Low-coordinate bismuth cations

Article abstract of DOI:10.1021/ic500113g

Chloride abstraction from the diamido-bismuth compound Bi(Me ₂Si{NAr}₂)Cl (1, Ar = 2,6-i-Pr₂C ₆H₃) using MCl₃ (M = Al, Ga) is a facile route to cationic species. Stoichiometric reactions afford the tetrachlorometallate salts [Bi(Me₂Si{NAr}₂)][MCl₄] (2a, M = Al; 3a, M = Ga), whereas reaction with 0.5 equiv of the group 13 reagent gives the μ-chlorido bridged cations [{Bi(Me₂Si{NAr}₂)} ₂(μ-Cl)][MCl₄] (2b, M = Al; 3b, M = Ga). The crystal structure of 2a shows a formally two-coordinate bismuth cation, with a Bi...Cl contact to the [AlCl₄]^- anion, whereas the structure of 3b shows a total of three Bi...Cl contacts to [GaCl ₄]^-. Both species associate as {1:1}₂ dimers in the solid state through additional Bi...Cl interactions. Attempted preparation of cationic complexes using either NaBR₄ (R = Ph, Et) or [HNEt₃][BPh₄] were unsuccessful. Instead of forming the borate salts, the neutral compounds Bi(Me₂Si{NAr}₂)R (4, R = Et; 5, R = Ph) were isolated as a result of aryl/alkyl transfer from boron to bismuth.

Full text of DOI:10.1021/ic500113g

Article
pubs.acs.org/IC
Low-Coordinate Bismuth Cations
Ryan J. Schwamm,† Benjamin M. Day,§ Martyn P. Coles,*,† and Christopher M. Fitchett‡
†School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand
§Department of Chemistry, University of Sussex, Falmer, Brighton BN1 9QJ, U.K.
‡Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch 8041, New Zealand
S
* Supporting Information
ABSTRACT: Chloride abstraction from the diamido-bismuth
compound Bi(Me2Si{NAr}2)Cl (1, Ar = 2,6-i-Pr2C6H3) using
MCl3 (M = Al, Ga) is a facile route to cationic species.
Stoichiometric reactions afford the tetrachlorometallate salts
[Bi(Me2Si{NAr}2)][MCl4] (2a, M = Al; 3a, M = Ga), whereas
reaction with 0.5 equiv of the group 13 reagent gives the μ-
chlorido bridged cations [{Bi(Me2Si{NAr}2)}2(μ-Cl)][MCl4]
(2b, M = Al; 3b, M = Ga). The crystal structure of 2a shows a
formally two-coordinate bismuth cation, with a Bi···Cl contact
to the [AlCl4]− anion, whereas the structure of 3b shows a
total of three Bi···Cl contacts to [GaCl4]−. Both species
associate as {1:1}2 dimers in the solid state through addi-
tional Bi···Cl interactions. Attempted preparation of cationic
complexes using either NaBR4 (R = Ph, Et) or [HNEt3][BPh4] were unsuccessful. Instead of forming the borate salts, the neutral
compounds Bi(Me2Si{NAr}2)R (4, R = Et; 5, R = Ph) were isolated as a result of aryl/alkyl transfer from boron to bismuth.
1. INTRODUCTION
Commercially available BiX3 compounds (X = halogen, triflate,
nitrate) are used as Lewis acidic reagents to promote a range of
organic transformations1 and polymerization reactions.2 More
recently cationic bismuth compounds have been investigated,3,4
developing the concept that an increased electrophilicity
associated with the positively charged metal center will enhance
the activity of the reagents. Due in part to the large radius of
the element [Shannon ionic radii Bi3+: 6-coordinate = 1.03 Å;
8-coordinate = 1.17 Å],5 much of the research on cationic
bismuth compounds has focused on the application of
multidentate ligands able to provide additional interactions to
support the metal center.6 Prominent among these examples
are the potentially tridentate systems based on either a
dianionic (C,E,C) framework (E = N, O, S),4,7 or the mono-
anionic (E,C,E)-system.8,9 Relatively little work has been
directed toward the study of low-coordinate bismuth cations.
A survey of the Cambridge Structural Database10 was con-
Figure 1. Graph showing the coordination number of structurally
ducted to examine the distribution of coordination numbers
characterized bismuth cations (bismuth clusters defined as compounds
associated with crystallographically characterized cationic
containing three or more Bi atoms in the structure).
bismuth compounds. The results, displayed in Figure 1, were
divided into three classes: bismuth(III), bismuth(V), and
number there is a fairly even split between Bi(III) and higher
nuclearity “cluster” compounds, with far fewer examples of Bi(V)
cations. The exception is the 4-coordinate species, for which a large
number of [BiAr4]+ cations have been structurally determined.
bismuth clusters (defined in this survey as species containing
three or more Bi atoms). Most examples have been reported in
which the bismuth is 4-coordinate (52.5%), with 6- and 8-
coordinate bismuth each representing 12.0% of the total
number of structures listed in the database. Both high- (>8-co-
ordinate: 7.6%) and especially low- (<4-coordinate: 3.8%) co-
ordinate species are poorly represented. For each coordination
Received: January 20, 2014
© XXXX American Chemical Society
A
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The only structurally characterized two-coordinated bismuth
cation is supported by the bulky diamido-ligand [Me2Si{Nt-Bu}2]2−
(I, Figure 2).11 The salt is generated by chloride abstraction
were complicated by transfer of the R-group and formation of
Bi(Me2Si{NAr}2)R.
2. EXPERIMENTAL SECTION
2.1. General. All manipulations were carried out under dry
nitrogen using standard Schlenk-line and cannula techniques, or in a
conventional nitrogen-filled glovebox. Solvents were dried over
appropriate drying agents and degassed prior to use. NMR spectra
were recorded using a Bruker Avance DPX 300 MHz spectrometer
at 300.1 (1H) and 75.4 (13C) MHz or a Varian VNMRS 500 MHz
spectrometer at 500.1 (1H), 160.4 (11B), 125.4 (13C), and 99.3 (29Si)
MHz. Proton and carbon chemical shifts were referenced internally
to residual solvent resonances. 29Si NMR chemical shifts were ob-
tained from 1H−29Si heteronuclear multiple-bond correlation
(HMBC) spectra. Elemental analyses were performed by S. Boyer at
London Metropolitan University. BiCl3 was freshly sublimed prior to
the synthesis of Bi(Me2Si{NAr}2)Cl (1), which was made according to
our previously published procedure.18 [HNEt3][BPh4] was synthe-
sized from [HNEt3]Cl and Na[BPh4] according to the procedure
described by Evans and co-workers.9 All other chemicals were
purchased from commercial sources and used as received.
2.2. Preparation of [Bi(Me2Si{NAr}2)][AlCl4] (2a). A solution of
1 (0.100 g, 0.15 mmol) in toluene (5 mL) was added dropwise to a
stirred suspension of AlCl3 (0.019 g, 0.15 mmol) in toluene (5 mL).
The resulting dark red solution was stirred for 4 h followed by
concentration and storage at −30 °C. After 24 h, dark red crystals were
obtained. Yield 0.105 g, 88%. Anal. Calcd. for C26H40N2AlBiCl4Si
(786.47): C, 39.71; H, 5.13; N, 3.56%. Found: C, 39.85; H, 5.01; N,
Figure 2. Examples of structurally characterized bismuth cations
containing tetrachlorometallate anions (see text for references).
3.68%. 1H NMR: δ 7.26 (d, 3JHH = 7.7 Hz, 4H, m-CH), 6.60 (t, 3JHH
=
7.7 Hz, 2H, p-CH), 3.49 (m br, 4H, CHMe2), 1.21 (br, 24H, CHMe2),
0.13 (s, 6H, SiMe2). 13C{1H} NMR: δ *, 148.5, 128.8, 122.5 (C6H3),
28.2 (CHMe2), 27.0 (br, CHMe2), 10.4 (SiMe). * o-C not observed.
29Si NMR: δ 38.0.
2.3. Generation of [{Bi(Me2Si{NAr}2)}2(μ-Cl)][AlCl4] (2b).
Method 1NMR Scale. A solution of 2a (0.020 g, 0.026 mmol) in
C6D6 (0.5 mL) was added to 1 (0.085 g, 0.013 mmol). The 1H NMR
spectrum indicated complete consumption of starting materials after
10 min at room temperature.
from the neutral Bi(III) precursor Bi(Me2Si{Nt-Bu}2)Cl,
using MCl3 (M = Al, Ga, and In), to afford the corresponding
tetrachlorometallate species. This strategy for cation production
has been applied to other bismuth systems.12−17 The aluminum
reagent AlCl3 dominates as the chloride abstraction agent, with
relatively few reports on the use of GaCl3,11,15,17 and only a
single report of this reactivity being achieved with InCl3;11
these trends presumably reflect the differing Lewis acidity of the
group 13 reagents.
The solid-state structure of the tetrachloroaluminate salt I
contains long-range Bi···Cl interactions between the [Bi(Me2Si-
{Nt-Bu}2)]+ cation and chlorides from two [AlCl4]− anions,
generating a polymeric chain parallel to the b-axis of the unit
cell. Such moderation of positive charge in bismuth salts
through the formation of intermolecular Bi···Cl contacts to the
[MCl4]− counterions is relatively common, and may be
augmented by additional associations in the solid state. For
example, the reaction of BiCl3 and AlCl3 in the presence of
hexamethyl benzene affords the {1:1}2 dimeric salt with an η3-
bonded aromatic ring (II),12 whereas generating the [BiCl2]+
cation in the presence of SbPh3, using toluene as solvent,
restricted the aggregation to the monobismuth species (III).16
The only structurally characterized tetrachlorogallate salt of
bismuth involves the N,N′,N′-tris(trimethylsilyl)hydrazido
ligand (IV).15 In this example bismuth is involved in three-
center four-electron bonding to the two ligands, precluding the
formation of interion Bi···Cl interactions with the [GaCl4]−
anion.
Method 2Preparative Scale. A solution of 1 (0.040 g, 0.061
mmol) in toluene (2 mL) was added to a stirring suspension of AlCl3
(0.004 g, 0.031 mmol) in toluene (2 mL). The resulting suspension
1
was stirred for 4 h followed by the removal of volatiles. H NMR
1
analysis of the crude product revealed formation of 2b. H NMR: δ
7.24 (d, 3JHH = 7.8 Hz, 4H, m-CH), 6.74 (t, 3JHH = 7.8 Hz, 2H, p-CH),
3
3.86 (br sept, 4H, CHMe2), 1.25 (d, JHH = 6.6 Hz, 24H, CHMe2),
0.20 (s, 6H, SiMe2).
2.4. Generation of [Bi(Me2Si{NAr}2)][GaCl4] (3a). Method
1NMR Scale. A solution of 2b (0.020 g, 0.026 mmol) in C6D6
(0.5 mL) was added to 1 (0.009 g, 0.013 mmol). The 1H NMR
spectrum indicated complete consumption of starting materials after
10 min at room temperature.
Method 2Preparative Scale. A solution of 1 (0.040 g, 0.061
mmol) in toluene (2 mL) was added to a solution of GaCl3 (0.011 g,
0.061 mmol) in toluene (2 mL). Removal of the volatiles followed by
1
1H NMR analysis of the crude products revealed formation of 3a. H
3
3
NMR: δ 7.28 (d, JHH = 7.8 Hz, 4H, m-CH), 6.58 (t, JHH = 7.8 Hz,
3
2H, p-CH), 3.51 (sept, JHH = 6.7 Hz, 4H, CHMe2), 1.24 (br, 24H,
CHMe2), 0.13 (s, 6H, SiMe2).
2.5. Preparation of [{Bi(Me2Si{NAr}2)}2(μ-Cl)][GaCl4] (3b). A
solution of 1 (0.100 g, 0.15 mmol) in toluene (4 mL) was added
dropwise to a stirring suspension of GaCl3 (0.013 g, 0.075 mmol) in
toluene (4 mL). The resulting dark red solution was stirred for 2 h
followed by concentration of the solution and storage at −30 °C. After
24 h, small dark red crystals of 3b were obtained. Yield 0.047 g, 40%.
Anal. Calcd. for C52H80N4Bi2Cl5GaSi2 (1482.34): C, 42.13; H, 5.44; N,
In this Contribution we examine the scope and limitations
of cation formation, using Bi(Me2Si{NAr}2)Cl, (1, Ar = 2,6-i-
Pr2C6H3),18 as a starting material. Compound 1 is stable under
anaerobic conditions, and we have demonstrated that the
chelating diamide ligand is a stable platform for further
derivation of the Bi−Cl bond. While formation of cationic
species is relatively straightforward using MCl3 (M = Al, Ga),
attempts at synthesizing salts containing borate anions [BR4]−
1
3.78%. Found: C, 41.97; H, 5.31; N, 3.90%. H NMR: δ 7.25 (d,
3
3JHH = 7.8 Hz, 4H, m-CH), 6.74 (t, JHH = 7.8 Hz, 2H, p-CH), 3.90
3
3
(sept, JHH = 6.8 Hz, 4H, CHMe2), 1.27 (d, JHH = 6.8 Hz, 24H,
CHMe2), 0.21 (s, 6H, SiMe2). 29Si NMR: δ 31.2. 13C{1H} NMR data
B
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could not be obtained due to decomposition of 3b in solution over
extended periods of time.
Cl (1) is most clearly evident from inequivalent SiMe2
resonances at δH 0.60 and 0.07 ppm.18 Formation of a planar
2-coordinate Bi cation would, however, generate a single set of
ligand resonances in the NMR spectrum, predicted for a C2h
ligand environment.
2.6. Preparation of Bi(Me2Si{NAr}2)Ph (4). Method 1Prepara-
tive Scale from Bi(Me2Si{NAr}2)Cl + NaBPh4. A solution of 1 (0.100 g,
0.15 mmol) in toluene (5 mL) was added dropwise to a stirring
suspension of NaBPh4 (0.051 g, 0.15 mmol) in toluene (5 mL). The
resulting solution was stirred for 72 h at 90 °C, followed by removal of
the volatiles. Extraction into hexane and filtering through Celite
resulted in a clear yellow solution. The solution was concentrated and
stored at −30 °C. After 24 h, a number of white crystals of BPh3 were
deposited. Further concentration and storage at −30 °C yielded a
second crop of crystals, identified as a mixture of BPh3 and 4. Yield
0.070 g, 67%.
The reaction between Bi(Me2Si{NAr}2)Cl and one equiv of
AlCl3 in toluene proceeds with an immediate color change
from yellow to deep red. Concentration and cooling of the
resultant solution to −30 °C afforded deep red crystals of the
tetrachloroaluminate salt, [Bi(Me2Si{NAr}2)][AlCl4] (2a,
1
Scheme 1). The H NMR spectrum shows a single sharp
Method 2NMR Scale from Bi(Me2Si{NAr}2)Et + [HNEt3][BPh4]. A
solution of 5 (0.020 g, 0.031 mmol) in C6D6 was added to
[HNEt3][BPh4] (0.013 g, 0.031 mmol). The 1H NMR spectrum
revealed complete formation of 4 and BPh3 after 0.5 h at room
temperature.
a
Scheme 1. Synthetic Routes to Bismuth Cations 2 and 3
Anal. Calcd. for C32H45N2BiSi (694.78): C, 55.32; H, 6.53; N,
4.03%. Found: C, 55.48; H, 6.64; N, 3.95%. 1H NMR: δ 8.48 (d, 3JHH
3
= 7.5 Hz, 2H, o-C6H5), 7.57 (t, JHH = 7.5 Hz, 1H, p-C6H5), 6.95 (t,
3JHH = 7.5 Hz, 2H, m-C6H5), 4.30 (sept, 3JHH = 6.8 Hz, 4H, CHMe2),
3
1.28 (d, JHH = 6.8 Hz, 24H, CHMe2), 0.63, 0.15 (s, SiMe2). 13C{1H}
NMR: δ 148.0 (br, C6H5), 147.2 (C6H3), 140.9 (C6H3), 136.2 (C6H5),
131.6 (C6H5), 129.4 (C6H3), 128.4 (C6H3), 124.5 (C6H5), 27.8 (br,
CHMe2), 25.1 (br, CHMe2), 17.5, 4.8 (SiMe). 29Si NMR: δ 19.5.
2.7. Preparation of Bi(Me2Si{NAr}2)Et (5). A solution of 1 (0.100 g,
0.15 mmol) in toluene (5 mL) was added dropwise to a stirring suspension
of NaBEt4 (0.023 g, 0.15 mmol) in toluene (5 mL). The resulting
solution was stirred for 24 h at room temperature, followed by removal
of the volatiles and extraction into hexane. The resulting suspension
was filtered through Celite and concentrated, followed by storage at
−30 °C. After 24 h, clear yellow crystals were formed. Yield 0.061 g,
63%. Anal. Calcd. for C28H45N2BiSi (646.73): C, 52.00; H, 7.01; N,
a
(i) 2MCl3 (2 M = Al; 3 M = Ga).
peak for the SiMe2 protons at δH 0.13 ppm and broad
resonances at δH 3.49 and 1.21 ppm for the iso-propyl methine
and methyl protons, respectively (Figure 3a). These data are
consistent with the formation of [Bi(Me2Si{NAr}2)]+, although
we recognize that a number of alternative structures involving
cation···anion interactions in the solution state also fit these
data (Supporting Information, Figure S1). There is a notable
low-field shift of the 29Si NMR resonance upon generation of
the cation, from δSi = 29.7 ppm in 1 to δSi = 38.0 in 2a (ΔδSi =
+8.3 ppm). This indicates that changes to the environment at
the bismuth center influence spectroscopic properties of the
remote silicon atom, which therefore serves as a convenient
handle to probe the electronic state of the metal in solution.
The analogous NMR scale reaction between 1 and GaCl3
(1 equiv) in C6D6 proceeded in a similar manner, with an
immediate color change on mixing to afford a deep red
1
4.33%. Found: C, 51.91; H, 7.12; N, 4.24%. H NMR: δ 7.19 (d,
3
3JHH = 7.6 Hz, 4H, m-CH), 6.99 (t, JHH = 7.6 Hz, 2H, p-CH), 4.28
3
3
(sept, JHH = 6.9 Hz, 4H, CHMe2), 2.47 (t, JHH = 8.1 Hz, 3H,
3
CH2CH3), 2.04 (q, JHH = 8.1 Hz, 2H, CH2CH3), 1.31 (br, 24H,
CHMe2), 0.42 (s, 3H, SiMe2), 0.04 (s, 3H, SiMe2). 13C{1H} NMR: δ
147.9, 141.4, 124.2, 123.5 (C6H3), 27.7 (CHMe2), 25.9, 25.4
(CHMe2), 15.6 (SiMe), 8.7 (CH2CH3), 5.2 (SiMe). BiCH2CH3 was
not observed. 29Si NMR: δ 17.8.
2.8. Crystal Structure Data. Crystals were covered in inert oil,
and suitable single crystals were selected under a microscope and
mounted on a Enraf Nonius Kappa CCD diffractometer (2a) or an
Agilent SuperNova diffractometer fitted with an Atlas detector (3b,
4, 5). Data was collected at 173(2) K (2a) or 120.01(10) K (3b, 4, 5)
using Mo Kα radiation at 0.71073 Å (2a, 4, 5) or Cu Kα radiation
at 1.5418 Å (3b). The structures were refined with SHELXL-97.19
Additional features of note are listed below:
[{Bi(Me2Si{NAr}2)}2(μ-Cl)][GaCl4] (3b). The compound crystallizes
with a molecule of hexane in the unit cell.
Bi(Me2Si{NAr}2)Ph (4). The toluene solvate was located on an
inversion center and was refined at half-occupancy; hydrogen atoms
were not included in this model.
1
solution. The H NMR spectrum was similar to that observed
for isolated 2a, with SiMe2, CHMe2, and CHMe2 resonances at
δH 3.51, 1.24, and 0.13 ppm, respectively, and are assigned to
the tetrachlorogallate analogue of 2a, [Bi(Me2Si{NAr}2)]-
[GaCl4], 3a (Figure 3d). Attempted isolation of 3a at −30 °C,
however, gave two visually distinct species that cocrystallized as
pale yellow and deep red solids. The lighter-colored solid was
1H NMR silent and had a melting point of 78−79 °C, con-
sistent with GaCl3 (mp 77.9 02 °C).20 Mechanical separation
enabled full characterization of the red crystals, including single-
crystal X-ray diffraction analysis, which identified the crystals as
the dibismuth cation [{Bi(Me2Si{NAr}2)}2(μ-Cl)][GaCl4]
(3b).
Bi(Me Si{NAr} )Et (5). The data solves in both the R3 and R3 space
̅
2
2
groups; the latter model (in which the molecule is located on an inver-
sion center) is presented. The disorder was modeled as alternative
positions of the BiEt/SiMe2 groups, with a single position for the NAr
groups. There are large solvent channels in the crystal structure
containing a poorly resolved and unidentified solvent; this was not
modeled in the solution.
1
The H NMR spectrum of an isolated sample of 3b is also
3. RESULTS AND DISCUSSION
consistent with a C2h symmetric structure in solution, with
selected peaks shifted notably downfield from the correspond-
ing resonances for the [Bi(Me2Si{NAr}2)]+ cation in 3a
(Figure 3c). These chemical shift differences are most prom-
inent for the p-C6H3 (δH 6.74 ppm), CHMe2 (δH 3.90 ppm),
and SiMe2 (δH 0.21 ppm) resonances in 3b, with ΔδH values of
3.1. Reaction of Bi(Me2Si{NAr}2)Cl with MCl3 (M = Al,
Ga, In). NMR spectroscopy is a convenient tool for the
detection of changes to the Bi environment in relation to the
chelating diamide ligand. The C1 symmetry imposed by the
pyramidal geometry of the bismuth atom in Bi(Me2Si{NAr}2)
C
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Figure 3. 1H NMR spectra of cationic Bi compounds 2a, 2b, 3a, and 3b. (a) 2a from isolated [Bi(Me2Si{NAr}2)][AlCl4]; (b) 2b from
[Bi(Me2Si{NAr}2)][AlCl4] + 1 equiv of Bi(Me2Si{NAr}2)Cl (1); (c) 3b from isolated [{Bi(Me2Si{NAr}2)}2(μ-Cl)][GaCl4]; (d) 3a from
[{Bi(Me2Si{NAr}2)}2(μ-Cl)][GaCl4] + 1 equiv of GaCl3.
0.16, 0.39, and 0.08 ppm, respectively. As for 2a, the 29Si NMR
resonance is shifted to low field (δSi = 31.2 ppm), although the
magnitude of the shift is much less than it is in the mono-
bismuth cation (ΔδSi = +1.5). These data show that the
bimetallic [{Bi(Me2Si{NAr}2)}2(μ-Cl)]+ cation is not retained
as a rigid unit in solution.
Addition of 1 equiv of GaCl3 to an NMR sample of 3b in
C6D6 resulted in complete conversion to 3a. In light of these
results, the aluminum system was re-examined to determine
whether similar interconversion between 2a and the tetra-
chloroaluminate analogue of 3b is possible. Addition of one
1
equiv of 1 to a solution of 2a gave a H NMR spectrum con-
sistent with [{Bi(Me2Si{NAr}2)}2(μ-Cl)][AlCl4] (2b, Figure 3b),
with a maximum Δδ of 0.04 ppm (CHMe2) compared with the
spectrum obtained from 3b.
Veith reported that Bi(Me2Si{Nt-Bu}2)Cl also underwent
chloride abstraction to afford the cation formed when reacted
Figure 4. Thermal ellipsoid plot (30% probability, H-atoms omitted)
of [Bi(Me2Si{NAr}2)][AlCl4] (2a).
with InCl3.11 However no color change was observed when
InCl3 was added to a solution of 1, and NMR analysis indicated
that no reaction had occurred. Attempts to promote cation
bond lengths and angles, along with those of the previously
reported structure of compound 1 are presented in Table 2.
The compound crystallizes as the {1:1} salt with the closest
Bi···Cl contact of 2.953(3) Å, considerably longer than the
terminal Bi−Cl bonds in 1 [2.556(1) Å and 2.4857(16) Å].
The Bi−N distances in 2a are within 3σ of those in the neutral
compound, albeit with a trend toward shorter bonds. The
bismuth atom in 2a deviates slightly from the N2Si least-squares
plane (0.09(1) Å), which contrasts with the endo conforma-
tion21 of 1 in which displacements of 0.294(6) and 0.229(8) Å
of the bismuth from this plane are observed. This shift con-
tributes to the larger ligand bite angle of 73.7(3)° in 2a
compared with values of 70.74(16)° and 71.78(11)° observed
in 1.
formation by heating the mixture to 80 °C afforded an
1
intractable mixture of species by H NMR, and no clean prod-
uct could be isolated. No detailed analysis of changes to the
electronic structure upon replacing the nitrogen substitutents
from t-Bu in Veith’s compound to 2,6-i-Pr2C6H3 in 1 have been
performed to explain this lack of reactivity. However, differences
in the steric profile of the ligands are evident from the solid-state
structures of the chlorides, where Bi(Me2Si{Nt-Bu}2)Cl forms a
one-dimensional (1-D) chain linked by Bi···Cl interactions and 1
is trimeric with Bi···aryl π-bonding interactions.
The molecular structure of the tetrachloroaluminate salt
[Bi(Me2Si{NAr}2)][AlCl4] 2a is shown in Figure 4, with crystal
structure and refinement data collected in Table 1; selected
D
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Table 1. Crystal Structure and Refinement Data for [Bi(Me2Si{NAr}2)][AlCl4] (2a), [{Bi(Me2Si{NAr}2)}2(μ-Cl)][GaCl4] (3b),
Bi(Me2Si{NAr}2)Ph (4), and Bi(Me2Si{NAr}2)Et (5)
2a
3b·C6H14
2(4)·C7(H8)
5
empirical formula
Mr
C26H40AlBiCl4N2Si
C58H94Bi2Cl5GaN4Si2
1568.48
C135H180Bi4N8Si4
2863.15
C28H45BiN2Si
646.73
786.45
T [K]
173(2)
120.01(10)
120.02(10)
120.0
crystal size [mm]
crystal system
space group
a [Å]
0.08 × 0.08 × 0.01
orthorhombic
0.10 × 0.08 × 0.02
triclinic
0.35 × 0.16 × 0.05
triclinic
0.21 × 0.15 × 0.14
trigonal
Pbcn (No.60)
P1 (No.2)
̅
P1 (No.2)
̅
R3 (No.148)
̅
28.7503(11)
24.9726(10)
12.8472(5)
17.0713(7)
17.4081(7)
117.739(4)
92.142(3)
12.9068(2)
15.6323(4)
17.3240(5)
108.940(2)
93.6783(18)
100.2794(18)
3224.91(14)
1
b [Å]
16.6486(4)
28.7503(11)
c [Å]
16.1717(6)
9.8541(5)
α [deg]
β [deg]
γ [deg]
90
90
90
90
90
90.447(3)
120
V [Å3]
6723.5(4)
3375.4(3)
7053.9(6)
Z
8
2
9
Dcalc. [mg m−3
]
1.55
1.54
1.47
1.37
absorption coefficient [mm−1
]
5.64
12.97
5.53
5.67
2θ range for data collection [deg]
reflections collected
7.02 to 54.16
26421
2.87 to 74.00
26092
5.32 to 60.0
66037
5.66 to 66.22
16452
independent reflections
reflections with I > 2σ(I)
data/restraints/parameters
final R indices [I > 2σ(I)]
final R indices (all data)
GOF on F2
7374 [Rint 0.161]
4578
13265 [Rint 0.034]
11200
18799 [Rint 0.035]
15967
5348 [Rint 0.072]
4288
7374/0/316
R1 = 0.077, wR2 = 0.163
R1 = 0.131 wR2 = 0.189
1.018
13265/36/671
R1 = 0.031, wR2 = 0.073
R1 = 0.040, wR2 = 0.080
1.036
18799/0/714
R1 = 0.024, wR2 = 0.053
R1 = 0.033, wR2 = 0.056
1.036
5348/114/179
R1 = 0.129, wR2 = 0.272
R1 = 0.151 wR2 = 0.280
1.323
a
largest diff. peak/hole [e Å−3
]
3.64 and −3.18
1.66 and −2.15
1.82 and −0.97
1.88 and −3.13
a
Close to Bi.
There is a relatively large range of Al−Cl bond lengths in the
Bi−Cl distances are longer than the terminal chloride bonds
in 1 and shorter than the closest Bi···Cl ion-contact in 2a,
suggesting an intermediate bonding type with delocalization
across the Bi−Cl−Bi moiety. The asymmetry is in good
agreement with the only other structurally characterized mono
chloride-bridged cation, [{t-BuN(CH2C6H4)2Bi}2(μ-Cl)][B-
(C6F5)4],7 for which ΔBiCl = 0.11 Å. As noted for 2a, there is
no significant decrease in Bi−N bond lengths upon generation
of the cation, and the Bi atoms are essentially coplanar with
the chelating diamide (deviation from the N2Si least-squares plane =
0.088(8) and 0.050(7) Å for Bi1 and Bi2, respectively), generating
relatively large ligand bite angles of 72.08(15)° and 72.21(15)°.
The interion Bi···Cl distances in the asymmetric unit of 3b
span the range of 3.3168(2)−3.5618(2) Å and are considerably
shorter than they are in the crystal structure of IV in which no
bismuth-to-tetrachlorogallate contacts are described.15 Two of
the interactions in 3b involve Bi2, also consistent with this
being the more positive metal. The Ga−Cl bond lengths (range
from 2.1622(14) Å to 2.1878(14) Å) span those reported for
IV and the series of [M(crown)n(THF)m][GaCl4] compounds
(M = Li/Na, crown = 12-c-4, n = 2, m = 0; M = Na, crown =
18-c-6, n = 1, m = 0; M = K, crown = 18-c-6, n = 1, m = 2).25
The difference in the Ga−Cl bond lengths within the anion
(ΔGaCl = 0.03 Å) is considerably smaller than the corresponding
difference in the Al−Cl distances of 2a, consistent with all four
chlorides being involved in Bi···Cl interactions. Indeed,
examination of the unit cell of 3b confirms that Cl4 is
associating with a second cation (Cl4···Bi1′ 3.3277(1) Å)
to generate the {1:1}2 aggregate bis{μ-chlorido-[N,N′-
dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido-1κN)]-
[N,N′-dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido-
2κN)]dibismuth(1+)}deca-μ-chlorido-1:3κ4Cl,1:4κ2Cl,1:5κ2Cl,
tetrachloroaluminate anion (ΔAlCl = 0.08 Å), reflecting differing
degrees of Bi···Cl interaction. The longest Al−Cl bond
(2.172(4) Å) involves chloride Cl1, which is most closely
associated with the bismuth. The shortest bond (Al−Cl2,
2.091(5) Å) is at the low end of the range noted for a series of
noncoordinated [AlCl4]− anions within the structurally char-
acterized compounds [M(crown)n(THF)m][AlCl4] (M = Li/Na,
crown =12-c-4, n = 2, m = 0; M = Na/K, crown =18-c-6, n = 1,
m = 2; M = K, crown =15-c-5, n = 2, m = 0: range of Al−Cl
bond lengths = 2.102(2)−2.1469(9) Å),22 consistent with a
terminal chloride ligand. The remaining Al−Cl bonds are
intermediate between these two values and involve chlorides
that are engaged in intermolecular Bi···Cl interactions to
another cation, resulting in an overall {1:1}2 molecular struc-
ture (Figure 5). The bonding mode of the [AlCl4]− anion in
hexa-μ-chlorido-1:3κ4Cl,1:4κ2Cl,2:3κ2Cl,2:4κ4Cl-dichlorido-
1κCl,2κCl-[N,N′-dimethylsilanediylbis(2,6-dipropan-2-ylpheny-
lamido-3κN)][N,N′-dimethylsilanediylbis(2,6-dipropan-2-
ylphenylamido-4κN)]dialuminiumdibismuth ([2a]2) is unusual,
but has been previously observed in polymeric tin23 and samarium24
complexes.
The bismuth component of the tetrachlorogallate salt 3b
consists of a μ-chlorido-bridged monocation in which each
pyramidal Bi atom retains a bidentate diamido-ligand. The inter-
planar angle between the SiN2Bi metallacycles is 144.03(11)°
with a trans−trans arrangement of the ligands with respect to
Si···Bi−Cl−Bi···Si. This unit is supported by three Bi···Cl
interactions to the [GaCl4]− anion (Figure 6). The Bi−Cl1
bond lengths within the cation are inequivalent (2.7888(12)
and 2.6902(12) Å to Bi1 and Bi2, respectively; ΔBiCl = 0.10 Å),
suggesting a localization of positive charge on Bi2. Both of the
E
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Table 2. Selected Bond Lengths (Å) for 2a and 3b, Presented
with Those of 1 for Comparison
a
b
c
1
2a
3b
Bi−N
2.132(3)
2.144(3)
2.181(3)
2.118(8)
2.120(8)
2.121(4)
2.131(3)
2.143(3)
2.152(3)
Bi−Cl
Bi···Cl
2.4857(16)
2.5560(10)
2.6902(12)
2.7888(12)
3.3168(14)
3.3277(13)
3.5373(16)
3.5618(14)
1.734(4)
Figure 6. Thermal ellipsoid plot (30% probability, H-atoms and
hexane solvate omitted) of [{Bi(Me2Si{NAr}2)}2(μ-Cl)][GaCl4] (3b).
2.953(3)
[N,N′-dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido-
4κN)][N,N′-dimethylsilanediylbis(2,6-dipropan-2-ylphenyla-
mido-5κN)][N,N′-dimethylsilanediylbis(2,6-dipropan-2-ylphe-
nylamido-6κN)]digalliumtetrabismuthate(2-) in the solid state
([3b]2, Figure 7). This is the only structurally characterized
Si−N
1.733(3)
1.735(3)
1.736(3)
1.763(9)
1.765(8)
1.736(4)
1.748(4)
1.752(4)
M−Cl
2.091(5)
2.134(4)
2.152(4)
2.172(4)
73.7(3)
2.1622(14)
2.1689(15)
2.1770(13)
2.1878(14)
72.08(15)
72.21(15)
92.67(17)
N−Bi−N
N−Si−N
Bi−N−Si
70.74(16)
71.78(11)
92.58(15)
93.3(2)
92.1(4)
97.17(14)
97.54(13)
97.71(14)
97.1(3)
97.0(3)
97.00(17)
97.64(18)
97.88(18)
98.16(17)
94.28(11)
97.56(11)
97.76(10)
101.12(11)
N−Bi−Cl
96.34(9)
96.37(9)
97.89(9)
94.2(2)
98.1(2)
a
b
c
1.5 molecules in the unit cell. M = Al. M = Ga.
Figure 7. Molecular structure of [3b]2, showing the bridging [GaCl4]−
anions (′ = −x, −y, −z; aryl groups reduced to show only ipso-carbon
atoms).
example of the tetrachlorogallate anion interacting through all
four chloride ligands.
3.2. Reaction with M[BR4] (M = Na, R = Ph, Et; M =
HNEt3, R = Ph). Evans and co-workers have shown that the
bis(aryl) bismuth chloride compound BiAr′2Cl (Ar′ = 2,6-
(Me2NCH2)2C6H3) is converted to the tetraphenylborate salt
upon reaction with NaBPh4 (Scheme 2). The cation is also
generated from the protonolysis reaction of the allyl compound
BiAr′2(CH2CHCH2) with [HNEt3][BPh4].9 Monitoring a
1
mixture of 1 and NaBPh4 by H NMR spectroscopy indicated
that the reaction did not proceed at room temperature. Heating
the reaction to 90 °C for 3 d, however, afforded a mixture of
yellow 4 and colorless crystals upon workup. Physical separa-
tion allowed pure samples of 4 to be prepared for analysis by
NMR spectroscopy, elemental analysis, and X-ray diffraction.
1H NMR data for 4 indicate a C1 symmetry structure, with
SiMe2 resonances at δH 0.63 and 0.15 ppm. Integration of the
aromatic region of the spectrum is consistent with the presence
Figure 5. Molecular structure of [2a]2, showing the bridging [AlCl4]−
anions (′ = 1 − x, y, 1/2 − z; aryl groups reduced to show only ipso-
carbon atoms).
1:6κ2Cl,2:4κ2Cl,2:5κ2Cl,2:6κ4Cl,3:4κ2Cl,5:6κ2Cl-[N,N′-
dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido-3κN)]-
F
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Scheme 2. Reaction of Bi(Me2Si{NAr}2)X (1 X = Cl, 5 X =
a
Et) with [A][BR4] (A = Na, R = Ph, Et; A = HNEt3, R = Ph)
a
(i) NaBPh4; (ii) NaBEt4; (iii) [HNEt3][BPh4].
of a single phenyl group, with the peaks assigned to the ortho-
protons at low field (δH = 8.48 ppm, C6D6). This chemical shift
is significantly different from that observed for the [BPh4]−
anion (e.g., [Bi(Ar′)2][BPh4]: δH = 6.99 ppm, CD3CN9) and
BiPh3 (δH = 7.73 ppm, C6D6). These data are consistent with
formation of the phenyl compound Bi(Me2Si{NAr}2)Ph,
confirmed by elemental analysis and an X-ray crystal structure
determination (vide infra). The colorless crystals that formed
during the reaction were identified as BPh3 by 11B NMR
spectroscopy (δB 68 ppm26) and by comparison of their unit
cell with published data.27
Figure 8. Thermal ellipsoid plot (30% probability) of Bi(Me2Si-
{NAr}2)Et, 5 (′ = 1 − x, 1 − y, −z; H-atoms omitted).
Aryl transfer reactions from [BAr4]− anions are well
documented,28 and the reaction of Na[BAr4″] (Ar″ = Ph,
p-tolyl, 4−F-C6H4) with bismuth(III) carboxylates has been
reported recently as a convenient route to BiAr3″ species.29 To
probe this mode of reactivity further we examined the reaction
of 1 with Na[BEt4], where the tetraethylborate anion is known
to behave as an alkyl transfer reagent.30 In this case the reaction
proceeded at room temperature, affording pale yellow crystals
1
on workup. H NMR data was consistent with the bismuth
ethyl compound Bi(Me2Si{NAr}2)Et (5) showing a C1
symmetry (SiMe2: δH = 0.42 and 0.04 ppm). The resonances
for methyl and methylene groups of the ethyl ligand appear as a
triplet and quartet at δH 2.47 and 2.04 ppm, respectively. The
29Si NMR resonances for 4 (δSi = 19.5 ppm) and 5 (δSi = 17.8
ppm) are shifted to higher field compared with 1 (ΔδSi = −10.2
ppm and −11.9 ppm, respectively), reflecting the relatively
electron-rich metallacycle upon exchanging the bismuth
substituent from chloride to aryl/alkyl groups.
Figure 9. Thermal ellipsoid plot (30% probability) of one of the
independent molecules of Bi(Me2Si{NAr}2)Ph, 4 (H-atoms and
toluene solvate omitted).
small energy difference between the two orientations of the
metallacycle with respect to the aryl substituents. As a result the
solution of the data is not of sufficient quality for a meaningful
discussion of bond lengths and angles; it does, however, con-
firm the connectivity of 5 as a rare example of a monomeric
bismuth-ethyl compound (Figure 8).31
The structures of 4 and 5 were determined by single-crystal
X-ray diffraction experiments (Tables 1 and 3; Figures 8 and 9).
Compound 4 crystallizes as the toluene solvate, with two
independent molecules in the unit cell that differ primarily with
respect to the orientation of the phenyl substituent (Figure 9).
Each molecule is monomeric with a pyramidal geometry of the
Bi atom and an essentially planar metallacycle (deviation of Bi
from mean SiN2 plane: Bi1 0.121(4) Å, Bi2 0.037(4) Å). The
Bi−N bond lengths in 4 are longer than in the other structures
examined during this study, resulting in a smaller average bite
angle of 70.68(7)° for the diamide ligand. The Bi−C bond
length (2.253(3) Å) is unexceptional and is within the range
noted for BiPh3 (2.237(7) to 2.273(8) Å).32
Comparing the two molecules within the unit cell we note
that phenyl groups are rotated in opposite directions along the
Bi−Cipso bond relative to the plane bisecting the metallacycle
through the silicon, bismuth, and Cipso atoms (molecule Bi1 =
+14.85(7)°; molecule Bi2 = −29.56(11)°, where +ve = clockwise
directionFigure 10a,b). This twisted orientation brings the
portion of the phenyl group located below the metallacycle into
close proximity with one of the i-Pr groups of the aryl sub-
stituents. The resulting steric conflict is alleviated by the nitrogen
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 4
Bi1−N1
Bi1−N2
Bi1−C27
Si1−N1
2.168(2)
2.177(2)
2.253(3)
1.713(2)
1.726(2)
70.50(7)
98.02(9)
100.50(9)
98.21(9)
97.49(9)
93.65(10)
Bi2−N3
Bi2−N4
Bi2−C58
Si2−N3
2.1790(19)
2.172(2)
2.252(3)
1.721(2)
1.731(2)
70.86(7)
100.32(8)
97.44(9)
97.63(9)
97.59(9)
93.90(10)
Si1−N2
Si2−N4
N1−Bi1−N2
N1−Bi1−C27
N2−Bi1−C27
Bi1−N1−Si1
Bi1−N2−Si1
N1−Si1−N2
N3−Bi2−N4
N3−Bi2−C58
N4−Bi2−C58
Bi2−N3−Si2
Bi2−N4−Si2
N3−Si2−N4
Unfortunately the data solution for compound 5 was
complicated by molecular disorder that was modeled in the
R3 space group as being about an inversion center (Supporting
̅
Information, Figure S2). This disorder is most likely caused by
the small size of the ethyl substituent compared to other
X-groups in the Bi(Me2Si{NAr}2)X compounds, resulting in a
G
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4. DISCUSSION
The paucity of low-coordinate bismuth cations is illustrated by
the facts that 2a is only the second formally two-coordinate Bi+
center to be structurally characterized and that 2a is a derivative
of the first example.11 This is perhaps not surprising given the
large radius of the element and the focus on multidentate
ligands in this area of chemistry. As a consequence, additional
interion (and other intermolecular) interactions become
important in the condensed (solid) state, as shown by the
Bi···Cl contacts present in the structures of 2a and 3b.
Previous work has quantified the bond order (BO) of Bi···Cl
interactions (eq 1),34 using values of r0 = 2.423 Å35 and
B = 0.39.36 We recently used this equation to show that the
intermolecular Bi···Cl BO between associated molecules in the
trimeric unit of 1 was 0.1418 and that this was significantly
less than that calculated for a similar Bi···Cl interaction in the
Nt-Bu analogue (BO = 0.20).37 Table 4 summarizes a series of
BOs for some bismuth chloride compounds and the cor-
responding cations, generated by halide abstraction using MCl3
(M = Al, Ga).
⎡
⎤
(r0 − r)
BO = exp
⎢
⎣
⎥
⎦
B
(eq 1)
According to eq 1, the terminal bismuth chloride bonds in 1
have BOs of 0.85 and 0.71, reflecting the relatively long Bi−Cl
distances. The smaller BO (weaker bond) corresponds to the
chloride involved in bridging interactions to another molecule,
showing the sensitivity of this measurement to small changes in
the environment of the bond. Given that these Bi−Cl BOs are
significantly less than unity, it is perhaps not surprising that
chloride abstraction and generation of bismuth cations is a
relatively facile process.
Conversion of 1 to the cation and association of the formally
positive bismuth metal and the tetrachloroaluminate
anion gives a BO of 0.26 for the primary Bi···Cl interaction,
suggesting a strongly associated ion pair in the solid state with a
reduction of ∼0.5 on generation of the cation (ΔBO = −0.59
and −0.45). Unfortunately, it is not possible to make a direct
comparison with the ΔBO in the corresponding Nt-Bu cation
(I, Figure 2), as the primary Bi−Cl bond in the neutral
compound (BO = 0.43) is already weakened by intermolecular
interactions along a 1-D chain in the crystal structure (vide
supra). Nevertheless a reduction is observed upon generation of
the cation, with the principal Bi···[Cl−AlCl3] BO of 0.19 in this
case approximately equal to the weaker Bi−Cl···Bi bridging
bond along the chain. The calculated BO values for the Bi···
[Cl−AlCl3] interactions of the associated dimer in 2 (Figure 5)
are 0.11 and 0.04 for Cl4 and Cl3, respectively. These values
indicate weak, nonsymmetrical bonding to the second bismuth
cation with values lower than the major interion interactions
in I.
Comparing these BOs with the corresponding values for
other ligand systems shows that the ΔBOs upon cation
generation are highly dependent on the ligand. For example,
the bulky cyclopentadienyl derivative [Bi(Cp″)Cl2]2 has BO
values of 0.75 for the terminal Bi−Cl bonds, with the BOs of
the nonsymmetrical bridging μ-chlorides being 0.53 and 0.19
(average from two crystal modifications). Formation of the
cation retains the dimeric unit, with only minor modifications
to the Bi(μ-Cl)Bi BOs (0.57 and 0.20), and the closest contact
to the [AlCl4]− corresponding to a BO of 0.06.
Figure 10. Schematic representations of the two molecules of 4,
showing (a) the different rotation of the phenyl ligand relative to the
Si···Bi−Cipso vector, (b) the displacement of one of the aryl groups out
of the plane of the metallacycle, and (c) the dimerization of molecule
Bi2 (′ = 2 − x, −y, 1 − z).
aryl-substituent being located above the BiNSiN-plane,
illustrated by the different angles that the N−Cipso bonds
adopt with respect to this plane (molecule Bi1: N1−C1 = 5.9°,
N2−C13 = 15.3°; molecule Bi2: N3−C34 = 9.3°, N4−C46 =
21.2°; see Supporting Information, Figure S3).
The twisting of the phenyl ligand is more pronounced in
molecule Bi2. Examination of the packing shows that this
molecule is involved in intermolecular interactions with a
symmetry generated equivalent positioned about an inver-
sion center (Figure 10c). The para-carbon atom of the
phenyl substituent (C61) is located at 3.629(3) Å from Bi2′
(′ = 2-x, -y, 1-z), within the range of distances previously
attributed to a bonding interaction within the series of
compounds [BiCl3·(C6H6‑nMen)] (Bi···C distances 3.168(7)
to 3.751(8) Å).33 However, the large ring slippage of 2.57 Å
from the centroid of the C6-ring suggests that it is the π−π
interactions between the two phenyl rings that dominate
(centroid−centroid distance 3.827(3) Å, plane-to-plane shift
1.295(5) Å), although the role of crystal packing forces
should not be dismissed.
H
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Table 4. Bond Orders (BOs) for Bi−Cl Bonds and Bi···Cl Interactions, Calculated Using eq 1
Bi−Cl
[Bi]···[Cl-MCl3]
compound
bond order (BO)
bond order (BO)
reference
18
a
[Bi(Me2Si{NAr}2)Cl]3 (1)
0.85
0.71
0.14 (μ-)
[Bi(Me2Si{NAr}2)][AlCl4] (2a)
0.26
0.11
0.04
this work
[Bi(Me2Si{Nt-Bu}2)Cl]∞
0.43 (μ-)
0.20 (μ-)
37
11
[Bi(Me2Si{Nt-Bu}2)][AlCl4] (I)
0.19
0.17
0.03
0.02
a
[Bi(Cp″)Cl2]2
0.75/0.74
0.48/0.57 (μ-)
0.22/0.16 (μ-)
0.57 (μ-)
14, 38
14
[Bi(Cp″)Cl][AlCl4]
0.06
0.06
0.20 (μ-)
Bi(N{SiMe3}N{SiMe3}2)2Cl
0.77
15
15
[Bi(N{SiMe3}N{SiMe3}2)2][GaCl4] (IV)
0.03
0.03
0.10
0.10
0.06
0.05
[{Bi(Me2Si{NAr}2)}2(μ-Cl)][GaCl4] (3b)
0.50 (μ-)
0.39 (μ-)
this work
a
Two different crystal modifications; Cp″ = [1,2,3,4-iPr4C5H]−.
The tetrachlorogallate salt 3b has a nonsymmetrically
AUTHOR INFORMATION
Corresponding Author
* E-mail: martyn.coles@vuw.ac.nz. Phone: +64 (0)4 4636357.
Author Contributions
The manuscript was written through contributions of all
authors.
■
bridging chloride in the cationic unit, with BOs of 0.50 and
0.39. Despite being aligned well within the dimeric unit
(Figure 7), the interion BOs for Bi···[Cl−GaCl3] are only 0.10
to 0.05, indicating a weak interaction. These are only slightly
more than the calculated BOs of 0.03 in [Bi(N{SiMe3}N-
{SiMe3}2)2][GaCl4] (IV).
Funding
In summary, the BOs associated with terminal Bi−Cl bonds
in neutral species are significantly less than those expected for a
single bond, being typically in the range of 0.7−0.8. In contrast
the intermolecular BOs calculated for Bi−Cl···Bi bridges during
the formation of μ,μ-dichlorobridged dimers can be as much as
∼0.55 and during the association of neutral molecules can be
up to ∼0.43. Surprisingly, formation of “contact” ion pairs does
not give such large values of BO between the Bi+ center and the
tetrachloroaluminate anion, despite the electrostatic attraction
between the ions. This is may be due to a delocalization of the
positive charge into the ancillary ligands at Bi (as noted for the
N,N′,N′-tris(trimethylsilyl)hyradzido salt IV) and the relative
exposure of the (long) terminal Bi−Cl bonds compared with
the much shorter Al−Cl bonds.
Victoria Master’s by thesis scholarship (R.J.S.)
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Dr. Richard Hartshorn for help in naming compounds 2a and
3b using the correct “kappa” nomenclature, as currently defined
by IUPAC.
REFERENCES
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ASSOCIATED CONTENT
■
S
* Supporting Information
Alternative solution-state structures for a C2h ligand environ-
ment; additional projections of the crystal structures of 4 and 5;
crystallographic information files (CIF format) for 2a (CCDC
990963), 3b (CCDC 990964), 4 (CCDC 990965), and 5
(CCDC 990966). This material is available free of charge via
the Internet at http://pubs.acs.org.
I
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