Ga[OSi(OtBu)3]3·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry

Article abstract of DOI:10.1039/c6dt01676f

The molecular precursor tris[(tri-tert-butoxy)siloxy]gallium, as the tetrahydrofuran adduct Ga[OSi(O^tBu)₃]₃·THF (1), was synthesized via the salt metathesis reaction of gallium trichloride with NaOSi(O^tBu)₃. This complex serves as a model for isolated gallium in a silica framework. Complex 1 decomposes thermally in hydrocarbon solvent, eliminating isobutylene, water, and tert-butanol to generate high surface area gallium-containing silica at low temperatures. When thermal decomposition was performed in the presence of P-123 Pluronic as a templating agent the generated material displayed uniform vermicular pores. Textural mesoporosity was evident in untemplated material. Co-thermolysis of 1 with HOSi(O^tBu)₃ in the presence of P-123 Pluronic led to materials with Ga : Si ratios ranging from 1 : 3 to 1 : 50, denoted UCB1-GaSi₃, UCB1-GaSi₁₀, UCB1-GaSi₂₀ and UCB1-GaSi₅₀. After calcination at 500 °C these materials exhibited decreasing surface areas and broadening pore distributions with increasing silicon content, indicating a loss of template effects. The position and dispersion of the gallium in UCB1-GaSi materials was investigated using ⁷¹Ga MAS-NMR, powder XRD, and STEM/EDS elemental mapping. The results indicate a high degree of gallium dispersion in all samples, with gallium oxide clusters or oligomers present at higher gallium content.

Full text of DOI:10.1039/c6dt01676f

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
t
Ga[OSi(O Bu) ] ·THF, a thermolytic molecular
3
3
precursor for high surface area gallium-containing
silica materials of controlled dispersion and
stoichiometry†
Cite this: Dalton Trans., 2016, 45,
11025
a,c
b
b,c
a,c
James P. Dombrowski, Gregory R. Johnson, Alexis T. Bell* and T. Don Tilley*
t
The molecular precursor tris[(tri-tert-butoxy)siloxy]gallium, as the tetrahydrofuran adduct Ga[OSi(O Bu)
3 3
] ·
t
THF (1), was synthesized via the salt metathesis reaction of gallium trichloride with NaOSi(O Bu)
3
.
This complex serves as a model for isolated gallium in a silica framework. Complex 1 decomposes
thermally in hydrocarbon solvent, eliminating isobutylene, water, and tert-butanol to generate high
surface area gallium-containing silica at low temperatures. When thermal decomposition was performed
in the presence of P-123 Pluronic as a templating agent the generated material displayed uniform vermi-
cular pores. Textural mesoporosity was evident in untemplated material. Co-thermolysis of 1 with HOSi
t
(
O Bu)
3
in the presence of P-123 Pluronic led to materials with Ga : Si ratios ranging from 1 : 3 to 1 : 50,
, UCB1-GaSi10, UCB1-GaSi20 and UCB1-GaSi50. After calcination at 500 °C these
denoted UCB1-GaSi
3
materials exhibited decreasing surface areas and broadening pore distributions with increasing silicon
Received 29th April 2016,
Accepted 10th June 2016
content, indicating a loss of template effects. The position and dispersion of the gallium in UCB1-GaSi
71
materials was investigated using Ga MAS-NMR, powder XRD, and STEM/EDS elemental mapping. The
DOI: 10.1039/c6dt01676f
results indicate a high degree of gallium dispersion in all samples, with gallium oxide clusters or oligomers
present at higher gallium content.
www.rsc.org/dalton
used as catalysts for several liquid phase reactions including
Introduction
3
–7
epoxidation and Friedel–Crafts alkylation.
Interestingly,
Zeolitic and mesoporous gallium-containing materials have gallosilicates appear to exhibit catalytic properties that are
attracted interest as heterogeneous catalysts for a variety of different from those of comparable aluminosilicates, though
1
industrially important transformations. For example, zeolites the former are relatively less studied. For example, the Friedel–
containing gallium have been widely studied as catalysts for Crafts benzylation of benzene with benzyl chloride occurs
propane dehydrogenation to propene and propene aromatiza- readily over gallium-incorporated mesoporous silicas, while
7
,8
tion, a reaction sequence commercialized as the Cyclar the aluminum analog is significantly less active. The reverse
1
,2
process. It has been proposed that both framework gallium, is found when benzyl alcohol is used as the alkylating
7
i.e. gallium directly occupying a silicon position in the crystal- reagent. These differences suggest that additional study of
line lattice, and extra-framework gallium play a role in this cat- gallium-containing silicas may yield important new discoveries
2
alysis. Mesoporous gallium-containing silicas have also been in catalysis.
A better understanding of the chemical properties associ-
ated with gallium centers should result from studies of
gallium siloxide molecular models, or molecular chemistry
a
Department of Chemistry, University of California, Berkeley, Berkeley, California
9
b
4720-1460, USA. E-mail: tdtilley@berkeley.edu
designed to provide well-defined, single-site gallium materials.
However, few molecular gallium siloxides are known, and
none have been used to generate gallium-containing silica
Department of Chemical and Biomolecular Engineering, University of California,
Berkeley, Berkeley, California 94720-1460, USA
c
Chemical Sciences Division, Lawrence Berkeley Laboratory, 1 Cyclotron Road,
9
,10
Berkeley, California 94720, USA
†
materials.
This laboratory has employed a synthetic strat-
Electronic supplementary information (ESI) available: NMR spectra of mole-
egy, termed the thermolytic molecular precursor (TMP)
method, to utilize appropriately designed molecular complexes
that serve as spectroscopic and structural models for an active
site, and as precursors to materials that possess such active
cular precursors, vibrational spectroscopy of precursors, powder XRD patterns of
all materials, HAADF-STEM images of all materials, crystallographic data, TG/
DTA data of precursor mixtures. CCDC 1477192. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c6dt01676f
This journal is © The Royal Society of Chemistry 2016
Dalton Trans., 2016, 45, 11025–11034 | 11025

View Article Online
Paper
Dalton Transactions
sites. This approach starts with an oxygen-rich molecular pre- and a ramp rate of 10 °C min− . Powder X-ray diffraction
1
cursor containing the active core of interest, using ligands that data was collected at the University of California-Berkeley,
model the oxide support. For example, a M–O–SiO
3
moiety is CHEXRAY instrumentation facility using a D8 Discover GADDS
linkage. Such tri(tert-butoxy) Powder XRD instrument with a fine-focus sealed source (Cu-Kα
siloxy complexes have been found to readily provide access to radiation). Ammonia-TPD measurements were performed at
materials containing M[–O–SiO sites, via thermal elimin- the Center for the Development of Precision Chemical
t
modeled by a M–O–Si(O Bu)
3
3 n
]
1
1
ation of isobutene and water. These precursors have been Materials housed at Chonnam National University.
used to generate bulk materials with high dispersion of the
Single-crystal X-ray crystallography
metal sites, or in surface modification reactions that introduce
1
2
such sites onto an oxide support.
This report describes new molecular precursor,
Single-crystal X-ray studies were performed at the University of
California-Berkeley CHEXRAY instrumentation facility using
a
a
tetrahydrofuran adduct of tris[(tri-tert-butoxy)siloxy]gallium, an Apex II Quazar instrument with a microfocus sealed source
t
3 3
Ga[OSi(O Bu) ] ·THF (1), as a thermolytic precursor to (Incoatec IµS; Mo-Kα radiation, λ = 0.71073 Å). Measurements
gallium-containing silica materials. Compound 1 represents were taken on a Bruker APEX II CCD area detector and the
the first precursor to gallium-silica materials containing solely data collection was computed and integrated using the Bruker
Ga–O–SiO covalent linkages and serves as a good spectro- APEX2 software package. Bruker SAINT was used for cell refine-
3
scopic model for gallium isolated on silica. As detailed below, ment and data reduction. The structure was solved using
complex 1 is also an effective, low-temperature precursor to SHELXS-97 (Sheldrick 2008) and was refined using
gallium-silica materials with variable Ga : Si ratios of 1 : 3 to SHELXL-2013 (Sheldrick 2013). A 0.06 mm × 0.08 mm ×
1
: 50. This TMP method is suitable for use with a templating 0.14 mm colorless plate-like crystal was used for the X-ray ana-
agent, P-123 Pluronic, which allows some control over the lyses in a frozen glass of paratone N hydrocarbon oil at 100(2)
material’s surface area and morphology.
K under a flow of nitrogen.
HAADF-STEM and STEM/EDS elemental mapping
Imaging by high-angle annular dark-field scanning trans-
mission electron microscopy (HAADF-STEM) and scanning
transmission electron microscopy energy dispersive spec-
troscopy (STEM-EDS) was performed at the Molecular Foundry
at the Lawrence Berkeley National Laboratory using an FEI
Titan electron microscope. Samples were prepared for imaging
by drop-casting 5 µL of an ethanol suspension of the sample
particles onto a lacey carbon Cu TEM grid. The grids were then
dried in a vacuum oven at 383 K for 1 h to evaporate the
solvent. All imaging was performed using a 200 kV accelerating
voltage. Elemental mapping by STEM-EDS was conducted
using a Bruker silicon drift detector that collected fluorescent
X-rays from 0 to 20 keV with a 140 eV energy resolution and 10
eV per channel dispersion. Processing and quantification of
the elemental maps was done using the Bruker Esprit software
program.
Experimental
General
All synthetic manipulations were performed under a nitrogen
atmosphere using Schlenk techniques or in a glovebox, unless
otherwise noted. Tetrahydrofuran (unstabilized, Macron),
pentane (Fisher Chemical HPLC grade) and toluene (Fisher
Chemical HPLC Grade) were dried using a JC Meyer Solvent
Column system and used without further treatment. Benzene-
d and toluene-d were used for all NMR experiments and were
6
8
deoxygenated with three freeze–pump–thaw cycles and dried
for a minimum of 24 h over 3 Å molecular sieves before use.
Calcinations were performed in a Lindberg 1200 °C three-zone
3
−1
tube furnace with a flow rate of 100 cm min using oxygen
99.96%). Gallium trichloride (99.999%, Strem Chemical) was
stored in a glovebox and used without further purification.
(
t
t
3 3
HOSi(O Bu) , NaOSi(O Bu) and SBA-15 were synthesized by
7
1
1
2–14
Ga MAS-NMR spectroscopy
literature methods.
7
1
Solid state Ga MAS-NMR spectroscopy was performed at the
NMR Facility at the University of California, Davis. The
Characterization
1
13
H and C NMR spectra were collected on a Bruker AVB-400 samples were run on a Bruker AVANCE 500 wide-bore NMR
NMR spectrometer at 400 MHz referenced internally to tetra- spectrometer equipped with a 11.74 T magnet. After hydration
methylsilane. All 2D-NMR spectra were collected on a Bruker in a saturated water atmosphere for a minimum of 48 h,
2
9
AV-500 NMR spectrometer at 500 MHz. Si NMR spectra were samples were packed into a 2.5 mm rotor for analysis. A
collected on a Bruker AV-600 NMR spectrometer at 600 MHz. 2.5 mm probe was used. A single pulse of 0.31 μs pulse length
IR spectra were collected on a Thermo Nicolet 6700 FTIR (corresponding to 45° tip-angle) and a relaxation delay of 0.1 s
spectrometer using NaCl as a background and a pentane film were used for data acquisition. Chemical shifts were externally
of 1 between NaCl plates as the sample. Raman spectra were referenced to a gallium trichloride solution. All samples were
collected on a Horiba Yvon Jobin labRAM HR confocal Raman run at 34 kHz. UCB1-GaSi was run with a dwell time of 1 μs
3
spectrometer with a wavelength of 633 nm. Thermogravimetric and 441 490 scans, UCB1-GaSi10 was run with a dwell time of
analyses were performed on a Seiko Instruments Inc. EXSTAR 1 μs and 565 621 scans, UCB1-GaSi50 was run with a dwell time
3
−1
6
000 series TG/DTA 6300 under a gas flow of 100 cm min
of 5 μs and 498 390 scans.
11026 | Dalton Trans., 2016, 45, 11025–11034
This journal is © The Royal Society of Chemistry 2016

View Article Online
Dalton Transactions
Paper
In situ FTIR spectroscopy with pyridine
ture the ampule was ruptured and the contents were emptied
onto an evaporation dish to air dry. After three days the
remaining solids were calcined at 500 °C under O for 3 h. The
2
solids were collected, ground with a mortar and pestle to form
a powder, and dehydrated at 120 °C under dynamic vacuum
for 12 h before being stored in a glovebox. Anal. Calcd for
In situ pyridine adsorption followed by FTIR spectroscopy was
performed using a Nicolet 6700 FTIR spectrometer equipped
with a Praying Mantis DRIFTS cell attachment (Harrick).
Samples were diluted with potassium bromide and loaded into
the DRIFTS cup of the High Temperature Reaction Chamber.
Samples were pretreated at 120 °C for a minimum of
2 3 2
Ga O ·3SiO : Ga, 25.45; Si, 30.75. Found: Ga, 22.2; Si, 28.2, C,
1.53; H, 0.85 (corresponds to a Ga : Si ratio of 1 : 3.16).
50 minutes under He flow (20 mL min−1) before 2 µL of pyri-
1
dine was vaporized into the He carrier gas and passed through
the sample. Spectra were recorded post-injection until no
changes between sequential spectra were observed. The areas
of absorbance bands corresponding to Brønsted acid sites
Synthesis of UCB1-GaSi materials with lower gallium content
A mixture of 1 and tris(tert-butoxy)silanol (0.600 g),) with the
ratios adjusted to afford the desired stoichiometry, was dis-
solved in a solution of 0.200 g of P-123 Pluronic in 6 mL of dry
toluene. This solution was then transferred to a 10 mL glass
ampule interfaced to a glass tube with a 14/20 ground glass
joint and a Teflon stopper through a Cajon adapter. The appar-
atus was removed from the glovebox, sealed under nitrogen,
and transferred to a Schlenk line. Three freeze–pump–thaw
cycles were performed before the ampule was flame-sealed
under vacuum while still frozen to prevent over-pressurization
during precursor thermolysis. After warming to room tempera-
ture the sealed ampule was placed in an oil bath at 135 °C for
(
∼1545) and Lewis acid sites (∼1455) were determined from
the subtraction result of spectra taken after helium treatment
at 120 °C and after pyridine adsorption signals had stabil-
15
ized. The Brønsted/Lewis acid site ratios were calculated
using the peak areas and their respective molar extinction
1
6
coefficients.
t
Synthesis of Ga[OSi(O Bu)
3
]
3
·THF (1)
t
A 30 mL THF solution of Na[OSi(O Bu) ] (2.156 g, 7.53 mmol)
3
3
was added dropwise over ten minutes to a 100 mL glass round-
bottom Schlenk flask containing a stirred solution of GaCl3
24 h, which resulted in the formation of a pale yellow gel. After
cooling to room temperature the ampule was ruptured and the
contents were emptied onto an evaporation dish to air dry.
After three days the remaining solids were calcined at 500 °C
under O for 3 h. The solids were collected, ground by mortar
2
and pestle to a powder, and dehydrated at 120 °C under
dynamic vacuum for 12 h before being stored in a glovebox.
Anal. Calcd for Ga O ·20SiO : Ga, 10.04; Si, 40.44. Found:
2 3 2
Ga, 8.18; Si, 32.5, C, 0.61; H, <0.2 (corresponds to a Ga : Si ratio
of 1 : 9.54).
2 3 2
Anal. Calcd for Ga O ·40SiO : Ga, 5.38; Si, 43.36. Found:
Ga, 4.81; Si, 38.7, C, 0.42; H, <0.2 (corresponds to a Ga : Si ratio
of 1 : 20.0).
(0.465 g, 2.64 mmol) in 10 mL of THF. During addition, an
opaque white suspension formed. After 90 minutes the solu-
tion was evaporated to dryness in vacuo leaving a white to pale-
yellow solid. Extraction with pentane and filtration followed by
evaporation to dryness in vacuo yielded a white solid (74%
yield, 1.72 g, 1.85 mmol). Recrystallization from THF at −30 °C
gave colorless crystals suitable for X-ray crystallography. Anal.
3
Calcd for C40H89GaO13Si : C, 51.54; H, 9.62. Found: C, 51.42;
H, 9.72. IR (pentane film between NaCl plates, KBr beamsplit-
ter, 500–3500 cm− ): 2972 s, 2929 wsh, 2872 wsh, 1460 w, 1387
w, 1363 m, 1238 msh, 1217 w, 1196 s, 1103 wsh, 1051 vs, 1026
ssh, 912 wbr, 864 wbr, 829 m, 804 vw, 702 m, 665 w, 515
1
2 3 2
Anal. Calcd for Ga O ·100SiO : Ga, 2.25; Si, 45.33. Found:
Ga, 1.95; Si, 38.8, C, 0.16; H, <0.2 (corresponds to a Ga : Si ratio
of 1 : 49.4).
−
1
w. Raman (633 nm laser, 100–2000 cm ): 1448 s, 1239 m,
191 wsh, 1030 wbr, 907 msh, 824 wsh, 800 ssh, 650 m, 535 w,
1
1
t
H NMR (benzene-d , 400 MHz, 20 °C): δ 1.51 (s, 81H, O Bu,
4
6
1
3
1
H, THF overlapping), δ 4.42 (bs, 4H, THF). C{ H} NMR Synthesis of untemplated Ga O ·3SiO material
2 3 2
t
6
(benzene-d , 400 MHz, 20 °C): δ 72.20 (THF), δ 32.41 (SiO Bu), δ
In a typical preparation, 0.600 g of 1 was dissolved in 6 mL of
dry toluene. This solution was then transferred to a 10 mL
glass ampule interfaced to a glass tube with a 14/20 ground
glass joint and a Teflon stopper through a Cajon adapter. The
2
9
2
5.34 (THF). Si NMR (benzene-d , 600 MHz, 20 °C): δ −94.75.
6
3
Synthesis of UCB1-GaSi material
In a typical preparation, in a drybox 0.600 g of 1 was dissolved apparatus was removed from the glovebox, sealed under nitro-
in a solution of 0.200 g of P-123 Pluronic in 6 mL of dry gen, and transferred to a Schlenk line. Three freeze–pump–
toluene. This solution was then transferred to a 10 mL glass thaw cycles were performed before the ampule was flame-
ampule interfaced to a glass tube with a 14/20 ground-glass sealed under vacuum while still frozen to prevent over-pressur-
joint and a Teflon stopper through a Cajon adapter. The appar- ization during precursor thermolysis After warming to room
atus was sealed under nitrogen, removed from the glovebox, temperature, the sealed ampule was placed in an oil bath pre-
and transferred to a Schlenk line. Three freeze–pump–thaw heated to 135 °C for 24 h. During this time, depending on the
cycles were performed before the ampule was flame-sealed sample, a clear, pale yellow gel formed. After cooling to room
under vacuum while still frozen to prevent over-pressurization temperature the ampule was ruptured and the contents were
during thermolysis. After warming to room temperature, the emptied onto an evaporation dish to air dry. After three days
sealed ampule was placed in a 135 °C oil bath for 24 h to the remaining solids were calcined at 500 °C under O
2
for 3 h.
produce a solid pale-yellow gel. After cooling to room tempera- The solids were then collected, ground with a mortar and
This journal is © The Royal Society of Chemistry 2016
Dalton Trans., 2016, 45, 11025–11034 | 11027

View Article Online
Paper
Dalton Transactions
pestle to a powder, and dehydrated at 120 °C under dynamic
vacuum for 12 h before being stored in a glovebox.
Results & discussion
Synthesis of 1
t
The complex Ga[OSi(O Bu)
3
]
3
·THF (1) was synthesized by
addition of 2.9 equivalents of sodium tris(tert-butoxy)silano-
late to gallium trichloride in THF. Following evaporation and
extraction with pentane, the product was recrystallized from
THF as analytically pure colorless crystals in 74% yield
(Scheme 1).
Single-crystal X-ray crystallographic characterization of 1
Fig. 1 Thermal ellipsoid plot of 1 at the 40% probability level. The
hydrogen atoms are omitted for clarity.
Single, plate-like crystals of 1 were obtained by recrystallization
from a concentrated THF solution at −30 °C. X-ray crystallo-
graphic analysis confirmed the complex to be the monomeric
THF adduct. Unfortunately, the structure exhibited total mole-
cular disorder, which prevents determination of precise bond-
lengths and angles; however, it is clear the gallium and silicon
atoms adopt approximately tetrahedral coordination and a
THF molecule is bound to the gallium center (Fig. 1).
benzene-d6 shows resonances diagnostic of tris(tert-butoxy)-
silanol and THF. An insoluble material, presumably hydrated
gallium oxide, was observed in the NMR tube. Monitoring a
1
benzene-d6 solution of complex 1 by H NMR spectroscopy
revealed that the complex began to thermally decompose
Stability and relevance of 1 as a thermolytic molecular precursor within six hours at 20 °C, with generation of a trace amount of
isobutene. Note that the aluminum analog of 1 also de-
composes at 20 °C with elimination of isobutene. Over 21 h
at 20 °C, decomposition of 1 in benzene-d occurred with the
6
formation of free tris(tert-butoxy)silanol and isobutene (3.9%
and 7.4% of available tert-butoxy groups, respectively) and
concurrent deposition of a gel. In the solid state, 1 begins to
decompose within six hours at 20 °C, indicated by the for-
mation of hydrocarbon-insoluble material.
The molecular precursor 1 fills a vacancy in the series of group
1
8
1
3 tris(tri-tert-butoxy)siloxide complexes in that similar deriva-
tives have previously been reported for boron, aluminum and
9
,17,18
indium.
Complexes of each type have been successfully
investigated as thermolytic precursors to group 13 element-
containing silica materials. Of the few reports regarding
gallium siloxide complexes, only one has described their use
as thermolytic precursors. Driess et al. reported the synth-
t
eses of [Me
2
Ga(OSiEt
3
)]
2
and [Me
2
Ga(OSi(O Bu)
3
)]
2
; however,
Thermogravimetric (TG/DTA) and NMR spectroscopic analyses
of 1
thermolysis of these compounds gave gallium oxide rather
9
than gallium-containing silica. Therefore, development of a
well-defined precursor for the thermolytic formation of The thermal instability observed at 20 °C suggested that 1 may
gallium-containing silicas has remained an unrealized goal.
be a thermolytic molecular precursor (TMP) to gallium-silica
The molecular precursor 1 is air-sensitive and thermally materials. Thermogravimetric analysis of 1 under O or N
2
2
unstable at room temperature. Treatment of 1 with one equi- indicated rapid mass loss associated with thermal decompo-
valent of water led to partial hydrolysis of the gallium–oxygen sition of the precursor around 110 °C (Fig. 2). Isobutylene for-
1
1
bonds. A H NMR spectrum recorded 15 minutes after mation is expected during this event based on H NMR
addition of one equivalent of water to a solution of 1 in experiments discussed above as well as previous studies,
which established the mechanism for thermolytic decompo-
1
9
sition of similar group 13 precursors. The tailing mass losses
from ∼170–1000 °C can be attributed to a loss of water gener-
ated during silanol condensation. The lack of any additional
major mass-loss events before 1000 °C indicated that co-
ordinated THF must have evaporated during the elimination
of tert-butoxy groups from 1. Indeed, the total mass loss
(
76.8%) is close to the expected value for loss of 9 equivalents
of isobutylene, 4.5 equivalents of water and coordinated THF
required losses for the complex to form Ga O ·6SiO : 70.6%).
(
2
3
2
Additional insight into the thermal decomposition was
gained through NMR spectroscopic observation of soluble
decomposition products. The gallium precursor 1 in toluene-
t
Scheme 1 Synthesis of Ga[OSi(O Bu)
3
]
3
·THF (1).
11028 | Dalton Trans., 2016, 45, 11025–11034
This journal is © The Royal Society of Chemistry 2016

View Article Online
Dalton Transactions
Paper
Dinitrogen-physisorption measurements were performed
on calcined samples of P-123-templated and untemplated
materials generated from solution thermolyses of 1 (UCB1-
GaSi
3 2 3 2
and Ga O ·6SiO , respectively). These measurements
indicated the presence of template effects for UCB1-GaSi , as
3
20
previously observed for several other UCB1 materials. High
2
−1
surface areas were observed for both samples (636 m g and
2
−1
5
07 m g for UCB1-GaSi and Ga O ·6SiO respectively), with
3 2 3 2
3
UCB1-GaSi having a much smaller average pore radius and a
narrower pore distribution. In addition, the dinitrogen-physi-
sorption measurement for un-templated Ga O ·6SiO exhibited
2
3
2
a shift in the hysteresis loop to significantly higher relative
pressures, indicative of textural mesoporosity rather than the
2
1
vermicular pores reported for UCB1 materials (Fig. 3).
Fig. 2 TGA mass-loss curve for 1 under nitrogen.
Powder X-ray diffraction (pXRD) experiments were per-
formed to look for evidence of crystalline oxide domains in
UCB1-GaSi3 and Ga O ·6SiO . The results indicate that
materials formed by direct thermolysis of 1 exhibit broad,
shoulder peaks at 2θ = ∼35° and ∼65° (see ESI, S5†). These
features are largely unchanged between the templated and
untemplated materials and lie in the general region for α-, γ-,
2
3
2
d was heated to 135 °C for 24 h, resulting in the total dis-
8
1
appearance of signals associated with
1
(by
H NMR
spectroscopy) along with a complicated mixture of organic
products, potentially due to additional reactivity between the
gallium centers and isobutene or tert-butanol. In addition, a
gallium-silica gel formed in the NMR tube. The elimination
products generated over the first 30 minutes of thermolysis
were collected by vacuum transfer from a sample of 1 that was
heated (135 °C) under vacuum. The volatile products were de-
δ-, ε- and β-Ga
vents definitive assignments. These peaks were observed in
pXRD spectra of UCB1-GaSi samples calcined at temperatures
2 3
O ; however, the broadness of the peaks pre-
22
3
as low as 200 °C, which is above the expected decomposition
temperature of P-123, but were not observed in the uncalcined
posited onto frozen benzene-d at −196 °C containing ferro-
23
6
samples (see ESI, S7†). Calcination of UCB1-GaSi at higher
3
1
cene as an internal standard. By H NMR spectroscopy,
temperatures (800 °C) resulted in growth of peaks associated
isobutene, tert-butanol, THF, and water were the major volatile
products accounting for 38% of the tert-butoxy groups and
with γ-Ga O . It is not clear whether the higher temperature
2
3
treatment leads to formation of larger particles of the same
5
4% of the THF present in the sample. These observations are
22,24
oxide phase observed at 500 °C or new, different phases.
consistent with previous studies on related TMP complexes
The observation that direct thermolysis of 1 leads to for-
mation of gallium-silica materials with small gallium oxide
domains was not unexpected given the relatively high Ga : Si
molar ratio dictated by the precursor. Thus to promote isolated
gallium sites it was of interest to examine UCB1-GaSi materials
1
1,17,18
containing tri-(tert-butoxy)siloxide groups.
In contrast to the clean thermolysis observed for 1, the
t
2 3 2 2 3 2
gallium siloxides [Me Ga(OSiEt )] and [Me Ga(OSi(O Bu) )]
investigated by Driess and coworkers exhibit complex multi-
step thermal degradations at high temperatures, which result
9
in gallium oxide formation. Comparing the reactivity of 1 to
t
[
Me Ga(OSiEt )] and [Me Ga(OSi(O Bu) )] suggests that the
2
3
2
2
3 2
methyl groups on gallium may interfere with the mechanism
for formation of gallium-silica materials.
Synthesis of gallium-containing silica materials
Initial investigations into the synthesis of gallium-containing
silica materials using 1 as a thermolytic molecular precursor
were performed by heating 1 in either a solution of toluene or
toluene/P-123 Pluronic at 135 °C. To remove the P-123 Pluronic
and drive off residual solvent after thermolysis, the resulting
gels were air-dried for three days to form white or pale yellow
2
monoliths that were then calcined at 500 °C in O for three
hours. The white calcined samples were then ground to a
powder by mortar and pestle. This synthetic protocol involving
P-123 Pluronic as template has previously been reported by
this laboratory to generate materials with uniform pore distri-
Fig. 3 Nitrogen adsorption–desorption isotherms and pore size distri-
butions (as change in pore volume with respect to pore radius, inset,
BJH desorption method) after calcination at 500 °C in O
templated gallium-silica (Ga ·6SiO ) and P-123-templated gallium-
silica (UCB1-GaSi ).
2
for un-
2
O
3
2
2
0
butions and narrow pore diameters.
3
This journal is © The Royal Society of Chemistry 2016
Dalton Trans., 2016, 45, 11025–11034 | 11029

View Article Online
Paper
Dalton Transactions
having higher contents of silicon, and in this regard it seemed (135 °C for 24 h) produced isobutene and small amounts of
possible to tune the gallium content by inclusion of a purely tert-butanol as the major soluble products even at the lowest
siliceous precursor during thermolysis.
loading of gallium, indicating complete consumption of the
Tris(tert-butoxy)silanol was selected as a siliceous diluent precursors (see ESI, S8†).
since it contains only tert-butoxy and hydroxyl substituents on
The wide range of metal loadings achievable using 1 as the
silicon that are readily lost in the thermolysis/condensation metal-containing precursor stands in contrast to the previous
process. Previous investigations into the co-thermolysis of work on tantala-silica materials described above. Addition of
i
tris(tert-butoxy)silanol with a tantalum(V) precursor, Ta(O Pr) - catalytic amounts of aluminum trichloride to TMP thermolysis
2
t
[
OSi(O Bu)
3
]
3
, found that over a narrow range of Ta : Si ratios reactions is known to induce thermolysis and decrease gela-
complete incorporation of the precursors into the materials tion times, and it appears that the gallium Lewis-acid centers
2
5
occurs. However, incomplete thermolysis of added tris(tert- present in 1 also exhibit an ability to catalyze the thermal
1
9,20,31
butoxy)silanol was observed if the Ta : Si ratio of the combined decomposition even at low loadings.
2
5
precursors decreased below 1 : 9.
approach was applied to generate materials with tunable Ga/Si thesized UCB1-GaSi materials with lower Ga : Si ratios
ratios in the presence of the P-123 Pluronic template with the (denoted UCB1-GaSi10 UCB1-GaSi20 and UCB1-GaSi50
goal of controlling the coordinate environment of the gallium revealed that the shoulder peaks observed in UCB1-GaSi were
This co-thermolysis
Powder X-ray diffraction (pXRD) studies of the newly syn-
,
,
)
3
centers.
The co-thermolysis of
absent. This indicates that the dilution was successful in mod-
with tris(tert-butoxy)silanol ulating the formation of gallium oxide domains (see ESI, S6†).
1
occurred in toluene in the presence of P-123 Pluronic by a
To investigate the dilution method using tris(tert-butoxy)-
method analogous to that used for the synthesis of UCB1- silanol as a means for suppressing the formation of gallium
7
1
GaSi
00 °C in O
and 1 : 50, denoted UCB1-GaSi , UCB1-GaSi , and UCB1- only tetrahedral gallium signals in lower gallium-loading
3
. The as-synthesized gels, once air-dried, were calcined at oxide, Ga MAS-NMR spectroscopy was performed on calcined
5
2
to give materials with Ga : Si ratios of 1 : 10, 1 : 20, UCB1-GaSi , UCB1-GaSi10, and UCB1-GaSi50. The presence of
3
1
0
20
GaSi50, respectively. Elemental analysis of the gallium to materials supports the elimination of large gallium oxide crys-
silicon ratios confirmed that the intended stoichiometries tallites in favor of tetrahedrally-coordinated gallium atoms
were achieved (Table 1). The accuracy with which gallium con- embedded in silica (Fig. 4). However, note that previous
tents may be targeted by this method is noteworthy, since reports suggest that not all gallium is necessarily observable
hydrothermal syntheses of gallium-containing silica by direct by NMR, especially if the gallium environments possess low
2
6
addition of a gallium precursor to a silica sol–gel often display symmetry or high disorder. Hydration of gallium silicates
2
6–29
lower than anticipated loadings in the final material.
The has been reported to assist in relaxing signals and sharpening
thermolytic method employed here, therefore, provides valu- peaks; therefore, these samples were stored under a saturated
2
6
able access to gallium-containing silica over a broad range of water atmosphere for a minimum of 48 h prior to analysis.
precise loadings.
As a reminder, tris(tert-butoxy)silanol boils above 205 °C,
therefore the observation of expected Ga : Si ratios following
3
0
calcination is significant. This result provides evidence of
total precursor decomposition and incorporation into the gel
during the co-thermolysis; any remaining free silanol would be
expected to boil out during calcination which would result in
higher Ga : Si ratios than targeted.
NMR investigations were performed to monitor the thermo-
lysis of both tris(tert-butoxy)silanol and 1 in solution for com-
pletion. Thermolysis in toluene-d under gelation conditions
8
Table 1 Elemental analyses and physisorption parameters for syn-
thesized materials
SA
Ave. pore
radius (nm)
Pore vol.
a
(m g−1)
2
3
−1
Material
Ga : Si
(cm g
)
UCB1-GaSi
3
1 : 3(3.16)
1 : 10(9.54)
1 : 20(20.0)
1 : 50(49.4)
1 : 3
636
497
379
293
507
2.0
3.9
7.2
13.7
5.3
0.65
0.99
1.25
1.57
1.44
UCB1-GaSi10
UCB1-GaSi20
UCB1-GaSi50
Untemplated
7
1
Fig. 4
Ga-MASNMR spectra of UCB1-GaSi
3
(1 : 3), UCB1-GaSi10 (1 : 10)
. Signals for
and UCB1-GaSi50 (1 : 50) after calcination at 500 °C in O
2
tetrahedral coordination (∼150 ppm and ∼123 ppm) and octahedral
coordination (∼0 ppm) are apparent.
a
Values in parentheses indicate measured ratios.
11030 | Dalton Trans., 2016, 45, 11025–11034
This journal is © The Royal Society of Chemistry 2016

View Article Online
Dalton Transactions
Paper
The results indicate the presence of two major peaks for tetra-
High-angle annular dark-field scanning transmission elec-
hedral gallium with maxima at ∼123 and ∼150 ppm along with tron microscopy (HAADF-STEM) images of all samples showed
a peak for octahedral gallium at ∼0 ppm in the UCB1-GaSi and porous structures as expected. However, the high energy of the
UCB1-GaSi10 samples. For UCB1-GaSi50 only the peak at electron beam and risk of beam-induced damage prevented
3
7
1
∼
123 ppm is present in the Ga MAS-NMR spectrum.
The broad signals present at ∼150 and ∼0 ppm in gallium- viously reported for this type of material would be observable
rich UCB1-GaSi samples are similar to literature reports of (see ESI, S13†).
magnification to an extent that vermicular pore structures pre-
7
1
Ga NMR shifts for γ-Ga O , and are tentatively assigned to
While STEM images were unable to provide evidence for
2
3
3
2
this oxide phase. They are inconsistent with gallium oxyhydr- structural differences between UCB1-GaSi samples, dinitrogen-
oxide structures which would be expected to exhibit only physisorption measurements clearly indicated changes in
signals attributed to octahedral Ga and have signals upfield porosity. It was observed that as the silicon content increases
from those reported for β-Ga
123 ppm was present in all three samples and was the only the hysteresis loops towards higher P/P
observable signal in UCB1-GaSi . This peak is tentatively silica content was also observed, along with changes in the
3
3
2
O
3
.
The sharp signal at in the UCB1-GaSi materials, surface areas decreases. A shift in
∼
0
values with increasing
5
0
assigned to an isolated gallium species; however, earlier pore radii distributions that showed broader pore size distri-
reports of “single-site” gallium on MCM-41 or SBA-15 describe butions and a shift to higher average radii (Fig. 6). While
2
6,28
a different tetrahedral signal located at ∼150 ppm.
indicates that the UCB1-GaSi materials may possess a different cations used for STEM, the dinitrogen-physisorption measure-
type of isolated species. ments taken of UCB1-GaSi are consistent with earlier reports
Elemental mapping STEM/EDS spectroscopy was performed of UCB1-type materials for which vermicular pores were obser-
This specific pore structures were unobservable at the magnifi-
3
2
0
on UCB1-GaSi
3
and UCB1-GaSi10 samples. No visible signs of vable by TEM.
The observation that pore uniformity is reduced with
the phase segregation of gallia particles from the silica matrix
were observed even in UCB1-GaSi3 (Fig. 5). This result is increasing silicon content is noteworthy. The narrow pore dis-
consistent with the broadness of the observed pXRD peaks for tributions of UCB1 materials were previously attributed to
these materials, and supports previous reports indicating that Lewis acid–base interactions between Lewis-acidic metal
the presence of pre-formed M[–O–SiO ] linkages in a single- centers in the molecular precursors and Lewis-basic oxygen
3
n
source precursor leads to highly dispersed metal oxides upon atoms of ethylene or propylene glycol monomers in the P-123
1
2,25
20
thermolysis.
It is interesting to note that samples with 1 : 3 Pluronic template. This interaction was proposed to lead to
and 1 : 10 Ga : Si ratios exhibit similar degrees of dispersion polymer unfolding. This hypothesis was put forth based on a
7
1
despite the differences in pXRD and Ga MAS-NMR spectra previous report by Soler-Illia and Sanchez, who postulated that
noted above. This suggests that any phase segregation in the under conditions involving limited water the hydrolysis of
UCB1-GaSi sample occurs on a scale smaller than that obser- various transition metal alkoxides to mesoporous materials
3
vable by elemental mapping without incurring beam damage containing vermicular pores was due to coordination of P-123
3
4
to the samples. The pixel edge is ∼3 nm in length, so it is esti- Pluronic to the metal precursors.
mated that oxide particles formed should be no larger than presumably results from the role played by the Lewis acid
0 nm in size.
An additional effect
1
Fig. 6 Nitrogen adsorption–desorption isotherms and pore size distri-
butions (as change in pore volume with respect to pore radius, inset)
Fig. 5 Elemental maps of (A) UCB1-GaSi
3
and (B) UCB1-GaSi10. The
2 3
after calcination at 500 °C in O for UCB1-GaSi (1 : 3), UCB1-GaSi10
first column from the left contains HAADF-STEM images of the mapped
region. The second (red) and third (green) columns are the Ga and Si
channels of the elemental maps, respectively.
(1 : 10), UCB1-GaSi20 (1 : 20), and UCB1-GaSi50 (1 : 50). Pore size distri-
butions are normalized for all samples (for un-normalized figure see ESI,
S11†).
This journal is © The Royal Society of Chemistry 2016
Dalton Trans., 2016, 45, 11025–11034 | 11031

View Article Online
Paper
Dalton Transactions
concentration, since oxide network formation is catalysed by the increased dispersion of the gallium atoms within the silica
3
+
4+
acid. Thus, at higher concentrations of Ga the oxide domains support. Insertion of Ga cations into tetrahedral Si posi-
condense more rapidly, such that the resulting structure is more tions necessitates protonation of the surface to maintain
strongly influenced by the template. The observation that charge balance. It is possible that gallium hydroxyl species are
there is a loss of templating in materials synthesized with formed on the surface as well (Fig. 7). On the other extreme, at
lower gallium content is therefore consistent with gallium- low silicon content gallium oxide particles formed on the
based Lewis acid sites playing a significant role in vermicular surface may block Brønsted acid sites.
pore formation.
The measured Brønsted acidities are similar to those of
The observed trend that surface area decreased with mesoporous silica (SBA-15) samples dehydrated under the
−
2
increasing silicon content stands in stark contrast to the same conditions (∼2 OH per nm ). For reference, the physical
trends observed in many post-synthetic and sol–gel based limit of hydration for a silica material is estimated at 4.6–4.9
2
7–29
2 35
methods for generating mesoporous gallium-silica.
In OH per nm .
general, it is found that increasing the loading of a metal by
The total acid site densities, as measured by ammonia
post-synthetic methods leads to lower surface areas due to temperature-programmed desorption, exhibit interesting
pore blockage by precursor deposition or, in extreme cases, trends in acid center strengths as indicated by the increased
sintering of metal particles and the formation of metal oxide prevalence of moderate strength acid sites and the decreased
phases separated from the high-surface area silica support. prevalence of strong acid sites as the gallium content of the
The materials described here display dramatically different material increases. Complex desorption profiles indicate the
trends in physical characteristics, which suggests that the presence of several types of acid sites in all samples (Fig. 6). At
factors controlling material formation by TMP methods signifi- low gallium loadings most of the acidity is associated with
cantly differ from those found in traditional hydrothermal and both weak (desorption temperature of ∼200 °C) and strong (de-
post-synthetic methodologies (Table 1).
sorption temperature of ∼600–700 °C) acid sites, with a small
amount of moderate strength sites (desorption temperature of
300–400 °C). Upon inclusion of more gallium, large desorption
peaks centered from 300–500 °C suggest that additional
gallium generates moderate-strength acid sites (Fig. 8).
Characterization of surface acidities of UCB1-GaSi materials
Gallium-silica materials are primarily of interest as acid cata-
lysts, therefore, the acidic properties of the materials were
probed by ammonia temperature-programmed desorption
While all ammonia desorption traces exhibit similar fea-
tures below 375 °C, notable differences in desorption peaks
(
NH -TPD) and pyridine-FTIR (Table 2). NH -TPD measure-
3
3
are observed at higher temperatures. In UCB1-GaSi a major
ments provide total acid content including both Lewis and
Brønsted acidic sites. Pyridine-FTIR can provide two IR-peaks
centered at ∼1455 and ∼1545, which after correction for inte-
grated molar extinction coefficients (IMEC) give the relative
3
peak is observed between 450–500 °C that remains only as a
trace signal upon dilution of the gallium content in UCB1-
GaSi . A new major signal is observed at higher temperatures
10
1
6
(578 °C) that also appears in even more gallium-poor UCB1-
GaSi20 and UCB1-GaSi50 (642 and 622 °C). This suggests the
presence of acid sites in UCB1-GaSi3 that are replaced with
stronger sites in more dilute samples.
ratios of Brønsted and Lewis acids. The combination of the
two methods allows for an estimation of the acidic site den-
sities on the surface when corrected for surface areas.
The Brønsted and Lewis acid site densities measured for
UCB1-GaSi materials revealed decreased Lewis acid densities
and increased Brønsted acid densities as the silicon content
increased (Table 2). This can be partially attributed to the
Several of the ammonia desorption peaks observed for
UCB1-GaSi materials are similar to previous reports of desorp-
tion peaks measured for gallium-containing silicas. Ammonia
desorption peaks observed in the range of 100–200 °C have
been attributed to weakly acidic Brønsted acid groups and the
high temperature peaks from 550–650 °C are tentatively
7
1
gallium oxide observed by Ga MAS-NMR that was not appar-
ent in samples with low gallium content. It has been reported
that γ-Ga O has a high ratio of Lewis acid sites to Brønsted
2
3
3
3
6
2
assigned to Brønsted acid sites as well. The broad peaks
attributed to moderate strength acid sites with maxima at
acid sites. In addition, the increasing Brønsted acid concen-
tration with increasing silicon content can be attributed to
3
7,38
∼300 °C have been assigned to Lewis acidic structures.
Table 2 Acid site densities of UCB1-GaSi materials
a
Total acidity
Bronsted acidity
(sites per nm )
Lewis acidity
2
2
2
Material
(sites per nm )
(sites per nm )
UCB1-GaSi
3
4.74
3.89
3.79
4.84
0.9
1.3
1.4
3.0
3.8
2.6
2.4
1.8
UCB1-GaSi10
UCB1-GaSi20
UCB1-GaSi50
a
Values measured by NH
3
-TPD. Bronsted and Lewis acid ratios deter- Fig. 7 Possible surface structures of gallium that would contribute to
mined by pyridine-FTIR.
Brønsted acidity.
11032 | Dalton Trans., 2016, 45, 11025–11034
This journal is © The Royal Society of Chemistry 2016

View Article Online
Dalton Transactions
Paper
lysis. Co-thermolysis of 1 with tris(tert-butoxy)silanol is poss-
ible over a wide range of gallium loadings and the targeted
loadings were achievable with a high degree of precision. In
addition, the coordination environments of the gallium
centers of the final materials may be controlled by varying the
t
relative ratio of 1 and HOSi(O Bu)
3
starting materials. At high
7
1
gallium content, pXRD and Ga MAS-NMR suggest the for-
mation of Ga O which is not present when the gallium
2
3
content is decreased. The precise control of metal loading in
these materials could be useful in studying the effects of
nuclearity on reactivity. High surface areas were observed in all
samples, and, unusually, surface areas increased with increas-
ing gallium content.
t
Co-thermolysis of 1 with HOSi(O Bu) in the presence of
3
P-123 Pluronic results in the loss of vermicular pore structures
as the silicon content increases. Based on literature precedent,
it is proposed that the Lewis acid centers coordinate to oxygen
centers in the polymer and this interaction, in combination
with more rapid thermolysis with more Lewis-acidic gallium
centers, is key in templating vermicular pore structures with
narrow size distributions.
Acknowledgements
Work at the Molecular Foundry was supported by the Office of
Science, Office of Basic Energy Sciences, of the U.S. Depart-
ment of Energy under Contract No. DE-AC02-05CH11231. We
Fig. 8 NH
3 3
-TPD curves and Gaussian curve fits for UCB1-GaSi (1 : 3),
UCB1-GaSi10 (1 : 10), UCB1-GaSi20 (1 : 20), and UCB1-GaSi50 (1 : 50). (A)
Overlay of all curves showing entire range used for acidity measure- gratefully acknowledge the support of the Director, Office of
ments. (B) 1 : 3, 5 peak fit, peak centers (°C): 127, 203, 292, 454, 874. (C)
Energy Research, Office of Basic Energy Sciences, Chemical
1
1
1
: 10, 7 peak fit, peak centers (°C): 118, 148, 223, 337, 475, 578, 1117. (D)
: 20, 7 peak fit, peak centers (°C): 115, 140, 184, 272, 375, 642, 828. (E)
: 50, 5 peak fit, peak centers (°C): 123, 158, 330, 362, 622.
Sciences Division, of the U.S. Department of Energy (DOE)
under Contract DE-AC02-05CH11231. We acknowledge the
National Institutes of Health for funding the UC Berkeley
CheXray X-ray crystallographic facility under Grant No. S10-
RR027172 and the UC Berkeley College of Chemistry NMR
facility under Grant No. SRR023679A and 1S10RR016634-01.
We acknowledge Neelay Phadke, Dr. Truman C. Wambach and
Andy L. Nguyen for helpful discussions. The authors would
also like to acknowledge Micah Ziegler for assistance with
crystal structure analysis.
Ultimately, the investigation of surface acidities serves to
inform the potential application of these materials for cataly-
sis. Initial investigations of UCB1-GaSi , which displays the
3
greatest density of Lewis acid sites, shows promise. Under reac-
tion conditions that have been employed for Friedel–Crafts
alkylations (40 °C, N
.25 mL benzyl chloride), complete conversion of benzyl chlor-
ide was achieved within 30 minutes, with 87% selectivity to
2
, 35 mg catalyst, 3.25 mL benzene,
0
diphenylmethane. For comparison, Vinu et al. reported 100% Notes and references
selectivity and 95% conversion using KIT-6 silica impregnated
1
R. Fricke, H. Kosslick, G. Lischke and M. Richter, Chem.
Rev., 2000, 100, 2303.
2 M. Guisnet and N. S. Gnep, Catal. Today, 1996, 31, 275.
E. G. Moschetta, N. A. Brunelli and C. W. Jones, Appl.
Catal., A, 2015, 504, 429.
with 30 wt% Ga O nanoparticles; however, even at a higher
2
3
temperature (50 °C) it took 75 minutes to achieve this conver-
3
9
sion. The application of these materials for Lewis acid cataly-
sis is ongoing.
3
4
S. Mandal, A. SinhaMahapatra, B. Rakesh, R. Kumar,
A. Panda and B. Chowdhury, Catal. Commun., 2011, 12,
Conclusions
7
34.
t
Ga[OSi(O Bu) ] ·THF (1) is an effective molecular precursor for
5 P. P. Pescarmona and P. A. Jacobs, Catal. Today, 2008,
3
3
the synthesis of gallium-silica materials. This is the first
example of a molecular gallium silanolate that can be used to
generate gallium-silica materials by low temperature thermo-
137, 52.
6 K. Bachari and O. Cherifi, J. Mol. Catal. A: Chem., 2006,
253, 187.
This journal is © The Royal Society of Chemistry 2016
Dalton Trans., 2016, 45, 11025–11034 | 11033

View Article Online
Paper
Dalton Transactions
7
M. J. Gracia, E. Losada, R. Luque, J. M. Campelo, D. Luna,
J. M. Marinas and A. A. Romero, Appl. Catal., A, 2008, 349,
48.
A. E. Ahmed and F. Adam, Microporous Mesoporous Mater.,
009, 118, 35.
K. Samedov, Y. Aksu and M. Driess, ChemPlusChem, 2012,
7, 663.
A. C. Hannon, E. R. Barney and R. I. Walton, Chem. – Eur.
J., 2013, 19, 2803.
1
23 D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson,
B. F. Chmelka and G. D. Stucky, Science, 1998, 279, 548.
24 V. N. Sigaev, N. V. Golubev, E. S. Ignat’eva,
B. Champagnon, D. Vouagner, E. Nardou, R. Lorenzi and
A. Paleari, Nanoscale, 2013, 5, 299.
8
9
2
7
1
0 D. Solis-Ibarra, M. de J. Velásquez-Hernández, R. Huerta- 25 R. L. Brutchey, C. G. Lugmair, L. O. Schebaum and
Lavorie and V. Jancik, Inorg. Chem., 2011, 50, 8907. T. D. Tilley, J. Catal., 2005, 229, 72.
1 (a) K. W. Terry, C. G. Lugmair and T. D. Tilley, J. Am. Chem. 26 C.-F. Cheng, H. He, W. Zhou, J. Klinowski,
1
Soc., 1997, 119, 9745; (b) K. L. Fujdala and T. D. Tilley,
J. Catal., 2003, 216, 265.
J. A. S. Gonçalves and L. F. Gladden, J. Phys. Chem., 1996,
100, 390.
1
2 (a) J. W. Kriesel and T. D. Tilley, J. Mater. Chem., 2001, 11, 27 Z. El Berrichi, B. Louis, J. P. Tessonnier, O. Ersen,
1
081; (b) K. L. Fujdala, R. L. Brutchey and T. D. Tilley, Top.
L. Cherif, M. J. Ledoux and C. Pham-Huu, Appl. Catal., A,
2007, 316, 219.
Organomet. Chem., 2005, 16, 69; (c) T. D. Tilley, J. Mol.
Catal. A: Chem., 2002, 182–183, 17; (d) D. A. Ruddy and 28 M. Selvaraj and S. Kawi, Catal. Today, 2008, 131, 82.
T. D. Tilley, J. Am. Chem. Soc., 2008, 130, 11088; 29 M. Chatterjee, T. Iwasaki, Y. Onodera, T. Nagase,
(e) C. Copéret, A. Comas-Vives, M. P. Conley, D. P. Estes,
H. Hayashi and T. Ebina, Chem. Mater., 2000, 12, 1654.
A. Fedorov, V. Mougel, H. Nagae, F. Núñez-Zarur and 30 H. J. Backer and H. A. Klasens, Recl. Trav. Chim. Pays-Bas.,
P. A. Zhizhko, Chem. Rev., 2016, 116, 323; (f) K. L. Fujdala
and T. D. Tilley, J. Am. Chem. Soc., 2001, 123, 10133.
3 Y. Abe and I. Kijima, Bull. Chem. Soc. Jpn., 1969, 42, 1118.
1942, 61, 500.
31 R. L. Brutchey, J. E. Goldberger, T. S. Koffas and
T. D. Tilley, Chem. Mater., 2003, 15, 1040.
1
1
4 M. Kruk, M. Jaroniec, C. H. Ko and R. Ryoo, Chem. Mater., 32 W. Lueangchaichaweng, N. R. Brooks, S. Fiorilli,
2
000, 12, 1961.
E. Gobechiya, K. Lin, L. Li, S. Parres-Esclapez, E. Javon,
S. Bals, G. Van Tendeloo, J. A. Martens, C. E. A. Kirschhock,
P. A. Jacobs and P. P. Pescarmona, Angew. Chem., Int. Ed.,
2014, 53, 1585.
1
1
1
5 B. Chakraborty and B. Viswanathan, Catal. Today, 1999, 49, 253.
6 C. A. Emeis, J. Catal., 1993, 141, 347.
7 K. L. Fujdala, A. G. Oliver, F. J. Hollander and T. D. Tilley,
Inorg. Chem., 2003, 42, 1140.
8 C. G. Lugmair, K. L. Fujdala and T. D. Tilley, Chem. Mater.,
33 L. A. O’Dell, S. L. P. Savin, A. V. Chadwick and M. E. Smith,
Appl. Magn. Reson., 2007, 32, 527.
1
1
2
2
2
002, 14, 888.
9 K. W. Terry, P. K. Ganzel and T. D. Tilley, Chem. Mater.,
992, 4, 1290.
34 G. J. de A. A. Soler-Illia and C. Sanchez, New J. Chem., 2000,
24, 493.
35 L. T. Zhuravlev, Colloids Surf., A, 2000, 173, 1.
1
0 J. W. Kriesel, M. S. Sander and T. D. Tilley, Chem. Mater., 36 T. Takeguchi, J. Kim, M. Kang, T. Inui, W. Cheuh and
001, 13, 3554. G. L. Haller, J. Catal., 1998, 175, 1.
1 K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, 37 B. Karmakar, A. Sinhamahapatra, A. B. Panda, J. Banerji
2
R. A. Pierotti, J. Rouquérol and T. Siemieniewska, Pure
Appl. Chem., 1985, 57, 603.
2 (a) M. Hirano, K. Sakoda and Y. Hirose, J. Sol-Gel Sci.
and B. Chowdhury, Appl. Catal., A, 2011, 392, 111.
38 S. J. Kim, K.-D. Jung and O.-S. Joo, J. Porous Mater., 2004,
11, 211.
2
Technol., 2016, 77, 348; (b) B. Zheng, W. Hua, Y. Yue and 39 H. Oveisi, C. Anand, A. Mano, S. S. Al-Deyab, P. Kalita,
Z. Gao, J. Catal., 2005, 232, 143; (c) H. Y. Playford,
A. Beitollahi and A. Vinu, J. Mater. Chem., 2010, 20, 10120.
11034 | Dalton Trans., 2016, 45, 11025–11034
This journal is © The Royal Society of Chemistry 2016