Isolation of Homoleptic Dicationic Tellurium and Monocationic Bismuth Analogues of Non-N-Heterocyclic Carbene Derivatives

Article abstract of DOI:10.1021/acs.organomet.9b00698

The first examples of Te analogues of non-N-heterocyclic carbene (non-NHC) derivatives, [(ppy)₂Te]·2ClO₄, [4]·2ClO₄, and[(ppy)₂Te]·2OTf, [5]·2OTf [where ppy = 2-(2′-pyridyl)phenyl and Tf = O₂SCF₃] are reported by the metathesis reaction of diorganoiodotelluronium(IV) cation, [(ppy)₂TeI]·I₃, [3]·I₃, with AgClO₄ and AgOTf, respectively. The metathesis reaction of ppyTeCl₃, 6, with an excess of AgClO₄ resulted in the isolation of [ppyTe(μ-O)]₂·2ClO₄, [8]·2ClO₄. The reaction of triorganotelluronium(IV) cation [(ppy)₃Te]·Br, [10]Br, with K₂PdCl₄ afforded [(ppy)₂TeCl]·[(ppy)PdCl₂], 11. The generality of the "ppy" group on stabilizing other main-group non-NHC analogues has been further established by synthesizing the second example of a Bi analogue of a non-NHC derivative, namely, bismuthenium ion, [(ppy)₂Bi]·Cl, [12]·Cl, using the same aryl group. All of the synthesized compounds are unambiguously authenticated by single-crystal X-ray diffraction studies. DFT calculations [natural bond orbital (NBO), atoms in molecules (AIM), and electron localization function (ELF)] indicate that the stability of the non-NHC carbenoids relies on the σ-hole participation of the Te/Bi atom with the strong intramolecular coordination ability of the pyridyl N atom of the aryl substituent.

Full text of DOI:10.1021/acs.organomet.9b00698

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Isolation of Homoleptic Dicationic Tellurium and Monocationic
Bismuth Analogues of Non-N-Heterocyclic Carbene Derivatives
Rajesh Deka, Arup Sarkar, Ray J. Butcher, Peter C. Junk, David R. Turner, Glen B. Deacon,*
and Harkesh B. Singh*
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ABSTRACT: The first examples of Te analogues of non-N-
heterocyclic carbene (non-NHC) derivatives, [(ppy)2Te]·2ClO4,
[4]·2ClO4, and[(ppy)2Te]·2OTf, [5]·2OTf [where ppy = 2-(2′-
pyridyl)phenyl and Tf = O2SCF3] are reported by the metathesis
reaction of diorganoiodotelluronium(IV) cation, [(ppy)2TeI]·I3,
[3]·I3, with AgClO4 and AgOTf, respectively. The metathesis
reaction of ppyTeCl3, 6, with an excess of AgClO4 resulted in the
isolation of [ppyTe(μ-O)]2·2ClO4, [8]·2ClO4. The reaction of
triorganotelluronium(IV) cation [(ppy)3Te]·Br, [10]Br, with
K2PdCl4 afforded [(ppy)2TeCl]·[(ppy)PdCl2], 11. The generality
of the “ppy” group on stabilizing other main-group non-NHC
analogues has been further established by synthesizing the second
example of a Bi analogue of a non-NHC derivative, namely,
bismuthenium ion, [(ppy)2Bi]·Cl, [12]·Cl, using the same aryl group. All of the synthesized compounds are unambiguously
authenticated by single-crystal X-ray diffraction studies. DFT calculations [natural bond orbital (NBO), atoms in molecules (AIM),
and electron localization function (ELF)] indicate that the stability of the non-NHC carbenoids relies on the σ-hole participation of
the Te/Bi atom with the strong intramolecular coordination ability of the pyridyl N atom of the aryl substituent.
analogues is very challenging, as the corresponding Te4+
cations are expected to be ambivalent in nature, i.e., being
INTRODUCTION
■
Inspired by the extraordinary success of N-heterocyclic
carbenes (NHCs), 1a in metal-based chemistry, significant
research has been carried out in the last few decades to isolate
and explore the reactivity of isovalent analogues of NHCs
highly electrophilic and possessing a lone pair of electrons at
the same time.2a In a groundbreaking report, Ragogna and co-
workers have utilized the strong σ-donating ability of the N
atoms of the diazabutadiene α-diimine ligand motifs for the
within p-block elements, collectively known as main-group
isolation of the Te analogues of NHC derivatives 1e.2b
NHC analogues (Chart 1).1 The interesting molecular
structures, versatile electronic properties, and reactivity
associated with the main-group NHC analogues have offered
abundant opportunities in main-group and coordination
chemistry.1 Compared to the group 14 and 15 NHC analogues
of period 5, i.e., 1b−1d, the isolation of group 16 NHC
In the case of NHCs, while the steric properties can be easily
fine-tuned by changing the substituents on the N atoms or by
changing the size of the ring, the choices of modifying the
electronic properties are limited.3 In this context, significant
research has been undertaken lately to understand and explore
the chemistry of “non-NHC” derivatives comprising a
backbone other than imidazol-2-ylidenes. From the seminal
work by Bertrand and co-workers, it is perceived that the non-
NHC frameworks can exhibit promising electronic features and
wide structural varieties which extend their applications in
various fields of contemporary chemistry.3 Among the main-
group non-NHC analogues of groups 14−16, reports on the
Chart 1. NHC (1a) and Other Main-Group NHC Analogues
of Period 5 (1b−1e)
Received: October 18, 2019
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Scheme 1. Synthesis of Dicationic Tellurium Analogues of Non-NHC Derivatives, [4]·2ClO4 and [5]·2OTf
heavier main-group analogues of group 15 and 16 non-NHC
derivatives are still scarce even though the chemistry of group
14 analogues is well studied.4 Very recently, Beckmann and co-
workers have reported the first examples of heavier group 15
analogues (Bi, Sb) of non-NHC derivatives, namely, the
bismuthenium ion [(2,6-Mes2C6H3)2Bi][BAr4] and the
stibenium ion [(2,6-Mes2C6H3)2Sb][B(C6F5)] [where Mes =
2,4,6-Me3C6H2 and Ar = 3,5-(CF3)2C6H3] stabilized by bulky
meta-terphenyl substituents and weakly coordinating anions.2a
The corresponding group 16 congeners have not been
reported. It is worth mentioning that, in recent times, various
cationic organotellurium and organobismuth compounds have
received enormous attention because of their fascinating
photoluminescence properties and promising applications in
photocatalysis.5
treated with an excess (ca. 5 equiv) of AgClO4/AgOTf in
acetonitrile solution at ambient temperature, the reaction
resulted in the precipitation of silver iodide as an off-white
solid. The precipitate was filtered off, and the resultant filtrate,
on slow evaporation at ambient temperature, afforded stable,
white crystalline solids of [4]·2ClO4/[5]·2OTf in ca. 90% yield
1
(Scheme 1). The H and 13C NMR spectra of [4]·2ClO4 and
[5]·2OTf confirmed the purity of the compounds with
characteristic signals and consistent integration values for the
2-(2′-pyridyl)phenyl moiety. Minute but perceptible changes
in chemical shifts were observed for [4]·2ClO4 and [5]·2OTf
in comparison to the precursor [3]·I3. In the 125Te NMR
spectra, [4]·2ClO4 and [5]·2OTf showed single resonances at
δ = 1107 and 1114 ppm, respectively. While these chemical
shift values are close to that of precursor [3]·I3 (δ = 1100
ppm), they are significantly upfield shifted in comparison to
the TeIV NHC analogue, 1e, reported by Ragogna and co-
workers (δ = 1736 ppm), as in the latter Te center was directly
bonded to two N atoms.2b
The molecular structure of [3]·I3 is represented in Figure 1.
Defined by a C2N2I donor set, the geometry around the
Te(IV) center is distorted trigonal bipyramidal, wherein the
iodine and N1 atoms occupy the axial positions and the C11,
C12, and N2 atoms occupy the equatorial positions.
Srivastava et al.6a and Beckmann and co-workers6b have
independently utilized the intramolecular chalcogen bonding
(IChB) approach for the isolation of diorganoiodotelluronium-
(IV) cations. We envisaged that the metathesis reaction of
these diorganoiodotelluronium(IV) cations with silver salts
with noncoordinating anions might lead to the isolation of
hitherto unknown Te analogues of non-NHC derivatives.
Accordingly, iodobis[2-(phenylazo)phenyl-C,N′]-
tellureniumtriiodide6a was treated with silver perchlorate in
acetonitrile/methanol. However, the reaction did not afford
the desired diorganotellurenium(IV) dication. We thought
that, by utilizing stronger IChB interactions, the isolation of
the desired diorganotellurenium(IV) dication could be
achieved. In this context, we planned to use [(ppy)2TeI]·I3,
[3]·I3 [where ppy = 2-(2′-pyridyl)phenyl], as the precursor. It
is worth mentioning that, by using a tellurium trichloride
derivative of the same substrate, i.e., ppyTeCl3, we have
recently succeeded in the isolation of the first example of
monomeric organotellurinic acid, wherein the lone pair of the
N atom of the pyridylphenyl ring strongly participated with the
Te center.7 Herein, by metathesis reaction of [3]·I3 with silver
salts (AgClO4 and AgOTf, Tf = O2SCF3), we report the first
examples of stable, homoleptic dicationic tellurium analogues
of “non-NHC” derivatives, namely, [(ppy)2Te]·2ClO4, [4]·
2ClO4, and [(ppy)2Te]·2OTf, [5]·2OTf.
Figure 1. Molecular structure of [3]·I3; thermal ellipsoids are set at
the 50% probability level. Selected bond distances and angles (Å,
deg): C1−Te 2.134(5), C12−Te 2.141(5), N1···Te 2.295(5), N2···
Te 2.636(5), I1−Te 2.9158(5), I2−I3 2.9736(7), I3−I4 2.8779(7),
C1−Te−C12 97.2(2), N1···Te···N2 85.1(2), N1···Te−I1 167.7(1),
N2···Te−I1 102.3(1), C1−Te−I1 95.2(1), C12−Te−I1 87.3(1), I2−
I3−I4 177.06(2).
RESULTS AND DISCUSSION
Precursor [3]·I3 was synthesized by the oxidative addition of
iodine with diorganotelluride (ppy)2Te, 2.8 When [3]·I3 was
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Figure 2. (a) Molecular structure of [4]·2ClO4; thermal ellipsoids are drawn at the 50% probability level. Selected bond distances and angles (Å,
deg): C1−Te 2.116(2), C12−Te 2.117(2), N1···Te 2.224(2), N2···Te 2.229(2), C1−Te−C12 92.68(9), C1−Te···N 77.04(8), C12−Te···N
77.37(8), N1···Te···N2 162.83(7). (b) Natural bond orbital (NBO) plot showing the lp(N) → p(Te) interaction, stabilization energy, ΔE = 122.5,
122.5 kcal/mol. (c) Electron localization function (ELF) for [4]+ drawing in the plane containing N, Te, and C atoms.
Figure 3. (a) Electrostatic surface potential (ESP) map, ρ = 0.001 au, showing an enhanced σ-hole region antipodal to the C−Te bond in the
absence of N → Te IChB interactions. (b) ESP of [4]+ showing diminution of the σ-hole region due to the presence of N → Te IChB interactions.
ESPs have been drawn on the Hirshfeld surface with potential in the range from 0.175 au (red) to 0.210 au (blue). (c) Atoms in molecules (AIM)
bond topology of [4]+.
Compound [3]·I3 exhibits significantly stronger N···Te IChB
interactions, as is evident from the corresponding N···Te
distances of 2.295(5) and 2.636(5) Å, which are considerably
shorter in comparison to that observed in similar
iodotellurium(IV) cations, namely, [(C6H5NNC6H4)2TeI]·I3
[2.481(11) and 2.756(13) Å; 2.476(13) and 2.796(28) Å] and
[(8-Me2NC10H6)2TeI]·I3 [2.743(7) and 3.20(1) Å].6 The
Te−I bond distance [2.9158(5) Å] and ∠C−Te−C [95.2(1)°]
in [3]·I3 are in good agreement with those in
[(C6H5NNC6H4)2TeI]·I3 [2.782(12)/2.778(15); 97.4(5)/
95.5(6)°] and [(8-Me2NC10H6)2TeI]·I3 [2.780(2) Å;
96.7(3)°].6
The molecular structures of [4]·2ClO4 and [5]·2OTf are
significantly similar; hence, the structure of only [4]·2ClO4 is
described here (Figure 2a; see the Supporting Information for
the structure of [5]·2OTf). The spatial arrangement of the
Te(IV) center is distorted square pyramidal taking the lone
pair of Te and N···Te IChB interactions into account. The
donor set C2N2 makes a spirocyclic arrangement around the
Te center with a C1−Te−C12 bond angle of 92.68(9)°, while
both N atoms make a transoid angle of 162.83(7)°. In the TeIV
NHC analogue 1e, the corresponding N−Te−N angle is
significantly larger with an angle of 172.8(2)°.2b The
interesting feature in the structure of [4]·2ClO4 is the N···
Te IChB interactions, which make five-membered TeNC3
rings with N···Te distances of 2.224(2) and 2.229(2) Å.
These distances are significantly shorter than those observed in
the precursor [3]·I3 [2.295(5) and 2.636(5) Å, vide supra].
The C−N−Te bond angles are 114.8(1) and 115.1(1)°. Both
of the perchlorate anions are involved in weak interactions with
the Te center with distances lying in the range 3.021(2)−
3.115(2) Å, and these distances are well within the sum of the
van der Waals radii of Te and O atoms [Σ rvdw(O, Te) = 3.49
Å].9
To shed light on the electronic structure of a TeIV cation and
to understand the role of the N atoms of the 2-(2′-
pyridyl)phenyl on the stability of the synthesized compounds,
DFT calculations were carried out using the Gaussian 0.9 (rev
A.02) program10 (functional: B3PW91;11 mixed basis set: Te,
SDB-cc-pVTZ;12 C/H/N/O, 6-31G**;13 Bi, cc-pVTZ-PP14).
After a geometry optimization starting from the crystal
coordinates, natural bond orbital (NBO) calculations were
performed for cation [4]+.15 The NBO analysis treats each N−
Te interaction in [4]+ as an lp(N) → p(Te) donor−acceptor
interaction (Figure 2b). A stabilization energy of ∼122 kcal/
mol of each N → Te interaction inferred that they contributed
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significantly to the overall stability of the compound. The
strong N → Te IChB in [4]+ was further validated by electron
localization function (ELF) calculation, wherein a continuum
of elevated ELF values was observed along the N → Te vectors
(Figure 2c).16
To probe the effect of N → Te IChB interactions on the
Te(IV) center in [4]+, the electrostatic surface potential
(ESP)17 was calculated for [4]+ and for a model compound
wherein the pyridyl rings were rotated away from the Te center
in such a way that no IChB was observed between the N and
Te atoms. The ESP of the model compound showed a broad
region of depleted electron density, known as the σ-hole
region, antipodal to the C−Te bond (Figure 3a). It is worth
mentioning that, in the case of group 14−16 compounds, along
the extension of a covalent bond, a highly directional and
localized region of depleted electron density (positive
electrostatic potential) is observed, due to the anisotropic
distribution of electron density, and is known as a σ-hole.18
These σ-holes are responsible for various noncovalent
interactions, such as chalcogen bonding (ChB), pnictogen
bonding (PnB), and tetrel bonding (TrB) to name a few. The
significant diminution of the original σ-hole in compound [4]+
after N → Te IChB (Figure 3b) unambiguously established the
direct involvement of the σ-hole in chalcogen bonding with the
lone pair of the nitrogen atom. To understand the nature of
interaction between the N and Te atoms, an atoms in
molecules (AIM) calculation has been carried out (Figure
3c).19 The analysis of the topological properties of the N···Te
bond critical point (bcp), such as a low electron density, ρ(r),
value of 0.129 e Å−3, Laplacian of electron density, ∇2ρ(r), value
of −0.018 e Å−3, a positive kinetic energy density over electron
density ratio [G(r)/ρ(r)] of 0.22 au, and a total energy density
over electron density ratio [H(r)/ρ(r)] of −0.66 au, infers a
dominant electrostatic interaction between the two atoms. The
“−G(r)/V(r)” value of 0.864 further suggests a predominantly
ionic character of the N···Te interaction with a significant
mixing of covalent character.20 This is further corroborated by
the natural population analysis (NPA) charge of −0.589 for
each N atom and 1.785 for the Te atom.
Figure 4. Molecular structure of [8]·2ClO4; thermal ellipsoids are set
at the 50% probability level. Selected bond distances and angles (Å,
deg): C−Te 2.11(1), N···Te 2.279(9), O1−Te 1.917(8), O2−Te
2.068(8), O11···Te 2.784(9), C−Te···N 76.0(4), O1−Te−O2
78.8(3), Te−O−Te 101.2(3).
longer than that in [4]·2ClO4 [2.224(2) Å] but shorter than
that in [3]·I3 [2.295(5) Å]. The Te−O distances of 1.917(8)
and 2.068(8) Å are in agreement with similar reported dimeric
compounds, namely, [Te(2,6-(Me2NCH2)(μ-O)]2·2ClO4
[1.987(4) and 1.996(4) Å] and [Te(6-Ph2P(O)-Ace-5-)(μ-
O)]2·2OTf [1.920(3)−2.070(3) Å, Ace = acenaphthyl].22 The
nonbonding distance between the two Te centers of 3.080(1)
Å is significantly shorter than the sum of the van der Waal radii
[Σ rvdw(Te, Te) = 3.98 Å].9
To compare the structural parameters of the diorganodica-
tions [4]·2ClO4 and [5]·2OTf with the corresponding
monocation (ppy)3Te+ and to explore the coordination ability
of the Te center, ppyBr, 9,23 was treated with BuLi followed
n
by TeCl4 to afford [(ppy)3Te]·Br, [10]·Br (Scheme 3).
Compound [10]·Br showed 125Te NMR resonance at 867
ppm, which is consistent with the value observed for similar
reported triorganotelluronium(IV) cations, namely, triphenyl-
telluronium chloride (773 ppm) and tris(8-quinolinyl)-
telluronium chloride (669 ppm).24 Interestingly, when [10]·
Br was treated with K2PdCl4, a reverse transmetalation was
observed, resulting in the formation of the PdII complex of
chlorotelluronium cation, namely, [(ppy)2TeCl]·[(ppy)-
PdCl2], 11. In the absence of any other possible explanation,
the stronger N···Te IChB in [10]·Br could be held responsible
for the reverse transmetalation in contrast to the Gabbaï and
co-workers report, wherein tris(8-quinolinyl) telluronium
chloride on reaction with a Pd(II) precursor resulted in the
formation of a 1:1 palladated complex with the telluronium ion
acting as a σ-acceptor ligand.24b In the 125Te NMR spectrum,
11 showed single resonance at 1309 ppm.
In an attempt to synthesize the tricationic species (ppyTe3+),
ppyTeCl3,21 6, was treated with an excess of AgClO4.
However, the desired compound [7]·3ClO4 was not stable
and the adventitious hydrolysis resulted in the formation of
ditelluroxonium bis(perchlorate) [ppyTe(μ-O)]2.2ClO4, [8]·
2ClO4 (Scheme 2). The ditelluroxonium cation [8]·2ClO4
shows 125Te NMR resonance at 1413 ppm.
Scheme 2. Isolation of [8]·2ClO4 by the Attempted
Synthesis of [7]·3ClO4
In the molecular structure of [10]·Br (Figure 5a), the
distortion from a regular octahedron is less [∠N−Te−C(trans)
163.4(3)−165.7(3)°] in comparison to that of the related
compound, tris(8-quinolinyl)telluronium chloride [∠N−Te−
C(trans) 146.7(2)−147.8(2)°].24b Again, the N···Te IChB
distances are significantly shorter [2.680(8)−2.689(7) Å] in
comparison to tris(8-quinolinyl)telluronium chloride
[2.950(5)−2.988(6) Å]. In the molecular structure of 11
(Figure 5b), the cationic entity, the halide site is mixed Cl/Br
with occupancies of 0.908(8):0.092(8). Hence, the structure is
described with respect to the Cl− ligand. The spatial
arrangement around the TeIV center is similar to that of
iodotelluronium cation, [3]·I3. In particular, the C−Te
The molecular structure of [8]·2ClO4 is presented in Figure
4, which reveals a dimeric structure with a crystallographically
imposed center of inversion. Each Te(IV) center is
coordinated to one ppy ligand in trans orientation with respect
to the other and forms a Te2O2 core with μ2-bridging oxygen
atoms. The N···Te distance of 2.279(9) Å is significantly
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Scheme 3. Synthesis of a Pd(II) Complex of Chlorotelluronium Cation, 11
Figure 5. Molecular structures of (a) [10]·Br and (b) 11; thermal ellipsoids are set at the 50% probability level. Selected bond distances and angles
(Å, deg): For [10]·Br, C1−Te 2.152(9), C12−Te 2.13(1), C23−Te 2.152(7), N1···Te 2.688(7), N2···Te 2.680(8), N3···Te 2.647(8), C1−Te···
N1 70.1(3), C12−Te···N2 70.4(3), C23−Te···N3 70.7(3), C1−Te···N2 164.3(3), C12−Te···N3 165.7(3), C23−Te···N1 163.4(3). For 11,
C11A−Pd 2.02(1), C11B−Te 2.14(1), C22B−Te 2.15(1), N1A−Pd 2.03(1), N1B···Te 2.291(9), N2B···Te 2.67(1), Pd−Cl1 2.37(1), Pd−Cl2
2.49(2), Te−Cl1B 2.57(1), Pd···Te 3.738(1), N1A−Pd−C11A 81.5(4), N1A−Pd−C12 96.1(5), N1A−Pd−Cl1 173.2(5), C11A−Pd−Cl2
176.7(5), N1B−Te−C11B 76.6(4), N2B−Te−C22B 70.5(4), N1B−Te−Cl1B 167.3(4), N2B−Te−Cl1B 104.1(3). In the cationic entity, the
halide site is mixed Cl/Br with occupancies of 0.908(8) (for Cl1B)/0.092(8) (for Br1B). In the anionic entity, the halide sites are mixed Cl/Br with
occupancies of 0.874(9) (for Cl1)/0.126(9) (for Br1) and 0.781(9) (for Cl2)/0.219(9) (for Br2).
distances [2.15(1), 2.14(1) Å] and N···Te distances [2.291(9),
2.67(1) Å] in 11 are in good agreement with those observed in
[3]·I3. The ∠C−Te−C [94.7(4)°] in 11 is slightly smaller than
that in [3]·I3 [97.2(2)°]. In the anionic entity, the geometry
around the PdII center is essentially square planar. The bond
lengths and associated bond angles of the ppy and Cl ligands
with the PdII center are in good agreement with the value
observed in similar related dichlorido Pd(II) complexes.25
Interestingly, an unsupported cation−anion interaction is
exhibited between the TeIV and PdII centers with a distance
of 3.738(1) Å, which is shorter than the sum of van der Waals
distances of the two atoms [Σ rvdw(Te, Pd) = 4.14 Å].9
Scheme 4. Synthesis of the Diorganobismuthenium
Chloride [12]·Cl
taking the lone pair of Bi and N···Bi intramolecular interactions
into account (Figure 6a). The Bi(III) ion sits on a
crystallographically imposed center of inversion, containing
two ppy groups in a trans arrangement. The N···Bi distance of
2.467(5) Å is well within the sum of the van der Waals radii of
the two elements [Σ rvdw(N, Bi) = 4.24 Å],9 indicating the
presence of strong N···Bi intramolecular interactions. The
∠C−Bi−C angle of 92.1(3)° is significantly smaller than that
observed in [(2,6-Mes2C6H3)2Bi][BAr4] [116.69(9)°] [where
Mes = 2,4,6-Me3C6H2 and Ar = 3,5-(CF3)2C6H3].2 The NBO
analysis indicates a strong lp(N) → p(Bi) donor−acceptor
interaction in [12]+, wherein each interaction contributes to
the stability of the compound by ΔE = 60.12 kcal/mol (Figure
6b). The ELF study on [12]+ lends further support to the N →
Bi interaction, which shows a considerable degree of electron
sharing between the N and Bi atoms (Figure 6c). It is
noteworthy that, while comparing with the ELF of [4]·2ClO4
(Figure 2c), the sharing of electrons between N and the
element center in [12]·Cl is less, which might be attributed to
To see the generality of the “ppy” group on stabilizing other
main-group non-NHC analogues and to further explore the
unique intramolecular interaction ability of the N atom of the
ppy group, we went on to synthesize (ppy)2BiCl, which was
planned to be used for the metathesis reaction in a subsequent
step to generate a cationic species. Interestingly, when 9 was
n
treated with BuLi followed by addition of BiCl3, a facile
autoionization took place, resulting in the formation of
diorganobismuthenium chloride, [(ppy)2BiIII]·Cl, [12]·Cl
(Scheme 4). [12]+ is only the second example of
bismuthenium ion reported so far after the Beckmann and
co-workers’ donor free bismuthenium ion, [(2,6-
Mes2C6H3)2Bi][BAr4] [where Mes = 2,4,6-Me3C6H2 and Ar
= 3,5-(CF3)2C6H3], stabilized by bulky aryl substituents.2a
An examination of the crystal structure of [12]·Cl indicates
that, similar to [4]·2ClO4 and [5]·2OTf, the coordination
geometry of the Bi(III) center is distorted square pyramidal,
E
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Figure 6. (a) Molecular structure of [12]·Cl; thermal ellipsoids are drawn at the 50% probability level. Selected bond distances and angles (Å, deg):
C1−Bi 2.292(6), N1···Bi 2.467(5), C1−Bi−C1′ 92.1(3), N1···Bi···N1′ 149.5(2), N1···Bi−C1 71.65(19). (b) Natural bond orbital (NBO) plot of
[12]+ showing the lp(N) → p(Bi) interaction, stabilization energy, ΔE = 60.12 kcal/mol for each N → Bi interaction. (c) ELF for [12]+ drawing in
the plane containing N, Bi, and C atoms.
Figure 7. (a) ESP map, ρ = 0.001 au, showing the enhanced σ-hole antipodal to the C−Bi bond in the absence of N → Bi intramolecular
interactions. (b) ESP of [12]+ showing diminution of the σ-hole region due to the presence of N → Bi intramolecular interactions. ESPs have been
drawn on the Hirshfeld surface with potential in the range from 0.08 au (red) to 0.115 au (blue). (c) AIM bond topology of [12]+.
the differences in the size of TeIV and BiIII cations. This is
further corroborated by the corresponding N → Te distance in
[4]·2ClO4 [2.224(2), 2.229(2) Å] and N → Bi distance in
[12]·Cl [2.467(5) Å] (vide supra).
The ESP studies indicate a significant reduction in the σ-
hole region due to the presence of N → Bi interaction (Figure
7b) in comparison to the model compound, wherein in the
absence of N → Bi interaction a large σ-hole region antipodal
to the C−Bi bond is observed (Figure 7a). The analysis of the
topological properties of the N → Bi bcp indicates a
predominant electrostatic interaction between the two atoms,
as suggested by a low electron density, ρ(r), value of 0.059
analogues of non-NHC derivatives. The stability of the
dicationic TeIV non-NHC derivatives was achieved by exposing
the σ-hole around the Te center to the N-lone pair of a rigid
and planar pyridylphenyl ring. The active participation of the
σ-hole with the lone pair of N-atoms through electrostatic
interaction serves the purpose of attenuating the excessive
electrophilicity around the TeIV center, which is generally
achieved by the strong σ-donating ability of the two N atoms
in NHC derivatives. The generality of the phenylpyridyl ring
on the stabilization of other main-group non-NHC analogues
was further established by synthesizing intramolecular
interactions stabilized bismuthenium cation. This is only the
second example of this compound class and the first one to
contain an intramolecularly coordinated substituent. Given the
tremendous interest in NHCs and their analogues over the last
few decades, this new family of compounds would be of
significant interest with respect to their synthetic utility and
reactivity.
e Å−3, a slightly positive Laplacian of electron density, ∇2
,
ρ(r)
value of 0.159 e Å−3, a positive kinetic energy density over
electron density ratio [G(r)/ρ(r)] of 0.800 au, and a total
energy density over electron density ratio [H(r)/ρ(r)] of
−0.125 au, a value close to 0 (Figure 7c). The predominant
electrostatic nature of the N → Bi interaction is further
corroborated by the “−G(r)/V(r)” value of 0.07.
EXPERIMENTAL SECTION
■
CONCLUSIONS
All manipulations were performed under a N2 atmosphere using
standard Schlenk techniques. Solvents were dried by following
standard methods. The starting materials and solvents were purchased
from commercial sources. (ppy)2Te was synthesized by the reaction
of (ppy)HgCl with ppyTeCl3 followed by the treatment with an
excess of hydrazine hydrate.8 (ppy)TeCl3 was synthesized following
the reported procedure using (ppy)HgCl and TeCl4.21 (Caution:
■
In conclusion, we have succeeded in isolating the first examples
of robust, IChB stabilized Te analogues of non-NHC
derivatives by metathesis reaction of diorganohalotelluronium-
(IV) cations with AgClO4/AgOTf. This novel series of
compounds fills the missing link in the period 5 main-group
F
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1
Organomercury compounds are highly toxic. Perchlorate salts with
organic ligands are potentially explosive. Adequate precaution should
be taken while handling such compounds.) (ppy)Br was synthesized
by the treatment of 2-phenylpyridine with Pd(OAc)2 and NBS.23 1H
(400 and 500 MHz), 13C (100 and 125 MHz), and 125Te (126 MHz,
158 MHz) NMR spectra were recorded on Bruker AV 400 MHz and
Bruker AV 500 MHz spectrometers at 25 °C. The chemical shifts
cited were referenced to TMS (1H, 13C) as internal and Me2Te
Yield 0.304 g (74%); mp >300 °C; H NMR (500 MHz, DMSO-
d6) δ 8.57 (d, J = 4.1 Hz, 2H), 8.12 (dd, J = 11.0, 8.0 Hz, 4H), 7.96
(td, J = 7.8, 1.6 Hz, 2H), 7.64 (d, J = 6.9 Hz, 2H), 7.49 (dd, J = 6.8,
5.1 Hz, 2H), 7.46−7.38 (m, 4H); 13C NMR (125 MHz, DMSO-d6) δ
156.02, 149.80, 147.99, 141.40, 138.48, 137.94, 129.39, 128.24,
127.25, 123.54, 121.09; 125Te NMR (157 MHz, DMSO-d6) δ 1413;
FT-IR (neat, cm−1) 3077 (vw), 2918 (vw), 1603 (w), 1444 (s), 1308
(vw), 1141 (s), 1089 (s), 1053 (s), 914 (vw), 876 (m), 764 (m), 736
(w), 654 (w), 632 (m), 622 (m), 539 (vw), 498 (w); MS(ESI+), m/z
Calcd for {[8]ClO4}+ (C22H16ClN2O6Te2), 696.86; Found, 696.89;
Anal. Calcd for C22H16Cl2N2O10Te2: C, 33.26, H, 2.03, N, 3.53;
Found C, 33.07, H, 1.93, N, 3.71.
(
125Te) as external standards. Electron spray mass spectra (ESI-MS)
were performed on a Q-Tof micro (YA-105) mass spectrometer.
Elemental analyses were performed on a Carlo Erba model 1106
elemental analyzer. Infrared spectra were recorded on a PerkinElmer
spectrometer.
Synthesis of Compound [10]·Br. A stirred solution of 923
(0.150 g, 0.643 mmol) in dry Et2O (25 mL) was treated dropwise
with 1.6 M solution of n-BuLi in hexane (0.482 mL, 0.772 mmol) at
−78 °C for 30 min. An Et2O (20 mL) solution of TeCl4 (0.043 g,
0.160 mmol) was added to the reaction mixture at −78 °C. The
reaction mixture was stirred for 14 h at room temperature. After
completion of the reaction, the solvent was removed under a vacuum
to get a light yellow solid, which is the mixture of [10]·Br and
(ppy)2Te. Dichloromethane (20 mL) was added to the solid, and the
resulting reaction mixture was filtered through Celite. The filtrate was
concentrated under a vacuum and washed with Et2O (3 × 15 mL)
which removed (ppy)2Te, and this afforded the analytically pure solid
of [10]·Br. Light yellow crystals of [10]·Br·2CHCl3 suitable for
single-crystal diffraction analysis were obtained by slow diffusion of
hexane into CHCl3 solution of [10]·Br.
Synthesis of Compound [3]·I3. A solution of 28 (0.100 g, 0.228
mmol) in dry dichloromethane (15 mL) was cooled to 0 °C. A
solution of iodine (0.115 g, 0.456 mmol) in carbon tetrachloride (15
mL) was added dropwise to it. After stirring at 0 °C for 1 h, the
reaction mixture was filtered off and the solvent was removed under a
vacuum to get a dark red solid of [3]·I3. Red colored crystals of [3]·I3
suitable for single-crystal diffraction analysis were obtained by slow
evaporation of a chloroform solution of [3]·I3 at room temperature.
Yield 0.176 g (82%); mp 192−194 °C; 1H NMR (500 MHz,
DMSO-d6) δ 9.26 (d, J = 5.6 Hz, 2H), 8.70 (d, J = 8.3 Hz, 2H), 8.57
(d, J = 7.9 Hz, 2H), 8.40 (d, J = 7.8 Hz, 2H), 8.26 (t, J = 7.8 Hz, 2H),
7.69−7.55 (m, 6H); 13C NMR (500 MHz, DMSO-d6) δ 153.66,
143.61, 139.66, 134.21, 132.06, 130.99, 130.95, 127.30, 127.01,
123.67, 122.09; 125Te NMR (126 MHz, DMSO-d6) δ 1100; FT-IR
(neat, cm−1) 3051 (w), 1589 (m), 1481 (m), 1459 (w), 1437 (m),
1418 (m), 1301 (m), 1283 (m), 1259 (w), 1156 (m), 1103 (w), 1063
(vw), 1015 (m), 793 (w), 752 (s), 658 (vw), 642 (m), 627 (m);
MS(ESI+), m/z Calcd for {3-I}+ (C22H16N2Te), 438.05; Found,
438.07; Anal. Calcd for C22H16I4N2Te: C, 28.00, H, 1.71, N, 2.97;
Found C, 28.13, H, 1.67, N, 3.09.
1
Yield 0.284 g (66%); mp 156 °C; H NMR (500 MHz, C6D6) δ
8.80 (dd, J = 7.9, 1.0 Hz, 3H), 8.41 (ddd, J = 4.9, 1.6, 0.9 Hz, 3H),
7.46 (dd, J = 7.8, 1.3 Hz, 3H), 7.27 (d, J = 8.2 Hz, 3H), 7.05−6.98
(m, 6H), 6.84 (td, J = 8.0, 1.4 Hz, 3H), 6.54 (ddd, J = 7.4, 4.9, 0.9 Hz,
3H); 13C NMR (125 MHz, C6D6) δ 156.81, 146.48, 141.35, 139.59,
137.07, 130.35, 127.53, 127.38, 122.52, 120.72, 112.75; 125Te NMR
(157 MHz, CDCl3) δ 867; FT-IR (neat, cm−1) 3051 (m), 1589 (s),
1476 (m), 1464 (m), 1434 (s), 1300 (m), 1157 (m), 1098 (m), 1071
(w), 1015 (w), 999 (m), 895 (w), 797 (m), 757 (s), 627 (m), 590
(w); MS(ESI+), m/z Calcd for [10]+ (C33H24N3Te), 592.11; Found,
592.10; Anal. Calcd for C33H24BrN3Te: C, 59.15, H, 3.61, N, 6.27;
Found C, 58.97, H, 3.54, N, 6.39.
Synthesis of [4]·2ClO4 and [5]·2OTf. To a solution of [3]·I3
(0.040 g, 0.042 mmol) in acetonitrile (15 mL) was added silver salt
[AgClO4 (0.044 g, 0.211 mmol) for [4]·2ClO4; AgOTf (0.054 g,
0.211 mmol) for [5]·2OTf]. The reaction mixture was stirred at room
temperature for 2 h. This resulted in an off-white precipitate. The
precipitate was filtered off. The resulting filtrate on slow evaporation
afforded colorless crystalline solids of [4]·2ClO4 and[5]·2OTf.
[4]·2ClO4. Yield 0.023 g (88%); mp >300 °C; 1H NMR (500 MHz,
DMSO-d6) δ 8.58−8.54 (m, 2H), 8.13 (dd, J = 11.8, 7.8 Hz, 4H),
7.97 (t, J = 7.0 Hz, 2H), 7.65−7.61 (m, 2H), 7.49 (dd, J = 10.8, 5.8
Hz, 2H), 7.42 (ddd, J = 15.0, 10.3, 4.3 Hz, 4H); 13C NMR (125 MHz,
DMSO-d6) δ 156.57, 150.35, 148.53, 141.95, 139.05, 138.48, 129.94,
128.79, 127.81, 124.10, 121.66; 125Te NMR (126 MHz, DMSO-d6) δ
1107; FT-IR (neat, cm−1) 3064 (vw), 2922 (vw), 1606 (m), 1486
(w), 1463 (w), 1443 (w), 1309 (w), 1293 (vw), 1139 (s), 1112 (s),
1089 (s), 761 (m), 739 (w), 634 (m), 626 (m); MS(ESI+), m/z Calcd
for {[4]ClO4 + H}+ (C22H17ClN2O4Te), 537.97; Found, 537.98;
Anal. Calcd for C22H16Cl2N2O8Te: C, 41.62; H, 2.54; N, 4.41; Found
C, 41.87; H, 2.22; N, 4.56.
Synthesis of Compound 11. To a THF solution of [10]·Br
(0.075 g, 0.118 mmol) was added a THF solution of K2PdCl4 (0.036
g, 0.112 mmol) at room temperature. The reaction mixture was
stirred for 12 h. The solvent was removed under a vacuum to get a
yellow solid. The solid was washed with CHCl3 (3 × 15 mL) and
Et2O (3 × 15 mL) to afford the analytically pure solid of 11. Yellow
crystals of 11 suitable for single-crystal diffraction analysis were
obtained by slow diffusion of benzene into a DMSO solution of 11 at
room temperature.
Yield 0.073 g (82%); mp 191 °C; 1H NMR (400 MHz, DMSO-d6)
δ 9.27 (d, J = 5.6 Hz, 1H), 8.70 (d, J = 8.3 Hz, 1H), 8.60−8.54 (m,
2H), 8.40 (d, J = 8.0 Hz, 1H), 8.30−8.22 (m, 1H), 8.14 (dd, J = 12.7,
4.9 Hz, 2H), 8.00−7.94 (m, 1H), 7.69−7.56 (m, 4H), 7.50 (ddd, J =
7.4, 4.8, 1.0 Hz, 1H), 7.43 (dtd, J = 16.6, 7.3, 1.5 Hz, 2H); 13C NMR
(400 MHz, DMSO-d6) δ 156.49, 154.16, 148.38, 144.11, 141.95,
140.17, 139.03, 138.35, 134.71, 132.55, 131.45, 129.93, 128.72,
127.80, 127.74, 127.51, 124.17, 124.09, 122.60, 121.55; 125Te NMR
(400 MHz, DMSO-d6) δ 1309; FT-IR (neat, cm−1) 3061 (w), 2922
(s), 2852 (s), 1600 (m), 1578 (m), 1485 (w), 1466 (vw), 1439 (w),
1422 (w), 1304 (w), 1288 (w), 1273 (w), 1156 (w), 1017 (w), 790
(w), 757 (s), 739 (m), 661 (vw), 630 (w); MS(ESI+), m/z Calcd for
[11-{(ppy)PdCl2}]+ (C22H16ClN2Te), 473.01; Found, 473.03.
Synthesis of [12]·Cl. A stirred solution of 923 (0.100 g, 0.429
mmol) in dry Et2O (20 mL) was treated dropwise with 1.6 M solution
of n-BuLi in hexane (0.322 mL, 0.515 mmol) at −78 °C for 30 min.
BiCl3 (0.067 g, 0.212 mmol) was added to the reaction mixture and
was stirred for 8 h. After completion of the reaction, the solvent was
removed under a vacuum to get a white solid. Dichloromethane (20
mL) was added to the solid, and the resulting reaction mixture was
filtered through Celite. The filtrate was concentrated under a vacuum
to afford the analytically pure solid of [12]·Cl. Colorless crystals of
[5]·2OTf. Yield 0.028 g (90%); mp >300 °C; 1H NMR (500 MHz,
DMSO-d6) δ 8.59−8.55 (m, 2H), 8.15−8.08 (m, 4H), 7.98−7.93 (m,
2H), 7.64 (dd, J = 7.1, 1.2 Hz, 2H), 7.51−7.47 (m, 2H), 7.46−7.38
(m, 4H); 13C NMR (125 MHz, DMSO-d6) δ 156.56, 150.35, 148.54,
141.95, 139.03, 138.49, 129.93, 128.79, 127.80, 124.09, 121.64; 125Te
NMR (126 MHz, DMSO-d6) δ 1114; FT-IR (neat, cm−1) 3054 (m),
3027 (m), 1600 (s), 1590 (s), 1483 (m), 1463 (m), 1438 (m), 1424
(m), 1306 (m), 1288 (m), 1261 (vw), 1171 (w), 1158 (w), 1105 (w),
1017 (m), 887 (w), 797 (w), 759 (s), 736 (m), 628 (m), 465 (m);
MS(ESI+), m/z Calcd for {[5]OTf + H}+ (C23H17F3N2O3STe),
587.99; Found, 587.96; Anal. Calcd for C24H16F6N2O6S2Te: C, 39.27;
H, 2.20; N, 3.82; Found C, 39.41; H, 2.17; N, 4.16.
Synthesis of Compound [8]·2ClO4. To a solution of 621 (0.200
g, 0.514 mmol) in acetonitrile (15 mL) was added AgClO4 (0.319 g,
1.542 mmol). The reaction mixture was stirred at room temperature
for 2 h. This resulted in an off-white precipitate. The precipitate was
filtered off. The resulting filtrate on slow evaporation at room
temperature afforded a colorless crystalline solid of [8]·2ClO4.
G
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[12]·Cl suitable for single-crystal diffraction analysis were obtained by
slow evaporation of a methanol solution of [12]·Cl at room
temperature.
Mumbai, India, and Monash University, Clayton,
Australia
Arup Sarkar − Indian Institute of Technology Bombay,
Mumbai, India
Ray J. Butcher − Howard University, Washington, DC
Peter C. Junk − IITB-Monash Research Academy,
Mumbai, India, and James Cook University, Townsville,
Australia; orcid.org/0000-0002-0683-8918
David R. Turner − IITB-Monash Research Academy,
Mumbai, India, and Monash University, Clayton,
Australia; orcid.org/0000-0003-1603-7994
1
Yield 0.169 g (71%); mp >300 °C; H NMR (500 MHz, DMSO-
d6) δ 8.99 (d, J = 4.7 Hz, 2H), 8.43 (d, J = 7.6 Hz, 2H), 8.38 (d, J =
8.2 Hz, 2H), 8.25 (t, J = 7.3 Hz, 2H), 7.90 (d, J = 7.2 Hz, 2H), 7.73−
7.69 (m, 2H), 7.52 (dt, J = 22.9, 7.0 Hz, 4H); 13C NMR (125 MHz,
DMSO-d6) δ 186.96, 161.65, 149.07, 145.28, 141.13, 138.19, 133.70,
130.15, 128.64, 124.67, 122.94; FT-IR (neat, cm−1) 3051 (m), 3013
(m), 1625 (vw), 1594 (m), 1479 (m), 1420 (m), 1277 (vw), 1246
(vw), 1153 (w), 1102 (w), 1014 (m), 1000 (w), 902 (vw), 846 (vw),
805 (w), 761 (s), 737 (m), 729 (m), 635 (w), 553 (w); MS(ESI+),
m/z Calcd for [12]+ (C22H16BiN2), 517.11; Found, 517.13; Anal.
Calcd for C22H16BiClN2: C, 47.80; H, 2.92; N, 5.07; Found C, 47.56;
H, 2.87; N, 5.26.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.9b00698
X-ray Crystallographic Study. The diffraction measurements for
compounds [3]·I3−[5]·2OTf and [8]·2ClO4−[12]·Cl were per-
formed on a Rigaku Saturn 724 diffractometer using graphite
monochromated Mo Kα radiation (λ = 0.7107 Å). The data
collection was carried out by the standard ω-scan technique, and
the data were evaluated and reduced by using CrystalClear-SM Expert
software. The structures were determined by routine heavy-atom
techniques using SHELXS-9726 and Fourier methods and were
refined by full-matrix least-squares with the anisotropic non-hydrogen
atoms and hydrogen atoms with a fixed isotropic thermal parameter of
0.07 Å2 using the SHELXL-97 program.27 SQUEEZE was applied to
the disordered solvent molecules in [10]·Br by using the PLATON
program.28
Computational Methodology. DFT calculations were carried
out using the Gaussian 0.9 (rev D.02) program10 (functional:
B3PW91;11 mixed basis set: Te, SDB-cc-pVTZ;12 C/H/N/O, 6-
31G**;13 Bi, cc-pVTZ-PP14). Frequency calculations were calculated,
and all of the structures were detected with minima such that no
negative frequencies were observed. The topological analyses were
carried out using Multiwfn software.29
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors would like to acknowledge Department of Science
and Technology (DST), India (J. C. Bose Fellowship
15DSTFLS002, Grant No. RD/0115-DSTFLS80-004) and
IITB-Monash Research Academy (IMURA 0242) for provid-
ing funding to carry out this research. A.S. acknowledges CSIR
for SRF. R.D. thanks Arijit and Asif for technical support. We
acknowledge the Super Computing facility of IIT Bombay,
Space Time-2, for the computational studies.
REFERENCES
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.9b00698.
■
sı
Spectroscopic data, crystallographic parameters, and
packing diagrams for [4]·2ClO4 and [12]·Cl (PDF)
Cartesian coordinates for [4]·2ClO4 and [12]·Cl (XYZ)
Accession Codes
CCDC 1949046−1949052 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: + 44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
Glen B. Deacon − IITB-Monash Research Academy,
Mumbai, India, and Monash University, Clayton,
Australia; Email: glen.deacon@monash.edu
Harkesh B. Singh − Indian Institute of Technology
Bombay, Mumbai, India, and IITB-Monash Research
Academy, Mumbai, India; orcid.org/0000-0002-
0403-0149; Email: chhbsia@chem.iitb.ac.in
Other Authors
Rajesh Deka − Indian Institute of Technology Bombay,
Mumbai, India, IITB-Monash Research Academy,
H
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Heterocyclic Nitrenium Cation Bound to a Nickel-Cyclam Core. J.
Am. Chem. Soc. 2014, 136, 582−585.
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