Controlling the Properties of a 2,2′-bipy-Platinum Dichloride Complex via Oxidation of a Peripheral Stibine Moiety

Article abstract of DOI:10.1021/acs.organomet.8b00296

Our interest in the chemistry of antimony derivatives has led us to investigate the synthesis and properties of 4-(diphenylstibino)-2,2′-bipyridine (L^SbPh2). This new ligand, which could be obtained by reaction of 4-lithio-2,2′-bipyridine with Ph₂SbCl, was treated with Pt(CH₃CN)₂Cl₂ to afford the platinum complex L^SbPh2PtCl₂ (1). Interestingly, the latter reacts with PhICl₂ to afford L^SbCl2Ph2PtCl₂ (2), a complex in which the peripheral stibine moiety has been converted into a dichlorostiborane. Complexes 1 and 2 have both been fully characterized. Computational, UV-vis, and cyclic voltammetry studies show that oxidation of the antimony atom leads to a lowering of the bipy-centered LUMO, indicating that 2 is more electron deficient than 1. A congruent picture emerges from reactivity studies, which show that 2 is a more active catalyst for the hydroarylation of ethyl propiolate by mesitylene.

Full text of DOI:10.1021/acs.organomet.8b00296

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Controlling the Properties of a 2,2′-bipy−Platinum Dichloride
Complex via Oxidation of a Peripheral Stibine Moiety
Ying-Hao Lo and Franc o̧ is P. Gabbaï*
Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
*
S Supporting Information
ABSTRACT: Our interest in the chemistry of antimony
derivatives has led us to investigate the synthesis and
SbPh2
properties of 4-(diphenylstibino)-2,2′-bipyridine (L
).
This new ligand, which could be obtained by reaction of 4-
lithio-2,2′-bipyridine with Ph SbCl, was treated with Pt-
2
SbPh2
(
(
L
CH CN) Cl to afford the platinum complex L
PtCl
2
3
2
2
1). Interestingly, the latter reacts with PhICl to afford
2
SbCl2Ph2
PtCl (2), a complex in which the peripheral stibine
2
moiety has been converted into a dichlorostiborane.
Complexes 1 and 2 have both been fully characterized.
Computational, UV−vis, and cyclic voltammetry studies show
that oxidation of the antimony atom leads to a lowering of the
bipy-centered LUMO, indicating that 2 is more electron
deficient than 1. A congruent picture emerges from reactivity studies, which show that 2 is a more active catalyst for the
hydroarylation of ethyl propiolate by mesitylene.
INTRODUCTION
A situation which has received less attention is that involving
transition-metal complexes where the antimony moiety is
positioned at the outer rim of a coordination complex as in the
■
Antimony(V) compounds are emerging as powerful Lewis acid
catalysts for a number of organic transformations. Earlier
studies showed that stibonium cations such as [Ph Sb]
catalyze the addition of isocyanates to epoxides. More
recently, stibonium cations have found use as catalysts for
the allylstannation and hydrosilylation of various aldehydes,
among other reactions. Antimony-based Lewis acids can also
8
+
case of C (Chart 1). A detailed study of this complex showed
4
1
that the antimony moiety, despite its large separation from the
metal center, alters the redox properties of the latter. Indeed,
we observed a net anodic shift in the Ru(II/III) redox couple
upon oxidation of the antimony center, leading us to conclude
that the high-valent antimony moiety is electron-withdrawing.
Building on these original results, we have chosen to
investigate antimony-substituted 2,2′-bipyridine (bipy) ligands
in order to determine if the redox activity of the peripheral
antimony center could be used to influence the reactivity of a
transition metal coordinated to the bipy ligand (Chart 2). In
this article, we describe the synthesis of an antimony-
substituted bipy ligand and its coordination to platinum. We
also describe how oxidation of the antimony center affects the
photophysical properties of the complex as well as its reactivity.
2
3
4
activate transition-metal catalysts by abstraction of an anionic
5
ligand. Such a possibility is illustrated by the properties of
6
7
complexes A and B, which catalyze reactions involving
alkynyl substrates (Chart 1). In both cases, we proposed that
the Lewis acidic antimony center of these complexes engages
the metal-bound chloride anion, leading to the generation of
an exposed, electrophilic metal center available for substrate
activation.
Chart 1. Transition Metal Complexes Featuring Lewis
Acidic Antimony Moieties
Chart 2. Outline of Work Mentioned Within
Received: May 8, 2018
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00296
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Article
RESULTS AND DISCUSSION
occurred at the antimony atom was provided by the resonance
of the antimony-bound Ph groups, which appear in the 7.2−
7.4 ppm range for 1 and the 7.5−7.8 ppm range for 2.
Oxidation of the antimony center was confirmed by the
structural characterization of 2 (vide infra). It is interesting to
■
The synthesis of the 4-(diphenylstibino)-2,2′-bipyridine ligand
SbPh2
(
L
) was achieved by lithiation of 4-bromobipyridine
9
followed by reaction with Ph SbCl (Scheme 1). This ligand is
2
Scheme 1. Synthesis of LSbPh2, 1, and 2
a
note that addition of up to 4 equiv of PhICl did not alter the
2
fate of this reaction, indicating that the platinum center resists
oxidation to the tetravalent state.
The structures of complexes 1 and 2 have been determined
using X-ray diffraction analysis (Figure 2 and 3). The
a
n
Legend: (a) 1.1 equiv of BuLi, Et O; 1 equiv of SbPh Cl, THF,
2
2
−
100 °C; (b) 1 equiv of Pt(CH CN)Cl , CH CN, 50 °C; (c) 1 equiv
3 2 3
of PhICl , DMSO.
2
1
an air-stable solid which could be easily crystallized. The H
NMR spectrum is consistent with that expected for a 4-
substituted 2,2′-bipyridine derivative with each hydrogen on
the ligand backbone being chemically distinct. This ligand
Figure 2. Structure of one of the two independent molecules in the
solid-state structure of 1. Thermal ellipsoids are drawn at the 50%
probability level. The hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and angles (deg): Sb1−C3 2.203(9), N1−Pt1
2.008(7), N2−Pt1 2.041(7), Pt1−Cl1 2.297(2), Pt1−Cl2 2.319(2),
N1−Pt1−N2 80.4(3).
crystallizes in the P2 /n space group with two nearly identical
1
molecules in the asymmetric unit. The geometry of the
antimony atom is close to that expected for a triarylstibine,
with C−Sb−C bond angles close to 90° (Figure 1).
Figure 1. Structure of one of the two independent molecules
Figure 3. Structure of one of the two independent molecules in the
solid-state structure of 1. Thermal ellipsoids are drawn at the 50%
probability level. The hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and angles (deg): Sb1−C3 2.127(9), N1−Pt1
SbPh2
observed for L
in the solid state. Thermal ellipsoids are drawn at
the 50% probability level. The hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg): Sb1−C3 2.161(2),
C11−Sb1−C3 95.14(7), C17−Sb1−C3 94.32(8), C17−Sb1−C11
2
.003(7), N2−Pt1 2.024(8), Pt1−Cl1 2.298(3), Pt1−Cl2 2.291(2),
96.39(8).
N1−Pt1−N2 80.4(3), Cl3−Sb1−Cl4 176.56(9).
This ligand reacts cleanly with [(CH CN) PtCl ] in
3
2
2
acetonitrile to afford the corresponding platinum(II) complex
asymmetric unit of both complexes contains two independent
molecules which display very similar geometries. In the case of
1, the two independent molecules are engaged in the formation
of an extended stack. Within this stack, the bipyridyl−platinum
dichloride units of the successive molecules are essentially
parallel to each other and are separated by an average distance
of 3.40 Å (see the Supporting Information). In the case of 2,
the two independent molecules form a stacked dimer with a
separation of 3.32 Å between the bipyridyl−platinum
dichloride units of the two molecules (see the Supporting
Information). In both complexes, the platinum(II) atoms are
tetracoordinated in a square-planar geometry, which is
10
1
as an air-stable yellow solid (Scheme 1). Inspection of the
1
H NMR spectrum of 1 shows that complexation of the
platinum ion induces a notable downfield shift of the proton
attached to the 3-position of the bipyridine backbone from 8.5
ppm to 8.7 ppm. Given that both the antimony and platinum
2c,4c,11
centers of 1 could be oxidized by two electrons,
we
became eager to interrogate the compound by addition of
iodobenzene dichloride (PhICl ). When attempted in
2
acetonitrile, this reaction gave an intractable mixture of
compounds, which we assign to the poor solubility of 1 in
this solvent. Gratifyingly, the reaction proceeded cleanly in
1
8
DMSO to afford complex 2 as the oxidized product. The H
consistent with a d electronic configuration. The N−Pt−N
bond angles for complexes 1 and 2 are compressed to averages
of 80.5(4) and 80.3(4)°, respectively, relative to the ideal value
NMR spectrum of complex 2 shows a further downfield shift of
1
the H NMR resonances. The first hint that oxidation had
B
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Article
of 90°, which is characteristic of Pt(II) bipyridine and diamine
Table 1. Frontier Molecular Orbitals (Isovalue 0.05) and
Energies (eV) of 1 and 2
1
2
complexes. Complex 2 contains a pentacoordinated anti-
mony center that adopts a distorted-trigonal-bipyramidal
geometry with the two chloride ligands occupying the axial
positions (average Cl−Sb−Cl = 176.12(13)°). This geometry
follows the apicophilicity of the electronegative halogen ligands
13
as typically observed for dihalotriarylstiboranes. The Pt−Cl
bonds involving the chlorine trans to the antimony-substituted
pyridine ring are marginally shorter in complex 2 than in
complex 1 (average 2.293(3) Å vs average 2.318(3) Å),
suggesting a reduction of the trans influence of the N1 atom
1
4
upon oxidation. This result suggests that the oxidation state
of the antimony center can be used to adjust the donor
strength of the bipyridine ligand.
The photophysical properties of platinum(II) complexes
featuring bipyridyl ligands can be used to map the electronic
15
structure of the complexes. Such complexes are characterized
by two main absorption features. The low-energy feature is a
metal to ligand charge transfer (MLCT) band which is
followed at higher energy by a ligand-centered π−π* transition
in 1 to 2.79 eV (444 nm) in 2, which is in good agreement
with the red shift observed by UV−vis spectroscopy.
The electronic absorption bands of 1 and 2 were examined
with time-dependent DFT (TD-DFT) calculations using the
solute electron density-based implicit solvation model (SMD)
with MeCN as a solvent. These calculations indicate that the
MLCT band in both complexes is dominated by a distinctly
intense single electronic excitation at 378 nm for 1 (f = 0.14)
and 382 nm for 2 (f = 0.15) (Figure 5). Weaker excitations are
1
6
(
Figure 4). While the π−π* transitions are often obscured by
Figure 4. Experimental UV−vis spectra of 1, 2, and (bipy)PtCl in
2
MeCN at room temperature.
other high-energy bands, the MLCT bands appear in an area
that does not suffer from such interferences. For this reason,
we decided to focus on the MLCT band. The λmax of the
MLCT band of 1 (387 nm) shows a small but noticeable red
Figure 5. Experimental UV−vis spectrum and calculated vertical
electronic transitions (represented by bars) of 1 and 2 in MeCN. The
wavelengths of the calculated transitions are plotted against the
oscillator strength.
shift in comparison to the parent complex (bipy)PtCl (383
2
nm). This small shift indicates that incorporation of the
diphenylantimony moiety alters the electronic properties of the
bipy ligand only to a very small extent. A more noticeable shift
of 10 nm is observed upon oxidation of the antimony center as
in (λmax(2) = 397 nm). This effect is consistent with a lowering
of the bipyridine π* orbitals upon oxidation of the antimony
center.
observed at 383 and 434 nm for 2 and 379 and 415 nm for 1.
Analysis of the TD-DFT output using the natural transition
orbital (NTO) methods shows that these low-energy
excitations have the expected MLCT character as indicated
by inspection of the dominant NTOs given in Table 2 for the
first three excited singlet states. It is also important to note that
the electronic excitations identified for 2 are lower in energy
than those of 1, again in agreement with the red shift observed
experimentally.
The density functional theory (DFT) optimized structures
of 1 and 2 are in reasonable agreement with the structures
determined experimentally (see the Supporting Information).
The contours and energies of the Kohn−Sham lowest
unoccupied molecular orbital (LUMO) and highest occupied
molecular orbital (HOMO) are presented in Table 1. In both
complexes, the HOMO can be described as an antibonding
Pt(d )−Cl(p ) π* orbital, the energy of which is lowered by
On the basis of the NTOs shown in Table 2, it appears that
transitions with low oscillator strengths are those for which the
platinum-centered donor orbital has poor overlap with the
ligand π* acceptor orbital. The most intense transitions in both
complexes are those involving the third donor orbital. The
oscillator strengths of these transitions are at least 10 times
larger than those of the first and second transition, a result that
can be explained on the basis of the apparent better overlap
yz
z
0
.14 eV upon oxidation. The LUMO of both complexes is
based on the antimony-substituted bipy ligand. This orbital,
which has π* character, shows a lowering of 0.21 eV upon
conversion of 1 into 2. The net effect of these changes is a
decrease of the HOMO−LUMO gap from 2.87 eV (432 nm)
17
existing between the donor and acceptor NTOs.
C
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Article
Table 2. Dominant NTOs, Calculated Wavelengths (λ), and
Oscillator Strengths (f) for the First Three Excited Singlet
States of 1 and 2
reduction of 1 and (bipy)PtCl , indicating that 2 is a more
electron deficient compound.
2
a
Having measured the effect of oxidation on the optoelec-
tronic properties of these complexes, we next became
interested in probing whether the reactivity of the platinum
center could also be affected by oxidation of the peripheral
antimony atom. We have observed such cooperative effects in
+
the case of the antimony gold complex D , which becomes
+
catalytically active upon conversion into E by oxidation of the
18
antimony atom (Scheme 2).
Scheme 2. Cooperative Effects in the Case of an Antimony
Gold Complex
In the present case, however, we questioned whether the
greater separation would cancel any cooperative effects
between antimony and platinum. To address this question,
we selected a simple reaction that would allow us to interrogate
the electrophilic character of the platinum center, especially
after oxidation. We selected the hydroarylation of ethyl
propiolate by mesitylene, a reaction known to be accelerated
a
The acceptor orbitals are the same for all three transitions.
The electrochemistry of 1, 2, and (bipy)PtCl was also
2
19
investigated using cyclic voltammetry (CV) (Figure 6).
by platinum catalysts. This reaction was carried out in
trifluoroacetic acid, and the results are compiled in Table 3. As
Table 3. Pt(II)-Catalyzed Hydroarylation of Ethyl
a
Propiolate with Mesitylene
b
yield (%)
entry
[cat.] (5 mol %)
temp (°C)
3
4
c
1
1
2
1
2
60
60
25
25
60
60
60
32
62
13
50
<1
30
31
33
c
2
21
trace
6
<1
25
22
d
3
d
4
c
5
SbPh Cl2
(bipy)PtCl2
3
c
6
c
7
(bipy)PtCl + Ph SbCl
2
2
3
a
Figure 6. Cyclic voltammograms of 1, 2, and (bipy)PtCl in DMF
2
Reaction conditions: mesitylene (0.28 mmol), ethyl propiolate (0.28
b
n
1
with 0.1 M [ Bu N][PF ] as electrolyte. The scan rate was 0.1 V/s,
4
6
mmol), TFA (1 mL). H NMR yields relative to 1,2-dichloroethane
c d
+
and potentials are referenced to Fc/Fc in the same solvent.
added at the end of the reaction. Reaction time = 4 h. Reaction time
24 h.
=
Compound 1 and (bipy)PtCl both display a quasi-reversible
2
reduction wave at E1/2 = −1.57 and −1.59 V, respectively,
shown by entries 1 and 2, catalyst 2 is markedly more active
than 1, leading to an ∼2-fold increase of the yield in the
monohydroarylation product 3 after 4 h. The reaction also
proceeded at room temperature over the course of 24 h
(entries 3 and 4). Under these conditions, a greater differential
was observed between the two catalysts, with again catalyst 2
affording a markedly higher yield of 3. Carrying out the
reaction at room temperature also improved the selectivity for
the monohydroarylation product. These results suggest that
oxidation of the antimony atom positively affects the catalytic
15
corresponding to the reduction of the bipyridine ligand. The
similarity of these potentials indicates that the diphenylanti-
mony moiety is innocent and only induces a very minor
perturbation of the electronic properties of the ligand. The
voltammogram of complex 2 features two irreversible
reduction events and thus differs markedly from that of 1
and (bipy)PtCl . While it is difficult to assign the nature of
2
these reductions, we will note that the first event occurs at E =
p
−1.2 V. This potential is distinctly more anodic than the first
D
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Article
properties of the metal center. The lack of reaction observed
when Ph SbCl is used alone underscores the catalytic function
of the platinum atom in these reactions (entry 5). We also
with a CCD area detector (graphite-monochromated Mo Kα
radiation, λ = 0.71073 Å, ω scans with a 0.5° step in ω). In each
case, a specimen of suitable size and quality was selected and mounted
onto a nylon loop. The semiempirical method SADABS was applied
for absorption correction. The structures were solved by direct
3
2
27
tested the catalytic activity of (bipy)PtCl and found it to be as
2
active as 1, suggesting that the diphenylantimony moiety
present in 1 has no influence on the catalytic activity of these
complexes (entry 6). Finally, we also tested the (bipy)PtCl2/
methods and refined by the full-matrix least-squares technique against
2
F
with anisotropic temperature parameters for all non-hydrogen
atoms. All H atoms were geometrically placed and refined using the
Ph SbCl system and found it to be as active as 1 and
3
2
riding model approximation. Data reduction and further calculations
28
(
bipy)PtCl (entry 7). This last experiment points to the
were performed using the Bruker Apex2 (2013) and SHELXTL
program packages. Structural refinements were performed using
2
importance of the intramolecular connection between the
29
Olex2.
diphenyldichloroantimony moiety and the bipy ligand in 2.
Electrochemistry. Electrochemical experiments were performed
with an electrochemical analyzer from CH Instruments (Model 610A)
with a glassy-carbon working electrode and a platinum auxiliary
electrode. The reference electrode was built from a silver wire inserted
into a small glass tube fitted with a porous Vycor frit at the tip and
filled with a THF solution containing tetrabutylammonium
hexafluorophosphate (TBAPF , 0.1 M) and AgNO (0.005 M). All
CONCLUSIONS
■
The results presented in this article demonstrate that the redox
activity of a stibine ligand installed at the periphery of a
bipyridine ligand can be used to influence the electronic
properties of the latter. This conclusion is supported by an
investigation of the corresponding platinum dichloride
complexes and the observation that oxidation of the stibine
induces a red shift of the MLCT UV−vis absorption band and
an anodic shift of the reduction potential. These experimental
observations are corroborated by DFT calculations, which
show that this antimony-centered oxidation lowers the energy
of the LUMO. Last, we have also measured the effect of these
changes on the reactivity of the platinum center using the
hydroarylation of ethyl propiolate by mesitylene as a
benchmark reaction. These results indicate that the oxidized
complex 2 is more electrophilic, leading to greater product
yields.
6
3
three electrodes were immersed in a deoxygenated DMF solution (5
mL) containing TBAPF (0.1 M) as a support electrolyte and the
6
platinum complex (1, 2, or (bipy)PtCl ) (0.001 M). Ferrocene was
2
used as an internal standard, and all potentials are reported with
+
respect to the Fc/Fc redox couple.
Synthesis of L. n-Butyllithium (1.0 mL, 2.6 M in hexane, 2.6
mmol) was added dropwise to an Et O (5 mL) solution of 4-bromo-
2
2,2′-bipyridine (510 mg, 2.17 mmol) cooled to −100 °C. Once
addition was complete, the resulting orange suspension was kept at
this temperature and stirred for an additional 30 min. This solution
was kept at −100 °C and combined with a THF (5 mL) solution of
Ph SbCl (0.82 g, 2.63 mmol), which was added slowly using a
2
cannula. The resulting mixture was stirred at −100 °C for an
additional 1 h, before being warmed to room temperature. After 12 h,
the solvents were evaporated under vacuum. The residue was taken
up in CH Cl (20 mL) and filtered through Celite. The filtrate was
EXPERIMENTAL SECTION
General Considerations. All preparations were carried out under
■
2
2
brought to dryness and the resulting thick oily product mixture
purified by flash chromatography on silica gel (mobile phase: 1% ethyl
acetate in hexanes). The third major fraction was evaporated to an
oily residue, which was washed with pentane to yield L as a white
solid. Yield: 620 mg (45%). Single crystals of L suitable for X-ray
an N atmosphere using standard Schlenk techniques unless otherwise
2
2
0,21
22
23
stated. 4-Bromobipyridine, Ph SbCl,
were prepared according to previously reported procedures. Et O and
THF were dried by refluxing under N over Na/K. CH CN was dried
PhICl2, and (bipy)PtCl2
2
2
2
3
over CaH . All other solvents were ACS reagent grade and were used
diffraction were obtained by evaporation of a pentane/CH
2
Cl
): δ
2
2
1
as received. All chemicals were purchased from Sigma-Aldrich, Merck,
or Spectrochem and used as received. Thin-layer chromatography was
performed on a Merck 60 F254 silica gel plate (0.25 mm thickness).
Column chromatography was performed on a Merck 60 silica gel
solution at room temperature. H NMR (499.42 MHz, CDCl
3
8.56 (d, J = 4.0 Hz, 1H), 8.52 (s, 1H), 8.49 (d, J = 4.7 Hz, 1H), 8.28
(d, J = 8.0 Hz, 1H), 7.72 (td, J = 7.8, 1.8 Hz, 1H), 7.42−7.36 (m,
4H), 7.28 (m, 6H), 7.21 (ddd, J = 7.4, 4.8, 1.0 Hz, 1H), 7.19−7.16
1
3
(
100−200 mesh). Ambient-temperature NMR spectra were recorded
(m, 1H). C NMR (125.58 MHz, CDCl ): δ 156.15, 155.18, 150.43,
3
1
on a Varian Unity Inova 500 FT NMR (499.42 MHz for H, 125.58
149.17, 148.74, 137.28, 136.87, 136.30, 130.58, 129.11, 128.99,
MHz for 13C) spectrometer. Chemical shifts (δ) are given in ppm and
128.85, 123.65, 121.32. Anal. Calcd for C22
H N Sb: C, 61.29; H,
17 2
1
13
are referenced against the solvent signals ( H, C). Elemental
analyses were performed at Atlantic Microlab (Norcross, GA).
Absorbance measurements were taken on a Shimadzu UV-2502PC
UV−vis spectrophotometer against a solvent reference.
Computational Details. DFT structural optimizations were
conducted using the Gaussian 09 program. In all cases, the
structures were optimized using the B3LYP functional which has been
3.97. Found: C, 61.59; H, 4.33.
Synthesis of 1. The ligand L (150 mg, 0.35 mmol) and
Pt(CH CN) Cl (115 mg, 0.33 mmol) were combined in acetonitrile
(5 mL). The resulting mixture was warmed to 50 °C and stirred for 5
h. The precipitate that was obtained was filtered, washed with CH Cl
O (3 × 2 mL), and dried under vacuum to give a
3
2
2
2
2
2
4
(3 × 2 mL) and Et
2
1 as a pale yellow solid. Yield: 240 mg (82%). Single crystals of 1
17,25
widely applied for the study of bipy-platinum complexes.
In order
suitable for X-ray diffraction were obtained by diffusion of pentane
1
to optimize the efficiency of our computations while still treating the
heavy atoms at a sufficient level of theory, we used the mixed basis
sets cc-pVTZ-PP for Sb/Pt, 6-31g for C/H/N, and 6-31g(d′) for Cl,
with effective core potentials for the heavy elements. Optimizations
with the MPW1PW91 functional and the same basis sets were
considered but abandoned because they afforded geometries
exhibiting large deviations from the experimental ones. For all
optimized structures, frequency calculations were carried out to
confirm the absence of imaginary frequencies. TD-DFT calculations
were carried out using the B3LYP functional and the SMD solvation
model. The molecular orbitals were visualized and plotted using the
into a solution of the compound in CH
NMR (499.42 MHz, (CD
J = 5.8 Hz, 1H), 8.71 (s, 1H), 8.36 (m, 2H), 7.81 (t, J = 6.1 Hz, 1H),
2
Cl
2
inside an NMR tube. H
) SO): δ 9.47 (d, J = 5.9 Hz, 1H), 9.29 (d,
3 2
1
3
7.58 (d, J = 5.9 Hz, 1H), 7.55−7.47 (m, 4H), 7.46−7.36 (m, 6H).
C
NMR (125.58 MHz, (CD SO): δ 156.66, 154.96, 148.45, 146.67,
)
3 2
140.49, 137.82, 136.21, 134.02, 131.19, 129.21, 129.15, 128.89,
127.62, 123.97. Anal. Calcd for C H N SbPtCl : C, 37.90; H, 2.46.
2
2
17
2
2
Found: C, 38.15; H, 2.55.
Synthesis of 2. Complex 1 (100 mg. 0.14 mmol) was dissolved in
DMSO (5 mL) and treated with a DMSO (1 mL) solution of PhICl2
(40 mg, 0.15 mmol). The resulting yellow suspension was stirred for 1
26
Jimp2 program.
h. The solution was extracted with pentane (3 × 3 mL) and Et O (3
2
Crystallography. All crystallographic measurements were per-
formed at 110(2) K using a Bruker SMART APEX II diffractometer
× 2 mL) and recrystallized from CH Cl /Et O to yield a yellow solid.
2
2
2
Yield: 70 mg (64%). Single crystals of 2 suitable for X-ray diffraction
E
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were obtained by diffusion of pentane into a solution of the
Robertson, A. P. M.; Burford, N.; Patrick, B. O.; McDonald, R.;
1
3+
compound in CH Cl inside an NMR tube. H NMR (499.42 MHz,
Ferguson, M. J. Bipyridine complexes of E (E = P, As, Sb, Bi):
2
2
I
V
(
CD ) SO): δ 9.50 (m, 2H), 8.68 (s, 1H), 8.35 (td, J = 7.9, 1.3 Hz,
strong Lewis acids, sources of E(OTf) and synthons for E and E
3
2
3
1
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C NMR (125.58 MHz, (CD ) SO): δ 166.56, 156.34, 155.65,
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2
2
+
2+
153.06, 148.65, 147.57, 140.91, 132.71, 132.14, 129.76, 128.43,
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2
17
2
4
H, 2.23. Found: C, 34.33; H, 2.31.
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1
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0% ethyl acetate in hexanes). The NMR data collected match those
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ASSOCIATED CONTENT
Supporting Information
■
*
S
6
5
4
6 5 4
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00296.
That Activates Strong Element-Fluorine Bonds. J. Am. Chem. Soc.
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Additional experimental details and NMR spectra for
SbPh2
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and 1−4 (PDF)
Cartesian coordinates of the optimized structures (XYZ)
Halostibines SbMeX and SbMe X: Lewis Acids or Lewis Bases?
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Accession Codes
CCDC 1843560−1843562 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(
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AUTHOR INFORMATION
Corresponding Author
E-mail for F.P.G.: francois@tamu.edu.
■
sensing by an Sb(V)-substituted cyclometalated Ru polypyridyl
complex. J. Organomet. Chem. 2017, 847, 154−161.
*
(9) Mizuno, T.; Takeuchi, M.; Hamachi, I.; Nakashima, K.; Shinkai,
S. A boronic acid-diol interaction is useful for chiroselective
transcription of the sugar structure to the [Δ]- versus [Λ]-
ORCID
Franc o̧ is P. Gabbaï: 0000-0003-4788-2998
Notes
III
3+
[
Co (bpy) ] ratio. J. Chem. Soc., Perkin Trans. 2 1998, 2281−2288.
3
(
10) Minghetti, G.; Stoccoro, S.; Cinellu, M. A.; Soro, B.; Zucca, A.
The authors declare no competing financial interest.
Activation of a C−H Bond in a Pyridine Ring. Reaction of 6-
Substituted 2,2′-Bipyridines with Methyl and Phenyl Platinum(II)
Derivatives: N′,C(3)-“Rollover” Cyclometalation. Organometallics
ACKNOWLEDGMENTS
This work was supported by the National Science Foundation
CHE-1566474), the Welch Foundation (A-1423), and Texas
■
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hydrolysis of nitriles giving metal-bound iminols. J. Chem. Soc., Dalton
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A&M University (Arthur E. Martell Chair of Chemistry).
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