Alkoxycarbonylmethyl derivatives of tellurium: Facile synthesis and structural studies

Article abstract of DOI:10.1016/j.jorganchem.2013.01.010

Methyl and t-butyl esters of α-bromoacetic acid added oxidatively to elemental tellurium in the presence of sodium iodide to give high yields of crystalline bis(alkoxycarbonylmethyl)tellurium(IV) diiodides, (ROCOCH ₂)₂TeI₂. The chloro and bromo analogs were prepared via their reduction into tellurides followed by dihalogen oxidation. Activation of the α-C_sp3-Br bond by ester functionality appears to be insufficient as methyl α-bromoacetate failed to add to Te(0) or aryltellurium(II) bromides. The nucleophilic substitution reaction of α-bromoesters with aryltellurolates, ArTe^-Na⁺ (Ar = 1-C₁₀H₇, Np; 2,4,6-Me₃C₆H ₂, Mes), gave (alkoxycarbonylmethyl)aryltellurides that were characterized as mixed diorganotellurium dihalides. Crystal structures of Np(MeOCOCH₂)TeBr₂, Mes(MeOCOCH₂)TeBr ₂ and Mes(t-BuOCOCH₂)TeCl₂ show that the functionalized organic moiety, ROCOCH₂, behaves as a (C, O) chelating ligand. The carbonyl O atom of the ester group in these compounds is involved in a 1,4-Te?O secondary bonding interaction. However, the functionalized ligands in the case of (MeOCOCH₂)₂TeI₂ are devoid of such an interaction. Surprisingly, one of the two organic ligands in (MeOCOCH₂)₂TeBr₂ takes part in an intramolecular 1,4-Te?O interaction, the other appears to involve an intermolecular Te?O interaction to result in a one-dimensional array of molecules in the crystal lattice.

Full text of DOI:10.1016/j.jorganchem.2013.01.010

Journal of Organometallic Chemistry 728 (2013) 38e43
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Alkoxycarbonylmethyl derivatives of tellurium: Facile synthesis and
structural studies
,
a
a
b
c
Ashok K.S. Chauhan a , Swami N. Bharti , Ramesh C. Srivastava , Ray J. Butcher , Andrew Duthie
*
a Department of Chemistry, University of Lucknow, Lucknow 226007, India
b Department of Chemistry, Howard University, Washington, DC 20059, USA
c School of Life and Environmental Sciences, Deakin University, Geelong 3217, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
Methyl and t-butyl esters of
sodium iodide to give high yields of crystalline bis(alkoxycarbonylmethyl)tellurium(IV) diiodides,
(ROCOCH2)2TeI2. The chloro and bromo analogs were prepared via their reduction into tellurides followed
a
-bromoacetic acid added oxidatively to elemental tellurium in the presence of
Received 16 November 2012
Received in revised form
10 January 2013
by dihalogen oxidation. Activation of the
methyl
reaction of
a-Csp3eBr bond by ester functionality appears to be insufficient as
Accepted 11 January 2013
a
-bromoacetate failed to add to Te(0) or aryltellurium(II) bromides. The nucleophilic substitution
a
-bromoesters with aryltellurolates, ArTeꢀNaþ (Ar ¼ 1-C10H7, Np; 2,4,6-Me3C6H2, Mes), gave
Keywords:
(alkoxycarbonylmethyl)aryltellurides that were characterized as mixed diorganotellurium dihalides.
Crystal structures of Np(MeOCOCH2)TeBr2, Mes(MeOCOCH2)TeBr2 and Mes(t-BuOCOCH2)TeCl2 show that
the functionalized organic moiety, ROCOCH2, behaves as a (C, O) chelating ligand. The carbonyl O atom of
the ester group in these compounds is involved in a 1,4-Te/O secondary bonding interaction. However, the
functionalized ligands in the case of (MeOCOCH2)2TeI2 are devoid of such an interaction. Surprisingly, one
of the two organic ligands in (MeOCOCH2)2TeBr2 takes part in an intramolecular 1,4-Te/O interaction, the
other appears to involve an intermolecular Te/O interaction to result in a one-dimensional array of
molecules in the crystal lattice.
Tellurium insertion
a
-Tellurated ester
Functionalized organotellurium
Nucleophilic telluration
Secondary bonding interaction
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
attributed to the inductive effect of the halogen atoms linked to it and
its propensity to take hypervalent bond state. This appears to result in
Reactions of active metals viz. Li and Mg with functionalized
organic substrates, as a route to C-metalated corresponding de-
rivatives, are not so straightforward due to the possible nucleophilic
attack of the Li/MgeC bond on the functional group. The less elec-
tropositive element Te inserts into the CeI bond of acylmethyl- and
amidomethyl iodides to afford functionalized organotellurium(IV)
the positive polarization of the carbon atom of the TeeC bond(s), in
spite of the greater electronegativity when compared to that of
a tellurium atom. Taking advantageof thisproperty, coupling reaction
of bis(a-carbonylmethyl)tellurium dichlorides, (RCOCH2)2TeCl2 with
lithium nitronates [LiC(NO2)R1R2], which provide nucleophilic sta-
bilized carbanions, has been devised and the coupling products
[RCOCH]CR1R2] isolated in high yields, though (ROCOCH2)2TeCl2
required higher reaction temperature to afford the coupling product
in modest yield [4]. The rare absence of 1,4-Te/O SBIs observed in
case of (PhOCOCH2)2TeCl2, [the only ester functionalized organo-
tellurium(IV) dihalide characterized crystallographically [4]] is
interesting and substantiates poor electrophilicity of Te(IV) center in
it. Also, the described synthesis of (ROCOCH2)2TeCl2, (R ¼ Me, Ph), the
only reported bis(alkoxycarbonylmethyl)tellurium(IV) dihalides, re-
quires initial preparation of the ketene silyl acetal [H2C]C(OR)
OSiMe3] from the enol of the parent acetic acid ester followed by
electrophilic substitution with moisture sensitive TeCl4 [5]. However,
different synthetic approaches in the past have been made to obtain
(alkoxycarbonylmethyl)tellurium(II) derivatives analogous to well
diiodides, (YCH2)2TeI2 (Y ¼ RCOe, R1R2NCOe).
a-Carbonyl activation
of the Csp3eBr bond of acylmethyl- and amidomethyl bromides has
also been exploited in our laboratory as a one-step synthetic protocol
to get analogous dibromides, (YCH2)2TeBr2 [1,2]. Crystallographic
structure determination of more than a dozen such diorganotellur-
ium(IV)halides revealed thatthe carbonyl O atom isalmostinvariably
involved in the intramolecular 1,4-Te/O secondary bonding in-
teractions (SBI), at least in the solid state [3]. The moderate oxophi-
licity exhibited by the tellurium atom in these compounds may be
* Corresponding author. Tel.: þ91 9415010763; fax: þ91 522 2338531.
E-mail addresses: akschauhan2003@yahoo.co.in, akschauhan@hotmail.com
(A.K.S. Chauhan), goswamiswaminath@yahoo.com (S.N. Bharti), rameshlko@
yahoo.co.nz (R.C. Srivastava), rbutcher99@yahoo.com (R.J. Butcher), aduthie@
deakin.edu.au (A. Duthie).
explored
a-organylselenoesters. a-Alkyltelluoesters were first pre-
pared by thermal decomposition of telluronium salts, [R2(ROCOCH2)
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.01.010

A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 728 (2013) 38e43
39
Te]þ Brꢀ [6,7]. Subsequent methods include reactions of organo-
mixed halide, (MeOCOCH2)2TeClBr by stirring an equimolar mix-
ture of 1a and NaBr did not succeed, however the isolated sample
showed three peaks (at 796, 775 and 748 ppm in 1:3:3 ratio) which
may be assigned to (MeOCOCH2)2TeCl2, (MeOCOCH2)2TeClBr and
(MeOCOCH2)2TeBr2 respectively.
tellurium reagents, prepared in situ, such as ArTeꢀ Mþ (M ¼ Li, Na)
and ArTeX (X ¼ Br, I) with
a-bromoesters [8,9] and lithium enolates
[10] or Reformatsky reagent, BrZnCH2COOR [11], respectively. Inter-
estingly, 1:1 addition of PhTeBr to ethyl diazoacetate provided
labile ethyl-
of bis(triphenylstannyl)telluride with
metrical telluroesters, (ROCOCH2)2Te [13]. Surprisingly, oxidative
addition of -haloesters to elemental tellurium, similar to the syn-
thetic protocol for Reformatsky reagents, has never been observed.
In the above context, it has been envisaged in the present
investigation to examine the potential of alkoxycarbonyl function-
a
-bromo-
a
-pheyltelluroacetate [12], while the reaction
The nucleophilic substitution reactions of a-bromoesters,
a-bromoesters provided sym-
ROCOCH2Br, used in the present study with aryltellurolates, ArTeꢀ
(Ar ¼ 1-C10H7, Np; 2,4,6-Me3C6H2, Mes) proceeded readily at room
temperature to afford alkylaryltellurides, Ar(ROCOCH2)Te (Ar ¼ Np
and R ¼ Me, 3; t-Bu, 4; Ar ¼ Mes and R ¼ Me, 5; t-Bu, 6) as yellow
oils or low melting solid (6). Oxidative addition of dihalogens gave
the dihalides, Ar(ROCOCH2)TeX2 (X ¼ Cl, 3ae6a; Br, 3be6b; I, 3ce
6c) (Scheme 1). These mixed diorganotellurium(IV) dihalides are
crystalline solids stable to air and moisture, except 3c and 5c which
decompose on standing at room temperature. In the 1H NMR
spectra, Te(II) compounds 4 and 6 showed a high field signal for the
methylene protons ((compared to the respective dihalides),
Ar(ROCOCH2)TeX2) in addition to the expected signals for aryl and
t-butyl protons. Presence of a single resonance owing to the two
ortho methyls of the mesityl ligand in 5 and 6 is consistent with the
free rotation of the aryl moiety about the TeeCMes bond. This is,
however, not so in the 1H NMR spectra of the dihalides, Mes(RO-
COCH2)TeX2, which show separate signals for each of the ortho
methyls as well as for the ring protons of the aryl ligand. Magnetic
inequivalence of methyl substituents of the aryl moiety among the
mesityltellurium(IV) dihalides is also evident from the separate
signals for the methyl carbons in their 13C NMR spectra. The pres-
ence of axial halo ligands in these mesityltellurium(IV) compounds
thus causes steric hindrance in the free rotation of the aryl moiety
about the TeeCMes bond. There is a single peak in the 125Te NMR
spectra of the examined tellurium(IV) dihalides and the chemical
shift values in the range 687e804 ppm appear to be more affected
by the nature of the halide than that of the organic ligands.
a
ality in the activation of
a
-Csp3eX (X ¼ I, Br) bond to insert elemental
tellurium and to determine the bonding mode of the organic ligands
in the resulting bis(alkoxycarbonylmethyl)tellurium(IV) dihalides.
The mixed (alkoxycarbonylmethyl)aryltellurium(IV) dihalides have
also been prepared for structural comparison.
2. Results and discussion
2.1. Synthesis
Elemental tellurium failed to react with a-bromoesters when
heated together up to w100 ꢁC. However, when a mixture of tel-
lurium powder, ROCOCH2Br and NaI was stirred overnight at room
temperature, bis(alkoxycarbonylmethyl)tellurium(IV) diiodides,
(ROCOCH2)2TeI2 (R ¼ Me, 1c; t-Bu, 2c) were obtained in very good
yields. On reduction in a biphasic medium with Na2S2O5, both
diiodides afforded the corresponding tellurides, (ROCOCH2)2Te
as yellow liquids which were characterized as their dihalides
(ROCOCH2)2TeX2 [X ¼ Cl (1a, 2a), Br (1b, 2b)] after halogenations
with SO2Cl2 and Br2 at 0 ꢁC (Scheme 1). The addition of a dichloro-
methane solution of MeOCOCH2Br to a stirred solution of mesi-
tyltellurium(II) bromide in the same solvent (prepared in situ by
mixing equimolar amounts of dimesityl ditelluride and Br2) sepa-
rated some elemental tellurium. Removal of the solvent from the
filtrate gave a light yellow residue. The 1H NMR spectrum of this
compound corresponded to that of dimesityltellurium dibromide
and was devoid of any signal due to tellurium-bound methylene
protons.
2.2. Crystal structures
The crystal structures determined by single-crystal diffraction for
(MeOCOCH2)2TeBr2,1b, (MeOCOCH2)2TeI2,1c, Np(MeOCOCH2)TeBr2,
3b, and Mes(MeOCOCH2)TeBr2, 5b, are unambiguous while t-butyl
group in case of Mes(t-BuOCOCH2)TeCl2, 6a, is two-fold disordered.
The ORTEP views of the molecular structures showing the atom
numbering are presented in Figs. 1e5. Hydrogen atoms are omitted
for clarity. The selected bond lengths and angles are summarized in
Table 1 and crystallographic data together with the structure
refinement details are given in Table 2. All of these compounds
exhibit putative see-saw geometry to the C2TeX2 core, characterized
by a hypervalent quasi-linear XeTeeX fragment. The planarity
of the skeletal frameworks of the alkoxycarbonylmethyl ligands
All the six dihalides are crystalline solids fairly stable at ambient
conditions and soluble in dichloromethane and chloroform. Their
1H NMR spectra consist of singlets for the methylene (
d
w4.4 ppm)
and alkoxy protons (
d w3.8 ppm, Me; w1.5 ppm, CMe3). Compound
1a has been prepared earlier by a different method, but the
assignment of peaks is erroneous [4]. The 13C chemical shifts of the
methylene carbon and the 125Te chemical shifts for the examined
compounds appear to be sensitive to the nature of halo ligands, but
the
d(
13C) values for the carbonyl carbons (164e166 ppm) are little
(methyleneCeC(O)OeCalkyl) is another common feature of these
affected. Compound 1b was also prepared by the metathetical re-
action between 1a and sodium bromide. Attempts to prepare the
ester-functionalized organotellurium(IV) dihalides. Despite the
similarity of the primary geometry around the Te(IV) atom in these
Scheme 1. Synthetic routes and interconversion reactions.

40
A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 728 (2013) 38e43
Fig. 1. ORTEP view of 3b showing the atom numbering scheme. Hydrogen atoms are
omitted for clarity.
Fig. 3. ORTEP view of 6a showing the atom numbering scheme. Hydrogen atoms are
omitted for clarity.
compounds, they crystallized in different space groups. The diversity
of space groups among these alkoxycarbonylmethyltellurium(IV)
dihalides suggests that the packing of these compounds is sensitive
to the nature of the ligands attached to the central atom.
Asymmetric units in the crystal structures of 3b and 6a each
consist of one molecule, but two in case of 5b. The molecular
structure in these mixed-diorganotellurium(IV) halides is charac-
terized by the presence of the functionalized ligand in (C,O) che-
lating mode involving intramolecular 1,4-Te/O secondary bonding
interaction (Figs. 1e3).
and (R2NCOCH2)2TeX2 [2], the C-bonded ester functionalized li-
gands in 1c are devoid of any intramolecular Te/O interactions as
observed earlier in the case of (PhCOCH2)2TeCl2 [5]. The skeletal
plane of each organic ligand is skewed away from the equatorial
plane of the central Te atom and becomes nearly orthogonal to it
[dihedral angles ¼ 65.1(1)ꢁ] (Fig. 4).
Absence of intramolecular Te/O interactions in the crystalline
state of 1c paves the way for intermolecular Te/I interactions. Each
central Te(IV) atom in the self assembly acquires coordination
number 6 (excluding its lone pair) via reciprocatory intermolecular
The attractive interaction between the carbonyl O atom of the
ester group and central Te(IV) atom results in a significantly shorter
ꢀ
ꢀ
Te/I interactions [d(Te, I) ¼ 3.655 A, cf. Srvdw(Te, I) ¼ 4.04 A;
:I/TeeCtrans ¼ 166.9ꢁ] with two adjacent molecules. A folded
ribbon like supramolecular architecture thus becomes evident in
the solid state of this compound (Fig. S1). Although the inter-
molecular Te/I linkages are longer compared to the primary TeeI
ꢀ
interatomic distance [d(Te,O), (A) ¼ 2.979(3), 3b; 3.074(3), 2.995(3),
5b; 2.938(1), 6a] in comparison to the sum of their van der Waal
ꢀ
radii [Srvdw(Te, O) ¼ 3.58 A]. The functionalized ligand orients itself
to become nearly coplanar with the CeTeeC plane [interplanar
angle, (ꢁ) ¼ 11.8(2), 3b; 37.2(2), 30.8(1), 5b; 22.4(4), 6a] and the O
atom lies almost in the equatorial plane [distance of O atom from
ꢀ
bonds [d(Te, I) ¼ 2.895(1) A], all the angles around Te atom in the
TeC2I4 moiety are quite close to the ideal value of 90ꢁ. The two
iodine atoms drawn from the adjacent molecules that lie in the
domain of the lone pair on the central Te(IV) atom in each molecule,
subtend an angle even smaller than the angle opposite to it
[:I/Te/I ¼ 90.8(1)ꢁ, :CeTeeC ¼ 94.8(1)ꢁ]. It may be concluded
that the self assembly via intermolecular Te/I interactions in the
crystalline state of this compound, ignores the Te(IV) lone pair
stereochemical activity, if any. The crystal structure of its bromo
analog, (MeOCOCH2)2TeBr2, 1b is interestingly somewhat different
(Fig. 5). While one of the organic ligands takes part in the intra-
molecular 1,4-Te/O interaction, the other is devoid of it. The
chelated organic ligand orients its plane suitably to become almost
coplanar with the CeTeeC plane [interplanar angle ¼ 16.9(1)ꢁ] and
its carbonyl O atom lies nearly trans to the other TeeC bond
ꢀ
the equatorial plane, (A) ¼ ꢀ0.377(4), 3b; 0.347(3), ꢀ0.491(4), 5b;
0.220(1), 6a] and occupies a position nearly trans to the TeeCaryl
bond [:O/TeeCaryl, (ꢁ) ¼ 150.9(2), 3b; 157.2(1), 157.3(1), 5b;
160.4(1), 6a]. Formation of the four-member chelate ring causes
angular distortion at the tellurium-bound C atom of the alkox-
ycarbonylmethyl ligand, as a consequence the measure of :Tee
C
sp3eCcarbonyl in these compounds [106.7(3)ꢁ, 3b; 104.7(3)ꢁ,
104.7(2)ꢁ, 5b; 105.0(1)ꢁ, 6a] is smaller to the ideal value of 109.5ꢁ.
The propensity of central Te(IV) atom to increase its coordination
number thus imparts an octahedral environment including its lone
pair around it, at least in the crystalline state of the alkox-
ycarbonylaryltellurium(IV) compounds. Besides, the steric demand
of an aryl ligand in these compounds widens the equatorial angle
[:CeTeeC, (ꢁ) ¼ 99.7(2), 3b; 107.6(1), 108.0(1), 5b; 108.0(1), 6a; cf.
96(3)ꢁ, the average value for a C2TeX2 core [14]] and makes the
Te(IV) atom inaccessible for the ubiquitous intermolecular Te/X
interactions.
ꢁ
ꢀ
[:O1A/TeeC1Btrans ¼ 145.5(1) ] at a distance of 3.003(3) A from
the Te(IV) center which is significantly shorter to the value of
Srvdw(Te, O). A comparison of the TeeCsp3eCcarbonyl angular mea-
sures for the two C-bonded ligands in this compound [106.6(3)ꢁ
versus 112.8(3)ꢁ] suggests a significant contraction at the methyl-
ene C atom of the chelated ligand owing to the attractive non
The ligational behavior of the functionalized organic ligands in
(MeOCOCH2)2TeI2, 1c is however exceptional. The asymmetric unit
in the crystal lattice comprises of half a molecule and unlike the
(C,O) chelating mode exhibited by acylmethyl and amidomethyl
ligands among analogous compounds, (RCOCH2)2TeX2 [1,3,15,16]
Fig. 2. ORTEP view of 5b (molecule 1) showing the atom numbering scheme.
Fig. 4. ORTEP view of 1c showing the atom numbering scheme. Hydrogen atoms are
Hydrogen atoms are omitted for clarity.
omitted for clarity.

A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 728 (2013) 38e43
41
of bromoacetic acid (synthesis grade) were procured from Merck,
Germany and used as such. Bis(1-naphthyl)ditelluride and dime-
sitylditellurides were prepared by the reported method [17,18].
Melting points were recorded in capillary tubes and are uncorrec-
ted. 1H NMR (300.13 MHz) spectra were recorded on a Bruker
DRX300 spectrometer and 13C{1H} (100.54 MHz) and 125Te{1H}
(126.19 MHz) NMR spectra on a JEOL Eclipse Plus 400 NMR spec-
trometer. CDCl3was used as NMR solvent and the reported 1H and
13C chemical shifts in ppm are against Me4Si while the 125Te
chemical shifts are against Me2Te. C, H analyses were carried out
using a Carlo Erba 1108 analyzer.
Fig. 5. ORTEP view of 1b showing the atom numbering scheme. Hydrogen atoms are
omitted for clarity.
4.2. Syntheses
4.2.1. Syntheses of bis(alkoxycarbonylmethyl)tellurium diiodides
A typical experiment is described. Te powder (1.3 g, 10 mmol),
2-bromomethylacetate (2.0 mL, 21.6 mmol) and sodium iodide
(3.0 g, 20 mmol) were stirred together for 72 h at room temper-
ature (the reaction is complete in 4e5 h when stirred at moderate
temperature w40e50 ꢁC). The resulting red colored paste
was dissolved in diethyl ether and filtered. The filtrate was freed
of solvent and the residue triturated with petroleum ether (40e
60 ꢁC). The red solid obtained was filtered and recrystallized
from dichloromethane to give 1c. Yield: 4.75 g (90%). M.p.: 72 ꢁC.
Anal. Calc. for C6H10O4TeI2 (527.55): C, 13.66; H, 1.91. Found: C,
bonded Te/O interaction. The skeletal plane of the second C-
bonded methoxycarbonylmethyl moiety in the solid state of this
compound is almost orthogonal to the CeTeeC plane [dihedral
angle ¼ 67.1(2)ꢁ]. The central Te atom in this molecule is accessible
and invokes intermolecular Te/ Bri SBI as supramolecular motif
[d(Te, Br ) ¼ 3.562(1) A, cf. Srvdw(Te, Br) ¼ 3.93 A; Br /Tee
C1Atrans ¼ 163.0(1)ꢁ; i ¼ x ꢀ 1/2, ꢀy þ 3/2, z ꢀ 1/2]. This inter-
action interlinks two rows of molecules in the crystal lattice in
a gear-teeth fashion. The carbonyl O atom of the organic ligand
(devoid of intramolecular Te/O interaction) from an adjacent
i
i
ꢀ
ꢀ
molecule also approaches the central Te(IV) atom so that the
13.76; H, 1.84. 1H NMR:
13C{1H} NMR: 41.0 (CH3), 54.0 (CH2), 166.4 (CO) ppm. 125Te{1H}
NMR: 687 ppm.
d 3.88 (s, 6H, CH3O), 4.48 (s, 4H, CH2) ppm.
interatomic distance is smaller [d(Te,O1Bii)
¼
3.512(4) A,
ꢀ
d
O1Bii/TeeC1Atrans ¼ 129.7(1)ꢁ; ii ¼ x þ 1/2, ꢀy þ 3/2, z ꢀ 1/2],
though marginally, compared to Srvdw(Te, O) value and may be said
to account for a weak intermolecular Te/O SBI on the distance
versus strength criteria (Fig. S2).
d
The use of t-butyl ester of bromoacetic acid in the synthesis
described above gave red crystals of 2c. Yield: 5.2 g (86%). M.p.:
93 ꢁC. Anal. Calc. for C12H22O4TeI2 (611.71): C, 23.56; H, 3.63. Found:
C, 23.88; H 3.91. 1H NMR:
13C{1H} NMR:
164.8(CO) ppm. 125Te{1H} NMR:
d
1.54 (s, 18H, t-Bu), 4.39 (s, 4H, CH2) ppm.
28.0 (CH3), 43.2 (CH2), 85.6 (quaternary C),
655 ppm.
3. Conclusion
d
d
The potential of an ester group to activate the a-Csp3eBr bond to
insert Te(0) and afford ester-functionalized organotellurium de-
rivatives is poor compared to an acyl or amido group. However,
stirring at room temperature of a mixture of an alkyl ester of
4.2.2. Syntheses of bis(alkoxycarbonylmethyl)tellurium dibromides
and dichlorides
The bromo and chloro analogs of 1c and 2c were prepared by
their reduction to the respective bis(alkoxycarbonylmethyl)tellu-
rides followed by oxidative halogenations with Br2 and SO2Cl2. In
a typical experiment, an aqueous solution of sodium meta-
bisulphite (0.19 g, 1.0 mmol) was added slowly under stirring to
a dichloromethane solution of 0.528 g (1.00 mmol) of the com-
pound 1c. The organic layer was separated within 15 min and
washed thrice with water and passed over a bed of anhydrous so-
dium sulfate. The filtrate was freed from the solvent to give yellow
oily telluride, 1. Addition of a solution of SO2Cl2 (0.12 mL, 1.5 mmol)
in n-hexane (w10 mL) to a cooled (0 ꢁC) light yellow solution of 1 in
the same solvent (20 mL) under stirring precipitated a white solid
which was filtered and recrystallized from dichloromethane to give
analytically pure 1a. Yield: 0.28 g (80%). M.p.: 60 ꢁC (lit. 50e55 ꢁC
[4]). Anal. Calc. for C6H10O4TeCl2 (344.65): C, 20.91; H, 2.92.
a
-bromoacetic acid, sodium iodide and tellurium powder provides
a convenient synthetic route to obtain the desired organotellurium
compounds. The delicate balance between the electronic factors
and crystal forces appear to direct the bonding mode of the
alkoxycarbonylmethyl ligands in the solid state. The secondary
bonding interactions involving Te(IV) atom with a lone pair, appear
to ignore the VSEPR rules at least in the crystalline state of the
functionalized organotellurium(IV) halides.
4. Experimental
4.1. General procedures
Preparative work was performed under dry nitrogen. All sol-
vents were purified and dried before use. Methyl and t-butyl esters
Found: C, 20.78; H, 2.85. 1H NMR:
d
3.87 (s, 6H, OCH3), 4.42 (s, 4H,
Table 1
ꢁ
ꢀ
Selected interatomic distances (A) and bond angles ( ) of 1b, 1c, 3b, 5b, and 6a.
Parameter
1b
2.129(5)
2.154(4)
93.2(2)
2.655(1)
2.670(1)
175.15(2)
3.003(3)
145.5(1)
1c
2.158(1)
3b
2.137(4)
2.115(4)
99.7(2)
2.705(1)
2.628(1)
173.30(2)
2.979(3)
150.9(2)
5b
6a
TeeCalkyl(C1/C1A, C1B)
TeeCalkyl (C1/1B) or TeeCaryl(C4/C4A, C4B)
2.148(3), 2.138(3)
2.131(3), 2.119(3)
107.6(1), 108.0(1)
2.693(1), 2.698(1)
2.644(1), 2.634(1)
173.92(2), 174.34(2)
3.074(3), 2.995(3)
157.2(1), 157.3(1)
2.127(1)
2.125(1)
108.02(6)
2.503(1)
2.512(1)
171.43(2)
2.938(1)
145.5(1)
2.158(1)
94.8(2)
2.895(1)
2.895(1)
176.50(2)
e
C
alkyleTeeCaryl
TeeX1
TeeX2
X1eTeeX2
Te/O1 (O1A, O1B) (<3.58)
O1 (O1A, O1B)/TeeCtrans
e

42
A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 728 (2013) 38e43
Table 2
Crystal data and structure refinement details of 1b, 1c, 3b, 5b, and 6a.
1b
1c
3b
5b
6a
Empirical formula
C6H10Br2O4Te
433.56
C6H10I2O4Te
527.54
C13H12Br2O2Te
487.65
C12H16Br2O2Te
479.67
C15H22Cl2O2Te
432.83
Formula mass (g molꢀ1
)
Temperature (K)
123(2)
0.71073
110(2)
0.71073
295(2)
0.71073
295(2)
0.71073
295(2)
0.71073
ꢀ
Wavelenth,
l
(A)
Crystal system
Crystal size (mm3)
Space group
Monoclinic
0.85 ꢂ 0.45 ꢂ 0.11
P 21/n
6.6483(2)
19.1797(6)
9.4488(5)
90
106.836(4)
90
1153.19(7)
4
Monoclinic
0.47 ꢂ 0.44 ꢂ 0.32
C 2/c
19.2748(9)
9.2967(5)
6.9406(3)
90
93.080(4)
90
1241.90(10)
4
Triclinic
Monoclinic
0.53 ꢂ 0.21 ꢂ 0.18
P 21/n
11.1424(4)
9.2479(3)
30.9878(13)
90
99.124(4)
90
3152.70(19)
8
Orthorhombic
0.55 ꢂ 0.22 ꢂ 0.17
P b c a
9.9930(3)
17.8639(6)
20.6867(5)
90
0.48 ꢂ 0.44 ꢂ 0.15
P ꢀ1
ꢀ
a (A)
7.2466(5)
9.4560(5)
12.4268(5)
72.137(4)
77.153(4)
70.577(5)
757.46(7)
2
ꢀ
b (A)
ꢀ
c (A)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
90
90
3
ꢀ
V (A )
3692.86(19)
8
1.557
Z
rcalcd (Mg mꢀ3
)
2.497
9.492
2.821
7.352
2.138
7.230
2.021
6.946
m
(MoK
a
, mmꢀ1
)
1.899
F(000)
800
944
456
1808
1712
h, k, l ranges collected
Reflection collected
ꢀ6 ꢃ h ꢃ 10
ꢀ26 ꢃ k ꢃ 29
ꢀ14 ꢃ l ꢃ 10
7235
ꢀ21 ꢃ h ꢃ 26
ꢀ11 ꢃ k ꢃ 9
ꢀ9 ꢃ l ꢃ 9
3062
ꢀ10 ꢃ h ꢃ 9
ꢀ12 ꢃ k ꢃ 14
ꢀ14 ꢃ l ꢃ 18
9110
ꢀ16 ꢃ h ꢃ 13
ꢀ12 ꢃ k ꢃ 13
ꢀ44 ꢃ l ꢃ 43
28,479
ꢀ15 ꢃ h ꢃ 14
ꢀ18 ꢃ k ꢃ 25
ꢀ26 ꢃ l ꢃ 30
19,592
Independent reflections
q
3780[R(int) ¼ 0.0399]
5.17 to 32.75
98.7
1447 [R(int) ¼ 0.0215]
4.75 to 29.39
98.9
4978 [R(int) ¼ 0.0356]
5.15 to 32.76
99.0
10,558 [R(int) ¼ 0.0525]
5.04 to 32.80
98.7
6236 [R(int) ¼ 0.0321]
5.07 to 32.66
99.1
range (ꢁ)
Completeness to qmax (%)
Absorption correction
Analytical
Semi-empirical from
equivalents
1.00000, 0.57455
Semi-empirical from
equivalents
1.00000, 0.15936
Semi-empirical from
equivalents
1.00000, 0.23326
Semi-empirical from
equivalents
1.00000, 0.72057
Max., min. transmission
0.338, 0.027
Refinement method
Full-matrix least-squares Full-matrix least-squares Full-matrix least-squares Full-matrix least-squares Full-matrix least-squares
on F2
on F2
on F2
on F2
on F2
Data/restraints/parameters 3780/0/121
1447/0/62
0.983
4978/0/165
0.917
10,558/0/316
0.860
6236/0/201
0.919
Goodness of fit on F2
1.033
Final R indices (I > 2
s(I))
R1 ¼ 0.0441,
wR2 ¼ 0.0906
R1 ¼ 0.0613,
wR2 ¼ 0.0992
2.751/ꢀ2.300
R1 ¼ 0.0242,
wR2 ¼ 0.0545
R1 ¼ 0.0333,
wR2 ¼ 0.0563
0.999/ꢀ0.852
R1 ¼ 0.0493,
wR2 ¼ 0.1120
R1 ¼ 0.0875,
wR2 ¼ 0.1225
1.503/ꢀ1.876
R1 ¼ 0.0411,
wR2 ¼ 0.0688
R1 ¼ 0.1223,
wR2 ¼ 0.0800
0.962/ꢀ0.755
R1 ¼ 0.0326,
wR2 ¼ 0.0694
R1 ¼ 0.0727,
wR2 ¼ 0.0761
0.622/ꢀ0.476
R indices (all data)
Largest diff peak/hole
ꢀꢀ3
(e A
)
CH2) ppm. 2a: yield: 86%. M.p.: 120 ꢁC. Anal. Calc. for C12H22O4TeCl2
(428.81): C, 33.61; H, 5.17. Found: C, 33.58; H, 4.93. 1H NMR:
1.53
(s, 18H, t-Bu), 4.32 (s, 4H, CH2) ppm. 13C{1H} NMR:
27.9 (CH3), 49.7
(CH2), 85.3 (quaternary C), 164.7 (CO) ppm. 125Te{1H} NMR:
4.2.4. Syntheses of aryl(alkoxycarbonylmethyl)tellurides
d
In a typical experiment, a solution of bis(1-naphthyl)ditelluride
(0.51 g, 1.0 mmol) in dry THF (20 mL) was cooled to 0 ꢁC in a two
neck 100 mL round bottom flask under a flow of dry nitrogen.
t-Butyl ester of 2-bromoacetic acid (0.45 mL, 2.7 mmol) was added
with stirring, followed by slow addition of a 5% aqueous solution of
sodium borohydride until the red color of the ditelluride faded. The
mixture was stirred at room temperature for a further 5 h. The
compound was extracted with dichloromethane (50 mL), washed
with distilled water (3 ꢂ 50 mL) and dried over anhydrous sodium
sulfate. The solvent was removed completely under reduced pres-
sure to result in a light orange oil of (1-naphthyl)(t-butox-
ycarbonylmethyl)telluride, 4. The product was added to a silica
column, eluted with n-hexane to wash out the unreacted ditellur-
ide and then with dichloromethane to obtain the purified product.
d
d
793 ppm.
1b: yield: 72%. M.p.: 61 ꢁC. Anal. Calc. for C6H10O4TeBr2 (433.55):
C, 16.62; H, 2.32. Found: C, 16.38; H, 2.35. 1H NMR:
d
3.88 (s, 6H,
44.9 (OCH3), 53.8
748 ppm. 2b: yield: 80%.
CH3O), 4.52 (s, 4H, CH2) ppm. 13C{1H} NMR:
(CH2), 166.3 (CO) ppm. 125Te{1H} NMR:
d
d
M.p.: 105 ꢁC. Anal. Calc. for C12H22O4TeBr2 (517.71): C, 27.84; H,
4.28. Found: C, 27.58; H, 4.12. 1H NMR:
4H, CH2) ppm.
d 1.54 (s, 18H, t-Bu), 4.41 (s,
4.2.3. Metathetical reactions of 1a and 2a with sodium bromide
Compounds 1b and 2b were also obtained by the halide ex-
change reaction between 1a or 2a and NaBr. A solution of 1a
(0.70 g 2.0 mmol) in dichloromethane (20 mL) was stirred with
sodium bromide (0.50 g, 4.9 mmol) for 6 h. The sodium halides
were removed by filtration. Concentration of the filtrate and
addition of petroleum ether (40e60 ꢁC) afforded 0.73 g (84%) of
1b as a light yellow solid, which when recrystallized from
chloroform gave yellow crystals. Compound 2b was obtained
similarly.
Attempts to prepare a pure sample of mixed halide, (MeO-
COCH2)2TeClBr by stirring 1a with NaBr in 1:1 molar ratio were
unsuccessful, though 125Te NMR of the isolated sample showed
three signals at 796, 748 and 775 (w1:3:3) ppm which may be
assigned to 1a, 1b and the mixed halide respectively.
Yield: 0. 61 g (81%); 1H NMR:
8.26e7.30 (m, 7H, aryl protons).
d 1.26 (s, 9H, t-Bu), 3.47 (s, 2H, CH2),
The other aryl(alkoxycarbonylmethyl)tellurides, 3, 5 and 6 were
prepared similarly. These tellurides are liquids at ambient tem-
perature, except 6 which is a low melting solid (M.p.: 33e34 ꢁC).
5: yield: 81%; 1H NMR:
d 2.29 (s, 3H, p-CH3), 2.62 (s, 6H, o-CH3),
3.38 (s, 2H, CH2); 3.52 (s, 3H, OCH3), 6.99 (s, 2H, m-aryl protons)
ppm.
6: yield: 86%; 1H NMR:
d 1.67 (s, 9H, t-Bu), 2.28 (s, 3H, p-CH3),
2.63 (s, 6H, o-CH3), 3.31 (s, 2H, CH2); 6.97 (s, 2H, m-aryl protons)
ppm.
The oxidative halogenations of the mixed diorganotellurides
(3e6) using SO2Cl2, Br2 and I2 by the procedure described above in

A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 728 (2013) 38e43
43
Section 4.2.2 gave the corresponding white chlorides, yellow bro-
mides and red iodides as stable crystalline solids, except 3c and 5c
which decompose on standing at room temperature.
3b, 5b and 6a at ambient temperature. Intensity data were collected
on an Oxford Diffraction Gemini CCD diffractometer with graphite-
ꢀ
monochromated Mo-K
a
(0.7107 A) radiation. Data were reduced
3a: yield: 80%. M.p.: 121e122 ꢁC. Anal. Calc. for C13H12O2TeCl2
and corrected for absorption using spherical harmonics, imple-
mented in SCALE3 ABSPACK scaling algorithm in the CrysA-
lisPro171.NET program from Oxford Diffraction Ltd. The structures
were solved by direct methods and difference Fourier synthesis
using SHELXS-97 [19]. Full-matrix least-squares refinements on
F2, using all data, were carried out with anisotropic displacement
parameters applied to non-hydrogen atoms. Hydrogen atoms
attached to carbon were included in geometrically calculated po-
sitions using a riding model and were refined isotropically. Crystal
data and structure refinement details are given in Table 1. In 6a,
methyl groups of t-butyl fragment are disordered over two con-
formations and each conformer was refined with occupancy factors
which summed to one. The ORTEP figures (omitting H atoms for
clarity and showing 50% probability displacement ellipsoids) were
generated using the WinGX 2002 platform [20].
(398.74): C, 39.16; H, 3.03. Found: C, 39.36; H, 3.18. 1H NMR:
d
3.93
(s, 3H, CH3O), 4.76 (s, 2H, CH2), 7.60e8.21 (m, 7H, aryl protons)
ppm. 13C{1H} NMR:
51.9 (OCH3), 54.0 (CH2), 126.5, 126.6, 127.4,
128.3, 129.5, 131.5, 131.8, 132.9, 134.3, 134.8 (aryl carbons), 166.2
(CO) ppm. 125Te{1H} NMR:
774 ppm.
3b: yield: 85%. M.p.: 139 ꢁC. Anal. Calc. for C13H12O2TeBr2
(487.64): C, 32.02; H, 2.48. Found: C, 31.86; H, 2.60. 1H NMR:
3.96
(s, 3H, CH3O), 4.89 (s, 2H, CH2), 7.62e8.18 (m, 7H, aryl protons) ppm.
13C{1H} NMR:
50.2 (OCH3), 54.2 (CH2), 126.5, 126.8, 127.5, 128.3,
129.5,131.0,131.4,132.3,132.8,134.3 (aryl carbons),166.3 (CO) ppm.
125Te{1H} NMR:
713 ppm.
4a: yield: 85%. M.p.: 106 ꢁC. Anal. Calc. for C16H18O2TeCl2
(440.82): C, 43.59; H, 4.12. Found: C, 44.05; H, 3.97. 1H NMR:
1.59
(s, 9H, t-Bu), 4.72 (s, 2H, CH2), 7.59e8.14 (m, 7H, aryl protons) ppm.
13C{1H} NMR in 4:1 CDCl3:DMSO-d6:
26.8 (CH3), 53.2 (CH2), 56.0
d
d
d
d
d
d
d
(quaternary C), 125.6, 125.8, 126.1, 126.9, 128.3, 130.5, 131.4, 131.5,
Acknowledgments
133.0, 133.9 (aryl carbons), 167.0 (CO) ppm. 125Te{1H} NMR:
d
792 ppm.
Financial assistance by the Department of Science and Tech-
nology, Government of India, New Delhi, is gratefully acknowl-
edged. The authors are thankful to the Head, Department of
Chemistry, University of Lucknow, for providing laboratory facilities
and the Sophisticated Analytical Instrument Facility (SAIF) at
C.D.R.I., Lucknow, for 1H NMR and C, H analyses.
4b: yield: 88%. M.p.: 126 ꢁC. Anal. Calc. for C16H18O2TeBr2
(529.72): C, 36.28; H, 3.42. Found: C, 35.93; H, 3.22. 1H NMR:
d 1.63
(s, 9H, t-Bu), 4.82 (s, 2H, CH2), 7.53e8.09 (m, 7H, aryl protons) ppm.
4c: yield: 84%. M.p.: 109 ꢁC. Anal. Calc. for C16H18O2TeI2 (623.72):
C, 30.81; H, 2.91. Found: C, 30.06; H, 2.82. 1H NMR:
d 1.61 (s, 9H,
t-Bu), 4.85 (s, 2H, CH2), 7.58e8.11 (m, 7H, aryl protons) ppm.
5a: yield: 85%; M.p.: 122e123 ꢁC. Anal. Calc. for C12H16O2TeCl2
Appendix A. Supplementary material
(390.76): C, 36.88; H, 4.13. Found: C, 36.70; H, 3.98. 1H NMR:
d 2.31
(s, 3H, p-CH3), 2.69 (s, 3H, o-CH3), 2.79 (s, 3H, o-CH3), 3.91 (s, 3H,
OCH3), 4.83 (s, 2H, CH2), 6.98 (s, 1H, m-proton), 7.03 (s, 1H, m-
CCDC 921596e921600 contain the supplementary crystallo-
graphic data for 1b,1c, 3b, 5b and 6a respectively. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
proton) ppm. 13C{1H} NMR:
d
20.9, 23.3, 23.4 (mesityl methyl car-
bons), 51.7 (OCH3), 53.9 (CH2), 130.4, 131.7, 135.4, 139.5, 141.0, 142.4
(mesityl ring carbons), 166.6 (CO) ppm. 125Te{1H} NMR:
798 ppm.
5b: yield: 83%. M.p.: 106e108 ꢁC. Anal. Calc. for C12H16O2TeBr2
(479.66): C, 30.05; H, 3.36. Found: C, 29.82; H 3.10. 1H NMR:
2.32
d
Appendix B. Supplementary data
d
(s, 3H, p-CH3), 2.66 (s, 3H, o-CH3), 2.76 (s, 3H, o-CH3), 3.92 (s, 3H,
OCH3), 4.97 (s, 2H, CH2), 6.96 (s, 1H, m-proton), 7.02 (s, 1H,
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.01.010.
m-proton) ppm. 13C{1H} NMR:
d 21.0, 23.2, 24.0 (mesityl methyl
carbons), 50.7 (OCH3), 54.1 (CH2), 130.5, 131.8, 132.2, 139.2, 141.2,
References
142.4 (mesityl ring carbons), 166.6 (CO) ppm. 125Te{1H} NMR:
[1] A.K.S. Chauhan, A. Kumar, R.C. Srivastava, R.J. Butcher, J. Organomet. Chem.
658 (2002) 169e175.
[2] S. Misra, A.K.S. Chauhan, P. Singh, R.C. Srivastava, A. Duthie, R.J. Butcher,
Dalton Trans. 39 (2010) 2637e3643.
d
721 ppm.
6a: yield: 85%. M.p.: 104e105 ꢁC. Anal. Calc. for C15H22O2TeCl2
(432.84): C, 41.62; H, 5.12. Found: C, 41.34; H 5.28. 1H NMR:
d 1.57 (s,
[3] A.K.S. Chauhan, P. Singh, R.C. Srivastava, R.J. Butcher, A. Duthie, J. Organomet.
Chem. 695 (2010) 2118e2125. and references therein.
[4] R. Tamura, H. Shimizu, N. Ono, N. Azuma, H. Suzuki, Organometallics 11
(1992) 954e958.
9H, t-Bu), 2.32 (s, 3H, p-CH3), 2.67 (s, 3H, o-CH3), 2.79 (s, 3H, o-CH3),
4.76 (s, 2H, CH2), 6.98 (s, 1H, m-proton), 7.02 (s, 1H, m-proton) ppm.
13C{1H} NMR:
d 21.0, 23.4, 23.5 (mesityl methyl carbons), 27.9
(t-Bu), 54.0 (CH2), 85.3 (quaternary C), 130.3, 131.6, 135.4, 139.7,
[5] I.D. Sadekov, A.A. Maksimenko, B.B. Rivkin, Zh. Org. Khim. 14 (1978) 874.
[6] M.P. Bafle, C.A. Chaplin, H. Phillips, J. Chem. Soc. (1938) 341e347.
[7] M.P. Bafle, K.N. Nandi, J. Chem. Soc. (1941) 70e72.
[8] L. Engman, Organometallics 5 (1986) 427e431.
[9] L.A. Silks III, J.D. Odom, R.B. Dunlap, Synth. Commun. 21 (1991) 1105e1119.
[10] T. Hiiro, N. Kambe, A. Ogawa, N. Miyoshi, S. Murai, N. Sonoda, Synthesis (1987)
1096e1097.
[11] Y. Ho, Z. Huang, X. Huang, Synth. Commun. 19 (1989) 1625e1629.
[12] M.J. Dabdoub, P.G. Guerrero Jr., J. Organomet. Chem. 460 (1993) 31e37.
[13] C.-J. Li, D.N. Harpp, Sulf. Lett. 13 (1991) 139e142.
[14] F.H. Allen, O. Kennard, Chem. Des. Automat. News 8 (1993) 31e37.
[15] A.K.S. Chauhan, P. Singh, A. Kumar, R.C. Srivastava, R.J. Butcher, A. Duthie,
Organometallics 26 (2007) 1955e1959.
141.1, 142.3 (mesityl ring carbons), 165.0 (CO) ppm. 125Te{1H} NMR:
d
804 ppm.
6b: yield: 86%. M.p.: 125e126 ꢁC. Anal. Calc. for C15H22O2TeBr2
(521.74): C, 34.53; H, 4.25. Found: C, 34.28; H, 4.07. 1H NMR:
d 1.58
(s, 9H, t-Bu), 2.30 (s, 3H, p-CH3), 2.52 (s, 3H, o-CH3), 2.64 (s, 3H, o-
CH3), 4.91 (s, 2H, CH2), 6.91 (s, 1H, m-proton), 6.98 (s, 1H, m-proton)
ppm.
6c: yield: 84%. M.p.: 101 ꢁC. Anal. Calc. for C15H22O2TeI2 (615.74):
C, 29.26; H, 3.60. Found: C 28.98, H 3.82; 1H NMR:
d 1.58 (s, 9H, t-
[16] A.K.S. Chauhan, P. Singh, R.C. Srivastava, A. Duthie, A. Voda, Dalton Trans.
(2008) 4023e4028.
[17] M.R. Detty, B.J. Murray, D.L. Smith, N. Zumbulyadis, J. Am. Chem. Soc. 105
(1983) 875e882.
Bu), 2.32 (s, 3H, p-CH3), 2.63 (s, 3H, o-CH3), 2.76 (s, 3H, o-CH3), 4.90
(s, 2H, CH2), 6.96 (s, 1H, m-proton), 7.01 (s, 1H, m-proton) ppm.
[18] M. Akiba, M.V. Lakshmikantham, K.-Y. Jen, M.P. Cava, J. Org. Chem. 49 (1984)
4819e4821.
4.3. Crystallography
[19] G.M. Sheldrick, SHELXL-97, Program for the Solution of Crystal Structures,
University of Göttingen, Göttingen (Germany), 2008.
Single crystals suitable for X-ray diffraction measurements were
grown by slow evaporation of dichloromethane solutions of 1b, 1c,
[20] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837e838.