Oxide-Supported Titanium Catalysts: Structure-Activity Relationship in Heterogeneous Catalysis, with the Choice of Support as a Key Step

Article abstract of DOI:10.1021/acs.organomet.0c00650

The reactions of tetrakis(neopentyl)titanium, TiNp4 (1), with the surface of three solid oxides, silica, silica-alumina, and alumina, all partially dehydroxylated at 500 °C under vacuum were achieved. The resulting supported organometallic species react with dihydrogen to form the corresponding supported hydrides. The preparation of supported titanium hydrides on alumina is described here in detail, and the species obtained were extensively characterized by FTIR, solid-state NMR and EPR spectroscopy, and mass-balance analysis. The supported titanium hydride species were tested in three important reactions for petrochemistry: epoxidation of 1-octene, depolymerization of Fischer-Tropsch waxes, and polymerization of ethylene. The activities of titanium hydrides supported on alumina were compared to those of their silica- and silica-alumina-supported analogues.

Full text of DOI:10.1021/acs.organomet.0c00650

pubs.acs.org/Organometallics
Article
Oxide-Supported Titanium Catalysts: Structure−Activity
Relationship in Heterogeneous Catalysis, with the Choice of Support
as a Key Step
́
Cherif Larabi,* Sebastien Norsic, Lhoussain Khrouz, Olivier Boyron, Kai Chung Szeto, Christine Lucas,
Mostafa Taoufik,* and Aimery De Mallmann*
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ABSTRACT: The reactions of tetrakis(neopentyl)titanium, TiNp4 (1), with the
surface of three solid oxides, silica, silica−alumina, and alumina, all partially
dehydroxylated at 500 °C under vacuum were achieved. The resulting supported
organometallic species react with dihydrogen to form the corresponding supported
hydrides. The preparation of supported titanium hydrides on alumina is described
here in detail, and the species obtained were extensively characterized by FTIR, solid-
state NMR and EPR spectroscopy, and mass-balance analysis. The supported
titanium hydride species were tested in three important reactions for petrochemistry:
epoxidation of 1-octene, depolymerization of Fischer−Tropsch waxes, and polymer-
ization of ethylene. The activities of titanium hydrides supported on alumina were
compared to those of their silica- and silica−alumina-supported analogues.
homogeneous catalysis, such as alkane metathesis,21 direct
conversion of ethylene to propylene,22 and metathetic
oxidation.23 The work of Basset, a pioneer of surface
organometallic chemistry, has exhaustively reviewed the
preparation and characterization of the highly reactive early-
transition-metal hydride species, supported on various
oxides.5,24
Among all investigated transition-metal systems, supported
Ti species with adequately tuned coordination spheres were
shown to play an important role in epoxidation,25,26 hydro-
amination,27 catalytic imido transfer,28 polymerization,29 and
depolymerization processes.11,12 Nevertheless, a detailed
description of the surface Ti species remains still difficult to
access. Previously, it has been suggested that a proper choice of
the dehydroxylation temperature of the support allows control
of the distribution of surface hydroxyl groups and tuning their
chemical reactivity.5 As a result, when they react with
organometallic compounds, such as tetrakis(neopentyl)-
titanium, mono- or bis-coordinated Ti alkyl species can be
selectively obtained, as a function of the surface silanol
density.30−32 A supported Ti hydride is a very important
INTRODUCTION
■
Typical heterogeneous catalysts are solid phases or consist of
active species (inorganic clusters or metal−organic complexes)
immobilized on solid supports such as silica,1 alumina,2 clay,3
zeolite,4 etc. Commercial heterogeneous catalysts suffer from
the presence of different and ill-defined active sites, due to the
heterogeneity of the surface and lack of a controlled
preparation procedure at the molecular level. Fundamental
understandings of the active sites and their coordination
spheres are essential in order to develop next-generation
catalysts with enhanced activities and selectivities. An
alternative approach to prepare molecularly well defined
species on a support has been proposed: surface organo-
metallic chemistry.5 Generally, this methodology offers access
to well-defined active sites on a solid surface. Moreover, the
interactions between the support and the active center, as well
as the mechanism of the catalytic reaction, can be elucidated by
standard spectroscopic methods very similarly to the case of
homogeneous catalysis.6 As a consequence, an opportunity to
tune the catalytic site reactivity (coordination sphere: supports,
ligands) toward a given reaction arises. Several essential
catalytic systems for processes such as alkene metathesis,7−9
imine metathesis,10 controlled depolymerization of waxes,11,12
methane coupling,13,14 alkane dehydrogenation,15,16 alkane
aromatization,17,18 2-butene dimerization,19 and alkene epox-
idation20 have been demonstrated using this strategy.
Importantly, catalysts prepared by this approach have also
led to the discovery of new reactions, unknown in
Received: September 28, 2020
https://dx.doi.org/10.1021/acs.organomet.0c00650
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glovebox into a tightly closed zirconia rotor. ESR X-band spectra were
recorded on a Bruker X-band spectrometer Elexsys E500 (T = 110 K,
power 4−16 mW, modulation amplitude 1 G, frequency ca. 9.42
GHz). For the correction of magnetic field values, a DPPH standard
was used. EasySpin software (Matlab) was used to simulate the EPR
spectra.35 For a quantitative evaluation, an integration of the
absorbance spectrum was performed and compared to the integration
of the spectrum of a vanadyl(IV) sulfate standard. Elemental analyses
were performed at the Catalysis Research Institute (IRC,
Villeurbanne, France), at the Central Analysis Service of the CNRS
(Solaize, France), and at LSEO Dijon. Three oxide supports were
used. AEROSIL200 silica from Evonik, silica−alumina (25% alumina,
Akzo Nobel), and AEROXIDE ALUC alumina from Evonik were
calcined for 24 h at 500 °C under a continuous flow of oxygen and
then thermally treated under vacuum (10−5 mbar) at 500 °C for a
intermediate among the reactions mentioned. Precisely, in
alkene epoxidation, it can undergo protonolysis of the alkyl
hydroperoxide, in polymerization, it could readily insert olefins,
and in depolymerization, it can readily activate the long-chain
hydrocarbon by σ-bond metathesis and cut C−C bonds by β-
alkyl transfer.11,12 Hence, this work comprises an extensive
study of Ti hydrides prepared on conventional supports.
Previously, Ti hydrides supported on silica and silica−alumina
have been reported.5,12 The major Ti hydride species is tris-
coordinated to the surface, as revealed by IR, solid-state NMR,
mass balance analysis, EPR, stoichiometric reactivity analysis,
and XAS. The synthesis of the titanium hydride supported on
alumina is presented here for the first time. These supported Ti
hydride materials have been investigated for 1-octene
epoxidation, ethylene polymerization, and depolymerization
of a Fischer−Tropsch wax (FT-wax).
minimum of 15 h for a partial dehydroxylation, leading to SiO2‑500
,
SiO2-Al2O3‑500 and Al2O3‑500, respectively. It was controlled by ESR
that the silica, silica−alumina, and alumina supports do not show any
important paramagnetic impurities such as Fe(III). The BET surface
of Al2O3‑500 is 105 m2/g and the OH density 0.65 mmol/g,
corresponding to ca. 3.7 OH/nm2.
Reaction of [Ti(CH2tBu)4] (TiNp4) with Different Supports.
The impregnation technique consists typically of stirring at 25 °C for
EXPERIMENTAL SECTION
■
General Procedures. For the organometallic synthesis, experi-
ments were carried out using standard Schlenk and glovebox
techniques. Solvents were purified and dried according to standard
procedures and stored over 3 Å molecular sieves. Ti(OEt)4 (99%,
Aldrich), 13CO2 (99% 13C, Cambridge Isotopes), tBuMgCl (1.7 M in
diethyl ether, Aldrich), LiAlH4 (95%, Aldrich), MgSO4 (Laurylab),
NaHCO3 (Prolabo), and Vilsmeier reagent (95%, Aldrich, stored
under argon) were used as received. tBuCH2Li was prepared from
tBuCH2Cl (98%, Lancaster) and Li wires (Aldrich). [Ti(CH2tBu)4]
was prepared according to the literature procedure.33 13C-labeled
[Ti(*CH2tBu)4] was prepared as already reported elsewhere.12,32
A TBHP (tBuOOH) anhydrous solution in pentane was prepared
according to the procedures reported by Sharpless et al.34 from a
commercial solution of 70% TBHP in water and stored under argon
over 3 Å molecular sieves prior to use. 1-Octene and dodecane were
provided from Aldrich and stored over molecular sieves (3 Å) under
argon after purification on a neutral alumina and elimination of solved
gases by the freeze−pump−thaw technique. tBuOH, 1,2-epoxyoctane,
and 1,2-octanediol were used as received for the gas chromatographic
peak identification and calibration. Isopropanol, acetic acid, sodium
iodide, and sodium thiosulfate were used as is for the iodometric
titration of the anhydrous solution of TBHP in pentane.34
4 h a mixture of the desired support (SiO2‑500, SiO2-Al2O3‑500
,
Al2O3‑500; 0.5−2.5 g) and a solution of the molecular complex (in
excess in comparison to the number of hydroxyl groups of the
support) in pentane within a double-Schlenk glass vessel, equipped
with a glass frit between its two compartments. After filtration, the
solid was kept in the first compartment and washed three times with
pentane distilled from the second compartment. All volatile
compounds were collected into a large 6 L glass vessel in order to
quantify the neopentane evolved during the grafting reaction. The
powder was finally dried under vacuum (10−5 mbar) for 4 h, at room
temperature, and stored in a glovebox. This protocol allows
elimination of the excess molecular complex, even traces of
physisorbed TiNp4 from the surface, and recovery of the gas emitted
during the reaction. The Ti contents of the three materials thus
obtained, [TiNpx]@SiO2‑500, [TiNpx]@SiO2-Al2O3‑500, and [TiNpx]
@Al2O3‑500, were respectively 1.23, 2.25, and 0.79 wt %.
Monitoring the Synthesis of [Ti(CH2tBu)x]@Al2O3‑500 and [Ti-
H]@Al2O3‑500 by In Situ FTIR. The oxide (25 mg) was pressed into a
self-supporting disk, adjusted in the sample holder, and introduced
into a cell equipped with CaF2 windows. The supports were calcined
overnight in air at 500 °C and dehydroxylated under vacuum (10−5
mmHg) at 500 °C. The complex (TiNp4) was then sublimed under
vacuum at 50 °C onto the oxide disk. The solid was then heated at 50
°C for 2 h, and the excess 1 was removed by reverse sublimation at 60
°C and condensed into a tube cooled by liquid nitrogen, which was
then sealed off using a blowtorch. An amount of H2 corresponding to
70 kPa was then introduced into the reactor, and the sample was
heated to 150 °C at a rate of 1 °C/min, maintained at this
temperature for 4 h, and then cooled to room temperature. An IR
spectrum was recorded at each step.
Analyses of organics (tBuOH, pentane, tBuOOH, 1-octene, 1,2-
epoxyoctane, and dodecane) were performed on a HP 6890 gas
chromatograph, equipped with a flame ionization detector (FID) and
a HP-1 column (30 m × 0.32 mm) with the following temperature
program: 3 min at 70 °C, 20 °C min−1 up to 200 °C and 5 min at 200
°C.
Gas-phase quantitative analyses of light alkanes (grafting, hydro-
genolysis) were performed on a Hewlett-Packard 5890 Series II gas
chromatograph equipped with a flame ionization detector and an
Al2O3/KCl on fused silica column (50 m × 0.32 mm). The amount of
dihydrogen evolved (protonolysis with tBuOH) was determined with
a Hewlett-Packard 6890 gas chromatograph equipped with a TCD
detector and a molecular sieve column (15 m × 0.32 mm).
Hydrogenolysis of Supported Titanium Complex. Typically,
the titanium surface organometallic complexes grafted onto
Infrared spectra were recorded on a Nicolet FT-IR Magna 550
spectrometer equipped with a cell designed for in situ preparations
under a controlled atmosphere. Solid-state NMR studies were carried
out on Bruker DSX 300 MHz and Avance 500 MHz spectrometers.
For all experiments, the rotation frequency was set to 10 kHz.
Chemical shifts are given with respect to TMS as an external standard,
with a precision of 0.2−0.3 and 1 ppm for 1H and 13C NMR,
respectively. Parameters used: (i) 1H MAS NMR spectra, pulse delay
2 s, 8−32 scans per spectrum; (ii) 13C CP/MAS NMR spectra, 90°
pulse on the protons (pulse length 3.8 μs), then a cross-polarization
step with a contact time typically set to 5 ms, and finally recording of
the 13C signal under high-power proton decoupling, pulse delay 2 s,
20000−100000 scans per spectrum, an apodization function
(exponential) corresponding to a line-broadening of 50 Hz applied
to the spectrum. Air-sensitive samples were transferred within a
dehydroxylated supports (SiO2‑500, SiO2-Al2O3‑500, and Al2O3‑500
)
were heated to 150 °C for 2 h in a Schlenk tube under H2 (550 Torr)
first purified on a deoxo/zeolite catalyst. The resulting solids, [Ti-H]
@SiO2‑500, [Ti-H]@SiO2Al2O3‑500, and [Ti-H]@Al2O3‑500, were
stored in the glovebox. The methane and ethane evolved were
further quantified by GC.
Protonolysis of Supported Titanium Hydrides. Protonolysis
consisted of the treatment of [Ti-H]@SiO2‑500, [Ti-H]@
SiO2Al2O3‑500, and [Ti-H]@Al2O3(500) samples with tert-butyl alcohol
(40 mbar) for 1 h at 30 °C, followed by a measurement of the amount
of evolved gases (H2, alkanes) by GC. During this treatment, titanium
hydrides disappeared while surface TiOtBu species appeared and no
modification of the amount of Ti(III) was observed (ESR spectrum
recorded less than 24 h after the protonolysis).
B
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Epoxidation of 1-Octene. In a typical run, the catalyst (ca. 10
μmol of titanium, between 20 and 60 mg of supported catalyst) was
transferred in a glovebox under an inert atmosphere into a 40 mL
Schlenk equipped with a septum for sample removals. 1-Octene (3000
equiv/mol of Ti) and dodecane (ca. 100 mg, the same amount was
used for the gas chromatographic standardization) were added via
syringe under argon into the Schlenk containing the catalyst, which
was then fitted with a condenser under argon, a magnetic stirrer, and a
thermometer. The mixture was stirred and was warmed to 80 °C over
1 h. An anhydrous TBHP solution in pentane (1.5 to 2.0 mmol, 150−
200 equiv/mol of Ti) was added dropwise over 2 min via a precision
syringe. Aliquots were removed at various time intervals and analyzed
by gas chromatography.
lower than that of the first step) with a proximate hydroxyl
group to form the bipodal species (−154 kJ/mol). The latter
reaction is unfavorable for W(C(tBu))(CH2tBu)3 supported
on alumina (100 kJ/mol). Interestingly, for the bipodal Zr
species, it has been observed that a neopentyl ligand transfer
may occur (practically barrierless, according to DFT
calculations) toward a Lewis Al site and generate the cationic
surface species [(AlSO)2Zr(CH2tBu)]+[(AlS(CH2tBu)]−. The
reactivity of Hf(CH2tBu)4 on alumina also gives mainly the
c a t i o n i c s u r f a c e s p e c i e s [ ( A l S O ) 2 H f -
(CH2tBu)]+[(AlS(CH2tBu)]−.41,42 In addition, neutral monop-
t
odal [(AlSO)Hf(CH2 Bu)3] and bipodal [(AlSO)2Hf-
Hydrogenolysis of a FT-Wax. General Procedure. Mechanical
mixtures of supported titanium hydrides (75 μmol of Ti) and wax
(400 mg; Aldrich, ASTM D87; mp 70 °C) were charged using a
glovebox into a stainless steel cylinder reactor. After connection to the
gas lines and a purge of the tubes, a flow of hydrogen (20 mL/min),
controlled by a mass flow controller (Brooks) under 1 bar of pressure,
was sent upward into the catalyst bed, which was heated to 180 °C.
Hydrocarbon products were stripped from the liquid medium by the
hydrogen flow. Light hydrocarbons were analyzed online by GC (HP
6890 chromatograph equipped with an Al2O3/KCl 50 m × 0.32 mm
capillary column and a FID detector for hydrocarbons). Liquid
products were condensed at 0 °C and analyzed off-line by GC (HP
5890 chromatograph equipped with an HP5 30 m × 0.32 mm
capillary column and a FID detector).
(CH2tBu)2] species have also been observed. The difference
in reactivity is associated with the steric occupancy of the
complex and the size of the transition-metal center. Thus, the
reactivity of Ti(CH2tBu)4 with alumina is expected to be
different from the former cases and is further investigated in
detail.
In Situ FTIR. The reaction of TiNp4 (1) with the surface of
partially dehydroxylated alumina Al2O3‑500 and the evolution of
the supported titanium complexes under hydrogen have been
followed by FT-IR (Figure 1). The solid changes from white
Polymerization Reaction. The polymerization reactions were
performed in a 100 mL glass-lined stainless steel autoclave, equipped
with a magnetic stirrer. The reactor was charged with 50 mg of the
supported catalyst (0.79, 1.23, and 2.25 wt % Ti on Al2O3‑500, SiO2‑500
,
and Al2O3-SiO2‑500, respectively) and 20 mL of dry toluene in the
glovebox. The autoclave was connected to a gas line which was
flushed with dry ethylene. The reactor was heated to 40 °C and filled
with 10 bar of ethylene. The pressure was kept constant for 30 min.
The gas and liquid phases were then analyzed in order to check for
the presence or absence of oligomers. The reaction was quenched by
removing the unreacted ethylene. The polymer was recovered and
dried at 50 °C overnight under reduced pressure before the final mass
was weighed. High-temperature size exclusion chromatography (HT-
SEC) analyses were performed in 1,2,4-trichlorobenzene (TCB) using
a Viscotek system (Malvern Instruments) equipped with three
columns (PLgel Olexis 300 mm × 7 mm from Agilent Technologies)
and a refractive index (RI) detector. DSC measurements were
performed on a Mettler Toledo DSC 1 apparatus.
RESULTS AND DISCUSSION
■
Grafting of TiNp4 on Al2O3‑500. A large number of works
have been dedicated to elucidate the surface structure of
alumina and its interaction with organometallic com-
plexes.36−42 Alumina is an ionic oxide where the hydroxyl
groups are bonded to several different aluminum atoms.
Different theoretical models of the surface of alumina have
been proposed.40,43−45 According to the model reported by
Sautet et al., five kinds of hydroxyl groups are present on the
surface of alumina.44 The reactivity of the different aluminum
hydroxyl groups depends on the organometallic complex. For
instance, for isoelectronic complexes of group 3B, Al(iBu)3
reacts with all kinds of hydroxyl groups,46 while Ga(iBu)3
consumes only part of the available hydroxyl groups.16 W(
C(tBu))(CH2tBu)3 reacts only with tetrahedrally coordinated
hydroxyl groups.47 On the other hand, Zr(CH2tBu)4 can
readily react with different hydroxyl groups.48 Theoretical
investigations have revealed that protonolysis of a neopentyl
ligand in Zr(CH2tBu)4 is highly favorable (−201 kJ/mol).
Furthermore, the monopodal Zr intermediate species can still
undergo a second reaction (having an activation barrier even
Figure 1. In situ FTIR spectra of (a) Al2O3‑500, activated at 500 °C
under vacuum overnight, (b) the sample in (a) after grafting of TiNp4
on Al2O3‑500, and (c) the sample in (b) after treatment of the resulted
supported species with hydrogen for 12 h at 150 °C. (d) Enlargement
showing the evolution of the νAlO−H area. (e) Enlargement of the
νAl−H and νTi−H area, obtained after subtraction of (a) from (c).
for the pure alumina to become yellow after the grafting
reaction. The FTIR data show that the peak at 3777 cm−1
characteristic of tetrahedral aluminum hydroxyls (HO-μ1-AlIV)
completely disappears (Figure 1d). Moreover, the absorption
bands around 3726−3680 cm−1 appear less modified but are
slightly red shifted to 3672 cm−1, probably due to interactions
of hydroxyls with C−H bonds of neopentyl ligands. New
bands appear between 2800 and 3000 cm−1, characteristic of
CH3 and CH2 νC−H vibrations, and from 1229 to 1464 cm−1,
ascribed to δCH bending vibration bands. They are attributed
x
C
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Scheme 1. Grafting Reaction of TiNp4 (1) onto Al2O3‑500 Leading to Neutral (2a) and Cationic (2b) Surface Species and
Preparation of Alumina-Supported Titanium Hydrides [Ti-H]@Al2O3‑500, Leading to Neutral Ti(IV) Hydride A, Ti(III) B, and
Ti(IV) Cationic Hydride C
to Ti neopentyl ligands of grafted surface species (2a and 2b,
shown in Scheme 1).
Upon treatment under hydrogen at 150 °C of the resulting
compounds, the intensities of νC−H and δC−H vibration bands,
attributed to neopentyl groups, strongly decrease but the
signals are still present, due to the remaining [AlS-Np]−
fragments (see species 2b and C in Scheme 1), as observed
in the case of ZrNpx@Al2O3‑500 and HfNpx@Al2O3‑500
supported analogues.41,48 In fact, it was observed that a
thermal treatment under H2 at a temperature over 250 °C is
needed to decompose such Al-alkyl fragments.46 In addition a
band centered at 1906 cm−1 is observed (Figure 1c,e). It is
attributed to Al−H stretching vibrations. This component
originates from a hydride transfer from Ti to Al (2a to A and B
in Scheme 1), not from the hydrogenolysis of a transferred
neopentyl ligand. Moreover, a broad signal is observed
between 1700 and 1500 cm−1 (Figure 1e), apparently
Figure 2. In situ FTIR spectra obtained after subtraction of the
composed of three bands at 1676, 1603, and 1543 cm−1
alumina support contribution: (a) [Ti-H]@Al2O3‑500; (b) [Ti-H]@
attributed to stretching vibrations of Ti−H groups, differently
Al2O3‑500 treated under D2 for 1 h at 25 °C; (c) sample in (b) under
coordinated to the surface of alumina. These assignments were
further confirmed by H−D exchange experiments and are in
agreement with the reactions presented in Scheme 1 that will
be described into more detail later in the text.
D2 overnight; (d) reaction of the sample in (c) with H2 for 1 h at 150
°C.
alumina surface OH groups has reacted (ca. 50%) with TiNp4
and the metal surface density for TiNpx@Al2O3‑500 is ca. 1.0
When the supported titanium hydride species are in contact
with deuterium gas (1 atm), the intensities of the bands
characteristic of a Ti−H stretching mode decreased and
shifted, with only slight changes in the shape and intensity of
the Al−H band (Figure 2a−c).
48
41
Ti/nm2, as for the grafting ZrNp4 or HfNp4 on Al2O3‑500
supports.
After hydrogenolysis of TiNpx@Al2O3‑500, methane and
ethane were released; their quantification gave CH4/Ti = 4.7
0.8 and C2H6/Ti = 1.7 0.3, respectively (−8.1 C/Ti). The
presence of a substantial amount of ethane is due to the fact
that Ti can only conduct β-alkyl transfer. Note that, according
to the mass balance analysis, ca. 2 C/Ti remains after
hydrogenolysis, which is due to Al neopentyl fragments
obtained after ligand transfer. This further suggests that the
grafting of Ti(CH2tBu)4 on Al2O3‑500 gives ca. 60%
[(AlSO)2Ti(CH2tBu)2] (2a in Scheme 1) and 40%
[(AlSO)2Ti(CH2tBu)]+[(AlS(CH2tBu)]− (2b in Scheme 1).
The latter distribution is further supported by IR, revealing
that ca. 22% of the νC−H band intensity remains, characteristic
of residual alkyl groups, after hydrogenolysis (Figure 1c).
The protonolysis of [Ti-H]@SiO2‑500 and [Ti-H]@
SiO2Al2O3‑500 with tBuOH only led to the emission of
dihydrogen (H2/Ti = 0.85) and traces of methane, while in
the case of [Ti-H]@Al2O3‑500, neopentane (NpH/Ti = 0.4) is
also evolved with dihydrogen (H2/Ti = 1.2) and traces of
The Ti−D vibration band expected at around 1150 cm−1
was not clearly observed, due to the presence of broad and
intense bands characteristic of the alumina framework
vibrations. A subsequent reaction with hydrogen reestablished
the Ti−H vibration bands (Figure 2d).
Mass Balance Analysis. The grafting of TiNp4 on Al2O3‑500
was performed by an impregnation method. A 485 mg amount
of TiNp4 (1.46 mmol) was reacted with 2 g of Al2O3‑500 (1.3
mmol of [AlSO-H]) in dry pentane for 2 h. Neopentane,
tBuCH3, was detected in the gaseous phase and quantified by
gas chromatography (0.69 mmol). After extraction of the
excess and drying at 25 °C under high vacuum, the amounts of
carbon and titanium were also measured and gave 1.95 wt %
(3.34 mmol) and 0.79 wt % (0.34 mmol), respectively (10 C/
Ti on the surface). These results suggest that, for each titanium
grafted, ca. 2.0 neopentane molecules are released and 2.0
neopentyl groups are left on the material. Thus, 0.68 mmol of
D
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methane, resulting from the protonolysis of Ti−H, AlS-Np, and
AlS-H surface species. This neopentane emission agrees in
particular with the presence of [(AlS(CH2tBu)]− surface
species which have not reacted with dihydrogen in the
conditions of the hydrogenolysis (2b and C in Scheme 1). [Ti-
H]@Al2O3‑500 was then characterized by NMR and ESR.
difficult to detect, while for the silica and silica−alumina
counterparts, resonances are observed at 4.4 ppm for Si−H
and at 8−9 ppm for Ti−H.5,12 In addition, the 13C CPMAS
spectrum (Figure 3c) features a broad resonance at 23 ppm
and corresponds to alkyl groups attached to aluminum,49
confirming the occurrence of a neopentyl transfer (leading to
[Np-AlS]− fragments; see species 2b and C in Scheme 1). This
type of aluminum alkyl fragment has been already reported to
be very stable at 150 °C under hydrogen.46
1
NMR Spectroscopy. The solid-state H NMR spectrum of
Ti-Npx@Al2O3‑500 comprises a rather broad resonance
centered at 1 ppm which is attributed to methyl and methylene
groups of the Ti−CH2C(CH3)3 and Al−CH2C(CH3)3 frag-
ments and residual AlS−OH sites (Figure S1), while the proton
Electron Spin Resonance (ESR). The nature of the
supported titanium complex on Al2O3‑500 was further studied
by the ESR technique (Figure 4).
signals of methyl and methylene groups are resolved in the case
12,32
of Ti-Npx@SiO2‑500 and Ti-Npx@SiO2-Al2O3‑500
.
The
complexity of the surface of the alumina support (relative to
silica) causes structural diversity in the grafted species,
40
1
resulting in broadening of the H NMR signals. The 13C
CPMAS solid-state NMR of TiNpx@Al2O3‑500 is also more
complex than those obtained on silica32 and silica−alumina.12
In order to enhance the signal, a labeled titanium tetrakis-
(neopentyl) organometallic complex was used. It was prepared
in five steps from labeled *CO2, as already reported
elsewhere.12,32 In Figure 3 are shown 13C NMR spectra of
Figure 4. ESR patterns of paramagnetic species on the surface of
Al2O3‑500: (a) TiNpx@Al2O3‑500 (black); (b) [Ti-H]@Al2O3‑500 (red);
(c) sample in (b) after the butanolysis of [Ti-H]@Al2O3‑500 (blue).
The ESR signal of TiNp4 on alumina shows an overall width
of ca. 800 G and an average ESR g factor (g ) of 1.95 (Figure
av
4). It is consistent with an unpaired electron in a metal-based
orbital typical of a Ti(III) radical.50 From a double integration
of the signal, in comparison to the integration of the spectrum
of a vanadyl sulfate standard, only a small fraction of Ti(III) is
present in this sample (ca. 1% of the total amount of supported
Ti). After hydrogenolysis, the signal observed (Figure 4b) is
much more intense and its integration indicates that ca. 30% of
the supported titanium is Ti(III). After the protonolysis of [Ti-
H]@Al2O3‑500 with tBuOH, the shape of the signal has
changed and is more symmetrical (Figure 4c), probably due to
the coordination of tBuOH on the Ti(III) sites as a L-type
ligand. Moreover, the intensity of the signal is not much
affected (ca. 28% of the supported Ti is Ti(III)), showing that
under these conditions tBuOH did not react with Ti(III).
After the hydrogenolysis of (AlSO)2TiNp2 (2a) and
[(AlSO)2TiNp]+[Np−AlS]− (2b), the resulting material, [Ti-
H]@Al2O3‑500, is composed of different surface species (see
A−C in Scheme 1): neutral tripodal hydrides, [(AlSO)3Ti-H]
(A, ca. 30%), formed concomitantly with AlS-H surface
fragments containing Ti(III) radicals, [(AlSO)3TiIII] (B, ca.
30%), and bipodal cationic hydrides, [(AlSO)2Ti-H]+[Np−
AlS]− (C, ca. 40%). This repartition was deduced from the
results of mass balance analysis, protonolysis with tBuOH
(NpH emission for C), and EPR (Ti(III) proportion for B). It
also agrees with the IR and NMR studies. These species will
lead to different catalytic reactivities. Their proportions are
summarized in Table 1. It should be noted that the cationic
species C only exists for the alumina support and the Ti(III)
Figure 3. 13C CP-MAS solid-state NMR spectra of a. TiNpx@
Al2O3‑500; b. 13C enriched TiNpx@Al2O3‑500 and c. [Ti-H]@Al2O3‑500
obtained from the hydrogenolysis of 13C enriched TiNpx@Al2O3‑500
.
t
[Ti(CH2‑ Bu)x]@Al2O3‑500 and [Ti(*CH2tBu)x]@Al2O3.
Peaks at 31 and 27 ppm are attributed to the methyl groups
of the neopentyl coordinated to titanium and aluminum,
respectively. The signal at 23 ppm is attributed to the
methylene groups of Al−CH2C(CH3)3 fragments.49 In
addition, the signals at 103 and 121 ppm (only observed for
the labeled sample) necessarily originate from methylene
groups of Ti−CH2C(CH3)3 with different environments,
including neutral or cationic species (2a and 2b in Scheme
1), as reported in the case of Zr and Hf systems.41,48
1
After hydrogenolysis, the H NMR spectrum of the sample
presents mainly a broad peak centered at 0.74 ppm attributed
to the remaining neopentyl groups bound to Al (Figure S1).
The broadening of this signal along with a slight shift is due to
the presence of Ti(III) paramagnetic species (vide infra) in the
sample. Due to the more complex nature of sites on the
alumina surface and the paramagnetism of [Ti-H]@Al2O3‑500
,
the characteristic Ti−H and Al−H signals, which should both
appear in the 3−12 ppm range, are also broadened and very
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Table 1. Proportions (%) of the Different Supported Species
in the Different Ti−H@oxide Materials
a
a
a
A
B
C
[Ti-H]@Al2O3‑500
30
85
85
30
15
15
40
0
0
12
[Ti-H]@SiO2-Al2O3‑500
5
[Ti-H]@SiO2
a
Structures of species A−C are presented in Scheme 1. The relative
error for each value is 15% (e.g., for C on Al2O3‑500, the proportion
is 40 6%).
proportion is ca. twice as great on alumina than on silica and
silica−alumina supports.
Catalytic Performances. In this part of the study, the
catalytic activities of titanium hydrides supported on different
oxides (silica, silica−alumina, alumina), denoted [Ti-H]@
SiO2, [Ti-H]@SiO2-Al2O3, and [Ti-H]@Al2O3, were inves-
tigated as polyfunctional catalysts in three different reactions:
the epoxidation of 1-octene to 1,2-epoxyoctane,51 the low-
temperature hydrogenolysis of a FT-wax,12 and the polymer-
ization of ethylene.52 These studies provide a direct
comparison of the support effect in the chosen reactions.
1-Octene Epoxidation. The catalytic performances for the
epoxidation of 1-octene by tert-butyl hydroperoxide (Scheme
S1) of these well-defined titanium hydride grafted species were
evaluated. A blank test with bare alumina showed no significant
epoxidation reaction at 80 °C and the occurrence of a slow
TBHP degradation:53 6% in 1 h; 12% in 4 h. The formation of
1,2-epoxyoctane and the TBHP consumption with time are
represented in Figure 5.
The initial activities, determined after less than 4 min, and
the turnover frequencies (TOF), obtained after 15 min of
reaction, for the titanium hydrides supported on the three
supports silica, silica−alumina, and alumina are summarized in
Table 2.
The conversion of TBHP versus time showed that the
reaction is faster in the presence of the catalyst supported on
silica in comparison to that on silica−alumina; indeed, after 60
min the yield of 1,2-epoxyoctane is more than 90%, while it is
about 60% for Ti-H@SiO2-Al2O3‑500 and it is only 5% for [Ti-
H]@Al2O3‑500 (Figure 5). The catalyst resulting from [Ti-H]@
SiO2‑500 is thus the most active and stable.
Figure 5. Activity of supported [Ti-H] species for 1-octene
epoxidation by TBHP, showing the yield of 1,2-epoxyoctane and
the conversion of TBHP: (a, top) [Ti-H]@SiO2‑500; (b, middle) [Ti-
H]@SiO2-Al2O3‑500; (c, bottom) [[Ti-H]@Al2O3‑500
.
Table 2. Initial Activities and TOFs after 15 min of Reaction
for the Epoxidation of 1-Octene by TBHP
initial activity (h−1
)
TOF (h−1) after 15 min
[Ti-H]@SiO2
[Ti-H]@SiO2-Al2O3
[Ti-H]@Al2O3
1050
310
34
465
210
28
This catalytic reaction should first involve a protonolysis of
Ti−H moieties by TBHP along with the formation of
hydrogen and a Ti−OOtBu active surface species (Scheme
S2). The formation of the epoxide consists of an oxygen
transfer to the olefin, as already reported in the literature.54−56
Ti(III) (species C) may also catalyze an epoxidation with
TBHP,57 but the reaction rate is reported to be rather low,
even for an allylic alcohol.
The results suggest that the support plays a central role in
the stability of the catalyst. In the case of the alumina support,
the limited activity seems to be due to a poisoning of the
catalytic site, most likely by strongly coordinated chelating
ligands as β-methoxy alcohols and diols. It is known that the
most electrophilic Lewis acid sites can catalyze the opening of
an epoxide at moderate temperatures.58−61 On the alumina
support, the most electrophilic cationic C type Ti sites may
play this role, thus producing β-alkoxy alcohol chelating ligands
strongly adsorbed on Ti sites that would lead to a deactivation
of the catalyst. On the other hand, the presence of water or the
resulting Ti−OH groups has been proposed for the ring
opening of epoxides and the formation of diols that tend to
deactivate the catalyst.62−64 The formation of water may come
from the reaction of tBuOH or TBHP with residual AlSOH
groups of alumina to form AlS−OR or AlS−OOR surface
species. In addition, pure alumina itself is known to also
catalyze epoxide opening with alcohols or water into β-alkoxy
alcohols and diols.65,66 However, an alcohol dehydration on
alumina would occur at higher temperatures.67,68 The current
findings suggest that aluminum-free supports are preferable in
this type of epoxidation reaction.
FT Wax Hydrogenolysis. The catalytic performances of the
three supported titanium hydrides, denoted [Ti-H]@SiO2‑500
,
[Ti-H]@SiO2-Al2O3‑500, and [Ti-H]@Al2O3‑500, were eval-
uated in the hydrogenolysis of paraffin waxes, an important
reaction in petrochemistry. The effect of the support itself in
the absence of the titanium hydrides was studied, and the
conversions were found to be negligible for the three oxides.
The evolution of the gaseous phase was followed by gas
chromatography, in particular for the C1−C4 gas cut (Figure
S2). The liquids were recovered in a specific compartment and
characterized. The reaction was considered to be over when no
more gas was detected by GC. In fact, the end of the reaction
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was observed for [Ti-H]@SiO2-Al2O3 and [Ti-H]@Al2O3 after
14 and 10 h, respectively (no more wax in the reactor), while
for [Ti-H]@SiO2‑500 the reaction was stopped, for a wax
conversion of only 30%, after 26 h.
The products of hydrogenolysis have been divided into three
fractions, gas (C1−C4), gasoline (C5−C9), and diesel (C10−
C22) cuts. The yields of the different fractions are highlighted
in Figure 6. As is shown, the titanium supported on silica is less
stable Ti−olefin π complex. This may explain the higher
activity observed for [Ti-H]@SiO2-Al2O3‑500 and [Ti-H]@
Al2O3‑500 in comparison to [Ti-H]@SiO2‑500
.
Ethylene Polymerization. The activities of the supported
hydrides toward ethylene polymerization were also studied.
The supported hydrides showed interesting activities at 40 °C
under 10 bar of ethylene without any cocatalyst (Table 3). The
titanium hydrides supported on alumina have an activity of 915
g mmol−1 h−1 which is more than 3 times higher than those for
the titanium hydrides supported on silica or silica−alumina.
Titanium hydride supported on silica are slightly more active
than that supported on silica−alumina (270 vs 220 g mmol−1
h−1).
In our protocol, the mass of the catalyst is the same but the
Ti amount is different and is differently distributed among the
three categories of surface sites (A−C, see Scheme 1 and Table
1): 13 μmol of Ti for [Ti-H]@SiO2‑500 (A, 11 μmol; B, 2
μmol; C, 0); 24 μmol of Ti for [Ti-H]@SiO2-Al2O3‑500 (A, 20
μmol; B, 4 μmol; C, 0); 8.3 μmol of Ti for [Ti-H]@Al2O3‑500
(A, 2.5 μmol; B, 2.5 μmol; C, 3.3 μmol). From these results it
can be deduced that the cationic species C is more active than
the Ti(IV) neutral species A and that increasing fractions of B
and C sites are correlated with increasing yields.
The mechanism of polymerization involves an insertion of
ethylene into the Ti−H bond, followed by the insertion of
ethylene into a Ti−alkyl bond, a propagation step, on a
preferably highly electron deficient center, in particular cationic
species. Importantly, cationic Ti−H type species such as C are
unknown in homogeneous catalysis, due to a rapid deactivation
through the formation of inactive dimeric species. This latter
deactivation scheme can be avoided with firmly anchored
supported species.
Figure 6. Yields of the three fractions gas, gasoline, and diesel during
the hydrogenolysis of a FT wax.
active and the reaction was not complete even after 26 h, while
for the two other supports it was complete. In the case of
alumina, slightly higher amounts of gas and gasoline were
obtained in comparison to the silica−alumina support, whereas
the diesel fraction was slightly more dominant in the presence
of silica−alumina than in alumina. The amounts of each
compound before and after the hydrogenolysis reaction are
highlighted in Figure S3.
While the same amount of Ti is used, the reaction rate is
lower for [Ti-H]@SiO2‑500, as can be observed for low reaction
times for C1−C4 gas production (Figure S2). The mechanism
proposed for such hydrogenolysis reactions catalyzed by group
4 metals is based on a C−H bond activation in the paraffinic
chain by the metal hydride in a d0 configuration through a σ-
bond metathesis, with the formation of a metal−alkyl complex
and liberation of dihydrogen. Then a β-alkyl transfer step,
leading to C−C bond cleavage with the formation of a new
metal−alkyl complex and an olefin with a smaller carbon chain,
would be the rate-limiting step, which is thermodynamically
unfavorable.69,70 The subsequent hydrogenation of the olefinic
double bond would provide the driving force to make the
process run. The proximity of a Lewis acid center and a
stronger electrophilicity of the metal site would then facilitate
the key β-alkyl transfer step of the proposed mechanism
through the weakening of a Cβ−alkyl bond by an additional
alkyl−Lewis acid interaction and the formation of a more
CONCLUSION
■
Titanium hydrides supported onto three different oxides
(silica, silica−alumina, and alumina) were successfully
prepared via the surface organometallic chemistry approach.
[Ti-H]@Al2O3‑500 is reported for the first time and has been
extensively characterized by IR, solid-state NMR, mass balance
analysis, and ESR. Their activities in three different reactions
(epoxidation of 1-octene, depolymerization of a FT-wax, and
polymerization of ethylene) were studied. The materials
prepared with this strategy have led to heterogeneous catalysts
operating under relatively mild conditions. This work
demonstrates that the activity and the selectivity of the
catalysts are related to the support. In the case of the
epoxidation reaction of 1-octene, it was shown that the
presence of aluminum (SiO2-Al2O3‑500 and Al2O3‑500 supports)
inhibited the reaction, due to the presence of Lewis and strong
Brønsted acid sites that can produce chelate-poisoning
molecules such as diols. The effect of the support on the
hydrogenolysis of FT-waxes was examined, and [Ti-H]@
Al2O3‑500 exhibited the highest activity with an important diesel
Table 3. Results Obtained for Ethylene Polymerization over [Ti-H] Species Supported on Different Oxides: [Ti-H]@SiO2‑500
[Ti-H]@SiO2-Al2O3‑500. and [Ti-H]@Al2O3‑500
,
a
b
c
activity (g mmolTi h−1
)
Mn (103 g mol−1
)
PDI (Mw/Mn)
Tm (°C)
−1
catalyst
Ti (wt %)
amt of PE (g)
[Ti-H]@SiO2‑500
[Ti-H]@SiO2-Al2O3‑500
[Ti-H]@Al2O3‑500
1.23
2.25
0.79
1.75
2.57
3.77
270
220
915
156
195
195
1.98
1.92
1.78
134
135
136
a
b
c
Experimental conditions: T = 40 °C, P = 10 bar, t = 30 min, V = 20 mL of toluene, catalyst 50 mg. From GPC. From DSC.
G
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Article
Author Contributions
selectivity, slightly higher than that of [Ti-H]@SiO2-Al2O3‑500
.
Conversely, [Ti-H]@SiO2‑500 was much less active, which was
attributed to the lower electrophilicity of Ti active centers and
the lack of acid sites surrounding the Ti−H active site. The
three different catalysts were shown to be active in ethylene
polymerization without any addition of cocatalyst. However,
the alumina-supported sample offered a more significant
amount of cationic Ti propagation sites and boosted the
polymerization activity. This study showed that a proper
choice of support may strongly alter the catalytic properties for
supported Ti−H species, due to the presence of neutral and/or
cationic supported Ti−H species.
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors wish to thank the CNRS, the French Ministry of
Higher Education and Research, and CPE-Lyon for financial
support.
REFERENCES
ASSOCIATED CONTENT
■
■
(1) Song, J.-R.; Wen, L.-X.; Shao, L.; Chen, J.-F. Preparation and
Characterization of Novel Pd/SiO2 and Ca-Pd/SiO2 Egg-Shell
Catalysts with Porous Hollow Silica. Appl. Surf. Sci. 2006, 253 (5),
2678−2684.
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00650.
1H NMR spectra of [TiNpx]@Al2O3‑500 and [Ti-H]@
Al2O3‑500, schemes presenting the epoxidation reaction
and a proposed mechanism, and figures showing the
evolution of cumulated C1−C4 gas products during the
hydrogenolysis of a FT-wax catalyzed by the three
catalysts and the whole product distributions before and
after the reaction (PDF)
(2) Barroso-Quiroga, M. M.; Castro-Luna, A. E. Catalytic Activity
and Effect of Modifiers on Ni-Based Catalysts for the Dry Reforming
of Methane. Int. J. Hydrog. Energy 2010, 35 (11), 6052−6056.
(3) Ramaswamy, V.; Malwadkar, S.; Chilukuri, S. Cu-Ce Mixed
Oxides Supported on Al-Pillared Clay: Effect of Method of
Preparation on Catalytic Activity in the Preferential Oxidation of
Carbon Monoxide. Appl. Catal., B 2008, 84 (1−2), 21−29.
(4) Long, J.; Wang, X.; Zhang, G.; Dong, J.; Yan, T.; Li, Z.; Fu, X. A
Mononuclear Cyclopentadiene-Iron Complex Grafted in the
Supercages of HY Zeolite: Synthesis, Structure, and Reactivity.
Chem. - Eur. J. 2007, 13 (28), 7890−7899.
AUTHOR INFORMATION
■
(5) Basset, J.-M.; Psaro, R.; Roberto, D. Modern Surface Organo-
metallic Chemistry; Wiley-VCH: Weinheim, 2009.
Corresponding Authors
Cherif Larabi − Université de Lyon, ESCPE Lyon, UMR 5265
CNRS, Université Claude Bernard Lyon 1, Laboratoire
C2P2, F-69626 Villeurbanne Cedex, France;
Email: cherif.larabi@univ-lyon1.fr
(6) Samantaray, M. K.; D’Eia, V.; Pump, E.; Falivene, L.; Harb, M.;
Chikh, S. O.; Cavallo, L.; Basset, J.-M. The Comparison between
Single Atom Catalysis and Surface Organometallic Catalysis. Chem.
Rev. 2020, 120 (2), 734−813.
Mostafa Taoufik − Université de Lyon, ESCPE Lyon, UMR
5265 CNRS, Université Claude Bernard Lyon 1, Laboratoire
C2P2, F-69626 Villeurbanne Cedex, France; orcid.org/
0000-0002-3627-5263; Email: mostafa.taoufik@univ-
lyon1.fr
Aimery De Mallmann − Université de Lyon, ESCPE Lyon,
UMR 5265 CNRS, Université Claude Bernard Lyon 1,
Laboratoire C2P2, F-69626 Villeurbanne Cedex, France;
orcid.org/0000-0002-8943-6403; Email: aimery.de-
mallmann@univ-lyon1.fr
(7) Popoff, N.; Mazoyer, E.; Pelletier, J.; Gauvin, R. M.; Taoufik, M.
Expanding the Scope of Metathesis: A Survey of Polyfunctional,
Single-Site Supported Tungsten Systems for Hydrocarbon Valor-
ization. Chem. Soc. Rev. 2013, 42 (23), 9035−9054.
(8) Larabi, C.; Merle, N.; Le Quemener, F.; Rouge, P.; Berrier, E.;
Gauvin, R. M.; Le Roux, E.; de Mallmann, A.; Szeto, K. C.; Taoufik,
M. New Synthetic Approach towards Well-Defined Silica Supported
Tungsten Bisoxo, Active Catalysts for Olefin Metathesis. Catal.
Commun. 2018, 108, 51−54.
(9) Larabi, C.; Szeto, K. C.; Bouhoute, Y.; Charlin, M. O.; Merle, N.;
De Mallmann, A.; Gauvin, R. M.; Delevoye, L.; Taoufik, M. Solvent-
Free Ring-Opening Metathesis Polymerization of Norbornene over
Silica-Supported Tungsten-Oxo Perhydrocarbyl Catalysts. Macromol.
Rapid Commun. 2016, 37 (22), 1832−1836.
(10) Barman, S.; Merle, N.; Minenkov, Y.; De Mallmann, A.;
Samantaray, M. K.; Le Quemener, F.; Szeto, K. C.; Abou-Hamad, E.;
Cavallo, L.; Taoufik, M.; Basset, J.-M. Well-Defined Silica Grafted
Molybdenum Bis(Imido) Catalysts for Imine Metathesis Reactions.
Organometallics 2017, 36 (8), 1550−1556.
(11) Norsic, S.; Larabi, C.; Delgado, M.; Garron, A.; de Mallmann,
A.; Santini, C.; Szeto, K. C.; Basset, J.-M.; Taoufik, M. Low
Temperature Hydrogenolysis of Waxes to Diesel Range Gasoline and
Light Alkanes: Comparison of Catalytic Properties of Group 4, 5 and
6 Metal Hydrides Supported on Silica-Alumina. Catal. Sci. Technol.
2012, 2 (1), 215−219.
(12) Larabi, C.; Merle, N.; Norsic, S.; Taoufik, M.; Baudouin, A.;
Lucas, C.; Thivolle-Cazat, J.; de Mallmann, A.; Basset, J.-M. Surface
Organometallic Chemistry of Titanium on Silica-Alumina and
Catalytic Hydrogenolysis of Waxes at Low Temperature. Organo-
metallics 2009, 28 (19), 5647−5655.
(13) Soulivong, D.; Norsic, S.; Taoufik, M.; Coperet, C.; Thivolle-
Cazat, J.; Chakka, S.; Basset, J.-M. Non-Oxidative Coupling Reaction
of Methane to Ethane and Hydrogen Catalyzed by the Silica-
Authors
́
Sebastien Norsic − Université de Lyon, ESCPE Lyon, UMR
5265 CNRS, Université Claude Bernard Lyon 1, Laboratoire
C2P2, F-69626 Villeurbanne Cedex, France
Lhoussain Khrouz − Université de Lyon, ENS de Lyon, CNRS
UMR 5182, Université Claude Bernard Lyon 1, Laboratoire
de Chimie, 69342 Lyon, France
Olivier Boyron − Université de Lyon, ESCPE Lyon, UMR
5265 CNRS, Université Claude Bernard Lyon 1, Laboratoire
C2P2, F-69626 Villeurbanne Cedex, France; orcid.org/
0000-0002-0386-5814
Kai Chung Szeto − Université de Lyon, ESCPE Lyon, UMR
5265 CNRS, Université Claude Bernard Lyon 1, Laboratoire
C2P2, F-69626 Villeurbanne Cedex, France
Christine Lucas − Université de Lyon, ESCPE Lyon, UMR
5265 CNRS, Université Claude Bernard Lyon 1, Laboratoire
C2P2, F-69626 Villeurbanne Cedex, France
Complete contact information is available at:
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Supported Tantalum Hydride: (SiO)2Ta-H. J. Am. Chem. Soc. 2008,
130 (15), 5044−5045.
(29) Popoff, N.; Espinas, J.; Pelletier, J.; Macqueron, B.; Szeto, K. C.;
Boyron, O.; Boisson, C.; Del Rosal, I.; Maron, L.; De Mallmann, A.;
Gauvin, R. M.; Taoufik, M. Small Changes Have Consequences:
Lessons from Tetrabenzyltitanium and -Zirconium Surface Organo-
metallic Chemistry. Chem. - Eur. J. 2013, 19 (3), 964−973.
(30) Rosier, C.; Niccolai, G.; Basset, J. Catalytic Hydrogenolysis and
Isomerization of Light Alkanes over the Silica-Supported Titanium
Hydride Complex (SiO)3TiH. J. Am. Chem. Soc. 1997, 119 (50),
12408−12409.
(14) Szeto, K. C.; Norsic, S.; Hardou, L.; Le Roux, E.; Chakka, S.;
Thivolle-Cazat, J.; Baudouin, A.; Papaioannou, C.; Basset, J.-M.;
Taoufik, M. Non-Oxidative Coupling of Methane Catalysed by
Supported Tungsten Hydride onto Alumina and Silica-Alumina in
Classical and H2 Permeable Membrane Fixed-Bed Reactors. Chem.
Commun. 2010, 46 (22), 3985−3987.
(15) Szeto, K. C.; Loges, B.; Merle, N.; Popoff, N.; Quadrelli, E. A.;
Jia, H.; Berrier, E.; De Mallmann, A.; Deleyoye, L.; Gauvin, R. M.;
Taoufik, M. Vanadium Oxo Organometallic Species Supported on
Silica for the Selective Non-Oxidative Dehydrogenation of Propane.
Organometallics 2013, 32 (21), 6452−6460.
(16) Szeto, K. C.; Jones, Z. R.; Merle, N.; Rios, C.; Gallo, A.; Le
Quemener, F.; Delevoye, L.; Gauvin, R. M.; Scott, S. L.; Taoufik, M.
A Strong Support Effect in Selective Propane Dehydrogenation
Catalyzed by Ga(i-Bu)3 Grafted onto Gamma-Alumina and Silica.
ACS Catal. 2018, 8 (8), 7566−7577.
(17) Szeto, K. C.; Gallo, A.; Hernandez-Morejudo, S.; Olsbye, U.;
De Mallmann, A.; Lefebvre, F.; Gauvin, R. M.; Deevoye, L.; Scott, S.
L.; Taoufik, M. Selective Grafting of Ga(i-Bu3 on the Silanols of
Mesoporous H-ZSM-5 by Surface Organometallic Chemistry. J. Phys.
Chem. C 2015, 119 (47), 26611−26619.
(18) Al Maksoud, W.; Gevers, L. E.; Vittenet, J.; Outd-Chikh, S.;
Telalovic, S.; Bhatte, K.; Abou-Hamad, E.; Anjum, D. H.; Hedhili, M.
N.; Vishwanath, V.; Alhazmi, A.; Atmusaiteer, K.; Basset, J. M. A
Strategy to Convert Propane to Aromatics (BTX) Using TiNp4
Grafted at the Periphery of ZSM-5 by Surface Organometallic
Chemistry. Dalton Trans. 2019, 48 (19), 6611−6620.
(31) Alladin, T.; Beaudoin, M.; Scott, S. Thermolysis of Silica-
Supported Bis(Neopentyl) Complexes of Titanium and Zirconium.
Inorg. Chim. Acta 2003, 345, 292−298.
(32) Bini, F.; Rosier, C.; Saint-Arroman, R. P.; Neumann, E.;
Dablemont, C.; de Mallmann, A.; Lefebvre, F.; Niccolai, G. P.; Basset,
J.-M.; Crocker, M.; Buijink, J.-K. Surface Organometallic Chemistry of
Titanium: Synthesis, Characterization, and Reactivity of (Si-O)nTi-
(CH2C(CH3)3)4-n (n = 1, 2) Grafted on Aerosil Silica and MCM-41.
Organometallics 2006, 25 (15), 3743−3760.
(33) Cheon, J.; Rogers, D.; Girolami, G. Mechanistic Studies of the
Thermolysis of Tetraneopentyltitanium(IV) 0.1. Solution Evidence
That Titanium Alkylidenes Activate Saturated Hydrocarbons. J. Am.
Chem. Soc. 1997, 119 (29), 6804−6813.
(34) Gao, Y.; Hanson, R.; Klunder, J.; Ko, S.; Masamune, H.;
Sharpless, K. Catalytic Asymmetric Epoxidation and Kinetic
Resolution-Modified Procedures Including Insitu Derivatization. J.
Am. Chem. Soc. 1987, 109 (19), 5765−5780.
(35) Stoll, S.; Schweiger, A. EasySpin, a Comprehensive Software
Package for Spectral Simulation and Analysis in EPR. J. Magn. Reson.
2006, 178 (1), 42−55.
(19) Szeto, K. C.; Merle, N.; Rios, C.; Rouge, P.; Castelbou, J. L.;
Taoufik, M. Tailoring the Selectivity in 2-Butene Conversion over
Supported d(0) Group 4, 5 and 6 Metal Hydrides: From
Dimerization to Metathesis. Catal. Sci. Technol. 2015, 5 (10),
4765−4771.
(36) Joubert, J.; Delbecq, F.; Sautet, P. Alkane Metathesis by a
Tungsten Carbyne Complex Grafted on Gamma Alumina: Is There a
Direct Chemical Role of the Support? J. Catal. 2007, 251 (2), 507−
513.
(37) Joubert, J.; Delbecq, F.; Thieuleux, C.; Taoufik, M.; Blanc, F.;
Coperet, C.; Thivolle-Cazat, J.; Basset, J.-M.; Sautet, P. Synthesis,
Characterization, and Catalytic Properties of Gamma-Al2O3-Sup-
ported Zirconium Hydrides through a Combined Use of Surface
Organometallic Chemistry and Periodic Calculations. Organometallics
2007, 26 (14), 3329−3335.
(20) Meunier, D.; Piechaczyk, A.; de Mallmann, A.; Basset, J. Silica-
Supported Tantalum Catalysts for Asymmetric Epoxidations of Allyl
Alcohols. Angew. Chem., Int. Ed. 1999, 38 (23), 3540−3542.
(21) Basset, J.-M.; Coperet, C.; Soulivong, D.; Taoufik, M.; Cazat, J.
T. Metathesis of Alkanes and Related Reactions. Acc. Chem. Res. 2010,
43 (2), 323−334.
(22) Taoufik, M.; Le Roux, E.; Thivolle-Cazat, J.; Basset, J.-M.
Direct Transformation of Ethylene into Propylene Catalyzed by a
Tungsten Hydride Supported on Alumina: Trifunctional Single-Site
Catalysis. Angew. Chem., Int. Ed. 2007, 46 (38), 7202−7205.
(23) Le Quemener, F.; Barman, S.; Merle, N.; Aljuhani, M. A.;
Samantaray, M. K.; Saih, Y.; Szeto, K. C.; De Mallmann, A.;
Minenkov, Y.; Huang, K.-W.; Cavallo, L.; Taoufik, M.; Basset, J.-M.
Metathetic Oxidation of 2-Butenes to Acetaldehyde by Molecular
Oxygen Using the Single-Site Olefin Metathesis Catalyst (SiO)2Mo-
(O)2. ACS Catal. 2018, 8 (8), 7549−7555.
(38) Szeto, K. C.; Merle, N.; Trebosc, J.; Taoufik, M.; Gauvin, R. M.;
Pourpoint, F.; Delevoye, L. Caveat on the Actual Robustness of
Heteronuclear NMR Methods for Probing the Surface of Gamma-
Alumina and Related Catalysts. J. Phys. Chem. C 2019, 123 (20),
12919−12927.
̈
(39) Knozinger, H.; Ratnasamy, P. Catalytic Aluminas - Surface
Models and Characterization of Surface Sites. Catal. Rev.: Sci. Eng.
1978, 17 (1), 31−70.
(40) Taoufik, M.; Szeto, K. C.; Merle, N.; Del Rosal, I.; Maron, L.;
Trebosc, J.; Tricot, G.; Gauvin, R. M.; Delevoye, L. Heteronuclear
NMR Spectroscopy as a Surface-Selective Technique: A Unique Look
at the Hydroxyl Groups of Gamma-Alumina. Chem. - Eur. J. 2014, 20
(14), 4038−4046.
(24) Samantaray, M. K.; Pump, E.; Bendjeriou-Sedjerari, A.; D’Elia,
V.; Pelletier, J. D. A.; Guidotti, M.; Psaro, R.; Basset, J.-M. Surface
Organometallic Chemistry in Heterogeneous Catalysis. Chem. Soc.
Rev. 2018, 47 (22), 8403−8437.
(41) Delgado, M.; Santini, C. C.; Elbecq, F.; Wischert, R.; Le
Guennic, B.; Tosin, G.; Spitz, R.; Basset, J.-M.; Sautet, P. Alumina as a
Simultaneous Support and Co Catalyst: Cationic Hafnium Complex
Evidenced by Experimental and DFT Analyses. J. Phys. Chem. C 2010,
114 (43), 18516−18528.
(42) Delgado, M.; Santini, C. C.; Delbecq, F.; Baudouin, A.; De
Mallmann, A.; Prestipino, C.; Norsic, S.; Sautet, P.; Basset, J.-M.
Characterization of Surface Hydride Hafnium Complexes on Alumina
by a Combination of Experiments and DFT Calculations. J. Phys.
Chem. C 2011, 115 (14), 6757−6763.
(43) Motta, A.; Szeto, K. C.; Taoufik, M.; Nicholas, C. P. Energetic
Pathways and Influence of the Metallacyclobutane Intermediates
Formed during Isobutene/2-Butene Cross-Metathesis over WH3/
Al2O3 Supported Catalyst. Catal. Sci. Technol. 2016, 6 (10), 3386−
3393.
(25) Clerici, M.; Bellussi, G.; Romano, U. Synthesis of Propylene-
Oxide from Propylene and Hydrogen-Peroxide Catalyzed by
Titanium Silicalite. J. Catal. 1991, 129 (1), 159−167.
(26) Buijink, J.; van Vlaanderen, J.; Crocker, A.; Niele, E. Propylene
Epoxidation over Titanium-on-Silica Catalyst - the Heart of the
SMPO Process. Catal. Today 2004, 93−95, 199−204.
(27) Aldrich, K. E.; Odom, A. L. Titanium-Catalyzed Hydro-
amination and Multicomponent Coupling with a Simple Silica-
Supported Catalyst. Organometallics 2018, 37 (23), 4341−4349.
(28) Zhizhko, P. A.; Pichugov, A. V.; Bushkov, N. S.; Rumyantsev, A.
V.; Utegenov, K. I.; Talanova, V. N.; Strelkova, T. V.; Lebedev, D.;
Mance, D.; Zarubin, D. N. Catalytic Imido-Transfer Reactions of
Well-Defined Silica-Supported Titanium Imido Complexes Prepared
via Surface Organometallic Chemistry. Organometallics 2020, 39 (7),
1014−1023.
I
https://dx.doi.org/10.1021/acs.organomet.0c00650
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
(44) Digne, M.; Sautet, P.; Raybaud, P.; Euzen, P.; Toulhoat, H.
Hydroxyl Groups on Gamma-Alumina Surfaces: A DFT Study. J.
Catal. 2002, 211 (1), 1−5.
(45) Raybaud, P.; Digne, M.; Iftimie, R.; Wellens, W.; Euzen, P.;
Toulhoat, H. Morphology and Surface Properties of Boehmite
(Gamma-AlOOH): A Density Functional Theory Study. J. Catal.
2001, 201 (2), 236−246.
(46) Mazoyer, E.; Trebosc, J.; Baudouin, A.; Boyron, O.; Pelletier, J.;
Basset, J.-M.; Vitorino, M. J.; Nicholas, C. P.; Gauvin, R. M.; Taoufik,
M.; Delevoye, L. Heteronuclear NMR Correlations To Probe the
Local Structure of Catalytically Active Surface Aluminum Hydride
Species on Gamma-Alumina. Angew. Chem., Int. Ed. 2010, 49 (51),
9854−9858.
(47) Taoufik, M.; Le Roux, E.; Thivolle-Cazat, J.; Coperet, C.;
Basset, J.-M.; Maunders, B.; Sunley, G. J. Alumina Supported
Tungsten Hydrides, New Efficient Catalysts for Alkane Metathesis.
Top. Catal. 2006, 40 (1−4), 65−70.
(48) Joubert, J.; Delbecq, F.; Sautet, P.; Le Roux, E.; Taoufik, M.;
Thieuleux, C.; Blanc, F.; Coperet, C.; Thivolle-Cazat, J.; Basset, J.-M.
Molecular Understanding of Alumina Supported Single-Site Catalysts
by a Combination of Experiment and Theory. J. Am. Chem. Soc. 2006,
128 (28), 9157−9169.
(49) Pelletier, J.; Espinas, J.; Vu, N.; Norsic, S.; Baudouin, A.;
Delevoye, L.; Trebosc, J.; Le Roux, E.; Santini, C.; Basset, J.-M.;
Gauvin, R. M.; Taoufik, M. A Well-Defined Silica-Supported
Aluminium Alkyl through an Unprecedented, Consecutive Two-
Step Protonolysis-Alkyl Transfer Mechanism. Chem. Commun. 2011,
47 (10), 2979−2981.
(50) Krizan, M.; Honzicek, J.; Vinklarek, J.; Ruzickova, Z.; Erben, M.
Titanocene(III) Pseudohalides: An ESR and Structural Study. New J.
Chem. 2015, 39 (1), 576−588.
(61) Williams, D. B. G.; Lawton, M. Aluminium triflate: a
remarkable Lewis acid catalyst for the ring opening of epoxides by
alcohols. Org. Biomol. Chem. 2005, 3, 3269−3272.
(62) Silvestre-Albero, J.; Domine, M. E.; Jorda, J. L.; Navarro, M. T.;
Rey, F.; Rodriguez-Reinoso, F.; Corma, A. Spectroscopic, Calori-
metric, and Catalytic Evidences of Hydrophobicity on Ti-MCM-41
Silylated Materials for Olefin Epoxidations. Appl. Catal., A 2015, 507,
14−25.
(63) Corma, A.; Domine, M.; Ganoa, J. A.; Jorda, J. L.; Navarro, M.
T.; Rey, F.; Perez-Pariente, J.; Tsuji, J.; McCulloch, B.; Nemeth, L. T.
Strategies to improve the epoxidation activity and selectivity of Ti-
MCM-41. Chem. Commun. 1998, 2211−2212.
(64) Saikia, L.; Satyarthi, J. K.; Srinivas, D.; Ratnasamy, P. Activation
and reactivity of epoxides on solid acid catalysts. J. Catal. 2007, 252,
148−160.
(65) Posner, G. A.; Rogers, D. A.; Kinzig, C. M.; Gurria, G. M.
Organic reactions at alumina surfaces. Displacement reactions effected
by alcohols, thiols, and acetic acid on dehydrated alumina.
Tetrahedron Lett. 1975, 16, 3597−3600.
(66) Posner, G. A.; Rogers, D. Z. J. Organic reactions at alumina
surfaces. Mild and selective opening of arene and related oxides by
weak oxygen and nitrogen nucleophiles. J. Am. Chem. Soc. 1977, 99,
8214−8218.
̈
̈
(67) Knozinger, H.; Kohne, R. Dehydration of Alcohols over
Alumina. 1. Reaction Scheme. J. Catal. 1966, 5 (2), 264−270.
(68) Roy, S.; Mpourmpakis, G.; Hong, D.-Y.; Vlachos, D. G.; Bhan,
A.; Gorte, R. J. Mechanistic Study of Alcohol Dehydration on
Gamma-Al2O3. ACS Catal. 2012, 2 (9), 1846−1853.
(69) Dufaud, V.; Basset, J. M. Catalytic Hydrogenolysis at Low
Temperature and Pressure of Polyethylene and Polypropylene to
Diesels or Lower Alkanes by a Zirconium Hydride Supported on
Silica-Alumina: A Step Toward Polyolefin Degradation by the
Microscopic Reverse of Ziegler-Natta Polymerization. Angew. Chem.,
Int. Ed. 1998, 37, 806−810.
(70) Mortensen, J. J.; Parrinello, M. J. A Density Functional Theory
Study of a Silica-Supported Zirconium Monohydride Catalyst for
Depolymerization of Polyethylene. J. Phys. Chem. B 2000, 104 (13),
2901−2907.
(51) Blanckenberg, A.; Malgas-Enus, R. Olefin Epoxidation with
Metal-Based Nanocatalysts. Catal. Rev.: Sci. Eng. 2019, 61 (1), 27−83.
(52) Ma, Z.; Yang, W.; Sun, W.-H. Recent Progress on Transition
Metal (Fe, Co, Ni, Ti and V) Complex Catalysts in Olefin
Polymerization with High Thermal Stability. Chin. J. Chem. 2017,
35 (5), 531−540.
(53) Gomez Bernal, H.; Cedeno Caero, L.; Finocchio, E.; Busca, G.
An FT-IR Study of the Adsorption and Reactivity of Tert-Butyl
Hydroperoxide over Oxide Catalysts. Appl. Catal., A 2009, 369 (1−2),
27−35.
(54) Deubel, D.; Frenking, G.; Gisdakis, P.; Herrmann, W.; Rosch,
N.; Sundermeyer, J. Olefin Epoxidation with Inorganic Peroxides.
Solutions to Four Long-Standing Controversies on the Mechanism of
Oxygen Transfer. Acc. Chem. Res. 2004, 37 (9), 645−652.
(55) Sharpless, K.; Williams, D.; Townsend, J. Mechanism of
Epoxidation of Olefins by Covalent Peroxides of Molybdenum(VI). J.
Am. Chem. Soc. 1972, 94 (1), 295−296.
(56) Bach, R.; Wolber, G.; Coddens, B. On the Mechanism of
Metal-Catalyzed Epoxidation - A Model for the Bonding in Peroxo
Metal-Complexes. J. Am. Chem. Soc. 1984, 106 (20), 6098−6099.
(57) Botubol-Ares, J. M.; Hanson, J. R.; Hernandez-Galan, R.;
Collado, I. G. Mild Epoxidation of Allylic Alcohols Catalyzed by
Titanium(III) Complexes: Selectivity and Mechanism. ACS Omega
2017, 2 (7), 3083−3090.
(58) Yu, Y.; Zhu, Y.; Bhagat, M. N.; Raghuraman, A.; Hirsekorn, K.
F.; Notestein, J. M.; Nguyen, S. T.; Broadbelt, L. J. Mechanism of
Regioselective Ring-Opening Reactions of 1,2-Epoxyoctane Catalyzed
by Tris(Pentafluorophenyl)Borane: A Combined Experimental,
Density Functional Theory, and Microkinetic Study. ACS Catal.
2018, 8 (12), 11119−11133.
(59) Parulkar, A.; Spanos, A. P.; Deshpande, N.; Brunelli, N. A.
Synthesis and Catalytic Testing of Lewis Acidic Nano Zeolite Beta for
Epoxide Ring Opening with Alcohols. Appl. Catal., A 2019, 577, 28−
34.
(60) Caron, M.; Sharpless, K. B. Ti(OiPr)4 Mediated Nucleophilic
Openings of 2,3-Epoxy Alcohols. A Mild Procedure for Regioselective
Ring-Opening. J. Org. Chem. 1985, 50, 1557−1560.
J
https://dx.doi.org/10.1021/acs.organomet.0c00650
Organometallics XXXX, XXX, XXX−XXX