Synthesis and characterization of neutral and cationic intramolecularly coordinated aluminum compounds. Structural determination of [(Pytsi)AlMe] +[MeB(C6F5)3]- [Pytsi = C(SiMe3)2</sub

Article abstract of DOI:10.1021/om050426s

The synthesis and structure of neutral and cationic aluminum compounds equipped with the intramolecular donating C(SiMe₃) ₂SiMe₂(2-C₅H₄N) ligand denoted by Pytsi is described. The compounds (Pytsi)AlM

Full text of DOI:10.1021/om050426s

6120
Organometallics 2005, 24, 6120-6125
Synthesis and Characterization of Neutral and Cationic
Intramolecularly Coordinated Aluminum Compounds.
Structural Determination of [(Pytsi)AlMe]+[MeB(C6F5)3]-
[(Pytsi ) C(SiMe3)2SiMe2(2-C5H4N)]
Olimpiu Stanga,‡ Clinton L. Lund,‡ Huan Liang,‡ J. Wilson Quail,§ and
Jens Mu¨ller*,‡
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon,
SK S7N 5C9 Canada, and Saskatchewan Structural Sciences Centre, University of
Saskatchewan, 110 Science Place, Saskatoon, SK S7N 5C9 Canada
Received May 27, 2005
The synthesis and structure of neutral and cationic aluminum compounds equipped with
the intramolecular donating C(SiMe3)2SiMe2(2-C5H4N) ligand denoted by Pytsi is described.
The compounds (Pytsi)AlMe2 (1), (Pytsi)AlEt2 (2), [(Pytsi)AlMe]+[MeB(C6F5)3]- (3), and
[(Pytsi)AlMe(thf)]+[MeB(C6F5)3]- (3‚thf) have been synthesized and characterized by standard
methods, and the molecular structures of 1, 2, and 3 have been determined by single-crystal
X-ray analyses. Compound 3 was obtained by an addition of 1 equiv of B(C6F5)3 to the
dimethyl species 1. The salt-like title compound 3 shows a methyl group in a bridging position
between Al and B atoms consisting of a long Al-C distance of 2.380(2) Å and a B-C bond
length of 1.681(3) Å.
Introduction
[B(C6F5)4]- is shielded by very bulky m-terphenyl sub-
stituents with C-Al-C angles of 159° and 157° found
in two different polymorphs. Jordan et al. reported in
1997 that three- and four-coordinated aluminum cations
Cationic aluminum species with coordination num-
bers from 2 to 7 are known.1 Those with low-coordinated
Al centers are strong Lewis acids and are potentially
useful as transition-metal-free olefin polymerization
catalysts or initiators. Bochmann et al. reported in 1996
that the aluminocenium cation in [Cp2Al]+[MeB(C6F5)3]-
initiates polymerization of isobutene and isobutene-
isoprene mixtures.2 Three years earlier, the decamethyl
derivative Cp*2Al+ was already characterized by
Schno¨ckel et al.3 From a formal viewpoint, aluminum
in the aluminocenium cation is 2-fold coordinated;
however, because of the pentahapto-coordinated Cp
rings the coordination number in [Cp2Al]+ is not well
defined. Reed et al. reported the synthesis of [Et2Al]+-
[CB11H6X6]- (X ) Cl, Br).4 On the basis of the X-ray
structural analyses, the Et2Al+ moiety is weakly coor-
dinated to two halogen atoms of the carborane unit with
C-Al-C angles of 130° (X ) Br) and 137° (X ) Cl). The
salt-like species [Et2Al]+[CB11H6X6]- has been shown
to be an extremely efficient catalyst for polymerization
of cyclohexene oxide.4 Recently, a quasi-two-coordinated
diorganoaluminum cation has been described by
Wehmschulte et al.5 The Al atom in [(2,6-Mes2C6H3)2Al]+-
-
equipped with N,N′-dialkylamidinate ligands RC(NR′)2
can be used for ethylene polymerization under mild
conditions.6 Comparable monoanionic N,N-bidentate
ligands,7-19 O,N-bidentate ligands,20-25 and C,N-biden-
(6) Coles, M. P.; Jordan, R. F. J. Am. Chem. Soc. 1997, 119, 8125-
8126.
(7) Ihara, E.; Young, V. G.; Jordan, R. F. J. Am. Chem. Soc. 1998,
120, 8277-8278.
(8) Cosledan, F.; Hitchcock, P. B.; Lappert, M. F. Chem. Commun.
1999, 705-706.
(9) Korolev, A. V.; Guzei, I. A.; Jordan, R. F. J. Am. Chem. Soc. 1999,
121, 11605-11606.
(10) Ong, C. M.; McKarns, P.; Stephan, D. W. Organometallics 1999,
18, 4197-4204.
(11) Radzewich, C. E.; Guzei, I. A.; Jordan, R. F. J. Am. Chem. Soc.
1999, 121, 8673-8674.
(12) Dagorne, S.; Guzei, I. A.; Coles, M. P.; Jordan, R. F. J. Am.
Chem. Soc. 2000, 122, 274-289.
(13) Korolev, A. V.; Ihara, E.; Guzei, I. A.; Young, V. G.; Jordan, R.
F. J. Am. Chem. Soc. 2001, 123, 8291-8309.
(14) Pappalardo, D.; Tedesco, C.; Pellecchia, C. Eur. J. Inorg. Chem.
2002, 621-628.
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2313.
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(17) Dagorne, S.; Bellemin-Laponnaz, S.; Welter, R. Organometallics
2004, 23, 3053-3061.
* To whom correspondence should be addressed. E-mail:
jens.mueller@usask.ca.
(18) Masuda, J. D.; Walsh, D. M.; Wei, P. R.; Stephan, D. W.
Organometallics 2004, 23, 1819-1824.
‡ Department of Chemistry, University of Saskatchewan.
§ Saskatchewan Structural Sciences Centre.
(19) Welch, G. C.; Piers, W. E.; Parvez, M.; McDonald, R. Organo-
metallics 2004, 23, 1811-1818.
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10.1021/om050426s CCC: $30.25 © 2005 American Chemical Society
Publication on Web 11/02/2005

Neutral and Cationic Aluminum Compounds
Organometallics, Vol. 24, No. 25, 2005 6121
tate ligands26 had been used to stabilize cationic Al
centers with low coordination numbers.
Eaborn and Smith and others have shown that the
sterically demanding trisyl ligand (trisyl ) tris(tri-
methylsilyl)methyl, C(SiMe3)3; commonly denoted as
Tsi) can be used to stabilize compounds with unusual
low coordination numbers.27 In addition to the bulkiness
of the trisyl ligand, R silyl effects contribute to a
stabilization of an attached metal center. Several trisyl
derivatives in which one or more methyl groups
are replaced by substituents with Lewis-base donor
capabilities are known, among which the pytrisyl
ligand, C(SiMe3)2SiMe2(2-C5H4N), is the most studied
example.28-33 Recently, we took advantage of the unique
properties of the bulky and intramolecularly stabilizing
pytrisyl ligand and synthesized [1]ferrocenophanes with
aluminum34 and gallium35 in bridging positions.
Within this report we describe the synthesis and
structural characterization of neutral and cationic
pytrisyl alanes.
Figure 1. Molecular structure of 2 with thermal ellipsoids
drawn at the 50% probability level. Selected bond lengths
[Å] and angles [deg]: Al1-N1 ) 2.0034(18), Al1-C16 )
2.017(2), Al1-C17 ) 1.994(2), Al1-C7 ) 2.043(2), C7-Si1
) 1.865(2), C7-Si2 ) 1.889(2), C7-Si3 ) 1.884(2), N1-
Al1-C7 ) 96.02(8), N1-Al1-C16 ) 103.66(9), N1-Al1-
C17 ) 102.73(9), C16-Al1-C7 ) 123.29(10), C17-Al1-
C7 ) 116.10(10), C17-Al1-C16 ) 110.47(10), Al1-C7-
Si1 ) 100.15(10), C7-Si1-C6 ) 103.11(9), Si1-C6-N1 )
114.61(15), C6-N1-Al1 ) 114.84(14).
Results and Discussion
The dimethyl alane 1 is readily accessible by metath-
esis starting with the known Li(thf)(Pytsi)28 and chloro-
dimethylalane (eq 1).
have similar shapes and sizes, and a disorder as found
for 1 is not unexpected. The diethyl alane 2, which we
synthesized similarly to compounds 1, does not exhibit
two similarly shaped molecular halves and, conse-
quently, is not disordered in the crystal lattice (Figure
1, Table 1). To model the disorder in 1, we used the
structure of compound 2. The terminal methyl groups
on the two ethyl groups were replaced by H atoms,
giving the same formula as 1. A rigid model of the so
modified molecule 2, with occupancies set at 0.50, was
used to refine the data for compound 1, resulting in an
R value of 7.9% with all atoms isotropic.
One methyl substituent of 1 can be abstracted by the
perfluorinated borane B(C6F5)3, resulting in the salt-
like compound [(Pytsi)AlMe]+[MeB(C6F5)3]- (3). Com-
pound 3 crystallizes in the monoclinic space group C2/c
with half a molecule of toluene in the asymmetric unit
(Figure 2, Table 1). The most interesting part of the
molecular structure of 3 is displayed by the Me group
bridging the Al and B atoms. The positions of the
hydrogen atoms of the bridging Me group were located
in ∆F maps and refined. The nearly linear bridge [Al1-
C17-B1 ) 163.76(17)°] consists of a long Al1-C17
distance of 2.380(2) Å and a B1-C17 bond length of
1.681(3) Å. To the best of our knowledge, structures of
salt-like compounds with a cationic Al center and
methyl group bridging to a B(C6F5)3 moiety are not
described in the literature. However, the structural
motif LnM- - -H3C-B(C6F5)3 is known for transition
metal species such as Ti,36-38 Zr,39-44 and Hf45 com-
Compound 1 had been described in a very recent
publication by Hill and Smith.33 The authors mentioned
a disorder of 1 in the crystal lattice; however, the
molecular structure of 1 was not described. We also
found disordered molecules 1 in the crystal lattice, but
could successfully model it. The structure of compound
1 is disordered about a plane of symmetry, bisecting the
ring along the Si2C plane in the (Me3Si)2C moiety. One-
half of the molecule reflects almost on top of the other
half of molecule. Both halves of the compound 1, one
with a SiMe2 group and the other with a Me2Al group,
(23) Dagorne, S.; Lavanant, L.; Welter, R.; Chassenieux, C.; Haquette,
P.; Jaouen, G. Organometallics 2003, 22, 3732-3741.
(24) Dagorne, S.; Janowska, I.; Welter, R.; Zakrzewski, J.; Jaouen,
G. Organometallics 2004, 23, 4706-4710.
(25) Pappalardo, D.; Mazzeo, M.; Montefusco, P.; Tedesco, C.;
Pellecchia, C. Eur. J. Inorg. Chem. 2004, 1292-1298.
(26) Engelhardt, L. M.; Kynast, U.; Raston, C. L.; White, A. H.
Angew. Chem., Int. Ed. Engl. 1987, 26, 681-682.
(27) Eaborn, C.; Smith, J. D. J. Chem. Soc., Dalton Trans. 2001,
1541-1552.
(28) Al-Juaid, S. S.; Eaborn, C.; Hitchcock, P. B.; Hill, M. S.; Smith,
J. D. Organometallics 2000, 19, 3224-3231.
(29) Eaborn, C.; Hill, M. S.; Hitchcock, P. B.; Smith, J. D. Chem.
Commun. 2000, 691-692.
(30) Al-Juaid, S. S.; Avent, A. G.; Eaborn, C.; El-Hamruni, S. M.;
Hawkes, S. A.; Hill, M. S.; Hopman, M.; Hitchcock, P. B.; Smith, J. D.
J. Organomet. Chem. 2001, 631, 76-86.
(31) Al-Juaid, S. S.; Avent, A. G.; Eaborn, C.; Hill, M. S.; Hitchcock,
P. B.; Patel, D. J.; Smith, J. D. Organometallics 2001, 20, 1223-1229.
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Soc., Dalton Trans. 2002, 2467-2472.
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1298-1300.
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J. J. Organomet. Chem. 2005, 690, 69-75.
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metallics 2000, 19, 2994-3000.
(34) Schachner, J. A.; Lund, C. L.; Quail, J. W.; Mu¨ller, J. Organo-
metallics 2005, 24, 785-787.
(38) Shafir, A.; Arnold, J. J. Am. Chem. Soc. 2001, 123, 9212-9213.
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metallics 2005, 24, 4483-4488.

6122 Organometallics, Vol. 24, No. 25, 2005
Table 1. Crystal and Structural Refinement Data for Compounds 1, 2, and 3
3‚0.5toluene
Stanga et al.
1
2
empirical formula
fw
wavelength, Å
cryst syst
C
16H34AlNSi3
C
18H38AlNSi3
C37.50H38AlBF15NSi3
351.69
379.74
909.75
0.71073
0.71073
triclinic
P1h (2)
0.71073
monoclinic
C2/c (15)
8
21.4717(3)
16.2706(2)
25.7972(4)
90
113.1518(7)
90
8286.6(2)
1.458
173(2)
0.233
3.34-26.37
13 405
8451 [R(int) ) 0.0329]
none
orthorhombic
Pnma (62)
4
space group (No.)
Z
2
a, Å
12.7464(4)
14.1803(4)
12.1479(3)
90
90
90
2195.71(11)
1.064
173(2)
0.252
3.20-22.0
2557
8.8068(2)
8.9623(2)
17.2181(4)
85.4238(8)
75.5482(9)
62.6172(8)
1167.59(5)
1.080
b, Å
c, Å
R, deg
â, deg
γ, deg
vol, Å3
d(calc), mg/m3
temp, K
173(2)
0.241
3.17-27.48
10 231
abs coeff, mm-1
θ range, deg
no. of reflns collected
no. of indep reflns
abs corr
1418
none
5339 [R(int) ) 0.0458]
none
ref method
full-matrix least-squares on F2
5339/0/218
no. of data/restr/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole, e Å-3
1418/0/38
1.260
R1 ) 0.0790, wR2 ) 0.2044
R1 ) 0.1105, wR2 ) 0.2890
0.702 and -0.946
8451/57/563
1.046
R1 ) 0.0453, wR2 ) 0.1043
R1 ) 0.0704, wR2 ) 0.1170
0.474 and -0.409
1.024
R1 ) 0.0472, wR2 ) 0.1044
R1 ) 0.0773, wR2 ) 0.1173
0.389 and -0.302
pounds. A textbook example is [Cp2ZrMe]+[MeB(C6F5)3]-
with an Zr-µMe distance being 0.30 Å longer than the
Zr-Meterm distance of 2.251(3) Å; the B-Me bond length
is 1.667(3) Å.42 In comparison, the Al1-C17 distance of
2.380(2) Å in 3 is 0.44 Å longer than that of the Al-
Meterm bond [Al1-C16 ) 1.943(3) Å]. This is a signifi-
cant difference, and the Al1-C17 distance is far too long
to be a covalent bond. Aluminum is 3-fold coordinated
by the bidentate pytrisyl ligand and the remaining Me
group plus weakly coordinated by the bridging Me
group. This intermediate coordination is also reflected
in the sum (342°) over the three angles between the C7,
N1, and C16 and the central Al atom. This value is
between the sum over the three corresponding angles
in compound 2 with 4-fold coordination (323°) and the
sum over three angles in an idealized trigonal planar
arrangement (360°).
We intended to characterize compound 3 in solution
by NMR spectroscopy. The reaction batch that we used
to obtain single crystals showed the typical pattern of
a pytrisyl ligand exhibiting a mirror plane on time
1
average in the H NMR spectrum. Unfortunately, we
could not measure a proton NMR spectrum of 3 free of
byproducts. However, if in an NMR tube a 1:1 mixture
of the solid starting materials 1 and B(C6F5)3, cooled to
-78 °C, is dissolved in precooled toluene-d8 (-78 °C),
1
low-temperature H, 11B, 19F, and 13C NMR spectra of
compound 3, nearly free of byproducts, can be obtained
(see Experimental Section and Supporting Information).
For example, the 1H NMR spectra show one singlet for
each of the AlMe, SiMe2, C(SiMe3)2, and BMe moieties
and four singlets for the pyridyl group. The chemical
shift of the Me group of the anion is temperature
dependent. It changes from δ 1.47 at -78 °C to δ 1.35
at -18 °C and is broadened at higher temperatures
before it disappears in the baseline at 12 °C. For the
AlMe group only insignificant changes of the chemical
shift can be observered in the range -78 to -18 °C, but
at higher temperatures, it behaves similar to the BMe
group and is also hidden in the baseline at 12 °C. At
temperatures above -8 °C new 1H NMR peaks ap-
peared, and prolonged exposure of the flame-sealed
NMR tube to ambient temperatures resulted in 1H NMR
Figure 2. Molecular structure of 3 with thermal ellipsoids
drawn at the 50% probability level. Solvent molecules are
omitted for clarity. Selected bond lengths [Å] and angles
[deg]: Al1-N1 ) 1.9485(18), Al1-C16 ) 1.943(3), Al1-
C17 ) 2.380(2), Al1-C7 ) 1.975(2), C7-Si1 ) 1.875(2),
C7-Si2 ) 1.912(2), C7-Si3 ) 1.893(2), B1-C17 )
(40) Baumann, R.; Davis, W. M.; Schrock, R. R. J. Am. Chem. Soc.
1997, 119, 3830-3831.
(41) Bazan, G. C.; Cotter, W. D.; Komon, Z. J. A.; Lee, R. A.;
Lachicotte, R. J. J. Am. Chem. Soc. 2000, 122, 1371-1380.
(42) Guzei, I. A.; Stockland, R. A.; Jordan, R. F. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 2000, 56, 635-636.
(43) Beck, S.; Lieber, S.; Schaper, F.; Geyer, A.; Brintzinger, H. H.
J. Am. Chem. Soc. 2001, 123, 1483-1489.
1.681(3), N1-Al1-C7
) 100.58(9), N1-Al1-C16 )
111.49(10), N1-Al1-C17 ) 93.91(8), C16-Al1-C7 )
129.77(10), C17-Al1-C7 ) 112.38(10), C17-Al1-C16 )
103.11(10), Al1-C7-Si1 ) 101.83(10), C7-Si1-C6 )
102.42(10), Si1-C6-N1 ) 115.93(15), C6-N1-Al1 )
113.66(15).
(44) Choukroun, R.; Wolff, F.; Lorber, C.; Donnadieu, B. Organo-
metallics 2003, 22, 2245-2248.
(45) Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 9462-
9475.

Neutral and Cationic Aluminum Compounds
Organometallics, Vol. 24, No. 25, 2005 6123
Chart 1. (a) Cation of 3‚thf; (b) NMR
Time-Averaged Molecular Symmetry of the Cation
of 3‚thf
of the coordinated thf at δ 1.35 (4H), 3.08 (2H), and 3.34
(2H). By increasing the temperature the chemical shifts
of the coordinated thf move closer to those of the
noncoordinated thf, so that at 100 °C (500 MHz) the
signals at higher field coalesced to one signal at δ 1.53
(CH2CH2O) and that at lower field still appeared as two
broad signals (δ 3.54 and 3.34). Coalescence phenomena
can be observed for the two sets of singlets for the
diastereotopic methyl group in SiMe2 and C(SiMe3)2,
respectively, which broaden with increasing tempera-
ture, and at 100 °C only two very broad singlets are
present. These NMR results show that a fast exchange
of the coordinated thf and noncoordinated thf occurs,
resulting in an inversion of the Al atom.
spectra with numerous signals; we could neither identify
a byproduct nor isolate one. This temperature sensitiv-
ity prevented a complete uncovering of the dynamic
behavior of 3 in solution. Similar dynamic behavior had
been observed for other salt-like species, e.g., [{HC-
(CMeNAr)2}AlMe][MeB(C6F5)3],11 and it was proposed
that an exchange of the Me groups occurs in solution
as illustrated in eq 2. We assume that such an equilib-
rium also exists for compound 3.
Conclusions
We have shown that one methyl group of the di-
methylalane 1 can be abstracted by the perfluorinated
borane B(C6F5)3, resulting in the salt-like compound
[(Pytsi)AlMe]+[MeB(C6F5)3]- (3). The molecular struc-
ture of 3 in the solid state shows a methyl group in a
bridging position between aluminum and boron with a
long Al-C distance of 2.380(2) Å. Compound 3 is not
stable in solution at ambient temperature; however, a
stable thf adduct can be obtained. These initial results
show that the pytrisyl ligand is capable of stabilizing
an aluminum cation with a low coordination number.
We started to change compound 3 systematically by
using different weakly coordinating anions, by exchang-
ing the remaining methyl group at aluminum by a
sterically more demanding group, and by increasing the
steric bulk of the pytrisyl ligand by introducing steri-
cally demanding groups in position 6 of the pyridine
ring. By fine-tuning compound 3, we hope to control the
reactivity of cationic pytrisyl alanes and make use of
them in catalytic processes such as olefin polymeriza-
tion.
The chemical shift of the Me group of [MeB(C6F5)3]-
for 3 is significantly downfield from those of salts of the
type A[MeB(C6F5)3], with A+ being an “innocent” cation.
Jordan et al. chose [NBu3Bz][MeB(C6F5)3] (δ 1.09;
toluene-d8)11 as a reference compound. We found a
chemical shift of δ 0.99 (toluene-d8) for the thf adduct
of compound 3, [(Pytsi)AlMe(thf)][MeB(C6F5)3], which
is discussed below. The downfield shift is indicative of
ion-pairing in solution and shows that compound 3,
dissolved in toluene, exhibits a molecular structure with
an Al-Me-B moiety, similar as that found in the crystal
lattice.
If the synthesis of compound 3 is performed in the
presence of 1 equiv of thf, a new compound, [(Pytsi)-
AlMe(thf)][MeB(C6F5)3] (3‚thf), is formed. The 1H NMR
spectrum reveals an asymmetric pytrisyl ligand: two
singlets for the C(SiMe3)2 moiety and two singlets for
the SiMe2 group. These NMR data are consistent with
the formation of the expected cation shown in Chart 1a.
The cation of the salt 3‚thf exhibits C1 point group
symmetry. Therefore, all H and C atoms of the coordi-
nated thf molecule are nonequivalent and, in principle,
should give one resonance each. The coordinated thf
moiety, however, shows only two 13C NMR peaks at δ
Experimental Section
General Procedures. All manipulations were carried out
using standard Schlenk techniques. Solvents were dried using
a Braun solvent purification system and stored under nitrogen
over 4 Å molecular sieves. All solvents for NMR spectroscopy
were degassed prior to use and stored under nitrogen over 4
Å molecular sieves. Li(thf)(Pytsi)28 [Pytsi ) C(SiMe3)2SiMe2-
(2-C5H4N)] and B(C6F5)346 were synthesized as described in the
literature. Me2AlCl and Et2AlCl were purchased from Aldrich
1
and used as received. H, 13C, 11B, 27Al, and 19F NMR spectra
1
24.75 and 74.69 and three multiplets in the H NMR
1
were recorded on a Bruker 500 MHz Avance. H (500 MHz)
spectrum at δ 1.35 (4H), 3.08 (2H), and 3.34 (2H). This
result can be interpreted as being due to the well-known
inversion of the envelope conformation of thf, resulting
in a time-averaged C2 symmetry of the cation (Chart
1b).
The NMR data show that the thf molecule does not
dissociate and reassociate fast on the NMR time scale;
a process like this would be accompanied by an inver-
sion at the Al atom. However, if 2 equiv of thf-d8 are
added to a NMR sample of 3‚thf in toluene-d8, two new
multiplets appear, unequivocally indicating noncoordi-
nated thf. In addition, the relative intensity of the sets
of signals of coordinated thf decreased respectively,
revealing that added thf-d8 replaces coordinated thf in
3‚thf. At ambient temperature the free thf resonates at
δ 1.48 and 3.48, which is downfield with respect to those
and 13C (125.8 MHz) chemical shifts were referenced to the
residual protons of the deuterated solvents. In the case of
toluene-d8, the peak of the Me group was used as a reference
(1H NMR δ 2.09; 13C NMR δ 20.40). Other nuclei were
referenced to an external standard dissolved in C6D6: 27Al
NMR (130.3 MHz; [Al(acac)3]), 11B NMR (165.5 MHz, BF3-
OEt2), 19F NMR (470.5 MHz, CFCl3). Samples were dissolved
in C6D6, and NMR spectra were obtained at ambient temper-
ature unless noted differently. We could not detect the 13C
NMR signal of the pytrisyl C atom directly bound to Al for
compounds 1, 2, and 4. Mass spectra were measured on a VG
70SE, and signals of the most abundant ions are listed.
Elemental analyses were performed on a Perkin-Elmer 2400
CHN elemental analyzer using V2O5 to promote complete
combustion.
(46) Lancaster, S. SyntheticPage 2003, 215.

6124 Organometallics, Vol. 24, No. 25, 2005
Stanga et al.
(Pytsi)AlMe2 (1). A solution of Me2AlCl (4.9 mL, 1 M in
hexanes) was added dropwise to a stirred solution of Li(thf)-
(Pytsi) (1.828 g, 4.9 mmol) in hexane (20 mL) at -78 °C. The
resulting solution was stirred for 20 min at -78 °C and then
allowed to warm to ambient temperature. After the reaction
mixture was stirred for 16 h, the solid was filtered off and
washed with hexane (3 × 5 mL). Removal of the solvent left a
light yellow solid, which was sublimed at 90 °C and high
vacuum to give the colorless crude product. Crystallization
from hexane (10 mL) at -30 °C resulted in colorless crystals,
suitable for single-crystal X-ray structural determination
(1.184 g, 69%). Compound 1 was first described in ref 33. Our
spectroscopic data were identical to those given earlier, but
we consider that amendments are required to assignments of
1H and 13C resonances from the pyridine moiety. Our assign-
ments were confirmed by 1H-1H COSY and HMQC experi-
ments. 1H NMR: δ -0.21 (s, 6H, AlMe2), 0.27 (s, 18H, SiMe3),
0.40 (s, 6H, SiMe2), 6.34 (pst, 1H, 5-H), 6.79 (pst, 1H, 4-H),
6.92 (d, 1H, 3-H), 7.93 (d, 1H, 6-H). 13C{1H} NMR: δ -3.16
(br, AlMe2), 4.35 (SiMe2), 6.57 (SiMe3), 124.39 (5-C), 129.22
(3-C), 138.37 (4-C), 145.88 (6-C), 174.05 (ipso-C). 27Al NMR:
δ 176 (w1/2 ) 2850 Hz). MS: m/z 336 (100, M - Me+), 264 (52,
C12H22NSi3+), 248 (20, C11H18NSi3+). Anal. Calcd for C16H34-
NAlSi3 (351.691): C, 54.64; H, 9.74; N, 3.98. Found: C, 54.67;
H, 10.11; N, 3.75.
Single crystals of 3 were obtained as follows (see Results
and Discussion). B(C6F5)3 (0.716 g dissolved in 10 mL of
toluene, 1.4 mmol) was added via a cannula to a solution of 1
(0.492 g, 1.4 mmol) in toluene (10 mL), and the resulting
reaction mixture was stirred for 1 h. The solvent was removed
in high vacuum from the clear, colorless solution, resulting in
a formation of a white wax. Trituration with hexane (2 × 20
mL) gave 3 as a white solid (0.938 g, 78%). Toluene (10 mL)
was added, and the flask was placed in the freezer (ca. -20
°C), resulting in the formation of two liquid layers and some
colorless crystals. The two liquid layers were syringed off, and
all remaining volatiles were removed in high vacuum. X-ray
analysis of the crystals revealed the desired compound.
(Pytsi)AlMe(thf)+[MeB(C6F5)3]- (3‚thf). B(C6F5)3 (0.472
g dissolved in 10 mL of toluene, 0.921 mmol) was added via a
cannula to a stirred solution of 1 (0.324 g, 0.921 mmol) and
thf (0.08 mL, ∼0.921 mmol) in toluene (10 mL). The reaction
mixture was stirred for 30 min, resulting in the formation of
two layers. All volatiles were removed in high vacuum.
Trituration with hexane (2 × 20 mL) did not result in the
formation of a solid, but gave a colorless sticky foam after the
remaining solvent was removed in high vacuum (0.789 g, 92%).
1H NMR (toluene-d8): δ -0.50 (s, 3H, AlMe), -0.17 (s, 9H,
SiMe3), 0.00 (s, 9H, SiMe3), 0.10 (s, 3H, SiMe), 0.29 (s, 3H,
SiMe), 0.99 (s, 3H, BMe), 1.35 (m, 4H, CH2CH2O), 3.08 (m,
2H, CH2O), 3.34 (m, 2H, CH2O), 7.00 (pst, 1 H, 5-H), 7.24 (d,
1H, 3-H), 7.38 (pst, 1H, 4-H), 7.80 (d, 1H, 6-H). 13C{1H} NMR
(toluene-d8): δ -7.89 (AlMe), 2.04 (SiMe), 4.01 (SiMe), 5.15
(SiMe3), 5.59 (SiMe3), 11.3 (br, BMe), 24.75 (CH2CH2O), 74.69
(CH2O), 126.53 (5-C), 130.1 (br, ipso-C6F5), 131.27 (3-C), 137.1
(Pytsi)AlEt2 (2). Li(thf)(Pytsi) (3.206 g, 8.6 mmol) was
dissolved in hexane (40 mL) at ambient temperature and
cooled with an acetone-dry ice bath. Et2AlCl (8.6 mL, 1 M in
hexane) was added over a period of 10 min using a syringe
and a septum, and the resulting solution was stirred for
another 20 min, before the dry ice bath was removed. The
reaction mixture was stirred overnight at ambient tempera-
ture. The solution was filtered, and the solid was washed with
hexane (3 × 10 mL). After the solvent was removed from the
filtrate in high vacuum, pale yellow crystals were obtained by
sublimation at 140 °C in high vacuum. The sublimed com-
pound was dissolved in hexane (25 mL), and crystallization
at ca. -20 °C resulted in colorless compound 2 (2.281 g, 70%).
1
(d/m, JCF ) 245 Hz, m-C6F5), 138.1 (d/m,1JCF ) 245 Hz,
1
p-C6F5), 142.22 (4-C), 145.46 (6-C), 149.21 (d/m, JCF ) 239
Hz, o-C6F5), 173.69 (ipso-C5H4N). 11B NMR (CDCl3): δ -15.1
(s, br). 19F NMR (CDCl3): δ -137.29 (d, 6 F, o-F), -168.90 (m,
3 F, p-F), -171.61 (m, 6 F, m-F).
X-ray Structural Analysis. For all three structures 1, 2,
and 3, data were collected at -100 °C on a Nonius Kappa CCD
diffractometer, using the COLLECT program.47 Cell refine-
ment and data reductions used the programs DENZO and
SCALEPACK.48 SIR9749 was used to solve the structure, and
SHELXL9750 was used to refine the structure. Except for the
bridge methyl protons in 3, H atoms were placed in calculated
positions with Uiso constrained to be 1.2 times Ueq of the carrier
atom for aromatic protons and 1.5 times Ueq of the carrier
atoms for methyl and methylene hydrogen atoms.
Because of the disorder of compound 1, the structure of
compound 2 was used as a model for compound 1 (see Results
and Discussion). A rigid model of the modified molecule 2, with
occupancies set at 0.50, was used to refine the data for
compound 1. Since the reflected half of 1 has atoms very close
to the other half of 1, it was not possible to allow the positions
to refine independently and it was also not possible to refine
the atoms anisotropically, because strong correlations result
in meaningless thermal ellipsoids. The crystal only diffracted
to 22 degrees. Only 38 parameters (6 to define the position
and orientation of the rigid molecule, temp factor on 21 non-H
atoms, and rotation of the 10 methyl groups plus scale) were
refined against 1418 reflections (1138 observed). For further
information see the Supporting Information.
2
1H NMR: δ 0.26 (s, 18H, SiMe3), 0.31 (d/q, 2H, JHH ) 14.3
Hz, 3JHH ) 8.1 Hz, AlCH2), 0.39 (s, 6H, SiMe2), 0.50 (d/q, 2H,
3
3
2JHH ) 14.3 Hz, JHH ) 8.1 Hz, AlCH2), 1.37 (d/d, 6H, JHH
)
8.1 Hz, AlCH2CH3), 6.34 (pst, 1H, 5-H), 6.78 (pst, 1H, 4-H),
6.92 (d, 1H, 3-H), 8.10 (d, 1H, 6-H). 13C{1H} NMR: δ 4.09
(SiMe2), 4.19 (br, AlCH2), 6.32 (SiMe3), 10.49 (AlCH2CH3),
123.61 (5-C), 129.15 (3-C), 138.09 (4-C), 146.09 (6-C), 173.83
(ipso-C). 27Al NMR: δ 173 (w1/2 ) 2400 Hz). MS (70 eV) m/z
(%) 364 (7, M - Me+), 350 (100, M - C2H5+), 295 (12) [PytsiH+],
280 (36, C13H26NSi3+, 264 (18, C12H22NSi3+), 248 (8, C11H18-
NSi3+). Anal. Calcd for C18H38AlNSi3 (379.745): C, 56.93; H,
10.09; N, 3.69. Found: C, 56.37; H, 9.47; N, 3.12.
(Pytsi)AlMe+[MeB(C6F5)3]- (3). A NMR tube, charged
with 1 (0.0176 g, 0.0500 mmol) and B(C6F5)3 (0.0256 g, 0.0500
mmol), was cooled to -78 °C, precooled toluene-d8 (1 mL, -78
°C) was added with a syringe, and the tube was carefully
shaken in such a way that a significant increase of the
temperature was avoided. The NMR tube containing a clear
and colorless solution was inserted into a cooled NMR probe
head (see Supporting Information for NMR spectra). 1H NMR
(225 K, toluene-d8): δ -0.12 (s, 18H, SiMe3), -0.09 (s, 3H,
AlMe), 0.04 (s, 6H, SiMe2), 1.40 (s, 3H, BMe), 6.40 (m, br, 1H,
4-H or 5-H), 6.51 (d, 1H, 3-H), 6.83 (m, 1H, 5-H or 4-H), 7.58
(d, 1H, 6-H). 13C{1H} NMR: δ -4.98 (AlMe), 1.16 (C(SiMe3)2),
2.57 (SiMe2), 4.63 (SiMe3), 12.1 (br, BMe), 125.65 (4-C or 5-C),
130.46 (3-C), 136.94 (d/m, 1JCF ) 241 Hz, m-C6F5), 141.36 (5-C
Acknowledgment. The authors thank the Natural
Sciences and Engineering Research Council of Canada
(NSERC Discovery Grant, J.M.), the Department of
(47) COLLECT; Nonius BV: Delft, The Netherlands, 1998.
(48) Otwinowski, Z.; Minor, W. In Macromolecular Crystallography,
Part A; Carter, C. W., Sweet, R. M., Eds.; Academic Press: London,
1997; Vol. 276, pp 307-326.
(49) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R.
J. Appl. Crystallogr. 1999, 32, 115-119.
(50) Sheldrick, G. M. SHELXL97; University of Go¨ttingen: Ger-
many, 1997.
1
or 4-C), 144.69 (6-C), 148.30 (d/m, JCF ) 241 Hz, o-C6F5),
171.96 (ipso-C5H4N); peaks for ipso-C6F5 and p-C6F5 are hidden
by the solvent signals. 11B NMR: δ -14.80 (s). 19F NMR: δ
-133.55 (d, 6F, o-F), -159.95 (m, 3F, p-F), -164.34 (m, 6F,
m-F); small amounts of B(C6F5)3 were detected at δ -128.66
(d, 6F, o-F), -140.43 (m, 3F, p-F), -159.75 (m, 6F, m-F) (see
ref 11).

Neutral and Cationic Aluminum Compounds
Organometallics, Vol. 24, No. 25, 2005 6125
Supporting Information Available: 1H, 13C, 19F, and 11
B
Chemistry, and the University of Saskatchewan for
their generous support. We thank the Canada Founda-
tion for Innovation (CFI) and the government of
Saskatchewan for funding of the X-ray and NMR
facilities in the Saskatchewan Structural Sciences Cen-
tre (SSSC). We thank Keith Brown for his support in
conducting NMR experiments.
NMR spectra of 3 (225 K, toluene-d8) and crystallographic data
for 1, 2, and 3 in CIF format. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM050426S