Structural characterization of a cationic zirconocene dimethylaniline complex and related catalytically relevant species

Article abstract of DOI:10.1021/om800783h

We report the first crystallographically characterized dimethylaniline complex of a group 4 metallocene. [(IPCF)ZrMe(NMe₂Ph)][B(C ₆F₅)₄] shows strongly coordinated NMe ₂Ph which does not interchange in solution. DFT calculations suggest that the Zr-N bond is 23 kJ mol^-1 stronger than the Zr-Me-Zr bond in [[(IPCF)ZrMe]₂(μ-Me)][MeB(C₆F₅) ₃], the structure of which is also reported (IPCF=Me ₂C(C₅H₄)(fluorenyl)).

Full text of DOI:10.1021/om800783h

Organometallics 2008, 27, 6371–6374
6371
Structural Characterization of a Cationic Zirconocene
Dimethylaniline Complex and Related Catalytically Relevant Species
Polly A. Wilson, Joseph A. Wright, Vasily S. Oganesyan, Simon J. Lancaster, and
Manfred Bochmann*
Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, UniVersity of East
Anglia, Norwich NR4 7TJ, U.K.
ReceiVed August 14, 2008
Summary: We report the first crystallographically characterized
dimethylaniline complex of a group 4 metallocene. [(IPCF)-
ZrMe(NMe2Ph)][B(C6F5)4] shows strongly coordinated NMe2Ph
which does not interchange in solution. DFT calculations
suggest that the Zr-N bond is 23 kJ mol-1 stronger than the
Zr-Me-Zr bond in [{(IPCF)ZrMe}2(µ-Me)][MeB(C6F5)3], the
structureofwhichisalsoreported(IPCF)Me2C(C5H4)(fluorenyl)).
One of the most widely used methods of generating cationic
metallocene alkyl complexes is the protonolysis of metallocene
dialkyls with ammonium salts.1-3 The reaction of zirconocene
dimethyls with dimethylanilinium tetraarylborate salts has found
particularly widespread application, and in early pioneering work
Turner was able to show that the use of [HNMe2Ph][B(C6F5)4]
as a cation generating agent resulted in particularly active
catalysts. This was thought to be due mainly to the low basicity
of dimethylaniline (pKb ) 8.85; cf. pKb ) 3.25 for NEt3)4 and
its correspondingly low ability to bind to the resulting cationic
group 4 metal center.
1
Figure 1. VT H NMR spectra of [(IPCF)Zr(Me)NMe2Ph]+[B-
(C6F5)4]- (2) in toluene-d8/1,2-difluorobenzene (1/1 v/v).
During studies directed at determining the kinetics of met-
allocene catalyst activation with anilinium and triphenylcar-
benium salts, we carried out reactions between (IPCF)ZrMe2
(1) and [HNMe2Ph][B(C6F5)4] in toluene (M ) Zr, Hf; IPCF )
Me2C(C5H4)(fluorenyl)) (eq 1).5 Combining the two reagents
gave a red-orange solution accompanied by the deposition of
some red oil. Cooling this mixture overnight at -26 °C afforded
red crystals of [(IPCF)ZrMe(NMe2Ph)][B(C6F5)4] (2) which
were suitable for single-crystal X-ray diffraction (see below).
coordinated dimethylaniline. These signals broaden above 0 °C,
and a spectrum recorded at 40 °C showed coalescence to a
singlet at δ 1.77. Dissociation and exchange of coordinated
dimethylaniline is evidently not a facile process. The signal
assigned to free dimethylaniline is found in the range δ 2.5-2.2
and is both temperature and concentration dependent. The
assignment was confirmed by the addition of excess NMe2Ph.
However, subsequent experiments revealed that excess
[HNMe2Ph]+[B(C6F5)4]- also appears at the same chemical shift:
i.e., it rapidly exchanges with and is indistinguishable from free
DMA. For this reason, the signal has been labeled simply as
DMAXS (Figure 1). There was no observed exchange of this
DMAXS resonance and the Zr-coordinated DMA over the
temperature range studied.
The structure of the cation in 2 · 2(toluene) is shown in Figure
2. The phenyl group of the coordinated aniline fits into the
groove of the fluorenyl moiety. The solid-state conformation is
consistent with the solution NMR data.
To the best of our knowledge there is no previous example
of a structurally characterized dimethylaniline complex of a
group 4 metallocene and only one example of a zirconium
nonmetallocene structure, Jordan’s [(F6-acen)Zr(CH2CMe3)-
(NMe2Ph)][B(C6F5)4] (F6-acen ) N,N′-ethylenebis(trifluoroacety-
lacetoneiminato)).6 This complex shows a comparable Zr-Naniline
distance of 2.441(4) Å; in CD2Cl2 solution the -NMe2 moiety
appears as a singlet at δ 2.86, and there is rapid exchange with
The aniline adduct proved surprisingly stable in solution at
room temperature and above. The variable-temperature 1H NMR
spectra of 2 are in agreement with C1 symmetry. An unexpected
feature was the presence below +20 °C of two separate
resonances for the two diastereotopic methyl groups of the
(1) Bochmann, M.; Wilson, L. M. J. Chem. Soc., Chem. Commun. 1986,
1610.
(2) Taube, R.; Krukowka, L. J. Organomet. Chem. 1988, 347, C9.
(3) Turner, H. W. (Exxon Chemicals) Eur. Pat. Appl. 0277004, 1988;
Chem. Abstr. 1989, 110, 58290a.
(4) CRC Handbook of Chemistry and Physics, 76th ed.; Lide, D. R.,
Ed., CRC Press: Boca Raton, FL, 1995; Section 8-45.
(5) Ewen, J. A.; Elder, M. J.; Jones, R. L.; Haspelagh, L.; Atwood, J. L.;
Bott, S. G.; Robinson, K. Makromol. Chem. Macromol. Symp. 1991, 48/
49, 253.
(6) Tjaden, E. B.; Swenson, D. C.; Jordan, R. F.; Petersen, J. L.
Organometallics 1995, 14, 371.
10.1021/om800783h CCC: $40.75
2008 American Chemical Society
Publication on Web 10/29/2008

6372 Organometallics, Vol. 27, No. 23, 2008
Notes
Figure 2. ORTEP representation of the [(IPCF)ZrMe(NMe2Ph)]+
cation, showing ellipsoids at the 50% probability level. Hydrogen
atoms have been omitted for clarity. Selected bond lengths (Å) and
angles (deg): Zr-N(1) ) 2.424(5), Zr-C(54) ) 2.255(6), Zr-CtCp
) 2.178, Zr-CtFlu ) 2.241; N(1)-Zr-C(54) ) 96.75(19), CtCp-Zr-
CtFlu ) 118.13 (Ct ) centroid of five-membered-ring ligand).
Figure 3. Structure of the [{(IPCF)Zr(µ-F)}2]2+ dication in 5.
Ellipsoids are drawn at the 50% probability level. Hydrogen atoms
have been omitted for clarity.
time scale.12 The low ethylene polymerization activity of
imino-oxazolinyl zirconium complexes is also thought to be
due to DMA coordination.13
Scheme 1
Extending the reaction of metallocene dimethyls with
[HNMe2Ph][B(C6F5)4] to the hafnocene (IPCF)HfMe2 showed that
the reaction is more complex and in fact proceeds in stages. In
this case a mixture of [(IPCF)HfMe(NMe2Ph)]+ (3) and the
binuclear cation [{(IPCF)HfMe}2(µ-Me)]+ (4) was obtained. The
binuclear species persisted over the temperature range from -30
to +20 °C and was only converted into the mononuclear cation
after standing for several hours at room temperature (see the
Supporting Information). Careful examination of the NMR spectra
of (IPCF)ZrMe2/[HNMe2Ph+][B(C6F5)4-] mixtures at -40 °C
showed that here too the methyl-bridged binuclear complex is
produced in low concentration but is much less stable than the Hf
analogue. It is clear therefore that the reaction of LnMMe2 with
HNMe2Ph+ involves [(LnMMe)2(µ-Me)]+ as the primary product,
which is cleaved by excess HNMe2Ph+ and DMA to give
[LnMMe(NMe2Ph)]+ (Scheme 1).
free DMA. Cooling to -80 °C was necessary to show separate
resonances for free and coordinated DMA; these signals coalesced
at approximately -40 °C.
A number of NMR spectroscopic studies have provided
evidence for dimethylaniline coordination. Schaper et al. have
studied the displacement of MeB(C6F5)3- by DMA in benzene,
giving an outer-sphere complex.7 However, of the zirconocenes
they studied, only in the case of the most open bis-Cp ligands
could an equilibrium species with coordinated DMA be identi-
fied; there was no coordination to bis-indenyl or bis-benzindenyl
species. A survey of the literature on spectroscopic studies of
Zr-DMA species produced a mixture of accounts reporting
either one or two NMe2 signals, with considerable variation in
their δ values. For example, in [(EBI)Zr(Me)(NMe2Ph)][B(4-
C6H4F)4] the resonances for the diastereotopic NMe2 group were
found upfield from free aniline (EBI ) rac-C2H4(1-Ind)2), at δ
1.83 and 1.34 (cf. δ 2.62 for free aniline, solvent C6D5Br at
-20 °C).8 Hollink et al. reported singlets at δ 3.20 and 3.03 in
CD2Cl2 for [Cp(tBu3PdN)Zr(Me)(NMe2Ph)][B(C6F5)4] but were
unable to isolate the compound in an analytically pure form.9
The spectroscopically observed DMA adducts [Me2Si(NBut)2-
ZrR(NMe2Ph)]+ show only single, very broad NMe2 signals with
highly solvent dependent chemical shifts (R ) CH2Ph, C3H6Ph,
CH2CHMeCH2Ph).10 Other relevant reports include the detection
by Buchwald of weak DMA coordination in [(EBTHI)M(H)-
NMe2Ph)][Co(C2B9H11)2] (M ) Zr, Hf)11 and that of Schrock
et al., who reported polydentate zirconium and hafnium amido
complexes where coordinated DMA (with equivalent methyl
groups) did not exchange readily with free DMA on the NMR
The reaction of 1 with [Ph3C][B(C6F5)4] in place of
[HNMe2Ph][B(C6F5)4] gives the ion pair [(IPCF)ZrMe+ · · ·
B(C6F5)4 ], which is, however, very unstable.14 Storing the red-
-
brown solution of this mixture in toluene/1,2-difluorobenzene
at -26 °C for prolonged periods of time produced green
needlelike crystals, along with a dark oily residue. The crystals
were very poorly soluble and very sensitive to solvent removal;
nevertheless, they were found to be suitable for X-ray analysis
and were crystallographically identified as [{(IPCF)Zr(µ-
F)}2][B(C6F5)4]2 · 2(toluene) (5 · 2(toluene)) (Figure 3). The
identity of the bridging atom was determined by refinement of
a number of possible candidates against the data set; the rest of
the model was unchanged during this process. Only fluorine
gave satisfactory displacement parameters after free refinement.
Marks et al. have previously identified monofluoro-bridged
complexes of the type [{(IPCF)ZrR}2(µ-F)]+ (R ) Me,15 C6F516
)
from similar reactions of 1 with various cation generating agents;
both of these contain near-linear Zr-F-Zr bridges with Zr-F
distances substantially shorter than those observed for 5 (ca.
(12) (a) Aizenberg, M.; Turculet, L.; Davis, W. M.; Schattenmann, F.;
Schrock, R. R. Organometallics 1998, 17, 4795. (b) Schrock, R. R.; Casado,
A. L.; Goodman, J. T.; Liang, L.-C.; Bonitatebus, P. J., Jr.; Davis, W. M.
Organometallics 2000, 19, 5325.
(13) Westmoreland, I.; Munslow, I. J.; Clarke, A. J.; Clarkson, G.; Scott,
P. Organometallics 2004, 23, 5066.
(7) Schaper, F.; Geyer, A.; Brintzinger, H.-H. Organometallics 2002,
21, 473.
(8) Horton, A. D.; Orpen, A. G. Organometallics 1991, 10, 3910.
(9) Hollink, E.; Wei, P.; Stephan, D. W. Organometallics 2004, 23, 1562.
(10) Horton, A. D.; de With, J. Organometallics 1997, 16, 5424.
(11) Grossman, R. B.; Doyle, R. A.; Buchwald, S. L. Organometallics
1991, 10, 1501.
(14) Chen, M. C.; Roberts, J. A. S.; Marks, T. J. J. Am. Chem. Soc.
2004, 126, 4605.

Notes
Organometallics, Vol. 27, No. 23, 2008 6373
Table 1. Selected Bond Lengths (Å) and Angles (deg) of the
Halide-Bridged Complexes [{(IPCF)Zr(µ-X)}2]2+[A–]2
X ) F, A )
B(C6F5)4 (5)
X ) Cl, A )
B(C6F5)4 (6)
X ) Br, A )
a
Al(C6F5)4
Zr-X
2.454(4)
2.481(5)
2.154
2.231
2.528
91.27(16)
88.73(16)
118.18
2.5898(11)
2.6046(11)
2.144
2.198
3.844
95.47(4)
84.53(4)
119.40
2.6772(13)
2.7155(13)
2.135
2.197
3.896
92.52(4)
87.48(4)
120.23
Zr-X′
Zr-CtCp
Zr-CtFlu
Zr · · · Zr′
Zr-X-Zr′
X-Zr-X′
Cpcent-Zr-Flucent
a Reference 15.
Figure 4. Structure of [{(IPCF)ZrMe}2(µ-Me)][MeB(C6F5)3] (7).
Ellipsoids are drawn at the 50% probability level.
Scheme 2
Table 2. Selected Bond Lengths (Å) and Angles (deg) of Ion Pairs
[{(IPCF)ZrMe}2(µ-Me)+][A–]
A ) MeB
A ) F
A ) (C6F5)3AlF-Al
a
a
(C6F5)3 (7) {Al(C6F5)3}2
(C12F9)3
Zr-Mebr
2.429(10)
2.257(8)
158.3(3)
4.857(10)
2.4179(3)
2.248(3)
180.0
4.8358(4)
180
2.418(17)(av)
2.253(18)
161.1(6)
4.836(17)
62.79
Zr-Meterm
Zr-Me-Zr′
Zr · · · Zr′
2.1-2.15 Å vs g2.45 Å for 5). The formation of 5 provides
evidence of yet another possible catalyst deactivation product
in this system.
Meterm-Zr-Zr′-Me′term 61.24
a Reference 15.
The chloro-bridged analogue [{(IPCF)Zr(µ-Cl)}2][B(C6F5)4]2 ·
difference of 23 kJ mol-1 is indicative of the surprisingly strong
DMA binding in 2.20 Pyridine, on the other hand, is bound much
some 47 kJ mol-1 more strongly than DMA, as befits a base that
is a powerful catalyst poison.
2(toluene) (6 · 2(toluene)) was isolated from a reaction of 1 with
-
[HNMe2Ph+][B(C6F5)4 ], which evidently contained a chloride
impurity.17 Pertinent structural parameters of 5 and 6 are
collected in Table 1 for comparison, together with those of the
known15 bromo analogue.
Whereas the formation of cationic species with HNMe2Ph+ or
CPh3+ salts is irreversible, the reaction of metallocene dimethyls
with neutral Lewis acids LA is characterized by a set of equilibria,
as studied by Brintzinger and co-workers for LA ) B(C6F5)3
(Scheme 2).18
Experimental Section
General Procedures. All manipulations were performed under
dry nitrogen gas using standard Schlenk techniques. Solvents were
purified by distillation under nitrogen from sodium-potassium alloy
(light petroleum, bp 40-60 °C), sodium (low-sulfur toluene), or
sodium-benzophenone (THF). [HNMe2Ph][B(C6F5)4] was synthe-
sized from NMe2Ph · HCl and Li[B(C6F5)4] in dichloromethane and
recrystallized from a dichloromethane/light petroleum solvent mixture.
Li[B(C6F5)4] was made from B(C6F5)3 and LiC6F5 in light petroleum21
and was free from other borate impurities within NMR detection limits
(19F, 11B) without further purification. The compounds (IPCF)MMe2
(M ) Zr (1), Hf) were synthesized following literature procedures.22
Deuterated toluene was dried by stirring over Na/K alloy followed by
trap-to-trap distillation; 1,2-F2C6H4 was degassed and dried over
activated 4 Å molecular sieves. NMR (1H, 13C, 19F, 11B) spectra were
recorded on a Bruker Avance DPX-300 spectrometer. Chemical shifts
were referenced to residual solvent peaks.
The position of this equilibrium is strongly dependent on the
size of LA: while for B(C6F5)3 the mononuclear product
(IPCF)ZrMe(µ-Me)B(C6F5)3 is preferred,19 bulkier anions such
as FPBB-, MePBB-, and [(C6F5)3Al-F-Al(C12F9)3]- stabilize
the binuclear cation [{(IPCF)ZrMe}2(µ-Me)]+ (PBB ) tris-
(perfluorobiphenylyl)borane).15,16 We now found that cooling
a mixture of 1 with B(C6F5)3in a molar ratio of 2:1 at 4 °C gives
crystalline [{(IPCF)ZrMe}2(µ-Me)][MeB(C6F5)3] (7) as orange
plates (Figure 4). The structure of the cation is similar to previously
reported examples but differs in the much more acute Zr-Me-Zr
angle and the Meterm-Zr-Zr-Meterm torsion angle (Table 2).
Isolation of 7 provides structural evidence for a hitherto missing
member of the reaction equilibrium.
In order to elucidate the strength of Zr-N and Zr-C bonding,
we carried out a series of DFT calculations on the cations in 2 and
7 and, for comparison, on the pyridine analogue of 2, [(IP-
CF)ZrMe(py)]+. The bonding energy of the [(IPCF)ZrMe]+
fragment and dimethylaniline in 2 was found to be -151 kJ mol-1,
significantly stronger than the Zr-C bond to the bridging methyl
ligand in the homobinuclear complex 7 (-128 kJ mol-1). Although
these calculations did not include the effect of solvation, the energy
Variable-temperature NMR spectra of ion pairs were recorded at
temperature intervals of 10 °C. Acquisition relaxation delay (d1) was
12 s and time domain size 65 536 data points. A total of 32-64 scans
were accumulated (1H). Sample concentration was typically in the
1
range 15-20 mM. For VT H NMR experiments, samples were
allowed to equilibrate at each temperature for 5-10 min. Stock
solutions of DMA in toluene-d8 were 0.1 M.
[(IPCF)ZrMe(NMe2Ph)][B(C6F5)4] (2). (IPCF)ZrMe2 (16.1 mg,
41 µmol) and [HNMe2Ph][B(C6F5)4] (31.5 mg, 39 µmol) were
dissolved in toluene (10 mL). This gave a red-orange solution, and a
dark red oily residue settled on the bottom of the Schlenk tube. When
(15) Chen, M. C.; Robertson, J. A. S.; Seyam, A. M.; Li, L.; Zuccaccia,
C.; Stahl, N. G.; Marks, T. J. Organometallics 2006, 25, 2833.
(16) Chen, Y. X.; Metz, M. V.; Li, L.; Stern, C. L.; Marks, T. J. J. Am.
Chem. Soc. 1998, 120, 6287.
(17) For details of the structure see the Supporting Information.
(18) (a) Haselwander, T.; Beck, S.; Brintzinger, H. H. In Ziegler
Catalysts-Recent Scientific InnoVations and Technological ImproVements;
Fink, G., Mu¨lhaupt, R., Brintzinger, H. H., Eds.; Springer: Berlin, 1995; p
181. (b) Beck, S.; Prosenc, M. H.; Brintzinger, H. H.; Goretzki, R.; Nerfert,
H.; Fink, G. J. Mol. Catal. A 1996, 111, 67.
(20) Strong DMA coordination was also observed in the reaction of
[HNMe2Ph][B(C6F5)4] with (SBI)ZrMe2: [(SBI)ZrMe(NMe2Ph)]+ shows two
signals for diastereotopic N-methyl groups around δ 2.1 and 1.5 (-30 to
+20 °C) which coalesce and exchange with free DMA on heating to 50 °C
(δ 1.95) (SBI ) rac-Me2Si(Ind)2).
(21) (a) Massey, A. G.; Park, A. J.; Stone, F. G. A. Proc. Chem. Soc.
[London] 1963, 212. (b) Massey, A. G.; Park, A. J. J. Organomet. Chem.
1964, 2, 245.
(19) Chen, M. C.; Roberts, J. A.; Marks, T. J. J. Am. Chem. Soc. 2004,
126, 4605.
(22) Ewen, J. A.; Jones, R. L.; Razavi, A.; Ferrara, J. D. J. Am. Chem.
Soc. 1988, 110, 6255.

6374 Organometallics, Vol. 27, No. 23, 2008
Notes
the temperature was lowered overnight to -26 °C, red crystals formed
on the sides of the vessel and, after a further couple of days, the solution
was observed to have lightened in color, turning a very pale red, and
more crystals had formed, identified crystallographically as 2 · 2(tolu-
ene). Because of the small crop of crystalline material, an elemental
analysis was not obtained. VT 1H NMR studies of a solution generated
from (IPCF)ZrMe2 (9.0 mg, 23 µmol) and [HNMe2Ph][B(C6F5)4] (18.2
mg, 23 µmol) in toluene-d8/1,2-difluorobenzene (1/1 v/v) were
conducted over the temperature range -30 to +20 °C. 1H NMR (300.1
MHz, 0 °C, toluene-d8/C6H4F2; 1/1): δ 7.4-6.1 (Flu, overlapped with
toluene, C6H4F2, Me2NPh and remaining C5H4 1H), 5.23 (m, 1H,
C5H4), 4.95 (m, 1H, C5H4), 4.87 (m, 1H, C5H4), 2.35 (s, 2H; free
NMe2), 1.90 (s, 3H, NMe), 1.83 (s, 3H, CMe), 1.60 (s, 3H, CMe),
1.34 (s, 3H, NMe), -0.78 (s, 3H, ZrMe).
In separate experiments, addition of DMA (5 µmol, 0.05 mL of
stock solution) to a mixture of (IPCF)ZrMe2 (4.9 mg, 13 µmol) and
[HNMe2Ph][B(C6F5)4] (9.8 mg, 12 µmol) in toluene-d8/1,2-difluo-
robenzene (1/1 v/v) caused the signal at δ 2.35 to increase in intensity,
accompanied by a downfield shift to δ 2.50 (at 0 °C). Warming to 40
°C resulted in coalescence of the NMe2 signals of coordinated DMA
at δ 1.77.
(300.1 MHz, 25 °C, toluene-d8/1,2-difluorobenzene; ca. 4/1): δ 7.8-6.0
(Flu, overlapped with toluene, DFB, DMA, and remaining C5H4 2H
signals), 5.6-4.8 (C5H4 multiplets, total of 6H), 1.80-1.69 (4s, total
of 12H, CMe), 1.25 (v br, s, 3H, MeB), -1.22 (s, 4H, ZrMe), -1.29
(s, 2H, ZrMe), -3.27 (s, 1H, µ-Me) and -3.39 (s, 2H, µ-Me).
Computational Details. The Gaussian-98 package was used for
all calculations.23 Calculations were carried out “in the gas phase”
with the gradient-corrected functional B3LYP and the Lanl2dz basis
set for all atoms. To establish comparison with the experiment, the
interaction energy was calculated as a function of the Zr-N bond
distance. The calculated equilibrium distance was shown to correspond
very closely to the crystallographically determined value.
X-ray Crystallography. In all cases, crystals were suspended in
perfluorinated polyether oil, mounted on a glass fiber, and transferred
directly to the cold N2 stream of the diffractometer. Data for compound
2 were collected on a Bruker-Nonius KappaCCD diffractometer
equipped with a Bruker-Nonius FR591 molybdenum rotating anode
(λ(Mo KR) ) 0.710 69 Å) and confocal mirrors; data collection and
processing were controlled by the DENZO and SCALEPACK pro-
grams.24 Diffraction data for compound 5 were collected on a Bruker
SMART APEX2 CCD diffractometer at Daresbury SRS station
16.2smx operating at the wavelength λ ) 0.797 70 Å; data collection
and processing were carried out using the APEX2 and SAINT
packages.25 For compounds 6 and 7, data collection took place on an
Oxford Diffraction Xcalibur-3 system equipped with a molybdenum
target and Enhance optics; collection and processing used the CrysAlis-
CCD and -RED packages.26
In all cases, structure solution was carried out by the direct methods
routines in the SIR-92 program27 and refined by full-matrix least-
squares methods on F2 in SHELXL28 within the WinGX program
suite.29 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. For crystal and refinement data see the Supporting Information
(Table S1).
In compound 7, the location of hydrogen atoms on the bridging
carbon C(1) could not be determined from the diffraction data. The
geometry at this carbon is also unlike that of the standard models for
hydrogen placement. These hydrogen atoms were therefore omitted
from the model, although they have been included in the calculation
of the molecular formula.
Freezing a mixture of solid [(IPCF)ZrMe2 (7.0 mg, 18 µmol) and
solid [HNMe2Ph][B(C6F5)4] (14.8 mg, 18 µmol)] prior to solvent
addition permitted the simultaneous formation of both 2 and 7 to be
observed over the range -30 to 0 °C. The latter was indicated by the
1
following H NMR singlet resonances (300.1 MHz, 0 °C): δ -1.19
(ZrMe), -1.25 (ZrMe), -3.22 (µ-Me), and -3.39 (µ-Me), ratio of
2:4:2:1 for the two diastereomers of the [{(IPCF)ZrMe}2(µ-Me)]+
cation. However, by the time the sample reached 20 °C, none of this
homodinuclear cation remained.
Reaction of (IPCF)HfMe2 with [HNMe2Ph][B(C6F5)4]. The
orange-red solution obtained from the reaction of (IPCF)HfMe2 (8.2
mg, 20 µmol) with [HNMe2Ph][B(C6F5)4] (8.2 mg, 20 µmol) in
1
toluene-d8/1,2-difluorobenzene (1/1 v/v) was studied by H NMR
spectroscopy over the temperature range -30 to +20 °C. Resonances
indicative of both [(IPCF)HfMe(NMe2Ph)]+ (3) and [{(IPCF)Hf-
Me}2(µ-Me)]+ (4) were observed which persisted over the entire
temperature range. An ambient-temperature 1H NMR spectrum
recorded after 24 h revealed predominantly signals belonging to 3,
with just a trace of 4 remaining. Cation 3: 1H NMR (300.1 MHz, 26
°C, toluene-d8/C6H4F2 1/1) δ 7.7-6.0 (Flu, overlapped with toluene,
difluorobenzene, DMA and remaining C5H4 1H), 5.52 (m, 1H, C5H4),
5.11 (m, 1H, C5H4), 4.87 (m, 1H, C5H4), 2.48 (s, 6H, free NMe2),
1.94 (s, 3H, CMe2), 1.83 (b, 3H, NMe2), 1.68 (s, 3H, CMe2), 1.49 (b,
Acknowledgment. This work was supported by the Engi-
neering and Physical Sciences Research Council. We thank Dr.
Louise Male (EPSRC National Crystallographic Service, Uni-
versity of Southampton) and Dr. Ross Harrington (Daresbury
Synchrotron) for collecting X-ray data for compounds 2 and 5,
respectively, and Prof. R. D. Cannon (UEA) for helpful
discussions.
1
3H, NMe2), -0.83 (s, 3H, HfMe). Cation 4: H NMR (300.1 MHz,
20 °C, toluene-d8//C6H4F2 1/1) HfMe signals, all singlets, ratio of 2/2/
1/1, -1.41 (HfMe), -1.45 (HfMe), -3.31 (µ-Me), -3.41 (µ-Me).
[{(IPCF)Zr(µ-F)}2][B(C6F5)4]2 (5). (IPCF)ZrMe2 (7.3 mg, 19
µmol) and [Ph3C][B(C6F5)4] (17.2 mg, 19 µmol) were dissolved in
toluene (5 mL). The red-brown solution was stored at 4 °C. After
several weeks, green needlelike crystals had formed, along with a dark
oily residue, and the solution had turned more pale. The crystals, green
blocks, were identified by single-crystal X-ray diffraction as 5 · 2(tolu-
ene).
Supporting Information Available: Figures, tables, and CIF
files giving NMR spectra of 2 and of hafnocene complexes and
X-ray data for compounds 2, 5, 6, and 7. This material is available
free of charge via the Internet at http://pubs.acs.org.
[{(IPCF)Zr(µ2-Cl)}2][B(C6F5)4]2 (6). In a 5 mm NMR tube
equipped with a Teflon seal, (IPCF)ZrMe2 (3.5 mg, 9 µmol) and
[HNMe2Ph][B(C6F5)4]. (7.2 mg, 9 µmol) were dissolved in toluene-
d8/C6H4F2 (1 mL, 4/1 v/v), giving a purple solution. The sample was
left at room temperature for several hours. During this time green
crystals of 6 · 2(toluene) were formed which were suitable for X-ray
diffraction.
OM800783H
(23) Frisch, M. J., et al. Gaussian98; Gaussian, Inc., Pittsburgh, PA, 1998.
(24) Otwinowski, Z.; Minor, W. In Methods in Enzymolology; Carter,
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276, pp 307-326.
(25) APEX2; Bruker AXS Inc., Madison, WI, 2004. SAINT; Bruker
AXS Inc., Madison, WI, 2004.
[{(IPCF)ZrMe}2(µ-Me)][MeB(C6F5)3] (7). (IPCF)ZrMe2 (32.5
mg, 83 µmol) and B(C6F5)3 (5.8 mL, 41 µmol, from a 71.3 mM stock
solution in toluene) were combined to give an orange-red solution,
which was stored at 4 °C. This yielded dark orange, featherlike crystals.
The solid was identified by X-ray diffraction. Anal. Calcd for
C64H48BF15Zr2: C, 59.35; H, 3.74. Found: C, 58.85; H, 4.31. 1H NMR
(26) CrysAlis-CCD and -RED; Oxford Diffraction Ltd., Abingdon,
Oxford, U.K., 2006.
(27) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl.
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(29) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.