Synthesis and characterization of intramolecularly coordinated alanes with new sterically demanding trisyl-based ligands

Article abstract of DOI:10.1139/V07-063

Five new intramolecularly coordinated aluminum species, whose molecular structures have been elucidated in solution by NMR spectroscopy and in the solid state by single crystal X-ray analysis, are described. All species are equipped with a trisyl-based ligand with a pyridyl donor group [Pytsi stands for -C(SiMe₃)₂SiMe₂(2-C₅H ₄N)]. While the compound (Pytsi)AlMeCl was accessible either from Li(THF)(Pytsi) and MeAlCl₂ or from (Pytsi)AlCl₂ and LiMe, the tert-butyl derivative (Pytsi)AltBuCl could only be obtained from Li(THF)(Pytsi) and tBuAlCl₂. Attempted synthesis of (Pytsi)AltBuCl from (Pytsi)AlCl₂ and LitBu or from (Pytsi)AlCl₂ and tBuMgCl failed. Three other compounds (3-5) were synthesized and can be described as derivatives of (Pytsi)AlMe₂ with additional groups in the ortho position of the pyridyl group. Compound 3 carried a Me group in the ortho position, while compounds 4 and 5 were equipped with Ph and 2,6-diisopropylphenyl moieties, respectively.

Full text of DOI:10.1139/V07-063

483
Synthesis and characterization of intramolecularly
coordinated alanes with new sterically demanding
trisyl-based ligands
Clinton L. Lund, Olimpiu Stanga, J. Wilson Quail, and Jens Müller
Abstract: Five new intramolecularly coordinated aluminum species, whose molecular structures have been elucidated in
solution by NMR spectroscopy and in the solid state by single crystal X-ray analysis, are described. All species are
equipped with a trisyl-based ligand with a pyridyl donor group [Pytsi stands for -C(SiMe3)2SiMe2(2-C5H4N)]. While
the compound (Pytsi)AlMeCl was accessible either from Li(THF)(Pytsi) and MeAlCl2 or from (Pytsi)AlCl2 and LiMe,
the tert-butyl derivative (Pytsi)AltBuCl could only be obtained from Li(THF)(Pytsi) and tBuAlCl2. Attempted synthesis
of (Pytsi)AltBuCl from (Pytsi)AlCl2 and LitBu or from (Pytsi)AlCl2 and tBuMgCl failed. Three other compounds (3–5)
were synthesized and can be described as derivatives of (Pytsi)AlMe2 with additional groups in the ortho position of
the pyridyl group. Compound 3 carried a Me group in the ortho position, while compounds 4 and 5 were equipped
with Ph and 2,6-diisopropylphenyl moieties, respectively.
Key words: aluminum, trisyl ligands, methyl alanes.
Résumé : On décrit cinq nouvelles espèces d’aluminium à coordination intramoléculaire dont on a déterminé les struc-
tures en solution par RMN et à l’état solide par diffraction des rayons X. Toutes les espèces incluent un ligand à base
d’un groupe trisyle comportant un groupe donneur pyridyle [Pytsi = -C(SiMe3)2SiMe2(2-C5H4N)]. Alors que le com-
posé (Pytsi)AlMeCl est accessible à partir du Li(THF)(Pytsi) et du MeAlCl2 ou du (Pytsi)AlCl2 et du LiMe, le dérivé
tert-butylé n’est disponible que par la réaction du Li(THF)(Pytsi) et du t-BuAlCl2. On n’a pas pu réaliser la synthèse
du (Pytsi)Alt-BuCl à partir du (Pytsi)AlCl2 et du Lit-Bu ou par réaction du (Pytsi)AlCl2 et du t-BuMgCl. On a réalisé
la synthèse de trois autres composés (3–5) qui peuvent être décrits comme des dérivés du (Pytsi)AlMe qui comportent
des groupes additionnels en position ortho du groupe pyridyle. Le composé 3 porte un groupe méthyle en position or-
tho alors que les composés 4 et 5 portent respectivement des groupes phényle et 2,3-diisopropylphényle.
Mots-clés : aluminium, ligands trisyles, méthylalanes.
[Traduit par la Rédaction] Lund et al. 490
Introduction
ligand (Fig. 1, Ar′). For example, employing the Ar′ ligand
gives access to well-defined, monomeric aluminium halides
(1). Azides of the heavier group 13 elements are usually oli-
gomers (2), however, the application of Ar′ and Pr′ (Fig. 1),
respectively, allowed for the preparation of the first
monomeric aluminum azides (3–5). The use of the Pr′ ligand
usually results in species of higher volatility than those
equipped with Ar′ ligands and respective Al, Ga, and In
azides had been employed as single-source precursors for
chemical vapor deposition (CVD) of nitrides (2, 6).
Group 13 element compounds EX3 are textbook examples
of Lewis acids. Usually, the electronic needs of the heavier
group members Al, Ga, and In cannot be satisfied intra-
molecularly through π bonds and, hence, oligomers are
found throughout their structural chemistry. By employing
ligands that are equipped with donor groups, Lewis acid–
base adducts are formed intramolecularly and oligomers can
be prevented. One of the most commonly used intramole-
cularly coordinating ligands is the “one-armed” phenyl
The tris(trimethylsilyl)methyl ligand, commonly referred
to as the trisyl ligand, is a widely used sterically demanding
ligand with electron-donor properties provided by three silyl
groups (β silyl effect) (7). Eaborn and co-workers (8) devel-
oped a series of trisyl-based ligands in which one of
the methyl groups is formally replaced by a substituent with
σ donor abilities. Modifications included ligands of the type
-C(SiMe3)2(SiMe2R) with R being MeO (7), Ph2P (7),
CH2PPh2 (7), Me2N (Fig. 1, Me2Ntsi) (7), and 2-C5H4N
(Fig. 1, Pytsi). Recently, we had shown that Pytsi and
Me2Ntsi (Fig. 1) stabilized alanes and gallanes can be used
for the preparation of [1]metallacyclophanes such as
[1]ferrocenophanes (9–11), [1]chromarenophanes (11), and
[1]vanadarenophanes (11). The type of intramolecularly co-
Received 21 March 2007. Accepted 4 May 20007. Published
on the NRC Research Press Web site at canjchem.nrc.ca on
11 July 2007.
C.L. Lund, O. Stanga1, and J. Müller.2 Department of
Chemistry, University of Saskatchewan, 110 Science Place,
Saskatoon, SK S7N 5C9, Canada.
J.W. Quail. Saskatchewan Structural Sciences Centre,
University of Saskatchewan, 110 Science Place, Saskatoon,
SK S7N 5C9, Canada.
1Present address: Akzo Nobel Polymer Chemicals bv,
Stationsstraat 77, 3811 MH Amersfoort, The Netherlands.
2Corresponding author (email: jens.mueller@usask.ca).
Can. J. Chem. 85: 483–490 (2007)
doi:10.1139/V07-063
© 2007 NRC Canada

484
Can. J. Chem. Vol. 85, 2007
Fig. 1. Intramolecularly coordinating ligands.
Fig. 2. Molecular structure of 1 with thermal ellipsoids at the
50% probability level. H atoms are omitted for clarity. Selected
bond lengths (Å) and angles (°): Al1–N1 = 1.962(2), Al–Cl1 =
2.1813(9), Al1–C7 = 2.008(2), Al1–C16 = 1.978(2), N1–Al1–Cl1 =
98.98(7), N1–Al1–C16 = 109.28(9), N1–Al1-C7 = 98.34(9), C7–
Al1–Cl1 = 113.42(7), C7–Al1–C16 = 125.37(10), Cl1–Al1–C16 =
107.68(7).
ordinating ligand is of crucial importance for getting
strained organometallic species: a change from the sterically
demanding Pytsi and MeNtsi, respectively, to the slimmer
Ar′
ligand
(Fig.
1)
resulted
in
unstrained
[1.1]ferrocenophanes (12, 13).
Because of the bulkiness and the β silyl effect, trisyl-type
ligands might be ideal to stabilize low-coordinated Lewis-
acid metal complexes. Starting with this working hypothesis,
we set out to explore cationic aluminum species equipped
with the Pytsi ligand. Cationic low-coordinated aluminum
compounds are potential catalysts or initiators for olefin
polymerizations (14–19). Recently, we described the synthe-
sis of a saltlike compound [(Pytsi)AlMe][MeB(C6F5)3] (19).
This species was obtained by a methyl abstraction reaction
from (Pytsi)AlMe2 with the perfluorinated borane B(C6F5)3,
however, this compound slowly decomposed in toluene at
ambient temperature. We planned to increase its stability by
shielding the Al centre more effectively with sterically de-
manding groups, either attached to aluminum directly or at-
tached to the backbone of the chelating ligand.
In this paper, we describe the synthesis and characteriza-
tion of new alanes equipped with trisyl-based intramole-
cularly coordinating ligands.
[1]
Results and discussion
Cations are commonly synthesized through halide abstrac-
tion reactions from suitable halogen containing precursors.
Often, silver salts of weakly coordinating anions are em-
ployed (20). Against this background, we intended to pre-
pare precursor species of the type (Pytsi)AlClR. First, we
prepared (Pytsi)AlClMe (1) from Li(THF)(Pytsi) and
MeAlCl2 (eq. [1]). A similar route had been previously em-
ployed for Ar′AlClMe (1). Compound 1 can also be synthe-
sized by a substitution reaction from (Pytsi)AlCl2 and LiMe.
Both routes to species 1 work comparably well (see Experi-
mental section). In accordance with the known synthesis of
Ar′AlCltBu (1), we attempted the synthesis of
(Pytsi)AlCltBu (2) from (Pytsi)AlCl2 (21) and LitBu in Et2O
or with tBuMgCl in Et2O. Both reactions proved unsuccess-
space group P 21/c. Figs. 2 and 3 depict their molecular
structures, and Table 1 shows their structural parameters.
Expectedly, the molecular structures are very similar. The
Al atoms are four-fold coordinated by two C atoms, one Cl
atom, and one N atom with nearly identical bond lengths
(Figs. 2 and 3). The major difference between 1 and 2 is due
to a different folding of the five-membered ring. For both
compounds, the five-membered ring adopts an envelope con-
formation with C7 being the tip of the envelope. However,
because of the stereogenic Al centre two different folding di-
rections of C7 are possible. While in compound 1 C7 is
folded away from the Cl atom, in compound 2 C7 is folded
towards the Cl atom. The conformer found for 2 places the
tBu group in an axial position and allows a maximum dis-
tance towards the two neighbouring SiMe3 groups, indicat-
ing that steric factors play the major role in finding a
particular isomer.
1
ful. In the case of LitBu, a very rich H NMR spectrum
hinted at complex reactions and showed that the target com-
pound 2 had not been formed. In the case of the Grignard re-
agent, no reaction happened at all. However, the target
molecule 2 was accessible in a moderate isolated yield of
54% by reacting Li(THF)(Pytsi) with tBuAlCl2 (eq. [1]).
Compounds 1 and 2 are asymmetric species as revealed
by NMR spectroscopy. For example, for both compounds the
SiMe2 and the two SiMe3 moieties give rise to two singlets,
As mentioned in the introduction, we attempted to shield
the Al centre more effectively with sterically demanding
groups. Therefore, we synthesized derivatives of
(Pytsi)AlMe2 (19, 21) in which the ortho position of the
pyridine ring carries a Me (3), Ph (4), or Dipp group (5)
(Dipp = 2,6-diisopropylphenyl). As illustrated in Scheme 1,
1
each in H NMR as well as in 13C{1H} NMR spectra. Com-
pounds 1 and 2, respectively, crystallize in the monoclinic
© 2007 NRC Canada

Lund et al.
485
Fig. 3. Molecular structure of 2 with thermal ellipsoids at the
50% probability level. H atoms are omitted for clarity. Selected
bond lengths (Å) and angles (°): Al1–N1 = 1.9765(14), Al–Cl1 =
2.1787(6), Al1–C7 = 2.0340(15), Al1–C16 = 2.0077(18), N1–
Al1–Cl1 = 103.92(4), N1–Al1–C16 = 103.92(7), N1–Al1–C7 =
96.43(6), C7–Al1–Cl1 = 115.31(5), C7–Al1–C16 = 127.95(7),
Cl1–Al1–C16 = 105.48(6).
pendicular to the pyridiyl moiety and is not rotating rapidly
on the NMR time scale.
The molecular structures of compounds 3–5 were deter-
mined with single crystal X-ray analysis (Figs. 4–6 and Ta-
ble 1). All species exhibit an envelope conformation of the
five-membered heterocycle with C7 being the tip of the en-
velope. In all compounds, aluminum is tetrahedrally sur-
rounded by a set of three C atoms and one N atom with very
similar bond lengths and angles (Figs. 4–6). For example,
the Al–N bond lengths are found in the narrow range be-
tween 2.0393(16) and 2.0587(15) Å, even though these do-
nor bonds are expected to be the most flexible bonds in the
molecules. A similar but slightly shorter Al–N bond was
found for (Pytsi)AlEt2 (Al-N = 2.0034(18) Å) (19). Reliable
bond lengths and angles are not available for the closely re-
lated dimethylalane (Pytsi)AlMe2, because it is disordered
about a plane of symmetry that bisects the molecule along
the Si2C plane in the C(SiMe3)2 group (19). In both halves
of the molecule the Me2Al- and the Me2Si moieties on one
side and the two halves of the pyridine ring on the other side
have similar sizes and shapes, which makes the disordering
understandable (19). Both halves of (Pytsi)AlMe2 can be
made dissimilar by either changing the alkyl groups at alu-
minum or adding a substituent to the pyridyl moiety; neither
(Pytsi)AlEt2 (19) nor compound 3 are disordered in the crys-
tal lattice.
Conclusion
compounds 3–5 have been prepared similarly as the known
(Pytsi)AlMe2 (19, 21). Of course, the methyl group in the 6
position of the pyridine ring is too small to sterically protect
the aluminum atom. However, compound 3 was the first test
case to determine if a small change to the pyridyl group has
an influence on the synthesis of the respective dimethyl
alane.
The preparation of 3–5 differs mainly in the way we syn-
thesized the ortho-lithiated pyridine (Scheme 1). In all cases
the ortho-lithiated pyridine derivative was prepared in situ.
However, for compounds 3 and 4, we generated it from a re-
spective bromopyridine and LiBu. For compound 5, we first
used a nickel catalyst cross-coupling of a Grignard reagent
(22, 23) followed by a selective deprotonation in the ortho
position, a method that had been previously applied to other
phenylpyridine derivatives (24) (Scheme 2).
We synthesized five new intramolecularly coordinated
aluminum species, whose molecular structures have been
elucidated in solution by NMR spectroscopy and in the solid
state by single crystal X-ray analysis. All species 1–5 are
equipped with a trisyl-based ligand with a pyridyl donor
group (Fig. 1, Pytsi). While the monomethyl compound
(Pytsi)AlMeCl (1) is accessible either from Li(THF)(Pytsi)
and MeAlCl2 (eq. [1]) or from (Pytsi)AlCl2 and LiMe, the
tert-butyl derivative (Pytsi)AltBuCl (2) could only be ob-
tained from Li(THF)(Pytsi) and tBuAlCl2 (eq. [1]). The lat-
ter result is in contrast to the synthesis of the related species
Ar′AltBuCl (Fig. 1, Ar′), which was synthesized from
Ar′AlCl2 and LitBu (1). The different substitution behavior
of (Pytsi)AlCl2 and Ar′AlCl2 towards LitBu can be inter-
preted as being due to the higher steric demand of Pytsi
compared with Ar′ (Fig. 1).
The dimethylalanes 3–5 were isolated in moderate to good
Compounds 3–5 can all be described as derivatives of
(Pytsi)AlMe2 with additional groups in the ortho position
of the pyridyl group. From the molecular structures of the
yields of 51% to 86% as crystalline colorless solids. All
1
three compounds reveal patterns in their H and 13C NMR
spectra that are consistent with time-averaged Cs symmetri-
cal species. The most noteworthy feature in all the spectra is
the appearance of the two isopropyl groups of the Dipp
ligand of compound 5. They show two doublets for the Me
groups (δ 0.82 and 1.34) and one multiplet for the CH group
Ph-substituted compound
4
(Fig. 5) and the 2,6-
diisopropylphenyl derivative 5 (Fig. 6) one gets the impres-
sion that the aromatic group in the ortho position of the
pyridyl ring might serve as a shield to help protect the Al
atom and, consequently, we intend to employ these species
as precursors for cationic aluminum compounds.
1
(δ 2.40) in the H NMR spectrum and two singlets for the
Me groups and one singlet for the CH groups in the 13C{1H}
NMR spectrum. This shows that both isopropyl groups are
chemically equivalent, but the methyl groups are nonequiva-
lent for each isopropyl group. As already mentioned above,
the NMR spectra can be rationalized by assuming compound
5 is a time-averaged Cs symmetrical species; e.g., the SiMe3
and the AlMe2 moieties each give rise to one singlet. All
facts combined prove that the Dipp ligand is oriented per-
Experimental
General procedures
All manipulations were carried out using standard
Schlenk techniques. Solvents were dried using a Braun Sol-
vent Purification System and stored under nitrogen over 4 Å
© 2007 NRC Canada

486
Can. J. Chem. Vol. 85, 2007
Table 1. Crystal and structural refinement data for compounds 1–5.
Compound
Empirical formula
Formula weight
Wavelength (Å)
Crystal system
Space group
Z
1
2
3
4
5
C15H31AlClNSi3
372.11
0.710 73
Monoclinic
P 21/c
C18H37AlClNSi3
414.19
0.710 73
Monoclinic
P 21/c
C17H36AlNSi3
365.72
0.710 73
Monoclinic
P 21/c
C22H38AlNSi3
427.78
0.710 73
Monoclinic
P 21/c
C28H50AlNSi3
511.94
0.710 73
Triclinic
P1
4
4
4
4
2
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
9.046 30(10)
9.315 60(10)
25.5316(4)
90
94.8075(5)
90
2144.02(5)
1.153
173(2)
0.382
2.26 to 27.55
17 648
4921 [R(int) =
0.0631]
9.0520(2)
16.7560(4)
18.2311(3)
90
118.6060(10)
90
2427.67(9)
1.133
173(2)
0.344
2.55 to 30.00
13 876
7071 [R(int) =
0.0298]
17.1251(3)
9.1309(2)
15.5683(3)
90
111.7240(10)
90
2261.48(8)
1.074
173(2)
0.247
2.57 to 28.20
42 198
5491 [R(int) =
0.0799]
13.8716(4)
9.7136(3)
18.6390(8)
90
90.394(2)
90
2511.42(15)
1.131
173(2)
0.232
2.78 to 27.48
10 258
5732 [R(int) =
0.0457]
8.5860(2)
12.0067(4)
16.6488(6)
71.2665(15)
80.8750(18)
75.5988(17)
1568.51(9)
1.084
173(2)
0.195
2.74 to 27.48
13 539
7178 [R(int) =
0.0238]
Volume (Å3)
Dcalcd (mg/m3)
Temperature (K)
Abs coeff. (mm–1)
θ range (°)
Reflections collected
Independent
reflections
Absorption correction Semi-empirical from Semi-empirical
Semi-empirical
from equivalents
Full-matrix least
squares on F2
5491, 0, 242
Semi-empirical
from equivalents
Full-matrix least
squares on F2
5732, 0, 254
Semi-empirical from
equivalents
Full-matrix least-
squares on F2
7178, 0, 312
equivalents
Full-matrix least-
squares on F2
4921, 0, 199
from equivalents
Full-matrix least-
squares on F2
Ref. method
Data, restraints,
parameters
7071, 0, 228
Goodness-of-fit on F2 1.043
1.058
1.042
1.024
1.001
Final R indices [I >
2σ(I)]
R indices (all data)
R1 = 0.0454, wR2 =
0.1053
R1 = 0.0749, wR2 =
0.1242
R1 = 0.0418, wR2 = R1 = 0.0442, wR2 = R1 = 0.0477, wR2 = R1 = 0.0448, wR2 =
0.0956 0.0943 0.1027 0.1096
R1 = 0.0634, wR2 = R1 = 0.0637, wR2 = R1 = 0.0843, wR2 = R1 = 0.0604, wR2 =
0.1050
0.1020
0.1205
0.1191
Largest diff. peak
and hole (e, Å–3)
0.635, –0.462
0.417, –0.275
0.369, –0.291
0.310, –0.355
0.503, –0.384
Scheme 1. Synthesis of compounds 3–5.
Scheme 2. Synthesis of the lithiopyridine for 5.
Aldrich) and LiBu (VWR) were titrated with 2,6-di-tert-
butylphenol–fluorene before usage (28). Silica Gel 60
(particle size 0.040–0.063 mm) was purchased from EMD
Chemicals. 1H, 13C, and 27Al NMR spectra were recorded on
a Bruker 500 MHz Avance at 25 °C in C6D6 unless noted
molecular sieves. All solvents for NMR spectroscopy were
degassed prior to use and stored under nitrogen over 4 Å
molecular sieves. HC(SiMe3)2(SiMe2Br) (8), Li(THF)(Pytsi)
[Pytsi = C(SiMe2)(SiMe3)2C5H4N)] (8), (Pytsi)AlCl2 (21), 2-
bromo-6-methylpyridine (25), 2-bromo-6-phenylpyridine
(24), and bromo-2,6-diisopropylbenzene (26) were synthesized
as described in the literature. tBuAlCl2 was synthesized sim-
ilar to tBuAlBr2 (27). 2-(2,6-Diisopropylphenyl)pyridine
was synthesized similar to 2-(2,6-diisopropylphenyl)-6-
methylpyridine (22). Me2AlCl and MeAlCl2 were purchased
from Sigma-Aldrich and used as received. LiMe (Sigma-
1
differently. H chemical shifts were referenced to the resid-
ual protons of the deuterated solvents (C6D6 at δ 7.15;
CDCl3 at δ 7.26), 13C chemical shifts were referenced to the
deuterated solvent (C6D6 signal at δ 128.0; CDCl3 signal at δ
77.0), and 27Al NMR spectra were referenced to [Al(acac)3]
dissolved in C6D6. Mass spectra were measured on a VG
70SE (m/z > 10% are listed for signals of the most abundant
© 2007 NRC Canada

Lund et al.
487
Fig. 6. Molecular structure of 5 with thermal ellipsoids at the
50% probability level. H atoms are omitted for clarity. Selected
bond lengths (Å) and angles (°): Al1–N1 = 2.0587(15), Al1–C7 =
2.0595(17), Al1–C16 = 1.965(2), Al1–C17 = 2.0390(19), C16–
Al1–C17 = 109.25(9), C7–Al1–C16 = 118.47(9), C7–Al1–C17 =
117.17(7), N1–Al1–C16 = 114.48(8), N1–Al1–C17 = 99.89(7),
N1–Al1–C7 = 95.32(6).
Fig. 4. Molecular structure of 3 with thermal ellipsoids at the
50% probability level. H atoms are omitted for clarity. Selected
bond lengths (Å) and angles (°): Al1–N1 = 2.0393(16), Al1–C7 =
2.0416(17), Al1–C16 = 1.976(2), Al1–C17 = 1.980(2), C16–Al1–
C17 = 110.30(10), C7–Al1–C16 = 116.94(8), C7–Al1–C17 =
118.49(8), N1–Al1–C16 = 112.74(8), N1–Al1–C17 = 99.94(8),
N1–Al1–C7 = 96.01(6).
Chloro{[dimethyl(pyrid-2-yl)silyl]bis(trimethyl-
silyl)methyl}methylaluminum (1)
Route 1: A solution of MeAlCl2 (4.2 mL, 1.0 mol/L in
Fig. 5. Molecular structure of 4 with thermal ellipsoids at the
50% probability level. H atoms are omitted for clarity. Selected
bond lengths (Å) and angles (°): Al1–N1 = 2.0537(19), Al1–C7 =
2.054(2), Al1–C16 = 1.983(2), Al1–C17 = 2.002(2), C16–Al1–
C17 = 111.50(11), C7–Al1–C16 = 117.62(9), C7–Al1–C17 =
113.27(9), N1–Al1–C16 = 110.26(9), N1–Al1–C17 = 106.83(9),
N1–Al1–C7 = 95.71(8).
hexane, 4.2 mmol) was added to
a
solution of
Li(THF)(Pytsi) (1.577 g, 4.220 mmol) in hexane at –78 °C.
After stirring for 20 min, the reaction mixture was allowed
to warm to ambient temperature and stirred for 16 h. The
solid was filtered off, extracted with Et2O (3 × 10 mL), the
combined organic extracts were reduced in volume to
10 mL, and crystallization at ca. –30 °C resulted in colorless
crystals of 1 (1.395 g, 88%).
Route 2: LiMe (4.4 mL, 0.93 mol/L, 4.1 mmol) was added
to (Pytsi)AlCl2 (1.625 g, 4.140 mmol) in Et2O (50 mL) at
–78 °C. The slurry was stirred for 30 min at –78 °C, allowed
to warm to ambient temperature, and stirred for 16 h. The
white solid was filtered off and the product extracted with
Et2O (3 × 10 mL). The combined extracts were reduced in
volume to 20 mL and kept at –30 °C to give colorless crys-
tals of 1 (1.257 g, 82%).
1H NMR (500 MHz) δ: 0.01 (s, 3H, AlMe), 0.15 (s, 9H,
SiMe3), 0.33 (s, 3H, SiMe2), 0.44 (s, 9H, SiMe3), 0.49 (s,
3H, SiMe2), 6.31 (pst, 1H, H-5), 6.77 (pst, 1H, H-4), 6.88
(d, 1H, H-3), 8.06 (d, 1H, H-6). 13C NMR (125.8 MHz) δ:
3.2 (SiMe), 4.2 (SiMe), 5.8 (SiMe3), 6.2 (SiMe3), 124.4 (C-
5), 129.0 (C-3), 138.9 (C-4), 145.8 (C-6), 173.1 (ipso-C).
27Al NMR (130.3 MHz) δ: 157 (w1/2 = 2000 Hz). MS
(70 eV) m/z (%): 356 (61) [M+ – CH3], 295 (13) [MH+ – Al
– Cl – CH3], 280 (37) [MH+ – Al – Cl – 2CH3], 264 (100)
+
+
[C12H22NSi3 ], 73 (11) [SiMe3 ]. Anal. calcd. for
C15H31AlClNSi3 (372.104): C 54.64, H 9.74, N 3.98; found:
C 54.67, H 10.11, N 3.75.
ions). Elemental analyses were performed on a PerkinElmer
2400 CHN Elemental Analyzer using V2O5 to promote com-
plete combustion.
tert-Butylchloro{[dimethyl(pyrid-2-yl)silyl]bis(trimethyl-
silyl)methyl}aluminum (2)
Li(THF)(Pytsi) (2.200 g, 5.887 mmol) was dissolved in
© 2007 NRC Canada

488
Can. J. Chem. Vol. 85, 2007
hexane (40 mL) and cooled to –78 °C. A solution of
tBuAlCl2 (0.913 g, 5.890 mmol) in hexane (30 mL) was
filled into a dropping funnel and added to the cooled solu-
tion of Li(THF)(Pytsi) over a period of 5 min. This resulted
in the formation of a slightly yellow solution with a white
precipitate. After stirring the reaction mixture for 30 min,
the cooling bath was removed and the solution was stirred
for another 2 h. The formed dark brown solution was filtered
and all volatiles were removed in high vacuum. Sublimation
at 150 °C in high vacuum produced a yellow-orange solid.
The sublimed solid was dissolved in hexane (35 mL) and
crystallization at ca. –30 °C resulted in pale yellow crystals
in high vacuum gave a white solid, which was extracted
with hexane (3 × 15 mL). The combined organic fractions
were separated from the solid remains by filtration. The or-
ganic phase was concentrated to 20 mL and kept at –30 °C
to give light yellow crystalline plates of 3 (1.132 g, 51%).
1H NMR (500 MHz) δ: –0.17 (s, 6H, AlMe2), 0.29 (s, 18H,
SiMe3), 0.42 (s, 6H, SiMe2), 2.26 (s, 3H, Me), 6.22 (d, 1H,
H-5), 6.78 (pst, 1H, H-4), 6.88 (d, 1H, H-3). 13C NMR
(125.8 MHz) δ: –1.9 (AlMe2), 4.5 (SiMe2), 6.4 (SiMe3),
23.0 (CH3), 125.3 (C-5), 126.3 (C-3), 138.1 (C-4), 157.4
(ipso-C-6), 173.8 (ipso-C-2). 27Al NMR (130.3 MHz) δ:
174.3 (w1/2 = 2750 Hz). MS (70 eV) m/z (%): 350 (100) [M+
1
+
of 2 (1.322 g, 54%). H NMR (500 MHz) δ: 0.30 (s, 9H,
– CH3], 278 (37) [M+ – Al – 4CH3], 262 (15) [C12H20NSi3 ].
SiMe3), 0.36 (s, 9H, SiMe3), 0.40 (s, 3H, SiMe2), 0.44 (s,
3H, SiMe2), 1.25 (s, 9H, C(CH3)3), 6.37 (pst, 1H, H-5), 6.81
(d, 1H, H-3), 6.92 (pst, 1H, H-4), 8.45 (d, 1H, H-6).
13C{1H} NMR (125.8 MHz) δ: 1.15 [br, C(SiMe3)2], 4.41
(SiMe2), 4.61 (SiMe2), 6.94 (SiMe3), 7.10 (SiMe3), 17.1
[C(CH3)3], 31.2 [C(CH3)3], 124.1 (C-5), 129.5 (C-3), 139.1
(C-4), 146.9 (C-6), 172.61 (ipso-C). 27Al (130.3 MHz) δ:
150 (w1/2 = 4300 Hz). MS (70 eV) m/z (%): 398 (6) [M+ –
Anal. calcd. for C17H36AlNSi3 (365.713): C 55.83, H 9.92,
N 3.83; found: C 55.16, H 10.57, N 3.63.
[Dimethyl(6-phenylpyrid-2-yl)silyl]bis(trimethyl-
silyl)methane
LiBu (2.2 mL, 2.8 mol/L in hexane, 6.2 mmol) was added
dropwise to a stirring solution of 2-bromo-6-phenylpyridine
(1.321 g, 5.643 mmol) in Et2O (15 mL) at –78 °C. The
resulting red solution was stirred for 20 min before a cold
solution (–78 °C) of CH(Me3Si)2(SiMe2Br) (1.712g,
5.755 mmol) in Et2O (15 mL) was added. The cold bath was
removed and the reaction mixture stirred overnight. The red-
brown liquid phase was separated from the solids by filtra-
tion. Removal of all volatiles at ambient temperature in high
vacuum from the liquid phase gave a red oil. The product
was collected as a golden yellow oil by a flask-to-flask con-
densation (bp 145–150 °C, 10–3 mbar, 1.339 g, 64%). The
fraction collected at 65–95 °C was discarded. 1H NMR
(500 MHz) δ: 0.11 (s, 18H, SiMe3), 0.17 (s, 1H, CH), 0.52
(s, 6H, SiMe2), 7.17(m, 2H, Py H-4, Ph H-5), 7.21 (d, 1H,
Py, H-3 or H-5), 7.27 (t, 2H, Ph, H-3, H-4), 7.30 (d, 1H, Py,
H-5 or H-3) 8.17 (d, 2H, Ph, H-2, H-6). 13C NMR
(125.8 MHz) δ: 1.4 (SiMe2), 1.7 (CH), 3.3 (SiMe3), 119.1
(Py, C-3 or C-5), 127.1 (Py, C-3 or C-5), 127.2 (Ph, C-2,
C-6), 128.8 (Ph, C-3, C-5), 129.0 (Py, C-4), 134.6 (Ph, C-4),
140.3 (Ph, ipso-C), 156.7 (Py, ipso-C-6), 169.8 (Py, ipso-C-2).
+
CH3], 356 (72) [M+ – tBu], 336 (16) [C15H31AlNSi3 ], 264
+
(100) [C12H22NSi3 ]. Anal. calcd. for C18H37AlClNSi3
(414.184): C 52.20, H 9.00, N 3.38; found: C 52.88, H 8.96,
N 3.18.
[Dimethyl(6-methylpyrid-2-yl)silyl]bis(trimethyl-
silyl)methane
LiBu (15.0 mL, 2.7 mol/L in hexane, 40.5 mmol) was
added dropwise to a solution of 2-bromo-6-methylpyridine
(8.796 g, 37.12 mmol) in Et2O (30 mL) at –78 °C to give a
dark red solution. The solution was stirred for 20 min before
being added to
a
cold solution (–78 °C) of
HC(SiMe3)2(SiMe2Br) (11.751 g, 39.505 mmol) in Et2O
(100 mL), which gave a brown solution. The cold bath was
removed and the reaction mixture was stirred for 16 h. After
the solvent was removed in vacuum, a dark-brown oil re-
mained, which was transferred onto a dry silica column. The
product was eluted with ethyl acetate and a subsequent
flask-to-flask condensation under inert gas atmosphere
yielded a light yellow oil [bp 82–84 °C, 10–3 mbar (1 bar =
{[Dimethyl(6-phenylpyrid-2-yl)silyl]bis(trimethyl-
silyl)methyl}dimethylaluminum (4)
1
100 kPa), 8.920 g, 77%]. H NMR (500 MHz) δ: 0.10 (s,
18H, SiMe3), 0.46 (s, 6H, SiMe2), 2.43 (s, 3H, o-Me), 6.64
(d, 1H, H-5), 7.06 (pst, 1H, H-4), 7.11 (d, 1H, H-3). 13C
NMR (125.8 MHz) δ: 1.5 (SiMe2), 3.4 (SiMe3), 24.8 (CH3),
121.8 (C-5), 125.7 (C-3), 134.0 (C-4), 158.0 (ipso-C-6),
169.2 (ipso-C-2).
LiMe (4.0 mL, 1.0 mol/L in THF–cumene, 4.0 mmol) was
added dropwise to a stirring solution of [dimethyl(6-
phenylpyrid-2-yl)silyl]bis(trimethylsilyl)methane (1.339 g,
3.602 mmol) in THF (30 mL) at ambient temperature result-
ing in the formation of gas and a red solution. After 1 h of
stirring at ambient temperature, the red solution was cooled
to 0 °C and Me2AlCl (5.0 mL, 1.0 mol/L in hexane,
5.0 mmol) was added dropwise to give a clear brown solu-
tion that was stirred for 16 h at ambient temperature.
Removal of all volatiles in high vacuum at ambient tempera-
ture yielded a light brown solid. The solid was extracted
with ether (3 × 20 mL), and the solvent was removed to give
a light brown solid, which was subsequently sublimed
(140 °C, 10–3 mbar) to give a white solid (1.171 g, 76%).
Crystallization from diethyl ether at –30 °C yielded colorless
{[Dimethyl(6-methylpyrid-2-yl)silyl]bis(trimethyl-
silyl)methyl}dimethylaluminum (3)
LiMe (6.6 mL, 1.0 mol/L in THF–cumene, 6.6 mmol) was
added dropwise to [dimethyl(6-methylpyrid-2-yl)silyl]bis(tri-
methylsilyl)methane (1.866 g, 6.026 mmol) in THF (30 mL)
at ambient temperature to give a red solution. Gas was given
off immediately. After 1 h of stirring, the solvent was
removed in vacuum to leave an oily residue behind, which
was dissolved in hexane (20 mL). The solution was cooled
to –78 °C and Me2AlCl (6.6 mL, 1.0 mol/L in hexane,
6.6 mmol) was added dropwise over 10 min. The cold bath
was removed and the reaction mixture stirred for 16 h at am-
bient temperature. Removal of all volatiles from the solution
1
crystals of 4 (1.095 g, 71%). H NMR (500 MHz) δ: –0.58
(s, 6H, AlMe2), 0.26 (s, 18H, SiMe3), 0.51 (s, 6H, SiMe2),
6.62 (d, 1H, H-5), 6.90 (pst, 1H, H-4), 7.05 (d, 1H, H-3),
7.10–7.11 (m, 3H, Ph), 7.20–7.22 (m, 2H, Ph). 13C NMR
© 2007 NRC Canada

Lund et al.
489
(125.8 MHz) δ: –2.3 (AlMe2, br), 4.7 (SiMe2), 6.3 (SiMe3),
125.7, (C-5), 127.7 (C-3), 128.4 (Ph), 129.1 (Ph) 129.7 (Ph,
ipso-C), 138.0 (C-4), 160.3 (ipso-C-6), 174.8 (ipso-C-2).
27Al NMR (130.3 MHz) δ: 182 (w1/2 = 4500 Hz). MS
(70 eV) m/z (%): 412 (100) [M+ – CH3], 340 (24) [M+ – Al
– 4CH3], 217 (16). Anal. calcd. for C22H38AlNSi3 (422.804):
C 61.77, H 8.95, N 3.27; found: C 61.09, H 8.88, N 3.18.
organic phase were subsequently removed in vacuum. Flask-
to-flask condensation of the orange oil at high vacuum gave
two fractions. The fraction at 85–125 °C was discarded. The
product was received as an oil (bp 135–140 °C, 10–3 mbar,
3.214 g, 68%), which turned into a light yellow solid upon
cooling to ambient temperature. 1H NMR (500 MHz) δ: 0.10
(s, 18H, SiMe3), 0.21 (s, 1H, CH), 0.47 (s, 6H, SiMe2), 1.12
(d, 6H, CH(CH3)CH3), 1.23 (d, 6H, CH(CH3)CH3), 2.72 (m,
2H, CH(CH3)CH3, 6.92 (d, 1H, Py, H-3 or H-5), 7.12 (pst,
1H, Ph, H-4), 7.20 (m, 3H, Ph H-3, H-5, Py H-3 or H-5),
7.30 (pst, 1H, Py H-4). 13C NMR (125.8 MHz) δ: 0.8 (CH),
1.3 (SiMe2), 3.3 (2 SiMe3), 23.9 (HC(CH3)CH3), 25.0
(HC(CH3)CH3), 30.7 (HC(CH3)CH3), 122.9 (Ph, 3-C, 5-C),
123.6 (Py, C-3 or C-5), 126.2 (Py, C-5 or C-3), 128.8 (Ph,
C-4), 133.6 (Py, C-4), 140.2 (Ph, ipso-C-1), 146.7 (Ph, ipso-
C-2, ipso-C-6), 160.3 (Py, ipso-C-6), 169.9 (Py, ipso-C-2).
2-(2,6-Diisopropylphenyl)pyridine
Bromo-2,6-diisopropylbenzene (6.115 g, 25.36 mmol) in
THF (10 mL) was added to Mg turnings (0.740 g,
30.45 mmol) in THF (20 mL) in a flask equipped with re-
flux condenser. Heat was used to start the Grignard reaction.
The mixture was refluxed for 24 h before being added to a
mixture of PtBu3 (0.1472 g, 0.7376 mmol), Ni(acac)2
(0.1684 g, 0.6555 mmol), and 2-bromopyridine (3.388 g,
21.44 mmol) in THF (100 mL) cooled to 0 °C, which re-
sulted in a brown solution. The solution refluxed for 24 h
and was subsequently poured into dilute HCl (200 mL;
0 °C). The organic phase was discarded and the aqueous
phase was extracted with Et2O (2 × 50 mL) and the Et2O
phase was discarded. K2CO3 was added to the aqueous
phase until the evolution of CO2 ceased during which the
color of the solution went from brown to yellow. The aque-
ous phase was extracted with dichloromethane (3 × 150 mL)
followed by the removal of volatiles in high vacuum from
the combined organic phases to leave a brown oil behind.
Flask-to-flask condensation under high vacuum at 120–
125 °C yielded a viscous yellow oil (2.467 g, 48%). 1H
NMR (500 MHz, CDCl3) δ: 1.06 (6 H, d, HC(CH3)CH3),
1.10 (d, 6 H, HC(CH3)CH3), 2.46 (m, 2H, HC(CH3)CH3),
7.19 (d, 1H, Ph), 7.25 (m, 2H, Py H-4, H-3), 7.33 (pst, 1H,
Ph), 7.71 (pst, 1H, Py H-5), 8.70 (d, 1H, Py H-6). 13C NMR
(125.8 MHz, CDCl3) δ: 23.9 (HC(CH3)CH3), 24.2
(HC(CH3)CH3), 30.3 (2 HC(CH3)CH3), 121.5 (Py, C-3 or C-
4), 122.6 (Ph, C-3, C-5), 124.9 (Py, C-4 or C-3), 128.5 (Ph,
C-4), 135.6 (Py, C-5), 138.6 (Ph, C-1), 146.4 (Py, ipso-C-6),
149.3 (Ph, C-2, C-6), 160.0 (Py, ipso-C-2).
{{[6-(2,6-Diisopropylphenyl)pyrid-2yl]dimethyl-
silyl}bis(trimethylsilyl)methyl}dimethylaluminum (5)
LiMe (2.6 mL, 1.0 mol/L in THF–cumene) was added
dropwise to {[6-(2,6-diisopropylphenyl)pyrid-2yl]dimethyl-
silyl}bis(trimethylsilyl)methane (0.984, 2.158 mmol) in THF
(20 mL). The solution was stirred for 4 h during which the
solution turned brown and gas evolved. Subsequently, the
flask was cooled to –78 °C and Me2AlCl (2.6 mL, 1.0 mol/L
in hexanes) was added dropwise. The cold bath was removed
and the reaction mixture stirred overnight. After removal of
volatiles from the clear yellow solution a yellow solid re-
mained, which was extracted with ether (10 mL), the extract
was filtered and volatiles were removed in vacuum from the
filtrate to give a light yellow solid. The solid was dissolved
in warm hexane (10 mL) and kept at –30 °C to give color-
1
less crystals of 5 (0.953 g, 86%). H NMR (500 MHz) δ:
–0.62 (s, 6H, AlMe2), 0.31 (s, 18H, SiMe3), 0.50 (s, 6H,
SiMe2), 0.82 (d, 6H, HC(CH3)CH3), 1.34 (d, 6H,
HC(CH3)CH3), 2.40 (m, 2H, HC(CH3)CH3), 6.91 (t, 1H, Py,
H-4,), 6.96 (d, 1H, Py, H-3 or H-5), 7.08 (d, H, Py, H-5 or
H-3), 7.11 (d, 2H, Ph, H-3, H-5), 7.26 (pst, 1H, Ph, H-4).
13C NMR (125.8 MHz) δ: –2.5 (AlMe2), 4.7 (SiMe2), 6.5 (2
SiMe3), 22.2 (HC(CH3)CH3), 26.4 (HC(CH3)CH3), 30.9
(HC(CH3)CH3), 123.1 (Ph, C-3, C-5), 127.8 (Py, C-3 or C-
5), 128.3 (Py, C-5 or C-3), 130.7 (Ph, C-4), 134.9 (Ph, C-1),
136.7 (Py, C-4), 147.3 (Ph, C-2, C-6), 159.5 (Py, C-6), 175.5
(Py, C-2). 27Al NMR δ: 179 (w1/2 = 4300 Hz). MS (70 eV)
m/z (%): 496 (10) [M+ – CH3], 455 (100) [MH+ – Al –
{[6-(2,6-Diisopropylphenyl)pyrid-2yl]dimethyl-
silyl}bis(trimethylsilyl)methane
LiBu (22.0 mL, 2.87 mol/L in hexane, 63.1 mmol) was
added dropwise to a solution of 2-dimethylaminoethanol
(2.802 g, 31.43 mmol) in hexane (30 mL) cooled to 0 °C,
and the resulting yellow solution was stirred for an addi-
tional 30 min. 2-(2,6-Diisopropylphenyl)pyridine (2.499 g,
10.44 mmol) in hexane (30 mL) was added and the color of
the reaction mixture changed immediately to red. After 1 h
of stirring at 0 °C, the mixture was cooled to –78 °C and
HC(SiMe3)2(SiMe2Br) (11.355 g, 38.17 mmol) in hexane
(30 mL) was added dropwise. The mixture was kept at
–78 °C for 1 h before the cold bath was removed and stirring
was continued for 16 h at ambient temperature. Deionized
H2O (100 mL) was added, and the aqueous phase was ex-
tracted with Et2O (3 × 100 mL). The combined extracts were
dried over MgSO4, filtered, and the volatiles from the
+
2CH3], 440 (35) [MH+ – Al –3CH3], 73 (13) [SiMe3 ]. Anal.
calcd. for C28H50AlNSi3 (511.94): C 65.69, H 9.84, N 2.74;
found: C64.89, H 9.42, N 2.38.
X-ray structural analysis for 1–5.3
Data was collected at –100 °C on a Nonius Kappa CCD
diffractometer, using the COLLECT program (29). Cell re-
finement and data reductions used the programs DENZO
and SCALEPACK (30). The program SIR97 (31) was used
to solve the structure and SHELXL97 (32) was used to re-
fine the structure. ORTEP-3 for Windows (33) was used for
3 Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository of
Unpublished Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 5183. For more
information on obtaining material refer to cisti-icist.nrc-cnrc.gc.ca/irm/unpub_e.shtml. CCDC 641212 and 641216 contain the crystallo-
graphic data for this manuscript. These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (Or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2007 NRC Canada

490
Can. J. Chem. Vol. 85, 2007
12. H. Braunschweig, C. Burschka, G.K.B. Clentsmith, T. Kupfer,
and K. Radacki. Inorg. Chem. 44, 4906 (2005).
13. J.A. Schachner, G.A. Orlowski, J.W. Quail, H.-B. Kraatz, and
J. Müller. Inorg. Chem. 45, 454 (2006).
14. M. Bochmann and D.M. Dawson. Angew. Chem. Int. Ed. 35,
2226 (1996).
15. M.P. Coles and R.F. Jordan. J. Am. Chem. Soc. 119, 8125 (1997).
16. M. Bruce, V.C. Gibson, C. Redshaw, A. Solan, J.P. White, and
D. J. Williams. Chem. Commun. (Cambridge), 2523 (1998).
17. D.A. Atwood. Coord. Chem. Rev. 176, 407 (1998).
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Soc. 124, 7662 (2002).
molecular graphics and PLATON (34) was used to prepare
material for publication. H atoms were placed in calculated
positions with Uiso constrained to be 1.5 times Ueq of the
carrier atom for all methyl H atoms and 1.2 times Uiso for all
other H atoms.
The three methyl groups on Si3 (compound 3) are disor-
dered and were modeled with occupancies of 0.72 and 0.28
for the two components. Only one position for the methyl
groups is shown in Fig. 4.
Acknowledgments
19. O. Stanga, C.L. Lund, H. Liang, J.W. Quail, and J. Müller.
We thank the Natural Sciences and Engineering Research
Council of Canada (JM, NSERC Discovery Grant), the De-
partment of Chemistry, and the University of Saskatchewan
for their generous support. We thank the Canada Foundation
for Innovation (CFI) and the government of Saskatchewan
for funding of the X-ray and NMR facilities in the Saskatch-
ewan Structural Sciences Centre (SSSC).
Organometallics, 24, 6120 (2005).
20. I. Krossing and I. Raabe. Angew. Chem. Int. Ed. 43, 2066
(2004).
21. J. Howson, C. Eaborn, P.B. Hitchcock, M.S. Hill, and J.D.
Smith. J. Organomet. Chem. 690, 69 (2005).
22. F. Speiser, P. Braunstein, and L. Saussine. Organometallics,
23, 2633 (2004).
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Herrmann. Angew. Chem. Int. Ed. 39, 1602 (2000).
24. P. Gros and Y. Fort. J. Org. Chem. 68, 2028 (2003).
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© 2007 NRC Canada