Functionalized organotellurium halides: Synthesis, characterization, and observation of intra- and intermolecular secondary bonding

Article abstract of DOI:10.1080/10426500590906319

Activated tellurium, but not selenium, reacts with para-substituted benzoylmethyl bromides as well as with iodoacetamide at their melting points in absence of a solvent to give bis(p-substituted benzoylmethyl)tellurium dibromides, (p-YC₆H₄

Full text of DOI:10.1080/10426500590906319

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Phosphorus, Sulfur, and Silicon
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Functionalized Organotellurium
Halides: Synthesis,
Characterization, and
Observation of Intra- and
Intermolecular Secondary
Bonding
Ashok K. S. Chauhan a , Arun Kumar a & R. C.
Srivastava a
a Chemistry Department, Lucknow University ,
Lucknow, India
Published online: 01 Feb 2007.
To cite this article: Ashok K. S. Chauhan , Arun Kumar & R. C. Srivastava (2005)
Functionalized Organotellurium Halides: Synthesis, Characterization, and Observation
of Intra- and Intermolecular Secondary Bonding, Phosphorus, Sulfur, and Silicon and
the Related Elements, 180:3-4, 1057-1062, DOI: 10.1080/10426500590906319
To link to this article: http://dx.doi.org/10.1080/10426500590906319
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Phosphorus, Sulfur, and Silicon, 180:1057–1062, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500590906319
Functionalized Organotellurium Halides: Synthesis,
Characterization, and Observation of Intra- and
Intermolecular Secondary Bonding
Ashok K. S. Chauhan
Arun Kumar
R. C. Srivastava
Chemistry Department, Lucknow University, Lucknow, India
Activated tellurium, but not selenium, reacts with para-substituted benzoyl-
methyl bromides as well as with iodoacetamide at their melting points in ab-
sence of a solvent to give bis(p-substituted benzoylmethyl)tellurium dibromides,
(p-YC6H4COCH2)2TeBr2, (Y = H, Me, and MeO) and bis(acetamido)tellurium diio-
dide, (H2NCOCH2)2TeI2, respectively. Quick reduction of (p-YC6H4COCH2)2TeBr2,
with sodium metabisulphite in
a two-phase system yields crystalline (p-
YC6H4COCH2)2Te. These tellurides undergo smooth oxidative addition of halo-
gens, interhalogen ICl or a pseudohalogen (SCN)2. Intramolecular coordination of
the carbonyl group in these functionalized diorganotellurium dihalides is evident
. . .
from IR spectra and shorter Te O (carbonyl) distances in comparison to the sum
of van der Waals radii and completes six coordination around Te atom. Not un-
. . .
expectedly, therefore, intermolecular secondary bonding effects of the type Te O,
. . .
. . .
Te X and X X are missing in (PhCOCH2)2TeBr2, (p-MeOC6H4COCH2)TeBr2
and (PhCOCH2)2TeI2. Instead, these compounds provide rare examples, among
. . .
organotellurium compounds, of supramolecular architecture, where C
H
Br and
. . .
C
H
O hydrogen bonds and π-π (phenyl ring) interactions appear to be the non-
covalent intermolecular associative forces that dominate the crystal packing.
Keywords Functionalized organotelluriums; organotellurium(IV) halides; secondary
bonding; supramolecular association
INTRODUCTION
Nonfunctionalized organotellurium halides almost invariably exhibit
. . .
a great propensity of tellurium to form intermolecular Te X and/or
. . .
X
X secondary bonds. In the solid state, such noncovalent secondary
Received January 22, 2004; accepted September 27, 2004.
We are thankful to the Department of Science & Technology, Government of India and
the University Grants Commission, New Delhi for financial support.
Address correspondence to Ashok K. S. Chauhan, University of Lucknow, Chemistry
Department, Lucknow 226007, India. E-mail: akschuhan@hotmail.com
1057

1058
A. K. S. Chauhan et al.
bonds (even clustered about the region thought to be occupied by the
lone pair) are responsible for the specific color of crystalline organotel-
lurium iodides1,2 and are believed to provide a new bonding motif for
supramolecular self-assembly and crystal engineering.3 The electronic
structure of secondary-bonded organotellurium halides has been ex-
plained either as a manifestation of hypervalence of tellurium in terms
of electron rich three-center bonding4–6 or as directional donor-acceptor
bonding,7–9 though the two approaches are, in fact, equivalent.10 When
the organic ligand attached to the tellurium is functionalized and pos-
sesses a nucleophillic atom A (viz. N, O, S or X) in close proximity,
. . .
intramolecular Te A secondary interactions are expected. The effect
of intramolecular secondary bonding on supramolecular association in-
. . .
volving intermolecular Te X secondary bonds has not been looked into.
The available routes to prepare functionalized organotellurium
halides involve moisture sensitive TeCl4 or n-BuLi together with rigor-
ous anhydrous oxygen-free atmosphere. We report here our successful
attempts of inserting elemental tellurium across Csp3- X bond activated
. . .
by an aroyl or amide group and the role of Te A secondary bonding in
the supramolecular motifs of some representative functionalized organ-
otellurium halides.
RESULTS AND DISCUSSION
As the Grignard reagents or organolithiums of organic substrates with
carbonyl functionality are not readily accessible, the direct reaction of
elemental tellurium with β-halocarbonyl compounds was attempted.
Thus tellurium (but not selenium) inserted across C(sp3)-Br bond is
activated by the presence of a benzoyl group to give crystalline (p-
YC6H4COCH2)2TeBr2 (Y = H, 1a; Me, 1b; OMe, 1c) (Eq. (1)). This
reaction is of particular relevance as it provides a route to function-
alized organotellurium halides directly from elemental tellurium and
an organic halide and involves the use of neither air/moisture sensi-
tive reagents like TeCl4 or n-BuLi nor deoxygenated N2/Ar atmosphere.
This also represents the only example of tellurium insertion across a
carbon-bromine bond though Me2TeI2 and cyclo-(CH2)nTeI2, (n = 4 or
5) have been prepared earlier by a similar insertion reaction with MeI14
or I(CH2)nI.15,16 However, failure of para-halobenzoylmethyl bromides
(Y = Cl, Br) to add oxidatively to Te(0) apparently demonstrates the
importance of having an activating substituent in para position of the
benzoyl group.
p-YC6H4COCH2Br + Te → (p-YC6H4COCH2)2TeBr2
Y = H, Me, OMe
(1)

Organotellurium (IV) Halides: Synthetic and Supramolecular Aspects
1059
Iodoacetamide also reacted in the sense of Eq. (1) to give the
crystalline bis(acetamido)tellurium(IV) diiodide, (NH2COCH2)2TeI2,
2, while iodoacetic acid failed to react in an analogous manner.
The ethylene ketal of benzoylmethyl bromide (the protected car-
bonyl compound), 2-bromoethanol, 2-bromoethoxy trimethylsilane, N-
bromoethylphthalimide, as well as 2-bromothiophene did not react with
elemental tellurium even on heating up to 100◦C for several hours. It
appears, therefore, that the insertion of elemental Te across the C(sp3)
-
Br bonds is facilitated by presence of an activating functionality like
the carbonyl group at the α-carbon atom.
Reduction of the newly synthesized bromides 1, could be achieved
with Na2S2O5 in a two phase system (CH2Cl2-H2O). Separation of the
yellow organic layer within 5 to 10 minutes afforded the correspond-
ing dialkyltellurides 3, which can be stored at low temperature for a
couple of weeks. Scheme 1 depicts oxidative additions of halogens, an
interhalogen and a pseudohalogen to 3, that have been affected in quan-
titative yields. The addition product of ICl with 3 affords satisfactory
elemental analyses and IR and NMR data while that of thiocyanogen
having insufficient solubility appears to be mixed with a small quantity
of thiocyanogen polymer. Interestingly, reaction of 3 with allyl bromide
resulted in the formation of the dibromides instead of the expected tel-
luronium salt [(p-YC6H4COCH2)2Te(C3H5)]+Br− but with HCl (from
CH3COCl + CH3OH) elemental tellurium separated.
SCHEME 1
Characterization of the bis(p-substituted benzoylmethyl)tellurium-
(IV and II) derivatives is based upon elemental analyses, IR and NMR,
(1H, 13C and 125Te) spectral data and has been substantiated by the
single-crystal X-ray diffraction data for the compounds 1a, 1c, and
4a.17,18 Significant lowering of the carbonyl stretching frequency
(ꢀυCO ∼ 40 cm−1) in the IR spectra of the dihalides indicates in-
tramolecular coordination of the carbonyl oxygen to the central Te(IV),
. . .
˚
which is also evident from the Te O distances (2.818–2.938 A) that are

1060
A. K. S. Chauhan et al.
˚
shorter than the sum of van der Waals radii (3.58 A) though longer than
˚
the sum of covalent radii (2.03 A) of the two atoms. Surprisingly, no sig-
nificant change in the υ(CO) is observed between the tellurium(IV) and
tellurium(II) though a comparison of δCH2 values clearly indicates that
the methylene protons in the Te(IV) species 1, 4, and 5 are more shielded
than the corresponding Te(II) compounds 3. The proton-decoupled 125Te
NMR spectra in CDCl3 show only a single resonance for 1 (∼677) and
3 (∼487 ppm relative to Me2Te) which is in accordance with enhanced
shielding of Te environment in the tellurides, 3 with respect to that in
the corresponding telluranes, 1. The 125Te MAS NMR chemical shift of
1a (635 ppm), 1b (667 ppm), and 1c (661 ppm) compare reasonably well
with the values observed in CDCl3 solution.
. . .
Molecular association via intermolecular Te X secondary bonding
is a characteristic feature of nonfunctionalized organotellurium(IV)
halides due to which the primary Te X bond lengths are affected.19,20
The longer and unequal apical Te X bond distances observed in case
of 1a, 1c, and 4a are typical of the reported bond lengths when in-
20,21
. . .
termolecular Te X secondary bonding is absent.
Crystal packing
. . .
in these compounds also is devoid of any intermolecular Te O sec-
ondary bonds and it is interesting to note that Te(IV) atom prefers
intramolecular donor-acceptor Te O interaction to complete its six
. . .
coordination even though it leads to the formation of strained four-
membered heterocyclic rings. The remarkable feature of solid state
structures of functionalized organotellurium(IV) halides is the presence
. . .
of C H A hydrogen bonds (A is an electronegative atom, O or Br). The
. . .
˚
chemically-meaningful (methylene)CH Br distance of 2.951 A in 1a
. . .
and (methylene/methoxy)CH O distances in the range between 2.45–
22
˚
. . .
2.68 A qualify the criterion for a bonafide C H A hydrogen bond.
The dominant noncovalent interaction in assembling the molecular
units leading to a supramolecular structure, therefore, appears to be
. . .
the stronger and energetically favorable C H A hydrogen bonds as
. . .
. . .
compared to Te X secondary bonds. Such C H A hydrogen bonds are
rare in organotellurium(IV) halides but common in case of organic23,24
and nonorganic crystals.25 The crystal packing analysis of 5a show no
such hydrogen bonding due to low electronegativity of iodine and prob-
ably π-π tacking26 appears to be the only noncovalent intermolecular
force that dominates secondary bonding involving electron rich heavier
atoms (Te and I).
EXPERIMENTAL
The commercial Te powder was washed with conc. HCl and water, dried
at ∼120◦C and grinded before use.

Organotellurium (IV) Halides: Synthetic and Supramolecular Aspects
1061
(a) Synthesis of (p-MeC6H4COCH2)2TeBr2, 1b: A mixture of Te powder
(10 mmol) and p-MeC6H4COCH2Br (22 mmol) was heated gently
with stirring until the mixture solidified. The solid was washed
with cold dichloromethane and then extracted with hot chloro-
form. Evaporation of the solvent followed by recrystallization with
CHCl3/pet.ether afforded 1b in about 65% yield.1a and 1c were
prepared similarly.
Because of the poor yield in absence of solvent, (NH2COCH2)2TeI2,
2 was prepared in refluxing toluene (yield ∼ 70%).
(b) Oxidative addition reactions of 3: to a cold solution of freshly-
prepared 3 (1.2 mmol) was slowly added Br2 (1.2 mmol) in CCl4
(10 mL). After stirring at ambient temperature for 2 h, the solvent
was removed and the residue crystallized from CHCl3/pet ether to
give the corresponding dibromides 1, which had same m.p. and IR
spectra as the ones prepared in (a). (p-YC6H4COCH2)2TeCl2, 4 and
(p-YC6H4COCH2)2TeI2, 5 were prepared similarly from the corre-
sponding 3 and SO2Cl2 and I2, respectively. Analogous oxidative
addition of ICl and (SCN)2 afforded (p-YC6H4COCH2)2TeICl and
(p-YC6H4COCH2)2Te(SCN)2.
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