Evaluation of bismuth-based dispersion energy donors-synthesis, structure and theoretical study of 2-biphenylbismuth(iii) derivatives

Article abstract of DOI:10.1039/c9cp06924k

A series of 2-biphenyl bismuth(iii) compounds of the type (2-PhC6H4)3-nBiXn [n = 0 (1); n = 1, X = Cl (2), Br (3), I (4), Me (5); n = 2, X = Cl (6), Br (7), I (8)] has been synthesized and analyzed with focus on intramolecular London dispersion interactions. The library of the compounds was set up in order to investigate the Bi?π arene interaction by systematic variation of X. The structural analysis in the solid state revealed that the triarylbismuth(iii) compound 1 shows an encapsulation of the metal atom but the distances between the bismuth atom and the phenyl centroids amount to values close to or larger than 4.0 ?, which is considered to be a rather week dispersion interaction. In the case of monomeric diorganobismuth(iii) compounds 2-5 the moderate crowding effectively hinders the formation of intermolecular donor-acceptor interactions, but allows for intramolecular dispersion-type interactions with the 2-biphenyl ligand. In contrast, the structures of the monoorganobismuth compounds 6-8 show the formation of Bi-X?Bi donor-acceptor bonds leading to the formation of 1D ribbons in the solid state. These coordination bonds are accompanied by intermolecular dispersion interactions with Bi?Phcentroid distances ?. In solution the diorganobismuth(iii) halides 2-4 show a broadening of their NMR signals (H-8, H-8′ and H-9, H-9′ protons of the 2-biphenyl ligand), which is a result of dynamic processes including ligand rotation. For further elucidation of these processes compounds 2, 4 and 7 were studied by temperature-dependent NMR spectroscopy. Electronic structure calculations at the density functional theory and DLPNO-coupled cluster level of theory were applied to investigate and quantify the intramolecular London dispersion interactions, in an attempt to distinguish between basic intramolecular interactions and packing effects and to shed light on the dynamic behavior in solution.

Full text of DOI:10.1039/c9cp06924k

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Preda, S. Scholz, M. Krasowska, K. Bhattacharyya, A. M. Toma, C. Silvestru, M. Korb, T. Rueffer, H. Lang
and A. A. Auer, Phys. Chem. Chem. Phys., 2020, DOI: 10.1039/C9CP06924K.
Volume 19
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Evaluation of bismuth-based dispersion
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/C9CP06924K
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donors – synthesis, structure and theoretical study of
2-biphenylbismuth(III) derivatives
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Ana-Maria Fritzsche,a,f Sebastian Scholz, Małgorzata Krasowska, Kalishankar
a
b
b
a,c
c
d,e
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Bhattacharyya, Ana Maria Toma, Cristian Silvestru, Marcus Korb, Tobias Rüffer,d
d,f
b
a,f
Heinrich Lang, Alexander A. Auer,* Michael Mehring*
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aTechnische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Chemie, Professur
Koordinationschemie, 09107 Chemnitz, Germany
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bMax-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr,
Germany
cBabeş-Bolyai University, Faculty of Chemistry and Chemical Engineering, Department of Chemistry,
Supramolecular Organic and Organometallic Chemistry Centre (SOOMCC), 11 Arany Janos, 400028
Cluj-Napoca, Romania
dTechnische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Chemie, Professur
Anorganische Chemie, 09107 Chemnitz, Germany
eThe University of Western Australia, Faculty of Science, School of Molecular Sciences, Crawley, Perth,
WA 6009, Australia
fCenter for Materials, Architectures and Integration of Nanomembranes (MAIN), Rosenbergstr. 6, 09126
Chemnitz
Email: Michael Mehring*- michael.mehring@chemie.tu-chemnitz.de
Email: Alexander Auer* - alexander.auer@kofo.mpg.de
* Corresponding authors
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Abstract
A series of 2-biphenyl bismuth(III) compounds of the type (2-PhC H ) BiX [n = 0 (1); n = 1,
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4 3-n
n
X = Cl (2), Br (3), I (4), Me (5); n = 2, X = Cl (6), Br (7), I (8)] has been synthesized and analyzed
with focus on intramolecular London dispersion interactions. The library of the compounds was
set up in order to investigate the Bi∙∙∙ arene interaction by systematic variation of X. The
structural analysis in the solid state revealed that the triarylbismuth(III) compound 1 shows an
encapsulation of the metal atom but the distances between the bismuth atom and the phenyl
centroids amount to values close to or larger than 4.0 Å, which is considered to be a rather
week dispersion interaction. In the case of monomeric diorganobismuth(III) compounds 2−5
the moderate crowding effectively hinders the formation of intermolecular donor-acceptor
interactions, but allows for intramolecular dispersion-type interactions with the 2-biphenyl
ligand. In contrast, the structures of the monoorganobismuth compounds 6−8 show the
formation of Bi−X∙∙∙Bi donor-acceptor bonds leading to the formation of 1D ribbons in the solid
state. These coordination bonds are accompanied by intermolecular dispersion interactions
with Bi···Phcentroid distances < 4.0 Å. In solution the diorganobismuth(III) halides 2−4 show a
broadening of their NMR signals (H-8,H-8’ and H-9, H-9’ protons of the 2-biphenyl ligand),
which is a result of dynamic processes including ligand rotation. For further elucidation of these
processes compounds 2, 4 and 7 were studied by temperature-dependent NMR spectroscopy.
Electronic structure calculations at the density functional theory and DLPNO-Coupled Cluster
level of theory were applied to investigate and quantify the intramolecular London dispersion
interactions, in an attempt to distinguish between basic intramolecular interactions and packing
effects and to shed light on the dynamic behavior in solution.
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Keywords: bismuth; 2-biphenyl; London dispersion interaction; single crystal X-ray structure;
DFT-D; DLPNO-CCSD(T); electronic structure calculations.
2
2
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2

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Introduction
Over the past several years, London dispersion interaction of main group elements has
witnessed increasing interest both experimentally1-9 and theoretically,10-16 and was
demonstrated to be relevant in the field of organometallic chemistry with regard to structure
and properties even of small molecules. In recent reports it is discussed that weak dispersion
interactions of the type metal∙∙∙ arene contribute significantly to the assembling processes of
molecular units in supramolecular structures, which might open up new directions of dynamic
structural evolution of supramolecular architectures.6-8 With regard to this and to build up a
better understanding of the basic principles intermolecular London dispersion interactions for
diverse arylbismuth compounds have been studied in our research groups,16-22 and the effect
on polymorphism and phase transition in compounds of the type Ar Bi (Ar = C H NMe, C H O,
1
1
1
1
1
1
1
1
1
1
2
0
1
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3
18, 21
C H S, C H Se) was demonstrated.
In the last years, the importance of intramolecular
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3
4
3
Bi··· arene interactions for the stabilisation of unusual organobismuth compounds, mainly
bearing ligands of the terphenyl type, has been demonstrated by several other research groups
(Scheme 1).23-32 Although it is now well accepted that dispersion interaction plays an important
role in structure formation, there is still need for systematic investigations in order to determine
the influence of e.g. the substituents X in organobismuth(III) compounds of the type Ar BiX
3
-n
n
(n = 0, 1, 2). A future aim is to make use of this type of interactions in supramolecular design
strategies controlled by the strength and nature of the interaction of aryl ligands with bismuth
and other heavy metals.
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1
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Scheme 1. Selected molecules showing intramolecular Bi··· arene interactions with
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significant impact on structure and reactivity.24, 27-32
To reach this goal theoretical work is necessary in addition to experimental studies. So far,
computational studies on pnictogen··· arene interactions address mainly intermolecular
interactions,13, 16, 20-21, 33 whereas only a limited number of studies on intramolecular interactions
of this type is reported.25, 29, 32 For example, intermolecular pnictogen··· arene interaction were
investigated earlier using computational methods (BP86-D3/def2-TZVPD level of theory) by
Frontera and coworkers on a series of systems involving different types of benzene derivatives
1
1
1
1
1
1
1
1
1
1
and the heavier pnictogenes ECl (E = As, Sb, Bi).14, 15 In a more recent paper we have
3
investigated the intermolecular interaction between various compounds of the type BiX (X =
3
H, Me, Ph, OH, OMe, F, Cl, Br) and C H (Scheme 2, A). These studies have shown that the
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nature and strength of the dispersion interaction is strongly influenced by the substituent X.16,
20
The higher the bismuth is polarized by X, the stronger is the interaction and the shorter is
the Bi···Phcentroid distance. The calculations revealed a pure dispersive interaction for the methyl
group, while the chlorine substituent induces a significant donor-acceptor behaviour. This
interplay between dispersion and donor-acceptor properties results from the (→σ*) charge
transfer. Another study was focused on the As, Sb and Bi adducts EX ···C H (X = Me, OMe,
3
6
6
4

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Cl) (Scheme 2, B) and it was analysed how the dispersion interaction strength is altered by
DOI: 10.1039/C9CP06924K
exchanging the pnictogen E. The interaction energies calculated at the DLPNO-CCSD(T) level
-1
-1
increase from As < Sb < Bi and range from -10 kJ mol to -40 kJ mol for ECl ···C H (E = As,
3
6
6
34
Sb, Bi). In a recent paper we have also discussed the interaction between BiCl and benzene
3
derivatives with either one or three substituents being R = CF , NO , NH , OH, OCH(O)
3
2
2
(Scheme 2, C). The results show that the substituents of the arene have a significant influence
on the interaction strength and structure of the formed adducts (e.g. BiCl ···C H R) and
3
6
5
especially substituents that increase the electron density in the aromatic ring increase the
strength of the donor-acceptor interaction and vice versa.35 The overall interaction energy
-1
1
1
0
1
might transcend -70 kJ mol in compounds of the type BiCl ···C H R .
3 6 3 3
R
R
R
R
Bi
X
E
X
Bi
Cl
Bi
Cl
R = CF , NO , NH , OH, OCOH
X
X
X
X
Cl
Cl
Cl
Cl
X = H, CH , Ph, OH,
E = As, Sb, Bi
3
3
2
2
OMe, F, Cl, Br
X = CH , OMe, Cl
3
A
B
C
1
1
2
3
Scheme 2. Different dispersion adducts of aromatic systems with trivalent heavy pnictogen
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1
1
1
1
1
2
2
2
2
2
4
5
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7
8
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0
1
2
3
4
compounds (EX3).16, 20, 34, 35
On the basis of our previous studies here the synthesis, characterization and the crystal
structures of the arylbismuth(III) compounds (2-PhC H ) BiX [n = 0 (1); n = 1, X = Cl (2), Br
6
4 3-n
n
(3), I (4), Me (5); n = 2, X = Cl (6), Br (7), I (8)] are reported (Scheme 3). They are composed
of bismuth acting as DED (Dispersion Energy Donor) and 2-biphenyl as a rigid intramolecular
ligand. The influence of the substituent X on the strength of the intramolecular bismuth···
arene interaction was analysed experimentally and by using electronic structure calculations.
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Results and Discussion
Synthesis
The first report on the synthesis of (2-PhC H ) Bi dates back to 1936, based on the reaction of
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4 3
3
6
the Grignard reagent 2-PhC H MgBr and BiCl . Later on, the synthesis of the related
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4
3
derivatives of the lighter pnictogens, i.e. (2-PhC H ) E (E = P, As and Sb) using the Wurtz-
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4 3
Fittig method, employing sodium was reported.37 However, neither the determination of the
crystal structures of these compounds nor of their halogen derivatives was published so far.
The compounds reported herein of the type (2-PhC H ) BiX [n = 0; (1); n = 1, X = Cl (2), Br
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4 3-n
n
(3), Me (5); n = 2, X = Cl (6), Br (7)] were prepared either via i) salt elimination reactions
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1
1
1
1
1
1
1
1
2
2
2
2
2
between 2-biphenyllithium and BiX (X = Cl, Br), (3:1, 2:1 and 1:1 molar ratio), or methyllithium
3
and (2-PhC H ) BiCl in Et O solution, at −78 °C (Method A, Scheme 3), or ii) solvent-free
6
4 2
2
redistribution reactions between (2-PhC H ) Bi and BiX (1:2 molar ratio) carried out at 130 °C
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4 3
3
(Method B, Scheme 3). The compounds were isolated as colorless crystalline solids in
moderate to good yields. Treatment of the organobismuth(III) bromides in EtOH with KI gave,
via halogen exchange reactions (Method C, Scheme 3), the iodides (2-PhC H ) BiI (4) and (2-
6
4 2
PhC H )BiI (8) as yellow and orange solids in good yields. The compound (2-PhC H ) Sb (9)
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4
2
6
4 3
was prepared using the same synthetic procedure as described for 1 and was obtained as a
colorless solid (Scheme 3). The compounds 1−9 are soluble in common organic solvents, but
the bismuth compounds are air and heat sensitive. In solution and in the solid state the
compounds slowly decompose and hence should at best be stored under inert conditions. The
stability of the organobismuth(III) halides was analysed by time dependent 1H NMR
spectroscopy (see ESI Figures S1 and S2). The compounds decompose in the course of five
to six days via redistribution reactions finally leading to the formation of biphenyl.
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R =
+
-
ECl3
R E E = Bi (1), Sb (9)
Method A
3
3:1
3LiCl
Et O
Et2O + BiBr3
-78 °C
:1
2
RBr
+
nBuLi
RLi
R BiBr (3)
2
2
2
h, -78 °C
-
2LiBr
+
BiBr3
RBiBr2 (7)
1:1
-
LiBr
Et O
2
MeLi
+
R BiCl
2
R BiMe (5)
2
-78 °C
-
LiCl
Method B
melt / 130 °C
:1
R BiX
2
X = Cl (2)
2
R Bi
3
+
BiX3
melt / 130 °C
:2
RBiX2
X = Cl (6), Br (7)
1
Method C
EtOH
:1
KBr
R BiBr
+
+
KI
R BiI (4)
2
2
1
-
EtOH
:2
2KBr
RBiBr2
KI
RBiI2 (8)
1
-
1
2
3
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5
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8
9
Scheme 3. Synthetic routes for the preparation of the organobismuth(III) compounds (2-
PhC H ) BiX (1−8) and (2-PhC H ) Sb (9).
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4 3-n
n
6
4 3
Molecular structures of the triarylpnictogen(III) compounds 1 and 9.
Single crystals suitable for X-ray diffraction analysis of 1 were grown from a n-hexane solution
and the molecular structure is illustrated in Figure 1. Selected bond lengths and angles are
listed in the Figure caption and the crystallographic data are given in Table S1. Compound 1
crystallizes in the monoclinic space group P2 /n and is isomorphous with (2-PhC H ) Sb (9)
1
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4 3
1
1
1
1
1
0
1
2
3
4
(see the ESI, Figure S3). A detailed discussion of the crystal structure of 9 is presented in the
ESI. The molecular structure of 1 shows a trigonal pyramidal geometry at the metal atom with
average C−E−C bond angles of 94.6° for 1. The average values of the Bi−C bond lengths of
20,38,39
2.261 Å are within the ranges reported for other arylbismuthine derivatives, i.e. Ph Bi,
3
40
41
Mes Bi and (p-tolyl) Bi.
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Compound 1 shows an encapsulation of the bismuth atom by the 2-biphenyl ligands
DOI: 10.1039/C9CP06924K
(Bi∙∙∙Phcentroid: 3.99 Å, 4.04 Å and 4.06 Å ), however, the Bi∙∙∙Phcentroid distances are found close
to 4.0 Å, which can be considered as the limit of significant London dispersion interaction for
35
these systems based on previous theoretical work. However, the structure of 1 revealed 1D
ribbon-like structures (Figure S4i) which are formed via C−H···Phcentroid intermolecular contacts
with a distance of C24−H24···Phcentroid 2.55 Å and an angle γ = 5.6° between the ring normal
and the vector between the ring centroid and the hydrogen atom. The 1D ribbons are further
connected via the C−H···Ph intermolecular contacts C43−H43···Phcentroid 3.06 Å (γ = 10.3°) to
give a 2D network in the solid state (see the ESI, Figure S4ii).
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Figure 1. Thermal ellipsoid model of (2-PhC H ) Bi (1) at 50% probability level. Hydrogen
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atoms are omitted for clarity. Selected bond lengths [Å]: Bi1−C1 2.258(3), Bi1−C21 2.267(3),
Bi1−C41 2.257(4), Bi1···Phcentroid(I) 4.06, Bi1···Phcentroid(II) 4.04, Bi1···Phcentroid(III) 3.99. Selected
bond angles [°]: C1−Bi1−C21 95.28(12), C1−Bi1−C41 96.04(12), C21−Bi1−C41 92.33(12),
Bi1−C1−C6 118.1(2), Bi1−C21−C26 118.0(3), Bi1−C41−C46 117.0(2).
Molecular structures of the diarylbismuth halides 2−4 and the diarylmethylbismuthine 5
Single crystals suitable for X-ray crystallography were isolated upon crystallization at ambient
temperature from a n-hexane solution (for 2, 3), from a CHCl solution (for 4) and by slow
3
diffusion of Et O into n-pentane solution at −28 °C (for 5). The molecular structures of the
2
diarylbismuth(III) halides are depicted in Figures 2−5, the selected bond lengths and angles
are listed in the Figure captions, and their crystallographic data are given in Table S1. The
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compounds crystallize in the triclinic space group P-1 (2 and 4) and the monoclinic space
DOI: 10.1039/C9CP06924K
groups P2 /n (3) and P2 (5). The asymmetric unit of 2 comprises two crystallographically
1
1
independent molecules, denoted as 2a (Bi1) and 2b (Bi2). Related bond length and angles of
2a and 2b differ by up to 2%, however, in the following we focus on data of 2a. All the
compounds show monomeric structures in the solid state with intramolecular dispersion
interactions of the type Bi··· arene. The corresponding Bi···Phcentroid distances are Bi1···
Phcentroid(I) 3.92 Å (2a, Figure 2i), Bi1···Phcentroid(I) 3.82 Å (3, Figure 3i) and for 4 Bi1···Phcentroid(I)
3.89 Å and Bi1···Phcentroid(II) 3.98 Å (Figure 4i). The angle ’, which is defined as the angle
between the ring normal and the vector between the ring centroid and the bismuth atom,
amounts to 46.5°. At least one of the Bi−C−C angles for 2a (Bi1−C13−C18 116.3(2)°), 3
(Bi1−C13−C18 114.6(3)°) and 4 (Bi1−C1−C6 116.2(8)°, Bi1−C13−C18 117.4()°) is slightly
compressed in comparison to the triorganobismuthine 1. This is indicative for a dispersion
interaction between bismuth and one phenyl moiety in 2−4.
1
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1
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0
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1
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1
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1
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2
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3
Figure 2. Thermal ellipsoid model of (2-PhC H ) BiCl (2) at 50% probability level showing: i)
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the molecular structure of 2a. Hydrogen atoms are omitted for clarity, except those involved
showing intra- or intermolecular contacts. Selected bond lengths [Å]: Bi1−C1 2.264(3),
Bi1−C13 2.263(3), Bi1−Cl1 2.519(1), Bi1···Phcentroid(I) 3.92 (γ‘ = 46.5°), Bi1···Phcentroid(II) 4.26,
H14···Cl1 2.81. Selected bond angles [°]: C1−Bi1−C13 93.30(12), C1−Bi1−Cl1 89.64(8),
C13−Bi1−Cl1 92.89(9), Bi1−C1−C6 120.8(2), Bi1−C13−C18 116.2(2). ii) dimer association:
C17−H17···Phcentroid 2.73 Å (γ = 2.9°), C20−H20···Phcentroid 2.93 Å (γ = 6.8°). Symmetry
transformations: a = 1 − x, −y, 1 –z.
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Due to the Bi··· arene interactions the geometry at the bismuth atoms is best described as
distorted pseudo−trigonal bipyramidal with the Phcentroid trans to the halogen atom
[Phcentroid−Bi1−Cl1 161.9° (for 2), Phcentroid−Bi1−Br1 161.5° (for 3)] and the carbon atoms placed
in the equatorial positions [C1−Bi1−C13 93.30(12)°, C1−Bi1−Cl1 89.64(8)°, C13−Bi1−Cl1
92.89(9)° (for 2a), C1−Bi1−C13 96.09(17)°, C1−Bi1−Br1 92.33(14)°, C13−Bi1−Br1 93.63(14)°
(for 3)].
9
0
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
Figure 3. i) Thermal ellipsoid model of (2-PhC H ) BiBr (3) at 60% probability level. Hydrogen
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4 2
1
2
3
4
5
6
7
8
9
0
1
2
3
4
atoms are omitted for clarity, except those involved showing intra- or intermolecular contacts.
Selected bond lengths [Å]: Bi1−C1 2.240(5), Bi1−C13 2.252(5), Bi1−Br1 2.655(7),
Bi1···Phcentroid(I) 3.82 (γ‘ = 43.4°), Bi1···Phcentroid(II) 4.06, H14···Br1 2.94. Selected bond angles
[°]: C1−Bi1−C13 96.09(17), C1−Bi1−Br1 92.33(14), C13−Bi1−Br1 93.63(14), Bi1−C1−C6
118.8(3), Bi1−C13−C18 114.6(3). ii) wire and stick model of 1D ribbons (view along the c-axis):
C20−H20···Phcentroid 2.94 Å (γ = 12.6°), C5a−H5aarene···Phcentroid 3.07 Å (γ = 14.5°). Symmetry
transformations: a = −1 + x, 1 + y, z.
Intramolecular Bi···Ph contacts in 4 lead to a distorted square pyramidal coordination geometry
at the bismuth atom, with the carbon atom C13 of one 2-biphenyl ligand placed in the axial
positions. The basal plane of the square pyramid is described by the two Phcentroid ligands, the
iodide atom and the carbon atom C1 of the second aryl ligand. This is supported by the bond
angles C1−Bi1−C13 of 94.9(4)°, C13−Bi1−I1 of 93.9(3)°, C13−Bi1−Phcentroid(I) of 72.9°,
C13−Bi1−Phcentroid(II) of 69.2°, Phcentroid(I)−Bi1−I1 of 158.8° and Phcentroid(II)−Bi1−C1 of 158.6°.
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Compounds 2a and 4 both form centrosymmetric dimers via two different C−H∙∙∙Ph
DOI: 10.1039/C9CP06924K
intermolecular contacts for 2a (C17b−H17barene···Phcentroid 2.73
Å
(γ
=
2.9°),
C20b−H20barene···Phcentroid 2.93 Å, γ = 6.8°, Figure 2ii) and for 4 (C22−H22arene···Phcentroid 2.77
Å, γ = 6.7°, see Figure 4ii). Moreover, the dimers in 2a are connected via two additional
intermolecular Cl···H contacts, Cl2a···H5c 2.75 Å and Cl1b···H21e 2.86 Å, which results in the
formation of a 2D network in the solid state (Figure S5). In 4 the dimeric associates are
connected via C−H···Phcentroid intermolecular contacts with C10−H10arene···Phcentroid distances
of 2.81 Å (γ = 10.7°) leading to the formation of 1D ribbon-like structures (view along the a-
axis, Figure S6). Noteworthy, compound 3 also forms a 1D ribbon (view along the c-axis) in
the solid state via two different C−H···Phcentroid intermolecular contacts with C20−H20···Phcentroid
2.94 Å (γ = 12.6°), C5a−H5a···Phcentroid 3.07 Å (γ = 14.5°) (Figure 3ii).
1
1
0
1
1
1
2
3
Figure 4. Thermal ellipsoid model of (2-PhC H ) BiI (4) at 50% probability level showing: i) the
6
4 2
1
1
1
1
1
1
2
4
5
6
7
8
9
0
molecular structure of 4. Hydrogen atoms are omitted for clarity, except those involved showing
intra- or intermolecular contacts. Selected bond lengths [Å]: Bi1−C1 2.264(11), Bi1−C13
2.248(11), Bi1−I1 2.8829(8), Bi1···Phcentroid(I) 3.89 (γ‘ = 48.5°), Bi1···Phcentroid(II) 3.98 (γ‘ = 39.9°),
C2−H2···I1 3.05. Selected bond angles [°]: C1−Bi1−C13 94.9(4), C1−Bi1−I1 94.7(3),
C13−Bi1−I1 93.9(3), Bi1−C1−C6 116.2(8), Bi1−C13−C18 117.4(8). ii) dimer association:
C22−H22···Phcentroid 2.77 Å (γ = 6.7°). Symmetry transformations: a = 1 − x, 1 − y, 1 – z.
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4
In addition the molecules of the monohalides 2a−4 reveal the presence of intramolecular
DOI: 10.1039/C9CP06924K
C−H···halogen contacts, with distances of C14−H14···Cl1 2.81 Å (for 2a, Figure 2ii),
C14−H14···Br1 2.94 Å (for 3, Figure 3i) and C2−H2···I1 3.05 Å (for 4, Figure 4i), which are
shorter than the sum of the van der Waals radii of the corresponding atoms (rvdW (H, Cl) =
4
2
5
6
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2
3
4
5
6
7
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9
3.02 Å, rvdW (H, Br) = 3.06 Å and rvdW (H, I) = 3.24 Å). Due to these intramolecular C−X···H
interactions, the molecules are arranged in such a way that the halogen atom is placed closer
to a 2-biphenyl ligand of the same molecular unit than to the bismuth atom of the neighbouring
molecule.
The heteroleptic triorganobismuth(III) compound 5 crystallises in the space group P2 with two
1
1
1
1
1
1
1
1
1
1
1
crystallographically independent molecules. Both molecules adopt a distorted trigonal
pyramidal geometry at the bismuth atom with average C−Bi−C bond angles of 93.0° (5a and
5b). In 5a the Bi···Phcentroid distances are 4.11 Å and 4.19 Å, and 4.10 Å and 4.24 Å in 5b. The
Bi−C−C angles are close to 120° [5a: Bi1−C14−C19 120.8(12)° and Bi1−C2−C7 121.0(12)°;
5a: Bi2−C44−C49 122.5(12)° and Bi1−C32−C37 120.1(13)°;], and thus not indicative for a
significant intramolecular interaction between bismuth and the phenyl groups. Intermolecular
Bi···Phcentroid contacts are neither found (Figure S7).
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1
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5
6
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8
9
Figure 5. Thermal ellipsoid model of (2-PhC H ) BiMe (5) at 30% probability level. Hydrogen
6 4 2
atoms are omitted for clarity. Selected bond lengths [Å]: 5a (left): Bi1−C1 2.25(2), Bi1−C2
2.263(18), Bi1−C14 2.249(14), Bi1···Phcentroid(I) 4.11 and Bi1···Phcentroid(II) 4.19. Selected bond
angles [°]: C1−Bi1−C2 95.0(7), C1−Bi1−C14 89.7(6), C2−Bi1−C14 94.4(6), Bi1−C2−C7
120.8(12), Bi1−C14−C19 121.0(12). 5b (right): Bi2−C31 2.23(2), Bi2−C32 2.285(17), Bi2−C44
2.265(16), Bi2···Phcentroid(I) 4.10 and Bi2···Phcentroid(II) 4.24. Selected bond angles [°]:
C31−Bi2−C32 95.6(7), C31−Bi2−C44 88.9(6), C32−Bi2−C44 94.5(6), Bi2−C32−C37
120.1(13), Bi2−C44−C49 122.5(12).
1
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1
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1
2
Figure 6. Comparison of the intramolecular Bi∙∙∙Phcentroid distances and the Bi−C−C bond
angles in the monomers of 2a, 3, 4 and5a as observed in the solid state.
3
4
5
6
7
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2
3
4
5
6
7
Analysis of the crystal structures of 2−5 reveals that the moderate crowding at the bismuth
atom hinders strong intermolecular donor-acceptor interactions and that weak C−H∙∙∙ arene
interactions determine the crystal packing. Intramolecular Bi···Ph contacts are observed in the
range 3.82 Å − 4.31 Å for the monomers, with the Bi···Phcentroid distances following the order 3
< 4 < 2 < 5 (Figure 6). It might be concluded, that these interactions hinder free rotation of the
biphenyl ligands, but the H···X contacts might also contribute to the stabilization of rotational
isomers. For the diorganobismuth halides 2−4, the Bi−C−C bond angles are significantly
compressed (deviation from ideal angle of 120°), while for 5 the Bi−C−C bond angles are close
to 120°. This implies that in the organobismuth(III) halides the bismuth∙∙∙ arene interaction is
significantly more attractive in comparison to the triorganobismuth(III) compound 5. However,
the trend for the Bi···Phcentroid distance does not follow the trend predicted for the interaction
between bismuth halides and a  arene ligand. This suggests that packing effects in the crystal
interfere with the weak intramolecular interaction. In order to assess, quantify and rationalize
1
1
1
1
1
1
1
1
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these results, an electronic structure calculations on the isolated molecular species was carried
DOI: 10.1039/C9CP06924K
out, which will be discussed in a following section.
Crystal structures of the arylbismuth(III) dihalides 6−8
Colorless, light yellow and orange single crystals suitable for X-ray crystallography were
isolated upon crystallization by slow diffusion of n-pentane into Et O solution at −28 °C (for 6),
2
at ambient temperature by slow diffusion of n-hexane into CHCl solution (for 7) and from a
3
CH Cl solution at ambient temperature (for 8), respectively. The molecular structures of the
2
2
arylbismuth(III) dihalides 6−8 are depicted in Figures 7−9, the selected bond lengths and
angles are listed in the Figure captions and their crystallographic data are given in Tables S1
and S2. The compounds crystallize in the orthorhombic space group P2 2 2 (for 6), the
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
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0
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6
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0
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5
6
7
8
1
1 1
monoclinic space group P2 /c (for 7) and triclinic space group P-1 (for 8) respectively.
1
Compound 7 shows a disorder of the 2-biphenyl group with an occupancy ratio of 0.59:0.41.
Thus, the supramolecular structures are shown and discussed only for the molecule that shows
the higher occupancy for the aryl ring. The asymmetric units of 6 and 7 comprise one molecule
of (2-PhC H )BiX , with Bi1‒C1, Bi‒X1 and Bi‒X2 bond lengths of: 2.230(7) Å, 2.684(2) Å and
6
4
2
2.476(2) Å (for 6); 2.234(11) Å, 3.124(1) Å and 2.610(1) Å (for 7). Compound 8 shows two
crystallographically independent molecules in the asymmetric unit with Bi1−C1, Bi1−I1 and
Bi1−I2 bond lengths of 2.247(5) Å, 3.0274(5) Å, 2.8353(5) Å and Bi2−C21, Bi2−I3 and Bi2−I4
bond lengths of 2.257(6) Å, 3.0191(5) Å and 2.8183(5) Å, respectively. The Bi−X bond lengths
are in accordance with those observed for primary and secondary Bi-X bonds in other
43, 44
arylbismuth dihalides such as [PhBiX (thf)] (X = Cl, Br, I).
The crystal structure analyses of
2
6 and 7 reveal long Bi···Phcentroid distances (Bi1···Phcentroid 3.94 Å for 6, Figure 7i and
Bi1···Phcentroid 3.86 Å for 7, Figure 8i). For the independent molecules of compound 8 the
intramolecular Bi···Phcentroid distances amount to 4.044 Å for molecule 8a and 3.911 Å for
molecule 8b (Figure 9i). An indication for the intramolecular dispersion type Bi··· arene
interaction are the Bi1−C1−C6 bond angles (6: 117.2(5)°, 7: 117.1(8)°, 8 116.7(4) and
Bi2−C21−C26 118.3(4)°), which deviate from the ideal angle of 120°. Significant differences
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2
3
were not observed for the intramolecular Bi···Phcentroid distances in 6−8; they are slightly larger
DOI: 10.1039/C9CP06924K
than those observed for compounds 2−4. However, a clear trend on the intramolecular
Bi···Phcentroid distances related to the nature of X does not become obvious.
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
Figure 7. i) Thermal ellipsoid model of (2-PhC H )BiCl (6) at 50% probability level and ii) 1D
6
4
2
ribbon-like structure (view along the a-axis). Hydrogen atoms are omitted for clarity, except
those involved showing intramolecular contacts. Selected bond lengths [Å]: Bi1−C1 2.230(7),
Bi1−Cl1 2.684(2), Bi1−Cl2 2.476(2), Bi1a−Cl1 2.909(2) Å, Bi1···Phcentroid(I) 3.94 (γ‘ = 50.7°),
intermolecular Bi1···Phcentroid(II) 3.42 Å (γ‘ = 8.9°), C2−H2···Cl2 2.739. Selected bond angles [°]:
C1−Bi1−Cl1 85.2(2), C1−Bi1−Cl2 93.6(2), Cl1−Bi1−Cl2 91.8(6), Cl1−Bi1a−Cl1a 165.6(4),
Cl1−Bi1a−Cl2a 95.3(6), Bi1−C1−C6 117.2(5), Bi1−Cl1−Bi1a 109.8(1). Symmetry
1
1
1
1
1
1
1
1
1
1
1
transformations: a = 2 − x, ∕ + y, ∕ – z.
2
2
The structures of the arylbismuth(III) dihalides show the formation of 1D ribbons which occurs
through short intermolecular Bi···X interactions approximately trans to the opposite halogen
atom from the neighbouring molecule (6: Cl1a−Bi1a···Cl1 165.6(4)°); 7: Br1a−Bi1a···Br1
167.59(2)°; 8: I1−Bi1···I3 176.3(14)°; I3a−Bi2a···I1 177.7(14)°). The secondary bridging Bi···X
distances are as follows; 6: Bi1a···Cl1 2.909(2) Å, (cf. rvdW(Bi, Cl) 3.82−4.36 Å,42, 45);
1
9
Bi1a···Br1 2.790(1) Å, (cf. rvdW(Bi, Br) 3.90−4.40 Å 42, 45); 8: Bi1···I3 3.221(5) Å, Bi2a···I1
2
2
2
0
1
2
3.209(2) Å; (rvdW(Bi, I) 4.05−4.58 Å 42, 45). The primary Bi−X distances in the X−Bi···X bridges
are, as expected, shorter (6: Bi1−Cl1 2.684(2) Å; 7: Bi1−Br1 3.1240(10) Å; 8: Bi1−I1 3.027(5)
Å, Bi2a−I3a 3.019(5) Å). In addition to these donor-acceptor Bi···X bonds for the dihalides 6−8,
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intermolecular Bi··· arene interactions between the bismuth atom and the phenyl ring of the
DOI: 10.1039/C9CP06924K
neighbouring molecule are established. In combination they lead to the formation of zig-zag
chains along the crystallographic axis (1D ribbons in Figures 7ii-9ii). The Bi···Phcentroid distances
amount to 3.42 Å (for 6), 3.70 Å (for 7), 3.56 Å (for 8) and are comparable to those observed
in [PhBiX (thf)], (X = Cl, Br, I; Bi···Ph
distances in the range between 3.43 Å and 3.54
centroid
2
Å).43, 44 The competition between donor-acceptor and dispersion interaction is commonly
observed for this type of ArBiX compounds. The crystal structures 6 and 7 show very similar
2
features, even they are not isostructural. The environment at the bismuth atom for 6 and 7
becomes distorted octahedral based on the core [(2-PhC H )BiX (Ph ) ], with the C1 atom
centroid 2
6
4
3
1
1
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4
of the biphenyl ligand, the Xbridging atoms and the intermolecular Phcentroid occupying the
equatorial positions. The Phcentroid involved in intramolecular interaction and the terminal
halogen atom are placed in the axial positions with Phcentroid−Bi1−Cl2 159.2° (for 6) and
Phcentroid−Bi1−Br2 162.3° (for 7). In 8 the Bi2 atom adopts a distorted square pyramidal
geometry with the carbon atom of the biphenyl ligand in apical position and the vector of the
intramolecular Bi···Phcentroid contact placed trans to the terminal iodide atom I4. This is reflected
in the bond angles of Phcentroid−Bi2−I4 150.0°, Phcentroid−Bi2−C21 69.6°, Phcentroid−Bi2−I3 112.4°
and C21−Bi2−I3 90.34(17)°. A distorted square pyramidal environment was observed for the
Bi1 atom, with the basal plane formed by the carbon atom C1 of the biphenyl ligand, two Ibridging
atoms and Phcentroid, while the axial position is occupied by I2 (cf. corresponding bond angles
Phcentroid−Bi1−C1 150.2°, I1−Bi1−I3 176.3°, I2−Bi1−C1 96.3°, I2−Bi1−I1 95.1°, I2−Bi3−I1 88.4°,
I2−Bi1−Phcentroid 112.4°.
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7
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9
0
Figure 8. i) Thermal ellipsoid model of (2-PhC H )BiBr (7) at 50% probability level and ii) 1D
6 4 2
ribbon-like structure (view along the a-axis). Hydrogen atoms are omitted for clarity, except H2
involved in intramolecular interaction with a bromine atom. Selected bond lengths [Å]: Bi1−C1
2.234(11), Bi1−Br1 3.1240(10), Bi1−Br2 2.6099(13), Bi1−Br1a 2.7911(10), Bi1···Phcentroid(I)
3.86 (γ = 51.1°), intermolecular Bi1···Phcentroid(II) 3.70 Å (γ‘ = 18.0°), C2−H2···Br2 2.991.
Selected bond angles [°]: C1−Bi1−Br1 79.9(7), C1−Bi1−Br2 96.9(7), C1−Bi1−Br1a 90.3(7),
Br1−Bi1−Br2 95.3(3), Br1−Bi1a−Br1a 167.59(2), Br2−Bi1−Br1a 93.4(3), Bi1−Br1−Bi1a
1
1
105.23(3) Bi1−C1−C6 117.1(8), Symmetry transformations: a = −x, ∕ + y, ∕ – z.
2
2
1
1
1
1
1
1
1
1
1
1
2
3
4
5
6
7
8
Figure 9. i) Thermal ellipsoid model of (2-PhC H )BiI (8) at 50% probability level showing
6 4 2
dimer association of molecules 8a and 8b and ii) 1D ribbon like structure. Hydrogen atoms are
omitted for clarity, except H2 and H10 involved in intramolecular interaction with the iodine
atoms. Selected bond lengths [Å]: Bi1−C1 2.247(5), Bi1−I1 3.0274(5), Bi1−I2 2.8353(5),
Bi2a−I1 3.2091(5) Å, Bi1−I3 3.2205(5) Å, Bi1···Phcentroid(I) 4.04, Bi2−C21 2.257(6), Bi2−I3
3.0191(5), Bi2−I4 2.8183(5), Bi2···Phcentroid(II) 3.91 (γ‘ = 48.7°), intermolecular Bi1···Phcentroid(III)
,
3.56 Å (γ‘ = 18.9°), C2−H2···I4 3.054, C10−H10···I2 3.054. Selected bond angles [°]:
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C1−Bi1−I1 92.88(14), C1−Bi1−I2 96.25(15), C1−Bi1−I3 84.07(14), C21−Bi2−I3 90.34(17),
DOI: 10.1039/C9CP06924K
C21−Bi2−I4 94.45(16), C21−Bi2−I1 90.34(14), I1−Bi1−I2 94.078(13), I1−Bi1−I3 176.289(12),
I2−Bi1−I3 88.367(13), I3−Bi2−I4 92.031(13), I3a−Bi2a−I1 177.743(12), Bi1−I3−Bi2
98.170(14), Bi1−I1−Bi2a 100.114(14), Bi1−C1−C6 116.7(4), Bi2−C21−C26 118.3(4). ii):
Symmetry transformations: a = 1 + x, y, z; b = − x, 1 − y, 1 – z.
Furthermore, a 2D network is formed based on short intermolecular C−H···Cl bonds (for 6)
and C−Harene···Ph contacts (for 7 and 8) between parallel 1D layers connected through C8-
H8b···Cl2a 2.80 Å (for 6, Figure S8), C11−H11···Phcentroid 2.84 Å (γ = 13.1°, for 7, Figure S9)
and C10−H1A···Phcentroid 2.87 Å (γ = 17.1°, for 8, Figure S10).
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
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7
Computational study of diarylbismuth halides 2-4 and the diarylmethlybismuthine 5
As one of the aims of this study is to rationalize intramolecular Bi··· arene interactions using
a library of flexible substituents, the crystallographic analyses are supplemented by
computational studies. While in most of the presented compounds intermolecular interactions
are dominating in the crystal structure, in compounds 2−5 intramolecular Bi··· arene
interactions seem to dominate. Hence, we start by discussing whether the trends observed in
the crystal structures are purely due to intramolecular interactions, or whether crystal packing
effects play a major role.
In order to assess the molecular structures of compounds 2-5, one has to take into account
that this particular system has several “soft” degrees of freedom leading to a rich variety of
possible conformers. In order to compare and assess the structures found by the
crystallographic analysis, first of all, an overview over the most important low energy
conformers has to be obtained. For this purpose, a conformational sampling approach recently
46
published by Grimme et al. was carried out. In this scheme, a multistep multilevel procedure
is used to screen a large part of the conformational space, select the lowest energy conformers
and refine them at a higher level of theory.
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Figure 10. Schematic representation of the four lowest energy conformers I for each
n
3
4
5
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0
1
2
3
4
5
compound (a) R BiCH (2), (b) R BiCl (3), (c) R BiBr (4), and (d) R BiI (5) (R = 2-PhC H ). The
2
3
2
2
2
6
4
lowest energy geometries of each compound are set to zero (energy in kJ/mol, structures see
Figs. 11 and 12).
The relative energies of the lowest energy conformations of 2-5 after a final optimization at the
PBE-D3/def2-TZVP level of theory are shown in Fig. 10. Note that previous studies have
shown that this level of theory provides a good balance between computational effort and
accuracy in comparison to high-level methods.34, 35 The structural parameters, i.e. the
computed Bi···Phcentroid distances and the BiCC angle, are displayed in Fig. 11. For all
compounds, the same structural motif with one close Bi···Ph contact is found as the lowest
energy structure. Given the crystal structures discussed in the previous sections, the results
for the fully relaxed structures are quite remarkable. From methyl to iodide, the bismuth-to-
phenyl centroid distance and the two BiCC angles with the organic substituents
1
1
1
1
1
1
1
6
monotonously decrease from 4.11 to 3.76 Å and from 120.6° to 116.0°, respectively, as might
be expected for an increasing strength of the intramolecular Bi··· arene interaction.
1
1
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1
Compound
d1(X···H) d2(Bi···Ph) d3(Bi···Ph) a1(Bi-C-C)
a2(Bi-C-C)
(
(
(
(
a) R BiCH (2) 2.68 Å 4.05 Å
4.11 Å
3.79 Å
3.77 Å
3.76 Å
119.4°
119.6°
119.3°
119.2°
120.6°
117.1°
116.5°
116.0°
2
3
b) R BiCl (3)
2.82 Å 4.05 Å
2.93 Å 4.04 Å
3.06 Å 4.04 Å
2
c) R BiBr (4)
2
d) R BiI (5)
2
2
3
4
5
6
7
8
9
Figure 11. Lowest energy structures of (a) R BiCH (2), (b) R BiCl (3), (c) R BiBr (4), and (d)
2
3
2
2
R BiI (5) (R = 2-PhC H ) calculated at the PBE-D3/def2-TZVP level of theory. Closest
2
6
4
Bi···Phcentroid distances and shortest halide-hydrogen bond lengths are given.
The question is why the structures observed in the crystal do not show the expected trends.
Figure 12 includes the structures found in the conformational search and in addition the
minimum geometries obtained by optimising the molecular structures as obtained from the
single crystal X-ray structure analysis.
1
1
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0
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2
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Figure 12. Molecular structures of the four lowest energy conformations of (a) R BiCH (2), (b)
2
3
3
4
5
6
R BiCl (3), (c) R BiBr (4), and (d) R BiI (5) (R = 2-PhC H ) R = (2-PhC H ) (in kJ/mol), and
2 2 2 6 4 6 4
comparison with geometries as obtained by optimization of the molecules geometries in the
solid state. Note that the small energy differences between equivalent structures are due to
the numerics of the geometry optimizations.
7
8
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0
1
2
3
4
Obviously, none of the conformers found in the crystal structure represents the most stable
conformer but the molecular structures derived from 5, the chloride 3 and iodide 5 resemble
each other.
1
1
1
1
1
Table 1. Relaxation energies (in kJ/mol) from the experimental crystal structure geometries
(with pre-optimized hydrogen atom postions) to the fully optimized conformer (middle column)
and comparison to the lowest energy conformer from the GFN-XTB simulation (right column).
All structures are optimized at PBE-D3/def2-TZVP level of theory R = (2-PhC H ).
6
4
Crystal Structure
Optimization at PBE-
Comparison with lowest
(experimental)
D3/def2-TZVP level
energy conformer
R BiCH (2)
-60.3
-11.0
-28.1
-56.1
-5.5
-3.2
-3.0
-4.6
2
3
R BiCl (3)
2
R BiBr (4)
2
R BiI (5)
2
22

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Physical Chemistry Chemical Physics
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DOI: 10.1039/C9CP06924K
1
2
3
4
5
6
7
8
9
In Table 1, the energy differences between molecules as present in the crystal (with optimized
hydrogen positions) and the fully optimized geometries along with the energy difference to the
lowest conformer are given. This energy difference arises at least partially from packing effects
but also includes the error of DFT in computing equilibrium geometries. While these two effects
might be difficult to disentangle, the size of the observed effect with around 10-70 kJ/mol
already allows to estimate that packing effects – especially due to CH···π and π···π interactions
in the crystal play a significant role for these structures. This has also been observed in
previous work on the crystal structures of arylbismuth(III) compounds in which computational
methods have been applied to quantify the effects of intermolecular interactions in crystal
1
1
0
1
structures. Here, it was found that typical Bi··· arene interactions for BiPh range in the order
3
1
2
of 30-40 kJ/mol while intermolecular CH··· and ··· interactions yield interaction energies of
1
1
1
1
1
1
1
2
2
3
4
5
6
7
8
9
0
1
similar strength, which results in a rich polymorphism observed in single crystal X-ray structure
analysis.20
Solution NMR studies of compounds 1−9.
1
13
1
Compounds 1−9 were investigated by solution H and C{ H} NMR spectroscopy at ambient
temperature in CDCl solution. The assignment of resonance signals is based on 2D NMR
3
(COSY, Figs. S14−S22; HSQC and HMBC) correlation spectra, according to the numbering
shown in Scheme 4.
2
2
2
3
Scheme 4. Compounds 1−9 and numbering scheme for NMR assignments.
23

Physical Chemistry Chemical Physics
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DOI: 10.1039/C9CP06924K
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
1
The H NMR spectra of compounds 1−9 show the expected resonance signals corresponding
to the aromatic protons of the 2-biphenyl ligand (Figs. 15 and 16). For the diarylbismuth(III)
1
halides 2−4 and the heteroleptic diaryl(methyl)bismuth(III) compound 5 the H NMR spectra
show only one set of signals indicating the equivalence of the organic ligands. A very large
downfield shift is observed for the resonance signals that belong to the H-6 proton placed in
the ortho position to the bismuth atom. The shift depends on the nature of X and increases
following the order 2-PhC H < Me < Cl < Br < I (Fig. 13). Characteristic shifts to δ = 8.86 ppm
6
4
for 2 (X = Cl), 8.96 ppm for 3 (X = Br) and 9.11 ppm for 4 (X = I) are observed, while the
triorganobismuth(III) compounds 1 and 5 show resonance signals at δ = 7.91 ppm and δ =
7.97 ppm, respectively. For comparison the corresponding triarylantimony(III) compound 9 was
prepared, which shows a resonance signal for the H-6 proton at δ = 7.37 ppm. Even more
pronounced downfield shifts were observed in the case of the monoarylbismuth(III) dihalides
6−8 showing a similar dependence (vide infra) on the nature of the substituent X attached to
the bismuth atom (Cl < Br < I, Fig. 14). The corresponding resonance signals for H-6 are
observed at δ = 9.78 ppm for 6 (X = Cl), 10.04 ppm for 7 (X = Br) and 10.42 ppm for 8 (X = I).
In the literature, a similar trend of the chemical shifts with regard to the halide was described
for arylbismuth(III) and arylantimony(III) halides for the signal belonging to the H-6 proton
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
placed in the ortho position to the metal atom. For example, in the series of compounds Ar EX
2
47, 48
and ArEX (E = Sb, Ar = 2-(Me NCH )C H , X = Ar, Cl, Br, I),
(E = Bi, Ar = 2-(Et NCH )C H ,
2 2 6 4
2
2
2
6
4
49
X = Ar, Cl, Br, I) the chemical shift depends on both the metal atom and on the nature of X,
but similar trends with regard to the nature of X are observed (Table 2). There is a small
difference between the chemical shifts in compounds of the type Ar BiX (Δ = 0.10 ppm for Cl
2
4
9
< Br and Br < I each, Ar = 2-(Et NCH )C H ), which is in good agreement with the
2
2
6
4
corresponding values for 2−4 (Δ = 0.10 ppm for Cl < Br and Δ = 0.15 ppm for Br < I). In the
49
case of the reported dihalides (Et NCH )C H )BiX the differences of the chemical shifts of Δ
2
2
6
4
2
= 0.14 ppm for Cl < Br and Δ = 0.28 ppm for Br < I are significantly smaller than those found
in the compounds 6−8 (Δ = 0.26 ppm for Cl < Br and Δ = 0.38 ppm for Br < I). To the best of
24

Page 25 of 52
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1
2
3
4
5
6
7
8
9
knowledge the chemical shift of δ = 10.42 ppm for H-6 in (2-PhC H )BiI is exceptional for
6 4 2
DOI: 10.1039/C9CP06924K
arylbismuth(III) halides.
An explanation for the large downfield shift of the hydrogen atom in ortho position to the
bismuth atom was given by Suzuki and coworkers. Firstly, they point at the participation of H-
6 in hydrogen bonds, i.e. the presence of a weak H···halogen interaction, and secondly to the
anisotropic deshielding effect due to the proximity of the hydrogen atom to the Bi−X bond as
discussed for the chiral bismuthines [2-(Me NCH )C H ][4-MeC H ]BiX (X = para-tolyl, F, Cl,
2
2
6
4
6
4
50
t
51
Br, I) and [2-( BuSO )C H ][4-MeC H ]BiX (X = Cl, Br). Note that our preliminary calculations
2
6
4
6
4
1
of the H NMR chemical shifts indicate that the downfield shift is not reproduced using a
nonrelativistic approach. It seems likely that the increasing downfield shift is mainly due to the
so-called Inverse Halogen Dependence (IHD) which is caused by spin orbit coupling on the
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
1
heavy halogen atom and its effect on the H NMR shift. Similar effects for through space
interactions and an IHD have been reported for iodo alkyl and aryl compounds by Kaupp et al.
and for ion pairs by Ariai et al.52, 53
13
1
The C{ H} NMR spectra of the di- and monoarylbismuth(III) halides also exhibit a downfield
shift for the C-6 carbon resonance signals, which follows the order Cl < Br < I (2: δ = 138.24
ppm, 3: δ = 139.77 ppm, 4: δ = 142.75 ppm, Figure S11, 6: δ = 138.02 ppm, 8: δ = 140.70
ppm, 9: δ = 146.35 ppm, Figure S12).
25

Physical Chemistry Chemical Physics
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1
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1
2
3
Table 2. H NMR chemical shifts and selected distances and angles of compounds 1−4 and
DOI: 10.1039/C9CP06924K
6−8 and compounds of the general formulas Ar EX and ArEX .
2
2
Compounds
Substituent
X
Chemical
shift
δ (ppm)
H∙∙∙X
distance
(Å)
C∙∙∙X
distance
(Å)
C−H∙∙∙X
angle (°)
Lit.
this work
Ar BiX
Ar (1)
7.91
-
-
2
6 4
Ar = 2-PhC H
this work
this work
this work
this work
Cl (2)
Br (3)
I (4)
Me (5)
Cl
8.86
8.96
9.11
7.97
8.30
2.808
2.943
3.034
3.458
3.560
3.727
126.4
125.1
130.9
-
-
-
-
-
-
Ar BiX
2
Ar = Ph
4
4
9
Br
I
Ar
8.36
8.41
7.70
2.820
3.505
-
129.0
-
-
-
-
4
Ar BiX
2
Ar =
2
-(Et
2
NCH
2
)C
6
H
4
49
49
49
47
Cl
Br
I
8.55
8.65
8.75
7.53
2.815
2.925
3.128
-
3.436
3.547
3.814
125.1
125.5
132.1
-
Ar SbX
Ar =
Ar
2
2
-(Me
2
NCH
2
)C
6
H
4
4
4
4
8
8
8
Cl
Br
I
7.86
7.90
7.96
9.78
2.724
2.838
3.104
2.739
3.360
3.481
3.769
3.727
126.3
125.8
129.9
130.9
this work
ArBiX
Ar = 2-PhC H
6 4
Cl (6)
2
this work
this work
Br (7)
I (8)
Cl
10.04
10.42
8.97
2.991
3.054
2.732
3.392
3.682
3.400
126.5
125.1
129.5
44
ArBiX
Ar = Ph
2
4
3
3
Br
I
9.12
9.22
2.774
2.948,
3.496
3.677,
3.694
-
132.6
133.0,
135.6
-
4
2955
49
ArBiX
Ar =
Cl
9.17
-
2
2
2 2 6 4
-(Et NCH )C H
4
9
9
Br
I
Cl
9.31
9.59
8.28
-
-
-
4
3.077
2.764
3.757
3.346
129.9
120.4
49
48
ArSbX
Ar =
2
2 2 6 4
2-(Me NCH )C H
4
8
8
Br
I
8.58
8.68
2.818
3.073
3.473
3.738
126.9
129.9
4
4
5
26

Page 27 of 52
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DOI: 10.1039/C9CP06924K
1
1
2
3
4
Figure 13. Comparison of H NMR spectra (aromatic region) in CDCl of compounds 1−5 and
3
9 showing a large downfield shifts for the resonance signals belonging to H-6 placed in ortho
position to the bismuth atom.
5
1
6
7
8
Figure 14. Comparison of H NMR spectra (aromatic region) in CDCl of compounds 6−8
3
showing a large downfield shift for the resonance signals belonging to H-6 placed in ortho
position to the bismuth atom.
27

Physical Chemistry Chemical Physics
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8
9
0
1
In the H NMR spectra of compounds 2−4 significant broadening of the NMR signals at ambient
temperature is observed, which is indicative for a dynamic process in solution. In order to study
1
the dynamic behavior, variable temperature H NMR spectra were recorded in CD Cl for
2
2
compounds 3 (Figure 15) and 4 (Figure S13), in the temperature range of 293 K to 178 K. At
1
ambient temperature the H NMR spectra of 3 and 4 show characteristic resonance signals at
δ = 7.11 ppm and δ = 7.10 ppm, respectively, which belong to the H-8 and H-8’ protons of the
biphenyl ligand. This might be interpreted as a result of a dynamic interaction of dispersion
type between bismuth and the aryl ligand.
1
1
1
1
1
1
1
1
1
1
1
2
3
4
5
6
7
8
Figure 15. Temperature dependent H NMR spectra of (2-PhC H ) BiBr (3) measured in
6
4 2
CD Cl showing the region for aromatic protons including the numbering scheme.
2
2
As the temperature was lowered, the resonances belonging to the H-8 and H-8’ protons further
coalesced, with a coalescence temperature (T ) of 233 K. The corresponding free energies of
c
activation ΔG are 42.8 kJ mol–1 for 3 and 43.3 kJ mol–1 for 4. For the signal assigned to the
‡
H-9 and H-9’ protons a broadening is observed above 243 K. By subsequent cooling of the
28

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3
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5
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7
8
9
solution to 178 K, the H NMR spectra show two sets of doublet resonances (integral ratio of
DOI: 10.1039/C9CP06924K
1:1), i.e. at δ = 6.51 for H-8 and at δ = 7.47 for H-8’ in 3, at δ = 6.66 for H-8 and δ = 7.44 for
H-8’ in 4 and two sets of triplet resonances (integral ratio of 1:1), i.e. at δ = 7.25 for H-9 and δ
= 7.41 for H-9’ in 3, and at δ = 7.26 for H-9 and at δ = 7.39 for H-9’ in 4. This assignment is
supported by a COSY NMR spectrum of compound 3 at 178 K (Fig. 16). For the aryl protons
(H-3 – H-6) belonging to the aromatic ring C H changes are not observed, being indicative for
6
4
a fast flip of the aryl ligand. These results indicate that at 293 K the aryl groups attached to the
bismuth atom are equivalent and free rotation of the phenyl rings around the C-C bond is
allowed, while at low temperature the dynamic process becomes slower, being consistent with
the nonequivalence of H-8 and H-8’ as well as H-9 and H-9’ protons. Thus, in solution the
rotation of the phenyl group is frozen, but the Bi··· arene interaction does not freeze. The 2-
1
1
1
1
1
1
1
0
1
2
3
4
5
6
1
biphenylbismuth dibromide 7 shows a small upfield shift of its H NMR signals (CD Cl ) at 178
2
2
K, but no significant changes in comparison to the spectrum measured at 293 K are observed,
which indicates the equivalence of H-8 and H-8’ as well as H-9 and H-9’ in the 2-biphenyl
ligand even at low temperature.
1
1
7
8
1
1
Figure 16. H− H COSY NMR spectrum (500.30 MHz) of (2-PhC H ) BiBr (3) recorded in
6
4 2
1
9
CD Cl at 178 K.
2 2
29