[Me2Al(THF)2]+[{Me2Si(NDipp) 2}2Zr2Cl5]- (Dipp = 2,6-diisopropylphenyl), an unusual zirconium/aluminum ion pair containing a THF-stabilized dimethylaluminum cation

Article abstract of DOI:10.1021/om0201819

The bulky chelating dianion Me₂Si(NDipp^-)₂ was used to synthesize [{Me₂Si(NDipp)₂}-ZrCl₂(THF)₂] (Dipp=2,6-diisopropylphenyl). The nitrogen atoms of the chelating diamide and the cis oxygen atoms of the THF ligands defined a plane around Zr. The reactions were conducted under an atmosphere of dry argon and manipulated either on a double-manifold vacuum line or in a dinitrogen-filled drybox.

Full text of DOI:10.1021/om0201819

3258
Organometallics 2002, 21, 3258-3262
[Me2Al(THF )2]+[{Me2Si(NDip p )2}2Zr 2Cl5]- (Dip p )
2,6-Diisop r op ylp h en yl), a n Un u su a l Zir con iu m /Alu m in u m
Ion P a ir Con ta in in g a THF -Sta bilized
Dim eth yla lu m in u m Ca tion
Michael S. Hill* and Peter B. Hitchcock
School of Chemistry, Physics and Environmental Science, University of Sussex, Falmer,
Brighton BN1 9QJ , U.K.
Received March 4, 2002
The bulky chelating dianion Me2Si(NDipp-)2 has been used to synthesize [{Me2Si(NDipp)2}-
ZrCl2(THF)2] (Dipp ) 2,6-diisopropylphenyl). Reaction of Al2Me6 and [{Me2Si(NDipp)2}ZrCl2-
(THF)2] affords the unusual ionic complex [Me2Al(THF)2]+[{Me2Si(NDipp)2}2Zr2Cl5]-.
We have recently begun an exploration of new kineti-
cation.8 It is now recognized that this active species is
merely a single component in a set of complex solution
equilibria that consist predominantly of dormant spe-
cies.9 The isolation and identification of defined reaction
products from treatment of typical zirconium “precata-
lysts” with stoichiometric quantities of trialkylalumi-
num reagents may provide insight into the nature of
these solution equilibria. For example, Stephan has
recently sought to model the interaction of zirconium
phosphinimide catalyst precursors with MAO by reac-
tion with AlMe3. This allowed the identification of the
zirconium cluster compounds (Cp*Zr)4(µ-Cl)5(Cl)(µ-CH)2
and (Cp*Zr)5(µ-Cl)6(µ-CH)3, which were presented as
possible products of catalyst decomposition pathways.10
With similar intent, we now wish to report the applica-
tion of 1 in the synthesis of the chelated diamido-
zirconium dichloride 3 and the stoichiometric reaction
of 3 with trimethylaluminum (Scheme 1).
cally stabilizing σ- and π-ligand systems with sufficient
bulk to enable the isolation of low-coordinate, reactive
metal centers and unusual group 3 containing bimetal-
lics.1,2 As part of this general program of research we
have now turned our attention to chelating silyl dia-
mides of the form Me2Si(RN-)2 (R ) alkyl, aryl). This
class of ligand has been extensively applied in the
synthesis of main-group and transition-metal com-
plexes.3 It is somewhat surprising, therefore, that the
dianion derived from the ligand precursor, 1 (Scheme
1), bearing the bulky yet readily available 2,6-diisopro-
pylphenyl substituent, has not been exploited previously
(despite the potential of 1 having been remarked upon
over a decade ago).4
The past few years have witnessed an increasing
interest in the use of polydentate amides as suitable
spectator ligands in zirconium(IV) chemistry.5 Many of
these reports are motivated by the application of these
complexes as new generation “nonmetallocene” olefin
polymerization catalysts.6 The catalytic species are
commonly generated in situ by activation with a large
(typically 500 equiv) excess of commercially available
methylalumoxane (MAO).7 This ill-defined material can
contain up to 40% unreacted trimethylaluminum and
produces, via a series of alkylation and alkide abstrac-
tion reactions, a catalytically active zirconium alkyl
Resu lts a n d Discu ssion
The amine precursor 1 was synthesized by a method
similar to that reported for [Me2Si(MesNH)2] (Mes )
2,4,6-trimethylphenyl).4 Compound 1 may be conve-
n
niently deprotonated with 2 equiv of BuLi in hexane.
Under these conditions 2 precipitates as a colorless
powder, giving NMR data identical with those of an
analytically pure crystalline sample obtained from
concentrated hexane solution. Crystals of the dilithium
derivative 2 were subjected to a single-crystal X-ray
diffraction study. Compound 2 crystallizes as discrete
dimeric molecules with no crystallographically imposed
symmetry. There are two independent but chemically
identical molecules in the asymmetric unit, one of which
is illustrated in Figure 1. The dimeric units of 2 are
reminiscent of those in the structure of [Me2Si(t-
BuNLi)2]2,11 in that the primary coordination of the
* To whom correspondence should be addressed. E-mail: m.s.hill@
sussex.ac.uk. Fax: (+44)1273-677196.
(1) Hill, M. S.; Hitchcock, P. B. Organometallics 2002, 21, 220.
(2) Hill, M. S.; Hitchcock, P. B. Angew. Chem., Int. Ed. 2001, 40,
4089.
(3) Veith, M. Chem. Rev. 1990, 90, 3.
(4) Chen, H.; Bartlett, R. A.; Rasika Dias, H. V.; Olmstead, M. M.;
Power, P. P. Inorg. Chem. 1991, 30, 2487.
(5) For example see: (a) Kempe, R. Angew. Chem., Int. Ed. 2000,
39, 469. (b) Cloke, F. G. N.; Hitchcock, P. B.; Love, J . B. J . Chem. Soc.,
Dalton Trans. 1995, 25. (c) Cloke, F. G. N.; Geldbach, T. J .; Hitchcock,
P. B.; Love, J . B. J . Organomet. Chem. 1996, 506, 343. (d) Baumann,
R.; Davis, W. M.; Schrock, R. R. J . Am. Chem. Soc. 1997, 119, 3830.
(e) Schattenmann, F. J .; Schrock, R. R.; Davis, W. M. Organometallics
1998, 17, 989.
(6) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428.
(7) Barron, A. R. Organometallics 1995, 14, 3581.
(8) Chen, E. Y.-X.; Marks, T. J . Chem. Rev. 2000, 100, 1391.
(9) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255.
(10) Yue, N.; Hollink, E.; Gue´rin, F.; Stephan, D. W. Organometallics
2001, 20, 4424. For a recent example in titanium chemistry see: Coles,
M. P.; Hitchcock, P. B. J . Chem. Soc., Dalton Trans. 2001, 1169.
10.1021/om0201819 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 06/25/2002

[Me2Al(THF)2]+[{Me2Si(NDipp)2}2Zr2Cl5]-
Organometallics, Vol. 21, No. 15, 2002 3259
Sch em e 1
lithium atoms is provided by the nitrogen centers. The
N4Li4 core is shown in Figure 2. Li(2) and Li(3) are
bound by three nitrogen atoms, which gives rise to
approximate trigonal-pyramidal coordination for these
metals. Li(1) and Li(4) are also coordinated by two short
Li-N interactions and by two close contacts to the ipso
carbon atoms of the Dipp substituents. While this
results in the loss of the approximate D2d symmetry
observed in [Me2Si(t-BuNLi)2]2,11 the formation of a
“ladder” structure, directed by the formation of η6-aryl
to lithium interactions, like that of [Me2Si(MesNLi)2]2,
is prevented by the greater steric demands of the
isopropyl groups.4
The highly sterically demanding Dipp susbstituent
has been employed in McConville’s chelated diamidozir-
conium olefin polymerization catalysts.12 Zirconium
complexes supported by silyl diamides similar to 2 but
bearing less sterically demanding substituents have
been reported previously,13 and N-substituted 2,6-
dimethylphenyl derivatives have been studied in the
context of olefin polymerization catalysis.14 Initial at-
tempts to synthesize base-free zirconium derivatives of
1 in wholly hydrocarbon solvents were unsuccessful.
However, reaction of 2 with 1 equiv of ZrCl4 in THF
provided, upon crystallization from toluene, the colorless
zirconium dichloride complex 3 in high (80%) yield. Like
the previously reported [{Me2Si(t-BuN)2}ZrCl2(THF)2]15
and [CH2(CH2NSiMe3)2ZrCl2(THF)2],16 complex 3 con-
tains two molecules of THF per zirconium center. 3 is
F igu r e 1. Molecular structure of 2 (25% probability
ellipsoids). H atoms were omitted for clarity. Selected bond
lengths (Å): Li(1)-N(1), 1.930(10); Li(1)-N(3), 1.959(10);
Li(1)‚‚‚C(1), 2.312(10); Li(1)‚‚‚C(25), 2.436(11); Li(2)-N(3),
1.993(10); Li(2)-N(2), 2.111(12); Li(2)-N(1), 2.269(14);
Li(3)-N(4), 2.028(10); Li(3)-N(1), 2.149(11); Li(3)-N(2),
2.222(11); Li(4)-N(4), 1.883(10); Li(4)-N(2), 1.952(10);
Li(4)‚‚‚C(13), 2.208(10).
1
robust in solution, and H NMR studies undertaken in
C6D6 or d8-toluene indicate none of the partial loss or
exchange of THF reported for [{Me2Si(t-BuN)2}ZrCl2-
(THF)2].15 The methyl groups of the isopropyl substit-
uents are diastereotopic and appear as two doublets in
the 1H NMR spectrum. We interpret this to be a
consequence of restricted rotation about the N-Cipso
bonds.12
Such steric interactions were also evident in the solid-
state structure of 3, determined by an X-ray diffraction
(11) Brauer, D. J .; Bu¨rger, H.; Liewald, G. R. J . Organomet. Chem.
1986, 308, 119.
(12) (a) Scollard, J . D.; McConville, D. H.; Vittal, J . J . Organo-
metallics 1995, 14, 5478. (b) Scollard, J . D.; McConville, D. H.; Vittal,
J . J . Organometallics 1997, 16, 4415.
(13) Brauer, D. J .; Burger, H.; Essig, E.; Geswandtner, W. J .
Organomet. Chem. 1980, 190, 343.
(14) Gibson, V. C.; Kimberley, B. S.; White, A. J . P.; Williams, D.
J .; Howard, P. Chem. Commun. 1998, 313.
(15) Horton, A. D.; de With, J . Organometallics 1997, 16, 5424.
(16) (a) Friedrich, S.; Gade, L. H.; Scowen, I. J .; McPartlin, M.
Organometallics 1995, 14, 5344. (b) Gade, L. H.; Friedrich, S.; Tro¨sch,
D. J . M.; Scowen, I. J .; McPartlin, M. Inorg. Chem. 1999, 38, 5295.
F igu r e 2. Ball and stick representation of the N4Li4
core of 2.

3260 Organometallics, Vol. 21, No. 15, 2002
Hill and Hitchcock
F igu r e 3. Molecular structure of 3 (25% probability
ellipsoids). H atoms were omitted for clarity. Selected bond
lengths (Å) and angles (deg): Zr-N(1), 2.050(2); Zr-N(2),
2.051(2); Zr-Cl(1), 2.473(1); Zr-Cl(2), 2.473(1); Zr-O(1),
2.312(2); Zr-O(2), 2.326(2); N(1)-Zr-N(2), 76.83(9); N(2)-
Zr-O(1), 170.98(9); N(1)-Zr-O(1), 95.21(8); N(2)-Zr-O(2),
95.37(9); N(1)-Zr-O(2), 170.58(10); O(1)-Zr-O(2), 92.93(8);
N(2)-Zr-Cl(2), 96.62(7); N(1)-Zr-Cl(2), 103.35(7); O(1)-
Zr-Cl(2), 80.95(6); O(2)-Zr-Cl(2), 82.60(7); N(2)-Zr-
Cl(1), 102.24(7); N(1)-Zr-Cl(1), 96.72(7); O(1)-Zr-Cl(1),
82.70(6); O(2)-Zr-Cl(1), 79.60(7); Cl(2)-Zr-Cl(1), 155.10(3).
F igu r e 4. Molecular structure of 4 (25% probability
ellipsoids). Isopropyl Me groups were omitted for clarity.
Selected bond lengths (Å) and angles (deg): Zr(1)-N(4),
2.014(5); Zr(1)-N(3), 2.029(4); Zr(1)-Cl(1), 2.457(2); Zr(1)-
Cl(3), 2.611(2); Zr(1)-Cl(4), 2.655(2); Zr(1)-Cl(5), 2.694(2);
Al-O(1), 1.822(7); Al-O(2), 1.849(5); Al-C(54), 1.924(11);
Al-C(53), 1.931(11); O(1)-Al-O(2), 97.0(3); O(1)-Al-
C(54), 104.4(6); O(2)-Al-C(54), 107.4(4); O(1)-Al-C(53),
109.2(5); O(2)-Al-C(53), 107.3(4); C(54)-Al-C(53), 127.4(7).
proposed by eq 1, in which Al2Me6 acts both as a
methylating reagent and as a Lewis acid capable of
abstracting residual THF from the coordination sphere
of 3.
study (Figure 3). This revealed distorted-octahedral
coordination at zirconium and confirmed the overall C2
symmetry inferred from the multinuclear NMR studies.
The nitrogen atoms of the chelating diamide and the
cis oxygen atoms of the THF ligands define a plane
around Zr (the rms deviation of the N1N2O1O2ZrSi
plane is 0.0831 Å). Despite the small bite of the diamido
chelate (N(1)-Zr-N(2) ) 76.84(2)°), the Cl(1)-Zr-Cl(2)
angle is somewhat bent from linearity (155.09(3)°) by
the steric compression caused by the large Dipp sub-
stituents.
Complex 4 was obtained as large colorless crystals in
ca. 60% isolated yield after reaction of 3 with 1 equiv of
Al2Me6 in toluene and crystallization from the same
solvent. 4 was shown by X-ray diffraction analysis to
be the ionic complex [Me2Al(THF)2]+[{Me2Si(NDipp)2}2-
Zr2Cl5]- (Figure 4). The solid-state structure of 4
comprises a bis-THF-solvated dimethylaluminum cation
and a dinuclear zirconium anion in which the coordina-
tion sphere of each six-coordinate zirconium center is
provided by chelation of a single diamido ligand, three
bridging chlorides, and a single terminal chloride.
Compound 4 may have formed as the result of a series
of reaction steps initiated by partial methylation of
zirconium to form Me2AlCl. Subsequent fast chloride
abstraction by the remaining 3 from Me2AlCl and
stabilization of the resultant alumocenium cation by
coordination of THF would then result in the formation
of 4. We have not yet been successful in the isolation of
other products from this reaction. However, examination
of the brown glassy solid remaining after evaporation
Although, to the best of our knowledge, the isolation
of an ion pair of this general structure is unprecedented,
complex equilibria that include similar alkylation reac-
tions have long been acknowledged as a characteristic
of both homogeneous and heterogeneous Ziegler-Natta
chemistry.17 Variable-temperature 1H and 13C NMR
studies in d8-toluene suggested that such equilibria may
be established upon redissolving a pure sample of 4 (see
the Supporting Information). The 1H and 13C NMR
spectra at 348 K revealed the presence of three species
that exist in an approximate 6:3:1 ratio. These were
identified by selective decoupling of the observed iso-
propyl methine protons at 3.83 (major), 3.24, and 2.72
ppm (minor) from the respective ligand methyl reso-
1
of volatiles from the mother liquor of 4 by H NMR in
C6D6 indicated a complex mixture containing the intact
diamido ligand and coordinated THF, along with mul-
tiple methylaluminum or methylzirconium environ-
ments. The isolated yield of 4 is consistent with an
overall reaction stoichiometry similar to that tentatively
1
nances at 1.24, 1.13, and 1.05 ppm in the H NMR. Spin
saturation transfer experiments at this temperature,
(17) Sinn, H.; Kaminsky, W. Adv. Organomet. Chem. 1980, 18, 99.

[Me2Al(THF)2]+[{Me2Si(NDipp)2}2Zr2Cl5]-
Organometallics, Vol. 21, No. 15, 2002 3261
was warmed to room temperature. This was filtered to remove
precipitated LiCl before evaporation of volatiles to yield 1 in
stoichiometric yield as a colorless viscous oil which crystallized
on standing. Anal. Calcd for C26H42N2Si: C, 76.01; H, 10.33;
however (using 2 s of irradiation on the peak of interest),
showed no sign of exchange between any of the solution
components. Although this behavior may also be a result
of decomposition at the elevated temperature of the
experiment, it is not currently possible to assign the
identity of any of these species to a structure corre-
sponding to compound 4. The observation of both bound
and free THF (in a 2:1 ratio by integration) indicates
that the integrity of the [Me2Al(THF)2]+ cation is also
not maintained in solution at 348 K. When a sample of
4 is cooled, complex reversible changes occur. At 248 K
at least six separate sets of signals (that broaden with
further cooling to 198 K) may be assigned to ligand
isopropyl groups. The upfield signals (>ca. -0.5 ppm)
arising from the aluminum-bonded methyl groups of 4
behave in a similarly complex manner. It is, however,
not possible to distinguish between Al-Me and Zr-Me
signals.
It is possible to regard compound 4 as an intermediate
in an alkylation sequence reminiscent of those proposed
for systems relevant to practical homogeneous olefin
polymerization. There has been recent interest in the
application of low-coordinate organoaluminum cations
as catalysts for olefin polymerization in their own
right,18 and organoaluminum cations of the form [R2-
Al(donor)2]+ have also been shown to act as activators
in polymerization catalysis.19 Studies of other model
systems have shown that alumoxanes themselves can
display Lewis base character.20 The formation of cationic
organoaluminum species effectively “immobilized” upon
the Al-O-Al framework of MAO, and the possible
mechanistic implications of their existence, cannot
therefore be discounted. Studies are continuing, to
discover the reactivity of 3 with other tri- and diorga-
noaluminum reagents and to clarify the behavior of 4
in solution.
1
N, 6.82. Found: C, 76.28; H, 10.50; N, 6.70. H NMR: δ 0.21
(s, 6H, SiMe2), 1.17 (d, 24H, CH(CH3)2), 2.63 (s, 2H, NH), 3.51
(sept, 4H, CH(CH3)2), 7.09 (d, 4H, Hmeta), 7.15 (s, 2H, Hpara).
13C{1H} NMR: δ 0.0 (SiMe2), 23.8 (CH(CH3)2), 28.6 (CH(CH3)2),
123.5 (Cmeta), 124.5 (Ar-iPr), 138.7 (Cipso), 144.5 (Cpara). 29Si
NMR: δ -8.3.
[Me2Si(Dip p NLi)2]2 (2). A solution of nBuLi (4.9 mL of a
2.5 M solution in hexane) was added dropwise to a stirred
solution of 1 (2.50 g, 6.10 mmol) in hexane (40 mL) at room
temperature, producing an exothermic reaction and a colorless
precipitate. Filtration and washing with hexane (25 mL)
yielded 2 as a colorless pyrophoric powder (2.11 g, 82%).
Crystals suitable for a single-crystal X-ray diffraction analysis
were isolated upon concentration of the combined hexane
washings. Anal. Calcd for C52H80Li4N4Si2: C, 73.88; H, 9.56;
N, 6.64. Found: C, 73.81; H, 9.54; N, 6.64. 1H NMR: δ 0.01
(s, 6H, SiMe2), 1.26 (d, 24H, CH(CH3)2), 3.71 (sept, 4H,
CH(CH3)2), 6.88 (t, 2H, Hpara), 7.01 (d, 4H, Hmeta). 13C{1H}
NMR: δ 4.0 (SiMe2), 24.6 (CH(CH3)2), 27.4 (CH(CH3)2), 121.0
7
(Ar-iPr), 125.2 (Cmeta), 144.1 (Cpara), 147.7 (Cipso). Li NMR: δ
1.97. 29Si NMR: δ -15.9.
[Me2Si(Dip p N)2Zr Cl2(THF )2] (3). A solution of 2 (0.98 g,
2.32 mmol) in THF (20 mL) was added dropwise to a solution
of ZrCl4 (0.54 g, 2.32 mmol) in THF (25 mL) at -78 °C. The
pale yellow reaction mixture was warmed to room temperature
and stirred for a further 2 h, after which the solvent was
removed under vacuum. The product was extracted with
toluene (30 mL) and filtered to remove LiCl. Concentration to
ca. 15 mL and crystallization at room temperature gave 3 as
colorless blocklike crystals suitable for an X-ray diffraction
analysis (1.31 g, 79.4%). Anal. Calcd for C34H50Cl2N2O2SiZr:
C, 57.55; H, 7.05; N, 3.95. Found: C, 57.58; H, 6.92; N, 3.86.
1H NMR: δ 0.45 (s, 6H, SiMe2), 1.07 (m, 8H, THF), 1.39 and
1.48 (d, 24H, CH(CH3)2), 3.77 (m, 8H, THF), 4.37 (sept, 4H,
CH(CH3)2), 7.08 (t, 2H, Hpara), 7.19 (d, 4H, Hmeta). 13C{1H}
NMR: δ 2.9 (SiMe2), 24.9 (THF), 25.7 (CH(CH3)2), 27.1 (CH-
(CH3)2), 27.4 (CH(CH3)2), 72.6 (THF) 123.9 (Ar-iPr), 124.5
(Cmeta), 143.8 (Cpara), 145.0 (Cipso). 29Si NMR: δ -33.7. MS: m/z
644 (25, M+ - THF).
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions were conducted
under an atmosphere of dry argon and manipulated either on
a double-manifold vacuum line or in a dintrogen-filled drybox
operating at less than 1 ppm of O2. Solvents were purified by
distillation from an appropriate drying agent (toluene and THF
from potassium, diethyl ether from Na/benzophenone, and
hexane from Na/K alloy). NMR spectra were recorded on a
Bruker AMX 500 instrument at 300.13 (1H), 125.8 (13C), 99.4
(29Si), and 116 MHz (7Li) from samples in C6D6, chemical shifts
are given relative to SiMe4 and aqueous LiCl, and intensities
of the quaternary and 29Si signals were enhanced by INEPT
polarization transfer. Mass spectra were obtained on a Fisons
Instruments VG Autospec spectrometer at 70 eV.
[Me2Al(THF )2][{Me2Si(NDip p )2}2Zr 2Cl5] (4). A solution
of 3 (0.85 g, 1.20 mmol) in toluene (30 mL) was treated at room
temperature with Al2Me6 (2.0 M in hexane, 0.60 mL) and the
resulting gray solution stirred for 2 h. Concentration to
incipient crystallization (ca. 15 mL) followed by warming and
slow cooling to room temperature produced 4‚3C7H8 as large
colorless crystals (0.45 g, 45%). A further crop of analytically
pure crystalline material (0.15 g, 15%) was obtained upon
cooling the residual mother liquor to -30 °C. Anal. Calcd for
C
83H126N4AlCl5O2Si2Zr2: C, 60.19; H, 7.61; N, 3.38. Found: C,
59.94; H, 7.52; N, 3.28.
Cr ysta llogr a p h ic Mea su r em en ts. Crystal data for 2:
Me2Si(Dip p NH)2 (1; Dip p ) 2,6-i-P r 2C6H3). A solution of
nBuLi (18.1 mL of a 2.5 M solution in hexane) was added to a
stirred solution of freshly distilled H2NDipp (8.0 g, 45.2 mmol)
in diethyl ether (150 mL) at -78 °C. The pale yellow solution
was warmed to room temperature before being recooled to -78
°C. Dropwise addition of a solution of Me2SiCl2 (2.92 g, 22.6
mmol) in diethyl ether (20 mL) produced a hazy solution that
C
52H80Li4N4Si2, Mr ) 845.14, triclinic, space group P1h (No. 2),
a ) 13.1790(8) Å, b ) 20.5792(9) Å, c ) 20.6279(13) Å, R )
86.418(4)°, â ) 86.917°, γ ) 75.749(4)°, U ) 5407.5(5) Å3, T )
250(2) K, Z ) 4, Dc ) 1.04 g cm-3, 26 135 reflections, 12 999
unique reflections (Rint ) 0.057), 9173 reflections with I > 2σ(I);
R1, wR2 ) 0.072, 0.191 (I > 2σ(I)) and 0.107, 0.214 (all data).
Crystal data for 3: C34H50N2O2Cl2SiZr, Mr ) 708.97, mono-
clinic, space group P21/c (No. 14), a ) 10.4851(3) Å, b )
18.5447(7) Å, c ) 19.1721(5) Å, â ) 95.139(2)°, U ) 3712(2)
Å3, T ) 173(2) K, Z ) 4, Dc ) 1.27 g cm-3, 16 064 reflections,
6532 unique reflections (Rint ) 0.053), 4945 reflections with I
> 2σ(I); R1, wR2 ) 0.041, 0.105 (I > 2σ(I)) and 0.064, 0.116
(all data). Crystal data for 4‚3(toluene): C83H126AlN4O2Cl5Si2-
Zr2, Mr ) 1654.73, triclinic, space group P1h (No. 2), a )
16.2531(9) Å, b ) 17.1893(9) Å, c ) 18.3172(10) Å, R )
79.160(3)°, â ) 67.470(2)°, γ ) 69.910(3)°, U ) 4429.9(4) Å3, T
(18) Dagorne, S.; Guzei, I. A.; Coles, M. P.; J ordan, R. F. J . Am.
Chem. Soc. 2000, 122, 274 and references therein. For theoretical
refutation of this observed reactivity see: Talarico, G.; Buscio, V.;
Budzelaar, P. H. M. Organometallics 2001, 20, 4721. Talarico, G.;
Budzelaar, P. H. M. Organometallics 2002, 21, 34.
(19) Klosin, J .; Roof, G. R.; Chen, E. Y.-X.; Abboud, K. A. Organo-
metallics 2000, 19, 4684. For a general review of cationic group 13
compounds see: Atwood, D. A. Coord. Chem. Rev. 1998, 176, 407.
(20) Harlan, C. J .; Bott, S. G.; Barron, A. R. J . Am. Chem. Soc. 1995,
117, 6465.

3262 Organometallics, Vol. 21, No. 15, 2002
Hill and Hitchcock
) 173(2) K, Z ) 2, Dc ) 1.24 g cm-3, 30 797 reflections, 15 489
unique reflections (Rint ) 0.059), 11 103 reflections with I >
2σ(I); R1, wR2 ) 0.072, 0.153 (I > 2σ(I)) and 0.107, 0.168 (all
data). Data were collected on a KappaCCD diffractometer
(µ(Mo KR) ) 0.710 73 Å). The structures were solved by direct
methods (SHELXS-97)21 and refined by full-matrix least
squares (SHELXL-97)22 with non-H atoms anisotropic and H
atoms included in the riding mode. In 2 an absorption
correction was not applied, and in 3 and 4 the data were
corrected for absorption effects using MULTISCAN.
Ack n ow led gm en t. We thank the Royal Society for
the provision of a University Research Fellowship
(M.S.H.) and Dr. A. G. Avent for assistance with NMR
spectra. The reviewers are thanked for helpful com-
ments and suggestions.
Su p p or t in g In for m a t ion Ava ila b le: Figures giving
1H and 13C NMR spectra of 4 at 248 and 348 K and tables
giving details of crystal data and structure refinement, atom
coordinates, equivalent isotropic displacement factors, bond
lengths and angles, and hydrogen coordinates for 2-4. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(21) Sheldrick, G. M. SHELXS-97: Program for the Solution of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany,
1997.
(22) Sheldrick, G. M. SHELXL-97: Program for the Refinement of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany,
1997.
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