From Mixed-Valent Phenyltellurenyl Bromide Ph(Br2)TeTePh to the

Article pubs.acs.org/Organometallics

From Mixed-Valent Phenyltellurenyl Bromide Ph(Br2)TeTePh to the Isolation of [{(C6H5)Te}19O24Br5]Br4 Sangeeta Yadav,† Harkesh B. Singh,*,† Matthias Zeller,‡ and Ray J. Butcher*,§ †

Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India Department of Chemistry, Youngstown State University, Youngstown, Ohio 44555, United States § Department of Chemistry, Howard University, Washington, D. C. 20059, United States ‡

S Supporting Information *

ABSTRACT: The σ-donor ligand selone L (L = 1,3dibutylbenzimidazolin-2-selone, C15H22N2Se) caused cleavage of the Te−Te bond of the mixed-valent phenyltellurenyl bromide {Ph(Br2)TeTePh} in THF to produce the selone adduct of a phenyltellurenyl cation with phenyltellurium dibromide anion, [PhTe(L)][PhTeBr2] (1). The adduct disproportionated in polar solvent (CH3CN), followed by hydrolysis with traces of water to give the largest telluroxane cluster, [{(C6H5)Te}19O24Br5]Br4, with a Te19O24 skeleton. The bowl-shaped telluroxane cluster dimerizes in the solid state, forming the molecular capsule {[{(C6H5)Te}19O24Br5]Br4}2. The cluster is amphipathic and has a hydrophilic cavity consisting of tellurium, oxygen, and bromide atoms, which contains 24H2O molecules.

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INTRODUCTION A variety of telluroxanes have been prepared by the hydrolysis of aryltellurium(IV) trihalide, RTeX3 (X = Cl, Br, I). The products of hydrolysis are polymeric in both solution and the solid state.1 The first discrete organotelluroxane cluster, [Li(THF)4][{(i-PrTe)12O16Br4{Li(THF)Br}4}Br]·2THF,2 was isolated by Giolando and co-workers during the attempted synthesis of isopropyl hex-1-ynyl telluride. Recently, wellcharacterized smaller discrete aryltellurium clusters containing six to eight tellurium atoms have been obtained by the hydrolysis of aryltellurium trihalides, which are stabilized by intramolecular coordination.3 The present work originated from our motivation of studying the reactivity of mixed-valent aryltellurenyl halides and to isolate the complexes of “RTe+”, an isoelectronic analogue of I+.4 The reaction of mixed-valent phenyltellurenyl bromide Ph(Br2)TeTePh5 with selone6 afforded the organotelluroxane cluster [{(C6H5)Te}19O24Br5]Br4. We herein present the synthesis of a novel organotelluroxane cluster containing a Te19O24 skeleton, which dimerizes in the solid state to form a molecular capsule, {[{(C6H5)Te}19O24Br5]Br4}2.

coordinated selone. In the ESI-MS spectrum, in positive mode, it exhibited a single cluster of peaks at m/z 515.0389, which corresponds to [C21H27N2SeTe]+, and in negative mode, another cluster at m/z 364.7741 corresponding to the [C5H6TeBr2]− fragment. However, in an attempt at recrystallization from CH3CN, when compound 1 was dissolved in CH3CN, the reddish solution rapidly afforded a pale yellow precipitate and a reddish supernatant solution. The pale yellow precipitate was characterized as novel cluster 2 and the reddish supernatant afforded, on fractional crystallization, compounds 3 and L2TeBr4. The synthesis of L2TeBr4 has been reported earlier by our group by an alternative route;6 however, its structure has not been reported (Figure S1 in the Supporting Information). Suitable yellow crystals of 2 could be obtained by slow evaporation of a solution of 1 in CH3CN. The structure of cluster 2 was established by X-ray diffraction studies. The schematic diagram of the [{(C6H5)Te}19O24Br5]4+ cluster is given in Figure 1. The complete precipitation of 2 requires ∼72 h. The formation and structural characterization of compound 2 is reproducible and confirmed. When a CH3CN solution of compound 1 was treated with water (2 mL) and the mixture stirred for 24 h, the reaction again afforded a light yellow precipitate of 2, indicating a key role of hydrolysis in the formation of 2. Compound 2 shows broad peaks in the aromatic region in 1H NMR and 13C NMR spectra; however, it shows only one sharp peak at 1516 ppm in 125Te NMR spectrum. This indicates that the cluster

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RESULTS AND DISCUSSION The reaction of Ph(Br 2 )TeTePh with L (L = 1,3dibutylbenzimidazolin-2-selone, C15H22N2Se) in THF at room temperature afforded the desired selone adduct [PhTe(L)]+[PhTeBr2]− (1) (Scheme 1). Compound 1 in CDCl3 solution shows two signals in the 125Te NMR spectrum at 1186 and 889 ppm for the cation and anion, respectively. The 77Se NMR spectrum showed one signal at 148 ppm for the © XXXX American Chemical Society

Received: December 22, 2016

A

DOI: 10.1021/acs.organomet.6b00953 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Scheme 1. Synthesis of Compound 1 and Its Disproportionated/Hydrolyzed Products

charge balance, and crystallizes around a crystallographic axis (the other cationic clusters are linked by the symmetry operation 1 − x, y, 1/2 − z). This unit is disordered over two conformations (Experimental Section in the Supporting Information), and the following discussion will only be referring to the major component. While it is relatively easy to pick out the components of the major part of the cluster, as there are eight Te atoms in common with both major and minor components and the remaining Te atoms are at 0.64 occupancy, it was much more difficult to pick out a complete minor cluster that matched the major cluster in every detail. In particular, it can be stated that Te2, Te5, Te6, Te15, Te16, Te17, Te18, and Te19 are common to both clusters. In the major/minor cluster are Te1/Te21, Te3/Te23, Te4/Te24, Te7/Te27, Te8/Te28, Te9/Te29, Te10/Te30, Te11/Te31, Te12/Te32, and Te14/Te34. Due to severe disorder it was not possible to pick out a complete fragment that matched up with Te13 (Figure S5 in the Supporting Information). The cationic clusters are linked into dimers by H···Br interactions and secondary interactions between the Te atoms in one unit with attached Br atoms in the symmetry-generated cluster, {[{(C6H5)Te}19O24Br5]Br4}2. In addition to the Te···Br interactions holding the clusters together, there are intercluster C−H···Br interactions (2.870(1) Å) involving H15D and Br5, which link these clusters into a zigzag ribbon along the a axis (Figure 2). The packing of the cationic cluster, the bromide anions, and the solvate water molecules viewed along the a, b, and c axes is shown in Figure S2 in the Supporting Information. The discussion of this novel structure will first concentrate on the more general aspects of the whole structure before an investigation is made into the finer details of the coordination environment of individual Te atoms. The best description of the overall shape of the cluster is a slightly flattened sphere. The overall dimensions of the cluster are 24.98 × 22.23 × 20.08 Å (i.e., 2.498 × 2.223 × 2.008 nm) with a Te19O24Br5 core of 18.28 × 18.28 × 4.00 Å; thus, this cluster can be considered as a small nanoparticle. The shell consists of hydrophobic phenyl groups aligned perpendicular to the surface of the capsule. The inner core consists of Te−O−Te and Te−Br moieties. As has been indicated above, the two molecules of the cluster are linked by numerous Te−Br bonds and interactions (Figure 3) as well as C−H···Br interactions: namely, Br1···H15B, Br2···H13F, and Br4···H15F (2.875(2), 2.832(2) and 2.631(1) Å, respectively) (Figure S3 in the Supporting Information). The Te−Br interactions can be divided into several groups. The first

Figure 1. [{(C6H5)Te}19O24Br5]4+ cluster.

does not remain intact in solution, and the identity of the species in solution remains unclear. The elemental analysis data are in agreement with the calculated values for the formula determined from X-ray crystallographic studies. X-ray Crystallographic Studies. The complex cluster crystallized in the monoclinic space group C2/c with 4 formula units in the unit cell, and thus only half the formula unit was unique.7 The overall cluster was comprised of 19 (C6H5)Te units linked by bridging oxygens, making up a flattenedspherical shape with the phenyl groups arranged externally and the interior containing both the attached Br atoms and Br− anions as well as numerous solvent water molecules, thus having an external hydrophobic area and an internal hydrophilic cavity.8 Within the hydrophilic cavity some of the solvent water molecules were relatively ordered and thus were included in the refinement. However, there was also a significant amount of solvent that was not ordered and could not be modeled, as is commonly found in other large structures such as those containing heteropolyanions9a and proteins.9b The structure consists of a complex cationic cluster of overall formula [{(C6H5)Te}19O24Br5]4+, with 4Br− making up the B

DOI: 10.1021/acs.organomet.6b00953 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

Figure 2. Diagram viewed along the a axis (major component only) showing how the clusters are packed into the unit cell. Hydrogen atoms are omitted for clarity.

Figure 3. Diagram of the major component only with phenyl rings and solvent molecules omitted for clarity showing (a, left) the Te···Br interactions linking the two cationic clusters and (b, right) the hydrophilic central cavity.

from 3.085 to 3.182 Å as well as weaker Te−Br interactions between Br and multiple Te atoms ranging from 3.540 to 3.663 Å similar to those found in the present case.2 A detailed analysis of the molecular structure of the [{(C6H5)Te}19O24Br5]4+ cluster (Figure 4) reveals several unique structural features. (i) The cluster bears 4+ charge formally located on Te11, Te17, O2, and O3 which is satisfied by 4 bromide ions. (ii) There are 5 bromine atoms in the cluster which are bound to 5 tellurium atoms. (iii) Peripheral −O−Te−O− atoms are arranged in a zigzag manner to form a 26-membered ring. (iv) The overall cage consists of 7 10membered rings and one 4-membered ring. (v) This has an inner core of 7 Te atoms (Te1 to Te7) and an outer core of 12 Te atoms (Te8 to Te19), where a symmetric “star shaped” inner Te6O6 ring is connected to a much less symmetric Te12O12 ring via μ-O or μ3-O bridges. (vi) All Te atoms are in

group involves Br1 through Br7. These Br aroms are involved in two types of interactions with Te atoms, one shorter and one longer. The shorter Te−Br distances range from 2.769 to 3.119 Å while Br1 to Br5 also bridge between the two molecules (to different tellurium in each unit) but asymmetrically with the shorter distances ranging from 2.769 to 3.003 Å and the longer distances ranging from 3.082 to 3.113 Å for Br2 to Br5 and 3.423 Å for Br1. Br6 and Br7 are on symmetry elements and bridge Te11 and Te17 in different asymmetric units at 3.098 and 3.074 Å, respectively. Atoms Br8, Br9, and Br10 bridge multiple Te atoms at distances ranging from 3.361 to 3.509 Å and thus can be considered as anionic and encapsulated in the hydrophilic pocket. These types of Te−Br interactions have been observed previously in the complex [Li(THF)4][{(iPrTe)12O16Br4{Li(THF)Br}4}Br]·2THF, containing a Te12O16 ring where there were stronger Te−Br interactions ranging C

DOI: 10.1021/acs.organomet.6b00953 Organometallics XXXX, XXX, XXX−XXX

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Te···Te interactions, namely Te1···Te2 and Te1···Te6, with bond lengths of 3.374(1) and 3.352(1) Å, respectively. Surface area, pore size, and pore volume were calculated by CO2 adsorption on compound 2. The BET surface area (Brunauer−Emmett−Teller) is 14.75 m2/g, and the Langmuir surface area is 33.62 m2/g. Compound 2 was found to be a porous solid with an average pore radius of 16.12 Å and a pore volume of 1.19 × 10−2 cm3/g. The CO2 gas uptake capacity of the cluster is 1.19 wt % (6.04 mL/g). The CO2 adsorption− desorption isotherm (Figure S6a in the Supporting Information) is completely reversible. The reversibility implies that the interactions between CO2 and the sorbent molecules are weak and regeneration of the compound is energetically favorable. UV−visible absorption (Figure S6b) and fluorescence spectra (Figure S6c) exhibited that the cluster shows absorbance at 269 nm and emission at 390 and 355 nm. In conclusion, we have presented the isolation and structural characterization of the largest organotelluroxane cluster as its bromide salt, [{(C6H5)Te}19O24Br5]Br4. It is worth noting that the largest telluroxane cluster is generated from in situ generated PhTeBr3 in a complex milieu of polar solvent CH3CN, ligand selone, etc., whereas the hydrolysis of preformed PhTeBr3 affords only insoluble products.

Figure 4. Structure of the [{(C6H5)Te}19O24Br5]4+ cation (major component only). Hydrogen atoms are omitted for clarity.

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the +4 oxidation state and have 3 coordination environments: (a) all Te atoms in the inner core have a (C6H5)TeO3 environment with all oxygen atoms involved in bridging 2 tellurium atoms, except for O2 and O3, which bridge 3 Te atoms; (b) in the outer ring there are 5 tellurium atoms (Te8, Te9 Te13, Te15, and Te19) which have a (C6H5)TeBrO2 environment; (c) Te10, Te12, Te14, Te16, and Te18 of the outer ring have a (C6H5)TeO3 environment; (d) the remaining Te11 and Te17 only have a (C6H5)TeO2 environment within the cluster but are involved in 2 longer bonds to both Br− anions in the cavity as well as Br atoms from the adjoining cluster (Te11−Br4 3.110 Å, Te11−Br3 3.088 Å generated by 1 − x, y, 1/2 − z; Te17−Br6 3.074 Å, Te17−Br7 3.119 Å generated by 1 − x, y, 1/2 − z). All of the Te−C bonds in the cluster are equivalent with an average bond length of 2.102 Å. The Te−O bond lengths vary a great deal in the cluster. However, this variation can be explained if the structure is divided into 3 building blocks: (i) a tellurinic acid part comprised of Te11 and Te17, (ii) an RTeO2Br part which consists of Te8, Te9, Te13, Te15, and Te19, and (iii) tellurinic anhydride composed of Te1−Te7, Te10, Te12, Te14, Te16, and Te18. For tellurinic acid moieties the four Te−O bonds are short and the average value is 1.915 Å, which depicts more than single-bond character in the bonds due to delocalization. However, in RTeO2Br moieties, there is one TeO bond with an average bond length of 1.888 Å and one Te−O bond with an average bond length of 1.988 Å. The Te−Br bond length is longer than a covalent bond and shorter than the sum of van der Waals radii. However, in tellurinic anhydride moieties there is one TeO bond with average bond length 1.921 Å. This indicates a decrease in bond order due to the delocalization. One Te−O bond with average bond length 2.055 Å indicates a purely single bond. One Te−O bond has an average bond length of 2.213 Å which is more than a Te−O single bond. This bond represents the coordination from oxygen of TeO of a neighboring moiety to Te: i.e., a TeO→Te bond. The increase in the bond length is due to the delocalization in the TeO bond of a neighboring moiety. In addition to these covalent bonds, there are nine Te···O secondary interactions ranging from 2.561 to 2.871 Å and two

EXPERIMENTAL SECTION

All manipulations were executed under a nitrogen or argon atmosphere using standard Schlenk techniques unless otherwise noted. Solvents were purified and dried by standard procedures and were distilled prior to use. Melting points were recorded on a Veego VMP-I melting point apparatus in capillary tubes and were uncorrected. Infrared spectra were obtained on a PerkinElmer Spectrum One FT-IR spectrometer as KBr diluted disks. 1H (400 MHz, 500 MHz), 13C (100.56 MHz, 126 MHz), 77Se (76 MHz, 95 MHz), and 125Te (126 MHz, 158 MHz) nuclear magnetic resonance spectra were recorded on Bruker AV 400 and Bruker AV 500 spectrometers at 25 °C. Chemical shifts are cited with respect to Me4Si as internal standard for 1H and 13C, Me2Se for 77Se, and Me2Te for 125 Te as external standards. Elemental analyses were performed on a Carlo Erba Model 1106 elemental analyzer. The ESI mass spectra were recorded on a Q-tof micro (YA-105) mass spectrometer. The bulk purity of the compounds has been established by elemental analysis, HRMS, and NMR spectroscopy. Thermogravimetric analysis were carried out on a PerkinElmer thermal analysis system, under a stream of nitrogen gas at a heating rate of 10 °C/min. Powder X-ray diffractions were recorded on a Philips X’pert Pro (PANAnalytical) diffractometer using Cu Kα radiation (λ, 1.54190 Å). Gas sorption and uptake measurements were performed on a Quantachrome Autosorb1C analyzer using UHP grade. CO2 adsorption measurements were performed at 273 K in a water bath. Prior to gas adsorption measurements, the samples were evacuated at 30 °C for 5−7 h under ultrahigh vacuum (10−8 mbar). The UV−visible spectrum measurements were carried out using a Varian Cary 100 bio spectrophotometer. Emission experiments were carried out using a PerkinElmer LS55 Luminescence spectrometer. Synthesis of Compounds 1−3 and L2TeBr4. In a roundbottomed flask, Ph(Br2)TeTePh (1.00 g, 1.76 mmol) was dissolved in 30 mL of THF and to this was added selone (L; 0.54 g, 1.76 mmol) at room temperature. The reaction mixture immediately changed from orange to red. The reaction mixture was stirred for 30 min at room temperature. The solvent was evaporated to give crude compound 1 and characterized as such without further purification. Compound 1 disproportionates while crystallizing and, therefore, could not be structurally characterized. Compound 1 (1.50 g) was dissolved in CH3CN, and the dissolution resulted in a rapid precipitation of compound 2 (0.09 g). Suitable crystals of 2 were obtained by the slow evaporation of a solution of 1 in CH3CN in 42% yield. The red supernatant was concentrated and D

DOI: 10.1021/acs.organomet.6b00953 Organometallics XXXX, XXX, XXX−XXX

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1421−1428. (c) Thavornyutikarn, P.; McWhinnie, W. R. J. Organomet. Chem. 1973, 50, 135−143. (2) Citeau, H.; Kirschbaum, K.; Conrad, O.; Giolando, D. M. Chem. Commun. 2001, 2006−2007. (3) (a) Srivastava, K.; Sharma, S.; Singh, H. B.; Singh, U. P.; Butcher, R. J. Chem. Commun. 2010, 46, 1130−1132. (b) Beckmann, J.; Bolsinger, J.; Duthie, A. Chem. - Eur. J. 2011, 17, 930−940. (c) Metre, R. K.; Kundu, S.; Sahoo, D.; Chandrasekhar, V. Organometallics 2014, 33, 2380−2383. (4) Yadav, S.; Raju, S.; Singh, H. B.; Butcher, R. J. Dalton Trans. 2016, 45, 8458−8467. (5) Beckmann, J.; Hesse, M.; Poleschner, H.; Seppelt, K. Angew. Chem., Int. Ed. 2007, 46, 8277−8280. (6) Manjare, S. T.; Yadav, S.; Singh, H. B.; Butcher, R. J. Eur. J. Inorg. Chem. 2013, 2013, 5344−5357. (7) Crystal data for 3 (123 K): C111H95Br9O36Te19, fw 5148.48, monoclinic, space group C2/c, yellow crystals, a = 31.6005(11) Å, b = 30.5468(11) Å, c = 37.0295(13) Å, α = 90°, β = 90.1590(10)°, γ = 90°, V = 35744(2) Å3, Z = 4, Dcalcd = 1.927 Mg/m3, R1 = 0.1922, wR2 = 0.2316 (all data), GOF = 1.040. (8) Mueller, A.; Garai, S.; Schaeffer, C.; Merca, A.; Boegge, H.; AlKarawi, A. J. M.; Prasad, T. K. Chem. - Eur. J. 2014, 20, 6659−6664. (9) (a) Wassermann, K.; Pope, M. T. Inorg. Chem. 2001, 40, 2763− 2768. (b) Yu, B.; Blaber, M.; Gronenborn, A. M.; Clore, G. M.; Caspar, D. L. D. Proc. Natl. Acad. Sci. U. S. A. 1999, 96, 103−108.

was dissolved in dichloromethane. After 24 h red crystals of L2TeBr4 (56%) were obtained. The remaining supernatant gave compound 3 in 28% yield. L2TeBr4 has been reported earlier by our group.6 Compound 1. Yield: 1.50 g (96%). 1H NMR (400 MHz, CDCl3): δ (ppm) 7.86 (broad, 4H), 7.50−7.42 (m, 4H), 7.21 (m, 2H), 7.10 (broad, 4H), 4.04 (t, J = 7.64 Hz, 4H), 1.65 (quin, J = 7.44 Hz, 4H), 1.24 (sext, J = 7.60 Hz, 4H), 0.86 (t, J = 7.45 Hz, 6H). 13C NMR (101 MHz, CDCl3): δ (ppm) 150.23 (NCN), 138.85, 131.98, 128.81, 128.51, 125.73, 115.07, 111.74, 47.13, 30.45, 19.57, 13.40. 77Se NMR (76 MHz, CDCl3): δ (ppm) 148 (s). 125Te NMR (126 MHz, CDCl3): δ (ppm) 1186, 889. Anal. Calcd for C27H32Br2N2SeTe2: C, 36.91; H, 3.67; N, 3.19. Found: C, 37.17; H, 4.12; N, 5.02. ESI-MS (positive mode): [M − C6H5TeBr2]+ m/z 515.0389 (observed), 515.0389 (calculated). ESI-MS (negative mode): [M − C21H27N2SeTe]− m/z 364.7741 (observed), 364.7783 (calculated). Compound 2. Yield: 0.21 g (42%). Mp: 220 °C dec. FT-IR: 3420 (O−H (H2O)), 3053 (C−H), 735 (Te−O), 686 (C−H), 664 (Te− O) cm−1. 1H NMR (500 MHz, DMSO-d6): δ (ppm) 8.76 (broad), 7.93 (d), 7.61 (broad), 7.10 (broad), 7.04 (broad), 6.82 (broad). 13C NMR (126 MHz, CDCl3): δ (ppm) 135.04, 132.79, 132.66, 131.94, 131.24, 130.38, 128.25, 127.79. 125Te NMR (158 MHz, CDCl3): δ (ppm) 1516. Anal. Calcd for C114H95Br9O24Te19: C, 27.43; H, 1.92. Found: C, 27.18; H, 1.87, ESI-MS (positive mode): [M − 4Br]4+ m/z 1176.6206 (observed), 1173.3659 (calculated). Compound 3. Yield: 0.19 g (28%). 1H NMR (400 MHz, CDCl3): δ (ppm) 7.94 (d, 2H), 7.48−7.39 (m, 4H), 7.16 (t, 1H), 6.98 (t, 2H), 4.11 (t, J = 7.53 Hz, 4H), 1.71 (quin, J = 7.53 Hz, 4H), 1.32 (sext, J = 7.60 Hz, 4H), 0.90 (t, J = 7.40 Hz, 6H). 13C NMR (101 MHz, CDCl3): δ (ppm) 153.62 (NCN), 141.14, 131.91, 128.38, 127.97, 124.84, 116.45, 11.07, 46.69, 30.16, 19.50, 13.33. 77Se NMR (76 MHz, CDCl3): δ (ppm) 129 (s, CSe). 125Te NMR (126 MHz, CDCl3): δ (ppm) 917. Anal. Calcd for C21H27N2SeTeBr: C, 42.47; H, 4.58; N, 4.72. Found: C, 42.50; H, 4.44; N, 6.58. ESI-MS (positive mode): [M − Br]+ m/z 515.0389 (observed), 515.0389 (calculated).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00953. X-ray crystallographic study, X-ray crystallographic data of L2TeBr4, packing, hydrogen bonding, and space-filling diagrams of 2, characterization of cluster 2, and spectral data (PDF) Accession Codes

CCDC 1449921−1449922 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for H.B.S.: [email protected]. *E-mail for R.J.B.: [email protected]. ORCID

Harkesh B. Singh: 0000-0002-0403-0149 Notes

The authors declare no competing financial interest.

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REFERENCES

(1) (a) Lederer, K. Ber. Dtsch. Chem. Ges. 1915, 48, 1345−1350. (b) Alcock, N. W.; Harrison, W. D. J. Chem. Soc., Dalton Trans. 1982, E

DOI: 10.1021/acs.organomet.6b00953 Organometallics XXXX, XXX, XXX−XXX