Selective tin-carbon bond cleavage reactions of trimethylstannylzirconocene dichloride with electrophiles

Article abstract of DOI:10.1021/ic991461s

The reaction of 5,5-bis(trimethylstannyl)cyclopentadiene with CpZrCl₃ (Cp = η⁵-C₅H₅) affords the monostan-nylated metallocene complex (η⁵-Me₃SnC₅H₄)CpZrCl₂ (1), accompanied by variable amounts of (η⁵-ClMe₂-SnC₅H₄)CpZrCl₂ (2). The complex (1) reacts with BCl₃ or with ICl to afford 2 (Sn-CH₃ cleavage), but with HCl, Cp₂ZrCl₂ is obtained instead (Sn-Cp cleavage). Depending on the reaction conditions, treatment of either 1 or 2 with BBr₃ affords (η⁵-BrMe₂SnC₅H₄)CpZrBr₂ (3) or (η⁵-Br₂MeSnC₅H₄)CpZrBr₂ (4). The reaction of 1 with excess I₂ affords the iodostannylated complex (η⁵-IMe₂SnC₅H₄)CpZrCl₂ (5). Two of the complexes (2·2C₆H₅CH₃ and 4·THF) are crystallographically characterized. The adduct 4·THF has a distorted trigonal bipyramidal geometry about tin with a long O-Sn distance of 2.655 A. We find overall that Me₃Sn substituents undergo electrophilic halodemethylation much more readily than corresponding Me₃Si substituents, whereas the reactivities of the halostannylated complexes toward nucleophiles such as airborne moisture are much lower than those of their halosilylated counterparts.

Full text of DOI:10.1021/ic991461s

Inorg. Chem. 2000, 39, 4921-4926
4921
Selective Tin-Carbon Bond Cleavage Reactions of Trimethylstannylzirconocene Dichloride
with Electrophiles
Xu Cheng, Carla Slebodnick, and Paul A. Deck*
Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061-0212
Damon R. Billodeaux1 and Frank R. Fronczek
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803-1804
ReceiVed December 21, 1999
The reaction of 5,5-bis(trimethylstannyl)cyclopentadiene with CpZrCl3 (Cp ) η5-C5H5) affords the monostan-
nylated metallocene complex (η5-Me3SnC5H4)CpZrCl2 (1), accompanied by variable amounts of (η5-ClMe2-
SnC5H4)CpZrCl2 (2). The complex (1) reacts with BCl3 or with ICl to afford 2 (Sn-CH3 cleavage), but with
HCl, Cp2ZrCl2 is obtained instead (Sn-Cp cleavage). Depending on the reaction conditions, treatment of either
1 or 2 with BBr3 affords (η5-BrMe2SnC5H4)CpZrBr2 (3) or (η5-Br2MeSnC5H4)CpZrBr2 (4). The reaction of 1
with excess I2 affords the iodostannylated complex (η5-IMe2SnC5H4)CpZrCl2 (5). Two of the complexes (2‚
2C6H5CH3 and 4‚THF) are crystallographically characterized. The adduct 4‚THF has a distorted trigonal
bipyramidal geometry about tin with a long O-Sn distance of 2.655 Å. We find overall that Me3Sn substituents
undergo electrophilic halodemethylation much more readily than corresponding Me3Si substituents, whereas the
reactivities of the halostannylated complexes toward nucleophiles such as airborne moisture are much lower than
those of their halosilylated counterparts.
Introduction
metallocene dibromides upon treatment with excess BBr3.5,6 We
now report the results of several reactions of a Me3Sn-substituted
zirconocene dichloride (1) with electrophiles (BBr3, BCl3, I2,
ICl, and HCl), and we compare the reactivities of the Me3Sn
and Me3Si substituents toward such electrophiles.
Group 4 metallocenes are an established class of homoge-
neous catalysts for olefin polymerization.2 During the past
several years, numerous structure-reactivity investigations have
yielded a better mechanistic understanding of metallocene-
catalyzed processes as well as a wider range of practical
applications. The growing availability of general synthetic routes
to a wide variety of metallocene structures has facilitated these
investigations.
We are exploring synthetic approaches to metallocene
complexes bearing highly electrophilic substituents.3,4 Such
species are useful intermediates for the synthesis of ansa-
metallocenes3b-d,5,6 and as precursors to surface-immobilized
metallocene catalysts.7 In earlier reports, we showed that Me3-
Si-substituted group 4 metallocene dichlorides undergo selective,
efficient conversion to the corresponding BrMe2Si-substituted
Experimental Section
General Procedures. Standard inert-atmosphere techniques were
used for all procedures. Reaction glassware sealed with either Krytox7
fluorinated lubricant or Kalrez7 O-rings and flamed out under vacuum
was used for reactions involving boron trihalides. BCl3 (1.0 M solutions
in hexanes or dichloromethane), BBr3, and ICl were used as received
from Aldrich. CpZrCl3 was used as received from Strem Chemical Co.
CpZrCl3C‚DME was prepared according to the procedure of Lund and
Livinghouse.8 5,5-Bis(trimethylstannyl)cyclopentadiene was prepared
by a published procedure,9 and its purity (>98%) was confirmed by
1H NMR analysis.10 A JEOL Eclipse instrument (500 MHz for 1H, 125
MHz for 13C) was used for all NMR measurements. NMR-scale
(1) Undergraduate research participant.
(2) (a) Hlatky, G. G. Coord. Chem. ReV. 1999, 181, 243. (b) Britovsek,
G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. Engl.
1999, 38, 429. (c) Locatelli, P. Trends Polym. Sci. 1996, 4, 326. (h)
Bochmann, M. Top. Catal. 1999, 7, 9. (i) Kaminsky, W. J. Chem.
Soc., Dalton Trans. 1998, 1413. (j) Soga, K.; Shiono, T. Prog. Polym.
Sci. 1997, 22, 1503. (k) Machima, K.; Nakayama, Y.; Nakamura, A.
AdV. Polym. Sci. 1997, 133, 1.
(3) (a) Cuenca, T.; Royo, P. Coord. Chem. ReV. 1999, 195, 447 and
references therein. (b) Alcalde, M. I.; Go´mez-Sal, M. P.; Royo, P.
Organometallics 1999, 18, 546. (c) De la Mata, F. J.; Giner, P.; Royo,
P. J. Organomet. Chem. 1999, 572, 155. (d) Gomez, R.; Gomez-Sal,
P.; Manzanero, A.; Royo, P. Polyhedron 1998, 17, 1055. (e) Su¨nkel,
K.; Schubert, S.; Hofmann, J. J. Organomet. Chem. 1997, 541, 199.
(f) Larkin, S. A.; Golden, J. T.; Shapiro, P. J.; Yap, G. P. A.; Foo, D.
M. J.; Rheingold, A. L. Organometallics 1996, 15, 2393. (g) Reetz,
M. T.; Willuhn, M.; Psiorz, C.; Goodard, R. J. Chem. Soc., Chem.
Commun. 1999, 1105. (h) Ashe, A. J.; Fang, X.-G.; Kampf, J. W.
Organometallics 1999, 18, 2288. (i) Stelck, D. S.; Shapiro, P. J.;
Basickes, N.; Rheingold, A. L. Organometallics 1997, 16, 4546.
(4) For lead references to nucleophile-functionalized metallocene com-
plexes, see: (a) Jutzi, P.; Redeker, T. Eur. J. Inorg. Chem. 1998, 6,
663. (b) Lehmus, P.; Kokko, E.; Harkki, O.; Leino, R.; Luttikhedde,
H. J. G.; Na¨sman, J. H.; Seppa¨la¨, J. V. Macromolecules 1999, 32,
3547. (c) Alt, H. G.; Jung, M. J. Organomet. Chem. 1998, 568, 127.
(d) Alt, H. G.; Fottinger, K.; Milius, W. J. Organomet. Chem. 1998,
564, 109. (e) Shin, J. H.; Hascall, T.; Parkin, G. Organometallics 1999,
18, 6.
(5) Deck, P. A.; Fisher, T. S.; Downey, J. S. Organometallics 1997, 16,
1193.
(6) Lofthus, O. W.; Slebodnick, C.; Deck, P. A. Organometallics 1999,
18, 3702.
(7) (a) Suzuki, N.; Asami, H.; Nakamura, T.; Huhn, T.; Fukuoka, A.;
Ichikawa, M.; Saburi, M.; Wakatsuki, Y. Chem. Lett. 1999, 4, 341.
(b) Abbenhuis, H. C. L. Angew. Chem., Int. Ed. 1999, 38, 1058. (c)
Arai, T.; Ban, H. T.; Uozumi, T.; Soga, K. J. Polym. Sci., Part A:
Polym. Chem. 1998, 36, 421.
(8) Lund, E. C.; Livinghouse, T. Organometallics 1990, 9, 2426.
10.1021/ic991461s CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/22/2000

4922 Inorganic Chemistry, Vol. 39, No. 21, 2000
Cheng et al.
experiments were carried out in J-Young resealable tubes. Elemental
analyses were performed by Desert Analytics (Tucson, AZ).
1.21 ppm, but instead we observed a broad signal at 1.02 ppm, which
we have tentatively assigned to Me2BCl.11 Because the initial reaction
was limiting in BCl3, we surmise that the byproduct MeBCl2 reacted
further with 1 to afford Me2BCl. Then, excess BCl3 was condensed
into the tube. After 10 min, all of the remaining substrate (1) had reacted
to produce the product (2). A broad signal at 1.21 ppm (br s, 3 H,
CH3) was tentatively assigned to the byproduct MeBCl2. No significant
Synthesis of (η5-Me3SnC5H4)(η5-C5H5)ZrCl2 (1). A suspension of
CpZrCl3‚DME (1.76 g, 5.0 mmol) and 5,5-C5H4(SnMe3)2 (1.96 g, 5.0
mmol) in 30 mL of toluene was stirred under reflux for 15 h. The
resulting yellow solution was evaporated, and the yellow residue was
recrystallized from hexane/tetrahydrofuran (THF) to obtain 1.13 g (2.5
mmol, 50%) of light golden plates in two crops. An otherwise identical
procedure using CpZrCl3 (1.31 g, 5.0 mmol) as the starting material
afforded 1.77 g (3.9 mmol, 78%) of 1. 1H NMR (CDCl3): δ 6.70 (m,
2 H, C5H4), 6.58 (m, 2 H, C5H4), 6.44 (s, 5 H, C5H5), 0.33 (s, 9 H,
SnMe3). 13C NMR (CDCl3): δ 127.1 (CH), 116.9 (CH), 116.1 (C),
115.8 (CH), -7.6 (CH3). Anal. Calcd for C13H18Cl2SnZr: C, 34.31;
H, 3.99. Found: C, 34.52; H, 3.93.
1
change was subsequently observed in the H NMR spectrum after 1
week at 25 °C.
NMR-Scale Reaction of 1 with BBr3. Under a nitrogen counter-
stream, about 0.1 mL of BBr3 was transferred to a 10-mg sample of 1
dissolved in about 0.7 mL of CDCl3 in a J-Young NMR tube. The
1
tube was sealed and shaken vigorously to mix its contents. The H
NMR spectrum obtained after 10 min showed that all of the starting
complex (1) had reacted, and a new complex (3) with signals at 6.85
(m, 2 H, C5H4), 6.60 (m, 2 H, C5H4), 6.55 (s, 5 H, C5H5), and 1.10
ppm (s, 6 H, SnMe2) had appeared, along with a byproduct that we
assigned to MeBBr2 based on one broad signal at 1.42 ppm.11 After 8
h, about three-fourths of the intermediate (3) was consumed, and new
signals at 7.01 (m, 2 H, C5H4), 6.64 (m, 2 H, C5H4), 6.61 (s, 5 H,
C5H5), and 1.70 ppm (s, 3 H, CH3) were assigned to the methyldibro-
mostannylated complex (4). Re-examination of the initial spectrum
showed that this complex was already present in a small amount after
only 10 min. After 15 h (total reaction time), nearly all of the remaining
intermediate (3) had been replaced by 4, with a concomitant increase
in the intensity of the MeBBr2 signal at 1.42 ppm. After 4 additional
days, only 4 was observed.
Synthesis of (η5-ClMe2SnC5H4)(η5-C5H5)ZrCl2 (2). A solution of
1 (0.50 g, 1.1 mmol) and BCl3 (10 mL, 1.0 M in CH2Cl2) in 15 mL of
CH2Cl2 (including 10 mL of solvent from the BCl3 solution) was stirred
at 25 °C for 10 min. The volatile components were then evaporated.
Recrystallization of the residue from hexane/toluene afforded 0.43 g
(0.90 mmol, 82%) of silver-gray plates in two crops. 1H NMR
(CDCl3): δ 6.73 (m, 2 H, C5H4), 6.63 (m, 2 H, C5H4), 6.49 (s, 5 H,
C5H5), 0.95 (s, 6 H, SnMe2). 13C NMR (CDCl3): δ 130.6 (C), 124.9
(CH), 116.4 (CH), 115.8 (CH), 0.5 (CH3). Anal. Calcd for C12H15Cl3-
SnZr: C, 30.31; H, 3.18. Found: C, 30.65; H, 3.04.
Synthesis of (η5-BrMe2SnC5H4)(η5-C5H5)ZrBr2 (3). A solution of
1 (0.50 g, 1.1 mmol) and BBr3 (2 mL, 21 mmol) in 10 mL of CH2Cl2
was stirred at 25 °C for 10 min, and then the volatile components were
evaporated. Recrystallization of the residue from hexane/toluene
afforded 0.57 g (0.94 mmol, 85%) of light green-yellow plates in two
crops. An otherwise identical procedure using 2 (0.30 g, 0.63 mmol)
NMR-Scale Reaction of 1 with I2. Under a nitrogen counterstream,
a small crystal of iodine was added to a 10-mg sample of 1 dissolved
in about 0.7 mL of CDCl3 in a J-Young NMR tube. The NMR tube
1
1
was sealed and shaken vigorously to mix its contents. The H NMR
as the starting material afforded 0.31 g (0.51 mmol, 82%) of 3. H
spectrum obtained after 10 min showed a partial conversion of 1 to a
single product assigned to 5 with signals at 6.72 (m, 2 H, C5H4), 6.61
(m, 2 H, C5H4), 6.49 (s, 5 H, C5H5), and 1.17 ppm (s, 6 H, SnMe2),
along with a byproduct that we assigned to CH3I based on a sharp
signal at 2.16 ppm (s, 3 H, CH3). The spectrum obtained after 1 day
showed complete conversion of 1 to 5, with a concomitant increase in
the CH3I signal.
NMR-Scale Reaction of 1 with ICl. In a nitrogen glovebox, 0.2
mL of a CDCl3 solution containing excess ICl was added to a 10-mg
sample of 1 dissolved in about 0.5 mL of CDCl3 in a J-Young NMR
tube. The tube was sealed and shaken vigorously to mix its contents.
The 1H NMR spectrum obtained after 10 min showed that ap-
proximately 80% of 1 had been converted to 2. A strong signal arising
from the byproduct CH3I was also observed. Neither 5 nor CH3Cl was
detected.
NMR (CDCl3): δ 6.85 (m, 2 H, C5H4), 6.60 (m, 2 H, C5H4), 6.55 (s,
5 H, C5H5), 1.10 (s, 6 H, SnMe2). 13C NMR (CDCl3): δ 129.0 (C),
125.5 (CH), 116.2 (CH), 115.3 (CH), 1.5 (CH3). Anal. Calcd for C12H15-
Br3SnZr: C, 23.67; H, 2.48. Found: C, 23.47; H, 2.40.
Synthesis of (η5-Br2MeSnC5H4)(η5-C5H5)ZrBr2 (4). A solution of
1 (0.30 g, 0.66 mmol) and BBr3 (2 mL) in CH2Cl2 (10 mL) was stirred
at 25 °C for 15 h. The volatile components were then evaporated.
Recrystallization of the brown residue from hexane/toluene afforded
0.29 g (0.43 mmol, 66%) of green-yellow plates. An otherwise identical
procedure using 2 (0.23 g, 0.47 mmol) as the starting material afforded
1
0.22 g (0.32 mmol, 68%) of 4. H NMR (CDCl3): δ 7.01 (m, 2 H,
C5H4), 6.64 (m, 2 H, C5H4), 6.61 (s, 5 H, C5H5), 1.70 (s, 3 H, SnCH3).
13C NMR (CDCl3): δ 126.6 (CH), 125.7 (C), 116.5 (CH), 114.3 (CH),
12.0 (CH3). Anal. Calcd for C11H12Br4SnZr: C, 19.61; H, 1.80.
Found: C, 19.80; H, 1.64.
NMR-Scale Reaction of 1 with CpZrCl3. A J-Young NMR tube
was charged with 4.6 mg (0.010 mmol) of 1 and 2.6 mg (0.010 mmol)
of CpZrCl3. Toluene (about 1 mL) was added, and the tube was sealed
and placed into an oil bath maintained at 100 °C. After 15 h, the toluene
was evaporated, and about 1 mL of CDCl3 was condensed into the
Synthesis of (η5-IMe2SnC5H4)(η5-C5H5)ZrCl2 (5). A solution of 1
(0.30 g, 0.66 mmol) and I2 (0.84 g, 3.3 mmol) in 10 mL of CH2Cl2
was stirred at 25 °C for 15 h. The volatile components were evaporated,
including most of the excess iodine. Recrystallization of the residue
from hexanes/toluene afforded dark red needles. Washing with hexanes
and drying under vacuum afforded 0.18 g (0.32 mmol, 48%) of a pale
1
tube. According to H NMR analysis, the resulting mixture contained
1, 2, and Cp2ZrCl2 in a ratio of approximately 3:1:5, respectively.
NMR-Scale Reaction of 1 with ZrCl4. A J-Young NMR tube was
charged with 4.6 mg (0.010 mmol) of 1 and 2.3 mg (0.010 mmol) of
ZrCl4. Toluene (about 1 mL) was added, and the tube was sealed and
placed into an oil bath maintained at 100 °C. After 15 h, the toluene
was evaporated, and about 1 mL of CDCl3 was condensed into the
1
yellow crystalline solid. H NMR (CDCl3): δ 6.72 (m, 2 H, C5H4),
6.61 (m, 2 H, C5H4), 6.49 (s, 5 H, C5H5), 1.17 (s, 6 H, SnMe2). 13C
NMR (CDCl3): δ 127.9 (C), 125.4 (CH), 116.3 (CH), 115.5 (CH), 0.8
(CH3). Anal. Calcd for C12H15Cl2ISnZr: C, 25.42; H, 2.67. Found: C,
25.71; H, 2.65.
NMR-Scale Reaction of 1 with BCl3. A small amount of BCl3 was
vacuum-transferred from a 1.0 M hexanes solution (Aldrich) to a 10-
mg sample of 1 in about 0.7 mL of CDCl3 in a J-Young NMR tube.
The NMR tube was then refilled with argon, sealed, and shaken
1
tube. The resulting H NMR spectrum revealed a complex mixture of
unidentified products; however, neither the unreacted starting material
(1) nor the chlorodemethylated complex (2) was observed.
Crystal Structures. Crystals of 2 were obtained by slow evaporation
of a 2:1 hexanes/toluene solution under air in a refrigerator at 5 °C.
1
vigorously to mix its contents. The H NMR spectrum obtained after
20 min showed a new set of signals assigned to 2 at 7.01 (m, 2 H,
C5H4), 6.64 (m, 2 H, C5H4), 6.61 (s, 5 H, C5H5), and 1.70 ppm (s, 6 H,
SnMe2). A signal arising from the byproduct MeBCl2 was expected at
(11) (a) No¨th, H.; Vahrenkamp, H. J. Organomet. Chem. 1968, 281, 23.
The chemical shifts reported were -1.00 ppm for Me2BCl, -1.21
ppm for MeBCl2, -1.14 ppm for Me2BBr, and -1.42 ppm for
MeBBr2, relative to TMS in CCl4. We believe that the correct chemical
shifts are +1.00, +1.21, +1.14, and +1.42 ppm in current shift
notation. This interpretation is supported by data for neat Me2BCl (τ
) 9.34) and neat MeBCl2 (τ ) 8.88); see: (b) de Moor, J. E.; van der
Kelen, G. P. J. Organomet. Chem. 1966, 6, 235.
(9) Pribytkova, I. M.; Kisin, A. V.; Luzikov, Yu. N.; Makoveyeva, N. P.;
Torocheshnikov, V. N.; Ustynyuk, Yu. A. J. Organomet. Chem. 1971,
30, C57.
(10) Grishin, Yu. A.; Luzikov, Yu. N.; Ustynyuk, Yu. A. Dokl. Akad. Nauk
SSSR 1974, 216, 321.

Reactions of Trimethylstannylzirconocene
Inorganic Chemistry, Vol. 39, No. 21, 2000 4923
Table 1. Crystallographic Data
2‚1/2(toluene)
toluene gave useful yields of 1. The adduct CpZrCl3‚DME reacts
much more slowly than CpZrCl3 with (SnMe3)2C5H4, probably
because the DME ligand decreases the electrophilicity of the
zirconium center. The complex (1) is ostensibly the first
stannylated zirconocene dichloride complex.
4‚THF
chemical formula C12H15Cl3SnZr‚2C7H8 C11H12Br4SnZr‚C4H8O
a (Å)
b (Å)
c (Å)
21.6517(15)
12.8720(10)
14.1878(9)
103.389(5)
3846.7(5)
8
20.6230(2)
8.3330(2)
11.9970(4)
102.5120(10)
2012.74(9)
4
Two byproducts, Cp2ZrCl2 and 2, were observed in the
reaction of CpZrCl3 and (SnMe3)2C5H4. The amounts of these
byproducts varied widely but were usually less than 10%,
although in one reaction 2 was the major product. We suspected
that Cp2ZrCl2 might arise from the reaction of (Me3SnC5H4)-
CpZrCl2 (1) with HCl, generated in situ via hydrolysis of
CpZrCl3 by adventitious moisture. This hypothesis was tested
using an NMR-scale experiment in which purified 1 was treated
directly with HCl to afford Cp2ZrCl2 and Me3SnCl (eq 1)
according to 1H NMR analysis. Stannylated aromatic compounds
often undergo electrophilic destannylation under similar condi-
tions.15 We suspected that 1 might undergo a Zr-Cl/Sn-Me
metathesis reaction with ZrCl4, a possible impurity in CpZrCl3.
A reaction of 1 with ZrCl4 in an NMR tube revealed a complex
mixture of several products, from which both the starting
material (1) and the chlorodemethylated complex (2) were absent
â (deg)
V (Å)3
Z
formula weight
space group
T (K)
521.57
C2/c
293(5)
0.71073
1.801
2.247
0.0384
0.0779
745.84
P21/c
100(2)
λ (Mo KR) (Å)
0.71073
2.461
a
F
calc (mg m-3
)
µ (mm-1
)
9.698
0.0484
0.1189
Rb
Rw [I > 2σ(I)]c
a Experimental crystal densities (Fobsd) were not obtained. b R )
∑||Fo| - |Fc||/∑|Fo|, observed data (>2σ(Io)). c Rw ) [∑[w(Fo2 - Fc2)2]/
2
∑[w(Fo )2]]2, all data.
Scheme 1
1
according to H NMR analysis. We also carried out an NMR-
tube reaction of purified 1 with 1 equiv of CpZrCl3 (eq 2) and
observed a significant amount of 2. Thus, the formation of 2
during the reaction of CpZrCl3 and (SnMe3)2C5H4 apparently
results from a further reaction of the desired product (1) with
unreacted CpZrCl3.
(2)
Crystals of 4 were grown from a 1:1 hexanes/THF solution by slow
evaporation in a refrigerator at 5 °C under air. Details of the
crystallographic experiments, data collection, and refinement are
contained in Table 1. Complete tables of crystal data, positional and
thermal parameters, bond distances, and bond angles are included in
the Supporting Information.
Electrophilic Halogenation Reactions. As shown in Scheme
1, the stannylated substrate (1) underwent rapid chlorodem-
ethylation with boron trichloride at 25 °C to afford the
corresponding chlorodimethylstannylated complex (2) in 82%
yield. When we followed the progress of this reaction in an
NMR tube-scale reaction using excess BCl3, the signals of 1
were absent after 10 min at 25 °C and were replaced by signals
assigned to 2. The product (2) complex can withstand exposure
to air for several days with negligible decomposition.
We next explored the reactions of 1 and 2 with BBr3 (Scheme
1). In NMR-scale reactions in CDCl3 at 25 °C, excess BBr3
converted both 1 and 2 to a common intermediate within 10
min. We assigned the observed spectrum to the tribrominated
species (3). This interpretation means that both tin and zirconium
undergo rapid transhalogenation. The propensity of the tin center
toward exchange is consistent with the ease of chlorodemethy-
lation of 1 using BCl3 discussed above, and transhalogenation
Results
Synthesis of Trimethylstannylzirconocene Dichloride. The
usual anionic ligand-substitution routes to metallocene com-
plexes such as 1 are closed, because trimethylstannylcyclopen-
tadiene reacts with bases such as n-butyllithium or sodium
hydride to afford products in which the Cp-Sn bond is
cleaved.12 Churakov and Kuz’mina prepared (Me3SnC5H4)TiCl3
using an alternative, the chlorotrimethylstannane-elimination
reaction of TiCl4 and (Me3Sn)2C5H4 at 25 °C.13 We adopted
this approach to prepare our desired substrate (1) from
(SnMe3)2C5H4 and CpZrCl3 (Scheme 1). However, neither
CpZrCl3 nor CpZrCl3‚DME reacted with (Me3Sn)2C5H4 at 25
°C, possibly because of the lower reactivity of the zirconium
half-metallocene complexes14 or because neither is soluble in
the reaction solvent (toluene). Extended reactions at 110 °C in
(14) (a) Winter, C. H.; Zhou, X.-X.; Dobbs, D. A.; Heeg, M. J. Organo-
metallics 1991, 10, 210. (b) Ciruelos, S.; Cuenca, T.; Gomez-Sal, P.;
Manzanero, A.; Royo, P. Organometallics 1995, 14, 177.
(15) Eaborn, C.; Jenkins, I. D.; Walton, D. R. M. J. Chem. Soc., Perkin
Trans. 2 1974, 596.
(12) Ko¨hler, F. H.; Geike, W. A.; Hertkorn, N. J. Organomet. Chem. 1987,
334, 359.
(13) Churakov, A. V.; Kuz’mina, L. G. Acta Crystallogr. 1996, C52, 3037.

4924 Inorganic Chemistry, Vol. 39, No. 21, 2000
Cheng et al.
Scheme 2
2
1
Table 2. JSnH and JSnC Coupling Constants for
Alkylhalostannanesa
2J (Hz)
1J (Hz)
entry complex 119Sn-1H 117Sn-1H 119Sn-13C 117Sn-13C
1
2
3
4
5
6
7
8
9
1
2
3
4
57.5
67.4
66.9
84.8
65.6
54.3b
58.5b
58.5b
66.0b
89.0b
54.8
64.6
63.7
81.1
62.8
52.0b
56.0b
56.0b
63.5b
85.0b
374
471
459
584
435
338c,d
379c
365c
460e
f
358
451
439
558
415
323c,d
365c
349c
420e
f
Figure 1. Thermal ellipsoid plot of 2 shown at 50% probability.
Hydrogen atoms and disordered toluene solvent molecule omitted.
Selected bond distances (Å) and angles (deg): Zr-Cl(1), 2.442(1); Zr-
Cl(2), 2.470(1); Zr-Cp(1), 2.193(6); Zr-Cp(2), 2.193(6); Cl(1)-Zr-
Cl(2), 95.3(4); Cp(1)-Zr-Cp(2), 129.6(4); Sn-Cl(3), 2.401(2); Sn-
C(6), 2.135(4); Sn-C(11), 2.115(5); Sn-C(12), 2.105(4); Cl(3)-Sn-
C(6), 97.8(1); Cl(3)-Sn-C(11), 103.8(2); Cl(3)-Sn-C(12), 103.5(2);
C(6)-Sn-C(11), 110.5(2); C(6)-Sn-C(12), 116.0(2); C(11)-Sn-
C(12), 121.2(2); Cl(3)-Sn-C(6)-C(7), 110.1(3) (torsion). Cp(1) is
the centroid of C(1), C(2), C(3), C(4), and C(5). Cp(2) is the centroid
of C(6), C(7), C(8), C(9), and C(10).
5
Me4Sn
Me3SnCl
Me3SnBr
Me2SnBr2
MeSnBr3
10
a Data for 1-5 were determined from spectral satellite positions.
b Data obtained in CDCl3 solution (ref 17). c Data obtained in CDCl3
solution (ref 18). d Data reported only for 119Sn. Estimated from
J(117Sn-13C) ) J(119Sn-13C)δ(117Sn)/δ(119Sn). e Estimated from a
single, averaged coupling constant (J ) 440 Hz) obtained in CH2Cl2
(ref 19). f No reported values found.
data with similar compounds reported elsewhere.17-19 Com-
parison of entries 2, 3, and 5 and comparison of entries 7 and
8 suggest that 2JSnH is relatively insensitive to the identity of
1
the halide, although a periodic trend toward decreasing JSnC
with the heavier halides is observed. Pairwise comparisons of
entries 1 and 8, 3 and 9, and 4 and 10 suggest that the
zirconocene dihalide moiety has an electronic effect similar to
that of bromide on the tin atom.
of the ZrCl2 moiety is also already known to be rapid under
these conditions.16 The signals assigned to 3 subsequently
disappeared over about 15 h at 25 °C and were replaced by an
additional set of signals assigned to the methyldibromostanny-
lated complex (4). By control of reaction times, preparative
reactions of 1 with BBr3 afforded either 3 (85% yield) or 4
(68% yield). A reaction of the substrate (1) with BBr3 in
chlorobenzene at 140 °C for 15 h failed to produce any of the
Crystal Structures of 2 and 4. Crystal data for 2 are
presented in Table 1. The unit cell contains a planar region of
electron density that presumably resulted from a badly disor-
dered toluene molecule and was modeled accordingly. Relatively
precise metric parameters were obtained nevertheless. Although
the structure of 2 (Figure 1) is not remarkable, inasmuch as 2
is the first structurally characterized stannylated zirconocene
dichloride complex, we wish to comment on the major features
of its structure. In an analogous complex, (Me3SiC5H4)2ZrCl2,20
the Cp-Zr distances were 2.199 and 2.209 Å, the Cp-Cl
distances were 2.476 and 2.505 Å, the Cp-Zr-Cl angle was
129.1°, and the Cl-Zr-Cl angle was 93.7°. Data presented in
Figure 1 for the metallocene “core” of 2 are nearly identical.
The Cp(ipso carbon)-Sn distance of 2 was 2.135(4) Å, which
is somewhat shorter than the corresponding distance of 2.169
Å observed in (Me3SnC5H4)TiCl3.13 The distorted tetrahedral
structure about Sn in 2 is typical of tetrahedral Sn compounds
having one chloride and three hydrocarbyl ligands. Of 41 such
Sn atoms in the Cambridge Crystallographic Database, the
median Cl-Sn-C angle was 101° (range, 91-108°), whereas
the median C-Sn-C angle was 116° (range, 104-128°).
1
anticipated Br3Sn-substituted complex, as determined by H
NMR analysis. Like the chlorodimethylstannylated complex (2),
complexes 3 and 4 withstand exposure to air for several days
without significant decomposition or hydrolysis.
We next investigated two iodinolysis reactions (Scheme 2).
In an NMR-scale reaction of 1 and excess I2 (CDCl3 solvent),
the signals assigned to 1 disappeared over about 1 day, whereas
new signals assigned to 5 and to the byproduct CH3I were
observed. When the reaction was carried out on a preparative
scale in CH2Cl2, a 48% yield of 5 was obtained. The reaction
of 1 with ICl was more rapid, proceeding quantitatively to 2
1
and CH3I after 10 min, according to H NMR analysis of a
reaction carried out in an NMR tube in CDCl3 solution. Because
this reaction did not afford different metallocene products, we
did not investigate it further on a preparative scale.
NMR Studies. The Sn-CH3 groups of the starting complex
(1) and the products (2, 3, 4, and 5) showed clear tin satellites
(17) van den Berghe, E. V.; van der Kelen, G. P. J. Organomet. Chem.
1966, 6, 575.
(18) Singh, G. J. Organomet. Chem. 1975, 99, 251.
(19) Mitchell, T. N. J. Organomet. Chem. 1973, 59, 189.
(20) Antinolo, A.; Lappert, M. F.; Singh, A.; Winterborn, D. J. W.;
Engelhardt, L. M.; Raston, C. L.; White, A. H.; Carty, A. J.; Taylor,
N. J. J. Chem. Soc., Dalton Trans. 1987, 1463.
1
in both the H and 13C NMR spectra. Table 2 compares these
(16) (a) Druce, P. M.; Kingston, B. M.; Lappert, M. F.; Spalding, T. R. S.;
Srivastava, R. C. J. Chem. Soc. A 1969, 2106. (b) Gassman, P. G.;
Winter, C. H. Organometallics, 1991, 10, 1592.

Reactions of Trimethylstannylzirconocene
Inorganic Chemistry, Vol. 39, No. 21, 2000 4925
Figure 3. Histogram plot of Sn-O distances (<2.7 Å) for trigonal
bipyramidal complexes having the general formula SnO(CH3)nX4-n, n
) 1-3, X ) Cl, Br, or I. Data obtained from the Cambridge
Crystallographic Data Centre.
Sn-O bond was part of a ring were excluded. A histogram plot
(Figure 3) for the resulting 72 structures shows the typical range
of Sn-O distances, and in this context, the Sn-O distance in
4‚THF is indeed long.
Discussion
General Comparisons of Tin and Silicon. Although tin and
silicon are formally valence-isoelectronic, many differences are
exhibited in the structure and reactivity of their respective
compounds. Tin has a larger sp3 covalent radius (1.40 Å) than
silicon (1.18 Å).26 The radial distributions of the Sn(5s) and
Sn(5p) orbitals are more diffuse than those of the Si(3s) and
Si(3p) orbitals, as reflected in the following: the lower first
ionization energy of Sn (708.2 kJ/mol) versus that of Si (786.3
kJ/mol), the higher polarizability of Sn (7.7 ( 25%) compared
to that of Si (5.38 ( 2%),27 lower homogeneous dissociation
energies of Sn-C bonds (69.3 kcal/mol for (CH3)3Sn-CH3)
compared to those of Si-C bonds (89.8 kcal/mol for (CH3)3-
Si-CH3),28 and the lower first ionization potential of Sn(CH3)4
(9.65 eV) versus that of Si(CH3)4 (10.23 eV).29
Reactivity of Si-Me versus Sn-Me Bonds toward Elec-
trophiles. The differences noted above are borne out in the
increased susceptibility of Sn-CH3 bonds toward Lewis acidic
cleavage relative to Si-CH3 bonds30 and are demonstrated
strikingly in the reactivities of the trimethylstannylated complex
(1) compared to those of trimethylsilylated analogues. Only
about 30% of one SiMe3 group on (Me3SiCp)2ZrCl2 was
converted into a chlorodimethylsilyl group (SiMe2Cl) upon
reaction with BCl3 at 100 °C for 2 days,6 whereas the conversion
of the single SnMe3 group of 1 to a SnMe2Cl group was
completed in a few minutes at 25 °C upon treatment with BCl3.
Despite the apparently high reactivity of the Me-Sn bonds, the
SnMe2Cl substituent did not undergo further substitution at 25
°C. However, as BBr3 is a stronger Lewis acid than BCl3,31 it
was reasonable (in hindsight) to discover that BBr3 could react
Figure 2. Thermal ellipsoid plot of 4‚THF shown at 50% probability.
Hydrogen atoms omitted. Selected bond distances (Å) and angles
(deg): Zr-Br(1), 2.6178(5); Zr-Br(2), 2.6001(5); Zr-Cp(1), 2.208-
(4); Zr-Cp(2), 2.197(4); Br(1)-Zr-Br(2), 95.23(2); Cp(1)-Zr-Cp-
(2), 128.7(1); Sn-Br(3), 2.5534(5); Sn-Br(4), 2.5139(5); Sn-C(1),
2.113(4); Sn-C(6), 2.111(5); Sn-O(1), 2.655(5); Br(3)-Sn-Br(4),
95.77(2); Br(3)-Sn-C(1), 100.1(1); Br(3)-Sn-C(1), 102.1(2); Br-
(3)-Sn-O(1), 178.5(2); Br(4)-Sn-C(1), 106.0(1); Br(4)-Sn-C(6),
108.0(1); Br(4)-Sn-O(1), 83.1(2); C(1)-Sn-C(6), 136.9(2); C(1)-
Sn-O(1), 79.4(2); C(6)-Sn-O(1), 79.3(2); Br(3)-Sn-C(1)-C(2),
-148.0(3) (torsion). Cp(1) is the centroid of C(1), C(2), C(3), C(4),
and C(5). Cp(2) is the centroid of C(7), C(8), C(9), C(10), and C(11).
Crystal data for 4‚THF are presented in Table 1. The lattice
THF molecule is associated with the tin atom (Figure 2), such
that the coordination environment about Sn is pseudo-trigonal-
bipyramidal (tbp), with the THF oxygen and one bromide ligand
in pseudoaxial positions and the Cp, methyl, and second bromide
ligands in the pseudoequatorial plane. The distortion from ideal
tbp geometry is evident in the displacement of the Sn from the
equatorial plane by 0.37 Å away from the weakly bound, neutral
oxygen ligand. The rest of the metallocene “core” exhibits
bonding geometries that are completely consistent with other
unbridged zirconocene dibromide complexes that have been
crystallographically characterized.20-22
The Sn-O distance in 4‚THF is rather long in comparison
to those observed in analogous structures selected from the
Cambridge Structural Database (CSD), such as ArCl3Sn‚THF
(2.357 Å),23 ArCl2MeSn‚DMSO (2.294 Å),24 and Br3MeSn‚
DMF (2.269 Å).25 We searched the Cambridge Structural
Database for tin atoms ligated by 1-3 halogens, 1-3 hydro-
carbyl groups, and exactly one oxygen. Compounds in which
either the tin or oxygen atoms were bridging or in which the
(26) Huheey, J. E.; Keiter, E. A.; Keiter, R. L. In Inorganic Chemistry,
Principles of Structures and Chemistry, 4th ed.; HarperCollins College
Publishers: New York, 1993; p 292.
(27) CRC Handbook of Chemistry and Physics, 78th ed.; Lide, D. R. et
al., Eds.; CRC Press: New York, 1997; pp 10-201.
(28) Jackson, R. A. J. Organomet. Chem. 1979, 166, 17.
(29) Aoyama, M.; Masude, S.; Ohno, K.; Harada, Y.; Yew, M. C. J. Phys.
Chem. 1989, 93, 1800.
(30) (a) Eaborn, C.; Pande, K. C. J. Chem. Soc. 1960, 1566. (b) Ponamarev,
S. V.; Machigin, E. V.; Lutsenko, I. F. Zh. Obshch. Khim. 1966, 36,
548. (c) Seyferth, D. Prog. Inorg. Chem. 1962, 3, 129.
(31) (a) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th
ed.; Wiley: New York, 1988; p 172. (b) Bowmaker, G. A.; Boyd, P.
D. W.; Sorrenson, R. J. J. Chem. Soc., Faraday Trans. 2 1985, 81,
1023.
(21) Petoff, J. L. M.; Bruce, M. D.; Waymouth, R. M.; Masood, A.; Lal,
T. K.; Quan, R. W.; Behrend, S. J. Organometallics 1997, 16, 5909.
(22) Buhl, M.; Hopp, G.; von Philipsborn, W.; Beck, S.; Prosenc, M.-H.;
Rief, U.; Brintzinger, H.-H. Organometallics 1996, 15, 778.
(23) Leonhardt, T.; Latscha, H. P. Z. Naturforsch., B 1997, 52, 25.
(24) Krishnamurti, R.; Kuivila, H. G.; Shaik, N. S.; Zubieta, J. Organo-
metallics 1991, 10, 423.
(25) Aslanov, L. A.; Ionov, V. M.; Attiya, V. M.; Permin, A. B.; Petrosyan,
V. S. Zh. Strukt. Khim. 1978, 19, 315.

4926 Inorganic Chemistry, Vol. 39, No. 21, 2000
Cheng et al.
Scheme 3
cleavage toward electrophiles such as BCl3.33 I2 and ICl also
cleave the Sn-Ar bonds of stannylated aromatic complexes to
produce iodoarenes.34 In the present study, only HCl cleaves
the Cp-Sn bond, whereas all the other electrophilic reagents
(BCl3, BBr3, I2, and ICl) cleave the Sn-Me bond of the
stannylated zirconocene dichloride complex. At first glance, it
appears that the electron-rich ferrocenes favor ring-substitution
processes, possibly by d-electron stabilization of a putative
Meisenheimer-type intermediate, whereas the group 4 systems,
which have no d-electrons, forbid Cp-E cleavage and allow
the slower E-Me cleavage process to be observed by default.
However, preliminary observations in a separate, ongoing study
have suggested that Me3Si-substituted cobaltocenium hexafluo-
rophosphates, which are isoelectronic with the ferrocenes,
undergo neither Cp-Si nor Si-Me cleavage when treated with
BBr3, even at 80 °C for several hours in CDCl3.
further to form the MeBr2Sn-substituted zirconocene complex
(4). In contrast, only one methyl group of the SiMe3 substituent
of (Me3SiC5H4)(Cp)ZrCl2 was replaced by bromine upon
reaction with BBr3 at 65 °C for 2 days.5,6
Conclusions
Reactivity of Si-X versus Sn-X bonds toward Nucleo-
philes. An interesting trend in the nucleophilic susceptibility
of E-X bonds (E ) Si, Sn and X ) Cl, Br, I) is also
demonstrated here. Whereas 2 is stable to air (ambient moisture)
for several days, complexes bearing BrMe2Si groups undergo
rapid hydrolysis in air to afford tetramethyldisiloxane linkages,3b-d
presumably via hydrolysis of the Si-Br bonds to form an
intermediate disilanol, which undergoes subsequent condensation
(discharged water is observed).6 Although tin halides are
susceptible to hydrolysis, the complexes reported here (2, 3, 4,
and 5) appear unusually unreactive in this respect. However,
the propensity for tin halides to form adducts with nucleophiles
is clearly demonstrated in the observed formation of a crystalline
THF adduct of 4, which retained the coordinated solvent for
more than a day in the absence of mother liquors prior to
crystallographic analysis.
Reactivity of Cp-E versus E-Me Bonds toward Elec-
trophiles. Periodic trends are emerging in the relative reactivities
(Scheme 3) of the Cp-E and E-Me bonds as a function of the
coordinated transition metal (M), the group 14 element (E), and
the reacting electrophile (AX). We showed earlier that Me3Si-
substituted ferrocenes undergo rapid cleavage of the Cp-Si bond
upon treatment with BCl3 at low temperature,6 whereas with
Me3Si-substituted zirconocene dichlorides, the Me-Si bonds
are cleaved instead.6 Manners and co-workers showed that Me3-
Sn-substituted ferrocenes are preferentially ortho-borylated by
chloroboranes.32 Corresponding Me3Si- and Me3Sn-substituted
aromatic hydrocarbons undergo rapid Ar-Si and Ar-Sn
The reactivity of a SnMe3 substituent on zirconocene dichlo-
ride toward Lewis acidic halodemethylation using BCl3 or BBr3
is much greater than the corresponding reactivity of the SiMe3
substituent. The SnMe3 group also undergoes selective iodi-
nolysis of a single Sn-CH3 bond. The resulting ClSnMe2-,
BrSnMe2-, ISnMe2-, and MeBr2Sn-substituted complexes are,
in contrast, surprisingly stable toward ambient moisture, con-
sidering the facility of hydrolysis demonstrated previously for
BrMe2Si-substituted complexes.
Acknowledgment. This project was supported by the
National Science Foundation (CHE-9875446) and by the
Research Corporation Cottrell Scholarship (CS0567).
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of 2‚2C6H5CH3 and 4‚
THF. This material is available free of charge via the Internet at
http://pubs.acs.org.
IC991461S
(32) Jakle, F.; Lough, A. J.; Manners, I. J. Chem. Soc., Chem. Commun.
1999, 5, 453.
(33) (a) Gross, U.; Kaufmann, D. Chem. Ber. 1987, 120, 991. (b) Kaufmann,
D. Chem. Ber. 1987, 120, 901. (c) Kaufmann, D. Chem. Ber. 1987,
120, 853.
(34) (a) Eaborn, C.; Najam, A. A.; Walton, D. R. M. J. Chem. Soc., Chem.
Commun. 1972, 840. (b) Eaborn, C.; Najam, A. A.; Walton, D. R. M.
J. Chem. Soc., Perkin Trans. 1 1972, 2481. (c) Yamamoto, Y.; Yanagi,
A. Chem. Pharm. Bull. 1982, 30, 1731. (d) Seitz, D. E.; Lee, S. H.;
Hanson, R. N.; Bottaro, J. C. Synth. Commun. 1983, 13, 121. (e) Lee,
S. H.; Hanson, R. N.; Seitz, D. E. Tetrahedron Lett. 1984, 25, 1751.