Efficient catalytic alkyne metathesis with a fluoroalkoxy-supported ditungsten(III) complex

Article abstract of DOI:10.3762/bjoc.14.220

The molybdenum and tungsten complexes M₂(OR)₆ (Mo2F6, M = Mo, R = C(CF₃)₂Me; W2F3, M = W, R = OC(CF₃)Me₂) were synthesized as bimetallic congeners of the highly active alkyne metathesis catalysts [MesC-M{OC(CF₃)_nMe_3-n}] (MoF6, M = Mo, n = 2; WF3, M = W, n = 1; Mes = 2,4,6-trimethylphenyl). The corresponding benzylidyne complex [PhC-W{OC(CF₃)Me2}] (W^PhF3) was prepared by cleaving the W-W bond in W2F3 with 1-phenyl-1-propyne. The catalytic alkyne metathesis activity of these metal complexes was determined in the self-metathesis, ring-closing alkyne metathesis and cross-metathesis of internal and terminal alkynes, revealing an almost equally high metathesis activity for the bimetallic tungsten complex W2F3 and the alkylidyne complex W^PhF3. In contrast, Mo2F6 displayed no significant activity in alkyne metathesis.

Full text of DOI:10.3762/bjoc.14.220

Efficient catalytic alkyne metathesis with a
fluoroalkoxy-supported ditungsten(III) complex
Henrike Ehrhorn, Janin Schlösser, Dirk Bockfeld and Matthias Tamm*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2018, 14, 2425–2434.
Institut für Anorganische und Analytische Chemie, Technische
Universität Braunschweig, Hagenring 30, 38106 Braunschweig,
Germany
doi:10.3762/bjoc.14.220
Received: 25 June 2018
Accepted: 27 August 2018
Published: 18 September 2018
Email:
Matthias Tamm* - m.tamm@tu-bs.de
This article is part of the thematic issue "Progress in metathesis chemistry
III".
* Corresponding author
Keywords:
Guest Editor: K. Grela
alkylidyne complexes; alkyne metathesis; catalysis; terminal alkynes;
tungsten
© 2018 Ehrhorn et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Abstract
The molybdenum and tungsten complexes M2(OR)6 (Mo2F6, M = Mo, R = C(CF3)2Me; W2F3, M = W, R = OC(CF3)Me2) were
synthesized as bimetallic congeners of the highly active alkyne metathesis catalysts [MesC≡M{OC(CF3)nMe3−n}] (MoF6,
M = Mo, n = 2; WF3, M = W, n = 1; Mes = 2,4,6-trimethylphenyl). The corresponding benzylidyne complex
[PhC≡W{OC(CF3)Me2}] (WPhF3) was prepared by cleaving the W≡W bond in W2F3 with 1-phenyl-1-propyne. The catalytic
alkyne metathesis activity of these metal complexes was determined in the self-metathesis, ring-closing alkyne metathesis and
cross-metathesis of internal and terminal alkynes, revealing an almost equally high metathesis activity for the bimetallic tungsten
complex W2F3 and the alkylidyne complex WPhF3. In contrast, Mo2F6 displayed no significant activity in alkyne metathesis.
Introduction
While the field of olefin metathesis has seen significant The contributions from our group to the development of alkyne
progress in the past decades [1-5], the synthetic potential of metathesis catalysts were initially based on a design strategy
alkyne metathesis has been growing only recently [6-11]. inspired by the structure of highly active olefin metathesis cata-
Alkyne metathesis represents a transition-metal-catalyzed trans- lysts, the Schrock-type molybdenum and tungsten alkylidene
formation in which carbon–carbon triple bonds are cleaved and complexes [13-15]. Imidazolin-2-iminato ligands were used to
formed under mild conditions via metallacyclobutadiene modify Schrock-type alkylidyne complexes, resulting in new
(MCBD) intermediates [12]. Ongoing progress in the develop- active alkyne metathesis catalysts such as I (Figure 1) [16-20].
ment of highly active homogeneous alkyne metathesis catalysts Initially, the neopentylidyne tungsten complex was synthesized
(Figure 1) has increased the value of this method in natural via the conventional “high-oxidation-state route” developed by
product and materials chemistry.
R. R. Schrock [16,17,21,22]; later, the “low-oxidation-state
2425

Beilstein J. Org. Chem. 2018, 14, 2425–2434.
Figure 1: Selected homogeneous catalysts for alkyne metathesis.
route”, starting from M(CO)6 (M = Mo, W), was employed, vantageous for the catalytic activity, since the removal of
which gave rise to the corresponding molybdenum and tung- coordinating solvents like THF or DME was facilitated [49].
sten benzylidyne complexes [18-20].
The molybdenum 2,4,6-trimethylbenzylidyne complex
[MesC≡Mo{OC(CF3)2Me}3] (Figure 1, MoF6) represents the
In addition to these, several well-defined alkylidyne complexes first alkyne metathesis catalyst capable of effective and highly
have been developed and successfully utilized in alkyne metath- selective terminal alkyne metathesis [49,51-53]. Later, a study
esis in the past decade. The molybdenum alkylidyne complex was conducted to determine the optimum degree of fluorination
with triphenylsiloxide ligands (type II) introduced by of the alkoxide ligands for tungsten alkylidyne complexes
A. Fürstner and co–workers is frequently used in the total syn- [53,54]. It was found that the tungsten alkylidyne complex
thesis of natural products [23-27]. A unique catalytic reactivity [MesC≡W{OC(CF3)Me2}3] (Figure 1, WF3) showed excellent
towards conjugated diynes was observed for the tungsten catalytic performance not only in the metathesis of internal but
benzylidyne complex with OSi(Ot-Bu)3 ligands (type III) [28- also, for the first time with the metal tungsten, terminal alkynes
30]. The catalyst III, which is capable of promoting conven- at room temperature [54]. Our studies clearly display a strong
tional alkyne metathesis [19], also proved to be highly active in dependency of the catalytic alkyne metathesis activity on the
the cross metathesis of symmetric 1,3-butadiynes to form un- metal-alkoxide combination. The electrophilicity of the metal
symmetrically substituted 1,3-butadiynes [30]. W. Zhang and sites can be controlled by the number of fluorine atoms of the
his group introduced several multidentate phenoxide ligands to ancillary fluoroalkoxide ligands [55-57]. The difference in the
molybdenum propylidyne precursors to form chelate com- optimum degree of fluorination for molybdenum and tungsten is
plexes of type IV [31-34]. These catalysts were especially suc- rationalized by the increased intrinsic electrophilicity of tung-
cessful in the construction of supramolecular materials such as sten compared to molybdenum [56].
ethynylene-linked polymers [11,35], porous networks [36] and
molecular cages [37-43]. Furthermore, living ring-opening Based on these insights into the structure–activity relationship
alkyne metathesis polymerization (ROAMP) has been intensely of alkyne metathesis catalysts, we wanted to establish an alter-
studied for different molybdenum alkylidyne complexes by the native and convenient access to highly active catalysts. Herein,
group of F. R. Fischer, who was able to monitor the influence of we report the systematic study on the metathesis performance of
both the alkylidyne moiety as well as the ancillary ligands [44- bimetallic hexaalkoxide complexes M2(OR)6 (M = Mo,
48].
R = OC(CF3)2Me, Mo2F6; M = W, R = OC(CF3)Me2, W2F3),
which draw upon the most catalytically active alkylidyne com-
More recently, we expanded the “low-oxidation-state route” to plexes MoF6 and WF3. R. R. Schrock synthesized the first
the synthesis of 2,4,6-trimethylbenzylidyne complexes of alkylidyne complex which was able to undergo alkyne metathe-
molybdenum and tungsten [18,49,50], which led to an in- sis, [t-BuC≡W(Ot-Bu)3] (V), originally from [NEt4][t-
creased steric demand at the metal center. This proved to be ad- BuC≡WCl4] [22,58-61]. Subsequently, he reported a protocol
2426

Beilstein J. Org. Chem. 2018, 14, 2425–2434.
to synthesize the alkylidyne complex V by a stoichiometric ture [61]. Thereby, the self-metathesis yield of 1-heptyne could
alkyne metathesis reaction of the ditungsten complex be increased to 80% at elevated temperatures. Based on this ap-
[(t-BuO)3W≡W(Ot-Bu)3] with MeC≡Ct-Bu (Scheme 1) [62]. proach, the dinuclear tungsten complex [W2(MMPO)6] (VI,
Even though Schrock’s catalyst V was the most established MMPO = 1-methoxy-2-methylpropan-2-ol) was isolated which
alkyne metathesis catalyst for many years [63,64], it does not catalyzed alkyne metathesis of 1-heptyne at elevated tempera-
promote terminal alkyne metathesis efficiently and leads to po- tures [68] and to date represents the only well-defined ditung-
lymerization initiated by intermediate deprotiometallacyclobu- sten complex which has been successfully used in alkyne me-
tadiene species [55,60,61,65-67]. Moreover, the bimetallic tathesis.
[(t-BuO)3W≡W(Ot-Bu)3] complex has not been directly em-
ployed in catalytic alkyne metathesis.
The organometallic chemistry of the M2X6 complexes (X = R
(alkyl), NR2, OR) with metal-metal triple bonds (M = Mo, W)
has attracted attention for many years (mainly during the 70s,
80s and 90s) [69]. A plethora of dinuclear compounds has been
published [70-78], and detailed studies on their reactivity have
been conducted [79-85]. Therefore, the reactivity of ditungsten
complexes towards alkynes has been known for quite some
time. The metal–metal triple bond of many ditungsten com-
plexes can be cleaved by alkynes in a metathesis-like reaction to
form the corresponding alkylidyne complexes [62,86]. Dinu-
clear Mo≡Mo complexes, however, have not yet been cleaved
efficiently by alkynes [87].
Results and Discussion
Complex synthesis
The dimeric molybdenum complex [Mo2Cl6(dme)2]
(dme = 1,2-dimethoxyethane) serves as an excellent starting
material for compounds of the type Mo2X6 (X = alkyl,
alkoxide) [73]. The desired hexakis(fluoroalkoxide) dimer
Scheme 1: Synthesis of alkylidyne complex V from bimetallic
[(t-BuO)3W≡W(Ot-Bu)3]; the catalytically active ditungsten complex
[W2(MMPO)6] (VI, MMPO = 1-methoxy-2-methylpropan-2-ol) [68].
A. Mortreux and his group found that the alkyne metathesis [Mo2{OC(CF3)2Me}6] (Mo2F6) was first isolated by D. Rogers
selectivity of Schrock’s original catalyst V can be enhanced by and his group by salt metathesis of [Mo2Cl6(dme)2] with
adding an external ligand like quinuclidine to the reaction mix- 6 equiv of NaOC(CF3)2Me (Scheme 2) [73]. This reaction
Scheme 2: Synthesis of hexakis(fluoroalkoxide) dimers Mo2F6 [73] and W2F3.
2427

Beilstein J. Org. Chem. 2018, 14, 2425–2434.
affords a red, sparingly soluble complex in moderate yield
(28%).
T h e b i m e t a l l i c t u n g s t e n a n a l o g u e t o W F 3 ,
[W2{OC(CF3)Me2}6] (W2F3), can be prepared by the reaction
of [NaW2Cl7(THF)5] with 6 equiv of NaOC(CF3)Me2 [86], but
this procedure requires one equivalent of toxic sodium
amalgam. Therefore, we decided to attempt the protonolysis of
hexakis(dimethylamido)ditungsten [W2(NMe2)6] with the
alcohol HOC(CF3)Me2 [71,88], which has been described very
briefly in the literature [89]. [W2(NMe2)6] is easily accessible
from WCl4 and LiNMe2 and has emerged as an important
starting material for various dinuclear tungsten compounds [90].
M. H. Chisholm and co-workers used 6 equiv of the free
alcohol to exchange the amide ligands and isolated the
bis(dimethylamino) adduct of the ditungsten complex [89]. The
amine ligands were liberated under reduced pressure and at
elevated temperature. However, in our hands, an excess of
HOC(CF3)Me2 was required to drive the reaction to
completion and led to the formation of the complex
[W2{OC(CF3)Me2}6(NHMe2)] (W2F3·NHMe2) (Scheme 2).
Figure 2: Molecular structure of W2F3·NHMe2 with thermal displace-
ment parameters drawn at 50% probability. Hydrogen atoms are
omitted for clarity.
The additional amine ligand stems from the protonolysis reac- negative NMe2 ligand and indicates a weak bond between
tion of the amide with the fluorinated alcohol. Brown crystals the tungsten and the nitrogen atom. Coordination of the
suitable for X-ray diffraction analysis were isolated from a satu- NHMe2 ligand to W1 affords markedly longer W1–O bonds
rated pentane solution at −40 °C. The molecular structure of this (1. 905(2)–1. 970(2) Å) than the W2–O bonds
complex was established by X-ray diffraction analysis. The (1.818(2)–1.930(2) Å). The W1 atom is coordinated in an
ORTEP diagram is shown in Figure 2, and selected bond almost square-pyramidal fashion (τ5 = 0.25) [92] while the W2
lengths and angles are displayed in Table 1.
atom adopts a nearly tetrahedral geometry (τ4 = 0.89) [93],
which is usually observed in X3W≡WX3 complexes [72,83,94].
The tungsten–tungsten triple bond of 2.3452(2) Å falls in the The coordination of one amine ligand after the protonolysis of
range of previously reported bond lengths of this type [69]. For the amide ligands in [W2(NMe2)6] has been observed before,
example, the W≡W distance in [W2{OC(CF3)2Me}]6 is e.g., in [W2(OAr)6(HNMe2)] (Ar = 3,5-dimethylphenoxide)
2.309(3) Å [78], 2.430(8) Å in [W2(MMPO)6] [68], and [95].
2.332(1) Å in [W2(OCHMe2)6(py)2] (py = pyridine) [90]. The
W1–N bond length of 2.270(3) Å is longer compared to the Complex W2F3·NHMe2 appeared to be rather unstable espe-
W–N distances in [W2(NMe2)6] (1.95(2)–1.99(2) Å) [71] and cially in hexane and pentane solutions. Over a period of 24 h, a
[W2Cl2(NMe2)4] (1.935(8)–1.937(9) Å) [91]. This is attributed color change from brown to bright red occurred in solution.
to the neutral nature of the NHMe2 ligand compared to the This observation indicates the loss of the additional amine
Table 1: Selected bond lengths [Å] and angles [°]:
Bond
Bond length [Å]
Bond angle
Angle [°]
Bond angle
Angle [°]
W1–W2
W1–O1
W1–O2
W1–O3
W1–N
2.3452(2)
1.905(2)
1.911(3)
1.970(2)
2.270(3)
1.930(2)
1.818(2)
1.872(2)
O1–W1–O2
O1–W1–O3
O2–W1–O3
O1–W1–N
O2–W1–N
O3–W1–N
O6–W2–O5
O6–W2–O4
93.75(11)
145.01(10)
91.61(11)
82.15(11)
159.81(11)
81.06(11)
110.53(11)
112.06(11)
O5-W2-O4
O1–W1–W2
O2–W1–W2
O3–W1–W2
N–W1–W2
O4–W2–W1
O5–W2–W1
O6–W2–W1
122.91(11)
104.75(8)
108.97(8)
106.06(7)
91.17(8)
W2–O4
W2–O5
W2–O6
98.33(7
99.29(7)
111.85(8)
2428

Beilstein J. Org. Chem. 2018, 14, 2425–2434.
ligand, and after recrystallization from pentane at −25 °C, the conversion observed after 28 minutes. Selected 19F NMR spec-
red complex W2F3 was isolated. The 1H NMR spectrum tra can be found in Figure S7 of Supporting Information File 1.
reveals the only expected signal at 1.51 ppm, which is in line
with the previously reported values, where W2F3 had been pre- The 1H NMR spectrum of WPhF3 displays two multiplets in the
pared from [NaW2Cl7(THF)5] [86]. The 13C and 19F NMR aromatic region for the benzylidyne hydrogen atoms and one
spectra are also consistent with literature values. Crystals of singlet for the methyl groups of the trifluoro-tert-butoxy ligand
W2F3 suitable for X-ray diffraction analysis were obtained at 1.65 ppm. In the 13C NMR spectrum, the signal of the
upon cooling a saturated pentane solution to −40 °C. Unfortu- carbyne carbon atom can be found at 266.9 ppm, which is in the
nately, the crystal structure suffers from severe disorder. Each range typically observed for RC≡W moieties [16-18,49,50,54].
tungsten atom is disordered over four positions, and additional- The 19F NMR spectrum only exhibits one singlet for the com-
ly, the alkoxide ligands are also disordered (for more details, plex with a chemical shift of −82.4 ppm. Crystals suitable for
see Supporting Information File 1). Therefore, the crystal struc- X-ray diffraction analysis were isolated from a saturated
ture only confirms the connectivity and does not allow the pentane solution at −40 °C; again, the crystal structure suffers
discussion of bond lengths and angles. This disorder pattern has from crystallographic problems: one alkoxide ligand is refined
been reported repeatedly for molybdenum and tungsten on two positions, while another one is refined on three posi-
hexaalkoxides and silanolates [73,78,83,96-98]. An ORTEP tions. The crystal structure, which is displayed in Figure 3, only
diagram of W2F3 is displayed in Supporting Information File 1 confirms the connectivity of this molecule, and discussion of
(Scheme S13).
any bond length is not meaningful (for more details, see Sup-
porting Information File 1). A similar crystal structure with the
As stated above, R. R. Schrock could generate alkyne metathe- 2,4,6-trimethylbenzylidyne moiety at the tungsten atom, which
sis catalysts of type V (Scheme 1) from the corresponding does not exhibit disorder, has been reported previously [54].
bimetallic complex [62,99]. Thus, we attempted the cleavage of
the M≡M bond of Mo2F6 and W2F3 by an alkyne to generate
the corresponding benzylidyne complexes. Unfortunately, as re-
ported in the past by Schrock [62,87], we could not achieve the
selective cleavage of the triple bond in Mo2F6 by internal or
terminal alkynes to isolate the corresponding alkylidyne com-
plex. In an NMR study on the cleavage of the Mo≡Mo triple
bond, in which Mo2F6 was treated with two equivalents of
1-phenyl-1-propyne, no signals corresponding to a possible
molybdenum alkylidyne complex were detected in the 1H and
19F NMR spectra over a period of three days.
In contrast, the reaction of the bimetallic tungsten complex
W2F3 with two equivalents of 1-phenyl-1-propyne in toluene
afforded the light yellow benzylidyne complex WPhF3
(Scheme 3) in satisfactory yield after recrystallization from
n-pentane. In a metathesis-like reaction, the W≡W bond is
cleaved, with 2-butyne forming as a side product. Following
this reaction by 1H and 19F NMR spectroscopy revealed fast
and selective formation of WPhF3, and after 14 minutes, most
of the starting material W2F3 was already consumed, with full
Figure 3: Molecular structure of WPhF3 with thermal displacement pa-
rameters drawn at 50% probability. Hydrogen atoms and minor compo-
nents of the disordered OC(CF3)Me2 groups are omitted for clarity.
Catalytic studies
With the bimetallic complexes Mo2F6 and W2F3 and the new
alkylidyne complex WPhF3 at hand, we aimed at systemati-
cally investigating the catalytic activity of those complexes.
Even though we failed in selectively cleaving the Mo≡Mo triple
bond, we attempted catalytic alkyne metathesis with Mo2F6.
Interestingly, a marginal catalytic activity could be detected for
complex Mo2F6: over the course of four days, the dimolyb-
Scheme 3: Preparation of the alkylidyne complex WPhF3.
2429

Beilstein J. Org. Chem. 2018, 14, 2425–2434.
denum complex achieved a conversion of 70% in the self-me-
tathesis of the standard substrate 3-pentynyl benzyl ether in tol-
uene in the presence of molecular sieves (MS 5 Å) as 2-butyne
scavenger. The conversion versus time diagram (Supporting
Information File 1, Figure S8) exhibits a sigmoidal curve
progression, which indicates the slow formation of a catalytical-
ly active species, presumably an alkylidyne complex, despite
our inability to monitor the formation of such a species by
NMR spectroscopy. We attribute the poor catalytic perfor-
mance of Mo2F6 to the low solubility in all common solvents
[73], since most of the compound still remained undissolved in
the reaction mixture after four days. However, all efforts to op-
timize the metathesis conditions and to achieve higher conver-
sions failed. Attempts to increase the solubility of Mo2F6 in
toluene by performing the metathesis reaction at 60 °C led to no
detectable conversion of the starting material. Furthermore, ca-
talysis in CH2Cl2 afforded even lower conversions compared to
toluene, while the metathesis failed completely in diethyl ether.
Figure 4: Conversion versus time diagram for the self-metathesis of
1-phenyl-1-propyne catalyzed by 0.5 mol % W2F3 (grey) and 1 mol %
WPhF3 (black).
For the potential tungsten catalysts, toluene solutions of
1-phenyl-1-propyne were treated with W2F3 (0.5 mol %) and cies were calculated from the conversion of 1-phenyl-1-propyne
WPhF3 (1 mol %) and stirred in the presence of molecular after one minute (TOF1min). The TOF of the alkylidyne com-
sieves (MS 5 Å) as 2-butyne scavenger and n-decane as internal plex WPhF3 reaches 78 min−1 (1.30 s−1), while W2F3 has a
standard at room temperature (Scheme 4). The catalysis was significantly lower TOF of 13 min−1 (0.21 s−1) after one
initially monitored over time through gas chromatography, minute; this value is based on the formation of two catalytically
affording the conversion versus time diagram depicted in active alkylidyne species upon treatment with the alkyne sub-
Figure 4.
strate. After 10 minutes, the alkylidyne complex WPhF3 has
accomplished nearly full conversion and after 20 minutes, cata-
lyst W2F3 achieves the same conversion of the starting materi-
al. The maximum conversion of around 97% is reached for both
catalysts within 60 minutes. Accordingly, we aimed at further
monitoring the substrate scope of the complexes including the
metathesis of terminal alkynes as well as ring-closing alkyne
metathesis (RCAM).
Table 2 summarizes the isolated yields for various self-metathe-
sis and RCAM reactions. These findings are in line with our
initial results regarding the conversion of 1-phenyl-1-propyne
(Table 2, entry 1). Both tungsten complexes afforded excellent
yields in the metathesis of different para-substituted phenyl-
propynes (Table 2, entries 2–4). For both catalysts, the yields
are identical within the error of the experiment. Furthermore,
Scheme 4: Self-metathesis of 1-phenyl-1-propyne derivatives by tung-
sten complexes W2F3 and WPhF3.
Figure 4 clearly shows that both tungsten complexes are active the well-established substrates 3-pentynyl (R = Me) and
in the metathesis of 1-phenyl-1-propyne, with the bimetallic 3-butynyl (R = H) benzyl ether (Table 2, entry 5) and
compound W2F3 (grey) showing a slower initiation rate com- 3-pentynyl (R = Me) and 3-butynyl (R = H) benzyl ester
pared to the alkylidyne complex WPhF3. For the bimetallic (Table 2, entry 6) afforded good isolated yields. The bimetallic
complex W2F3, an additional initiation step is required, in complex W2F3 is even capable of metathesizing terminal
which the W≡W triple bond is cleaved and catalytically active alkynes at room temperature and performs in the same manner
alkylidyne species are formed. Therefore, the conversion of the as the alkylidyne complex WPhF3. Additional conversion
substrate with catalyst W2F3 is significantly slower at the versus time diagrams are displayed in Figures S9 and S10 in
beginning of the reaction. The initial catalyst turnover frequen- Supporting Information File 1. Finally, the ditungsten catalyst
2430

Beilstein J. Org. Chem. 2018, 14, 2425–2434.
Table 2: Alkyne metathesis of different substrates.a
Entry
Substrate
Product
Cat.
R
Yield [%]
W2F3
WPhF3
96
95
1
2
3
4
W2F3
WPhF3
95
96
W2F3
WPhF3
94
97
W2F3
WPhF3
98
97
R = Me
R = H
96
88
W2F3
WPhF3
W2F3
5
6
R = Me
R = H
94
88
R = Me
R = H
93
79
R = Me
R = H
94
72
WPhF3
W2F3
WPhF3
86
84
7
8
W2F3
WPhF3
93
96
aSelf-metathesis: substrate (0.5 mmol), catalyst (0.5 mol % W2F3; 1 mol % WPhF3), toluene (internal alkynes: 2.5 mL, 200 mM; terminal alkynes:
24 mL, 21 mM), MS 5 Å (500 mg), 25 °C, 2 h. RCAM: substrate (0.5 mmol), catalyst (1 mol % W2F3; 2 mol % WPhF3), toluene (24 mL, 21 mM),
MS 5 Å (1.0 g), 25 °C, 2 h.
W2F3 was also employed in alkyne cross-metathesis (ACM), a Conclusion
reaction which is of large interest for the application of alkyne Previously, we have reported the optimum level of fluorination
metathesis, but often leads to product mixtures. Therefore, (tri- in MoF6 and WF3 as the most catalytically active alkylidyne
methylsilyl)propyne and (trimethylsilyl)acetylene were chosen complexes [54]. Thus, we intended to study the catalytic activi-
as reaction partners in ACM, since this reaction proved to be ty of the well-known bimetallic molybdenum and tungsten com-
quite efficient in the past [25,54,100]. A toluene solution of plexes bearing the same fluoroalkoxide ligands. Indeed, W2F3
both substrates (1:2 ratio, TMS–alkyne in excess) was charged as the bimetallic analogue to mononuclear WF3 is highly active
with the catalyst W2F3 (0.5–1 mol %) in the presence of mo- in the metathesis of internal and even terminal alkynes and also
lecular sieves 5 Å and stirred for two hours at room tempera- promotes alkyne cross-metathesis efficiently. The Mo2F6 com-
ture. The isolated yields of the ACM are summarized in plex, however, does not exhibit satisfactory alkyne metathesis
Table 3. The depicted reactions selectively afforded the unsym- activity, which we attribute to its low solubility. Furthermore,
metrical alkynes, corroborating that the bimetallic tungsten the corresponding mononuclear benzylidyne complex WPhF3 is
complex W2F3 is able to introduce a trimethylsilyl protecting easily accessible from the dinuclear W2F3 complex and
group to alkynes.
performs equally well compared to the latter.
2431

Beilstein J. Org. Chem. 2018, 14, 2425–2434.
Table 3: Alkyne cross metathesis (ACM) with catalyst W2F3.a
Entry
1
Substrates
Product
Cat.
Yield [%]
87
0.5 mol %
2
3
1 mol %
82
93
0.5 mol %
4
0.5 mol %
92
aSubstrate (0.5 mmol), TMS-propyne or TMS-acetylene (1 mmol), toluene (internal alkynes: 2.5 mL, terminal alkynes: 24 mL), MS 5 Å (500 mg),
25 °C, 2 h.
References
1. Fürstner, A. Angew. Chem., Int. Ed. 2000, 39, 3012–3043.
The finding that W2F3 is a highly active alkyne metathesis pre-
catalyst and does not have to be converted into an alkylidyne
doi:10.1002/1521-3773(20000901)39:17<3012::aid-anie3012>3.3.co;
species prior to catalysis could be beneficial for future applica-
2-7
tions of alkyne metathesis since this protocol represents a con-
2. Connon, S. J.; Blechert, S. Angew. Chem., Int. Ed. 2003, 42,
venient approach to alkyne metathesis catalysts in two steps
1900–1923. doi:10.1002/anie.200200556
starting from WCl4.
3. Grela, K. Olefin Metathesis; John Wiley & Sons: Hoboken, NJ, U.S.A.,
2014. doi:10.1002/9781118711613
4. Hoveyda, A. H.; Zhugralin, A. R. Nature 2007, 450, 243–251.
Supporting Information
doi:10.1038/nature06351
5. Grubbs, R. H.; Wenzel, A. G.; O'Leary, D. J.; Khosravi, E., Eds.
CCDC 1850924−1850926 contain the supplementary
crystallographic data for this paper. These data can be
obtained free of charge via
Handbook of Metathesis; Wiley-VCH Verlag GmbH: Weinheim,
Germany, 2015. doi:10.1002/9783527674107
6. Fürstner, A.; Davies, P. W. Chem. Commun. 2005, 2307–2320.
doi:10.1039/b419143a
http://www.ccdc.cam.ac.uk/data_request/cif.
7. Mortreux, A.; Coutelier, O. J. Mol. Catal. A: Chem. 2006, 254, 96–104.
doi:10.1016/j.molcata.2006.03.054
Supporting Information File 1
8. Zhang, W.; Moore, J. S. Adv. Synth. Catal. 2007, 349, 93–120.
doi:10.1002/adsc.200600476
Experimental section, NMR spectra, catalysis procedure
and product characterization, crystallographic details for
W2F3·(NHMe2), W2F3 and WPhF3.
9. Wu, X.; Tamm, M. Beilstein J. Org. Chem. 2011, 7, 82–93.
doi:10.3762/bjoc.7.12
10. Fürstner, A. Angew. Chem., Int. Ed. 2013, 52, 2794–2819.
doi:10.1002/anie.201204513
[https://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-14-220-S1.pdf]
11. Yang, H.; Jin, Y.; Du, Y.; Zhang, W. J. Mater. Chem. A 2014, 2,
5986–5993. doi:10.1039/c3ta14227b
12. Katz, T. J.; McGinnis, J. J. Am. Chem. Soc. 1975, 97, 1592–1594.
doi:10.1021/ja00839a063
Acknowledgements
13. Schrock, R. R.; Hoveyda, A. H. Angew. Chem., Int. Ed. 2003, 42,
4592–4633. doi:10.1002/anie.200300576
H.E. wishes to thank the Fonds der Chemischen Industrie (FCI)
for a Chemiefonds Fellowship. This work was funded by the
Deutsche Forschungsgemeinschaft (DFG) through project TA
189/12−1 (“Mechanistic studies on the catalytic metathesis of
internal and terminal alkynes and diynes”). The authors wish to
thank Dr. M. Freytag for the crystal structure determination of
W2F3·(NHMe2).
14. Schrock, R. R.; Czekelius, C. Adv. Synth. Catal. 2007, 349, 55–77.
doi:10.1002/adsc.200600459
15. Cortez, G. A.; Schrock, R. R.; Hoveyda, A. H. Angew. Chem., Int. Ed.
2007, 46, 4534–4538. doi:10.1002/anie.200605130
16. Beer, S.; Hrib, C. G.; Jones, P. G.; Brandhorst, K.; Grunenberg, J.;
Tamm, M. Angew. Chem., Int. Ed. 2007, 46, 8890–8894.
doi:10.1002/anie.200703184
17. Beer, S.; Brandhorst, K.; Hrib, C. G.; Wu, X.; Haberlag, B.;
Grunenberg, J.; Jones, P. G.; Tamm, M. Organometallics 2009, 28,
1534–1545. doi:10.1021/om801119t
ORCID® iDs
Dirk Bockfeld - https://orcid.org/0000-0003-1084-8577
Matthias Tamm - https://orcid.org/0000-0002-5364-0357
2432

Beilstein J. Org. Chem. 2018, 14, 2425–2434.
18. Haberlag, B.; Wu, X.; Brandhorst, K.; Grunenberg, J.; Daniliuc, C. G.;
Jones, P. G.; Tamm, M. Chem. – Eur. J. 2010, 16, 8868–8877.
doi:10.1002/chem.201000597
42. Ortiz, M.; Cho, S.; Niklas, J.; Kim, S.; Poluektov, O. G.; Zhang, W.;
Rumbles, G.; Park, J. J. Am. Chem. Soc. 2017, 139, 4286–4289.
doi:10.1021/jacs.7b00220
19. Lysenko, S.; Haberlag, B.; Daniliuc, C. G.; Jones, P. G.; Tamm, M.
ChemCatChem 2011, 3, 115–118. doi:10.1002/cctc.201000355
20. Lysenko, S.; Daniliuc, C. G.; Jones, P. G.; Tamm, M.
J. Organomet. Chem. 2013, 744, 7–14.
43. Ortiz, M.; Yu, C.; Jin, Y.; Zhang, W. Top. Curr. Chem. 2017, 375, 69.
doi:10.1007/s41061-017-0156-1
44. Paley, D. W.; Sedbrook, D. F.; Decatur, J.; Fischer, F. R.;
Steigerwald, M. L.; Nuckolls, C. Angew. Chem., Int. Ed. 2013, 52,
4591–4594. doi:10.1002/anie.201300758
doi:10.1016/j.jorganchem.2013.03.035
21. Clark, D. N.; Schrock, R. R. J. Am. Chem. Soc. 1978, 100,
6774–6776. doi:10.1021/ja00489a049
45. Bellone, D. E.; Bours, J.; Menke, E. H.; Fischer, F. R.
J. Am. Chem. Soc. 2015, 137, 850–856. doi:10.1021/ja510919v
46. von Kugelgen, S.; Bellone, D. E.; Cloke, R. R.; Perkins, W. S.;
Fischer, F. R. J. Am. Chem. Soc. 2016, 138, 6234–6239.
doi:10.1021/jacs.6b02422
22. Schrock, R. R.; Clark, D. N.; Sancho, J.; Wengrovius, J. H.;
Rocklage, S. M.; Pedersen, S. F. Organometallics 1982, 1,
1645–1651. doi:10.1021/om00072a018
23. Heppekausen, J.; Stade, R.; Goddard, R.; Fürstner, A.
J. Am. Chem. Soc. 2010, 132, 11045–11057. doi:10.1021/ja104800w
24. Heppekausen, J.; Stade, R.; Kondoh, A.; Seidel, G.; Goddard, R.;
Fürstner, A. Chem. – Eur. J. 2012, 18, 10281–10299.
doi:10.1002/chem.201200621
47. von Kugelgen, S.; Sifri, R.; Bellone, D.; Fischer, F. R.
J. Am. Chem. Soc. 2017, 139, 7577–7585. doi:10.1021/jacs.7b02225
48. Jeong, H.; von Kugelgen, S.; Bellone, D.; Fischer, F. R.
J. Am. Chem. Soc. 2017, 139, 15509–15514.
doi:10.1021/jacs.7b09390
25. Persich, P.; Llaveria, J.; Lhermet, R.; de Haro, T.; Stade, R.;
Kondoh, A.; Fürstner, A. Chem. – Eur. J. 2013, 19, 13047–13058.
doi:10.1002/chem.201302320
49. Haberlag, B.; Freytag, M.; Daniliuc, C. G.; Jones, P. G.; Tamm, M.
Angew. Chem., Int. Ed. 2012, 51, 13019–13022.
doi:10.1002/anie.201207772
26. Willwacher, J.; Heggen, B.; Wirtz, C.; Thiel, W.; Fürstner, A.
Chem. – Eur. J. 2015, 21, 10416–10430.
50. Haberlag, B.; Freytag, M.; Jones, P. G.; Tamm, M. Adv. Synth. Catal.
2014, 356, 1255–1265. doi:10.1002/adsc.201400051
51. Hötling, S.; Bittner, C.; Tamm, M.; Dähn, S.; Collatz, J.;
Steidle, J. L. M.; Schulz, S. Org. Lett. 2015, 17, 5004–5007.
doi:10.1021/acs.orglett.5b02461
doi:10.1002/chem.201501491
27. Schaubach, S.; Gebauer, K.; Ungeheuer, F.; Hoffmeister, L.;
Ilg, M. K.; Wirtz, C.; Fürstner, A. Chem. – Eur. J. 2016, 22,
8494–8507. doi:10.1002/chem.201601163
52. Estes, D. P.; Bittner, C.; Àrias, Ò.; Casey, M.; Fedorov, A.; Tamm, M.;
Copéret, C. Angew. Chem., Int. Ed. 2016, 55, 13960–13964.
doi:10.1002/anie.201605129
28. Lysenko, S.; Volbeda, J.; Jones, P. G.; Tamm, M.
Angew. Chem., Int. Ed. 2012, 51, 6757–6761.
doi:10.1002/anie.201202101
53. Estes, D. P.; Gordon, C. P.; Fedorov, A.; Liao, W.-C.; Ehrhorn, H.;
Bittner, C.; Zier, M. L.; Bockfeld, D.; Chan, K. W.; Eisenstein, O.;
Raynaud, C.; Tamm, M.; Copéret, C. J. Am. Chem. Soc. 2017, 139,
17597–17607. doi:10.1021/jacs.7b09934
29. Li, S. T.; Schnabel, T.; Lysenko, S.; Brandhorst, K.; Tamm, M.
Chem. Commun. 2013, 49, 7189–7191. doi:10.1039/c3cc43108h
30. Tamm, M.; Schnabel, T.; Melcher, D.; Brandhorst, K.; Bockfeld, D.
Chem. – Eur. J. 2018, 24, 9022–9032. doi:10.1002/chem.201801651
31. Jyothish, K.; Zhang, W. Angew. Chem., Int. Ed. 2011, 50, 3435–3438.
doi:10.1002/anie.201007559
54. Bittner, C.; Ehrhorn, H.; Bockfeld, D.; Brandhorst, K.; Tamm, M.
Organometallics 2017, 36, 3398–3406.
doi:10.1021/acs.organomet.7b00519
32. Jyothish, K.; Wang, Q.; Zhang, W. Adv. Synth. Catal. 2012, 354,
2073–2078. doi:10.1002/adsc.201200243
55. Freudenberger, J. H.; Schrock, R. R.; Churchill, M. R.;
Rheingold, A. L.; Ziller, J. W. Organometallics 1984, 3, 1563–1573.
doi:10.1021/om00088a019
33. Yang, H.; Liu, Z.; Zhang, W. Adv. Synth. Catal. 2013, 355, 885–890.
doi:10.1002/adsc.201201105
56. Buhro, W. E.; Chisholm, M. H. Adv. Organomet. Chem. 1987, 27,
311–369. doi:10.1016/s0065-3055(08)60030-1
34. Du, Y.; Yang, H.; Zhu, C.; Ortiz, M.; Okochi, K. D.; Shoemaker, R.;
Jin, Y.; Zhang, W. Chem. – Eur. J. 2016, 22, 7959–7963.
doi:10.1002/chem.201505174
57. Schrock, R. R. Chem. Rev. 2002, 102, 145–180.
doi:10.1021/cr0103726
35. Hu, K.; Yang, H.; Zhang, W.; Qin, Y. Chem. Sci. 2013, 4, 3649–3653.
doi:10.1039/c3sc51264a
58. Wengrovius, J. H.; Sancho, J.; Schrock, R. R. J. Am. Chem. Soc.
1981, 103, 3932–3934. doi:10.1021/ja00403a058
59. Schrock, R. R. J. Organomet. Chem. 1986, 300, 249–262.
doi:10.1016/0022-328x(86)84064-5
36. Yang, H.; Zhu, Y.; Du, Y.; Tan, D.; Jin, Y.; Zhang, W.
Mater. Chem. Front. 2017, 1, 1369–1372. doi:10.1039/c6qm00359a
37. Zhang, C.; Wang, Q.; Long, H.; Zhang, W. J. Am. Chem. Soc. 2011,
133, 20995–21001. doi:10.1021/ja210418t
60. Bray, A.; Mortreux, A.; Petit, F.; Petit, M.; Szymanska-Buzar, T.
J. Chem. Soc., Chem. Commun. 1993, 197–199.
doi:10.1039/c39930000197
38. Wang, Q.; Zhang, C.; Noll, B. C.; Long, H.; Jin, Y.; Zhang, W.
Angew. Chem., Int. Ed. 2014, 53, 10663–10667.
61. Coutelier, O.; Mortreux, A. Adv. Synth. Catal. 2006, 348, 2038–2042.
doi:10.1002/adsc.200606116
doi:10.1002/anie.201404880
39. Wang, Q.; Yu, C.; Long, H.; Du, Y.; Jin, Y.; Zhang, W.
Angew. Chem., Int. Ed. 2015, 54, 7550–7554.
62. Listemann, M. L.; Schrock, R. R. Organometallics 1985, 4, 74–83.
doi:10.1021/om00120a014
doi:10.1002/anie.201501679
63. Fürstner, A.; Seidel, G. Angew. Chem., Int. Ed. 1998, 37, 1734–1736.
doi:10.1002/(sici)1521-3773(19980703)37:12<1734::aid-anie1734>3.0
.co;2-6
40. Yu, C.; Long, H.; Jin, Y.; Zhang, W. Org. Lett. 2016, 18, 2946–2949.
doi:10.1021/acs.orglett.6b01293
41. Wang, Q.; Yu, C.; Zhang, C.; Long, H.; Azarnoush, S.; Jin, Y.;
Zhang, W. Chem. Sci. 2016, 7, 3370–3376. doi:10.1039/c5sc04977f
64. Nicolaou, K. C.; Bulger, P. G.; Sarlah, D. Angew. Chem., Int. Ed.
2005, 44, 4490–4527. doi:10.1002/anie.200500369
2433

Beilstein J. Org. Chem. 2018, 14, 2425–2434.
65. McCullough, L. G.; Listemann, M. L.; Schrock, R. R.; Churchill, M. R.;
Ziller, J. W. J. Am. Chem. Soc. 1983, 105, 6729–6730.
doi:10.1021/ja00360a040
89. Budzichowski, T. A.; Chisholm, M. H.; Tiedtke, D. B.; Huffman, J. C.;
Streib, W. E. Organometallics 1995, 14, 2318–2324.
doi:10.1021/om00005a033
66. Freudenberger, J. H.; Schrock, R. R. Organometallics 1986, 5,
1411–1417. doi:10.1021/om00138a019
90. Akiyama, M.; Chisholm, M. H.; Cotton, F. A.; Extine, M. W.;
Haitko, D. A.; Little, D.; Fanwick, P. E. Inorg. Chem. 1979, 18,
2266–2270. doi:10.1021/ic50198a043
67. Mortreux, A.; Petit, F.; Petit, M.; Szymanska-Buzar, T.
J. Mol. Catal. A: Chem. 1995, 96, 95–105.
91. Chisholm, M. H.; Cotton, F. A.; Extine, M.; Millar, M.; Stults, B. R.
J. Am. Chem. Soc. 1976, 98, 4486–4491. doi:10.1021/ja00431a026
92. Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C.
J. Chem. Soc., Dalton Trans. 1984, 1349–1356.
doi:10.1016/1381-1169(94)00004-2
68. Coutelier, O.; Nowogrocki, G.; Paul, J.-F.; Mortreux, A.
Adv. Synth. Catal. 2007, 349, 2259–2263.
doi:10.1002/adsc.200700104
doi:10.1039/dt9840001349
69. Chisholm, M. H.; Cotton, F. A. Acc. Chem. Res. 1978, 11, 356–362.
doi:10.1021/ar50129a006
93. Yang, L.; Powell, D. R.; Houser, R. P. Dalton Trans. 2007, 955–964.
doi:10.1039/b617136b
70. Chisholm, M. H.; Cotton, F. A.; Frenz, B. A.; Reichert, W. W.;
Shive, L. W.; Stults, B. R. J. Am. Chem. Soc. 1976, 98, 4469–4476.
doi:10.1021/ja00431a024
94. Chisholm, M. H.; Parkin, I. P.; Huffman, J. C.; Lobkovsky, E. M.;
Folting, K. Polyhedron 1991, 10, 2839–2846.
doi:10.1016/s0277-5387(00)86188-4
71. Chisholm, M. H.; Cotton, F. A.; Extine, M.; Stults, B. R.
J. Am. Chem. Soc. 1976, 98, 4477–4485. doi:10.1021/ja00431a025
72. Coffindaffer, T. W.; Rothwell, I. P.; Huffmann, J. C. Inorg. Chem.
1985, 24, 1643–1646. doi:10.1021/ic00205a010
95. Coffindaffer, T. W.; Niccolai, G. P.; Powell, D.; Rothwell, I. P.
J. Am. Chem. Soc. 1985, 107, 3572–3583. doi:10.1021/ja00298a029
96. Chisholm, M. H.; Folting, K.; Hampden-Smith, M.; Smith, C. A.
Polyhedron 1987, 6, 1747–1755. doi:10.1016/s0277-5387(00)86546-8
97. Cayton, R. H.; Chisholm, M. H. Inorg. Chem. 1991, 30, 1422–1425.
doi:10.1021/ic00006a051
73. Gilbert, T. M.; Landes, A. M.; Rogers, R. D. Inorg. Chem. 1992, 31,
3438–3444. doi:10.1021/ic00042a020
74. Su, K.; Tilley, T. D. Chem. Mater. 1997, 9, 588–595.
doi:10.1021/cm960413s
98. Chisholm, M. H.; Gallucci, J. C.; Hollandsworth, C. B. Polyhedron
2006, 25, 827–833. doi:10.1016/j.poly.2005.07.010
99. Schrock, R. R.; Listemann, M. L.; Sturgeoff, L. G. J. Am. Chem. Soc.
1982, 104, 4291–4293. doi:10.1021/ja00379a061
75. Chisholm, M. H.; Folting, K.; Wu, D.-D. Chem. Commun. 1998,
379–380. doi:10.1039/a708268a
76. Radius, U.; Attner, J. Eur. J. Inorg. Chem. 1998, 299–303.
doi:10.1002/(sici)1099-0682(199803)1998:3<299::aid-ejic299>3.0.co;
2-q
100.Lhermet, R.; Fürstner, A. Chem. – Eur. J. 2014, 20, 13188–13193.
doi:10.1002/chem.201404166
77. Budzichowski, T. A.; Chisholm, M. H.; Tiedtke, D. B.; Gruhn, N. E.;
Lichtenberger, D. L. Polyhedron 1998, 17, 705–711.
doi:10.1016/s0277-5387(97)00360-4
License and Terms
78. Gilbert, T. M.; Bauer, C. B.; Bond, A. H.; Rogers, R. D. Polyhedron
1999, 18, 1293–1301. doi:10.1016/s0277-5387(98)00433-1
79. Chetcuti, M. J.; Chisholm, M. H.; Huffman, J. C.; Leonelli, J.
J. Am. Chem. Soc. 1983, 105, 292–293. doi:10.1021/ja00340a025
80. Chisholm, M. H.; Huffman, J. C.; Ratermann, A. L. Inorg. Chem. 1983,
22, 4100–4105. doi:10.1021/ic00168a055
This is an Open Access article under the terms of the
Creative Commons Attribution License
(http://creativecommons.org/licenses/by/4.0). Please note
that the reuse, redistribution and reproduction in particular
requires that the authors and source are credited.
81. Chisholm, M. H.; Conroy, B. K.; Eichhorn, B. W.; Folting, K.;
Hoffman, D. M.; Huffman, J. C.; Marchant, N. S. Polyhedron 1987, 6,
783–792. doi:10.1016/s0277-5387(00)86884-9
The license is subject to the Beilstein Journal of Organic
Chemistry terms and conditions:
82. Chisholm, M. H.; Eichhorn, B. W.; Folting, K.; Huffman, J. C.;
Ontiveros, C. D.; Streib, W. E.; van der Sluys, W. G. Inorg. Chem.
1987, 26, 3182–3186. doi:10.1021/ic00266a024
(https://www.beilstein-journals.org/bjoc)
83. Chisholm, M. H.; Cook, C. M.; Huffman, J. C.; Streib, W. E.
J. Chem. Soc., Dalton Trans. 1991, 929–937.
The definitive version of this article is the electronic one
which can be found at:
doi:10.1039/dt9910000929
doi:10.3762/bjoc.14.220
84. Chisholm, M. H.; Huang, J.-H.; Huffman, J. C.; Parkin, I. P.
Inorg. Chem. 1997, 36, 1642–1651. doi:10.1021/ic961429n
85. Budzichowski, T. A.; Chisholm, M. H.; Folting, K.; Huffman, J. C.;
Streib, W. E.; Tiedtke, D. B. Polyhedron 1998, 17, 857–867.
doi:10.1016/s0277-5387(97)00290-8
86. Girolami, G. S.; Sattelberger, A. P., Eds. Inorganic Syntheses: Volume
36; Inorganic Syntheses; John Wiley & Sons, Inc.: Hoboken, NJ,
U.S.A., 2014. doi:10.1002/9781118744994
87. Strutz, H.; Schrock, R. R. Organometallics 1984, 3, 1600–1601.
doi:10.1021/om00088a030
88. Fackler, J. P., Ed. Inorganic syntheses; Wiley: New York, NY, U.S.A.,
1982; Vol. 21. doi:10.1002/9780470132524
2434