Stereoelectronic influence of the type of bifunctional ansa- monocyclopentadienyldimethylsilylamido ligand on the molecular structures displayed by zirconium dichloride and 1,4-diphenylbutadiene complexes

Article abstract of DOI:10.1021/ic040001i

A series of organozirconium dichloride and 1,4-diphenylbutadiene complexes featuring a dianionic bifunctional ligand with a cyclopentadienyl-type functionality and an appended amido N donor have been prepared and structurally characterized. [(C₅H₄)SiMe₂(N-t-Bu)]ZrCl ₂, 1, [(C₉H₆)SiMe₂(N-t-Bu)]ZrCl ₂, 2, and [(C₅Me₄)SiMe₂(N-i-Pr)] ZrCl₂, 3, were prepared in two steps, with ligand chelation accomplished by an amine elimination reaction followed by treatment of the diamido Zr intermediate with an excess of SiMe₃Cl. X-ray structural analyses reveal that in the solid state 2 is monomeric, whereas 1 and 3 are centrosymmetric dimers linked by a pair of bridging chlorides. The level of asymmetry displayed by the central Zr₂(μ-Cl)₂ moiety is indicated by the variation in the pair of independent bridging Zr-Cl bond distances, which are 2.618(1) and 2.657(1) A in 1 and 2.542(1) and 2.745(1) A in 3, respectively. The metathetical reactions of [Mg(C ₄H₄Ph₂)(THF)₃]_n with 1, 2, 3, and [(C₅Me₄)SiMe₂(N-t-Bu)]ZrCl ₂ proceed to afford the corresponding 1,4-diphenylbutadiene derivatives 4, 5, 6, and 7, respectively. Solution NMR data show that 6 is obtained exclusively as the supine isomer, whereas compounds 4, 5, and 7 exist as >20:1, 6:1, and 2:1 mixtures of the supine and prone isomers at ambient temperature. The molecular structures of the supine forms of 4, 5, 6, and 7 are appreciably folded (70-80°) along the line of intersection between the plane containing the Zr and the two terminal butadiene carbons and the plane of the cis-butadiene fragment. An increase in the folding is accompanied by a decrease in the difference between the average Zr-C(terminal) and Zr-C(internal) bond distances and leads to a more pronounced long-short-long C-C bond sequence within the coordinated butadiene.

Full text of DOI:10.1021/ic040001i

Inorg. Chem. 2004, 43, 3976−3987
Stereoelectronic Influence of the Type of Bifunctional
ansa-Monocyclopentadienyldimethylsilylamido Ligand on the Molecular
Structures Displayed by Zirconium Dichloride and 1,4-Diphenylbutadiene
Complexes
Leonie F. Braun,1 Thorsten Dreier,1 Matthew Christy, and Jeffrey L. Petersen*
C. Eugene Bennett Department of Chemistry, West Virginia UniVersity,
Morgantown, West Virginia 26505-6045
Received January 5, 2004
A series of organozirconium dichloride and 1,4-diphenylbutadiene complexes featuring a dianionic bifunctional ligand
with a cyclopentadienyl-type functionality and an appended amido N donor have been prepared and structurally
characterized. [(C H )SiMe2(N-t-Bu)]ZrCl2, 1, [(C H )SiMe2(N-t-Bu)]ZrCl2, 2, and [(C Me4)SiMe2(N-i-Pr)]ZrCl2, 3, were
5
4
9
6
5
prepared in two steps, with ligand chelation accomplished by an amine elimination reaction followed by treatment
of the diamido Zr intermediate with an excess of SiMe3Cl. X-ray structural analyses reveal that in the solid state
2 is monomeric, whereas 1 and 3 are centrosymmetric dimers linked by a pair of bridging chlorides. The level of
asymmetry displayed by the central Zr2(µ-Cl)2 moiety is indicated by the variation in the pair of independent bridging
Zr−Cl bond distances, which are 2.618(1) and 2.657(1) Å in 1 and 2.542(1) and 2.745(1) Å in 3, respectively. The
metathetical reactions of [Mg(C H Ph2)(THF)3]n with 1, 2, 3, and [(C Me4)SiMe2(N-t-Bu)]ZrCl2 proceed to afford the
4
4
5
corresponding 1,4-diphenylbutadiene derivatives 4, 5, 6, and 7, respectively. Solution NMR data show that 6 is
obtained exclusively as the supine isomer, whereas compounds 4, 5, and 7 exist as >20:1, 6:1, and 2:1 mixtures
of the supine and prone isomers at ambient temperature. The molecular structures of the supine forms of 4, 5, 6,
and 7 are appreciably folded (70−80°) along the line of intersection between the plane containing the Zr and the
two terminal butadiene carbons and the plane of the cis-butadiene fragment. An increase in the folding is accompanied
by a decrease in the difference between the average Zr−C(terminal) and Zr−C(internal) bond distances and leads
to a more pronounced long−short−long C−C bond sequence within the coordinated butadiene.
Introduction
extended Bercaw’s findings to Group 4 metals and indepen-
dently prepared a series of 14-electron ansa-cyclopentadi-
enylamido metal complexes, [(C5R4)L(NR′)]MCl2, with M
) Ti, Zr, Hf; R ) H, alkyl; R′ ) alkyl, aryl, which, upon
activation with methylalumoxane, afford highly active Zie-
gler-Natta catalysts for the copolymerization of ethylene
and 1-alkenes or styrene. The catalytic performance of these
“constrained-geometry” catalysts varies with the electronic
and steric features of the cyclopentadienyl and amido
functionalities and the type of bridging linkage (L).3-5
The incorporation of an ansa-cyclopentadienylamido-type
ligand is typically accomplished by a conventional metathesis
The Lewis acidity of early-transition-metal metallocenes
is enhanced by the replacement of the two cyclopentadienyl
rings with a bifunctional ansa-cyclopentadienylamido ligand,
such as [(C5Me4)SiMe2(N-t-Bu)]2-, which reduces the steric
congestion and the formal electron count at the electrophilic
center. This ligand modification was originally introduced
by Bercaw and co-workers2 and led to their development of
one-component scandium-based ethylene polymerization
catalysts. Researchers at The Dow Chemical Co.3 and Exxon4
* Author to whom correspondence should be addressed. E-mail: jpeterse@
wvu.edu.
(1) Institut fu¨r Organische Chemie, University of Mu¨nster, visiting student.
(2) (a) Shapiro, P. J.; Cotter, W. D.; Schaefer, W. P.; Labinger, J. A.;
Bercaw, J. E. J. Am. Chem. Soc. 1994, 116, 4623-4640. (b) Piers,
W. E.; Shapiro, P. J.; Bunel, E. E.; Bercaw, J. E. Synlett 1990, 2,
74-84. (c) Shapiro, P. J.; Bunel, E. E.; Schaefer, W. P.; Bercaw, J.
E. Organometallics 1990, 9, 867-869.
(3) Stevens, J. C.; Timmers, F. J.; Rosen, G. W.; Knight, G. W.; Lai, S.
Y. Eur. Patent Appl. EP 0 416 815 A2, 1991.
(4) Canich, J. M. Eur. Patent Appl. EP 0 420 436 A1, 1991.
(5) McKnight, A. L.; Masood, M. A.; Waymouth, R. M.; Straus, D. A.
Organometallics 1997, 16, 2879-2885.
3976 Inorganic Chemistry, Vol. 43, No. 13, 2004
10.1021/ic040001i CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/27/2004

Influence of ansa-Cyclopentadienylamido Ligands on Metallocenes
reaction of a suitable dilithio salt, a diGrignard reagent of
[(C5R4)L(NR′)]2- with an appropriate metal chloride,2-7 or
by a thermally induced amine elimination reaction of
(C5R4H)L(NHR′) and a metal tetraamide.8-11 The conversion
of the intermediate metal diamido complex to the corre-
sponding dichloride derivative may be accomplished by the
addition of excess SiMe3Cl. This latter approach has led to
the development of efficient syntheses for [(C5H4)SiMe2(N-
butadiene adopts the Z configuration. Related Ti and Zr 1,3-
butadiene complexes may also be prepared by the corre-
sponding metathetical reactions of [(C5Me4)SiMe2(NR)]-
MCl2, R ) t-Bu,17 CHMe(1-C10H7),17 or [(C5H4)SiMe2(N-
t-Bu)]MCl2,18 with [Mg(C4H6)(THF)2]n.
The X-ray structural analyses of [(C5Me4)SiMe2(N-t-Bu)]-
Zr(C4H6)17 and [(C5H4)SiMe2(N-t-Bu)]Zr(C4H6)18 revealed
that the replacement of C5Me4 with the C5H4 ring has a
dramatic influence on the solution and solid-state structures
displayed by these compounds. Solution NMR data for [(C5-
Me4)SiMe2(N-t-Bu)]Zr(C4H6) indicate the presence of an 85:
15 mixture of the supine and prone isomers, whereas for
[(C5H4)SiMe2(N-t-Bu)]Zr(C4H6), only the supine isomer is
observed. In the solid state, the supine isomer of [(C5Me4)-
SiMe2(N-t-Bu)]Zr(C4H6) is mononuclear.17 Alternatively,
[(C5H4)SiMe2(N-t-Bu)]Zr(C4H6) is tetranuclear,18 with four
unsymmetrically bridging butadiene groups. To avoid the
formation of oligomeric species, such as observed in the solid
state for [(C5H4)SiMe2(N-t-Bu)]Zr(C4H6), a series of mono-
nuclear Zr 1,4-diphenylbutadiene complexes, [(Ring)-
SiMe2(NR)]Zr(C4H4Ph2), Ring ) C5H4, C5Me4, C9H6; R )
i-Pr or t-Bu, were prepared. The results of our X-ray
structural analyses have provided the opportunity to evaluate
the stereoelectronic influence of the type of cyclopentadienyl
functionality and the size of the alkyl substituent, R, on the
relative importance of the η4-π diene and the η2-σ2,π diene
representations for the metal-butadiene bonding interaction.
10
12
t-Bu)]TiCl2 and [(C5Me4)SiMe2(N-t-Bu)]ZrCl2 and was
used to prepare the ansa-monocyclopentadienyldimethyl-
silylamido Zr dichloride complexes reported herein. Leung
and co-workers11 reported that treatment of enantiomerically
pure R(-)- or S(+)-[(C5Me4)SiMe2(NCH(Me)Ph)]Zr(NMe2)2
with SiMe3Cl initially led to the isolation of the RR- and
SS-dichloro-bridged dimers, respectively, which upon sub-
limation (10-2 Torr, 200 °C) yield the respective monomeric
R- and S-[(C5Me4)SiMe2(NCH(Me)Ph)]ZrCl2 complexes.
Teuben and co-workers subsequently found that the modified
13
amine elimination reaction of Zr(NMe2)2Cl2(THF)2 with
(C5H5)(CH2)nNHR, n ) 2, 3, affords [(C5H4)(CH2)n(NR)]-
ZrCl2, R ) i-Pr, t-Bu, directly in one step.14
The [(C5Me4)SiMe2(NR)]TiCl2 complexes are highly at-
tractive precursors for the generation of olefin copolymer-
ization catalysts.15 Treatment of [(C5Me4)SiMe2(NR1)]TiCl2
with 2 equiv of n-BuLi in the presence of excess diene
allowed researchers at The Dow Chemical Co. in collabora-
tion with Marks and co-workers15a at Northwestern Univer-
sity to prepare a series of organotitanium diene complexes,
Results and Discussion
[(C5Me4)SiMe2(NR1)]Ti(R2CHdCHCHdCHR3)] (R1
)
t-Bu, Ph; R2 ) H, Me; R3 ) H, Me). The stoichiometric
addition of B(C6F5)3 converts these Ti-diene complexes
into zwitterionic complexes [(C5Me4)SiMe2(NR1)]Ti+R2-
CHdCHCHdCHR3B-(C6F5)3, which function as single-
component copolymerization catalysts. Cowley and co-
workers16 used a similar approach to prepare [(C5Me4)-
SiMe2(N-t-Bu)]M+CHMedCHCHdCH2B-(C6F5)3, M ) Ti,
Zr, and observed that the π-allyl unit within the cisoid
Synthesis and Characterization of Several ansa-Mono-
cyclopentadienylamido-Type Zr Dichloride Complexes.
The attachment of a bifunctional monocyclopentadienyldim-
ethylsilylamido-type ligand to Zr is conveniently carried out
by the thermally induced amine elimination reaction of
(RingH)SiMe2(NHR) with Zr(NMe2)4 (eq 1). For Ring )
C5H4, C5Me4 and R ) i-Pr, t-Bu, this reaction is best
performed by heating a neat 1:1 reaction mixture while
purging the released NMe2H with nitrogen. As these reactions
proceed to completion, the [(Ring)SiMe2(NR)]Zr(NMe2)2
complexes are sufficiently volatile to collect on the upper
cool portion of the reaction flask and may be readily purified
by sublimation. In contrast, the neat amine elimination
reaction of (C9H7)SiMe2(NH-t-Bu) with Zr(NMe2)4 affords
a dark orange, viscous oil.9 These bis(dimethylamido) Zr
intermediates were identified by solution NMR measure-
ments.
The [(Ring)SiMe2(NR)]Zr(NMe2)2 complexes are readily
converted to [(Ring)SiMe2(NR)]ZrCl2 by heating the respec-
tive toluene solution in the presence of excess SiMe3Cl
overnight at 60 °C (eq 2). These reactions proceed with
elimination of NMe2SiMe3, which is readily removed under
vacuum. The overall yields obtained from this two-step
reaction sequence range from 70 to 85% for [(C5H4)SiMe2-
(N-t-Bu)]ZrCl2, 1, [(C9H6)SiMe2(N-t-Bu)]ZrCl2, 2, [(C5Me4)-
(6) (a) Okuda, J. Chem. Ber. 1990, 123, 1649-1651. (b) Okuda, J.;
Schattenmann, F. J.; Wocadlo, S.; Massa, W. Organometallics 1995,
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(7) Strickler, J. R.; Power, J. M. U.S. Patent 5,359,105, 1994.
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12, 1936-1945. (b) Sinnema, P.-J.; van der Veen, L.; Spek, A. L.;
Veldman, N.; Teuben, J. H. Organometallics 1997, 16, 4245-4247.
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482, 169-181.
(10) Carpenetti, D. W.; Kloppenburg, L.; Kupec, J. T.; Petersen, J. L.
Organometallics 1996, 15, 1572-1581.
(11) Leung, W.-P.; Song, F.-Q.; Zhou, Z.-Y.; Xue, F.; Mak, T. C. W. J.
Organomet. Chem. 1999, 575, 232-241.
(12) Kloppenburg, L. Ph.D. dissertation, University of Mu¨nster, 1997.
(13) Brenner, S.; Kempe, R.; Arndt, P. Z. Anorg. Allg. Chem. 1995, 621,
2021-2024.
(14) (a) Sinnema, P.-J.; Liekelema, K.; Stall, O. K. B.; Hessen, B.; Teuben,
J. H. J. Mol. Catal. 1998, 128, 143-153. (b) Sinnema, P.-J. Ph.D.
dissertation, University of Gro¨ningen, 1999.
(15) (a) Devore, D. D.; Timmers, F. J.; Hasha, D. L.; Rosen, R. K.; Marks,
T. J.; Deck, P. A.; Stern, C. L. Organometallics 1995, 14, 3132-
3134. (b) Devore, D. D.; Stevens, J. C.; Timmers, F. J.; Rosen, R. K.
U.S. Patent 5,539,068, 1996.
(16) (a) Cowley, A. H.; Hair, G. S.; McBurnett, B. G.; Jones, R. A. J.
Chem. Soc., Chem. Commun. 1999, 437-438. (b) Hair, G. S.; Jones,
R. A.; Cowley, A. H.; Lynch, V. Inorg. Chem. 2001, 40, 1014-1019.
(17) Dahlmann, M.; Schottek, J.; Fro¨hlich, R.; Kunz, D.; Nissinen, M.;
Erker, G.; Fink, G.; Kleinschmidt, R. J. Chem. Soc., Dalton Trans.
2000, 1881-1886.
(18) Strauch, J. W.; Petersen, J. L. Organometallics 2001, 20, 2623-2630.
Inorganic Chemistry, Vol. 43, No. 13, 2004 3977

Braun et al.
Figure 1. Perspective view and the atom labeling scheme for the dimeric
structure of [(C5H4)SiMe2(N-t-Bu)]ZrCl2, 1. The thermal ellipsoids are
scaled to enclose 30% probability. This dimeric structure is constrained by
a crystallographic center of inversion.
Figure 2. Perspective view of the molecular structure and the atom labeling
scheme for [(C9H6)SiMe2(N-t-Bu)]ZrCl2, 2. The thermal ellipsoids are scaled
to enclose 30% probability.
SiMe2(N-i-Pr)]ZrCl2, 3, and [(C5Me4)SiMe2(N-t-Bu)]ZrCl2.
[(C5Me4)SiMe2(N-t-Bu)]ZrCl2 and 2 may be purified by
sublimation, whereas compounds 1 and 3 were recrystallized
by cooling a hot toluene solution. These four compounds
were characterized by 1H and 13C NMR measurements, and
their molecular structures were verified by X-ray crystal-
lography.
Figure 3. Perspective view and the atom labeling scheme for the dimeric
structure of [(C5Me4)SiMe2(N-i-Pr)]ZrCl2, 3. The thermal ellipsoids are
scaled to enclose 30% probability. This dimeric structure is constrained by
a crystallographic center of inversion.
0.689 Å from the plane defined by the terminal Cl atom,
the two bridging Cl atoms, and the amido N atom. In
contrast, because the N-Zr-Clinner angle is ca. 30° greater
than the Clt-Zr-Clouter angle in 3, the two legs defined by
the Zr-N and Zr-Clinner bond vectors are directed farther
away from each other, whereas the other two legs defined
by the Zr-Clt and Zr-Clouter bond vectors are more disposed
toward one another than in 1.
The Zr-Cl bond distances for the outer and inner bridging
chlorides within the central Zr2(µ-Cl)2 moiety of 1 are 2.618-
(1) and 2.657(1) Å with a terminal Zr-Clt distance of 2.453-
(1) Å. The corresponding bridging Zr-Cl distances in 3 of
2.542(1) and 2.745(1) Å reflect a substantially higher degree
of asymmetry. A comparable level of asymmetry exists in
RR-{[(C5Me4)SiMe2(NCH(Me)Ph)]ZrCl(µ-Cl)}2,11 with the
two outer bridging Zr-Cl bonds being 2.541(2) and 2.547-
(2) Å and the two inner bridging Zr-Cl bonds being 2.760-
(2) and 2.807(2) Å for the nearly planar Zr2(µ-Cl)2 core. The
weaker dative ZrrClinner interaction of 3 is compensated by
a 0.076 Å decrease in the Zr-Clouter distance and a 0.02 Å
reduction of the Zr-Clt distance to 2.434(1) Å and is
accompanied by a ca. 10° increase in the N-Zr-Clinner angle
The solution NMR spectra of 1 and 3 exhibit mirror
symmetry consistent with the presence of mononuclear
structures in solution. The introduction of the indenyl group
in 2 results in the appearance of two well-separated sets
of proton and carbon resonances for the inequivalent
methyl substituents of the dimethylsilyl bridge. Whereas
the mononuclear structure of 2 is retained in the solid state,
the molecular structures of 1 and 3 are centrosymmetric
dimers, held together by a pair of bridging Cl ligands.
Perspective views of the molecular structures of 1, 2, and 3
are depicted in Figures 1, 2, and 3, respectively, with the
atom labeling scheme provided for the independent non-
hydrogen atoms.
The coordination geometry about each Zr atom in 1 and
3 resembles a four-legged piano stool, with the appended
amido N atom trans to the inner bridging Clinner atom and
the terminal Clt (i.e. Cl(2)) atom disposed opposite to the
outer bridging Clouter (i.e., Cl(1)). In 1, the Zr atom is disposed
3978 Inorganic Chemistry, Vol. 43, No. 13, 2004

Influence of ansa-Cyclopentadienylamido Ligands on Metallocenes
from 144.48(7) to 154.33(8)° and a ca. 19° decrease in the
Clt-Zr-Clouter angle from 143.38(3) to 124.62(4)° for 1 and
3, respectively. The perpendicular displacements of the
terminal Cl ligands from the planar Zr2(µ-Cl)2 core are 1.06
and 1.81 Å for 1 and 3, respectively.
In contrast, the four-coordinate geometry of 2 resembles
that of a distorted tetrahedron and is similar to that displayed
by [(C5Me4)SiMe2(N-t-Bu)]ZrCl2.10 The position of the
indenyl group is such that the plane passing through the
bridgehead C, Si, and N atoms bisects the Cl-Zr-Cl angle.
The replacement of the indenyl group of 2 with the better
π-donating C5Me4 ring19 leads to a ca. 0.03 Å decrease in
the Zr-Cp(c) distance, a 0.01 Å increase in the Zr-N(amido)
distance, and a pair of nearly equal Zr-Cl bonds. However,
the lower coordination number and formal electron count of
Zr in 2 and [(C5Me4)SiMe2(N-t-Bu)]ZrCl2 allow the Cl
ligands to π donate more effectively to the electrophilic Zr,
thus producing a 0.04-0.06 Å decrease in their correspond-
ing Zr-Cl bond distances.
The X-ray crystallographic data of compounds 1, 2, and
3 reflect the structural changes that occur during the transition
from a symmetric dimer, 1, through an intermediate asym-
metric dimer, 3, to two non-interacting, well-separated four-
coordinate monomers, such as observed for 2 and [(C5Me4)-
SiMe2(N-t-Bu)]ZrCl2. Dissociation of the symmetric dimer
proceeds with elongation of the Zr-Clinner distance and with
concomitant reduction in the Clt-Zr-Clouter angle and the
Zr-Clouter distance. As this process proceeds with further
weakening of the dative ZrrClinner interaction, the Clt-Zr-
Clouter bond angle approaches 105°, and the difference in the
Zr-Ct and Zr-Clouter distances diminishes as their respective
values approach 2.40 Å, a typical value for a terminal Zr-
Cl bond distance in 14-electron, four-coordinate, monocy-
clopentadienyl Zr complexes.20,21
Characterization of the 1,4-Diphenylbutadiene Zr Com-
plexes. The solution NMR data for [(C5H4)SiMe2(N-t-Bu)]-
Zr(C4H4Ph2), 4, and [(C5Me4)SiMe2(NR)]Zr(C4H4Ph2), R )
i-Pr (6), t-Bu (7), are consistent with the presence of mirror
symmetry. The indenyl group in [(C9H6)SiMe2(N-t-Bu)]Zr-
(C4H4Ph2), 5, makes this compound chiral, as evidenced by
the appearance of well-separated proton and carbon reso-
nances for the two methyl substituents of the SiMe2 bridge.
For 4, 6, and 7, the chemically equivalent meso and anti
protons of each 1,4-diphenylbutadiene ligand produce two
well-separated multiplets, consistent with an AA′XX′ cou-
pling system. The independent JH-H coupling constants were
determined by computer simulation.22 The magnitude of the
3Jmeso-meso and 3Jmeso-anti coupling constants of 10-12 Hz is
consistent with a cis- rather than a trans-butadiene back-
bone.23 The splitting patterns for the meso and anti protons
of 4, 6, and 7 are similar and resemble the one that is
simulated in Figure 4a. The loss of mirror symmetry in 5
leads to the appearance of two second-order multiplets
centered at δ 6.16 and 6.10 for the chemically inequivalent
meso protons of its major isomer, as shown in Figure 4b,
and of two well-separated pseudo doublets of doublets for
the chemically inequivalent anti protons. The corresponding
ortho, meta, and para protons of the phenyl rings of 4, 5, 6,
and 7 exhibit an AA′BB′C splitting pattern with six
independent coupling constants. The JH-H coupling constants
between the ortho, meta, and para phenyl ring protons were
also determined by computer simulation.22
General Synthesis of [(Ring)SiMe2(NR)]Zr(C4H4Ph2)
Complexes (Ring ) C5H4, C5Me4, and C9H6; R ) t-Bu,
i-Pr). The metathetical reactions of [(Ring)SiMe2(NR)]ZrCl2
(Ring ) C5H4, C5Me4, C9H6; R ) t-Bu, i-Pr) with a 5%
excess of 1,4-diphenylbutadiene magnesium were carried out
in toluene (eq 3). As each reaction proceeded, the color of
the reaction mixture became dark red. The resultant 1,4-
diphenylbutadiene compounds, [(Ring)SiMe2(NR)]Zr(C4H4-
Ph2), were soluble in toluene, moderately soluble in pentane,
and only modestly soluble in hexamethyldisiloxane. Purifica-
tion of these butadiene compounds was accomplished by
recrystallization from toluene or pentane, leaving dark red
crystals. The identity of each compound was verified by
The 1H NMR spectra reveal that compound 6 exhibits one
primary species in solution, whereas compounds 4, 5, and 7
afford >20:1, 6:1, and 2:1 mixtures, respectively, of two
conformational isomers, which differ in terms of the orienta-
tion of the butadiene cup with respect to the cyclopentadienyl
functionality. The supine structure has the open end of the
diene cup directed toward the cyclopentadienyl functionality,
whereas the alternative prone structure has the opening of
the diene cup directed away from the cyclopentadienyl ring.
The magnitude of the chemical shift difference, ∆δH, between
the downfield meso (δmeso) and upfield anti (δanti) protons
of the cis-butadiene of the supine structure is typically 2-3
times greater than that for the prone isomer. The chemical
shifts of the meso and anti butadiene protons of 4 (major
and minor), 5 (major and minor), 6, and 7 (major and minor)
and the JH-H coupling constants are summarized in Table 1.
The range of the chemical shift difference observed for 4
(major), 5 (major), 6, and 7 (major) is 4.3-5.0 ppm, which
1
solution H and 13C NMR measurements, and the peak
assignments were made by examination of the observed
cross-peaks in the corresponding 2D HETCOR and COSY
NMR spectra.
(19) (a) Gassman, P. G.; Winter, C. H. J. Am. Chem. Soc. 1988, 110, 6130-
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T.; Eyler, J. R.; Siedle, A. R. J. Am. Chem. Soc. 1996, 118, 11244-
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(22) SpinWorks, version 2.1 (Professor Kirk Marat, Department of
Chemistry, University of Manitoba, Manitoba, Canada R3T 2N2),
permits off-line processing of 1D and 2D NMR data and may be used
for the simulation and analysis of complex second-order spectra and
dynamic NMR spectral data.
(23) Benn, R.; Schroth, G. J. Organomet. Chem. 1982, 228, 71-85.
Inorganic Chemistry, Vol. 43, No. 13, 2004 3979

Braun et al.
Two representations, η4-π diene and η2-σ2,π diene, have
been invoked to describe the nature of the metal-butadiene
bonding interaction. Two different approaches have been
used to evaluate the relative importance of these two
representations from an examination of the X-ray crystal-
lographic data. Erker and co-workers24 observed for a series
of Group 4 metallocene butadiene complexes that η4-π diene
complexes are recognized by shorter M-C(internal) and
C(terminal)-C(internal) bond distances and by smaller
M-C(terminal)-C(internal) bond angles than the values
of these three parameters in η2-σ2,π diene complexes.
For example, the corresponding values of 2.550(5) Å, 1.445-
(2) Å, and 81.8(1)° for Cp2Zr(η4-1,2,5,6-tetramethyl-3,4-
dimethylenetricyclo[3.1.0.02.6]hexane)24b are compatible with
the η4-π diene representation, whereas the substantially larger
values of 2.885(4) Å, 1.48(1) Å, and 95.8° for Cp2Zr-
(indanediyl)25 are indicative of a pure η2-σ2 interaction
lacking a π-bonding component. From their examination of
the values of these three structural parameters for M(η4-
C4H6)Ph[N(SiMe2CH2PMe2)2] (M ) Zr, 2.466(11) Å, 1.42-
(2) Å, 76.3(7)°; M ) Hf, 2.456(7) Å, 1.429(12) Å, 76.5(5)°),
Fryzuk and co-workers26 concluded that these two complexes
exhibit a higher degree of η4-π character than that found in
Group 4 metallocene diene complexes. The corresponding
structural data (2.400(5) Å, 1.437(8) Å, 73.6° (av)) for the
Hf dibutadiene complex, Hf(C4H6)2(dmpe),27 also reflect the
prevalence of the η4-π diene interaction.
Figure 4. (a) Simulated (top) and experimental (bottom) AA′XX′ splitting
pattern observed for the chemically equivalent meso-butadiene protons of
4 (major) and (b) simulated (top) and experimental (bottom) second-order
splitting pattern observed for the chemically inequivalent meso-butadiene
protons of 5 (major).
is substantially larger than the ∆δH range of 2.2-2.4 ppm
for the minor isomers of 4, 5, and 7. On the basis of these
solution NMR data, compounds 4 (major), 5 (major), 6, and
7 (major) conform to the supine structure, whereas 4 (minor),
5 (minor), and 7 (minor) are assigned to the alternative prone
structure.
The alternative approach28 used to evaluate the nature of
the metal-diene bonding interaction involves a correlation
between the dihedral angle, R (defined as the angle between
the plane passing through the four diene carbons and the
plane through the metal and two terminal carbons of the
diene), and the ∆M-C distance (defined as the difference
between the average of the pair of M-C(terminal) and
M-C(internal) bond distances). Group 4 metallocene com-
plexes with appreciable η4-π diene character24 typically
exhibit values of R > 110°, with ∆M-C varying from -0.3
to -0.5 Å. For late-transition-metal η4-π diene complexes,
the values of R and ∆M-C typically range from 75 to 90°
and from -0.1 to 0.1 Å, respectively.28 The values of R and
∆M-C observed for M ) Zr of 98.9° and -0.171 Å and
for M ) Hf of 97.5° and -0.193 Å in M(η4-C4H6)Ph[N-
(SiMe2CH2PMe2)2]26 provide further indication of greater
η4-π character than that in Group 4 metallocene diene
complexes.
Description of the Molecular Structures of the 1,4-
Diphenylbutadiene Zr Complexes. The molecular structures
of [(C5H4)SiMe2(N-t-Bu)]Zr(C4H4Ph2), 4, [(C9H6)SiMe2(N-
t-Bu)]Zr(C4H4Ph2), 5, [(C5Me4)SiMe2(N-i-Pr)]Zr(C4H4Ph2),
6, and [(C5Me4)SiMe2(N-t-Bu)]Zr(C4H4Ph2), 7, were deter-
mined by analyses of X-ray diffraction data collected while
cooling the samples at -50 °C (Table 2). The crystals used
for these structural analyses were grown at ambient temper-
ature by slow removal of solvent from a saturated solution
of the respective compound. Perspective views of the
molecular structures with the appropriate atom labeling
scheme are depicted in Figures 5, 6, 7, and 8, respectively.
The Zr coordination environment in each complex is
comprised of the π-bonded cyclopentadienyl ring functional-
ity, the anionic amido N-donor of the corresponding bifunc-
tional ligand, and a 1,4-diphenylbutadiene moiety. The open
cup of the cis-diene ligand is directed toward the cyclopen-
tadienyl functionality, consistent with the supine conforma-
tion. The metal-diene bonding interaction and spatial
orientation of the diene unit are compatible with the
structures reported by Erker and co-workers17 for [(C5Me4)-
SiMe2(NCHMe(1-C10H7))]Zr(C4H6) and the major isomer of
[(C5Me4)SiMe2(N-t-Bu)]Zr(C4H6) and by Strauch and Pe-
tersen18 for [(C5Me4)SiMe2(N-i-Pr)]Zr(C4H6). The planar
phenyl substituents of the cis-diene ligand in 4-7 are directed
laterally from the terminal butadiene carbons, with their
planes rotated 25-40° from being coplanar with the plane
defined by the four central carbons of the coordinated diene.
(24) (a) Erker, G.; Kru¨ger, C.; Mu¨ller, G. AdV. Organomet. Chem. 1985,
24, 1-39. (b) Erker, G.; Engel, K.; Kru¨ger, C.; Mu¨ller, G. Organo-
metallics 1984, 3, 128-133. (c) Kru¨ger, C.; Mu¨ller, G.; Erker, G.;
Dorf, U.; Engel, K. Organometallics 1985, 4, 215-223. (d) Erker,
G.; Engel, K.; Kru¨ger, C.; Chiang, A.-P. Chem. Ber. 1982, 115, 3311-
3323. (e) Erker, G.; Wicher, J.; Engel, K.; Rosenfeldt, F.; Dietrich,
W.; Kru¨ger, C. J. Am. Chem. Soc. 1980, 102, 6346-6348.
(25) Lappert, M. F.; Martin, T. R.; Atwood, J. L.; Hunter, W. E. J. Chem.
Soc., Chem. Commun. 1980, 476-477.
(26) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J. Organometallics 1989, 8,
1723-1732.
(27) Wreford, S. S.; Whitney, J. F. Inorg. Chem. 1981, 20, 3918-3924.
(28) (a) Yasuda, H.; Nakamura, A.; Kai, Y.; Kasai, N. Topics in Physical
Organometallic Chemistry; Freund Publishing House: Tel Aviv, 1987;
Vol. 2. (b) Yasuda, H.; Tatsumi, K.; Okamoto, T.; Mashima, K.; Lee,
K.; Nakumura, A.; Kai, Y.; Kanehisa, N.; Kasai, N. J. Am. Chem.
Soc. 1985, 107, 2410-2422.
3980 Inorganic Chemistry, Vol. 43, No. 13, 2004

Influence of ansa-Cyclopentadienylamido Ligands on Metallocenes
1
Table 1. Summary of H NMR Data for the Meso and Anti Protons of the 1,4-Diphenylbutadiene Ligands in 4-7
compound
structure
δmeso
6.28
δanti
1.97
J(H-H), Hza
4 (major)
4 (minor)
5 (major)
supine
prone
supine
J(m-m′) ) 9.94(6), J(m-a′) ) -2.12(8), J(a-a′) ) 0.22(5), J(a-m) ) 11.18(1)
J(m-m′) ) 11.44(7), J(m-a′) ) -1.8(1), J(a-a′) ) 0.29(6), J(a-m) ) 12.59(1)
J(m1-m2) ) 10.70(7), J(m1-a2) ) 1.34(7), J(m2-a1) ) 1.17(7),
5.12
2.70
6.15 (m1)
6.11 (m2)
5.31 (m1)
4.42 (m2)
6.22
1.72 (a1)
1.25 (a2)
2.58 (a1)
2.43 (a2)
1.70
J(a1-a2) ) 0.16(7), J(m1-a1) ) 11.84(7), J(m2-a2) ) 12.03(7)
5 (minor)
prone
J(m1-m2) ) 11.5(2), J(m1-a2) ) 1.6(2), J(m2-a1) ) 1.3(2),
J(a1-a2) ) 0.2(2), J(m1-a1) ) 12.3(2), J(m2-a2) ) 12.5(2)
6
supine
supine
prone
J(m-m′) ) 10.77(5), J(m-a′) ) -2.26(7), J(a-a′) ) 0.60(4), J(a-m) ) 10.96(1)
J(m-m′) ) 10.55(7), J(m-a′) ) -2.2(1), J(a-a′) ) 0.43(6), J(a-m) ) 11.28(1)
J(m-m′) ) 11.41(9), J(m-a′) ) -1.5(1), J(a-a′) ) 0.24(7), J(a-m) ) 13.05(3)
7 (major)
7 (minor)
6.38
5.01
1.37
2.83
a The esd’s determined from the computer simulation are given in parentheses.
bonding distance of the electrophilic Zr center, thus resulting
in ∆Zr-C values varying from -0.09 Å (6) to -0.14 Å
(7). The smallest dihedral angle, R, is accompanied by the
smallest ∆Zr-C value, and vice versa. The methine H atom
of the isopropyl substituent on the amido N of 6 is directed
toward the diene ligand. Consequently, the replacement of
the tert-butyl substituent in 7 with the sterically less
demanding isopropyl group enhances the π-bonding contri-
bution to the Zr-diene interaction and affords greater
π-donation from the amido N donor. The resultant structural
adjustments include a 0.03 Å decrease in the average Zr-
C(internal) bond distance, a nearly 11° decrease in the
dihedral angle, R, and a 0.035 Å decrease in the Zr-N bond
distance.
Coordination of a cis η4-π diene to an electrophilic metal
often leads to a long-short-long sequence for the three
C-C bonds within the butadiene ligand.24,26-28 With the
exception of 7, the central C-C bond is 0.04-0.07 Å shorter
than the outer two C-C bonds of the coordinated diene.
Compound 6, which has the smallest dihedral angle, R, and
shortest pair of Zr-C(internal) distances, also exhibits the
shortest internal C-C bond distance of 1.374(5) Å. This
long-short-long C-C bond variation may be rationalized
by treating 4-7 as Zr(II) η4-diene rather than as Zr(IV)
enediyl complexes. On the basis of the former description,
one anticipates that as the dihedral angle, R, decreases toward
90°, the degree of π-back-donation from the filled Zr-dπ
orbital to the empty lower-lying π* antibonding orbital of
the neutral diene should increase. Because the two nodes in
this diene π* orbital lie between the C(terminal)-C(internal)
bonds, an increase in π-back-donation would be expected
to enhance the long-short-long variation of the C-C
distances within the coordinated diene. The structural data
provided in Table 4 are consistent with this description.
The Zr-C(terminal) bond distances in these butadiene
complexes range from 2.30 to 2.35 Å and are modestly
longer than the corresponding values of 2.300 (av), 2.300-
(5), and 2.278(6) Å observed in [(C5Me4)SiMe2(NCHMe-
(1-C10H7))]Zr(C4H6),17 [(C5Me4)SiMe2(N-t-Bu)]Zr(C4H6),17
and [(C5Me4)SiMe2(N-i-Pr)]Zr(C4H6),18 respectively, which
are more typical of a Zr-C σ-bond. For example, the bond
distances for the Zr-C σ-bonds in (C5H5)2ZrMe2 and (C9H6)2-
ZrMe2 are 2.273(5), 2.280(5)29 and 2.251(6) Å,30 respectively.
Figure 5. Perspective view of molecular structure of the supine isomer
of [(C5H4)SiMe2(N-t-Bu)]Zr(C4H4Ph2), 4, and the atom labeling scheme.
The thermal ellipsoids are scaled to enclose 30% probability.
Figure 6. Frontal view of the molecular structure of the supine isomer of
[(C9H6)SiMe2(N-t-Bu)]Zr(C4H4Ph2), 5, and the atom labeling scheme. The
thermal ellipsoids are scaled to enclose 30% probability.
The structural data summarized in Table 4 indicate that
the four Zr-1,4-diphenylbutadiene complexes 4-7 also
exhibit pronounced η4-π diene character. The average Zr-
C(internal) distances range from 2.42 to 2.46 Å, the average
C(terminal)-C(internal) distances vary from 1.4 to 1.46 Å,
and the average Zr-C(terminal)-C(internal) bond angles fall
between 69 and 79°. The five-membered ZrC4 moieties are
appreciably folded with the dihedral angle, R, ranging from
100° (6) to 110.8° (7). The substantial folding of this
molecular unit places all four butadiene carbons within a
(29) Hunter, W. E.; Hrncir, D. C.; Vann Bynum, R.; Penttila, R. A.;
Atwood, J. L. Organometallics 1983, 2, 750-755.
(30) Atwood, J. L.; Hunter, W. E.; Hrncir, D. C.; Samuel, E.; Alt, H.;
Rausch, M. D. Inorg. Chem. 1975, 14, 1757-1762.
Inorganic Chemistry, Vol. 43, No. 13, 2004 3981

Braun et al.
3982 Inorganic Chemistry, Vol. 43, No. 13, 2004

Influence of ansa-Cyclopentadienylamido Ligands on Metallocenes
Table 3. Selected Interatomic Distances (Å) and Bond Angles (°) for
Complexes 1-3
1
2
3
A. Interatomic Distances
Zr-Cp(c)a
Zr-N
2.181
2.190
2.181
2.052(3)
2.453(1)
2.618(1)
2.657(1)
1.866(4)
1.734(3)
2.042(3)
2.394(1), 2.400(1)
2.052(3)
2.434(1)
2.542(1)
2.745(1)
1.874(3)
1.730(3)
Zr-Clt
Zr-Clouter
Zr-Clinner
b
Si-Cb
Si-N
1.878(4)
1.752(3)
B. Bond Angles
Cp(c)-Zr-N
Cp(c)-Zr-Clt
Cp(c)-Zr-Clouter
Cp(c)-Zr-Clinner
Cb-Si-Nb
100.6
109.2
104.8
114.1
92.86(13)
95.69(8)
91.05(8)
144.48(7)
102.4
114.2, 115.5
100.4
117.6
115.9
104.4
91.49(13)
94.50(8)
89.10(8)
154.33(8)
93.1(2)
110.33(9), 109.19(9)
N-Zr-Clt
N-Zr-Clouter
N-Zr-Clinner
Clt-Zr-Clt
105.21(5)
Clt-Zr-Clinner
Clinner-Zr-Clouter
Clt-Zr-Clouter
Si-N-Zr
80.69(4)
73.29(4)
143.38(3)
107.22(13)
129.0(2)
123.6(2)
79.75(3)
74.35(4)
124.62(4)
108.07(12)
129.8(2)
122.1(2)
106.0(2)
128.2(2)
125.7(2)
Ca-N-Sic
Ca-N-Zrc
Figure 7. Perspective view of the molecular structure of the supine isomer
of [(C5Me4)SiMe2(N-i-Pr)]Zr(C4H4Ph2), 6, and the atom labeling scheme.
The thermal ellipsoids are scaled to enclose 30% probability.
a Cp(c) corresponds to the centroid of the cyclopentadienyl ring. b Cb
corresponds to the bridgehead carbon. c Ca corresponds to the carbon of
the alkyl substituent at the amido nitrogen.
Table 4. Selected Interatomic Distances (Å) and Bond Angles (°) for
Complexes 4-7
4
5
6
7
A. Interatomic Distances
Zr-Cp(c)a
Zr-N
2.173
2.198
2.170
2.195
2.086(3)
2.329(4)
2.451(4)
2.445(4)
2.317(4)
1.440(5)
1.380(5)
1.430(5)
2.091(2)
2.308(2)
2.444(2)
2.465(2)
2.347(2)
1.436(3)
1.393(3)
1.474(3)
2.074(3)
2.333(4)
2.421(4)
2.416(4)
2.327(4)
1.443(5)
1.374(5)
1.448(5)
2.109(2)
2.301(3)
2.448(3)
2.459(3)
2.324(2)
1.393(4)
1.403(4)
1.400(4)
b
Zr-C1
Zr-C2
Zr-C3
Zr-C4
C1-C2
C2-C3
C3-C4
B. Bond Angles
101.6
Cp(c)-Zr-N
C1-Zr-C4
Si-N-Zr
101.5
102.0
79.82(14)
102.1
84.19(9)
81.71(15)
82.06(7)
Figure 8. Perspective view of the molecular structure of the supine isomer
of [(C5Me4)SiMe2(N-t-Bu)]Zr(C4H4Ph2), 7, and the atom labeling scheme.
The thermal ellipsoids are scaled to enclose 30% probability. The methyl
groups of the tert-butyl substituent suffer from a 75:25 two-site Star-of-
David disorder. The atoms are only shown for the major site.
103.96(14) 103.08(7) 105.47(15) 103.92(9)
Cb-Si-Nc
Zr-C1-C2
C1-C2-C3
C2-C3-C4
C3-C4-Zr
Cipso-C1-Zr
Cipso-C4-Zr
Cipso-C1-C2
Cipso-C4-C3
94.8(2)
77.2(2)
94.2(2)
77.7(1)
124.6(2)
126.1(2)
77.2(1)
129.1(1)
132.4(1)
124.0(2)
121.7(2)
105.2
93.5(2)
69.0(2)
124.3(3)
123.7(3)
68.9(2)
129.9(3)
128.7(3)
123.0(3)
122.8(3)
100.0
94.6(1)
78.8(2)
127.3(3)
127.5(3)
78.4(2)
133.0(2)
130.7(2)
120.7(3)
121.3(2)
110.8
125.9(4)
124.8(4)
77.5(2)
132.6(3)
128.2(3)
123.4(4)
125.1(4)
This modest increase in the Zr-C(terminal) bond distances
may reflect an enhancement of the η4-π diene contribution
arising from the placement of a phenyl substituent at each
terminal diene carbon. This remark is supported by a
comparison of the pertinent structural parameters provided
in Table 5 for [(C5Me4)SiMe2(N-i-Pr)]Zr(C4H6) and 6. These
data indicate that the introduction of the phenyl substituents
leads to a lengthening of the Zr-C(terminal) bonds and a
concomitant shortening of the corresponding Zr-C(internal)
bonds, ultimately leading to a nearly 0.10 Å reduction in
∆Zr-C. The subsequent decrease in the dihedral angle, R,
from 110 to 100° is also accompanied by a more pronounced
long-short-long C-C bond sequence.
dihedral angle, R 104.9
a Cp(c) corresponds to the centroid of the cyclopentadienyl ring. b C1
and C4 are the two terminal carbons and C2 and C3 represent the two internal
carbons of the 1,4-diphenylbutadiene ligand. c Cb corresponds to the
bridgehead carbon.
butadiene), where R ) i-Pr, t-Bu, also exhibit the supine
conformation. The respective values of R and ∆Zr-C of
108.7°, -0.249 Å and of 116.5°, -0.377 Å are also
consistent with an appreciable η4-diene interaction in these
two complexes. However, the shorter average Zr-C(termi-
nal) distances of 2.285(3) and 2.263(6) Å, respectively,
Stephan and co-workers21 recently reported that the related
cis-diene complexes, (C5Me5)Zr(NPR3)(η4-2,3-dimethyl-
Inorganic Chemistry, Vol. 43, No. 13, 2004 3983

Braun et al.
Table 5. Structural Parameters for [(C5Me4)SiMe2(N-i-Pr)]Zr(C4H4R2);
R ) H, Ph
Experimental Section
Reagents. The hydrocarbon and ethereal solvents were purified
by standard methods.32 Toluene and pentane were refluxed over
Na/K under a nitrogen flush and transferred to separate storage
flasks containing [(C5H5)2Ti(µ-Cl)2]2Zn33 or Na/K benzophenone
ketyl. Hexamethyldisiloxane and diethyl ether were dried over
LiAlH4. The deuterated solvents C6D6 (Cambridge Isotopes, 99.5%)
and CDCl3 (Aldrich, 99.8%) were dried over activated 4A molecular
sieves.
[(C5Me4)SiMe2(N-i-Pr)]Zr(C4H6)
6
Zr-C(terminal) (Å)
Zr-C(internal) (Å)
∆Zr-Ca (Å)
C-C (outer) (Å)
C-C (inner) (Å)
∆C-Cb (Å)
Zr-Cp(c) (Å)
Zr-N (Å)
dihedral angle, R (°)
2.278(6)
2.463(5)
-0.185
1.413(7)
1.386(8)
0.027
2.163
2.117(6)
110.0
2.330 (av)
2.419 (av)
-0.089
1.445 (av)
1.374(5)
0.071
2.170
2.074(3)
100.0
Starting materials such as ZrCl4 (Alfa), LiNMe2 (Aldrich, 95%),
n-BuLi (Aldrich, 1.6 M in hexane), indene (Aldrich), trans-1,4-
diphenylbutadiene (Aldrich), and 2,3-dimethyl-1,3-butadiene (Al-
drich) were used without further purification. SiMe2Cl2 (Acros),
SiMe3Cl (Acros), NH2-t-Bu (Acros), and NH2-i-Pr (Acros) were
vacuum distilled prior to use and stored over 4A molecular sieves.
[(C5H4)SiMe2(N-t-Bu)]Zr(NMe2)2,10 [(C5Me4)SiMe2(N-t-Bu)]ZrCl2,10
(C9H7)SiMe2(N(H)-t-Bu),9 (C5Me4H)SiMe2(N(H)-i-Pr),34 and Zr-
a ∆Zr-C corresponds to the difference between the Zr-C(terminal) and
Zr-C(internal) bond distances. b ∆C-C corresponds to the difference
between the C-C (outer) and C-C (inner) bond distances.
reflect a greater contribution from the σ2,π-diene representa-
tion than observed in compounds 4-7.
35
(NMe2)4 were prepared using literature procedures.
The bifunctional monocyclopentadienylamido ligands in
4, 6, and 7 are symmetrically disposed to afford structures
with Cs symmetry, consistent with the NMR spectral data
for these three compounds. The plane of symmetry passes
through the bridgehead C, Si, N, and Zr atoms and the
midpoint of the central C-C bond of the cis-diene ligand.
Within each pair of shorter Zr-C(terminal) and longer Zr-
C(internal) bonds, the bond distances are essentially equal.
In contrast, the introduction of the unsymmetrical indenyl
functionality in 5 leads to a significant lateral displacement
of the SiMe2 bridge. As a result, the plane passing through
the bridgehead C, Si, and N atoms of 5 does not bisect the
C(16)-Zr-C(19) bond angle. The perpendicular displace-
ment of the Si atom from lying in the plane passing through
the Zr and the midpoints of the central C(17)-C(18) bond
and the C(16)‚‚‚C(19) line segment of 5 is 1.207 Å. An
analogous distortion is observed in the molecular structure
of the Ti analogue, [(C9H6)SiMe2(N-t-Bu)]Ti(C4H4Ph2), in
which the η4-π diene ligand adopts the alternative prone
conformation.31 The asymmetric coordination environment
about the Zr atom of 5 is further reflected by a 0.04 Å
difference in the two independent Zr-C(terminal) bond
distances. The absence of mirror symmetry is consistent with
the observation of four distinct proton and carbon resonances
for the four chemically inequivalent H and C atoms of the
central diene unit of 5.
Instrumentation. The 1H NMR spectra of the zirconium
dichloride compounds 1, 2, and 3 were measured with a JEOL
Eclipse 270 MHz NMR spectrometer, whereas the 1H NMR spectra
of the zirconium 1,4-diphenylbutadiene compounds 4, 5, 6, and 7
were measured with a Varian 600 Inova NMR spectrometer. All
of the 13C NMR spectra were measured with a JEOL Eclipse 270
NMR spectrometer, operating in the FT mode at 67.5 MHz. The
1H chemical shifts are referenced to the residual proton peaks of
benzene-d6 at δ 7.15 (vs TMS) or chloroform-d1 at δ 7.24 (vs TMS),
whereas the central peak of the triplet for benzene-d6 at δ 128.0
(vs TMS) and the central peak of the triplet for chloroform-d1 at δ
77.0 (vs TMS) were used as internal 13C NMR references. Computer
1
simulations of H NMR splitting patterns were performed with
SpinWorks, version 2.1.22
General Procedures. All syntheses were carried out on a double-
manifold, high-vacuum line or in a Vacuum Atmospheres glovebox
equipped with an HE-493 Dri-Train. Reactions were typically
carried out in pressure-equalizing filter frits equipped with high-
vacuum Teflon stopcocks and Solv-seal joints. Nitrogen was
purified by passage over reduced BTS catalyst and activated 4A
molecular sieves. All glassware was thoroughly oven dried and
flame dried under vacuum prior to use. NMR sample tubes were
sealed under approximately 500 Torr of nitrogen. Elemental
analyses were performed by Complete Analysis Laboratories Inc.,
E+R Microanalytical Division, Parsippany, NJ 07054.
Preparation of [(C5H4)SiMe2(N-t-Bu)]ZrCl2, 1. A 4.30 g
sample (11.5 mmol) of freshly sublimed [(C5H4)SiMe2(N-t-Bu)]-
Zr(NMe2)2 was placed in a 100 mL Solv-seal flask. Toluene (25
mL) and 4.0 mL (31.5 mmol, 37% excess) of SiMe3Cl were added
by vacuum transfer. The stirred solution was heated at 65 °C
overnight. After removal of the toluene and the excess of SiMe3-
Cl, washing of the crude product with pentane left 1 as a white
finely divided solid. Yield: 3.70 g (91%). Suitable crystals for
structural analysis were grown by cooling a saturated toluene
The structural analyses of 4-7 have shown that the cis-
1,4-diphenylbutadiene ligand prefers the supine over the
prone orientation. The level of the η4-π bonding contribution
is enhanced by replacement of the t-Bu substituent on the
amido N atom with the sterically less demanding i-Pr group
and is reflected by decreases in the dihedral angle, R, and
∆Zr-C. The asymmetry introduced by the indenyl ligand
leads to a lateral displacement of the SiMe2 linker and a
detectable variation in the two terminal Zr-C bond distances.
1
3
solution. H NMR (CDCl3): δ 6.91, 6.44 (t, 2H, C5H4, JH-H
)
2.2 Hz), 1.38 (s, 9H, NCMe3), 0.54 (s, 6H, SiMe2). Gated non-
decoupled 13C NMR (CDCl3): δ 122.1, 121.2 (C5H4, d, J ) 175
Hz), 109.8 (bridgehead, s), 57.7 (NCMe3, s), 32.6 (NCMe3, q, J )
(31) The bond distances for the pair of terminal and internal Ti-C distances
are 2.204(4); 2.244(4) Å and 2.311(4); 2.320(4) Å, respectively, with
∆Ti-C being -0.09 Å. The dihedral angle, R, is 106.1°. The 1H NMR
spectrum features two multiplets centered at δ 5.01; 4.01 for the meso
protons and two pseudo doublets of doublets centered at δ 3.56; 3.32
for the anti protons of the cis-1,4-diphenylbutadiene ligand. Morgan,
J. B.; Petersen, J. L, unpublished results.
(32) Gordon, A. J.; Ford, R. A. The Chemist’s Companion; Wiley-
Interscience: New York, 1972; pp 431-436.
(33) Sekutowski, D. G.; Stucky, G. D. Inorg. Chem. 1975, 14, 2192-2199.
(34) A procedure analogous to that described previously for (C5Me4H)-
SiMe2(N(H)-t-Bu)10 was used to prepare (C5Me4H)SiMe2(N(H)-i-Pr).
(35) Diamond, G. M.; Rodewald, S.; Jordan, R. F. Organometallics 1995,
14, 5-7.
3984 Inorganic Chemistry, Vol. 43, No. 13, 2004

Influence of ansa-Cyclopentadienylamido Ligands on Metallocenes
125 Hz), 0.90 (SiMe2, q, J ) 120 Hz). Anal. Calcd for C11H19Cl2-
NSiZr: C, 37.17; H, 5.39; N, 3.94. Found: C, 37.27; H, 5.67; N,
4.10.
Preparation of [Mg(C4H4Ph2)(THF)3]n.36 A 3.05 g sample of
activated Mg and 2.50 g of trans-1,4-diphenylbutadiene were added
to a 100-mL round-bottom Solv-seal flask. Following evacuation
of the filter frit assembly, THF (60 mL, dried over Na/K benzo-
phenone ketyl) was added via vacuum distillation. The flask
containing the reaction mixture was placed in a thermostatically
controlled water bath to maintain the temperature at 15 °C. The
reaction mixture was stirred continuously for 5 days. The filter frit
assembly was placed on the vacuum line, and the red solution was
filtered, leaving an orange solid and Mg chips. THF was removed
into a liquid nitrogen-cooled trap. The THF was redistilled back to
extract the remaining product. After the THF was removed under
vacuum, the orange pyrophoric product was washed several times
with pentane. Yield: 4.70 g (89%)
Preparation of [(C5H4)SiMe2(N-t-Bu)]Zr(C4H4Ph2), 4. A 0.50
g (1.41 mmol) sample of [(C5H4)SiMe2(N-t-Bu)]ZrCl2 and 0.64 g
(1.48 mmol, 5% excess) of [Mg(C4H4Ph2)(THF)3]n were combined
in a 100 mL Solv-seal flask that was then attached to a swivel frit
assembly. Toluene (30 mL) was added via vacuum distillation. After
the reaction mixture was stirred for 3 h at room temperature, the
solution was filtered. The solvent was removed slowly into a liquid
nitrogen-cooled trap, leaving dark red crystals. The product was
recrystallized from toluene. Yield: 0.55 g (80%). Anal. Calcd for
Preparation of [(C9H6)SiMe2(N-t-Bu)]ZrCl2, 2. A 1.89 g
sample (7.00 mmol) of Zr(NMe2)4 was combined with 1.73 g (7.00
mmol) of (C9H7)SiMe2(N(H)-t-Bu) in a 100 mL Solv-seal flask.
The neat reaction mixture was heated to 120 °C and stirred for 2
days. A modest purge of N2 and periodic evacuation of the reaction
mixture removed the volatile NMe2H. The reaction proceeded with
formation of 3.0 g of [(C9H6)SiMe2(N-t-Bu)]Zr(NMe2)2 as a dark
orange oil.9 The entire product was dissolved in 20 mL of toluene.
SiMe3Cl (2.7 mL, 50% excess) was added by vacuum transfer, and
the reaction was stirred for 24 h at 65 °C. The resulting product
was washed twice with pentane and then purified by sublimation
at 55 °C and 10-4 Torr. Yield: 2.34 g (83%). Slow removal of
CH2Cl2 from a saturated solution provided crystals suitable for
X-ray crystallographic analysis. 1H NMR (CDCl3): δ 7.75 (d, 2H,
3
3JH-H ) 8.5, aromat CH), 7.36, 7.26 (t, 1H, JH-H ) 6.5, 8.5,
3
aromat CH), 7.09, 6.62 (d, 1H, JH-H ) 3.1, olefin. CH), 1.33 (s,
9H, NCMe3), 0.88, 0.62 (s, 3H, SiMe2). Gated non-decoupled 13
C
NMR (CDCl3): δ 132.9, 132.8 (s, aromat), 127.7, 127.5, 126.4,
125.6 (d, CH, aromat, J ) 161 Hz), 126.4, 111.1 (d, CH, olefin.,
J ) 175, 169 Hz), 94.0 (s, bridgehead), 57.1 (s, CMe3), 32.7 (q,
CMe3, J ) 125 Hz), 3.92, 1.78 (q, SiMe2, J ) 119 Hz). Anal.
Calcd for C15H21Cl2NSiZr: C, 44.43; H, 5.22; N, 3.45. Found: C,
44.37; H, 5.29; N, 3.54.
C
30.5H37SiZrN (536.92): C, 68.23; H, 6.95; N, 2.60. Found: C,
1
68.01; H, 6.75; N, 2.65. Major isomer, H NMR (599.67 MHz,
C6D6): δ 7.23 (mult., 4Hm, meta Ph), 7.05 (mult., 4Ho, ortho Ph),
6.92 (tt, 2Hp, para Ph), 6.28 (mult., 2Hmeso, meso butadiene), 5.95
(t, 2H, C5H4,3JH-H ) 2.3), 5.74 (t, 2H, C5H4, JH-H ) 2.3), 1.97
Preparation of [(C5Me4)SiMe2(N-i-Pr)]ZrCl2, 3. A 1.00 g
sample of freshly sublimed Zr(NMe2)4 was combined with 0.90 g
of (C5Me4H)SiMe2(N(H)-i-Pr) in a 100 mL Solv-seal flask. The
neat reaction mixture was heated to 100 °C while under a modest
N2 flush and within an hour a light yellow crystalline product
formed. The NMR data indicated that this amine elimination
reaction was essentially quantitative. Crude isolated yield: 1.45 g,
93.5%. 1H NMR (C6D6): δ 3.81 (septet, 1H, 3JH-H ) 7.1, CHMe2),
2.88 (s, 12H, NMe2), 2.15, 1.90 (s, 6H, C5Me4), 1.19 (d, 6H, 3JH-H
) 7.1, CHMe2), 0.59 (s, 6H, SiMe2). Gated non-decoupled 13C
NMR (C6D6): δ 127.6, 124.0 (s, C5Me4), 101.1 (s, bridgehead C
of C5Me4), 50.7 (d, CHMe2, J ) 132 Hz), 44.1 (q, NMe2, J ) 131
Hz), 28.7 (q, CHMe2, J ) 126 Hz), 13.9, 11.0 (q, C5Me4, J ) 126
Hz), 6.1 (q, SiMe2, J ) 118 Hz).
3
(mult., 2Hanti, anti butadiene), 0.98 (s, 9H, CMe3), 0.20 (s, 6H,
SiMe2). Proton coupling constants (Hz) determined by computer
simulation of the phenyl protons: Jm-m′ ) 1.05(6), Jm-p ) 7.30-
(5), Jm-o ) 7.13(8), Jo-m′ ) 1.21(1), Jp-o ) 1.15(5), Jo-o′ ) 0.32-
(6). Proton coupling constants (Hz) determined by computer
simulation of the butadiene protons: Jmeso-meso′ ) 9.94(6), Jmeso-anti′
) -2.12(8), Janti-anti′ ) 0.22(5), Janti-meso ) 11.18(1). Gated non-
decoupled 13C NMR (67.5 MHz, C6D6): δ 143.1 (s, ipso Ph), 129.3
(d, meta Ph, J ) 153), 122.5 (d, para Ph, J ) 154), 121.6 (d, ortho
Ph, J ) 153), 120.1 (d, meso butadiene, J ) 158), 116.8 (d, C5H4,
J ) 162), 116.3 (d, C5H4, J ) 170), 110.8 (s, bridgehead), 75.0 (d,
anti butadiene, J ) 138), 59.4 (s, CMe3), 36.1 (q, CMe3, J ) 123),
2.2 (q, SiMe2, J ) 118). 2D HETCOR (C6D6): δ 129.3/7.23 (meta
Ph), 122.5/6.92 (para Ph), 121.6/7.05 (ortho Ph), 120.1/6.28 (meso
butadiene), 116.8/5.95 (C5H4), 116.3/5.74 (C5H4), 75.0/1.97 (anti
butadiene), 36.1/0.98 (CMe3), 2.2/0.20 (SiMe2). Minor isomer, 1H
NMR (599.67 MHz, C6D6): δ 7.3-6.9 (Ph), 5.86 (t, 2H, C5H4,3JH-H
) 2.5), 5.47 (t, 2H, C5H4, 3JH-H ) 2.5), 5.12 (mult., 2Hmeso, meso
butadiene), 2.70 (mult., 2Hanti, anti butadiene), 1.10 (s, 9H, CMe3),
0.31 (s, 6H, SiMe2). Proton coupling constants (Hz) determined
The 1.45 g sample of [(C5Me4)SiMe2(N-i-Pr)]Zr(NMe2)2 was
used without further purification and transferred to a 100 mL Solv-
seal flask. Toluene (25 mL) and 1.14 g of SiMe3Cl (50% excess)
were added via vacuum transfer. After the reaction mixture was
stirred for 2 days at ambient temperature, the volatiles were removed
and the product residue was washed with a small amount of pentane.
Yield: 1.25 g (90%). The cooling of a saturated toluene solution
1
by computer simulation for the butadiene protons: Jmeso-meso′
11.44(7), Jmeso-anti′ ) -1.76(10), Janti-anti′ ) 0.29(6), Janti-meso
12.59(1).
)
)
afforded crystals suitable for X-ray crystallographic analysis. H
3
NMR (C6D6): δ 4.03 (sept., CHMe2, JH-H ) 6.4), 2.05, 1.94 (s,
3
C5Me4), 1.19 (d, CHMe2, JH-H ) 6.4), 0.39 (s, SiMe2). 13C{1H}
Preparation of [(C9H6)SiMe2(N-t-Bu)]Zr(C4H4Ph2), 5. A 0.50
g (1.23 mmol) sample of [(C9H6)SiMe2(N-t-Bu)]ZrCl2 and 0.56 g
(1.29 mmol, 5% excess) of [Mg(C4H4Ph2)(THF)3]n were added to
a 100 mL Solv-seal flask. The reaction mixture was stirred in 30
mL of toluene for 3 h at room temperature and then filtered through
a filter frit. While the solvent was removed slowly, crystals formed
on the wall of the flask. Larger dark red crystals were obtained by
recrystallization with pentane. Yield: 0.43 g (64%). Anal. Calcd
for C34.5H39SiZrN (586.98): C, 70.59; H, 6.70; N, 2.39. Found:
C, 70.31; H, 6.85; N, 2.28.
NMR (C6D6): δ 134.5, 130.4 (C5Me4), 101.8 (bridgehead C of
C5Me4), 50.7 (CHMe2), 26.1 (CHMe2), 14.9, 11.8 (C5Me4), 4.8
(SiMe2). Anal. Calcd for C14H25Cl2NSiZr: C, 42.30; H, 6.34; N,
3.52. Found: C, 42.35; H, 6.52; N, 3.30.
Preparation of Activated Mg. A 100 mL Solv-seal flask was
charged with 6.00 g (0.25 mol) of Mg chips and 0.30 g of iodine.
THF (60 mL, dried over Na/K benzophenone ketyl) was added to
the reaction flask via vacuum transfer. Approximately 1.0 mL of
2,3-dimethyl-1,3-butadiene was condensed into the reaction flask.
The reaction mixture was heated to 65 °C and stirred for 1.5 days.
The yellowish-green solution was filtered, leaving gray Mg chips,
which were washed with THF (2 × 10 mL).
(36) Yasuda, H.; Kajihara, Y.; Mashima, K.; Nagasuna, K.; Lee, K.;
Nakamura, A. Organometallics 1982, 1, 388-396.
Inorganic Chemistry, Vol. 43, No. 13, 2004 3985

Braun et al.
167), obscured, 124.4 (proximal and distal C5Me4), 101.4 (s,
bridgehead), 75.4 (d, anti butadiene, J ) 137), 53.5 (d, CHMe2, J
) 125), 28.8 (q, CHMe2, J ) 125), 12.8, 10.7 (q, C5Me4, J )
125), 6.8 (q, SiMe2, J ) 119). 2D HETCOR (C6D6): δ 128.6/7.22
(meta Ph), 124.1/6.22 (meso butadiene), 122.4/6.94 (para Ph), 123.6/
6.89 (ortho Ph), 75.4/1.70 (anti butadiene), 53.5/4.14 (CHMe2),
28.8/0.96 (CHMe2), 12.8, 10.7/1.67 (C5Me4), 6.8/0.41 (SiMe2).
Preparation of [(C5Me4)SiMe2(N-t-Bu)]Zr(C4H4Ph2), 7. A 100
mL Solv-seal flask was charged with 0.50 g (1.22 mmol) of [(C5-
Me4)SiMe2(N-t-Bu)]ZrCl2 and 0.56 g (1.28 mmol, 5% excess) of
[Mg(C4H4Ph2)(THF)3]n. Following the addition of 30 mL of toluene,
the reaction mixture was stirred for 3 h at room temperature. The
resulting reaction mixture was filtered, and the solvent was removed
slowly into a liquid nitrogen-cooled trap. The dark reddish-brown
product contained a mixture of two isomers. After the solid was
washed with pentane, the major isomer was recrystallized from
1
Major isomer, H NMR (599.67 MHz, C6D6): δ 7.28 (mult.,
2Hm, Ph1), 7.06 (mult., 2Ho, Ph1), 6.93 (tt, Hp, Ph1), 7.16 (mult.,
2Hm, Ph2), 6.98 (tt, Hp, Ph2), 6.56 (mult., 2Ho, Ph2), 7.57, 7.09,
6.84, 6.51, 6.32, 5.71 (dq, dt, ddd, ddd, d, dd; H3, H6, H4, H5, H1,
H2; J1,2 ) 3.3, J2,3 ) 0.9, J3,4 ) 8.4, J3,5 ) 1.2, J3,6 ) 1.0, J4,5
)
6.6, J4,6 ) 1.2, J5,6 ) 8.5 Hz), 6.15, 6.11 (mult., 2H, meso
butadiene), 1.72, 1.25 (mult., 2H, anti butadiene), 0.92 (s, 9H,
CMe3), 0.65, 0.20 (s, 6H, SiMe2); proton coupling constants (Hz)
determined by computer simulation for Ph1: Jm-m′ ) 0.93(8), Jm-p
) 7.31(6), Jm-o ) 7.21(9), Jo-m′ ) 0.96(1), Jp-o ) 1.28(6), Jo-o′
) 0.34(8). Proton coupling constants (Hz) determined by computer
simulation for Ph2: Jm-m′ ) 0.9(1), Jm-p ) 7.1(1), Jm-o ) 7.0(2),
Jo-m′ ) 0.86(2), Jp-o ) 1.3(1), Jo-o′ ) 0.3(1). Proton coupling
constants (Hz) determined by computer simulation of the butadiene
protons: Jmeso1-meso2 ) 10.70(7), Jmeso1-anti1 ) 11.84(7), Jmeso2-anti1
) 1.17(7), Jmeso1-anti2 ) 1.34(7), Jmeso2-anti2 ) 12.03(7), Janti1-anti2
) 0.16(7). 13C{1H} NMR (67.5 MHz, C6D6): δ 143.9, 142.5 (ipso-
Ph), 133.2, 129.6 (quat. C, indenyl), 125.1, 124.6, 124.5, 124.2,
121.7, 107.0 (C6, C3, C5, C4, C1, C2), 128.8, 123.2, 122.9 (2Cm,
2Co, Cp of Ph1), 127.4, 125.3, 122.7 (2Cm, 2Co, Cp of Ph2), 122.6,
117.5 (meso butadiene), 96.5 (bridgehead C, indenyl), 79.6, 77.1
(anti butadiene), 59.1 (CMe3), 35.8 (CMe3), 6.3, 2.2 (SiMe2). 2D
HETCOR (C6D6): δ 125.1/7.09, 124.6/7.57, 124.5/6.84, 124.2/6.51,
121.7/6.32, 107.0/5.71 (CH, indenyl), 128.8/7.28, 123.2/7.06, 122.9/
6.93 (CH, Ph1), 127.4/7.16, 125.3/6.56, 122.7/6.98 (CH, Ph2), 122.6/
6.11, 117.5/6.15 (CH, meso butadiene), 79.6/1.72, 77.1/1.25 (CH,
anti butadiene), 35.8/0.92 (CMe3), 6.3/0.65, 2.2/0.20 (SiMe2). Minor
isomer, 1H NMR (599.67 MHz, C6D6): δ 7.5-6.4 (mult., 16H, Ph
and indenyl rings), 5.31, 4.42 (mult., 2H, meso butadiene), 2.58,
2.43 (mult., 2H, anti butadiene), 1.10 (s, 9H, CMe3), 0.69, 0.40 (s,
6H, SiMe2). Proton coupling constants (Hz) determined by computer
simulation of the butadiene protons: Jmeso1-meso2 ) 11.5(2),
Jmeso1-anti1 ) 12.3(2), Jmeso2-anti1 ) 1.3(2), Jmeso1-anti2 ) 1.6(2),
Jmeso2-anti2 ) 12.5(2), Janti1-anti2 ) 0.2(2).
1
toluene. Yield: 0.63 g (94%). Major isomer, H NMR (599.67
MHz, C6D6): δ 7.22 (mult., 4Hm, meta Ph), 7.00 (mult., 4Ho, ortho
Ph), 6.96 (tt, 2Hp, para Ph), 6.38 (mult., meso butadiene), 1.78 (s,
6H, C5Me4), 1.64 (s, 6H, C5Me4), 1.37 (mult., anti butadiene), 1.14
(s, 9H, CMe3), 0.48 (s, 6H, SiMe2). Proton coupling constants (Hz)
determined by computer simulation of the phenyl protons: Jm-m′
) 1.13(15), Jm-p ) 7.01(11), Jm-o ) 6.50(18), Jo-m′ ) 1.21(3),
Jp-o ) 1.17(11), Jo-o′ ) 0.29(11). Proton coupling constants (Hz)
determined by computer simulation of the butadiene protons:
Jmeso-meso′ ) 10.55(7), Jmeso-anti′ ) -2.2(1), Janti-anti′ ) 0.43(6),
Janti-meso ) 11.28(1). 13C{1H} NMR (67.5 MHz, C6D6): δ 145.4
(ipso Ph), 128.4 (meta Ph), 124.8 (ortho Ph), 124.0 (meso
butadiene), 122.8 (para Ph), 125.6, 125.3 (proximal and distal C5-
Me4), 103.3 (bridgehead C5Me4), 76.3 (anti butadiene), 55.8
(CMe3), 36.5 (CMe3), 13.1, 11.2 (C5Me4), 7.8 (SiMe2). 2D
HETCOR (C6D6): δ 128.4/7.22 (meta Ph), 124.8/7.00 (ortho Ph),
122.8/6.96 (para Ph), 124.0/6.38 (meso butadiene), 76.3/1.37 (anti
butadiene), 36.5/1.14 (CMe3), 13.1/1.78 (C5Me4), 11.2/1.64 (C5Me4),
7.8/0.48 (SiMe2). Minor isomer, 1H NMR (599.67 MHz, C6D6): δ
7.3-7.1 (mult., 10H, Ph), 5.01 (mult., meso butadiene), 2.83 (mult.,
anti butadiene), 1.75 (s, 6H, C5Me4), 1.37 (s, 6H, C5Me4), 1.21 (s,
9H, CMe3), 0.56 (s, 6H, SiMe2). Proton coupling constants (Hz)
determined by computer simulation of the butadiene protons:
Jmeso-meso′ ) 11.41(9), Jmeso-anti′ ) -1.5(1), Janti-anti′ ) 0.24(7),
Janti-meso ) 13.05(3). 13C{1H} NMR (67.5 MHz, C6D6): δ 144.2
(ipso Ph), 128.7, 126.8, 124.0 (Ph), 129.8, 124.3 (proximal and
distal C5Me4), 105.1 (meso butadiene), 99.2 (bridgehead), 77.7 (anti
butadiene), 55.6 (CMe3), 36.3 (CMe3), 13.2, 11.0 (C5Me4), 7.9
(SiMe2). 2D HETCOR (C6D6): δ 128.7/7.14, 126.8/7.30, 124.0/
7.25 (Ph); 105.1/5.01 (meso butadiene), 77.7/2.83 (anti butadiene),
36.3/1.21 (CMe3), 13.2/1.75 (C5Me4), 11.0/1.37 (C5Me4), 7.9/0.56
(SiMe2).
Description of the X-ray Structural Analyses. The crystals for
1-3 were sealed in glass capillary tubes under a nitrogen
atmosphere. The data collections for {[(C5H4)SiMe2(N-t-Bu)]ZrCl-
(µ-Cl)}2 and [(C9H6)SiMe2(N-t-Bu)]ZrCl2 were performed at ambi-
ent temperature, whereas that of {[(C5Me4)SiMe2(N-i-Pr)]ZrCl(µ-
Cl)}2 was carried out while cooling the sample at -80 °C, with a
stream of nitrogen gas provided by an LT-2 low-temperature
attachment. The reflections that were used for the unit-cell
determination were located and indexed by the automatic peak
search routine provided with XSCANS.37 The lattice parameters
and orientation matrix for the unit cells were calculated from a
nonlinear least-squares fit of the orientation angles of at least 35
reflections. The X-ray diffraction data for [(C9H6)SiMe2(N-t-Bu)]-
Preparation of [(C5Me4)SiMe2(N-i-Pr)]Zr(C4H4Ph2), 6. A 20
mL cylindrical Solv-seal tube was charged with 0.10 g (0.25 mmol)
of [(C5Me4)SiMe2(N-i-Pr)]ZrCl2 and 0.12 g (0.26 mmol, 5% excess)
of [Mg(C4H4Ph2)(THF)3]n. The reaction mixture was stirred in 15
mL of toluene for 1 h at 0 °C before being warmed to room
temperature and then stirred for an additional hour. The reaction
mixture was filtered, and the solvent was removed slowly under
reduced pressure, leaving the product as dark red crystals. Yield:
0.12 g (88%) Anal. Calcd for C30H39SiZrN (532.93): C, 67.61; H,
7.38; N, 2.63. Found: C, 67.47; H, 7.47; N, 2.56. 1H NMR (599.67
MHz, C6D6): δ 7.22 (mult., 4Hm, meta Ph), 6.94 (tt, 2Hp, para
Ph), 6.89 (mult., 2Ho, ortho Ph), 6.22 (mult., 2H, meso butadiene),
4.14 (sept., 1H, CHMe2,3JH-H ) 6.4), 1.70 (mult., 2H, anti
butadiene), 1.67 (s, 12H, C5Me4), 0.96 (d, 6H, CHMe2,3JH-H
)
6.4), 0.41 (s, 6H, SiMe2). Proton coupling constants (Hz) determined
by computer simulation of the phenyl protons: Jm-m′ ) 1.04(7),
Jm-p ) 7.24(5), Jm-o ) 7.00(8), Jo-m′ ) 1.19(1), Jp-o ) 1.17(5),
Jo-o′ ) 0.31(7). Proton coupling constants (Hz) determined by
computer simulation of the butadiene protons: Jmeso-meso′ ) 10.77-
(5), Jmeso-anti′ ) -2.26(7), Janti-anti′ ) 0.60(4), Janti-meso ) 10.96-
(1). Gated non-decoupled 13C NMR (67.5 MHz, C6D6): δ 145.0
(s, ipso Ph), 128.6 (d, meta Ph, J ) 154), 124.1 (d, meso butadiene,
J ) 154), 123.6 (d, ortho Ph, J ) 152), 122.4 (d, para Ph, J )
(37) XSCANS (version 2.0) is a diffractometer control system developed
by Bruker AXS, Inc., Madison, WI.
3986 Inorganic Chemistry, Vol. 43, No. 13, 2004

Influence of ansa-Cyclopentadienylamido Ligands on Metallocenes
ZrCl2 were initially collected using an I-centered monoclinic unit
cell and later transformed to the conventional C-centered monoclinic
cell.
methyls of the tert-butyl substituent bound to the amido N in [(C5-
Me4)SiMe2(N-t-Bu)]Zr(C4H4Ph2) suffered from a two-site 75:25
disorder. Idealized positions for the hydrogen atoms were included
as fixed contributions using a riding model, and the positions of
the methyl hydrogen atoms were optimized by a rigid rotating group
Intensity data were measured with graphite-monochromated Mo
KR radiation (λ ) 0.71073 Å) and variable ω scans. Background
counts were measured at the beginning and at the end of each scan
with the crystal and counter kept stationary. The combined
intensities of three standard reflections, which were measured after
every 100 reflections, did not show any indication of crystal
movement or decay. The raw data were corrected for Lorentz-
polarization effects. An empirical absorption correction based on
the measurement of six PSI scans was applied to the data collected
for {[(C5H4)SiMe2(N-t-Bu)]ZrCl(µ-Cl)}2.
refinement with idealized tetrahedral angles. Full-matrix least-
2
squares refinement based upon the minimization of ∑wi| Fo
-
Fc2 | , with weighting given by the expression wi-1 ) [σ2(Fo ) +
2
2
(aP)2 + bP], where P ) (Max(Fo ,0) + 2Fc2)/3, converged to give
2
the values of the final discrepancy indices40 provided in Table 2.
Selected interatomic distances and bond angles are summarized in
Tables 3 and 4 for the Zr dichloride complexes 1-3 and the Zr
1,4-diphenylbutadiene derivatives 4-7, respectively.
The crystals of 4-7 were coated with the perfluoropolyether
PFO-XR75 (Lancaster) and then sealed under nitrogen in glass
capillary tubes. Each sample was optically aligned on the four-
circle of a Siemens P4 diffractometer equipped with a graphite
monochromatic crystal, a Mo KR radiation source (λ ) 0.71073
Å), and a SMART CCD detector held at 5.054 cm from the crystal.
The samples were cooled to -50 °C. Four sets of 20 frames each
were collected using the ω scan method, with a 10 s exposure time.
Integration of these frames followed by reflection indexing and
least-squares refinement produced a crystal orientation matrix and
preliminary lattice parameters.
Data collection involved the measurement of a total of 1650
frames of 30 s duration in five different runs covering a hemisphere.
The program SMART (version 5.6)38 was used for diffractometer
control, frame scans, indexing, orientation matrix calculations, least-
squares refinement of cell parameters, and data collection. All of
the raw data frames were read by the program SAINT (version
5/6.0)38 and integrated using 3D profiling algorithms. An absorption
correction was applied using the SADABS routine available in
SAINT. The data were corrected for Lorentz and polarization
effects, as well as any crystal decay.
Initial coordinates for all of the non-hydrogen atoms were
determined by a combination of direct methods and difference
Fourier methods with the use of SHELXL-93 or SHELXTL 6.1.39
The molecular structures of {[(C5H4)SiMe2(N-t-Bu)]ZrCl(µ-Cl)}2
and {[(C5Me4)SiMe2(N-i-Pr)]ZrCl(µ-Cl)}2 are constrained in the
solid state by a crystallographic center of inversion. The structural
analyses of [(C5Me4)SiMe2(N-t-Bu)]Zr(C4H4Ph2) and [(C5H4)SiMe2-
(N-t-Bu)]Zr(C4H4Ph2) revealed the presence of toluene, which was
disordered about a crystallographic center of inversion. The three
Acknowledgment. Financial support for this research was
provided by the donors of the Petroleum Research Fund,
administered by the American Chemical Society. J.L.P.
gratefully acknowledges the financial support provided by
the Eberly College of Arts and Sciences and the C. Eugene
Bennett Department of Chemistry and the unrestricted
research funds provided by Union Carbide Corp. and The
Dow Chemical Co. to acquire a SMART CCD detector for
the Siemens P4 X-ray diffractometer at West Virginia
University. Funds for the recent acquisition of a Varian 600
Inova NMR spectrometer at West Virginia University were
provided through the NSF-EPsCOR program.
Note Added after ASAP: The version of this paper
posted ASAP May 27, 2004, was missing the Results and
Discussion section heading. The corrected version appeared
June 7, 2004.
Supporting Information Available: Complete tables of the
results from the X-ray crystallographic analyses performed on
compounds 1-7. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC040001I
(39) SHELXTL-93 and SHELXTL 6.1 are crystallographic software
packages developed by Professor G. Sheldrick, Institut fur Anorga-
nische Chemie, University of Go¨ttingen, D-37077 Go¨ttingen, Germany,
for Bruker AXS, Inc., Madison, WI.
(40) The equations for the R-factors are R1 ) ∑(|Fo | - | Fc|)/∑| Fo | and
2
2
2
wR2 ) [∑[w(Fo - Fc )2]/∑[wFo ]]1/2. The expression for the
“goodness-of-fit” is GOF ) [∑[w(Fo2 - Fc )2]/(n - p)]1/2, where n is
the number of reflections and p is the total number of parameters that
2
(38) The SMART 5.6 and SAINT 5/6.0 programs are part of the Bruker
AXS crystallographic software package used for single-crystal data
collection, reduction, and preparation.
were varied during the last refinement cycle.
Inorganic Chemistry, Vol. 43, No. 13, 2004 3987