Synthesis and formal ring-opening reactions of (η5-C 5Me5)Zr[η2-CH2CH(C 6H5)][N(iPr)C(Me)N(iPr)], a base-free η2-styrene complex of zirconium

Article abstract of DOI:10.1021/om0508785

Synthesis of a base-free η²-styrene complex of zirconium has been achieved and its molecular structure analyzed by X-ray crystallography. This compound undergoes protonolysis and σ-bond metathesis of a formal zirconacyclopropane ring with a variety of reagents. With phenylacetylene, ring opening occurs on the more substituted side, while Me₃MCl (M = Si, Sn) effect ring opening on the least substituted side. Hydrogenolysis further proceeds rapidly to provide a zirconanorbornadiene derivative in high yield under conditions where a structurally related dimethyl complex remains inert.

Full text of DOI:10.1021/om0508785

Organometallics 2006, 25, 531-535
531
Synthesis and Formal Ring-Opening Reactions of
(η5-C5Me5)Zr[η2-CH2CH(C6H5)][N(iPr)C(Me)N(iPr)], a Base-Free
η2-Styrene Complex of Zirconium
Denis Kissounko, Albert Epshteyn, James C. Fettinger, and Lawrence R. Sita*
Department of Chemistry and Biochemistry, UniVersity of Maryland, College Park, Maryland 20742
ReceiVed October 11, 2005
Synthesis of a base-free η2-styrene complex of zirconium has been achieved and its molecular structure
analyzed by X-ray crystallography. This compound undergoes protonolysis and σ-bond metathesis of a
formal zirconacyclopropane ring with a variety of reagents. With phenylacetylene, ring opening occurs
on the more substituted side, while Me3MCl (M ) Si, Sn) effect ring opening on the least substituted
side. Hydrogenolysis further proceeds rapidly to provide a zirconanorbornadiene derivative in high yield
under conditions where a structurally related dimethyl complex remains inert.
We have recently documented that, in contrast to zircono-
cenes, the mono(cyclopentadienyl), mono(amidinate) ligand set
appears to be well suited for the stabilization of neutral and
cationic zirconium(IV) complexes bearing alkyl substituents with
â-hydrogens, even though these non-metallocene compounds
formally possess electron counts lower than those of their
zirconocene counterparts.7,8 These results encouraged us to
investigate the stability and reactivity of formal Zr(II) η2-alkene
complexes that are supported by the same ligand com-
bination. Herein, we now present the synthesis and structural
characterization of a formal 14-electron, base-free η2-styrene
complex of zirconium. We further present a preliminary inves-
tigation of the reactivity of this complex that involves formal
ring opening of a zirconacyclopropane ring via protonolysis and
σ-bond metathesis.
Introduction
Since the mid-1980s, systematic investigations of the chemical
reactivities of η2-alkene and η2-alkyne complexes of bis-
(cyclopentadienyl)zirconium, i.e., “Cp2Zr” (Cp ) η5-C5H5) (also
known as zirconocene), by Negishi, Takahashi, and Buchwald,
to name just a few, have led to the development of a rich
collection of useful transformations for organic synthesis.1 In
practice, two limiting structures within the Dewar-Chatt-
Duncanson model of bonding,2 i.e., either a Zr(II) metal-alkene
complex or a Zr(IV) metallacyclopropane, are often interchange-
ably invoked to fit different mechanistic schemes, with the result
that a certain degree of ambiguity still exists regarding the nature
of the primary steps involved in many key transformations. For
instance, the zirconocene-catalyzed hydrosilylation and hydro-
genation of alkenes have alternatively been proposed as
proceeding either through oxidative addition/reductive elimina-
tion reactions involving Cp2Zr(II) metal centers or through
σ-bond metathesis reactions involving Zr(IV) metallacyclopro-
panes.3 Complicating this picture further is that electron-deficient
zirconocene η2-alkene complexes do not appear to be stable
toward isolation, and accordingly, to date, the only solid-state
structural parameters that are available are for a few examples
(i.e., η2-ethene, η2-diphenylethene, and η2-styrene) that have
been stabilized as 18-electron species with the addition of strong
σ-donors (i.e., PR3, THF, and pyridine, also known as “bases”).4
In the case of non-zirconocenes, only η2-ethene complexes have
so far been isolated and, once again, only as adducts with strong
σ-donors, albeit in a few cases with electron counts of <18.5,6
Results and Discussion
As shown in Scheme 1, the successful synthesis of a
η2-styrene complex was achieved through reaction of the known
dichloride starting material 17 with 2 equiv of (â-lithioethyl)-
benzene9 to provide dark green 2 in 76% isolated yield. A single-
crystal X-ray analysis of 2 was conducted, and Table 1 provides
a summary of the X-ray data obtained, while Figure 1 and Table
2 present the molecular structure and a listing of selected
structural parameters, respectively.10 From an analysis of these
latter data, it would appear that this compound possesses
substantial metallacyclopropane character (cf. bond distances
(Å): Zr(1)-C(1) ) 2.280(3), Zr(1)-C(2) ) 2.300(3), and
C(1)-C(2) ) 1.449(5) in 2 vs the corresponding values of 2.36-
(2), 2.43(2), and 1.38(2) in Cp2Zr(η2-PhCHCHPh)(PMe3)4b and
2.35(1), 2.35(2), and 1.46(2) in Cp2Zr(η2-CH2CHPh)(PMe3)4c).
(1) For reviews, see: (a) Buchwald, S. L.; Nielsen, R. B. Chem. ReV.
1988, 88, 1047-1058. (b) Negishi, E.; Takahashi, T. Acc. Chem. Res. 1994,
27, 124-130. (c) Marek, I., Ed. Titanium and Zirconium in Organic
Synthesis; Wiley-VCH: New York, 2002.
(2) (a) Dewar, M. J. S. Bull. Soc. Chim. Fr. 1951, 18, C79. (b) Chatt, J.;
Duncanson, L. A. J. Chem. Soc. 1953, 2939-2947.
(5) (a) Schrock, R. R.; Baumann, R.; Reid, S. M.; Goodman, J. T.;
Stumpf, R.; Davis, W. M. Organometallics 1999, 18, 3649-3670. (b)
Fryzuk, M. D.; Duval, P. B.; Rettig, S. J. Can. J. Chem. 2001, 79, 536-
545.
(3) See for instance: (a) Negishi, E.; Huo, S. In ref 1c, p 43. (b) Ura,
Y.; Hara, R.; Takahashi, T. Chem. Lett. 1998, 195-196. (c) Takahashi, T.;
Bao, F.; Gao, G.; Ogasawara, M. Org. Lett. 2003, 5, 3479-3481.
(4) (a) Alt, H. G.; Denner, C. E.; Thewalt, U.; Rausch, M. D. J.
Organomet. Chem. 1988, 356, C83-C85. (b) Takahashi, T.; Murakami,
M.; Kunishige, M.; Saburi, M.; Uchida, Y.; Kozawa, K.; Uchida, T.;
Swanson, D. R.; Negishi, E. Chem. Lett. 1989, 761-764. (c) Binger, P.;
Mu¨ller, P.; Benn, R.; Rufinska, A.; Gabor, B.; Kru¨ger, C.; Betz, P. Chem.
Ber. 1989, 122, 1035-1042. (d) Fisher, R. A.; Buchwald, S. L. Organo-
metallics 1990, 9, 871-873. (e) Fischer, R.; Walther, D.; Gebhardt, P.;
Go¨rls, H. Organometallics 2000, 19, 2532-2540. (f) Lee, H.; Hascall, T.;
Desrosiers, P. J.; Parkin, G. J. Am. Chem. Soc. 1998, 120, 5830-5831.
(6) For Cp*2Ti(η2-ethylene) (Cp* ) η5-C5Me5), see: Cohen, S. A.;
Bercaw, J. E. Organometallics 1985, 4, 1006-1014.
(7) Keaton, R. J.; Koterwas, L. A.; Fettinger, J. C.; Sita, L. R. J. Am.
Chem. Soc. 2002, 124, 5932-5933.
(8) Harney, M. B.; Keaton, R. J.; Sita, L. R. J. Am. Chem. Soc. 2004,
126, 4536-4537.
(9) Negishi, E.; Swanson, D. R.; Rousset, C. J. J. Org. Chem. 1990, 55,
5406-5409.
(10) Details are provided in the Supporting Information.
10.1021/om0508785 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 12/17/2005

532 Organometallics, Vol. 25, No. 2, 2006
Kissounko et al.
Scheme 1
Table 1. Crystallographic Data for Compounds 2 and 7
2
7
formula
Mr
T, K
cryst syst
space group
a, Å
C26H40N2Zr
471.82
173(2)
monoclinic
P21/n
8.9534(3)
19.0468(7)
14.3058(5)
90
91.9270(10)
90
2438.24
4
C26H42N2Zr
473.84
293(2)
triclinic
P1h
8.7602(3)
9.7735(4)
15.5841(6)
79.2240(10)
82.0160(10)
69.5270(10)
1224.03(8)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
Figure 1. Molecular structure (30% thermal ellipsoids) of com-
pound 2. All hydrogen atoms have been removed for the sake of
clarity.
F(000)
D
1000
1.285
504
1.286
calcd, g/cm3
λ, Å
0.710 73
0.465
27.50
0.710 73
0.463
27.50
Table 2. Selected Structural Parameters for Compound 2
µ, mm-1
θ
max, deg
index ranges
Bond Lengths (Å)
Zr(1)-CNT1a
Zr(1)-N(1)
Zr(1)-N(2)
Zr(1)-C(1)
Zr(1)-C(2)
2.2210(11)
2.2413(19)
2.260(2)
Zr(1)-C(3)
N(1)-C(9)
N(2)-C(9)
C(1)-C(2)
C(2)-C(3)
2.644(2)
1.342(3)
1.332(3)
1.449(5)
1.425(4)
h
k
-11 to +11
-24 to +24
-18 to +18
21 850
5604 (R(int) ) 0.0471)
4100
5604
3
425
R1 ) 0.0344
wR2 ) 0.0791
R1 ) 0.0659
wR2 ) 0.0905
1.078
-11 to +11
-12 to +12
-20 to +20
19 750
5616
4850
5616
15
433
R1 ) 0.0304
wR2 ) 0.0772
R1 ) 0.0404
wR2 ) 0.0816
1.073
l
2.280(3)
RCa
2.300(3)
IRCb
IRCGTc
no. of data
no. of restraints
no. of params
R for IRCGT
Bond Angles (deg)
N(1)-Zr(1)-N(2)
C(1)-Zr(1)-C(2)
C(2)-C(1)-Zr(1)
59.80(7)
36.89(12)
72.29(16)
C(1)-C(2)-Zr(1)
C(3)-C(2)-Zr(1)
C(3)-C(2)-C(1)
70.82(16)
87.13(16)
120.8(3)
a CNT1 is the calculated centroid of the Cp* fragment.
R for IRC
Scheme 2
goodness of fit
largest diff peak and
hole, e Å-3
1.090 and -0.501
0.938 and -0.452
a RC ) number of reflections collected. b IRC ) number of independent
RC. c IRCGT ) number of IRC with I > 2σ(I).
On closer inspection, there is also a relatively close approach
between Zr(1) and C(3) of the phenyl ring at 2.644(2) Å which
might be taken as evidence of a secondary bonding interaction
between the electron-deficient metal center and the styrene
fragment that contributes to further stabilization of the complex.
In contrast, no close metal-phenyl ring interactions appear in
the corresponding 18-electron, base-stabilized η2-styrene zir-
conocene, Cp2Zr(η2-CH2CHPh)(PMe3).4c
provided a calculated barrier to rotation of the phenyl ring about
q
the C(2)-C(3) bond, ∆Gc (Tc ) 292 K), of 12.5 kcal mol-1
.
To probe the existence and strength of a possible η3 mode of
bonding of the styrene fragment that is suggested by the solid-
state structure of 2, the structure of this compound in solution
was probed by variable-temperature 1H NMR (400 MHz,
toluene-d8) spectroscopy. To begin, it was determined that
compound 2 is quite robust in solution at elevated temperatures
of up to 100 °C. Furthermore, the spectra recorded at 25 °C
and above provide no evidence for rotation of the η2-styrene
fragment about a zirconium-alkene axis that might be possible
within a classical Zr(II) metal η2-alkene complex, thus lending
additional support to the conclusion that 2 possesses substantial
Zr(IV) metallacyclopropane character. With respect to the
possible existence of any additional secondary bonding interac-
tions involving the styrene fragment and the metal center in
solution, the collection of variable-temperature 1H NMR spectra
However, the magnitude of this barrier can just as easily be
accounted for on the basis of nonbonded steric interactions
involved with rotation of the phenyl group within the ligand
environment as it can be rationalized in terms of a weak
secondary bonding interaction. Accordingly, for the purposes
of this work, we choose to think of 2 in terms of having a η2-
styrene interaction with the metal center.
As Scheme 2 reveals, reaction of 2 with 1 equiv of phen-
ylacetylene led to a quantitative yield of the yellow crystalline
acetylide complex 3 through formal protonolysis of the zir-
conacyclopropane ring at the carbon atom bearing the phenyl
substituent. Cohen and Bercaw6 reported similar protonolysis
of a titanocene η2-ethene complex with terminal alkynes, and
Negishi and co-workers11 demonstrated that a high yield of 1,2-

A Base-Free η2-Styrene Complex of Zirconium
Organometallics, Vol. 25, No. 2, 2006 533
Scheme 3
Scheme 4
diphenylethane is produced when in situ generated Cp2Zr-
(η2-PhCHCHPh) is treated in solution with HCl. A crystal
structure of 3 confirms the structural assignment that is shown
in Scheme 2, and the molecular structure of this compound
displays no unusual geometric features.10 Surprisingly, however,
although compound 3 was found to be stable in solution for
short periods of time (<24 h), benzene solutions of this complex
become noticeably purple-tinged after 1 day, and heating a
toluene solution for 48 h at 60 °C subsequently provided the
purple crystalline zirconacyclopent-3-ene complex 4, which was
also structurally characterized by single-crystal X-ray analysis.10
Although no specific mechanistic details are yet known regard-
ing this transformation, it can be noted that 4 is formally an
isomeric product expected from alkyne insertion of pheny-
lacetylene into 2. Given this, we tentatively propose that 3 can
undergo intramolecular â-hydrogen abstraction by the acetylide
R-carbon to regenerate 2 and phenylacetylene. Reinsertion of
the latter back into the least hindered Zr-C bond of 2 could
then form the zirconacyclopent-1-ene product shown in Scheme
3, which subsequently undergoes isomerization to the potentially
more thermodynamically stable zirconacyclopent-3-ene isomer
4. In this regard, the solid-state structure of 4 is strongly
suggestive of a σ2,π interaction of the formal butadiene fragment
with the metal center.7,12 It can be mentioned that Cohen and
Bercaw6 also observed the room-temperature isomerization of
the initial titanocene alkyl acetylide complex Cp*2Ti(Et)-
(CHCHMe) (Cp* ) η5-C5Me5), arising from protonolysis of
Cp*2Ti(η2-CH2CH2) with propene, to an analogous titanacy-
clopent-1-ene, which serves to support a more general nature
for the first two steps in Scheme 3.
Scheme 5
5 f 6 isomerization is most likely driven by relief of steric
interactions.
Hydrogenolysis of 2 with dihydrogen in pentane proceeded
rapidly at room temperature to provide the η2-arene complex 7
in near-quantitative yield according to Scheme 5.10,13 Once
again, compound 7 was subjected to crystallographic analysis
and Table 1 provides a summary of the X-ray data obtained,
while Figure 2 and Table 3 provide the molecular structure and
As shown in Scheme 4, reaction of 2 with Me3MCl (M )
Si, Sn) effected formal metallacyclopropane ring opening
through σ-bond metathesis on the least hindered side. More
specifically, with Me3SiCl in toluene at 40 °C, 1H NMR analysis
revealed initial formation of a 5:1 mixture of two diastereomeric
products, which over the course of 18 h converted entirely to
the initial minor species. Recrystallization of the crude product
then afforded a 93% yield of 6a, which was structurally
characterized by X-ray analysis.10 In the case of Me3SnCl, the
reaction with 2 was carried out in Et2O at -30 °C to
quantitatively provide diastereomer 5b, which crystallographic
analysis confirmed to have the stereochemistry depicted in
Scheme 4.10 As with 5a, this kinetic product was then observed
Figure 2. Molecular structure (30% thermal ellipsoids) of com-
pound 7. All hydrogen atoms have been removed for the sake of
clarity.
1
by H NMR to quantitatively isomerize in solution through
a listing of selected structural parameters, respectively. These
crystallographic data confirm that the structure of 7 is best
represented as a Zr(IV) zirconanorbornadiene rather than as a
Zr(II) η4- or η6-arene complex, which is somewhat surprising,
given the formal 14-electron count that this high-oxidation-state
metal-centered epimerization to the more thermodynamically
stable product 6b at room temperature. Analysis of space-
filling representations of structural models suggest that the
(11) Negishi, E.; Cederbaum, F. E.; Takahashi, T. Tetrahedron Lett. 1986,
27, 2829-2832.
(12) Erker, G.; Kruger, C.; Muller, G. AdV. Organomet. Chem. 1985,
24, 1-39.
(13) Ortiz, C. G.; Abboud, K. A.; Cameron, T. M.; Boncella, J. M. Chem.
Commun. 2001, 247-248.

534 Organometallics, Vol. 25, No. 2, 2006
Kissounko et al.
Table 3. Selected Structural Parameters for Compound 7
Preparation of Compound 2. To a solution of 0.75 mL (5.17
mmol) of (2-iodoethyl)benzene in 50 mL of Et2O cooled to -78
°C was added 7.3 mL of 1.5 M tBuLi (11.0 mmol) in pentane. The
reaction mixture was then warmed to ambient temperature over 1
h, whereupon it was cooled to -30 °C and 1.08 g (2.46 mmol) of
1 was added. The reaction mixture was stirred overnight at ambient
temperature, and then all the volatiles were removed under vacuum,
the green residue was extracted with pentane, and the extract filtered
through Celite and re-evaporated. The green solid material was
taken up into a small (ca. 10 mL) amount of pentane, passed through
a small pad of Celite, and crystallized at -30 °C to give 0.89 g
Bond Lengths (Å)
Zr(1)-CNT1a
Zr(1)-N(1)
Zr(1)-N(2)
Zr(1)-C(1)
Zr(1)-C(2)
Zr(1)-C(3)
Zr(1)-C(4)
Zr(1)-C(5)
2.2658(9)
2.2989(15)
2.2886(15)
2.313(2)
Zr(1)-C(6)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(1)
2.5190(19)
1.444(4)
1.357(4)
1.438(3)
1.469(3)
1.358(3)
1.457(3)
2.510(2)
2.514(2)
2.3501(19)
2.5597(18)
Bond Angles (deg)
N(2)-Zr(1)-N(1)
C(1)-Zr(1)-C(4)
C(2)-C(1)-Zr(1)
C(6)-C(1)-Zr(1)
C(3)-C(4)-Zr(1)
C(5)-C(4)-Zr(1)
57.86(6)
75.74(8)
80.22(13)
80.36(12)
79.17(12)
80.59(11)
C(2)-C(1)-C(6)
C(3)-C(4)-C(5)
C(1)-C(2)-C(3)
C(1)-C(6)-C(5)
C(4)-C(3)-C(2)
C(6)-C(5)-C(4)
112.9(2)
113.5(2)
120.9(2)
122.4(2)
122.1(2)
119.44(18)
1
(76% yield) of 2 as a deep green crystalline material. H NMR
(benzene-d6, 25 °C): δ 0.11, 0.88, 1.06, 1.28 (d, 3 H, J ) 6.8 Hz,
CHMe2); 1.35, 2.16 (br s, 1 H, CHAHBCHPh); 1.43 (s, 3 H, CMe);
1.84 (s, 15 H, C5Me5); 3.53 (br s, 1 H, CHAHBCHPh); 2.99, 3.75
(sept, 1 H, J ) 6.8 Hz, CHMe2); 6.24 (br s, 2 H, o-Ph); 6.41 (t, 1
H, J ) 7.2 Hz, p-Ph); 6.97 (t, 2 H, J ) 7.2 Hz, m-Ph). 13C{1H}
NMR (benzene-d6, 25 °C): δ 11.7 (C5Me5); 12.3 (CMe); 23.0, 24.6,
25.7, 25.8 (CHMe2); 47.2, 50.4 (CHMe2); 60.1 (CHAHBCHPh); 81.2
(CHAHBCHPh); 118.4 (C5Me5); 116.2, 130.9, 139.1, 146.4 (Ph);
164.1 (CMe). Anal. Calcd for C26H40N2Zr: C, 66.18; H, 8.54; N,
5.94. Found: C, 65.80; H, 8.57; N, 6.01.
a CNT1 is the calculated centroid of the Cp* fragment.
designation requires vs either a 16- or 18-electron count that
the alternative reduced metal structural formalizations pro-
vide.13,14 Further support for a zirconanorbornadiene structure
is provided by the observed thermal robustness of 7, which fails
to undergo arene substitution in toluene at 100 °C, and by the
1H chemical shifts of the resonances for the metallanorborna-
diene fragment (i.e., C6H5Et), which occur between 3.64 and
3.86 ppm.13 Mechanistically, since no styrene production is
observed and 7 cannot function as a catalyst for the hydrogena-
tion of styrene, we propose that the 2 f 7 transformation pro-
ceeds through initial σ-bond metathesis of the metallacyclo-
propane to provide a zirconium alkyl hydride that then under-
goes π-assisted reductive elimination, followed by formal arene
reduction, to generate 7 (see Scheme 5). Of final note, this facile
hydrogenolysis of 2 stands in sharp contrast to the inertness of
the structurally related dimethyl complex Cp*Zr(Me)2[N(iPr)C-
(Me)N(iPr)], which remains unchanged under identical condi-
tions.
Preparation of Compound 3. To a solution of 0.13 g (0.28
mmol) of 2 in 5 mL of Et2O cooled to -30 °C was added 3.0 µL
(0.28 mmol) of phenylacetylene. The reaction mixture was then
warmed to ambient temperature over 1 h, whereupon it was
evaporated to dryness. The residue was taken up into a small (ca.
5 mL) amount of pentane, passed through a small pad of Celite,
and crystallized at -30 °C to give 0.10 g (62% isolated yield) of
1
3a as a yellow crystalline material. On a smaller scale, H NMR
1
revealed the reaction to have proceeded quantitatively. H NMR
(benzene-d6, 25 °C): δ 0.65, 0.99 (t of d, 1 H, 1J ) 12.8 Hz, 2J )
5.2 Hz, CH2CH2Ph); 1.14 (br s, 12 H, CHMe2); 1.55 (s, 3 H, CMe);
2.09 (s, 15 H, C5Me5); 3.29 (sept, 2 H, J ) 6.8 Hz, CHMe2); 3.69
1
2
and 3.74 (t of d, 1 H, J ) 11.0 Hz, J ) 5.2 Hz, CH2CH2Ph);
6.97-7.53 (m, 10 H, CH2CH2Ph, CCPh). 13C{1H} NMR (benzene-
d6, 25 °C): δ 12.2 (C5Me5); 12.3 (CMe); 23.9 (CHMe2); 24.4 (CH2-
CH2Ph); 32.2 (CH2CH2Ph); 48.1 (CHMe2); 72.7 (CCPh); 108.8
(CCPh); 121.7 (C5Me5); 124.7, 126.2, 125.5, 127.4, 127.6, 131.1,
148.2, 150.4 (CH2CH2Ph, CCPh); 175.9 (CMe). Anal. Calcd for
C34H46N2Zr: C, 71.15; H, 8.08; N, 4.88. Found: C, 70.44; H, 8.12;
N, 5.07.
Conclusion
In summary, a new, base-free η2-styrene complex of zirco-
nium bearing the mono(cyclopentadienyl), mono(amidinate)
ligand set has been prepared. A preliminary survey of reactivity
has revealed that this compound can formally undergo ring
opening of a zirconacyclopropane ring via either protonolysis,
in the case of phenylacetylene, or σ-bond metathesis, in the case
of group 14 metal chlorides and hydrogenolysis. Additional
studies of this compound, and in particular, insertion chemistry
of alkenes to form zirconacyclopentanes, will be published in
due course.
Preparation of Compound 4. A solution of 0.13 g (0.28 mmol)
of 3 in 5 mL of toluene was heated at 60 °C for 48 h, whereupon
it was evaporated to dryness. The residue was taken up into a small
(ca. 10 mL) amount of pentane, passed through a small pad of
Celite, concentrated to a volume of ca. 5 mL, and crystallized at
-30 °C. The mother liquor was decanted, concentrated to 0.5 mL
volume, and crystallized at -30 °C to give 0.04 g (31% yield) of
4 as a purple crystalline material. 1H NMR (benzene-d6, 25 °C): δ
-0.08, 0.75, 0.77, 0.95 (d, 3 H, CHMe2); 0.50, 0.81 (dd, 1 H, 1J )
2
8.0 Hz, J ) 0.2 Hz, CH2Ph); 1.29 (s, 3 H, CMe); 1.69 (d, 1 H, J
Experimental Details
) 8.0 Hz, CHPh); 1.87 (s, 15 H, C5Me5); 2.22 (d, 1 H, J ) 8 Hz,
dCH); 3.0, 3.24 (sept, 1 H, J ) 6.8 Hz, CHMe2); 6.97-7.53 (m,
10 H, CH2CH2Ph, CCPh). 13C{1H} NMR (benzene-d6, 25 °C): δ
11.6 (C5Me5); 12.2 (CMe); 25.7, 24.8, 23.8, 23.0 (CHMe2); 13.8
(CH2Ph); 22.3 (CHPh); 46.1, 47.0 (CHMe2); 58.4 (dCH); 74.6
(dCPh); 119.4 (C5Me5); 119.9, 121.1, 123.7, 124.4, 125.5, 127.9,
144.9, 145.8 (Ph); 157.4 (CMe). Anal. Calcd for C34H46N2Zr: C,
71.15; H, 8.08; N, 4.88. Found: C, 71.27; H, 7.99; N, 5.07.
General Considerations. All manipulations were carried out in
a glovebox or using standard Schlenk-line techniques under an
atmosphere of dinitrogen. All solvents were dried (Na/benzo-
phenone for diethylether and pentane, Na for toluene, CaH2 for
chlorobenzene) and distilled under dinitrogen prior to use. Benzene-
d6 and toluene-d8 were vacuum-transferred from NaK alloy, and
chlorobenzene-d5 was vacuum-transferred from CaH2 prior to use
as NMR solvents. Cp*ZrCl2[iPrNC(Me)NPri] (1) was prepared
according to previously published procedures.7 1H and 13C{1H}
NMR spectra were recorded at 400 and 100 MHz, respectively.
Elemental analyses were performed by Midwest Microlab.
Preparation of Compound 5b. To a solution of 0.20 g (0.46
mmol) of 2 in 20 mL of Et2O cooled to -30 °C was added 0.09 g
(0.23 mmol) of trimethyltin chloride. Immediately after that the
reaction mixture was evaporated to dryness while the solution was
kept at 0 °C, the residue was extracted with a 5:1 pentane/toluene
mixture, the extracts were filtered through a small pad of Celite,
and then the solvents were removed in vacuo to provide a crude
(14) For titananorbornadiene complexes, see: (a) Hagadorn, J. R.; Arnold,
J. Angew. Chem., Int. Engl. 1998, 37, 1729-1731. (b) Ozerov, V.; Patrick,
B. O.; Ladipo, F. T. J. Am. Chem. Soc. 2000, 122, 6423-6431.

A Base-Free η2-Styrene Complex of Zirconium
Organometallics, Vol. 25, No. 2, 2006 535
1
material that was recrystallized at -30 °C from a 5:1 pentane/
toluene mixture (ca. 4 mL) to give 0.13 g (41% yield) of 5b as an
orange crystalline material. 1H NMR (toluene-d8, -10 °C): δ 0.18
(s, 9 H, SnMe3); 1.07, 1.11, 1.25, 1.39 (d, 3 H, J ) 6.8 Hz, CHMe2);
1.42 (s, 3 H, CMe); 1.23 and 1.74 (dd, 1 H, 1J ) 16.0 Hz, 2J ) 8.0
(∼100% yield) of 6b as an orange crystalline material. H NMR
(benzene-d6, 25 °C): δ -0.06 (s, 9 H, SnMe3); 1.04, 1.09, 1.29,
1.36 (d, 3 H, J ) 6.8 Hz, CHMe2); 1.21 (dd, 1 H, 1J ) 16.0 Hz, 2J
) 4.0 Hz, CHAHBSnMe3); 1.54 (s, 3 H, CMe); 1.74 (dd, 1 H, 1J )
16.0 Hz, 2J ) 8.0 Hz, CHAHBSnMe3); 1.85 (s, 15 H, C5Me5);
2.32 (dd, 1 H, J1 ) 8.0 Hz, J2 ) 4.0 Hz, CHPh); 3.35, 3.52
(sept, 1 H, J ) 6.8 Hz, CHMe2); 6.83-7.16 (m, 5 H, Ph). 13C{1H}
NMR (benzene-d6, 25 °C): δ -8.0 (SnMe3); 12.2 (C5Me5); 12.9
(CHAHBSnMe3); 14.7 (CMe); 23.8, 23.9, 24.4, 25.6 (CHMe2); 47.5,
48.7 (CHMe2); 79.4 (CHPh); 122.3 (C5Me5), 122.6, 122.7, 127.8,
149.8 (Ph); 174.2 (CMe). Anal. Calcd for C29H49ClN2SnZr: C,
51.90; H, 7.36; N, 4.17. Found: C, 51.72; H, 7.30; N, 4.20.
Preparation of Compound 7. A solution of 0.12 g (0.24 mmol)
of 2 in 10 mL of Et2O was pressurized with dihydrogen at 40 psi.
The color immediately changed to brown, whereupon the solution
was evaporated to dryness. The residue was taken up into a small
(ca. 5 mL) amount of pentane, passed through a small pad of
Celite, and crystallized at -30 °C to give 0.11 g (92.2% yield) of
7 as a brown crystalline material. 1H NMR (benzene-d6, 25 °C): δ
0.87, 1.20 (d, 6 H, J ) 6.8 Hz, CHMe2); 0.89 (t, 3 H, J ) 7.6 Hz,
CH3CH2C6H5); 1.37 (q, 2 H, J ) 7.6 Hz, CH3CH2C6H5); 1.52 (s,
3 H, CMe); 1.85 (s, 15 H, C5Me5); 3.32 (sept, 2 H, J ) 6.8 Hz,
CHMe2); 3.64-3.86 (m, 5 H, CH3CH2C6H5). 13C{1H} NMR
(benzene-d6, 25 °C): δ 12.6 (C5Me5); 13.7 (CH3CH2C6H5); 13.8
(CMe); 25.3, 26.6 (CHMe2); 28.6 (CH3CH2C6H5); 47.1 (CHMe2);
94.0, 95.2, 111.5, 112.2 (CH2CH2C6H5); 126.3 (C5Me5); 171.9
(CMe). Anal. Calcd for C26H42N2Zr: C, 65.90; H, 8.93; N, 5.91.
Found: C, 65.20; H, 8.96; N, 5.29.
1
Hz, CHAHBSnMe3); 1.95 (s, 15 H, C5Me5); 2.52 (d, 1 H, J ) 8.6
Hz, CHPh); 3.45 (sept, 2 H, J ) 6.8 Hz, CHMe2); 6.83-7.21 (m,
5 H, Ph). 13C{1H} NMR (benzene-d6, 25 °C): δ -8.7 (SnMe3);
9.5 (CHAHBSnMe3); 12.5 (C5Me5); 15.1 (CMe); 23.7, 234.0, 24.9,
25.9 (CHMe2); 47.0, 49.2 (CHMe2); 78.7 (CHPh); 122.2 (C5Me5),
122.9, 127.4, 128.2, 149.5 (Ph); 174.5 (CMe).
Preparation of Compound 6a. A solution of 0.11 g (0.23 mmol)
of 2 and 29 µL (0.23 mmol) of trimethylchlorosilane in 5 mL of
toluene was kept overnight at 40 °C. After that the reaction mixture
was evaporated to dryness, the residue was extracted with a 5:1
pentane/toluene mixture, the extracts were filtered through a small
pad of Celite, and then solvents were removed in vacuo to provide
a crude material that was recrystallized at -30 °C from a 5:1
pentane/toluene mixture (ca. 4 mL) to give 0.12 g (93% yield) of
6a as an orange crystalline material. Note: single-crystal X-ray
analysis provided a 0.09% Br occupancy at the Cl (0.91%) site in
the refined solid-state structure of 6a.10 At the present time, we do
not know the source of this contaminant, but we note that the
chemical analysis of 6a (vide infra) did not reflect this level of
1
bromide contamination within the bulk material. H NMR (ben-
zene-d6, 25 °C): δ -0.08 (s, 9 H, SiMe3); 1.00, 1.03, 1.27, 1.36
1
2
(d, 3 H, J ) 6.8 Hz, CHMe2); 1.21 (dd, 1 H, J ) 14.6 Hz, J )
1
2
2.4 Hz, CHAHBSiMe3); 1.40 (dd, 1 H, J ) 14.6 Hz, J ) 2.4 Hz,
CHAHBSiMe3); 1.51 (s, 3 H, CMe); 1.81 (s, 15 H, C5Me5); 2.56
1
2
(dd, 1 H, J ) 14.6 Hz, J ) 12.4 Hz, CHPh); 3.31, 3.49 (sept, 1
H, J ) 6.8 Hz, CHMe2); 6.82-7.16 (m, 5 H, Ph). 13C{1H} NMR
(benzene-d6, 25 °C): δ 0.0 (SiMe3); 11.9 (C5Me5); 13.5 (CMe);
13.9 (CHAHBSiMe3); 23.3, 23.7, 24.5, 25.0 (CHMe2); 47.2, 48.5
(CHMe2); 78.6 (CHPh); 121.8 (C5Me5), 122.6, 127.4, 127.9, 149.1
(Ph); 174.0 (CMe). Anal. Calcd for C29H49ClN2SiZr: C, 60.0; H,
8.51; N, 4.82. Found: C, 59.90; H, 8.59; N, 4.88.
Acknowledgment. Funding for this work was provided by
the NSF (Grant No. CHE-0092493), for which we are grateful.
Supporting Information Available: Details of the crystal-
lographic analyses of 2-4, 5b, 6a, and 7, including tables of atomic
positions, isotropic thermal parameters, and anisotropic thermal
displacement coefficients; crystal data are also given as CIF files.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Preparation of Compound 6b. A solution of 0.13 g (0.19 mmol)
of 5b was dissolved in benzene-d6 and kept overnight at an ambient
temperature, whereupon complete isomerization of 5b into 6b was
observed. All the volatiles were removed in vacuo to give 0.13 g
OM0508785