Stepwise construction of silica-supported tantalum/iridium heteropolymetallic catalysts using surface organometallic chemistry

Article abstract of DOI:10.1016/j.jcat.2020.10.016

A stepwise surface organometallic chemistry (SOMC) methodology consisting in using a silica-supported tantalum species, [(≡SiO)Ta(CH^tBu)(CH₂^tBu)₂], as a reactive center to coordinate an iridium site, was developed to construct tantalum/iridium heterobimetallic edifices. The resulting material, MAT-2, exhibits enhanced catalytic performances - both in H/D isotopic exchange and alkane metathesis reactions - in comparison to MAT-1, which was prepared from the direct grafting on silica of a well-defined heterobimetallic Ta/Ir complex. We projected that the difference in catalytic activity was due to the presence of distinct active sites and we used a combination of advanced spectroscopic methods (IR, solid-state NMR and XAS spectroscopies) as well as modeling (computational studies and molecular models) to identify the structure of these surface species. These investigations point towards the presence of three types of active sites at the surface of MAT-2: the heterobimetallic surface species, [≡SiOTa(CH₂^tBu)₂{IrH₂(Cp*)}] 2-s, which is also found in MAT-1, as well as an unanticipated heterotrimetallic species, [≡SiOTa(CH₂^tBu)₂{IrH₂(Cp*)}], 3-s along with some unreacted monometallic Ta sites [(≡SiO)Ta(CH^tBu)(CH₂^tBu)₂], 1-s. The well-defined trimetallic surface species 3-s was independently prepared and characterized to support this hypothesis. This study highlights the importance of the synthetic methodology used for the preparation of heterobimetallic species through SOMC, and the difficulty to obtain true single-sites surface species.

Full text of DOI:10.1016/j.jcat.2020.10.016

Journal Pre-proofs
Stepwise Construction of Silica-supported Tantalum/Iridium Heteropolyme-
tallic Catalysts Using Surface Organometallic Chemistry
Sébastien Lassalle, Ribal Jabbour, Iker Del Rosal, Laurent Maron, Emiliano
Fonda, Laurent Veyre, David Gajan, Anne Lesage, Chloé Thieuleux, Clément
Camp
PII:
S0021-9517(20)30422-X
https://doi.org/10.1016/j.jcat.2020.10.016
YJCAT 13942
DOI:
Reference:
To appear in:
Journal of Catalysis
Received Date:
Revised Date:
Accepted Date:
14 August 2020
9 October 2020
13 October 2020
Please cite this article as: S. Lassalle, R. Jabbour, I. Del Rosal, L. Maron, E. Fonda, L. Veyre, D. Gajan, A.
Lesage, C. Thieuleux, C. Camp, Stepwise Construction of Silica-supported Tantalum/Iridium Heteropolymetallic
Catalysts Using Surface Organometallic Chemistry, Journal of Catalysis (2020), doi: https://doi.org/10.1016/
j.jcat.2020.10.016
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Stepwise Construction of Silica-supported Tantalum/Iridium
Heteropolymetallic Catalysts Using Surface Organometallic Chemistry.
a
b
c
c
d
Sébastien Lassalle, Ribal Jabbour, Iker Del Rosal, Laurent Maron, Emiliano Fonda, Laurent
a
b
b
a
a
Veyre, David Gajan, Anne Lesage, Chloé Thieuleux and Clément Camp*
a
Laboratory of Chemistry, Catalysis, Polymers and Processes, C2P2 UMR 5265, Université de Lyon, Institut de Chimie de Lyon, CNRS, Université Lyon 1,
CPE Lyon, 43 Bd du 11 Novembre 1918, F-69616 Villeurbanne, France.
*clement.camp@univ-lyon1.fr
b
Université de Lyon, Centre de RMN à Hauts Champs de Lyon CRMN, FRE 2034, Université de Lyon, CNRS, ENS Lyon, UCB Lyon 1, 69100
Villeurbanne, France.
c
LPCNO (IRSAMC), Université de Toulouse, INSA, UPS, CNRS (UMR 5215); Institut National des Sciences Appliquées, 135 avenue de Rangueil, F-
3
1077 Toulouse, France.
d
Synchrotron SOLEIL, L’Orme des Merisiers, Saint Aubin BP-48, 91192 Gif sur Yvette, France.
ABSTRACT
A
stepwise surface organometallic chemistry (SOMC) methodology consisting in using
a
silica-supported tantalum species,
t
t
[(≡SiO)Ta(CH Bu)(CH Bu) ], as a reactive center to coordinate an iridium site, was developed to construct tantalum/iridium heterobimetallic
2 2
edifices. The resulting material, MAT-2, exhibits enhanced catalytic performances - both in H/D isotopic exchange and alkane metathesis
reactions - in comparison to MAT-1, which was prepared from the direct grafting on silica of a well-defined heterobimetallic Ta/Ir complex. We
projected that the difference in catalytic activity was due to the presence of distinct active sites and we used a combination of advanced
spectroscopic methods (IR, solid-state NMR and XAS spectroscopies) as well as modeling (computational studies and molecular models) to
identify the structure of these surface species. These investigations point towards the presence of three types of active sites at the surface of
t
MAT-2: the heterobimetallic surface species, [≡SiOTa(CH
2
Bu)
2
{IrH
2
(Cp*)}] 2-s, which is also found in MAT-1, as well as an unanticipated
t
t
t
heterotrimetallic species, [≡SiOTa(CH
2
Bu)
2
{IrH
2
(Cp*)}], 3-s along with some unreacted monometallic Ta sites [(≡SiO)Ta(CH Bu)(CH
2
Bu)
2
], 1-s.
The well-defined trimetallic surface species 3-s was independently prepared and characterized to support this hypothesis. This study highlights
the importance of the synthetic methodology used for the preparation of heterobimetallic species through SOMC, and the difficulty to obtain
true single-sites surface species.
KEYWORDS
Surface OrganoMetallic Chemistry (SOMC); early/late heterobimetallic species; supported Dual-Atom Catalysts (DACs); hydrogen isotope
exchange (HIE); alkane metathesis; hydrides; tantalum; iridium.
address this challenge, surface organometallic chemistry
1
. Introduction
(SOMC) is a method of choice since it allows to generate well-
defined surface species from tailored molecular complexes
and thus combines the advantages of homogeneous and
heterogeneous approaches.[11,12]
Heterometallic systems attract substantial interest due to their
original structures and their capability to promote new
chemistry, different from that of their monometallic
constituents, through metal-metal synergistic effects.[1–9]
Homogeneous approaches are particularly powerful to
prepare sophisticated bimetallic complexes featuring a precise
and controlled structure. Yet the bottleneck of these systems
resides in the use of elaborated on-purpose ligands which are
particularly efficient to direct the assembly of the two metals,
but can limit their accessibility and therefore their interest in
catalysis.[3] Heterogeneous approaches offer numerous
advantages, among which the possibility to access low
coordinated metallic sites not achievable in solution.[10]
However classical heterogeneous systems are generally ill-
defined and as a result the exact nature of the catalytically
active species often remain elusive which hampers the precise
understanding of the cooperative bimetallic mechanisms in
place, and thus the rational design of new systems. To
Two main synthetic methodologies can be envisioned to
prepare well-defined supported heterobimetallic species
through SOMC. First, a heterobimetallic complex can be
prepared in solution through the condensation of two
monometallic precursors. This molecular heterobimetallic
derivative can then be grafted onto the solid support in a
second step (Scheme 1, route A). This approach was
successfully developed in our group recently to prepare
original silica-supported Ta-Ir species with excellent
performances in catalytic H/D isotope exchange reactions.[10]
Another elegant methodology to access silica-supported
heterobimetallic species consists first in grafting an oxophilic
monometallic complex onto the oxide support and then, in a
second step, in using this supported organometallic species as
a
reactive center to introduce the second metal, as
1

summarized in Scheme 1, route B. This strategy has only been
explored in very rare instances[13–18] and is different from
sequential co-grafting or co-impregnation methods in which
both metal sites are orthogonally attached to the support,
independently of one another, and are typically converted to
supported alloys or nanoparticles after thermal treatment.[19–
dehydroxylated[11] at 700°C according to the reported
procedures.[10] The preparation of [(CH CHCH Si
is detailed in SI and is adapted from literature
procedure.[45] Propane was dried and deoxygenated over
freshly regenerated R311G BASF catalyst/molecular sieves
(4Å) prior to use. All other reagents were acquired from
commercial sources and used as received.
3
)
2
2
]
7
8
O12OH
a
2
8][29–32] The purpose of this article is to compare both
routes (A and B) in the case of a tantalum-iridium system. We
demonstrate that, although homogeneously distributed
heterometallic species are formed using both approaches, the
nature of the obtained surface species, and therefore the
catalytic performances of these materials, are affected by the
chosen synthetic methodology. Note that this work falls
within the emerging area of research of supported Dual-Atom
Catalysts (DACs),[33,34] although the mild SOMC catalyst
preparation approach is drastically different from classically
used high temperature (750-1200°C) pyrolytic treatment of
metal-organic precursors leading to carbon-derived materials
containing dual M-M’ sites.[35–39]
2
2
.2 Syntheses
.2.1 Synthesis of {( Bu)
i
t
tBu)
7
Si
7
O
12SiO)}Ta(CH Bu)(CH
2
2
], 1-
POSS.
The preparation of 1-POSS was adapted from a literature
procedure.[43] pentane (8 mL) solution of
[(CH CHCH 12OH (1.460 g, 1.75 mmol) was added
dropwise to a dark brown pentane (8 mL) solution of 1
(814 mg, 1.75 mmol). The reaction mixture was stirred 24
hours at room temperature and then 30 min at 60°C yielding a
pale yellow solution. The volatiles were removed under
vacuum, affording a yellow oil. The crude product was
dissolved in the minimum amount of HMDSO and stored at -
A
] Si O
2 7 8
3
)
2
MXn+2
+
M'X'n+1
route A
XnM M'X'
40°C for 3 days yielding orange crystals of 1-POSS (1,825 g,
-
XX'
1
1
.48 mmol, 85%). H NMR (300 MHz, C
6
D
6
) δ 4.75 (s, 1H,
n
t
Ta=CH), 2.30 – 1.98 (m, 7H, CH(CH
3
)
2
), 1.42 (s, 9H, Bu), 1.22
H
O
O
Xn+1M M'X'n
t
(s, 18H, Bu), 1.13 (d, J = 6.6 Hz, 18H, α- CH(CH ) ), 1.07 (m, J =
3
2
6
0
C
(
.6Hz, 24H, β- CH(CH
.84 (d, J = 7.0 Hz, 8H, β-SiCH
245.1 (Ta=CHC(CH
Ta=CHC(CH ), 34.8-34.0 (CH ), 26.1 (CH
2.9 (SiCH ). Elemental analysis calcd (%) for C43
3
)
2
), 0.90 (d, J = 7.0 Hz, 6H, α-SiCH
2
),
). C{ H} NMR (101 MHz,
), 95.9 (Ta-CH ), 45.7
), 24.4 (CH(CH ),
Ta:
oxide support
- HX
oxide support
1
3
1
2
6
D
6
)
δ
3
)
3
2
MXn+2
M'X'n+1
XX'
3
)
3
3
3
3 2
)
-
HX
MXn+1
-
2
2
H
95
O13Si
8
O
C 42.13, H 7.81; found: C 42.19, H 7.84.
route B
oxide support
i
tBu)
2
.2.2 Synthesis of {( Bu)
7
Si
7
O12SiO)}Ta(CH
2
2
{IrH
2
(Cp*)}],
Scheme 1. Methodologies to access heterobimetallic surface
2-POSS.
species through a SOMC approach.
A colorless toluene (8 mL) solution of Cp*IrH
4
(89.5 mg, 0.27
mmol) was added dropwise to an orange toluene (8 mL)
solution of 1-POSS (364 mg, 0.29 mmol). The reaction mixture
was stirred 2 hours at room temperature and volatiles were
removed in vacuo to yield an orange oil. The residue was
dissolved in the minimum amount of HMDSO and stored at -
2
. Materials and Methods
2
.1 General considerations.
Unless otherwise noted, all reactions and characterization
were performed under inert atmosphere either using high-
vacuum lines (10-5 mBar) Schlenk line techniques or in an
MBraun glovebox under an atmosphere of purified argon (<1
4
0°C overnight to yield red crystals identified as 3-POSS. The
mixture was filtered off to remove 3-POSS and the filtrate
was concentrated and stored at -40°C for 3 days to yield 2-
1
POSS as red crystals (323 mg, 0.22 mmol, 75%). H NMR (300
2 2
ppm O /H O). Glassware and cannulæ were stored in an oven
MHz, C
6
D
6
3
)
2
at ∼100 °C for at least 12 h prior to use. Toluene and n-
pentane were purified by passage through a column of
activated alumina, dried over Na/benzophenone, vacuum-
transferred to a storage flask and freeze-pump-thaw degassed
prior to use. Hexamethyldisiloxane (HMDSO) was refluxed
and distilled from CaH
stored over 4Å molecular sieves prior to use. C
over Na/benzophenone vacuum-transferred to a storage flask
and freeze-pump-thaw degassed prior to use. Fluorobenzene
was freeze-pump-thaw degassed and stored over molecular
t
)
6
, 1.29 (d, J = 14.1Hz, 2H, Ta-CH
.7 Hz, 18H, α-CH(CH
CH(CH ), 0.97 (d, J = 7.0 Hz, 6H, α-SiCH
H, β-SiCH ), 0.18 (d, J = 14.1 Hz, 2H, Ta-CH
2
3
)
2
8
1
3
1
Ir-H). C{ H} NMR (101 MHz, THF-d
2
, freeze-pump-thaw degassed and
was dried
(
C
5
Me
5
), 35.2 (C(CH
6
D
6
(CH(CH
3
)
2
calcd (%) for C48
3
8.68, H 6.91.
t
t
2.2.3
{( Bu)
Synthesis
of
sieves (4Å) prior to use. Cp*IrH
4
,[40] Ta(CH Bu)(CH
] 1-s,[42,43] and MAT-1,[10] were
prepared using literature procedures. The SBA-15
mesoporous silica was synthesized[44] and
2 3
Bu) ,[41]
i
t
t
t
7
Si
7
O
2 2 2 5 2
12SiO)}Ta(CH Bu) {Ir H (Cp*) }], 3-POSS.
2 2
[(≡SiO)Ta(CH Bu)(CH Bu)
A colorless pentane (5 mL) solution of Cp*IrH
4
(50 mg, 0.15
mmol) was added dropwise to an orange pentane (5 mL)
2

t
solution of 1-POSS (93.3 mg, 0.08 mmol). The reaction
mixture was stirred for 2 hours at room temperature and the
volatiles were removed in vacuo to yield an orange oil. The
residue was dissolved in the minimum amount of HMDSO
and stored at -40°C overnight to yield red crystals identified
NMR (400 MHz, C
6
D
6
) δ 2.15 (s, 30H, Cp*), 1.56 (s, 27H, Bu),
), -11.14 (s, 5H, Ir-H).
) δ 93.4 (Ta-CH ), 93.3 (C Me ),
C(CH ), 34.2 (CH C(CH ), 32.1
t
1.33 (s, 9H, Bu), 1.08 (s, 2H, Ta-CH
2
1
3
1
C{ H} NMR (101 MHz, C
72.8 (OC(CH ), 35.6 (CH
(OC(CH )), 11.2 (C Me ).
.2.6 Preparation of MAT-2.
2 3
Powder [≡SiOTa(CH ], 1-s, (801 mg, 0.49 mmol
tBu)(CH tBu)
Ta, 1 eq.) is charged in one compartment of a two-sided
Schlenk reaction vessel equipped with a sintered glass filter
4
(163 mg, 0.49 mmol, 1 eq.) is placed in the other
compartment. The double-Schlenk vessel is then evacuated
6
D
6
2
5
5
3
)
3
2
3
)
3
2
3 3
)
3
)
3
5
5
1
as 3-POSS (104 mg, 0.06 mmol, 82%). H NMR (300 MHz,
2
C
6
D
6
) δ 2.20 (s, 7H, CH(CH
3
)
2
), 2.14 (s, 30H, Cp*), 1.28 (s, 9H,
), 1.12 (m, 24H, β-
), 0.88 – 0.82 (m, 8H, β-
), -11.02 (s, 5H,Ir-H). C{ H} NMR (101 MHz, C ) δ
3.6 (Ta-CH ), 93.6 (C Me ), 35.2-33.3 (C(CH ), 26.3-25.0
CH ), 24.5 (CH(CH ), 23.2-22.8 (SiCH ), 11.1 (C Me ).
Elemental analysis calcd (%) for C53 Ta: C 36.49, H
2
t
Bu), 1.20 (d, J = 6.6 Hz, 18H, α-CH(CH
CH(CH
SiCH
9
(
3 2
)
3
)
2
), 0.93 – 0.89 (m, 6H, α-SiCH
2
1
3
1
2
6 6
D
and Cp*IrH
2
5
5
3 3
)
3
3
)
2
2
5
5
-5
(
10 mBar) and dry pentane (15 mL) is added in both
compartments via vacuum distillation. The colorless solution
H
2 8
109Ir O13Si
6
.30; found: C 35.93, H 6.32.
.2.4 Synthesis of [(CH t
Bu)Ta{Ir
tBu)
], 1.
of complex Cp*IrH
4
is transferred through the frit to the
2
2
2
H
5
(Cp*)
2
}], 3.
t
t
[
≡SiOTa(CH
2
Bu)(CH
2
Bu)
3
] powder suspension and stirred at
t
From [Ta(CH Bu)(CH
2
3
room temperature for 2 h. After the reaction, the pale red
supernatant is filtered away from the solid. The solid is
washed with fresh pentane and the supernatant is removed
again. This procedure is repeated 6 times to ensure removal of
A colorless pentane solution (10 mL) of Cp*IrH
4
(171 mg,
(120 mg,
0
.52 mmol, 2 eq.) was added dropwise to a dark-brown
pentane solution (10 mL) of Ta(CH Bu)(CH Bu)
2
t
t
3
4
any unreacted Cp*IrH . The volatile components are then
0
.26 mmol, 1 eq.). The reaction mixture turned dark orange
condensed in a 6.7 liters round bottom flask, propane (3.2
mmol) is introduced as internal standard and the neopentane
evolved during the grafting is quantified by G.C. (0.43 mmol,
.9 eq). The resulting pale yellow powder is dried under
vacuum (10 mBar) for 2 hours at room temperature to yield
and was stirred at room temperature for 24h. The volatiles
were removed in vacuo to yield a red/orange solid (253 mg).
The crude product was dissolved in the minimum amount of
pentane and stored at -40°C overnight to yield orange needles
crystals of 3 (223 mg, 0.23 mmol, 88%). Single crystals suitable
for X-ray diffraction were obtained similarly.
0
-5
1
9
15 mg of MAT-2. H MAS SSNMR (500 MHz, 293 K) δ = 2.1
t
13
(Cp*), 1.0 (CH
2
Bu), -11.3 (Ir-H).
C
CPMAS SSNMR
From [{Ta(CH
A colorless pentane solution (8 mL) of Cp*IrH
.07 mmol, 1 eq.) was added dropwise to an orange pentane
2 3 2
tBu)
}{IrH (Cp*)}], 2.
t
(
9
2
126 MHz, 293 K) δ = 110.4 (Ta-CH
2
), 93.9 (C
5
Me
5
), 33.5 ( Bu),
4
(23 mg,
-1
.1 (C
5
Me
5
). DRIFT (293K, cm ) ν 2956 (s, νC-H), 2904 (s, νC-H),
863 (m, νC-H), 2065 (m, νIr-H), 2020 (s, νIr-H), 1947 (m, νIr-H).
0
solution (8 mL) of 2 (50 mg, 0.07 mmol, 1 eq.). The reaction
mixture turned dark orange and was stirred at room
temperature for 24h. The volatiles were removed in vacuo to
yield a red/orange solid. The crude product was dissolved in
the minimum amount of pentane and stored at -40°C
overnight to yield orange needles crystals of 3 (60 mg,
Elemental analysis calcd (%) for MAT-2: C 12.66, H 2.07, Ir
1
0.13, Ta 9.54; found: C 12.85, H 2.13, Ir 9.51, Ta 9.72.
2
.2.7 Preparation of MAT-3.
-5
SBA-15700 (300 mg dehydroxylated at 700°C under 10 mBar
vacuum for 10 hours, 0.24 mmol of OH, 1.0 eq.) is charged in
one compartment of a two-sided Schlenk reaction vessel
equipped with a sintered glass filter and complex 3 (262 mg,
0.26 mmol, 1.1 eq.) is placed in the other compartment. The
1
0
3
5
.06 mmol, 87%). H NMR (400 MHz, 293K, C
6
D
2
6
) δ 2.11 (s,
), -10.52 (s,
) δ = 107.9 (Ta-
). DRIFT (293K,
cm ) ν = 2949 (s, νC-H), 2898 (s, νC-H), 2854 (s, νC-H), 2734 (m,
C-H), 2084 (s, νIr-H), 2043 (s, νIr-H), 2018 (s, νIr-H), 1996 (s, νIr-H),
t
0H, Cp*), 1.33 (s, 18H, Bu), 0.62 (s, 4H, Ta-CH
1
3
1
H, Ir-H). C{ H} NMR (101 MHz, 293K, C
6 6
D
-5
double-Schlenk vessel is then evacuated (10 mBar) and dry
pentane (15 mL) is added to 3 via vacuum distillation. The
intense red solution of complex 3 is transferred through the
frit to the SBA-15700 powder and stirred at room temperature
for 2 h upon which time the material turns pale yellow. After
the reaction the pale red supernatant is filtered away from the
solid. The solid is washed with fresh pentane and the
supernatant is removed again. This procedure is repeated 6
times to ensure removal of any unreacted 3. The volatile
components are then condensed in a 6.7 liters round bottom
flask, propane (3.5 mmol) is introduced as internal standard
and the neopentane evolved during the grafting is quantified
by G.C. (0.20 mmol, 0.9 eq). The resulting pale yellow powder
CH
2
), 93.3 (C Me ), 35.6 (C(CH ), 11.0 (C Me
5
5
3
)
3
5
5
-1
ν
1
1
967 (s, νIr-H), 1457 (s), 1380 (s), 1353 (s), 1220 (s), 1073 (m),
069 (m), 1027 (s). Elemental analysis calcd (%) for
C
30
H57Ir
2
Ta: C 36.65, H 5.84; found: C 36.67, H 5.87.
t
2
.2.5 Synthesis of [{(CH t
TBS.
2
Bu)Ta(OSi(O Bu)
3
)}{Ir
2
H
5
2
(Cp*) }], 3-
t
A colorless pentane solution of HOSi(O Bu)
3
(13 mg, 0.05
mmol, 1 eq.) was added dropwise to another orange pentane
(
50 mL) solution of 3 (50 mg, 0.05 mmol, 1 eq.). After 4 hours
stirring at r.t. the volatiles were remove under vacuum
yielding a light orange crude solid (58 mg). The solid was
dissolved in the minimum amount of pentane and stored at -
-5
is dried under vacuum (10 mBar) for 2 hours at room
1
temperature to yield 420 mg of compound MAT-3. H MAS
4
0°C for 3 days yielding crystals of unreacted complex 3.
t
SSNMR (500 MHz, 293 K) δ 2.1 (Cp*), 0.9 (CH
2
Bu), -11.3 (Ir-
Me ), 33.1
). DRIFT (293K, cm ) ν 2951 (s, νC-H), 2911 (s,
These crystals were filtered off, the filtrate was concentrated
13
H). C CPMAS SSNMR (126 MHz, 293 K) δ 93.2 (C
5
5
by half under vacuum and stored at -40°C for another 3 days
t
-1
(
Bu), 9.2 (C
5
Me
5
1
yielding 3-TBS as orange crystals (42 mg, 0.03 mmol, 67%). H
ν
C-H), 2864 (s, νC-H), 2030 (s, νIr-H), 1947 (s, νIr-H), 1865 (s, δC-H).
3

Elemental analysis calcd (%) for MAT-3: C 10.84, H 1.67, Ir
In a typical experiment, MAT-2 (52 mg, 0.027 mmol of Ta)
was charged in a 500 mL batch reactor under argon. After
evacuation of the gas phase, propane (730 mBar, 530 eq.) was
introduced and the batch reactor was heated at 200°C. The gas
phase was sampled periodically and analyzed by GC to
monitor quantity of products and their distribution during
the reaction. The turnover number (TON) is calculated as
follows: TON = n /(3n ) where n is the total number of
1
3.88, Ta 6.53; found: C 11.12, H 1.79, Ir 13.80, Ta 6.45.
2
2
.3 Catalysis
.3.1 Hydrogen-deuterium catalytic exchange reaction using
6 5 6 6
C H F as substrate and C D as deuterium source.
In a typical experiment, MAT-2 (7.7 mg, 0.004 mmol of Ta)
was charged in a J. Young NMR tube and suspended in a
stock solution composed of fluorobenzene (6.6 mg,
C
Ta
C
moles of carbon atoms arising from all the reaction products
(methane, ethane, butanes and pentanes) and nTa is the
number of moles of Ta introduced in the experiment.
0
.069 mmol), hexamethyldisiloxane (6.0 mg, 0.037 mmol) as
internal standard and C (0.58 mL). The NMR tube was
6
D
6
sealed under argons and the reaction was then heated at 70°C
2
.4 Characterizations
1
inside a NMR spectrometer and periodically monitored by H
1
9
2.4.1 IR spectroscopy.
NMR and F NMR spectroscopy. The monitoring of the
catalytic activity was realized on independently prepared
catalysts with excellent reproducibility.
Samples were prepared in a glovebox (diluted in KBr for
molecular compounds, pure for silica-supported species),
sealed under argon in a DRIFT cell equipped with KBr
windows and analyzed on a Nicolet 6700 FT-IR spectrometer.
2
.3.2 Split test
MAT-2 (10.5 mg, 0.0056 mmol Ta) was charged in a J. Young
NMR tube and suspended in stock solution of
fluorobenzene (9.0 mg, 0.094 mmol) and
hexamethyldisiloxane (6.4 mg, 0.039 mmol) as internal
standard in C (0.58 mL). The NMR tube was sealed under
argon and the solution was heated in a 70 ± 2°C silicone oil
2
.4.2 Elemental analyses.
a
ICP-MS and combustion analyses were performed under inert
atmosphere either at the School of Human Sciences, Science
6
D
6
Center,
Mikroanalytisches Labor Pascher, Germany.
.4.3 X-ray diffraction structural determinations.
London
Metropolitan
University
or
at
1
19
bath and periodically monitored by H NMR and F NMR
spectroscopy. After 3 hours reaction (30% conversion) the
supported catalyst was removed by filtration through a dry
glass microfiber filter under argon and the filtrate was
transferred into another J. Young NMR tube which was again
heated in a 70 ± 2°C silicone oil bath and periodically
2
Experimental details regarding XRD measurements are
provided in SI. CCDC 2018037-2018040 contain the
supplementary crystallographic data for this paper. These
data are provided free of charge by the Cambridge
Crystallographic Data Centre.
1
19
monitored by H NMR and F NMR spectroscopy. No further
conversion (30%) of fluorobenzene was observed after 48
hours. Analysis of this liquid filtrate by ICP-MS showed
undetectable amount of Ta and Ir metals in solution (below
detection limit <0.001 wt% Ir, <0.001 wt% Ta). Analysis of the
spent solid catalyst by TEM showed good integrity of the
material structure with the absence of metal nanoparticles and
a homogeneous distribution of Ta and Ir in equimolar ratio as
seen by EDX.
2
.4.4 NMR Spectroscopy.
Solution NMR spectra were recorded on Bruker AV-300,
AVQ-400 and AV-500 spectrometers. Chemical shifts were
measured relative to residual solvent peaks, which were
assigned relative to an external TMS standard set at 0.00 ppm.
1
13
1
1
H and C NMR assignments were confirmed by H− H
1
13
COSY and H− C HSQC and HMBC experiments.
The proton solid-state NMR spectra were obtained on a
Bruker 700 MHz narrow-bore spectrometer using a double
resonance 2.5 mm MAS probe. The samples were introduced
under argon in a zirconia rotor, which was then tightly
closed. Ultra-dry nitrogen gas was used to spin the samples to
avoid sample degradation. For all the proton multiple-
quantum experiments, the spinning frequency was set to 18
kHz. The 2D proton DQ-SQ correlation spectra were recorded
according to the following general scheme: excitation of DQ
2
.3.3 Catalyst reuse
MAT-2 (10.5 mg, 0.0056 mmol Ta) was charged in a J. Young
NMR tube and suspended in stock solution of
fluorobenzene (9.0 mg, 0.094 mmol) and
hexamethyldisiloxane (5.5 mg, 0.034 mmol) as internal
standard in C (0.57 mL). The NMR tube was sealed under
argon and the solution was heated in a 70 ± 2°C silicone oil
a
6
D
6
1
19
bath and periodically monitored by H NMR and F NMR
spectroscopy. After 24 hours reaction (96.0% conversion) the
NMR tube was transferred to the Ar atmosphere glovebox.
Fluorobenzene (9.0 mg, 0.094 mmol) was added to the NMR
tube which was again heated in a 70 ± 2°C silicone oil bath.
1
coherences, t evolution and reconversion into observable
magnetization, Z-filter, and detection. DQ excitation and
reconversion were achieved using the POST-C7 pulse
sequence.[46–48] The length of the POST-C7[49] excitation
and reconversion block was set to 160 μs (corresponding to
After 24 hours reaction, 92.4% conversion was reached. Initial
TOFs were identical for run#1 and run#2 (1.59 h-1 and 1.56 h-1
seven basic POST-C7 cycles). Quadrature detection in ω
achieved using the States-TPPI method.[50] A recycle delay of
s was used. The spectral width in the indirect dimension
1
was
respectively) showing good reuse of the catalyst without
deactivation (see Figure S31).
2
was set to 70000 Hz. The 2D proton TQ-SQ correlation spectra
was recorded according to the following general scheme:
2
.3.4 Propane metathesis catalysis.
4

excitation of TQ coherences, t
1
evolution, reconversion into
pentane solution of 2. This led to material MAT-1 which
observable magnetization, Z-filter, and detection.[51–55] TQ
excitation was achieved by the sequential application of first a
contains the well-defined silica-supported monopodal surface
t
species [≡SiOTa(CH
2
Bu)
2
{IrH
2
(Cp*)}], 2-s (Scheme 2).[10]
9
0° proton pulse followed by a DQ POST-C7 pulse sequence
In order to explore the feasibility of route B, i.e. the stepwise
construction of supported heterobimetallic edifices directly on
silica, we first prepared the monometallic monopodal silica-
as previously described in the literature. The length of the
POST-C7 excitation and reconversion block was also set to 160
μs. Quadrature detection in ω
TPPI method.[50] A recycle delay of 2 s was used and the
spectral width in the indirect dimension was 120000 Hz.
1
was achieved using the States-
t
t
supported tantalum species [(≡SiO)Ta(CH Bu)(CH
Scheme 2), based on previous knowledge from our lab.[42,43]
Reaction monitoring by infrared spectroscopy shows that the
2 2
Bu) ], 1-s
(
-1
2
.4.5 X-ray Absorption Spectroscopy.
characteristic sharp band at 3741 cm (ν(O-H)) from SBA-15700
has completely disappeared in the first step, indicating the
full consumption of the isolated surface silanols through
grafting of the Ta monometallic precursor (Figure 1). New
The samples (in the form of powders) were compacted and
sealed under argon in glass capillaries to prevent exposure to
air or moisture. The X-ray absorption measurements were
performed on the SAMBA beamline at the Synchrotron
SOLEIL (Gif sur Yvette, France) in transmission mode. The
energy calibration was made versus a tantalum foil standard.
Data analysis was performed using Demeter software
package.[56] The theoretical modelization and fit of the
EXAFS spectra within Demeter software were done using
corresponding crystallographic and DFT structures.
-1
signals are found at 2960-2860 cm and are assigned to ν(C-H)
stretches of the neopentyl/neopentylidene ligands from 1-s.
This supported species exhibits the same reactive
neopentylidene and neopentyl ligands as those found in 1,
and we thus anticipated analogous alkane elimination
reactivity towards acidic iridium hydrides than that leading
to the heterobimetallic complex 2 (Scheme 2).
Upon treatment of the monometallic grafted tantalum
complex 1-s with a pentane solution of Cp*IrH at room
4
2
.4.6 Computational Details.
All DFT calculations were carried out with the Gaussian 09
suite of programs.[57] Geometries were fully optimized in gas
phase without symmetry constraints, employing the B3PW91
functional.[58,59] The nature of the extrema was verified by
analytical frequency calculations. The calculation of electronic
energies and enthalpies of the extrema of the potential energy
surface (minima and transition states) were performed at the
same level of theory as the geometry optimizations. IRC
calculations were performed to confirm the connections of the
optimized transition states. Iridium and Tantalum atoms were
treated with a small-core effective core potential (60 MWB),
associated with its adapted basis set[60] augmented with a
temperature, using a Ta:Ir stoichiometric ratio of 1:1, the pale
yellow powder turns immediately into a more intense yellow-
colored material, noted MAT-2. 0.9 equiv. of neopentane is
released per surface Ta atom, as titrated by gas
chromatography (GC). This analysis is consistent with the
chemical reaction of the iridium molecular precursor,
4
Cp*IrH , with the tantalum surface species 1-s yielding new
Ta/Ir surface species through alkane elimination observed for
the preparation of 2 in solution. This is further supported by
the IR spectroscopy analysis of MAT-2, with the appearance
of a new set of bands, assigned to ν(Ir-H) stretches, in the
-1
2
080-1940 cm region (Figure 1).[68,69] It is worth mentioning
that Cp*IrH does not react with silica in the absence of Ta
see Figure S30).
f
polarization function (ζ = 0.938 and 0.790 respectively for Ir
and Ta). Si atoms were treated with a Stuttgart effective core
potential[61] augmented with a polarization function (ζd =
4
(
0
.284).[62] For the other elements (H, C and O), Pople's
double-ζ basis set 6-31G(d,p) was used.[63–66] The
vibrational frequencies were calculated using a scaling factor
of 0.9575 as proposed by Irikura et al.[67]
3
. Results and discussion
3
.1 Materials preparation
We recently reported an efficient and clean synthetic
methodology to access original tantalum/iridium
heterobimetallic species, based on the alkane elimination
reaction between a nucleophilic early metal alkyl/alkylidene
t
t
derivative Ta(CH Bu)(CH
2
3
Bu) , 1, and a late metal Brønsted
acidic hydride, Cp*IrH
4
, affording the bimetallic complex
Figure 1. Diffuse Reflection Infrared Fourier Transform
spectra of SBA-15700 (green line), 1-s (grey line) and MAT-2
t
[
{Ta(CH
2
Bu)
3
}{IrH
2
(Cp*)}], 2 (Scheme 2).[10] Complex 2 was
successfully grafted onto silica upon treatment of a SBA-15
silica support dehydroxylated at 700 °C (SBA-15700) with a
(red line) recorded on powder materials under argon.
5

tBu
tBu
tBu
tBu
Ta
1
route A
Cp*IrH4 1 eq.
pentane, r.t.
-
C(CH3)4
H
H
H
tBu
H
tBu
Ta Ir
tBu
Ta Ir
tBu
H
O
O
O
tBu
2
O
O
Si
O
O
O
O
O
O
Si
O
pentane, r.t.
Si
Si
O
Si
O
O
Si
O
O
O
- C(CH3)4
O
O
SBA-15700
2-s
MAT-1
Ta(CH Bu)(CH2tBu)3
t
pentane, r.t.
-
C(CH3)4
tBu
H
H
Ta Ir
O
route B
H
H
H
tBu
tBu
Ir
H
tBu
tBu
O
H
tBu
tBu
O
Cp*IrH , 1 eq.
pentane, r.t.
Ta Ir
tBu
4
Ta tBu
Ta
+
+
O
-
C(CH3)4
O
O
O
O
O
O
O
O
O
O
Si
O
Si
Si
O
O
O
O
Si
O
O
O
Si
O
O
O
O
Si
O
Si
O
O
Si
O
O
Si
Si
Si
Si
O
O
O
O
O
O
O
O
O
2
-s
3-s
22 5%
1-s
31 5%
1-s
4
7 7%
MAT-2
Scheme 2. Preparation of silica-supported species.
The elemental analysis of MAT-2 (Expected: Ir:Ta ratio =
.0(1), C:Ta ratio = 20.0(1), Found: Ir:Ta ratio = 0.9(1), C:Ta
-
1
2 x
tantalum hydride species [(≡SiO) TaH ] (TOF = 0.42 h , 30%
1
conversion in 24 hours), which were tested as benchmarks for
this reaction (Figure 2). This suggests that metal-metal
cooperative effects are present and beneficial for catalysis.
ratio = 19.7(1)) is similar to that for MAT-1 (Ir:Ta ratio = 1.0(1),
C:Ta ratio = 19.9(1)). The total Ta content in MAT-2 (4.7
mol%) is analogous to that measured by elemental analysis
for the monometallic material 1-s (4.5 mol%), showing that
no, or undetectable negligible amount of Ta was detached
from the surface during the preparation of MAT-2. Taken
together, these analyses suggest that, globally, one iridium
center has reacted with one tantalum center in route B.
However this is not sufficient to claim that routes A and B are
equivalent on a molecular level.
In order to assess the robustness of catalyst MAT-2, a split test
experiment at 30% conversion has been carried out and no
evolution of the substrate conversion was observed after
filtration of the solid catalyst, showing that there is no active
metal species in solution. In addition undetectable amount
(
below detection limit <0.001 wt%) of both Ta and Ir was
observed in the analysis of the liquid phase via ICP-MS,
which indicates that no leached inactive metal species are
present in solution as well. Analysis of the spent catalyst by
TEM shows the absence of metal nanoparticles and EDX
shows that the weight percent of Ta and Ir as well as the Ta/Ir
ratio before and after catalysis are the same, which further
suggests that the catalyst integrity is maintained throughout
H/D exchange catalysis.
3
.2 Catalytic activity
First hints of the dissimilarities between MAT-1 and MAT-2
were gained through the analysis of their catalytic
performances. As reported by our group, the Ta/Ir sites from
MAT-1 are able to perform catalytic Hydrogen Isotope
Exchange (HIE) reactions with excellent performances that
rivals those of the best systems reported to date.[10] We thus
compared the catalytic HIE activity of MAT-1 and MAT-2 in
Furthermore catalyst MAT-2 reuse has been performed.
6.0% conversion was obtained in the first reaction run (24
9
hours reaction) and 92.4% conversion was reached in the
second reaction run (24 hours reaction). Initial TOFs were
identical for run 1 and run 2 (1.59 h and 1.56 h respectively)
showing a good reuse of the catalyst without substantial
deactivation (see Figure S31).
6 6
the benchmark H/D scrambling reaction between C D and
-1
-1
C
6
H
5
F at 70°C using 6 mol% of Ta. As shown on Figure 2,
-
MAT-2 exhibits a significant increase in activity (TOF = 1.59 h
1
,
95 % conversion in 24 hours) compared to the previously
-1
reported material MAT-1 (TOF = 1.04 h , 70% conversion in
Supported tantalum alkyls and hydrides on silica are known
to catalyze linear or branched alkanes metathesis.[70,71]
Therefore, we have also compared the catalytic activity of
MAT-1 and MAT-2 in propane metathesis. The tests were
carried out at 200°C in a batch reactor with a tantalum loading
of 0.1 mol%. The reaction was monitored by GC and GC-MS
over time to quantify and identify the reaction products. Here
2
4 hours), thereby suggesting the existence of different active
species in both materials. Noteworthy, the supported Ta/Ir
heteropolymetallic species from MAT-1 and MAT-2 both
show a substantially enhanced catalytic activity compared to
monometallic silica-supported tantalum analogues, such as
the alkyl/alkylidene species 1-s (which is inactive) and the
6

again, MAT-2 displayed a significantly enhanced catalytic
activity compared to MAT-1, with TONs after 40 hours
-1
-1
reaction of 118 vs 50, and TOFs of 8.3 h vs 3.2 h , respectively
Figure 3). During the initial stage of the reaction we observe
(
the release of neopentane in the gas phase. This suggests that
the incoming propane reacts with the surface Ta-neopentyl
groups to generate, through sigma-bond metathesis, Ta-
propyl moieties and liberate neopentane. This proposed C-H
bond activation is typical of surface Ta-alkyl complexes, and
is the first step in the reported propane metathesis mechanism
2
with monometallic Ta/SiO species.[71] Methane, ethane,
butanes and pentanes account for all of the reaction products
with excellent mass balance. No significant difference in
product selectivity is observed between MAT-1 and MAT-2:
both catalysts are more selective towards C2 (50-60%) and C4
(
30-40%) homologues, while C1 and C5 products are formed
Figure 3. Propane metathesis at 200°C in batch reactor (700
mBar, 0,2 mol% Ta). MAT-1 ( ), MAT-2 ( ), MAT-3 ( ),
in lower amounts (below 5%), which is a typical behavior for
Ta and W propane metathesis catalysts.[16,19,70–72] Given
the similarity in products distribution, a reaction mechanism
analogous to that classically accepted for propane metathesis
[
=
h .
(≡SiO)
2
1
TaH] ( ). TOFs determined using initial rates: MAT-2
-
-1
-1
8.3 h ; MAT-1 = 3.2 h ; MAT-3 = 0.6 h ; [(≡SiO)
2
TaH] = 4.4
-
1
2
catalyzed by monometallic Ta/SiO active sites is plausible.
Overall the catalytic results suggest that the active sites in
Note that HRTEM analyses of MAT-2 prior and after catalysis
excluded the formation of metal nanoparticles during the
material preparation or in the course of catalysis, which
testify the high robustness of the heterometallic surface sites
t
MAT-2 are different from the [≡SiOTa(CH
2
Bu)
2
{IrH
2
(Cp*)}]
sites, 2-s, found in MAT-1. In order to better understand these
phenomena, molecular models were synthesized and
advanced characterizations of these materials were carried
out. These investigations, detailed below, support the
coexistence of several surface species in MAT-2, and in
particular the formation of bimetallic as well as trimetallic
assemblies through route B as shown in Scheme 2.
(see SI).
3
.3 Molecular models
In order to better understand the reactivity of Cp*IrH
4
towards the silica-supported tantalum alkyl alkylidene
species 1-s, we first turned our attention to molecular models.
Organometallic siloxy derivatives, and in particular those
belonging to the polyhedral oligomeric silsesquioxanes
(
POSS) family, have been used with some success as
molecular models for silica-grafted species.[43,45,73–77] For
instance, the silsesquioxane cage (c-C Si 12SiOH, which
5
H
9
)
7
7
O
mimics the isolated silanol sites found at the surface of silica
dehydroxylated at 700°C, was reacted with the tantalum
complex 1 to elucidate the reaction pathway leading to the
surface species 1-s.[43] In analogy with this previous study,
i
t
t
we prepared complex {( Bu)
7
Si
7
O
12SiO)}Ta(CH Bu)(CH
2
Bu)
. As
shown on Scheme 3, when 1-POSS is reacted with 0.5
2
,
Figure 2. Conversion of fluorobenzene as a function of
1-POSS and scrutinized its reactivity towards Cp*IrH
4
reaction time. The H/D exchange experiments were carried
out in C
, MAT-3 ( ), [(≡SiO)
conditions.
6
D
6
at 70°C with 6 mol% of Ta. MAT-1 ( ), MAT-2 (
equivalent of Cp*IrH
4
in C
6
D
6
at room temperature, the
)
2
TaH] ( ). 1-s is inactive under these
heterobimetallic
species
2-POSS,
i
tBu)
{( Bu)
7
Si
7
O12SiO)}Ta(CH
2
2
{IrH
2
(Cp*)}],
is
obtained selectively as the sole Ir-containing species.
However, when higher amounts of Cp*IrH are used, a
{Ir (Cp*) }],
-POSS, is formed, along with 2-POSS and unreacted 1-
POSS. Complex 3-POSS can be obtained quantitatively when
-POSS is treated with 2 equivalents Cp*IrH . The trimetallic
aggregate 3-POSS arises from the addition of Cp*IrH
4
i
t
trimetallic species {( Bu)
7
Si
7
O
12SiO)}Ta(CH
2
Bu)
2
2
H
5
2
3
1
4
4
onto 2-
7

POSS, which competes with the addition of Cp*IrH
POSS. This ultimately results in the formation of a mixture of
4
onto 1-
between the various hydrides at the temperature of the
experiment (298 K).
species when Ta:Ir stoichiometric ratios close to 1:1 are used
Single crystals of 2-POSS and 3-POSS suitable for X-ray
diffraction were grown from saturated HDMSO solutions
stored for 24 hours at -40°C. As seen in Figure 4, the solid-
state structure of 2-POSS displays a very short Ta-Ir distance
(2.350(2) Å) which is more than 0.2 Å shorter than the sum of
the respective metallic radii (Ta: 1.343 Å; Ir: 1.260 Å; sum =
2.603 Å). The formal shortness ratio (FSR) is low (0.90) and
suggests a strong metal-metal interaction with a multiple Ta-
Ir bond order, analogous to that found in 1. Even if the
hydrides could not be located in the XRD Fourier Map, their
existence was confirmed by other spectroscopic methods.
Moreover, hint of their presence is given by the marked tilting
of the Cp* ligand with respect to the Ta-Ir bond (Cp*centroid-Ir-
Ta angle of 146(1)°), as a result of the three-legged piano-stool
coordination geometry around the Ir center which is
(Scheme 3).
The identities of 2-POSS and 3-POSS were confirmed by
1
13
infrared spectroscopy, H and C solution NMR as well as by
1
X-ray diffraction studies. The H-NMR spectrum for 2-POSS
displays a high-field resonance corresponding to the Ir-H
hydrides at δ = -11.70 ppm and two singlets at δ = 1.23 and
t
2
.31 ppm attributed to the Bu and Cp* moieties respectively.
The introduction of the POSS ligand induces some rigidity
1
and a loss of symmetry, as indicated by the H resonances of
the tantalum-bound methylene groups from the two
2
neopentyl ligands (Ta-CH ) appearing as two diastereotopic
doublets corresponding to two protons, with distinct chemical
2
2
shifts and strong JHH couplings (δ = 0.18 and 1.29 ppm, JHH
=
1
4.2 Hz). In the case of compound 3-POSS, the NMR
spectroscopic features of the isobutyl ligands from the POSS
archetypal
of
pentamethylcyclopentadienyl
iridium
cage as well as those of the neopentyl and Cp* ligands are
complexes.[78] The Ta-CNp and Ta-O bond lengths (average
value 2.145(1) Å and 1.876(6) Å, respectively) are in the
expected range for classical Ta-neopentyl and Ta-siloxy
groups.[76,79,80]
1
similar to those of 2-POSS. The H NMR resonance for the
hydrides in 3-POSS appears as a singlet at δ = -11.02
corresponding from integration to five protons. This is
indicative of a rapid exchange on the NMR time scale
tBu
tBu
R
Si
O H
Ta
O
Si
O
H
O

O
Si
R
O
Si
t
t
Si
R
O
Ta(CH Bu)(CH Bu)
tBu
O Si
O


2
3
R
Si
O
=


O
pentane, r.t.
- C(CH3)4
Si
O
O
O
R


1-POSS
Si
Si
O
R
R
n Cp*IrH4
C6D6, r.t.
i
R = Bu
-
n C(CH3)4
H
H
H
H
H
tBu
Ir
H
tBu
tBu
tBu
H
tBu
+
Ta
Ir
+
Ta
Ir
Ta
O
O
O
Si
tBu
Si
Si
1
-POSS
2-POSS
3-POSS
0%
stoichiometry
n = 0.5
n = 0.9
n = 2.1
50%
5%
50%
90%
0%
selectivity
5%
0%
100%
Scheme 3. Reaction of the tantalum molecular model 1-POSS with Cp*IrH
POSS and 3-POSS, respectively.
4
yielding the bimetallic and trimetallic complexes 2-
8

the contrary, the FSR for Ta1-Ir2 is slightly higher than unity
1.003) and although a direct metal-metal interaction cannot
(
be excluded (reported Ta-Ir single bond distances span the
range 2.53-2.85 Å),[81–83] the close proximity between Ta1
and Ir2 is most likely the result of the presence of bridging
hydrides. The approximately linear Cp*centroid-Ir2-Ta1 angle
(
177.83°) suggests the presence of 3 bridging hydrides across
the two metals, arranged to favor a three-legged piano stool
coordination geometry around the {Cp*Ir2} core whereas the
clear tilting of the Cp* ligand with respect to the Ta1-Ir1 bond
(
Cp*centroid-Ir1-Ta1 angle of 151.38°) suggests two terminal
hydrides. All other metric parameters are for most part
similar to those observed in 1 and 2-POSS.
2
-POSS and 3-POSS provide good structural models for the
immobilized surface heterotrimetallic complexes 2-s and 3-s,
but equally important, 2-POSS and 3-POSS can serve as
references to decipher the spectroscopic data recorded on the
functionalized materials and corroborate the assignments
proposed below.
Computational studies have been carried out at the density
functional theory (DFT) level using the B3PW91 functional, to
confirm the precise location of the hydride ligands (see SI),
with good correlation between the crystallographic and
calculated structures. The DFT analysis is also in agreement
with the IR data.
Ir2
C1
Ir1
Ta1
O1
Following the observation that high nuclearity systems could
be formed on silsesquioxanes, we then explored the reaction
between the tantalum tris-neopentyl neopentylidene complex
Si1
t
t
2 3
Ta(CH Bu)(CH Bu) and the iridium tetrahydride complex
Cp*IrH
4
in a 1:2 stoichiometric ratio. The reaction affords
t
cleanly the trinuclear complex [{Ta(CH
which is isolated in 88% yield (Scheme 4). H NMR
2
Bu)
2
}{Ir
2
H
5
(Cp*)
2
}], 3,
1
6 6
monitoring of the reaction in C D solvent shows that two
equivalents of neopentane are released, as expected.
Evolution over time of the characteristics high field
resonances of Ir-hydride protons highlights the fast formation
of 2 as intermediate product (δIrH = -11.98 ppm). The latter is
Figure 4. Solid-state molecular structures of 2-POSS (top) and
-POSS (bottom) determined by X-ray diffraction. Ellipsoids
3
are represented with 30% probability. Hydrogen atoms have
been omitted for clarity. Two independent complexes are
found in the asymmetric unit for 2-POSS, only one is
represented. Selected bond distances (Å) and angles (°) for 2-
POSS: Ta1-Ir1 2.350(2), Ta1-O1 1.876(6), Ta1-CNp 2.15(1), Ir1-
Cp*centroid 1.946(8), Ta1-Ir1-Cp*centroid 146(1), Ta1-O1-Si1 164(5).
For 3-POSS: Ta1-Ir1 2.3893(5), Ta1-Ir2 2.6113(4), Ta1-O1
then slowly converted into
3
(δIrH = -10.52 ppm) by
protonolysis of one Ta-neopentyl bond from 2 by an external
acidic iridium-hydride from excess of Cp*IrH . Accordingly,
4
the reaction of 2 with one equivalent of Cp*IrH in pentane at
4
room temperature affords quantitatively complex 3 with
evolution of one equivalent of neopentane, as projected and
confirmed by elemental analysis (Scheme 4).
1
1
1
.902(5), Ta1-C2 2.185(9), Ir1-Cp*centroid 1.927(1), Ir2-Cp*centroid
.855(1), Ta1-Ir1-Cp*centroid 151.38(1), Ta1-Ir2-Cp*centroid
77.83(1), Ir1-Ta1-Ir2 112.05(2), Ta1-O1-Si1 152.6(4).
The structure of 3 was elucidated by 1H and 13C solution
NMR spectroscopy, infrared spectroscopy, elemental analysis
1
and X-ray diffraction studies. The H NMR spectrum of a
solution of 3 in C
6
D
6
t
0
.62 ppm assigned to the Cp*, Bu, and Ta-CH
The most striking feature of the solid-state structure of 3-
POSS, shown on Figure 4, is the disparity in the intermetallic
distances and geometries. The Ta1-Ir1 distance (2.3898(5) Å) is
more than 0.2 Å shorter than the Ta1-Ir2 distance
respectively. In addition,
corresponding to five protons upon integration is observed at
a single hydride resonance
1
2
98 K (singlet, δIrH = -10.52 ppm). Variable temperature H-
8
NMR measurements, performed in toluene-d solution in the
(
2.6113(4) Å). The Ta1-Ir1 distance displays a FSR of 0.92 and
range 228-298 K, did not enable to decoalesce this resonance,
indicating rapid chemical exchange on the NMR time scale
between bridging and terminal hydride sites. Vibrational IR
suggests the same strong metal-metal interaction with a
multiple Ta1-Ir1 bond order as observed in 1 and 2-POSS. On
9

spectroscopy exhibits a series of M-H stretching vibration
-
1
signals between 2088-1968 cm , which are assigned to Ir-H
3
.4 Rational preparation of heterotrimetallic Ta/Ir
2
surface
stretching vibrations. For comparison, the characteristic
absorption bands of terminal iridium hydrides are 2150 cm
species
-1
The isolation of 3 offers a unique entry point towards the
clean preparation of well-defined trimetallic surface species.
In order to anticipate the reactivity of 3 with silica, we
investigated first the protonolysis reaction of 3 with tris(tert-
-1
for
CH
Cp*IrH
4
[40],
2095
[84] and 2056 cm for 2,[10] Thus the
supports the
cm
for
2
(Cp) Ta(μ-
-1
2
)
2
Ir(SiEt )(H)(CO)
3
2
broad signal distribution in complex
3
concomitant presence of bridging and terminal hydrides.
butoxy)silanol. The reaction is carried out in
a 1:1
stoichiometric ratio in pentane at room temperature and
affords exclusively the monosiloxy heterotrimetallic complex
H
tBu
tBu
H
Cp*IrH 1 eq.
pentane, r.t.
4
t
t
3-TBS
[{IrH
3
(Cp*)}{Ta(CH
2
Bu)(OSi(O Bu)
3
)
2
}{IrH
2
(Cp*)}]
tBu
tBu
Ta Ir
tBu
1
tBu
Ta
1
(Scheme 5). H NMR reaction monitoring shows that 1.0
equiv. of neopentane is released in the course of the reaction,
as expected. The spectroscopic and structural features of 3-
TBS closely match those of 3-POSS (see SI).
- C(CH3)4
tBu
2
Cp*IrH 1 eq.
4
pentane, r.t.
-
C(CH3)4
H
H
H
H
Cp*IrH 2 eq.
Ir
4
pentane, r.t.
H
H
H
tBu
H
H
H
H
Ta
Ir
Ir
Ir
H
t
H
HOSi(O Bu) 1 eq.
-
2 C(CH3)4
3
H
tBu
H
tBu
t
Ta
Ir
Ta
Ir
pentane, r.t.
- C(CH3)4
tBu
3
O
tBu
( BuO) Si
3
Scheme 4. Synthesis of the Ta-Ir heteropolymetallic hydride
species 2 and 3 through alkane elimination.
3
3-TBS
Single crystals suitable for X-ray diffraction were grown from
a saturated solution of 3 in pentane stored for 24 hours at -
H
H
H
H
Ir
4
0°C. As for 3-POSS, the solid-state structure of 3, reproduced
H
tBu
Ta
Ir
on Figure 5, displays a strong disparity in the intermetallic
distances and geometries. Metric parameters for 3 and 3-
POSS are for most part similar. The formal shortness ratio for
Ta-Ir1 (0.93) is in agreement with a multiple Ta-Ir1 bond and
the market tilting of the Cp* ligand with respect to the Ta-Ir1
bond suggests the presence of terminal hydrides on Ir1, as
observed for 3-POSS. Conversely, the formal shortness ratio
H
O
O
O
O
3
Si
O
O
O
O
O
Si
O
Si
O
O
O
O
Si
Si
O
O
pentane, r.t.
- C(CH3)4
Si
O
O
O
O
SBA15-700
3-s
MAT-3
Scheme 5. Protonolysis reactivity of complex 3.
for Ta-Ir2 (0.99) indicates
a weaker metal-metal bond
interaction and the alignment of the Cp*centroid with the Ta-
Ir2 bond suggests the presence of bridging hydrides, as
confirmed by DFT studies (see SI).
The clean protonolysis reaction occurring with 3 led us
consider the covalent grafting of 3 onto silica. Upon treatment
of SBA-15700 with
a pentane solution of 3 at room
temperature, the powder turns immediately yellow and 0.9
equiv. of neopentane is evolved per grafted Ta, as quantified
by GC. DRIFT spectroscopy analysis of the resulting material,
-1
noted MAT-3, shows that the ν(O-H) signal at 3747 cm
assigned to isolated silanols disappears, indicating the full
consumption of the isolated surface silanols through grafting,
while new signals attributed to ν(C-H) stretches of the
-1
neopentyl and Cp* ligands at 2960-2860 cm and signals
-1
assigned to ν(Ir-H) stretches at 2020 and 1947 cm appear.
The elemental analysis of MAT-3 is in excellent agreement
with the proposed formula (expected %C 10.84, %H 1.67 %Ir
Figure 5. Solid-state molecular structure of 3 determined by
X-ray diffraction. Ellipsoids are represented with 30%
probability. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (°): Ta1-Ir1 2.4291(9),
Ta1-Ir2 2.5891(9), Ta1-C1 2.17(2), Ta1-C2 2.18(2), Ir1-Cp*centroid
1
3.88 %Ta 6.53; found %C 11.12, %H 1.79 %Ir 13.80 %Ta 6.45).
These analyses are consistent with the chemical grafting of the
precursor onto silica via protonolysis of one Ta-Np bond by a
surface silanol group, yielding a monopodal surface species 3-
s (Scheme 5).
1
.929(1), Ir2-Cp*centroid 1.857(1), Ta1-Ir1-Cp*centroid 156.16(1),
Ta1-Ir2-Cp*centroid 178.93(1), Ir1-Ta1-Ir2 113.57(2).
1
0

Materials MAT-1, MAT-2 and MAT-3 were then subjected to
advanced characterization to uncover the structural identity
of their Ta/Ir surface sites.
vibrational domain is slightly shifted to lower-frequency
-1
(2060– 1824 cm ). Thus, these results make also a case for the
presence of heterobimetallic (2-s) and heterotrimetallic (3-s)
surface species in MAT-2. It is interesting to note that the M-
H stretching frequencies are directly correlated with the
length of the Ir-H bonds.
3
.5 Infrared Spectroscopy
Substantial disparities are found in the ν(Ir-H) vibrational
signatures of MAT-1, MAT-2 and MAT-3 (Figure 6a). The
ν(Ir-H) signal of MAT-1 shows two bands at 2037 and 2064
3
.6 Solid-state NMR spectroscopy
-1
cm and is clearly different from that of MAT-3, which is
Proton solid-state NMR spectroscopy under Magic Angle
Spinning (MAS) was applied in order to further support these
more complex and spans a larger wavenumbers range (2020-
-1
1
1
947 cm ). The higher number of Ir-H stretches in MAT-3 is
conclusions. The 1D H spectra of MAT-2 (Figure S17) and
in adequation with its more complex structure, featuring both
bridging and terminal hydrides. These IR spectra differences
parallel those for the molecular analogues 2-POSS vs 3-POSS
described above. Remarkably, the ν(Ir-H) signature recorded
for MAT-2 (Figure 6a) appears as a linear combination of that
for MAT-1 and MAT-3. This clearly indicates that route A
and route B lead to different surface hydride species, and
MAT-3 (Figure S20) both display two intense signals at 2.1
and 0.9 ppm that are assigned to the CH (Cp*) and CH (Np)
3 3
moieties respectively, as well as one well-defined signal at
around -11.3 ppm with a small shoulder at high field
1
3
corresponding to the hydride protons. The C solid-state CP-
MAS NMR spectrum of MAT-2 shows four resonances at
2
110.4, 93.9, 33.5 and 9.1 ppm assigned to the CH (Np), C(Cp*),
suggests that
a
mixture of heterobimetallic (2-s) and
CH (Np) and CH (Cp*) carbons respectively (Figure S18).
3
3
heterotrimetallic (3-s) surface species is present in MAT-2, in
agreement with what is observed with the molecular models
chemistry.
This NMR signature is almost identical to that observed for
MAT-3 (Figure S21), as expected as the surface species 2-s and
1
13
3-s bear similar organic ligands. The H and C NMR spectra
of MAT-1 also displayed the same set of resonances.[10] Thus,
it is extremely difficult to differentiate MAT-1, MAT-2 and
MAT-3 from one-dimensional solid-state NMR studies. In
order to unambiguously determine the number of hydride
protons attached to the metal centers and probe structural
information inherent to proton-proton dipolar couplings, two-
dimensional (2D) proton double-quantum (DQ) and triple-
quantum (TQ) correlation spectra were recorded on MAT-2
and MAT-3. These experiments enable the detection of spatial
proximities between pairs (DQ) or triplets (TQ) of dipolar-
coupled protons, with correlations at the sum of the
individual frequencies in the indirect dimension. For hydride
protons with degenerate chemical shifts, auto-correlation
1 2 1 2
peaks along the ω = 2ω (DQ) or ω = 3ω (TQ) diagonal
reveal the presence of pools of (at least) two or three protons
respectively. The proton DQ spectra of MAT-2 (Figure S19)
and MAT-3 (Figure S22) are similar, with auto-correlations
for the CH
correlations between the CH
3
(Cp*), CH
3
(Np) and hydride protons. Off-diagonal
and hydride protons are also
3
observed. These spectra are also similar to that of MAT-1,[10]
and do not allow one to confirm that route A and B yield
different surface species. The evidence is clearly provided by
proton TQ NMR spectroscopy. The SQ-TQ spectrum of MAT-
2 is shown in Figure 7. The observation of an auto-correlation
along the diagonal at (−11.3 ppm, −33.9ppm) demonstrates
unambiguously that 2-s is not the only species formed in
route B, and that additional organometallic complexes
bearing a higher number of hydrides are present. While this
correlation was absent from the SQ-TQ spectrum of MAT-
Figure 6. a) Diffuse reflection infrared Fourier transform
spectra (Ir-H stretching region) of materials MAT-1 (black
line), MAT-2 (red line) and MAT-3 (blue line) recorded on
powder materials under argon. The SBA-15700 signal has been
subtracted to remove contribution from the support. b)
Calculated Ir–H vibrational frequencies of IR-active normal
mode of vibrations for MAT-1 (black) and MAT-3 (blue).
In Figure 6b are reported all the calculated Ir–H vibrational
frequencies of IR-active normal mode of vibrations for
different optimized rotamers of MAT-1 and MAT-3. In MAT-
1
,[10] it is clearly visible in the spectrum of MAT-3 (Figure
S23), supporting the presence of both heterobi- and
heterotrimetallic surface species in MAT-2. A color code has
been added in Figure 7 to facilitate its interpretation
considering the presence of both 2-s and 3-s. The elongated
shape of the autocorrelation indicates that the broadening of
1
and MAT-3. There are respectively two and five distinct
ν(Ir-H) normal modes, one per Ir-H bond. In MAT-1, the Ir-H
stretching modes lie between 2122 and 2017 cm ,
-1
independently of the considered rotamer. In MAT-3, the
1
1

the hydride resonance is inhomogeneous, i.e. corresponds to a
distribution of chemical shifts due to slight structural
heterogeneity likely originating from the support. We also
note that fast exchange on the NMR time scale between
hydrides is very likely to occur, leading to the observation of
a distribution of average chemical shifts.
Figure 8. Ta LIII (top) and Ir L
(black line); MAT-2 (red line); MAT-3 (blue line) and 1-s
green line) in q-space.
I
(bottom) XANES data of MAT-
1
(
The results of the extended X-ray absorption fine structure
EXAFS) analysis at the Ta LIII edge of MAT-1, MAT-2 and
MAT-3 are detailed below. Note that Ta and Ir have
(
Figure 7. Proton SQ-TQ NMR spectrum (700 MHz, 2.5 mm
probe, 18 kHz MAS frequency) of MAT-2. A total of 300 t
1
intertwined L-edges thus XAS measurement at the Ir LIII edge
increments of 8.3 μs with 96 scans each were recorded. The
(
11215 eV) is not feasible since it overlaps with the Ta LII and
total experimental time was 16 h. The trace above the 2D plot
Ta L edges (11136 and 11680 eV respectively). The Ta-O, Ta-C
I
1
corresponds to the one-dimensional H NMR spectrum. The
and Ta-Ir scattering paths used in our models correspond to
the nearest neighbors around the Ta center in each sample.
The amplitude of the reduction term So² (0.7) was determined
using XAS data recorded on molecular complexes 2 and 3 as
standards, featuring a well-known structure.
1 2
dotted orange line corresponds to the ω =3ω diagonal. The
spectrum has been zoomed by a factor 32 in the hydride
region to clearly show the autocorrelation at around (−11.3
ppm, −33.9 ppm). The correlations between the hydride and
CH (Np) and CH (Cp*) protons at around (−11.3 ppm, −21
3 3
ppm) and (−11.3 ppm, −8 ppm) are also indicated. The other
Several candidate models were considered to fit the EXAFS
data at the Ta LIII edge of MAT-1 (see SI). The best fit, shown
in Figure 9, gives a first shell of 4 neighbors around Ta, with
one oxygen atom at 1.91(1) Å, one iridium at 2.37(1) Å and
two carbons at 2.05(1) and 2.18(1) Å. All these distances (Table
experimental conditions are described in detail in section
2
.4.4.
3
.7 X-Ray absorption spectroscopy
1
) are in perfect agreement with the metrical parameters
We performed XAS experiments at the Ta LIII edge to get
more insight into the local structure and oxidation states of
the surface species. X-ray absorption near-edge (XANES)
spectra for MAT-1, MAT-2 and MAT-3 display edge features
at ca. 9880.5 eV (Figure 8-top) and are nearly identical to that
of the monometallic Ta(V) surface species 1-s, thus indicating
that the oxidation state of Ta in these materials is similar.
Similarly, XANES spectra for MAT-1, MAT-2 and MAT-3
determined by X-ray crystallography on the molecular model
2-POSS and with DFT models (Ta=Ir = 2.370 Å)[10] (see Table
S1 is SI for more details). This supports the presence of 2-s
single sites at the surface of MAT-1. Inclusion of an additional
oxygen atom in the model is detrimental to the fitting (see SI),
therefore the coordination of Ta to a nearby siloxane bridge
from the silica surface, as seen in other SOMC systems,[42,85]
is unlikely here.
I
recorded at the Ir L edge are alike (Figure 8-bottom) and thus
suggest that the Ir oxidation state is comparable in all these
samples.
1
2

Table 1. Fitting parameters obtained from simulation of the
EXAFS data of MAT-1.
Table 2. Fitting parameters obtained from simulation of the
EXAFS data of MAT-3.
Neighbor
Na
r [Å]b
σ [Å 2]c
0.001(1)
0.003(1)
0.001(1)
0.001(1)
Neighbor
Na
r [Å]b
σ [Å 2]c
O
Ir
C
C
1.2(2)
1*
1.91(1)
2.37(1)
2.05(2)
2.18(2)
O
Ir
Ir
C
1.5 (3)
1*
1.91(1)
2.40(1)
2.60(1)
2.20(2)
0.002(1)
0.002(1)
0.003(1)
0.002(1)
1*
1*
1*
1*
[
[
a] Number of neighbors. [b] Distance between the Ta center and the neighbor.
c]Debye-Waller factor. * Fixed parameters in the fit
[
a] Number of neighbors. [b] Distance between the Ta center and the neighbor.
c]Debye-Waller factor. * Fixed parameters in the fit
[
Figure 9. EXAFS Ta LIII edge experimental data (solid lines)
and fit (dashed lines) of MAT-1 in R-space (top) and K-space
Figure 10. EXAFS Ta LIII edge experimental data (solid lines)
and fit (dashed lines) of MAT-3 in R-space (top) and K-space
(bottom).
(bottom).
EXAFS studies performed on MAT-3 (Figure 10) show a first
shell containing two different Ir atoms (Ta-Ir1 = 2.40(1) Å; Ta-
Ir2 = 2.60(1) Å), confirming the presence of a strong metal-
metal interaction with a multiple Ta-Ir1 bond (FSR = 0.92) and
a weaker interaction with Ir2 (FSR = 1) arising from the
presence of bridging hydrides. Note that imposing two
equivalent iridium atoms bound to Ta in the model, either at
short (2.39(2) Å) or long (2.63(2) Å) distance, significantly
worsen the EXAFS fit (see SI), which further supports the
presence of two non-equivalent Ta-Ir interactions. The first
coordination sphere of the Ta center is completed by about
one carbon (Ta-C = 2.20(2) Å) and one oxygen (Ta-O = 1.91(1)
Å) atoms. All these distances (Table 2) are again in excellent
agreement with the crystal structure of the molecular
analogue 3-POSS confirming therefore the proposed structure
for 3-s.
Modelling the EXAFS data recorded for MAT-2 using a single
contribution for the calculation failed due to the poor quality
of fit. To elucidate the structure of the metallic sites present at
the surface of MAT-2 we thus performed a linear combination
fitting analysis of the XANES and EXAFS regions. All
t
combinations using 1-s, 2, 2-s, 3, 3-s and [≡SiOTa-(CH2
Bu)H{IrH (Cp*)}][10] data as standards were explored (see SI).
2
Excellent fitting of the XAS data for MAT-2 was obtained in
both regions using the triple combination of 2-s (47±7%), 3-s
(22±5%) and 1-s (31±5%) (Figure 11). The goodness of fit factor
2
(reduced χ ) increases of 50%, when reducing the fit to two
standards only (see SI). In light of this XAS data analysis for
MAT-2, the contribution from the three species 1-s, 2-s, and 3-
s is clearly established and supports the presence of these
three surface sites on MAT-2.
1
3

performances. Note that the cooperativity between two types
of metallic sites (Zr/W and Ti/W) co-anchored on silica has
been described previously and resulted in drastic
improvement of the catalytic activity in propane
metathesis.[19,20] Tandem alkane-dehydrogenation/olefin-
metathesis systems, involving two independent metal
catalysts which are not necessarily in close proximity, have
also proven successful for alkane metathesis or alkane/alkene
coupling.[86–89] Another hypothesis is that an unidentified
minor surface species, which could not be detected despite
our efforts to provide an advanced characterization of these
materials, is also formed and is responsible for this increase in
catalytic activity.
4
. Conclusions
Different routes for the preparation of tantalum/iridium
heterometallic species at the surface of SBA-15 silica
dehydroxylated at 700°C have been investigated by elemental
analysis, IR, advanced solid-state NMR spectroscopy, XAS,
DFT computations and the synthesis of molecular models.
The data are fully consistent with the formation of only one
type of well-defined surface species when pre-formed
bimetallic or trimetallic complexes are first prepared in
solution and then grafted to the surface through the formation
of a Ta-O-Si linkage. However a mixture of bimetallic (2-s)
and trimetallic (3-s) species are obtained (along with some
unreacted monometallic Ta sites 1-s) using a stepwise
approach which consists in exploiting the reactivity of a Ta
organometallic site pre-grafted on silica with a Ir hydride
complex. Quite strikingly, the material featuring both
bimetallic and trimetallic sites (MAT-2) outperforms those
featuring only one type of site in H/D exchange and alkane
metathesis catalytic transformations. It is still unclear at the
moment if this rise in activity is due to synergistic effects
between the three types of metallic sites at the surface of the
material (1-s + 2-s + 3-s), or if additional surface active species,
which could not be detected despite our efforts to provide an
advanced characterization of these materials, are also formed
and are responsible for this increase in catalytic performances.
Figure 11. EXAFS Ta LIII edge linear combination fitting of
MAT-2 using MAT-1, MAT-3 and 1-s as standards.
Experimental data (solid grey lines) and fit (dashed black
lines) in q-space (top) and K-space (bottom).
Taken together, the advanced characterization of these
materials through state of the art spectroscopic methods (IR,
NMR and XAS):
(
(
(
i)
is in excellent agreement with the proposed
structures for the surface species 2-s and 3-s,
ii)
iii)
validates the use of molecular analogues as
structural models for these surface species and
supports the concomitant presence of several
surface sites in MAT-2 (1-s + 2-s + 3-s).
Strikingly, in both HIE and propane metathesis catalytic tests,
the activity of MAT-3, which contains solely the well-defined
trimetallic surface species 3-s, is inferior to that of MAT-2 (see
Figures 2 and 3). Therefore, the enhanced catalytic activity of
MAT-2 cannot be easily explained by the sole presence of the
trimetallic species 3-s. One possible explanation is that a
synergistic effect arises from the simultaneous presence of 1-s,
This study highlights the importance of the synthetic
methodology used for the preparation of heterobimetallic
species through SOMC, and the difficulty to obtain true
single-sites.[90] It also points out a paradox: ill-defined
species are often not desired since, due to their more complex
nature, they are difficult to comprehend and rationalize; but
at the same time, these species should not systematically be
disregarded since they can have better catalytic performances.
Efforts devoted to the understanding of these complex
systems often paves the way to unexpected discoveries.
2
-s and 3-s active sites. The classically accepted reaction
mechanism for alkane metathesis involves the combination of
a) an alkane dehydrogenation cycle followed by (b) an olefin
metathesis cycle which redistributes the carbon chains among
the transient alkene products and finally (c)
(
a
rehydrogenation step which produces the mixture of longer-
chain and shorter-chain alkanes. If some of the metal surface
sites described in the present work are more effective in the
dehydrogenation/hydrogenation process and others are more
effective in the olefin metathesis cycle then their use in
combination in MAT-2 could result in enhanced catalytic
Declaration of Competing Interest
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
1
4

[12]
C. Copéret, M. Chabanas, R. Petroff Saint-Arroman, J.-M. Basset,
Homogeneous and heterogeneous catalysis: bridging the gap
through surface organometallic chemistry., Angew. Chemie Int. Ed.
Acknowledgements
4
2 (2003) 156–181. https://doi.org/10.1002/anie.200390072.
We thank the "Centre de diffractométrie Henri Longchambon,
Université de Lyon", and in particular Erwan Jeanneau for the
single-crystal X-ray diffraction analyses. We acknowledge
SOLEIL for provision of synchrotron radiation facilities and
the beamline SAMBA staff for assistance. We thank Tanya K.
Todorova for helpful discussions. L.M. is member of the
Institut Universitaire de France. We gratefully acknowledge
financial support from the “Programme Avenir Lyon Saint-
Etienne de l’Université de Lyon”, as part of the
[13]
K. Weiss, W. Guthmann, M. Denzner, Investigation of polymerisation
and metathesis reactions. Part XIII1 1 Part XII, K. Weiss, R. Goller and
G. Lössei, J. Mol. Catal., 46 (1988) 267.: Heterogeneous bimetallic
metathesis catalysts by reactions of differently substituted Fischer-
type tungsten, J. Mol. Catal. 46 (1988) 341–349.
https://doi.org/10.1016/0304-5102(88)85106-X.
[14]
K. Weiss, M. Denzner, Untersuchungen von Polymerisations- und
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https://doi.org/10.1016/0022-328X(88)89029-6.
[
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16]
K. Weiss, W. Guthmann, S. Maisuls, Heterogeneous, Bimetallic
Metathesis Catalysts by Reaction of Fischer-type Carbene Complexes
with Reduced Phillips Catalyst, Angew. Chemie Int. Ed. 27 (1988)
“
Investissements d’Avenir” program (ANR-11-IDEX-0007),
2
75–277. https://doi.org/10.1002/anie.198802751.
the CNRS-MOMENTUM 2017 program, the TGIR-RMN-THC
Fr3050 CNRS and SOLEIL synchrotron (SAMBA beamline,
proposal 20181971). This work was performed using HPC
resources from CALMIP (Grant 2016-p0833).
[
F. Rataboul, C. Copéret, L. Lefort, A. De Mallmann, J. Thivolle-Cazat,
J.M. Basset, Synthesis, characterization and propane metathesis
activity of a tantalum-hydride prepared on high surface area “silica
supported zirconium hydroxide,” J. Chem. Soc. Dalt. Trans. 9 (2007)
9
23–927. https://doi.org/10.1039/b616921j.
[17]
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(1998) 620–625. https://doi.org/10.1021/cm9706199.
Supplementary data to this article can be found online.
[18]
[19]
[20]
I.B. Moroz, P. Florian, J. Viger-Gravel, C.P. Gordon, A. Lesage, C.
Copéret, Silica-Grafted Tris(neopentyl)aluminum: A Monomeric
Aluminum Solid Co-catalyst for Efficient Nickel-Catalyzed Ethene
Dimerization, Angew. Chemie - Int. Ed. (2020) anie.202006285.
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Graphical abstract:
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Research Highlights:
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Two routes to prepare Ta-Ir/SiO catalysts via surface organometallic chemistry.
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In-depth structural characterization of Ta, Ta-Ir and Ta-Ir surface sites.
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Improved catalytic performances in H/D isotope exchange and propane metathesis.
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