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Keywords:

  • Copper(I) vinylsilane π;
  • complexes;
  • Crystal structure;
  • Thermal stability and kinetic lability

Abstract

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

Two new copper(I) olefin complexes, [Cu6Cl6(MTrVS)2] (1) and [Cu2Cl2(DMVSP)2] (2), of tridentate bridging methyltrivinylsilane (MTrVS) and bidentate chelating 2-[dimethyl(vinyl)silyl]pyridine (DMVSP) have been synthesized and characterized by single-crystal X-ray structure analysis, IR and 1H NMR spectroscopy. It has been shown that using the alkenylsilanes with required electronic properties, molecular symmetry and conformational flexibility, it is possible to control the formation of optimal copper(I) halide oligomers. The obtained results, together with relevant literature data, also illustrate how the coordination mode of vinylsilanes is related to Cu–(C=C) bond strengthening and, consequently, to stability of the organometallic compounds. In particular, we suggest that, together with Cu–Cα distance shortening accompanied by a segmentation of π-conjugated chelate ring, complex shows an increased lability to form probably an alkenylcopper intermediate in the homocoupling reaction of alkenyl(2-pyridyl)silanes. At the same time, no appreciable reduction of thermal stability of π-conjugated chelate complex 2 with respect to bridged compound 1 emerges.


Introduction

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

Copper(I)-alkenylsilane adducts are among the most versatile organometallic intermediates in the organosilicon chemistry.1 From a synthetic chemistry point of view, at least four facts attracted our attention. Firstly, the vinylsilanes can be obtained in good yields by reaction of perhalogenated alkylsilanes with powdered copper;2 secondly, the copper(I) catalyzes a highly regioselective synthesis of branched vinylsilanes;3 thirdly, the CuCl catalyzed three-component coupling reaction of allylsilanes, olefins and amines involves the migration of the C=C double bond to form vinylsilane derivatives.4 The fourth fact is that copper(I) chloride has proved to be successful to facilitate the transfer of silicon-substituted carbenes to a variety of alkenes and cycloalkenes including functionalized vinylsilanes. And this is particularly interesting because almost solely E-vinylsilanes were obtained in the presence of CuCl, whereas other catalysts gave mainly Z-alkenes.5 Thus, it cannot be excluded that intermediate CuI olefin complexes are formed in each case, and that Cu···(C=C)–Si conjugated systems are probably thermodynamically stable. On the other hand, vinylsilanes are excellent initial products that can undergo a variety of different transformations, including electrophilic substitution, metathesis, cross-coupling, homo-coupling and many others. So copper(I) chloride as a co-catalyst significantly increased the catalytic activity of ruthenium hydride complex in silylative coupling of vinylsiloxanes with styrene.6 Moreover, the reaction proceeded as above, with complete chemo- and stereoselectivity producing only E-silylstyrene. Also, copper(I) chloride was found to promote the homo-coupling reaction of unsaturated or aromatic organosilanes resulted in conjugated products including 1,3-dienes.7,8 Although it is suggested that this process occurs via transmetalation of organosilanes to afford organocopper species, there is no scientific consensus on the mechanism by which extended π-conjugated systems can be stabilized. Besides, multivinylsilicon compounds are even more often used for synthesis and subsequent reinforcement of elastomeric networks because they can be employed not only as initial polymers (polysiloxanes with regular9 or terminal10 vinyl groups), but also as crosslinking agents.11 And though there are many crosslinking methods, the hydrosilylation is one of the most convenient routes to cross-linked polymers. Copper(I) halide complexes are also used as a catalyst precursors for addition of Si–H groups across unsaturated bonds,12 but they still do not achieve the high productivity and selectivity observed for late transition metal-based hydrosilylation catalysts and definitely need to be improved.13

Thus, the unique properties of copper(I)-alkenylsilane systems provide a number of reasons to obtain and study the CuI olefin complexes. It has been over 40 years since Fitch et al. first showed that alkylvinylsilane-copper(I) chloride π complexes appear to be among the most stable olefin CuI adducts. This general feature does not seem to depend on low ligand volatility, but is most likely produced by an unusual bonding mode of unsaturated organosilicon compounds.14 Unfortunately, there is no common opinion concerning the nature of chemical interactions not only in such organometallic systems, but even in vinylsilicon ligands.15 For example, it is well known that hyperconjugation is more important for organoelement compounds than for their carbon analogues. Nevertheless, the relative contributions of conjugation and hyperconjugation to the decrease of free energy of these systems are uncertain. Until now, very little is known about the structural properties of these complexes. All the above-mentioned facts have encouraged us to direct our attention to the complexation of alkenylsilicon compounds by d10 metal atoms. We previously showed that a silicon atom acts as an amplifier of copper-olefin interaction to enhance the thermal stability of organometallic complexes.16 Undoubtedly, these effects will also depend upon the coordination mode of unsaturated silicon containing ligand: bridging or chelating. To examine how these structural differences are related to the Cu–(C=C) bond strengthening and consequently to functional properties of these organometallic compounds we have managed to prepare and characterize two new copper(I) chloride π complexes, [Cu3Cl3(MTrVS)] (1) and [Cu2Cl2(DMVSP)] (2), containing vinylsilanes, one of which, namely methyltrivinylsilane (MTrVS), cannot be involved in the stable CuI chelation and other one, 2-[dimethyl(vinyl)silyl]pyridine (DMVSP), is well capable of chelating metal ion to form the five-membered ring.

Results and Discussion

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

Synthesis and Characterization of CuCl Complexes

All organic compounds used in this work were available commercially and were employed in the process without further purification. The synthesis of complexes 1 and 2 was optimized to obtain single crystals suitable for X-ray diffraction analysis. Because of this, the yield of the title complexes dropped to about 41 % (1) and 14 % (2). While the complex 2 was prepared by simple dissolution of CuCl in an excess of TVMSP, the diffraction-quality crystals of 1 could be obtained only through redox reaction. The CuII reduction was probably carried out according to the following Scheme

  • equation image((1))

Here the tin ions act not only as reducing substance, but also as stabilizing agent to prevent premature precipitation of sparingly soluble copper(I) chloride complexes. To test the efficiency of the method, we recently applied it also to growing single crystals of CuCl complexes with tetravinylsilane and dimethyltetravinyldisiloxane.16 Due to the insolubility of complex 1, the deuterated chloroform solutions of CuCl and MTrVS in the molar ratios 1:1 and 2:1 were examined. But, with further increasing the CuCl content, the solution became turbid and a precipitate was formed. The ligands and organometallic compounds were characterized by 1H NMR, and FTIR spectroscopy. In all proton spectra the H-H coupling constants for vinyl protons increase in the expected order: 2Jgem << 3Jcis < 3Jtrans, but their changes caused by coordination with copper(I) are not always evident. Furthermore, the vinyl α proton has highest coordination induced shifts in both complexes. Finally, the minor chemical shift differences for vinyl protons in coordinated and free DMVSP were observed in deuterated dimethyl sulfoxide that suggest the solvent-ligand exchange.

Crystal Structure of [Cu6Cl6(MTrVS)2] (1)

As can be seen from Figure 1, the structure of 1 contains two different centrosymmetric clusters, Cu2Cl2 and Cu4Cl4, linked through π bridging molecules of MTrVS into an infinite zigzag chain. The running crosswise (along [1 1 1] and [1 1equation image 1]) one-dimensional metal-organic frameworks are arranged in a three-dimensional structure by both weak hydrogen bonds (Cl2···H21B' 2.89 Å, Cl2···C21' 3.796(3) Å, Cl2···H21B′–C2' 165.5°) and self-association of tetramers Cu4Cl4 in the [1 0 0] direction (Cu1···Cl1' 3.3288(7) Å). The occurrence of two different sources of separate CunCln species in the same structure points out that the cuprous halide clusters are highly prone to rearrangement depending on the coordination behavior and steric properties of an unsaturated ligand. For this reason, tetravinylsilane (TVS) bridges two Cu4Cl4 units in the structure of [Cu4Cl4(TVS)],16 whereas a lack of one of the vinyl groups does not allow self-assembling of Cu2Cl2 dimers in 1. On the other hand, tetraallylsilane (TAS), the molecule with a longer spacer arm, was found to be efficient for cross-linking and formation of four inter-Cu5Cl5-cluster bridges in the structure of complex [Cu5Cl5(TAS)].17 Thus, it becomes possible to design optimal copper(I) halide oligomers using the organic component with required electronic properties, molecular symmetry and conformational flexibility. For example, the Cu4Cl4 chair-like units show in 1 as well as in [Cu4Cl4(TVS)] the twisting conformation (torsion angles –164.8°, 78.1°, 15.5°, –100.7°) which is partly a result of excellent electron π-acceptor properties of vinylsilanes.16 Indeed, an increase in π*C=C [LEFTWARDS ARROW] dCu back bonding interaction promotes the planarity of the CuI coordination sphere, causing elongation of the Cu···Cl lateral bonds (see Cu2–Cl2 bond length in Table 1) and, consequently, distortion of chair-like tetranuclear clusters.

thumbnail image

Figure 1. Part of the infinite zigzag chain of 1. All hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at 50 % probability level.

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Table 1. Selected bond lengths /Å and angles /° for 1 and 2.
Bondlength /Åbond angle
  1. a

    a) mi is the middle of the Ci1=Ci2 bond.

Cu1–Cl12.2590(6)Cl1–Cu1–Cl2′101.13(2)
Cu1–Cl2′2.2774(6)Cl1–Cu1–m1129.31
Cu1–C112.042(2)Cl2′–Cu1–m1128.55
Cu1–C122.043(2)C11–Cu1–C1238.6(1)
Cu1–m1a)1.928Cl1–Cu2–Cl2′106.32(2)
Cu2–Cl1′2.2890(6)Cl1–Cu2–Cl291.45(3)
Cu2–Cl2′2.3004(6)Cl2′–Cu2–Cl286.16(3)
Cu2–Cl22.8103(7)Cl1–Cu2–m2128.32
Cu2–C212.059(2)Cl2′–Cu2–m2123.45
Cu2–C222.074(2)Cl2–Cu2–m2103.96
Cu2–m21.952C21–Cu2–C2238.3(1)
Cu3–Cl32.2611(9)Cl3–Cu3–Cl3′96.92(3)
Cu3–Cl3′2.2784(8)Cl3–Cu3–m3136.91
Cu3–C312.018(3)Cl3′–Cu3–m3126.13
Cu3–C322.045(3)C31–Cu3–C3239.0(2)
Cu3–m31.915  
C=C1.350(3)–1.356(3)C–Si1–C106.2(1)–113.6(1)
Si1–C1.850(3)–1.876(2)Si1–C=C125.0(2)–126.4(2)
Cu1–Cl12.2746(6)Cl1–Cu1–Cl1′97.32(2)
Cu1–Cl1′2.5143(6)Cl1–Cu1–N1106.29(5)
Cu1–N12.020(2)Cl1′–Cu1–N1100.22(5)
Cu1–C112.094(3)Cl1–Cu1–m1127.16
Cu1–C122.060(3)N1–Cu1–m1111.49
Cu1–m11.965Cl1′–Cu1–m1110.43
C11=C121.348(4)C11–Cu1–C1237.1(1)
Si1–C1.840(3)-C–Si1–C102.8(1)–
 1.884(2) 112.4(2)
N1–C1.337(2),Si1–C12=C11126.6(3)
 1.360(2)C1–N1–C5119.1(2)
Cpyr–Cpyr1.366(3)–1.378(3)N1–Cpyr–Cpyr119.6(2), 123.1(2)
  Cpyr–Cpyr–Cpyr118.1(2)–120.5(2)

The inorganic moiety of 1 is formed from three crystallographically independent copper(I) atoms, two of them (Cu1, Cu3) are very similar from the coordination point of view and possess a trigonal planar environment of two bridging chlorine atoms and C=C group of MTrVS molecule. The third copper atom (Cu2), contained in the tetramer, adopts trigonal pyramidal arrangement of olefin bond and three bridging chlorine atoms, one of which, Cl2, is situated in the apical position. For this reason, C=C bonds are slightly inclined with the respect to the Cl–Cl–m basal plane (m is the middle of C=C bond). And, the more the copper atom displacement out of this plane, Cu3 0.025 Å, Cu1 0.120 Å, Cu2 0.171 Å, the stronger is the C=C group inclination, 2.68°, 4.26°, 8.94° respectively.

Crystal Structure of [Cu2Cl2(DMVSP)2] (2)

According to the X-ray analysis, complex 2 has molecular structure and consists of dimeric units [Cu2Cl2(DMVSP)2] located around a crystallographic symmetry center (Figure 2). The introduction of 2-pyridyl group into vinylsilane moiety, as one would expect, favors the chelating behavior of these ligands and leads to the formation of five-membered chelate rings with metal ions. The copper atom is coordinated by two bridging chlorine atoms and one C=C,N-chelating DMVSP ligand to form a distorted tetrahedron (see Table 1). Thus, one chlorine atom (Cl1′) occupies the axial position resulting in shortening of the distance from the copper atom to the basal plane, Δ, to 0.467 Å. Because the copper–olefin interaction in 2 is weaker than that in 1, the C=C bond becomes shorter, whereas the Cu–m distance increases, reducing overall the C–Cu–C angle (Table 1). Nevertheless, the olefin group tends to align in the plane of basal ligands and the deviation from planarity does not exceed 0.012 Å.

thumbnail image

Figure 2. Molecular structure of 2. All hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at 50 % probability level.

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The pyridyl groups of two adjacent DMVSP molecules are involved in a face-to-face π–π stacking interaction with a centroid–centroid distance of 3.761(3) Å. This aromatic embrace between the complex molecules, lying across centers of inversion, is accompanied by a perfect alignment of pyridyl rings with zero offset distance and leads to 1D supramolecular chain of dimers running along [1 1 0]. Moreover, we assume that N-coordinated CuI atom could serve as a primary electron acceptor which amplifies an uneven charge distribution across pyridyl rings, thus facilitating the appearance of additional centers of symmetry by the above stacking interactions and, as a consequence, by close packing of molecules in the C-centered monoclinic cell.

Copper–Olefin Interaction and Complex Stability

The unequal Cu–C bond lengths found in the title compounds are similar to those reported for other η2-alkene complexes. But it is noteworthy that the α-carbon atom (next to silicon atom) in 2 is significantly closer to the metal atom than the β-carbon atom. The findings are contrary to the conventional view of lengthening of the Cu–Cα distance (d) as a steric hindrance effect of non-hydrogen substituent on the double bond. From these results it is possible to suggest that five-membered chelate ring is primarily responsible for the unusual geometry of Cu–(C=C) fragment. However, we did not find any evidence for this in the CSD database. On the contrary, three CuI complexes containing Cu–(C=C)–C–C–Y (Y = two-electron donor center) chelate unit were characterized by common geometric features, i.e. d(Cu–Cα) > d(Cu–Cβ). At the same time, two compounds with Cu–(C=C)–Si–C–Y chelate rings reported in CSD, [Cu2I2(2-(2-p-tolylvinyl)dimethylsilyl)pyridine)2] (3),18 and [Cu2Br2(2,2-dimethyl-2-silabut-3-enyldiphenylphosphine)2] (4),19 did not differ strongly from the title complex 2 according to the above mentioned parameters and showed the shortening of the Cu–Cα distance (see Table 2). Moreover, similar trends were observed in the case of even less strained sixe-membered chelate cycle Cu–(C=C)–C–Si–C–Y in complex [Cu2I2(2-(allyldimethylsilyl)pyridine)2].20 We believe that this unexpected result can be explained, in the first place, by a positive inductive effect of the silicon atom and its π-acceptor properties, and secondly, by steric constraints of the Y, C=C-chelating ligands, although it is generally difficult to separate these factors. It is interesting to note also that the shortening of the Cu–Cα distance has been as well observed in the complexes containing five-membered chelate rings with another soft bases such as sulfur atom21 or N–N group of pyrazole ring.22 In addition, the crystal structures with silicon containing chelates share one common feature: the silicon atom is always located at the opposite side from the axial ligand (Lax), as though moving to occupy an additional coordination site on the copper(I) atom. Certainly, the trigonal bipyramidal environment of CuI formed in this way is strongly distorted, but Lax–Cu–Cα–Si torsion angle (φ) values by far exceed 90° (Table 2). Both the Cu–Cα bond shortening and the silicon atom position, may be attributed not only to the (dSi+σ*Si–C) [LEFTWARDS ARROW]π*C=C [LEFTWARDS ARROW] dCu conjugation, which we reported earlier,16 but also, probably, to the dSi [LEFTWARDS ARROW] dCu π-donation. In addition, the strengthening of the Cu–(C=C) interaction, observed in the series 4 [RIGHTWARDS ARROW] 3 [RIGHTWARDS ARROW] 2 (see ω(Cα-Cu–Cβ) values in Table 2) and determined mainly by steric requirements of coligands and ligand substituents, favors more planar orientation of the chelate ring (see maximum deviations from planarity, Δring, in Table 2), greatly facilitating the π-conjugation.

Table 2. Comparison of geometric parameters for selected CuI complexes with vinylsilanes.
Parameter1234
d(Cu–Cα) /Å2.043–2.074(2)2.060(3)2.150(8)2.246(8)
d(Cu–Cβ) /Å2.018–2.059(2)2.094(3)2.298(8)2.266(8)
d(Cu–m) /Å1.915–1.9521.9652.1192.166
ω(Cα–Cu–Cβ) /°38.3(2)–39.0(2)37.1(1)35.0(3)32.5(3)
φ(Lax–Cu–Cα–Si) /°139.1136.5134.6163.5
d(Cu···Si) /Å3.164–3.234(1)2.968(1)3.031(3)3.303(2)
Δring-0.180.440.48

The degree of the trigonal distortion of the CuI coordination tetrahedron is correlated with the strength of copper–olefin interaction estimated from Cα-Cu–Cβ angle (ω): pseudo tetrahedral geometry in 2 (37.1(1)°), trigonal pyramidal (38.3(1)°) and triangular planar (38.6(1)°, 39.0(2)°) coordination in 1. These results are in some disagreement with the data obtained by FTIR spectroscopy. The low-frequency shifts of the C=C stretching mode for both complexes are nearly equal, 89 cm–1 for 1 and 91 cm–1 for 2, and correspond well with very similar values for C=C bond length, 1.350(3)–1.356(3) Å for 1 and 1.348(4) Å for 2. Thus, the magnitude of the C–Cu–C angle seems to be more adequate to measure of Cu–(C=C) bonding because it allows for more complete (dSi+σ*Si–C) [LEFTWARDS ARROW]π*C=C [LEFTWARDS ARROW] dCu conjugation. This could explain the strengthening of the copper-olefin interaction without corresponding C=C bond stretching. Unlike IR spectroscopy, the 1H NMR analysis provides a more reliable source of information because all olefinic proton resonances may be shifted to high-field due to a partial conversion from sp2- to sp3- hybridized carbon atoms in the first place.23 The 1H NMR spectrum of complex 2 in CDCl3 shows three olefinic proton signals (δ) which are slightly upfield shifted (Δδ = –0.12 to –0.24 ppm) as compared to those of the free DMVSP confirming moderate Cu–(C=C) interaction. The vinyl proton signals in system CDCl3–CuCl–MTrVS shift upfield, the higher the molar ratio CuCl:MTrVS, Δδ is equal about –0.08 ppm (1:1) and –0.25 ppm (2:1). It would suggest that copper–alkene bonding in 1 (3:1) is slightly stronger than in 2. In addition, the decrease of the 3J(H,H) coupling constants caused by the Cu–(C=C) interaction approximates to 1 Hz in 2CuCl:MTrVS, whereas in 2 it does not exceed 0.4 Hz. And since the vicinal coupling constants are known to depend on the H–C=C–H dihedral angles,24 the observed changes may be due to a strengthening of the dCu [RIGHTWARDS ARROW] π*C=C backbonding in 1, which results in a partial hybridization conversion of vinyl carbons from sp2 to sp3. An analogous trend was observed for tetravinylsilane copper(I) hexafluoroacetylacetonate complexes of various stoichiometry.25 In addition, in this case, the Δδ values increased to about –1.2 ppm, while the C–Cu–C angles reached even 41.0(3)°. For the complexes of more soft π-bases with vinylsilanes the high field shifts can be still more evident, for example, for Ni0 complex with bridging dimetyldivinylsilane it is equal –3.0 ppm.26 The decomposition temperatures (Td) of the above adducts with copper(I) hexafluoroacetylacetonate and Ni0 were around 403 K and 363–367 K respectively at normal pressure. Why, then, is the complex 2 (Td = 371 K) more thermodynamically stable than might be expected? We believe that this can be attributed to the above described chelate effect which due to π-conjugation causes complex to be thermodynamically more stable despite a weakened Cu–(C=C) interaction.

Structure of Copper(I) Halide Complexes with Alkenyl(2-pyridyl)silanes in Light of Homocoupling Reaction

Investigation of the homocoupling reaction of alkenyl(2-pyridyl)silanes mediated by CuX/CsF (X = Cl, Br, I) indicated that the 2-pyridyl group has strong directing effect, thus allowing to efficiently realize the Si–to–Cu transmetalation.18 A wide variety of multisubstituted butadienes has been obtained in this manner using different copper(I) halides. It has appeared that the anion type affects significantly the reaction yields of both olefin intermediate and diene product: 99 % for X = I, 59–84 % for Br and 40 % (first stage of reaction) for Cl.18 This is in accord with our conclusions about the enhancement of hyperconjugation due to the reduction of steric repulsion by replacement of the bulky iodide anion with the smaller chloride anion. And since the metal olefin interaction in [Cu2I2(TVMSP)2] is weaker than 2, the Cu–(C=C) triangle shows here more pronounced asymmetry (Table 2), to generate a quasi-η1 complex which probably facilitates the subsequent Si–C bond breaking and the formation of alkenylcopper species. Besides it, the asymmetry of Cu–C bond lengths also has some influence on the decrease of C–Cu–C angle value, and thus on the thermodynamic complex stability. Contrary to this, chloro-containing complex 2, where the values of ω(C–Cu–C) are higher and Cu–(C=C) triangle is nearly isosceles, should be thermodynamically more stable and therefore less effective as an intermediate in the above mentioned homocoupling process.

Conclusions

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

Finally, it can be assumed that the coordination mode of vinylsilanes is related to Cu–(C=C) bond strengthening and, consequently, to stability of these organometallic compounds. On the other hand, the cuprous halide clusters are highly prone to rearrangement depending on electronic properties, molecular symmetry and conformational flexibility of an unsaturated ligand. The shortening of Cu–Cα distance in Cu–(C=C)–Si–C–Y chelate ring may indicate that the complexation is labile to form an alkenylcopper intermediate and that the segmentation of π-conjugated system is associated with a stereochemical alteration of the CuI coordination sphere. This is accompanied by CunXn aggregate transformation, which provides a structural dynamics of intermediate complex.

Experimental Section

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

General Procedures: Anhydrous copper(II) chloride was obtained by dehydrating the dihydrate (Chempur, 96 % pure) at 90 °C/50 Torr for 30 min. Copper(I) chloride was freshly prepared every time before use by the reduction of copper(II) with sulfite anions according to the standard procedure.27 The decomposition points (uncorrected) of crystalline solids were measured using Boetius microscope with a heating table. The IR spectrum was recorded with a Philips PU 9800 FT instrument in the range 400–4000 cm–1 employing KBr pellet technique (complexes 1 and 2) and MTrVS and DMVSP as liquid sample. 1H NMR spectra were recorded with a Bruker Ultrashield spectrometer operating at 400.13 MHz.

Synthesis of [Cu6Cl6(MTrVS)2] (1): The anhydrous CuCl2 (0.054 g, 0,4 mmol) was dissolved in the mixture of MTrVS (0.240 mL, about 2.0 mmol, Aldrich, 97 % pure) and ethyl alcohol (0.200 mL, Poch, 99,8 % pure). Subsequently, the small amount of crystalline anhydrous SnCl2 (0.035 g, about 0.17 mmol, Chempur, 98.0 % pure) was added little by little to this green solution until it becomes almost colorless. After 10 hours the column-shaped colorless crystals of 1 suitable for X-ray investigation appeared at room temperature. During the samples heating the decomposition was observed microscopically at 366 K. The compound does not dissolve unchanged in common organic solvent but decomposes slowly in water. Total yield: 0.023 g (40.7 %). IR (KBr): equation image = 3420 (s, very broad), 1918(vw), 1618(m, broad), 1504(m), 1405(w), 1349(m), 1257(w), 1026(w), 966(w), 794(s), 749(m), 697(m), 547(w, broad) cm–1. For comparison purposes, MTrVS: IR (KBr): equation image = 3456 (w), 3052(s), 3010(m), 2969(s), 2947(s), 1911(w), 1593(m), 1405(s), 1251(s), 1008(s), 954(s), 799(vs), 743(s), 681(s), 697(m), 541(m) cm–1.

Synthesis of [Cu2Cl2(DMVSP)2] (2): The freshly synthesized CuCl (0.050 g, about 0,5 mmol) was dissolved in DMVSP (0.300 mL, about 1.8 mmol) at room temperature. The prismatic colorless crystals of complex 2 were observed in 10 min. The compound is equally soluble in both chloroform and dimethylsulfoxide. Its thermal decomposition takes place at about 371 K. Total yield: 0.019 g (14.4 %). IR (KBr): equation image = 3449 (s, broad), 3360(s, broad), 3053(w), 2956(m), 2924(w), 1634(w, broad), 1586(m), 1559(w), 1503(w), 1456(w), 1426(m), 1359(m), 1246(m), 1142(m), 1089(w), 1015(m), 968(m), 924(w), 847(vs), 818(s), 751(vs), 735(w), 719(m), 691(m), 603(w), 471(w), 404(m) cm–1. For comparison purposes, DMVSP: IR (KBr): equation image = 3449 (w), 3051(m), 2988(w), 2960(m), 2902(w), 1594(w), 1575(m), 1405(m), 1247(s), 1139(m), 1046(m), 1009(m), 988(m), 954(m), 822(vs), 781(s), 749(s), 702(m), 611(m), 527(m) cm–1.

X-ray Structure Determination: Single crystals of the complexes 1 and 2 were selected directly from the products obtained during their syntheses and mounted on a Xcalibur diffractometer (Mo-Kα radiation, λ = 0.71073 Å, graphite monochromator) equipped with a CCD detector. 115 ω oscillation images with an increment of 0.5 frame width and 20 s (1), 25 s (2) exposure per image were collected at 293 K, crystal-to-detector distance 60 mm. After integration the data were corrected for Lorentz and polarization effects,28 but not for absorption. Cell parameters were obtained by a least-squares refinement based on reflection angles in the range 5.8 < 2θ < 59°. Structures were solved by direct methods applying SHELX program package.29 Hydrogen atoms were added geometrically and refined in a riding model with isotropic temperature factors of 1.2 times (1.5 times for methyl groups) the Ueq value of the parent atoms. All non-hydrogen atoms were located from difference Fourier synthesis and refined by least-squares method in the full-matrix anisotropic approximation. The crystallographic data for compounds 1 and 2 and details of X-ray experiment are collected in the Table 3. Structure drawings were prepared by using the DIAMOND program.30

Table 3. Crystallographic data and conditions of X-ray experiment for 1 and 2.
Compound12
Empirical formulaC7H12Cl3Cu3SiC9H13ClCuNSi
M421.23262.28
F(000)912604
Space groupI2/aC2/c
a13.4731(5)14.743(1)
b7.2302(2)11.2975(5)
c27.4910(15)15.591(1)
β94.258(5)113.383(6)
V32670.6(2)2383.5(3)
Z88
Crystal size /mm0.28 × 0.12 × 0.120.40 × 0.30 × 0.30
Dcalc /g·cm–32.30951.462
Detection methodω scanω scan
min;2θmax5.8; 59.06.1; 58.8
Index ranges0 ≤ h ≤ 180 ≤ h ≤ 20
 –9 ≤ k ≤ 8–15 ≤ k ≤ 12
 0 ≤ l ≤ 370 ≤ l ≤ 21
Number of reflections:  
Measured34133055
Independent with F > 4σ(F)25271588
Number of refined parameters127139
R; Rw (for I > 2σ(I))0.0233; 0.05460.0286; 0.0497
Goodness-of-fit0.9160.818
Δρmax/Δρmin /e·Å–30.56/–0.600.31/–0.20

813847 http://www.ccdc.cam.ac.uk/data_request/cif and -813848 http://www.ccdc.cam.ac.uk/data_request/cif contain the supplementary crystallographic data for 1 and 2 respectively. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223-336-033; E-mail: deposit@ccdc.cam.ac.uk.

Supporting Information (see footnote on the first page of this article): 1H NMR spectroscopic data for free ligands and complexes.

Acknowledgements

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

We are grateful to Dr. Dorota Wieczorek and Mgr. Marek Grzymek (Department of Chemistry, Opole University, Poland) for help with the 1H NMR and FTIR measurements.

Supporting Information

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

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