Reductive Coupling of an Indenylidene with Calcium to Form Bis(indenyl) ansa-Metallocenes: Molecular Structures of trans-Ph2C2H2-rac-(η 5-4,7-Me2C9H4) 2Ca(THF)2 and trans-Ph2C2H2-rac-(η 5-4,7-Me2C9H4)2Fe

Article abstract of DOI:10.1021/om980990l

1-E-benzylidene-4,7-dimethylindene (1) is reductively coupled by activated calcium to form two isomers, trans-Ph₂C₂H₂-rac-(η ⁵-4,7-Me₂-C₉H₄) ₂Ca(THF)₂ (trans-rac-2) and cis-Ph₂C₂H₂-meso-(η⁵-4,7-Me ₂-C₉H₄)₂Ca(THF)₂ (cis-meso-2) in an approximately 1:1 ratio. Reaction of the calcium species with FeCl₂ produces a mixture of the corresponding trans-rac and cis-meso ferrocenophane species (3) along with another ferrocenophane isomer that is presumed to be either the trans-meso or cis-rac isomer. Thus, the relative geometry of the indenyl rings is not retained entirely during the transfer of the ligand framework from calcium to iron. A complete scrambling of the indenyl ring geometry appears to occur upon transfer of the ligand framework from calcium to zirconium. The results of X-ray crystal structure determinations of 1-E-benzylidene-4,7-dimethylindene, trans-Ph₂C₂H₂-rac-(η ⁵-4,7-Me₂-C₉H₄) ₂Ca(THF)₂, and trans-Ph₂C₂H₂-rac-(η ⁵-4,7-Me₂-C₉H₄)₂Fe are described.

Full text of DOI:10.1021/om980990l

3468
Organometallics 1999, 18, 3468-3473
Red u ctive Cou p lin g of a n In d en ylid en e w ith Ca lciu m To
F or m Bis(in d en yl) a n sa -Meta llocen es: Molecu la r
Str u ctu r es of
tr a n s-P h 2C2H2-r a c-(η5-4,7-Me2C9H4)2Ca (THF )2 a n d
tr a n s-P h 2C2H2-r a c-(η5-4,7-Me2C9H4)2F e
Pamela J . Shapiro,* Kevin M. Kane, Ashwani Vij, Dan Stelck, Gilbert J . Matare,
Robert L. Hubbard, and Brett Caron
Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343
Received December 7, 1998
1-E-benzylidene-4,7-dimethylindene (1) is reductively coupled by activated calcium to form
two isomers, trans-Ph2C2H2-rac-(η5-4,7-Me2-C9H4)2Ca(THF)2 (trans-rac-2) and cis-Ph2C2H2-
meso-(η5-4,7-Me2-C9H4)2Ca(THF)2 (cis-meso-2) in an approximately 1:1 ratio. Reaction of
the calcium species with FeCl2 produces a mixture of the corresponding trans-rac and cis-
meso ferrocenophane species (3) along with another ferrocenophane isomer that is presumed
to be either the trans-meso or cis-rac isomer. Thus, the relative geometry of the indenyl
rings is not retained entirely during the transfer of the ligand framework from calcium to
iron. A complete scrambling of the indenyl ring geometry appears to occur upon transfer of
the ligand framework from calcium to zirconium. The results of X-ray crystal structure
determinations of 1-E-benzylidene-4,7-dimethylindene, trans-Ph2C2H2-rac-(η5-4,7-Me2-
C9H4)2Ca(THF)2, and trans-Ph2C2H2-rac-(η5-4,7-Me2-C9H4)2Fe are described.
In tr od u ction
hydrogens. Described herein are the preparation and
molecular structures of 1-E-benzylidene-4,7-dimethyl-
indene, its calcocene coupling product, and a ferrocene
complex derived therefrom.
We reported recently the facile reductive coupling of
phenylfulvene with activated calcium to yield a mixture
of ansa-calcocenes with cis- and trans-diphenylethano
bridges.1 The predominant trans isomer was isolated by
fractional recrystallization, and its structure was con-
firmed by X-ray crystallography. This new calcocene has
been shown to be a versatile precursor for the prepara-
tion of C2-symmetric metallocenes of iron,1 chromium,2
and zirconium.1 An elegant and even more direct
application of fulvene coupling to the synthesis of group
4 ansa-metallocene dichlorides was also recently re-
ported by Eisch and co-workers.3 In this case the
reductive coupling is accomplished by the divalent group
4 transition metal dihalides themselves.
The formation of 1,1′-(1,2-trans-diphenylethanediyl)-
calcocene as the major isomer in the coupling of phen-
ylfulvene by activated calcium led us to investigate the
possibility of preparing a single C2-symmetric product
selectively. Our initial efforts were directed at increas-
ing the steric bulk of the 6-aryl group of the fulvene in
order to promote formation of the trans-coupling prod-
uct, but this met with only limited success. As a result,
we turned to an indenyl fulvene analogue that we hoped
would impose additional steric limitations on the ster-
eochemistry of the coupling reaction, in addition to
meeting the limitation discovered in our previous
work: that the fulvene must be devoid of abstractable
Resu lts
Syn th esis a n d Str u ctu r e of 1-E-Ben zylid en e-4,7-
d im eth ylin d en e. There are four calcocene diastereo-
mers that could arise from the coupling of a benzylide-
neindene by calcium since either a cis or trans stereo-
chemistry within the 1,2-diphenylethano bridge can be
combined with either a meso or rac orientation of the
indenyl rings (Scheme 1). We sought to limit the number
of isomers which could form by introducing methyl
substituents at the 4- and 7-benzenoid positions of the
indenyl molecule in order to block isomerization of the
benzylideneindene from an E to a Z geometry during
the reductive coupling reaction. Our limited knowledge
of the mechanistic details of the fulvene coupling
notwithstanding, our subsequent attempts to couple the
simpler 1-E-benzylideneindene with activated cacium
resulted in an ill-defined mixture of products, the 1H
NMR spectrum of which could not be attributed solely
to the trans-rac and cis-meso isomers.
Using a modification of the method reported by
Friguelli et al. for the synthesis of 1-E-benzylidenein-
dene,4 we synthesized 1-E-benzylidene-4,7-dimethylin-
dene (1) from 4,7-dimethylindene. Although the prepa-
ration of this compound has been mentioned previously,5,6
(1) Kane, K. M.; Shapiro, P. J .; Cubbon, R.; Vij, A.; Rheingold, A. L.
Organometallics 1997, 16, 4567.
(2) Matare, G. J .; Foo, D. M.; Kane, K. M.; Wagener, M.; Shapiro,
P. J .; Concolino, T.; Rheingold, A. L. Manuscript in preparation.
(3) Eisch, J . J .; Shi, X.; Owuor, F. A. Organometallics 1998, 17, 5219.
(4) Fringuelli, F.; Pani, G.; Pizzo, F. Tetrahedron 1994, 50, 11499.
(5) Herz, W. J . Am. Chem. Soc. 1953, 75, 73.
(6) Riedel, M.; Erker, G.; Bosch, B.; Bertuleit, A. Ger. Patent DE
19632919 A1 980219, 1996.
10.1021/om980990l CCC: $18.00 © 1999 American Chemical Society
Publication on Web 07/24/1999

Reductive Coupling of an Indenylidene with Calcium
Organometallics, Vol. 18, No. 17, 1999 3469
Sch em e 1. F ou r P ossible Isom er s fr om th e
Red u ctive Cou p lin g of Ben zylid en ein d en e w ith
Ca lciu m
about the C(9)-C(12) bond would be significantly
hindered by the methyl group at C(5).
1H and 13C NMR assignments for 1 (Experimental
Section) were based on a combination of HETCOR,
COSY, and APT experiments and by comparison with
spectral data for dimethylindene and earlier assign-
ments for E-1-benzylidene-1H-indene.4
P r ep a r a tion a n d NMR Ch a r a cter iza tion of a n sa -
Ca lcocen e a n d a n sa -F er r ocen e Com p lexes. The
reaction of 1 with activated calcium takes several hours,
which contrasts with the reductive coupling of phenyl-
fulvene (complete in 45 min).1 The ansa-calcocene 2 is
isolated as a tan powder which is stable in the solid
state under a nitrogen atmosphere if stored at -25 °C.
At room temperature the solid darkens to brown over
days. In this respect, 2 is less stable than its bis-
cyclopentadienyl analogue, which undergoes a similar
discoloration much more slowly, over months of storage
at room temperature.
its synthesis and characterization have not yet been
fully described.
The fulvene is a yellow, crystalline compound that can
be recrystallized from hot ethanol or purified by subli-
mation in yields approaching 60%. The 1H and 13C NMR
assignments for 1 were determined from a combination
of HETCOR and COSY experiments. Whereas Fringuel-
li et al. determined the orientation of the phenyl group
in 1-E-benzylideneindene using NOE experiments,4 we
were able to isolate an X-ray quality crystal of 1 that
confirms the E-configuration of the phenyl moiety.
There are four independent molecules in the unit cell.
This is a consequence of the crystal packing, in which
two independent chains of molecules having no true
symmetry relation stack parallel to the [100] direction.
In each chain, the normals to the fused rings make an
angle of approximately 45° with the [100] direction.
However, in each chain, the normals to the phenyl
groups are alternately parallel and perpendicular to
[100]. Thus, with two crystallographically independent
molecules per chain, and two independent chains, a Z
) 4 is obtained. An ORTEP drawing of the four
molecules is shown in Figure 1 alongside a packing
diagram of the crystal. Crystallographic data for 1 are
given in Table 1 and selected bond lengths and angles
for one of the indenylidene molecules, C1-C18, are
presented Table 2.
Examples of crystallographically characterized inde-
nylidenes are few.7-9 The molecular structure of 1 is
most comparable to that of trans-1,1′-bis(indenylidene),7
which differs from 1 by the absence of methyl substit-
uents at the 4,7-positions of the indene rings and by the
constrained coplanarity of the substituents about the
fulvene double bond. The exocyclic fulvene bond lengths
for the two molecules are similar (1.340(5) Å for 1 and
1.342(4) Å for the bis(indenylidene). The pattern of C-C
double and single bonds within the indene rings of the
two molecules are also similar. In both molecules, the
π-electrons of the benzenoid portion of the indene rings
are delocalized, as revealed by the fairly uniform lengths
of their C-C bonds.
Although a crystal structure determination of 2
1
revealed only the trans-rac isomer (vide infra), the H
NMR spectrum of the isolated product indicated that
another isomer, the cis-meso isomer, was also present
since a total of four distinct methyl resonances were
observed (eq 1).
(1)
The presence of either the trans-meso and cis-rac
isomers could be eliminated since each individual isomer
would have contributed four methyl peaks to the
spectrum. A roughly 50:50 ratio of the trans-rac and cis-
meso isomers was indicated by the relative intensities
of the methyl resonances at δ 3.04, 2.95, 2.32, 2.30 in
1
the H NMR spectrum of the mixture in benzene-d6.
The reaction of 2 with FeCl2 produces a variable
mixture of isomers of the ferrocenophane complex 3 (eq
2).
(2)
Two isomers are formed predominantly, and we
assign these as the trans-rac and cis-meso isomers based
The features of the molecular structure of 1 most
relevant to the chemistry described herein are the
nonbonded distances between C(11) and C(12) (3.246 Å)
and between C(12) and C(16) (4.259 Å). The greater
span of the C(12)-C(16) distance indicates that rotation
1
on the number of distinct methyl peaks in the H NMR
spectrum of the mixture in benzene-d6 (two singlets for
the trans-rac isomer at δ 2.71, 2.22 and two singlets for
the cis-meso isomer at δ 2.53, 1.92) and on the number
of peaks corresponding to hydrogens on the cyclopen-
tadienyl portion of the indenyl ring (two doublets for
the trans-rac isomer at δ 5.06, 3.97 and two doublets
for the cis-meso isomer at δ 4.68, 4.47). Our assignment
(7) Capparelli, M. V.; Machado, R.; de Sanctis, Y.; Arce, A. J . Acta
Crystallogr. 1996, C52, 947.
(8) Erhardt, W. D.; Ammon, H. L. Tetrahedron Lett. 1975, 3997.
(9) Ferna´ndez-G., J . M.; Solorzano-Maldonado, K.; Rodr´ıguez-
Romero, A.; Soriano-Garc´ıa, M. Acta Crystallogr. 1996, C52, 460.

3470 Organometallics, Vol. 18, No. 17, 1999
Shapiro et al.
F igu r e 1. (a) Molecular structures of four independent molecules in the crystal of 1 with atom labelings. Thermal ellipsoids
are plotted at 50% probability. (b) Crystal packing diagram.
(THF)2.1 On occasion, additional peaks due to another
isomer of 3 appear in the methyl and indenyl regions
Ta ble 1. Cr ysta llogr a p h ic Da ta for 1 a n d
tr a n s-r a c-3
of the 1H NMR spectrum of the ferrocenophane product.
We tentatively assign this isomer as either the trans-
meso or the cis-rac form of 3 based on the pattern of
four distinct methyl resonances in the benzene-d6 1H
NMR spectrum at δ 2.85, 2.57, 2.11, 2.03. This ad-
ditional isomer has appeared in some preparations in
amounts approaching that of the cis-meso isomer. As
with the calcocene complex, the crystal of the ferrocene
complex selected for X-ray analysis contained only the
trans-rac isomer (vide infra).
1
trans-rac-3
C36H32Fe
520.47
orthorhombic
Pbca
12.9203(4)
17.2732(4)
23.6686(7)
formula
mol wt
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C18H16
232.31
triclinic
P1
10.0013(2)
15.0257(3)
18.4490(2)
82.371(1)
78.313(1)
78.958(1)
2651.95(8)
4
90
90
90
5282.2(3)
8
Z
T (K)
213(2)
0.701 73 (Mo KR)
1.164
0.065
992
213(2)
0.701 73 (Mo KR)
1.309
0.594
2192
Compound 3 is isolated as a purple precipitate upon
addition of petroleum ether to a toluene solution of the
compound. The compound is extremely air-sensitive as
compared with the other [2]ferrocenophanes,10-18 turn-
ing light brown immediately upon exposure to air in
either the solid state or in solution. The compound
appears to be light-sensitive as well, decomposing from
a purple benzene-soluble solid to an insoluble brown
solid, even upon storage in a nitrogen atmosphere, if it
is not protected from light. The exceptional instability
of this compound can probably be attributed to the
propensity of the indenyl ring toward (η5-η3) slippage
in combination with the strain imposed by the interan-
nular bridge.
λ (Å)
Fcalcd (g/cm3)
µ (mm-1
)
F000
cryst size
θ range (deg)
hkl limits
no. reflcns collected 11 106
no. indep reflcns
data/restraints/
param
0.10 × 0.10 × 0.05
0.10 × 0.10 × 0.05 mm
1.38-23.28
1.72-25.00
-11/10; -16/16; -20/15 -14/16; -17/22; -31/29
23 031
4642 (Rint ) 0.2051)
2075/317/335
7087 (Rint ) 0.0502)
7084/0/650
GOF
1.049
0.0800 (F > 2σ(F))
0.1918
1.229
0.0856 (F > 2σ(F))
0.1440
R(Fo)a
2
b
wR(Fo
largest diff peak/
hole (e Å-3
)
0.413/-0.352
0.379/-0.309
)
a
b
R ) ∑|Fo - Fc|/∑|Fo|. wR ) {[∑w(Fo - Fc)2]/[∑w(Fo)2]}1/2; w
) 1/σ2(Fo)2 + (xP)2 + (yP)2], where P ) (Fo + 2Fc2)/3.
2
X-r a y Str u ctu r es of tr a n s-P h 2C2H2-r a c-(η5-4,7-
Me2C9H4)2Ca (THF )2 a n d tr a n s-P h 2C2H2-r a c-(η5-4,7-
Me2C9H4)2F e. Two unique calcocene molecules and a
free molecule of THF were found in the unit cell of the
crystal of 2 that was characterized. Both calcocene
molecules exhibit a trans-rac stereochemistry. The X-ray
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 1
C(1)-C(9)
C(1)-C(6)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
1.490(5)
1.405(5)
1.398(5)
1.394(6)
1.383(6)
1.394(6)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(9)-C(12)
C(12)-C(13)
1.471(6)
1.332(6)
1.483(5)
1.340(5)
1.465(5)
(10) Yasufuku, K.; Aoki, K.; Yamazaki, H. Inorg. Chem. 1997, 16,
6624.
(11) Aggarwal, V. K.; J ones, D.; Turner, M. L.; Adams, H. J .
Organomet. Chem. 1996, 524, 263.
(12) Nelson, J . M.; Rengel, H.; Manners, I. J . Am. Chem. Soc. 1993,
115, 7035.
(13) Lentzner, H. L.; Watts, W. E. Tetrahedron 1971, 27, 4343.
(14) Tan, T. S.; Fletcher, J . L.; McGlinchey, M. J . J . Chem. Soc.
Chem. Commun. 1975, 771.
(15) Vyacheslav V.; Dement’ev, F. C.-L.; Parkanyi, L.; Sharma H.;
Pannell, K. H.; Nguyen, M. T.; Diaz, A. Organometallics 1993, 12, 1983.
(16) Finckh, W.; Tang, B.-Z.; Foucher, D. A.; Zamble, D. B.; Ziem-
binski, R.; Lough, A.; Manners, I. Organometallics 1993, 12, 823.
(17) Laing, M. B.; Trueblood, K. N. Acta Crystallogr. 1965, 19, 373.
(18) Heberhold, M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1837.
C(1)-C(2)-C(10)
C(3)-C(2)-C(10)
C(3)-C(2)-C(1)
C(4)-C(5)-C(6)
C(6)-C(5)-C(11)
C(4)-C(5)-C(11)
124.4(4)
C(5)-C(6)-C(7)
C(1)-C(9)-C(12)
C(1)-C(9)-C(8)
C(8)-C(9)-C(12)
C(9)-C(12)-C(13)
C(2)-C(1)-C(9)
129.1(4)
128.8(3)
104.2(3)
126.9(4)
128.6(4)
131.7(4)
119.6(4)
116.0(4)
116.0(4)
121.9(4)
122.1(4)
of peaks for the two isomers is based on the assumption
that the trans-rac species is the predominant of the two
and is the isomer that is enriched upon recrystallization
of the isomer mixture. We base this assumption on our
experience with trans- and cis-Ph2C2H2(η5-C5H4)2Ca-

Reductive Coupling of an Indenylidene with Calcium
Organometallics, Vol. 18, No. 17, 1999 3471
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
two tetrahydrofuran (THF) molecules in the equatorial
wedge to adopt more of a mutually coplanar arrange-
ment as opposed to the mutually perperpendicular
orientation encountered in the cyclopentadienyl ana-
logue. The planar nature of one of the coordinated THF
molecules in molecule 1 (O(1), C(37)-C(40)) and its
relatively large thermal ellipsoids indicate that it is
positionally disordered.
(d eg) for tr a n s-r a c-2 a n d tr a n s-r a c-3
trans-rac-2
(M ) Ca, L ) OC5H8)
trans-rac-3
molecule 1 molecule 2 (M ) Fe, L ) none)
Average Bond Distance (Å)
M-L
M-Cp(centroid)
2.339(5)
2.452(3)
2.346(20)
2.458(14)
- - -
1.64(4)
Bond Angle (deg)
The molecular structure of trans-rac-3 is shown in
Figure 3. Crystallographic data and selected bond
distances and angles are listed in Tables 1 and 3,
respectively. In contrast to [m]ferrocenophanes, there
are few reported structures of bridged bis(indenyl)iron
complexes.20,21,27,28 Distortions in ferrocenophanes are
typically described by the tilt angle R, between the ring
planes, and by the angle fomed by the metal and the
ring centroids, δ. The values for R and δ for trans-rac-
3, 22.9° and 164.4°, respectively, are comparable with
those exhibited by other carbon bridged [2]ferro-
cenophanes.10,11,17,18 The average Fe-Cp(centroid) dis-
tance of 1.64 Å is also normal. Nevertheless, some ring
slippage is evident from the large variation in distances
between the iron and the coordinated carbons of the
indenyl rings. In general, the benzenoid carbons (C(1),
C(5), C(26), C(30)) are slipped farthest from the iron
center with distances of 2.079(9)-2.119(9) Å; however,
C(4) and C(29), at 2.045(9) and 2.072(8) Å, are also
somewhat distant from the iron center as compared with
C(2), C(3), C(27), and C(28), which range from 1.961(9)
Å to 2.022(9) Å. This additional slippage can be at-
tributed to the strain imposed by the two-carbon bridge
on the metallocene structure, which is also evident from
the large deviations of C(2) and C(27), the bridgehead
carbons, from the mean planes of the indenyl rings by
0.030(5) and 0.033(5) Å, respectively. The Ind-C-C-
Ind torsion angle of 39.5° is quite large when compared
to that of 1,1′-tetramethyleneferrocene,16 in which the
corresponding Cp-C-C-Cp torsion angle is 25°. Con-
sequently, the C5 rings trans-rac-3 are more staggered
(Figure 3b), by approximately 18° as compared to the
9-10° angle of staggering in 1,1′-tetramethylenefer-
rocene.
L-M-L
90.2(2)
93.2(2)
118.8
66.0(3)
86.5(2)
- - -
cent-M-cent (δ) 118.5
164.2°
22.9(4)
71.0(2)
Cp-Cp bend(R)
Ph-Ph twist
66.4(3)
47.2(3)
Torsion Angle (deg)
Ph-C-C-Phb
Ind-C-C-Indc
50.4(9)
56.7(8)
54.7(8)
47.5(8)
66(1)
39.5(9)
F igu r e 2. Molecular structure of one of the trans-rac-
calcocene molecules in the crystal of 2. Thermal ellipsoids
are plotted at 50% probability.
crystal structure has not yet been completely refined19
due to our inability to identify and refine a long chain
molecule that is also present in the crystal. Neverthe-
less, the core structures show definitive atom connectiv-
ity and reasonable bond lengths and angles. An ORTEP
drawing of one of the calcocene molecules (molecule 1)
is shown in Figure 1. Selected bond distances and angles
for both molecules are listed in Table 3 (All crystal-
lographic details available up to the writing of this
manuscript are in the Supporting Information).
Discu ssion a n d Con clu sion
Although the reductive coupling of 1-E-benzylidene-
4,7-dimethylindene with activated calcium to form an
ansa-bis(indenyl)calcium complex is stereoselective,
forming only two of four possible diastereomers through
a retention of the E geometry about the fulvene C-C
bond, we were disappointed by the lack of selectivity of
the coupling for the C2-symmetric trans-rac isomer.
Surprisingly, formation of the trans isomer is less
favored in this case than in the synthesis of Ph2C2H2-
(η5-C5H4)2Ca(THF)2.
Poor rac:meso ratios have generally been obtained in
the kinetic products of the synthesis of group 4 ansa-
metallocene complexes from dianions of bridged, sym-
metrically substituted dicyclopentadiene ligands and
bridged bis(indene) ligands. Brintzinger has attributed
these poor stereoselectivities to the formation of inter-
mediates with one η1-bonded ring, in which there would
The indenyl rings in trans-rac-2 (Figure 2) adopt a
more open bent-sandwich structure as compared with
the structure of the cyclopentadienyl analogue, trans-
Ph2C2H2(η5-C5H4)2Ca(THF)2.1 This is reflected in the
narrower cent-Ca-cent angles (118.5°and 118.8° as
compared to 119.9°) and the larger angles between the
indenyl ring planes (66.4°and 66.0° as compared to
58.0°). The average Ca-Cp(centroid) distance of 2.45 Å
is comparable to the 2.42 Å distance found in the
cyclopentadienyl analogue. The Ca-O distances are
comparable to those of trans-Ph2C2H2(η5-C5H4)2Ca-
(THF)2. The greater bending angle between the indenyl
rings of 2 is accompanied by wider O-Ca-O angles
(90.2°and 93.2° as compared to 84.7°). This allows the
(19) Crystal data for 2: space group P21/n; monoclinic; a ) 23.1634(4)
Å; b ) 15.0033(3) Å; c ) 28.3090(2) Å; â ) 104.836(1)°; V ) 9510.2(3)
Å3; Z ) 12; R indices at current level of refinement [I > 2σ(I), R1
)
0.0932, wR2 ) 0.2342 for 13 431 independent reflections; GOF ) 1.051.
The structure will be submitted for publication to Cambridge Crystal
Structure Data Base upon completion.
(20) Scott, P.; Rief, U.; Diebold, J .; Brintzinger, H. H. Organome-
tallics 1993, 12, 3094.
(21) Dewan, J . C. Organometallics 1983, 2, 83.

3472 Organometallics, Vol. 18, No. 17, 1999
Shapiro et al.
F igu r e 3. (a) Side view of molecular structure of trans-rac-3. (b) Top view of a partial structure showing the staggered
conformation of the metallocene rings and the degree of twist in the two-carbon bridge. Thermal ellipsoids are plotted at
50% probability.
be negligible steric interaction between the substituents
on the rings.22 Although the fulvene reductive coupling
probably involves a different mechanism of ligand
assembly about the metal, this method offered no real
improvement in diastereolectivity in the synthesis of the
title calcocene complex. Eisch likewise obtained a 1:1
mixture of meso- and rac-benzometallocene isomers in
the coupling of 1′,1′-dimethylbenzofulvene with zirco-
nium chloride. Nevertheless, his employment of the
transition metal itself as the template for fulvene
coupling is preferable to having an additional trans-
metalation step, not only because it is more direct but
also because we have found that the transmetalation
results in additional loss of stereochemistry.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
using a combination of glovebox, high-vacuum, or Schlenk
techniques. All solvents were distilled under nitrogen over
sodium benzophenone ketyl (tetrahydrofuran, toluene, meth-
ylcyclohexane) or CaH2 (petroleum ether). The solvents were
then stored in line-pots from which they were either vacuum-
transferred from sodium benzophenone ketyl or cannulated
directly. NMR solvents (Isotech): Benzene-d6 and CDCl3 were
dried over activated 4 Å molecular sieves. Argon was purified
by passage over oxy tower BASF catalyst (Aldrich) and 4 Å
molecular sieves. 4,7-Dimethylindene was prepared as de-
scribed by Erker et al..25 Cetylammonium bromide (Aesar),
calcium granules (Strem), HgCl2 (Aldrich), and FeCl2 (Aldrich),
were used as received from the supplier. NMR spectra were
recorded on an IBM NR-300 (300 MHz 1H, 75 MHz 13C) an
IBM NR-200 (200 MHz 1H, 50 MHz 13C), and a Varian Gemini
Transfer of the bis-indenyl ligand framework from
calcium to iron occurs with some loss of stereochemistry,
since a third isomer besides the trans-rac and cis-meso
ferrocenophane isomers appears in the reaction product.
An even greater loss of stereochemistry was encountered
upon transferring the ligand framework from calcium
to either ZrCl4(SMe2)2 or ZrCl4(THF)2. Both reactions
produced a complex mixture of products which could not
300 (300 MHz H, 75 MHz 13C).
P r ep a r a t ion of E-1-b en zylid en e-1H -4,7-d im et h ylin -
d en e, 1. Using a modification of the method reported by
1
1
be distinguished by their peaks in the H NMR spec-
trum and which could not be separated or even enriched
in one species by crystallization. Thus, achieving a
diastereochemically pure racemic form of an ansa-bis-
(indenyl)calcium complex (either through the stereose-
lective reductive coupling of indenylfulvenes with acti-
vated calcium or the separation of a isomeric mixture)
does not guarantee that this stereochemistry is retained
upon transfer of the ligand framework from the calcium
center to a transition metal. Complete retention of meso
or rac stereochemistry upon transmetalation is guar-
anteed only with stannyl or silyl derivatives of the
ligand framework.23,24
Fringuelli et al.,4 dimethylindene (23.5 g, 0.16 mol) was added
slowly to a mixture of 0.61 g of cetyltriethylammonium
bromide in 250 mL of 0.25 M NaOH. After stirring rapidly for
10 min, benzaldehyde (17.3 g, 0.16 mol) was added dropwise
to the mixture over a 3 h period. The mixture was stirred
overnight, and the resultant yellow solid was isolated by
filtration. The product was washed with water several times,
allowed to air-dry, and then crystallized from hot ethanol to
give bright yellow needles. A second crop was obtained by
(22) Wiesenfeldt, H.; Reinmuth, A.; Barsties, E.; Evertz, K.; Brintz-
inger, H.-H. J . Organomet. Chem. 1989, 369, 359.
(23) Hu¨ttenhofer, M.; Schaper, F.; Brintzinger, H. H. Angew. Chem.,
Int. Ed. Engl. 1998, 110, 2378.
(24) Resconi, L.; Piemontesi, F.; Camurati, I.; Balboni, D.; Sironi,
A.; Moret, M.; Rychlicki, H.; Ziegler, R. Organometallics 1996, 15, 5046.
(25) Erker, G.; Psiorz, C.; Fro¨hlich, R.; Grehl, M.; Kru¨ger, C.; Nolte,
M. Tetrahedron 1995, 51, 4347.

Reductive Coupling of an Indenylidene with Calcium
Organometallics, Vol. 18, No. 17, 1999 3473
concentrating the filtrate and cooling: total yield, 22.4 g (60%);
mp, 58-59 °C. H NMR (CDCl3): δ 7.68 (s, 1H, fulvenyl-H);
pin was mounted on a goniometer head. Crystals of 2 were
grown by slow diffusion of petroleum ether into a THF solution
of the compound. A suitable crystal was mounted in a glass
capillary under a nitrogen atmosphere. Crystals of 3 were
grown from a concentrated benzene solution that was cooled
at 5 °C for several days. After the benzene was decanted from
the crystals, they were coated with mineral oil. A suitable
crystal was mounted on a pin with silicon grease, and the pin
was mounted on a goniometer head and immediately placed
under a nitrogen stream.
1
7.54-7.64 (m, 2 H, H2′, H6′); 7.41-7.50 (m, 2H, H3′, H5′), 7.32-
7.40 (m, 1H, H4′), 7.10 (dd, 1H, H5 or H6), 6.88-7.2 (m, 3H,
H2, H3, and H5 or H6), 2.68, 2.45 (s, each 3H, CH3). 13C NMR
(CDCl3): δ 143.1, 141.6, 137.7, 133.0, 130.4, 128.1 (C1, C4, C7,
C8, C9, and C1′), 133.0 (CHPh), 130.4 (C2′ and C6′), 128.9 (C2
or C3), 131.5 (C2 or C3), 126.3 (C5 or C6), 128.4 (C3′ and C5′),
127.8(C4′), 21.4, 18.0 (CH3). Anal. Calcd for C18H16: C, 93.0;
H, 6.7. Found: C, 93.0; H, 6.9.
P r ep a r a tion of P h 2C2H2-(η5-4,7-Me2C9H4)2Ca (THF )2, 2.
Calcium granules (0.65 g, 16 mmol) were activated with HgCl2
(0.047 g, 0.17 mmol) by combining the two solids in 150 mL
THF, letting the mixture sit undisturbed for 1 h, under a
blanket of argon, and then rapidly stirring the mixture for 1
h. The fulvene 1 (1.7 g, 7.3 mmol) was added to the solution
at room temperature with stirring. On addition of the fulvene
the solution initially turned green then grayish-brown. The
mixture was stirred at room temperture for 8 h. The excess
calcium was removed by filtration, and the filtrate was
evaporated to dryness to yield a beige foam that was washed
twice with hexane. The solid was resuspended in diethyl ether,
cooled at -78 °C, and filtered cold to afford 2 as a white,
flocculent solid (yield, 1.3 g, 55%). 1H NMR (C6D6); mixture of
Data were collected using a Siemens (Bruker) SMART CCD
(charge coupled device) based diffractometer equipped with an
LT-2 low-temperature apparatus operating around -54 °C. A
total of 1271 frames of data were collected using ω scans with
a scan width of 0.3° per frame for 30 s. Additional parameters
are available in the cif file. The first 50 frames were recollected
at the end of data collection to monitor for decay. Cell
parameters were retrieved using SMART software (V. 4.050,
Bruker Analytical X-ray Systems, Madison, WI, 1995) and
refined using SAINT (V. 4.050, Bruker Analytical X-ray
Systems, Madison, WI, 1995) on all observed reflections. Data
reduction was performed using the SAINT software which
corrects for Lp and decay. Absorption corrections were applied
using SADABS (Program for absorption corrections using
Siemens CCD based on the method of Robert Blessing26). The
structures were solved by the direct method using the SHELXS-
97 program (Sheldrick, G. M., University of Go¨ttingen, Ger-
many, 1997) and refined by the least-squares method on F2
using SHELXL-97, which is incorporated in SHELXTL-PC V
5.10 (PC/UNIX-Version, Bruker Analytical X-ray Systems,
Madison, WI, 1995). All non-hydrogen atoms were refined
anisotropically. Hydrogen positions were calculated by geo-
metrical methods and refined as a Riding model. In each case,
the crystals used for the diffraction studies showed no decom-
position during data collection.
3
isomers): δ 7.83 (d,3J HH ) 7.1 Hz, Ph-H); 7.59 (d, J HH ) 6.9
3
Hz, Ph-H); 7.29 (d, J HH ) 3.4 Hz, H5 and H6); 7.13-6.94 (m,
H5 or H6 and Ph-H); 6.82 (s, PhCHCp), 6.59-6.43 (m, H2 and
3
H3 and Ph-H); 6.11, 5.98 (d, J HH ) 3.4 Hz, H2 and H3); 6.03
(s, PhCHCp); 3.04, 2.95, 2.32, 2.30 (s, 4,7-CH3); 2.88, 1.15 (br,
THF). 13C NMR (C6D6; mixture of isomers): δ 130.3, 129.6 (C5
and C6); 126.4, 126.2, 125.4, 125.0, 124.8, 120.5, 120.0, 119.8,
118.0 (C1, C4, C5, C6, C8, C9 and phenyl carbons); 117.0, 114.5,
95.1, 94.0 (C2 and C3); 68.5, 24.8 (THF); 55.0, 50.5 (PhCHCp);
22.8, 21.6, 19.2 (4,7-CH3). Anal. Calcd for C44H48O2Ca: C,
81.44; H, 7.45. Found: C, 81.07; H, 7.12.
P r ep a r a tion of P h 2C2H2-(η5-4,7-Me2C9H4)2F e, 3. THF (50
mL) was vacuum-transferred onto a mixture of FeCl2 (0.20 g,
1.5 mmol) and 2 (1.0 g, 1.5 mmol) at -78 °C, and the reaction
mixture was warmed to room temperature and stirred over-
night with the entire reaction vessel wrapped in aluminum
foil to exclude light. The resulting deep purple solution was
dried under vacuum, and the product was redissolved in 50
mL of toluene and filtered to remove the CaCl2 byproduct. The
CaCl2 was washed repeatedly with toluene, and the combined
filtrate and washings were concentrated to 10 mL and cooled
to -78 °C to precipitate 3 as a purple solid: yield, 0.31 g, 40%.
1H NMR (C6D6; trans-rac and cis-meso isomers): δ 7.42, 6.91-
7.18 (m, phenyl-H). 1H NMR (C6D6; trans-rac isomer): δ 6.85,
Ack n ow led gm en t. P.J .S. is grateful to the National
Science Foundation for a CAREER grant (No. CHE-
9502739) in support of this work. The establishment of
the Single-Crystal X-ray Dirffraction Laboratory at the
University of Idaho was supported by the NSF-Idaho
EPSCoR Program, the National Science Foundation,
and the M. J . Murdock Charitable Trust of Vancouver,
WA. We thank Prof. Roger Willett (Washington State
University) and Dr. Roland Fro¨hlich (Westfa¨lischen
Wilhelms Universita¨t, Mu¨nster) for examining and
commenting on the validity of the X-ray crystal struc-
ture of compound 1. We also thank Dr. Gary Knerr
(University of Idaho) for his assistance in acquiring
NMR data.
3
6.59 (d, J H-H ) 6.3 Hz, H5 and H6), 6.04 (s, PhCHCp), 5.06,
3.97 (d, 3J H-H ) 2.5 Hz, H2 and H3), 2.71, 2.22 (s, 4,7-CH3). 1H
NMR (C6D6; cis-meso isomer): δ 6.67, 6.37 (d, 3J H-H ) 6.5 Hz,
3
H5 and H6), 6.59 (s, PhCHCp), 4.68, 4.47 (d, J H-H ) 2.6 Hz,
Su p p or tin g In for m a tion Ava ila ble: Details of the struc-
ture determinations for 1, trans-rac-2, and trans-rac-3, includ-
ing tables listing atomic coordinates, thermal parameters, and
bond distances and angles, figures showing structures, and
text giving details of the packing analysis. This material is
available free of charge via the Internet at http://pubs/acs.org.
H2 and H3), 2.53, 1.92 (s, 4,7-CH3). 1H NMR (C6D6; third, minor
isomer (trans-meso or cis-rac): δ 5.09 (s, PhCHCp), 2.85, 2.57,
2.11, 2.03 (s, 4,7-CH3). 13C NMR (C6D6-d6): δ 129.2, 128.4,
128.2, 126.7 (Ph-C). 13C NMR (trans-rac isomer): δ 126.3,
121.4 (C5 and C6), 75.2, 68.2 (C2, C3), 58.7 (PhCHCp), 22.3,
18.3 (4,7-CH3). 13C NMR (cis-meso isomer): δ 124.8, 119.0 (C5
and C6), 73.6, 59.0 (C2, C3), 54.8 (PhCHCp) 21.1, 17.8 (4,7-
CH3). Anal. Calcd for C36H32Fe: C, 83.07; H, 6.20. Found: C,
83.49; H, 6.51.
OM980990L
(26) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(27) Al´ıas, F. M.; Barlow, S.; Tudor, J . S.; O’Hare, D.; Perry, R. T.;
Nelson, J . M.; Manners, I. J . Organomet. Chem. 1997, 528, 47.
(28) Tudor, J .; Barlow, S.; Payne, B. R.; O’Hare, D.; Nguyen, P.;
Evans, C. E. B.; Manners, I. Organometallics 1999, 18, 2281.
X-r a y Cr ysta l Str u ctu r e Deter m in a tion s. For compound
1, a suitable crystal chosen from a batch grown from hot
ethanol was mounted on a pin with silicon grease, and the