Syntheses and structural characterization of a LAl(N3)N[μ- Si(N3)tBu]2NAl(N3)L and a monomeric aluminum hydride amide LAlH(NHAr) (L = HC[(CMe)(NAr)]2, Ar = 2,6-iPr 2C6H3</su

Article abstract of DOI:10.1021/om050698v

Reactions between the aluminum(I) monomer LA1 (L = HC[(CMe)(NAr)] ₂, Ar = 2,6-iPr₂C₆H₃) and organic azides (RN₃, R = C₁₀H₁₅ (adamantyl), Ph ₃Si; tBuSi(N₃)

Full text of DOI:10.1021/om050698v

6420
Organometallics 2005, 24, 6420-6425
Syntheses and Structural Characterization of a
LAl(N3)N[µ-Si(N3)(tBu)]2NAl(N3)L and a Monomeric
Aluminum Hydride Amide LAlH(NHAr) (L )
HC[(CMe)(NAr)]2, Ar ) 2,6-iPr2C6H3)
Hongping Zhu, Zhi Yang, Jo¨rg Magull, Herbert W. Roesky,*
Hans-Georg Schmidt, and Mathias Noltemeyer
Institut fu¨r Anorganische Chemie der Universita¨t Go¨ttingen,
Tammannstrasse 4, D-37077 Go¨ttingen, Germany
Received August 12, 2005
Reactions between the aluminum(I) monomer LAl (L ) HC[(CMe)(NAr)]2, Ar ) 2,6-
iPr2C6H3) and organic azides (RN3, R ) C10H15 (adamantyl), Ph3Si; tBuSi(N3)3) are reported.
LAl reacted with the bulky azide RN3 in toluene in a temperature range of -50 to 25 °C,
resulting in the compound LAl[(NR)2N2] (R ) C10H15 (1), Ph3Si (2)) instead of the expected
AldN multiple bond species, while the reaction with tBuSi(N3)3 gave LAl(N3)N[(µ-Si-
(N3)(tBu)]2NAl(N3)L (3). Compounds 1-3 have been fully characterized by mass spectrometry
and IR and multinuclear NMR spectroscopy (1H, 13C, and 29Si) as well as by single-crystal
X-ray crystallography. The structural analysis of 1 and 2 reveals an AlN4 planar five-
membered ring compound, suggesting a [2 + 3] cycloaddition of the AldN multiple bond
species with a molecule of RN3 despite the steric bulk of the L and R substituents. Compound
3 shows a bonding of the N3 group to the Al and a formation of the N2Si2 central core, implying
the migration of N3 and a [2 + 2] cycloaddition in the reaction sequence. In addition, the
solvent-free reaction of an aluminum dihydride LAlH2 with ArNH2 was also investigated at
elevated temperatures (150-290 °C), and a monomeric aluminum hydride amide, LAlH-
(NHAr) (4), was obtained as the only isolable product. The Al-H and N-H groups of 4 are
shown in the IR and 1H NMR spectra. The corresponding X-ray structural analysis exhibits
the Al-H and N-H bonds that are nearly arranged in position trans to the Al-NNHAr bond.
Introduction
initially formed imide LAlNAr* further reacts intramo-
lecularly under C-H bond activated addition and [2 +
2] cycloaddition involving the methyl and phenyl group,
respectively.6 However, the reaction of (Cp*Al)4 with
Me3SiN3 at elevated temperature yielded Cp*[(Me3-
Si)2N]AlN(µ-AlCp*)(µ-Al[N(SiMe3)2])NAlCp*2; the re-
lated mechanism is still under investigation.3 These
examples demonstrate an extensive reaction chemistry
between heavier group 13 metal(I) species and organic
azides. Moreover, it has been shown that the steric
demand of the substituents at M (M(I) species) and N
(organic azide) has a great influence on the formation
of the products. Herein we report on the reaction of the
aluminum(I) monomer LAl with the bulky azide RN3
and the isolation of the AlN4 five-membered-ring com-
pound LAl[(NR)2N2] (R ) C10H15 (adamantyl) (1), SiPh3
(2)). Treatment of LAl with tBuSi(N3)3, however, gener-
ates the compound LAl(N3)N[(µ-Si(N3)(tBu)]2NAl(N3)L
(3), different from the previously reported results on
related reactions. In addition, the investigation of the
H2 elimination reaction using an aluminum dihydride
LAlH2 and a primary amine ArNH2 at elevated tem-
peratures is also presented, in which a monomeric
aluminum hydride amide, LAlH(NHAr) (4), was ob-
tained as the only isolable product.
The reactions of monovalent heavier group 13 com-
pounds with organic azides are of general interest. In
these reactions, an interaction between the metal center
and the N3 group results in an elimination of N2 and
the formation of a M-N bond with a multiple bond
character.1 Such M-N bonded species are highly reac-
tive and can further react through dimerization,2 by
C-H bond activation,3 by 1,3-dipolar addition,4 and
alternatively by cycloaddition with another molecule of
azide.5 More recently, we have reported on a reaction
of LAl with Ar*N3 (L ) HC[(CMe)(NAr)]2, Ar* ) 2,6-
Ar2C6H3, Ar ) 2,6-iPr2C6H3) at low temperatures. The
* To whom correspondence should be addressed. E-mail:
hroesky@gwdg.de.
(1) (a) Hardman, N. J.; Cui, C.; Roesky, H. W.; Fink, W. H.; Power,
P. P. Angew. Chem. 2001, 113, 2230-2232; Angew. Chem., Int. Ed.
2001, 40, 2172-2174. (b) Wright, R. J.; Phillips, A. D.; Allen, T. L.;
Fink, W. H.; Power, P. P. J. Am. Chem. Soc. 2003, 125, 1694-1695.
(2) Schulz, S.; Voigt, A.; Roesky, H. W.; Ha¨ming, L.; Herbst-Irmer,
R. Organometallics 1996, 15, 5252-5253.
(3) Schulz, S.; Ha¨ming, L.; Herbst-Irmer, R.; Roesky, H. W.; Sheld-
rick, G. M. Angew. Chem. 1994, 106, 1052-1054; Angew. Chem., Int.
Ed. Engl. 1994, 33, 969-971.
(4) Jutzi, P.; Neumann, B.; Reumann, G.; Stammler, H.-G. Orga-
nometallics 1999, 18, 2037-2039.
(5) (a) Cui, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer, M.
Angew. Chem. 2000, 112, 4705-4707; Angew. Chem., Int. Ed. 2000,
39, 4531-4533. (b) Cui, C.; Ko¨pke, S.; Herbst-Irmer, R.; Roesky, H.
W.; Noltemeyer, M.; Schmidt, H.-G.; Wrackmeyer, B. J. Am. Chem.
Soc. 2001, 129, 9091-9098.
(6) Zhu, H.; Chai, J.; Chandrasekhar, V.; Roesky, H. W.; Magull,
J.; Vidovic, D.; Schmidt, H.-G.; Noltemeyer, M.; Power, P. P.; Merrill,
W. A. J. Am. Chem. Soc. 2004, 126, 9472-9473.
10.1021/om050698v CCC: $30.25 © 2005 American Chemical Society
Publication on Web 11/01/2005

Monomeric Aluminum Hydride Amide
Organometallics, Vol. 24, No. 26, 2005 6421
128.0, 128.2, 128.5, 128.9, 129.2, 129.3, 137.2, 137.3, 137.5,
138.1, 140.7, 143.7, 145.8 (Ar-C6H3, SiPh3, PhMe), 172.2 (CN).
29Si NMR (99.36 MHz, C6D6, 298 K, ppm): δ -20.6, -15.1.
EI-MS: m/z (%) 717.4 (100, [M+ - Ph3SiN3]). Anal. Calcd (%)
for C72H79AlN6Si2 (2‚PhMe, Mr ) 1111.62): C, 77.80; H, 7.16;
N, 7.56. Found: C, 77.79; H, 7.25; N, 7.34.
Note: The reaction of LAl and C10H15N3 (or Ph3SiN3) in a
molar ratio of 1:1 even in the temperature range of -78 °C to
room temperature still resulted in the formation of 1 (or 2).
Experimental Section
General Procedures. All manipulations were carried out
under a purified nitrogen atmosphere using Schlenk tech-
niques or inside an Mbraun MB 150-GI glovebox filled with
dry nitrogen where the calibrated values of O2 and H2O were
strictly controlled below 1 ppm. All solvents were dried by
standard methods prior to use. Commercially available chemi-
cals were purchased from Aldrich or Fluka and used as
received except for ArNH2. ArNH2 was distilled prior to use.
The other compounds mentioned in this paper were prepared
according to published procedures: Ph3SiN3,2 LAl,7 tBuSi(N3)3,8
LAlH2.9 Elemental analyses were performed by the Analytis-
ches Labor des Instituts fu¨r Anorganische Chemie der Uni-
Synthesis of LAl(N3)N[µ-Si(N3)(tBu)]2NAl(N3)L (3). A
precooled toluene solution (10 mL) of tBuSi(N3)3 (0.11 g, 0.5
mmol) was added to a toluene solution (20 mL) of LAl (0.22 g,
0.5 mmol) at -50 °C. The mixture was stirred and allowed to
warm to room temperature. The color of the solution changed
from red to yellow, and finally to colorless. After stirring for
an additional 12 h, the solution was concentrated (ca. 5 mL),
and to this solution n-hexane (15 mL) was added. The colorless
crystalline solid of 3 was immediately formed and collected
by filtration (0.10 g). The filtrate was stored at 4 °C for three
weeks to afford another crop of X-ray quality crystals of 3‚
1
versita¨t Go¨ttingen. H (300.13 and 500.13 MHz), 13C (125.76
MHz), and 29Si (99.36 MHz) NMR spectra were recorded on a
Bruker AM 300 or 500 spectrometer and IR spectra on a Bio-
Rad Digilab FTS-7 spectrometer. EI mass spectra were
measured on a Finnigan MAT 8230 or a Varian MAT CH5
instrument. Melting points were measured in sealed glass
tubes and were not corrected.
1
PhMe (0.17 g). Total yield: 0.26 g, 83% of 3. Mp: 320 °C. H
Synthesis of LAl[(NC10H15)2N2] (1). Precooled toluene (30
mL) was added to a mixture of LAl (0.20 g, 0.45 mmol) and
C10H15N3 (0.16 g, 0.90 mmol) at -50 °C. The suspension was
allowed to warm to room temperature and stirred for 12 h. A
yellow solution developed. The solvent from the solution was
removed in vacuo, and the residue was washed with n-hexane
(5 mL) to afford a yellow crystalline solid of 1. Yield: 0.29 g,
NMR (300.13 MHz, D8-toluene, 298 K, ppm): δ 0.27 (s, 18 H,
tBu), 1.07 (d, 4 × 3 H, 3JHH ) 6.8 Hz, CH(CH3)2), 1.14 (d, 8 ×
3
3
3 H, JHH ) 6.8 Hz, CH(CH3)2), 1.21 (d, 4 × 3 H, JHH ) 6.8
Hz, CH(CH3)2), 1.64 (s, 4 × 3 H, â-CH3), 3.16 (sept, 4 × 1 H,
3JHH ) 6.8 Hz, CH(CH3)2), 3.26 (sept, 4 × 1 H, 3JHH ) 6.8 Hz,
CH(CH3)2), 4.76 (s, 2 × 1 H, γ-CH), 6.94-7.20 (m, 12 H, Ar-
C6H3). 13C{1H} NMR (125.76 MHz, D8-toluene, 298 K, ppm):
δ 1.36 (tBu), 22.5, 23.0, 24.2, 24.6, 24.8, 27.1, 28.6, 29.1, 32.0
(CH(CH3)2, â-CH3), 94.3 (γ-C), 123.5, 125.1, 127.9, 128.1, 137.4,
141.3, 142.7, 144.4 (Ar-C6H3), 172.2 (CN). 29Si NMR (99.36
MHz, D8-toluene, 298 K, ppm): δ -21.5, -20.8. EI-MS: m/z
(%) 1255 (30, [M+]), 1198 (100, [M+ - tBu]). IR (KBr plate,
Nujol mull, cm-1): ν 2113, 2076 (m, N3). Anal. Calcd (%) for
C66H100Al2N18Si2 (Mr ) 1255.79): C, 63.12; H, 8.03; N, 20.01.
Found: C, 63.08; H, 8.08; N, 20.04.
1
84%. Mp: 384 °C. H NMR (500.13 MHz, D8-toluene, 298 K,
3
ppm): δ 1.06 (d, 2 × 3 H, JHH ) 6.8 Hz, CH(CH3)2), 1.18 (d,
3
3
2 × 3 H, JHH ) 6.8 Hz, CH(CH3)2), 1.24 (d, 2 × 3 H, JHH
)
6.8 Hz, CH(CH3)2), 1.25 (d, 2 × 3 H, 3JHH ) 6.8 Hz, CH(CH3)2),
1.33-1.49 (m), 1.77-1.84 (m), 2.22 (br) (15 H, C10H15), 1.62
3
(s, 2 × 3 H, â-CH3), 3.32 (sept, 2 × 1 H, JHH ) 6.8 Hz,
CH(CH3)2), 3.88 (sept, 2 × 1 H, 3JHH ) 6.8 Hz, CH(CH3)2), 5.20
(s, 1 H, γ-CH), 6.90-7.18 (m, 6 H, Ar-C6H3). 13C{1H} NMR
(125.76 MHz, D8-toluene, 298 K, ppm): δ 24.5, 24.6, 25.2, 25.5,
25.6, 29.2, 30.1, 31.0 (CH(CH3)2, â-CH3), 36.9, 37.8, 44.6, 52.5,
53.6 (C10H15), 101.8 (γ-C), 124.9, 125.1, 127.8, 128.1, 129.2,
141.1, 143.0, 146.1 (Ar-C6H3), 171.8 (CN). EI-MS: m/z (%)
Synthesis of LAlH(NHAr) (4). A mixture of LAlH2 (1.34
g, 3 mmol) and ArNH2 (0.57 mL, 3 mmol), with stirring, was
slowly heated to ca. 150 °C for 1 h. H2 evolution was observed
and ceased after 1 h. When cooled to room temperature, the
solidified product was dissolved in toluene (15 mL). The solvent
from the solution was removed in vacuo, and the residue was
washed with n-hexane (2 × 2 mL), affording the light yellow
crystalline solid of 4 (yield >95%). Mp: 134 °C. 1H NMR
(300.13 MHz, D8-toluene, 298 K, ppm): δ 0.95 (d, 4 × 3 H,
770.5 (100, [M+]). Anal. Calcd (%) for C49H71AlN6 (Mr
)
771.13): C, 76.32; H, 9.28; N, 10.90. Found: C, 76.34; H, 9.24;
N, 10.74. X-ray quality single crystals of 1‚Et2O were grown
from a mixture of solvents (Et2O:n-hexane ) 1:3) at 4 °C for
one week.
Synthesis of LAl[(NSiPh3)2N2]‚PhMe (2‚PhMe). The
synthetic route is similar to that of 1. LAl (0.44 g, 1 mmol)
and Ph3SiN3 (0.60 g, 2 mmol) are used. After workup, a
colorless solution developed. The solution was concentrated (ca.
5 mL), and to it n-hexane (10 mL) was added. The solution
was kept at 4 °C for three weeks to afford X-ray quality
3
3JHH ) 6.8 Hz, CH(CH3)2), 1.10 (d, 2 × 3 H, JHH ) 6.8 Hz,
3
CH(CH3)2), 1.11 (d, 2 × 3 H, JHH ) 6.8 Hz, CH(CH3)2), 1.13
3
3
(d, 2 × 3 H, JHH ) 6.8 Hz, CH(CH3)2), 1.26 (d, 2 × 3 H, JHH
) 6.8 Hz, CH(CH3)2), 1.55 (s, 2 × 3 H, â-Me), 2.43 (sept, 2 ×
3
1 H, JHH ) 6.8 Hz, CH(CH3)2), 2.93 (s, 1 H, NH), 3.32 (sept,
crystals of 2‚PhMe. Yield: 0.89 g, 80%. Mp: 220 °C. 1H NMR
3
4 × 1 H, JHH ) 6.8 Hz, CH(CH3)2), 4.97 (s, 1 H, γ-CH), 5.50
3
(500.13 MHz, C6D6, 298 K, ppm): δ 0.61 (d, 2 × 3 H, JHH
)
(br, 1 H, Al-H), 6.69-6.72, 6.92-7.10 (m, 9 H, Ar-C6H3). 13C-
{1H} NMR (125.76 MHz, D8-toluene, 298 K, ppm): δ 23.4, 24.4,
24.5, 24.6, 24.7, 25.2, 28.4, 28.7, 28.9 (CH(CH3)2, â-CH3), 97.9
(γ-C), 117.5, 123.0, 124.6, 125.0, 125.6, 128.2, 128.5, 129.2,
129.3, 135.4, 137.5, 140.7, 144.0, 144.5, 145.3 (Ar-C6H3), 170.6
(CN). EI-MS: m/z (%): 621 (22, [M+]), 578 (100, [M+ - iPr]).
IR (KBr plate, Nujol mull, cm-1): ν 1821 (w, Al-H), 3358 (w,
N-H). Anal. Calcd (%) for C41H60AlN3 (Mr ) 621.93): C, 79.18;
H, 9.72; N, 6.76. Found: C, 79.12; H, 9.74; N, 6.61. X-ray single
crystals of 4‚PhMe were obtained by recrystallization of 4 from
a mixture of toluene and n-hexane (3:2).
6.8 Hz, CH(CH3)2), 0.76 (d, 2 × 3 H, 3JHH ) 6.8 Hz, CH(CH3)2),
3
0.87 (d, 2 × 3 H, JHH ) 6.8 Hz, CH(CH3)2), 1.01 (d, 2 × 3 H,
3JHH ) 6.8 Hz, CH(CH3)2), 1.27 (s, 2 × 3 H, â-CH3), 2.10 (s, 3
H, PhMe), 2.47 (sept, 2 × 1 H, 3JHH ) 6.8 Hz, CH(CH3)2), 3.66
(sept, 2 × 1 H, 3JHH ) 6.8 Hz, CH(CH3)2), 3.91 (s, 1 H, γ-CH),
6.96-7.26 (m, 41 H, Ar-C6H3, SiPh3, PhMe). 13C{1H} NMR
(125.76 MHz, C6D6, 298 K, ppm): δ 21.4, 24.7, 25.0, 25.6, 28.3,
28.8 (CH(CH3)2, â-CH3, PhMe), 102.3 (γ-C), 125.1, 125.8, 126.0,
(7) Cui, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer, M.; Hao,
H.; Cimpoesu, F. Angew. Chem. 2000, 112, 4444-4446; Angew. Chem.,
Int. Ed. 2000, 39, 4274-4276.
(8) The compound tBuSi(N3)3 was prepared using tBuSiCl3 and
excess NaN3 with reference to that of Ph3SiN3 in ref 2. The physical
and spectroscopic data are shown here: colorless liquid, mp -10 °C;
1H NMR (300.13 MHz, C6D6, 298 K, ppm) δ 0.70; IR (KBr plate, Nujol
mull, cm-1) ν 2185, 2156 (vs, N3).
X-ray Structure Determination and Refinement. The
crystallographic data for compounds 1‚Et2O, 2‚PhMe, and 3‚
PhMe were collected on a Stoe IPDS II-array detector system
and for compound 4‚PhMe on a Stoe-Siemens-Huber four-circle
diffractometer coupled to a Siemens CCD area detector. In both
cases graphite-monochromated Mo KR radiation (λ ) 0.71073
Å) was used. All structures were solved by direct methods
(9) Cui, C.; Roesky, H. W.; Hao, H.; Schmidt, H.-G.; Noltemeyer,
M. Angew. Chem. 2000, 112, 1885-1887; Angew. Chem., Int. Ed. 2000,
39, 1815-1817.

6422 Organometallics, Vol. 24, No. 26, 2005
Table 1. Crystallographic Data for Compounds 1‚Et2O, 2‚PhMe, 3‚PhMe, and 4‚PhMe
Zhu et al.
1‚Et2O
2‚PhMe
3‚PhMe
4‚PhMe
formula
fw
C
53H81AlN6O
C72H79AlN6Si2
1111.57
C
73H108Al2N18Si2
C48H68AlN3
845.22
1347.91
714.03
temp (K)
cryst syst
space group
a (Å)
133(2)
orthorhombic
Pbca
17.413(1)
21.173(1)
26.774(1)
133(2)
133(2)
200(2)
monoclinic
P2(1)/n
14.476(3)
22.773(5)
18.766(4)
triclinic
triclinic
P1h
P1h
12.923(1)
16.568(1)
19.751(1)
102.65(1)
99.84(1)
10.071(2)
11.630(2)
19.851(4)
91.56(3)
90.86(3)
110.81(3)
2172(1)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
93.20(3)
99.24(1)
9871(1)
6177(2)
3978(1)
Z
8
4
2
2
Fc (Mg/m3)
1.137
1.195
1.125
1.427
µ (mm-1
F(000)
)
0.084
0.119
0.118
0.110
3696
2376
1452
1020
θ range (deg)
1.52-25.01
-20 e h e 20
-23 e k e 25
-30 e l e 31
91 750
1.41-24.99
-17 e h e 16
-25 e k e 26
-22 e l e 22
62 011
1.76-25.17
-12 e h e 15
-19 e k e 19
-23 e l e 23
40 310
3.52-22.47
-10 e h e 10
-12 e k e 12
-21 e l e 21
9308
index ranges
no. of reflns collected
no. of indep reflns (Rint
)
8688 (0.0571)
8688/0/562
1.036
0.0418, 0.1057
0.0586, 0.1124
0.203/-0.265
10 804 (0.0903)
10 804/0/735
1.025
0.0480, 0.1183
0.0608, 0.1258
0.491/-0.413
13 529 (0.0561)
13 529/1/853
1.082
0.0629, 0.1770
0.0837, 0.1925
1.177/-0.845
5648 (0.0761)
5648/0/488
1.015
0.0495, 0.1318
0.0615, 0.1464
0.258/-0.234
no. of data/restraints/params
GoF/F2
R1,a wR2b (I > 2σ(I ))
R1,a wR2b (all data)
largest diff peak/hole (e‚Å-3
)
2
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo - Fc )2/∑w(Fo2)]1/2
.
Scheme 1
(SHELXS-96)10 and refined against F2 using SHELXL-97.11 All
non-hydrogen atoms were located by difference Fourier syn-
thesis and refined anisotropically except for those of toluene
molecules in 2‚PhMe and 3‚PhMe, which were refined isotro-
pically using a part treatment (the PhMe molecule was located
in two positions with the respective 0.50 occupation) for 2‚
PhMe and a rigid model of benzene and distance restraints
treatment for 3‚PhMe. Thus, the residual electronic density
of the difference Fourier synthesis in 3‚PhMe is somewhat high
(1.177 e‚Å-3). We were not able to improve this value by the
collection of the reflection data on another diffractometer. All
hydrogen atoms were included using the riding model with
Uiso tied to the Uiso of the parent atoms, except for the Al-H
hydrogen in 4, which was located by difference Fourier
synthesis and refined isotropically. A summary of cell param-
eters, data collection, and structure solution and refinement
is given in Table 1.
Scheme 2
Results and Discussion
Reactions of LAl with RN3 (R ) C10H15 (adaman-
tyl), Ph3Si) and tBuSi(N3)3. The reaction of LAl with
2 equiv of bulky azide and RN3 in toluene in the
temperature range -50 to 25 °C resulted in the forma-
tion of the five-membered-ring compound LAl[(NR)2N2]
(R ) C10H15 (1), Ph3Si (2)), a result similar to that in
the previously reported reaction of LAl with the less
bulky Me3SiN3.5 Treatment of such a mixture in 1:1
molar ratio in a lower temperature range (-78 to 25
°C) in an attempt to isolate a LAlNR species was not
successful, and LAl[(NR)2N2] was always formed as the
only isolable product. This indicates that the steric bulk
of the C10H15 and Ph3Si substituents is still not suf-
ficient enough to stabilize the LAlNR monomer; instead,
such AldN multiple bonded species further react under
[2 + 3] cycloaddition with another molecule of the azide
(Scheme 1). Undoubtedly, in view of our work in this
field,5-7 the alternation of the bulky azide further
evidences the high reactivity of the AldN multiple
bonded species despite the steric bulk of the substitu-
ents at both Al and N atoms. Further exploration of the
reaction of LAl with tBuSi(N3)3 interestingly led under
similar conditions to LAl(N3)N[µ-Si(N3)(tBu)]2NAl(N3)L
(3). This result is completely different from the previ-
ously reported ones.2-6 Here we were able to deduce that
the formation of 3 may proceed through the initial N2
elimination to yield the AldN multiple bonded inter-
mediate A. A further rearranges under migration of one
N3 group from the Si to the Al atom to form the NdSi
species B. Finally B reacts in a [2 + 2] cycloaddition to
yield 3 (Scheme 2). Obviously, the high reactivity of A
initiates this intramolecular N3 migration. Moreover,
the chelating character and the bulk of L at Al compared
to those of the N3 and tBu groups at N may be
(10) Sheldrick, G. M. SHELXS-90, Program for Structure Solution.
Acta Crystallogr., Sect. A 1990, 46, 467-473.
(11) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.

Monomeric Aluminum Hydride Amide
Organometallics, Vol. 24, No. 26, 2005 6423
Figure 1. Molecular structure of 1. Thermal ellipsoids are
drawn at the 50% level, and hydrogen atoms are omitted
for clarity.
Figure 2. Molecular structure of 2. Thermal ellipsoids are
drawn at the 50% level, and hydrogen atoms are omitted
for clarity.
responsible for the different reaction products. This
proposed rearrangement can be compared to the result
reported on the 1,3-dipolar addition of Me3SiN3 to the
GadN multiple bonded intermediate.4 Compounds con-
taining the NdSi double bond are known,12 and [2 + 2]
cycloaddition reactions of these systems have been well
documented.13
Compounds 1 and 2 were obtained in high yield as a
yellowish crystalline solid and colorless crystals, respec-
tively. The latter crystallized with a toluene molecule.
1 has a high melting point (384 °C), and EI-MS indicates
the highest peak for the molecular ion. In contrast, 2
melts at 220 °C, and the most intense peak in the EI-
MS of 2 was observed corresponding to the LAlNSiPh3
fragment without any other related ions indicative of
the composition of 2 in the gas phase.
The single-crystal X-ray diffraction studies clearly
reveal that 1 and 2 both have an AlN4 five-membered-
ring structure. The molecular structures of 1 and 2 are
shown in Figures 1 and 2. Selected bond lengths and
angles are listed in Table 2. In the structures of 1 and
2, the Al center is involved as part of two fused rings
(AlC3N2 and AlN4) that are in almost orthogonal array
(dihedral angle: 90.6° 1; 87.1° 2). The AlN4 ring exhibits
a perfect plane (least-squares plane ∆ ) 0.0069 Å 1;
0.0188 Å 2). The corresponding parameters within this
plane (Al-N: 1.818(1), 1.854(1) Å 1; 1.842(2), 1.871(2)
Å 2; N-N: 1.390(2), 1.272(2), 1.391(2) Å 1; 1.412(2),
1.259(2), 1.427(2) Å 2) indicate that the AlN4 ring in 1
is more densely packed than that in 2. This may give
rise to the difference of the above-mentioned physical
properties between 1 and 2. The Al-N bond lengths
within the AlN4 ring are a little shorter compared to
that in the AlNC2 ring (1.876(2) Å), which is formed by
[2 + 2] cycloaddition of an AldN and the CdC bond of
a phenyl ring.6
Figure 3. Molecular structure of 3. Thermal ellipsoids are
drawn at the 40% level, and hydrogen atoms are omitted
for clarity.
Table 2. Selected Bond Distances (Å) and Angles
(deg) for 1‚Et2O and 2‚PhMe
1‚Et2O 2‚PhMe
1‚Et2O
2‚PhMe
Al(1)-N(1) 1.907(1) 1.892(2) N(1)-Al(1)-N(2) 95.38(5) 96.99(7)
Al(1)-N(2) 1.895(1) 1.896(2) N(3)-Al(1)-N(6) 85.08(5) 87.38(8)
Al(1)-N(3) 1.818(1) 1.871(2) Al(1)-N(6)-N(5) 110.96(9) 108.94(12)
Al(1)-N(6) 1.854(1) 1.842(2) N(6)-N(5)-N(4) 115.99(12) 117.51(15)
N(3)-N(4) 1.391(2) 1.412(2) N(5)-N(4)-N(3) 115.63(11) 117.22(16)
N(4)-N(5) 1.272(2) 1.259(2) N(4)-N(3)-Al(1) 112.31(9) 108.77(12)
N(5)-N(6) 1.390(2) 1.427(2)
in n-hexane. It has a high melting point (320 °C). EI-
MS data (m/z (%): 1255 (30, [M+]), 1198 (100, [M+
-
tBu])) are consistent with the formulation of 3, which
was unambiguously established by single-crystal X-ray
diffraction. This indicates a thermal stability of 3,
although this compound contains four N3 groups.
Compound 3 crystallizes with two half toluene mol-
ecules in space group P1h. The molecular structure of 3
is shown in Figure 3. Selected bond lengths and angles
are listed in Table 3. In the structure of 3, each Al atom
is coordinated by the chelating â-diketiminato L and one
N3 group and one N atom from the Si2N2 ring and
appears in a distorted tetrahedral geometry. The central
Si2N2 ring is formed in an approximate square (Si-N:
Compound 3 is a colorless crystalline solid that has a
good solubility in toluene and benzene but a poor one
(12) Power, P. P. Chem. Rev. 1999, 99, 3463-3503, and references
therein.
(13) (a) Walter, S.; Klingebiel, U. Coord. Chem. Rev. 1994, 130, 481-
508, and references therein. (b) Hemme, I.; Klingebiel, U. Adv.
Organomet. Chem. 1996, 39, 159-192, and references therein. (c) Xiao,
Y.; Son, D. Y. Organometallics 2004, 23, 4438-4443.

6424 Organometallics, Vol. 24, No. 26, 2005
Zhu et al.
a variety of products. One of the classic routes,17 the
reaction of group 13 metal hydride and/or alkyl (R′MR2,
R ) organic group or H) with primary amine R′′NH2,
has been widely studied. Work in this field has been
extensively reported by No¨th,18 Power,19 Roesky,20 and
Schulz.21 In these reactions, the [R′MR(NHR′′)]m is
thought to be an intermediate in the formation of the
corresponding metal imide [R′MNR′′]n (m, n g 2) with
regard to the stepwise elimination of H2 or alkane,
whereas the orthometalation in some cases is observed
resulting in C-H activated derivatives.19a,b However,
[R′MR(NHR′′)]m is thermally unstable. Studies on these
systems have shown that its stability is strongly influ-
enced by the steric bulk of R′ and R′′ at both M and N
atoms, especially in the case of R ) H.17 [R2Al(NHtBu)]2
(R ) H or D) is stable only at room temperature.18
[Mes*AlH(µ-NHR*)]2 containing bulky substituents R*
) CH2Mes, SiPh3, Mes ) 2,4,6-Me3C6H2, and Mes* )
2,4,6-tBu3C6H2 decomposes in the range 125 to 200 °C
to the corresponding aluminum imides.19d Recent stud-
ies on the reaction of Me3N‚AlH3 and ArNH2 indicate
that the Me3N‚AlH(NHAr)2 intermediate gives under
reflux in pentane [ArHNAl(H)-µ-NHAr]2 and Me3N‚Al-
(NHAr)3, respectively.21 Nonetheless, there are only a
few of such compounds known, and they are only
sparingly studied by X-ray structural analysis.22 Herein
we show the preparation and structural characterization
of the monomeric compound LAlH(NHAr) (4) derived
from a solvent-free reaction of LAlH2 and ArNH2.
A mixture of LAlH2 and 1 equiv of ArNH2 in the
absence of solvent was treated at elevated temperature
(150 °C) until H2 evolution ceased. This reaction smoothly
afforded a monomeric aluminum hydride amide, LAlH-
(NHAr) (4), as a light yellow crystalline solid in almost
quantitative yield (>95%) (eq 1).
Table 3. Selected Bond Distances (Å) and Angles
(deg) for 3‚PhMe
Al(1)-N(1)
Al(1)-N(3)
N(6)-Si(1)
Si(1)-N(7)
Al(2)-N(7)
Al(2)-N(14)
N(3)-N(4)
N(8)-N(9)
N(11)-N(12)
N(16)-N(17)
1.912(3)
1.839(3)
1.748(2)
1.737(2)
1.812(2)
1.902(3)
1.190(4)
1.227(4)
1.223(4)
1.207(4)
Al(1)-N(2)
Al(1)-N(6)
N(6)-Si(2)
Si(2)-N(7)
Al(2)-N(16)
Al(2)-N(15)
N(4)-N(5)
N(9)-N(10)
N(12)-N(13)
N(17)-N(18)
1.909(3)
1.808(2)
1.734(2)
1.749(2)
1.851(3)
1.921(3)
1.150(4)
1.139(4)
1.140(4)
1.151(4)
N(1)-Al(1)-N(2)
Si(1)-N(6)-Si(2)
Si(1)-N(7)-Si(2)
97.07(11) N(3)-Al(1)-N(6)
88.37(11) N(6)-Si(1)-N(7)
88.22(11) N(6)-Si(2)-N(7)
101.16(12)
91.66(12)
91.72(11)
N(7)-Al(2)-N(16) 102.90(11) N(14)-Al(2)-N(15) 97.55(11)
N(3)-N(4)-N(5) 176.0(3) N(8)-N(9)-N(10) 174.6(4)
N(11)-N(12)-N(13) 174.6(4) N(16)-N(17)-N(18) 176.7(3)
1.734(2),1.737(2),1.748(2),1.749(2)Å;N-Si-N: 91.66(12),
91.72(11)°; Si-N-Si: 88.37(11), 88.22(11)°; ∆ ) 0.0101
Å). A notable feature is that the two tBu groups bound
to Si atoms are arranged on one side of the Si2N2 ring,
whereas the N3 groups are located on the opposite side
of the ring. This structural character is hardly observed
among the known Si2N2 ring compounds13 and gives rise
to the two LAl moieties bonded to the respective N atom
also in a position syn to the Si2N2 ring due to the steric
effect caused by the two tBu groups, whereas the two
N3 groups at the respective Al center are arranged in
trans position. The Al-N bond lengths range from
1.808(2) to 1.921(3) Å (Al-Nâ-diketiminato ) 1.902(3)-
1.921(3) Å; Al-NN3 ) 1.839(3)-1.851(3) Å; Al-NSi2N2
) 1.808(2)-1.812(2) Å). The Al-Nâ-diketiminato bond
lengths are close to those in 1 and 2 (1.895(1)-1.907(1)
Å), and the Al-NN3 bond distances are a little shorter
than those terminal ones in R2AlN3 (R ) 2-(Me2NCH2)-
C6H4, 1.864(6) Å; (CH2)3NMe2, 1.897(2) Å)14 and Me2-
Al(N3)NH2tBu (1.901(1) Å).15 The Al-NSi2N2 bond lengths
compare well with those in Cp*{(Me3Si)2N}AlN(µ-AlCp*)-
(µ-Al{N(SiMe3)2})NAlCp*2 (1.781-1.819 Å).3 The N-N
bond lengths (1.139(4)-1.227(4) Å) and N-N-N angles
(174.6(4)-176.7(3)°) of the N3 groups are consistent with
those in the literature.14,15 The IR spectrum confirms
the characteristic frequencies of the terminal N3 groups
(2113, 2076 cm-1).
Compound 4 is soluble in aromatic solvents, but
sparingly soluble in such hydrocarbons as n-pentane
and n-hexane. It melts at 134 °C. The most intense peak
in the EI-MS of 4 appeared at m/z 578 [M+ - iPr], and
the signal at m/z 621 (22%) was assigned to the
molecular ion [M+]. In the 1H NMR spectrum, a singlet
at 3.01 ppm corresponds to the N-H proton resonance
Solvent-Free Reaction of LAlH2 with ArNH2.
Among the syntheses of heavier group 13 imido com-
pounds, the reaction of monovalent group 13 metal
species with organic azides can be considered as a direct
synthetic route under the elimination of N2,16 although
the high reactivity of such monomeric species can cause
(14) Mu¨ller, J.; Fischer, R. A.; Sussek, H.; Pilgram, P.; Wang, R.;
Pritzkow, H.; Herdtweck, E. Organometallics 1998, 17, 161-166.
(15) Fischer, R. A.; Miehr, A.; Sussek, H.; Pritzkow, H.; Herdtweck,
E.; Mu¨ller, J.; Ambacher, O.; Metzger, T. J. Chem. Soc., Chem.
Commun. 1996, 2685-2686.
(17) Cesari, M.; Cucinella, S. In The Chemistry of Inorganic Homo-
and Heterocycles; Haiduc, I., Sowerby, D. B., Eds.; Academic Press:
New York, 1982; Vol. 1, Chapter 6, pp 167-190.
(18) No¨th, H.; Wolfgardt, P. Z. Naturforsch. B 1976, 31, 697-708.
(19) Selected examples: (a) Waggoner, K. M.; Power, P. P. J. Am.
Chem. Soc. 1991, 113, 3385-3393. (b) Wehmschulte, R. J.; Power, P.
P. J. Am. Chem. Soc. 1996, 118, 791-797. (c) Wehmschulte, R. J.;
Power, P. P. Inorg. Chem. 1998, 37, 2106-2109. (d) Wehmschulte, R.
J.; Power, P. P. Inorg. Chem. 1998, 37, 6906-6911. (e) Wehmschulte,
R. J.; Power, P. P. Polyhedron 2000, 19, 1649-1661.
(16) In organometallic chemistry, azides are commonly used as
precursor for nitrene in the synthesis of transition metal imido
complexes. Selected examples: (a) Nugent, W. A.; Meyer, J. M. Metal-
Ligand Multiple Bonds; John Wiley and Sons: New York, 1988. (b)
Parkin, G.; van Asselt, A.; Leahy, D. J.; Whinnery, L.; Hua, N. G.;
Quan, R. W.; Henling, L. M.; Schaefer, W. P.; Santarsiero, B. D.;
Bercaw, J. E. Inorg. Chem. 1992, 31, 82-85. (c) Proulx, G.; Bergman,
R. G. J. Am. Chem. Soc. 1995, 117, 6382-6383. (d) Fickes, M. C.; Davis,
W. M.; Cummins, C. C. J. Am. Chem. Soc. 1995, 117, 6384-6385. (e)
Proulx, G.; Bergman, R. G. Organometallics 1996, 15, 684-692. (f)
Hanna, T. A.; Baranger, A. M.; Bergman, R. G. Angew. Chem. 1996,
108, 693-696; Angew. Chem., Int. Ed. Engl. 1996, 35, 653-655. (g)
Gavenonis, J.; Tilley, T. D. J. Am. Chem. Soc. 2002, 124, 8536-8537.
(h) Gavenonis, J.; Tilley, T. D. Organometallics 2002, 21, 5549-5563.
(20) (a) Belgardt, T.; Waezsada, S. D.; Roesky, H. W.; Gornitzka,
H.; Ha¨ming, L.; Stalke, D. Inorg. Chem. 1994, 33, 6247-6251. (b)
Belgardt, T.; Storre, J.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-
G. Inorg. Chem. 1995, 34, 3821-3822. (c) Belgardt, T.; Storre, J.;
Klemp, A.; Gornitzka, H.; Ha¨ming, L.; Schmidt, H.-G.; Roesky, H. W.
J. Chem. Soc., Dalton Trans. 1995, 3747-3751.
(21) Bauer, T.; Schulz, S.; Hupfer, H.; Nieger, M. Organometallics
2002, 21, 2931-2939.

Monomeric Aluminum Hydride Amide
Organometallics, Vol. 24, No. 26, 2005 6425
1.37-1.75 Å observed for terminal aluminum hy-
drides.21-23 The Al-NNHAr bond length (1.817(2) Å) is
shorter than those of Al-Nâ-diketiminato bonds (1.905-
(2), 1.922(2) Å). The Al-H and N-H bonds are nearly
arranged in trans position to the Al-NNHAr bond.
Compound 4 contains the Al-H and N-H functional-
ities, which are commonly thought to be highly reactive.
Therefore, 4 was further treated at higher temperatures
(150-290 °C) for 5 h; however, no H2 gas evolution was
1
observed. The melting point and spectroscopic (IR, H
NMR) measurements indicated that, during the heating,
compound 4 did not change its composition.
Conclusion
In summary, LAl reacts with bulky azide RN3 to yield
the five-membered ring compound LAl[(NR)2N2] (R )
C10H15 (1), Ph3Si (2)), while with tBuSi(N3)3 LAl(N3)N-
[µ-Si(N3)(tBu)]2NAl(N3)L (3) is formed. The former ap-
pears to proceed by a [2 + 3] cycloaddition of a reactive
LAldNR species and an azide molecule, although the
L and R substituents are rather bulky. The latter may
occur with a further rearrangement of LAldNSi(tBu)-
(N3)2 (A) to LAl(N3)NdSi(tBu)(N3) (B) and finally is
completed by [2 + 2] cycloaddition. The steric demand
of the â-diketiminato ligand L at Al and the R group at
N hinders the oligomerization of the AldN intermedi-
ates; however, the AldN system is reactive enough to
allow the cyclic addition, the N3 migration, or the C-H
activation. In some cases this is influenced by the
reaction temperature.6 In contrast, the reaction of LAlH2
with ArNH2 yields only the monomeric aluminum
hydride amide LAlH(NHAr) (4). Further condensation
of 4 at elevated temperatures was not observed.
Figure 4. Molecular structure of 4. Thermal ellipsoids are
drawn at the 40% level, and hydrogen atoms of the L ligand
and Ar group are omitted for clarity.
Table 4. Selected Bond Distances (Å) and Angles
(deg) for 4‚PhMe
Al(1)-N(1)
1.905(2)
1.817(2)
95.57(8)
Al(1)-N(2)
1.922(2)
1.482
119.1
Al(1)-N(3)
Al(1)-H(1)
N(1)-Al(1)-N(2)
N(3)-Al(1)-H(1)
and one broad resonance centered at 5.50 ppm to the
Al-H proton, characteristic for amidoaluminum hy-
drides.22a The IR spectrum clearly shows the respective
N-H (3358 cm-1) and Al-H (1821 cm-1) absorption
bands.
The structural analysis revealed 4 as monomeric with
the coordination of the aluminum center completed by
the chelating â-diketiminato ligand, one NHAr group,
and one H atom in a distorted tetrahedral geometry.
The molecular structure of 4 is shown in Figure 4.
Selected bond lengths and angles are listed in Table 4.
The Al-H bond length (1.482 Å) is located in the range
Acknowledgment. We are grateful for financial
support of the Go¨ttinger Akademie der Wissenschaften.
Supporting Information Available: CIF files for com-
pounds 1‚Et2O, 2‚PhMe, 3‚PhMe, and 4‚PhMe are available
free of charge via the Internet at http://pubs.acs.org.
OM050698V
(22) Compounds of the type EHAlNHR (E ) Cl, H) are structurally
characterized in the form of intramolecular stabilized heterocycles. (a)
Atwood, J. L.; Lawrence, S. M.; Raston, C. L. J. Chem. Soc., Chem.
Commun. 1994, 73-74. (b) Gardiner, M. G.; Lawrence, S. M.; Raston,
C. L. Inorg. Chem. 1995, 34, 4652-4659. (c) Gardiner, M. G.; Lawrence,
S. M.; Raston, C. L. Inorg. Chem. 1996, 35, 1349-1354. Me3N‚AlH-
(NHAr)2, [ArHNAlH(µ-NHAr)]2, and ArHNAlH(µ-NHAr)(µ-NAr)AlH-
(NMe2Et) are reported as monomeric and dimeric, respectively: see
ref 21.
(23) Selected examples: (a) Linti, G.; No¨th, H.; Rahm, P. Z.
Naturforsch. B 1988, 43, 1101-1112. (b) Cowley, A. H.; Isom, H. S.;
Decke, A. Organometallics 1995, 14, 2589-2592. (c) Gardiner, M. G.;
Lawrence, S. M.; Raston, C. L. J. Chem. Soc., Dalton Trans. 1996,
4163-4169. (d) Wehmschulte, R. J.; Power, P. P. Inorg. Chem. 1996,
35, 3262-3267. (e) Zhu, H.; Chai, J.; Roesky, H. W.; Noltemeyer, M.;
Schmidt, H.-G.; Vidovic, D.; Magull, J. Eur. J. Inorg. Chem. 2003,
3113-3119.