Syntheses and structures of the arylaluminum chalcogenides (ArAIE)2 (Ar = 2-(NEt2CH2)-6-MeC6H3, E = Se; Ar = 2,6-(NEt2CH2)2C6H3, E = Se, Te)

Article abstract of DOI:10.1021/ic000255d

Two intramolecular stabilized arylaluminum dihydrides, {2-(NEt₂CH₂)-6-MeC₆H₃}AlH₂ (1) and {2,6-(NEt₂-CH₂)₂C₆H₃}AlH₂ (2), were prepared

Full text of DOI:10.1021/ic000255d

3678
Inorg. Chem. 2000, 39, 3678-3681
Syntheses and Structures of the Arylaluminum Chalcogenides (ArAlE)2 (Ar )
2-(NEt2CH2)-6-MeC6H3, E ) Se; Ar ) 2,6-(NEt2CH2)2C6H3, E ) Se, Te)†
Chunming Cui, Herbert W. Roesky,* Mathias Noltemeyer, and Hans-Georg Schmidt
Institute of Inorganic Chemistry, University of Go¨ttingen, Tammannstrasse 4,
D-37077 Go¨ttingen, Germany
ReceiVed March 7, 2000
Two intramolecular stabilized arylaluminum dihydrides, {2-(NEt2CH2)-6-MeC6H3}AlH2 (1) and {2,6-(NEt2-
CH2)2C6H3}AlH2 (2), were prepared by reducing the corresponding dichlorides with an excess of LiAlH4 in
diethyl ether. Reactions of 1 and 2 with elemental selenium afforded the dimeric arylaluminum selenides [{2-
(NEt2CH2)-6-MeC6H3}AlSe]2 (3) and [{2,6-(NEt2CH2)2C6H3}AlSe]2 (4). Reaction of 2 with metallic tellurium
gave the dimeric arylaluminum telluride [{2,6-(NEt2CH2)2C6H3}AlTe]2 (5). The possible reaction pathway is
discussed, and molecular structures determined by single-crystal X-ray analyses are presented for 3 and 5.
Introduction
These ligands can effectively control the geometry of a metal
center and prevent association, as has been demonstrated by
the synthesis of monomeric aluminum and gallium hydrides
using the tridentate 2,6-(Me2NCH2)2C6H3 ligand.7,8 However
group 13 element chalcogenides with this type of ligand have
not yet been reported. The only related compound is dimeric
(Mes*AlS)2 (Mes* ) 2,4,6-(t-Bu)3C6H2).9 Herein we report the
first examples of arylaluminum selenides and a telluride of the
general formula (ArAlE)n.
Heavier group 13 element chalcogenides are potential single-
source precursors for group 13-16 materials.1 The synthesis
and characterization of this class of compounds have been one
of the interesting research fields in recent years. Although
numerous publications have discussed a variety of aluminum
compounds containing heavier group 16 elements,2 only a
handful of the compounds with the formula (RAlE)n (R )
organic group, E ) Se, Te)3 are known because of the lack of
a general synthetic route. We recently reported that organoalu-
minum dihydrides are possible precursors for compounds of the
formula (RAlE)n.4 As an extension of the utilization of this route,
we are now interested in employing bulky bidentate and
tridentate ligand systems to generate monomeric RAlE moieties
by intramolecular stabilization.
Experimental Section
All manipulations were carried out under a purified nitrogen
atmosphere using standard Schlenk techniques. The solvents were dried
by standard methods. Chemicals were purchased from Aldrich or Fluka
and used as received. 2,6-(Et2NCH2)2C6H3Br and its lithium salt were
prepared as described in the literature.5
Elemental analyses were performed by the Analytisches Labor des
Instituts fu¨r Anorganische Chemie der Universita¨t Go¨ttingen. A Bruker
AM 200 spectrometer was used to record the 1H NMR (200.13 MHz)
and 13C NMR (125.76 MHz) spectra. EI mass spectra were obtained
on a Finnigan MAT 8230 instrument. Melting points were measured
in sealed glass capillaries and were not corrected.
Aryl ligands of the type 2,6-(R2NCH2)2C6H3 and 2-(R2-
NCH2)C6H4 (R ) Me, Et, i-Pr, or other organic group) with
one or two donor sidearms have been widely used in late
transition chemistry,5 and some group 13 and 14 element
compounds with this type of ligand have also been reported.6
† Dedicated to Professor Richard Neidlein on the occasion of his 70th
birthday.
Synthesis of 2-(Et2NCH2)-6-MeC6H3Br (a). 2-(Et2NCH2)-6-MeC6H3-
Br was obtained as a byproduct from the synthesis of 2,6-(Et2NCH2)2-
C6H3Br in ca. 10% yield. Bp: 76 °C/0.05 Torr. H NMR (C6D6): δ
0.78 (t, Et), 2.23 (Et), 2.60 (Me), 3.45 (CH2), 6.8-7.25 (m, Ph).
Synthesis of {2-(Et2NCH2)-6-MeC6H3}AlH2 (1). A solution of {2-
(Et2NCH2)-6-MeC6H3}Li prepared from a (0.76 g, 3 mmol) and BuLi
(3 mL in hexane, 3 mmol) in diethyl ether (20 mL) was added to a
solution of AlCl3 (0.40 g, 3 mmol) in diethyl ether (10 mL) at -78
°C. The mixture was allowed to warm to room temperature and then
(1) For a review, see: Barron, A. R. AdV. Mater. Opt. Electron. 1995, 5,
1
245.
(2) For leading references, see, for example: (a) Oliver, J. P.; Kumar,
R.; Taghiof, M. In Coordination Chemistry of Aluminum; Robinson,
G. H., Ed.; VCH: New York, 1993; p 167. (b) Rahbarnoohi, H.;
Kumar, R.; Heeg, M. J.; Oliver, J. P. Organometallics 1995, 14, 3869.
(c) Barron, A. R. Comments Inorg. Chem. 1993, 14, 123.
(3) (a) Schulz, S.; Roesky, H. W.; Koch, H. J.; Sheldrick, G. M.; Stalke,
D.; Kuhn, A. Angew. Chem. 1993, 105, 1828; Angew. Chem., Int. Ed.
Engl. 1993, 32, 172. (b) Harlan, C. J.; Gillan, E. G.; Bott, S. G.; Barron,
A. R. Organometallics 1996, 15, 5479.
(4) (a) Cui, C.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G.
Organometallics 1999, 18, 5120. (b) Cui, C.; Roesky, H. W.; Hao,
H.; Schmidt, H.-G.; Noltemeyer, M. Angew. Chem. 2000, 112, 1885;
Angew. Chem. Int. Ed. 2000, 39, 1815.
(5) For example: (a) van Beek, J. A. M.; van Koten, G.; Dekker, G. P.
C. M.; Wissing, E. J. Organomet. Chem. 1990, 394, 659. (b) van Beek,
J. A. M.; van Koten, G.; Ramp, M. J.; Coenjaarts, N. C.; Grove, D.
M.; Goubitz, K.; Zoutberg, M. C.; Stam, C. H.; Smeets, W. J. J.; Spek,
A. L. Inorg. Chem. 1991, 30, 3059. (c) van de Kuil, L. A.; Luitjes,
H.; Grove, D. M.; Zwikker, J. W.; van der Linden, J. G. M.; Roelofsen,
A. M.; Jenneskens, L. W.; Drenth, W.; van Koten, G. Organometallics
1994, 13, 468.
(6) For example: (a) Mu¨ller, J.; Englert, U. Chem. Ber. 1995, 128, 493.
(b) Dam, M. A.; Akkerman, O. S.; Bickelhaupt, F.; Veldman, N.; Spek,
A. L. Main Group Metal Chem. 1995, 18, 633. (c) Probst, R.; Leis,
C.; Gamper, S.; Herdtweck, E.; Zybill, C.; Auner, N. Angew. Chem.
1991, 103, 1155; Angew. Chem., Int. Ed. Engl. 1991, 30, 1132. (d)
Isom, H. S.; Cowley, A. H.; Decken, A.; Sissingh, F.; Gorbelin, S.;
Lagow, R. J. Organometallics 1995, 14, 2400.
(7) Cowley, A. H.; Gabbai, F. P.; Atwood, D. A. J. Am. Chem. Soc. 1994,
116, 1559.
(8) Contreras, L.; Cowley, A. H.; Gabbai, F. P.; Jones, R. A.; Carrano,
C. J.; Bond, M. R. J. Organomet. Chem. 1995, 489, C1.
(9) Wehmschulte, R. F.; Power, P. P. J. Chem. Soc., Chem. Commun.
1998, 335.
10.1021/ic000255d CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/07/2000

Arylaluminum Chalcogenides
Inorganic Chemistry, Vol. 39, No. 16, 2000 3679
stirred overnight. After filtration, the filtrate was added to a suspension
of LiAlH4 (0.30 g, 8 mmol) in diethyl ether (10 mL) at room
temperature. The mixture was stirred at room temperature for 15 h.
All volatiles were removed in vacuo, and the residue was extracted
with n-hexane (50 mL). The extract was concentrated to incipient
crystallization at -30 °C to give white crystals of 1 (0.40 g, 65%).
Table 1. X-ray Crystallographic Data for Compounds 3 and 5
0.5 3‚C7H8
0.5 5
formula
fw
C19H26AlNSe
374.35
C16H27AlN2Te
401.98
temp (K)
133(2)
203(2)
cryst syst, space group monoclinic, P21/n
monoclinic, P21/c
1
Mp: 92-93 °C. H NMR (C6D6): δ 0.62 (t, 6 H, J ) 7.3 Hz, Et),
a, b, c (Å)
12.498(3), 11.556(2), 10.542(2), 11.726(3),
2.35 (q, 4 H, J ) 6.2 Hz, Et), 2.57 (s, 3 H, Me), 4.60 (br s, 2 H, AlH2),
7.02-7.23 (m, 3 H, Ph). 13C NMR (C6D6): δ 8.75 (Et), 25.7 (Me),
45.8 (Et), 61.1 (CH2), 121.1, 127.8, 128.3, 144.2, 146.5 (Ph), 149.3
(AlC). EI-MS: m/e 204 (M+ - H). Anal. Calcd for C12H20AlN: C,
70.24; H, 9.76; N, 6.83. Found: C, 69.47; H, 9.80; N, 6.72.
14.256(3)
90, 114.03(3), 90
1880.4(7), 4
1.187
2.041
776
1.00 × 0.80 × 0.70
2.36-27.50
-16 e h e 14, 0 e
k e 14, 0e l e 18
4301
4301 (0.0000)
4296/0/203
14.580(4)
90, 105.04(2), 90
1740.8(7), 4
1.534
1.753
808
0.60 × 0.60 × 0.20
3.52-25.01
-12e h e 12, -13 e
k e 13, -17 e l e 17
9371
3066 (0.0479)
3066/0/185
R, â, γ (deg)
V (Å3), Z
d
calcd (Mg/m3)
abs coeff (mm-1
F(000)
)
Synthesis of {2,6-(Et2NCH2)2C6H3}AlH2 (2). {2,6-(Et2NCH2)2C6H3}-
AlH2 was prepared similarly to 1. 2,6-(Et2NCH2)2C6H3Br (3.26 g, 10
mmol), BuLi (10 mL in n-hexane, 10 mmol), AlCl3 (1.33 g, 10 mmol),
and LiAlH4 (0.85 g, 22.5 mmol) were used. The crude product was
crystallized from toluene/pentane (1/1) to give white crystals (1.8 g,
cryst size (mm)
θ range (deg)
limiting indices
no. of reflns collected
no. of indep reflns (Rint
no. of data/restraints/
params
1
)
65.2%). Mp: 65-67 °C. H NMR (C6D6): δ 0.90 (t, 12 H, J ) 7.2
Hz, Et), 2.75 (q, 8 H, J ) 7.1 Hz, Et), 3.42 (s, 4 H, CH2), 4.4 (br s, 2
H, AlH2), 6.90 (d, 2 H, J ) 7.3 Hz, Ph), 7.31 (t, 1 H, J ) 7.2 Hz, Ph).
13C NMR (C6D6): δ 9.27 (Et), 46.3 (Et), 60.0 (CH2), 122.2, 128.3,
146.0 (Ph), 150.1 (AlC). EI-MS: m/e 275 (M+ - H). Anal. Calcd for
C16H29AlN2: C, 69.53; H, 10.57; N, 10.13. Found: C, 69.35; H, 10.54;
N, 9.88.
GOF/F2
1.117
0.0435, 0.1016
1.111
0.0282, 0.0759
R indices [I > 2σ(I)]:
R1, wR2
R indices (all data):
R1, wR2
0.0627, 0.1147
0.0289, 0.0768
largest diff peak/hole
0.880/-0.563
0.984/-1.234
Synthesis of [{2-(Et2NCH2)-6-MeC6H3}AlSe]2 (3). To a mixture
of 1 (0.25 g, 1.22 mmol) and selenium (0.10 g, 1.26 mmol) was added
toluene (20 mL) at room temperature. The mixture was stirred at 80
°C for 10 h and filtered to remove small amounts of precipitate. The
filtrate was concentrated and stored at -20 °C for 2 d to give color-
less crystals of 3‚C7H8, which easily lost solvent under vacuum to
give 3 as a white solid (0.27 g, 78.2%). Mp: 220-222 °C. 1H
NMR (C6D6): δ 0.85 (t, 6 H, Et), 2.72 (q, 4 H, Et), 2.94 (s, 3 H, Me),
3.43 (s, 2 H, CH2), 7.00-7.30 (m, 3 H, Ph). 13C NMR (C6D6): δ
9.01 (Et), 25.1 (Me), 46.6 (Et), 58.9 (CH2), 121.6, 128.7, 129.3, 142.8,
146.2 (Ph), 147.7 (AlC). EI-MS: m/e 566 (M+). Anal. Calcd for
C12H18AlNSe: C, 51.06; H, 6.38; N, 4.96. Found: C, 50.74; H, 6.32;
N, 5.03.
(e Å-3
)
Results and Discussion
Aluminum dihydrides can be easily prepared by the reduction
of the corresponding dihalides.6d,8 The reactions of 2-(Et2NCH2)-
6-MeC6H3Li and 2,6-(Et2NCH2)2C6H3Li with equal amounts of
AlCl3 yielded the aluminum dichlorides, and reductions with
excess amounts of LiAlH4 in diethyl ether afforded the intra-
molecular stabilized arylaluminum dihydrides 2-(Et2NCH2)-6-
MeC6H3AlH2 (1) and 2,6-(Et2NCH2)2C6H3AlH2 (2), respec-
tively, in modest yields (Scheme 1). The dichlorides were not
isolated and characterized but were directly reduced in situ to
yield 1 and 2. The similar aluminum dichlorides 2,6-(Me2-
NCH2)2C6H3AlCl2 and 2-(Me2NCH2)C6H4AlCl2, prepared in an
analogous way, have been reported.6d,8 Dihydrides 1 and 2 were
characterized by 1H NMR, 13C NMR, and EI-MS spectroscopy
as well as elemental analyses. The EI mass spectra of 1 and 2
each give the highest peak corresponding to the [M+ - H]
fragment, indicating that both compounds are monomeric in the
gas phase. The 1H NMR spectra of 1 and 2 each show a broad
hydride resonance, which is characteristic for aluminum hy-
drides. Compound 2 might also be monomeric in the solid state,
as was reported for 2,6-(Me2NCH2)2C6H3AlH2.8
Reactions of 1 and 2 with selenium at 80 °C respectively
afforded the first examples of arylaluminum selenides [{2-(Et2-
NCH2)-6-MeC6H3}AlSe]2 (3) and [{2,6-(Et2NCH2)2C6H3}-
AlSe]2 (4) in good yields. We have briefly mentioned the
mechanism of this type of reaction in our previous publication.4a
The isolation of an aluminum-SeH compound LAl(SeH)2 (L
) Ar′NC(Me)CHC(Me)NAr′, Ar′ ) 2,6-i-Pr2C6H3)4b suggests
that this reaction proceeds through an aryl aluminum-SeH
intermediate. It is proposed that the coordination of an Se2 unit
to the aluminum atom forms a hypervalent aluminum center12
and that the activated Se2 unit is concertedly reduced by the
two hydride ligands to yield ArAl(SeH)2, which reacts im-
mediately with another molecule of ArAlH2 to eliminate
hydrogen (Scheme 2). When 2 equiv of selenium is used for
the reaction, only half of the selenium is consumed. This
observation indicates that, in this case, the reaction of ArAl-
(SeH)2 with ArAlH2 is much faster. In contrast, when a very
Synthesis of [{2,6-(Et2NCH2)2C6H3}AlSe]2 (4). [{2,6-(Et2-
NCH2)2C6H3}AlSe]2 was prepared similarly to 3. Compound 2 (0.33
g, 1.2 mmol) and selenium (0.10 g, 1.2 mmol) were used for the
preparation. Crystallization from hot toluene (10 mL) gave colorless
1
crystals of 4 (0.28 g, 66%). Mp: 160-162 °C. H NMR (CDCl3): δ
1.08 (t, 12 H, J ) 7.2 Hz, Et), 2.97 (q, 8 H, J ) 7.1 Hz, Et), 3.96 (s,
4 H, CH2), 7.2 (m, 3 H, Ph). 13C NMR (CDCl3): δ 11.06 (Et), 47.29
(Et), 59.70 (CH2), 124.2, 128.7, 145.5 (Ph), 145.8 (AlPh). EI-MS: m/e
708 (M+). Anal. Calcd for C16H27AlN2Se: C, 54.38; H, 7.70; N, 7.93.
Found: C, 54.19; H, 7.73; N; 7.89.
Synthesis of [{2,6-(Et2NCH2)2C6H3}AlTe]2 (5). A suspension of 2
(0.28 g, 1.04 mmol) and tellurium (0.13 g, 1.04 mmol) in toluene (20
mL) was refluxed for 8 h. After filtration to remove small amounts of
precipitate, the filtrate was concentrated and stored at room temperature
for 1 week to give large plates of 5 suitable for single-crystal X-ray
analysis (0.33 g, 79%). Mp: 233-235 °C. 1H NMR (CDCl3): δ 1.20
(t, 12 H, J ) 7.1 Hz, Et), 3.03 (q, 8 H, J ) 7.2 Hz, Et), 3.96 (s, 4 H,
CH2), 7.23 (m, 3 H, Ph). 13C NMR (CDCl3): δ 11.3 (Et), 47.4 (Et),
59.1 (CH2), 124.1, 128.6, 145.3 (Ph), 144.6 (AlC). EI-MS: m/e 804
(M+). Anal. Calcd for C16H27AlN2Te: C, 47.85; H, 6.78; N, 6.97.
Found: C, 48.63; H, 6.79; N, 6.97.
X-ray Structure Determinations and Refinements. Data for the
crystal structures of 3 and 5 were collected on a Stoe-Siemens four-
circle diffractometer using Mo KR radiation (λ ) 0.710 73 Å). The
structures were solved by direct methods (SHELXS-96)10 and refined
against F2 using SHELXL-97.11 All heavy atoms were refined aniso-
tropically. Hydrogen atoms were included by using a riding model with
each Uiso related to the Uiso of the parent atom. Crystal data, data
collection details, and solution and refinement procedures are sum-
marized in Table 1.
(10) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(11) Sheldrick, G. M. SHELXL: Program for Crystal Structure Refinement;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(12) Raston, C. L. J. Organomet. Chem. 1994, 475, 15.

3680 Inorganic Chemistry, Vol. 39, No. 16, 2000
Cui et al.
Scheme 1
Scheme 2
(3), (4)
bulky chelating group L is used, the reaction of LAl(SeH)2 with
LAlH2 is markedly slowed due to the steric effect of the ligand.
Unfortunately, we are unable to monitor this reaction because
of its heterogeneous nature. Reaction of 2 with tellurium in
refluxing toluene gave the arylaluminum telluride [{2,6-(Et2-
NCH2)2C6H3}AlTe]2 (5) in good yield. The mechanism might
be similar to that for the reaction of the hydrides with selenium.
Compounds 3 and 4 are inert to donor reagents such as
phosphine, pyridine, and tmeda ((Me2NCH2)2). They are only
poorly soluble in toluene, THF, and DME and have a very
limited solubility in CHCl3.
The three compounds were fully characterized by multinuclear
NMR spectroscopy, EI mass spectra, and elemental analyses.
The MS spectra of 3-5 show the dimeric molecular ion peaks,
and the NMR spectra exhibit the expected resonances. To
elucidate the role of the NEt2 donors, single-crystal X-ray
determinations of compounds 3 and 5 were carried out. Single
crystals suitable for X-ray crystal studies of 3 and 5 were
obtained from toluene at -20 °C and at room temperature,
respectively.
Compound 3 crystallizes as a dimer with a crystallographi-
cally required inversion center in the solid state (Figure 1).
Selected bond lengths and angles are listed in Table 2. The NEt2
arms are coordinated to the aluminum atoms with Al-N
distances of 2.052(3) Å, which is in line with that of (Me2-
NCH2)C6H4AlCl2.6b The Se(1)-Al(1) and Se(1)-Al(1A) dis-
tances differ (by ca. 0.014 Å) probably because of different steric
effects at the two sides of the aryl ligand. They are slightly
longer than those of the dimeric compound [{N(SiMe3)C(Ph)C-
(SiMe3)2}AlSe]2 (average 2.35 Å).4a The Al(1)-Se-Al(1A)
internal angle is acute, with a value of 77.52°, which is nearly
equal to that of [{N(SiMe3)C(Ph)C(SiMe3)2}AlSe]2.
Figure 1. Molecular structure of 3 in the crystal. The solvent C7H8
and hydrogen atoms have been omitted for clarity.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Compound 3
Se(1)-Al(1A)
Se(1)-Al(1)
2.352(7)
2.366(4)
Al(1)-C(11)
Al(1)-N(1)
1.960(3)
2.052 (3)
Al(1A)-Se(1)-Al(1)
C(11)-Al(1)-N(1)
77.52(4) N(1)-Al(1)-Al(1A)
126.9(9)
86.79(12) Se(1A)-Al(1)-Al(1A) 51.45(3)
C(11)-Al(1)-Se(1A) 122.99(11) Se(1)-Al(1)-Al(1A)
N(1)-Al(1)-Se(1A) 115.58(8) Se(1A)-Al(1)-Se(1)
51.03(3)
102.48(4)
C(11)-Al(1)-Se(1)
N(1)-Al(1)-Se(1)
119.58
108.70
C(11)-Al(1)-Al(1A) 146.00(11)
ligand is coordinated to an aluminum atom and the other arm
is in a dangling position. However, the 1H and 13C NMR spectra
show only one set of signals for the Et2NCH2 group; it is
assumed that, in solution, a rapid exchange of coordination and
dissociation of the two NEt2 groups takes place. Unfortunately,
due to the low solubility of these compounds, we were not able
to perform low-temperature NMR studies. Similar behavior has
already been observed for the dimeric gallium compound (2,6-
(NMe2CH2)2C6H3GaPSiPh3)2.13 Compound 5 is the third struc-
turally characterized organoaluminum telluride with the formula
(RAlTe)n; the others are (Cp*AlTe)4 (Cp* ) C5Me5) and [{N-
(SiMe3)C(Ph)C(SiMe3)2}AlTe]2 reported by our group.3a,4a The
Te(1)-Al(1) (2.589 Å) and Te(1)-Al(1A) (2.582 Å) distances
are only marginally different from each other. They are shorter
Compound 5 crystallizes in the monoclinic P21/c space group
as a centrosymmetric dimer (Figure 2). Selected bond lengths
and angles are listed in Table 3. The most interesting structural
feature is that only one arm of the two NEt2 sites of the aryl
(13) Cowley, A. H.; Jones, R. A.; Mardones, M. A.; Ruiz, J.; Atwood, J.
L.; Bott, S. G. Angew. Chem. 1990, 102, 1169; Angew. Chem., Int.
Ed. Engl. 1990, 29, 1150.

Arylaluminum Chalcogenides
Inorganic Chemistry, Vol. 39, No. 16, 2000 3681
(Ph)C(SiMe3)2}AlSe]2 (averages 102.4, 77.6°) despite the longer
Al-Te distances.
Conclusions and Remarks
The results of the syntheses for compounds 4 and 5 indicate
that the dimeric form with one dangling NEt2 group is ener-
getically favored in comparison to the corresponding monomeric
species with two chelating arrangements at the aluminum atom.
Using the more bulky aryl ligand (2,6-{(t-Bu)(Me)NCH2}2C6H3),
the dimeric form was also obtained (according to mass spectra).
The 1H NMR spectrum shows a broad singlet for the t-Bu and
Me groups, indicating that the bulky substituents at the nitrogen
atoms are responsible for the slower exchange (coordination
and dissociation) on the NMR time scale.14 The dimeric
compounds 3-5 as well as [{N(SiMe3)C(Ph)C(SiMe3)2}AlE]2
(E ) Se, Te) are thermally quite stable systems. They do not
dissociate in polar solvents (THF, DME), even under reflux
conditions. In addition, strong donors such as pyridine, tmeda,
or phosphine have no effect on the dissociation of the dimers.
The utilization of the bulky bidentate ligand N(Ar′)C(Me)CHC-
(Me)N(Ar′) (Ar′ ) 2,6-i-Pr2C6H3) unexpectedly leads to the
isolation of the first example of an aluminum-SeH compound.
Inspired by this result, we are now exploring the possibility of
synthesizing the donor-free compounds R2AlEH (E ) S, Se,
Te; R ) monodentate anion). The deprotonation of this class
of compounds might give anionic [R2AlE]- species, which may
possess π-bonding character between aluminum and the chal-
cogen atom.15 This work is presently in progress.
Figure 2. Molecular structure of 5 in the crystal. Hydrogen atoms
have been omitted for clarity.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Compound 5
Te(1)-Al(1A)
Te(1)-Al(1)
2.581(8)
2.588(7)
Al(1)-C(11)
Al(1)-N(2)
1.976(3)
2.054(2)
Al(1A)-Te(1)-Al(1) 76.30(3) C(11)-Al(1)-Te(1) 119.59(7)
109.22(6)
C(11)-Al(1)-N(2)
86.74(9) N(2)-Al(1)-Te(1)
C(11)-Al(1)-Te(1A) 122.62(8) Te(1A)-Al(1)-Te(1) 103.70(3)
N(2)-Al(1)-Te(1A) 113.80(6)
than those of the cubic (Cp*AlTe)4 derivative (2.688-2.750
Å) due to the low coordination number of the Te atom in
compound 5, and they are only slightly longer than those in
[{N(SiMe3)C(Ph)C(SiMe3)2}AlTe]2 (2.562-2.577 Å). The Al-
(1)-C(11) distance (1.976(3) Å) is only slightly longer than
that of compound 3 (1.960 Å), and both are in the range of
those reported for {(Me2NCH2)C6H4}AlCl2‚THF (1.987 Å) and
dimeric [{(Me2NCH2)C6H4}AlCl2]2 (1.941 Å).6 The Te-Al-
Te (103.70(3)°) and Al-Te-Al (76.30(3)°) angles are quite
similar to those of dimeric [{N(SiMe3)C(Ph)C(SiMe3)2}AlTe]2
(103.12(4), 76.88(4)°) even though the Al2Te2 core binds to
quite different ligands in the two compounds. In addition, the
angles of the Al2Te2 unit are also nearly equal to those of Al2-
Se2 for compound 3 (102.48(4), 77.52(4)°) and [{N(SiMe3)C-
Acknowledgment. This work was supported by the Deutsche
Forschungsgemeinschaft.
Supporting Information Available: X-ray crystallographic files,
in CIF format, for compounds 3 and 5. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC000255D
(14) The compounds 2,6-{(t-Bu)(Me)NCH2}2C6H3AlH2 (b) and [2,6-{(t-
Bu)(Me)NCH2}2C6H3AlSe]2 (c) were prepared similarly to compounds
2 and 4. Data for b: mp 91-92 °C; EI-MS m/e 303 (M+ - H). Data
for c: mp 322-323 °C; 1H NMR (CDCl3) δ 1.35 (s, 18 H, t-Bu),
2.57 (s, 6 H, Me), 4.04 (s, 4 H, CH2), 7.21 (m, 3 H, Ph); 77Se NMR
(CDCl3) δ -14.2, -13.8; EI-MS m/e 764 (M+).
(15) Power, P. P. Chem. ReV. 1999, 99, 3463.