Efficient heterogeneous dual catalyst systems for alkane metathesis

Article abstract of DOI:10.1002/adsc.200900539

A fully heterogeneous and highly efficient dual catalyst system for alkane metathesis (AM) has been developed. The system is comprised of an alumina-supported iridium pincer catalyst for alkane dehydrogenation/olefin hydrogenation and a second heterogeneous olefin metathesis catalyst. The iridium catalysts bear basic functional groups on the aromatic backbone of the pincer ligand and are strongly adsorbed on Lewis acid sites on alumina. The heterogeneous systems exhibit higher lifetimes and productivities relative to the corresponding homogeneous systems as catalyst/catalyst interactions and bimolecular decomposition reactions are inhibited. Additionally, using a two-pot device, the supported Ir catalysts and metathesis catalysts can be physically separated and run at different temperatures. This system with isolated catalysts shows very high turnover numbers and is selective for the formation of high molecular weight alkanes.

Full text of DOI:10.1002/adsc.200900539

FULL PAPERS
DOI: 10.1002/adsc.200900539
Efficient Heterogeneous Dual Catalyst Systems for Alkane
Metathesis
a
a
a
a,
Zheng Huang, Eleanor Rolfe, Emily C. Carson, Maurice Brookhart, *
b,
b
c
Alan S. Goldman, * Sahar H. El-Khalafy, and Amy H. Roy MacArthur
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
a
Fax : (+1)-919-962-2388; e-mail: mbrookhart@unc.edu
Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ 08854, USA
b
Fax : (+1)-732-445-5312; e-mail: alan.goldman@rutgers.edu
Department of Chemistry, United States Naval Academy, Annapolis, MD 21402, USA
c
Received: July 31, 2009; Revised: November 20, 2009; Published online: December 18, 2009
Abstract: A fully heterogeneous and highly efficient decomposition reactions are inhibited. Additionally,
dual catalyst system for alkane metathesis (AM) has using a “two-pot” device, the supported Ir catalysts
been developed. The system is comprised of an alu- and metathesis catalysts can be physically separated
mina-supported iridium pincer catalyst for alkane de- and run at different temperatures. This system with
hydrogenation/olefin hydrogenation and a second isolated catalysts shows very high turnover numbers
heterogeneous olefin metathesis catalyst. The iridium and is selective for the formation of high molecular
catalysts bear basic functional groups on the aromat- weight alkanes.
ic backbone of the pincer ligand and are strongly ad-
sorbed on Lewis acid sites on alumina. The heteroge-
neous systems exhibit higher lifetimes and productiv- Keywords: alkane metathesis; alumina; dehydrogen-
ities relative to the corresponding homogeneous sys- ation; heterogeneous catalysis; olefin metathesis;
tems as catalyst/catalyst interactions and bimolecular pincer iridium
Introduction
ACHTUNGTRENNUNG
[
5]
Application of the Fischer–Tropsch (F-T) process to conversion pathways. Heavy hydrocarbons can be
produce synthetic fuel will likely become increasingly converted (unselectively) to liquid alkanes via hydro-
important as petroleum reserves dwindle. The feed- cracking. Unfortunately, there is currently no practical
stock for the F-T process, H /CO (syngas), can be de- method to upgrade the low-MW alkanes to F-T
2
rived from various carbon sources including coal, nat- diesel. Alkane metathesis (AM) can potentially be
ural gas, shale oil and biomass. Conversion of coal to employed to selectively convert low-MW hydrocar-
liquid hydrocarbons is of particular interest due to the bons into diesel and thus improve the diesel yields via
[
1]
worldꢀs vast coal reserves. Production of diesel fuel F-T synthesis.
using the F-T process is attractive since the product is Examples of AM have been previously reported by
highly paraffinic with a very low sulfur content two groups. In 1973, Burnett and Hughes showed
[
6]
(
<1 ppm) and thus burns more cleanly than petroleum- that passage of n-butane over a mixture of alumina-
[2,3]
based diesel.
Furthermore, diesel engines run supported platinum (a hydrogenation/dehydrogena-
tion catalyst) and silica-supported WO3 (an olefin
Although F-T technology has been in use for nearly metathesis catalyst) at 3998C resulted in the forma-
a century, diesel production is still limited due to its tion of hydrocarbons in the C –C range with pro-
~
30% more efficiently than gasoline engines.
1
8+
high cost. A major problem is that the F-T process pane and pentane as the major products (25 wt% and
yields alkane mixtures with no molecular weight 16 wt%, respectively). Methane, branched hydrocar-
(
MW) control while only linear hydrocarbons in the bons, and olefins were produced in addition to the
[
7–10]
C –C range are useful as diesel fuel. n-Alkanes linear alkanes. More recently, Basset et al.
report-
9
19
lower than ca. C suffer from high volatility and lower ed single component Ta or W catalysts for AM which
9
[
4]
ignition quality (cetane number). In addition to F-T function at much lower temperatures. For example,
product mixtures, low-carbon number, low-MW al- propane can be converted at 1508C to a mixture of C1
Adv. Synth. Catal. 2010, 352, 125 – 135
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
125

Zheng Huang et al.
FULL PAPERS
[
16]
Schrock-type olefin metathesis catalysts and an iri-
dium catalyst afforded efficient homogeneous AM
systems. For instance, a reaction conducted at 1258C
converted ca. 125–200 equiv of n-hexane to a range of
[
11]
C to C n-alkanes after 1 day. The Schrock catalyst
2
15
was found to decay much faster than the Ir catalyst
[11,16]
and its early decomposition limited conversion.
Alumina-supported Re O can be used as a hetero-
2
7
geneous metathesis catalyst, and when used in combi-
nation with iridium pincer catalysts, provides a more
stable and longer lived AM dual catalyst system. For
example, heating an n-decane solution of 4 and tert-
Scheme 1.
to C alkanes by using an alumina-supported tungsten butylethylene at 1758C over Re O /Al O gave linear
6
2
7
2
3
hydride catalyst but low turnover frequencies are ob- alkane products in the C –C range with 485 turn-
2
34
[8]
[11]
served (ca. 1/h). These systems are proposed to op- overs after 9 days. We showed in these systems that
erate via the reaction of metal with alkanes to form iridium complexes were partially or completely ad-
[
10]
alkylidene hydride complexes and olefins.
result, both branched and linear hydrocarbons, as well tions led us to study alumina-supported iridium
as methane, are generated. pincer complexes (Figure 2) for catalytic transfer de-
As a sorbed on the Re O alumina support. These observa-
2 7
We have reported both homogeneous and hetero- hydrogenation. We showed that iridium pincer com-
geneous tandem catalytic systems which operate as plexes, especially those bearing basic functional
shown in Scheme 1. Alkane metathesis was achieved groups in the para-position of the pincer ligands
at moderate temperatures (125–1758C) with complete (structures 3–7), bind to g-alumina through a Lewis
[
11]
[17]
selectivity for linear alkanes.
The iridium-based acid/Lewis base interaction.
These alumina-sup-
pincer complexes (Figure 1), reported by Jensen, ported catalysts are thermally robust and recyclable,
[12,13]
[14,15]
Kaska
and our own groups,
serve as the and display high activities for alkane transfer dehy-
alkane dehydrogenation/olefin hydrogenation cata- drogenation. The goal of the work reported here is to
lysts. The combination of an Mo olefin metathesis cat- combine such catalysts with heterogeneous olefin
alyst, Mo
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(CHR)
A
T
N
T
E
N
N
(NAr)[OC
A
H
U
G
R
N
U
(CH )
A
H
U
G
R
N
U
G
(Mo-F12) metathesis catalysts to generate a fully heterogeneous
3
3 2 2
[
11]
(
R=CMe Ph, Ar=2,6-diisopropylphenyl), or other catalyst system for AM.
2
We report here an investigation of heterogeneous
AM using six g-alumina-supported iridium pincer cat-
alysts in combination with the heterogeneous olefin
metathesis catalyst Re O /Al O . These heterogene-
2
7
2
3
ous catalyst systems show significantly higher activity
for alkane metathesis than homogeneous systems ex-
amined earlier. The results show that addition of alu-
mina can prevent the interaction between the iridium
catalyst and olefin metathesis catalysts which includes
both the heterogeneous catalyst Re O /Al O and the
2
7
2
3
homogeneous catalyst Mo-F . Since the Re O /Al O
1
2
2
7
2
3
catalyst is longer-lived and operates more efficiently
at temperatures substantially below the optimum tem-
peratures for the Ir pincer catalysts, another approach
to this problem relied on the construction of a device
Figure 1. Structures of (POCOP)Ir and (PCP)Ir complexes.
Figure 2. Structures of iridium pincer complexes with basic functional groups in the para-position.
126
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Adv. Synth. Catal. 2010, 352, 125 – 135

Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis
in which the catalysts can be isolated from one anoth- hydridochloride complex with sodium tert-butoxide in
er and operate at different temperatures. This system the presence of ethylene produced 8 (53% yield).
with physically separated catalysts is long-lived, at
least partially recyclable, and quite efficient for AM,
exhibiting total turnover numbers (TONs) up to 7000. Alkane Metathesis with 1 and Re O /Al O
2
7
2
3
When this device is used the product distribution
favors heavy alkanes and shows few or no secondary Catalytic alkane metathesis reactions were run using
AM products. A readily available heterogeneous n-decane as the solvent in combination with unsubsti-
olefin metathesis catalyst, MoO /CoO/Al O , has also tuted iridium catalyst 1 and solid-phase olefin meta-
3
2
3
been investigated for AM. High activity is achieved thesis catalyst Re O on alumina. Reactions were car-
2
7
with alumina-supported iridium and MoO catalysts ried out under argon and monitored by GC with hexa-
3
isolated and operated at different temperatures.
methylbenzene or mesitylene used as an internal stan-
dard [Eq. (1)]. Results are summarized in Table 1. In-
Results and Discussion
Iridium Pincer Catalysts Used in AM with Re O /
2
7
Al O3
2
Iridium pincer complexes used as hydrogen transfer
catalysts in this study include unsubstituted complexes itial runs at 125 and 1758C (entries 1 and 2) employed
and 2 and pincer complexes bearing basic function- 23 mmol 1 with a 1:2.5 molar ratio of 1:Re O (540 mg
1
2
7
ality in the para position of the arene ring, 3, 5–7. The Re O /Al O , 5 wt% Re O ). At 1258C very low pro-
2
7
2
3
2
7
syntheses of these catalysts have been previously re- ductivity was observed (14 turnovers after 4 days)
[11,17]
ported.
from 4,6-dihydroxypyrimidine has also been exam- numbers (TONs) were observed after 5 days. All sub-
ined. Its synthesis is outlined in Scheme 2. sequent runs were thus carried out at 1758C. In runs 1
In addition, a new catalyst, 8, derived compared to the run at 1758C where 140 turnover
The pyrimidine-based POCOP-type ligand, 9, was and 2 we noted that n-decane solutions of 1 were
synthesized in 79% crude yield by reaction of 4,6-di- orange prior to addition of Re O /Al O . When
2
7
2
3
hydroxypyrimidine with di-tert-butylchlorophosphine Re O /Al O was added, these solutions lightened and
2
7
2
3
and excess triethylamine. NMR analysis shows a 15% became nearly colorless, suggesting that most of 1 was
impurity presumed to be the monophosphinite. Iridi- adsorbed on the alumina.
um hydridochloride complex, 10, was obtained from
Entries 3–7 in Table 1, all run with similar amounts
the reaction of excess [(COD)IrCl] with the ligand in of 1 in n-decane, show that a critical feature in deter-
2
mesitylene for 20 h at 1708C (60% yield). The impuri- mining the productivity of these reactions is the
ty observed in the ligand does not undergo metalla- amount of alumina present. For example, when a
tion, and thus does not interfere with the isolation of 1:4.3 molar ratio of 1:Re O (1020 mg Re O /Al O ,
2
7
2
7
2
3
pure 10. The square pyramidal geometry at the metal 5 wt% Re O ) was used (entry 3) TONs are more
2
7
center, in which hydrogen occupies the apical posi- than doubled relative to entry 2; however, when the
tion, was confirmed by single crystal X-ray diffraction same conditions as in entry 2 are used but 506 mg of
analysis (see Experimental Section). Treatment of the pure alumina is added (entry 4, bringing total alumina
Scheme 2.
Adv. Synth. Catal. 2010, 352, 125 – 135
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
127

Zheng Huang et al.
FULL PAPERS
[a]
Table 1. Total turnover numbers (TONs) and concentration of products from the metathesis of n-decane (2.5 mL, 5.12M)
by 1 (21 to 25 mmol) and various loadings of Re O /Al O with or without additional Al O .
2
7
2
3
2
3
AHCTUNGTRENNUNG[ Product]/M (TONs)
[b]
Entry Temp. [1]
Re O
Re O /Al O
[mg/wt%]
Added Al O 3 h: M
5 days: M
(TONs)
End of reaction:
(TONs) (time)
M
2
7
2
7
2
3
2
3
[
8C] [mmol] [mmol]
[mg]
(TONs)
[
c]
1
2
3
4
5
6
7
125
175
175
175
175
175
175
23
23
25
23
21
22
21
57
57
108
57
35
69
35
540 mg/5%
540 mg/5%
0
0
0
506
0
0
415
trace
–
0.13 (14.2) (4 days)
1.59 (177) (9 days)
4.51 (451) (11 days)
2.92 (321) (8 days)
0.04 (4.8) (2 days)
0.436 (49) (3 days)
1.70 (202) (9 days)
0.153 (17) 1.28 (140)
0.295 (30) 3.63 (363)
0.281 (31) 2.65 (291)
1020 mg/5%
542 mg/5%
128 mg/13%
255 mg/13%
130 mg/13%
trace
trace
–
–
0.196 (23) 1.29 (154)
[
[
[
a]
TONs relative to Ir.
When the system has lost activity completely.
Less than 1 TO.
b]
c]
to 1021 mg), a similar increase in TONs is observed. pected to inhibit the interaction between the iridium
In entry 6, a 1:Re O molar ratio of 1:3.1 was used catalyst and the olefin metathesis catalyst at least as
2
7
(
similar to entry 2) except a 13 wt% loading of Re O
much as was seen in the case of the weakly adsorbed
unsubstituted complex 1.
2
7
[
18–20]
on Al O was employed
, so only 222 mg of Al O
2
3
2
3
were required. Very poor productivity was observed.
In combination with Re O /Al O (5 wt% of
2
7
2
3
Finally compare entries 5 and 7. A 1:1.6 molar ratio Re O ), catalysts 3, 5 and 6 were screened for AM
2
7
of 1:Re O was used in each case, but in entry 7 addi- using n-decane. In most runs ca. 24 mmol Ir were used
2
7
tional Al O3 (415 mg) had been added. With no together with ca. 550 mg of Re O /Al O which corre-
2
2
7
2
3
added alumina (entry 5), productivity was poor but sponds to a 1:2.4 molar ratio of Ir:Re O . Reactions
2
7
with added alumina (entry 7) productivity was equal were carried out at 1758C and monitored by GC at
to that of entry 2 even though a significantly lower 3 h, 1 day and 7 days. Table 2 summarizes the total
molar quantity of Re O was used.
concentration of alkane products (C –C plus C –C )
2
7
2 9 11 34
These results argue strongly that as the fraction of and TONs. In runs 1, 3, and 6 the iridium complex
1
that is supported on alumina increases, the AM pro- was added to n-decane and was adsorbed on Re O /
2
7
ductivity of the system increases. Importantly, in Al O . In these runs the reaction rates and productivi-
2
3
single-catalyst systems, catalysts 1 and Re O /Al O
ties were significantly increased by using 3, 5 or 6 rel-
2
7
2
3
each show decreased catalytic activity (for transfer de- ative to 1 (Table 2, entries 1, 3 and 6). For example,
hydrogenation and olefin metathesis, respectively) in after 3 h at 1758C, AM with 3 and 6 gave 265 and
[
17–20]
the presence of added alumina.
Thus the observa- 208 TONs, respectively. Under identical conditions,
tion of increased activity due to added alumina in the only 17 TONs were obtained in the reaction using 1
present tandem system strongly indicates that the alu- (Table 1, entry 2). The reactions with 5 and 6 formed
mina is preventing unfavorable catalyst-catalyst inter- alkane products in 79% yield (406 and 402 TONs, re-
actions leading to decomposition and/or catalyst in- spectively) after 7 days (Table 2, entries 3 and 6). In
hibition.
contrast, when the reaction with 1 was terminated at
9
days, the total conversion was only 31%
(
177 TONs).
AM with g-Alumina-Supported Iridium Complexes 3,
The effect of added alumina was also investigated
in these systems by using ca. 500 mg of alumina to
support iridium complexes 3, 5 and 6 prior to the ad-
5
and 6
Our previous studies indicated that iridium pincer dition of the Re O /Al O catalyst. Using the para-
2
7
2
3
complexes containing basic functional groups in the methoxy-supported system 3 supported on the Re O /
2
7
[
17]
para-position are adsorbed strongly on g-alumina.
Al O particles, catalysis was finished after ca. 1 day,
2 3
For example, a COA suspension of 6/Al O was fil- as heating an additional 6 days resulted in only 19 ad-
2
3
tered at 2008C. ICP-MS analysis indicated that only ditional TONs (Table 2, entry 1). Supporting 3 on
.02% of the Ir had leached into solution. The para- 502 mg Al O prior to exposure to Re O /Al O re-
0
2
3
2
7
2
3
substituted alumina-supported catalysts are highly sulted in a significant increase in catalyst lifetime with
active for transfer dehydrogenation of alkanes and TONs reaching 434 at 7 days (entry 2). The effect on
[
17]
can be efficiently recycled.
The strong adsorption productivity of supporting the iridium catalyst on alu-
of these iridium complexes by alumina would be ex- mina is more significant for the para-dimethylamino-
128
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Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis
Table 2. Total TONs and concentration of products from the metathesis of n-decane (2.5 or 10 mL, 5.12M) by Re O /Al O
3
2
7
2
(
ca. 540 mg, 5 wt% of Re O ) and iridium catalysts 3, 5, or 6 (24 to 27 mmol) with or without additional Al O at 1758C.
2
7
2
3
AHCTUNGTRENNUNG
2
7
2
7
2
3
2
3
1
2
3
4
5
6
7
3
3
5
5
5
6
6
24
24
24
24
25
24
27
60
58
58
57
57
57
56
570 mg
550 mg
547 mg
538 mg
540 mg
538 mg
530 mg
0 mg
502 mg
0 mg
503 mg
503 mg
0 mg
2.49 (265)
2.15 (226)
–
2.22 (231)
0.69 (277)
2.02 (208)
3.36 (311)
3.06 (326)
3.10 (326)
3.07 (320)
4.30 (448)
2.05 (827)
–
3.24 (345)
4.12 (434)
3.88 (406)
4.75 (495)
2.67 (1080)
3.85 (402)
4.55 (421)
[
[
[
a]
a]
a]
[b]
506 mg
3.92 (363)
[
[
a]
Two equiv. (relative to 5) of tert-butylethylene were added as the H acceptor.
With 10 mL of n-decane as starting material.
2
b]
supported 5/Al O and para-oxide-supported systems ing this homogeneous system at 1258C gave only
2
3
6
6
/Al O . For example, the productivity using catalyst 4.4 TONs after 1 day (Table 3, entry 3). This activity
was significantly increased by the presence of addi- using 5 was much lower than that obtained with the
2 3
tional alumina (208 vs. 311 TONs after 3 h). Among unsubstituted PCP catalyst 2 under the same condi-
these systems, the para-dimethylamino catalyst 5 sup- tions (38 TONs; Table 3, entry 1), although catalysts 2
ported by additional alumina was most productive and 5 are comparably active for (single-catalyst)
[
17]
and gave 495 TONs after 7 days (entry 4). Remarka- alkane dehydrogenation. Presumably this low activ-
bly, the n-decane starting alkane was present in lower ity is due to the interaction between the dimethylami-
molar quantities than n-nonane, n-octane and n-hep- no group of 5 and the Schrock catalyst Mo-F . How-
1
2
tane, with measured C :C :C :C :C molar ratios of ever, upon addition of 100 mg of g-Al O , productivity
7
8
9
10
11
2
3
1.9:1.5:1.1:1.0:0.7 (Figure 3). Encouraged by these significantly increased; heating this suspension at
high productivities, the substrate n-decane was in- 1258C gave a TON of 40 after 1 day (Table 3,
creased from 2.5 mL to 10 mL using the same quanti- entry 4). The conversion was even greater with great-
ties of 5, alumina and Re O /Al O (entry 5). After er amounts of added alumina. For example, AM with
2
7
2
3
7
2
days at 1758C, the product concentration reached 200 and 300 mg of alumina gave 177 and 225 TONs,
.67M with a total of 1080 TONs. respectively, after 1 day at 1258C (entries 5 and 6).
These results show that iridium complexes bearing Thus the presence of alumina resulted in a 50-fold in-
polar groups in the para-position adsorb strongly on crease in TON in catalysis by 5 plus Mo-F , to give
1
2
alumina and perform much better in AM than the TONꢀs much greater than were obtained under the
weakly adsorbed parent complex 1. Although the same conditions with unsubstituted catalyst
complexes bind strongly to the Re O /Al O particles, (Table 3, entry 2). The solutions were nearly colorless
2
2
7
2
3
the reaction rates and productivities are improved by in the presence of alumina, suggesting that both com-
independently adsorbing Ir complexes on additional plex 5 and Mo-F12 were adsorbed by alumina. Thus,
alumina prior to exposure to Re O /Al O .
as higher fractions of the catalysts are adsorbed on
alumina, interaction between the two complexes is ap-
parently inhibited, leading to higher productivity in
2
7
2
3
AM Using Schrock Olefin Metathesis Catalyst Mo-F12 AM. In contrast, the productivity of 2 was only slight-
ly improved by the presence of 200 mg of alumina (46
A solution-phase AM reaction as shown in Eq. (2) vs. 38 TONs; Table 3, entries 1 and 2), much less than
was conducted with n-hexane as the substrate/solvent, the increase resulting from addition of alumina when
using p-dimethylamino-substituted PCP catalyst 5, using 5 (177 vs. 4.4 TONs; entries 3 and 5).
olefin metathesis catalyst Mo-F , and two equiv. of
Thus we see that in the absence of alumina, the di-
12
tert-butylethylene (TBE) as hydrogen acceptor. Heat- methylamino group of 5 has a very deleterious effect
on the combination of 5 and Mo-F . The same dime-
1
2
thylamino group, however, binds strongly to alumina,
precluding interactions of Mo-F12 with either the di-
methylamino group itself or any other interactions
with the Ir catalyst. For comparison, we note that in
the absence of an olefin metathesis catalyst, 5 acts as
a catalyst for the transfer dehydrogenation of n-
octane under conditions similar to those in the experi-
Adv. Synth. Catal. 2010, 352, 125 – 135
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129

Zheng Huang et al.
FULL PAPERS
Figure 3. GC trace of product mixture resulting from the metathesis of n-decane (solvent) by 5/Al O and Re O /Al O after
2
3
2
7
2
3
7
days at 1758C (see Table 2). * The molar ratio is obtained by multiplying the GC integral ratio by the response factor of
each alkane.
ments of Table 3. Under such conditions catalyst bind- lysts, show that Mo-F12 is active for olefin metathesis
ing to alumina is clearly observed but there is no dra- in the presence of alumina (and apparently complete-
matic effect on dehydrogenation rate. For example, ly adsorbed to it), but it is less active than solution
1
00 mg alumina added to 1.0 mL n-octane solution of phase Mo-F . Thus the respective individual catalytic
12
5
result in an increase in dehydrogenation TONꢀs of activities of 5 and Mo-F12 are either decreased or not
[17]
less than 50%. This compares with entry 5 in which significantly increased by alumina; however, for the
the addition of 200 mg alumina to 2.0 mL n-hexane AM catalysis system, comprised of both these cata-
solution of 5 and Mo-F result in a 40-fold increase in lysts, the presence of alumina increases TONꢀs ca. 40-
12
the TON for AM (see entry 3). Likewise, control ex- fold. As noted above for the system of 1 and Re O ,
2
7
periments, in the absence of dehydrogenation cata- these results are clearly supportive of the conclusion
that adsorption by alumina prevents bimolecular cata-
lyst-catalyst degradation and/or inhibition reactions.
In the case of unsubstituted complex 2 the situation
Table 3. n-Alkane products (equiv. relative to Ir) from the may be much more complex, with several factors in
metathesis of n-hexane (2.0 mL, 7.6M) by
2
and
5
play. Interactions of Mo-F12 with 2 in solution are
(
20 mmol), TBE (40 mmol), and Mo-F12 (32 mmol; 12.8 mM) probably real although less severe than with 5. Addi-
with or without additional Al O after 24 h at 1258C.
2
3
tion of alumina presumably decreases these (less im-
portant) interactions, but possibly this smaller advant-
Product (TONs)
age is offset by unfavorable interactions of the alumi-
Entry Ir Al O [mg] C–C5 C –C C10 C –C
Total
2
3
7
9
11
15
[17]
na with the iridium center of 2
.
1
2
3
4
5
6
2
2
5
5
5
5
0
200
0
100
200
300
16
15
1.8
14
70
97
12
24
0.9
23
96
9
1.3
38
46
4.4
40
177
225
Selectivity for the formation of C relative to other
10
2.9 4.4
1.4 0.3
1.9 1.2
6.6 4.2
8.5 5.5
heavier alkanes (C +C +C ) was decreased by
7
8
9
adding alumina. Thus the runs using either 2 or 5
without alumina formed n-decane with moderate se-
lectivity [43% and 61%, respectively, entries 1 and 3;
we define selectivity here as the molar ratio of C10 to
114
130
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Adv. Synth. Catal. 2010, 352, 125 – 135

Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis
the sum (C +C +C +C )]. In the runs using 2 and Table 5. Distribution of C
to C34 n-alkane products (equiv
relative to Ir) from the metathesis of n-decane (2.5 mL,
7
8
9
10
2
5
with 200 mg of alumina, the selectivity for the for-
5
5
.12M) by 6, 7 or 8 (4.2 mmol) and Re O /Al O (ca. 540 mg,
mation of C was only 11% and 6%, respectively (en-
tries 2 and 5). Our previous results have shown that g-
alumina can isomerize 1-olefins to internal olefins;
2 7 2 3
10
wt% of Re O ; no additional Al O ) at 1758C after 7 days.
2
7
2
3
[
17]
Entry Ir C –C C –C C –C C –C C>18 Total TON
2
5
6
9
11
14
15
18
this may give rise to the lower selectivity in the reac-
tions with alumina. Alternatively, any differences be-
tween Mo-F12 on alumina vs. solution-phase Mo-F12,
including different rates for the various possible
olefin metathesis reactions, may be responsible for
the lower selectivity.
1
2
3
6
7
8
160
402
366
727
939
834
376
542
553
121
225
235
35
67
69
1420
2180
2060
productivity but activity is reduced after 24 h. At long
times catalyst 7 clearly outperforms both 6 and 8. We
do not fully understand the reaction profiles, but we
AM with Low Loading of Iridium Catalysts 6, 7 and 8
[
17]
note that previous ICP-MS experiments suggest the
As demonstrated above, using additional alumina to phosphinite system is most strongly adsorbed on alu-
support the iridium catalysts prevents interaction be- mina relative to 6.
tween iridium catalysts and Re O /Al O . An alterna-
Heterogeneous AM reactions with n-decane as sub-
2
3
2
3
tive approach to minimize these presumed interac- strate form products in the C –C range. Table 5 sum-
2
34
tions is to decrease the loading of iridium catalyst on marizes the alkane product distributions formed using
Re O /Al O . Complex 6 together with iridium com- catalysts 6, 7 and 8 after 7 days (entries 1, 2, and 3,
2
7
2
3
plexes 7, bearing a phosphinite group in the para-po- Table 5). Selectivity for the desirable products, ethane
sition, and 8 possessing a pyrimidine backbone in the and n-C H is low and may be attributable to olefin
1
8
38,
pincer ligand, were tested under these low-load condi- isomerization, which is known to be catalyzed by the
tions. Complexes 6 and 7 have previously been shown iridium complexes and may also be catalyzed by
to adsorb strongly on alumina through a Lewis acid/ Re O /Al O and even Al O itself. Alkanes heavier
2
7
2
3
2
3
[
17]
Lewis base interaction.
A similar phenomenon than n-C H must be produced via secondary alkane
18 38
occurs with 8, which most likely binds to acidic sites metathesis since they are derived from metathesis of
on the alumina through the basic nitrogen atoms in at least one olefin of Cn>10, which is necessarily a
the pincer backbone. In these AM reactions, only product of primary alkane metathesis.
4
.2 mmol of 6, 7 or 8 was combined with Re O /Al O
2 7 2 3
(
ca. 540 mg) in n-decane (2.5 mL) without additional
alumina and heated at 1758C. Results are summarized AM Using Physically Separated 6/Al O and Re O /
2
3
2
7
in Table 4. Catalysis with 6 gave 291 TONs after 3 h Al O or MoO /CoO/Al O
3
2
3
3
2
and 1670 TONs after 14 days (entry 1). Among the
three systems, the initial rate using 8 was fastest, af- A disadvantage of using Al O -supported iridium cat-
2
3
fording 1910 TONs after 1 day (64% conversion); alysts together with Re O /Al O in the same pot is
2
7
2
3
however, activity dramatically decreased after ca. that the Ir catalysts function at optimal rates well
1
1
day and heating for 6 more days resulted in only above 1008C while the rhenium metathesis catalysts
[
19–22]
50 additional TONs (see Table 4). The system em- function most effectively at 20–1008C
and de-
ploying phosphinite catalyst 7 appears to be the most grade moderately rapidly at temperatures above
[
20]
stable and long-lived. After 7 days, the catalyst was 808C. Thus, carrying out reactions at 1758C results
still active for AM and TONs up to 2440 (81% con- in decay of the rhenium catalyst while even 1758C is
version) were obtained after 14 days.
lower than optimum for the highly stable iridium cat-
All three catalysts show good initial activity at alysts. Furthermore, interactions between the Ir and
early reaction times. Catalyst 8 shows highest initial Re O catalysts in the one-pot system accelerate the
2
7
Table 4. Total TONs and concentration of products from the metathesis of n-decane (2.5 mL, 5.12M) by Re O /Al O (ca.
2
7
2
3
5
40 mg, 5 wt% of Re O ) and iridium catalysts 6, 7 or 8 (4.2 mmol) without additional Al O at 1758C.
2
7
2
3
Entry Ir [Ir]
Re O
[mmol]
Re O /Al O [mg/
wt.%]
3 h: M
(TONs)
1 day: M
(TONs)
7 days: M
(TONs)
14 days: M
(TONs)
2
7
2
7
2
3
[mmol]
1
2
3
6
7
8
4.2
4.2
4.2
57
57
57
544 mg/5%
546 mg/5%
544 mg/5%
0.489 (291)
0.366 (218)
0.687 (609)
1.20 (715)
2.32 (1380)
3.22 (1910)
2.38 (1420)
3.65 (2180)
3.46 (2060)
2.81 (1670)
4.10 (2440)
–
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asc.wiley-vch.de
131

Zheng Huang et al.
FULL PAPERS
After 52 h, a TON of 3910 was observed. After solu-
tions were removed from each pot and the device re-
charged, the first recycle produced 1370 turnovers
after 52 h. A second recycle gave 670 turnovers after
1
8 h. The decrease in activity of the system could be
due to the loss of olefins upon removal of the solution
at least 1 equiv. of olefin is required to support the
(
catalytic cycle). Therefore, twenty equiv. of 1-octene
were added to the n-octane charge. After 28 h of ad-
ditional heating the TON for this cycle was up to
1620, which is actually a greater TON than was ach-
ieved after the first recycle (the total TON was 6900
for the three cycles). These results suggest that the
loss of olefin is clearly a factor affecting recyclability,
though it may not be the only factor.
Figure 4. A two-pot device for alkane metathesis.
decomposition of both catalysts and decrease produc-
tivity (although this is mitigated by strongly binding Alkane Product Distributions Using the Two-Pot
para-substituents on the pincer ligand of the Ir com- Device
plexes). To circumvent these problems we have de-
signed a simple apparatus shown in Figure 4 which Using the two-pot system avoids the build-up of
allows physical separation and operation of the two heavy alkanes via secondary alkane metathesis. Al-
catalysts at two different temperatures. The device
ACHTUNGTRENNkUG anes n-C H and n-C H are the only two observa-
15 32 16 34
contains two “pots” connected by two tubes as shown. ble products of secondary alkane metathesis and are
The upper, larger diameter tube is heavily insulated. present in very small amounts (19 equiv. total after
The lower pot is loaded with the Ir catalyst and the 52 h in the first cycle). The yield of alkanes above C14
upper pot is loaded with Re O /Al O . The lower is low because olefins heavier than octenes are diffi-
2
7
2
3
tube contains a frit at the mouth of the upper pot to cult to distill and therefore they are less likely to
prevent the rhenium catalyst from being washed into reach the upper pot containing the olefin metathesis
the lower pot. When the lower pot is heated, hydro- catalyst. Consequently, the heavier olefins (C )
>
8
carbons distill through the upper insulated tube and seldom undergo metathesis and serve primarily as hy-
condense in the upper pot which is stirred and held at drogen acceptors in the lower pot. Moreover, the
a lower temperature (508C). Olefin metathesis occurs alkane product distribution is concentrated in the C9–
readily at these temperatures and product returns to C range relative to the distributions in the “one-pot”
1
4
the lower pot through the lower tube.
reaction. Such a skew in the distribution is favorable
Table 6 summarizes the results of an experiment for diesel production. The molar ratio of C –C n-al-
9
14
using n-octane (6590 equiv. relative to Ir) and Re O / kanes to C –C n-alkanes obtained from octane in the
2
7
2
7
Al O (540 mg, 5 wt% of Re O ) in the upper pot two-pot reactor is 1.3:1. In contrast, alkane metathesis
2
3
2
7
(
508C) and the alumina-supported Ir catalyst 6 by the mixed catalysts favors the formation of alkanes
(
2.8 mmol on 280 mg Al O ) in the lower pot (2208C). lighter than the starting alkane. For example, meta-
2
3
thesis of n-decane by 6 and Re O /Al O in the one-
2
3
2
3
pot system (Table 5, entry 1) forms heavier alkanes
C –C and lighter alkanes C –C n-alkanes in a
Table 6. Distribution of C to C16 n-alkane products (equiva-
lents relative to Ir) from the metathesis of n-octane (3 mL,
11
18
2
9
2
0.56:1 molar ratio. This favorable change in hydrocar-
6
.15M) by alumina-supported 6 (2.8 mmol) and Re O /Al O
bon distribution arises from the fact that the lower
molecular weight olefins are more volatile and can be
repeatedly distilled into the upper pot for secondary
metathesis, while the heavy olefins tend to remain in
the lower pot and serve as hydrogen acceptors.
2
7
2
3
(
540 mg, 5 wt% of Re O ) using a two-pot reactor.
2 7
Time C –C4 C –C C –C
C –C
12
C ,C
15
Total TON
2
5
7
9
11
14
16
1
5
1
1
5
2
1
8 h 88
2 h 300
st recycle
8 h 48
2 h 109
nd recycle
8 h 33
642
1421 1775
717
114
392
1
19
1560
3910
While Re O /Al O is an efficient heterogeneous
2
7
2
3
catalyst when operated at 20–1008C, heterogeneous
284
479
357
653
58
122
1
3
748
1370
molybdenum and tungsten catalysts are known to op-
[
19,21,22]
erate above these temperatures.
MoO /CoO/
3
Al O was particularly attractive in that it is commer-
2
3
205
375
61
0
0
674
cially available at low cost and so this catalyst was
screened in AM. MoO /CoO/Al O pellets (Strem)
addition of 20 equiv. of 1-octene
8 h 139 506 817 162
3
2
3
2
1620
were calcined at 5508C under air prior to use. Follow-
132
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Adv. Synth. Catal. 2010, 352, 125 – 135

Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis
Table 7. Total TONs of products from the metathesis of n- Experimental Section
decane (2.5 mL)/n-octane (3 mL) by alumina-supported 6
(
2
2.5 mmol Ir, 310 mg Al O ) and MoO /CoO/Al O (240 mg,
43 mmol Mo).
2 3 3 2 3
General Considerations
All manipulations were carried out using standard Schlenk,
high-vacuum and glovebox techniques. Argon was purified
by passage through columns of BASF R3-11 (Chemalog)
and 4 ꢂ molecular sieves. Tetrahydrofuran (THF) was dis-
tilled under a nitrogen atmosphere from sodium benzophe-
none ketyl prior to use. Pentane and toluene were passed
through columns of activated alumina. Triethylamine, THF-
d , and toluene-d were dried with 4 ꢂ molecular sieves and
Entry System
Temp. [8C]
Product/TONs
day 2 days 4 days 9 days
1
–
1
2
Mixed
Separated 220/100
175
–
120
–
1026 1753 2450 3130
8
8
degassed by freeze-pump-thaw cycles. Anhydrous decane
was purchased from Aldrich, dried with 4 ꢂ molecular
sieves and degassed by freeze-pump-thaw cycles. Mesitylene,
n-hexane, n-octane, and tert-butylethylene were purchased
ing calcining these pellets showed excellent activity in
olefin metathesis at 1758C. Initial AM experiments
were carried out by mixing the MoO /CoO/Al O
3
3
2
from Aldrich, dried with Na or LiAlH , and vacuum trans-
4
(
240 mg, 243 mmol of Mo) catalyst with alumina-sup-
ferred into sealed flasks. Ammonium perrhenate was pur-
ported 6 (2.5 mmol of Ir on 310 mg of alumina) in n-
decane (5130 equiv. relative to Ir) and heating at
chased from Aldrich and used as received. g-Al O (97.7%)
2
3
and MoO /CoO/Al O were purchased from Strem and cal-
3
2
3
1758C. AM activity was low with only 120 TONs seen
cined as noted below. Schrock catalyst Mo-F12 was pur-
[
11]
after 4 days (Table 7, entry 1). Remarkably, when the chased from Strem and used as received. Complexes 1,
[17]
[17]
[17]
[23]
metathesis catalyst was isolated from the iridium cata- 5, 6, 7, and [(COD)IrCl]2 were synthesized as pre-
lyst by using the two-pot device, the productivity was viously reported. All other reagents were purchased from
very significantly increased. In a typical experiment, Sigma–Aldrich or Strem and used as received.
NMR spectra were recorded on Bruker DRX-400,
n-octane (7390 equiv. relative to Ir) was heated with
alumina-supported 6 (2.5 mmol of Ir on 310 mg of alu-
AVANCE-400, and Bruker DRX-500 MHz spectrometers.
1
13
H and C NMR spectra were referenced to residual protio
mina) at 2208C in the lower pot and the Mo catalyst
240 mg) was heated in the upper pot at 1008C. After
days, TONs up to 3130 were obtained (Table 7).
3
1
solvent peaks. P chemical shifts were referenced to an ex-
ternal H PO standard. Elemental analyses were carried out
(
3
4
9
by Robertson Microlit Laboratories, NJ.
These results indicate that in the one-pot system
there must be interaction between the Ir and Mo cat-
alysts which significantly decreases catalyst activity
GC analyses (FID detection) was performed according to
the following methods: Agilent 6850 Series GC System
fitted with an Agilent HP-1 column (100% dimethylpolysi-
and stability and that this can be circumvented by loxane, 30 mꢃ0.32 mm i.d., 0.25 mm film thickness). Typical
À1
À1
physically separating the catalysts. The mode and temperature program: 5 min isothermal at 338C, 20 8Cmin
nature of this deleterious interaction is unknown.
heat up, 10 min isothermal at 3008C, flow rate: 1 mLmin
(
He), split ratio: 400, inlet temperature: 2508C, detector
temperature: 2508C.
Conclusions
In summary, several g-alumina-supported iridium sys-
tems were investigated for alkane metathesis. The Ir
catalysts, which adsorb strongly on alumina through a
Lewis acid/Lewis base interaction, exhibit unprece-
dented high activity for alkane metathesis in combina-
Synthesis of Pyrimidine-Based POCOP Pincer
Ligand {C H N -[OP ACHTUNGRTNEUNG( t-Bu) ] -4,6} (9)
4
1
2
2 2
To a cloudy, pale yellow suspension of 400 mg (3.57 mmol)
,6-dihydroxypyrimidine in 40 mL THF were added 3.6 mL
4
tion with Re O /Al O . Addition of alumina was (25.90 mmol) Et N and 1.5 mL (7.85 mmol) di-tert-butyl-
2
7
2
3
3
found to improve the productivity and catalyst stabili- chlorophosphine, both via syringe. The reaction mixture was
ty by minimizing the potential interaction between heated to 808C and was allowed to reflux overnight. The
solvent was removed under high vacuum, yielding the crude
the iridium species and Re O /Al O or the Schrock
2
7
2
3
product as a pale yellow solid. The product was extracted in
catalyst Mo-F . Using a “two-pot” device, the sup-
ported Ir catalysts and the metathesis catalysts, in-
cluding Re O /Al O and the commercially available
MoO /CoO/Al O , can be isolated and run at differ-
ent temperatures. The system with separated Ir and
Re O catalysts is at least partially recyclable, highly
1
2
4
0 mL toluene and filtered through a pad of celite. Toluene
was removed under vacuum; the product was obtained as
2
7
2
3
pale yellow crystals (ca. 85% purity by NMR); yield: 1.13 g
3
2
3
1
(
2.81 mmol, 79%). H NMR (400 MHz, 238C, toluene-d ):
8
3
d=7.10 (s, 1H, H2), 6.98 (s, 1H, H5), 1.11 (d, JP, H
1.6 Hz, 36H, 4ꢃt-Bu); P{ H} NMR (162 MHz, 238C, tolu-
=
31
1
2
7
1
efficient, and shows selectivity for heavy alkane prod-
ucts. The AM process holds promise for selective con-
ene-d ): d=158.4 (15%, monophosphorylated impurity),
8
1
3
1
1
57.5 (85%); C{ H} NMR (101 MHz, 238C, CDCl ): d=
3
version of the less useful n-alkanes in the C –C range 172.6 (d, JP,C =8.1 Hz, C4 and C6), 158.2 (s, C2), 94.2 (t,
3
8
to heavier alkanes in the diesel range.
JC,C =5.1 Hz), 35.5 [C , m, C ACHTUNRTGNNEG(U CH ) ], 27.2 (CH , m, 4ꢃt-Bu).
q 3 3 3
Adv. Synth. Catal. 2010, 352, 125 – 135
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asc.wiley-vch.de
133

Zheng Huang et al.
FULL PAPERS
Synthesis of Hydridochloride Complex
ysis, calcd. for C22
H
41
N
2
O
2
P
2
Ir (619.74): C 42.64, N 4.52, H
6
.67; found: C 42.85, N 4.38, H 6.43.
(
POCOP)IrHCl (10)
The ligand (530 mg, 1.32 mmol) and [(COD)IrCl ] (387 mg,
2
0.58 mmol) were suspended in 25 mL mesitylene; this mix-
ture was heated at 1708C for 20 h. Solvent was removed
under vacuum. The pure product was extracted by washing
with toluene (methylene chloride could also be used). Sol-
vent was removed under vacuum, the product was obtained
as a mixture of red-orange powder and burgundy crystals
which were subject to X-ray diffraction analysis; yield:
Procedures for Alkane Metathesis Reactions
Table 1 and Table 2: A flask was charged with the Ir cata-
lyst (21–27 mmol), Re O on alumina (5 wt% or 13 wt%),
2
7
2
.5 mL (12.8 mmol) of n-decane, and hexamethylbenzene
(
ca. 60 mmol) as internal standard. In the entries 3–5 of
4
93.7 mg (0.86 mmol, 60%). An ORTEP diagram of 10 is
Table 2, two equiv. of tert-butylethylene relative to the Ir
catalyst (48–50 mmol) were added. In the entries of Table 1
where additional alumina was introduced, the alumina was
added together with solid starting material prior to the addi-
tion of decane. In the entries of Table 2, the alumina was
added to the decane solution of Ir catalyst. After the solu-
tion turned to colorless, Re O /Al O and the internal stan-
[24] 1
shown in Figure 5.
H NMR (400 MHz, 238C, toluene-d ):
8
2
d=8.29 (s, 1H), 1.16 (m, 36H, 4ꢃt-Bu), À40.14 (t, J
=
P, H
3
1
1
1
2.8 Hz, 1H, IrH); P{ H} NMR (162 MHz, 238C, CDCl ):
3
d=172.4; elemental analysis. calcd. for C H N O P ClIr
2
0
38
2
2 2
(
5
628.15): C 38.24, N 4.46, H 6.10; found: C 37.63, N 4.47, H,
.67.
2
7
2
3
dard were added. The flask was sealed tightly with a teflon
plug under an argon atmosphere, and the solution stirred in
a 1758C oil bath. Periodically, the flask was removed from
the bath and cooled in an ice bath. An aliquot was removed
from the flask, and analyzed by GC. Turnover numbers
were calculated for each aliquot.
Synthesis of (POCOP)Ir CAHTUNGTRNENUG( C H ) (8)
2 4
A flask containing 200 mg (0.318 mmol) 9 and 33.9 mg
0.352 mmol) sodium tert-butoxide was placed under posi-
(
tive argon pressure. Next, the flask was placed under posi-
tive ethylene pressure via a needle connected to the ethyl-
ene hose; after several minutes, 25 mL toluene were added
via syringe, producing a cloudy, red-orange solution. The
needle connected to the ethylene hose was submerged in
the suspension, and the solution was allowed to stir for 5 h.
After 3 h, the reaction mixture was a deep burgundy color.
The solution was cannula transferred and filtered through a
pad of celite. The solvent was removed under vacuum; the
Table 3: A flask was charged with the Ir catalyst (20
mmol), TBE (40 mmol), Mo-F12 (32 mmol), a varied loading
of alumina (0–200 mg), 2.0 mL (15.2 mmol) of n-hexane,
and mesitylene as internal standard. The flask was sealed
tightly with a teflon plug under an argon atmosphere, and
the solution stirred in a 1258C oil bath. Periodically, the
flask was removed from the bath and cooled in an ice bath.
An aliquot was removed from the flask, and analyzed by
GC. Turnover numbers were calculated for each aliquot.
Table 4 and Table 5: A flask was charged with the Ir cata-
lyst (4.2 mmol), ~540 mg Re O /Al O , 2.5 mL (12.8 mmol)
1
pure product was isolated as a red-orange powder. H NMR
3
(
400 MHz, 238C, toluene-d ): d=8.61 (s, 1H), 2.95 (t, J
=
8
P, H
3
1
1
2
Hz, 4H, C H ), 1.15 (m, 36H, 4ꢃt-Bu); P{ H} NMR
2 4
13 1
2
7
2
3
(
162 MHz, 238C, toluene-d ): d=177.1;
C{ H} NMR
8
of n-decane, and mesitylene (ca. 70 mmol) as internal stan-
dard. The flask was sealed tightly with a teflon plug under
an argon atmosphere, and the solution stirred in a 1758C oil
bath. Periodically, the flask was removed from the bath and
cooled in an ice bath. An aliquot was removed from the
flask, and analyzed by GC. Turnover numbers were calculat-
ed for each aliquot.
(
101 MHz, 238C, CDCl ): d=179.7 (C , vt, C4 and C6),
3
q
153.7 (CH, s, C2), 127.0 (C , m, C5), 42.2 (C , vt, 4 ꢃ t-Bu ),
q q 2
3
8.1 (CH , s, C H ), 28.6 (CH , vt, 2ꢃt-Bu ); elemental anal-
2
2
4
3
2
Table 6: The lower pot of the two-pot apparatus was
charged with g-alumina-supported iridium catalyst 6 (2.8
mmol), hexamethylbenzene (60 mmol) and 3 mL of n-octane.
The upper pot was charged with 540 mg of Re O /Al O
3
2
7
2
(
5 wt%). The device was sealed tightly with two teflon plugs
under an argon atmosphere. The lower pot was heated at
208C and the upper pot was heated at 508C. Periodically,
2
the flask was removed from the bath and cooled in an ice
bath. An aliquot was removed from the flask, and analyzed
by GC. Turnover numbers were calculated for each aliquot.
The heterogeneous catalysts can be recycled. After each
cycle, the solution was syringed out and the solid was
washed 3 times with pentane and n-octane, respectively.
Fresh n-octane and internal standard were then added.
Table 7: For the one-pot system, the procedure was simi-
lar to that in Table 4 except 240 mg of MoO /CoO/Al O
3
Figure 5. ORTEP diagram of 10. The bond distances around
the metal center are 1.988(7) ꢂ (Ir1ÀC10), 2.3031(19) ꢂ
3
2
(
Ir1ÀP1), 2.2968 (Ir1ÀP2), and 2.392(2) ꢂ (Ir1ÀCl1). Select-
were used as the olefin metathesis catalyst. For the two-pot
ed bond angles (deg): 158.77(7) (P1ÀIr1ÀP2), 79.6(2) (C10À system, the procedure was similar to than in Table 6 except
Ir1ÀP1), 79.1(2) (C10ÀIr1ÀP2), 175.3(2) (C10ÀIr1ÀCl). Hy-
240 mg of MoO /CoO/Al O were charged in the upper pot
3 2 3
drogen on the Ir center cannot be located.
of the device.
134
asc.wiley-vch.de
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Adv. Synth. Catal. 2010, 352, 125 – 135

Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis
Acknowledgements
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