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Article

Diorganotin(IV) Complexes of Organoselenolato Ligands with Pyrazole Moieties—Synthesis, Structure and Properties †

by
Melinda Tamas
1,
Roxana A. Butuza
1,
Monica Dan
2 and
Anca Silvestru
1,*
1
Supramolecular Organic and Organometallic Chemistry Centre (CCSOOM), Chemistry Department, Faculty of Chemistry and Chemical Engineering, “Babeş-Bolyai” University, 400028 Cluj-Napoca, Romania
2
National Institute for Research and Development of Isotopic and Molecular Technologies, 400293 Cluj-Napoca, Romania
*
Author to whom correspondence should be addressed.
†
Dedicated to Prof. Hans J. Breunig at his 80th birthday.
Molecules 2025, 30(7), 1648; https://doi.org/10.3390/molecules30071648
Submission received: 16 March 2025 / Revised: 1 April 2025 / Accepted: 3 April 2025 / Published: 7 April 2025
(This article belongs to the Special Issue Recent Advances in the Synthesis, Functionalization and Applications of Pyrazole-Type Compounds III)
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Versions Notes

Abstract

:
Diorganotin(IV) compounds of types RR′Sn(SeCH2CH2pz)2 [R = R′ = nBu (2), Ph (3); R = 2-(Me2NCH2)C6H4, R′ = Me (4), nBu (5), Ph (6)], and RR′SnX(SeCH2CH2pz) [R = 2-(Me2NCH2)C6H4, R′ = nBu, X = Cl (7), R′ = Me, X = SCN (9)], as well as [2-(Me2NCH2)C6H4](Me)Sn(NCS)2 (8), and the tin(II) Sn(SeCH2CH2pz)2 (10) (pz = pyrazole), were prepared by salt metathesis reactions between the appropriate diorganotin(IV) dichloride or dipseudohalide and Na[SeCH2CH2pz], with the latter freshly prepared from (pzCH2CH2)2Se2 (1). The solution behaviour of these compounds was investigated by multinuclear NMR (1H, 13C, 77Se, 119Sn), and the NMR spectra showed the existence of the Se–Sn bonds in solution. Compounds 4 and 5 showed decomposition in a solution of chlorinated solvents with the formation of selenium bridged dimeric species of type {[2-(Me2NCH2)C6H4](R’)Se}2 [R′ = Me (4-a), nBu (5-a)], as the single-crystal X-ray diffraction studies revealed, in contrast with compound 9, for which a monomeric structure was observed with the desired composition. The solid state structures of 4-a, 5-a, 8, and 9 revealed N→Sn intramolecular coordination of the nitrogen atom in the pendant CH2NMe2 arm. The NMR spectra suggested such a coordination at room temperature only for compound 7.

1. Introduction

The potential of the organotin and the organoselenium compounds in biology, catalysis, and materials science determined over the past decades a continuously increasing interest to develop new chemical species, with an appropriate combination of organic groups and ligands, which might improve thermal and hydrolytic stability and enhance specific properties. Organoselenium compounds showed significant antioxidant, anti-inflammatory, and antiproliferative activity [1,2,3], were used as catalysts in organic synthesis [4,5], and were successfully employed as starting materials for precursors for nanoparticles or thin films [6]. On the other hand, organotin species displayed antitumor activity against several types of cancer [7,8,9], are used in catalysis [10,11], and have proven to be valuable precursors for nanomaterials [12] as well. These facts have sparked interest in obtaining chemical species which contain both tin and selenium in the same molecule, thus promising enhanced potential both for biological applications and nanomaterials.
Tin(II) and tin(IV) complexes with Sn–Se bonds displayed structural features and properties which recommended them as valuable single-source precursors for binary SnSe or SnSe2 thin films and nanoparticles [13,14,15]. SnSe is a p-type semiconductor, with a direct band gap of 0.9 eV and an indirect band gap of 1.3 eV [16,17], while SnSe2 is an n-type semiconductor with an indirect band gap of 1.0 eV [18]. Both show excellent thermoelectric and optoelectronic properties based on their intrinsic anisotropy [19]. The large number of applications of tin chalcogenides for optoelectronic devices, gas sensors, or anode materials for Li/Na-ion batteries determined a significant interest to find new single-source precursors, which allow for better control upon the thermal behaviour, structure, and phase composition when compared with dual-source precursors [20].
Several tin(II) complexes, e.g., 1∞[Sn(SePh)2] [17], Sn[SeSi(SiMe3)3] [21], and [Sn(2-Sepy)2] [22], were observed to undergo a single-step thermal decomposition to yield SnSe, while the tin(IV) complexes lead to SnSe nanoparticles by pyrolysis, i.e., [Sn(SePh)4] [23], or decomposed to SnSe2, i.e., [Sn(2-Sepy)4] [22]. The tin(IV) complexes [SnCl2{(SeCH2CH2)2NMe}] and [Sn{(SeCH2CH2)2NMe}2] were used as single-source precursors for SnSe nanoparticles, either by microwave-assisted solvothermal processes or by thermolysis [19]. Dinuclear triorganotin(IV) compounds, with bulky organic groups attached to tin, e.g., (Ph3Sn)2Se [24,25] and diorganotin(IV) species, either dinuclear, e.g., [{(Me2Si)2CH}2Sn(μ-Se)]2 [26], or mononuclear derivatives of types R2Sn(SeAr)2 and R2SnCl(SeAr) (R = Me, Et, nBu, tBu; Ar = C5H4N, C5H3(3-Me)N, C5H3(5-Me)N, C4H(4,6-Me2)2N2), were also studied by thermal decomposition or pyrolysis to obtain SnSe or SnSe2 nanoparticles [27,28,29]. In addition, atmospheric pressure chemical vapour deposition (APCVD) or aerosol-assisted CVD (AACVD) were employed to obtain SnSe thin films and nanosheets from diorganotin bis(organoselenolates) [29,30,31].
In this context, there still is significant interest in designing new compounds with thermal stability and high volatility, and to choose the most suitable combinations of organic groups attached both to tin and selenium, which not only enable a neat thermal decomposition, but also allow us to obtain nanocrystals, nanosheets, or thin films of tin selenides with homogeneous structures and compositions. It was shown that the use of organic groups decorated with pendant arms bearing nitrogen donor atoms capable for intramolecular coordination has a significant influence not only on the structure of the organometallic species, either organotin or organoselenium, but, more important, on their reactivity and specific behaviour in the above-mentioned fields [32,33,34]. As a consequence, various organic groups capable of behaving as C,N (e.g., 2-(Me2NCH2)C6H4) or N,C,N (e.g., 2,6-(Me2NCH2)C6H3) chelating moieties were employed both in organotin [35,36,37,38] and organoselenium [39,40,41,42] chemistry.
Previously, we reported on the tin complexes Sn[SeC6H4(CH2NMe2)-2][N(SiMe3)2] and Sn(SePh)2[N(SiMe3)2] [43], obtained by the reactions of Sn[N(SiMe3)2]2 with the corresponding diorganodiselenide, as well as homo- and heteroleptic di- and triorganotin(IV) complexes with pseudohalido ligands, i.e., [2-(Me2NCH2)C6H4]RSn(NCE)2 [E = S, Se; R = nBu, Ph, 2-(Me2NCH2)C6H4] and [2-(Me2NCH2)C6H4]R2Sn(NCE) (E = S, Se, R = Me, Ph) [44], or dithiocarbamato ligands, i.e., RR′Sn(S2CNR″2)Cl [R = R′ = Me, nBu; R″ = Me, Et; R = 2-(Me2NCH2)C6H4, R′ = Me, R″ = Me, Et] and RR′Sn(S2CNR″2)(NCS) [R = R′ = Me, nBu, R″ = Me, Et; R = 2-(Me2NCH2)C6H4, R′ = Me, nBu, R″ = Me, Et [45], prepared by salt metathesis reactions. Recently, we reported on diorganotin(IV) compounds with organoselenolato ligands bearing alkyl groups with pyrazole moieties, namely R2Sn(SeCH2CH2pz)2 [R = Me, 2-(Me2NCH2)C6H4], and we investigated their antiproliferative activity against murine colon carcinoma C26 cells [46]. As a continuation of our research on this topic, the present work reports on the synthesis and structural characterization of new homo- and heteroleptic diorganotin(IV) bis(organoselenolates) with pyrazole containing organic groups, namely RR′Sn(SeCH2CH2pz)2 [R = R′ = nBu (2), Ph (3); R = 2-(Me2NCH2)C6H4, R′ = Me (4), nBu (5), Ph (6)], [2-(Me2NCH2)C6H4](nBu)SnCl(CH2CH2Se) (7), [2-(Me2NCH2)C6H4](Me)Sn(NCS)2 (8), and [2-(Me2NCH2)C6H4](Me)Sn(NCS)(SeCH2CH2pz) (9), as well as the tin(II) complex Sn(SeCH2CH2pz)2 (10).

2. Results and Discussion

2.1. Synthesis

Diorganotin(IV) compounds of types RR′SnL2 [L = SeCH2CH2pz, R = R′ = nBu (2), Ph (3), R = 2-(Me2NCH2)C6H4, R′ = Me (4), nBu (5), Ph (6)], and RR′SnXL [L = SeCH2CH2pz, R = 2-(Me2NCH2)C6H4, R′ = nBu, X = Cl (7); R′ = Me, X = NCS (9)], as well as [2-(Me2NCH2)C6H4](Me)Sn(NCS)2 (8) and the tin(II) compound Sn(SeCH2CH2pz)2 (10), were prepared by salt metathesis reactions, as depicted in Scheme 1. The sodium organoselenolate was freshly prepared, starting from (pzCH2CH2)2Se2 (1). Compounds 4, 8, 9, and 10 were isolated as solid species, while the other compounds were oils.

2.2. Spectroscopic Characterization

Solution Behaviour

All compounds were characterized by multinuclear NMR (1H, 13C{1H}, 77Se{1H}, and 119Sn{1H}, as appropriate) spectroscopy and mass spectrometry. The NMR spectra suggested in each case the presence of the desired species in solution.
Both the 1H and the 13C{1H} NMR spectra show the expected resonances for the organic groups attached to tin and to selenium, respectively (see the Supplementary Information (SI), Figures S1–S6). The 1H NMR spectra display for the CH2 groups in the pzCH2CH2Se− ligands two multiplet resonances (see the Supplementary Information, Figures S1, S3, S5 and S6), with a splitting pattern determined by the non-equivalence of the two protons in each CH2 group.
The resonances of the protons and the carbon atoms in the proximity of tin or selenium are accompanied by 117/119Sn and 77Se satellites, respectively, and display characteristic coupling constants. The 1JSnC coupling constant for compound 2, which has two aliphatic carbons attached to tin, is given in Table 1. This value was used to calculate the C–Sn–C angle and to assign a distorted tetrahedral coordination geometry to tin in solution [47,48].
The 119Sn{1H} spectra of all compounds bearing the organoselenolato ligand show a singlet resonance in each case, accompanied by 1JSeSn coupling constants. The 119Sn{1H} resonance of compound 9 has a different pattern (see the Supplementary Information, Figure S7), the splitting suggesting dipolar interactions with the two quadrupolar 14N nuclei and 119Sn-14N spin–spin coupling, as previously described by Wrackmeyer [49]. The 77Se{1H} spectra show a singlet resonance for each compound, accompanied by 1J117SnSe and 1J119SnSe coupling constants. The values for the 1JSeSn coupling constants, along with the 119Sn and the 77Se chemical shifts for compounds 1–10, and the starting diorganotin halides, are given in Table 2, while the 119Sn{1H} and the 77Se{1H} resonances for compound 2, as an example, are displayed in Figure 1. Based on the NMR spectra, we can conclude that in each case, the organoselenolato ligand is attached to tin by selenium.
For the heteroleptic diorganotin(IV) compounds 4–9, the presence of the 2-(Me2NCH2)C6H4 group might determine an increase in the coordination number at the tin atom, due to an intramolecular N→Sn coordination, in which the CH2N(CH3)2 pendant arm is involved. Such a secondary interaction should be observed in the 1H and the 13C NMR spectra by the no more equivalent CH2 protons and the two methyl groups in the CH2N(CH3)2 pendant arm. We noted this behaviour in solution, at room temperature, only for compound 7, where the resonance for the CH2 protons appears as an AB spin system (δA 3.35 and δB 3.99 ppm, 2JHH 13.1 Hz), and the two methyl groups give two singlet resonances (δN(CH3)2 2.23 and 2.45 ppm; δN(CH3)2 44.7 and 46.1 ppm) both in the 1H and the 13C NMR spectra (see the Supplementary Material, Figure S6). This behaviour, namely a N→Sn interaction, might be expected in solution for all the heteroleptic compounds described in this study, but it could not be observed at the room temperature NMR time scale due to a very fast process involving de-coordination, inversion at the nitrogen atom, and re-coordination [55].
Valuable data about the coordination number at the tin atom in solution is available for the 119Sn NMR spectra as well, as reported previously by Holeček [50] and Otera [56]. Based on the 119Sn NMR resonances observed in CDCl3 solutions, we can assign a monomeric structure for compounds 4–7 with pentacoordinate Sn atoms. For the tin complexes, the chemical shifts in the 119Sn NMR resonances are close to those observed for the starting diorganotin(IV) dichlorides, for which a structure with pentacoordinate tin was assigned previously [37,50,51,52,53,54]. Moreover, the 1H and the 13C NMR spectra of compound 7 at room temperature clearly show the intramolecular coordination of the nitrogen atom in the CH2N(CH3)2 pendant arm to tin. The 119Sn NMR resonance for 7 (δ = −104.6 ppm) has a very similar value with those observed for compounds 5 and 6, and close to that observed for compound 4. Anyway, the 119Sn chemical shifts for our compounds fall in the range reported by Otera for pentacoordinate diorganotin(IV) species (−90 ÷ −330 ppm). In this way, we can assume the existence of pentacoordinated tin atoms in solution, with C,N-chelating ligands, similarly with the solid state structures determined for the decomposition products 4-a and 5-a.
In the case of compound 9, the CH2N(CH3)2 protons give very broad 1H NMR resonances at room temperature, thus suggesting a dynamic behaviour in solution, as described above, but slower at room temperature than observed in compounds 4–6. To further investigate this behaviour, we performed low temperature 1H NMR experiments (see the Supplementary Information, Figure S8), and we could observe that at low temperatures, the CH2N protons and the two N(CH3)2 groups, respectively, are no more equivalent (at −30 °C δ(1H)Me 2.24 and 2.46 ppm, and δA(1H)CH2 3.47 and δB(1H)CH2 3.94 ppm). We could calculate the free enthalpy, ΔG# = 58.7 KJ/mol, at the coalescence temperature Tc = 15 °C, for the dynamic process suffered by the CH2 protons in the CH2N(CH3)2 pendant arm, and a ΔG# = 70.8 KJ/mol at Tc = 10 °C for the two methyl groups. We can conclude that for compound 9, the variable-temperature 1H NMR spectra proved that under 0 °C, the nitrogen atom in the CH2N(CH3)2 pendant arm remains coordinated with tin, while above this temperature the compound undergoes a dynamic process. In this way, we assume that at low temperatures compound 9 has the same molecular structure as that one determined in solid state by single-crystal X-ray diffraction, as discussed below. For compound 8, we can assume a similar behaviour, where the N→Sn coordination involving the nitrogen atom in the pendant arm is present at low temperatures as well, while at room temperature the compound exhibits fluxionality in solution, and we expect for this compound, at low temperatures, a similar structure with that determined by single-crystal X-ray diffraction. Moreover, the chemical shift values of the 119Sn resonances for these two compounds suggest the existence of intramolecularly coordinated pendant arms, which results in five-coordinate tin atoms [56]. The 119Sn chemical shift for 8 at −252.7 ppm is close to those observed previously for the related [2-(Me2NCH2)C6H4](nBu)Sn(NCS)2 (−266.6 ppm) and [2-(Me2NCH2)C6H4](Ph)Sn(NCS)2 (−329.3 ppm) [44], while for 9 the 119Sn resonance was observed at −161.8 ppm. These values are consistent with pentacoordinate Sn compounds [56], similarly to their solid state structure.
′The ESI+ mass spectra show for all compounds of type RR′Sn(SeCH2CH2pz)2 the base peak for the cation [RR′Sn(SeCH2CH2pz)]+, formed during ionization, at the m/z values 407.02210 for cpd. 2 (calcd. 407.01935 for C13H25N2SeSn), 446.06921 for 3 (calcd. 446.94169 for C17H15N2SeSn), 441.99945/441.99963 for compounds 4 and 9 (calcd. 441.99895/441.99915 for C15H22N3SeSn), 484.04724/484.04731 for compounds 5 and 7 (calcd. 484.04590 for C18H28N3SeSn), and 504.01658 for 6 (calcd. 504.01460 for C20H24N3SeSn), while for [2-(Me2NCH2)C6H4](Me)Sn(SCN)2 (8) was observed the base peak for the cation [M-SCN]+ at m/z 326.99713 (calcd. 326.99724 for C11H15N2SSn). For the tin(II) compound Sn(SeCH2CH2pz)2 (10), the mass spectrum showed the base peak at m/z 292.87903 (calcd. 292.87850 for C5H7N2SeSn).

2.3. X-Ray Diffraction Studies

2.3.1. Crystal and Molecular Structure of {[2-(Me2NCH2)C6H4](Me)SnSe}2 (4-a) and {[2-(Me2NCH2)C6H4](nBu)SnSe}2 (5-a)

Our attempts to grow single-crystals of compound 4 from a mixture of CH2Cl2 and n-hexane resulted in a decomposition solid product with a dimeric structure, namely {[2-(Me2NCH2)C6H4](Me)SnSe}2 (4-a). Compound 5, which was isolated as an oil, decomposed in CDCl3 solution in a similar way, and we observed the formation of a solid microcrystalline product in the NMR tube after several days. The X-ray diffraction studies also revealed for this compound the formation of the dimeric species {[2-(Me2NCH2)C6H4](nBu)SnSe}2 (5-a). We have to mention that it was previously reported that in CHCl3 or CH2Cl2 solutions, the tin(IV) complex [Sn(S2CNEt2)4] decomposed with the formation of the dimeric [SnS(S2CNEt2)2]2 with a planar Sn2S2 core, and S(S2CNEt2)2 [57], in a way similar to what we found for compounds 4 and 5. The dimeric structure of compound 4-a is depicted in Figure 2, while that of 5-a is given in the Supplementary Information, Figure S9. Important interatomic distances and bond angles are given in Table 3.
Several similarities in the molecular structures of these compounds can be pointed out.
The molecules are associated in dimeric units by bridging selenium atoms, which interact at very similar distances with both tin atoms (range 2.5033(3) Å–2.6545(3) Å, vs. Σrcov(Sn,Se) 2.59 Å and ΣrvdW(Sn,Se) 4.24 Å) [58]. These values are suggestive of a tin–selenium primary interaction of type [RR′Sn+–Se−] for each selenium atom, with the calculated bond order for such an interaction being 2.57 Å, vs. the much shorter value (2.37 Å) calculated for an [RR′Sn=Se] structure [16]. A single Sn–Se bond can be assigned for compounds 4 and 5 in solution as well, based on the 1JSnSe coupling constant, which falls in the range typical for single Sn–Se bonds reported for other tin organoselenolates [36]. In this way, planar Sn2Se2 cores are formed in each compound, with Se–Sn–Se angles of 94.73(1)°, and 94.45(1)° in 4-a, and 5-a, respectively, and the organic groups displayed trans each other, above and beneath the Sn2Se2 plane. Moreover, the tin atoms are very close each other, at Sn···Sn distances of 3.4952(4) Å, and 3.5183(4) Å in 4-a, and 5-a, respectively, much shorter than ΣrvdW(Sn,Sn) of 4.84 Å [58].
The nitrogen atoms in the pendant arms are intramolecularly coordinated to tin, thus resulting in tin(IV) hypercoordinated species, namely 10-Sn-5 in 4-a and 5-a [59].
In both compounds, the five atoms attached to tin are displayed in a distorted trigonal bipyramidal coordination environment (τ5 = 0.81 [60]), with the nitrogen atom in the pendant arm and the selenium of the partner molecule in the dimer in apices (N1–Sn1–Se1′ 173.16(1)° in 4-a and 172.01(6)° in 5-a).
The coordination geometry of selenium is angular, with Sn–Se–Sn angles of 85.27(1)°, and 85.55(1)° in compounds 4-a and 5-a, respectively.
As a result of the intramolecular N→Sn coordination, a non-planar SnC3N five membered ring is formed, and consequently the compounds display planar chirality [61], where nitrogen is the pilot atom and the C6H4 ring is the chiral plane, thus resulting in RN and SN isomers, with respect to the two SnC3N five membered rings in a dimeric unit. In addition, due to the positions of the two selenium atoms, one in apices and the other in the equatorial plane, the tin atom becomes chiral itself, and in this way each dimer in the crystal displays C/A isomerism as well [61]. As a consequence, the crystal structures contain dimers formed by CSnRN1 and ASn′SN1′ isomers, both in 4-a and 5-a.
A close look at the crystals of these compounds revealed chain-like supramolecular associations with dimers (see the Supplementary Information, Figures S10 and S11). The chains are formed by CH···Se interactions in 4-a (H5···Se 3.028 Å, vs. ΣrvdW(H,Se) 3.10 Å [58]. In 5-a, a CH2 proton in the nBu group is involved in inter-dimer π HCH···Cg contacts (H10B···Cg 2.81 Å, γ = 5.8°, C10–H10B···Cg 141°) [62,63].

2.3.2. Crystal and Molecular Structure of [2-(Me2NCH2)C6H4](Me)Sn(NCS)2 (8) and [2-(Me2NCH2)C6H4](Me)Sn(NCS)(SeCH2CH2pz) (9)

The crystal of compound 8 contains two very similar independent molecules in the unit cell. A thermal ellipsoid representation of molecule 8a is given in Figure 3, and that of molecule 8b is given in the Supplementary Information, Figure S12, while the molecular structure of 9 is depicted in Figure 4. Important interatomic distances and bond angles for the two independent molecules in 8 are given in Table 4, while those for the complex 9 are given in Table 3. In both species, the 2-(Me2NCH2)C6H4 group acts as a C,N-chelating moiety, while the NCS ligands behave as isothiocyanato moieties.
In the molecule of 9, the organoselenolato pzCH2CH2Se− ligand behaves as a κSe monodentate moiety [61], with a Sn–Se interatomic distance of 2.5298(3) Å, which is slightly shorter than those observed in R2Sn(2-SeC5H4N)2 (R = Me, 2.615(3), 2.618(3), 2.595(3) and 2.585(3) Å in the two independent molecules; R = tBu, 2.622(2) Å) [28], but it is of the same magnitude as those found in 4-a and 5-a, and typical for a single Sn–Se bond. In this way, compounds 8 and 9 can be described as 10-Sn-5 hypercoordinate species. The coordination geometry about tin is a distorted square pyramide in 8a (τ5 = 0.26) and 8b (τ5 = 0.16), with N2 and N5, respectively, in apices, and a distorted trigonal bipyramide in 9 (τ5 = 0.70), with N1 and N2 in apices (N1–Sn1–N2 169.64(1)°).
The intramolecular N→Sn coordination generates NC3Sn five-membered rings, which are not planar, but folded about the Sn···CH2 imaginary axis (Sn1···C7 in 8a and in 9, Sn2···C19 in 8b), and, as a consequence, this induces planar chirality, which determines a racemic mixture of RN and SN isomers in the crystal [61]. Moreover, the tin atom becomes chiral itself, and the presence of C/A enantiomers [61] should be taken into account as well. Based on these considerations, the crystal of 8 contains racemic mixtures of ASn1,RN1/CSn1,SN1 and CSn2,SN4/ASn2,RN4, while 9 contains a racemic mixture of ASn,SN1 and CSn,RN1 isomers. The isothiocyanato ligands are essentially linear in both compounds, with N=C=S angles in the range 177.35(1)–179.58(1)°.
In the crystal of 8, the molecules are associated in polymeric chains (see Supplementary Information, Figure S13) by NCS ligands (S3···Sn1 3.2876(6) Å vs. Σrcov(Sn,S) 2.44 Å and ΣrvdW(Sn,S) 4.31 Å [58]). If we take into account this interaction as well, the coordination geometry about tin becomes distorted octahedral, and the molecules can be described as a hypercoordinate 12-Sn-6 species with bridging NCS ligands. Further, S···H contacts (S4···H21A 2.919 Å, S4···H17 2.717 Å, and S4···H7A 3.008 Å, vs. ΣrvdW(S,H) 3.10 Å) lead to a 3D supramolecular network (see the Supplementary Information, Figure S14).
A close look at the crystal of 9 revealed π H2CH···Cg interactions with the participation of a proton from the methyl group attached to tin, namely H10C···Cg(C1-C6) = 3.01 Å (see Supplementary Information Figure S15).

2.4. Thermal Behaviour

In order to assess the potential of our compounds for the formation of tin selenides, we investigated the thermal decomposition of compound 4 (M = 616.12) both in inert atmosphere (argon) and in synthetic air. In argon atmosphere, no mass loss was observed until 200 °C, but after this, temperature decomposition occurs until 346 °C, with a mass loss of 76.48% (471 g/mol) and a residue of 145 g/mol (23.52%). The massive mass loss of 76.48% suggests the elimination of Sn(SeCH2CH2pz)2 (M = 467). In a second step, after a plateau, almost all the residue was volatilised above 800 °C. As the weight of the residue after the first step was significantly below the mass of the expected SnSe, we investigated the thermal behaviour of the tin(II) complex Sn(SeCH2CH2pz)2.(cpd. 10,) in the same conditions. In this case, we observed a mass loss of 58.65%, which might be assigned to the diorganoselenide Se(CH2CH2pz)2, and a final residue corresponding to SnSe (m = 193 g/mol, 41.35%), which is close to the calculated SnSe content (m = 196, 41.97%) in the precursor. The low weight of the residue remaining from compound 4 might be explained by a partial sublimation of the tin compound before decomposition, taking into account that most of the organotin complexes are volatile species [32].
Further thermogravimetric analyses were performed in air for both compounds, and almost the same behaviour was observed in the range of 200–400 °C, as described above for the experiments under argon, but the weight of the final residue corresponded to metallic tin; namely, for compound 4, the remaining residue of 19.07% corresponded to a mass of 117 g/mol. Apparently, the decomposition proceeds in a similar way both under argon and in air, but we have to consider a more complex pathway under an air flow, based on the formation of oxidized species in the presence of oxygen, as long as both tin and selenium are prone to oxidation.
The thermal behaviour of compounds 8 and 9 was investigated in synthetic air as well, and the final residue corresponded, in both cases, to metallic tin. For compound 9 (M = 500.11), in a first degradation step, most of the compound was eliminated, and a mass loss of 70.74% (m = 355.11) could be assigned formally to Sn(SeCH2CH2pz)(SCN) (M = 350.88, calcd. 72.18%), resembling the behaviour of compound 4. The thermograms of compounds 4, 8, 9, and 10 are displayed in the Supplementary Information, Figures S16 and S17. The experimental results suggest that the investigated compounds are volatile species, which either sublime before decomposition, or decompose easily with the elimination of organoselenium species. Their high volatility recommend them as potential candidates for CVD processes. The behaviour of our compounds resembles that observed during the thermogravimetric analyses of other tin(IV) organoselenolates, i.e., R2Sn{SeC5H3(Me-5)N}2 (R = Me, Et, tBu) [29], [Sn(SePh)2]n [64], [(PhSe)2Sn{N(SiMe3)2}2], [{(Me3Si)2N}2Sn(μ2-Se)]2 [65], and Me2Sn{2-SeC5H2(Me-4,6)2N}2 [66], where the SnSe quantity recovered as a residue from the starting precursors was lower than the theoretical content, due to a significant volatilisation before thermal decomposition.

3. Materials and Methods

3.1. General

All synthetic manipulations involving air-sensitive compounds were carried out under argon atmosphere by using Schlenk techniques. Solvents were dried and distilled under argon prior to use. Starting materials such as N,N-dimethylbenzylamine, NaBH4, nBuLi (1.6 M solution in n-hexane), KSCN, Bu2SnCl2, Ph2SnCl2, and SnCl2 were commercial products, and they were used as received, while the diorganodiselenide (pzCH2CH2)2Se2 (1) [46] and the diorganotin(IV) dichlorides were prepared according to literature procedures [37,50,51,52,53,54]. Elemental analyses (CHN) were performed on a Flash EA 1112 analyser (Thermo Scientific, Waltham, MA, USA). Melting points were measured with an Electrothermal 9200 apparatus and were not corrected. The 1H, 13C{1H}, 77Se{1H}, and 119Sn{1H} NMR spectra, at room temperature, as well as the VT 1H NMR spectra for compound 9, were recorded in CDCl3, on a Bruker AVANCE III instrument (Bruker, Billerica, MA, USA), operating at 400.13, 100.61, 76.31, and 149.21 MHz, respectively. The 1H and 13C{1H} chemical shifts are reported in δ units (ppm) relative to the residual peak of the solvent in the 1H NMR spectra (CHCl3, 7.26 ppm), and to the peak of the deuterated solvent (CDCl3, 77.16 ppm) in the 13C{1H} NMR spectra. They were assigned based on 2D correlation experiments (H,H-COSY, H,C-HSQC, and H,C-HMBC), according to the numbering shown in Scheme 2. The 77Se{1H} and 119Sn{1H} NMR resonances are reported in ppm relative to Me2Se and Me4Sn, respectively. The NMR spectra were processed using the MestReNova software (version 14) [67]. The APCI+ and ESI+ mass spectra were recorded on a Thermo Scientific LTQ-Orbitrap XL spectrometer (Waltham, MA, USA) equipped with a standard ESI/APCI source, and were processed with Thermo Xcalibur software (version 3.1) [68]. Thermogravimetric analyses (TGA) were performed in synthetic air (100 mL/min, 12 vol.% O2 in N2) or in argon (100 mL/min), using an SDT Q600 instrument (TA Instruments, USA), in the temperature range 25–1000 °C, using a heating rate of 10 °C/min.

3.2. Synthesis

3.2.1. nBu2Sn(SeCH2CH2pz)2 (2)

To a yellow solution of (pzCH2CH2)2Se2 (0.131 g, 0.376 mmol) in 30 mL absolute ethanol, we added NaBH4 (0.035 g, 0.925 mmol, 23% excess) at ice bath temperature. A colourless solution was obtained within a few minutes. After the hydrogen release had subsided, ethanol was removed at reduced pressure, and the remaining colourless solid was washed with hexane (3 × 5 mL), dried and redissolved in ethanol. Bu2SnCl2 (0.1142 g, 0.376 mmol) was added to the ethanol solution, and the stirring continued for 1.5 h. After the evaporation of ethanol, 20 mL of dry dichloromethane was added. After filtration, the solvent was removed under vacuum, and the colourless oil was washed with hexane (3 × 5 mL) and finally dried under vacuum. Yield: 0.214 g (98%); elemental anal.: calcd. for C18H32N4Se2Sn (MW 581.11): C 37.20, H 5.55, N 9.64%; found: C 37.35, H 5.63, N 9.88%; 1H NMR, δ: 0.90 (t, 6H, CH2CH2CH2CH3, 3JHH 7.3 Hz), 1.30–1.39 (m, 4H, CH2CH2CH2CH3), 1.43–1.53 (m, 4H, CH2CH2CH2CH3), 1.54–1.62 (m, 4H, CH2CH2CH2CH3), 3.02–3.13 (m, CH2CH2Se), 4.32–4.38 (m, 4H, CH2CH2Se), 6.23 (t, 2H, pz-H2, 3JHH 1.9 Hz), 7.44 (d, 2H, pz-H1, 3JHH 2.0 Hz), 7.51 (d, 2H, pz-H3, 3JHH 1.5 Hz); 13C{1H} NMR, δ: 13.72 (CH2CH2CH2CH3), 18.55 (CH2CH2CH2CH3, 1J117SnC 326.4, 1J119SnC 341.4 Hz), 18.80 (CH2CH2Se, 1JSeC 15.5 Hz), 26.73 (CH2CH2CH2CH3, 2J117SnC 71.3 Hz, 2J119SnC 74.4 Hz), 28.89 (CH2CH2CH2CH3, 3J119SnC 25.4 Hz), 54.75 (CH2CH2Se, 3J119SnC 11.1 Hz), 105.42 (pz-C2), 129.61 (pz-C1), 139.79 (pz-C3); 77Se{1H} NMR, δ: −177.7 (s, 1J117SnSe 1177.1, 1J119SnSe 1232.2 Hz); 119Sn{1H} NMR, δ: 79.9 (s, 1JSeSn 1231.9 Hz); APCI+ MS (MeOH): m/z (%) 409.02182 (100) [M-SeCH2CH2pz]+ (409.01994, calcd. for C13H25N2SeSn), 294.88016 (52) [pzCH2CH2SeSn]+ (294.87909 calcd. for C5H7N2SeSn).
Compounds 3–6 were prepared similarly to compound 2.

3.2.2. Ph2Sn(SeCH2CH2pz)2 (3)

Ph2Sn(SeCH2CH2pz)2 (3) was isolated as a colourless oil from (pzCH2CH2)2Se2 (0.158 g, 0.454 mmol), NaBH4 (0.042 g, 1.11 mmol, 22% excess), and Ph2SnCl2 (0.156 g, 0.454 mmol). Yield: 0.189 g (67%); elemental anal., calcd. for: C22H24N4Se2Sn (MW 621.1): C 42.54, H 3.90, N 9.02%; found: C 42.97, H 4.12, N 9.21%. 1H NMR, δ: 3.02–3.15 (m, 4H, CH2CH2Se), 4.21–4.29 (m, 4H, CH2CH2Se), 6.17 (t, 2H, pz-H2, 3JHH 2.1 Hz), 7.19 (d, 2H, pz-H1, 3JHH 2.3 Hz), 7.41–7.49 (m, 8H, pz-H3 + C6H5-Hm+p), 7.52–7.72 (m, 4H, C6H5-Ho, 3JSnH 64 Hz); 13C{1H} NMR, δ: 19.7 (CH2CH2Se, 1JSeC 61.4 Hz), 54.39 (CH2CH2Se), 105.42 (pz-C2), 129.42 (C6H5-Cm, 4JSnC 63.7 Hz), 129.47 (pz-C1), 130.60 (C6H5-Cp), 136.07 (C6H5-Co, 2J119SnC 48.7 Hz), 137.01 (C6H5-Ci), 139.8 (pz-C3); 77Se{1H} NMR, δ: −182.3 (s, 1J117SnSe 1261.7, 1J119SnSe 1321.3 Hz); 119Sn{1H} NMR, δ: −23.5 (s, 1JSeSn 1320.3 Hz); APCI+ MS (MeOH): m/z (%) 448.95909 (100) [M-SeCH2CH2pz]+ (448.95734 calcd. for C17H17N2SeSn), 174.97755 (35) [pzCH2CH2Se]+.

3.2.3. [2-(Me2NCH2)C6H4](Me)Sn(SeCH2CH2pz)2 (4)

[2-(Me2NCH2)C6H4](Me)Sn(SeCH2CH2pz)2 (4) was isolated as a colourless solid product from (pzCH2CH2)2Se2 (0.150 g, 0.430 mmol), NaBH4 (0.045 g, 1.2 mmol, 20% excess), and [2-(Me2NCH2)C6H4](Me)SnCl2 (0.146 g, 0.430 mmol). For compounds 4–6, the product was extracted in toluene, instead of dichloromethane. Yield: 0.177 g (67%). M.p. 53 °C. Elemental anal., calcd. for C20H29N5Se2Sn (MW 616.12): C 38.99, H 4.74, N 11.37%; found: C 38.72, H 4.87, N 11.55%. 1H NMR, δ: 0.96 (s, 3H, SnCH3, 2J117SnH 63.2, 2J119SnH 66.5 Hz), 2.24 (s, 6H, CH2NCH3), 3.00–3.11 (m, 4H, CH2CH2Se), 3.56 (s, 2H, C6H4CH2N-H7), 4.26–4.35 (m, 4H, CH2CH2Se), 6.19 (t, 2H, pz-H9, 3JHH 1.9 Hz), 7.10–7.17 (m, 1H, C6H4-H3), 7.31–7.35 (m, 2H, C6H4-H4,5), 7.37 (d, 2H, pz-H8, 3JHH 2.1 Hz), 7.48 (d, 2H, pz-H10, 3JHH 2.0 Hz), 7.75–7.98 (m, C6H4-H6, 3JSnH 72.9 Hz); 13C{1H} NMR, δ: 1.58 (SnCH3, 1J117SnC 479.6, 1J119SnC 501.5 Hz), 19.41 (CH2CH2Se, 1JSeC 13.1, 2JSnC 63.8 Hz), 45.1 (CH2NCH3), 54.8 (CH2CH2Se, 2JSeC 11.7 Hz), 63.9 (Me2NCH2-C7, 3JSnC 27.9 Hz), 105.26 (pz-C9), 128.11 (C6H4-C3 + C6H4-C5), 129.43 (pz-C8), 130.2 (C6H4-C4, 4JSnC 14.2 Hz), 137.38 (C6H4-C6, 2JSnC 55.6 Hz), 138.41 (C6H4-C1), 139.5 (pz-C10), 142.97 (C6H4-C2, 2JSnC 36.9 Hz); 77Se{1H} NMR, δ: −163.6 (s, 1J117SnSe 1066.3, 1J119SnSe 1117.5 Hz); 119Sn{1H} NMR, δ: −74.2 (s, 1JSnSe 1116.4 Hz); ESI+ MS (MeOH), m/z (%): 443.99945 (100) [M-SeCH2CH2pz]+ (443.99954 calcd. for C15H22N3SeSn).

3.2.4. [2-(Me2NCH2)C6H4](nBu)Sn(SeCH2CH2pz)2 (5)

[2-(Me2NCH2)C6H4](nBu)Sn(SeCH2CH2pz)2 (5) was obtained from (pzCH2CH2)2Se2 (0.200 g, 0.572 mmol), NaBH4 (0.056 g, 1.51 mmol) and [2-(Me2NCH2)C6H4](nBu)SnCl2 (0.436 g, 1.144 mmol). The title compound was isolated as a colourless oil after separation by column chromatography, using a mixture of ethyl acetate and dichloromethane (1:1, v/v). Yield: 0.233 g (62%). Elemental anal., calcd. for C23H35N5Se2Sn (MW 658.20): C 41.97, H 5.36, N 10.34%; found: C 42.44, H 5.62, N 10.35%. 1H NMR, δ: 0.92 (t, 3H, SnCH2CH2CH2CH3, 3JHH 7.4 Hz), 1.34–1.43 (m, 2H, SnCH2CH2CH2CH3), 1.56–174 (m, 4H, SnCH2CH2CH2CH3), 2.26 (s, 6H, CH2NCH3), 3.01–3.12 (m, 4H, CH2CH2Se), 3.54 (2H, C6H4CH2N-H7), 4.29–4.38 (m, 4H, CH2CH2Se), 6.21 (t, 2H, pz-H9, 3JHH 2.1 Hz), 7.13–7.17 (m, 1H, C6H4-H3), 7.30–7.37 (m, 2H, C6H4-H4,5), 7.43 (d, 2H, pz-H8, 3JHH 2.2 Hz), 7.49 (d, 2H, pz-H10, 3JHH 1.6 Hz), 7.86–7.91 (m, 1H, C6H4-H6, 3JSnH 71.6 Hz); 13C{1H} NMR, δ: 13.8 (SnCH2CH2CH2CH3), 19.3 (CH2CH2Se, 1JSeC 14.4 Hz), 21.6 (CH2CH2CH2CH3), 24.1 (CH2CH2CH2CH3), 26.7 (CH2CH2CH2CH3), 45.3 (CH2NCH3), 54.7 (CH2CH2Se), 64.3 (Me2NCH2-C7), 105.2 (pz-C9), 127.9 (C6H4-C4), 128.5 (C6H4-C6), 129.9 (C6H4-C5), 130.3 (pz-C8), 137.4 (C6H4-C3), 139.4 (pz-C10), 140.7 (C6H4-C1), 143.3 (C6H4-C2); 77Se{1H} NMR, δ: −183.2 (s, 1J117SnSe 1317.4, 1J119SnSe 1375.5 Hz); 119Sn{1H} NMR, δ: −52.2 (s, 1JSnSe 1145.2 Hz); ESI+ MS (MeOH), m/z (%): 486.04759 (100) [M-SeCH2CH2pz]+ (486.04649 calcd. for C18H25N3SeSn).

3.2.5. [2-(Me2NCH2)C6H4](Ph)Sn(SeCH2CH2pz)2 (6)

[2-(Me2NCH2)C6H4](Ph)Sn(SeCH2CH2pz)2 (6) was isolated as a yellow oil from (pzCH2CH2)2Se2 (0.202 g, 0.580 mmol), NaBH4 (0.053 g, 1.43 mmol), and [2-(Me2NCH2)C6H4](Ph)SnCl2 (0.232 g, 0.580 mmol). Yield: 0.263 g (67%); elemental anal., calcd. for C25H31N5Se2Sn (MW 678.19): C 44.28, H 4.61, N 10.33%; found: C 44.72, H 4.62, N 10.44%. 1H NMR, δ: 1.88 (s, 6H, CH2NCH3), 2.87–3.03 (m, 4H, CH2CH2Se), 3.49 (s, 2H, C6H4CH2N-H7), 4.05–4.18 (m, 4H, CH2CH2Se), 6.12 (t, 2H, pz-H9, 3JHH 2.02 Hz), 7.14 (d, pz-H8, 3JHH 2.0 Hz), 7.14–7.17 (m, 1H, C6H4-H3), 7.35–7.44 (m, 5H, C6H5-Hm+p + C6H4-H4), 7.42 (d, 2H, pz-H10, 3JHH 1.8 Hz), 7.52–7.73 (m, 2H, C6H5-Ho, 2JSnH 71.3 Hz), 7.92–8.11 (m, 1H, C6H4-H6, 2JSnH 76.9 Hz); 13C{1H} NMR, δ: 19.6 (CH2CH2Se, 1JSeC 12.5 Hz), 45.2 (CH2NCH3), 54.6 (CH2CH2Se), 63.7 (Me2NCH2-C7), 105.1 (pz-C9), 128.19 (C6H4-C3), 128.27 (C6H4-C5), 128.88 (C6H5-Cm), 129.04 (C6H5-Cp), 129.07 (pz-C8), 129.16 (C6H4-C4), 129.78 (pz-C10) 130.3 (C6H4-Cp), 134.7 (C6H5-Co), 137.7 (C6H4-C6), 139.9 (C6H4-C1), 142.9 (C6H4-C2); 77Se{1H} NMR, δ: −182.4 (s, 1J117SnSe 1121.7, 1J119SnSe 1173.4 Hz; 119Sn{1H} NMR, δ: −107.2 (s, 1JSnSe 1171.5 Hz); ESI+ MS (MeOH), m/z (%): 506.01622 (100) [M-SeCH2CH2pz]+ (506.01519 calcd. for C20H24N3SeSn).

3.2.6. Synthesis of [2-(Me2NCH2)C6H4](nBu)SnCl(SeCH2CH2pz) (7)

To a yellow solution of (pzCH2CH2)2Se2 (0.200 g, 0.572 mmol) in 30 mL absolute ethanol, we added NaBH4 (0.047 g, 1.27 mmol) at ice bath temperature. A colourless solution was obtained within a few minutes. After the hydrogen release had subsided, ethanol was removed at reduced pressure, and then the remaining colourless solid was washed with hexane (3 × 5 mL), dried, and redissolved in ethanol. The obtained solution was added dropwise to a solution of [2-(Me2NCH2)C6H4](nBu)SnCl2 (0.436 g, 1.145 mmol) in ethanol (15 mL), and the stirring continued for 2 h. After the evaporation of ethanol, 20 mL of dry toluene was added. After removing the resulting solid by filtration, the solvent was removed under vacuum, and the remaining yellow oil was washed with hexane (3 × 5 mL) and dried at reduced pressure. Yield: 0.233 g (54%). Elemental anal., calcd. for C18H28ClN3SeSn (MW 519.56): C 41.61, H 5.43, N 8.09%; found: C 42.37, H 5.78, N 8.24%. 1H NMR, δ: 0.93 (t, 3H, SnCH2CH2CH2CH3, 3JHH 7.2 Hz), 1.37–1.50 (m, 2H, SnCH2CH2CH2CH3), 1.58–176 (m, 2H, SnCH2CH2CH2CH3), 1.80–1.90 (m, 2H, CH2CH2CH2CH3), 2.23 (s, 3H, CH2NCH3), 2.45 (s, 3H, CH2NCH3), 3.08–3.27 (m, 2H, CH2CH2Se), AB spin system, with δA 3.35 and δB 3.99 (2H, C6H4CH2N-H7, 2JHH 13.1 Hz), 4.19–4.33 (m, 2H, CH2CH2Se), 6.15 (t, 2H, pz-H9, 3JHH 2.1 Hz), 7.12–7.22 (m, 1H, C6H4-H3), 7.25 (d, 2H, pz-H8, 3JHH 2.2 Hz), 7.35–7.44 (m, 2H, C6H4-H4,5), 7.45 (d, 2H, pz-H10, 3JHH 1.6 Hz), 8.11–8.34 (m, 1H, C6H4-H6, 3JSnH 74.3 Hz); 13C{1H} NMR, δ: 13.8 (SnCH2CH2CH2CH3), 20.1 (CH2CH2Se, 1JSeC 17.4 Hz), 24.14 (CH2CH2CH2CH3), 26.6 (CH2CH2CH2CH3, 2J117SnC 104.1, 2J119SnC 110.7 Hz), 28.35 (CH2CH2CH2CH3, 3JSnC 36.7 Hz), 44.7 (CH2NCH3), 46.1 (CH2NCH3), 54.58 (CH2CH2Se, 2JSnC 8.9 Hz), 64.2 (Me2NCH2-C7, 3JSnC 30 Hz), 105.1 (pz-C9), 127.4 (C6H4-C6, 2JSnC 65.2 Hz), 128.6 (C6H4-C5, 3JSnC 74.5 Hz), 129.7 (pz-C8), 130.4 (C6H4-C4, 4JSnC 14.0 Hz), 137.6 (C6H4-C3, 3JSnC 50.6 Hz), 139.4 (pz-C8), 139.8 (C6H4-C1), 141.9 (C6H4-C2, 2JSnC 43.3 Hz); 77Se{1H} NMR, δ: −160.9 (s, 1J117SnSe 1317.4, 1J119SnSe 1374.9 Hz); 119Sn{1H} NMR, δ: −104.6 (s, 1JSeSn 1374.4 Hz). ESI+ MS (MeOH), m/z (%): 486.04744 (100) [M-SeCH2CH2pz]+ (486.04649 calcd. for C18H25N3SeSn).

3.2.7. Synthesis of [2-(Me2NCH2)C6H4](Me)Sn(SCN)2 (8)

A solution of KSCN (0.486 g, 5.00 mmol) in 25 mL methanol was added to [2- (Me2NCH2)C6H4](Me)SnCl2 (0.847 g, 2.500 mmol) in dichloromethane (20 mL), at room temperature, and the reaction mixture was stirred for 3 h. The solvent was removed in vacuum, and the remaining solid was treated with CH2Cl2 (25 mL). KCl was separated by filtration, and the solvent was removed at reduced pressure. The resulting colourless solid was washed with n-hexane (3 × 5 mL). Yield: 0.816 g (85%); M.p. 150 °C; elemental anal., calcd. for C12H15N3S2Sn (MW 384.11): C, 37.52, H, 3.94, N, 10.94%, found: C, 37.77, H, 4.12, N, 11.12%. 1H NMR, δ: 1.12 (s, 3H, SnCH3, 2J117SnH 78.7, 2J119SnH 82.3 Hz), 2.47 (s, 6H, CH2NCH3), 3.78 (s, 2H, C6H4CH2N-H7), 7.18–7.31 (m, 1H, C6H4-H3, 4JSnH 34.8 Hz), 7.43–7.54 (m, 2H, C6H4-H4,5), 7.83–8.10 (m, 1H, C6H4-H6, 3JSnH 90.1 Hz); 13C{1H} NMR, δ: 2.4 (br., SnCH3), 45.2 (CH2NCH3), 63.32 (Me2NCH2-C7, 3JSnC 44.7 Hz, 127.7 (C6H4-C6, 2JSnC 78.8 Hz), 129.5 (C6H4-C5, 3JSnC 96.2 Hz), 132.0 (C6H4-C4, 4JSnC 15.7 Hz), 134.7 (br., C6H4-C2), 136.8 (C6H4-C3, 3JSnC 62.4 Hz), 140.9 (C6H4-C1, 1JSnC 55.2 Hz), 143.50 (br., NCS). 119Sn{1H} NMR, δ: −252.7 (s, br.); ESI+ MS (MeOH), m/z (%):326.99719 (100) [M-SCN]+ (m/z 326.99724 calcd. for C11H15N2SSn), 136.11211 (44) [2-(Me2NCH2)C6H4].

3.2.8. Synthesis of [2-(Me2NCH2)C6H4](Me)Sn(SCN)(SeCH2CH2pz) (9)

To a solution of (pzCH2CH2)2Se2 (0.132 g, 0.379 mmol) in 20 mL degassed absolute ethanol, NaBH4 (0.032 g, 0.834 mmol) was added at ice bath temperature. Afterwards, the solvent was removed, and the remaining colourless solid was washed with n-hexane (3 × 5 mL). After redissolution in ethanol, the obtained solution was added dropwise to a solution of [2-(Me2NCH2)C6H4](Me)Sn(SCN)2 (0.291 g, 0.758 mmol) in ethanol (10 mL), and the stirring continued overnight. The next day, ethanol was removed at reduced pressure, and 20 mL of dry toluene was added. The solid residue was separated by filtration, and, from the clear solution, the solvent was removed under vacuum. The obtained colourless solid product was washed with n-hexane (3 × 5 mL). Yield: 0.265 g (70%); M.p. 75 °C; elemental anal., calcd. for C16H22N4SSeSn (MW 500.11): C, 38.43, H, 4.43, N, 11.20%, found: C, 38.22, H, 4.14, N, 11.38%. 1H NMR (20 °C), δ: 1.01 (s, 3H, SnCH3, 2J117SnH 71.3, 2J119SnH 74.6 Hz), 2.34 (s, br., 6H, CH2NCH3), 3.06–3.25 (m, 2H, CH2CH2Se), 3.66 (v.br., 2H, C6H4CH2N-H7), 4.26–4.34 (m, 2H, CH2CH2Se), 6.18 (t, 2H, pz-H9, 3JHH 2.0 Hz), 7.12–7.25 (m, 1H, C6H4-H3), 7.41 (d, 1H, pz-H8, 3JHH 2.1 Hz), 7.40–7.48 (m, 2H, C6H4-H4,5), 7.46 (d, 1H, pz-H10, 3JHH 1.8 Hz), 7.9–8.1 (m, 1H, C6H4-H6, 3JSnH 78.1 Hz). 1H NMR (−50 °C), δ: 1.04 (s, 3H, SnCH3, 2J117/119SnH 74.3 Hz), 2.26 (s, 3H, CH2NCH3), 2.49 (s, 3H, CH2NCH3), 3.01–3.20 (m, 2H, CH2CH2Se), AB spin system with δA 3.47 and δB 3.94 (2H, C6H4CH2N-H7, 2JHH 14.1 Hz), 4.28–4.38 (m, 2H, CH2CH2Se), 6.21 (br., 1H, pz-H9), 7.18–7.27 (m, 1H, C6H4-H3), 7.33 (d, 1H, pz-H8, 3JHH 2.1 Hz), 7.44–7.50 (m, 2H, C6H4-H4,5), 7.51 (br., 1H, pz-H10), 7.9–8.1 (m, 1H, C6H4-H6, 3JSnH 76.5 Hz).13C{1H} NMR (20 °C), δ: 1.42 (SnCH3, 1J117SnC 568.3, 1J119SnC 595.3 Hz), 19.9 (CH2CH2Se, 1JSeC 20.7 Hz), 45.2 (br., CH2NCH3), 54.3 (CH2CH2Se, 2JSeC 13.6 Hz), 63.8 (Me2NCH2-C7, 3JSnC 38.6 Hz), 105.4 (pz-C9), 127.44 (C6H4-C3, 3JSnC 69.2 Hz), 129.1 (C6H4-C5), 130.1 (pz-C8), 131.0 (C6H4-C4, 4JSnC 14.7 Hz), 136.9 (C6H4-C6, 2JSnC 47.7 Hz), 137.0 (C6H4-C1), 139.6 (pz-C10), 141.4 (C6H4-C2). The resonance for (SCN) was not observed; 77Se{1H} NMR (20 °C), δ: −167.1 (s, 1J117SnSe 1353.7, 1J119SnSe 1422.3 Hz); 119Sn{1H} NMR (20 °C), δ: −161.8 (br., 1JSeSn 1427.1); ESI+ MS (MeOH): m/z (%) 443.99915 (100) [M-SCN]+ (443.99954 calcd. for C15H20N3SeSn).

3.2.9. Synthesis of Sn(SeCH2CH2pz)2 (10)

To a solution of (pzCH2CH2)2Se2 (0.302 g, 0.867 mmol) in absolute ethanol, NaBH4 (0.078 g, 2.11 mmol) was added. Subsequently, SnCl2 (0.164 g, 0.867 mmol) was added. The mixture was stirred for 2 h under argon. Then, EtOH was removed under vacuum, and the compound was redissolved in toluene. The remaining solid residue was separated by filtration, and, from the clear solution, the solvent was removed at reduced pressure. The title compound resulted in a yellow solid. Yield: 0.169 g (42%); M.p. 195 °C. Elemental anal., calcd. for C10H14N4Se2Sn (MW 466.90): C, 25.73, H, 3.02, N, 12.00%, found: C, 25.54, H, 3.48, N, 11.89%. 1H NMR, δ: 3.18–3.39 (m, 4H, CH2CH2Se), 4.39–4.52 (m, 4H, CH2CH2Se), 6.23 (t, 2H, pz-H2, 3JHH 2.1 Hz), 7.43 (d, 2H, pz-H1, 3JHH 2.1 Hz), 7.53 (d, 2H, pz-H3, 3JHH 1.6 Hz); 13C{1H} NMR, δ: 23.0 (CH2CH2Se, 1JSeC 19.5 Hz), 54.0 (CH2CH2Se, 2JSeC 16 Hz), 105.7 (pz-C2), 129.9 (pz-C1), 140.1 (pz-C3); 77Se{1H} NMR, δ: −11.5 (s, 1J117SnSe 1447.1, 1J119SnSe 1513.5 Hz); 119Sn{1H} NMR, δ: −167.6 (s, 1JSeSn 1511.4 Hz); ESI+ MS (MeOH), m/z (%):293.03705 (100) [M-SeCH2CH2pz]+ (293.87127 calcd. for C5H7N2SeSn), 174.97684 (38) [SeCH2CH2pz]+.

3.3. Crystal Structure Determination

Single crystals suitable for X-ray diffraction were obtained by slow diffusion from a mixture of solvents, namely CH2Cl2/n-hexane (1:3 ν/ν), for {[2-(Me2NCH2)C6H4](Me)SnSe}2 (4-a), [2-(Me2NCH2)C6H4](nBu)Sn(NCS)2 (8), and [2-(Me2NCH2)C6H4]2(Me)Sn(NCS)(SeCH2CH2pz) (9), while single crystals of {[2-(Me2NCH2)C6H4](nBu)SnSe}2 (5-a) were formed in the NMR tube from a CDCl3 solution of 5. Details of the crystal structure determination and refinement are given in the Supporting Information (SI), Tables S1 and S2. The data were collected on a Bruker D–8 Venture diffractometer, using graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) from a IµS 3.0 microfocus source with multilayer optics, at 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 APEX3 Software Package was used [69]. Intermolecular secondary bonding interactions were found with PLATON [62,63]. The drawings were created with the Diamond programme [70]. CCDC 2429261, 2429262, 2429264, and 2429265 contain the supplementary crystallographic data for compounds 4-a, 5-a, 8, and 9, respectively. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif (accessed on 12 March 2025).

4. Conclusions

The diorganotin(IV) bis(organoselenolates) RR′Sn(SeCH2CH2pz)2 [R = R′ = nBu (2), Ph (3); R = 2-(Me2NCH2)C6H4, R′ = Me (4), nBu (5), Ph (6)], [2-(Me2NCH2)C6H4](nBu)SnCl(CH2CH2Se) (7), [2-(Me2NCH2)C6H4](Me)Sn(NCS)2 (8), and [2-(Me2NCH2)C6H4](Me)Sn(NCS)(CH2CH2Se) (9), as well as the tin(II) complex Sn(SeCH2CH2pz)2 (10), were prepared and structurally characterized in solution and in solid state. The 119Sn and the 77Se NMR spectra showed only one resonance for each compound, accompanied by 1JSeSn and 1JSnSe coupling constants, thus suggesting that the organoselenolato ligands behave as monodentate κSe moieties. The 1H and the 13C NMR spectra gave no clear evidence of C,N-coordination behaviour of the 2-(Me2NCH2)C6H4 group at room temperature, except for compound 7, while a VT 1H NMR experiment for compound 9 revealed intramolecularly coordinated Me2NCH2 pendant arms at low temperatures. The ESI+/APCI+ HRMS spectra showed the base peak for the cations [RR′Sn(SeCH2CH2pz)]+ resulting from ionization.
Single-crystal X-ray diffraction studies evidenced the C,N-chelating behaviour of the 2-(Me2NCH2)C6H4 group in the dimeric species 4-a and 5-a, resulted from the formal elimination of Se(CH2CH2pz)2 among each two molecules of 4 and 5, respectively. The C,N-chelating behaviour of the 2-(Me2NCH2)C6H4 group was observed in the solid state structures of 8 and 9 as well.
Based on the 1JSnC coupling constant in the 13C NMR spectrum of 2, we could assign a distorted tetrahedral coordination geometry about the tin atom in solution, and we can assume a similar coordination geometry for compound 3, both being liquids at room temperature. For the compounds bearing a 2-(Me2NCH2)C6H4 group attached to tin, based on the NMR spectra, we assume a temperature dependent dynamic process in solution which involves decoordination, inversion at nitrogen, and re-coordination to tin. The single-crystal molecular structure of compounds 4-a, 5-a, 8, and 9 are consistent with hypercoordinated 10-Sn-5 species.
Preliminary thermogravimetric experiments showed that the solid species 4, 8, 9, and 10 might be considered as potential molecular precursors for tin chalcogenides, mostly in CVD processes, due to their high volatility. Further investigations are necessary to establish the thermal behaviour of these molecular species.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/molecules30071648/s1: NMR spectra (Figures S1–S8), Single-crystal X-ray structures (Figures S9–S15), Thermogravimetric analysis data (Figures S16 and S17), and Crystallographic data (Tables S1 and S2). Supplementary Material corresponding to the X-ray structure has been deposited in the CCDC as CCDC 2429261, 2429262, 2429264, and 2429265 (see Section 3.3).

Author Contributions

Conceptualization, A.S.; methodology, A.S., R.A.B., and M.D.; validation, A.S. and M.D.; formal analysis, A.S., M.T., R.A.B., and M.D.; investigation, A.S., M.T., R.A.B., and M.D.; resources, A.S.; writing—original draft preparation, A.S. and R.A.B.; writing—review and editing, A.S., supervision, A.S.; project administration, A.S.; funding acquisition, A.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Romanian Ministry of Education and Research (UEFISCDI) through the grants PN-III-P4-ID-PCE-2020-1028 and PN-IV-P1-PCE-2023-0966.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Original experimental data not provided in the Supplementary Information are available from the authors on request.

Conflicts of Interest

The authors declare no conflict of interest.

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Molecules 30 01648 sch001
Scheme 1. Synthesis of the tin complexes.
Scheme 1. Synthesis of the tin complexes.
Molecules 30 01648 sch001
Molecules 30 01648 g001
Figure 1. 77Se{1H} (a) and 119Sn{1H} (b) resonances for compound 2.
Figure 1. 77Se{1H} (a) and 119Sn{1H} (b) resonances for compound 2.
Molecules 30 01648 g001
Molecules 30 01648 g002
Figure 2. Thermal ellipsoid representation of a dimeric unit in compound 4-a. Hydrogen atoms are omitted for clarity. Symmetry equivalent positions (-x,1-y,-z) are given by “prime”.
Figure 2. Thermal ellipsoid representation of a dimeric unit in compound 4-a. Hydrogen atoms are omitted for clarity. Symmetry equivalent positions (-x,1-y,-z) are given by “prime”.
Molecules 30 01648 g002
Molecules 30 01648 g003
Figure 3. Thermal ellipsoid representation of molecule a in compound 8. Hydrogen atoms are omitted for clarity.
Figure 3. Thermal ellipsoid representation of molecule a in compound 8. Hydrogen atoms are omitted for clarity.
Molecules 30 01648 g003
Molecules 30 01648 g004
Figure 4. Thermal ellipsoids representation of a molecule in compound 9. Hydrogen atoms, except that one involved in the intramolecular interaction, are omitted for clarity.
Figure 4. Thermal ellipsoids representation of a molecule in compound 9. Hydrogen atoms, except that one involved in the intramolecular interaction, are omitted for clarity.
Molecules 30 01648 g004
Molecules 30 01648 sch002
Scheme 2. Numbering scheme for NMR assignments.
Scheme 2. Numbering scheme for NMR assignments.
Molecules 30 01648 sch002
Table 1. 1J119SnC coupling constant, and calculated C–Sn–C angle in solution, for compound 2.
Table 1. 1J119SnC coupling constant, and calculated C–Sn–C angle in solution, for compound 2.
Compound13C{1H} NMR
1J(119Sn,13C)C–Sn–C
2341.4106.7° a
108.8° b
a 1J = 11.4θ–875; b 1J = 9.99θ–746.
Table 2. 77Se and 119Sn NMR resonances for compounds 1–10 and the starting RR′SnCl2.
Table 2. 77Se and 119Sn NMR resonances for compounds 1–10 and the starting RR′SnCl2.
Cpd.δ77Se
(ppm)		1J117SnSe/1J119SnSe
(Hz)		δ119Sn
(ppm)		1JSe119Sn
(Hz)		RR′SnCl2δ119Sn
(ppm)
1292.1 [25]-----
2−177.71177.1 (117Sn)
1232.2 (119Sn)		79.91231.9nBu2SnCl2126.3 [50]
3−182.31261.7 (117Sn)
1321.3 (119Sn)		−23.51320.3Ph2SnCl2−26.7 [51]
4−163.61066.3 (117Sn)
1117.5 (119Sn)		−74.21116.4R′MeSnCl2−97.3 [52,53]
5−161.01317.4 (117Sn)
1375.5 (119Sn)		−104.81380.5R′nBuSnCl2−103 [37]
6−182.41121.7 (117Sn)
1173.4 (119Sn)		−107.21171.5R′PhSnCl2−170 [54]
7−160.91317.4 (117Sn)
1374.9 (119Sn)		−104.61374.4R′nBuSnCl2−103
8 −252.7 R′MeSnCl2−97.3
9−167.11353.7 (117Sn)
1422.3 (119Sn)		−161.81427.1R′MeSn(SCN)2−252.7
10−11.51447.1 (117Sn)
1513.5 (119Sn)		−167.61511.4
Table 3. Important interatomic distances and bond angles in 4-a, 5-a, and 9.
Table 3. Important interatomic distances and bond angles in 4-a, 5-a, and 9.
Bond/Angle4-a5-a 9
Sn1–Se12.5033(3)2.5317(2)Sn1–Se12.5298(3)
Sn1–Se1′2.6545(3)2.6475(4)Sn1–N12.4110(3)
Sn1–N12.5633(3)2.6046(2)Sn1–N22.2410(2)
Sn1–C12.1434(2)2.1528(1)Sn1–C12.1231(2)
Sn1–C102.1365(2)2.1662(1)Sn1–C102.1202(2)
Se1–Se1′3.7960(4)3.8025(5)N2–C111.1354(1)
Sn1–Sn1′3.4952(4)3.5183(4)S1–C111.6273(2)
Se1–Sn1–Se1′94.73(1)94.45(1)N1–Sn1–Se189.85(1)
N1–Sn1–Se188.60(1)87.11(1)C1–Sn1–Se1114.92(1)
N1–Sn1–Se1′173.16(1)172.01(6)C1–Sn1–C10127.58(1)
N1–Sn1–C173.83(1)72.89(1)C10–Sn1–Se1116.46(1)
N1–Sn1–C1085.76(1)84.82(1)N2–Sn1–Se193.37(1)
C1–Sn1–Se1114.27(1)111.92(1)N2–Sn1–C192.91(1)
C1–Sn1–Se1′99.35(1)99.30(7)N2–Sn1–C1093.86(1)
C1–Sn1–C10124.23(1)123.22(1)N2–Sn1–N1169.64(1)
C10–Sn1–Se1116.50(1)118.42(1)N2–C11–S1179.09(1)
C10–Sn1–Se1′98.05(1)101.23(7)
Sn1–Se1–Sn1′85.27(1)85.55(1)
Table 4. Important interatomic distances and bond angles in 8.
Table 4. Important interatomic distances and bond angles in 8.
Bond/Angle8a 8b
Sn1–N12.3926(1)Sn2–N42.3804(1)
Sn1–N22.1183(1)Sn2–N52.1567(1)
Sn1–N32.1874(1)Sn2–N62.1848(1)
Sn1–C12.1082(1)Sn2–C132.1178(1)
Sn1–C102.1075(1)Sn2–C222.1051(1)
N2–C111.1460(1)N5–C231.1615(1)
N3–C121.1605(1)N6–C241.1229(1)
S1–C111.6094(1)S3–C231.6159(1)
S2–C121.6241(1)S4–C241.6229(1)
Sn1′–S33.2876(6)Sn2–S23.1441(7)
N1–Sn1–N286.74(1)N4–Sn2–N584.37(1)
N1–Sn1–N3170.38(1)N4–Sn2–N6167.92(1)
N2–Sn1–N388.58(1)N5–Sn2–N687.47(1)
N1–Sn1–C177.63(1)N4–Sn2–C1376.63(1)
N1–Sn1–C1094.07(1)N4–Sn2–C2293.64(1)
C1–Sn1–C10154.39(1)C13–Sn2–C22158.17(1)
N2–Sn1–C199.80(1)N5–Sn2–C1399.24(1)
N2–Sn1–C10103.91(1)N5–Sn2–C2299.18(1)
N3–Sn1–C194.91(1)N6–Sn2–C1395.97(1)
N3–Sn1–C1095.22(1)N6–Sn2–C2296.45(1)
N2–C11–S1177.35(1)N5–C23–S3178.85(1)
N3–C12–S2179.23(1)N6–C24–S4179.58(1)
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Tamas, M.; Butuza, R.A.; Dan, M.; Silvestru, A. Diorganotin(IV) Complexes of Organoselenolato Ligands with Pyrazole Moieties—Synthesis, Structure and Properties. Molecules 2025, 30, 1648. https://doi.org/10.3390/molecules30071648

AMA Style

Tamas M, Butuza RA, Dan M, Silvestru A. Diorganotin(IV) Complexes of Organoselenolato Ligands with Pyrazole Moieties—Synthesis, Structure and Properties. Molecules. 2025; 30(7):1648. https://doi.org/10.3390/molecules30071648

Chicago/Turabian Style

Tamas, Melinda, Roxana A. Butuza, Monica Dan, and Anca Silvestru. 2025. "Diorganotin(IV) Complexes of Organoselenolato Ligands with Pyrazole Moieties—Synthesis, Structure and Properties" Molecules 30, no. 7: 1648. https://doi.org/10.3390/molecules30071648

APA Style

Tamas, M., Butuza, R. A., Dan, M., & Silvestru, A. (2025). Diorganotin(IV) Complexes of Organoselenolato Ligands with Pyrazole Moieties—Synthesis, Structure and Properties. Molecules, 30(7), 1648. https://doi.org/10.3390/molecules30071648

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