Stoichiometric and catalytic cross dimerization between butadiene and methyl acrylate promoted by a Ruthenium(0) complex

Article abstract of DOI:10.1021/om100822n

Treatment of Ru(η⁴-butadiene)(η⁴-1,5-COD) (NCMe) (1a) with methyl acrylate in benzene for 3 h at 6 °C produces Ru{cisoid-η⁴-(2E,4E)-(methyl hepta-2,4-dienoate)} (η⁴-1,5-COD)(NCMe) (2a) in 97% yield. Complex 1a (2 mol %) catalyzes the chemoselective cross dimerization between butadiene and methyl acrylate in benzene to give a mixture of the regioisomers of methyl heptadienoate in 43% yield by the oxidative coupling reaction.

Full text of DOI:10.1021/om100822n

Organometallics 2010, 29, 5741–5743 5741
DOI: 10.1021/om100822n
Stoichiometric and Catalytic Cross Dimerization between Butadiene and
Methyl Acrylate Promoted by a Ruthenium(0) Complex
Masafumi Hirano,* Yasutomo Arai, Nobuyuki Komine, and Sanshiro Komiya
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of
Agriculture and Technology, 2-24-26 Nakacho, Koganei, Tokyo 184-8588, Japan
Received August 24, 2010
Summary: Treatment of Ru(η4-butadiene)(η4-1,5-COD)(NCMe)
(1a) with methyl acrylate in benzene for 3 h at 6 °C produces
Ru{cisoid-η4-(2E,4E)-(methyl hepta-2,4-dienoate)}(η4-1,5-COD)-
(NCMe) (2a) in 97% yield. Complex 1a (2 mol %) catalyzes
the chemoselective cross dimerization between butadiene and
methyl acrylate in benzene to give a mixture of the regio-
isomers of methyl heptadienoate in 43% yield by the oxidative
coupling reaction.
Chart 1
Selective dimerizations of substituted olefins catalyzed
by cationic Ru(II) complexes with Cp or Cp* ligands are
regarded as one of the promising zero-emission processes for
preparing monomers for condensation polymerization as
well as other starting materials.1 Although a highly Lewis
basic Ru(0) species is expected to enhance the susceptibility
toward the oxidative coupling reaction, the mechanism is not
well understood and explored. We recently obtained explicit
examples in support of oxidative coupling of acrylates on
a zerovalent ruthenium compound, Ru(η6-naphthalene)-
(η4-1,5-COD)2 (COD = cyclooctadiene (C8H12)), by the
addition of ancillary ligands such as PMe3 or MeCN to
the catalytic system, giving {κ4-(methyl methacrylate)}-
{η2-(methyl methacrylate)}ruthenium(0) (I) in the case of
methyl methacrylate3 and trans-2,5-bis(methoxycarbonyl)-
ruthenacyclopentane (II) in the case of methyl acrylate4
(Chart 1). Notably, II is an effective catalyst for the tail-to-
tail type coupling reaction of methyl acrylate.
Scheme 1
One promising and valuable outlet of olefin dimerization
reactions is chemoselective cross dimerization of substituted
olefins, since it would provide an easy and versatile synthetic
methodology for a variety of organic molecules having functional
groups. Herein we disclose the stoichiometric and catalytic chemo-
selective cross dimerization of butadiene and methyl acrylate.
Treatment of Ru(η4-butadiene)(η4-1,5-COD)L5 (1a: L =
MeCN) with methyl acrylate in benzene at 6 °C followed by
workup procedures produced a brown oil of Ru{cisoid-η4-
(2E,4E)-(methyl hepta-2,4-dienoate)}(η4-1,5-COD)L (2a: L =
MeCN) in 97% yield (Scheme 1).
Complex 2a was characterized by H NMR and H-1H
COSY.6 The most interesting feature of 2a is the ethyl group
attached to the conjugated diene moiety. It is worthy to note
that a conjugated diene fragment is produced by the coupling
reaction of the coordinated butadiene with methyl acrylate.
The methylene protons in the ethyl group are observed as
diastereotopic, suggesting the conjugated diene moiety is
coordinated to the ruthenium center. These observations are
consistent with the formation of the η4-(2E,4E)-methyl
hepta-2,4-dienoate fragment on ruthenium. The formation
of the conjugated diene moiety was also confirmed by the
iodolysis of 2a to give (2E,4E)-methyl hepta-2,4-dienoate7 in
80% yield.
1
1
*To whom correspondence should be addressed. Tel and fax: þ81 423
88 7044. E-mail: hrc@cc.tuat.ac.jp.
(1) Trost, B. M.; Toste, F. D.; Pinkerton, A. B. Chem. Rev. 2001, 101,
2067, and references therein.
(2) (a) Bennett, M. A.; Neumann, H.; Thomas, M.; Wang, X.-Q.;
Pertici, P.; Salvadori, P.; Vitulli, G. Organometallics 1991, 10, 3237.
(b) Crocker, M.; Green, M.; Howard, J. A. K.; Norman, N. C.; Thomas, D. M.
J. Chem. Soc., Dalton Trans. 1990, 2299. (c) Vitulli, G.; Pertici, P.;
Salvadori, P. J. Chem. Soc., Dalton Trans. 1984, 2255.
(3) Hirano, M.; Hiroi, Y.; Komine, N.; Komiya, S. Organometallics
2010, 29, 3690.
(6) 1H NMR (300 MHz, C6D6, rt):δ 0.82 (s, 3H, NCMe), 0.99 (t, JH-H
7.2 Hz, 3H, 7-Me), 1.22 (q, JH-H = 7.0 Hz, 1H, 5-CH), 1.30 (dqui, JH-H
13.8, 7.0 Hz, 1H, 6-CH2), 1.39 (d, JH-H = 7.1 Hz, 1H, 2-CH), 1.48 (dqui,
JH-H = 13.8, 7.0 Hz, 1H, 6-CH2), 1.95-2.1 (m, 4H, COD), 2.15-2.3 (m,
2H, COD), 2.4-2.55 (m, 2H, COD), 3.0-3.1 (m, 1H, COD), 3.3-3.45
(m, 2H, COD), 3.49 (s, 3H, OMe), 4.52-4.57 (m, 1H, COD), 4.86 (dd,
JH-H = 7.0, 5.1 Hz, 1H, 4-CH), 6.10 (dd, JH-H = 7.1, 5.1 Hz, 1H, 3-CH).
=
=
(4) Hirano, M.; Sakate, Y.; Komine, N.; Komiya, S.; Bennett, M. A.
Organometallics 2009, 28, 4902.
(5) Bennett, M. A.; Wang, X.-Q. J. Organomet. Chem. 1992, 428, C17.
r
2010 American Chemical Society
Published on Web 10/08/2010
pubs.acs.org/Organometallics

5742 Organometallics, Vol. 29, No. 22, 2010
Hirano et al.
Figure 1. Molecular structure of 2c with numbering schemes. Ellipsoids indicate 50% probability. Hydrogen atoms in the 1,5-COD
ligand are omitted for clarity.
This compound was more unambiguously characterized
by the X-ray structure analyses of its PPh3 and CO analo-
gues. For example, exposure of 2a to an atmosphere of CO
(0.1 MPa) for 3 h at room temperature followed by workup
procedures involving recrystallization from cold Et2O gave
pale yellow needles of 2c (L = CO) in 53% yield. The overall
molecular structure consists of the cisoid-η4-(2E,4E)-methyl
hepta-2,4-dienoate complex of Ru(0) with 1,5-COD and CO
ligands (Figure 1).8
dimerization reaction between butadiene and methyl acry-
late was achieved by 1a (2 mol %) at 80 °C for 4 h to give
(2E,5Z)-methyl hepta-2,5-dienoate10 (32%) and (2E,4E)-
methyl hepta-2,4-dienoate (11%) with a trace of the isomers
(eq 2).11
˚
The bond distances C(1)-C(2) [1.509(5) A] and C(2)-C(3)
[1.509(3) A] clearly show their single-bond character, and
˚
˚
˚
C(3)-C(4) [1.416(3) A], C(4)-C(5) [1.407(3) A], and C(5)-
C(6) [1.431(4) A] suggest a slight contribution of the ene-diyl
˚
type coordination. The IR spectrum of 2c in KBr shows an
intense band at 1976 cm-1, which is assignable to the
stretching vibration of the CO ligand. Since a monocarbonyl
complex of Ru(0), Ru(η4-1,5-COD)(η4-1,3,5-COT)(CO),
has been reported to show a νCO band at 1985 cm-1,9 the
νCO band in 2c suggests the formal zerovalent state of 2c.
Treatment of 2b with excess butadiene at room tempera-
ture released (2E,4E)-methyl hepta-2,4-dienoate in 49%
yield by re-formation of a cisoid-η4-butadiene complex,
Ru(η4-butadiene)(η4-1,5-COD)(PPh3) (1b), in 80% yield
(eq 1).
When 2b was employed in this reaction, (2E,5Z)-methyl
hepta-2,5-dienoate (27%) and (2E,4E)-methyl hepta-2,4-
dienoate (5%) were produced, suggesting the isolated 2b to
also be an active catalyst. It is notable that the dominant
product in catalysis is (2E,5Z)-methyl hepta-2,5-dienoate,
while the stoichiometric reaction exclusively gives (2E,4E)-
methyl hepta-2,4-dienoate (vide infra). Such cross dimeriza-
tion has also been catalyzed by (allyl)cobalt(I)12 and in situ-
formed (hydrido)ruthenium(II) species,13 but they give
(3E,5Z)-methyl hepta-3,5-dienoate as the dominant pro-
duct, which is not observed in the present catalysis. Both
(10) Feldman, K. S.; Grega, K. C. J. Organomet. Chem. 1990,
381, 251.
(11) The moderate total yield (43%) is probably due to deactivation of
the active species. A stoichiometric reaction of 2a with excess butadiene
produced a homocoupling complex of butadiene, supine,prone-[Ru(η3:η3-
2,7-octadiene-1,8-diyl)(η4-1,5-COD)] (54%), with liberation of (2E,4E)-
methyl hepta-2,4-dienoate (49%). The η3:η3-2,7-octadiene-1,8-diyl com-
plex is a very stable compound under these conditions. Therefore, we
believe the oxidative coupling reaction between butadiene molecules on
Ru(0) to be the major deactivation process. The comprehensive oxidative
coupling reactions of conjugated dienes on Ru(0) will be reported else-
where.
Encouraged by this stoichiometric reaction, the catalytic
cross dimerization was performed. The chemoselective cross
(7) (a) Tolstikov, G. A.; Dzhemilev, U. M.; Khusnutdinov, R. I. Zh.
Obshch. Khim. 1975, 45, 1322. (b) Ma, D.; Lu, X. Tetrahedron 1990, 46,
3189.
(8) Selected crystallographic and physical data for 2c: triclinic, P1,
˚
˚
˚
a = 7.715(4) A, b = 8.091(4) A, c = 14.138(7) A, R = 101.756(4)°, β =
3
˚
€
95.319(4)°, γ = 108.580(6)°, V = 807.1(7) A , Z = 2, temp = 200.0 K,
reflns number total = 3590, parameters = 287, GOF = 1.072, R1 =
0.0281, wR2 = 0.0744.
(12) (a) Bonnemann, H.; Grard, C.; Kopp, W.; Pump, W.; Tanaka,
€
K.; Wilke, G. Angew. Chem., Int. Ed. Engl. 1973, 12, 964. (b) Bonnemann,
H.; Grard, C.; Kopp, W.; Wilke, G. Pure Appl. Chem. 1971, 6, 265.
(13) Mitsudo, T.; Zhang, S.-W.; Kondo, T.; Watanabe, Y. Tetra-
hedron Lett. 1992, 33, 341.
(9) Deganello, G.; Mantovani, A.; Sandrini, P. K.; Pertici, P.; Vitulli,
G. J. Organomet. Chem. 1977, 135, 215.

Communication
Scheme 2. Proposed Catalytic Cycle
Organometallics, Vol. 29, No. 22, 2010 5743
by the oxidative coupling. An analogous ruthenacyclopentane
is also formed in the selective dimerization of methyl acrylate
(Chart 1).4 The σ-π rearrangement of the allyl produces
the intermediate D. The η3-allylic moiety should have an
anti configuration to reflect the cisoid conformation of the
η4-butadiene ligand in B. Then, the β-hydride elimination and
successive reductive elimination produces the intermediate F.
This unconjugated diene ligand may be labile, and the presence
of butadiene induces facile liberation of the unconjugated
diene. This scenario well accounts for the predominant forma-
tion of (2E,5Z)-methyl hepta-2,5-dienoate in the catalysis. On
the other hand, the intermediate F can also cause further
isomerization to give the more thermodynamically stable con-
jugated species I by the C-H bond cleavage reaction process.
This process accounts for the exclusive formation of 2a by the
stoichiometric reaction in the absence of butadiene.
In summary, the present work provides a ruthenium-
promoted stoichiometric and catalytic chemoselective cross
dimerization reaction between butadiene and methyl acry-
late via an oxidative coupling mechanism. The chemoselec-
tivity is probably induced by the facile η4-coordination of
butadiene on ruthenium(0) followed by the η2-coordination
of electron-withdrawing methyl acrylate on the Lewis basic
site. Further detailed mechanistic studies and tolerance of
substrates are now in progress.
reports have brought forward the hydrido-insertion mecha-
nism without detailed experimental support.
Acknowledgment. We are grateful to Prof. M. A. Bennett
(Australian National University) for discussions. We thank
Ms. S. Kiyota for elemental analysis.
The present chemoselective cross dimerization is consis-
tent with the catalytic cycle as shown in Scheme 2. In the first
step, facile liberation of MeCN from 1a initiates the catalysis
to give A. The highly basic zerovalent ruthenium(0) species A
favors coordination of an electron-withdrawing methyl acry-
late to give B. Formation of such a (κ4-conjugated compound)-
(η2-conjugated compound)ruthenium(0) complex has been
demonstrated in the mechanistic study of catalytic tail-to-tail
dimerization of methyl methacrylate promoted by ruthenium-
(0) by us (Chart 1).3 Then a ruthenacyclopentane C is formed
Supporting Information Available: Text, tables, and figures
giving full experimental details involving the characterizations
of 2a, 2b, 2c, and 1b, 1H NMR spectrum of 2a, reactions of 2a,
2b, and 2c with iodine and butadiene, GLC chart for catalysis
between butadiene and methyl acrylate, and crystallographic
analyses of 2b and 2c and CIF files giving X-ray crystal data.
This material is available free of charge via the Internet at http://
pubs.acs.org.