Systematic synthesis and crystal structures of tetraaryltellurium compounds Ar4TeIV

Article abstract of DOI:10.1246/bcsj.20180380

Hypervalent tetraaryltellurium(IV) compounds of the type Ar₄Te^IV(1: Ar = C₆H₅; 2: Ar = p-H₃CC₆H₄; 3: Ar = p-t-BuC₆H₄; 4: Ar = p-F₃CC₆H₄) were prepared via a convenient one-pot reaction between the isolated corresponding ArLi reagent and TeCl₄. X-ray crystallographic analyses of 14 revealed distorted pseudo-trigonal-bipyramidal (TBP) structures for Ar₄Te and the TBP character was analyzed by the dihedral angle method.

Full text of DOI:10.1246/bcsj.20180380

Document type: Article
Short Article
Systematic Synthesis and Crystal
Structures of Tetraaryltellurium
Compounds Ar4TeIV #
Sho Kobayashi, Koh Sugamata,
and Mao Minoura*
Figure 1. 1-4 and related organochalcogen(IV) compounds.
Department of Chemistry, College of Science,
washed with
hexane
M. Minoura
Rikkyo University, 3-34-1 Nishi-Ikebukuro,
Toshima-ku, Tokyo 171-8501, Japan
+
ArX
n-BuLi
ArLi
hexane
Et2O
white solid
(X = Br or I)
E-mail: minoura@rikkyo.ac.jp
Received: December 4, 2018; Accepted: December 8, 2018;
Web Released: December 15, 2018
recryst. with
Et2O
+
Ar4Te
TeCl4
4.5 ArLi
yellow solid
Scheme 1. Synthesis of 1-4.
Abstract
Hypervalent tetraaryltellurium(IV) compounds of the
type Ar4TeIV (1: Ar = C6H5; 2: Ar = p-H3CC6H4; 3: Ar =
p-t-BuC6H4; 4: Ar = p-F3CC6H4) were prepared via a convenient
one-pot reaction between the isolated corresponding ArLi rea-
gent and TeCl4. X-ray crystallographic analyses of 1-4 revealed
distorted pseudo-trigonal-bipyramidal (TBP) structures for Ar4Te
and the TBP character was analyzed by the dihedral angle
method.
effective and powerful stabilization method for hypervalent com-
pounds has been established by Martin et al.; the bidentate Martin
ligand can stabilize hypervalent chalcogen(IV) molecules by the
construction of five-membered rings containing the hypervalent
atom and the strong electron-withdrawing properties of the ligand,
although oxygen atom(s) are bound to the chalcogen(IV) atom
in the ring system (Figure 1).9 The paucity of bonding parameters
on hypervalent tetraorganotellurium(IV) compounds in which the
tellurium atom is bound to carbon substituents stimulated us to
synthesize tetraaryltellurium compounds of the type Ar4TeIV
(1: Ar = C6H5; 2: Ar = p-H3CC6H4; 3: Ar = p-t-BuC6H4; 4: Ar =
p-F3CC6H4) in order to elucidate their crystal structures and
examine their hypervalent bonds.
Keywords: Hypervalent
j
Tellurium
j
Berry pseudorotation
1. Introduction
Organotellurium compounds have attracted interest as potential
precursors for organic synthesis1 and tellurium-containing nano-
materials.2 Moreover, the structural chemistry of organotellurium
compounds has also received substantial attention due to the
variable oxidation states of tellurium.3 Given that divalent organo-
tellurium compounds have been characterized extensively by
X-ray crystallography (>1000 examples), it is rather surprising
that only four examples of structurally defined tetraorganotellu-
rium(IV) compounds have been reported,4 especially considering
that significant attention has been focused on the structural prop-
erties of the so-called hypervalent bonds in chalcogen(IV) com-
pounds.5 In 1982, Ziolo et al. reported a distorted pseudo-trigonal-
bipyramidal (TBP) crystal structure for Ph4Te with long apical and
short equatorial C-Te bonds.4a It should be noted that this first
characterization of the solid-state structure of such a tetraorgano-
tellurium(IV) compound was only achieved 30 years after the first
isolation of Ph4Te by Wittig in 1952.6 The lack of systematic
structural studies to examine hypervalent bonds in detail is mainly
due to the instability of tetraorganotellurium(IV) compounds.4,5
For example, Ph4Te easily decomposes in the presence of atmos-
pheric moisture and/or oxygen, halogen-containing solvents, and
upon heating.7 As for the isolation of Ph4Te, the only method
suitable for its purification is recrystallization.4-7 Hellwinkel et al.
have developed a stabilization method that is based on the forma-
tion of five-membered rings containing a chalcogen(IV) atom,
using a biphenylene ligand instead of two phenyl groups.8 Another
2. Results and Discussion
During the course of our study of hypervalent compounds, we
have found that impurities such as alkyl halides or excess Li
reagent accelerate the deterioration of Ar4TeIV; therefore, we used
the isolated ArLi reagent instead of the in-situ-generated ArLi
reagent for the isolation of 1-4.10 The ArLi reagents were prepared
by treatment of the corresponding ArX (X = Br or I) with n-BuLi
in hexane for 1 h at 0 °C. The thus obtained white ArLi reagents
were collected by filtration and subsequently extracted into Et2O.
Then, LiX was removed by filtration to afford ArLi as white solids
after the removal of the solvent in vacuo. 1-4 were obtained from
the reaction of TeCl4 with the corresponding ArLi in Et2O at
¹78 °C. This one-pot reaction afforded 1-4 in moderate yield as
pale yellow crystalline solids after recrystallization from Et2O
(Scheme 1).
The 125Te NMR resonances of 1-4 were observed at 512, 500,
1
515, and 504 ppm, respectively. In the H and 13C spectra of 1-4
(and the 19F NMR spectrum of 4), only one set of aryl groups was
observed at room temperature in C6D6 (Figure 2), suggesting rapid
Berry pseudorotation (BPR)11 in solution between TBP structures
via square pyramidal (SP) transition structures (Figure 3), which is
common for pentaorgano-element compounds.12 In this sense, each
of the spectra reflects an averaged structure in the BPR and the
dynamic nature of such tetraorganotellurium(IV) compounds.
Bull. Chem. Soc. Jpn. 2019, 92, 661–663 | doi:10.1246/bcsj.20180380
© 2019 The Chemical Society of Japan | 661

The unambiguous identification of 1-4 was accomplished by
X-ray crystallographic analysis (Figure 4).13 For 1-4, pseudo-TBP
structures with elongated Capical-Te bonds and Cequatorial-Te bonds
were observed (vide infra). Although the previously reported
crystal structure of Ph4Te¢1/8C6H6 revealed four independent
molecules per P-1 unit cell with half a molecule of benzene,
crystals of 1 contain only one independent molecule of Ph4Te in a
lattice of higher symmetry (P21/n), even when the single crystals
were obtained from a benzene solution.
shortest Te-Te and Te-element distances (1: 4.181 ¡ (Te), 3.202
(H); 2: 4.639 (Te), 3.231 (H); 3: 5.735 (Te), 3.858 (H); 4: 9.081
(Te), 3.633 (F)). The corresponding sums of the van der Waals
radii (¡) are 4.12 (Te£Te), 3.26 (Te£H), and 3.53 (Te£F).14 All
Capical-Te bonds in 1-4 are significantly longer than the Cequatorial
-
Te bonds and the substituents at the para-positions of the aryl rings
induce only small differences among 1-4 and a clear trend in the
C-Te bond lengths was not observed. In an ideal TBP structure, the
Capical-Te-Capical bond angle should be 180°; yet, narrower bond
angles were observed around the Te atom in 1-4 due to repulsion
between the C-Te bonding electrons and the corresponding lone
pair of electrons (Table 1).
In the unit cells of 1-4, the tellurium centers exhibit weak
intermolecular contacts in the crystalline state, evident from the
The TBP character (%) of 1-4 and that of previously reported
Ph4Te¢1/8C6H6 were calculated by the dihedral angle method15
based on the observed bond angles around the Te atoms.
It is noteworthy that the tellurium environment of 1 showed low
TBP character (55%), while those in 2 (84%), 3 (93%), 4 (87%),
and Ph4Te¢1/8C6H6 (93%) exhibit high TBP character. This may
be rationalized considering the differences in the packing lattice
energy of the crystalline state of Ph4Te (P21/n vs. P-1).16
3. Conclusions
We have developed a convenient one-pot route to hypervalent
tetraorganotellurium compounds 1-4. The results of NMR spectros-
copy measurements and X-ray crystallographic analyses indicate
that 1-4 exhibit a dynamic behavior and Berry pseudorotation in
solution. Different trigonal bipyramidal character values were cal-
culated for 1-4 in the solid state and attributed to different packing
arrangements.
Figure 2. 1H NMR spectrum of 2.
a: apical
b: basal
e
We are currently carrying out further structural characterizations
of these reactive hypervalent molecules and the corresponding
results will be reported elsewhere in due course.
a
b
b
e: equatorial
e
e
e
pivot
pivot
pivot
a
a
TBP
b
e
4. Experimental
TBP
SP
(Transision structure)
Preparation of Ph4Te (1). A solution of PhI (10.0 g, 5.46 mL,
49.0 mmol) in hexane (100 mL) was treated with n-BuLi (31.2 mL,
49.0 mmol, 1.57 M) at 0 °C. After the mixture was stirred for 30
min at 0 °C and 1 h at room temperature, the reaction mixture was
filtered and extracted with Et2O. After removal of all volatiles, the
residue was washed with hexane and filtered to give PhLi as a
white solid. A solution of PhLi (3.34 g, 37.0 mmol) in Et2O (40
mL) was added to a solution of TeCl4 (2.38 g, 8.82 mmol) in Et2O
(100 mL) at ¹78 °C. After stirring for 2 h at room temperature, the
mixture was filtered and recrystallized from Et2O at ¹35 °C to
give Ph4Te (2.21 g, 5.0 mmol, 57.5%) as a pale yellow solid: mp
Figure 3. Schematic view of the Berry pseudorotation inter-
conversion between two trigonal bipyramidal (TBP) structures
via a square pyramidal (SP) transition structure.
1
118 °C; H NMR (400 MHz, C6D6, 298 K) δ 6.97-7.01(m, 12H),
7.42-7.47 (m, 8H); 13C NMR (100 MHz, C6D6, 298 K) δ 128.8,
133.5, 149.8; signals for the para-carbon atom could not be iden-
tified due to overlap with solvent signals; 13C NMR (100 MHz,
CD3CN, 298 K) δ 128.6, 129.4, 133.7, 150.6; 125Te NMR (126
MHz, C6D6, 298 K) δ 512.3.
X-ray Crystal Structure Analysis. Pale yellow single crystals
of 1-4 suitable for X-ray diffraction measurements were obtained
Figure 4. ORTEP drawings of 1-4 with thermal ellipsoids at
50% probability.
Table 1. Selected bond lengths (¡) and angles (°) of 1-4 and (C6H5)4Te¢1/8C6H6
Compound
(C6H5)4Te (1)
(p-H3CC6H4)4Te (2) 2.279(2) 2.303(2) 2.123(3) 2.132(3)
(p-t-BuC6H4)4Te (3) 2.281(2) 2.296(2) 2.134(2) 2.130(2)
(p-F3CC6H4)4Te (4) 2.271(2) 2.291(2) 2.135(2) 2.143(2)
C1ap-Te C2ap-Te C3eq-Te C4eq-Te C1ap-Te-C2ap C3eq-Te-C4eq R-factor
Z Z'
Space Gp.
2.245(3) 2.239(3) 2.162(3) 2.161(3)
157.3(1)
172.26(8)
166.10(8)
161.78(8)
168.3(4)
129.3(2)
104.85(9)
110.96(9)
114.41(8)
110.0(4)
2.22
3.07
2.94
2.38
6.5
4 1
2 1
4 2
2 1
8 4
P21/n
-
P1
-
P1
-
P1
-
4a
(C6H5)4Te·1/8C6H6 2.27(1) 2.30(1) 2.13(1) 2.16(1)
P1
662 | Bull. Chem. Soc. Jpn. 2019, 92, 661–663 | doi:10.1246/bcsj.20180380
© 2019 The Chemical Society of Japan

a) Ph4Te¢0.125C6H6: C. S. Smith, J. S. Lee, D. D. Titus, R. F.
Ziolo, Organometallics 1982, 1, 350. b) Bis(2,2¤-Biphenylylene)Te: S.
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were collected at ¹173 °C using a Bruker APEX II diffractometer
equipped with an APEX II CCD detector with MoKα radiation.
A wavelength of - = 0.71069 ¡ and single crystals of 0.10 ©
0.10 © 0.10 mm3 were selected in order to reduce absorption. Data
reduction was performed using Bruker SAINT. Structures were
solved by direct methods (SHELXT-2014)17a and refined against F2
by weighted full-matrix least-squares (SHELXL-2014).17b
The crystal data, data correction, and refinement details are
summarized in Table S1.
5
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This work was supported by the Japanese Ministry of Education,
Culture, Sports, Science, and Technology (MEXT) via a Grant-in-
Aid for Science Research on Innovative Areas (15H00962; Stimuli-
Responsive Chemical Species), by the MEXT-supported Program
for the Strategic Research Foundation at Private Universities
(2013-2017), the Japan Society for the Promotion of Science
(JSPS) via KAKENHI grants JP24550063 and JP15K05439, and by
the Collaborative Research Program of the Institute for Chemical
Research, Kyoto University (grants 2017-102 and 2018-106).
M. M. is grateful for financial support from the Rikkyo University
Special Fund for Research.
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Supporting Information
General experimental procedures and materials, as well as
X-ray crystallographic and spectroscopic data (1H, 13C, 19F, and
125Te NMR spectra) are available in the Supporting Informa-
tion. This material is available on https://doi.org/10.1246/bcsj.
20180380.
9
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10 All manipulations were carried out in an argon-filled glovebox
with heavy-walled Schlenk flasks. CAUTION: Solid ArLi compounds
may be explosive, especially those that contain fluorine.
11 R. S. Berry, J. Chem. Phys. 1960, 32, 933.
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1
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The optimized structure of 1 (NIMAG = 0, SCF = verytight,
3
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2.2568; C3eq-Te: 2.1358; C4eq-Te: 2.1358¡; C1ap-Te-C2ap: 168.4;
C3eq-Te-C4eq: 108.4 (°). The atom cooridinates were shown in
Table S2.
17 a) G. M. Sheldrick, Acta Crystallogr., Sect. C 2015, 71, 3.
b) G. M. Sheldrick, Acta Crystallogr., Sect. A 2015, 71, 3.
4
Compounds containing C-Te bonds were analyzed in
Cambridge Structural Database (CSD); Ver. 5.39, May, 2018.
Bull. Chem. Soc. Jpn. 2019, 92, 661–663 | doi:10.1246/bcsj.20180380
© 2019 The Chemical Society of Japan | 663