Coordination complexes of bismuth triflates with tetrahydrofuran and diphosphine ligands

Article abstract of DOI:10.1021/ic400875a

The reaction of CH₃OSO₂CF₃ (MeOTf) with BiBr₃ in tetrahydrofuran (THF) yields (THF)₂BiBr ₂(OTf) (1), which is converted to (dmpe)BiBr₂(OTf) (2Br) upon displacement of the THF ligands with bis(dimethylphosphino)ethane (dmpe). The chloride derivatives (dmpe)BiCl₂(OTf) (2Cl) and (dmpe)BiCl(OTf)₂ (3) are obtained from the reaction of BiCl ₃ and dmpe with 1 and 2 equiv of Me₃SiOSO ₂CF₃ (TMSOTf), respectively. The complexes readily decompose in solution to give elemental bismuth and a mixture of products. The solid-state structures reveal dimeric units bridged by both triflate O-S-O interactions and weak Bi-X-Bi interactions (X = Cl, Br). Comparison of the solid-state structures illustrates that both cis and trans configurations of halides are possible in complexes of the form L₂BiX₂(OTf), depending upon the denticity of the ligand. The experimentally observed configurations are consistent with minima calculated at the MP2 level for the triflate-free cations in the gas phase. Examination of the MP2-calculated electronic structure of 3 reveals the presence of low-lying π-type orbitals that may result in Z-type ligand activity. However, the attempted coordination of 3 with the electron-rich metal center in K₂PdCl₄, via metal-to-ligand back-donation, leads instead to halide abstraction, giving [(dmpe)₂Pd][(CH₃CN)₂Bi₂Cl ₆(OTf)₂] (8). The anion in 8 consists of two octahedral bismuth environments bridged along one edge by two triflate anions. The results illustrate new coordination chemistry for bismuth.

Full text of DOI:10.1021/ic400875a

Article
pubs.acs.org/IC
Coordination Complexes of Bismuth Triflates with Tetrahydrofuran
and Diphosphine Ligands
Saurabh S. Chitnis,† Neil Burford,*,† Andreas Decken,‡ and Michael J. Ferguson§
†Department of Chemistry, University of Victoria, Victoria, British Columbia, Canada V8W 3V6
‡Department of Chemistry, University of New Brunswick, Fredericton, New Brunswick, Canada E3A 6E2
§Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
S
* Supporting Information
ABSTRACT: The reaction of CH3OSO2CF3 (MeOTf) with BiBr3 in tetrahydrofuran (THF)
yields (THF)2BiBr2(OTf) (1), which is converted to (dmpe)BiBr2(OTf) (2Br) upon
displacement of the THF ligands with bis(dimethylphosphino)ethane (dmpe). The chloride
derivatives (dmpe)BiCl2(OTf) (2Cl) and (dmpe)BiCl(OTf)2 (3) are obtained from the
reaction of BiCl3 and dmpe with 1 and 2 equiv of Me3SiOSO2CF3 (TMSOTf), respectively.
The complexes readily decompose in solution to give elemental bismuth and a mixture of
products. The solid-state structures reveal dimeric units bridged by both triflate O−S−O
interactions and weak Bi−X−Bi interactions (X = Cl, Br). Comparison of the solid-state
structures illustrates that both cis and trans configurations of halides are possible in complexes of the form L2BiX2(OTf),
depending upon the denticity of the ligand. The experimentally observed configurations are consistent with minima calculated at
the MP2 level for the triflate-free cations in the gas phase. Examination of the MP2-calculated electronic structure of 3 reveals the
presence of low-lying π-type orbitals that may result in Z-type ligand activity. However, the attempted coordination of 3 with the
electron-rich metal center in K2PdCl4, via metal-to-ligand back-donation, leads instead to halide abstraction, giving
[(dmpe)2Pd][(CH3CN)2Bi2Cl6(OTf)2] (8). The anion in 8 consists of two octahedral bismuth environments bridged along
one edge by two triflate anions. The results illustrate new coordination chemistry for bismuth.
(THF)2BiBr2(OTf) (1), (dmpe)BiBr2(OTf) (2Br), (dmpe)-
BiCl2(OTf) (2Cl), and (dmpe)BiCl(OTf)2 (3). The new
compounds are bismuth derivatives of recently reported
antimony complexes.3 Moreover, the compounds are analogous
to the recently reported cationic ligands of the form [LPR2]+
and [L3P]3+ (L = carbene), in which the low-lying vacant
acceptor orbitals and the lone pair at the phosphorus atom
impart unusual catalytic behavior to their complexes with
electron-rich late transition metals.16−18 In this context, we
have also examined the potential interaction of 3(OTf)2 with
K2PdCl4, leading to the dianion [(CH3CN)2Bi2Cl6(OTf)2]2−.
INTRODUCTION
■
Coordination chemistry of the p-block elements is superficially
developed in comparison to that of the transition elements but
offers interesting bonding features, especially for the pnictogens
and chalcogens, in which it is possible for the Lewis-acidic
acceptor site to also possess a lone pair of electrons. A variety of
phosphine complexes of low-valent phosphorus,1 arsenic,2 or
antimony3−5 acceptors have recently been reported in which
the Lewis acidity of the lone-pair-bearing acceptor has been
enhanced by the introduction of a cationic charge, illustrating
new structure and bonding and unusual redox chemistry. The
analogous coordination chemistry for bismuth is evidenced
only by [(Ph3P)2BiPh2][PF6]6 and the spectroscopic character-
ization of [Ph3PBiPh2][PF6]6 and [Ph3PBiCl2][AlCl4].7 In view
of the diverse coordination chemistry that is developing for
bismuth with amine donors,8,9 and the established phosphine
complexes of neutral [Bi2Br6(PMe3)4, Bi4Br12(PEt3)4,
Bi2 Br6 (dmpe)2 , Bi2 Br6 (PPhMe2 )2 (OPPhMe2 )2 ,1 0
Bi2Cl6(dppm)2, Bi4Cl12(dppe)5, Bi2Cl6(dppe)3],11 [BiX3{o-
C6H4(PPh2)2}] (X = Br, I), and [BiX3{o-C6H4(PMe2)2}] (X
= Cl, Br, I)12 and anionic ([Bi2Br7(PMe3)2]−,13
[BiI4(dmpe)]−,14 and [BiI4(PhPMe2)]−15) bismuth halides,
we have examined trifluoromethanesulfonate (triflate or OTf)
derivatives of bismuth halides with the expectation of
augmenting the Lewis acidity at bismuth (dmpe = 1,4-
tetramethyldiphosphinoethane, dppm = 1,3-tetraphenyldiphos-
phinomethane, and dppe = 1,4-tetraphenyldiphosphinoethane).
Here we report the synthesis and structural characterization of
EXPERIMENTAL SECTION
■
Reactions were carried out in an Innovative Technologies or MBraun
glovebox under an atmosphere of dry and deoxygenated N2. Large-
scale reactions were performed on a Schlenk line using standard inert-
air techniques under an atmosphere of dry and deoxygenated argon.
Dichloromethane (DCM), toluene, hexane, and n-pentane were
purified on an MBraun solvent purification system. High-performance
liquid chromatography grade MeCN was purchased from Aldrich and
dried by distillation from CaH2 under an atmosphere of argon.
Tetrahydrofuran (THF) was distilled from sodium/benzophenone
under an atmosphere of argon. All solvents were stored over freshly
activated 4 Å molecular sieves. Deuterated solvents were purchased
from Aldrich and dried using 4 Å molecular sieves. MeOTf (>98%)
and dmpe (97%) were obtained from Aldrich and used after
Received: April 9, 2013
© XXXX American Chemical Society
A
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distillation. BiBr3 (Strem Chemicals, 99.999%), BiCl3 (Strem
Chemicals, 99.999%), and K2PdCl4 (Aldrich, 99.99%) were used as
received. TMSOTf (99%) was purchased from Aldrich and distilled
prior to use. NMR spectra were obtained at room temperature, unless
otherwise stated, on a Bruker AVANCE 500 1H (500.13 MHz, 11.7 T)
and a Bruker AVANCE 300 1H (300.15 MHz, 7.02 T). Chemical shifts
(δ) are reported in ppm. 13C (125.76 MHz) chemical shifts are
referenced to δTMS = 0.00 ppm, and 31P (202.46 and 121.56 MHz)
chemical shifts are referenced to δH PO (85%) = 0.00 ppm. Spectra were
(dmpe)BiCl2(OTf) (2Cl). A solution of dmpe (0.150 g, 1 mmol) in
toluene (5 mL) was added dropwise to a suspension of BiCl3 (0.316 g,
1 mmol) and TMSOTf (0.222 g, 1 mmol) in toluene (10 mL). A
yellow precipitate was observed immediately. The reaction was
allowed to stir for 2 h to yield a yellow precipitate under a clear and
colorless supernatant, which was filtered and washed with pentane (3
× 5 mL). Removal of the solvent over 16 h yielded a fine yellow
powder, which was recrystallized from a minimum amount of CH3CN
at −30 °C over 48 h to yield large crystalline blocks, identified as
2Cl·CH3CN using X-ray crystallography. Yield (crystals): 0.337 g,
54%. Mp: 220 °C (dec). 1H NMR (500 MHz, CD3CN, 298 K): δ 2.30
3
4
obtained in an appropriate deuterated solvent in 5 mm tubes that were
capped and sealed with Teflon and Parafilm prior to removal from the
inert atmosphere. Melting points were recorded on an electrothermal
apparatus in sealed capillary tubes under N2. Elemental analyses of
selected samples were performed by Canadian Microanalytical Services
Ltd., Delta, British Columbia, Canada. Single-crystal X-ray diffraction
was carried out using either a Bruker AXS P4/SMART 1000 or a
PLATFORM/APEX II CCD diffractometer under a stream of cold N2.
Computational Details. Quantum-chemical calculations were
performed using Gaussian09.19 All structures were optimized without
symmetry constraints at the MP2 level using the cc-pWCVDZ basis
set20 and the Stuttgart−Cologne fully relativistic ECP (ECP60MDF)21
for bismuth. All other atoms were modeled using the cc-PVDZ basis
set. Structures were characterized as true minima by analytical
frequency calculations that showed zero negative frequencies.
2
(d, 12H, Me2PCH2CH2PMe2, JP−H = 14.7 Hz), 3.10 (m,
Me2PCH2CH2PMe2, 4H). 13C{1H} NMR (125 MHz, CD3CN, 298
1
K): δ 9.8 (d, 1JP−C = 28 Hz), 31.3 (d, JP−C = 29 Hz). 31P NMR (200
MHz, CD3CN, 298 K): δ 80.7 (br). Raman: the sample decomposes in
the laser beam.
(dmpe)BiCl(OTf)2 (3). A solution of dmpe (0.150 g, 1 mmol) in
toluene (10 mL) was added dropwise to a suspension of BiCl3 (0.316
g, 1 mmol) and TMSOTf (0.444 g, 2 mmol) in toluene (10 mL). A
yellow precipitate was observed immediately. The reaction was
allowed to stir for 1 h to yield a yellow suspension. The product
was filtered and washed with pentane (3 × 5 mL). Removal of the
solvent over 24 h yielded a fine yellow powder, which was
recrystallized from a minimum amount of CH3CN at −30 °C to
yield colorless crystalline blocks, identified as dmpeBiCl-
(OTf)2·CH3CN using X-ray crystallography. Yield (crystals): 0.496
g, 68%. Mp: 207−212 °C (dec). Elem anal. Calcd (found) for
(THF)2BiBr2(OTf) (1). BiBr3 (11.217 g, 25 mmol) was dissolved in
THF (50 mL) in a Schlenk bulb and stirred to obtain a clear, golden-
yellow solution. A solution of MeOTf (4.103 g, 25 mmol) in THF (12
mL) was added over 20 min through an addition funnel with an oil
bubbler attached to vent CH3Br. Gaseous evolution and a slight
exotherm were observed over the course of the addition. Stirring for an
additional 16 h at room temperature produced a viscous white
suspension. The slurry was pumped to dryness over 16 h under a
dynamic vacuum to yield a sticky light-gray solid (15.303 g). This
product was recrystallized from a 1:1 (v/v) mixture of DCM/Et2O at
−30 °C over 72 h, and the shiny, translucent blocks obtained were
isolated by decantation. The crystals were identified as 1 using X-ray
crystallography. Because of the high degree of disorder in the THF
molecules, precise bond lengths and angles could not be obtained. The
identity of the bulk was established via elemental analysis and NMR
spectroscopy, which confirmed that the coordinated THF molecules
are not removed even after prolonged exposure to high vacuum at
room temperature. Yield (crystals): 10.031 g, 78%. Mp: 108−110 °C.
1
3·CH3CN: C, 16.37 (16.20); H, 2.61 (2.79). H NMR (CD3CN, 300
MHz, 298 K): δ 1.94 (s, 3H, CH3CN), 2.33 (d, 12H,
Me2PCH2CH2PMe2), 3.19 (m, Me2PCH2CH2PMe2, 4H). 13C{1H}
NMR (CD3CN, 75 MHz, 298 K): δ 10.2 (d, 1JP−C = 29 Hz), 31.5 (d,
1JP−C = 27 Hz). 31P NMR (CD3CN, 120 MHz, 298 K): δ 90.8 (br).
NMR Detection of (dppm)BiCl2(OTf). TMSOTf (0.111 g, 0.5
mmol) was added to a light-orange solution of BiCl3 (0.157 g, 0.5
mmol) and dppm (0.197 g, 0.5 mmol) in CD2Cl2 (3 mL). A clear,
dark-orange solution was obtained upon stirring at room temperature
for 30 min. The solution was analyzed by NMR spectroscopy. A
parallel experiment with 2 equiv of TMSOTf (0.222 g, 1 mmol)
yielded identical NMR spectra. 1H NMR (CD2Cl2, 300 MHz, 298 K):
δ 4.97 (t, 2JP−H = 8.7 Hz, 2H), 7.38 (m, 12H), 7.59 (m, 8H). 13C{1H}
1
NMR (CD2Cl2, 75 MHz, 298 K): δ 25.2 (s), 116.8 (q, CF3, JP−C
=
319.8 Hz), 128.8 (t, 4.6 Hz), 129.7 (t, 12.4 Hz), 131.4 (s), 133.7 (t, 6.9
Hz). 31P NMR (CD2Cl2, 120 MHz, 298 K): δ 18.6 (br).
1
Elem anal. Calcd (found) for 1: C, 15.90 (16.33); H, 2.61 (2.44). H
NMR Detection of [(dmpe)2Pd][(CH3CN)2Bi2Cl6(OTf)2] (8).
K2PdCl4 (0.066 g, 0.2 mmol) and 3(OTf)2 (0.147 g, 0.2 mmol)
were combined in a vial. Upon the addition of 1 mL of CH3CN, a gray
suspension was formed immediately, which was allowed to stir for 1 h
and then settle. The clear, light-orange supernatant was removed via
pipet and the gray solid washed with an additional 1 mL of CH3CN.
The wash was combined with the supernatant, and the clear solution
was analyzed by 31P NMR spectroscopy and found to contain only one
signal, assigned to the [dmpe2Pd]2+ cation. 31P NMR (CH3CN2, 120
MHz, 298 K): δ 38.9 (literature δ 38.3, CD3NO2).46 The identity of
the product was confirmed from crystals obtained directly from the
NMR aliquot, which were analyzed as 8 by X-ray crystallography.
Despite repeated recrystallization attempts, it was not possible to
completely remove KOTf from its mixture with 8 and obtain the latter
as a pure substance.
NMR (300 MHz, CD2Cl2, 298 K): δ 2.00 (m, 4H, THF), 4.15 (m, 4H,
THF). 13C{1H} NMR (75 MHz, CD2Cl2, 298 K): δ 26.1 (s), 71.1 (s),
1
116.8 (q, CF3, JP−C = 319.8 Hz). Raman (cm−1, [relative intensity]):
84.1 [45], 93.1 [28], 191.9 [52], 212.1 [100], 322.1 [6], 346.8 [5],
352.4 [11], 519.7 [1], 578.1 [3], 763.3 [24], 854.2 [6], 922.7 [6],
1022.6 [60], 1041.7 [4], 1185.4 [4], 1224.7 [7], 1347.0 [1], 1368.4
[4], 1450.3 [4], 1487.3 [5], 2880.5 [11], 2902.9 [18], 2936.6 [19],
2954.6 [17], 2991.6 [23].
(dmpe)BiBr2(OTf) (2Br). 1 (0.662 g, 1 mmol) in toluene (5 mL)
was added dropwise to a solution of dmpe (0.150 g, 1 mmol) in
toluene (5 mL). A bright-yellow precipitate was obtained immediately.
The reaction was allowed to stir for an additional 1 h to yield a light-
gray precipitate, which was filtered and washed with pentane (3 × 5
mL). Removal of the solvent over 4 h gave a light-gray powder
together with some insoluble black precipitate. The crude product was
recrystallized from a minimum amount of CH3CN at −30 °C to yield
translucent blocks, which were identified as 2Br·CH3CN using X-ray
crystallography. Yield (crystals): 0.548 g, 77%. Mp: 225 °C (dec).
Elem anal. Calcd (found) for 2Br·CH3CN: C, 15.25 (16.54); H, 2.70
(2.65); the sample shows visible decomposition (formation of an
insoluble brown/black powder) under vacuum (10−2 mbar) and,
consequently, attempts to obtain better analytical results were
unsuccessful. 1H NMR (500 MHz, CD3CN, 298 K): δ 2.41 (d,
RESULTS AND DISCUSSION
■
An equimolar combination of BiBr3 and MeOTf in THF results
in exothermic elimination of gaseous MeBr and formation of 1.
The reaction mixture becomes gelatinous over the course of the
reaction because of Lewis-acid-catalyzed ring-opening polymer-
ization of THF, which is a well-known mode of reactivity for
metals in ethereal solvents.22 Nevertheless, single crystals of the
compound were obtained in 78% yield (isolated crystals) upon
recrystallization from 1:1 Et2O/DCM. The crystalline solid
2
12H, Me2PCH2CH2PMe2, JP−H = 14.5 Hz), 3.06 (m, 4H,
Me2PCH2CH2PMe2). 31P NMR (200 MHz, CD3CN, 298 K): δ 50.8
(br). Raman: the sample decomposes in the laser beam.
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Figure 1. Views of the feature compounds in the solid state (i) 1, (ii) 2Br, (iii) 2Cl, and (iv) 3 showing the geometry at bismuth and interion
contacts through the O−S−O moiety of the triflate anions resulting in dimeric association. Thermal ellipsoids are drawn at the 50% probability level.
Hydrogen atoms and noninteracting portions of the triflate anions have been omitted for clarity. For facile comparison, the atom labels in this figure
are different from those in the CIF files.
Table 1. Selected Solid-State Structural Parameters for Compounds 1, 2Cl, 2Br, and 3 and Related Compounds 4Cl[BiCl4]23
a
4Br[BiBr4],24 5[SbCl6]2,37 THF3BiBr3,25 [Bi2X4][AlX4]2 (X = Cl, Br),26 [BiCl2][W6Cl13],27 and [BiCl][W6Cl14]28
Bi−Cl-Containing Compounds
2Cl
3
4Cl[Bi2Cl8]0.5 [BiCl2][W6Cl13] [Bi2Cl4][AlCl4]2 [BiCl2]+ 5[SbCl6]2 [BiCl][W6Cl14] [BiCl]2+
P/O−Bi
2.6754(9) PA
2.6634(10) PB
[2.680]
2.6730(10) PA
2.6671(12) PB
[2.709]
[2.689]
P−Bi−P
Bi−Cl
77.95(3)
77.15(3)
[80.5]
[79.3]
2.6802(10) ClA
2.6348(10) ClB
3.623 ClA′ [2.626]
168.77(3)
2.4990(22)
2.501(6)
91.0(2)
2.441(4)
2.459(3)
2.392(2)
2.663(2)
2.671(2)
77.95(6)
93.99(9)
102.06(6)
[2.360]
[100.0]
2.479(6)
2.489(3)
[2.276]
[2.435]
Cl−Bi−Cl
91.38
[155.3]
Bi---O
3.010(3) OA
2.844(2) OB
2.858(4) OB
2.645(3) OC
2.744(4) OA
Bi−Br-Containing Compounds
4Br[BiBr4] THF3BiBr3 [THFBiBrPh2] [THFBiBr2Ph]x
[Bi2Br4]
[AlBr4]2
1
2Br
[BiBr2]+
BiBr3
P/O−Bi
2.4059(5) OC
2.4070(5) OD
[2.382]
2.6883(14) PA
2.6750(13) PB
[2.690]
2.62(9)
2.635(7)
2.700(7)
2.600(8)
90.6(3)
2.589(7)
2.671(8)
P/O−Bi−P/ 158.5(5) OC−Bi− 77.97(4)
O
OD
85.4(2)
[174.1]
[79.9]
89.7(2)
Bi−Br
Br−Bi−Br
Bi---O
2.6068(17) BrA
2.6073(17) BrB
[2.579]
2.8332(6) BrA
2.7871(6) BrB
3.625 BrA′ [2.778]
168.09(2)
2.666(5)
92.4(1)
2.628(5)
2.6834(13)
2.6623(11)
92.0(2)
2.741(1)
2.684(1)
2.555(1)
2.779(1)
2.859(1)
89.41(4)
95.36(4)
[2.506]
[101.4]
2.636(4)
2.660(3)
2.692(3)
88.19(10)
90.08(11)
96.29(11)
93.73(6)
92.6(6)
[100.4]
[162.3]
95.45(5)
2.7862(5) OA
2.8299(7) OB
2.995(4) OA
2.838(4) OB
a
Calculated values in square brackets are for the gas-phase, triflate-free cations at the MP2 level.29
C
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retains THF under vacuum (5 × 10−2 mbar) at room
temperature, as confirmed by NMR spectroscopy and
elemental analysis data. When the crystals are heated under
vacuum, an insoluble dark-brown powder is formed.
The reaction of 1 with dmpe in toluene results in quantitative
(as shown by 31P NMR spectra of the reaction mixtures)
formation of 2Br with displacement of THF by the chelating
ligand. Crystals of 2Br·CH3CN were obtained by recrystalliza-
tion from CH3CN at −30 °C, but solutions at room
temperature deposit black insoluble powder within days.
Isolated crystals of 2Br·CH3CN are thermally stable under an
inert atmosphere at room temperature for weeks.
substituent, and three cis-configured interion contacts to
oxygen atoms of separate triflate anions.
The range of Bi---OOTf distances in compounds 1, 2Cl, 2Br,
and 3 [2.645(3)−3.010(3) Å] is significantly longer than the
sum of the covalent radii [Bi−O = 2.25 Å] and significantly
shorter than the sum of the van der Waals radii [Bi---O = 3.80
Å]. While the structure of Bi(OTf)3 has not been reported, the
observed Bi---OOTf distances are generally consistent with those
reported for representative bismuth triflate compounds
[2.473(5)−3.553(6) Å in Ph2Bi(OTf),30 2.386(11)−
2.879(15) Å in (THF)4ClBi(OTf)2,31 and 2.54(5)−2.84(3) Å
in (H2O)4Bi(OTf)332] and are generally longer than the Bi−O
distances in the covalent oxide α-Bi2O3 [2.08(3)−2.80(2) and
3.25(4) Å]33 or alkoxide Bi(OCPh3)3 [2.070(4)−2.081(4)
Å].34 We conclude that while the Bi---OOTf distances in
compounds 1, 2Cl, 2Br), and 3 are generally longer than a
formal covalent Bi−O bond, the compounds are best
formulated as pseudohalide complexes of the type
[L2BiXn(OTf)3−n
]
rather than ionic salts of the type
2
[L2BiXn]2[OTf]2(3−n)
.
To further assess the structural influences of the Bi---triflate
interion contacts, we performed ab initio calculations (MP2)29
to obtain the gas-phase structures of the triflate-free cations of
1, 2Br, 2Cl, and 3 (see Table 1, values in square brackets). The
optimized geometry at the bismuth center in the cations of 1,
2Br, and 2Cl is a distorted seesaw, consistent with a AX4E
VSEPR geometry with a stereochemically active lone pair.
Further evidence of lone-pair activity in the gas-phase structures
comes from the observation that the halide substituents in the
cations of 2Br and 2Cl are bent back toward the dmpe ligands
(Br−Bi−Br = 162.3°; Cl−Bi−Cl = 155.3°) and the THF
ligands in the cation of 1 (O−Bi−O = 174.1°) are bent back
toward the bromide substituents. The corresponding exper-
imental values for the X−Bi−X bond angle [168.09(2)° for 2Br
and 168.77(3)° for 2Cl] or the O−Bi−O bond angle
[158.5(5)° for 1(OTf)] are significantly larger than those of
the cations in the gas phase, consistent with reduced lone-pair
stereochemical activity in the solid state. We did not observe
gas-phase minima for the hypothetical tetrahedral geometries
for the cations in 1, 2Br, and 2Cl (AX4 VSEPR). By
comparison, a tetrahedral geometry was calculated and
observed in the solid state39 for the recently reported
[(Me3P)2SnCl2]2+ dication, consistent with an AX4 VSEPR
geometry. The trans-THF2 structure observed for the cation in
the solid-state structure of 1 is calculated to be a minimum for
the cation of 1 in the gas phase, while there is no minimum
evident for the hypothetical cis-THF2 structure with trans-
bromine substituents. The calculated P−Bi bond lengths and
angles for the cations of 2Br, 2Cl, and 3 are very similar to
those observed in the solid state, while the calculated Bi−X (X
= Cl or Br) bonds are significantly shorter than those observed
in the solid state. We conclude that interactions with the triflate
ion suppress the lone-pair stereochemical activity at bismuth
and attenuate the overall Lewis acidity of the metal centers in
the solid state, leading to lengthened Bi−X bonds.
Attempts to isolate (THF)2BiCl2(OTf) from BiCl3 and
MeOTf in THF were unsuccessful because of the rapid
+
thickening of the solvent, suggesting that BiCl2 is a more
+
potent polymerization catalyst than BiBr2 . Therefore, 2Cl was
prepared directly from equimolar mixtures of BiCl3, TMSOTf,
and dmpe in toluene and precipitated as an insoluble yellow
powder. When BiCl3 was reacted with dmpe in the presence of
excess TMSOTf, 3 was obtained. Single crystals of each
compound were obtained by recrystallization from CH3CN at
−30 °C because both compounds exhibit thermal instability in
solution at room temperature, as judged by the deposition of
elemental bismuth within hours. Both compounds are thermally
stable for weeks in the solid state under an inert atmosphere.
The solid-state structures of 1, 2Cl, 2Br, and 3 (Figure 1) all
involve dimeric arrangements by virtue of Bi---OOTf contacts,
which provide two O−S−O bridges between two bismuth
centers. The distorted octahedral environment at bismuth is
more regular in 1 than in the structures of 2Cl, 2Br, and 3, in
which the axially configured halide centers are slanted to
accommodate long intermolecular Bi---Cl contacts. The
geometry at bismuth in each structure shows no evidence of
lone-pair stereochemical activity. Selected structural parameters
for each compound are summarized in Table 1 together with
analogous parameters for some related compounds.
The structure of 1 is at low resolution because of disorder
but is consistent with elemental analysis data and is sufficient to
illustrate the connectivity as a cis-configured dibromobismuth
center with two trans-configured THF ligands and two cis-
configured contacts to oxygen atoms of separate triflate anions.
In contrast, the solid-state structures of compounds 2Cl and
2Br involve trans-configured halide substituents imposed by the
chelating (cis-configured) dmpe ligand. Compound 3 features a
bismuth center with a chelating dmpe ligand, one chlorine
In the solid state, the cis Bi−Br bonds in 1 [Br−Bi−Br =
93.73(6)°] are shorter than those in 4Br, (THF)3BiBr3, BiBr3,
(THF)BiPh2Br, and [(THF)BiPhBr2]x and are similar to those
in [Bi2Br6][AlBr4]2, all of which feature cis Bi−Br bonds. The
trans configuration of bromine atoms in 2Br is accompanied by
substantially longer Bi−Br bonds, likely because of a trans
influence, which is also predicted by the MP2-optimized
structure of the cation of 2Br in the gas phase. Consistently, the
D
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Inorganic Chemistry
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Table 2. Crystal Data for the Featured Compounds
1
2Br·CH3CN
2Cl·CH3CN
3·CH3CN
8
empirical formula
fw
C9H16BiBr2SO5F3
662.08
C9H19BiBr2F3O3P2SN
709.05
C9H19BiCl2F3NO3P2S
620.13
C10H19BiClF6NO6P2S2
733.75
C18H38Bi2Cl6F6N2O6P4PdS2
1417.56
space group
a (Å)
P1
C2/c
C2/c
P2(1)/n
12.6020(15)
16.2877(19)
12.8527(15)
90
P1
̅
̅
8.088(2)
10.539(4)
11.746(3)
106.091(5)
97.960(4)
106.559(3)
896.1(4)
2
21.1892(16)
15.3454(16)
12.6533(11)
90
21.2850(16)
15.2439(16)
12.3056(10)
90
8.9289(4)
9.8177(4)
13.9674(6)
106.6802(4)
94.1676(5)
107.2454(5)
1103.37
1
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
94.694(2)
90
95.629(2)
90
118.648(1)
90
4100.5(6)
8
3973.5(6)
8
2315.2(5)
4
ρ (g cm−3
)
2.454
2.297
2.073
2.105
2.133
λ (Å)
0.71073
188(1)
0.71073
198(1)
0.71073
198(1)
0.71073
173(1)
0.71073
173
T (K)
GOF
1.048
1.032
1.037
1.058
1.106
a
R1
0.0498
0.0397
0.0274
0.0320
0.0136
a
wR2
0.1222
0.0922
0.0583
0.0663
0.0331
a
2
4
R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = [∑w(Fo − Fc2)2/∑w(Fo )]1/2
.
trans-configured Bi−Cl bonds [Cl−Bi−Cl = 168.77(3)°] in
2Cl are also significantly longer than those in related species,
including neutral BiCl3 [2.500(18) Å]35 and 6 [2.5116(8) and
2.5269(8) Å],36 which feature a cis configuration of chlorine
centers at the bismuth center. As expected, the Bi−Cl bond in 3
[2.4990(22) Å] is markedly shorter than that in 2Cl and is only
marginally longer than those observed in the related 5
[2.479(6) Å]37 and [BiCl][W6Cl14] [2.489(3) Å].28 By
comparison, the shortest Bi−Cl bond reported in the
Cambridge Structural Database to date is 2.394 Å in the
neutral arene complex (p-xylene)2Bi2Cl6,38 and the MP2-
optimized value for the hypothetical gas-phase diatomic
[BiCl]2+ is 2.276 Å.
The observed and calculated P−Bi bond lengths in 2Br, 2Cl,
and 3 are essentially equivalent, suggesting that these are
insensitive to the Lewis acidity of the bismuth center, despite
the greater electronegativity of the chlorine substituents and the
greater charge in 3. Moreover, the P−Bi bond lengths in 2Cl
and 2Br are similar to those in neutral and anionic compounds
containing P−Bi bonds (Table 1). Therefore, the substantially
shorter Bi−Cl and Bi---OOTf distances in 3 compared to those
in 2Cl preferentially compensate for the enhanced Lewis acidity
at the metal center. The differing sensitivity of the E−X and E−
P bonds to the charge at the metal center is consistent with
observations for cationic P−SbXn and P−SnXn complexes and
may be a general feature of phosphine complexes of main-
group halides.3,39 The Lewis basicity and configuration of the
phosphine ligands is, nevertheless, important. Thus, the more
basic dmpe ligand results in substantially shorter P−Bi
distances than those found in [(Ph3P)2BiPh2][PF6] [2.968(3)
and 2.937(3) Å],6 which bears trans-configured phosphine
ligands.
The structure of 2Cl is consistent with that of the antimony
derivative [(dmpe)SbCl2][OTf] (7)3 with trans-configured
chlorine substituents imposed by the stereochemically active
lone pair. While the average E−Cl and E−P bond lengths
[2.6678(20) and 2.6694(19) Å, respectively] are predictably
longer in 2Cl than in 7 [2.5625(8) and 2.5657(8) Å,
respectively] because of the larger covalent radius of bismuth
(1.48 Å, compared to that of antimony at 1.39 Å), the average
of two contacts to the triflate anions are ca. 0.05 Å shorter for
2Cl [2.927(5) Å] than for 7 [2.9746(28) Å], because of the
lesser steric restriction at the larger bismuth atom and the lower
stereochemical activity of the Bi 6s lone pair compared to the
5s lone pair in 7. In this context, the dimeric structure adopted
by 2Cl is not observed for 7, which adopts a complex network
structure where the two interacting triflate anions bridge
different metal centers in the extended solid-state structure
(Table 2).3
Recently, it has been shown that, because of the combination
of low-lying vacant acceptor orbitals and a lone pair at the
central phosphorus atom, ligands of the type [LPR2]+ and
[L3P]3+ (L = carbene) can coordinate with electron-rich late
transition metals,40 classifying these main-group cations as a
novel family of π-accepting ligands with demonstrated
applications in catalysis.41 Transition-metal complexes bearing
cationic ligands of the type [R3P−P−PR3]+ have also been
characterized by NMR spectroscopy.42 However, despite the
well-established use of neutral stibine and bismuthine43 ligands
in transition-metal chemistry, investigations of their Z-type
ligand abilities are limited. Only two instances of well-
established bismuth−metal coordinate bonds have been
reported, both employing P−Bi−P-type pincer ligands to
bind gold(I) in a tridentate fashion, such that the P−Au
interaction assists in enforcing the Au−Bi interaction.44a,b
Analysis of the bonding situation showed that in both cases the
Au−Bi bonding was driven by transfer of the electron density
from the gold atom to the Bi−Cl σ* antibonding orbital.
Fernandez et al. have also reported a long Bi−Au [3.7284(5)
The Bi−OTHF lengths in 1 are approximately 0.23 Å shorter
than those in the neutral adducts (THF)3BiBr3, (THF)BiPh2Br,
or polymeric [(THF)BiPhBr2]x, reflecting a stronger Bi−OTHF
interaction in the triflate complex despite the trans config-
uration of the ether ligands. Taken together with the short Bi−
Br bonds in 1 (vide supra), these features demonstrate that the
bismuth center in this complex is highly Lewis acidic even in
the presence of the triflate contacts.
+
−
Å] interaction between the cation [Bi(C6H4CH2NMe2 2)2]
and the anion [Au(C6F5)2]−, without the need for a pincer
framework or other structure-directing features to enforce the
Bi−Au contact.45
E
dx.doi.org/10.1021/ic400875a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Following an analysis of the electronic structure of 3 at the
MP2 level, we reasoned that, analogous to the cases above, the
low-lying vacant p-orbitals centered at the bismuth atom in 3
(Figure 2a) may also serve as π-acceptor orbitals with electron-
dimers.48 −50 The last of these best describes
[(CH3CN)2Bi2Cl6(OTf)2]2−, which crystallizes as a centrosym-
metric edge-sharing bioctahedron via two O−S−O linkages
between adjacent bismuth centers. The preference for
phosphine/halide exchange (metathesis) over Bi−Pd Z-type
coordination evidences a substantially higher Lewis acidity at
the bismuth center in 3(OTf)2 (p-orbitals as acceptor
molecular orbitals) than in the formally more highly charged
phosphorus-centered cations (p-orbital-derived acceptor mo-
lecular orbitals) or in the neutral halobismuthines (Bi−X σ*-
acceptor molecular orbitals). Moreover, whereas the 3s lone
pair in cationic phosphines readily engages the transition metal,
leading to synergistic σ donation and π back-donation, the
contracted 6s lone pair at the bismuth center in 3 is a much
weaker Lewis base and likely does not benefit from such an
interaction. It is therefore unlikely that bismuth complexes such
as 3 can be used as ligands in the absence of additional
structure-enforcing factors such as pincer chelation.
Figure 2. Surface plots (|isovalue| = 0.02) of (a) 3LUMO (−9.63 eV)
and 3LUMO+1 (−9.74 eV) and (b) 3HOMO (−18.12 eV).
rich, late-transition-metal donors, enhanced by localization of
the highest occupied molecular orbital (HOMO) on the
bismuth atom (Figure 2b), prompting an assessment of the σ-
donor/π-acceptor ligand capabilities of 3.
The addition of a CH3CN solution of 3(OTf)2 to 1 equiv of
K2PdCl4 results in the formation of a clear orange solution,
which shows a single peak at δ 38.9 in the 31P NMR spectrum
of the reaction mixture, consistent with formation of the known
[dmpe2Pd]2+ cation.46 Concentration of the solution under
vacuum yields a large quantity of light-gray powder and
crystalline blocks. The identity of the crystalline material was
confirmed by X-ray crystallography to be 8 (Figure 3). The gray
CONCLUSIONS
■
In summary, the synthesis and characterization of compounds
featuring bismuth acceptors stabilized by THF or dmpe ligands
are described. In the solid state, the triflate-containing
compounds 1, 2Br, 2Cl, and 3 crystallize as dimers involving
Bi---OOTf and Bi---X interactions. The Bi−X bond lengths
exhibit a greater sensitivity to the formal Lewis acidity of the
bismuth center than do the Bi−P bond lengths. The strong
trans influence of the halide ligands is also documented. A
comparison of homologous Sb/Bi structures 2Cl and 7
illustrates the structural consequences of relative lone-pair
stereochemical activity. In solution, the compounds behave as
classic coordination complexes, as illustrated by the ligand
substitution reaction that yields 2Br from a solution of 1 with
dmpe. An assessment of the electronic structure of 3 suggests
that it may behave as a Z-type ligand because of the presence of
both a lone pair and vacant p orbitals at the bismuth center.
However, experimental attempts to realize such reactivity were
unsuccessful and led instead to the discovery of a metathesis
reaction highlighting an important distinction between the
chemistry of phosphorus and bismuth cations, with the latter
showing a substantially greater Lewis acidity even with lower
formal charges and more strongly interacting counterions.
These insights provide direction for the further development
and diversification of the coordination chemistry of bismuth.
Figure 3. View of the solid-state structure of 8. Thermal ellipsoids are
drawn at the 30% probability level. Noninteracting portions of the
t r i fl a t e a n i o n h a v e b e e n o m i t t e d . T h e a n i o n
[(CH3CN)2Bi2Cl6(OTf)2]2− is centrosymmetric. Select bond lengths
(Å) and angles (deg) are as follows: Bi−Cl(A) = 2.5074(6), Bi−Cl(B)
= 2.5192(6), Bi−Cl(C) = 2.5171(6), Bi−O(A) = 2.6617(18), Bi−
O(B) = 2.6724(18), Bi−N1 = 2.757(2); Cl(A)−Bi−Cl(B) =
94.400(19), O(A)−Bi−O(B) = 84.30(6), O(A)−Bi−Cl(B) =
171.49(6), O(B)−Bi−Cl(A) = 172.14(5), N(A)−Bi−Cl(C) =
171.49(6). For facile comparison, the atom labels in this figure are
different from those in the CIF file.
ASSOCIATED CONTENT
* Supporting Information
■
S
Cartesian coordinates for gas-phase-optimized compounds and
CIF files. This material is available free of charge via the
Internet at http://pubs.acs.org.
powder showed no signals in its H or 31P NMR spectrum,
1
AUTHOR INFORMATION
Corresponding Author
*E-mail: nburford@uvic.ca. Phone: +1 250 721 7150.
Notes
■
consistent with its formulation as a mixture of KOTf and
unreacted K2PdCl4, implying the overall reaction shown in
Scheme 1.
The [Bi2Cl8]2− dianion is a well-known formulation that is
observed as dimers,23 a polymer,47 and ligand-supported
The authors declare no competing financial interest.
Scheme 1. Reaction between 3 and K2PdCl4
F
dx.doi.org/10.1021/ic400875a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
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ACKNOWLEDGMENTS
■
The authors gratefully acknowledge the Natural Sciences and
Engineering Council of Canada for financial support and the
Vanier Canada Graduate Scholarships Program for a graduate
scholarship (to S.S.C.).
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