Stereospecific chlorotelluration of terminal acetylenes

Article abstract of DOI:10.1016/j.jorganchem.2012.02.025

Chlorotelluration of terminal acetylenes, RCHCH (R = Ph, 1; 4-MeC ₆H₄, 2; t-Bu, 3) with aryltellurium trichlorides and TeCl₄ in refluxing toluene affords (2-chloro-2-organylvinyl) tellurium(IV) dichlorides, Ar[R(Cl)CCH]TeC

Full text of DOI:10.1016/j.jorganchem.2012.02.025

Journal of Organometallic Chemistry 708-709 (2012) 75e81
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Stereospecific chlorotelluration of terminal acetylenes
,
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:
Chlorotelluration of terminal acetylenes, RCH^CH (R ¼ Ph, 1; 4-MeC6H4, 2; t-Bu, 3) with aryltellurium
trichlorides and TeCl4 in refluxing toluene affords (2-chloro-2-organylvinyl)tellurium(IV) dichlorides, Ar
[R(Cl)C]CH]TeCl2 (Ar ¼ 1-C10H7, 1Aae3Aa; 2,4,6-Me3C6H2, 1Bae3Ba; 4-MeOC6H4, 1Ca) and [t-Bu(Cl)C]
CH]2TeCl2, 3a respectively. These Te(IV) derivatives on reduction with Na2S2O5 give the corresponding
vinyltellurides as oils, except (2,4,6-Me3C6H2)[Ph(Cl)C]CH]Te (1B) which is a crystalline solid. The
dibromides (1Abe3Ab, 1Bbe3Bb, 3b) and diiodides (1Ace3Ac, 1Bce3Bc, 1Cc) were obtained by the
oxidative addition of dihalogens to the tellurides. The stereochemistry of the products has been estab-
lished with the help of X-ray diffraction studies of 1Aa, 1Ba, 1Bc, 1Cc, 3Aa, 3a and 1B. Intramolecular
Te/Cl attractive interactions appear to favor the (Z) conformation adopted by the 2-chloro-2-
organylvinyltellurium group irrespective of the steric demand of the aryl ligand of the Te(IV) electro-
phile and the terminal acetylene substituent. The intermolecular Te/X secondary bonding interactions
give rise to dimeric units in the lattices of 1-naphthyl- and anisyltellurium(IV) derivatives, but are absent
among the mesityl analogues, consistent with the larger steric requirement of the latter ligand.
Ó 2012 Elsevier B.V. All rights reserved.
Received 31 October 2011
Received in revised form
17 February 2012
Accepted 21 February 2012
Keywords:
Vinyltellurium
Chlorotelluration
Secondary bonding interaction
Steric role
1. Introduction
addition product of aryltellurium trichloride and 1-alkynes, gives
aryl vinyl tellurides and thus provides an alternative route to their
The first report on the reaction of TeCl4 with mono and disub-
stituted acetylenes to give -chlorovinyltellurium(IV) trichlorides
synthesis.
Although the major products obtained in the addition of elec-
b
appeared in 1962 [1]. The highly regiospecific and stereospecific
features of the electrophilic addition reaction of tellurium tetra-
chloride to alkylphenylacetylenes and propargyl alcohol were
recognized by Uemura et al. in 1979 [2] and this paved the way to
the applications of organotellurium compounds in organic
synthesis. The vinyltellurium(II) compounds have been recognized
as important organotellurium precursors in transmetallation and
palladium-catalyzed coupling reactions [3]. These facts stimulated
studies on the electrophilic addition of tellurium(IV) halides to
a C^C bond and during the last two decades, the reactions of
substituted 1-alkynes have been extended to tellurium tetra-
bromide [4], organotellurium trichlorides [5], -tribromides [6,7]
and even to the poorly electrophilic aryltellurium triiodides [8,9].
The reduction of aryl(2-halovinyl)tellurium(IV) dihalides, the
trophilic tellurium species to aliphatic and aromatic alkynes are
more often (Z)-isomers [10e12], formed through a concerted syn
addition that involves a four-center transition state [Chart 1 e (I)],
the stereoselectivity of the regioselective addition reaction of
aryltellurium tribromides to ReC^CeH (R ¼ Ph, CH3COCH2) was
reported to depend upon the polarity of the solvent employed.
Thus, the reaction of aryltellurium tribromides with alkynes in
methanol afforded (E)-(2-bromovinyl)aryltellurium(IV) dibro-
mides, but in benzene yielded the (Z)-isomer [6]. However, in the
case of the addition of RTeX3 (X ¼ Br, I) to ferrocenylacetylene,
while the electron-donor ability of the ferrocenyl moiety facilitated
the reaction, its bulkiness presumably undermined the influence of
solvent polarity as the (Z)-isomers were invariably obtained [9]. The
regio- and stereochemistry of the addition reactions of TeCl4 or
oganotellurium trichlorides to 3-hydroxyalkynes is however,
reported to be influenced by the electronic factor of the hydroxyl
group and the steric congestion at the propargylic position. In
reactions with the unsubstituted propargyl alcohol the structures
of the isolated products indicated the formation of a mixture of (Z)-
and (E)- isomers with the expected regiochemistry [7,13]. Recently,
* 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).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.02.025

76
A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 708-709 (2012) 75e81
R
C
CH
the structural characterization of the isolated product in the
chlorotelluration reaction of PheC^CeH with 4-MeC6H4TeCl3 even
in a nonpolar solvent like benzene has also shown an (E) configu-
ration for the vinyl group [14]. Formation of the (E)-isomer has been
rationalized in terms of the addition of Te(IV) chlorides to the triple
bond in an anti fashion to give a telluronium ion [Chart 1 e (II)] as
an intermediate. The chloride ion attacks preferentially the
hydroxymethyl substituted carbon of the telluronium ion to give
the product with the expected regiochemistry but in the presence
of steric congestion at the vicinal carbon atom it attacks the
unsubstituted terminal carbon of the alkynes resulting in the (E)-
isomer with the opposed regiochemistry [13,15,16].
In spite of a number of studies, it appears that the regio- and
stereoselectivity of the addition reaction of aryltellurium trihalides
is not always predictable. The role of steric hindrance of the aryl
ligand bound to tellurium on the regio- and stereoselectivity of the
addition reaction of aryltellurium trichlorides to terminal acety-
lenes has not been examined. Moreover, only a few vinyl-
tellurium(II) derivatives have been structurally characterized and
their configurations established in the solid state [13,17]. In
continuation of our interest in functionalized organotelluriums
[18,19], the adducts of 1-naphthyl-, mesityl- and anisyltellurium
trichloride with phenylacetylene were, therefore, isolated and
characterized structurally in the present investigation. The chlor-
otelluration of t-butylacetylene with these ArTeCl3 as well as with
TeCl4 under similar conditions was also studied for comparison.
TeCl4
CCl4, reflux
ArTeCl3
MeC6H5, reflux
R = Ph, 1; 4-MeC6H4, 2; t-Bu, 3
R
H
Cl
Ar
t-Bu
H
H
t-Bu
Te
1Aa, 1Ba, 1Ca
Cl
C10H7, A;
2Aa 2Ba
,
,
Te
Cl Cl
Ar
Cl
2,4,6-Me3C6H2, B;
4-MeOC6H4, C.
Cl
Cl
3Aa,
3a
NaBr
NaI / KI
NaBr
Ph
Cl
H
Ph
Cl
H
Br
I
Na2S2O5
Ph
SO2Cl2
t-Bu
H
H
t-Bu
Te
Te
Ar
Ar
1Bc 1Cc
Te
Br Br
Cl
Cl
Br
H
I
1Bb, 1Cb,
,
3b
Te
Cl
I2
Br2
Ar
1A, 1B, 1C
Scheme 1. Synthetic routes and interconversion reactions.
In the 1H and 13C NMR spectra, separate signals for the ortho
methyl protons and carbons of the Te bound mesityl ligand in
mesityltellurium(IV) derivatives 1Ba, 1Bb, 1Bc and 2Ba are indica-
tive of restricted rotation along the TeeCmesityl bond. The vinylic
proton is deshielded due to the presence of the vicinal aryltellurium
(ArTe) substituent, with the deshielding being greater when Ar is 1-
naphthyl or mesityl than anisyl. This observation is consistent with
the steric requirement of the aryl ligand bound to Te atom.
Reduction of dichloromethane solutions of the synthesized vinyl-
tellurium(IV) dichlorides with aqueous sodium metabisulfite gives
the corresponding vinyl tellurides as oils, except for (2-chloro-2-
phenyllvinyl)mesityl telluride (1B) which was obtained as a crys-
talline solid. Compound 1B has a high field 125Te signal compared to
the Te(IV) derivatives and its vinyl group also has the (Z) configu-
ration (vide infra). Addition of Br2 or I2 to dichloromethane solu-
tions of these tellurides oxidizes them to the corresponding
vinyltellurium(IV) dibromides (1Abe3Ab, 1Bbe3Bb, 3b) and diio-
dides (1Ace3Ac,1Bce3Bc,1Cc), which are sharp melting solids that
are soluble in chloroform and dichloromethane. The diiodides can
also be prepared by halide exchange between the dichlorides or
dibromides and NaI. Interestingly, the halide exchange between
1Ba and NaI (to give 1Bc) does not alter the configuration of the
vinyl group as has been reported in the halide exchange reaction
between (4-MeC6H4)(PhC(Cl)C]CH)TeCl2 and Br2/I2 [14]. The 1H
and 13C NMR signals for the methine group are observed at low
field. The 125Te chemical shifts for the vinyltellurium(IV) derivatives
are consistent with the electronegativity of the halogen atoms.
2. Results and discussion
2.1. Synthesis
Insertion of terminal acetylenes, RC^CH (R ¼ Ph, 4-MeC6H4, t-
Bu) into a TeeCl bond of aryltellurium trichlorides, ArTeCl3 (Ar ¼ 1-
C10H7, 2,4,6-Me3C6H2, 4-MeOC6H4) and TeCl4 leads to the formation
of the corresponding vinyltellurium(IV) dichlorides (Scheme 1) as
colorless crystalline solids that are fairly soluble in chloroform or
dichloromethane. As evident from the structural characterization of
1Aa, 1Ba, 3Aa and 3a in the solid state, these vinyl derivatives exist
as the (Z)-isomer. It implies that in the presence of a bulky aryl
group at the electrophilic Te(IV) species or at the acetylenic carbon
atom, the 1,2-addition of TeeCl across a triple bond in a non polar
solvent proceeds in a syn fashion via a concerted four-centered
mechanism and the reaction is invariably regio- and stereospecific.
This observation is interesting as the major product that has been
isolated and characterized by single-crystal diffraction studies in
the reaction of phenylacetylene with 4-MeOC6H4TeCl3 is the (Z)-
isomer [11], while reaction with 4-MeC6H4TeCl3 gave the (E)-
isomer [14]. The isolation of (E)-isomer of (4-MeC6H4)(PhC(Cl)C]
CH)TeCl2, though had been attributed to the opposite inductive
effect of Me substituent compared to that of MeO, it is an exception
as its bromo and iodo analogues also possess (Z) conformation in
solid state [14].
Cl
R
R = C6H5
H
R = CH2OH
R
Cl
+
Te Cl(Ar)
Cl
Cl
Te
Cl
(Ar)Cl
Cl
(I)
(II)
Fig. 1. Molecular structure of 3a (molecule A) showing the atom numbering scheme.
Hydrogen atoms are omitted for clarity. Symmetry operation used to generate equiv-
alent atoms ¼ x, 0.5 ꢀ y, z.
Chart 1. Probable transition state (I) in the syn and intermediate ion (II) in the anti
chlorotelluration of 1-alkynes.

A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 708-709 (2012) 75e81
77
Fig. 2. Molecular structure of 3Aa showing the atom numbering scheme. Hydrogen
atoms are omitted for clarity.
Fig. 4. Molecular structure of 1Cc (molecule A) showing the atom numbering scheme.
Hydrogen atoms are omitted for clarity.
2.2. Molecular and crystal structures
stereospecificity of the addition reaction and (b) intramolecular
Te/Cl interactions contribute to the realization of the (Z)-confor-
mation of the vinyl group. The latter observation is supported by
a similar inference made earlier where the intramolecular Te/O
Except for compound 1Aa, the crystal structures of all
compounds examined in the present study are free from any
disorder. The Cl atom of the vinyl group in 1Aa is two-fold disor-
dered with positional occupancies of 0.713(3) (Cl3A) and 0.287(3)
(Cl3B). The asymmetric units in the lattices of 1Aa, 1Ba, 1Bc, 3Aa
and 1B each consist of a single molecule, while in the cases of 1Cc
and 3a there are two crystallographically independent molecules.
ORTEP diagrams for the molecular structures of 3a, 3Aa, 1Ba, 1Cc
and 1B are presented in Figs. 1e5 and those of 1Aa and 1Ba
(Figures S1 And S2) are given in the supplementary material. The
solid state structure of all compounds contain the customary planar
vinyl group, C(Cl)C]C(H)Te, with the maximum deviation of its
constituent atoms from their mean plane limited to 0.13 Å. The
observed C]C bond lengths (1.286(6)e1.330(4) Å) do not exceed
the value (1.337 Å) in free ethylene. The 2-chloro-2-organylvinyl
ligand bound to Te atom displays (Z) stereochemistry in each of
the vinyltellurium derivatives for which X-ray diffraction data have
been solved in the present study. The (Z) conformation of the vinyl
group provides an opportunity for the secondary bonding inter-
actions (SBIs) between the cis positioned Te and Cl atoms. The
shorter intra vinyl group 1,4-Te/Cl distance, which varies in the
range 3.204(6) (1Aa) to 3.362(3) Å (1B), compared to S rvdw(Te, Cl)
of 3.83 Å [20] and nearly linear Clviny/TeeCtrans alignment
[: Clviny/TeeCtrans measures in between 145.42(7) (1B) and
interaction led to the isolation of the (Z)-isomer of
b-tri-
fluoroacetylvinyl-2-(ethoxycarbonyl)ethyltelluride characterized
by X-ray diffraction [17]. Furthermore, the (Z)-stereochemistry is
retained among 1Bc,1Cc and 1B. The exchange of the chloro ligands
of 1Ba with iodo to give 1Bc or their removal to provide mesi-
tylvinyltellurium(II) compound 1B does not alter the vinyl group
conformation. This is interesting in the light of a recent report
where treating (4-MeC6H4)(Ph(Cl)C]CH)TeCl2 with Br2 or I2
resulted in change of vinyl group conformation from (E) in the
parent dichloride to (Z) among the dibromide and the diiodide [14].
In all the diorganotellurium dihalides, the primary geometry
around the Te atom is j-trigonal bipyramidal with halo ligands at
the apical positions. Relevant bond parameters are listed in Table 1.
The two TeeCsp2 bonds, each measuring 2.080(5) or 2.083(5) Å in
the two independent molecules of 3a, are also almost equal in 1Cc
{2.111(4), 2.109(4) Å and 2.101(4), 2.106(5) Å in its two independent
molecules} but differ appreciably in 1Aa (2.085(2), 2.118(2) Å), 1Ba
(2.083(3), 2.125(3) Å), 1Bc (2.092(4), 2.142(4) Å) and 3Aa (2.087(2),
2.118(2) Å). The steric demand of 1-naphthyl and mesityl ligands
appears to cause lengthening of the TeeCaryl bond compared to the
TeeCvinyl. Steric repulsion due to the presence of bulky aryl ligand
among the 1-naphthyl and mesityltellurium(IV) compounds also
causes widening of the equatorial CeTeeC angle when compared to
that of 3a, 1Cc or 1B (Table 1). It is more obvious among the
153.43(7)ꢁ (1Aa)], suitable for an n(Cl) ꢀ
s*(TeeCtrans) orbital
interaction, indicate the presence of an attractive interaction that
favors the observed conformation. It implies that addition of Te(IV)
chlorides, ArTeCl3 and TeCl4, to the terminal alkynes to give 1Aa,
1Ba, 3Aa and 3a occurs preferentially in a syn fashion in refluxing
toluene. It may be safely inferred that (a) the steric demand of the
organic moieties bound either to the 2-carbon atom of the terminal
alkyne or the electrophilic Te center does not affect the regio- and
mesitylvinyltellurium dihalides. The exocyclic angles
:
TeeC9eC10 and : TeeC9eC14 at the ipso carbon atom of the
mesityl ligand in 1Ba [114.4(2)ꢁ, 124.3(2)ꢁ] and 1Bc [111.6(2)ꢁ,
128.4(4)ꢁ] when compared to those in 1B [118.8(2)ꢁ, 120.4(2)ꢁ]
reveal significant deviation from their putative value of 120ꢁ. This
substantiates the loss of local C2 symmetry of the mesityl group
Fig. 3. Molecular structure of 1Ba showing the atom numbering scheme. Hydrogen
Fig. 5. Molecular structure of 1B showing the atom numbering scheme. Hydrogen
atoms are omitted for clarity.
atoms are omitted for clarity.

78
A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 708-709 (2012) 75e81
Table 1
Bond parameters (Å, ꢁ) of 1Aa, 3Aa, 3a, 1Cc, 1Ba, 1Bc, and 1B.
1Aa
2.085(2)
2.118(2)
101.01 (8)
172.51(2)
2.538(1)
3Aa
2.087(2)
3a Mol1, Mol2
1Cc Mol1, Mol2
1Ba
2.083(3)
1Bc
2.092(4)
1B
2.098(3)
2.135(3)
93.35(9)
TeeCvinyl
TeeCaryl/vinyl
CeTeeC
XeTeeX
TeeX1
2.080(5), 2.083(5)
2.080(5), 2.083(5)
95.87(19), 95.19(18)
168.43(8), 168.03(8)
2.505(3), 2.507(2)
2.507(3), 2.503(3)
3.246(2) each,
3.249(2) each
149.72(13) each,
148.84(13) each
2.111(4), 2.101(4)
2.109(4), 2.106(5)
96.38(17), 5.52(19)
177.94(1), 178.04(2)
2.949(1), 2.948(1)
2.913(1), 2.890(1)
3.280(1) each,
3.273(1) each
147.20(12) each,
146.33(12) each
2.118(2)
98.39(7)
173.06(2)
2.476(1)
2.525(1)
3.250(1)
2.125(3)
99.52(9)
175.93(3)
2.487(1)
2.524(1)
3.335(1)
2.142(4)
107.07(14)
177.23(1)
2.914(1)
2.943(1)
3.270(1)
TeeX2
Te/Clvinyl
2.485(1)
3.234(2)a
3.204(6)a
153.43(7)a
153.10(11)a
3.362(3)
ClvinyleTe∙∙∙Ctrans
ClvinyleTe∙∙∙Ctrans
147.26(5)
146.58(7)
151.67(11)
145.42(7)
a
For the two disordered positions: Cl3A and Cl3B.
about the TeeC axis, as inferred from the separate signals for the
ortho methyl protons and carbon atoms in their 1H and 13C NMR
spectra (vide supra).
and aryltellurium trichlorides used in the present work were
prepared by chlorination of tellurium powder and the corre-
sponding diaryltellurides with SO2Cl2, respectively. The terminal
acetylenes procured commercially were used after distillation. 1H
NMR spectra were recorded at 300.13 MHz in CDCl3 on a Bruker
DRX300 spectrometer using Me4Si as the internal standard. 13C{1H}
(100.54 MHz) and 125Te{1H} (126.19 MHz) NMR spectra were
recorded on a JEOL Eclipse Plus 400 NMR spectrometer, using Me4Si
and Me2Te as internal standards. CDCl3was used as the NMR
The steric demand of 1-naphthyl and mesityl ligands appears to
affect the self assembly via intermolecular interactions involving
the Te atom in lattices of the Te(IV) compounds. The intramolecular
Te/Cl SBIs impart six-coordination to the central Te(IV) atom in (t-
BuCCl]CH)2TeCl2 (3a) (Fig. 1) and its lattice is devoid of intermo-
lecular Te/Cl interactions. Among the lattices of 1-naphthyl- and
anisyltellurium(IV) derivatives (3Aa, 1Aa and 1Cc), formation of
zero-dimensional supramolecular dimeric units by means of
intermolecular Te/X SBIs highlights the propensity of Te(IV) to
complete its coordination number of six.
solvent and the reported values of chemical shifts (d) are in ppm.
Microanalyses for C, H content were carried out using a Carlo Erba
1108 analyzer and Te content in some of the compounds was
determined volumetrically.
While the aryl ligands in case of 1Cc are oriented on the same
side of the Te2I2 quadrilateral formed by the pairs of primary TeeI
and secondary Te/I bonds (Fig. 6), the 1-naphthyl ligands, due to
the greater steric demand, are on opposite sides of the Te2Cl2
parallelograms among the centrosymmetric pairs of molecules
realized via intermolecular Te/Cl interactions in the lattices of 3Aa
and 1Aa (Fig. 7 and S3). In the case of the analogous mesityl
derivatives, 1Ba and 1Bc, the bulkier aryl group hinders the access
of halo ligands of the neighboring molecules to the central five-
coordinate tellurium atom and no similar supramolecular dimers
could be identified in their lattices.
3.1. Syntheses
3.1.1. Electrophilic addition of Te(IV) chlorides to the terminal
alkynes
TeCl4 or ArTeCl3 (Ar ¼ 1-C10H7, 2,4,6-Me3C6H2, 4-MeOC6H4)
adds across the CeC triple bond of phenyl-, p-tolyl- or t-butylace-
tylene to give (RCCl]CH)2TeCl2 or Ar(RCCl]CH)TeCl2. In a typical
experiment, 2.00 mmol of phenylacetylene (0.22 mL) was added to
a solution of 1-naphthyltellurium trichloride (0.72 g, 2.00 mmol) in
dry toluene (20 mL) and refluxed for 12 h. The solvent was reduced
3. Experimental
Preparative work was performed under dry nitrogen. Melting
points were recorded in capillary tubes and are uncorrected. All
solvents were purified and dried before use. Tellurium tetrachloride
Fig. 6. Zero-dimensional supramolecular unit realized through intermolecular Te/I
interaction in the crystal lattice of 1Cc. Hydrogen atoms (except for vinyl) omitted for
clarity.
Fig. 7. Zero-dimensional supramolecular unit realized through intermolecular Te/Cl
interaction in the crystal lattice of 3Aa. Hydrogen atoms (except for vinyl) omitted for
clarity.

A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 708-709 (2012) 75e81
79
to approximately 3e4 mL by distillation under reduced pressure
and the resulting sticky mass on trituration with petroleum ether
(40e60 ꢁC) afforded a colorless solid that was recrystallized from
chloroform to give colorless crystals of (1-C10H7)(PhCCl]CH)TeCl2
(1Aa). Yield: 0.75 g (81%). M.p.: 190 ꢁC. Anal. Calc. for C18H13Cl3Te
(463.25): C, 46.67; H, 2.83; Te, 27.54. Found: C, 46.41; H, 2.60; Te,
aqueous solution of Na2S2O5 (0.19 g, 1.0 mmol) for 20 min. The
organic layer gradually turned yellow and it was separated, washed
with water (4 ꢂ 50 mL) and dried over anhydrous Na2SO4. The
solution was concentrated to about 5 mL and pet. ether (40e60 ꢁC)
(10 mL) added to precipitate a colorless solid that was recrystallized
from hexane as cream color crystals of (2,4,6-Me3C6H2)(PhCCl]CH)
Te (1B). Yield: 0.32 g (85%). M.p.: 80 ꢁC. Anal. Calc. for C17H17ClTe
27.86. 1H NMR:
d
7.47e7.79 (8H, m, aryl), 7.97 (1H, d, 3J ¼ 8.1 Hz,
naphthyl), 8.04 (1H, s, vinyl), 8.08 (1H, d, 3J ¼ 8.1 Hz, naphthyl), 8.16
(1H, d, 3J ¼ 8.1 Hz, naphthyl) 8.34 (1H, d, 3J ¼ 7.8 Hz, naphthyl) ppm.
(384.37): C, 53.12; H, 4.46. Found: C, 53.44; H, 4.54. 1H NMR:
d 2.31
(3H, s, mesityl p-Me), 2.55, 2.61 (6H, d, mesityl o-Me), 7.02 (2H, s,
13C{1H} NMR:
d 123.5, 126.5 (vinyl), 126.7, 127.3, 127.5, 128.1, 128.8,
mesityl m-H), 7.17 (1H, s, vinyl), 7.25e7.50 (5H, m, Ph), ppm. 13C{1H}
129.5, 131.4, 131.5, 132.1, 132.8, 134.4, 134.5, 135.7, 147.9 (aryl) ppm.
NMR:
d 20.9 (p-Me), 29.7 (o-Me), 108.1, 117.9 (vinyl), 125.8, 127.7,
125Te{1H} NMR:
d
741 ppm.
128.1, 128.3, 137.0, 137.6, 139.6, 145.2 (aryl) ppm. 125Te{1H} NMR:
Compounds 1Ba, 1Ca, 2Aa, 2Ba, 3Aa and 3a were prepared
d
389 ppm.
following the same procedure.
Under similar conditions reduction of 1Aa and 1Ca afforded the
tellurides 1A and 1C as viscous liquids that were vacuum dried.
3.1.1.1. (2,4,6-Me3C6H2)(PhCCl]CH)TeCl2 (1Ba). Yield: 0.73 g (80%).
M.p.: 165 ꢁC. Anal. Calc. for C17H17Cl3Te (455.28): C, 44.85; H, 3.76;
3.1.2.1. (1-C10H7)(PhCCl]CH)Te (1A). Yield: 0.32 g (82%). Anal. Calc.
Te, 28.03. Found: C, 44.78; H, 3.80; Te, 28.06. 1H NMR:
d
2.33 (3H, s,
for C18H13ClTe (392.4): C, 55.10; H, 3.34. Found: C, 55.50; H, 3.12. 1H
p-Me), 2.83 (3H, s, o-Me), 2.84 (3H, s, o-Me), 7.00 (1H, s, m-H), 7.07
NMR:
naphthyl), 7.87, 7.90 (1H, d, naphthyl), 8.21, 8.24 (1H, d, naphthyl)
8.27, 8.29 (1H, d, naphthyl) ppm. 13C{1H} NMR:
107.9, 116.9 (vinyl),
126.0, 126.5, 127.3, 128.3, 129.0, 130.3, 132.5, 133.7, 140.2 ppm 125Te
{1H} NMR:
515 ppm.
d 7.24e7.58 (8H, m, aryl), 7.35 (1H, s, vinyl), 7.80, 7.81 (1H, d,
(1H, s, m-H), 7.45e7.70 (5H, m, Ph), 8.30 (1H, s, vinyl) ppm. 13C{1H}
NMR:
128.8, 130.5, 131.2, 131.8, 135.0, 136.8, 139.3, 141.0, 142.2, 145.2 (aryl)
ppm. 125Te{1H} NMR:
757 ppm.
d
21.0 (p-Me), 23.5 (o-Me), 23.8 (o-Me), 120.8, 127.3 (vinyl),
d
d
d
3.1.1.2. (4-MeOC6H4)(PhCCl]CH)TeCl2 (1Ca). Yield: 0.74 g, (83%).
M.p.: 135e136 ꢁC (lit 134e135 ꢁC; authentic 1H spectrum [5]). 125Te
NMR: 821 ppm.
3.1.2.2. (4-MeOC6H4)(PhCCl]CH)Te (1C). Yield: (0.31 g, 83%). Anal.
Calc. for C15H13ClOTe (372.3): C, 48.39; H, 3.52. Found: C, 48.50; H,
3.30. (authentic 1H spectrum [5]). 125Te{1H} NMR:
d 616 ppm.
3.1.1.3. (1-C10H7)(4-MeC6H4CCl]CH)TeCl2 (2Aa). Yield: 0.74 g,
3.1.3. Oxidative halogen addition reactions of the diorganotellurides
A 1.0 mmol solution of Br2 (0.05 mL) or I2 (0.25 g) in dichloro-
methane (10 mL) was added drop wise to a solution of the appro-
priate telluride (1B or 1C) obtained by the reduction of 1.0 mmol of
1Ba (0.46 g) or 1Ca (0.44 g) in the same solvent (20 mL) under
stirring at 0 ꢁC. Concentration of the resulting yellow to orange
colored solution, followed by addition of n-hexane yielded the
corresponding Te(IV) dibromides (1Bb or 1Cb) or diiodides (1Bc or
1Cc). Recrystallization with CH2Cl2/CHCl3 gave analytically pure
samples.
(82%). M.p.: 150 ꢁC. Anal. Calc. for C19H15Cl3Te (477.28): C, 47.81; H,
3.17. Found: C, 47.50; H, 3.20. 1H NMR:
d 2.43 (3H, s, p-Me)
7.26e7.96 (8H, m, aryl), 7.99 (1H, s, vinyl), 8.08 (1H, d, 3J ¼ 8.1 Hz,
naphthyl), 8.16 (1H, d, 3J ¼ 8.1 Hz, naphthyl), 8.34 (1H, d, 3J ¼ 7.8 Hz,
naphthyl) ppm. 13C{1H} NMR:
d 21.4 (p-Me), 122.2, 126.5 (vinyl),
126.7, 127.2, 127.4, 128.1, 129.4, 129.5, 131.3, 131.42, 132.1, 132.7,
134.4, 135.8, 142.2, 148.2 (aryl) ppm. 125Te{1H} NMR:
d
743 ppm.
3.1.1.4. (2,4,6-Me3C6H2)(4-MeC6H4CCl]CH)TeCl2
(2Ba). Yield:
0.61 g, (65%). M.p.: 170 ꢁC. Anal. Calc. for C18H19Cl3Te (469.3): C,
46.07; H, 4.08. Found: C, 46.50; H, 4.10. 1H NMR:
d
2.30 (3H, s,
3.1.3.1. (2,4,6-Me3C6H2)(PhCCl]CH)TeBr2 (1Bb). Yield: 0.39 g (72%).
M.p.: 170e171 ꢁC. Anal. Calc. for C17H17Br2ClTe (544.18): C, 37.52; H,
mesityl p-Me), 2.44 (3H, s, tolyl p-Me), 2.70 (3H, s, o-Me), 2.82 (3H,
s, o-Me), 6.94 (1H, s, mesityl m-H), 7.03 (1H, s, mesityl m-H), 7.33
(2H, d, 3J ¼ 7.5 Hz, tolyl m-H), 7.56 (2H, d, 3J ¼ 7.8 Hz, tolyl o-H), 8.21
3.15. Found: C, 37.89; H, 3.17. 1H NMR:
d 2.34 (3H, s, p-Me), 2.80 (3H,
s, o-Me), 2.83 (3H, s, o-Me), 6.99 (1H, s, mesityl m-H), 7.07 (1H, s,
(1H, s, vinyl) ppm. 13C{1H} NMR:
d
20.9 (mesityl p-Me), 21.6 (tolyl p-
mesityl m-H), 7.48e7.68 (5H, m, Ph), 8.42 (1H, s, vinyl) ppm. 13C{1H}
Me), 23.0 (o-Me), 23.6 (o-Me), 121.4, 128.2 (vinyl), 129.9, 130.4,
NMR:
130.6, 131.2, 131.9, 133.7, 135.0, 139.0, 141.2, 142.2, 144.8 (aryl) ppm.
125Te{1H} NMR:
688 ppm.
d 21.0 (p-Me), 23.6 (o-Me), 24.1 (o-Me), 117.1, 127.3, 128.8,
131.9, 133.8, 136.2, 139.3, 141.6, 141.9, 142.2, 144.7 (aryl) ppm. 125Te
{1H} NMR:
d
773 ppm.
d
3.1.1.5. (1-C10H7)(t-BuCCl]CH)TeCl2 (3Aa). Yield: 0.69
g
(78%).
3.1.3.2. (4-MeOC6H4)(PhCCl]CH)TeBr2 (1Cb). Yield: 0.40 g (90%).
M.p.: 149e151 ꢁC. Anal. Calc. for C15H13Br2ClTe (443.22): C, 33.86; H
M.p.: 195 ꢁC. Anal. Calc. for C16H17Cl3Te (443.27): C, 43.35; H, 3.87.
Found: C, 43.50; H, 3.80. 1H NMR
d
1.39 (9H, s, t-Bu), 7.60e7.73 (3H,
2.46. Found: C, 33.78; H, 2.50. 1H NMR:
d 3.89 (3H, s, MeO), 7.06 (2H,
m, naphthyl), 7.58 (1H, s, vinyl), 7.96 (1H, d, 3J ¼ 8.1 Hz, naphthyl),
d, 3J ¼ 8.4 Hz, anisyl o-H), 7.44e7.49 (3H, m, Ph), 7.70 (2H, d,
8.06 (1H, d, 3J ¼ 8.1 Hz, naphthyl), 8.13 (1H, d, 3J ¼ 8.1 Hz, naphthyl),
3J ¼ 6.0 Hz, Ph o-H), 7.83 (1H, s, vinyl), 8.22 (2H, d, 3J ¼ 8.4 Hz, anisyl
3
8.23 (1H, d, J ¼ 9.0 Hz, naphthyl) ppm.
m-H) ppm. 13C{1H} NMR:
d 55.6 (MeO), 115.9, 118.4 (vinyl), 121.9,
127.4, 128.8, 131.4, 134.2, 136.5, 147.2, 162.3 (aryl) ppm. 125Te{1H}
NMR: 780 ppm.
3.1.1.6. (t-BuCCl]CH)2TeCl2 (3a). Yield: (0.48 g, 55%). M.p.:
223e225 ꢁC. Anal. Calc. for C12H20Cl4Te (433.7): C, 33.23; H, 4.65.
d
Found: C, 33.50; H, 4.80. 1H NMR:
d
1.31 (18H, s, t-Bu), 7.42 (2H, s,
28.41 (t-Bu), 40.77 (t-Bu),120.79,160.50
711 ppm.
3.1.3.3. (2,4,6-Me3C6H2)(PhCCl]CH)TeI2 (1Bc). Yield: 0.56 g (87%).
vinyl) ppm. 13C{1H} NMR:
(vinyl). 125Te{1H} NMR:
d
M.p.: 106 ꢁC. Anal. Calc. for C17H17I2ClTe (638.18): C, 31.99; H, 2.68.
d
Found: C, 32.00; H, 2.70. 1H NMR:
d 2.33 (3H, s, p-Me), 2.70 (6H, s, o-
Me), 7.00 (2H, s, mesityl m-H), 7.46 (5H, s, aryl), 8.42 (1H, s, vinyl)
ppm.
3.1.2. Reduction of (2-chloro-2-phenyllvinyl)tellurium(IV)
dichlorides to diorganotellurides
(2-chloro-2-phenylvinyl)mesityltellurium(IV) dichloride (1Ba)
(0.455 g,1.0 mmol) in dichloromethane (50 mL) was shaken with an
3.1.3.4. (4-MeOC6H4)(PhCCl]CH)TeI2 (1Cc). Yield: 0.52 g (84%).
M.p.: 165 ꢁC. Anal. Calc. for C15H13I2ClTe (626.13): C, 28.77; H, 2.09.

80
A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 708-709 (2012) 75e81
Found: C, 28.78; H, 2.10. 1H NMR:
d
3.88 (3H, s, MeO), 7.00 (2H, d,
collected on an Oxford Diffraction Gemini CCD diffractometer with
graphite-monochromated Mo-K (0.7107 Å) radiation. Data were
3J ¼ 8.7 Hz, anisyl o-H), 7.44e7.49 (3H, m, Ph), 7.69 (2H, d,
a
3J ¼ 6.6 Hz, Ph o-H), 7.75 (1H, s, vinyl), 8.20 (2H, d, 3J ¼ 9.0 Hz, anisyl
reduced and corrected for absorption using spherical harmonics,
implemented 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 [21]. 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
positions using a riding model and were refined isotropically.
Crystal data and structure refinement details are given in Table 2.
Figs. (1e5 and S1-S2) of molecular structures (omitting H atoms for
clarity and showing 50% probability displacement ellipsoids) were
generated using ORTEP-3 version 2.02 [22].
m-H) ppm. 13C{1H} NMR:
d 55.6 (MeO), 112.7, 115.6 (vinyl), 116.3,
127.2, 128.8, 131.2, 134.8, 138.2, 146.7, 162.1 (aryl) ppm. 125Te{1H}
NMR: 820 ppm.
d
3.1.4. Metathetical reactions of 1Ca, 1Cb or 3a with sodium
bromide or sodium/potassium iodide
In a typical experiment, a solution of 3a (0.87 g, 2 mmol) in
dichloromethane (25 mL) was stirred with NaBr (0.50 g, 4.9 mmol)
for 6 h. The sodium halides were removed by filtration and the
filtrate concentrated. Petroleum ether (40e60 ꢁC) was added to
afford (t-BuCCl]CH)2TeBr2 (3b) as a light yellow solid that was
recrystallized from chloroform. Yield: 0.90 g (86%). M.p.: 175 ꢁC.
Anal. Calc. for C12H20Cl2Br2Te (522.6): C, 27.58; H, 3.86. Found: C,
27.70; H, 3.91. 1H NMR:
13C{1H} NMR:
28.3 (t-Bu), 40.9 (t-Bu), 117.3, 160.5 (vinyl) ppm.
125Te{1H} NMR:
655 ppm.
d 1.30 (18H, s, t-Bu), 7.95 (2H, s, vinyl) ppm.
4. Conclusions
d
Terminal acetylenes, RC^CH (R ¼ Ph, 4-MeC6H4, t-Bu), insert
into the TeeCl bond of aryltellurium trichlorides, ArTeCl3 (Ar ¼ 1-
C10H7, 2,4,6-Me3C6H2, 4-MeOC6H4) and TeCl4 to form the corre-
sponding vinyltellurium(IV) dichlorides with Z conformation irre-
spective of the steric requirement of the aryl ligand at the Te or t-
butyl group at the acetylene. The Z conformation of the vinyl
moiety is retained among the arylvinyltellurium(II) compounds
formed by reduction of the parent dichlorides and among the
dihalides obtained by oxidative addition of dihalogens to the
tellurides. While intramolecular Te/Cl secondary bonding inter-
action (SBI) between the cis-positioned Te and Cl atoms favors by
the Z conformation of the vinyl group, intermolecular Te/Cl SBIs
d
Compound 1Cc prepared either from 1Ca or 1Cb gave an
authentic melting point and the yields were comparable.
3.2. Crystallography
Single crystals suitable for X-ray diffraction measurements were
grown by slow evaporation of chloroform solutions of 1Aa, 1Ba,
3Aa, 3a, 1Bc and 1Cc at ambient temperature. In the case of tellu-
ride 1B, suitable crystals were obtained by cooling a dichloro-
methane/hexane (1:4) solution to ꢀ10 ꢁC. Intensity data were
Table 2
Crystal data and structure refinement details of 1Aa, 3Aa, 3a, 1Cc, 1Ba, 1Bc, and 1B.
1Aa
3Aa
3a
1Cc
1Ba
1Bc
1B
Empirical formula
Formula mass (g molꢀ1
Temperature (K)
C18H13Cl3Te
463.23
295(2)
C16H17Cl3Te
443.25
123(2)
C12H20Cl4Te
433.68
295(2)
C15H13I2ClTe
626.10
295(2)
C17H17Cl3Te
455.26
295(2)
C17H17I2ClTe
638.16
110(2)
C17H17ClTe
384.36
110(2)
)
Wavelenth,
l
(Å)
0.71073
Monoclinic
0.71073
Monoclinic
0.71073
Orthorhombic
0.71073
Triclinic
0.71073
Monoclinic
0.71073
Monoclinic
0.71073
Orthorhombic
Crystal system
Crystal size (mm3)
Space group
a (Å)
b (Å)
c (Å)
0.48 ꢂ 0.36 ꢂ 0.28 0.50 ꢂ 0.35 ꢂ 0.26 0.47 ꢂ 0.35 ꢂ 0.32 0.52 ꢂ 0.45 ꢂ 0.15 0.49 ꢂ 0.41 ꢂ 0.18 0.49 ꢂ 0.28 ꢂ 0.23 0.53 ꢂ 0.28 ꢂ 0.22
P 21/n
P 2/c
P n m a
9.4741(13)
13.4412(11)
12.9060(14)
90
90
90
3489.0(3)
8
1.651
Pꢀ1
P 21/n
C 2/c
P b c a
8.5555(2)
10.4188(3)
20.2706(5)
90
101.289(2)
90
1771.93(8)
4
1.736
7.7903(2)
19.9754(5)
11.8084(3)
90
107.003(3)
90
1757.24(8)
4
1.675
23.4241(9)
25.0297(9)
5.9509(3)
89.915(3)
82.973(2)
88.008(2)
1833.97(9)
4
8.6442(2)
14.6987(4)
14.5998(4)
90
103.485(3)
90
1803.88(8)
4
1.676
14.9212(6)
20.5948(4)
14.2715(6)
90
119.448(5)
90
3819.0(2)
8
2.220
14.8108(5)
8.5584(3)
24.5404(10)
90
90
90
3110.68(18)
8
1.641
a
b
g
(deg)
(deg)
(deg)
V (Å3)
Z
rcalcd (Mg mꢀ3
)
2.268
5.128
m
(Mo-K
a
, mmꢀ1
)
2.124
2.137
2.298
2.084
4.924
2.069
F(000)
896
864
1696
1144
888
2352
1504
h, k, l ranges collected
Reflection collected
ꢀ12 ꢃ h ꢃ 10
ꢀ11 ꢃ k ꢃ 15
ꢀ29 ꢃ l ꢃ 25
15 297
ꢀ11 ꢃ h ꢃ 7
ꢀ30 ꢃ k ꢃ 27
ꢀ15 ꢃ l ꢃ 17
13 917
ꢀ31 ꢃ h ꢃ 34
ꢀ38 ꢃ k ꢃ 33
ꢀ8ꢃ l ꢃ 8
17 321
ꢀ16 ꢃ h ꢃ 16
ꢀ18 ꢃ k ꢃ 16
ꢀ20 ꢃ l ꢃ 20
23 970
ꢀ12 ꢃ h ꢃ 12
ꢀ17 ꢃ k ꢃ 22
ꢀ21 ꢃ l ꢃ 13
15 067
ꢀ21 ꢃ h ꢃ 20
ꢀ31 ꢃ k ꢃ 27
ꢀ20 ꢃ l ꢃ 21
13 495
ꢀ22 ꢃ h ꢃ 13
ꢀ11 ꢃ k ꢃ 12
ꢀ36 ꢃ l ꢃ 37
14 851
Independent reflections
5906 [R(int) ¼
0.0243]
4.70e32.66
99.2
5846 [R(int) ¼
0.0253]
5.13e32.79
98.9
5991 [R(int) ¼
0.0393]
5.04e32.75
98.7
11 946 [R(int) ¼
6015 [R(int) ¼
0.0317]
4.85e32.8
99.2
6346 [R(int) ¼
0.0237]
4.77e32.75
99.2
5193 [R(int) ¼
0.0305]
4.76e32.64
99.2
0.0283]
q
range (ꢁ)
4.65e32.70
98.7
Completeness to qmax (%)
Absorption correction
Max., min. transmission
Refinement method
Semi-empirical from equivalents
1.00000, 0.68590 1.00000, 0.71531 1.00000, 0.76102 1.00000, 0.22001 1.00000, 0.88380 1.00000, 0.27730 1.00000, 0.70697
Full-matrix least-squares on F2
Data/restraints/parameters
5906/0/203
1.023
5846/0/184
0.983
5991/0/169
1.214
11 946/0/358
1.021
6015/0/193
0.879
6346/0/194
1.028
5193/0/175
1.052
Goodness of fit on F2
Final R indices (I > 2
s
(I))
R1 ¼ 0.0315,
wR2 ¼ 0.0659
R1 ¼ 0.0561,
wR2 ¼ 0.0710
R1 ¼ 0.0258,
wR2 ¼ 0.0546
R1 ¼ 0.0396,
wR2 ¼ 0.0574
0.744/ꢀ0.880
R1 ¼ 0.0704,
wR2 ¼ 0.1205
R1 ¼ 0.0973,
wR2 ¼ 0.1269
1.073/ꢀ1.690
R1 ¼ 0.0489,
wR2 ¼ 0.1002
R1 ¼ 0.1016,
wR2 ¼ 0.1139
0.941/ꢀ0.928
R1 ¼ 0.0341,
wR2 ¼ 0.0622
R1 ¼ 0.0727,
wR2 ¼ 0.0680
0863/ꢀ0.631
R1 ¼ 0.0359,
wR2 ¼ 0.0824
R1 ¼ 0.0512,
wR2 ¼ 0.0873
2.075/ꢀ1.785
R1 ¼ 0.0352,
wR2 ¼ 0.0743
R1 ¼ 0.0562,
wR2 ¼ 0.0743
1.304/ꢀ2.304
R indices (all data)
Largest diff peak/hole (e Åꢀ3) 0.603/ꢀ0.789

A.K.S. Chauhan et al. / Journal of Organometallic Chemistry 708-709 (2012) 75e81
81
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1032e1076.
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10 (1991) 845e846.
are present among the lattices of 1Aa, 3Aa, 1Cc, but absent in those
of the mesityl analogues due to its larger steric size.
Acknowledgments
[6] X. Huang, Y.-P. Wang, Tetrahedron Lett. 37 (1996) 7417e7420.
[7] J. Zukerman-Schpector, H.A. Stefani, D. deO. Silva, A.L. Braga, L. Dornelles, C.
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Financial assistance by the Department of Science and Tech-
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[9] Y. Torubaev, P. Mathur, A.A. Pasynskii, J. Organomet. Chem. 695 (2010)
1300e1306.
Appendix A. Supplementary material
[10] J. Zukerman-Schpector, E.E. Castellano, G. Oliva, J.V. Comasseto, H.A. Stefani,
Acta Crystallogr. C47 (1991) 960e962.
[11] J. Zukerman-Schpector, J.V. Comasseto, H.A. Stefani, Acta Crystallogr. C51
(1995) 861e863.
[12] J. Zukerman-Schpector, R.L. Camillo, J.V. Comasseto, R.A. Santos, I. Caracelli,
Acta Crystallogr. C55 (1999) 1577e1579.
[13] G. Zeni, A. Chieffi, R.L.O.R. Cunha, J. Zukerman-Schpector, H.A. Stefani,
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[14] I. Caracelli, J. Zukerman-Schpector, S.H. Maganhi, H.A. Stefani, R. Guadagnin,
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[15] J. Zukerman-Schpector, R.L. Camillo, J.V. Comasseto, R.L.O.R. Cunha, A. Chieffi,
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[16] R.L.O.R. Cunha, J. Zukerman-Schpector, I. Caracelli, J.V. Comasseto,
J. Organomet. Chem. 691 (2006) 4807e4815.
ORTEP figures of the molecular structures of 1Aa and 1Ba
(Figures S1 and S2) together with the supramolecular dimeric unit
identified in the crystal lattice of 1Aa (Figure S3) are given as
supplementary information. This material is available free of charge
via the Internet at http://pubs.acs.org.
CCDC 111111e111117 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
[17] X.-S. Mo, Y.-Z. Huang, Y.-R. Zhao, J. Chem. Soc. Chem. Commun. (1994)
2769e2770.
Appendix B. Supplementary material
[18] S. Misra, A.K.S. Chauhan, P. Singh, R.C. Srivastava, A. Duthie, R.J. Butcher,
Dalton Trans. 39 (2010) 2637e3643.
[19] A.K.S. Chauhan, P. Singh, R.C. Srivastava, R.J. Butcher, A. Duthie, J. Organomet.
Chem. 695 (2010) 2118e2125.
Supplementary material associated with this article can be found,
in the online version, at doi:10.1016/j.jorganchem.2012.02.025.
[20] L. Pauling, The Nature of the Chemical Bond, third ed. Cornell University Press,
Ithaca, New York, 1960.
[21] SHELXL-97 G.M. Sheldric, Program for the Solution of Crystal Structures,
University of Göttingen, Göttingen (Germany), 2008.
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