Reactivity of TerN(SiMe3)BiCl2 - Synthesis of an Aminobismuthenium Cation and TerN(SiMe3)Bi(N3)2

Article abstract of DOI:10.1021/acs.organomet.8b00318

The reaction of TerN(SiMe₃)BiCl₂ (1) (Ter = 2,6-bis(2,4,6-trimethylphenyl)phenyl) with Lewis acids such as GaCl₃ and Ag[OTf] (OTf = OSO₂CF₃) was studied. While the reaction of 1 with GaCl₃ led to decomposition into bismuth black, TerNH₂·GaCl₃, and [TerNH₃][GaCl₄], the reactions of 1 with 1 and 2 equiv of Ag[OTf] resulted in methyl/triflate exchange reactions affording TerN(SiMe₂OTf)Bi(Me)Cl (2) and TerN(SiMe₂OTf)Bi(Me)OTf (3). To circumvent the methyl/triflate exchange, the diiodide compound TerN(SiMe₃)BiI₂ (5) and the azide-substituted derivatives TerN(SiMe₃)Bi(Cl)N₃ (6) and TerN(SiMe₃)Bi(N₃)₂ (7) were prepared, although it was not possible to isolate pure 7 because of small impurities of 6. All of the bismuth compounds (1-7) were characterized by single-crystal X-ray diffraction and NMR, IR, and Raman spectroscopy. According to quantum-chemical calculations, 3 can be regarded as a donor-stabilized aminobismuthenium cation with OTf^- as the counterion. As expected for bismuth compounds with aromatic scaffolds, Bi···-arene interactions were observed. The influence of the substitution at the bismuth atom on the strength of this intramolecular interaction with the terphenyl moiety was studied by experimental (crystal structures) and theoretical methods. A correlation between the Lewis acidity (NBO charge) and the Bi···-arene distance could be established.

Full text of DOI:10.1021/acs.organomet.8b00318

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Reactivity of TerN(SiMe3)BiCl2Synthesis of an
Aminobismuthenium Cation and TerN(SiMe3)Bi(N3)2
Jonas Bresien,† Christian Hering-Junghans,† Axel Schulz,*,†,‡ Max Thomas,† and Alexander Villinger†
†Abteilung Anorganische Chemie, Institut fu
̈
r Chemie, Universitat Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany
̈
‡Materialdesign, Leibniz-Institut fu
̈
r Katalyse an der Universitat Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
̈
S
* Supporting Information
ABSTRACT: The reaction of TerN(SiMe3)BiCl2 (1) (Ter = 2,6-
bis(2,4,6-trimethylphenyl)phenyl) with Lewis acids such as GaCl3 and
Ag[OTf] (OTf = OSO2CF3) was studied. While the reaction of 1 with
GaCl3 led to decomposition into bismuth black, TerNH2·GaCl3, and
[TerNH3][GaCl4], the reactions of 1 with 1 and 2 equiv of Ag[OTf]
resulted in methyl/triflate exchange reactions affording TerN-
(SiMe2OTf)Bi(Me)Cl (2) and TerN(SiMe2OTf)Bi(Me)OTf (3). To
circumvent the methyl/triflate exchange, the diiodide compound
TerN(SiMe3)BiI2 (5) and the azide-substituted derivatives TerN(SiMe3)Bi(Cl)N3 (6) and TerN(SiMe3)Bi(N3)2 (7) were
prepared, although it was not possible to isolate pure 7 because of small impurities of 6. All of the bismuth compounds (1−7)
were characterized by single-crystal X-ray diffraction and NMR, IR, and Raman spectroscopy. According to quantum-chemical
calculations, 3 can be regarded as a donor-stabilized aminobismuthenium cation with OTf− as the counterion. As expected for
bismuth compounds with aromatic scaffolds, Bi···π-arene interactions were observed. The influence of the substitution at the
bismuth atom on the strength of this intramolecular interaction with the terphenyl moiety was studied by experimental (crystal
structures) and theoretical methods. A correlation between the Lewis acidity (NBO charge) and the Bi···π-arene distance could
be established.
Scheme 1. Examples of Low-Valent Nitrogen−Bismuth
Compounds Exhibiting Silyl Amine Functionalities (R = t-
Bu, Dipp = 2,6-Diisopropylphenyl)
INTRODUCTION
■
Nitrogen−bismuth compounds have been in the focus of main-
group chemistry for more than three decades,1−16 especially
aminobismuthanes (bismuth amides), which were shown to be
valuable starting materials in element organic chemistry.17 Ever
since the early works of Errington, Norman, and co-
workers,18,19 the number of structurally characterized amino-
bismuthanes has grown steadily. Notably, derivatives featuring
bulky substituents such as 2,4,6-tri-tert-butylphenyl (Mes*)5,20
or 2,6-bis(2,4,6-trimethylphenyl)phenyl (Ter)20−22 groups
have been utilized to stabilize highly labile nitrogen−bismuth
compounds but also Bi−E species (E = group 14−16
element).2,9,23,24
Lately there has been great interest in nitrogen−bismuth
compounds containing silyl groups attached to the nitrogen
atom, such as those depicted in Scheme 1. These compounds
are versatile starting materials for the synthesis of low-valent
(nitrogen−)bismuth compounds.7,11,25−31
In particular, N-(trimethylsilyl)aminobismuthanes with
different sterically demanding groups at the nitrogen atom
have been studied intensively. The Me3Si group was
introduced to increase the steric protection of the precursor,
but at the same time, “Me3Si+”, also known as “big proton”, can
easily be removed by strong nucleophiles such as X− (X =
halogen, OR) to afford, for instance, low-valent N−Bi
cations.11,20,25,28 However, on some occasions the elimination
of the Me3Si group was impossible,28 contrary to results
obtained with lighter congeners (RN(SiMe3)PnCl2; Pn = P,
As; R = Mes*).32−34 In these cases, use of stannylated species
rather than silylated species often represented a more favorable
reaction pathway.35
Our quest for a salt bearing the bismadiazonium cation (R−
NBi+), which could be used to generate an unknown cyclic
tetrazabismuthole (RN4Bi) in a [3 + 2] cycloaddition reaction
with a covalent azide, led to our specific interest in the
reactivity of N-(trimethylsilyl)aminodichlorobismuthanes of
the type RN(SiMe3)BiCl2. RN(SiMe3)BiCl2 compounds
seemed to be suitable precursors for the generation of R−
NBi+ species because the lighter congeners of the
tetrazapnictole series (RN4Pn; Pn = P,36 As,34,37 Sb38) had
already been successfully prepared by elimination of a
trimethylsilyl group from RN(SiMe3)PnX2 (X = Cl, OTf)
Received: May 16, 2018
© XXXX American Chemical Society
A
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followed by Cl− ion abstraction or isomerization by means of a
strong Lewis acid (Scheme 2).
but also for the investigation of intramolecular Bi···π-arene
interactions.
RESULTS AND DISCUSSION
Scheme 2. General Approach for the Synthesis of
Tetrazapnictoles (R = Ter, Mes*; Pn = P, As, Sb; LA =
Lewis Acid)
■
Synthesis. TerN(SiMe3)BiCl2 (1), a compound with a
formally hidden N−Bi double bond, which can be generated
by Me3SiCl elimination, was synthesized according to a
literature procedure by the reaction of in situ-generated
TerN(SiMe3)Li with BiCl3 in Et2O (Scheme 4).20
Scheme 4. Synthesis of TerN(SiMe3)BiCl2 (1)
Addition of a Lewis acid such as GaCl3 is one of the easiest
ways to trigger Me3SiCl elimination from silyl amino-
dichloropnictanes.32,34,36,37 Indeed, upon addition of GaCl3
at −80 °C (Scheme 5), Me3SiCl elimination was observed, but
Hence, TerN(SiMe3)BiCl2 (1), a molecule featuring both a
bulky terphenyl group and an aminosilyl group, is a promising
candidate for the preparation of low-valent Bi−N compounds,
especially Ter−NBi+. Aside from their steric protection,
terphenyls are also capable of stabilizing bismuth compounds
by π-arene interactions with the bismuth center, a typical
structural motif frequently found in bismuth compounds. This
long-known phenomenon (also known as “Menshutkin”
interactions or “Menshutkin-type” complexes) is not limited
to bismuth but is also observed for antimony and arsenic
compounds39,40 and has been intensively investigated by
experimental and theoretical studies.41−43 Often, such
interactions are intermolecular (e.g., with solvent mole-
cules),20,42 but some examples of intramolecular Menshutkin-
type complexes are known in bismuth compounds bearing
bulky arene substituents.23,35,44,45 It has been demonstrated
that such π-arene interactions have a significant stabilizing
effect, for example, on highly reactive aminochlorobismuthe-
nium cations.28
Scheme 5. Reaction of 1 with GaCl3
unfortunately, the in situ-generated Ter−NBiCl species
decomposed readily into TerNH2·GaCl3 and [TerNH3]-
[GaCl4] (both isolated as colorless, block-shaped crystals)
and a violet-black oil of unknown composition (a complex
1
mixture according to H NMR spectroscopy). The decom-
position took place very fast even at low temperatures. Hence,
no intermediates could be identified. The origin of the protons
could not be determined doubtlessly. However, it is possible
that the decomposition of the Bi−N compound involved the
formation of radical species, as was discussed previously in the
synthesis of Mes*N(SiMe3)BiCl2.20 Thus, the protons might
be abstracted from the solvent (CH2Cl2).
Bi···π-arene interactions have been the focus of numerous
studies.39,42,46−50 It was Hobza and co-workers who elucidated
that the main contribution to these element···π-system
interactions are dispersion interactions in addition to a small
contribution from electron transfer.41 This electron transfer
can be discussed in terms of σ-hole bonding (Scheme 3). The
Since the elimination of Me3SiCl in the presence of a Lewis
acid was unsuccessful, the synthesis of TerN(SiMe3)Bi(Cl)-
OTf was attempted. In this case, Me3SiOTf elimination was
expected to generate a species bearing a Bi−N double bond. It
is known that the closely related antimony compound
Mes*N(SiMe3)Sb(OTf)2 is intrinsically unstable toward
Me3SiOTf elimination.52 To facilitate the synthesis of
TerN(SiMe3)Bi(Cl)OTf, 1 was treated with 1 equiv Ag[OTf]
at low temperatures (−25 °C), resulting in an immediate color
change from orange to red. Upon warming to ambient
temperature, the suspension turned yellow. Upon warming to
room temperature, the formed suspension turned yellow.
Attempts to crystallize the reaction product from toluene
failed, but X-ray-quality crystals could be grown from a
saturated benzene solution in rather good yield (68%). The X-
ray structure revealed the formation of a methyl/triflate
exchange product (2 in Scheme 6 and Figure 1). Strangely
enough, when 1 was reacted with 2 equiv of Ag[OTf] in a
similar fashion, Me3SiOTf elimination could not be achieved
either. The two chlorine atoms at the bismuth atom could be
abstracted, though, leading to the formation of 3 (Scheme 6
Scheme 3. A Bi···π-Arene Complex
Bi···π-arene interaction should be stronger when the Lewis
acidity of the Bi atom increases. One possibility to extremely
enhance the Lewis acidity is to generate a bismuthenium
cation. It was previously shown that such bismuthenium
cations can be stabilized by aromatic π systems.28,51 Cationic
Bi species were synthesized by abstracting a chloride ion
utilizing Lewis acids or silver salts of weakly coordinating
anions (WCAs). To that end, the behavior of 1 in the presence
of GaCl3 and Ag[OTf] was investigated. Moreover, the
terphenyl compounds presented herein are interesting
contributions not only for the development of N−Bi chemistry
B
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three constitutional isomers of species 3 are possible:
TerN(SiMe3)Bi(OTf)2, TerN[SiMe2(OTf)]Bi(Me)OTf, and
TerN[SiMe(OTf)2]BiMe2 but again the thermodynamic
product is formed: TerN[SiMe2(OTf)]Bi(Me)OTf (3) is
favored by 6.6 and 5.9 kcal/mol over TerN(SiMe3)Bi(OTf)2
and TerN[SiMe(OTf)2]BiMe2, respectively (see the Support-
ing Information).
Scheme 6. Reaction of 1 with Ag[OTf] and Formation of
Methyl/Triflate Exchange Products 2 and 3
The formation of 2 and 3 was not entirely unexpected since
such methyl/triflate exchange reactions for the corresponding
arsenic53 and antimony54 congeners were already known. To
avoid the methyl/triflate exchange reaction, generation of
TerN(SiMe3)Bi(OTf)2 by reacting TerN(SiMe3)Li with
Bi(OTf)3 was then attempted. Unfortunately, decomposition
was observed. Bismuth black was identified as the major
product besides TerNH2 and a small amount of colorless
crystals. Intriguingly, single-crystal diffraction of those colorless
crystals revealed the formation of compound 4, a C−C
coupling product of two TerNH2 moieties (see the Supporting
Information). Since 4 was only formed in traces, analytical data
1
are limited to structural (X-ray) and H NMR data.
Transformation of the chloride derivative 1 into the iodide
derivative prior to the triflate reaction was another approach to
get a clean reaction with Ag[OTf] without methyl/triflate
exchange. To that end, 1 was reacted with 2 equiv of Me3SiI,
which yielded the iodido species TerN(SiMe3)BiI2 (5) (Figure
3), as depicted in Scheme 7. The mixed halogenated species,
Figure 1. Ball-and-stick representation of the molecular structure of 2
in the crystal. H atoms have been omitted for clarity. Selected bond
lengths (Å) and angles (deg): Bi−N 2.232(2), Bi−C27 2.231(2), Bi−
Cl 2.5345(7), N−Si 1.705(2), O1−Si 1.771(2), O1−S 1.511(2);
C27−Bi−Cl 89.91(8), C27−Bi−N 101.62(9), N−Bi−Cl 97.57(6),
Si−N−Bi 125.0(1), S−O1−Si 134.7(1).
and Figure 2), which is also a product featuring methyl/triflate
exchange, but with only one methyl group. Migration of a
Figure 2. Ball-and-stick representation of the molecular structure of 3
in the crystal. H atoms have been omitted for clarity. Selected bond
lengths (Å) and angles (deg): Bi−N 2.224(2), Bi−C1 2.219(2), O3−
Bi 2.375(2), N−Si 1.709(2), O4−Si 1.751(2); C1−Bi−O3 83.05(6),
C1−Bi−N 101.87(6), N−Bi−O3 93.38(5), Si−N−Bi 128.17(9), S1−
O3−Bi 124.05(8), S2−O4−Si 130.7(1).
Figure 3. Ball-and-stick representation of the molecular structure of 5
in the crystal. H atoms have been omitted for clarity. Selected bond
lengths (Å) and angles (deg): B1−N1 2.166(3), B1−I1 2.8992(3),
Bi1−I2 2.8455(4), Bi1−I1′ 3.695(4), N1−Si1 1.762(3), C1−N1
1.431(5), B1−Ct1 3.7048(4), I1−Ct1 3.6643(4); N1−Bi1−I1
97.29(8), N1−Bi1−I2 110.07(8), I1−Bi1−I2 92.25(1), I1−Bi1−I1′
80.573(9), C1−N1−Bi1 110.9(2), C1−N1−Si1 123.7(3), Si1−N1−
Bi1 125.4(2). Symmetry code (′): −x, −y, 1 − z.
second methyl group was not observed, leaving one triflate
attached to the bismuth center. Presumably, the first equivalent
of Ag[OTf] results in abstraction of a chloride ion to afford a
Bi+ center, after which migration of the methyl group is favored
over binding of the OTf− ion directly to the positive bismuth
center. Finally, after migration of the methyl group, the triflate
gets attached to the positive Si center in accord with computed
thermodynamic data favoring the exchange product 2 over the
expected Bi−OTf species by 7.9 kcal/mol (see the Supporting
Information (SI)). With the second equivalent of Ag[OTf],
again chloride abstraction occurs in species 2, but in this case
formation of the bismuth−triflate bond is favored. Formally,
Scheme 7. Synthesis of 5
C
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TerN(SiMe3)Bi(Cl)I, was not obtained, even in a reaction of 1
with only 1 equiv of Me3SiI. In that case, always a 1:1 mixture
of 1 and 5 was observed.
Compound 5 was unstable in CH2Cl2 or fluorobenzene
solution at ambient temperature; however, it could be stored as
a solid under an argon atmosphere in the dark at −35 °C for
approximately 3 weeks. Longer storage resulted in the
formation of a black solid and the free amine according to
1H NMR spectroscopy. 5 was also sensitive toward light.
Therefore, Raman spectra had to be collected at −80 °C.
Because of the instability of 5, especially in solution, it was
impossible to carry out follow-up chemistry.
All of the above-discussed reactions aimed to generate a
bismadiazonium salt that could be used in a [3 + 2]
cycloaddition with an azide. Because of the obviously high
reactivity and instability of the intermediates, e.g., with respect
to methyl/triflate exchange, a new approach was chosen.
Instead of generation of a bismadiazonium salt and subsequent
addition of azide, the corresponding aminoazidobismuthanes
were prepared. In this case, the N3 functionality is already part
of the molecule, which could give rise to an intramolecular
[3 + 2] cycloaddition. Hence, in a second series of experiments
we tried to generate tetrazabismutholes starting from
substituted bismuth azides as illustrated in Scheme 2, a
reaction which worked nicely for the antimony analogue. For
this purpose, compound 1 was stirred with 1 or 2 equiv of
NaN3 in tetrahydrofuran (THF) to synthesize TerN(SiMe3)-
Bi(Cl)N3 (6) and TerN(SiMe3)Bi(N3)2 (7) (Scheme 8),
respectively.
Figure 4. Ball-and-stick representation of the molecular structure of 6
in the crystal. H atoms have been omitted for clarity. Selected bond
lengths (Å) and angles (deg): N1−Bi1 2.180(1), N2−Bi1 2.218(2),
Cl1−Bi1 2.5642(3), N1−Si1 1.751(1), C1−N1 1.420(2), N2−N3
1.207(2), N3−N4 1.150(2); N1−Bi1−Cl1 95.02(3), N1−Bi1−N2
92.31(4), N2−Bi1−Cl1 89.89(3), C1−N1−Bi1 115.38(8), C1−N1−
Si1 127.66(9), Si1−N1−Bi1 115.60(5), N3−N2−Bi1 116.1(1), N4−
N3−N2 177.0(2), Cl1′−Bi1 3.3483(5), Cl1−Bi1−Cl1′ 83.07(2),
Bi1−Cl1−Bi1′ 96.93(2). Symmetry code (′): 2 − x,1 − y, −z.
Scheme 8. Synthesis of the Azide-Substituted Compounds
TerN(SiMe3)Bi(Cl)N3 (6) and TerN(SiMe3)Bi(N3)2 (7)
The chloride/azide exchange reaction using NaN3 (Scheme
8) yielded monoazide 6 (Figure 4) in a straightforward
synthesis but turned out to be more complicated for the
generation of diazide 7 (Figure 5). In the reaction of 1 with 2
equiv of NaN3, 7 could be obtained only in a mixture with 6
(6:7 ≈ 1:5). Even a reaction of 1 with a huge excess of NaN3
led to such a mixture. Hence, complete conversion into 7 could
not be achieved. In an attempt to obtain pure 7, silver azide
was used instead of sodium azide. However, this reaction
always led to decomposition into bismuth black, TerNH2, and
Figure 5. Ball-and-stick representation of the molecular structure of 7
in the crystal. H atoms have been omitted for clarity. Selected bond
lengths (Å) and angles (deg): N1−Bi1 2.184(2), N2−Bi1 2.287(5),
N5−Bi1 2.214(2), N1−Si1 1.753(2), C1−N1 1.420(2), N2−N3
1.227(3), N3−N4 1.152(3), N5−N6 1.214(2), N6−N7 1.146(2);
N1−Bi1−N2 96.8(2), N1−Bi1−N5 92.26(5), N5−Bi1−N2 83.9(2),
Si1−N1−Bi1 113.39(6), N3−N2−Bi1 122.7(4), N6−N5−Bi1
166.7(1), N4−N3−N2 175.6(3), N7−N6−N5 176.2(2). Symmetry
code (′): 1 − x, −y, 1 − z.
1
TerN(SiMe3)H, as confirmed by H NMR spectroscopy. To
date it has not been possible to generate pure 7. Nevertheless,
we treated both azides with a Lewis acid in order to form a
tetrazabismuthole as depicted in Scheme 2 for antimony.
Unfortunately, reactions of 6 and 7 with a Lewis acid always
resulted in decomposition to afford mainly bismuth black and
TerNH2.
intermolecular interaction with the solvate molecules can be
discussed, but the terphenyl substituent is arranged in such a
fashion that one of the mesitylenes is in the proximity of the Bi
center, allowing intramolecular π-arene interactions (vide
infra), which can be best described as a [2 + 2 + 2]
coordination mode. Both species feature an eclipsed, bent
R1(R2)Bi−N−SiMe2(OTf) frame (Bi−N−Si = 125.0(1) in 2
and 128.20(9)° in 3) with trigonal-pyramidal Bi, trigonal-
planar N, and strongly distorted tetrahedral Si centers (Table
1). Both the Bi−N and Si−O distances are in the typical range
of strongly polarized Bi−N and Si−O bonds.55 However, the
Bi−OTf bond in compound 3 (Bi1−O3, 2.375(2) Å; Figure 2)
is significantly longer than expected for a strongly polarized
Bi−O single bond (the sum of the covalent radii is ∑rcov(Bi−
Structure and Bonding. Compound 2, TerN-
[SiMe2(OTf)]Bi(Cl)Me, crystallized in the orthorhombic
space group P212121 with four formula units in the unit cell
as the benzene solvate 2·2C6H6, while for 3, TerN-
[SiMe2(OTf)]Bi(OTf)Me, a triclinic cell and space group P1
̅
with Z = 2 were found. Compound 3 crystallized as
monobenzene solvate. The structures of 2 and 3 without the
solvates are shown in Figures 1 and 2. For both compounds, no
D
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Table 1. Selected Parameters for the Description of the Bi−
a
X Interaction in Compounds 2 and 3
parameter
2
3
X−Bi/∑rcov[X−Bi] [%]
∑∠(Bi) [deg]
101
111
289.1
97.57(6)
0.51
278.3
93.38(5)
0.28
∠(X−Bi−N) [deg]
b
QCT X → RBiMe [e]
c
lone valence at Bi
no
yes
ρ(r) at the BCP [e]
∇2ρ(r) at the BCP
0.065
0.143
+75
0.062
0.236
+78
d
D298,hom [kcal/mol]
d
D298,het [kcal/mol]
+152
+107
a
b
c
Figure 6. Two-dimensional cross section through the N1−Bi1−O3
plane of the electron localization function (ELF) of 3.
2, X = Cl; 3, X = OTf. Based on NBO charges. From NBO
d
analysis. Computed dissociation free energies for the homolytic
(hom) and heterolytic (het) dissociation processes.
O) = 2.14 Å)55 because of the weakly coordinating character of
the OTf group. Additionally, the Bi−O3 bond is located
opposite to the π-arene system; the same holds true for the Cl
atom attached to Bi in compound 2. Hence, the elongation of
the Bi−O bond might also be discussed in terms of a
hyperconjugative effect.46,56 Because of the strong ionic
bonding between the triflate and the formal Bi+ compound,
3 can be regarded as an aminobismuthenium cation stabilized
by a triflate anion. According to natural bond orbital (NBO)
analysis, the triflate group carries an overall charge of −0.72e,
which corresponds to a charge transfer of 0.28e onto the
TerN[SiMe2(OTf)]Bi(Me)+ fragment, in accord with a highly
polarized Bi−O bond or even an ion pair description. Further
NBO analysis data support the latter idea by describing the
bismuth atom with an empty valence 6p orbital, that is, as
bismuthenium cation, as depicted in Scheme 9 by Lewis
Figure 7. Plot of the Laplacian along the O3−Bi1 axis and position of
the bond critical point (BCP) and valence-shell charge concentration
(VSCC).
Scheme 9. Major Lewis Representations of the Bi−X
Interaction According to NBO Analysis
(∇2ρ(r) = 0.236), which is also an indicator of ionic
bonding.57−63
Table 1 summarizes some essential parameters of the Bi−X
interaction in 2 (X = Cl) and 3 (X = OTf) to compare the
chloride with the triflate substituent. When all of the bond
indicators are taken into account, triflate derivative 3 can be
regarded as a donor-stabilized bismuthenium cation while
compound 2 is best described as chlorobismuthane with a
highly polarized Bi−Cl bond.
representation B. Interestingly, stabilization of the Bi+ fragment
bearing an electron sextet by hyperconjugation (n(O) →
p(Bi), 96 kcal/mol; formula A) is much more pronounced
than stabilization by formation of a Bi−N double bond (10
kcal/mol; formula C). The natural localized molecular orbital
(NLMO) picture, which displays all of the delocalization
effects, also features stabilization of the bismuthenium cation
by donation of electron density of the adjacent lone pairs of
the O atom into the formal empty p orbital located on the
bismuth atom. Additionally, the computed electron localization
function (ELF) supports the ionic description, since the
localized electron density of O3 is roughly spherical and not
directed toward Bi1 (Figure 6).
A topological analysis of the electron density along the O3−
Bi1 axis revealed only one valence-shell charge concentration
(VSCC) in the Laplacian (Figure 7), also suggesting a mainly
ionic interaction between O3 and Bi1,57 which is in agreement
with the NBO and ELF results (vide supra). Also, the
calculated electron density at the bond critical point (BCP) is
quite low (ρ(r) = 0.062e) and the Laplacian is positive
Compound 5 was crystallized from the reaction mixture
without further purification (Figure 3) in the triclinic space
̅
group P1 with two molecules in the unit cell. In the crystal,
compound 5 forms centrosymmetric dimers with formal Bi2I2
rings as a result of long-range Bi···I intermolecular coordina-
tion (Bi1′−I1 = Bi1−I1′ = 3.6950(4) Å; cf. ∑rvdW(Bi···I) = 4.4
Å).64 Moreover, within compound 5 two slightly different Bi−
I1 and Bi−I2 distances (Bi1−I1 = 2.8992(3) Å; Bi1−I2 =
2.8455(4) Å) are observed that are close to the sum of the
covalent radii (∑rcov(I−Bi) = 2.84 Å).55 The Bi−N distance
(2.166(3) Å) is in the range of a polarized Bi−N single bond
(∑rcov(N−Bi) = 2.22 Å)55 and comparable to those found in
species 2 (2.232(2) Å) and 3 (2.224(2) Å).20 The angular sum
at the bismuth atom (∑∠(Bi1) = 299.6°) is significantly larger
than in 1 (282.0°) and other aminodichlorbismuthanes.20 This
might be due to the very large iodine atoms, in accord with
Bent’s rule.65,66 Again the Bi center is stabilized by η2
coordination (vide infra) with one mesitylene ring, as depicted
in Figure 3. Moreover, the iodine atom is also close to the
arene, leading to I···Carene π interactions.
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Article
Both azido compounds 6 and 7 crystallized from a saturated
benzene solution at room temperature as benzene solvates
(Figures 4 and 5; see Table S2). There are no intermolecular
interactions between the bismuth atoms and benzene solvate
molecules in the crystal structure, but again, in both cases the
Bi center is stabilized by coordination to one mesitylene ring of
the terphenyl substituent (vide infra). Compound 6 crystal-
̅
lized in the triclinic space group P1 with two molecules in the
unit cell, while the mixture of 6 and 7 crystallized in the
monoclinic space group P21/n with four molecules per unit
cell, both featuring centrosymmetric dimers in the solid state.
We do want to stress that it was impossible to crystallize pure
diazide 7. The structural parameters of 6 and 7 are similar, and
therefore, 6 can easily cocrystallize with 7. The amino
nitrogen−bismuth distance in 7 (Bi1−N1 = 2.184(2) Å) is
the same as in 6 (2.180(1) Å) within the standard deviation
and in the expected range for a polarized Bi−N single bond
(∑rcov(N−Bi) = 2.22 Å),55 The same holds true for the
distance of Bi1 to the nonbridging azido nitrogen (2.218(2) Å
in 6 vs 2.214(2) Å in 7). However, in 7 the distance to the
bridging azido nitrogen (Bi1−N2 = 2.287(5) Å) is significantly
longer, as it bridges both monomers in a μ1,1 fashion (cf.
Bi(N3)3, dav(Bi−N) = 2.316 Å).67 The distance between Bi1
and N2′ of the adjacent molecule (B1···N2′ = 3.120(5) Å) lies
well within the sum of the van der Waals radii (∑rvdW(Bi···N)
= 3.9 Å).64 Interestingly, the Nγ of the azide group covalently
bound to the bismuth atom in both species lies in the
proximity to the adjacent Bi1′ atom (3.411(2) in 6 and
3.281(2) Å in 7; cf. ∑rvdW(Bi···N) = 3.9 Å), and therefore,
these azides can also be considered as bridging groups but in a
μ1,3 mode (Figures 4 and 5).
All of the azide groups in 6 and 7 are in a trans-bent
arrangement with N−N−N angles smaller than 180° (175−
177°), and therefore, a small covalent contribution to the
bismuth azide bonds can be discussed, in agreement with NBO
analysis (see the Supporting Information), which features
highly polarized Bi−N bonds (in the Bi−N NBO, ca. 83% of
the electron density is localized at nitrogen and 17% at the
bismuth center). In the case of compound 6, the chlorine atom
bridges the two monomeric units instead of the azide group,
with a Bi1−Cl1 distance of 2.5642(3) Å, which is significantly
longer than the sum of the covalent radii (∑rcov(Bi−Cl) = 2.50
Å55) (Figure 4), while the second, much longer Bi1−Cl1′
distance of 3.3483(4) Å lies well within the sum of the van der
Waals radii (∑rvdW(Bi−Cl) = 4.1 Å).64
Bismuth-arene Interactions. All of the studied com-
pounds feature a Bi−X bond (X = Cl, I, N, O) that is nearly
perpendicular to one o-mesitylene ring system. As indicated by
NBO analysis, the π system of the aromatic ring interacts with
the antibonding orbital of the Bi−X bond (as shown in Figure
8 for species 1 as an example). Since this work led to several
structurally characterized compounds featuring intramolecular
Menshutkin-type interactions,20,39,45,68−74 the influence of the
substituents at the bismuth atom on the interaction could be
studied in detail. Table 2 lists the minimum, maximum,
average, and centroid (Ct) distances of the closest mesitylene
ring system to the bismuth atom. Since it is rather difficult to
give correct connectivities (hapticities) of asymmetrically
coordinated mesitylenes to the bismuth center, we have used
the criterion d(Bi···Cmesitylene) < 4.2 Å (cf. ∑rvdW(Bi···C) = 4.0
Å), resulting in a formal hapticity value of 6 for all of the
considered species except 5 (Figure 3), for which competition
between iodine and bismuth for the arene interaction leads to
Figure 8. Bi···π-arene interaction in 1 in the NLMO picture (left) and
in a simplified orbital picture (right).
Table 2. Bi···Mesitylene Distances (Minimum, Maximum,
Average, Centroid, in Å) in Compounds 1−3 and 5−7
b
dmin
dmax
dav
dCt
cm
η
a
1
2
3
5
6
7
2.940(4)
2.994(3)
2.871(2)
3.119(4)
2.842(2)
2.878(2)
3.637(4)
4.206(3)
4.089(2)
4.668(5)
3.444(2)
3.468(2)
3.33
3.63
3.51
3.92
3.20
3.23
3.03
3.38
3.26
3.71
2.88
2.91
2 + 2 + 2
2 + 2 + 2
2 + 2 + 2
2 + 2
3 + 3
3 + 3
6
6
6
4
6
6
a
b
Structural data were taken from ref 5. cm = coordination mode.
hapticities of 4 for Bi and 3 for iodine (cf. ∑rvdW(I···C) = 3.8
Å) (Table 3).64 Interestingly, the I−Ct distance is even smaller
(3.66 Å compared with 3.70 Å for Bi−Ct). A closer look at the
distances for all species revealed often either a [2 + 2 + 2] or [3
+ 3] coordination mode of the mesitylene with the Bi center.
The interaction of the mesitylene ring system with the Bi
atom is also manifested in the NLMO picture (Figure 8). For
example, the π system of the arene in 1 donates electron
density into one of the antibonding σ*(Bi−Cl) orbitals.
We tried to find a correlation between the substituents of the
bismuth atom and the strength of the Bi···π-arene interaction.
To compare the studied bismuth compounds, the bismuth
partial charge was plotted as a function of the Bi···CMes(min)
distance.75 The partial charges at the bismuth atoms (Table 4
and Figure 9) were computed at the PBE0/def2svp level of
theory76−78 including the D3(BJ) empirical dispersion.48 In
general, the Bi···CMes(min) distance correlates well with the
NBO charge at the Bi center: the shorter the Bi···mesitylene
contact, the larger the calculated positive NBO charge at Bi
(Figure 9). The only exception was found for the diazido
compound 7. Although this compound exhibits the largest
NBO charge at Bi, the Bi···CMes(min) distance is slightly longer
than in 3 and 6.
CONCLUSION
■
Even though the presented compounds turned out to be
unsuited for the generation of a tetrazabismuthole, we could
synthesize interesting derivatives of TerN(SiMe3)BiCl2 (1) via
different routes, which allowed the study of the reactivity of
aminobismuthanes.
Reactions with Ag[OTf] led to a methyl/triflate exchange
reaction, indicating an extremely Lewis acidic transient species
whose nature could not be established. In fact, a highly Lewis
acidic, anion-stabilized aminobismuthenium salt, 3, could be
synthesized by substituting the remaining chloride in the
methyl/triflate exchange product 2 by a second triflate using a
second equivalent of Ag[OTf]. When TerN(SiMe3)Li and
Bi(OTf)3 were utilized to synthesize TerN(SiMe3)Bi(OTf)2,
small amounts of a C−C coupling product were observed.
F
DOI: 10.1021/acs.organomet.8b00318
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Article
Table 3. Bi/I···Mesitylene Distances in Compound 5 [Å]
C1
C2
C3
C4
C5
C6
Bi
I
3.119(3)
3.683(4)
3.277(4)
3.762(4)
3.832(3)
3.858(5)
4.070(4)
4.009(4)
4.534(4)
4.050(4)
4.668(5)
4.148(4)
Caution! Silver azide (AgN3) is explosive and sensitive toward shock,
heat, and electrical discharge. All manipulations with AgN3 should be
carried out wearing appropriate protective clothing.
Table 4. Summary of NBO Analysis Data (QBi and Qmes in e,
Localization of the Bi−N Bond and Bi Lone Pair in %)
c
d
e
QBi
∑Qmes
Bi−N
Bi−LP
Synthesis of TerN(SiMe2OTf)Bi(Me)Cl (2). To a stirred solution
of TerN(SiMe3)BiCl2 (0.200 g, 0.28 mmol) in toluene (2 mL) was
added a solution of Ag[OTf] (0.072 g, 0.28 mmol) in toluene (1 mL)
dropwise at −25 °C. Upon warming to room temperature, the
reaction mixture was stirred for 1.5 h and filtered (F4). The solvent
was removed in vacuo, and the resulting yellow solid was
recrystallized from benzene at room temperature. Washing with n-
hexane (0.2 mL) and drying in vacuo for 3 h afforded 2·1/2C6H6
(0.152 g, 0.19 mmol, 68.4% yield) as pale-yellow to colorless crystals.
Crystals obtained by recrystallization from benzene were suitable
for single-crystal diffraction. 2 crystallized with two molecules of
benzene. Drying in vacuo led to partial loss of solvent molecules (only
half a molecule of benzene per molecule of 2 was found in the NMR
spectra and CHN analysis).
a
b
b
a
a
a
1
2
3
5
6
7
+1.50
+1.43
+1.64
+1.16
+1.64
+1.73
0.04
0.03
0.07
0.05
0.06
0.05
18
18
16
19
17
16
95
88
89
95
95
95
a
b
Calculated as the dimer. Calculated as monomers as found in the
c
crystal. Sum of the natural charges (NBO-based) at the coordinating
Mes group (in e). Localization of the Bi−N σ bond at Bi (in %). 6s
character of the lone pair (LP) at Bi (in %).
d
e
Mp: 110 °C (decomp.). CHN calcd (found) in %: C 44.69
(44.61), H 4.48 (4.24), N 1.68 (1.65), S 3.85 (4.33). 1H NMR (298.2
K, CD2Cl2, 300.13 MHz, δ): −0.19 (broad, 3H, Si(CH3)(CH3)OTf),
0.18 (broad, 3H, Si(CH3)(CH3)OTf), 1.19 (s, 3H, Bi(CH3)), 2.25
(broad, 12H, o-CH3 from Mes), 2.35 (broad, 6H, p-CH3 from Mes),
6.99−7.07 (broad (three resonances), 7H, arom. CH), 7.36 (s, 3H,
1/2C6H6). 19F{1H} NMR (298.2 K, CD2Cl2, 282.38 MHz, δ): −76.80
(s).
Synthesis of TerN(SiMe2OTf)Bi(Me)OTf (3). At −40 °C, a
solution of Ag[OTf] (0.154 g, 0.60 mmol) in toluene (1 mL) was
added to a stirred solution of TerN(SiMe3)BiCl2 (0.200 g, 0.29
mmol) in toluene (2 mL). The reaction mixture was warmed to room
temperature and stirred for 2.5 h. Upon filtration (F4), the solvent
was removed in vacuo, and the resulting yellow solid was
recrystallized from benzene at room temperature. The crystals were
washed with n-hexane (0.2 mL) and dried in vacuo for 3 h, affording
3·1/2C6H6 (0.178 g, 0.20 mmol, 70.0% yield) as a yellow solid.
Crystals obtained by recrystallization from benzene were suitable
for single-crystal diffraction. 3 crystallized with one molecule of
benzene. Drying in vacuo led to partial loss of solvent molecules (only
half a molecule of benzene per molecule of 3 was found in the NMR
spectra and CHN analysis).
Figure 9. Correlation between the NBO charge at Bi1 and the closest
Bi···mesitylene contact.
It was also shown that exchange of the chlorine atoms in 1
by other halogens (e.g., iodine) and pseudohalogens (e.g.,
azide) was possible. Pseudohalogens can be introduced using
the respective sodium salts, but full conversion into the doubly
substituted pseudohalogen derivative turned out to be difficult.
All of the compounds were structurally characterized and
displayed either monomeric molecular species or centrosym-
metric dimers when a halogen or pseudohalogen was present.
All of the species featured classic bismuth···arene interactions
stabilizing the bismuth compounds. Additionally, for the iodine
species 5 a competition between Bi and I for arene interactions
was found since the iodine also interacts with arenes.
Moreover, a simple correlation between the positive charge
at the bismuth and the shortest Bi···CMes distance was
established in accord with previous studies and the description
of the Bi···π-arene interaction as a Lewis acid−base pair.
Mp: 80 °C. CHN calcd (found) in %: C 40.59 (40.70), H 3.94
(3.77), N 1.48 (1.62), S 6.77 (6.80). 1H NMR (298.2 K, C6D6,
300.13 MHz, δ): 0.19 (broad, 6H, Si(CH3)2OTf), 1.47 (broad, 3H,
Bi(CH3)OTf), 2.07 (broad, 6H, Ter-CH3), 2.13 (broad, 6H, Ter-
CH3), 2.24 (broad, 6H, Ter-CH3), 6.64−6.99 (broad, 7H, Arom.
1
CH), 7.16 (s, 3H, /2C6H6). 19F{1H} NMR (298.2 K, C6D6, 282.38
MHz, δ): −77.43 (s, CF3), −76.32 (s, CF3).
Synthesis of TerN(SiMe3)BiI2 (5). To a stirred solution of
TerN(SiMe3)BiCl2 (0.188 g, 0.16 mmol) in CH2Cl2 (3 mL) is added
Me3SiI (0.065 g, 0.32 mmol, neat) dropwise at −40 °C. The dark red
solution is stirred 15 min at this temperature and concentrated at −40
°C afterward. Storage at −80 °C for 8 h results in the deposition of
red crystals of 5. Removal of the supernatant by syringe, washing with
n-hexane (0.1 mL) at −40 °C and drying in vacuo at room
temperature for 2 h yields 0.044 g (0.05 mmol, 31.9%) 5.
Mp.: 151 °C (Decomp.). CHN calc. (found) in %: C 37.56
1
(37.18), H 3.97 (3.65), N 1.62 (1.58). H NMR (298.2 K, CD2Cl2,
EXPERIMENTAL SECTION
300.13 MHz): − 0.08 (s, 9H, Si(CH3)3), 2.14 (s, 6H, CH3), 2.23 (s,
6H, CH3), 2.36 (s, 6H, CH3), 6.98−7.05 (m, 7H, arom. CH.
Synthesis of TerN(SiMe3)Bi(Cl)N3 (6). TerN(SiMe3)BiCl2
(0.362 g, 0.50 mmol) and NaN3 (0.033 g, 0.50 mmol) were mixed
together as solids and suspended in THF (4 mL) afterward. The
reaction mixture was stirred for 17 h at room temperature. Upon
removal of the solvent in vacuo, the resulting residue was extracted
■
General Considerations. All of the manipulations were carried
out under oxygen- and moisture-free conditions under argon using
standard Schlenk or drybox techniques.
Detailed information regarding experimental procedures and a full
set of analytical data (including IR and Raman spectroscopy, melting
points, etc.) can be found in the Supporting Information.
G
DOI: 10.1021/acs.organomet.8b00318
Organometallics XXXX, XXX, XXX−XXX

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with benzene (3 mL) and filtered (F4). Concentration and storage at
room temperature for 2 h led to the deposition of orange crystals
(needles). The supernatant was removed by syringe and discarded.
Washing with n-hexane (0.2 mL) and drying in vacuo for 3 h afforded
6·1/12C6H6 (0.196 g, 0.29 mmol, 57.1% yield) as an orange solid.
Crystals of 6 obtained from benzene were suitable for single-crystal
diffraction. 6 crystallized with 1 equiv of benzene. Drying in vacuo led
to partial loss of solvent molecules (only 1/12 of a molecule of benzene
per molecule of 6 was found in the NMR spectra and CHN analysis).
Mp: 175 °C (decomp.; red melt and gas evolution). CHN calcd
Synthesis, X-Ray Crystal Structures and Theoretical Calculations. Eur.
J. Inorg. Chem. 2009, 2009, 2247−2253.
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Binaren Molekulverbindungen der Gruppe 15 Elemente Mit P2As2-,
PSb2-, PBi2-, PBi3- und P2Bi4-Gerust. Z. Anorg. Allg. Chem. 2009, 635,
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Phosphaniminato-Komplexe von Bismut(III). Die Kristallstrukturen
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1
(found) in %: C 47.62 (47.58), H 5.01 (4.72), N 8.08 (7.65). H
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NMR (298.2 K, CD2Cl2, 300.13 MHz, δ): −0.19 (broad, 9H,
Si(CH3)3), 2.22 (broad, 12H, o-CH3), 2.37 (broad, 6H, p-CH3),
1
6.94−7.15 (broad, 7H, arom. CH), 7.36 (s, 0.5H, /12C6H6). 29Si
INEPT NMR (298.2 K, CD2Cl2, 59.63 MHz, δ): 10.9 (m).
Reaction of TerN(SiMe3)BiCl2 (1) with an Excess of NaN3.
TerN(SiMe3)BiCl2 (0.200 g, 0.29 mmol) and NaN3 (0.039 g, 0.60
mmol) were mixed together as solids and suspended in THF (4 mL).
The reaction mixture was stirred for 23 h at room temperature, and
the solvent was removed in vacuo afterward. The residue was
extracted with benzene (4 mL) and filtered (F4). Concentration and
storage at room temperature for 3 h led to the deposition of orange
crystals containing 83% 7 and 17% 6. Addition of more NaN3 (0.020
g, 0.31 mmol), stirring in THF (4 mL) over 18 h, and workup as
described above led to orange crystals containing 88% 7 and 12% 6. It
was not possible to synthesize pure 7 with this method. Spectra of the
mixed compound are given in the Supporting Information.
(7) Veith, M.; Bertsch, B.; Huch, V. Zur Element-Stickstoff-
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Bonding Modes for Boraamidinate Ligands in Heavy Group 15
Complexes: Fluxional Behavior of the 1:2 Complexes, LiM[PhB-
(NtBu)2]2 (M = As, Sb, Bi). Inorg. Chem. 2007, 46 (7), 2627−2636.
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of the Cyclic Amido Bismuth Imide, {[(Me3Si)2N]Bi[μ-N(SiMe3)]}2,
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00318.
■
S
Synthesis of starting materials and compounds,
description of additional experiments, NMR, IR, and
Raman spectra, details of the X-ray structures and
ORTEP depictions, and computational details (PDF)
Cartesian coordinates (XYZ)
Accession Codes
CCDC 1841999−1842005 and 1854602 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by e-mailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, U.K.; fax: +44 1223
336033.
(13) Burford, N.; Cameron, T. S.; Macdonald, C. L. B.; Robertson,
K. N.; Schurko, R.; Walsh, D.; McDonald, R.; Wasylishen, R. E.
Dissociation of 2,4-Bis(2,4,6-Tri-Tert-Butylphenyl)-Cyclo-1,3-Dipnic-
ta-2,4-Diazanes (Pnict = P, As, Sb) Imposed by Substituent Steric
Strain: A Cyclobutane/Olefin Analogy. Inorg. Chem. 2005, 44 (22),
8058−8064.
(14) Burford, N.; Landry, J. C.; Ferguson, M. J.; McDonald, R.
Synthesis of Cyclo-2,4,6-Triarsa-1,3,5-Triazanes from Cyclo-2,4-
Diarsa-1,3-Diazanes Demonstrating the General Influence of Sub-
stituent Steric Strain on the Relative Stability of Pnictazane
Oligomers. Inorg. Chem. 2005, 44 (16), 5897−5902.
(15) Burford, N.; Cameron, T. S.; Lam, K.-C.; LeBlanc, D. J.;
Macdonald, C. L. B.; Phillips, A. D.; Rheingold, A. L.; Stark, L.;
Walsh, D. Synthesis and Characterization of an Homologous Series of
Bis(Amido)Diazadipnictetidines (Pnict = P, As, Sb, Bi). Can. J. Chem.
2001, 79 (3), 342−348.
(16) Raston, C. L.; Skelton, B. W.; Tolhurst, V.-A.; White, A. H.
Geminal Arsa(III)Amide and Trisubstituted Antimony and Bismuth
Amides from the Sterically Hindered, N-Functionalised Amido
Ligand [{2-(6-Me)C5H3N}NSiMe3]−. J. Chem. Soc. Dalt. Trans.
2000, 2 (8), 1279−1285.
AUTHOR INFORMATION
Corresponding Author
*E-mail for A.S.: axel.schulz@uni-rostock.de.
ORCID
Axel Schulz: 0000-0001-9060-7065
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
We thank Dr. Dirk Michalik, Brigitte Goronzi, and Heike
Borgwald for measuring the NMR spectra. Universitat Rostock
is acknowledged for providing access to the high-performance
computing facilities.
■
̈
(17) Suzuki, H.; Matano, Y. Organobismuth Chemistry; Elsevier:
Amsterdam, 2001.
(18) Clegg, W.; Compton, N. A.; Errington, R. J.; Norman, N. C.;
Wishart, N. Synthesis and X-Ray Crystal Structure of a Homoleptic
Bismuth Amide. Polyhedron 1989, 8 (12), 1579−1580.
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