Low-temperature synthesis of aluminum sulfide as the solvate Al4S6(NMe3)4 in hydrocarbon solution

Full text of DOI:10.1021/ja972111c

9566
J. Am. Chem. Soc. 1997, 119, 9566-9567
elimination of Me2SiH2.8 In addition, direct interaction of the
elemental chalcogens Se and Te with Me3N‚AlH3 has been
shown to afford {Me3N‚Al(H)(µ2-E)}2 (E ) Se or Te).9
Reaction of Me3N‚AlH3 and S(SiMe3)2 in toluene at 90-95
°C according to eq 1 affords 1‚PhMe in 67% purified yield.10a
X-ray data11a show that its structure (Figure 1) is a bicyclic Al4S5
[3.3.1] array in which two fused six-membered AlS rings have
a boat conformation. Each Al is bound to a Me3N donor (av
Al-N ) 2.021(7) Å) as well as to two µ2-sulfides (av Al-S )
2.223(11) Å). In addition, the two bridgehead Al atoms (Al(1)
and Al(3)) are linked by a µ2-sulfide (av Al-S ) 2.232(2) Å),
whereas Al(2) and Al(4) each carry a hydrogen (av Al-H )
1.54(5) Å). Thus, all aluminums in 1‚PhMe have distorted
tetrahedral coordination. Spectroscopic data (1H, 13C, and 27Al
NMR and IR) are in harmony with the formula established for
1‚PhMe by X-ray crystallography. 1H NMR spectroscopy
reveals a 1:1 ratio of 1 and PhMe and a 2:1 ratio of Me3N and
Al-H groups. IR absorptions for the Al-H and Al-S bonds
Low-Temperature Synthesis of Aluminum Sulfide
as the Solvate Al4S6(NMe3)4 in Hydrocarbon
Solution
Rudolf J. Wehmschulte and Philip P. Power*
Department of Chemistry
UniVersity of California
DaVis, California 95616
ReceiVed June 26, 1997
Aluminum sulfide, Al2S3, a moisture-sensitive colorless solid,
has a variety of structures in the crystalline phase1 and is
synthesized by the direct reaction of the elements at elevated
temperature. The moisture sensitivity and the high-temperature
synthesis are features common to most binary heavier main
group 13-15 and 13-16 compounds.2 Their high lattice
energy,3 however, precludes solubility at ambient temperature
in media with which they do not react. The isolation and
purification of stoichiometric neutral cage fragments of such
lattices under mild conditions is thus an important synthetic
challenge, since many binary group 13-15 and 13-16 com-
pounds have interesting electronic properties.4 One approach
to the problem involves the generation of such substances by a
homogeneous reaction in solution followed by their stabilization
and crystallization as a complex with neutral donor ligands.
Some neutral lithium halide fragments have been synthesized
by this method.5 This general approach has also been applied
to a number of cages of the heavier chalcogenides such as
were observed at 1782 and 503 cm-1
.
Complete elimination of Al hydrogen is observed in the
reaction of Me3N‚AlH3 with a slight excess of S(SiMe3)2 over
the required stoichiometry (i.e., >1.5 S per Al).10b The structure
of the product Al4S6(NMe3)4 (2)11b features an adamantanyl
Al4S6 framework with each bridgehead Al complexed to Me3N
(Al-N ) 1.991(4) Å) and three µ2-sulfides (Al-S ) 2.2235-
(7) Å) (Figure 2). The coordination at the aluminums is thus
distorted tetrahedral (S-Al-S ) 114.61(2)°, S-Al-N )
103.65(3)°), and the two-coordinate sulfurs feature an Al-S-
Al angle of 97.82(6)°. Attempts to convert 1 to 2 via reaction
of 1 equiv of S(SiMe3)2 have been only partially successful.
The major problem arose from attempted redissolution of
1‚PhMe in PhMe which results in the deposition of an (as yet
6a
Cu50S25{P(tBu)2Me}16 and Cu146Se73(PPh3)30.6b To date,
however, it has not proven possible to synthesize cage com-
plexes in which both the metal ion and counteranion have high
formal charges as in group 13-15 or 13-16 binary species.7 It
is now shown that the reaction between Me3N‚AlH3 and
S(SiMe3)2 at relatively low temperature leads to the aluminum
sulfide complexes Al4S5(H)2(NMe3)4‚PhMe (1‚PhMe) and Al4S6-
(NMe3)4 (2) in moderate yields.
(7) However, related cage species (e.g., Cd32Se14(SePh)36(PPh3)4 or
Cu96P30{P(SiMe3)2}6(PEt3)18) having multiply-charged anionic ligands have
been synthesized. See: Behrens, S.; Bettenhausen, M.; Deveson, A. C.;
Eichhofer, A.; Fenske, D.; Lohde, A.; Woggon, U. Angew. Chem., Int. Ed.
Engl. 1996, 35, 2215. Fenske, D.; Holstein, W. Angew. Chem., Int. Ed.
Engl. 1994, 33, 1290.
(8) Wehmschulte, R.; Power, P. P. J. Am. Chem. Soc. 1997, 119, 8387.
(9) Gardiner, M. G.; Raston, C. L.; Tolhurst, V.-A. J. Chem. Soc., Chem.
Commun. 1995, 2501.
The preparative routes to 1 and 2 involve the stoichiometries
given in eqs 1 and 2. The use of S(SiMe3)2 as the chalcogenide
(10) All manipulations were carried out under anaerobic and anhydrous
conditions. Both 1 and 2 gave satisfactory C, H, and N elemental analyses.
(a) Al4S5(H)2(NMe3)4‚PhMe (1‚PhMe). A solution of 0.36 g (4.0 mmol) of
H3AlNMe310c in toluene (25 mL) was treated with 1.06 mL (5.0 mmol) of
(Me3Si)2S10d at room temperature and heated to 90-95 °C for 24 h. The
small amount of voluminous, grayish precipitate was separated, and the
clear, colorless supernatant liquid was concentrated to ca. 3 mL and cooled
in a -20 °C freezer for 3 days to afford 0.40 g of colorless crystals of
1‚PhMe. Recrystallization from toluene (20 mL) gave 0.16 g of the pure
product as colorless crystals of sufficient quality for X-ray crystallography.
Yield: 27%. The crystals turn opaque at mp ) 75-90 °C (desolvation),
foams at ca. 250 °C, and do not melt below 315 °C. 1H NMR (C6D6):
7.05 (m, toluene, 5H), 4.9 (s, br, w1/2 ) 170 Hz, Al-H, 2H), 2.47 (s, Me3N,
18H), 2.29 (s, Me3N, 18H), 2.10 (s, toluene, 3H). 13C{1H} NMR (C6D6):
47.2 (Me3N). 27Al NMR (C6D6, νo ) 78.34047 MHz): 146 (s, w1/2 ≈ 1900
Hz). IR (Nujol mull): 1782 (st, Al-H). (b) Al4S6(NMe3)4, 2. (Me3Si)2S
(1.27 mL, 6.0 mmol) was added to a solution of H3AlNMe3 (0.36 g, 4.0
mmol) in toluene (25 mL), and the mixture was heated to 110-115 °C for
ca. 17 h. The clear, colorless solution was separated from the small amount
of voluminous precipitate and heated to 110-115 °C for an additional 4 d
to afford a colorless, crystalline solid, which was washed with n-pentane
(20 mL) and dried under reduced pressure. This solid consists of at least
two different compounds: bundles of thin plates or needles which still
contain the Al-H function (by IR) and clear blocks of approximately cubo-
octahedral shape with a maximum size of 0.2 mm in an estimated 60:40
ratio. The blocks were of sufficient quality for X-ray diffraction. Yield:
0.26 g. This compound does not melt below 315 °C. (c) Ruff, J. K.;
Hawthorne, M. F. J. Am. Chem. Soc. 1960, 82, 2141. (d) Armitage, D. A.;
Clark, M. J.; Sinden, A. W.; Wingfield, J. N.; Abel, E.W.; Louis, E. J.
Inorg. Synth. 1974, 15, 207.
4Me3N‚AlH3 + 5S(SiMe3)2 PhMe8
Al4S5(H)2(NMe3)4 + 10Me3SiH (1)
1
4Me3N‚AlH3 + 6S(SiMe3)2 PhMe8
Al4S6(NMe3)4 + 12Me3SiH (2)
2
transfer agent was prompted by the reaction of the alane
(Mes*AlH2)2 (Mes*)-C6H2-2,4,6-(tBu)3)withthesiloxane(Me2-
SiO)3 to afford the alumoxane (Mes*AlO)4 in high yield with
(1) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Clarendon:
Oxford, 1984; p 764.
(2) Taylor, M. J.; Brothers, P. J. In Chemistry of Aluminum, Gallium,
Indium and Thallium; Downs, A. J., Ed.; Blackie-Chapman Hall: London,
1993; Chapter 3, pp 161, 168.
(3) The lattice energy for an ionic compound may be estimated by using
the Kapustinskii equation. This shows that the lattice energies of species
such as Al2S3 with multiply-charged ions are often more than an order of
magnitude greater than the simplest ionic species such as NaCl. Kapustinskii,
A. F. Z. Phys. Chem. (Leipzig) 1933, B22, 257.
(4) Grant, I. R. In ref 2, Chapter 5.
(5) (a) Barr, D.; Snaith, R.; Wright, D. S.; Mulvey, R. E.; Wade, K. J.
Am. Chem. Soc. 1987, 109, 7891. (b) Barr, D.; Doyle, M. J.; Mulvey, R.
E.; Rathby, P. R.; Reed, D.; Snaith, R.; Wright, D. S. J. Chem. Soc., Chem.
Commun. 1989, 318. (c) Veith, M.; Hobein, P.; Huch, V. J. Chem. Soc.,
Chem. Commun. 1995, 213.
(11) Crystal data at 130 K with Cu KR (λ ) 1.541 78 Å) radiation: (a)
1‚PhMe, C19H46Al4N4S5, Mr ) 598.82, orthorhombic, space group Pna21,
a ) 11.8936(12) Å, b ) 27.252(2) Å, c ) 10.042(2) Å, V ) 3255.0(7) Å3,
Dcalcd ) 1.222 g cm-3, Z ) 4, R ) 0.0253 for 2189 (I > 2σ(I)) reflections;
(b) Al4S6(NMe3)4 (2), C12H36Al4N4S6, Mr ) 536.73, cubic, space group
I4h3m, a ) 11.4095(9) Å, V ) 1485.3(2) Å3, Dcalcd ) 1.200 g cm-3, Z ) 2,
R ) 0.0305 for 172 (I > 2σ(I)) reflections.
(6) (a) Fenske, D.; Dehnen, S. Chem. Eur. J. 1996, 2, 1407. (b)
Krautscheid, H.; Fenske, D.; Baum, G.; Semmelmann, M. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 1303.
S0002-7863(97)02111-2 CCC: $14.00 © 1997 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 119, No. 40, 1997 9567
NAl(H)(µ2-E)}2 (E ) Se or Te).9 The Al-S distances in 1
and 2 (ca. 2.22 Å) are shorter than those in the recently reported
12
{(Me2EtC)AlS}4 (ca. 2.31 Å) which involves µ3-S sulfides
in an Al4S4 cubane arrangement, but are longer than those in
S[Al{CH(SiMe3)2}2]2 (Al-S ) 2.187(4) Å)13 or Al(SMes*)3
(av Al-S ) 2.185(5) Å)14 where, although the sulfide or thiolate
has a two-coordinate S, the Al is three-coordinate. The closest
15
known structure to 2 is the adamantanyl species Al4I4(SMe)4S2
in which four of the six core sulfurs are derived from thiolates.
The Al-µ2-S (sulfide) distances average 2.18(2) Å which, owing
to the higher standard deviations, cannot be regarded as
appreciably shorter than the Al-S bond length in 2. The ternary
compound TlAlS2 has also been described as isomorphous to
TlGaSe2,16 which consists of layers of corner-sharing adaman-
tane-like [M4X10] (M ) Al, Ga, In; X ) S, Se)17 supertetrahedra,
but no additional details were given.
Figure 1. Thermal ellipsoidal (30%) plot of 1. Hydrogen atoms are
not shown except for H(1) and H(2). Selected bond distances (Å) and
angles (deg) are the following: Al(1)-S(1) ) 2.208(2), Al(1)-S(4)
) 2.221(2), Al(1)-S(5) ) 2.230(2), Al(2)-S(1) ) 2.232(2), Al(2)-
S(2) ) 2.229(2), Al(3)-S(2) ) 2.214(2), Al(3)-S(3) ) 2.202(2), Al-
(3)-S(5) ) 2.233(2), Al(4)-S(3) ) 2.225(2), Al(4)-S(4) ) 2.235(2),
Al(1)-N(1) ) 2.032(2), Al(2)-N(2) ) 2.022(4), Al(3)-N(3) ) 2.017-
(4), Al(4)-N(4) ) 2.013(3), Al(2)-H(1) ) 1.58(4), Al(4)-H(2) )
1.51(5), Al(1)-S(1)-Al(2) ) 99.50(6), Al(1)-S(5)-Al(3) ) 96.35-
(5), S(1)-Al(1)-S(4) ) 115.37(6), S(1)-Al(1)-S(5) ) 114.22(6),
S(4)-Al(1)-S(5) ) 114.06(6), S(1)-Al(1)-N(1) ) 104.76(11), S(4)-
Al(1)-N(1) ) 103.97(11).
Although the stoichiometry of the Al4S6 core in 2 corresponds
to the formula of Al2S3, the coordination of the Al in 2 involves
three sulfides and one amine nitrogen. It thus differs from the
18
essentially tetrahedral AlS4 environment found in Al2S3 and
the related anionic salts TlAlS2,16a Tl3Al7S12,19 and Tl3Al13S21,16b
whose structures consist of corner-sharing Al-centered AlS4
tetrahedra. Nonetheless, the adamantanyl core of 2 is composed
of S3AlN tetrahedra in which the sulfide corners are also shared.
Thus, 2 is the smallest neutral unit with the correct Al2S3
stoichiometry which resembles the structure of Al2S3.
A
putatively smaller neutral Al2S3(NMe3)2 fragment would prob-
ably be different in the sense that its structure would consist of
an Al2S3 trigonal bipyramid with face- rather than corner
sharing-NAlS3 tetrahedra. Attempted sublimation of 2 at low
pressure and ca. 250 °C results in the elimination of NMe3 and
the deposition of an amorphous form of Al2S3.
Acknowledgment. We thank the Donors of the Petroleum Research
Fund administered by the American Chemical Society and the National
Science Foundation for financial support.
Supporting Information Available: Tables of data collection
parameters, atom coordinates, bond distances, angles, anisotropic
thermal parameters, and hydrogen coordinates (21 pages). See any
current masthead page for ordering and Internet access instructions.
JA972111C
(12) Harlan, C. J.; Gillan, E. G.; Bott, S. G.; Barron, A. R. Organome-
tallics 1996, 15, 5479.
Figure 2. Thermal ellipsoidal (30%) plot of 2. Hydrogen atoms are
not shown. Selected bond distances (Å) and angles (deg) are the
following: Al(1)-S(1) ) 2.2235(7), Al(1)-N(1) ) 1.991(4), Al(1)-
S(1)-Al(1a) ) 97.82(6), S(1)-Al(1)-S(1a) ) 114.61(2), S(1)-Al-
(1)-N(1) ) 103.65(3).
(13) Uhl, W.; Vester, A.; Hiller, W. J. Organomet. Chem. 1993, 443,
9-17.
(14) Ruhlandt-Senge, K.; Power, P. P. Inorg. Chem. 1991, 30, 2633.
(15) Boardman, A.; Small, R. W. H.; Worrall, I. J. Inorg. Chim. Acta
1986, 120, L23-L24.
(16) (a) Mu¨ller, D.; Hahn, H. Z. Anorg. Allg. Chem. 1978, 438, 258. (b)
Krebs, B.; Greiwing, H. Acta Chem. Scand. 1991, 45, 833.
(17) Krebs, B.; Voelker, D.; Stiller, K.-O. Inorg. Chim. Acta 1982, 65,
L101-L102.
unidentified) insoluble solid but having both Al-H and Al-S
IR absorptions.
The Al-N and Al-S structural parameters in 1 and 2 are
consistent with currently available data on related complexes.
For example, the Al-N distances in 1 (2.032(7) Å) and 2 (1.991-
(4) Å) may be compared to the 2.011(9) Å observed in {Me3-
(18) A new high-temperature hexagonal modification of Al2S3 involves
half of the aluminum atoms in trigonal bipyramidal coordination, how-
ever: Krebs, B.; Schiemann, A.; La¨ge, M. Z. Anorg. Allg. Chem. 1993,
619, 983.
(19) Krebs, B.; Greiwing, H. Z. Anorg. Allg. Chem. 1992, 616, 145.