Si-N Heterodehydrocoupling with a Lanthanide Compound

Article abstract of DOI:10.1021/acs.organomet.8b00372

[La{N(SiMe₃)₂}₃THF₂] (1) is an effective precatalyst for the heterodehydrocoupling of silanes and amines. Coupling of primary and secondary amines with aryl silanes was achieved with a loading of 0.8 mol % of [L

Full text of DOI:10.1021/acs.organomet.8b00372

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Si−N Heterodehydrocoupling with a Lanthanide Compound
Michael P. Cibuzar and Rory Waterman*
Department of Chemistry, University of Vermont, Burlington, Vermont 05405-0125, United States
S
* Supporting Information
ABSTRACT: [La{N(SiMe3)2}3THF2] (1) is an effective precatalyst for
the heterodehydrocoupling of silanes and amines. Coupling of primary and
secondary amines with aryl silanes was achieved with a loading of 0.8 mol
% of [La{N(SiMe3)2}3THF2]. With primary amines, generation of tertiary
and sometimes quaternary silamines was facile, often requiring only a few
hours to reach completion, including new silamines Ph3Si(nPrNH) and
Ph3Si(iPrNH). Secondary amines were also available for heterodehy-
drocoupling, though they generally required longer reaction times and, in
some instances, higher reaction temperatures. This work expands upon the
utility of f-block complexes in heterodehydrocoupling catalysis.
ligands in coordination chemistry.32,33 Heterodehydrocoupling
INTRODUCTION
■
is an attractive avenue for silamine preparation versus salt
Catalysis is a critical step in sustainable processes, but the
metathesis because the H2 byproduct is easily separated and
relative abundance of the catalyst is a key factor in its overall
simplifies workup. However, selectivity in dehydrocoupling is
utility.1 A common approach for reducing the demand for
also challenging as an excess of amine is required. Recently,
precious metals in catalysis is to replace them with base metals.
improved selectivity has been achieved with dehydrocoupling
This methodology has met with some success, but significant
catalysts, though it remains challenging without designer
challenges, including achieving comparable turnover metrics
ligands.34,35 Overall, dehydrocoupling is a potentially more
with similar catalyst loadings, remain. In fewer cases, rare earth
atom economic process for the generation of silamines, which
metals have been used instead of base metals. Despite being
argues for its continued study.
labeled as rare earth elements, some lanthanides, lanthanum,
The primary aim of this work was an investigation of a more
cerium, and neodymium, for example, are more abundant in
earth-abundant, simple lanthanum compound for this trans-
the earth’s crust than some base metals such as cobalt.2,3
formation. Due in part to commercial availability, the
Unsurprisingly, exploration of lanthanide-based catalysis has
lanthanum(III) derivative, [La{N(SiMe3)2}3], became the
been an exciting area of growth.4
focus of this study, which has shown excellent activity in
Organolanthanides have been shown to be viable catalysts
different main group bond-forming transformations.14,36
for a variety of transformations with some critical advances in
alkene polymerization,5−10 but main group relevant trans-
RESULTS AND DISCUSSION
formations including dehydrocoupling11 and heterofunctional-
■
Treatment of lanthanum trichloride with 3 equiv of lithium
ization12−16 have been reported, as well. In 1999, Takaki and
bis(trimethylsilyl)amide in THF for 6 h at ambient temper-
co-workers first demonstrated heterodehydrocoupling of
ature affords the five-coordinate compound, [La{N-
(SiMe3)2}3THF2] (1; eq 1), as a colorless powder upon
silanes with amines using [Yb(η2-Ph2CNAr)(hmpa)n] (Ar =
2, 6-diisopropylphenyl, hmpa = hexamethylphosphoramide),
focusing on quaternary silamines from tertiary silanes.17 In
2012, Cui and co-workers demonstrated that a different
ytterbium catalyst, [IMesYb{N(SiMe3)2}2] (IMes = 1,3-
dimesitylimidazol-2-ylidene), could successfully heterodehy-
drocouple primary and secondary silanes with amines.18 Sadow
has expanded upon Si−N coupling with lanthanides, reporting
that [Ln{C(SiHMe2)3}2ImtBu] (Ln = Yb, Sm; ImtBu = 1,3-di-
tert-butylimidazol-2-ylidene) are also active catalysts for this
transformation.19 To date, however, there are no reports of
more abundant lanthanides catalyzing the heterodehydrocou-
pling of silanes and amines.
sublimation. Alternatively, 1 can be prepared by dissolving
commercially available La{N(SiMe3)2}3 in THF followed by
removal of solvent under reduced pressure. The THF-solvated
species has increased solubility in a variety of organic solvents,
Special Issue: Organometallic Complexes of Electropositive Ele-
ments for Selective Synthesis
Silamines are utilized as mild, sterically hindered bases,20
protecting groups for silanes21−23 and amines,24,25 and
silylating reagents.26−29 Polysilazanes are precursors for
silicon-nitride-based ceramics.30,31 Silamines are also important
Received: May 31, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00372
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Article
including benezene-d6 and thus was the preferred complex for
this study.
Tertiary silanes were the most challenging substrates for this
system. Reaction of 2:1 mixture of n-propylamine and
triphenylsilane with 0.8 mol % of 1 at ambient temperature
affords Ph3Si(nPrNH) over a period of 24 h. Conducting this
reaction at 60 °C, however, gave complete conversion in less
than 3 h. These initial reactions prompted a broader
investigation, and a family of silanes and amine substrates
were screened based on their appearance in previous
studies.18,19,34,37−40
More sterically encumbering amine substrates, isopropyl-
amine, aniline, and tert-butylamine, were tested (Table 2).
Similar to the n-propylamine reactions, optimal conversions
with isopropylamine required an increased amine/silane ratio.
Reactions with aniline and tert-butylamine with phenylsilane
required a slight excess of amine to achieve quantitative
conversions. For secondary silanes, reaction at 60 °C provided
optimal product formation in less than 2 h. In reactions with
aniline, clean formation of the tertiary and quaternary silane
products was possible from secondary silane substrates,
depending only on reaction times.
Due to the steric pressure around silicon, quaternary
silamines have been challenging to make by dehydrocoupling.
A 2:1 mixture of isopropylamine with triphenylsilane in the
presence of 0.8 mol % of 1 at 60 °C gives Ph3Si(iPrNH)
quantitatively in 1.5 h (Table 2, entry 4). Under the same
conditions, the analogous reaction with n-propylamine and
triphenylsilane gave Ph3Si(nPrNH) quantitatively in 2.75 h
(Table 1, entry 4; eq 3). To the best of our knowledge, this is
Compound 1 was tested as a Si−N heterodehydrocoupling
catalyst. Treatment of a 3:1 mixture of n-propylamine and
phenylsilane with 5 mol % of 1 at 25 °C resulted in immediate
effervescence of H2. In fewer than 10 min, PhSi(nPrNH)3 was
produced, but additional ill-defined byproducts were also
present. Reducing the catalyst loading to 0.8 mol % and
increasing the amine/silane ratio to 4:1 increased the
conversion to the desired product to 85% with only a slight
increase in reaction time (Table 1). Further increasing the
amine/silane ratio had no significant impact on yield.
Table 1. Coupling of Silanes with n-Propylamine Catalyzed
a
by [La{N(SiMe3)2}3THF2] (1)
b
entry
silane
equiv
product
conversion
c
1
PhSiH3
PhSiH3
MePhSiH2
Ph2SiH2
Ph3SiH
3
4
4
4
2
PhSi(nPrNH)3
PhSi(nPrNH)3
MePhSi(nPrNH)2
Ph2Si(nPrNH)2
Ph3Si(nPrNH)
40−50
85
96
100
100
2
3
4
d
5
a
Conditions: 0.8 mol % of 1 at 25 °C in benzene-d6 solution.
Products were characterized by H, 29Si, and H−29Si HSQC NMR
1
1
spectroscopy. Conversion determined by integration of 1H NMR
b
c
spectra. Equivalents of amine per equivalent of silane. 5 mol % of 1.
d
t = 60 °C.
Secondary silanes were also effective substrates. Reaction of
a 4:1 mixture of n-propylamine and methylphenylsilane with
0.8 mol % of 1 provided the quaternary silane, MePhSi-
(nPrNH)2, in 96% conversion, as measured by 1H NMR
spectroscopy (Scheme 1). Trace amounts of a byproduct were
Scheme 1. Dehydrocoupling of Methylphenylsilane and n-
Propylamine by 1 (Table 1, entry 2)
the first time Ph3Si(nPrNH) and Ph3Si(iPrNH) have been
synthesized by any method. Both aniline and tert-butylamine
reacted with triphenylsilane but required forcing conditions.
Increased catalyst loading (4 mol % of 1), temperature (90
°C), and reaction times (36−48 h) were needed for even
minimal conversions. Although NMR spectra demonstrated
consumption of silane in all cases, low conversions thwarted
product identification. Ultimately, coupling with triphenylsi-
lane was largely dependent on the identity of the amine.
Generation of a quaternary silamine from a primary or
secondary silane is also possible. By slightly increasing the
amine/silane ratio to 4:1 and heating the reaction to 90 °C,
reaction of aniline and phenylsilane in the presence of 0.8 mol
% of 1 provides quantitative conversion to PhSi(PhNH)3
(Table 2, entry 6). Due to the increased steric pressure of
aniline over isopropylamine, the reactions with secondary
silanes take considerably longer. MePhSi(PhNH)2 and PhSi-
(PhNH)3 have been synthesized before but not by
heterodehydrocoupling.41,42
observed in the 1H and 1H−29Si HSQC NMR spectra at δ 5.19
and δ −12.6, respectively. Although we cannot provide
n
definitive data, this product is most consistent with PrN-
i
(MePhSiH)2 based on Sadow’s reported preparation of PrN-
(MePhSiH)2 by magnesium-catalyzed reaction of 2 equiv of
methylphenylsilane with isopropylamine.34 Increasing the
amine/silane ratio continued to provide the quaternary silane
with the same byproduct. However, treatment of a 4:1 solution
of n-propylamine and diphenylsilane with 0.8 mol % of 1
produced the expected product, Ph2Si(nPrNH)2, quantitatively,
according to NMR spectroscopy.
Reactivity with secondary amines was also largely dependent
on the identity of the amine. Diethylamine was readily coupled
with primary and secondary silanes (Table 3). Use of a bulkier
amine, bis(trimethylsilyl)amine, required up to 24 h reaction
time for complete conversion under the conditions tested
(Table 3). Coupling of tertiary silanes with secondary amines
was not achieved under conditions screened. In reactions
between secondary silanes and bis(trimethylsilyl)amine, even
B
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a
Table 2. Coupling of Silanes with More Sterically Encumbered Amines by 1
b
c
entry
silane
amine
equiv
temp (°C)
product
conversion
time (h)
d
1
2
PhSiH3
iPrNH2
iPrNH2
iPrNH2
iPrNH2
PhNH2
PhNH2
PhNH2
PhNH2
PhNH2
PhNH2
tBuNH2
tBuNH2
tBuNH2
6
25
25
25
60
25
90
60
60
60
60
25
60
60
PhSi(iPrNH)3
90
0.5
0.5
0.5
1.5
0.5
24
3
36
1.5
72
1.5
3
MePhSiH2
Ph2SiH2
Ph3SiH
4
MePhSi(iPrNH)2
Ph2Si(iPrNH)2
Ph3Si(iPrNH)
100
100
100
100
100
100
76
100
100
100
100
100
3
4
4
2
5
6
7
8
PhSiH3
PhSiH3
3.1
4
Ph(PhNH)2SiH
PhSi(PhNH)3
MePhSiH2
MePhSiH2
Ph2SiH2
Ph2SiH2
PhSiH3
2.1
2.1
2.1
2.1
3.1
2.1
2.1
MePh(PhNH)SiH
MePhSi(PhNH)2
Ph2(PhNH)SiH
Ph2Si(PhNH)2
Ph(tBuNH)2SiH
MePh(tBuNH)SiH
9
10
11
12
13
MePhSiH2
Ph2SiH2
Ph2(tBuNH)SiH
1.5
a
b
d
1
1
Conditions: 0.8 mol % of 1 at T °C in benzene-d6 solution. Products were characterized by H, 29Si, and H−29Si HSQC NMR spectroscopy.
c
Equivalents of amine per equivalent of silane. For conversions less than 100%, reactions were not complete (i.e., no byproducts observed).
Mixture of several silamines.
a
Table 3. Coupling of Silanes and Secondary Amines by 1
b
entry
silane
amine
Et2NH
Et2NH
Et2NH
Et2NH
equiv
temp (°C)
product
conversion
time (h)
1
2
3
4
PhSiH3
PhSiH3
MePhSiH2
Ph2SiH2
Ph3SiH
3.1
3.1
2.1
2.1
1.1
3.1
2.1
2.1
1.1
60
60
90
90
90
90
90
90
90
Ph(Et2N)SiH2
Ph(Et2N)2SiH
MePh(Et2N)SiH
Ph2(Et2N)SiH
none
97
97
100
100
0
100
0
0
0.5
24
1.5
1.5
72
24
24
24
24
c
5
Et2NH
6
PhSiH3
HN(SiMe3)2
HN(SiMe3)2
HN(SiMe3)2
HN(SiMe3)2
Ph{N(SiMe3)2}SiH2
none
c
7
MePhSiH2
Ph2SiH2
Ph3SiH
c
8
c
none
none
9
0
a
1
1
Conditions: 0.8 mol % of 1 at T °C in benzene-d6 solution. Products were characterized by H, 29Si, and H−29Si HSQC NMR spectroscopy.
b
c
1
Conversion was determined by integration of H NMR spectra. Equivalents of amine per equivalent of silane. 4 mol % of 1.
after extended reaction times (24 h or longer), increased
catalyst loading (4%), and higher temperatures (90 °C), no
consumption of starting materials was observed. Based on
these trends, the decrease of reactivity with bis(trimethylsilyl)-
amine is likely a result of increased steric crowding at nitrogen
or decreased basicity/nucleophilicity compared to diethyl-
amine.
Competitive dehydrocoupling of the bis(trimethylsilyl)-
amide ligands on 1 and less sterically hindered amines was
not observed except for the reaction of diethylamine and
phenylsilane. In this reaction, approximately 2% conversion to
Ph{N(SiMe3)2}SiH2 was observed.18 Neither MePh{N-
(SiMe3)2}SiH nor Ph2{N(SiMe3)2}SiH were observed in the
reaction between methylphenylsilane or diphenylsilane with
diethylamine, respectively.43 In addition, there are no cases in
which bis(trimethylsilyl)amine was coupled with silamine
products.
It is likely that the mechanism of dehydrocoupling with 1 is
similar to that which Sadow and co-workers proposed for
[ToMMgMe] (ToM = tris(4,4-dimethyl-2-oxazolinyl)-
phenylborate).34 The observation of bis(trimethylsilyl)amine
in all reactions by NMR spectroscopy suggests in situ amide
exchange at 1 that affords the presumed active catalyst,
N(SiMe3)3−x(RNH)xLa(THF)z (z = 0−2). It is also possible
that one or both THF molecules may dissociate in this step. It
is difficult to differentiate bound versus free THF in this
system by 1H NMR spectroscopy. Then Si−N bond formation,
by either amine attack at silicon or σ-bond metathesis, ensues
to generate a hydride intermediate. A Ln−H bond would be
primed to react with another equivalent of the amine to
regenerate the catalyst. The difference between reactions of
methylphenyl and diphenylsilane provides some insight into
the mechanism of the Si−N bond-forming step. Despite being
more sterically crowded, the reaction time to completion for
more electrophilic diphenylsilane with aniline and tert-
butylamine was shorter than that with methylphenylsilane
(NB: This reaction time is, at best, merely a proxy for relative
rate; Table 2, entries 7, 9, 13, and 14). As such, these
observations give a preliminary indication that nucleophilic
amide attack on silicon followed by rapid β-hydride transfer to
lanthanum may be more likely than σ-bond metathesis.
To better compare the activity of 1 to that of the other
lanthanide catalysts, turnover number (TON) and turnover
frequency (TOF) were calculated. Turnover frequency was
calculated using total reaction time. We acknowledge that total
reaction time, rather than initial rate, significantly under-
estimates the activity, but these data are available, providing a
benchmark to compare catalysts.44 A second feature to
consider in the dehydrocoupling of silanes with amines is
selectivity. As a result, two different TOFs were calculated. The
first is the traditional calculation:
mols product
(mols catalyst) × (reaction time)
TOF =
(4)
This calculation describes the turnover frequency of the
reaction as it relates to selectivity for a given product. In this
C
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calculation, moles of product are defined as only the primary
reaction product. A second turnover frequency, TOFSiN, was
calculated to approximate the total Si−N coupling events for
each catalyst, which approximates overall activity. This is
calculated by
but they are more selective and therefore continue to have
utility in a variety of applications.
Similar trends exist with more sterically encumbered primary
and secondary amines (Table 5). In bulkier systems, reactions
catalyzed by 2 are complete in approximately the same amount
of time as that for 1. Again, the reason for the large differences
in TOF and TOFSiN is catalyst loading. Cui and co-workers
catalyze reactions with 5 mol % of 2, whereas 1 can be utilized
with loadings less than 1 mol %. The result is approximately a
5-fold increase in TOF and TOFSiN for 1 versus 2. Analyzing
TOF and TOFSiN becomes further convoluted when reaction
conditions change. Appropriate TOF and TOFSiN comparisons
for reactions of diethylamine with phenylsilane or diphenylsi-
lane are difficult because the reaction temperatures are
different for all catalysts. Overall, 1 has generally high TOF
and TOFSiN with mild reaction conditions.
There are several possible explanations why 1 is an active
catalyst. Many d0 metal complexes have demonstrated the
capacity to be Si−N heterodehydrocoupling catalysts.34,45−52
The decreased electronegativity of these catalysts is likely an
important contributor in their reactivity. This trend is similar
in the f-block, where La and Yb are among the least
electronegative elements. One potential difference among
these compounds are the carbene ligands common to
compounds 2 and 3, whereas 1 lacks such strongly electron-
donating ligands. The relative donation to the metal could be
an important factor in either N−H bond activation or N−Si
bond formation. Similarly, the oxidation state of these catalysts
likely has a large effect on reactivity. Compounds 2 and 3 are in
the +2 oxidation state, whereas 1 is in its +3 oxidation state.
Similar to having more donating ligands, a decreased oxidation
state may slow N−H activation to regenerate the active
catalyst. An alternative rationale for increased activity of 1
could be the potential difference in the number of active sites.
Up to three bis(trimethylsilyl)amido ligands could be labilized
at 1. Presuming the ancillary ligand of 2 and 3 does not
dissociate, there would only be up to two actives sites. Further
investigation of these differences may yield design features for
future catalysts.
In summary, 1, which is easily obtained in a one-step
synthesis or by addition of THF to commercial [La{N-
(SiMe3)2}3], is perhaps the most active lanthanide-based
precatalyst for the heterodehydrocoupling of amines and
silanes. With catalyst loadings below 1 mol %, dehydrocoupling
was efficient in most cases. Coupling silanes with propylamines
occurred on the minute time scale, though sometimes yield
was lowered due to generation of poorly identified products.
Generating quaternary silamines from triphenylsilane with
propylamines was also achieved for the first time. Reactivity
with bulkier amines was also facile, making tertiary silamines
readily. In some cases, even new silamines were generated.
Lastly, less sterically bulky secondary amines were readily
transformed into silamines in the presence of 1 and primary
and secondary silanes.
(mols product) × (Si−N bonds formed)
TOFSiN
=
(mols catalyst) × (reaction time
(5)
The TOFSiN value speaks to the Si−N coupling potential of
each reaction. Naturally, this term somewhat underappreciates
the ability of these catalysts to selectively make certain
silamines, which is a general goal of this catalysis. It is critical
to note that these terms are highly related, essentially
rephrasing the same activity values, but these do allow for a
comparison between activity and selectivity. With these two
terms, however, some general comparative statements can be
made about lanthanide-based amine−silane heterodehydro-
coupling catalysts (Figure 1).
Figure 1. Lanthanide-based Si−N heterodehydrocoupling catalysts.
Compound 1 and the reported lanthanide-based catalysts,
Cui’s [IMesYb{N(SiMe3)2}2] catalyst (2)18 and Sadow’s
[Ln{C(SiHMe2)3}2ImtBu] (Ln = Yb (3a), Sm (3b))
catalysts,19 demonstrate excellent reactivity in the coupling of
silanes with isopropylamine (Table 4). For the generation of
Table 4. TON and TOFs of Lanthanum-Based Si−N
i
Heterodehydrocoupling Catalysts with PrNH2
a
a
entry
silane
catalyst
product
TON
TOF
225
TOFSiN
b
1
2
3
4
5
6
7
PhSiH3
PhSiH3
PhSiH3
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
1
2
PhSiR3
PhSiR3
PhSiR3
Ph2SiR2
Ph2RSiH
Ph2RSiH
Ph2RSiH
337.5
59.4
37.8
250
20
675
10
378
500
20
c
3.3
c
3a
126
250
20
<1
<1
b
1
2
c
c
3a
8.7
8.8
<1
<1
c
3b
a
b
c
Per hour, 2,18 3a,b.19 Catalyst loading = 0.8 mol %. Catalyst
loading = 5 mol %.
PhSi(iPrNH)3, it is evident that 1 is the most active catalyst,
nearly doubling the TOF and TOFSiN as compared to the next
most active catalyst. Compared to 3a and 3b, 2 is more active
for coupling secondary silanes with amines. In the reaction
between diphenylsilane and isopropylamine, the monoaddition
product, Ph2(iPrNH)SiH, is generated by 2, 3a, and 3b with
TOFs of 20, <1, and <1, respectively. The double-addition
product, Ph2Si(iPrNH)2, is generated by 1 with a TOF of 250,
an order of magnitude greater than that of 2. Though high
TOF is desirable, selectivity is also of high utility. When the
ratio of amine to silane approaches unity, selectivity decreases
for 1 (vide supra). The TOFs may be lower for 2, 3a, and 3b,
EXPERIMENTAL SECTION
■
General Information. All manipulations were performed under a
nitrogen atmosphere with dry, oxygen-free solvents using an M. Braun
glovebox or standard Schlenk techniques. Benzene-d6 was purchased
from Cambridge Isotope Laboratory and then degassed and dried
over NaK alloy. Tetrahydrofuran was dried over sodium and vacuum
transferred. NMR spectra were recorded with a Bruker AXR 500 MHz
or Varian 500 MHz spectrometer. Reported 1H NMR resonances are
D
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Table 5. Coupling of Amines with PhSiH3 and Ph2SiH2
a
a
entry
catalyst
loading (mol %)
amine
product
TON
TOF
TOFSiN
1
2
3
1
0.8
5
tBuNH2
tBuNH2
tBuNH2
tBuNH2
tBuNH2
tBuNH2
Et2NH
Et2NH
Et2NH
Et2NH
Et2NH
Et2NH
Et2NH
Ph(tBuNH)2SiH
Ph(tBuNH)2SiH
Ph(tBuNH)2SiH
Ph2(tBuNH)SiH
Ph2(tBuNH)SiH
Ph2(tBuNH)SiH
Ph(Et2N)SiH2
Ph(Et2N)2SiH
Ph(Et2N)2SiH
Ph(Et2N)2SiH
Ph2(Et2N)SiH
Ph2(Et2N)SiH
Ph2(Et2N)SiH
250
40
83
20
167
40
2
2
3a
1
5
36.8
125
20
1.2
b
4
0.8
5
83
20
<1
242
20
1
83
20
<1
243
40
2
5
6
2
3a
1
2
3a
3b
1
10
0.8
5
5
5
0.8
5
5
8.7
b
7
8
9
10
11
12
13
121
40
32.8
32.4
125
20
1
2
c
83
20
<1
83
20
<1
2
3a
8.2
a
b
c
Per hour, 2,18 3a,b.19 Reaction performed at 60 °C. Reaction performed at 90 °C.
referenced to the residual solvent resonance (benzene-d6 = δ 7.16).
ESI-mass spectra were collected on an AB-Sciex 4000 QTrap Hybrid
triple quadrupole/linear ion trap mass spectrometer. IR data were
collected on a Bruker Alpha FTIR spectrometer as neat samples.
Phenylsilane (Oakwood Chemicals), methylphenylsilane (Sigma-
Aldrich), diphenylsilane (Acros Organics), and triphenylsilane
(Gelest) were used as received. N-Propylamine (Sigma-Aldrich),
isopropylamine (Alfa Aesar), tert-butylamine (Alfa Aesar), aniline
(Sigma-Aldrich), and diethylamine (Acros Organics) were dried by
being stirred over calcium hydride followed by distillation. Bis-
(trimethylsilyl)amine (Acros Organics) was used as received.
Preparation of Ph3Si(iPrNH). Isopropylamine (38.1 mg, 0.644
mmol) and triphenylsilane (83.9 mg, 0.322 mmol) in 0.5 mL of
benzene-d6 were added to 1 (2 mg, 2.6 × 10−3 mmol). The reaction
was heated at 60 °C. Over 1.5 h, Ph3Si(iPrNH) was observed in 100%
yield. Volatiles were removed, and the residue was dissolved in
hexanes. The hexanes solution was filtered through a bed of Celite
and concentrated until the first signs of precipitation. The hexanes
solution was warmed until all solids redissolved. The solution was
then cooled to −20° for 24 h. The resulting colorless precipitate was
isolated by decanting the hexanes solution and washing with minimal,
cold hexanes. Ph3Si(iPrNH) was isolated as a white solid in 93% yield.
1H NMR (benzene-d6, 500 MHz): δ 7.72 (m, 6H), 7.22 (m, 9H),
3.14 (m, 1H), 0.96 (d, 6H), 0.92 (br, 1H). 13C NMR (benzene-d6,
126 MHz): δ 136.8, 136.0, 129.7, 128.1, 43.9, 27.8. 29Si NMR
(benzene-d6, 99 MHz): δ −17.86. IR (neat, cm−1): 3387, 3065, 2955,
2924, 2863, 1427, 1379, 1165, 1111, 1017, 871, 739, 699, 523, 497.
MS (ESI): 318.2.
Preparation of MePhSi(PhNH)2. Dichloromethylphenylsilane
(0.511g, 2.67 mmol) and aniline (1.0 g, 10.7 mmol) were stirred in
15 mL of diethyl ether for 24 h. The diethyl ether solution was filtered
through a bed of Celite and concentrated until the first signs of
precipitation. The hexanes solution was warmed until solids
redissolved. The solution was then cooled to −20 °C for 24 h. The
resulting colorless precipitate was isolated by decanting the hexanes
solution and washing with minimal, cold hexanes. MePhSi(PhNH)2
was isolated as colorless block crystals in 47% yield. 1H NMR
(benzene-d6, 500 MHz): δ 7.61 (m, 2H), 7.16 (m, 3H), 7.05 (m, 4H),
6.73 (m, 2H), 6.69 (m, 4H), 3.52 (s, 2H), 0.45 (s, 3H). 13C NMR
(benzene-d6, 126 MHz): δ 146.3, 136.2, 134.4, 130.5, 129.6, 128.5,
119.2, 117.4. 29Si NMR (benzene-d6, 99 MHz): δ −19.80. IR (neat,
cm−1): 3375, 3041, 1599,1497, 1376, 1284, 1114, 902, 751, 692, 471.
MS (ESI): 305.2.
[La{N(SiMe3)2}3THF2]53 (1). Over 20 min, lithium bis-
(trimethylsilyl)amide (4.092 g, 24.45 mmol) in 25 mL of THF was
slowly added to LaCl3 (2.000 g, 8.15 mmol) in 25 mL of THF. The
reaction was stirred for 6 h. Solvent was removed, and the residue was
extracted with hexanes. Removal of solvent and vacuum sublimation
at 80−90 °C provided the product as a colorless powder in 60% yield
1
(3.735 g, 4.89 mmol). H NMR (benzene-d6, 500 MHz): δ 3.64 (m,
8H), 1.26 (m, 8H), 0.37 (s, 54H).
Catalysis Experiments. All reactions were conducted using a J-
Young type polytetrafluoroethylene-valved NMR tube in benzene-d6
1
solution. Upon obtaining an initial H NMR spectrum, the reaction
mixture was placed in an oil bath at the listed temperature. All NMR
spectra were collected at 25 °C.
General Method for Heterodehydrocoupling Reactions. In a
N2-filled drybox, appropriate amounts of an amine and silane were
measured and mixed in ca. 0.5 mL of benzene-d6. This solution was
then pipetted into a vial containing 1. The solution was quickly
transferred into a J-Young-type polytetrafluoroethylene-valved NMR
tube. An initial NMR spectrum was collected, and then the sample
was placed in an oil bath at the listed temperature. The reaction was
monitored by NMR spectroscopy until reactivity had ceased.
Preparation of Ph3Si(nPrNH). n-Propylamine (38.1 mg, 0.644
mmol) and triphenylsilane (83.9 mg, 0.322 mmol) in 0.5 mL of
benzene-d6 were added to 1 (2 mg, 2.6 × 10−3 mmol). The reaction
was then heated at 60 °C. Over 2.75 h, Ph3Si(nPrNH) was produced
in 100% yield. Volatile materials were removed under reduced
pressure, and the resultant colorless residue was dissolved in hexanes.
The hexanes solution was filtered through a bed of Celite and
concentrated until the first signs of precipitation. The hexanes
solution was warmed until all solid was dissolved. The solution was
then cooled to −20 °C for 24 h. The resulting colorless precipitate
was isolated by decanting the hexanes solution and washing with
minimal, cold hexanes. Ph3Si(nPrNH) was isolated as a white solid in
Preparation of PhSi(PhNH)3. Phenylsilane (113.3 mg, 1.005
mmol) and aniline (389.9 mg, 4.19 mmol) in 0.5 mL of benzene-d6
were added to 1 (8 mg, 1.05 × 10−2 mmol). The reaction was heated
at 90 °C for 24 h. Solvent was removed, and the colorless solid was
washed with pentane. PhSi(PhNH)3 was collected as a colorless solid
in 86% yield. 1H NMR (benzene-d6, 500 MHz): δ 7.78 (m, 2H), 7.13
(m, 1H), 7.08 (m, 2h), 7.02 (m, 6H), 6.74 (m, 9H), 3.84 (s, 3H). 13C
NMR (benzene-d6, 126 MHz): δ 145.5, 134.9, 134.0, 130.9, 129.6,
128.6, 119.7, 117.6. 29Si NMR (benzene-d6, 99 MHz): δ −41.47. IR
(neat, cm−1): 3371, 3042, 1599, 1496, 1475, 1383, 1280, 1118, 905,
890, 752, 692, 490, 464. MS (ESI): 382.2.
1
96% yield. H NMR (benzene-d6, 500 MHz): δ 7.72 (m, 6 H), 7.22
ASSOCIATED CONTENT
* Supporting Information
■
(m, 9 H), 2.85 (q, 2 H), 1.31 (sextet, 2 H), 0.99 (br, 1 H), 0.71 (t, 3
H). 13C NMR (benzene-d6, 126 MHz): δ 136.5, 136.0, 129.8, 128.1,
44.8, 27.8, 11.4. 29Si NMR (benzene-d6, 99 MHz): δ 16.48. IR (neat,
cm−1): 3402, 3066, 2954, 2922, 2852, 1427, 1396, 1110, 1008, 830,
736, 698, 521, 498. MS (ESI): 318.2.
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00372.
E
DOI: 10.1021/acs.organomet.8b00372
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Experimental details, characterization data and reaction
Article
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AUTHOR INFORMATION
Corresponding Author
*E-mail: rory.waterman@uvm.edu.
ORCID
Rory Waterman: 0000-0001-8761-8759
Notes
The authors declare no competing financial interest.
■
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ACKNOWLEDGMENTS
■
This work was funded by the U.S. National Science
Foundation (CHE-1565658). The authors thank Monika
Ivancic for NMR spectroscopy assistance, and Bruce O’Rourke
for MS acquisition.
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