Reactivity of Me3M (M = A1, Ga, In) with benzylamine to form the dimers, [Me2MN(H)CH2Ph]2, and the hexamers, [MeA1NCH2Ph]6 and [MeGaNCH2Ph]6: Molecular structures of t

Article abstract of DOI:10.1016/S0022-328X(02)01125-7

1:1 Equimolar mixtures of Me₃Al, Me₃Ga, or Me₃In and benzylamine, when heated to 90-120 °C in toluene solution, undergo methane elimination to yield the respective dimers, [Me₂MN(H)CH₂Ph]₂,

Full text of DOI:10.1016/S0022-328X(02)01125-7

Journal of Organometallic Chemistry 649 (2002) 78–85
www.elsevier.com/locate/jorganchem
Reactivity of Me3M (M=Al, Ga, In) with benzylamine to form
the dimers, [Me2MN(H)CH2Ph]2, and the hexamers,
[MeAlNCH2Ph]6 and [MeGaNCH2Ph]6: molecular structures of
trans-[Me2MN(H)CH2Ph]2 and [MeAlNCH2Ph]6
Eric K. Styron a, Charles H. Lake b, David H. Powell c, Larry K. Krannich a,*,
Charles L. Watkins a
a Department of Chemistry, Uni6ersity of Alabama at Birmingham, Birmingham, AL 35294-1240, USA
b Department of Chemistry, Indiana Uni6ersity of Pennsyl6ania, Indiana, PA 15705, USA
c Department of Chemistry, Uni6ersity of Florida, Gaines6ille, FL 32611, USA
Received 20 August 2001; received in revised form 27 November 2001; accepted 27 November 2001
Abstract
1:1 Equimolar mixtures of Me3Al, Me3Ga, or Me3In and benzylamine, when heated to 90–120 °C in toluene solution, undergo
methane elimination to yield the respective dimers, [Me2MN(H)CH2Ph]2, where M=Al, Ga, or In. These dimers exist as 1:1
mixtures of cis and trans isomers in toluene-d8 solution, over the temperature range 30–90 °C, consistent with the results of
Beachley [1] for the aluminum derivative. However, single-crystal X-ray data indicate the dimers each crystallize in the trans form.
The structure of each dimer exhibits a center of symmetry and each M2N2 core has a slightly distorted square planar geometry.
The 1H- and 13C-NMR chemical shift assignments were made for the cis and trans isomers of the three compounds using a
combination of 1D- and 2D-NMR techniques. Thermolysis of the 1:1 mixtures at higher temperatures (120–180 °C) generates the
more condensed hexameric species, [MeAlNCH2Ph]6 and [MeGaNCH2Ph]6. [MeAlNCH2Ph]6 crystallizes in a rhombohedral
structure where the AlꢀN cage consists of two six-membered (AlN)3 rings linked together by six transverse AlꢀN bonds. The
results of these thermolyses involving benzylamine are compared with the results of analogous reactions employing dibenzylamine,
where an orthometalated product, [MeMN(CH2Ph)-m-(CH2C6H4)]2, (M=Al, Ga), is obtained. © 2002 Elsevier Science B.V. All
rights reserved.
Keywords: Trimethylaluminum; Trimethylgallium; Trimethylindium; Thermolysis; Benzylamine; Dibenzylamine
dimers, [Me2AlR%]2, via methane elimination [14]. Simi-
lar reactions with Me3Ga lead to the synthesis and
1. Introduction
characterization of ten aminogallanes [8]. However,
The chemical reactivity of organoaluminum, -gal-
when the secondary amines contain the more sterically
lium, and -indium compounds toward amines has been
demanding groups R%=NiPr2, NsBu2, and N(CH2Ph)2,
investigated extensively over the past sixty years [1–13].
the corresponding aminogallanes could not be synthe-
Our research group has reported the synthesis and
sized by thermolysis, but were obtained by the reaction
characterization of four series of R3M·secondary amine
of Me2GaCl with the appropriate lithium amide. Care-
adducts (M=Al, Ga, In; R=Me, Et) [14–16] and
three series of aminoalane and aminogallane dimers
[8,14,16]. Thermolysis of 1:1 mixtures of Me3Al with
each of thirteen secondary amines, R%H, proceeds
ful monitoring of the thermolysis of a 1:1 Me3Ga/
1
HN(CH2Ph)2 mixture at 120 °C by H-NMR indicates
that partial conversion of the initial product
[Me2GaN(CH2Ph)]2 to a more condensed GaꢀN species
occurs before adduct consumption is complete. Subse-
quent thermolysis of the Me3Ga/HN(CH2Ph)2 mixture
at 150 °C yields the orthometalated dimer
smoothly to yield the corresponding aminoalane
* Corresponding author. Fax: +1-205-943-2543.
E-mail address: krannich@uab.edu (L.K. Krannich).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(02)01125-7

E.K. Styron et al. / Journal of Organometallic Chemistry 649 (2002) 78–85
79
[Me2GaN(CH2Ph)-m-(CH2C6H4)]2 [17]. Thermolysis of
mixtures of Me3Al with diphenylamine and of Me3Al
with dibenzylamine have also been reported to produce
Al2N2-containing orthometalated dimers [18,19]. Al-
though [Me2InNMe2]2 was synthesized initially by ther-
molysis of Me3In with HNMe2 [2c], other aminoindane
dimers, with more sterically demanding secondary
amine functions, have been synthesized primarily by
other methods [5]. Several attempts at the preparation
of [Me2InN(CH2Ph)]2 in our laboratory by thermolysis
of Me3In/HN(CH2Ph)2 mixtures led to poor product
yield. However, thermolysis of mixtures of Me3M
(M=Al, Ga, In) with the sterically hindered primary
amine 2-aminobiphenyl, NH2Bp, gives quantitative
yields of the respective dimers, [Me2MN(H)Bp]2 [20,21].
Because the synthesis of [Me2AlN(H)CH2Ph]2 results
from the thermolysis of a mixture of Me3Al and
H2NCH2Ph [1], we wanted to determine whether the
corresponding gallium- and indium-containing dimers
could be synthesized by thermolysis using benzylamine
instead of dibenzylamine. Also, a comparison of the
structural and spectroscopic properties for the
[Me2AlN(H)CH2Ph]2 (1), [Me2GaN(H)CH2Ph]2 (2),
and [Me2InN(H)CH2Ph]2 (3) in excellent yields. The
synthesis data for 1 are in agreement with those of
Beachley [1]. The dimeric nature of 1, 2, and 3 has been
confirmed by NMR, mass spectral, and single crystal
X-ray data. In comparison, the corresponding thermol-
ysis reactions of Me3M with dibenzylamine, where there
is the substitution of a second benzyl group for the
amine hydrogen, led to an acceptable yield of isolated
dimer product for [Me2AlN(CH2Ph)2]2 only [8,14,22].
1
The H- and 13C-NMR spectra for the three dimers
each suggest the presence of both cis and trans isomers
with respect to the four-membered M2N2 ring in solu-
tion. For example, the RT-1H-NMR methyl group
resonance for each dimer consists of three singlets in a
1:2:1 ratio. The two resonances of equal intensity are
assigned to the two non-equivalent methyl groups on
the two sides of the M2N2 ring in the cis isomer and the
third methyl resonance arises from the two symmetry
1
equivalent methyl groups in the trans isomer. The H-
NMR spectral assignments for the individual cis and
trans isomers were made from the 1D- and 2D-H,H-
1
[Me2MN(CH2Ph)2]2
series,
(M=Al,
Ga,
In)
COSY- and H,H-NOESY-NMR spectra. The two H-
[8,14,19,22], with those of the [Me2MN(H)CH2Ph]2 se-
ries could be relevant in terms of understanding the
steric requirements of the benzyl group.
NMR cis isomer methyl resonances can be separated by
H,H-NOESY experiments into those on the NH side of
the M2N2 ring and to those on the NCH2Ph side of the
ring. The cis methyl resonances for 1–3 which show
NOESY crosspeaks to the amine NH group occur at
slightly higher magnetic fields. Each of the three dimers
exists as a 1:1 mixture of cis–trans geometrical isomers
from 30–90° in toluene-d8 solution. These unusual 1:1
non-temperature dependent isomer ratios suggest that
the dimer complexes are not sterically hindered in terms
of the benzyl group and that the benzyl group only
minimally affects transition state energies and entropies
Thermolysis of mixtures of Me3M (M=Al, Ga, In)
with a variety of primary amines (H2NR¦) yields ini-
tially the species [Me2MN(H)R¦]n (n=2, 3) via meth-
ane elimination. Thermolysis at higher temperatures
may result in additional methane elimination with the
formation of more condensed species such as
[MeMNR¦]n (n=3, 4, 6–8) [3,4,6,7,10–12,19,23–
26,28–32] or alternately, cyclometalated dimers
[7,11,20,27,28]. The results of these studies suggest that
the nature and the degree of aggregation of the product
obtained are dependent on the steric nature of the alkyl
or aromatic group attached to the amine nitrogen and
the metal present. Therefore, we investigated the ther-
molysis of the three Me3M/benzylamine systems at
temperatures above those required for dimer formation
to determine whether a more condensed species,
[MeMNCH2Ph]n, or possibly an orthometalated dimer,
as in the reactions of Me3Al and Me3Ga with dibenzy-
lamine, would be obtained.
1
for isomer interconversion [1,12,13,31b,34,35]. The H-
and 13C-NMR chemical shifts of the methyl groups in
1–3 are dependent on the metal present (higher to
1
lower magnetic field: H, Al\Ga\In; 13C, Al\In\
Ga), consistent with our previous observations on
Me3M·secondary amine adducts [15] and the
[Me2MN(CH2Ph)2]2 series [8,14,22]. The 13C-NMR
chemical shift assignments were made from the 1H-
NMR assignments; 1D- and DEPT-NMR experiments;
and the 2D-C,H-COSY- and H,C-HMBC-NMR exper-
iments. The 13C-NMR cis isomer methyl resonance
which arises from the methyl group on the same side of
the ring as the amine hydrogen occurs at slightly lower
2. Results and discussion
1
magnetic fields, in contrast to the respective H-NMR
2.1. Synthesis and characterization of
[Me2AlN(H)CH2Ph]2 (1), [Me2GaN(H)CH2Ph]2 (2),
and [Me2InN(H)CH2Ph]2 (3)
resonances. Slight differences in the ipso and ortho
aromatic 13C-NMR resonances for the cis and trans
isomers allowed the assignment of their individual 13C-
NMR chemical shifts from H,C-HMBC-NMR experi-
ment correlations with the methylene protons of the
Thermolysis of 1:1 mol ratio mixtures of Me3M,
M=Al, Ga, and In, and benyzlamine in toluene pro-
ceed smoothly to produce the respective dimers
1
benzyl group. The H- and 13C-NMR chemical shifts
for the methyl and methylene groups in 1–3 are consis-

80
E.K. Styron et al. / Journal of Organometallic Chemistry 649 (2002) 78–85
tent with, but to higher magnetic field than the corre-
sponding resonances for the [Me2MN(CH2Ph)2]2 series
[8,14,22].
The mass spectral data for 4 and 5 and the single
crystal X-ray data for 4, as discussed below, are consis-
tent with hexamer formation (x=6). The major fea-
tures of the mass spectrum of [MeAlNCH2Ph]6 are an
[M+−Me] ion peak at m/z=867, similar to the mass
spectra for 1–3, as discussed above; a small ion peak at
m/z=426, assignable to [M+−2Me]/2, or trimer for-
mation; and the ion peaks associated with
C6H5CH2NH+ (m/z=106) and its decomposition. The
EI-MS of [MeGaNCH2Ph]6 is rich in spectral features
showing an envelope of ion peaks representing [M+],
starting at m/z=1134. The isotopically derived spec-
trum, based on C48H60N6Ga6, is in excellent agreement
with the experimental spectrum. The [MeGaNCH2Ph]6
parent ion fragments more readily than that for
[MeAlNCH2Ph]6. There is a series of ion peak clusters
representing the sequential loss of a monomer unit
leading from pentamer down to monomer. Within each
cluster is an additional series of ion peaks resulting
from the loss of methyl and benzylamino groups.
Me2Ga+ peaks at m/z=99 and 101 are prominent in
the spectrum, as in the mass spectrum of 2.
The expected molecular ion peaks [M+] for 1–3 are
not present in the electron impact mass spectral (EI-
MS) data. Instead, [M+−Me] peaks are observed,
which is consistent with reported data on other series of
aminoalane and aminogallane dimers [8,9,14,36,37]. Ion
peaks related to the benzylamino moiety are a signifi-
cant feature of the three mass spectra. The ion peak at
m/z=106, arising from C6H5CH2NH+ [38], is the base
peak for 1 and 2. Characteristic ion peaks for alkylben-
zenes, such as C7H+7 at m/z=91, are also observed.
Interestingly, significant concentrations of the monomer
species, [M+/2−Me], are observed for 2 and 3, but not
for 1. This observation is consistent with the reported
EI-MS data for aminoindane dimers which show sig-
nificant concentrations of both monomer and dimer
species, with an increasing ratio of monomer as the
steric bulk of the amide ligand is increased [5], and with
the relative enthalpies of dative bond formation for
Me3M·NMe3 (AlꢀN\GaꢀN:InꢀN) [2h]. The EI-MS
for [Me2AlN(CH2Ph)2]2, obtained under the same ex-
perimental conditions, shows significant formation of
[M+/2−Me] and related ion peaks, which suggests that
there is significantly more steric strain in [Me2AlN-
(CH2Ph)2]2 than in 1.
Imidoalanes, [MeAlNR¦]n, derived from the reaction
of Me3Al with primary amines (H2NR¦) are oligomeric,
where n=3, 4, 6, 7, and
8 [3,4,6,7,10–12,23–
26,28,29,30b,c,32b]. The degree of aggregation, n, de-
pends strongly on the nature of the R¦ group attached
to nitrogen. For arylamines, n=6 for R¦=phenyl [25],
but by adding more sterically demanding groups to the
aromatic ring, imidoalanes with n=4 (R¦=1,3,5-tri-
methylphenyl) and n=3 (R¦=2,6-di-isopropylphenyl)
have been synthesized [28]. Likewise, values of n=4, 6,
2.2. Synthesis and characterization of [MeAlNCH2Ph]6
(4) and [MeGaNCH2Ph]6 (5)
Equimolar mixtures of Me3M and benzylamine in
toluene were heated from 120 to 180 °C and monitored
and
8
have been reported for imidogallanes,
1
by H-NMR to establish experimental conditions for
[MeGaNR¦]n [24,30a,c,31,32], where the sterically de-
methane elimination and product formation of a highly
condensed species. Thermolysis of the mixtures led to
the formation of [MeAlNCH2Ph]6 (4) at 135 °C and
[MeGaNCH2Ph]6 (5) at 175 °C. All attempts at obtain-
ing a higher condensed indium-nitrogen containing
compound were unsuccessful. The 1H-NMR spectra
were simple, consisting of one single resonance (area=
3) for the methyl group, a single resonance for the CH2
group (area=2), and a spectral pattern characteristic
of a monosubstituted aromatic group. These data and
the accompanying 13C-NMR data suggest the forma-
tion of an imidoalane and an imidogallane and not an
orthometalated species, as in the higher-temperature
thermolysis reactions of Me3Al and Me3Ga mixtures
with dibenzylamine. Recent work in our laboratory has
shown that the rate of the orthometalation reaction for
HN(tBu)CH2Ph with Me3Al at 120 °C is much faster
than the corresponding reaction of dibenzylamine with
Me3Al at 150 °C due to the incorporation of the steri-
t
manding groups R¦=i-propyl, Bu, and trimethylsilyl
display an oligimerization of n=4; the groups R¦=4-
i
fluorophenyl, Bu, and n-propyl require n=6; and n=
8 for R¦=methyl. Therefore, hexamer formation,
[MeMNCH2Ph]6, for R¦=benzyl is in agreement with
the literature values for n.
2.3. Crystal Structures for 1a, 2a, 3a, and 4
The X-ray crystal data for 1a, 2a, and 3a are given in
Table 1. The ORTEP drawing of the molecular structure
and the atom labeling scheme for trans-
[Me2InN(H)CH2Ph]2 (3a), are shown in Fig. 1. Selected
,
bond lengths (A) and angles (°) from the X-ray data are
summarized in Table 2 for 1a, 2a, and 3a and are
comparable with literature values for structurally simi-
lar aminoalane [3,4,6,7,9,16,18–21,25,28,36,40], amino-
gallane [3,8,11,13,18,28,31b,41–43], and aminoindane
dimers [3,5,20,34,35]. The three dimers each crystallize
in the trans conformation with a planar, almost square,
M2N2 core. The M(1)ꢀN(1) and M(1)ꢀN(1A) bond
distances forming the four-membered ring are slightly
t
cally bulky Bu group [39]. Therefore, substitution of
the less sterically demanding hydrogen for a benzyl
group would arguably make orthometalation a non-
competitive process in these systems.

E.K. Styron et al. / Journal of Organometallic Chemistry 649 (2002) 78–85
81
,
,
0.029(6) A (Ga), and 0.034(8) A (In); the NꢀMꢀN
angles increase 3.1(3)° (Al), 2.9(3)° (Ga), and 3.4(3)°
(In) with a corresponding decrease in the MꢀNꢀM
angles; and the external CꢀMꢀC angles decrease 3.6(4)°
(Al), 3.8(5)° (Ga), and 2.3(6)° (In). Another effect of
the substitution of the benzyl group is to distort the
M2N2 ring so that it is no longer planar, but folded
along the N···N axis by 4.0° (Al), 2.7° (Ga), and 4.6°
(In). Therefore, in these three series increasing the steric
bulk of the amido group is accommodated by small
increases in the MꢀN distances, changes in the internal
angles, significant decreases in the external CꢀMꢀC
angles, and folding of the M2N2 rings along the N···N
different for each of the three dimers. The NꢀMꢀN and
MꢀNꢀM bond angles deviate from 90°, with the devia-
tions being greatest for 3a and least for 1a. The
NꢀMꢀN bond angles are less than 90° and the MꢀNꢀM
bond angles are greater than 90°; therefore, the M2N2
cores are slightly elongated along the M···M axis. These
data are in agreement with structural data reported for
aminoalanes and aminogallanes with the general for-
mula [Me2MN(H)R¦]2 [7,8,13,20,21,25,28,31b,42,43a].
Significant structural changes occur when the amine
hydrogen is replaced by the more sterically demanding
benzyl group to form [Me2MN(CH2Ph)2]2 [8,19,22]. On
,
the average: the MꢀN bonds lengthen 0.028(6) A (Al),
Table 1
Crystal data and structure refinement parameters for 1a, 2a, 3a, and 4
Empirical formula
Crystal system
Space group
C
18H28Al2N2
C18H28Ga2N2
Orthorhombic
Pbca
C18H28In2N2
Triclinic
C48H60Al6N6
Rhombohedral
Orthorhombic
Pbca
(
(
P1
R3
Unit cell dimensions
,
a (A)
10.7484(12)
8.3002(12)
22.1151(28)
10.7231(15)
8.3057(15)
22.0896(38)
9.2085(11)
10.4239(11)
12.8026(19)
70.743(10)
85.474(11)
63.568(9)
1035.5(5)
1
16.7118(20)
14.9796(30)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
1973.0(10)
2
1967.4(10)
4
3623(2)
3
Z
Crystal size (mm)
0.30×0.10×0.05
0.146
0.45×0.35×0.30
2.737
0.30×0.30×0.30
2.226
0.40×0.30×0.30
0.172
Absorption coefficent (mm−1
)
,
Radiation (Mo–Ka), u (A)
2q range (°)
Scan type
0.71073
2.0–45.0
0.71073
2.0–45.0
0.71073
2.0–45.0
ꢀ–2q
0.71073
1.0–45.0
ꢀ–2q
ꢀ
ꢀ
Index ranges
05h511, 05k58,
−235l523
05h511, 05k58,
−235l523
−95h59, −115k511, −175h517,
−135l513
−175k517,
−165l516
Reflections collected
Independent reflections
Observed reflections
Final R indices (observed data)
R indices (all data)
2530
2539
5381
6270
1286 (Rint=5.68%)
666 (F\3.0|(F))
R=8.75%, Rw=9.11%
1285 (Rint=4.57%)
829 (F\6.0|(F))
R=3.62%, Rw =4.14%
R=6.72%, Rw=7.46%
0.52 and −0.38
2691 (Rint=3.69%)
2187 (F\6.0|(F))
R=4.34%, Rw=4.72%
R=5.26%, Rw=7.43%
1.19 and −1.22
1049 (Rint=2.82%)
711 (F\6.0|(F))
R=4.02%, Rw=4.21%
R=7.56%, Rw=5.64%
0.27 and −0.24
Largest differential peak and
0.51 and −0.40
−3
,
hole (e A
)
Fig. 1. Molecular structure of 3a.

82
E.K. Styron et al. / Journal of Organometallic Chemistry 649 (2002) 78–85
Table 2
,
Selected bond lengths (A) and bond angles (°) for 1a, 2a, and 3a (M=Al, Ga, In)
[Me2AlN(H)CH2Ph]2
[Me2GaN(H)CH2Ph]2
[Me2InN(H)CH2Ph]2
Bond lengths
M(1)ꢀN(1)
M(1)ꢀC(1)
1.949(8)
1.931(12)
1.955(10)
2.817(5)
1.961(7)
1.422(11)
2.005(6)
1.960(8)
1.951(7)
2.924(1)
2.024(5)
1.479(8)
2.205(9)
2.161(7)
2.144(7)
3.292(1)
2.222(6)
1.455(9)
M(1)ꢀC(2)
M(1)···M(1A)
M(1)ꢀN(1A)
N(1)ꢀC(10)
Bond angles
N(1)ꢀM(1)ꢀC(1)
N(1)ꢀM(1)ꢀC(2)
C(1)ꢀM(1)ꢀC(2)
N(1)ꢀM(1)ꢀN(1A)
C(1)ꢀM(1)ꢀN(1A)
C(2)ꢀM(1)ꢀN(1A)
M(1)ꢀN(1)ꢀC(10)
M(1)ꢀN(1)ꢀM(1A)
C(10)ꢀN(1)ꢀM(1A)
N(1)ꢀC(10)ꢀC(11)
111.5(4)
111.8(4)
121.6(4)
87.8(3)
109.6(4)
109.3(4)
121.9(6)
92.2(3)
110.9(3)
106.5(3)
125.4(3)
87.0(2)
108.2(3)
112.1(3)
118.3(4)
93.0(2)
108.4(4)
107.1(3)
131.4(4)
84.0(3)
106.4(3)
109.3(3)
116.9(5)
96.0(3)
120.1(6)
117.2(8)
117.4(4)
116.7(5)
115.3(5)
117.5(6)
axes. These observations are in agreement with re-
ported correlations of the steric properties of functional
groups attached to the amine nitrogen with the corre-
was sublimed prior to use. Benzylamine, benzene-d6,
and toluene-d8, Aldrich, were stored over molecular
1
sieves. H- and 13C-NMR spectra were obtained on a
sponding
40,41,43b].
dimer
geometries
[5,7–9,25,28,35,36,
Bruker DRX-400 NMR spectrometer, using benzene-d6
as solvent and internal reference for the room tempera-
ture (r.t.) studies. Toluene-d8 was used as the solvent
The ORTEP drawing of the molecular structure and
the atom labeling scheme for [MeAlNCH2Ph]6 (4), is
shown in Fig. 2 and selected bond lengths (A) and
angles (°) are summarized in Table 3. [MeAlNCH2Ph]6
crystallizes in a rhombohedral structure where the
(AlN)6 cage consists of two six-membered (AlN)3 rings
linked by six transverse AlꢀN bonds. The AlꢀN bonds
in the two six-membered rings (1.890(7) A, average) are
shorter than the transverse bonds (1.985(3) A, average)
1
for the variable-temperature studies. The H- and 13C-
,
NMR chemical shift assignments were made based on
normal 1D- and 13C-DEPT- and 2D-H,H-COSY-,
H,H-NOESY-, C,H-COSY-, and H,C-HMBC-NMR
,
,
consistent with the structural data for other imidoalane
hexamers of the form [MeAlNR]6, where R=i-propyl
[23], phenyl [25], 4-fluorophenyl [30c], and C2H4NMe2
[12]. The NꢀAlꢀN bond angles in the two six-membered
rings are significantly smaller (114.2(2)°) than the
AlꢀNꢀAl bond angles (125.3(1)°), whereas the trend is
opposite for the bond angles in the four-membered
rings.
3. Experimental details
3.1. General experimental conditions
Standard inert-atmosphere techniques were used for
the synthesis, solution preparation, and manipulation
of all compounds. Trimethylaluminum, Texas Alkyls,
was used as obtained; trimethylgallium, Morton Ad-
vanced Materials, was distilled under vacuum prior to
use; and trimethylindium, Morton Advanced Materials,
Fig. 2. Molecular structure of 4.

E.K. Styron et al. / Journal of Organometallic Chemistry 649 (2002) 78–85
83
Table 3
dimers above, except that greater thermolysis tempera-
tures were required. The reaction conditions were: com-
pound 4, 0.673 g Me3Al with 1.000 g benzylamine at
135 °C for 2.0 days (1.14 g, 83% yield); and 5, 1.060 g
Me3Ga with 1.000 g benzylamine at 175 °C for 3.0
days (0.85 g, 48% yield). X-ray quality crystals were
obtained for 4 only. We were unsuccessful in synthesiz-
ing the corresponding indium hexamer from either the
thermolysis of 1:1 Me3In/benzylamine mixtures or ther-
molysis of 3.
o
,
Selected bond lengths (A) and bond angles ( ) for [MeAlNCH2Ph]6
(4)
Bond lengths
Al(1)ꢀN(1)
Al(1)···Al(1A)
Al(1)ꢀN(1C)
N(1)ꢀC(10)
1.893(4) Al(1)ꢀC(1)
2.703(2) Al(1)···Al(1B)
1.888(3) Al(1)ꢀN(1B)
1.508(5) N(1)ꢀAl(1A)
1.935(3)
2.703(1)
1.985(3)
1.985(3)
Bond angles
N(1)ꢀAl(1)ꢀC(1)
C(1)ꢀAl(1)ꢀN(1C)
N(1C)ꢀAl(1)ꢀN(1B)
Al(1)ꢀN(1)ꢀAl(1A)
Al(1)ꢀN(1)ꢀAl(1D)
Al(1A)ꢀN(1)ꢀAl(1D)
118.8(2) N(1)ꢀAl(1)ꢀN(1C)
119.7(2) C(1)ꢀAl(1)ꢀN(1B)
91.4(1) Al(1)ꢀN(1)ꢀC(10)
88.3(1) C(10)ꢀN(1)ꢀAl(1A) 117.1(2)
125.3(1) C(10)ꢀN(1)ꢀAl(1D) 114.3(2)
114.2(2)
113.5(1)
115.5(2)
3.4. Characterization data
88.5(1) N(1)ꢀC(10)ꢀC(11)
115.6(3)
3.4.1. [Me2AlN(H)CH2Ph]2 (1) [1]
M.p.: 87–89 °C (65–68 °C) [1]. 1H-NMR (1a): l
−0.53 (s, 12H, AlCH3), 0.99 (t, 2H, NH), 3.66 (d, 4H,
NCH2), 6.96 (m, 4H, H12, H16), 7.09 (m, 4H, H13,
1
experiments. IR spectra were obtained using split mull
samples in Nujol and Kel-F (halocarbon) on KBr
plates. EI-MS data were obtained on a Finnigan
MAT95Q mass spectrometer with an electron energy of
70 eV. The samples were introduced using a direct-in-
sertion probe under inert-atmosphere conditions. Ele-
H15), 7.02 (m, 2H, H14); H-NMR (1b): l −0.58 (s,
6H, AlCH3), −0.48 (s, 6H, AlCH3), 0.90 (t, 2H, NH),
3.68 (d, 4H, NCH2), 6.96 (m, 4H, H12, H16), 7.09 (m,
4H, H13, H15), 7.02 (m, 2H, H14). 13C-NMR (1a): l
−10.44 (AlCH3), 47.10 (NCH2), 141.57 (C11), 127.02
(C12, C16), 128.83 (C13, C15), 127.35 (C14); 13C-NMR
(1b): l −12.34 (AlCH3), −8.54 (AlCH3), 47.19
(NCH2), 141.55 (C11), 126.92 (C12, C16), 128.83 (C13,
C15), 127.33 (C14). MS; m/z: 311 [M+−15].
mental
analyses
were
performed
by
E&R
Microanalytical Laboratory, Inc., Parsippany, NJ.
Melting points were obtained in capillaries under nitro-
gen and are uncorrected.
3.4.2. [Me2GaN(H)CH2Ph]2 (2)
M.p.: 82–86 °C. H-NMR (2a): l −0.19 (s, 12H,
GaCH3), 1.04 (t, 2H, NH), 3.71 (d, 4H, NCH2), 6.96
1
3.2. Synthesis of [Me2AlN(H)CH2Ph]2 (1),
[Me2GaN(H)CH2Ph]2 (2), and [Me2InN(H)CH2Ph]2 (3)
(m, 4H, H12, H16), 7.10 (m, 4H, H13, H15), 7.03 (m,
2H, H14); H-NMR (2b): l −0.21 (s, 6H, GaCH3),
1
Compounds 1 [1], 2, and 3 were synthesized by
thermolysis of 1:1 equimolar mixtures of the respective
Me3M (M=Al, Ga, In) with benzylamine dissolved in
15 ml of toluene. Each mixture was put into a high-
pressure tube which was placed in an oil bath at a
selected temperature. The progress of each reaction was
−0.17 (s, 6H, GaCH3), 0.995 (t, 2H, NH), 3.72 (d, 4H,
NCH2), 6.96 (m, 4H, H12, H16), 7.10 (m, 4H, H13,
H15), 7.03 (m, 2H, H14). 13C-NMR (2a): l −8.01
(GaCH3), 48.87 (NCH2), 142.54 (C11), 126.90 (C12,
C16), 128.72 (C13, C15), 127.07 (C14); 13C-NMR (2b):
l −10.77 (GaCH3), −5.32 (GaCH3), 49.00 (NCH2),
142.51 (C11), 126.89 (C12, C16), 128.72 (C13, C15),
127.07 (C14). IR (cm−1): 3307 (w), 3028 (w), 2944 (w),
2884 (m), 2823 (w), 1950 (w), 1661 (w), 1199 (s), 1156
(m), 1078 (m), 1039 (s), 1023 (s), 961 (m), 848 (s), 734
(vs), 694 (s), 620 (m), 578 (s). MS; m/z: 395, 397, 399
[M+−15]. Anal. Calc. for C18H28Ga2N2: C, 52.49; H,
6.85; N, 6.80. Found: C, 52.63; H, 6.90; N 6.80%.
1
monitored by H-NMR. The reaction conditions were:
compound 1, 0.673 g Me3Al with 1.000 g benzylamine
at 90 °C for 1.5 days (1.47 g, 96% yield); 2, 1.072 g
Me3Ga with 1.000 g benzylamine at 120 °C for 3.0
days (1.89 g, 98% yield); and 3, 1.492 g Me3In with
1.000 g benzylamine at 90 °C for 2.0 d (2.03 g, 87%
yield). In solution, each of the dimers exists as a 1:1
mixture of trans (a) and cis (b) isomers. Crystals were
obtained from each of the reaction mixtures upon
standing at r.t. The crystals were dried under vacuum
and recrystallized from toluene at −15 °C. In each
case, only solid trans (a) isomer was obtained as evi-
denced by single crystal X-ray structural analysis.
3.4.3. [Me2InN(H)CH2Ph]2 (3)
1
M.p.: 80–82 °C. H-NMR (3a): l −0.15 (s, 12H,
InCH3), 0.91 (t, 2H, NH), 3.79 (d, 4H, NCH2), 6.95 (m,
4H, H12, H16), 7.11 (m, 4H, H13, H15), 7.02 (m, 2H,
1
H14); H-NMR (3b): l −0.16 (s, 6H, InCH3), −0.13
3.3. Synthesis of [MeAlNCH2Ph]6 (4) and
[MeGaNCH2Ph]6 (5)
(s, 6H, InCH3), 0.87 (t, 2H, NH), 3.81 (d, 4H, NCH2),
6.95 (m, 4H, H12, H16), 7.11 (m, 4H, H13, H15), 7.02
(m, 2H, H14). 13C-NMR (3a): l −9.30 (InCH3), 50.60
(NCH2), 144.62 (C11), 126.72 (C12, C16), 128.79 (C13,
C15), 126.98 (C14); 13C-NMR (3b): l −11.26 (InCH3),
The aluminum and gallium hexamers were synthe-
sized and crystals obtained in a manner similar to the

84
E.K. Styron et al. / Journal of Organometallic Chemistry 649 (2002) 78–85
−7.34 (InCH3), 50.72 (NCH2), 144.57 (C11), 126.69
(C12, C16), 128.79 (C13, C15), 126.98 (C14). IR
(cm−1): 3297 (m), 3061 (w), 3023 (w), 2963 (m), 2911
(m), 2852 (w), 1943 (w), 1802 (w), 1599 (m), 1294 (m),
1189 (s), 1158 (m), 1145 (s), 1077 (m), 1043 (s), 1025
(vs), 968 (s), 810 (s), 728 (s), 692 (vs), 508 (s). MS; m/z:
487 [M+−15]. Anal. Calc. for C18H28In2N2: C, 43.06;
H, 5.62; N, 5.58. Found: C, 43.39; H, 5.92; N 5.69%.
data collection and refinement processes are provided in
Table 1.
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 132624, 132625, 132626, and
132627 for trans-[Me2AlN(H)CH2Ph]2, trans-[Me2-
3.4.4. [MeAlNCH2Ph]6 (4)
1
M.p. (dec.): 328 °C. H-NMR (4): l −0.44 (s, 18H,
GaN(H)CH2Ph]2,
trans-[Me2InN(H)CH2Ph]2,
and
AlCH3), 4.22 (s, 12H, NCH2), 7.13 (m, 12H, H12,
H16), 7.20 (m, 12H, H13, H15), 7.16 (m, 6H, H14).
13C-NMR (4): l −13.52 (AlCH3), 49.95 (NCH2),
143.72 (C11), 127.4 (C12, C16), 128.9 (C13, C15), 126.9
(C14). IR (cm−1): 3083 (vw), 3058 (w), 3026 (w), 2927
(w), 2884 (w), 2853 (w), 1946 (w), 1869 (w), 1802 (w),
1661 (w), 1310 (m), 1246 (m), 1198 (m), 1180 (m), 1005
(s), 992 (s), 976 (s), 905 (m), 746 (s), 734 (s), 691 (s), 531
(s). MS; m/z: 867 [M+−15]. Anal. Calc. for
C48H60Al6N6: C, 65.29; H, 6.85; N, 9.52. Found: C,
65.19; H, 6.88; N, 9.39%.
[MeAlNCH2Ph]6, respectively. Copies of this informa-
tion may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax:
+44-1223-336033;
e-mail:
deposit@ccdc.
cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
This work was supported in part by a US Depart-
ment of Education GAANN Fellowship to E.K.S.
3.4.5. [MeGaNCH2Ph]6 (5)
1
M.p. (dec.): 290 °C. H-NMR (4): l −0.28 (s, 18H,
References
GaCH3), 4.28 (s, 12H, NCH2), 7.16 (m, 12H, H12,
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13C-NMR (4): l −12.69 (GaCH3), 53.13 (NCH2),
144.50 (C11), 126.83 (C12, C16), 128.71 (C13, C15),
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