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Keywords:

  • Chalcogen ligands;
  • Tin;
  • Octahedral complexes;
  • Crystal structure

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

The metathetical reactions between SnBr4 and Li2[E'C(PPh2E)2] in toluene produce the homoleptic tin(IV) complexes Sn[E′C(PPh2E)2]2 [E = E′ = S (1b); E = S, E′ = Se (1c)], which were isolated as red crystals and structurally characterized by X-ray crystallography. The metrical parameters of these octahedral complexes are compared with those of the all-selenium analog Sn[E′C(PPh2E)2]2 (E = E′ = Se, 1a), which was prepared previously by a different route.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

Three years ago we reported synthesis and X-ray crystal structure of the octahedral tin(IV) complex Sn[SeC(PPh2Se)2]2 (1a), which was obtained unexpectedly from the reaction of SnCl2 and TMEDA.Li[(H)C(PPh2Se)2] via a process that involves selenium-proton exchange as well as a redox transformation.1 The dianion [SeC(PPh2Se)2]2– in this complex represents a new class of trichalcogenido-centered PCP-bridged ligand. The potentially wide scope of these tridentate ligands in the coordination chemistry of both main group and transition metals led us to the development of the direct synthesis of the dilithium derivatives of analogous all-sulfur and mixed sulfur/selenium reagents Li2[E′C(PPh2S)2] (E′ = S, Se) by the reaction of the well-known Le Floch reagent Li2[C(PPh2S)2]2 with the appropriate chalcogen.3 To date the synthesis of the all-selenium analogue Li2[SeC(PPh2Se)2] has proved to be elusive because the generation of the selenium derivative of the Le Floch reagent, i.e. Li2[C(PPh2Se)2], via double deprotonation of H2C(PPh2Se)2 with organolithium reagents is accompanied by P–Se bond cleavage.4

Preliminary investigations of the metathetical reactions of the new reagents Li2[E′C(PPh2S)2] (E′ = S, Se) with main group metal or metalloid halides have produced heteroleptic complexes of indium(III) and tellurium(IV),5,6 which have been structurally characterized. Interestingly, redox behavior is observed in the corresponding reactions with CuCl2 which produce dinuclear CuI-CuI complexes of the oxidized ligand involving an elongated central chalcogen–chalcogen bond.7,8,9 In this short communication we describe the synthesis of the homoleptic tin (IV) complexes Sn[E′C(PPh2E)2]2 [E = E′ = S (1b); E = S, E′ = Se (1c)] via metathesis and we compare the solid-state structures of 1b and 1c with that of the all-selenium analog 1a.

Results and Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

Synthesis and NMR Spectra of Sn[E′C(PPh2E)2]2 [E = E′ = S (1b); E = S, E′ = Se (1c)]

The reaction of the in situ reagents [{Li(tmeda)}2{E′C(PPh2S)2}2] (E′ = S, Se) with SnBr4 in a 2:1 molar ratio in toluene produced 1b and 1c as red, air-stable solids in low (ca. 20 %) yields (Scheme 1). In both syntheses the 31P NMR spectra of reaction mixtures revealed the presence of the neutral precursor CH2(PPh2S)2 (δ = 35.5 ppm) and, in the case of 1c, the dianionic diselenide [{Li(tmeda)}{SeC(PPh2S)2}]2 (δ = 50.63), presumably formed via a competing redox process. The concomitant formation of these by-products undoubtedly accounts for the low isolated yields of 1b and 1c. For comparison, the synthesis of the previously reported all-selenium analogue [Sn{SeC(PPh2Se)2}2] (1a)1 by a different route is also illustrated in Scheme 1.

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Scheme 1. Synthesis of 1a, 1b, and 1c.

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Leung and co-workers have shown that the reaction of SnCl4 with the magnesium reagent MgC(PPh2S)2(THF)2 produces the tin(IV) complex Sn[C(PPh2S)2]2, in which the ligand is bonded in a tridentate (S, C,S) fashion to tin.10 Interestingly, in this work we isolated small amounts of complex 1b from the reaction of the dilithium reagent Li2[C(PPh2S)2] with SnBr4. The formation of 1b in this case may result from the insertion of sulfur (formed as a by-product) into the tin–carbon bonds of Sn[C(PPh2S)2]2; the preparation of monomeric lead(II) complexes of trichalcogenido PCP-bridged ligands Pb[E′C(PPh2S)2] (E′ = S, Se) via chalcogen insertion into Pb–C bonds has been reported previously by Leung et al.11

The 31P NMR spectra of 1b and 1c in CD2Cl2 show a single resonance at δ = 54.9 and 57.6 ppm, respectively, cf. δ = 61.6 for 1a in CD2Cl2. The values for 1b and 1c are deshielded in comparison with those of the corresponding dilithium complexes, [{Li(tmeda)}2{SC(PPh2S)2}] (δ = 44.0 ppm)3 and [{Li(tmeda)}2{SeC(PPh2S)2}] (δ = 43.5 ppm),3 and the heteroleptic indium(III) complexes (TMEDA)InCl[(S)C(PPh2S)2] (δ = 48.0 ppm)5 and (TMEDA)InCl[(Se)C(PPh2S)2] (δ = 48.4 ppm).5 The (31P, 117, 119Sn) coupling constants for 1b and 1c are 28.0 and 35.6 Hz. As was observed for 1a1 the 1H NMR spectra of 1b and 1c exhibited only the typical pattern for phenyl groups, and no signal for PC(H)P hydrogen was observed. The very low solubility of 1b and 1c in organic solvents precluded the acquisition of 119Sn and, in the case of 1c, 77Se NMR spectra. The reason for the poor solubility of 1b and 1c is not evident, since there are no significant intermolecular interactions in the solid-state structures (vide infra).

Crystal Structures of Sn[E′C(PPh2E)2]2 [E = E′ = S (1b); E = S, E′ = Se (1c)]

The structures of 1b and 1c were determined by single-crystal X-ray crystallography. Crystal data and structure refinement details are presented in Table 1. Compound 1b crystallizes in the centrosymmetric space group (C2/c), while 1c forms in the chiral space group (P21). The asymmetric unit of 1b contains half of the unit of 1b and a solvent dichloromethane molecule. In contrast, the molecule [Sn{SeC(PPh2S)2}2] and two toluene solvent molecules were present in the asymmetric unit of 1c. This difference is also reflected in the tin-bridged bond angles [S1–Sn1–S1 = 180.0°; S2–Sn1–S2 = 180.0°; S3–Sn1–S3 = 180.0° for 1b and Se2–Sn1–Se1 = 175.22(4)°; S1–Sn1–S3 = 175.15(8)°; S2–Sn1–S4 = 176.39(9)° for 1c].

Table 1. Crystal data and structure refinement details for 1b and 1c.
 1b·2CH2Cl21c·2C7H8
Empirical formulaC52H44Cl4P4S6SnC64H56Se2P4S4Sn
Formula weight1245.601353.82
Temperature /K123(2)123(2)
Wavelength /Å0.710730.71073
Crystal systemmonoclinicmonoclinic
Space groupC2/cP21
Unit cell dimensions  
a28.6520(3)15.5180(3)
b11.2320(3)11.3930(3)
c22.1870(5)16.2630(3)
β128.6350(10)91.2030(12)
V35577.5(2)2874.61(11)
Z42
Calculated density /g·cm–31.4831.564
Absorption coefficient /mm–11.0242.009
F(000)25201364
Crystal size /mm0.25 × 0.22 × 0.130.12 × 0.11 × 0.08
Limiting indices–36 ≤ h ≤ 36–19 ≤ h ≤ 19
 –14 ≤ k ≤ 14–14 ≤ k ≤ 14
 –28 ≤ l ≤ 27–20 ≤ l ≤ 20
Reflections collected/unique21039 / 6072 [R(int) = 0.0490]23331 / 12477 [R(int) = 0.0671]
Completeness to theta99.6 %99.8 %
Max. and min. transmission0.8784 and 0.78380.8558 and 0.7946
Refinement methodFull-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters6072 / 0 / 30412477 / 20 / 672
Goodness-of-fit on F21.1601.109
Final R indices  
R1, wR2 [I>2σ (I)]0.0526, 0.12040.0627, 0.1177
R1, wR2 (all data)0.0616, 0.12510.0793, 0.1277
Largest diff. peak and hole /e·Å31.319 and –0.8931.187 and –0.565

The molecular structures of 1b and 1c are shown in Figure 1 and Figure 2, respectively, and the structural parameters for 1b, 1c, and the previously reported complex 1a are compared in Table 2. All three complexes are comprised of a central tin atom that is coordinated to two tridentate (E,E′,E) ligands. The arrangement around the tin atom is octahedral with coordination environments SnSe6 for 1a, SnS6 for 1b, and SnS4Se2 for 1c. Small distortions result from the disparity in the Sn–E′(C) and Sn–E(P) distances; the former are shorter by ca. 0.20 Å for 1b (E = E′ = S) and ca. 0.17 Å for 1a (E = E′ = Se). The mean Sn–S(P) distances in 1b and 1c are essentially equal [2.650(1) versus 2.662(2) Å] as are the Sn–Se(C) bond lengths in complexes 1a [2.637(1) Å] and 1c [2.601 (1) Å]; the latter are comparable to the value of 2.5917(3) Å found for hexacoordinate complex [{(C5H4N)Se}2SnCl2].12 The C–S bond length of 1.771(4) Å in 1b is significantly shorter in comparison with those of the main group metal complexes of the same ligand, i.e. (TMEDA)InCl[(S)C(PPh2S)2] [1.803(7) Å]5 and [Pb{SC(PPh2S)2}] [1.801(8) Å],11 but longer with respect to the value 1.732(11) Å reported for [TeBr2{SC(PPh2S)2}] [1.732(11) Å].6 The C–Se bond lengths of 1a [1.929(6) Å] and 1c [1.911(8) Å] are within the range of values found for other complexes of the mixed chalcogen ligand, cf. [Pb{SeC(PPh2S)2}] [1.917(1) Å],11 (TMEDA)InCl[(Se)C(PPh2S)2] [1.938(9) Å],5 and [{Li(TMEDA)}2{SeC(PPh2S)2}] [1.970(3) Å].3

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Figure 1. Molecular structure of 1b. Solvent dichloromethane molecules and hydrogen atoms of phenyl groups are omitted for the sake of clarity.

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Figure 2. Molecular structure of 1c. Solvent toluene molecules and hydrogen atoms of phenyl groups are omitted for the sake of clarity.

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Table 2. Selected bond lengths /Å and angles /° for 1a1c.
 
  1. a

    a) Data taken from reference1. b) The use of E′ and E′′ indicates the inequivalent Se atoms bonded to carbon in 1c.

 E = E′ = Se (1a) a)E = E′ = S (1b)E = S; E′ = Se (1c) b)
Sn1–E12.812(1)2.6350(10)2.658(2)
Sn1–E22.810(1)2.6650(10)2.656(2)
Sn1–E32.662(3)
Sn1–E42.672(2)
Sn1–E2.637(1)2.4456(10)2.6012(11)
Sn1–E′'2.6011(11)
P1–E12.181(2)2.0270(15)2.015(3)
P2–E22.187(2)2.0150(14)2.022(3)
P3–E32.019(3)
P4–E42.022(3)
C1–E1.929(6)1.771(4)1.916(8)
C26–E′′1.906(8)
P1–C11.749(6)1.750(4)1.727(10)
P2–C11.749(5)1.750(4)1.757(8)
P3–C261.764(9)
P4–C261.734(8)
    
P1–C1–P2123.1(3)119.4(2)121.0(5)
P3–C26–P4119.0(4)
P1–C1–E108.3(4)107.9(2)108.2(4)
P2–C1–E109.4(3)107.6(2)107.2(5)
P3–C26–E′′107.2(4)
P4–C26–E′′109.4(4)
P1–E1–Sn194.61(5)95.10(5)108.2(4)
P2–E2–Sn194.33(5)93.88(4)107.2(5)
P3–E3–Sn1107.2(4)
P4–E4–Sn1109.4(4)
C1–E′–Sn194.01(17)96.46(13)92.1(3)
C26–E′′–Sn192.9(3)

The disparity between the P–S and P–C bond lengths is insignificant when the chalcogen changes from sulfur to selenium in the complexes [Sn{E′C(PPh2S)2}2] [2.0261(1) (1b), 2.020(3) (1c) Å and 1.750(4) (1b), 1.745(9) (1c) Å, respectively]. As expected, these metrical parameters are longer and shorter, respectively, in comparison with the corresponding distances in the parent molecule CH2(PPh2S)2 [1.9506(9) and 1.825(2) Å].13

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

Metathetical reactions can be used to generate the tin(IV) complexes of dianionic trichalcogenido PCP-bridged ligands 1b and 1c, which allow a structural comparison of their octahedral architectures with that of the known all-selenium complex 1a. Although heteroleptic complexes with InIII5 and TeIV,6 as well as monomeric PbII derivatives,11 were previously known, the SnIV examples 1b and 1c represent the first homoleptic complexes of these interesting ligands with p-block metals or metalloids. However, the low isolated yields and detection of the diselenide [{Li(tmeda)}{SeC(PPh2S)2}]2 among the by-products signals the concomitant occurrence of redox reactions as has been observed for reactions of the dianions [E′C(PPh2S)2]2– (E′ = S, Se) with CuCl2.7,8,9

Experimental Section

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

General Procedures: All reactions and manipulations were carried out in an argon atmosphere by using standard Schlenk techniques. Solvents were dried with and distilled from CaH2 (CH2Cl2) and Na/benzophenone (toluene). MeLi (1.6 M in Et2O), potassium hydride, CH2(PPh2)2, tin(IV) bromide, selenium and sulfur powder were purchased from Aldrich Chemical Co. and used without further purification. Elemental analyses were performed by the Analytical Services Laboratory, Department of Chemistry, University of Calgary.

Spectroscopic Methods: 1H, 13C, and 31P NMR spectra were recorded with Bruker 400 spectrometers. The chemical shifts were referenced externally to 85 % H3PO4 (δ = 0 ppm) for 31P nucleus and Me4Si (δ = 0 ppm) for 1H and 13C nuclei, respectively.

Synthesis of Sn[E'C(PPh2E)2]2 [E = E′ = S (1b); E = S, E′ = Se (1c)]: One equivalent of chalcogen (0.021 g of sulfur or 0.053 g of selenium; 0.66 mmol) in toluene (5 mL) was slowly added to in situ-generated [{Li(tmeda)}2{C(PPh2S)2}] (0.67 mmol)2 (prepared from 0.30 g of [CH2(PPh2S)2]; 0.84 mL of 1.6 M MeLi in Et2O; 0.155 g of tmeda) in toluene at –78 °C. The mixture was stirred for 10 min at –78 °C and further at 23 °C for 1 h. The resulting solution of [{Li(tmeda)}2{E′C(PPh2S)2}2] (E′ = S, Se) was slowly transferred by cannula into a flask containing stannic bromide (0.146 g, 0.33 mmol) at –78 °C and this mixture was stirred at ambient temperature for 12 h. A red insoluble solid was separated from the yellow solution by filtration. The crude red solid was washed twice with toluene (10 mL) and extracted with dichloromethane (50 mL) to remove lithium bromide. Crystalline samples were obtained by diffusion of toluene into dichloromethane solutions to give 1b (0.084 g, 23 %) and 1c (0.069 g, 18 %).

Characterization Data for 1b·C7H8: After recrystallization from toluene: C57H48P4S6Sn: calcd. C 58.62; H 4.12 %; found: C, 59.25; H, 4.58 %. 31P NMR (400 MHz, CD2Cl2, 25 °C): δ = 54.94 [s, 2, 3J(31P, 117, 119Sn) = 28.0 Hz]. 1H NMR (400 MHz, CD2Cl2, 25 °C): δ = 8.22–8.14 (m, 8 H, Ph), 7.56–7.66 (m, 8 H, Ph), 6.99–7.28 (m, 16 H, Ph), 6.87–6.93 (m, 8 H, Ph). 13C NMR (400 MHz, CD2Cl2, 25 °C): δ = 125.8 (s), 128.5–129.0 (m, br), 129.6 (s), 131.8–132.1 (m), 132.3 (br., m), 133.2 (m, br) ppm.

Characterization Data for 1c: After washing with toluene, extraction with dichloromethane and pumping under vacuum for an extended period: C50H40P4S4Se2Sn: calcd. C 51.34; H 3.45 %; found: C, 50.93; H, 3.65 %. 31P NMR (400 MHz, CD2Cl2, 25 °C): δ = 57.55 [s, 2, 3J(31P, 117, 119Sn) = 28.0 Hz]. 1H NMR (400 MHz, CD2Cl2, 25 °C): δ = 8.24–8.17 (m, 8 H, Ph), 7.59–7.66 (m, 8 H, Ph), 6.99–7.40 (m, 16 H, Ph), 6.86–6.91 (m, 8 H, Ph) ppm.

X-ray Structure Determinations: X-ray quality crystals were grown by slow diffusion of toluene into a dichloromethane solution of 1b or 1c at –20 °C. Data were collected with a Nonius Kappa CCD diffractometer with use of monochromated Mo-Kα radiation (λ = 0.71073 Å) at 123 K. The structures were solved by direct methods using the program SHELXS-97 and refined with SHELXL-9714 and by full-matrix least-squares with anisotropic thermal parameters for the non-hydrogen atoms. In 1c, one of the carbon atoms of a phenyl group (C43) attached to phosphorus and the carbon atoms of solvent toluene molecules (C57–C59, and C63) were disordered over two positions which were fixed satisfactorily. Crystal data and structure refinement details are presented in Table 1.

Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies of the data can be obtained free of charge on quoting the depository numbers CCDC-964575 http://www.ccdc.cam.ac.uk/data_request/cif and CCDC-964576 http://www.ccdc.cam.ac.uk/data_request/cif for 1b and 1c (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

Financial support of this work by NSERC (Canada) is gratefully acknowledged.

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