Synthesis of Alkyne Metathesis Catalysts from Tris(dimethylamido)tungsten Precursors

Article abstract of DOI:10.1002/ejic.202000835

Benzylidyne tungsten systems bearing a combination of alkoxide and amide ligands were readily obtained by partial alcoholysis of amido-supported tungsten complexes. Benzylidyne tris(dimethylamido)tungsten was treated with fluorinated alcohols Me₂(CF₃)COH, Me(CF₃)₂COH, and (CF₃)₃COH, and also with silanols (tBuO)₃SiOH, and Ph₃SiOH, all of which resulted in complexes of the type [PhC≡W(NHMe₂)(NMe₂)(OR)₂]. Full displacement of the amido ligands was also achieved in [PhC≡W(NHMe₂){OC(CF₃)₂Me}{OSi(O-tBu)₃}₂] and [PhC≡W(NHMe₂)(OSiPh₃)₃]. In addition, reaction of the three fluorinated alcohols with hexakis(dimethylamido)ditungsten yielded isomeric mixtures of bimetallic complexes [W₂(NMe₂)₄(OR)₂], which bear two electron-donating ligands and one electron-withdrawing ligand per tungsten atom. All amido-substituted compounds are active in the self-metathesis of 5-benzyloxy-2-pentyne, although [W₂(OR)₂(NMe₂)₄] complexes require longer initiation times depending on the degree of fluorination of the tert-butoxide ligand.

Full text of DOI:10.1002/ejic.202000835

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Alkyne Metathesis
Synthesis of Alkyne Metathesis Catalysts from
Tris(dimethylamido)tungsten Precursors
[a]
[a]
[a]
[a]
[a]
Daniel Melcher, Òscar Àrias, Matthias Freytag, Peter G. Jones, and Matthias Tamm*
Dedicated to Professor Richard R. Schrock on the occasion of his 75th birthday
Abstract: Benzylidyne tungsten systems bearing a combination (NHMe )(OSiPh ) ]. In addition, reaction of the three fluorinated
2
3 3
of alkoxide and amide ligands were readily obtained by partial alcohols with hexakis(dimethylamido)ditungsten yielded iso-
alcoholysis of amido-supported tungsten complexes. Benzylid- meric mixtures of bimetallic complexes [W (NMe ) (OR) ], which
2
2 4
2
yne tris(dimethylamido)tungsten was treated with fluorinated bear two electron-donating ligands and one electron-withdraw-
alcohols Me (CF )COH, Me(CF ) COH, and (CF ) COH, and also ing ligand per tungsten atom. All amido-substituted compounds
2
3
3 2
3 3
with silanols (tBuO) SiOH, and Ph SiOH, all of which resulted are active in the self-metathesis of 5-benzyloxy-2-pentyne, al-
3
3
in complexes of the type [PhC≡ W(NHMe )(NMe )(OR) ]. Full though [W (OR) (NMe ) ] complexes require longer initiation
2
2
2
2
2
2 4
displacement of the amido ligands was also achieved in times depending on the degree of fluorination of the tert-butox-
[
PhC≡ W(NHMe ){OC(CF ) Me}{OSi(O-tBu) } ] and [PhC≡ W- ide ligand.
2
3 2
3 2
Introduction
Alkyne metathesis, discovered half a century ago,[1] has for a
long time remained in the shadow of the much more familiar
olefin metathesis. Its potential, however, has become clear with
the development of suitable synthetic approaches to tungsten
[
2]
and molybdenum alkylidyne complexes. Especially for tung-
sten, three main precursors can be highlighted (Scheme 1). Pre-
cursor [Me CC≡ W(Cl) (dme)] (1; dme = 1,2-dimethoxyethane)
3
3
was prepared by Schrock et al. via the “high-oxidation-state”
[
3]
route, and gave access to a long series of tungsten alkylidyne
complexes bearing a variety of alkoxide ligands. Starting from
WCl , versatile complex 1 is obtained in three steps, and can
6
be reacted further via salt metathesis to generate different
tungsten alkylidyne complexes. A major drawback is the lack
of variability in the alkylidyne fragment, which may however
[
4]
subsequently be exchanged by cross-metathesis with alkynes.
This disadvantage is overcome in the “low-oxidation-state”
route. Thereby, addition of lithium salts to metal carbonyls
forms Fischer-type carbene complexes, which may be further
[
5]
oxidized to give [ArC≡ W(Br) (dme)] (2; Ar = aryl).
3
[
a] Dr. D. Melcher, Dr. Ò. Àrias, Dr. M. Freytag, Prof. Dr. P. G. Jones,
Prof. Dr. M. Tamm
Institut für Anorganische und Analytische Chemie, Technische Universität
Braunschweig,
Hagenring 30, 38106 Braunschweig, Germany
Scheme 1. Selected precursors for the synthesis of tungsten alkylidyne com-
plexes. Abbreviations: Ar, aryl; DME, 1,2-dimethoxyethane; R, alkyl chain; red,
reductant (preferably Sn); TMS, trimethylsilyl.
E-mail: m.tamm@tu-braunschweig.de
https://www.tu-braunschweig.de/iaac/personal/prof-dr-m-tamm
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.202000835.
The third method, the ditungsten route,[6] has received less
attention than the other two and is based on dinuclear precur-
sors [W (NMe ) ] (3a) and [W (OR) ] (3b). Synthesis of 3a is
©
2020 The Authors. European Journal of Inorganic Chemistry published by
2
2 6
2
6
Wiley-VCH GmbH. · This is an open access article under the terms of the
Creative Commons Attribution License, which permits use, distribution and
reproduction in any medium, provided the original work is properly cited.
[
7]
achieved by salt metathesis of WCl with LiNMe . WCl can
4
2
4
[
8]
be synthesized from WCl via reduction with tin. In contrast
6
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to the high- and low-oxidation-state routes, the amido ligands
are exchanged simply by alcoholysis to generate 3b, a reaction
[
8b,9]
that was intensively studied by Chisholm.
In particular, the
was recently re-
[
6h]
fluorinated derivative [W (OC(CF )Me ) ]
2
3
2 6
ported to be highly efficient in the metathesis of internal and
terminal alkynes. An alternative route to 3b was developed by
[
6a]
Schrock, who investigated the metathesis reactions of these
ditungsten complexes with alkynes, during which the tung-
sten–tungsten bond is formally oxidized to yield the corre-
sponding alkylidyne complexes.[6a,6c,6h] Nevertheless, the range
of convenient alcohols is limited because they require a mini-
mum steric bulk to prevent deactivation by bridging ligands,
and need to comply with the electronic characteristics for cata-
lytic activity. Moreover, because of overcrowding, not every
bulky ligand is able to substitute completely all the dimethyl-
amido ligands.
Scheme 3. Classical synthesis of “push-pull” complexes 9; conditions: a) lith-
ium 1,3-di-tert-butylimidazolin-2-iminato, – LiOR , – DME.
F
A potentially easier way to generate mixed ligand systems
[
10]
[11]
involves the alcoholysis of 4a or 4b. Thus, partial substitu-
tion of the dimethylamido ligands would result in complexes
of the form [RC≡ W(NMe ) (OR′)3–n] (n = 1, 2), which combine,
2 n
respectively, one or two electron-donating ligands (NMe ) with
2
two or one electron-withdrawing ligands (OR′). We investigated
these reactions employing fluorinated tert-butoxides
A
less investigated tungsten alkylidyne precursor is
[
RC≡ W(NMe ) ] (4a, R = tBu; 4b, R = Et), which combines the
2
3
(
OC(CF )Me , OC(CF ) Me, and OC(CF ) ) and siloxy-based li-
advantage of ligand substitution via alcoholysis with the pres-
ence of an alkylidyne moiety so that the steric hindrance associ-
ated with ditungsten species is reduced. This type of complex
was first synthesized by Schrock by salt metathesis of
3 2 3 2 3 3
gands (OSiPh3 and OSi(O-tBu) ). This ligand selection was
3
guided by the special abilities of tungsten and molybdenum
complexes supported by such ligands. For example,
[
10]
[PhC≡ W{OSi(O-tBu) } ] (10) is able to perform efficiently alkyne
(
NEt )[Me CC≡ W(Cl) ] (5)
or [EtC≡ W(O-tBu)3] (6a) with
An alternative was reported by
3 3
4
3
4
[
16]
[
6a,11]
and 1,3-diyne metathesis,
11) and [MesC≡ Mo{OC(CF ) Me} ] (12) are excellent cata-
whereas [MesC≡ W{OC(CF )Me } ]
LiNMe (Scheme 2, top).
3
2 3
2
[
17]
[18]
(
McElwee-White, who synthesized [N≡ W(NMe ) ] (4c) from
3 2
3
2
3
lysts for internal and terminal alkyne metatheses. Moreover, re-
[
N≡ W(O-tBu) ] (7) in a ligand exchange reaction with 0.75
3
[
19]
[20]
[
12]
lated ether and N-heterocyclic carbene adducts have been
employed in ring-opening alkyne metathesis polymerisation or
alkyne homometathesis reactions. Molybdenum complexes of
equivalents of [Zr(NMe ) ] or [Ti(NMe ) ] (Scheme 2).
How-
2
4
2 4
ever, the attention in those years was focused on the “high-
oxidation-state” route, and so compounds 4a and 4b were ne-
glected, although alcoholysis is an established method to ex-
change arylamido ligands in analogous molybdenum alkyl-
[
21]
the type [ArC≡ Mo(OSiPh ) ] (13)
proved to be all-rounders
3 3
and perform comparatively well not only in internal and termi-
[
22]
[
13]
nal alkyne metathesis, but also in ring-closing diyne metath-
idyne complexes.
Compound 4c is used in another context
esis. Interestingly, their tungsten equivalents[21] are so far un-
[23]
[
14]
to create tungsten oxide surfaces and nanotubes.
known.
Results and Discussion
Preparation and Characterization of Complex 4d
Alkylidyne complex [PhC≡ W(NMe ) ] (4d) was targeted as a pre-
2
3
cursor for the synthesis of mixed ligand complexes. Its synthesis
was optimized from methods reported by Schrock and
McElwee-White (see Scheme 2). In a first attempt, Schrock's salt
metathesis procedure was adapted. Thus, the tert-butoxide li-
[
6a,6c,24]
gands in [PhC≡ W(O-tBu) ] (6b)
were substituted at ambi-
3
Scheme 2. Synthetic strategies of tris(dimethylamido)tungsten complexes.
ent temperature employing three equivalents of LiNMe
2
(
0
Scheme 4). On the following day, the solvent was removed at
°C to prevent sublimation of volatile 4d, which was then
This old, yet interesting precursor is perfectly suited to syn-
thesize hybrid, “push-pull” systems; these are metal alkylidyne
compounds carrying two electron-withdrawing ligands and
one-electron donating ligand, and have proved to be very effi-
extracted with cold pentane. The by-product of the reaction,
[
2d,2e,5c,15]
cient in alkyne metathesis.
Such complexes were con-
structed in two steps from 1 or 2 via salt metathesis with
M(OC(CF ) Me) (M = Li or K) to give [RC≡ W(dme){OC(CF ) Me} ]
3
2
3 2
3
(
8a, R = tBu; 8b, R = Ar). Subsequent addition of lithium imidaz-
olin-2-iminato salts resulted in the substitution of one alkoxide
group and the formation of “push-pull” systems 9a and 9b
(
Scheme 3).
Scheme 4. Synthesis of triamido precursor 4d.
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LiO-tBu, was filtered off, and complex 4d was isolated from the the apical position (C–W–N angles between 101.51(12)° and
filtrate in 70 % yield as a yellow powder.
104.03(12)°). The W1–C1 bond length of 1.757(3) Å is virtually
In the second procedure, following McElwee-White, oxophilic equal to that of 6b (1.758(5) Å).[24b] The nearly linear angle
tetrakis(dimethylamido)titanium promoted the ligand exchange W1–C1–C2 (174.8(2)°) is in accordance with the triple bond
to generate 4d in 60 % yield after 2 h under mild conditions character of the alkylidyne moiety. The W–N distances of
1
(
Scheme 4). The H NMR spectrum exhibited the characteristic 1.947(3)–1.957(3) Å are in the expected range for an amide
[
26]
signals for the phenyl group in the aromatic region (6.92– bond.
In addition, a second polymorph of 4d crystallized
7
.36 ppm) and a singlet at 3.38 ppm corresponding to the from a cold pentane solution in the orthorhombic space group
amido methyl groups. All necessary resonances were also ob- Pnma. The structure (see Figure S1) displays C symmetry, with
s
1
3
served in the C NMR spectrum. In particular, the methyl the asymmetric unit containing only half a molecule. Structural
groups appeared at 49.8 ppm, and the alkylidyne carbon atom parameters are similar to the first polymorph except for a
(
W≡ C) was considerably more deshielded (276.4 ppm) than in shorter W1–C1 bond of 1.713(8) Å, and an elongated C1–C2
[
24a]
6
4
b (257 ppm)
a (288.3 ppm).
but less deshielded than in Schrock's complex bond (1.478(10) Å).
Single crystals suitable for X-ray diffraction
[
10]
analysis were obtained from a solution of 4d in dichloro-
methane at –35 °C; the structure is presented in Figure 1.
Preparation and Characterization of Complexes
F
[
PhC≡ W(NHMe )(NMe )(OR ) ]
2
2
2
The combination of electron-withdrawing fluorinated ligands
and electron-donating amido ligands should provide a basis for
the desired “push-pull” effect. Thus, addition of two equivalents
of 1,1,1-trifluoro-, 1,1,1,3,3,3-hexafluoro-, or nonafluoro-tert-but-
anol to a solution of 4d yielded the corresponding disubsti-
F
tuted complexes [PhC≡ W(NHMe )(NMe )(OR ) ] in moderate to
2
2
2
F
F
excellent yields (14a, R = C(CF )Me , 53 %; 14b, R = C(CF ) Me,
4 %; 14c, R = C(CF ) , 94 %; Scheme 5, center). It should be
3
2
3 2
F
9
3 3
noted that one dimethylamine molecule – released as a by-
product – remained coordinated, giving pentacoordinate tung-
sten complexes.
1
H NMR spectroscopy of compounds 14a, 14b (in C D ), and
6
6
1
4c (in [D ]toluene) showed two singlets for the methyl groups
8
of the amido ligands (at 2.75, 2.87 and 3.05 ppm, and at 3.99,
4.05 and 4.34 ppm, respectively), which suggests a hindered
rotation around the W–N bonds. A similar situation was ob-
served for the dimethylamine moiety, which gave rise to a
broad singlet at 2.19 ppm for 14a, and to two singlets in the
other congeners (14b: 2.15 and 2.18 ppm; 14c: 2.26 and
Figure 1. Molecular structure of 4d with thermal displacement parameters
drawn at the 50 % probability level. Relevant bond lengths [Å] and angles
[
deg]: W1–C1 1.757(3), W1–N1 1.948(3), W1–N2 1.947(3), W1–N3 1.957(3), C1–
C2 1.456(4); W1–C1–C2 174.8(2), C1–W1–N1 104.03(12), C1–W1–N2
1
1
01.51(12), C1–W1–N3 103.61(12), N1–W1–N2 115.32(11), N1–W1–N3
14.46(11), N2–W1–N3 115.40(11).
Complex 4d crystallized in the orthorhombic space group 2.28 ppm). The corresponding amine protons featured chemical
Pbca. The geometry of the complex is best described as dis- shifts of 2.19 ppm (14a), 2.47 ppm (14b), and 2.75 ppm (14c),
[
25]
torted trigonal pyramidal (τ = 0.917(2)),
whereby the three which, as observed for all other resonances, increased with the
nitrogen atoms form the base with N–W–N angles between degree of fluorination. Furthermore, while the diastereotopic
14.46(11)° and 115.40(11)°, and the alkylidyne group occupies methyl groups of the trifluorinated alkoxide ligands in complex
4
1
Scheme 5. Synthesis of mixed ligand complexes 14a–14c, 15–18.
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1
4a produced two resonances at 1.26 and 1.54 ppm, the methyl electronic situation in 16 is very similar to that of complex 14a,
protons of the OC(CF ) Me fragments in complex 14b appeared and the carbon resonances seem scarcely affected by the sup-
3
2
as a single multiplet at 1.49 ppm. These observations indicate a porting ligands. The silanolate ligands in both complexes give
1
3
Cs molecular symmetry with a trans coordination of the alkoxide only one set of signals in the C NMR spectrum, which indi-
ligands. Accordingly, only one singlet was observed in the cates the chemical equivalency of these ligands and is consist-
1
9
1
F{ H} NMR spectra of 14a (–82.30 ppm) and 14c (–73.3 ppm), ent with C symmetric structures in solution.
s
4
whereas two quartets at –78.4 and –77.2 ppm ( J = 9.7 Hz)
Crystallographic analysis of complexes 15 and 16 was frus-
FF
were assigned to the diastereotopic CF groups in complex 14b. trated because of poor crystal quality and, again, the indistin-
3
1
3
1
In the C{ H} NMR spectra of 14a, 14b, and 14c, the alkylid- guishable amido–amino situation, but the expected trans ar-
yne carbon atoms resonate at low field at 271.1, 273.4, and rangement of the silanolate ligands could be established. The
2
79.1 ppm, respectively. Because of the hindered rotation molecular configuration of complex 15 was confirmed chemi-
around the W–N bonds, the methyl groups of the amido ligands cally by treatment of 15 with Me(CF ) COH, which selectively
3
2
appeared as two singlets at 43.4 and 59.4 ppm (14a), 42.1 and substituted the basic amido ligand (Scheme 5, left). Complex
9.4 ppm (14b), and 41.7 and 59.6 ppm (14c). In contrast, the [PhC≡ W(NHMe ){OC(CF ) Me}{OSi(O-tBu) } ] (17) precipitated as
5
2
3 2
3 2
amine moieties gave rise to only one broadened resonance at orange crystals from a pentane solution at –35 °C in 75 % yield.
4
0.0, 39.9, and 40.0 ppm, respectively. The crystal structure de- The crystals are triclinic (space group P 1¯ ) and contain two inde-
termination of compound 14b was attempted, and it verified pendent molecules per unit cell. The molecular structure (Fig-
the trans configuration of the fluorinated ligands (see Support- ure 2) shows a distorted square pyramidal geometry around
[
28]
ing Information, Figure S2). Unfortunately, the results were un- the tungsten atom (τ5 = 0.333(5) and 0.324(4))
satisfactory; in particular, the hydrogen atom of the proposed alkylidyne moiety in the apical position and proves that the
dimethylamine ligand was not located.
amine ligand is still coordinated. The siloxy ligands are aligned
with the
In order to get a satisfactory crystal structure, replacement trans to each other, but at an angle that deviates strongly from
of the amine ligand in 14b was attempted (see the Supporting 180° (142.98(14) Å, 143.38(12) Å). The W1–C1 bond length of
Information for details, pp S3–S4). By reaction with DME a few 1.762(5) Å and 1.752(4) Å is typical for a tungsten alkylidyne
crystals were obtained; however, X-ray crystallographic analysis bond. The angles between C1 and the alkoxide ligands are par-
revealed a dimeric structure (complexes cis-S1 and trans-S1; see ticularly wide (104.26°–107.60°), and the W–O distances are sig-
Figures S3–S4), in which the amine ligand is still coordinated, nificantly elongated (1.918(3)–1.942(3)), probably because of
and two methoxy groups bridge the tungsten complexes. These steric hindrance.
methoxy fragments may have originated from activation of a
DME molecule, which substituted one alkoxide ligand and the
amido ligand.
Preparation and Characterization of Complexes
[
PhC≡ W(NHMe )(NMe )(OSiR ) ]
2 2 3 2
Siloxy-based catalysts, as demonstrated by 1,3-dyine metathesis
[
15f,15h,16b]
[21,27]
promoter 10
and by Fürstner's complex 13,
are
highly active and exhibit a remarkable functional group toler-
ance. Therefore, the combination of these promising silanolate
ligands with the amido ligands was also explored. Complexes
[
PhC≡ W(NHMe )(NMe )(OSiR ) ] (15, R = O-tBu; 16, R = C H ;
2
2
3 2
6 5
Scheme 5, top) were then obtained by slow addition of two
equivalents of the corresponding, commercially available alco-
Figure 2. Molecular structure of one of the two independent molecules of 17
with thermal displacement parameters drawn at the 30 % probability level;
hydrogen atoms (except at N1) are omitted for clarity. Relevant bond lengths
hols (R SiOH) to a solution of 4d in pentane (15) or toluene
3
(
9
16). After extraction with pentane, complex 16 was isolated in
1 % yield as a deep green powder, whereas complex 15 was
[Å] and angles [deg]: W1–C1 1.762(5), W1′–C1′ 1.752(4), W1–N1 2.234(4),
W1′–N1′ 2.231(4), W1–O1 1.937(3), W1′–O1′ 1.942(3), W1–O5 1.918(3), W1′–
O5′ 1.918(3), W1–O9 1.939(3), W1′–O9′ 1.933(3), C1–C2 1.438(7), C1′–C2′
recrystallized from diethyl ether at –35 °C to give orange crys-
tals in 85 % yield.
1
.457(6); W1–C1–C2 177.6(4), W1′–C1′–C2′ 175.7(4), C1–W1–N1 92.66(18),
C1′–W1′–N1′ 92.78(17), C1–W1–O1 106.63(17), C1′–W1′–O1′ 105.18(16), C1–
W1–O5 106.60(16), C1′–W1′–O5′ 107.60(16), C1–W1–O9 104.26(17), C1′–W1′–
O9′ 104.26(17), N1–W1–O1 80.83(13), N1′–W1′–O1′ 80.69(13), N1–W1–O5
81.80(13), N1′–W1′–O5′ 81.83(13), N1–W1–O9 162.97(15), N1′–W1′–O9′
1
The H NMR spectra of both compounds show the character-
istic splitting of the methyl groups of the amino and the amido
moieties, and a general shift into the high field in complex 16
162.81(13), O1–W1–O5 142.98(14), O1′–W1′–O5′ 143.38(12), O1–W1–O9
92.30(12), O1′–W1′–O9′ 92.49(12), O5–W1–O9 94.94(12), O5′–W1′–O9′
94.89(12). Values for the second molecule are distinguished by primes.
(
(
NHMe : 2.73, 2.75 (15), 2.13, 2.15 (16) ppm; NMe : 3.29, 4.41
2
2
15), 2.75, 3.90 (16) ppm; NHMe : 4.86 (15), 2.29 (16) ppm). In
2
comparison with complexes 14a–14c all resonances in 15 are
clearly more deshielded, which can be ascribed to the higher
Substitution of the amido group by the fluorinated alkoxide
electronegativity of the OSi(O-tBu) ligands and, hence, a higher (δH = 2.03 ppm, δF = –76.2 ppm) is also observed by NMR
3
electron-pushing effect of the amido ligand. In contrast, the spectroscopy. In addition, the amine protons are considerably
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deshielded. The W≡ C signal at 281.3 ppm is slightly low-field crystallizes in the monoclinic space group C2/c, and its coordi-
shifted compared to 15 (δ = 278.1 ppm).
nation geometry can be described as distorted square-pyrami-
C
[
28]
dal (τ = 0.263(4), base angles 144.59(11)° and 160.37(12)°).
5
The alkylidyne moiety occupies the apical position with a nor-
mal W–C triple bond length of 1.762(4). The W–N bond
(2.250(3) Å) is moderately elongated compared to complex 17
Preparation and Characterization of Complex
[
PhC≡ W(NHMe )(OSiPh ) ]
2 3 3
(
2.23 Å), which is probably associated with the increased size of
So far, tungsten complexes of type [RC≡ W(OSiPh ) ] have not
been described in the literature. For example, addition of
3
3
the third alkoxide ligand.
KOSiPh3 to tribromido precursor 2 led to the formation of
[
21,29]
K[PhC≡ W(OSiPh ) ]·dme (dme = 1,2-dimethoxyethane),
a
3
4
tungstate complex bearing four siloxy ligands. Instead, reaction Preparation of Tetrakis(dimethylamido)bis(fluoro-tert-
of our triamido precursor 4d with three equivalents of Ph SiOH butoxide)ditungsten Complexes
3
in toluene (Scheme 5, bottom right) resulted in the formation
Attempts to prepare inverse push-pull analogs – containing two
of neutral [PhC≡ W(NHMe )(OSiPh ) ] (18) in 88 % yield as a
2
3 3
amido ligands and one alkoxide substituent – of complexes
4–16 from 4d were unsuccessful, and resulted only in the
brownish-pink solid. As in former complexes 14–17, the NMR
spectra indicate one dimethylamine molecule bonded to the
1
known disubstitution reactions, but with halved yields. A valid
alternative was found in the ditungsten route. Through direct
metal atom (NHMe , δH = 1.80 and 1.82 ppm; NHMe , δ =
2
2
H
2.73 ppm). The expected low-field shifted signal for the alkylid-
alcoholysis of bimetallic complex 3a, compounds of the type
yne carbon atom is observed at δ = 277.9 ppm. Unfortunately,
C
F
[
W (NMe ) (OR ) ] were successfully prepared using four equiv-
2
2 2
4
NMR analyses show that the complex is unstable in solution
and slowly decomposes generating hexaphenyldisiloxane (see
Figure S17).
Pale red crystals suitable for X-ray diffraction analysis were
obtained from a concentrated dichloromethane solution at
F
[6f,9,30]
alents or an excess of the alcohol (R OH).
In line with
this, we expected substitution of just two amido ligands to be
possible if only two equivalents of the fluorinated alcohols were
used (Scheme 6). Indeed, after sublimation of the crude prod-
F
ucts at 120 °C, compounds with the formula [W (NMe ) (OR ) ]
2
2 4
2
–
35 °C; the structure is displayed in Figure 3. The compound
were isolated as yellow to orange solids in good yields (19a,
F
F
F
R = C(CF )Me , 68 %; 19b, R = C(CF ) Me, 60 %; 19c, R =
3
2
3 2
C(CF ) , 70 %).
3
3
The NMR spectra (Supporting Information, pp S30–S33)
show a series of diastereoisomers, which prevents signal assign-
ment, but integration of the characteristic regions in the 1
H
NMR spectra is consistent with the substitution of two amido
ligands in 3a and the expected formation of complexes 19a–
19c. Additional evidence for the correct composition was pro-
vided by combustion analysis. However, unsymmetrical substi-
F
tution at the ditungsten core, i.e., 1,1-[W (NMe ) (OR ) ] (C
2
2 4
2
s
symmetry), should be also considered. Only in the case of com-
plex 19b, two singlets at 1.75 and 1.78 ppm for the methyl
protons of the alkoxide ligand indicate the existence of mainly
two conformers in a 2:1 ratio. In the fluorine NMR spectrum,
the major isomer displays a single peak at –78.6 ppm, whereas
the CF groups of the second isomer split into two quartets at
3
–
78.2 and –78.9 ppm and, therefore, they should be diastereo-
2 2
Figure 3. Molecular structure of 18·(CH Cl )3.5 with thermal displacement pa-
topic. Thus, the latter isomer must be the C -symmetric rac-1,2–
19b (gauche conformation), and the major isomer is probably
meso-1,2–19b (C2h symmetry, anti-conformation).
rameters drawn at the 50 % probability level; co-crystallized dichloromethane
molecules are omitted for clarity. Relevant bond lengths [Å] and angles [deg]:
W1–C1 1.762(4), W1–N1 2.250(3), W1–O1 1.927(3), W1–O2 1.939(3), W1–O3
2
1
.941(3), C1–C2 1.458(6); W1–C1–C2 177.6(4), C1–W1–N1 94.05(16), C1–W1–
O1 106.17(16), C1–W1–O2 105.48(15), C1–W1–O3 104.79(16), N1–W1–O1
1.95(12), N1–W1–O2 160.37(12), N1–W1–O3 79.13(12), O1–W1–O2 94.18(12),
O1–W1–O3 144.59(11), O2–W1–O3 93.75(12).
In addition, crystals suitable for X-ray diffraction analysis
were grown from a saturated Et O solution at –35 °C, confirm-
ing the structure of complexes 19a–19c (Figure 4, Figure 5, and
8
2
Scheme 6. Synthesis of ditungsten complexes 19a–19c produced a mixture of isomers.
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Figure 6). The products crystallized, respectively, in the space
groups P 1¯ , P2 /n, and P2 /n, the latter two being isotypic, and
1
1
they all contain half a molecule in the asymmetric unit (the
other half being generated by inversion). All three molecules
show a staggered conformation with an anti-periplanar orienta-
tion (180°) of the fluorinated ligands. The W1–O1 distances are,
respectively, 1.907(2) Å, 1.936(2) Å, and 2.0058(17) Å, with the
latter being considerably longer than other reported tungsten–
[
6f,26]
alkoxide bonds (1.868–1.934 Å).
The W1–W1# bond lengths
(
2.3155(3) Å, 2.3144(3) Å, 2.28593(18) Å) are comparable with
[
6f,9]
those of analogous structures
for a tungsten–tungsten triple bond.
and are in the typical range
[
31]
Figure 6. Molecular structure of meso-1,2–19c with thermal displacement
parameters drawn at the 50 % probability level; symmetry operator –x + 1,
–
y + 1, –z + 1. Only one position of the disordered CF
Relevant bond lengths [Å] and angles [deg]: W1–W1# 2.28593(18), W1–N1
.931(2), W1–N2 1.931(2), W1–O1 2.0058(17); N1–W1–N2 111.84(9), N1–W1–
O1 117.61(8), N1–W1–W1# 100.53(6), N2–W1–O1 119.74(8), N2–W1–W1#
00.58(6), O1–W1–W1# 102.01(5).
3
groups is shown.
1
1
so, the simple synthetic approach makes these complexes inter-
esting targets as alkyne metathesis promoters, and their cata-
lytic behavior is presented in the next section.
Catalytic Activity in Internal Alkyne Metathesis
The activity of all ten complexes 14–19 in alkyne metathesis
was investigated with respect to the homodimerization of our
Figure 4. Molecular structure of meso-1,2–19a with thermal displacement pa-
rameters drawn at the 50 % probability level; symmetry operator –x + 1, –y
benchmark substrate BnO(CH ) C≡ CMe (Bn
=
benzyl,
2
2
+
1, –z + 2. Only one position of the disordered alkoxide group is shown.
Relevant bond lengths [Å] and angles [deg]: W1–W1# 2.3155(3), W1–N1
.950(3), W1–N2 1.951(3), W1–O1 1.907(2); N1–W1–N2 116.40(12), N1–W1–
O1 111.18(12), N1–W1–W1# 102.57(9), N2–W1–O1 111.61(12), N2–W1–W1#
02.06(9), O1–W1–W1# 112.30(8).
[
5c]
C H CH ) in the presence of molecular sieves under standard
6
5
2
[
15h]
1
conditions (Scheme 7).
1
Scheme 7. Self-metathesis of 5-benzyloxy-2-pentyne (250 μmol) catalyzed by
complexes 14–19 (cat.); conditions: ambient temperature, toluene (1.25 mL),
molecular sieves 5 Å (250 mg), n-decane (0.05 mL) as internal standard.
For all complexes, the conversion was monitored by GC ana-
lyses at specified time intervals, and the results are plotted in
Figure 7, Figure 8, and Figure 9. In addition, to confirm the
Figure 5. Molecular structure of meso-1,2–19b with thermal displacement
parameters drawn at the 50 % probability level; symmetry operator –x + 1,
–y + 1, –z + 1. Relevant bond lengths [Å] and angles [deg]: W1–W1# 2.3144(3),
W1–N1 1.940(3), W1–N2 1.932(3), W1–O1 1.936(2); N1–W1–N2 115.51(12),
N1–W1–O1 110.34(11), N1–W1–W1# 102.93(9), N2–W1–O1 111.27(11), N2–
W1–W1# 102.13(9), O1–W1–W1# 114.27(7).
Despite the molecular structure determinations, the NMR
analyses discussed above indicate that the bulk materials con-
sist of isomeric mixtures. Indeed, the gauche conformer of 19a,
rac-1,2-[W (NMe ) (OC(CF )Me ) ], was also characterized crys-
2
2 4
3
2 2
Figure 7. GC conversion–time diagram of the self-metathesis of 5-benzyloxy-
tallographically (see Supporting Information, Figure S5). Hence,
2
-pentyne using 1 mol-% of 14a–14c (and 9b for comparison); conditions:
the structure of compounds 19a–19c is not well-defined. Even
see Scheme 7.
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maximal conversion, isolated yields were determined for almost complexes,[17,18c] the degree of fluorination does not seem to
all reactions except for the two least active compounds (17 and affect the catalytic performance of these systems. Among
1
8); the values are summarized in Table 1 and agree with the them, complex 14c showed the highest activity (TOF
=
10 min
–1
GC data.
8.4 min ) and its conversion rate is comparable to other push-
[
5c,32]
pull species such as 9b (see Scheme 3).
chromatography (GPC) traces of the crude reaction mixtures
see Figures S22–S26) confirmed full conversion to the dimeric
The gel permeation
(
species and the absence of oligomers.
Silanolate-based benzylidyne complexes 15–18 behaved
substantially differently in the self-metathesis of 5-benzyloxy-2-
–1
pentyne (Figure 8). The fastest initiation (TOF10 min = 8.7 min )
and highest conversion (97 % in 2 h) was achieved by tri(tert-
butoxy)silanolate complex 15. The analogous push–pull com-
–1
plex 16 initiated similarly fast (TOF10 min = 7.9 min ) but
reached only a lower conversion of about 90 % after 2 h. Substi-
tution of the third amido ligand as in complexes 17 and 18
caused a reduced catalytic performance, probably for steric rea-
sons. A significant activity decrease was observed for triphenyl-
silanolate-supported complex 18, which reached only 16 %
conversion after 3 h and a 50 % maximum conversion after sev-
eral days. The reason might be slow deactivation of 18 by the
aforementioned formation of hexaphenyldisiloxane. In addition,
the GPC trace of the crude reaction mixture after catalysis using
complex 18 revealed the production of polymers (see Figure
S30).
Figure 8. GC conversion–time diagram of the self-metathesis of 5-benzyloxy-
2
-pentyne using 1 mol-% of 15–18; conditions: see Scheme 7.
Bimetallic species 19a–19c are precatalysts that first have to
be oxidized by the alkyne to form the corresponding active
tungsten alkylidyne complex. This activation step is the rate-
determining step and it is relatively slow, so the amount of
active species is small at the beginning. As concluded in previ-
[
17,18c,20c]
ous studies,
the initiation time increases with the de-
gree of fluorination of the alkoxy ligands (Figure 9), which is
consistent with the increasing electrophilicity at the metal
cores. Thus, using complex 19a the alkyne substrate was con-
verted to 93 % within 1 h (according to GC), whereas complex
Figure 9. GC conversion–time diagram of the self-metathesis of 5-benzyloxy-
-pentyne using 0.5 mol-% of 19a–19c; conditions: see Scheme 7.
2
1
9b reached a similar conversion only after about 3 h. Complex
Table 1. GC conversions (%), isolated yields (%), and TOF10 min (min–1) of the
self-metathesis of 5-benzyloxy-2-pentyne using complexes 14–19.
19c exhibited the longest initiation period (no conversion was
detected in the first 4 h), and required 10 h to achieve a conver-
sion of 95 %.
Catalyst
GC conversion [t/h][a]
Isolated yield[b] TOF10 min
In principle, the series of compounds 19 may be used as
1
1
1
1
1
1
1
1
1
1
4a
4b
4c
5
6
7
95 [2]
93 [2]
97 [2]
98 [3]
92 [3]
78 [3]
16 [3]
97 [3]
92 [4]
95 [10]
93
94
96
96
80
n.d.
n.d.
95
91
94
7.1
7.2
8.4
8.7
7.9
5.2
0.2
n.d.
n.d.
n.d.
[
13c–13g]
two-component systems by in situ generation
from 3a
and the corresponding alcohol. Because of its simplicity, this
approach is certainly promising and will be investigated.
[
[
c]
c]
8
[
[
[
c]
c]
c]
9a
9b
9c
Conclusion
Alkyne metathesis promoters featuring a hybrid ligand environ-
ment have been readily and selectively synthesized by alcoholy-
sis of tris(dimethylamido) tungsten complexes with silanols and
fluorinated tert-butanols. Among the tungsten benzylidyne ver-
sions (14–18), the perfluorinated tert-butoxide (14c) and the
tri(tert-butoxy)siloxide (15) based complexes allowed for nearly
full conversion in the self-metathesis of 5-benzyloxy-2-pentyne
[
a] Calculated from the area counts ratio of the substrate to n-decane at
time t; conditions: ambient temperature, 1 mol-% 14–18 or 0.5 mol-% 19a–
9c, toluene (1.25 mL), molecular sieves 5 Å (250 mg), n-decane (0.05 mL) as
1
internal standard. [b] Conditions as in [a] without n-decane, isolated by filtra-
tion through Celite and neutral alox followed by column chromatography
purification, if necessary. [c] Not determined.
Fluorinated complexes 14a–14c exhibited an almost equiva- after 2 h at catalyst loadings of 1 mol-%. In addition, push-pull
lent reaction progress (Figure 7), and after 2 h reached excellent ditungsten complexes 19a–19c were obtained directly from
conversions of 95 %, 93 %, and 97 %, respectively. In contrast hexakis(dimethylamido)ditungsten (3a), but only 1,1,1-trifluoro-
to the trend observed for other fluorinated tungsten alkylidyne tert-butoxide complex 19a performed efficiently in alkyne me-
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tathesis. In future studies, addition of alkynes to open these graphic parameters and further structural details are summarized
in the Supporting Information (Table S1, pp S5–S7; for special fea-
species and generate alkylidyne complexes will be further in-
vestigated. We are optimistic that the present work will increase
the popularity of the alcoholysis synthetic approach and the
tures and exceptions, see pp S7–S8). The program XP (Siemens)[
37]
was used for graphical representations.
use of amido-supported tungsten precursors in the alkyne me- Deposition Numbers 2026935 (for 4d, Pbca polymorph), 2026936
tathesis community.
(for 4d, Pnma polymorph), 2026937 (for 14b), 2026938 (for cis-S1),
026939 (for trans-S1), 2026940 (for 17), 2026941 (for 18), 2026942
for meso-1,2–19a), 2026943 (for rac-1,2–19a), 2026944 (for 19b),
026945 (for 19c) contain the supplementary crystallographic data
for this paper. These data are provided free of charge by the joint
Cambridge Crystallographic Data Centre and Fachinformations-
zentrum Karlsruhe Access Structures service www.ccdc.cam.ac.uk/
structures.
2
(
2
Experimental Section
General. All operations with air- and moisture-sensitive compounds
were performed in a glovebox in a dry argon atmosphere (MBraun
2
00B) or on a high vacuum line using Schlenk techniques. Solvents
(except THF) were purified by a solvent purification system
Other analytical techniques. Elemental analyses (C, H, N) were
determined by combustion and gas chromatographic analysis on a
Vario MICRO cube (Elementar) instrument equipped with WLD and
IR detectors using argon as carrier gas. Values are reported in %
and as an average of three runs. Gas chromatography (GC) analyses
were executed on a Shimadzu GC2010 device equipped with a Ze-
bron ZB-5MS column (30 m × 0.25 mm × 0.25 μm) and FID detector.
Samples (1 μL) were injected at 250 °C with a split/splitless ratio of
1:10 and heated in the column from 50 to 300 °C with a heating
rate of 10 °C min and using helium as carrier gas (30 cm s ). For
calibration, n-decane was used as an internal standard. GPC analy-
ses were performed at 35 °C at a flow rate of 1 mL/min through
PSS SDV (Lux) THF-GPC columns (5 μm, 100 Å and 1000 Å) using a
light scattering detector (Agilent Series 1200) and a polystyrene
standard for calibration.
(
MBraun) and stored over molecular sieves (4 Å) prior to use. THF
[
33]
and deuterated solvents were dried by conventional methods
and stored over molecular sieves. Unless otherwise indicated, all
starting materials obtained from Sigma-Aldrich, Acros or Chempur
were used without further purification. Celite diatomaceous earth
was stored for at least 3 d in an oven at 120 °C. Powdered molecular
sieves 5 Å (particle size < 50 μm, Sigma-Aldrich) used for alkyne
metathesis reactions were dried for at least 24 h at 180 °C under
[
8a]
[7b,7c]
high vacuum prior to use. WCl ,
[W (NMe ) ],
[W (O-
4
2
2 6
[34]
2
–
1
–1
tBu)6],[ [PhC≡ W(O-tBu)3],
7c]
[6a,6c]
and [Ti(NMe2)4]
were prepared
according to slightly modified literature procedures (see Supporting
Information for details, pp S2–S3), and 5-benzyloxy-2-pentyne
was prepared according to the literature procedure.
[
5c]
NMR spectroscopy. NMR spectra were recorded with Bruker DPX
00 (200 MHz, room temperature), Bruker AV II 300 (300 MHz, room
2
Experimental details
temperature), AV III HD 300 (300 MHz, room temperature), and
Bruker AV II 600 (600 MHz, 303 K) devices. 1H and C{ H} NMR
13
1
[
PhC≡ W(NMe ) ], 4d. The preparation was based on published syn-
2 3
spectra were referenced relative to the (residual) solvent signals.
[11]
[12]
theses by Schrock
or McElwee-White.
Based on McElwee-
1
9
1
F{ H} NMR spectra were referenced relative to virtual internal
CFCl (the observation frequencies of a dilute solution of CFCl in
White's route: [Ti(NMe ) ] (0.75 equiv., 341.6 mg, 1.5238 mmol) was
2
4
3
3
added to a solution of [PhC≡ W(O-t-Bu) ] (1000 mg, 2.031 mmol) in
3
the deuterated solvents were determined earlier). Chemical shifts
(
(
attached to each carbon atom was determined by C-DEPT135 ex-
periments. Coupling constants (J) are reported in Hertz (Hz), and
splitting patterns are indicated as s (singlet), d (doublet), t (triplet),
q (quartet), sep (septet), m (multiplet), and br (broad).
Et O (60 mL). After stirring for 2 h at ambient temperature the solu-
2
δ) are expressed in parts per million (ppm). The number of protons
n) for a given resonance is indicated by nH. The number of protons
tion was cooled to 0 °C in an ice-water bath. The solvent was then
removed carefully under reduced pressure to prevent sublimation
of [PhC≡ W(NMe ) ]. The resulting gray-brown residue was sus-
1
3
2
3
pended in small amounts of cold n-pentane, stirred for 5 min, and
collected on a frit. The collected solid was washed three times with
small amounts of cold n-pentane and dried under vacuum to obtain
a deep yellow powder in 60 % yield (493.8 mg, 1.2187 mmol). Based
on Schrock's route: LiNMe2 (3.05 equiv., 316 mg, 6.19 mmol) was
added in portions to a stirred solution of [PhC≡ W(O-t-Bu)3]
X-ray Diffraction Studies
Single crystals were examined and mounted in perfluorinated inert
oil and transferred to the cold gas stream of the diffractometer.
Data were recorded on an Oxford Diffraction Nova A diffractometer,
using mirror-focused Cu-K radiation (1.54184 Å; compound 18) or
an Oxford Diffraction Xcalibur Eos diffractometer using graphite-
monochromated Mo-K radiation (0.71073 Å; compounds 4d (both
polymorphs), 14b, 17, meso-1,2–19a, rac-1,2–19a, 19b, 19c, cis-S1,
trans-S1). Absorption corrections were performed on the basis of
multiscans. All structures were solved using SHELXS-97
fined anisotropically by full-matrix least-squares procedures on F
(
1000 mg, 2.031 mmol) in Et O (60 mL). The reaction mixture was
2
stirred overnight at ambient temperature and then cooled to 0 °C
in an ice-water bath. The solvent was removed under reduced pres-
sure, and the residue was suspended in small amounts of cold
n-pentane, stirred for 5 min, and collected on a frit. The collected
solid was washed three times with small amounts of cold n-pentane
and dried under vacuum. The product was isolated as a deep yellow
powder in 70 % yield (576 mg, 1.422 mmol). Crystals suitable for X-
ray diffraction analysis were obtained from a concentrated solution
α
α
[35]
and re-
2
[36]
using the SHELXL-2018/3 program.
located and refined isotropically (amine proton in compounds 17,
8, cis-S1, and trans-S1), included as idealized methyl groups al-
Hydrogen atoms were either
in dichloromethane (P
polymorph) or n-pentane (Pnma poly-
bca
1
morph) at –35 °C. H NMR (300.1 MHz, C D ): δ = 3.38 (s, 18H;
6
6
1
3
4
6
× CH ), 6.92 (tt, J
= 7.4 Hz, J
= 1.3 Hz, 1H; para-H), 7.17–
3
H,H
H,H
lowed to rotate but not tip (all methyls with the exception of disor-
dered methyl groups in meso-1,2–19a and in compound cis-S1), or
placed geometrically and allowed to ride on their attached carbon
atoms (all other H atoms). If possible, disordered groups were re-
fined on two or more positions; appropriate restraints were em-
ployed to improve refinement stability, but the dimensions of disor-
dered groups should always be interpreted with caution. Crystallo-
1
3
7.24 (m, 2H; Ar-H), 7.30–7.36 (m, 2H, Ar-H); C NMR (75.5 MHz,
C D ): δ = 49.8 (CH ), 125.5 (Ar-CH), 127.9 (Ar-CH), 130.4 (Ar-CH)
6
6
3
1
48.2 (Ar-C ), 276.4 (W≡ C); elemental analysis calcd. (%) for
q
C H N W: C 38.54, H 5.72, N 10.37; found C 38.18, H 5.65, N 10.13.
13 23 3
[PhC≡ W(NHMe )(NMe ){OC(CF )Me } ], 14a. A solution of 1,1,1-
2
2
3
2 2
trifluoro-tert-butanol (2.0 equiv., 128.4 mg, 1.002 mmol) in a small
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amount of n-pentane was added slowly to a solution of 4d sure, and stored at –35 °C. The product was isolated as orange
1
(203.0 mg, 501.0 μmol) in n-pentane (15 mL). After stirring the reac-
crystals in 85 % yield (373.0 mg, 419.6 μmol). H NMR (300.1 MHz,
tion mixture for 3 h at ambient temperature, the solvent was re- C D ): δ = 1.48 (s, 54H; 6 × OC(CH ) ), 2.73 (s, 3H; NH(CH )Me), 2.75
6
6
3 3
3
moved under reduced pressure. The residue was dissolved in a
small amount of diethyl ether and stored in a freezer at –35 °C,
which resulted in precipitation of the product as yellow needles.
The mother liquor was removed by decantation, and the crystals
(s, 3H; NHMe(CH )), 3.29 (s, 3H; N(CH )Me), 4.42 (s, 3H; NMe(CH )),
3 3 3
4.86 (br m, 1H; NHMe ), 6.77–6.85 (m, 1H; para-H), 7.24–7.33 (m,
2
1
3
4H; 4 × Ar-H); C NMR (75.5 MHz, C D ): δ = 31.9 (OC(CH ) ), 40.8
6
6
3 3
(NH(CH ) ), 43.6 (N(CH )Me), 60.6 (NMe(CH )), 72.3 (OCMe ), 125.5
3
2
3
3
3
1
were dried in high vacuum. Yield: 53 % (163.9 mg, 265.9 μmol). H
(Ar-CH), 127.1 (Ar-CH), 132.5 (Ar-CH), 147.7 (Ar-C ), 278.1 (W≡ C); ele-
q
NMR (600.1 MHz, C D ): δ = 1.26 (s, 6H; 2 × C(CF )Me(CH )), 1.54 (s,
mental analysis calcd. (%) for C H N O Si W: C 47.29, H 8.16, N
6
6
3
3
35 72 2 8 2
6
H; 2 × C(CF )(CH )Me), 2.19 (br s, 7H; NH(CH ) ), 2.75 (s, 3H;
3.15; found C 47.40, H 8.31, N 2.98.
3
3
3 2
3
= 7.4 Hz, 4JH,H
NMe(CH )), 3.99 (s, 3H; N(CH )Me), 6.82 (tt, J
=
3
3
H,H
[PhC≡ W(NHMe )(NMe )(OSiPh ) ], 16. A solution of triphenyl-
2
2
3 2
1
.3 Hz, 1H; para-H), 6.98–7.01 (m, 2H; Ar-H), 7.17–7.21 (m, 2H; Ar-H);
silanol (2.0 equiv., 238.7 mg, 863.6 μmol) in toluene (10 mL) was
added slowly to a stirred solution of 4d (175.0 mg, 431.8 μmol) in
toluene (20 mL). After 3 h, the solvent was removed under reduced
pressure, and the residue was dried in high vacuum to give a deep
1
3
C NMR (150.9 MHz, C D ): δ = 25.6 (C(CF )(CH )Me), 25.9
6
6
3
3
(C(CF )Me(CH )), 40.0 (br, NHMe ), 43.4 (NMe(CH )), 59.4 (N(CH )Me),
3 3 2 3 3
2
7
9.3 (q, JC,F = 27.6 Hz; C(CF )Me ), 126.0 (para-CH), 127.8 (ortho-
3 2
1
CH), 128.9 (q, J = 273 Hz; CF ), 131.2 (meta-CH), 147.5 (ipso-C ),
1
C,F
3
q
green solid in 91 % yield (358.9 mg, 393.1 μmol). H NMR
2
71.1 (W≡ C); 19F NMR (376.8 MHz, C D ): δ = –83.02; elemental
6 6
(300.3 MHz, [D ]toluene): δ = 2.13 (s, 3H; NH(CH )Me), 2.15 (s, 3H;
8
3
analysis calcd. (%) for C H F N O W: C 37.03, H 4.91, N 4.55;
found C 36.63, H 4.67, N 4.31.
1
9
30
6
2
2
NHMe(CH )), 2.29 (br s, 1H; NHMe ), 2.75 (s, 3H; N(CH )Me), 3.90 (s,
3 2 3
3
7
4
H; NMe(CH )), 6.73–6.83 (m, 3H; Ar-H), 7.13–7.21 (m, 20H; Ar-H),
.82–7.91 (m, 12H; Ar-H); C NMR (75.5 MHz, [D ]toluene): δ =
3
1
3
8
[PhC≡ W(NHMe )(NMe ){OC(CF ) Me} ], 14b.
A
solution of
2
2
3 2
2
0.7 (NHMe ), 42.7 (N(CH )Me), 59.8 (NMe(CH )), 127.4 (PhC≡ ), 128.0
2
3
3
1
,1,1,3,3,3-hexafluoro-2-methylpropan-2-ol (2.0 equiv., 269.6 mg,
(
(
SiPh ), 129.3 (PhC≡ ), 129.6 (SiPh ), 131.7 (PhC≡ ), 136.0 (SiPh ), 138.7
3 3 3
1
.481 mmol) in a small amount of n-pentane was added slowly to
SiPh ), 148.1 (PhC≡ ), 275.9 (W≡ C); elemental analysis calcd. (%) for
3
a solution of 4d (300 mg, 740.4 μmol) in n-pentane (20 mL). After
stirring the reaction mixture for 3 h at ambient temperature, the
solvent and unreacted starting materials were removed under re-
duced pressure, which resulted in a pale brown solid. Yield: 94 %
C H N O Si W: C 61.84, H 5.30, N 3.07; found C 61.89, H 5.191, N
47 48 2 2 2
2
.71.
[PhC≡ W(NHMe
COH (1.0 equiv., 134.8 mg, 0.740 mmol) in a small amount
of n-pentane was added slowly to a solution of 15 (658.2 mg,
){OC(CF ) Me}{OSi(O-t-Bu) } ], 17. A solution of
3 2 3 2
2
504.0 mg, 696.0 μmol). 1H NMR (300.1 MHz, C D ): δ = 1.49 (m, Me(CF
)
3 2
(
6
6
6
H; 2 × C(CF ) CH ), 2.15 (s, 3H; NH(CH )Me), 2.18 (s, 3H;
3 2 3 3
NHMe(CH )), 2.47 (br s, 1H; NHMe ), 2.87 (s, 3H; N(CH )Me), 4.05 (s, 740.4 μmol) in n-pentane (30 mL). After stirring for 2 h at ambient
3
2
3
3
4
3H; NMe(CH )), 6.79 (tt, J
= 7.4 Hz, J
= 1.3 Hz, 1H; para-H), temperature, the reaction mixture was concentrated under reduced
3
H,H
H,H
13
6
.94–7.02 (m, 2H; Ar-H), 7.11–7.21 (m, 2H; Ar-H); C NMR (75.5 MHz,
pressure and stored at –35 °C. The product was isolated as orange
C D ): δ = 20.2 (C(CF ) (CH )), 39.9 (NHMe ), 42.1 (N(CH )Me), 59.4 crystals in 75 % yield (569.7 mg, 555.3 μmol). The crystals were
6
6
3 2
3
2
3
2
1
1
(
2
1
NMe(CH )), 81.5 (sept, JC,F = 28 Hz; C(CF ) Me), 124.5 (q, JC,F
=
suitable for X-ray diffraction analysis. H NMR (300.1 MHz, C
δ = 1.45 (s, 54H; 6 × C(CH )), 2.03 (br m, 3H; OC(CF CH ), 2.78 (s,
3H; NH(CH )Me), 2.80 (s, 3H; NHMe(CH )), 5.61 (sept, JH,H = 5.8 Hz,
1H; NHMe ), 6.70 (tt, JH,H = 7.4 Hz, JH,H = 1.4 Hz, 1H; para-H), 7.14–
7.19 (m, 2H (overlapped with the solvent residual signal); Ar-CH),
6 6
D ):
3
3 2
88 Hz; 2 × CF ), 125.3 (q, 1J = 289 Hz; 2 × CF ), 127.1 (Ar-CH),
)
3
C,F
3
3
3
2
3
1
9
3
27.9 (Ar-CH), 131.5 (Ar-CH), 146.4 (Ar-C ), 273.4 (W≡ C). F NMR
3
3
q
4
3
4
(188.3 MHz, C D ): δ = –78.4 (q, JF,F = 9.7 Hz, 6F; 2 × CF ) –77.2
2
6
6
3
4
(
q, JF,F = 9.7 Hz, 6F; 2 × CF ); elemental analysis calcd. (%) for
3
1
3
C H F N O W: C 31.51, H 3.34, N 3.87; found C 31.29, H 3.20, N 7.22–7.30 (m, 2H; Ar-CH); C NMR (75.5 MHz, C
D
): δ = 21.2
), 73.2 (CMe ), 82.9 (m;
OC(CF ) CH ), 124.9 (q, J = 290 Hz; CF ), 127.0 (Ar-CH), 127.3 (Ar-
19 24 12 2 2
6
6
3
.92.
(OC(CF
3
)
2
CH
3
), 31.9 (C(CH
3
)
3
), 42.2 (NHMe
2
3
1
3
2
3
C,F
3
[PhC≡ W(NHMe )(NMe ){OC(CF ) } ], 14c. A solution of perfluoro-
19
2
2
3 3 2
CH), 133.9 (Ar-CH), 145.4 (Ar-C ), 281.3 (W≡ C); F NMR (188.3 MHz,
q
tert-butanol (2.0 equiv., 156.1 mg, 0.661 mmol) in a small amount
of toluene was added slowly to a solution of 4d (134.0 mg,
C D ): δ = –76.2 (CF ).
6
6
3
Synthesis of [PhC≡ W(NHMe )(OSiPh ) ], 18.
A solution of
2
3 3
3
30.7 μmol) in toluene (10 mL). After stirring the reaction mixture
Ph SiOH (3.0 equiv., 1.023 g, 3.702 mmol) in toluene (10 mL) was
3
for 3 h at ambient temperature, the solvent and unreacted starting
materials were removed under reduced pressure, which resulted in
a pale brown solid. Yield: 94 % (258.9 mg, 311.1 μmol). H NMR
added to a solution of 4d (500 mg, 1.2340 mmol) in toluene
(40 mL). The reaction mixture was stirred overnight at ambient tem-
1
perature, and the solvent was removed under reduced pressure.
The remaining residue was stirred for 20 min in n-pentane (20 mL),
filtered, and then the collected solid was washed with n-pentane
(300.3 MHz, [D ]toluene): δ = 2.26 (s, 3H; NH(CH )Me), 2.28 (s, 3H;
8
3
NHMe(CH )), 2.75 (br s, 1H; NHMe ), 3.05 (s, 3H; N(CH )Me), 4.34 (s,
3
2
3
3
4
3H; NMe(CH )), 6.73 (tt, J
= 7.4 Hz, J = 1.3 Hz, 1H; para-H),
3
H,H
H,H
(3 × 5 mL) and dried under high vacuum to give a brownish-pink
13
6
.94–7.03 (m, 2H; Ar-H), 7.06–7.15 (m, 2H; Ar-H); C NMR (75.5 MHz,
solid in 88 % yield (1.242 g, 1.085 mmol). Red single crystals were
obtained from a concentrated dichloromethane solution at –35 °C.
[D ]toluene): δ = 40.0 (NHMe ), 41.7 (N(CH )Me), 59.6 (NMe(CH )),
8 2 3 3
1
8
3.0 (m; C(CF ) ), 122.0 (q, J = 294 Hz; CF ), 127.5 (Ar-CH), 132.3
3 3 C,F 3
1
H NMR (300.1 MHz, C D ): δ = 1.80 (s, 3H; NH(CH )Me), 1.82 (s, 3H;
6
6
3
3
(Ar-CH), 145.4 (Ar-C ), 279.1 (W≡ C), the resonance for one aryl-CH
q
NHMe(CH )), 2.73 (sept, J
2
= 5.9 Hz, 1H; HNMe ), 6.43–6.48 (m,
3
H,H
2
carbon atom overlaps with the solvent signal and was not ob-
3
4
H; Ar-H), 6.69 (tt, J
= 7.4 Hz, J
= 1.2 Hz, 1H; para-H), 6.87
served; 19F NMR (282.5 MHz, [D ]toluene): δ = –73.3 (CF ); elemen-
H,H
H,H
8
3
(br t, 6H; Ar-H), 6.99–7.10 (m, 15H; Ar-H), 7.10–7.22 (m, 6H (over-
tal analysis calcd. (%) for C H F N O W: C 27.42, H 2.18, N 3.37;
found C 27.46, H 2.19, N 3.32.
1
9 18 18 2 2
lapped with the solvent residual signal); Ar-H), 7.74–7.78 (m, 2H;
Ar-H), 7.82–7.87 (m, 6H; Ar-H), 7.87–7.94 (m, 12H; Ar-H); 13C NMR
(75.5 MHz, C D ): δ = 42.3 (NHMe ), 126.9 (PhC≡ ), 127.9 (SiPh ),
[PhC≡ W(NHMe )(NMe ){OSi(O-t-Bu) } ], 15.
A
solution of
2
2
3 2
6
6
2
3
(
tBuO) SiOH (2.0 equiv., 261.1 mg, 987.2 μmol) in a small amount
128.1 (SiPh ), 128.2 (PhC≡ ), 129.5 (SiPh ), 129.9 (SiPh ), 133.9 (PhC≡ ),
3
3 3 3
of n-pentane was added slowly to a solution of 4d (200.0 mg,
136.2 (SiPh ), 136.4 (SiPh ), 137.4 (SiPh ), 137.7 (SiPh ), 145.9 (PhC≡ ),
3 3 3 3
4
93.6 μmol) in n-pentane (20 mL). The reaction mixture was stirred 277.9 (W≡ C); elemental analysis calcd. (%) for C H NO Si W:
63 57 3 3
for 2 h at ambient temperature, concentrated under reduced pres-
C 66.13, H 5.02, N 1.22; found C 65.75, H 4.96, N 1.21.
Eur. J. Inorg. Chem. 0000, 0–0
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© 2020 The Authors. European Journal of Inorganic Chemistry
published by Wiley-VCH GmbH

Full Paper
doi.org/10.1002/ejic.202000835
EurJIC
European Journal of Inorganic Chemistry
[
W (NMe ) {OC(CF )Me } ], 19a. A solution of 1,1,1-trifluoro-tert-
Conflict of Interest
2
2 4
3
2 2
butanol (2.0 equiv., 40.5 mg, 316.4 μmol) in toluene (2 mL) was
The authors declare no competing financial interest.
added slowly to a solution of [W (NMe ) ] (3a, 100 mg, 0.158 mmol)
2
2 6
in toluene (10 mL). After stirring the reaction mixture for 8 h at
ambient temperature, the solvent was removed under reduced
pressure, and the remaining solid was sublimed at 120 °C and
Acknowledgments
–3
1
0
mbar to give a yellow microcrystalline solid in 68 % yield We thank to Dr. Dirk Bockfeld for determination of the X-ray
(
85.4 mg, 107.0 μmol). Single crystals were obtained from a concen- crystal structure of meso-1,2-19c. Financial support by the Deut-
trated n-pentane solution at –35 °C. Elemental analysis calcd. (%)
for C H F N O W : C 24.08, H 4.55, N 7.02; found C 24.28, H 4.24,
N 6.96.
sche Forschungsgemeinschaft (DFG) through grant Ta 189/12-1
is gratefully acknowledged. Open access funding enabled and
organized by Projekt DEAL.
16
36
6
4
2
2
[
W (NMe ) {OC(CF ) Me} ], 19b. A solution of 1,1,1,3,3,3-hexa-
2
2 4
3 2
2
fluoro-2-methylpropan-2-ol (2.0 equiv., 230 mg, 1.266 mmol) in tol-
uene (5 mL) was added slowly to a solution of 3a (400.0 mg,
Keywords: Alkylidyne complexes · Alkyne metathesis ·
Metal–metal triple bonds · Tungsten · Homogeneous
catalysis
6
32.8 μmol) in toluene (40 mL). After stirring the reaction mixture
for 8 h at ambient temperature, the solvent was removed under
reduced pressure, and the remaining solid was sublimed at 120 °C
and 10–3 mbar to give a yellow microcrystalline solid in 70 % yield
[
1] F. Pennella, R. L. Banks, G. C. Bailey, Chem. Commun. 1968, 1548–1549.
(
401.4 mg, 443.0 μmol). Single crystals were obtained from a con-
1
[2] a) A. Fürstner, P. W. Davies, Chem. Commun. 2005, 2307–2320; b) A. Mor-
treux, O. Coutelier, J. Mol. Catal. A 2006, 254, 96–104; c) W. Zhang, J. S.
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Today 2010, 28, 60–63; e) X. Wu, M. Tamm, Beilstein J. Org. Chem. 2011,
centrated n-pentane solution at –35 °C. H NMR (600.1 MHz, C D ):
6
6
δ = 1.75 (m, 6H; 2 × C(CF ) (CH ), meso-1,2–19b), 1.78 (m, 3H;
3
2
3
2
4
4
1
5
2
× C(CF ) (CH ), rac-1,2–19b), 2.11–2.63 (br m, 12H
+
6H;
3
2
3
× N(CH )Me, meso/rac-1,2–19b), 3.80–4.46 (br m, 12H + 6H;
3
7
, 82–93; f) A. Fürstner, Angew. Chem. Int. Ed. 2013, 52, 2794–2819;
13
× NMe(CH ), meso/rac-1,2–19b); C NMR (150.9 MHz, C D ): δ =
3
6
6
Angew. Chem. 2013, 125, 2860; g) C. Deraedt, M. d'Halluin, D. Astruc, Eur.
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3190–3208; k) D. Lee, I. Volchkov, S. Y. Yun, Alkyne Metathesis. In Organic
Reactions, Vol. 102 (Ed.: P. A. Evans), John Wiley & Sons, Hoboken, NJ
(USA), 2020, p. 613–931.
9.5 (C(CF ) (CH )), 20.3 (C(CF ) (CH )), 38.8 (NMe ), 45.4 (NMe ),
3
2
3
3 2
3
2
2
1
9.1 (NMe ), 61.7 (NMe ), 82.0 (m; OC(CF )Me), 124.6 (q, JC,F
=
2
2
3
1
1
90 Hz; CF ), 124.7(q, J = 288 Hz; CF ), 124.9 (q, J = 288 Hz;
3
C,F
3
C,F
19
4
CF3); F NMR (376.8 MHz, C D ): δ = –78.2 (q, J = 9.4 Hz, 3F;
6
6
F,F
2
× CF , rac-1,2–19b), –78.6 (s, 12F; 4 × CF , meso-1,2–19b), –78.9
3
3
4
(q, J = 9.4 Hz, 3F; 2 × CF , rac-1,2–19b), the isomeric mixture of
F,F 3
[
[
3] a) R. R. Schrock, J. Sancho, S. F. Pederson, S. C. Virgil, R. H. Grubbs,
meso-1,2–19b and rac-1,2–19b has a 2:1 ratio; elemental analysis
2
,2-Dimethylpropylidyne Tungsten(VI) Complexes and Precursors for their
calcd. (%) for C H F N O W : C 21.21, H 3.34, N 6.18; found
16
30 12
4
2
2
Syntheses. In Inorganic Syntheses, Vol. 26 (Ed.: H. D. Kaesz), John Wiley &
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1984, 3, 1563–1573.
C 21.08, H 3.14, N 5.72. Although the nitrogen content is not suffi-
ciently accurate, it is provided to illustrate the best value obtained
to date.
4] J. H. Freudenberger, R. R. Schrock, Organometallics 1986, 5, 1411–1417.
[
W (NMe ) {OC(CF ) } ], 19c. A solution of perfluoro-tert-butanol
2 2 4 3 3 2
[5] a) A. Mayr, G. A. McDermott, J. Am. Chem. Soc. 1986, 108, 548–549;
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(2.0 equiv., 97 mg, 0.411 mmol) in toluene (2 mL) was added slowly
to a solution of 3a (130.0 mg, 0.206 mmol) in toluene (10 mL). After
stirring the reaction mixture for 8 h at ambient temperature, the
solvent was removed under reduced pressure, and the remaining
[
6] a) R. R. Schrock, M. L. Listemann, L. G. Sturgeoff, J. Am. Chem. Soc. 1982,
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–
3
solid was sublimed at 120 °C and 10 mbar to give an orange solid
in 70 % yield (146 mg, 0.144 mmol). Single crystals were obtained
from a concentrated n-pentane solution at –35 °C. Elemental anal-
ysis calcd. (%) for C H F N O W : C 18.95, H 2.39, N 5.53; found
16
24 18
4
2
2
C 19.15, H 2.51, N 5.54.
7
05–711; g) M. H. Chisholm, Chem. Rec. 2001, 1, 12–23; h) H. Ehrhorn, J.
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434.
Standard procedure for the self-metathesis of 5-benzyloxy-2-
pentyne. In an argon-filled glovebox, a 5 mL flask was charged
with powdered molecular sieves 5 Å (250 mg), n-decane (0.05 mL),
2
[
7] a) F. A. Cotton, B. R. Stults, J. M. Troup, M. H. Chisholm, M. W. Extine, J.
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5
(
-benzyloxy-2-pentyne (0.25 mmol), and toluene (1.5 mL). A sample
0.05 mL) was then taken for the GC reference. After addition of the
catalyst (14–18, 1 mol-%, 2.5 μmol; 19, 0.5 mol-%, 1.25 μmol),
0
.05 mL aliquots were collected at defined time intervals (1, 2, 3, 4,
5
, 10, 20, 30, 60, 120, and 180 min). Additional aliquots were col-
lected every 30 min (the final sample after 600 min) for complexes
9. All samples were filtered directly through neutral alox and
1
[
6
8] Also other reducing agents, such as antimony, mercury, [W(CO) ], or red
rinsed three times with diethyl ether. The filtrate was analyzed via
GC, and the crude reaction mixtures at the end of the metathesis
reactions were analyzed via GPC (see pp S35–S39).
phosphorus, have been employed; see: a) V. Kolesnichenko, D. C. Swen-
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[
3 3
9] M. H. Chisholm, C. B. Hollandsworth, X M≡ MX Compounds of Molyb-
Supporting Information (see footnote on the first page of this
article): Additional experimental details, including solid-state struc-
ture determinations, NMR spectra and GPC traces.
rd
denum and Tungsten. In Multiple Bonds Between Metal Atoms, 3 ed.
(Eds.: F. A. Cotton, C. A. Murillo, R. A. Walton), Springer US, Boston, MA,
2005, p. 203–250.
Eur. J. Inorg. Chem. 0000, 0–0
www.eurjic.org
10
© 2020 The Authors. European Journal of Inorganic Chemistry
published by Wiley-VCH GmbH

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doi.org/10.1002/ejic.202000835
EurJIC
European Journal of Inorganic Chemistry
[
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2
2
011, 123, 3497; f) K. Jyothish, Q. Wang, W. Zhang, Adv. Synth. Catal.
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Received: September 3, 2019
Eur. J. Inorg. Chem. 0000, 0–0
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© 2020 The Authors. European Journal of Inorganic Chemistry
published by Wiley-VCH GmbH

Full Paper
doi.org/10.1002/ejic.202000835
EurJIC
European Journal of Inorganic Chemistry
Alkyne Metathesis
D. Melcher, Ò. Àrias, M. Freytag,
P. G. Jones, M. Tamm* ................... 1–12
Synthesis of Alkyne Metathesis Cat-
alysts from Tris(dimethylamido)-
tungsten Precursors
Mixed ligand systems for alkyne me- synthesized via partial alcoholysis of
tathesis. Tungsten alkyne metathesis tris(dimethylamido)tungsten
pre-
catalysts bearing a combination of alk- cursors such as [PhC≡ W(NMe ) ] and
2
3
oxide and amide ligands were readily [W (NMe ) ].
2
2 6
doi.org/10.1002/ejic.202000835
Eur. J. Inorg. Chem. 0000, 0–0
www.eurjic.org
12
© 2020 The Authors. European Journal of Inorganic Chemistry
published by Wiley-VCH GmbH