Double N-H bond activation of N,N′-bis-substituted hydrazines with stable N-heterocyclic silylene

Article abstract of DOI:10.1039/c1dt11708d

The reaction of N-heterocyclic silylene (NHSi) L [L = CH{(CCH ₂)(CMe)(2,6-iPr₂C₆H₃N) ₂}Si] with benzoylhydrazine, 1,2-dicarbethoxyhydrazine, 1,2-diacetylhydrazine and 1,2-bis(tert-butoxycarbonyl)hydra

Full text of DOI:10.1039/c1dt11708d

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PAPER
Double N–H bond activation of N,N¢-bis-substituted hydrazines with stable
N-heterocyclic silylene†
Ramachandran Azhakar, Rajendra S. Ghadwal, Herbert W. Roesky,* Jakob Hey and Dietmar Stalke*
Received 8th September 2011, Accepted 24th October 2011
DOI: 10.1039/c1dt11708d
The reaction of N-heterocyclic silylene (NHSi) L [L = CH{(C CH2)(CMe)(2,6-iPr2C6H3N)2}Si] with
benzoylhydrazine, 1,2-dicarbethoxyhydrazine, 1,2-diacetylhydrazine and 1,2-bis(tert-butoxycarbonyl)-
hydrazine in 1 : 1 molar ratio resulted in compounds 1–4 with an almost quantitative yield and five
coordinate silicon atoms. Compounds 1–4 were formed by double N–H bond activation by deliberate
selection of N,N¢-bis-substituted hydrazine compounds bearing the –C(O)NHNH– unit. Compounds
1–4 were characterized by NMR spectroscopy, EI-MS and elemental analysis. The molecular structures
of compounds 1–3 were unambiguously established by single crystal X-ray structural analysis.
the activation of the other N–H bond. The reaction of the four
Introduction
hydrazine derivatives with L proceeds as expected, i.e. with the
N–H bond activation has been the subject of many studies because
activation of two N–H bonds. Herein, we report on the double
of the prevalence of nitrogen-containing compounds for pharma-
N–H bond activation of N,N¢-bis-substituted hydrazines by NHSi
(L) leading to compounds 1–4 with five coordinate silicon atoms.
ceutical and other fine chemicals.1 Moreover, the activation of
N–H bonds is less studied compared to the activation of C–H2 or
O–H3 bonds. Finally the double N–H bond activation of hydrazine
Results and discussion
based molecules is still rare.4 Recently Hartwig et al. reported
double N–H bond activation by an iridium(I) complex.4 Previously
we published studies on the N–H bond activation of ammonia5
and hydrazines,6,7 and Driess et al. outlined the activation for
organoamines1g by utilizing the stable N-heterocyclic silylene
(NHSi) L [L = CH{(C CH2)(CMe)(2,6-iPr2C6H3N)2}Si]. In the
case of ammonia, hydrazine and N-methyl hydrazine we observed
only a single N–H bond activation. However, in the reaction of
L with 1,2-diphenylhydrazine, a spirocyclic product formed with
the elimination of molecular hydrogen. Formation of this product
occurred by the activation of one N–H and one C(aromatic)–
H bond instead of another N–H bond, which is attributed to
the steric strain within the ring.7 With this in mind, we selected
the N,N¢-bis-substituted hydrazine molecules, benzoylhydrazine,
1,2-dicarbethoxyhydrazine, 1,2-diacetylhydrazine and 1,2-bis(tert-
butoxycarbonyl)hydrazine bearing the –C(O)NHNH– unit, that
would favor the double N–H bond cleavage. The choice of the
above mentioned substituted hydrazines is based on the fact that
the presence of the –NHNH– unit leads to activation of one of
the N–H bonds and the presence of the carbonyl group with
the –C(O)NHNH– unit ultimately favors the formation of a five-
membered ring with L leading to the spirocyclic compound and
Reaction of L with benzoylhydrazine, 1,2-dicarbethoxyhydrazine,
1,2-diacetylhydrazine and 1,2-bis(tert-butoxycarbonyl)hydrazine
in 1 : 1 molar ratios resulted in the formation of compounds 1–4
with five coordinate silicon atoms in quantitative yield (Scheme 1)
and the proposed mechanism is given in Scheme 2. In all the cases,
N,N¢-bis-substituted hydrazines have been converted to hydrazone
derivatives. The formation of compounds 1–4 was supported by
NMR spectroscopy, EI-MS and elemental analysis. The molecular
structures of compounds 1–3 were unequivocally confirmed by
single crystal X-ray structural analysis.
Institut fu¨r Anorganische Chemie der Universita¨t Go¨ttingen, Tam-
mannstrasse 4, 37077, Go¨ttingen, Germany. E-mail: hroesky@gwdg.de,
dstalke@chemie.uni-goettingen.de
† CCDC reference numbers 817514, 817515 and 843520 for compounds 1,
2 and 3. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/c1dt11708d
Scheme 1 Double N–H bond activation of benzoylhydrazine, 1,2-dicarb-
ethoxyhydrazine, 1,2-diacetylhydrazine and 1,2-bis(tert-butoxycar-
bonyl)hydrazine by L to form compounds 1–4.
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Fig. 1 Molecular structure of 1·0.52 hexane with anisotropic displace-
ment parameters depicted at the 50% probability level. The solvent hexane
molecule, the methyl carbons of isopropyl groups and all of the hydrogen
atoms except at Si1 an◦d N3 are omitted for clarity. Selected bond lengths
˚
(A) and bond angles ( ): Si1–N1 1.9437(12), Si1–N2 1.8371(11), Si1–N3
1.7391(12), Si1–O1 1.7667(10), Si1–H1S 1.376(15), N3–N4 1.4021(16),
N4–C31 1.2873(17), C31–O1 1.3395(16); N1–Si1–N2 91.74(5), N3–Si1–O1
83.70(5), N2–Si1–N3 128.58(6), N1–Si1–O1 172.69(5), N3–Si1–H1S
126.5(6), O1–Si1–H1S 94.6(6), N2–Si1–H1S 104.9(6), N1–Si1–H1S
91.3(6).
Scheme 2 Proposed mechanism for the formation of compounds 1–4.
The structural index t which defines the extent of deviation
from trigonal bipyramidal to square pyramidal geometry (t =
1 for perfect trigonal bipyramidal; t = 0 for perfect square based
pyramid10) is 0.74 indicating small deviation from the regular TBP
geometry. The overall geometrical features of 1 correspond to
those determined earlier.11 The sum of angles of the equatorial
atoms around Si1 equals 360.0◦. The silicon atom is shifted out
of the plane defined by N1, C1, C2, C3 and N2 significantly by
Compounds 1–4 are soluble in n-hexane, n-pentane, toluene and
benzene. They are stable in the solid state as well as in solution
without any decomposition under an inert gas atmosphere. The
29Si NMR spectra of 1–4 each exhibit a single resonance between
d -110.92 and -103.75, which are upfield shifted compared to L (d
88.4). This is due to the higher coordination of the silicon atoms
in 1–4. The resonances are upfield shifted compared to those of
the other species with four coordinate silicon,5–8 but they are in
agreement with those formed for other five coordinate silicon
compounds obtained from L.9 A further proton resonance of
NCCH3 in the region of d 1.45 to 1.49 for six hydrogen atoms
and the absence of a signal for the protons in NCCH2 of 1–4,
indicates the protonation of the methylene group in the ligand
backbone of L. The Si–H proton in the 1H NMR spectra of 1–4
shows a single resonance in the d 6.36 to 6.47 region, which was
corroborated by a 1H–29Si HSQC (heteronuclear single-quantum
correlation) experiment. In 1 the resonances for both g-CH and
˚
0.7116(15) A. There are two types of Si–N bonds present in 1,
˚
one is shorter (N2–Si1: 1.8371(11) A) and the other one is longer
˚
(N1–Si1: 1.9437(12) A). There is an appreciable change in the N1–
Si1–N2 bite angle of 1 (128.58(6)◦), when compared with that of L
(99.317(54)◦). These changes are attributed to the protonation of
the methylene group at the backbone of the b-diketiminate ligand.
˚
The Si1–N3 bond length is 1.7391(12) A indicating a single bond
character.12 The Si1–O1 bond length is 1.7667(10) A, which is
˚
comparable to the Si–O single bond distances observed in five
coordinate silicon complexes.13a The position of the silicon bound
hydrogen atom was taken from the Fourier difference map and was
1
N–H protons in the H NMR spectrum are observed at d 4.93.
The 1H–15N HSQC experiment shows strong coupling between the
resonance at d 4.93 and a 15N resonance, indicating that the proton
is nitrogen bound. In 2–4 the resonances for g-CH are observed as
a single resonance each in the region at d 4.88 to 4.92. Compounds
1–4 exhibit their molecular ion in the mass spectra at m/z 580, 620,
560 and 676.
˚
refined freely. The Si–H distance of 1.376(15) A is considerably
shorter than the related distance in the structurally characterized
˚
silicon(II) monohydride of 1.47342(11) A determined from charge
density investigations.13b The higher coordination around Si1 and
the higher formal oxidation state of Si1 in 1 indicates much more
covalent bonding when compared with the latter where the Si–H
˚
bond is highly polar. The N3–N4 bond length is 1.4021(16) A,
indicating a N–N single bond of hydrazine or of a hydrazone
derivative as reported in literature.14 The C31–N4 distance of
Molecular structure of 1
1.2873(17) A compares well with a C N double bond14 and the
˚
Compound 1 forms as yellow crystals in the monoclinic space
group P21/n (Table 1), and the molecular structure is shown
in Fig. 1. The silicon atom is five coordinate and features a
distorted trigonal bipyramidal geometry (TBP), made up from
three nitrogen atoms, a single oxygen atom and a hydrogen atom.
The three nitrogen atoms arranged at the silicon atom originate
from the hydrazone moiety and from the b-diketiminate ligand.
15
˚
C31–O1 bond length of 1.3395(16) A with a single bond.
Molecular structure of 2
Compound 2 crystallizes in the monoclinic space group P21/c
and the molecular structure is shown in Fig. 2. Similar to 1, the
1530 | Dalton Trans., 2012, 41, 1529–1533
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Table 1 Crystal and structure refinement parameters for compounds 1, 2 and 3
Parameters
1·0.52 n-hexane
39.12H55.24N4OSi
625.65
2
3
Empirical formula
Formula weight
Crystal system
Space group
C
C35H52N4O4Si
620.90
C33H48N4O2Si
560.84
Monoclinic
P21/n
Monoclinic
P21/c
Orthorhombic
P212121
˚
˚
˚
˚
˚
˚
˚
Unit cell dimensions
a = 11.4828(8) A
a = 13.2681(14) A
a = 13.816(2) A
b = 12.0258(9) A
b = 12.0341(12) A
b = 14.387(2) A
˚
˚
c = 26.1609(19) A
c = 21.837(2) A
c = 15.751(3) A
b = 94.746(2)◦
b = 94.780(5)◦
3
3
3
˚
˚
˚
Volume, Z
3600.2(5) A , 4
3476.6(6) A , 4
3130.8(9) A , 4
Density (calcd)
Absorption coefficient
F (000)
1.154 g cm-3
1.187 g cm-3
1.190 g cm-3
0.101 mm-1
0.065 mm-1
0.110 mm-1
1360
1344
1216
Crystal size
q range for data collection
Limiting indices
0.22 ¥ 0.16 ¥ 0.12 mm3
0.18 ¥ 0.14 ¥ 0.11 mm3
0.1 ¥ 0.05 ¥ 0.04 mm3
1.56 to 26.11◦
1.22 to 21.06◦
1.92 to 27.13◦
-14 £ h £ 14, -14 £ k £ 14,
-32 £ l £ 32
57531
-16 £ h £ 16, -15 £ k £ 15,
-27 £ l £ 27
97129
-14 £ h £ 17, -18 £ k £ 18,
-20 £ l £ 18
26322
Reflections collected
Independent reflections
Completeness to q
7146 (Rint = 0.0368)
99.8% (q = 26.11)
Full-matrix least-squares on F2
7146/2/434
7620 (Rint = 0.0576)
99.7% (q = 21.07)
Full-matrix least-squares on F2
7620/4/440
6906 (Rint = 0.0778)
99.8% (q = 27.13)
Full-matrix least-squares on F2
6906/2/379
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
R indices (all data)
1.042
1.099
1.023
R1 = 0.0367, wR2 = 0.0908
R1 = 0.0452, wR2 = 0.0955
R1 = 0.0456, wR2 = 0.1119
R1 = 0.0600, wR2 = 0.1181
R1 = 0.0393, wR2 = 0.0873
R1 = 0.0461, wR2 = 0.0914
0.04(8)
Absolute structure parameter21
Largest diff. peak and hole
-3
-3
-3
˚
˚
˚
0.306 and -0.363 e A
0.337 and -0.334 e A
0.324 and -0.258 e A
˚
one is (axial) 1.9272(14) A. The silicon atom is shifted out of
the N2C3-plane of the SiN2C3 six-membered ring by 0.4862(18)
˚
A. Again, the position of the silicon bound hydrogen atom was
taken from the Fourier difference map and refined freely. The Si–
˚
H distance of 1.371(19) A in 2 is very similar to that determined
in 1.13c The N3–Si1–N4 bite angle at the silicon atom of the b-
◦
˚
diketiminate ligand is 94.72(6) . The N–N [N1–N2 1.4275(19) A]
˚
and C–O [C1–O1 1.340(2) A] bond lengths present in the newly
formed five-membered ring of 2 are quite comparable to those
in similar compounds reported in the literature.15 The distance
˚
between C1–N1 is 1.272(2) A indicating C N double bond
character.14
Molecular structure of 3
Compound 3 crystallizes in the orthorhombic space group P212121
and the molecular structure is given in Fig. 3. Like 1 and 2,
the silicon atom in 3 is five coordinate comprising three nitrogen
atoms, one oxygen atom and one hydrogen atom. The bond lengths
Fig. 2 Molecular structure of 2 with anisotropic displacement parameters
depicted at the 50% probability level. All hydrogen atoms except at Si1,
the methyl carbons of isopropyl groups and one carbon atom of the ethyl
˚
groups are omitted for clarity. Selected bond lengths (A) and bond angles
(◦): Si1–O1 1.7205(12), Si1–N3 1.8078(14), Si1–N2 1.8405(14), Si1–N4
1.9272(14), Si1–H1S 1.371(19), N1–N2 1.4275(19), N1–C1 1.272(2),
C1–O1 1.340(2); O1–Si1–N3 108.85(6), O1–Si1–N2 83.74(6), N3–Si1–N2
100.83(6), O1–Si1–N4 85.23(6), N3–Si1–N4 94.72(6), N2–Si1–N4
163.19(6), O1–Si1–H1S 135.7(8), N3–Si1–H1S 115.4(8), N2–Si1–H1S
90.7(8), N4–Si1–H1S 88.4(8).
˚
of Si–N(equatorial) and the Si–N(axial) are 1.8059(14) A and
˚
1.9250(14) A. The structural index t is 0.53. The silicon atom is
shifted out of the N2C3–plane of the SiN2C3 six-membered ring by
˚
˚
0.4478(18) A. The Si–H distance of 1.476(13) A, was taken from
the Fourier difference map and refined freely. The N–Si–N bite
angle at the silicon atom with the backbone ligand is 93.94(6)◦.
˚
˚
The N–N [N3–N4 1.4107(19) A] and C–O [C30–O1 1.365(2) A]
bond lengths present in the newly formed five-membered ring of
3 are quite comparable to those in similar compounds reported in
silicon atom in 2 is five coordinate comprising three nitrogen
atoms (two from the b-diketiminate ligand and one from the
hydrazone moiety), one oxygen atom and one hydrogen atom. The
structural index t is 0.46. This is caused by the axial substituents
N4 and N2 that have an angle of 163.19(6)◦ with Si1. The sum
of angles between the equatorial ligands around Si1 is 360.0◦.
As in 1, there are two types of Si–N bonds observed from the
the literature.15 The distance between C30–N4 is 1.274(2) A.
˚
In all reported reactions, the SiN2CO five-membered ring has
been formed. The dihedral angles between the planes of the six-
and five-membered rings are 34.31(6)◦, 83.21(6)◦ and 79.93(5)◦,
in compounds 1, 2 and 3, respectively. A hydrogen atom has been
transferred to the silicon atom in all cases.
˚
supporting ligand. One (equatorial) is 1.8078(14) A and the other
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3.43 (m, 1H, CH(CH3)2), 4.93 (b, 2H, NH, g-CH), 6.39(s, 1H,
SiH), 6.91–7.12 (m, 6H, 2 ¥ iPr2C6H3), 7.47–7.50 (m, 5H, C6H5)
◦
1
ppm. 29Si{ H} NMR (59.63 MHz, C6D6, 25 C): d -110.92 ppm.
EI-MS: m/z 580 (M+).
Synthesis of 2
n-Hexane (60 mL) was added to a 100 mL Schlenk flask containing
L (0.26 g, 0.59 mmol) and 1,2-dicarbethoxyhydrazine (0.11 g, 0.62
mmol). The reaction mixture was stirred at room temperature for
12 h. The solution was filtered and the solvent was reduced in vacuo
to 30 mL and stored in a freezer at -32 ◦C for 15 days to obtain
colorless single crystals. (0.28 g, 76%). Mp 150–153 ◦C (decomp).
Elemental analysis (%) calcd for C35H52N4O4Si (620.90): C, 67.70;
H, 8.44; N, 9.02. Found: C, 67.10; H, 8.15; N, 9.31. 1H NMR (200
MHz, C6D6, 25 ◦C): d 0.83 (t, 3H, J = 7 Hz, CH2CH3), 1.01 (t, 3H,
J = 7 Hz, CH2CH3), 1.06 (d, 6H, J = 7 Hz, CH(CH3)2), 1.18 (d,
6H, J = 7 Hz, CH(CH3)2), 1.43 (d, 6H, J = 7 Hz, CH(CH3)2), 1.46
(s, 6H, NC(CH3)), 1.54 (d, 6H, J = 7 Hz, CH(CH3)2), 3.21–3.47
(m, 4H, CH(CH3)2), 3.80 (q, 2H, J = 7 Hz, –OCH2), 4.12 (q, 2H,
J = 7 Hz, –OCH2), 4.88 (s, 1H, g-CH), 6.41 (s, 1H, SiH), 7.10–7.23
Fig. 3 Molecular structure of 3 with anisotropic displacement parameters
depicted at the 50% probability level. All hydrogen atoms except at
Si3 and the methyl carbons of isopropyl g◦roups are omitted for clarity.
˚
Selected bond lengths (A) and bond angles ( ): Si3–O1 1.7109(12), Si3–N2
1.8059(14), Si3–N3 1.8573(14), Si3–N1 1.9250(14), Si1–H3S 1.476(13),
N3–N4 1.4107(19), N4–C30 1.274(2), C30–O1 1.365(2); O1–Si3–N2
108.26(6), O1–Si3–N3 84.03(6), N3–Si3–N2 99.58(6), O1–Si3–N1
87.00(6), N2–Si3–N1 93.94(6), N3–Si3–N1 165.58(6), O1–Si3–H3S
133.6(6), N2–Si3–H3S 118.1(6), N3–Si3–H3S 90.6(7), N1–Si3–H3S
87.4(7).
1
(m, 6H, 2 ¥ iPr2C6H3) ppm. 29Si{ H} NMR (59.36 MHz, C6D6,
25 ◦C): d -103.75 ppm. EI-MS: m/z 620 (M+).
Synthesis of 3
Experimental section
n-Hexane (60 mL) was added to a 100 mL Schlenk flask containing
L (0.32 g, 0.72 mmol) and 1,2-diacetylhydrazine (0.09 g, 0.77
mmol). The reaction mixture was stirred at room temperature for
12 h. The solution was filtered and the solv◦ent was reduced in vacuo
to 20 mL and stored in a freezer at -32 C for 2 days to obtain
colorless single crystals. (0.34 g, 84%). Mp 163–165 ◦C (decomp).
Elemental analysis (%) calcd for C33H48N4O2Si (560.85): C, 70.67;
H, 8.63; N, 9.99. Found: C, 70.62; H, 8.56; N, 9.82. 1H NMR (500
MHz, C6D6, 25 ◦C): d 1.07 (d, 6H, J = 7 Hz, CH(CH3)2), 1.20
(d, 6H, J = 7 Hz, CH(CH3)2), 1.28 (d, 6H, J = 7 Hz, CH(CH3)2),
1.49 (s, 6H, NC(CH3)), 1.52 (d, 6H, J = 7 Hz, CH(CH3)2), 1.84(s,
3H, CH3), 1.94 (s, 3H, CH3), 3.21 (m, 2H, CH(CH3)2), 3.46 (m,
2H, CH(CH3)2), 4.92 (s, 1H, g-CH), 6.47 (s, 1H, SiH), 7.09–7.18
All manipulations were carried out in an inert atmosphere of
dinitrogen gas using standard Schlenk line techniques and in
a dinitrogen gas filled glove box. Solvents were purified by
an MBRAUN solvent purification system MB SPS-800. All
chemicals were purchased from Aldrich, Alfa Aeser, or ABCR
and used without further purification. L was prepared as reported
in literature.15 1H and 29Si NMR spectra were recorded with a
Bruker Avance DPX 200, a Bruker Avance DRX 300 or a Bruker
Avance DRX 500 spectrometer, using C6D6 as solvent. Chemical
shifts d are given relative to SiMe4. EI-MS spectra were obtained
using a Finnigan MAT 8230 instrument. Elemental analyses were
performed by the Institut fu¨r Anorganische Chemie, Universita¨t
Go¨ttingen. Melting points were measured in a sealed glass tube
on a Bu¨chi B-540 melting point apparatus.
1
(m, 6H, 2 ¥ iPr2C6H3) ppm. 29Si{ H} NMR (99.36 MHz, C6D6,
25 ◦C): d -104.39 ppm. EI-MS: m/z 560 (M+).
Synthesis of 4
Synthesis of 1
n-Hexane (60 mL) was added to a 100 mL Schlenk flask containing
L (0.45 g, 1.01 mmol) and 1,2-bis(tert-butoxycarbonyl)hydrazine
(0.24 g, 1.03 mmol). The reaction mixture was stirred at room
temperature for 12 h. The solution was filtered and the solvent was
reduced in vacuo to 30 mL and stored in a freezer at -32 ◦C for 15
days to obtain a crystalline product of 4. (0.52 g, 76%). Mp 145–
148 ◦C (decomp). Elemental analysis (%) calcd for C39H60N4O4Si
(677.00): C, 69.19; H, 8.93; N, 8.28. Found: C, 69.12; H, 8.86;
n-Hexane (60 mL) was added to a 100 mL Schlenk flask containing
L (0.30 g, 0.68 mmol) and benzoylhydrazine (0.10 g, 0.73 mmol)
and the reaction mixture was stirred at room temperature for
12 h. The solution was filtered and the solvent was reduced
in vacuo to about 30 mL and stored at -32 ◦C for a week in a
freezer to obtain yellow colored single crystals. (0.30 g, 77%). Mp
215–218 ◦C (decomp). For elemental analysis, 1·0.52 n-hexane
was treated under vacuum for six hours to remove the hexane
molecules. Elemental analysis (%) calcd for C36H48N4OSi (580.88):
C, 74.44; H, 8.33; N, 9.65. Found: C, 74.22; H, 8.05; N, 9.37.
1H NMR (300 MHz, C6D6, 25 ◦C): d 1.03 (d, 3H, J = 7 Hz,
CH(CH3)2), 1.17 (d, 6H, J = 7 Hz, CH(CH3)2), 1.19 (d, 3H, J = 7
Hz, CH(CH3)2), 1.21 (d, 6H, J = 7 Hz, CH(CH3)2), 1.31 (d, 3H, J =
7 Hz, CH(CH3)2), 1.45 (s, 6H, NC(CH3)2, 1.48 (d, 3H, J = 7 Hz,
CH(CH3)2), 3.25 (m, 1H, CH(CH3)2), 3.30 (m, 2H, CH(CH3)2),
N, 8.23. H NMR (500 MHz, C6D6, 25 ◦C): d 1.05 (d, 6H, J =
1
7 Hz, CH(CH3)2), 1.20 (d, 6H, J = 7 Hz, CH(CH3)2), 1.25 (s,
9H, C(CH3)3), 1.44 (d, 6H, J = 7 Hz, CH(CH3)2), 1.45 (s, 15H,
NC(CH3), C(CH3)3), 1.55 (d, 6H, J = 7 Hz, CH(CH3)2, 3.29 (m,
2H, CH(CH3)2), 3.42 (m, 2H, CH(CH3)2), 4.88 (s, 1H, g-CH),
1
6.36 (s, 1H, SiH), 7.13–7.20 (m, 6H, 2 ¥ iPr2C6H3) ppm. 29Si{ H}
NMR (99.36 MHz, C6D6, 25 ◦C): d -104.63 ppm. EI-MS: m/z
676 (M+).
1532 | Dalton Trans., 2012, 41, 1529–1533
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Crystal Structure Determination
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Suitable single crystals for X-ray structural analysis of 1, 2 and
3 were mounted at low temperature in inert oil under an argon
atmosphere by applying the X-Temp2 device.16 The data of 1,
2 and 3 were collected at 100 K on a Bruker D8 three circle
diffractometer equipped with a SMART APEX II CCD detector
and an INCOATEC Mo microsource with INCOATEC Quazar
mirror optics.17 The data were integrated with SAINT18 and an
empirical absorption correction with SADABS19 was applied.
The structures were solved by direct methods (SHELXS-97) and
refined against all data by full-matrix least-squares methods on
F2 (SHELXL-97).20 All non hydrogen atoms were refined with
anisotropic displacement parameters. The hydrogen atoms were
refined isotropically on calculated positions using a riding model
with their Uiso values constrained to 1.5Ueq of their pivot atoms
for terminal sp3 carbon atoms and 1.2 times for all other carbon
atoms. The positions of hydrogen atoms located at the silicon
atoms were taken from the Fourier difference map. Their Uiso
value was constrained to be the 1.5Ueq of the silicon atom in the
case of 2, 1.2Ueq in the case of 3 and refined freely in the case of 1.
The site occupation factor for several lattice n-hexane molecules
located on an inversion center in the unit cell was refined in the
case of 1 leading to non-integer numbers in the empirical formula.
Conclusions
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In summary, we have demonstrated the double N–H bond
activation by the reaction of NHSi with substituted hydrazines
leading to compounds 1–4 in high yield where each silicon is five
coordinate. The driving force for this reaction is the oxidative
addition at the silicon(II) centers to yield the five coordinate
silicon(IV) products.
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12 N. Kocher, J. Henn, B. Gostevskii, I. Kost, I. Kalikhman, B. Engels
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Acknowledgements
We are thankful to the Deutsche Forschungsgemeinschaft for
supporting this work. R. A. is thankful to the Alexander von
Humboldt Stiftung for a research fellowship. D. S. and J. H. are
grateful to the DNRF funded Center for Materials Crystallography
(CMC) for support and the Land Niedersachsen for providing a
fellowship in the Catalysis of Sustainable Synthesis (CaSuS) PhD
program.
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