Reactions between base-stabilized AlH3 and diisopropylphenylamine: Syntheses and X-ray structures of amino- and iminoalanes

Article abstract of DOI:10.1021/om020080a

Reactions between amine-stabilized H₃Al (amine = NMe₃, NMe₂Et) and DippNH₂ (Dipp = 2,6-(i-Pr)₂C₆H₃) were studied at different reaction temperatures and in different molar ratios.

Full text of DOI:10.1021/om020080a

Organometallics 2002, 21, 2931-2939
2931
Rea ction s betw een Ba se-Sta bilized AlH3 a n d
Diisop r op ylp h en yla m in e: Syn th eses a n d X-r a y
Str u ctu r es of Am in o- a n d Im in oa la n es
Tillmann Bauer, Stephan Schulz,* Heike Hupfer, and Martin Nieger
Institut fu¨r Anorganische Chemie der Universita¨t Bonn, Gerhard-Domagk-Strasse 1,
D-53121 Bonn, Germany
Received J anuary 31, 2002
Reactions between amine-stabilized H3Al (amine ) NMe3, NMe2Et) and DippNH2 (Dipp
) 2,6-(i-Pr)2C6H3) were studied at different reaction temperatures and in different molar
ratios. Lewis base stabilized heterocyclic iminoalanes [base‚HAlNDipp]2 (base ) NMe3 (1),
NMe2Et (7)), monomeric aminoalanes Me3N‚(H3-x)Al(N(H)Dipp)x (x ) 2 (2), 3 (4)) and base-
free, heterocyclic aminoalanes [Dipp(H)NAl(H)-µ-N(H)Dipp]2 (3), respectively, were obtained
in high yields. The NMe3 group of 2 can be thermally removed, yielding a mixture of 3 and
4, while that of 4 can be replaced by 4-(dimethylamino)pyridine (dmap), giving dmap‚Al-
(N(H)Dipp)3 (5). In addition, Li(OEt2)Al[N(H)Dipp]4 (6) and the amine-stabilized heterocycle
DippN(H)Al(H)N(Dipp)AlH(NMe2Et)N(H)Dipp (8) were synthesized. The new compounds
1-8 were fully characterized by IR, mass, and multinuclear NMR spectroscopy (1H, 13C);
2-4, 6, and 8 were also characterized by single-crystal X-ray structure analyses.
Sch em e 1. In itia l Stu d ies by Wiber g et a l. on th e
Rea ction of AlH3 a n d NH3
In tr od u ction
Since the first synthesis of H3Al‚NMe3 by Stecher and
Wiberg in 1942,1 tertiary amine-alane adducts of the
type H3Al‚NR3 have been studied in detail for more than
half a century due to their fascinating structural
chemistry2 and their versatility in organic and inorganic
syntheses.3 More recently, their potential to serve as
molecular precursors (single-source precursors) for the
synthesis of a variety of solid-state materials was
demonstrated, restimulating fundamental research on
this class of compounds.4 Several alanes such as H3Al‚
NMe3, H3Al‚NMe2Et, H3Al‚NEt3, H3Al‚(NMe3)2, H3Al‚
TMEDA, and Me2AlH‚NMe2Et were shown to be prom-
ising candidates for the deposition of Al films and of
various III-V material films by MOCVD technology
(metalloorganic chemical vapor deposition).5 However,
the utility of amine-alane adducts in materials science
also was initially studied by Wiberg et al. They inves-
tigated in detail the equimolar reaction of AlH3 and
NH3, demonstrating the complete range of amine-alane
chemistry. First, the simple Lewis acid-base adduct
H3Al‚NH3 is formed, which is only stable at low tem-
perature (-80 °C). Raising the temperature subse-
quently leads to H2 elimination reactions, resulting in
the stepwise formation first of the aminoalane [H2-
AlNH2]x and, at higher temperatures, of the iminoalane
[HAlNH]x. At 150 °C, the reaction finally gives alumi-
num nitride, AlN.6 The reaction of AlH3 with an excess
of NH3 results in the formation of Al(NH2)3,7 which also
can be thermally converted into AlN (Scheme 1).
Unfortunately, the solid-state structures of the oli-
gomeric amino- and iminoalane as well as of Al(NH2)3
remained unknown, due to their unsatisfactory crys-
tallizing properties and their tendency to undergo
consecutive H2 or NH3 elimination reactions. Therefore,
reactions of base-stabilized AlH3 with secondary amines
R2NH were studied in detail in order to obtain struc-
tural information on as-prepared oligomeric amino-
alanes. The reaction temperature, the stoichiometry of
the reactants, and the steric demand of the substituents
bound to N were found to play key roles in what degree
of oligomerization was attained. Monomeric aminoalanes
* To whom correspondence should be addressed. Fax: + 49 228-
735327. E-mail: sschulz@uni-bonn.de.
(1) (a) Stecher, O.; Wiberg, E. Ber. Dtsch. Chem. Ges. 1942, 75, 2003.
(b) Wiberg, E.; Amberger, E. Hydrides of the Elements of Main Groups
I -IV; Elsevier: Amsterdam, 1971.
(2) (a) J ones, C.; Koutsantonis, G. A.; Raston, C. L. Polyhedron 1993,
12, 1829. (b) Gardiner, M. G.; Raston, C. L. Coord. Chem. Rev. 1997,
166, 1. (c) Downs, A. J . Coord. Chem. Rev. 1999, 189, 59. (d) Aldridge,
S.; Downs, A. J . Chem. Rev. 2001, 101, 3305.
8
9
of the type base‚Al(H)2NR2 and Al(NR2)3 ), as well as
(3) Hudlicky, M. In Reductions in Organic Chemistry, 2nd ed.;
American Chemical Society: Washington, DC, 1996.
(4) For a recent review see, for example: J egier, J . A.; Gladfelter,
W. L. Coord. Chem. Rev. 2000, 206-207, 631.
(5) (a) Gladfelter, W. L.; Boyd, D. C.; J ensen, K. F. Chem. Mater.
1989, 1, 339. (b) Wee, A. T. S.; Murell, A. J .; Singh, N. K.; O’Hare, D.;
Ford, J . S. J . Chem. Soc., Chem. Commun. 1990, 11. (c) Baum, T. H.;
Larson, C. E.; J ackson, R. L. Appl. Phys. Lett. 1989, 55, 1264.
(6) Wiberg, E.; May, A. Z. Naturforsch., B 1955, 10, 229.
(7) Wiberg, E.; May, A. Z. Naturforsch., B 1955, 10, 231.
(8) (a) Atwood, J . L.; Kousantonis, G. A.; Lee, F.-C.; Raston, C. L.
J . Chem. Soc., Chem. Commun. 1994, 91. (b) Gardiner, M. G.;
Lawrence, S. M.; Raston, C. L. Inorg. Chem. 1995, 34, 4652. (c) Dias,
H. V. R.; J in, W.; Ratcliff, R. E. Inorg. Chem. 1995, 34, 6100. (d)
Gardiner, M. G.; Lawrence, S. M.; Raston, C. L. Inorg. Chem. 1996,
35, 1349.
10.1021/om020080a CCC: $22.00 © 2002 American Chemical Society
Publication on Web 06/11/2002

2932 Organometallics, Vol. 21, No. 14, 2002
Bauer et al.
oligomeric aminoalanes such as [H2AlNR2]x,10 [HAl-
(NR2)2]x,11 and [Al(NR2)3]2,12 were obtained, mainly in
the form of four- and six-membered heterocycles.13 In
contrast, equimolar reactions of H3Al‚NR3 with primary
amines RNH2 preferentially yielded iminoalanes [HAl-
NR]x or mixed imino- and aminoalanes rather than
aminoalanes [H2AlN(H)R]x, depending on their instabil-
ity toward further H2 elimination reactions. Several
Al-N cages (x ) 4, 6-8) were structurally character-
ized,14 clearly showing the influence of the steric
demand of the substituents on the degree of oligomer-
ization. In contrast, monomeric compounds have been
synthesized to a far lesser extent. Monomeric imino-
alanes of the type HAlNR are completely unknown,15
while aminoalanes of the type H2AlN(H)R are only
known in the form of intramolecular stabilized hetero-
cycles.8b,d In addition, the monomeric bis- and tris-
(amino)alanes HAl[N(H)R]2 and Al[N(H)R]3 also have
not been structurally characterized, to date.16 Several
attempts to prepare them have been made, but reactions
of AlCl3 with LiNHR (R ) Dipp, tBu) yielded monomeric
Li aluminates of the type LiAl[N(H)R]4,17 and reactions
of LiAlH4 with DippNH2 gave heterocyclic compounds.18
We became interested in monomeric compounds of
the types mentioned above not only because of their
underexplored structural chemistry but also due to
the fact that monomeric compounds usually show
higher volatilities compared to heterocyclic or cage
compounds. This, of course, is of fundamental impor-
tance for potential applications of such compounds
in CVD processes. In addition, carbon contamination of
the resulting material generally can be reduced by use
of H-substituted precursors, as was shown in different
studies.
The most common pathway for the preparation of
monomeric aminoalanes makes use of very bulky sub-
stituents such as Mes* and Dipp (Mes* ) 2,4,6-(t-
Bu)3C6H2, Dipp ) 2,6-(i-Pr)2C6H3), leading to the for-
mation of kinetically stabilized moieties.19 More recently,
we have shown that monomeric group 13/15 compounds
also can be electronically stabilized. The heterocycles
[R2MER′2]x (M ) Al, Ga; E ) P, As, Sb, Bi), which may
be described as head-to-tail adducts, generally can be
converted into their monomeric form by addition of a
Lewis base, which coordinates to the group 13 metal.20
Combining these two general pathways, we became
interested in the reaction of amine-stabilized AlH3 with
DippNH2, which contains the bulky Dipp group, in order
to synthesize monomeric amine-stabilized amino- and
iminoalanes containing both Al-H and N-H function-
alities.
(9) (a) Brothers, P. J .; Wehmschulte, R. J .; Olmstead, M. M.;
Ruhlandt-Senge, K.; Parkin, S. R.; Power, P. P. Organometallics 1994,
13, 2792. (b) Sheldrick, G. M.; Sheldrick, W. S. J . Chem. Soc. A 1969,
2279.
(10) (a) Downs, A. J .; Duckworth, D.; Machell, J . C.; Pulham, C. R.
Polyhedron 1992, 11, 1295. (b) Dumichen, U.; Gelbrich, V.; Sieler, J .
Z. Anorg. Allg. Chem. 1999, 625, 262. (c) Kuhn, N.; Fuchs, S.;
Steimann, M. Z. Anorg. Allg. Chem. 2000, 626, 1387. (d) Hair, G. S.;
Battle, S. L.; Decken, A.; Cowley, A. H.; J ones, R. A. Inorg. Chem. 2000,
39, 27. (e) Klein, C.; No¨th, H.; Tacke, M.; Thomann, M. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 886. (f) Bensiek, S.; Bangel, M.; Neumann, B.;
Stammler, H.-G.; J utzi, P. Organometallics 2000, 19, 1292. (g) Atwood,
J . L.; Lawrence, S. M.; Raston, C. L. J . Chem. Soc., Chem. Commun.
1994, 73.
We report here reactions of AlH3‚NMe3 and AlH3‚
NMe2Et with DippNH2, leading to several new amino-
and iminoalanes, which were obtained either as hetero-
cycles or Lewis base stabilized monomers. The products
were investigated in detail by elemental analyses, IR,
mass, and multinuclear NMR spectroscopy (1H, 13C); five
compounds were also characterized by single-crystal
X-ray diffraction.
(11) (a) Ouzounis, K.; Riffel, H.; Hess, H.; Kohler, U.; Weidlein, J .
Z. Anorg. Allg. Chem. 1983, 504, 67. (b) Chang, C.-C.; Li, M.-D.; Chiang,
M. Y.; Peng, S.-M.; Wang, Y.; Lee, G.-H. Inorg. Chem. 1997, 36, 1955.
(c) J anik, J . F.; Wells, R. L.; Rheingold, A. L.; Guzei, I. A. Polyhedron
1998, 17, 4101.
Resu lts a n d Discu ssion
(12) Waggoner, K. M.; Olmstead, M. M.; Power, P. P. Polyhedron
1990, 9, 257.
Depending on the molar ratio of H3Al‚NMe3 and
DippNH2 and the reaction temperature, the hydridic H
atoms of AlH3 can be substituted by one, two, or three
amino groups (Scheme 2).
(13) For
a
recent review see for example: Chang, C.-C.;
Ameerunisha, M. S. Coord. Chem. Rev. 1999, 189, 199.
(14) (a) Veith, M. Chem. Rev. 1990, 90, 3. (b) Perego, G.; del Piero,
G.; Cesari, M.; Zazzetta, A.; Dozzi, G. J . Organomet. Chem. 1975, 87,
53. (c) del Piero, G.; Cesari, M.; Dozzi, G.; Mazzei, A. J . Organomet.
Chem. 1977, 129, 281. (d) Cesari, M.; Perego, G.; del Piero, G.;
Cucinella, S.; Cernia, E. J . Organomet. Chem. 1974, 78, 203. (e) del
Piero, G.; Perego, G.; Cucinella, S.; Cesari, M.; Mazzei, A. J . Organomet.
Chem. 1977, 136, 13. (f) Perego, G.; Dozzi, G. J . Organomet. Chem.
1981, 205, 21. (g) Perego, G.; Cesari, M.; del Piero, G.; Balducci, A.;
Cernia, E. J . Organomet. Chem. 1975, 87, 33. (h) del Piero, G.;
Cucinella, S.; Cesari, M. J . Organomet. Chem. 1979, 173, 263. (i)
Harlan, C. J .; Bott, S. G.; Barron, A. R. J . Chem. Soc., Dalton Trans.
1997, 637.
The equimolar reaction between H3Al‚NMe3 and
DippNH2 probably yielded first Me3N‚H2AlN(H)Dipp,21
which, however, could not be isolated due to its lability
toward a second H2-elimination reaction, subsequently
yielding the base-stabilized iminoalane [Me3N‚HAlN-
1
Dipp]2 (1). The H and 13C NMR spectra of 1 show two
sets of resonances due to the nonequivalent i-Pr groups
(15) The only monomeric iminoalane was recently synthesized by
reaction of a low-valent alane and a sterically encumbered azide:
Hardman, N. J .; Cui, C.; Roesky, H. W.; Fink, W. H.; Power, P. P.
Angew. Chem., Int. Ed. 2001, 40, 2172.
(16) Al[N(H)Mes*]3 (Silverman, J . S.; Carmalt, C. J .; Cowley, A. H.;
Culp, R. D.; J ones, R. A.; McBurnett, B. G. Inorg. Chem. 1999, 38,
296) and Al[N(H)t-Bu]3 (Brask, J . K.; Chivers, T.; Yap, G. P. A. Chem.
Commun. 1998, 2543) have been synthesized, but no structural details
are given in the original contribution. However, the severely disordered
structure of Al[N(H)t-Bu]3 cocrystallized with Li[Al(Nt-Bu)(NHt-Bu)2]2‚
(t-BuLi) was recently reported, showing Al[N(H)t-Bu]3 to form a dimer
in the solid state (Brask, J . K.; Chivers, T.; Schatte, G.; Yap, G. P. A.
Organometallics 2000, 19, 5683).
(17) (a) Silverman, J . S.; Carmalt, C. J .; Neumeyer, D. A.; Cowley,
A. H.; McBurnett, B. G.; Decken, A. Polyhedron 1998, 17, 977. (b)
Beswick, M. A.; Choi, N.; Harmer, C. N.; McPartlin, M.; Mosquera, M.
E. G.; Raithby, P. R.; Tombul, M.; Wright, D. S. Chem. Commun. 1998,
1383.
(18) Montero, M. L.; Wessel, H.; Roesky, H. W.; Teichert, M.; Uson,
I. Angew. Chem., Int. Ed. 1997, 36, 629.
(19) (a) Waggoner, K. M.; Ruhlandt-Senge, K.; Wehmschulte, R. J .;
He, X.; Olmstead, M. M.; Power, P. P. Inorg. Chem. 1993, 32, 2557.
(b) Wehmschulte, R. J .; Power, P. P. J . Am. Chem. Soc. 1996, 118,
791. (c) Li, X.-W.; Su, J .; Robinson, G. H. Chem. Commun. 1998, 1281.
(d) Rutherford, D.; Atwood, D. A. J . Am. Chem. Soc. 1996, 118, 11535.
For a recent review, see for example: Power, P. P. Chem. Rev. 1999,
99, 3463.
(20) (a) Schulz, S.; Nieger, M. Organometallics 2000, 19, 2640. (b)
Kuczkowski, A.; Thomas, F.; Schulz, S.; Nieger, M. Organometallics
2000, 19, 5758. (c) Thomas, F.; Schulz, S.; Nieger, M. Eur. J . Inorg.
Chem. 2001, 161.
(21) It should be noted that for the synthesis of all compounds
described in this contribution it is crucial to maintain the correct
stoichiometry between the reactants. This can be a problem due to
the tendency of H3Al‚NMe3 to decompose at elevated temperatures,
giving polymeric (AlH3)x. If such an impure H3Al‚NMe3 sample is used,
higher substituted compounds are formed due to an excess of DippNH2.
To avoid their formation, all reactions can be performed using a slight
excess (<10%) of H3Al‚NMe3.

Amino- and Iminoalanes
Organometallics, Vol. 21, No. 14, 2002 2933
Sch em e 2. Rea ction of H3Al‚NMe3 a n d Dip p NH2 in Differ en t Mola r Ra tios
of the Dipp ligands. The IR spectrum of 1 displays a
strong Al-H absorption band at 1799 cm-1, while no
N-H absorption band is detected. The EI mass spec-
trum does not show a molecular ion peak, but peaks
with low intensity due to [M+/2] and [M+/2 - NMe3] are
observed. In addition, a fragment peak (m/z 812)
indicates the presence of the heterocubane [HAlNDipp]4,
whose formation starting from 1 after loss of the NMe3
group followed by dimerization of the thus-formed base-
free iminoalane [HAlNDipp]2 seems reasonable.
Me3N-free Al-N compound was formed in low yield,
while no resonances due to 3 were observed. The
unknown Me3N-free compound might be the iminoalane
[HAlNDipp]4, whose formation in the gas phase was
shown in the mass spectra of 1 and 2. However, further
studies aimed at the isolation and identification of
this particular compound are needed. Since the syn-
thesis of 3 by heating 2 in pentane solution was
accompanied by the formation of 4, we were interested
in a more straightforward, byproduct-free synthesis and,
therefore, investigated the 2:1 molar reaction between
DippNH2 and H3Al‚NMe3 in more detail. Pure 3 was
obtained in high yield when the reaction was performed
at 25 °C in pentane, followed by storage of the resulting
solution at 0 °C. Obviously, the higher reaction tem-
perature favors the dissociation of (weakly bound)
NMe3, which agrees with what was observed when 2
was heated in refluxing pentane. The 1H NMR spectrum
of 3 obtained at ambient temperature shows resonances
due to N-H and Al-H groups. Broad resonances of the
bridging NHDipp groups point to exchange reactions
between the nonequivalent Me groups, which could be
resolved at lower temperature. At -30 °C two doublets
at 0.76 and 1.48 ppm and two septets were observed,
which coalesce at about 0 °C. Further heating to 60 °C
led to one well-resolved doublet and one septet. At this
temperature, the exchange reactions between the i-Pr
protons are fast on the NMR time scale. Comparable
findings were observed in temperature-dependent 13C
NMR spectra. Figure 1 displays the 1H NMR spectra
obtained between -30 and 60 °C.
Reaction of H3Al‚NMe3 and 2 equiv of DippNH2 was
accompanied by H2 elimination, resulting in the forma-
tion of the Lewis base stabilized bis(amino)alane NMe3‚
Al(H)[N(H)Dipp]2 (2). Its IR spectrum shows strong
N-H (3408, 3363 cm-1) and Al-H (1832 cm-1) absorp-
tion bands. The 1H NMR spectrum of 2 also displays
resonances due to N-H and Al-H groups. In addition,
resonances due to the Dipp protons and the NMe3 group
in a 2:1 molar ratio were detected, indicating the
stability of the Lewis base stabilized bis(amino)alane 2
in solution at ambient temperature. In contrast, its EI
mass spectrum does not show the molecular ion peak
due to consecutive reactions of 2 in the gas phase. In
an attempt to initiate the dissociation of NMe3, a
solution of 2 was heated in pentane at reflux for about
2 h. Evaporation of all volatiles in vacuo gave a colorless
solid, whose 1H NMR spectrum proved the complete
conversion of 2 into equal amounts of the base-free
heterocycle [Dipp(H)NAl(H)-µ-N(H)Dipp]2 (3) and the
base-stabilized tris(amino)alane Me3N‚Al[N(H)Dipp]3
(4). Pure 3 was obtained after recrystallization from
hexane at 0 °C. In contrast, heating 2 to 100 °C in the
absence of solvent for 1 h did not give 3. According to
1H NMR studies, 2 was quantitatively converted to the
iminoalane 1 and the tris(amino)alane 4. An additional
Reaction of 3 equiv of DippNH2 and H3Al‚NMe3
yielded the Me3N-stabilized tris(amino)alane Me3N‚Al-
[N(H)Dipp]3 (4), which was obtained as a colorless
crystalline solid after crystallization at -10 °C. Its IR

2934 Organometallics, Vol. 21, No. 14, 2002
Bauer et al.
Figu r e 2. Molecular structure and atom-numbering scheme
of compound 2. Thermal ellipsoids are drawn at the 50%
probability level. H atoms, except those attached to N and
Al, have been omitted for clarity. Selected bond lengths (Å)
and angles (deg): Al1-N101 ) 1.827(2), Al1-N201 )
1.833(2), Al1-N1 ) 2.019(2), Al1-H1 ) 1.501(12), N101-
H101 ) 0.847(14), N201-H201 ) 0.855(14); N101-Al1-
N201 ) 105.7(1), N101-Al1-N1 ) 104.6(1), N201-Al1-
N1 ) 101.7(1).
Al centers coordinated by one NMe3 group. This result
is interesting, in view of the fact that the degree of
oligomerization of iminoalanes [RAlNR′]x generally
depends on the steric bulk of the substituents: (small)
four-membered rings are usually formed with sterically
bulky ligands bound to both the Al and the N centers,
while use of smaller ligands generally results in the
formation of more highly associated cyclic (six-mem-
bered rings) or cage compounds (x g 4). In 1, only the
N centers are substituted by a bulky Dipp group, while
the Al centers each only carry a H atom. Clearly, the
coordination of NMe3 stabilizes the four-membered
heterocycle. The formation of 1 proves the principle of
electronic stabilization to be very powerful for the
synthesis of lower associated iminoalanes. In addition,
due to the use of one reactive ligand (H) and a coordi-
natively bound Lewis base, which might be eliminated
under specific conditions, electronically stabilized imi-
noalanes such as 1 promise to show a much higher
reactivity and potential for further synthetic studies
compared to kinetically stabilized iminoalanes contain-
ing very bulky substituents.
Colorless crystals of 2 suitable for an X-ray structure
analysis were obtained from hexane at 0 °C. Figure 2
shows its solid-state structure. Compound 2 crystallizes
in the triclinic space group P1h (No. 2). The central
skeleton of 2 is built by two N(H)Dipp groups and
one H atom bound to the Al center. Coordination of
the Lewis base NMe3 allows Al to reach the stable
coordination number 4. The Al-N σ-bonds are signifi-
cantly shorter (1.827(2), 1.833(2) Å) compared to the
Al-N dative bond (2.019(2) Å). However, they fall
within typical ranges for dative Al-N bonds and for
Al-N σ-bonds between 3-fold-coordinated N and 4-fold-
coordinated Al centers. Intermolecularly stabilized
[N-methyl-N′,N′′-bis(trimethylsilyl)diethylenetriamino]-
alane, [(Me3SiNCH2CH2)2NMe]AlH, also shows signifi-
cantly different Al-N bond distances (1.832, 2.014 Å).22
F igu r e 1. Temperature-dependent 1H NMR spectra of 3
recorded between -30 and 60 °C in toluene-d8.
spectrum does not show Al-H but strong N-H absorp-
1
tion bands. The H NMR spectrum of 4 also shows only
resonances due to DippNH and NMe3 protons in the
expected 3:1 stoichiometry. Its EI mass spectrum does
not show the molecular ion but peaks due to the
fragments AlN(H)Dipp and Al(NHDipp)2. Peaks with
higher molecular masses (m/z 580 [Al2(NHDipp)3], 758
[Al2(NHDipp)4], 781 [Al3(NDipp)4]) demonstrate the
lability of 4 toward loss of NMe3, followed by consecutive
gas-phase oligomerization reactions. The lability of the
NMe3 group was also demonstrated in the reaction of 4
with 4-(dimethylamino)pyridine (dmap). This particular
Lewis base, whose capacity to stabilize monomeric group
13/15 compounds has been demonstrated previously,20
displaces the NMe3 ligand, giving dmap-coordinated
dmap‚Al[N(H)Dipp]3 (5) in quantitative yield. Its 1H
NMR spectrum shows typical resonances due to the
dmap group, while the resonance of NMe3 disappeared.
The IR spectrum of 5 is very similar to that of 4, also
showing strong N-H absorption bands.
To examine the solid-state structures of the new
imino- and aminoalanes, considerable efforts were
undertaken to grow single crystals of the compounds.
Several data sets of colorless crystals of 1 were recorded
but could not be refined, due to severe disorder prob-
lems. Therefore, no information with respect to bond
lengths and angles can be given. However, the collected
data sets unambiguously confirmed the connectivity of
1, containing a planar four-membered ring with both
(22) Emig, N.; Nguyen, H.; Krautscheid, H.; Reau, R.; Cazaux,
J .-B.; Bertrand, G. Organometallics 1998, 17, 3599.

Amino- and Iminoalanes
Organometallics, Vol. 21, No. 14, 2002 2935
F igu r e 4. Reduced ORTEP plot of 3 showing the non-
planar Al2N2 ring and the all-cis orientation of the sub-
stituents. Only the ipso-C atoms of the Dipp ligands are
shown for clarity.
Figu r e 3. Molecular structure and atom-numbering scheme
of compound 3. Thermal ellipsoids are drawn at the 50%
probability level. i-Pr-groups and H atoms, except those
attached to ring N and Al, have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Al1-N1 )
1.970(3), Al1-N2 ) 1.972(3), Al1-N3 ) 1.809(3), Al1-
H1Al ) 1.446(16), Al2-N4 ) 1.801(3), Al2-N1 ) 1.956(3),
Al2-N2 ) 1.979(3), Al2-H2Al ) 1.447(16), N1-H1N )
0.906(16), N2-H2N ) 0.859(16), N3-H3 ) 0.885(17), N4-
H4 ) 0.882(17); N3-Al1-N1 ) 106.2(2), N3-Al1-N2 )
106.7(2), N1-Al1-N2 ) 84.3(2), N4-Al2-N1 ) 104.4(2),
N4-Al2-N2 ) 107.5(2), N1-Al2-N2 ) 84.5(2), C11-N1-
Al2 ) 126.3(2), C11-N1-Al1 ) 128.3(2), Al2-N1-Al1 )
93.8(2), C21-N2-Al1 ) 125.6(2), C21-N2-Al2 ) 129.0(2),
Al1-N2-Al2 ) 93.0(2).
Figu r e 5. Molecular structure and atom-numbering scheme
of compound 4. Thermal ellipsoids are drawn at the 50%
probability level. H atoms, except those attached to N, have
been omitted for clarity. Selected bond lengths (Å) and
angles (deg): Al1-N201 ) 1.823(2), Al1-N101 ) 1.839(2),
Al1-N301 ) 1.840(2), Al1-N1 ) 2.038(2), N101-H101 )
0.899(16),N201-H201 )0.853(17),N301-H301 )0.888(17);
N201-Al1-N101 ) 119.1(2), N201-Al1-N301 ) 120.4(2),
N101-Al1-N301 ) 104.5(1), N201-Al1-N1 ) 102.2(1),
N101-Al1-N1 ) 103.2(1), N301-Al1-N1 ) 105.1(2).
To the best of our knowledge, 2 is the first monomeric
bis(amino)alane stabilized by an external Lewis base.
2 contains vicinal Al-H and N-H functionalities, a
structural motif that was found only in oligomeric Li
aluminates,18,23 heterocycles,24 or cages14b,f and in Lewis
acid-base adducts such as 2,2,6,6-tetramethylpiperi-
dine-alane25 and (2,6-t-Bu-4-Me-C6H2O)2AlH‚NH2t-Bu,
thus far.26
Colorless crystals of 3 of X-ray quality were obtained
from hexane at -20 °C (Figures 3 and 4). Compound 3
crystallizes in the monoclinic space group C2/c (No. 15).
Its central unit is the nonplanar four-membered Al2N2
ring containing a bridging N(H)Dipp moiety. A second
N(H)Dipp group and an H atom are terminally bound
to each Al atom. The terminal substituents and the
bridging N-Dipp groups are arranged in a cisoid orien-
tation. The formation of a planar, centrosymmetric
Al2N2 ring with the ligands adopting all-trans positions
likely would lead to increased repulsive interactions
between the very bulky Dipp groups. The Al-N dis-
tances differ significantly, according to the different
coordination numbers (CN) between terminal (CN 3)
and bridging N centers (CN 4). The Al-N distance
within the ring (1.969(3) Å) is elongated by about 0.16
Å compared to that of the terminal N(H)Dipp group
(1.805(3) Å). The same findings were observed in [Me2N-
Al(H)-µ-NMe2]2,11a to the best of our knowledge the only
bis(amino)alane containing identically substituted amino
groups in terminal (1.805 Å) and bridging positions
(1.965 Å), and in the mixed aminoalane [i-Pr2NAl(H)-
µ-NEt2]2.11b The endocyclic N-Al-N angles (84.4°)
found in 3 are smaller than the endocyclic Al-N-Al
angles (93.4°), as is typical for Al2N2 rings.
Colorless crystals of 4 were obtained from hexane at
0 °C. The solid-state structure of 4, which crystallizes
in the monoclinic space group P21/c (No. 14), is shown
in Figure 5. Compound 4 is the first structurally
characterized monomeric tris(amino)alane. The Al-N
σ-bonds are about 0.2 Å shorter than the dative Al-N
bond. The average Al-N σ-bond distances of 2 and 4
are almost identical, despite the greater steric demand
of three N(H)Dipp groups in 4 compared to the two
N(H)Dipp groups in 2. The N-Al-N bond angles
between the N(H)Dipp ligands are significantly larger
compared to those between the N(H)Dipp and NMe3
substituents, clearly showing the higher steric demand
of the σ-bound N(H)Dipp groups compared to that of the
coordinatively bound NMe3 group. The unexpectedly
(23) Al-J uaid, S. S.; Eaborn, C.; Gorrell, I. B.; Hawkes, S. A.;
Hitchcock, P. B.; Smith, J . D. J . Chem. Soc., Dalton Trans. 1998, 2411.
(24) (a) Atwood, J . L.; Lawrence, S. M.; Raston, C. L. J . Chem. Soc.,
Chem. Commun. 1994, 73. (b) Gardiner, M. G.; Lawrence, S. M.;
Raston, C. L. Inorg. Chem. 1995, 34, 4652. (c) Gardiner, M. G.;
Lawrence, S. M.; Raston, C. L. Inorg. Chem. 1996, 35, 1349.
(25) (a) Atwood, J . L; Koutsantonis, G. A.; Lee, F.-C.; Raston, C. L.
J . Chem. Soc., Chem. Commun. 1994, 91. (b) Krossing, I.; No¨th, H.;
Schwenk-Kircher, H.; Seifert, T.; Tacke, C. Eur. J . Inorg. Chem. 1998,
1925.
(26) Healy, M. D.; Mason, M. R.; Gravelle, P. W.; Bott, S. G.; Barron,
A. R. J . Chem. Soc., Dalton Trans. 1993, 441.

2936 Organometallics, Vol. 21, No. 14, 2002
Bauer et al.
Figu r e 6. Molecular structure and atom-numbering scheme
of compound 6. Thermal ellipsoids are drawn at the 50%
probability level. H atoms, except those attached to N, have
been omitted for clarity. Only one orientation of the
disordered Et2O molecule is shown. Selected bond lengths
(Å) and angles (deg): Al1-N2 ) 1.827(2), Al1-N1 )
1.912(2), N1-Li1 ) 2.036(3), N1-H1 ) 0.889(15), N2-H2
) 0.861(14), O1-Li1 ) 1.847(8); N2′-Al1-N2 ) 119.8(2),
N2′-Al1-N1 ) 119.3(1), N2-Al1-N1 ) 100.7(1), N1-
Al1-N1′ ) 95.4(1), Al1-N1-Li1 ) 88.3(2).
Figu r e 7. Molecular structure and atom-numbering scheme
of compound 8. Thermal ellipsoids are drawn at the 50%
probability level. H atoms, except those attached to N, have
been omitted for clarity. Only one orientation of the
disordered i-Pr group (terminal NHDipp substituent) is
shown. Selected bond lengths (Å) and angles (deg): Al1-
N1 ) 2.010(3), Al1-N3 ) 1.925(3), Al1-N4 ) 1.804(2),
Al1-H2Al ) 1.43(3), Al2-N2 ) 1.812(3), Al2-N3 )
2.026(3), Al2-N4 ) 1.854(2), Al2-H1Al ) 1.53(3), N2-
H2N ) 0.90(4), N3-H3N ) 0.86(3), N4-C29 ) 1.406(4),
N3-C17 ) 1.449(4); N4-Al1-N3 ) 90.4(2), N4-Al1-N1
) 106.9(2), N3-Al1-N1 ) 109.7(2), N2-Al2-N4 ) 107.5(2),
N2-Al2-N3 ) 123.8(2), N4-Al2-N3 ) 85.9(2), C17-N3-
Al1 ) 125.3(2), C17-N3-Al2 ) 129.6(2), Al1-N3-Al2 )
87.2(2), C29-N4-Al1 ) 138.8(2), C29-N4-Al2 ) 124.2(2),
Al1-N4-Al2 ) 96.4(2).
large variation of about 15° indicates substantial re-
pulsive interactions between the very bulky substitu-
ents.
In a single case, the reaction of H3Al‚NMe3 with 3
equiv of DippNH2 led to a mixture of 4 and, in low yield,
the second product 6, which was isolated by recrystal-
lization from toluene. Figure 6 shows the solid-state
structure of 6. Compound 6 crystallizes in the mono-
clinic space group C2/c (No. 15). It contains an anionic
Al center bound to four N(H)Dipp groups and a Li
cation, which is 3-fold-coordinated by one Et2O molecule
and two N(H)Dipp groups. Obviously, 6 is formed from
a H3Al‚NMe3 sample which was partially contamined
with LiAlH4‚OEt2. This is reasonable, since the synthe-
sis of H3Al‚NMe3 starts from a solution of LiAlH4 in
Et2O. 6 is isostructural with the corresponding THF
complex17b and shows almost the same structural
parameters. The Al-N bond distances clearly show the
different coordination numbers of the N atoms. Those
distances to the 4-fold-coordinated N are about 0.09 Å
elongated compared to those to the 3-fold-coordinated
NHDipp group. The bond angles vary between 95.4(1)
and 119.8(2)°, with the smallest angle being between
the 4-fold-coordinated N centers.
In an attempt to overcome the crystallographic dis-
order problems observed for the iminoalane 1, we
reacted DippNH2 with H3Al‚NMe2Et. The equimolar
reaction yielded the iminoalane [NMe2Et‚Al(H)NDipp]2
(7). Its 1H NMR spectrum shows resonances due to
Al-H and NMe2Et groups and two doublets due to the
nonequivalent i-Pr groups. The IR spectrum also proves
the presence of Al-H groups (1802 cm-1), while N-H
absorption bands were not detected. However, several
attempts to obtain single crystals of 7 suitable for an
X-ray crystal structure analysis were unsuccessful.
We also reacted H3Al‚NMe2Et with 0.5 and 1.5 equiv
of DippNH2 in pentane in order to obtain Al-rich or
N-rich aminoalanes. While the reaction of H3Al‚NMe2-
Et with 0.5 equiv of DippNH2 yielded 7 as the only
isolable product, the reaction with 1.5 equiv of DippNH2
gave the unsymmetrically substituted aminoalane 8.
The IR spectrum of 8 shows strong absorption bands
due to N-H and Al-H groups, while the 1H NMR
spectrum obtained at ambient temperature displays a
very complex peak pattern due to the presence of several
chemically nonequivalent i-Pr groups. To obtain further
structural information on the solid-state structure of 8,
single crystals, which were obtained from pentane at 0
°C, were investigated by X-ray diffraction (Figures 7 and
8). Compound 8 crystallizes in the monoclinic space
group P21/n (No. 14). Its central structural unit contains
a planar four-membered Al2N2 ring with both the Al and
N centers in different chemical environments. Its back-
bone is built by a DippN unit, to which two Al(H)N(H)-
Dipp units are covalently bound. One Al center is
intermolecularly stabilized by a NMe2Et base, while the
second Al atom is intramolecularly stabilized by coor-
dination of the N(H)Dipp group bound to the first Al
center. The synthesis of 8 can be rationalized according
to a reaction sequence as described in Scheme 4.
8 shows two long Al-N dative bonds (2.010(3),
2.026(3) Å), while the Al-N σ-bonds toward the 3-fold
coordinated N centers are significantly shorter (1.804(2),

Amino- and Iminoalanes
Organometallics, Vol. 21, No. 14, 2002 2937
and for potential applications as single-source precur-
sors in MOCVD processes are currently under investi-
gation.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were per-
formed in a glovebox under an N2 atmosphere or with standard
Schlenk techniques. Solvents were dried over sodium/potas-
sium and degassed prior to use. DippNH2 was purchased from
Aldrich, dried over KOH and distilled and stored under Ar.
H3Al‚NMe3 and H3Al‚NMe2Et27 were prepared according to
literature methods. A Bruker AMX 300 spectrometer was used
for NMR spectroscopy. 1H and 13C{1H} NMR spectra were
referenced to internal C6D5H (1H, δ 7.154; 13C, δ 128.0), while
temperature-dependent NMR spectra were measured in toluene-
d8 (1H, δ 2.03 (q), 6.98 (m), 7.00 (br), 7.09 (m); 13C, δ 20.4 (sept),
125.2 (t), 128.0 (t), 128.9 (t), 137.5 (s) ppm). Mass spectra (EI)
were recorded on a VG Masslab 12-250 spectrometer. Infrared
spectra were recorded in Nujol between KBr plates with a
Nicolet Magna 550 and are reported in wavenumbers. Melting
points were measured in sealed capillaries and were not
corrected. Elemental analyses were performed at the Mikro-
analytisches Labor der Universita¨t Bonn. Please note that
amino- and iminoalanes generally tend to give low percentage
numbers for C and N due to the formation of aluminum carbide
and/or nitride. Yields are given for the pure products and are
based on the amount of AlH3‚NR3 used.
F igu r e 8. Reduced ORTEP plot of 8 showing the planar
Al2N2 ring. The i-Pr groups of the Dipp ligands are omitted
for clarity.
Sch em e 3. Rea ction of H3Al‚NMe2Et a n d Dip p NH2
in Differ en t Mola r Ra tios
[Me3N‚Al(H)NDip p ]2 (1). A 0.18 g (2 mmol) portion of
AlH3‚NMe3 was dissolved in 20 mL of pentane, cooled to -40
°C, and combined with 0.35 g (2 mmol) of DippNH2. Slow
warming to ambient temperature within 2 h occurred with gas
evolution. The resulting colorless solution was stored at -20
°C, to give colorless crystals.
Yield: 0.42 g (81%). Mp: >270 °C. Anal. Found (calcd) for
C30H54N4Al2 (524.7): H, 10.28 (10.37); C, 68.24 (68.67); N, 10.31
1
3
(10.68). H NMR (C6D6, 300 MHz): δ 1.34 (d, J HH ) 7.0 Hz,
Sch em e 4. P r op osed Rea ction Cou r se for th e
Syn th esis of 8
12H, CH(CH3)2), 1.48 (d, 3J HH ) 6.6 Hz, 12H, CH(CH3)2), 1.79
3
(s, 18H, N(CH3)3), 4.44 (sept, J HH ) 6.8 Hz, 4H, CH(CH3)2),
6.96-7.22 (6H, Hring). 13C NMR (C6D6, 74 MHz): δ 25.4 (CH-
(CH3)2), 26.8 (CH(CH3)2), 27.4 (CH(CH3)2), 45.8 (NMe3), 117.7
(Cring), 123.8 (Cring), 141.6 (Cring), 150.2 (N-Cring). IR (Nujol):
νj 1799 (Al-H), 1587, 1103, 997, 698 cm-1. EI-MS (20 eV,
100 °C): m/z 59 (60) (NMe3+), 162 (10) (Dipp+), 177 (100)
(DippNH2+), 203 (1) (HAlNDipp+), 262 (5) (Me3N‚HAlNDipp+),
769 (1) ((HAlNDipp)4 - i-Pr), 812 (2) ((HAlNDipp)4+).
+
Me3N‚Al(H)[N(H)Dip p ]2 (2). A 0.71 g (4 mmol) portion of
DippNH2 was added at -30 °C to a solution of 0.18 g (2 mmol)
of AlH3‚NMe3 in 20 mL of hexane. Warming to ambient
temperature within 3 h resulted in gas evolution. The colorless
solution was stored at -10 °C to give colorless crystals.
Yield: 0. 76 g (87%). Mp: 112 °C. Anal. Found (calcd) for
1.812(3), 1.854(2) Å). The sum of the bond angles of N4
(359.3°) clearly proves the absence of any H atom. Al-H
and N-H distances are comparable to those found in
other compounds described herein. However, in par-
ticular the Al-H distances show a relatively large
variation.
C
27H46N3Al (439.7): H, 10.43 (10.55); C, 73.28 (73.75); N, 9.32
3
(9.56). 1H NMR (C6D6, 300 MHz): δ 1.33 (d, J HH ) 6.8 Hz,
24H, CH(CH3)2), 1.78 (s, 9H, N(CH3)3), 2.85 (s, 2H, NH), 3.54
3
(sept, J HH ) 6.8 Hz, 4H, CH(CH3)2), 4.2 (s (br), Al-H), 6.94-
7.17 (6H, Hring). 13C NMR (C6D6, 74 MHz): δ 23.6 (CH(CH3)2),
29.2 (CH(CH3)2), 46.7 (NMe3), 118.6 (Cring), 123.5 (Cring), 136.8
(Cring), 146.1 (N-Cring). IR (Nujol): νj 3406, 3363 (NH), 1832
(AlH), 1591, 1429, 1338, 1107, 991, 891, 758 cm-1. EI-MS (25
eV, 150 °C): m/z 59 (20) (NMe3+), 162 (10) (Dipp+), 177 (100)
(DippNH+), 203 (5) (AlN(H)Dipp+).
Con clu sion s. Reactions of the amine-stabilized alanes
H3Al‚NMe3 and H3Al‚NMe2Et and the primary amine
DippNH2 were investigated in detail. Depending on the
reaction temperature and stoichiometry, base-stabilized
dimeric iminoalanes and monomeric aminoalanes as
well as heterocyclic aminoalanes were obtained. In
Me3N‚Al[N(H)Dipp]3, the NMe3 group is only weakly
bound and can be thermally removed or replaced by
4-(dimethylamino)pyridine (dmap). The as-prepared
compounds demonstrate the principle of electronic
stabilization to be very useful for the preparation of low
associated amino- and iminoalanes containing Al-H
and N-H functionalities. Investigations concerning the
potential of such compounds for consecutive reactions
[Dip p (H)NAl(H)-µ-N(H)Dip p ]2 (3). A 0.18 g (2 mmol)
portion of AlH3‚NMe3 was dissolved in 20 mL of pentane and
combined with 0.71 g (4 mmol) of DippNH2. Strong gas
evolution resulted. The resulting colorless solution was stirred
for 30 min. After storage at 0 °C for 12 h, colorless crystals of
3 were obtained.
Yield: 0.59 g (78%). Mp: 115 °C dec. Anal. Found (calcd)
for C48H74Al2N4 (761.1): H, 9.59 (9.80); C, 75.53 (75.75); N,
(27) Kovar, R. A.; Callaway, J . O. Inorg. Synth. 1977, 17, 36.

2938 Organometallics, Vol. 21, No. 14, 2002
Bauer et al.
1
3
7.29 (7.36). H NMR (C6D6, 300 MHz): δ 1.09 (d, J HH ) 6.6
Hz, 24H, CH(CH3)2 (term.)), 1.21 (s (br), 24 H, CH(CH3)2 (µ-
Yield: 0.12 g (93%). Mp: 220 °C dec. Anal. Found for
C43H64N5Al (678.0): H, 9.38 (9.52); C, 75. 98 (76.18); N, 10.16
(10.33). H NMR (C6D6, 300 MHz): δ 1.28 (d, J HH ) 6.7 Hz,
36H, CH(CH3)2), 1.74 (s, 9H, N(CH3)3), 3.26 (s, 3H, NH), 3.49
3
1
3
NHDipp)), 2.71 (sept, J HH ) 6.6 Hz, 4H, CH(CH3)2 (term.)),
3.37 (s, 2H, NH), 3.44 (sept (br), 4H, CH(CH3)2 (µ-NHDipp)),
4.21 (s, 2H, NH), 4.8 (s (br) AlH), 6.77-7.03 (12H, Hring). 13C
NMR (C6D6, 74 MHz): δ 23.0 (CH(CH3)2 (term.)), 25.0 (br,
CH(CH3)2 (µ-NHDipp)), 29.7 (CH(CH3)2 (µ-NHDipp)), 30.7 (CH-
(CH3)2 (term.)), 118.4, 123.4, 124.3, 125.2, 134.3, 136.8 (Cring),
139.0, 144.8 (N-Cring). IR (Nujol): νj 3389, 3244 (NH), 1937,
1916 (AlH), 1591, 1341, 1168, 930, 870, 740, 691 cm-1. EI-MS
(70 eV, 350 °C): m/z 73 (20) (NMe2Et+), 162 (10) (Dipp),
177 (100) (DippNH2+), 234 (30) (Dipp(H)N(AlH)2+), 721 (6)
(M+ - i-Pr), 762 (10) (M+), 805 (6) (Al2(NHDipp)6+ - 3 i-Pr -
3
3
(sept, J HH ) 6.7 Hz, 6H, CH(CH3)2), 5.64 (d, J HH ) 6.7 Hz,
3
2H, dmap), 6.94-7.19 (9H, Hring), 8.37 (d, J HH ) 6.7 Hz, 2H,
dmap). 13C NMR (C6D6, 74 MHz): δ 23.9 (CH(CH3)2), 28.9 (CH-
(CH3)2), 38.0 (NMe2), 106.2 (C3dmap), 118.6 (CDipp), 123.3 (CDipp),
137.9 (CDipp), 147.0 (N- CDipp), 147.5 (C2dmap). IR (Nujol): νj
3389, 3348 (NH), 1628, 1586, 1550, 1342, 862, 797, 738 cm-1
.
EI-MS (70 eV, 300 °C): m/z 121 (10) (dmap+), 162 (20) (Dipp+),
176 (100) (DippNH+), 203 (30) (AlN(H)Dipp+), 379 (5) (Al-
(NHDipp)2+), 555 (1) (M+ - dmap), 678 (1) (M+).
+
Dipp), 981 (2) (Al2(NHDipp)6 - 3 i-Pr), 1024 (2) (Al2-
(NHDipp)6 - 2 i-Pr).
Li(OEt2)AlN(H)Dip p 4 (6). Anal. Found (calcd) for C52H82
-
+
AlLiN4O (813.1): H, 9.99 (10.17); C, 76.21 (76.81); N, 6.58
3
Tem p er a t u r e-Dep en d en t NMR Sp ect r a . The most
important parts of the 1H NMR spectra are displayed in
Figure 1.
(6.89). 1H NMR (C6D6, 300 MHz): δ 0.63 (t, J HH ) 6.7 Hz,
6H, (CH3CH2)2O), 1.20 (d, 3J HH ) 6.8 Hz, 36H, CH(CH3)2), 1.92
(s, 9H, N(CH3)3), 2.85 (q, 3J HH ) 6.7 Hz, 6H, (CH3CH2)2O), 3.26
3
243 K: 1H NMR (toluene-d8, 300 MHz) δ 0.76 (d, 3J HH ) 5.0
(s, 4H, NH), 3.40 (sept, J HH ) 6.8 Hz, 6H, CH(CH3)2), 6.80-
7.13 (12H, Hring). 13C NMR (C6D6, 74 MHz): δ 24.4 (CH(CH3)2),
29.2 (CH(CH3)2), 123.7 (Cring), 125.6 (Cring), 136.1 (Cring), 137.8
(N-Cring).
Hz, 12H, CH(CH3)2 (µ-NHDipp)), 1.02 (d, 3J HH ) 6.4 Hz, 24H,
3
CH(CH3)2 (term.)), 1.48 (d, J HH ) 5.0 Hz, 12H, CH(CH3)2 (µ-
NHDipp)), 2.52 (sept, J HH ) 6.4 Hz, 4H, CH(CH3)2 (term.)),
3
2.72 (sept (br), 2H, CH(CH3)2 (µ-NHDipp)), 3.36 (s, 2H, NH),
4.00 (sept (br), 2H, CH(CH3)2 (µ-NHDipp)), 4.14 (s, 2H, NH),
4.76 (s (br) AlH), 6.72-6.95 (12H, Hring); 13C NMR (toluene-
d8, 74 MHz) δ 22.6 (CH(CH3)2 (term.)), 23.4 (CH(CH3)2 (µ-
NHDipp)), 26.0 (CH(CH3)2 (µ-NHDipp)), 29.4 (CH(CH3)2 (µ-
NHDipp)), 29.8 (CH(CH3)2 (µ-NHDipp)), 30.8 (CH(CH3)2 (term.)),
117.9, 123.2, 124.1, 126.1, 133.4, 136.5 (Cring), 137.7, 139.5,
144.8 (N-Cring).
[Me2EtN‚Al(H)NDip p ]2 (7). A 0.21 g (2 mmol) portion of
AlH3‚NMe2Et was dissolved in 15 mL of pentane, cooled to
-40 °C, and combined with 0.35 g (2 mmol) of DippNH2. Slow
warming to ambient temperature within 2 h occurred with gas
evolution. The resulting colorless solution was stored at -10
°C to give colorless crystals.
Yield: 0.46 g (83%). Mp: 110 °C dec. Anal. Found (calcd)
for C32H58N4Al2 (552.8): H, 10.52 (10.58); C, 69.48 (69.53); N,
273 K: 1H NMR (toluene-d8, 300 MHz) δ 0.8-1.3 (CH(CH3)2
1
3
1.09 (10.14). H NMR (C6D6, 300 MHz): δ 0.36 (t, J HH ) 7.3
3
3
(µ-NHDipp, very br)), 1.01 (d, J HH ) 6.4 Hz, 24H, CH(CH3)2
Hz, 6H, NCH2CH3), 1.35 (d, J HH ) 6.8 Hz, 12H, CH(CH3)2),
(term.)), 2.56 (sept, 3J HH ) 6.4 Hz, 4H, CH(CH3)2 (term.)), 3.31
(s, 2H, NH), 4.12 (s, 2H, NH), 4.7 (s (br) AlH), 6.70-6.92 (12H,
1.50 (d, 3J HH ) 6.8 Hz, 12H, CH(CH3)2), 1.91 (s, 12H, N(CH3)3),
3
3
2.23 (q, J HH ) 7.3 Hz, 4H, NCH2CH3), 4.46 (sept, J HH ) 6.8
Hz, 4H, CH(CH3)2), 6.92-7.22 (6H, Hring). 13C NMR (C6D6, 74
MHz): δ 7.8 (NCH2CH3), 25.6 (CH(CH3)2), 26.8 (CH(CH3)2),
27.4 (CH(CH3)2), 42.0 (NMe2), 7.8 (NCH2CH3), 117.9 (Cring),
123.9 (Cring), 141.9 (Cring), 150.4 (N-Cring). IR (Nujol): νj 1895,
1802 (AlH), 1259, 908, 8629, 795, 699 cm-1. EI-MS (70 eV,
250 °C): m/z 59 (40) (NMe3+), 162 (100) (Dipp+), 176 (60)
(DippNH2+), 204 (5) (AlN(H)Dipp+).
H
ring); 13C NMR (toluene-d8, 74 MHz) δ 22.8 (CH(CH3)2 (term.)),
24-26 (CH(CH3)2 (µ-NHDipp, very br)), 29.7 (CH(CH3)2 (µ-
NHDipp, br)), 30.8 (CH(CH3)2 (term.)), 118.1, 123.3, 124.2,
133.7, 136.7 (Cring), 137.4, 144.8 (N-Cring).
3
333 K: 1H NMR (toluene-d8, 300 MHz) δ 1.00 (d, J HH
)
3
6.7 Hz, 24H, CH(CH3)2 (term.)), 1.15 (d, J HH ) 6.6 Hz,
3
24H, CH(CH3)2 (µ-NHDipp)), 2.65 (sept, J HH ) 6.6 Hz, 4H,
3
CH(CH3)2 (term.)), 3.23 (s, 2H, NH), 3.39 (sept, J HH ) 6.6
Dip p N(H)Al(H)N(Dip p )AlH(NMe2Et)N(H)Dip p (8). A
0.21 g (2 mmol) portion of AlH3‚NMe2Et was dissolved in 15
mL of pentane, cooled to -40 °C, and combined with 0.53 g (3
mmol) of DippNH2. Slow warming to ambient temperature
within 3 h was accompanied by gas evolution. After the
colorless solution was stirred for 2 h and stored at -20 °C for
10 h, colorless crystals were obtained.
Hz, 4H, CH(CH3)2 (µ-NHDipp)), 4.10 (s, 2H, NH), 4.5 (s
(very br) AlH), 6.62-6.94 (12H, Hring); 13C NMR (toluene-d8,
74 MHz) δ 23.2 (CH(CH3)2 (term.)), 25.1 (CH(CH3)2 (µ-
NHDipp)), 29.8 (CH(CH3)2 (µ-NHDipp)), 30.8 (CH(CH3)2 (term.)),
118.6, 123.4, 124.4, 125.3, 134.7, 137.0 (Cring), 139.4, 144.9
(N-Cring).
Me3N‚Al[N(H)Dip p ]3 (4). A 0.18 g (2 mmol) portion of
AlH3‚NMe3 was dissolved in 20 mL of hexane, cooled to -40
°C, and combined with 1.06 g (6 mmol) of DippNH2. Warming
to ambient temperature within 1 h was accompanied by strong
gas evolution. The resulting colorless solution was stored at
-10 °C to give colorless crystals.
Yield: 0.52 g (79%). Crystal turns brown above 90 °C
without melting and decomposes at 171 °C. Anal. Found (calcd)
for C40H66Al2N4 (656.9): H, 10.01 (10.13); C, 72.96 (73.14); N,
3
8.38 (8.53). 1H NMR (C6D6, 300 MHz): δ 0.27 (t, J HH ) 7.2
3
Hz, 3H, NCH2CH3), 0.89 (d, J HH ) 6.6 Hz, 6H, CH(CH3)2),
3
3
1.16 (d, J HH ) 6.6 Hz, 6H, CH(CH3)2), 1.30 (d, J HH ) 7.0 Hz,
12H, CH(CH3)2), 1.46 (m, 6H, CH(CH3)2), 1.62 (d, 3J HH ) 6.9 Hz,
6H, CH(CH3)2), 1.70 (s, 3H, NCH3), 1.79 (s, 3H, NCH3), 2.16
Yield: 1.12 g (91%). Mp: 178 °C. Anal. Found (calcd) for
C
39H63N4Al (614.9): H, 10. 31 (10.33); C, 76.09 (76.18); N, 9.02
3
3
3
(9.11). 1H NMR (C6D6, 300 MHz): δ 1.21 (d, J HH ) 6.7 Hz,
(q, J HH ) 7.2 Hz, 4H, NCH2CH3), 2.90 (sept, J HH ) 6.8 Hz,
36H, CH(CH3)2), 1.92 (s, 9H, N(CH3)3), 2.78 (s, 3H, NH), 3.45
2H, CH(CH3)2), 2.98 (sept, 3J HH ) 6.8 Hz, 1H, CH(CH3)2), 3.14
3
(sept, 3J HH ) 6.7 Hz, 6H, CH(CH3)2), 6.93-7.11 (9H, Hring). 13
C
(s, 1H, NH), 4.06 (s, 1H, NH), 4.06 (sept, J HH ) 6.8 Hz, 1H,
3
NMR (C6D6, 74 MHz): δ 23.9 (CH(CH3)2), 29.0 (CH(CH3)2), 48.1
(NMe3), 119.6 (Cring), 123.5 (Cring), 138.3 (Cring), 145.7 (N-Cring).
IR (Nujol): νj 3404, 3354, 3321 (NH), 1591, 1432, 1327, 1200,
1105, 987, 889, 863, 750 cm-1. EI-MS (20 eV, 250 °C): m/z 59
(30) (NMe3+), 162 (100) (Dipp+), 177 (70) (DippNH2+), 204 (1)
(AlN(H)Dipp+), 378 (3) (Al(NHDipp)2+), 580 (4) (Al2(NHDipp)3+),
758 (2) (Al2(NHDipp)4+), 781 (5) (Al3(NDipp)4+).
d m a p ‚Al[N(H)Dip p ]3 (5). A 0.12 g (0.2 mmol) portion of 4
and 0.02 g (0.2 mmol) of 4-(dimethylamino)pyridine were
dissolved in 25 mL of hexane and stirred at ambient temper-
ature for 5 h. The solvent was removed in vacuo, and 5 was
obtained as a colorless, crystalline solid.
CH(CH3)2), 4.29 (sept, J HH ) 6.8 Hz, 2H, CH(CH3)2), 4.8 (s
(br), AlH), 6.80-7.28 (9H, Hring). IR (Nujol): νj 3376, 3298, 2956
(NH), 1869, 1808 (AlH), 1589, 1247, 1169, 922, 829, 702 cm-1
.
MS (70 eV, 300 °C): m/z 43 (15) (i-Pr+), 73 (10) (NMe2Et+),
162 (100) (Dipp+), 177 (40) (DippNH2+), 202 (25) (AlNDipp+),
378 (10) (DippNAlNHDipp+), 581 (10) (M+ - NMe2Et - H2).
X-r a y Str u ctu r e Solu tion a n d Refin em en t. Crystal-
lographic data of 2-4, 6, and 8 are summarized in Table 1.
Figures 2-8 show ORTEP diagrams of the solid-state struc-
tures of 2-4, 6, and 8. Data were collected on a Nonius Kappa-
CCD diffractometer. The structures were solved by Patterson
methods (SHELXS-97)28 and refined by full-matrix least

Amino- and Iminoalanes
Organometallics, Vol. 21, No. 14, 2002 2939
Ta ble 1. Cr ysta llogr a p h ic Deta ils for 2-4, 6, a n d 8
2
3
4
6
8
e
empirical formula
mol mass
cryst syst
space group
a (Å)
C
439.7
27H46AlN3
C48H74Al2N4
761.1
C39H63AlN4‚(hexane) C52H82AlLiN4Od
C40H66Al2N4
656.9
monoclinic
701.1
813.1
triclinic
P1h (No. 2)
8.4309(1)
9.8406(2)
17.2348(3)
90.714(1)
97.038(1)
105.249(1)
1367.66(4)
2
monoclinic
C2/c (No. 15)
22.1181(24)
13.3759(12)
32.2007(35)
90
103.829(5)
90
9250.4(16)
8
monoclinic
P21/c (No. 14)
13.6724(2)
23.8819(4)
13.5283(2)
90
monoclinic
C2/c (No. 15)
22.7354(5)
11.5512(2)
22.0804(5)
90
P21/n (No.14)
11.1631(2)
25.2828(4)
15.1317(3)
90
b (Å)
c (Å)
R (deg)
â (deg)
93.298(1)
90
120.148(1)
90
103.684(1)
90
4149.46(13)
4
γ (deg)
V (Å3)
4409.98(12)
4
5014.38(18)
4
Z
T (K)
123(2)
123(2)
123(2)
123(2)
123(2)
radiation (λ (Å))
Mo KR (0.710 73) Mo KR (0.710 73) Mo KR (0.710 73)
Mo KR (0.710 73) Mo KR (0.710 73)
µ (mm-1
)
0.092
1.068
50
0.098
1.093
50
0.079
1.056
50
0.079
1.077
50
0.100
1.052
50
Dcalcd (g cm-3
2θmax (deg)
)
cryst dimens (mm)
no. of rflns
no. of unique rflns
Rmerg
0.60 × 0.50 × 0.15 0.20 × 0.10 × 0.10 0.25 × 0.20 × 0.10
0.40 × 0.35 × 0.30 0.50 × 0.40 × 0.30
24 422
4799
21 606
7403
33 640
7660
19 114
4379
41 846
7274
0.0313
0.1160
505/6
0.0639
0.1089
0.879
0.0444
460/106
0.0581
0.1728
1.071
0.0397
286/80
0.0490
0.1338
1.071
0.0458
424/224
0.0574
0.1552
1.068
no. of params refined/restraints 289/3
R1a
0.0405
0.1113
1.038
wR2b
goodness of fitc
final max/min ∆F (e Å-3
)
0.381/-0.321
0.209/-0.257
0.688/-0.587
0.214/-0.308
0.416/-0.553
R1 ) ∑(||Fo| - |Fc||)/∑|Fo| (for I > 2σ(I)). wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
c Goodness of fit ) {∑[w(|Fo | - |Fc |)2]/(Nobservns
-
a
b
2
2
2
d
N
params)}1/2
.
The coordinated Et2O molecule is disordered. e One i-Pr group of the terminal NHDipp substituent is disordered.
squares on F2 (SHELXL-97).29 All non-hydrogen atoms were
refined anisotropically and hydrogen atoms by a riding model.
The crystallographic data of 2-4, 6, and 8 (excluding structure
factors) have been deposited with the Cambridge Crystal-
lographic Data Centre as Supplementary Publication Nos.
CCDC-144769 (2), CCDC-144769 (3), CCDC-144768 (4), CCDC-
144767 (6), and CCDC-144770 (8). Copies of the data can be
obtained free of charge on application to the CCDC, 12 Union
Road, Cambridge CB21EZ, U.K. (Telefax, (+44) 1223/336033;
E-mail, deposit@ccdc.cam-ak.uk).
Ack n ow led gm en t. S.S. gratefully acknowledges
generous financial support by the Deutsche Forschungs-
gemeinschaft (DFG), the Fonds der Chemischen Indus-
trie (FCI), and the Bundesministerium fu¨r Bildung,
Wissenschaft, Forschung and Technologie (BMBF) and
Prof. E. Niecke, Universita¨t Bonn.
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
distances, bond angles, anisotropic temperature factor param-
eters, and fractional coordinates for 2-4, 6, and 8. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(28) Sheldrick, G. M. SHELXS-97, Program for Structure Solution.
Acta Crystallogr., Sect. A 1990, 46, 467.
(29) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997.
OM020080A