Stable iso-osmabenzenes from a formal [3+3] cycloaddition reaction of metal vinylidene with alkynols

Article abstract of DOI:10.1002/anie.201006442

The magic of Os: An unprecedented formal [3+3] cycloaddition reaction of 1 with alkynols affords stable iso-osmabenzenes at room temperature (see scheme). The phosphonium substituent at the C_β position and the 18e ^- nature of the compound play key roles in the origin of the high thermal stability of the products. Isomerization of iso-osmabenzenes into η⁵-cyclopentadienyl complexes through metalated cyclopentadiene intermediates is also described.

Full text of DOI:10.1002/anie.201006442

Communications
DOI: 10.1002/anie.201006442
Cycloaddition
Stable Iso-osmabenzenes from a Formal [3+3] Cycloaddition Reaction
of Metal Vinylidene with Alkynols**
Qianyi Zhao, Lei Gong, Chunfa Xu, Jun Zhu,* Xumin He, and Haiping Xia*
The investigation on the synthesis and reactivity of metal
vinylidene complexes has always been an active area,[1]
especially given their applications as well-known catalysts
for metathesis and carbon–carbon and carbon–heteroatom
coupling reactions.[1b,e,2] Compared with other reactions of
metal vinylidenes, the cyclization reactions are underdevel-
oped. Previous studies showed that the
of H2O/CH3OH (3:2 v/v) at reflux produced the osmium
hydride vinylidene complex 2, which was isolated as a light-
yellow solid in 60% yield (Scheme 1). The other product,
1
PhCHO, was detected by H NMR (d = 9.3 ppm; PhCHO)
and GC analysis of the reaction mixture (see Figure S1 in the
Supporting Information). Complex 2 was characterized by
NMR spectroscopy and elemental analysis, and the structure
was additionally confirmed by single-crystal X-ray diffraction
(Figure S2).
=
vinylidene M Ca bond participated in cyclo-
additions (see a) as key steps in carbon–
carbon coupling reactions,[3] and some cyclo-
addition products have also been isolated.[4]
Interestingly, similar reactions of the metal
[5]
=
vinylidene Ca Cb bond (see b) have been realized as well.
However, cyclizations of the skeleton of metal vinylidene
=
=
(M Ca Cb) as a unit (see c) remain scarce. In fact, the
reported cyclization is a formal [3+2] cycloaddition reac-
tion.[5c] To the best of our knowledge, the [3+3] cyclization
reactions of metal vinylidene to construct six-membered rings
have not been reported.
Scheme 1. Preparation of osmium hydride vinylidene 2.
Moreover, since the first isolation of metallabenzene was
achieved by Roper and co-workers,[7a] considerable research
interest has been attracted in this field.[6,7] Nevertheless, the
metallabenzene analogue isometallabenzene, which can be
seen as a metal-containing 1,2,4-cyclohexatriene, has not been
thoroughly explored. Until now, only the 16eÀ isometalla-
Complex 2 is thermally stable in the solid state but highly
ꢀ
reactive in solution. Treatment of 2 with HC CCH(OH)Ph in
dichloromethane or chloroform at room temperature led to a
fast color change from light yellow to brown red. The
unexpected iso-osmabenzene 3 was generated from a formal
[3+3] cycloaddition and isolated in high yield (93%).
= =
À
À
=
ꢀ
=
benzene
[Os{ C C(Ph) CH(Ph) CH C(CH2Ph)}Cl-
Similarly, when 2 reacted with HC CCH(OH)CH CH2 or
ꢀ
(PiPr3)2], prepared by double coupling reactions, was
reported by Esteruelas and co-workers in 2004.[8] Herein,
we report an unprecedented formal [3+3] cycloaddition
reaction between the hydride vinylidene complex [OsHCl2-
HC CCH(OH)CH2CH3 under the same reaction conditions,
the other two iso-osmabenzenes, 4 (88% yield) and 5 (80%
yield), were also formed (Scheme 2).
= =
{ C CH(PPh3)}(PPh3)2] (2) and alkynols under mild condi-
tions to give stable 18eÀ iso-osmabenzenes. The origin of the
unexpected stability of these iso-osmabenzene complexes and
their isomerization into h5-cyclopentadienyl complexes
through metalated cyclopentadiene intermediates is also
described.
Stirring of the osmium hydride alkenylcarbyne complex
[9]
ꢀ À
=
[OsHCl2( C C(PPh3) CHPh)(PPh3)2]BF4 (1) in a mixture
[*] Q. Zhao, L. Gong, C. Xu, Prof. Dr. J. Zhu, Prof. Dr. X. He,
Prof. Dr. H. Xia
State Key Laboratory of Physical Chemistry of Solid Surfaces
College of Chemistry and Chemical Engineering
Xiamen University, Xiamen, 361005 (P.R. China)
Fax: (+86)592-218-6628
Scheme 2. Preparation of iso-osmabenzene 3–5.
E-mail: jun.zhu@xmu.edu.cn
The structure of 3 was characterized by single-crystal
X-ray diffraction analysis.[10] As shown in Figure 1, the six-
membered ring is almost planar. The deviations, in ꢀ, from
the best plane are 0.0410 (Os1), 0.0003 (C1), 0.0515 (C2),
hpxia@xmu.edu.cn
[**] This work was financially supported by the National Science
Foundation of China (Nos. 20872123 and 20925208).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201006442.
=
0.0571 (C3), 0.0022 (C4), and 0.0491 (C5). The Os1 C1 bond
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Angew. Chem. Int. Ed. 2011, 50, 1354 –1358

metal hydride complexes is the insertion of terminal alkynes
[16]
À
into their M H bonds.
Solid samples of 3, 4, and 5 show air and moisture
stabilities; they can be heated in air at 1008C for 5 hours
without notable decomposition. In solution, complex 3 is
thermally stable to some extent, and tolerant to bases such as
Na2CO3 and NaOH; however 3 is sensitive to acids such as
HCl and HBF4. In contrast to 3, complexes 4 and 5 are less
stable. When 4 was continuously stirred in chloroform at
room temperature, it rearranged slowly into the h5-cyclo-
pentadienyl complex 7 after three days (Scheme 3). The
Figure 1. X-ray crystal structure of 3 (ellipsoids shown at the 50%
probability level). Some of the hydrogen atoms are omitted for clarity.
Selected bond lengths [ꢀ] and angles [deg]: Os1–Cl1 2.487(2), Os1–Cl2
2.492(3), Os1–P1 2.393(3), Os1–P2 2.398(3), Os–C1 1.781(11), Os1–
C5 2.043(12), C1–C2 1.339(13), C2–C3 1.563(14), C3–C4 1.507(13),
C4–C5 1.351(14); C1-Os1-C5 78.3(4), Os1-C1-C2 155.1(8), C1-C2-C3
114.2(9), C2-C3-C4 111.6(9), C3-C4-C5 128.6(10), C4-C5-Os1 131.4(8).
= =
Scheme 3. Preparation of 6–8.
length (1.781(11) ꢀ) is at the low-end of the typical Os C
CRR’ (1.78–1.90 ꢀ)[11] and Os Ccarbene (1.78–2.14 ꢀ) bonds.[12]
=
The Os1–C5 bond length (2.043(12) ꢀ) is within the range
observed for typical Os–Cvinyl bonds.[13] The C1 C2, C4 C5,
C2–C3, and C3–C4 bond lengths are typical for carbon–
carbon double and single bonds. The Os–C and C–C bond
lengths within the six-membered ring indicate that the
metallacycle has a localized nature. The Os1-C1-C2 angle of
155.1(8)8 is comparable to that of Esteruelasꢁ iso-osmaben-
zene (158.5(3)8)[8] and Jiaꢁs osmabenzyne (148.7(3)–
154.9(9)8)[14] or osmanaphalyne (151.1(5)8 and 155.0(3)8).[15]
In keeping with the solid-state structure of 3, the 1H NMR
analysis showed no signal for the carbene proton. Two proton
isomerization of 5, which led to 8, was faster and accom-
plished in quantitative yield within two days. The solution of 3
behaved similarly to give 6, but very slowly as the trans-
formation took more than one week. By comparing the
above-mentioned results, the stability of 3, 4, and 5 follows
the sequence 3 > 4 > 5, which is mainly influenced by the
substituents on the sp3-carbon atom.
DFT calculations have been carried out to gain insight
into the relative stabilities of 3, 4, and 5. Compounds 3’, 4’, and
5’ are model complexes in which the PPh3 ligand is replaced
with PH3. The computed relative free energies for 3’, 4’, and 5’
with respect to the model h5-cyclopentadienyl complexes 6’,
7’, and 8’ are 11.7, 13.5, and 19.6 kcalmolÀ1 (Scheme 4a),
respectively, and are consistent with the experimental obser-
vations. For comparison, we also calculated the energy
=
=
=
signals for the Os–CH CH unit were observed at d = 8.3 and
4.7 ppm, respectively, with a coupling constant of 9.5 Hz,
which indicates a cis geometry.
Mainly attributed to the chirality of the sp3-carbon atom
C3, the 31P{1H} NMR spectrum of 3 displayed the same
characteristic AB spin system as did Esteruelasꢁ isometalla-
benzene;[8] the resonances were centered at d = À3.4 (d,
= =
À
difference for the first iso-osmabenzene [Os{ C C(Ph)
[8]
À
=
CH(Ph) CH C(CH2Ph)}Cl(PiPr3)2] (model complex Os1’)
relative to the h5-Cp complex Os1(Cp)’ (38.2 kcalmolÀ1,
Scheme 4b).
2
2J(PP) = 360.5 Hz) and À7.9 ppm (d, J(PP) = 360.5 Hz) for
each of the two OsPPh3, respectively. The signal at
d = 3.9(s) ppm was assigned to CPPh3. Unfortunately, the
poor solubility of 3 and 4 prevented 13C{1H} NMR character-
ization. Isoosmabenzenes 4 and 5 have similar NMR spec-
troscopic characteristics as 3.
To probe the origin of the relatively high stability of 3’, we
additionally constructed three more model complexes,
+
namely 3-PH3 ’, 3-ClÀ’, and 3-PH3’, to examine the role of
the phosphonium substituent and different electron counts
(Scheme 4c). Interestingly, when the phosphonium substitu-
ent is replaced by a hydrogen atom, the relative energy of
A plausible mechanism for the formation of 3, 4, and 5 is
shown in Scheme 2. The insertion of terminal alkynes into
Os H bond should afford intermediate A. The subsequent
dehydration and C–C coupling between the Cb of the
vinylidene fragment and the hydroxy-linked carbon atom in
A led to the formal [3+3] cycloaddition iso-osmabenzene
products. It should be mentioned that the typical reaction of
3-PH3 ’ is increased from 11.7 kcalmolÀ1 to 26.3 kcalmolÀ1
+
À
compared to 3’, indicating that the phosphonium substituent
plays a crucial role in stabilizing iso-osmabenzene complexes.
Moreover, when one ClÀ or PH3 ligand is deliberately
removed from 3’ to form a 16eÀ iso-osmabenzene 3-ClÀ’ or
Angew. Chem. Int. Ed. 2011, 50, 1354 –1358
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Communications
h5-cyclopentadienyl model complexes 6’, 7’, and 8’, respec-
tively (Scheme 4a).
To capture the intermediate in this reaction, CO was
introduced to stabilize B. A flask containing a solution of 3
was placed in an ice bath and under a CO atmosphere, and the
mixture was stirred, thus leading to 9 (Scheme 5). Complex 9
was characterized by NMR spectroscopy, elemental analysis,
and single-crystal X-ray diffraction (Figure 2).[10] The forma-
Scheme 5. Preparation of 9.
Scheme 4. Relative free energies (kcalmolÀ1, in the solvent of chloro-
form) of iso-osmabenzenes compared with Cp complexes.
Figure 2. X-ray crystal structure of 9 (ellipsoids shown at the 50%
probability level).
3-PH3’, respectively, their stabilities relative to the h5-com-
plexes are decreased to 34.5 and 25.4 kcalmolÀ1, respectively,
suggesting that the contribution to the stability from the 18eÀ
rule is not negligible. Taken together, both the phosphonium
substituent at the Cb position and the 18eÀ nature of 3
contribute to the high stability.
Additional studies showed that complexes 6, 7, and 8
could also be produced by heating 3, 4, and 5, respectively, in
chloroform for hours. By changing the counteranion of 8 to
BPh4À, complex 8a was prepared and confirmed by X-ray
diffraction (Figure S3). Furthermore, the complexes 6, 7, 8,
and 8a were characterized by NMR spectroscopy and
elemental analysis.
tion of 9 suggests that iso-osmabenzenes rearranged via
metalated cyclopentadiene intermediates.
At first glance, isometallabenzene D is similar to metal-
labenzene C and metallabenzyne E, particularly the reso-
nance structure E’ (Scheme 6). Compared with metallaben-
zyne E, metallabenzene C and isometallabenzene D have a
lower degree of unsaturation. Although metallabenzenes and
metallabenzynes are familiar to us, isometallabenzenes are
extremely rare. In this regard, isolation of the isometallaben-
zenes 3, 4, and 5 will definitely enrich the chemistry of six-
membered metallacycles.
It is well known that metallabenzenes can undergo
carbene migratory insertion reactions into cyclopentadienyl
complexes.[17] A similar process can be detected in the
isomerization of isometallabenzenes (Scheme 3). The pro-
posed mechanism shows that it may go through the metalated
cyclopentadiene intermediate B. As a result of its instability,
the 16eÀ five-coordinated B immediately undergoes H-shift
Scheme 6. Metallabenzene, isometallabenzene, and metallabenzyne.
À
onto the Ca atom of the Os-Cvinyl followed by Os C bond
cleavage, giving the stable h5-cyclopentadienyl complexes 6, 7,
and 8. Indeed, the computed data for the metalated cyclo-
pentadiene B6’, B7’, and B8’ model complexes are less stable
by 8.7, 10.0, and 14.0 kcalmolÀ1 relative to the corresponding
In summary, isometallabenzenes were isolated from the
novel [3+3] cycloaddition reactions of a metal vinylidene
complex with alkynols in high yields at room temperature.
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Angew. Chem. Int. Ed. 2011, 50, 1354 –1358

Mereiter, R. Schmid, K. Kirchner, Organometallics 1999, 18,
1011; c) M. Murakami, S. Hori, J. Am. Chem. Soc. 2003, 125,
4720; d) Y. J. Park, B.-I. Kwon, J.-A. Ahn, H. Lee, C.-H. Jun, J.
Am. Chem. Soc. 2004, 126, 13892.
This method provides a simple and efficient route to prepare
stable isometallabenzenes. The origin of the unexpected
stability was probed by using DFT calculations, which suggest
that both the phosphonium substituent at the Cb position and
the 18eÀ nature of the complex are the stabilizing factors. We
also found that these isometallabenzenes could isomerize into
h5-cyclopentadienyl complexes via a metalated cyclopenta-
diene intermediate. The new reaction pattern between metal
vinylidene and alkynols represents a promising synthetic
method to construct other metallacycles. Expansion of
cyclizations of vinylidene complexes to heteroatom-contain-
ing metallacycles is ongoing.
[4] a) R. Beckhaus, I. Strauß, T. Wagner, P. Kiprof, Angew. Chem.
1993, 105, 281; Angew. Chem. Int. Ed. Engl. 1993, 32, 264; b) R.
Beckhaus, I. Strauß, T. Wagner, Angew. Chem. 1995, 107, 738;
Angew. Chem. Int. Ed. Engl. 1995, 34, 688; c) R. Beckhaus, J.
Sang, T. Wagner, B. Ganter, Organometallics 1996, 15, 1176;
d) M. Yamaguchi, Y. Arikawa, Y. Nishimura, K. Umakoshi, M.
Onishi, Chem. Commun. 2009, 2911.
[5] For examples: a) P. Alvarez, E. Lastra, J. Gimeno, M. Bassetti,
L. R. Falvello, J. Am. Chem. Soc. 2003, 125, 2386; b) P. Braꢄa, J.
Gimeno, J. A. Sordo, J. Org. Chem. 2004, 69, 2544; c) J.
Ipaktschi, J. Mohseni-Ala, A. Dꢅlmer, S. Steffens, C. Witten-
burg, J. Heck, Organometallics 2004, 23, 4902; d) Y.-S. Yen, Y.-C.
Lin, S.-L. Huang, Y.-H. Liu, H.-L. Sung, Y. Wang, J. Am. Chem.
Soc. 2005, 127, 18037.
Experimental Section
ꢀ À
2: The osmium hydride-alkenylcarbyne complex [OsHCl2( C C-
=
(PPh3) CHPh)(PPh3)2]BF4 (1) (506 mg, 0.405 mmol) was stirred in a
[6] For reviews, see: a) G. Jia, Acc. Chem. Res. 2004, 37, 479;
b) C. W. Landorf, M. M. Haley, Angew. Chem. 2006, 118, 4018;
Angew. Chem. Int. Ed. 2006, 45, 3914; c) L. J. Wright, Dalton
Trans. 2006, 1821; d) J. R. Bleeke, Acc. Chem. Res. 2007, 40,
1035.
mixture of CH3OH (20 mL) and H2O (30 mL) under reflux for about
12 h to give a light-yellow suspension, which was collected by
filtration, washed with methanol and diethyl ether, and then dried
1
under vacuum. Yield: 261 mg, 60%. H NMR (400.1 MHz, CDCl3):
d = À8.0 (td, J(P,H) = 15.6 Hz, J(P,H) = 4.0 Hz, 1H, OsH), 7.7–
6.6 ppm (m, 45H, PPh3), 0.6 ppm (br, 1H, OsCCHPPh3); 31P{1H}
NMR (162.0 MHz, CDCl3): d = 7.6 (d, J(P,P) = 4.9 Hz OsPPh3),
À1.06 ppm (t, J(P,P) = 4.9 Hz, CPPh3); elemental analysis (%) calcd
for C56H47P3Cl2Os: C 62.62, H 4.41; found: C 62.32, H 4.31.
[7] For examples: a) G. P. Elliott, W. R. Roper, J. M. Waters, J.
Chem. Soc. Chem. Commun. 1982, 811; b) U. Englert, F.
Podewils, I. Schiffers, A. Salzer, Angew. Chem. 1998, 110, 2196;
Angew. Chem. Int. Ed. 1998, 37, 2134; c) C. E. F. Rickard, W. R.
Roper, S. D. Woodgate, L. J. Wright, Angew. Chem. 2000, 112,
766; Angew. Chem. Int. Ed. 2000, 39, 750; d) U. Effertz, U.
Englert, F. Podewils, A. Salzer, T. Wagner, M. Kaupp, Organo-
metallics 2003, 22, 264; e) E. ꢆlvarez, M. Paneque, M. L. Poveda,
N. Rendꢂn, Angew. Chem. 2006, 118, 488; Angew. Chem. Int. Ed.
2006, 45, 474; f) G. R. Clark, P. M. Johns, W. R. Roper, L. J.
Wright, Organometallics 2008, 27, 451; g) A. F. Dalebrook, L. J.
Wright, Organometallics 2009, 28, 5536; h) K. C. Poon, L. Liu, T.
Guo, J. Li, H. H. Y. Sung, I. D. Williams, Z. Lin, G. Jia, Angew.
Chem. 2010, 122, 2819; Angew. Chem. Int. Ed. 2010, 49, 2759;
i) G. R. Clark, L. A. Ferguson, A. E. McIntosh, T. Sꢇhnel, L. J.
Wright, J. Am. Chem. Soc. 2010, 132, 13443.
3: HC ꢀ CCH(OH)Ph (55.4 mL, 0.447 mmol) was added to a
solution of 2 (400 mg, 0.372 mmol) in CH2Cl2 or CHCl3 (15 mL). The
reaction mixture was stirred at room temperature for about 1 h at
which point a brown-red solution was obtained. A red solid was
collected after the solvent was evaporated to dryness under vacuum
and the resulting residue was washed by diethyl ether and then dried
1
under vacuum. Yield: 412 mg, 93%. H NMR (500.2 MHz, CDCl3):
d = 8.3
(dd,
J(H,H) = 9.5 Hz,
J(H,H) = 2.0 Hz,
1H,
OsCHCHCH(Ph)), 7.5–6.6 (m, 50H, Ph), 5.2 (m, 1H,
OsCHCHCH(Ph)), 4.7 ppm (m, OsCHCHCH(Ph)); 31P{1H} NMR
(202.5 MHz, CDCl3): d = 3.9 (s, CPPh3), À3.4 (d, J(P,P) = 360.5 Hz,
OsPPh3), À7.9 ppm (d, J(P,P) = 360.5 Hz, OsPPh3); elemental anal-
ysis (%) calcd for C65H53Cl2P3Os: C 65.71, H 4.50; found: C 65.70, H
4.33.
[8] P. Barrio, M. A. Esteruelas, E. Oꢄate, J. Am. Chem. Soc. 2004,
126, 1946.
[9] B. Liu, H. Wang, H. Xie, B. Zeng, J. Chen, J. Tao, T. B. Wen, Z.
Cao, H. Xia, Angew. Chem. 2009, 121, 5538; Angew. Chem. Int.
Ed. 2009, 48, 5430.
For details of the preparation of 4, 5, 6, 7, 8, 8a, and 9, see the
Supporting Information.
[10] CCDC 796181 (3) and CCDC 796183 (9) contains the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. See the
Supporting Information for details.
[11] a) T. B. Wen, W. Y. Hung, Z. Y. Zhou, M. F. Lo, I. D. Williams, G.
Jia, Eur. J. Inorg. Chem. 2004, 2837; b) R. Castarlenas, M. A.
Esteruelas, R. Lalrempuia, M. Olivꢃn, E. Oꢄate, Organometal-
lics 2008, 27, 795.
Received: October 14, 2010
Published online: January 5, 2011
Keywords: cycloaddition · density functional calculations ·
.
metallacycles · osmium · vinylidenes
[12] a) R. Castarlenas, M. A. Esteruelas, E. Oꢄate, Organometallics
2005, 24, 4343; b) T. Bolaꢄo, R. Castarlenas, M. A. Esteruelas, E.
Oꢄate, Organometallics 2007, 26, 2037; c) R. Castarlenas, M. A.
Esteruelas, E. Oꢄate, Organometallics 2007, 26, 2129.
[13] a) M. A. Esteruelas, F. J. Fernꢃndez-Alvarez, M. Olivꢃn, E.
Oꢄate, J. Am. Chem. Soc. 2006, 128, 4596; b) L. Zhang, L. Dang,
T. B. Wen, H. H.-Y. Sung, I. D. Williams, Z. Lin, G. Jia,
Organometallics 2007, 26, 2849.
[14] a) T. B. Wen, Z. Y. Zhou, G. Jia, Angew. Chem. 2001, 113, 2005;
Angew. Chem. Int. Ed. 2001, 40, 1951; b) T. B. Wen, S. M. Ng,
W. Y. Hung, Z. Y. Zhou, M. F. Lo, L.-Y. Shek, I. D. Williams, Z.
Lin, G. Jia, J. Am. Chem. Soc. 2003, 125, 884; c) T. B. Wen, W. Y.
Hung, H. H. Y. Sung, I. D. Williams, G. Jia, J. Am. Chem. Soc.
2005, 127, 2856; d) W. Y. Hung, J. Zhu, T. B. Wen, K. P. Yu,
[1] For reviews, see: a) M. I. Bruce, Chem. Rev. 1991, 91, 197;
b) M. C. Puerta, P. Valerga, Coord. Chem. Rev. 1999, 193–195,
977; c) M. A. Esteruelas, A. M. Lꢂpez, M. Olivꢃn, Coord. Chem.
Rev. 2007, 251, 795; d) C.-M. Che, C.-M. Ho, J.-S. Huang, Coord.
Chem. Rev. 2007, 251, 2145; e) P. Dixneuf, C. Bruneau, Metal
Vinylidenes and Allenylidenes in Catalysis: From Reactivity to
Applications in Synthesis, Wiley-VCH, Weinheim, 2008.
[2] For reviews, see: a) C. Bruneau, P. H. Dixneuf, Acc. Chem. Res.
1999, 32, 311; b) H. Katayama, F. Ozawa, Coord. Chem. Rev.
2004, 248, 1703; c) H. Werner, Coord. Chem. Rev. 2004, 248,
1693; d) C. Bruneau, P. H. Dixneuf, Angew. Chem. 2006, 118,
2232; Angew. Chem. Int. Ed. 2006, 45, 2176.
[3] For examples: a) C. Slugovc, K. Mereiter, R. Schmid, K.
Kirchner, J. Am. Chem. Soc. 1998, 120, 6175; b) C. Slugovc, K.
Angew. Chem. Int. Ed. 2011, 50, 1354 –1358
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
1357

Communications
H. H. Y. Sung, I. D. Williams, Z. Lin, G. Jia, J. Am. Chem. Soc.
2006, 128, 13742.
O. Blacque, T. Fox, C. M. Frech, H. Berke, Organometallics 2009,
28, 4670.
[15] a) G. He, J. Zhu, W. Y. Hung, T. B. Wen, H. H.-Y. Sung, I. D.
Williams, Z. Lin, G. Jia, Angew. Chem. 2007, 119, 9223; Angew.
Chem. Int. Ed. 2007, 46, 9065; b) B. Liu, H. Xie, H. Wang, L. Wu,
Q. Zhao, J. Chen, T. B. Wen, Z. Cao, H. Xia, Angew. Chem. 2009,
121, 5569; Angew. Chem. Int. Ed. 2009, 48, 5461.
[16] a) M. A. Esteruelas, A. M. Lꢂpez, E. Oꢄate, Organometallics
2007, 26, 3260; b) R. Ghosh, T. J. Emge, K. Krogh-Jespersen,
A. S. Goldman, J. Am. Chem. Soc. 2008, 130, 11317; c) Y. Jiang,
[17] a) J. Yang, W. M. Jones, J. K. Dixon, N. T. Allison, J. Am. Chem.
Soc. 1995, 117, 9776; b) H.-P. Wu, S. Lanza, T. J. R. Weakley,
M. M. Haley, Organometallics 2002, 21, 2824; c) H.-P. Wu, D. H.
Ess, S. Lanza, T. J. R. Weakley, K. N. Houk, K. K. Baldridge,
M. M. Haley, Organometallics 2007, 26, 3957; d) P. M. Johns,
W. R. Roper, S. D. Woodgate, L. J. Wright, Organometallics
2010, 29, 5358.
1358
www.angewandte.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 1354 –1358