Group 2 metal (Mg, Ca, Sr) silylamides supported by a cyclen-derived macrocyclic polyamine

Article abstract of DOI:10.1039/c7dt01727h

Heteroleptic bis(silyl)amides of magnesium and calcium [(L)M{N(SiMe₃)₂}] [M = Mg, Ca; LH = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane; (Me₃TACD)H] were previously synthesized from LH and [M{N(SiMe₃)₂}₂]. Strontium bis(silyl)amides [Sr{N(SiMe₃)₂}₂(thf)₂] and [Sr{N(SiHMe₂)₂}₂(thf)_2/3] reacted with LH to give different types of products, depending on the presence of the β-SiH function. While the former underwent protonolysis to give the amido-bridged dimer [(L)Sr{N(SiMe₃)₂}]₂ (1), the latter gave the adduct [(LH)Sr{N(SiHMe₂)₂}₂] (2) as a stable solid. 2 slowly underwent an intramolecular Si-H/H-N dehydrocoupling in solution to give [{(L)SiMe₂N(SiHMe₂)}Sr{N(SiHMe₂)₂}] (3) by liberating H₂. The results of transamination of 1 with HN(SiHMe₂)₂ depended on the relative stoichiometric ratio. A 1 : 1 mixture in n-pentane gave [{(L)SiMe₂N(SiHMe₂)}Sr{N(SiMe₃)₂}] (4) and H₂, while excess HN(SiHMe₂)₂ gave the adduct 2 under similar conditions. Compounds 2 and 3 exhibit Sr? H-Si interactions according to X-ray crystallography, NMR, and IR spectroscopy. Lighter congeners of elusive [(L)Sr{N(SiHMe₂)₂}] were isolable for Mg (5) and Ca (6).

Full text of DOI:10.1039/c7dt01727h

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PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
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Group 2 metal (Mg, Ca, Sr) silylamides supported by a cyclen-
derived macrocyclic polyamine
Debabrata Mukherjee,a Satoru Shirase,b Klaus Beckerle,a Thomas P. Spaniol,a Kazushi Mashimab
and Jun Okudaa,*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Heteroleptic bis(silyl)amides of magnesium and calcium [(L)M{N(SiMe3)2}] [M = Mg, Ca; LH = 1,4,7-trimethyl-1,4,7,10-
tetraazacyclododecane; (Me3TACD)H] were previously synthesized from LH and [M{N(SiMe3)2}2]. Strontium bis(silyl)amides
[Sr{N(SiMe3)2}2(thf)2] and [Sr{N(SiHMe2)2}2(thf)2/3] reacted with LH to give different types of products, depending on the
www.rsc.org/
presence of the
β-SiH function. While the former underwent protonolysis to give the amido-bridged dimer
[(L)Sr{N(SiMe3)2}]2 (1), the latter gave the adduct [(LH)Sr{N(SiHMe2)2}2] (2) as a stable solid. 2 slowly underwent an
intramolecular Si−H/H−N dehydrocoupling in solution to give [{(L)SiMe2N(SiHMe2)}Sr{N(SiHMe2)2}] (3) by liberating H2.
Results of transamination of 1 with HN(SiHMe2)2 depended on the relative stoichiometric ratio. A 1:1 mixture in n-pentane
gave [{(L)SiMe2N(SiHMe2)}Sr{N(SiMe3)2}] (4) and H2, while excess HN(SiHMe2)2 gave the adduct 2 under similar condition.
Compounds 2 and 3 exhibit Sr↼H−Si interactions according to X-ray crystallography, NMR, and IR spectroscopy. Lighter
congeners of elusive [(L)Sr{N(SiHMe2)2}] were isolable for Mg (5) and Ca (6).
hexamethyl bis(silyl)amide [N(SiMe3)2; HMDS] complexes of
magnesium and calcium [(L)M{N(SiMe3)2}] (M = Mg, Ca).6b
Here we report on the HMDS and TMDS [tetramethyl
Introduction
Homogeneous catalysts based on earth-abundant and non-
toxic alkaline earth metals are increasingly important in
transition metal-free chemistry.1 Homo- and heteroleptic
group 2 silylamides act as precatalysts for the dehydrogenative
bis(silyl)amide; N(SiHMe2)2] derivatives of the heavier
strontium as well as on the TMDS derivatives of magnesium
and calcium and conduct a systematic comparison between
the three metals.
Si
metathesis and
containing -hydrogens received special attention, as they
exhibit 3-center-2-electron M Si agostic interactions that
lead to unusual structures and reactivity.3 For the heavier
group 2 metals, -agostic interactions of a N(SiHMe2)2 group
−
N bond formation reactions that typically involve M
−N/H−Si
M
−
H/H
−N
protonolysis.2 Silylamides
β
Results and discussion
↼H−
Reactions of LH with [Sr(HMDS)2] and [Sr(TMDS)2].
β
Me3Si
N
could instigate better stability compared to the bulkier
N(SiMe3)2 ligand.4
Me3Si
N
N
N
N
[Sr{N(SiMe3)2}2(thf)2]
N
Sr
Sr
N
Heteroleptic bis(silyl)amides, especially of the heavier
congeners Ca, Sr, and Ba, require kinetic stabilization using
appropriate co-ligands.4a,5 The cyclen derived macroyclic
1/2
toluene
25 °C, 2 h
N
SiMe3
N
SiMe3
N
Me
Me
Me
−HN(SiMe3)2
N
N
N
1
, 81%
polyamine
1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane
[(Me3TACD)H = LH] is a tetradentate monoanionic proligand
forming stable complexes with main group, transition, and rare
earth metals.6 We have previously described the heteroleptic
NH
LH
N
N
[Sr{N(SiHMe2)2}2(thf)2/3
]
HN
N
Sr
THF/n-pentane
(1:9)
Me2HSi
SiHMe2
N
N
25 °C, 15 min
a.Dr. D. Mukherjee, Dr. Klaus Beckerle, Dr. T. P. Spaniol, Prof. Dr. J. Okuda*
Institute of Inorganic Chemistry, RWTH Aachen University
Landoltweg 1, 52056, Aachen (Germany)
Me2HSi
SiHMe2
, 92%
2
E-mail: jun.okuda@ac.rwth-aachen.de
Scheme 1. Synthesis of the strontium silylamides 1 and 2.
b.S. Shirase, Prof. Dr. K. Mashima
Graduate School of Engineering Science
Osaka University, Toyonaka, Osaka 560-8531 (Japan)
An equimolar mixture of [Sr{N(SiMe3)2}2(thf)2] and LH in
toluene at 25 ˚C gave [(L)Sr{N(SiMe3)2}]2 ) as colorless
† Electronic Supplementary Information (ESI) available: Description of compounds
1-6, spectroscopic data, and crystallographic data files. CCDC 1537652-1537656.
(1
crystals in 81% yield (Scheme 1). It is soluble in THF but
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/x0xx00000x.
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insoluble in aliphatic and aromatic hydrocarbons.
Contrastingly, treating [Sr{N(SiHMe2)2}2(thf)2/3] with LH in
THF/n-pentane (1:9) solvent mixture precipitated the adduct
[(LH)Sr{N(SiHMe2)2}2] (
2) as colorless crystals in 92% yield
(Scheme 1). Complex
2 is soluble in both THF and aromatic
hydrocarbons.
1
The H NMR spectrum of
1 in THF-d8 shows the expected
resonances of L in addition to a singlet at δ −0.07 ppm (18 H)
for the terminal N(SiMe3)2 ligand. Complex is stable in the
solid state but decomposes in benzene or THF with H2
evolution to give [{(L)SiMe2N(SiHMe2)}Sr{N(SiHMe2)2}] ( ) in
88% yield (Scheme 2). This Si N bond formation reaction is
slow at room temperature allowing the spectroscopic
characterization of , and can be accelerated by heating. A
freshly prepared benzene-d6 solution of shows the
resonances of a coordinated LH. The NH proton appears as a
multiplet at 2.85 ppm. The two chemically equivalent
0.57
2
3
−
2
2
δ
terminal N(SiHMe2)2 groups are detected as a doublet at
δ
2
ppm (3JHH = 2.8 Hz, JSiH = 9.5 Hz, 24 H, SiMe) and a septet at
δ
3
5.08 ppm (1JSiH = 158 Hz, 4 H, SiH). The spectroscopic data for
are similar to those of the homologous calcium derivative
reported previously (vide infra).6b
Scheme 3. Transamination of 1 with HN(SiHMe2)2.
From the coupling constants 1JSiH in the 1H NMR spectra the
extent of 3-center-2-electron M Si bonding interactions
↼H−
1
can be estimated.4a The value of JSiH = 158 Hz in
2
suggests a
Scheme 2. Intramolecular dehydrogenative Si−H/H−N coupling of 2 to give 3.
weak
β
is also weakly
-agostic interaction. The terminal N(SiHMe2)2 group in
3
. The
is a
β
-agostic (1JSiH = 157 Hz), similar to that in
2
pendant N(SiHMe2) (1JSiH = 173 Hz) in both
3 and 4
Transamination of 1 with [HN(SiHMe2)2].
‘classical’ silylamide. This is also corroborated by their solid-
state IR spectra (see ESI). The SiH stretching band of is broad,
while has two overlapping SiH bands indicating the presence
of both agostic as well as non-agostic SiH bonds. Complex
The outcome of the transamination of
1 with the smaller
ν
ν
2
amine HN(SiHMe2)2 containing β-hydrogens depended on the
relative stoichiometric ratio of the reactants. Stirring a 1:1
3
4
mixture as a suspension in n-pentane for 24 h gave the mixed
exhibits a sharp νSiH band due to the single non-agostic
N(SiHMe2) unit.
ligand compound [{(L)SiMe2N(SiHMe2)}Sr{N(SiMe3)2}] (
4) in
93% yield (Scheme 3). Both 1 and 4 are insoluble in n-pentane
and the mixture remained heterogeneous throughout the
reaction. This is most likely a stepwise process, whereby the
proton in HN(SiHMe2)2 is first transferred to the amido
function of the monoanionic L, generating an undetectable
X-ray crystallography.
Complexes
diffraction.
1
-
4
were characterized by single crystal X-ray
1
has a dimeric structure with a central Sr2N2 unit
intermediate [(LH)Sr{N(SiHMe2)2}{N(SiMe3)2}]
structurally related to is probably unstable and releases H2
to give . Reaction with a fourfold excess of HN(SiHMe2)2 in
identical fashion gave instead but did not convert further
into due to its insolubility in n-pentane (Scheme 3). This also
likely goes through the same intermediate that may react
faster with additional HN(SiHMe2)2 in intermolecular fashion,
rather than undergoing Si H/H N dehydrocoupling. Complex
is related to with a terminal N(SiMe3)2 group instead of
N(SiHMe2)2, showing a similar 1H NMR spectrum in benzene-d6
with a singlet at 0.44 ppm (18 H) for the N(SiMe3)2 protons.
Isolated can be converted into by transamination with
(
A
)
that is
around a crystallographic center of inversion, while the
magnesium and calcium homologs were monomeric.6b Amido
nitrogens of the two L ligands connect the strontium atoms
(Figure 1). Each terminal N(SiMe3)2 ligand shows one
2. A
4
2
3
significant Sr↼C−Si interaction giving a capped octahedron
geometry to each strontium. These are evident from a short
A
Sr1
−
−
C12 distance [3.147(3) Å], a nearly planar arrangement of
N6 Si1 C12 (torsion angle 3.8˚), and Sr1 N6 Si1
Sr1 N6 Si2 [130.63(11)].
crystallizes in space group C2/c with a
−
−
4
Sr1
−
−
∠
−
−
3
[106.53(10)] being more acute than
∠
−
−
Complex
2
δ
monomeric molecular structure (Figure 2). Crystallographic C2-
symmetry makes the N(SiHMe2)2 ligands identical, but causes
disorder to the carbon atoms of the L fragment. In the
4
3
HN(SiHMe2)2 in benzene (Scheme 3).
2 | J. Name., 2012, 00, 1-3
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refinement, the disorder could be modelled with split and the terminal N(SiHMe2)2 ligand make the strontium-center
positions. The formally six-coordinate strontium-center shows formally six-coordinate (Figure 3). One of the two terminal
two Sr
antiprismatic geometry at the metal center. These are octahedral geometry for strontium, as indicated by the short
manifested by the small angle Sr1 N5 Si1 [102.17(7)] Sr1 H3 distance of 2.984(3) Å and by the smaller angle of
compared to Sr1 N5 Si2 [124.75(8)], the short Sr1 H1 Sr1 N6 Si3 [107.09(9)] compared to Sr1 N6 Si4
H1 motif [117.15(10)]. The pendant Si2 H2, although pointing towards
↼
H−
Si agostic interactions creating
a
square Si−H bonds shows an agostic interaction to give a capped
∠
−
−
−
∠
−
−
−
∠
−
−
∠
−
−
distance [2.814(19) Å], and the planar Sr1
−
N5−
Si1−
−
(torsion angle 1.4˚).
the metal, is non-agostic as suggested by the metric
parameters and is consistent with the NMR and IR spectral
data.
Figure 1. Molecular structure of 1. The carbon atoms of the disordered L ligands are
shown with one split position. Hydrogens atoms are omitted for clarity. Displacement
parameters are drawn at 50% probability. Selected bond distances (Å): Sr1−N1' =
Sr1'−N1 2.598(2); Sr1−N1 = Sr1'−N1' 2.641(2); Sr1−N6 = Sr1'−N6' 2.627(2); Sr1−C12 =
Sr1'−C12' 3.147(3). Selected bond angles (˚): ∠Sr1−N6−Si1 = ∠Sr1'−N6'−Si1' 106.53(10);
Figure 3. Molecular structure of 3. Hydrogen atoms except the SiH units are omitted for
clarity. Displacement parameters are drawn at 50% probability. Selected bond
distances (Å): Sr1−N1 2.8127(18); Sr1−N2 2.7609(18); Sr1−N3 2.7667(18); Sr1−N4
2.6991(19); Sr1−N5 2.5218(18); Sr1−N6 2.5073(19); Sr1−H3 2.984(3). Selected bond
angles (˚): ∠Sr1−N6−Si3 = 107.09(9); ∠Sr1−N6−Si4 117.15(10). Selected torsion angles
(˚): ∠Sr1−N6−Si3−H3 −6.7; ∠Sr1−N3'−Si1'−H1' −1.3.
∠Sr1−N6−Si2
=
∠Sr1'−N6'−Si2' 130.63(11). Selected torsion angles (˚):
∠Sr1−N6−Si1−C12 = ∠Sr1'−N6'−Si1'−C12' 3.76(14).
The molecular structure of
distorted octahedral geometry (Figure 4). The pendant and
non-agostic Si2 H2 bond in is pointing away from the metal
center, probably due to steric hindrance from the bulkier
terminal N(SiMe3)2 group. The respective Sr N bond lengths in
and are comparable.
4 is similar to that of 3 with a
−
4
−
3
4
Figure 2. Molecular structure of 2. The carbon atoms of the disordered L ligands are
shown with one split position. Hydrogens atoms except the SiH units are omitted for
clarity. The hydrogen atom at N1 is not shown due to disorder in the Me3TACD ligand.
Displacement parameters are drawn at 50% probability. Selected bond distances (Å):
Sr1−N5 = Sr1−N5' 2.5334(15); Sr1−H1 = Sr1−H1' 2.814(19). Selected bond angles (˚):
∠Sr1−N5−Si1 = ∠Sr1−N5'−Si1' 102.17(7); ∠Sr1−N5−Si2 = ∠Sr1−N5'−Si2' 124.75(8).
Selected torsion angles for 2 (˚): ∠Sr1−N5−Si1−H1 = ∠Sr1−N5'−Si1'−H1' 1.4.
Figure 4. Molecular structure of 4. Hydrogen atoms except the SiH are omitted for
clarity. Displacement parameters are drawn at 50% probability. Selected bond
distances (Å): Sr1−N1 2.774(6); Sr1−N2 2.713(6); Sr1−N3 2.770(6); Sr1−N4 2.892(7);
Sr1−N5 2.522(6); Sr1−N6 2.523(5).
Both compounds 3 and 4 are monomeric in the solid-state.
is isostructural with its calcium homolog.6b The
Complex
3
nitrogen atoms of the L, the pendant NSiMe2(SiHMe2) group,
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N
N
N
N
Comparison with magnesium and calcium.
HN(SiHMe2)2
N
N
N
N
Ca
N
Ca
n-pentane, 25 °C
<5 min
− HN(SiMe3)2
Heteroleptic [(L)M{N(SiMe3)2}] (M = Mg, Ca) had been
synthesized before via protonolysis.6b The previously unknown
N
Me2HSi
SiHMe2
Me3Si
SiMe3
compound [(L)Mg{N(SiHMe2)2} (5) was obtained in 86% yield
6
, 86%
via protonolysis or by transamination from [(L)Mg{N(SiMe3)2}]
with HN(SiHMe2)2 (Scheme 4).
THF/benzene
25 °C, 2 h
N
N
N
N
HN(SiHMe2)2
N
N
N
N
N
Mg
N
unidentified
+
n-pentane, 25 °C
<5 min
− HN(SiMe3)2
Ca
N
Me2Si
calcium species
SiHMe2
N
N
N
N
Mg
N
Me3Si
SiMe3
SiHMe2
Me2HSi
LH
Me2HSi
SiHMe2
[Mg{N(SiHMe2)2}2]
Scheme 5. Synthesis of [(L)Ca(TMDS)] (6) and its decomposition in solution.
n-pentane, 25 °C
<5 min
5, 86%
− HN(SiHMe2)2
The calcium TMDS precursor [Ca{N(SiHMe2)2}2(thf)] was
Scheme 4. Synthesis of [(L)Mg(TMDS)] (5) by protonolysis and transamination.
previously reported to readily undergo Si−H/H−N
dehydrocouling with LH instead of protonolysis, directly
providing [{(L)SiMe2N(SiHMe2)}Ca{N(SiHMe2)2}] within 30 min
at 25 ˚C in benzene.6b We have now synthesized
1
The NMR (1JSiH = 173 Hz) and IR (νSiH = 2045 cm− , sharp)
spectroscopic data of 5 suggest a 'classical' bis(silyl)amide
[(L)Ca{N(SiHMe2)2}] (
[(L)Ca{N(SiMe3)2}] with HN(SiHMe2)2 (Scheme 5). The H NMR
spectrum of a freshly prepared benzene-d6 solution of
showed broad signals for the CH2 units of L and for the methyl
groups of the TMDS ligand. The well-resolved septet for Si at
6) in 86% yield by transamination of
structure, in agreement with the results of X-ray
crystallography (Figure 5). The five-coordinate magnesium
center has a distorted square pyramidal geometry with the
1
6
Mg−N bonds being shorter than the Sr−N distances in
complexes 1-3.
H
1
δ
4.97 ppm (3JHH = 2.8 Hz, JSiH = 164 Hz) suggests a weak
agostic interaction. This was supported by a broad νSiH
absorption in the IR spectrum. is only stable as a solid and
decomposed in benzene solution within to give
β-
6
2
h
[{(L)SiMe2N(SiHMe2)}Ca{N(SiHMe2)2}] and an unidentified
calcium species in 1:1 ratio (Scheme 5). The decomposition
occurred possibly through a series of ligand exchange steps
and was complete in THF within 5 min.
The decomposition of
6 in toluene-d8 was slow at low
temperature according to a variable temperature NMR
analysis. Decrease in temperature resulted in splitting of the
SiHMe2 resonances at the coalescence temperature Tc = 253 K
(see ESI). An Eyring plot derived from a line shape analysis
provided the activation parameters as ꢀ
H‡ = 9.7±0.8 kcal mol−1
1
1
and
ꢀ
S‡
=
−
8.0±0.4 cal mol− K− which led to
ꢀ
G‡
=
253K
Figure 5. Molecular structure of 5. Hydrogen atoms except the SiH units are omitted for
clarity. Displacement parameters are drawn at 50% probability. Selected bond
distances (Å): Mg1−N1 1.991(2); Mg1−N2 2.276(2); Mg1−N3 2.209(2); Mg1−N4
2.280(2); Mg1−N5 2.016(2); Si1−H1 1.42(2); Si2−H2 1.36(2).
1
11.7±0.9 kcal mol− at Tc (see ESI). This behavior is similar to
that of the homoleptic [Ca{N(SiHMe2)2}2] in toluene-d8 with
G‡
1
ꢀ
= 9.6 kcal mol− at Tc = 253 K.7 [Ca{N(SiHMe2)2}2] is
253K
trimeric in solution and the decoalescence results from
dynamic Ca Si interactions. The instability of and
substantially negative
S‡ imply that additional processes
other than the intramolecular -agostic interaction might be
responsible for the decomposition at room temperature. A
single crystal X-ray diffraction of could not be obtained.
↼
H−
6
ꢀ
β
6
Several stable and structurally characterized heteroleptic
CaTMDS complexes are known.4c,4d,6b,7-8 VT-NMR spectroscopic
analysis was reported for only two of them which do not show
any decoalescence.4d,7 The instability of
6 compared to
[(L)Ca(HMDS)] contrasts observations by Carpentier et al. that
the phenolate complexes [(LO3)M{N(SiHMe2)2}] (M = Ca, Sr, Ba,
4 | J. Name., 2012, 00, 1-3
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(LO3)H = 2-{1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)- standard
methods.
LH,6a
[Sr(HMDS)2(thf)2]4a
methyl}-4,6-di-tert-butylphenol) with TMDS ligand were [Sr(TMDS)2(thf)2/3],4a [Mg(TMDS)2],10 [(L)M(HMDS)] (M = Mg,
obtained in yield up to 70%, while the corresponding HMDS Ca)6b were synthesized according to the literature procedures.
derivatives were not accessible.4a
HN(SiMe3)2 and HN(SiHMe2)2 were purchased from Gelest and
Silylamines HN(SiMe3)2 and HN(SiHMe2)2 as well as the dried and degassed before storing over molecular sieves inside
macrocyclic polyamine LH are all secondary amines and their the glovebox. 1H, 13C{1H}, and 29Si{1H} NMR spectra were
relative pKa values govern the formation of the amide recorded on a Bruker Avance-III spectrometer at ambient
complexes of magnesium, calcium, and strontium. The lower temperature unless otherwise mentioned. Chemical shifts (
1
δ
in
p
Ka value of HN(SiHMe2)2 (22.6) compared to that of ppm) of the H and 13C{1H} NMR spectra were referenced to
HN(SiMe3)2 (25.8) explains why transamination of HMDS with the residual signals of the deuterated solvents. 29Si{1H} spectra
HN(SiHMe2)2 is facile.4a,9 The relative acidity of LH is also were referenced to an external standard of SiMe4.
critical but a valid comparison is not so trivial due to the Abbreviations for NMR spectra: s (singlet), d (doublet), t
macrocyclic nature of LH. The synthesis and transamination (triplet), q (quartet), sep (septet), br (broad). FT-IR spectra
reactivity pattern of all three metals are different from each were recorded using KBr pellets with an AVATAR 360 FT-IR
other. Both magnesium precursors undergo protonolysis with spectrometer. Elemental analyses were performed on an
LH. The Mg−N(SiMe3)2 bond in [(L)Mg(HMDS)] has the highest elementar vario EL machine. X-ray diffraction data were
basicity and undergoes transamination to give [(L)Mg(TMDS)]. collected on a Bruker APEX II diffractometer. Single crystal
For calcium, while [Ca(HMDS)2] reacted via protonolysis, diffraction data are reported in crystallographic information
[Ca(TMDS)2] readily underwent Si−
Similar to the situation for magnesium, the Ca
H/H
−
N dehydrocoupling. files (cif).
N(SiMe3)2 bond [(L)Sr{N(SiMe3)2}]2 (1). A 5 mL toluene solution of LH (0.077 g,
−
in [(L)Ca(HMDS)] is the most basic site and hence was 0.362 mmol) and [Sr{N(SiMe3)2}2(thf)2] (0.200 g, 0.362 mmol)
transaminated with HN(SiHMe2)2. While [Sr(HMDS)2] behaves was stirred for 2 h at room temperature. Colorless crystals that
like the homologous compounds of magnesium and calcium, precipitated during this time were isolated by filtration and
[Sr(TMDS)2] reacts with LH to give the adduct [(LH)Sr(TMDS)2]. washed with toluene (3 × 5 mL). Drying the solid under
Contrary to magnesium and calcium, the Sr
amide bond in [(L)Sr(HMDS)] is more basic than Sr
probably due to the bridging nature. Thus it is first protonated diffraction were obtained by reactive crystallization from
upon reaction with HN(SiHMe2)2. The resulting intermediate
toluene at room temperature under diluted condition. 1H NMR
is unstable and either releases H2 or undergoes another round (400 MHz, THF-d8): δ −0.07 (s, 18 H, SiMe3), 2.15-2.31 (m, 6 H,
−
N(Me3TACD) vacuum afforded analytically pure
1 (0.135 g, 0.293 mmol, 80.9
−
N(SiMe3)2, % yield) as a colorless powder. Single crystals suitable for X-ray
A
of transamination with excess HN(SiHMe2)2 at the terminal
C
H2), 2.32 (s, 3 H, NMe), 2.39 (s, 6 H, NMe), 2.53-2.58 (m, 2 H,
H2), 2.72-2.82 (m, 4 H, CH2), 3.12-3.22 (m, 4 H, CH2). 13C{1H}
N(SiMe3)2 ligand. Notably, the intramolecular Si−H/H
−N
C
dehydrocoupling occurring at the calcium and strontium NMR (100 MHz, THF-d8):
centers is markedly different from the intermolecular metal (NMe), 52.5 ( H2), 57.0 (
amide-hydrosilane metathesis.2a The
proton clearly NMR (80 Hz, THF-d8): δ −19.4 (SiMe3). Anal. Calcd. for
becomes more acidic upon metal coordination.6f In addition, C18H43N5Si2Sr1: C, 44.26; H, 9.39; N, 15.18. Found: C, 44.28; H,
Si interactions could enhance the hydridicity of the 9.42; N, 15.05.
's. Two other heteroleptic CaTMDS complexes are also [(L)Sr{N(SiHMe2)2}2] (2). A 5 mL solution of
δ
6.5 (SiMe3), 44.5 (NMe), 48.0
C
C
H2), 57.8 ( H2), 63.9 (
C
C
H2). 29Si{1H}
N
H
M↼H−
SiH
n-pentane/THF
known to react with externally added primary amines in a (9:1) of LH (0.073 g, 0.340 mmol) and [Sr{N(SiHMe2)2}2(thf)2/3
]
similar manner.8b
(0.136 g, 0.340 mmol) was stirred for 5 min at room
temperature. Colorless crystals that precipitated during this
time were isolated by filtration and washed with -pentane (3
× 5 mL). Drying under vacuum afforded in analytically pure
n
Conclusions
2
form (0.176 g, 0.311 mmol, 91.5% yield) as a colorless powder.
Single crystals suitable for X-ray diffraction were obtained by
In conclusion, we have synthesized a series of HMDS and
TMDS complexes of magnesium, calcium, and strontium
supported by a tetradentate macrocyclic polyamine. The
systematic study of their synthesis, structure, and reactivity
demonstrates the individuality of these three metals despite
their divalent oxidation state and gradually increasing
electropositive character.
reactive crystallization from n-pentane/THF (9:1) at room
temperature under diluted condition. 1H NMR (400 MHz,
3
0.57 (d, JHH = 2.8 Hz, 24 H, SiHMe2), 1.72-2.45
benzene-d6): δ
(multiple broad multiplets, 16 H, CH2), 2.25 (s, 6 H, NMe), 2.29
1
(m, 3 H, NMe), 5.08 (sept, JSiH = 158 Hz, 1 H, SiHMe2). 13C{1H}
NMR (benzene-d6, 100 MHz):
δ 6.1 (SiHMe2), 43.7 (NMe), 45.3
(NMe), 46.7 (CH2), 53.4 (CH2), 54.0 (
NMR (80 MHz, benzene-d6): δ −27.0 (SiHMe2). IR (KBr, cm− ):
C
H2), 56.0 (
C
H2). 29Si{1H}
1
Experimental
νSiH 2036 (sh), 2006 (s). Anal. Calcd. for C19H54N6Si4Sr: C, 40.27;
H, 9.61; N, 14.83. Found: C, 39.85; H, 9.64; N, 15.08.
General considerations. All reactions were performed under a
dry argon atmosphere using standard Schlenk techniques or in
a glovebox. Prior to use, glassware were dried overnight at 130
°C and solvents were dried, distilled, and degassed using
[{(L)SiMe2N(SiHMe2)}Sr{N(SiHMe2)2}] (3). A solution of
2
(0.150 g, 0.265 mmol) in 1 mL of benzene was heated at 60 ˚C
for 6 h. After cooling, all volatiles were removed under
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DOI: 10.1039/C7DT01727H
ARTICLE
Journal Name
reduced pressure and a colorless solid was obtained. The solid C15H39N5Si2Mg: C, 48.69; H, 10.63; N, 18.93. Found: C, 48.33; H,
was washed with -pentane (3 × 5 mL) and dried under 10.45; N, 19.05.
vacuum to give analytically pure (0.131 g, 0.232 mmol, 87.5 [(L)Ca{N(SiHMe2)2}] (6). To a solution of [(L)Ca{N(SiMe3)2}]
% yield) as a colorless powder. Single crystals suitable for X-ray (0.400 g, 0.968 mmol) in 3 mL of -pentane, a solution of
diffraction were obtained from -pentane diffusion into a HN(SiHMe2)2 (0.129 mg, 0.968 mmol) in 2 mL of -pentane was
concentrated THF solution at
35 ˚C. 1H NMR (400 MHz, added. A colorless solid immediately precipitated upon mixing.
benzene-d6): -pentane (3 × 5 mL).
0.33 (s, 6 H, SiMe2, pendant), 0.54 (d, 3JHH = 2.8 The solid was isolated and washed with
Hz, 12 H, SiHMe2, terminal), 0.58 (d, 3JHH = 2.8 Hz, 6 H, SiHMe2
Drying under vacuum afforded analytically pure (0.320 g,
n
3
n
n
n
−
δ
n
,
6
1
pendant), 1.68-2.71 (multiple broad multiplets, 16 H, CH2), 0.830 mmol, 85.7% yield) as a voluminous colorless solid. H
2.12 (s, 6 H, NMe), 2.19 (s, 3 H, NMe), 5.07 (sept, 1JSiH = 157 Hz, NMR (400 MHz, benzene-d6):
δ 0.57 (br, 12 H, SiHMe2), 1.83-
1
2 H, Si
H
Me2, terminal), 5.44 (sept, JSiH = 173 Hz, 1 H, Si
H
Me2, 3.26 (multiple broad multiplets, 16 H, CH2), 2.33 (s, 6 H, NMe),
4.3 (SiMe2
2.36 (s, 3 H, NMe), 4.97 (sept, 3JHH = 2.8 Hz, 1JSiH = 164 Hz, 2 H,
pendant), 5.9 (SiHMe2, terminal and pendant), 43.7 (NMe), Si 6.7 (SiHMe2),
Me2). 13C{1H} NMR (benzene-d6, 100 MHz):
46.4 (NMe), 46.4 ( H2), 53.8 ( H2), 53.9 ( H2), 56.1 ( H2). 47.0 (NMe), 47.8 (NMe), 50.5 ( H2), 54.2 ( H2), 54.4 ( H2), 60.6
29Si{1H} NMR (80 MHz, benzene-d6): δ −10.4 (SiMe2, pendant), H2). 29Si{1H} NMR (80 MHz, benzene-d6): δ −27.2 (SiHMe2). IR
27.5 (SiHMe2, terminal),
pendant). 13C{1H} NMR (benzene-d6, 100 MHz):
δ
,
H
δ
C
C
C
C
C
C
C
(
C
1
−
−
31.1 (SiHMe2, pendant). IR (KBr, (KBr, cm− ): νSiH 2043 (sh), 2007 (s). Anal. Calcd. for
1
cm− ): νSiH 2106 (br, sh), 2036 (s), 1977 (br, s), 1903 (br, sh). C15H39N5Si2Ca: C, 46.70; H, 10.19; N, 18.16. Found: C, 46.44; H,
Anal. Calcd. for C19H52N6Si4Sr: C, 40.42; H, 9.28; N, 14.88. 10.63; N, 18.37.
Found: C, 39.98; H, 9.36; N, 14.64.
[{(L)SiMe2N(SiHMe2)}Sr{N(SiMe3)2}] (4). A suspension of
1
Acknowledgements
(0.200 g, 0.434 mmol) in 3 mL of n-pentane was mixed with
HN(SiHMe2)2 (0.056 g, 0.434 mmol) and stirred at room
temperature for 24 h. Removing all volatiles under reduced
We thank the Deutsche Forschungsgemeinschaft through the
International Research Training Group “Selectivity in Chemo-
and Biocatalysis” for financial support and the Alexander von
Humboldt Foundation for a fellowship to D. M. We also thank
K.-N. Truong and Prof. U. Englert for collecting the X-ray data.
pressure gave a colorless solid. The solid was washed with
pentane (3 × 5 mL) and dried under vacuum to give analytically
pure (0.240 g, 0.405 mmol, 93.3 % yield) as a colorless
powder. Single crystals suitable for X-ray diffraction were
obtained by diffusion of -pentane into a concentrated THF
solution at 0.32 (s, 6
35 ˚C. 1H NMR (400 MHz, benzene-d6):
n-
4
n
−
δ
Notes and references
H, pendant SiMe2), 0.44 (s, 18 H, SiMe3), 0.60 (d, 3JHH = 2.9 Hz,
6 H, pendant SiHMe2), 1.59-2.69 (multiple broad multiplets, 16
1
(a) S. Harder, Chem. Rev., 2010, 110, 3852-3876; (b) A. G. M.
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=
173 Hz, 1 H, pendant Si
MHz): 4.3 (pendant SiMe2), 6.0 (pendant SiHMe2), 7.5
(SiMe3), 45.7 (NMe), 46.02 (NMe), 46.5 ( H2), 53.9 ( H2), 54.3
H2), 56.5 (
H2). 29Si{1H} NMR (80 MHz, benzene-d6): δ −10.0
(pendant SiMe2), 17.7 (terminal SiMe3), 30.2 (pendant
H
Me2). 13C{1H} NMR (benzene-d6, 100
δ
C
C
(C
C
−
−
1
SiHMe2). IR (KBr, cm− ): νSiH 2000 (s). Anal. Calcd. for
C21H56N6Si4Sr: C, 42.56; H, 9.52; N, 14.18. Found: C, 42.22; H,
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n-pentane was stirred for 30 min at room temperature. All
volatiles were removed under reduced pressure and a
colorless solid was obtained. This was recrystallized from a
concentrated n-pentane solution at −35 ˚C. The crystalline
solids were isolated from the mother liquor and dried under
3
(a) R. Anwander, O. Runte, J. Eppinger, G. Gerstberger, E.
Herdtweck and M. Spiegler, J. Chem. Soc., Dalton Trans.,
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vacuum to give analytically pure 5 (0.220 g, 0.595 mmol, 86.0
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3
0.51 (d, JHH = 3.0 Hz, 12 H, SiHMe2), 1.52-1.59 (m, 2 H, CH2),
δ
1.62-1.68 (m, 2 H, CH2), 1.89-1.95 (m, 5 H, NMe and CH2), 2.22-
2.30 (m, 10 H, NMe and CH2), 2.82-2.89 (m, 2 H, CH2), 3.13-
3.20 (m, 2 H, CH2), 3.34-38 (m, 2 H, CH2), 5.03 (sept, 3JSiH = 173
Hz, 1 H, Si
H
Me2). 13C{1H} NMR (100 MHz, benzene-d6):
δ
(SiHMe2), 44.1 (NMe), 46.7 (NMe), 50.4 (CH2), 52.9 (CH2), 55.2
5.4
Anwander, Inorg. Chem., 2011, 50, 7217-7228; (f) T.
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(
C
H2), 63.2 (
C
H2). 29Si{1H} NMR (80 MHz, benzene-d6): δ −21.4
1
(
SiHMe2). IR (KBr, cm− ): νSiH 2045 (s). Anal. Calcd. for
6 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C7DT01727H
TOC
Group 2 metal (Mg, Ca, Sr) silylamides supported by a cyclen-derived macrocyclic
polyamine
Debabrata Mukherjee,a Satoru Shirase,b Klaus Beckerle,a Thomas P. Spaniol,a Kazushi Mashima,b and
Jun Okudaa,*
Me
Me
N
N
Sr(HMDS)2
Sr(TMDS)2
−HMDSH
NH
N
Me
(LH)
HMDS = N(SiMe3)2
TMDS = N(SiHMe2)2
[M{N(SiMe3)2}2] and [M{N(SiHMe2)2}2] (M = Mg, Ca, Sr) reacted with the macrocyclic
NNNN-type polyamine (Me3TACD)H (LH) to give different types of products, especially
with the
β-SiH function, exhibiting the individuality of these alkaline earths within the
identical ligand sets.