Synthesis, characterization and oxidizing properties of a diorgano tellurone carrying bulky aromatic substituents

Article abstract of DOI:10.1039/b811112j

Bis(2,4,6-triisopropylphenyl) tellurone (Tip₂TeO₂) was prepared, fully characterized by spectroscopic and X-ray crystallographic analyses, as well as theoretical calculations, and found to be an effective oxidizing agent that was capable of converting alcohols into carbonyl compounds under mild reaction conditions. The Royal Society of Chemistry.

Full text of DOI:10.1039/b811112j

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COMMUNICATION
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Synthesis, characterization and oxidizing properties of a diorgano
tellurone carrying bulky aromatic substituentsw
Makoto Oba,a Yasunori Okada,a Kozaburo Nishiyama,*a Shigeru Shimadab and
Wataru Ando*b
Received (in Cambridge, UK) 30th June 2008, Accepted 7th August 2008
First published as an Advance Article on the web 17th September 2008
DOI: 10.1039/b811112j
Bis(2,4,6-triisopropylphenyl) tellurone (Tip2TeO2) was pre-
pared, fully characterized by spectroscopic and X-ray crystallo-
graphic analyses, as well as theoretical calculations, and found
to be an effective oxidizing agent that was capable of converting
alcohols into carbonyl compounds under mild reaction
conditions.
Diorgano tellurones (R2TeO2), the tellurium analogues of
sulfones, are a novel class of organochalcogen oxides that
have not yet been fully characterized. Since 1920, few attempts
have been made to prepare tellurones by the oxidation of
diorgano tellurides with hydrogen peroxide,1 which probably
Scheme 1 Synthesis of Tip2TeO2 (2). Reagents and conditions: (a)
NaIO4 (2.25 equiv.), EtOH–H2O, 98%; (b) NaIO4 (1 equiv.),
EtOH–H2O, 83%; (c) as in (b), 90%.
resulted in the formation of the hydrogen peroxide adducts of
the telluroxides.2 In 1982, Engman and Cava reported the
preparation of bis(4-methoxyphenyl) tellurone, which gave
satisfactory analytical data for the first time, by periodate
oxidation of the corresponding telluroxide.3 More recently, a
similar approach towards diorgano tellurones, using sodium
hypochlorite as an oxidant, was reported by Khurana and co-
workers.4 However, considering the highly polarizable nature
of the tellurium–oxygen bond, it is doubtful whether the
reported tellurones were obtained in a monomeric form. We
prepared bis(4-methoxyphenyl) tellurone according to Cava’s
procedure, and the product was analyzed by NMR spectro-
chalcogen oxide capable of oxidizing alcohols to their corres-
ponding carbonyl compounds.
When a solution of bis(2,4,6-triisopropylphenyl) telluride
(Tip2Te, 1) in ethanol was treated with an aqueous solution of
sodium periodate (2.25 equiv.) at room temperature overnight,
bis(2,4,6-triisopropylphenyl) tellurone (Tip2TeO2, 2) was iso-
lated in 98% yield by precipitation from water (Scheme 1).
Tellurone 2 could be also obtained via the corresponding
telluroxide, 3 (Tip2TeO), in a stepwise manner. The use of
other oxidizing agents, such as hypochlorite, hydrogen per-
oxide and meta-chloroperbenzoic acid, resulted in either a low
yield or a complex mixture. Diphenyl telluride and bis(2,4,6-
trimethylphenyl) telluride (Mes2Te) were also subjected to the
above oxidation conditions; however, the former gave an
oligomeric mixture, as in the case of 4-methoxyphenyl deriva-
tive, and the latter afforded only the corresponding telluroxide
(Mes2TeO) in 87% yield.
The structure of 2 was confirmed by 1H, 13C and 125Te
NMR, MS and IR spectroscopy, as well as elemental ana-
lysis.z The 125Te NMR spectrum of 2 revealed a signal at d
1326, which is shifted slightly downfield from that of the
corresponding telluroxide, 3 (d 1314).5 The FAB-MS spectrum
of 2 showed a parent ion peak at m/z = 569 (MH)+. The IR
spectrum of 2 in benzene revealed two absorptions at 835 and
805 cmꢀ1, which are in good agreement with the calculated
asymmetrical and symmetrical stretching vibrational frequen-
cies of the O–Te–O group (834 and 799 cmꢀ1, respectively),6
computed at the B3LYP/6-31G(d)+LANL2DZdp(Te)y level
and scaled by 0.98.7
1
scopy. The H, 13C and 125Te NMR spectra exhibited all the
characteristics of oligomeric compounds, with extremely
broad 1H signals, and many 13C and 125Te signals being
observed, despite the compound’s highly symmetrical struc-
ture. These findings led us to speculate that we were dealing
with an oligomeric mixture of the telluroxane type. It is
reasonable to expect that bulky substituents placed on the
tellurium atom would force the tellurone to retain its mono-
meric form. In this Communication, we report the synthesis
and the first crystal structure of a diorgano tellurone. The
bulky diaryl tellurone obtained in this work is also the first
a Department of Materials Chemistry, Tokai University, 317 Nishino,
Numazu, Shizuoka 410-0395, Japan.
E-mail: nishiyam@wing.ncc.u-tokai.ac.jp; Fax: +81 55 968 1155;
Tel: +81 55 968 1111
b National Institute of Advanced Industrial Science and Technology,
1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
E-mail: wataru.ando@aist.go.jp; Fax: +81 29 861 4511;
Tel: +81 29 861 6244
w Electronic supplementary information (ESI) available: General
experimental procedures, and 1H, 13C and 125Te NMR spectra. CCDC
691356. For ESI and crystal data for tellurone 2 in CIF or other
electronic format, see DOI: 10.1039/b811112j
The crystal structure of 2 was established by X-ray crystallo-
graphy (Fig. 1).z The two Te–O distances of 1.801(2) and
ꢁc
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Table 1 Oxidation of alcohols to carbonyl compounds using Tip2-
TeO2 (2)
Tip2TeO2ð2 equiv:Þ
alcohol ꢀ!carbonyl compound
hexane;reflux
Run
Alcohol
Time/h
Product (%)a
1b
2
4-BrC6H4CH2OH
4-BrC6H4CH2OH
8
1
4-BrC6H4CHO (96)
4-BrC6H4CHO
(quant.)
3
4
PhCH2OH
4-MeOC6H4CH2OH
1
1
PhCHO (quant.)
4-MeOC6H4CHO
(quant.)
Fig. 1 An ORTEP drawing of Tip2TeO2 (2), showing 50% prob-
ability ellipsoids for the non-hydrogen atoms. Water of crystallization
is omitted for clarity. Selected bond lengths (A) and angles (1):
Te(1)–O(1) 1.801(2), Te(1)–O(2) 1.802(3), Te(1)–C(1) 2.127(4),
Te(1)–C(16) 2.126(3), O(1)–Te(1)–O(2) 111.17(13), C(1)–Te(1)–C(16)
106.12(15), O(1)–Te(1)–C(1) 114.01(13), O(1)–Te(1)–C(16) 105.58(13),
O(2)–Te(1)–C(1) 105.65(15), O(2)–Te(1)–C(16) 114.41(13).
5
6
4-O2NC6H4CH2OH
4
1
4-O2NC6H4CHO
(94)
trans-
PhCHQCHCHO
(quant.)
trans-2-Dodecen-1-
al (quant.)
PhCH2CH2CHO
(quant.)
trans-PhCHQCHCH2OH
7
8
trans-2-Dodecenol
1
2
PhCH2CH2CH2OH
1.802(3) A are shorter than those found in Ph2TeO (Te–O
1.871(18) A)8 and (C6F5)2TeO (Te–O 1.875(3) A),9 which
adopt dimeric structures bonded by secondary Te–O intera-
ctions (Te–O 2.563(21) and 2.214(2) A, respectively). The two
Te–C distances of 2.127(4) and 2.126(3) A are comparable to
those commonly found in diaryl telluroxides such as (4-
MeOC6H4)2TeO (Te–O 2.126(2) A).10 The atoms arranged
around the tellurium atom are in the shape of a regular
tetrahedron, with angles ranging from 105.58(13) to
114.41(13)1. In the crystal lattice, two Tip2TeO2 molecules
interact via two water molecules, where the two protons in
each water molecule are oriented in such a way that they point
towards two different oxygen atoms of different tellurones,
and two O–Te–O planes are nearly perpendicular (96.71) to
each other. The distance between the tellurone and the water
molecules is typical of a weak hydrogen bond, with an average
O–O distance of 2.84 A.
9
10
11
12
1-Dodecanol
2-Dodecanol
PhCHOHCH3
PhCHOHCO2Me
6
2
4
8
1-Dodecanal (97)
No reaction
PhCOCH3 (87)
PhCOCO2Me (77)
a
b
Determined by 1H NMR. The reaction was carried out in refluxing
pentane (36 1C).
allylic alcohols. Therefore, the corresponding aldehydes were
obtained in quantitative yields (runs 3, 4, 6 and 7), although
4-nitrobenzyl alcohol required a longer reaction time (run 5).
Note that non-activated alcohols, such as 3-phenylpropanol
and 1-dodecanol, were found to undergo oxidation to alde-
hydes with excellent yields (runs 8 and 9). Moderate reactivity
was observed in the oxidation of secondary benzylic alcohols,
giving acetophenone and methyl phenylglyoxylate in 87 and
77% yields, respectively (runs 11 and 12), whereas non-acti-
vated secondary alcohols such as 2-dodecanol were unreactive
(run 10).
A
theoretical calculation6 on
2 at the B3LYP/6-
31G(d)+LANL2DZdp(Te)y level efficiently reproduced the
experimental structure (calculated bond lengths (A) and angles
(1): Te–O 1.787, Te–C 2.165, O–Te–O 116.98, C–Te–C
105.89). The deviation of the observed O–Te–O angle
(111.17(13)1) from the calculated value (116.981) can be
attributed to the interaction with the water molecules in the
crystal lattice.
We have already reported that the corresponding tellur-
oxide, 3, could oxidize benzylic and allylic alcohols; however,
the reaction should be carried out in refluxing xylene (140 1C).5
In addition, 3 could not oxidize non-activated alcohols, even
at a higher temperature, suggesting an enhanced reactivity of
2 in comparison with 3.
In conclusion, we have prepared and fully characterized the
first monomeric diorgano tellurone, 2, with the help of bulky
aromatic substituents. It has also been demonstrated that 2 is
highly reactive towards alcohols, giving the corresponding carbo-
nyl compounds in good yields. Further studies are in progress to
broaden the potential of 2 as an oxidizing reagent and to elucidate
the reason for its increased alcohol-oxidizing competence.
Financial support from Tokai University is gratefully
acknowledged by M. O.
Further structural proof for 2 was obtained by the oxidation
of triphenylphosphine with 0.5 equiv. of 2 in refluxing CDCl3.
The 31P and 1H NMR spectra of the reaction mixture revealed
quantitative formation of triphenylphosphine oxide, along
with the complete recovery of Tip2Te (1), suggesting that 2
involves two reactive Te–O bonds.
The most prominent feature of 2 is its alcohol-oxidizing
activity.11 When a pentane solution of 4-bromobenzyl alcohol
and 2 equiv. of 2 were heated to reflux (36 1C) for 8 h, 4-
bromobenzaldehyde was obtained in 96% yield (Table 1, run 1).
A similar reaction in refluxing hexane (69 1C) was completed
within 1 h to give a quantitative yield of the aldehyde (run 2).
Other alcohols were also employed as substrates, and repre-
sentative results are listed in Table 1. In order to shorten
turnaround times, all reactions were performed in refluxing
hexane. Tellurone 2 was highly reactive toward benzylic and
Notes and references
z Colorless crystals, mp 108–110 1C. 1H NMR (CDCl3): d 1.12 (d,
J = 7 Hz, 24H), 1.21 (d, J = 7 Hz, 12H), 2.88 (sept, J = 7 Hz, 2H),
4.09 (sept, J = 7 Hz, 4H) and 7.14 (s, 4H). 13C NMR (CDCl3): d
23.57, 24.26, 32.74, 34.24, 124.79, 137.82 (d satellite, JTe–C = 81 Hz),
152.19 and 154.87. 125Te NMR (CDCl3):
d 1326. FAB-MS
ꢁc
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(m-NBA): m/z = 569 (MH+). IR (KBr): nmax = 3470 (O–H), 3050
Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R.
(C–H), 2960 (C–H), 825 (Te–O) and 800 (Te–O) cmꢀ1. IR (benzene):
Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J.
B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J.
J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M.
C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A.
Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M.
W. Gill, B. G. Johnson, W. Chen, M. W. Wong, C. Gonzalez and
J. A. Pople, GAUSSIAN 03 (Revision D.02), Gaussian, Inc.,
Wallingford, CT, 2004.
n
max = 2960 (C–H), 835 (Te–O) and 805 (Te–O) cmꢀ1. Anal. calc. for
C30H46O2TeꢂH2O: C, 61.67; H, 8.28. Found: C, 61.82; H, 8.39%.
y The LANL2DZdp effective core potential basis set was used for Te,
while the 6-31G(d) basis set was used for C, H and O. This combina-
tion is denoted as 6-31G(d)+LANL2DZdp(Te).
z X-Ray data were collected on a Bruker SMART diffractometer. The
structure was solved by direct methods (SHELXS-97) and refined with
CRYSTALS. Crystallographic data for 2: C30H46O2TeꢂH2O, Mr
=
584.31, 0.16
ꢃ
0.12 ꢃ 0.08 mm, monoclinic, C2/c (#15), a =
24.4967(19), b = 16.1761(12), c = 16.3546(12) A, b = 111.4460(10)1,
V = 6032.0(8) A3, Z = 8, rcalc = 1.287 g cmꢀ3, m = 1.012 mmꢀ1, MoKa
(l = 0.71069 A), 153(2) K, 2ymax = 56.51. Of the 18 070 reflections that
were collected, 6755 were unique (Rint = 0.043). R = 0.0756 (all
reflections), R1 = 0.0378 [I 4 2s(I)], wR2 = 0.0911 (all reflections),
GOF = 1.052, residual electron density between ꢀ0.89 and 1.30 eA3.
CCDC 691356. See the ESI.w
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11 A typical experimental procedure for the oxidation of alcohols
with tellurone 2 is as follows. A solution of 4-bromobenzyl alcohol
(94.1 mg, 0.503 mmol) and 2 (584 mg, 1.03 mmol) in hexane (5 ml)
was refluxed for 1 h. 1H NMR analysis of the concentrated
reaction mixture showed the quantitative formation of 4-bromo-
benzaldehyde. Purification of the product was performed by flash
column chromatography on silica gel and elution with hexane
afforded 4-bromobenzaldehyde (90.4 mg, 0.489 mmol) in 97%
yield. The structure was confirmed by comparison of the obtained
1H NMR spectrum and GC retention times with those of an
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ꢁc
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5380 | Chem. Commun., 2008, 5378–5380