Lewis-base stabilized diiodine adducts with N-heterocyclic chalcogenamides

Article abstract of DOI:10.1039/c3dt51309b

Oxidation reactions of stable chalcogenamides with iodine are intriguing due to their broad application in various organic syntheses. In the present study we report on the utilization of N-heterocyclic carbene and cyclic-alkyl-amino carbenes L^1-3

Full text of DOI:10.1039/c3dt51309b

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Lewis-base stabilized diiodine adducts with
N-heterocyclic chalcogenamides†
Cite this: Dalton Trans., 2013, 42, 12940
Mykyta Tretiakov,a Yuriy G. Shermolovich,b Amit Pratap Singh,a Prinson P. Samuel,a
Herbert W. Roesky,*a Benedikt Niepötter,a Arne Visschera and Dietmar Stalke*a
Oxidation reactions of stable chalcogenamides with iodine are intriguing due to their broad application
in various organic syntheses. In the present study we report on the utilization of N-heterocyclic carbene
and cyclic-alkyl-amino carbenes L1–3: (L1: = :C[N(2,6-iPr2-C6H3)CH]2, L2: = :C(CH2)(CMe2)(C6H10)N-2,6-iPr2-
C6H3, L3: = :C(CH2)(CMe2)2N-2,6-iPr2-C6H3) for the syntheses of chalcogenamides L1–3vE (E = S, Se, Te)
1–4 and zwitterionic adducts L1–3vE–I–I 5–8. The synthesis of compounds 1–4 involved the addition
reaction of ligand L1–3: and elemental chalcogen. Treatment of 1–4 with iodine resulted in the formation
of adducts 5–8. Compounds 5–8 are well characterized with various spectroscopic methods and single-
crystal X-ray structural analysis.
Received 20th May 2013,
Accepted 31st May 2013
DOI: 10.1039/c3dt51309b
www.rsc.org/dalton
The motivation for using L1–3vE (L1: = :C[N(2,6-iPr2-C6H3)-
CH]2, L2: = :C(CH2)(CMe2)(C6H10)N-2,6-iPr2-C6H3, L3: = :C(CH2)-
Introduction
The reactions of elemental halogens (I2, Br2) and interhalogens (CMe2)2N-2,6-iPr2-C6H3) compounds as precursors for the reac-
(IBr, ICl) with organic molecules (L) containing group 16 tion with iodine was the possibility of forming an oxidized
donor atoms of composition LvE (L = organic framework, diiodide E(I)2 instead of the non-oxidized E–I–I adduct.
E = S, Se, Te) have gained particular interest in recent years.
Herein, we report on the synthesis and spectroscopic
They are used in various fields of research ranging from syn- characterization of novel chalcogenamides 1–4 as well as the
thetic chemistry to materials and industrial chemistry.1–17 The synthesis, structural, and spectroscopic characterization of
adduct formation of a donor (group 16 atom) with diiodine novel zwitterionic iodine compounds 5–8 with the N-hetero-
(LvE–I–I) stabilizes the lone pair of electrons of the donor by cyclic thioamides L1vS (1), L2vS (2), selenoamide L3vSe (3),
mixing its orbital with the σ* anti-bonding orbital of I2.18 As a and telluroamide L3vTe (4).
result a coordination bond forms and the double bond of the
chalcogenone group as well as the iodine–iodine single bond
are lengthened. A direct relationship was found to exist
between these three bond lengths: if the E–I bond length is
short, then the C–E bond length and I–I bond length will be
Results and discussion
The N-heterocyclic carbene ligands L1–3: are treated with
long and the donor functionality is strong. Furthermore the
νI–I frequencies are linearly correlated with the I–I bond
lengths. It is also worth mentioning that a zwitterionic struc-
ture is formed with the positive charge at the organic frame-
work and the negative charge at the I2 unit with the result that
a lengthening of the CvE double bond is observed. Therefore,
chalcogenamides are particularly good donors. Generally, the
greater the stabilizing ability of the N-alkyl or -aryl groups, the
stronger the resulting diiodine complex will be.19
elemental chalcogens (S, Se, Te) to form carbon–chalcogen
double bonds (Scheme 1). The rate of reaction of carbenes
with chalcogens increases in the order Se < Te < S in accord-
ance with the increase of the chalcogen solubility. All the pre-
pared chalcogenamides can be extracted with hot hexane and
recrystallized from THF. Chalcogenamides 1–4 are further
treated with diiodine in a molar ratio of 1 : 1 in toluene at
room temperature to give the diiodine adducts 5–8 (Scheme 2).
The present research is devoted to the comparison of the struc-
tural data between diiodine adducts of thio- (1, 2), seleno- (3)
and telluro- (4) amides.
aInstitut für Anorganische Chemie, Georg-August-Universität, Tammannstraβe 4,
The reactions of elemental sulfur with L1: as well as L2: are
complete after 12 hours at room temperature to give 1 and 2,
respectively, as colorless pure compounds in moderate yields.
Selenoamide 3 as well as telluroamide 4 were prepared under a
nitrogen atmosphere in moderate yields by the reaction
37077-Göttingen, Germany. E-mail: hroesky@gwdg.de, dstalke@gwdg.de
bInstitute of Organic Chemistry NAS of Ukraine, Murmanskaya Str. 5, 02094 Kiev,
Ukraine
†CCDC 933418 (5), 933419 (6), 933420 (7), 933421 (8). For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c3dt51309b
12940 | Dalton Trans., 2013, 42, 12940–12946
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Scheme 1 Synthesis of compounds 1–4.
between L3: and grey selenium and tellurium, respectively, in a
The 1H NMR chemical shift of the CH(CH3)2 proton in com-
molar ratio of 1 : 1.3 in THF at room temperature. The diiodine pound 5 is shifted upfield to 2.65 ppm when compared with
adducts 5–8 were obtained in good yields by reacting diiodine that of 1 (2.75 ppm). In the case of compound 6, the chemical
with 1–4, respectively, in a molar ratio of 1 : 1 in toluene under shift of the characteristic N-C(Me2)CH2– protons is shifted to
a nitrogen atmosphere. Compounds 5–8 are stable under nitro- low field (2.67 ppm) when compared with that of 2 (2.27 ppm).
gen for more than 3 months.
The ‘carbene’ carbon atom in compound 7 shows the
The 13C NMR measurements showed distinct differences in resonance at 231.7 ppm which is more than 10 ppm downfield
the chemical shifts between free carbenes L1–3: and chalcogen- compared with that of 3 (219.8 ppm). However, the 77Se NMR
amides L1–3vE (E = S, Se, Te). The ‘carbene’ carbon resonance resonance for selenoamide 3 (492.43 ppm) and the corres-
is shifted more than 50 ppm upfield on converting the ligand ponding diiodine adduct 7 (491.26 ppm) are nearly the same.
L to a respective chalcogenamide. For instance, in the Compound 8 has a very weak solubility in most of the organic
13C NMR spectra, the difference in ‘carbene’ carbon resonance solvents, and therefore the 13C NMR spectrum as well as the
between L1: (220.6 ppm) and 1 (167 ppm) is 53.6 ppm, and 125Te NMR spectrum were silent.
between L2: (309.4 ppm) and 2 (213.6 ppm) is 95.8 ppm. Com-
All the chalcogenamides are stable in open air. All the di-
parable chemical shifts are observed for the ‘carbene’ carbon iodine adducts of chalcogenamides are stable under a nitrogen
atoms of compounds 3 (219.8 ppm) and 4 (215.4 ppm) while atmosphere.
the corresponding resonance in L3: is 304.2 ppm.
In order to establish unambiguously the structural features
of compounds 5–8, single crystal X-ray structural analyses were
carried out. Suitable single crystals of 5–8 were obtained from
saturated toluene solutions.
Compound 5 crystallizes in the monoclinic crystal system
with space group C2/c, and compound 6 crystallizes in the
ˉ
triclinic crystal system with space group P1 (Table 1).
The molecular structures of compounds 5 and 6 are shown in
Fig. 1 and 2, respectively. No significant differences in bond
lengths and angles were observed in compounds 5 and 6. The
I(1)–S(1) and I(1)–I(2) bond lengths for compound 5 are 2.6981(7)
Å and 2.8662(6) Å, respectively, while the S(1)–I(1)–I(2) bond
angle is 176.805(13)°. The I(1)–S(1) and I(1)–I(2) bond lengths
for compound 6 are 2.8121(7) Å and 2.8282(6) Å, respectively,
while the S(1)–I(1)–I(2) bond angle is 173.783(10)° which is
close to that in 5. Both iodine atoms I(1) and I(2) in compounds
5 and 6 are not perpendicular to the C–S bond (C(1)–S(1)–I(1) =
101.47(7)° (5), 118.08(6)° (6)). In compound 5 the C–S bond
length is 1.706(2) Å, which is nearly the same as that in
6 (1.6961(16) Å). It is clear from the above discussion that the
difference in the organic framework does not have a consider-
able influence on the structural features of the CvS–I–I part of
the molecules.
Scheme 2 Synthesis of compounds 5–8.
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Dalton Trans., 2013, 42, 12940–12946 | 12941

Table 1 Crystal and structure refinement parameters for compounds 5–8
Parameters
5
6
7
8
CCDC No.
933418
C34H44I2N2S
766.57
100(2) K
0.56086 Å
Monoclinic
C2/c
933419
C23H35I2NS
611.38
933420
C20H31I2NSe
618.22
933421
C20H31I2NTe
666.86
100(2) K
0.56086 Å
Monoclinic
P21/n
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
100(2) K
0.56086 Å
Triclinic
100(2) K
0.56086 Å
Triclinic
ˉ
P1
ˉ
P1
Unit cell dimensions
a = 37.684(3) Å
b = 11.414(2) Å
c = 16.103(2) Å
α = 90.00°
a = 9.520(2) Å
b = 11.141(2) Å
c = 12.138(2) Å
α = 91.69(2)°
β = 100.62(2)°
γ = 103.70(2)°
1225.7(4) Å3
a = 9.8690(10) Å
b = 9.876(2) Å
c = 11.9680(10) Å
α = 92.040(10)°
β = 100.33(2)°
a = 11.108(2) Å
b = 16.440(2) Å
c = 12.754(2) Å
α = 90.00°
β = 100.24(2)°
γ = 90.00°
β = 99.76(2)°
γ = 90.00°
γ = 93.280(10)°
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
6816.0(16) Å3
8
1144.4(3) Å3
2295.4(6) Å3
2
2
4
1.494 Mg m−3
1.027 mm−1
1.657 Mg m−3
1.412 mm−1
1.794 Mg m−3
2.303 mm−1
1.930 Mg m−3
2.116 mm−1
3072
604
596
1264
0.178 × 0.133 × 0.063 mm3
0.867 to 23.633°
−53 ≤ h ≤ 53, −16 ≤ k ≤ 16,
−22 ≤ l ≤ 22
0.118 × 0.102 × 0.088 mm3
1.351 to 25.679°
−14 ≤ h ≤ 14, −17 ≤ k ≤ 17,
−18 ≤ l ≤ 18
0.128 × 0.061 × 0.047 mm3
1.366 to 21.395°
−12 ≤ h ≤ 12, −12 ≤ k ≤ 12,
−15 ≤ l ≤ 15
0.090 × 0.085 × 0.058 mm3
1.609 to 24.813°
−16 ≤ h ≤ 16, −24 ≤ k ≤ 24,
−19 ≤ l ≤ 19
108 910
Reflections collected
103 802
50 088
33 744
Independent reflections
Completeness to theta = 19.665°
Absorption correction
Max. and min. transmission
Refinement method
10 410 [R(int) = 0.0635]
100.0%
Semi-empirical from equivalents
0.7449 and 0.6452
Full-matrix least-squares on F2
10 410/0/361
9450 [R(int) = 0.0454]
100.0%
Analytical
1.0000 and 0.8996
Full-matrix least-squares on F2
9450/0/250
5274 [R(int) = 0.0361]
100.0%
Semi-empirical
0.8618 and 0.8043
Full-matrix least-squares on F2
5274/0/225
8016 [R(int) = 0.0922]
100.0%
Analytical
0.8140 and 0.7503
Full-matrix least-squares on F2
8016/3/230
Data/restraints/parameters
Goodness-of-fit on F2
1.027
1.054
1.031
1.064
Final R indices [I > 2σ(I)]
R indices (all data)
Extinction coefficient
R1 = 0.0304, wR2 = 0.0654
R1 = 0.0397, wR2 = 0.0687
n/a
R1 = 0.0255, wR2 = 0.0527
R1 = 0.0357, wR2 = 0.0552
n/a
R1 = 0.0194, wR2 = 0.0390
R1 = 0.0247, wR2 = 0.0407
n/a
R1 = 0.0313, wR2 = 0.0458
R1 = 0.0484, wR2 = 0.0492
0.00047(6)
Largest diff. peak and hole
1.439 and −0.997 e Å−3
1.162 and −0.947 e Å−3
0.769 and −0.746 e Å−3
0.829 and −0.748 e Å−3

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Fig. 3 Solid state structure of L3vSe–I–I (7). Hydrogen atoms are omitted for
clarity. Anisotropic displacement parameters are depicted at the 50% probability
level. Selected bond lengths (Å) and angles (°): I(1)–Se(1) 2.8192(6), I(1)–I(2)
2.8943(5), Se(1)–C(1) 1.854(2), N(1)–C(1) 1.315(3); Se(1)–I(1)–I(2) 171.456(8),
C(1)–Se(1)–I(1) 111.89(6), C(1)–N(1)–C(4) 124.08(17), C(1)–N(2–C(3) 109.61(16).
Fig. 1 Solid state structure of L1vS–I–I (5). Hydrogen atoms are omitted for
clarity. Anisotropic displacement parameters are depicted at the 50% probability
level. Selected bond lengths (Å) and angles (°): I(1)–S(1) 2.6981(7), I(1)–I(2)
2.8662(6), S(1)–C(1) 1.706(2), N(1)–C(1) 1.358(3); S(1)–I(1)–I(2) 176.805(13),
C(1)–S(1)–I(1) 101.47(7), C(1)–N(1)–C(2) 109.53(16), C(1)–N(2–C(3) 109.61(16).
Fig. 4 Solid state structure of L3vTe–I–I (8). Hydrogen atoms are omitted for
clarity. Anisotropic displacement parameters are depicted at the 50% probability
level. Selected bond lengths (Å) and angles (°): I(1)–Te(1) 2.8244(4), I(1)–I(2)
3.0964(4), Te(1)–C(1) 2.100(2), N(1)–C(1) 1.305(3); Te(1)–I(1)–I(2) 177.431(8),
C(1)–Te(1)–I(1) 105.71(6), C(1)–N(1)–C(9) 124.2(2).
Fig. 2 Solid state structure of L2vS–I–I (6). Hydrogen atoms are omitted for
clarity. Anisotropic displacement parameters are depicted at the 50% probability
level. Selected bond lengths (Å) and angles (°): I(1)–S(1) 2.8121(7), I(1)–I(2)
2.8282(6), S(1)–C(1) 1.6961(16), N(1)–C(1) 1.324(2); S(1)–I(1)–I(2) 173.783(10),
C(1)–S(1)–I(1) 118.08(6), C(1)–N(1)–C(12) 122.47(13).
ˉ
Compound 7 crystallizes in the triclinic space group P1 and C–Se and C–Te bonds, but have angles of 111.89° and 105.71(6)°,
compound 8 in the monoclinic space group P21/n (Table 1). respectively. In compound
7 the C–Se bond length is
The molecular structure of compounds 7 and 8 are shown in 1.854(2) Å, which is about 0.25 Å shorter than the C–Te found
Fig. 3 and 4, respectively. Notable differences in the corres- in 8 (2.100(2) Å) due to the difference in the atomic radii
ponding bond lengths and angles in compounds 7 and 8 were between selenium and tellurium. The structural differences in
observed. The Se(1)–I(1) and I(1)–I(2) bond lengths in com- CvE–I–I (E = Se, Te) bonds and angles are dictated by the
pound 7 are 2.8192(6) Å and 2.8943(5) Å, respectively, while difference of the atomic radii of chalcogens.
the Se(1)–I(1)–I(2) bond angle is 171.456(8)°. The Te(1)–I(1)
From the above discussed structural details the bonding
and I(1)–I(2) bond lengths for compound 8 are 2.8244(4) Å and situation in compounds 5–8 can be explained as follows. The
3.0964(4) Å, respectively, while the Te(1)–I(1)–I(2) bond angle bond formation between chalcogenamide and iodine occurs
(177.431(8)°) is more obtuse than the corresponding bond through donation of electron density from the chalcogen atom
angle in compound 7 (Se(1)–I(1)–I(2) = 171.456(8)°). The I(1)–I(2) to the iodine unit. This results in a partial positive charge at
bonds in compounds 7 and 8 are not perpendicular to the the chalcogen atom and some negative charge in the iodine
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part (Scheme 2). The involvement of the nitrogen lone pair in was stirred overnight. The dark red solution was evaporated to
a CvN double bond causes a positive charge on the nitrogen dryness. The residue was extracted with boiling hexane (2 ×
with partial compensation of the electron density of the chal- 50 mL), filtered and dried to yield light yellow pure 2 (yield
cogen atom resulting in a final weak zwitterionic structure 1.27 g, 58%). Mp 138 °C (dec.). Elemental analysis (%) calcd
with the positive nitrogen atom and the negative I–I part. As a for C27H36N2S (357.60): C, 77.25; H, 9.87; N, 3.92. Found: C,
result of this electronic delocalization, the C–N and C–E bond 77.43; H, 9.42; N, 4.05. 1H NMR (200 MHz, THF-d8, TMS,
lengths show a partial double bond character. The C–N bond 25 °C): δ 7.30–7.11 (m, 3H, CHar), 2.82 (sept, 2H, Ar–
lengths in compounds 5–8 are very close to the CvN double CH(CH3)2), 2.27 (s, 2H, CH2), 2.16–1.00 (m, 10 H, CH2), 1.29 (s,
bond distance which indicates that the positive charge density 6 H, CH3), 1.25 (d, J = 6.9 Hz, 6 H, CH3), 1.17 (d, J = 6.9 Hz,
is mainly located on the nitrogen atom. This is further evi- 6 H, CH3) ppm. 13C NMR (126 MHz, THF-d8, TMS, 25 °C):
denced by the almost planar geometry around the nitrogen δ 213.6, 148.2, 138.5, 129.3, 124.5, 96.4, 69.7, 55.5, 39.6, 32.9,
atom in compounds 5–8. In 5, the C–N bond distance is 1.358(3) 30.0, 27.3, 26.4, 23.5 ppm. EI-MS: m/z 357.2 (M+) (100%).
Å which is longer than the corresponding bond lengths in 6
Synthesis of L3vSe (3)
(1.324(2) Å), 7 (1.315(3) Å) and 8 (1.305(3) Å). This is due to the
two nitrogen atoms which are present in compound 5, and Compound 3 was synthesized by the reaction of L3: (1.00 g,
both of them participate in the charge delocalization whereas 3.5 mmol) in THF with grey selenium (0.36 g, 4.55 mmol) at
in the latter compounds only one nitrogen atom is present.
room temperature under a nitrogen atmosphere. The mixture
was stirred for 4 days. The dark solution was evaporated to
dryness. The residue was extracted with boiling hexane (2 ×
40 mL), filtered and dried to yield light yellow colorless pure 3
(yield 0.84 g, 66%). Mp 150 °C. Elemental analysis (%) calcd
for C20H31NSe (364.43): C, 65.92; H, 8.57; N, 3.84. Found: C,
66.78; H, 8.60; N, 3.85. 1H NMR (200 MHz, THF-d8, TMS,
25 °C): δ 7.34–7.23 (m, 3H, CHar), 2.80 (sept, 2H, Ar–
CH(CH3)2), 2.27 (s, 2H, CH2), 1.46 (s, 6 H, CH3), 1.31 (s, 6 H,
CH3), 1.27 (d, J = 5.7 Hz, 6 H, CH3), 1.24 (J = 5.7 Hz, 6 H, CH3)
ppm. 13C NMR (126 MHz, THF-d8, TMS, 25 °C): δ 219.8, 147.6,
135.4, 129.5, 125.3, 72.6, 54.0, 51.4, 32.3, 30.1, 29.1, 27.3,
23.9 ppm. 77Se NMR (95 MHz, THF-d8, TMS, 25 °C): δ
492.43 ppm. EI-MS: m/z 365 (M+) (100%).
Experimental section
All manipulations were performed in a dry and oxygen free
atmosphere (N2) using standard Schlenk-line techniques and
inside an MBraun MB 150-GI glove box maintained at or below
1 ppm of O2 and H2O. All solvents were dried by an MBraun
solvent purification system prior to use. N-Heterocyclic
carbene L1: and cyclic-alkyl-amino carbene L2,3: were syn-
thesized using reported procedures.20,21 Sulfur was sublimed
before using, and grey selenium, tellurium and iodine were
1
purchased and used as received. The H, 13C, 77Se, and 127Te
NMR spectra were recorded on a Bruker Avance DRX instru-
ment (300 or 500 MHz). The chemical shifts δ are given in
ppm with tetramethylsilane as an external standard. Elemental
analyses were performed at the Analytisches Labor des Insti-
tuts für Anorganische Chemie der Universität Göttingen.
Synthesis of L3vTe (4)
Compound 4 was synthesized by the reaction of L3: (1.00 g,
3.5 mmol) in THF with tellurium (0.58 g, 4.55 mmol) at room
temperature under a nitrogen atmosphere. The mixture was
stirred for 2 days until the color of the solution turned dark.
The solution was evaporated to dryness. The residue was
extracted with boiling hexane (2 × 40 mL), filtered and dried to
yield orange pure 4 (yield 0.90 g, 62%). Mp 162 °C. Elemental
analysis (%) calcd for C20H31NTe (413.07): C, 58.15; H, 7.56; N,
3.39. Found: C, 58.98; H, 7.84; N, 3.36. 1H NMR (500 MHz,
toluene-d8, TMS, 25 °C): δ 7.13–7.03 (m, 3H, CHar), 2.76 (sept,
2H, Ar–CH(CH3)2), 1.77 (s, 2H, CH2), 1.48 (d, J = 11 Hz, 6 H,
CH3), 1.41 (s, 6 H, CH3), 1.18 (d, J = 11 Hz, 6 H, CH3), 0.98 (s,
6 H, CH3) ppm. 13C NMR (126 MHz, toluene-d8, TMS, 25 °C):
δ 215.4, 146.3, 136.9, 129.1, 125.2, 75.8, 58.7, 49.6, 33.1, 29.7,
28.3, 27.9, 24.1 ppm. 125Te NMR (95 MHz, toluene-d8, TMS,
25 °C): δ 472.04 ppm. EI-MS: m/z 415 (M+) (100%).
Synthesis of L1vS (1)
Compound 1 was synthesized from the reaction of N-hetero-
cyclic carbene L1: (3.00 g, 7.72 mmol) in THF with elemental
sulfur (0.37 g, 11.58 mmol) at room temperature in open air.
The mixture was stirred overnight. The solvent was removed
in vacuum. The residue was extracted with hot hexane
(2 × 50 mL), filtered and dried to yield colorless pure 1
(yield 2.23 g, 69%). Mp 298 °C (dec.). Elemental analysis (%)
calcd for C27H36N2S (420.59): C, 73.22; H, 6.93; N, 4.38. Found:
C, 73.43; H, 7.02; N, 4.25. 1H NMR (200 MHz, CDCl3, TMS,
25 °C): δ 7.60–7.29 (m, 6H, CHar), 6.84 (s, 2H, CH–N), 2.75
(sept, 4H, CH), 1.31 (d, J = 6.8 Hz, 12 H, CH3), 1.21 (d, J =
6.8 Hz, 12 H, CH3) ppm. 13C NMR (126 MHz, CDCl3, TMS,
25 °C): δ 167.0, 146.5, 133.8, 130.1, 124.2, 119.0, 28.9, 24.2,
23.4 ppm. EI-MS: m/z 420.2 (M+) (100%).
Synthesis of L1vS–I–I (5)
For the synthesis of compound 5 a mixture of crystalline
iodine (0.097 g, 0.38 mmol) and L1vS (1) (0.16 g, 0.38 mmol)
was dissolved in toluene (20 mL) at room temperature. The
Synthesis of L2vS (2)
Compound 2 was synthesized from the reaction of L2: (2.00 g, color of the solution turned dark immediately. The solution
7 mmol) in THF with elemental sulfur (0.29 g, 9.1 mmol) at was stirred for 3 days and then filtered and the filtrate was
room temperature under a nitrogen atmosphere. The mixture evaporated to dryness. The residue was dissolved in toluene
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(10 mL) and stored at −32 °C for 3 days in a freezer to give 1.44 (s, 6 H, CH3), 1.32 (d, J = 6.6 Hz, 6 H, CH3), 1.26 (d, J =
brown crystals of 5 suitable for single crystal X-ray structural 6.6 Hz, 6 H, CH3) ppm. EI-MS: m/z 415 (M+ − 2I) (100%).
analysis (yield 0.25 g, 99%). Mp 180 °C (dec.). 1H NMR
Crystal structure determination
(200 MHz, THF-d8, TMS, 25 °C): δ 7.50–7.33 (m, 8H, CHar
+
CH–N), 2.65 (sept, 4H, Ar–CH(CH3)2), 1.38 (d, J = 6.8 Hz, 12 H, Suitable single crystals for X-ray structural analysis of 5, 6, 7,
CH3), 1.20 (d, J = 6.8 Hz, 12 H, CH3) ppm. 13C NMR (126 MHz, and 8 were mounted at low temperature in inert oil under an
THF-d8, TMS, 25 °C): δ 157.0, 146.8, 133.7, 131.6, 125.2, 124.1, argon atmosphere by applying the X-Temp2 device.22 The data
30.0, 23.9 ppm. EI-MS: m/z 420 (M+ − 2I) (100%).
were collected on a Bruker D8 three circle diffractometer
equipped with a SMART APEX II CCD detector and an INCOA-
TEC Ag microfocus source with INCOATEC Quazar mirror
optics.23 The data were integrated with SAINT24 and a semi-
empirical (for 5, 7) and an analytical (for 6, 8) absorption correc-
tion with SADABS25 were applied. The structure was solved by
direct methods (SHELXS-97) and refined against all data by
full-matrix least-squares methods on F2 (SHELXL-97).26 All
non-hydrogen-atoms were refined with anisotropic displace-
ment parameters. The hydrogen atoms were refined isotropi-
cally on calculated positions using a riding model with their
Uiso values constrained to 1.5Ueq of their pivot atoms for term-
inal sp3 carbon atoms and 1.2 times for all other carbon
atoms. The disordered parts were refined using distance
restraints and restraints for the anisotropic displacement
parameters.
Synthesis of L2vS–I–I (6)
For the synthesis of compound 6, crystalline iodine (0.21 g,
0.84 mmol) was added to a solution of L2vS (2) (0.3 g,
0.84 mmol) in toluene (15 mL) at room temperature. The color
of the solution turned dark red immediately. The solution was
stirred for 1 day and then filtered and the filtrate was evapo-
rated to dryness. The residue was dissolved in 10 mL of
toluene and stored at −32 °C for 3 days in a freezer to give
dark brown crystals of 6 suitable for single crystal X-ray struc-
tural analysis (yield 0.15 g, 29%). Mp 146 °C (dec.). 1H NMR
(200 MHz, THF-d8, TMS, 25 °C): δ 7.26 (m, 3H, CHar), 2.81
(sept, 2H, Ar–CH(CH3)2), 2.67 (s, 2 H, CH2), 1.83–1.45 (m, 10 H,
CH2), 1.32 (s, 6 H, CH3), 1.26 (d, 6 H, CH3), 1.18 (d, 6 H, CH3)
ppm. 13C NMR (126 MHz, THF-d8, TMS, 25 °C): δ 209.4, 145.4,
138.4, 128.9, 124.4, 85.3, 73.0, 53.8, 35.2, 30.5, 29.1, 26.8, 26.4,
22.5 ppm. EI-MS: m/z 357.3 (M+ − 2I) (100%).
Conclusions
Synthesis of L3vSe–I–I (7)
The synthesis and reactivity of compounds with heavier group
For the synthesis of compound 7, crystalline iodine (0.58 g, 16 elements is a rapidly growing field in chemistry because of
2.30 mmol) was added to a solution of L3vSe (3) (0.84 g, their extensive use in various applications. In the present
2.3 mmol) in toluene (20 mL) at room temperature. The color study we show that an N-heterocyclic carbene L1: as well as
of the solution turned immediately dark. The solution was cyclic-alkyl-amino carbenes L2–3: react with chalcogens to form
stirred for 2 days and then the precipitate was filtered and air stable chalcogenamides 1–4. All the chalcogenamides
dried. The product was dissolved in toluene (10 mL) and regardless of the organic framework or chalcogen are able to
stored at −32 °C for 3 days to give dark brown crystals of 7 suit- form diiodine adducts with the general formula LvE–I–I.
able for single crystal X-ray structural analysis (yield 1.10 g, These experiments show the easy access to this class of com-
77%). Mp 232 °C (dec.). 1H NMR (200 MHz, THF-d8, TMS, pounds. Compounds 5–8 are well-characterized with various
25 °C): δ 7.56–7.35 (m, 3H, CHar), 2.73 (sept, 2H, Ar– spectroscopic methods and single-crystal X-ray analyses. These
CH(CH3)2), 2.40 (s, 2 H, CH2), 1.70 (s, 6 H, CH3), 1.30 (m, 18 H, compounds might prove to be promising candidates for the
CH3) ppm. 13C NMR (126 MHz, THF-d8, TMS, 25 °C): δ 231.7, synthesis of iodine containing compounds, which are sensitive
146.7, 133.1, 131.1, 126.5, 77.2, 55.0, 51.9, 30.6, 30.5, 30.2, to elemental iodine. The formation of an oxidized E(I)2 com-
27.0, 25.3 ppm. 77Se NMR (95 MHz, THF-d8, TMS, 25 °C): δ pound which we were aiming at was not observed due to the
491.26 ppm. EI-MS: m/z 365 (M+ − 2I) (100%).
low oxidation potential of iodine.
Synthesis of L3vTe–I–I (8)
Acknowledgements
For the synthesis of compound 8, crystalline iodine (0.46 g,
1.81 mmol) was added to a solution of L3vTe (4) (0.75 g,
1.81 mmol) in toluene (20 mL) at room temperature. The color
of the solution turned dark and a precipitate was formed
immediately. The solution was stirred for 2 days, and the pre-
cipitate was filtered and dried in vacuo. The saturated solution
of 8 in DMSO was stored at room temperature for 3 days to
give black crystals of 8 suitable for single crystal X-ray struc-
tural analysis (yield 1.20 g, 99%). Mp 206 °C (dec.). 1H NMR
(300 MHz, DMSO-d6, TMS, 25 °C): δ 7.50 (m, 3H, CHar), 2.64
(sept, 2H, Ar–CH(CH3)2), 2.10 (s, 2 H, CH2), 1.67 (s, 6 H, CH3),
H.W.R. thanks the Deutsche Forschungsgemeinschaft for
financial support. Dedicated to Professor Bernt Krebs on the
occasion of his 75th birthday.
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