Novel alkylidenating agents via the α lithiation of monoalkyl group 4 metal derivatives: Methylidene-metal complexes and their active lithiated precursors

Article abstract of DOI:10.1002/ejoc.200400808

The interaction of the Group 4 metal chlorides, MCl₄, where M = Ti, Zr, Hf, with two equiv. of methyllithium at -78 °C in toluene has led to the corresponding methylidene-metal complex, H₂C=MCl₂, possibly complexed with LiCl. That this complex was stable to at least -40 °C was demonstrated by adding chemical trapping agents at this temperature: 1) benzophenone was quantitatively converted into 1,1-diphenylethylene when M = Ti or Zr; with the Hf analogue, a 1:3 mixture of 1,1-diphenylethylene and 1,1-diphenylethanol was produced; 2) propiophenone reacted with the methylidene complex to yield 2-phenyl-1-butene, 38% (M = Ti) or 25% (M = Zr), with the majority of the propiophenone being recovered (the unreacted ketone is attributed to enolate salt formation competing with the methylidenation); 3) diphenylacetylene reacted with H₂C=TiCl₂ by cycloaddition in 50% yield, ultimately to give a 1:1 mixture of α-methyl-cis-stilbene and α-methyl-trans-stilbene; and finally 4) norbomene was polymerized in a ROMP process by either the methylidenetitanium or methylidene-zirconium complex, but the titanium catalyst exhibited higher activity. The stability of such methylidene complexes proved to be highly temperature- and solvent-dependent: 1) the methylidene complex in toluene was no longer detectable by chemical trapping when the reaction mixture was warmed to 0 °C or above; 2) the generation of the methylidene complex in THF was uniformly unsuccessful even at -78 °C or above. From these observations this study concludes that in toluene the free methylidene complex, H₂C=MCl ₂, is not present but rather the agent is still bonded to LiCl. At higher temperatures in toluene or even at -78 °C in THF, the LiCl dissociates from such complexation and the free methylidene dimerizes to [Cl₂M-CH₂]₂, as is known in the case of Cp ₂Ti=CH₂. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejoc.200400808

SHORT COMMUNICATION
Novel Alkylidenating Agents via the α Lithiation of Monoalkyl Group 4 Metal
Derivatives: Methylidene-Metal Complexes and Their Active Lithiated
Precursors[‡]
John J. Eisch*[a] and Adetenu A. Adeosun[a]
Keywords: Group 4 metals / Methyl derivatives / Methylidene complexes / Lithiation / ROMP catalyst
The interaction of the Group 4 metal chlorides, MCl4, where
M = Ti, Zr, Hf, with two equiv. of methyllithium at –78 °C
in toluene has led to the corresponding methylidene-metal
complex, H2C=MCl2, possibly complexed with LiCl. That this
complex was stable to at least –40 °C was demonstrated by
adding chemical trapping agents at this temperature: 1)
benzophenone was quantitatively converted into 1,1-diphen-
ylethylene when M = Ti or Zr; with the Hf analogue, a 1:3
mixture of 1,1-diphenylethylene and 1,1-diphenylethanol
was produced; 2) propiophenone reacted with the methyli-
dene complex to yield 2-phenyl-1-butene, 38% (M = Ti) or
25% (M = Zr), with the majority of the propiophenone being
recovered (the unreacted ketone is attributed to enolate salt
formation competing with the methylidenation); 3) diphenyl-
acetylene reacted with H2C=TiCl2 by cycloaddition in 50%
yield, ultimately to give a 1:1 mixture of α-methyl-cis-stilbene
and α-methyl-trans-stilbene; and finally 4) norbornene was
polymerized in a ROMP process by either the methylidene-
titanium or methylidene-zirconium complex, but the titanium
catalyst exhibited higher activity. The stability of such meth-
ylidene complexes proved to be highly temperature- and sol-
vent-dependent: 1) the methylidene complex in toluene was
no longer detectable by chemical trapping when the reaction
mixture was warmed to 0 °C or above; 2) the generation of
the methylidene complex in THF was uniformly unsuccessful
even at –78 °C or above. From these observations this study
concludes that in toluene the free methylidene complex,
H2C=MCl2, is not present but rather the agent is still bonded
to LiCl. At higher temperatures in toluene or even at –78 °C
in THF, the LiCl dissociates from such complexation and the
free methylidene dimerizes to [Cl2M–CH2]2, as is known in
the case of Cp2Ti=CH2.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
As a novel, general approach to transition metal-alkylid-
enes we have initiated the study of base-mediated α,µ dehy-
drohalogenations[2] in monoalkyl Group 4 metal trihalides
2 as depicted in Scheme 1. A straightforward and known
route to such monomethyl derivatives as 2 is the interaction
of Group 4 metal tetrachlorides MCl4 (1a–1c, M = Ti, Zr,
Hf) with a methylating agent (MeMgX, MeLi, MenAlCl3–n
,
Me2Zn, or Cp2TiMe2) in a 1:1 ratio.[3] With excess
MeMgX, for example, further methylation of 2 can yield
successively Me2MCl2, Me3MCl and Me4Ti.[4] The impetus
for the present investigation was the question of whether an
excess of methyllithium might act on 2, not as a methylating
agent, but a lithiating agent to produce 3 and ultimately
methylidene 4 by an α,µ elimination of LiCl (Scheme 1, R
= H). In several previous reports the action of two equiv.
of methyllithium was assumed to yield Me2TiCl2 (5) directly
but without corroborating evidence.[5]
Scheme 1.
In order to determine which course of reaction might
take place, either preferentially or randomly, we have
studied the behavior of the individual halides, TiCl4, ZrCl4,
and HfCl4, with two equiv. of methyllithium in an ether/
toluene medium at low temperatures. We had hoped to de-
cide whether the methyl analogs of 3 and 4, namely 5 and
6, would thereby be formed by means of chemical trapping
with benzophenone (7). From the extensive work of Reetz
and coworkers on titanium alkyls,[6]5, if formed, should in-
sert the C=O group of 7 into the C–M bond and give alco-
holate 8, and upon hydrolysis, alcohol 9 (Scheme 2). On the
other hand, were 6 (or its lithiated precursor; cf. infra) pres-
ent, then a smooth methylidenation leading to 1,1-diphenyl-
[‡] Organic Chemistry of Subvalent Transition Metal Complexes,
32. Part 31: Ref.[1]
[a] State University of New York at Binghamton, Department of
Chemistry,
P. O. Box 6000, Binghamton, NY 13902-6000, USA
Fax: +1-607-777-4865
E-mail: jjeisch@binghamton.edu
Eur. J. Org. Chem. 2005, 993–997
DOI: 10.1002/ejoc.200400808
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
993

J. J. Eisch, A. A. Adeosun
SHORT COMMUNICATION
ethylene (10) should ensue. Such expectations have their the active agent, then alcoholate 14 would result. Its decom-
firm substantiation in the extensive studies of the Tebbe rea- position with elimination would afford some amounts of
gent and its many analogs.[7]
three isomeric olefins 13, 15, and 16 (path b). In the actual
trial only olefin 13 was observed with either the Ti or Zr
reagent. This finding reinforces the conclusion that the
structure of the active agent is H2C=MCl2 in both cases.
However, it is important to note that yields of olefin 13
were modest (Ti, 38%; Zr, 25%) and much of ketone 9 was
recovered (62–75%). The most straightforward explanation
for much remaining ketone in this reaction is that some
base has generated the enolate salt of 12. Corroboration for
the presence of the enolate of 12 comes from a reaction
mixture of 9 with 6a, which was worked up with D2O: the
methylene group of 9 was Ͼ90% monodeuterated (cf. in-
fra).
Scheme 2.
Results
Addition of two equiv. of methyllithium in ether to a
solution or suspension of one equiv. of MCl4 (1a–1c, M =
Ti, Zr, or Hf) in toluene and cooled to –78 °C resulted in
a red-brown (Ti) or milky-white suspension (Zr, Hf). The
mixture was allowed to warm to –40 °C and then treated
with 0.90 equiv. of benzophenone (7). Hydrolytic workup
gave a quantitative yield of 1,1-diphenylethylene (10) with
TiCl4 and with ZrCl4. In the case of HfCl4 the yield of 10
was only 27% and the balance of the product was 1,1-di-
phenyl-1-ethanol (9) [73%]. With Scheme 3 as the reference,
the methylidene complex 6a,6b, or 6c (or its lithiated pre-
cursor) was clearly formed, in whole or in part, in each case
and was trapped via intermediate 11 by the benzophe-
none.[8] As will be mentioned below, there is reason to attri-
bute the high yield of the alcohol 9 in the Hf case to the
greater thermal stability of the C–Hf bond in 11 and hence
its partial persistence to the hydrolysis step.[9]
Scheme 4.
Further corroboration for the presence of a methylidene-
like complex in the titanium case was sought by the ad-
dition of one equiv. of diphenylacetylene (17) to the puta-
tive H2C=TiCl2 reagent at –40 °C. Hydrolytic workup re-
vealed that 50% of 17 had been converted into a 1:1 mix-
ture of α-methyl-cis-stilbene (20a) and α-methyl-trans-stil-
bene (20b). In chemical behavior well-precedented by the
reactions of Tebbe-like reagents with acetylenes,[7e,10] such
an outcome supports the cycloaddition reaction proposed
in Scheme 5 to form 18 with subsequent ring opening to
produce conformationally isomeric vinylcarbene complexes
19a and 19b. Random protolytic workup of such equilibrat-
ing conformers would nicely provide a 1:1 cis,trans-mixture
of olefins 20a and 20b.
In a preliminary study it has also been shown that either
H2C=TiCl2 (6a) or H2C=ZrCl2 (6b) in toluene is capable of
reacting as a ROMP catalyst towards norbornene at –40 °C.
Scheme 3.
The white solid obtained upon hydrolytic workup was
1
In order to substantiate that the methylidenating agent shown in both cases to exhibit H and 13C NMR spectra
active in converting benzophenone (7) into 1,1-diphenyleth- identical with those of cis-polynorbornene, as produced by
ylene (10) was 6 or its lithium precursor, rather than 5, pro- known ROMP polymerizations.[11] Apparently, 6a and 6b
piophenone (12) was allowed to react with the titanium or initiate ROMP processes by [2+2] cycloaddition to norbor-
zirconium methylidenating reagent in a 1:1 molar ratio at nene, quite analogous to the manner in which 6a adds to
–40 °C. As shown in Scheme 4, were H2C=MCl2 (6a–6b, M diphenylacetylene (17) to form 18 in Scheme 5 below. How-
= Ti, Zr) the sole active agent, then only olefin 13 would ever, it is noteworthy that the titanium analog 6a was much
be formed (path a). If on the other hand Me2MCl2 (5) were more reactive than the zirconium catalyst 6b.
994
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 993–997

Methylidene-Metal Complexes and Their Active Lithiated Precursors
SHORT COMMUNICATION
gested neutral methylidenating agent is 4 (R = H). However,
the presence of uncomplexed 4 seems unlikely in view of
the known behavior of titanocene methylene (25), as exhib-
ited when generated from the Tebbe reagent[13] or the
Grubbs titanacyclobutane (24) adducts.[14] Rapid dimeriza-
tion to the less reactive 1,3-dititanacyclobutane (26) occurs
(Scheme 7).
Scheme 5.
Scheme 7.
Accordingly, we propose that the active methylidenating
agent generated from MCl4 and methyllithium in toluene is
not free 6 (or, 4, R = H) but a complex of 6 with LiCl,
either as σ complex 27 or π complex 28.
The foregoing findings leave little doubt that some form
of the methylidene complex, 6a–6b, resulted from the 2:1
interaction of methyllithium and MCl4 and was present at
–40 °C when various substrates were added. Nevertheless,
one must still consider whether the dimethylmetal dichlo-
ride 5 might have been the primary reaction product formed
at –78 °C but then decomposed upon warming to –40 °C to
yield 6 (Scheme 6). To address this, TiCl4 in toluene at
–78 °C was treated with two equiv. of MeLi and after 30 min
at that temperature, two equiv. of I2 were then added. Were
5 present, it would have undergone iodinolysis to generate
methyl iodide (21). On the other hand, had 5 already de-
composed to 6, iodinolysis should have led to 22 and then
to ethylene (23), as other methylenedimetallics, such as 25
or 26 have been shown to react.[12] In the present experi-
ment no trace of methyl iodide has been detected and there-
fore no Me2TiCl2 was generated even at –78 °C.
The organolithium form of 6, such as 27, could be re-
sponsible for the extensive enolate salt formation observed
as a side reaction in the methylidenation of propiophenone
(12) [Equation (1)].
(1)
Furthermore, the failure to observe any methylidenation
of ketones in THF or in toluene at 20 °C can be ascribed
to the promoted dissociation of LiCl from 27 or 28 and the
subsequent formation of the unreactive dimer of 6, namely
29.
Scheme 6.
As a fitting subject for continuing studies, a pronounced
solvent effect must be noted: when the MCl4 was dissolved
or dispersed at –78 °C in THF, rather than toluene, and the
methyllithium added, the reaction was then brought either
to –40 °C or to –20 °C and the benzophenone added. In
neither case did any of the benzophenone react. Yet the
hydrolysis of such reaction runs gave copious evolutions of
methane gas, which showed that methyl–metal bonds were
still present. Even for reactions in toluene, when the benzo-
phenone was added at room temperature, rather than
–20 °C, again no reaction of the ketone was observed.
Clearly, the active reagent 6 decomposes above –20 °C.
In line with this interpretation, the reaction given in
Scheme 1 is under continuing study. Our hope is to obtain
both NMR spectroscopic evidence and deuterium-labeling
upon hydrolysis with D2O as support for the presence of
intermediate 29. Furthermore, by conducting the reaction
of MCl4 with methyllithium in the presence of phosphanes,
we hope that such phosphanes will displace LiCl from 27
or 28 to produce a stable monomeric form of 6 useful in
diverse methylidenations.
Finally, it should be borne in mind that in keeping with
their alkylidenating activity both H2C=TiCl2 (6a) and
H2C=ZrCl2 (6b) have exhibited ROMP catalytic activity to-
ward norbornene, and that accordingly, more stable phos-
Discussion
The foregoing results are consistent with the reaction phane derivatives of 6 would be worthy of evaluation as
pathway in toluene as depicted in Scheme 1, where the sug- catalysts in future ROMP processes.
Eur. J. Org. Chem. 2005, 993–997
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
995

J. J. Eisch, A. A. Adeosun
SHORT COMMUNICATION
(10) was obtained in quantitative yield as shown by 1H and 13C
spectroscopy.
Experimental Section
Instrumentation, Analysis, and Starting Reagents: All reactions were
carried out under a positive pressure of anhydrous, oxygen-free ar-
gon. All solvents employed with organometallic compounds were
dried and distilled from a sodium metal-benzophenone ketyl mix-
ture prior to use.[15] The IR spectra were recorded with a Perkin–
Elmer instrument (model 457), and samples were measured either
as mineral oil mulls or as KBr films. The NMR spectra (1H and
13C) were recorded with a Bruker spectrometer (model EM-360)
and tetramethylsilane (Me4Si) was used as the internal standard.
The chemical shifts reported are expressed on the δ scale in parts
per million (ppm) from the Me4Si reference signal. The GC/MS
measurements and analyses were performed with a Hewlett–Pack-
ard GC 5890/Hewlett–Packard 5970 mass-selective-detector instru-
ment. The gas chromatographic analyses were carried out with a
Hewlett–Packard instrument (model 5880) provided with a 2-m
OV-101 packed column or with a Hewlett–Packard instrument
(model 4890) having a 30-m SE-30 capillary column. Melting
points were determined on a Thomas–Hoover Unimelt capillary
melting point apparatus and are uncorrected. In all reaction work-
ups a satisfactory material balance of at least 95% of the expected
mass was obtained. In most cases such reaction mixtures were ana-
lyzed directly by integration of appropriate signals in their 1H
NMR spectra.
Reaction of Methyllithium with Hafnium(IV) Chloride in Toluene: To
anhydrous hafnium(iv) chloride (580 mg, 1.8 mmol) suspended in
toluene (60 mL) at –78 °C was added slowly methyllithium (2.60
mL of 1.4 m solution, 3.6 mmol) in diethyl ether solution at –78 °C
under argon. The resulting white mixture was allowed to stir at
–78 °C for 2h before allowing it to warm up to –40 °C.
A toluene solution of benzophenone (7) [0.33g, 1.81 mmol] was
added to the foregoing solution of assumed complex 6c (M = Hf)
[2.0 mmol] in toluene at –40 °C, and the resulting white mixture
was allowed to warm to room temperature overnight. Upon hydro-
lytic workup, a liquid mixture of 1,1-diphenylethylene (10) [27%]
and 1,1-diphenylethanol (9) [73%] was obtained as shown by 1H
and 13C NMR spectroscopy. 1,1-Diphenylethanol (9): 1H NMR
(CDCl3): δ = 7.00–7.50 (Ar), 2.60 (s, 1 H), 1.80 (s, Me) ppm. 13C
NMR (CDCl3): δ = 148.00, 128.10, 126.87, 125.84 (Ar), 76.16
(COH), and 30.75 (CH3) ppm.
Chemical Trapping of Group 4 Methylidenes with Propiophenone
Titanium-methylidene 6a (M = Ti): A toluene solution of propio-
phenone (12) [1.31 mL, 10 mmol] was added to complex 6a (M =
Ti) [10 mmol] in toluene at –40 °C, and the resulting mixture was
allowed to warm to room temperature overnight. Upon hydrolytic
workup, a liquid mixture of 2-phenyl-1-butene (13) and recovered
propiophenone (12) was obtained in 38% and 62% yields, respec-
tively, as shown by 1H and 13C NMR spectroscopy. 2-Phenyl-1-
butene (13): 1H NMR (CDCl3): δ = 1.10 (t, 3 H), 2.50 (q, 2 H), 5.05
(s, 1 H), 5.27 (s, 1 H), 7.1–7.5 (m, 5 H) ppm. 13C NMR (CDCl3): δ
= 12.92, 28.04, 110.90, 125.98, 127.22, 128.19, 141.51, 150.01 ppm.
Reaction of Methyllithium with Titanium(IV) Chloride in Toluene:
To anhydrous titanium(iv) chloride (1.1 mL, 10 mmol) dissolved in
toluene (60 mL) at –78 °C was added slowly methyllithium
(14.3 mL of 1.4 m solution, 20.0 mmol) in diethyl ether solution
at –78 °C under argon. The resulting reddish-brown mixture was
allowed to stir at –78 °C for a few minutes before being allowed to
warm to –40 °C.
In a reaction run identical with the foregoing, the reaction mixture
1
was worked up with D2O. In the H NMR spectrum of the propio-
A toluene solution of benzophenone (7) [1.82 g, 10 mmol] was
added to the foregoing solution of assumed complex 6a (M = Ti)
[11.1 mmol] in toluene at –40 °C and the resulting reddish-brown
mixture was allowed to warm to room temperature overnight.
Upon hydrolytic workup, 1,1-diphenylethylene (10) was obtained
phenone the integration of the CH2 signal versus the CH3 reso-
nance gave a ratio of 1.05:3.00. This ratio indicates that the methyl-
ene group was Ͼ90% monodeuterated.
Zirconium-methylidene 6b (M = Zr): A toluene solution of propio-
phenone (12) [0.77 mL, 5.9 mmol] was added to a solution of
complex 6b (M = Zr) [5.9 mmol] in toluene at –40 °C, and the
resulting mixture was allowed to warm to room temperature over-
night. Upon hydrolytic workup, a liquid mixture of 2-phenyl-1-but-
ene (13) and recovered propiophenone (12) was obtained in 25%
1
in quantitative yield as shown by H and 13C NMR spectroscopy.
1,1-Diphenylethylene (10):1H NMR (CDCl3): δ = 7.31 (Ar, 10 H),
5.4 (s, 2 H) ppm. 13C NMR (CDCl3): δ = 150.09 (C), 141.49,
128.23, 128.13, 127.65 (Ar), 114.17 (CH2) ppm.
An identical reaction at –78 °C between TiCl4 (10 mmol) in toluene
(60 mL) and methyllithium (20 mmol) in diethyl ether was con-
ducted for 30 min with stirring. Thereupon, at the same tempera-
ture, diiodine (2.2 equiv.) was introduced and the mixture allowed
to come to 25 °C overnight. Hydrolysis and excess iodide removal
with aqueous NaHSO3 and drying of the toluene layer with anhy-
drous NaSO4 yielded a separated toluene layer. Without any evapo-
1
and 75% yields, respectively, as shown by H and 13C NMR spec-
troscopy.
Reaction of Titanium-methylidene 6a (M = Ti) with Diphenylacety-
lene (17): A solution of diphenylacetylene (17) [1.78 g, 10 mmol] in
toluene (60 mL) was added to a solution of complex 6a (M = Ti)
[10 mmol] in toluene at –40 °C, and the resulting reddish-brown
mixture was allowed to warm to room temperature overnight.
Upon hydrolytic workup, a colorless solid residue consisting of di-
phenylacetylene (17), α-methyl-cis-stilbene (20a), and α-methyl-
trans-stilbene (20b) was obtained in amounts of 50%, 25% and
25% yields, respectively, as shown by 1H and 13C NMR spec-
troscopy. Diphenylacetylene (17): 1H NMR (CDCl3): δ = 7.51,
7.41–7.22 (Ar, 10 H) ppm. 13C NMR (CDCl3): δ = 131.59, 128.33,
128.26, 123.31, 89.43 (C=C) ppm.
1
ration the H and 13C NMR spectra of this layer was recorded and
revealed no detectable signals for methyl iodide.
Reaction of Methyllithium with Zirconium(IV) Chloride in Toluene:
To anhydrous zirconium(iv) chloride (1.73 g, 7.4 mmol) suspended
in toluene (60 mL) at –78 °C was added slowly methyllithium
(10.6 mL of 1.4 m solution, 14.8 mmol) in diethyl ether solution
at –78 °C under argon. The resulting milky-white mixture of 6b (M
= Zr) and LiCl was allowed to stir at –78 °C for 2h before allowing
it to warm up to –40 °C.
α-Methyl-cis-stilbene (20a):1H NMR (CDCl3): δ = 7.12–6.9 (Ar, 10
H), 6.84(H), 2.18(3H) ppm. 13C NMR (CDCl3): δ = 144.37–126.4,
17.6 (CH3) ppm.
A toluene solution of benzophenone (7) [1.08 g, 5.9 mmol] was
added to the foregoing solution of assumed of complex 6b (M =
Zr) [7.4 mmol] in toluene at –40 °C. The resulting white mixture
was then allowed to warm to room temperature overnight, and
upon hydrolytic workup, the clear liquid of 1,1-diphenylethylene
α-Methyl-trans-stilbene (20b):1H NMR (CDCl3): δ = 7.25–6.75
(11H); 2.22 (3H) ppm. 13C NMR (CDCl3): δ = 144.37–126.40, 27.3
(CH3) ppm.
996
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 993–997

Methylidene-Metal Complexes and Their Active Lithiated Precursors
SHORT COMMUNICATION
[5] Publications that have assumed that TiCl4 reacts with two
equiv. of methyllithium to form Me2TiCl2 are the following: a)
J. Liu, D. Zhang, H. Huang, Y. Qian, A. S. C. Chan, J. Polym.
Sci. Polym. Chem. Ed .2000, 38, 1639–1641; and b) D. Duncan,
T. Livinghouse, Organometallics 1999, 18, 4421–4428. In the
latter work the supposed “(CH3)2TiCl2” was employed as a
metallating agent for an amino functionality (R–NH2 Ǟ [R–
N=TiCl2]). It should be noted that intermediates 6 or 27 would
be expected to react in a similar way with R–NH2.
Reactions of Methyllithium with Group 4 Chlorides in THF: Individ-
ual reactions, similar to the foregoing, of methyllithium (2 molar
equiv.) with either TiCl4 or ZrCl4 (1 equiv.), but in a THF media,
were conducted at –78 °C. Subsequent treatment of the reaction
mixture, either at –40 °C or at room temperature, gave no product
upon workup. Nevertheless, hydrolyses of such reaction mixtures
gave copious evolution of methane gas; such gas evolution shows
that a C1 carbon–titanium bond was present in the mixture.
[6] M. T. Reetz, “Organotitanium Chemistry”, in Organometallics
in Synthesis (Eds.: M. Schlosser), Wiley, New York, 2002, ch.
7, pp. 107.
[7] a) F. N. Tebbe, G. W. Parshall, G. S. Reddy, J. Am. Chem. Soc.
1978, 100, 3611–3613; b) K. C. Ott, R. H. Grubbs, J. Am. chem.
Soc. 1981, 103, 5922–5923; c) N. A. Petasis, E. I. Bzowej, J.
Am. Chem. Soc. 1990, 112, 6392–6394; d) L. R. Gillion, R. H.
Grubbs, J. Am. Chem. Soc. 1986, 108, 733–735; e) J. J. Eisch,
A. Piotrowski, Tetrahedron Lett. 1983, 24, 2043–2046.
ROMP Process with Norbornene
With H2C=TiCl2 (6a): Anhydrous norbornene (4.71g, 50 mmol) in
toluene (25 mL) was added to the toluene solution (60 mL) of com-
plex 6a (5 mmol) at –40 °C, and the resulting reddish-brown mix-
ture was allowed to warm to room temperature over 10h. After
adding the very dark brown reaction mixture to methanol (60 mL)
at room temperature with vigorous stirring, a white amorphous
solid (1.04 g) precipitated. This was confirmed to be cis-polynor-
[8] a) A preliminary report on certain aspects of the 2:1 reaction
of MeLi and TiCl4 has appeared in published form in a mono-
graph dedicated to the memory of Professor Kazuo Soga: J. J.
Eisch, F. A. Owuor, P. O. Otieno, A. A. Adeosun, in Progress
and Development of Catalytic Olefin Polymerization (Eds.: T.
Sano, T. Uozumi, H. Nakatani, M. Terano), Technology and
Education Publishers, Tokyo, 2000, pp. 88–97; b) Interaction
of methyllithium in diethyl ether with the complex TiCl4·2THF
in toluene at –40 °C in various ratios has been assumed to pro-
duce methyltitanium chlorides of the type, MenTiCl4–n: J. Liu,
D. Zhang, J. Huang, Y. Qian, A. S. C. Chan, J. Poly. Sci. A
Poly. Chem. 2000, 38, 1639–1641. Particularly, a 2:1 molar ratio
of MeLi and TiCl4 was found to act as a potent catalyst for
ROMP processes with dicyclopentadiene. The authors have
proposed that such active catalysts arose from the generation
of Me2TiCl2, which then decomposed in situ to produce
Cl2Ti=CH2. Our work supports the direct formation of
Cl2Ti=CH2 without the intermediacy of Me2TiCl2. Incompat-
ible with the instability ascribed by these authors to Me2TiCl2
at –40 °C is the report that Me2TiCl2, prepared from TiCl4 and
Cp2TiMe2, is a violet-black compound volatile without decom-
position at 25 °C at 0.2 Torr. Its thermal decomposition at
higher temperatures leads to TiCl2 and methane (E. H. de-
Butts, U. S. Patent 3,021,349, 1959/62). It is sufficiently stable
1
bornene by comparison of its H and 13C NMR values with those
in the literature.[8]cis-Polynorbornene: 13C NMR (CDCl3): δ =
134.006, 132.928 (CH), 43.106, 41.401, 38.474, 32.477 (CH2) ppm.
With H2C=ZrCl2 (6b): Anhydrous norbornene (6.71g, 71 mmol) in
toluene (20 mL) was added to the toluene solution (20 mL) of com-
plex 6b (7.1 mmol) at –40 °C, and the resulting colorless solution
was allowed to warm up to room temperature over 10 h. Quenching
the very dark brown mixture with methanol (60 mL) at room tem-
perature with vigorous stirring precipitated a white amorphous so-
lid (0.15 g). This was confirmed to be cis-polynorbornene by com-
parison of its 13C NMR values with literature values for cis-poly-
norbornene.[8]
Acknowledgments
This research has been conducted with the financial support of the
U.S. National Science Foundation, a Senior Scientist Award to
J.J.E. from the Alexander von Humboldt Stiftung of Bonn, Ger-
many, as well as a grant from the Solvay Corporation of Brussels,
Belgium. Furthermore, we are indebted to former group members,
Dr. Fredrick Owuor and Dr. Peter Otieno, and present group mem-
bers, Messrs. Somnath Dutta and John N. Gitua, for valuable ori-
enting experiments.
1
to have its H NMR spectrum recorded at 35 °C (J. F. Hanlan,
J. D. McCowan, Can. J. Chem. 1972, 50, 747–754).
[9] The relative thermal stability of σ C–Hf bonds, compared with
C–Ti and C–Zr bonds, is evidenced by the fact that hafnocene
catalysts in polymerization of olefins lead to polymers of higher
molecular weight because the cationic catalyst site, Cp2Hf+–R,
being of greater thermal stability, can insert a greater number
of olefin monomers. Cf. J. A. Ewen, R. L. Jones, A. Razavi, J.
Am. Chem. Soc. 1988, 110, 6255–6256.
[1] J. J. Eisch, P. R. Munson, J. N. Gitua, Origins Life Evol. Bio-
sphere 2004, 34, 441–454.
[2] By the term, α,µ dehydrohalogenation, we mean to specify the
stepwise proton-removal from an α-carbon atom, followed by
the loss of halide anion from the adjacent metal (µ) to form a
π C=M linkage.
[3] a) K. H. Thiele, K. Jacob, Z. Anorg. Allg. Chem. 1968, 356,
195–201; b) M. T. Reetz, S. H. Kung, M. Hüllmann, Tetrahe-
dron 1986, 42, 2931; c) C. Beerman, H. Bestian, Angew. Chem.
1959, 71, 618–623; d) H. deVries, Recueil Trav. Chim. 1961, 80,
866–878; e) E. H. LeButts, U. S. Patent 3,021,349, 1959/62.
[4] S. Berger, W. Bock, G. Frenking, V. Jonas, F. Müller, J. Am.
Chem. Soc. 1995, 117, 3820–3829. Indeed, because of the ease
with which CH3TiCl3 reacts with any excess of CH3MgI to
form successively (CH3)2TiCl2, (CH3)3TiCl, and (CH3)4Ti, the
preparation of none of the partially methylated derivatives,
(CH3)nTiCl4-n, was attempted in such a reaction. Instead (CH3)4-
Ti was prepared from four equiv. of CH3MgI and TiCl4 at
–40 °C. Then the various (CH3)nTiCl4-n derivatives were ob-
tained at –78 °C by the redistribution reaction between TiCl4
and (CH3)4Ti in the proper stoichiometric ratios.
[10] F. N. Tebbe, R. L. Harlow, J. Am. Chem. Soc. 1980, 102, 6149–
6151.
[11] A. J. Brandolini, D. D. Hills, NMR Spectra of Polymers and
Polymer Additives, Marcel Dekker, New York, 2000.
[12] In their communication: K. C. Ott, R. H. Grubbs, J. Am.
Chem. Soc. 1981, 103, 5922–5923, the authors report that 25
and its dimer 26, prepared in two steps from the Tebbe reagent,
react with I2 to yield Cp2TiI2, 78% of ethylene, and 22% of
methane.
[13] F. N. Tebbe, G. W. Parshall, D. W. Ovenall, J. Am. Chem. Soc.
1979, 101, 5074–5076.
[14] J. B. Lee, T. R. Howard, R. H. Grubbs, J. Am. Chem. Soc. 1980,
102, 6876–6878.
[15] A detailed description for conducting organometallic reactions
in a safe and reproducible manner is given in: J. J. Eisch, Or-
ganometallic Syntheses, Academic Press, New York, 1981, vol.
2, pp. 1–84.
Received November 11, 2004
Eur. J. Org. Chem. 2005, 993–997
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
997