Control of N- or C-bridging mode in dimeric butylmagnesium silylamides

Article abstract of DOI:10.1021/om200587n

The simple approach to cleave 4,5-dihydro-2-furyl with lithiated primary amines yields a wide range of N-alkyl-substituted (aminomethyl)silazanes. These are easily deprotonated by dibutylmagnesium, resulting in either magnesium disilylamides or butylmagne

Full text of DOI:10.1021/om200587n

ARTICLE
pubs.acs.org/Organometallics
Control of N- or C-Bridging Mode in Dimeric Butylmagnesium
Silylamides
Victoria P. Colquhoun, Bors C. Abele, and Carsten Strohmann*
Anorganische Chemie, Technische Universit€at Dortmund, Otto-Hahn-Strasse 6, 44227 Dortmund, Germany
S Supporting Information
b
ABSTRACT: The simple approach to cleave 4,5-dihydro-2-
furyl with lithiated primary amines yields a wide range of
N-alkyl-substituted (aminomethyl)silazanes. These are easily de-
protonated by dibutylmagnesium, resulting in either magne-
sium disilylamides or butylmagnesium silylamides upon
variation of the stochiometric ratios and reaction temperatures.
The obtained dimeric butylmagnesium silylamide compounds
[{(CH3)2Si(CH2NC5H10)(NR)}Mg(n-Bu)]2 (R = t-Bu, i-Pr),
examined by single-crystal X-ray diffraction analysis, exhibit different bridging modes MgꢀElꢀMg (El = C, N) according to the
steric demand of the ligand. This observation has been studied using theoretical methods.
Scheme 1. Synthesis of (Piperidinomethyl)silazanes
’ INTRODUCTION
The NꢀH bond of silazanes is easily deprotonated by metal
alkyl reagents, resulting in new compounds, for example, metal
bisamides or mixed alkylmetal amides. Alkylmetal amides are suitable
as alkylation or deprotonation reagents in organic synthesis, and
metal bisamides are of interest as molecular precursors for new
materials or lactide polymerization catalysts.1ꢀ4 To enhance their
reactivity, a precoordination of the metal is achieved by a side arm
with a coordinating donor atom as for example in (aminomethyl)
silazanes.5 Additionally, the chelating aminomethyl moiety already
occupies one coordination site of the metal atom, providing ample
stability to prevent oligomerization. Thereby the creation of small
volatile molecules suitable for chemical vapor deposition (CVD)
applications is possible.6 Considering dibutylmagnesium as a de-
protonation reagent for these silazanes, either just one or both butyl
groups are expected to be substituted by the ligand. Until now, only
a few small intermediates with similar bidentate nitrogen ligands still
bearing a butyl group and thereby maintaining one functionality are
known.2,7 As shown by Chong and co-workers these intermediates
possess interesting applicabilities, e.g., as enantioselective alkylation
reagents for aldehydes.2 The deprotonation of two amines contain-
ing an additional side arm with another coordinating amine function
yields small four-coordinate magnesium compounds, which are
potential CVD precursors.6,8 Starting from the same ligand, the
selective synthesis of either an intermediate still bearing one
functionality or the 2-fold deprotonation product would be desirable.
This simplifies the large-scale preparation of similar compounds.
We herein report a general three-step synthetic route for
silazanes such as 4a,b,c, which exhibit different alkyl substituents
at the amine moieties. With this preparation method, more varied
silazanes can easily be designed to suit a specific purpose. These
silazane ligands were successfully used for the selective synthesis of
magnesium disilylamides 5a,b,c and butylmagnesium silylamides
6a,b by deprotonation with dibutylmagnesium. We obtained new
magnesium silylamide compounds displaying interesting structural
features. Controlled by the sterical demand of the silazane ligand,
two different bridging modes for the dimeric alkylmagnesium
silylamide species are formed. Due to these unexpected structural
features, these compounds may potentially be used as alkylation
reagents in organic synthesis.
’ RESULTS AND DISCUSSION
Synthesis of Silazanes with Different Alkyl Substituents at
the Amine Moieties. The introduction of the protecting group
4,5-dihydro-2-furyl at the silicon center marks the first step of
this synthesis with a simplified experimental procedure already
developed by Chan and co-workers.9 In the following reaction
step, the amination of the chloromethyl group with a secondary
amine, in this case piperidine, yields compound 3. In this synthesis
Received: July 4, 2011
Published: September 26, 2011
r
2011 American Chemical Society
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Scheme 2. Syntheses of Butylmagnesium Silylamides and
Magnesium Disilylamides
Figure 2. Molecular structure of compound 5c (left) and schematic
display of compounds 5a,b,c (right). Selected bond lengths (Å) and
angles (deg) (symmetry operation: ꢀx+3/2, y, ꢀz+1/2): MgꢀN2
2.014(2), MgꢀN1 2.232(2), Si1ꢀN2 1.689(2), N2ꢀC9 1.455(3),
N1ꢀMgꢀN2 92.30(6), N2ꢀMgꢀN20130.25(10), N1ꢀMgꢀN10
110.07(10), N2ꢀMgꢀN10 116.23(6).
Figure 3. Molecular structure and schematic display of compound 6a.
Selected bond lengths (Å) and angles (deg) (symmetry operation: ꢀx
+1, ꢀy+2, ꢀz+1): MgꢀN1 2.000(2), MgꢀN2 2.185(2), MgꢀC13
2.276(3), MgꢀC130 2.260(3), SiꢀN1 1.688(2), N1ꢀC3 1.468(3),
MgꢀC13ꢀMg0 75.28(9), C13ꢀMgꢀC130 104.72(9), N1ꢀMgꢀN2
92.17(7), N1ꢀMgꢀC13 119.04(9), N1ꢀMgꢀC130 121.91(9),
C13ꢀMgꢀN2 106.61(8), C130ꢀMgꢀN2 110.72(9).
Figure 1. Molecular structure of compounds 5a (left) and 5b (right).
Selected bond lengths (Å) and angles (deg) of 5a: MgꢀN2 2.252(2),
MgꢀN4 2.219(2), MgꢀN1 2.030(2), MgꢀN3 2.033(2), Si1ꢀN1
1.689(2), Si2ꢀN3 1.691(2), N1ꢀC3 1.479(3), N3ꢀC15 1.476(3),
N1ꢀMgꢀN2 93.06(7), N1ꢀMgꢀN3 137.60(8), N1ꢀMgꢀN4
110.53(7), N2ꢀMgꢀN3 116.01(7), N2ꢀMgꢀN4 103.61(7), N3ꢀ
MgꢀN4 92.71(7); 5b: MgꢀN2 2.223(1), MgꢀN4 2.250(1), MgꢀN1
2.004(1), MgꢀN3 2.014(1), Si1ꢀN1 1.692(1), Si2ꢀN3 1.683(1),
C3ꢀN1 1.469(2), C14ꢀN3 1.475(2), N1ꢀMgꢀN2 92.57(5),
N1ꢀMgꢀN3 126.18(5), N1ꢀMgꢀN4 116.30(5), N2ꢀMgꢀN3
119.04(5), N2ꢀMgꢀN4 111.37(5), N3ꢀMgꢀN4 92.66(5).
compound 5a. The selective synthesis of compounds 6a,
b, however, was achieved by slowly adding a solution of the
silazane ligand in pentane to dibutylmagnesium at ꢀ10 °C and
subsequent storage at ꢀ30 °C. These butylmagnesium silyl-
amide complexes 6a,b could be isolated as colorless crystals with
yields of 42% and 91%, respectively. The reaction of 0.5 equiv of
dibutylmagnesium with 4a,b,c and subsequent storage at room
temperature (5a,b) or 0 °C (5c) results in colorless crystals
of compounds 5a,b,c exclusively, with a minimum yield of
63% (Scheme 2). With the exception of compound 5c, which
required dilution of the silazane ligand in pentane, no additional
solvent was added in both the butylmagnesium silylamide
and magnesium disilylamide syntheses to obtain the crystalline
products.
two equivalents of amine are necessary to bind the generated
hydrochloric acid. Finally, the protection group is removed via
reaction with 1 equiv of lithiated primary amine [tert-butylamine
(a), isopropylamine (b), and cyclohexylamine (c)]. As stated by
Chan and co-workers, lithiated reagents are necessary to cleave
the SiꢀC bond of the protecting 4,5-dihydro-2-furyl moiety.
Subsequent addition of ammonium chloride, as a nonhydrolytic
protonation reagent, yields the desired silazane ligands 4a,b,c
(Scheme 1). This proves to be a remarkably simple reaction
pathway with an overall yield of 52%.
Compounds 5a,b,c crystallize in the monoclinic crystal
system, space group P21/n (a), P21/c (b), and P2/n (c). The
central magnesium atom exhibits contacts to both nitrogen
atoms of two ligand molecules, resulting in a four-coordinate
magnesium center. The dative MgꢀN bonds of the intramo-
lecularly coordinated piperidinomethyl substituents are con-
siderably longer (approximately 0.2 Å) than the MgꢀN bonds to
the silicon-bonded nitrogen atom with a largely electrostatic attrac-
tion. Deprotonation of the silazane leads to strongly shortened
SiꢀN bond lengths [1.683(1)ꢀ1.694(1) Å] due to an increase of
Selective Syntheses of Magnesium Disilylamide or Alter-
natively Butylmagnesium Silylamide Compounds. Treatment
of compound 4a with 1 equiv of commercially available dibutyl-
magnesium solution in heptane at ꢀ20 °C and subsequent storage
at room temperature for 12 h results in the formation of not
only the butylmagnesium silylamide compound 6a (inter-
mediate) but a crystalline mixture of both the magnesium
disilylamide and butylmagnesium silylamide 5a and 6a. Both
compounds could be distinguished by their differing crystal
shape, small elongated blocks for 6a and large square blocks for
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ARTICLE
ionic bond character. The ideal tetrahedral environment at the
magnesium center is strongly distorted by the sterically demanding
tert-butyl (a), isopropyl (b), and cyclohexyl (c) substituents as well
as the five-membered ring formed by chelation of the aminomethyl
side arm (Figures 1 and 2). The observed structural parameters are
similar to comparable published magnesium disilylamides bearing
an additional donor function, for example, Mg[{(CH3)3Si}N-
(CH2)3N(CH3)2]2.6,8c,10 While compounds 5a,b are well soluble
in noncoordinating solvents (benzene-d6), compound 5c displays
a considerably reduced solubility. Therefore the characterization
of 5c via 29Si and 13C NMR could be achieved only by correla-
tion methods. Additionally, signals of the starting material, the
silazane, which is formed by decomposition of the magnesium
amide bond become more dominant after a prolonged mea-
surement time. The n-butyl-bearing compounds 6a,b show no
solubility in benzene or toluene at all. Since the use of
coordinating solvents (thf) results in the formation of a com-
plex mixture of thf adducts, the NMR characterization of
compounds 6a,b was not possible.11
The molecular structures of compounds 6a,b are both those of
strictly centrosymmetric dimers, which crystallized in the triclinic
crystal system, space group P1. Their most salient difference is
their bridging mode. The central four-membered ring comprises
two carbon and two magnesium atoms for compound 6a
(C-bridge) and two nitrogen and two magnesium atoms for com-
pound 6b (N-bridge) (Figure 3 and Figure 4). The bridging
moiety changes from the n-butyl group in compound 6a to the
silylamide in compound 6b. As expected, the MgꢀN1/MgꢀN10
bond lengths of the bridging, four-coordinate amide nitrogens in
compound 6b are slightly larger compared to the MgꢀN1 bond
length of compound 6a, in which the silicon-bonded nitrogen
centers are still three-coordinate. Still, the magnesium amide
bonds are shorter than the dative MgꢀN2 and MgꢀN20 bonds
of the chelating piperidinomethyl arm. At 2.276(3) and 2.260(3)
Å, the bridging MgꢀC13 bond in 6a is quite long compared to
the sum of the covalent radii [2.17 Å] of magnesium and carbon
and the nonbridging MgꢀC12 bond of compound 6b. To the
author’s knowledge, there are no directly comparable systems
with bridging alkyl groups known, but dimeric structures with the
Figure 4. Molecular structure and schematic display of compound 6b.
Selected bond lengths (Å) and angles (deg) (symmetry operation: ꢀx,
ꢀy+2, ꢀz+1): MgꢀN1 2.184(2), MgꢀN10 2.151(2), MgꢀN20
2.298(2), MgꢀC12 2.148(2), SiꢀN1 1.728(2), C9ꢀN1 1.491(2),
C12ꢀMgꢀN10 121.36(7), C12ꢀMgꢀN1 120.95(8), N10ꢀMgꢀN1
92.19(6), C12ꢀMgꢀN20 110.45(8), N10ꢀMgꢀN20 93.02(6),
N1ꢀMgꢀN20 114.84(6), C9ꢀN1ꢀSi 119.40(12), C9ꢀN1ꢀMg0
115.35(11), SiꢀN1ꢀMg0 108.49(8), C9ꢀN1ꢀMg 104.90(11), SiꢀN1ꢀMg
116.77(8), Mg0ꢀN1ꢀMg 87.81(6).
Scheme 3. Energy Needed to Break Dimers into Monomers
Figure 5. Relative difference in energy for optimized structures
[B3LYP/6-31+G(d)] of tert-butyl-substituted compounds with C-brid-
ging (6a) and N-bridging modes (6aN) (hydrogens omitted for clarity).
Figure 6. Relative difference in energy for optimized structures [B3LYP/6-31+G(d)] of isopropyl- (left) and methyl-substituted (right) compounds
with C-bridging (6bC and 6dC) and N-bridging modes (6b and 6dN) (hydrogens omitted for clarity).
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Table 1. Crystal Data and Structure Refinement Parameters for 5a,b,c and 6a,b
5a
5b
5c
6a
6b
formula
C
24H54MgN4Si2
C22H50MgN4Si2
451.15
C28H58MgN4Si2
531.27
C32H72Mg2N4Si2
617.74
C30H68Mg2N4Si2
589.68
fw [g molꢀ1
]
479.20
3
T [K]
173(2)
193(2)
173(2)
173(2)
173(2)
wavelength [Å]
cryst syst
space group
Z
0.71073
monoclinic
P21/n
0.71073
monoclinic
P21/c
0.71073
0.71073
0.71073
monoclinic
P2/n
triclinic
triclinic
P1
P1
4
4
4
1
1
a [Å]
9.8598(12)
17.856(2)
17.272(2)
90
16.189(4)
10.5506(13)
16.739(3)
90
15.5428(6)
10.1316(4)
20.2967(10)
90
9.121(2)
10.235(2)
10.943(2)
97.28(4)
102.20(4)
92.947(4)
987.2(4)
1.039
8.5742(14)
10.2417(17)
10.7960(18)
83.090(3)
88.234(3)
74.707(3)
907.8(3)
1.079
b [Å]
c [Å]
α [deg]
β [deg]
γ [deg]
V [Å3]
106.098(2)
90
101.37(2)
90
102.192(4)
90
2921.6(6)
1.089
2803.1(9)
1.069
3124.1(2)
1.130
F
calc [g cmꢀ3
μ [mmꢀ1
]
3
]
0.161
0.164
0.156
0.146
0.156
θ range [deg]
2.16ꢀ26.00
15 169
2.29ꢀ27.00
28 963
2.26ꢀ26.00
33 942
1.92ꢀ26.00
8729
1.90ꢀ27.00
9322
no. of reflns
no. of indep reflns/Rint
params
5735/0.0428
290
6069/0.0454
270
6143/0.0497
321
3823/0.0318
195
3863/0.0258
185
R1/wR2 indices [I > 2σ(I)]
R1/wR2 for all reflns
GooF on F2
0.0521/0.1170
0.0769/0.1319
1.069
0.0519/0.1419
0.0560/0.1464
1.054
0.0412/0.0855
0.0815/0.0892
1.025
0.0507/0.1302
0.0656/0.1436
1.020
0.0503/0.1281
0.0628/0.1388
1.069
largest diff peak/hole [e Åꢀ3
]
0.313/ꢀ0.202
0.287/ꢀ0.397
0.281/ꢀ0.531
0.337/ꢀ0.194
0.397/ꢀ0.192
3
β-diketiminato ligand, which displays a different electronic
structure, show similar MgꢀC bond lengths.12 The SiꢀN bond
length for compound 6a [1.688(2) Å] is comparable to those of
compounds 5a,b,c, whereas the length of the SiꢀN bond in 6b is
slightly longer [1.728(2) Å] as a result of the dimerization via the
amide nitrogen bridge. Due to the restricting cyclic structures
and sterically demanding tert-butyl and isopropyl groups, the
ideal tetrahedral arrangements at the magnesium atoms are
strongly distorted.
To determine the relative difference in energy concerning
these two possible bridging modes for the tert-butyl- as well as the
isopropyl-substituted compounds, DFT calculations were per-
formed at the B3LYP/6-31+G(d) level.13
61 kJ molꢀ1 compared to the C-bridged compound (6dC)
(Figure 6).
3
The sterical restrictions of both the calculated structures and
the corresponding synthesized compounds 6a,b indicate en-
hanced energy levels compared to sterically undemanding struc-
tures. This should result in an enhancement of reactivity of 6a,b
compared to less sterically clustered structures. To evaluate the
reactivity of these compounds, the energy consumed by splitting
the dimers into monomers was calculated using their energeti-
cally most stable dimeric structures (6a,b) and the dimeric
methyl-substituted model structure 6dN (Scheme 3). These
calculations revealed that the sterically unrestricted structure
6dN needs 112 kJ molꢀ1 to be separated into monomers. The
3
Due to the strong sterical demand of a tert-butyl group, the
dimeric compounds 6a and 6b, however, are split at the cost of
unusual carbon bridge (6a) is highly favored [80 kJ molꢀ1
]
38kJ molꢀ1 (a) and 46kJ molꢀ1 (b), respectively. These calcula-
3
3
3
compared to a nitrogen bridge (6aN) (Figure 5). This is in
agreement with the determined crystal structure of 6a, although
most dimeric magnesium compounds found in the literature
usually prefer the most electronegative atom as the bridging
tions are in accordance with the proposed higher reactivities
for those compounds, especially the carbon-bridged tert-butyl-
substituted dimer 6a.
unit.2,6,14 An energy difference of 14 kJ molꢀ1 was calculated for
3
’ CONCLUSION
the carbon-bridged compound 6bC and the favored nitrogen-
bridged compound 6b. This is consistent with the experimental
result of a dimerization via the nitrogen atom observed in the
crystal structure (Figure 6). Additionally, this rather small value
might indicate that the sterical restriction is still quite significant.
To verify the steric influence on the bridging mode, the model
structures 6dC (C-bridge) and 6dN (N-bridge), which feature a
small methyl group [R = Me] instead of the sterically demanding
tert-butyl or isopropyl groups, were calculated at the same level.
As expected, these model structures without sterically demand-
ing groups also favor a nitrogen bridge (6dN) with a difference of
The synthesis of more varied (aminomethyl)silazanes, which
exhibit different alkyl substituents at the amine moieties, has been
a preparative challenge in organosilicon chemistry. Chan and co-
workers have demonstrated that the protecting group 4,5-
dihydro-2-furyl is easily cleaved using alkyl lithium reagents.
This method was applied and extended to the synthesis of
(aminomethyl)silazanes. By cleaving this protecting group with
lithiated primary amines, a wide range of N-alkyl-substituted
(aminomethyl)silazanes is now accessible. Since previous re-
search demonstrates an extensive practical potential of metal
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Organometallics
ARTICLE
amides and mixed alkylmetal amides, the prepared (amino-
methyl)silazanes were deprotonated by the 2-fold base dibutyl-
magnesium. This reaction yields either magnesium disilylamides
(5a,b,c) or butylmagnesium silylamides (6a,b) selectively upon
variation of the stochiometric ratios and reaction temperatures.
The examination of the obtained dimeric butylmagnesium
silylamide compounds by single-crystal X-ray diffraction analysis
reveals different bridging modes. According to the steric demand
of the ligand, either a carbon- or nitrogen-bridged dimer is
formed. In consequence, by changing the substituent of the
(aminomethyl)silazane from isobutyl to tert-butyl the mode of
aggregation can be controlled. While sterically undemand-
ing substituents lead to a nitrogen-bridged dimer, commonly
observed in similar magnesium complexes, sterically demanding
substituents form an unusual carbon-bridged dimer. The calcu-
and afterward extracted with diethyl ether (5 ꢁ 50 mL). After drying the
combined organic fractions over Na2SO4 the solvent was removed and
the oily residue distilled in vacuo to give 10.2 g (58 mmol, 90%) of a
colorless liquid (36 °C, 1 ꢁ 10ꢀ2 mbar).
Synthesis of (4,5-Dihydrofuran-2-yl)(piperidinomethyl)
dimethylsilane (3). A 9.0 g (51 mmol) portion of 2 was dissolved
in 50 mL of toluene, and 10.1 mL (8.7 g, 102 mmol) of piperidine was
added. The reaction mixture was stirred under reflux for 55 h. The
precipitation was removed via filtration and washed with 100 mL of
pentane. After removal of the solvent the oily residue was distilled
in vacuo to give 10.3 g (46 mmol, 90%) of a colorless liquid (60 °C, 1 ꢁ
10ꢀ2 mbar). 1H NMR (300.1 MHz, CDCl3): δ 0.21 [s, 6H; Si(CH3)2],
1.33ꢀ1.40 [m, 2H; NCH2CH2CH2], 1.51ꢀ1.58 [m, 4H; NCH2CH2-
CH2], 2.03 [s, 2H; SiCH2N], 2.32ꢀ2.36 [m, 4H; NCH2CH2CH2], 2.59
[td, 2H, 3JHH = 9.6 Hz, 3JHH = 2.6 Hz; SiCCHCH2CH2O], 4.27 [t, 2H,
3JHH = 9.6 Hz; SiCCHCH2CH2O], 5.26 [t, 1H, 3JHH = 2.6 Hz; SiCCH-
CH2CH2O]. 13C NMR (75.5 MHz, CDCl3): δ ꢀ3.6 [Si(CH3)2], 23.7
[NCH2CH2CH2], 26.2 [NCH2CH2CH2], 30.7 [SiCCHCH2CH2O],
49.2 [SiCH2N], 58.2 [NCH2CH2CH2], 70.3 [SiCCHCH2CH2O],
111.8 [SiCCHCH2CH2O], 161.3 [SiCCHCH2CH2O]. 29Si NMR
(59.6 MHz, CDCl3): δ ꢀ13.0. GC-EI(+)MS, tR = 4.98 min, m/z [%]:
225 (3) [M+], 98 (100) [(CH2NC5H10)+]. Anal. Calcd: C, 63.94; H,
10.28; N, 6.21. Found: C, 64.0; H, 10.1; N, 6.1.
lated energy difference of 80 kJ molꢀ1 between the two possible
3
bridging modes of compound 6a featuring tert-butyl groups
illustrates the impact of steric effects, which control the aggrega-
tion mode.
’ EXPERIMENTAL SECTION
General Procedures. All reactions were carried out under argon
using a standard Schlenk line. All solvents were dried by standard
methods. NMR spectra were recorded on Bruker Avance-500, Bruker
DRX 500, Bruker Avance-400, Bruker DRX 400, Bruker DPX 300, and
Varian Inova 500 spectrometers. 1H NMR spectra are referenced to the
Synthesis of (tert-Butylamino)(piperidinomethyl)dime-
thylsilane (4a). A 9.3 mL (15 mmol, 1.6 M in hexane) amount of
n-BuLi was added to a solution of 3.4 mL (2.2 g, 30 mmol) of tert-
butylamine in 50 mL of thf at ꢀ50 °C. The mixture was allowed to warm
to 0 °C before adding 2.5 g (11 mmol) of 3. The reaction mixture was
stirred for 30 min at 0 °C, and then 0.8 g (15 mmol) of ammonium
chloride was added. After removal of the solvent the residue was
dissolved in pentane. The solid was filtered off under argon. Afterward
the solvent of the filtrate was removed and the residual oil purified via
bulb-to-bulb distillation (65 °C, 4.2 ꢁ 10ꢀ2 mbar) to give 1.8 g (8 mmol,
71%) of a colorless liquid. 1H NMR (300.1 MHz, C6D6): δ 0.20 [s, 6H;
Si(CH3)2], 0.96 [br, 1H; SiNHC(CH3)3], 1.16 [s, 9H; SiNHC(CH3)3],
1.28ꢀ1.36 [m, 2H; NCCCH2], 1.51ꢀ1.58 [m, 4H; NCCH2C], 1.84 [s,
2H; SiCH2N], 2.36 [br, 4H; NCH2CC]. 13C NMR (75.5 MHz, C6D6):
δ 2.7 [Si(CH3)2], 24.8 [NCCCH2], 27.3 [NCCH2C], 34.3 [SiNC-
(CH3)3], 49.6 [SiNC(CH3)3], 52.9 [SiCH2N], 59.1 [NCH2CC]. 29Si
NMR (59.6 MHz, C6D6): δ ꢀ6.0. Anal. Calcd: C, 63.09; H, 12.35; N,
12.26. Found: C, 62.0; H, 12.1; N, 12.0.
internal standards C6D5H at 7.16 ppm or CHCl3 at 7.27 ppm, and 13
C
NMR spectra are referenced to C6D5H at 128.39 ppm or CHCl3 at 77.00
ppm (external standard: TMS). The 29Si NMR spectra are referenced to
the external standard TMS. The GC-MS spectra were measured with the
gas chromatography column HP 6890 [J. & W. Scientific; 25 m length,
i.d. 0.2 mm, helium gas, 2.06 bar; temperature progam: 50 °C (1 min) to
40 °C/min to 300 °C (5 min)] and a HP mass selective detector 5973
(EI(+)-MS, 70 eV). The elemental analysis was conducted on a Leco
CHNS-932/O VTF-900 analyzer. All chemicals were used as purchased
with the exception of ammonium chloride, which was purified and dried
by sublimation prior to use.
Crystal Structure Determination of Compounds 5a,b,c
and 6a,b. The crystals of all compounds were mounted in an inert
oil (perfluoropolyalkyl ether) at ꢀ60 °C (N2 stream), using the
X-TEMP 2 device.15 5a and 6a,b: Bruker Apex CCD diffractometer;
programs used for data collection, cell determination, and cell refinement:
Smart V. 5622 (Bruker AXS, 2001), integration: SaintPlus V. 6.02 (Bruker
AXS, 1999), empiricalabsorptioncorrection:SadabsV. 2.01(BrukerAXS,
1999). 5b: StoeIPDS diffratometer; datacollection: ExposeinIPDS (Stoe
& Cie, 1999), cell determination and refinement: Cell in IPDS (Stoe &
Cie, 1999), integration: Integrate in IPDS (Stoe & Cie, 1999), numerical
absorption correction: Faceit in IPDS (Stoe & Cie, 1999). 5c: Oxford
Diffraction Xcalibur S, programs used for data collection, cell determina-
tion, and cell refinement: CrysAlis (Oxford, 2008); CrysAlis RED
(Oxford, 2008), empirical absorption correction: Scale3 Abspack (Oxford,
2008). The structures were solved using direct methods (SHELXS90);
structural refinement was done with SHELXL97.
Synthesis of (Isopropylamino)(piperidinomethyl)dime-
thylsilane (4b). The synthetic approach was identical to the procedure
described above: 20.0 mL (32 mmol, 1.6 M in hexane) of n-BuLi, 5.6 mL
(3.8 g, 65 mmol) of isopropylamine in 50 mL thf, 4.5 g (20 mmol) of 3,
2.0 g (37 mmol) of ammonium chloride. Bulb-to-bulb distillation at
60 °C and 5 ꢁ 10ꢀ2 mbar gave 3.0 g (14 mmol, 70%). 1H NMR (300.1
MHz, C6D6): δ 0.15 [s, 6H; Si(CH3)2], 0.34 [br, 1H; SiNHCH-
3
(CH3)2], 1.01 [d, 6H, JHH = 6.3 Hz; SiNHCH(CH3)2], 1.28ꢀ1.36
[m, 2H; NCCCH2], 1.51ꢀ1.59 [m, 4H; NCCH2C], 1.85 [s, 2H;
3
SiCH2N], 2.36 [br, 4H; NCH2CC], 3.01 [septd, 1H, JHH = 6.3 Hz,
3JHH = 10.2 Hz; SiNHCH(CH3)2]. 13C NMR (75.5 MHz, C6D6): δ 0.1
[Si(CH3)2], 24.8 [NCCCH2], 27.3 [NCCH2C], 28.6 [SiNCH(CH3)2],
43.7 [SiNCH(CH3)2], 52.2 [SiCH2N], 59.3 [NCH2CC]. 29Si NMR
(59.6 MHz, C6D6): δ ꢀ2.4. Anal. Calcd: C, 61.62; H, 12.22; N, 13.06.
Found: C, 61.2; H, 12.0; N, 13.1.
Synthesis of (Chloromethyl)(4,5-dihydrofuran-2-yl)dime-
thylsilane (2). The synthesis was carried out using a simplified pro-
cedure developed by Chan and co-workers. Analytical data are identical
and not listed here.9 A 5.5 mL (5.1 g, 73 mmol) sample of 2,3-
dihydrofuran was disssolved in 60 mL of thf and cooled to ꢀ60 °C.
After addition of 29.0 mL (72.5 mmol, 2.5 M in hexane) of n-BuLi the
reaction mixture was stirred for 1 h and warmed to 0 °C. This reaction
mixture was added to a solution of 9.2 g (64 mmol) of (chloromethyl)
dimethylchlorosilane in 30 mL of thf cooled to ꢀ60 °C. After stirring for
1 h and warming to 0 °C the reaction was quenched with 70 mL of water
Synthesis of (Cyclohexylamino)(piperidinomethyl)dim-
ethylsilane (4c). The synthetic approach was identical to the proce-
dure described above: 17.5 mL (28 mmol, 1.6 M in hexane) of n-BuLi,
4.0 mL (3.5 g, 35 mmol) of cyclohexylamine in 50 mL of thf, 4.3 g (19
mmol) of 3, 1.6 g (30 mmol) of ammonium chloride. Bulb-to-bulb
distillation at 90 °C and 1.4 ꢁ 10ꢀ2 mbar gave 2.8 g (11 mmol, 59%).
1H NMR (500.1 MHz, C6D6): δ 0.18 [s, 6H; Si(CH3)2], 0.51 [d, 1H,
3JHH = 8.0 Hz; SiNHCHC6H10], 0.94ꢀ1.09 [m, 3H; SiNHCHC6H10],
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Organometallics
ARTICLE
1.16ꢀ1.25 [m, 2H; SiNHCHC6H10], 1.30ꢀ1.35 [m, 2H; NCCCH2],
1.46ꢀ1.51 [m, 1H; SiNHCHC6H10], 1.54ꢀ1.58 [m, 4H; NCCH2C],
1.60ꢀ1.66 [m, 2H; SiNHCHC6H10], 1.88 [s, 2H; SiCH2N], 2.38
[br, 4H; NCH2CC], 2.61ꢀ2.68 [m, 1H; SiNHCHC6H10]. 13C NMR
(125.8 MHz, C6D6): δ 0.3 [Si(CH3)2], 24.8 [NCCCH2], 26.3
[SiNHCHCCH2C], 26.6 [SiNHCHCCCH2], 27.3 [NCCH2C], 39.5
[SiNHCHCH2CC], 51.2 [SiNHCHCH2CC], 52.3 [SiCH2N], 59.3
[NCH2CC]. 29Si NMR (59.6 MHz, C6D6): δ ꢀ2.3. Anal. Calcd: C,
66.07; H, 11.88; N, 11.01. Found: C, 65.7; H, 11.6; N, 10.8.
of pentane and cooled to ꢀ60 °C. Retaining the temperature, a solution
of 164 mg of 4b (0.76 mmol) in 5 mL of pentane was added slowly, while
the reaction mixture was warmed to ꢀ30 °C. Storage at ꢀ30 °C for 20 h
yielded 207 mg (0.35 mmol, 92%) of colorless crystals of 6a suitable for
X-ray analysis. Anal. Calcd: C, 61.11; H, 11.62; N, 9.50. Found: C, 59.8;
H, 11.6; N, 9.5.
’ ASSOCIATED CONTENT
Synthesis of Magnesium Disilylamide 5a. To 131 mg (0.57
mmol) of 4a cooled to ꢀ60 °C was added 0.29 mL (0.30 mmol, 1.0 M in
heptane) of n-Bu2Mg, and the mixture was allowed to warm to room
temperature. Storage for 20 h yields 86 mg (0.18 mmol, 63%) of
S
Supporting Information. Crystallographic data in CIF
b
format and figures giving thermal ellipsoid plots of 5a,b,c and
6a,b. Total energies and Cartesian coordinates for all computed
structures. This material is available free of charge via the Internet
at http://pubs.acs.org.
1
colorless crystals of 5a suitable for X-ray analysis. H NMR (300.1
MHz, C6D6): δ 0.27 + 0.40 [s, 12H; Si(CH3)2], 1.15ꢀ1.57 [m, 12H;
NCH2CH2CH2], 1.59 [s, 18H; NC(CH3)3], 1.67 + 2.05 [AB-system,
’ AUTHOR INFORMATION
2
4H, JHH = 14.3 Hz; SiCH2N], 2.18ꢀ2.25 [m, 2H; NCH2CH2CH2],
2.74ꢀ2.87 [m, 4H; NCH2CH2CH2], 3.14ꢀ3.23 [m, 2H; NCH2CH2-
CH2]. 13C NMR (100.6 MHz, C6D6): δ 6.8 + 7.5 [Si(CH3)2], 20.1
[NCH2CH2CH2], 20.6 [NCH2CH2CH2], 24.7 [NCH2CH2CH2], 38.3
[NC(CH3)3], 47.0 [SiCH2N], 52.4 [NC(CH3)3], 54.6 [NCH2CH2-
CH2], 58.6 [NCH2CH2CH2]. 29Si NMR (59.6 MHz, C6D6): δ ꢀ16.9.
Anal. Calcd: C, 60.16; H, 11.36; N, 11.69. Found: C, 59.5; H, 11.4; N, 11.5.
Synthesis of Magnesium Disilylamide 5b. To 160 mg (0.75
mmol) of 4b cooled to ꢀ60 °C was added 0.38 mL (0.40 mmol, 1.0 M in
heptane) of n-Bu2Mg, and the reaction mixture was allowed to warm to
room temperature. Storage for 20 h yielded 128 mg (0.28 mmol, 75%) of
colorless crystals of 5b suitable for X-ray analysis. 1H NMR (400.1 MHz,
C6D6): δ 0.24 + 0.42 [s, 12H; Si(CH3)2], 1.01ꢀ1.14 [m, 2H; NCH2CH2-
CH2], 1.53ꢀ1.60 [m, 2H; NCH2CH2CH2], 1.47 + 1.49 [d, 12H, 3JHH = 6.3
Hz; NCH(CH3)2], 1.65ꢀ1.71 [m, 2H; NCH2CH2CH2], 1.63 + 1.75 [AB-
system, 4H, 2JHH =14.2Hz;SiCH2N], 1.84ꢀ2.00 [m, 6H; NCH2CH2CH2],
2.58ꢀ2.64 [m, 2H; NCH2CH2CH2], 3.40ꢀ3.44 [m, 2H; NCH2CH2CH2],
Corresponding Author
*E-mail: mail@carsten-strohmann.de.
’ ACKNOWLEDGMENT
We thank the Deutsche Forschungsgemeinschaft, the Fonds
der Chemischen Industrie, and Wacker Chemie AG for their
support. Additionally the authors wish to express their gratitude
toward Jana Becker and Patricia Gollas.
’ REFERENCES
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3.73 [sept, 2H, JHH = 6.2 Hz; NCH(CH3)2]. 13C NMR (100.6 MHz,
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C6D6): δ 5.5 + 6.5 [Si(CH3)2], 22.8 [NCH2CH2CH2], 24.0 [NCH2CH2-
CH2], 24.3 [NCH2CH2CH2], 31.6 [NCH(CH3)2], 32.0 [NCH(CH3)2],
48.5 [NCH(CH3)2], 52.2 [SiCH2N], 56.2 [NCH2CH2CH2], 60.7 [NCH2-
CH2CH2]. 29Si NMR (59.6 MHz, C6D6):δꢀ15.7. Anal. Calcd: C, 58.57; H,
11.17; N, 12.42. Found: C, 58.0; H, 11.0; N, 12.3.
Synthesis of Magnesium Disilylamide 5c. To a solution of 67
mg (0.26 mmol) of 4c in 5 mL of pentane cooled to ꢀ60 °C was added
0.13 mL (0.13 mmol, 1.0 M in heptane) of n-Bu2Mg, and the reaction
mixture was allowed to warm to 0 °C. After 20 h 47 mg (0.09 mmol,
69%) of colorless crystals of 5c suitable for X-ray analysis was obtained.
1H NMR (300.1 MHz, C6D6): δ 0.26, 0.43 [s, 12H; Si(CH3)2], 0.88ꢀ
1.93 [m, 14H; NCH2CH2CH2, SiNCHC6H10], 1.60 + 1.78 [AB-system,
2JHH = 14.3 Hz, 4H; SiCH2N], 2.14 [br, 2H; NCH2CH2CH2], 2.60 [br,
1H; SiNCHC6H10], 3.07 [br, 1H; NCH2CH2CH2], 3.48ꢀ3.53 [m, 1H;
NCH2CH2CH2]. 13C NMR (125.8 MHz, C6D6): δ 5.9, 6.7 [Si(CH3)2],
23.1ꢀ30.7 [NCH2CH2CH2, NCHCH2CH2CH2], 42.5 [NCHCH2-
CH2CH2], 52.9 [SiCH2N], 56.6 [NCH2CH2CH2], 58.1 [NCHCH2-
CH2CH2], 61.1 [NCH2CH2CH2]. 29Si NMR (59.6 MHz, C6D6):
δ ꢀ16.0. Anal. Calcd: C, 63.30; H, 11.00; N, 10.55. Found: C, 62.8; H,
11.2; N, 10.3.
Synthesis of Butylmagnesium Silylamide 6a. A 0.44 mL
(0.44 mmol, 1.0 M in heptane) amount of n-Bu2Mg was diluted in 5 mL
of pentane and cooled to ꢀ60 °C. Retaining the temperature, a solution
of 101 mg of 4a (0.44 mmol) in 5 mL of pentane was added slowly, while
the reaction mixture was warmed to ꢀ30 °C. Storage at ꢀ30 °C for 20 h
yielded 57 mg (0.09 mmol, 42%) of colorless crystals of 6a suitable for
X-ray analysis. Anal. Calcd: C, 62.22; H, 11.75; N, 9.07. Found: C, 61.3;
H, 11.5; N, 8.6.
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1
Synthesis of Butylmagnesium Silylamide 6b. A 0.76 mL
(0.76 mmol, 1.0 M in heptane) sample of n-Bu2Mg was diluted in 5 mL
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