Carbynehydridoruthenium complexes as catalysts for the selective, ring-opening metathesis of cyclopentene with methyl acrylate

Full text of DOI:10.1002/(SICI)1521-3773(19981231)37:24<3421::AID-ANIE3421>3.0.CO;2-U

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Carbynehydridoruthenium Complexes as
Catalysts for the Selective, Ring-Opening
Metathesis of Cyclopentene with
Methyl Acrylate**
Wolfram Stüer, Justin Wolf, Helmut Werner,*
Peter Schwab, and Michael Schulz
Dedicated to Professor Ernst-Otto Fischer
on the occasion of his 80th birthday
ˆ
Carbeneruthenium complexes of the type [RuCl2( CHR)-
(PR3')2], which were first prepared by Grubbs and co-workers,
are not only highly efficient catalysts for olefin metathesis,[1]
but are also increasingly used in organic synthesis.[2] In
contrast to related catalytically active compounds of molyb-
denum and tungsten, the ruthenium complexes have the
advantage of tolerating substrates containing polar functional
groups.[3] The disadvantage, however, is the low activity in the
metathesis of electron-poor olefins such as acrylic acid and
derivatives thereof. We are particularly interested in the
selective ring-opening metathesis (ROM) of cyclopentene
with various acyclic olefins as chain transfer reagents (CTA);
the desired products are not telechelic polymers as in previous
work,[4] but linear functionalized olefins with a chain length of
up to 20 carbon atoms. Owing to the work by Blechert, Crowe
and co-workers it is known that the Grubbs-type catalysts are
unsuitable for metathesis with electron-poor acyclic olefins as
CTA, whereas the catalytically active carbene complexes of
the Schrock-type can be applied to some extent.[5] Here we
describe the first catalysts based on ruthenium which are able
to catalyze the selective ROM of cyclopentene with methyl
acrylate as an electron-poor olefin, thereby leading to the
formation of long-chain functionalized olefins as the main
products.[6]
cationic carbene complexes of the general composition
‡
ˆ
[RuCl( CHCH2R)(PCy3)2] (with A as anion). These 14-
electron species could be the counterparts of the compound
‡
[Ru(Ph)(CO)(PtBu2Me)2] , which was recently described by
Caulton et al.[10] Therefore, when a solution of complex 2 in
CH2Cl2/Et2O was treated with an excess of a solution of HBF4
in Et2O at 808C and then worked-up in an appropriate way,
a yellow solid was obtained. This compound is not the
ˆ
anticipated cationic ethylidene derivative [RuCl( CHCH3)-
(PCy3)2]BF4 but, in agreement with the NMR spectra, the
carbynehydrido complex 6. The 1H spectrum displays no
signal in the low-field region, which would be expected for the
a-hydrogen atom of an ethylidene ligand, but a triplet
resonance at d ˆ 6.91 (2J(P,H) ˆ 15 Hz), assigned to a
metal-bonded hydride. In the 13C NMR spectrum of 6 the
signal of the a-carbon atom of the carbyne ligand appears as a
triplet at d ˆ 316.1 (2J(C,P) ˆ 9 Hz), and that of the b-carbon
atom as a singlet at d ˆ 41.4. Moreover, some resonances are
observed which are assigned to an Et2O ligand. This ligand is,
however, only weakly coordinated and easily displaced by
H2O to give 7. Analogous to the formation of 6, compound 2
also reacts with [HNMe2Ph][B(C6F5)4] and [H(OEt2)2]-
[B{C6H3(CF3)2}4][11] to afford the corresponding carbyne
complexes 8 and 9, which differ in the counterion and the
donor ligand L. In addition to the spectroscopic data, the
composition of 6 ± 9 is supported by their reactivity towards
soluble chloride sources. Instead of the neutral carbynehy-
Recently, we reported an efficient one-pot synthesis of the
ˆ
carbeneruthenium complexes [RuCl2( CHCH2R)(PCy3)2]
(R ˆ H (4), Ph (5); Cy ˆ cyclohexyl) from RuCl3, Mg, PCy3,
H2, HC CR, and H2O.[7] For establishing this synthesis it was
ꢀ
important to recognize that upon treatment of 1[8] with
1-alkynes initially the hydridovinylidene compounds 2 and 3[9]
are formed, which then react with HCl or a synthetic
equivalent thereof to afford the desired carbene complexes
4 and 5, respectively (L ˆ PCy3).
ꢀ
drido complex [RuHCl2( CCH3)(PCy3)2] the isomeric car-
bene complex 4 is formed in quantitative yield.
Following this observation, we were interested to find out
whether the reaction of the hydridovinylidene compounds 2
and 3 with acids HA, containing an anion that does not
coordinate to a metal center, would lead to the formation of
[*] Prof. Dr. H. Werner, Dipl.-Chem. W. Stüer, Dr. J. Wolf
Institut für Anorganische Chemie der Universität
Am Hubland, D-97074 Würzburg (Germany)
Fax: (‡49)931-8884605
E-mail: helmut.werner@mail.uni-wuerzburg.de
Dr. P. Schwab, Dr. M. Schulz
BASF Aktiengesellschaft, Ammoniaklaboratorium
D-67056 Ludwigshafen (Germany)
To the best of our knowledge, compounds 6 ± 9 are the first
[**] This work was supported by the Deutsche Forschungsgemeinschaft
(SFB 347) and the BASF AG. W.S. thanks the Fonds der Chemischen
cationic carbynehydrido complexes of ruthenium. With re-
1
spect to the characteristic H and 13C NMR spectroscopic
Â
Industrie for a Kekule scholarship. We are grateful to Dr. A. Schäfer
ꢀ
data, they are related to the compound [OsHCl( CCH2Ph)-
and Dr. M. Schäfer for helpful discussions, and to Dr. W. Buchner for
2
recording the H NMR spectra.
(OH2)(PiPr3)2]BF4, the only carbynehydridoosmium complex
Angew. Chem. Int. Ed. 1998, 37, No. 24
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reported as yet.[12a] Some uncharged compounds of the
acrylate [Eq. (1)]. Hereby a mixture of the first members of
the homologous series of multiply unsaturated esters
ꢀ
general composition [OsHCl2( CCH2R)(PiPr3)2] are also
known.[12b, c] Since for the corresponding osmium complex
with R ˆ Ph the cis disposition of the hydrido and carbyne
ligands has been confirmed by a single-crystal X-ray structure
analysis,[12b] we assume that for 6 ± 9 a similar configuration
exists. Density functional theory (DFT) calculations for 6 are
in agreement with the proposed cis arrangement of the
hydrido and carbyne ligands.[13]
With regard to the mechanism of formation of compounds
6 ± 9, two possibilities are conceivable. The protonation of 2
either takes place at the b-carbon atom of the vinylidene
ligand, or the attack of the proton is initially directed to the
metal leading to the formation of the intermediate
C7H11CO2CH3, C12H19CO2CH3, and C17C27CO2CH3 are
formed with a selectivity of 50, 40, and 10%. Compounds 4
and 11 are catalytically inactive in this process.
The cationic carbynehydrido complexes reported here are
the first ruthenium compounds which are able to catalyze the
metathesis of electron-poor olefins. Further applications of
6 ± 9, for example, for the cross-metathesis of alkynes,[15] are
now being studied in our laboratory. Weiss[16a] as well as
Fürstner[16b] and co-workers have recently shown that the
‡
ˆ ˆ
[RuH2Cl( C CH2)(PCy3)2] , which subsequently isomerizes
to the respective carbynehydrido complex by a 1,3-hydrogen
shift. A labeling experiment, based on the reaction of 2 with
[DNMe2Ph][B(C6F5)4], clearly confirms that the protonation
2
follows the first pathway. As the H NMR spectrum reveals,
ꢀ
ꢀ
the deuterated compound [RuHCl( CCH2D)(NMe2Ph)-
carbynetungsten complex [W( CCMe3)(OCMe3)3] is a highly
(PCy3)2][B(C6F5)4] ([D1]8) is exclusively formed, while an
isotopomer with the deuterium bonded to the metal center
cannot be detected.
active catalyst both for the metathesis of acyclic diynes
(ADIMET) and for the ring-closing reaction of diynes to
cycloalkynes. For the neutral carbyneruthenium compounds
ꢀ
Compounds 6 ± 9 are yellow air-sensitive solids which in
solution at room temperature completely decompose within
20 ± 30 min. The stability depends only slightly on the counter-
ion A , but is strongly influenced by the donor ligand L. Thus,
the analogue of 6 with L ˆ THF is significantly more labile in
solution than the adduct with Et2O. In this respect, it is
important to note that the stability of the carbynehydrido
derivatives increases considerably (up to several hours) upon
addition of excess of L or HA to the solution. We therefore
believe that the decomposition of 6 ± 9 in solution is initiated
both by the dissociation of L as well as by deprotonation.
The aforementioned lability of 6 ± 9 possibly explains why
these compounds are not accessible by halide abstraction
from 4 with silver or thallium salts. At low temperature, no
reaction between 4 and AgX or TlX occurs, and at room
temperature unidentified mixtures of products are formed.
However, if 4 is treated with a large excess (ca. 100-fold) of
HBF4 in Et2O the carbynehydrido complex 6 is surprisingly
generated in about 20% yield. As a by-product the phospho-
nium salt [HPCy3]BF4 (10) has been isolated.
[RuCl( CR)(CO)(PPh3)2], which have been prepared by
[17]
ˆ
Roper et al. from [RuCl2( CCl2)(CO)(PPh3)2] and LiR,
a
similar catalytic activity is unknown. Besides 6 ± 9, most
recently also cationic allyl- and allenylideneruthenium com-
plexes were described which partly catalyze olefin metathesis
upon activation with diazoalkanes.[18]
Since the lifetime of the catalysts 6 ± 9 is still lower than that
of 4 or 11, we are currently attempting to improve the stability
by modifying the phosphane as well as the coordinated
anionic ligand. The use of isocyanate or phenolate instead of
chloride seems to be promising.
Experimental Section
6: Compound 2 (102 mg, 0.14 mmol) was dissolved in a mixture of CH2Cl2
(5 mL) and Et2O (5 mL). The red-brown solution was then treated at
808C with an excess of HBF4 in Et2O (ca. 0.1 mL of a 1.6m solution of
HBF4 in Et2O). The reaction mixture was slowly warmed to 08C, the
solvent was removed in vacuo, and Et2O (5 mL) was added to the brown
residue. After a few minutes a yellow solid precipitated, which was filtered
and washed with Et2O (5 mL). Yield: 90 mg (72%). Equivalent conduc-
tivity in CH2Cl2: 47 cm2 W 1mol 1. The NMR spectra were measured in the
presence of a small amount of Et2O and [HPCy3]BF4 at room temperature
(see text). 1H NMR (400 MHz, CD2Cl2): d ˆ 4.77 (q, 3J(H,H) ˆ 7.0 Hz, 4H,
RuOCH2CH3), 2.52 ± 2.46 and 2.01 ± 1.30 (both m, 75H, PCy3,
RuOCH2CH3 and RuCCH3), 6.91 (t, 2J(P,H) ˆ 15 Hz, 1H, RuH); 31P
NMR (162 MHz, CD2Cl2): d ˆ 55.5 (s); 19F NMR (376.4 MHz, CD2Cl2):
d ˆ 151.1 (s); 13C NMR (100.6 MHz, CD2Cl2): d ˆ 316.1 (t, 2J(C,P) ˆ
9 Hz, RuCCH3), 84.6 (s, RuOCH2CH3), 41.4 (s, RuCCH3), 35.7 (vt, N ˆ
22 Hz, C1 of PCy3), 31.6, 30.4 (both s, PCy3), 27.6, 27.3 (both vt, N ˆ 10 Hz,
C2 of PCy3), 26.2 (s, PCy3), 12.7 (s, RuOCH2CH3).
Compounds 6 ± 9 are highly efficient catalysts for olefin
metathesis. We investigated in particular the catalytic activity
of complex 6, which catalyzes the ring opening metathesis
polymerization (ROMP) of cyclic olefins such as cyclopen-
tene, cyclooctene, cyclooctadiene, dicyclopentadiene, and
oxanorbornene derivatives even more effectively than the
[14]
ˆ
Grubbs compound [RuCl2( CHPh)(PCy3)2] (11). A com-
parison experiment reveals that ROMP of cyclooctene (room
temperature, ccat. ˆ 10 3 m, time: 3 min, yield 90%) with 6 as
catalyst is about 20 times faster than with 11. The molecular-
weight distribution and the polydispersity index of the
polymer (amount of trans olefin 76%) is presently under
investigation. From some preliminary experiments it can be
concluded that the activity of 7 ± 9 is comparable to that of 6.
However, the carbynehydrido complexes 6 ± 9 also catalyze
the cross-olefin metathesis of cyclopentene with methyl
7: A solution of 6 (80 mg, 0.09 mmol) in CH2Cl2 (5 mL) was shaken with
degassed H2O (3 mL) for 1 min. The organic phase was separated, and the
solvent was removed in vacuo to provide a yellow solid. Yield: 61 mg
(81%). 1H NMR (400 MHz, CD2Cl2, 608C): d ˆ 2.49 ± 2.39 and 2.00 ± 1.09
2
(both m, 71H, PCy3, OH2, CH3), 6.48 (brt, J(P,H) ˆ 12 Hz, 1H, RuH);
31P NMR (162 MHz, CD2Cl2, 608C): d ˆ 56.2 (s); 13C NMR (100.6 MHz,
CD2Cl2, 608C): d ˆ 314 (brs, RuCCH3), 40.8 (s, RuCCH3), 34.1 (vt, N ˆ
22 Hz, C1 of PCy3), 30.6, 29.0, 26.8, 26.5, and 25.4 (all s, PCy3).
3422
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Angew. Chem. Int. Ed. 1998, 37, No. 24

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8:
A
solid sample of
2
(72 mg, 0.10 mmol) was mixed with
1124 ± 1126; b) Verfahren zur Herstellung von Rutheniumkomplexen,
BASF AG, O.Z.0050/48279.
[8] M. L. Christ, S. Sabo-Etienne, B. Chaudret, Organometallics 1994, 13,
3800 ± 3804.
[HNMe2Ph][B(C6F5)4] (80 mg, 0.10 mmol) and treated at 808C with of
CD2Cl2 (2 mL). According to the NMR spectra, the generated yellow
solution contained exclusively complex 8. 1H NMR (200 MHz, CD2Cl2,
608C): d ˆ 7.32 ± 6.97 (m, 5H, Ph-H), 3.0 (brs, 6H, NCH3), 2.39 ± 1.24 (m,
69H, PCy3 and RuCCH3), 6.33 (t, 2J(P,H) ˆ 15 Hz, 1H, RuH); 31P NMR
(162 MHz, CD2Cl2, 708C): d ˆ 56.6 (s); 13C NMR (100.6 MHz, CD2Cl2,
Â
[9] M. Olivan, O. Eisenstein, K. G. Caulton, Organometallics 1997, 16,
2227 ± 2229.
[10] D. Huang, W. E. Streib, O. Eisenstein, K. G. Caulton, Angew. Chem.
1997, 109, 2096 ± 2098; Angew. Chem. Int. Ed. Engl. 1997, 36, 2004 ±
2006.
[11] M. Brookhart, B. Grant, A. F. Volpe, Organometallics 1992, 11, 3920 ±
3922.
[12] a) M. Bourgault, A. Castillo, M. A. Esteruelas, E. OnÄate, N. Ruiz,
Organometallics 1997, 16, 636 ± 645; b) J. Espuelas, M. A. Esteruelas,
F. J. Lahoz, L. A. Oro, N. Ruiz, J. Am. Chem. Soc. 1993, 115, 4683 ±
1
708C): d ˆ 311.9 (brs, RuCCH3), 147.4 (d, J(C,F) ˆ 239 Hz, C6F5), 137.7
(d, 1J(C,F) ˆ 245 Hz, C6F5), 135.7 (d, 1J(C,F) ˆ 247 Hz, C6F5), 129.0 (s,
NPh), 123.2, 118.1 and 113.4 (all brs, NPh), 41.5 (brs, NCH3), 40.2 (s,
RuCCH3), 34.0 (vt, N ˆ 23 Hz, C1 of PCy3), 30.6, 28.9, 26.7, 26.4, and 25.3
(all s, PCy3).
9: Analogous to the synthesis of 8, compound
quantitative yield from (20 mg, 0.028 mmol) and [H(OEt2)2]-
9 was prepared in
2
Â
4689; c) G. J. Spivak, J. N. Coalter, M. Olivan, O. Eisenstein, K. G.
[B{C6H3(CF3)2}4] (28 mg, 0.028 mmol) in CD2Cl2 and characterized spec-
troscopically at room temperature. 1H NMR (200 MHz, CD2Cl2): d ˆ 7.75,
7.59 (both m, 12H, B{C6H3(CF3)2}4), 3.36 (q, 3J(H,H) ˆ 6.6 Hz, 8H,
OCH2CH3), 2.7 ± 1.2 (m, 69H, PCy3 and RuCCH3), 1.19 (t, 3J(H,H) ˆ
Caulton, Organometallics 1998, 17, 999 ± 1001.
[13] Dr. A. Schäfer, BASF AG, unpublished results.
[14] W. Stüer, Dissertation, Universität Würzburg, to be submitted, 1998.
[15] Some examples of alkyne metathesis reactions with a carbyne- or
alkylidynemetal complex as catalyst are known: a) R. R. Schrock,
Acc. Chem. Res. 1986, 19, 342 ± 348; b) R. R. Schrock, Polyhedron
1995, 14, 3177 ± 3195; c) K. Weiss in Carbyne Complexes (Eds.: H.
Fischer, P. Hofmann, F. R. Kreissl, R. R. Schrock, U. Schubert, K.
Weiss), VCH, Weinheim, 1988, pp. 205 ± 228.
[16] a) K. Weiss, A. Michel, E.-M. Auth, U. H. F. Bunz, T. Mangel, K.
Müllen, Angew. Chem. 1997, 109, 522 ± 525; Angew. Chem. Int. Ed.
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[17] M. A. Gallop, W. R. Roper, Adv. Organomet. Chem. 1986, 25, 121 ±
198.
6.6 Hz, 12H, OCH2CH3), 6.57 (t, J(P,H) ˆ 15 Hz, 1H, RuH); 31P NMR
2
(81 MHz, CD2Cl2): d ˆ 57.2 (s).
Selective ROM of cyclopentene with methyl acrylate: A solution of 2
(56 mg, 0.077 mmol) in a mixture of CH2Cl2 (2 mL), Et2O (2 mL), and
0.5 mL of a 1.6m solution of HBF4 in Et2O was added to a mixture of methyl
acrylate (50 mL, 0.552 mol) and cyclopentene (4 mL, 0.045 mol) at room
temperature. After the solution was stirred for 2 h at room temperature, the
solvent and excess of substrate were distilled off at normal pressure, the
remaining residue was treated with pentane (10 mL), and upon addition of
Et2O (60 mL) the solution was filtered through aluminum oxide (neutral,
activity grade III). After removal of the solvent, a colorless liquid (2.5 g)
was obtained, the composition of which was investigated by GC/MS. The
liquid contained the first members of a homologous series of long-chain
multiply unsaturated esters C7H11CO2CH3, C12H19CO2CH3, and
C17C27CO2CH3 in ratios of 50, 40, and 10%.
[18] a) W. A. Herrmann, W. C. Schattenmann, O. Nuyken, S. C. Glander,
Angew. Chem. 1996, 108, 1169 ± 1170; Angew. Chem. Int. Ed. Engl.
1996, 35, 1087 ± 1088; b) A. Fürstner, M. Picquet, C. Bruneau, P. H.
Dixneuf, Chem. Commun. 1998, 1315 ± 1316.
Received: July 10, 1998 [Z12124IE]
German version: Angew. Chem. 1998, 110, 3603 ± 3606
Keywords: carbyne complexes ´ metathesis ´ ruthenium ´
vinylidene complexes
Rapid Assembly of Oligosaccharides: Total
Synthesis of a Glycosylphosphatidylinositol
Anchor of Trypanosoma brucei**
[1] a) S. T. Nguyen, L. K. Johnson, R. H. Grubbs, J. Am. Chem. Soc. 1992,
114, 3974 ± 3975; b) G. C. Fu, S. T. Nguyen, R. H. Grubbs, J. Am.
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Â
Daniel K. Baeschlin, Andre R. Chaperon,
Virginie Charbonneau, Luke G. Green, Steven V. Ley,*
Ulrich Lücking, and Eric Walther
Glycoproteins and glycolipids are major components of the
outer surface of eukaryotic cells and play a vital role in
fundamental biological processes such as viral, bacterial, and
parasitic infections, immune defence, and inflammation.[1]
Intensive research into the biological role of carbohydrates
has led to an increased need for the synthesis of natural and
modified glycoconjugates. Although remarkable progress has
been made in the field of oligosaccharide synthesis,[2] further
innovations are still required since the synthesis of complex
oligosaccharides remains a highly specialized and time con-
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b) W. E. Crowe, Z. J. Zhang, J. Am. Chem. Soc. 1993, 115, 10998 ±
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[*] Prof. Dr. S. V. Ley, D. K. Baeschlin, Dr. A. R. Chaperon,
V. Charbonneau, Dr. L. G. Green, U. Lücking, Dr. E. Walther
Department of Chemistry, University of Cambridge
Lensfield Road, Cambridge CB21EW (UK)
Fax: (‡44)1223-336442
E-mail: svl1000@cam.ac.uk
[**] This work was supported by a BP Endowment, a Novartis Research
Fellowship, the Zeneca Strategic Research Fund, the Glaxo-Welcome
Research Fund (S.V.L.), the Swiss National Science Foundation
(D.K.B., A.C., and E.W.), and the EU (U.L.).
[6] Kationische Rutheniumkomplexe, Verfahren zu ihrer Herstellung und
ihre Verwendung, BASF AG, NAE19980187.
[7] a) J. Wolf, W. Stüer, C. Grünwald, H. Werner, P. Schwab, M. Schulz,
Angew. Chem. 1998, 110, 1165 ± 1167; Angew. Chem. Int. Ed. 1998, 37,
Angew. Chem. Int. Ed. 1998, 37, No. 24
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