Novel valence expansion reactions using KC8: A new route to hexavalent organotellurium compounds from divalent tellurium

Article abstract of DOI:10.1246/cl.2002.288

Hexavalent tellurium compounds, Ar₅(CH₃)Te, Ar₄(CH₃)₂Te, and Ar₂(CH₃)₄Te (Ar = 4-CF₃C₆H₄, Ph, 4-CH₃C₆H₄

Full text of DOI:10.1246/cl.2002.288

288
Chemistry Letters 2002
Novel Valence Expansion Reactions Using KC8: A New Route to Hexavalent Organotellurium
Compounds from Divalent Tellurium
Masataka Miyasato, Mao Minoura,y Yohsuke Yamamoto, and Kin-ya AkibaÃyy
Department of Chemistry, Graduate School of Science, Hiroshima University,
1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526
yDepartment of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato, Sagamihara 228-8555
yyAdvanced Research Center for Science and Engineering, Waseda University, 3-4-1 Ohkubo, Tokyo 169-8555
(Received December 18, 2001; CL-011272)
Hexavalent
tellurium
compounds,
Ar5(CH3)Te,
Ar4(CH3)2Te, and Ar2(CH3)4Te (Ar ¼ 4-CF3C6H4, Ph, 4-
CH3C6H4), were synthesized by the reaction of Ar2-n(CH3)nTe
(n ¼ 0{1) or Ar3-m(CH3)mTeþXÀ (m ¼ 0{2) with KC8 followed
by the treatment with CH3I.
Valence of main group element compounds are generally
exalted higher byoxidizing reagents such as halogens and valence
shell expansion takes place in certain cases. For example,
Ph4F2Te was prepared by treatment of Ph4Te with XeF2 as an
oxidant.1 However, reactions of R2Te or R4Te with alkyl halides
did not yield hypervalent tellurium compounds but the corre-
sponding oniums R3Teþ.2 Here we report one-pot novel valence
expansion reactions from Ar2-n(CH3)nTe(II) (n ¼ 0{1) or
Ar3-m(CH3ÞmTeþXÀ(IV) (m ¼ 0{2) to Ar5(CH3)Te(VI),
Ar4(CH3)2Te(VI), and Ar2(CH3)4Te(VI) (Ar ¼ 4-CF3C6H4,
Ph, 4-CH3C6H4) by use of KC8 followed by treatment with CH3I.
The reaction of (4-CF3C6H4)2Te(II) with potassium graphite
(KC8)3 (ca. 15 equiv) was carried out at À78 ꢀC in THF for 5 min
and the reaction mixture was treated with CH3I (ca. 30 equiv) to
afford several hexavalent tellurium compounds, that is, (4-
CF3C6H4)5(CH3)Te (1)(4%), (4-CF3C6H4)4(CH3)2Te (trans-2)
(9%), and (4-CF3C6H4Þ2(CH3)4Te (trans-3) (10%) (Scheme
1).4{6 These hexavalent tellurium compounds are stable to
atmospheric moisture and could be separated by recycling HPLC.
They were characterized by spectroscopies and elemental
analyses. X-ray analysis of trans-2 and trans-3 confirmed that
these were octahedral and the two methyl groups in trans-2 and
the two 4-CF3C6H4 groups in trans-3 were located trans to each
other. The ORTEP drawing of trans-3 is shown in Figure 1.7
Figure 1. X-ray structure of trans-3 (30% thermal
ellipsoid). The structure is almost perfectly octahedral;
bond angles for each cis group is in the range of 90 Æ 0:7 ꢀ
and for each trans group is in the range of 180 Æ 1:4 ꢀ.
ꢀ
Selected bond lengths (A): Te-C(1) 2.25(1), Te-C(8)
2.19(1), Te-C(9) 2.18(1), Te-C(10) 2.18(1).
Table 1. Yields of the reaction of organotellurium compounds with KC8
(CH3K, PhCH2K) after treatment with CH3l
Scheme 1. Synthesis of hexaorganotellurium compunds.
The reaction of (4-CF3C6H4)3TeþClÀ with KC8 followed by
treatment with CH3I afforded a similar mixture of the hexavalent
tellurium compounds (1: 21%, trans-2: 7%, and trans-3: 7%)
(Table 1). When (4-CF3C6H4)(CH3)Te, (4-CF3C6H4)2-
(CH3)TeþOTfÀ, and (4-CF3C6H4)(CH3)2TeþIÀ were used
instead of homoleptic materials as mentioned above, i.e., (4-
CF3C6H4)2Te and (4-CF3C6H4)3TeþClÀ, monomethylated 1
was not obtained at all but di- and tetramethylated compounds
(trans-2 and trans-3) were obtained with increased yields. For
example, trans-2 (31%) and trans-3 (4%) were obtained from (4-
CF3C6H4)2(CH3ÞTeþOTfÀ and only trans-3 was obtained from
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
289
(4-CF3C6H4Þ(CH3)2TeþIÀ and (4-CF3C6H4)(CH3)Te in low
yields. These results clearly indicate that the unique valence
expansion took place by electron transfer from KC8 and was
applicable for the synthesis of new hexavalent tellurium
compounds with mixed carbon ligands. In fact, Ph6-n(CH3)nTe
(n ¼ 1, 4;8 n ¼ 2, trans-59) and (4-CH3C6H4)6-n(CH3)nTe
(n ¼ 1, 6;10 n ¼ 2, trans-7) were obtained from Ph3TeþBrÀ
and (4-CH3C6H4)3TeþClÀ as shown in Table 1.
Dedicated to Prof. Teruaki Mukaiyama on the occasion of his
75th birthday.
References and Notes
1
R. S. Michalak, S. R. Wilson, and J. C. Martin, J. Am. Chem. Soc., 106,
7529 (1984); K. Alam and A. F. Janzen, J. Fluorine Chem., 27, 467
(1985); L. Ahmed and J. A. Morrison, J. Am. Chem. Soc., 112, 7411
(1990); S. Sato, T. Yamashita, E. Horn, and N. Furukawa, Organome-
tallics, 15, 3526 (1996); M. Minoura, T. Sagami, K.-y. Akiba, C.
Modrakowski, A. Sudau, K. Seppelt, and S. Wallenhauer, Angew.
Chem., Int. Ed. Engl., 35, 2660 (1996); S. Sato, T. Yamashita, E. Horn,
O. Takahashi, and N. Furukawa, Tetrahedron, 53, 12183 (1997).
G. A. Olah, K. K. Laali, Q. Wang, and G. K. S. Prakash, in ‘‘Onium
Ions,’’ John Wiley & Sons, New York (1998), p 167; D. Hellwinkel,
Ann. N.Y. Acad. Sci., 192, 158 (1972).
Instead of KC8, C H K11 or PhCH2K12 could be used for the
3
reaction (Table 1), and trans-2 was obtained from (4-
CF3C6H4)2Te even by the use of PhCH2K. Therefore, PhCH2K
and CH3K should behave as an electron donor similar to KC8.
In order to elucidate the mechanism of the reaction, we
examined the effects of the equivalents of the reagents of KC8 and
CH3I in the reaction with (4-CF3C6H4)2Te on the yield of
hexavalent tellurium compounds. These results are shown in
Table 2. The generation of (4-CF3C6H4)TeÀ was suggested by
the formation of (4-CF3C6H4)(CH3)Te in the initial stage of the
reaction (entry 2 in Table 2). By use of a large excess of KC8 the
number of the Te-Ar bond clevaged increased. The 125Te NMR of
the reaction mixture from (4-CF3C6H4)2Te and a large excess of
KC8 at À78 ꢀC before the addition of CH3I showed a signal at ꢀ
360 ppm, which can be assigned as that for a dianion (4-
CF3C6H4)4Te2ÀÁ2(KþC8), generated independently by the reac-
tion of (4-CF3C6H4)5(CH3)Te with KC8.5 The signal at ꢀ
362 ppm was also observed in the reaction of (4-CF3C6H4)2Te
with CH3K before the addition of CH3I, therefore, it is confirmed
that CH3K acts as an electron donor. The detailed reaction
mechanism is not clear yet but a possible mechanism is illustrated
in Scheme 2.
2
3
For example, see: A. Furstner, Angew. Chem., Int. Ed. Engl., 32, 164
¨
¨
(1993); R. Csuk, B. I. Glanzer, and A. Furstner, Adv. Organomet. Chem.,
28, 85 (1988); D. Savoia, C. Trombini, and A. Umani-Ronchi, Pure
Appl. Chem., 57, 1887 (1985); H. Selig and L. B. Ebert, Adv. Inorg.
Chem. Radiochem., 23, 281 (1980); J.-M. Lalancette, G. Rollin, and P.
Dumas, Can. J. Chem., 50, 3058 (1972).
4
General procedure;
A
THF solution of Ar2-n(CH3)nTe or
Ar3-m(CH3)mTeþXÀ (Ar: 4-CF3C6H4, Ph, 4-CH3C6H4) {aryl halide
was also added in some cases (see Table 1)g was added to freshly
prepared KC8 (ca. 15 equiv) at À78 ꢀC. After 5 min of stirring, CH3I (ca.
30 equiv) was added at the same temperature, and the reaction mixture
was allowed to warm to room temperature. Graphite powder was filtered
off, and volatile materials were evaporated. Hexavalent oraganotellur-
ium species could be isolated by recycling HPLC(Japan Analytical
Industry LC-908, 1,2-dichloroethane as an eluent). The yields are
summarized in Table 1.
5
6
M. Miyasato, M. Minoura, and K.-y. Akiba, Angew. Chem., Int. Ed., 40,
2674 (2001).
trans-3; mp. 224 ꢀC (dec.); 1H NMR(400 MHz, CDCl3, 25 ꢀC) ꢀ1.88(s,
12H), 7.64 (d, 4H, J ¼ 8:3 Hz), 7.85 (d, 4H, J ¼ 8:3 Hz); 13CNMR
1
(100 MHz, CDCl3, 25 ꢀC) ꢀ 36.3 (q, JCTe ¼ 7:1 Hz), 124.2 (q,
2
1JCF ¼ 272 Hz), 124.9 (d), 129.6 (q, JCF ¼ 33 Hz), 130.5 (d), 165.9
Table 2. Effects of the equivalents of the reagents (KC8 and CH3I) in the
reaction with (4-CF3C6H4)2Te
(s, 1JCTe ¼ 173 Hz);19F NMR(376 MHz, CDCl3, 25 ꢀC) ꢀÀ63:0; 125Te
NMR [126 MHz, CDCl3, 25 ꢀC, (C H )2Te] ꢀ 119.
Data were collected at 200 K on a Mac Science DIP2030 imaging plate
3
7
equipped with graphite-monochromated Mo-Kꢁ radiation (ꢂ ¼
ꢀ
0:71073 A). Unit cell parameters were determined by autoindexing
several images in each data set separately with program DENZO. For
each data set, rotation images were collected in 3 ꢀ increments with a
total rotation of 180 ꢀ about ꢃ. Data were processed by using
SCALEPACK. The structure was solved using the teXsan system and
refined by full-matrix least-squares. Crystal data for trans-3: monoclinic
ꢀ
system, space group C2=c (no. 15), a ¼ 12:1390ð8Þ A, b ¼
ꢀ
ꢀ
ꢀ
ꢀ 3
18:359ð1Þ A, c ¼ 9:4980ð5Þ A, ꢄ ¼ 118:067ð4Þ , V ¼ 1867:8ð2Þ A ,
Z ¼ 4, ꢅcalc ¼ 1:70 g cmÀ3. R ¼ 0:0654 (Rw ¼ 0:1305) for 1925
observed reflections (116 parameters) with I > 3ꢆðIÞ. Goodness of
fit ¼ 1:311
8
9
M. Minoura, T. Mukuda, T. Sagami, and K.-y. Akiba, J. Am. Chem. Soc.,
121, 10852 (1999).
trans-5; mp. 246 ꢀC (dec.); 1H NMR(400 MHz, CDCl3, 25 ꢀC) ꢀ2.14(s,
6H), 7.20 (t, 8H, J ¼ 6:8 Hz), 7.28 (t, 4H, J ¼ 6:8 Hz), 7.32 (d, 8H,
J ¼ 6:8 Hz); 13C NMR (100 MHz, CDCl3, 25 ꢀC) ꢀ 29.5 (q,
1JCTe ¼ 16:6 Hz), 127.1 (d), 127.5 (d), 132.6 (d), 157.5 (s,
1JCTe ¼ 74:6 Hz); 125Te NMR [126 MHz, CDCl3, 25 ꢀC, (C H)2Te] ꢀ
3
274.
10 6; mp. 226 ꢀC (dec.); 1H NMR (400 MHz, CDCl3, 25 ꢀC) ꢀ 2.16 (s, 3H),
2.24 (s, 3H), 2.31 (s, 12H), 6.95 (d, 2H, J ¼ 7:8 Hz), 6.97 (d, 8H,
J ¼ 7:8 Hz), 7.27 (d, 8H, J ¼ 7:8 Hz), 7.50 (d, 2H, J ¼ 7:8 Hz); 13C
NMR (100 MHz, CDCl3, 25 ꢀC) ꢀ 21.0 (q), 21.1 (q), 33.0 (q,
1JCTe ¼ 12:4 Hz), 127.7 (d), 127.9 (d), 133.1 (d), 133.7 (d), 137.0 (s),
137.1 (s), 148.5 (s, 1JCTe ¼ 16:6 Hz), 151.9 (s, 1JCTe ¼ 49:8 Hz); 125Te
Scheme 2. Possible mechanism.
NMR [126 MHz, CDCl3, 25 ꢀC, (C H )2Te] ꢀ 341.
This work was supported by Grants-in-Aid for Scientific
Research (No. 11304044 and 12740352) from the Ministry of
Education, Culture, Sports, Science, and Technology of the
Japanese Government. The support of the Nishida Research Fund
for Fundamental Organic Chemistry (to M. Minoura) is also
acknowledged.
3
11 C. Eaborn, P. B. Hitchcock, K. Izod, A. J. Jaggar, and J. D. Smith,
Organometallics, 13, 753 (1994); E. Weiss and G. Sauermann, Chem.
Ber., 103, 265 (1970); E. Weiss and G. Sauermann, Angew. Chem., Int.
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12 M. Schlosser, Pure Appl. Chem., 60, 1627 (1988); M. Schlosser and J.
Hartmann, Angew. Chem., Int. Ed. Engl., 12, 508 (1973).