Reactions of hydridochlorosilanes with 2,2′ -bipyridine and 1.10-phenanthroline: Complexation versus dismutation and metal-catalyst-free 1.4-hydrosilylation

Article abstract of DOI:10.1021/ic901620e

Stable in the solid state and isolable in high yields are adducts of H ₂SiCI₂, HSiCl₃, and RSiCl₃ (R = Me, Ph) with the N, N'-chelating ligands 1,10-phenanthroline (phen; 1c), 2,2'-bipyridine (bipy; 1b), and (to a limited extent) N,N,N, Ntetramethylethylenediamine (tmeda; 1a). The products were comprehensively characterized via multinuclear solution and solid-state NMR spectroscopy, including analysis of the ²⁹Si NMR chemical shift anisotropy tensors, Raman spectroscopy, elemental analyses, and, for SiCI₄(phen) (2c), HSiCl₃(bipy) (3b), H₂SiCl₂(bipy) (4b), MeSiCl₃(phen) (5c), and PhSiCl₃(phen) (6c), single-crystal X-ray structure analyses. The latter revealed that the nonchlorine substituents (i.e., H, Me, and Ph) are exclusively trans-disposed to the N-donor atoms of the chelating ligands. A dismutation of the complexes HXSiCl₂(bipy) and HXSiCl₂(tmeda) (X = H or Cl) was observed in polar solvents at elevated temperatures. This reaction is more pronounced when phen is used instead of bipy or tmeda. For MeHSiCl₂(phen), in addition to undergoing H-Cl redistribution accompanied by the formation of 5c, an unexpected 1,4-hydrosilylation was observed. The latter was proven NMR-spectroscopically and by a single-crystal X-ray structure analysis of the product MeSiCl ₂(4H-phen) (7), a pentacoordinated silicon compound with a trigonal-bipyramidal arrangement of the subsituents and the methyl group located in an equatorial position.

Full text of DOI:10.1021/ic901620e

Inorg. Chem. 2010, 49, 2667–2673 2667
DOI: 10.1021/ic901620e
Reactions of Hydridochlorosilanes with 2,20-Bipyridine and 1,10-Phenanthroline:
Complexation versus Dismutation and Metal-Catalyst-Free 1,4-Hydrosilylation
†
†
†
†
‡
,†
€
Gerrit W. Fester, Jana Eckstein, Daniela Gerlach, Jorg Wagler, Erica Brendler, and Edwin Kroke*
†Institut fu€r Anorganische Chemie, ‡Institut fu€r Analytische Chemie, TU Bergakademie Freiberg, Leipziger
Strasse 29, 09596 Freiberg, Germany
Received August 13, 2009
Stable in the solid state and isolable in high yields are adducts of H2SiCl2, HSiCl3, and RSiCl3 (R = Me, Ph) with the N,
N0-chelating ligands 1,10-phenanthroline (phen; 1c), 2,20-bipyridine (bipy; 1b), and (to a limited extent) N,N,N0,N0-
tetramethylethylenediamine (tmeda; 1a). The products were comprehensively characterized via multinuclear solution
and solid-state NMR spectroscopy, including analysis of the 29Si NMR chemical shift anisotropy tensors, Raman
spectroscopy, elemental analyses, and, for SiCl4(phen) (2c), HSiCl3(bipy) (3b), H2SiCl2(bipy) (4b), MeSiCl3(phen)
(5c), and PhSiCl3(phen) (6c), single-crystal X-ray structure analyses. The latter revealed that the nonchlorine
substituents (i.e., H, Me, and Ph) are exclusively trans-disposed to the N-donor atoms of the chelating ligands. A
dismutation of the complexes HXSiCl2(bipy) and HXSiCl2(tmeda) (X = H or Cl) was observed in polar solvents at
elevated temperatures. This reaction is more pronounced when phen is used instead of bipy or tmeda. For
MeHSiCl2(phen), in addition to undergoing H-Cl redistribution accompanied by the formation of 5c, an unexpected
1,4-hydrosilylation was observed. The latter was proven NMR-spectroscopically and by a single-crystal X-ray structure
analysis of the product MeSiCl2(4H-phen) (7), a pentacoordinated silicon compound with a trigonal-bipyramidal
arrangement of the subsituents and the methyl group located in an equatorial position.
Scheme 1. Reaction of Trichlorosilane with tmeda
Introduction
Hydridochlorosilanes of the type HxSiCl4-x play a crucial
role in the production process of ultrapure silicon (the
Siemens process), in addition to being starting materials
for numerous organosilicon compounds.1 Among products
molecular structures of which have been analyzed carefully,3
derived from hydridochlorosilanes, adducts with additional
donor molecules have attracted particular attention.2 This
might imply that compounds of the type HxSiCl4-x(donor)2
with x = 1 or 2 are already well-known from the literature. In
contrast to pyridine adducts HxSiCl4-x(Rpy)2 (Rpy = pyridine
and substituted pyridines), which have been studied and the
only two structurally characterized complexes HxSiCl4-x
-
(donor) comprising a bidentate N,N0-chelating ligand have
been described so far: In the 1960s, Campell-Fergusson and
Ebsworth reported the reaction of N,N,N0,N0-tetramethyl-
ethylenediamine (tmeda) with SiHCl3 in a 1:1 ratio to give
(tmeda)SiHCl3 (Scheme 1):
The poor solubility of the reaction product indicated
polymeric or ionic structures.4 X-ray diffraction analysis,
however, revealed the monomeric structure of the complex.5
In sharp contrast with related hydridochlorosilane com-
plexes, the products of the reactions of silicon tetrahalides with
2,20-bipyridine (bipy) and 1,10-phenanthroline (phen) as che-
lating N(sp2)N0(sp2)-donor building blocks are well-known.6
*To whom correspondence should be addressed. E-mail: edwin.kroke@
chemie.tu-freiberg.de. Fax: (þ49)3731-39-4058.
(1) (a) Klockner, H. J.; Eschwey, M. Chem.-Ing.-Tech. 1988, 60, 815–821.
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74, 621–625. (c) Seth, K. K. U.S. Patent 4,395,389, 1983. (d) Morimoto, S. U.S.
Patent 4,613,489, 1985. (e) Litteral, C. J. DE Patent 2162537, 1972. (f) Bakay, C. J.
DE Patent 2507864, 1975. (g) Vorotyntsev, V. M. RU Patent 2152902, 2000.
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P. J. Organomet. Chem. 1990, 400, 81–106. (c) Corriu, R. J. P.; Guerin, C.;
Henner, B.; Wang, Q. Inorg. Chim. Acta 1992, 198-200, 705–713. (d) Chuit, C.;
Corriu, R. J. P.; Reye, C.; Young, J. C. Chem. Rev. 1993, 93, 1371–1448.
(3) (a) Wannagat, U.; Schwarz, R.; Voss, H.; Knauff, K. G. Z. Anorg.
Allg. Chem. 1954, 227, 73–88. (b) Burg, A. B. J. Am. Chem. Soc. 1954, 76,
2674–2675. (c) Fleischer, H.; Hensen, K.; Stumpf, T. Chem. Ber. 1996, 129, 765–
(4) Campell-Fergusson, H. J.; Ebsworth, E. A. V. J. Chem. Soc. A 1966,
1508–1514. Campell-Fergusson, H. J.; Ebsworth, E. A. V. J. Chem. Soc. A 1967,
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Soc. 1964, 238–244. (b) Wannagat, U.; Hensen, K.; Petsch, P.; Vielberg, F.
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Soc. 1998, 120, 10402–10408. (e) Hensen, K.; Kettner, M.; Stumpf, T.; Bolte, M.
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r
2010 American Chemical Society
Published on Web 02/16/2010
pubs.acs.org/IC

2668 Inorganic Chemistry, Vol. 49, No. 6, 2010
Fester et al.
In this context, it was pointed out that the compounds SiX4-
(bipy) and SiX4(phen) are more stable than their pyridine
analogues SiX4(py)2, a principle of general applicability.7
Kummer et al. reported that, with reference to the same silane,
the complex stability increases in the order py < bipy < phen.8
In another particular case, a comparative study showed that
dissociation of the crystalline adduct of silicon tetrachloride
with bipy commences at noticeably higher temperatures than a
similar decomposition of the pyridine adduct,9 and computa-
tional studies support these findings.10
Whereas in trans-N-donor-substituted silanes (e.g., with
pyridine ligands) the four formally covalently bound groups,
e.g., Si-X and Si-H, are forced to arrange in the equatorial
plane of an almost octahedral coordination sphere, investi-
gations on bipy and phen complexes of silanes still lack the
information as to which coordination sites (trans- or cis-N)
will be occupied by Si-X (X = F, Cl, Br), Si-H, and Si-C
groups.11
Herein we report the systematic investigation of hexa-
coordinated silicon compounds from hydridochlorosilanes
(H2SiCl2, HSiCl3, MeHSiCl2, and PhHSiCl2) and chlorosi-
lanes (SiCl4, MeSiCl3, and PhSiCl3) with the N,N0-chelating
ligands tmeda, bipy, and phen. Differences between bipy and
phen with respect to complexation versus dismutation as
competitive reactions became clear, and an unexpected 1,4-
hydrosilylation was found to take place at the phen ligand.
placed in idealized positions and isotropically refined (riding
model). Si-bound H atoms were found by analysis of the
residual electron density and refined without bond-length
restraints. Structure solution and refinement of F2 against all
reflections were carried out with the software SHELXS-97
€
€
and SHELXL-97 [G. M. Sheldrick, Universitat Gottingen
(1986-1997)]. The structure of 5c was determined from a data
set collected from a twin [twin law: (1, 0, 0)(0, 1, 0)(0, 0, -1),
populations 58% and 42%], the twinning of which resulted
from the monoclinic angle being close to 90°. In a similar
manner, compound 4b crystallized as a twin because of the
combination of very similar crystallographic axes a and b,
together with very similar angles R and β. Thus, the structure
was refined using the twin matrix (0, 1, 0)(1, 0, 0)(0, 0, 1),
resulting in a population of 3% for a twin component and
a significant decrease of the R factor (by ca. 0.01). Data of
the structural determination and refinement for the herein-
presented crystal structures are summarized in the supporting
Information (Tables S1 and S2).
Starting materials H2SiCl2 (Degussa), HSiCl3 (Acros),
SiCl4 (Acros), HSiCl2Me (Aldrich), HSiCl2Ph (Aldrich),
MeSiCl3 (Merck), PhSiCl3 (ABCR), 1,10-phenanthroline
(Chempur), 2,20-bipyridine(ABCR), N,N,N0,N0-tetramethyl-
ethylenediamine (Merck), and pyridine (Riedel de Haen)
were commercially available. Solid compounds were dried
under vacuum for several hours. All chlorosilanes were used
as supplied.
General Procedure for the Syntheses of 3-4a, 2-4b, and 2-4c.
The respective silane (5 mmol) was dissolved in toluene (20 mL)
and stirred at -78 °C, and the desired N,N0-chelating ligand
(10 mmol) was added as a solid (tmeda as a liquid). The products
precipitated as colorless solids. The suspension was stirred for
1 h at -78 °C and then allowed to slowly adjust to ambient
temperature. The white precipitate was filtered off, washed with
toluene, and dried under vacuum. Modifications to this proce-
dure are outlined if applicable.
The compounds 5-6b, 5-6c, and 2a were prepared according
to the following general route: To the solid N,N0-chelating
ligand (10 mmol), which was stirred at -78 °C, was added the
silane (4 mL). The products precipitated as colorless solids. The
suspension was stirred for 1 h at -78 °C and was then allowed to
slowly adjust to ambient temperature. The precipitate was
filtered off, washed with the respective silane, and dried under
vacuum. Modifications to this procedure are outlined if applic-
able. Spectroscopic and analytical details are provided in the
Supporting Information.
Experimental Section
All reactions were carried out under an atmosphere of dry
argon using the Schlenk technique. Solvents were dried and
purified by standard methods.
Cross-polarization/magic angle spinning (CP/MAS)
NMR spectra were recorded on a 400 MHz Bruker Avance
WB spectrometer using a 7 mm probe with zirconia rotors
and KelF inserts operating at 400.23, 100.61, and 79.51 MHz
1
for H, 13C, and 29Si NMR spectra, respectively. Chemical
shiftsare reported inppmrelativetotetramethylsilane(TMS)
using Q8M8 [octakis(trimethylsiloxy)octasilsesquioxane] and
adamantane as the external standard for 29Si and 13C NMR,
respectively. If not otherwise mentioned, CP/MAS spectra
wererecorded atνspin = 4 kHz and13C NMR usingtheTOSS
sequence.
Raman spectra were recorded on a Bruker RFS 100/S
instrument operating with a Nd/YAG laser. Determination
of the chlorine content of compounds 3b and 4b was per-
formed by hydrolysis of 0.19 g of 3b and of 0.21 g of 4b in
100 mL of a diluted sodium hydroxide solution, followed by
chloride quantification with ion chromatography (Dionex
ICS-2000, eluent 22 mM KOH, column AS11_HC, electrical
conductivity measurement). C, H, and N analyses were
performed using a vario microcube (Elementar).
Yields for Compounds 2-6b, 2c, 5-6c, and 2-4a. SiCl4(bipy)
(2b): 1.58 g (4.85 mmol; 97%). HSiCl3(bipy) (3b): 1.44 g (4.94
mmol; 99%). H2SiCl2(bipy) (4b): 1.35 g (4.96 mmol; 99%).
MeSiCl3(bipy) (5b): 1.48 g (4.84 mmol; 96.8%). PhSiCl3(bipy)
(6b): 0.92 g (2.50 mmol; 50%). SiCl4(phen) (2c): 1.72 g (4.91
mmol; 98.3%). MeSiCl3(phen) (5c): 1.57 g (4.76 mmol; 95.2%).
PhSiCl3(phen) (6c): 1.0 g (2.55 mmol; 51.1%). SiCl4(tmeda)
(2a): 1.20 g (4.2 mmol; 83.9%). HSiCl3(tmeda) (3a): 1.20 g
(4.80 mmol; 95.4%). H2SiCl2(tmeda) (4a): 1.05 g (4.8 mmol;
96.7%).
Single-crystal X-ray diffraction data were collected on a
Bruker Nonius X8 APEX2 CCD diffractometer using Mo
KRradiation. Structuresweresolvedwithdirectmethodsand
refined with full-matrix least-squares methods. All non-H
atoms were anisotropically refined. C-bound H atoms were
Results and Discussion
In analogy to the previously described direct reaction of
3f
12
H2SiCl2 and HSiCl3 with pyridines, the straightforward
formation of the octahedrally coordinated silicon compounds
of bipy (2-4b) and phen (2-4c) was expected (Scheme 2, top).
Furthermore, tmeda was used as an N,N0-chelating ligand
(Scheme 2, bottom).
(7) Davydova, E. I.; Timoshkin, A. Yu.; Sevast’yanova, T. N.; Suvorov,
A. V.; Schaefer, H. F. Russ. J. Gen. Chem. 2003, 11, 1742–1750.
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29–54.
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Zh. Obshch. Khim. 2002, 72, 64.
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A. V.; Frenking, G. Int. J. Quantum Chem. 2004, 100, 419–425.
(11) Kummer, D.; Chaudhry, S. C.; Debaerdemaeker, T.; Thewalt, U.
Chem. Ber. 1990, 123, 945–951.
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Chem. 2008, 5020–5023. (b) Fester, G. W.; Wagler, J.; Brendler, E.; Bohme, U.;
Gerlach, D.; Kroke, E. J. Am. Chem. Soc. 2009, 131, 6855–6864.

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2669
Scheme 2. Reactions of Various Chlorosilanes with bipy, phen, and
tmeda
4b appear particularly noteworthy because this feature
clearly distinguishes bipy complexes such as 3b from the
related tmeda complex 3a, which was reported to com-
prise fac-arranged Si-Cl bonds and a trans-Cl-situated
Si-H bond. An explanation as to the origin of the
configurational difference between 3b and 3a is provided
by the steric demand of the chelating ligands. Whereas in
compound 3b (the same holds for 4b) intermolecular
interactions between the axial Cl atoms and the H atoms
of neighboring bipy moieties stabilize the crystal packing,
the Cl-Si-H axis in 3a obviously serves the minimization
of intramolecular repulsive forces between the tmeda
methyl groups and the Si-bound monodentate substitu-
ents. In 5c, the Si-bound phenyl group is arranged almost
perpendicularly to the phen ligand, most likely in order to
minimize steric repulsion. A similar donor atom arrange-
ment (that is, two Si-Cl bonds trans to each other in
addition to a Si-bound phenyl group trans-disposed to an
imine N atom) has been described previously.17
The silicon-complex stability of the N,N0-chelating ligands
under investigation increases in the order tmeda < py < bipy
< phen. Whereas tmeda fails to form stable adducts with
MeSiCl3 or PhSiCl3 (target products 5a and 6a, respectively),
thus limiting our series of XYSiCl2(tmeda) complexes, the
desired products 2-6b and 2-6c were accessible from bipy
and phen, respectively. (The tetrachlorosilane adducts of
bipy, phen, and tmeda have already been reported in the
literature.6,13) CP/MAS 29Si NMR spectra revealed hexa-
coordination of the Si atoms of all of the above products,14
and coordination of the tmeda ligand [two N(sp3)-donor
atoms] is accompanied by a significant downfield shift of the
resonance with respect to the signals of the bipy and phen
complexes of the same silane [comprising two N(sp2)-donor
atoms]. The poor solubilities of these complexes rendered
solution NMR spectroscopy unsuitable. Retention of the
Si-bound H atoms (if applicable) is supported by Raman
spectroscopy (Table 1).
Crystal Structures of the Hexacoordinated Silicon Com-
plexes. In addition to the spectroscopic characterization
described above, recrystallization of the bipy complexes
3b and 4b as well as the phen adducts 2c, 5c, and 6c
afforded crystals suitable for X-ray diffraction analyses
(Figure 1 and Table 2). Despite the different chelators
used and the different non-Cl substituents bound to the Si
atom, these five complexes exhibit a number of mutual
structural features. In addition to their slightly distorted
octahedral Si-coordination sphere, all of them have a
Cl-Si-Cl axis in common, which is directed almost
perpendicularly to the idealized plane of and slightly bent
toward the chelating ligand. Furthermore, the lengths
of the Si-Cl bonds, which are trans-disposed to one
another, are significantly longer than the trans-N-situated
Si-Cl bonds of 3b, 2c, 5c, and 6c. Both the trans-Cl-
and the trans-N-situated Si-Cl bonds are significantly
longer than those in tetracoordinated chlorosilanes
(e.g., 201.9 pm for tetrachlorosilane15). Even in the case
of the phen complexes, the (more or less) rigid phen
moiety responds to the coordinative requirements of the
Si atom as a Lewis acidic center: e.g., in the case of 2c, the
angles N1-C12-C11 and N2-C11-C12 decreased from
117.1(1)° and 119.0(1)°16 to 115.5(2)° and 115.7(2)°. The
trans-N-situated Si-bound H atom(s) of adducts 3b and
In addition to the isotropic 29Si NMR shift, the chemical
shift anisotropy (CSA) tensor components of the hydrido-
chlorosilane adducts 3b and 4b were extracted from spin-
ning side-band spectra, and the directions of the principal
components with respect to the Si-coordination spheres
were analyzed with the aid of computational analyses based
on the crystal structures of these complexes.
The experimentally obtained data (entries “exp” in
Table 3) are reproduced very well with both B3LYP
and HF (with a particularly good match of the B3LYP
results) in the case of the dichlorosilane complex 4b,
whereas B3LYP fails to provide satisfactory data for
the trichlorosilane(bipy) adduct 3b. The use of HF instead
of B3LYP helps to reduce these errors only in part. The
general shape of the CSA tensor, however, is reproduced
to an extent that allows for a discussion of its orientation
with respect to the Si-coordination sphere (Figure 2).
Whereas the CSA tensor for the trichlorosilane(bipy)
adduct 3b is surprisingly similar to that of the adduct
HSiCl3(4-tert-butylpyridine)2, which comprises trans-
disposed N-donor sites instead of the cis N-Si-N situa-
tion of 3b, the change from trans- to cis-disposed N-donor
sites effects the CSA tensor properties of the dichloro-
silane complexes noticeably. In particular, the 29Si NMR
resonance is shifted to higher field upon transition to the
chelate complex. This shift of the isotropic signal is
mainly caused by an even more pronounced upfield shift
of principal component (11). In complexes HRSiCl2-
(4-tert-butylpyridine)2 (R = H, Cl), this CSA tensor
component was shown to point along the Cl-Si-Cl axis,
being particularly influenced by the orthogonal substitu-
ents (N and H donors). The same directionality applies to
4b, with (11) pointing along the Cl-Si-Cl axis and the
very similar components (22) and (33) being situated in
the SiN2H2 plane. Thus, in complex 4b, this pronounced
upfield shift of the 29Si NMR resonance [with respect to
H2SiCl2(4-tert-butylpyridine)2] can be attributed to the
strong chelating effect of the bipy ligand. The develop-
(13) Beattie, I. R.; Webster, M. J. Chem. Soc. 1963, 4285–4287.
(14) Kintzinger, J. P.; Marsmann, C. NMR;Basic Principles and
Progress; Springer-Verlag: Berlin, 1981; Vol. 17.
(15) Donald, K. J.; Bohm, M. C.; Lindner, H. J. THEOCHEM 2005, 713,
215–226.
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1935–1942.
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1998, 17, 887–892.
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1980, 186, 13–17.

2670 Inorganic Chemistry, Vol. 49, No. 6, 2010
Fester et al.
Table 1. CP/MAS 29Si NMR Data and ν(Si-H) Raman Bands [cm-1] for Compounds 2a-2c, 3a-3c, 4a-4c, 5b, 5c, 6b, and 6c
tmeda
bipy
phen
silane
SiCl4
29Si NMR [ppm]
ν(Si-H) [cm-1
]
29Si NMR [ppm]
ν(Si-H) [cm-1
]
29Si NMR [ppm]
ν(Si-H) [cm-1
]
2a
3a
2b
3b
4b
5b
6b
2c
3c
4c
5c
6c
-160.1
-145.3
-131.5
-179.5
-169.5
-161.0
-155.2
-153.5
-179.7
-171.1
-163.3
-152.4
-153.1
HSiCl3
2145, 2174
2080, 2205
2137
a
a
H2SiCl2
MeSiCl3
PhSiCl3
4a
2050, 2081
5ab
6ab
a Dismutation. b Not stable at room temperature and under cooling.
Figure 1. Molecular structures of 3band 4b(on top fromlefttoright) and2c (oneofthe two independentcomplex molecules in2c2 MeCN), 5c(ina crystal
3
of 5c THF), and 6c (bottom from left to right). ORTEP drawing with 50% probability thermal ellipsoids. H atoms omitted for clarity in the case of 2c, 5c,
3
and 6c. Atoms C13 and Cl3 in compound 5c are disordered with sof of 46% and 54%.
reports,5 represent a serious competitor to hydridochloro-
silane complexation in polar solvents. The reactions of
Table 2. Selected Bond Lengths and Angles for Compounds 3b, 4b, 2c, 5c, and 6c
3b
4b
2c
5c
6c
trichlorosilane and dichlorosilane with tmeda and bipy
led to the formation of hexacoordinated silicon com-
pounds 3a and 3b as well as 4a and 4b, respectively. Under
the synthesis conditions applied (-78 °C), compounds 4a
and 4b precipitated immediately. There was no indication
for dismutation reactions even upon variation of the
solvent used (toluene and n-hexane). The same observa-
tion was made for the reaction of trichlorosilane and
dichlorosilane with tmeda.
Si-N1 [pm]
Si-N2 [pm]
Si-Cl1 [pm]
Si-Cl2 [pm]
Si-Cl3 [pm]
Si-Cl4 [pm]
Si-C13 [pm]
193.6(2) 196.0(4) 197.3(2) 202.1(6) 200.4(2)
196.7(2) 196.2(4) 197.1(2) 199.6(6) 202.4(2)
222.6(1) 227.9(2) 218.5(1) 222.4(3) 223.0(1)
222.1(1) 225.3(2) 220.5(1) 222.2(3) 221.9(1)
217.2(1)
214.3(1) 214.6(4) 218.9(1)
214.4(1)
183.7(19) 191.7(2)
N1-Si-N2 [deg] 80.87(8) 79.02(17) 81.84(7) 80.12(19) 80.13(6)
Cl1-Si-Cl2 [deg] 172.55(4) 174.71(9) 172.08(3) 169.34(11) 166.94(3)
In the Raman spectrum, as expected, the target pro-
ducts exhibit their characteristic Si-H valence vibration
bands. The shift to larger wave numbers for the trichloro-
silane complexes (with reference to the related dichloro-
silane complex) can be explained by electron withdrawal
from the Si-H bond, hence bond strengthening, caused
by the additional halide substituent.21 Furthermore, the
Si-H valence vibration bands of these complexes are
shifted to lower wave numbers with respect to the tetra-
coordinated silanes H2SiCl2 and HSiCl3. This shift is
accompanied by broadening of the signal, which can be
attributed to increased ionic contributions to the Si-H
bonding situation.3f
ment of the CSA characteristics of the trichloro-
silane complex HSiCl3(4-tert-butylpyridine)2 upon chela-
tion by bipy, however, hints at another (at least one) effect
on the shielding of the Si nuclei in these complexes, which
might be capable of overcompensating for the stronger
shielding caused by the chelator. It is known from various
examples of hexacoordinated silicon complexes that
the introduction of five-membered chelate rings in the
Si-coordination sphere causes a downfield shift of the 29Si
NMR resonance with reference to similar systems bearing
six-membered chelates, e.g., those depicted in Scheme 3.
Thus, the introduction of the five-membered bipy chelate
can be expected to exert similar effects on the shielding of the
Si nuclei in the herein reported complexes.
(20) Herzfeld, J.; Berger, A. E. J. Chem. Phys. 1980, 73, 6021–6030.
(21) Weinmann, M.; Gehrig, A.; Schiemenz, B.; Huttner, G.; Nuber, B.;
Rheinwald, G.; Lang, H. J. Organomet. Chem. 1998, 563, 61–72.
Dismutation of Hydridochlorosilanes. Si-Cl versus
Si-H dismutation reactions, as pointed out in previous

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2671
Table 3. Experimental CP/MAS 29Si NMR Data of Selected Compounds silane (L)
3
Ω c
κ c
b
silane
L
a
δiso
δ11
δ22
δ33
HSiCl3
bipy
exp
-169.5
-160.8
-169.2
-170.0
-161.0
-161.8
-164.5
-149.6
-123.4
-119.4
-126.8
-126.6
-85.1
-86.3
-93.0
-49.5
-178.1
-163.0
-180.4
-183.3
-194.2
-194.2
-197.3
-189.3
-207.0
-200.0
-200.4
-202.0
-203.4
-204.9
-203.2
-210.0
83.6
80.6
73.6
75.5
118.4
118.6
110.2
160.5
-0.31
-0.08
-0.46
-0.45
-0.84
-0.82
-0.89
-0.70
B3LYP
HF
exp
12
HSiCl3
H2SiCl2
(4-tert-butylpyridine)2
bipy
exp
B3LYP
HF
exp
3f
H2SiCl2
(4-tert-butylpyridine)2
a Method: exp = experimental, B3LYP = calculated on the B3LYP/6-311Gþ(2d,p) level, and HF = calculated on the HF/6-311Gþ(2d,p) level.
Both CSA tensor calculations on the B3LYP and HF levels were performed on the molecular structures obtained from X-ray diffraction analyses
after optimization of the H-atom positions on the MPW1PW91/6-311G(d,p) level. b Chemical shift in the solid state. c Herzfeld-Berger convention,20
Ω = δ11 - δ33, κ = 3 (δ22 - δiso)/Ω.
Scheme 4. Dismutation of 4c in Solution
Figure 2. Orientation of the 29Si CSA tensor components δ11, δ22, and
δ33 with respect to the molecules 3b (left) and 4b (right). Atomic spheres
are drawnatarbitrary size, Clatoms are black, andN atoms are filledwith
circles.
Scheme 3. Cationic Silicon Trichelate Complexes Bearing Exclusively
Five-Membered [Si(trop)3]þ18 (Left) and Six-Membered O,O-Chelates
[Si(acetylacetonato)3]þ19 (Right)a
a CP/MAS 29Si NMR spectroscopic data (δiso) are given below the
formulas. Note: Although the six Si-O bonds in each of above com-
pounds are almost equal among each other, the ketoenolate canonical
form was chosen to illustrate the similarities between the O,O ligands,
i.e., three O,O-ketoenolate monoanionic ligands with an unsaturated
[C(sp2)] backbone.
Figure 3. CP/MAS 29Si NMR spectrum of the solid product obtained
by the reaction of phen with dichlorosilane in THF at 65 °C after 1 h
(asterisks mark spinning side bands of 3c).
In contrast with the formation of bipy adducts 3b and
4b, the reactions of H2SiCl2 and HSiCl3 with phen, e.g., in
n-hexane or toluene, resulted in Si-H versus Si-Cl
redistribution, including complexation of dismutation
products (Scheme 4).
In addition to the pronounced susceptibility of mono-
chlorosilane to dismutation reactions, the tendency for
complexation of hydridosilanes with N-containing ligands
decreases from tetrachlorosilane to monosilane.22 This
combination of effects is presumably the major reason for
monochlorosilane(phen) adducts still being unobserved in
the course of our investigations. (Note: The potential
redistribution product monosilane was not observed so
far during our investigations.)
The reaction of H2SiCl2 with phen to produce 4c in
tetrahydrofuran (THF; under reflux or at room tempera-
ture) results in the formation of dismutation products as
well. A solid consisting of a mixture of 3c and 4c was
obtained, as indicated by CP/MAS 29Si NMR spectroscopy
(Figure 3).
The supernatant, a red solution, exhibited a signal at
δ = -99 ppm in the 29Si NMR spectrum, which indicates
the formation of at least one additional byproduct, a
compound comprising a pentacoordinated silicon com-
pound.23
Hydrosilylation of phen with Organohydridochlorosi-
lanes. Because the formation of a pentacoordinated
silicon compound in a reaction between dichlorosilane
and phen was completely unexpected, further attention
was paid to this phenomenon. Kummer et al. have
already observed a rearrangement reaction of an Si-X
moiety in the phen coordination clamp, i.e., a silyl shift
(X being a silyl substituent) to the phen ligand back-
bone.24 In related studies dealing with Si-H activation
in higher coordinated silicon compounds, hydride
shifts to CdN and NdN moieties have also been
(23) Kintzinger, J. P.; Marsmann, C. NMR;Basic Principles and
Progress; Springer-Verlag: Berlin, 1981; Vol. 17.
(24) Kummer, D.; Chaudry, S. C.; Depmeier, W.; Mattern, G. Chem. Ber.
1990, 123, 2241–2245.
(22) (a) Fleischer, H. Eur. J. Inorg. Chem. 2001, 393–404. (b) Timoshkin, A.
Yu.; Sevast'yanova, T. N.; Davydova, E. I.; Suvorov, A. V.; Scheafer, H. F., III
Russ. J. Gen. Chem. 2002, 72, 1911–1915.

2672 Inorganic Chemistry, Vol. 49, No. 6, 2010
Fester et al.
observed.25 A hydrosilylation of a phen CdN bond
(i.e., rearrangement of the Si-H bond) would provide
an explanation for the formation of the pentacoordi-
nated silicon compound. Because the pentacoordinated
silicon complex lacks an Si-H bond (vide infra), the
dismutation product HSiCl3(phen) may be considered
as a key intermediate, which underwent Si-H cleavage
in the case of an intramolecular hydride rearrangement.
In addition to trichlorosilane, organodichlorosilanes
RHSiCl2 should exhibit the same capability of trans-
ferring the H atom of a Si-H moiety onto an imine
(or phen) CdN moiety, with the obvious advantage of
their lower susceptibility to hydrogen versus chlorine
dismutation.
The reaction between methyldichlorosilane and phen in
THF at -5 °C resulted in the formation of a poorly
soluble crystalline compound, which dissolved upon
heating and afforded a yellowish crystalline solid upon
cooling. The CP/MAS 29Si NMR spectrum of this solid
revealed the formation of one hexacoordinated silicon
compound (δiso = -151.6 ppm). Raman spectroscopic
data indicated the absence of the characteristic Si-H
valence vibration. Both of these spectroscopic data and
the determination of the unit cell parameters proved
this solid to be the dismutation product 5c, which was
obtained in high yield (60% with respect to a quantitative
formation of MeSiH3 þ 2MeSiCl3 as dismutation
products). For comparison, the synthesis of 5c from
MeSiCl3 and phen in THF under similar conditions (the
same ratio of MeSiCl3-THF) resulted in a similar yield
(63%), thus rendering the observed yields (ca. 40% less
than theoretical) a matter of solubility in THF.
Figure 4. Molecular structure of 7 (ORTEP diagram with 50% prob-
ability ellipsoids). Atoms Si1, Cl1, N1, N2, and C3-C12 of the molecule
are situated on a crystallographically imposed mirror plane. Hence, the
positions of C1, C2, C13, and Cl2 (not located in this plane) suffer from
symmetry-imposed disorder with a sof of 0.5 for each position. Selected
bond lengths [pm] and angles [deg]: Si1-Cl1 221.1(1), Si1-Cl2 203.0(3),
Si1-C13 189.5(14), Si1-N1177.6(2), Si1-N2200.4(2), N1-C1 142.2(3),
N1-C12 140.6(3), C1-C2 133.9(4), C2-C3 149.7(4), C3-C4 150.5(3);
N2-Si1-Cl1 178.3(1), N1-Si1-Cl1 95.2(1), N1-Si1-C13 117.3(7).
Scheme 5. Two Alternative Routes toward 7: Intramolecular Hydro-
gen Shift (A) and Intermolecular Hydrogen Transfer from a Hydrido-
silane (e.g., MeH2SiCl) to 5c (Route B)
29Si NMR spectra of the remaining solution revealed
signals at δ = -68.2, -73.7, -76.3, -76.8, and -78.5 ppm.
A Raman spectrum of the solid obtained upon removal of
the solvent lacks the characteristic Si-H valence vibration.
Additionally, a CP/MAS 29Si NMR spectrum recorded
upon removal of the solvent supported the formation of
pentacoordinated silicon compounds (δ = -79 ppm,
broad) rather than the signal in solution being a result of
rapid equilibration between compounds with tetra- and
hexacoordinated Si atoms. From this solution, further
crystalline solids were obtained that, in addition to yellowish
crystals of 5c, contained a few red crystals. An X-ray
diffraction analysis of the latter confirmed both the forma-
tion of a pentacoordinated silicon compound (7) and the
hydride shift to the phen ligand (Figure 4).
In contrast with the silyl rearrangement found by
Kummer et al.24 and the hydride shifts reported by Kost
et al., Kawashima et al., and Wagler et al.,25 all of which
are 1,3-shift reactions, the rearrangement of a Si-bound
hydride, giving rise to the formation of 7, represents a
1,5 shift, i.e., a 1,4 addition of the Si-H moiety to phen
(Scheme 5). Our observations, i.e., (i) the predominant
formation of MeSiCl3 as the dismutation product (as
its phen adduct 5c), (ii) the emergence of various 29Si
NMR signals characteristic of pentacoordinated silicon
complexes, (iii) the preference for trans-N-located Si-H
bonds in 3b and 4b, and (iv) the crystallographically
proven formation of a 1,4-dihydrophenanthroline ligand
supporting the hypothesis that the hydride Si-H transfer
to the phen moiety occurs in an intermolecular fashion
(reaction of 5c with MeHnSiCl3-n, route B) rather than
intramolecularly upon formation of MeHSiCl2(phen)
(route A; Scheme 5).
For the reaction between phenyldichlorosilane and phen
in THF, a similar reaction was observed. A red solution and
a poorly soluble crystalline compound were obtained. The
CP/MAS 29Si NMR spectrum of the latter indicated the
formation of a hexacoordinated silicon compound (δiso
=
-153.1 ppm; 6c). Raman spectroscopic data again demon-
strated a lack of the characteristic Si-H valence vibration.
29Si NMR spectra of the remaining solution revealed a signal
at δ = -85.3 ppm. Final evidence for the general possibility
of an intermolecular Si-H transfer to the phen backbone is
provided by the reaction between 5c and PhHSiCl2. Whereas
ligand exchange [under formation of PhHSiCl2(phen)] and
subsequent intramolecular rearrangement should produce a
silicon compound with a characteristic 29Si NMR signal at
(25) (a) Kertsnus-Banchik, E.; Kalikhman, I.; Gostevskii, B.; Deutsch, Z.;
Botoshansky, M.; Kost, D. Organometallics 2008, 27, 5285–5294. (b) Lippe,
K.; Gerlach, D.; Kroke, E.; Wagler, J. Organometallics 2009, 28, 621–629. (c)
Yamamura, M.; Kano, N.; Kawashima, T. Tetrahedron Lett. 2007, 48, 4033–
4036.

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2673
-85 ppm, intermolecular hydrogen transfer from PhHSiCl2
to the MeSiCl3-coordinated phen backbone and chlorine
transfer from the MeSiCl3 moiety to the phenylsilicon
moiety should deliver a compound that produces a 29Si
NMR signal at ca. -77 ppm. The 29Si NMR spectrum
acquired from a mixture obtained by the reaction of 5c with
PhHSiCl2 in THF exhibited signals at 13.8 ppm (MeSiCl3),
-0.3 ppm (PhSiCl3), and -76.6 ppm but no signal in the
range -80 to -90 ppm, thus providing an additional hint at
an intermolecular Si-H transfer to the phen ligand.
So far, there are no crystallographic data available
for silicon complexes of 1,4-dihydrophenanthroline.
The coordination behavior of this 4H-phen derivative,
however, is closely related to the manner in which 1,2,3,4-
tetrahydrophenanthroline is setting up trigonal-bipyra-
midal coordination spheres about halide-substituted
silicon centers,26 thus rendering extensive discussion of
the molecular structure of 7 superfluous.
which was formed by the unexpected 1,4-hydrosilylation
reaction (or hydrogen 1,5 shift), was presented. In addition
to the formal hydride 1,5 shift, further experimental data
support the hydrogenation of thephen ligand to arise froman
intermolecular hydrogenation reaction that involves dis-
mutation products. Trichlorosilane and dichlorosilane may
exhibit the same reactivity patterns.
The first crystallographic evidence was delivered for
hydridochlorosilane complexes of bipy. In contrast with the
already known HSiCl3(tmeda) complex, the silane(bipy)
adducts exhibit Si-H bonds trans-situated with respect to
the N-donor sites. In addition to this difference, the tmeda
complexes, although accessible as stable solids, were found to
be noticeably less stable than the bipy complexes with respect
to their Si-N bonds. That is, dissociation into tmeda and the
respective silane was found in solution.
The synthetic potential of the reversible complexation-
dissociation, with particular focus on Si-H activation
and the use of Si-coordinated ligands as precursors in
ligand-hydrogenation reactions, will be the subject of
further investigations.
Conclusions
Hydridochlorosilanes were shown to undergo various
reactions with the bidentate chelators bipy and phen,
i.e., complexation, dismutation, and hydrosilylation of the
ligand. Whereas the reactivity patterns of tetrachlorosilane
and organotrichlorosilanes with the above ligands are limited
to adduct formation, organodichlorosilanes proved unstable
in the bipy and phen braces. In particular, RSiHSiCl2(bipy)
underwent dismutation to yield RSiCl3(bipy). In contrast to
these two alternatives, hydrosilylation of the ligand was
found as a reasonable alternative in related phen systems.
Rather than being a competitor with dismutation, this
hydrosilylation appears to be a subsequent reaction upon
dismutation. In this context, the first crystal structure of a
silicon complex bearing a 1,4-dihydrophenanthroline ligand,
Acknowledgment. The German Research Foundation
(DFG, Bonn, Germany) and TU Bergakademie Freiberg
are acknowledged for financial support of this research.
Supporting Information Available:
Further details of the
experimental procedures, CP/MAS 29Si NMR data of compounds
2-4a, 2-6b, 2c, 5-6c, and 7, and X-ray structure analysis data and
CIF files for 2c, 3b, 4b, 5c, 6c, and 7. This material is available free of
charge via the Internet at http://pubs.acs.org. Crystallographic data
(excluding structure factors) for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Centre as
supplementary publication nos. CCDC-733072 (2c), CCDC-733074
(3b), CCDC-733071 (4b), CCDC-733076 (5c), CCDC-733073 (6c),
and CCDC-733075 (7). Copies of the data can be obtained free of
charge by contacting The Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, U.K., via www.ccdc.cam.ac.
uk/data_request/cif, fax (international) þ44-1223/336-033, or e-mail
deposit@ccdc.cam.ac.uk.
(26) (a) Klebe, G.; Bats, J. W.; Hensen, K. J. Chem. Soc., Dalton Trans.
1985, 1–4. (b) Klebe, G.; Bats, J. W.; Fuess, H. J. Am. Chem. Soc. 1984, 106,
5202–5208. (c) Klebe, G.; Hensen, K.; Fuess, H. Chem. Ber. 1983, 116, 3125–
3132.