Synthesis of Organoaluminum Chalcogenides [RAl(μ-E)]2 (R = N(SiMe3)C(Ph)C(SiMe3)2, E = Se, Te) from Aluminum Dihydride [RAlH(μ-H)]2

Article abstract of DOI:10.1021/om9904807

1-Azaallylaluminum dihydride [RAlH(μ-H)]₂ (1) (R = N(SiMe₃)C(Ph)C(SiMe₃)₂) has been prepared in nearly quantitative yield from the reduction of RAlBr₂ with an excess of LiAlH₄ in diethyl ether. Reaction of 1 with elemental Se or Te in toluene afforded the novel organoaluminum chalcogenide [RAl(μ-E)]₂ (E = Se (2); Te (3)) in good yield. The structures of compounds 1, 2, and 3 in the solid state have been characterized by X-ray diffraction analyses. Compounds 2 and 3 have a dimeric structure featuring three novel fused planar four-membered ring systems with a central Al₂E₂ core. Based on ¹H and ²⁹Si NMR data and crystal structural analysis of 2 and 3, an equilibrium of the trans and cis isomers in solution is proposed for the two compounds due to the relative orientation of the two chelating rings of the bidentate R ligands.

Full text of DOI:10.1021/om9904807

5120
Organometallics 1999, 18, 5120-5123
Syn th esis of Or ga n oa lu m in u m Ch a lcogen id es [RAl(µ-E)]2
(R ) N(SiMe3)C(P h )C(SiMe3)2, E ) Se, Te) fr om
†
Alu m in u m Dih yd r id e [RAlH(µ-H)]2
Chunming Cui, Herbert W. Roesky,* Mathias Noltemeyer, and
Hans-Georg Schmidt
Institut fu¨r Anorganische Chemie der Universita¨t Go¨ttingen, Tammannstrasse 4,
D-37077 Go¨ttingen, Germany
Received J une 22, 1999
1-Azaallylaluminum dihydride [RAlH(µ-H)]2 (1) (R ) N(SiMe3)C(Ph)C(SiMe3)2) has been
prepared in nearly quantitative yield from the reduction of RAlBr2 with an excess of LiAlH4
in diethyl ether. Reaction of 1 with elemental Se or Te in toluene afforded the novel
organoaluminum chalcogenide [RAl(µ-E)]2 (E ) Se (2); Te (3)) in good yield. The structures
of compounds 1, 2, and 3 in the solid state have been characterized by X-ray diffraction
analyses. Compounds 2 and 3 have a dimeric structure featuring three novel fused planar
1
four-membered ring systems with a central Al2E2 core. Based on H and 29Si NMR data and
crystal structural analysis of 2 and 3, an equilibrium of the trans and cis isomers in solution
is proposed for the two compounds due to the relative orientation of the two chelating rings
of the bidentate R ligands.
In tr od u ction
mula (R′AlE)n (R′ ) organic group; E ) Se, Te), namely,
the structurally characterized aluminum-selenium (tel-
lurium) cage compounds (Cp*AlE)4 (E ) Se or Te)2 and
(Me2EtCAlSe)4.3b Although the reaction of aluminum
hydride Me3N‚AlH3 or (Mes*AlH2)2 (Mes* ) 2,4,6-t-
Bu3C6H2) with organochalcogenides has been reported,5
the reactions of organoaluminum dihydrides with el-
emental Se and Te have not been investigated. There-
fore this reaction would be an alternative route to
generate organoaluminum chalcogenides of formula
(R′AlE)n. Herein we report the synthesis and structure
of 1-azaallylaluminum dihydride and its facile reaction
with elemental Se and Te to give dimeric organoalumi-
num chalcogenides in good yields.
Previously we described the basic chemistry of 1-azaal-
lyl aluminum compounds.1 It seems that this very bulky
chelating ligand R (R ) N(SiMe3)C(Ph)C(SiMe3)2) has
unique steric and electronic properties, therefore leading
to the isolation of the first dimeric aluminum difluoride
[RAlF(µ-F)]2. Consequently we developed the chemistry
of the RAl moiety to synthesize RAlH2 and to examine
its reaction with the heavier group 16 elements (Se, Te).
It is well-known that aluminum chalcogenides with a
cubane structure can be prepared by the reaction of the
appropriate aluminum alkyls with either H2Se or
elemental Se and Te and moreover by the reaction of
(Cp*Al)4 (Cp* ) C5Me5) with elemental Se and Te.2
However, so far, the former route involving elemental
chalcogens (Se, Te) and Al(III) alkyls can only be
employed using (t-Bu)3Al and (Me2EtC)3Al.3 In other
cases, elemental Se or Te can insert only into one of the
aluminum-carbon bonds, under forcing conditions; the
final products are a mixture of organic-substituted
chalcogenides.4 Overall there are only a few fully
characterized organometallic compounds with the for-
Exp er im en ta l Section
All operations were carried out under purified N2 atmo-
sphere by using Schlenk techniques. Solvents were purified
and dried by distillation from K or LiAlH4 under N2 prior to
use. RAlBr2 was prepared according to the published proce-
dure.1 Elemental selenium and tellurium were purchased from
Aldrich and used as received.
1H NMR (250.130 MHz), 13C NMR (100.600 MHz), 29Si NMR
(79.460 MHz), and 27Al NMR (65.170 MHz) spectra were
recorded on a Bruker AM 200 or a Bruker AM 250 spectrom-
eter. The chemical shifts were externally referenced to SiMe4
or AlCl3 (27Al). EI (70 eV) mass spectra were measured on a
Finnigan MAT 8230 or a Varian MAT CH5 instrument.
Elemental analyses were performed by the Analytisches Labor
des Instituts fu¨r Anorganische Chemie der Universita¨t Go¨t-
tingen. Melting points were measured in sealed glass tubes
and were not corrected.
† Dedicated to Professor Ulrich Mu¨ller on the occasion of his 60th
birthday.
(1) Cui, C.; Roesky, H. W.; Noltemeyer, M.; Lappert, M. F.; Schmidt,
H.-G.; Hao, H. Organometallics 1999, 18, 2256.
(2) Schulz, S.; Roesky, H. W.; Koch, H. G.; Sheldrick, G. M.; Stalke,
D.; Kuhn, A. Angew. Chem. 1993, 105, 1828; Angew. Chem., Int. Ed.
Engl. 1993, 32, 1729.
(3) (a) Cowley, A. H.; J ones, R. A.; Harris, P. R.; Atwood, D. A.;
Contreras, L.; Burek, C. J . Angew. Chem. 1991, 103, 1164; Angew.
Chem., Int. Ed. Engl. 1991, 30, 1143. (b) Harlan, C. J .; Gillan, E. G.;
Bott, S. G.; Barron, A. R. Organometallics 1996, 15, 5479.
(4) (a) Zakharkin, L. I.; Gavrilenko, V. V. Bull. Acad. Sci. USSR,
Div. Chem. Sci. (Engl. Transl.) 1960, 1294. (b) Kozikowski, A. P.; Ames,
A. J . Org. Chem. 1978, 43, 2735. (c) Bottomley, F.; Day, R. W.
Organometallics 1991, 10, 2560. (d) Power, M. B.; Ziller, J . W.; Tyler,
A. N.; Barron, A. R. Organometallics 1992, 11, 1055. (e) Kumar, R.;
Dick, D. G.; Ghazi, S. U.; Taghiof, M.; Heeg, M. J .; Oliver, J . P.
Organometallics 1995, 14, 1601.
[{N(SiMe3)C(P h )C(SiMe3)2}AlH(µ-H)]2 (1). A solution of
RAlBr2 (5.22 g, 10 mmol) in diethyl ether (30 mL) was added
(5) (a) Gardiner, M. G.; Raston, C. L.; Tolhurst, V.-A. J . Chem. Soc.,
Chem. Commun. 1995, 1457. (b) Wehmschulte, R. J .; Power, P. P. J .
Chem. Soc., Chem. Commun. 1998, 335.
10.1021/om9904807 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 11/04/1999

Synthesis of Organoaluminum Chalcogenides
Organometallics, Vol. 18, No. 24, 1999 5121
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for Com p ou n d s 1, 2, a n d 3
1
2
3
formula
fw
C
34H68Al2N2Si6
C34H64Al2N2Se2Si6
881.29
C34H64Al2N2Si6Te2
978.57
727.40
temp (K)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
153(2)
monoclinic
P21/n
14.014(2)
9.1980(13)
18.175(3)
90
106.760(15)
90
2243.3(6)
2
1.077
0.249
792
150(2)
triclinic
P1h
213(2)
triclinic
P1h
8.7959(10)
11.6070(15)
23.153(4)
100.984(10)
92.014(13)
91.248(9)
2318.1(6)
2
9.0522(15)
11.666(2)
23.149(7)
99.55(3)
91.415(14)
92.158(12)
2407.8(9)
2
Z
d(calcd) (Mg/m3)
1.263
1.813
920
1.350
1.421
992
abs coeff (mm-1
F(000)
)
cryst size (mm)
θ range (deg)
limiting indices
0.90 × 0.70 × 0.40
3.67-22.52
-15 e h e 15
-8 e k e 9
-18 e l e 19
3590
2912 (Rint ) 0.0449)
2911/0/216
1.038
1.00 × 0.70 × 0.60
3.51-25.04
-10 e h e 10
-13 e k e 13
-24 e l e 27
9658
8160 (Rint ) 0.0323)
8160/0/433
1.047
0.60 × 0.40 × 0.20
3.51-25.05
-10 e h e 10
-13 e k e 13
-10 e l e 27
8518
8518 (Rint ) 0.0000)
8518/0/435
1.032
no. of reflns collected
no. of indep reflns
no. of data/restraints/params
GOF/F2
R indices [I > 2σ(I)]
R1 ) 0.0289
wR2 ) 0.0733
R1 ) 0.0310
wR2 ) 0.0757
0.246/-0.193
R1 )0.0363
wR2 ) 0.0946
R1 ) 0.0422
wR2 ) 0.1018
0.630/-0.590
R1 ) 0.0431
wR2 ) 0.1050
R1 ) 0.0587
wR2 ) 0.1190
1.024/-0.837
R indices (all data)
largest diff peak/hole (e Å-3
)
to a suspension of LiAlH4 (1.14 g, 30 mmol) in diethyl ether
(10 mL) at 0 °C. The mixture was allowed to warm to room
temperature and stirred overnight. The volatiles were removed
under vacuum, and the residue was extracted with toluene
(30 mL). The extract was concentrated and then stored at -30
°C overnight to give white crystals (3.4 g, 94%). Mp: 82 °C.
Anal. Calcd for C34H68Al2N2Si6: C, 56.09; H, 9.42; N, 3.85.
toluene (15 mL) was heated to 80 °C for 8 h and then refluxed
for 4 h. After filtration, the solvent was evaporated to dryness,
and the green residue was crystallized from benzene/pentane
(2:1) to give greenish crystals (0.60 g, 78.6%). Mp: 176 °C (dec).
Anal. Calcd for C34H64Al2N2Si6Te2: C, 41.70; H, 6.59; N, 2.86.
1
Found: C, 40.96; H, 6.72; N, 3.10. H NMR (C6D6): δ 0.34 (d,
18 H, NSiMe3), 0.48 (d, 36 H, SiMe3), 6.82-7.00 (m, 6 H, Ph),
7.30-7.40 (m, 4 H, Ph). 29Si NMR (C6D6): δ -2.7, -2.4 (s,
SiMe3), 8.6, 9.1 (s, NSiMe3). MS (EI): m/z 976 (M+, 100), 488
(M+/2, 10).
1
Found: C, 56.14; H, 9.56; N, 3.89. H NMR (C6D6): δ -0.40
(s, 9 H, NSiMe3), 0.25 (s, 18 H, SiMe3), 4.72 (s, 2 H, AlH), 6.9-
1
7.0 (3 H, Ph), 7.3 (d, 2 H, Ph). H NMR (toluene-d8, 295 K): δ
-0.03 (s, 9 H, NSiMe3), 0.22 (s, 18 H, SiMe3), 4.61 (s, 2 H,
X-r a y Str u ctu r a l Deter m in a tion s a n d Refin em en ts for
1, 2, a n d 3. Data for crystal structures of compounds 1, 2,
and 3 were collected on a Stoe-Siemens four-circle diffracto-
meter using Mo KR radiation (λ ) 0.71073 Å). All structures
were solved by direct methods (SHELXS-96)6 and refined
against F2 using SHELXL-97.7 All heavy atoms were refined
anisotropically. Hydrogen atoms were included using the
riding model with Uiso tied to the Uiso of the parent atoms. A
summary of cell parameters, data collection, and structure
solutions is given in Table 1.
1
AlH), 7.01, 7.20-7.30 (m, 5 H, Ph). H NMR (toluene-d8, 233
K): δ 0.04 (s, 9 H, NSiMe3), 0.35 (s, 18 H, SiMe3), 4.75 (s, 2 H,
1
AlH), 7.06, 7.20-7.30 (m, 5 H, Ph). H NMR (toluene-d8, 193
K): δ 0.13 (s, 9 H, NSiMe3), 0.48 (s br, 18 H, SiMe3), 4.80 (s
br, 2 H, AlH), 7.07, 7.27 (s br, 5 H, Ph). 13C NMR (C6D6): δ
0.34 (NSiMe3), 2.74 (SiMe3), 48.8 (br s, CSi2), 127.0, 128.2,
130.6 (s, Ph), 142.9 (s, ipso-C), 209.8 (s, CN). 29Si NMR
(C6D6): δ 3.59 (s, CSi2), 5.69 (s, NSiMe3). 27Al NMR (toluene-
d8, 296 K): δ 131.6 (ν1/2 ) 2100 Hz).
[{N(SiMe3)C(P h )C(SiMe3)2}Al(µ-Se)]2 (2). To a mixture
of 1 (0.64 g, 0.89 mmol) and selenium (0.14 g, 1.79 mmol) was
added toluene (15 mL) at room temperature. After the mixture
was heated to 80 °C and stirred for 8 h, it was filtered. The
filtrate was concentrated (3 mL), and n-hexane (5 mL) was
added. Cooling of the solution to -30 °C overnight afforded
colorless crystals, which were collected by filtration and dried
(0.56 g, 71.3%). Mp: 247 °C (dec). Anal. Calcd for C34H64Al2N2-
Se2Si6: C, 46.34; H, 7.32; N, 3.18. Found: C, 45.92; H, 7.23;
Resu lts a n d Discu ssion
Syn th esis a n d Molecu la r Str u ctu r e of [RAlH(µ-
H)]2 (1). Reaction of RAlBr2 with an excess of LiAlH4
in diethyl ether afforded [RAlH(µ-H)]2 (1) in nearly
quantitative yield. 1 was characterized by H, 13C, and
1
29Si NMR, elemental analysis, and X-ray structural
analysis. Single crystals of 1 were grown from n-hexane
at 0 °C. The selected bond distances and angles are
listed in Table 2. 1 adopts a dimeric structure in the
solid state (Figure 1); as a consequence, the whole
structure features three fused four-membered rings with
asymmetric 1-azaallyl ligands in trans configuration.
Each aluminum atom is 5-fold coordinated, and the
geometry of the Al atoms can be described as trigonal
1
N, 3.26. H NMR (C6D6): δ 0.28 (d, 18 H, NSiMe3), 0.48 (br s,
36 H, SiMe3), 6.82-6.90 (m, 6 H, Ph), 7.35 (m, 4 H, Ph). 1H
NMR (toluene-d8, 295 K): δ 0.25 (d, 18 H, NSiMe3), 0.44 (d,
36 H, SiMe3), 7.01, 7.30-7.50 (m, 10 H, Ph). 1H NMR (toluene-
d8, 233 K): δ 0.27 (d, 18 H, NSiMe3), 0.50 (br s, 36 H, SiMe3),
7.06, 7.30-7.50 (m, 10 H, Ph). 1H NMR (toluene-d8, 193 K): δ
0.29 (s, 18 H, NSiMe3), 0.55 (s, 36 H, SiMe3), 7.08, 7.35 (br s,
10 H, Ph). 29Si NMR (C6D6): δ -2.5, -2.2 (s, SiMe3), 7.9, 8.4 (s,
NSiMe3). MS (EI): m/z 882 (M+, 100), 867 (M+ - Me, 4), 441
(M+/2, 5).
(6) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(7) Sheldrick, G. M. SHELXL, Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
[{N(SiMe3)C(P h )C(SiMe3)2}Al(µ-Te)]2 (3). A mixture of
1 (0.56 g, 0.78 mmol) and tellurium (0.20 g, 1.56 mmol) in

5122 Organometallics, Vol. 18, No. 24, 1999
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d An gles (d eg) for Com p ou n d 1
Cui et al.
Al(1)-H(1) 1.603
Al(1)-N(1) 2.026(2)
Al(1)-C(1) 2.418(2)
C(1)-N(1) 1.301(2)
H(1A)-Al(1)-N(1) 165.6
N(1)-Al(1)-C(2) 70.39
Al(1)-H(2) 1.509
Al(1)-H(1A) 1.966
C(1)-C(2) 1.495(2)
H(1)-Al(1)-H(1A) 76.3
H(1)-Al(1)-H(2) 117.2
Al(1)-C(2) 2.058(2)
Al(1)-Al(1A) 2.8154(11)
H(1)-Al(1)-N(1) 100.1
F igu r e 2. Molecular structure of 2 in the crystal. H atoms
have been omitted for clarity.
F igu r e 1. Molecular structure of 1 in the crystal. H atoms
except those in central core have been omitted for clarity.
may be comparable to those of group 13 alkyls with
elemental Se and Te, where products [R′2M(µ-ER′)]2 (R′
) alkyl, M ) Al, Ga) can be isolated.4d In a similar way,
this reaction presumably involves a hydroselenolate
(hydrotellurolate) intermediate,4c followed by elimina-
tion of hydrogen. The related reactions of the cleavage
of element-element bonds of group 16 using an alumi-
num hydride include the reactions of diorganodis-
elenides or -ditellurides with i-Bu2AlH12 or Me3N‚
AlH3.5a Compounds 2 and 3, which are very air and
moisture sensitive, but thermally quite stable as indi-
cated by their high melting points and EI mass spectra,
in which 100% M+ was observed for both compounds,
bipyramidal with the axis going through H(1A)-Al(1)-
N(1) (165.6°). The two bridging Al-H bonds at the same
aluminum atom differ in length by 0.363 Å due to the
asymmetry of the bulky ligand, which is in sharp
contrast to compound (Mes*AlH2)2, where the two
bridging Al-H bonds are nearly equal.8 The terminal
Al-H bonds (1.509 Å) are comparable to that (1.52(2)
Å) in compound [HAl(NMe2)3]-,9 while the two shorter
bridging Al-H bonds (1.603 Å) are shorter than those
observed in compounds [Me2Al(µ-H)]2 (1.68(2) Å)10 and
[o-(Me2NCH2)C6H4]AlH(µ-H)]2 (1.688 Å).11 The two other
bridging Al-H separations (1.966 Å) of 1 are much
longer than the sum of the covalent radii of Al and H
(1.67 Å) and the longest observed in organoaluminum
dihydrides, indicating only weak bonding interaction
1
have been characterized by H and 29Si NMR spectros-
copy, elemental analysis, and EI mass spectra. The
structures of the two compounds have been determined
by X-ray diffraction analyses as well, and one of those
is shown in Figure 2 (2 and 3 are isostructural) with
the atom-labeling scheme. The selected bond lengths
and angles for 2 and 3 are given in Table 3. Crystals of
X-ray diffraction quality of 2 (colorless) or 3 (greenish)
were obtained from toluene/n-hexane solution at -20
°C or benzene/n-hexane at 6 °C, respectively. 2 and 3
crystallize in the triclinic unit cell P1h group. The two,
essentially equal molecules in the unit cell, only mar-
ginally different in bond lengths and angles, are crys-
tallographically centrosymmetric (Figure 2 shows only
one molecule of 2). The structure of 2 consists of three
fused four-membered rings with a central Al(1)-Se(1)-
Al(1A)-Se(1A) core (the mean deviation of the plane ∆
) 0.000, the sum of the internal angles ) 360.01°, the
central core of the other molecule in the unit cell is
represented by Al(2)-Se(2)-Al(2A)-Se(2A)), nearly
perpendicular to the two other rings (the angles between
two adjacent planes in the two different molecules are
92.7° and 91.8°, respectively). The Al-Se distances
(2.3424-2.3563 Å) are shorter than those in cubane
compounds (Cp*AlSe)4 (2.462-2.497 Å) and (Me2-
EtCAlSe)4 (2.444-2.481 Å) due to the lower coordination
number of Se (two) atoms in 2. The Al-Al separations
1
between the two monomers. The H NMR spectra (C6D6
and toluene-d8) at room temperature show only one
sharp signal for AlH protons, and the 27Al NMR
resonance (δ 131.6 ppm) indicates that a 4-fold coordi-
nated aluminum center is present in solution. Therefore
a monomeric structure of 1 in solution is proposed. At
low temperature (193, 233 K) the signal for AlH only
broadens as the other singlets in the spectra, and there
is no observation of a dynamic process, indicating that
the monomeric structure is maintained at these tem-
peratures.
Syn th esis a n d Str u ctu r e of [RAl(µ-E)]2 (E ) Se
(2), Te (3)). The reaction of 1 with selenium or metallic
tellurium proceeded smoothly in toluene at elevated
temperature to afford dimeric aluminum selenide (2) or
telluride (3) in good yield (eq 1).
[RAlH(µ-H)]2 + 2/x Ex f [RAl(µ-E)]2 + 2 H2 (1)
E ) Se (2), Te (3)
This reaction type obviously represents a new and facile
route to organoaluminum chalcogenides. The detailed
reaction pathway is currently unknown. The reaction
(8) Wehmschulte, R. J .; Power, P. P. Inorg. Chem. 1994, 33, 5611.
(9) Linti, G.; No¨th, H.; Rahm, P. Z. Naturforsch. 1988, B43, 1101.
(10) Uhl, W. Z. Anorg. Allg. Chem. 1989, 37, 570.
(11) Isom, H. S.; Cowley, A. H.; Decken, A.; Sissingh, F.; Corbelin,
S.; Lagow, R. J . Organometallics 1995, 14, 2400.
(12) (a) Sasaki, K.; Aso, Y.; Otsubo, T.; Ogura, F. Chem. Lett. 1989,
607. (b) Sasaki, K.; Mori, T.; Doi, Y.; Kawachi, A.; Aso, Y.; Otsubo, T.;
Ogura, F. Chem. Lett. 1991, 415. (c) Inoue, T.; Takeda, T.; Kambe, N.;
Ogawa, A.; Ryu, I.; Sonoda, N. Organometallics 1994, 13, 4543.

Synthesis of Organoaluminum Chalcogenides
Organometallics, Vol. 18, No. 24, 1999 5123
Ta ble 3. Selected Bon d Dista n ces (Å) a n d Bon d An gles (d eg) for Com p ou n d s 2 a n d 3
[RAl(µ-Se)]2 (2)
Al(1)-Se(1A) 2.3527(9)
Al(1)-Al(1A) 2.9412(16)
Al(2)-Se(2) 2.3469(8)
Al(1)-Se(1) 2.3424(8)
Al(1)-C(2) 2.051(3)
Al(1)-N(1) 1.948(2)
N(1)-C(1) 1.308(3)
C(1)-C(2) 1.491(4)
Al(2)-Se(2A) 2.3563
Al(2)-N(2) 1.953(2)
Se(1)-Al(1)-Se(1A) 102.42(2)
Se(2)-Al(2)-Se(2A) 102.39(3)
Al(2)-C(4) 2.052(3)
Al(2)-Al(2A) 2.9473(15)
N(1)-Al(1)-C(2) 72.01(10)
C(2)-Al(1)-Se(1) 123.17(8)
Al(1)-Se(1)-Al(1A) 77.58(3)
Al(2)-Se(2)-Al(2A) 77.61(3)
[RAl(µ-Te)]2 (3)
Al(1)-Te(1A) 2.5768(14)
Al(1)-N(1) 1.946(3)
Al(1)-Te(1) 2.5619(12)
Al(2)-Te(2A) 2.5765(14)
N(1)-C(1) 1.319(5)
N(1)-Al(1)-Te(1) 110.03(11)
C(2)-Al(1)-Te(1) 123.06(12)
Al(2)-Te(2) 2.5753(12)
Al(1)-C(2) 2.064(4)
C(1)-C(2) 1.484(6)
N(1)-Al(1)-C(2) 71.80(15)
Al(1)-Te(1)-Al(1A) 76.88(4)
Al(2)-Te(2)-Al(2A) 77.21(4)
Te(1)-Al(1)-Te(1A) 103.12(4)
Te(2)-Al(2)-Te(2A) 102.79(4)
Sch em e 1
(2.9412(16), 2.9473(15) Å) are slightly longer than that
in the starting material 1 (2.8154(11) Å) due to longer
Al-Se bonds than the bridging Al-H bonds even though
the aluminum atoms in the latter is 5-fold coordinated.
The internal angles at Al (102.42(3)°, 102.39(3)°) are
more open than at Se (77.58(3)°, 77.61(3)°) due to acute
angles N-Al-C (72.01(10)°, 71.74(10)°), which are only
slightly more open than those in the 5-fold coordinated
aluminum atoms of 1. 2 crystallizes as a trans isomer
with the backbone of the ligands in trans configuration.
Compound 3 is the second example of a monoorga-
noaluminum telluride to be fully structurally character-
ized. The only previous example is the tetrameric
(Cp*AlTe)4 reported by our group, which has an Al4Te4
cubane structure with Al-Te distances in the range
from 2.688 to 2.750 Å. The longer Al-Te bond lengths
in that compound are due to the higher coordination
number of Te (three). The short Al-Te distances
(2.5619-2.5768 Å) in 3 are similar to those observed in
the compound [{(SiMe3)2HC}2Al]2Te (2.549 Å).14 It is
noteworthy that the internal angles at Al and at Te in
3 are quite similar to those at Al and at Se in 2,
respectively, despite the longer Al-Te bond lengths
compared to the Al-Se bonds (the central cores of the
two different molecules in the unit cell of 3 are repre-
sented by Al(1)-Te(1)-Al(1A)-Te(1A) and Al(2)-Te-
(2)-Al(2A)-Te(2A), respectively; see Table 3).
observed at this temperature. Due to the ligand back-
bone, which is arranged nearly perpendicular to the
central core, two possible isomers (trans and cis) are
given in Scheme 1. The ratio of the two isomers (1:2)
for both 2 and 3 at room temperature is estimated by
1
using the H NMR spectra. Because of the flexibility of
the ligand R, the M-C bond cleavage mechanism has
been proposed to explain the dynamic processes of
compounds (ClMR)2 (M ) Sn, Pb)14 and [RAlF(µ-F)]2.1
In a similar manner, the Al-C bond dissociation/
association process might also be responsible for the
conversion of the two isomers in solution.
Con clu sion
The reaction of RAlH2 with elemental Se and Te has
been shown to be an efficient and facile route to
synthesize organoaluminum chalcogenides. Due to the
chelating and bulky nature of R, low aggregation
products (RAlE)2 were obtained. We will further explore
the reactivities of the two dimeric compounds.
1
Both H and 29Si NMR spectra indicate the existence
of an equilibrium of two isomers of 2 and 3, respectively,
in C6D6 solution, which is probably caused by the
relative orientation of the ligand chelating rings. The
Ack n ow led gm en t. We are grateful to the Deutsche
Forschungsgemeinschaft for generous financial support.
1
variable-temperature (193-295 K) H NMR spectra of
2 indicate that the conversion of the two isomers in
toluene-d8 becomes slow at 193 K, as indicated by the
fact that only one singlet for NSiMe3 and SiMe3 can be
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and refinement details, bond lengths, bond angles, and
thermal parameters for 1-3. This material is available free
of charge via the Internet at http://pubs. acs. org.
(13) Uhl, W.; Schu¨tz, U. Z. Naturforsch. 1994, B49, 931.
(14) Hitchcock, P. B.; Lappert, M. F.; Layh, M. Inorg. Chim. Acta
1998, 269, 181.
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