1,3-doubly bridged group 4 metallocenes by intramolecular reductive coupling of pendant olefins

Article abstract of DOI:10.1021/om9905411

The new precursors M(NMe₂)₂Cl₂(dme) (M = Zr (3), Hf (4)) react with the dilithium derivative of the silyl-bridged bis(1-indenyl) ligand bearing pendant 4-pentenyl groups Li₂-[3,3′-⁵R₂-SBI] (2) in toluene at -35°C to provide the corresponding bis(dimethylamido) metallocenes with rac/meso ratios of 6-7:1. Subsequent treatment of the substantially racenriched zirconocene mixture with excess TMS-Cl in dichloromethane in the presence of a catalytic amount of anhydrous HCl provides rac-[3,3′-⁵R₂-SBI]ZrCl₂ (7) in 40% isolated yield free from its meso isomer. Similar reactions of Li₂[SBI]·OEt₂ and of Li₂[EBI]·OEt₂ with 3 and 4 also lead to selective formation of the rac-metallocenes with rac/meso ratios as high as 20:1 for [SBI]Zr(NMe₂)₂ (10). Sodium amalgam reduction of rac-[3,3′-⁵R₂-SBI]ZrCl₂ (7) in THF results in the intramolecular tail-to-tail coupling of the pendant olefins to provide the crystallographically characterized α,α′-disubstituted zirconacyclopentane 13 in 95% isolated yield. In contrast, reduction of rac-[3,3′-⁵R₂-SBI]HfCl₂ (8) (prepared from 2 and HfCl₄ in toluene) leads to both the symmetric α,α′-disubstituted and the unsymmetric α,β′-substituted hafnacyclopentanes (14 and 15, respectively) in a 1:1 ratio. Zirconacycle 13 reacts with [HNMe₂Ph]⁺[OTf]^- to give the monotriflate 17, in which one of the 4-pentenyl arms is released and the other is formally protonated at its terminal carbon atom to give this thermally stable secondary alkyl complex. Formation of 17 is best understood as proceeding through a mono-olefin intermediate 16, which can be trapped with 2-butyne to form the corresponding zirconacyclopentene 18. Reaction of 13 with the organometallic Lewis acid B(C₆F₅)₃ results in the formal abstraction of a hydride from the 3-position of one arm to form [HB(C₆F₅)₃]^- and a THF-bound π-allyl cation 19, in which one pendant alkene is also free.

Full text of DOI:10.1021/om9905411

Organometallics 2000, 19, 127-134
127
1,3-Dou bly Br id ged Gr ou p 4 Meta llocen es by
In tr a m olecu la r Red u ctive Cou p lin g of P en d a n t Olefin s
Timothy H. Warren, Gerhard Erker,* Roland Fro¨hlich,† and Birgit Wibbeling†
Organisch-Chemisches Institut der Universita¨t Mu¨nster, Corrensstrasse 40,
D-48149 Mu¨nster, Germany
Received J uly 12, 1999
The new precursors M(NMe2)2Cl2(dme) (M ) Zr (3), Hf (4)) react with the dilithium
derivative of the silyl-bridged bis(1-indenyl) ligand bearing pendant 4-pentenyl groups Li2-
[3,3′-5R2-SBI] (2) in toluene at -35 °C to provide the corresponding bis(dimethylamido)
metallocenes with rac/meso ratios of 6-7:1. Subsequent treatment of the substantially rac-
enriched zirconocene mixture with excess TMS-Cl in dichloromethane in the presence of a
catalytic amount of anhydrous HCl provides rac-[3,3′-5R2-SBI]ZrCl2 (7) in 40% isolated yield
free from its meso isomer. Similar reactions of Li2[SBI]‚OEt2 and of Li2[EBI]‚OEt2 with 3
and 4 also lead to selective formation of the rac-metallocenes with rac/meso ratios as high
as 20:1 for [SBI]Zr(NMe2)2 (10). Sodium amalgam reduction of rac-[3,3′-5R2-SBI]ZrCl2 (7)
in THF results in the intramolecular tail-to-tail coupling of the pendant olefins to provide
the crystallographically characterized R,R′-disubstituted zirconacyclopentane 13 in 95%
isolated yield. In contrast, reduction of rac-[3,3′-5R2-SBI]HfCl2 (8) (prepared from 2 and
HfCl4 in toluene) leads to both the symmetric R,R′-disubstituted and the unsymmetric R,â′-
substituted hafnacyclopentanes (14 and 15, respectively) in a 1:1 ratio. Zirconacycle 13 reacts
with [HNMe2Ph]+[OTf]- to give the monotriflate 17, in which one of the 4-pentenyl arms is
released and the other is formally protonated at its terminal carbon atom to give this
thermally stable secondary alkyl complex. Formation of 17 is best understood as proceeding
through a mono-olefin intermediate 16, which can be trapped with 2-butyne to form the
corresponding zirconacyclopentene 18. Reaction of 13 with the organometallic Lewis acid
B(C6F5)3 results in the formal abstraction of a hydride from the 3-position of one arm to
form [HB(C6F5)3]- and a THF-bound π-allyl cation 19, in which one pendant alkene is also
free.
In tr od u ction
reactions.7 Many of the above applications employ C2-
symmetric ansa-metallocenes, either in their racemic
or optically resolved forms,6d,8 which emphasizes the
importance of efficient routes to this important family
of catalyst precursors.
The C2-symmetric environment of group 4 rac-met-
allocenes based on symmetrically bridged indenyl or
tetrahydroindenyl ligands plays host to a number of
stereoselective C-C and/or C-H bond-forming pro-
cesses.1 Such reactions include isotactic R-olefin polym-
erization,2 asymmetric hydrogenation of alkenes3 and
imines,3 asymmetric hydrosilylation of ketones,5 asym-
metric carbomagnesation of cyclic allyl ethers and
amines,6a-c enantioselective carboalumination of
alkenes,6d and asymmetric catalysis of Diels-Alder
Focusing on the extremely rapid C-C and C-H bond-
forming reactions that metallocene cations mediate in
the polymerization of R-olefins, we became interested
in exploring potentially new reactivity patterns9 that
could result from the physical separation of the two
equivalent sites in a metallocene complex. The X-ray
structure of the ansa-zirconocene 1, which bears an
unusually long 12-carbon bridge, shows such a separa-
tion, as the bridge spans the front side of the coordina-
tion wedge rather than appearing opposite to it (Scheme
1).10 Unfortunately, this conformation is not maintained
in solution due to rotation of the indenyl rings.11 To
ensure that this desired conformation is rigorously
† X-ray crystal structure analyses.
(1) For an overview, see: Hoveyda, A. H.; Morken, J . P. Angew.
Chem. 1996, 108, 1378-1401; Angew. Chem., Int. Ed. Engl. 1996, 35,
1262-1284.
(2) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem. 1995, 107, 1255-1283; Angew. Chem.,
Int. Ed. Engl. 1995, 34, 1143-1170.
(3) Troutman, M. V.; Appella, D. H.; Buchwald, S. L. J . Am. Chem.
Soc. 1999, 121, 4916-4917.
(4) Willoughby, C. A.; Buchwald, S. L. J . Am. Chem. Soc. 1994, 116,
11703-11714.
(7) J aquith, J . B.; Guan, J .; Wang, S.; Collins, S. Organometallics
1995, 14, 1079-1081.
(5) Carter, M. B.; Schiøtt, B.; Gutie´rrez, A.; Buchwald, S. L. J . Am.
Chem. Soc. 1994, 116, 11667-11670.
(8) (a) Ringwald, M.; Stu¨rmer, R.; Brintzinger, H. H. J . Am. Chem.
Soc. 1999, 121, 1524-1527, and references therein. (b) Kondakov, D.
Y.; Negishi, E. J . Am. Chem. Soc. 1995, 117, 10771-10772. (c) Erker,
G.; Aulbach, M.; Knickmeier, M.; Wingbermu¨hle, D.; Kru¨ger, C.; Nolte,
M.; Werner, S. J . Am. Chem. Soc. 1993, 115, 4590-4601.
(9) Bertuleit, A.; Fritze, C.; Erker, G.; Fro¨hlich, R. Organometallics
1997, 16, 2891-2899.
(6) (a) Xu, Z. M.; J ohannes, C. W.; Houri, A. F.; La, D. S.; Cogan D.
A.; Hofilena, G. E.; Hoveyda, A. H. J . Am. Chem. Soc. 1997, 119,
10302-10316. (b) Heron, N. M.; Adams, J . A.; Hoveyda, A. H. J . Am.
Chem. Soc. 1997, 119, 6205-6206. (c) Visser, M. S.; Heron, N. M.;
Didiuk, M. T.; Sagal, J . F.; Hoveyda, A. H. J . Am. Chem. Soc. 1996,
118, 4291-4298. (d) Kondakov, D. Y.; Negishi, E. J . Am. Chem. Soc.
1995, 117, 10771-10772; 1996, 118, 1577-1578.
(10) Erker, G.; Mollenkopf, C.; Grehl, M.; Fro¨hlich, R.; Kru¨ger, C.;
Noe, R.; Riedel, M. Organometallics 1994, 13, 1950-1955.
10.1021/om9905411 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 12/16/1999

128 Organometallics, Vol. 19, No. 2, 2000
Warren et al.
Sch em e 1
Sch em e 2a
preserved in solution, we sought the synthesis of a 1,3-
doubly bridged analogue in which rotation of the indenyl
rings would be prevented.
Although synthetic routes to 1,2-doubly bridged met-
allocenes have been developed to provide ansa-metal-
locenes with a greater degree of rigidity,12 these methods
were not expected to be as successful in the preparation
of a 1,3-doubly bridged metallocene due to the greater
required length of the linker and the entropic challenges
that entail. Our strategy was to employ silyl-bridged
ansa-metallocenes bearing pendant groups in the 3- and
3′-positions which would be ammenable to coupling
reactions, thus using the bent metallocene geometry as
a template to bring these functionalities into mutual
proximity. We describe herein our efforts utilizing
terminal alkenyl pendants, chosen both for their com-
patibility with standard synthetic methods in the prepa-
ration of substituted indenyl ligands and their group 4
metallocenes13 and due to the wide range of potential
methods to couple these functionalities.14,15
a(i) 1 equiv of BuLi/THF, then ROTs/0 °C; (ii) BuLi/Et2O,
then 0.5 equiv of Me2SiCl2/-78 °C to room temperature; (iii)
2 equiv of BuLi/pentane.
Sch em e 3
Resu lts a n d Discu ssion
Scouting experiments were performed to determine
suitable group 4 metal complex precursors that would
allow the convenient isolation of the corresponding rac-
metallocene dichlorides derived from the dilithium salt
2. Although the metallocenes may by be prepared by
reaction between 2 and MCl4 (M ) Zr, Hf) in toluene,
the overall conversion is low (ca. 35%) and devoid of
stereoselectivity (rac/meso ) 1:1). In an attempt to boost
the overall conversion using two metal-based “protecting
groups”,16 the known Zr(NEt2)2Cl2(THF)217 reagent was
used. This led to much higher formation (ca. 90% crude)
of the red [3,3′-5R2-SBI]Zr(NEt2)2, but again as a 1:1
rac/meso mixture.
Reaction of the lithium salt 2 with the new, toluene-
soluble precursors M(NMe2)2Cl2(dme) (M ) Zr (3), Hf
(4)), which we prepared by reaction of M(NMe2)4 with 2
equiv of TMS-Cl in ether in the presence of 3-5 equiv
of dme, led as well to high conversion to the correspond-
ing [3,3′-5R2-SBI]M(NMe2)2 (M ) Zr (5), Hf (6)) com-
plexes, but in much higher rac/meso ratios estimated
at 6-7:1 (Scheme 3).18 Without requiring isolation, the
bis(dimethylamido)zirconocene 5 may be conveniently
converted to rac-[3,3′-5R2-SBI]ZrCl2 (7) by reaction with
excess TMS-Cl in the presence of a catalytic amount
Syn th esis of Silyl-Br id ged Liga n d s a n d a n sa -
Meta llocen e Com p lexes. The silyl-bridged ligand
employed in this study bearing two 5-carbon pendant
terminal olefin chains was prepared in a three-step
reaction sequence (Scheme 2). Deprotonation of indene
in THF with n-butyllithium followed by addition of
4-pentenyl tosylate afforded the corresponding 4-pen-
tenyl indene, which was isolated primarily as its
1-substituted isomer after distillation. Subsequent depro-
tonation with n-butyllithium in ether followed by the
addition of 0.5 equiv of Me2SiCl2 at -78 °C provided
the silyl-bridged bis(indene) ligand H2[3,3′-5R2-SBI] as
a yellow oil following flash chromatography. The cor-
responding dilithium salt Li2[3,3′-5R2-SBI] (2) was
prepared by deprotonation of the bis(indene) system in
pentane with n-butyllithium and is conveniently iso-
lated by filtration in roughly 60% overall yield (two
steps).
(11) Mollenkopf, C. Dissertation, University of Mu¨nster, 1994.
(12) (a) Mengele, W.; Diebold, J .; Troll, C.; Ro¨ll, W.; Brintzinger,
H.-H. Organometallics 1993, 12, 1931-1935. (b) Cano, A.; Cuenca, T.;
Go´mez-Sal, P.; Royo, B.; Royo, P. Organometallics 1994, 13, 1688-
1694.
(13) (a) Alt, H. G.; J ung, M. J . Organomet. Chem. 1999, 580, 1-16.
(b) Alt, H. G.; J ung, M. J . Organomet. Chem. 1998, 562, 229-253. (c)
Spence, R. E. v. H.; Piers, W. E. Organometallics 1995, 14, 4617-4624.
(14) Schuster, M.; Blechert, S. Angew. Chem. 1997, 109, 2124-2144;
Angew. Chem., Int. Ed. Engl. 1997, 36, 2037-2056. (b) Marsella-M.
J .; Maynard, H. D.; Grubbs, R. H. Angew. Chem. 1997, 109, 1147-
1150; Angew. Chem., Int. Ed. Engl. 1997, 36, 1101-1103.
(15) (a) Taber, D. F.; Louey, J . P.; Wang, Y.; Nugent, W. A.; Dixon,
D. A.; Harlow, R. L. J . Am. Chem. Soc. 1994, 116, 9457-9463. (b)
Negishi, E.; Takahashi, T. Acc. Chem. Res. 1994, 27, 124-130.
(16) Warren, T. H.; Schrock, R. R.; Davis, W. M. Organometallics
1998, 17, 308-321.
(17) Brenner, S.; Kempe, R.; Arndt, P. Z. Anorg. Allg. Chem. 1995,
621, 2021-2024.
(18) Similar diastereoselectivities were also observed using the
known Zr(NMe2)2Cl2(THF)2, but the new M(NMe2)2Cl2(dme) reagents
employed here were chosen for their ease of preparation and better
solubility in toluene.

1,3-Doubly Bridged Group 4 Metallocenes
Organometallics, Vol. 19, No. 2, 2000 129
Sch em e 4a
Sch em e 5
a(i) 1 equiv of Li2[SBI]‚OEt2; (ii) 1 equiv of Li2[EBI]‚OEt2
toluene/-35 °C to room temperature.
of anhydrous HCl. Although the zirconocene dichloride
7 may be isolated free from its meso isomer in ca. 40%
yield, similar conversion of hafnocene 6 to the desired
rac-[3,3′-5R2-SBI]HfCl2 (8) proved unreliable. rac-[3,3′-
5R2-SBI]HfCl2 (8) is instead best prepared directly from
2 and HfCl4 in toluene and is isolated isomerically pure
in 10-15% yield following one recrystallization.
To test the generality of the stereoselectivity observed
in the transmetalation of the bis(1-indenyl) ligand 2
observed above, a similar protocol was tried with two
related bis(indenyl) ligands. Reactions of Li2[SBI]‚OEt2
and Li2[EBI]‚OEt2 with M(NMe2)2Cl2(dme) (3 and 4)
provide the corresponding bis(dimethylamido)metal-
locenes 9-12 in ca. 90% purity (1H NMR) and in rac/
meso ratios of over 20:1 in the case of [SBI]Zr(NMe2)2
(9) (Scheme 4). Simple removal of the volatiles in vacuo
followed by recrystallization of the residue from toluene
after filtration provided the pure rac-metallocenes in
about 50% overall yield (unoptimized).
disubstituted hafnacyclopentane 14 could be identified
from the H NMR spectrum of this mixture by compari-
1
son of its three characteristic indenyl 2-H, Me2Si, and
Hf-CHR signals (δ 5.35, 0.55, and -1.99 ppm, respec-
tively) with corresponding resonances from 13. Further-
more, the 600 MHz 1H 1D-TOCSY NMR spectrum
obtained by irradiation of the resonance assigned to the
Hf-CHR group of the symmetric isomer 14 at δ -1.99
ppm reveals metallacycle resonances that are essen-
tially superimposable on those appearing in the 1H
NMR spectrum of its zirconium analogue 13. In contrast
to the symmetric 13 and 14, the absence of C2-symmetry
in the other hafnacycle 15 results in two 1H NMR
signals at δ 5.51 and 5.29 ppm as well as at δ 0.64 and
0.47 ppm for its inequivalent indenyl 2-H and Me2Si
groups, respectively. Furthermore, complete assignment
of the coupled pendants based on a series of 1H-1H and
1H-13C correlation NMR spectra as well as 1H 1D-
TOCSY NMR spectra reveals both Hf-CHR (δ 1.11
ppm) and Hf-CHaHbR (δ -0.16 and -1.73 ppm) groups,
identifiying metallacycle 15 as derived from the head-
to-tail coupling of the pendant olefins.
In tr a m olecu la r Red u ctive Olefin Cou p lin g. Re-
duction of rac-[3,3′-5R2-SBI]ZrCl2 (7) bearing the 5-car-
bon arms was effected with sodium amalgam in THF.
It results in the intramolecular tail-to-tail coupling of
the two pendant olefins to provide the C2-symmetric
R,R′-disubstituted zironacyclopentane 13 in 90% isolated
yield (Scheme 5). The 1H NMR spectrum of 13 lacks
characteristic terminal alkenyl resonances, and al-
though two diastereomeric R,R′-disubstituted zironacy-
clopentanes are possible, singlets observed for the
indenyl 2-H and Me2Si groups (δ 5.49 and 0.54 ppm,
respectively) suggest the presence of a single diastere-
1
omer. In conjuction with H-1H correlation spectra, the
single upfield resonance at δ -2.14 ppm is assigned to
the secondary Zr-CHR groups. The metallacyclopen-
1
tane formulation is further corroborated by the J CH
coupling constants of 122.5 and 124.5 Hz for the carbon
atoms R and â to zirconium, respectively.19 1H NOE
NMR experiments as well as rudimentary molecular
modeling studies favor the diastereomer shown in
Scheme 5, and this was confirmed by an X-ray crystal
structure analysis (see below).
X-r a y Cr ysta l Str u ctu r a l An a lyses. The asym-
metric units of the isostructural complexes 13 and 14
contain both enantiomers of the corresponding C2-
symmetric bis(indenyl) metallocene, of which one of
these enantiomers shows positional disorder for the
carbon atoms â and γ to the indenyl rings. The non-
disordered molecule of zirconacyclopentane 13 (Figure
1) clearly shows the coupling of the two formerly
pendant ω-alkenes to form a C-C single bond with a
C(12)-C(32) distance of 1.541(7) Å [Hf complex 14:
In contrast, the analogous reduction of rac-[3,3′-5R2-
SBI]HfCl2 (8) leads to a ca. 1:1 ratio of two products in
90% overall yield (Scheme 5). The symmetric R,R′-
(19) Takahashi, T.; Fischer, R.; Xi, Z.; Nakajima, K. Chem. Lett.
1996, 357-358.

130 Organometallics, Vol. 19, No. 2, 2000
Warren et al.
Sch em e 6a
F igu r e 1. DIAMOND representation (50% probability
level) of the nondisordered molecule found in the X-ray
study of 13. Selected bond distances (Å) and angles (deg):
Zr(1)-C(11), 2.286(5), Zr(1)-C(31) 2.294(5), C(12)-C(32)
1.541(7), C(11)-C(12) 1.542(7), C(31)-C(32) 1.547(7), C(11)-
Zr(1)-C(31) 87.36(17), Zr(1)-C(11)-C(12) 97.4(3), Zr(1)-
C(31)-C(32) 99.2(3), C(11)-C(12)-C(32) 112.1(4), C(12)-
C(32)-C(31) 115.0(4), Zr(1)-C(31)-C(30) 124.0(3), Zr(1)-
C(11)-C(10) 125.2(3).
a(i) 1-5 equiv of [HMe2NPh]+[OTf]-/benzene-d6; (ii) 10 equiv
of 2-butyne/benzene-d6/overnight.
Rea ctivity of th e Meta lla cyclop en ta n es. With
closure of the two indenyl-bound alkenyl arms effected
by the metallocene centers, we felt that we might be
able to simply remove the coupled alkyl chains in 13-
15 from the metal center by protonation with 2 equiv
of an HCl source. Ideally, this would provide 1,3-doubly
bridged metallocene dichlorides bearing either a 10
(from 13 and 14) or nine (from 15) carbon chain
spanning the metallocene coordination wedge. Whereas
reaction with anhydrous HCl in toluene did not lead to
any tractible products at temperatures spanning from
-78 °C to room temperature, the benzene-soluble
[HNMe2Ph]+[OTf]- reacts slowly with zirconacycle 13
to produce the ring-opened product 17, in which one of
the ω-alkenyl arms is released from the metal center
and the terminal carbon of a bound pendant alkene is
protonated (Scheme 6). The reaction is relatively slow,
occurring over 20 min at room temperature in benzene-
d6 (ca. 0.05 M in 13, 0.3 M in [HNMe2Ph]+[OTf]-), and
the new secondary alkylmetallocene complex 17 is
surprisingly stable in the presence of excess anilinium
F igu r e 2. SCHAKAL representation of 13 highlighting
the 10-carbon bridge which results upon metallacycle
formation.
1.511(8) Å].20 These bond distances lie comfortably
within the range established, 1.502(5)-1.560(3) Å, for
other structurally characterized group 4 metallacyclo-
pentanes.15a,19,21,22 The Zr-C distances of 2.286(5) and
2.294(5) Å [Hf: 2.258(5), 2.282(5) Å] as well as the
C-Zr-C angle of 87.36(17)° [Hf: 86.2(2)°] are also
comparable to those distances and angles found in other
related zirconacyclopentanes (2.275(2)-2.347(4) Å and
81.2(1)-89.2(1)°, respectively). There does not appear
to be any appreciable ring strain in the metallacycle
itself, as both 13 and 14 exhibit ring angles in the range
109-115°, and the Cp(centr)-M-Cp(centr) angles of
127.4(2)° (13) and 128.0(2)° (14) also reveal no unusual
distortion. It would thus appear that the 4-pentenyl
arms were ideally situated to couple, forming the R,R′-
disubstituted metallacyclopentanes 13 and 14.
1
salt. Whereas olefinic H NMR resonances centered at
δ 5.73 and 4.95 ppm clearly reveal the dissociation of
one pendant alkenyl arm, a multiplet of relative inten-
sity 1 at δ -1.79 ppm shows that one secondary Zr-
CH unit has remained intact. Protonation of the termi-
nal carbon of this “bound” pendant has resulted in a
doublet at δ 0.88 ppm coupled solely to the Zr-CH
group (3J HH ) 8.4 Hz). Furthermore, the unsymmetric
nature of 17 is reflected in the observation of diaste-
reotopic indenyl 2-H (δ 6.24 and 5.08 ppm) as well as
Me2Si groups (δ 0.65 and 0.53 ppm). In contrast to 13,
no reaction occurs between 14 or 15 and [HNMe2Ph]+-
[OTf]- over hours under similar conditions.
The surprising inertness of 13 toward protonolytic
cleavage of the Zr-C σ-bond is probably due to severe
steric crowding at the central core of the molecule. The
observed mode of protonation of 13 seemed to indicate
reversibility of the metallacycle formation and even the
dissociation of a pendant olefin from the metallacycle
to form the alleged mono-olefin metallocene intermedi-
ate 16 (Scheme 6). This assumption was supported by
a trapping reaction with excess 2-butyne. Reaction of
13 with 10 equiv of 2-butyne in benzene slowly leads to
the formation of zirconacyclopentene 18, in which 1
(20) Complete structural details from the X-ray crystal structure
determination of 14 can be found in the Supporting Information.
(21) (a) Knight, K. S.; Wang, D.; Waymouth, R. M.; Ziller, J . J . Am.
Chem. Soc. 1994, 116, 1845-1854. (b) Mashima, K.; Sakai, N.; Takaya,
H. Bull. Chem. Soc. J pn. 1991, 64, 2475-2483. (c) Schmidt, J . R.;
Duggan, D. M. Inorg. Chem. 1981, 20, 318-323.
(22) In the structures of the zirconacyclopentanes rac-[EBTHI]Zr-
(CHPhCH2CHPhCH2) and rac-[EBTHI]Zr(C4H8), disorder in either one
or both of the Câ atoms results in abnormally short Câ-Câ distances
of 1.331(6) and 1.451(7) Å, respectively. Mansel, S.; Thomas, D.;
Lefeber, C.; Heller, D.; Kempe, R.; Baumann, W.; Rosenthal, U.
Organometallics 1997, 16, 2886-2890.

1,3-Doubly Bridged Group 4 Metallocenes
Organometallics, Vol. 19, No. 2, 2000 131
Sch em e 7
13 (δ 35.7, 65.1, and 29.6 ppm; C-10 to C-12, respec-
tively).
In conclusion, we have demonstrated an effective new
method for the stereoselective synthesis of rac-metal-
locenes through the reaction of dilithium salts of bridged
bis(indenyl) systems with the easily prepared reagents
M(NMe2)2Cl2(dme) (M ) Zr (3), Hf (4)). Complementary
to the route described by J ordan employing the free
ansa-metallocene ligand and M(NMe2)4,26 this new
method holds promise in cases where the desired ansa-
metallocene ligand is either too bulky or not acidic
enough to undergo efficient and complete aminolysis.
The bent sandwich geometry of related silyl-bridged
ansa-metallocenes rac-[3,3′-5R2-SBI]MCl2 (M ) Zr (7),
Hf (8)) may be used to bring substituents in the 3- and
3′-positions into mutual proximity. Simple reduction of
7 and 8 with sodium amalgam effects the coupling of
the 4-pentenyl arms leading to 1,3-doubly bridged
metallocenes through metallacyclopentane formation
and illustrates how ligand systems may be further
functionalized after transmetalation.
Sch em e 8
equiv of alkyne formally adds to the intermediate 16.
In the H NMR spectrum of 18, two methyl resonances
Exp er im en ta l Section
1
All reactions involving butyllithium or group 4 metal
compounds were carried out under argon using Schlenk-type
glassware or in a glovebox. Solvents were purified by standard
techniques, while deuterated NMR solvents were dried and
stored over activated 4 Å molecular sieves before use. NMR
spectra were recorded on either a Bruker AC 200P (1H, 200.13;
13C, 50.3 MHz; 11B, 64.2 MHz) or on a Varian Unity Plus (1H,
599.9; 13C, 150.8; 19F, 471.0 MHz) NMR spectrometer in which
1H and 13C assignments were in some cases confirmed through
GCOSY, GHSQC, GHMBC, and one-dimensional TOCSY
spectra.27 All NMR spectra were recorded at room temperature
unless otherwise noted. Proton and carbon NMR spectra were
referenced internally by the 1H or 13C signal of the solvent
relative to trimethylsilane. Fluorine and boron spectra were
referenced externally to neat CFCl3 and BF3 etherate, respec-
tively. Coupling constants J are reported in Hz. Melting points
were obtained using a TA Instruments DSC 2010 differential
scanning calorimeter, and elemental analyses were obtained
using a Foss-Heraeus CHN-Rapid microanalyzer.
at δ 1.39 and 1.27 ppm indicate the incorporation of 1
equiv of 2-butyne into the metallacycle that still bears
one secondary Zr-CH group (δ 0.26 ppm), and the
olefinic multiplets centered at δ 5.74 and 4.95 ppm
establish the dissociation of one pendant alkene. The
observation of both two indenyl 2-H (δ 6.04 and 5.49
ppm) and two Me2Si (δ 0.70 and 0.69 ppm) H NMR
signals serves to further illustrate the unsymmetric
nature of 18.
Although 14 and 15 do not readily incorporate 2-bu-
tyne under similar conditions, evidence that pendant
olefin complexes are accessible in the hafnium system
comes from heating a ca. 1:1 mixture of the hafnacycles
14 and 15 in benzene-d6. After 18 h at 65 °C, equilib-
rium is established in favor of the symmetric isomer 14
(K ) 6), indicating that interconversion between these
two hafnacycles does take place and is most reasonably
mediated by an intermediate analogous to 16 (Scheme
7).
1
X-ray data sets were collected with a Nonius KappaCCD
diffractometer, using a rotating anode generator FR591.
Programs used: data collection Collect, data reduction Denzo-
SMN, absorption correction SORTAV, structure solution
SHELXS-97, structure refinement SHELXL-97, graphics DIA-
MOND and SCHAKAL-92.28
Reaction with the organometallic Lewis acid B(C6F5)3
follows an unusual course. Rather than abstracting23
a
secondary carbon from the zirconacycle 13 or adding to
the terminal carbon24 in the mono-olefin intermediate
16, a hydride is formally abstracted from the middle
carbon of one bound pendant arm (probably at the stage
of the reactive intermediate 16). The [H-B(C6F5)3]-
anion results (11B NMR: δ 24.9 ppm, (d))25 as well as
the π-allylmetallocene cation 19, which is stable when
generated in the presence of THF (Scheme 8). Whereas
the allyl unit in 19 could be assigned by a combination
of 1D-TOCSY NMR and correlation NMR spectra, its
cationic nature is strongly suggested by the dramatic
downfield shifts of the 13C NMR signals of the allylic
carbon atoms (δ 88.2, 131.4, and 107.8 ppm) when
compared to their resonances in the neutral zirconacycle
Tris(pentafluorophenyl)borane29 as well as M(NMe2)4 (M )
Zr,26e Hf26b) were prepared according to literature proceedures.
(26) (a) Christopher, J . N.; J ordan, R. F.; Petersen, J . L.; Young, V.
G. Organometallics 1997, 16, 3044-3050. (b) Diamond, G. M.; J ordan,
R. F.; Petersen, J . L. Organometallics 1996, 15, 4030-4037. (c)
Christopher, J . N.; Diamond, G. M.; J ordan, R. F.; Petersen, J .
Organometallics 1996, 15, 4038-4044. (d) Diamond, G. M.; J ordan,
R. F.; Petersen, J . L. Organometallics 1996, 15, 4045-4053. (e)
Diamond, G. M.; J ordan, R. F.; Petersen, J . L. J . Am. Chem. Soc. 1996,
118, 8024-8033. (f) Diamond, G. M.; Rodewald, S.; J ordan, R. F.
Organometallics 1995, 14, 5-7.
(27) Braun, S.; Kalinowski, H.; Berger, S. 100 and More Basic NMR
Experiments; VCH: Weinheim, 1996, and references therein.
(28) Programs used: Data collection: COLLECT: Nonius B.V., 1998.
Data reduction: Denzo-SMN: Otwinowski, Z.; Minor, W. Methods
Enzymol. 1997, 276, 307-326. Absorption Correction: SORTAV:
Blessing, R. H. Acta Crystallogr. 1995, A51, 33-37; J . Appl. Crystal-
logr. 1997, 30, 421-426. Structure Solution: SHELXS-97: Sheldrick,
G. M. Acta Crystallogr. 1990, A46, 467-473. Sheldrick, G. M. Uni-
versita¨t Go¨ttingen, 1997. Structure refinement: SHELXL-97: Sheld-
rick, G. M. Universita¨t Go¨ttingen, 1997. Graphics: DIAMOND: Bran-
denburg, K. Universita¨t Bonn, 1996; SCHAKAL-92: Keller, E.
Universita¨t Freiburg, 1997.
(23) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1991,
113, 3623-3625.
(24) Sun, Y. M.; Piers, W. E.; Rettig S. J . Chem. Commun. 1998,
127-128.
(25) Blaschke, U.; Erker, G.; Nissinen, M.; Wegelius, E.; Fro¨hlich,
R. Organometallics 1999, 18, 1224-1234.

132 Organometallics, Vol. 19, No. 2, 2000
Warren et al.
Directly before use, indene (Fluka, g90%) was either freshly
distilled or purified by passage of a ca. 10% v/v pentane
solution through silica gel followed by removal of pentane in
vacuo. Me2SiCl2 was distilled from N,N-dimethylaniline under
argon after stirring overnight to remove HCl. Li2[EBI]‚OEt2
and Li2[SBI]‚OEt2 were prepared by adding 2 equiv of n-
butyllithium to the corresponding bis(indenes)26c,30 in ether and
then isolating the product by filtration. [HNMe2Ph]+[OTf]- was
prepared by adding freshly opened triflic acid (Aldrich, 98%)
to a equimolar solution of N,N-dimethylaniline in pentane at
0 °C after decanting this solution from 4 Å molecular sieves.
4-P en ten yl Tosyla te.31 Freshly ground potassium hydrox-
ide (170 g, 2.95 mol) was slowly added over 30 min to a stirring
solution of 4-penten-1-ol (21.2 g, 246 mmol) and tosyl chloride
(56.3 g, 296 mmol) in 600 mL of ether at 0 °C. After stirring
for an additional 1.5 h, the mixture was quenched with ice
water (ca. 300 mL) until all of the remaining KOH dissolved.
The organic fraction was separated and the aqueous phase
washed with ether (2 × 150 mL). After drying the combined
organic extracts over MgSO4, removal of the volatiles in vacuo
rinsed with pentane (300 mL). The volatiles were removed in
vacuo to give a 1:1 rac/meso mixture of Me2Si(1-(3-(4-pentenyl)-
indene)2). The yellow oil was then taken up in 250 mL of
pentane and sparged with argon. Butyllithium (83 mL, 131
mmol, 1.58 M in hexane) was added at 0 °C, and after ca. 1
h the product began to precipitate. After 4 h, the precipitate
was collected by filtration, rinsed with pentane, and dried in
vacuo. The solid was then dispersed in pentane (200 mL), and
the suspension was stirred for 3 h to remove all traces of
butyllithium. The solid was again collected by filtration,
washed with pentane (50 mL), and dried in vacuo to yield 18.8
1
g (62%) of the product as slightly off-white powder. H NMR
(C6D6/THF-d8, ca. 10:1, 200 MHz): δ 8.08 (m, 2, Ar), 7.71 (m,
2, Ar), 7.01 (s, 2, 2-H), 5.93 (m, 2, CHdCH2), 5.02 (m, 4, CHd
CH2), 3.05 (t, 4, ind-CH2), 2.27 (q, 4, CH2), 1.93 (q, 4, CH2),
0.97 (SiMe2). 13C NMR (C6D6/THF-d8, ca. 10:1, 50 MHz): δ
140.0, 134.5, 130.1, 123.9, 122.2, 118.3, 115.5, 115.2, 114.1,
109.9, 96.6, 34.7, 32.4, 28.4, 3.0. Anal. Calcd for C30H38Li2Si
(440.6): C, 81.78; H, 8.69. Found: C, 81.54; H, 8.54.
Zr (NMe2)2Cl2(d m e) (3). Chlorotrimethylsilane (9.77 mL,
77.0 mmol) was added to a solution of Zr(NMe2)4 (10.30 g, 38.5
mmol) in ether (200 mL) with dme (20 mL). After stirring
overnight, the solution was concentrated to ca. 30 mL and
allowed to crystallize at -30 °C. Decanting the mother liquors
followed by drying the very pale yellow crystals in vacuo gave
a first crop of 8.89 g. A second crop of 3 could be obtained by
further concentration and crystallization of the mother liquors
1
afforded 55.4 g (94%) of the tosylate as colorless oil. H NMR
(CDCl3, 200 MHz): δ 7.74 (d, 2, Ar-H), 7.30 (d, 2, Ar-H), 5.66
(m, 1, CHdCH2), 4.92 (m, 2, CHdCH2), 3.98 (t, 2, OCH2), 2.40
(s, 3, Ar-CH3), 2.03 (q, 2, CH2), 1.69 (q, 2, CH2). 13C NMR
(CDCl3, 50 MHz): δ 144.7, 136.6, 133.1, 129.8, 127.8, 115.8,
69.8, 29.3, 27.9, 21.6. Anal. Calcd for C12H16O3S (240.3): C,
59.98; H, 6.70. Found: C, 59.34; H, 6.72.
1
to give a total yield of 10.35 g (76%). H NMR (C6D6/THF-d8,
3-(4-P en ten yl)in d en e. Butyllithium (146 mL, 231 mmol,
1.58 M in hexane) was slowly added to a solution of indene
(26.7 g, 230 mmol) in 250 mL of THF at 0 °C. After stirring
for 3 h, a solution of 4-pentenyl tosylate (53.9 g, 224 mmol) in
50 mL of THF was added dropwise over 45 min at 0 °C. The
solution was stirred overnight, allowing to slowly warm to
room temperature. After addition of a few drops of water, the
suspension was concentrated by rotary evaporation and then
extracted with water (250 mL) and ether (400 mL). The organic
phase was separated and the aqueous phase washed twice with
ether (100 mL). The organic extracts were dried over MgSO4
and then concentrated to dryness. A small amount of unre-
acted tosylate was removed by dissolving the orange oil in
pentane (100 mL) and filtering through a pad of silica gel,
which was then rinsed with pentane (300 mL). Fractional
distillation (80 °C, 0.1 mbar) gave the product as a colorless
liquid (28.1 g, 67%) containing a small amount (6%) of the 1,1-
disubstituted indene. 1H NMR (CDCl3, 200 MHz): δ 7.50-
7.15 (m, 4, Ar), 6.24 (t, 1, 2-H), 5.91 (m, 1, CHdCH2), 5.07 (m,
2, CHdCH2), 3.35 (d, 2, ring CH2), 2.60 (t, 2, ind-CH2), 2.21
(q, 2, CH2), 1.83 (q, 2, CH2). 13C NMR (CDCl3, 50 MHz): δ
144.5, 144.3, 138.6, 133.0, 127.8, 125.9, 124.43, 123.7, 118.9,
114.7, 37.7, 33.6, 27.2, 27.1. (Extra peaks appear in this 13C
NMR spectrum due to the presence of the disubstituted isomer
and cannot be assigned with utmost certainty to the product.)
Anal. Calcd for C14H16 (184.3): C, 91.26; H, 8.74. Found: C,
91.25; H, 9.16.
ca. 10:1, 200 MHz): δ 3.28 (br, 4, OCH2), 3.27 (s, 12, NMe2),
3.12 (s, 6, OCH3). 13C NMR (C6D6/THF-d8, ca. 10:1, 50 MHz):
δ 74.9 (v br, OCH2), 62.1 (OCH3), 44.6 (NMe2). Mp: 89 °C. Anal.
Calcd for C8H22N2Cl2O2Zr (340.4): C, 28.23; H, 6.51; N, 8.23.
Found: C, 28.15; H, 6.71; N, 8.04.
Hf(NMe2)2Cl2(d m e) (4). Chlorotrimethylsilane (7.04 mL,
55.5 mmol) was added to a solution of Hf(NMe2)4 (9.85 g, 27.8
mmol) in ether (100 mL) with dme (15 mL). After stirring
overnight, the solution was concentrated to ca. 30 mL and
allowed to crystallize at -30 °C. Decanting the mother liquors
followed by drying the colorless crystals in vacuo gave a yield
of 9.50 g (80%). 1H NMR (C6D6/THF-d8, ca. 10/1, 600 MHz): δ
3.40 (s, 12 H, NMe2), 3.10 (s, 6 H, OCH3), 3.12 (s, 4 H, OCH2).
13C NMR (C6D6/THF-d8, ca. 10:1, 150 MHz): δ 71.6 (OCH2),
62.1 (OCH3), 44.2 (NMe2). Mp: 95 °C. Anal. Calcd for C8H22N2-
Cl2HfO2 (427.7): C, 22.47; H, 5.18; N, 6.55. Found: C, 22.15;
H, 4.90; N, 6.38.
r a c-[3,3′-5R2-SBI]Zr Cl2 (7). Chilled toluene (70 mL, -30
°C) was added to a solid mixture of 2 (5.53 g, 12.7 mmol) and
3 (4.32 g, 12.7 mmol). The suspension immediately became
red and was allowed to warm to room temperature with
stirring. After 2 h, the red solution was filtered through Celite
and concentrated to ca. 10 mL. An aliquot measured by 1H
NMR spectroscopy showed that the major species in solution
was rac-[3,3′-5R2-SBI]Zr(NMe2)2 (5), whose Me2Si resonance
appears at δ 0.87 ppm. Integrating the largest indenyl 2-H
resonance (δ 6.12 ppm) against the second largest (δ 6.20 ppm)
in this region afforded a conservative estimate of 6:1 for the
rac/meso ratio of this mixture. Dichloromethane (60 mL) was
added followed by TMS-Cl (6.43 mL, 50.7 mmol). The solution
was chilled to 0 °C, after which anhydrous HCl (0.63 mL, 0.63
mmol, 1.0 M in ether) was added with stirring. After 10 min,
the red color of the solution faded to orange, signaling
conversion to the dichloride. In some preparations the color
did not change after addition of 5 mol % HCl, requiring the
addition of another portion or two to effect complete conver-
sion. The solution was concentrated to dryness, and the residue
was washed with pentane and then crystallized from toluene
to give 2.83 g (38%) of the product 7 as orange microcrystals.
1H NMR (C6D6, 600 MHz): δ 7.38 (d of t, 2 H, 4-H), 7.27 (d of
t, 2 H, 7-H), 7.14 (m, 2 H, 5-H), 6.88 (m, 2 H, 6-H), 5.72 (s, 2
H, 2-H), 5.67 (m, 2 H, 11-H), 4.92 (m, 4 H, 12-CH2), 2.83 (t, 4
H, 8-CH2), 1.92 (m, 4 H, 10-CH2), 1.53 (m, 4 H, 9-CH2), 0.65
Li2[Me2Si(1-(3-(4-p en ten yl)in d en e)2)] (Li2[3,3′-5R2-SBI])
(2). Butyllithium (88.1 mL, 139 mmol, 1.58 M in hexane) was
slowly added to a solution of 3-(4-pentenyl)indene (28.1 g, 139
mmol) in 150 mL of ether at 0 °C. After stirring for 3 h, the
solution was chilled to -78 °C, and a solution of Me2SiCl2 (8.98
g, 69.6 mmol) in ether (50 mL) was added dropwise over 45
min. The solution was stirred overnight, slowly allowing to
warm to room temperature. The volatiles were removed in
vacuo, and the remaining oil was taken up in pentane (100
mL) and filtered through a pad of silica gel, which was then
(29) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2, 245-
250.
(30) Collins, S.; Kuntz, B. A.; Taylor, N. J .; Ward, D. G. J .
Organomet. Chem. 1988, 342, 21-29.
(31) An established method was employed: Brandsma, L. Prepara-
tive Acetylenic Chemistry, 2 ed.; Elsevier: Amsterdam, 1988; pp 256-
257.

1,3-Doubly Bridged Group 4 Metallocenes
Organometallics, Vol. 19, No. 2, 2000 133
(SiMe2). 13C NMR (C6D6, 150 MHz): δ 138.5 (C-11), 133.0 (C-
3a), 131.4 (C-3), 128.2 (C-7a), 126.8 (C-5), 126.6 (C-6), 124.9
(C-7), 124.7 (C-4), 117.1 (C-2), 115.0 (C-12), 85.7 (C-1), 33.9
(C-9), 29.6 (C-10), 28.2 (C-8), -1.8 (SiMe2). Mp: 200 °C. Anal.
Calcd for C30H34Cl2SiZr (584.8): C, 61.61; H, 5.86. Found: C,
61.67; H, 6.58.
123.7, 123.6 (C-6 and C-7), 123.1 (C-4), 122.6 (C-3), 118.9 (C-
2), 79.9 (C-1), 65.1 (1J CH ) 122.5, C-11), 35.7 (1J CH ) 122.0,
C-10), 29.6 (1J CH ) 124.5, C-12), 28.5 (C-9), 26.2 (C-8), -2.1
(SiMe2). Mp: 147 °C (decomp). Anal. Calcd for C30H34SiZr
(513.9): C, 70.12; H, 6.67. Found: C, 69.97; H 6.95. X-ray
crystal structure analysis of 13: formula C30H34SiZr, M )
513.88, 0.50 × 0.30 × 0.30 mm, a ) 14.352(1) Å, b ) 10.216-
r a c-[3,3′-5R2-SBI]HfCl2 (8). Chilled (-35 °C) toluene (75
mL) was added to a solid mixture of HfCl4 (2.95 g, 9.21 mmol)
and 2 (4.02 g, 9.21 mmol). The suspension became yellow once
stirring commenced and was allowed to warm to room tem-
perature. After stirring overnight, the yellow suspension was
filtered through Celite, concentrated to ca. 15 mL, and chilled
to -35 °C. A first crop of ca. 1.5 g consisting of a 85:15 rac/
meso mixture was recrystallized from Et2O/dichloromethane
(50:50) to give 0.77 g (12%) of the product as bright yellow
(1) Å, c ) 32.489(1) Å, â ) 92.42(1)°, V ) 4759.3(6) Å3, Fcalc
)
1.434 g cm-3, µ ) 5.29 cm-1, empirical absorption correction
(0.778 e T e 0.858), Z ) 8, monoclinic, space group P21/n (No.
14), λ ) 0.71073 Å, T ) 198 K, ω and æ scans, 18 828
reflections collected ((h, (k, (l), [(sin θ)/λ] ) 0.67 Å-1, 8784
independent (Rint ) 0.058) and 7852 observed reflections [I g
2 σ(I)], 619 refined parameters, R ) 0.058, wR2 ) 0.129, max.
residual electron density 0.63 (-0.76) e Å-3, two independent
molecules in the asymmetric unit being enantiomers, checking
of λ/2 gives no indication of cell doubling, positional disorder
in the carbon chain of the second molecules refined with
restraints (0.57(1):0.43(1); 0.53(1):047(1)), hydrogens calculated
and refined as riding atoms.
1
microcrystals. H NMR (C6D6, 600 MHz): δ 7.37 (d of t, 2 H,
7-H), 7.33 (d of t, 2 H, 7-H), 7.11 (m, 2 H, 5-H), 6.87 (m, 2 H,
6-H), 5.69 (s, 2 H, 2-H), 5.67 (m, 2 H, 11-H), 4.92 (m, 4 H,
12-CH2), 2.83 (t, 4 H, 8-CH2), 1.92 (m, 4 H, 10-CH2), 1.53 (m,
4 H, 9-CH2), 0.66 (SiMe2). 13C NMR (C6D6, 150 MHz): δ 138.5
(C-11), 132.2 (C-3a), 129.1 (C-3), 126.9 (C-7a), 126.7 (C-5),
126.5 (C-6), 124.9 (C-7), 124.5 (C-4), 115.3 (C-2), 114.9 (C-12),
86.1 (C-1), 33.9 (C-9), 29.6 (C-10), 28.1 (C-8), -1.7 (SiMe2).
Anal. Calcd for C30H38Cl2SiHf (676.1): C, 53.29; H, 5.67.
Found: C, 53.62; H, 5.11.
r a c-[SBI]Zr (NMe2)2 (9). Chilled (-35 °C) toluene (25 mL)
was added to a solid mixture of Li2[SBI]‚OEt2 (0.593 g, 1.58
mmol) and 3 (0.593 g, 1.50 mmol). The suspension turned red
rapidly and was allowed to warm to room temperature with
stirring. After 3 h, the volatiles were removed in vacuo, and
the residue was extracted with toluene (20 mL). The extracts
were filtered through Celite, and the filtrate was concentrated
to ca. 5 mL and was allowed to crystallize overnight at -30
°C. The mother liquors were then decanted and the crystals
dried in vacuo to provide 0.49 g (66%, unoptimized) of the
product as red crystals. 1H NMR analysis26 of the toluene
extracts prior to crystallization indicated a rac/meso ratio of
greater than 20.
Ha fn a cyclop en ta n es 14 a n d 15. Chilled THF (120 mL,
-30 °C) was added to a solid mixture of 8 (1.60 g, 2.38 mmol)
and freshly prepared sodium amalgam (44 g, 9.5 mmol, 0.5%
Na in Hg). Rapid stirring at 0 °C resulted in a darkening of
the solution to forest green and dispersion of the amalgam.
After ca. 1 h, the solution became yellow again and was stirred
overnight. The volatiles were removed in vacuo, the residue
was extracted with toluene (50 mL), and then the extracts were
filtered through Celite. Removal of the volatiles in vacuo
provided 1.28 g (89%) of the product as yellow microcrystals.
Crystals of 14 suitable for an X-ray crystal structure analysis
were obtained by slow evaporation of a benzene solution
containing a mixture of 14 and 15. Spectral data for symmetric
hafnacyclopentane 14: 1H NMR (C6D6, 600 MHz, atom num-
bering as in Scheme 7): δ 7.45 (d of t, 2 H, 4-H), 7.04 (m, 2 H,
5-H), 6.93 (d of t, 2 H, 7-H), 6.70 (m, 2 H, 6-H), 5.39 (s, 2 H,
2-H), 2.99 (m, 2 H, 8-CH2), 2.74 (m, 2, 8-CH2), 2.11 (m, 2 H,
10-CH2), 2.01 (m, 2 H, 9-CH2), 1.67 (m, 2 H, 12-CH2), 1.51 (m,
4 H, 9-CH2, 12-CH2), 1.38 (m, 2, 10-CH2), 0.55 (s, 6 H, SiMe2),
-1.99 (m, 2 H, 11-H). 13C NMR (C6D6, 150 MHz): δ 127.7 (C-
3a), 125.3 (C-7a), 124.5 (C-5), 124.0, 123.8 (C-6 and C-7), 123.5
(C-4), 121.9 (C-3), 117.8 (C-2), 82.3 (C-1), 67.0 (C-11), 35.3 (C-
10), 30.1 (C-12), 28.4 (C-9), 25.9 (C-8), -2.1 (SiMe2). Spectral
data for the unsymmetrical isomer 15: 1H NMR (C6D6, 600
MHz): δ 7.70 (d of t, 1 H, 4-H), 7.66 (d of t, 1 H, 4′-H), 7.29 (d
of t, 1 H, 7′-H), 7.12 (d of t, 1 H, 7-H), 7.03 (m, 1 H, 5′-H), 6.93
(m, 2 H, 5-H), 6.69 (m, 2 H, 6-H and 6′-H), 5.51 (s, 1 H, 2′-H),
5.29 (s, 1 H, 2-H), 3.37 (m, 1 H, 8′-CH2), 3.17 (m, 1 H, 8-CH2),
2.97 (m, 1 H, 8′-CH2), 2.72 (m, 1 H, 11′-H), 2.54 (m, 1 H, 9′-
CH2), 2.18 (m, 2 H, 9-CH2 and 10-CH2), 2.03 (m, 1 H, 9′-CH2),
1.98 (m, 1 H, 8-CH2), 1.87 (m, 1 H, 10′-CH2), 1.77 (m, 1 H,
12-CH2), 1.67 (m, 1 H, 12-CH2), 1.66 (m, 1 H, 10′-CH2), 1.44
(m, 1 H, 9-CH2), 1.11 (m, 1 H, 11-H), 0.64 (SiMe2), 0.45 (SiMe2),
0.28 (m, 1 H, 10-CH2), -0.16 (m, 1 H, 12′-CH2), -1.73 (m, 1
H, 12′-CH2). 13C NMR (C6D6, 150 MHz): δ 131.1 (C-3a), 130.3
(C-3a′), 128.2 (C-7a), 126.7, 125.4, 125.1, 125.1, 124.9, 124.5
(C-7a′), 123.9, 123.7, 123.0, 122.8 (C-2′), 119.9 (C-3), 119.2 (C-
3′), 117.9 (C-2), 86.1 (C-1′), 81.2 (C-1), 59.0 (C-12′), 58.7 (C-
11), 39.0 (C-10′), 34.7 (C-12), 33.3 (C-11′), 33.1 (C-10), 29.5 (C-
8′), 28.5 (C-8), 26.0 (C-9′), 25.5 (C-9), 0.3, -3.2 (SiMe2) (four
aromatic resonances could not be assigned unequivocally).
r a c-[SBI]Hf(NMe2)2 (10). 10 was prepared analogously to
9 employing Li2[SBI]‚OEt2 (0.51 g, 1.37 mmol) and 4 (0.65 g,
1.37 mmol) to provide 0.13 g (35%) of the product as orange-
1
yellow crystals in two crops. H NMR analysis26 indicated an
initial rac/meso ratio of ca. 16:1.
r a c-[EBI]Zr (NMe2)2 (11). 11 was prepared analogously to
9 employing Li2[EBI]‚OEt2 (0.52 g, 1.50 mmol) and 3 (0.51 g,
1.45 mmol) to provide 0.33 g (50%) of the product as red-orange
crystals. 1H NMR analysis26 indicated an initial rac/meso ratio
of ca. 5:1.
r a c-[EBI]Hf(NMe2)2 (12). 12 was prepared analogously to
9 employing Li2[EBI]‚OEt2 (0.34 g, 1.00 mmol) and 4 (0.43 g,
1.00 mmol) to provide 0.28 g (54%) of the product as yellow
crystals. 1H NMR analysis26 indicated an initial rac/meso ratio
of ca. 8:1.
Zir con a cycle (13). Chilled THF (120 mL, -30 °C) was
added to a solid mixture of 7 (2.16 g, 3.79 mmol) and freshly
prepared sodium amalgam (63 g, 14 mmol, 0.5% Na in Hg).
Rapid stirring at 0 °C resulted in a darkening of the solution
and dispersion of the amalgam. After 1 h, the solution was
dark orange and was stirred for another hour. The volatiles
were removed in vacuo, the residue was extracted with toluene
(50 mL), and then the extracts were filtered through Celite.
Removal of the volatiles in vacuo provided 1.81 g (95%) of the
product as orange microcrystals. Crystals suitable for X-ray
analysis were obtained by slow evaporation of a benzene
Mp: 220 °C (decomp, crystals of 14). Anal. Calcd for C30H34
-
SiHf (601.2): C, 59.94; H, 5.70. Found C, 59.46; H, 5.88.
X-ray crystal structure analysis of 14: formula C30H34SiHf,
M ) 601.15, 0.50 × 0.30 × 0.30 mm, a ) 14.346(1) Å, b )
10.195(1) Å, c ) 32.544(1) Å, â ) 92.62(1)°, V ) 4754.8(6) Å3,
Fcalc ) 1.680 g cm-3, µ ) 44.55 cm-1, empirical absorption
correction (0.214 e T e 0.348), Z ) 8, monoclinic, space group
P21/n (No. 14), λ ) 0.71073 Å, T ) 198 K, ω and æ scans, 18 862
reflections collected ((h, (k, (l), [(sin θ)/λ] ) 0.71 Å-1, 12 601
independent (Rint ) 0.024) and 11 061 observed reflections
1
solution of 13. H NMR (C6D6, 600 MHz): δ 7.39 (d of t, 2 H,
4-H), 7.03 (m, 2 H, 5-H), 6.91 (d of t, 2 H, 7-H), 6.69 (m, 2 H,
6-H), 5.49 (s, 2 H, 2-H), 2.99 (m, 2 H, 8-CH2), 2.75 (m, 2, 8-CH2),
2.00 (m, 2 H, 9-CH2), 1.71 (m, 2 H, 10-CH2), 1.57 (m, 2 H,
9-CH2), 1.42 (m, 2 H, 12-CH2), 1.33 (m, 2, 12-CH2), 1.28 (m, 4,
10-CH2), 0.54 (s, 6 H, SiMe2), -2.14 (m, 2 H, 11-H). 13C NMR
(C6D6, 150 MHz): δ 127.9 (C-3a), 125.9 (C-7a), 124.2 (C-5),

134 Organometallics, Vol. 19, No. 2, 2000
Warren et al.
[I g 2 σ(I)], 619 refined parameters, R ) 0.041, wR2 )
0.080, max. residual electron density 1.96 (-2.14) e Å-3
close to Hf, two independent molecules in the asymmetric
unit being enantiomers, checking of λ/2 gives no indication
of cell doubling, positional disorder in the carbon chain of
the second molecules refined with restraints (0.57(1):0.43(1);
0.53(1):0.47(1)), hydrogens calculated and refined as riding
atoms.
132.3 (C-13), 129.7, 128.9, 128.2, 126.7, 125.6, 125.3, 125.1,
124.7, 124.4, 123.8, 123.5, 123.2, 123.2, 121.8, 119.7, 118.3,
114.9 (aromatic), 83.6 (C-1′), 82.4 (C-1), 61.0 (C-11), 36.2 (C-
12), 34.1 (C-9′), 33.3 (C-10), 30.1 (C-10′), 28.3 (C-9), 27.4 (C-
8′), 26.7 (C-8), 22.0 (C-16), 19.9 (C-14), -0.2 (SiMe2), -2.6
(SiMe2).
Ca tion ic π-a llylzir con ocen e (19). A chilled (-35 °C)
solution of B(C6F5)3 (0.013 g, 0.025 mmol) in ca. 0.7 mL of
toluene-d8 was added to a chilled solution of 13 (0.012 g, 0.024
mmol) in ca. 0.7 mL of toluene-d8 containing 10 µL (4 equiv)
of THF-d8. The solution darkened to red, and a portion of the
solution was immediately transferred to an NMR tube and
Mon otr ifla te (16). A benzene-d6 solution (ca. 0.7 mL) of
13 (0.030 g, 0.59 mmol) was added to a vial containing
[HMe2NPh]+[OTf]- (0.030 g, 0.11 mmol) and was subsequently
transferred to an NMR tube. After standing at room temper-
ature for approximately an hour, conversion to the product
16 was complete. 16 is stable in the presence of excess
anilinium for several hours at room temperature. 1H NMR
(C6D6, 600 MHz): δ 7.30, 7.24, 7.17, 6.92 (dd, 1 H each, 4-H,
4′-H, 7-H, 7′-H), 7.07, 7.05, 6.97, 6.92 (m, 1 H each, 5-H, 5′-H,
6-H, 6′H), 6.24 (s, 1 H, 2-H or 2′H), 5.73 (m, 1 H, 11′-H), 5.08
(s, 1 H, 2′-H or 2-H), 4.95 (m, 2 H, 12′-CH2), 3.30 (m, 1 H,
8′-CH2), 3.05 (m, 1 H, 8′-CH2), 2.64 (m, 1 H, 8-CH2), 2.43 (m,
1 H, 8-CH2), 2.00 (m, 2 H, 10′-CH2), 1.68 (m, 1 H, 9-CH2), 1.59
(m, 2 H, 9′-CH2), 1.49 (m, 1 H, 10-CH2), 1.3 (m, 1 H, 10-CH2),
1
cooled to -78 °C. H NMR spectra at -35 °C showed incom-
plete conversion to product. Warming to room temperature
affored spectrally clean conversion to product, and later
inspection of the NMR tube revealed a red-purple oil, which
1
had separated. H NMR (toluene-d8, 600 MHz): δ 7.05, 6.99,
6.93, 6.87 (d of t, 1 H each, 4-H, 4′-H, 7-H, 7′-H), 7.05, 6.75,
6.67, 6.62 (m, 1 each, 5-H, 5′-H, 6-H, 6′-H), 5.89 (s, 1 H, 2-H
or 2′-H), 5.65 (m, 1 H, 11′-H), 5.16 (m, 1 H, 11-H), 4.94 (m, 2,
12′-CH2), 4.78 (s, 1 H, 2′-H or 2-H), 4.34 (d, 1 H, 12-CH2), 3.25
(d, 1H, 12-CH2), 2.73 (m, 2 H, 8′-CH2 and 8-CH2), 2.63 (dd, 1
H, 9-CH2), 2.48 (dd, 1 H, 9-CH2), 2.20 (m, 1 H, 8′-CH2), 1.91
(q, 2 H, 10′-CH2), 1.67 (m, 1 H, 9-CH2), 1.51 (m, 2 H, 9′-CH2),
0.73 (s, 3 H, SiMe2), 0.66 (s, 3, SiMe2), -1.75 (dd, 1H, 10-H).
Partial 13C NMR (toluene-d8, 600 MHz): δ 131.4 (C-11),
127.0, 126.1, 123.6, 121.0, 121.02, 120.4, 120.1, 116.8, 115.6
(C-12′), 107.8 (C-12), 107.5 (C-2′or C-2), 90.1 (C-1 or C-1′), 88.2
(C-10), 84.9 (C-1′or C-1), 34.5 (C-9), 33.3 (C-10′), 30.7, 26.2,
25.9, 23.4 (C-8), -1.0 (SiMe2), -4.1 (SiMe2). (B(C6F5)3 reso-
nances omitted) 11B NMR (toluene-d8, 64.2 MHz): δ -24.9 (d).
3
1.10 (m, 1 H, 9-CH2), 0.88 (d, J HH ) 8.4, 3 H, 12-CH3), 0.64
(SiMe2), 0.53 (SiMe2), -1.79 (m, 1 H, 11-H). 13C NMR (C6D6,
150 MHz): δ 138.3 (C-11′), 134.3, 131.0, 129.6, 128.9, 127.3,
126.4, 126.1, 125.0, 124.3, 123.2, 122.9, 122.4, 119.5 (C-2 or
C-2′), 115.1 (C-12′), 114.1 (C-2′or C2), 84.1, 82.7 (C-1 and C-1′),
71.6 (C-11), 35.9 (C-10), 33.8 (C-10′), 31.0 (C-9′), 28.1 (C-9),
27.2 (C-8′), 26.6 (C-8), 18.7 (12-CH3), -0.7, -3.1 (SiMe2) (the
triflate CF3 resonance was not found). 19F NMR (C6D6, 471
MHz): δ -75.1.
Zir con a cyclop en ten e (18). 2-Butyne (15 µL, 0.19 mmol)
was added to a solution of 13 (0.015 g, 0.029 mmol) in 0.7 mL
of benzene-d6 and transferred to an NMR tube and sealed with
a Teflon cap. The solution was allowed to stand at room
temperature overnight, after which conversion to the monoin-
sertion product 18 was complete. Removal of the volatiles in
vacuo provided spectra free of excess 2-butyne. 1H NMR (C6D6,
600 MHz): δ 7.48 (d of t, 1 H, 4-H), 7.43 (d of t, 1 H, 4′-H),
7.37 (d of t, 1 H, 7-H), 7.21 (d of t, 1 H, 7′-H), 6.96 (m, 1 H,
5′-H), 6.83 (m, 1 H, 6-H), 6.79 (m, 1 H, 5-H), 6.73 (m, 1 H,
6′-H), 6.04 (s, 1 H, 2′-H), 5.74 (m, 1 H, 11′-H), 5.49 (s, 1 H,
2-H), 4.97 (m, 2 H, 12′-CH2), 2.95 (m, 1 H, 8-CH2), 2.77 (m, 1
H, 8′-CH2), 2.60 (m, 1 H, 8′-CH2), 2.37 (m, 1, 8-CH2), 2.02 (q,
2 H, 10′-CH2), 1.96 (m, 2 H, 9-CH2 and 12-CH2), 1.71 (m, 2 H,
9′-CH2), 1.64 (m, 1 H, 10-CH2), 1.46 (d of d, 1 H, 12-CH2), 1.39
(s, 3 H, 16-CH3), 1.32 (m, 1 H, 9-CH2), 1.26 (s, 3, 14-CH3), 1.00,
(m, 1 H, 10-CH2), 0.70 (SiMe2), 0.69 (SiMe2), 0.26 (m, 1 H, 11-
H). 13C NMR (C6D6, 150 MHz): δ 183.7 (C-15), 138.7 (C-11′),
Ackn owledgm en t. Financial support from the Fonds
der Chemischen Industrie and the Deutsche For-
schungsgemeinschaft is gratefully acknowledged. T.H.W
expresses gratitude to NSF-NATO, DAAD, and the
Alexander von Humboldt Foundation for their generous
support of his stay in Germany and thanks Dr. Klaus
Bergander for many stimulating discussions as well as
assistance in obtaining high-field NMR spectra.
Su p p or tin g In for m a tion Ava ila ble: Additional NMR
data for complexes 7, 8, and 13-19. Details on the X-ray
crystal structure determinations of complexes 13 and 14. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM9905411