Mesityltellurenyl cations stabilized by triphenylpnictogens [MesTe(EPh 3)]+ (E = P, As, Sb)

Article abstract of DOI:10.1021/ic3017722

The homoleptic 1:1 Lewis pair (LP) complex [MesTe(TeMes₂)]O ₃SCF₃ (1) featuring the cation [MesTe(TeMes ₂)]⁺ (1a) was obtained by the reaction of Mes ₂Te with HO₃SCF₃.

Full text of DOI:10.1021/ic3017722

Article
pubs.acs.org/IC
Mesityltellurenyl Cations Stabilized by Triphenylpnictogens
[MesTe(EPh3)]+ (E = P, As, Sb)†
Jens Beckmann,*,‡,§ Jens Bolsinger,§ Andrew Duthie,⊥ Pamela Finke,‡,§ Enno Lork,‡ Carsten Ludtke,§
̈
Ole Mallow,‡,§ and Stefan Mebs*,§
‡Institut fur Anorganische und Physikalische Chemie, Universitat Bremen, Leobener Strasse, D-28359 Bremen, Germany
̈
̈
̈
§Institut fur Chemie und Biochemie, Freie Universitat Berlin, Fabeckstrasse 34/36, D-14195 Berlin, Germany
̈
⊥School of Life and Environmental Sciences, Deakin University, Pigdons Road, Waurn Ponds 3217, Australia
S
* Supporting Information
ABSTRACT: The homoleptic 1:1 Lewis pair (LP) complex [MesTe(TeMes2)]-
O3SCF3 (1) featuring the cation [MesTe(TeMes2)]+ (1a) was obtained by the
reaction of Mes2Te with HO3SCF3. The reaction of 1 with Ph3E (E = P, As, Sb,
Bi) proceeded with substitution of Mes2Te and provided the heteroleptic 1:1 LP
complexes [MesTe(EPh3)]O3SCF3 (2, E = P; 3, E = As) and [MesTe(SbPh3)]-
[Ph2Sb(O3SCF3)2] (4) featuring the cations [MesTe(EPh3)]+ (2a, E = P; 3a, E =
As; 4a, E = Sb) and the anion [Ph2Sb(O3SCF3)2]− (4b). In the reaction with
Ph3Bi, the crude product contained the cation [MesTe(BiPh3)]+ (5a) and the
anion [Ph2Bi(O3SCF3)2]− (5b); however, the heteroleptic 1:1 LP complex
[MesTe(BiPh3)][Ph2Bi(O3SCF3)2] (5) could not be isolated because of its
limited stability. Instead, fractional crystallization furnished a large amount of
Ph2BiO3SCF3 (6), which was also obtained by the reaction of Ph3Bi with
HO3SCF3. The formation of the anions 4b and 5b involves a phenyl group
migration from Ph3E (E = Sb, Bi) to the MesTe+ cation and afforded MesTePh as the byproduct, which was identified in the
mother liquor. The heteroleptic 1:1 LP complexes 2−4 were also obtained by the one-pot reaction of Mes2Te, Ph3E (E = P, As,
Sb) and HO3SCF3. Compounds 1−4 and 6 were investigated by single-crystal X-ray diffraction. The molecular structures of 1a−
4a were used for density functional theory calculations at the B3PW91/TZ level of theory and studied using natural bond order
(NBO) analyses as well as real-space bonding descriptors derived from an atoms-in-molecules (AIM) analysis of the theoretically
obtained electron density. Additionally, the electron localizability indicator (ELI-D) and the delocalization index are derived from
the corresponding pair density.
pincer ligands featuring S donor atoms.9 More recently, highly
charged chalcogen(II) dications were obtained by the reaction
of in situ generated chalcogen(II) triflates with 1,4-diaryl-1,4-
INTRODUCTION
■
Like silylenes (R2Si), the isoelectronic phosphenium cations
(R2P+) and sulfonium dications (R2S2+) as well as their heavier
diaza-1,3-butadiene (R2DAB) ligands, diiminopyridine
congeners are unsaturated (six-valence-electron) species
(R2DIMPY) ligands, bis(arylimino)acenaphthene (R2BIAN)
possessing a vacant p orbital and one lone pair and accordingly
ligands, two monodentate pyridines, two NHCs, and chelating
may react as Lewis acid and base. Phosphenium cations can be
stabilized using strong σ-donor ligands, such as phosphines and
N-heterocyclic carbenes (NHCs), as exemplified by the 1:1
Lewis pair (LP) complexes [Ph2P(PPh3)]O3SCF3 and [Ph2P-
bis(phosphino) and bis(arsino) ligands.10
Tellurenyl ions (RTe+) are unsaturated (six-valence-
1
electron) species having not only a vacant p orbital but also
two lone pairs, which raises the prospect of an interesting
(CR2)]AlCl4 (CR2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-
ylidene).2 For related arsenium (R2As+), stibenium (R2Sb+),
reactivity.
There have been a number of reports on intramolecularly11,12
and bismuthenium (R2Bi+) cations, similar homoleptic 1:1
and intermolecularly13−21 σ-donor-stabilized tellurenyl cations.
The fully characterized di- and trinuclear tellurium compounds
[MesTe(TeMes2)n]SbF6 (n = 1, 2) were regarded as
homoleptic 1:1 and 1:2 LP complexes of the mesityltellurenyl
cation MesTe+ and the Lewis base Mes2Te (Mes = 2,4,6-
Me3C6H2).13,14 Mesityltellurenyl cations stabilized by trialkyl-
complexes, e.g., [PhMeAs(AsPh3)]O3SCF3,3 and [Me2Sb-
(SbMe3)]MeSbBr3,4 and heteroleptic 1:1 LP complexes, e.g.,
[Ph2E(PPh3)]PF6 (E = As, Sb, Bi),5−8 were reported. For the
heavier pnictogens, also 1:2 LP complexes, e.g., [Ph2E(PPh3)2]-
PF6 (E = Sb, Bi), were described.5−8 For [Ph2E(PPh3)n]+ (n =
1, 2), the bonding situation was investigated in terms of bond
dissociation energies, bond decomposition, and molecular
orbital (MO) analyses.8 The first highly charged chalcogen(IV)
dications were stabilized by intramolecularly coordinating
Received: August 13, 2012
Published: November 7, 2012
© 2012 American Chemical Society
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phosphine selenides [MesTe(SeP-t-Bu2-i-Pr)n]SbF6 (n = 1, 2)
were characterized by multinuclear NMR spectroscopy, but no
structural information was disclosed.14 A similar 4-tolyltellur-
enyl cation stabilized by a trialkylphosphine selenide, [4-
MeC6H4Te(SeP-t-Bu-i-Pr2)]4-MeC6H4TeI2 was claimed; how-
ever, because of the short Te−Te interaction, this compound
might be better viewed as a σ-donor-stabilized mixed-valent 4-
tolyltellurenyl halide [(t-Bu-i-Pr2PSe)(4-MeC6H4)TeTeI2(4-
MeC6H4)].15 Previously, two tributylphosphine-stabilized orga-
notellurenyl cations, [4-FC6H4Te(PBu3)]BF4 and [MeTe-
(PBu3)]ClO4, were obtained as oils and characterized only
tentatively by 31P and 125Te NMR spectroscopy,16 whereas the
lighter organochalcogenyl(II) cations were already known, as
exemplified by the fully characterized perchlorate salts [PhS-
RESULTS AND DISCUSSION
■
The reported homoleptic 1:1 LP complex [MesTe(TeMes2)]-
SbF6 was prepared by the reaction of Mes2Te, MesTeTeMes,
Br2, and AgSbF6 (Mes = 2,4,6-Me3C6H2).13,14 This reaction
most likely involves the formation of unstable mesityltellurenyl
bromide MesTeBr as the reaction intermediate. We have now
found a more straightforward synthetic protocol avoiding the
use of bromine and silver salts for the preparation of an
analogue, namely, [MesTe(TeMes2)]O3SCF3 (1) featuring the
same cation 1a. Compound 1 was obtained by the reaction of
Mes2Te with triflic acid in acetonitrile (MeCN) and isolated by
crystallization as a brownish dark-red solid in 87% yield (eq 1).
2Mes2Te + HO3SCF ⎯⎯⎯⎯⎯⎯→ [MesTe(TeMes2)]O3SCF
3
3
−MesH
1
17
(PPh3)]ClO4 and [MeSe(PPh3)]ClO4.18 The lack of
(1)
structural information on tellurenyl cations stabilized by strong
σ donor atoms prompted us to investigate phosphine and NHC
complexes in more detail. In preceding work, we already
described the NHC-stabilized m-terphenyltellurenyl cation
[2,6-Mes2C6H3Te(CR2)]X (X = 2,6-Mes2C6H3TeCl2, 2,6-
Mes2C6H3TeBr2, I; CR2 = 1,3,4,5-tetramethylimidazole-2-
ylidene) that was prepared starting from the (mixed-valent)
m-terphenyltellurenyl halides (2,6-Mes2C6H3)TeTeX2(2,6-
Mes2C6H3) (X = Cl, Br) and 2,6-Mes2C6H3TeI.19 Comple-
menting the experimental work, we also disclosed calculated
gas-phase structures, dissociation energies, and the results of
natural bond order (NBO) analyses of NHC- and phosphine-
stabilized phenyltellurenyl cations [PhTe(CR2)]+ and [PhTe-
(PMe3)]+ (CR2 = 1,3,4,5-tetramethylimidazol-2-ylidene).19
During the course of this work, aryltellurenyl cations were
trapped using acetylenes, affording tellurenium ions [RTe-
(CR′)2]+.20 The lighter thiiranium and seleniranium ions
[RE(CR′)2]+ (E = S, Se) were already previously known and
have recently attracted considerable attention in organic
syntheses.21 Very recently, aryltellurenyl cations were also
trapped using butadienes, giving rise to the formation of
telluronium ions incorporated into cyclopropenes.22 In the
latter report, the first fully characterized phosphine-stabilized
aryltellurenyl cations [BbtTe(PPh3)]X [X = O3SCF3, BF4,
N(O3SCF3)2; Bbt = 2,6-{(Me3Si)2CH}2-4-{(Me3Si)3C}C6H2]
were also described, which have been obtained by the reaction
of (mixed-valent) bulky aryltellurenyl halides with triphenyl-
phosphine in the presence of silver salts AgX or trimethylsilanes
Me3SiX.22
We have now found a simple and convenient synthetic
protocol for preparation of the homoleptic 1:1 LP complex
[MesTe(TeMes2)]+ (1a) that readily underwent nucleophilic
substitution reactions with triphenylpnictogens Ph3E (E = P,
As, Sb, Bi) to give a series of archetypical σ-donor-stabilized
tellurenyl cations [MesTe(EPh3)]+ (2a, E = P; 3a, E = As; 4a, E
= Sb; 5a, E = Bi). Density functional theory (DFT) calculations
and state-of-the-art analytical methods, including NBO, atom-
in-molecules (AIM), and electron localizability indicator (ELI-
D), of homo- and heteroleptic 1:1 LP complexes 1a−4a were
carried out in an effort to shed some light on the electronic
structure and the formal dative Te−E bonds (E = Te, P, As,
Sb). Analysis of the Te−E bonds (E = main-group and
transition metals) is of substantial current interest because they
are prominently featured within metal ditelluroimidodiphos-
phinates,23 polyfunctional Lewis acids,24 and redox-active
dinuclear complexes.25
The mesitylene formed as a side product was removed, together
with the solvent from the reaction mixture, by vacuum
distillation and identified by NMR spectroscopy. Regardless
of whether an excess of triflic acid was applied, the reaction
always stopped when half of Mes2Te was consumed.
Apparently, protonation of Mes2Te produced a (solvated)
mesityltellurenyl cation, MesTe+, which immediately formed a
1:1 LP complex with the second half of Mes2Te. To the best of
our knowledge, selective aryl cleavage reactions involving group
16 compounds using triflic acid are unprecedented; however,
we are aware that this reaction type is a standard tool for
functionalization of group 14 organyls.26 The reaction
mechanism of these cleavage reactions involves an electrophilic
ipso substitution at the aromatic ring in which triorganoelement
cations R3E+ (E = Si, Ge, Sn; R = alkyl, aryl) play an important
role. A similar mechanism involving tellurenyl cations RTe+
may be operative for the reaction of Mes2Te with triflic acid.
Unlike [MesTe(TeMes2)]SbF6,13,14 1 is readily soluble in
organic solvents, such as CH2Cl2, CHCl3, tetrahydrofuran
(THF), and MeCN, thus enabling characterization in solution.
The 125Te NMR spectrum (CDCl3) showed two signals at
844.8 (ω1/2 = 293 Hz) and 376.5 ppm with an integral ratio of
1:1, which were unambiguously assigned to the MesTe+ and
Mes2Te moieties, respectively. The assignment was supported
by an NMR experiment, in which small amounts of Mes2Te
were successively added to a solution of 1. Each addition
increased the intensity of the signal originally at 376.5 ppm,
which was shifted toward the 125Te NMR chemical shift of pure
Mes2Te (250.5 ppm), while the position and intensity of the
signal at 844.8 ppm remained almost the same. No evidence
was found for the formation of the homoleptic 1:2 LP complex
[MesTe(TeMes2)2]O3SCF3. Apparently, the exchange between
coordinated and free Mes2Te is fast on the 125Te NMR time
scale. The electrospray ionization mass spectrometry (ESI-MS)
spectrum (MeCN, positive detection mode) of 1 revealed only
one prominent mass cluster at m/z 617.2 for 1a. Conductivity
measurements confirmed that electrolytic dissociation of 1 into
1a and triflate ions occurs in solution. The molar conductivity
(MeCN, c = 5 × 10−7 mol L−1) of 1 (Λ = 360 Ω−1 cm2 mol−1)
is in agreement with the presence of 1:1 electrolytes.27 The
crystal structure of 1 is shown in Figure 1, and selected bond
parameters are collected in the caption of the figure.
Similar to [MesTe(TeMes2)]SbF6, 1 forms a macrocycle
comprised of two 1a cations and two triflate anions, which are
associated with secondary Te···O contacts of 2.651(4) and
3.091(5) Å that lie between the sum of covalent radii (2.04
Å)28 and the sum of van der Waals radii (3.58 Å).29 In general,
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ppm, respectively. These chemical shifts are generally
consistent with those reported for [4-FC6H4Te(PBu3)]BF4
(360 ppm)16 and [BbtTe(PPh3)]O3SCF3 (464 ppm),22
respectively. The 1J(125Te−31P) coupling constant of 2
compares well with those of [4-FC6H4Te(PBu3)]BF4 (1071
Hz), [MeTe(PBu3)]ClO4 (1046 Hz),16 and [BbtTe(PPh3)]-
O3SCF3 (1387 Hz).22 The lack of a J(125Te−31P) coupling
1
constant in CD3CN is tentatively attributed to the kinetic
lability of 2a on the NMR time scale. Dissociation and
association of Ph3P may be fast on the NMR time scale in
competition with the σ-donor solvent. The 31P NMR spectrum
(CDCl3) of 2 showed a singlet at 6.0 ppm, which is significantly
shifted from that of free Ph3P (−4.1 ppm). No evidence was
found for the formation of a 1:2 LP complex by NMR
spectroscopy. The 125Te NMR chemical shift (CDCl3)
remained nearly unchanged when more equivalents of Ph3P
were successively added to a solution of 2. Upon addition, the
31P NMR signal of 2 shifted toward that of free Ph3P. The
exchange between complexing and free Ph3P appears to be fast
on the NMR time scale. The 31P NMR spectrum (CD3CN) of
2 displayed a singlet at 4.7 ppm. The fact that the latter value
lies between the chemical shifts of 2 in CDCl3 and free Ph3P
tentatively supports the idea that acetonitrile is to some extent a
competitive σ donor. The ESI-MS spectra (MeCN, positive
detection mode) of 2 and 3 show prominent mass clusters at
m/z 511.1 and 555.2 for 2a and 3a, respectively. The molar
conductivity (MeCN, c = 5 × 10−7 mol l−1) of 2 (Λ = 400 Ω−1
cm2 mol−1) is consistent with the presence of 1:1 electrolytes.27
The crystal structures of 2 and 3 are shown in Figures 2 and 3.
Figure 1. Molecular structure of 1 showing 50% probability ellipsoids
and the crystallographic numbering scheme (symmetry code used to
generate crystallographically related atoms: a = 2 − x, −y, −z).
Selected bond parameters (Å and deg): Te1···O2a 3.091(5), Te1−Te2
2.808(1), Te1−C10 2.127(5), Te1−C20 2.135(5), Te2···O1 2.651(4),
Te2−C30 2.134(5); C10−Te1−C20 101.4(2), C10−Te1−Te2
114.4(1), C20−Te1−Te2 94.6(1), C30−Te2−Te1 84.7(1).
the bond parameters of 1a are very similar in both complexes;
however, the Te−Te bond length of 1 [2.808(1) Å] is
somewhat longer than that of [MesTe(TeMes2)]SbF6
[2.7645(5) Å].13
It was proposed that [MesTe(TeMes2)]SbF6 could be of
significance for the synthesis of new cationic organotellurium
compounds.13 With this idea in mind, we investigated the
reactivity of 1 toward the σ donors Ph3E (E = P, As, Sb, Bi).
The reaction of 1 with Ph3P and Ph3As proceeded with
smooth substitution of Mes2Te, which precipitated from the
reaction mixture, providing the heteroleptic 1:1 LP complexes
[MesTe(EPh3)]O3SCF3 (2, E = P; 3, E = As) featuring the
cations [MesTe(EPh3)]+ (2a, E = P; 3a, E = As). Compounds
2 and 3 were isolated by crystallization as orange solids in 79
and 26% yield (Scheme 1). Notably, 2 and 3 were also prepared
by the one-pot reaction of Mes2Te, Ph3E (E = P, As), and
HO3SCF3, albeit in somewhat lower yields.
Scheme 1. Synthesis of 2 and 3
Figure 2. Molecular structure of 2 showing 50% probability ellipsoids
and the crystallographic numbering scheme. Selected bond parameters
(Å and deg): Te1···O1 2.829(3), Te1−P1 2.467(1), Te1−C10
2.127(3), P1−C20 1.802(3), P1−C30 1.802(3), P1−C40 1.798(3);
C10−Te1−P1 91.29(9).
Selected bond parameters of 2 and 3 are collected in the
caption of the figures. As in [BbtTe(PPh3)]X [X = O3SCF3,
BF4, N(O3SCF3)2], 2 and 3 exhibit T-shaped structures. The
Te−E bond lengths of 2 [2.467(1) Å; E = P] and 3 [2.5799(6)
Å; E = As] are close to the sum of covalent radii (2.45 Å, E = P;
2.57 Å, E = As)28 and account for bond orders of about 1. The
C−Te−E bond angles of 2 [91.29(9)°, E = P] and 3
[92.10(6)°, E = As] are smaller than that of [BbtTe(PPh3)]-
O3SCF3 [103.25(8)°],22 presumably because of steric repulsion
involving the bulky Bbt substituent in the latter compound. In
Compound 2 is an analogue of the very recently
communicated complexes [BbtTe(PPh3)]X [X = O3SCF3,
BF4, N(O3SCF3)2] containing a bulkier aryl substituent and
different counterions.22 Compounds 2 and 3 are readily soluble
in a number of organic solvents including CH2Cl2, CHCl3,
THF, and MeCN. The 125Te NMR spectrum (CDCl3) of 2
1
showed a doublet at 393.0 ppm with a J(125Te−31P) coupling
of 1148 Hz, whereas the 125Te NMR spectra (CD3CN) of 2
and 3 exhibited singlets at 385.6 (ω1/2 = 185 Hz) and 408.5
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(MeCN, positive and negative detection modes) of 4 exhibits
the most intense mass clusters (except that for the triflate ion at
m/z 148.6) at m/z 601.1 and 572.8 for the cation 4a and the
anion 4b, respectively. The molar conductivity (MeCN, c = 5 ×
10−7 mol L−1) of 4 (Λ = 480 Ω−1 cm2 mol−1) is somewhat
higher than those measured for 1 and 2, accounting for the
presence of 1:1 electrolytes. The molecular structure of 4 is
shown in Figure 4, and selected bond parameters are collected
in the caption of the figure. The molecular structure of 4a
closely resembles those of 2a and 3a. The Te−Sb bond lengths
of 4a [2.708(1) Å] compare well with the sum of covalent radii
(2.77 Å).28 In 2 and 3, the triphenylpnictogens and triflate ions
are situated in trans positions around the Te atoms (Figures 2
and 3). A similar arrangement was recently encountered within
the 1:1 LP complex [Cl2Sb(AsMe3)]O3SCF3, in which Me3As
is situated in the trans position to the triflate ion.31 In 4, the
cation 4a interacts in the trans position with the π system of the
mesityl group of an adjacent cation 4a [closest distance
Te1···C13b 3.501(3) Å]. A similar π interaction was recently
observed for the 1:1 LP complex [Cl2Bi(SbPh3)]AlCl4·toluene,
in which the toluene molecule coordinates to the Bi atom in the
trans position of Ph3Sb.32 In addition, 4 shows a contact
between the cation 4a and a triflate moiety of the anion 4b in a
side-on fashion. The related Te1···O2a [3.153(1) Å] and
Sb1···O2a [3.106(3) Å] distances are shorter than the sum of
van der Waals radii (3.58 and 3.64 Å, respectively). Owing to
the stereochemically active lone pair at the SbIII atom, the
spatial arrangement of the Sb atom of the anion 4b is trigonal-
bipyramidal and defined by a C2O2 donor set for the primary
coordination sphere, in which C and O atoms occupied the
equatorial and axial positions, respectively.
Figure 3. Molecular structure of 3 showing 50% probability ellipsoids
and the crystallographic numbering scheme. Selected bond parameters
(Å and deg): Te1···O1 2.792(3), Te1−As1 2.5799(6), Te1−C10
2.126(2), As1−C20 1.916(2), As1−C30 1.920(2), As1−C40
1.927(2); C10−Te1−As1 92.10(6).
[MesTe(EPh3)]O3SCF3 (2, E = P; 3, E = As), the cations 2a
and 3a are associated with the triflate anions by secondary
Te···O contacts of 2.829(3) and 2.792(3) Å that are shorter
than the sum of van der Waals radii (3.58 Å).29 In
[BbtTe(PPh3)]O3SCF3, this contact is longer [3.1898(3) Å],
probably because of the greater bulkiness of the Bbt
substituent.22 The C−Te−O angle is almost linear in 2 and
3, as well as in [BbtTe(PPh3)]O3SCF3.22
The reaction of 1 with 2 equiv of Ph3Sb produced the
heteroleptic 1:1 LP complex [MesTe(SbPh3)][Ph2Sb-
(O3SCF3)2] (4), which features the cation [MesTe(SbPh3)]+
(4a) and the anion [Ph2Sb(O3SCF3)2]− (4b). Variation of the
stoichiometry had no influence on the outcome of the reaction;
e.g., no evidence for the formation of [MesTe(SbPh3)]O3SCF3
was found. After removal of Mes2Te, 4 was isolated by
crystallization as a ruby-red solid in 46% yield (Scheme 2). The
In addition to the two primary Sb−O bonds, there are two
secondary Sb···O contacts related to the two triflate moieties,
completing the coordination sphere of the Sb. The Sb···O bond
lengths [3.573(3) and 3.390(3) Å] are longer than the sum of
covalent radii but significantly shorter than the sum of van der
Waals radii (3.64 Å).29 Interestingly, two cations 4a are further
associated with π stacking involving two phenyl rings and two
mesityl rings that adopt nearly parallel conformations. The
closest distance between the aryl rings is 3.268(6) Å for C11
and C35.
Scheme 2. Synthesis of 4
In the solid state, 1−4 possess an indefinite bench stability
when stored at room temperature under argon. Compound 4
can even be handled in air for short periods of time, while the
other compounds degrade rapidly. In solution, 1−4 are
moderately stable and decompose under precipitation of Te
powder. The relative stability decreases in the order 4 ≫ 1 > 2
≫ 3. The stability depends on the solvent and decreases in the
order THF > MeCN > CHCl3 ≈ CH2Cl2.
The reaction of 1 with 2 equiv of Ph3Bi most likely provided
the heteroleptic 1:1 LP complex [MesTe(BiPh3)][Ph2Bi-
(O3SCF3)2] (5), featuring the cation [MesTe(BiPh3)]+ (5a)
and the anion [Ph2Bi(O3SCF3)2]− (5b), but could not be
isolated in pure form (Scheme 3). The crude reaction mixture
consisting of 5 was investigated immediately after removal of
most Mes2Te by crystallization and the solvent by vacuum
evaporation. The ESI-MS spectrum (MeCN, positive detection
mode) of 5 exhibits three intense mass clusters at m/z 363.1,
689.2, and 731.2 that were unambiguously assigned to the
cations Ph2Bi+ (6a), 5a, and [Ph2Bi(TeMes2)]+, respectively.
The ESI-MS spectrum (MeCN, negative detection mode) of 5
displays only one intense mass cluster at m/z 660.8 for the
anion 5b. The 125Te NMR spectrum (CD3CN) of crude 5
formation of the anion 4b implies that a phenyl group
migration from half of triphenylantimony to half of the
mesityltellurenyl cation had occurred. The migration of aryl
groups is not unprecedented in tellurium chemistry, which
holds particularly true for mesityltellurium compounds.14 The
formation of the anion 4b can be rationalized when the
assumed Sb product of the phenyl group migration,
Ph2SbO3SCF3, reacted with additional triflate ions. The Te
product of the phenyl group migration, the unsymmetrical
diaryltelluride MesPhTe, was identified in the mother liquor by
its 125Te NMR chemical shift (419.7 ppm) after most of the
Mes2Te and 4 were removed by crystallization. To support the
identification, MesTePh (a colorless oil), was independently
prepared by the reaction of MesTeI (obtained in situ by the
reaction of MesTeTeMes with iodine)30 with PhMgBr. More
efficiently, 4 was prepared by the one-pot reaction of Mes2Te,
Ph3Sb, and HO3SCF3 and isolated in 92% yield.
The 125Te NMR spectrum (CD3CN) of 4 shows a signal at
418.4 ppm that is close to those of 1−3. The ESI-MS spectrum
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Figure 4. Molecular structure of 4 showing 50% probability ellipsoids and the crystallographic numbering scheme (symmetry codes used to generate
crystallographically related atoms: a = x, 1 + y, z; b = 1 − x, −y, 1 − z). Selected bond parameters (Å and deg): Te1···O2a 3.156(3), Te1−Sb1
2.708(1), Te1−C10 2.125(3), Te1···C13b 3.501(3), Sb1···O2a 3.106(3), Sb1−C20 2.108(3), Sb1−C30 2.109(3), Sb1−C40 2.102(3), Sb2a−O1a
2.325(2), Sb2a···O2a 3.573(3), Sb2a−O4a 2.323(2), Sb2a···O5a 3.390(3), Sb2a−C50a 2.147(3), Sb2a−C60a 2.136(3); C10−Te1−Sb1 90.30(7),
O1a−Sb2a−O4a 166.73(7), O1a−Sb2a−C50a 87.0(1), O1a−Sb2a−C60a 83.9(1), O4a−Sb2a−C50a 87.5(1), O4a−Sb2a−C60a 84.7(1), C50a−
Sb2a−C60a 96.5(1).
the ESI-MS spectrum also reveals a mass cluster at m/z 379.1,
which was assigned to the cation [Ph2Bi(O)]+ (6b), which
apparently formed by air oxidation of 6a. The crystal structure
of 6 is shown in Figure 5, and selected bond parameters of 6 are
Scheme 3. Attempted Synthesis of 5 and Synthesis of 6
displays a main signal at δ 422.4 ppm, which matches well the
125Te NMR chemical shifts observed for 2−4 (see above). Also
visible was a minor signal at 250.5 ppm, which was assigned to
Mes2Te. No evidence was found for the 1:1 LP complex cation
[Ph2Bi(TeMes2)]+ by 125Te NMR spectroscopy (see below).
All attempts to isolate 5 by fractional crystallization failed but
provided Ph2BiO3SCF3 (6) as colorless crystals in 71% yield.
The fact that the yield exceeds 50% suggests that not only the
anion 5b but also the cation 5a are the sources of 6. This is
tentatively attributed to a degradation process involving phenyl
group migration from Bi to Te within 5a.
It is worth noting that similar aryl scrambling reactions
between Bi and Te species are well-known and have been
utilized for preparative purposes, e.g., the synthesis of
diaryltellurides from triarylbismuth.33 More rationally, 6 was
obtained by the reaction of Ph3Bi with triflic acid in 93% yield
by a slightly modified literature procedure (Scheme 3).34 We
now add spectroscopic and structural details. Compound 6 is
readily soluble in polar solvents such as MeCN, in which it
undergoes electrolytic dissociation into 6a and triflate ions. The
molar conductivity (MeCN, c = 5 × 10−7 mol L−1) of 6 (Λ =
460 Ω−1 cm2 mol−1) is consistent with the presence of 1:1
electrolytes. The ESI-MS spectra (MeCN, positive and negative
detection modes) of 6 show only intense mass clusters at m/z
363.1 and 660.8, belonging to the cation 6a and the anion 5b,
respectively. Interestingly, when a solution of 6 in MeCN was
exposed to the atmosphere for 1 h prior to the measurement,
Figure 5. Crystal structure of 6 showing 50% probability ellipsoids and
the crystallographic numbering scheme (symmetry code used to
generate crystallographically related atoms: a = −1 − x, −1 − y, 0.5 +
z). Selected bond parameters (Å and deg): Bi1−O1 2.531(6),
Bi1···O1a 3.480(6), Bi1−O2a 2.473(5), Bi1···O3 3.553(6), Bi1−C10
2.233(7), Bi1−C20 2.223(7); O1−Bi1−O2a 168.5(2), O1−Bi1−C10
86.2(2), O1−Bi1−C20 86.5(2), O2a−Bi1−C10 88.6(2), O2a−Bi1−
C20 84.0(2), C10−Bi1−C20 97.2(3).
collected in the caption of the figure. It comprises a 1D
polymer containing sequences of ion-paired cations 6a and
triflate anions. Bearing in mind the stereochemically active lone
pair, the spatial arrangement of the Bi atoms is trigonal-
bipyramidal, whereby the first coordination sphere is defined by
a C2O2 donor set. The primary Bi−O bond lengths of 6
[2.473(5) and 2.531(6) Å] are slightly longer than those of 2,6-
(t-BuO)2C6H3Bi(O3SCF3)2 [2.389(7) and 2.393(6) Å].35
There are also two secondary Bi···O contacts [3.480(6) and
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Figure 6. MO isosurface plots (0.04 au densities) of 2a and corresponding energies (eV).
3.553(6) Å], completing the coordination sphere of the Bi
atom of 6. In an effort to prepare the 1:1 LP complex
[Ph2Bi(TeMes2)]O3SCF3, the NMR scale reaction of 6 and
Mes2Te was carried out in CD3CN at room temperature, the
125Te NMR spectrum of which shows only the presence of
Mes2Te. Attempts to isolate a 1:1 LP complex by fraction
crystallization afforded crops of the reactants. In contrast to the
heteroleptic 1:1 and 1:2 LP complexes [Ph2Bi(PPh3)n]PF6 (n =
1, 2),5−8 the desired 1:1 LP complex [Ph2Bi(TeMes2)]-
(O3SCF3) is apparently not favored in the solid state.
DFT Calculations and NBO, AIM, and ELI-D Analyses.
Like the homo- and heteroleptic group 15 LP complexes
[R2E(E′R3′)n]+ (E, E′ = P, As, Sb, Bi; R, R′ = alkyl, aryl; n = 1,
2),1,3−8 the bismesityltelluride-stabilized mesityltellurenyl cati-
on 1a and the triphenylpnictogen-stabilized mesityltellurenyl
cations [MesTe(EPh3)]+ (2a, E = P; 3a, E = As; 4a, E = Sb) are
archetypical examples of p-block compounds comprising formal
dative bonds, which makes them worthwhile candidates for
detailed bond analyses.
To get a deeper insight into the bond situation, single-point
calculations of the cationic 1:1 LP complexes 1a−4a were
performed on the DFT level of theory. The (vertical) bond
dissociation energies of the complexes increases in the order 1a
(243.4 kJ mol−1) < 4a (289.3 kJ mol−1) < 3a (303.4 kJ mol−1)
< 2a (322.6 kJ mol−1). These energies are in the same order of
magnitude as the dissociation energy of the fully optimized 1:1
LP complex [PhTe(PMe3)]+ (328.6 kJ mol−1) published in our
preceding work.19 The homoleptic 1:1 LP complex 1a has the
lowest dissociation energy, which is consistent with the results
of the substitution experiments, leading to the formation of the
more stable heteroleptic 1:1 LP complexes [MesTe(EPh3)]+
(2a, E = P; 3a, E = As; 4a, E = Sb). Characteristic MOs of 1a
and [MesTe(EPh3)]+ (2a, E = P; 3a, E = As; 4a E = Sb) were
visualized, and a representative selection of 2a is shown in
Figure 6. The MOs of 1a, 3a, and 4a are of similar shape and
energy (see S4 in the Supporting Information). For all four 1:1
LP complexes, the highest occupied molecular orbital
(HOMO) is a p-like lone pair situated at the Te cation and
the lowest unoccupied molecular orbital is comprised of an
antibonding combination of p orbitals at the donor atoms E (E
= Te, P, As, Sb) and the acceptor atom Te (Figure 6a,b and S4
in the Supporting Information). Because of strong electron
delocalization involving the aryl groups, no single MO for the
Te−E bond was found. Instead, there are a number of MOs
indicating the binding character of the Te−E bond. These were
analyzed by orbital contribution analysis of the corresponding
disynaptic ELI-D bonding basins and canonical molecular
orbital (CMO) analysis according to the NBO scheme.
Analysis of the electron density (ED) distribution provides
complementary information to quantum-mechanical-based
approaches and empirical bonding schemes like the valence-
shell electron-pair repulsion model. The ED is an observable
and can thus, in principle, not only be calculated but also
obtained experimentally by high-resolution X-ray diffraction at
low temperatures and subsequent asperical atom refinement,
e.g., based on the Hansen−Coppens multipole formalism.36 An
ED obtained by either calculation or experiment can be
analyzed topologically by the AIM theory37 of Bader, which by
the introduction of surfaces of zero electron flux generates
atomic basins and enables a straightforward quantitative
interpretation of atomic and bonding properties. This approach
has been applied to a large number of chemical systems in the
last 2 decades.38,39 The molecular or crystalline ED of any given
assemblage of atoms typically exhibits bond paths [and related
bond critical points (bcp’s)] linking adjacent atoms. In
covalently bonded systems, these bond paths unambiguously
correspond to the molecular graph, which intuitively would be
drawn by chemists.
Moreover, bond paths are found for all types of chemical
interactions, including ionic, metallic, and intermolecular
hydrogen-bonded and van der Waals bonded systems.
However, for multicenter-bonded systems like supported
metal carbonyls and clusters of main-group elements like
boranes, this one-to-one relationship is not valid anymore.40,41
Becuase of this, further bond descriptors that do not rely on the
existence of bcp's are required. Integrated bonding descriptors
like the delocalization index [δ(x,y)],42,43 which is a measure of
the electron sharing between two atoms, are not sensitive to the
topology. Moreover, parallel to ED analysis, different types of
localization functions appeared, which divide space into regions
of localized electron pairs instead of atoms and therefore greatly
complement the AIM theory. The ELI-D44 applied here is a
further development of the prominent electron localization
function (ELF).45,46 To the best of our knowledge, there is only
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a
Table 1. Topological Bond Descriptors
ρ(rbcp) [e Å−3
MesTe+: Te−C
]
∇2ρ(rbcp) [e Å−5
]
d [Å]
d1 [Å]
d2 [Å]
ε
G/ρ(rbcp) [h e−1
]
H/ρ(rbcp) [h e−1
]
0.71
0.0
2.133
2.140
1.099
1.103
1.034
1.038
0.07
0.10
0.52
0.49
−0.51
−0.52
Mes2Te: Te−C
0.71
−0.3
Ph3E: E−C
E = P
0.97
0.85
0.67
−5.8
−2.3
1.4
1.832
1.954
2.149
0.733
0.946
1.083
1.099
1.008
1.066
0.16
0.08
0.06
0.60
0.49
0.61
−0.98
−0.66
−0.48
E = As
E = Sb
LP Complex: Te−E
1a
0.39
0.54
0.48
0.44
−0.1
−0.8
−0.5
−0.4
2.807
2.481
2.580
2.708
1.456
1.224
1.272
1.350
1.355
1.257
1.308
1.358
0.21
0.25
0.23
0.26
0.30
0.34
0.31
0.31
−0.31
−0.43
−0.38
−0.36
2a
3a
4a
LP Complex: Te−C
1a
0.72
0.74
0.73
0.72
−0.6
−0.6
−0.7
−0.7
2.133
2.114
2.123
2.124
1.111
1.101
1.107
1.110
1.022
1.012
1.016
1.015
0.04
0.02
0.02
0.03
0.46
0.47
0.46
0.46
−0.52
−0.53
−0.52
−0.52
2a
3a
4a
LP Complex: E−C
1a
2a
3a
4a
0.74
1.05
0.92
0.73
−1.3
−7.8
−3.5
0.5
2.132
1.804
1.921
2.107
1.122
0.738
0.956
1.083
1.010
1.066
0.965
1.024
0.10
0.11
0.09
0.08
0.42
0.51
0.43
0.56
−0.53
−1.01
−0.67
−0.51
a
For all bonds, ρ(rbcp) is the ED at the bcp; ∇2ρ(rbcp) is the corresponding Laplacian; d is the distance of the two bonded nuclei, d1 and d2 are the
distances from atoms x and y to the bcp; ε is the bond ellipticity [ε = (λ1/λ2) − 1; λ1 > λ2 ]; G/ρ(rbcp) and H/ρ(rbcp) are the kinetic and total energy
densities over ρ ratios, respectively.
one report utilizing ELI-D in tellurium chemistry, namely, to
describe the bond situation in the complex Te10[Ir(TeCl4)-
(TeCl3)]2.47 For both ELF and ELI-D, the partitioning follows
the same rules as those used by AIM to separate atoms from
each other. Thus, it is space-filling and discrete, providing
reliable integrated electron numbers of both core shells and
(non)bonded valence electrons. Valence basins connecting two
core basins are called disynaptic, whereas lone pairs and H
atoms exhibit so-called (protonated) monosynaptic valence
basins. The disadvantage of ELF, not comparable between
different molecules because localization is always related to the
uniform electron gas of the very same compound, was
discarded with the introduction of ELI-D. The bond
topological properties of 1a−4a are collected in Table 1 and
reveal all occurring bond types (C−E and Te−E; E = P, As, Sb,
Te) to be of polar covalent nature. Representations of the ELI-
D basins of 1a−4a are shown in Figure 7
The ED at the bcp’s lies between 0.39 e Å−3 (the polar
covalent Te−Te bond of 1a) and 1.05 e Å−3 (the mainly
covalent P−C bonds of 2a), with all Laplacians being slightly
negative, which is a sign of covalency, or almost zero. The
covalency is also reflected in the negative value of the total
energy over the density ratio H/ρ(rbcp), which is again the
largest for the P−C bonds. In the line P, As, Sb, and Te, the
ρ(rbcp) values of all C−E and Te−E bonds show a trend of
decreasing density, which is essentially related to the increasing
bond lengths. Upon complex formation, all E−C (E = P, As,
Sb) and Te−C bonds become shorter, thus leading to higher
ρ(rbcp) values. The large bond ellipticities of the Te−E bonds
(0.21−0.25) reflect their diffuse and delocalized nature.
Figure 7. ELI-D of 1a (γ = 1.30), 2a (γ = 1.50), 3a (γ = 1.40), and 4a
(γ = 1.30).
part S5.1 in the Supporting Information). In the uncharged free
donor molecules, there is also a pronounced internal charge
polarization, in that the donor atoms E are significantly positive
(0.47 e, E = Te; 1.51 e, E = P; 0.93 e, E = As; 1.12 e, E = Sb)
and the aryl substituents are negative. Interestingly, Ph3As does
not follow the trend suggested by the results for P, Sb, and Te,
which is attributed to the influence of the filled 3d shell. Upon
LP complex formation, 0.67−0.83 e are transferred from Ph3E
In terms of AIM partitioning, the positive charge of the free
mesityltellurenyl cation is to 61% located at the Te atom (Table
2); the rest is evenly distributed over the mesityl group (see
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a
be tuned with the electron donors not only by variation of the
donor atom type but also by different numbers of nonbonding
electron pairs at the donor atom. As the E−C bonds (E = P, As,
Sb, Te) of the donor molecules become shorter upon complex
formation (see above), they gain small amounts of charge (0.1−
0.25 e). For estimation of the bond polarities of the Te−E
bonds, the quite new concept of overlapping ELI-D valence
basins with AIM atoms is helpful, which is expressed by the
Jansen index J.48 For homopolar bonds, e.g., the C−C bond in
ethane, the electrons within the C−C bonding basin are to 50%
located within each C atom; thus, J = 50%. With increasing
bond polarity, one finds an increasing amount of electron
populations located within the more electronegative atom (J >
50%). With this concept, one can discriminate polar covalent
interactions (50% < J < 95%) from dative bonds (J > 95%), and
by quantification of the ED in the ELI-D basin parts, it allows a
reliable estimation of the charge transfer between Lewis base
and acid.49 The Jansen index J confirms that all listed bond
types are polar covalent, because all relative electron
populations lie within the boundaries of 50% and 95% (Table
3). Moreover, it shows that all bonds are less polar upon
complex formation because all values come closer to 50%. For
the E−C bonds of the donor molecules, this effect is more
pronounced than that for the Te−C bond of the cation.
In 2a, orbital contribution analysis of the Te−P ELI-D basin
shows that the ED of this basin stems mainly from the MOs a54,
a99, a87, a93, a102, and a111 (12.0, 10.0, 9.7, 7.2, 7.0, and 6.5%,
respectively; Figure 6c−f). CMO analysis shows larger
contributions of the Te−P bonding NBO to MOs a99, a54,
a87, a102, and a93 (13.2, 10.2, 10.1, 7.1, and 5.5%, respectively).
While in orbital a54, the ED is equally distributed around the
Te−P bond, the orbitals a111, a102, a93, and a87 show EDs along
the Te−P bond mostly concentrated toward the P atom,
resembling the lone pair of the triphenylphosphine moiety.
Orbital a99 shows a π interaction of the MesTe+ unit with a
deformed p-like orbital at the P atom, which could be
interpreted as π-back-donation of the lone pair at the tellurium
to the donor. In addition, MO a108 reflects a nonpolar covalent
binding with the ED equally distributed between the two atoms
(but this orbital corresponds only to 3.4% to the Te−P basin).
For the LP complexes 3a and 4a and with minor limitations
also 1a, orbitals with comparable shape and energy could also
be found (see S4 in the Supporting Information, for example),
so that, in summary, the bonding situation in all of these
complexes could be described as polar covalent. The overall
MO interpretation of these complexes is in good comparison
with that described for the 1:1 LP complexes [Ph2E(PPh3)]+ (E
= P, As, Sb, Bi).8
Table 2. AIM Net Charges (e)
R−E
E
Te+
Te−R
∑R3/2−E ∑TeMes
Single Components
MesTe+
0.61
0.39
1.00
Mes2Te
Ph3P
−0.24
−0.50
−0.31
−0.37
0.47
1.51
0.93
1.12
0.00
0.00
0.00
0.00
Ph3As
Ph3Sb
LP Complexes
1a
2a
3a
4a
−0.05
0.83
1.72
1.08
1.39
0.36
0.42
0.38
0.26
−0.09
−0.10
−0.09
−0.09
0.72
0.67
0.72
0.83
0.27
0.33
0.28
0.17
−0.35
−0.12
−0.18
a
The AIM net charges are the difference of the integrated number of
electrons within the zero flux surface, ∮ x∩y′ around the atom and
electrons of the isolated atom.
(E = P, As, Sb) to the mesityltellurenyl cation. This leads to a
less positive Te atom of the cation (0.26−0.42 e instead of 0.61
e) and a slightly negative mesityl group (ca. −0.1 e instead of
0.39 e); see Table 2 for details. As expected, the phenyl groups
of the triphenylpnictogens Ph3E become less negative upon
complex formation, while the donor atoms E = Te, P, As, Sb
become even more positively charged (electron loss of about
0.2−0.3 e), which leads to a strong charge polarization between
the Te atom of the cation and the donating atoms and
concomitantly to polar covalent Te−Te and Te−E bonds. This
is essentially in accordance with the bond topological
properties.
The integrated bond properties (Table 3) give a detailed
view of the charge redistributions upon complex formation and
complement analysis of the topological bond properties and
atomic charges. The free mesityltellurenyl cation MesTe+
stabilizes its charge by exhibiting an electronic structure,
which may be described as partially quinoid: Te(C−C/C′
C/C′−C)ring. The TeC double-bond character is reflected in
large values for δ(Te,C) = 1.44 and ELI-D population = 2.30 e,
compared to 1.02 and 1.91 e in Mes2Te. The results for the
mesityl group are given in part S6.2 of the Supporting
Information. Upon complex formation, the Te−C bond
becomes a single bond and the mesityl fragment recovers its
aromatic character (see Scheme S7 in the Supporting
Information). The two nonbonding electron pairs of the Te
atom of the mesityltellurenyl cation MesTe+ behave unexpect-
edly. Instead of gaining charge from the donor molecules, they
each (slightly) lose 0.02 e (1a) to 0.14 e (2a). The charge
donation from Lewis base to the cation is most clearly visible in
the significant decrease of the electron population within the
former lone pairs of the Te, P, As, and Sb atoms of free Mes2Te
and Ph3E (E = P, As, Sb). These electron-pair basins are
connecting Lewis acid and base comprising the Te−E bond.
The charge depletion becomes more and more dominant with
increasing size of the donor atom E (0.70 e, E = Te; 0.16 e, E =
P; 0.37 e, E = As; 0.44 e, E = Sb). Because the initial electron
population also increases in the series P, As, and Sb, the Te−E
bonds (E = P, As, Sb) show quite similar bond characteristics.
The Te−Te bond is an exception with a very small electron
population of 1.61 e compared to 1.89−1.95 e for Te−E bonds
(E = P, As, Sb). This is presumably due to the influence of the
second lone pair of the Mes2Te donor, which upon complex
formation carries the large amount of 2.60 e. This lets us
surmise that stabilization of the mesityltellurenyl cations may
CONCLUSIONS
■
Starting from simple reactants [e.g., Mes2Te, Ph3E (E = P, As,
Sb) and HO3SCF3], the 1:1 LP complexes 1−4 were prepared
and fully characterized. Compounds 1−4 comprise the
archetypical σ-donor-stabilized mesityltellurenyl cations 1a
and [MesTe(EPh3)]+ (2a, E = P; 3a, E = As; 4a, E = Sb)
containing polar covalent Te−E bonds (E = Te, P, As, Sb),
which have been analyzed by DFT calculations and analysis
methods, including NBO, AIM, and ELI-D. These show that
most of the positive charge is situated at the donor atoms E,
which, in fact, suggests that the complexes are best described as
telluronium (1a), phosponium (2a), arsonium (3a), and
stibonium cations (4a). The HOMOs of 1a−4a are p-like
lone pairs situated at the mesityltellurenyl cations. We are
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a
Table 3. Integrated Bond Descriptors
δ(x,y)
ELI-Dpop [e]
V
[Å−3
]
ELImax
γ
ΔELI [Å]
pop1
pop2
J2 [%]
ELI
001
MesTe+
LP1
2.40
2.40
17.8
1.83
1.90
LP2
18.5
Mes2Te
LP1
2.31
2.31
16.7
16.9
1.80
1.84
LP2
Ph3E: LP E
E = P
2.05
2.31
2.39
16.5
18.5
23.0
2.67
2.29
2.10
E = As
E = Sb
Ph3E: E−C
E = P
0.84
0.91
0.86
2.14
2.14
2.15
4.9
5.4
7.0
1.89
1.77
1.75
0.059
0.069
0.044
0.459
0.658
0.526
1.679
1.478
1.623
78.5
69.2
75.4
E = As
E = Sb
Mes2Te
Te−C
MesTe+
Te−C
1.01
1.44
1.91
2.30
5.1
1.65
1.59
0.079
0.012
0.546
0.696
1.362
1.605
71.0
69.8
10.6
LP Complexes: Lone Pairs at Te
1a, LP1
2.39
2.37
2.60
2.25
2.27
2.30
2.31
2.32
2.33
17.1
17.6
18.1
15.0
15.2
15.6
15.8
15.9
16.3
1.75
1.82
1.78
1.75
1.73
1.75
1.74
1.72
1.71
1a, LP2
1a, LP Mes2Te
2a, LP1
2a, LP2
3a, LP1
3a, LP2
4a, LP1
4a, LP2
LP Complexes: Te−E
1a
0.98
0.95
0.95
0.97
1.61
1.89
1.94
1.95
5.8
6.5
7.3
9.7
1.36
1.72
1.44
1.32
0.270
0.056
0.045
0.138
0.448
0.550
0.502
0.577
1.156
1.339
1.432
1.276
71.9
70.8
73.8
65.4
2a
3a
4a
LP Complexes: Te−C
1a
1.04
1.04
1.05
1.05
1.93
1.92
1.90
1.87
5.2
5.1
5.0
4.8
1.60
1.60
1.60
1.59
0.010
0.019
0.017
0.012
0.633
0.640
0.639
0.636
1.294
1.279
1.260
1.232
67.1
66.6
66.3
65.9
2a
3a
4a
LP Complexes: E−C
1a
2a
3a
4a
0.96
0.84
0.90
0.85
1.97
2.24
2.23
2.23
5.2
5.5
6.0
7.9
1.60
1.89
1.71
1.66
0.090
0.012
0.020
0.031
0.795
0.630
0.910
0.779
1.169
1.608
1.317
1.447
59.4
71.8
59.1
65.0
a
ELI
001
For all bonds, δ(x,y) is the delocalization index of atoms x and y; ELI-Dpop is the electron population of the ELI-D basins; V is the corresponding
volume cut at an ED value of 0.001 au; ELImax γ is the corresponding ELI-D value at the attractor position; ΔELI is the distance of the attractor
position perpendicular to the xy axis; pop1 and pop2 are the absolute numbers of electrons of an ELI-D basin within an AIM atom, respectively, and
J2 is the Jansen index, which is given relative to pop2.
currently exploring the possibility of utilizing 1−4 as electron-
pair donors for the synthesis of transition-metal complexes.50
For instance, preliminary work has shown that the reaction of 4
with Fe(CO)5 gives rise to a crude product, the ESI-MS
spectrum (MeCN, positive detection mode) of which shows a
mass cluster at m/z 769.0, which was assigned to the cation
[MesTe(SbPh3)(Fe(CO)4)]+ based on the correct isotopic
pattern. Similar “push−pull” complexes were recently reported
for NHC-stabilized silylenes,51 germylenes,52,53 and stanny-
lenes.53
EXPERIMENTAL SECTION
■
General Procedures. The starting material Mes2Te [δ(125Te) =
250.5 ppm]54 was prepared according to literature procedures,
whereas Ph3E (E = P, As, Sb, Bi) and triflic acid were obtained
commercially and used as received. The H, 13C, and 125Te NMR
1
spectra were recorded at room temperature (unless otherwise stated)
using a Bruker Avance-360 spectrometer and are referenced to SiMe4
(1H and 13C), 85% H3PO4 (31P), and Me2Te (125Te). As secondary
references, solutions of 100 mg samples of Ph2Se2 [δ(77Se) = 464.0
ppm] in CDCl3 and Te(OH)6 [δ(125Te) = 707.0 ppm] in D2O were
used. The ESI-MS spectra were obtained with a Bruker Esquire-LC
ion-trap mass spectrometer. Acetonitrile solutions (c = 1 × 10−6 mol
L−1) were injected directly into the spectrometer at a flow rate of 3 μL
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Inorganic Chemistry
Article
min−1. Nitrogen was used both as a drying gas and for nebulization
with flow rates of approximately 5 L min−1 and a pressure of 5 psi,
respectively. The pressure in the mass analyzer region was usually
about 1 × 10−5 mbar. Spectra were collected for 1 min and averaged.
The nozzle−skimmer voltage was adjusted individually for each
measurement. Elemental analyses were obtained using a HEKAtech
Euro EA-CHNS analyzer. Because of the limited stability, reasonable
results were obtained only for 4. All conductivity measurements have
been carried out with a WTW Cond 330i at 25 °C.
Synthesis of [MesTe(SbPh3)][Ph2Sb(O3SCF3)2] (4). Method A.
To a solution of 1 (0.95 g, 1.25 mmol) in dry CH3CN (30 mL) was
added Ph3Sb (0.44 g, 1.25 mmol). The red solution was stirred for 72
h, precipitated Mes2Te was filtered off, and the solvent was removed
under reduced pressure. Crystallization (CH2Cl2/n-hexane) afforded 4
as red crystals (0.68 g, 0.58 mmol, 46%; mp 122−125 °C). Method B.
Mes2Te (0.50 g, 1.36 mmol) and Ph3Sb (0.95 g, 2.70 mmol) were
dissolved in CH3CN (35 mL), and triflic acid (0.41 g, 2.70 mmol) was
slowly added. The red solution was stirred for 24 h and the solvent
removed under reduced pressure. Crystallization (CH2Cl2/n-hexane)
afforded 4 as ruby-red crystals (1.47 g, 1.25 mmol, 92%; mp 122−125
°C).
Synthesis of [MesTe(TeMes2)]O3SCF3 (1). To a continuously
stirred suspension of Mes2Te (1.00 g, 2.73 mmol) in dry CH3CN (60
mL) was slowly added triflic acid (0.21 g, 1.37 mmol). The deep-red
solution was stirred overnight and the solvent as well as residual acid
removed under reduced pressure. Crystallization (CH2Cl2/n-hexane)
afforded 1 as brownish dark-red crystals (0.91 g, 1.19 mmol, 87%; dec
at 168 °C without melting).
1H NMR (CD3CN): δ 7.54 (m, 6H), 7.46 (m, 17H), 6.84 (m, 4H),
2.45 (s, 6H), 2.34 (s, 3H). 13C{1H} NMR (CD3CN): δ 147.5, 145.0,
138.6, 136.6, 136.1, 133.2, 131.2, 131.0, 130.0, 129.3, 128.9, 128.7,
127.7, 127.3, 31.4, 21.2. 125Te NMR (CD3CN): δ 418.4. 125Te NMR
(CDCl3): δ 425.5. ESI-MS (CH3CN, positive mode): m/z 601.1
[C27H26SbTe]+ for [MesTe(SbPh3)]+ (4a). ESI-MS (CH3CN,
negative mode): m/z 572.8 [C14H10F6O6S2Sb]− for 4b. Molar
conductivity (CH3CN, c = 5 × 10−7 mol L−1): Λ = 480 Ω−1 cm2
mol−1. Anal. Calcd for [MesTe(SbPh3)]+[Ph2Sb(O3SCF3)2]−,
1176.96: C, 41.95; H, 3.09; S, 5.46. Found: C, 42.08; H, 3.38; S, 5.18.
Synthesis of MesTePh. A solution of MesTeI [freshly prepared by
the addition of solid iodine (1.02 g, 8.04 mmol) to a solution of
(MesTe)2 (1.97 g, 4.00 mmol) in toluene (30 mL), which was allowed
to react for 1h] was treated with a solution of phenylmagnesium
bromide [prepared from bromobenzene (1.26 g, 8.03 mmol) and
activated Mg turnings (0.26 g, 10.69 mmol) in THF (30 mL)]. The
solution was stirred overnight and then quenched with a Na2SO3
solution (10%, 20 mL). The organic layer was separated and dried
over Na2SO4.
1H NMR (CD3CN): δ 7.07 (s, 2H), 7.01 (s, 4H), 2.23 (s, 9H), 2.13
1
(s, 18H). H NMR (CDCl3): δ 6.95 (s, 2H), 6.90 (s, 4H), 2.30 (s,
9H), 2.17 (s, 18H). 13C{1H} NMR (CD3CN): δ 149.1, 144.6, 144.3,
144.2, 138.7, 131.5, 129.2, 127.8, 119.2, 118.4, 30.5, 25.6, 21.3, 21.2,
20.9. 13C{1H} NMR (CDCl3): δ 148.2, 143.7, 143.5, 142.1, 138.0,
130.2, 128.6, 127.2, 119.9, 118.0, 30.2, 26.4, 21.3, 21.2, 21.0. 125Te
NMR (CD3CN): δ 932.1 (ω1/2 = 222 Hz), 396.3. 125Te NMR
(CDCl3): δ 844.8 (ω1/2 = 293 Hz), 376.5. ESI-MS (CH3CN, positive
mode): m/z 617.2 (C27H33Te2) for MesTe(TeMes2)]+ (1a). Molar
conductivity (CH3CN, c = 5 × 10−7 mol L−1): Λ = 360 Ω−1 cm2
mol−1.
Synthesis of [MesTe(PPh3)]O3SCF3 (2). Method A. To a solution
of 1 (0.95 g, 1.25 mmol) in dry CH3CN (30 mL) was added Ph3P
(0.33 g, 1.25 mmol). The orange solution was stirred for 72 h,
precipitated Mes2Te (0.09 g, 0.25 mmol) was filtered off, and the
solvent was removed under reduced pressure. Crystallization
(CH2Cl2/n-hexane) afforded 2 as orange crystals (0.65 g, 0.99
mmol, 79%; mp 76 °C). Method B. Mes2Te (0.50 g, 1.36 mmol) and
Ph3P (0.36 g, 1.36 mmol) were dissolved in dry CH3CN (35 mL), and
triflic acid (0.20 g, 1.36 mmol) was slowly added. The orange solution
was stirred for 24 h, and the solvent was removed under reduced
pressure. Crystallization (CH2Cl2/n-hexane) afforded 2 as orange
crystals (0.69 g, 1.00 mmol, 77%; mp 76 °C).
After removal of the solvent in vacuum, the crude product was
purified by column chromatography (silica/n-hexane) to give
MesTePh as a colorless oil (1.61 g, 4.98 mmol, 62%).
1H NMR (CDCl3): δ 7.31 (2H, m), 7.13 (3H, m), 7.00 (2H, s),
2.52 (6H, s), 2.32 (3H, s). 13C{1H} NMR (CDCl3): δ 145.4, 139.4,
134.6, 129.4, 127.6, 126.6, 118.3, 116.3, 29.4, 21.0. 125Te NMR
(CDCl3): δ 419.7.
Attempted Synthesis of [MesTe(BiPh3)][Ph2Bi(O3SCF3)2] (5).
To a solution of 1 (0.95 g, 1.25 mmol) in dry CH3CN (30 mL) was
added Ph3Bi (0.55 g, 1.25 mmol). The yellow solution was stirred for
48 h, precipitated Mes2Te removed by filtration, and the solvent
removed under reduced pressure.
1H NMR (CD3CN): δ 7.76 (m, 3H), 7.60 (m, 12H), 6.87 (s, 2H),
2.29 (s, 3H), 2.19 (s, 6H). 1H NMR (CDCl3): δ 7.69 (t, 3H), 7.51 (m,
6H), 7.36 (m, 6H), 6.81 (s, 2H), 2.22 (s, 3H), 2.13 (s, 6H). 13C{1H}
2
NMR (CD3CN): δ 147.8, 143.5, 135.6, 135.0 (d, J(13C−31P) = 11.4
125Te NMR (CD3CN): δ 422.4. 125Te NMR (CDCl3): δ 414.2. ESI-
MS (CH3CN, positive mode): m/z 731.2 [C30H32BiTe]+ for
[Ph2Bi(TeMes2)]+, 689.2 [C27H26BiTe]+ for [MesTeBiPh3]+ (5a),
363.1 [C12H10Bi]+ for [Ph2Bi]+ (6a). ESI-MS (CH3CN, negative
mode): m/z 660.8 [C14H10BiF6O6S2]− for [Ph2Bi(O3SCF3)2]− (5b).
Crystallization (CH2Cl2/n-hexane) afforded 6 as colorless crystals
(0.41 g, 0.88 mmol, 71%; dec at 152 °C without melting).
Synthesis of Ph2BiO3SCF3 (6). A solution of Ph3Bi (2.20 g, 5.00
mmol) in CH2Cl2 (50 mL) was cooled to −78 °C, and triflic acid
(0.75 g, 5.00 mmol) was added. After the solution was stirred for 10
min at low temperature, it was warmed to room temperature and
stirred for another 10 h. Quick evaporation of the solvent afforded a
white solid, which was recrystallized from CH3CN to yield 6 as
colorless crystals (2.38 g, 4.65 mmol, 93%; dec at 152 °C without
melting).
3
Hz), 130.9 (d, J(13C−31P) = 12.7 Hz), 129.3, 128.7, 127.6, 117.3,
29.9, 21.0. 13C{1H} NMR (CDCl3): δ 147.1, 142.7, 135.0 (d,
2
1J(13C−31P) = 1.7 Hz), 133.7 [d, J(13C−31P) = 5.3 Hz], 130.1 (d,
3J(13C−31P) = 6.5 Hz), 128.6, 120.2, 119.5, 114.9, 29.3, 20.9. 31P{1H}
NMR (CD3CN): δ 4.7. 31P{1H} NMR (CDCl3): δ 6.0. 125Te NMR
(CD3CN): δ 385.6 (ω1/2 = 185 Hz). 125Te NMR (CDCl3): δ 393.0
(1J(125Te−31P) = 1148 Hz). ESI-MS (CH3CN, positive mode): m/z
511.1 (C27H26PTe) for [MesTe(PPh3)]+ (2a). Molar conductivity
(CH3CN, c = 5 × 10−7 mol L−1): Λ = 400 Ω−1 cm2 mol−1.
Synthesis of [MesTe(AsPh3)]O3SCF3 (3). Method A. To a
solution of 1 (0.95 g, 1.25 mmol) in diethyl ether (30 mL) was added
Ph3As (0.38 g, 1.25 mmol). The orange solution was stirred for 72 h,
precipitated Mes2Te was filtered off, and the solvent was removed
under reduced pressure. Crystallization (diethyl ether/n-hexane)
afforded 3 as orange crystals (0.23 g, 0.33 mmol, 26%). Method B.
Mes2Te (0.50 g, 1.36 mmol) and Ph3As (0.42 g, 1.36 mmol) were
dissolved in dry diethyl ether (35 mL), and triflic acid (0.20 g, 1.36
mmol) was slowly added. The orange solution was stirred for 24 h and
the solvent removed under reduced pressure. Crystallization (CH2Cl2/
n-hexane) afforded 3 as orange crystals (0.21 g, 0.30 mmol, 22%).
1H NMR (CD3CN): δ 7.62 (m, 3H), 7.46 (m, 12H), 6.82 (s, 2H),
2.32 (s, 6H), 2.22 (s, 3H). 13C{1H} NMR (CD3CN): δ 147.8, 143.5,
138.6, 133.9, 133.8, 131.0, 129.1, 128.7, 127.7, 127.1, 30.6, 21.2. 125Te
NMR (CD3CN): δ 408.5. 125Te NMR (CDCl3): δ 414.8. ESI-MS
(CH3CN, positive mode): m/z 555.2 [C27H26AsTe]+ for [MesTe-
(AsPh3)]+ (3a).
1H NMR (CD3CN): δ 8.45 (d, 4H), 7.82 (t, 4H), 7.48 (t, 2H).
13C{1H} NMR (CD3CN): δ 139.2, 133.6, 130.0. ESI-MS (CH3CN,
positive mode): m/z 363.1 [C12H10Bi]+ for [Ph2Bi]+ (6a). ESI-MS
(CH3CN, negative mode): m/z 660.8 [C14H10BiF6O6S2]− for 5b.
Molar conductivity (CH3CN, c = 5 × 10−7 mol L−1): Λ = 460 Ω−1 cm2
mol−1.
X-ray Crystallography. Intensity data were collected on a STOE
IPDS 2T area detector (1) and a Siemens P4 diffractometer (2−4 and
6) fitted with a Siemens LTII at 173 K with graphite-monochromated
Mo Kα (0.7107 Å) radiation. All structures were solved by direct
methods and refined based on F2 by use of the SHELX program
package.55 All non-H atoms were refined using anisotropic displace-
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Inorganic Chemistry
Article
ment parameters. H atoms attached to C atoms were included in
geometrically calculated positions using a riding model. Crystal and
refinement data are collected in Table S1 in the Supporting
Information. Figures were created using DIAMOND.56 Crystallo-
graphic data (excluding structure factors) for the structural analyses
have been deposited with the Cambridge Crystallographic Data
Centre, CCDC 886605 (1), 886606 (2), 886607 (3), 886608 (4), and
886609 (6). Copies of this information may be obtained free of charge
from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
U.K. (fax +44-1223-336033; e-mail deposit@ccdc.cam.ac.uk, or
http://www.ccdc.cam.ac.uk).
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Computational Methodology. Single-point calculations of the
cationic complexes 1a, 2a, 3a, and 4a applying the DFT/B3PW9157
functional were performed using the crystallographic geometry with
the program package Gaussian09.58 For Te and Sb atoms, an
ECP28MDF electron core potential and the appropriate cc-pVTZ
basis set were applied; for all other atoms, the 6-311+G(2df,p) basis
set was used.59 Calculations of the donors, Mes2Te,60 Ph3P,61 Ph3As,62
and Ph3Sb63 were equally performed using the structural data taken
from the CCDC database. If there was more than one symmetry-
inequivalent molecule in the unit cell, one representative was chosen
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the isolated MesTe+ cation was taken from complex 1. C−H distances
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2
of all substances were set to neutron diffraction data (Csp −H 1.083 Å;
Csp −H 1.059 Å) prior to processing.64 NBO analyses were performed
3
using NBO 5.9.65 For the AIM analyses, wave function files were
generated along with single-point calculations and analyzed using
AIMAll.66 DGrid was used to analyze the ELI-D, revealing the
integrated bond descriptors using a 0.05 au grid and a 3.0 au box
around the molecule.67 Figures of the ELI-D were generated with the
program MolIso.68
Hanninen, M. M.; Dutton, J. L.; Tuononen, H. M.; Ragogna, P. J.
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ASSOCIATED CONTENT
■
(14) Jeske, J.; du Mont, W.-W.; Ruthe, F.; Jones, P. G.; Mercuri, L.
M.; Deplano, P. Eur. J. Inorg. Chem. 2000, 1591−1599.
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S
* Supporting Information
Crystal data and structure refinement of compounds 1−4 and 6
as well as details of the computations including geometries,
total energies, MO plots for compounds 1a−4a, detailed AIM
charges and integrated bond descriptors, plots of the ELI-D,
and a comparison of the delocalization indices and the ELI-D
population of the mesityl fragment in the complexes. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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AUTHOR INFORMATION
(20) Poleschner, H.; Seppelt, K. Angew. Chem., Int. Ed. 2008, 47,
6461−6464.
■
Corresponding Author
(21) (a) Huang, X.; Batchelor, R. J.; Einstein, F. W. B.; Bennet, A. J. J.
Org. Chem. 1994, 59, 7108−7116. (b) Lucchini, V.; Modena, G.; Pasi,
M.; Pasquato, L. J. Chem. Soc., Chem. Commun. 1994, 1565−1566.
(c) Lucchini, V.; Modena, G.; Pasi, M.; Pasquato, L. J. Org. Chem.
1997, 62, 7018−7020. (d) Wirth, T.; Fragale, G.; Spichty, M. J. Am.
Chem. Soc. 1998, 120, 3376−3381. (e) Fachini, M.; Lucchini, V.;
Modena, G.; Pasi, M.; Pasquato, L. J. Am. Chem. Soc. 1999, 121, 3944−
3950. (f) Uehlin, L.; Fragale, G.; Wirth, T. Chem.Eur. J. 2002, 8,
1125−1133. (g) Denmark, S. E.; Collins, W. R.; Cullen, M. D. J. Am.
Chem. Soc. 2009, 131, 3490−3492. (h) Denmark, S. E.; Vogler, T.
Chem.Eur. J. 2009, 15, 11737−11745. (i) Denmark, S. E.; Kalyani,
D.; Collins, W. R. J. Am. Chem. Soc. 2010, 132, 15752−15765.
(22) Sugamata, K.; Sasamori, T.; Tokitoh, N. Eur. J. Inorg. Chem.
2012, 775−778.
(23) (a) Chivers, T.; Konu, J.; Ritch, J. S.; Copsey, M. C.; Eisler, D.
J.; Tuononen, H. M. J. Organomet. Chem. 2007, 692, 2658−2668.
(b) Ritch, J. S.; Chivers, T. Dalton Trans. 2008, 957−962.
(c) Robertson, S. D.; Chivers, T. Dalton Trans. 2008, 1765−1772.
(d) Robertson, S. D.; Chivers, T.; Tuononen, H. M. Inorg. Chem.
2008, 47, 10634−10643. (e) Robertson, S. D.; Chivers, T.; Tuononen,
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*E-mail: j.beckmann@uni-bremen.de (J.B.), stebs@chemie.fu-
berlin.de (S.M.). Tel.: ++49(0)421 218-63160. Fax: ++49(0)
421 218-9863160.
Notes
The authors declare no competing financial interest.
DEDICATION
■
†Dedicated to Professor Rudiger Mews on the occasion of his
̈
70th birthday.
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