Pentacoordinate mono(β-diketonato)- and hexacoordinate bis-(β-diketonato)-silicon(IV) complexes obtained from (thiocyanato-N) hydridosilanes

Article abstract of DOI:10.1016/j.poly.2012.04.030

Three novel neutral hypercoordinate silicon(IV) complexes containing the O,O′-donor deprotonated β-diketone ligands 1,3-diphenylpropane-1,3- dione (HL¹) and 1-phenylbutane-1,3-dione (HL²) were synthesized starting from the hitherto unknown diphenyl(thiocyanato-N)silane [HPh₂Si(NCS)] and methyldi(thiocyanato-N)silane [HMeSi(NCS) ₂], a class of silicon source with Si-NCS and Si-H reactive functionalities. The reaction of HL¹ with the new starting material HPh₂Si(NCS) only afforded a neutral pentacoordinate silicon complex containing one β-diketonato ligand coordinated in a bidentate fashion (complex 16). The reaction of HL¹ and HL² with HMeSi(NCS)₂ yielded bis-β-diketonato neutral hexacoordinate silicon complexes (17 and 18, respectively). The three compounds 16-18 were characterized using solution ¹H, ¹³C and ²⁹Si INEPT NMR and FT-IR spectroscopies, and compounds 17 and 18 were also studied using solid-state ²⁹Si CP/MAS NMR. Elemental analysis and single-crystal X-ray diffraction were used to establish the composition and the structure of all of the new complexes. The ²⁹Si INEPT NMR solution studies confirmed that compounds 16-18 maintain the same hypercoordination in solution that they have in the solid state. Compound 16 has a SiO ₂NC₂ coordinating framework and represents the first example of a pentacoordinate silicon β-diketonato whose X-ray single crystal structure has been elucidated, and compounds 17 and 18 are the first neutral, non-zwitterionic, hexacoordinate silicon complexes with a SiO ₄NC coordinating framework bearing only one -NCS functionality. The usefulness of the (thiocyanato-N)hydridosilanes HPh₂Si(NCS) and HMeSi(NCS)₂ as starting materials for the preparation of hypercoordinate organosilicon complexes is confirmed.

Full text of DOI:10.1016/j.poly.2012.04.030

Polyhedron 41 (2012) 127–133
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Pentacoordinate mono(b-diketonato)- and hexacoordinate
bis-(b-diketonato)-silicon(IV) complexes obtained from
(thiocyanato-N)hydridosilanes
Gerardo González-García a, Eleuterio Álvarez b, J. Alfredo Gutiérrez a,
⇑
a Departamento de Química, Universidad de Guanajuato, Noria Alta s/n, 36050 Guanajuato, Gto., Mexico
b Instituto de Investigaciones Químicas, CSIC – Universidad de Sevilla, Avda. Américo Vespucio, 49, Isla de La Cartuja, 41092 Sevilla, Spain
a r t i c l e i n f o
a b s t r a c t
Three novel neutral hypercoordinate silicon(IV) complexes containing the O,O0-donor deprotonated
b-diketone ligands 1,3-diphenylpropane-1,3-dione (HL1) and 1-phenylbutane-1,3-dione (HL2) were syn-
thesized starting from the hitherto unknown diphenyl(thiocyanato-N)silane [HPh2Si(NCS)] and meth-
yldi(thiocyanato-N)silane [HMeSi(NCS)2], a class of silicon source with Si–NCS and Si–H reactive
functionalities. The reaction of HL1 with the new starting material HPh2Si(NCS) only afforded a neutral
pentacoordinate silicon complex containing one b-diketonato ligand coordinated in a bidentate fashion
(complex 16). The reaction of HL1 and HL2 with HMeSi(NCS)2 yielded bis-b-diketonato neutral hexacoor-
dinate silicon complexes (17 and 18, respectively). The three compounds 16–18 were characterized using
solution 1H, 13C and 29Si INEPT NMR and FT-IR spectroscopies, and compounds 17 and 18 were also stud-
ied using solid-state 29Si CP/MAS NMR. Elemental analysis and single-crystal X-ray diffraction were used
to establish the composition and the structure of all of the new complexes. The 29Si INEPT NMR solution
studies confirmed that compounds 16–18 maintain the same hypercoordination in solution that they
have in the solid state. Compound 16 has a SiO2NC2 coordinating framework and represents the first
example of a pentacoordinate silicon b-diketonato whose X-ray single crystal structure has been eluci-
dated, and compounds 17 and 18 are the first neutral, non-zwitterionic, hexacoordinate silicon com-
plexes with a SiO4NC coordinating framework bearing only one –NCS functionality. The usefulness of
the (thiocyanato-N)hydridosilanes HPh2Si(NCS) and HMeSi(NCS)2 as starting materials for the
preparation of hypercoordinate organosilicon complexes is confirmed.
Article history:
Received 12 December 2011
Accepted 25 April 2012
Available online 7 May 2012
Keywords:
Silicon
Hypercoordinate
Hydridosilanes
(Thiocyanato-N)silanes
b-Diketones
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
some cases, 1H or 13C NMR [3b,4,7], molecular weight determina-
tions [3,8,9] and mass spectrometry [8,9]. Thus, several structural
The chemistry of hypercoordinate b-diketonato silicon(IV) com-
plexes encompasses compounds containing one [1], two [2–14] and
three [15,16] b-diketonato ligands. This type of compound has been
known since Dilthey reported the reaction of silicon tetrachloride
with acetylacetone (Hacac) to obtain the cationic hexacoordinate
complex tris-(acetylacetonato), [Si(acac)3]+ (1), more than one hun-
dred years ago [15]. The family of hypercoordinate silicon b-diket-
onates has continued to grow [1,14]; however, only hexacoordinate
complexes have been structurally characterized using single crystal
X-ray diffraction [1,10–14] (see below), and no examples of
pentacoordinate silicon b-diketonates have been studied with this
technique. In fact, for several years, hypercoordinate silicon b-
diketonates have been characterized mainly with the help of IR
and UV–Vis spectroscopies, elemental analyses [2–5,7–9] and, in
features of these compounds remain unknown. It was only in rela-
tively recent times that silicon complexes began to be systemati-
cally studied by means of solution 29Si NMR spectroscopy: Cella
et al. concluded that this analytical tool is very powerful for deter-
mining the coordination number in silicon compounds after analyz-
ing several previously synthesized penta- and hexa-coordinate
silicon complexes and a number of new hypercoordinate silicon
complexes that they had prepared [6].
A search in the Cambridge Structural Data Base (CSD) revealed
that the first X-ray crystal structures for silicon b-diketonatos were
reported from 1979 to 1993, and these structures correspond to
several examples of the hexacoordinate cation [Si(acac)3]ꢀ+ (1),
which only differs in the counterion (ClO4ꢀ, C12H4N4ꢀ, HCl2 and
Ag2Cl42ꢀ) [16]. In addition to 1 [16], the CSD showed that the
hexacoordinate compounds 2 [10], 3 [11], 4 [12], 5 [13], 6, 7 [14]
and 8–10 [1] (Chart 1) are the only silicon b-diketonates that have
been studied using X-ray single crystal diffractometry.
⇑
Corresponding author. Tel./fax: +52 473 732 0006x8134.
E-mail address: jagutier@ugto.mx (J.A. Gutiérrez).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.04.030

128
G. González-García et al. / Polyhedron 41 (2012) 127–133
R
O
Si
To the best of our knowledge, no structural information has
R
X
Y
been reported for pentacoordinate silicon b-diketonato complexes
[5,6]. Therefore, we are now reporting the preparation and detailed
characterization of the first example of this type of compound,
starting from the hitherto unknown silane HPh2Si(NCS) (15). We
also report the synthesis and X-ray crystal structure of two new
neutral bis-b-diketonato hexacoordinate silicon complexes, which
were prepared from the already known silane reagent HMe-
Si(NCS)2 (11) [19,20] and which, like 15, also contain the useful
Si–H functionality.
R
R
R
2
Me
Me
-NCS -NCS
-NCO
O
O
O
Y
3
4
-NCO
tBu Me Me
R
R
X
R
O
Si
O
R
O
O
O
O
O
O
1-O-C(Ph)2C(=O)-O1-
1-O-C6H4-C(=O)-O1-
5
6
7
Ph
Me
2. Results and discussion
R
R
1-O-CH2-C(=O)-O1-
Me
The new starting material, diphenyl(thiocyanato-N)silane
[HPh2Si(NCS), 15] was obtained as a colorless liquid in 64% yield
by treating HPh2SiCl with an excess of NH4NCS (25%). Complex
15 reacts with the b-diketone ligand HL1 (1,3-diphenylpropane-
1,3-dione) only via the Si–H functionality to yield complex 16
(Scheme 1) in a 44% yield as a yellow crystalline solid and H2 as
a byproduct (evidenced by a pressurization of the reaction vessel
and the explosive combustion of a small balloon filled with the
gas liberated). Complex 16 was the only silicon complex isolated
from this reaction in spite of the fact that two equivalents of the
b-diketone were added without displacement of the Si–NCS func-
tional group that could yield the bis-b-diketonato silicon complex
Ph2Si(L1)2 (Scheme 2), which is an analog of the previously re-
ported Ph2Si(acac)2 [7].
R
R'
S
Me Me
8
9
10
O
O
N
O
Ph
Me
Ph
Ph
Si
Ph
R'
Chart 1. Silicon(IV) b-diketonates studied by single-crystal X-ray diffraction.
In the first studies with silicon b-diketonatos, it has been ob-
served that silicon acetylacetonato complexes are prone to decom-
position [2,4,5] or the production of silicon dienolates [7,17]; these
problems can be circumvented by using b-diketone-bearing groups
without enolizable protons, such as dibenzoylmethane (1,3-
diphenylpropane-1,3-dione) [3c,5,7,13] 2-thenoyltrifluoroacetone
[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione] [3c] and dipi-
valoylmethane (2,20,6,60-tetramethylheptane-3,5-dione) [12]. An-
other strategy to stabilize the silicon b-diketonatos is to increase
the Lewis acidity of the silicon atom with the use of electron-with-
drawing groups [18] such as chloro [2], carboxylatos [3,13,14], alk-
oxides [14] and catecholatos [9] as well as N-thiocyanato (–NCS)
[8,10] and N-cyanato (–NCO) [11] anions. Tacke et al. have demon-
strated the high synthetic potential of Si(NCO)4 and Si(NCS)4 as
starting materials for the synthesis of hypercoordinate silicon com-
plexes [10,11] because the –NCX ligands (X = O, S) are able to easily
stabilize the hypercoordination of the silicon center (as was ob-
served earlier by Narula in the case of –NCS [8]), but they are also
good as leaving groups; thus, the hexacoordinate bis-(b-diketonato)
complexes 2 [10] and 3 [11] (Chart 1) can be obtained from Si(N-
CO)4 and Si(NCS)4, respectively. In this regard, we recently reported
the preparation of (thiocyanato-N)hydridosilane, HMeSi(NCS)2 (11)
[19], which contains a labile Si–H functionality in addition to Si–
NCS bonds, making it a suitable reagent for nucleophilic substitu-
tion at the silicon center with byproducts that are easily eliminated.
We demonstrated the usefulness of 11 in the preparation of neutral
penta- and hexacoordinate silicon complexes with SiON3C and
SiON4C coordinating frameworks by its reaction with tridentate
N,N,O-donor Schiff base ligands (12 and 13, respectively; Scheme
1) [19] as well as a silicon complex with a SiO2N3C coordinating
framework (14, Scheme 1) by the reaction of 11 with a salen-type
ligand [20]. In fact, one can consider that the hydridosilane func-
tionality, Si–H, provides a strong base (Hꢀ) that easily and cleanly
abstracts acidic protons from the b-diketone ligands (see below),
thus avoiding the use of bases such as pyridine [2], triethylamine
[17] or imidazole, which may give rise to complex reactions in
the presence of b-diketones [7], or other strategies that require
the prior preparation of a deprotonated derivative of the b-diketone
[1,2,5,12,21].
Complex 16 crystallizes in the space group Pc with two inde-
pendent molecules in the asymmetric unit. The silicon coordina-
tion polyhedron is a nearly perfect trigonal bipyramid (TBP) with
98.9% of ideal TBP [22]. The maximum deviations from the ideal
90° and 180° angles of 16 are 4.26(7)° and 4.34(7)°, respectively.
The sum of the bond angles around the Si1 atom, which form the
equatorial plane (C16, C22, O2), is 359.93(8)°. The structure com-
plex 16 is depicted in Fig. 1, and the crystal data and the experi-
mental parameters used for the crystal structure analysis are
summarized in Table 1.
In the TBP complex 16, the silicon atom is coordinated in the
equatorial positions by two phenyl ligands (Si1–C16, Si1–C22)
and one oxygen in the b-diketonato ligand (Si1–O2), whereas the
axial positions are occupied by the thiocyanato-N ligand (Si1–
NCS) and the second oxygen in the b-diketonato ligand (Si1–O1).
As expected, the Si1–O1 bond in the axial position [1.8792(13)]
is significantly longer than the Si1–O2 bond in the equatorial posi-
tion [1.6957(14)]. The two molecules in the asymmetric unit of
complex 16 show intermolecular
p–p
and Hꢁ ꢁ ꢁ
p interactions (see
supplementary information for details), but these molecules are
not structurally identical. A slight difference in the dihedral angle
of one phenyl ring of the order of 28.99(9)°, probably either to
avoid intermolecular steric hindrance or to increase the aromatic
interactions (edge-to-face or offset stacked orientations), is enough
to break the inversion symmetry for this structure; the former sit-
uation originates that complex 16 crystallizes in a non-centrosym-
metric space group (Pc).
In a CDCl3 solution, the 29Si INEPT NMR spectrum of a sample of
16 in a sealed tube under high vacuum exhibits only one sharp sig-
nal at d ꢀ99.9, which indicates that this pentacoordinate silicon(IV)
complex exists only as one diastereomer in this solvent at room
temperature. The 29Si NMR signal of 16 is shifted significantly up-
field (ca. 70 ppm) with respect to the starting material 11, which is
consistent with a strong O–Si–O coordination by the b-diketonato
ligand. Attempts to study 16 using solid state 29Si NMR failed;
although the sample for the NMR measurements was prepared un-
der a N2 atmosphere, two signals developed at d ꢀ109.7 (broad)
and d ꢀ38.9 (sharp) during the first minutes of the spectral

G. González-García et al. / Polyhedron 41 (2012) 127–133
129
NCS
12
Me
R = H R' = benzyl
Si
N
+
HMeSi(NCS)2
Ph
N
O
- H2 - HNCS
N
OH
NCS
13
NR
R'
N
N
R = R' = methyl
Si
+
HMeSi(NCS)2
- H2
Me
O
NCS
NCS
14
Ph
Ph
Ph
Ph
N
N
O
N
O
N
+
HMeSi(NCS)2
Si
- H2 - HNCS
O
OH
H
Me
OMe
OMe
OMe
OMe
Scheme 1. Preparation of some hypercoordinate silicon complexes from (thiocyanato-N)hydridosilanes as silicon sources.
H
Ph Si Ph
Cl
Ph2Si(L1)2
+ NH4NCS
- NH4Cl
- HNCS
X
+ 2 HL1
- H2
Ph
O
Ph
H
O
+ HL1
- H2
Ph
Ph Si Ph
NCS
Si
Ph
NCS
16
15
Scheme 2. Preparation of diphenyl(thiocyanato-N)silane (15) and its reaction with
1,3-diphenylpropane-1,3-dione (HL1).
Fig. 1. ORTEP view of compound 16 drawn at the 50% probability level. The
crystallographic asymmetric unit presents two independent molecules of com-
pound 16 which only differ slightly in the dihedral angle of one phenyl ring; only
one independent molecule is shown. The hydrogen atoms have been omitted for
clarity. Selected bond lengths [Å] and angles [°]: Si1–N1 1.8716(17), Si1–O1
1.8792(13), Si1–O2 1.6957(14), Si1–C16 1.8641(19), Si1–C22 1.8664(19), N1–C28
1.163(2), S1–C28 1.6160(18); N1–Si1–O1 175.74(7), O2–Si1–C16 116.73(8), O2–
Si1–C22 121.85(8), C16–Si1–C22 121.34(8), C28–N1–Si1 173.51(16), N1–C28–S1
179.70(18), O2–Si1–N1 85.66(7), C16–Si1–N1 93.99(7), C22–Si1–N1 92.96(8), O2–
Si1–O1 90.31(6), C16–Si1–O1 89.07(7), C22–Si1–O1 87.98(7).
acquisition, indicating the fast decomposition of 16, probably cat-
alyzed by traces of oxygen or water. The 29Si chemical shift of com-
plex 16 is similar to that of analogous neutral pentacoordinate
silicon complexes with a SiO2NC2 skeleton containing O,N,O-donor
Schiff base ligands and two phenyl [23–25] or two vinyl ligands
[25].
Compound 16 could be considered to be a stable intermediate
species in
a nucleophilic substitution reaction to produce
bis-(b-diketonato)hexacoordinate silicon compounds (see below);
the Si–NCS functionality that is present in 16 could be useful in fur-
ther condensation [20,26,27] or substitution [14,28–31] reactions
to prepare novel hypercoordinate silicon compounds.
good elemental analyses; this was particularly hard in the case of
compound 17 (see Section 4).
The reaction of one equivalent of HMeSi(NCS)2 (11) with two
equivalent of 1,3-diphenylpropane-1,3-dione (HL1) or 1-phenylbu-
tane-1,3-dione (HL2) at 25 °C in acetonitrile leads to the formation
of the neutral hexacoordinate silicon(IV) complexes 17 and 18 in
70% and 73% yield, respectively (see Scheme 3). All the compounds
here reported are very reactive making difficult the obtainment of
The molecular structures of 17 and 18 in a crystal are shown in
Figs. 2 and 3, respectively; selected bond distances and angles are
given in the figure legends. The crystal data and the experimental
parameters used for the crystal structure analyses of 17 and 18
are given in Table 1. Both complexes crystallize in the space group
P21/c.

130
G. González-García et al. / Polyhedron 41 (2012) 127–133
Table 1
Summary of the crystallographic data and structure refinement results for 16–18.
Complexes
16
17
18
Formula
C
28H21NO2SSi
C32H25NO4SSi
547.68
100(2)
C22H21NO4SSi
423.55
100(2)
Formula mass (g molꢀ1
Collection T (K)
)
463.61
100(2)
k (Mo K
a
) (Å)
0.71073
monoclinic
Pc
13.6456(6)
10.6108(6)
17.5293(10)
112.184(2)
2350.2(2)
4
0.71073
monoclinic
P21/c
14.7078(9)
9.8037(6)
19.9540(12)
108.146(2)
2734.1(3)
4
0.71073
monoclinic
P21/c
12.8759(7)
14.4162(8)
11.6962(7)
109.579(2)
2045.5(2)
4
Crystal system
Space group
a (Å)
b (Å)
c (Å)
b (°)
V (Å3)
Z
q
(Calc.) (Mg mꢀ3
)
1.310
1.331
1.375
F(000)
968
1144
888
Crystal dimensions (mm)
h range (°)
0.50 ꢂ 0.40 ꢂ 0.30
3.25–31.85
39705
12211/595
0.0399
0.0378
0.0980
1.060
+0.388/ꢀ0.346
0.54 ꢂ 0.50 ꢂ 0.26
2.91–30.91
33822
8584/353
0.0484
0.0436
0.1302
1.002
0.384 and ꢀ0.368
0.50 ꢂ 0.16 ꢂ 0.11
2.33–30.57
45448
6259/265
0.0708
0.0472
0.1529
1.024
0.416 and ꢀ0.477
No. of collected reflections
No. of independent reflections/parameters
Rint
R1(F) [F2 > 2
r
(F2)]a
wR2(F2)b (all data)
Sc (all data)
max./min. residual electron density (e Åꢀ3
)
P
P
R1ðFÞ ¼ ðjFoj ꢀ jFcjÞ= jFoj for the observed reflections [F2 > 2
r
(F2)].
a
b
c
P
P
2
2 1=2
wR2ðF2Þ ¼ f ½wðFo2 ꢀ Fc2Þ ꢃ= wðFo2Þ g
.
P
2
S ¼ f ½wðF2o ꢀ F2c Þ ꢃ=ðn ꢀ pÞg1=2; (n = number of reflections, p = number of parameters).
R'
R
R'
R
R
O
2
H
SCN Si Me
NCS
O
O
O
O
O
Si
- H2
- HNCS
Me
R'
NCS
R
R'
11
HL1
HL2
Ph Ph
R
R'
Me
Ph
Ph Ph
17
18
Me
Ph
Scheme 3. Reaction of methyldi(thiocyanato-N)silane (15) with 1,3-diphenylpro
pane-1,3-dione (HL1) and with 1-phenylbutane-1,3-dione (HL2).
The Si-coordination polyhedron for the two neutral hexacoordi-
nate silicon complexes 17 and 18 can be described as a distorted
octahedron with a SiO4NC coordinating framework with two b-
diketonato ligands located in a relative cis position. As expected,
the Si–C and Si–N distances, as well as the analogous angles and
Si–O distances in the coordinating framework for complexes 17
and 18, are quite similar; for instance, the shorter Si–O distance
for both complexes is that for a Si–O bond trans to another Si–O
bond (Si1–O1 1.7883 Å for 17 and Si1–O2 1.7858 Å for 18); simi-
larly, the angles formed by the O–Si–C trans bonds are O(2)–
Si(1)–C(32) 177.90(7) for 17 and O(1)–Si(1)–C(21) 176.92(9) for
18, and the angles of the O–Si–N trans bonds are O(4)–Si(1)–N(1)
175.13(6) for 17 and O(4)–Si(1)–N(1) 171.03(9) for 18. In the case
of the complex with the unsymmetrical b-diketonato ligand (18,
see Fig. 3), it can be observed that each pair of analogous groups
on the two b-diketonato ligands (phenyl groups or methyl groups),
are mutually located in a relative cis position with respect to the
silicon center.
Fig. 2. ORTEP view of compound 17 drawn at the 50% probability level. Selected
bond lengths [Å] and angles [°]: Si1–N1 1.8843(15), Si1–O1 1.7883(13), Si1–O2
1.8111(11), Si1–O3 1.8017(13), Si1–O4 1.8171(12), Si1–C32 1.8875(15), N(1)–C31
1.171(2), S(1)–C31 1.6079(17); O(4)–Si(1)–N(1) 175.13(6), O(1)–Si(1)–O(3)
172.69(5), O(2)–Si(1)–C(32) 177.90(7), O(1)–Si(1)–O(2) 89.36(5), O(3)–Si(1)–O(2)
83.51(5), O(3)–Si(1)–C(32) 95.91(7), O(1)–Si(1)–C(32) 91.27(7).
(2019 cmꢀ1) and 15 (2066 cmꢀ1). Similar behavior has been ob-
served for some hexacoordinate b-diketonato silicon complexes
[8a] and was ascribed to the predominance of the N„C–Sdꢀ cano-
nical form in the silicon hypercoordinate complexes, whereas for
11 and 15, the dꢀN@C@S canonical form must have a higher contri-
bution; this observation is consistent with C–N and C–S crystallo-
graphic distances for the –NCS ligand in complexes 16–17 as
The FT-IR signals of the C–N stretching mode of the N-thiocya-
nato ligands in the hexacoordinate silicon complexes 16, 17 and 18
appear at 2099, 2085 and 2113 cmꢀ1, respectively, and are shifted
to higher energy with respect to the starting materials 11

G. González-García et al. / Polyhedron 41 (2012) 127–133
131
According to the literature, the anionic (19 [32] and 20 [33]) and
the zwitterionic (21 [34] and 22 [35]) silicon complexes shown in
Chart 2, are the only analogous hexacoordinate silicon complexes
of 17 and 18 with a SiO4NC coordinating framework that have been
structurally characterized using single-crystal X-ray diffraction.
It is interesting to compare some structural data for the SiO4NC
skeleton of the neutral hexacoordinate silicon complexes 17 and
18 with those of complexes 19–21 whose silicon centers are for-
mally charged (ꢀ1). Although they possess a SiO4NC skeleton, com-
pound 22 has Si–C and Si–N bonds in a relative trans position,
whereas the corresponding bonds in complexes 17–21 are in a rel-
ative cis position. Table 2 shows the data for some comparable
bonds distances for the above-mentioned compounds.
According to the data in Table 2, the Si–C and Si–N bonds in
complexes 19–21 are consistently longer, and three of the four
Si–O bonds are consistently shorter, compared with the analogous
bond distances for 17 and 18 (of the two Si–O bonds that are mutu-
ally trans for all complexes in Table 2, the shorter bonds have sim-
ilar values, whereas the longer bonds are slightly shorter for 19–
21). This difference in bond distances can be explained by consid-
ering the presence of the two dianionic O,O0-donor catecholato li-
gands for compounds 19–21, which in virtue of their charge (ꢀ1)
on each oxygen atom, act as very strong donors toward the silicon
center, and this is particularly favored by the presence of a neutral
amino donor atom of the second ligand that, compared with the –
NCS ligand, is a relatively poor donating atom. In the case of each
b-diketonato ligand of 17 and 18, only one of the oxygen donor
atoms formally has a ꢀ1 charge, whereas the second atom is for-
mally neutral. However, these complexes also contain a strong N-
donor anionic ligand, –NCS, in addition to the methyl ligand, which
is also an electron donating (+I) group [36]. These latter two factors
diminish the average donating power of the b-diketonate ligands,
which is reflected in three larger Si–O distances for 17 and 18 with
respect to the bis-catecholate complexes 19–21.
In the reaction of the Si–H bond of tetravalent hydridosilanes 10
and 15 with the b-diketones HL1 and HL2 to yield the five- and six-
coordinate silicon complexes 16–18, the question arises as to
whether these are acid–base reactions or nucleophilic substitutions
at the silicon center through a hypercoordinate silicon intermedi-
ate. This subject was analyzed by Corriu in the case of the reactions
of a set of pentacoordinate dihydridosilicates [H2Si(OR)3]ꢀ with
alcohols (ROH) to yield the corresponding pentacoordinate silicates
[HSi(OR)4]ꢀ, and he concluded that a nucleophilic substitution reac-
tion mechanism at the silicon atom was occurring via a hexacoordi-
nate intermediate [18a,37]. By analogy, in the present case, it can be
considered that the reaction initiates with a nucleophilic attack at
the silicon atom of hydridosilanes 10 and 15 by the sp3 enolic oxy-
gen of the b-diketone ligand (the ketonic oxygen with an sp2
hybridization is more electronegative [38] and thus less basic) to
yield a pentacoordinate intermediate; the intramolecular reaction
between the hydride and the enol proton then follows with the
coordination of the second oxygen of the ligand to yield a neutral
pentacoordinate complex. In the three reactions that produce com-
plexes 16–18, the acid base reaction for the former step can be ruled
out by considering that this pathway would produce a low-valent
tricoordinate silicon intermediate [37]. However, two pathways fol-
low: in the case of the hydridosilane 15, a second molecule of the b-
diketone ligand would be unable to carry out an additional nucleo-
philic attack at the silicon center of complex 16 due to steric hin-
drance, causing the reaction to end at this point; in the case of
the pentacoordinate intermediates derived from the hydridosilane
11, a second molecule of the b-diketones HL1 and HL2 could attack
at the intermediate via one of their oxygen atoms, following the lib-
eration of HNCS and the coordination of the second oxygen atom to
yield hexacoordinate complexes 17 and 18.
Fig. 3. ORTEP view of compound 18 drawn at the 50% probability level. Selected
bond lengths [Å] and angles [°]: Si1–N1 1.8591(19), Si1–O1 1.8304(17), Si1–O2
1.7858(14), Si1–O3 1.8103(15), Si1–O4 1.8166(15), Si1–C21 1.881(2), N(1)–C22
1.161(3), S(1)–C22 1.605(2); O(4)–Si(1)–N(1) 171.03(9), O(2)–Si(1)–O(3) 175.04(8),
O(1)–Si(1)–C(21) 176.92(9), O(1)–Si(1)–O(2) 91.38(7), O(1)–Si(1)–O(3) 83.66(7),
O(3)–Si(1)–C(21) 93.27(9), O(2)–Si(1)–C(21) 91.68(9).
compared, for instance, with those corresponding to the tetracoor-
dinate compound Si(NCS)4 [10].
Complexes 17 and 18 were studied using solution and solid-
state 29Si NMR. In the solid state, the isotropic 29Si chemical shifts
obtained in the CP/MAS NMR studies are quite similar for both
complexes (17: d ꢀ169.0; 18: d ꢀ170.0) and are in good agreement
with the 29Si chemical shifts obtained in solution [17 (CDCl3): d
ꢀ174.2; 18 (CDCl3): d ꢀ174.8, (C6D6): d ꢀ175.5)]. These results
indicate that compounds 17 and 18 maintain the hexacoordination
of the silicon atom in solution and that only one diastereomer is
present in both cases. The 29Si chemical shift resonance of com-
plexes 17 and 18 (SiO4NC skeleton) are in the expected region for
hexacoordinate silicon complexes containing two b-diketonato li-
gands; some examples of this type of compound that illustrate this
fact are the following (skeleton, chemical shift, solvent): SiO4CCl, d
ꢀ149.5, CDCl3 [6]; SiO4C2, d ꢀ161.7, THF-d8 [7]; SiO4N2 (2), d
ꢀ208.7, CDCl3 [10]; SiO4N2 (3), d ꢀ204.2, CD2Cl2 [11]; SiO4C2 (4),
d ꢀ138.87, C6D6 [12]; SiO6 (5), d ꢀ176.1, CD2Cl2 [13]; SiO6 (6), d
ꢀ190.3, CD2Cl2 [14]; SiO6 (7), d ꢀ174.1, CD2Cl2 [14]; (see Chart 1
for the structures of 2–7). As observed from the above data, the
presence of two –NCS or –NCO ligands in these complexes causes
a large high-field chemical shift of the 29Si resonance (complexes
2 [10] and 3 [11]).
N
Ph
Me
2N
Me2N
_
_
O
O
O
Si
Si
R
O
O
O
O
N
O
Ph
N
Me2
+
22
R
H
19
20
21
CH2NMe2
+
CH2NHMe2
Chart 2. Hexacoordinate silicon complexes with a SiO4NC skeleton.

132
G. González-García et al. / Polyhedron 41 (2012) 127–133
Table 2
Comparison of some crystallographic bond distances (Å) for some silicon compounds with a SiO4NC coordinating framework.
Bond
17
18
19a
20b
21c
Si–C
1.885
1.881
1.917
1.943
1.954
Si–N
1.884
1.859
2.157
2.085
2.173
Si–O trans to Si–C
Si–O trans to Si–N
Si–O mutually trans
1.811
1.817
1.788, 1.801
1.830
1.816
1.785, 1.810
1.776
1.785
1.779, 1.785
1.771
1.778
1.768, 1.796
1.795
1.767
1.787, 1.793
a
b
c
Reference [32].
Reference [33].
Reference [34]. See Scheme 2 for structures of 17 and 18 and Chart 2 for structures of 19–21.
and were recrystallized in ethanol and dried for 2 h in a vacuum
before use. The HPh2SiCl (90%) was purchased from Aldrich and
was distilled before use.
3. Concluding remarks
The (thiocyanato-N)hydridosilanes HPh2Si(NCS) and HMe-
Si(NCS)2 proved to be useful silicon sources for the production of
novel neutral penta- and hexa-coordinate silicon compounds con-
taining b-diketonato ligands; in a more general sense, the primary
usefulness of the (thiocyanato-N)hydridosilanes will be in those
cases in which anionic protonated ligands are involved, which, to
avoid the presence of acidic protons during the synthesis, require
the use of external bases such as pyridine, triethylamine or imidaz-
ole or the preparation of a deprotonated derivative of the b-diketo-
nate ligand. In this regard, the synthetic route exemplified here
with HPh2Si(NCS) and HMeSi(NCS)2 as starting materials could
be extended to prepare other novel pentacoordinate and hexacoor-
dinate silicon complexes by the displacement of the hydride ligand
from the silicon atom upon reaction with protonated monoanionic
bidentate ligands. This type of reaction could be extended, for in-
stance, to other chelating monoanionic, hard-donor ligands, analo-
gous to b-diketones such as those of the type R2P(O)-X-P(O)R2
(X = NH) [39]. Alternatively, given the fact that complexes 16–18
retain one –NCS group in the coordination sphere, this functional-
ity could be used, for instance, in further Wurtz-type coupling or
substitution reactions to obtain novel hypercoordinate silicon
complexes.
4.2. Synthesis of diphenyl(thiocyanato-N)silane (15)
Chloro(diphenyl)silane (9.7 g, 44.0 mmol) was added at 20 °C to
a stirred suspension of ammonium thiocyanate (4.2 g, 55.0 mmol)
in toluene (30 mL). The reaction mixture was stirred under reflux
for 4 h. After the mixture was cooled to 20 °C, the resulting precip-
itate was filtered off and discarded. The solvent was removed from
the filtrate by distillation at normal pressure, and the residue was
distilled in a vacuum to yield a colorless liquid (bp: 98–100 °C/
20 mbar). Yield: 64% (6.8 g, 28.0 mmol). 1H NMR (200 MHz, CDCl3):
d 5.5 (s, 1H, SiH; satellites: d 1J (1H–29Si) 233.5 Hz), 7.5–7.7 (m,
10H, SiPh). 13C NMR (50 MHz, CDCl3): d 128.51, 131.36, 134.58
(CH aromatic); 129.83 (Cipso–Si); 144.28 (NCS). 29Si INEPT NMR
(56.9 MHz, CDCl3): d ꢀ30.0. FT-IR:
m ; m(Si–H)
(–NCS) 2066 cmꢀ1
2169 cmꢀ1 (C–H) 3072, 3053 cmꢀ1. Anal. Calc. for C13H11NSSi
;
m
(FW 241.38): C, 64.69; H, 4.59; N, 5.80; S, 13.28. Found: C, 64.94;
H, 4.99; N, 5.60; S, 13.51%.
4.3. Synthesis of diphenyl-[1,3-diphenylpropan-1,3-dionato(1ꢀ)-O,O
0](thiocyanato-N)silicon(IV) (16)
1,3-Diphenylpropane-1,3-dione (HL1, 1.40 g, 6.24 mmol) was
added at 25 °C to a stirred solution of HPh2Si(NCS) (0.75 g,
3.11 mmol) in acetonitrile (10 mL). The reaction mixture was stir-
red for 72 h at 20 °C and produced a yellow crystalline solid. The
solid product was filtered and recrystallized in acetonitrile
(20 mL) by slow cooling from 80 to ꢀ20 °C. The yellow crystals
formed were filtered, washed with diethyl ether (10 mL) and dried
4. Experimental
4.1. General procedures
The reactions were performed under an inert atmosphere of dry
nitrogen using standard Schlenk techniques. The organic solvents
were dried and purified according to standard procedures and
stored under a nitrogen atmosphere. The 1H and 13C solution
NMR spectra were recorded at room temperature on either a Var-
ian Gemini 200 (200 MHz 1H and 50 MHz 13C) or a Varian Unity
Plus 300 spectrometer. CDCl3 and C6D6 were used as solvents for
the NMR experiments and were dried using 4A molecular sieve (Al-
drich). The chemical shifts (d) were determined relative to the
residual signal of the solvent (CDCl3: 1H d 7.26; 13C d 77.0). The
assignment of the 13C NMR data was supported by DEPT 135
experiments. The solution (CDCl3 or C6D6) 29Si INEPT NMR and
the solid-state 29Si CP/MAS spectra were recorded on a Varian
Unity Plus 300 spectrometer (29Si, 59.6 MHz), and the chemical
shifts (d) were determined relative to external TMS (d 0.0). The
FT-IR spectra were recorded on a Perkin Elmer Spectrum 100 FT-
IR spectrometer using Nujol mulls for 11 and 15, and a KBr disk
for complexes 16–18. The melting points were determined in
sealed capillaries and are not corrected, and the elemental analyses
were performed by ALS Environmental (Tucson, USA) or using a
LECO TruSpec CHNS instrument at the Instituto de Investigaciones
Químicas CSIC, Universidad de Sevilla, Spain. The starting material,
HMeSi(NCS)2, was prepared as reported in the literature [19]. The
b-diketone ligands L1H and L2H were purchased from Aldrich
under
a vacuum (0.01 mbar) for 2 h. Yield 46.3% (0.67 g,
1.44 mmol); mp: 220–222 °C. 1H NMR (300 MHz, CDCl3): d 7.18
(s, 1H, O–C@CH), 7.25–8.17 (m, 20H, CH aromatic). 13C NMR
(50 MHz, CDCl3): d 95.61 (O–C@CH); 127.66, 128.65, 129.22,
129.48, 134.32 (CH aromatic); 133.62 (Cipso–Si); 138.90 (Cipso
–
C@O); 183.40 (Cipso–C@O); resonance signal of –NCS ligand not de-
tected. 29Si INEPT NMR (79.5 MHz, CDCl3): d ꢀ99.9. FT-IR:
m(–NCS)
2099 cmꢀ1 (C–H) 3013, 3064 cmꢀ1. Anal. Calc. for C28H21NO2SSi
; m
(FW 463.62): C, 72.54; H, 4.57; N, 3.02; S, 6.92. Found: C, 72.72;
H, 4.87; N, 2.98; S, 7.26%.
4.4. Synthesis of methyl-bis[1,3-diphenylpropan-1,3-dionato(1ꢀ)-O,O
0](thiocyanato-N)silicon(IV) (17)
1,3-Diphenylpropane-1,3-dione (HL1, 3.72 g, 16.72 mmol) at
room temperature was added to a solution of HMeSi(NCS)2
(1.31 g, 8.17 mmol) in acetonitrile (30 mL). The reaction mixture
was stirred at 25 °C for 24 h. The precipitate solid that formed
was recrystallized by slow cooling from 80 to 20 °C, and the crys-
talline solid obtained was filtered and washed with diethyl ether
(20 mL) and then dried in a vacuum (0.01 mbar for 2 h). Yield

G. González-García et al. / Polyhedron 41 (2012) 127–133
133
70% (3.14 g, 5.73 mmol); mp >250 °C (dec). 1H NMR (200 MHz,
CDCl3): d 0.61 (s, 3H, SiCH3); 7.04 (s, 2H, O–C@CH), 7.3–8.2 (m,
20H, CH aromatic; two broad signals). 13C NMR (50.3 MHz, CDCl3):
d 12.20 (SiCH3); 93.83 (O–C@CH); 128.23, 128.77, 133.56, (CH aro-
matic); 135.1 (Cipso), 183.30 broad (C@O); resonance signal of –NCS
ligand not detected. 29Si INEPT NMR (59.6 MHz, CDCl3): d ꢀ174.2.
[2] R. West, J. Am. Chem. Soc. 80 (1958) 3246.
[3] (a) R.M. Pike, R.R. Luongo, J. Am. Chem. Soc. 87 (1965) 1403;
(b) C.E. Holloway, R.R. Luongo, R.M. Pike, J. Am. Chem. Soc. 88 (1966) 2060;
(c) R.M. Pike, R.R. Luongo, J. Am. Chem. Soc. 88 (1966) 2972.
[4] D.W. Thompson, Inorg. Chem. 8 (1969) 2015.
[5] G. Schott, K. Golz, Z. Anorg. Allg. Chem. 383 (1971) 314.
[6] J.A. Cella, J.D. Cargioli, E.A. Williams, J. Organometal. Chem. 186 (1980) 13.
[7] K.M. Taba, W.V. Dahlhoff, J. Organometal. Chem. 280 (1985) 27.
[8] (a) S.P. Narula, R. Shankar, B. Kaur, S. Soni, Polyhedron 10 (1991) 2463;
(b) S.P. Narula, S. Soni, R. Shankar, Main Group Met. Chem. 15 (1992) 293.
[9] K. Yamaguchi, K. Ueno, H. Ogino, Chem. Lett. (1998) 247.
[10] O. Seiler, R. Bertermann, N. Buggisch, C. Burschka, M. Penka, D. Tebbe, R. Tacke,
Z. Anorg. Allg. Chem. 629 (2003) 1403.
[11] R. Tacke, R. Bertermann, M. Penka, O. Seiler, Z. Anorg. Allg. Chem. 629 (2003)
2415.
[12] C. Xu, T.H. Baum, A.L. Rheingold, Inorg. Chem. 43 (2004) 1568.
[13] O. Seiler, M. Penka, R. Tacke, Inorg. Chim. Acta 357 (2004) 1955.
[14] O. Seiler, C. Burschka, T. Fenske, D. Troegel, R. Tacke, Inorg. Chem. 46 (2007)
5419.
29Si CP/MAS NMR (59.6 MHz): d ꢀ169.0 (broad). FT-IR:
m(–NCS)
2085 cmꢀ1 (C–H) 3063 cmꢀ1. Anal. Calc. for C32H25NO4SSi (FW
; m
547.69): C, 70.17; H, 4.60; N, 2.56; S, 5.85. Found: C, 70.02; H,
4.66; N, 2.39; S, 4.85%.
4.5. Synthesis of methyl-bis[1-phenylbutan-1,3-dionato(1ꢀ)-O,O0]
(thiocyanato-N)silicon(IV) (18)
1-Phenylbutane-1,3-dione (1.47 g, 9.07 mmol) at room temper-
ature was added to a solution of HMeSi(NCS)2 (0.73 g, 4.53 mmol)
in acetonitrile (30 mL); the reaction mixture was stirred at 25 °C
for 2 h; the precipitate solid that formed was recrystallized by slow
cooling from 80 to ꢀ20 °C in acetonitrile (40 mL). The crystalline
solid obtained was filtered and washed with diethyl ether
(20 mL) and dried in a vacuum (0.01 mbar for 2 h). Yield 73%
(1.40 g, 3.30 mmol); mp >150 °C (dec). 1H NMR (200 MHz, CDCl3):
d 0.38 (s, 3H, SiCH3), 2.23 (s, 6H, O@C–CH3); 6.26 (s, 2H, O–C@CH);
7.40–8.19 (m, 10H, CH aromatic).13C NMR (75 MHz, CDCl3): d 9.65
(SiCH3), 26.6 (O@C–CH3), 97.46 (O–C@CH); 128.22, 128.76, 134.48
(CH aromatic); 133.54 (O@C–Cipso); 134.87 (–NCS). 29Si INEPT NMR
(59.6 MHz) CDCl3, d ꢀ174.8; C6D6, d ꢀ175.5. 29Si CP/MAS NMR
[15] W. Dilthey, Chem. Abstr. (1903) 162105.
[16] Cambridge Structural Data Base (CSD, version 5.32; November 2010): F.H.
Allen, Acta Crystallogr. B58 (2002) 380. The references cited in CSD concerning
the X-ray crystal structures of the cation [Si(aca)3]+ with different anions are
the following: (a) Anion ClO4ꢀ: T. Adam, T. Debaerdemaeker, U. Thewalt, Eur.
ꢀ
Cryst. Meeting
5
(1979) 325; (b) Anion C12H4N4
:
K. Ueyama, G.-E.
Matsubayashi, J. Chem. Res. 48 (1985) 801; (c) Anion HCl2ꢀ: U. Thewalt, U.
Link, Z. Naturforsch. B Chem. Sci. 46 (1991) 293; (d) Anion Ag2Cl42ꢀ: D.
Hogerle, U. Link, U. Thewalt, Z. Naturforsch. B Chem. Sci. 48 (1993) 691.
[17] J.A. Cella, T.D. Mitchell, J. Organometal. Chem. 244 (1983) C5.
[18] (a) C. Chuit, R.J.P. Corriu, C. Reye, J.C. Young, Chem. Rev. 93 (1993) 1371;
(b) D. Kotz, I. Kalikhman, in: Z. Rappoport, Y. Apeilgon (Eds.), The Chemistry of
Organosilicon Compounds, vol. 2, John Wiley and Sons, Ltd, 1998 (Chapter 2).
[19] G. Gonzalez-Garcia, J.A. Gutierrez, S. Cota, S. Metz, R. Bertermann, C. Burschka,
R. Tacke, Z. Anorg. Allg. Chem. 634 (2008) 1281.
[20] G. Gonzalez-Garcıa, E. Alvarez, A.M. Marcos-Fernandez, J.A. Gutierrez, Inorg.
Chem. 48 (2009) 4231.
(59.6 MHz):
d
ꢀ170.0. FT-IR:
m ; m(C–H)
(–NCS) 2113 cmꢀ1
[21] N. Serpone, K.A. Hersh, J. Organometal. Chem. 84 (1975) 177.
[22] N. Kano, A. Kikuchi, T. Kawashima, Chem. Commun. (2001) 2096.
[23] J. Wagler, E. Brendler, Z. Naturforsch. 62b (2007) 225.
[24] U. Böhme, B. Günther, Inorg. Chem. Commun. 10 (2007) 482.
[25] U. Böhme, S. Wiesner, B. Günther, Inorg. Chem. Commun. 9 (2006) 806.
[26] K. Tamao, M. Asahara, T. Saeki, A. Toshimitsu, Angew. Chem., Int. Ed. 38 (1999)
3316.
2966 cmꢀ1. Anal. Calc. for C22H21NO4SSi (FW 423.56): C, 62.38; H,
5.00; N, 3.31; S, 7.57. Found: C, 62.51; H, 5.36; N, 3.40; 7.55%.
4.6. Crystallographic structure determination
[27] F. Mucha, U. Bohme, Chem. Commun. (1998) 1289.
[28] K. Junold, C. Burschka, R. Bertermann, R. Tacke, Dalton Trans. 39 (2010) 9401.
[29] S. Metz, C. Burschka, R. Tacke, Organometallics 27 (2008) 6032.
[30] S. Metz, B. Theis, C. Burschka, R. Tacke, Chem. Eur. J. 16 (2010) 6844.
[31] C. Breliere, R.J.P. Corriu, G. Royo, W.W.C. Wong Chi Man, J. Zwecker,
Organometallics 9 (1990) 2633.
[32] F. Carré, G. Cerveau, C. Chuit, R.J.P. Corriu, C. Réyé, Angew. Chem., Int. Ed. 28
(1989) 489.
[33] F. Carré, C. Chuit, R.J.P. Corriu, A. Mehdi, C. Reyé, J. Organomet. Chem. 446
(1993) C6.
[34] F. Carré, C. Chuit, R.J.P. Corriu, A. Fanta, A. Mehdi, C. Reyé, Organometallics 14
(1995) 194.
[35] I. Kalikhman, V. Kingston, O. Girshberg, D. Kost, Organometallics 20 (2001)
4713.
[36] J. March, Advanced Organic Chemistry. Reaction, Mechanisms, and Structure,
fourth ed., John Wiley and Sons, New York, 1992. p. 18.
Suitable single crystals of 16–18 were obtained by slow cooling
in acetonitrile, after which they were coated with dry perfluoro-
polyether and mounted on a glass fiber under a cold nitrogen
stream [T = 100(2) K]. Data collection was performed on a Bru-
ker-Nonius X8APEX-II CCD diffractometer using monochromated-
graphite radiation k (Mo Ka) = 0.71073 Å by means of x and /
scans. The structures were resolved using direct methods with a
SIR 2004 [40] and refined using full-matrix least-squares proce-
dures utilizing SHELXL-97 [41].
Acknowledgments
[37] R.J.P. Corriu, C. Guerin, B.J.L. Henner, Q. Wang, Organometallics 10 (1991)
3200.
[38] J.E. Huheey, E.A. Keiter, R.L. Keiter, Inorganic Chemistry. Principles of Structure
and Reactivity, fourth ed., Harper Collins College Publishers, New York, 1993.
p. 187 (Chapter 5).
[39] M. Correa-Ascencio, E.K. Galvan-Miranda, F. Rascon-Cruz, O. Jimenez-
Sandoval, S.J. Jimenez-Sandoval, R. Cea-Olivares, V. Jancik, R.A. Toscano, V.
Garcıa-Montalvo, Inorg. Chem. 49 (2010) 4109.
[40] M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascarano, L.G.C. De
Caro, G. Polidori, R. Spagna, J. Appl. Crystallogr. 38 (2005) 381.
[41] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
Financial support from PROMEP (Secretaría de Educación Públi-
ca) is acknowledged. G.G.G. gratefully acknowledges a Ph.D. schol-
arship from Consejo Nacional de Ciencia y Tecnología (CONACYT)
and the Universidad de Guanajuato. We are grateful to the Consejo
Superior de Investigaciones Científicas (CSIC) of Spain for the
award of a license for the use of the Cambridge Crystallographic
Data Base (CSD).
References
[1] S. Metz, C. Burschka, R. Tacke, Organometallics 28 (2009) 2311.