Preparation and reactions of monocyclic bis(cyclopentadienyl)titanacyclopentenes and -pentadienes

Article abstract of DOI:10.1016/S0022-328X(01)01072-5

A combination of Cp₂TiCl₂-2EtMgBr was found to be very effective for the formation of monocyclic titanacyclopentenes in excellent yields. On the other hand, a combination of Cp₂TiCl₂-2n-BuLi was used for intermolecular coupling of two alkynes to form titanacyclopentadienes in good to excellent yields. A reaction temperature range from -10 to -30°C was critical for the success of the combinations. Reactions of these in situ-prepared titanacycles show interesting similarities to or differences from their zirconacycle analogs.

Full text of DOI:10.1016/S0022-328X(01)01072-5

Journal of Organometallic Chemistry 633 (2001) 18–26
www.elsevier.com/locate/jorganchem
Preparation and reactions of monocyclic
bis(cyclopentadienyl)titanacyclopentenes and -pentadienes
Kimihiko Sato a,b, Yasushi Nishihara a,b, Shouquan Huo a,b, Zhenfeng Xi c,
Tamotsu Takahashi a,b,
*
a Catalysis Research Center and Graduate School of Pharmaceutical Sciences, Hokkaido Uni6ersity, Hokkaido, Japan
b CREST, Science and Technology Corporation (JST), Sapporo 060-0811, Japan
c Department of Chemistry, Peking Uni6ersity, Beijing 100871, China
Received 16 January 2001; received in revised form 31 May 2001; accepted 15 June 2001
Abstract
A combination of Cp2TiCl2–2EtMgBr was found to be very effective for the formation of monocyclic titanacyclopentenes in
excellent yields. On the other hand, a combination of Cp2TiCl2–2n-BuLi was used for intermolecular coupling of two alkynes to
form titanacyclopentadienes in good to excellent yields. A reaction temperature range from −10 to −30 °C was critical for the
success of the combinations. Reactions of these in situ-prepared titanacycles show interesting similarities to or differences from
their zirconacycle analogs. © 2001 Published by Elsevier Science B.V.
Keywords: Titanacyclopentene; Titanacyclopentadiene; Intermolecular coupling; Titanocene–ethylene complex
1. Introduction
coupled with various unsaturated compounds to give
zirconacycles [3]. For example, zirconacyclopentenes
can be easily generated in high yields and with high
pair-selectivity from the intermolecular coupling of
Cp2Zr(CH2ꢀCH2) with an acetylene (Scheme 1 (1)) [5].
On the other hand, a combination of Cp2ZrCl2 with
two equivalents of n-BuLi has proven very effective for
intermolecular coupling of two alkyne molecules or
intramolecular coupling of diynes to form mono or
bicyclic zirconacyclopentadienes [6]. The reactive spe-
cies of this combination of Cp2ZrCl2–2n-BuLi (Negishi
reagent) has been proposed to be a zirconocene–butene
complex, which has shown a very different reactivity
towards various substrates from the aforementioned
Organometallic compounds of the group 4 metals
(Ti, Zr, Hf), which are dominated by the use of cy-
clopentadienyl ligands, have proven very useful as
reagents or catalysts in synthetic chemistry [1,2]. In
recent years, we have studied the preparation and reac-
tions of bis(cyclopentadienyl)zirconacycles, including
zirconacyclopentanes, -pentenes and -pentadienes [3].
Zirconocene dichloride, Cp2ZrCl2, reacted with two
equivalents of EtMgBr to give a zirconocene–ethylene
complex Cp2Zr(CH2ꢀCH2) [4], which intermolecularly
zirconocene–ethylene
complex
Cp2Zr(CH2ꢀCH2)
(Scheme 1 (2)). Although not studied as much, combi-
nations of Cp2HfCl2–2EtMgBr [7] and Cp2HfCl2–2n-
BuLi [6b,7] have been successfully applied for the
preparation of hafnacyclopentenes and -pentadienes
(Scheme 1). However, surprisingly, analogous inter-
molecular coupling reactions using Cp2TiCl2–2EtMgBr
and Cp2TiCl2–2n-BuLi to give titanacyclopentenes and
titanacyclopentadienes have not been developed. In this
paper, we would like to report the following: (i) titana-
Scheme 1.
* Corresponding author. Tel.: +81-11-7062911; fax: +81-11-
7063274.
E-mail address: tamotsu@cat.hokudai.ac.jp (T. Takahashi).
0022-328X/01/$ - see front matter © 2001 Published by Elsevier Science B.V.
PII: S0022-328X(01)01072-5

K. Sato et al. / Journal of Organometallic Chemistry 633 (2001) 18–26
19
clopentadienes [8,10]. Among these, an aryloxytitanium
compound [8], (Ar¦O)2Ti, generated in situ from
(Ar¦O)2TiCl2–Na, and an alkoxytitanium–olefin com-
plex [9], (h2-propene)Ti(O-i-Pr)2, generated in situ from
Ti(O-i-Pr)4–2i-PrMgCl have shown interesting reactiv-
ity towards a variety of substrates. Combinations of
bis(cyclopentadienyl) or bis(pentamethylcyclopentadi-
enyl)titanocene dichloride with various reducing
reagents including EtMgBr and n-BuLi have been stud-
ied [11–15]. However, these combinations have been
used almost exclusively as a source of Cp2TiH for
hydrotitanation or hydromagnesation reactions, iso-
merization reactions or a source of a ‘Cp2Ti’ equivalent
for intramolecular coupling reactions of unsaturated
compounds. One major reason for the difficulty of the
intermolecular coupling is the labile nature of the olefin
on titanocene. Binger et al. clearly indicated the differ-
ence between a titanocene–butene and a zirconocene–
butene complex [16]. In order to realize an
intermolecular coupling reaction pattern, we used Et-
MgBr and carried out its coupling reaction at low
temperature. Fortunately, we were able to observe the
intermolecular coupling of ethylene derived from Et-
MgBr with alkynes using titanocene. Titanacyclopen-
tene derivatives (1) were formed in excellent NMR
yields, as shown in Scheme 2. Hydrolysis of the reac-
tion mixture with 3 N HCl afforded compounds 2.
Deuterolysis instead of hydrolysis of the reaction mix-
ture gave 3a in 94% yield with more than 98% of D
incorporation. Results are summarized in Table 1.
It is noteworthy that in all cases, coupling products
of ethylene derived from EtMgBr with an alkyne were
Scheme 2.
cyclopentenes were prepared in high yields and with
high pair-selectivity by an intermolecular coupling of
Cp2TiCl2, EtMgBr and an alkyne; (ii) two molecules of
alkynes intermolecularly coupled to form titanacy-
clopentadienes using a combination of Cp2TiCl2–2n-
BuLi. In addition, reactions of the titanacycles
prepared here are presented.
2. Results and discussion
2.1. Preparation of bis(cyclopentadienyl)-
titanacyclopentenes by an intermolecular coupling of
Cp2TiCl2, EtMgBr and an alkyne
Divalent titanium Ti(II) complexes with ligands other
than cyclopentadienyl have been reported and applied
for the preparation of titanacyclopentenes and titanacy-
Table 1
Formation of titanacyclopentene compounds by the reaction of Cp2TiCl2 with EtMgBr and an alkyne

20
K. Sato et al. / Journal of Organometallic Chemistry 633 (2001) 18–26
2.2. Unexpected formation of cyclopropane deri6ati6es
from reaction of silylated acetylenes with
Cp2TiCl2–2EtMgBr
When a silylated acetylene such as 1-trimethylsilyl-1-
propyne was used to react with Cp2TiCl2–2EtMgBr,
the expected titanacyclopentene was not formed. Sur-
prisingly, instead, 1-methyl-1-(trimethylsilyl)methyl cy-
clopropane (5) was obtained in 84% yield after
hydrolysis of the reaction mixture with 3 N HCl at
−30 °C (Scheme 4). This result was different from that
obtained in the case of the zirconocenes and
hafnocenes, in which a zirconacyclopentene or hafnacy-
clopentene was formed. Deuterolysis of the reaction
mixture instead of hydrolysis afforded a bis-deuterated
product (5D) in 94% yield with \98% D incorpora-
Scheme 3.
1
tion. In comparison with the H-NMR spectrum of (5),
1
the H-NMR spectrum of 5D indicated that the signal
at 0.78 ppm in 5 assignable to two protons of the CH2
next to the trimethylsilyl group was deuterated in 5D.
The 13C-NMR spectrum of 5D showed a quintet at
27.16 ppm assignable to the CD2 moiety. Attempts to
isolate the titanium-containing intermediate of this re-
action have been so far unsuccessful. a-Silylated titana-
cyclopentene (6) and a titanocene carbene compound
(7) are proposed to be the key intermediates. Cyclo-
propane formation by Michael addition-type reaction
of the MꢁC bond (M=Zr or Ti) to the CꢀC bond with
an electron-withdrawing group has been observed in
the case of zirconium [18]. In the case of titanium,
titanocene carbene complex formation by Michael addi-
tion-type reaction in the titanacycle has been reported
[19a,b]. A type of complex similar to 7 has been pro-
posed as the key intermediate [19].
Scheme 4.
formed in excellent yields. No formation of the alkyne
dimer was observed. We have already reported that
zirconocene dichloride reacted with two equivalents of
EtMgBr to give a zirconocene–ethylene complex,
which immediately reacted with one equivalent of an
alkyne to afford a zirconacyclopentene [5]. However, in
some cases formation of zirconacyclopentadienes was
observed in 3–5% yields. In order to completely sup-
press the formation of zirconacyclopentadienes, intro-
duction of ethylene was required [17]. However, in the
case of this titanocene, addition of ethylene was not
necessary. Yields and pair-selectivity of the formation
of titanacyclopentenes were the same or higher than
those in the cases of the corresponding zirconacy-
clopentenes.
2.3. Titanium-mediated intermolecular coupling of an
alkyne, EtMgBr (or ethylene) and CO. Formation of
cyclopentenone deri6ati6es 6ia CO insertion into
titanacyclopentenes
It was necessary to keep the mixture at a low tem-
perature (−30 °C) during the reaction. When the re-
action was carried out at 0 °C and at room
temperature for 3 h, the yields of 2a decreased to 86
and 68%, respectively. The use of other Grignard
reagents such as n-BuMgCl, PrMgCl did not give ti-
tanacyclopentene compounds. This is probably because
butene or propene formed in situ on titanocene is more
labile.
The reaction mechanism for the formation of titana-
cyclopentenes (1) from the combination of Cp2TiCl2/
2EtMgBr/alkyne is proposed to be analogous with that
for zircona- and hafna-cyclopentenes [5]. It involves
the formation of a titanocene–ethylene complex (4) by
b-hydrogen abstraction from Cp2TiEt2, followed by
intermolecular coupling of the ethylene with an alkyne
(Scheme 3).
Titanocene and zirconocene-mediated coupling of
enynes with CO-forming bicyclic cyclopentenones have
been reported via insertion of CO into titana- or zir-
cona-cyclopentenes [3,6,9,20,22]. For the intermolecular
coupling pattern, we and others have reported zir-
conocene-mediated reactions [5,21]. However, since
there was no titanocene-mediated method for the pair-
selective intermolecular coupling of olefins with alky-
nes, the formation of cyclopentenones by inter-
molecular coupling of an alkyne, an olefin, and CO
mediated by titanocene (Cp2Ti) has not been developed.
Although the reactivity of titanacyclopentenes is quite
different in many cases from that of zirconacyclopente-
nes, insertion of CO into titanacyclopentenes prepared
in situ afforded cyclopentenones (Eq. (3)), as already
observed for the zirconacyclopentene cases [5]. This

K. Sato et al. / Journal of Organometallic Chemistry 633 (2001) 18–26
21
2.4. Preparation of bis(cyclopentadienyl)-
titanacyclopentadienes by intermolecular coupling of
alkynes using Cp2TiCl2–2n-BuLi
represents the first example of titanocene-mediated in-
termolecular coupling of an alkyne, an ethylene and
CO to form monocyclic useful a,b-disubstituted cy-
clopentenones [13]. The cyclopentenones were formed
in excellent yields when the CO insertion reaction was
carried out at −30 °C for 3–6 h. Results are given in
Table 2. When the reaction was carried out at room
temperature, yields of cyclopentenones decreased.
As mentioned previously, monocyclic titanacyclopen-
tadienes with ligation other than cyclopentadienyl [8–
11] and bicyclic titanacyclopentadienes with various
ligands including cyclopentadienyl [13,14,23,24] have
been prepared via intermolecular coupling of two alky-
nes or via intramolecular coupling of diynes. Although
the combination of Cp2ZrCl2–2n-BuLi (Negishi
reagent) has proven to be the most effective and practi-
cal for the preparation of mono and bicyclic zirconacy-
clopentadienes [6], an analogous combination of
Cp2TiCl2–2n-BuLi has not been reported as a reagent
for the preparation of titanacyclopentadienes. In the
case of Cp2ZrCl2–2n-BuLi, addition of two equivalents
of the same alkynes or one equivalent of a diyne readily
affords mono or bicyclic zirconacyclopentadienes at
room temperature in quantitative yields normally
within 1 h [6]. Hydrolysis of the reaction mixture with
3 N HCl easily gives the corresponding dienes in almost
quantitative yields. However, in a simple application of
the Cp2ZrCl2–2n-BuLi–two alkynes system, the same
conditions and its work-up procedure for the prepara-
tion of titanacyclopentadienes did not work well. The
reason is that Cp2TiBu2 is not stable at room tempera-
ture. As reported, it may be easily converted into
Cp2TiBu or Cp2TiH. Binger reported the formation of
a Cp2Ti(butene) complex from Cp2TiBu2 and the labil-
ity of the butene. We carried out the reaction at lower
temperature. As we expected, when the reaction tem-
perature was lowered, the yields of titanacyclopentadi-
enes increased. Finally, the range from −10 to
−30 °C was found to be the most effective for the
formation of titanacyclopentadienes (Eq. (4)). Follow-
ing these conditions, monocyclic titanacyclopentadienes
were prepared intermolecularly in good to excellent
NMR yields (Table 3).
(3)
It has been pointed out that in order to obtain the
desired cyclopentenones from the reaction of zirconacy-
clopentenes with CO, treatment of the reaction mixture
with I2 is necessary [5,21]. Normal quenching with 3 N
HCl gives a mixture of the cyclopentenones and their
corresponding alcohols. The use of I2 and its removal
from the extracts are often troublesome. However, in-
terestingly, just normal quenching with 3 N HCl was
good enough to obtain cyclopentenones exclusively
from the reaction of titanacyclopentenes with CO. No
alcohols were obtained. Without I2, the work-up was
simplified and time-saving. In addition, compared with
the case of zirconacyclopentenes, the reaction of titana-
cyclopentenes with CO afforded the corresponding cy-
clopentenones in remarkably higher isolated yields,
since titanacyclopentenes (1) were cleanly formed and
their further reactions with CO afforded no by-
products.
Table 2
Formation of cyclopentenones by insertion of CO into titanacy-
clopentenes
(4)
It is noteworthy that, unlike zirconacyclopentadienes,
hydrolysis of titanacyclopentadienes with 3 N HCl
gives the corresponding dienes in relatively low yields.
Although the reason is not clear yet, isomerization or
oligomerization in the process of hydrolysis is assumed
to be responsible for the low yields of dienes.
The reaction mechanism for the formation of titana-
cyclopentadienes from the combination of Cp2TiCl2–
2n-BuLi–two alkynes is proposed to be essentially the
same as that for the formation of zirconacyclopentadi-
enes from the combination of Cp2ZrCl2–2n-BuLi–two
alkynes, as shown in Scheme 5.

22
K. Sato et al. / Journal of Organometallic Chemistry 633 (2001) 18–26
Table 3
3. Conclusions
Formation of monocyclic titanacyclopentadienes by intermolecular
coupling
We have demonstrated in this paper that: (i) Combi-
nations of Cp2TiCl2–2EtMgBr and Cp2TiCl2–2n-BuLi
are effective reagents for the intermolecular coupling of
ethylene with alkynes to form monocyclic titanacy-
clopentenes, and for intermolecular coupling of two
alkynes to form titanacyclopentadienes. These methods
enable easy access to titanacycles and thus will promote
studies of their chemistry. (ii) Lower reaction tempera-
ture than that in the zirconocene cases is critical for the
success of this development. (iii) b-Hydrogen abstrac-
tion from Cp2TiEt2 and Cp2TiBu2 to generate the ti-
tanocene–ethylene complex or the titanocene–butene
complex is easier than that from their zirconocene
analogs. b-Hydrogen abstraction takes place at lower
temperature (−30 to −10 °C).
2.5. Reaction of titanacyclopentadienes with alkynes in
the presence of CuCl
As a demonstration of the different reactivities be-
tween zircona- and titana-cyclopentadienes, reactions
of titanacyclopentadienes with a third alkyne such as
DMAD was carried out, expecting formation of ben-
zene derivatives [25]. We have recently reported that
zirconacyclopentadienes react with a third alkyne to
form benzene derivatives in the presence of CuCl (Eq.
(6)) [26]. However, surprisingly, the reaction of titana-
cyclopentadienes with DMAD in the presence of CuCl
did not give benzene derivatives; instead, linear trienes
(11) were formed in good yields (Eq. (5)).
Scheme 5.
4. Experimental
4.1. General methods
All reactions involving organometallic compounds
were carried out under nitrogen atmosphere using stan-
dard Schlenk tube techniques. Tetrahydrofuran (THF)
was distilled and dried with sodium benzophenone
ketyl. Titanocene dichloride (Cp2TiCl2) was purchased
from Aldrich. EtMgBr (0.96 M solution in THF) and
n-BuLi (1.60 M solution in hexane) were purchased
from Kanto Chemical Co. Inc. Unless otherwise noted,
chemicals were used without further purification.
1H- and 13C-NMR spectra were recorded with a 400
MHz Bruker NMR spectrometer. The NMR yields
were determined using mesitylene as an internal stan-
dard. GC analyses were performed on a Shimadzu
GC-14B equipped with a flame ionization detector us-
ing a Shimadzu capillary column (CBPI-M25-025). The
GC yields were determined using suitable hydrocarbon
as internal standards.
(5)
(6)

K. Sato et al. / Journal of Organometallic Chemistry 633 (2001) 18–26
23
4.2. Preparation of titanacyclopentenes and isolation of
hydrolyzed products
4.2.6. Bis(cyclopentadienyl)-2,3-dipropyl-1-
titanacyclopentene (1c)
1
NMR yield 98%. H-NMR (C6D6, Me4Si): l 5.96 (s,
10H, Cp). 13C-NMR (C6D6, Me4Si): l 14.7, 15.3, 21.9,
23.8, 35.5, 36.2, 38.0, 58.3, 113.8 (10C), 135.9, 194.2.
HRMS calc. for C20H28Ti 316.1670, found 316.1692.
Hydrolysis of the reaction mixture afforded 2c. GC
yield 97%, isolated yield 68%. The NMR data of 2c are
the same as those reported [5a].
4.2.1. A general procedure
EtMgBr (2.4 mmol, 1.0 M THF solution, 2.4 ml) was
added dropwise with a syringe to a THF (5 ml) solution
of Cp2TiCl2 (1.2 mmol, 299 mg) at −78 °C (dry
ice–acetone bath) in a 20 ml Schlenk tube. After the
addition was complete, the reaction mixture was stirred
at −78 °C for 1 h. To the reaction mixture, an alkyne
(1.0 mmol) was added and stirred for 3 h at −30 °C.
Titanacyclopentenes (1) were formed and determined
by 13C-NMR. Only the Cp signals were determined by
1H-NMR because several peaks overlapped with THF
signals. Hydrolysis of the reaction mixture with 3 N
HCl followed by normal work-up afforded 2.
4.2.7. Preparation of 1d
Two regioisomers were obtained in a ratio of 3:1.
Combined NMR yield 83%. NMR data for the major:
1H-NMR (C6D6, Me4Si): l 6.07 (s, 10H, Cp). 13C-
NMR (C6D6, Me4Si): l 14.3, 23.3, 31.4, 34.5, 37.8, 60.2,
115.1, 126.4, 138.5, 150.3, 192.5. HRMS calc. for
C24H28Ti 364.1670, found 364.1670.
Hydrolysis of the reaction mixture afforded a mix-
ture of two regioisomers in a ratio of 3:1. Their NMR
data are the same as those reported [17].
4.2.2. General notes
We have reported the formation and NMR data for
compounds 2 (for 2a,b,d,e, see Ref. [17]; for 2c, see Ref.
[5a]). All these compounds show the same NMR spec-
tra as those reported.
4.2.8. Preparation of 1e
Two regioisomers were obtained in a ratio of 10:1.
Combined NMR yield 88%. NMR data for the major:
1H-NMR (C6D6, Me4Si): l 6.16 (s, 10H, Cp). 13C-
NMR (C6D6, Me4Si): l 20.1, 39.9, 59.1, 115.0, 122.6,
125.8, 127.5, 133.6, 150.6, 191.7. HRMS calc. for
C21H22Ti 322.1201, found 322.1193.
Hydrolysis of the reaction mixture afforded a mix-
ture of two regioisomers in a ratio of 10:1. Their NMR
data are the same as those reported [17].
4.2.3. Bis(cyclopentadienyl)-2,3-diphenyl-1-
titanacyclopentene (1a)
NMR yield 99%. H-NMR (C6D6, Me4Si): l 2.83 (t,
2H, J=6.6 Hz), 6.28 (s, 10H), 6.9–6.4 (m, 10H).
13C-NMR (C6D6, Me4Si): l 40.7, 60.6, 115.6 (10C),
123.1, 125.3, 127.3, 127.5, 128.0, 129.2, 139.7, 144.4,
150.4, 194.8. HRMS calc. forC26H25Ti [M+H]
385.1436, found 385.1446.
1
Hydrolysis of the reaction mixture afforded 2a. GC
yield 95%. The NMR data of 2b are the same as those
reported [17].
4.3. Reaction of 1-trimethylsilyl-1-propyne with
Cp2TiCl2–2EtMgBr. Isolation of cyclopropane
deri6ati6es (5)
4.2.4. Isolation of 3a
4.3.1. A general procedure
The procedure is essentially the same as described
above for the isolation of 2.
Deuterolysis instead of hydrolysis afforded 3a in 94%
GC yield. Isolated yield 90%. 1H-NMR (CDCl3,
Me4Si): l 1.09–1.13 (tt, 2H, J=8.1, 2.2 Hz), 2.55 (t,
2H, J=8.0 Hz), 6.96–6.99 (m, 2H), 7.07–7.13 (m, 3H),
7.19–7.22 (m, 2H), 7.26–7.35 (m, 3H). 13C-NMR
(CDCl3, Me4Si): l 12.70 (t, J=20.1 Hz), 33.52, 125.06
(t, J=24.2 Hz), 126.13, 126.90, 127.89, 128.56, 128.63,
129.07, 137.60, 141.63, 144.93. HRMS calc. for
C16D2H14 210.1375, found 210.1379.
4.3.2. 1-Methyl-1-(trimethylsilyl)methylcyclopropane (5)
Colorless liquid, GC yield 84%, isolated yield 51%.
1H-NMR (CDCl3, Me4Si): l 0.15 (s, 9H), 0.33–0.37 (m,
4H), 0.73 (s, 2H), 1.16 (s, 3H). 13C-NMR (CDCl3,
Me4Si): l −0.06, 13.09, 14.96, 25.87, 28.16. HRMS
calc. for C8H18Si 142.1178, found 142.1178.
4.2.5. Bis(cyclopentadienyl)-2,3-dibutyl-1-
titanacyclopentene (1b)
NMR yield 99%. H-NMR (C6D6, Me4Si): l 6.18 (s,
4.3.3. 1-Methyl-1-bisdeutero(trimethylsilyl)-
methylcyclopropane (5D)
1
10H, Cp). 13C-NMR (CDCl3, Me4Si): l 14.1, 14.2, 23.4,
24.0, 31.0, 33.0, 35.0, 36.2, 57.9, 114.0, 135.8, 193.8.
HRMS calc. for C22H32Ti 344.1983, found 344.1971.
Hydrolysis of the reaction mixture afforded 2b. GC
yield 90%. The NMR data of 2b are the same as those
reported [17].
Deuterolysis instead of hydrolysis afforded 5D. Col-
orless liquid, GC yield 94%, isolated yield 69%. 1H-
NMR (CDCl3, Me4Si): l 0.05 (s, 9H), 0.22–0.26 (m,
4H), 1.05 (s, 3H). 13C-NMR (CDCl3, Me4Si): l −0.13,
12.94, 14.82, 25.75, 27.16 (quintet, J=17.4 HZ).
HRMS calc. for C8H16D2Si 144.1301, found 144.1315.

24
K. Sato et al. / Journal of Organometallic Chemistry 633 (2001) 18–26
4.4. Insertion of CO into titanacyclopentenes.
Preparation of h,i-disubstituted cyclopentenones (8)
(CDCl3, Me4Si): l 13.81, 22.95, 23.83, 29.83, 30.45,
34.25, 127.19, 128.86, 129.29, 36.75, 141.32, 167.04,
209.76. HRMS calc. for C15H18O 214.1358, found
214.1348.
4.4.1. A general procedure
Into a THF solution of titanacyclopentenes (1.0
mmol) prepared in situ as described above, was slowly
bubbled CO gas at −30 °C for 3 h. The reaction
mixture was then quenched with 3 N HCl and extracted
with EtOAc. The combination of extracts was washed
with water and brine, and dried over MgSO4. Purifica-
tion by column chromatography (silica gel, hexane–
Et2O=4:1) afforded pure cyclopentenones.
4.4.7. Isolation of 8e
Cyclopentenone (8e) was obtained as a mixture of
two regioisomers (10:1). Combined GC yield 81%, com-
bined isolated yield 67%. NMR data for the major:
1
2-phenyl-3-methylcyclopenten-1-one. H-NMR (CDCl3,
Me4Si): l 2.14 (s, 3H), 2.48–2.53 (m, 2H), 2.60–2.63
(m, 2H), 7.26–7.43 (m, 5H). 13D-NMR (CDCl3,
Me4Si): l 18.29, 31.75, 34.81, 127.53, 128.19, 129.09,
131.84, 140.21, 171.96, 207.54. NMR data for the mi-
nor: 2-Methyl-3-phenylcyclopenten-1-one. 1H-NMR
(CDCl3, Me4Si): l 1.97 (s, 3H), 2.540–2.56 (m, 2H),
2.91–2.94 (m, 2H), 7.42–7.54 (m, 5H). 13C-NMR
(CDCl3, Me4Si): l 9.94, 29.27, 34.02, 127.56, 128.63,
129.48, 136.43, 136.54, 166.60, 209.86.
4.4.2. A general note
We have reported the preparation and characteriza-
tion of 8a–c,e [5b].
4.4.3. 2,3-Dipheylcyclopenten-1-one (8a)
Colorless liquid, GC yield 88%, isolated yield 81%.
1H-NMR (CDCl3, Me4Si): l 2.62–2.64 (m, 2H), 2.96–
2.98 (m, 2H), 7.18–7.31 (m, 10H). 13C-NMR (CDCl3,
Me4Si): l 29.18, 34.46, 127.46, 127.73, 128.08, 128.10,
129.12, 129.48, 132.04, 135.34, 139.44, 167.73, 207.10.
4.5. Preparation of monocyclic titanacyclopentadienes
4.5.1. A general procedure
n-BuLi (2.4 mmol, 1.6 M hexane solution, 1.5 ml)
was added dropwise with a syringe to a THF (5 ml)
solution of Cp2TiCl2 (1.25 mmol, 299 mg) at −78 °C
(dry ice–acetone bath) in a 20 ml Schlenk tube. After
the addition was complete, the reaction mixture was
stirred at −78 °C for 1 h. To the reaction mixture, an
alkyne (2.0 mmol) was added, then stirred for 3 h at
−10 °C (NH4Cl–ice bath). The formation of titanacy-
clopentadienes was determined by 13C-NMR. Only the
4.4.4. 2,3-Dibutylcyclopenten-1-one (8b)
Colorless liquid, GC yield 97%, isolated yield 90%.
1H-NMR (CDCl3, Me4Si): l 0.89 (t, 3H, J=7.1 Hz),
0.95 (t, 3H, J=7.2 Hz), 1.27–1.42 (m, 6H), 1.48–1.56
(m, 2H), 2.15 (t, 2H, J=7.1 Hz), 2.34–2.50 (m, 6H).
13C-NMR (CDCl3, Me4Si): l 13.66, 13.66, 22.55, 22.57,
22.64, 28.71, 29.44, 30.60, 30.67, 34.00, 140.18, 173.63,
209.69.
1
Cp peaks were detected by H-NMR, because several
4.4.5. 2,3-Dipropylcyclopenten-1-one (8c)
peaks overlapped with the THF peaks.
Colorless liquid, GC yield 99%, isolated yield 83%.
1H-NMR (CDCl3, Me4Si): l 0.89 (t, 3H, J=7.3 Hz),
0.98 (t, 3H, J=7.4 Hz), 1.36–1.44 (m, 2H), 1.52–1.63
(m, 2H), 2.13–2.17 (t, 2H, J=7.6 Hz), 2.34–2.40 (m,
2H), 2.41–2.44 (t, 2H, J=7.8 Hz), 2.50–2.52 (m, 2H).
13C-NMR (CDCl3, Me4Si): l 13.85, 13.90, 20.57, 21.60,
24.84, 28.63, 32.90, 33.97, 140.13, 173.63, 209.74.
4.5.2. Bis(cyclopentadienyl)-2,3,4,5-tetramethyl-
1-titanacyclopentadiene (9a)
1
NMR yield 92%. H-NMR (C6D6, Me4Si): l 1.30 (s,
6H), 1.65 (s, 6H), 5.83 (s, 10H). 13C-NMR (C6D6,
Me4Si): l 19.5, 92.2, 98.6, 112.2 (5C), 114.7. HRMS
calc. for C18H22Ti 286.1201, found 286.1194.
4.4.6. Isolation of 8d
4.5.3. Bis(cyclopentadienyl)-2,3,4,5-tetraethyl-
1-titanacyclopentadiene (9b)
NMR yield 93%. H-NMR (C6D6, Me4Si): l 0.99 (t,
6H, J=7.5 Hz), 1.10 (t, 6H, J=7.4 Hz), 1.48 (q, 4H,
J=7.3 Hz), 2.07 (q, 4H, J=7.5 Hz), 5.96 (s, 10H).
13C-NMR (C6D6, Me4Si): l 14.8, 15.5, 21.0, 27.9, 111.8
(5C), 131.9, 200.7. HRMS calc. for C22H30Ti 342.1827,
found 342.1856.
Cyclopentenone (8d) was obtained as mixture of two
regioisomers (3:1). Combined GC yield 76%, combined
isolated yield 63%. NMR data for the major: 2-Phenyl-
1
1
3-butylcyclopenten-1-one. H-NMR (CDCl3, Me4Si): l
0.88 (t, 3H, J=7.3 Hz), 1.29–1.35 (m, 2H), 1.50–1.58
(m, 2H), 2.49–2.54 (m, 4H), 2.65 (t, 2H, J=4.4 Hz),
7.22–7.41 (m, 5H). 13C-NMR (CDCl3, Me4Si): l 13.61,
22.45, 28.88, 29.60, 31.25, 34.51, 127.33, 128.04, 128.90,
131.87, 140.22, 175.76, 207.73. NMR data for the mi-
4.5.4. Bis(cyclopentadienyl)-2,3,4,5-tetrapropyl-
1-titanacyclopentadiene (9c)
nor:
2-Butyl-3-phenylcyclopenten-1-one.
1H-NMR
1
(CDCl3, Me4Si): l 0.87 (t, 3H, J=7.4 Hz), 1.26–1.50
(m, 4H), 2.37 (t, 2H, J=7.5 Hz), 2.50–2.53 (m, 2H),
2.89 (t, 2H, J=4.6 Hz), 7.26–7.46 (m, 5H). 13C-NMR
NMR yield 75%. H-NMR (C6D6, Me4Si): l 0.91 (t,
6H, J=7.2 Hz), 1.03 (t, 6H, J=7.2 Hz), 1.31–1.42 (m,
8H), 1.67–1.73 (m, 4H), 1.94–1.99 (m, 4H), 5.96 (s,

K. Sato et al. / Journal of Organometallic Chemistry 633 (2001) 18–26
25
10H). 13C-NMR (C6D6, Me4Si): l 15.0, 15.5, 24.0, 24.4,
31.0, 38.8, 112.1 (5C), 131.1, 199.8. HRMS calc. for
C26H38Ti 398.2453, found 398.2436.
130.76, 132.45, 138.79, 147.81, 150.42, 165.91, 168.48.
HRMS calc. for C22H36O4 364.2612, found 364.2597.
4.6.4. Isolation of triene (11c)
Isolated yield 54%. 1H-NMR (CDCl3, SiMe4): l
0.85–0.93 (m, 12H), 1.27–1.34 (m, 16H), 2.01–2.19 (m,
8H), 3.70 (s, 3H), 3.76 (s, 3H), 5.27 (t, 1H, J=7.3 Hz),
5.77 (s, 1H). 13C-NMR (CDCl3, SiMe4): l 13.94, 14.02,
22.50, 22.66, 22.75, 23.36, 27.91, 30.22, 30.51, 30.69,
30.87, 31.18, 31.54, 51.64, 52.11, 121.09, 130.71, 132.41,
138.70, 147.81, 150.56, 165.87, 168.48. HRMS calc. for
C26H44O4 420.3237, found 420.3262.
4.5.5. Bis(cyclopentadienyl)-1,3-dimethyl-
2,4-diphenyl-1-titanacyclopentadiene (9d)
NMR yield 92%. H-NMR (C6D6, Me4Si): l 1.22 (s,
3H), 1.47 (s, 3H), 5.90 (s, 10H), 7.26–6.89 (m, 10H).
13C-NMR (C6D6, Me4Si): l 18.9, 22.3, 112.8, 113.4
(10C), 114.1, 123.6, 125.6, 126.8 (2C), 128.1 (2C), 129.6
(2C), 130.2, 135.7, 143.2, 148.7, 195.5, 198. HRMS calc.
for C28H26Ti 410.1514, found 410.1540.
1
4.5.6. Bis(cyclopentadienyl)-1,3-dibutyl-2,4-diphenyl-
1-titanacyclopentadiene (9e)
NMR yield 86%. H-NMR (C6D6, Me4Si): l 0.57 (t,
Acknowledgements
1
A part of this work was supported by the Ministry of
Education, Science, Sport and Culture, Japan. ZX
thanks the National Natural Science Foundation of
China (29702001) and the National Science Fund for
Distinguished Young Scholars (29825105) for financial
support of a part of this work. The authors appreciate
Xuechuan Hong for his experiment.
6H, J=7.0 Hz), 0.71 (t, 6H, J=6.8 Hz), 1.23–2.06 (m,
12H), 6.00 (s, 10H), 7.29–6.93 (m, 10H). 13C-NMR
(C6D6, Me4Si): l 13.9, 14.0, 23.0, 23.9, 30.5, 32.9, 33.0,
37.4, 112.4, 113.3 (10C), 114.3, 123.6, 125.5, 126.5 (2H),
128.1 (2C), 130.0 (2C), 132.5, 135.5, 143.3, 149.0, 196.5,
204.3. HRMS calc. for C34H38Ti 494.2453, found
494.2470.
4.6. Reaction of titanacyclopentadienes with DMAD in
the presence of CuCl. Isolation of trienes (11)
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