Chemistry of half-sandwich compounds of zirconium: Evidence for the formation of the novel ansa cationic-zwitterionic complex [Zr(η:η-C5H4CMe2C6H 4Me-p)(μ-MeB(C6F5)3)]

Article abstract of DOI:10.1021/om990499+

The compound [Zr(η-C₅H₄CMe₂C₆H ₄Me-p)Cl₃(dme)] (1) has been prepared. Methylation affords the compound [Zr(η-C₅H₄CMe₂C₆H ₄Me-p)Me

Full text of DOI:10.1021/om990499+

482
Organometallics 2000, 19, 482-489
Ch em istr y of Ha lf-Sa n d w ich Com p ou n d s of Zir con iu m :
Evid en ce for th e F or m a tion of th e Novel a n sa
Ca tion ic-Zw itter ion ic Com p lex
[Zr (η:η-C5H4CMe2C6H4Me-p)(µ-MeB(C6F 5)3)]+[MeB(C6F 5)3]-
J . Sassmannshausen†
Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, U.K.
Received J une 29, 1999
The compound [Zr(η-C5H4CMe2C6H4Me-p)Cl3(dme)] (1) has been prepared. Methylation
affords the compound [Zr(η-C5H4CMe2C6H4Me-p)Me3] (2), and benzylation of 1 yields [Zr-
(η-C5H4CMe2C6H4Me-p)(CH2Ph)3] (3). Reaction of 2 with [Ph3C]+[B(C6F5)4]- at -60 °C gives
the ansa complex [Zr(η:η-C5H4CMe2C6H4Me-p)Me2]+[B(C6F5)4]- (4a ), which has been char-
acterized by 1D and 2D NMR spectroscopy. Reaction of 2 with an excess (1.5 equiv) of B(C6F5)3
yields not only the ansa complex [Zr(η:η-C5H4CMe2C6H4Me-p)Me2]+[MeB(C6F5)3]- (4b) but
also the novel cationic zwitterionic ansa complex [Zr(η:η-C5H4CMe2C6H4Me-p)(µ-MeB-
(C6F5)3)]+[MeB(C6F5)3]- (5). The dynamic behavior of complexes 4b and 5 was extensively
studied by NMR spectroscopy. Reaction of 3 with [Ph3C]+[B(C6F5)4]- at -60 °C yields the
ansa complex [Zr(η:η-C5H4CMe2C6H4Me-p)(CH2Ph)2]+[B(C6F5)4]- (6), containing σ-bound
benzyl ligands.
In tr od u ction
solid-state structure of [Zr(η-C5H3(SiMe3)2-1,3)(η-tolu-
ene)Me2]+. Recently, Rausch12,17 has reported the 16-
electron ansa complex [Zr(η:η-C5Me4CH2CH2C6H5)Me2]+-
[B(C6F5)4]- and used this complex as a model for styrene
polymerization. In this model the cationic complex [Zr-
(η:η-C5Me4CH2CH2C6H5)Me2]+ is considered to be the
resting state for styrene polymerization; the incoming
monomer displaces the coordinated phenyl ring and
subsequently inserts into the metal-carbon bond (see
Scheme 1).
Competitive complexation to the metal of the tethered
phenyl ring and the phenyl ring attached to the growing
chain can be expected, since other cationic half-
sandwich complexes of zirconium are known18 in which
the benzyl moiety is coordinated in an η3 and η7 fashion,
respectively.
To investigate the coordination mode of the benzyl
moiety and the pendant phenyl group, the compound
[Zr(η-C5H4CMe2C6H4Me-p)(CH2Ph)3] (3) was prepared.
Here, the methyl group in the para position of the
tethered phenyl ring serves as an NMR probe.
Since Rausch’s cation [Zr(η:η-C5Me4CH2C6H4Me-p)-
Me2]+ formally has the same electronic configuration as
the neutral zirconocene compound [Zr(η-C5R5)2Me2] (R
) H, Me), we sought to investigate the possibility of the
formation of zwitterionic complexes similar to the well-
known metallocene complexes [Zr(η-C5R5)2Me(µ-Me)B-
(C6F5)3] (R ) H, Me).19,20 For this purpose the compound
[Zr(η-C5H4CMe2C6H4Me-p)Me3] (2) was prepared.
Cationic zirconocene complexes are of great interest
as catalysts for hydrogenation,1 isomerization,2 and
especially olefin polymerization reactions.3-11 The donr-
free 14-electron [Zr(η-C5H5)2R]+ cation is believed to be
an active species in Ziegler-Natta type olefin polym-
erization. However, these species are extremely reactive
and have not been isolated.
The half-sandwich complexes [M(η-Cp′)R3] (Cp′ )
C5H5, substituted Cp; M ) Ti, Zr, Hf) have received less
attention, although they are used as precursors for the
catalytic polymerization of styrene12 and propene.13
Baird et al. have demonstrated the formation of arene
adducts [M(η-C5Me5)Me2(η-arene)]+ (arene ) benzene,
toluene, m- and p-xylene, anisole, styrene, mesitylene;
M ) Ti, Zr, Hf).14,15 Bochmann et al.16 reported the
† Present address: Max-Planck Institut fu¨r Kohlenforschung, Kaiser-
Wilhelm-Platz 1, D-45470 Mu¨lheim an der Ruhr, Germany. E-mail:
sassy1@gmx.de. Fax: (+49)208-3062980.
(1) Qian, Y.; Li, G.; Huang, Y. J . Mol. Catal. 1989, 54, L 19.
(2) Qian, Y.; Lu, J .; Xu, W. J . Mol. Catal. 1986, 34, 31.
(3) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 225-270.
(4) Kaminsky, W.; Arndt, M. Adv. Polym. Sci. 1995, 127, 144-187.
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Chem. 1996, 518, 155-166.
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(15) Gillis, D. J .; Quyoum, R.; Tudoret, M. J .; Wang, Q.; J eremic,
D.; Roszak, A. W.; Baird, M. C. Organometallics 1996, 15, 3600-3605.
(16) Bochmann, M.; Robinson, O. B.; Lancaster, S. J .; Hursthouse,
M. B.; Coles, S. J . Organometallics 1995, 14, 2456-2462.
(17) Blais, M. S.; Chien, J . C. W.; Rausch, M. D. Organometallics
1998, 17, 3775-3783.
(12) Flores, J . C.; Wood, J . S.; Chien, J . C. W.; Rausch, M. D.
Organometallics 1996, 15, 4944-4950.
(13) Sassmannshausen, J .; Bochmann, M.; Ro¨sch, J .; Lige, D. J .
Organomet. Chem. 1997, 548, 23-28.
(14) Gillis, D. J .; Tudoret, M. J .; Baird, M. C. J . Am. Chem. Soc.
1993, 115, 2543-2545.
(18) Pellecchia, C.; Immirzi, A.; Pappalardo, D.; Peluso, A. Orga-
nometallics 1994, 13, 3773-3775.
10.1021/om990499+ CCC: $19.00 © 2000 American Chemical Society
Publication on Web 01/28/2000

Half-Sandwich Compounds of Zirconium
Organometallics, Vol. 19, No. 4, 2000 483
Sch em e 1a
of the phenyl hydrogen atoms, which is indicative of η
coordination of the phenyl ring to the cationic zirconium
center (see Scheme 3). Similar observations have been
made previously.12,22 The complete assignment of 4a
1
was performed by H, 13C, HMQC (heteronuclear mul-
tiple quantum coherence), and NOESY (nuclear Over-
hauser enhancement spectroscopy) spectroscopy, and
the data are collected in Table 1.
The NOESY spectrum (see Experimental Section)
clearly shows a correlation between the Cp(1,2) (see
Table 1 for labeling) and the Ph(12,13) hydrogen atoms
with the zirconium-methyl groups, respectively (cf.
Figure 1). A correlation between the CMe2 group and
the Cp(3,4) and Ph(10,11) hydrogen atoms was ob-
served, thus enabling complete assignment of the cation
4a .
More interesting was the reaction of 2 with 1.5 equiv
of B(C6F5)3 in CD2Cl2 at -60 °C, which was monitored
by NMR spectroscopy. At this temperature not only the
cation 4b was observed but also the new compound 5
(see Figure 2).
a
R ) growing polymer chain.
Sch em e 2a
The 11B NMR spectrum of 5 at -60 °C indicates the
presence of two distinct four-coordinate boron species,
one having a chemical shift of δ -15 ppm which has
-
previously been attributed to the free MeB(C6F5)3
anion,14 and a second species having a chemical shift of
δ -13 ppm. At -40 °C this second peak is no longer
present, indicating that it is associated with a thermally
sensitive compound. We postulate this to be the new
zwitterionic-cationic complex 5 (Scheme 3).
5 can be considered to be a Lewis acid-base adduct
between the 16-electron complex 4b and the strong
Lewis base B(C6F5)3, similar to other known zwitterionic
complexes such as [Zr(η-C5H5)Me(µ-Me)B(C6F5)3]19,20
and [Zr{η-C5H3(SiMe3)2-1,3}2Me(µ-Me)B(C6F5)3].23 The
proposed structure of 5 is further supported by the
observation of a peak at δ 0.97 ppm in the 1H NMR
spectrum, which correlates with a peak at δ 37.5 ppm
in the 13C NMR spectrum. This peak can be assigned
a
Legend: (i) (a) ZrCl4(dms)2, CH2Cl2, room temperature, (b)
dme; (ii) MgMeCl, Et2O, -78 °C; (iii) Mg(CH2Ph)Cl, Et2O, room
temperature.
Resu lts a n d Discu ssion
1
to a Me group bridging the Zr and B atoms. The J CH
The compound [Zr(η-C5H4CMe2C6H4Me-p)Cl3(dme)]
(1) was prepared by a modified literature procedure21
by reacting the ligand C5H4(SiMe3)(CMe2C6H4Me-p)
with [ZrCl4(Me2S)2] in dichloromethane followed by
precipitation of the zirconium compound 1 as the di-
methoxyethane adduct. 1 was used without further puri-
fication. Methylation of 1 was performed with MgMeCl
in diethyl ether at -78 °C to furnish the compound [Zr-
(η-C5H4CMe2C6H4Me-p)Me3] (2) as an air- and moisture-
sensitive dark brown microcrystalline solid, which is
best handled under argon (Scheme 2).Benzylation of 1
was performed with Mg(CH2Ph)Cl in diethyl ether at
ambient temperature; the product [Zr(η-C5H4CMe2C6H4-
Me-p)(CH2Ph)3] (3) crystallizes as yellow needles from
light petroleum.
coupling constant for this bridging methyl group is 115
Hz, compared to 125 Hz for the nonbridging ZrMe
group. Because of the bridging methyl group, complex
5 is chiral and all of the expected resonances are
observed. Full assignment of 5 was possible using
COSY, HMQC, and NOESY/EXSY (exchange spectros-
copy) spectroscopy.
To investigate a possible exchange between complex
4b and 5, a NOESY/EXSY spectrum was recorded (see
Experimental Section). The spectrum recorded at -60
°C indicates an exchange not only between 4b and 5
(see Scheme 4 and Figure 3) but also between the two
sides of complex 5.
The exchange between complexes 4b and 5 is indi-
cated by the cross-peak between the two different CpH,
CMe2, and PhH signals, respectively, suggesting a
reversible process (see Figure 3). This exchange is
clearly seen from the cross-peak exchanging Ph(12,13)
(δ 8.01 ppm) of 4b with Ph(12) (δ 8.57 ppm) and Ph(13)
(δ 8.05 ppm, underneath Ph(12,13) peak) of 5 (see Table
The reaction of 2 with [Ph3C]+[B(C6F5)4]- in CD2Cl2
was monitored by NMR spectroscopy. At -60 °C the
reaction proceeds cleanly to the ansa-metallocene [Zr-
-
(η:η-C5H4CMe2C6H4Me-p)Me2]+ (4a ; B(C6F5)4 counte-
rion). Typical for such complexes is the low-field shift
(19) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1991,
113, 3623.
(20) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
(22) Sassmannshausen, J . New Substitued Cyclopentadienyl Com-
plexes as 1-Alkene Polymerisation Catalysts; University of Leeds:
Leeds, U.K., 1997.
(23) Bochmann, M.; Lancaster, S. J .; Hursthouse, M. B.; Maik, K.
M. A. Organometallics 1994, 13, 2235-2243.
116, 10015-10033.
(21) Lund, E. C.; Livinghouse, T. Organometallics 1990, 9, 2426-
2427.

484 Organometallics, Vol. 19, No. 4, 2000
Sassmannshausen
Sch em e 3a
a
Legend: (i) [Ph3C]+[B(C6F5)4]-, CD2Cl2, -60 °C; (ii) 1.5 equiv of B(C6F5)3, CD2Cl2, -60 °C.
-
1 for labeling). Similarly, Ph(10,11) (δ 7.22 ppm) of 4b
exchanges with Ph(11) (δ 7.82 ppm) and Ph(10) (δ 7.27
ppm, underneath Ph(10,11) peak). The weaker cross-
peak at F1 δ 8.05 ppm, F2 δ 7.22 ppm is due to COSY
breakthrough; the even weaker cross-peak at F1 δ 8.57
ppm and F2 δ 7.22 ppm is due to NOESY.
the MeBX3 moiety is weakly bonded via agostic hy-
drogens to the cationic metal center.23 Thus, the rather
labile anion can be readily displaced by stronger Lewis
bases. This displacement has been recently demon-
strated by Green et al. in the formation of cationic26 and
dicationic27 zirconocene complexes stabilized by in-
tramolecular phenyl coordination. In these complexes
the (di)cationic zirconium center is stabilized by agostic
interaction of the ortho hydrogen of the phenyl ring (see
Chart 1).
Similar observations can be made for the cyclopen-
tadienyl protons of complexes 4b and 5. More detailed
information about the processes involved can be ob-
tained by examining the aliphatic region of the spec-
-
-
trum, in particular the ZrMe and MeBX3 (X ) C6F5)
If we take this into account, the free anion MeBX3
of 4b could be sufficiently Lewis basic to replace the
coordinated anion MeBX3 in 5.
peaks.
-
Figure 4 shows an expansion of this region, which
-
indicates an exchange between the free MeBX3 with
Complex 5 can convert into 4b by loss of BX3, which
could recoordinate to form the inverted version of 5 (cf.
Scheme 4) in a manner similar to that observed by
Marks et al.24,25 Indeed, the 19F NMR spectrum shows
the presence of three compounds: B(C6F5)3 (δ -133.4,
-149.2, and -166.6 ppm), the solvated [MeB(C6F5)3]-
(δ -139.4, -169.9, and -172.7 ppm), and the chemical
shift difference ∆δ(m,p-F) 2.8 ppm, indicative of a
noncoordinated anion as previously described by Hor-
ton.28 Values for ∆δ(m,p-F) between 3 and 6 ppm
indicate coordination of the anion, while values <3 ppm
indicate noncoordination of the anion. The third species
in the spectrum can be assigned to be the bridging MeB-
(C6F5)3 group and has absorptions centered at δ -140.7,
-163.9, and -169.5 ppm with a value for ∆δ(m,p-F) of
5.6 ppm, indicating coordination of the anion.28
the ZrMe2 group of complex 4b and with the ZrMe and
Zr(µ-Me)BX3 moieties of complex 5. A similar ion pair
dissociation/reabstraction and symmetrization has been
observed previously and thoroughly investigated by
Marks.24,25 From careful analysis of the NMR spectra
of the complex [M({η-C5H3Me2-1,2)Me][MeB(C6F5)3] (M
) Zr, Hf) at various temperatures, two processes which
lead to exchange of the methyl group in the metallocene
wedge could be identified. The first process, more
dominant in polar solvents and for M ) Zr, cleaves the
Zr-µ-Me interaction and flips the terminal Zr-Me
group from one side of the metallocene girdle to the
other and is followed by reassociation of the anion. The
second process permutes both the diastereotopic ring
sites and the bridging/terminal methyl groups by an
initial dissociation of B(C6F5)3 by Me-B bond cleavage
and coordination to the other terminal methyl group of
the zirconocene. This process is more facile when M )
Hf, probably due to greater M-C bond strength (see
Scheme 5).
The lability of 5 is demonstrated by the temperature
sensitivity of the complexswarming the solution to -40
°C leads to the formation of 4b with loss of 5.
The reaction of 2 equiv of B(C6F5)3 and 1 equiv of 2
could not be monitored by NMR spectroscopy due to the
very low solubility of 5 at -60 °C.
A similar mechanism can be suggested here: the free
-
-
MeBX3 displaces the coordinated MeBX3 of complex
5, resulting in an exchange between free and coordi-
nated MeBX3-. It is known from the zwitterionic
complex [Zr{η-C5H3(SiMe3)2-1,3}2Me(µ-Me)B(C6F5)3] that
The reaction of 3 with [Ph3C]+[B(C6F5)4]- in CD2Cl2
was monitored by NMR spectroscopy. At -40 °C the
(26) Doerrer, L. H.; Ha¨ussinger, D.; Green, M. L. H.; Sassmann-
shausen, J . J . Chem. Soc., Dalton Trans. 1999, 2111-2118.
(27) Green, M. L. H.; Sassmannshausen, J . J . Chem. Soc., Chem.
Commun. 1999, 115-116.
(28) Horton, A. D.; de With, J .; van der Linden, A. J .; van de Weg,
H. Organometallics 1996, 15, 2672-2674.
(24) Deck, P. A.; Marks, T. J . J . Am. Chem. Soc. 1995, 117, 6128-
6129.
(25) Deck, P. A.; Beswick, C. L.; Marks, T. J . J . Am. Chem. Soc.
1998, 120, 1772-1784.

Half-Sandwich Compounds of Zirconium
Organometallics, Vol. 19, No. 4, 2000 485
plex [Zr(η-C5H5)(CH2Ph)2]+[B(CH2Ph)(C6F5)3]-, in which
the anion is η6-coordinated to the cationic zirconium
center. The J CH coupling constant for this species is
Ta ble 1. NMR Da ta for Ca tion ic Com p lexes 4a ,b, 5,
a n d 6
1
reported to be 122 Hz, which is very similar to that
observed for 6.
These findings explain the observed lower activity of
these compounds for styrene12,17 and ethylene22,37 po-
lymerization; the coordinated phenyl ring blocks the
vacant coordination site and hinders complexation of the
monomer. It also shows that coordination of a phenyl
ring from the growing chain is unlikely.
Unfortunately, the triphenylethane byproduct ham-
1
pered the observation of the aromatic region in the H
NMR spectrum.
The reaction of 3 with B(C6F5)3 in CD2Cl2 at -60 °C
did not lead to a clean product, and the 1H NMR
spectrum only consisted out of broad, featureless peaks.
Con clu sion
We have prepared the half-sandwich zirconium trichlo-
ride complex 1, which has a pendant phenyl group.
Methylation of 1 leads to the formation of the trimethyl
compound 2, while treatment with PhCH2MgCl leads
to the tribenzyl compound 3.
The reaction of 2 with 1 equiv of [Ph3C]+[B(C6F5)4]-
in CD2Cl2 furnishes the cationic ansa complex 4a with
the phenyl group η6-coordinated to the cationic zirco-
nium center. The structure of 4a could be unambigu-
ously assigned by 2D NMR spectroscopy and NOESY
experiments.
Reaction of 2 with more than 1 equiv of B(C6F5)3 leads
not only to the formation of 4b but also to the formation
of the novel cationic zwitterionic ansa zirconocene
complex 5. This complex has a methyl group bridging
the zirconium and boron atoms in a manner similar to
that for the zwitterionic group 4 metallocene complexes
previously observed. Complexes 4a ,b are thus formally
related to the neutral group 4 metallocene compounds
and provide yet another example of the rich and often
quite unusual chemistry of B(C6F5)3.38 NOESY/EXSY
spectroscopy indicates that complexes 4b and 5 are in
rapid equilibrium with each other. Similar exchange
processes have been observed for zwitterionic group 4
metallocene complexes.24,25
The tribenzyl compound 3 reacts with [Ph3C]+[B-
(C6F5)4]- in CD2Cl2 to yield the ansa complex 6, in which
the pendant phenyl ring is coordinated to the cationic
zirconium center and the benzyl groups are σ-bound to
the metal. These results, and those obtained by Rausch
et al.12 for styrene and by us22 for ethylene polymeri-
zation, are consistent with the lower activity of these
a
b
500 MHz. 125.7 MHz. c Obscured by triphenylethane.
formation of 1 equiv of Ph3CCH2Ph, the byproduct of
the abstraction of a benzyl group, and of 1 equiv of the
cationic species 6 is observed. The reaction is fairly
clean, toluene resulting from hydrolysis being the only
byproduct observed. The protons for the pendant phenyl
ring generate signals at δ 7.69 and 8.12 ppm, while that
for the attached methyl group is shifted from δ 2.29 ppm
to δ 2.65 ppm, similar to that observed for 4a at δ 2.76
ppm. The 1J CH coupling constant found for the Zr-CH2-
Ph group is 127 Hz and is typical for a benzyl group
σ-coordinated to zirconium, rather than the η2 coordina-
tion previously observed for metallocene complexes.23,29-35
On the basis of the evidence of NMR spectroscopy, we
suggest that the structure of 6 is similar to that of 4a ;
the phenyl ring is coordinated to the cationic zirconium,
and the benzyl moieties are σ-bound to the zirconium.
Similar cationic half-sandwich complexes have been
observed before, notably by Pellecchia36 for the com-
(30) J ordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echols, S. F.; Willet,
R. J . Am. Chem. Soc. 1987, 109, 4111-4113.
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Organometallics 1990, 9, 1539.
(32) Davis, G. R.; J arvis, J . A.; Kilburn, B. T.; Piols, A. J . P. J . Chem.
Soc., Chem. Commun. 1971, 677.
(33) Davis, G. R.; J arvis, J . A.; Kilburn, B. T. J . Chem. Soc., Chem.
Commun. 1971, 1511.
(34) Mintz, E. A.; Moloy, K. G.; Marks, T. J . J . Am. Chem. Soc. 1982,
104, 4692.
(35) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell, I.
P.; Huffman, J . C. Organometallics 1985, 4, 902.
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tallics 1993, 12, 4473-4478.
(37) Bochmann, M. Top. Catal. 1999, 7, 9-22.
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640.

486 Organometallics, Vol. 19, No. 4, 2000
Sassmannshausen
F igu r e 1. NOESY NMR spectrum of 4a .
F igu r e 2. 1H NMR spectra: (a) reaction of 2 with [Ph3C]+[B(C6F5)4]-; (b) reaction of 2 with 1.5 equiv of B(C6F5)3. Peaks
belonging to 5 are denoted in italics.
NOESY/EXSY spectra were recorded using a standard
NOESY pulse program with 2K of data points for the FID, a
sweep range of 4665 Hz with a 90° pulse, an initial pulse delay
of 1.5 s, and a mixing time of 0.67 s. Eight scans per increment
were recorded, and 512 increments were collected.
class of compounds compared with related unsubsti-
tuted species.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All experiments were carried out
under a nitrogen atmosphere by using standard Schlenk
techniques. Solvents were dried over sodium (toluene, low in
sulfur), sodium/potassium alloy (diethyl ether, light petroleum
ether, bp 40-60 °C), sodium/benzophenone (thf), and calcium
hydride (dichloromethane). NMR solvents were dried over
activated molecular sieves, freeze-thawed, and stored in
Young’s-Tap sealed ampules.
P r ep a r a tion of [Zr (η-C5H4CMe2C6H4Me-p)Cl3(d m e)] (1).
The compound [Zr(η-C5H4CMe2-p-C6H4Me)Cl3(dme)] was pre-
pared by a modified literature procedure.21 The compound
ZrCl4(Me2S)2, prepared from freshly sublimed ZrCl4 (12.07 g,
51.8 mmol) and dimethyl sulfide (7.60 cm3, 103.6 mmol) in 120
cm3 of dichloromethane, was treated with C5H4(SiMe3)(CMe2-
p-C6H4Me) (14.0 g, 51.8 mmol) at 0 °C. The reaction mixture
was stirred for 10 days at room temperature; a white precipi-
tate was formed. Dimethoxyethane (5.4 mL) was added, and
the reaction mixture was concentrated and stored at 3 °C for
2 days. The off-white product was collected by filtration and
washed with 50 cm3 of diethyl ether. The product was dried
under reduced pressure and was used without further puri-
fication. Yield: 20.12 g, 41.5 mmol; 80%. Anal. Found: C, 41.2;
H, 5.2; Cl, 25.2. Calcd for C19H27Cl3O2Zr: C, 47.1; H, 5.6; Cl,
NMR spectra were recorded on a Bruker AM300 or a
VARIAN UnityPlus 500 spectrometer and referenced to the
1
residual protio solvent peak for H. Chemical shifts are quoted
in ppm relative to tetramethylsilane. 13C NMR spectra were
referenced to the solvent peak relative to TMS and were
proton-decoupled using a WALTZ sequence. CH coupling
constants were measured by coupled HMQC. 11B NMR spectra
were referenced to BF3‚Et2O (δ 0 ppm).
1
21.9. H NMR (CDCl3, 300 MHz, 20 °C; δ (ppm)): 1.93 (s, 6H,

Half-Sandwich Compounds of Zirconium
Organometallics, Vol. 19, No. 4, 2000 487
Sch em e 4
F igu r e 3. NOESY/EXSY NMR spectrum of 4b and 5. Peaks belonging to 5 are denoted in italics.
CMe2); 2.28 (s, 3H, PhMe); 3.88 (br, 6H, dme); 4.09 (br, 4H,
dme); 6.52 (“t”, 2H, Cp); 6.58 (“t”, 2H, Cp); 7.02 (“s”, 4H, Ph).
13C NMR (CDCl3, 125.7 MHz, 20 °C; δ (ppm)): 20.8 (PhMe);
27.8 (CCH3); 40.8 (CCH3); 118.4 (Cp′); 125.7 (Ph′); 128.7 (Ph′);
135.1 (i-C Cp); 145.7 (i-C PhMe); 148.7 (i-C Ph).
residue was extracted into 130 cm3 of hot light petroleum. The
clear, dark yellow solution was cooled to -80 °C. The brown
microcrystalline solid formed was collected by filtration. The
compound is very air-sensitive and is best handled under an
argon atmosphere. Yield: 1.96 g, 5.9 mmol; 30%. Anal.
Found: C, 63.6; H, 7.5. Calcd for C18H26Zr: C, 64.8; H, 7.9. 1H
NMR (CDCl3, 500 MHz, 20 °C; δ (ppm)): 0.25 (s, 9H, ZrMe);
1.58 (s, 6H, CMe2); 2.29 (s, 3H, PhMe); 6.18 (“t”, 2H, Cp′); 6.21
(“t”, 2H, Cp′); 7.07 (d, 2H, Ph′); 7.15 (d, 2H, Ph′). 13C NMR
(CDCl3, 125.7 MHz, 20 °C; δ (ppm)): 20.8 (PhMe); 29.8 (CCH3);
39.0 (CCH3); 45.3 (ZrMe); 106.8 (Cp′); 110.8 (Cp′); 125.8
(Ph′); 128.8 (Ph′); 135.4 (i-C Cp); 142.7 (i-C PhMe); 147.1
(i-C Ph).
P r ep a r a tion of [Zr (η-C5H4CMe2C6H4Me-p)Me3] (2). The
compound [Zr(η-C5H4CMe2-p-C6H4Me)Cl3(dme)] (9.52 g, 19.6
mmol) was suspended in 120 cm3 of diethyl ether and cooled
to -78 °C. The Grignard reagent MgClMe (19.6 cm3, 58.9
mmol, 3 mol/L in thf) was slowly added via syringe. The
reaction mixture was stirred at -78 °C for 30 min, slowly
warmed to room temperature, and stirred for 2 h. The volatiles
were removed under reduced pressure, and the dark brown

488 Organometallics, Vol. 19, No. 4, 2000
Sassmannshausen
F igu r e 4. NOESY/EXSY spectrum of 4b and 5. Peaks belonging to 5 are denoted in italics.
Sch em e 5
into light petroleum yielded a yellow microcrystalline solid,
which was pure by NMR spectroscopy. Yield: 5.58 g, 9.9 mmol;
45% Anal. Found: C, 76.7; H, 6.8. Calcd for C36H38Zr: C, 77.0;
Ch a r t 1
1
H, 6.8. H NMR (CDCl3, 500 MHz, 20 °C; δ (ppm)): 1.54 (s, 6
H, CH2Ph); 1.66 (s, 6H, CCH3); 2.30 (s, 3H, PhMe); 5.25 (“t”,
2H, Cp1); 5.99 (“t”, 2H, Cp2); 6.50 (d, 6H, o-H Bz); 7.01 (t, 3H,
p-H Bz); 7.09 (d, 2H, Ph′); 7.14 (t, 6H, m-H Bz); 7.17 (d, 2H,
Ph′). 13C NMR (CDCl3, 125.7 MHz, 20 °C; δ (ppm)): 20.9
(PhCH3); 30.3 (CCH3); 39.7 (CCH3); 66.6 (ZrCH2Ph, J CH ) 127
Hz); 109.8 (Cp2); 111.5 (Cp1); 123.2 (p-C Bz); 126.0 (Ph′); 127.5
(o-C Bz); 128.8 (Ph′); 129.5 (m-C Bz); 135.5 (i-C PhMe); 141.0
(i-C Cp); 143.3 (i-C Bz); 147.0 (i-C Ph′).
Low -Tem p er a tu r e NMR Stu d ies on Ca tion ic Com -
p ou n d s. Because of the sensitivity of the cationic complexes,
the complexes were generated in situ, and isolation was not
attempted.
P r ep a r a tion of [Zr (η-C5H4CMe2-p-C6H4Me)(CH2P h )3]
(3). The compound [Zr(η-C5H4CMe2-p-C6H4Me)Cl3(dme)] (10.6
g, 22 mmol) was added to a solution of MgCl(CH2Ph) (80 mmol)
in 200 cm3 of diethyl ether at room temperature. The color
changed immediately to bright yellow. The mixture was stirred
for 12 h. The volatiles were removed under reduced pressure
to form a dark brown solid. The solid was extracted into hot
light petroleum (3 × 70 cm3). The extract was taken to dryness
and extracted into hot light petroleum. Repeated extraction
The general procedure was as follows. The zirconocene
compound (ca. 0.1 mmol) was dissolved in 0.25 cm3 of CD2Cl2,
and the solution was transferred into a precooled (-78 °C)
NMR tube. The cation-generating agent B(C6F5)3 or [Ph3C]+-
[B(C6F5)4]- (ca. 0.11 mmol) was dissolved in 0.28 cm3 of

Half-Sandwich Compounds of Zirconium
Organometallics, Vol. 19, No. 4, 2000 489
1
CD2Cl2 andtransferred onto the zirconocene solution in the
NMR tube. The tube was sealed and shaken vigorously to
ensure complete mixing. The sample was placed into the
precooled (-60 °C) probe of the NMR spectrometer. 1D and
2D NMR spectra were recorded at -60 °C, unless otherwise
stated. The sample was warmed to ambient temperature at
increments of 20 K, and at each step a H NMR spectrum was
recorded.
Ack n ow led gm en t. I thank Prof. M. L. H. Green for
valuable discussion and continuous support.
OM990499+