Metalations with group 4 alkylmetal(IV) halides: Expeditious route to metallocene and nonmetallocene procatalysts

Article abstract of DOI:10.1021/om0104621

Group 4 alkylmetal(IV) halides of the type Bu₂M_tCl₂, generated in hydrocarbon media at -78°C by treating M_tCl₄ with 2 equiv of n-butyllithium, function as strong bases toward a variety of Br?nsted acids, E-H, where E = cyclopentadienyl or substituted cyclopentadienyl, 1-alkynyl, indenyl, alkoxy, aryloxy, and disubstituted amino, to form metallocene and nonmetallocene procatalysts, E₂MCl₂, expeditiously and generally in high yield.

Full text of DOI:10.1021/om0104621

4132
Organometallics 2001, 20, 4132-4134
Meta la tion s w ith Gr ou p 4 Alk ylm eta l(IV) Ha lid es:
Exp ed itiou s Rou te to Meta llocen e a n d Non m eta llocen e
P r oca ta lysts1
J ohn J . Eisch,* Fredrick A. Owuor, and Peter O. Otieno
Department of Chemistry, The State University of New York at Binghamton,
Binghamton, New York 13902-6016
Received J une 4, 2001
Summary: Group 4 alkylmetal(IV) halides of the type
Bu2MtCl2, generated in hydrocarbon media at -78 °C
by treating MtCl4 with 2 equiv of n-butyllithium, function
as strong bases toward a variety of Brønsted acids, E-H,
where E ) cyclopentadienyl or substituted cyclopenta-
dienyl, 1-alkynyl, indenyl, alkoxy, aryloxy, and disub-
stituted amino, to form metallocene and nonmetallocene
procatalysts, E2MCl2, expeditiously and generally in high
yield.
1-butene,10 toward a wide variety of unsaturated organic
substrates (6; E ) O, NR, cyclopentadienylidene), such
as ketones, imines, and fulvenes.11 The resulting met-
allocene or nonmetallocene group 4 metal derivatives
(7) constitute a variegated structural array of olefin
polymerization procatalysts12 (Scheme 1).
Our most recent studies have now uncovered yet a
third type of most useful and versatile reactions for the
kinetically stable alkyls Bu2MtCl2 (1), and this is their
facile metalation of a broad range of Brønsted acids,
E-H (8), even at -78 °C in hydrocarbon media. With
E equal to cyclopentadienyl or substituted cyclopenta-
dienyl, to 1-alkynyl, alkoxy (RO), or aryloxy (ArO), and
to disubstituted amino (R2N) groups, the corresponding
metalated derivative E2MtCl2 (9) is formed rapidly and
completely (Scheme 1). These metalations represent an
extraordinarily expeditious route to metallocene and
nonmetallocene procatalysts for olefin polymerization.12
In a one-flask operation MtCl4 dispersed in a hydrocar-
bon medium at -78 °C is treated with 2 equiv of
n-butyllithium to form Bu2MtCl2 (1), and shortly there-
after 2-3 equiv of E-H (8) is added and the mixture
warmed to 20 °C or higher.13 The solvent is removed
under reduced pressure, and E2MtCl2 extracted away
from the LiCl byproduct with hot toluene in a Soxhlet
apparatus. In most cases E2MtCl2 (9) can be recovered
from the toluene extract essentially quantitatively and
pure by NMR spectral criteria.
Because of the central importance of the σ carbon-
transition-metal bond, C-Mt, as the active site in both
Ziegler-Natta heterogeneous2 and metallocene homo-
geneous olefin polymerization catalysts,3 our group has
been exploring the synthesis and chemical reactivity of
early transition metal alkyls over the past decade.4-7
Such studies have led to the discovery of an extraordi-
nary and most useful kinetic solvent effect. As exempli-
fied by the di-n-butylmetal dichlorides of the group 4
metals, Bu2MtCl2 (1), such alkyls synthesized in ether
solvents at -78 °C from MtCl4 and 2 equiv of n-
butyllithium undergo a ready reductive elimination of
its alkyl groups8 upon warming to 0 °C and provide
MtCl2 (2) quantitatively.5,9 MtCl2 can be utilized to
achieve a useful variety of reductions in organic syn-
thesis5,7 or can effect the metalative dimerization of
fulvenes, such as the 6,6-dimethyl derivative 3, to form
the corresponding ansa-metallocene (4) in high yield9
(Scheme 1). In contrast to this mode of decomposition,
when 1 is generated in hydrocarbon media such as
hexane or toluene it shows a remarkable stability
toward reductive elimination (1 f 2) and instead
behaves as a hydrometalating agent, with loss of
The titanium, zirconium, and hafnium derivatives of
Bu2MtCl2 all reacted readily in toluene at -78 °C with
freshly distilled cyclopentadiene or substituted cyclo-
pentadienes (10) to provide quantitatively the corre-
(10) The 1-butene evolved was trapped by passing through a CCl4
solution of Br2 and the 1,2-dibromobutane identified by NMR spec-
troscopy.
(11) Eisch, J . J .; Owuor, F. A.; Shi, X. Organometallics 1999, 18,
1583. The hydrometalating action of Bu2MtCl2 (1) on organic substrates
could conceivably occur via two routes: (1) dissociation by elimination
of 1-butene into H2MtCl2 and subsequent hydrometalation and/or (2)
direct transfer of an H-Mt bond to the organic substrate via a six-
membered ring complex of 1 with the substrate. Which mechanism
prevails remains to be determined.
* To whom correspondence should be addressed. Fax: 607-777-4865.
E-mail: jjeisch@binghamton.edu.
(1) Organic Chemistry of Subvalent Transition Metal Complexes.
23. Part 22: Eisch, J . J .; Gitua, J . N.; Otieno, P. O.; Shi, X. J .
Organomet. Chem. 2001, 624, 229.
(2) Boor, J ., J r. Ziegler-Natta Catalysts and Polymerizations;
Academic Press: New York, 1979; Chapter 11.
(3) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew Chem., Int. Ed. Engl. 1995, 34, 1143.
(4) Eisch, J . J .; Piotrowski, A. M.; Brownstein, S. K.; Gabe, E. J .;
Lee, F. L. J . Am. Chem. Soc. 1975, 107, 7219.
(5) Eisch, J . J .; Boleslawski, M. P. J . Organomet. Chem. 1987, 334,
C1.
(6) Eisch, J . J .; Shi, X.; Lasota, J . Z. Naturforsch. 1995, 50b, 342.
(7) Eisch, J . J .; Shi, X.; Alila, J . R.; Thiele, S. Chem. Ber./ Recl. 1997,
130, 1175.
(8) The butyl groups are lost as a mixture of butane and 1-butene,
which were identified in the condensed ether solvent at -78 °C, by a
combination of 1H and 13C NMR and IR spectral analysis as well as
the chemical trapping of 1-butene with Br2.
(12) Such procatalysts must be admixed with a cocatalyst, such as
RnAlX3-n or MAO, to produce the olefin polymerization catalyst
containing the crucial C-Mt bond.
(13) With indenes and amines (R2NH), prolonged reaction times at
20 °C or heating is required to attain higher yields of E2MtCl2. With
1-alkynes, such as phenylacetylene, the metalation reaction with
Bu2ZrCl2 took place smoothly and cleanly in hexane. Proof of metala-
tion was obtained by treating such a reaction mixture with D2O and
isolating PhCtCD. In toluene, however, even at low temperatures the
reaction between phenylacetylene and Bu2ZrCl2 gives only a mixture
of cyclotrimers and polymer. Heating should be minimal, since it
promotes the decomposition of Bu2MtCl2 into MtCl2.
(9) Eisch, J . J .; Shi, X.; Owuor, F. A. Organometallics 1998, 17, 5219.
10.1021/om0104621 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 08/31/2001

Communications
Organometallics, Vol. 20, No. 20, 2001 4133
Sch em e 1
sponding metallocene dichlorides (11) (eq 1).14a With
indene, the reaction with 1 to produce bis(indenyl)metal
lecular bis-metalation of the isomeric 1,2-dicyclopenta-
dienylethanes with Bu2TiCl2 led smoothly to the ansa-
metallocene dichloride 13.15 Second, 1,2-diols such as
meso-hydrobenzoin react readily with Bu2ZrCl2 to form
the cyclic ansa-nonmetallocene derivative 14.16 The
success of such bis-metalations may well prove ap-
plicable to the synthesis of heteroatom-tethered transi-
tion-metal procatalysts of constrained geometry.17 Ac-
cordingly, our efficient metalations with Bu2MtCl2
reported here offer a novel and facile access to both
ansa-metallocenes and a number of transition-metal
procatalysts of constrained geometry.
Finally, the ready reaction of hydroxy Brønsted acids
(15), such as alcohols or phenols, with Bu2MtCl2 (1)
(14) (a) A typical procedure for the preparation of zirconocene
dichloride is as follows: A suspension of 20 mmol of ZrCl4 in 150 mL
of hexane or toluene, under argon and cooled to -78 °C, was treated
slowly with 40 mmol of BuLi in hexane. The stirred light brown
mixture of Bu2ZrCl2 and LiCl was warmed to 20 °C over 8 h. The
mixture was recooled to -78 °C and then treated with 2.5 equiv of
freshly distilled cyclopentadiene. After 1 h at -78 °C and 4 h at gentle
reflux, the cooled mixture was filtered to remove the LiCl. LiCl was
extracted with portions of pentane-methylene chloride (3:1 v/v), and
the combined filtrate and extracts were freed of volatiles under reduced
pressure. The residue consisted of pure zirconocene dichloride (>95%).
1H and 13C NMR data for the metallocene dichlorides obtained (10, R
) H): Ti, 6.59 and 120.1 ppm; Zr, 6.50 and 116.0 ppm; Hf, 6.40 and
114.5 ppm. (b) Other modifications of solvent, temperature, or possible
catalysts have proved ineffectual or deleterious: (1) heating 1 and
indene in refluxing heptane (bp 98 °C) led to lower yields of 12 because
of the thermal decomposition of Bu2MtCl2 (1) to MtCl2 (2);9 (2) even
dissolution of 1 in toluene at 25 °C accelerated the alkylative reduction
of 1 to 2, possibly due to the π-basicity of toluene promoting the
reductive elimination of the butyl groups from 1; (3) in CH2Cl2, with
or without an additional Lewis acid such as MeAlCl2, the yield of 12
dropped markedly, most likely because of the known cationic polym-
erization of indenes by Lewis acids: Sigwalt, P. J . Polym. Sci. 1961,
52, 15.
dichlorides (12) proceeded less readily and both pro-
longed stirring at 20 °C and heating in hexane at 65 °C
was necessary to give yields of metallocenes ranging
upward of 75% of 12.14b Likewise, 1-alkynes such as
(15) The isomeric 1,2-dicyclopentadienylethanes were prepared ac-
cording to the literature method: Smith, J . A.; Brintzinger, H. H. J .
Organomet. Chem. 1981, 218, 159. Compound 13 was obtained as dark
red crystals (80%). 1H NMR (CDCl3): 6.87 (4H); 6.05 (4H); 3.22 (4H).
(16) Interaction of a hexane-benzene suspension of 10 mmol of 1
(Mt ) Zr), containing the LiCl byproduct, with 1 equivalent of meso-
hydrobenzoin at 50 °C under argon for 1 h led to gas evolution. The
warm suspension was filtered to remove the LiCl, and then the residual
LiCl was extracted further with warm benzene. Solvent removal from
the combined filtrate and extracts left a 95% yield of 14 as a colorless
solid. 1H NMR (C6D6): δ 4.06 (H), 6.89 (5H). 13C NMR: δ 54, 127.3,
128.1, 128.4, 128.7. IR (mineral oil mull): no O-H absorption in the
3300-3500 cm-1 region. The 1H NMR peaks of meso-hydrobenzoin
occur at δ 1.23, 4.31, and 6.77-6.90 and the 13C peaks at δ 79.1, 128.5,
128.7, 129.0, and 129.3.
phenylacetylene reacted cleanly in hexane at 20 °C to
give high yields of (RCtC)2MtCl2. On the other hand,
reaction of 1 under various conditions with fluorene
failed to give any significant amounts of the expected
bis(9-fluorenyl)metal dichloride.
Two classes of diprotic Brønsted acids proved to be
particularly advantageous substrates for reaction with
these novel Bu2MtCl2 metalating agents. First, as
demonstrated specifically with Bu2TiCl2, an intramo-

4134 Organometallics, Vol. 20, No. 20, 2001
Communications
(structure 14 and eq 2) and the slower reaction with
secondary amines (16) (eq 3) provide a reliable and
equiv of TiCl4 in anhydrous toluene at -78 °C and under
argon is added 2 equiv of BuLi in hexane in order to
form Bu2TiCl2. After 30 min of stirring at -78 °C, 2
equiv of anhydrous isopropyl alcohol in hexane is slowly
added to produce Cl2Ti(OPri)2.23 After 30 min of stirring
and warming to 0 °C, the mixture is recooled to -78 °C
and then treated with an additional 2 equiv of BuLi to
yield Bu2Ti(OPri)2. After subsequent warming to 20 °C
the mixture turns black, signaling the formation of
Ti(OPri)2. The volatiles are removed under reduced
pressure, and anhydrous, deoxygenated toluene is added.
The LiCl is filtered off to provide a toluene solution of
black Ti(OPri)2, free of any byproduct lithium salts. Here
again, all of the foregoing chemical transformations can
be conducted in a one-flask operation.
In summary, by the metalating action of group 4
metal derivatives of the type Bu2MtCl2 on various
Brønsted acids, a wide array of both metallocene and
nonmetallocene olefin polymerization procatalysts has
become readily accessible and a highly convenient route
to subvalent transition-metal carbenoid reagents for
organic synthesis has been established.
convenient preparation of group 4 metal complexes
bearing different ligands, such as 17 and 18, which
ligands can be selectively displaced by reaction with a
main-group organometallic reagent. Such derivatives as
17 and 18 can be directly combined with MAO or an
aluminum alkyl to generate a modified olefin polymer-
ization catalyst system,12 or they can be treated with
2 equiv of n-butyllithium in THF to effect selective
loss of the chloride ligands and the formation of the
labile complexes 19 and 20 (eqs 4 and 5). J ust as the
Ack n ow led gm en t. Our research on this topic over
the past decade has been supported at various times
by Akzo Corporate Research America, the U.S. National
Science Foundation, Solvay, SA, Brussels, Belgium, and
the Alexander von Humboldt Stiftung, Bonn, Germany.
Technical advice and assistance have been provided by
Mr. J ohn N. Gitua.
Bu2MtCl2 derivatives themselves, 19 and 20 decompose
cleanly above -78 °C to the corresponding group 4
derivatives (RO)2Mt and (R2N)2Mt. Such so-called tran-
sition-metal carbenoids have been shown to add readily
to CdC, CdO, and related linkages in a process termed
epimetalation18 and have shown great promise in or-
ganic synthesis.19-21 As an illustration of the great
utility of epimetalation in synthesis, consider the con-
version of ethylene (22), via its epimetalation adduct
23, into 24 by means of two different insertions of
reagents into its vicinal C-Ti bonds (eq 6).19
OM0104621
(17) Heteroatom-tethered constrained-geometry catalysts are cov-
ered in the following Dow European patent application: Stevens, J .
C.; Timmers, F. C.; Wilson, D. R.; Schmidt, G. F.; Nickias, P. N.; Rosen,
R. K.; Knight, G. W.; Lai, S. Eur. Patent EP-416-815-A2, March 13,
1991.
(18) Eisch, J . J . J . Organomet. Chem. 2001, 617-618, 14.
(19) Eisch, J . J .; Gitua, J . N.; Otieno, P. O.; Shi, X. J . Organomet.
Chem. 2001, 624, 229.
(20) Kulinkovich, O. G.; Meijere, A.d. Chem. Rev. 2000, 100, 2789.
(21) Sato, F.; Urabe, H.; Okamoto, S. Chem. Rev. 2000, 100, 2835.
(22) (a) Although Ti(OPri)2 can be and indeed has been generated
from the action of 2 equiv of n-butyllithium on Ti(OPri)4 at -78 °C in
hexane, toluene, or THF,19 the generated byproduct, 2 equiv of LiOPri,
is soluble in the hydrocarbon or ether medium and hence cannot be
separated from the Ti(OPri)2 reagent. The LiOPri can by its strongly
basic character interfere with the reactions of Ti(OPri)2 with unsatur-
ated organic substrates. (b) The sequence of steps described here starts
with 20 mmol of TiCl4 dissolved in 80 mL of THF, which at -78 °C
under argon is treated with 40 mmol of n-butyllithium in 25 mL of
hexane.
(23) Titanium(IV) compounds bearing different ligands, such as
ClTi(OPri)3 and Cl2Ti(OPri)2, have previously been shown to be readily
prepared by a redistribution reaction between appropriate molar ratios
of TiCl4 and Ti(OPri)4 at 0 °C: Reetz, M. T.; Westermann, J .; Steinbach,
R.; Wenderoth, B.; Peter, R.; Ostarek, R.; Maus, S. Chem. Ber. 1985,
118, 1421. The method for preparing Cl2Ti(OPri)2 reported here does
not require the synthesis of the Ti(OR)4 component beforehand and
hence is easily extensible to the preparation of other Cl2Ti(OR)2 species
by simply treating Bu2TiCl2 with 2 equiv of the requisite alcohol, ROH.
The preparation of titanium(II) isopropoxide (21) free
of any undesirable LiOPri byproduct22a illustrates the
ease and efficiency of the method.22b To a solution of 1