Unraveling the Mechanism of 1,3-Diyne Cross-Metathesis Catalyzed by Silanolate-Supported Tungsten Alkylidyne Complexes

Article abstract of DOI:10.1002/chem.201801651

The benzylidyne complex [PhC≡W{OSi(OtBu)₃}₃] (1) catalyzed the cross-metathesis between 1,4-bis(trimethylsilyl)-1,3-butadiyne (2) and symmetrical 1,3-diynes (3) efficiently, which gave access to TMS-capped 1,3-diynes RC≡C?C≡CSiMe

Full text of DOI:10.1002/chem.201801651

A Journal of
Accepted Article
Title: Unraveling the Mechanism of 1,3-Diyne Cross-Metathesis
Catalyzed by Silanolate-Supported Tungsten Alkylidyne
Complexes
Authors: Matthias Tamm, Tobias Schnabel, Daniel Melcher, Kai
Brandhorst, and Dirk Bockfeld
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201801651
Link to VoR: http://dx.doi.org/10.1002/chem.201801651
Supported by

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
Unraveling the Mechanism of 1,3-Diyne Cross-Metathesis Cata-
lyzed by Silanolate-Supported Tungsten Alkylidyne Complexes
Tobias M. Schnabel, Daniel Melcher, Kai Brandhorst, Dirk Bockfeld, and Matthias Tamm*[a]
diynes,[33–35] such as Cadiot-Chodkiewicz coupling and the
Fritsch-Buttenberg-Wiechell rearrangement,[37] which usually
involve the generation of reactive bromoalkynes or
dibromoenyne species, respectively. These methods suffer
from a limited substrate scope, and formation of bromide-
containing side products is less economical and
environmentally benign. Therefore, direct metal-catalyzed
cross-coupling of two terminal alkynes represents an attractive
alternative;[34,35] however, low selectivity towards the formation
of the desired unsymmetrical diyne will typically yield
significant amounts of the corresponding homocoupled diynes
as side products. Optimization was achieved by using one
alkyne in large excess, e.g., 4- to 6-fold in Cu-,[38–40] Ni/Cu-[41]
and Fe/Cu-catalyzed[42] reactions. Recently, several protocols
were established which display larger heteroselectivity and
provide sufficient yields of the unsymmetrical diyne with
application of the major alkyne in only two-fold or even lower
excess.[35] Heterogeneous[43–45] and homogeneous[46–48]
[36]
Abstract: The benzylidyne complex [PhCW{OSi(OtBu)
catalyzed the cross-metathesis between 1,4-bis(trimethylsilyl)-
,3-butadiyne (2) and symmetrical 1,3-diynes (3) efficiently, which
gave access to TMS-capped 1,3-diynes RCC–CCSiMe (4).
Diyne cross-metathesis (DYCM) studies with C-labeled diyne
}
3 3
] (1)
1
3
13
13
13
PhC C– CCPh (3*) revealed that this reaction proceeds
through reversible carbon-carbon triple-bond cleavage and
formation according to the conventional mechanism of alkyne
metathesis. The reaction between 1 and 3* afforded the 3-
13
13
3 3
phenylpropynylidyne complex PhC C– CW{OSi(OtBu) } ] (5*),
indicating that alkynylalkylidyne complexes are likely to act as
catalytically active species. Attempts to isolate 5* from mixtures of
1
and 3* afforded crystals of the ditungsten 2-butyne-1,4-diylidyne
13
13
13
13
complex [(tBuO)
3
3 3 3
SiO} W C– C C– CW{OSi(OtBu) } ] (6*),
which was additionally characterized by X-ray diffraction analysis.
Depolymerization-macrocyclization of carbazole-butadiyne
a
polymer, obtained from 3,6-diethynyl-9-dodecylcarbazole (7)
under copper-catalyzed Hay coupling conditions, was also
efficiently catalyzed by 1 and afforded a mixture of mono-, diyne-
and triyne-containing tetrameric macrocycles, revealing that diyne
disproportionation into monoynes and triynes occurs as a slow
side reaction that interferes with a high diyne metathesis selectivity.
Potential catalytic pathways were studied by means of quantum-
chemical calculations, and kinetic studies were performed to
substantiate an ,-mechanism for the catalytic diyne metathesis
reaction, which involves intermediate alkynylalkylidyne and ,’-
dialkynylmetallacyclobutadiene intermediates.
copper and gold catalysts as well as bimetallic Pd/Cu- and
Ni/Ag-based systems[
49,50]
were succesfully employed for
these transformations. Propargylic and homopropargylic
alkohols, ethers and esters are particularly useful substrates
for these heterocouplings,[46,47,50] since selective and
subsequent alkyne activation is mediated by oxygen-metal
interaction.[50]
Introduction
Conjugated diynes and polyynes constitute important core
structures
compounds,[
in
4–13]
natural
materials and polymers.
products,[1–3]
supramolecular
[14–27]
Numerous
methods exist for the construction of the rigid diyne moiety,
with metal-catalyzed oxidative homocoupling of terminal
alkynes, e.g., Glaser, Eglinton and Hay coupling reactions,
representing the most important method for the preparation of
symmetrical 1,3-diynes (Scheme 1).[28–32] More elaborate
methods are required for the synthesis of unsymmetrical
[
a]
T. Schnable, Dr. D. Melcher, Dr. K. Brandhorst, D. Bockfeld, Prof.
Dr. Matthias Tamm
Institut für Anorganische und Analytische Chemie
Technische Universität Braunschweig
Hagenring 30, 38106 Braunschweig, Germany
E-mail: m.tamm@tu-bs.de.
Scheme 1. Synthesis of symmetrical and unsymmetrical 1,3-diynes.
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
Despite these advances, the irreversible formation of the
carbon-carbon bond in these oxidative alkyne cross-coupling
reactions is still a major drawback, since the corresponding
homocoupled diynes will also form inevitably and need to be
discarded, if only the unsymmetrical diyne is of further use. We
have introduced an alternative reversible method for the
synthesis of conjugated diynes that built on the recent
remarkable advances in the development and application of
moieties from a diyne polymer under alkyne metathesis
conditions.[
85]
To rationalize the high selectivity of 1 towards diyne
formation, we proposed
a mechanism based on the
conventional mechanism of alkyne metathesis via
metallacyclobutadiene (MCBD) intermediates.[
86,87]
Thus,
diyne
metathesis
likely
involves
alkynylalkylidyne
intermediates (MC–CCR), which could reversibly undergo
[2+2]-cycloaddition with the respective 1,3-diynes to afford
,’-dialkynyl-MCBD species ( and ’ refer to the 1,3-
positions in the metallycycle, and  denotes the 2-position).
Although this so-called ,-mechanism was substantiated by
[51–62]
homogeneous alkyne metathesis catalysts.
Apart from
Schrock-type[
63,64]
molybdenum and tungsten alkylidyne
complexes supported by fluoroalkoxides,[65–77] our group has
also introduced silanolate complexes such as 1 (Scheme 1) as
efficient catalysts for the metathesis and ring-closing
13
reaction of 1 with the C-monolabeled 1,4-diphenyl-1,3-
1
3
metathesis
respectively.[
of
78,79]
internal
alkynes
and
,-diynes,
butadiyne PhC C–CCPh, an alternative mechanism
Moreover, 1 was found to promote the
involving alkylidyne and -monoalkynyl-MCBD intermediates
could not be excluded (-mechanism).[
80]
With both
metathesis of methyl-capped conjugated diynes of the type
RCC–CCMe, which was originally anticipated to afford
mechanistic scenarios, the selectivity towards diyne
metathesis is explained satisfactorily, whereas diyne
disproportionation can be rationalized only by deviation from
the ,-mechnism, e.g., with triyne formation via an ,-
dialkynyl-MCBD. To further validate these assumptions, we
triynes
(
RCC–CC–CCR
together
with
2-butyne
MeCCMe).[80] High selectivity towards the formation of
symmetrical diynes (RCC–CCR) was found instead; these
reactions afforded stoichiometric amounts of 2,4-hexadiyne
81]
(
dimethyldiacetylene, DMDA),[ which was removed from the
would like to present in this contribution a combined
equilibrium by adsorption on molecular sieves (5 Å) or by
evaporation. The usefulness of this diyne homometathesis
reaction should be questioned for good reason, since the loss
experimental and theoretical study that will help to further
unravel the mechanism of the 1,3-diyne metathesis reaction,
which we regard as an important expansion of the increasingly
important field of alkyne metathesis.[
51–60,62]
6
of a C -building block effects poor atom economy. We
concluded, however, that the reversibility of carbon-carbon
triple-bond formation under thermodynamic control will
potentially allow to exploit this reaction for the construction of
macrocyclic or polymeric diyne materials, which was in fact
demonstrated by ring-closing diyne metathesis (RCDYM).[
Subsequently, this reactivity was also observed for silanolate-
supported molybdenum alkylidyne complexes and employed
in the total synthesis of naturally ocurring cyclo-1,3-
diynes.[82,83]
Turning diyne metathesis into a useful reaction can also
be achieved by cross-metathesis of two symmetrical 1,3-
diynes (diyne cross-metathesis, DYCM), which are each
conveniently accessible by copper-catalyzed homocoupling of
the corresponding terminal alkynes (Scheme 1). Accordingly,
Results and Discussion
80]
Diyne cross-metathesis (DYCM)
For expanding the scope of diyne cross-metathesis, we
investigated the equilibrium reaction between 1,4-
bis(trimethylsilyl)-1,3-butadiyne (2) and various symmetrical
aromatic and aliphatic 1,3-diynes (3). These reactions provide
access to unsymmetrical TMS-capped diynes RCC–
3
CCSiMe (4), which are useful synthetic intermediates and
may serve as synthons for terminal or metalated butadiyne
[88]
derivatives.
reactions,
As described previously for other DYCM
preliminary NMR experiments were carried out
1
proved capable to promote the equilibrium reaction between
[84]
various 1,4-diaryl- and 1,4-dialkyl-1,3-butadiynes.[
84]
To
for the reaction between
2
H
and 1,4-bis(4-methoxy)-1,3-
4
) to establish the equilibrium
increase the yield of the desired unsymmetrical diyne, one
substrate is usually used in excess, e.g., 4 : 1, and the isolated
yields fall in the range expected theoretically for just slightly
exergonic reactions. In contrast to copper-catalyzed cross-
couplings, the symmetrical diyne starting materials can be
recycled and used again in the equilibrium metathesis reaction.
While catalyst 1 showed remarkably high selectivity towards
metathetical diyne formation, slow diyne disproportionation
into the corresponding monoynes and triynes (and
subsequently into polyynes) was observed after prolonged
reaction times.[84] As observed by Gross and Moore, this
disproportionation is significantly faster in the presence of
other alkylidyne catalyst systems, which explains the isolation
butadiyne (3a, R = p-MeOC
6
2
constant K = [4a] /([2][3a]) (Table 1, see also Table 2, Entry 1).
The reaction in CH
2
Cl
2
was initially followed by gas
chromatography, revealing that the equilibrium for this diyne
combination is established within ca. 100 minutes at room
temperature in the presence of 2 mol% of catalyst 1 (see the
Supporting Information, Section S8.1). The reaction was then
performed under the same conditions in CD
2
Cl
2
for various
ratios of the starting concentrations [2]
0
: [3a]
0
. Integration of
1
the sufficiently well separated H NMR signals for the OCH
3
groups in 3a (6H, δ  3.82 ppm) and 4a (3H, δ  3.81 ppm)
allows to determine their relative concentrations and the
resulting equilibrium constant K (Table 1). In accordance with
Le Chatelier’s principle, increasing the excess of 2 over 3a
from 1 : 1 to 4 : 1 shifts the equilibrium towards the desired
2 4
of tetrameric macrocycles with yne (C ) and diyne (C )
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
unsymmetrical diyne 4a with an increasing [4a] : [3a] ratio. For
all four experiments, K is satisfactorily well reproduced with an
average value of K = 4.2. As expected, the corresponding
Table 2. Diyne cross-metathesis of symmetrical to unsymmetrical 1,3-
diynes catalyzed by 1 with a 4 : 1 ratio of 2 and 3.[
a]
-1
Gibbs free energy (ΔG298K < –1 kcal mol ) indicates that the
formation of the unsymmetrical 1,3-diyne is only slightly
exergonic. It should be noted that this experiment shall merely
confirm that we are dealing with an almost thermoneutral
equilibrium reaction and that the error of K and ΔG298K must be
ascribed to the limit of accuracy of integrating the respective
Educt
Product 4
Time
min.]
Yield[b]
[%]
[
1
H NMR signals.
3
a
b
100
120
88
91
Table 1. NMR study of an quilibrium diyne cross-metathesis reaction.[a]
3
ΔG298K
Yield[d]
[%]
[
b]
[4a] : [3a][c]
[2]
0
: [3a]
0
K
-
1
[kcal mol ]
3 [
c
c]
60
89
82
88
1
2
3
4
: 1
: 1
: 1
: 1
1.70
4.70
6.74
8.12
2.89
5.08
4.66
4.08
–0.63
–0.96
–0.91
–0.83
46
70
77
80
3d
25
3e
3f
200
[a] Reaction between 1,4-bis(trimethylsilyl)-1,3-butadiyne (2) and 1,4-
bis(4-methoxyphenyl)-1,3-butadiyne (3a) affording 4-(4-methoxyphenyl)-
230
83
1,3-butadiyn-1-yltrimethylsilane (4a, R = 4-MeOC
6 4
H ; see Table 2, Entry
1
); for a detailed protocol and relevant equations, see the Supporting
[
84]
Information (Section S5) and previous work. [b] Ratio of the starting
[
2 2
a] Conditions: 2 (0.1 M), 3 (0.025 M), catalyst 1 (2 mol%), CH Cl , room
concentrations. [c] Ratio of the equilibrium concentrations determined by
temperature; see the Supporting Information (Section S6) for full details. [b]
Yield of product 4 isolated after filtration through alumina and purification
by column chromatography; the yields are based on the conversion of the
minor substrate 3; the unconsumed starting materials 2 and 3 are largely
recovered. [c] The molecular structure was determined by X-ray diffraction
analysis (see Supporting Information, Section S1).
1
integration of the OCH
3
H NMR signals in 3a (6H) and 4a (3H).
[d] Calculated yield based on the conversion of 3a.
DYCM with 2 was then studied for the diynes 3a–3f
shown in Table 2, which were obtained from the
corresponding terminal alkynes by CuCl-catalyzed
homocoupling.[ Initially, conversion versus time diagrams
were recorded for each diyne combination to establish the
optimum reaction time (see the Supporting Information,
Section S8). The reactions were then performed on
preparative scale (2.60 mmol 2, 0.65 mmol 3, 0.065 mmol
13C-Labeling studies
89]
We had previously reported diyne homometathesis of 13C-
1
3
13
monolabeled 1,3-pentadiyn-1-yl-2- C-benzene (PhC C–
CCMe), which afforded monolabeled 1,4-diphenyl-1,3-
1
3
13
[80]
butadiyne-2- C (PhC C–CCPh).
The absence of any
detectable amounts of doubly labeled 1,4-diphenyl-1,3-
1); after equilibration, the reaction mixtures were filtered
1
3
13
13
butadiyne-2,3- C (PhC C– CCPh, 3b*) confirmed that
the metathesis reaction proceeds through carbon-carbon
triple-bond cleavage and formation, ruling out any mechanism
involving alkynyl group exchange.[94] Here, 3b* obtained by
through alumina, and the diynes were separated by column
chromatography. The isolated yields of 4 are based on the
conversion of the minor diyne component 3 and range from
82% (4d) to 91% (4b). In all cases, the unconverted starting
13
copper-catalyzed
phenylacetylene (PhC CH) was employed in DYCM with 2.
Initially, a 1 : 1 mixture of both alkynes was dissolved in CD Cl
together with 2 mol% of 1. The 13C NMR spectrum (see the
Supporting Information, Section S9.11) was recorded after 2 h
reaction time, revealing the presence of the doubly labeled
homocoupling
of
C-labeled
material 2 could be largely recovered and used in further
DYCM reactions. The isolated yield of 4a (88%) is larger
than the yield determined by NMR spectroscopy for a
1
3
2
2
4
: 1 mixture of 2 and 3a (80%, see Table 1), which we
ascribe to the error of the NMR experiment and to the
different reaction conditions. Overall, our new method for the
preparation TMS-capped 1,3-butadiynes is clearly able to
compete with alternative procedures employing, among
others, Cadiot-Chodkiewicz- or Sonogashira-type coupling
reactions.[90–93]
1
3
13
13
13
butadiynes Me
(
3
SiC C– CCSiMe
3
(2*), PhC C– CCPh
1
3
13
3b*) and PhC C– CCSiMe
form via the equilibrium reactions shown in Scheme 2. The
carbon atoms of the labeled positions give rise to singlets at
8.2 ppm for 2* and 74.0 ppm for 3b*, whereas two doublets
at 88.0 and 74.3 ppm with 1JCC = 148 Hz are found for
3
(4b*), which are expected to
1
3
C
8
13
asymmetric 4b*. Full experimental and simulated C NMR
spectra of all the three labeled diynes with the assignment of
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
all signals are presented in the Supporting Information
complexes and contain tungsten in the formal oxidation state
+IV. Closer inspection of the full 13C NMR spectrum of 5* (see
the Supporting Information, Section S9.12) reveals the
presence of only very minor amounts of other labeled polyyne
species. A signal at 89.3 ppm is assigned to the acetylenic unit
of diphenylacetylene (tolane), which must form as a side
product in stoichiometric amounts. Its formation was
additionally confirmed by UV/vis spectroscopy, which also
indicated the absence of the starting material 1,4-diphenyl-1,3-
butadiyne and of the higher polyyne 1,6-diphenyl-1,3,5-
hexatriyne[96,101] (see the Supporting Information, Section S10).
(
Section S9). Repeating the metathesis between 2 and 3b* on
a preparative scale under the reaction conditions mentioned in
Table 2 (four-fold excess of 2) afforded a mixture of 4b*/4b in
8
9% yield after chromatographic work-up. Figure 1 shows an
1
3
excerpt from the resulting C NMR spectrum; the singlets at
the positions marked C1, C2, C3 and C4 are assigned to
unlabeled 4b, while the two doublets for the labeled positions
C2 and C3 in 4b* (see above) come along with two doublets
of doublets for the unlabeled carbon atoms C1 and C4, which
display 1JCC/ JCC couplings of 147/18 Hz and 196/25 Hz,
respectively. It should be noted that the DYCM protocol
2
provides
convenient
access
to
symmetrical
and
1
3
unsymmetrical doubly C-labeled 1,3-butadiynes which are
difficult to be obtained by other methods.[95,96]
Figure 1. Excerpt from the 13C NMR spectrum of 4b*/4b in CD
asterisk denotes an impurity of 2*.
2 2
Cl ; the
Unfortunately, the complexes 5 and 5* could not be
isolated in pure form, since all attempts to crystallize these
highly soluble compounds, e.g., from hexamethyldisiloxane or
toluene, afforded dark red crystals of 6 or 6* in ca. 30% yield
Scheme 2. Diyne metathesis with 13C-labeled diphenylbutadiyne (3b*). The
asterisks indicate labeled position; the corresponding complexes 5 and 6
are formed from unlabeled diphenylbutadiyne (3b).
(
Scheme 2). The molecular structure of 6 was confirmed by X-
1
3
ray diffraction analysis, revealing the formation of a C -bridged
4
As previously described for monolabeled PhC C–
CCPh,[
80]
13
ditungsten complex (Figure 3). The asymmetric unit contains
two halves of two independent centrosymmetric molecules
with similar geometric parameters. The W–C1–C2 and C1–
C2–C2’ angles are close to linearity (176°–179°), and the W–
C1 bond lengths of 1.780(4) Å (molecule A) and 1.777(6) Å
(molecule B) indicate the presence of tungsten-carbon triple
doubly
C-labeled 3b* was treated with an
. The 13C NMR spectrum
equimolar amount of 1 in CD Cl
2 2
indicated the formation of the 3-phenylpropynylidyne complex
5
9
2
* (Scheme 2), which displays two doublets at 251.8 and
6.0 ppm (1JCC = 94 Hz) for the W C– CCPh unit (Figure
13
13
1
83
). The tungsten satellites reveal couplings with the
W
1
2
bonds in comparison with a just slightly shorter W–C1 bond of
isotope of JCW = 300 Hz and JCW = 61 Hz, which is in good
agrement with the previously established values for the
78]
1
.745(2) Å in 1.[
Accordingly, the C1–C2 bonds are
13
13
[80]
significantly longer than the C2–C2’ bonds, revealing the
presence of a bis(alkylidyne) complex with a WC–CC–CW
moiety. This assignment is also confirmed by the observation
W C–CCPh and WC– CCPh congeners.
A similar
1
coupling ( JCW = 296 Hz) was reported for the quinuclidine
adduct of the related complex [(tBuO)
formed in a similar fashion from [(tBuO)
octadiyne.[97] It should be noted that other tungsten 3-
3
WC–CCEt], which
13
of two doublets of doublets for the fully labeled W C–
3
WCMe] and 3,5-
1
3
13
13
13
C C– CW moiety in the C NMR spectrum of 6* (see the
Supporting Information, Section S9.14), which appear at 247.0
(C ) and 88.7 ppm (C
) with 1JCC and 2JCC couplings of 64 and
2 Hz, respectively.
5
phenylpropynylidyne complexes, e.g., [PhCC–CW(CO X]
X = Cl, Br, I),[98–100]


(
represent classical Fischer-type carbyne
4
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
W(dppe)
W(CO) (dppe)X
Re(PMe (CCSiMe
exhibits significantly shorter metal-carbon bonds than the
2
I
(dppe
=
bis(diphenylphosphino)ethane),
(X
=
Cl,
I),[
108,109]
and
2
+
[110]
[
6
3
)
4
3
)] .
It should be noted, however, that
previous ditungsten complexes, in which the formal oxidation
state +IV is assigned to the metal atoms. Therefore, 6
represents the first example of a 2-butyne-1,4-diylidyne
complex terminated by two tungsten(VI) metal atoms.
The formation of 6 from 1 and 1,4-diphenyl-1,3-butadiyne
(
3b) can be rationalized by initial formation of alkynylalkylidyne
complex 5 (as evidenced by 13C NMR spectroscopy for 5*) with
release of one equivalent of diphenylacetylene (tolane).
Reaction of 5 with additional diyne could then furnish 1,6-
diphenyl-1,3,5-hexatriyne and 1, which will further form 6 and
and additional tolane, presumably via
a 5-phenyl-2,4-
pentadiynylidyne species (WC–CC–CC–Ph). Accordingly,
a 1 : 1 reaction between 1 and 1,4-diphenyl-1,3-butadiyne
furnishes 1.5 equivalents of tolane, which was the only side
product that could be identified unambiguously, e.g., by UV/vis
spectroscopy. It should be noted that the observed fast
formation of 5/5* supports the prevalence of the ,-
mechanism of diyne metathesis, whereas the subsequent
slow disproportionation must proceed through an ,-MCBD,
in which the alkylidyne and alkynyl moieties reside in
neighboring positions. The final formation of 6 may then
quickly proceed according to the ,-mechanism, which
explains our inability to monitor the intermediate formation of
PhC C– C C– CC–Ph and W C– C C– CC–Ph
species, if labeled diphenylbutadiyne (3b*) is employed. The
observation of all labeled carbon atoms in the C4 bridge of 6*
rules out any other mechanistic scenario that does not involve
the cleavage and formation of carbon-carbon triple bonds.
Figure 2. Excerpt from the 13C NMR spectrum of a 1 : 1 mixture of 1 and
3
2 2
b* in CD Cl showing the signals of the - and -carbon atoms of the
13
13
W C– CCPh unit in 5*.
Si3'
Si1
O1
O9'
1
3
13
13
13
13
13
13
13
W
C1 C2
Si2'
O5
Si2
C2' C1' W'
O1'
O5'
O9
Si3
Si1'
Diyne depolymerization-macrocyclization
Despite the high selectivity of catalyst 1 in diyne metathesis,
the isolation of 6/6* confirmed the possibility of slow diyne
disproportionation into monoynes and triynes (and
subsequently into polyynes) as reported previously.[84] This
side reaction is also responsible for the formation of tetrameric
Figure 3. Molecular structure of 6 (molecule A) with thermal displacement
parameters drawn at 50% probability; methyl groups and minor components
of disordered groups were omitted for clarity. The asymmetric unit contains
two halves of two independent molecules; selected bond lengths [Å] and
angles [°] in molecule A/B: W–C1 1.780(4)/1.777(6), C1–C2
1.361(7)/1.371(9), C2–C2’ 1.238(9)/1.224(13); W–C1–C2 176.0(4)/
78.0(5), C1–C2–C2’ 176.8(6)/179.3(10).
macrocycles with yne (C
carbazole-butadiyne polymer
EtCMo{N(Ar)tBu} ]/Ph SiOH. With this catalyst system, the
2
) and diyne (C
4
) moieties from a
1
in the presence of
[
3
3
compound with four 1,3-butadiyne-1,4-diyl units was detected
only as a minor product by MALDI-TOF mass spectrometry,
which also revealed the formation of a mixture of tetramers
The ditungsten complex 6 represents a new carbon-rich
transition metal complex, in which sp carbon chains terminate
-bridged systems,
with carbon-metal bonds.[18,102–104] For C
4
2 4
with varying amounts of C and C units incorporated in the
complexes with an even number of electrons may exist in three
conjugated forms, i.e. M–CC–CC–M (1,3-butadiyne-1,4-
diyl), M=C=C=C=C=M (1,2,3-butatriene-1,4-diylidene) and
MC–CC–CM (2-butyne-1,4-diylidyne). The 1,3-butadiyne-
,4-diyl form is most common, and two- and four-electron
oxidation would formally afford the 1,2,3-butatriene-1,4-
diylidene and 2-butyne-1,4-diylidyne species.[104–106] The
macrocycle.[85] Since we expected a higher selectivity of
catalyst 1 towards diyne formation, we studied its performance
in the depolymerization of a related polycarbazole system.
Therefore, 3,6-diethynyl-9-dodecylcarbazole (7)[111,112] was
prepared and subjected to polymerization under copper-
catalyzed Hay coupling conditions (Scheme 3).[85] According
to gel permeation chromatography (GPC), the resulting
1
dicarbyne form as realized in 6 has been stabilized only in a
n
polymer 8 had a M of 27 kDa, a polydispersity index (PDI) of
few ditungsten and dirhenium complexes, e.g., with M =
Tp’ (Tp’= hydridotris(3,5-dimethylpyrazolyl)borate),[107]
1.7 and a degree of polymerization of 51 (Table 3).
W(CO)
2
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
the GPC trace indicates the conversion of polycarbazole 8 to
a (quasi-)monodisperse lower molecular weight oligomer
(
(
Figure 4, Table 3). Analysis of this product by MALDI-MS
Figure 5) revealed that the depolymerization-macro-
cyclization reaction did not exclusively produce the expected
tetramer 9 (m/z = 1525), but also afforded the tetrameric
species 9+C
2
(m/z = 1549), 9–C
2
(m/z = 1501), 9–C
4
(
m/z = 1477). Again, the formation of 9 with four diyne units as
the main product confirms the ability of 1 to act as a rather
selective diyne-metathesis catalyst. However, the prolonged
reaction times required for complete depolymerization lead to
substantial diyne disproportionation as an undesired side
reaction, which also furnishes the tetrameric species with one
C
6
and three C
as well as two C
compound should exist as a mixture of two structural isomers
Scheme 3). It is obvious that diyne disproportionation
4
units (9+C
2
), one C
2
and three C
4 2
units (9–C )
2
and two C
4
units (9–C
4
). In principle, the latter
(
constitutes an unavoidable, albeit slow side-reaction, and in
future experiments, further adjustment regarding the degree of
polymerization, catalyst loading, and reaction time is required
to apply this catalytic diyne metathesis methodology efficiently
in supramolecular chemistry.
Scheme 3. Polymerisation of carbazole
7 and depolymerization-
macrocyclisation of polycarbazole 8 to cyclic tetramers 9.
Table 3. Gel permeation chromatography data.[a,b]
Figure 4. GPC traces of polymer 8 and of the mixture containing tetramers
9
after 22 h.
Compound
Monomer 7
Polymer 8
M
n
[kDa]
M
w
[kDa]
M
w
/M
n
P [
c]
n
0.55
27.9
2.5
0.55
47.8
2.5
1.0
1.7
1.0
-
51
-
Tetramers 9d
[
a] Reactions conditions: toluene, 10 wt% 1, 22 h, rt. [b] Based on polystyrene
standards, see the Supporting Information (Section S11) for details. [c]
Degree of polymerization P = M (polymer)/M (monomer). [d] Mixture of
n
n
n
tetramers 9 with all distributions shown in Scheme 3.
A toluene solution of the diyne-bridged polycarbazole 8
was treated with a catalytic amount of 1 (10 wt%) and stirred
at room temperature for 22 h (Scheme 3). The resulting crude
reaction mixture was passed through a short pad of neutral
aluminium oxide to remove the catalyst. Recrystallization from
THF solution at –30 °C afforded a white powder in 75% yield;
Figure 5. Partial MALDI-TOF mass spectrum of the mixture containing the
tetramers 9–C (m/z = 1477) 9–C (m/z = 1501), 9 (m/z = 1525) and 9+C
m/z = 1549) shown in Scheme 3.
4
,
2
2
(
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
Scheme 4. Possible catalytic cycles for the metathesis of conjugated diynes. Microscopic reversibility is expected for all reaction steps; the direction of arrows
1
1
2
2
shall indicate constructive reaction paths towards the cross-metathesis of two symmetrical diynes R CC–CCR and R CC–CCR .
Quantum chemical modeling of diyne metathesis reactions
on the right-hand side. As previously stated,[80] both mechanisms
allow to rationalize the selectivity towards the formation of 1,3-
diynes during their homo- and cross-metathesis, whereas the
1
3
The diyne metathesis studies employing the C-labeled diynes
PhC C–CCMe, PhC C–CCPh,
(
1
3
13
[80]
13
13
and PhC C– CCPh
vide supra) rule out any mechanistic scenario that does not
observed side reaction, slow diyne disproportionation into mono-
and triynes (and subsequently into polyynes),[
84,85]
is explained by
involve the cleavage and formation of carbon-carbon triple bonds
according to the established mechanism of the alkyne metathesis
reaction, which involves intermediate metallacyclobutadiene
deviation from the two alternative mechanistic pathways and by
the occurrence of ,-dialkynyl-MCBDs. Overall, the ,-
mechanism is more likely, since the formation of the latter species
does also require alkynylalkylidyne intermediates, which were
identified unambiguously by NMR spectroscopy as 13C-labeled
W C–CCPh, WC– CCPh and W C– CCPh units (vide
supra). It must be emphasized, however, that their observation
under the reaction conditions in the NMR tube cannot be regarded
as conclusive proof, and therefore, we tried to disclose the
mechanism of diyne metathesis by density functional theory
(DFT) calculations.
Since the tungsten complex 1 is currently the only alkylidyne
complex that is capable to promote the metathesis of diynes
efficiently, the ancillary silanolate ligands seem to be crucial for
the observed catalytic activity and selectivity and need to be fully
included in the quantum chemical calculations. Because of the
enormous size and nature of the silanolate ligands in complex 1,
(
MCBD) species.[86] It is therefore reasonable to assume that the
metathesis of conjugated diynes also proceeds through a
combination of reversible [2+2] cycloaddition and cycloreversion
steps. However, the situation is less clear-cut, since two
alternative catalytic cycles can be entered from a pre-catalyst (like
13
13
13
13
1
in this paper), which involve different catalytically active species.
As shown in Scheme 4, initiation by cycloaddition of a diyne to the
pre-catalyst can afford either an - or a -MCBD, which differ in
the position of the alkynyl group. Subsequent cycloreversion will
lead to alkynylalkylidyne (Scheme 4, left) or alkylidyne complexes
(
Scheme 4, right), which each appear as intermediates in one of
the two catalytic cycles. On the left, catalytic turnover proceeds
further via ,’-dialkynyl-MCBDs (“,-mechanism”), whereas -
monoalkynyl-MCBDs (“-mechanism”) are exclusively involved
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
appropriate consideration of dispersion effects are of particular
importance to predict the catalytic activity, and therefore, we
decided to employ the PW6B95-D3 functional together with the
def2-TZVP basis for the calculation of all reported electronic
energies.[113–117] Unfortunately this level of theory turned out to be
too demanding for running geometry optimizations and frequency
calculations, and we had to resort to the M06[118] functional and
the rather small double-zeta basis set 6-31G(d,p) for this task.
Therefore, all reported values correspond to pure electronic
energies computed at the PW6B95-D3/def2-TZVP level of theory
at the geometries optimized at the M06/6-31G(d,p) level of theory.
For details see Supporting Information (Section S15).
MCBD is kinetically and thermodynamically preferred compared
to triyne and monoyne formation via an ,-MCBD, In conclusion,
our computations predict that alkynylalkylidyne complexes
represent the catalytically active species and that diyne
metathesis follows the ,-mechanism, whereas the formation of
higher polyynes is disfavoured.

E [kcal mol-1
]
40
30
20


30.4
22.2
14.6
In line with previous studies,[65–67,72,87] we have computed all
relevant intermediates and transition states for the two considered
catalytic cycles for a model reaction of the tungsten ethylidyne
1
4.6
10
0
4
.2
complex [MeCW{OSi(OtBu)
3
}
3
2
]
with 2,4-hexadiyne as the
0.0
0.0
1
substrate (Scheme 4, R = R = Me). In addition, alternative
reaction pathways for diyne disproportionation were studied
computationally. Figure 6 shows the calculated potential-energy
profiles for the two alternative initiation steps via - and -MCBDs
-10
-
9.6
-13.0
15.1
-
13.0
-
-20
(
Scheme 4, upper part), which indicates that the formation of an
-1
alkynylalkylidyne complex is favored by 4.9 kcal mol .
Furthermore, the transition states for the cycloaddition and
cycloreversion via the α-MCBD are much lower in energy than the
respective transition states for the β-addition. Overall, the -
addition of the diyne is predicted to be kinetically preferred over
the -addition, and the formation of the alkynylalkylidyne
intermediate is kinetically and thermodynamically preferred.
Figure 7. Potential-energy profiles for the α- (black) and β-addition (red) of 2,4-
hexadiyne to the tungsten 2-butynylidyne complex [MeCC–
CW{OSi(OtBu)
3 3
} ]; the black profile corresponds to the ,-mechanism shown
in Scheme 4 for R = R2 = Me. All reported values are electronic energies
1
computed at the PW6B95-D3/def2-TZVP level of theory.

E [kcal mol-1
]
4
3
2
1
0
0
0
0


W
O2
3
3.8
33.8
O1
2
2.8
W
14.6
TS
1
5.7
O1
O2
0
.0
W
0
10
20
0
.0
0.0
4.9
[
3 3
MeCCCW{OSi(OtBu) } ]
-
+ 2,4-hexadiyne
-
-
-8.1
-8.1
-
13.0
-
12.2

,-MCBD
-17.3
Figure 8. Ball-and-stick presentation of relevant stationary points for the ,-
MCBD formation by using the M06 density functional; methyl groups were
omitted for clarity. Selected bond lengths [Å] in TS/,-MCBD: W–O1
2
.212/2.027, W–O2 2.199/2.578.
Figure 6. Potential-energy profiles for the α- (black) and β-addition (red) of 2,4-
]; the red
profile corresponds to the -mechanism shown in Scheme 4 for R1 = R2 = Me.
All reported values are electronic energies computed at the PW6B95-D3/def2-
TZVP level of theory.
3 3
hexadiyne to the tungsten ethylidyne complex [MeCW{OSi(OtBu) }
Finally, it should be mentioned that an appropriate
consideration of dispersion interactions seems to be of utmost
importance, since inspection of the calculated structures reveals
secondary interactions for various stationary points, which involve
the coordination of the silanolate ligand in a chelating fashion
through an additional oxygen atom of one of the SiOtBu groups.
This is illustrated in Figure 8 for the three relevant stationary
points for the formation of the ,-MCBD from the
alkynylalkylidyne complex and 2,4-hexadiyne (Figure 7, left part).
The alkynylalkylidyne complex does not show secondary
For the alkynylalkylidyne complex to be catalytically active the
subsequent reaction with 2,4-hexadiyne must be considered, too.
As shown in Figure 7, the cycloaddition reaction can either afford
,- or ,-MCBDs, and cycloreversion of the latter will then lead
to the formation of triynes. Again, the -addition is kinetically
preferred over the -addition, and diyne metathesis via ,-
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
tungsten–oxygen interactions, and the calculated W–O bond
lengths of 1.899 Å are in perfect agreement with those established
for 1 experimentally by X-ray diffraction analysis, i.e. 1.8809(14)–
kinetic study with a further reduced catalyst loading of 0.5 mol%.
The resulting concentration-time diagram qualitatively shows the
same behaviour, albeit with lower reaction rates (Figure 10). The
ratio between the fitted rate constants kpre = 4.4 10-4 s-1 and
1
.8882(14) Å.[78] In contrast, both the transition state (TS) and the

,-MCBD contain one silanolate ligand bound in a chelating
k
std = 1.8 10-4 s-1 show again a significant accelaration by a factor
of 2.4 for the “premixed” catalyst solution, while the ratios
2
OSi{OSi(OtBu)
3
}
3
- O
fashion. Surprisingly, the two W–O
distances are almost identical in the TS structure (2.212 and
.199 Å), whereas the MCBD features a shorter W–O1 (2.199 Å)
and a longer W–O2 bond (2.578 Å), which resembles the situation
found in the complex [MesCW{OSi(OtBu) }{OC(CF
].[73]
These findings indicate that secondary interactions with the
silanolate ligand play a crucial role in the stabilization of transition
states and intermediates and are potentially a key factor for the
understanding of the observed high diyne metathesis selectivity
of catalyst 1.
kpre,2%/kpre,0.5% = 4.5 and kstd,2%/kstd,0.5% = 3.5 reflect the four times
2
lower catalyst loading quite well. These results indicate that diyne
metathesis reactions can be carried efficiently at low catalyst
loading, which was additionally exemplified by the DYCM
reactions between 1,4-diphenyl-1,3-butadiyne and 1,4-bis(4-
methoxyphenyl)-1,3-butadiyne or dodecadiyne (see Supporting
Information, Section S14).
3
3 3 2
) }
-
3
-1
k
k
pre = 2.0 10
k = 2.0e-03/s
s
0.1
-4
-1
k == 66 . .33 e1 -00 4 /ss
std
Kinetic study of diyne metathesis
0.08
Si
Si
Si
Although the DFT calculations predict a preference for the ,-
over the -mechanism, we finally devised a kinetic study of the
diyne cross-metathesis (DYCM) reaction between 1,4-
0
0
0
.06
.04
.02
0
bis(trimethylsilyl)-1,3-butadiyne
butadiyne (3b). Since the
(2) and 1,4-diphenyl-1,3-
C-labeling experiments clearly
13
indicated the fast formation of the 3-phenylpropynylidyne complex
upon mixing the pre-catalyst 1 and 3b (Scheme 2), we
5
monitored the progress of the DYCM reaction by gas
chromatography (GC) for two different experimental procedures:
The standard procedure is identical to that described in Table 2
with addition of 2 mol% of 1 to the reaction mixture, while the
alternative procedure involved pre-mixing of equimolar amounts
of 1 and substrate 3b in dichloromethane for 10 min, followed by
addition of this pre-mixed or active catalyst solution to the reaction
mixture. Thus, the reaction mixtures contain either the alkylidyne
or predominantly the alkynylalkylidyne species at the beginning of
the DYCM reaction (t = 0), which will afford different kinetic
profiles, if only one of the tungsten compounds is catalytically
active.
0
20
40
60
80
100
120
Time [min.]
Figure 9. Concentration-time diagram of the diyne cross-metathesis (DYCM)
reaction of 1,4-bis(trimethylsilyl)-1,3-butadiyne (2) with 1,4-diphenyl-1,3-
butadiyne (3b) in a 4 : 1 ratio under standard conditions (dashed line) and with
a pre-mixed catalyst solution (solid line) at 2 mol% catalyst loading.
-
4
-1
k
k
pre = 4.4 10
k = 4.4e-04/s
s
0.1
.08
.06
-4 -1
k == 11 . .88 e1 -00 4 /ss
std
Comparison of the respective concentration-time diagrams
recorded for a catalyst loading of 2 mol% (Figure 9) reveals that
the premix protocol (pre) effects a significantly faster conversion
0
0
Si
Si
Si
than the standard protocol (std) employing the pristine alkylidyne
catalyst solution. The respective rate constants kpre = 2.0 10-3
s
-1
and kstd = 6.3 10-4 s-1 have been obtained by an exponential fit
0.04
corresponding to an observed first-order kinetic, indicating that
“
premixing” leads to an accelaration by a factor of ca. 3.2
0.02
compared to the “standard” reaction. Since both catalytic
experiments only differ in the initial concentration of the 3-
phenylpropynylidyne complex 5, this species is responsible for
the observed higher catalytic activity, corroborating that the
DYCM reactions proceeds most likely through the ,-
mechanism and involves alkynylalkylidyne intermediates
0
0
20
40
60
80
100
120
Time [min.]
Figure 10. Concentration-time diagram of the diyne cross-metathesis (DYCM)
reaction of 1,4-bis(trimethylsilyl)-1,3-butadiyne (2) with 1,4-diphenyl-1,3-
butadiyne (3b) in a 4 : 1 ratio under standard conditions (dashed line) and with
a pre-mixed catalyst solution (solid line) at 0.5 mol% catalyst loading.
(
Scheme 4, left side). This result is consistent with the DFT
calculations and all experiments reported above.
Knowing that the DYCM reaction rate is increased by
“
premixing” the alkylidyne complex with a diyne at higher
concentrations prior to the actual catalysis, we repeated the
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
Conclusions
Acknowledgements
The ability of the tungsten alkylidyne complex 1 to promote
not only the metathesis of internal alkynes,[78] but also the
metathesis of 1,3-diynes,[80,84] has been further exploited by diyne
cross-metathesis (DYCM) between 1,4-bis(trimethylsilyl)-1,3-
butadiyne and symmetrical 1,3-diynes. The resulting
trimethylsilane derivatives may serve as useful synthons for the
preparation of terminal or functionalized 1,3-diynes, and
accordingly, we regard this new diyne metathesis methodology as
an important addition to the plethora of methods available in
preparative acetylenic chemistry for the construction of
conjugated diynes and polyynes. Furthermore, this method
provides convenient access to unusual symmetrical and
We are grateful to Priv.-Doz. Dr. Christian Kleeberg and to Dr.
Kerstin Ibrom for helpful discussions regarding the NMR
spectroscopic data. We also acknowledge the X-ray
crystallographic support provided by Prof. Dr. Peter G. Jones and
Dr. Matthias Freytag. We thank Dr. Manfred Nimtz (Helmholtz
Centre for Infection Research, Braunschweig) for recording the
MALDI-TOF mass spectra. This work was funded by the
Deutsche Forschungsgemeinschaft (DFG) through grant TA
189/12-1.
Keywords: Alkyne Metathesis • Diyne Cross-Metathesis •
Diynes • Alkylidyne Complexes • Tungsten
13
unsymmetrical C-labeled 1,3-diyne species. In contrast to
alternative routes such as irreversible cross-coupling of terminal
alkynes, the reversible diyne metathesis reaction occurs under full
thermodynamic control, which allows to shift the equilibrium in a
favorable manner by employing one of the diyne substrates in
excess. Unreacted starting materials can be recovered and used
again for subsequent DYCM reactions. Although catalyst 1
exhibits a remarkably high selectivity towards diyne metathesis,
diyne disproportionation into monoynes and triynes, and
subsequently into higher polynes, occurs as a slow side reaction,
which was demonstrated by catalytic depolymerization-
macrocyclization of a carbazole-butadiyne polymer, which does
[
1]
A. L. K. Shi Shun, R. R. Tykwinski, Angew. Chem. Int. Ed. 2006, 45,
034–1057.
1
[
[
[
2]
3]
4]
B. W. Gung, C. R. Chim. 2009, 12, 489–505.
W. Shi, COCAT 2015, 2, 2–13.
J. S. Moore, Acc. Chem. Res. 1997, 30, 402–413.
[5]
[6]
C. Grave, A. D. Schlüter, Eur. J. Org. Chem. 2002, 3075–3098.
Y. Yamaguchi, Z.-i. Yoshida, Chem. Eur. J. 2003, 9, 5430–5440.
S. Höger, Chem. Eur. J. 2004, 10, 1320–1329.
[
[
[
[
7]
8]
9]
W. Zhang, J. S. Moore, Angew. Chem. Int. Ed. 2006, 45, 4416–4439.
E. L. Spitler, C. A. J. Ii, M. M. Haley, Chem. Rev. 2006, 106, 5344–5386.
10] C. N. Carroll, J. J. Naleway, M. M. Haley, D. W. Johnson, Chem. Soc.
Rev. 2010, 39, 3875–3888.
not only afford the desired C
macrocycles with a mixture of C -, C
Since the 13C-labeling studies in this and in a previous study
clearly indicated fast formation of alkynylalkylidyne complexes
MC–CC–CR) upon mixing 1 and 1,3-diyne substrates, a
4
-bridged tetramers, but also
[
11] M. Iyoda, J. Yamakawa, M. J. Rahman, Angew. Chem. Int. Ed. 2011, 50,
2
4
- and C -bridges.
6
10522–10553.
[80]
[12] D. Zhao, J. S. Moore, Chem. Commun. 2003, 807–818.
[13] S. Míguez-Lago, M. M. Cid, Synthesis 2017, 49, 4111–4123.
[
[
[
[
14] U. H. F. Bunz, Y. Rubin, Y. Tobe, Chem. Soc. Rev. 1999, 28, 107–119.
15] U. H. F. Bunz, Chem. Rev. 2000, 100, 1605–1644.
(
mechanism was substantiated that involves alkynylalkylidyne
complexes as catalytically active species and ,-dialkynyl-
MCBD intermediates (,-mechanism). The disproportionation
into monoynes and triynes can then be rationalized by deviation
from this mechanism through formation ,-dialkynyl-MCBD,
which according to our theoretical calculations is clearly kinetically
and thermodynamically disfavored. The role of catalytically active
alkynylalkylidyne species is also in agreement with a kinetic study
that reveals significantly higher catalytic activity if pre-catalyst 1
and a 1,3-diyne substrate are premixed and then added to the
reaction mixture. However, all attempts to isolate
alkynylalkylidyne complexes in pure form by fractional
crystallization were prevented by the high solubility owing to the
16] V. Maraval, R. Chauvin, Chem. Rev. 2006, 106, 5317–5343.
17] M. M. Haley, R. R. Tykwinski, Carbon-rich compounds. From molecules
to materials, Wiley-VCH, Weinheim, 2006.
[
[
18] S. Szafert, J. A. Gladysz, Chem. Rev. 2006, 106, PR1-PR33.
19] M. M. Haley, Pure Appl. Chem. 2008, 80, 117.
[20] M. Akita, T. Koike, Dalton Trans. 2008, 3523–3530.
[21] J. Liu, J. W. Y. Lam, B. Z. Tang, Chem. Rev. 2009, 109, 5799–5867.
[
[
[
[
22] W. A. Chalifoux, R. R. Tykwinski, C. R. Chim. 2009, 12, 341–358.
23] F. Diederich, M. Kivala, Adv. Mat. 2010, 22, 803–812.
24] R. Gleiter, D. B. Werz, Chem. Rev. 2010, 110, 4447–4488.
25] F. Cataldo (Ed.) Polyynes. Synthesis, properties, and applications,
Taylor & Francis, Boca Raton, 2006.
[
[
26] L. Zang, Y. Che, J. S. Moore, Acc. Chem. Res. 2008, 41, 1596–1608.
27] Z. Chen, C. Molina-Jirón, S. Klyatskaya, F. Klappenberger, M. Ruben,
Ann. Phys. 2017, 318, 1700056.
3
presence of the OSi(OtBu) ligand, and only the 2-butyne-1,4-
diylidyne ditungsten complex 6 that is slowly formed could be
isolated in crystalline from.
[28] Siemsen, Livingston, Diederich, Angew. Chem. Int. Ed. 2000, 39, 2632–
657.
29] H. A. Stefani, A. S. Guarezemini, R. Cella, Tetrahedron 2010, 66, 7871–
918.
2
[
We fell that diyne metathesis with the level of selectivity
provided by catalyst 1 is clearly competitive with other methods
for the preparation of symmetrical and unsymmetrical diynes,
since it allows to establish carbon-carbon triple bonds in a
reversible fashion under thermodynamic control. This will be
particularly useful for the construction of macrocyclic diyne and
7
[
[
30] F. Alonso, M. Yus, ACS Catal. 2012, 2, 1441–1451.
31] S. E. Allen, R. R. Walvoord, R. Padilla-Salinas, M. C. Kozlowski, Chem.
Rev. 2013, 113, 6234–6458.
[
32] K. S. Sindhu, G. Anilkumar, RSC Adv 2014, 4, 27867–27887.
[33] J. A. Marsden, M. M. Haley in Metal-Catalyzed Cross-Coupling
Reactions, WILEY-VCH Verlag GmbH, 2008.
oligo(diyne) formation in view of the great recent success of
catalytic alkyne metathesis in supramolecular chemistry.[59–62]
[34]
35] J. Lei, L. Su, K. Zeng, T. Chen, R. Qiu, Y. Zhou, C.-T. Au, S.-F. Yin,
Chem. Eng. Sci. 2017, 171, 404–425.
W. Shi, A. Lei, Tetrahedron Lett. 2014, 55, 2763–2772.
[
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
[
36] K. S. Sindhu, A. P. Thankachan, P. S. Sajitha, G. Anilkumar, Org. Biomol.
Chem. 2015, 13, 6891–6905.
[74] S. von Kugelgen, D. E. Bellone, R. R. Cloke, W. S. Perkins, F. R. Fischer,
J. Am. Chem. Soc. 2016, 138, 6234–6239.
[
[
37] E. Jahnke, R. R. Tykwinski, Chem. Commun. 2010, 46, 3235–3249.
38] D. Wang, J. Li, N. Li, T. Gao, S. Hou, B. Chen, Green Chem. 2010, 12,
[75] S. von Kugelgen, R. Sifri, D. Bellone, F. R. Fischer, J. Am. Chem. Soc.
2017, 139, 7577–7585.
4
5–48.
[76] H. Jeong, S. von Kugelgen, D. Bellone, F. R. Fischer, J. Am. Chem. Soc.
2017, 139, 15509–15514.
[
[
39] R. Xiao, R. Yao, M. Cai, Eur. J. Org. Chem. 2012, 2012, 4178–4184.
40] J. R. Suárez, D. Collado-Sanz, D. J. Cárdenas, J. L. Chiara, J. Org.
Chem. 2015, 80, 1098–1106.
[77] M. Koy, I. Elser, J. Meisner, W. Frey, K. Wurst, J. Kästner, M. R.
Buchmeiser, Chem. Eur. J. 2017, 23, 15484–15490.
[
[
41] W. Yin, C. He, M. Chen, H. Zhang, A. Lei, Org. Lett. 2009, 11, 709–712.
42] X. Meng, C. Li, B. Han, T. Wang, B. Chen, Tetrahedron 2010, 66, 4029–
[78] S. Lysenko, B. Haberlag, C. G. Daniliuc, P. G. Jones, M. Tamm,
ChemCatChem 2011, 3, 115–118.
4
031.
[79] B. Haberlag, M. Freytag, P. G. Jones, M. Tamm, Adv. Synth. Catal. 2014,
356, 1255–1265.
[
43] M. Nasr-Esfahani, I. Mohammadpoor-Baltork, A. R. Khosropour, M.
Moghadam, V. Mirkhani, S. Tangestaninejad, V. Agabekov, H. A.
Rudbari, RSC Adv 2014, 4, 14291–14296.
[80] S. Lysenko, J. Volbeda, P. G. Jones, M. Tamm, Angew. Chem. Int. Ed.
2012, 51, 6757–6761.
[
[
[
[
[
[
44] L. Liu, T. Matsushita, P. Concepción, A. Leyva-Pérez, A. Corma, ACS
Catal. 2016, 6, 2211–2221.
[81] E. F. Meyer, J. J. Meyer, J. Chem. Eng. Data 1986, 31, 273–274.
[82] F. Ungeheuer, A. Fürstner, Chem. Eur. J. 2015, 21, 11387–11392.
[83] S. Schaubach, K. Gebauer, F. Ungeheuer, L. Hoffmeister, M. K. Ilg, C.
Wirtz, A. Fürstner, Chem. Eur. J. 2016, 22, 8494–8507.
[84] S. T. Li, T. Schnabel, S. Lysenko, K. Brandhorst, M. Tamm, Chem.
Commun. 2013, 49, 7189–7191.
45] B. Vilhanová, J. Václavík, L. Artiglia, M. Ranocchiari, A. Togni, J. A. van
Bokhoven, ACS Catal. 2017, 7, 3414–3418.
46] H. Peng, Y. Xi, N. Ronaghi, B. Dong, N. G. Akhmedov, X. Shi, J. Am.
Chem. Soc. 2014, 136, 13174–13177.
47] L. Su, J. Dong, L. Liu, M. Sun, R. Qiu, Y. Zhou, S.-F. Yin, J. Am. Chem.
Soc. 2016, 138, 12348–12351.
[85] D. E. Gross, J. S. Moore, Macromolecules 2011, 44, 3685–3687.
[86] T. J. Katz, J. McGinnis, J. Am. Chem. Soc. 1975, 97, 1592–1594.
[87] J. Zhu, G. Jia, Z. Lin, Organometallics 2006, 25, 1812–1819.
[88] L. Brandsma, Preparative Acetylenic Chemistry, Elsevier Science,
Burlington, 1988.
48] A. Sagadevan, P.-C. Lyu, K. C. Hwang, Green Chem. 2016, 18, 4526–
4
530.
49] Y. Liu, P. Liu, N. Gu, J. Xie, Y. Liu, B. Dai, Chin. J. Chem. 2016, 34, 895–
00.
9
[89] K. Yin, C. Li, J. Li, X. Jia, Green Chem. 2011, 13, 591.
[90] A. Zeiler, M. J. Ziegler, M. Rudolph, F. Rominger, A. S. K. Hashmi, Adv.
Synth. Catal. 2015, 357, 1507–1514.
[
[
[
[
[
[
[
[
50] A. Mohanty, S. Roy, Chem. Commun. 2017, 53, 10796–10799.
51] R. R. Schrock, C. Czekelius, Adv. Synth. Catal. 2007, 349, 55–77.
52] W. Zhang, J. S. Moore, Adv. Synth. Catal. 2007, 349, 93–120.
53] X. Wu, M. Tamm, Beilstein J. Org. Chem. 2011, 7, 82–93.
54] K. Jyothish, W. Zhang, Angew. Chem. Int. Ed. 2011, 50, 8478–8480.
55] A. Fürstner, Angew. Chem. Int. Ed. 2013, 52, 2794–2819.
56] R. R. Schrock, Chem. Commun. 2013, 49, 5529.
[91] Y.-X. Xue, Y.-Y. Zhu, L.-M. Gao, X.-Y. He, N. Liu, W.-Y. Zhang, J. Yin,
Y. Ding, H. Zhou, Z.-Q. Wu, J. Am. Chem. Soc. 2014, 136, 4706–4713.
[92] S. Mo, X.-B. Shao, G. Zhang, Q.-H. Li, RSC Adv. 2017, 7, 27243–27247.
[93] X. Li, X. Xie, N. Sun, Y. Liu, Angew. Chem. Int. Ed. 2017, 56, 6994–6998.
[94] S. Pulst, F. G. Kirchbauer, B. Heller, W. Baumann, U. Rosenthal, Angew.
Chem. Int. Ed. 1998, 37, 1925–1927.
57] C. Deraedt, M. d'Halluin, D. Astruc, Eur. J. Inorg. Chem. 2013, 4881–
4
908.
[95] P. Bichler, W. A. Chalifoux, S. Eisler, A. L. K. Shi Shun, E. T. Chernick,
R. R. Tykwinski, Org. Lett. 2009, 11, 519–522.
[
[
58] A. Fürstner in Modern Alkyne Chemistry, Wiley-VCH Verlag GmbH & Co.
KGaA, 2014.
[96] R. Tykwinski, T. Luu, Synthesis 2012, 44, 1915–1922.
[97] M. L. Listemann, R. R. Schrock, Organometallics 1985, 4, 74–83.
[98] F. H. Köhler, H. J. Kalder, E. O. Fischer, J. Organomet. Chem. 1976, 113,
11–22.
59] Y. Jin, Q. Wang, P. Taynton, W. Zhang, Acc. Chem. Res. 2014, 47,
1575–1586.
[
[
60] H. Yang, Y. Jin, Y. Du, W. Zhang, J. Mater. Chem. A 2014, 2, 5986–5993.
61] Q. Wang, C. Yu, C. Zhang, H. Long, S. Azarnoush, Y. Jin, W. Zhang,
Chem. Sci. 2016, 7, 3370–3376.
[99] F. H. Köhler, H. J. Kalder, E. O. Fischer, J. Organomet. Chem. 1975, 85,
C19-C22.
[
[
[
[
62] M. Ortiz, C. Yu, Y. Jin, W. Zhang, Top. Curr. Chem. 2017, 375, 69.
63] R. R. Schrock, Acc. Chem. Res. 1986, 19, 342–348.
[100] E. O. Fischer, H. J. Kalder, F. H. Köhler, J. Organomet. Chem. 1974, 81,
C23-C27.
64] R. R. Schrock, Chem. Rev. 2002, 102, 145–180.
[101] S. Eisler, R. R. Tykwinski, J. Am. Chem. Soc. 2000, 122, 10736–10737.
[102] A. Ceccon, S. Santi, L. Orian, A. Bisello, Coord. Chem. Rev. 2004, 248,
683–724.
65] S. Beer, C. G. Hrib, P. G. Jones, K. Brandhorst, J. Grunenberg, M. Tamm,
Angew. Chem. Int. Ed. 2007, 46, 8890–8894.
[
[
[
[
[
[
[
[
66] S. Beer, K. Brandhorst, C. G. Hrib, X. Wu, B. Haberlag, J. Grunenberg,
P. G. Jones, M. Tamm, Organometallics 2009, 28, 1534–1545.
67] B. Haberlag, X. Wu, K. Brandhorst, J. Grunenberg, C. G. Daniliuc, P. G.
Jones, M. Tamm, Chem. Eur. J. 2010, 16, 8868–8877.
[103] K. Venkatesan, O. Blacque, H. Berke, Dalton Trans. 2007, 1091–1100.
[104] P. Aguirre-Etcheverry, D. O'Hare, Chem. Rev. 2010, 110, 4839–4864.
[105] M. I. Bruce, P. J. Low, K. Costuas, J.-F. Halet, S. P. Best, G. A. Heath,
J. Am. Chem. Soc. 2000, 122, 1949–1962.
68] X. Wu, C. G. Daniliuc, C. G. Hrib, M. Tamm, J. Organomet. Chem. 2011,
[106] H. Jiao, K. Costuas, J. A. Gladysz, J.-F. Halet, M. Guillemot, L. Toupet,
F. Paul, C. Lapinte, J. Am. Chem. Soc. 2003, 125, 9511–9522.
[107] B. E. Woodworth, P. S. White, J. L. Templeton, J. Am. Chem. Soc. 1997,
119, 828–829.
696, 4147–4151.
69] B. Haberlag, M. Freytag, C. G. Daniliuc, P. G. Jones, M. Tamm, Angew.
Chem. Int. Ed. 2012, 51, 13019–13022.
70] S. Lysenko, C. G. Daniliuc, P. G. Jones, M. Tamm, J. Organomet. Chem.
[108] S. N. Semenov, O. Blacque, T. Fox, K. Venkatesan, H. Berke, J. Am.
Chem. Soc. 2010, 132, 3115–3127.
2013, 744, 7–14.
71] D. P. Estes, C. Bittner, Ò. Àrias, M. Casey, A. Fedorov, M. Tamm, C.
Copéret, Angew. Chem. Int. Ed. 2016, 55, 13960–13964.
72] C. Bittner, H. Ehrhorn, D. Bockfeld, K. Brandhorst, M. Tamm,
Organometallics 2017, 36, 3398–3406.
[109] S. N. Semenov, S. F. Taghipourian, O. Blacque, T. Fox, K. Venkatesan,
H. Berke, J. Am. Chem. Soc. 2010, 132, 7584–7585.
[110] Y. Li, O. Blacque, T. Fox, S. Luber, W. Polit, R. F. Winter, K. Venkatesan,
H. Berke, Dalton Trans. 2016, 45, 5783–5799.
73] D. P. Estes, C. P. Gordon, A. Fedorov, W.-C. Liao, H. Ehrhorn, C. Bittner,
M. L. Zier, D. Bockfeld, K. W. Chan, O. Eisenstein et al., J. Am. Chem.
Soc. 2017, 139, 17597–17607.
[111] Y. Takihana, M. Shiotsuki, F. Sanda, T. Masuda, Macromolecules 2004,
37, 7578–7583.
[112] Y. You, S. H. Kim, H. K. Jung, S. Y. Park, Macromolecules 2006, 39,
349–356.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
[
[
113] Y. Zhao, D. G. Truhlar, J. Phys. Chem. A 2005, 109, 5656–5667.
114] S. Grimme, S. Ehrlich, L. Goerigk, J. Comput. Chem. 2011, 32, 1456–
1
465.
115] S. Grimme, J. Antony, S. Ehrlich, H. Krieg, J. Chem. Phys. 2010, 132,
54104.
[
1
[
[
[
116] F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys. 2005, 7, 3297–3305.
117] F. Weigend, Phys. Chem. Chem. Phys. 2006, 8, 1057–1065.
118] Y. Zhao, D. G. Truhlar, Theor. Chem. Acc. 2008, 120, 215–241.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201801651
FULL PAPER
Entry for the Table of Contents
FULL PAPER
The benzylidyne complex
T. M. Schnabel, D. Melcher, K.
[
PhCW{OSi(OtBu)
3
}
3
] catalyzes the
Brandhorst, D. Bockfeld, and M. Tamm*
cross-metathesis between 1,4-
bis(trimethylsilyl)-1,3-butadiyne and
symmetrical 1,3-diynes efficiently,
giving access to TMS-capped 1,3-
Page No. – Page No.
Unraveling the Mechanism of 1,3-
Diyne Cross-Metathesis Catalyzed by
Silanolate-Supported Tungsten
Alkylidyne Complexes
3
diynes RCC–CCSiMe .
Experimental and theoretical studies
reveal a mechnism that involves
reversible carbon-carbon triple-bond
cleavage and formation according to
the conventional mechanism of alkyne
metathesis.
This article is protected by copyright. All rights reserved.