Selective synthesis and derivatization of alkali metal silanides MSi(SiH3)3

Article abstract of DOI:10.1002/chem.201201253

Greetings from silicon valley: Alkali metal silanides (H3Si)3Si-M+ were shown to be selectively accessible for the first time by the reaction of neopentasilane SiACHTUNGTRENUNG(SiH3)4 with tBuOM or iPr2NLi. The method allows the convenient derivatization of higher silicon hydrides and provides a simple access for unprecedented systematic studies on the chemical behavior of hydro-ACHTUNGTRENUNGpolysilanes (see scheme).

Full text of DOI:10.1002/chem.201201253

DOI: 10.1002/chem.201201253
Selective Synthesis and Derivatization of Alkali Metal Silanides MSiACHTUNTRGNEUNG(SiH3)3
Harald Stueger,*[a] Thomas Mitterfellner,[a] Roland Fischer,[a] Christoph Walkner,[a]
Matthias Patz,[b] and Stephan Wieber[b]
Solution-based deposition and processing techniques for
silicon attracted considerable attention just recently, because
they allow significant reduction of processing costs in the
manufacture of devices, such as light-emitting diodes, thin-
film transistors, or solar cells, compared with standard
vacuum-based approaches, such as the chemical vapor depo-
sition (CVD) method.[1] Open-chained and cyclic silicon hy-
drides of the composition SinH2n+2 or SinH2n, respectively,
are potential precursors in this context, and silicon layers
have been deposited successfully from solutions containing
hydrosilane oligomers obtained by photochemical or ther-
mal decomposition of cyclopentasilane Si5H10, cyclohexasi-
heteroatom dopants covalently linked to silicon (single-
source precursors).[6,7] The only compounds of this type de-
scribed in the literature so far are silyl phosphanes and ar-
sanes containing H3Si or H5Si2 groups, such as (H3Si)nEH3Àn
ACTHNUTRGNEUNG
(E=P, As),[8] H5Si2EH2,[9] (H5Si2)3P, [10] or H5Si2P(SiH3)2[11], in
which only (H3Si)3P and H3SiPH2 are accessible in prepara-
tive quantities.[12] Both compounds, however, are not ideal
as single-source precursors for liquid-phase Si deposition,
because their high volatility makes evaporation prior to
thermal decomposition during the film-forming process and,
therefore, considerable loss of the dopant element rather
likely. This problem could be circumvented, if the dopant
lane Si6H12, or neopentasilane Si
(SiH3)4 (Scheme 1).[2–4]
was attached to larger and less volatile Si H fragments. In
À
this context, the detailed investigation of chemical proper-
ties of selected higher silicon hydrides is of particular impor-
tance.
Although their synthesis and their physical properties are
well documented,[13,14] only few reports on chemical transfor-
mations involving higher silicon hydrides are described in
the literature including the partial halogenation of di-, tri-,
tetra-, and cyclohexasilane.[6,15] Redistribution reactions of
Si2H6 or Si3H8 under the influence of MSiH3 (M=Na, K) to
give sodium and potassium silanides MSinH2n+1 (M=Na, K;
n=3–5) containing branched oligosilanyl anions are also de-
scribed. These methods, however, require the handling of
pyrophoric gases, such as SiH4 and Si2H6, and usually afford
product mixtures, which are difficult or even impossible to
separate and frequently could only be analyzed after further
derivatization of the initial products.[16] Herein, we present
an alternative approach for the highly selective synthesis
and the derivatization of the alkali-metal silanides MSi-
Scheme 1. Deposition of silicon layers starting from Si5H10.[2]
n- or p-Doped silicon films can also be made by using this
method, if the hydrosilane precursor is mixed with appropri-
ate dopants, such as P4 or B10H14, prior to photo-oligomeri-
zation.[5] To prevent non-uniform dopant distribution and to
improve the electrical properties of the resulting semicon-
ductor film, it has been suggested to use hydrosilane precur-
sors for silicon-film deposition, which contain one or more
ACHTUNERGN(UNG SiH3)3 (M=Li, Na, K) starting from SiCAHTUNTGERN(NUGN SiH3)4, which is
easily accessible in preparative quantities by a standard liter-
ature procedure.[17]
In close analogy to Si
tBuOK under cleavage of one Si Si bond to give KSi-
(SiMe3)3 and tBuOSiMe3,[18] the reaction of Si
(SiH3)4 and
ACHTUGNTERN(NUNG SiMe3)4, which cleanly reacts with
[a] Prof. Dr. H. Stueger, Dr. T. Mitterfellner, Dr. R. Fischer,
Dr. C. Walkner
À
G
ACHTUNGTRENNUNG
Institute of Inorganic Chemistry
Graz University of Technology
Stremayrgasse 9, 8010 Graz (Austria)
Fax : (+43)31687332103
tBuOM (M=Li, Na, K) in coordinating solvents, such as di-
ethyl ether, DME, THF, or bis(2-methoxyethyl) ether (di-
glyme) at À308C afforded the alkali-metal silanides 1–3
along with tBuOSiH3 which quickly disproportionates to
give tBuO2SiH2 and SiH4 (Scheme 2).
E-mail: harald.stueger@tugraz.at
[b] Dr. M. Patz, Dr. S. Wieber
Creavis, Technologies & Innovation
Evonik Industries AG
Paul Baumannstrasse 1, 45764 Marl (Germany)
1
Thus, in the H NMR spectra of the reaction mixtures re-
corded after stirring SiACHTNUGTRNEUG(N SiH3)4 and tBuOM in a molar ratio
of 1:1 in THF for 30 min at À308C only one sharp signal in
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201253.
the typical range for SiH3 groups near d=3.4 ppm appeared,
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Chem. Eur. J. 2012, 18, 7662 – 7664

COMMUNICATION
Scheme 2. Synthesis of MSi
Si(SiH3)4.
ACHTUNGTRNE(NUNG SiH3)3 (M=Li, Na, K) (1–3) starting from
ACHTUNGTRENNUNG
whereas the coupled 29Si NMR spectra showed a quartet of
heptets centered at d=À77 ppm for the H3Si groups and
a multiplet close to d=À280 ppm for the central silicon
atom in 1–3 along with the signals of the secondary products
1
(tBuO)2SiH2 (d=À52.0 ppm, t, JSiÀH =241.3 Hz) and SiH4
1
(d=À94.8 ppm, p, JSiÀH =203.2 Hz). NMR parameters ob-
tained for 3 are consistent with literature data.[16c] The lithi-
um silanide 1 turned out to be accessible equally well from
Scheme 4. Derivatization of 1–3 with C- and Si-containing electrophiles.
SiACHTUNGTRENNUNG(SiH3)4 and iPr2NLi. However, in this case, iPr2NSiH3 is
formed as the second product (Scheme 3), which is some-
times advantageous, because after derivatization of 1,
iPr2NSiH3 can be separated from the desired product by
acid hydrolysis as the ammonium salt in contrast to
(tBuO)2SiH2.
dependent on the substituents attached to the chlorosilane
substrate. Although Ph3SiCl exclusively afforded 1,1,1-tri-
phenylneopentasilane (5), PhMe2SiCl and PhH2SiCl gave
the expected compounds 6 and 8 along with the disubstitut-
ed products 7 and 9 (Scheme 5).
Scheme 3. Synthesis of 1 through iPr2NLi.
Scheme 5. Mechanism proposed for the formation of the disubstitution
products 7 and 9.
Attempts to obtain crystals of 1–3 for X-ray crystallogra-
phy either by concentration of the solutions in vacuo or by
the addition of hydrocarbon solvents only led to the forma-
tion of insoluble yellow solids, which already has been ob-
served by Fehꢁr et al.[16c,d] Etheral solutions of 1–3, however,
can be stored and handled at room temperature at least for
several hours without any noticeable decomposition and
thus can be used directly for further derivatization reactions.
A summary of successful derivatization reactions of 1–3 per-
formed in this work is given in Scheme 4. Experimental de-
tails and analytical data can be found in the Supporting In-
formation.
Compounds 1–3 cleanly react in the expected way with
various C- and Si-containing electrophiles, which provides
an uncomplicated and easy-to-perform preparative access to
isotetrasilane and neopentasilane derivatives on a multigram
scale. Treatment of 1, for example, with methyl tosylate af-
The formation of 7 and 9 could be strongly suppressed, if
proper precautions are taken to prevent an excess of the
alkali-metal silanide in the reaction mixture, which is in line
with the mechanism proposed in Scheme 5. Thus, 6 and 8
could be synthesized with selectivities of 90 and 80%, re-
spectively, if the metal silanide solution is slowly added to
the chlorosilane, and if the reaction temperature is raised
from À30 to 08C. A similar tendency for the formation of
increased amounts of byproducts in the presence of excess
metal silanide has been observed earlier for the reaction of
KSiH3 with MeI or Me3EX (E=Si, Ge, Sn; X=Cl, Br).[20]
Compounds 4–9 were characterized by standard spectro-
scopic techniques. The molecular structure of 5 was further
investigated by single-crystal X-ray crystallography
(Figure 1).[21] Compounds 5 crystallizes in the trigonal space
forded MeSiACHTUNGTRENNUNG(SiH3)3 (5) nearly quantitatively, whereas the
¯
À
substitution reaction of 1–3 with phenylchlorosilanes
PhnR3ÀnSiCl (R=Me, H) gave the neopentasilanes 5–9. In
this case, product distribution turned out to be somewhat
group R3. The Si SiH3 distance of 233.4 pm agrees well
[16e]
with the values observed for MeSi
(SiH3)3
and
[16f]
SiG
in the gas phase. The tetrahedral geometry
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H. Stueger et al.
[4] S. Wieber, M. Patz, R. Carius, T. Bronger, M. Cçlle, Evonik Degussa
GmbH, WO2011/061106 A2, 2011.
[5] a) H. Tanaka, H. Iwasawa, D. Wang, N. Toyoda, T. Aoki, I. Yudasa-
ka, Y. Matsuki, T. Shimoda, M. Furusawa, Jpn. J. Appl. Phys. 2007,
46, L886; b) M. Furusawa, T. Aoki (Seiko Epson Corp.),
JP2003318119, 2003.
[6] D. Schulz, X. Dai, K. J. Nelson, P. Boudjouk (NDSU Research
Foundation), WO2009/148878 A2, 2009.
[7] a) Y. Matsuki (JSR Corp.), EP1092755 A1, 2001; b) V. K. Dioumaev
(Kovio Inc.), US2007/0078252, 2007; c) F. Zuercher, W. Guo, J.
Rockenberger, V. K. Dioumaev, B. Ridley, K. Kunze, J. M. Cleeves
(Kovio Inc.), US2008/7314513B1, 2008.
[8] a) E. Amberger, H. Boeters, Angew. Chem. 1962, 74, 32; Angew.
Chem. Int. Ed. Engl. 1962, 1, 52; b) E. Amberger, H. Boeters,
Angew. Chem. 1962, 1, 293; Angew. Chem. Int. Ed. Engl. 1962, 1,
268; c) D. Sudrashan, S. D. Gokhale, W. L. Jolly, Inorg. Chem. 1965,
4, 596; d) J. E. Drake, J. Simpson, J. Chem. Soc. A 1968, 1039; e) C.
Glidewell, G. M. Sheldrick, J. Chem. Soc. A 1969, 350; f) J. E.
Drake, J. W. Anderson, J. Chem. Soc. A 1970, 3131; g) G. Fritz, H.
Schꢂfer, Z. Anorg. Allg. Chem. 1971, 385, 243.
[9] a) J. E. Drake, N. Goddard, J. Simpson, Inorg. Mater. Inorg. Nucl.
Chem. Letters 1968, 4, 361; b) A. D. Norman, Chem. Commun. 1968,
812.
[10] a) J. E. Drake, N. Goddard, J. Chem. Soc. A 1969, 662; b) D. E.
Wingeletz, A. D. Norman, Phosphorus, Sulfur, and Silicon 1988, 39,
123.
Figure 1. Molecular structure of 5 in the crystal (50% thermal probability
À
ellipsoids). Selected bond lengths [pm] and angles [8]: Si1 Si2 234.4(1),
À
Si2 Si3 233.4 (1); Si3-Si2-Si3 111.3(1), Si3-Si2-Si1 107.6(1).
[11] J. E. Drake, J. W. Anderson, J. Chem. Soc. A 1971, 2246.
[12] a) J. B. Tice, A. V. G. Chizmeshya, J. Tolle, V. R. D’Costa, J. Menen-
dez, J. Kouvetakis, Dalton Trans. 2010, 39, 4551; b) G. Becker, B. Es-
chbach, D. Kꢂshammer, O. Mundt, Z. Anorg. Allg. Chem. 1994, 620,
29.
around Si2 is slightly distorted with Si-Si-Si bond angles of
À
111.38 and 107.68 and a slightly elongated Si1 Si2 bond
length.
In summary, we have discovered a novel method for the
selective synthesis and isolation of branched higher silicon
hydrides on a preparative scale starting from SiACHTNUTRGNE(UNG SiH3)4,
[13] For
a discussion and leading references, see: a) E. Hengge in
Gmelin Handbook of Inorganic Chemistry, Vol. 15(B1) (Ed.: U.
Krꢃerke), Springer, Berlin, 1982, p.203; b) J. H. Lorenz, Sol. Energy
Res. Inst., Report, Energy Res. Abstr. 1984, 9, Abstr. No. 18359;
c) H. G. Horn, Chemikerzeitung 1986, 4, 142.
which is easily accessible from commercially available Si2Cl6
in preparative quantities by a standard literature procedure.
Our simple preparative approach avoids the handling of py-
rophoric gases, such as SiH4 and Si2H6, and thus offers con-
siderable potential for the systematic investigation of physi-
cal and chemical properties of defined higher silicon hy-
drides and their derivatives, which are of fundamental im-
portance for future applications of this class of compounds
for the deposition of n- or p-doped silicon layers.
[14] a) E. Hengge, G. Bauer, Angew. Chem. 1973, 85, 304; b) E. Hengge,
D. Kovar, Angew. Chem. 1977, 89, 417.
[15] An excellent summary on known halogenation reactions of higher
silicon hydrides can be found in Ref. [13a].
[16] a) F. Fehꢁr, R. Freund, Inorg. Nucl. Chem. Lett. 1973, 9, 937; b) F.
Fehꢁr, R. Freund, Inorg. Nucl. Chem. Lett. 1974, 10, 561; c) F. Fehꢁr,
M. Krancher, Z. Naturforsch. 1985, 40b, 1301; d) F. Fehꢁr, M.
Krancher, M. Fehꢁr, Z. Anorg. Allg. Chem. 1991, 606, 7; e) T. Lo-
breyer, J. Oeler, W. Sundermeyer, H. Oberhammer, Chem. Ber.
1993, 126, 665; f) T. Lobreyer, W. Sundermeyer, H. Oberhammer,
Chem. Ber. 1994, 127, 2111.
[17] a) J. P. Cannady, X. Zhou (Dow Corning Corp.), WO2008/051328,
2008; b) S. Wieber, M. Trocha, H. Rauleder, E. Mꢃh, H. Stꢃger, C.
Walkner (Evonik Degussa GmbH), DE102009053804, 2011.
[18] C. Marschner, Eur. J. Inorg. Chem. 1998, 221.
Keywords: doping · hydrides · metallation · silanes · silicon
[1] For a discussion and leading references on solution-based Si deposi-
tion, see: a) Solution Processing of Inorganic Materials (Ed.: D. B.
Mitzi), Wiley, Hoboken, 2011; b) J. Sun, B. Zhang, H. E. Katz, Adv.
Funct. Mater. 2011, 21, 29.
[2] T. Shimoda, Y. Matsuki, M. Furusawa, T. Aoki, I. Yudasaka, H.
Tanaka, H. Iwasawa, D. Wang, M. Miyasaka, Y. Takeuchi, Nature
2006, 440, 783.
[3] S. Han, X. Dai, P. Loy, J. Lovaasen, J. Huether, J. M. Hoey, A.
Wagner, J. Sandstrom, D. Bunzow, O. F. Swenson, I. S. Akhatov,
D. L. Schulz, J. Non-Cryst. Solids 2008, 354, 2623.
[19] a) F. Fehꢁr, D. Schinkitz, J. Schaaf, Z. Anorg. Allg. Chem. 1971, 383,
303; b) F. Fehꢁr, F. Ocklenburg, D. Skrodzki, Z. Naturforsch. 1980,
35b, 869.
[20] E. Amberger, E. Mꢃhlhofer, J. Organomet. Chem. 1968, 12, 55.
[21] CCDC-860495 (5) contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Received: April 12, 2012
Published online: May 21, 2012
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