Unprecedented formation of μ-vinylidene complexes from phospharuthenocene and acyl chloride via activation of the C=O double bond

Article abstract of DOI:10.1021/om701063k

A novel reaction mode of phosphametallocenes was discovered. The phospharuthenocenes with cyclohexyl substituents at the α-positions of the η⁵-phospholide(s) reacted with acyl electrophiles by an initial electrophilic attack to the ruthenium to produce the μ-alkenylidene species with activation of the acyl C=O double bond and elimination of an α-hydrogen.

Full text of DOI:10.1021/om701063k

6698
Organometallics 2007, 26, 6698–6700
Unprecedented Formation of µ-Vinylidene Complexes from
Phospharuthenocene and Acyl Chloride via Activation of the CdO
Double Bond
Masamichi Ogasawara,*,† Takeshi Sakamoto,† Azumi Ito,‡ Yonghui Ge,†
Kiyohiko Nakajima,§ Tamotsu Takahashi,*,† and Tamio Hayashi*,‡
Catalysis Research Center and Graduate School of Life Sciences, Hokkaido UniVersity, and SORST,
Japan Science and Technology Agency (JST), Kita-ku, Sapporo 001-0021, Japan, Department of
Chemistry, Graduate School of Science, Kyoto UniVersity, Sakyo, Kyoto 606-8502, Japan, and Department
of Chemistry, Aichi UniVersity of Education, Igaya, Kariya, Aichi, 448-8542, Japan
ReceiVed October 23, 2007
Scheme 1. Reactions of Diphosphametallocenes with Acetyl
Electrophile
Summary: A noVel reaction mode of phosphametallocenes was
discoVered. The phospharuthenocenes with cyclohexyl substit-
uents at the R-positions of the η5-phospholide(s) reacted with
acyl electrophiles by an initial electrophilic attack to the
ruthenium to produce the µ-alkenylidene species with actiVation
of the acyl CdO double bond and elimination of an R-hydrogen.
Recently, phosphametallocenes have attracted considerable
attention in organometallic chemistry.1 Because a phosphorus
atom in an η5-phospholide possesses a lone pair on it, phos-
phametallocenes are Lewis basic. Thus, they have been utilized
as nucleophilic catalysts2 or a new class of P-donor ligands with
unique electronic/steric properties.3,4 Although many interesting
applications of these compounds have been reported so far,
studies on their reactivity are still relatively limited. In general,
phosphametallocenes are “aromatic”, as seen in (η5-cyclopen-
tadienyl)metal complexes, and serve as good substrates for
electrophilic substitution reactions,5 such as Friedel–Crafts
acylation or Vilsmier formylation. In this report, we would like
to describe an unprecedented reaction of phosphametallocene
species.Duringourstudiesonreactivityofphospharuthenocenes,4l,6,7
it was found that a reaction between a phospharuthenocene and
an acyl electrophile produced a novel µ-vinylidene species,
where the vinylidene moiety bridged the Ru center and the
phosphorus atom, via activation of the acyl CdO double bond.
* To whom correspondence should be addressed. E-mail:
ogasawar@cat.hokudai.ac.jp; tamotsu@cat.hokudai.ac.jp; thayashi@
kuchem.kyoto-u.ac.jp.
Treatment of the 1,1′-diphospharuthenocene 1 with 2 equiv
of an acetyl electrophile, which was generated from CH3COCl
and AlCl3, in refluxing dichloromethane for 24 h gave the pale
yellow crystalline product 2 in 46% yield together with
recovered 1 (30%) and a small amount of the Friedel–Crafts
acetylation product 3 in 15% yield (Scheme 1, top). The
products 2 and 3 were air- and moisture-stable and easily
purified by silica gel column chromatography. The product 2
showed two signals of equal intensity at δ –26.6 and –21.2 in
† Hokkaido University.
‡ Kyoto University.
§ Aichi University of Education.
(1) For reviews of phosphametallocenes, see: (a) Mathey, F.; Fischer,
J.; Nelson, J. H. Struct. Bonding (Berlin) 1983, 55, 153. (b) Mathey, F.
NouV. J. Chim. 1987, 11, 585. (c) Mathey, F. Coord. Chem. ReV. 1994,
137, 1. (d) Mathey, F. J. Organomet. Chem. 2002, 646, 15. (e) Carmichael,
D.; Mathey, F. Top. Curr. Chem. 2002, 220, 27. (f) Le Floch, P. Coord.
Chem. ReV. 2006, 250, 627.
(2) (a) Garrett, C. E.; Fu, G. C. J. Org. Chem. 1997, 62, 4534. (b) Wang,
L.-S.; Hollis, T. K. Org. Lett. 2003, 5, 2543.
1
the 31P NMR spectrum. The H NMR spectrum of 2 showed
(3) (a) Sava, X.; Ricard, L.; Mathey, F.; Le Floch, P. Organometallics
2000, 19, 4899. (b) Melaimi, M.; Mathey, F.; Le Floch, P. J. Organomet.
Chem. 2001, 640, 197.
four doublets in the olefinic/phospholyl region [δ 5.40 (d, JPH
) 3.9 Hz, 2H), 5.55 (d, JPH ) 17.0 Hz, 2H), 6.02 (d, JPH
)
(4) As chiral ligands for asymmetric reactions, see: (a) Qiao, S.; Fu,
G. C. J. Org. Chem. 1998, 63, 4168. (b) Ganter, C.; Glinsböckel, C.; Ganter,
B. Eur. J. Inorg. Chem. 1998, 1163. (c) Ganter, C.; Kaulen, C.; Englert, U.
Organometallics 1999, 18, 5444. (d) Shintani, R.; Lo, M. M.-C.; Fu, G. C.
Org. Lett. 2000, 2, 3695. (e) Tanaka, K.; Qiao, S.; Tobisu, M.; Lo, M. M.-
C.; Fu, G. C. J. Am. Chem. Soc. 2000, 122, 9870. (f) Ogasawara, M.;
Yoshida, K.; Hayashi, T. Organometallics 2001, 20, 3917. (g) Tanaka, K.;
Fu, G. C. J. Org. Chem. 2001, 66, 8177. (h) Shintani, R.; Fu, G. C. Org.
Lett. 2002, 4, 3699. (i) Shintani, R.; Fu, G. C. Angew. Chem., Int. Ed. 2003,
42, 4082. (j) Shintani, R.; Fu, G. C. J. Am. Chem. Soc. 2003, 125, 19778.
(k) Suárez, A.; Downey, W.; Fu, G. C. J. Am. Chem. Soc. 2005, 127, 11244.
(l) Ogasawara, M.; Ito, A.; Yoshida, K.; Hayashi, T. Organometallics 2006,
25, 2715.
64.1 Hz, 1H), 6.83 (d, JPH ) 35.5 Hz, 1H)] with a 2:2:1:1
1
integration ratio. In the phosphorus-decoupled H NMR spec-
trum, these four signals are turned into four singlets. The HRMS
(6) (a) Ogasawara, M.; Nagano, T.; Yoshida, K.; Hayashi, T. Organo-
metallics 2002, 21, 3062. (b) Ogasawara, M.; Yoshida, K.; Hayashi, T.
Organometallics 2003, 22, 1783.
(7) (a) Carmichael, D.; Ricard, L.; Mathey, F. J. Chem. Soc., Chem.
Commun. 1994, 1167. (b) Carmichael, D.; Mathey, F.; Ricard, L.; Seeboth,
N. Chem. Commun. 2002, 2976. (c) Carmichael, D.; Klankermayer, J.;
Ricard, L.; Seeboth, N. Chem. Commun. 2004, 1144. (d) Carmichael, D.;
Ricard, L.; Seeboth, N.; Brown, J. M.; Claridge, T. D. W.; Odell, B. Dalton
Trans. 2005, 2173. (e) Carmichael, D.; Ricard, L.; Seeboth, N. Organo-
metallics 2007, 26, 2964. (f) Loschen, R.; Loschen, C.; Frank, W.; Ganter,
C. Eur. J. Inorg. Chem. 2007, 553. (g) Carmichael, D.; Goldet, G.;
Klankermayer, J.; Ricard, L.; Seeboth, N.; Stankevicˇ, M. Chem.-Eur. J.
2007, 13, 5492.
(5) (a) Mathey, F.; Mitschler, A.; Weiss, R. J. Am. Chem. Soc. 1977,
99, 3537. (b) Mathey, F. Tetrahedron Lett. 1976, 17, 4155. (c) Mathey, F.
J. Organomet. Chem. 1977, 139, 77. (d) de Lauzon, G.; Deschamps, B.;
Mathey, F. NouV. J. Chim. 1980, 4, 683. (e) de Lauzon, G.; Deschamps,
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994.
10.1021/om701063k CCC: $37.00
2007 American Chemical Society
Publication on Web 12/04/2007

Communications
Organometallics, Vol. 26, No. 27, 2007 6699
Scheme 2. Scope and Limitation of Preparing µ-Alkenylidene
Ruthenium Complexes
Figure 1. ORTEP drawing of 2 with 30% thermal ellipsoids. All
hydrogen atoms except H(1) and H(2) are omitted for clarity.
Selected bond lengths (Å) and angles (deg): Ru(1)–P(1) (nonbond-
ing) ) 2.6360(11), Ru(1)–P(2) ) 2.4345(10), Ru(1)–C(1) )
2.152(4), P(1)–C(1) ) 1.747(4), P(1)–O(1) ) 1.479(3), C(1)–C(2)
) 1.315(6); Ru(1)–C(1)–P(1) ) 84.42(17), C(3)–P(1)–C(6) )
93.03(19), Ru(1)–C(1)–C(2) ) 141.8(3), P(1)–C(1)–C(2) )
133.7(3).
Scheme 3. Possible Reaction Pathway of Formation of 2
from 1 and AcCl/AlCl3
analysis suggested a chemical formula of C34H50OP2Ru for 2,
which was identical to that of the Friedel–Crafts acetylation
product 3.
Recrystallization of 2 from hot ethyl acetate grew prismatic
crystals suitable for X-ray structure analysis. The result of the
crystallography is shown in Figure 1. One of the two phospholyl
ligands in 2 is oxidized at P(1), and the phosphorus shows
distorted tetrahedral geometry. There is no bonding interaction
between Ru(1) and P(1) with the Ru(1)-P(1) distance of
2.6360(11) Å. The P(1)C(3)C(4)C(5)C(6) core coordinates to
Ru(1) at the η4-diene moiety with the envelope-like bent
structure; the dihedral angle between the P(1)C(3)C(6) plane
and the C(3)C(4)C(5)C(6) plane is 16.33°, and P(1) lies out of
the C(3)C(4)C(5)C(6) plane by 0.360 Å away from Ru(1). The
vinylidene moiety C(1)dC(2)H(1)H(2) bridges between Ru(1)
and P(1). The CdCH2 plane is nearly perpendicular to the η5-
phospholyl plane (85.50°), which makes the two hydrogens at
the vinylidene terminus inequivalent to each other. The C(1)-C(2)
bond length is 1.315(6) Å, that is, within a normal range for
typical CdC double bonds. Analogous η4-coordination of a
P-oxo-phospholide can be seen in an iron complex reported by
Mathey and co-workers.8
in phosphaferrocenes were more reactive than the ꢀ-positions
to electrophilic substitution.9 The low yield of 5 can be attributed
to the cyclohexyl groups, which block the more reactive R-sites
in 4. The unfavorable formation of 3 in the reaction of 1
(Scheme 1, top) could be partly ascribed to the shielding of the
R-phospholyl positions in 1 by the four Cy groups in the same
way. Indeed, monophospharuthenocenes 9, which had an
R-hydro- or an R-silyl-phospholide, were reported to be active
substrates for the Friedel–Crafts acylation with (CF3CO)2O/
BF3 · OEt2, and the corresponding R-trifluoroacetylphospha-
ruthenocene species 10 were obtained in good yields (Scheme
2, middle).7b On the other hand, the monophospharuthenocene
species 6 provided the µ-vinylidene species 7 in 56% yield by
the reaction with CH3COCl/AlCl3. The structure of 7 was
unambiguously determined by various NMR measurements and
X-ray crystallography (see Supporting Information). The forma-
tion of the µ-vinylidene complex 7 is more selective for 6: a
Friedel–Crafts acetylation product 8 was obtained in less than
3%, and the unreacted 6 was recovered in 37% yield (Scheme
2, top).
The use of propionyl chloride for a reaction with 1 under
otherwise identical conditions also afforded the µ-alkenylidene
species 11 albeit in low yield (13%). Complex 11 was obtained
as the E-isomer predominantly (E/Z ) >97/<3 determined by
1H and 31P NMR; Scheme 2, bottom).
A possible mechanism for the formation of the µ-vinylidene
complex 2 is shown in Scheme 3. Because all the R-phospholide
positions are blocked by the cyclohexyl substituents in 1, the
acetyl electrophile attacks the ruthenium center instead of the
With free rotation of the η5-phospholyl ligand around the
Ru(1)-phospholyl axis, complex 2 is Cs symmetric in solution,
1
and the H, 13C, and 31P NMR spectra are consistent with the
solid-state structure.
The origin of O(1) and the µ-vinylidene could be ascribed to
acetyl chloride; that is, the phosphorus and the ruthenium atoms
in 1 cooperatively activated the CdO double bond in CH3COCl
during the transformation to 2. The ruthenium center and the
cyclohexyl substituents at the R-positions of the phospholides
in 1 play important roles for formation of this unique µ-
vinylidene complex 1. Treatment of the homologous diphos-
phaferrocene 4, which is isostructural to 1, under the identical
conditions afforded the Friedel–Crafts acetylation product 5 in
21% yield (Scheme 1, bottom). Complex 5 was the sole
detectable product, and the unreacted 4 was recovered in 73%
yield. It was reported that the R-positions of η5-phospholides
(8) Deschamps, B.; Fischer, J.; Mathey, F.; Mitschler, A. Inorg. Chem.
1981, 20, 3252.
(9) (a) Mathey, F. J. Organomet. Chem. 1977, 139, 77. (b) Roberts,
R. M. G.; Wells, A. S. Inorg. Chim. Acta 1987, 130, 93.

6700 Organometallics, Vol. 26, No. 27, 2007
Scheme 4. Reactivity of µ-Vinylidene Complex 2
Communications
η5-phospholide.10 An intramolecular nucleophilic attack of the
phospholide at the acetyl carbonyl carbon, which may be
activated by AlCl3, followed by a nucleophilic abstraction of
–
one of the hydrogens in the acetyl moiety by the AlCl4 anion
affords the µ-vinylidene complex 2. The final step in Scheme 3
is somewhat similar to the mechanism of the well-known
Arbuzov reaction. Apparently, the orientation of the electrophilic
(ruthenium) and the nucleophilic (phosphorus) cites in close
proximity is an important factor in realizing the reaction.
Complex 2 possesses a lone pair on the phosphorus of the
η5-phospholide. Indeed, treatment of 2 with excess Fe2(CO)9
in boiling benzene-d6 showed a partial conversion (ca. 50%)
Figure 2. ORTEP drawing of 14 with 30% thermal ellipsoids. All
hydrogen atoms except for those on C(1) and C(2) are omitted for
clarity. Selected bond lengths (Å) and angles (deg): Ru(1)–P(1)
(nonbonding) ) 2.6103(10), Ru(1)–P(2) ) 2.4278(14), Ru(1)–C(1)
) 2.229(4), P(1)–C(1) ) 1.760(4), P(1)–O(1) ) 1.484(3), C(1)–C(2)
) 1.510(7); Ru(1)–C(1)–P(1) ) 80.83(17), C(3)–P(1)–C(6) )
97.03(19), Ru(1)–C(1)–C(2) ) 121.9(3), P(1)–C(1)–C(2) )
119.7(3).
1
into the Fe(CO)4 adduct 13.11 The H NMR spectrum of the
mixture of 2 and 13 showed broadened resonances due to a
slow exchange between the two (Scheme 4). Although 13 was
not isolable because of weak coordination of 2 to the iron atom,
the downfield shift of one of the two signals in the 31P NMR
spectrum clearly indicated the coordination of the Fe(CO)4
fragment in 13.12
The C(1)-C(2) bond length and the H(1)C(2)H(2) angle
(114(4)°) suggest olefinic character of the µ-vinylidene moiety
in 2. Indeed, the CdC double bond is smoothly hydrogenated
under 1 atm of H2 in the presence of Pd/C to give the
µ-ethylidene complex 14 in 93% isolated yield (Scheme 4). The
X-ray crystal structure of 14 is shown in Figure 2. The C(1)
atom, which bridges between P(1) and Ru(1), changes its
hybridization mode from sp2 to sp3 upon hydrogenation of the
C(1)dC(2) double bond in 2. Thus, some distortion can be
detected in the local structure around C(1) in 14. The overall
structure of 14 is, however, very similar to that of 2. Complex
14 is insensitive to both oxygen and moisture and can be handled
in air without appreciable decomposition.
In summary, an unprecedented reaction mode of phospha-
metallocenes was discovered. The phospharuthenocenes, which
have 2,5-dicyclohexylphospholide(s), react with an acetyl or a
propionyl electrophile by an initial electrophilic attack at the
ruthenium and afford the µ-alkenylidene species with activation
of the acyl CdO double bond and elimination of an R-hydrogen.
Acknowledgment. A part of this work was supported by
a Grant-in-Aid for Scientific Research on Priority Areas
“Synergistic Effects for Creation of Functional Molecules”
from the Ministry of Education, Culture, Sports, Science and
Technology, Japan, and the Nagase Science and Technology
Foundation (to M.O.).
(10) It has been suggested that the initial electrophilic attack to ferrocene
can occur at two different sites, a carbon atom of a cyclopentadienyl ring
or the iron center, in electrophilic substitution of ferrocenes; see: (a) Watts,
N. E. In ComprehensiVe Organometallic Chemistry; Wilkinson, G., Stone,
F. G. A., Abel, E. N., Eds.; Pergammon: New York, 1982; Vol. 8, Chapter
59, pp 1019–1021. (b) 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; pp 173–174.
(11) (a) Mathey, F. J. Organomet. Chem. 1978, 154, C13. (b) Fischer,
J.; Mitschler, A.; Ricard, L.; Mathey, F. J. Chem. Soc., Dalton Trans. 1980,
2522.
Supporting Information Available: Detailed experimental
procedures, compound characterization data, and crystallographic
data in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
(12) 2, 31P NMR (C6D6): δ–26.4 and–19.3; 13, 31P NMR (C6D6):
δ–16.2 and 38.2.
OM701063K