Facile cleavage of the silicon-oxygen bond leading to unusual dinuclear aluminum complexes

Article abstract of DOI:10.1021/om990698t

Reactions of Me₂Si(OR)(NHR′) (R = 2,6-Me₂-Ph; R′ = Cy (2a), Ph (2b)) with AlMe₃ in pentane at room temperature afford unusual dinuclear aluminum complexes (Me₂Al)₂[(μ-OR)(μ-NR′SiMe₃)] (R = 2,6-Me₂Ph; R′ = Cy (3a), Ph (36)) that contain both nitrogen- and oxygen-bridging groups. Meanwhile, the corresponding reaction of Me₂Si(OR)(NHR′) (R, R′ = 2,6-Me₂Ph (2c)) yields a monomeric N,O-chelated aluminum species [Me₂Si(OR)(NR′)]AlMe₂ (3c). It is most likely that two AlMe₃ molecules are associated with the facile cleavage of the Si-O bond to form the stable four-membered (μ-N)Al₂(μ-O) ring of 3a,b, but the analogous reaction does not occur in 2c, having a bulkier N-substituent. The crystal structure of 3a is reported.

Full text of DOI:10.1021/om990698t

Organometallics 1999, 18, 5713-5716
5713
F a cile Clea va ge of th e Silicon -Oxygen Bon d Lea d in g to
Un u su a l Din u clea r Alu m in u m Com p lexes
Choong Hoon Lee and J oon Won Park*
Department of Chemistry, Center for Biofunctional Molecules, Pohang University of Science
and Technology, San 31 Hyoja-dong, Pohang, 790-784, Korea
Received September 1, 1999
Sch em e 1
Summary: Reactions of Me2Si(OR)(NHR′) (R ) 2,6-Me2-
Ph; R′ ) Cy (2a ), Ph (2b)) with AlMe3 in pentane at room
temperature afford unusual dinuclear aluminum com-
plexes (Me2Al)2[(µ-OR)(µ-NR′SiMe3)] (R ) 2,6-Me2Ph; R′
) Cy (3a ), Ph (3b)) that contain both nitrogen- and
oxygen-bridging groups. Meanwhile, the corresponding
reaction of Me2Si(OR)(NHR′) (R, R′ ) 2,6-Me2Ph (2c))
yields a monomeric N,O-chelated aluminum species
[Me2Si(OR)(NR′)]AlMe2 (3c). It is most likely that two
AlMe3 molecules are associated with the facile cleavage
of the Si-O bond to form the stable four-membered (µ-
N)Al2(µ-O) ring of 3a ,b, but the analogous reaction does
not occur in 2c, having a bulkier N-substituent. The
crystal structure of 3a is reported.
In tr od u ction
Recently, there is much attention on neutral alumi-
num complexes that are chelated by bi- or tridentate
anionic ligands.1 The related efforts have explored a
wide range of novel organoaluminum compounds with
well-defined structures and chemical reactivity. In
particular, N,N′-bidentate amidinate ligands of the type
[RC(NR′)2]- (R, R′ ) alkyl, aryl) with a π-delocalized
NCN fragment are extensively used to coordinate an
electrophilic Al center.2
) C6H11 (2a ), Ph (2b), 2,6-Me2Ph (2c)) for use in
organoaluminum chemistry. Interestingly, reactions of
2a ,b with AlMe3 undergo a facile cleavage of the
silicon-oxygen bond and form unusual dinuclear alu-
minum complexes (Me2Al)2[(µ-OR)(µ-NR′SiMe3)] (R )
2,6-Me2Ph; R′ ) Cy (3a ), Ph (3b)).
Similarly, N,O-substituted (oxydimethylsilyl)amides
of [Me2Si(OR)(NR′)]- that contain a localized N-anion
with a pendant neutral O-donor also act as attractive
chelating ligands. It is previously known that the N,O-
bis(tert-butyl) ligand of [Me2Si(OtBu)(NtBu)]- is useful
for stabilizing main group metals, but not including
aluminum.3 In this regard, we here report bulky N,O-
chelate ligands (Me2Si(OR)(NHR′), R ) 2,6-Me2Ph; R′
Resu lts a n d Discu ssion
R ea ct ion s of (Ar yloxyd im et h ylsilyl)a m id es
(2a -c) w ith Tr im eth yla lu m in u m . The N,O-ligands
(2a -c) were prepared from the reaction between 2,6-
dimethylphenol and excess dichlorodimethylsilane, fol-
lowed by treatment with appropriate amines, cyclohex-
ylamine, aniline, and 2,6-dimethylaniline, respectively,
in a stepwise fashion.4
When 2a was allowed to react with an equimolar
amount of AlMe3 in pentane at room temperature, a
white solid precipitated in 12 h (Scheme 1). Surpris-
ingly, X-ray crystallographic (vide infra) and elemental
analyses showed that the product is an unprecedented
dinuclear species, (Me2Al)2[(µ-O-2,6-Me2Ph)(µ-NCySiMe3)]
(3a ), in which each aluminum center is connected with
both an alkylamide- and an alkoxide-bridging group.
Homo- and hetero-2D COSY spectra confirmed that the
solid-state structure is maintained in solution as well.
Two sets of proton and 13C resonances for Al-Me groups
are in harmony with the four-membered cyclic struc-
ture.
(1) For recent reports: (a) Cosle´dan, F.; Hitchcock, P. B.; Lappert,
M. F. Chem. Commun. 1999, 705. (b) Bruce, M.; Gibson, V. C.;
Redshaw, C.; Solan, G. A.; White, A. J . P.; Williams, D. J . Chem.
Commun. 1998, 2523. (c) Aeilts, S. L.; Coles, M. P.; Swenson, D. C.;
J ordan, R. F. Organometallics 1998, 17, 3265. (d) Radzewich, C. E.;
Coles, M. P.; J ordan, R. F. J . Am Chem. Soc. 1998, 120, 9384. (e) Qian,
B.; Ward, D. L.; Smith, M. R. Organometallics 1998, 17, 3070. (f)
Gibson, V. C.; Redshaw, C.; White, A. J . P.; Williams, D. J . J .
Organomet. Chem. 1998, 550, 453. (g) Emig, N.; Nguyen, H.; Kraut-
scheid, H.; Re´au, R.; Cazaux, J .-B.; Bertrand, G. Organometallics 1998,
17, 3599. (h) Ihara, F.; Young, V. G., J r.; J ordan, R. F. J . Am. Chem.
Soc. 1998, 120, 8277. (i) Emig, N.; Re´au, R.; Krautscheid, H.; Fenske,
D.; Bertrand, G. J . Am. Chem. Soc. 1996, 118, 5822. (j) Dias, H. V. R.
D.; J in, W.; Ratcliff, R. E. Inorg. Chem. 1995, 34, 6100. (k) Fryzuk, M.
D.; Giesbrecht, G. R.; Olovsson, G.; Rettig, S. J . Organometallics 1996,
15, 4832. (l) McMahon, C. N.; Francis, J . A.; Bott, S. G.; Barron, A. R.
J . Chem. Soc., Dalton Trans. 1999, 67.
(2) (a) Coles, M. P.; Swenson, D. C.; J ordan, R. F. Organometallics
1998, 17, 4042. (b) Coles, M. P.; J ordan, R. F. J . Am Chem. Soc. 1997,
119, 8125. (c) Coles, M. P.; Swenson, D. C.; J ordan, R. F. Organome-
tallics 1997, 16, 5183.
(3) Veith, M. Angew. Chem., Int. Ed. Engl. 1987, 26, 1, and other
references therein.
(4) Preparation of a similar ligand, Me2Si(O-t-Bu)(NH-t-Bu), has
been reported. Please see: Veith, M.; Ro¨sler, R. J . Organomet. Chem.
1982, 229, 131.
10.1021/om990698t CCC: $18.00 © 1999 American Chemical Society
Publication on Web 12/02/1999

5714 Organometallics, Vol. 18, No. 26, 1999
Notes
Sch em e 2
The same behaviors are also observed for the corre-
sponding reaction of 2b to give a dinuclear species, (Me2-
Al)2[(µ-O-2,6-Me2Ph)(µ-NPhSiMe3)] (3b ). Elemental
analysis and NMR spectra of 3b at room temperature
are consistent with the dinuclear species. In particular,
only seven 13C peaks for the aromatic groups were
observed in benzene-d6. However, the expected eight
peaks were recorded in CDCl3. A peak at 127.9 ppm
must overlap one of the benzene-d6 peaks. For 3b, the
large difference between chemical shifts (δ -0.24 and
-0.43 ppm in 1H NMR; -3.00 and -5.44 ppm in 13C
NMR) of the nonequivalent Al-Me groups is presum-
ably due to the anisotropic environment invoked by the
phenyl ring current.
To our knowledge, the dinuclear aluminum species
(3a ,b) are very unusual in that most of dinuclear
aluminum complexes [R1 Al(µ-E)]2 (E ) NR2 , OR2, SR2;
2
2
R1, R2 ) alkyl, aryl) consist of equivalent monomeric
units. Meanwhile, (Me2Al)2[(µ-OMe)(µ-iPrNC(Me)NiPr)]
with a methoxy and an amidinate bridging group has
been reported as a rare analogue.6 3a ,b must originate
from the reaction of the intermediates (I), [Me2Si(OR)-
(NR′)]AlMe2 (R ) 2,6-Me2Ph; R′ ) Cy and Ph, respec-
tively), with the second AlMe3 molecule (Scheme 2). The
driving force of the latter reaction must be a large
energy gain from the Al-O bond (585 kJ /mol)7 forma-
tion, which is sufficient to compensate for the Si-O bond
(439 kJ /mol)8 cleavage. Similar cleavage in organo-
siloxanes9 and tris(trimethylsilyl) phosphate10 has been
observed, but only under rigorous heating conditions.
Compared with the previous examples, the cleavage in
2a ,b occurs even at 0 °C, showing the kinetic amenabil-
ity.
Variable-temperature NMR spectra showed that the
four-membered cycle of 3b is fluxional. As the solution
of 3b in toluene-d8 was gradually heated, two signals
of the Al-Me groups become broadened and finally
coalesced at 58 °C, from which ∆Gq for exchange of the
methyl groups is estimated to be about 16 kcal mol-1 5
.
To follow the Si-O bond cleavage, an equimolar
amount of AlMe3 was added to a C6D6 solution of 2a in
an NMR tube at room temperature. Immediately after
the mixing, downfield shifts of the silicon-methyl and
N-Cipso protons of 2a were observed, indicating the
transient formation of an adduct, [Me2Si(O-2,6-Me2Ph)-
(NHCy)]‚(AlMe3)n (n ) 1 or 2). In 2 h, new proton signals
appeared, and the formation of about 40% (NMR yield
based on the consumed AlMe3) of 3a was observed in
24 h. In the NMR reaction of 2b with an equimolar
amount of AlMe3, formation of 3b is much faster than
that observed for 3a . The conversion is almost quantita-
tive in 2 h, leaving half of the ligand 2b intact. The
remaining ligand can also be transformed into 3b by
the subsequent addition of AlMe3.
To understand these features further, control experi-
ments were carried out and followed by 1H NMR
spectroscopy. AlMe3 was mixed with 2,6-dimethylphenol
and cyclohexyltrimethylsilylamine in the ratio of 2:1:1
at room temperature. The reaction afforded a mixture
of products, but 3a was not observed in the mixture.
Additionally, heating 2,6-Me2PhOSiMe3 with excess
AlMe3 to 80 °C did not show any sign of cleavage of the
Si-O bond in 24 h. These observations confirm that the
The mechanism could be either unimolecular or bi-
molecular, and the latter must be associated with two
molecules of the binuclear species or extra ligands such
as coordinating solvents. To probe the possibility,
coalescence temperature (Tc) was measured at several
concentrations. It is found that Tc is independent of the
concentration of 3b. Also, tetrahydrofuran was added
to find out whether the coordinating solvent assists the
exchange process. Almost the same Tc (50 °C) in the
presence of a catalytic amount of THF (10 mol %)
indicates that the exchange process is not associated
with the extra coordinating ligand. Addition of 4 equiv
of THF generated four new peaks for the Al-Me group
with concurrent disappearance of the original two
1
resonances. When the H NMR spectrum was taken in
THF-d8, only one resonance for the Al-Me group was
observed. Therefore, it seems that the dissociation into
mononuclear species has occurred in the presence of a
large excess of THF, and the final products are labile
and/or fluxional enough to show one resonance for the
1
Al-Me group in H NMR.
Therefore, a unimolecular process is the most prob-
able mechanism. Considering the rather high activation
energy to cleave either the aluminum-oxygen bond or
the aluminum-nitrogen bond, a concerted mechanism,
in which bond breakage and the formation occur simul-
taneously while the N(SiMe3)Ph rotates about the N-O
vector, must be plausible.
(6) Chang, C.-C.; Hsiung, C.-S.; Su, H.-L.; Srinivas, B.; Lee, G.-H.;
Wang, Y. Organometallics 1998, 17, 1595.
(7) Chemistry of Aluminum, Gallium, Indium and Thallium; Downs,
A. J ., Ed.; Blackie Academic & Professional: London, 1993; p 3.
(8) Baldwin, J . C.; Lappert, M. F.; Pedley, J . B.; Poland, J . S. J .
Chem. Soc., Dalton Trans. 1972, 1943.
(9) Apblett, A. W.; Barron, A. R. Organometallics 1990, 9, 2137.
(10) Pinkas, J .; Chakraborty, D.; Yang, Y.; Murugavel, R.; Noltem-
eyer, M.; Roesky, H. W. Organometallics 1999, 18, 523.
(5) Friebolin, H. Basic One- and Two-Dimensional NMR Spectros-
copy; VCH: Weinheim, 1993; p 287.

Notes
Organometallics, Vol. 18, No. 26, 1999 5715
and nearly trigonal planar, respectively. As expected,
the Al-N-AlA angle (89.58(9)°) is more acute than the
Al-O-AlA angle (97.80(9)°), and the angles are com-
parable to those found in the dimeric aluminum com-
pounds [R1 Al(µ-E)]2 (E ) NR2 , OR2; R1, R2 ) alkyl,
2
2
aryl). The Al-N (2.0035(16) Å) and Al-O (1.8731(13)
Å) bond lengths are close to the standard values (1.95
and 1.85 Å, respectively)11 of Al-E (E ) N, O) bonds
featuring similar bonding character.
Su m m a r y
We observed the facile cleavage of the Si-O bond
promoted by two molecules of AlMe3 to form unusual
dinuclear aluminum complexes (Me2Al)2[(µ-OR)(µ-NR′-
SiMe3)] (R ) 2,6-Me2Ph; R′ ) Cy, Ph) that contain both
an alkoxide and an alkylamide bridge. Meanwhile, a
bulkier substituent on the nitrogen atom gives a N,O-
chelated mononuclear aluminum species, instead. The
above approach seems to be quite useful for the forma-
tion of hetero-bridged dinuclear aluminum complexes
as long as the steric bulkiness on the nitrogen atom can
be avoided.
F igu r e 1. ORTEP diagram of the structure of (Me2Al)2-
[(µ-O-2,6-Me2Ph)(µ-NCySiMe3)] (3a )
Ta ble 1. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for
(Me2Al)2[(µ-O-2,6-Me2P h )(µ-NCySiMe3)] (3a )a
bond distances
bond angles
Al-N
2.0035(16)
1.8731(13)
1.949(3)
1.959(2)
1.804(2)
1.410(3)
1.539(3)
2.8229(12)
N-Al-O
85.07(6)
112.40(13)
119.96(12)
112.59(11)
89.58(9)
108.09(12)
115.32(17)
116.37(8)
97.80(9)
Al-O
C(9)-Al-C(10)
N-Al-C(9)
O-Al-C(9)
Al-N-AlA
Al-N-C(13)
Si-N-C(13)
Al-N-Si
Al-C(9)
Al-C(10)
N-Si
O-C(1)
N-C(13)
Al-AlA
Exp er im en ta l Section
Gen er a l P r oced u r e. All manipulation of air- and/or mois-
ture-sensitive compounds was carried out with use of standard
Schlenk or vacuum-line techniques. Argon was purified by
passing through columns of Ridox oxygen scavenger (R31-3,
Fisher) and Linde 4-Å molecular sieves. Solids were trans-
ferred and stored in an N2-filled Vacuum Atmospheres glove-
box equipped with a HE-493 Dri-Train, a CS-40 Dri-Cold, and
an oxygen analyzer (model 315, Teledyne Analytical Instru-
ments).
Anhydrous toluene, tetrahydrofuran, and diethyl ether were
purchased from Aldrich and transferred to sodium/benzophe-
none ketyl without prior treatment. Pentane were stirred over
concentrated H2SO4, dried over CaH2, and then transferred
to sodium/benzophenone ketyl. Dried deoxygenated solvents
were vacuum-transferred to dry glass vessels equipped with
a J -Young valve and stored under argon. Benzene-d6 was
transferred from purple sodium/benzophenone ketyl. CDCl3
was predried under CaH2 and vacuum-transferred. Cl2SiMe2
and AlMe3 were used as received from Aldrich. 2,6-Dimethyl-
aniline, aniline, and cyclohexylamine were dried under KOH
and distilled. 2,6-Dimethylphenol was purified through vacuum
sublimation.
NMR spectra were recorded on Bruker DPX300 (300 MHz,
1H) spectrometers. Chemical shifts are reported in δ, refer-
enced to residual solvent signals. Elemental analyses were
performed at Pohang University of Science and Technology
(Elementar Vario-EL). High-resolution mass spectral analyses
were preformed at Korea Basic Science Institute (J EOL
SX102). Melting points were measured in sealed glass tubes
and were not corrected.
P r ep a r a tion of 2,6-Me2P h OSiMe2Cl (1). n-BuLi (97.0 mL,
1.32 M in hexane, 128 mmol) was slowly added to sublimed
2,6-dimethylphenol (15.6 g, 128 mmol) dissolved in diethyl
ether (100 mL) at -45 °C. The reaction mixture was warmed
to room temperature and stirred for 2 h. The solution was
cooled again to -45 °C, and Cl2SiMe2 (54.0 mL, 445 mmol)
was slowly added. Immediately white precipitates were formed.
The mixture was warmed to room temperature and stirred
overnight. The solution was filtered, and the filtrate was
evacuated to afford pale yellow oil. Colorless oil 1 (22.1 g,
Al-O-AlA
Al-O-C(1)
130.87(5)
a
Symmetry transformation used to generate equivalent atoms:
A, x, -y, z.
formation of two separate fragments, the aluminum
alkoxide and the aluminum alkylamide, is not on the
reaction pathway, and the chelation leading to the four-
membered metallacycle is important for the facile
cleavage.
In contrast, when 2c reacted with 1 equiv of AlMe3,
the four-coordinate aluminum complex [Me2Si(O-2,6-
Me2Ph)(N-2,6-Me2Ph)]AlMe2 (3c) was immediately ob-
served as a white solid. The proton and carbon NMR
spectra of 3c display the singlets of the AlMe2 moiety
at -0.31 and -5.54 ppm, respectively. Integration of the
proton resonances clearly showed that the 1:1 complex
was formed, and the singlet resonance in the NMR
spectra is in harmony with the resulting symmetric
molecular structure. The stability of the mononuclear
complex 3c against AlMe3 should be associated with the
larger N-substituent, which might inhibit the formation
of the transition state like II.
St r u ct u r es of (Me2Al)2[(µ-O-2,6-Me2P h )(µ-NCy-
SiMe3)] (3a ). The structure of 3a was determined by
X-ray crystallography. The molecular structure is shown
in Figure 1, and selected bond lengths and angles are
summarized in Table 1. 3a is a dinuclear aluminum
species with the two molecular units of Me2AlO(2,6-Me2-
Ph) and Me2AlN(Cy)(SiMe3) being associated with each
other. The molecule has crystallographic m symmetry
with a mirror plane passing through the N, O, C(11),
and C(16) atoms and the 2,6-dimethylphenyl group. The
four-membered Al2NO ring is planar within 0.10 Å.
Each aluminum center is 1.411(2) Å away from the
mirror plane and adopts a distorted tetrahedral geom-
etry with an N-Al-O angle of 85.07(6)°. The geometry
of nitrogen and oxygen atoms is distorted tetrahedral
(11) Robinson, G. H. Coordination Chemistry of Aluminum; VCH:
New York, 1993; Chapter 1.

5716 Organometallics, Vol. 18, No. 26, 1999
Notes
80.4%) was obtained by vacuum distillation (30 mTorr, 40 °C).
1H NMR (CDCl3): δ 7.04 (d, 2H), 6.90 (t, 1H), 2.28 (s, 6H),
0.63 (s, 6H). 13C NMR (CDCl3): δ 153.2, 128.9, 122.1, 121.5,
50.9, 38.9, 26.0, 18.4, -0.71.
P r ep a r a tion of Me2Si(O-2,6-Me2P h )(NHCy) (2a ). Cyclo-
hexylamine (6.50 mL, 56.8 mmol) was slowly added to an ether
(200 mL) solution of compound 1 (6.10 g, 28.4 mmol) at 0 °C.
Immediately, white precipitates were formed, and the mixture
was stirred overnight at room temperature. The solution was
filtered, and a pale yellow oil was obtained by evacuating the
filtrate. Colorless oil 2a (5.6 g, 71%) was isolated by vacuum
distillation (85 °C, 30 mTorr). 1H NMR (C6D6): δ 6.96 (d, 2H),
6.81 (t, 1H), 2.62 (m, 1H), 2.25 (s, 6H), 1.69 (m, 2H), 1.56 (m,
2H), 1.41 (m, NH), 1.14-0.82 (m, 6H), 0.20 (s, 6H). 13C NMR
(C6D6): δ 153.3, 128.8, 128.7, 121.6, 50.7, 38.7, 26.0, 25.9, 18.3,
-0.95. MS (EI, 70 eV): m/z 105 (21), 178 (63), 234 (61), 253
(100), 277 (M+, 13). HRMS (EI, 70 eV): calcd for C16H27NOSi
277.1862, found 277.1848.
temperature. Formation of a white precipitate was observed
in 1 h. The resulting solution was reduced to 5 mL, and a white
solid of 3b (0.90 g, 80% based on the consumed chelate) was
obtained by filtration and washing with pentane. Meanwhile,
addition of AlMe3 (0.74 mL, 7.72 mmol) into the solution of
2b (1.00 g, 3.68 mmol) produced 1.25 g of 3b (yield ) 85%).
1
Melting point: 139 °C. H NMR (C6D6): δ 6.97-6.80 (m, 8H,
P r ep a r a tion of Me2Si(O-2,6-Me2P h )(NHP h ) (2b). 2b was
obtained using compound 1 (6.10 g, 28.4 mmol) and aniline
(5.20 mL, 57.1 mmol) with a similar procedure for 2a . Vacuum
distillation (105 °C, 30 mTorr) of the crude product afforded
aromatic), 2.31 (br s, 6H, benzylic), 0.22 (s, 9H, SiMe3), -0.24
(s, 6H, AlMe), -0.43 (s, 6H, AlMe). 13C NMR (C6D6): δ 148.9,
143.0, 131.6, 130.1, 129.9, 125.0, 124.6, 18.8 (benzylic), 2.46
(SiMe3), -3.00 (AlMe), -5.44 (AlMe). 13C NMR (CDCl3): 149.0,
143.3, 131.8, 130.4, 130.1, 127.9, 125.1, 124.4, 19.1 (benzylic),
2.98 (SiMe3), -3.00 (AlMe), -5.23(AlMe). Anal. Calcd for
1
pure colorless oil (5.2 g, 68%). H NMR (C6D6): δ 7.10 (t, 2H),
6.93 (d, 2H), 6.83-6.73 (m, 4H), 3.46 (br s, NH), 2.19 (s, 6H),
0.17 (s, 6H). 13C NMR (C6D6): δ 152.6, 146.0, 129.5, 129.0,
128.8, 122.2, 119.2, 117.5, 17.7, -1.78. MS (EI, 70 eV): m/z
150 (18), 163 (18), 178 (100), 271 (M+, 57). HRMS (EI, 70 eV):
calcd for C16H21NOSi 271.1385, found 271.1392.
C
21H35NOSiAl2: C, 63.12; H, 8.83; N, 3.51. Found: C, 63.38;
H, 8.72; N, 3.35.
P r ep a r a t ion of [Me2Si(O-2,6-Me2P h )(N-2,6-Me2P h )]-
AlMe2 (3c). AlMe3 (0.97 mL, 10 mmol) was added dropwise
to a pentane (30 mL) solution of 2c (3.0 g, 10 mmol) at room
temperature. After the addition, a white precipitate started
to appear. The mixture was stirred overnight. The volume of
the solution was reduced, and the white precipitate of 3c (3.2
g, 90%) was filtered. Analytically pure colorless crystals could
be isolated from the saturated pentane solution at -20 °C.
P r epar ation of Me2Si(O-2,6-Me2P h )(NH-2,6-Me2P h ) (2c).
n-BuLi (15.2 mL, 1.6 M in hexane, 24.3 mmol) was slowly
added to a THF (20 mL) solution of 2,6-dimethylaniline (3.0
mL, 24.4 mmol) at -40 °C. The resulting yellowish white
suspension was warmed to room temperature and stirred for
1 h. The solution was again cooled to 0 °C, and compound 1
(5.0 g, 23.3 mmol) was added. The mixture was stirred
overnight at room temperature. The solution was condensed
under vacuum and extracted with pentane. The filtrate was
evaporated to afford pale yellow crude oil. Colorless viscous
oil 2c (6.0 g, 82%) was obtained by vacuum distillation (20
mTorr, 115 °C). 1H NMR (CDCl3): δ 7.11 (m, 4H), 6.95 (m,
2H), 3.14 (br s, NH), 2.39 (s, 6H), 2.36 (s, 6H), 0.34 (s, 6H).
13C NMR (CDCl3): δ 153.0, 142.6, 132.4, 129.1, 129.0, 128.8,
122.7, 122.1, 20.1, 18.4, -0.32. MS (EI, 70 eV): m/z 121 (79),
163 (26), 178 (100), 196 (20), 299 (M+, 92). HRMS (EI, 70 eV):
calcd for C18H25NOSi 299.1697, found 299.1705.
P r ep a r a tion of (Me2Al)2[(µ-O-2,6-Me2P h )(µ-NCySiMe3)]
(3a ). AlMe3 (1.05 mL, 11.0 mmol) was added dropwise to a
pentane (50 mL) solution of 2a (3.00 g, 10.8 mmol) at room
temperature. The resulting pale yellow solution was stirred
overnight. Formation of white precipitate was observed. White
solid of 3a (1.3 g, 59% based on the consumed chelate) was
obtained by filtration and washing with pentane. Meanwhile,
addition of AlMe3 (0.72 mL, 7.51 mmol) into the solution of
2a (1.00 g, 3.60 mmol) gave 1.10 g of 3a (yield ) 75%).
Analytically pure and X-ray suitable colorless crystals could
be obtained from toluene solution stored at -45 °C. Melting
point: 136 °C. 1H NMR (C6D6): δ 6.86 (d, 2H), 6.82 (t, 1H),
3.50 (m, 1H, cyclohexyl axial d), 2.40 (s, 6H, benzylic), 1.86
(br d, 2H, cyclohexyl equatorial e), 1.55 (br d, 2H, cyclohexyl
equatorial h), 1.45 (m, 3H, cyclohexyl axial f and equatorial
i), 1.20 (m, 2H, cyclohexyl axial g), 1.02 (m, 1H, cyclohexyl axial
j), 0.39 (s, 9H, SiMe3), -0.35 (s, 6H, AlMe), -0.36 (s, 6H, AlMe).
13C NMR (C6D6): δ 148.9 (phenylic, ipso), 130.1 (phenylic,
ortho), 129.9 (phenylic, meta), 124.4 (phenylic, para), 61.6
(NCH), 38.7 (NCHCH2), 27.4 (NCHCH2CH2), 25.8 (NCHCH2-
CH2CH2), 18.7 (benzylic CH3), 7.07 (SiMe3), -4.80 (AlMe),
-5.80 (AlMe). Anal. Calcd for C21H41NOSiAl2: C, 62.18; H,
10.19; N, 3.45. Found: C, 62.16; H, 9.77; N, 3.30.
1
Melting point: 178 °C. H NMR (C6D6): δ 7.17 (d, 2H), 6.95
(t, 1H), 6.78 (s, 3H), 2.55 (s, 6H), 2.27 (s, 6H), 0.09 (s, 6H),
-0.31 (s, 6H). 13C NMR (C6D6): δ 147.3, 143.7, 135.1, 130.4,
130.0, 128.7, 125.6, 122.3, 20.5, 17.9, 3.49, -5.54. Anal. Calcd
for C20H30NOSiAl: C, 67.56; H, 8.51; N, 3.94. Found: C, 67.28;
H, 8.51; N, 3.94.
X-r a y Cr ysta llogr a p h ic Deter m in a tion for 3a . A crystal
sealed in a capillary tube was mounted on a Siemens SMART
diffractometer equipped with a graphite-monochromated Mo
KR (λ ) 0.71073 Å) radiation source and a CCD detector.
Fifteen frames of two-dimensional diffraction images were
collected and processed to deduce a cell parameter and
orientation matrix. Data collection was performed at 293 K.
A total of 1271 frames of two-dimensional diffraction images
were collected, and each of which was measured for 20 s. The
frame data were processed to produce conventional intensity
data by the program SAINT. The intensity data were corrected
for Lorentz and polarization effects. An absorption correction
was also applied based on ψ scans. The structures were solved
by a combination of Patterson and difference Fourier methods
provided by the program package SHELXTL. All the non-
hydrogen atoms were refined anisotropically.
Ack n ow led gm en t. This work is supported by the
Korea Foundation of Science and Engineering. The
authors are grateful to Mr. J ungseok Heo for X-ray
crystallographic analysis.
Su p p or tin g In for m a tion Ava ila ble: Tables S1-S4 list-
ing full experimental details for data collection and refinement,
atomic coordinates, bond distances and bond angles, and
anisotropic parameters. This material is available free of
charge via the Internet at http://pubs.acs.org.
P r ep a r a tion of (Me2Al)2[(µ-O-2,6-Me2P h )(µ-NP h SiMe3)]
(3b). AlMe3 (0.58 mL, 6.0 mmol) was added dropwise to a
pentane (20 mL) solution of 2b (1.52 g, 5.60 mmol) at room
OM990698T