Generation of stoichiometric ethylene and isotopic derivatives and application in transition-metal-catalyzed vinylation and enyne metathesis

Article abstract of DOI:10.1002/chem.201303668

Ethylene is one of the most important building blocks in industry for the production of polymers and commodity chemicals. ¹³C- and D-isotope-labeled ethylenes are also valuable reagents with applications ranging from polymer-structure determination, reaction-mechanism elucidation to the preparation of more complex isotopically labeled compounds. However, these isotopic derivatives are expensive, and are flammable gases, which are difficult to handle. We have developed a method for the controlled generation of ethylene and its isotopic variants including, for the first time, fully isotopically labeled ethylene, from simple alkene precursors by using Ru catalysis. Applying a two-chamber reactor allows both the synthesis of ethylene and its immediate consumption in a chemical transformation permitting reactions to be performed with only stoichiometric amounts of this two carbon olefin. This was demonstrated in the Ni-catalyzed Heck reaction with aryl triflates and benzyl chlorides, as well as Ru-mediated enyne metathesis. Why more when less works! A method for the controlled generation of ethylene including the fully isotopically labeled derivative is described, as well as their use in three transition-metal-catalyzed reactions. Applying a two-chamber reactor, only stoichiometric amounts of ethylene are required, which allows the simple installment of deuterium and ¹³C in the product (see scheme).

Full text of DOI:10.1002/chem.201303668

FULL PAPER
DOI: 10.1002/chem.201303668
Generation of Stoichiometric Ethylene and Isotopic Derivatives and
Application in Transition-Metal-Catalyzed Vinylation and Enyne Metathesis
Geanna K. Min,[a] Klaus Bjerglund,[a] Søren Kramer,[a] Thomas M. Gøgsig,*[a]
Anders T. Lindhardt,*[b] and Troels Skrydstrup*[a]
Abstract: Ethylene is one of the most
important building blocks in industry
for the production of polymers and
commodity chemicals. 13C- and D-iso-
tope-labeled ethylenes are also valu-
sive, and are flammable gases, which
are difficult to handle. We have devel-
oped a method for the controlled gen-
eration of ethylene and its isotopic var-
iants including, for the first time, fully
isotopically labeled ethylene, from
simple alkene precursors by using Ru
catalysis. Applying a two-chamber re-
actor allows both the synthesis of ethyl-
ene and its immediate consumption in
a chemical transformation permitting
reactions to be performed with only
stoichiometric amounts of this two
carbon olefin. This was demonstrated
in the Ni-catalyzed Heck reaction with
aryl triflates and benzyl chlorides, as
well as Ru-mediated enyne metathesis.
ACHTUNGTRENNUNGable reagents with applications ranging
from polymer-structure determination,
reaction-mechanism elucidation to the
preparation of more complex isotopi-
cally labeled compounds. However,
these isotopic derivatives are expen-
Keywords: deuterium · ethylene ·
Heck reaction · isotopic labeling ·
metathesis
Introduction
two-carbon fragment.[5–10] In addition, such isotopic deriva-
tives serve as a two-carbon building block for the construc-
tion of more complex organic compounds with site-specific
isotope labeling.[11]
Ethylene is an industrially important platform chemical pro-
duced from the petrochemical feedstock by steam crack-
ing.[1] It is the most commercially produced organic com-
pound in the world, and its global production in 2011
reached an astonishing 141000000 tons.[2] Most of the main
synthetic polymers arise directly or indirectly from this
simple olefin, and it is estimated that approximately 30% of
all commodity chemicals have their origins from ethylene.[3]
Being a plant hormone, ethylene has an additionally impor-
tant industrial role as a food-ripening agent.[4]
Isotopically labeled variants of ethylene incorporating
deuterium or 13C have many valuable applications for indus-
trial and academic research. Such applications include reac-
tion-pathway elucidations, rate studies of catalytic reactions
with ethylene as a substrate, and tools for the structure de-
termination of products, such as polymers derived from this
The development of new synthetic transformations em-
ploying ethylene catalyzed by transition-metal complexes is
still of high importance.[12–19] Despite the relatively straight-
forward handling of ethylene gas from a cylinder or lecture
bottle, there are still some considerations in relation to its
use.[1] Generally, a large excess of the gas is applied (and in
some cases, under high pressures). Furthermore, it is not
simple to perform a reaction in which a specific or limiting
amount of ethylene is applied. Finally, replacement with iso-
topically labeled variants of ethylene complicates the situa-
tion even more due to their high costs, or even absence as
a commercial reagent, such as fully isotopically labeled eth-
ylene (1,2-[13C2]-1,1,2,2-[D4]ethylene).
Of significant value would be to identify operating condi-
tions, in which ethylene including isotopic variants could be
generated and subsequently applied as a stoichiometric re-
agent in an ensuing reaction. We sought to find a viable so-
lution, in which the desired isotopically labeled ethylene is
synthesized in a controlled manner from an easily accessible
terminal alkene, applying a transition-metal-mediated olefin
metathesis in a two-chamber system.[21–27] Hence, the Ru-cat-
alyzed homodimerization of a vinyl arene 1 (Scheme 1), in-
cluding its deuterium and/or 13C isotope analogs labeled at
the terminal position of the olefin, would generate ethylene
and its isotopic derivatives in a convenient manner. Per-
forming this reaction in one of the two reaction chambers of
a closed two-chamber system would allow the produced eth-
ylene to diffuse into the second chamber to which a second
reaction has been set up, exploiting the gaseous olefin as
[a] Dr. G. K. Min, K. Bjerglund, Dr. S. Kramer, Dr. T. M. Gøgsig,
Prof. Dr. T. Skrydstrup
Center for Insoluble Protein Structures (inSPIN)
Interdisciplinary Nanoscience Center (iNANO)
and Department of Chemistry, Aarhus University
Gustav Wieds Vej 14, 8000 Aarhus C (Denmark)
Fax: (+45)4189 3001
E-mail: goegsig@chem.au.dk
ts@chem.au.dk
[b] Dr. A. T. Lindhardt
Interdisciplinary Nanoscience Center (iNANO)
Biological & Chemical Engineering, Department of Engineering
Aarhus University, Finlandsgade 22, 8200 Aarhus N (Denmark)
E-mail: lindhardt@chem.au.dk
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201303668.
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revealed that vinyl arenes 3 and 4 (Scheme 2) released eth-
ylene in various commonly used organic solvents, such as
toluene (94% after 2 h at 208C and 100% after 20 min at
1008C).[28] Compounds 3 and 4 therefore represent suitable
candidates as ethylene precursors, not only because they re-
leased ethylene in high yields, but because it was possible to
synthesize in few steps, by using standard literature proto-
cols, variants 5, 6, and 7 with isotope labeling on the termi-
nal carbon position.[29–31] Upon subjection to the Hoveyda–
Grubbs II generation catalyst, vinyl arenes 5, 6, and 7 would
allow the simple preparation of 1,2-[13C2]- and 1,1,2,2-
[D4]ethylene, as well as the fully isotopically labeled deriva-
tive (1,2-[13C2]-1,1,2,2-[D4]ethylene). For two other examples
of internal ethylene precursors and the gas-measurement
setup, see the Supporting Information.[32]
Although there is no doubt that gaseous ethylene, provid-
ed from a pressurized cylinder, serves as the most cost-effi-
cient alternative, the presented protocol provides the possi-
bility of performing small-scale experiments in a simple
setup with near-quantitative amounts of ethylene. As seen
from the ethylene precursors tested, these have clearly not
been chosen from an atom-economical point of view. In-
stead, they have been designed with the aim to be easily
handled and with the ability to synthesize the deuterium
and/or 13C-labeled versions. Finally, whenever an experiment
has been performed by using the described method,
a simple switch from the ethylene precursor to its isotopical-
ly labeled counterparts would allow efficient incorporation
of the deuterium and/or 13C-label under identical conditions.
With the ethylene generation in hand, its incorporation
into organic substrates was next examined applying the two-
chamber reactor.[33] Three transformations were selected, as
depicted in Schemes 3–5 with the goal of identifying reac-
tion conditions, which operate well by applying only stoi-
chiometric amounts of ethylene. The indicated loading of
ethylene applied in Schemes 3–5 corresponds to the relative
amount generated from the precursors shown in Scheme 2
(see the Supporting Information for conditions).We initially
studied the possibility of a Ni-catalyzed Heck reaction be-
tween aryl triflates and stoichiometric ethylene in analogy
to similar work by using electron-rich olefins.[34] With com-
pound 3 as the ethylene precursor, various styrene deriva-
tives 8–13 could be prepared from their corresponding aryl
triflate by using this approach (Scheme 3). Hence, one
chamber was loaded with 3 and the Hoveyda-Grubbs II gen-
eration catalyst (2 mol%) in cyclopentyl methyl ether
(CPME), and in the other chamber, the aryl triflate,
a nickel(0) complex, the diphosphine, and the amine base
were dissolved in toluene. Sealing the flask and heating to
1008C for 20 h gave the desired styrenes in 56–90% yield.
Only a slight excess of ethylene gas generated in the second
chamber was employed for these reactions to achieve good
to excellent yields. Functional groups, such as amides, esters,
and nitriles, were tolerated under the reaction conditions.
Switching to the alternative ethylene precursor 4 provided
similar coupling yields. Gratifyingly, when the 13C-labeled
compound 5 was used for the generation of 1,2-[13C2]eth-
Scheme 1. Generation and application of ethylene.
a stoichiometric reagent in a similar manner to our recent
work on palladium-catalyzed carbonylation reactions.[24–27] In
this way, no storage of the flammable gas in a flask with or
without isotope labeling is required, and furthermore, they
can be produced easily when required and in stoichiometric
amounts.
Results and Discussion
Several substrates were evaluated for their ability to act as
efficient ethylene precursors. In the presence of the Hovey-
da-Grubbs II generation catalyst, gas-measurement studies
Scheme 2. Ethylene and its isotope-labeled versions.
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Generation of Stoichiometric Ethylene and Isotopic Derivatives
FULL PAPER
Scheme 5. Ru-catalyzed enyne metathesis of alkynes with ethylene.
by the addition of the benzylic chloride, triethylsilyl tri-
AHCTUNTGRENfGUNN luoroAHCTUNRTGEGmNNNU ethaneACHTUNGTRENsNUGN ulfonate (TESOTf), and NEt3, gave the allyl-
ic arenes 15, 16, and 17 in acceptable to good yields after
a reaction time of only 2 h at 208C. Increasing the reaction
times did not improve the yields. Interestingly, Jamison and
co-workers observed an a/b mixture for compound 15. How-
ever, with this system and applying only stoichiometric eth-
ylene, only the allylic naphthalene was produced. Finally,
when the ethylene precursor is switched to the isotopically
labeled compound 5, the double 13C-labeled allylic benzene
18 could be secured in a satisfactory 56% yield.
Scheme 3. Ni-catalyzed vinylation of aryl triflates.
In the last reaction, the enyne metathesis between ethyl-
ene and two internal alkynes was studied.[21,22,35] Initial re-
sults demonstrated that 1.5 equivalents of ethylene originat-
ing from either 3 or 4 in the ethylene-producing chamber,
was enough to produce near-quantitative yields of the buta-
dienes 19 and 20 in the second chamber after heating for
20 h at 1008C in the presence of 5 mol% of the Hoveyda–
Grubbs II generation catalyst (Scheme 5).
These high yields are remarkable considering that
throughout the reaction course in essence three C=C double
bonds are broken, and three are formed with respect to eth-
ylene production and reaction, in addition to the fact that
ethylene must diffuse from one chamber to another. Fur-
thermore, near-quantitative yields were obtained for the
double 13C-labeled butadiene 21 by using ethylene precursor
5, and the tetradeuterated product 22 from compound 6. In
the latter case, there was a small leakage of the isotope la-
beling (96% deuterium incorporation), the origins of which
have not yet been determined.[36]
Scheme 4. Ni-catalyzed vinylation of benzylic chlorides.
As can be seen from Scheme 6, the 1,4-dienes could be
further utilized in a Diels–Alder reaction to generate double
13C-labeled aromatic systems. Hence, butadiene 21 could be
transformed in two steps to the phenyl dicarboxylate 24 via
an initial Diels–Alder reaction with dimethyl acetylenedicar-
boxylate followed by oxidation. Alternatively, a formal
[4+2] cycloaddition with phenyl nitrile promoted by Ni-cat-
alysis provided the double labeled pyridine 25 in a 77%
yield.[37] The tetradeuterated butadiene 22 underwent effi-
cient cyclization with N-phenylmaleimide in hot anisole to
generate the bicycle 26 in a 95% yield. Last but not least,
enyne metathesis with the fully isotopically labeled two
ylene, the double 13C-labeled vinyl biphenyl 14 was obtained
in a good yield (64%).
In an alternative reaction, we examined the use of the
two-chamber method in the Ni-catalyzed vinylation of ben-
zylic chlorides under an ethylene atmosphere, as was report-
ed by Jamison and co-workers in 2011.[17] In this transforma-
tion, Jamison et al. reported that the catalyst must be ma-
tured with ethylene prior to the addition of the benzylic
halide. Applying our setup (Scheme 4), we found that pre-
mixing of the catalyst for 15 min with only 2.2 equivalents of
ethylene generated from either precursors 3 or 4, followed
Chem. Eur. J. 2013, 19, 17603 – 17607
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T. M. Gøgsig, A. T. Lindhardt, T. Skrydstrup et al.
Hoveyda–Grubbs II generation catalyst (16.9 mg, 0.03 mmol) was dis-
solved in CPME (2 mL) and thereafter added to Chamber 2. Chamber 2
was sealed immediately with a screw cap fitted with a Teflon seal (Hov-
eyda–Grubbs II generation catalyst must be the very last reagent added
to the two-chamber system).
The loaded two-chamber system was then heated to 1008C for 20 h. The
reaction mixture was cooled to RT, concentrated, and purified by flash
chromatography (pentanes) giving compound 14 as a colorless solid
(34.7 mg, 64% yield). M.p. 119.0–121.08C; 1H NMR (400 MHz, CDCl3):
d=H 7.56–7.62 (m, 4H), 7.42–7.50 (m, 4H) 7.32–7.37 (m, 1H), 6.76 (ddd,
J=154.0, 17.8, 10.8 Hz, 1H), 5.79 (dddd, J=154.1, 17.6, 2.9, 0.88 Hz,
1H), 5.27 ppm (dd, J=160.3, 10.9 Hz, 1H); 13C NMR (100 MHz, CDCl3):
d=C 140.9, 140.7, 136.6, 136.5 (13C-labeled, J=69.5 Hz), 128.9, 127.5,
127.4 (d, J=4.5 Hz), 127.1, 126.8 (dd, J=4.9, 2.4 Hz), 114.0 ppm (13C-la-
beled, J=69.5 Hz); HRMS [M+H] calcd: 183.1079; found: 183.1079.
Acknowledgements
We thank Danish National Research Foundation (Grant number
DNRF59), Villum Foundation, Danish Council for Independent Re-
search: Technology and Production Sciences, Lundbeck Foundation, the
Carlsberg Foundation, and Aarhus University for generous financial sup-
port of this work.
Scheme 6. Application of labeled 1,4-dienes; DDQ=2,3-dichloro-5,6-di-
cyano-1,4-benzoquinone.
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Conclusion
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A simple and effective method for the generation of ethyl-
ene and its isotopic derivatives was developed, in addition
to demonstrating their use in a number of synthetic transfor-
mations. In this way, reactions can be carried out by using
only stoichiometric amounts of this olefin, without having to
handle the gas. We anticipate that this method for ethylene
production will be applicable to many fields in chemical syn-
thesis. Further work is ongoing to examine the preparation
and application of other small alkenes by using this ap-
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Experimental Section
Synthesis of [13C-a,b] 4-vinyl-1,1’-biphenyl (14): [Ni
ACTHNUTRGNEU(NG cod)2] (cod=1,5-cy-
clooctadiene; 8.3 mg, 0.03 mmol), 1,1’-bis(diphenylphosphino)ferrocene
(DPPF; 33.3 mg, 0.06 mmol), [1,1’-biphenyl]-4-yl trifluoromethanesulfo-
nate (90.3 mg, 0.30 mmol), Cy2NMe (Cy=cyclohexyl; 0.19 mL,
0.9 mmol), and CPME (2 mL) were added respectively to Chamber 1 of
the COware. Chamber 1 was sealed with a screw cap fitted with a Teflon
seal in the glove box under an argon atmosphere.
[20] A number of isotopically labeled variants of gaseous ethylene are
commercially available in small gas cylinders ranging from 0.1 to
1 L, and prices are generally high, or the company must be contact-
ed for this information (F. ex. Cambridge Isotopes provides 0.25 L
of 1,2-13C2-ethylene for $422.00). Fully labeled ethylene is not com-
mercially available.
13C-a-4-Vinylphenyl 4-methylbenzenesulfonate (5; 330.4 mg, 1.20 mmol)
was added to Chamber 2 in the glove box under an argon atmosphere.
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Generation of Stoichiometric Ethylene and Isotopic Derivatives
FULL PAPER
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Ref. [2]). However, one should possess the required equipment and
techniques for handling such gasses, including their use in stoichio-
metric amounts to avoid waste when using large excesses as is com-
monly employed. Our method allows the simple use and reaction of
ethylene in stoichiometric amounts without handling the gas gener-
ated. Furthermore, the simple set-up allows multiple two-chamber
systems to be set up to allow rapid screening of reaction conditions.
Finally, although some reports disclose the use of balloon tech-
niques, it cannot be advised to carry out reactions by using balloons
carrying a flammable gas.
[32] Only half the amount of Hoveyda–Grubbs II catalyst was required
to attain complete ethylene production by using the internal precur-
sors (see the Supporting Information).
[33] The two-chamber reactor, COware, is commercially available from
Sigma–Aldrich and SyTracks.
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high yield but with the same percentage of hydrogen incorporation,
suggesting that the isotope leakage must come from another source.
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[31] One could argue that the bulk production of isotopically labeled
ethylene is cheaper than the described procedure. For example, the
production of 1,1,2,2-[D4]ethylene comes from either calcium car-
bide by hydrolysis and deuteration of the intermediate acetylene, or
Received: September 18, 2013
Published online: November 14, 2013
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