The first structurally characterized aluminum compound with two SH groups: [LAI(SH)2] (L = N(Ar)C(Me)CHC(Me)N(Ar), Ar = 2,6-i-Pr2C6H3) and the catalytic properties of the sulfur P(NMe2)3 system

Article abstract of DOI:10.1021/ja028801k

Surprisingly stable is the bis(hydrogen sulfide) of aluminum LAl(SH)₂ with two terminal arranged SH groups. The insertion of sulfur into the Al-H bonds is catalyzed by SP(NMe₂)₃. A possible mechanism is discussed. Copyright

Full text of DOI:10.1021/ja028801k

Published on Web 01/18/2003
The First Structurally Characterized Aluminum Compound with Two SH
Groups: [LAl(SH)2] (L ) N(Ar)C(Me)CHC(Me)N(Ar), Ar ) 2,6-i-Pr2C6H3) and the
Catalytic Properties of the Sulfur P(NMe2)3 System
Vojtech Jancik, Ying Peng, Herbert W. Roesky,* Jiyang Li, Dante Neculai, Ana M. Neculai, and
Regine Herbst-Irmer
Institute of Inorganic Chemistry, UniVersity of Goettingen, Tammannstrasse 4, D-37077 Goettingen, Germany
Received October 3, 2002 ; E-mail: hroesky@gwdg.de
Organoaluminum chalcogenides have attracted great attention
in recent years as important precursors in chemical vapor deposition
(CVD) and catalysts.1 Our success in preparing the unique
monomeric [LAl(SeH)2], where L is the â-diketiminato ligand
N(Ar)C(Me)CHC(Me)N(Ar) (Ar ) 2,6-i-Pr2C6H3)2 led us to explore
new species of this kind including sulfur analogues. In fact,
aluminum hydrides form aluminum sulfides with S8, H2S, or
S(SiMe3)2, that are either dimeric, tetrameric, or hexameric in the
solid state in which sulfur acts as a µ or µ3 ligand.3 Nonetheless,
there are no reports on organoaluminum compounds with Al-SH
bonds. Only few examples of structurally known species are those
of transition-metal complexes (Pd, Pt, Ru, Rh, Re, Cr, Fe, Ni, Ti,
and Zr) containing two terminal hydrogen sulfide groups.4 Among
the main group metals, only Ge has been reported to yield the stable
Figure 1. Molecular structure of 2. Hydrogen atoms with the exception of
the protons of the SH units, are omitted for clarity. Selected bond lengths
[Å] and angles [deg]: Al(1)-N(1) 1.891(1), Al(1)-S(1) 2.223(1), Al(1)-
(C6H11)3GeSH derivative,5 while Ga forms the dimeric [t-Bu2Ga-
(µ-SH)]2.6
S(2) 2.217(1), S(1)-H(1) 1.20 (2), S(2)-H(2) 1.21(3); N(1)-Al(1)-N(1A)
Thus, LAlH2 (1), prepared from LH and AlH3‚NMe3,2 reacted
97.3(1), N(1)-Al(1)-S(1) 114.3 (1), N(1)-Al(1)-S(2) 112.9 (1), S(1)-
Al(1)-S(2) 105.4(1), Al(1)-S(1)-H(1) 97 (1), Al(1)-S(2)-H(2) 91(2).
with elemental sulfur to give a mixture of several products.
However, a small amount of [LAl(SH)2] (2) formed after a reaction
time of 72 h at ambient temperature. Addition of a small amount
Scheme 1. Synthesis of [LAl(SH)2]
of P(NMe2)3 significantly increased the reaction rate. After 5 h,
the reaction was complete, and the yield of 2 increased to 90%
(Scheme 1).7 Furthermore, 2 was unexpectedly thermal stablesno
changes were observable after 3 h of heating at 80 °C. This can be
explained by the steric and electronic stabilizing properties of the
bulky â-diketiminato ligand.
AldS give the values for Al-S(H) (2.160 Å), S-H (1.33 Å), and
Al-S-H (96.0°), respectively.10 The latter angle is almost similar
to those in 2 (97 and 91°).
Compound 2 was characterized by analytical, spectroscopic and
single-crystal X-ray diffraction studies. The 1H NMR spectrum of
2 showed a high-field singlet (δ -0.88 ppm) which can be, by
comparison with the selenium analogue, assigned to the SH protons.
The IR spectrum exhibited a weak peak at 2549 cm-1 that is
comparable with the stretching bands of S-H in other metal-SH
bonded complexes (2520-2596 cm-1),4c-e,g,h but it is significantly
lower than the literature data for H2S (2615 cm-1).8 The mass
spectrum gave the molecular ion peak at m/e ) 510.
The unambiguous molecular geometry of 2 was determined by
X-ray crystallography. The pale yellow crystals of 2 were obtained
by slow cooling of its saturated solution in toluene. The structure
of 2 is shown in Figure 1.
Compound 2 is isostructural to the Se analogue. Taking the
difference in covalent radii (0.14 Å)9 into account, the Al-S bonds
(2.223 and 2.217 Å) are comparable with the Al-Se bonds (2.331
and 2.340 Å). Furthermore, the angle S-Al-S (105.4°) is very
similar to the Se-Al-Se angle (103.7°).2 The Al-S bond distances
are also comparable with those of bridging aluminum-(µ-S)-sulfides,
and the S-Al-S angle is in the range of those reported in the
literature.3a,c-f The S-H bond (1.2 Å) falls in the range (0.99-
1.40 Å) of those for terminal S-H groups in other metal
complexes.4d-f,5 SCF/3-21G* calculations for monomeric H-S-
To investigate the role of phosphine in the reaction, the 1H and
1
31P NMR spectroscopy was periodically monitored. From the H
NMR kinetic studies, it is evident that the reaction proceeds via an
unstable reactive intermediate [LAl(H)SH] to completion (Figure
2).
The 31P NMR spectrum showed that all of the phosphine is
immediately oxidized to SP(NMe2)3 (31P NMR δ 82.4 ppm;
literature12 81.5 ppm), indicating its role as a catalyst in the reaction.
This hypothesis was confirmed by carrying out another experiment
directly with SP(NMe2)3 as a catalyst, instead of P(NMe2)3, and
conversion of 1 to 2 was observed. However, no reaction between
1 and SP(NMe2)3 occurred when the components are used in a molar
ratio of 1:2 without adding additional sulfur. Therefore, we believe
that SP(NMe2)3 reacts in the first step by a [2 + 1] cycloaddition
with sulfur to form the reactive intermediate (S2)P(NMe2)3. Forma-
tion of such a species is also favored from theoretical calculations
for the model compound SPH3 using the RHF/3-21 G* method,
where ∆E is -183.0 kJ/mol for the reaction of SPH3 and S to (S2)-
PH3. It is most likely that (S2)P(NMe2)3 forms a complex with 2
by opening the S-S bond and, consequently, inserts into one of
the Al-H bonds to yield [LAl(H)-S-P(SH)(NMe2)3] as an inter-
9
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J. AM. CHEM. SOC. 2003, 125, 1452-1453
10.1021/ja028801k CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen
Industrie (predoctoral fellowship to V. J.) for funding.
Supporting Information Available: Full experimental data for
compound 2 (PDF), and details of the X-ray structure determination
of 2 (CIF). This material is available free of charge via Internet at http://
pubs.acs.org.
References
(1) Reviews: (a) Barron, A. R. AdV. Mater. Opt. Electron. 1995, 5, 245. (b)
Oliver, J. P.; Kumar, R.; Taghiof, M. In Coordination Chemistry of
Aluminum; Robinson, G. H., Ed.; VCH: New York, 1993; p 167.
(2) Cui, C.; Roesky, H. W.; Hao, H.; Schmidt, H.-G.; Noltemeyer, M.; Angew.
Chem. 2000, 112, 1885; Angew. Chem., Int. Ed. 2000, 39, 1815.
(3) (a) Wehmschulte, R. J.; Power, P. P. J. Am. Chem. Soc. 1997, 119, 9566.
(b) Harlan, C. F.; Gillan, E. G.; Bott, S. G.; Barron, A. R. Organometallics
1996, 15, 5479. (c) Schnitter, C.; Klemp, A.; Roesky, H. W.; Schmidt,
H.-G.; Ro¨pken, C.; Herbst-Irmer, R.; Noltemeyer, M. Eur. J. Inorg. Chem.
1998, 2033. (d) Ecker, A.; Ko¨ppe, R.; U¨ ffing, C.; Schno¨ckel, H. Z. Anorg.
Allg. Chem. 1998, 624, 817. (e) Wehmschulte, R. J.; Power, P. P. Chem.
Commun. 1998, 335. (f) Uhl, W.; Vester, A. J. Organomet. Chem. 1993,
443, 9. (g) Taghiof, M.; Heeg, M. J.; Bailey, M.; Dick, D. G.; Kumar, R.;
Hendershot, D. G.; Rahbarnoohi, H.; Oliver, J. P. Organometallics 1995,
14, 2903.
Figure 2. 1H NMR kinetic study of the conversion of 1 to [LAl(SH)2] (2).
Resonances between δ 1.5 and 1.55 ppm are assigned to the backbone
methyl groups (O), and the doublets belong to the anisotropic methyl groups
of the i-Pr moieties (×).
Scheme 2. Proposed Mechanism for Insertion of Sulfur into the
Al-H Bonds by Using P(NMe2)3 and Sulfur as a Catalytic System
(4) (a) Briant, C. E.; Hughes, G. R.; Minshall, P. C.; Michael, D.; Mingos, P.
J. Organomet. Chem. 1980, 202, C18. (b) Ghiraldi, C. A.; Midollini, S.;
Nuzzi, F.; Orlandini, A. Transition Met. Chem. 1983, 8, 73. (c) Arif, A.
M.; Hefner, J. G.; Jones, R. A.; Koschmieder, S. U. J. Coord. Chem.
1991, 23, 13. (d) Khorasani-Motlag, M.; Safari, N.; Pamplin, C. B.; Patrick,
B. O.; James, B. R. Inorg. Chim. Acta 2001, 320, 184. (e) Bottomley, F.;
Drummond, D. F.; Egharevba, G. O.; White, P. S. Organometallics 1986,
5, 1620. (f) Jessop, P. G.; Lee, C.-L.; Rastar, G.; James, B. R.; Lock, C.
J. L.; Faggiani, R. Inorg. Chem. 1992, 31, 4601. (g) Schwarz, D. E.;
Dopke, J. A.; Rauchfuss, T. B.; Wilson, S. R. Angew. Chem. 2001, 113,
2413. Angew. Chem., Int. Ed. 2001, 40, 2351. (h) Howard, W. A.; Parkin,
G. Organometallics 1993, 12, 2363.
(5) Brisse, F.; Be´langer-Garie´py, F.; Zacharie, B.; Gareau, Y.; Steliou, K.
mediate. In the latter step, an “umpolung” of the hydridic to the
protonic form of the hydrogen atom takes place. Finally, a proton
transfer occurs from one sulfur atom to another, and thus the catalyst
is regenerated (Scheme 2).
NouV. J. Chim. 1983, 7, 391.
(6) Power, M. B.; Barron, A. R. J. Chem. Soc., Chem. Commun. 1991, 1315.
(7) Toluene (15 mL) was added to a mixture of 1 (1.063 g, 2.230 mmol) and
sulfur (0.147 g, 4.572 mmol), and after complete dissolution of the sulfur,
P(NMe2)3 (0.03 mL, 0.02 mmol) was added. The reaction mixture was
stirred for an additional 5 h, concentrated to ∼3 mL, and stored overnight
at -32 °C. The resulting pale yellow crystals of 2 were filtered off, washed
with cold toluene (1 mL), and dried in vacuo. Yield 1.09 g (90%); mp
218 °C dec; 1H NMR (benzene-d6, 200.131 MHz): δ 7.13-7.11 (m, 6H;
Ar-H), 4.88 (s, 1H; γ-H), 3.47 (sept, 4H, 3JH-H ) 6.8 Hz; CHMe2), 1.51
(s, 6H; Me), 1.44 (d, 12H, 3JH-H ) 6.7 Hz; CHMe2), 1.10 (d, 12H, 3JH-H
) 6.8 Hz; CHMe2), -0.88 (s, 2H; SH). 13C NMR (benzene-d6, 50.325
MHz): δ 171.43 (CN), 144.44, 138.74, 127.51, 124.54 (Ar), 98.70 (γ-
C), 28.59 (CHMe2), 25.49 (CHMe2), 24.69 (CHMe2), 23.96 (Me).
(8) Allen, H. C., Jr.; Blaine, L. R.; Plyler, E. K. J. Chem. Phys. 1956, 24, 35;
J. Chem. Phys. 1956, 25, 1132.
To sum up, this work constitutes the first report on the synthesis
and structural characterization of species containing Al-SH units
of which we are aware. This work could be developed into new
strategies for the synthesis of mixed metal organometallics, due to
the latent acidic nature of the SH protons, and preparation of
aluminum sulfide clusters. Since SP(NMe2)3 was found to be an
excellent catalyst for the insertion of sulfur into Al-H bonds, further
investigations of this catalyst on insertion reactions of sulfur into
metal-hydrogen bonds, instead of the reaction with toxic H2S, is
therefore warranted. Such studies are currently underway in our
laboratories.
(9) Huheey, J. E. In Inorganic Chemistry: Principles of Structure and
ReactiVity; Harper & Row: New York, 1983; p 73.
(10) (a) Zyubina, T. S.; Charkin, O. P. Zh. Neorg. Khim. 1991, 36, 3083; Russ.
J. Inorg. Chem. 1991, 36, 1731. (b) Zyubina, T. S.; Charkin, O. P. Zh.
Neorg. Khim. 1991, 36, 752; Russ. J. Inorg. Chem. 1991, 36, 425.
(11) Tolkmith, H. J. Am. Chem. Soc. 1963, 85, 3246.
Acknowledgment. This work is dedicated to Professor Heinz
Georg Wagner on the occasion of his 75th birthday. We thank the
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