Synthesis, structures, and ring-opening polymerization reactions of substituted cyclopentadienyl complexes of zinc

Article abstract of DOI:10.1021/om020690a

The reaction of 2 equiv of the new pyrrole-substituted cyclopentadienyl ligand cyclo-C₄H₄-NSiMe₂C₅ H₅ (2a, Cp^pyH) with Zn[N(SiMe₃)₂]₂ gives the bis(cyclopentadienyl)zinc complex Zn(Cp^py)₂ (3a). The reaction of 2a and the related derivatives cyclo-2,5-Me₂C₄ H₂NSiMe₂C₅H₅ (2b, Cp^pymeH) and 3,5-Me₂C₆H₃ CH₂CMe₂C₅H₅ (2c, Cp^mesH) with dibutylmagnesium gives the corresponding magnesocenes MgCp^R₂ (3a-c). Prolonged heating of the appropriate cyclopentadiene with zinc dialkyls in toluene, or alternatively stirring with [XZnN(SiMe₃)₂]₂ in toluene at 40°C for 1 h, gives the monocyclopentadienyl zinc alkyl complexes Cp^RZnX (6a, Cp^R = Cp^py, X = Me; 6c, Cp^R = Cp^mes, X = Me; 7a, Cp^R = Cp^py, X = Et; 7c, Cp^R = Cp^mes, X = Et), which provide spectroscopic evidence for a Zn...(hetero)arene interaction. Addition of tetramethylethylenediamine (TMEDA) gives Cp^RZnX(TMEDA) (8a, b, X = Me; 9a-c, X = Et). The crystal structures of 8b and 9c show η²-bound cyclopentadienyl ligands, with one long and one short Zn-C interaction. The reaction of 7c with B(C₆F₅)₃ in toluene proceeds with alkyl/C₆F₅ exchange to give Cp^mes Zn(C₆F₅) (10). Treatment of 9c with B(C₆F₅)₃ in toluene results in an ionic product, [Cp^mesZn(TMEDA)]⁺[EtB(C₆ F₅)₃]^- (11). On the other hand, the reaction of 9a with B(C₆F₅)₃ in toluene or dichloromethane proceeds with β-H abstraction, with concomitant loss of ethene, as well as both ethyl and cyclopentadienyl abstraction. Both 11 and 9a/B(C₆ F₅)₃ mixtures catalyze the polymerization of cyclohexene oxide and ε-caprolactone.

Full text of DOI:10.1021/om020690a

Organometallics 2003, 22, 797-803
797
Syn th esis, Str u ctu r es, a n d Rin g-Op en in g P olym er iza tion
Rea ction s of Su bstitu ted Cyclop en ta d ien yl Com p lexes of
Zin c
Dennis A. Walker, Timothy J . Woodman, Mark Schormann,
David L. Hughes, and Manfred Bochmann*
Wolfson Materials and Catalysis Centre, School of Chemical Sciences,
University of East Anglia, Norwich, NR4 7TJ , U.K.
Received August 22, 2002
The reaction of 2 equiv of the new pyrrole-substituted cyclopentadienyl ligand cyclo-C4H4-
NSiMe2C5H5 (2a , CppyH) with Zn[N(SiMe3)2]2 gives the bis(cyclopentadienyl)zinc complex
Zn(Cppy)2 (3a ). The reaction of 2a and the related derivatives cyclo-2,5-Me2C4H2NSiMe2C5H5
(2b, CppymeH) and 3,5-Me2C6H3CH2CMe2C5H5 (2c, CpmesH) with dibutylmagnesium gives
the corresponding magnesocenes MgCpR (3a -c). Prolonged heating of the appropriate
2
cyclopentadiene with zinc dialkyls in toluene, or alternatively stirring with [XZnN(SiMe3)2]2
in toluene at 40 °C for 1 h, gives the monocyclopentadienyl zinc alkyl complexes CpRZnX
(6a , CpR ) Cppy, X ) Me; 6c, CpR ) Cpmes, X ) Me; 7a , CpR ) Cppy, X ) Et; 7c, CpR ) Cpmes
,
X ) Et), which provide spectroscopic evidence for a Zn‚‚‚(hetero)arene interaction. Addition
of tetramethylethylenediamine (TMEDA) gives CpRZnX(TMEDA) (8a , b, X ) Me; 9a -c, X
) Et). The crystal structures of 8b and 9c show η2-bound cyclopentadienyl ligands, with
one long and one short Zn-C interaction. The reaction of 7c with B(C6F5)3 in toluene proceeds
with alkyl/C6F5 exchange to give CpmesZn(C6F5) (10). Treatment of 9c with B(C6F5)3 in toluene
results in an ionic product, [CpmesZn(TMEDA)]+[EtB(C6F5)3]- (11). On the other hand, the
reaction of 9a with B(C6F5)3 in toluene or dichloromethane proceeds with â-H abstraction,
with concomitant loss of ethene, as well as both ethyl and cyclopentadienyl abstraction.
Both 11 and 9a /B(C6F5)3 mixtures catalyze the polymerization of cyclohexene oxide and
ꢀ-caprolactone.
In tr od u ction
stabilized ion pairs, [R2Al(OEt2)2]+[RB(C6F5)3]-, which
have been used as activators in high-temperature alk-
ene polymerizations.6 As we showed recently, zinc
dialkyls behave similarly and rapidly undergo ligand
exchange with B(C6F5)3 in aromatic solvents to give
Zn(C6F5)2(arene), while in ether the ion pairs [RZn-
(OEt2)3]+X- (X ) RB(C6F5)3 or B(C6F5)4, R ) Me, Et,
Whereas the reaction of transition metal alkyls with
B(C6F5)3 is well documented to proceed with alkyl
abstraction to give catalytically active metal complexes,1
main group alkyls tend to react predominantly under
alkyl/C6F5 exchange. A prime example is the synthesis
of Al(C6F5)3 from AlMe3 and B(C6F5)3 in hydrocarbon
solvents.2 Similar exchange reactions are observed
between M(C6F5)3 and MAO (or MMAO) (M ) B, Al)3
and with AlR3 and [Ph3C][B(C6F5)4] (R ) Me, Et and
iBu).4 Mixtures of AlEt3 and B(C6F5)3 exhibit modest
ethene polymerization activity.5 In coordinating solvents
alkyl exchange is suppressed; for example, aluminum
trialkyls and B(C6F5)3 in diethyl ether give solvent-
t
and Bu) are obtained.7 Cationic zinc alkyls have previ-
ously been prepared by the addition of nitrogen macro-
cycles or crown ethers to zinc alkyls in the presence of
AlR3 or tetraphenylcyclopentadiene, to give [RZn-
(crown)]+X- (X ) AlR4, C5HPh4),8 and by the protolysis
of ZnEt2 with the ammonium salt [Bz3TACH]+[PF6]-,
which yields [(Bz3TAC)ZnEt]+[PF6]- (Bz3TAC ) 1,3,5-
tribenzyl-1,3,5-triazacyclohexane).9 The triflate complex
ZnMe(OTf)[H2C2(NtBu)2] is neutral in the solid state but
ionizes in THF or benzene.10
(1) (a) Yang, X.; Stern, C. L. Marks, T. J . J . Am. Chem. Soc. 1991,
113, 3623. (b) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc.
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B.; Malik, K. M. A. Organometallics 1994, 13, 2235. (d) Bochmann,
M. J . Chem. Soc., Dalton Trans. 1996, 255. (e) Luo, L.; Marks, T. J .
Top. Catal. 1999, 7, 97. (f) Bochmann, M. Top. Catal. 1999, 7, 9. (e)
Chen, E. Y. X.; Marks, T. J . Chem. Rev. 2000, 100, 1391.
(2) Biagini, P.; Lugli, G.; Abis, L.; Andeussi, P. (Enichem). U.S.
Patent 5,602,269, 1997.
The coordination of arenes in Zn(C6F5)2(arene) and
the potential of cationic zinc alkyls as catalysts for ring-
(6) Klosin, J .; Roof, G. R.; Chen, E. Y. X.; Abboud, K. A. Organo-
metallics 2000, 19, 4684.
(7) Walker, D. A.; Woodman, T. J .; Hughes, D. L.; Bochmann, M.
Organometallics 2001, 20, 3772.
(3) (a) Chen, E. Y. X.; Kruper, W. J .; Roof, G. (Dow Chemical Co.).
PCT Int. Appl. WO 00 09515. (b) Lee, C. H.; Lee, S. J .; Park, J . W.;
Kim, K. H.; Lee, B. Y.; Oh, J . S. J . Mol. Catal., A: Chem. 1988, 132,
231. (c) Carnahan, E. M.; Chen, E. Y. X.; J acobsen, G. B.; Stevens, J .
C. (Dow Chemical Co.). PCT Int. Appl. WO 99 15534.
(4) Bochmann, M.; Sarsfield, M. J . Organometallics 1998, 17, 5908.
(5) Kim, J . S.; Wojcinski, L. M.; Liu, S.; Sworen, J . C.; Sen, A. J .
Am. Chem. Soc. 2000, 122, 5668.
(8) (a) Fabicon, R. M.; Pajerski, A. D.; Richey, H. G. J . Am. Chem.
Soc. 1991, 113, 6680. (b) Fabicon, R. M.; Parvez, M.; Richey, H. G.
Organometallics 1999, 18, 5163. (c) Tang, H.; Parvez, M.; Richey, H.
G. Organometallics 2000, 19, 4810.
(9) Haufe, M.; Ko¨hn, R. D.; Kociok-Ko¨hn, G.; Filippou, A. C. Inorg.
Chem. Commun. 1998, 1, 263.
(10) Wissing, E.; Kaupp, M.; Boersma, J .; Spek, A. L.; van Koten,
G. Organometallics 1994, 13, 2349.
10.1021/om020690a CCC: $25.00 © 2003 American Chemical Society
Publication on Web 01/18/2003

798 Organometallics, Vol. 22, No. 4, 2003
Walker et al.
Sch em e 1
sensitive but can be stored at -20 °C under nitrogen
with no obvious degradation. Recrystallization from
light petroleum provides analytically pure samples.
The protolysis of zinc dialkyls is less facile. A reaction
between 2a and ZnMe2 in a molar ratio of 1:1 in toluene-
d8 in an NMR tube kept at 90 °C showed that after 2
days all the signals associated with 2a had disappeared
and the solution contained CppyZnMe (6a ), with some
unidentified impurities. All attempts to generate the
zincocene 3a by refluxing excess 2a with ZnMe2 in
toluene failed.
opening polymerization reactions of epoxides and lac-
tones prompted us to investigate whether cationic zinc
species could be stabilized by means of pendant aryl
substituents, to give, for example, ansa-arene-Cp struc-
tures with electron-rich arenes or heteroarenes, as
indicated in Scheme 1. Here we report the synthesis of
new zinc complexes with pendant silylpyrrolyl and 3,5-
dimethylphenylethyl substituents, their reactions with
cation-generating agents, and their reactivity in ring-
opening polymerizations of epoxides and lactones.
An alternative route to 6a involves the reaction of 2a
with MeZnN(SiMe3)2 (5). This has the advantage of
proceeding at much lower temperatures, typically 40 °C
for 1 h. However, repeated attempts generated 6a only
as an impure oil. MeZnN(SiMe3)2 was prepared by
comproportionating equimolar amounts of ZnMe2 and
Zn[N(SiMe3)2]2 in light petroleum. Removal of the
volatiles after ca. 5 min provides a white solid, which
can be sublimed at 0.5 mmHg and 40 °C to give colorless
crystals in high yield. The compound forms an amido-
bridged dimer in the solid state (Figure 3). Although
X-ray crystallography was able to ascertain the overall
geometry, the crystals were of poor quality, and the
structural parameters will not be discussed further.
Following the same procedure as for 6a , CpmesZnMe
(6c) was generated from 2c and either ZnMe2 (toluene-
d8, 80 °C, 48 h) or MeZnN(SiMe3)2 (toluene-d8, 40 °C, 1
h) and was characterized spectroscopically. Attempts to
isolate 6a and 6c on a preparative scale led to the
formation of impure yellow oils, which were extremely
soluble in all solvents; consequently neither compound
could be obtained analytically pure. Similarly, the ethyl
zinc complexes CppyZnEt (7a ) and CpmesZnEt (7c) were
generated in solution and characterized by NMR spec-
troscopy.
Resu lts a n d Discu ssion
Liga n d Syn th esis. The addition of lithium pyrrolide
salts to a 10-fold excess of Me2SiCl2 in light petroleum
affords 1-(chlorodimethylsilyl)pyrrole (1a ) and 2,5-di-
methyl-1-(chlorodimethyl)silylpyrrole (1b), respectively.
Subsequent reaction of 1a and 1b with NaCp(thf) in
tetrahydrofuran gave the new N-pyrrolyl-substituted
cyclopentadienyl compounds cyclo-C4H4NSiMe2C5H5 (2a,
CppyH) and cyclo-2,5-Me2C4H2NSiMe2C5H5 (2b, Cp-
pymeH) as yellow oils, which are conveniently purified
by distillation under reduced pressure (Scheme 2). The
3,5-dimethylbenzyl-substituted cyclopentadiene 2c (Cp-
mesH) was prepared using a modification of a literature
method11 by the addition of 3,5-dimethylbenzyllithium
to dimethylfulvene in tetrahydrofuran as a bright-yellow
oil. All three compounds are obtained as a mixture of
isomers and can be stored at -20 °C with no evidence
of Diels-Alder dimerization. NMR data of ligands and
complexes are given in the Supporting Information.
Zin c Com p lexes. Treatment of 2a with zinc bis-
(bistrimethylsilylamide) in light petroleum at 40 °C gave
the zincocene complex Cppy2Zn (3a ) as a white micro-
crystalline precipitate, which was purified by recrys-
tallization from toluene (Scheme 3). Previously reported
zincocenes tend to show “slipped sandwich” structures
containing both η1- and η5-cyclopentadienyl ligands,12-15
which undergo rapid haptotropic exchange in solution,
as shown by NMR studies. The 1H NMR of 3a at
ambient temperature shows both cyclopentadienyl
ligands to be equivalent; on cooling to -60 °C the
resonances broaden but could not be fully resolved. The
magnesocenes 4a -c were similarly prepared from 2a -c
and MgBu2 in light petroleum as colorless solids which
precipitate from the solution during the course of the
reaction. All three compounds are very air and moisture
Treatment of light petroleum solutions of 6a or 7a
with a slight excess of TMEDA generated the adducts
CppyZnR(TMEDA) (8a , R ) Me; 9a , R ) Et). Both
complexes have only limited solubility in petroleum and
precipitated immediately from solution. Recrystalliza-
tion at -20 °C from light petroleum with a minimum
amount of diethyl ether provided 8a as a colorless
crystalline solid, while 9a was obtained as yellow
crystals. In similar fashion, CppymeZnR(TMEDA) (8b, R
) Me; 9b, R ) Et) and CpmesZnEt(TMEDA) (9c) were
obtained as yellow to red crystalline solids after recrys-
tallization from light petroleum/diethyl ether mixtures.
A crystal of 8b suitable for single-crystal X-ray
diffraction was grown from light petroleum/diethyl ether
at -20 °C (Figure 1), while a suitable crystal of 9c was
obtained from light petroleum at room temperature
(Figure 2). Selected bond lengths and angles are col-
lected in Table 1. In both structures the zinc atom is in
an essentially five-coordinate arrangement. The coor-
dination sphere comprises the two nitrogen atoms of the
TMEDA ligand, the alkyl ligand, and two carbons from
the cyclopentadienyl rings. In both complexes there is
one short and one long Zn-C interaction to the cyclo-
pentadienyl ligands, with Zn-C distances of 2.185(2)
and 2.562(2) Å for 8b and 2.167(2) and 2.558(2) Å for
9c. The shortest bonds are to the carbon atoms furthest
removed from the pendant cyclopentadienyl substitu-
ents. These distances are slightly longer than those
(11) Djakovitch, L.; Herrmann, W. A. J . Organomet. Chem. 1997,
545, 399.
(12) Blom, R.; Haaland, A.; Weidlein, J . J . Chem. Soc., Chem
Commun. 1985, 266.
(13) Blom, R.; Boersma, J .; Budzelaar, P. H. M.; Fischer, B.;
Haaland, A.; Volden, H. V.; Weidlein, J . Acta Chem. Scand. 1986, A40,
113.
(14) Fischer, B.; Wijkens, P.; Boersma, J .; van Koten, G.; Smeets,
W. J . J .; Spek, A. L.; Budzelaar, P. H. M. J . Organomet. Chem. 1989,
376, 223.
(15) Burkey, D. J .; Hanusa, T. P. J . Organomet. Chem. 1996, 512,
165.

Substituted Cyclopentadienyl Complexes of Zinc
Organometallics, Vol. 22, No. 4, 2003 799
Sch em e 2
F igu r e 1. Structure of 8b showing the atomic numbering
scheme. Thermal ellipsoids are drawn at the 50% prob-
ability level.
F igu r e 2. Structure of 9c showing the atomic numbering
scheme. Thermal ellipsoids are drawn at the 50% prob-
ability level.
Sch em e 3
F igu r e 3. Structure of MeZnN(SiMe3)2 (5). Thermal
ellipsoids are drawn at the 30% probability level.
Sch em e 4
The Zn-Me distance in 8b of 1.985(2) Å is typical of
zinc methyl complexes, for example, in [MeZnNMe-
(CH2)3NMe2]2 [1.982(7) and 1.976(7) Å], [MeZn{NMe-
(CH2)2NMe2}]2 [1.978(4) and 1.991(4) Å], and Me2Zn-
[(CH2NMe)3]2 [1.984(5) Å].17,18 Similarly, the Zn-Et
distance in 9c of 2.001(2) Å compares well with litera-
ture values, e.g., [EtZnNMe(CH2)3NMe2]2 [2.024(4) and
2.010(3) Å] and [EtZnNMe(CH2)2NMe2]2 [1.989(3) Å].17
The cationic zinc ethyl complexes [EtZn(OEt2)3]+[B(C6-
F5)4]- 7 and [EtZn(1,3,5-tribenzyl-1,3,5-triazacyclo-
hexane)]+[PF6]- 9 both show shorter Zn-Et distances
(1.964(3) and 1.930(4) Å, respectively). The Zn-N bond
distances to the TMEDA ligands of 2.189(2) and 2.231-
(2) Å in 8b and 2.2020(14) and 2.245(2) Å in 9c are
found in polymeric [Cp2Zn]n, at 2.047 and 2.484 Å.16
A
similar Cp bonding mode is also found in solid [MeZn-
(µ-η2-Cp)]n, while the monomeric molecule in the gas
phase prefers η5-Cp. Other zinc cyclopentadienyl com-
pounds show η1,η5-hapticity, e.g., Zn(η1-Cp′)(η5-Cp′) (Cp′
) C5H4SiMe3, C5Me5, and C5Me4Ph).13,14 For example,
the Zn-C distances to the η1-C5Me5 ligand in Zn(C5-
Me5)2 are 2.094(3), 2.592(3), 2.509(3), 3.112(3), and
3.066(3) Å, with only the first considered as strongly
bonding.
(17) Azad Malik, M.; O’Brien, P.; Motevalli, M.; J ones, A. C. Inorg.
Chem. 1997, 36, 5076.
(16) Budzelaar, P. H. M.; Boersma, J .; van der Kerk, G. J . M.; Spek,
A. L.; Duisenberg, A. J . M. J . Organomet. Chem. 1985, 281, 123.
(18) O’Brien, P.; Hursthouse, M. B.; Motevalli, M.; Walsh, J . R.;
J ones, A. C. J . Organomet. Chem. 1993, 449, 1.

800 Organometallics, Vol. 22, No. 4, 2003
Walker et al.
(TMEDA)]+[EtB(C6F5)3]- (11), along with some minor
impurities. The [EtB(C6F5)3]- anion has NMR charac-
teristics closely similar to that in [EtZn(OEt2)3]+[EtB-
(C6F5)3]-,7 with a small chemical shift difference be-
tween the o-F and p-F 19F NMR resonances (∆δ 2.5
ppm), indicative of a noncoordinating borate.19 Reactions
of 7c with [H(OEt2)2]+[B(C6F5)4]-, [CPh3]+[B(C6F5)4]-,
or [PhNMe2H]+[B(C6F5)4]- produced complex mixtures
and could not be characterized.
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for 8b a n d 9c
(cyclo-2,5-Me-C4H2NSiMe2C5H4)ZnMe(TMEDA) (8b)
Zn(1)-N(1)
2.189(2)
1.985(2)
2.185(2)
1.422(3)
1.385(3)
1.361(3)
1.362(3)
1.837(2)
33.67(7)
129.86(8)
113.63(7)
110.97(8)
Zn(1)-N(2)
2.231(2)
2.562(2)
1.411(3)
1.420(3)
1.401(2)
1.403(3)
1.407(2)
1.800(2)
107.28(7)
82.57(6)
111.59(7)
Zn(1)-C(3)
Zn(1)-C(42)
Zn(1)-C(43)
C(41)-C(42)
C(43)-C(44)
N(71)-C(72)
C(73)-C(74)
C(75)-N(71)
Si(1)-N(71)
C(3)-Zn(1)-C(42)
N(1)-Zn(1)-N(2)
C(3)-Zn(1)-N(2)
C(42)-C(43)
C(44)-C(45)
C(72)-C(73)
C(74)-C(75)
Si(1)-C(41)
C(42)-Zn(1)-C(43)
C(3)-Zn(1)-C(43)
C(3)-Zn(1)-N(1)
N(71)-Si(1)-C(41)
Treatment of a toluene-d8 solution of 9a with B(C6F5)3
afforded a yellow oil, which separated from the toluene.
The NMR spectra of this product in CD2Cl2 were
complicated, with evidence for the presence of three
discrete borate anions, as shown by the 11B and 19F
NMR. Apart from the [EtB(C6F5)3]- anion, the 11B
spectrum contains two further signals, a broad singlet
at δ -11.8 and a doublet at δ -21.1 (J HB ) 84.8 Hz).
The first is thought likely to arise from [CppyB(C6F5)3]-;
this is supported by the presence in the 1H NMR
spectrum of signals associated with an η1-bonded cy-
clopentadienyl ring. The doublet is assigned to the
[HB(C6F5)3]- anion via abstraction of a â-H from the
ethyl ligand, with loss of ethene, which was identified
(3,5-Me2C6H3CH2CMe2C5H4)ZnEt(TMEDA) (9c)
2.2020(14) Zn(1)-N(2)
Zn(1)-N(1)
Zn(1)-C(61)
2.245(2)
2.167(2)
1.427(3)
1.392(2)
1.526(2)
2.001(2)
2.558(2)
1.435(3)
1.420(2)
1.536(2)
34.11(6)
109.58(7)
111.73(6)
Zn(1)-C(31)
C(31)-C(35)
C(32)-C(33)
C(33)-C(41)
Zn(1)-C(32)
C(31)-C(32)
C(33)-C(34)
C(61)-C(611)
C(32)-Zn(1)-C(31)
C(61)-Zn(1)-C(32)
C(61)-Zn(1)-N(1)
C(61)-Zn(1)-C(31)
N(1)-Zn(1)-N(2)
C(61)-Zn(1)-N(2)
132.10(7)
82.32(6)
111.50(7)
Zn(1)-C(61)-C(611) 116.71(13) C(33)-C(41)-C(511) 108.34(14)
similar to those found in related complexes, for example,
ZnMe2(TMEDA) [2.278 and 2.260 Å].18
1
in the H NMR spectrum as a sharp singlet at δ 5.41.
The 19F NMR spectra are in agreement with this
assignment and suggest the presence of free anions. In
conclusion, the reaction of 9a with B(C6F5)3 is nonselec-
tive and proceeds with â-H, ethyl, and cyclopentadienyl
abstraction. While the first two processes will result in
the same cationic species, the last will not. Why 9a
reacts with B(C6F5)3 in this fashion whereas 9c gener-
ates almost exclusively 11 is not clear, although it is
noted that an attempt to repeat the formation of 11 on
a preparative scale did give evidence of both cyclopen-
tadienyl and â-H abstraction as minor products.
P olym er iza tion Stu d ies. Zinc complexes have at-
tracted much interest as single-site catalysts for the
ring-opening polymerization of epoxides and lactones.20,21
Specifically some complexes have been employed as
catalysts for the alternating copolymerization of carbon
dioxide and epoxides to produce aliphatic polycar-
bonates.20b Darensbourg et al. recently reported zinc
halide and acetate complexes with amino-substituted
cyclopentadienyl ligands but found only low to modest
activity for the polymerization of cyclohexene oxide and
propylene oxide and CO2 copolymerizations.20e The use
of cationic complexes has the advantage of increasing
the Lewis acidity of the metal center and thus providing
a greater driving force toward monomer coordination.
For this reason it was hoped that the cationic complexes
11 and those arising from the reaction of 9a with
B(C6F5)3 would provide active catalysts. The cationic
species were generated in toluene solution and then
It is evident from the crystal structures of 8b and 9c
that in neither complex is there any interaction between
the zinc atom and the pendant aromatic or heteroaro-
matic ring. This is not surprising since the TMEDA
ligand will satisfy any coordination requirements. What
is more interesting is the question of interactions in the
TMEDA-free complexes. As none of these complexes
could be obtained as crystals suitable for X-ray analysis,
only NMR evidence is available. However, the addition
of TMEDA to 6a causes a significant low-field shift of
the pyrrolyl protons (notably the ortho-H, which shift
from δ 6.76 ppm to 7.27 ppm, ∆δ 0.51 ppm) and suggests
some degree of coordination of the pyrrolyl substituents.
In view of the high solubility of these compounds in
hydrocarbons, this interaction is more probably in-
tramolecular, to give an ansa-sandwich structure, rather
than intermolecular as in a coordination polymer.
Similar chemical shift changes are seen for 7a (∆δ 0.48
ppm).
Ca tion ic Sp ecies. Treatment of toluene-d8 solutions
of 6a with B(C6F5)3, [CPh3][B(C6F5)4], or [H(OEt2)2]-
[B(C6F5)4] led to the formation of complicated mixtures,
which could not be characterized. When the TMEDA
adduct 8a was used, a white solid deposited, which
proved to be insoluble, even in dichloromethane. It
seems likely that this white solid is a coordination
polymer, resulting from intermolecular coordination of
the pyrrole to zinc, although bridging TMEDA ligands
cannot be ruled out.
An NMR-scale reaction of CpmesZnEt (7c) with B(C6F5)3
in toluene-d8 led to the formation of CpmesZn(C6F5) (10)
as the result of ligand exchange, along with EtB(C6F5)2
and some traces of Et2B(C6F5) and Et3B, as shown by
comparison to previous spectra.7 Compound 10 was
subsequently prepared in toluene and recrystallized
from light petroleum as a white microcrystalline solid.
This facile ligand exchange is common for dialkyl zinc
species.7 When the TMEDA adduct 9c was treated with
B(C6F5)3 in toluene-d8, a red oil separated, which was
soluble in dichloromethane-d2 and identified as [CpMesZn-
(19) Horton, A. D.; de With, J .; van der Linden, A. J .; van de Weg,
H. Organometallics 1996, 15, 2672.
(20) (a) Cheng, M.; Attygalle, A. B.; Lobkovsky, E. B.; Coates, G.
W. J . Am. Chem. Soc. 1999, 121, 11583. (b) Cheng, M.; Lobkovsky, E.
B.; Coates, G. W. J . Am. Chem. Soc. 1999, 121, 11018. (c) Chisholm,
M. H.; Eilerts, N. W.; Huffman, J . C.; Iyer, S. S.; Pacold, M.;
Phomphrai, K. J . Am. Chem. Soc. 2000, 122, 11845. (d) Chisholm, M.
H.; Gallucci, J . C.; Zhen, H. Inorg. Chem. 2001, 40, 5051. (e) Darens-
bourg, D. J .; Wildeson, J . R.; Yarbrough, J . C. Organometallics 2001,
20, 4413. (f) Cheng, M.; Moore, D. R.; Reczek, J . J .; Chamberlain, B.
M.; Lobkovsky, E. B.; Coates, G. W. J . Am. Chem. Soc. 2001, 123, 8738.
(21) Hannant, M. D.; Schormann, M.; Bochmann, M. J . Chem. Soc.,
Dalton Trans. 2002, 4071.

Substituted Cyclopentadienyl Complexes of Zinc
Organometallics, Vol. 22, No. 4, 2003 801
Ta ble 2. P olym er iza tion Resu lts Usin g 11 a n d 9a /B(C6F 5)3
b
b
initiator (I) (µmol)
monomer (M)
M/I ratio
temp, °C
time, min
conversion %
TONa
Mw
Mw/Mn
9a /B(C6F5)3 (25)c
11c (25)c
CHO
CHO
ꢀ-CL
ꢀ-CL
S
S
PO
PO
2000
2000
1000
1000
1000
1000
1000
1000
0
0
5
5
3
100
100
1.0
8.0
trace
trace
0
24 000
24 000
210
59 700
102 000
30 400
46 100
6.1
1.6
2.0
1.2
9a /B(C6F5)3 (50)d
11c (50)d
65
65
25
25
25
25
3
1610
9a /B(C6F5)3 (50)e
11c (50)e
180
180
2880
2880
9a /B(C6F5)3 (25)f
11c (25)f
0
a
Turnover numbers in mol monomer (mol Zn)-1 h-1
.
b Determined by GPC relative to polystyrene standards. c Polymerization conditions
d
for CHO: 25 µmol of initiator (I); [M]/[I] ) 2000; toluene 25 mL. Polymerization conditions for ꢀ-CL: 50 µmol of initiator (I); [M]/[I] )
1000; toluene 30 mL. e Polymerization conditions for styrene: 50 µmol of initiator (I); [M]/[I] ) 1000; toluene 10 mL. f Polymerization
conditions for CHO: 25 µmol of initiator (I); [M]/[I] ) 1000; toluene 5 mL.
22
23
(SiMe3)2 and Zn[N(SiMe3)2]2 were prepared according to
literature procedures. TMEDA was dried over CaH2 and
distilled before use.
tested with a variety of monomers. The results of these
tests are collected in Table 2.
The complexes are inactive for the polymerization of
propylene oxide at 25 °C and gave only traces of
polystyrene. However, the polymerization of cyclohexene
oxide was rapid, and at 0 °C the monomer was quan-
titatively consumed within 5 min. The polymer produced
1-(Ch lor od im eth ylsilyl)p yr r ole (1a ). A solution of pyrrole
(20.0 g, 20.7 mL, 298 mmol) in diethyl ether (500 mL) at -78
°C was treated with nBuLi (186 mL, 1.6 M in hexanes, 298
mmol) over ca. 20 min. The reaction was allowed to reach room
temperature and stirred for a further 2 h. The resulting white
precipitate was collected via filtration and pumped in vacuo
for 1 h. This solid was slowly added to a rapidly stirred solution
of dimethyldichlorosilane (200 mL, 213 g, 1.65 mol) in light
petroleum (300 mL). After complete addition the reaction was
stirred for a further 10 h. The solids were filtered off and the
filtrate was reduced in vacuo to leave 1a as a colorless oil,
contaminated by approximately 10% (C4H4N)2SiMe2 (2), as
shown by NMR. 1a is slightly volatile at 0.5 mmHg. Yield 85%.
2,5-Dim eth yl-1-(ch lor od im eth ylsilyl)p yr r ole (1b). Fol-
lowing the method described for 1a , 1b was prepared as a light
yellow oil in 78% yield. Neither 1a nor 1b was fully purified
but were used in situ.
by 11 was of reasonably high molecular weight (Mh w
)
102 000), with a narrow polydispersity (Mh w/Mh n ) 1.6).
It is perhaps significant that the system 9a /B(C6F5)3
produces poly(cyclohexene oxide) with a lower molecular
weight (Mh w ) 59 700) and a much wider polydispersity
(Mh w/Mh n ) 6.1), possibly as a consequence of the presence
of several cationic species in the solution. Both 11 and
9a /B(C6F5)3 polymerized ꢀ-caprolactone at 65 °C to give
good quality polymers with narrow polydispersities. The
cationic Cpmes complex 11 proved to be significantly
more reactive than the 9a /B(C6F5)3 catalyst.
cyclo-C4H4NSiMe2C5H5 (2a ). A solution of freshly prepared
1a (10.1 g, 63.2 mmol) in light petroleum (200 mL) was slowly
added to a solution of NaCp(THF) (10.1 g, 63.1 mmol) at 0 °C.
After stirring for 16 h the reaction was quenched with water
(100 mL). The organic layer was separated, dried over mag-
nesium sulfate, and reduced in vacuo to leave crude 2a as a
slightly yellow oil. Distillation at 60-80 °C, 0.5 mmHg,
provided pure 2a as a pale yellow oil. Yield: 8.14 g (68.0%).
Anal. Calcd for C11H15NSi: C, 69.78; H, 7.99; N, 7.40. Found:
C, 69.61; H, 7.94; N, 8.00.
cyclo-2,5-Me2C4H2NSiMe2C5H5 (2b). Following the method
described for 2a , 2b was prepared as a yellow oil in 87.1%
yield. 2b was purified by distillation at 80-100 °C/0.7 mmHg.
Anal. Calcd for C13H19NSi: C,71.83; H, 8.81; N, 6.44. Found:
C, 71.46; H, 8.45; N, 6.67.
Con clu sion
The starting point of this work was the desire to
synthesize zinc ansa-sandwich complexes of the type
[Zn(Cp-bridge-D)]+, where D ) π-donor such as an
electron-rich arene or heteroarene. Although the solu-
bility characteristics of neutral complexes of this kind
precluded crystallization and structural characteriza-
tion, there is spectroscopic evidence for likely arene-
zinc interactions. The facile C6F5 exchange between
perfluoroarylborate reagents and zinc alkyls is only
suppressed by the presence of donors such as TMEDA.
Cationic zinc cyclopentadienyl complexes such as
[CpMesZn(TMEDA)]+[EtB(C6F5)3]- are readily accessible
in solution. Both [CpMesZn(TMEDA)]+[EtB(C6F5)3]- and
CppyZnEt(TMEDA)/B(C6F5)3 provide active initiators for
the polymerization of cyclohexene oxide and ꢀ-caprolac-
tone to high molecular weight polymers.
3,5-Me2C6H3CH2CMe2C5H5 (2c). To a solution of mesity-
lene (20 g, 166 mmol) in light petroleum (200 mL) at 0 °C was
added rapidly nBuLi (104 mL, 1.6 M in hexanes, 166 mmol),
followed by dry TMEDA (25 mL, 166 mmol). The reaction
mixture was stirred overnight to give a bright yellow precipi-
tate, which was filtered off and dissolved in THF (200 mL).
The solution was cooled to 0 °C, and dimethylfulvene (17.6 g,
166 mmol) was added rapidly. The reaction mixture was
allowed to reach room temperature, stirred for 12 h, quenched
with a saturated aqueous solution of ammonium chloride, and
extracted with diethyl ether (3 × 100 mL). The organic
fractions were dried over magnesium sulfate, filtered, and
taken to dryness in vacuo. The residue was distilled under
reduced pressure to afford the product as a yellow-orange oil,
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
under nitrogen using standard Schlenk and glovebox tech-
niques. Solvents were distilled under nitrogen from sodium
(toluene), sodium benzophenone (diethyl ether, tetrahydrofu-
ran), and sodium-potassium alloy (light petroleum, bp 40-
60 °C). Deuterated solvents were stored over 4 Å molecular
sieves and degassed by several freeze-thaw cycles. NMR
spectra were recorded on a Bruker Avance DPX300 spectro-
meter. 1H NMR spectra are referenced to residual solvent
protons, 19F (282.2 MHz) relative to CFCl3, and 11B (96.2 MHz)
relative to BF3‚OEt2. Pyrrole, 2,5-dimethylpyrrole, dichloro-
dimethylsilane, ZnMe2 (2.0 M solution in toluene), and ZnEt2
(1.1 M solution in hexanes) were used as purchased. EtZnN-
1
bp 100 °C/0.1 mmHg. H NMR indicates the presence of two
isomers. Yield: 15.0 g (40.0%). Anal. Calcd for C17H22
90.20; H, 9.80. Found: C, 90.23; H, 9.82.
: C,
(22) Budzelaar, P. H. M.; Boersma, J .; van der Klerk, G. J . M.; Spek,
A. L. Organometallics 1984, 3, 1187.
(23) Bochmann, M.; Bwembya, G.; Webb, K. J . Inorg. Synth. 1997,
31, 19.

802 Organometallics, Vol. 22, No. 4, 2003
Walker et al.
(C4H4NSiMe2C5H4)2Zn (3a ). A solution of Zn[N(SiMe3)2]2
(2.78 g, 7.20 mmol) in light petroleum (20 mL) was treated
with 2a (2.72 g, 14.4 mmol), heated at 45 °C for 2 h, and then
stirred at room temperature for a further 16 h. The resulting
white precipitate was filtered off, washed with light petroleum
(2 × 20 mL), and pumped to dryness in vacuo. Yield: 2.15 g
(67.6%). Anal. Calcd for C22H28N2Si2Zn: C, 59.78; H, 6.34; N,
6.39. Found: C, 59.45; H, 6.41; N, 6.25.
sample of the product on a preparative scale were frustrated
by the oily nature and high solubility of this compound.
(C4H4NSiMe2C5H4)Zn Me(TMEDA) (8a ). A mixture of
MeZnN(SiMe3)2 (3.10 g, 12.9 mmol) and 2a (2.41 g, 12.7 mmol)
in light petroleum (90 mL) was stirred at 40 °C for 2 h. After
removal of volatiles the oily residue was dissolved in light
petroleum (30 mL) and TMEDA (1.60 g, 13.8 mmol) was added,
causing the immediate separation of a pale pink oil, which was
collected and pumped in vacuo for 2 h, after which time it
solidified. The pale pink powder was extracted with light
petroleum (40 mL). Concentration and cooling to -20 °C
overnight gave 8a as a colorless crystalline solid, yield 2.45 g
(49.3%). Anal. Calcd for C18H33N3SiZn: C, 56.16; H, 8.64; N,
10.92. Found: C, 56.47; H, 8.37; N, 10.27.
(C4H4NSiMe2C5H4)2Mg (4a ). A solution of 2a (2.00 g, 10.6
mmol) in light petroleum (40 mL) at 0 °C was treated with
MgBun (5.28 mL, 1.0 M solution in heptane, 5.28 mmol). The
2
reaction was stirred at room temperature for 16 h. Concentra-
tion to ca. 20 mL and cooling to -20 °C provided 4a as a white
microcrystalline solid, yield 3.05 g (71.8%). Anal. Calcd for
C
22H28N2Si2Mg: C, 65.90; H, 7.04; N, 6.99. Found: C, 65.45;
(2,5-Me2C4H2NSiMe2C5H4)Zn Me(TMEDA) (8b). Follow-
ing the procedure for 8a , 8b was prepared from MeZnN-
(SiMe3)2 (2.05 g, 8.51 mmol), 2b (1.85 g, 8.51 mmol), and
TMEDA (1.05 g, 9.04 mmol) as a pale yellow crystalline solid
after recrystallization from light petroleum/diethyl ether at
-20 °C, yield 2.52 g (71.7%). Anal. Calcd for C20H37N3SiZn:
C, 58.16; H, 9.03; N, 10.17. Found: C, 57.33; H, 8.86; N, 9.85.
(C4H4NSiMe2C5H4)Zn Et(TMEDA) (9a). A mixture of ZnEt2
(9.86 mL, 1.1 M in toluene, 10.8 mmol) and 2a (2.00 g, 10.8
mmol) in toluene (80 mL) was heated to reflux for 24 h.
Removal of the volatiles gave a dark brown oil, which was
dissolved in light petroleum. Addition of TMEDA (1.50 g, 12.9
mmol) caused the immediate formation of a light brown
precipitate, which was filtered off, dried in vacuo for 2 h, and
recrystallized from light petroleum to give 9a as a yellow
microcrystalline solid, yield 2.39 g (55.5%). Anal. Calcd for
H, 7.03; N, 6.56.
(2,5-Me2C4H2NSiMe2C5H4)2Mg (4b). A solution of 2b (2.06
g, 9.45 mmol) in light petroleum (100 mL) at 0 °C was treated
with MgBun2 (4.70 mL, 1.0 M solution in heptane, 4.70 mmol).
The reaction rapidly became yellow and was stirred at room
temperature for 16 h. Concentration to ca. 30 mL and cooling
to -20 °C overnight gave 4b as a white microcrystalline solid,
yield 3.11 g (72.0%). Anal. Calcd for C26H36N2Si2Mg: C, 68.32;
H, 7.94; N, 6.13. Found: C, 68.58; H, 8.04; N, 6.34.
(3,5-Me2C6H3CH2CMe2C5H4)2Mg (4c). A solution of Cp-
mesH (1.47 g, 6.49 mmol) in light petroleum (20 mL) at 0 °C
was treated with MgBun (3.25 mL, 1.0 M in hexanes). The
2
reaction mixture was stirred vigorously for 7 h followed by
concentration of the solvent under reduced pressure. The
reaction mixture was cooled to -20 °C to give 4c a white
crystalline solid, yield 0.95 g (31.0%). Anal. Calcd for C34H42
Mg: C, 85.97; H, 8.91. Found: C, 84.98; H, 8.89.
-
C
19H35N3SiZn: C, 57.20; H, 8.84; N, 10.53. Found: C, 57.37;
H, 8.53; N, 10.18.
MeZn N(SiMe3)2 (5). A solution of ZnMe2 (4.5 mL, 2 M in
toluene, 9.0 mmol) in light petroleum (20 mL) was treated with
Zn[N(SiMe3)2]2 (3.48 g, 3.63 mL, 9.0 mmol). After stirring for
30 min the volatiles were removed in vacuo. The resulting
sticky white residue was sublimed at 50 °C/0.7 mmHg to give
5 as colorless crystals, yield 2.41 g (55.6%). Anal. Calcd for
C7H21NSi2Zn: C, 34.92; H, 8.79; N, 5.82. Found: C, 34.78; H,
8.43; N, 5.88.
Gen er a tion of (C4H4NSiMe2C5H4)Zn Me (6a ). Meth od a .
To a solution of ZnMe2 (0.015 g, 0.157 mmol) in toluene-d8 (0.3
mL) was added a solution of 2a (0.030 g, 0.158 mmol) also in
toluene-d8 (0.3 mL). The reaction was maintained at 90 °C,
progress being monitored by 1H NMR. After 48 h at this
temperature the signals for 2a had disappeared and the
solution contained mainly 6a and CH4 with some unidentified
side products.
Meth od b. To a solution of 5 (0.030 g, 0.125 mmol) in
toluene-d8 (0.3 mL) was added a solution of 2a (0.024 g, 0.127
mmol) also in toluene-d8 (0.3 mL). The reaction was monitored
at 40 °C by 1H NMR spectroscopy. After 1 h the solution
contained mainly 6a and HN(SiMe3)2.
Gen er a tion of (2,5-Me2C6H3CH2CMe2C5H4)Zn Me (6c).
To a solution of MeZnN(SiMe3)2 (0.030 g, 0.125 mmol) in C6D6
(0.3 mL) was added a solution of CpmesH (0.028 g, 0.125 mmol)
in C6D6 (0.3 mL). The reaction mixture was maintained at a
temperature of 50 °C. After 1.5 h the reaction was >90%
complete (NMR). Attempts to isolate an analytically pure
sample of the product on a preparative scale were frustrated
by the oily nature of this compound.
(2,5-Me2C4H2NSiMe2C5H4)Zn Et(TMEDA) (9b). A mixture
of EtZnN(SiMe3)2 (2.01 g, 7.89 mmol) and 2b (1.75 g, 8.05
mmol) in light petroleum (50 mL) was stirred at 40 °C for 2 h.
Removal of volatiles left an oil, which was dissolved in light
petroleum (40 mL) and treated with TMEDA (1.20 g, 10.3
mmol). A red oil separated from the solvent, which was
isolated. Drying in vacuo for 2 h gave a red powder, which
was extracted with light petroleum (50 mL). The extract was
reduced in vacuo and cooled to -20 °C overnight to give 9b as
orange crystals, yield 2.51 g (74.5%). Anal. Calcd for C21H39N3-
SiZn: C, 59.07; H, 9.21; N, 9.84. Found: C, 58.52; H, 8.85; N,
9.31.
(3,5-Me2C6H3CH2CMe2C5H4)Zn Et(TMEDA) (9c). A solu-
tion of EtZnN(SiMe3)2 (1.85 g, 7.25 mmol) in light petroleum
(20 mL) was treated with CpmesH (1.64 g, 7.25 mmol) at 50 °C
for 2 h. Removal of the volatiles in vacuo, afforded a yellow
oil, which was dissolved in light petroleum and treated with
dry TMEDA (1.09 mL, 7.25 mmol). The mixture was stirred
for 16 h, during which time a thick white precipitate formed,
which was filtered off and washed with light petroleum (10
mL) to give 9c, yield 2.10 g (68.0%). Anal. Calcd for C25H37N2-
Zn: C, 68.87; H, 9.71; N, 6.43. Found: C, 68.20; H, 9.66; N,
6.26.
Rea ction of Cp m esZn Et w ith B(C6F 5)3 in Tolu en e-d 8. An
NMR tube was charged with CpmesH (0.022 g, 0.098 mmol)
and EtZnN(SiMe3)2 (0.025 g, 0.098 mmol). The reactants were
dissolved in toluene-d8 (0.5 mL), and the sealed tube was
heated at 60 °C for 3 h, with the progress of the reaction
followed by 1H NMR spectroscopy. Upon completion of the
reaction, the volatiles were carefully removed from the NMR
tube in vacuo, and a solution of B(C6F5)3 (0.050 g, 0.098 mmol)
in toluene-d8 (0.5 mL) was added. The 11B NMR spectrum
Gen er a tion of (C4H4NSiMe2C5H4)Zn Et (7a ). Following
the procedures described for 6a , 7a was similarly generated
from 2a and either ZnEt2 or EtZnN(SiMe3)2 and characterized
spectroscopically in solution.
indicated ligand exchange leading to the formation of Cpmes
-
ZnC6F5 (10) and EtB(C6F5)2 with small amounts of BEt3 and
BEt2(C6F5), which are characterized by comparison with
literature spectra.6
(3,5-Me2C6H3CH2CMe2C5H4)Zn (C6F 5) (10). A solution of
B(C6F5)3 (1.17 g, 2.29 mmol) in toluene (10 mL) was treated
with a solution of CpmesZnEt (2.20 g, 6.88 mmol) in toluene
Gen er a tion of (3,5-Me2C6H3CH2CMe2C5H4)Zn Et (7c). To
a solution of EtZnN(SiMe3)2 (0.032 g, 0.125 mmol) in C6D6 (0.3
mL) was added CpmesH (0.028 g, 0.125 mmol) in C6D6 (0.3 mL).
The reaction mixture was heated to 50 °C and the progress of
the reaction monitored by H NMR. After 2 h, NMR indicated
a conversion of >90%. Attempts to obtain an analytically pure
1

Substituted Cyclopentadienyl Complexes of Zinc
Organometallics, Vol. 22, No. 4, 2003 803
(10 mL). The mixture was stirred for 1 h, followed by removal
of the volatiles in vacuo. The residue was recrystallized from
light petroleum, affording an off-white solid, yield 1.35 g
X-r a y Cr ysta llogr a p h y. From a sample under dried per-
fluoropolyether, a crystal was mounted on a glass fiber and
fixed in the cold nitrogen stream on a Rigaku R-Axis II image
plate diffractometer equipped with a rotating anode X-ray
source (Mo KR radiation) and graphite monochromator. Data
were processed using the DENZO/SCALEPACK programs.24
The structure was determined by the direct methods routines
in the XS program25 and refined by full-matrix least-squares
methods, on F2’s, in XL.24 The non-hydrogen atoms were
refined with anisotropic thermal parameters. Hydrogen atoms
were included in idealized positions, and their Uiso values were
set to ride on the Ueq values of the parent carbon atoms, except
for H(32) and H(33) for 9c and H(42) and H(43) for 8b, which
were refined freely. For those methyl groups for which a
staggered conformation was not possible to calculate, the group
was allowed to rotate about the C-C bond. In the final
difference map, the highest peaks (to ca. 0.23 e Å-3) were close
to the zinc atom. In the final difference map, the highest peaks
(to ca. 0.32 e Å-3) were close to the Zn-N(1) bond. Scattering
factors for neutral atoms were taken from ref 26. Computer
programs were run on a Silicon Graphics Indy at the Univer-
sity of East Anglia.
(40.7%). Anal. Calcd for
C23H21F5Zn: C, 60.34; H, 4.62.
Found: C, 59.88; H, 4.64. 19F NMR (282.4 MHz, benzene-d6,
20 °C): δ -113.2 (m, 2 F, o-F), -153.8 (t, 1 F, p-F), -161.2
(m, 2 F, m-F).
Rea ction of Cp m esZn Et(TMEDA) w ith B(C6F 5)3 in Tol-
u en e-d 8. An NMR tube was charged with B(C6F5)3 (0.030 g,
59 µmol) and 9c (0.025 g, 59 µmol). The reactants were
dissolved in toluene-d8 (0.5 mL), and the progress of the
reaction was monitored by NMR spectroscopy. A red oil was
observed to precipitate from the solution and was isolated and
dissolved in CD2Cl2. NMR spectroscopy indicated the formation
of [CpMesZn(TMEDA)]+[EtB(C6F5)3]- (11) as the main product.
11B{1H} NMR (96.2 MHz, CD2Cl2, 20 °C): δ -9.4 [EtB(C6F5)3]-.
19F NMR (282.4 MHz, CD2Cl2, 20 °C): δ -133.1 (d, 6 F, J FF
)
22.6 Hz, o-F), -165.4 (t, 3 F, J FF ) 22.6 Hz, p-F), -168.0 (t, 6
F, J FF ) 22.6 Hz, m-F).
Rea ction of Cp p yZn Et(TMEDA) w ith B(C6F 5)3 in Tol-
u en e-d 8. To an NMR tube containing B(C6F5)3 (0.030 g, 59
µmol) and 9a (0.023 g, 59 µmol) was added toluene-d8 (0.5 mL).
An orange oil precipitated after ca. 5 s, which was isolated
and dissolved in CD2Cl2. NMR spectroscopy showed a compli-
cated mixture of products. 11B and 19F NMR showed the
presence of three different anions, identified as [EtB(C6F5)3]-,
[HB(C6F5)3]-, and [CppyB(C6F5)3]-. [EtB(C6F5)3]- is character-
ized by the following parameters: 11B{1H} NMR (96.2 MHz,
CD2Cl2, 20 °C): δ -9.6. 19F NMR (282.4 MHz, CD2Cl2, 20 °C):
Cr ysta l d a ta for 8b: C20H37N3SiZn, fw 413.0; crystal size
0.5 × 0.3 × 0.3 mm; monoclinic, space group P21/c, a ) 10.776-
(1) Å, b ) 11.755(1) Å, c ) 18.419(1) Å; â ) 104.40(1)°; V )
2259(3) Å3; Z ) 4, Dcalcd ) 1.214 g cm-3; µ ) 1.15 mm-1; 8034
reflections collected, of which 4131 were unique (Rint ) 0.0348)
and 3490 with I > 2σ(I) were observed; final R1 [I > 2σ(I)] )
0.0272, wR2 (all data) ) 0.0725, w ) [σ2(Fo2) + (0.0266P)2 +
δ -131.6 (d, 6 F, J FF ) 22.6 Hz, o-F), -164.8 (t, 3 F, J FF
)
22.6 Hz, p-F), -167.8 (t, 6 F, J FF ) 22.6 Hz, m-F). [CppyB-
(C6F5)3]-: 11B{1H} NMR (96.2 MHz, CD2Cl2, 20 °C): δ -11.4.
0.606P]-1 with P ) (Fo + 2Fc2)/3. Goodness of fit S ) 1.063
2
for 239 parameters.
19F NMR (282.4 MHz, CD2Cl2, 20 °C): δ -132.9 (d, 6 F, J FF
)
Cr ysta l d a ta for 9c: C25H42N2Zn, fw 435.98; crystal size
0.5 × 0.6 × 0.9 mm; monoclinic, space group P21/c, a ) 11.142-
(2) Å, b ) 16.157(3) Å, c ) 14.667(3) Å; â ) 107.52(3)°; V )
2517(9) Å3; Z ) 4, Dcalcd ) 1.150 g cm-3; µ ) 0.987 mm-1; 9002
reflections collected, of which 4607 were unique (Rint ) 0.024)
and 3739 with I > 2σ(I) were observed; final R1 [I > 2σ(I)] )
0.0284, wR2 (all data) ) 0.0743; w ) [σ2(Fo2) + (0.0266P)2 +
22.6 Hz, o-F), -165.6 (t, 3 F, J FF ) 22.6 Hz, p-F), -168.2 (t, 6
F, J FF ) 22.6 Hz, m-F). [HB(C6F5)3]-: 11B{1H} NMR (96.2 MHz,
CD2Cl2, 20 °C): -21.1 (d, J HB ) 84.8 Hz). 19F NMR (282.4 MHz,
CD2Cl2, 20 °C): δ -134.2 (d, 6 F, J FF ) 22.6 Hz, o-F), -164.3
(t, 3 F, J FF ) 22.6 Hz, p-F), -167.5 (t, 6 F, J FF ) 22.6 Hz,
1
m-F). The H spectrum could not be fully assigned due to the
large number of peaks, although there is clear evidence of an
η1-bonded cyclopentadienyl ligand with several multiplets
between δ 6.0 and 7.2 ppm.
0.606P]-1 with P ) (Fo + 2Fc2)/3. Goodness of fit S ) 1.029
2
for 260 parameters.
Reaction of CppyZn Et(TMEDA) with B(C6F5)3 in Dich lo-
r om eth a n e-d 2. To an NMR tube containing B(C6F5)3 (0.030
g, 59 µmol) and 9a (0.023 g, 59 µmol) was added CD2Cl2 (0.5
mL). The reaction was followed by multinuclear NMR spec-
troscopy. The product distribution was essentially the same
as when the reaction was carried out in toluene-d8 (vide supra).
Also present in the 1H NMR was a sharp singlet at δ 5.41,
which is assigned to ethene formed as the result of â-H
abstraction.
Gen er a l P r oced u r e for P olym er iza tion . A magnetically
stirred 50 mL Schlenk tube was flame-dried in vacuo prior to
being charged with the required volume of dry and degassed
toluene and monomer. To this was added a solution of the
initiator (either 11 or 9a /B(C6F5)3) in a small amount of
toluene. For the styrene, cyclohexene oxide, and ꢀ-caprolactone
polymerizations the reaction was terminated by the injection
of 2 mL of methanol. The polymer was precipitated with
acidified methanol, washed with methanol, and dried in vacuo
for 24 h. The propylene oxide tests were monitered by NMR
spectroscopy.
Ack n ow led gm en t. This work was supported by the
Engineering and Physical Sciences Research Council
and the European Commission (Contract no. HPRN-CT-
2000-00004).
Su p p or tin g In for m a tion Ava ila ble: 1H and 13C NMR
data for new compounds and crystallographic data for com-
pounds 8b and 9c. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM020690A
(24) Otwinowski, Z.; Minor, W. Methods Enzymol. 1996, 276, 307.
(25) Sheldrick, G. M. SHELXTL Package, including XS for structure
determination, XL for refinement, and XP for molecular graphics;
Siemens Analytical Inc., 1995.
(26) International Tables for X-ray Crystallography; Kluwer Aca-
demic Publishers: Dordrecht, 1992; Vol. C, pp 500, 219, and 193.