Synthesis and structure of seven-membered metallacycloalkynes

Article abstract of DOI:10.1002/ejic.201201245

Seven-membered metallacycloalkyne compounds were synthesized. The reaction of the zirconocene-ethylene complex and (Z)-1,4-bis(trimethylsilyl)buta-1,2,3- triene gave a mixture of 1-zirconacyclopent-3-yne and 1-zirconacyclohept-3-yne. In contrast, zirconocene-alkyne complexes, such as those of 1-(trimethylsilyl) prop-1-yne and diphenylacetylene, gave 1-zirconacyclohept-2-en-5-yne in good yields. Consideration of structural parameters suggests that both a seven-membered cyclic alkyne and a five-membered structure contribute to generation of this complex. Coupling of benzyne and [3]cumulenes on a metal was also found to afford the corresponding metallacycles. Seven-membered metallacycloalkyne compounds were synthesized and structurally characterized. Zirconocene-alkyne complexes, such as those of 1-(trimethylsilyl)prop-1-yne and diphenylacetylene reacted with [3]cumulene to give 1-zirconacyclohept-2-en-5-yne in good yields. Coupling of benzyne and [3]cumulenes on the metal also gave the corresponding metallacycles. Copyright

Full text of DOI:10.1002/ejic.201201245

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DOI:10.1002/ejic.201201245
Synthesis and Structure of Seven-Membered
Metallacycloalkynes
Noriyuki Suzuki,*[a,b] Takashi Tsuchiya,[a] Naoto Aihara,[c]
Masakazu Iwasaki,[c] Masahiko Saburi,[c] Teiji Chihara,[b][‡] and
Yoshiro Masuyama[a]
COVER PICTURE
Keywords: Metallacycles / Zirconium / Titanium / Alkyne ligands / Cycloalkynes / Cumulenes
Seven-membered metallacycloalkyne compounds were syn-
thesized. The reaction of the zirconocene–ethylene complex
and (Z)-1,4-bis(trimethylsilyl)buta-1,2,3-triene gave a mix-
ture of 1-zirconacyclopent-3-yne and 1-zirconacyclohept-3-
yne. In contrast, zirconocene–alkyne complexes, such as
those of 1-(trimethylsilyl)prop-1-yne and diphenylacetylene,
gave 1-zirconacyclohept-2-en-5-yne in good yields. Con-
sideration of structural parameters suggests that both a
seven-membered cyclic alkyne and a five-membered struc-
ture contribute to generation of this complex. Coupling of
benzyne and [3]cumulenes on a metal was also found to af-
ford the corresponding metallacycles.
Introduction
Transition metal complexes of [n]cumulene (n Ն 3) have
attracted the attention of many coordination chemists be-
cause they demonstrate a variety of possible coordination
modes. For example, most rhodium complexes of [3] and
[5]cumulenes show η2-π-coordination.[1] Iron metal reacts
with cumulenes to form various complexes such as mono-
and multinuclear iron complexes;[2] in one instance C=C
bond cleavage even occurred.[2h] We recently reported that
[3]cumulenes coordinate to group IV metals to form five-
membered cycloalkyne compounds, specifically 1-metall-
acyclopent-3-ynes [Equation (1)].[3] We also demonstrated
that zirconocene complexes of [5]cumulene compounds are
capable of achieving two coordination modes, specifically
those characteristic of η2-π complexes and 1-zirconacyclop-
ent-3-yne compounds.[4] Metallacyclic compounds 1 are
surprisingly stable despite the highly strained nature of their
alkyne moieties. These compounds could be isolated as
crystals and their molecular structures were unambiguously
determined.
(1)
The 1-metallacyclopent-3-yne complex 1 resembles 1-
metallacyclopenta-2,3,4-triene complexes 4 in terms of their
molecular structures (Scheme 1). Complexes of the type 4
were reported by Rosenthal and co-workers, which are de-
rived from divalent zirconocenes or titanocenes and 1,3-di-
ynes. These complexes have a highly strained cyclic cumu-
lene structure yet are stable at room temperature.[5] Such
small metallacyclic allenes have received much attention not
only from organometallic chemists but also from organic
chemists by virtue of the juxtapositioning of their high sta-
bility and significantly strained structures.[4a,6] Buchwald
[a] Department of Materials and Life Sciences, Faculty of Science
and Technology, Sophia University,
Kioi-cho 7-1, Chiyoda-ku, Tokyo 102-8554, Japan
E-mail: norisuzuki@sophia.ac.jp
Homepage: www.mls.sophia.ac.jp/~orgsynth/
[b] Materials Characterization Team, RIKEN Advanced Science and Rosenthal independently reported that two 1,3-diyne
Institute,
molecules coupled to zirconium form “seven-membered cu-
Wako, Saitama 351-0198, Japan
mulene complex” 5.[5a,7] Such cumulene complexes may be
[c] Department of Applied Chemistry, Faculty of Engineering,
Graduate School of Saitama Institute of Technology,
1690 Fusaiji, Fukaya, Saitama 369-0293, Japan
[‡] Current address: Graduate School of Science and Engineering,
Saitama University,
in equilibrium with α-alkynyl metallacyclopentadienes of
the form 6. The corresponding titanium complex, indeed,
showed no interaction between the triple bond and the tita-
nium metal according to X-ray diffraction analyses
(Scheme 2).[8] An equilibrium between α-vinylzirconacyclo-
pentanes and seven-membered rings has been proposed.[9]
Shimo-Okubo 255, Sakura-ku, Saitama-city, Saitama, 338-
8570, Japan
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201201245.
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Erker and co-workers have reported the coupling of dimerization of cumulenes.[12] In this reaction they pro-
benzyne and 1,3-diyne on zirconium to form seven-mem- posed the formation of a nickellacycle species that was
bered cumulene derivatives accompanied by formation of formed by two cumulene molecules coupled on the nickel
2,4-bisalkynyl-1-zirconacyclopenta-2,4-diene as a minor atom, although the putative complex was not observed or
isomeric complex [Equation (2)].[10,11]
identified. These facts prompted us to investigate the reac-
tivity of cumulenes with group IV metals, particularly with
respect to coupling of cumulenes with alkenes and alkynes.
Seven-membered cyclo[3]cumulene compounds were
formed by the coupling of alkynes and 1,3-diynes on a
metal atom suggesting that coupling of an alkyne and [3]-
cumulene may give seven-membered metallacycloalkynes.
Synthesis and characterization of such species offered us
the chance to gain significant insight into the chemistry of
metallacycles and clearly warranted both interest and effort.
The synthesis and isolation of small cyclic alkynes has
long attracted organic chemists[13] and some examples of
isolable seven-membered cyclic alkynes have been reported.
Hydrocarbyl cycloheptynes have been isolated and spectro-
scopically characterized,[14] as well as heterocyclic alkynes
such as 1-thiacyclohept-4-ynes[15] and 1-silacyclohept-4-
ynes.[13a] However, examples that have been structurally
characterized by X-ray diffraction analysis are very
rare.[16–19] To the best of our knowledge, there have been no
examples of 1-metallacyclohept-3-ynes. Herein, we report
the synthesis and structure of seven-membered metallacy-
cloalkyne complexes generated by the coupling of [3]cumu-
lene and either an alkyne or an alkene on the metal. Earlier
portions of this work have been previously communi-
cated.[20]
Scheme 1. Zirconium complexes of 1,3-diynes.
Results and Discussion
We have reported the reactions of zirconocene-but-1-ene
complex 2, which is generated in situ from reaction of Negi-
shi reagent, Cp2Zr(nBu)2, with [3]cumulene derivatives 3 to
give the 1-zirconacyclopent-3-yne derivative 1 as a represen-
tative five-membered cycloalkyne [Equation (1)]. Replace-
ment of but-1-ene with the [3]cumulene 3 abolished the de-
sired coupling.[3a] Alternatively, when starting with
Cp2Zr(ethylene) 7, generated in situ from Cp2ZrEt2,[21] cou-
pling of ethylene and 3 on the zirconium atom was observed
leading to major product 1 (46%) through a ligand ex-
change involving ethylene and 3. NMR monitoring of the
reaction mixture indicated that the seven-membered metall-
acyclic product 8 was formed in 29% yield after 18 h at
Scheme 2. 2-Alkynyl-1-metallacyclopenta-2,4-diene vs. 1-metall-
acyclohepta-2,3,4,6-tetraene.
1
room temperature (Scheme 3). In the H NMR spectrum,
two singlets attributable to nonequivalent cyclopentadienyl
rings were observed at δ = 5.34 and 5.38 ppm, and the α-
methine proton appeared at δ = 1.50 ppm as a doublet (J
= 7 Hz) indicative of long-range coupling with another
methine proton (multiplet, 2.0–2.1 ppm). In the 13C NMR
spectrum, two quaternary carbons were observed at 96.36
and 104.05 ppm. Alkyne carbons that appeared downfield
suggest their interaction with the metal. Two methylene car-
(2)
In contrast, little is known about reductive coupling of bons appearing at δ = 37.07 and 45.10 ppm support the
cumulenes with other unsaturated hydrocarbons on transi- seven-membered structure. NMR data revealed a predomi-
tion metals. Iyoda and co-workers reported nickel-catalyzed nance of one stereoisomer of 8 whose isomerization could
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not be observed on the NMR timescale at room tempera-
ture. This is in sharp contrast to 1, where the initially
formed cis complex readily isomerized to the trans-isomer
at room temperature.[22] Although no stereochemical as-
signments have been made, we postulate that this easily iso-
merizable isomer bears the syn-form considering the results
of compound 12 and 16 (vide infra). Hydrolysis of the reac-
tion mixture with hydrochloric acid gave corresponding al-
kyne 10 as well as 9. Deuterolysis afforded dideutero prod-
uct [D2]-10 with 98% and Ͼ 99% D incorporation at the
1- and 6-positions, respectively. These results support the
assigned seven-membered structure of 8. Although 8 was
fully characterized by NMR spectroscopy in solution, its
low yield prohibited isolation. Accordingly, we studied the
reaction using alkyne complexes instead of the ethylene
complex. Zirconocene–alkyne complex Cp2Zr(Me3Si–
CϵC–Me)(PMe3) (11),[23] was prepared and reacted with 3
(Scheme 4). After heating at 80 °C for 1 h, the formation of
12 in 60–74% yield was detected by NMR spectroscopy.
Hydrolysis of 12 gave 1,4-enyne product 14. The ligand ex-
change was suppressed and 1 was formed in low yield (15%
Scheme 4. Preparation of 1-zirconacyclohept-2-en-5-yne 12 and the
byproducts.
1
by H NMR). Interestingly, we identified one minor prod-
uct 13 that appears to be an isomer of 12 (vide infra). It
is noteworthy that 1 failed to react when treated with 1-
(trimethylsilyl)prop-1-yne.
19 was not formed probably due to steric repulsions be-
tween the tetramethylcyclopentylidene moieties of 17 and
the phenyl/cyclopentadienyl groups of the zirconium spe-
cies.
Scheme 5. Preparation of 1-zirconacyclohept-2-en-5-yne 16 from
diphenylacetylene.
Scheme 3. Formation of a seven-membered metallacycloalkyne.
We next employed zirconocene–diphenylacetylene com-
plex 15.[24] The reaction predominantly gave seven-mem-
bered compound 16 in good yield accompanied by Ͻ1% of
1. No formation of byproducts such as 13 was observed
(Scheme 5) suggesting that diphenylacetylene more strongly
coordinates zirconium than does 1-(trimethylsilyl)prop-1-
yne. When a [3]cumulene with tert-butyl groups, 2,2,7,7-
tetramethylocta-3,4,5-triene was used instead of 3, starting
complex 15 failed to react. Addition of [5]cumulene deriva-
tive 17 to complex 15 afforded 1-zirconacyclopent-3-yne 18
as the only product (Scheme 6).[4b] Seven-membered alkyne Scheme 6. Reaction of zirconocene 15 with [5]cumulene compound.
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Recrystallization from hexane solution gave yellow crys- 110.05 (12) and 98.75, 104.34 (16) ppm in the 13C NMR
tals of 12 and 16, and their molecular structures were un- spectrum. The chemical shifts suggest that they are alkyne
ambiguously determined by X-ray diffraction analyses. The carbons. The signal for C1 was observed at 38.8 (12) and
complexes have a distorted seven-membered metallacyclic 34.6 (16) ppm. Infrared absorption signals attributable to
structure (Figure 1). The stereochemistry for two of the tri- the triple bond were observed at 2028 and 2025 cm–1 for 12
methylsilyl groups was syn. The formation of the anti-iso- and 16, respectively. These results support the seven-mem-
mer was negligible based on NMR spectra of the reaction bered enyne structure of 12 and 16. It should be noted that
mixture. The lengths of Zr–C1 [12: 2.580(2), 16 2.538(3) Å] these complexes are thermally stable and their crystals
indicate the existence of the metal–carbon bond. The C2– could be stored under an inert atmosphere for months, al-
C3 bonds are short enough [12: 1.239(3), 16: 1.231(3) Å] to though a sensitivity to air and moisture has been noted.
be regarded as triple bonds, whereas the C1–C2 bond (1.38–
Interestingly, there were orange crystals in the crop of 12,
1.39 Å) is significantly longer than is C2–C3. The angles and these crystals were found to be isomeric compound 13.
C1–C2–C3 and C2–C3–C4 are in the range of 155–161° and This minor product was collected from the crystal crop in
thus, much larger than 120°. These results support the 1- 6% isolated yield and its molecular structure unambigu-
metallacyclohept-2-en-5-yne structure. On the other hand, ously determined by X-ray diffraction. Compound 13 was
the alkyne moieties are bent toward the metals, showing characterized by a fused bicyclic structure implying that it
their interaction with the zirconium atom. The C1–C2 was also the coupled product of [3]cumulene 3 and alkyne
bonds are too short to be regarded as single bonds. The (Figure 2). 1H and 13C NMR spectroscopic data for the
short Zr–C2 and Zr–C3 distances also support metal–car- orange crystals support the results of the X-ray analysis.
bon interactions. These data suggest a contribution to Zr– The structure of 13 is similar to known butadiene com-
C interactions from the five-membered structure, 4-vinyl- plexes of zirconium.[25]
idene-1-zirconacyclopent-2-ene.
Figure 2. The molecular structure of 13. Drawn with 50% prob-
ability. Hydrogen atoms are partly omitted for clarity.
Although the mechanistic pathway for the formation of
13 is presently unclear, it is likely that coupling of the triple
bond of the alkyne with the internal double bond of the [3]-
cumulene 3 at the zirconium atom constitutes the initial
step, whereas 12 appears to arise from coupling of the ter-
minal double bond of 3 with the alkyne. A plausible route
is depicted in Scheme 7. When 3 was coupled with the 1-
(trimethylsilyl)prop-1-yne on zirconium, the coupling oc-
curred at its 2,3-positions to give initial complex 20. Re-
ductive elimination then formed the cyclobutene ring, fol-
lowed by isomerization; the resulting 1,3-diene compound
coordinated to the metal ultimately affording 13.
Figure 1. The molecular structures of 12 (top) and 16 (bottom).
To better understand the utility of the rather unstable
alkynes as coupling partners, we examined the zirconocene–
benzyne complex that is generated in situ from di-
Drawn with 50% probability. Hydrogen atoms are partly omitted
for clarity.
In the H NMR spectra, the methine protons at C1 ap- phenylbis(η5-cyclopentadienyl)zirconium 21.[26] Complex
peared at 2.17 (12) and 2.03 (16) ppm, showing their sp3 21 was heated at 100 °C for 3 h in the presence of 3. NMR
character. The C2 and C3 signals appeared at 101.36, spectra suggested the formation of coupled complex 22 in
1
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Scheme 7. A plausible pathway for the formation of 13.
64% yield. This species was obtained as a mixture of stereo-
isomers (syn/anti), probably because 3 isomerized during
the reaction. The ratio of stereoisomers ranged from 7:3 to
9:1, and was not very reproducible. Hydrolysis of the reac-
tion mixture gave 1-phenyl-1,4-bis(trimethylsilyl)but-2-yne
(Scheme 8). Although 22 was not isolated as crystals, its
structure was characterized by NMR spectroscopy (1H, 13C,
DEPT, COSY, HMQC and HMBC). Methine protons were
observed at δ = 1.85 and 3.95 ppm as doublets, with long-
range coupling (5.7 Hz) between them. Quaternary carbons
assignable to the “alkyne” moiety appeared at 103.4 and
99.6 ppm. These chemical shifts are similar to those of com-
pounds 12 and 16 (Table 1). Hydrolysis of 22 afforded 23.
Reaction of 21 with a butatriene bearing tert-butyl
groups, (Z)-2,2,7,7-tetramethylocta-3,4,5-triene, afforded 24
in 43% yield. This is the first example of a seven-membered
zirconacycloalkyne that consists of a [3]cumulene other
Scheme 8. Seven-membered alkyne from the benzyne complex.
than 3. Starting from Cp2TiPh2,[27] titanium analogue 25 workers support this hypothesis.[29] The propargyl moiety
1
was formed in 68% yield as determined by H NMR (Fig- of 12 and 16 resembles that of 26. However, Zr–C1 in 12
ure 3). These compounds have not been isolated as crystals, [2.580(2) Å] and 16 [2.538(3) Å] are shorter than Zr–C1 in
although 1H, 13C and two-dimensional NMR spectroscopic 26, and Zr–C3 in 12 and 16 [2.425(2) and 2.436(2) Å,
data support their proposed structures (vide infra).
respectively] are longer than Zr–C3 in 26. In addition, the
The synthesis and structure of Cp2Zr(Me)(CH2CϵCPh) C1–C2 distances in 12 and 16 [1.383(3) and 1.389(3) Å] are
(26) was reported by Wojcicki and co-workers (Figure 4).[28] significantly longer than that of 26 [1.344(5) Å]. Addition-
They proposed a structural contribution from allenyl struc- ally, the C2–C3 distances [1.239(3) and 1.231(3) Å for 12
ture 26Ј that takes into account the long Zr–CH2(C1) bond and 16] are shorter than is the case for 26 [1.259(4) Å].
[2.658(4) Å] and a short Zr–CPh(C3) distance [2.361(3) Å]. However, the contribution from B cannot be considered
Theoretical studies reported by Jemmis, Rosenthal and co- negligible (Figure 4). Thus, we have concluded that both
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1
Table 1. Chemical shifts of metallacycloalkynes in H and 13C NMR spectroscopy.
M
1H NMR/ppm
13C NMR/ppm
1
5JHH [Hz]
4
1
2
3
4
5
6
12
Zr
Zr
Zr
Zr
Ti
Ti
2.17
2.03
1.85
3.34
3.52
3.43
5.2
5.2
5.7
4.0
5.7
5.7
3.68
4.10
3.95
4.37
3.79
3.87
38.8
34.6
32.7
62.6
73.2
74.3
110.1
104.3
103.4
112.9
171.7
159.4
101.4
98.8
99.6
106.6
124.0
124.1
52.1
43.4
40.9
71.6
43.3
43.8
162.4
154.3
163.1
160.2
148.8
150.6
172.5
175.6
175.3
177.0
191.6
190.8
16
22
24
25 (major)[a]
25 (minor)[a]
[a] Two sets of signals were observed and are attributable to cis- and trans-isomers, although the stereochemistry was not determined.
Figure 3. Seven-membered alkynes from benzyne complexes.
structures A and B contribute to this complex, although the
former structure must be more important. In the 1,3-diyne-
dimerized metallacyclic complexes, the zirconium com-
plexes have seven-membered zirconacyclocumulene scaffold
5 whereas the titanium analogues are characterized by 2-
Figure 4. Possible resonance structures.
alkynyl-1-titanacyclopenta-2,4-diene
structure
6Ti
1
(Scheme 2). In the present study, H and 13C NMR spectra
for the zirconium complexes and the titanium complex 25
(Table 1) are compared. Titanium complex 25 was formed
as a 53:47 mixture of stereoisomers. NMR spectroscopy re-
vealed two sets of signals for each isomer. Although we have
not determined the stereochemistry of each isomer, signals
could be assigned to one of the isomers on the basis of two-
dimensional NMR spectra. It is noteworthy that chemical
shifts of the quaternary carbons of alkynes (2 and 3 in
Table 1) appeared significantly downfield in the titanium
structural contribution from the 5-vinylidene-1-zirconacy-
clopent-2-ene structure cannot be ruled out. Unstable al-
kynes such as benzyne were also compatible to these cou-
pling conditions. Studies of the corresponding titanium
compounds revealed a greater contribution to reaction
products by the 5-vinylidene-1-titanacyclopent-2-ene struc-
ture.
complexes relative to those in the zirconium compounds. Experimental Section
The methine protons at the α-position (1) also appeared
General: Manipulations involving organometallic species were car-
downfield in 25, as well as C-1. These observations imply
that the titanium complex is best described as 5-allenyl-1-
titanacyclopent-2-ene (25Ј).
ried out under an inert atmosphere using standard Schlenk tech-
niques or in a glove-box. Tetrahydrofuran was purchased from
Kanto Chemical Co., Inc. (dehydrated grade) and purified using a
Glass-Contour Solvent SystemsTM (SG Water USA) prior to use.
Anhydrous hexane was purchased from Kanto Chemical Co., Inc.
and degassed prior to use. Dichlorobis(η5-cyclopentadienyl)zirco-
nium and 1-(trimethylsilyl)prop-1-yne were purchased from Sigma–
Aldrich Co. Ltd. and used as received. Diphenylacetylene, ethyl-
magnesium bromide (0.89 m THF solution), phenyllithium (1.15 m
cyclohexane/diethyl ether solution) and n-butyllithium (1.6 m hex-
Conclusions
In summary, we have prepared seven-membered zircon-
acycloalkyne compounds by coupling of alkynes and [3]cu-
mulene on the metal; their molecular structures and spec-
troscopic data indicate a cycloalkyne structure, although a ane solution) were purchased from Kanto Chemical Co., Inc. (Z)-
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1,4-Bis(trimethylsilyl)buta-1,2,3-triene 3 and (Z)-2,2,7,7-tetrameth- (99 MHz, C6D6): δ = 2.00, 18.42 (JPC = 15.7 Hz, PMe3), 23.46 (JPC
ylocta-3,4,5-triene were prepared according to the literature.[30] 1,4-
Bis(2,2,5,5-tetramethylcyclopentylidene)buta-1,2,3-triene 17 was
prepared by the reported method.[12] Infrared spectra were re-
corded with TravelIR total reflection infrared equipment (SensIR
= 2.5 Hz, CMe), 102.53 (Cp), 166.96 (q, JPC = 7.4 Hz), 174.56 (q,
JPC = 21.4 Hz) ppm. 31P NMR (in C6D6): δ = 2.0 ppm.
1
Spectroscopic Data of 12: H NMR (400 MHz, C6D6): δ = 0.17 (s,
4
3 H), 0.27 (s, 3 H), 0.51 (s, 3 H), 1.95 (d, J = 0.7 Hz, 3 H), 2.17
1
Technologies) and Shimadzu FTIR-8300. H and 13C NMR spec-
4
(d, 5J = 5.2 Hz, 1 H), 3.68 (dd, 5J = 5.2, J = 0.7 Hz, 1 H), 5.52 (s,
tra were recorded with JEOL EX-270, AL-300, ECX 300, AL400,
Lambda 500 and ECA 500 spectrometers. 1H NMR yields were
determined by using either pyrene or toluene as an internal stan-
dard for calibration.
5 H), 5.64 (s, 5 H) ppm. 13C NMR (99 MHz, C6D6): δ = –1.02,
1.39, 5.61 (Me3Siϫ3), 26.23, 38.84, 52.12, 101.36 (q), 105.60,
107.29 (Cpϫ2), 110.05 (q), 162.41 (q), 172.50 (q) ppm. IR (neat,
ATR): ν = 752.5, 787.2, 829.7, 1017, 1243, 1260, 1302, 1441, 1509,
˜
2028, 2800, 2896, 2952 cm–1. C26H42Si3Zr (530.09): calcd. C 58.91,
H 7.99; found C 58.75, H 7.98.
Preparation of 8: To a solution of dichlorobis(η5-cyclopentadienyl)-
zirconium(IV) (292 mg, 1.0 mmol) in THF (5 mL) was added ethyl-
magnesium bromide (0.89 m THF solution, 2.0 mmol) dropwise at
–78 °C. Then 3 (196 mg, 1.0 mmol) was added and the mixture was
warmed to room temp., and stirred for 18 h. The formation of 8 in
29% yield was observed by 1H NMR at this stage, accompanied
by the zirconacyclopentyne compound 1 in 46%. The volatiles were
removed in vacuo and the residue was dissolved in C6D6 for pur-
1
Byproduct 13: H NMR (300 MHz, C6D6, Me4Si): δ = –0.99 (s, 1
H, C1H), –0.24 (d, 4J = 1.4 Hz, C6H), 0.307 [s, 9 H, Si-
(CH3)3], 0.314 [s, 9 H, Si(CH3)3], 0.40 [s, 9 H, Si(CH3)3], 2.58 (m,
2
1 H, C4H), 4.31 (br., 1 H, C7H), 4.71 (d, J = 1.4 Hz, 1 H, C7H),
5.17 (s, 5 H, Cp), 5.43 (s, 5 H, Cp) ppm. 13C NMR (75 MHz,
C6D6): δ = –0.56 ppm (SiMe3), 2.98 (SiMe3), 3.36 (SiMe3), 44.13
(C4), 53.53 (C6), 55.33 (C1), 95.29 (C7), 104.09 (Cp), 105.54 (Cp),
1
poses of NMR spectroscopy. H NMR (270 MHz, C6D6): δ = 0.25
(s, 9 H), 0.26 (s, 9 H), 1.50 (d, J = 7 Hz, 1 H), 1.68–1.80 (m, 2 H),
2.00–2.10 (m, 1 H), 2.22–2.32 (m, 1 H), 2.88–2.96 (m, 1 H), 5.34
(s, 5 H), 5.38 (s, 5 H) ppm. 13C NMR (67.8 MHz, C6D6): δ = –2.31
(SiMe3), 1.63 (SiMe3), 26.38, 29.60, 37.07, 45.10, 96.36, 104.05,
105.38, 106.66 ppm.
126.18 (C3), 142.09 (C2/5), 149.81 (C2/5) ppm. IR (KBr): ν = 756,
˜
949, 1049, 1350, 1462, 1639, 2893, 3090 cm–1.
Hydrolysis of 8: 1,4-Bis(trimethylsilyl)hex-2-yne (10): A reaction
mixture described above containing 3 and 8 was treated with 1 n
HCl at room temp., and the mixture was extracted with diethyl
ether. The organic layer was dried with magnesium sulfate, the
solution then filtered and the volatiles were removed in vacuo. Col-
umn chromatography on silica gel deactivated with 10 v/v% water
using hexane as eluent gave 10 as a yellow liquid in 26% yield
based on total number of Zr atoms. As previously reported, 1,4-
bis(trimethylsilyl)but-2-yne (9) was formed from 1 in 41% yield
based on Zr (GC). Deuterolysis was similarly carried out with 20%
DCl in D2O. The ratio of D incorporation was determined by 13C
NMR using the pulse sequence that suppresses the nuclear Over-
Hydrolysis of 12: (E)-1,3,6-Tris(trimethylsilyl)-2-methylhex-1-en-4-
yne (14): Isolated compound 12 (304 mg, 0.524 mmol) was dis-
solved in THF (2 mL), and H2O (1 mL) was added at room temp.
After it was stirred for 3 min, the mixture was extracted with di-
ethyl ether (10 mLϫ3). The organic layers were combined and
dried with magnesium sulfate. The solution was filtered, and the
solvent was removed in vacuo. The yellow oily residue was dis-
solved in hexane, and purification by column chromatography
using silica gel (deactivated with 10 v/v% of water) and hexane as
an eluent gave 105.8 mg of pure 14 as a colorless liquid in 65%
yield based on 12. Hydrolysis with aqueous HCl resulted in higher
yield (97% by GC), although it caused desilylation of the product
during the purification. 1H NMR (400 MHz, C6D6, Me4Si): δ =
0.08 (s, 3 H), 0.15 (s, 3 H), 0.19 (s, 3 H), 1.42 (s, 1 H), 1.45 (m, 1
H), 1.46 (m, 1 H), 1.83 (s, 3 H), 5.90 (s, 1 H) ppm. 13C NMR
(99 MHz, C6D6): δ = –2.34, –1.90, 0.36 (SiMe3 ϫ3), 7.56, 22.49,
36.37, 78.53, 80.78 (q), 121.89, 153.01 (q) ppm. HRMS: calcd. for
C16H34Si3, 310.1968, found 310.1964.
1
hauser enhancement. H NMR (270 MHz, CDCl3): δ = 0.03 (s, 9
H), 0.07 (s, 9 H), 1.04 (t, J = 7 Hz, 3 H), 1.44 (s, 2 H), 1.46 (m, 1 H),
1.25–1.33 (m, 1 H), 1.42–1.50 (m, 1 H) ppm. 13C NMR (67.8 MHz,
CDCl3): δ = –3.01 (JCSi = 52 Hz), –2.02 (JCSi = 52 Hz), 7.27 (JCSi
47 Hz), 14.44, 22.19 (JCSi = 49 Hz), 23.10, 77.59, 79.99 ppm. High-
resolution mass spectrometry (HRMS): calcd. for
C12H26Si2226.1573, found 226.1568.
=
Preparation of 12 and 13: To a solution of dichlorobis(η5-cyclopen-
tadienyl)zirconium(IV) (589 mg, 2.0 mmol) in THF (10 mL) was
added n-butyllithium (1.67 m in hexane, 4.2 mmol) dropwise at
–78 °C. Then 1-(trimethylsilyl)prop-1-yne (224 mg, 2.0 mmol) and
trimethylphosphane (183 mg, 2.4 mmol) was added, and the mix-
ture was warmed to room temp. The solution was stirred at 50 °C
for 1 h. Quantitative formation of Cp2Zr(Me3SiCϵCMe)(PMe3)
(11) was observed by 1H NMR spectroscopy. To this mixture, 3
(410 mg, 2.1 mmol) was added and stirring continued at 80 °C for
1 h. During this stage, the formation of 12 in 74% accompanied by
about 11% of the zirconacyclopentyne 1 was observed by 1H NMR
spectroscopy. Volatiles were then removed in vacuo and the residue
was dissolved in hexane and filtered. The filtrate was concentrated
and cooling to –20 °C afforded yellow crystals of 12 accompanied
by orange crystals of 13 (46%). The crystals of 13 were picked up
from the crop (6%).
Preparation of 16: Dichlorobis(η5-cyclopentadienyl)zirconium
(588 mg, 2.01 mmol) was dissolved in tetrahydrofuran (10 mL) and
cooled to –78 °C. To this solution, n-butyllithium (1.57 m in hexane,
2.7 mL, 4.2 mmol) was added dropwise, and the mixture was stirred
at –78 °C for 1 h. Trimethylphosphane (0.25 mL, 2.4 mmol) and
diphenylacetylene (368 mg, 2.0 mmol) in THF (2 mL) were then
added and the mixture allowed to warm to room temp. The reac-
tion was then stirred at 50 °C for 1 h. The quantitative formation
of 15 was observed by 1H NMR spectroscopy.[24a,24b] Then (Z)-
1,4-bis(trimethylsilyl)buta-1,2,3-triene 3 (410 mg, 2.09 mmol) was
added, and the solution was stirred at 80 °C for 1 h. 1H NMR
Spectroscopic Data of Cp2Zr(PMe3)(Me3SiCϵCMe) (11): 1H spectroscopy showed the formation of title compound 16 in 88%
NMR (400 MHz, C6D6): δ = 0.20 (s, 9 H), 1.36 (d, JPH = 5.7 Hz,
at this stage. The zirconacyclopent-3-yne complex 1 was not formed
(Ͻ 1%) judging from the H spectroscopy. Volatiles were removed
9 H), 2.37 (s, 3 H), 5.24 (d, JPH = 1.7 Hz, 10 H) ppm. 13C NMR
1
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in vacuo and the remaining residue was dissolved in hexane and
filtered. The filtrate was concentrated, and kept at –30 °C to give
yellow crystals of the title compound (644 mg, 54%). 1H NMR
(300 MHz, C6D6, Me4Si): δ = –0.05 ppm (s, 9 H), 0.29 (s, 9 H),
title compound was observed by 1H NMR spectroscopy (43%, a
70:30 mixture of stereoisomers). The spectroscopic data for the
major isomer is shown. 1H NMR (500 MHz, C6D6, Me4Si): δ =
1.09 (s, 9 H), 1.17 (s, 9 H), 3.34 (d, J = 4.0 Hz, 1 H), 4.37 (d, J
= 4.0 Hz, 1 H), 5.15 (s, 5 H), 5.66 (s, 5 H), 7.12–7.70 (m, 4 H) ppm.
5
5
5
5
2.03 (d, J = 5.2 Hz, 1 H), 4.10 (d, J = 5.2 Hz, 1 H), 5.22 (s, 5 H),
5.72 (s, 5 H), 6.82–7.23 (m, 10 H) ppm. 13C NMR (75 MHz, C6D6, 13C NMR (125 MHz, C6D6, Me4Si): δ = 29.83, 32.74, 34.56, 36.53,
Me4Si): δ = –3.32, –0.01, 34.64, 43.43, 98.75 (q, CϵC) 104.34 (q, 62.55 (CH), 71.55 (CH), 106.63 (q, CϵC) 112.94 (q, CϵC), 106.11
CϵC), 104.54 (Cp), 106.47 (Cp), 120.98, 123.72, 125.77, 125.94,
126.27, 126.60, 141.61 (q), 153.69 (q), 154.33 (q), 175.63 (q) ppm.
(Cp), 107.32 (Cp), 122.86, 124.27, 126.06, 143.24, 160.17 (q),
176.97 (q) ppm.
IR (KBr): ν = 698, 768, 845, 1049, 1246, 1300, 1439, 1477, 1593,
˜
Hydrolysis Product of 24: A solution of product 24 was treated with
1 n HCl at room temp., and extracted by diethyl ether. Formation
of the title compound was confirmed by gas chromatography (36%
based on number of Zr atoms). The organic layers were combined
and dried with MgSO4, and the solvents evaporated. Column
chromatography (hexane) on silica gel gave the title compound as
a colorless oil (54 mg, 11% isol.). 1H NMR (500 MHz, CDCl3,
Me4Si): δ = 0.97 (s, 9 H), 1.02 (s, 9 H), 2.11 (d, J = 2.4 Hz, 2
H), 3.40 (t, J = 2.4 Hz, 1 H), 7.16–7.35 (m, 5 H) ppm. 13C NMR
(125 MHz, CDCl3, Me4Si): δ = 27.70, 29.14, 31.36 (q), 34.04 (CH2),
35.12 (q), 49.93 (CH), 81.68 (q) 82.65 (q), 126.43, 127.42, 129.66,
2025, 2789, 2955, 3074 cm–1. C34H40Si2Zr (596.08): calcd. C 68.51,
H 6.76; found C 68.25, H 6.83.
Reaction of [5]Cumulene with 15, Formation of 18: To a solution of
15 (1.0 mmol) in THF (5 mL) was added [5]cumulene 17 (282 mg,
1
1.0 mmol) and the mixture sealed and stirred for 17 h at 90 °C. H
NMR indicated formation of 18 in 43% yield as the only major
product. Complex 18 was prepared by an alternative method[4b]
and the spectroscopic data were compared. The molecular struc-
ture was determined by X-ray analysis. 1H NMR (500 MHz, C6D6,
Me4Si): δ = 1.44 (s, 12 H), 1.55 (s, 12 H), 1.72–1.79 (m, 8 H), 5.37
(s, 10 H) ppm. 13C NMR (125 MHz, C6D6, Me4Si): δ = 29.39, 29.68
[C(CH3)3 ϫ2], 38.61, 40.43 (CH2 ϫ2), 46.69, 48.06 (qϫ2), 99.55
(CϵC), 105.14 (Cp), 152.78 (q), 167.81 (q) ppm. IR (neat, ATR):
140.17 (q) ppm. IR (NaCl): ν = 640, 702, 729, 783, 891, 1030, 1076,
˜
1219, 1366, 1393, 1454, 1600, 1732, 1805, 1944, 2866, 3028 cm–1.
HRMS: calcd. for C18H26 242.2035, found 242.2039.
ν = 787, 1014, 1021, 1258, 1356, 1458, 1625, 1957 (w), 2858,
˜
Preparation of the Titanium Complex with Benzyne 25: To a
solution of dichlorobis(η5-cyclopentadienyl)titanium (125 mg,
0.5 mmol) in toluene (5 mL) was added dropwise phenyllithium
(1.15 m in diethyl ether, 0.93 mL, 1.07 mmol) at –78 °C. The mix-
ture was stirred for 1 h, and then warmed up to room temp. (Z)-
1,4-Bis(trimethylsilyl)buta-1,2,3-triene (3) (118 mg, 0.6 mmol) was
added and the mixture was stirred at 90 °C for 3 h. Two sets of
signals were observed in NMR spectra in a 53:47 ratio (68% by 1H
NMR). These can be attributed to the cis- and trans-isomers, al-
though the stereochemistry could not be determined.
2952 cm–1. C32H42Zr (517.90): calcd. C 74.21, H 8.17; found C
74.49, H 8.38.
Preparation of Benzyne Complex 22: To a solution of dichlo-
robis(η5-cyclopentadienyl)zirconium (587 mg, 2.01 mmol) in THF
(10 mL) was added dropwise phenyllithium (1.15 m in cyclohexane/
diethyl ether, 3.70 mL, 4.25 mmol) at –78 °C. The mixture was
stirred for 1 h, and then warmed up to room temp. and stirred for
an additional 1 h. To this mixture (Z)-1,4-bis(trimethylsilyl)buta-
1,2,3-triene 3 (390 mg, 2.0 mmol) was added and the mixture was
stirred at 100 °C for 3 h. The formation of the title compound was
observed by 1H NMR spectroscopy (64%). Ratios of stereoisomers
1
25 (major): H NMR (500 MHz, C6D6, Me4Si): δ = 0.15 (s, 9 H),
0.24 (s, 9 H), 3.52 (d, 5J = 5.7 Hz, 1 H), 3.79 (d, 5J = 5.7 Hz, 1 H),
ranged from 7:3 to 9:1 (the spectroscopic data for the major isomer
5.88 (s, 5 H), 6.01 (s, 5 H), 6.79–6.96 (m, 3 H), 7.2–7.45 (m, 1
1
is shown). H NMR (500 MHz, C6D6, Me4Si): δ = 0.02 (s, 9 H), H) ppm. 13C NMR (125 MHz, C6D6, Me4Si): δ = 0.55, 1.42, 43.34
0.18 (s, 9 H), 1.85 (d, J = 5.7 Hz, 1 H), 3.95 (d, J = 5.7 Hz, 1 H),
(CH), 73.17 (Ti–CH), 115.20 (Cp), 115.53 (Cp), 124.00 (q, CϵC),
123.50, 125.00, 129.50, 135.24, 148.84 (q), 171.73 (q, CϵC), 191.57
5.20 (s, 5 H), 5.50 (s, 5 H), 6.97–7.60 (m, 4 H) ppm. 13C NMR
(125 MHz, C6D6, Me4Si): δ = –2.01, 1.67, 32.72, 40.93, 99.61 (q, (q, Ti-C) ppm.
CϵC) 103.44 (q, CϵC), 106.09 (Cp), 107.51 (Cp), 123.18, 123.34,
123.52, 143.70, 163.07 (q), 175.33 (q) ppm.
1
25 (minor): H NMR (500 MHz, C6D6, Me4Si): δ = 0.19 (s, 9 H),
0.23 (s, 9 H), 3.43 (d, 5J = 5.7 Hz, 1 H), 3.87 (d, 5J = 5.7 Hz, 1 H),
5.71 (s, 5 H), 5.99 (s, 5 H), 6.79–6.96 (m, 3 H), 7.2–7.45 (m, 1
H) ppm. 13C NMR (125 MHz, C6D6, Me4Si): δ = –0.21, 0.66, 43.78
(CH), 74.29 (Ti-CH), 113.71 (Cp), 114.36 (Cp), 124.05 (q, CϵC),
123.589, 125.66, 129.06, 136.55, 150.58 (q), 159.42 (q, CϵC),
190.77 (q, Ti-C) ppm.
Hydrolysis of 22 (23): The solution of product 22 was treated with
1 n HCl at room temp., and extracted by diethyl ether. Quantitative
formation of 23 was confirmed by gas chromatography. The or-
ganic layers were combined and dried with MgSO4, and the sol-
vents evaporated. Column chromatography (hexane) on silica gel
afforded title compound as a yellow oil (150 mg, 27% isol.). 1H
NMR (300 MHz, CDCl3, Me4Si): δ = 0.06 (s, 9 H), 0.17 (s, 9 H),
1.59 (d, J = 2.8 Hz, 1 H), 3.14 (t, J = 2.8 Hz, 1 H), 7.13–7.27 (m,
5 H) ppm. 13C NMR (75 MHz, CDCl3, Me4Si): δ = –3.20, –1.88,
7.35, 29.68, 78.00 (q), 79.68 (q), 123.75, 126.98, 127.92, 140.60
X-ray Crystallographic Analysis of 12: Single crystals were obtained
by recrystallization from a hexane solution. A yellow block crystal
(0.7ϫ0.5ϫ0.3 mm) was mounted in a nylon loop and coated with
liquid paraffin. Data were collected with a Rigaku RAXIS-RAPID
Imaging Plate diffractometer with graphite-monochromated Mo-
Kα radiation at 108 K. The structure was solved by direct meth-
ods[31] and expanded using Fourier techniques.[32] The refinements
were carried out by a least-squares method on F2. Some of the
hydrogen atoms (H1 and H4) were found by difference Fourier syn-
theses, and the others were placed at the calculated positions and
not refined. All calculations were performed using the teXsan soft-
ware package.[33] Crystallographic data are summarized in Table
S1.
(q) ppm. IR (NaCl): ν = 698, 845, 1250, 1493, 1597, 1693, 1728,
˜
2901, 2959 cm–1. HRMS: calcd. for C16H26Si2: 274.1567, found
274.1573.
Preparation of Benzyne Complex 24: To a solution of dichlo-
robis(η5-cyclopentadienyl)zirconium (588 mg, 2.01 mmol) in THF
(10 mL) was added dropwise phenyllithium (1.15 m in cyclohexane/
diethyl ether, 3.70 mL, 4.25 mmol) at –78 °C. The mixture was
stirred for 1 h, and then warmed up to room temp. (Z)-2,2,6,6-
Tetramethylocta-3,4,5-triene (338 mg, 2.06 mmol) was then added
and the mixture was stirred at 100 °C for 4 h. The formation of the
X-ray Crystallographic Analysis of 13: Single crystals were obtained
by recrystallization from a hexane solution. An orange block crys-
Eur. J. Inorg. Chem. 2013, 347–356
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FULL PAPER
tal (0.1ϫ0.1ϫ0.2 mm) was mounted on a nylon loop and coated
with liquid paraffin under nitrogen. Data were collected with a
Rigaku R-AXIS CS Imaging Plate diffractometer with graphite-
monochromated Mo-Kα radiation at 173 K. The structure was
solved by heavy-atom Patterson methods[34] and expanded using
Fourier techniques. The non-hydrogen atoms were refined aniso-
tropically. Some hydrogen atoms were found by the difference Fou-
rier syntheses, and others were placed at the calculated positions
and not refined. The final cycle of full-matrix least-squares refine-
ment on F2 was based on 4861 observed reflections and 331 vari-
able parameters. All calculations were performed using Crystal-
Structure[35] crystallographic software package except for refine-
ment, which was performed using SHELXL-97.[36] Crystallo-
graphic data are summarized in Table S1.
Ms. Y. Shimizu (Sophia Univ.) is acknowledged for providing mass
spectrometry expertise and Dr. D. Hashizume (RIKEN) is greatly
acknowledged for assistance in X-ray diffraction studies. This work
was financially supported by JSPS KAKENHI (grant number
22350022) and by the Asahi Glass foundation.
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[4]
X-ray Diffraction Analyses of 18: Crystals were obtained from a
hexane solution by slow evaporation of solvent. A yellow platelet
crystal (0.60ϫ0.20ϫ0.05 mm) was mounted in a nylon loop and
coated with paraffin. All data were collected with a Rigaku Saturn
CCD area detector with graphite-monochromated Mo-Kα radia-
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expanded using Fourier techniques.[38] Some non-hydrogen atoms
were refined anisotropically and the rest were refined isotropically.
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consisted of two crystallographically independent molecules of 18,
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SHELXL-97.[36] Crystallographic data are summarized in Table S1.
[5]
[6]
CCDC-266423 (for 12), -904355 (for 13), -904357 (for 16) and
-904356 (for 18) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Supporting Information (see footnote on the first page of this arti-
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Acknowledgments
The authors thank Ms. K. Yamada (RIKEN) and Ms. S. Machish-
ima (Sophia Univ.) for assistance in performing elemental analyses.
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Received: October 13, 2012
Published Online: December 19, 2012
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