Halogenation of Diorganotelluride [2,6-(Me2NCH2)2C6H3]TenBu: Synthesis, Molecular and Electronic Structural Investigation of Monoorgano Dihalotelluronium(IV) Cation

Article abstract of DOI:10.1002/ejic.202000910

A simple methodology for the synthesis of heteroleptic diorganotelluride [2,6-(Me₂NCH₂)₂C₆H₃]TenBu (1) and homoleptic diorganotelluride [2,6-(Me₂NCH₂)₂C₆H₃]₂Te (2) is reported. The halogenation reactions of diorganotelluride 1 are studied. In particular, the reaction of 1 with Br₂ resulted in the isolation of a monoorgano dibromotelluronium(IV) cation, namely [2,6-(Me₂NCH₂)₂C₆H₃TeBr₂]·Br₃ ([3]·Br₃). The reaction of [3]·Br₃ with K₂PdCl₄ afforded a monoorgano mixed dihalotelluronium(IV) cation, [2,6-(Me₂NCH₂)₂C₆H₃TeClBr]·PdBr₄ ([4]·PdBr₄). When diorganotelluride 1 was treated with I₂, the reaction afforded the tellurenium(II) cation, [2,6-(Me₂NCH₂)₂C₆H₃Te]·I₂·I₃ ([5]·I₂·I₃). The reaction of 1 with HgCl₂ resulted in the isolation of dimeric diorganoditelluroxonium(IV) cation, [2,6-(Me₂NCH₂)₂C₆H₃Te(μ-O)]₂·Hg₂Cl₆ ([6]·Hg₂Cl₆). A similar diorganoditelluroxonium(IV) cation, namely [2,6-(Me₂NCH₂)₂C₆H₃Te(μ-O)]₂·2Br ([6]·2Br) was also obtained by the reaction of 1 with Br₂ and NaOH. The crystallographic studies suggest that for each compound, both the N atoms from the pendant arms make strong Intramolecular Chalcogen Bonding (IChB) interactions with the Te center(s). The presence of a strong N→Te IChB interaction in the synthesized compounds was further validated by DFT calculations.

Full text of DOI:10.1002/ejic.202000910

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Monorgano Dihalotelluronium Cation
Halogenation of Diorganotelluride [2,6-(Me2NCH2)2C6H3]TenBu:
Synthesis, Molecular and Electronic Structural Investigation of
Monoorgano Dihalotelluronium(IV) Cation
Rajesh Deka,[a] Anand Gupta,[a] Arup Sarkar,[a] Ray J. Butcher,[b] and Harkesh B. Singh*[a]
Abstract: A simple methodology for the synthesis of hetero- (Me2NCH2)2C6H3Te]·I2·I3 ([5]·I2·I3). The reaction of 1 with HgCl2
leptic diorganotelluride [2,6-(Me2NCH2)2C6H3]TenBu (1) and resulted in the isolation of dimeric diorganoditelluroxonium(IV)
homoleptic diorganotelluride [2,6-(Me2NCH2)2C6H3]2Te (2) is re- cation,
[2,6-(Me2NCH2)2C6H3Te(μ-O)]2·Hg2Cl6
([6]·Hg2Cl6).
ported. The halogenation reactions of diorganotelluride 1 are A similar diorganoditelluroxonium(IV) cation, namely [2,6-
studied. In particular, the reaction of 1 with Br2 resulted in the (Me2NCH2)2C6H3Te(μ-O)]2·2Br ([6]·2Br) was also obtained by the
isolation of a monoorgano dibromotelluronium(IV) cation, reaction of 1 with Br2 and NaOH. The crystallographic studies
namely [2,6-(Me2NCH2)2C6H3TeBr2]·Br3 ([3]·Br3). The reaction suggest that for each compound, both the N atoms from the
of [3]·Br3 with K2PdCl4 afforded a monoorgano mixed di- pendant arms make strong Intramolecular Chalcogen Bonding
halotelluronium(IV) cation, [2,6-(Me2NCH2)2C6H3TeClBr]·PdBr4 (IChB) interactions with the Te center(s). The presence of a
([4]·PdBr4). When diorganotelluride 1 was treated with I2, strong N→Te IChB interaction in the synthesized compounds
the reaction afforded the tellurenium(II) cation, [2,6- was further validated by DFT calculations.
Introduction
B-type), monoorgano dihalotelluronium(IV) cation (C-type) and
monoorgano mixed dihalotelluronium cation (D-type) (Fig-
ure 1). While the chemistry of both A- and B-type halotelluro-
nium(IV) cations are sparingly studied, reports on C- and D-type
dihalotelluronium(IV) cations are still elusive in the literature.
Tellurium, known as a maverick among the group 16 ele-
ments,[1] and its various organometallic compounds, (i.e., orga-
notellurium compounds) have gained profound interest in
modern organometallic chemistry.[2] Amidst various organote-
llurium species, cationic tellurium species have become a topic
of promising research with respect to the challenges associated
with their syntheses, bonding and diverse reactivity aspects.[3]
To synthesize such cationic species, in particular to minimize
the high electrophilicity associated with the Te center, different
approaches, such as steric (bulky substituents) and electronic
[Intramolecular Chalcogen Bonding (IChB) interaction] ap-
proaches have been undertaken.[3] Among various cationic tel-
lurium species explored so far, a class of compounds which has
gained relatively less attention is the halotelluronium(IV) cation.
A compound with the highly electrophilic Te center, which is
covalently bonded to electronegative halogen atom(s), is syn-
thetically more challenging. Depending on the number of or-
ganic substituents or the halogen atoms bonded to the Te
atom, four different types of halotelluronium(IV) cations are
possible, namely, diorganohalotelluronium(IV) cations (A- and
Figure 1. Types of halotelluronium(IV) cations [R, R′ = aryl/alkyl; X, X′ = halo-
gen].
McWhinnie and co-workers have reported the first example of
a structurally characterized diorganochlorotelluronium(IV) cation
namely, [(ppy)(PhOEt)TeCl]+·HgCl3– (A-type) by the reaction of p-
ethoxyphenyltellurium(IV) trichloride with ppyHgCl [ppy = 2-(2′-
pyridyl)phenyl].[3b,4] Detty et al., reported the synthesis of dior-
ganohalotelluronium(IV) cations [(2-NMe2CH2C6H4)(Ph)TeX]+·X–
(X = Br/I) (A-type) by the oxidative addition of halogen (Br2/I2)
to the diorganotelluride (2-NMe2CH2C6H4)TePh.[5] Our group has
reported the isolation of structurally characterized diorganoiodo-
[a] R. Deka, A. Gupta, A. Sarkar, Prof. Dr. H. B. Singh
Department of Chemistry, Indian Institute of Technology Bombay,
Mumbai 400076, India
E-mail: chhbsia@chem.iitb.ac.in
http://ether.chem.iitb.ac.in/~chhbsia
[b] R. J. Butcher
–
telluronium(IV) cation of B-type, namely [(2-PhNNC6H4)2TeI]+·I3
by the oxidative addition of molecular iodine to IChB stabilized
diorganotelluride (2-PhNNC6H4)2Te.[6] A similar observation was
also made by Beckmann and co-workers, wherein the reaction
of (8-Me2NC10H6)2Te with X2 (X = Cl, Br, I) resulted into the isola-
tion of diorganohalotelluronium(IV) cations, [(8-Me2NC10H6)2-
TeX]+·X– (X = Cl, Br, I) (B-type).[7] Recently, we have reported the
synthesis and structural characterization of a diorganoiodotellu-
Department of Chemistry, Howard University,
Washington, D.C. 20059, USA
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.202000910.
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ronium(IV) cation namely, [(ppy)2TeI]+·I3– (B-type) by the reaction tellurenium(II) cation where the Te is T-shaped and involved in
of (ppy)2Te with I2.[3o] Detty et al., and Beckmann and co-workers a 3-centered-4-electron bond. As such, we wish to explore
gave detailed mechanistic investigation of the halogenation the chemistry of this substrate for the synthesis of
pathway of diorganotelluride to generate different halotelluro- unprecedented Te(IV) derivatives, and accordingly investigated
nium cations.[5,7] These studies suggested that halogenation of the reactions of heteroleptic diorganotelluride, namely [2,6-
diorganotelluride (R2Te, R = aryl, alkyl) presumably proceeds (Me2NCH2)2C6H3]TenBu, with different halogenating agents. We
through the initial formation of a molecular complex, R2Te···X–X anticipated that, due to the presence of strong N→Te IChB in-
(X = halogen). The molecular complex in the subsequent step teractions from two auxiliary arms of a single substituent and
undergoes dissociation of a halide ion to afford the desired di- considering the lability of the Te–nBu bond, the reaction might
organohalotelluronium(IV) cation [R2TeX]+. Beckmann and co- lead to the isolation of novel, rather unstable organotellu-
workers have reported that in case of IChB stabilized substrate, rium(IV) species under suitable reaction conditions. Herein, by
the dissociation of the halide ion from the molecular complex the halogenation of [2,6-(Me2NCH2)2C6H3]TenBu, we report the
was facilitated by strong D→Te interactions (D = donor atom isolation of first examples of IChB stabilized monoorgano di-
from the pendant arm of the aryl substrate), which results in the halotelluronium(IV) cations of both C- and D-types. The de-
significant elongation of X–X bond in the molecular complex, tailed electronic structural properties of the hitherto unknown
R2Te···X–X.[7] The D→Te IChB interactions also offer considerable dihalotelluronium(IV) cations are studied by Density Functional
stability to the final compound by donating a pair of electrons, Theory. In addition, we have also explored the hydrolysis reac-
resulting in considerable attenuation of electrophilicity around tions of [2,6-(Me2NCH2)2C6H3]TenBu, which led to the isolation
the Te center.
of diorganoditelluroxonium(IV) cations. All the synthesized
compounds are thoroughly characterized by multinuclear NMR
spectroscopy (1H, 13C and 125Te), ESI-MS and single-crystal X-ray
diffraction studies.
Recently, we investigated the reactivity of homoleptic di-
organotelluride [2,6-(Me2NCH2)2C6H3]2Te with SO2Cl2:K2PdCl4.[8]
We observed that the diorganotelluride underwent IChB medi-
ated Te-dearylation to afford the first example of a Pd(II) com-
plex [2,6-(Me2NCH2)2C6H3]TePdCl3, with any organotellure-
nium(II) cation as a ligand. It is interesting to note that there is
Results and Discussion
no report available on organotellurium halide for this substrate The starting material, 2,6-(Me2NCH2)2C6H3Br, LBr was synthe-
[i.e., 2,6-(Me2NCH2)2C6H3], wherein the Te is in +4 oxidation sized by the treatment of 2-bromo-1,3-bis(bromomethyl)-
state. This may be due to the formation of the extremely stable benzene with dimethylamine as reported in the literature.[9]
Rajesh Deka, born in Pathsala, Assam (India), completed his B.Sc. (2010) from B. Borooah College, Assam and M.Sc. (2012) from Gauhati University,
Assam. He received his Ph. D. from IITB-Monash Research Academy, a joint Ph. D. venture between IIT Bombay, India and Monash University,
Australia, under the supervision of Prof. H. B. Singh (IITB), Prof. Glen B. Deacon (Monash Academy) and Dr. David Turner (Monash Academy).
Currently he is working as a Research Associate with Prof. H. B. Singh in Department of Chemistry, IIT Bombay, India. His research interests include
design, synthesis, and electronic structural studies of organomain group compounds and monomeric lanthanoid complexes.
Anand Gupta completed his B.Sc. (2005) and M.Sc. (2008) from Deen Dayal Upadhyay Gorakhpur University, Uttar Pradesh, India. He received his
Ph. D. degree from Department of Chemistry, IIT Bombay (2016), under the supervision of Prof. H. B. Singh. Currently he is working as an Assistant
Professor in undergraduate college in Uttar Pradesh, India.
Arup Sarkar, born in Kolkata, India completed his B.Sc. (2012) from Seth Anandram Jaipuria College, Kolkata. He obtained his M.Sc. (2014) from
University of Calcutta, Kolkata and then moved to IIT Bombay to pursue his Ph. D. under Prof. Gopalan Rajaraman. His research interest covers
the area of investigation of magnetic anisotropy in single-ion magnets containing transition metals or lanthanoid elements through ab initio or
DFT calculation.
Raymond (Ray) J. Butcher, born in Greymouth, New Zealand (1945) and educated at Shirley Boy's High School in Christchurch, New Zealand
received his B.Sc. (Hons) in chemistry in 1968 and Ph. D. in Inorganic Chemistry with Prof. C. J. Wikins in 1974 from the University of Canterbury,
New Zealand. He then held Instructor/Post-doctoral fellowships with Prof. E. Sinn at University of Virginia, Charlottesville from 1974 to 1976, and
with Prof. M. T. Pope at Georgetown University, Washington DC from 1976 to 1977. He was appointed as Assistant Professor of Chemistry at
Howard University, Washington DC in 1977, and became full Professor in 1997. He held Fulbright Fellowships to India in 1989, 2009, and 2019. He
was elected as a Fellow of the Royal Society of Chemistry in 2018.
Harkesh B. Singh, born in 1956 in Uttar Pradesh, India, obtained his Ph. D. (1979) at Lucknow University with Prof. T. N. Srivastava. He then
pursued his second Ph. D. (1979–1983) at Aston University, Birmingham, under the supervision of Prof. W. R. McWhinnie. After a brief stay at IIT
Delhi, as Pool Scientist with Prof. B. L. Khandelwal, he joined IIT Bombay, in 1984 as a lecturer and became a full professor in 1995. Recently, he
has been conferred with prestigious J. C. Bose National Fellowship by Department of Science and Technology, India. He is a Fellow of the National
Academy of Sciences (FNASc), Indian Academy of Sciences (FASc), Indian National Academy of Science (FNA), and Royal Society of Chemistry
(FRSC). The primary theme of his research includes design, synthesis, and structural studies of novel organometallic derivatives of sulfur, -selenium,
and -tellurium and their applications.
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LBr was then treated with 1.1 equiv. of nBuLi to afford the telluride 1 was treated with Br2, the reaction resulted into the
lithiated product, i.e., 2,6-(Me2NCH2)2C6H3Li (Scheme 1). In the isolation of the first example of a monoorgano dibromotelluro-
subsequent step, 2,6-(Me2NCH2)2C6H3Li was treated with Te nium(IV) cation, [3]·Br3 (C-type) (Scheme 2). To explore the liga-
powder at –114 °C and the reaction mixture was stirred for ting properties of [3]·Br3, when it was treated with K2PdCl4, to
12 h. After completion of the reaction, a usual aqueous workup our interest, the reaction underwent a halogen exchange reac-
afforded a yellowish liquid which was then separated by col- tion resulting into the formation of first examples of a mono-
umn chromatography using petroleum ether (60–80°) and ethyl organo mixed dihalotelluronium(IV) cation [4]·PdBr4 (D-type),
acetate (10 %) as eluent. The first fraction was heteroleptic di- stabilized by a Pd(II) bromide anion. Moving down the group,
organotelluride 1, isolated as a yellow liquid with 66 % yield. when diorganotelluride 1 was treated with molecular iodine
The second fraction isolated was homoleptic diorganotelluride, in identical reaction conditions, the reaction resulted into the
2 as a white solid with 31 % yield. It is worth mentioning that formation of the tellurenium(II) cation, [5]·I2·I3. It is worth men-
similar debutylation of nBuLi followed by butylation at Te cen- tioning that Furukawa and co-workers reported that the reac-
ter was also observed by du Mont and co-workers.[10] Hetero- tion of diorganotelluride 1 with Br2 in a 1:1 ratio, in presence
leptic diorganotelluride 1 was synthesized by Furukawa and of KF6 at 0 °C resulted into the isolation of tellurenium(II) cation
co-workers by the treatment of lithiated product, 2,6- [2,6-(Me2NCH2)2C6H3Te]·PF6.[11] Contrarily, the present study re-
(Me2NCH2)2C6H3Li with nBuTeCN.[11] We have recently reported veals that with higher stoichiometry of Br2 (ca. 3 equivalent)
the synthesis of homoleptic diorganotelluride 2 by the treat- and at low reaction temperature, the diorganotelluride 1 af-
ment of 2,6-(Me2NCH2)2C6H3Li with Te(dtc)2, [dtc =diethyldithia- forded a dibromotelluronium(IV) cation, [3]·Br3. We believe that
carbamate].[8] What is particularly interesting about the current at low temperature, the dissociation of the bromide ions from
methodology is that the lithiated product, 2,6-(Me2NCH2)2- the molecular complex is not feasible, leading to the isolation
C6H3Li on treatment with Te powder resulted into formation of of an unprecedented dibromotelluronium(IV) cation. However,
both heteroleptic diorganotelluride 1 and homoleptic diorga- in the case of iodination reaction, the formation of a tellure-
notelluride 2 in reasonably good yields.
nium(II) cation instead of a monoorgano diiodotelluronium(IV)
cation might be attributed to the weaker oxidizing nature of
iodine and its larger size than bromine.
The 1H and 13C NMR spectra of [3]·Br3, [4]·PdBr4 and [5]·I2·I3
are consistent with the proposed structures, each compound
showing characteristic signals with consistent integration val-
1
ues for the aryl moiety (L). In particular, in the H NMR spectra,
compounds [3]·Br3, [4]·PdBr4 and [5]·I2·I3, showed a singlet
resonance at ca. 2 ppm corresponding to the -N(CH3)2 protons
from the N,N-dimethylbenzylamine moiety. Sharp signals were
observed in the range of 3–4 ppm for [3]·Br3, [4]·PdBr4 and
Scheme 1. Synthesis of heteroleptic diorganotelluride 1 and homoleptic di-
organotelluride 2.
In an attempt to explore the chlorination reaction of the [5]·I2·I3, which correspond to the benzylic (-ArCH2) protons at-
heteroleptic diorganotelluride, we have treated compound 1 tached to the –N(CH3)2 group. The aromatic protons corre-
with SO2Cl2. However, the reaction resulted in a highly moisture sponding to the substituent L showed resonances in the ex-
sensitive species with an indefinite composition, which could pected regions of 7–8 ppm with consistent integration values
not be adequately characterized. Interestingly, when diorgano- (vide infra). Similarly, the 13C NMR spectra of [3]·Br3, [4]·PdBr4
Scheme 2. Synthesis of monoorgano dibromotelluronium(IV) cation [3]·Br3, monoorgano mixed dihalotelluronium(IV) cation [4]·PdBr4 and tellurenium(II)
cation [5]·I2·I3.
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and [5]·I2·I3 showed expected number of signals supporting and 1480 ppm, respectively. These values are in good agree-
the formulation of the compounds. In the 125Te NMR spectra, ment to that of the chemical shift value observed in related
dihalotelluronium(IV) cations [3]·Br3 and [4]·PdBr4 showed res- dimeric diorganoditelluroxonium(IV) cation, namely [ppyTe-
onance at δ = 1706 ppm and 1641 ppm, respectively. These (μ-O)]2·2ClO4 (δ = 1413 ppm).[3o]
chemical shift values are significantly downfield shifted in com-
parison to the values observed in halotelluronium(IV) cations,
namely [(2-PhNNC6H4)2TeI]+·I3 (δ
=
1163 ppm),[6] [(8-
–
X-ray Crystallographic Studies
Me2NC10H6)2TeX]+·X– [δ = 1197 ppm (X = Cl); δ = 1198 ppm
The molecular structure of [3]·Br3 contains both
a
–
(X = Br), δ = 1184 ppm (X = I)],[7] [(ppy)2TeI]+·I3 (δ =
–
[C12H19Br2N2Te]+ cation and Br3 anion (Figure 2) and it repre-
sents the first example of structurally characterized mono-
organo dihalotelluronium(II) cation of C-type. The geometry
around the central Te is distorted square pyramidal due to the
sterically active lone pair, as reflected in the angles subtended
at the Te center, which range from 75.48(8)° to 95.06(5)° for the
cis angles and 152.04(7)° and 177.093(10)° for the trans angles.
However, there is a weak axial interaction between Te and Br3
of the anion [Te···Br3 3.5759(3) Å, C1–Te···Br3 148.16(7) Å]. The
Te–N distances are 2.372(2) Å and 2.435(2) Å, which are longer
than the sum of their covalent radii [Σrcov (Te, N) = 2.09 Å].[14]
However, these distances are significantly shorter in comparison
to the sum of their van der Wall radii [Σrvdw (Te, N) = 3.63 Å],
indicating strong IChB interactions from the N atoms to the Te
center.[15] The Te–Br distances are 2.6471(3) Å and 2.6905(3) Å,
which are longer than sum of their covalent radii [Σrcov (Te,
Br) = 2.58 Å]. These distances are in good agreement to the
Te–X (X = Cl, Br) distances observed in Ph2TeCl2 [2.506(2) Å] and
Ph2TeBr2 [2.618(6) Å].[16,17] In addition to the Te···Br3 interaction,
the telluronium cation [3]+ is further stabilized by extensive
weak H-bonding between H8A–Br3/H7B–Br3/H7B–Br4 with cor-
responding distances 3.081(30)/2.979(30)/2.929(30) Å, which are
well within the sum of the van der Waals radii of the two ele-
ments [Σrvdw (H, Br) = 3.05 Å] (Figure S2, Supporting Informa-
tion).[15]
1100 ppm).[3o] The 125Te NMR chemical shift value of δ =
1890 ppm observed for [5]·I2·I3 is comparable to the chemical
shift value observed in similar tellurenium(II) cations, namely
[2,6-(CH2NMe2)2C6H3Te]+·PF6 (δ = 1950 ppm)[11] and [2,6-
–
(Me2NCH2)2C6H3Te]2+[HgCl4]2– (δ = 1928 ppm).[8]
From literature studies it is perceived that IChB stabilized
diorganotellurides on treatment with various reagents, undergo
labilisation of Te–C bond trans to the IChB interactions leading
to the isolation of various cleaved product(s).[3o,12] In line with
this fact, as mentioned in the introduction section, we have
recently observed that reactions of homoleptic diorganotellur-
ide 2 with HgCl2 and SO2Cl2:K2PdCl4:KOH resulted into the
cleavage of trans Te–C bond affording a tellurenium(II) cation
[2,6-(Me2NCH2)2C6H3Te]·HgCl4 and Pd complex of a tellure-
nium(II) cation [2,6-(Me2NCH2)2C6H3]TePdCl3, respectively.[8] To
explore the effect of trans lablisation in the case of heteroleptic
diorganotelluride, we have treated diorganotelluride 1 with
HgCl2 (Scheme 3). Interestingly, due to the adventitious uptake
of moisture, the reaction resulted in the isolation of dimeric
diorganoditelluroxonium(IV) cation, [6]·Hg2Cl6. An identical re-
sult was also observed, when the reaction was carried out in
presence of air. To see the generality of the substrate for the
tendency to form hydrolyzed product, we have performed the
reactions of 1 with Br2:NaOH in presence of air. We observed
that the reaction resulted into a similar diorganoditelluroxo-
nium(IV) cation stabilized by bromide anion, i.e., [6]·2Br. It is
worth mentioning that Furukawa and co-workers have reported
a
similar diorganoditelluroxonium(IV) cation namely, [2,6-
–
(Me2NCH2)2C6H3Te(μ-O)]2+·PF6 from diorganotelluride 1 using
the oxidizing agent NOPF6.[13]
Figure 2. Diagram of [3]·Br3 containing a [C12H19Br2N2Te]+ cation and Br3
anion showing weak Te···Br and C–H···Br interactions.
–
Scheme 3. Synthesis of the diorganoditelluroxonium(IV) cations, [6]·Hg2Cl6
and [6]·2Br.
Similar to [3]·Br3, [4]·PdBr4 and [5]·I2·I3, the 1H and 13C NMR
For [4]·PdBr4, the two axial positions in the cation are occu-
spectra of [6]·Hg2Cl6 and [6]·2Br exhibit resonances with con- pied by both Cl and Br. In one position, the Cl/Br ratio is
sistent integration values for the aryl moiety (L), supporting the 0.848(5)/0.152(5) and for the other position, the Cl/Br ratio is
formulation of the compounds. In the 125Te NMR spectra, com- 0.458(5)/0.542(5), so the major component has both Cl and Br
pounds [6]·Hg2Cl6 and [6]·2Br showed signal at δ = 1472 ppm attached to Te as shown in Figure 3. The spatial arrangement
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with respect to the coordination sphere of the Te atom in the
cationic species is distorted square pyramidal with the N1, N2,
Br1/Br1A-b or N1, N2, Br2/Cl2A-b forming a distorted base,
while C1 is situated at apex. Similar to [3]+, Te1–Cl2A-b/Te1–
Br1A-b bond length of 2.529(13)/2.627(17) Å in [4]+ is closer to
Ph2TeCl2 [2.506(2) Å] and Ph2TeBr2 [2.618(6) Å].[16,17] Both the N
atoms of the aryl substrate (L) in [4]+ are involved in Te–N IChB
forming two five-membered cyclic rings with Te1–N1/Te1–N2
distances of 2.421(4)/2.370(4) Å. For [4]·PdBr4, a weakly coordi-
2–
nating anion (WCA) PdBr4 anion is present and located on a
center of inversion, indicating that only two Br atoms are
unique. This provides a secondary coordination sphere having
a Te–Pd separation of 3.938(4) Å, which is closer to the sum of
the van der Waals radii of the two elements [Σrvdw (Te, Pd) =
3.92 Å].[15] This interaction might be attributed to the overlaps
of the lone pair orbitals of the Te(IV) atoms with the dz2 orbital
of the Pd(II). The PdBr4 anion is twisted with respect to the
X–Te–X axis to minimize steric interactions between the halo-
gen atoms.
Figure 4. Diagram of [5]·I2·I3 showing the [C12H19N2Te]+ cation I3 anion and
–
I2 molecule linked by Te···I and I···I secondary interactions (for I12 only one
position shown).
2–
[Hg2Cl6]2–, [6]·Hg2Cl6 crystallized in the orthorhombic crystal
system, while [C24H38N4O2Te2]2+·2Br–, [6]·2Br crystallized in the
triclinic crystal system. The cationic entity, [2,6-(Me2NCH2)2-
+
C6H3Te(μ-O)]2 is similar in both these structures, so only that
in [6]·Hg2Cl6 will be described in detail and will be compared
to similar reported structures. There are only four reports avail-
able till date containing a cation with the Te2O22+ core. The first
report on the molecular structure of a dimeric diorganoditellu-
roxonium(IV) cation was made by Furukawa and co-workers,
+
which contains a cation [2,6-(Me2NCH2)2C6H3Te(μ-O)]2 stabi-
–
lized by a PF6 salt.[13] Beckmann and co-workers reported the
molecular structure of [(6-Ph2P(O)–Ace-5-)Te(μ-O)]2·2OTf
[Ace = acenaphthyl].[3m] Recently, we have reported the molec-
ular structures of IChB stabilized diorganoditelluroxonium(IV)
cation, namely [ppyTe(μ-O)]2·2ClO4 and [2,6-(Me2NCH2)2C6H3Te-
Figure 3. Diagram of [4]·PdBr4 containing a [C12H19BrClN2Te]+ cation and
PdBr4 anion showing the twist of the anion with respect to the cation and
the C–H···Br interactions.
2–
(μ-O)]2+·[PdCl3(DMSO)]– .[3o,12h]
2
In the molecular structure of [6]·Hg2Cl6, there is a cis arrange-
ment of the aryl rings of the attached 2,6-[(dimethylamino)me-
thyl)]phenyl substituents (Figure 5). This is in contrast to that
Compound [5]·I2·I3 i.e., [C12H19N2Te]+·I3 ·I2 crystallized in the
–
monoclinic space group C2/c with Z = 4 (i.e., Z′ = 0.5), indicating
crystallographically imposed symmetry where the central Te is
on a 2-fold axis and the I3– anion and I2 molecules lie on centers
–
observed in the structure of [2,6-(Me2NCH2)2C6H3Te(μ-O)]2+·PF6 ,
wherein the cation lies on a center of inversion and thus the aryl
groups are in a trans configuration.[13] The Te–N bond lengths
lying in the range from 2.467(6)-2.473(6) Å for [6]·Hg2Cl6 are
–
of inversion (Figure 4). In the case of the I3 anion, the central
iodine (I12) is not exactly on the inversion center being dis-
placed by 0.104 Å. The cation is planar with two five membered
chelating rings. The Te–N bond length is 2.3459(17) Å and is
less than that for the recently reported similar tellurenium(II)
cation, [2,6-(CH2NMe2)2C6H3Te]2·HgCl4 [2.392(7) Å].[8] This bond
length is less than the sum of the Te, N van der Waal radii [Σrvdw
(Te, N) = 3.63 Å] but it is larger than that of the sum of their
covalent radii [Σrcov (Te, N) = 2.09Å].[14,15] The anion and I2 have
in good agreement with the values observed in [2,6-
–
(Me2NCH2)2C6H3Te(μ-O)]2+·PF6
[2.475(5)-2.486(5) Å].[13] In
[6]·Hg2Cl6, the dihedral angles between the Te2O2 plane and aryl
rings are 83.7(2)° and 85.4(2)°, respectively, while the dihedral
angle between the two aryl rings is 10.9(3)° indicating that the
two aryl groups are not coplanar, and too far apart to form π···π
stacking interactions (closest contact is between C1a and C1b at
3.730 Å). Thus, the driving force for the adoption of this sterically
unfavorable cis conformation appears to be the formation of
Te···Cl cation···anion interactions which would not be possible if
the trans conformation was adopted. In this case, Cl1 from the
anion makes a bifurcated bond to both the Te atoms of the
cation [Te1···Cl1 3.389(2) Å; Te2···Cl2 3.575(2) Å]. A similar obser-
–
close contacts of 3.4475(2) Å with an I–I(I2)···I(I3 ) angle of
177.205(5) Å and an I–I(I3 )···I(I2) angle of 89.74(13) Å. The I3
–
–
anion is involved in H5A···I11 and H7A···I12 secondary interac-
tions with bond lengths of 3.381(2) Å and 3.278(81) Å, respec-
tively. As a result of these interactions, the I2 molecule comes
closer to Te with a Te···I distance of 4.2521(3) Å. In addition, the
extensive I···I halogen interactions form zig-zag ribbons in the
a direction (Figure S4, Supporting Information).
vation was also made in the recently reported diorganoditellu-
+
roxonium(IV) cation, namely [2,6-(Me2NCH2)2C6H3Te(μ-O)]2
·
The molecular structures of [6]·Hg2Cl6 and [6]·2Br represent [PdCl3(DMSO)]– , wherein due to the extensive cation···anion in-
2
rare examples of structurally characterized dimeric diorganodi- teractions, a cis orientation of the pincer ligands were ob-
telluroxonium(IV) cations. The molecular salt [C24H38N4O2Te2]2+ served.[12h] In contrast, in the case of [2,6-(Me2NCH2)2C6H3Te-
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–
(μ-O)]2+·PF6 , no such cation···anion interactions are present and Computational Studies
hence, the more sterically favorable trans conformation has been
In order to gain insight into the electronic structure of a mono-
adopted.[13] In the other two related structures containing the
organo dihalotelluronium(IV) cation, in particular, to understand
the role of the N-atoms of the 2,6-(dimethylamino)methyl}phenyl
(L) moiety on the stability of the synthesized compounds, single
point DFT calculations were carried out on [3]+, [4]+ and [5]+
using Gaussian 09 (Rev A.02) program[19] (functional: B3PW91;[20]
mixed basis set: Te: SDB-cc-pVTZ;[21] C/H/N/O/Cl/Br: 6-31G**[22]).
Examination of the Natural Bond Orbital (NBO)[23] plots reveals
that in cation [3]+, each N atom donates its lone pair of electrons
to the vacant p orbital (p*) of the Te atom, resulting in an
lp(N)→p*(Te) donor-acceptor interaction (Figure 6), wherein the
Te atom acts as the acceptor of the electrons from the N atoms.
The second-order stabilization energies of 92.2 kcal/mol and 81.3
of kcal/mol of the two N→Te interactions inferred that they con-
tributed significantly to the overall stability of the compound. In
case of cation [4]+, NBO analysis treats each N→Te interaction
as an lp(N)→Ry*(Te) donor-acceptor interaction with stabilization
energies of 91.2 kcal/mol and 78.7 kcal/mol. In case of tellure-
nium(IV) cation [5]+, each N→Te bond is attributed to
lp(N)→p*(Te) donor-acceptor interaction which contributes to
the stability of the compound by 82.4 kcal/mol.
2+
Te2O2 core, the same cis configuration has been adopted to
allow the formation of interionic Te···O interactions.[3m,3o]
In case of cation [3]+, two non-identical Te–Br interactions are
obtained from NBO analysis (Figure 7). In one case, one Br atom
is bonded to the Te atom by two centered, covalent sigma bond
(Figure 7a), while the NBO analysis treats the second Te–Br bond
as a lp(Br)→σ*(Te–Br) donor–acceptor interaction (Figure 7b). Inter-
estingly, in the case of [4]+, both Te–Cl and Te–Br interactions
are attributed to two centered, covalent sigma bonds (Figure 7c).
The presence of strong N→Te IChB in cations [3]+, [4]+and
[5]+, was further validated by electron localization function (ELF)
calculation,[24] wherein a continuum of elevated ELF values was
observed along the N→Te vectors (Figure 8).
Figure 5. The molecular structure of [6]·Hg2Cl6, showing cis conformation
adopted by phenyl rings.
Similar to [6]·Hg2Cl6, due to the extensive cation···anion inter-
actions, the arrangement of the aryl substituents in the molec-
ular structure of [6]·2Br are cis to each other (Figure S1, Support-
ing Information). Here, Br1 atom, from the anion moiety makes
a bifurcated bond to both the Te atoms of the cation [Te1···Br1
3.3946(11) Å, Te2···Br1 3.8497(11) Å]. It is worth mentioning that
in case of related organoantimony analogues bearing similar
NCN pincer ligands, a trans conformation of the pincer ligands
is observed. In particular, in the molecular structure of
The Wiberg bond order calculations reveal that in the cases
{2,6-[MeN(CH2CH2)2NCH2]2C6H3Sb(μ-O)}2 and [2,6-(Me2NCH2)2- of dihalotelluronium(IV) cations, [3]+ and [4]+, the C–Te bond
C6H3Sb(μ-O)]2, the pincer ligands adopted a trans orientation orders are almost equal to 1 (1.05 for [3]+; 1.06 for [4]+). A slightly
with respect to the central Sb2O2 cores.[18a,18b] However, in case higher C–Te bond order (1.10) is observed in tellurenium(II) cat-
of molecular structure of the corresponding Bi analogue, i.e., ion [5]+. In the case of [3]+, the calculated Wiberg bond orders
{2,6-[MeN(CH2CH2)2NCH2]2C6H3Bi(μ-O)}2, the pincer ligands are for the Te–Br bonds are 1.11and 1.17. A similar pattern is also
placed mutually in cis positions with regard to the four-mem- observed in the Te–Cl/Br bond orders of [4]+. In particular, the
bered Bi2O2 core.[18a] Interestingly, in case of both bismuth and calculated Te–Cl bond order is 1.11, while Te–Br bond order is
antimony compounds of related NCN pincer ligands containing slightly higher with a value of 1.20. The natural charges (in a.u.)
E2S2 (E=Sb, Bi) core such as, [2,6-(MeOCH2)2C6H3Sb(μ-S)]2, obtained from Natural Population Analysis (NPA) reveal that in
[2,6-(MesOCH2)2C6H3Sb(μ-S)]2 and [2,6-(Me2NCH2)2C6H3Bi(μ-O)]2, dibromotelluronium(IV) cation [3]+, a positive charge of +1.512
a trans orientation of pincer ligands was observed with regard is centered on the Te(IV) atom (Figure 9). The natural charges on
to the planar E2S2 (E=Sb, Bi) core.[18c–18d]
respective first coordination sphere atoms are Br (–0.436, –0.418),
Figure 6. The prominent natural bond orbital (NBO) plots of (a) [3]+, (b) [4]+, and (C) [5]+ showing strong N→Te interactions.
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Figure 7. NBO plots of (a–b) [3]+ and (c) [4]+ showing Te–X (X = Cl, Br) interactions.
Figure 8. Electron localization function (ELF) for (a) [3]+, (b) [4]+ and (c) [5]+ drawing in the plane containing N, C and Te atoms.
N (–0.505, –0.497) and C (–0.396). A similar distribution of NPA charges on N (–0.494) and C (–0.327) in [5]+ are in good agree-
charges is observed in the corresponding atoms in dihalotelluro- ment with that of [3]+ and [4]+.
nium(IV) cation [4]+. In particular, while the Te (IV) atom adheres
a positive charge of +1.572, there are accumulation of negative
charges of the values –0.477 at Cl, –0.448 at Br, (–0.504 and
–0.499) at N atoms, –0.382 at C atom. In case of tellurenium(II)
cation [5]+, almost half equivalent of positive charge is accumu-
lated (+0.730) at the Te(II) center, as compared to that of dihalo-
telluronium(IV) cations [3]+ and [4]+. The corresponding NPA
The frontier molecular orbitals for cations, [3]+, [4]+ and [5]+
are shown in Figure 10. The plots of frontier molecular orbitals
reveal that for both the dihalotelluronium(IV) cations [3]+ and
[4]+, the 2,6-(dimethylamino)methyl}phenyl (L) moiety makes
the major contribution to the HOMO (Figure 10a–b), whereas
in tellurenium(II) cation [5]+ contributions of both L and Te are
observed (Figure 10c). In each cation, the LUMO is localized
primarily on the Te center. For all the three cations, the HOMO-
Figure 9. NPA atomic charges of the atoms on the optimized structure of
compound (a) [3]+, (b) [4]+ and (c) [5]+. Colour code: Te-golden yellow,
Cl-bright green, Br-dark red, N-deep blue, C- dark grey and H-light grey.
Figure 10. Frontier molecular orbitals of (a) [3]·Br3, (b) [4]·PdBr4 and
(c) [5]·I2·I3 and their HOMO–LUMO energy gaps.
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ent temperature. The reaction was quenched by addition of water.
The reaction mixture was extracted with Et2O, the organic phase
was washed with H2O, dried with Na2SO4 and concentrated under
vacuum to get a yellow liquid. The liquid, in the next step, was
separated by column chromatography using petroleum ether (60–
80 °C) and ethyl acetate in 9:1 ratio as eluent. The first fraction
isolated was diorganotelluride 1, as a yellow liquid. The second frac-
tion isolated was diorganotelluride, 2 as a white solid.
LUMO energy gaps are similar and lie in the range of ΔE =
101.8 kcal/mol – 104.3 kcal/mol.
Conclusion
In conclusion, we have succeeded in isolating the first example
of a monoorgano dibromotelluronium(IV) cation of C-type,
[3]·Br3, by the reaction of heteroleptic diorganotelluride [2,6-
(Me2NCH2)2C6H3]TenBu (1) with molecular bromine. In an at-
tempt to explore the ligating properties of [3]·Br3, when it is
treated with K2PdCl4, the reaction results into the formation
of first example of a monoorgano mixed dihalotelluronium(IV)
cation [4]·PdBr4 (D-type), stabilized by a Pd(II) bromide anion.
When diorganotelluride 1 is treated with molecular iodine in
identical reaction conditions, the reaction results into the for-
mation of tellurenium(II) cation, [5]·I2·I3. Particularly interesting
aspect of the molecular structures of dihalotelluronium(IV) cat-
ions [3]·Br3 and [4]·PdBr4 is that the geometry around Te(IV)
center is distorted square pyramidal considering the Te lone
pair of electrons and N→Te interactions into account. The N–Te
bond lengths in each cases are well within the sum of the van
der Waals radii of the two elements (Te, N), indicating the pres-
ence of strong IChB interactions between the two atoms. In
line with Beckmann and co-workers' observation, these N→Te
interactions not only facilitate the formation of the desired di-
1
1: Yield: 1.84 g (66 %); H NMR (400 MHz, CDCl3): δ (ppm) 7.28 (d,
1H, Ar-H), 7.15–7.12 (m, 2H, Ar-H), 3.66 (s, 4H, Ar-CH2), 2.55 (t, 2H,
Bu-CH2), 2.23 (s, 12H, NMe2), 1.69–1.67 (m, 2H, Bu-CH2), 1.34–1.33
(m, 2H, Bu-CH2), 0.85 (t, 3H, Bu-CH3); 13C NMR (100 MHz, CDCl3): δ
(ppm) 145.17, 127.70, 127.46, 123.13, 68.77, 45.00, 34.02, 25.45,
13.67, 9.38; 125Te NMR (126 MHz, CDCl3): δ (ppm) 284 (lit. 287);[11]
MS(ESI+), m/z Calcd for [C16H29N2Te]+: 379.1385, found 379.1384.
2: Yield: 1.18 g (31 %); M.p. 127 °C (lit. 120–122 °C);[8] 1H NMR
(400 MHz, CDCl3): (ppm) 7.21–7.18 (m, 2H, Ar-H), 7.14–7.11 (m, 4H,
Ar-H), 3.18 (s, 8H, Ar-CH2), 2.13 (s, 24H, NMe2); 13C NMR (100 MHz,
CDCl3): δ (ppm) 144.15, 130.05, 127.54, 126.42, 65.45, 43.95; 125Te
NMR (126 MHz, CDCl3): δ (ppm) 374; MS(ESI+), m/z Calcd for
[C24H38N4Te]+: 512.2158, found 512.2161.
General procedure for the synthesis of [2,6-(Me2NCH2)2-
C6H3TeBr2]·Br3, [3]·Br3 and [2,6-(Me2NCH2)2C6H3]·I2·I3, [5]·I2·I3
To
a CCl4 (15 mL) solution of diorganotelluride 1 (0.20 g,
0.53 mmol), a CCl4 (10 mL) solution of Br2 (0.26 g, 85 μL, 1.65 mmol)
(for [3]·Br3) or I2 (0.42 g, 1.65 mmol) (for [5]·I2·I3) was added drop-
halotelluronium cations, but also attenuates the electrophilicity wise at –78 °C. After stirring the reaction mixture for 6 h at the
same temperature, the solvent was removed under vacuum. The
precipitate thus obtained was filtered off, washed with hexane
(5 mL × 2) and Et2O (10 mL × 3). The compound thus obtained was
dried under vacuum to afford analytically pure dark yellow solid of
[3]·Br3/red solid of [5]·I2·I3.
around the Te(IV) center. The active participation of N→Te inter-
actions in the stabilization of the compounds is corroborated
by detailed NBO and ELF analysis. It is noteworthy that al-
though various organotellurium species of the substrate, “2,6-
(Me2NCH2)2C6H3” have been widely studied in the literature, the
present work displays the first examples of any monomeric
Te(IV) cationic species of this substrate. We believe that the
availability of a monoorgano dihalotelluronium(IV) cation spe-
cies will stimulate exciting activity in the area of organometal-
lics, with respect to its synthetic design and reactivity profile.
[3]·Br3: Yield: 0.31 g (82 %); M.p. 165–167 °C; 1H NMR (400 MHz,
CDCl3): δ (ppm) 7.33 (d, 1H, Ar-H), 7.29–7.27 (m, 2H, Ar-H), 3.63 (d,
2H, Ar-CH2), 3.58 (d, 2H, Ar-CH2), 2.17 (s, 6H, NMe2), 2.13 (s, 6H,
NMe2); 13C NMR (100 MHz, CDCl3): δ (ppm) 135.84, 131.78, 128.10,
127.34, 66.04, 46.69; 125Te NMR (126 MHz, CDCl3): δ (ppm) 1706;
Anal. Calc. for C12H19Br5N2Te: C, 20.06, H, 2.67, N, 3.90; Found C,
20.19, H, 2.53, N, 4.01; MS(ESI+), m/z Calcd for [C12H19Br2N2Te]+:
480.8957, found 480.8961.
Experimental Section
[5]·I2·I3: Yield: 0.44 g (86 %); M.p. 173 °C; 1H NMR (400 MHz, CDCl3):
δ (ppm) 7.43–7.42 (m, 3H, Ar-H), 3.26 (s, 4H, Ar-CH2), 2.03 (s, 12H,
NMe2); 13C NMR (100 MHz, CDCl3): δ (ppm) 132.57, 132.40, 128.42,
125.94, 64.04, 48.98; 125Te NMR (126 MHz, CDCl3): δ (ppm) 1890;
Anal. Calc. for C12H19I5N2Te: C, 15.12, H, 2.01, N, 2.94; Found C, 14.97,
H, 2.12, N, 3.05; MS(ESI+), m/z Calcd for [C12H19N2Te]+: 321.0610,
found 321.0608.
All manipulations were performed under an N2 atmosphere using
standard Schlenk techniques unless otherwise noted. Solvents were
dried by following standard methods.[25] The starting materials and
solvents were purchased from commercial sources. 1H (400 and
500 MHz), 13C (100 and 125 MHz) and 125Te (126 MHz, 158 MHz)
NMR spectra were recorded on Bruker AV 400 MHz and Bruker AV
500 MHz spectrometers at 25 °C. Chemical shifts cited were refer-
enced to TMS (1H, 13C) as internal and Me2Te (125Te) as external
standard. Electron spray mass spectra (ESI-MS) were performed on
a Q-Tof micro (YA-105) mass spectrometer. Elemental analyses were
performed on a Carlo Erba Model 1106 elemental analyzer.
Synthesis of [2,6-(Me2NCH2)2C6H3TeClBr]·PdBr4, [4]·PdBr4
K2PdCl4 (0.05 g, 0.15 mmol) was added to a THF (10 mL) suspension
of [3]·Br3 (0.10 g, 0.14 mmol) at ambient temperature. The reaction
mixture was allowed to stir for 8 h at ambient temperature. After
that, solvent was removed under vacuum, resulting in a dark red
precipitation. The precipitate was filtered off, washed with CH2Cl2
(5 mL × 2) and Et2O (10 mL × 3) to obtain red solid of [4]·PdBr4.
Synthesis of [2,6-(Me2NCH2)2C6H3]TenBu,
1
and [2,6-
(Me2NCH2)2C6H3]2Te, 2
To a Et2O (20 mL) solution of 2-bromo-1,3-bis[(dimethylamino)-
methyl]benzene, LBr (2.00 g, 7.37 mmol), 1.6 concentration of
M
Yield: 0.14 g (78 %); M.p. 179 °C; 1H NMR (400 MHz, [D6]DMSO):
nBuLi (5.07 mL, 8.11 mmol) was added dropwise at 0 °C under δ (ppm) 7.36 (t, 1H, Ar-H), 7.12–7.09 (m, 2H, Ar-H), 3.59 (d, 2H,
nitrogen atmosphere and stirred for 30 min. The lithiated reaction Ar-CH2), 3.51 (d, 2H, Ar-CH2), 2.13 (s, 6H, NMe2), 2.09 (s, 6H, NMe2);
mixture was further cooled to –114 °C and Te powder (1.11 g, 13C NMR (100 MHz, [D6]DMSO): δ (ppm) 138.18, 131.09, 126.58,
8.85 mmol) was added to it and stirred for additional 12 h at ambi-
124.81, 61.26, 43.81; 125Te NMR (126 MHz, [D6]DMSO): δ (ppm) 1641;
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MS(ESI+), m/z Calcd for [C12H19BrClN2Te]+: 434.9482, found [6]·2Br) contain the supplementary crystallographic data for this
434.9489.
paper. These data are provided free of charge by the joint Cam-
bridge Crystallographic Data Centre and Fachinformationszentrum
Karlsruhe Access Structures service www.ccdc.cam.ac.uk/structures.
Note: Despite multiple efforts, the elemental analysis of [4]·PdBr4
was not satisfactory. This might be due to the incomplete combus-
tion of the heavy metal (i.e., Pd) during the recording of the sample.
Conflicts of interest
Synthesis of [2,6-(Me2NCH2)2C6H3Te(μ-O)]2·Hg2Cl6, [6]·Hg2Cl6.
The authors declare no conflict of interest.
To a solution of 1 (0.20 g, 0.53 mmol) in THF (10 mL), HgCl2 (0.22 g,
0.82 mmol) in THF (5 mL) was added dropwise at ambient tempera-
ture. After complete addition, the reaction mixture was stirred at
this temperature for 12 h in open air. To this, hexane (10 mL) was
added, resulting in a white solid. The white solid was filtered off,
washed with CH2Cl2 (10 mL × 3) and Et2O (5 mL × 3) and finally
dried under vacuum to afford [6]·Hg2Cl6.
Acknowledgments
H. B. S. gratefully acknowledges the Department of Science and
Technology, New Delhi, for the J. C. Bose Fellowship. A. G. is
thankful to the UGC for scholarship. A. S. acknowledges CSIR
for SRF.
Yield: 0.63 g (93 %); M.p. 159 °C; 1H NMR (500 MHz, [D6]DMSO):
δ (ppm) 7.39 (t, 2H, Ar-H), 7.10–7.06 (m, 4H, Ar-H), 3.83 (d, 4H, Ar-
CH2), 3.75 (d, 4H, Ar-CH2), 2.63 (s, 12H, NMe2), 2.49 (s, 12H, NMe2);
13C NMR (125 MHz, [D6]DMSO): δ (ppm) 139.75, 133.12, 129.87,
124.94, 71.04, 53.71; 125Te NMR (158 MHz, [D6]DMSO): δ (ppm) 1472;
Anal. Calc. for C24H38Cl6Hg2N4O2Te2: C, 22.46, H, 2.98, N, 4.36; Found
C, 22.69, H, 2.86, N, 4.41; MS(ESI+), m/2z Calcd for [C12H19N2OTe]+:
336.0545, found 336.0547.
Keywords: Dihalotelluronium(IV) cation ·
Diorganotellurides · Intramolecular chalcogen bonding ·
Structure elucidation · Density functional calculations
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Synthesis of [2,6-(Me2NCH2)2C6H3Te(μ-O)]2·2Br, [6]·2Br
A solution of Br2 (0.09 g, 29 μL, 0.58 mmol) in CCl4 (5 mL) was
added dropwise to the solution of 1 (0.20 g, 0.53 mmol) in CCl4
(15 mL) at 0 °C. The reaction mixture was stirred at same tempera-
ture for 4 h, resulting into the formation of yellow solid. The result-
ing solid was further treated with NaOH (0.02 g, 0.58 mmol) at room
temperature. After stirring for 12 h in open air, the solvent was
removed under vacuum resulting in precipitation of the crude
complex. This was washed with CH2Cl2 (10 mL × 3) and Et2O
(10 mL × 3) to give white solid of [6]·2Br.
1
Yield: 0.39 g (89 %); M.p. 143 °C; H NMR (500 MHz, [D6]DMSO):
δ (ppm) 7.30 (t, 2H, Ar-H), 7.15–7.11 (m, 4H, Ar-H), 3.77 (d, 4H, Ar-
CH2), 3.68 (d, 4H, Ar-CH2), 2.60 (s, 12H, NMe2), 2.28 (s, 12H, NMe2);
13C NMR (125 MHz, [D6]DMSO): δ (ppm) 134.25, 127.32, 127.12,
125.44, 69.14, 47.80; 125Te NMR (158 MHz, [D6]DMSO): δ (ppm) 1480;
Anal. Calc. for C24H38Br2N4O2Te2: C, 34.75, H, 4.62, N, 6.75; Found C,
34.59, H, 4.66, N, 6.87. (Anal. Calc. was carried out on crystals; the
compound lost the ethanol molecule of solvation and the water of
crystallization upon drying under vacuum); MS(ESI+), m/z Calcd for
[C24H38BrN4O2Te2]+: 751.0285, found 751.0283.
X-ray crystallographic study
X-ray diffraction for compound [3]·Br3, [4]·PdBr4 and [5]·I2·I3 was
collected on a Bruker Ape × 2 CCD diffractometer with Mo Kα radia-
tion. X-ray diffraction for [6]·Hg2Cl6 and [6]·2Br were collected on
a Xcalibur Gemini-R diffractometer with Cu Kα radiation. The data
collection was carried out by standard ω-scan technique and were
evaluated and reduced by using either CrystalClear-SM Expert or
CrysAlisPro software. The crystallographic data and structure refine-
ment parameters are given in ESI. The structures were refined by
full-matrix least-square with the anisotropic non-hydrogen atoms
and hydrogen atoms with fixed isotropic thermal parameter of 0.07
Å2 using the SHELXL program.[26] Due to the cell metrical parame-
ters emulating a monoclinic cell for [6]·2Br the data was incorrectly
collected in this cell and consequently was incomplete. By the time
this was noticed, the crystals had decayed and could not be re-
collected. Hence, the structure of [6]·2Br is included in ESI (Figure
S1).
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Received: September 29, 2020
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