Coupling reaction of a cyclopentadienyl ligand with a dienyl or alkenyl moiety on titanocene

Article abstract of DOI:10.1021/om101020u

Coupling reactions of a cyclopentadienyl (Cp) ligand with a dienyl or alkenyl ligand on dienyl-or alkenyltitanocenes proceeded to give dienylcyclopentadiene or alkenylcyclopentadiene derivatives in good to high yields. Dienyltitanocene derivatives were prepared by protonation of bis(cyclopentadienyl)titanacyclopentadienes with carboxylic acids. Chlorodienyltitanocene derivatives were formed by the reaction of titanacyclopentadienes with NCS. Alkenyltitanocene derivatives were prepared by the reaction of titanacyclopentene, which were prepared from Cp ₂TiEt₂ and alkynes, with t-BuOH. The structure of the alkenyltitanocene (in the case of 1,2-diphenylethenyl) was determined by X-ray analysis of the single crystal. These dienyl-, chlorodienyl-, or alkenyltitanocenes were treated with azobenzene at 50 °C for 6 h, and the corresponding dienylcyclopentadienes, chlorodienylcyclopentadienes, and alkenylcyclopentadiene derivatives were obtained in good to high yields. This result supports the existence of the stepwise mechanism for the coupling reaction of a Cp ligand with a diene moiety of titanacyclopentadienes, giving indene derivatives in the presence of azobenzene.

Full text of DOI:10.1021/om101020u

844 Organometallics 2011, 30, 844–851
DOI: 10.1021/om101020u
Coupling Reaction of a Cyclopentadienyl Ligand with a Dienyl
or Alkenyl Moiety on Titanocene
Zhiyi Song,† Yi-Fang Hsieh,† Ken-ichiro Kanno,† Kiyohiko Nakajima,‡ and
Tamotsu Takahashi*,†
†Catalysis Research Center and Graduate School of Life Science, Hokkaido University, and
Seed’s Innovation, Japan Science and Technology Corporation (JST ), Kita-ku Sapporo 001-0021,
Japan, and ‡Department of Chemistry, Aichi University of Education, Igaya, Kariya, Aichi,
448-8542, Japan
Received October 28, 2010
Coupling reactions of a cyclopentadienyl (Cp) ligand with a dienyl or alkenyl ligand on dienyl- or
alkenyltitanocenes proceeded to give dienylcyclopentadiene or alkenylcyclopentadiene derivatives in
good to high yields. Dienyltitanocene derivatives were prepared by protonation of bis(cyclo-
pentadienyl)titanacyclopentadienes with carboxylic acids. Chlorodienyltitanocene derivatives were
formed by the reaction of titanacyclopentadienes with NCS. Alkenyltitanocene derivatives were
prepared by the reaction of titanacyclopentene, which were prepared from Cp2TiEt2 and alkynes,
with t-BuOH. The structure of the alkenyltitanocene (in the case of 1,2-diphenylethenyl) was
determined by X-ray analysis of the single crystal. These dienyl-, chlorodienyl-, or alkenyltitanocenes
were treated with azobenzene at 50 °C for 6 h, and the corresponding dienylcyclopentadienes,
chlorodienylcyclopentadienes, and alkenylcyclopentadiene derivatives were obtained in good to high
yields. This result supports the existence of the stepwise mechanism for the coupling reaction of a Cp
ligand with a diene moiety of titanacyclopentadienes, giving indene derivatives in the presence of
azobenzene.
1. Introduction
formation by oxidation of the Rosenthal type of complex.
C-C cleavage of the Cp ligand was detected by 13C-enriched
experments.3b Furthermore, complexes 1 reacted with TiCl4
to afford chlorodihydroindene derivatives without C-C
cleavage on the Cp ligand.3c More recently, we reported that
the once cleaved C-C bond of Cp was recombined in the
indene product when the Rosenthal-type complex was trea-
ted with azobenzene.3d The unusual reaction of the Cp ligand
was also found to occur smoothly in a zirconium analogue
when it bears the indenyl or substituted Cp ligands.3e
Very recently we clearly indicated from the kinetic study
and 13C labeled experiment that the coupling of Cp with the
diene moiety occurred without the ring-opening of the Cp
ligand giving 2 as the first step (Scheme 3).3d In the second
step, the coupling product was gradually converted into the
Cp ring-opening product 3. We also indicated that there was
equilibrium between complexes 2 and 3. For this conversion,
we proposed the metathesis mechanism to explain the Cp
ring-opening reaction on titanium.3d
However, as for the coupling of the Cp ligand and the diene
moiety of the titanacyclopentadiene, there are two possible
pathways (Scheme 4). One is a concerted mechanism, such as
a Diels-Alder-type reaction of a carbon-carbon double bond
of a slipped Cp ligand on titanium(II) with the diene moiety.
The other is a stepwise coupling reaction of the Cp ligand
with the diene moiety on titanium(IV).
Although there are several coupling reactions of a Cp
ligand with a diene moiety2,3 and a theoretical study for
the coupling,4 there is no such study on the coupling
The cyclopentadienyl ligand has been believed to be “inert”
for various reactions for a long time.1 Rosenthal and his co-
workers reported a pioneer work of the coupling reaction of
the Cp ligand with a diene moiety of titanacyclopentadienes
and a rearranged dihydroindene titanium complex as shown
in Scheme 1.2
Recently we found titanacyclopentadienes 1 reacted with
benzonitrile, leading to double C-C cleavage of one Cp
ligand into two units, a 2C unit annualized with a diene moiety
to give benzene derivatives and a 3C unit constructing
pyridine derivatives with the added nitrile (Scheme 2).3a
We also reported a novel alkyl group migrated indene
*To whom correspondence should be addressed. E-mail: tamotsu@
cat.hokudai.ac.jp.
(1) Recent review article on metallocenes; see: Takahashi, T.; Kanno,
K. Metallocene in Regio- and Stereoselective Synthesis. In Topics in
Organometallic Chemistry; Takahashi, T., Ed.; Springer: Berlin, 2005; Vol.
8, p 217. For reactions of Cp ligand except titanacyclopentadienes, see:
(c) Giolando, D. M.; Rauchfuss, T. B. J. Am. Chem. Soc. 1984, 106, 6455.
(d) Crowe, W. E.; Vu, A. T. J. Am. Chem. Soc. 1996, 118, 5508. (e)
Dzwinniel, T. L.; Stryker, J. M. J. Am. Chem. Soc. 2004, 126, 9184.
(2) (a) Tillack, A.; Baumann, W.; Lefeber, O. C.; Spannenberg, A.;
Kempe, R.; Rosenthal, U. J. Organomet. Chem. 1996, 520, 187. Several
related reports from Prof. Rosenthal's group; see: (b) Rosenthal, U.; Burlakov,
V. V.; Arndt, P.; Baumann, W.; Spannenberg, A. Organometallics 2003, 22,
884. (c) Rosenthal, U.; Lefeber, C.; Arndt, P.; Tillack, A.; Baumann, W.;
Kempe, R.; Burlakov, V. V. J. Organomet. Chem. 1995, 503, 221. (d)
Thomas, D.; Peulecke, N.; Burlakov, V. V.; Heller, B.; Baumann, W.;
Spannenberg, A.; Kempe, R.; Rosenthal, U.; Beckhaus, R. Z. Anorg. Allg.
Chem. 1998, 624, 919.
r
pubs.acs.org/Organometallics
Published on Web 02/03/2011
2011 American Chemical Society

Article
Organometallics, Vol. 30, No. 4, 2011 845
Scheme 1. Rosenthal’s Pioneer Work for the Formation of Dihydroindenyl Titanium Complexes from Titanacyclopentadienes
Scheme 2. Various Products from Titanacyclopentadienes 1 and a Zirconium Analogue
Scheme 3. Coupling of the Cp Ligand with the Diene Moiety and Rearrangement of the Dihydroindenyl Moiety
Scheme 4. Concerted Mechanism and Stepwise Mechanism for
the Coupling of Cp with the Diene Moiety of Titanacyclopenta-
dienes
coupling reaction of the Cp ligand on titanium, as shown
in Scheme 5.
2. Results
2.1. Coupling Reaction of a Cp Ligand with a Dienyl
Ligand on Titanocene. Dienyltitanocene complexes 4 were
prepared by protonation of titanacyclopentadiene 1 with
carboxylic acids.5 For example, preparation and quenching
of dienyltitanocene 4b4 are shown in Scheme 6. In THF,
bis(cyclopentadienyl)titanacyclopentadiene 1b was treated
with 1 equiv of dichloroacetic acid to afford 4b4 in 93% yield.
NMR study of the dienyltitanocene 4b4 revealed an alkenyl
proton at 4.73 ppm as a triplet in the 1H NMR spectrum and
four alkenyl carbons at 129.4 (CH), 144.1 (C), 147.1 (C), and
192.8 (C-Ti) ppm in the 13C NMR spectrum. The chemical
shift of 192.8 ppm is very characteristic and is easily assigned
to the carbon attached to the titanium metal center. Deuterolysis
reaction of the Cp ligand with an alkenyl or dienyl moiety
group on titanocene as shown in eq 1, to the best of our
knowledge.
(3) Our related reports on this topic; see: (a) Xi, Z.; Sato, K.; Gao, Y.;
Lu, J.; Takahashi, T. J. Am. Chem. Soc. 2003, 125, 9568. (b) Takahashi, T.;
Kuzuba, Y.; Kong, F.; Nakajima, K.; Xi, Z. J. Am. Chem. Soc. 2005, 127,
17188. (c) Takahashi, T.; Song, Z.; Sato, K.; Kuzuba, Y.; Nakajima, K.;
Kanno, K. J. Am. Chem. Soc. 2007, 129, 11678. (d) Takahashi, T.; Song, Z.;
Hsieh, Y.-F.; Nakajima, K.; Kanno, K. J. Am. Chem. Soc. 2008, 130, 15236.
(e) Ren, S.; Igarashi, E.; Nakajima, K.; Kanno, K.; Takahashi, T. J. Am.
Chem. Soc. 2009, 131, 7492.
(4) Suresh, C. H.; Koga, N. Organometallics 2006, 25, 1924.
(5) Titanacyclopentadienes 1 and titanacyclopentenes 10 were pre-
pared according to the following literature. See: Sato, K.; Nishihara, Y.;
Huo, S.; Xi, Z.; Takahashi, T. J. Organomet. Chem. 2001, 633, 18.
This situation prompted us to investigate the coupl-
ing reaction of the Cp ligand with dienyl or alkenyl
groups on titanocene complexes. We found such cou-
pling reactions occurred smoothly and were facilitated
by azobenzene. In this paper we would like to report the

846 Organometallics, Vol. 30, No. 4, 2011
Song et al.
Scheme 5
Scheme 6. Generation and Quenching of Dienyltitanocene 4b4
and iodination of 4b4 gave the corresponding deuterated and
iodinated dienes in 75% yield with >95% deuterium incor-
poration and 85% NMR yield, respectively. These results
unambiguously showed the formation of dienyltitanocene 4b
in high yield.
When in situ prepared dienyltitanocene 4b4 was heated at
50 °C for 6 h in THF, the corresponding coupling product,
dienylcyclopentadiene 5b, was obtained as a mixture of the
double-bond positional isomers in 38% combined yield after
protonolysis.
In the coupling reaction of Cp with diene moiety giving
indene derivatives from titanacyclopentadienes, the driving
force was the sterical hindrance. Zr analogues did not show
such coupling reactions. But when the t-Bu group was
introduced to the Cp ligand of zirconacyclopentadienes,
even in the case of Zr, the coupling reaction proceeded.
Therefore, the driving force of the coupling reaction of Cp
with alkenyl or dienyl on Ti is the sterical hindrance around
the Ti center.
2.2. Coupling of a Cp Ligand with a Chlorodienyl Moiety
on Titanium. In a further investigation, N-chlorosuccinimide
(NCS) was employed to cleave one of the two Ti-C bonds of
a titanacyclopentadiene instead of hydrolysis (Scheme 7).7
Chlorodienyltitanocenes 6 were prepared by treatment of
titanacyclopentadienes 1 with 1.2 equiv of NCS. The formation
of complex 6b was checked by protonolysis, deuterolysis,
and iodonation. Protonolysis with concentrated HCl af-
forded chlorobutadiene in 92% NMR yield. Deuterolysis
and iodonation gave the corresponding deuterated products
in 85% yield (85% D) and chloroiodobutadiene in 90% yield.
Then the formed complex 6b was heated at 50 °C for 6 h.
After workup, the coupling product 7b was obtained as a
mixture of two double-bond positional isomers in 35% com-
bined yield. When azobenzene was added to the reaction, the
yield dramatically increased to 80% (Table 2, entry 2).
The coupling reaction was applied to various substrates,
and the results are summarized in Table 2. The reactions of
6a and 6c with azobenzene afforded the corresponding
products 7a and 7c in 85% and 91% yields, respectively
(entries 1 and 8). The cyclic 6d gave the coupling product 7d
in 75% yield (entry 9).
As we reported in the communication,3d the coupling
reaction of a Cp ligand and the diene moiety of titanacyclo-
pentadienes giving indene derivatives was facilitated by addi-
tion of azobenzene. Surprisingly, the same positive effect of
azobenzene was observed in this case. The yield of 5b was
remarkably improved to 92% when 4b4 was heated in the
presence of azobenzene (Table 1, entry 5).
Various carboxylic acids were employed for the reaction
with 1b to afford 4b1-9, as shown in Table 1. Complexes
4b1-9 were treated with azobenzene to give coupling product
5b in yields of 45-95% (entries 3-10).
Under the optimized conditions, complexes 1a-d were
treated first with dichloroacetic acid at -15 °C. The mixture
was gradually warmed to room temperature and stirred over-
night to afford 4a-d. After addition of 2 equiv of azobenzene,
the reaction mixture was stirred at 50 °C for 6 h. Hydrolysis
of the reaction mixture gave 5a-d in excellent yields from
92% to 98% (entries 1, 5, 12, and 13). When picolinic acid-d1
was employed to generate 4b9-D, 5b-D was obtained in 83%
yield with 86% deuterium incorporation (entry 11).6
(6) Gilbert, A. M.; Failli, A.; Shumsky, J.; Yang, Y.; Severin, A.;
Singh, G.; Hu, W.; Keeney, D.; Petersen, P. J.; Katz, A. L. J. Med. Chem.
2006, 49, 6027.
(7) Kanno, K.; Igarashi, E.; Zhou, L.; Nakajima, K.; Takahashi, T.
J. Am. Chem. Soc. 2008, 130, 5624.

Article
Organometallics, Vol. 30, No. 4, 2011 847
Table 1. Formation of Dienylcyclopentadienes 5
a Dienyltitanium 4 were prepared in situ by the reaction of carboxylic acid with 1. b A mixture of double-bond regioisomers. c Combined NMR yields
of two isomers. Isolated yields are in parentheses.
Scheme 7. Synthesis of Bis(cyclopentadienyl)chlorodienyltitanocene Derivatives
As for a facilitation effect, various reagents were examined
instead of azobenzene, and it was found that allyl chloride
and propargyl bromide also showed a similar effect. The
results are shown in Table 2. When 6b was treated with allyl
chloride and propargyl bromide, 7b was obtained in high
yields (entries 3 and 4). Pyrazine and triphenylphosphine

848 Organometallics, Vol. 30, No. 4, 2011
Table 2. Coupling Reaction of a Cyclopentadienyl Ligand with a Chlorodienyl Ligand on Titanocene
Song et al.
a Compounds 6 were prepared in situ by the reaction of 1 with NCS. b A mixture of two double-bond regioisomers. c Combined NMR yields of
isomers. Isolated yields are in parentheses. Entries 3 and 4 are GC yields.
Scheme 8. Formation of Alkenyltitanocene from Titanacyclo-
pentene 10 by the Reaction with t-BuOH
also showed small effects (entries 5 and 6), compared with the
control experiment without additives (entry 7). Since the
coupling reaction can be regarded as reductive elimination,
reagents that can oxidize the Ti(II) metal center have positive
effects. Allyl chloride or propargyl bromide plays a role in
the oxidation of the Ti metal center by oxidative addition. On
the other hand, azobenzene, pyrazine, or triphenylphosphine
coordinates to the Ti(II) metal center to push two ligands
together on titanium toward the coupling reaction and
stabilize the resulting titanium complex. However to our
disappointment, the identification of the remaining “CpTi”
species after the reductive elimination has not been successful
at this moment, since several peaks appear in the Cp area in
the proton NMR spectrum.
2.3. Preparation of Alkenyltitanocenes and Coupling of the
Cp Ligand with the Alkenyl Moiety on Titanium. The results
obtained above prompted us to investigate the coupling of
the Cp ligand with a simpler alkenyl ligand than the dienyl
ligand as an sp2 carbon. We tried to prepare alkenyltitano-
cenes by protonation of titanacyclopentenes 10, which we
previously prepared.5 It is interesting to note that when a
titanacyclopentene, which was conveniently prepared from
Cp2TiEt2 andanalkyne,wastreatedwitht-BuOH,theexpected
1,2-disubstituted butenyltitanocene was not formed. Instead,
disubstituted ethenyltitanocene 8 was obtained (Scheme 8).
The structure of one of the complexes (R = Ph, 8e) was
determined by X-ray analysis, as shown in Figure 1. This
suggests that titanacyclopentene 8 is in equilibrium with the
titanocene(alkyne)(ethylene) complex.8 Ethylene was eliminated
by addition of t-BuOH, and protonolysis of alkyne on titanium
proceeded to afford the alkenyltitanocene derivative 8.
The prepared alkenyltitanocene 8 was treated with azo-
benzene. As expected, alkenylcyclopentadienes 9 were ob-
tained as a mixture of two isomers when R was an alkyl
group (Scheme 9).
(8) Takahashi, T.; Hasegawa, M.; Suzuki, N.; Saburi, M.; Rousset,
C. J.; Fanwick, P. E.; Negishi, E. J. Am. Chem. Soc. 1991, 113, 8564.

Article
Table 3 shows the result of the Cp coupling reaction with
an alkenyl ligand on titanium. The complex 10a, which was
prepared by our reported method,5 was treated with t-BuOH
at room temperature for 24 h to afford complex 8a. Azobenzene
Organometallics, Vol. 30, No. 4, 2011 849
was added, and the reaction mixture was stirred at 50 °C for
an additional 6 h. After workup, alkenyl-Cp derivative 9a
was obtained as two isomers in 71% combined yield. Ethy-
lene was released in this reaction. Without azobenzene, only
10% of product 9a was formed.
Instead of t-BuOH, n-BuOH, sec-BuOH, and EtOH were
used (Table 3, entries 2-4), and the same coupling product
was obtained in those cases in comparable yields.
It is interesting to note that complex 8e (R=Ph) did not
give the corresponding coupling product. This reaction requires
electron-donating substituents. Complexes 10b,c,d with other
alkyl substituents reacted with alcohol and azobenzene in this
order to give the corresponding products 9b,c,d in yields of
76%, 64%, and 65%, respectively (entries 5-7).
When n-BuOD was employed to react with 10a at room
temperature, and then azobenzene was added, deuterated
product 9a-D was obtained in 55% yield with 98% deuter-
ium incorporation (Scheme 10).
3. Conclusion
We observed the coupling reaction of a dienyl or alkenyl
ligand with a Cp ligand on titanium metal. In the formation
of dihydroindenyl titanium complexes 2 from titanacyclo-
pentadienes 1, this result indicates that a stepwise mechanism
Figure 1. Perspective View of Diphenylethenyltitanocene 8e.
Scheme 9. Coupling of the Cp Ligand with an Alkenyl Moiety on
Titanocene
Scheme 10. Formation of Deuterated Alkenyltitanocene and Its
Coupling Reaction
Table 3. Coupling of the Cp Ligand with an Alkenyl Ligand of Alkenyltitanocene
a Complexes 8 were prepared in situ by the reaction of 10 with alcohol. b A mixture of two double-bond regioisomers. c Combined NMR yields of
isomers. Isolated yields are in parentheses. d The product 9d polymerized in net.

850 Organometallics, Vol. 30, No. 4, 2011
Song et al.
that involves coupling of a dienyl moiety on titanium is
possible.
2.4 mmol of azobenzene, the mixture was heated to 50 °C and
stirred for 6 h. The resulting solution was cooled to room
temperature, and aqueous NaHCO3 (2 mL) was added to
quench the reaction. The mixture was extracted with hexane,
and the organic phase was dried over MgSO4. After removal of
volatiles in vacuo, the residue was analyzed by 1H NMR
spectroscopy in benzene-d6 with dichloromethane or dioxane
as an internal standard. Then the residue was subjected to
column chromatography on silica gel (hexane containing 3%
of Et3N as eluent) to afford cyclopentadienyl derivatives 5.
(2Z,4E)-2-(Cyclopentadienyl)-3,4-dimethylhexa-2,4-diene
(5a). Product 5a was obtained as a mixture of double-bond
positional isomers of the cyclopenadienyl moiety. Combined
NMR yield of 98%. Isolated yield of 86%. Colorless oil.
The ratio of two isomers major:minor = 2.2:1. 1H NMR
(C6D6, Me4Si): 1.44 (qq, J=6.8 Hz, 1.5 Hz, major - 3 H), 1.48
(qq, J=6.8 Hz, 2.2 Hz, minor - 3 H), 1.61-1.64 (m, major - 3 H),
1.66-1.70 (m, minor - 3 H), 1.78-1.82 (m, major - 3 H,
minor - 3 H), 1.87-1.91 (m, major - 3 H), 1.93-1.95 (m, minor -
3 H), 2.81-2.85 (m, minor - 2 H), 3.05-3.09 (m, major - 2 H),
5.21 (qq, J=6.8 Hz, 1.5 Hz, major - 1 H), 5.30 (qq, J=6.8 Hz,
1.5 Hz, minor - 1 H), 6.05-6.09 (m, minor - 1 H), 6.22-6.28
(m, major- 1H, minor- 1 H), 6.37-6.42 (m, major - 1 H), 6.46-
6.51 (m, major - 1 H), 6.64 (dq, J=5.3 Hz, 1.5 Hz, minor - 1 H).
13C NMR (C6D6, Me4Si): 13.5, 13.7, 15.5, 15.8, 18.8, 19.36,
19.39, 20.8, 40.9, 43.7, 121.1, 123.0, 125.3, 125.4, 127.4, 129.3,
131.0, 131.7, 132.6, 135.8, 136.5, 136.9, 139.1, 140.3, 149.6,
149.9. HRMS: calcd for C13H18, 174.1409; found, 174.1398.
Reaction of 1b with Picolinic Acid-d1. Complex 1b was treated
with 1 equiv of picolinic acid-d1 to give 4b-D, which was
followed by quenching with an excess amount of methanesul-
fonic acid (0.5 mL) to afford deuterated diene in 80% yield with
70% deuterium incorporation.
Complex 4b-D reacted with azobenzene to afford 5b-D and
5b0-D in the combined NMR yield of 83% and were isolated as a
colorless oil in a yield of 75% with 86% deuterium incorporation.
The ratio of two isomers major:minor =1.5:1. 1H NMR
(C6D6, Me4Si): 0.82-1.10 (m, major - 12 H, minor - 12 H), 1.89-
2.02 (m, major - 2 H, minor - 2 H), 2.04-2.27 (m, major - 4 H,
minor - 4 H), 2.29-2.40 (m, major - 2 H, minor - 2 H), 2.80-
2.84 (m, minor - 2 H), 3.04-3.08 (m, major - 2 H), 6.07-6.11
(m, minor - 1 H), 6.21-6.26 (m, major - 1 H, minor - 1 H),
6.40-6.43 (m, major - 1 H), 6.46-6.50 (m, major - 1 H), 6.61-
6.66 (m, minor - 1 H).
Representative Procedure for Preparation Chlorodienyl-Cp
Derivatives 7 from the in Situ Formed Chlorodienyltitanocene 6.
To a solution of bis(cyclopentadienyl)titanacyclopentadiene 1,
which was prepared from Cp2TiCl2 (598 mg, 2.4 mmol) in 10 mL
of THF, n-BuLi (1.58 M in hexane, 4.8 mmol), and an alkyne
(4.0 mmol) or a diyne (2.0 mmol) was added 2.4 mmol of NCS,
and the mixture was stirred for 2 h at -10 °C to afford the
chlorodienyltitanocenes 6. After addition of 4 mmol of azoben-
zene, the mixture was heated to 50 °C and stirred for 6 h. The
resulting solution was cooled to room temperature, and aqueous
NaHCO3 (2 mL) was added to quench the reaction. The mixture
was extracted with hexane, and the organic phase was dried over
MgSO4. After removal of volatiles in vacuo, the residue was
analyzed by 1H NMR spectroscopy in benzene-d6 with dichloro-
methane or dioxane as an internal standard. Then the residue
was subjected to column chromatography on silica gel (hexane
containing 3% of Et3N as eluent) to afford a mixture of
cyclopentadienyl derivatives 7.
4. Experimental Section
General Procedures. All manipulations were carried out under
an atmosphere of nitrogen using standard Schlenk line techni-
ques. Unless otherwise noted, all starting materials were com-
mercially available and were used without further purification.
Tetrahydrofuran (THF), benzene, toluene, and hexane were
refluxed and distilled from sodium benzophenone ketyl under a
nitrogen atmosphere. Pyridine-2-carboxylic acid was deuterated
through recrystallization in D2O.6 Bis(cyclopentadienyl)tit-
anacyclopentadiene 1 and bis(cyclopentadienyl)titanacyclopentene
10 were prepared as we reported before.5
Preparation of 4b4. A solution of Cp2TiCl2 (598 mg, 2.4 mmol)
in THF (10 mL) was cooled to -78 °C, and n-BuLi (1.58 M in
hexane, 3.0 mL, 4.8 mmol) was added dropwise to the solution.
After stirring for 1 h at -78 °C, 3-hexyne (4.0 mmol) was added
and the mixture was stirred for 3 h at -10 °C, to form bis-
(cyclopentadienyl)titanacyclopentadiene 1b in the dark green
solution. The solvent was removed under reduced pressure. To
the residue was added 8 mL of hexane, the precipitated LiCl was
removed by filtration, and the filtrate was concentrated to
afford a yellow-green solid, 1b.
A capped 5 mm NMR tube was charged with 0.5 mL of a
benzene-d6 solution of the above prepared 1b (21 mg, 66 μmol)
under argon, and dichloromethane (6.4 μL, 100 μmol) was
added as the internal standard. After the NMR measurement,
the mixture was treated with dichloroacetic acid (5.4 μL,
66 μmol), and the color of the mixture changed instantly from
1
yellow-green to red. H NMR spectroscopy revealed that 4b4
was formed in >93% yield. To this 4b4 was added additional
dichloroacetic acid (10.8 μL, 132 μmol), and the color of the
mixture changed instantly to yellow with the formation of dienyl
derivative in 96% yield.
Furthermore, to the in situ generated 4b4 was added 0.1 mL of
a benzene-d6 solution of azobenzene (0.3 mmol), the sealed
NMR tube was treated at 50 °C for 6 h, and the dienyl-Cp
derivative 5b was formed in 72% yield (the characterization of
5b is listed in the following sections).
4b4: 1H NMR (C6D6, Me4Si) 0.88 (dt, J=7.5, 1.6 Hz, 3 H),
0.97 (dt, J=7.5, 1.6 Hz, 3 H), 0.99 (dt, J=7.0, 1.2 Hz, 3 H), 1.06
(dt, J=7.5, 1.6 Hz, 3 H), 1.52-1.56 (m, 2 H), 1.67-1.86 (m, 6 H),
4.73 (t, J=7.0 Hz, 1 H), 5.41 (s, 1 H), 5.76 (s, 10 H); 13C NMR
(C6D6, Me4Si) 12.9, 14.5, 14.6, 16.0, 21.6, 25.5, 26.1, 26.3, 68.3,
115.0, 129.4, 144.1, 147.1, 166.1, 192.8.
Deuterolysis and Iodination of 4b4. To a dark green solution of
bis(cyclopentadienyl)titanacyclopentadiene 1b, which was pre-
pared in 2.0 mmol scale, was added 2.0 mmol of dichloroacetic
acid, and the mixture was stirred for 1.5 h at -15 °C to afford a
red solution of 4b4. The reaction mixture was treated with 1 mL
of D2SO4 (10% D2O solution) at this temperature and was
allowed to warm to room temperature overnight. The mixture
was diluted with 5 mL of water, extracted with hexane, dried
over MgSO4, and concentrated. The residue was analyzed by
1H NMR spectroscopy in benzene-d6 with dichloromethane
(63.8 μL, 1.0 mmol) as an internal standard to reveal the
formation of deuterated diene in 75% yield (>95% D) and 5b
in 25% yield. When 4b4 was treated with I2 (3.0 mmol) and CuCl
(1.0 mmol), the iododiene was formed in 85% NMR yield.
Representative Procedure for Preparation of Dienyltitanocenes
4 and the Following Coupling Reaction to Form Dienyl-Cp 5. To a
solution of bis(cyclopentadienyl)titanacyclopentadiene 1, which
was prepared from Cp2TiCl2 (598 mg, 2.4 mmol) in 10 mL of
THF, n-BuLi (1.58 M in hexane, 4.8 mmol), and an alkyne (4.0
mmol) or a diyne (2.0 mmol) was added 2.0 mmol of dichloro-
acetic acid, and the mixture was stirred for 5 h at room
temperature to afford complexes 4 (small amount of the cou-
pling products 5 were formed unavoidably). After addition of
(2Z,4Z)-5-Chloro-2-(cyclopentadienyl)-3,4-dimethylhexa-2,4-
diene (7a). Product 7a was obtained as a mixture of double-bond
positional isomers. Combined NMR yield of 85%. Isolated
yield of 67%. Light yellow oil.
The ratio of two isomers major:minor = 2.2:1. 1H NMR
(C6D6, Me4Si): 1.50 (q, J=1.1 Hz, major - 3 H), 1.55 (q, J =
1.1 Hz, minor - 3 H), 1.80 (q, J=1.1 Hz, major - 3 H), 1.80-
1.89 (m, major - 6 H, minor - 9 H), 2.80 (br d, J=1.4 Hz,

Article
Organometallics, Vol. 30, No. 4, 2011 851
minor - 2 H), 3.06 (dq, J=1.4, 23 Hz, major - 1 H), 3.19 (dq, J=
1.4, 23 Hz, major - 1 H), 6.19-6.23 (m, minor - 1 H), 6.24-
6.29 (m, major - 1 H, minor - 1 H), 6.47-6.54 (m, major - 2 H),
6.74 (dq, J=1.5, 5.2 Hz, minor - 1 H). 13C NMR (C6D6, Me4Si):
18.0, 18.22, 18.27, 18.5, 18.7, 19.0, 21.8, 21.9, 41.2, 42.8, 123.9,
124.1, 126.2, 126.5, 128.2, 129.4, 132.3, 132.51, 132.54, 132.7, 133.2,
134.3, 135.7, 136.2, 148.4, 148.6. HRMS: calcd for C13H17Cl,
208.1018; found, 208.1013.
Reaction of 6b with Propargyl Bromide to Afford 7b. To a THF
solution of tetraethyltitanacyclopentadiene 1b (1.0 mmol scale)
was added NCS (160 mg, 1.2 mmol) at 0 °C, and the mixture was
stirred for 2 h. To the mixture was added propargyl bromide
(0.18 mL, 2.0 mmol), and the mixture was stirred at 50 °C for 6 h.
The reaction was quenched with 3 M aqueous HCl solution and
extracted with hexane. The organic phase was washed with
water, aqueous saturated NaHCO3, and brine and dried over
anhydrous sodium sulfate. After removal of the solvent in vacuo,
the residue was purified by column chromatography on silica gel
with hexane as an eluent to afford chlorobutadienylcyclopenta-
diene 7b as a colorless oil (218 mg, 92% GC yield; 82% isolated
yield). Compound 7b was obtained as a mixture of the double-bond
positional isomers in the cyclopentadiene ring in a ratio of 63:37.
The reactions with other organic halides also produced the
same compound 7b.
Representative Procedure for Preparation of Alkenyl-Cp Deri-
vatives 9. A solution of bis(cyclopentadienyl)titanacyclopentene
10 was prepared as we described for 10e from Cp2TiCl2 (598 mg,
2.4 mmol), EtMgBr (1.0 M in THF, 4.8 mmol), and an alkyne
(2.0 mmol). To the reaction mixture was added azobenzene (4
mmol), and the mixture was stirred at 50 °C for 8 h. After
cooling to room temperature, the reaction mixture was
quenched with aqueous saturated NaHCO3 (2 mL). The mixture
was extracted with hexane, and the organic phase was dried over
MgSO4. After removal of volatiles in vacuo, the residue was
analyzed by 1H NMR spectroscopy in benzene-d6 with dichlo-
romethane or dioxane as an internal standard. Then the residue
was subjected to column chromatography on silica gel (hexane
containing 3% of Et3N as eluent) to afford a mixture of
cyclopentadienyl derivatives 9.
(E)-4-(Cyclopentadienyl)-oct-4-ene (9a). Product 9a was ob-
tained as a mixture of double-bond positional isomers. Com-
bined NMR yield of 71%. Isolated yield of 55%. Colorless oil.
The ratio of two isomers major:minor = 2.9:1. 1H NMR
(C6D6, Me4Si): 0.89-1.08 (m, major - 6 H, minor - 6 H), 1.38-
1.53 (m, major - 2 H, minor - 2 H), 1.55-1.70 (m, major - 2 H,
minor - 2 H), 2.10-2.25 (m, major - 2 H, minor - 2 H), 2.36-
2.53 (m, major - 2 H, minor - 2 H), 2.96 (br s, minor - 2 H),
3.06 (br s, major - 2 H), 5.72 (t, J=7.2 Hz, major - 1 H), 5.95 (t,
J=7.2 Hz, minor - 1 H), 6.18-6.24 (m, major - 1 H, minor -
1 H), 6.38-6.44 (m, major - 1 H, minor - 1 H), 6.51-6.57 (m,
major - 1 H), 6.93-6.98 (m, minor - 1 H). 13C NMR (C6D6,
Me4Si): 14.10, 14.12, 14.4, 14.5, 22.8, 23.0, 23.3, 23.4, 30.60,
30.63, 31.0, 31.3, 40.7, 41.7, 124.9, 126.40, 126.48, 128.5, 130.7,
132.1, 133.1, 133.4, 135.4, 136.3, 147.6, 149.4. HRMS: calcd for
C13H20, 176.1565; found, 176.1571.
Formation of 8e by the Reaction of Bis(cyclopentadienyl)tit-
anacyclopentene 10e with t-BuOH. It should be noted that in the
case of diphenyltitanacyclopentene 10e, the coupling reaction
did not proceed to 9e under the same conditions as for 9a-d.
Complex 10e reacted with t-BuOH to afford air-stable yellow
crystals of 8e with a loss of ethylene. The structure of 8e was
determined by X-ray analysis. The deuterolysis of 8e gave
deuterated cis-stilbene in 96% GC yield, and the isolated yield
was 89% with >99% deuterium incorporation. The same
product was obtained again when 10e reacted with t-BuOD
followed by quenching with 3 N HCl.
To a THF solution of bis(cyclopentadienyl)titanacyclopentene
10e, which was obtained in the same way as above, was added
t-BuOH (2.4 mmol), and the mixture was stirred at 50 °C for 3 h.
After removal of volatiles in vacuo, the residue was subjected to
column chromatography on silica gel (hexane/ethyl acetate =
3:1 as eluent) to afford a yellow powder, 8e. Suitable crystals for
X-ray diffraction were obtained by dissolving 8e in toluene and
keeping it at -30 °C.
8e: 1H NMR (C6D6, Me4Si) 1.11 (s, 9 H), 6.06 (s, 10 H), 6.75
(s, 1 H), 7.01-7.53 (m, 10 H); 13C NMR (C6D6, Me4Si) 31.3, 83.7,
112.8, 123.6, 125.0, 126.3, 128.2, 128.6, 128.8, 133.7, 140.0, 155.5,
188.6; HRMS calcd for C28H30OTi, 430.1776; found, 430.1777.
Reaction of Bis(cyclopentadienyl)titanacyclopentene 10a with
n-BuOD. The reaction was carried out in a similar method to the
above method using n-BuOD reacted with 10a. Product 9a-D
was obtained as a mixture of double-bond positional isomers.
Combined NMR yield of 71%. Isolated yield of 55% (98% D).
Colorless oil.
The ratio of two isomers major:minor = 2.9:1. 1H NMR
(C6D6, Me4Si): 0.89-1.08 (m, major - 6 H, minor - 6 H), 1.38-
1.53 (m, major - 2 H, minor - 2 H), 1.55-1.70 (m, major - 2 H,
minor - 2 H), 2.10-2.25 (m, major - 2 H, minor - 2 H), 2.36-
2.53 (m, major - 2 H, minor - 2 H), 2.96 (br s, minor - 2 H),
3.06 (br s, major - 2 H), 5.72 (t, J=7.2 Hz, major - 1 H, 98% D
incorporation), 5.95 (t, J = 7.2 Hz, minor - 1 H, 98% D
incorporation), 6.18-6.24 (m, major - 1 H, minor - 1 H), 6.38-
6.44 (m, major - 1 H, minor - 1 H), 6.51-6.57 (m, major - 1
H), 6.93-6.98 (m, minor - 1 H).
Supporting Information Available: Experimental part for com-
pounds 5b-d, 7b-d, and 9b-d, NMR spectra of new com-
pounds, and X-ray analytical data for 8e. This material is
available free of charge via the Internet at http://pubs.acs.org.