New route to organoaluminium sulfides: Synthesis of (Mes*AlS)2 (Mes* = -C6H2But3-2,4,6) and its dimethyl sulfoxide adduct [Mes*AlS(OSMe2)]2

Article abstract of DOI:10.1039/a707142f

Treatment of the alane (Mes*AlH₂)₂ (Mes* = -C₆H₂Bu^t₃2,4,6) with S(SiMe₃)₂ in refluxing toluene affords the novel organoaluminium sulfide (Mes*AlS)₂ 1 which has a previously unobserved dimeric structure; treatment of 1 with 2 equiv. of Me₂SO furnishes the complex [Mes*AlS(OSMe₂)]₂ 2 in which a dimeric configuration is retained, and which shows weak intermolecular interactions between neighboring dimers.

Full text of DOI:10.1039/a707142f

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New route to organoaluminium sulfides: synthesis of (Mes*AlS)2 (Mes* =
-C6H2But3-2,4,6) and its dimethyl sulfoxide adduct [Mes*AlS(OSMe2)]2
Rudolf J. Wehmschulte and Philip P. Power*
Department of Chemistry, University of California, Davis, California 95616, USA
Treatment of the alane (Mes*AlH2)2 (Mes* = -C6H2But3-
2,4,6) with S(SiMe3)2 in refluxing toluene affords the novel
organoaluminium sulfide (Mes*AlS)2 1 which has a pre-
viously unobserved dimeric structure; treatment of 1 with 2
equiv. of Me2SO furnishes the complex [Mes*AlS(OSMe2)]2
2 in which a dimeric configuration is retained, and which
shows weak intermolecular interactions between neighbor-
ing dimers.
The angle between the normals to the (AlS)2 and aromatic ring
planes is 89.3°.
The dimeric structure of 1 may be contrasted with the
tetrameric structure of the corresponding oxide species
(Mes*AlO)44 which features an almost planar, eight-membered
Al4O4 ring with wide (ca. 151°) Al–O–Al angles. The lower
aggregation in 1 thus, may be a consequence of the reluctance of
the S atoms to hybridize which imposes a narrower interbond
angle. This leads to greater steric congestion in the molecule
which results in the lower degree of aggregation observed for 1.
Apparently, 1 is only the second example of a mono-
organoaluminium sulfide to be fully structurally characterized.
The only previous example is the tetrameric species [(Me2Et-
Group 13 organometallic chalcogenide species of formula
(RME)n (R = alkyl, aryl; M = Al, Ga, In; E = O–Te) are
usually synthesized with use of the organometallic precursors
MR3.1 For the heavier chalcogenide derivatives, direct inter-
action of the elements themselves (i.e. S, Se, Te) with the metal
trialkyls has afforded several new compounds which have three-
dimensional cage structures.2 For the lighter oxide derivatives,
however, the reaction between water (or water complexed in
metal salts)3 remains the preferred method of synthesis of
(RMO)n compounds.† Recently, it has been shown that
aluminium hydride compounds are also useful precursors for
2d
C)AlS]4 which has an Al4S4 cubane structure with Al–S
distances in the range 2.295(8)–2.319(9) Å. The longer Al–S
distances in that compound are due to the higher coordination
numbers of both Al (four) and S (three). The short Al–S
distances in 1 are similar to those observed in the low-
6
coordinate compounds Al(SMes*)3 [Al–S 2.172(2)–2.191(2)
7
Å], S[Al{CH(SiMe3)2}]2
[Al–S 2.187(4) Å] and
the synthesis of organoalumoxanes.4 Thus, the reaction of the
Al4I4S2(SMe)48 [Al–S (two-coordinate) 2.16(1)–2.20(1) Å].
The dimethyl sulfoxide adduct 2 was prepared by the addition
of 2 equiv. of Me2SO to 1 in benzene. Complex 2 was formed
essentially instantaneously and it is precipitated from benzene at
room temperature. Heating the solution to reflux temperature
resulted in redissolution of the precipitate and cooling slowly
resulted in crystals suitable for X-ray crystallography. The
X-ray data for 2 show that the dimeric Al2S2 core structure (Fig.
2) remains intact and that the metals are each complexed by one
dimethyl sulfoxide molecule which are disposed on opposite
sides of the Al2S2 core. This results in an increase of ca. 0.05 Å
in the Al–S bond lengths which span the narrow range
2.243(2)–2.259(2) Å. The Al–C distances are lengthened by
about the same amount; from 1.956(2) Å in 1 to an average of
2.022(8) Å in 2. The average Al–O distance is 1.86(1) Å, which
is within the range found in related complexes.9 Also, the Al2S2
core is folded slightly (fold angle 167.5°) along the S(1)···S(2)
axis. Although each Al is complexed by one Me2SO, it can be
seen from Fig. 2 that the relative orientation of each donor
molecule is different. Thus, the Me2SO containing O(1) is
oriented such that the SMe2 moiety lies above the Al2S2 core
whereas the O(2) containing Me2SO is oriented away from the
core. These different orientations are reflected in different Al–
O–S angles of 114.2(2)° at O(1) and 130.0(2) at O(2). It seems
that this unusual arrangement is a result of some weak
intermolecular interactions involving the Me2SO donor contain-
ing O(2). These interactions involve relatively short O···H
distances [e.g. O(2)···H(40E) 2.89 Å, O(2)···H(39F) 2.63 Å],
and S···H distances [e.g. S(1)···H(39C) 3.04 Å, S(2)···H(40E)
3.02 Å]. Another notable feature of the structure of 2 is the
distorted geometry at the ipso-C atoms of the Mes* ligands. The
averaged aromatic ring planes are bent by ca. 25° from the Al–C
vector lines. Similar distortions have been observed in other
Mes* group 13 derivatives.10
5
hydride (Mes*AlH2)2 (Mes*
=
-C6H2But3-2,4,6) with
(Me2SiO)3 affords the unique tetramer (Mes*AlO)4 with
elimination of SiH2Me2. We now report that the reaction of
(Mes*AlH2)2 with S(SiMe3)2‡ affords the unique, dimeric,
heavier chalcogenide derivative (Mes*AlS)2 1 and that treat-
ment of 1 with Me2SO does not effect dissociation of the
dimeric structure but affords the adduct [Mes*AlS(OSMe2)]2,
2.
Compound 1, which displays high thermal stability (mp >
200 °C), can be synthesized§ in almost quantitative yield by
5
refluxing (Mes*AlH2)2 with 2 equiv. of S(SiMe3)2 in either
toluene or n-octane. X-Ray crystallographic data¶ for 1 show
that it crystallizes as dimeric units (Fig. 1) which have a
crystallographically required inversion center. The planar Al2S2
core is characterized by almost equal Al–S distances of
2.2083(9) and 2.2107(14) Å and internal ring angles of
78.09(3)° at S and 101.91(3)° at Al. The external S–Al–C
angles, 127.94(7) and 130.14(7)°, are quite similar, so that the
sum of the angles at Al is 359.99° indicating strictly planar
coordination at Al. However, there are also short (2.26–2.33 Å)
interactions between a number of ortho-But H atoms and Al.
Fig. 1 Thermal ellipsoidal (30%) plot of 1 with H atoms not shown. Some
important bond distances (Å) and angles (°): Al(1)–S(1) 2.2083(9), Al(1)–
S(1A) 2.2107(14), Al–C(1) 1.956(2), Al(1)···Al(1A) 2.7835(13); Al(1)–
S(1)–Al(1A) 78.09(3), S(1)–Al(1)–S(1A) 101.91(3), S(1)–Al(1)–C(1)
127.94(7), S(1A)–Al(1)–C(1) 130.14(7).
Finally, although no dissociation of the dimeric 1 was
effected by the addition of Me2SO, attempted redissolution of
isolated 2 results in its partial decomposition and production of
Chem. Commun., 1998
335

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1 or 1·PhMe: A solution of (Mes*AlH2)25 (1.05 g, 1.91 mmol) in toluene
(25 ml) was heated with (Me3Si)2S (0.81 ml, 3.82 mmol, 0.68 g) at room
temp. The clear, colorless solution was heated to 100–105 °C for ca. 21 h
during which time large colorless plates of 1·PhMe formed. Yield: 1.25 g,
93%. Mp: turns opaque at 120–140 °C (desolvation), melts at 305–310 °C.
Crystals of unsolvated 1 suitable for X-ray diffraction studies were obtained
via a similar procedure by the reaction of (Mes*AlH2)2 with (Me3Si)2S in
n-octane at 115–120 °C for 38 h. Yield: 42%. Mp: turns slowly opaque at
250–280 °C, melts at 310–312 °C. 1H NMR (C6D6, 85 °C): d 7.51 (s, m-H,
4 H), 1.81 (s, o-CH3, 36 H), 1.36 (s, p-CH3, 18 H).
2: Dimethyl sulfoxide (0.06 ml, 0.8 mmol, 0.062 g) was added to a slurry
of finely ground 1·PhMe (0.16 g, 0.23 mmol) in benzene (25 ml) at room
temp. to give an almost clear solution from which after a few seconds a fine,
colorless solid precipitates. This was dissolved by heating to reflux for ca.
1 min to afford a clear colorless solution from which, after 3 days at room
temp. ca. 0.04 g of colorless plates could be isolated. Yield: 23%. Mp: turns
red at 235 °C, gradually darkens to almost black at 300 °C, does not melt
below 300 °C.
It is noteworthy that 1 is practically insoluble in hydrocarbon solvents. It
can be solubilized by the addition of Me2SO or HMPA at elevated
temperatures (the range 60–80 °C works best). From these solutions crystals
are usually obtained upon cooling to room temp. These crystals do not
redissolve without decomposition.
¶ Crystal data at T = 130 K with Mo-Ka, (l = 0.71073 Å) radiation for 1
and Cu-Ka, (l = 1.54178 Å) radiation for 2: 1, C36H58Al2S2, M = 608.9,
monoclinic, space group C2/c, a = 26.924(5), b = 9.845(2), c = 16.780(3)
Å, b = 125.86(3)°, U = 3064(1) Å3, m = 0.219 mm21, Z = 4 (8/2), wR2
= 0.119 for all 4149 data, R1 = 0.047 for 3164 [I > 2s(I)] data; 2,
C
40H70Al2O2S4, M = 765.2 monoclinic, space group P21/n, a = 18.374(5),
Fig. 2 Computer generated drawing of 2. H atoms, except those involved in
intermolecular interactions, are not shown. Some important bond distances
(Å) and angles (°): Al(1)–S(1) 2.259(2), Al(1)–S(2) 2.243(2), Al(2)–S(1)
2.258(2), Al(2)–S(2) 2.247(2), Al(1)–O(1) 1.869(2), Al(2)–O(2) 1.847(3),
Al(1)–C(1) 2.014(4), Al(2)–C(21) 2.029(4), S(3)–O(1) 1.553(3), S(4)–O(2)
1.548(3), Al(1)···Al(2) = 2.999(2), S–C(Me) av 1.766(8); S(1)–Al(1)–S(2)
95.91(6), S(1)–Al(2)–S(2) 95.84(6), Al(1)–S(1)–Al(2) 83.20(5), Al(1)–
S(2)–Al(2) 83.83(5), S(1)–Al(1)–C(1) 118.79(12), S(2)–Al(1)–C(1)
118.25(12), O(1)–Al(1)–C(1) 115.30(14), O(2)–Al(2)–C(21) 115.16(14),
S(3)–O(1)–Al(1) 114.2(2), S(4)–O(2)–Al(2) 130.0(2).
b = 9.883(2), c = 24.587(3) Å, b = 91.16(2)°, U = 4464(2) Å3, m = 2.560
mm21, Z = 4, wR2 = 0.143 for all 5830 data, R1 = 0.053 for 4550 [I >
2s(I)] data. CCDC 182/706.
1 A. R. Barron, Comments Inorg. Chem., 1993, 14, 123.
2 (a) A. H. Cowley, R. A. Jones, P. R. Harris, D. A. Atwood, L. Contreras
and C. J. Burek, Angew. Chem., Int. Ed. Engl., 1991, 30, 1143; (b)
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1315.
an orange–red solid. Attempts to identify the composition of
this solid are currently underway.
We thank the National Science Foundation and the Donors of
the Petroleum Research Fund administered by the American
Chemical Society for financial support.
3 M. K. Mason, J. M. Smith, S. G. Bott and A. R. Barron, J. Am. Chem.
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5 R. J. Wehmschulte and P. P. Power, Inorg. Chem., 1994, 33, 5611.
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7 W. Uhl, A. Vester and W. Miller, J. Organomet. Chem., 1993, 443,
9.
8 A. Boardman, R. W. H. Small and I. J. Worrall, Inorg. Chim. Acta, 1986,
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Organometallics, 1990, 9, 3086.
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Notes and References
*E-mail: pppower@ucdavis.edu
† Alumoxanes of formula R2AlOAlR2 can be synthesized by the reaction of
triorganoaluminium compounds with species containing reactive oxygen
such as CO2, RC(O)NR2, MeCO2H and Me2SO. See: H. Sinn and W.
Kaminsky, Adv. Organomet. Chem., 1980, 18, 99; W. Uhl, M. Koch, W.
Hiller and M. Heckel, Angew. Chem., Int. Ed. Engl., 1995, 34, 989.
‡ The compound S(SiMe3)2 has been extensively used recently in the
synthesis of several transition metal sulfide cluster compounds. See: D.
Fenske and S. Dehnen, Chem. Eur. J., 1996, 2, 1407.
§ All manipulations were carried out under anaerobic and anhydrous
conditions. The compound (Mes*AlH2)2 was synthesized as described in
5
the literature and S(SiMe3)2 was purchased from Aldrich and used as
received.
Received in Bloomington, IN, USA, 2nd October 1997; 7/07142F
336
Chem. Commun., 1998