Efficient metathesis of terminal alkynes

Article abstract of DOI:10.1002/anie.201207772

Despite remarkable recent advances in the development of well-defined homogeneous catalysts for alkyne metathesis with regard to their activity, functional-group tolerance, and required reaction temperature,[1] this method is largely limited to the use of internal alkynes, RC≡CR' (R=alkyl, aryl; R'≠6 H). Commonly, methyl-capped alkynes (R'=Me) are employed,[2] resulting in the formation of RC≡CR and volatile 2-butyne, which can be removed by evaporation (b.p.=278C) or adsorption on molecular sieves (MS 5 A)[3,4] to drive these equilibrium reactions to completion.[5] In contrast, terminal alkyne metathesis (TAM) has rarely been achieved,[2c, 6] since many high-oxidation-state, Schrock-type alkylidyne complexes are known to degrade in the presence of terminal alkyne substrates. For most cases, it was suggested that deactivation occurs through deprotonation of intermediate metallacyclobutadiene species with formation of " deprotiometallacycles" (DMCs),[7, 8] which can be stabilized and made isolable by addition of donor (Don) molecules (Scheme 1).[9] These DMCs can be regarded as containing a chelating alkynylalkylidene ligand, and it was proposed that such carbene complexes are responsible for the observed high activity towards the polymerization of terminal alkynes.[8b, 10] In addition, dimerization of methylidyne complexes [HC-MX3] and formation of dimetallatetrahedrane species [X3M- (m-C2H2)MX3] should be considered as an alternative deactivation path.

Full text of DOI:10.1002/anie.201207772

Angewandte
Chemie
DOI: 10.1002/anie.201207772
Alkyne Metathesis
Efficient Metathesis of Terminal Alkynes
Birte Haberlag, Matthias Freytag, Constantin G. Daniliuc, Peter G. Jones, and Matthias Tamm*
Despite remarkable recent advances in the development of
well-defined homogeneous catalysts for alkyne metathesis
with regard to their activity, functional-group tolerance, and
required reaction temperature,[1] this method is largely
competing polymerization was observed.[8a] For 1-heptyne,
the metathesis yield could be enhanced by addition of
quinuclidine as an external ligand, and up to 80% conversion
to 6-dodecyne was observed within 1 min at 808C and
4 mol% catalyst loading.[12] Furthermore, a bimetallic com-
plex containing a hemilabile alkoxy ether ligand [W2-
(MMPO)6] (MMPO = 1-methoxy-2-methyl-2-propanolato)
gave similar results for the metathesis of 1-heptyne.[13]
We are not aware of any other reports on TAM and wish
to present herein the first catalyst capable of promoting not
only the efficient metathesis of a wide variety of terminal
alkynes, but also the unprecedented terminal ring-closing
alkyne metathesis (TRAM) of a,w-diacetylenes. The novel
catalyst was discovered during our attempts to enhance the
stability of our catalyst series, which consists of molybdenum
and tungsten benzylidyne complexes with imidazolin-2-imi-
nato,[14] phosphoraneiminato,[15] and silanolate[16] ligands.
Therefore, we aimed at the preparation of the corresponding
2,4,6-trimethylbenzylidyne complexes in a similar manner
from [Mo(CO)6] and [W(CO)6].[14a] Addition of mesityl-
lithium (MesLi) to solutions of [M(CO)6] in diethyl ether,
followed by an aqueous solution of NMe4Br, afforded the
stable acyl complexes [NMe4][(MesCO)M(CO)5] (Scheme 2).
ꢀ
limited to the use of internal alkynes, RC CR’ (R = alkyl,
aryl; R’ ¼ H). Commonly, methyl-capped alkynes (R’ = Me)
are employed,[2] resulting in the formation of RC CR and
ꢀ
volatile 2-butyne, which can be removed by evaporation
(b.p. = 278C) or adsorption on molecular sieves (MS 5 ꢀ)[3,4]
to drive these equilibrium reactions to completion.[5] In
contrast, terminal alkyne metathesis (TAM) has rarely been
achieved,[2c,6] since many high-oxidation-state, Schrock-type
alkylidyne complexes are known to degrade in the presence of
terminal alkyne substrates. For most cases, it was suggested
that deactivation occurs through deprotonation of intermedi-
ate metallacyclobutadiene species with formation of “depro-
tiometallacycles” (DMCs),[7,8] which can be stabilized and
made isolable by addition of donor (Don) molecules
(Scheme 1).[9] These DMCs can be regarded as containing
Scheme 1. Formation of deprotiometallacyclobutadienes (DMCs).
a chelating alkynylalkylidene ligand, and it was proposed that
such carbene complexes are responsible for the observed high
activity towards the polymerization of terminal alkynes.[8b,10]
ꢀ
In addition, dimerization of methylidyne complexes [HC
MX3] and formation of dimetallatetrahedrane species [X3M-
(m-C2H2)MX3] should be considered as an alternative deac-
tivation path.[2c,8a,11]
The only known examples in which TAM was promoted
by homogeneous tungsten catalysts were reported by Mor-
treux and co-workers; the neopentylidyne complex [Me3C-
ꢀ
C W(OtBu)3] was able to catalyze the metathesis of various
aliphatic alkynes such as 1-pentyne, 1-hexyne, and 1-heptyne
in diethyl ether, although only little metathesis activity and
Scheme 2. Synthesis of 2,4,6-trimethylbenzylidyne complexes.
Treatment with oxalyl bromide in CH2Cl2 at low temperature
(ꢁ908C) gave the intermediate Fischer carbyne complexes
[17]
[*] Dipl.-Chem. B. Haberlag, Dr. M. Freytag, Dr. C. G. Daniliuc,
Prof. Dr. P. G. Jones, Prof. Dr. M. Tamm
ꢀ
trans-[MesC M(CO)4Br],
which can be directly reacted
with bromine and DME at ꢁ908C to produce the tribromides
Institut fꢀr Anorganische und Analytische Chemie
Technische Universitꢁt Braunschweig
Hagenring 30, 38106 Braunschweig (Germany)
E-mail: m.tamm@tu-bs.de
[18]
ꢀ
[MesC MBr3(dme)] 1a and 1b
as orange or yellow
crystalline solids in about 80% overall yield. The molecular
structures of 1a and 1b were determined by X-ray diffraction
analyses (see the Supporting Information), clearly confirming
the expected distorted octahedral geometries with a meri-
dional arrangement of the bromine atoms.
Homepage: http://www.tu-braunschweig.de/iaac
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201207772.
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13019

.
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Communications
The reaction of the Mo complex 1a with KOC(CF3)2Me in
THF for 12 h resulted in the formation of the solvent-free
To investigate the potential of 2a and 2b as alkyne
metathesis catalysts, we first performed the homodimeriza-
tion of the test substrate 3-pentynyl benzyl ether (3), employ-
ing the molecular-sieve method to adsorb 2-butyne.[3] Thus,
toluene solutions (200 mm) of 3 (0.5 mmol), 2a/2b (1 mol%),
and molecular sieves (MS 5 ꢀ) were stirred for 60 min.
Surprisingly, full conversion to 4 was only observed for the
molybdenum catalyst 2a, whereas the tungsten congener 2b
proved completely inactive, which we tentatively ascribe to
the high electrophilicity of the latter species as already
indicated by the difficulty of solvent removal.
Therefore, all subsequent experiments were performed
exclusively with 2a. Additionally, the conversion of 3 (R =
Me) into 4 was monitored by gas chromatography (GC) in the
presence of 2a (1 mol%), and the resulting conversion versus
time diagram is shown in Figure 2. Within one minute, 93% of
the dimer had formed, and the reaction was complete within
ꢀ
complex [MesC Mo{OC(CF3)2Me}3] (2a) after evaporation
and crystallization from pentane. Related dme-free com-
ꢀ
plexes of the type [RC Mo{OC(CF3)2Me}3] (R = Me, Et, iPr,
tBu) had already been isolated by Schrock by sublimation of
the dme-containing precursors under high vacuum (10ꢁ2 mm
Hg) and at higher temperature or from the alkyne metathesis
reaction between the neopentylidyne complex [Me3C-
[7b]
ꢀ
ꢀ
C Mo{OC(CF3)2Me}3] and RC CR (R = Me, Et, iPr).
Similar tungsten complexes were only isolated as dme
adducts,[19] which is in line with our observation that the
preparation of the corresponding unsolvated tungsten com-
plex 2b turned out to be more difficult. After treatment of 1b
with LiOC(CF3)2Me in THF, evaporation afforded the ether-
ate 2b (thf)x with varying amounts of coordinated THF (x =
0.5–1), and the solvent-free complex 2b could only be
obtained after repeated crystallization from hexamethyldisi-
loxane (HMDS) at ꢁ358C, albeit in moderate yield (35%).
The 13C NMR spectra (in C6D6) of the Mo and W
complexes 2 show characteristic low-field resonances at
317.6 (2a) and 293.7 ppm (2b) for the alkylidyne carbon
atoms, which fall in the range reported for related complex-
es.[7b,19] Both structures were also confirmed by X-ray
diffraction analysis (yellow single crystals were isolated at
ꢁ358C from pentane and HMDS solution, respectively),
revealing the formation of monomeric complexes with
slightly distorted tetrahedral geometries. Since the structure
of 2b suffered from disorder of two CF3 groups (see the
Supporting Information), only the molecular structure of 2a
will be discussed below (Figure 1). As expected, a short
Figure 2. Conversion versus time diagram for the metathesis of the
benzyl ethers 3 (R=Me: 0.5 mmol; R=H: 0.25 mmol) in toluene
(R=Me: 2.5 mL; R=H: 12 mL) catalyzed by 1 mol% of 2a in the
presence of molecular sieves 5 ꢂ. The conversion was monitored by
GC using n-decane as an internal standard.
ꢀ
Mo C1 bond of 1.7438(16) ꢀ together with an almost linear
Mo-C1-C2 axis of 177.40(13)8 is observed, which is in good
agreement with the values reported for the molybdenum
ꢀ
alkylidyne complex [EtC Mo(OAd)3] (Ad = adamantyl,
1.743(3) ꢀ, 177.4(3)8).[20]
ten minutes. Thus, the initial turnover frequency (TOF) of
93 minꢁ1 exceeds even that of highly active phosphoranimi-
nato complexes (TOF = 45 minꢁ1), established under identi-
cal conditions.[15] After workup, 4 was isolated as a colorless
oil in 98% yield.
Since we routinely check new catalyst systems for their
potential to catalyze the metathesis of terminal alkynes, 2a
was tested with respect to metathesis of the corresponding 3-
butynyl ether 3 (R = H). Much to our surprise, rapid
conversion to 4 was also observed with optimum results
obtained when the reaction was performed at significantly
higher dilution (21 mm). Despite the lower substrate and
catalyst concentration, 87% conversion was achieved within
one minute, confirming the outstanding catalyst performance
in the early stage of the reaction. After 10 min, 90%
conversion was determined, and workup afforded 4 in the
same yield (Figure 2).
Similar results were obtained for the metathesis of the
functionalized 3-pentynyl (R = Me) and 3-butynyl (R = H)
benzoic esters 5 bearing various substituents in the 4-position
of the phenyl ring (5a, X = Cl; 5b, X = OMe; 5c, X = SMe).
In a typical experiment, the substrate 5 was dissolved in
Figure 1. ORTEP diagram of 2a (ellipsoids drawn at the 50% proba-
bility level). Selected bond lengths [ꢂ] and angles [8]: Mo–C1
1.7438(16), Mo–O1 1.8946(11), Mo–O2 1.9243(11), Mo–O3
1.8963(11); O1-Mo-O2 115.11(5), O1-Mo-O3 117.45(5), O2-Mo-O3
113.21(5),C1-Mo-O1 104.83(6), C1-Mo-O2 97.13(6), C1-Mo-O3
106.04(6), Mo-C1-C2 177.40(13).
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Table 2: Ring-closing metathesis of internal and terminal alkynes.
Substrate Product Yield [%]
toluene and stirred at room temperature in the presence of 2a
(1 mol%) and molecular sieves (5 ꢀ)[21] under the conditions
given in Table 1. After 30 or 60 min, the reaction mixture was
filtered through a short pad of alumina, and the solvent was
R=Me
R=H
99[a]
95[b]
Table 1: Homodimerization of internal and terminal alkynes.
98[a]
96[c]
Compound
Yield [%]
X
R=Me[a]
R=H[b]
96[a]
88[c]
a
b
c
Cl
OMe
SMe
96
96
92
89
95
91[c]
[a] Substrate (0.5 mmol), catalyst 2a (1 mol%), toluene (2.5 mL), MS
5 ꢂ (500 mg), 258C, 30 min. [b] Substrate (0.25 mmol), catalyst 2a
(1 mol%), toluene (12 mL), MS 5 ꢂ (250 mg), 258C, 60 min. [c] Sub-
strate (0.5 mmol), catalyst 2a (1 mol%), toluene (2.5 mL), MS 5 ꢂ
(500 mg), 258C, 60 min.
[a] Substrate (0.5 mmol), catalyst 2a (2 mol%), toluene (21 mm,
24 mL), MS 5 ꢂ (1 g), 258C, 1 h. [b] Substrate (0.25 mmol), catalyst 2a
(2 mol%), toluene (21 mm, 12 mL), MS 5 ꢂ (500 mg), 2 h. [c] Substrate
(0.25 mmol), catalyst 2a (2 mol%), toluene (4.5 mm, 56 mL), MS 5 ꢂ
(500 mg), 2 h.
evaporated to afford the pure diesters (6a–c) in very good
yields (89–96%). These results indicate a functional-group
tolerance similar to that of imidazolin-2-iminato and silano-
late complexes, as established by our group.[14,16] However, the
metathesis of a related isonicotinic acid pentynyl ester was
not successful, indicating that catalyst 2a might not be
compatible with strongly coordinating groups such as the
pyridine functionality.
It should emphasized that the metathesis reactions
employing terminal alkynes were again performed at signifi-
cantly higher dilution (21 mm); under these conditions no
undesired polymerization product was observed. However,
when the reaction was conducted at the concentration used
for the internal alkynes (200 mm), the diesters 6 were isolated
in lower yield (by approximately 10%), which might be
ascribed to side reactions such as polymerization. In this
context, it is important to note that the metathesis of
phenylacetylene was not successfully catalyzed by 2a, and
polymer formation was immediately observed after addition
of the catalyst to the substrate solution. The isolated red solid
was identified as poly(phenylacetylene).[22]
Encouraged by the results described above for the
homodimerization of internal and terminal alkynes, we also
attempted ring-closing alkyne metathesis (RCAM) for the
a,w-diynes 7, 9, and 11 bearing either two 3-pentynyl (R =
Me) or two 3-butynyl (R = H) groups (Table 2). The reactions
were performed in toluene solution (21 mm or 4.5 mm) with
a catalyst loading of 2 mol% in the presence of molecular
sieves for adsorption of 2-butyne or acetylene. After the
reaction mixture had been stirred for 1 h (R = Me) or 2 h
(R = H), workup afforded in all cases the cycloalkynes 8, 10,
and 12 in excellent yields, with the terminal alkynes leading to
only slightly lower yields of isolated products. To the best of
our knowledge this is the first time that TRAM has been
accomplished; the formation of a cycloalkyne in 25% yield by
ꢀ
ring-closure of the mixed terminal/internal diyne HC C-
ꢀ
ꢀ
(CH2)3O(CH2)2C CC3H7 in the presence of [Me3CC W-
(OtBu)3]·quinuclidine represents the only other related
example.[12]
The discovery that the mesityl-substituted alkylidyne
complex [MesC Mo{OC(CF3)2Me}3] (2a) catalyzes the meta-
thesis of both internal and terminal alkynes efficiently
appears to be long overdue, since the closely related neo-
pentylidyne complexes [Me3CC Mo{OC(CF3)2Me}3(dme)]
ꢀ
ꢀ
ꢀ
and its dme-free congener [Me3CC Mo{OC(CF3)2Me}3] had
been described in the 1980s by Schrock and co-workers, with
the latter complex representing “one of the best acetylene
metathesis catalysts containing molybdenum”[7b] that had
been prepared by that group. The advance presented here
relies on the introduction of the mesityl group, which
significantly facilitates the isolation of the solvent-free com-
plex 2a, and its activity in internal alkyne metathesis might
have been predictable in view of the earlier work.[7]
We assume that its additionally discovered exceptional
activity in terminal alkyne metathesis (TAM) is based on the
following factors: 1) The absence of coordinating solvents
such as dme or thf results in a highly active metal species with
tetrahedral coordination; its rate of alkyne metathesis is
significantly faster than its rate of deactivation, for example,
by formation of deprotiometallacyclobutadienes (DMC,
Scheme 1). The latter reaction is hindered in the case of 2a,
since it was clearly demonstrated that alcohol elimination and
DMC formation are favored in the presence of donor
ligands.[7,9] 2) The relatively low basicity of the hexafluoro-
tert-butanolato, OC(CF3)2Me, ligands can also be expected to
disfavor DMC formation in contrast to the reactivity
observed for complexes containing more basic alkoxides or
silanolates such as OCMe3 or OSiPh3.[8,9] 3) Performing TAM
reactions at higher dilution seems to be of critical importance,
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.
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Communications
5999 – 6005; d) M. R. Churchill, J. W. Ziller, J. Organomet.
Chem. 1985, 281, 237 – 248; e) L. G. McCullough, M. L. Liste-
mann, R. R. Schrock, M. R. Churchill, J. W. Ziller, J. Am. Chem.
Soc. 1983, 105, 6729 – 6730.
since polymerization and/or intermolecular deactivation
processes are suppressed. In this context, it should be noted
again that the metathesis of terminal aromatic alkynes is still
not possible, since rapid polymerization of phenylacetylene in
the presence of catalytic amounts of 2a was observed. Despite
this limitation, we feel that a promising catalyst system is now
available for a wider application of TAM in organic synthesis.
Moreover, 2a and related species might also be considered as
promising catalysts for nitrile–alkyne cross-metathesis
(NACM) in view of the encouraging results that were
obtained by use of related Mo and W alkylidyne species.[23]
[8] a) A. Mortreux, F. Petit, M. Petit, T. Szymanska-Buzar, J. Mol.
Catal. A 1995, 96, 95 – 105; b) A. Bray, A. Mortreux, F. Petit, M.
Petit, T. Szymanska-Buzar, J. Chem. Soc. Chem. Commun. 1993,
197 – 199.
[9] J. Heppekausen, R. Stade, A. Kondoh, G. Seidel, R. Goddard, A.
Fꢁrstner, Chem. Eur. J. 2012, 18, 10281 – 10299.
[10] A ring-expansion mechanism has also been proposed, see: S.
Sarkar, K. P. McGowan, S. Kuppuswamy, I. Ghiviriga, K. A.
Abboud, A. S. Veige, J. Am. Chem. Soc. 2012, 134, 4509 – 4512.
[11] a) M. H. Chisholm, B. K. Conroy, B. W. Eichhorn, K. Folting,
D. M. Hoffman, J. C. Huffman, N. S. Marchant, Polyhedron
1987, 6, 783 – 792; b) M. H. Chisholm, K. Folting, D. M. Hoff-
man, J. C. Huffman, J. Am. Chem. Soc. 1984, 106, 6794 – 6805.
[12] O. Coutelier, A. Mortreux, Adv. Synth. Catal. 2006, 348, 2038 –
2042.
Received: September 26, 2012
Published online: November 14, 2012
Keywords: alkyne metathesis · alkynes ·
.
molybdenum complexes · ring-closing metathesis ·
tungsten complexes
[13] O. Coutelier, G. Nowogrocki, J.-F. Paul, A. Mortreux, Adv.
Synth. Catal. 2007, 349, 2259 – 2263.
[14] a) B. Haberlag, X. Wu, K. Brandhorst, J. Grunenberg, C. G.
Daniliuc, P. G. Jones, M. Tamm, Chem. Eur. J. 2010, 16, 8868 –
8877; b) S. Beer, K. Brandhorst, C. G. Hrib, X. Wu, B. Haberlag,
J. Grunenberg, P. G. Jones, M. Tamm, Organometallics 2009, 28,
1534 – 1545; c) S. Beer, C. G. Hrib, P. G. Jones, K. Brandhorst, J.
Grunenberg, M. Tamm, Angew. Chem. 2007, 119, 9047 – 9051;
Angew. Chem. Int. Ed. 2007, 46, 8890 – 8894.
[1] a) K. Jyothish, W. Zhang, Angew. Chem. 2011, 123, 8628 – 8630;
Angew. Chem. Int. Ed. 2011, 50, 8478 – 8488; b) X. Wu, M.
Tamm, Beilstein J. Org. Chem. 2011, 7, 82 – 93; c) M. Tamm, X.
Wu, Chem. Today 2010, 28, 60 – 63; d) A. Fꢁrstner, Chem.
Commun. 2011, 47, 6505 – 6511; e) A. Fꢁrstner, Angew. Chem.,
DOI: 10.1002/ange.201204513; Angew. Chem. Int. Ed., DOI:
10.1002/anie.201204513.
[15] X. Wu, C. G. Daniliuc, C. G. Hrib, M. Tamm, J. Organomet.
Chem. 2011, 696, 4147 – 4151.
[2] a) W. Zhang, J. S. Moore, Adv. Synth. Catal. 2007, 349, 93 – 120;
b) R. R. Schrock, C. Czekelius, Adv. Synth. Catal. 2007, 349, 55 –
77; c) A. Mortreux, O. Coutelier, J. Mol. Catal. A 2006, 254, 96 –
104; d) R. R. Schrock, Chem. Commun. 2005, 2773 – 2777;
e) U. H. F. Bunz, Science 2005, 308, 216 – 217; f) R. R. Schrock,
Chem. Rev. 2002, 102, 145 – 179; g) A. Fꢁrstner, P. Davis, Chem.
Commun. 2005, 2307 – 2320; h) R. R. Schrock, A. Hoveyda,
Angew. Chem. 2003, 115, 4740 – 4782; Angew. Chem. Int. Ed.
2003, 42, 4592 – 4633; i) A. Fꢁrstner in Handbook of Metathesis,
Vol. 2 (Ed.: R. Grubbs), Wiley-VCH, Weinheim, 2003, pp. 432 –
462; j) R. R. Schrock in Handbook of Metathesis, Vol. 1 (Ed.: R.
Grubbs), Wiley-VCH, Weinheim, 2003, pp. 173 – 189.
[16] S. Lysenko, B. Haberlag, C. G. Daniliuc, P. G. Jones, M. Tamm,
ChemCatChem 2011, 3, 115 – 118.
[17] a) E. O. Fischer, A. Schwanzer, H. Fischer, D. Neugebauer, G.
Huttner, Chem. Ber. 1977, 110, 53 – 66; b) E. O. Fischer, G. Kreis,
Chem. Ber. 1976, 109, 1673 – 1683.
[18] F. Furno, T. Fox, H. W. Schmalle, H. Berke, Organometallics
2000, 19, 3620 – 3630.
[19] a) J. H. Freudenberger, R. R. Schrock, M. R. Churchill, A. L.
Rheingold, J. W. Ziller, Organometallics 1984, 3, 1563 – 1573;
b) L. G. McCullough, R. R. Schrock, J. Am. Chem. Soc. 1984,
106, 4067 – 4068.
[20] Y.-C. Tsai, P. L. Diaconescu, C. C. Cummins, Organometallics
2000, 19, 5260 – 5262.
[21] The use of molecular sieves with smaller pore size (3 and 4 ꢀ)
proved inferior to the use of MS 5 ꢀ and usually led to
incomplete substrate conversion.
[3] J. Heppekausen, R. Stade, R. Goddard, A. Fꢁrstner, J. Am.
Chem. Soc. 2010, 132, 11045 – 11057.
[4] The possibility of conducting catalytic alkyne metathesis in the
presence of molecular sieves had been previously addressed,
although 4 ꢀ MS were used, see: a) V. Huc, R. Weihofen, I.
Martin-Jimenez, P. Ouliꢂ, C. Lepetit, G. Lavigne, R. Chauvin,
New J. Chem. 2003, 27, 1412 – 1414; b) V. Maraval, C. Lepetit,
A.-M. Caminade, J.-P. Majoral, R. Chauvin, Tetrahedron Lett.
2006, 47, 2155 – 2159.
[5] It is also possible to perform precipitation-driven alkyne meta-
thesis, see: a) W. Zhang, J. S. Moore, J. Am. Chem. Soc. 2005,
127, 11863 – 11870; b) W. Zhang, M. Brombosz, J. L. Mendoza,
J. S. Moore, J. Org. Chem. 2005, 70, 10198 – 10201; c) W. Zhang,
J. S. Moore, J. Am. Chem. Soc. 2004, 126, 12796.
[6] M. Sauthier, P. Zinck, A. Mortreux, C. R. Chim. 2010, 13, 304 –
314.
[7] a) J. H. Freudenberger, R. R. Schrock, Organometallics 1986, 5,
1411 – 1417; b) L. G. McCullough, R. R. Schrock, J. C. Dewan,
J. C. Murdzek, J. Am. Chem. Soc. 1985, 107, 5987 – 5998; c) H.
Strutz, J. C. Dewan, R. R. Schrock, J. Am. Chem. Soc. 1985, 107,
[22] Mw = 55.693 gmolꢁ1; Mw/Mn = 1.69; elemental analysis (%): C
92.69, H 6.32; 1H NMR (300 MHz, CDCl3, 258C): d = 5.77 (CH),
6.88 (Ar-CH), 7.08 ppm (Ar-CH), see Ref. [10] for comparison.
[23] a) A. M. Geyer, M. J. Holland, R. L. Gdula, J. E. Goodman,
M. J. A. Johnson, J. W. Kampf, J. Organomet. Chem. 2012, 708 –
709, 1 – 9; b) E. S. Wiedner, K. J. Gallagher, M. J. A. Johnson,
J. W. Kampf, Inorg. Chem. 2011, 50, 5936 – 5945; c) A. M. Geyer,
E. S. Wiedner, J. B. Gary, R. L. Gdula, N. C. Kuhlmann, M. A.
Johnson, B. D. Dunietz, J. W. Kampf, J. Am. Chem. Soc. 2008,
130, 8984 – 8999; d) A. M. Geyer, R. L. Gdula, E. S. Wiedner,
M. J. A. Johnson, J. Am. Chem. Soc. 2007, 129, 3800 – 3801;
e) R. L. Gdula, M. J. A. Johnson, J. Am. Chem. Soc. 2006, 128,
9614 – 9615; f) R. L. Gdula, M. J. A. Johnson, N. W. Ockwig,
Inorg. Chem. 2005, 44, 9140 – 9142.
13022 www.angewandte.org
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