Angewandte
Chemie
Compounds 1–5 are readily soluble in most common
organic solvents. At ꢀ408C, the 125Te NMR spectrum
([D8]toluene) of PhBr2TeTePh (1) shows two equally intense,
broad signals at d = 1291.0 and 823.7 ppm, which suggests that
the molecular structure is retained in solution.[16] However, no
spectrum of 1 was obtained at room temperature, which
points to a dynamic exchange processes taking place under
these conditions. The 125Te NMR spectrum (CDCl3) of
RBr2TeTeR (3, R = 2,6-Mes2C6H3) exhibits only one sharp
resonance at d = 1683.8 ppm, which is consistent with the idea
that 3 undergoes a reversible, presumably entropically
favored rearrangement reaction to 2,6-Mes2C6H3TeBr (3a)
Experimental Section
1–5: A solution of the appropriate diarylditelluride (PhTeTePh:
0.410 g, 1.00 mmol for 1, RTeTeR (R = 2,6-Mes2C6H3):[12] 0.882 g,
1.00 mmol for 2–5) in Et2O or CH2Cl2 (30 mL) was cooled to 08C and
slowly treated with the appropriate halogen or synthetic equivalent
(Br2: 160 mg, 1.00 mmol for 1, SO2Cl2: 135 mg, 1.00 mmol for 2, Br2:
160 mg, 1.00 mmol for 3, I2: 253 mg, 1.00 mmol for 4, I2: 761 mg,
3.00 mmol for 5). Analytically pure samples were obtained by
crystallization from CH2Cl2/pentane (1), diethyl ether (2–4) and
THF (5). Yields 550 mg, 0.96 mmol of 1 (96%, m.p. 408C); 858 mg,
0.90 mmol of 2 (90%); 990 mg, 0.95 mmol of 3 (95%); 1.08 g,
1.90 mmol of 4 (95%), 1.50 g, 1.82 mmol of 5 (91%). Compounds 2–5
decompose without melting.
Analytical data: 1: 125Te NMR (126 MHz, [D8]-toluene, ꢀ408C):
d = 1291.0 (integral 50%), 823.7 ppm (integral 50%). UV (Et2O,
0.1 mmol): lmax = 422 nm. Elemental analysis (%) calcd for
C12H10Br2Te2 (569.22 gmolꢀ1): C 25.32, H 1.77; found: C 25.19, H 1.71.
2: 125Te NMR (126 MHz, CDCl3): d = 1374.9 (integral 37%),
1090.4 (integral 26%), 1027.3 ppm (integral 37%). UV (Et2O,
0.1 mmol): lmax = 534 nm. Elemental analysis (%) calcd for
C48H50Cl2Te2 (953.09 gmolꢀ1): C 60.49, H 5.29; found: C 60.20, H 5.02.
3: 1H NMR (400 MHz, CDCl3): d = 7.37 (t, J = 7 Hz, 1H, Ar),
7.07 (d, J = 7 Hz, 2H, Ph), 6.84 (s, 4H, Mes), 2.27 (s, 6H, CH3),
1.99 ppm (s, 12H, CH3). 13C NMR (100 MHz, CDCl3): d = 148.2,
139.0, 137.8, 136.4, 130.9, 128.4, 128.3, 128.0 (Ar), 21.2, 20.8 ppm
(CH3). 125Te NMR (126 MHz, CDCl3): d = 1683.8 ppm. UV (Et2O,
0.1 mmol): lmax = 559 nm. Elemental Analysis (%) calcd for
C48H50Br2Te2 (1042.00 gmolꢀ1): C 55.33, H 4.84; found: C 54.95, H
4.82.
upon dissolution.[16] The Te Br and Te Te bonds appear to be
kinetically labile.
ꢀ
ꢀ
To estimate the relative stabilities of monomeric species
REX, mixed-valent dinuclear species RX2EER, and the
disproportionation products REX3 and REER (E = S, Se,
Te ; X = F, Cl, Br, I), ab initio calculations[17,18] of suitable
model compounds with R = CH3 were performed; the results
are summarized in Table 1. Within the fluoride series, there is
Table 1: Zero-point-energy-corrected reaction energies per chalcogen
atom of the dimerization DE1 and disproportionation DE2 of H3CEX.[a]
F
Cl
Br
I
4: 1H NMR (400 MHz, CDCl3): d = 7.49 (t, J = 8 Hz, 1H, Ar),
7.14 (d, J = 8 Hz, 2H, Ph), 6.96 (s, 4H, Mes), 2.37 (s, 6H, CH3),
2.07 ppm (s, 12H, CH3). 13C NMR (100 MHz, CDCl3): d = 149.6,
140.5, 137.6, 136.1, 130.9, 128.3, 128.0, 112.8 (Ar), 21.2, 21.0 ppm
(CH3). 125Te NMR (126 MHz, CDCl3): d = 1018.0 ppm. UV (Et2O,
0.1 mmol): lmax = 622 nm. Elemental analysis (%) calcd for C24H25ITe
(568.00 gmolꢀ1): C 50.75, H 4.44; found: C 50.35, H 4.41.
S
ꢀ11.93
ꢀ13.40
ꢀ2.19
ꢀ1.13
0.05
0.27
ꢀ0.87
ꢀ0.06
Se
Te
ꢀ14.42
ꢀ14.22
ꢀ6.12
ꢀ3.22
ꢀ4.50
ꢀ1.82
ꢀ8.01
ꢀ4.23
5: 1H NMR (400 MHz, CDCl3): d = 7.15 (t, J = 8 Hz, 1H, Ar),
6.98 (d, J = 8 Hz, 2H, Ph), 6.95 (s, 4H, Mes), 2.29 (s, 6H, CH3),
2.19 ppm (s, 12H, CH3). 13C NMR (100 MHz, CDCl3): d = 138.2,
136.4, 135.7, 131.0, 129.0, 128.7, 127.8, 127.7, (Ar), 21.2, 21.0 ppm
(CH3). 125Te NMR (126 MHz, CDCl3): d = 905.1; (C6D6): d =
945.6 ppm. UV (toluene, 0.1 mmol): lmax = 496 nm. Elemental anal-
ysis (%)calcd for C24H25I3Te (821.81 gmolꢀ1): C 35.08, H 3.07; found:
C 35.24, H 3.32.
ꢀ19.44
ꢀ18.74
ꢀ12.58
ꢀ8.72
ꢀ11.11
ꢀ6.93
ꢀ8.29
ꢀ4.44
[a]Upper value: DE1 for dimerization, 2H3CEX!H3CX2EECH3 + 2DE1.
Lower value: DE2 for disproportionation, 3H3CEX!H3CEX3
H3CEECH3 + 3DE2. E=S, Se, Te; X=F, Cl, Br, I. Values in kcalmolꢀ1
+
.
Received: May 29, 2007
Revised: July 11, 2007
Published online: September 18, 2007
a strong thermodynamic driving force of the monomers
H3CEF (E = S, Se, Te) to undergo dimerization and dispro-
portionation reactions to form either H3CF2EECH3 or
H3CEF3 and H3CEECH3, respectively. For both processes,
the associated reaction energies per chalcogen atom (DE1/
DE2) are almost identical and range between ꢀ11.93 and
ꢀ19.44 kcalmolꢀ1, which is consistent with the observation
that an equilibrium exists between F3CSF and F3CF2SSCF3
prior to disproportionation to F3CSF3 and F3CSSCF3.[2]
Amongst all other halides, the tellurenyl species H3CTeCl
and H3CTeBr reveal the highest propensity to undergo
dimerization to form H3CCl2TeTeCH3 (DE1 = ꢀ12.58 kcal
molꢀ1) and H3CBr2TeTeCH3 (DE1 = ꢀ11.11 kcalmolꢀ1),
respectively, while the alternative disproportion reactions
are less favored (DE2 = ꢀ8.72 and ꢀ6.93 kcalmolꢀ1). In all
remaining cases, the driving force to undergo rearrangement
reactions is appears to be too small (DE1, DE2 > ꢀ10 kcal
molꢀ1), which explains the stability of most monomeric
tellurenyl iodides and selenenyl halides.[5,17]
Keywords: halides · hypervalent compounds ·
.
mixed-valent compounds · structure elucidation · tellurium
b) M. V. Carlowitz, H. Oberhammer, H. Willner, J. E. Boggs, J.
[3]a) W. L. Dorn, A. Knöchel, P. Schulz, G. Klar, Z. Naturforsch. B
[4]G. N. Ledesma, E. S. Lang, E. M. Vµzquez-López, U. Abram,
[5]a) W.-W. du Mont, H. U. Meyer, S. Kubinoik, S. Pohl, W. Saak,
Angew. Chem. Int. Ed. 2007, 46, 8277 –8280
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim