Silicon version of enamines: Amino-substituted disilenes by the reactions of the disilyne RSiSiR (R = SiiPr[CH(SiMe3) 2]2) with amines

Article abstract of DOI:10.1016/j.jorganchem.2010.07.008

The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4- diisopropyltetrasila-2-yne 1 with secondary or primary amines produced amino-substituted disilenes R(R₂′N)SiSiHR 2a-d (R = Si ⁱPr[CH(SiMe₃)₂]₂, R ₂′NEt₂N (2a), (CH₂CH₂) ₂N (2b), ^tBu(H)N (2c), and Ph₂N (2d)). Spectroscopic and X-ray crystallographic analyses of 2 showed that 2a-c have a nearly coplanar arrangement of the SiSi double bond and the amino group, giving π-conjugation between the SiSi double bond and the lone pair on the nitrogen atom, whereas 2d has a nearly perpendicular arrangement precluding such conjugation. Theoretical calculations indicate that π-conjugation between the π-orbital of the SiSi double bond and the lone pair on the nitrogen atom is markedly influenced by the torsional angle between the SiSi double-bond plane and the amino-group plane.

Full text of DOI:10.1016/j.jorganchem.2010.07.008

Journal of Organometallic Chemistry 696 (2011) 1156e1162
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Silicon version of enamines: Amino-substituted disilenes by the reactions of the
disilyne RSi^SiR (R ¼ SiiPr[CH(SiMe3)2]2) with amines
*
Katsuhiko Takeuchi, Masao Ikoshi, Masaaki Ichinohe, Akira Sekiguchi
Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne
1
with
secondary or primary amines produced amino-substituted disilenes R(R20N)Si]SiHR 2aed (R ¼ SiiPr[CH
(SiMe3)2]2, R20N]Et2N (2a), (CH2CH2)2N (2b), tBu(H)N (2c), and Ph2N (2d)). Spectroscopic and X-ray
crystallographic analyses of 2 showed that 2aec have a nearly coplanar arrangement of the Si]Si double
Received 14 June 2010
Received in revised form
7 July 2010
Accepted 7 July 2010
bond and the amino group, giving
the nitrogen atom, whereas 2d has a nearly perpendicular arrangement precluding such conjugation.
Theoretical calculations indicate that -conjugation between the -orbital of the Si]Si double bond and
p-conjugation between the Si]Si double bond and the lone pair on
Keywords:
Addition reaction
Disilene
Disilyne
Siliconesilicon double bond
Siliconesilicon triple bond
p
p
the lone pair on the nitrogen atom is markedly influenced by the torsional angle between the Si]Si
double-bond plane and the amino-group plane.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
We have succeeded in the isolation of the first crystalline dis-
ilyne 1, RSi^SiR (R ¼ SiiPr[CH(SiMe3)2]2), whose characteristic
The chemistry of multiply bonded compounds containing
heavier group 14 elements has been developed since the isolation
of the stable distannene Dsi2Sn]SnDsi2 (Dsi ¼ CH(SiMe3)2) by
Lappert in 1973 [1], tetramesityldisilene Mes2Si]SiMes2 (Mes ¼
2,4,6-trimethylphenyl) [2] and the silene (Me3Si)2Si]C(OSiMe3)Ad
(Ad ¼ 1-adamantyl) in 1981 [3,4]. Despite extensive experimental
efforts directed towards the synthesis of triply bonded compounds
of heavier group 14 elements, heavier analogues of alkynes, such as
eE^Ce and eE^Ee (E ¼ Si, Ge, Sn, and Pb), remained unknown
until recently [5]. In 2000, Power reported the synthesis and
structural characterization of the lead analogue of the alkyne
analogue [6]. Subsequently, tin [7] and germanium [8] analogues
were also synthesized by the same group in 2002 using bulky
terphenyl ligands (2,6-diarylphenyl groups) and by Tokitoh group
using the Bbt substituent (C6H2-2,6-[CH(SiMe3)2-4-C(SiMe3)3) for
the germanium analogue [9]. In 2004, we [10] and Wiberg’s group
[11] reported the synthesis of the triply bonded silicon species,
disilynes, which are stabilized kinetically by very bulky silyl groups.
Very recently, Tokitoh’s group reported the synthesis of an aryl-
substituted disilyne by the use of the Bbt [12].
trans-bent structure was determined by X-ray crystallography as
well as by solid-state NMR spectroscopy [10,12]. Disilyne 1 has two
nondegenerate occupied
p-MOs and two unoccupied antibonding
p*-MOs with a relatively small HOMOeLUMO gap [10]. Thus, dis-
ilyne 1 is very reactive towards alkenes [13], alkynes [14], tBuLi [15],
alkali metals [15,16], nitriles [17], silylcyanides [18,19], and 9-bor-
abicyclo[3.3.1]nonane (9-BBN) [20] to give 1,2-disilacyclobutenes,
1,2-disilabenzene derivatives, a disilenyllithium, anion radicals,
triaza-1,4-disilabicyclo[2.2.2]oct-2,5,7-triene derivatives, disilyne-
silylisocyanide bis-adducts, 1,4-diaza-2,3-disilabenzene deriva-
tives, and a boryl-substituted disilene, respectively. Thus, we have
shown that the disilyne 1 provides a new highly effective route for
the synthesis of various types of unsaturated organosilicon
compounds that are very difficult to prepare by the usual method
for disilenes.
To our knowledge, there are three methods to synthesize
heteroatom-substituted disilenes: a) homocoupling of amino-
substituted silylenes [21]; b) photochemical isomerization of bicyclo
[1.1.0]butane derivatives Si3E (E ¼ S, Se, and Te) [22]; and c) the
reaction of a disilenide derivative with haloboranes [23]. The reduc-
tion of L:SiCl4 (L ¼ 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene)
to afford a new type of disilene, L:Si]Si:L, was also reported recently
[24]. However, the syntheses of heteroatom-substituted disilenes are
very limited for synthetic reasons [4]. Recently, we reported0 the
* Corresponding author.
E-mail address: sekiguch@chem.tsukuba.ac.jp (A. Sekiguchi).
0
synthesisoftwoamino-substituteddisilenesR(R2 N)Si]SiHR(R2 N¼
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.07.008

K. Takeuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1156e1162
1157
Scheme 1.
Et2N (2a) and Ph2N (2d)) by the reaction of disilyne 1 with diethyl-
amine or diphenylamine (Scheme 1), providing a new access route to
the efficient synthesis of amino-substituted disilenes [20]. In this
paper, we report a detailed study on the synthesis and physical
properties (NMR, UV, and X-ray) of amino-substituted disilenes, the
silicon version of enamines, by the reactions of disilyne RSi^SiR (R ¼
SiiPr[CH(SiMe3)2]2) with amines, including a cyclic amine (pyrroli-
between the amino-group plane and the Si]Si double-bond plane,
which reduces -conjugation. The fact that the Si1eN1 bond lengths
of 2a, 2b, and 2c (1.717(2),1.703(4), and 1.7103(16) Å, respectively) are
shorter thanthatof 2d(1.775(3) Å)alsoshows that2a, 2b, and 2chave
p
p-conjugation, while 2d has almost no
p-conjugation. However, the
Si]Sidouble-bondlengths of 2 reflectstericeffectsratherthanthe
p-
conjugation effect. The Si]Si double-bond lengths of 2c (2.1949(7) Å)
and 2d (2.1790(14) Å), both of which have relatively bulky substitu-
ents on the nitrogen atom, are longer than those of the other amino-
substituted disilenes 2a (2.1647(2) Å) and 2b (2.1596(17) Å).
dine) and a primary amine. We also discuss the
p-conjugation
between the Si]Si -bond and the lone pair on the nitrogen atom,
p
together with theoretical calculations.
The NMR spectra of amino-substituted disilenes 2b and 2c
recorded in C6D6 as solvent indicate the contribution of zwitterionic
structure B, which has anionic character on the H-substituted Si
atom, as found in 2a (Chart 1). In the 29Si NMR spectra of 2b and 2c,
two characteristic signals of skeletal silicon atoms were observed;
chemical shifts at lower field (159.0 and 136.5 ppm, respectively)
correspond to the skeletal low-coordinate silicon atom that is
bonded to the amino group (NeSi]Si) and the shifts at higher field
(ꢀ34.1 and ꢀ47.2 ppm, respectively) correspond to another skeletal
low-coordinate silicon atom that is bonded to a hydrogen atom
(HeSi]Si). These signals are similar to those of 2a (170.5 ppm for
NeSi]Si and ꢀ39.3 ppm for HeSi]Si), and the latter value drasti-
cally shifted to high field, in contrast to that for previously reported
unsymmetrical disilenes (63.3e154.5 ppm) [4c,27]. This is explain-
able based on the anionic charge on the H-substituted silicon atom
from the contribution of the zwitterionic structure B in Chart 1. In
contrast, the 29Si NMR resonances of the skeletal silicon atoms of 2d
at 136.4 (NeSi]Si) and 66.6 ppm (HeSi]Si) are in typical regions
2. Results and discussion
2.1. Synthesis, structure, and physical properties (NMR, UV,
and X-ray) of amino-substituted disilenes
The reactions of the disilyne 1 with various amines are summa-
rized in Scheme 1. We have previously described the reaction of
disilyne 1 with a slight excess of diethylamine or diphenylamine in
toluene or C6D6 to give the corresponding amino-substituted dis-
0
0
ilene R(R2 N)Si]SiHR (R2 N ¼ Et2N (2a) and Ph2N (2d)) [20]. Treat-
ment of the disilyne 1 with a slight excess of pyrrolidine, which is
sterically smaller than diethylamine, in toluene from ꢀ78 ꢁC to ꢀ50
ꢁC also yielded an orange solution of the amino-substituted disilene
R(CH2CH2)2NSi]SiHR (2c), which was isolated as air- and moisture-
sensitive orange crystals in 72% yield. A similar addition reaction of
the primary amine tert-butylamine to the disilyne 1 in toluene
afforded the amino-substituted disilene R[tBu(H)N]Si]SiHR (2c) in
54% yield. Both reactions producing 2b or 2c completed promptly
even at ꢀ78 ꢁC, similar to the case of diethylamine. The reaction of 1
with diphenylamine in C6D6 to give 2d was very slowand it took one
month for completion because of steric hindrance.
for unsymmetrical disilenes, showing that 2d has only weak
p-
conjugation in solution, as in the solid state. The contribution of the
zwitterionic structure B in 2a, 2b, and 2c is also suggested by their
high-field shifted 1H NMR resonances of SieH (2.97, 3.10, and 2.80
ppm, respectively) compared with that of 2d (4.54 ppm).
Although amino-substituted disilenes 2a, 2c, and 2d did not
react with excess amine because of their steric hindrance, the
smallest pyrrolidino group-substituted disilene 2b reacted with
a second pyrrolidine molecule to afford 3 in 85% yield (Scheme 1).
This reaction is similar to the reaction of disilyne 1 with alcohols,
which only gives 1,1-dialkoxydisilanes [25].
UVeVis spectroscopy of amino-substituted disilenes 2aed
revealed large red shifts of the longest-wavelength absorptions (438,
433, 411, and 440 nm, respectively), which are assigned to the pe
p*
electronic transition of the Si]Si double bond, compared with that of
RLiSi]SiHR (390 nm) [15]. The narrowing of the HOMOeLUMO gap
associated with such long-wavelength shifts is accepted as evidence
The crystal structures of 2aed have been determined by X-ray
crystallography; ORTEP drawings being shown in Figs. 1e4 with
selected structural parameters listed in Table 1. The coordination of
the nitrogen in all of the amino-substituted disilenes is almost planar
in each molecule with angular sums at nitrogen (SꢁN) of nearly 360ꢁ
that are characteristic of monosilyl-substituted amines [26]. The
amino-group planes of2a and 2bwere approximately parallel totheir
Si]Si double-bond planes with torsional angles Si2eSi1eN1eC1 of
for
p
-conjugation in 2a, 2b, and 2c. However, 2d shows the longest-
wavelength absorption, despite its weak
p-conjugation. Several
reasons have been considered for the red shift of 2d: a decrease in the
LUMO energy level by the relatively strong electron-withdrawing
diphenylamino group, and/or twisting of the Si]Si double bond
because of the steric effects of its very bulky substituents.
ca. 7ꢁ and 12ꢁ, which suggest the presence of
p-conjugation. In
contrast, 2dhas anamino-group planethatisalmost perpendicular to
the Si]Si double-bond plane with a torsional angle Si2eSi1eN1eC1
of ca. 67ꢁ, because of the two bulky phenyl groups. In 2c, the amino-
group plane is moderately twisted from the Si]Si double-bond plane
withatorsionalangleSi2eSi1eN1eC35ofca. 29ꢁ. Thus, acomparison
shows that bulky amino groups tend to have large twist angles
Chart 1.

1158
K. Takeuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1156e1162
Fig. 3. ORTEP drawing of 2c (30% thermal ellipsoids). Hydrogen atoms except H1 on
N1 and for H2 on Si2 are omitted for clarity.
Fig. 1. ORTEP drawing of 2a (30% thermal ellipsoids). Hydrogen atoms except for H2 on
Si2 are omitted for clarity.
essentially more stable as a slightly twisted structure than as
a completely planar structure. However, the energy differences
2.2. Theoretical calculations
between the model disilenes with
1.0 kcal/mol). Although the relative energies of the model disilenes
rise steeply with an increase in the dihedral angle
from about 45ꢁ
because of the decrease in the stabilizing effects of -conjugation
-orbital,
q
< 45ꢁ are very small (less than
While the experimental results of amino-substituted disilenes
q
indicate the presence of a contribution of
Si]Si double bond and the lone pair on the nitrogen atom, the
structural parameters are not fully explained by -conjugation
because of steric effects. Therefore, to provide an estimate of the
relationshipbetween -conjugationandthetwistingangleof theSi]
p-conjugation between the
p
between the lone pair of the nitrogen atom and the Si]Si
p
p
the most destabilizing
q
¼ 90ꢁ model disilene is only 4.4 kcal/mol
less stable than the energy minimum. The effect of
p-conjugation
p
between the Si]Si double bond and the amino group is also sup-
Si double-bond plane and amino-substituent plane in the amino-
substituted disilenes, we optimized a model compound Me3Si(Me2N)
ported by structural parameters (Fig. 5b and c): as the dihedral
angle
q q
increases (30ꢁ < < 90ꢁ), the Si]Si double bond becomes
Si]Si(H)SiMe3 20 in which the dihedral angles
q between the amino-
shortened and the SieN bond becomes elongated, reflecting the
decrease of the contribution of zwitterionic structure B.
group plane and the Si]Si double-bond plane were frozen at every
15ꢁ from 0ꢁ to 90ꢁ (Fig. 5). These theoretical studies were carried out
using density functional theory with the B3LYP [28,29] functional, as
implemented in the Gaussian 03 software with the 6-31G(d) level
basis set.
To further explore the effect of p-conjugation between the Si]
Si double bond and the lone pair on the nitrogen atom, correlated
with the torsional angle between the Si]Si double-bond plane and
the amino group, we performed GIAO calculations of the optimized
model disilenes 20 using the B3LYP/6-311G(3d) [30] level basis set.
As shown in Fig. 5a, the potential surface has a local minimum at
about 30ꢁ and shows that the amino-substituted disilene is
The calculated
atoms as a function of the dihedral angles
d(
29Si) chemical shifts of the two skeletal silicon
q
are plotted in Fig. 5d. As
Fig. 2. ORTEP drawing of 2b (30% thermal ellipsoids). Hydrogen atoms except for H2
Fig. 4. ORTEP drawing of 2d (30% thermal ellipsoids). Hydrogen atoms are omitted for
on Si2 are omitted for clarity.
clarity.

K. Takeuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1156e1162
1159
¼ 90ꢁ) and the planarization (SꢁSi ¼ 325ꢁ for
q
¼ 0ꢁ,
Table 1
ꢀ0.154 for
350ꢁ for
q
Selected bond lengths (Å) and angles (ꢁ) of 2a, 2b, 2c and 2d.
q
¼ 90ꢁ) of the H-substituted silicon atom.
Compound
2a
2b
2c
2d
Bond lengths (Å)
3. Conclusion
Si1eSi2
Si1eSi3
Si1eN1
Si2eSi8
Si2eH2
N1eC1
N1eC
2.1647(10)
2.1596(17)
2.3888(16)
1.703(4)
2.3481(16)
1.44(5)
1.466(6)
1.468(6)
(N1eC4)
2.1949(7)
2.3761(7)
1.7103(16)
2.3804(6)
1.43(2)
2.1790(14)
2.4320(14)
1.775(3)
2.3966(9)
1.717(2)
2.3550(10)
1.45(4)
1.463(3)
1.470(3)
(N1eC3)
We have demonstrated the reaction of the disilyne 1 with
diethylamine, pyrrolidine, tert-butylamine, and diphenylamine to
produce amino-substituted disilenes 2aed. The spectroscopic and
structural features for the series 2aed and a computational study of
the model compound of amino-substituted disilene 20 clearly
2.3723(15)
1.431(5)
1.428(5)
(N1eC7)
1.482(2)
(N1eC35)
indicate that
p-conjugation between the p-orbital of the Si]Si
Bond angles (ꢁ)
double bond and the lone pair on the nitrogen atom is markedly
influenced by the torsional angle between the Si]Si double-bond
plane and the amino-group plane.
Si2eSi1eSi3 116.14(4)
Si2eSi1eN1 122.41(8)
Si3eSi1eN1 120.10(8)
Si1eSi2eSi8 141.72(4)
Si1eSi2eH2 104.8(17)
Si8eSi2eH2 108.4(17)
117.60(7)
121.43(14)
120.05(14)
141.23(7)
101.6(19)
114.0(19)
124.4(3)
116.65(3)
131.19(6)
107.37(6)
144.35(3)
95.6(9)
122.60(6)
116.92(12)
118.31(12)
143.36(6)
101.7(9)
4. Experimental
Si1eN1eC1
Si1eN1eC
123.46(17)
120.72(18)
121.0(3)
122.0(2)
127.9(3)
130.90(12)
(Si1eN1eC3) (Si1eN1eC4) (Si1eN1eC35) (Si1eN1eC7)
4.1. General procedures
C1eN1eC
115.8(2)
107.7(4)
116.5(3)
(C1eN1eC3)
(C1eN1eC4)
(C1eN1eC7)
All experiments were performed using high-vacuum line tech-
niques or in an argon atmosphere using an MBRAUN MB 150B-G glove
box. All solvents were dried and degassed over potassium mirror in
vacuum prior to use. NMR spectra were recorded on Bruker AC-300FT
NMR (1H NMR at 300.1 MHz; 13C NMR at 75.5 MHz; 29Si NMR at 59.6
MHz) and AV-400FT NMR spectrometers (1H NMR at 400 MHz; 13C
NMR at 100.6 MHz; 29Si NMR at 79.5 MHz). High-resolution mass
spectra were performed on Bruker Daltonics micrOTOF mass spec-
trometer with APCI (atmospheric pressure chemical ionization
method). UVeVis spectrawererecordedonSimadzuUV-3150UVeVis
spectrophotometer in hexane. 1,1,4,4-Tetrakis[bis(trimethylsilyl)
methyl]-1,4-diisopropyltetrasila-2-yne 1 was prepared according to
the published procedure [10].
the dihedral angle
q
increases, the calculated
d(
29Si) values of the H-
substituted silicon atom are significantly shifted to low field, from
ꢀ63.5 (
q
¼ 0ꢁ) to 100.1 ppm (
q
¼ 90ꢁ), compared with those of the
N-substituted silicon atom (from 252.1 ppm for
q
¼ 0ꢁ to 204.0 ppm
for
q
¼ 90ꢁ). These results suggest that the localization of anionic
character on the H-substituted silicon atom by the contribution of
zwitterionic structure B becomes larger as the amino-group plane
becomes parallel to the Si]Si double bond. This localization of
anionic character with lower dihedral angles
decrease in the anionic charge (Mulliken charge: ꢀ0.270 for
q is also evident by the
q
¼ 0ꢁ,
Fig. 5. Theoretical calculations on H3Si(Me2N)Si]Si(H)SiH3 20 as a function of the dihedral angle between the Si]Si and the amino-group planes; a) relative energies, b) SieN bond
lengths, c) Si]Si double-bond lengths, and d) chemical shifts of skeletal silicon atoms calculated by the GIAO method.

1160
K. Takeuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1156e1162
4.1.1. Synthesis of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-
diisopropyl-2-diethylamino-2-tetrasilene (2a)
9.1 (CH(SiMe3)2 ꢂ 2), 16.3 (CH(CH3)2), 17.2 (CH(CH3)2), 21.0 (CH
(CH3)2), 22.2 (CH(CH3)2), 33.4 (HNeCCH3), 52.2 (HNeCCH3); 29Si
Dry oxygen-free Et2NH (0.25 ml, 177 mg, 2.4 mmol) was added
by vacuum transfer to a dry oxygen-free toluene solution (1.0 ml) of
1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-
2-yne 1 (50 mg, 0.06 mmol) and the mixture was stirred from ꢀ78
ꢁC to room temperature over 5 h. The color of the solution changed
to orange from the emerald green of 1. After evaporation of the
solvent and the remaining Et2NH, the residue was recrystallized
from pentane (0.5 ml) at ꢀ30 ꢁC to give 2a as air- and moisture-
sensitive orange crystals (43 mg, 78% yield). M.p. 134.4e135.9 ꢁC;
NMR (C6D6):
d
ꢀ47.2 (1JSieH ¼ 139 Hz, ]SieH), ꢀ0.6 (SiMe3), ꢀ0.4
(SiMe3), 0.0 (SiMe3), 0.2 (SiMe3), 3.0 (SiiPrDsi2), 17.0 (SiiPrDsi2),
136.5 (]SieN); HRMS: m/z calcd for C38H102NSi12 (M þ H)þ
908.5238, found 908.5239; UV/Vis (hexane) lmax/nm (3) 411 (3600).
4.1.4. Synthesis of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-
diisopropyl-2-(N,N-diphenylamino)-2-tetrasilene (2d)
Dry oxygen-free C6D6 (0.5 ml) was added by vacuum transfer to
a mixture of 1 (50 mg, 0.06 mmol) and Ph2NH (17 mg, 0.1 mmol) in
an NMR tube and the reaction mixture was monitored by 1H NMR
spectroscopy. After one month, the disilyne 1 was consumed and
the color of the solution changed to orange. After evaporation, the
residue was recrystallized from toluene (0.5 ml) at ꢀ30 ꢁC to give
2d as air- and moisture-sensitive orange crystals (20 mg, 33% yield).
M.p. 160.5e161.4 ꢁC. In the 1H NMR spectrum, one of the CH
(SiMe3)2 groups was not observed because of the very broad signal.
1H NMR (C6D6):
d 0.10 (s, 2H, CH(SiMe3)2), 0.19 (s, 2H, CH(SiMe3)2),
0.39 (s, 18H, CH(SiMe3)2), 0.40 (s, 18H, CH(SiMe3)2), 0.42 (s, 18H, CH
(SiMe3)2), 0.49 (s, 18H, CH(SiMe3)2), 1.06 (t, J ¼ 7.0 Hz, 6H, N
(CH2CH3)2), 1.34 (d, J ¼ 7.0 Hz, 12H, CH(CH3)2 ꢂ 2), 1.50 (sep, J ¼ 7.0
Hz, 1H, CH(CH3)2), 1.73 (sep, J ¼ 7.0 Hz, 1H, CH(CH3)2), 2.97 (s, 1 H,
SiH), 3.26 (q, J ¼ 7.0 Hz, 6H, N(CH2CH3)2); 13C NMR (C6D6):
d 5.3
(SiMe3), 5.7 (SiMe3), 6.2 (SiMe3 ꢂ 2), 9.1 (CH(SiMe3)2 ꢂ 2), 13.1 (N
(CH2CH3)2), 17.0 (CH(CH3)2), 17.3 (CH(CH3)2), 22.3 (CH(CH3)2 ꢂ 2),
1H NMR (C6D6):
d 0.00 (s, 2H, CH(SiMe3)2), 0.31 (s,18H, CH(SiMe3)2),
45.0 (N(CH2CH3)2); 29Si NMR (C6D6):
d
ꢀ39.3 (1JSieH ¼ 157 Hz, Si]
0.36 (s, 18H, CH(SiMe3)2) 0.40 (s, 18H, CH(SiMe3)2), 0.85 (br, 6H, CH
(CH3)2), 1.21 (sept, J ¼ 7.0 Hz, 1H, CH(CH3)2), 1.32 (br, 6H, CH(CH3)2),
1.50 (sept, J ¼ 7.0 Hz, 1H, CH(CH3)2), 4.54 (s, 1H, SiH), 6.83 (t, J ¼ 8.0
Hz, 2H, p-CH), 7.10 (t, J ¼ 8.0 Hz, 4H, m-CH), 7.52 (t, J ¼ 8.0 Hz, 4H, o-
SieH), ꢀ0.5 (SiMe3), ꢀ0.4 (SiMe3), 0.1 (SiMe3), 0.5 (SiMe3), 2.8
(SiiPrDsi2), 14.7 (SiiPrDsi2), 170.5 (Si]SieN); HRMS (APCI): m/z
calcd for C38H102NSi12 (M þ H)þ 908.5238, found 908.5235; UV/Vis
(hexane) lmax/nm (3) 438 (9740).
CH); 13C NMR (C6D6):
d 5.3 (SiMe3), 5.8 (SiMe3), 6.0 (SiMe3), 6.4
(SiMe3), 9.5 (CH(SiMe3)2 ꢂ 2), 17.4 (CH(CH3)2), 17.7 (CH(CH3)2), 21.9
4.1.2. Synthesis of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-
diisopropyl-2-(pyrrolidino)-2-tetrasilene (2b)
(CH(CH3)2 ꢂ 2), 122.8 (p-CH), 126.1 (o-CH), 129.2 (m-CH), 150.4
(ipso-CH); 29Si NMR (C6D6):
d
ꢀ0.41 (SiMe3), ꢀ0.35 (SiMe3), ꢀ0.1
Dry oxygen-free pyrrolidine (0.01 ml, 8.7 mg, 0.12 mmol) was
added by microsyringe to a dry oxygen-free toluene solution (1.0
ml) of 1 (50 mg, 0.06 mmol) and the mixture was stirred from ꢀ78
ꢁC to ꢀ50 ꢁC over 10 min. The color of the solution immediately
changed to orange from the emerald green of 1. After evaporation of
the solvent and the remaining pyrrolidine, the residue was
recrystallized from pentane (0.5 ml) at ꢀ30 ꢁC to give 2b as air- and
moisture-sensitive orange crystals (39 mg, 72% yield). M.p.
(SiMe3), 0.5 (SiMe3), 15.9 (SiiPrDsi2), 17.9 (SiiPrDsi2), 66.6 (1JSieH
¼
160 Hz, ]SieH), 136.4 (]SieN); HRMS: m/z calcd for C46H102NSi12
(M þ H)þ 1004.5238, found 1004.5239; UV/Vis (hexane) lmax/nm
(3) 339 (2250), 440 (4430).
4.1.5. Synthesis of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-
diisopropyl-2,2-(dipyrrolidino)tetrasilane (3)
Dry oxygen-free pyrrolidine (0.25 ml, 217 mg, 3.1 mmol) was
added by vacuum transfer to a dry oxygen-free toluene solution (1.0
ml) of 1 (50 mg, 0.06 mmol) and the mixture was stirred at room
temperature for 2 h. The color of the solution immediately changed
to orange from the emerald green of 1, and then gradually decol-
orized. After evaporation of the solvent and the remaining pyrro-
lidine, the residue was recrystallized from pentane (0.5 ml) at ꢀ30
ꢁC to give 3 as a colorless powder (50 mg, 85% yield). M.p.
123.7e124.4 ꢁC; 1H NMR (C6D6):
d 0.12 (s, 2H, CH(SiMe3)2), 0.21 (s,
2H, CH(SiMe3)2), 0.38 (s, 18H, CH(SiMe3)2), 0.39 (s, 18H, CH
(SiMe3)2), 0.41 (s, 18H, CH(SiMe3)2), 0.49 (s, 18H, CH(SiMe3)2), 1.34
(d, J ¼ 7.0 Hz, 12H, CH(CH3)2 ꢂ 2), 1.56 (sep, J ¼ 7.0 Hz, 1H, CH
(CH3)2), 1.61e1.66 (m, 4H, N(CH2CH2)2), 1.79 (sep, J ¼ 7.0 Hz, 1H, CH
(CH3)2), 3.10 (s, 1H, SiH), 3.20e3.34 (m, 4H, N(CH2CH2)2); 13C NMR
(C6D6):
d 5.5 (SiMe3), 5.9 (SiMe3), 6.1 (SiMe3), 6.2 (SiMe3), 7.2 (CH
(SiMe3)2), 9.1 (CH(SiMe3)2), 16.8 (CH(CH3)2), 17.3 (CH(CH3)2), 20.7
(CH(CH3)2), 22.6 (CH(CH3)2), 26.8 (N(CH2CH2)2), 53.8 (N(CH2CH2)2);
158.1e160.3 ꢁC; 1H NMR (C6D6):
d 0.14 (s, 2H, CH(SiMe3)2), 0.35 (s,
18H, CH(SiMe3)2), 0.37 (s, 2H, CH(SiMe3)2), 0.40 (s, 18H, CH
(SiMe3)2), 0.41 (s, 18H, CH(SiMe3)2), 0.42 (s, 18H, CH(SiMe3)2), 1.24
(d, J ¼ 7.0 Hz, 6H, CH(CH3)2), 1.43 (d, J ¼ 7.0 Hz, 6H, CH(CH3)2), 1.49
(sep, J ¼ 7.0 Hz, 1H, CH(CH3)2), 1.53 (sep, J ¼ 7.0 Hz, 1H, CH(CH3)2),
1.73 (q, J ¼ 4.0 Hz, 8H, N(CH2CH2)2), 3.22 (q, J ¼ 4.0 Hz, 8H, N
29Si NMR (C6D6):
d
ꢀ34.1 (1JSieH ¼ 149 Hz, ]SieH), ꢀ0.5 (SiMe3),
ꢀ0.4 (SiMe3), 0.2 (SiMe3), 0.5 (SiMe3), 2.1 (SiiPrDsi2), 14.7 (SiiPrDsi2),
159.0 (]SieN); HRMS: m/z calcd for C38H100NSi12 (M þ H)þ
906.5081, found 906.5084; UV/Vis (hexane) lmax/nm (3) 433 (3670).
(CH2CH2)2), 3.50 (s, 2H, SiH2); 13C NMR (C6D6):
d 4.1 (CH(SiMe3)2),
4.1.3. Synthesis of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-2-(tert-
butylamino)-1,4-diisopropyl-2-tetrasilene (2c)
5.1 (SiMe3), 5.3 (SiMe3), 6.1 (SiMe3), 6.4 (SiMe3), 8.8 (CH(SiMe3)2),
16.9 (CH(CH3)2), 17.4 (CH(CH3)2), 21.3 (CH(CH3)2), 22.0 (CH(CH3)2),
Dry oxygen-free tBuNH2 (0.50 ml, 348 mg, 4.8 mmol) was added
by vacuum transfer to a dry oxygen-free toluene solution (1.0 ml) of
1 (100 mg, 0.12 mmol) and the mixture was stirred from ꢀ78 ꢁC to
room temperature over 5 h. The color of the solution changed to
orange from the emerald green of 1. After evaporation of the
26.4 (N(CH2CH2)2), 50.3 (N(CH2CH2)2); 29Si NMR (C6D6):
d
ꢀ101.5
(1JSieH ¼ 156 Hz, SiH2), ꢀ1.3 (SiiPrDsi2), ꢀ0.3 (SiMe3 ꢂ 2), 0.1
(SiMe3), 8.0 (SiiPrDsi2) 18.6 (SieN); HRMS: m/z calcd for
C42H107N2Si12 (MeH)þ 975.5660, found 975.5625.
t
solvent and the remaining BuNH2, the residue was recrystallized
4.2. Crystal structure analyses of the compounds (2a, 2b, 2c, 2d)
from pentane (0.5 ml) at ꢀ30 ꢁC to give 2c as air- and moisture-
sensitive orange crystals (60 mg, 54% yield). M.p.118.5e119.8 ꢁC; 1H
The single crystals of compounds 2a, 2b, 2c, and 2d for X-ray
diffraction study were grown from a toluene solution. Diffraction
data were collected at 120 K for 2a and 2c and 150 K for 2b and 2d
on a Mac Science DIP2030 Image Plate Diffractometer with
a rotating anode (50 kV, 90 mA) employing graphite-mono-
NMR (C6D6):
d 0.10 (s, 2H, CH(SiMe3)2), 0.12 (s, 2H, CH(SiMe3)2),
0.39 (s, 36H, CH(SiMe3)2 ꢂ 2), 0.43 (s, 18H, CH(SiMe3)2), 0.50 (s, 18H,
t
CH(SiMe3)2), 1.346 (s, 9H, Bu), 1.355 (d, J ¼ 7.0 Hz, 6H, CH(CH3)2),
1.38 (d, J ¼ 7.0 Hz, 6H, CH(CH3)2),1.56 (sep, J ¼ 7.0 Hz,1H, CH(CH3)2),
1.70 (sep, J ¼ 7.0 Hz,1H, CH(CH3)2), 2.80 (s,1H, SiH), 2.83 (s,1H, NH);
chromatized Mo K
solved by the direct method, using SIR-92 program [31], and refined
a
radiation (
l
¼ 0.71070 Å). The structures were
13C NMR (C6D6):
d 5.4 (SiMe3), 5.8 (SiMe3), 6.0 (SiMe3), 6.4 (SiMe3),

K. Takeuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1156e1162
1161
Table 2
Crystallographic data and experimental parameters for the structure analysis of 2a, 2b, 2c and 2d.
Compound
2a
2b
2c
2d
Empirical formula
Formula mass (g molꢀ1
Crystal size/mm
Crystal color
C38H101NSi12
909.28
C38H99NSi12
907.26
(C38H101NSi12)2$C7H8
1910.69
C46H101NSi12
1005.36
)
0.3 ꢂ 0.25 ꢂ 0.05
0.15 ꢂ 0.15 ꢂ 0.1
0.35 ꢂ 0.25 ꢂ 0.2
0.25 ꢂ 0.20 ꢂ 0.05
Orange
Orange
Orange
Orange
Collection temperature (K)
(Mo K ) (Å)
Crystal system
Space group
120
0.71070
Monoclinic
P 21/c
150
120
0.71070
Monoclinic
P 21/c
150
l
a
0.71070
Triclinic
Pꢀ1
0.71070
Monoclinic
Cc
Unit cell parameters
a (Å)
b (Å)
c (Å)
15.2050(5)
11.6020(4)
32.7160(6)
90
95.385(2)
90
5745.9(3)
4
1.051
11.4560(8)
15.2840(5)
16.6910(11)
89.118(4)
79.321(3)
90.020(4)
2871.5(3)
2
16.7020(5)
11.5470(2)
31.4360(8)
90
96.3150(10)
90
6025.9(3)
2
1.053
20.5790(9)
17.7230(6)
19.8080(8)
90
119.906(2)
90
6262.4(4)
4
1.066
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
V (Å3)
Z
Dcalc (g cmꢀ3
F(000)
)
1.049
1004
0.295
2016
0.295
2116
0.284
2208
0.277
m
(mmꢀ1
)
Collected reflections
Independent reflections
Rint
60156
12967
0.0690
12967
465
0.0529
0.1392
1.007
28411
12660
0.0590
12660
465
0.0758
0.2042
1.012
57100
13501
0.0430
13501
528
0.0434
0.1180
1.026
32869
7500
0.0590
7500
Reflections used (I > 2.00s(I))
Parameters
533
a
R1 [I > 2
s
(I)]
0.0447
0.1188
1.056
wR2b (all data)
Sc
a
R1 ¼ SkFoj ꢀ jFck/SjFoj.
wR2 ¼ fS½wðFo2 ꢀ Fc2Þ2ꢃ=S½wðFo2Þ2ꢃg0:5
:
b
S ¼ fS½wðFo2 ꢀ Fc2Þ2ꢃ=ðn ꢀ pÞg0:5; where n is the number of reflections and p is the number of parameter.
c
(c) J. Escudié, H. Ranaivonjatovo, Adv. Organomet. Chem. 44 (1999) 113;
(d) M. Weidenbruch, in: Z. Rappoport, Y. Apeloig (Eds.), The Chemistry of
Organic Silicon Compounds, vol. 3, Wiley, Chichester, U.K., 2001 (Chapter 5);
(e) K. Klinkhammer, in: Z. Rappoport (Ed.), The Chemistry of Organic
Germanium, Tin and Lead Compounds, vol. 2, Wiley, Chichester, U.K., 2002
Part 1, (Chapter 4);
(f) N. Tokitoh, R. Okazaki, in: Z. Rappoport (Ed.), The Chemistry of Organic
Germanium, Tin and Lead Compounds, vol. 2, Wiley, Chichester, U.K., 2002
Part 1, (Chapter 13);
by the full-matrix least-squares method by SHELXL-97 program
[32]. The crystal data and experimental parameters for the X-ray
analysis of 2aed are listed in Tables 1 and 2.
4.3. Computational method
All calculations were carried out using the Gaussian 03 program
[29]. Calculations were performed with hybrid density functional
theory at the B3LYP level [27,28], using the 6-31G(d) basis set for
geometry optimization and the 6-311G(3d) basis set for the GIAO
method.
(g) M. Weidenbruch, Organometallics 22 (2003) 4348;
(h) V.Ya. Lee, A. Sekiguchi, Organometallics 23 (2004) 2822;
(i) M. Kira, T. Iwamoto, Adv. Organomet. Chem. 54 (2006) 73;
(j) V.Ya. Lee, A. Sekiguchi, J. Escudié, H. Ranaivonjatovo, Chem. Lett. 39
(2010) 312.
[5] Recent reviews on triple bond chemistry of heavier group 14 elements:
(a) P.P. Power, Chem. Rev. 99 (1999) 3463;
(b) M. Weidenbruch, J. Organomet, Chembiochem 646 (2002) 39;
(c) P.P. Power, Chem. Commun. (2003) 2091;
Acknowledgements
(d) M. Weidenbruch, Angew. Chem. Int. Ed. Engl. 43 (2004) 2;
(e) P.P. Power, Appl. Organomet. Chem. 19 (2005) 488;
(f) P.P. Power, Organometallics 26 (2007) 4362;
(g) A. Sekiguchi, Pure. Appl. Chem. 80 (2008) 447;
(h) P.P. Power, Nature 463 (2010) 171.
This work was supported by a Grant-in-Aid for Scientific
Research (Nos. 19105001, 21350023, 21108502) from the Ministry
of Education, Science, Sports, and Culture of Japan.
[6] L. Pu, B. Twamley, P.P. Power, J. Am. Chem. Soc. 122 (2000) 3524.
[7] (a) M. Stender, A.D. Phillips, R.J. Wright, P.P. Power, Angew. Chem. Int. Ed.
Engl. 41 (2002) 1785;
Appendix A. Supplementary material
(b) R.C. Fischer, L. Pu, J.C. Fettinger, M.A. Brynda, P.P. Power, J. Am. Chem. Soc.
128 (2006) 11366.
[8] A.D. Phillips, R.J. Wright, M.M. Olmstead, P.P. Power, J. Am. Chem. Soc. 124
(2002) 5930.
[9] Y. Sugiyama, T. Sasamori, Y. Hosoi, Y. Furukawa, N. Takagi, S. Nagase,
N. Tokitoh, J. Am. Chem. Soc. 128 (2006) 1023.
[10] A. Sekiguchi, R. Kinjo, M. Ichinohe, Science 305 (2004) 1755.
[11] N.Wiberg,S.K.Vasisht, G.Fischer, P.Mayer,Z.Anorg.Allg. Chem. 630(2004)1823.
[12] T. Sasamori, K. Hironaka, Y. Sugiyama, N. Takagi, S. Nagase, Y. Hosoi,
Y. Furukawa, N. Tokitoh, J. Am. Chem. Soc. 130 (2008) 13856.
[13] V. Kravchenko, R. Kinjo, A. Sekiguchi, M. Ichinohe, R. West, Y.S. Balazs,
A. Schmidt, M. Karni, Y. Apeloig, J. Am. Chem. Soc. 128 (2006) 14472.
[14] R. Kinjo, M. Ichinohe, A. Sekiguchi, N. Takagi, M. Sumimoto, S. Nagase, J. Am.
Chem. Soc. 129 (2007) 7766.
[15] R. Kinjo, M. Ichinohe, A. Sekiguchi, J. Am. Chem. Soc. 129 (2007) 26.
[16] A. Sekiguchi, R. Kinjo, M. Ichinohe, Synt. Met. 159 (2009) 773.
[17] K. Takeuchi, M. Ichinohe, A. Sekiguchi, J.-D. Guo, S. Nagase, Organometallics 28
(2009) 2658.
CCDC 770875 (2a), CCDC 780524 (2b), CCDC 780525 (2c) and
CCDC 770876 (2d); contain 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.
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