Selective linear coupling reaction of acetylene and acrylonitrile catalyzed by the well-defined metallacyclopentadiene complex C5Me5(PPh3)(Cl)RuCH=CHCH=CH

Article abstract of DOI:10.1021/om9800647

The metallacyclopentadiene complex C₅Me₅(PPh₃)(Cl)RuCH=CHCH=CH (1) was found to catalyze the linear coupling reaction of acetylene and acrylonitrile to give predominantly 2(E),4(Z),6-heptatrienenitrile (3; TON = 15, 85% se

Full text of DOI:10.1021/om9800647

Organometallics 1998, 17, 1257-1259
1257
Selective Lin ea r Cou p lin g Rea ction of Acetylen e a n d
Acr ylon itr ile Ca ta lyzed by th e Well-Defin ed
Meta lla cyclop en ta d ien e Com p lex
C5Me5(P P h 3)(Cl)Ru CHdCHCHdCH
Chae S. Yi,* J . Roman Torres-Lubian, and Nianhong Liu
Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881
Arnold L. Rheingold and Ilia A. Guzei
Department of Chemistry, The University of Delaware, Newark, Delaware 19716-2522
Received February 2, 1998
Summary: The metallacyclopentadiene complex C5Me5-
ruthenacyclopentadiene species C5Me5(PPh3)(Cl)Ru-
(PPh3)(Cl)RuCHdCHCHdCH (1) was found to catalyze
the linear coupling reaction of acetylene and acrylonitrile
to give predominantly 2(E),4(Z),6-heptatrienenitrile (3;
TON ) 15, 85% selectivity). The coupling reaction is
proposed to occur via an initial PPh3 dissociation from
1 and the subsequent insertion of acrylonitrile.
CHdCHCHdCH (1) selectively catalyzes the 2:1 linear
coupling reaction of acetylene and acrylonitrile to form
heptatrienenitrile.
We recently reported the synthesis of the chiral
ruthenium-vinylidene complex C5Me5(PPh3)(Cl)Rud
CdCHPh from the reaction of C5Me5Ru(PPh3)2Cl (2)
with PhCtCH.4b An analogous treatment of 2 with
excess HCtCH (1 atm) at room temperature in THF
resulted in the formation of the ruthenacyclopentadiene
complex 1,5 which was conveniently isolated in 54%
yield by treating with 1.2 equiv of CuCl2 (eq 1).6 The
Transition-metal-mediated coupling reactions of al-
kynes are well-known to form a variety of cyclic com-
pounds.1,2 Metallacyclopentadiene complexes have been
commonly considered as important intermediate species
in these reactions.1a,b In contrast, only a few examples
of the linear co-oligomerization reactions of alkynes and
alkenes have been reported.3 The selective linear
coupling reactions of alkynes and functionalized alkenes
would in principle lead to a variety of conjugated olefins.
As a part of an ongoing effort to extend the ruthenium-
mediated alkyne coupling reactions,4 we have begun to
explore the co-oligomerization reactions of alkynes and
alkenes. Herein we report that the newly synthesized
(1)
1H NMR of 1 in C6D6 exhibited an unusually downfield
shifted R-proton at δ 10.20 (J PH ) 6.0 Hz), which was
strongly coupled with both the phosphorus atom and
the Câ proton. The carbon resonances at δ 200.9 and
177.5 (d, J PC ) 27.7 Hz) were assigned to the R- and
â-metallacyclic carbon atoms.7 The metallacyclopenta-
diene structure of 1 was confirmed by X-ray crystal-
lography (Figure 1).8 The molecular structure of 1
showed a distorted-trigonal-bipyramidal geometry with
Cp* and PPh3 groups each occupying apical positions.
(1) (a) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.;
Wiley: New York, 1992. (b) Bo¨nnemann, H.; Brijoux, W. In Applied
Homogeneous Catalysis with Organometallic Compounds; Cornils, B.,
Herrmann, W. A., Eds.; VCH: New York, 1996; Vol. 2. (c) Melikyan,
G. G.; Nicholas, K. M. In Modern Acetylene Chemistry; Stang, P. J .,
Diederich, F., Eds.; VCH: New York, 1995. (d) Collman, J . P.; Hegedus,
L. S.; Norton, J . R.; Finke, R. G. Principles and Applications of
Organotransition Metal Chemistry; University Science Books: Mill
Valley, CA, 1987. (e) Grotjahn, D. B. In Comprehensive Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon Press: New York, 1994; Vol. 12. (f) Trost, B. M. Angew.
Chem., Int. Ed. Engl. 1995, 34, 259. (g) Schore, N. E. In Comprehensive
Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: New York, 1990;
Vol. 5. (h) Vollhart, K. P. C. Angew. Chem., Int. Ed. Engl. 1984, 23,
539.
(2) For recent examples on the metal-mediated intermolecular
alkyne coupling reactions, see: (a) Takeda, A.; Ohno, A.; Kadota, I.;
Gevorgyan, V.; Yamamoto, Y. J . Am. Chem. Soc. 1997, 119, 4547. (b)
Gevorgyan, V.; Takeda, A.; Yamamoto, Y. J . Am. Chem. Soc. 1997,
119, 11313. (c) J ohnson, E. S.; Balaich, G. J .; Fanwick, P. E.; Rothwell,
I. P. J . Am. Chem. Soc. 1997, 119, 11086. (d) O’Connor, J . M.; Hiibner,
K.; Merwin, R.; Gantzel, P. K.; Fong, B. S.; Adams, M.; Rheingold, A.
L. J . Am. Chem. Soc. 1997, 119, 3631. (e) van Belzen, R.; Hoffmann,
H.; Elsevier: C. J . Angew. Chem., Int. Ed. Engl. 1997, 36, 1743.
(3) (a) Wakatsuki, Y.; Aoki, K.; Yamazaki, H. J . Am. Chem. Soc.
1974, 96, 5284. (b) Wakatsuki, Y.; Aoki, K.; Yamazaki, H. J . Am. Chem.
Soc. 1979, 101, 1123. (c) Mitsudo, T.; Zhang, S.-W.; Nagao, M.;
Watanabe, Y. J . Chem. Soc., Chem. Commun. 1991, 598. (d) Trost, B.
M.; Indolese, A. F.; Mu¨ller, T. J . J .; Treptow, B. J . Am. Chem. Soc.
1995, 117, 615. (e) Bianchini, C.; Caulton, K. G.; J ohnson, T. J .; Meli,
A.; Peruzzini, M.; Vizza, F. Organometallics 1995, 14, 933.
(4) (a) Yi, C. S.; Liu, N. Organometallics 1996, 15, 3968. (b) Yi. C.
S.; Liu, N.; Rheingold, A. L.; Liable-Sands, L. M.; Guzei, I. A.
Organometallics 1997, 16, 3729. (c) Yi, C. S.; Liu, N.; Rheingold, A.
L.; Liable-Sands, L. M. Organometallics 1997, 16, 3910.
(5) See the Supporting Information for the characterization data of
complexes 1, 3, 4, and 6.
(6) CuCl2 has been known to form a stable adduct with PPh3. For a
recent example, see: Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J . Am.
Chem. Soc. 1997, 119, 3887 and references therein.
(7) Two metallacyclic carbon resonances were reported at δ 201.3
and 141.3 for the similar ruthenacyclopentadiene complex Cp(Br)(L)-
RuC(Ph)dCHCHdC(Ph) (L ) HN(CH2CH2)2O) in: Albers, M. O.;
deWaal, D. J . A.; Liles, D. C.; Robinson, D. J .; Singleton, E.; Wiege,
M. B. J . Chem. Soc., Chem. Commun. 1986, 1680.
(8) Crystal data for 1‚C6H6: C38H40ClPRu, monoclinic, P21/ c, a )
9.825(4) Å, b ) 22.411(7) Å, c ) 15.412(5) Å, â ) 108.440(19)o, V )
3219(3) Å3, Z ) 4, T ) 295(2) K, Dcalcd ) 1.370 g/cm3, R(F) ) 3.63% for
3354 observed independent reflections (2 e 2θ e 22.5°).
S0276-7333(98)00064-8 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/06/1998

1258 Organometallics, Vol. 17, No. 7, 1998
Communications
was completely determined by spectroscopic methods.5
The cis stereochemistry of 3 was established from a
relatively small coupling constant between two adjacent
vinyl protons (J H -H ) 11.3 Hz).
c
d
The formation of 3 was found to be dependent on both
the concentration of acetylene and the reaction temper-
ature. For example, the reaction at a higher concentra-
tion of HCtCH (4.4 mmol, ∼2 atm) resulted in the
formation of a complex mixture of products containing
3 (∼60%) and higher amounts of oligomeric products
(∼40%) as detected by GC-MS. A similar reaction at
room temperature was found to be quite sluggish (TON
< 2), while the reaction in THF (1 mL) resulted in
mostly insoluble polyacetylene and other oligomeric
products.13
The metallacyclopentadiene complex 1 can also be
obtained from the reaction of a ruthenium-alkene
complex with acetylene (eq 3). The ruthenium-alkene
F igu r e 1. Molecular structure of 1 drawn with 30%
thermal ellipsoids. Selected bond lengths (Å) and bond
angles (deg): Ru-C(29), 2.092(4); Ru-C(32), 2.059(5);
C(29)-C(30), 1.321(6); C(30)-C(31), 1.414(8); Ru-Cl, 2.439-
(8); Ru-P, 2.381(4); C(32)-Ru-C(29), 74.1(2); C(29)-Ru-
Cl, 136.02(12); C(32)-Ru-P, 113.23(12); P-Ru-Cl, 81.24-
(6).
Both relatively long Ru-to-CR bond distances (Ru-C(29)
) 2.092(4) Å, Ru-C(32) ) 2.059(5) Å) and a planar
metallacyclopentadiene ring geometry (mean deviation
) 0.026(7) Å) suggested a slight contribution from the
metallacyclopentatriene resonance structure.9 These
structural data are also comparable to the those for
previously reported mono- and dinuclear ruthenacyclo-
pentadiene species.7,10
Complex 1 was found to catalyze the linear coupling
reaction of acetylene and acrylonitrile. In a typical
reaction, the treatment of HCtCH (2.3 mmol) with a
catalytic amount of 1 (13 mg, 0.022 mmol) in acryloni-
trile (1.0 mL) at 70 °C for 3.5 h produced the predomi-
nantly linear product 2(E),4(Z),6-heptatrienenitrile (3)
(TON ) 15; ∼85% selectivity) (eq 2).11 Small amounts
(3)
complexes (R ) CN (4a ), COMe (4b)) were readily
prepared from the reaction of 2 with CH2dCHR (2.5
equiv) in THF at room temperature (85-97% isolated
yields), and their structures were established by spec-
troscopic methods.5 The molecular structure of 4b, as
defined by X-ray crystallography, showed a typical
three-legged piano stool geometry.14 The treatment of
complex 4a with HCtCH (1 atm) in THF at room
temperature cleanly yielded the metallacyclopentadiene
complex 1. Also, complex 1 was readily converted to
the alkene complex 4a by treating with 1.2 equiv of
acrylonitrile in C6D6 at room temperature. The olefin
complexes 4a and 4b were shown to be equally active
for the linear coupling reaction.
While a detailed mechanism of the reaction still
remains to be established, the above results are consis-
tent with the mechanism shown in Scheme 1. Two
different mechanisms have been commonly proposed for
the coupling step of a metallacyclopentadiene species
with an alkyne: an insertion of an alkyne into the
metallacyclopentadiene via a cycloheptatriene interme-
diate or a [4 + 2] cycloaddition between a metallacy-
clopentadiene and an alkyne.1,15 In our case, a facile
interconversion between 1 and 4a suggested that the
PPh3 ligand is readily dissociated from 1. The fact that
(2)
of higher oligomers of both homo- and heterocoupling
products were also formed (∼15%), but none of the cyclic
products such as 2-vinylpyridine or benzene derivatives
were detected by GC-MS.12 The organic product 3 was
isolated by column chromatography and its structure
(9) For discussion and examples of the metallacyclopentatriene
complexes, see: (a) Pu, L.; Hasegawa, T.; Parkin, S.; Taube, H. J . Am.
Chem. Soc. 1992, 114, 2712. (b) Pu, L.; Hasegawa, T.; Parkin, S.; Taube,
H. J . Am. Chem. Soc. 1992, 114, 7609. (c) Hirpo, W.; Curtis, M. D. J .
Am. Chem. Soc. 1988, 110, 5218. (d) Kerschner, J . L.; Fanwick, P. E.;
Rothwell, I. P. J . Am. Chem. Soc. 1988, 110, 8235.
(10) (a) Campion, B. K.; Heyn, R. H.; Tilley, T. D. Organometallics
1990, 9, 1106. (b) Braun, T.; Laubender, M.; Gevert, O.; Werner, H.
Chem. Ber. 1997, 130, 559.
(11) TON ) turnover number ) mol of product (mol of catalyst)-1
h-1. The numbering scheme of 3 is
(13) The dark brown insoluble product was isolated after washing
with THF and CH2Cl2. The IR data (KBr, νC-H
) 1009 cm-1
)
bend
matched well with the previously reported values of trans-polyacety-
lene: (a) Ito, T.; Shirakawa, H.; Ikeda, S. J . Polym. Sci., Polym. Chem.
Ed. 1974, 12, 11. (b) Landon, S. J .; Shulman, P. M.; Geoffroy, G. L. J .
Am. Chem. Soc. 1985, 107, 6739.
(14) See the Supporting Information for the molecular structure of
4b. Crystal data for 4b: C32H36ClOPRu, monoclinic, P21/ n, a ) 17.043-
(5) Å, b ) 10.417(3) Å, c ) 17.088(6) Å, â ) 113.54(2)o, V ) 2781.5(15)
Å3, Z ) 4, T ) 248(2) K, Dcalcd ) 1.443 g/cm3, R(F) ) 4.77% for 2746
observed independent reflections (2 e 2θ e 22.5°).
(12) The volatile portion of the solution contained mostly unreacted
acetylene and only a trace amount of acetylene homooligomers as
analyzed by GC-MS.

Communications
Organometallics, Vol. 17, No. 7, 1998 1259
Sch em e 1
incorporation at the terminal vinyl position (Hf) is
consistent with the insertion of an alkene into the
metallacyclopentadiene species 5.17 The preferential
formation of the cis-alkene product 3 also suggests that
the reaction occurs via the formation of metallacyclo-
pentadiene species 5 from the coupling of two acety-
lenes. The subsequent steps of the reaction, the â-H
elimination and the reductive elimination of the product
3, are well-established in alkyne coupling reactions.1d,e,3
In a preliminary investigation, we also found that
complex 1 effectively catalyzed the linear coupling
reaction of HCtCH and CH2dCHCO2Me. In this case,
the rate of the coupling reaction was considerably higher
than that of the acrylonitrile reaction, and the reaction
produced a 2:1 mixture of methyl 2(E),4(Z),6-hep-
tatrienoate (6a ) and methyl 2(Z),4(Z),6-heptatrienoate
(6b; TON ) 24; 89% combined yield based on HCtCH).5
Efforts are currently underway to determine both the
scope and selectivity of the coupling reaction by employ-
ing substituted alkynes and other functionalized al-
kenes.
addition of PPh3 (9 mg, 1.5 mol %) to the reaction
mixture virtually inhibited the coupling reaction under
otherwise similar reaction conditions also supports the
reversible dissociation of PPh3. When the coupling
reaction was run in CD2dCDCN (98% D, Cambridge
Ack n ow led gm en t. Financial support from Mar-
quette University, Committee-on-Research, is gratefully
acknowledged. J .R.T.-L. acknowledges a postdoctoral
fellowship from the Mexican Government (CONACYT
program).
1
Isotopes), the H NMR of the isolated product 3 showed
selective deuterium incorporation at three vinyl posi-
tions: Ha, Hb, and Hf.16 The selective deuterium
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystallographic data for 1 and 4b and text giving character-
ization data for 1, 3, 4, and 6 (16 pages). Ordering information
is given on any current masthead page.
(15) For recent examples of η4-arene species and their implication
in alkyne cyclotrimerization reactions, see: (a) Bianchini, C.; Caulton,
K. G.; Chardon, C.; Doublet, M.-L.; Eisenstein, O.; J ackson, S. A.;
J ohnson, T. J .; Meli, A.; Peruzzini, M.; Streib, W. E.; Vacca, A.; Vizza,
F. Organometallics 1994, 13, 2010. (b) Bianchini, C.; Caulton, K. G.;
Folting, K.; Meli, A.; Peruzzini, M.; Polo, A.; Vizza, F. J . Am. Chem.
Soc. 1992, 114, 7290. (c) Bianchini, C.; Caulton, K. G.; Chardon, C.;
Eisenstein, O.; Folting, K.; J ohnson, T. J .; Meli, A.; Peruzzini, M.;
Rauscher, D. J .; Streib, W. E.; Vizza, F. J . Am. Chem. Soc. 1991, 113,
5127. (d) Bruck, M. A.; Copenhaver, A. S.; Wigley, D. E. J . Am. Chem.
Soc. 1987, 109, 6525.
OM9800647
(17) As a reviewer pointed out, an alternate mechanism involving
a metallacyclopentene species generated from the coupling of acetylene
and an alkene is also consistent with the deuterium-labeling result.
While this mechanism seems less likely, since it requires the prefer-
ential insertion of acetylene over the elimination of â-CH2 hydrogen,
we cannot rigorously rule out this mechanism at this time.
(16) An approximately equal amount (> 95%) of deuterium has been
incorporated at all three vinyl positions of 3, as determined by 1H NMR.