1,4-Dihydropyridyl complexes of magnesium: Synthesis by pyridine insertion into the magnesium-silicon bond of triphenylsilyls and catalytic pyridine hydrofunctionalization

Article abstract of DOI:10.1039/c8dt01466c

Magnesium bis(triphenylsilyl) [Mg(SiPh₃)₂(THF)₂]·THF (1) reacted with a stoichiometric amount of pyridine to give the magnesium 4-(triphenylsilyl)dihydropyridyl complex [Mg(NC₅H₅-4-SiPh₃)₂(THF)₃] (2). Using an excess of pyridine, a mixture of magnesium dihydropyridyl [Mg(NC₅H₆)₂(py)₄] (3) and 4-(triphenylsilyl)pyridine was formed. Complex 3 underwent exchange with pyridine-d₅ at 25 °C to give [Mg(NC₅D₅H-4)₂(py-d₅)₄] (3-HD). Analogous reactions with Me₃TACD-supported magnesium triphenylsilyls [(Me₃TACD)Mg(SiPh₃)] (4) and [(Me₃TACD·AlEt₃)Mg(SiPh₃)] (6) ((Me₃TACD)H = Me₃[12]aneN₄: 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane) with pyridine gave [(Me₃TACD)Mg(NC₅H₅-4-SiPh₃)] (5), [(Me₃TACD·AlEt₃)Mg(NC₅H₅-4-SiPh₃)] (7) and a mixture of [(Me₃TACD)Mg(NC₅H₆)] (8) and 4-(triphenylsilyl)pyridine. Complex 8 is also formed by reacting 3 with (Me₃TACD)H and underwent exchange with pyridine-d₅ at higher temperatures. The activation energy for the exchange is about 25 kJ mol^-1 higher than that for the exchange reaction of 3 to 3-HD. Complexes 2, 3, 3-HD, 5, 7 and 8 were characterized by NMR spectroscopy and 3, 5 and 8 by single crystal structure analysis. Complex 3 was found to be slightly active in the hydrosilylation of pyridine using phenylsilane, whereas complex 8 showed no activity. Both complexes 3 and 8 were active in the hydroboration of pyridine with pinacolborane.

Full text of DOI:10.1039/c8dt01466c

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Efficient extraction of sulfate from water using
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ARTICLE
1,4-Dihydropyridyl complexes of magnesium: synthesis by
pyridine insertion into the magnesium-silicon bond of
triphenylsilyls and catalytic pyridine hydrofunctionalization
Received 00th January 20xx,
Accepted 00th January 20xx
L. E. Lemmerz,a T. P. Spaniola and J. Okudaa*
DOI: 10.1039/x0xx00000x
Magnesium bis(triphenylsilyl) [Mg(SiPh3)2(THF)2]·THF (1) reacted with stochiometric amount of pyridine to give the
magnesium 4-(triphenylsilyl)dihydropyridyl complex [Mg(NC5H5-4-SiPh3)2(THF)3] (2). Using an excess of pyridine, a mixture
of magnesium dihydropyridyl [Mg(NC5H6)2(py)4] (3) and 4-(triphenylsilyl)pyridine was formed. Complex 3 underwent
exchange with pyridine-d5 at 25 °C to give [Mg(NC5D5H-4)2(py-d5)4] (3-HD). Analogous reactions with Me3TACD-supported
magnesium triphenylsilyls [(Me3TACD)Mg(SiPh3)] (4) and [(Me3TACD·AlEt3)Mg(SiPh3)] (6) ((Me3TACD)H = Me3[12]aneN4:
1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane) with pyridine gave [(Me3TACD)Mg(NC5H5-4-SiPh3)] (5), [(Me3TACD·AlEt3)-
Mg(NC5H5-4-SiPh3)]) (7) and a mixture of [(Me3TACD)Mg(NC5H6)] (8) and 4-(triphenylsilyl)pyridine. Complex 8 is also
formed by reacting 3 with (Me3TACD)H and underwent exchange with pyridine-d5 at higher temperatures. The activation
energy for the exchange is about 25 kJ·mol-1 higher than for the exchange reaction of 3 to 3-HD. Complexes 2, 3, 3-HD, 5, 7
and 8 were characterized by NMR spectroscopy and by single crystal structure analysis for 3, 5 and 8. Complex 3 was found
to be slightly active in the hydrosilylation of pyridine using phenylsilane, whereas complex 8 showed no activity. Both
www.rsc.org/
complexes
3
and
8
were
active
in
the
hydroboration
of
pyridine
with
pinacolborane.
pyridyls were prepared43-46 and the hydrocarbon soluble
lithium tert-butyl-dihydropyridyl was found to catalyze the
hydroboration of aldehydes and ketones with pinacolborane.47
When the molecular calcium silyl [Ca(SiPh3)2(THF)4] was
treated with excess pyridine, calcium 1,4-dihydropyridyl
[Ca(NC5H6)2(py)n] (py = pyridine) was obtained along with
stoichiometric amount of 4-(triphenylsilyl)pyridine (Scheme
1).48
Introduction
In the context of bio-inspired hydride transfer reagents,
dihydropyridines such as Hantzsch ester have been studied
quite intensively.1-4 Hydrofunctionalization of pyridine is useful
for the synthesis of nitrogen-containing heterocycles and a
number of transition metal catalysts have been reported which
are active in the hydrosilylation5-13 and hydroboration12, 14-19 of
pyridine. More recently, some main group metal complexes
have been reported to hydrosilylate20, 21 and hydroborate20, 22-
pyridine
H
H
[Ca(SiPh3)2(THF)4]
N
Ca(py)n
+
2
N
SiPh3
25 °C, 2 h
2
27
pyridine. Magnesium dihydropyridyl complexes have been
23, 25, 28-35
[Mg(NC5H6)2(py)2], obtained
Scheme 1. Reaction of [Ca(SiPh3)2(THF)4] with an excess of pyridine.
known for decades.20,
from the reaction of activated MgH2 with pyridine by Ashby et
al. and De Koning et al. was found to reduce aldehydes,
ketones, enols and imines.28-31, 36 Lansbury’s reagent Li+[Al(1,4-
NC5H6)4]−37-39 formed starting from LiAlH4 with excess pyridine
is thought to contain a mixture of 1,2- and 1,4-isomers,
depending on the reaction conditions and can also be used as
highly selective stoichiometric reducing agent.
This reaction can be regarded as
a
regioselective
hydrosilylation of pyridine, followed by hydride transfer from
the intermediate 1,4-dihydropyridyl [Ca(NC5H5-4-SiPh3)2(L)n] (L
= THF, py). Mechanistically, this reaction probably involves
insertion of pyridine into both metal-silyl and metal-hydride
bond. Pyridine insertion into metal-silyl49 and metal-hydride
bonds17, 20, 21, 23, 25, 28-31, 34, 35, 37, 50 are known and the formation
of a metal-hydride intermediate is regarded to be crucial in the
hydrofuctionalization of pyridine.15-17, 19, 21-24, 51
Snaith and Mulvey were able to isolate [2-
(nBuC5H5N)Li·(py)2] from the reaction of nBuLi with excess
pyridine which acted as a lithium hydride source.40-42 More
recently, lithium, sodium and potassium tert-butyl-dihydro-
We report here on the results of the reaction of two
magnesium triphenylsilyls with pyridine to give 1,4-
dihydropyridyls along with their catalytic activity in the
hydrosilylation and hydroboration of pyridine.
Results and discussion
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Reaction of magnesium bis(triphenylsilyl)
to give 2-(n-butyl)pyridine and [Li(NC5H6)2(py)2]2.42 The
formation of [Mg(NC5H6)2(py)4] ( ) could only be observed with
3
The
reaction
of
the
52
magnesium
triphenylsilyl
an excess of pyridine, suggesting that the second mechanism is
more probable (Scheme 3 b). The formation of a magnesium
hydride intermediate was postulated by Hill et al. for the
[Mg(SiPh3)2(THF)2]·THF (
1)
with one equivalent of pyridine
(Scheme 2) gave [Mg(NC5H5-4-SiPh3)2(THF)3] (
yellow powder in excellent yields.
2) isolated as a
reaction
HC[C(Me)N(2,6-iPr2-C6H3)]2) with phenylsilane in the presence
of pyridine giving the dihydropyridyl complex
[(DIPPnacnac)Mg(NC5H6)(py)].32
Pure [Mg(NC5H6)2(py)4] ( ) without 4-(triphenylsilyl)pyridine
of
[(DIPPnacnac)MgnBu]
(DIPPnacnac
=
3
contamination was isolated following the method of De
Koning:29, 30 Activated MgH253 was stirred in the presence of an
excess of pyridine at room temperature for 18 h to give only
the 1,4-dihydropyridyl complex in 69% yield after
recrystallization from pyridine/n-hexane. De Koning et al.
reported the formation of the 1,2-dihydropyridyl species at
shorter reaction times. The 1H NMR spectra in THF-d8 and
Scheme 2. Synthesis of [Mg(NC5H5-4-SiPh3)2(THF)3] (
and 4-(triphenylsilyl)pyridine.
2) and [Mg(NC5H6)2(py)4] (3)
benzene-d6 are identical with that of [Mg(NC5H6)2(py)4] (
obtained from the reaction of [Mg(SiPh3)2(THF)2]·THF ( ) with
an excess of pyridine. The 1H NMR spectrum of
shows signals
for free pyridine which indicate that the coordination of
pyridine in is labile.
3)
Analogous insertion of pyridine into metal-silicon bonds are
known in the literature.48, 49 The reaction of
with an excess of
pyridine gave [Mg(NC5H6)2(py)4] ) and 4-(triphenylsilyl)-
1
1
3
(
3
pyridine which precipitated from the reaction mixture as pale
yellow solid and was identified by NMR spectroscopy.
3
Complete separation of
not possible. Upon repeated crystallizations from pyridine/n-
hexane, was obtained in 70% yield still containing 6 mol% of
4-(triphenylsilyl)pyridine. Complexes and are derived from
3 from 4-(triphenylsilyl)pyridine was
3
2
3
1,4-insertion of pyridine into the Mg−Si bond. No indication for
the formation of the 1,2-insertion products was found.
Nevertheless, the formation of 1,2-insertion products as
1
intermediates cannot be unequivocally ruled out. The H NMR
spectroscopic data for
Electronic Supplementary Information). The 1H NMR
spectroscopic data in pyridine-d5 of is comparable to that of
the bis(pyridine) complex [Mg(NC5H6)2(py)2] in pyridine-d5.29, 30
mechanism for the formation of [Mg(NC5H5-4-
SiPh3)2(THF)3] ( ) and [Mg(NC5H6)2(py)4] ( ) was proposed in
analogy to the formation of [Ca(NC5H6)2(py)n]48 (Scheme 3).
2 and 3 are summarized in Table S1 (see
3
A
2
3
Scheme 4. Exchange of
3 with pyridine-d5 to 3-HD at 25°C. The reaction is
monitored by 1H NMR spectroscopy (t = 10 min; t = 15 h; t = 70 h).
Scheme 3. Proposed mechanisms for the formation of group
dihydropyridyl complexes: a) formation of a metal hydride intermediate or b)
hydride transfer to a coordinated pyridine molecule and re-aromatization.
2 metal 1,4-
Complex
[Mg(NC5D5H-4)2(py-d5)4] (
reversible as HD reacts with protio-pyridine to 3
3
undergoes an exchange with pyridine-d5 to give
HD) (Scheme 4). The exchange is
as
3-
Formation of
a magnesium hydride intermediate or a
3
-
1
mechanism through re-aromatization initiated by the
coordination of a second pyridine followed by hydride transfer
are conceivable (Scheme 3). A hydride transfer to an incoming
monitored by H NMR spectroscopy in THF-d8 (See Electronic
Supplementary Information). The exchange follows pseudo-
first order kinetics and the reaction rates at 298 K, 313 K and
333 K were obtained: k1(298 K) = (1.29±0.01)·10−5 s−1; k1(313 K)
n
pyridine molecule was also reported for [Li(NC5H5 Bu-2)(py)2]
2 | J. Name., 2012, 00, 1-3
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= (7.12±0.08)·10−5 s−1; k1(333 K) = (5.59±0.10)·10−4 s−1. The [Mg(NC5H6)]2·(py)2}23
ARTICLE
(PARA
=
[(2,6-
activation energy for the exchange of to 3-HD was iPr2C6H3)NC(Me)C(H)C(Me)N]2-(p-C6H4))
determined as EA
(70.1±0.6)·kJ·mol-1 (See Electronic 1.9986(15) Å); [(PIA)Mg(NC5H6)(py)]34 (PIA
Supplementary Information). A possible mechanism for the C6H3)NC(Me)]CHP(Cy2)]N(2,6-Me2-C6H3)) (1.999(6) Å).
exchange of to HD consist of two steps. After exchange of
the labile pyridine ligands by pyridine-d5, hydride transfer from Triphenylsilyl Complex with a Me3TACD ligand
dihydropyridyl to pyridine-d5 occurs to generate HD. Such an In analogy to the reaction of with pyridine, reactions of the
exchange between dihydropyridyl and pyridine was also found Me3TACD-containing magnesium triphenylsilyls
for NN-{[Mg(NC5H6)(py)]2} (NN [(2,6- [(Me3TACD)Mg(SiPh3)] and [(Me3TACD·AlEt3)Mg(SiPh3)]
iPr2C6H3)NC(Me)−CHC(Me)N−]2) and [Li(NC5H5 Bu-2)(py)2].23, 42
((Me3TACD)H = Me3[12]aneN4: 1,4,7-trimethyl-1,4,7,10-
Over a period of 15 days a very slow reaction of
HD in tetraazacyclododecane)56 with pyridine were performed
pyridine-d5 to the completely deuterated species (Scheme 5).
[Mg(NC5D6)2(py-d5)4] ( ) was observed at 25 °C. This may be
3
(1.9893(15)-
=
=
(2,6-iPr2-
3
3-
3
-
1
=
(4)
n
52
(6)
3
-
3-D
due to the primary kinetic isotopic effect.54 Allyl complexes
[K(NC5H5-4-η1-C3H5)] and [K([18]crown-6)]2[Zn(η1-C3H5)4] were
reported also to undergo a reversible exchange reaction with
pyridine-d5.55
N
N
N
N
+ pyridine
N
N
N
N
Mg
Mg
N
THF, 25°C
SiPh3
[Mg(NC5D5H)2(py-d5)4] (3-HD) was independently obtained in
82% yield from the reaction of activated MgH2 with an excess
of pyridine-d5 and characterized by NMR spectroscopy. Highly
4
SiPh3
5
, 89%
temperature sensitive single crystals of [Mg(NC5H6)2(py)4] (
were obtained from pyridine/n-hexane at −30 °C over a period
of 48 h. Complex crystallizes with three additional molecules
of pyridine per formula unit of
3)
+ AlEt3
THF, 25°C
+ AlEt3
THF, 25°C
b)
3
3.
N
a)
N
N
N
+ pyridine
THF, 25°C
N
N
Mg
N
N
AlEt3
Mg
AlEt3
N
SiPh3
6
SiPh3
7
, a): 81%; b): 72%
Scheme
5
Synthesis
of
[(Me3TACD·AlEt3)Mg(NC5H5-4-SiPh3)] (
[(Me3TACD)Mg(NC5H5-4-SiPh3)]
).
(
5)
and
7
Complexes
[(Me3TACD)Mg(NC5H5-4-SiPh3)]
AlEt3)Mg(NC5H5-4-SiPh3)] (
can also be obtained in 72% yield by adding
AlEt3 to a solution of in THF (Scheme 5b). The products and
are derived from 1,4-insertion of pyridine into the
(
5
)
and
[(Me3TACD
·
7) were isolated in good
yields. Complex
7
5
5
7
magnesium-silicon bond. Again, no indication for the
formation of the 1,2-insertion products was found which might
be attributed to the high steric demands of the Me3TACD
ligand as well as the triphenylsilyl group. The formation of 1,2-
insertion products as intermediates cannot be completely
ruled out. An analogous reaction was observed when the allyl
complex [(Me3TACD)Mg(η1-C3H5)] was treated with one
equivalent of pyridine.57
Figure 1. Molecular structure of [Mg(NC5H6)2(py)4] (3). Displacement ellipsoids
are shown at the 50% probability level. Hydrogen atoms, except for the
dihydropyridyl rings, are omitted for clarity. Selected bond lengths [Å] and angles
[°]: Mg1–N1 2.1186(13), Mg1–N2 2.1396(13), Mg1–N3 2.2538(13), Mg1-N4
2.2509(13), Mg1–N5 2.3861(13), Mg1–N6 2.3799(13), N1-Mg1-N2 176.21(5), N3-
Mg1-N4 176.15(5) N5-Mg1-N6 177.56(5).
Complex 5 is soluble in THF and benzene, whereas complex 7 is
[Mg(NC5H6)2(py)4]
(3) shows an octahedral coordination
soluble in THF but decomposes in benzene at r.t over a period
of 24 h. The 1H NMR spectroscopic data for the 1,4-
geometry for magnesium ligated to four pyridine and two 1,4-
dihydropyridyl ligands. The four pyridine rings form a square
plane around the magnesium center whereas the apical
positions are occupied by the two 1,4-dihydropyridyl ligands.
The 1,4-dihydropyridyl ligands are rotated by 37° relative to
each other. The Mg-N1 and Mg-N2 distances of 2.1186(13) Å
and 2.1396(13) Å are slightly longer compared to distances in
dihydropyridyl ring in
Electronic Supplementary Information).
Single crystals of were obtained by layering n-hexane on a
toluene solution at −30 °C. Complex crystallizes with one
additional molecule of toluene per formula unit of
[(Me3TACD)Mg(NC5H5-4-SiPh3)] ( ) is monomeric with a square
5 and 7 are given in Table S1 (See
5
5
5.
5
other
([(DIPPnacnac)Mg(NC5H6)(py)]32
[Mg(NC5H6)]2·(py)2}23
(2.0035(9)
magnesium
1,4-dihydropyridyl
complexes
pyramidal coordination geometry for magnesium (Figure 2).
The 4-(triphenylsilyl)pyridyl group and four nitrogen atoms of
the monoanionic Me3TACD ligand are coordinated to the
(1.993(2)
Å);
{NN-
Å);
{PARA-
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magnesium center (structural parameter τ = 0.16). The Mg-N5
N
N
distance of 2.022(2) Å lies in the range of known magnesium
32, 34
The L3X-type ligand Me3TACD
N
pyridine
N
a)
pyridyl complexes.23,
N
+
N
SiPh3
N
N
N
Mg
Mg
60 °C, 3 d
displays the usual bonding parameters.
N
SiPh3
4
H
H
8
H2
pyridine
THF, 2 h
N
N
H
H
H
H
b)
N
Mg N
+
(Me3TACD)H
N
N
3
Scheme 6. Formation of [(Me3TACD)Mg(NC5H6)] (8).
Again, the separation of 4-(triphenylsilyl)pyridine was difficult.
The 1H NMR spectrum of the product mixture contains besides
signals for 4-(triphenylsilyl)pyridine, signals characteristic for
[(Me3TACD)Mg(NC5H6)]
protons in 2-, 3- and 4-position
respectively. Complex was obtained without the by-product
(
8)
including the dihydropyridyl
δ
4.05, 4.57 and 6.38 ppm,
8
4-(triphenylsilyl)pyridine by reacting [Mg(NC5H6)2(py)4] (
one equivalent of (Me3TACD)H (Scheme 6b).
3) with
Figure 2. Molecular structure of [(Me3TACD)Mg(NC5H5-4-SiPh3)]
(5).
Displacement ellipsoids are shown at the 50% probability level. Hydrogen atoms,
except for the pyridyl ring, are omitted for clarity. Selected bond lengths [Å] and
angles [°]: Mg1–N1 1.993(3), Mg1–N2 2.284(2), Mg1–N3 2.1866(17), Mg1-N4
2.294(3), Mg1–N5 2.022(2), C14-H14 1.00(4), C14-Si1 1.892(2), N1-Mg1-N3
111.38(8), N2-Mg1-N4 144.53(8).
The formation of [(Me3TACD·AlEt3)Mg(NC5H6)] was not
possible starting from in pyridine due to decomposition of
6
6
at 60 °C. A similar complex [(Me3TACD·AliBu3)Mg(NC5H6)] was
obtained from the reaction of [(Me3TACD·AliBu3)MgH] with
pyridine in 53% yield.35
To investigate whether the formation of the 1,4-insertion
products
products, the reaction of [(Me3TACD)Mg(SiPh3)] (
different pyridine derivatives was performed in THF-d8.
Complex reacted with 3-picoline to give the 1,4-insertion
product, whereas the reaction with 2-picoline proceeded
slowly. After 7 days about 50% of was converted into the 1,4-
5
and
7
proceeds via intermediate 1,2-insertion
4) with
[(Me3TACD)Mg(NC5H6)] (
8) showed no exchange with pyridine-
d5 to give [(Me3TACD)Mg(NC5D5H)] (
8
-HD) at 25 °C but at 60 °C
4
exchange was observed and follows pseudo-first order
kinetics. The reaction rates at different temperatures were
determined for 333 K, 343 K and 353 K: k1(333 K) =
(2.48±0.06)·10−5 s−1; k1(343 K) = (7.30±0.13)·10−5 s−1; k1(353 K)
4
insertion product and the residual 50% underwent C-H bond
activation to form [(Me3TACD)Mg(CH2NC5H4)] and triphenyl-
silane. The C-H bond activation or metalation of the methyl
group as competition to the insertion reaction was reported
for the reaction of bis(allyl)calcium with pyridine derivatives.58
With 4-picoline and 2,6-lutidine exclusive C-H bond activation
was observed without any formation of 1,2 insertion products.
The reaction with 2,6-lutidine was slow and after 11 days only
=
(1.72±0.02)·10−4 s−1 (see Electronic Supplementary
Information). The exchange reaction of with pyridine-d5 is
slower than that of complex . The activation energy for the
exchange of to 8-HD was determined as EA
(94.7±1.9)·kJ·mol-1 and can be seen to be about 25 kJ·mol-1
8
3
8
=
higher than that for the exchange of complex
(70.1±0.6)·kJ·mol-1.
3 with EA =
50% of
reaction occurred after 3 days at 60 °C.
When [(Me3TACD)Mg(SiPh3)] ( ) was stirred in pyridine for 3
days at room temperature, the formation of only was
observed. Heating this reaction mixture to 60 °C for 3 days
4 were consumed. With 2,6-di-tert-butylpyridine no
Single crystals of [(Me3TACD)Mg(NC5H6)] (8) were obtained
from toluene/n-hexane at −30 °C over a period of 24 h.
4
5
gave [(Me3TACD)Mg(NC5H6)] (
(Scheme 6a).
8) and 4-(triphenylsilyl)pyridine
4 | J. Name., 2012, 00, 1-3
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Table 1. Hydroboration of pyridine derivatives with HBpin catalyzed by 3,
[(Me3TACD·AliBu3)Mg(NC5H6)]25
8 and
.
R
H
R
R
N
O
O
10 mol% [cat]
80°C, 72 h
+
H
H
+
BH
N
N
BPin
BPin
1,4-isomer
1,2-isomer
Entry
Complex
R
1,2-:1,4-
isomers [%]
Conversiona
[%]
52
1
3
8
8
8
8
H
H
3:97
4:96
2
3b
74
H
10:90
27:73
47:53
3:97
68
4
tBu
tBu
H
75
5b,c
6d
75
Figure 3. Molecular structure of [(Me3TACD)Mg(NC5H6)] (8). Displacement
[LMg(DHP)]25
70
ellipsoids are shown at the 50% probability level. Hydrogen atoms, except for the
dihydropyridyl ring, are omitted for clarity. Selected bond lengths [Å] and angles
[°]: Mg1–N1 1.986(2), Mg1–N2 2.297(2), Mg1–N3 2.180(2), Mg1-N4 2.285(2),
Mg1–N5 2.017(2), N1-Mg1-N3 112.20(9), N2-Mg1-N4 145.07(8).
a
Relative to hexamethylbenzene as internal standard in THF-d8. Determined by
1H NMR spectroscopy. In benzene-d6. pinB-1,4-DHP is also detected due to
release of pyridine by 8. d [LMg(DHP)]= [(Me3TACD·AliBu3)Mg(NC5H6)].
b
c
[(Me3TACD)Mg(NC5H6)] (
8) is monomeric with a distorted
square pyramidal coordination geometry for magnesium (
τ
=
[Mg(NC5H6)2(py)4]
[(Me3TACD·AliBu3)Mg(NC5H6)]25
hydroboration of pyridine using HBpin. Complex
(
3
), [(Me3TACD)Mg(NC5H6)]
(
8
)
and
the
and
0.25). The magnesium center is coordinated by one 1,4-
dihydropyridyl ligand and four nitrogen atoms of the
monoanionic Me3TACD ligand. The Mg-N5 distance of 2.017(2)
Å is slightly shorter when compared to the Mg-N distances of
are active
in
8
[(Me3TACD·AliBu3)Mg(NC5H6)]25 are slightly more active than
complex and their results in the hydroboration of
3
the 1,4-dihydropyridyl ligand in complex 3 and lies in the range
pinacolborane are comparable to those of the magnesium
complexes [(DipNHPPh2)MgH)4]20, [(DIPPnacnac)MgnBu]22 and
of other magnesium1,4-dihydropyridyl complexes reported in
the literature.23, 32, 34
NN-{[Mg(NC5H6)(py)]2}
(NN
=
[(2,6-iPr2C6H3)NC(Me)-
CHC(Me)N−]2),23 whereas [Mg(THF)6][HBPh3]2 is considerably
more active. Finally, 4-tert-butylpyridine was hydroborated in
THF-d8 or benzene-d6 at 80°C with 75% conversion using 10
26
Hydrofunctionalization of pyridine
[Mg(NC5H6)2(py)4]
(
3
), [(Me3TACD)Mg(NC5H6)]
(
8
)
and
[(Me3TACD·AliBu3)Mg(NC5H6)]25 were tested as catalysts for
mol% of complex
8 as catalyst over a period of 72 h. In THF-d8
the hydrosilylation of pyridine. At a catalyst loading of 10 mol%
a higher selectivity towards the 1,4-isomer was observed
(Entry 2/3 and 4/5).
[(Me3TACD)Mg(NC5H6)]
[(Me3TACD·AliBu3)Mg(NC5H6)]25 showed no activity at 80 °C in
the hydrosilylation of pyridine using phenylsilane after 72 h.
Diketiminato-supported magnesium dihydropyridyls were also
(
8
)
and
β
-
Conclusion
33
not active.22,
Hill et al. assumed that the presence of
Pyridine was found to insert into the Mg−Si bond of the
additional strongly coordinating pyridine ligands prevented the
interaction of phenylsilane with the magnesium center.
molecular magnesium triphenylsilyl
magnesium 4-(triphenylsilyl)pyridyls 2, 5 and
Products of 1,2-insertion were not detected. With an excess of
pyridine, magnesium 1,4-dihydropyridyl complexes and
1, 4
and 652 to give the
7, respectively.
[Mg(NC5H6)2(py)4] (3) was found to be active at 80°C in the
hydrosilylation of pyridine with phenylsilane and after 72 h a
mixture consisting of [(1,4-NC5H6)2PhSiH] (12%), [(1,2-
NC5H6)2PhSiH] (9%) and [(1,4-NC5H6)PhSiH2] (14%) was
obtained. These results are comparable to those using
{[(DipNHPPh2)MgH]4} (Dip = 2,6-iPr2C6H3) which produced a
mixture of [(1,4-NC5H6)2PhSiH], [(1,2-NC5H6)2PhSiH] and [(1,2-
NC5H6)(1,4-NC5H6)PhSiH] at 80 °C after 48 h with a total
conversion of 52%.20
3
8
along with 4-(triphenylsilyl)pyridine were formed. The facile
hydride transfer from the 1,4-(triphenylsilyl)dihydropyridyl to
pyridine may be accounted for by stabilizing effect by a silyl
substituent in the re-aromatized pyridine. In the literature the
triphenylsilyl group is described to have an electron
withdrawing effect when substituted in the para-position of an
aromatic ring.59
Furthermore, [Mg(NC5H6)2(py)4] (3), [(Me3TACD)Mg(NC5H6)] (8)
As expected, the introduction of the macrocyclic ligand
Me3TACD resulted in significant stabilization of the 1,4-
dihydropyridyl complexes. The presence of a Lewis acid at the
amido nitrogen had no effect, as observed previously in other
Me3TACD magnesium complexes.52
and [(Me3TACD·AliBu3)Mg(NC5H6)]25 were tested as catalysts
for the hydroboration of pyridine. For pyridine hydroboration
with pinacolborane (HBpin) 10 mol% of the complexes were
used and the conversions were monitored by 1H NMR
spectroscopy (Table 1).
Whilst complex
8 was not active in the hydrosilylation of
pyridine using phenylsilane,
a
mixture of hydrosilylated
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dihydropyridines were obtained with complex 3. It was also benzene-d6 but identified by HSQC), 129.7 (para-Ph), 136.2
active in the hydroboration of pyridine using pinacolborane, (ipso-Ph), 137.1 (br., N(CH)2(CH)2CH), 137.4 (ortho-Ph) ppm. 1H
whereas complex
8
showed activity comparable to that of NMR (THF-d8; 400.1 MHz):
δ
N(CH)2(CH)2CH), 3.81 (m, 1H, N(CH)2(CH)2CH), 5.57 (m, 2H,
=
3.71-3.74 (m, 2H,
catalysts reported in the literature.20, 22, 23, 26
N(CH)2(CH)2CH), 7.22-7.30 (m, 18H, meta-/para-Ph), 7.67-7.69
(m, 12H, ortho-Ph) ppm. 13C{1H} NMR (THF-d8; 100.6 MHz):
δ =
Experimental
26.6 (N(CH)2(CH)2CH), 98.5 (N(CH)2(CH)2CH), 128.1 (meta-Ph),
129.4 (para-Ph), 137.5 (ipso-Ph), 137.7 (ortho-Ph), 140.3
General considerations
(N(CH)2(CH)2CH) ppm. 29Si{1H} NMR (THF-d8; 79.5 MHz):
δ =
All operations were performed under inert atmosphere of dry
argon using standard Schlenk techniques or glovebox
techniques. THF, n-pentane, n-hexane and toluene were
purified using a MB SPS-800 solvent purification system or
distilled under argon from sodium/benzophenone ketyl prior
to use. Pyridine was dried over CaH2 and distilled under argon
prior to use. Deuterated solvents (THF-d8, benzene-d6) were
distilled under argon from sodium/benzophenone ketyl prior
to use. The starting materials activated MgH2,53
23.0 ppm. Anal. calc. for C58H64N2O3Si2Mg (917.64 g·mol-1): C,
75.92; H, 7.03; N, 3.05; Mg, 2.65. Found: C, 74.51; H, 6.94; N,
3.23; Mg, 2.67%.
[Mg(NC5H6)2(py)4] (3)
Method A. [Mg(SiPh3)2(THF)2]·THF (1) (380 mg; 0.5 mmol) was
dissolved in pyridine (4 mL). After 2 h, a slightly yellow solid
precipitated from the red solution. The solid, which was
identified as 4-(triphenylsilyl)pyridine, was filtered off and the
red filtrate was reduced to a volume of 2 mL. The filtrate was
cooled to −30 °C and more of the byproduct precipitated. The
reaction solution was filtered again and cooled down to −30°C.
[Mg(SiPh3)(THF)2]·THF
(
1
), [(Me3TACD)Mg(SiPh3)]
52
(
4
)
and
[(Me3TACD·AlEt3)Mg(SiPh3)] (
6
)
were prepared according to
literature procedures. NMR spectra were recorded on a Bruker
Avance II 400 or a Bruker Avance III HD 400 spectrometer at 25
[Mg(NC5H6)2(py)4] (3) (174 mg; 0.35 mmol) crystallized from
°C in J. Young-type NMR tubes. Chemical shifts (δ in ppm) in
the solution at −30 °C as orange crystals over a period of 48 h
in a yield of 70%. The product still contained 6 mol% of 4-
(triphenylsilyl)pyridine as impurity. Thermally highly sensitive
crystals suitable for X-ray analysis were obtained from
pyridine/n-hexane over a period of 48 h at −30 °C.
Method B.29, 30 Activated MgH2 (33 mg, 1.25 mmol) was stirred
in pyridine (2 mL) at room temperature for 18 h. The reaction
solution was reduced and cooled at −30 °C for 24 h.
1
the H, 13C{1H} and 29Si{1H} NMR spectra were referenced to
the residual proton signals of the deuterated solvents and
reported relative to tetramethylsilane. The resonances in the
1H and 13C NMR spectra were assigned on the basis of two-
dimensional NMR experiments (COSY, HSQC, HMBC).
Combustion analyses were performed with an Elementar Vario
EL. The low carbon content for 2, 3 and 8 may be ascribed to
incomplete combustion due to possible formation of
incombustible magnesium carbide or carbonate. Similar
problems are reported for earth alkaline metal complexes in
[Mg(NC5H6)2(py)4] (3) (470 mg; 0.94 mmol) was obtained as
orange-brown crystals in 75% yield.
1H NMR (THF-d8; 400.1 MHz):
δ
=
3.21 (m, 4H,
the literature.52, 60 The magnesium contents of
determined by complexometric titrations and were carried out
according to the published procedure.61 Metal contents of
and were determined by inductively coupled plasma mass
2, 3 and 5 were
N(CH)2(CH)2CH2), 3.75 (m, 4H, N(CH)2(CH)2CH2), 5.84 (m, 4H,
N(CH)2(CH)2CH2), 7.28 (pyridine), 7.69 (pyridine), 8.55
7
(pyridine) ppm. 13C{1H} NMR (THF-d8, 100.6 MHz):
δ = 26.2
8
(N(CH)2(CH)2CH2), 92.2 (N(CH)2(CH)2CH2), 124.6 (pyridine),
136.8 (pyridine), 139.9 (N(CH)2(CH)2CH2), 150.9 (pyridine) ppm.
spectrometry using a Spectro ICP Spectroflame D instrument.
A defined amount of sample was dissolved in 8 mL of 40%
hydrofluoric acid, 2 mL of concentrated sulfuric acid, and 40
mL of water.
1H NMR (benzene-d6; 400.1 MHz):
δ = 3.81 (m, 4H,
N(CH)2(CH)2CH2), 4.54 (m, 4H, N(CH)2(CH)2CH2), 6.44 (m, 4H,
N(CH)2(CH)2CH2), 6.66 (pyridine), 6.96 (pyridine), 8.57
(pyridine) ppm. 1H NMR (pyridine-d5; 400.1 MHz):
δ = 3.83 (m,
[Mg(NC5H5-4-SiPh3)2(THF)3] (2)
4H, N(CH)2(CH)2CH2), 4.32 (m, 4H, N(CH)2(CH)2CH2), 6.38 (m,
4H, N(CH)2(CH)2CH2), 7.23 (pyridine), 7.59 (pyridine), 8.74
A solution of pyridine (63 mg; 0.8 mmol) in THF (2 mL) was
added to a solution of [Mg(SiPh3)2(THF)2]·THF (1) (304 mg; 0.4
(pyridine) ppm. 13C{1H} NMR (pyridine-d5, 100.6 MHz):
δ = 26.8
mmol) in THF (2 mL). The reaction mixture turned orange and
was stirred for 3 h at room temperature. The solvent was
removed under reduced pressure and the orange oil washed
with n-pentane (3 x 3mL) until it became a solid. [Mg(NC5H5-4-
(N(CH)2(CH)2CH2), 92.6 (N(CH)2(CH)2CH2), 124.5 (pyridine),
136.5 (pyridine), 141.3 (N(CH)2(CH)2CH2), 150.8 (pyridine) ppm.
Anal. calc. for C30H32N6Mg (500,93 g·mol-1): C, 71.93; H, 6.44;
N, 16.78; Mg, 4.85. Found: C, 70.39; H, 6.47; N, 16.70; Mg,
4.77%.
SiPh3)2(THF)3] (2) (343 mg; 0.37 mmol) was obtained as a
yellow powder; yield 93%.
1H NMR (C6D6; 400.1 MHz):
δ
= 1.34 (THF), 3.53 (THF), 4.00 (br.
[Mg(NC5D5H)2(py-d5)4] (3-HD)
s, 1H, N(CH)2(CH)2CH), 4.56 (br. s, 2H, N(CH)2(CH)2CH), 5.95 (br.
s, 2H, N(CH)2(CH)2CH), 7.20-7.23 (m, 18H, meta-/para-Ph),
7.88-7.89 (m, 12H, ortho-Ph) ppm. 13C{1H} NMR (C6D6; 100.6
Activated MgH2 (33 mg, 1.25 mmol) was stirred in pyridine-d5
(2 mL) at room temperature for 8 h. The reaction solution was
concentrated and cooled to −30°C for 24 h. [Mg(NC5D5H)2(py-
d5)4] (3-HD) (545 mg; 1.03 mmol) was obtained as orange-red
crystals in 82% yield. The crystals melt at room temperature.
MHz): δ = 25.3 (N(CH)2(CH)2CH), 26.0 (THF), 69.1 (THF), 98.5
(N(CH)2(CH)2CH), 128.2 (meta-Ph, overlapped by the signal of
6 | J. Name., 2012, 00, 1-3
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1H NMR (THF-d8; 400.1 MHz):
δ
=
3.18 (m, 2H,
(
2
) (58 mg; 0.1 mmol) in THF (2 mL). The reaction solution was
stirred for 2 h at room temperature. The solvent was removed
25.5 (N(CD)2(CD)2CDH, overlapped by the signal of THF-d8 but under reduced pressure and the oily residue was washed with
identified by HSQC) ppm. 1H NMR (pyridine-d5; 400.1 MHz):
n-pentane (3 x 3mL). [(Me3TACD·AlEt3)Mg(NC5H5-4-SiPh3)] (
3.80 (m, 2H, N(CD)2(CD)2CDH) ppm. 13C{1H} NMR (pyridine-d8; (50 mg; 0.07 mmol) was obtained in 72% yield as a yellow
N(CD)2(CD)2CDH) ppm. 13C{1H} NMR (THF-d8; 100.6 MHz):
δ =
δ
=
7)
100.6 MHz):
ppm. 1H NMR (benzene-d6; 400.1 MHz):
δ = 25.5 (N(CD)2(CD)2CDH, just identified by HSQC) powder.
3
= −0.17 (q, JHH = 8.03 Hz, 6H,
δ
= 3.89 (m, 2H, 1H NMR (THF-d8, 400.1 MHz):
δ
= 3.00 (br. Al(CH2CH3)2), 1.07 (t, JHH = 8.03 Hz, 9H, Al(CH2CH3)2), 2.35 (s,
N(CD)2(CD)2CDH) ppm. 2D NMR (THF; 400.1 MHz):
δ
s, N(CD)2(CD)2CDH), 3.60 (br. s, N(CD)2(CD)2CDH), 5.70 (br. s, 3H, Me), 2.39 (s, 6H, Me), 2.42-2.56 (m, 8H, CH2), 2.70-2.81 (m,
3
N(CD)2(CD)2CDH) ppm.
6H, CH2), 2.97-3.03 (m, 2H, CH2), 3.77-3.80 (m, 3H,
N(CH)2(CH)2CH), 5.76-5.78 (m, 2H, N(CH)2(CH)2CH), 7.25-7.30
(m, 9H, meta-/para-Ph), 7.69-7.71 (m, 6H, ortho-Ph) ppm.
[(Me3TACD)Mg(NC5H5-4-SiPh3)] (5)
A solution of pyridine (20 mg; 0.25 mmol) in THF (2 mL) was 13C{1H} NMR (THF-d8, 100.6 MHz):
δ = 2.1 (Al(CH2CH3)2), 12.1
4) (124 mg; 0.25 (Al(CH2CH3)2), 26.0 (N(CH)2(CH)2CH), 44.1 (Me), 45.5 (Me), 47.8
added to a solution of [(Me3TACD)Mg(SiPh3)](
mmol) in THF (2 mL). The color of the reaction mixture turned (CH2), 54.1 (CH2), 54.3 (CH2), 56.8 (CH2), 92.3 (N(CH)2(CH)2CH),
yellow and the reaction mixture was stirred for 1 h at room 128.2 (meta-Ph), 129.2 (ipso-Ph), 129.4 (para-Ph), 137.7
temperature. The solvent was removed under reduced (ortho-Ph), 140.7 (N(CH)2(CH)2CH) ppm. 29Si{1H} NMR (THF-d8,
pressure and the solid residue was washed with n-pentane (3 x 79.5 MHZ):
3 mL). [(Me3TACD)Mg(NC5H5-4-SiPh3)] (
) (128 mg; 0.22 mmol) (690.30 g·mol-1): C, 69.60; H, 8.76; N, 10.15; Mg, 3.52; Al, 3.91.
was obtained in 89% yield as a yellow powder. Found: C, 69.56; H, 8.61; N, 9.79; Mg, 3.52; Al, 3.66%.
1H NMR (THF-d8, 400.1 MHz):
= 2.24-2.28 (m, 2H, CH2), 2.37-
δ = −27.2 ppm. Anal. calc. for C40H60N5SiMgAl
5
δ
2.46 (m, 4H, CH2), 2.40 (s, 3H, Me), 2.41 (s, 6H, Me), 2.53-2.55 [(Me3TACD)Mg(NC5H6)] (8)
(m, 2H, CH2), 2.70-2.78 (m, 4H, CH2), 2.86-2.94 (m, 4H, CH2), Method A. [(Me3TACD)Mg(SiPh3)] (
4) was dissolved in pyridine
3.69-3.71 (m, 2H, N(CH)2(CH)2CH), 3.75-3.77 (m, 1H, (2 mL) and stirred at 60 °C for 3 days. The color of the solution
N(CH)2(CH)2CH), 5.72-5.74 (m, 2H, N(CH)2(CH)2CH), 7.23-7.30 turned from orange to red-brown. The solvent was removed
(m, 9H, meta-/para-Ph), 7.71-7.73 (m, 6H, ortho-Ph) ppm. under reduced pressure and the red-brown solid residue was
13C{1H} NMR (THF-d8, 100.6 MHz):
δ = 26.8 (N(CH)2(CH)2CH), washed with n-pentane (3 x 3 mL) and dried under vacuum.
43.8 (Me), 46.9 (Me), 51.2 (CH2), 53.0 (CH2), 55.8 (CH2), 63.8 The product mixture of [(Me3TACD)Mg(NC5H6)] (8) and 4-
(CH2), 92.0 (N(CH)2(CH)2CH), 128.1 (meta-Ph), 129.3 (para-Ph), (triphenylsilyl)pyridine could not be separated.
137.7 (ortho-Ph), 137.7 (ipso-Ph), 140.5 (N(CH)2(CH)2CH) ppm. Method B. (Me3TACD)H (140 mg; 0.65 mmol) in THF (1 mL)
29Si{1H} NMR (THF-d8, 79.5 MHZ): = −27.4 ppm. 1H NMR was added to a solution of [Mg(NC5H6)2(py)4] (
) (328 mg; 0.65
(benzene-d6, 400.1 MHz): = 1.38-1.48 (m, 4H, CH2), 1.65 (s, mmol) in THF (2 mL) and stirred at room temperature for 2 h.
δ
3
δ
3H, Me) 1.74-1.80 (m, 2H, CH2), 2.04 (s, 6H, Me), 2.09-2.17 (m, A color change of the solution from red to pale red-orange was
4H, CH2), 2.75-2.90 (m, 4H, CH2), 3.26-3.30 (m, 2H, CH2), 4.43- observed. The solvent was removed under reduced pressure
4.44 (m, 3H, N(CH)2(CH)2CH), 6.02-6.03 (m, 2H, and the red-brown oily residue was washed with n-pentane (3x
N(CH)2(CH)2CH), 7.23-7.26 (m, 9H, meta-/para-Ph), 8.09-8.12 3mL) until it became a solid. The solid was dried under vacuum
(m, 6H, ortho-Ph), ppm. 13C{1H} NMR (benzene-d6, 100.6 MHz): to give [(Me3TACD)Mg(NC5H6)] (
= 26.8 (N(CH)2(CH)2CH), 43.3 (Me), 46.6 (Me), 50.4 (CH2), pale brown powder in 92% yield.
52.6 (CH2), 54.9 (CH2), 63.2 (CH2), 92.8 (N(CH)2(CH)2CH), 128.2 1H NMR (benzene-d6, 400.1 MHz):
8
) (192 mg; 0.60 mmol) as a
δ
δ
= 1.37-1.48 (m, 4H, CH2),
(meta-Ph), 129.3 (para-Ph), 137.7 (ortho-Ph), 137.5 (ipso-Ph), 1.69 (s, 3H, Me) 1.73-1.79 (m, 2H, CH2), 2.07 (s, 6H, Me), 2.08-
140.4 (N(CH)2(CH)2CH) ppm. 29Si{1H} NMR (benzene-d6, 79.5 2.17 (m, 4H, CH2), 2.76-2.83 (m, 2H, CH2), 2.86-2.93 (m, 2H,
MHZ):
δ = −25.7 ppm. Anal. calc. for C34H45N5SiMg (576,16 CH2), 3.29-3.33 (m, 2H, CH2), 4.04-4.05 (m, 2H,
g·mol-1): C, 70.88; H, 7.87; N, 12.16; Mg, 4.22. Found: C, 70.09; N(CH)2(CH)2CH2), 4.55-4.59 (m, 2H, N(CH)2(CH)2CH2), 6.37-6.39
H, 7.85; N, 11.68; Mg, 4.05%.
(m, 2H, N(CH)2(CH)2CH2) ppm. 13C{1H} NMR (benzene-d6, 100.6
MHz): = 26.6 (N(CH)2(CH)2CH2), 43.4 (Me), 46.6 (Me), 50.3
(CH2), 52.6 (CH2), 54.9 (CH2), 63.2 (CH2), 92.9 (N(CH)2(CH)2CH2),
140.2 (N(CH)2(CH)2CH2) ppm. 1H NMR (THF-d8, 400.1 MHz):
δ
[(Me3TACD·AlEt3)Mg(NC5H5-4-SiPh3)] (7)
δ
=
Method A. A solution of pyridine (16 mg; 0.2 mmol) in THF (2
2.23-2.30 (m, 2H, CH2), 2.40-2.48 (m, 4H, CH2), 2.44 (s, 9H,
Me), 2.53-2.59 (m, 2H, CH2), 2.71-2.79 (m, 4H, CH2), 2.86-2.95
(m, 4H, CH2), 3.19-3.21 (m, 2H, N(CH)2(CH)2CH2), 3.67-3.99 (m,
2H, N(CH)2(CH)2CH2), 5.90-5.92 (m, 2H, N(CH)2(CH)2CH2) ppm.
mL) was added to a solution of [(Me3TACD·AlEt3)Mg(SiPh3)] (6)
(122 mg; 0.2 mmol) in THF (2 mL). The color of the reaction
mixture turned yellow. The reaction mixture was stirred for 1 h
at room temperature. The solvent was removed under
reduced pressure and the solid residue was washed with n-
13C{1H} NMR (THF-d8, 100.6 MHz):
δ = 26.3 (N(CH)2(CH)2CH2),
43.8 (Me), 46.7 (Me), 51.2 (CH2), 53.1 (CH2), 55.8 (CH2), 63.8
(CH2), 91.7 (N(CH)2(CH)2CH2), 140.2 (N(CH)2(CH)2CH2) ppm.
Anal. calc. for C16H31N5Mg (317,76 g·mol-1): C, 60.48; H, 9.83;
N, 22.04; Mg, 7.65. Found: C, 60.55; H, 9.90; N, 21.35; Mg,
7,01%.
pentane (3 x 3 mL). [(Me3TACD·AlEt3)Mg(NC5H5-4-SiPh3)] (7)
(112 mg; 0.16 mmol) was obtained in 81% yield as a yellow
powder.
Method B. A solution of AlEt3 (11.5 mg; 0.1 mmol) in THF (2
mL) was added to a solution of [(Me3TACD)Mg(NC5H5-4-SiPh3)]
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20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
L. Fohlmeister and A. Stasch, Chem. Eur. J., 2016, 22
10235-10246.
J. Intemann, H. Bauer, J. Pahl, L. Maron and S. Harder,
Chem. Eur. J., 2015, 21, 11452-11461.
M. Arrowsmith, M. S. Hill, T. Hadlington, G. Kociok-Köhn
and C. Weetman, Organometallics, 2011, 30, 5556-5559.
J. Intemann, M. Lutz and S. Harder, Organometallics,
2014, 33, 5722-5729.
C. Weetman, M. S. Hill and M. F. Mahon, Polyhedron,
2016, 103, 115-120.
S. Schnitzler, T. P. Spaniol and J. Okuda, Inorg. Chem.,
2016, 55, 12997-13006.
D. Mukherjee, S. Shirase, T. P. Spaniol, K. Mashima and J.
Okuda, Chem. Commun., 2016, 52, 13155-13158.
M. Rauch, S. Ruccolo and G. Parkin, J. Am. Chem. Soc.,
2017, 139, 13264-13267.
A. J. de Koning, J. Boersma and G. J. M. van der Kerk, J.
Organomet. Chem., 1980, 186, 173-184.
A. J. de Koning, J. Boersma and G. J. M. van der Kerk, J.
Organomet. Chem., 1980, 186, 159-172.
,
4-(Triphenylsilyl)pyridine
1H NMR (benzene-d6, 400.1 MHz):
δ = 7.12-7.14 (m, 6H, meta-
Ph), 7.18-7.22 (m, 3H, para-Ph), 7.26-7.27 (m, 2H,
N(CH)2(CH)2), 7.52-7.54 (m, 6H, ortho-Ph), 8.56-8.58 (m, 2H,
N(CH)2(CH)2) ppm. 13C{1H} NMR (benzene-d6, 100.6 MHz):
δ =
128.8 (meta-Ph), 130.6 (para-Ph), 131.3 (N(CH)2(CH)2), 133.5
(ipso-Ph), 137.1 (ortho-Ph), 144.4 (ipso-Ph), 150.0
(N(CH)2(CH)2) ppm. 29Si{1H} NMR (benzene-d6, 79.5 MHZ):
14.3 ppm. Anal. calc. for C23H19NSi (337,50 g·mol-1): C, 81.85;
H, 5.67; N, 4.15. Found: C, 80.48; H, 5.67; N, 4.33%.
δ =
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
A. J. de Koning, P. H. M. Budzelaar, B. G. K. van Aarssen, J.
Boersma and G. J. M. van der Kerk, J. Organomet. Chem.,
1981, 217, C1-C4.
We thank the Deutsche Forschungsgemeinschaft for financial
support.
31.
32.
33.
34.
35.
36.
E. C. Ashby and A. B. Goel, J. Organomet. Chem., 1981,
204, 139-145.
M. S. Hill, D. J. MacDougall and M. F. Mahon, Dalton
Trans., 2010, 39, 11129-11131.
M. S. Hill, G. Kociok-Kohn, D. J. MacDougall, M. F. Mahon
and C. Weetman, Dalton Trans., 2011, 40, 12500-12509.
H. Xie, X. Hua, B. Liu, C. Wu and D. Cui, J. Organomet.
Chem., 2015, 798, 335-340.
S. Schnitzler, T. P. Spaniol, L. Maron and J. Okuda, Chem.
Eur. J., 2015, 21, 11330-11334.
A. J. De Koning, P. H. M. Budzelaar, J. Boersma and G. J.
M. van der Kerk, J. Organomet. Chem., 1980, 199, 153-
169.
P. T. Lansbury and J. O. Peterson, J. Am. Chem. Soc., 1963,
85, 2236-2242.
K. Hensen, A. Lemke, T. Stumpf, M. Bolte, H. Fleischer, C.
R. Pulham, R. O. Gould and S. Harris, Inorg. Chem., 1999,
38, 4700-4704.
Notes and references
1.
2.
R. Lavilla, J. Chem. Soc., Perkin Trans. 1, 2002, 1141-1156.
C. Zheng and S.-L. You, Chem. Soc. Rev., 2012, 41, 2498-
2518.
3.
4.
S. J. Connon, Org. Biomol. Chem, 2007, 5, 3407-3417.
S. G. Ouellet, A. M. Walji and D. W. C. Macmillan, Acc.
Chem. Res., 2007, 40, 1327-1339.
5.
6.
L. Hao, A.-M. Lebuis, J. F. Harrod, H.-G. Woo and E.
Samuel, Chem. Commun., 1998, 2013-2014.
L. Hao, J. F. Harrod, A. M. Lebuis, Y. Mu, R. Shu, E. Samuel
and H. G. Woo, Angew. Chem. Int. Ed., 1998, 37, 3126-
3129.
37.
38.
7.
8.
J. F. Harrod, R. Shu, H.-G. Woo and E. Samuel, Can. J.
Chem., 2001, 79, 1075-1085.
D. V. Gutsulyak, A. v. d. Est and G. I. Nikonov, Angew.
Chem. Int. Ed., 2011, 50, 1384-1387.
9.
10.
K. Osakada, Angew. Chem. Int. Ed., 2011, 50, 3845-3846.
S.-H. Lee, D. V. Gutsulyak and G. I. Nikonov,
Organometallics, 2013, 32, 4457-4464.
C. D. F. Königs, H. F. T. Klare and M. Oestreich, Angew.
Chem. Int. Ed., 2013, 52, 10076-10079.
39.
40.
41.
42.
43.
44.
D. D. Tanner and C. M. Yang, J. Org. Chem., 1993, 58,
1840-1846.
D. Barr, R. Snaith, R. E. Mulvey and D. Reed, Polyhedron,
1988, , 665-668.
11.
12.
13.
14.
15.
16.
17.
18.
19.
7
D. R. Armstrong, R. E. Mulvey, D. Barr, R. Snaith and D.
Reed, J. Organomet. Chem., 1988, 350, 191-205.
R. E. Mulvey, L. Dunbar, W. Clegg and L. Horsburgh,
Angew. Chem. Int. Ed., 1996, 35, 753-755.
S. D. Robertson, A. R. Kennedy, J. J. Liggat and R. E.
Mulvey, Chem. Commun., 2015, 51, 5452-5455.
D. R. Armstrong, C. M. M. Harris, A. R. Kennedy, J. J.
Liggat, R. McLellan, R. E. Mulvey, M. D. T. Urquhart and S.
D. Robertson, Chem. Eur. J., 2015, 21, 14410-14420.
S. A. Orr, A. R. Kennedy, J. J. Liggat, R. McLellan, R. E.
J. L. Lortie, T. Dudding, B. M. Gabidullin and G. I. Nikonov,
ACS Catal., 2017, 7, 8454-8459.
S. Park and S. Chang, Angew. Chem. Int. Ed., 2017, 56
7720-7738.
N. C. Cook and J. E. Lyons, J. Am. Chem. Soc., 1966, 88
,
,
3396-3403.
K. Oshima, T. Ohmura and M. Suginome, J. Am. Chem.
Soc., 2012, 134, 3699-3702.
A. S. Dudnik, V. L. Weidner, A. Motta, M. Delferro and T. J.
Marks, Nat. Chem., 2014, 6, 1100.
A. Kaithal, B. Chatterjee and C. Gunanathan, Org. Lett.,
2016, 18, 3402-3405.
F. Zhang, H. Song, X. Zhuang, C.-H. Tung and W. Wang, J.
Am. Chem. Soc., 2017, 139, 17775-17778.
H. Liu, M. Khononov and M. S. Eisen, ACS Catal., 2018, 8,
45.
Mulvey and S. D. Robertson, Dalton Trans., 2016, 45
,
6234-6240.
46.
47.
R. McLellan, A. R. Kennedy, S. A. Orr, S. D. Robertson and
R. E. Mulvey, Angew. Chem. Int. Ed., 2017, 56, 1036-1041.
R. McLellan, A. R. Kennedy, R. E. Mulvey, S. A. Orr and S.
D. Robertson, Chem. Eur. J., 2017, 23, 16853-16861.
3673-3677.
8 | J. Name., 2012, 00, 1-3
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ARTICLE
48.
49.
50.
51.
52.
53.
V. Leich, T. P. Spaniol, L. Maron and J. Okuda, Chem.
Commun., 2014, 50, 2311-2314.
H.-G. Woo and T. Don Tilley, J. Organomet. Chem., 1990,
393, C6-C9.
A. McSkimming and S. B. Colbran, Chem. Soc. Rev., 2013,
42, 5439-5488.
M. S. Hill, D. J. Liptrot and C. Weetman, Chem. Soc. Rev.,
2016, 45, 972-988.
L. E. Lemmerz, V. Leich, D. Martin, T. P. Spaniol and J.
Okuda, Inorg. Chem., 2017, 56, 14979-14990.
G. D. Barbaras, C. Dillard, A. E. Finholt, T. Wartik, K. E.
Wilzbach and H. I. Schlesinger, J. Am. Chem. Soc., 1951,
73, 4585-4590.
54.
R. Macomber, Organic Chemistry−Chemical Behavior of
Orgnaic Compounds and Multi-step Organic Synthesis,
University Science Books, Sausalito, 1996.
C. Lichtenberg, T. P. Spaniol, L. Perrin, L. Maron and J.
Okuda, Chem. Eur. J., 2012, 18, 6448-6452.
55.
56.
D. Mukherjee and J. Okuda, Chem. Commun., 2018, 54
2701-2714.
,
57.
58.
D. Martin, Dissertation, RWTH Aachen University, 2015.
P. Jochmann, T. S. Dols, T. P. Spaniol, L. Perrin, L. Maron
and J. Okuda, Angew. Chem. Int. Ed., 2010, 49, 7795-7798.
R. A. Benkeser, C. E. DeBoer, R. E. Robinson and D. M.
Sauve, J. Am. Chem. Soc., 1956, 78, 682-686.
A. Causero, G. Ballmann, J. Pahl, H. Zijlstra, C. Färber and
S. Harder, Organometallics, 2016, 35, 3350-3360.
E. Merck, Komplexometrische Bestimmungsmethoden mit
Titriplex Merck, Darmstadt, 1975.
59.
60.
61.
This journal is © The Royal Society of Chemistry 20xx
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TOC
1,4-Dihydropyridyl Complexes of Magnesium: Synthesis by Pyridine Insertion into the
Magnesium-Silicon Bond of Triphenylsilyls and Catalytic Pyridine
Hydrofunctionalization
Lara Lemmerz, Thomas P. Spaniol and Jun Okuda*
Magnesium triphenylsilyl complexes [Mg(SiPh3)2(THF)2] and
[(Me3TACD)Mg(SiPh3)] ((Me3TACD)H = Me3[12]aneN4: 1,4,7-
trimethyl-1,4,7,10-tetraazacyclododecane) serve as precursors
for 1.4-dihydropyridyl complexes of magnesium which are
active in the hydroboration of pyridine using pinacolborane.