resonance at 8.18 ppm for the ArN=CH proton.

The methyl resonances of the iso-propyl groups in the SIMPY complexes 1–5 are broad and do not show two distinct resonances in ¹H and ¹³C spectra as it is usually observed in related Dipp-substituted complexes. The ditriflate 6, however, shows two distinct ¹³C resonances for these methyl groups, which are nevertheless isochronous in the ¹H spectrum. Similarly, only the methyl resonances in chloride complexes 7 and 12 and in the tin bromide 9 appear as two sets of signals in the ¹H and ¹³C spectra, but are not resolved in the germanium bromide 8 and the tin iodide 10. Spectroscopic evidence therefore points towards a rapid exchange of the axial and equatorial halide substituents in the [SIMPY·EX₂] complexes and a similar positional exchange in the cationic fragments [DIMPY·EX]⁺, which is faster for the heavier halogen atoms.

2.2.2 X-ray crystallography

The solid-state structures of the complexes 1–5, 7, 9 and 11 were authenticated by means of single crystal X-ray diffraction analyses. All SIMPY based compounds crystallize as undissociated, neutral, binary complexes [L·EX₂]. In contrast, the DIMPY complexes of the group 14 dihalides form separated ion pairs [DIMPY·EX]⁺[EX₃]⁻ upon auto-ionization. The DIMPY tin ditriflate 11, however, crystallizes as a neutral, undissociated complex with two independent molecules per asymmetric unit in which one of the tin centers is five-coordinate, while the second tin atom is six-coordinate via interaction with a THF donor molecule. A summary of crystallographic data is given in Table 1.

The complexes [SIMPY·EX₂] (EX₂=GeCl₂, GeBr₂, SnCl₂, SnBr₂) crystallize in the monoclinic space group P2₁/n whereas the iodide SIMPY SnI₂ crystallizes in the triclinic space group P1̅. All tetrel centers in the SIMPY complexes are four-coordinate and adopt a distorted disphenoidal structural motif (AB₄Ë-type structure according to VSEPR rules) around the tetrel atom, which is coordinated by two halide ions and two nitrogen donors of the SIMPY ligand. Both nitrogen atoms and one halide ion are located in plane with the central tetrel atom while the second halide ion is located at right angle to this plane (Fig. 2).

Fig. 2:

Schematic drawing of the group 14 element coordination in the complexes 1–5, 7 and 9 with the numbering scheme used in the text.

In all cases, two distinctly different E–N bond lengths are observed, where the E–N2 separation between the group 14 atom and the nitrogen atom of the pyridine ring is significantly shorter than the E–N1 distance between the tetrel and the imino nitrogen of the side arm. Furthermore, the tetrel halogen distances E–X1 (perpendicular to the N1/N2/E plane) and E–X2 (in plane) differ notably in all SIMPY group 14 derivatives.

In all compounds studied crystallographically, the longer E–X2 bond is found in trans position with respect to the weaker imino nitrogen donor atom N1 and lies in the plane E–N1–C1–C2–N2. The shorter E–X1 bond invariably involves the second halide atom, which is located in an almost perpendicular position with respect to the same plane. A summary of bond lengths and angles is given in Table 2.

The largest difference in E–X bond lengths in compounds 1–5 is observed in the bromides 2 and 4. In 2, the Ge1–Br2 distance amounts to 2.6104(4) Å and is thus 0.1781 Å longer that the out-of-plane Ge1–Br1 bond. Somewhat less pronounced is the difference in 4, where 2.7478(2) Å for Sn1–Br2 and 2.5955(3) Å for Sn1–Br1 are found. Similarly, the two E–N distances vary notably, with a short E–N(pyridine) distance and an elongated E–N(imine) contact. A comparison of the chlorides 1 (Fig. 3) and 3 with the bromides 2 and 4 shows that shorter and therefore stronger E–N1 interactions as in 2 vs. 1 correlate to longer and weaker E–X2 distances in trans-position which ultimately results in the dissociation of the E–X2 bond in the DIMPY complexes and the modified SIMPY ligand based complexes [^6-MeOSIMPY·EX]⁺[EX₃]⁻ (E=Ge; Sn, X=Cl) and hence formation of ion pairs [39]. The coordination in the tin diiodide 5, where the tin-halogen interaction is characterized as a soft-soft Lewis acid-base interaction, is different. Notably, it exhibits not only the shortest Sn1–N1 and Sn1–N2 bonds, but also the most symmetrical bonding situation with differences of 0.175 Å for the Sn–N bonds and only 0.095 Å for the two tin iodide bonds. The N1–C1 distance, which is diagnostic for the electron density transfer from the metal center towards the ligand does not vary significantly in the chlorides and bromides 1–4 and is similar to that of the uncomplexed ligand. In contrast, the C1–N1 distance is ca. 0.04 Å longer in the iodide complex 5.

Fig. 3:

Molecular structure of [SIMPY·GeCl₂], 1, in the solid state. Ellipsoids are drawn at the 50% probability level, hydrogen atoms are omitted for clarity.

With respect to the germanium dichloride complex 1, the germanium-nitrogen distances of 2.070(4) Å for Ge1–N1 and 2.045(4) Å for Ge1–N2 in the crystallographically characterized, methoxy substituted SIMPY complex [^6-MeOSIMPY·GeCl]⁺[GeCl₃]⁻ are found to be short and more symmetrical [39]. Moreover, the Ge–Cl distance in the tricoordinate cation is also ca. 0.06 Å shorter than in 1. The differences are a direct consequence of the lower coordination number and the positive charge in [^6-MeOSIMPY·GeCl]⁺ compared to 1.

The introduction of a second donor side arm as present in the DIMPY ligand apparently tips the balance towards auto-ionization and results in the formation of the ion pairs 7–10 and 12. Similar to [^Me2DIMPY·EX]⁺[EX₃]⁻ [36] and [^6-MeOSIMPY·EX]⁺[EX₃]⁻ [39], the bonding situation is characterized by rather short and symmetrical bonds E–N1 and E–N2 towards the imino nitrogen donors and an even shorter E–N3 distance. In the solid state, the halogen atom is invariably located below the N1–N2–N3–E plane and forms three angles N–E–X near 90°.

The molecular structures of 7, 9, previously reported 12 and the Me-DIMPY species [^Me2DIMPY·EX]⁺[EX₃]⁻ [36] contain well separated ion pairs in which the anion [EX₃]⁻ is strictly pyramidal with a sum of angles of 286.8(2)° in 7 and 284.2(1)° in 9 (Fig. 4). The cations contain four-coordinate tetrel centers, with two longer E–N separations towards the imino nitrogen atoms N1 and N2 and a short E–N3 distance towards the pyridine nitrogen atom. The fourth coordination site is occupied by a halogen atom. In 7, the Ge1–N1 and Ge1–N2 distances are 2.255(6) Å and 2.316(6) A, whereas the Ge1–N3 distance is only 2.075(4) Å. In the tin bromide complex 9, the respective distances are 2.453(2) and 2.457(2) Å (Sn1–N1 and Sn1–N2) which are slightly elongated compared to the tin chloride complex 12 based on the identical ligand, where Sn1–N1 and Sn1–N2 are 2.414(2) and 2.453(2) Å. The Sn1–N3 distance in 9 is conversely slightly shorter at 2.280(3) Å compared to the 2.302(2) Å observed in 12. In any case, both the E–N(pyridine) and the E–N(imine) bonds observed in the DIMPY complexes are longer than in the SIMPY complexes. The N3–E–N1/N2 angles are more acute for the germanium complexes than for the respective tin complexes, which is a direct consequence of the smaller atomic radius of germanium.

Fig. 4:

Molecular structure of [DIMPY·SnBr]⁺[SnBr]⁻, 9, in the solid state. Ellipsoids are drawn at the 50% probability level, hydrogen atoms are omitted for clarity.

Interestingly, the molecular structure of the tin ditriflate derivative 11 (space group P1̅, Fig. 5) is strikingly different, as is does not consist of ion pairs but of two structurally independent [DIMPY·Sn(OTf)₂] complexes per asymmetric unit. One of the complexes features a five-coordinate tin(II) center with essentially symmetrical interactions between the tin atom and the imino nitrogen atoms (Sn2–N4: 2.515(5) and Sn2–N6 2.501(5) Å) and a rather short Sn–N5(pyridine) distance of 2.314(5) Å. Moreover, the triflate groups are both engaged in short, direct interactions with the tin center with distances of 2.379(8) and 2.394(7) Å and are located above and below the basal plane of the DIMPY ligand containing the tin atom.

The second, structurally independent molecule features a six-coordinate tin(II) center in which all substituents are located at large distances. The Sn–imino distances are notably different and amount to 2.477(6) and 2.772(6) Å. The Sn1–N3 distance between to the pyridine nitrogen atom is also longer with 2.357(6) Å. Furthermore the Sn–O distances towards the triflate groups differ in lengths, one being shorter (2.248(8) Å) than both Sn–O distances in the five-coordinate species while the other distance is significantly elongated (2.611(6) Å). The THF molecule is weakly coordinated as the Sn–O(THF) distance is 2.725 Å. The Sn–O distances are in good agreement with the distances found in [^Me2DIMPY·SnOTf₂] (2.350(2) and 2.554(2) Å) and in [^MeOSIMPY·SnOTf₂] (2.3822(9) and 2.443(2) Å). For comparison, the Sn–O distance in the mixed species [^MeOSIMPY·SnCl]⁺OTf⁻ is significantly elongated at 3.042(2) Å [41].

A summary of bond lengths and angles in the DIMPY complexes is given in Table 3.

2.2.3 ¹¹⁹Sn Mössbauer spectroscopy

The ¹¹⁹Sn Mössbauer spectrum of 11 (78 K data, Fig. 6) shows two distinct signals in an almost perfect 1:1 ratio with isomer shifts (δ) of 3.52(1) mm s⁻¹ and 3.45(1) mm s⁻¹ (Table 4), which clearly indicate the oxidation state +II for tin. Furthermore, the electric quadrupole splitting (ΔE_Q) of the two signals differs notably and amounts to 1.28(2) mm s⁻¹ and 1.77(2) mm s⁻¹ demonstrating the unsymmetrical coordination around the tin atom in both cases. These values compare to isomer shifts of 2.94(1) and 3.18(1) mm s⁻¹ with electric quadrupole splittings of 1.63(1) and 1.64(1) mm s⁻¹, respectively, for the ion pair 12 [42]. Concerning the shifts of the ion pair 12, the signal at δ=2.94 mm s⁻¹ can be attributed to the tin(II) atom within the DIMPY complex while the second signal at δ=3.18 mm s⁻¹ can be assigned to the trichlorostannate(II) anion [43], [44]. For comparison, the neutral complex [DIMPY·Sn⁽⁰⁾] exhibits a quadrupole split signal at δ=2.64 mm s⁻¹ with ΔE_Q=2.11 mm s⁻¹ at 78 K [42]. The sample shows a small contribution (ca. 1%) of a tetravalent tin species (isomer shifts around 0 mm s⁻¹), most likely due to hydrolyses of the sample and formation of SnO₂ [45].

Synthesis of [SIMPY·GeCl₂] (1)

GeCl₂·dioxane (434 mg, 1.84 mmol, 1 eq) was dissolved in 4 mL THF and the SIMPY ligand 2-[ArN=CH](NC₅H₄) (Ar=C₆H₃-2-ⁱPr₂) (500 mg, 1.84 mmol, 1 eq) was added at room temperature. Color change was immediate as the solution went from clear transparent to a bright orange. The solvent was removed and the solid then dried under vacuum. Orange needle-like crystals suitable for X-ray analysis were obtained by recrystallization in THF and storing at −30°C. Yield: 99%; m. p.: 153°C. – ¹H NMR (300.22 MHz, C₆D₆): δ=8.84 (d, 1H, PyH), 8.65 (s, 1H, HC=N), 7.97 (d, 1H, PyH), 7.22 (m, 4H, CH arom), 6.83 (t, 1H, PyH), 3.18 (sept, 2H, CHⁱPr), 1.23 (d, 12H, CH₃ⁱPr). – ¹³C NMR (75.50 MHz, C₆D₆): δ=163.87 (C=N, imine), 149.98 (ArH), 148.35 (ArH), 140.39 (ArH), 139.24 (ArH), 127.09 (ArH), 125.48 (ArH), 123.93(ArH), 123.10 (ArH), 28.47 (CHⁱPr), 24.07 (CH₃ⁱPr). – Elemental analysis (%) for C₁₈H₂₂Cl₂N₂Ge (409.92): calcd. C 52.74, H 5.41, N 6.83; found C 51.51, H 5.25, N 6.49.

Synthesis of [SIMPY·GeBr₂] (2)

Procedure as described for [SIMPY·GeCl₂]. GeBr₂·dioxane (241 mg, 0.75 mmol, 1 eq) was dissolved in 4 mL THF and the SIMPY ligand (200 mg, 0.75 mmol, 1 eq) was added at room temperature. Dark orange crystals were obtained after recrystallizing in a THF-benzene mixture (2:1) at room temperature. Yield: 97%. m. p.: 169.9–171.9°C. – ¹H NMR (300.22 MHz, C₆D₆): δ=8.85 (d, 1H, PyH), 8.49 (s, 1H, HC=N), 7.87 (d, 1H, PyH), 7.21 (m, 4H, CH arom), 6.76 (t, 1H, PyH), 3.17 (sept, 2H, CHⁱPr), 1.22 (d, 12H, CH₃ⁱPr). – ¹³C NMR (75.50 MHz, C₆D₆): δ=161.57 (C=N, imine), 150.67 (ArH), 148.50 (ArH), 139.54 (ArH), 138.17 (ArH), 126.48 (ArH), 126.15 (ArH), 124.46 (ArH), 123.59 (ArH), 28.28 (CHⁱPr), 23.73 (CH₃ⁱPr). – Elemental analysis (%) for C₁₈H₂₂Br₂N₂Ge (498.83): calcd. C 43.34, H 4.45, N 5.62; found C 43.17, H 4.39, N 5.68.

Synthesis of [SIMPY·SnCl₂] (3)

Procedure as described for [SIMPY·GeCl₂]. SnCl₂ (338 mg, 1.84 mmol, 1 eq) was dissolved in 4 mL THF and the SIMPY ligand (500 mg, 1.84 mmol, 1 eq) was added at room temperature. Orange crystals were obtained after recrystallizing in THF at −30°C. Yield: 98%; m. p.: 205°C. – ¹H NMR (300.22 MHz, D₂O capillary/THF)): δ=9.18 (d, 1H, PyH), 8.50 (s, 1H, HC=N), 8.32 (d, 1H, PyH), 8.11 (t, 1H, PyH), 7.68 (t, 1H, PyH), 7.26 (d, 1H, CH arom), 7.22 (t, 1H, CH arom), 3.13 (sept, 2H, CHⁱPr), 1.27 (d, 12H, CH₃ⁱPr). – ¹³C NMR (75.50 MHz, D₂O capillary/THF): δ=163.28 (C=N, imine), 149.94 (ArH), 137.87 (ArH), 137.49 (ArH), 126.09 (ArH), 124.78 (ArH), 123.27 (ArH), 122.97 (ArH), 27.99 (CHⁱPr), 23.22 (CH₃ⁱPr). – ¹¹⁹Sn NMR (112.17 MHz, D₂O capillary/THF): δ=−216.3. – Elemental analysis (%) for C₁₈H₂₂Cl₂N₂Sn (456.00): calcd. C 47.41, H 4.86, N 6.14; found C 45.87, H 4.68, N 5.91.

Synthesis of [SIMPY·SnBr₂] (4)

Procedure as described for [SIMPY·GeCl₂]. SnBr₂ (209 mg, 0.75 mmol, 1 eq) was dissolved in 4 mL THF and the SIMPY ligand (200 mg, 0.75 mmol, 1 eq) was added at room temperature. Red cubic crystals were obtained after recrystallizing in a THF-benzene mixture (2:1) at room temperature. Yield: 84%; m. p.: 208°C. – ¹H NMR (300.22 MHz, CDCl₃): δ=9.94 (d, 1H, PyH), 8.38 (s, 1H, HC=N), 8.18 (t, 1H, PyH), 7.95 (d, 1H, PyH), 7.74 (t, 1H, PyH), 7.18 (m, 3H, CH arom), 2.94 (sept, 2H, CHⁱPr), 1.12 (d, 12H, CH₃ⁱPr). – ¹³C NMR (75.50 MHz, CDCl₃): δ=160.82 (C=N, imine), 151.77 (ArH), 149.24 (ArH), 141.18 (ArH), 138.85 (ArH), 128.17 (ArH), 126.85 (ArH), 123.84 (ArH), 123.26 (ArH), 28.41 (CHⁱPr), 24.41 (CH₃ⁱPr). – ¹¹⁹Sn NMR (112.17 MHz, D₂O capillary/THF): δ=−80.1. – Elemental analysis (%) for C₁₈H₂₂Br₂N₂Sn (544.90): calcd. C 39.68, H 4.07, N 5.14; found C 39.80, H 4.02, N 5.22.

Synthesis of [SIMPY·SnI₂] (5)

Procedure as described for [SIMPYGeCl₂]. SnI₂ (932 mg, 2.50 mmol, 1 eq) was dissolved in 4 mL THF and the SIMPY ligand (400 mg, 2.50 mmol, 1eq) was added at room temperature. Dark red cubic crystals were obtained after recrystallizing in a THF-benzene mixture (2:1) at room temperature. Yield: 79%; m. p.: 191.4–192.3°C. – ¹H NMR (300.22 MHz, C₆D₆): δ=9.21 (d, 1H, PyH), 8.37 (s, 1H, HC=N), 8.00 (d, 1H, PyH), 7.82 (t, 1H, PyH), 7.36 (t, 1H, PyH), 7.07 (m, 4H, CH arom), 3.00 (sept, 2H, CHⁱPr), 1.08 (d, 12H, CH₃ⁱPr). – ¹³C NMR (75.50 MHz, C₆D₆): δ=163.16 (C=N, imine), 151.60 (ArH), 151.18 (ArH), 138.89 (ArH), 137.81 (ArH), 126.58 (ArH), 125.32 (ArH), 124.91 (ArH), 124.49 (ArH), 123.09 (ArH), 27.96 (CHⁱPr), 23.34 (CH₃ⁱPr). – ¹¹⁹Sn NMR (112.17 MHz, D₂O capillary/THF): δ=317.2 broad signal. Elemental analysis (%) for C₁₈H₂₂I₂N₂Sn (638.91): calcd. C 33.84, H 3.41, N 4.38; found C 31.45, H 2.73, N 3.84.

Synthesis of [SIMPY·SnOTf₂] (6)

SIMPY ligand (0.5 g, 1.88 mmol, 1 eq) was dissolved in 5 mL THF and SnOTf₂ (0.78 g, 1.88 mmol, 1 eq) was added. The light yellow solution turned bright orange. All volatile components were removed in vacuo and a bright orange powder was obtained. Yield: 93%; m. p.: 67.5–68.6°C. – ¹H NMR (300.22 MHz, C₆D₆): δ=9.43 (broad s, 1H, HC=N), 8.19 (broad d, 1H, PyH), 7.58 (broad s, 1H, PyH), 7.18 (m, 3H, CH arom), 2.65 (broad sept, 2H, CHⁱPr), 1.24 (broad d, 12H, CH₃ⁱPr). – ¹³C NMR (75.50 MHz, C₆D₆): δ=167.22 (C=N, imine), 150.72 (ArH), 147.77 (ArH), 144.97 (ArH), 142.17 (ArH), 141.02 (ArH), 129.51 (ArH), 124.34 (ArH), 122.29 (ArH), 118.06 (ArH), 28.16 (CHⁱPr), 23.18 (CH₃ⁱPr), 23.14 (CH₃ⁱPr). – ¹¹⁹Sn NMR (112.17 MHz, C₆D₆-THF): δ=−27.8. Elemental analysis (%) for C₁₉H₂₂F₃N₂O₉S₃Sn (694.28): calcd. C 32.87, H 3.19, N 4.03; found C 32,58; H 3.23; N 3.99.

Synthesis of [DIMPY·GeCl]⁺[GeCl₃]^– (7)

GeCl₂·dioxane (0.51 g, 2.20 mmol, 2 eq) was dissolved in 5 mL THF and DIMPY (0.50 g, 1.10 mmol, 1 eq) was added at room temperature. Color change was immediate as the solution went from clear transparent to orange. The solvent was reduced and the solid then dried under vacuum. Orange needle-like crystals suitable for X-ray analysis were obtained by recrystallization in a mixture of THF-benzene at room temperature. Yield: 98%; m. p.: 158.6–160.7°C. ¹H NMR (300.22 MHz, C₆D₆): δ=8.61(s, 1H, HC=N), 8.55 (s, 1H, HC=N), 8.44 (t, 1H, PyH), 8.30 (td, 1H, PyH), 7.15 (m, 6H, CH arom), 3.15 (broad sept, 4H, CHⁱPr), 1.25 (broad d, 12H, CH₃ⁱPr), 1.16 (broad d, 12H, CH₃ⁱPr). – ¹³C NMR (75.50 MHz, C₆D₆): δ 162.87 (C=N, imine), 159.75 (C=N, imine), 154.67 (ArH), 148.66 (ArH), 146.34 (ArH), 139.57 (ArH), 137.13 (ArH), 136.19 (ArH), 132.67 (ArH), 128.18 (ArH), 124.77 (ArH), 123.15 (ArH), 122.19 (ArH), 28.08 (CHⁱPr), 23.14 (CH₃ⁱPr). – Elemental analysis (%) for C₃₁H₃₉Cl₄N₃Ge₂ (740.75): calcd. C 50.26, H 5.31, N 5.67; found C 51.47, H 6.66, N 7.03.

Synthesis of [DIMPY·GeBr]⁺[GeBr₃]^– (8)

Procedure as described for [DIMPYGeCl]⁺[GeCl₃]⁻ (7). GeBr₂·dioxane (0.28 g, 0.88 mmol, 2 eq) was dissolved in 5 mL THF and DIMPY (0.20 g, 0.44 mmol, 1 eq) was added at room temperature. Orange needle like crystals suitable for X-ray analysis were obtained by recrystallization in a mixture of THF-benzene at room temperature. Yield: 98%; m. p.: 171.7–172.5°C. – ¹H NMR (300.22 MHz, C₆D₆): δ=8.61(s, 1H, HC=N), 8.55 (s, 1H, HC=N), 8.44 (t, 1H, PyH), 8.30 (td, 1H, PyH), 7.15 (m, 6H, CH arom), 3.15 (broad sept, 4H, CHⁱPr), 1.25 (broad d, 12H, CH₃ⁱPr), 1.16 (broad d, 12H, CH₃ⁱPr). – ¹³C NMR (75.50 MHz, C₆D₆-THF): δ 160.06 (C=N, imine), 148.41 (ArH), 146.34 (ArH), 141.71 (ArH), 140.28 (ArH), 139.58 (ArH), 132.43 (ArH), 129.45 (ArH), 128.16 (ArH), 124.48 (ArH), 124.27 (ArH), 30.02 (CHⁱPr), 28.64 (CH₃ⁱPr). – Elemental analysis (%) for C₃₁H₃₉Cl₄N₃Ge₂ (740.75): calcd. C 50.26, H 5.31, N 5.67; found C 50.33, H 4.59, N 4.44.

Synthesis of [DIMPY·SnBr]⁺[SnBr₃]^– (9)

SnBr₂ (0.61 g, 2.20 mmol, 2 eq) was dissolved in 5 mL THF and DIMPY (0.50 g, 1.10 mmol, 1 eq) was added at room temperature resulting in an immediate color change from pale yellow to orange. The solvent was removed and the solid then dried under vacuum. Dark orange needles were obtained after recrystallizing in a THF-benzene mixture (2:1) at room temperature. Yield: 78%; m. p.: 196.6–197.8°C. – ¹H NMR (300.23 MHz, C₆D₆): δ=8.61 (s, 1H, HC=N), 8.48 (s, 1H, HC=N), 8.38 (d, 1H, PyH), 8.18 (t, 1H, PyH), 7.92 (d, 1H, PyH), 7.24 (m, 6H, CH arom.), 3.21 (broad sept, 4H, CHⁱPr), 1.33 (d, 12H, CH₃ⁱPr), 1.23 (d, 12H, CH₃ⁱPr) ppm. – ¹³C NMR (75.50 MHz, C₆D₆): δ=162.83 (C=N, imine), 159.39 (C=N, imine), 154.63 (Ar-CH), 148.12 (Ar-CH), 146.08 (Ar-CH), 140.30 (Ar-CH), 139.58 (Ar-CH), 137.00 (Ar-CH), 132.09 (Ar-CH), 128.31 (Ar-CH), 124.78 (Ar-CH), 124.37 (Ar-CH), 123.15 (Ar-CH), 122.23 (Ar-CH), 28.07 (CHⁱPr), 25.40 (CH₃ⁱPr), 23.13 (CH₃ⁱPr) ppm. – ¹¹⁹Sn NMR (111.92 MHz, C₆D₆): δ=98.2 (DimpySnBr), −405.8 (SnBr₃⁻ anion) ppm. – Elemental analysis (%) for C₃₁H₃₉Br₄N₃Sn₂·4THF (1299.14): calcd. C 43.45, H 5.51, N 3.23; found: C 43.28, H 5.29, N 3.31.

Synthesis of [DIMPY·SnI]⁺[SnI₃]^– (10)

Procedure as described for [DIMPYGeCl]⁺[GeCl₃]⁻ (7). SnI₂ (0.82 g, 2.20 mmol, 2 eq) was dissolved in 5 mL THF and the ligand DIMPY (0.50 g, 1.10 mmol, 1 eq) was added at room temperature. Yield: 91%; m. p.: 196.6–197.8°C. – ¹H NMR (300.23 MHz, C₆D₆): δ=9.24 (d, 1H, PyH), 8.40 (s, 1H, HC=N), 8.04 (d, 1H, PyH), 7.86 (t, 1H, PyH), 7.38 (t, 2H, CH arom.), 7.08 (m, 4H, CH arom.), 3.02 (broad sept, 4H, CHⁱPr), 1.09 (d, 24H, CH₃ⁱPr) ppm. – ¹³C NMR (75.50 MHz, C₆D₆): δ=163.30 (C=N, imine), 162.82 (Ar-CH), 159.36 (Ar-CH), 151.03 (Ar-CH), 146.00 (Ar-CH), 139.58 (Ar-CH), 137.88 (Ar-CH), 132.76 (Ar-CH), 127.97 (Ar-CH), 126.87 (Ar-CH), 125.49 (Ar-CH), 123.16 (Ar-CH), 122.59 (Ar-CH), 27.98 (CHⁱPr), 23.45 (CH₃ⁱPr) ppm. – Elemental analysis (%) for C₃₃H₄₇I₄N₃Sn₂ (1230.80): calcd. C 32.20, H 3.85, N 3.41; found C 33.61, H 3.77, N 4.33.

Synthesis of [DIMPY·SnOTf₂] (11)

DIMPY ligand (0.5 g, 1.10 mmol, 1 eq) was dissolved in 5 mL THF and SnOTf₂ (0.46 g, 1.10 mmol, 1 eq) was added. The solvent was reduced in vacuo and an orange powder was obtained. Cubic orange crystals were obtained via recrystallizing in THF-benzene mixture at room temperature. Yield: 78%; m. p.: 202.7–204.9°C. – ¹H NMR (300.23 MHz, C₆D₆): δ=8.18 (s, 2H, HC=N), 7.31 (t, 1H, PyH), 7.14 (m, 8H, CH arom.), 3.52 (broad sept, 4H, CHⁱPr), 1.27 (d, 24H, CH₃ⁱPr) ppm. – ¹³C NMR (75.50 MHz, C₆D₆): δ=163.48 (C=N, imine), 151.07 (Ar-CH), 144.48 (Ar-CH), 141.53 (Ar-CH), 131.03 (Ar-CH), 128.46 (Ar-CH), 124.79 (Ar-CH), 122.28 (Ar-CH), 118.05 (Ar-CH), 27.62 (CHⁱPr), 24.65 (CH₃ⁱPr) ppm. – ¹¹⁹Sn NMR (111.92 MHz, C₆D₆): δ=−46.4 ppm. – Elemental analysis (%) for C₃₉H₅₇F₆N₃O₆S₂Sn (960.72): calcd. C 48.76, H 5.98, N 4.37; found C 47.01, H 4.93 N 4.42.