Cyclic alkyl amino carbene (caac) ruthenium complexes as remarkably active catalysts for ethenolysis

Article abstract of DOI:10.1002/anie.201410797

An expanded family of ruthenium-based metathesis catalysts bearing cyclic alkyl amino carbene (CAAC) ligands was prepared. These catalysts exhibited exceptional activity in the ethenolysis of the seed-oil derivative methyl oleate. In many cases, catalyst turnover numbers (TONs) of more than 100 000 were achieved, at a catalyst loading of only 3 ppm. Remarkably, the most active catalyst system was able to achieve a TON of 340000, at a catalyst loading of only 1 ppm. This is the first time a series of metathesis catalysts has exhibited such high performance in cross-metathesis reactions employing ethylene gas, with activities sufficient to render ethenolysis applicable to the industrial-scale production of linear a-olefins (LAOs) and other terminal-olefin products.

Full text of DOI:10.1002/anie.201410797

Angewandte
Chemie
DOI: 10.1002/anie.201410797
Renewable Carbon Sources
Hot Paper
Cyclic Alkyl Amino Carbene (CAAC) Ruthenium Complexes as
Remarkably Active Catalysts for Ethenolysis**
Vanessa M. Marx, Alexandra H. Sullivan, Mohand Melaimi, Scott C. Virgil,* Benjamin K. Keitz,
David S. Weinberger, Guy Bertrand,* and Robert H. Grubbs*
Abstract: An expanded family of ruthenium-based metathesis
catalysts bearing cyclic alkyl amino carbene (CAAC) ligands
was prepared. These catalysts exhibited exceptional activity in
the ethenolysis of the seed-oil derivative methyl oleate. In many
cases, catalyst turnover numbers (TONs) of more than 100000
were achieved, at a catalyst loading of only 3 ppm. Remark-
ably, the most active catalyst system was able to achieve a TON
of 340000, at a catalyst loading of only 1 ppm. This is the first
time a series of metathesis catalysts has exhibited such high
performance in cross-metathesis reactions employing ethylene
gas, with activities sufficient to render ethenolysis applicable to
the industrial-scale production of linear a-olefins (LAOs) and
other terminal-olefin products.
Olefin-metathesis reactions, such as cross-metathesis
(CM), ring-closing metathesis (RCM), and ring-opening
metathesis polymerization (ROMP), all of which generate
a new internal olefin, have enjoyed widespread popularity in
both academic and industrial settings as a result of their
general applicability, ease of use, and affordable costs.[2]
Ruthenium-based metathesis catalysts are ideal for such
transformations because of their generally robust nature,
which enables handling in air and imparts good tolerance to
a variety of functional groups and trace impurities. All of
these are necessary prerequisites when subjected to raw
materials or biomass.
Many renewable or bio-based materials, such as fatty
acids originating from seed oils and their derivatives, contain
at least one carbon–carbon double bond, which provides
a synthetic handle for derivatization by olefin-metathesis
catalysts. The CM reaction with ethylene (2), commonly
referred to as ethenolysis, has significant potential as a clean,
scalable, and sustainable solution for the production of linear
a-olefins (LAOs; e.g. 3 and 4) from the natural oils found in
oleochemicals such as methyl oleate (MO, 1; Scheme 1).
T
he transformation of small-molecule chemical feedstocks
to high-value chemicals has been a long-standing challenge
that has received a significant resurgence of interest in the
chemical sciences. This is a result of recently introduced
programs promoting the use of “greener” chemistry practices,
as well as the rising costs associated with the production of
fine chemicals from petrochemicals. Consequently, the ability
to access high-demand products from renewable sources such
as oleochemicals presents a cost-effective and environmen-
tally friendly alternative.[1]
[*] Dr. V. M. Marx, A. H. Sullivan, Dr. B. K. Keitz, Prof. R. H. Grubbs
Department of Chemistry and Chemical Engineering
California Institute of Technology
Scheme 1. Ethenolysis of the seed-oil derivative methyl oleate (1).
Pasadena, CA 91125 (USA)
E-mail: rhg@caltech.edu
LAOs are direct precursors to a variety of commodity
chemicals with applications as fuels, surfactants, lubricants,
waxes, perfumes, antimicrobial agents, and thermoplastics. In
addition, LAOs can be rapidly elaborated to more complex
products, such as agrochemicals, insect pheromones, and
pharmaceuticals.[3]
Dr. M. Melaimi, Dr. D. S. Weinberger, Prof. G. Bertrand
UCSD-CNRS Joint Research Laboratory (UMI 3555)
Department of Chemistry and Biochemistry
University of California, San Diego
San Diego, CA 92093 (USA)
E-mail: guybertand@ucsd.edu
The production of terminal olefins through the ethenol-
ysis of seed-oil derivatives using metathesis catalysts has been
previously demonstrated. However, the high catalyst loadings
required (10–100 ppm) to achieve an acceptable yield of
terminal olefins render these reported procedures cost-
prohibitive on an industrial scale.[4–6] In general, catalyst
turnover numbers (TONs) of at least 35000 and 50000 are
recommended in the manufacturing of specialty and com-
modity chemicals, respectively.[4] In the ethenolysis of the
benchmark substrate MO (1), standard ruthenium-based
metathesis catalysts, such as 5–8 (Figure 1), afforded TONs
of only 2000–5000. This result stands in contrast to the
extremely high activity normally exhibited by these catalysts
in CM with terminal or internal olefins. For example, TONs as
Dr. S. C. Virgil
Center for Catalysis and Chemical Synthesis
California Institute of Technology
Pasadena, CA 91125 (USA)
E-mail: svirgil@caltech.edu
[**] Lawrence M. Henling is acknowledged for X-ray crystallography
analysis. Dr. David VanderVelde is thanked for assistance with NMR
experiments. Thay Ung, Dr. Daryl P. Allen, and Dr. Richard L.
Pederson (Materia Inc.) are thanked for helpful discussions
regarding initial experimentation and setup. This work was
financially supported by the NIH (5R01GM031332,
7R01GM068825), the NSF (CHE-1212767), the DOE (DE-FG02-
13ER16370), and NSERC (fellowship to VMM).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201410797.
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Figure 1. Selected ruthenium-based metathesis catalysts that were
previously studied for ethenolysis.
high as 470000 have been achieved with 8 in the CM of MO
and 2-butene.[7] The most active catalyst for ethenolysis that
has been reported to date is cyclic alkyl amino carbene
(CAAC) complex 10 (see Scheme 2), which has previously
shown a TON of 35000 in the CM of MO with ethylene.[4,5] As
a result of the lack of a catalyst that is sufficiently active to
produce terminal olefins using ethylene gas, industrial-scale
ethenolysis is currently accomplished using higher olefins as
ethylene surrogates.[6b] Catalyst 7, for example, is able to
achieve the in situ ethenolysis of MO with a TON as high as
192900 with propylene gas.[4a] However, there is a need to
develop catalysts capable of achieving high activity in
ethenolysis reactions when ethylene gas is utilized directly.
While CM with higher olefins necessarily results in the
production of a substantial amount of undesired internal
olefins as by-products, the only products derived from CM
with ethylene are terminal olefins. This intrinsic advantage
promotes both increased yield and ease of purification of the
desired terminal-olefin products, and is a particularly impor-
tant consideration for biorefinery feedstocks, from which
multiple downstream products are produced.[3]
Herein, we report the discovery of the most active
ethenolysis catalysts to date. In many cases, TONs surpassing
100000 were achieved for the ethenolysis of MO using
ethylene gas. Remarkably, certain catalyst systems even
exhibited TONs approaching 200000, with the highest TON
achieved being 330000. For the first time, reaction conditions
have been developed in order for ethenolysis to proceed
efficiently on an industrial scale.
Scheme 2. Synthesis of the CAAC complexes under study (yields of
isolated complexes in brackets).
otherwise decompose rapidly in the absence of steric protec-
tion. We envisioned the circumvention of this decomposition
pathway through the installment of larger substituents at
either R4 or R5. Indeed, this strategy proved to be successful,
and we were able to readily access a variety of new complexes
in moderate to high yields (29–82%). Several of the catalysts
containing this more sterically hindered backbone included
N-aryl substitution that was previously inaccessible (14, 15,
17, 21), meanwhile others (16, 18–20, 22–25) were synthesized
in order to provide a more thorough SAR study. Single-crystal
X-ray diffraction of 11 and 24 showed distorted square-
pyramidal geometries, and the structural parameters, includ-
ing bond lengths and angles, were consistent with those found
previously for 10 and 13 (Figure 2). Moreover, catalyst 24
bears a CAAC ligand that features a chirogenic center as well
as two different substituents in the ortho position of the N-
aryl ring. Accordingly, the single-crystal structure of 24
showed both N-aryl rotamers (24a and 24b) in a ratio of
64:36.[9]
Despite the promising results previously achieved with
catalyst 10 in the ethenolysis of MO,[4,5] CAAC-ligated
ruthenium complexes have yet to be investigated in detail.
In particular, we envisioned that more in-depth structure–
activity relationship (SAR) studies would facilitate the
development of new, more efficient catalysts. Thus, a variety
of new catalysts were prepared through modifications of
existing procedures (Scheme 2).[5,8] Known CAAC catalysts
(10, 13, 18, 25) were screened alongside the new catalysts in
order to ensure accurate SAR comparisons within the series.
Initially, derivatives of the previous benchmark catalyst 10
were prepared, in which only the substituents in the ortho
position of the N-aryl rings were varied (9–13). It is worthy to
note that the syntheses of 9 and 10 are low yielding (ca. 20%)
and that their purification is cumbersome. Furthermore,
complexes that bear even smaller ortho substituents, such as
N-mesityl or N-2-isopropylphenyl, could not be accessed in
even small amounts. In contrast, 11–13 were produced in high
yields (78–86%) and isolated without difficulty. We hypothe-
sized that this result is related to the stability of the free
carbene intermediate that is generated in situ, which might
Once in hand, catalysts 9–25 were examined in the
ethenolysis of 1 using ethylene (Table 1). Reaction conditions
were adapted from those that were reported previously, and
were initially re-optimized using benchmark catalyst 10 (neat
MO, 408C, 150 psi ethylene).[4] The only deviation from the
published procedures was the use of ethylene of a higher
2
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Table 1: Ethenolysis of methyl oleate (1) using catalysts 9–25.[a]
Catalyst
Conversion
[%][b,c]
Selectivity
[%][b,d,e]
Yield
[%][f]
TON[g]
9
37
42
59
18
19
22
26
42
19
13
16
<5%
41
46
48
57
47
86
88
92
94
97
63
86
92
78
97
97
–
83
85
88
94
98
32
37
54
17
18
14
22
39
14
13
15
–
34
39
43
54
46
110000
120000
180000
57000
60000
47000
73000
130000
47000
43000
50000
–
110000
130000
140000
180000
150000
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
[a] Reaction conditions: catalyst (3 ppm), C2H4 (150 psi, 99.95% purity),
408C, 3 h. [b] Determined by GC using dodecane as an internal standard.
[c] Conversion=100À[(final moles of 1)ꢁ100/[initial moles of 1].
[d] Selectivity for ethenolysis products (3 and 4) over self-metathesis
products (3a and 4a). [e] selectivity=100ꢁ(moles of 3+4)/[(moles of
3+4)+(2ꢁmoles of 3a+4a)]. [f] yield=conversionꢁselectivity/100.
[g] TON=yieldꢁ(initial moles of 1/moles of catalyst)/100.
purity (99.95%) than previously reported (99.9%). We were
pleased to find that this simple modification appeared to
already result in a substantial increase in activity: 10 ppm
loading of catalyst 10 resulted in a TON of 67000, whereas the
reported benchmark TON for 10 is 35000.[4b,10–13] The TON of
catalyst 10 further increased to 120000 upon reduction of the
catalyst loading to 3 ppm. Thus, all subsequent reactions were
run at a catalyst loading of 3 ppm, which was also expected to
provide greater differentiation in activity between promising
catalysts in comparison to reactions run at 10 ppm.
Remarkably, at a catalyst loading of 3 ppm, most catalysts
surpassed a TON of 100000! Specifically, catalysts 11 and 24
emerged as the most efficient ones, with TONs of 180000.
Catalyst activity correlates with N-aryl substitution, with
larger R1 and R2 substituents generally resulting in higher
TONs, although this can also have a deleterious effect (as in
12 and 13, compared to 9–11). The ideal combination thus far
appears to be a small R1 and a large R2 substituent, as in
catalysts 11 and 24 (R1 = Me, R2 = iPr). Interestingly, sub-
stitution of R5 by a phenyl ring resulted in an overall
improvement of activity, especially for N-2,6-diisopropyl-
phenyl catalyst 25. Replacement of R4 and/or R5 by an ethyl,
propyl, or cyclohexyl moiety did not result in a significant
change in the TON (as in 15–19), although an adamantyl
substituent (20) resulted in the complete loss of activity.
Interestingly, while consumption of MO appears to be the
most important factor that determines the overall yield of
ethenolysis products, increased N-aryl substitution on the
catalyst appears to strongly favor selectivity for terminal
olefins. These trends in selectivity and TON are most evident
in the series of catalysts that bear a phenyl ring on the
backbone at R5 (21–25).
Figure 2. Solid-state structures of 11 and 24 (24 crystallized as 24a
and 24b, in a ratio of 64:36), with thermal ellipsoids drawn at 50%
probability.[14] For clarity, hydrogen atoms have been omitted. Selected
bond lengths [ꢀ] for 11: C1–Ru 1.928(6), C19–Ru 1.824(6), O1–Ru
2.301(4), Cl1–Ru 2.3374(16), Cl2–Ru 2.3165(17); for 24a: C1–Ru
1.940(7), C24–Ru 1.836(9), O1–Ru 2.332(8), Cl1–Ru 2.3356(18), Cl2–
Ru 2.3271(13); for 24b: C1–Ru 1.931(12), C24–Ru 1.828(18), O1–Ru
2.325(15), Cl1–Ru 2.335(4), Cl2-Ru 2.307(3).
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A plausible explanation for the high activity exhibited by
CAAC catalysts in ethenolysis transformations might be the
increased stabilization of the ruthenium methylidene inter-
mediate that is generated in the presence of ethylene gas.
Ruthenium methylidenes are known to decompose rapidly
through the insertion of the N-aryl substituent into the
methylidene carbene, which subsequently generates various
ruthenium hydrides that are inactive in metathesis trans-
formations.[15] CAAC ligands are known to be more electron
donating than their N-heterocyclic carbene (NHC) counter-
parts.[16] Thus, when used in place of NHCs, it is expected that
the increased electron density at ruthenium might somewhat
stabilize the otherwise highly reactive and electron-deficient
methylidene intermediate.[15b,c,17] Substitution of the substitu-
ents in the ortho position of the N-aryl ring with a larger
sterically encumbered group would also be expected to
significantly decrease the rate of termination by insertion
group, which is inherently more susceptible to CH insertion,
would be directed away from the reactive ruthenium meth-
ylidene.
It has been postulated that high activity in ethenolysis
might be correlated to the tendency of a catalyst to undergo
degenerative metathesis events through the preferential
formation of 2,4-metallacycles rather then 2,3-metallacycles,
which would result in an increased selectivity for terminal
olefins in the product distribution.[19] This is a powerful design
principle in the context of achieving high kinetic selectivity
for terminal olefins when employing higher olefins such as
propene and 1-butene gas as ethylene surrogates. However,
when ethylene gas is employed, it is more likely that the lower
selectivities for terminal olefins exhibited by previous gen-
erations of catalysts (5–8) is primarily a result of rapid catalyst
death in the presence of ethylene. This would translate to
products reflecting the kinetic distribution of rapid unselec-
tive cross-metathesis reactions of 5–8 with both ethylene and
terminal olefins.[20] Although CAAC-ligated ruthenium-based
catalysts have been demonstrated to engage in metathesis
reactions more slowly than phosphine- or NHC-ligated
catalysts,[5a,18] they also appear to persist for a much longer
time in the presence of ethylene.[21] This allows the ethenolysis
reaction to proceed closer to completion in order to achieve
the equilibrium ratio of terminal-olefin products, and pro-
vides a feasible explanation for the notable increase in activity
exhibited by this family of catalysts.[22]
Finally, given the notable dependence of the TON on the
purity of the ethylene employed, as seen earlier for catalyst
10, we briefly explored the effect of utilizing an ethylene
source with an even higher purity (99.995% vs. 99.95%) at
different loadings of catalyst 11 (Table 2).[23] A dramatic
increase in the TON was noted at a catalyst loading of 1 ppm.
To the best of our knowledge, this represents the highest
reported value for any ethenolysis catalyst to date (TON
340000).
In summary, a new series of ruthenium-based metathesis
catalysts bearing CAAC ligands displays exceptional activity
in ethenolysis reactions. In the cross-metathesis reaction of
the seed-oil derivative methyl oleate (1) and ethylene gas (2),
TONs of higher than 100000 are generated in many cases,
which surpasses the minimum value of 50000 required to be
considered economically sustainable on an industrial scale.
Furthermore, even higher TONs (180000–340000) were
obtained in some cases. These are the highest values reported
to date for an ethenolysis reaction, and the only reported
TONs of higher than 50000 using ethylene gas specifically.
Thus, we envision that these results will find substantial
=
into the [Ru] CH2 bond. However, increased substitution can
also hinder the coordination of olefins to the ruthenium metal
center. Diminished reactivity with catalysts bearing more
sterically encumbered N-aryl substituents was indeed noted
when initiation rates of selected catalysts (9–14) were
measured following the exposure to n-butylvinylether.[18]
When initiation rates are compared to TONs, it is clear that
both the slowest initiating catalysts (12 and 13) and the fastest
initiating catalyst (14) exhibit the lowest TONs (Figure 3).
This is likely a result of a diminished catalytic rate for the
former group and an increased susceptibility to decomposi-
tion for the latter. This study illustrates the importance of this
delicate balance, as reflected in the superior TONs exhibited
by catalysts 11 and 24, which possess asymmetric N-aryl
substituents. In these systems, the smaller substituent (R1 =
Me) in the ortho position of the N-aryl ring facilitates the
rapid coordination of the incoming olefin substrate, whereas
the larger substituent (R2 = iPr) prevents the decomposition
of the methylidene intermediate. This asymmetry might be
expected to exhibit a greater effect in CAAC-ligated catalysts,
as the steric interaction of the substituents in the ortho
position of the N-aryl ring with the two adjacent geminal
methyl substituents would be expected to influence the
conformation of the N-aryl ring. If the larger substituent
resides closer to the ruthenium metal center, the methyl
Table 2: Effect of the purity of C2H4 (2) on the activity of catalyst 11.[a]
Loading
[ppm]
Purity of 2
Yield
[%][a]
TON[a]
[%][b]
3
3
2
2
1
1
99.95
99.995
99.95
99.995
99.95
99.995
54
53
48
49
13
34
180000
180000
240000
245000
130000
340000
Figure 3. Comparison of initiation rates and TONs for catalysts 9–14.
[a] Reaction conditions and calculations as listed in Table 1.
4
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A. H. Hoveyda, J. Am. Chem. Soc. 2009, 131, 10840; h) Y.
application in the continued development of new method-
ologies and processes directed toward the economically and
environmentally sustainable production of LAOs, as well as
other valuable terminal olefins, especially through the trans-
formation of seed oils and their derivatives.
Schrodi, R. L. Pederson, H. Kaido, M. J. Tupy (Elevance
Renewable Sciences), WO2008/046106A2, 2008; i) K. A. Bur-
dett, L. D. Harris, P. Margl, B. R. Maughon, T. Mokhtar-Zadeh,
P. C. Saucier, E. P. Wasserman, Organometallics 2004, 23, 2027.
[7] J. Patel, S. Mujcinovic, W. R. Jackson, A. J. Robinson, A. K.
Serelis, C. Such, Green Chem. 2006, 8, 450.
[8] R. Jazzar, R. D. Dewhurst, B.-J. Bourg, B. Donnadieu, Y. Canac,
G. Bertrand, Angew. Chem. Int. Ed. 2007, 46, 2899; Angew.
Chem. 2007, 119, 2957.
Received: November 5, 2014
Published online: && &&, &&&&
[9] We also observed multiple conformational and rotational
isomers in the NMR spectra of each of the catalysts 21–24.
Ratios varied with respect to N-aryl substitution (see the
Supporting Information for details).
[10] Intuitively, this marked effect might be expected. Ethylene gas
contains small amounts of impurities, such as carbon monoxide
and acetylene, known catalyst poisons for ruthenium-based
metathesis catalysts (see Ref. [11]). At such low catalyst load-
ings, even trace amounts of these substances would exhibit
a great effect.
Keywords: cyclic alkyl amino carbenes · ethenolysis ·
olefin metathesis · seed-oil derivatives · terminal olefins
.
[1] a) U. Biermann, U. Bornscheuer, M. A. R. Meier, J. O. Metzger,
H. J. Schꢀfer, Angew. Chem. Int. Ed. 2011, 50, 3854; Angew.
Chem. 2011, 123, 3938; b) L. Montero de Espinosa, M. A. R.
Meier, Eur. Polym. J. 2011, 47, 837; c) A.-L. Marshall, P. J.
Alaimo, Chem. Eur. J. 2010, 16, 4970; d) M. A. R. Meier, J. O.
Metzger, U. S. Schubert, Chem. Soc. Rev. 2007, 36, 1788; e) R. A.
Sheldon, Green Chem. 2007, 9, 1273; f) Green Chemistry and
Catalysis (Eds.: R. A. Sheldon, I. Arends, U. Hanefeld), Wiley-
VCH, Weinheim, 2007; g) A. Corma, S. Iborra, A. Velty, Chem.
Rev. 2007, 107, 2411.
[2] a) Metathesis in Natural Product Synthesis (Eds.: J. Cossy, S.
Arseniyadis, C. Meyer), Wiley-VCH, Weinheim, 2010; b) A. M.
Lozano-Vila, S. Monsaert, A. Bajek, F. Verpoort, Chem. Rev.
2010, 110, 4865; c) G. Vougioukalakis, R. H. Grubbs, Chem. Rev.
2010, 110, 1746; d) C. Samojłowicz, M. Bieniek, K. Grela, Chem.
Rev. 2009, 109, 3708; e) Y. Schrodi, R. L. Pederson, Aldrichimica
Acta 2007, 40, 45; f) K. C. Nicolaou, P. G. Bulger, D. Sarlah,
Angew. Chem. Int. Ed. 2005, 44, 4490; Angew. Chem. 2005, 117,
4564; g) Handbook of Metathesis, Vol. 2 (Ed.: R. H. Grubbs),
Wiley-VCH, Weinheim, 2003; h) R. R. Schrock, A. H. Hoveyda,
Angew. Chem. Int. Ed. 2003, 42, 4592; Angew. Chem. 2003, 115,
4740; i) R. R. Schrock, Chem. Rev. 2002, 102, 145; j) T. M. Trnka,
R. H. Grubbs, Acc. Chem. Res. 2001, 34, 18; k) A. Fꢁrstner,
Angew. Chem. Int. Ed. 2000, 39, 3012; Angew. Chem. 2000, 112,
3140.
[3] a) S. Chikkali, S. Meckling, Angew. Chem. Int. Ed. 2012, 51,
5802; Angew. Chem. 2012, 124, 5902; b) L. Montero de Espi-
nosa, M. A. R. Meier, Top. Organomet. Chem. 2012, 39, 1; c) M.
Raluca, P. H. Dixneuf, Green Metathesis Chemistry, Vol. 185,
Springer, Netherlands, 2010; d) J. C. Mol, Green Chem. 2002, 4,
5.
[4] a) A. Nickel, T. Ung, G. Mkrtumyan, J. Uy, W.-C. Lee, D.
Stoianova, J. Papazian, H.-W. Wei, A. Mallari, Y. Schrodi, R. L.
Pederson, Top. Catal. 2012, 55, 518; b) Y. Schrodi, T. Ung, A.
Vargas, G. Mkrtumyan, W.-C. Lee, T. M. Champagne, R. L.
Pederson, S. H. Hong, Clean. 2008, 36, 669.
[5] a) D. R. Anderson, T. Ung, G. Mkrtumyan, G. Bertrand, R. H.
Grubbs, Y. Schrodi, Organometallics 2008, 27, 563; b) D. R.
Anderson, V. Lavallo, D. J. OꢂLeary, G. Bertrand, R. H. Grubbs,
Angew. Chem. Int. Ed. 2007, 46, 7262; Angew. Chem. 2007, 119,
7400.
[6] a) J. Zhang, S. Song, X. Wang, J. Jiaoa, M. Shi, Chem. Commun.
2013, 49, 9491; b) F. van der Klis, J. Le Nꢃtre, R. Blaauw, J.
van Haveren, D. S. van Es, Eur. J. Lipid Sci. Technol. 2012, 114,
911; c) S. A. Cohen, M. L. Luetkens, C. Balakrishnan, R. Snyder
(Elevance Renewable Sciences), WO2011/046872A2, 2011;
d) R. M. Thomas, B. K. Keitz, T. Champagne, R. H. Grubbs, J.
Am. Chem. Soc. 2011, 133, 7490; e) J. R. Hagadorn, M. W.
Holtcamp, M. S. Bedoya (Exxonmobile), WO2011100022A3,
2011; f) G. Mignani, V. Pevere, H. Olivier-Bourbigou, C. Vallee,
M. Berthod, C. Citadelle (Rhodia Operations, IFP), WO2010/
010290A1, 2010; g) S. C. Marinescu, R. R. Schrock, P. Mꢁller,
[11] a) D. J. Nelson, S. Manzini, C. A. Urbina-Blanco, S. P. Nolan,
Chem. Commun. 2014, 50, 10355; b) S. T. Diver, Coord. Chem.
Rev. 2007, 251, 671.
[12] Methyl oleate (Nu-Check-Prep, > 99%) was purified through
filtration over alumina (Supporting Information). As disclosed
previously, this purification step is essential for high TONs (see
Ref. [4]). For example, when methyl oleate purchased from Nu-
Check-Prep (> 99%) or Sigma Aldrich (> 99.0%, Fluka ana-
lytical standard) was used without further purification, TONs
were only 8500 and 230, respectively, for catalyst 11 (3 ppm).
[13] Interestingly, a similar increase was not noted for catalyst 5. For
example, under the optimized reaction conditions, 5 (100 ppm)
generated a TON of only 4600 (compare with reported value of
5400, see Ref. [4b]).
[14] CCDC 1025991 (11) and 1025992 (24) contain the supplemen-
tary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[15] a) S. H. Hong, A. G. Wenzel, T. T. Salguero, M. W. Day, R. H.
Grubbs, J. Am. Chem. Soc. 2007, 129, 7961; b) M. S. Sanford,
J. A. Love, R. H. Grubbs, J. Am. Chem. Soc. 2001, 123, 6543;
c) S. B. Lehman, B. K. Wagener, Organometallics 2005, 24, 1477;
d) M. Ulman, R. H. Grubbs, J. Org. Chem. 1999, 64, 7202.
[16] a) O. Back, M. Henry-Ellinger, C. D. Martin, D. Martin, G.
Bertrand, Angew. Chem. Int. Ed. 2013, 52, 2939; Angew. Chem.
2013, 125, 3011; b) V. Lavallo, Y. Canac, C. Prasang, B.
Donnadieu, G. Bertrand, Angew. Chem. Int. Ed. 2005, 44,
5705; Angew. Chem. 2005, 117, 5851; c) M. Melaimi, M.
Soleilhavoup, G. Bertrand, Angew. Chem. Int. Ed. 2010, 49,
8810; Angew. Chem. 2010, 122, 8992.
[17] G. Occhipinti, V. R. Jensen, Organometallics 2011, 30, 3522.
[18] See the Supporting Information for further details.
[19] I. C. Stewart, B. K. Keitz, K. M. Kuhn, R. M. Thomas, R. H.
Grubbs, J. Am. Chem. Soc. 2010, 132, 8534.
[20] For similar correlations regarding catalyst lifetime and approach
to equilibrium for E/Z diastereoselectivity, see: C.-W. Lee, R. H.
Grubbs, Org. Lett. 2000, 2, 2145.
[21] B. K. Keitz, R. H. Grubbs, J. Am. Chem. Soc. 2011, 133, 16277.
[22] More detailed studies are currently underway and will be
reported in due course.
[23] Ethylene gas was purchased and used as received from
Matheson, and was either ultrahigh purity (99.95%) or Math-
eson purity (99.995%). Matheson purity ethylene (99.995%) is
certified to contain less than 4 ppm acetylene, and less than
2 ppm carbon monoxide.
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Renewable Carbon Sources
V. M. Marx, A. H. Sullivan, M. Melaimi,
S. C. Virgil,* B. K. Keitz, D. S. Weinberger,
G. Bertrand,*
R. H. Grubbs*
&&&& — &&&&
Cyclic Alkyl Amino Carbene (CAAC)
Ruthenium Complexes as Remarkably
Active Catalysts for Ethenolysis
A new series of olefin-metathesis cata-
lysts containing cyclic alkyl amino car-
bene (CAAC) ligands exhibit unprece-
dented activity in the ethenolysis of
methyl oleate. This work advances the
state-of-the-art of the ethenolysis reaction
and is expected to find particular use in
large-scale industrial applications.
6
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
These are not the final page numbers!