Heterometallic Palladium(II)-Indium(III) and -Gallium(III) Acetate-Bridged Complexes: Synthesis, Structure, and Catalytic Performance in Homogeneous Alkyne and Alkene Hydrogenation

Article abstract of DOI:10.1021/acs.inorgchem.8b01313

The reaction of Pd₃(OOCMe)₆ with indium(III) and gallium(III) acetates was studied to prepare new Pd^II-based heterometallic carboxylate complexes with group 13 metals. The heterometallic palladium(II)-indium(III) acetate-bridged complexes Pd(OOCMe)₄In(OOCMe) (1) and Pd(OOCMe)₄In(OOCMe)·MeCOOH (1a) were synthesized and structurally characterized with X-ray crystallography and extended X-ray absorption fine structure in the solid state and solution. A similar Pd-Ga heterometallic complex formed by the reaction of Pd₃(OOCMe)₆ with gallium(III) acetate in a dilute acetic acid solution, as evidenced by atmospheric pressure chemical ionization mass and UV-vis spectrometry, was unstable at higher concentrations and in the solid state. Complex 1 catalyzes the liquid-phase-selective phenylacetylene and styrene hydrogenation (1 atm of H₂ at 20 °C) in acetic acid, ethyl acetate, and N,N-dimethylformamide solutions, while no Pd metal was formed until alkyne and alkene hydrogenation ceased.

Full text of DOI:10.1021/acs.inorgchem.8b01313

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Heterometallic Palladium(II)−Indium(III) and −Gallium(III) Acetate-
Bridged Complexes: Synthesis, Structure, and Catalytic Performance
in Homogeneous Alkyne and Alkene Hydrogenation
Igor P. Stolarov,† Ilya A. Yakushev,† Andrei V. Churakov,† Natalia V. Cherkashina,†
Nadezhda S. Smirnova,† Evgeny V. Khramov,‡ Yan V. Zubavichus,‡ Victor N. Khrustalev,‡,§
Alexander A. Markov,† Alla P. Klyagina,† Alexey B. Kornev,∥ Vyacheslav M. Martynenko,∥
Alexander E. Gekhman,† Michael N. Vargaftik,*,† and Ilya I. Moiseev†
†Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, Russian Federation
‡National Research Center, Kurchatov Institute, Moscow, Russian Federation
§Peoples’ Friendship University of Russia (RUDN University), Moscow, Russian Federation
∥Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow, Russian Federation
S
* Supporting Information
ABSTRACT: The reaction of Pd3(OOCMe)6 with indium-
(III) and gallium(III) acetates was studied to prepare new
PdII-based heterometallic carboxylate complexes with group
13 metals. The heterometallic palladium(II)−indium(III)
acetate-bridged complexes Pd(OOCMe)4In(OOCMe) (1)
and Pd(OOCMe)4In(OOCMe)·MeCOOH (1a) were syn-
thesized and structurally characterized with X-ray crystallog-
raphy and extended X-ray absorption fine structure in the
solid state and solution. A similar Pd−Ga heterometallic
complex formed by the reaction of Pd3(OOCMe)6 with
gallium(III) acetate in a dilute acetic acid solution, as
evidenced by atmospheric pressure chemical ionization mass and UV−vis spectrometry, was unstable at higher concentrations
and in the solid state. Complex 1 catalyzes the liquid-phase-selective phenylacetylene and styrene hydrogenation (1 atm of H2 at
20 °C) in acetic acid, ethyl acetate, and N,N-dimethylformamide solutions, while no Pd metal was formed until alkyne and
alkene hydrogenation ceased.
1. INTRODUCTION
2. RESULTS AND DISCUSSION
Currently, multimetallic,1a particularly heterobimetallic PdII-
and PtII-based complexes, are attracting increasing attention as
single-molecular precursors to the mixed-metal nanoparticles
and heterogeneous catalysts.1b−g Unlike this, such hetero-
bimetallic complexes are less commonly used as unsupported
homogeneous catalysts.2 Recently, we found unexpectedly that
the unsupported heterobimetallic acetate-bridged complexes
PtII(μ-OOCMe)4MII(HOOCMe)4 (M = Ca, Sr, Ba) efficiently
2.1. UV−Vis Observation of Complexation. Normally,
indium(III) and gallium(III) triacetates are poorly soluble in
acetic acid. We found that In(OOCMe)3 and Ga(OOCMe)3
readily dissolve in glacial acetic acid containing Pd3(OOCMe)6
upon stirring at 60−80 °C. The reaction is accompanied by
systematical changes in time of the UV−vis spectrum of the
solution (Figure 1a−c).
These observations implied complexation of palladium(II)
acetate with indium(III) and gallium(III) acetates. The reaction
with indium(III) acetate proceeds to completion (Figure 1a).
Unlike this, the reaction with gallium(III) acetate observable at
low concentrations (Figure 1b) is not completed at higher
concentrations (Figure 1c), preventing preparation of the
crystalline heterometallic complex (see below).
catalyze partial alkyne hydrogenation the liquid phase.3a
A
similar catalytic effect was also found for the earlier synthesized
Pd-based analogues PdII(μ-OOCMe)4MII(HOOCMe)4 (M =
Ca, Sr, Ba).3b In this work, we attempted to extend the range of
complementary to PdII metals with group 13 elements in view of
the expected catalytic potential of new PdII-based heterometallic
complexes. One example of such complexes, Pd(OOCMe)4Tl-
(μ-OOCMe), has been reported,4a,b whereas the PdII-based
carboxylates with InIII and GaIII were unknown.
2.2. Mass Spectrometry (MS) Data. Additional evidence
of the formation of the Pd-based heterometallics with indium-
(III) and gallium(III) acetates gave MS analysis of the products
Received: May 16, 2018
© XXXX American Chemical Society
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Figure 1. Time profiles of the UV−vis spectra of the reaction solutions [Pd:In (Ga) = 1:1; glacial acetic acid; 80 °C]: (a) (Pd3(OOCMe)6 +
In(OOCMe)3, 0.965 × 10−3 mol L−1 each; (b) (Pd3(OOCMe)6 + Ga(OOCMe)3, 0.965 × 10−3 mol L−1 each; (c) reaction at high (Pd3(OOCMe)6 +
Ga(OOCMe)3 concentrations, 21 × 10−3 mol L−1 each (reaction solution probes diluted with acetic acid to 0.462 × 10−3 mol L−1 for spectral
recording).
Figure 2. (a) Positive region of the APCI-MS spectrum of the Pd3(OOCMe)6 + In(OOCMe)3 reaction product. (b) Negative region of the APCI-MS
spectrum of the Pd3(OOCMe)6 + In(OOCMe)3 reaction product.
of the Pd + In (Ga) reaction. The atmospheric pressure chemical
ionization MS (APCI-MS) spectrum of the product of the Pd +
In reaction in acetic acid revealed a high-intensity isotope cluster
with a maximum at m/z 517 in the positive region corresponding
to the protonated complex PdIn(OOCMe)5H+ and a smaller
isotope cluster with a maximum at m/z 457 corresponding to the
heterometallic ion PdIn(OOCMe)4+ (Figure 2a).
maximum at m/z 473 in the positive region corresponding to the
protonated molecule PdGa(OOCMe)5H+ (Figure 3a).
The negative region (Figure 3b) contains the main peak at m/
−
z 473 corresponding to the ion PdGa(OOCMe)5 .
2.3. Preparation of the Heterometallic Complexes. The
reaction between Pd3(OOCMe)6 and In(OOCMe)3 in glacial
acetic acid produced the crystalline complex Pd(OOCMe)4In-
(OOCMe)·HOOCMe (1a) as the crystal solvate in the yield
49% based on Pd. Recrystallization of 1a from benzene
produced the solvent-free complex Pd(OOCMe)4In(OOCMe)
(1) in the yield 36% based on Pd. Both 1 and 1a were
The negative region (Figure 2b) contains the main peak at m/
z 516 corresponding to the ion PdIn(OOCMe)5− and the low-
−
intensity peak at m/z 351 corresponding to the ion In(OAc)4 .
The APCI-MS spectrum of the product of the Pd + Ga
reaction in acetic acid detected an isotope cluster with a
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Figure 3. (a) Positive region of the APCI-MS spectrum of the Pd3(OOCMe)6 + Ga(OOCMe)3 reaction product. (b) Negative region containing the
−
main peak at m/z 473 corresponding to the ion PdGa(OOCMe)5 .
Figure 4. (a) Molecular structure of complex 1a showing disordering of the Pd and In surroundings. (b) Structure of complex 1 with solvation acetic
acid molecules. Displacement ellipsoids are shown at the 35% probability level (H atoms are omitted for clarity; for crystal data and structure
refinement, see Table 3). (c) Crystal packing of complex 1a.
structurally characterized with X-ray crystallography (see
below).
Unlike this, palladium(II)−gallium(III) complexation
through the reaction of Pd3(OOCMe)6 with Ga(OOCMe)3
was observed only in a fairly dilute (∼10−3 mol L−1) acetic acid
solution, which was evidenced by UV−vis spectrometry and
APCI-MS (see sections 2.1 and 2.2). However, numerous
attempts to concentrate the reaction solution for isolation of the
crystalline palladium(II)−gallium(III) heterometallic complex
were unsuccessful.
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Figure 5. Molecular structure of complex 1 with displacement ellipsoids shown at the 50% probability level (H atoms are omitted for clarity; for crystal
data and structure refinement, see Table 3).
Table 1. Selected Geometric Parameters of Complexes PdM(OOCMe)5 (M = Ga, In, Tl) in Angstroms
a
complex
method
Pd−Oeq
Pd−M
2.674
M−Oeq
M−O1
M−O2
ref
ax
PdGa(OAc)5
PBE0/def2-SVP
PBE0/MCP-TZP
M06/def2-SVP
PBE0-D3/MCP-TZP
PBE0/def2-SVP
PBE0-D3/MCP-TZP
exp. XRD
PBE0/def2-SVP
PBE0/MCP-TZP
PBE0-D3/MCP-TZP
exp. XRD
2.007
2.019
2.029
1.990 0.008
1.960 0.010
1.987 0.009
1.960 0.010
2.213 0.007
2.180 0.010
2.060(3)−2.200(3)
2.323 0.006
2.278 0.009
2.273 0.009
2.269(14)
1.833
1.800
1.825
1.799
2.171
2.124
2.186(7)
2.242
2.189
3.041
3.035
2.998
3.021
2.322
2.285
2.248(1)
2.406
2.368
2.362
2.353
2.637
2.710
2.641
2.790
2.760
2.7438(2)
2.781
2.746
2.750
2.702
2.017 0.001
2.005 0.002
2.016 0.003
1.995(3)−2.119(3)
2.003 0.001
2.015 0.002
2.014 0.002
2.003(7)
PdIn(OAc)5
PdTl(OAc)5
this work
4b
2.187
2.249
a
Mean values are shown with mean absolute deviations.
The failure origin is not clear. Most likely, this is due to the
aluminum(III) heterometallic complex by the reaction of
Pd3(OOCMe)6 with Al(OOCMe)3.
Hence, further studies were performed with the palladium-
known tendency of gallium(III) salts, particularly gallium(III)
acetate, to form unreactive, poorly dissolved gallium hydroxo
complexes through hydrolytic polymerization:5a−c
(II)−indium(III) complex 1.
2.4. X-ray Crystallography of 1 and 1a. The molecular
structure of complex 1a was determined with two parallel single-
crystal X-ray diffraction (XRD) techniques: (1) larger crystals
(0.20 × 0.16 × 0.06 mm) were studied using a Bruker SMART
Apex II laboratory diffractometer (Center of Shared Equipment
of the Kurnakov Institute) and (2) smaller crystals (0.15 × 0.07
× 0.04 mm) were studied on the Belok beamline of the
Kurchatov Synchrotron Radiation Source at the National
Research Center, Kurchatov Institute (Moscow, Russian
Federation). Both crystals 1 and 1a were prepared in
independent synthetic runs, and the results of both experiments
are very close each other.
Pd3(OOCMe)6 + Ga(OOCMe)3
F Pd(OOCMe)4Ga(OOCMe)
(i)
Ga(OOCMe)3 + H2O → {Ga(OH)(OOCMe)2}n
(ii)
In the synthesis, stage (i) seems to be reversible. Seemingly,
irreversible hydrolytic stage (ii) removes gallium(III) acetate
when the water content, even in the thoroughly dehydrated
(≤0.05 wt %) glacial acetic acid, is sufficient to shift left the
equilibrium stage (i). This obstacle was insignificant at the initial
period of the reaction at low reactant concentration (Figure 1b),
while it became prevailing in the synthetic runs at higher gallium
acetate concentration (Figure 1c) probably because of reaction
(ii) acceleration. We met the more hydrolytic confinement in an
attempt to prepare the acetate-bridged palladium(II)−
Analysis of the Fourier electron density synthesis for crystal 1a
revealed that the metal atoms are disordered over two positions
with nearly equal occupancies (Figure 4a). The distance
between two positions in structure 1a is approximately 0.6 Å.
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Figure 6. (a) Time profile for phenylacetylene hydrogenation (1 atm of H2 at 20 °C; PhCCH initial concentration 0.36 mol L−1) in 0.4 × 10−3 mol
L
−1 of complex 1 in an acetic acid solution: styrene accumulation (curve 1, red curve) and ethylbenzene accumulation (curve 2, black curve). (b) Time
profile for styrene-to-ethylbenzene hydrogenation (1 atm of H2 at 20 °C; PhCHCH2 initial concentration 0.35 mol L−1) in a 0.2 × 10−3 mol L−1
solution of complex 1 in different solvents: 1, acetic acid (red curve); 2, ethyl acetate (black curve); 3, DMF (green curve).
The crystal cell contains one disordered complex molecule
with a solvated acetic acid molecule, as shown in Figure 4a−c.
The solvent-free complex 1 was prepared by recrystallization
of 1a from dry benzene. The structure of crystal 1 (0.25 × 0.20 ×
0.02 mm) was studied with a Bruker SMART Apex II
diffractometer. The crystal cell contains one crystallographically
independent complex molecule without disorder, with relatively
short contact between the Pd and O atoms of the bridging acetic
group of adjacent molecule 1 [2.8361(2) Å].
The heterometallic molecule Pd(μ-OOCMe)4In(OOCMe)
in crystals 1a and 1 has a paddlewheel structure (Figure 5)
similar to that of the precedential palladium(II)−thallium(III)
complex Pd(OOCMe)4Tl(μ-OOCMe).4a,b
In both structures, the Pd−O, In−O, C−O, and Pd−In
interatomic distances are almost identical with each other and
the Pd atoms have a square-plane environment [distortion from
the O plane: 0.005(1)−0.038(2) Å in 1 and 1a] of four O atoms
belonging to the bridging acetate ligands connecting to the Pd
and In atoms [Pd−O 1.995(3)−2.119(3) Å; In−O 2.060(3)−
2.200(3) Å). The In atom has a six-coordinated environment in
1 [In−O 2.186(7)−2.248(13) Å] with the terminal acetate
group and a rather short Pd−In distance [2.7438(2) Å].
2.5. Density Functional Theory (DFT) Calculations of
PdM(OOCMe)5 (M = Ga, In, Tl). The equilibrium structure of
PdGa(OOCMe)5 acetate-bridged complex was calculated at
various computational levels (Table 1; see section 3.2.3 for
computational details). According to the calculations, the
interatomic distances R(Ga−Oeq) are significantly shorter (by
0.03−0.07 Å) than those in the other heterobimetallic
complexes. Similarly, the distance R(Pd−Ga) is also the shortest
among the considered complexes. Another feature of complex
PdGa(OOCMe)5 is monodentate coordination of the acetate
ligand. We were unable to calculate the equilibrium geometry of
PdIn(OOCMe)5 with the M06 functional and at PBE0/MCP-
TZP level, but the data obtained using the dispersion-corrected
PBE0 functional are in satisfactory agreement with the
experimental data. The same can be said with some caution
for complex PdTl(OOCMe)5. The calculated distance R(Pd−
Tl) in the equilibrium structures is significantly longer, by 0.04−
0.08 Å, compared to the XRD data.
with 3d transition6a−e and 4f rare-earth and alkaline-earth
metals.3a,7a−d Some of these complexes were successfully
practiced as precursors to supported catalysts for hydrogenation,
reductive dehydration, and other gas-phase and liquid-phase
reactions.8a−h
In this work, we unexpectedly found that unsupported
complex 1 catalyzes itself the partial alkyne and alkene
hydrogenation with H2 in the liquid phase. Generally,
monometallic palladium(II) complexes are easily reduced to
metallic Pd just by feeding of gaseous H2, whereas the catalytic
reaction proceeds over metallic Pd.9a−c
We also found that complex 1 was reduced by H2 in acetic
acid, N,N-dimethylformamide (DMF), and other solvents.
However, no reduction to Pd metal was observed when
phenylacetylene or styrene was preliminarily added to the
solution of 1 in acetic acid, ethyl acetate, and DMF, while alkyne
hydrogenation proceeded in homogeneous conditions without
the formation of Pd metal (Figure 6a,b).
H2/1
H2/1
PhC CH ⎯⎯⎯⎯→ PhCHCH2 ⎯⎯⎯⎯→ PhCH2CH3
Apparently, phenylacetylene and styrene acted as π ligands,
stabilizing an active form of the heterometallic complex. Just
after completion of hydrogenation, PdII was reduced to Pd
metal.
In our experiments, the initial rate (turnover frequency, TOF)
of styrene-to-ethylbenzene hydrogenation in an acetic acid
solution of Pd3(OOCMe)6 (just after its fast reduction with H2)
was 200 h−1, whereas in the solution of complex 1, the TOF was
at least 2400 h−1.
The catalytic ability of complex 1 is apparently due to the
influence of the complementary metal. In the crystal, the Pd and
In atoms are positioned at a rather short Pd−In distance,
2.7438(2) Å. It was of interest what happens upon passage of
molecule 1 to a solution in which it displayed catalytic behavior.
For this reason, we studied by extended X-ray absorption fine
structure (EXAFS) the structural changes in molecule 1 upon
transfer from a crystal to a solution.
2.7. EXAFS Study: Comparison of 1 in the Solid State
and Solution. Some information on the behavior of complex 1
in catalytic solutions could give EXAFS data. The Pd K-edge
EXAFS spectra showed that the coordination environment of
the Pd atom in 1 is retained upon dissolution in benzene and
glacial acetic acid (Figure 7).
2.6. Catalysis in Homogeneous Hydrogenation. Earlier
we synthesized and structurally characterized a series of
crystalline PdII-based heterometallic carboxylate complexes
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coordination to Pd atom of the alkene molecule, facilitating its
hydrogenation.
Figure 7. Pd K-edge EXAFS spectra of solid 1 (red dotted curve) and
0.91 × 10−3 mol L−1 solutions of 1 in glacial acetic acid (dark-red solid
curve) and benzene (black solid curve).
Figure 8. Pd K-edge EXAFS spectra of 0.91 × 10−3 mol L−1 solutions of
1 in DMF (gray thin line) and in glacial acetic acid (dark-red thick line).
Therefore, the mechanism of catalytic hydrogenation in a
solution of 1 needs additional investigation.
The atomic radial distribution functions around Pd atoms of
the solid 1 and its solutions in benzene and acetic acid have
coinciding maxima (Figure 7). The Fourier transforms of
EXAFS spectra have three main maxima for all of the samples.
The highest maximum corresponds to the coordination sphere
of Pd−O. The next peak was attributed to the distance between
the Pd and In atoms. The broad peak in the range between 3 and
4 Å (in the R−δ scale) is related to a set of Pd−O and Pd−C
distances.
Simulation of the Fourier transform of the EXAFS spectra for
1 showed that the Pd first coordination sphere has four
neighboring O atoms with a mean distance of 2.00 Å. A slight
increase in the coordination number for a Pd−O sphere in the
model for the solid sample is likely due to some disorder of its
structure. The model spectrum of solid 1 also confirms the
presence of a single In atom at the distance of 2.73 Å. The fitting
results show that dissolution of the complex in benzene or acetic
acid does not change noticeably its original structure (Table 2).
Unlike this, the Pd K-edge EXAFS spectrum of 1 in a DMF
solution (Figure 8) implies a distortion of the bimetallic
structure 1 in this medium, which possibly promotes
3. EXPERIMENTAL SECTION
3.1. Reagents and Solvents. Solvents [glacial acetic acid,
benzene, DMF, and acetonitrile (all reagent grade, Sigma-Aldrich)]
were purified by standard procedures.10 Glacial acetic acid for synthetic
runs was additionally dehydrated by reflux with B(OOCMe)3, followed
by rectification; the water content [gas chromatography (GC) analysis]
was at most 0.05%. Gaseous H2 (high purity, PGS service, Moscow,
Russian Federation) was fed at 1 atm from the cylinder through a
pressure regulator.
Palladium(II) acetate Pd3(OOCMe)6 was prepared by the oxidation
of Pd black [prepared by the reduction of PdCl2 (reagent grade,
Reakhim, Russia) with NaBH4] with concentrated HNO3 in glacial
acetic acid by a known procedure.11 The raw reaction product was
purified from the admixture of palladium(II) nitrite complexes by
refluxing in glacial acetic acid with a fresh portion of Pd black until NO2
evolution ceased, followed by recrystallization from hot acetic acid.
Gallium(III) and Indium(III) Acetates. A synthetic difficulty was the
high moisture sensitivity and fast aging of these chemicals. For that
reason, we used the starting materials prepared according to the
following protocols.
Ga(OOCMe)3. Gallium nitrate Ga(NO3)3·8H2O (4.29 g, 10 mmol)
prepared from high-purity gallium oxide (Sigma-Aldrich) was refluxed
in 50 mL of acetic anhydride until complete removal of nitrogen oxide
(2 h). The solution was evaporated to dryness on a rotary evaporator (1
mm, 70 °C in the bath) and dry-stored in a vacuum desiccator over
KOH. Yield: 2.58 g (97.6%). Anal. Calcd for GaC6H9O6: C, 29.18; H,
3.65. Found: C, 28.34; H, 4.46. IR (ATR, ν/cm−1): 1700 m, 1630 s,
1535 s, 1440 s, 1405 s, 1342 m, 1317 m, 1235 w, 1049 w, 1026 m, 968 w,
673 s, 632 s, 618 s.
Table 2. Results of Modeling of the EXAFS Spectra for Solid 1
and Its Solutions in Acetic Acid and Benzene (R =
Interatomic Distance, N = Coordination Number, σ2 = Debye
Factor, and R Factor = Matching Factor between the
Experimental and Model Spectra)
scattering pathway
R, Å
N
σ2, Å2
ΔE0, eV R factor, %
In(OOCMe)3. Indium nitrate In(NO3)3·4.5H2O (3.818 g, 10 mmol)
prepared from high-purity indium oxide (Sigma-Aldrich) was refluxed
for 3 h in 50 mL of acetic anhydride until complete removal of nitrogen
dioxide. The solution was evaporated to dryness on a rotary evaporator
(1 mm, 70 °C in the bath) and dry-stored in a vacuum desiccator over
KOH. Yield: 2.850 g (97.5%). The composition corresponds to water-
free In(OOCMe)3. Anal. Calcd for InC6H9O6: C, 24.68; H, 3.11.
Found: C, 24.83; H, 3.04. FTIR (ATR, cm−1): νas(COO) 1538,
νs(COO) 1410.
Solid 1
a
Pd−O
Pd−In
2.00
2.73
4.9
1.0
0.001
0.010
0.2
0.3
0.2
2.5
2.0
3.3
a
Solution of 1 in Acetic Acid
a
Pd−O
Pd−In
2.00
2.73
4.0
1.0
0.002
0.009
a
Solution of 1 in Benzene
a
Pd−O
Pd−In
1.99
2.76
4.0
1.0
0.003
0.012
a
3.2. Physical Measurements. Elemental analysis (C, H, and N)
was performed on an automated C,H,N-analyzer (EA3000, EvroVec-
tor, EU). UV−vis spectrometry was monitored on a Varian Cary 50
a
Fixed values in modeling.
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spectrophotometer with a standard built-in adjustable Peltier thermo-
stat in a quartz cell (10 mm) with a magnetic stirrer at 25−80 °C ( 0.1
°C). Attenuated-total-reflectance (ATR) IR spectra were recorded on a
Nicolet Nexus spectrometer with a Pike micro-ATR accessory.
3.2.1. XRD Analysis. The experimental intensities for 1 and 1a were
collected on a Bruker SMART APEX II and those for 1a on a Belok
beamline of the National Research Center, Kurchatov Institute, using a
Rayonix SX165 CCD detector at 150 and 100 K, respectively. Data
reductions were performed using SAINT software,12 and the
iMOSFLM utility in the CCP4i package for synchrotron studies.13
Absorption corrections based on measurements of equivalent
reflections were used.14 The structures were solved by direct methods
and refined by full-matrix least squares on F2 with anisotropic thermal
parameters for all non-H atoms.15 The In and Pd atoms were found to
be disordered over two proximal positions with almost equal
occupancies. They were refined with common thermal parameters
(EADP). All H atoms were placed in calculated positions and refined
using a riding model. Detailed crystallographic data are given in Table 3.
Crystallographic data for 1 and 1a have been deposited with the
Cambridge Crystallographic Data Center (CCDC 1841645−
1841647).
acetonitrile immediately before analysis (J. T. Baker, Phillipsburg, NJ;
stored over preactivated 4 Å molecular sieves) or glacial acetic acid to a
concentration of 0.1 mg mL−1. The solution was directly injected into
the mass spectrometer. The heat block was maintained at 150 °C and
the desolvation line at 150 °C. Nitrogen was used as the nebulizing and
drying gas (1.5 and 15 L min−1, respectively). The electrospray
interface voltage was set at 3.0 kV for positive ions and at −3.0 kV for
negative ions. The spectral range was m/z 200−2000. Shimadzu
LabSolutions software was used for data analysis.
3.2.3. Quantum-Chemical Calculations. The equilibrium geo-
metries of complexes PdM(CH3COO)5 (M = Ga, In, Tl) were found
using DFT functionals PBE016 and M0617 within spin-restricted
formalism. Grimme’s empirical dispersion correction scheme D39a was
used in conjunction with the PBE0 functional, as implemented18b in
GAMESS-US.19 The model core potential basis set MCP-TZP20 and
Ahlrich’s def2-SVP21a all-electron basis set for all atoms, except Pd, for
which the effective core potential was employed, were used. The def2-
SVP basis set was obtained from EMSL Basis Set Exchange Library.21b
All calculations were performed with the GAMESS-US package. We
used Jmol22 with POV-Ray software for visualization and figure
preparation.
3.2.4. XAFS. The XAFS spectra were measured on the Structural
Materials Science beamline on the synchrotron radiation source Sibir-2
at the National Research Center, Kurchatov Institute (Moscow,
Russian Federation). The X-ray beam (energy resolution ΔE/E ≈ 2
× 10‑4) was monochromatized using a silicon single crystal (220) with
the “butterfly” cut-out. The XAFS absorption spectra of Pd K-edge of
liquid and solid samples were recorded in transmission mode. The
XAFS spectra of solutions were collected in a quartz cuvette with an
optical path length of 5 cm. Two ionization chambers filled with argon
and xenon were used as detectors. The spectra were processed using the
IFEFFIT program package.23 The modeling of EXAFS spectra was
carried out in R space. The Fourier transforms of EXAFS oscillations
were taken in a range of k = 3−12 Å−1 with the weight coefficient k2 and
approximated in a range of R = 1.1−2.8 Å.
3.2.2. MS Characterization. Electrospray and DUIS MS spectra
were obtained with a Shimadzu LCMS-2020 instrument (Shimadzu
Scientific Instruments, Kyoto, Japan). Samples were dissolved in
Table 3. Crystal Data and Structure Refinement for 1a and 1
1a
1a
1
X-ray source
type
fine-focus sealed
tube
synchrotron
fine-focus sealed
tube
empirical
formula
C12H19InO12Pd
C12H19InO12Pd
C10H15InO10Pd
fw
576.49
576.49
100(2)
516.44
150(2)
temperature, K 150(2)
3.3. Syntheses. 3.3.1. Pd(μ-OOCMe)4InOOCMe·AcOH (1a). A
mixture of palladium acetate (224 mg, 1 mmol based on Pd) and
indium acetate (292 mg, 1 mmol) was stirred under reflux in 7 mL of
glacial acetic acid until a clear yellow-orange solution was formed (0.5
h). The reaction progress was monitored by UV−vis spectrometry of
the reaction solution probes. The resulting solution was cooled to room
temperature. An orange fine-crystalline precipitate was filtered off,
washed with dry ether, and dried in a vacuum desiccator over KOH.
Yield of 1a: 280 mg, 49% based on Pd. Anal. Calcd for PdInC12H19O12:
C, 25.00; H, 3.32. Found: C, 25.47; H, 3.50. IR (ATR, ν/cm−1): 3015
br w, 1722 w, 1701 m, 1589 s, 1395 s, 1347 m, 1265 m, 1229 m, 1049 m,
1028 m, 960 w, 922 m, 692 s, 626 s, 606 w, 574 w.
3.3.2. Pd(μ-OOCMe)4InOOCMe (1). Recrystallization of 1a from
benzene produced the solvent-free complex 1 in a yield of 36% based on
Pd. Anal. Calcd for PdInC10H15O10: C, 23.25; H, 2.92. Found: C, 24.02;
H, 2.86. IR (ATR, ν/cm−1): 1689 w, 1585 s, 1552 sh, 1445 w, 1414 s,
1396 s, 1351 m, 1296 m, 1047 m, 960 w, 972 m, 694 s, 628 m, 609 w,
593 w, 564 w, 551 m.
cryst size, mm
wavelength, Å
cryst syst
space group
a, Å
b, Å
c, Å
α, deg
β, deg
0.20 × 0.16 × 0.06 0.15 × 0.07 × 0.04 0.25 × 0.20 × 0.02
0.71073
triclinic
0.96990
triclinic
0.71073
triclinic
P1
̅
P1
̅
P1
̅
7.2405(8)
8.2457(9)
8.5297(10)
94.6170(10)
108.447(2)
104.6270(10)
460.23(9)
1
7.2309(15)
8.2458(17)
8.5495(17)
94.618(10)
108.59(2)
104.522(18)
460.51(17)
1
7.2536(8)
8.7112(10)
12.8212(15)
84.983(2)
84.397(2)
73.875(2)
773.01(15)
2
γ, deg
V, Å3
Z
density (calcd), 2.080
2.079
2.219
Mg mm−3
μ, mm−1
2.288
5.231
2.701
F(000)
θ range, deg
index range
282
282
500
2.59−27.79
4.244−38.427
2.44−29.00
Both 1 and 1a were structurally characterized with X-ray
crystallography.
−9 ≤ h ≤ 9, −10 −9 ≤ h ≤ 9, −10 −9 ≤ h ≤ 9, −11
≤ k ≤ 10, −11 ≤
≤ k ≤ 10, −10 ≤
≤ k ≤ 11, −17 ≤
3.3.3. Pd(μ-OOCMe)4Ga(OOCMe)·2AcOH (2). Palladium acetate
(105 mg, 0.47 mmol) and gallium acetate (116 mg, 0.47 mmol) in a
mixture of water-free acetic acid containing 0.3% acetic anhydride (40
mL) and n-octane (30 mL) and) were stirred at 80 °C for 80 min. The
reaction progress was monitored by UV−vis spectrometry of the
reaction solution probes. The resulting light-yellow solution was filtered
off and carefully evaporated almost to dryness on a rotary evaporator
with a membrane rotor pump (vacuum 9 Torr, evaporator water bath
20−30 °C, and receiver flask −10 °C). The soggy residue was stored in
a fridge (+5 °C) for 12 h, aimed at obtaining the crystalline Pd−Ga
complex. As a result, we obtained a yellow amorphous solid containing
no crystal phase. The yield of dry 2 is 245 mg (81% based on Pd). Anal.
Calcd for PdGaC16H24O16: C, 29.63; H, 3.73. Found: C, 29.55; H, 3.78.
IR (ATR, ν/cm−1): 20937 br w, 1713 w, 1599 s, 1566 sh, 1416 s, 1351
m, 1267 w, 1225 w, 1046 m, 973 m, 737 691 s, 671 s, 623 m, 580 w, 561
l ≤ 11
l ≤ 10
l ≤ 17
reflns collected 4762
indep reflns
8131
1847 (Rint
0.0762)
1523
8607
4078 (Rint
0.0156)
3718
2215 (Rint
0.0108)
2140
=
=
=
reflns obsd
R1/wR2 [I >
2σ(I)]
0.0367/0.0840
0.0375/0.0843
1.375
0.0286/0.0656
0.0180/0.0424
R1/wR2 (all
0.0407/0.0711
0.0206/0.0436
data)
GOF on F2
1.090
1.050
extinction coeff 0.000
min/Tmax 0.6576/0.8749
0.0121(17)
0.490/0.802
0.481/−0.913
0.000
0.5516/0.9480
0.575/−0.657
T
Δρmax/Δρmin, e 1.120/−0.808
Å−3
G
DOI: 10.1021/acs.inorgchem.8b01313
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
w, 553 w. Numerous synthetic runs attempting isolation of the
crystalline complex by varying the reaction conditions resulted in a
noncrystalline reaction product only.
Ilya A. Yakushev: 0000-0001-6784-947X
Andrei V. Churakov: 0000-0003-3336-4022
Natalia V. Cherkashina: 0000-0002-5435-2226
Nadezhda S. Smirnova: 0000-0001-6911-0070
Evgeny V. Khramov: 0000-0002-7111-5628
Yan V. Zubavichus: 0000-0003-2266-8944
Victor N. Khrustalev: 0000-0001-8806-2975
Alexander A. Markov: 0000-0002-7035-0490
Alla P. Klyagina: 0000-0003-4326-6573
Alexey B. Kornev: 0000-0002-4217-4063
Vyacheslav M. Martynenko: 0000-0003-0901-0590
Alexander E. Gekhman: 0000-0002-5081-9095
Michael N. Vargaftik: 0000-0001-6574-4906
Ilya I. Moiseev: 0000-0002-8954-7322
3.4. Catalysis. Catalytic experiments were carried out in a glass
temperature-controlled (water-jacketed), magnetically stirred flask of
50 mL volume (5 mL of reaction solution, liquid/gas ratio 1:10, and
stirring rate 600 rpm). A solution of phenylacetylene (410 mg, 4 mmol)
or styrene (208 mg, 2 mmol) in acetic acid, ethyl acetate, or DMF
containing complex 1 (1 mg, 0.002 mmol, or 0.5 mg, 0.001 mmol, for
phenylacetylene and styrene, respectively) was stirred under H2 (1 atm)
at 20 °C, while the reaction solution remained homogeneous and clear.
After 100% styrene conversion, Pd metal sediment and/or a black thin
coating on glass appeared. The reaction solution was periodically
sampled and monitored by GC (Shimadzu GC-17A, 25 m capillary
column, XE-60 phase).
4. CONCLUSIONS
Notes
This study was originally intended to challenge the lack of
palladium and platinum carboxylate-bridged heterometallics
with 13 group metals from In to Al, being encouraged by the
earlier successful synthesis of the palladium−thallium acetate
from Pd3(OOCMe)6 and Tl(OOCMe)3 by van der Ploeg et al.4a
and Balch et al.4b Our experiments showed that only one of the
three candidates, indium(III), readily forms a Pd-based acetate-
bridged heterometallic complex 1. An analogous complex with
gallium(III) acetate Pd(OOCMe)4Ga(OOCMe) was detected
in a dilute (∼10−3 mol L−1) acetic acid solution; however, it was
not separated as a crystalline solid from more concentrated
solutions seemingly because of high hydrolytic susceptibility
even at the minor water content (≤0.05%) in glacial acetic acid.
We met more hydrolytic obstruction in attempts to prepare a
Pd-based complex with aluminum(III) acetate.
The heterometallic Pd−In complex 1 was structurally
characterized with X-ray crystallography and EXAFS in the
solid state and solution using both the standard laboratory and
synchrotron XRD techniques. Unexpectedly, we found that the
unsupported complex 1 catalyzes itself in partial phenyl-
acetylene and styrene hydrogenation in the liquid phase,
whereas no Pd metal was formed until alkyne and alkene
hydrogenation ceased. This fact emphasizes the significant role
of supplementary nontransition metals in homogeneous
catalysis with noble metals24a−c but needs more detailed
investigation.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are thankful for financial support to the Russian
Foundation for Basic Research (Projects 17-03-00355, 18-03-
00228, and 18-33-00632) and, in part, by the RUDN University
Program “5-100”. Synchrotron-radiation-based single-crystal
XRD measurements were performed at the unique scientific
facility Kurchatov Synchrotron Radiation Source supported by
the Ministry of Education and Science of the Russian Federation
(Project Code RFMEFI61917X0007).
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ASSOCIATED CONTENT
* Supporting Information
■
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̀
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The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01313.
Crystal data and structure refinement for 1a and 1 (PDF)
Accession Codes
CCDC 1841645−1841647 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
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AUTHOR INFORMATION
Corresponding Author
*E-mail: wahr36@gmail.com (M.N.V.).
■
ORCID
Igor P. Stolarov: 0000-0002-3756-7938
H
DOI: 10.1021/acs.inorgchem.8b01313
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