Generation of homogeneous (sp3-C1)-bridged Cp/amido and Cp/phosphido group 4 metal Ziegler-Natta catalyst systems [2]

Full text of DOI:10.1021/ja0029634

J. Am. Chem. Soc. 2001, 123, 6181-6182
6181
Generation of Homogeneous (sp3-C1)-Bridged
Cp/Amido and Cp/Phosphido Group 4 Metal
Chart 1
Ziegler-Natta Catalyst Systems
Klaus Kunz, Gerhard Erker,* Steve Do¨ring,
Roland Fro¨hlich,‡ and Gerald Kehr
Organisch-Chemisches Institut, UniVersita¨t Mu¨nster
Corrensstrasse 40, D-48149 Mu¨nster, Germany
Scheme 1
ReceiVed August 9, 2000
The silylene-bridged Cp/amido group 4 metal complexes have
played an important role in the development of homogeneous
Ziegler-Natta catalysis. Such “constrained geometry” catalysts,
derived from e.g. 1 (MIVX2 ) ZrCl2 or TiCl2) have been of great
interest because of their polymerization and, especially, copo-
lymerization behavior of R-olefins and other reactive alkenes.1
Cp/amido ligands with larger bridging moieties have been
described,2 but it is remarkable that the corresponding chemistry
of the methylene- and alkylidene-(sp3-C1)-bridged Cp/amido
systems (2) appears not at all developed.3 We here wish to disclose
two rather simple and straightforward synthetic routes to such
systems (2) and their Cp/phosphido relatives (3) and describe first
examples of their use in homogeneous Ziegler-Natta catalysis
(Chart 1).
“constrained geometry” system 1 was obtained by treatment of
tetramethylfulvene 97 with Li[HN(CMe3)] (5b) followed by
deprotonation with tert-butyllithium and transmetalation to Zr to
give [Cp*-CH2-N(CMe3)]Zr(NEt2)2 (2c) in 66% yield [1H/13C
NMR: δ 4.34/68.6 (Cp*CH2N)]6 (Scheme 1).
The first route starts with a “non-enolizable” fulvene, such as
6-tert-butylfulvene (4).4 Addition of, for example, lithium 4-meth-
ylanilide (5a) yields the functionalized lithium cyclopentadienide
6a. Subsequent deprotonation (LDA) gave the dianionic sp3-C1-
bridged “constrained geometry” ligand 7a. Analogous treatment
of the fulvene 4 with lithium tert-butylamide (5b) followed by
deprotonation with tert-butyllithium gave 7b. Transmetalation to
zirconium employing the [Cl2Zr(NEt2)2(THF)2] reagent (8a)5a
proceeded without problems to yield the complexes 2a (66%)
and 2b (71%), respectively. Due to the chiral bridge each of these
complexes exhibits four diastereotopic 1H NMR Cp methine
resonances [2a: δ 6.38, 5.93 (R-CH), 6.10, 6.07 (â-CH)] and
pairs of diastereotopic -N(CH2AB)- signals [2a: δ 3.31, 3.28,
3.19, 3.08].6
Our second route to “CpC1N” systems starts with “non-
enolizable” 6-aminofulvenes, such as 10.8a Treatment of 6-di-
methylaminofulvene (10) with lithium anilide 5c results in an
addition/elimination sequence to cleanly yield the formimino-
substituted Cp-anion system 11 (isolated as a THF adduct in 91%
yield).8b Addition of p-tolyllithium yields the “dianionic” ligand
system isolated as the dilithio compound 12 (94%). Subsequent
transmetalation by treatment with [Cl2Zr(NEt2)2(THF)2] (8a) then
1
gave the “CpC1N”ZrX2 system 2d [75% isolated, H NMR: δ
6.03 (µ-sp3-CH), Cp signals at δ 6.14, 5.90 (R-CH), 6.00, 5.96
AB
(â-CH), four diastereotopic Zr-NCH2 resonances at δ 3.38,
The related sp3-C1-bridged Cp/amido metal complex analogue
2c (“Cp*C1N”ZrX2) of the silylene-bridged (“Cp*Si1N”ZrX2)
3.37, 3.28, and 3.16].
The reagent 11 adds 1 equiv of methyllithium to yield the
“CpC1N”Li2 reagent 13 (96%), which was transmetalated by treat-
ment with [Cl2Ti(NMe2)2] (8b)5b to give the “CpC1N”Ti(NMe2)2
complex 2e (69% isolated). Single crystals of 2e that were suited
for an X-ray crystal structure analysis9 were obtained from
dichloromethane at -20 °C during several days (Scheme 2).
In the crystal complex 2e exhibits a close to tetrahedral
coordination geometry of the central titanium atom. The fused
cyclopentadienide ligand is η5-coordinated, exhibiting a slightly
unsymmetrical array of Ti-C bonds, with Ti-C1 (2.266(2) Å)
being slightly shorter than the Ti-C2/C5 (2.314(2), 2.351(2) Å)
and Ti-C3/C4 bonds (2.402(2), 2.424(2) Å). The C1-C6 vector
(1.505(2) Å) forms an angle of 155.3° with the Cp-plane (Cp-
* Author for correspondence. E-mail: erker@uni-muenster.de.
‡ X-ray crystal structure analysis.
(1) Reviews: McKnight, A. L.; Waymouth, R. M. Chem. ReV. 1998, 98,
2587-2598. Okuda, J.; Eberle, T. Half-Sandwich Complexes as Metallocene
Analogues. In Metallocenes: Synthesis, ReactiVity, Applications; Togni, A.,
Haltermann, R. L., Eds.; Wiley-VCH: Weinheim, 1998; Vol. 1, pp 415-
453.
(2) (a) Diaz, H. V. R.; Wang, Z.; Bott, S. G. J. Organomet. Chem. 1996,
508, 91-99. Enders, M.; Rudolph, R.; Pritzkow, H. J. Organomet. Chem.
1997, 459, 251-256. Sinnema, P.-J.; van der Veen, L.; Spek, A. L.; Veldman,
N.; Teuben, J. H. Organometallics 1997, 16, 4245-4247. Witte, P. T.;
Meetsma, A.; Hessen, B.; Budzelaar, P. H. M. J. Am. Chem. Soc. 1997, 119,
10561-10562. Gomes, P. T.; Green, M. L. H.; Martins, A. M. J. Organomet.
Chem. 1998, 551, 133-138. (b) Rieger, B. J. Organomet. Chem. 1991, 420,
C17-C20. Christie, S. D. R.; Man, K. W.; Whitby, R. J.; Slawin, A. M. Z.
Organometallics 1999, 18, 348-359. (c) For sp2-C1-bridged analogues see:
Duda, L.; Erker, G.; Fro¨hlich, R.; Zippel, F. Eur. J. Inorg. Chem. 1998, 1153-
1162. Bertuleit, A.; Ko¨nemann, M.; Duda, L., Erker, G.; Fro¨hlich, R. Top.
Catal. 1999, 7, 37-44.
(6) Typical example: 2c: 290 mg (66%) of 2c isolated as a colorless oil.
Anal. Calcd for C22H43N3Zr (440.8): C, 59.95; H, 9.83; N, 9.53. Found: C,
59.10; H, 10.54; N, 9.67. 1H NMR (THF-d8, 200 MHz): δ 4.34 (s, 2H, CH2),
3.5-3.2 (m, 8H, NCH2CH3), 2.08, 2.06 (s, each 6H, CpCH3), 1.15 (s, 9H,
CMe3), 0.97 (t, 12H, NCH2CH3). 13C NMR (THF-d8, 150 MHz): δ 119.5
(ipso-C), 68.6 (CH2), 55.6/29.4 (CMe3), 43.5/15.2 (NCH2CH3), 11.2/10.5
(CpCH3).
(3) Ko¨nemann, M.; Erker, G.; Fro¨hlich, R.; Wu¨rthwein, E.-U. J. Am. Chem.
Soc. 1997, 119, 11155-11164.
(4) (a) Stone, K. L.; Little, R. D. J. Org. Chem. 1984, 49, 1849-1853. (b)
For Cp-anion syntheses by nucleophilic addition to fulvenes see, e.g.: Ziegler,
K.; Scha¨fer, W. Liebigs Ann. Chem. 1934, 511, 101-109. Ziegler, K.; Gellert,
H.-G.; Martin, H.; Nagel, K.; Schneider, J. Liebigs Ann. Chem. 1954, 589,
91-121. Sullivan, M. F.; Little, W. F. J. Organomet. Chem. 1967, 8, 277-
285. Renaut, P.; Tainturier, G.; Gautheron, B. J. Organomet. Chem. 1978,
148, 35-42.
(7) (a) Hashimoto, H.; Tobita, H.; Ogino, H. Organometallics 1993, 12,
2182-2187. See also: Do¨ring, S.; Erker, G. Synthesis 2001, 43-45. (b)
Heidemann, T.; Jutzi, P. Synthesis 1994, 777-778.
(8) (a) Hafner, K.; Schulz, G.; Wagner, K. Liebigs Ann. Chem. 1964, 678,
39-53. See also: Hafner, K.; Vo¨pel, K. H.; Ploss, G.; Ko¨nig, C. Org. Synth.
1967, 47, 52-54. (b) Kunz, K.; Erker, G.; Kehr, G.; Fro¨hlich, R. Organo-
metallics 2001, 20, 392-400.
(5) (a) Kempe, P.; Brenner, S.; Arndt, P. Z. Anorg. Allg. Chem. 1995, 621,
2021-2024. (b) Benzing, E.; Kornicker, W. Chem. Ber. 1961, 94, 2263-
2267.
(9) For details, see the Supporting Information.
10.1021/ja0029634 CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/20/2001

6182 J. Am. Chem. Soc., Vol. 123, No. 25, 2001
Communications to the Editor
Table 1. Selected Alkene Polymerization Reactions That Were
Carried Out with “CpC1N”MX2 and “CpC1P”MX2/MAO
Ziegler-Natta Catalystsa
Scheme 2
complex
M
mg[cat]b
g polymer
ethene/octenec
actd
ethene polymerization (60 °C):
1ae
2a
Zr
Zr
Zr
Zr
Ti
Zr
17.1
20.0
20.0
21.5
21.0
21.0
2.4
1.1
-
-
-
-
-
-
29
13
53
101
114
910
1be
2b
3a
4.9
6.3g
13.5
21.0h
3b
ethene/1-octene copolymerization (90 °C):
3a
Ti
Zr
Zr
Zr
Zr
Zr
16.0
20.0
19.0
18.0
20.0
21.0
0.5f,i
3.3
5:1
4:1
13:1
4:1
3:1
6:1
22
37
47
660
420
2240
2b
2c
4.2
1ae
1be
3b
28.8f,k
10.3f,i
51.5f,i
a Ethene polymerizations carried out in toluene at 60 °C, copoly-
merizations in toluene/1-octene (1:1) at 90 °C/1 h, 2 bar ethene unless
indicated; Al:Zr ≈ 700. b mg zirconium or titanium complex. c Com-
ponent ratio in the obtained copolymer determined by 13C NMR
analysis. d In g polymer/mmol [Zr] or [Ti]‚h‚bar. e “Cp*Si1N”ZrCl2 (1a)
f
and “Cp*Si1N”Zr(NMe2)2 (1b) used for a comparison. At 1 bar ethene
Figure 1. Molecular structure of 2e. Selected bond lengths (Å) and angles
(deg): C1-C2 1.413(2), C2-C3 1.394(3), C3-C4 1.400(3), C4-C5
1.399(3), C1-C5 1.407(2), C6-C7 1.517(2), N8-C9 1.387(2), N15-
C16 1.449(3), N15-C17 1.449(3), N18-C19 1.445(2), N18-C20
1.452(2), C1-C6-N8 99.1(1), C1-C6-C7 112.8(1), C6-N8-Ti 104.3(1),
C6-N8-C9 119.1(1), C9-N8-Ti 136.2(1), N8-Ti-N15 105.8(1), N8-
Ti-N18 112.8(1), N15-Ti-N18 102.3(1).
pressure. g Reaction time: 40 min. h Reaction time: 15 min. i Reaction
time: 30 min. k Reaction time: 45 min.
NR/PR group, but were often found to be higher as compared to
the conventional “Cp*Si1N”Zr-derived catalysts under comparable
laboratory conditions. Especially the new sp3-C1-bridged Cp/
phosphidozirconium systems show increased polymerization
activities (see Table 1). The new systems also form active catalysts
for ethene/1-octene copolymerization. At 90 °C a considerable
uptake of the linear 1-alkene was observed (up to ∼20% 1-octene
found incorporated in the copolymer under the applied nonopti-
mized conditions; see Table 1) leading to long-chain-branched
polymer structures.1c,13 Again, the “CpC1P”Zr-derived catalyst
system is remarkably active also in ethene/1-octene copolymer-
ization, relative to the conventional reference systems 1b and 1a/
MAO under comparable conditions.
Scheme 3
This study shows that the “CpC1N”MIVX2 carbon relatives (2)
and their “CpC1P”MIVX2 analogues (3) of the well established
“Cp*Si1N”MIVX2 “constrained geometry” Cp/amido systems (1)1c
are readily available in good yields by means of rather straight-
forward synthetic routes. These new complexes serve as suitable
components for the generation of active new Ziegler-Natta cata-
lyst systems that show an interesting potential in CC-bond forming
catalysis. The application-profile of the new “CpC1N” and
“CpC1P” metal catalysts is currently explored in our laboratory.
(centroid)-C1-C6). The C1-C6-N8 angle amounts to 99.1(1)°,
and the adjacent C6-N8 bond length is 1.476(2) Å. The N8-Ti
distance is found at 2.006(1) Å, which is markedly longer than
the adjacent Ti-N15 (1.911(2) Å) and Ti-N18 (1.898(1) Å)
bonds. The observed lengthening of the Ti-N8 bond may indicate
some increased constraint of the “CpC1N”Ti framework of 2e,
which is also reflected by the markedly reduced N8-Ti-Cp-
(centroid) angle of 95.6° relative to that of the “CpSi1N”MIV
frameworks of the otherwise closely related complexes [Cp*-
SiMe2-N(CMe3)]Zr(NMe2)2 at 100.2° or [Cp-SiMe2-N(CMe3)]-
Ti(NMe2)2 at 105.5°10 (Figure 1).
Acknowledgment. Financial support from the Fonds der Chemischen
Industrie and the Deutsche Forschungsgemeinschaft is gratefully ac-
knowledged.
The analogous alkylidene-bridged Cp/phosphido (“CpC1P”)
constrained geometry Ti and Zr systems 3 were prepared starting
by deprotonation of cyclohexylphosphine, followed by the addi-
tion to 6,6-dimethylfulvene to yield 15 (accompanied by ∼20%
of the 2-propenyl-CpLi deprotonation product).7b,11 Subsequent
deprotonation of 15 with LDA followed by transmetalation using
8a or 8b gave good yields of the “CpC1P”MX2 complexes 3b
(Zr, 72%) and 3a (Ti, 62%)12 (Scheme 3).
Supporting Information Available: Spectroscopic data of the new
compounds, including 13C NMR spectra of the obtained copolymers, and
details of the X-ray crystal structure analysis of complex 2e (PDF). This
material is available free of charge via the Internet at http://pubs.acs.org.
JA0029634
(12) 3b: 312 mg (72%) isolated as a red oil. Anal. Calcd for C22H41N2PZr
1
(455.8): C, 57.98; H, 9.07. Found: C, 58.27; H, 8.61%. H NMR (toluene-
The “CpC1N”MIV(NR2)2 and “CpC1P”MIV(NR2)2 complexes 2
and 3 gave active homogeneous Ziegler-Natta catalysts when
treated with excess methylalumoxane. Ethene polymerization
activities with the new catalyst systems depended on the specific
d8, 600 MHz, 298 K): δ 5.92, 5.47 (m, each 2 H, â- and R-H of Cp), 3.26,
3.15 (m, each 8 H, NCH2), 1.62 (d, 3JPH ) 10 Hz, CMe2), 1.99-1.23 (m, 11
H, C6H11), 0.93 (t, 3J ) 6.0 Hz, 12 H, NCH2CH3). 13C NMR (toluene-d8, 150
MHz, 298 K): δ 124.0 (ipso-C of Cp), 108.1 (â-CH of Cp), 106.4 (3JPC
3.6 Hz, R-CH of Cp), 42.5 (3JPC e 2 Hz, NCH2), 33.2 (CMe2), 30.9 (2JPC
)
)
13 Hz, C(CH3)2), 35.6 (1JPC ) 38 Hz, CH of C6H11), 36.0 (2JPC ) 16 Hz),
27.6 (3JPC ) 11 Hz), 26.9 (CH2 of C6H11), 16.1 (NCH2CH3). 31P NMR (toluene-
d8, 81 MHz, 298 K): δ -11.5.
(10) Carpenetti, D. W.; Kloppenburg, L.; Kupec, J. T.; Petersen, J. L.
Organometallics 1996, 15, 1572-1581.
(11) For metal complexes containing monoanionic Cp-CMe2-PHR- ligands
see: Koch, T.; Blaurock, S.; Somoza, F. B., Jr.; Voigt, A.; Kirmse, R.; Hey-
Hawkins, E. Organometallics 2000, 19, 2556-2563.
(13) Wang, W.-J.; Kolodka, E.; Zhu, S.; Hamielec, A. E. J. Polym. Sci.,
Part A: Polym. Chem. 1999, 37, 2949-2957. Liu, W.; Ray III, D. G.; Rinaldi,
P. L. Macromolecules 1999, 32, 3817-3819.