Uncovering alternative reaction pathways taken by group 4 metallocene cations: Facile intramolecular CH activation of Cp-(dimethylamino)alkyl substituents by a methylzirconocene cation

Article abstract of DOI:10.1021/om970164x

Alkyl- and aryllithium reagents add cleanly to the electrophilic carbon center C6 of 6-(N,N-dimethylamino)fulvenes to yield the corresponding substituted cyclopentadienyllithium systems Li[C₅H₄-CR¹R²NMe₂]. Subsequent treatment with ZrCl₄·2THF gives the corresponding Cp-functionalized zirconocene dichlorides. These were reacted with methyllithium to give the (C₅H₄CR¹R²NMe₂) ₂Zr(CH₃)₂ complexes 11a (R¹ = R¹ = CH₃) and 11b (R¹ = CH₃, R² = Ph), respectively. Treatment of 11 with tris(pentafluorophenyl)borane was carried out to generate the corresponding alkylmetallocene cations (12), which turned out to be unstable under the reaction conditions applied (-20 °C) with regard to liberation of 1 equiv of methane by CH activation at a methyl group adjacent to nitrogen and formation of the spiro-metallocene complex systems 13. CH activation may be a major reaction pathway open to alkylzirconocene cation systems under suitable reaction conditions.

Full text of DOI:10.1021/om970164x

Organometallics 1997, 16, 2891-2899
2891
Un cover in g Alter n a tive Rea ction P a th w a ys Ta k en by
Gr ou p 4 Meta llocen e Ca tion s: F a cile In tr a m olecu la r CH
Activa tion of Cp -(Dim eth yla m in o)a lk yl Su bstitu en ts by
a Meth ylzir con ocen e Ca tion
Axel Bertuleit, Cornelia Fritze, Gerhard Erker,* and Roland Fro¨hlich
Organisch-Chemisches Institut der Universita¨t Mu¨nster, Corrensstrasse 40,
D-48149 Mu¨nster, Germany
Received February 28, 1997X
Alkyl- and aryllithium reagents add cleanly to the electrophilic carbon center C6 of 6-(N,N-
dimethylamino)fulvenes to yield the corresponding substituted cyclopentadienyllithium
systems Li[C5H4-CR1R2NMe2]. Subsequent treatment with ZrCl4‚2THF gives the corre-
sponding Cp-functionalized zirconocene dichlorides. These were reacted with methyllithium
to give the (C5H4CR1R2NMe2)2Zr(CH3)2 complexes 11a (R1 ) R1 ) CH3) and 11b (R1 ) CH3,
R2 ) Ph), respectively. Treatment of 11 with tris(pentafluorophenyl)borane was carried
out to generate the corresponding alkylmetallocene cations (12), which turned out to be
unstable under the reaction conditions applied (-20 °C) with regard to liberation of 1 equiv
of methane by CH activation at a methyl group adjacent to nitrogen and formation of the
spiro-metallocene complex systems 13. CH activation may be a major reaction pathway
open to alkylzirconocene cation systems under suitable reaction conditions.
In tr od u ction
taken to suppress the prevailing tendency for insertion
reactions.3 Side chains that contain potentially coor-
dinating groups have been attached to the Cp rings of
group 4 metallocenes previously,4 and it was hoped to
alter the metallocene cation chemistry by the ensuing
internal coordination. However, the methods of group
4 metallocene cation formation used in those studies
were apparently not compatible with the pendent
functional groups.5 We have now prepared a related
series of titanocene and zirconocene complexes having
substituted (dimethylamino)methyl substituents at their
Cp rings and activated them by treatment with the
strong organometallic Lewis acid tris(pentafluorophen-
yl)borane.6 When the Cp-functionalized group 4 met-
allocene cations are generated in this way, an important
alternative reaction pathway becomes apparent, which
to our knowledge has remained dormant in previous
studies due to other, more favorable alternatives.
Alkylzirconocene cations play a prominent role as the
active species in the homogeneous Ziegler polymeriza-
tion of alkenes.1 Their chemistry, as it is known so far,
has been dominated by the enormous ease with which
these systems undergo insertion reactions into the metal
to carbon bond (and the metal to hydrogen bond,
respectively).2 Much less is known about other reaction
patterns of alkyl- or hydridozirconocene cation systems
that might become favored when suitable measures are
* FAX: +49 251 8339772. E-mail: erker@uni-muenster.de.
X Abstract published in Advance ACS Abstracts, May 15, 1997.
(1) Sinn, H.; Kaminsky, W. Adv. Organomet. Chem. 1980, 18, 99.
J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325. Aulbach, M.;
Ku¨ber, F. Chem. Unserer Zeit 1994, 28, 197. Brintzinger, H.-H.;
Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R. Angew. Chem.
1995, 107, 1255; Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255 and references
cited in these articles.
(2) (a) Examples of experimental studies: Guram, A. S.; J ordan, R.
F. J . Org. Chem. 1993, 58, 5595. Guram, A. S.; J ordan, R. F.
Organometallics 1990, 9, 2190. Eisch, J . J .; Caldwell, K. R.; Werner,
S.; Kru¨ger, C. Organometallics 1991, 10, 3417. Eshuis, J . J . W.; Tan,
Y. Y.; Meetsma, A.; Teuben, J . H. Organometallics 1992, 11, 362. Guo,
Z.; Swenson, D. C.; J ordan, R. F. Organometallics 1994, 13, 1424.
Kreuder, C.; J ordan, R. F.; Zhang, H. Organometallics 1995, 14, 2993.
(b) Theoretical studies: J olly, C. A.; Marynick, D. S. J . Am. Chem.
Soc. 1989, 111, 7968. Kawamura-Kuribayashi, H.; Koga, N.; Moro-
kuma, K. J . Am. Chem. Soc. 1992, 114, 8687. Prosenc, M.-H.; J aniak,
C.; Brintzinger, H.-H. Organometallics 1992, 11, 4036. J aniak, C. J .
Organomet. Chem. 1993, 452,63. Woo, T. K.; Fan, L.; Ziegler, T.
Organometallics 1994, 13, 432; 2252. Meier, R. J .; van Doremaele, G.
H. J .; Iarlori, S.; Buda, F. J . Am. Chem. Soc. 1994, 116, 7274. Fan, L.;
Harrison, D.; Woo, T. K.; Ziegler, T. Organometallics 1995, 14, 2018.
J ensen, V. R.; Børve, K. J .; Ystenes, M. J . Am. Chem. Soc. 1995, 117,
4109. Yoshida, T.; Koga, N.; Morokuma, K. Organometallics 1995, 14,
746. Hyla-Kryspin, I.; Niu, S.; Gleiter, R. Organometallics 1995, 14,
964. Lohrenz, J . C. W.; Woo, T. K.; Ziegler, T. J . Am. Chem. Soc. 1995,
117, 12793. Støvneng, J . A.; Rytter, E. J . Organomet. Chem. 1996,
519, 277. Margl, P.; Lohrenz, J . C. W.; Ziegler, T.; Blo¨chl, P. E.
J . Am. Chem. Soc. 1996, 118, 4434 and references cited in these
articles.
(3) (a) See for representative examples of addition reactions to
functional groups: Bochmann, M.; Wilson, L. M.; Hursthouse, M. B.;
Motevalli, M. Organometallics 1988, 7, 1148. Borkowsky, S. L.; J ordan,
R. F.; Hinch, G. D. Organometallics 1991, 10, 1268. Horton, A. D.;
Orpen, A. G. Organometallics 1992, 11, 8. Horton, A. D. Organome-
tallics 1992, 11, 3271. Borkowsky, S. L.; Baenziger, N. C.; J ordan, R.
F. Organometallics 1993, 12, 486. Alelyunas, Y. W.; Guo, Z.; La Pointe,
R. E.; J ordan, R. F. Organometallics 1993, 12, 544. Guram, A. S.; Guo,
Z.; J ordan, R. F. J . Am. Chem. Soc. 1993, 115, 4902. (b) Pyridine
activation: J ordan, R. F.; Taylor, D. F. J . Am. Chem. Soc. 1989, 111,
778. J ordan, R. F.; Guram, A. S. Organometallics 1990, 9, 2116. Guram,
A. S.; J ordan, R. F.; Taylor, D. F. J . Am. Chem. Soc. 1991, 113, 1833.
Guram, A. S.; J ordan, R. F. Organometallics 1991, 10, 3470. Guram,
A. S.; J ordan, R. F. J . Org. Chem. 1992, 57, 5994. Rodewald, S.; J ordan,
R. F. J . Am. Chem. Soc. 1994, 116, 4491. (c) Allyl complex formation:
Christ, C. S.; Eyler, J . R.; Richardson, D. E. J . Am. Chem. Soc. 1988,
110, 4038; 1990, 112, 596. Alameddin, N. G.; Ryan, M. F.; Eyler, J . R.;
Siedle, A. R.; Richardson, D. E. Organometallics 1995, 14, 5005. (d)
Organometallic adduct formation: Bochmann, M.; Lancaster, S. J .
Angew. Chem. 1994, 106, 1715; Angew. Chem., Int. Ed. Engl. 1994,
33, 1634. Bochmann, M.; Lancaster, S. J . J . Organomet. Chem. 1995,
497, 55. Deck, P. A.; Marks, T. G. J . Am. Chem. Soc. 1995, 117,
6128.
S0276-7333(97)00164-7 CCC: $14.00 © 1997 American Chemical Society

2892 Organometallics, Vol. 16, No. 13, 1997
Bertuleit et al.
Sch em e 1
Resu lts a n d Discu ssion
locenes used for this study bear differently substituted
(dimethylamino)methyl substituents at their Cp-ligand
systems. The specific systems differ with regard to the
substituents that they have attached at the single
carbon center that connects the Cp ring and the NMe2
functional group. For the preparation of these Cp-
functionalized group 4 metallocene complexes we de-
vised a new synthesis based on the general fulvene
route7 to Cp-ligand systems.
As a typical example bis[[1-(N,N-dimethylamino)-
ethyl]cyclopentadienyl]zirconium dichloride (9a ) was
prepared in the following way starting from 6-(dimethyl-
amino)fulvene (5) (Scheme 1). The amino-substituted
fulvene system 5 is readily available according to Hafner
et al.8 by treatment of the (N,N-dimethylamino)meth-
oxymethyl cation (3; which in turn was prepared from
N,N-dimethylformamide by alkylation with dimethyl
sulfate) with sodium cyclopentadienide. Addition of
methyllithium to the fulvene 5 produced the substituted
cyclopentadienyl ligand system 7a in excellent yield.
The anionic ligand system 7a was then reacted with
ZrCl4‚2THF in a 2:1 molar ratio in diethyl ether.
P r ep a r a tion of th e Cp -(Dim eth yla m in o)a lk yl-
Su bstitu ted Meta llocen e Com p lexes. The metal-
(4) For typical examples, see, e.g.: (a) Tueting, D. R.; Iyer, S. R.;
Schore, N. E. J . Organomet. Chem. 1987, 320, 349. Bensley, D. M.;
Mintz, E. A.; Sussangkam, S. J . J . Org. Chem. 1988, 53, 4417. Qian,
Y.; Li, G.; Chen, W.; Li, B.; J in, X. J . Organomet. Chem. 1989, 373,
185. Huang, Q.; Quian, Y.; Tang, Y. J . Organomet. Chem. 1989, 368,
277. Paolucci, G.; Fischer, R. D.; Benetollo, F.; Seraglia, R.; Bombieri,
G. J . Organomet. Chem. 1991, 412, 327. Wang, T.-F.; Lee, T.-Y.; Wen,
Y.-S.; Lin, L.-K. J . Organomet. Chem. 1991, 403, 353. Wang, T.-F.;
Lee, T.-Y.; Chou, J .-W.; Ong, C.-W. J . Organomet. Chem. 1992, 423,
31. Wang, T.-F.; Wen, Y.-S. J . Organomet. Chem. 1992, 439, 155.
Herrmann, W. A.; Anwander, R.; Munck, F.; Scherer, W. Chem. Ber.
1993, 126, 331. Kettenbach, R. T.; Bonrath, W.; Butenscho¨n, H. Chem.
Ber. 1993, 126, 1657. J utzi, P.; Dahlhaus, J .; Kristen, M. O. J .
Organomet. Chem. 1993, 450, C1. J utzi, P.; Dahlhaus, J . Synthesis
1993, 684. Paolucci, G.; D’Ippolito, R.; Ye, C.; Qian, C.; Gra¨per, J .;
Fischer, D. R. J . Organomet. Chem. 1994, 471, 97. van der Hende, J .
R.; Hitchcock, P. B.; Lappert, M. F.; Nile, T. A. J . Organomet. Chem.
1994, 472, 79. Paolucci, G.; Ossola, F.; Bettinelli, M.; Sessoli, R.;
Benetollo, F.; Bombieri, G. Organometallics 1994, 13, 1746. Dahlhaus,
J .; Bangel, M.; J utzi, P. J . Organomet. Chem. 1994, 474, 55. J utzi, P.;
Bangel, M. J . Organomet. Chem. 1994, 480, C18. Herrmann, W. A.;
Morawietz, M. J . A.; Priermeier, T. Angew. Chem. 1994, 106, 2025;
Angew. Chem., Int. Ed. Engl. 1994, 33, 1938. Siemeling, U.; Neumann,
B.; Stammler, H.-G. Z. Naturforsch. 1994, 49b, 683. J utzi, P.; Kle-
imeier, J . J . Organomet. Chem. 1995, 486, 287. Fryzuk, M. D.; Mao,
S. S. H.; Duval, P. B.; Rettig, S. J . Polyhedron 1995, 14, 11. Siemeling,
U.; Vorfeld, U.; Neumann, B.; Stammler, H.-G. Chem. Ber. 1995, 128,
481. Blais, M. S.; Rausch, M. D. J . Organomet. Chem. 1995, 502, 1.
Christoffers, J .; Bergman, R. G. Angew. Chem. 1995, 107, 2423; Angew.
Chem., Int. Ed. Engl. 1995, 34, 2266. Luttikhedde, H. J . G.; Leino, R.
P.; Wile´n, C.-E.; Na¨sman, J . H.; Ahlgre´n, M. J .; Pakkanen, T. A.
Organometallics 1996, 15, 3092 and references cited in these articles.
(b) Stahl, K. P.; Boche, G.; Massa, W. J . Organomet. Chem. 1984, 277,
113. Morcos, D.; Tikkanen, W. J . Organomet. Chem. 1989, 371, 15.
Schenk, W. A.; Labunde, C. Chem. Ber. 1989, 122, 1489. Szymoniak,
J .; Kubicki, M. M.; Besanc¸on, J .; Moise, C. Inorg. Chim. Acta 1991,
180, 153. Schenk, W. A.; Neuland-Labunde, C. Z. Naturforsch. 1991,
46b, 573. Tikkanen, W.; Ziller, J . W. Organometallics 1991, 10, 2266.
Ogasa, M.; Rausch, M. D.; Rogers, R. D. J . Organomet. Chem. 1991,
405, 279. Tikkanen, W.; Kim, A. L. Lam, K. B.; Ruekert, K. Organo-
metallics 1995, 14, 1525. Plenio, H.; Burth, D. J . Organomet. Chem.
1996, 519, 269. (c) Okuda, J .; Zimmermann, K. H. J . Organomet. Chem.
1988, 344, C1. Erker, G.; Aul, R. Organometallics 1988, 7, 2070. Alt,
H. G.; Han, J . S. Thewalt, U. J . Organomet. Chem. 1993, 456, 89.
Butakoff, K. A.; Lemenovskii, D. A.; Mountford, P.; Kuz’mina, L. G.;
Churakov, A. V. Polyhedron 1996, 15, 489.
(5) Reviews: J utzi, P.; Dahlhaus, J . Phosphorus, Sulfur Silicon
Relat. Elem. 1994, 87, 73. J utzi, P.; Dahlhaus, J . Coord. Chem. Rev.
1994, 137, 179. Okuda, J . Comments Inorg. Chem. 1994, 16, 185. J utzi,
P.; Siemeling, U. J . Organomet. Chem. 1995, 500, 175.
(6) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994, 116,
10015 and references cited therein. Temme, B.; Erker, G.; Fro¨hlich,
R.; Grehl, M. Angew. Chem. 1994, 106, 1570, Angew. Chem., Int. Ed.
Engl. 1994, 33, 1480. Temme, B.; Karl, J .; Erker, G. Chem. Eur. J .
1996, 2, 919.
(7) Ziegler, K.; Scha¨fer, W. J ustus Liebigs Ann. Chem. 1934, 511,
101. Ziegler, K.; Gellert, H.-G.; Martin, H.; Nagel, K.; Schneider, J .
J ustus Liebigs Ann. Chem. 1954, 589, 91. Sullivan, M. F.; Little, W.
F. J . Organomet. Chem. 1967, 8, 277. Renaut, P.; Tainturier, G.;
Gautheron, B. J . Organomet. Chem. 1978, 148, 35, 43. Brickhouse,
M. D.; Squires, R. R. J . Am. Chem. Soc. 1988, 110, 2706. Okuda, J .
Chem. Ber. 1989, 122, 1075. Clark, T. J .; Killian, C. M.; Luthra, S.;
Nile, T. A. J . Organomet. Chem. 1993, 462, 247. Squires, R. R. Acc.
Chem. Res. 1992, 25, 461.
(8) Hafner, K.; Vo¨pel, K. H.; Ploss, G.; Ko¨nig, C. Org. Synth. 1967,
47, 52 and references cited therein.

Group 4 Metallocene Cation Reaction Pathways
Organometallics, Vol. 16, No. 13, 1997 2893
Extraction with dichloromethane gave the correspond-
ing 1,1′-bis[1-(N,N-dimethylamino)ethyl]-substituted zir-
conocene dichloride (9a ) as a 1:1 mixture of the meso-
and rac-diastereomers in a combined yield of 44%.
In a similar way the 1-(N,N-dimethylamino)pentyl-
substituted metallocene system 9b was prepared start-
ing from the fulvene 5, to which n-butyllithium was
added. Again, the corresponding zirconocene dichloride
(9b) was obtained as a 1:1 mixture of meso-9b and rac-
9b. In this case, however, it was possible to separate
the rac-9b isomer from the mixture and obtain it pure,
albeit in a low yield of 8%. By applying a solvent dif-
fusion method, single crystals of the chiral metallocene
complex 9b could even be obtained that were suited for
an X-ray crystal structure determination (see below).
An analogous synthetic route was then started from
N,N-dimethylacetamide. O-Methylation followed by
condensation with NaCp gave the fulvene 6. To this
was added methyllithium to yield the Li[C5H4CMe2-
NMe2] reagent (8a ). Subsequent treatment with ZrCl4‚-
2THF then gave the zirconium complex 10a in good
yield (∼70% isolated).
F igu r e 1. View of the molecular geometry of the metal-
locene enantiomer (R,R)-9b with nonsystematic atom-
numbering scheme. Selected bond lengths (Å) and angles
(deg): Zr-Cl 2.4529(5), Zr-C1 2.542(2), Zr-C2 2.496(2),
Zr-C2a 2.522(2), Zr-C3 2.477(2), Zr-C3a 2.515(2), C1-
C4 1.518(3), C4-N 1.477(3), C4-N-C9 113.7(2), C4-N-
C9a 114.6(2), C9-N-C9a 111.4(2), torsional angles C2-
C1-C4-N 96.2(2), C2-C1-C4-C5 -29.8(3), C1-C4-N-
C9 66.1(3).
Addition of phenyllithium to 6-(N,N-dimethylamino)-
6-methylfulvene (6) furnished 8b. Subsequent treat-
ment with ZrCl4‚2THF gave a 1:1 mixture of meso-10b
and rac-10b (36% combined yield). In this case it was
also possible to obtain the pure rac-10b diastereomer
separated and isolated (∼15% yield).
is 131.7°. The 1-(N,N-dimethylamino)pentyl side chains
are found in a relative conformational arrangement that
places the two N(CH3)2 groups at the utmost intramo-
lecular distance from the zirconium center. The side
chains themselves are both oriented in the lateral
positions at the bent metallocene wedge.9 The overall
metallocene conformation is bis-lateral:anti.10 Taken
together the torsional arrangement of the groups at the
bent metallocene backbone indicates that the charac-
teristic structural appearance of (R,R)-9b seems to be
governed primarily by steric factors. The tertiary amino
group does not appear to interact as a specific functional
group with the formally electron-deficient zirconium
center in its immediate vicinity.
Alkylzirconocene cations were later to be generated
from the zirconocene systems 10a and rac-10b. There-
fore, the respective metallocene dichloride complexes
were converted to the dimethylmetallocenes by treat-
ment with methyllithium. The corresponding com-
plexes 11a and rac-11b were isolated in 82% and 75%
yield, respectively. The dimethylmetallocene complex
11b was characterized by X-ray diffraction (see below).
X-r a y Cr ysta l Str u ctu r e An a lyses. Single crystals
of isomerically pure 9b samples were obtained by the
diffusion method. In this case a clear solution of the
pure diastereomer rac-9b in dichloromethane was pre-
pared, into which pentane was allowed to diffuse during
a period of several weeks at ambient temperature.
Large crystals formed quite reproducibly in this way.
It turned out that the chiral bent metallocene complex
rac-9b crystallized under these conditions with spon-
taneous enantiomeric separation. Several crystals from
the same as well as different crystallizations were
investigated by X-ray diffraction. In each case the
crystal scanned contained a single enantiomer of the
chiral 9b diastereomer, with its experimental disclosure
apparently being statistical. The structure depicted in
Figure 1 is of the R,R-configured enantiomer.
The remarkable feature about the structure of (R,R)-
9b is that it is not distinguished in its most character-
istic structural parameters from the majority of known
16-electron zirconium(IV) bent metallocene complexes.
That means that, the tertiary amino groups present at
the side chains that are attached to the Cp rings do not
at all interact directly with the electron-deficient early
transition metal center, neither intra- nor intermolecu-
larly. In the crystal the zirconium center of (R,R)-9b
has attained a pseudotetrahedral coordination geom-
etry. The molecular symmetry is C2. The Zr-Cl bond
distance is 2.4529(5) Å, the Cl-Zr-Cl angle 97.70(3)°.
The average Zr-C(Cp) distance amounts to 2.510 Å, and
the corresponding Cp(centroid)-Zr-Cp(centroid) angle
The orientation of the amino groups away from the
16-electron zirconium center seems to be a general
(9) For examples of related bent metallocene conformational ar-
rangements see, e.g.: Petersen, J . L.; Dahl, L. F. J . Am. Chem. Soc.
1975, 97, 6422. Dusausoy, Y.; Protas, J .; Renaut, P.; Gautheron, B.;
Tainturier, G. J . Organomet. Chem. 1978, 157, 167. Howie, R. A.;
McQuillan, G. P.; Thompson, D. W. J . Organomet. Chem. 1984, 268,
149. Howie, R. A.; McQuillan, G. P.; Thompson, D. W.; Lock, G. A. J .
Organomet. Chem. 1986, 303, 213. Antinolo, A.; Lappert, M. F.; Singh,
A.; Winterborn, D. J . W.; Engelhardt, L. M.; Raston, C.; White, A. H.;
Carty, A. J .; Taylor, N. J . J . Chem. Soc., Dalton Trans. 1987, 1463.
Okuda, J . J . Organomet. Chem. 1988, 356, C43. Benn, R.; Grondey,
H.; Nolte, R.; Erker, G. Organometallics 1988, 7, 777. Erker, G.; Nolte,
R.; Tainturier, G.; Rheingold, A. Organometallics 1989, 8, 454. Erker,
G.; Nolte, R.; Kru¨ger, C.; Schlund, R.; Benn, R.; Grondey, H.; Mynott,
R. J . Organomet. Chem. 1989, 364, 119. Broussier, R.; Da Rold, A.;
Gautheron, B.; Dromzee, Y.; J eannin, Y. Inorg. Chem. 1990, 29, 1817.
Mallin, D. T.; Rausch, M. D.; Mintz, E. A.; Rheingold, A. L. J .
Organomet. Chem. 1990, 381, 35. Benn, R.; Grondey, H.; Erker, G.;
Aul, R.; Nolte, R. Organometallics 1990, 9, 2493. Winter, C. H.; Dobbs,
D. A.; Zhou, X.-X. J . Organomet. Chem. 1991, 403, 145. J aniak, C.;
Schumann, H. Adv. Organomet. Chem. 1991, 33, 291. Kru¨ger, C.; Nolte,
M.; Erker, G.; Thiele, S. Z. Naturforsch. 1992, 47B, 995. Kru¨ger, C.;
Lutz, F.; Nolte, M.; Erker, G.; Aulbach, M. J . Organomet. Chem. 1993,
452, 79. Sitzmann, H.; Zhou, P.; Wolmersha¨user, G. Chem. Ber. 1994,
127, 3.
(10) For definitions of conformational metallocene descriptors and
selected examples, see: Erker, G.; Aulbach, M.; Knickmeier, M.;
Wingbermu¨hle, D.; Kru¨ger, C.; Nolte, M.; Werner, S. J . Am. Chem.
Soc. 1993, 115, 4590. Waymouth, R. M.; Coates, G. W. Science 1995,
267, 222. Hauptmann, E.; Waymouth, R. M.; Ziller, J . W. J . Am. Chem.
Soc. 1995, 117, 11586. Knickmeier, M.; Erker, G.; Fox, T. J . Am. Chem.
Soc. 1996, 118, 9623.

2894 Organometallics, Vol. 16, No. 13, 1997
Bertuleit et al.
(pentafluorophenyl)borane13 at -20 °C. A rapid reac-
tion was observed to take place that proceeds with the
evolution of a gas (probably methane, see below).14
A
single organometallic product is formed that separates
from the reaction mixture as an oil. Workup, including
prolonged stirring with pentane, eventually led to
isolation of a solid product (84% yield). The product was
identified as 13a . The asymmetric spiro-metallocene
complex 13a shows very characteristic NMR spectra.
In the 1H NMR spectrum of the cationic spiro-metal-
locene the signals of the eight pairwise diastereotopic
cyclopentadienyl methine hydrogen atoms appear (at
253 K in dichloromethane-d2 solution) at δ 6.56, 6.51,
6.25, 5.95, 5.93, 5.75 (double intensity), and 5.54 [cor-
responding 13C NMR Cp resonances (dichloromethane-
d2, 208 K) at δ 113.0, 112.0, 110.0, 109.3, 106.5, 104.1,
99.5, 99.2 (CH) and δ 123.6, 115.2 (ipso-C of Cp),
respectively]. As a result of the spiro-metallocene
structure both C(CH3)2 methyl pairs (1H/13C NMR
signals at δ 1.60, 1.50, 1.49, 1.36/17.3, 24.6, 24.0, 24.2)
and the N(CH3)2 methyl pair are diastereotopic. To-
gether with the signal of the remaining single N-CH3
group consequently three resonances due to methyl
F igu r e 2. Projections of the independent molecules of 11b
as found in the crystal. Selected bond lengths (Å) and
angles (deg): Zr1-C11 2.272(7), Zr2-C31 2.274(7), Zr1-
C1 2.562(6), Zr1-C2 2.490(6), Zr1-C3 2.480(6), Zr1-C4
2.547(5), Zr1-C5 2.603(5), Zr2-C21 2.541(6), Zr2-C22
2.478(6), Zr2-C23 2.498(7), Zr2-C24 2.552(6), Zr2-C25
2.612(6), C5-C6 1.516(8), C25-C26 1.515(8), C6-N8
1.505(7), C26-N28 1.503(8), C11-Zr1-C11* 91.3(4), C31-
Zr2-C31* 91.2(5), centroid(C1-C5)-Zr1-centroid(C1*-
C5*) 132.6, centroid(C21-C25)-Zr2-centroid(C21*-C25*)
132.9, torsional angles C1-C5-C6-N8 104.0(6), C21-
C25-C26-N28 60.3(7), C4-C5-C6-N8 -61.3(6), C24-
C25-C26-N28 -105.9(6).
1
groups at nitrogen are observed for 13a in both the H
and 13C NMR spectrum (δ 2.30, 2.31, 2.44/43.3, 47.1,
47.6). The remaining methylene group that bridges
between zirconium and nitrogen (Zr-CH2-N) gives rise
to a single 13C NMR resonance at δ 48.8. The corre-
sponding pair of hydrogen atoms is again diastereotopic
due to the chiral spirocyclic ring structure of the
structural feature of this class of compounds. A very
similar arrangement of the C(CH3)[N(CH3)2]Ph substit-
uents is found for the dimethylzirconocene complex 11b.
Single crystals of 11b were formed when the pure rac-
11b diastereomer was slowly crystallized from dichlo-
romethane. Again, the large substituents at the Cp
rings are arranged anti to each other in opposite lateral
sectors at the bent metallocene backbone with the
N(CH3)2 groups both oriented toward the outside, away
from the bent metallocene core (see Figure 2). There
are two independent molecules of 11b in the crystal,
both being chemically equivalent. Their characteristic
structural parameters are very similar (see Figure 2).
We conclude that it appears that there is no direct
interaction between the 16-electron zirconium center
and the substituted (N,N-dimethylamino)methyl sub-
stituents attached to the Cp ligands of these specific
zirconocene complexes.11 This seems to hold for the
zirconocene dichlorides 9 and 10 and for the probably
slightly more electrophilic dimethylzirconocene com-
plexes 11, as well. The situation changes drastically
when a methyl anion becomes abstracted from the
zirconium center in 11, initially generating a cationic
zirconium complex with a formal 14-electron count.12
Zir con ocen e Ca tion System s Der ived fr om 11.
The dimethylzirconocene complex 11a was suspended
in toluene and treated with 1 molar equiv of tris-
1
metallacyclic system. It gives rise to an AX pair of H
resonances at δ 2.27 and 1.57 (2J ) 9.6 Hz) at 253 K in
dichloromethane-d2. In addition, the characteristic
NMR signals of the CH3B(C6F5)3 anion were monitored
(see Experimental Section for further details).
The specific chirality information contained in com-
plex 13a is not completely persistent, though. Raising
the temperature from 253 to 303 K (i.e., the highest
temperature chosen in dichloromethane-d2 solution)
rapidly leads to a (reversible) broadening and coales-
cence of the Zr-CH2-N AX system in the 1H NMR
spectrum. At the same time the four C(CH3)2 signals
get broad as do the N(CH3)2 pair of resonances and also
the Cp-methine signals. Only the single N-CH3 1H
NMR signal at δ 2.48 ppm appears to remain unaffected
by the dynamic NMR behavior of complex 13a ; it
remains a sharp singlet at all temperatures.
A brief investigation of the dynamic 1H NMR spectra
of complex 13a in bromobenzene at 200 MHz has
confirmed the pairwise coalescence of the diastereotopic
(12) J ordan, R. F.; Bajgur, C. S.; Willett, R.; Scott, B. J . Am. Chem.
Soc. 1986, 108, 7410. Lin, Z.; LeMarechal, J . F.; Sabat, M.; Marks, T.
J . J . Am. Chem. Soc. 1987, 109, 4127. Straus, D. A.; Zhang, C.; Tilley,
T. D. J . Organomet. Chem. 1989, 369, C13. Bochmann, M.; J aggar, A.
J .; Nicholls, J . C. Angew. Chem. 1990, 102, 830; Angew. Chem., Int.
Ed. Engl. 1990, 29, 780. Aleyunas, Y. W.; J ordan, R. F.; Echols, S. F.;
Borkowsky, S. L.; Bradley, P. K. Organometallics 1991, 10, 1406.
Amorose, D. M.; Lee, R. P.; Petersen, J . L. Organometallics 1991, 10,
2191. Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1991,
113, 3623. Chien, J . C. W.; Tsai, W.-M.; Rausch, M. D. J . Am. Chem.
Soc. 1991, 113, 8570. Hlatky, G. G.; Eckman, R. R.; Turner, H. W.
Organometallics 1992, 11, 1413. Boudjouk, P.; Bahr, S. R. J . Org.
Chem. 1992, 57, 5545. J ia, L.; Yang, X.; Ishihara, A.; Marks, T.
Organometallics 1995, 14, 3135.
(11) J utzi, P.; Kristen, M. O.; Dahlhaus, J . Neumann, B.; Stammler,
H. G. Organometallics 1993, 12, 2980. J utzi, P.; Kristen, M. O.;
Neumann, B.; Stammler, H.-G. Organometallics 1994, 13, 3854. Flores,
J . C.; Chien, J . C. W.; Rausch, M. D. Organometallics 1994, 13, 4140.
du Plooy, K. E.; Moll, U.; Wocadlo, S.; Massa, W.; Okuda, J . Organo-
metallics 1995, 14, 3129. Herrmann, W. A.; Morawietz, M. J . A.;
Priermeier, T.; Mashima, K. J . Organomet. Chem. 1995, 486, 291.
J utzi, P.; Dahlhaus, J .; Neumann, B.; Stammler, H. G. Organometallics
1996, 15, 747. Okuda, J .; du Plooy, K. E.; Massa, W.; Kang, H.-C.; Rose,
U. Chem. Ber. 1996, 129, 275. Enders, M.; Rudolph, R.; Pritzkow, H.
Chem. Ber. 1996, 129, 459. van der Zeijden, A. A. H. J . Organomet.
Chem. 1996, 518, 147. Mu, Y.; Piers, W. E.; MacQuarrie, D. C.;
Zaworotko, M. J .; Young, V. G., J r. Organometallics 1996, 15, 2720.
(13) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2,
245.
(14) See for a comparison: Temme, B.; Erker, G. J . Organomet.
Chem. 1995, 488, 177. Ro¨ttger, D.; Erker, G.; Fro¨hlich, R.; Kotila, S.
J . Organomet. Chem. 1996, 518, 17. Horton, A. D. Organometallics
1996, 15, 2675. See also: Ro¨ttger, D.; Schmuck, S.; Erker, G. J .
Organomet. Chem. 1996, 508, 263. Ro¨ttger, D.; Erker, G.; Grehl, M.;
Fro¨hlich, R. Organometallics 1994, 13, 3897.

Group 4 Metallocene Cation Reaction Pathways
Organometallics, Vol. 16, No. 13, 1997 2895
Sch em e 2
C(CH3)2 and N(CH3)2 pairs at higher temperatures.
Thus, complex 13a undergoes a thermally induced
reversible symmetrization process that is rapid on the
NMR time scale. Most likely this is to be explained by
a process initiated by rupture of the Zr-N bond in 13a
leading to a monocyclic organometallic intermediate
(14a ) that can easily undergo conformational equilibra-
tion9,10,15 before the reverse reaction takes place by the
electrophilic cationic zirconium center capturing and
coordinating to the N(CH3)2 group close by to re-form
the thermodynamically favored spiro-metallocene struc-
ture 13a (see Scheme 2).
The stereochemical situation is altered if persistent
chirality centers at carbon are introduced. This has
been the case when rac-11b was employed as the
starting material. Its reaction with B(C6F5)3 also
proceeds very cleanly to generate the respective spiro-
metallocene complex 13b with loss of methane. In this
case two diastereomers (13b, 13b′) (both with relative
configurations R*,R* at carbon and S* or R* at zirco-
nium, respectively) could in principle occur, but only a
single diastereomer was observed within the accuracy
of the NMR analysis. It remains to be revealed which
of the two possible diastereomers is the thermodynami-
cally preferred one that is obtained, but it is clear that
the Cp-CMePh[N] substituent pattern chosen here has
shifted the equilibrium situation depicted in Scheme 3
so far to one side that this spiro-metallocene product
appears as being static on the NMR time scale.
Although a thorough mechanistical investigation has
still to come, the following description of the reaction
course taken in the formation of the spiro-metallocenes
13 involving a CH-activation step appears likely. Obvi-
ously, the reaction sequence is initiated by the abstrac-
tion of a methyl group from the zirconium center in 11
by the B(C6F5)3 Lewis acid.6,14 The resulting methylzir-
conocene cation (12) seems to be extremely reactive with
regard to an intramolecular CH-activation reaction.16
All attempts to at least observe the intermediate 12 by
carrying out the methyl transfer reaction under direct
NMR control at low temperature have not proven
successful so far. We thus conclude that the methylzir-
conocene cation 12 encounters a situation set up for a
very favorable subsequent reaction due to the presence
of the substituted (dimethylamino)methyl substituents
attached to the Cp ligands. Undoubtedly, the essential
step of this reaction sequence involves CH activation.
In view of the electronic situation present at the
d0-configurated zirconium center17 in 12 the most com-
monly observed pathway for CH activation by means
of oxidative addition of the C-H bond to the metal
center18 is very unlikely to occur.
(16) Hlatky, G. G.; Turner, H. W.; Eckman, R. R. J . Am. Chem. Soc.
1989, 111, 2728. Ruwwe, J .; Erker, G.; Fro¨hlich, R. Angew. Chem. 1996,
108, 108; Angew. Chem., Int. Ed. Engl. 1996, 35, 80. See also:
Bochmann, M. Angew. Chem. 1992, 104, 1206; Angew. Chem. Int. Ed.
Engl. 1992, 31, 1181.
(15) Luke, W. D.; Streitwieser, A. J . Am. Chem. Soc. 1981, 103, 3241.
Okuda, J . Top. Curr. Chem. 1991, 160, 97 and references cited therein.

2896 Organometallics, Vol. 16, No. 13, 1997
Bertuleit et al.
Sch em e 3
Sch em e 4
It is, however, possible that a direct C-H activation
at the N-CH3 group is taking place, involving a four-
centered transition state (see eq 1). Similar “σ-metath-
esis” reactions have been observed to occur in the
reactions of very electrophilic Cp*2ScR reagents.19 But
it should be noted that such processes often prefer
activation of σ-bonds that exhibit high s-character.20
Also, in the reaction of 12 we note a very specific C-H
activation selectivity as only the CH3 groups adjacent
to nitrogen and not to carbon are involved.
A specific mechanistic involvement of the amino
nitrogen of 12 in the observed C-H activation process
(17) Lauher, J . W.; Hoffmann, R. J . Am. Chem. Soc. 1976, 98, 1729.
Guo, Z.; Swenson, D. C.; Guram, A. S.; J ordan, R. F. Organometallics
1994, 13, 766 and references cited therein. See also: Guram, A. S.;
Swenson, D. C.; J ordan, R. F. J . Am. Chem. Soc. 1992, 114, 8991.
Hurlburt, P. K.; Rack, J . J .; Luck, J . S.; Dec, S. F.; Webb, J . D.;
Anderson, O. P.; Strauss, S. H. J . Am. Chem. Soc. 1994, 116, 10003.
Antonelli, D. M.; Tjaden, E. B.; Stryker, J . M. Organometallics 1994,
13, 763. Temme, B.; Erker, G.; Karl, J .; Luftmann, H.; Fro¨hlich, R.;
Kotila, S. Angew. Chem. 1995, 107, 1867; Angew. Chem., Int. Ed. Engl.
1995, 34, 1755.
(18) Activation and Functionalization of Alkanes; Hill, C. L., Ed.;
Wiley: New York, 1989. Principles and Applications of Organotransi-
tion Metal Chemistry, 2nd ed.; Collman, J . P.; Hegedus, L. S.; Norton,
J . R.; Finke, R. G. University Science Books: Mill Valley, CA, 1987.
(19) Thompson, M. E.; Baxter, S. M.; Bulls, R.; Burger, B. J .; Nolan,
M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J . Am. Chem.
Soc. 1987, 109, 203.
could take place by either of two effects. Intramolecular
coordination of the tertiary amino functionality to the
cationic zirconium center could be involved. This would
simply bring the N-CH3 group into the vicinity of the
Zr-CH3 base, and this might open up a viable pathway
of a concerted methane elimination (15 f 16). Alter-
natively one might also consider a stepwise process
leading from 15 to 16 via 17, followed by a classical
reductive coupling step (pathway b, see Scheme 4).
All it requires to form the final product is the
intramolecular attack of the zirconium(II) center of the
(20) See, however: Bochmann, M.; Cuenca, T.; Hardy, D. T. J .
Organomet. Chem. 1994, 484, C10.

Group 4 Metallocene Cation Reaction Pathways
Organometallics, Vol. 16, No. 13, 1997 2897
Sch em e 5
resulting complex 16 with its electron pair serving as a
nucleophile to the electrophilic carbon center of the
adjacent iminium ion functional group that is attached
to the Cp-ring system.21 This reaction bears a great
similarity to the central step of the Mannich reaction
and may just be regarded as an analogously proceeding
organometallic aminomethylation reaction. It just em-
ploys an organometallic nucleophile instead of the
typical organic nucleophilic reagents used in the com-
mon Mannich reaction.22
But it should also be noted that non-ligand-stabilized
alkylzirconocene cations bear a great similarity to
reactive carbenium ions: they are very electrophilic
reagents, and their respective σ-bonds, the zirconium-
carbon and zirconium-hydrogen bond, respectively, are
thermodynamically very strong.23 Therefore, it is pos-
sible that donor-ligand free methylzirconocene cations
such as 12 have a tendency for hydride abstraction24
from mildly activated C-H linkages, especially when
such a bond is brought into close spatial contact with
the electrophilic metal center, as is the case here. The
hydride abstraction reaction consequently leads to the
formation of the hydrido(methyl)zirconocene species 17,
which is now ideally set up for reductive elimination of
methane to generate 16, which is then converted to the
final product 13 as outlined above (Scheme 5).
it brings a C-H bond that is activated toward hydride
abstraction into the close vicinity of the electrophilic
zirconium cation center. Nevertheless, the observed
very rapid hydride transfer from carbon to zirconium,
which is followed by methane formation, indicates that
CH activation may be another important reaction type
that is induced by group 4 bent metallocene cations.
This reaction appears to point to some essential similar-
ity between the 14-electron bent metallocene cation
systems and the carbenium ions. It would be tempting
to try to use this related reactivity to uncover novel
catalytic reaction pathways other than the well-studied
insertion reactions of the bent metallocene cations that
involve CH activation.3b Doing this stoichiometrically
seems to be unproblematic, as shown by the organome-
tallic aminomethylation reaction observed in this study,
as long as a thermodynamically favorable reaction is
found to close the overall reaction cycle. Catalytically
this can potentially be done by combining the CH-
activation reaction of a suitable organic substrate,
induced by the electrophilic zirconocene cation, with one
of the established insertion reactions at such electro-
philic metallocene catalyst species.25 Studies aimed at
developing such novel catalytic reaction patterns of
alkylzirconocene cation systems are currently being
carried out in our laboratory.
The metallocene cation system 12 encountered in this
study admittedly is of a rather special constitution as
Exp er im en ta l Section
All reactions involving organometallic reagents or substrates
were carried out in an inert atmosphere (argon) using Schlenk-
type glassware or in a glovebox. Solvents were dried and
distilled under argon prior to use. The following instruments
were used for physical characterization of the compounds.
Bruker AC 200 P, Bruker ARX 300, and Varian Unity Plus
600 NMR spectrometers; Nicolet 5 DXC FT-IR spectrometer;
DuPont 2910 (STA Instruments) DSC. Elemental analyses:
Foss-Heraeus CHN-O-Rapid. X-ray crystal structure analy-
(21) Hart, W. P.; Macomber, D. W.; Rausch, M. D. J . Am. Chem.
Soc. 1980, 102, 1196. Hart, W. P.; Shihua, D.; Rausch, M. D. J .
Organomet. Chem. 1985, 282, 111. Rausch, M. D.; Lewison, J . F.; Hart,
W. P. J . Organomet. Chem. 1988, 358, 161. J ones, S. S.; Rausch, M.
D.; Bitterwolf, T. E. J . Organomet. Chem. 1990, 396, 279. Ogasa, M.;
Mallin, D. T.; Macomber, D. W.; Rausch, M. D.; Rogers, R. D.; Rollins,
A. N. J . Organomet. Chem. 1991, 405, 41. J ones, S. S.; Rausch, M. D.;
Bitterwolf, T. E. J . Organomet. Chem. 1993, 450, 27. Oberhoff, M.;
Duda, L.; Karl, J .; Mohr, R.; Erker, G.; Fro¨hlich, R.; Grehl, M.
Organometallics 1996, 15, 4995. Reviews: Macomber, D. W.; Hart, W.
P.; Rausch, M. D. Adv. Organomet. Chem. 1982, 21, 1. Coville, N. J .;
Pickl, W. Coord. Chem. Rev. 1992, 116. 1.
(22) For a modern variant of the Mannich reaction, see, e.g.: Martin,
S. F.; Barr, K. J . J . Am. Chem. Soc. 1996, 118, 3299.
(25) Young, J . R.; Stille, J . R. Organometallics 1990, 9, 3022. Piers,
W. E.; Bercaw, J . E. J . Am. Chem. Soc. 1990, 112, 9406. Piers, W. E.;
Shapiro, P. J .; Bunel, E. E.; Bercaw, J . E. Synlett 1990, 74. Molander,
G. A.; Hoberg, J . O. J . Am. Chem. Soc. 1992, 114, 3123. Gagne´, M. R.;
Stern, C. L.: Marks, T. J . J . Am. Chem. Soc. 1992, 114, 275. Gagne´,
M. R.; Brard, L.; Conticello, V. P.; Giardello, M. A.; Stern, C. L.; Marks,
T. J . Organometallics 1992, 11, 2003. Li, Y.; Fu, P.-F.; Marks, T. J .
Organometallics 1994, 13, 439. Lea, N. E.; Buchwald, S. L. J . Am.
Chem. Soc. 1994, 116, 5985. Willoughby, C. A.; Buchwald, J . Am.
Chem. Soc. 1994, 116, 8952. Thiele, S.; Erker, G. Chem. Ber. 1997,
130, 201. Shaughnessy, K. H.; Waymouth, R. M. J . Am. Chem. Soc.
1995, 117, 5873. Kondokov, D. Y.; Negishi, E. J . Am. Chem. Soc. 1995,
117, 10771. Molander, G. A.; Nichols, P. J . J . Am. Chem. Soc. 1995,
117, 4415. Christoffers, J .; Bergman, R. G. J . Am. Chem. Soc. 1996,
118, 4715 and references cited therein.
(23) Kochi, J . K. Organometallic Mechanism and Catalysis; Aca-
demic Press: New York, 1978. Connor, J . A. Top. Curr. Chem. 1977,
71, 71. Metal-Ligand Bonding Energetics in Organotransition Metal
Compounds; Marks, T. J ., Ed.; Polyhedron Symposium in print; 1988;
Vol. 7. Bonding Energetics in Organometallic Compounds; Marks, T.
J ., Ed.; ACS Symposium Series 428; American Chemical Society:
Washington, DC, 1990. Drago, R. S.; Wong, N. M.; Ferris, D. C. J . Am.
Chem. Soc. 1992, 114, 91.
(24) Bartlett, P. D.; Condon, F. E.; Schneider, A. J . Am. Chem. Soc.
1944, 66, 1531. Dauben, H. J ., J r.; Gadecki, F. A.; Harmon, K. M.;
Pearson, D. L. J . Am. Chem. Soc. 1957, 79, 4557. Nenitzescu, C. D. In
Carbonium Ions; Olah, G. A., Schleyer, P. v. R., Eds.; Wiley: New York,
1970; Vol. II, pp 463-520.

2898 Organometallics, Vol. 16, No. 13, 1997
Bertuleit et al.
ses: Enraf-Nonius CAD4 diffractometer (programs used in-
clude SHELX 86, SHELX 93, and XP). The organic starting
materials 6-(N,N-dimethylamino)fulvene (5) and 6-(N,N-di-
methylamino)-6-methylfulvene (6) were prepared according to
the procedures published by Hafner et al.8
24H, NMe2), 1.24, 1.26 (each d, 3J ) 6.8 Hz, 12H, CH3). 1H
NMR (CDCl3): δ 6.42, 6.25 (m, each 4H, Cp), 3.93 (m, 4H, CH),
2.12, 2.13 (s, each 12H, NMe2), 1.28, 1.29 (d, 3J ) 6.8 Hz, each
6H, CH3). 13C NMR (benzene-d6): δ 134.6, 134.2 (ipso-C of
Cp), 118.3, 118.1, 116.1, 116.0, 113.1, 112.9, 110.6, 109.8 (CH
of Cp), 58.3 (CH), 40.4 (NMe2), 12.2 (CH3).
[[1-(N,N-Dim eth yla m in o)eth yl]cyclop en ta d ien yl]lith -
iu m (7a ). Ethereal methyllithium (51 mL of a 1.6 M solution,
77.0 mmol) was added dropwise with stirring to a solution of
9.3 g (77.0 mmol) of 6-(N,N-dimethylamino)fulvene (5) in 120
mL of ether at -40 °C. The reaction mixture was allowed to
warm to room temperature overnight with stirring. A light
brown suspension was obtained. The product (7a ) was simply
collected by filtration to give 9.8 g (89%) of 7a , that was
characterized by NMR spectroscopy. 1H NMR (benzene-d6/
Bis[η5-[1-(N,N-dim eth ylam in o)pen tyl]cyclopen tadien yl]-
zir con iu m Dich lor id e (r a c/m eso-9b Mixtu r e). A solution
of ZrCl4‚2THF (1.45 g, 3.83 mmol) in 30 mL of tetrahydrofuran
was slowly added to a stirred suspension of 7b (1.42 g, 7.67
mmol) in 150 mL of ether at 0 °C. The mixture was stirred
for 5 min at 0 °C and then the solvent removed in vacuo. The
brown viscous residue was dissolved in chloroform and then
kept at -30 °C overnight to precipitate the lithium chloride.
The precipitate was removed by filtration. Solvent was then
removed from the clear filtrate in vacuo to yield 0.69 g (35%)
of the ca. 90% pure rac-9b/meso-9b 1:1 mixture. 1H NMR
(CDCl3): δ 6.48, 6.36, 6.17, 6.08 (m, each 4H, Cp), 3.73, 3.68
(m, each 2H, CH), 2.06, 2.07 (s, each 12H, NMe2), 1.9-1.1 (br
m, 24H) and 0.9 (br t, 12H, n-butyl). 13C NMR (CDCl3): δ
132.7, 132.2 (ipso-C of Cp), 117.7, 116.9, 116.4, 115.7, 114.9,
114.7, 108.6, 107.7 (CH of Cp), 62.6 (CH-NMe2), 40.7 (NMe2),
30.7, 30.1 (CH-CH2-), 22.6, 29.1 (-CH2-CH2-), 14.1 (CH3).
r a c-Bis[η5-[1-(N,N-d im eth yla m in o)p en tyl]cyclop en ta -
d ien yl]zir con iu m Dich lor id e (r a c-9b). A cooled (0 °C)
suspension of ZrCl4 (1.96 g, 8.4 mmol) in 40 mL of toluene was
added to a stirred solution of the cyclopentadienyllithium
reagent 7b (4.63 g, 25 mmol) in 100 mL of toluene at 0 °C.
The mixture was stirred overnight. Lithium chloride was
filtered off through Celite and the residue washed with
dichloromethane. Solvent was removed from the combined
organic phases. The resulting oil was dissolved in pentane.
During 2 weeks a precipitate was formed at +6 °C, and it was
collected by filtration to yield 0.35 g (8%) of the rac-9b isomer
as a solid. Anal. Calcd for C24H40N2Cl2Zr (518.7): C, 55.57;
H, 7.77; N, 5.40. Found: C, 54.15; H, 7.54; N, 5.14. 1H NMR
(benzene-d6): δ 6.08, 6.02, 5.89, 5.61 (m, each 2H, Cp), 3.94
(m, 2H, CH), 2.00 (s, 12H, NMe2), 1.3-1.9 (br m, 12H) and
0.97 (br t, 6H, n-butyl). 13C NMR (CDCl3): δ 132.7 (ipso-C of
Cp), 117.0, 116.4, 114.9, 107.4 (CH of Cp), 62.6 (CH-NMe2),
40.8 (NMe2), 30.1, 29.1, 22.6, 14.1 (n-butyl).
3
THF-d8, 5:1): δ 5.81, 5.74 (m, each 2H, Cp), 3.59 (q, J ) 6.8
Hz, 1H, CH), 2.14 (s, 6H, NMe2), 1.39 (d, 3J ) 6.8 Hz, 3H,
CH3). 13C NMR (benzene-d6/THF-d8, 5:1): δ 120.9 (quat. C of
Cp), 110.2, 103.8 (CH of Cp), 60.7 (CH), 41.8 (NMe2), 17.2
(CH3).
[[1-(N,N-Dim eth yla m in o)p en tyl]cyclopen ta dien yl]lith -
iu m (7b). n-Butyllithium (1.6 M solution in hexane, 26.1 mL,
41.8 mmol) was added dropwise with stirring to a solution of
6-(N,N-dimethylamino)fulvene (5, 5.1 g, 41.7 mmol) in 40 mL
of tetrahydrofuran at -40 °C. The reaction mixture was
allowed to warm to room temperature overnight. Solvent was
removed in vacuo from the resulting clear brown colored
solution to give a highly viscous oil. Pentane (30 mL) was
added and the mixture stirred for 12 h to give a precipitate of
solid 7b. Pentane was decanted and the remaining solid dried
in vacuo to give 7.3 g (95%) of 7b as a light brownish colored
powder, which was characterized by NMR spectroscopy. 1H
NMR (benzene-d6/THF-d8, 3:1): δ 5.92, 5.80 (m, each 2H, Cp),
3.52 (m, 1H, CH), 2.18 (s, 6H, NMe2), 1.92, 1.68, 1.43 (m, 2H
each), and 0.89 (br t, 3H, n-butyl). 13C NMR (benzene-d6/THF-
d8, 3:1): δ 117.5 (quat. C of Cp), 104.7, 102.5 (CH of Cp), 65.4
(CH), 41.7 (NMe2), 34.0, 31.0, 23.2, 14.7 (n-butyl).
[[1-(N,N-Dim eth yla m in o)-1-m eth yleth yl]cyclop en ta d i-
en yl]lith iu m (8a ). Analogously as described for the synthesis
of 7a above, the fulvene 6 (7.72 g, 57.2 mmol), dissolved in
120 mL of ether, was treated with 33.2 mL of a 1.72 M ethereal
methyllithium solution (57.2 mmol) to yield 8a (7.3 g, 82%) as
a light brown colored powder. The product 8a was character-
ized by NMR spectroscopy. 1H NMR (benzene-d6/THF-d8, 10:
1): δ 6.00, 5.94 (m, each 2H, Cp), 2.19 (s, 6H NMe2), 1.53 [s,
6H, C(CH3)2]. 13C NMR (benzene-d6/THF-d8, 10:1): δ 124.5
(quat. C of Cp), 103.3, 102.5 (CH of Cp), 57.1 (CMe2), 39.8
[N(CH3)2], 26.2 [C(CH3)2].
[[1-(N,N-(Dim eth yla m in o)-1-m eth ylben zyl]cyclop en ta -
d ien yl]lith iu m (8b). Analogously as described above, the
fulvene 6 (solution of 2.9 g, 21.2 mmol, in 50 mL of ether) was
treated with phenyllithium (20.1 mmol) to yield 3.9 g (84%) of
8b as a slightly brownish colored powder, characterized by
NMR spectroscopy. 1H NMR (benzene-d6/THF-d8, 3:1): δ 7.84,
7.15, 7.00 (m, 5H, Ph), 5.92, 5.86 (m, each 2H, Cp), 2.25 (s,
6H, NMe2), 1.78 (s, 3H, CH3). 13C NMR (benzene-d6/THF-d8,
3:1): δ 153.8 (ipso-C of Ph), 128.5, 127.3, 124.9 (CH of Ph),
129.2 (ipso-C of Cp), 103.8, 102.4 (CH of Cp), 64.4 (quat.
C-NMe2), 40.3 (NMe2), 27.2 (CH3).
Bis[η5-[1-(N,N-dim eth ylam in o)eth yl]cyclopen tadien yl]-
zir con iu m Dich lor id e (r a c/m eso-9a Mixtu r e). A cooled (0
°C) suspension of ZrCl4‚2THF (2.50 g, 10.7 mmol) in 20 mL of
ether was added in several portions to a suspension of 3.25 g
(22.6 mmol) of the cyclopentadienyllithium reagent 7a in 50
mL of ether at 0 °C. The mixture was stirred for 15 min at 0
°C and then filtered. The ethereal solution contained only very
much contaminated product and was, therefore, discarded. The
solid was extracted with dichloromethane until the liquid
remained colorless. Solvent was removed from the dichlo-
romethane extract to yield 2.03 g (44%) of the rac-9a /meso-9a
1:1 mixture, mp 180 °C (dec, DSC). Anal. Calcd for C18H28N2-
Cl2Zr (434.6): C, 49.75; H, 6.49; N, 6.45. Found: C, 49.08; H,
6.68; N, 6.47. 1H NMR (benzene-d6): δ 6.2 (br m, 8H) and 5.8
(br m, 8H, Cp), 4.1 (two overlapping quartets, 4H, CH), 2.0 (s,
X-r a y Cr ysta l Str u ctu r e An a lysis of th e 9b En a n ti-
om er s. The pure rac-9b diastereomer was dissolved in
dichloromethane. Pentane was allowed to diffuse slowly into
this solution at ambient temperature. Over a period of several
weeks, long colorless needles of the product were obtained. The
chiral 9b diastereomer crystallized with spontaneous resolu-
tion of enantiomers. Several samples checked by X-ray
diffraction revealed that single crystals contained the pure
enantiomers (R,R)-9b or (S,S)-9b , respectively: formula
C
24H40N2ZrCl2, M ) 518.70, 0.5 × 0.3 × 0.25 mm, a ) 13.767-
(1) Å, b ) 14.207(1) Å, c ) 6.471(1) Å, V ) 1265.6(2) Å3, Fcalc
)
1.361 g cm-3, µ ) 6.58 cm-1, no absorption correction, Z ) 2,
orthorhombic, space group P21212 (No. 18), λ ) 0.710 73 Å,
ω/2θ scans, 2189 reflections collected ((h, +k, -l), [(sin θ)/
λ]max ) 0.62 Å-1, 2062 independent and 1990 observed reflec-
tions [I g 2σ(I)], 136 refined parameters, R ) 0.023, wR2
)
0.060, Flack parameter -0.03(4), maximum residual electron
density 0.58 (-0.69) e Å-3, hydrogens calculated and riding.
Bis[η5-[1-(N,N-d im et h yla m in o)-1-m et h ylet h yl]cyclo-
p en ta d ien yl]zir con iu m Dich lor id e (10a ). A cooled (0 °C)
suspension of ZrCl4‚2THF (6.82 g, 18.1 mmol) in 60 mL of ether
was added in portions to a stirred suspension of 5.71 g (36.1
mmol) of the cyclopentadienyllithium reagent 8a in 250 mL
of ether at 0 °C. The mixture was stirred for 15 min at 0 °C.
The precipitate was collected by filtration and washed with
ether (3 × 20 mL). The solid residue was extracted with
dichloromethane. Solvent was removed from the dichlo-
romethane extracts to give 4.44 g (53%) of 10a as a solid. The
combined ethereal phases were concentrated in vacuo to ca.
50% of their original volume and kept overnight at -30 °C to
precipitate additional 10a , which was collected by filtration
(1.51 g, 18%), mp 210 °C dec. Anal. Calcd for C20H32N2Cl2Zr

Group 4 Metallocene Cation Reaction Pathways
Organometallics, Vol. 16, No. 13, 1997 2899
(462.2): C, 51.93; H, 6.97; N, 6.06. Found: C, 49.61; H, 6.75;
N, 6.12. 1H NMR (dichloromethane-d2): δ 6.47, 6.37 (m, each
4H, Cp), 1.96 (s, 6H, NMe2), 1.51 [s, 6H, C(CH3)2]. 13C NMR
(CDCl3): δ 121.0 (ipso-C of Cp), 117.7, 111.8 (CH of Cp), 56.3
(C-NMe2), 39.0 (NMe2), 24.2 (CH3).
(ipso-C of Cp), 115.5, 114.8, 107.8, 107.1 (CH of Cp), 62.9 (C-
NMe2), 39.4 (NMe2), 32.4 (Zr-CH3), 12.8 (C-CH3).
X-r a y Cr ysta l Str u ctu r e An a lysis of 11b. Single crystals
of the chiral 11b diastereomer were obtained from toluene-
d8: formula C32H42N2Zr, M ) 545.90, 1.2 × 1.0 × 0.7 mm, a )
15.150(2) Å, b ) 25.215(3) Å, c ) 14.893(2) Å, â ) 90.19(1)°, V
) 5689.2(13) Å3, Fcalc ) 1.275 g cm-3, µ ) 4.08 cm-1, empirical
absorption correction via ψ-scan data (0.810 e C e 0.998), Z
) 8, monoclinic, space group C2/c (No. 15), λ ) 0.710 73 Å,
ω/2θ scans, 5993 reflections collected (-h, +k, (l), [(sin θ)/
λ]max ) 0.62 Å-1, 5773 independent and 4143 observed reflec-
Bis[η5-[1-(N,N-d im eth yla m in o)-1-m eth ylben zyl]cyclo-
p en ta d ien yl]zir con iu m d ich lor id e (r a c/m eso-10b Mix-
tu r e). A cold (0 °C) suspension of ZrCl4‚2THF (3.59 g, 9.5
mmol) in 50 mL of ether was added in portions to a suspension
of 4.18 g (19.0 mmol) of 8b in 250 mL of ether at -30 °C. The
mixture was stirred for an additional 2 h at -30 °C. The
precipitate was collected by filtration, washed with ether (3
× 10 mL), and then extracted with dichloromethane. Solvent
was removed from the extract. The residue was stirred for
15 min with 20 mL of a 1:1 ether/pentane mixture. The solid
product was recovered by filtration and dried in vacuo to yield
2.00 g (36%) of the rac-10b/meso-10b 1:1 mixture, mp 174 °C,
dec. Anal. Calcd for C30H36N2Cl2Zr (586.8): C, 61.41; H, 6.18;
N, 4.77. Found: C, 59.44; H, 6.13; N, 4.20. 1H NMR (dichloro-
methane-d2): δ 7.5-7.3 (br m, 12H) and 7.77, 7.73 (m, each
4H, Ph), 6.26, 6.20 (m, each 4H), 6.40, 6.12, 5.01, 3.66 (m, each
2H, Cp), 1.78, 1.83 (s, each 12H, NMe2), 1.77, 1.75 (s, each
6H, CH3).
r a c-Bis[η5-[1-(N,N-d im eth yla m in o)-1-m eth ylben zyl]cy-
clop en ta d ien yl]zir con iu m Dich lor id e (r a c-10b). To a
cooled (-30 °C) suspension of 3.39 g (15.5 mmol) of 8b in 50
mL of ether was added in portions a precooled (0 °C) suspen-
sion of 2.92 g (7.7 mmol) of ZrCl4‚2THF in 50 mL of ether.
The mixture was then stirred for 2 h at -30 °C and the
precipitate collected by filtration and washed with ether (3 ×
10 mL). The remaining solid was extracted with dichlo-
romethane until the extracts became colorless. Solvent was
removed from the dichloromethane phase to give a brown solid.
Pentane (15 mL) was added and the mixture stirred for 15
min. The solid was collected by filtration and dried in vacuo
to yield 0.68 g (15%) of rac-10b, mp 182 °C dec. Anal. Calcd
for C30H36N2Cl2Zr (586.8): C, 61.41; H, 6.18. Found: C, 60.93;
H, 6.07. 1H NMR (dichloromethane-d2): δ 7.77, 7.39, 7.33 (m,
10H, Ph), 6.40, 6.27, 6.12, 3.66 (m, each 2H, Cp), 1.78 (s, 12H,
NMe2), 1.77 (s, 6H, CH3). 13C NMR (dichloromethane-d2): δ
146.4 (ipso-C of Ph), 129.1, 128.3, 127.6 (CH of Ph) 140.5
(ipso-C of Cp), 126.2, 118.5, 114.1, 108.7 (CH of Cp), 63.2 (C-
NMe2), 39.3 (NMe2), 12.0 (CH3).
Bis[η5-[1-(N,N-d im et h yla m in o)-1-m et h ylet h yl]cyclo-
p en ta d ien yl]d im eth ylzir con iu m (11a ). A 4.0 mL volume
of a 1.68 M ethereal methyllithium solution (6.7 mmol) was
added dropwise with stirring to a suspension of 1.56 g (3.4
mmol) of 10a in 250 mL of ether at -40 °C. The suspension
was allowed to warm to -20 °C over a period of 2 h and then
stirred for an additional 1 h at room temperature. The solid
was removed by filtration through Celite. The clear filtrate
was concentrated in vacuo until the solution became turbid.
Precipitation of the product was then achieved at -30 °C.
Complex 11a (1.17g, 82%) was collected by filtration and dried
in vacuo, mp 189 °C (dec, DSC). Anal. Calcd for C22H38N2Zr
(421.8): C, 62.65; H, 9.08; N, 6.64. Found: C, 60.12; H, 8.65;
N, 6.60. 1H NMR (benzene-d6): δ 5.89, 5.80 (m, each 4H, Cp),
2.00 (s, 12H, NMe2), 1.25 [s, 12H, C(CH3)2], -0.01 [s, 6H, Zr-
(CH3)2]. 13C NMR (benzene-d6): δ 131.6 (ipso-C of Cp), 110.2,
109.6 (CH of Cp), 56.7 (C-NMe2) 39.3 (NMe2), 32.1 (Zr-CH3),
25.3 (C-CH3).
r a c-Bis[η5-[1-(N,N-d im eth yla m in o)-1-m eth ylben zyl]cy-
clop en t a d ien yl]d im et h ylzir con iu m (r a c-11b ). Analo-
gously as described above, 0.34 g (0.6 mmol) of rac-10b was
reacted with 0.7 mL of a 1.68 M ethereal methyllithium
solution (1.2 mmol of CH3Li) in 60 mL of ether to yield 0.23 g
(75%) of the product rac-11b, mp 176 °C (dec, DSC). Anal.
Calcd for C32H42N2Zr (545.9): C, 70.40; H, 7.75; N, 5.13.
Found: C, 68.23; H, 7.74; N, 4.80. 1H NMR (benzene-d6): δ
7.62, 7.14, 7.07 (m, 10 H, Ph), 6.33, 6.13, 5.16, 3.91 (m, each
2H, Cp), 1.83 (s, 12H, NMe2), 1.55 (s, 6H, C-CH3), -0.05 [s,
6H, Zr(CH3)2]. 13C NMR (benzene-d6): δ 147.5 (ipso-C of Ph),
127.7, 127.1 (CH of Ph, remaining signal under solvent), 135.2
tions [I g 2σ(I)], 325 refined parameters, R ) 0.084, wR2
0.247, maximum residual electron density 0.243 (-2.28) e Å-3
)
,
hydrogens calculated and riding. Accuracy is reduced due to
absorption of the large sample crystal. Cutting leads to a great
broadening of reflection profiles.
Rea ction of 11a w ith Tr is(p en ta flu or op h en yl)bor a n e.
F or m a tion of 13a . A solution of 0.82 g (1.6 mmol) of tris-
(pentafluorophenyl)borane in 30 mL of toluene was added to
a suspension of 0.68 g (1.6 mmol) of 11a in 30 mL of toluene
at -20 °C. Evolution of a gas was observed directly upon the
addition. The mixture was stirred for 2 h at -20 °C. During
this time a second oily phase separated. The toluene layer
was decanted from the oil. Pentane (80 mL) was added to the
oil and the mixture stirred for 2 days at ambient temperature
to solidify the product. The solid product was collected by
filtration and dried in vacuo to yield 1.2 g (84%) of the spiro-
metallocene 13a , mp 90 °C (dec DSC). Anal. Calcd for C38H34
-
BN2F15Zr (905.7): C, 50.39; H, 3.78; N, 3.09. Found: C, 49.87;
H, 3.79; N, 2.86. 1H NMR (600 MHz, 223 K, dichloromethane-
d2): δ 6.53, 5.90, 5.73 (m, each 2H) and 6.23, 5.52 (m, each
1H, Cp), 2.41 (s, 3H, N-CH3, 2.27 [s, 6H, N(CH3)2], 1.53, 2.21
2
(AX-system, J ) 9.6 Hz, -CH2-N), 1.58, 1.47, 1.46, 1.32 [s,
each 3H, C(CH3)2], 0.43 [br s, 3H, (C6F5)3B-CH3]. 13C NMR
(150 MHz, 223 K, dichloromethane-d2): δ 148.8 (1J CF ) 237
Hz), 138.0 (1J CF ) 252 Hz), 136.9 (1J CF ) 244 Hz), 128.3 (C6F5),
123.8, 115.4 (ipso-C of Cp), 113.1, 112.0, 110.2, 109.7, 106.7,
104.2, 99.7, 99.4 (CH of Cp), 60.6, 58.2 (CMe2), 49.1 (CH2), 47.7,
47.2 [N(CH3)2], 43.5 (N-CH3), 24.8, 24.3, 24.1, 17.5 [C(CH3)2],
9.5 (B-CH3).
Tr ea tm en t of r a c-11b w ith Tr is(p en ta flu or op h en yl)-
bor a n e. F or m a tion of 13b. Dichloromethane-d2 (0.5 mL)
was added to a mixture of the solid reagents rac-11b (27.3 mg,
0.5 mmol) and B(C6F5)3 (25.6 mg, 0.5 mmol) at ambient
temperature. A rapid gas evolution was observed. The
formation of the single 13b diastereomer was quantitative as
judged by NMR. 1H NMR (600 MHz, 303 K, dichloro-
methane): δ 7.3-7.5 (m, 10H, Ph), 6.83, 6.58, 6.40, 6.23, 6.14,
5.97, 5.85, 5.80 (m, each 1H, Cp), 2.97 (s, 3H, N-CH3), 2.55,
2.21 [s, each 3H, N(CH3)2], 2.51, 1.85 (AX-system, 2J ) 9.6
Hz, N-CH2-), 1.845, 1.841 (s, each 3H, C-CH3), δ 0.50 (br s,
3H, B-CH3). 13C NMR (150 MHz, 303 K, dichloromethane-
d2, signals of the cation are given only): δ 141.7, 140.1 (ipso-C
of Ph), 129.1, 128.3, 127.6, 127.3 (several signals overlapping,
CH of Ph), 121.6, 117.0 (ipso-C of Cp), 121.4, 113.3, 112.6,
109.7, 107.0, 104.5, 104.0, 100.4 (CH of Cp), 67.5, 67.1 (C-
CH3), 56.6 (CH2), 52.0 (N-CH3), 49.2, 49.0 [N(CH3)2], 29.1, 28.6
[C(CH3)2].
Ackn owledgm en t. Financial support from the Fonds
der Chemischen Industrie, the Krupp-Stiftung, the
Wissenschaftsministerium des Landes Nordrhein-West-
falen, and the Hoechst AG is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Details of the X-ray
crystal structure analyses of 9b and 11b and selected NMR
spectra of complexes 9-11 and 13 (40 pages). Ordering
information is given on any current masthead page.
OM970164X