Preparation and pyrolysis of poly(allyl iminoalane-co-ethyl iminoalane)s [HAlN(allyl)]m[HAlNEt]n

Article abstract of DOI:10.1016/j.jorganchem.2006.07.004

Poly(allyl iminoalane-co-ethyl iminoalane)s {[HAlN(allyl)]_m[HAlNEt]_n; Allyl/Et-alanes}, have been prepared by reactions of lithium hydridoaluminate (LiAlH₄) with a mixture of allylamine hydrochloride (CH₂{double bond, long}CHCH₂NH₂ · HCl; allylNH₂ · HCl) and ethylamine hydrochloride (CH₃CH₂NH₂ · HCl; EtNH₂ · HCl) with various allyl/Et ratios. Spectroscopic analyses indicate that Allyl/Et-alane(1/3) (allyl/Et = 1/3) contains octamers possessing Al-H and C-H groups as well as C{double bond, long}C, Al-N, and C-N bonds. The loss of aluminum during pyrolysis of Allyl/Et-alane(1/3) at 1600 °C under an Ar atmosphere is 15%, which is less than the value reported for the pyrolysis of poly(ethyliminoalane) (36%). The suppression can be ascribed to cross-linking reactions involving allyl groups (hydroalumination and polymerization of the allyl groups), judging from infrared (IR) and solid-state nuclear magnetic resonance (NMR) spectroscopy.

Full text of DOI:10.1016/j.jorganchem.2006.07.004

Journal of Organometallic Chemistry 691 (2006) 4289–4296
www.elsevier.com/locate/jorganchem
Preparation and pyrolysis of poly(allyl iminoalane-co-ethyl
iminoalane)s [HAlN(allyl)]m[HAlNEt]n
*
Yusuke Mori, Yasuhiro Kumakura, Yoshiyuki Sugahara
Department of Applied Chemistry, School of Science and Engineering, Waseda University, Ohkubo-3-4-1, Shinjuku-ku, Tokyo 169-8555, Japan
Received 18 February 2006; received in revised form 27 June 2006; accepted 7 July 2006
Available online 14 July 2006
Abstract
Poly(allyl iminoalane-co-ethyl iminoalane)s {[HAlN(allyl)]m[HAlNEt]n; Allyl/Et-alanes}, have been prepared by reactions of lithium
hydridoaluminate (LiAlH4) with a mixture of allylamine hydrochloride (CH2@CHCH2NH2 Æ HCl; allylNH2 Æ HCl) and ethylamine
hydrochloride (CH3CH2NH2 Æ HCl; EtNH2 Æ HCl) with various allyl/Et ratios. Spectroscopic analyses indicate that Allyl/Et-alane(1/3)
(allyl/Et = 1/3) contains octamers possessing Al–H and C–H groups as well as C@C, Al–N, and C–N bonds. The loss of aluminum dur-
ing pyrolysis of Allyl/Et-alane(1/3) at 1600 ꢀC under an Ar atmosphere is 15%, which is less than the value reported for the pyrolysis of
poly(ethyliminoalane) (36%). The suppression can be ascribed to cross-linking reactions involving allyl groups (hydroalumination and
polymerization of the allyl groups), judging from infrared (IR) and solid-state nuclear magnetic resonance (NMR) spectroscopy.
ꢁ 2006 Elsevier B.V. All rights reserved.
Keywords: Precursor; Poly(allyl iminoalane-co-ethyl iminoalane)s; Pyrolysis; Hydroalumination; Aluminum nitride
1. Introduction
In order to prepare soluble precursors with relatively
high ceramic yields, oligomers possessing reactive groups
can be employed. Yive et al. reported that the cross-linking
reactions (e.g. hydrosilylation) during pyrolysis of soluble
oligovinylsilazane [Si(CH2@CH)(H)NH]n led to a higher
ceramic yield and a even lower loss of silicon (0.5%) in
comparison with that for the pyrolysis of soluble oligo-
methylsilazane [SiMe(H)NH]n (46%) [6]. If the appropriate
reactive groups (for example, Si–H, B–H, N–H and Al–H
groups, or unsaturated organic groups) are introduced into
precursors, therefore, cross-linking reactions before the
volatilization can occur facilely, leading to exhibiting rela-
tively high ceramic yields and suppressing the loss of the
elemental components (in particular, metals) introduced
into precursors drastically.
Poly(alkyliminoalane)s [(HAlNR)n; PIAs] are well-
known cage-type oligomers possessing an Al–N backbone,
and their preparation procedures, structural characteriza-
tion, various properties (such as reactivity and thermody-
namic properties, etc.) and applications have been
extensively investigated [7–9]. The pyrolytic conversion
of PIAs into AlN has scarcely been reported, though
Pyrolytic conversion of precursors, which are typically
organometallic and/or inorganic polymers possessing
metal–nitrogen and/or metal–carbon backbones, is an
established route to obtaining non-oxide ceramics and
ceramics-based composites [1–5]. Desirable precursors
should be fusible at relatively low temperatures or soluble
in common organic solvents, since these properties are nec-
essary for fabrications into ceramic materials with desirable
shapes, including coatings and fibers. Precursors, more-
over, should exhibit high ceramic yields in order to reduce
shrinkage and cracks caused by gaseous species, which are
generally hydrocarbons (or even gases containing metals),
evolved during pyrolysis [1,3,5]. Since precursors with high
ceramic yields generally possess highly cross-linked struc-
tures, however, the solubility is very low, which is a large
drawback for the desired applications.
*
Corresponding author. Tel./fax: +83 5286 3204.
E-mail address: ys6546@waseda.jp (Y. Sugahara).
0022-328X/$ - see front matter ꢁ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.07.004

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Y. Mori et al. / Journal of Organometallic Chemistry 691 (2006) 4289–4296
numerous AlN precursors have been developed for past
few decades [10–12]. We have prepared AlN from cage-
type PIAs [13–16] and revealed the pyrolytic behavior at
lower temperatures [17,18]. Although PIAs possess reactive
Al–H groups, however, the loss of aluminum during pyro-
lysis of PIAs was relatively high because of the volatiliza-
tion of low molecular mass species, including PIAs, at
relatively low temperatures. The loss of aluminum during
pyrolysis at 1600 ꢀC was 36% [poly(ethyliminoalane),
(HAlNEt)n, n is mainly 8] and 55% [poly(isopropyliminoa-
lane), (HAlNiPr)n, n is mainly 6] [14,15]. It is therefore
expected that the loss of aluminum can be suppressed by
designing the cage-type compounds via introduction of
additional reactive groups.
Here we report the preparation of poly(allyl iminoalane-
co-ethyl iminioalane)s {[HAlN(allyl)]m[HAlNEt]n; Allyl/
Et-alanes}, from lithium hydridoaluminate (LiAlH4), allyl-
amine hydrochloride (CH2@CHCH2NH2 Æ HCl; allylNH2 Æ
HCl) and ethylamine hydrochloride (CH3CH2NH2 Æ HCl;
EtNH2 Æ HCl) with various allyl/Et ratios. The residues
pyrolyzed at low temperatures (200–400 ꢀC) are spectro-
scopically characterized to explore the pyrolytic behavior.
We focus in particular on the reactions of the allyl groups
(CH2@CH–CH2–) in the precursors at low temperatures,
leading to suppressing the loss of aluminum. The charac-
terization results of the residue pyrolyzed at 1600 ꢀC are
also presented.
Fig. 1. IR spectra of: (A) Et-alane, (B) Allyl/Et-alane(1/7), (C) Allyl/Et-
alane(1/3), (D) Allyl/Et-alane(1/1) and (E) Allyl-alane. The bands marked
by asterisks are due to hexachloro-1,3-butadiene (hcb).
2. Results and discussion
Table 1
The assignments of the adsorption bands in the IR spectra
2.1. Spectroscopic characterizations of poly(allyl
iminoalane-co-ethyl iminoalane)s
Wavenumber/cmꢀ1
Assignment
–
3078
mCH @CH
2
3000–2760
1860–1820
1635
1470–1450
1420
mCH
mAlH
mC@C
The IR spectra of the Allyl/Et-alanes, poly(ethyliminoa-
lane) [(HAlNEt)n, Et-alane] and poly(allyliminoalane)
{[HAlN(allyl)]n, Allyl-alane} are shown in Fig. 1. (The
assignments are listed in Table 1.) The IR spectra of the
dCH ; dCH
2
3
–
dCH @CH
2
Allyl/Et-alanes exhibit adsorption bands at 3078 cmꢀ1
1378
dCH
3
1140–1080
ꢁ720
mCN
mAlN
–
ðmCH @CH
Þ
[19], 3000–2760 cmꢀ1 (mCH
)
[19], 1860–
2
1820 cmꢀ1 (mAlH
) ) [19], 1140–
[7], 1635 cmꢀ1 (mC@C
1080 cmꢀ1 (mCN) [19] and ꢁ720 cmꢀ1 (mAlN) [20,21]. The
appearance of these bands suggests the presence of Al–H
and C–H groups as well as C@C, Al–N, and C–N bonds
in the Allyl/Et-alanes. Since the IR spectra of all the
Allyl/Et-alanes show similar profiles, only spectroscopic
characterization of Allyl/Et-alane(1/3) (allyl/Et = 1/3) is
represented below.
52–48 (CH2@CHCH2–N) ppm. The resonances of the ethyl
groups are also observed at 45–38 (CH3CH2–N) and 23–18
(CH3CH2–N) ppm. The chemical shifts of the ethyl groups
in Allyl/Et-alane(1/3) are similar to those in Et-alane.
Allyl/Et-alane(1/3) was also characterized by mass spec-
troscopy and cryoscopy. In the mass spectrum of the pre-
cursor (as shown in Fig. 4), the ionization peaks at m/e
567, 579, 591 and 603 are assignable to [(HAlNEt)8-1]+,
{[HAlN(allyl)][HAlNEt]7-1}+, {[HAlN(allyl)]2[HAlNEt]6-
1}+ and {[HAlN(allyl)]3[HAlNEt]5-1}+, respectively (Table
3). The average relative molecular mass of the precursor
determined by cryoscopy is 7.6 · 102. Based on these obser-
vations, we conclude that Allyl/Et-alane(1/3) contains
mainly [HAlN(allyl)]m[HAlNEt]n (m + n = 8) oligomers,
suggesting that essentially no cross-linking reactions, such
The 27Al NMR spectra of Allyl/Et-alane(1/3) and Et-
alane are shown in Fig. 2. The 27Al NMR spectrum of
Allyl/Et-alane(1/3), as well as that of Et-alane, exhibits
one broad signal at 135 ppm, which is assignable to the
HAlN3 environments [7,14,15,17].
The 13C NMR spectra of Allyl/Et-alane(1/3) and Et-
alane are shown in Fig. 3. (The assignments are listed in
Table 2.) In the 13C NMR spectrum of Allyl/Et-alane(1/
3), the resonances of the allyl group are observed at 141–
135 (CH2@CHCH2–N), 120–114 (CH2@CHCH2–N) and

Y. Mori et al. / Journal of Organometallic Chemistry 691 (2006) 4289–4296
4291
Fig. 4. Mass spectrum of Allyl/Et-alane(1/3).
Table 3
Mass spectrum of Allyl/Et-alane(1/3) under electron ionization
m/e
Assignment
[HAlN(allyl)]m[HAlNEt]n
567
579
591
603
[(HAlNEt)8-1]+
m = 0, n = 8
m = 1, n = 7
m = 2, n = 6
m = 3, n = 5
{[HAlN(allyl)][HAlNEt]7-1}+
{[HAlN(allyl)]2[HAlNEt]6-1}+
{[HAlN(allyl)]3[HAlNEt]5-1}+
Fig. 2. 27Al NMR spectra of (A) Et-alane and (B) Allyl/Et-alane(1/3).
as hydroalumination and/or polymerization of the allyl
groups, occur during the preparation of the precursor.
No evidence for the occurrence of the cross-linking reac-
tions is provided by the NMR results in accordance with
the consideration of the molecular mass.
2.2. Conversion of precursors into ceramic residues
The TG curves of the Allyl/Et-alanes, Allyl-alane, and
Et-alane are shown in Fig. 5. The ceramic yields of Allyl/
Et-alane(1/3), Allyl/Et-alane(1/7) (allyl/Et = 1/7), Allyl/Et-
alane(1/1) (allyl/Et = 1/1), Allyl-alane and Et-alane up to
Fig. 3. 13C NMR spectra of (A) Et-alane and (B) Allyl/Et-alane(1/3).
Table 2
The assignments of the chemical shifts in the 13C NMR spectra
Chemical shift/ppm
Assignment
141–135
120–114
52–48
CH2@CHCH2–N
CH2@CHCH2–N
CH2@CHCH2–N
CH3CH2–N
45–38
Fig. 5. TG curves of: (A) Allyl/Et-alane(1/3), (B) Allyl/Et-alane(1/7), (C)
Allyl/Et-alane(1/1), (D) Allyl-alane and (E) Et-alane under Ar flow.
23–18
CH3CH2–N

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Y. Mori et al. / Journal of Organometallic Chemistry 691 (2006) 4289–4296
900 ꢀC are 73.1, 70.8, 68.6, 65.8 and 61.6 mass%, respec-
tively. Thus, the ceramic yield of Allyl/Et-alane(1/3) is the
highest among the precursors containing the allyl groups.
Both Allyl/Et-alane(1/3) and Et-alane (M = 568) without
the allyl groups [15] contain mainly octamers, but the cera-
mic yield of Allyl/Et-alane(1/3) is slightly higher than that
of Et-alane. Since the mass loss cannot be observed above
500 ꢀC, it is therefore assumed that the cross-linking reac-
tions involving the allyl groups occur at low temperatures
(below 500 ꢀC).
Table 4 shows the compositions of Allyl/Et-alane(1/3) and
the residue pyrolyzed at 1600 ꢀC. The loss of aluminum dur-
ing pyrolysis can be calculated by the following equation,
based on the aluminum in the ceramic residue (CAl), the alu-
minum in the precursor (PAl) and the ceramic yield (Y).
LossðAlÞ ½%ꢂ ¼ ½ðPAl ꢀ Y ꢃ CAlÞ=PAlꢂ ꢃ 100
The loss of aluminum [Loss(Al)] during pyrolysis of
Allyl/Et-alane(1/3) is 15%, which is much smaller than that
for the pyrolysis of Et-alane (36%) [15]. This observation
suggests that the evolution of aluminum-containing species
can be suppressed by the introduction of the allyl groups
into the precursor.
Fig. 6. IR spectra of d-Allyl/Et-alane(1/3) pyrolyzed at 200 ꢀC.
2.3. Pyrolytic behavior of poly(allyl iminoalane-co-ethyl
iminoalane)s at low temperatures
shoulder at 130 ppm and the signal at 111 ppm are attrib-
utable to the HAlN3 [7] and AlN4 environments [25],
respectively. The signals at 32 and 0 ppm is assignable to
the six-coordinated aluminum environment, because the
resonances of the AlN6 environment appear in the range
between 6 and 45 ppm [26]. The signal at 70 ppm is tenta-
tively assigned to the five-coordinated aluminum environ-
ment, because the resonances of the AlN5 environment
appear at ꢁ83 ppm [26].
The IR spectra (not shown) of the residues pyrolyzed at
400 ꢀC reveal that the mCH @CH band at 3078 cmꢀ1 has
2
vanished. Fig. 6 shows the IR spectrum of deuterated
Allyl/Et-alane(1/3) [DAlN(allyl)]m[DAlNEt]n (allyl/Et =
1/3) [hereafter abbreviated as d-Allyl/Et-alane(1/3)] pyro-
lyzed at 200 ꢀC. The IR spectrum exhibits a mCD band at
2264 cmꢀ1 [19].
Fig. 7 shows the solid-state 13C NMR spectra of the
pyrolyzed residues. (The assignments are listed in Table
5.) Two signals at 137 and 115 ppm, which can be assigned
to the allyl groups, decrease gradually as the temperature
increases in comparison with the signals assignable to the
ethyl groups at 40 and 20 ppm. In addition, the solid-state
13C NMR spectra exhibit two new signals. One signal at
10 ppm is assignable to the CH3C(sp3) environment
[22,23]. The other signal at 26 ppm is attributable to the
–CH2C(sp3) and/or @CHC(sp3) environments [22–24].
Fig. 8 shows the solid-state 27Al NMR spectra of the
pyrolyzed residues. (The assignments are listed in Table
6.) The spectra at 200–400 ꢀC exhibit five signals at 111,
95, 70, 32 and 0 ppm and one shoulder at 130 ppm. The
As for the assignment of the shoulder at 95 ppm, the
broad signal of the CAlN3 environment in (EtAlNH)n
obtained by pyrolysis of (Et2AlNH2)3 at 200 ꢀC was
observed at 100 ppm for the measurement at 14 T [27]. It
is generally known that a smaller quadrupolar shift is
observed by applying a higher magnetic field for 27Al
NMR [28]. Actually, the chemical shift of the AlN4 envi-
ronment is observed at 114–117 ppm (at 14 T) [29],
110 ppm (at 9.4 T) [25] and 103 ppm (at 4.7 T) [30]. For
the signal assigned to the asymmetric OAlN3 environment,
the quadrupolar shift (106 ppm at 14 T [29], 93 3 ppm at
9.4 T [31]) is also observed. Thus, the shoulder at 95 ppm
measured at 9.4 T seems to be attributable to the CAlN3
environment.
Table 4
The compositions of Allyl/Et-alane(1/3) and the residue pyrolyzed at 1600 ꢀC
Sample
Elemental analysis/mass%
Compositional formula
Al
N
C
H
O
Total
Allyl/Et-alane(1/3)
Calculated [Allyl/Et-alane(1/3)]
36.0
36.4
18.6
18.9
36.0
36.5
7.7
8.2
–
–
98.3
100.0
AlNC2.25H5.74
AlNC2.25H6.00
1600 ꢀC
49.2
22.8
22.7
–
4.5
99.2
AlN0.89C1.04O0.15

Y. Mori et al. / Journal of Organometallic Chemistry 691 (2006) 4289–4296
4293
Fig. 7. Solid-state 13C NMR spectra of Allyl/Et-alane(1/3) pyrolyzed at:
(A) 200 ꢀC, (B) 300 ꢀC and (C) 400 ꢀC. Spinning side bands are marked
with asterisks.
Fig. 8. Solid-state 27Al NMR spectra of Allyl/Et-alane(1/3) pyrolyzed at:
(A) 200 ꢀC, (B) 300 ꢀC, (C) 400 ꢀC and (D) 1600 ꢀC. Spinning side bands
are marked with asterisks.
Table 5
The assignments of the chemical shifts in the solid-state 13C NMR spectra
Table 6
Chemical shift/ppm
Assignment
The assignments of the chemical shifts in the solid-state 27Al NMR spectra
137
115
46
40
26
CH2@CHCH2–N
CH2@CHCH2–N
CH2@CHCH2–N
CH3CH2–N
Chemical shift/ppm
Assignment
130
HAlN3
111–110
95
AlN4
CAlN3
–CH2C(sp3), @CHC(sp3)
CH3CH2–N
20
10
70
32, 0
AlN5 (tentative)
AlN6
CH3C(sp3)
In the temperature range from 200 to 400 ꢀC, as indi-
cated by the resonances and the bands assignable to the
allyl groups in the results of the IR and solid-state 13C
NMR spectra, most of the allyl groups in Allyl/Et-
alane(1/3) are reacted. Thus, it is expected that the cross-
linking reactions involving the allyl groups, such as
hydroalumination and/or polymerization of the allyl
groups, could occur.
Hydroalumination forms new Al–C bonds from Al–H
groups and C@C bond. If hydroalumination, which is a
reaction between Al–D groups and C@C bond, occurs dur-
ing pyrolysis of d-Allyl/Et-alane(1/3), the formation of new
C–D bonds is expected. Correspondingly, in the IR spec-
trum of the residue pyrolyzed of d-Allyl/Et-alane(1/3), the
mCD band at 2264 cmꢀ1 is observed. In the solid-state
27Al NMR spectra of the pyrolyzed residues of Allyl/Et-
alane(1/3), the shoulder assigned to the CAlN3 environ-
ment is observed, indicating that the residues possess new
Al–C bonds. In the solid-state 13C NMR spectra, more-
over, a signal assignable to the CH3C(sp3) environment
[22,23] is observed at 10 ppm. The 13C NMR spectra also
exhibit the signal at 26 ppm, which is attributed to the –
CH2C(sp3) and/or @CHC(sp3) environments [22–24]. The
formation of the CH3C(sp3) (10 ppm) and @CHC(sp3)
environments (26 ppm) is due to the a-addition on hydroa-
lumination, while that of the –CH2C(sp3) environment
(26 ppm) is due to the b-addition on hydroalumination.
Based on these observations, it can be concluded that
hydroalumination occurs to form new Al–C bonds during
pyrolysis (Scheme 1a).
As far as polymerization of the allyl groups is con-
cerned, this forms –CH(R)–CH2–CH(R)–CH2– [from
head–tail (or tail–head) polymerization] and/or –CH2–
CH(R)–CH(R)–CH2– [from head–head (or tail–tail) poly-
merization] linkages (R; CH2–N„). In the solid-state 13C
NMR spectra of the pyrolyzed residues, a signal centered
at 26 ppm, which is assignable to the –CH2C(sp3) and/or
@CHC(sp3) environments [22–24], is observed. Although

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Y. Mori et al. / Journal of Organometallic Chemistry 691 (2006) 4289–4296
Fig. 9. XRD pattern of Allyl/Et-alane(1/3) pyrolyzed at 1600 ꢀC.
Scheme 1. Possible reactions during pyrolysis.
these environments can be formed via hydroalumination
(as described above), they can also be obtained via poly-
merization of the allyl groups. We consequently could
not exclude the possible polymerization of the allyl groups
during pyrolysis (Scheme 1b).
The results of IR and solid-state NMR suggest that the
allyl groups lead to the occurrence of the cross-linking
reactions, involving hydroalumination and possibly poly-
merization of the allyl groups, during pyrolysis. It is conse-
quently reasonable to assume that the cross-linking
reactions make a significant contribution to the suppres-
sion of the loss of aluminum.
The Al–C bonds formed by hydroalumination and the
C–C bonds formed by polymerization of the allyl groups
should link the oligomers {[HAlN(allyl)]m[HAlNEt]n,
(m + n = 8)}. If these bonds are cleaved at the tempera-
tures for the volatilization of low molecular mass species,
such as the oligomers {the volatilization generally occur
below ꢁ300 ꢀC in the case of the pyrolysis of Et-alane
and poly(isopropyliminoalane) [(HAlNiPr)n]}, the volatili-
zation of the oligomers should occur easily and, conse-
quently, a considerable portion of aluminum in the
precursors should be lost. It is therefore speculated that
one possible reason for the suppression of the loss of alumi-
num is that the formed Al–C (and possibly C–C bonds) can
survive at the temperatures for the volatilization of low
molecular mass species at least partly.
Fig. 10. Raman spectrum of Allyl/Et-alane(1/3) pyrolyzed at 1600 ꢀC.
characterization of the various carbon phases [33–39]. The
Raman spectrum of the residue exhibits two bands at 1337
and 1595 cmꢀ1, which are consistent with the Raman spec-
trum of amorphous carbon [40,41]. Based on these results,
it is suggested that the pyrolyzed residue contains crystal-
line AlN and amorphous carbon.
The pyrolysis of precursors possessing both an Al–N
backbone and Al–C bonds under an inert atmosphere led
to the formation of AlN without any Al–C bonds [and alu-
minum carbide (Al4C3)] in the residues [12]. In this study,
the result of the solid-state 27Al NMR spectrum indicates
that no Al–C bonds are present in the residue pyrolyzed
at 1600 ꢀC, indicating that the Al–C bonds formed by
hydroalumination in the intermediates (i.e., the residue
pyrolyzed at low temperatures) are cleaved during pyroly-
sis at high temperatures.
2.4. Characterizations of the residue pyrolyzed at 1600 ꢀC
The residue of Allyl/Et-alane(1/3) pyrolyzed at 1600 ꢀC
was characterized by solid-state 27Al NMR, Raman, XRD
and elemental analysis. As shown in Fig. 8, the solid-state
27Al NMR spectrum of the residue exhibits one signal at
110 ppm, which can be assigned to the AlN4 environment
[25]. Fig. 9 shows the XRD pattern of the residue. The
XRD pattern is consistent with that of crystalline AlN [32].
The residue was also analyzed with Raman spectroscopy
(Fig. 10), which is one of the most sensitive methods for the
The ceramic yield of Allyl/Et-alane(1/3) up to 1600 ꢀC is
62 mass%, which exceeds that of Et-alane (50 mass%) [15].
As shown in Table 4, a relatively high amount of carbon is
present in the residue of Allyl/Et-alane(1/3) (22.7 mass%).

Y. Mori et al. / Journal of Organometallic Chemistry 691 (2006) 4289–4296
4295
(The carbon in the residue of Et-alane is 17.1 mass% [15].)
Based on these observations, it is assumed that the increase
in the ceramic yield can be ascribed to both the suppression
of the loss of aluminum and the increase in the carbon
yield.
sphere (purity: >99.999%) and pyrolyzed at 200, 300 and
400 ꢀC with no holding time. The heating and cooling rate
was 5 ꢀC/min. For the pyrolysis at 1600 ꢀC, Allyl/Et-
alane(1/3) (1.2 g) was placed on a BN boat in an alumina
tube under an argon atmosphere. The heating rate was
10 ꢀC/min from room temperature to 200 ꢀC and 5 ꢀC/
min from 200 to 1600 ꢀC. The temperature was maintained
at 1600 ꢀC for 2 h, and the pyrolyzed residue was then
cooled to room temperature at 5 ꢀC/min (yield: 62 mass%).
3. Experimental
All the manipulations were performed under a protec-
tive nitrogen atmosphere (purity: >99.9995%) using the
standard Schlenk technique [42] or a nitrogen-filled glove
box. Toluene (Kanto Chemical) was distilled over sodium
and benzophenone under a nitrogen atmosphere.
3.3. Characterizations of poly(allyl iminoalane-co-ethyl
iminoalane)s and the pyrolyzed residues
The Allyl/Et-alanes were characterized by infrared (IR)
spectroscopy (JASCO, FT/IR-460), nuclear magnetic reso-
nance (NMR) spectroscopy (JEOL, JNM-Lambda 500)
and mass (MS) spectroscopy (JEOL, JMS-AUTOMASS).
The IR spectra of the precursors were recorded using the
hexachloro-1,3-butadiene (C4Cl6; hcb) technique. The 13C
NMR (125.65 MHz) spectra of the precursors were
recorded as a benzene-d6 solution using tetramethylsilane
[(CH3)4Si, TMS, 0 ppm] as an external standard. The
27Al NMR (130.20 MHz) spectra of the precursors were
recorded on the same apparatus using [Al(H2O)6]3+
(0 ppm) as an external standard. The mass spectra of the
precursors were obtained by electron ionization in the
range of 10–1000 amu. The ionization energy was 70 eV
and the ionization temperature was 300 ꢀC. The average
masses of the precursors were measured by cryoscopy using
distilled benzene. Thermogravimetry (TG, Perkin–Elmer,
TGA-7) was carried out at a heating rate of 10 ꢀC/min
under flowing argon up to 900 ꢀC.
The residues of Allyl/Et-alane(1/3) pyrolyzed at 200–
400 ꢀC were characterized by IR and solid-state NMR
spectroscopy (JEOL, NM-GSX 400). The IR spectra of
the pyrolyzed residues were recorded using the hcb tech-
nique. The solid-state 13C NMR spectra of the pyrolyzed
residues were obtained at 100.54 MHz (13C) with cross
polarization and magic angle spinning (CP/MAS) tech-
niques. The solid-state 27Al NMR (104.17 MHz) spectra
were recorded with the MAS technique only. Five hundred
scans were accumulated with a pulse delay of 5 s (13C) or
1 s (27Al) and a spinning rate of 7 kHz (13C) or 9 kHz
(27Al). The residues pyrolyzed at 200–400 ꢀC were packed
in sample tubes in a nitrogen-filled glove box and kept
under flowing nitrogen during the measurements.
3.1. Preparation of poly(allyl iminoalane-co-ethyl
iminoalane)s
Poly(allyl iminoalane-co-ethyl iminoalane)s (Allyl/Et-
alanes) were synthesized by reacting lithium hydridoalumi-
nate (Wako Pure Chemical Industries) with allylamine
hydrochloride (Tokyo Kasei Kogyo) and ethylamine
hydrochloride (Tokyo Kasei Kogyo) as described below.
(m+n) LiAlH4 +m allylNH2 ꢄHCl+n EtNH2 ꢄHCl
!½HAlNðallylÞꢂm½HAlNEtꢂn þ ðm þ nÞ LiCl þ 3ðm þ nÞ H2
The d-Allyl/Et-alane(1/3) was also prepared from lithium
deuteridoaluminate (LiAlD4, Acros), allylamine hydro-
chloride and ethylamine hydrochloride.
The preparation of Allyl/Et-alane(1/3) is described
below as a representative procedure, since the other precur-
sors, Allyl/Et-alane(1/7) and Allyl/Et-alane(1/1), were pre-
pared in a similar manner. The reaction was conducted in
a three-necked round-bottomed flask equipped with a gas
inlet tube, a glass stopper and a reflux condenser. After it
was carefully purged with nitrogen, the apparatus was
charged with LiAlH4 (9.259 g, 0.244 mol) and distilled tol-
uene. Allylamine hydrochloride (5.707 g, 0.061 mol) and
ethylamine hydrochloride (14.92 g, 0.183 mol) were then
dried under reduced pressure for 3 h and added to this sus-
pension. The mixed suspension was stirred overnight at
0 ꢀC and then gradually heated to 110 ꢀC. After stirring
at 110 ꢀC for 16 h, the product was filtered to remove insol-
uble components. Toluene was removed from the clear
solution by trap-to-trap distillation under reduced pressure
to yield a white solid.
The residue of Allyl/Et-alane(1/3) pyrolyzed at 1600 ꢀC
was characterized by solid-state 27Al NMR spectroscopy,
Raman spectroscopy (Thermo Electron, Nicolet Almega
XR) and X-ray diffraction (XRD, Rigaku, Rint-2500) anal-
ysis. The solid-state 27Al NMR spectrum of the residue was
recorded on the same instrument employing the conditions
described above. The X-ray diffraction pattern of the resi-
due was obtained using monochromated Cu Ka radiation.
The amounts of aluminum in the precursors and the res-
idue pyrolyzed at 1600 ꢀC were determined using induc-
tively coupled plasma (ICP) emission spectrometry
For comparison with Allyl/Et-alanes, Et-alane and
Allyl-alane were also prepared. Et-alane was synthesized
by the methods reported previously [15]. Allyl-alane was
obtained from LiAlH4 and allylamine hydrochloride in
the similar manner to the preparation of Allyl/Et-alanes.
3.2. Pyrolysis of poly(allyl iminoalane-co-ethyl iminoalane)s
For the pyrolysis at 200–400 ꢀC, Allyl/Et-alane(1/3) was
placed on a BN boat in a quartz tube under an argon atmo-

4296
Y. Mori et al. / Journal of Organometallic Chemistry 691 (2006) 4289–4296
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and hydrogen in the precursor were determined with a Per-
kin–Elmer PE 2400-II instrument. The amounts of carbon,
nitrogen and oxygen in the residue pyrolyzed at 1600 ꢀC
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Poly(allyl iminoalane-co-ethyl iminoalane)s have been
prepared through reactions between LiAlH4, ally-
lNH2 Æ HCl and EtNH2 Æ HCl with the allyl/Et ratios. All
the Allyl/Et-alanes possess Al–H and C–H groups as well
as C@C, Al–N, and C–N bonds, as revealed by the IR
spectra. Spectroscopic analyses and cryoscopy indicate that
Allyl/Et-alane(1/3) comprises oligomers, mainly the octa-
mers [HAlN(allyl)]m[HAlNEt]n (m = 0–3, n = 8 ꢀ m). Dur-
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aluminum (15%) can be suppressed in comparison with
that for the pyrolysis of Et-alane (36%). The suppression
can be ascribed to hydroalumination and possibly poly-
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results suggest that the introduction of the allyl groups into
oligomeric cage-type polyiminoalane is effective in sup-
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