Robust Alkyne Metathesis Catalyzed by Air Stable d2Re(V) Alkylidyne Complexes

Article abstract of DOI:10.1021/jacs.0c06581

We report in this communication the first example of catalytic alkyne metathesis reactions mediated by well-defined non-d0 alkylidyne complexes. The air-stable d2 Re(V) alkylidyne complex Re4, bearing two PO-chelating ligands and a labile pyridine ligand, could catalyze homometathesis of internal alkynes with a broad substrate scope, including alcohols, amines, and even carboxylic acids. The catalyst can tolerate heating, air, and moisture in both solid and solution states, and the catalytic metathesis reactions could proceed normally in wet solvents.

Full text of DOI:10.1021/jacs.0c06581

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Communication
Robust Alkyne Metathesis Catalyzed by
Air Stable d2 Re(V) Alkylidyne Complexes
Mingxu Cui, WEI BAI, Herman H. Y. Sung, Ian D. Williams, and Guochen Jia
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.0c06581 • Publication Date (Web): 16 Jul 2020
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Robust Alkyne Metathesis Catalyzed by Air Stable d Re(V) Alkyli-
dyne Complexes
†
†
†
,†
,†,‡
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Mingxu Cui, Wei Bai, Herman H. Y. Sung, Ian D. Williams* and Guochen Jia*
†
Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
HKUST Shenzhen Research Institute, Shenzhen, 518057, China
‡
Supporting Information Placeholder
ABSTRACT: We report in this communication the first example
of catalytic alkyne metathesis reactions mediated by well-defined
Scheme 1. Selected Homogeneous Transition Metal Catalysts for
Alkyne Metathesis Reactions.
0
2
non-d alkylidyne complexes. The air-stable d Re(V) alkylidyne
complex Re4, bearing two PO-chelating ligands and a labile pyri-
dine ligand, could catalyze homo-metathesis of internal alkynes
with a broad substrate scope, including alcohols, amines and even
carboxylic acids. The catalyst can tolerate heating, air and moisture
in both solid and solution states and the catalytic metathesis reac-
tions could proceed normally in wet solvents.
2
It was recently reported that the air stable d Re(V) alkylidyne
Alkyne metathesis has shown great potential in synthesis of
1
2 , 3
complexes Re(≡CR')Cl
PMe Ph) could undergo stoichiometric metathesis reactions with
alkynes.
2 3 3 3 2
(PR ) (R' = aryl, alkyl; PR = PMePh ,
natural products, functional polymers
and supramolecular
4
2
materials. Classical homogeneous alkyne metathesis catalysts could
2
8, 29
The interesting observation promoted us to explore the
be classified into two categories: the “in situ” catalytic system based
5
, 6
potential of Re(V) alkylidyne complexes for catalytic alkyne me-
tathesis reactions.
The catalytic property of Re(≡CCH Ph)Cl (PMePh ) (Re1,
Scheme 2) was firstly evaluated by using the self-metathesis reaction
of p-tolyl-1-propyne (1a) as the model reaction. The complex Re1
only showed marginal activity at 150 C with neat 1a or very poor
activity at 100 C in 0.1 M toluene (Table 1, entries 1, 2). The
complex Re[≡CCH (o-C H Br)]Cl (PMe Ph) behaved similarly
on Mo(CO) /phenol or “Mortreux catalyst” (e.g. Scheme 1, A)
6
0
and well-defined high valent d Schrock-type alkylidyne complexes
e.g. Scheme 1, B). The former has the advantage of user-
7
2 2 2 3
(
friendliness. The latter displays remarkable efficiency and a broader
substrate scope, which was more commonly used and studied in
the past 4 decades. Modifications on Schrock-type alkylidyne cata-
o
8
o
lysts have been carried out continually aiming to obtain more ro-
bust systems with high efficiency and broader substrate scope to
benefit the wide popularity of alkyne metathesis. Many valuable
2
6
4
2
2
3
9
(Table S1, entry 2).
In an alternative way to modify the catalytic property of Re(V)
alkylidyne complexes, the ligand substitution reaction of Re1 with
the bidentate ligand, (2-hydroxyphenyl)diphenyl phosphine
ideas emerged during this period and remarkable improvements in
the efficiency and stability of alkyne metathesis catalysts based on
0
high valent d alkylidyne complexes have been achieved. Examples
(
Scheme 2, L1) was carried out to obtain the Re(V) alkylidyne
of the newly developed novel systems include Mo(VI) alkylidyne
1
0, 11, 12, 13,14 ,15
complex Re2 with two PO bidentate ligands. Subsequent experi-
ments showed that the complex Re2 displayed significantly im-
proved catalytic activity in self-metathesis reaction of 1a (Table 1,
entry 3). Re2 also has appreciable activity in promoting the model
reaction in a toluene solution at 100 C (Table 1, entry 4).
It was suspected that association of the mono phosphine ligand
PMePh in Re2 may increase the reaction barrier for the catalytic
metathesis reaction. Thus, catalytic reactions in the presence of CuI
(which could act as a phosphine sponge) were performed. As ex-
pected, the Re2-catalyzed self-metathesis reaction of p-tolyl-1-
propyne (1a) was accelerated in the presence of CuI. After heating
of neat 1a at 100 C for 8 h in the presence of 2 mol% of Re2 and
2 mol% of CuI, the conversion reached to 47% (Table 1, entries 5,
6).
catalysts with tridentate ligands,
pyridine or phenan-
1
6 , 17 , 18
throline stabilized bench-stable Mo(VI) precatalysts,
supported heterogeneous Mo(VI) alkylidyne catalysts,
silica
and
19 , 20
Mo(VI) or W(VI) alkylidyne complexes bearing imidazolin-2-
o
21
22
23
iminato ligands, NHC ligands or silyloxy ligands. Some of the
systems can even efficiently promote the metathesis of challenging
2
4
2
terminal alkynes.
Although alkyne metathesis reactions mediated by high valent
0
0
d alkylidyne complexes are now well established and many non-d
25, 26
alkylidyne complexes are known,
to the best of our knowledge,
catalytic alkyne metathesis reactions mediated by well-defined non-
o
0
d alkylidyne complexes have not been reported yet. In contrast,
0
olefin metathesis could be promoted by both d metal (e.g. Ta(V),
4
Mo(VI)) alkylidenes and d Ru(IV) carbenes (a carbene ligand is
2
7
viewed as a dianionic ligand). Herein, we report the first example
0
Scheme 2. Synthesis of Rhenium (V) Alkylidene Catalysts.
of alkyne metathesis reactions catalyzed by a non-d metal alkyli-
2
dyne complex, specifically, the d Re(V) alkylidyne complex Re4
(Scheme 1, C).
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Table 1. Rhenium (V) Alkylidenes Catalyzed Homo-metathesis of
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
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4
4
4
4
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5
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5
5
5
5
6
p-Tolyl-1-propyne
[
d]
T
( C)
t
(h)
yield
entry catalyst(s)
solvent
o
(%)
[
a]
1
2
3
Re1
Re1
neat
toluene
neat
150
8
8
19
[b]
100
150
trace
60
15
21
47
11
98
82
85
95
96
0
1
2
3
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0
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0
1
2
3
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7
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0
1
2
3
4
5
6
7
8
9
0
[
a]
Re2
2
[
b]
4
5
6
Re2
toluene
neat
100
8
[
a]
a]
b]
Re2
100
8
[
Re2/CuI
Re3
neat
100
8
[
7
8
9
toluene
toluene
1,4-dioxane
100
8
[b]
b]
Re4
100
8
[
Re4
100
20
20
48
48
[
b]
i
1
0
Re4
BuOH
100
[
c]
c]
1
1
Re4
wet toluene
reflux
reflux
[
i
12
Re4
wet BuOH
[
[
a]
Condition: alkyne (0.2 mmol), catalyst (2 mol%), without 5 Å MS;
b]
The above observation hinted that analogs of Re2 free of
Condition: alkyne (0.2 mmol), catalyst (2 mol%), 5 Å MS (250
[
c]
PMePh ligand may be catalytically more active. Attempts have
mg), 0.1 M; Condition: alkyne (0.2 mmol), catalyst (2 mol%),
2
3
1
been made to prepare the pyridine (py) complex
without 5 Å MS, wet solvents, 0.1 M, refluxed under N ;
2
[
d]
1
Re(≡CCH Ph)Cl (o-OC H -PPh ) (py) complex by reacting Re2
Conversions were determined by H NMR using CH
internal standard.
Br as the
2 2
2
2
6
4
2 2
with pyridine in the presence of CuI. The in-situ NMR experi-
ments indicated that the desired pyridine complex might be
30
formed. Unfortunately, pure samples of the desired alkylidyne
The higher activity of the pyridine-coordinated complex Re4
compared with that of the corresponding PMePh analog can be
attributed to the relative lability of pyridine and PMePh for substi-
tution reactions. This hypothesis was supported by ligand exchange
reactions of Re4 and cis-Re3 (Scheme 3). The ligand exchange
complex from the reaction could not be obtained due to the diffi-
culty in completely removing the Cu-containing side product.
To facilitate the isolation of pyridine-coordinated alkylidyne
complexes, the PO ligand was modified by introducing two CF3
groups to the phenyl groups (Scheme 2, L2), which was expected to
differentiate the solubility of the pyridine-coordinated alkylidyne
2
2
reaction of Re4 with trimethylphosphine (PMe
) (10 equiv.) oc-
curred at 60 C and was completed at 80 C within 6 hours to give
the PMe -coordinated complex Re4’ (Figure S1). On the other
hand, the ligand substitution reaction of cis-Re3 with PMe (10
3
o
o
complex from CuI(PMePh ) in non-polar solvents. The reaction of
3
2
Re1 with the modified ligand [bis(3,5-bis(trifluoromethyl)-
3
o
o
phenyl)phosphanyl] phenol (L2) at 100 C for 3 h gave a mixture of
equiv.) could only slowly take place at 100 C and proceeded with
an appreciable rate at 120 C (Figure S2).
o
isomers cis-Re3 and trans-Re3, which can be separated by recrystal-
lization. The isomers cis-Re3 and trans-Re3 can interconvert with
o
each other when heated above 80 C in toluene, giving an equilib-
Scheme 3. Ligand Exchange Experiments of Re4 and cis-Re3.
rium mixture with a molar ratio of 3 : 2. Subsequent ligand ex-
change reaction of Re3 with pyridine in the presence of CuI pro-
duced the desired pyridine supported complex Re4, which could
then be easily separated from the Cu-containing side product
CuI(PMePh ) by diethyl ether extraction. The complex Re4 has
2
been characterized both spectroscopically and crystallographically.
It is an air-stable golden-yellow solid that can be stored in air for
months in the solid state and for weeks in solutions without appre-
ciable decomposition. In addition, the complex Re4 remain un-
o
changed after heating in wet degassed toluene-d at 100 C for 16
8
hours as indicated by in-situ NMR spectroscopy.
Subsequent experiments showed that the performance of Re3
in catalytic self-metathesis reaction of p-tolyl-1-propyne (1a) is simi-
lar to that of Re2 (Table 1, entry 7). On the other hand, the pyri-
dine complex Re4 has a significantly improved activity compared
with Re1 - Re3. The model reaction of 1a was essentially completed
The Re4-catalyzed reaction could proceed in strongly coordi-
nating solvents like 1,4-dioxane with only slight decrease in the
reactivity (Table 1, entry 9). Furthermore, the metathesis reaction
promoted by Re4 can tolerate protic solvents like isobutanol with-
out significant decline in yield (Table 1, entry 10). Most interesting-
o
within 8 hours at 100 C in toluene solution with 2 mol% of Re4
(
Table 1, entry 8).
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ly, the catalytic metathesis reactions in wet toluene or isobutanol
could also take place (Table 1, entries 11, 12). Control experiments
indicate that the catalyst Re4 has nearly equal activity in wet and
dry toluene. After refluxing the reaction mixtures containing 1a
and 2 mol% of Re4 for 16 hours, the one in wet toluene gave 73%
of NMR yield, while the one in dry toluene gave 77% of NMR
yield (Table S1, entries 12, 13). The Re(V) alkylidyne catalytic sys-
tem represents the first example of air and moisture stable alkyli-
dyne catalysts with demonstrated metathesis activity for unstrained
(1g). The metathesis reaction of the more challenging substrate, 2-
propynylthiophene (1h), also proceeded well and produced 2h in
excellent yield. 4-Propynylbenzaldehyde (1i), a tough substrate that
1
2
3
4
5
6
7
8
9
0
was well-known to destroy some high valent d alkylidyne cata-
1
1
lysts, could be metathesized by Re4 efficiently to give 2i in excel-
lent yield.
Apart from aryl alkynes, metathesis reactions of alkyl alkynes
were also tested. For example, the popular alkyl alkyne substate 1l
was metathesized by Re4 to give 2l in high isolated yield. Propar-
gylic alcohol derivatives are another class of problematic sub-
32
alkynes.
3
3
The outstanding air and moisture stability of Re4 hints that
the catalyst has the potential to promote metathesis of substrates
containing coordinating, polar or protic functional groups. The
substrate scope of metathesis reactions mediated by Re4 was next
investigated, especially for substrates with potential problematic
functional groups (Chart 1). In most cases, the catalytic reactions
were conducted in dry toluene with 2 mol% of the catalyst and
activated 5 Å MS as butyne absorber. Some reactions were carried
out in wet toluene (e.g. 1k, 1o). For those substrates with strong
coordination ability, higher catalyst loading (3 mol%) and pro-
longed reaction time (16 h) were employed.
strates. To the best of our knowledge, the self-metathesis reaction
of the propargylic alcohol derivative 1m has never been reported.
With Re4 as the catalyst, the substrate 1m could be metathesized to
give 2m in moderate yield.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
The metathesis of alkyne substrates with protic groups, such as
hydroxy and amino groups, was well-recognized as a challenging
0
task for high valent d alkylidyne catalysts. Most catalytic systems
reported before are either incompatible with such groups or show
0
low efficiency. In contrast, the non-d alkylidyne catalyst Re4 is
inherently tolerant to protic environments, and promotes self-
metathesis reactions of protic substrates like 4-propynylphenol (1j)
and 4-propynylaniline (1k) smoothly to give corresponding prod-
ucts in good isolated yields with only 3 mol% of catalyst loading.
Moreover, the alkyl alkyne substrate 1n with an “unhindered pri-
Chart 1. Scope of Metathesized Alkynes Promoted by Re4.
1
5
mary alcohol” could also be metathesized normally by Re4 to give
the product 2n in excellent yield. Encouraged by these successes,
we extended the substrate scope to the unprotected carboxylic acid
substrate 1o. Surprisingly, the self-metathesis product 2o was
formed either in dry or wet toluene and isolated in good yields. To
the best of our knowledge, Re4 is the first catalyst with demon-
strated metathesis activity for substrate with a carboxylic acid func-
tional group.
The alkyne metathesis reaction mediated by Re4 presumably
proceeds through ligand dissociation, reversible cycloaddition of
Re(V) alkylidyne intermediate with alkyne, and re-association of
2
8, 34
ligand.
Consistent with the proposed mechanism, the in-situ
3
1
1
P{ H} NMR spectra after catalytic reactions showed signals assign-
able to new Re(V) alkylidyne complexes analogous to Re4. For
instance, Re5 was isolated in 80% yield in the reaction of Re4 with
5
equiv. of 2-propynylthiophene (1h), the structure of which was
confirmed by X-ray diffraction (Scheme 4). The isolated complex,
Re5, was found to be equally active as Re4 for catalytic self-
metathesis reaction of 2-propynylthiophene.
Scheme 4. Stoichiometric alkyne metathesis of Re4 with 2-
propynylthiophene (1h).
[
a]
Conditions: alkyne (0.2 mmol), Re4 (2 mol%), 5 Å MS (250 mg),
[
b]
dry toluene (2 mL), 100 °C, 8 h; Conditions: alkyne (0.2 mmol),
Re4 (3 mol%), 5 Å MS (250 mg), dry toluene (2 mL), 100 °C, 16 h.
[c]
31
Conditions: alkyne (0.2 mmol), Re4 (3 mol%), wet toluene (2
In summary, this communication demonstrated the first exam-
1
0
mL), reflux, 48 h. Conversions were determined by H NMR using
CH Br as the internal standard. Isolated yields are given in paren-
ple of alkyne metathesis reactions promoted by non-d transition
2
metal alkylidyne complexes. The d Re(V) alkylidyne complex Re4
2
2
theses. Only isolated yields are provided for products with poor
solubilities.
prepared in this work has remarkable stability to both air and mois-
ture and can effect metathesis of alkynes with a broad substrate
scope, including alcohols, amines and even carboxylic acids. The
0
As shown in Chart 1, a variety of alkyne products can be ob-
tained by Re4-promoted self-metathesis of internal alkynes. All of
the products were isolated in moderate to excellent yields. The
complex Re4 is compatible with substrates containing functional
groups such as ether (1c), ketone (1d), ester (1f) and tertiary amine
results indicated that development of non-d alkylidyne-based cata-
lysts can provide an alternative approach toward user-friendly al-
kyne metathesis reactions. Fine-tuning of catalyst activity and elab-
oration of the mechanistic features of these systems are in progress.
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ASSOCIATED CONTENT
Supporting Information
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The Supporting Information is available free of charge on the ACS
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AUTHOR INFORMATION
Corresponding Authors
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56.
(4) Selected examples of supermolecular materials synthesized by alkyne
metathesis: (a) Cencer, M. M.; Greenlee, A. J.; Moore, J. S., Quantifying
Error Correction through a Rule-Based Model of Strand Escape from an
*
*
E-mail: chjiag@ust.hk.
E-mail: chwill@ust.hk.
[n]-Rung Ladder. J. Am. Chem. Soc. 2020, 142, 162-168. (b) Ortiz, M.; Cho,
ORCID
S.; Niklas, J.; Kim, S.; Poluektov, O. G.; Zhang, W.; Rumbles, G.; Park, J.,
Through-Space Ultrafast Photoinduced Electron Transfer Dynamics of a
C70-Encapsulated Bisporphyrin Covalent Organic Polyhedron in a Low-
Dielectric Medium. J. Am. Chem. Soc. 2017, 139, 4286-4289. (c) Lee, S.;
Chenard, E.; Gray, D. L.; Moore, J. S., Synthesis of
Cycloparaphenyleneacetylene via Alkyne Metathesis: C70 Complexation
and Copper-Free Triple Click Reaction. J. Am. Chem. Soc. 2016, 138, 13814-
13817. (d) Wang, Q.; Yu, C.; Long, H.; Du, Y.; Jin, Y.; Zhang, W.,
Solution-phase dynamic assembly of permanently interlocked
aryleneethynylene cages through alkyne metathesis. Angew. Chem., Int. Ed.
Mingxu Cui: 0000-0002-3701-7696
Wei Bai: 0000-0001-8585-9321
Ian D. Williams: 0000-0001-8743-401X
Guochen Jia: 0000-0002-4285-8756
Present Addresses
Department of Chemistry, The Hong Kong University of Science
and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
E-mail: chjiag@ust.hk
2
015, 54, 7550-7554.
Notes
( 5 ) (a) Mortreux, A.; Blanchard, M., Metathesis of alkynes by a
molybdenum hexacarbonyl–resorcinol catalyst. J. Chem. Soc., Chem. Commun.
The authors declare no competing financial interests.
1
974, 19, 786-787. (b) Bencheick, A.; Petit, M.; Mortreux, A.; Petit, F.,
ACKNOWLEDGMENT
New active and selective catalysts for homogeneous metathesis of
disubstituted alkynes. J. Mol. Catal. 1982, 15, 93-101.
This work was supported by the Hong Kong Research Grants
Council (Project No.: 602113, 16321516) and National Natural
Science Foundation of China (Project No.: 21971218)
(6) (a) Kloppenburg, L.; Song, D.; Bunz, U. H. F., Alkyne Metathesis with
Simple Catalyst Systems: Poly(p-phenyleneethynylene)s. J. Am. Chem. Soc.
1998, 120, 7973-7974. (b) Pschirer, N. G.; Bunz, U. H. F., Alkyne
metathesis with simple catalyst systems: High yield dimerization of
propynylated aromatics; scope and limitations. Tetrahedron Lett. 1999, 40,
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481-2484. (c) Brizius, G.; Bunz, U. H., Increased activity of in situ catalysts
for alkyne metathesis. Org. Lett. 2002, 4, 2829-2831. (d) Grela, K.;
Ignatowska, J., An improved catalyst for ring-closing alkyne metathesis
based on molybdenum hexacarbonyl/2-fluorophenol. Org. Lett. 2002, 4,
(1) Selected examples of synthesizing natural products involving alkyne
metathesis: (a) Meng, Z.; Fürstner, A., Total Synthesis of (-)-Sinulariadiolide.
A Transannular Approach. J. Am. Chem. Soc. 2019, 141, 805-809. (b)
Schaubach, S.; Gebauer, K.; Ungeheuer, F.; Hoffmeister, L.; Ilg, M. K.;
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747-3749. (e) Sashuk, V.; Ignatowska, J.; Grela, K., A fine-tuned
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( 7 ) (a) Wengrovius, J. H.; Sancho, J.; Schrock, R. R., Metathesis of
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1
03, 3932-3934. (b) Pedersen, S. F.; Schrock, R. R.; Churchill, M. R.;
Wasserman, H. J., Reaction of tungsten(VI) alkylidyne complexes with
acetylenes to give tungstenacyclobutadiene and cyclopentadienyl complexes.
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(8) Selected reviews see: (a) Lee, D.; Volchkov, I.; Yun, S. Y.; Cha, J. K.,
Alkyne Metathesis. Org. React. 2020, 102, 613-931. (b) Ehrhorn, H.; Tamm,
M., Well-Defined Alkyne Metathesis Catalysts: Developments and Recent
Applications. Chem. Eur. J. 2019, 25, 3190-3208. (c) Fürstner, A., Alkyne
metathesis on the rise. Angew. Chem., Int. Ed. 2013, 52, 2794-2819. (d)
Schrock, R. R., Alkyne metathesis by molybdenum and tungsten alkylidyne
complexes. Chem. Commun. 2013, 49, 5529-5531.
2
016, 22, 8494-8507. (c) Fuchs, M.; Fürstner, A., trans-Hydrogenation:
application to a concise and scalable synthesis of brefeldin A. Angew. Chem.,
Int. Ed. 2015, 54, 3978-3982. (d) Hotling, S.; Haberlag, B.; Tamm, M.;
Collatz, J.; Mack, P.; Steidle, J. L.; Vences, M.; Schulz, S., Identification and
synthesis of macrolide pheromones of the grain beetle Oryzaephilus
surinamensis and the frog Spinomantis aglavei. Chem. Eur. J. 2014, 20,
3
183-3191. (e) Hickmann, V.; Alcarazo, M.; Fürstner, A., Protecting-group-
free and catalysis-based total synthesis of the ecklonialactones. J. Am. Chem.
Soc. 2010, 132, 11042-11044.
(2) Selected examples of conjugated polymers synthesized by metathesis of
acyclic diynes: (a) Zhang, W.; Moore, J. S., Synthesis of Poly(2,5-
thienyleneethynylene)s by Alkyne Metathesis. Macromolecules 2004, 37,
(
9) Selected reviews or perspectives see: (1) Jyothish, K.; Zhang, W., To-
wards highly active and robust alkyne metathesis catalysts: recent develop-
ments in catalyst design. Angew. Chem., Int. Ed. 2011, 50, 8478-8080. (2)
Bunz, U. H. F., How are alkynes scrambled? Science 2005, 308, 216-217.
(10) Du, Y.; Yang, H.; Zhu, C.; Ortiz, M.; Okochi, K. D.; Shoemaker, R.;
Jin, Y.; Zhang, W., Highly Active Multidentate Ligand-Based Alkyne
Metathesis Catalysts. Chem. Eur. J. 2016, 22, 7959-7963.
3
973-3975. (b) Bunz, U. H. F., Poly(p-phenyleneethynylene)s by Alkyne
Metathesis. Acc. Chem. Res. 2001, 34, 998-1010. (c) Brizius, G.; Pschirer, N.
G.; Steffen, W.; Stitzer, K.; zur Loye, H.-C.; Bunz, U. H. F., Alkyne Metath-
esis with Simple Catalyst Systems: Efficient Synthesis of Conjugated Poly-
mers Containing Vinyl Groups in Main or Side Chain. J. Am. Chem. Soc.
(
11) Yang, H.; Liu, Z.; Zhang, W., Multidentate Triphenolsilane-Based
2
000, 122, 12435-12440.
Alkyne Metathesis Catalysts. Adv. Synth. Catal. 2013, 355, 885-890.
(12) Jyothish, K.; Wang, Q.; Zhang, W., Highly Active Multidentate Alkyne
Metathesis Catalysts: Ligand-Activity Relationship and Their Applications
(
3) Selected examples of ROAMP of cyclic alkynes: (a) Jeong, H.; von
Kugelgen, S.; Bellone, D.; Fischer, F. R., Regioselective Termination
Reagents for Ring-Opening Alkyne Metathesis Polymerization. J. Am. Chem.
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in Efficient Synthesis of Porphyrin-Based Aryleneethynylene Polymers. Adv.
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13 ) Jyothish, K.; Zhang, W., Introducing a podand motif to alkyne
metathesis catalyst design: a highly active multidentate molybdenum(VI)
catalyst that resists alkyne polymerization. Angew. Chem., Int. Ed. 2011, 50,
13019-13022. (b) Lhermet, R.; Fürstner, A., Cross-metathesis of terminal
alkynes. Chem. Eur. J. 2014, 20, 13188-13193. (c) Bittner, C.; Ehrhorn, H.;
Bockfeld, D.; Brandhorst, K.; Tamm, M., Tuning the Catalytic Alkyne
(
Metathesis
Trimethylbenzylidyne
3 n
OC(CF ) Me3–n (n = 0–3). Organometallics 2017, 36, 3398-3406. (d)
Activity
of
Molybdenum
and
Tungsten
2,4,6-
Complexes
with
Fluoroalkoxide
Ligands
3
435-3438.
(14) Paley, D. W.; Sedbrook, D. F.; Decatur, J.; Fischer, F. R.; Steigerwald,
M. L.; Nuckolls, C., Alcohol-promoted ring-opening alkyne metathesis
polymerization. Angew. Chem., Int. Ed. 2013, 52, 4591-4594.
Ehrhorn, H.; Schlosser, J.; Bockfeld, D.; Tamm, M., Efficient catalytic
alkyne metathesis with a fluoroalkoxy-supported ditungsten(III) complex.
Beilstein J. Org. Chem. 2018, 14, 2425-2434.
(
15) (a) Hillenbrand, J.; Leutzsch, M.; Fürstner, A., Molybdenum Alkylidyne
(25) Shi, C.; Jia, G., Chemistry of rhenium carbyne complexes. Coord. Chem.
Rev. 2013, 257, 666-701.
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Complexes with Tripodal Silanolate Ligands: The Next Generation of
Alkyne Metathesis Catalysts. Angew. Chem., Int. Ed. 2019, 58, 1-8. (b)
Hillenbrand, J.; Leutzsch, M.; Yiannakas, E.; Gordon, C. P.; Wille, C.;
Nöthling, N.; Copéret, C.; Fürstner, A., "Canopy Catalysts" for Alkyne
Metathesis: Molybdenum Alkylidyne Complexes with a Tripodal Ligand
Framework. J. Am. Chem. Soc. 2020, 142, 11279-11294.
(16) Bindl, M.; Stade, R.; Heilmann, E. K.; Picot, A.; Goddard, R.; Fürstner,
A., Molybdenum nitride complexes with Ph3SiO ligands are exceedingly
practical and tolerant precatalysts for alkyne metathesis and efficient nitro-
gen transfer agents. J. Am. Chem. Soc. 2009, 131, 9468-9470.
0
(26) Selected recent works on non-d metal alkylidyne complexes: (a) Hill, A.
F.; Manzano, R. A., Dimetallapoly-yn-diylidynes: Ln M≡C-(C≡C)x -
C≡MLn (x=0-4). Angew. Chem., Int. Ed. 2019, 58, 15354-15357. (b) Frogley,
B. J.; Hill, A. F., Flexible Platinum(0) Coordination to a Ditungsten
Ethanediylidyne. Angew. Chem., Int. Ed. 2019, 58, 8044-8048. (c) Luo, M.;
Long, L.; Zhang, H.; Yang, Y.; Hua, Y.; Liu, G.; Lin, Z.; Xia, H., Reactions
of Isocyanides with Metal Carbyne Complexes: Isolation and
Characterization of Metallacyclopropenimine Intermediates. J. Am. Chem.
Soc. 2017, 139, 1822-1825. (d) Buil, M. L.; Cardo, J. J.; Esteruelas, M. A.;
Oñate, E., Square-Planar Alkylidyne-Osmium and Five-Coordinate
Alkylidene-Osmium Complexes: Controlling the Transformation from
Hydride-Alkylidyne to Alkylidene. J. Am. Chem. Soc. 2016, 138, 9720-8728.
(27) (a) Chauvin, Y., Olefin metathesis: the early days (Nobel Lecture).
Angew. Chem., Int. Ed. 2006, 45, 3740-3747. (b) Schrock, R. R., Multiple
metal-carbon bonds for catalytic metathesis reactions (Nobel Lecture).
Angew. Chem., Int. Ed. 2006, 45, 3748-3759. (c) Grubbs, R. H., Olefin-
metathesis catalysts for the preparation of molecules and materials (Nobel
Lecture). Angew. Chem., Int. Ed. 2006, 45, 3760-3765.
(
17) Heppekausen, J.; Stade, R.; Goddard, R.; Fürstner, A., Practical new
silyloxy-based alkyne metathesis catalysts with optimized activity and
selectivity profiles. J. Am. Chem. Soc. 2010, 132, 11045-11057.
(
18) Heppekausen, J.; Stade, R.; Kondoh, A.; Seidel, G.; Goddard, R.;
Fürstner, A., Optimized synthesis, structural investigations, ligand tuning
and synthetic evaluation of silyloxy-based alkyne metathesis catalysts. Chem.
Eur. J. 2012, 18, 10281-10299.
(19) (a) 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., Molecular and Silica-Supported Molybdenum
Alkyne Metathesis Catalysts: Influence of Electronics and Dynamics on
Activity Revealed by Kinetics, Solid-State NMR, and Chemical Shift Analy-
sis. J. Am. Chem. Soc. 2017, 139, 17597-17607. (b) Estes, D. P.; Bittner, C.;
Àrias, Ò .; Casey, M.; Fedorov, A.; Tamm, M.; Copéret, C., Alkyne Metathe-
sis with Silica-Supported and Molecular Catalysts at Parts-per-Million Load-
ings. Angew. Chem., Int. Ed. 2016, 55, 13960-13964.
(28) Bai, W.; Lee, K.-H.; Sung, H. H. Y.; Williams, I. D.; Lin, Z.; Jia, G.,
Alkyne Metathesis Reactions of Rhenium(V) Carbyne Complexes.
Organometallics 2016, 35, 3808-3815.
(29) Bai, W.; Wei, W.; Sung, H. H. Y.; Williams, I. D.; Lin, Z.; Jia, G.,
Syntheses of Re(V) Alkylidyne Complexes and Ligand Effect on the
Reactivity of Re(V) Alkylidyne Complexes toward Alkynes. Organometallics
2018, 37, 559-569.
31
1
(
20) Weissman, H.; Plunkett, K. N.; Moore, J. S., A highly active, heteroge-
neous catalyst for alkyne metathesis. Angew. Chem., Int. Ed. 2006, 45, 585-
88.
21) (a) Haberlag, B.; Wu, X.; Brandhorst, K.; Grunenberg, J.; Daniliuc, C.
(30) The P{ H} NMR spectrum of the crude product displays two signals at
46.3 and 30.9 ppm, in addition to a broad peak at -32.3 ppm assignable to
1
5
(
CuI(PMePh ). The H NMR spectrum shows characteristic peaks of Re≡
2
2
CCH Ph at 2.88 (dt, J = 18.9, 3.2 Hz) and 2.58 (dt, J = 18.9, 3.6 Hz) ppm
G.; Jones, P. G.; Tamm, M., Preparation of imidazolin-2-iminato
molybdenum and tungsten benzylidyne complexes: a new pathway to highly
active alkyne metathesis catalysts. Chem. Eur. J. 2010, 16, 8868-8877. (b)
Beer, S.; Brandhorst, K.; Hrib, C. G.; Wu, X.; Haberlag, B.; Grunenberg, J.;
Jones, P. G.; Tamm, M., Experimental and Theoretical Investigations of
Catalytic Alkyne Cross-Metathesis with Imidazolin-2-iminato Tungsten
Alkylidyne Complexes. Organometallics 2009, 28, 1534-1545. (c) Beer, S.;
Hrib, C. G.; Jones, P. G.; Brandhorst, K.; Grunenberg, J.; Tamm, M.,
Efficient room-temperature alkyne metathesis with well-defined imidazolin-
and a doublet at 8.31 (J = 5.7 Hz) ppm which is assignable to a pyridine
ligand. The NMR data are similar to those of the isolated pyridine-
coordinated complex Re4.
(
31) Commercial A.R. grade toluene or isobutanol stored in air without any
drying process was bubbled with N for 10 minutes before use. Because 5Å
2
MS cannot be employed to absorb 2-butyne in wet solvents, refluxing condi-
tion was utilized to remove the byproduct 2-butyne which will cause pro-
longed reaction times. See: reference 17.
(32) There’s one example of moisture stable alkylidyne catalyst for ring
opening alkyne metathesis polymerization. See: reference 14. Besides, it
2
8
-iminato tungsten alkylidyne complexes. Angew. Chem., Int. Ed. 2007, 46,
890-8894.
should also be mentioned that some Mo(CO) /phenol-based systems have
6
(
22) (1) Elser, I.; Groos, J.; Hauser, P. M.; Koy, M.; van der Ende, M.; Wang,
been reported to operate without exclusion of air or moisture. See: refer-
ences 6a, 6b and 6d).
(33) Schaubach, S.; Gebauer, K.; Ungeheuer, F.; Hoffmeister, L.; Ilg, M. K.;
Wirtz, C.; Fürstner, A., A Two-Component Alkyne Metathesis Catalyst
System with an Improved Substrate Scope and Functional Group Tolerance:
Development and Applications to Natural Product Synthesis. Chem. Eur. J.
2016, 22, 8494-507.
(34) Zhu, J.; Jia, G.; Lin, Z., Theoretical Investigation of Alkyne Metathesis
Catalyzed by W/Mo Alkylidyne Complexes. Organometallics 2006, 25, 1812-
1819.
D.; Frey, W.; Wurst, K.; Meisner, J.; Ziegler, F.; Kästner, J.; Buchmeiser, M.
R., Molybdenum and Tungsten Alkylidyne Complexes Containing Mono-,
Bi-, and Tridentate N-Heterocyclic Carbenes. Organometallics 2019, 38,
4
133-4146. (2) Koy, M.; Elser, I.; Meisner, J.; Frey, W.; Wurst, K.; Kastner,
J.; Buchmeiser, M. R., High Oxidation State Molybdenum N-Heterocyclic
Carbene Alkylidyne Complexes: Synthesis, Mechanistic Studies, and
Reactivity. Chem. Eur. J. 2017, 23, 15484-15490.
(
23) (a) Lysenko, S.; Haberlag, B.; Daniliuc, C. G.; Jones, P. G.; Tamm, M.,
Efficient Catalytic Alkyne Metathesis with a Tri(tert-butoxy)silanolate-
Supported Tungsten Benzylidyne Complex. ChemCatChem 2011, 3 , 115-
1
18. (b) Li, S. T.; Schnabel, T.; Lysenko, S.; Brandhorst, K.; Tamm, M.,
Synthesis of unsymmetrical 1,3-diynes via alkyne cross-metathesis. Chem.
Commun. 2013, 49, 7189-7191.
(
24) (a) Haberlag, B.; Freytag, M.; Daniliuc, C. G.; Jones, P. G.; Tamm, M.,
Efficient metathesis of terminal alkynes. Angew. Chem., Int. Ed. 2012, 51,
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