Amido Ca(II) complexes supported by Schiff base ligands for catalytic cross-dehydrogenative coupling of amines with silanes

Article abstract of DOI:10.1039/c8dt01130c

A series of amido Ca complexes LCa[N(SiMe₃)₂](THF) (1-4) coordinated by Schiff base ligands L^1-4 were synthesized via an amine elimination reaction between proligands L^1-4H and a bisamido complex Ca[N(SiMe₃

Full text of DOI:10.1039/c8dt01130c

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ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
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ARTICLE
Amido Ca(II) complexes supported by Schiff base ligands for
catalytic cross-dehydrogenative coupling of amines with silanes
Natalia V. Forosenko,a Ivan V. Basalov,a Anton V. Cherkasov,a Georgy K. Fukin,a Elena S. Shubina,b
Alexander A. Trifonova,b,*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
A series of amido Ca complexes LCa[N(SiMe3)2](THF) (1−4) coordinated by Schiff base ligands L1−4 were synthesized via
amine elimination reaction between proligands L1−4H and bisamido complex Ca[N(SiMe3)2]2(THF)2 in good yields. Unlike
Ca[N(SiMe3)2]2(THF)2 the reactions of M[N(SiMe3)2]2(THF)2 (M = Yb, Sm) with proligands L1−4H do not lead to the formation
of the target Ln(II) amido complexes. The reaction of Yb[N(SiMe3)2]2(THF)2 with L1H is accompanied by intramolecular C-H
bond activation of a quinoline ring and results in the formation of complex 6 coordinated by a new trianionic [NNNNOO]
ligand. The reactions of amido complexes 1 and 4 with PhSiH3 do not allow for preparing the related hydrides but afford
homoleptic bis(phenolate) complexes 5 and 7 due to ligand redistribution reaction. Amido complexes 1−4 were evaluated
as precatalysts for cross-dehydrogenative coupling of silanes (PhSiH3, Ph(Me)SiH2, Ph3SiH) and aliphatic, aromatic and
cyclic amines (RNH2, R2NH).
www.rsc.org/
examples of catalytic dehydrogenative cross-coupling of
silanes with amines promoted by Pt40, Rh41, Ru42, Ti43, Cu44,
and U45 complexes, Lewis acids46 and bases47 affording
Introduction
Calcium is the fifth most abundant element in the Earth's
crust, and the third most abundant metal.1 Despite a number
of very important advantages which make this metal an
extremely attractive candidate for investigation in catalysis
untill very recently the catalytic potential of calcium complexes
did not receive considerable attention and the examples of
their application were mainly limited to Lewis-acidic catalysis.2
The communications on catalytic activity of calcium complexes
silazanes have been reported to date. Amido and alkyl metal
complexes of s-block and rare-earth metals proved to be able
to catalyze this reaction48-54 too. Ca amido complexes
supported by readily accessible iminophenolate55 ligands,
whose electronic and steric properties can be easily modified
in a wide range, are worthy candidates for catalysis of cross-
dehydrogenative coupling of amines with silanes.
Herein we report on the synthesis of a series of new
heteroleptic amido complexes of Ca(II) supported by
multidentate Schiff base ligands. Moreover, the effect of the
redox-active nature of the metal and ligand on the result of
the reactions of bis-amides of Ca and Yb with Schiff bases is
considered. The results of cross-dehydrogenative coupling of
amines with silanes catalysed by heteroleptic amido Ca(II)
complexes and the influence of electronic and steric properties
of both substrates is discussed.
in
ring-opening
polymerization,3-8
hydrogenation,9
hydroboration,10 hydroamination,11-17 hydrosilylation,18-21
hydrophosphination22-28 of unsaturated substrates as well as in
amine-borane dehydro-coupling29-34 began to appear in the
first decade of XXI century. Furthermore, the current trend
toward development of new synthetic approaches promoted
by non-toxic, inexpensive and earth-abundant metals
stimulates development in chemistry of biogenic and
environmentally friendly calcium35. New efficient atom-
economic and ecologically friendly methods for catalytic
formation of Si-N bonds and synthesis of silazanes can be one
of the prospective fields of application of calcium complexes.
Silazanes are widely used as silylating agents,36 ligands in
organometallic chemistry,37 as well as precursors for the
production of heavy-duty non-oxide ceramics38, 39. A number
Results and discussion
Synthesis of complexes. The heteroleptic amido complexes
LCa[N(SiMe3)2](THF)n coordinated by polydentate Schiff-base
ligands L1-4 were synthesized via one step amine elimination
reaction of proligands LH1-4 and bisamido complex
Ca[N(SiMe3)2]2(THF)2 in toluene (Scheme 1).
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ARTICLE
Journal Name
X
(Me Si)2N
3
OH
tBu
X
tBu
Toluene
THFn
Ca
O
N
N
- HN(SiMe3)2
tBu
+ Ca[N(SiMe3)2]2(THF)2
tBu
Ph
L1, n=2 (1), 90%
X
L2, n=0 (2), 91%
O
N
N
N
N
O
N
3
3
L , n=1 ( ), 86%
L4, n=0 (4), 95%
N
N
L1
L3
L4
L2
Scheme 1. Synthesis of complexes 1-4
Complex was isolated after recrystallization from
THF/hexane solution as dark-red crystals. Complexes and
were obtained from THF/hexane mixture as bright-yellow
.
1
2
4
microcrystalline powders. Crystallization of complex
toluene afforded dark-purple microcrystalline powder.
3 from
Complexes
Darensbourg and co-workers56 in 2008 by one-pot salt
metathesis reaction of Schiff base ligand, equiv of
1 and 3 were previously synthesized by
Figure 1. Molecular structure of
1. Hydrogen atoms,
2
methylene fragments of the THF molecules, and methyl
substituents of tBu groups are omitted for clarity; thermal
ellipsoids drawn at the 30% probability level. Bond lengths (Å)
and angles (deg): Ca(1)−O(1) 2.238(2), Ca(1)−N(1) 2.500(2),
Ca(1)−N(2) 2.593(2), Ca(1)−N(3) 2.367(2), Ca(1)−O(2) 2.383(2);
NaN(SiMe3)2 and 1 equiv of CaI2 in THF and characterized by
NMR spectroscopy. Complexes were isolated after
recrystallization from dichloromethane in 83.8 and 47.9%
yield. We proposed an approach which allows for increasing
the products yields up to 90 and 86% respectively. Complexes
1-4 are well-soluble in THF, DME, Et2O, toluene and slightly
soluble in hexane. Complexes are stable in both solid state and
in toluene solution under conditions excluding contact with
oxygen and moisture. No evidences for ligand redistribution
O(1)−Ca(1)−N(1)
N(2)−Ca(1)−N(3)
O(1)−Ca(1)−N(3)
72.61(5),
106.37(5),
116.30(5),
N(1)−Ca(1)−N(2)
O(1)−Ca(1)−O(2)
O(2)−Ca(1)−N(3)
65.05(5),
86.37(5),
97.77(5),
O(3)−Ca(1)−N(3) 93.90(5), Si(1)−N(3)−Si(2) 121.54(9).
1
tBu
reaction typical for calcium compounds were detected. The H
and 13C{1H} NMR spectra of 1-4 display single sets of
resonances in the 0 to 75 °C temperature range, consistent
with the presence of a single C1-symmetric species in solution.
tBu
(Me Si)2N
3
N
O
N
Ca
The single crystal samples of
1 suitable for X-ray diffraction
Toluene
THF2
tBu
N
N
N
0.5
+ PhSiH3
Ca
O
study were obtained by slow concentration of THF/hexane
solution at room temperature. The molecular structure of
N
- PhSiH2N(SiMe3)2
- 0.5 CaH2
O
- THF
complex
refinement data are listed in the Table S1 (see Supporting
Information). crystallizes in triclinic crystal system, P-1 space
group The six-coordinate metal centre in adopts a distorted
1 is depicted in Figure 1 and the crystal and structural
tBu
5, 20%
tBu
1
tBu
.
1
square-bipyramidal geometry. Two nitrogen and one oxygen
atoms of the iminophenolate ligand and one nitrogen atom of
amido group are located in the base and two oxygen atoms of
THF molecules occupy the axial vertices. The Ca(1)−N(3)silylamido
Scheme 2. Reaction of complex
1 with PhSiH3.
Crystals of complex 5, suitable for X-ray diffraction study, were
obtained by slow concentration of its solution in toluene at
room temperature. According to the X-ray diffraction data,
bond length in
typical for six-coordinate Ca complexes with terminal
N(SiMe3)2 ligands57-59
1 (2.367(2) Å) fall into the range of values
complex
5
crystallizes in the space group P2(1)/c as a solvate
is monomeric, the calcium ion is
5∙C7H8. Complex
5
.
coordinated by two iminophenolate ligands (Figure 2). The
bond lengths between Ca(II) and oxygen and nitrogen atoms of
the salicylaldiminate unit (Ca(1)−O(1) (2.205(2), Ca(1)−N(2)
In order to obtain a heteroleptic hydrido derivative of Ca
containing tridentate iminophenolate ligand complex was
treated with 1.3 equiv. of PhSiH3 (toluene, 20° C, 24h).
However, homoleptic bis(phenolate) calcium complex was
1
2.455(2) Å) in
5 fall into the range normally measured in the
5
related six-coordinated calcium complexes with Schiff base
ligands.8, 61, 62
isolated from the reaction mixture as dark-red crystals in 20%
yield (Scheme 2) together with insoluble off-white powder of
CaH2. Most likely the formation of
5 is a result of the ligand
redistribution reaction of the coordinatively labile hydrido
intermediate [L1CaH].60
2 | J. Name., 2012, 00, 1-3
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Journal Name
ARTICLE
tBu
tBu
H
N
O
OH
N
N
Toluene, RT
tBu
N
YbIII
- HN(SiMe3)2
N
-0.5 [(Me3Si)2N]2Yb(THF)2
N
THF
tBu
O
tBu
+ [(Me3Si)2N]2YbII(THF)2
6
20%
tBu
Scheme 3. Synthesis of complex
6.
Monocrystalline samples of 6 suitable for X-ray analysis were
obtained by slow concentration of a DME/hexane solution at
room temperature. The X-ray study established the order of
connectivity of the atoms in the molecule; however, the poor
quality of the crystals does not allow us to discuss the
Figure 2. Molecular structure of
5. Hydrogen atoms and
methyl substituents of tBu groups are omitted for clarity;
thermal ellipsoids drawn at the 30% probability level. Bond
lengths (Å) and angles (deg): Ca(1)−O(2) 2.182(2), Ca(1)−O(1)
2.205(2), Ca(1)−N(2) 2.455(2), Ca(1)−N(3) 2.471(2), Ca(1)−N(4)
2.480(2), Ca(1)−N(1) 2.525(2); O(2)−Ca(1)−O(1) 113.57(6),
geometric parameters of
depicted in Figure 3.
6. The crystal structure of 6 is
N(2)−Ca(1)−N(4)
165.76(6),
O(1)−Ca(1)−N(3)
92.12(6),
O(2)−Ca(1)−N(1) 90.14(6).
Ca(II) and Yb(II) ions due to their hard Lewis acidity,
64
oxophilicity, low polarizability63,
and close values of ionic
radii65 exhibit strong similarities in the structures and
reactivity66. Despite this fact our attempts to synthesize
ytterbium analogue failed. Instead of the expected Yb(II)
amido complex L1Yb[N(SiMe3)2](THF)n the reaction afforded a
bis(alkoxo) Yb(III) complex
6
coordinated by new trianionic
half of
[OONNNN]3- ligand and HN(SiMe3)2 while
a
Yb[N(SiMe3)2]2(THF)2 remained unreacted (Scheme 3).
Interestingly within first 10 min of the reaction the formation
of equimolar amounts of homoleptic bis(phenolate) and
bis(amido) Yb(II) complexes was evidenced by 1H NMR
spectroscopy. The attempts to detect the target amido
phenolate L1Yb[N(SiMe3)2](THF)n in solution failed. Moreover,
according to 1H NMR spectroscopic monitoring in ~1 h at room
temperature paramagnetic species appeared in the reaction
Figure 3. Molecular structure of
6. Hydrogen atoms,
methylene fragments of the THF molecule and methyl
substituents of tBu groups are omitted for clarity.
The reaction of complex
4
with 1.3 equiv. of PhSiH3 in toluene
resulted in the
mixture. Most likely the assembling of new ligand in
6 can be
at room temperature similarly to that of
1
rationalized by a sequence of transformations in the
formation of equimolar mixture of homoleptic bis(phenolate)
and CaH2. After recrystallization of the reaction products from
coordination sphere of ytterbium: intramolecular oxidation of
Yb(II) by redox active iminophenolate ligand67 followed by the
formation of Yb(III)-N bond and C-H bond activation resulted in
the formation of a new bond between imino carbon and the
carbon atom in ortho-position of quinoline ring.
mixture DME/hexane (1:1) calcium bis(phenolate) complex
7
was isolated in 38% yield (Scheme 4). Monitoring of the
1
reaction of
NMR spectroscopy revealed that the reaction is completed in
0.5 h to afford an equimolar mixture of PhSiH2N(SiMe3)2 and
4 with PhSiH3 (1:1 molar ratio, C6D6, 20 °C) by H
Formation of
6 in the reaction of Yb(III) tris(amide)
7.
Yb[N(SiMe3)2]3 with equimolar amount of L1H (THF, 40 °C) has
been formerly reported by Shen.68 In this case C-H bond
activation occurred along with elimination of HN(SiMe3)2 while
valent state of ytterbium ion remained unchanged. The
attempts of synthesis of heteroleptic Ln(II) (Ln = Yb, Sm) amido
complexes supported by ligands L2-L4 failed. The reactions
resulted in the formation of intractable oily products
containing both LnII and LnIII species.
No evidence for the presence of a transient hydrido species
[L4CaH] was detected. This observation suggests that the σ-
bond metathesis reaction is rather slow, while the ligand
redistribution occurs fast.
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ARTICLE
Journal Name
tBu
O
N
N
tBu
O
O
O
N
(Me3Si)2N
OH
tBu
tBu
O
O
O
Toluene
Ca
tBu
2
Ca
Toluene
tBu
N
O
THF
THF
O
+ PhSiH3
- 2 HN(SiMe3)2
Ca
N
- PhSiH2N(SiMe3)2
- 0.5 CaH2
tBu
O
O
N
O
tBu
O
tBu
+ Ca[N(SiMe3)2]2(THF)2
8
, 89%
tBu
tBu
7, 38%
tBu
Scheme 5. Synthesis of complex
According to the X-ray analysis in complex
sphere of eight-coordinated calcium ion is composed by two
[ONO] L4 ligands and two THF molecules (Figure 5).
distinctive feature of is the presence of short distances
8.
Scheme 4. Reaction of complex
4 with PhSiH3.
8
the coordination
Complex 7 is well soluble in aromatic hydrocarbons, THF and
DME but poorly soluble in hexane. Crystals of suitable for X-
ray analysis were obtained by slow concentration of
DME/hexane solution at room temperature. The molecular
7
A
8
between the aromatic rings at the nitrogen atom of the
phenolate ligands. Nearly coplanar orientation of 2-MeO-5-
MeC6H3N rings of two ligands (dihedral angle is 11.2o) together
structure of complex
and structural refinement data are listed in the Table S2
(Supporting Information). The asymmetric unit of contains
7 is depicted in Figure 4 and the crystal
7
two crystallographically independent molecules. The metal with short distance between the ring centroids (3.67(3) Å) are
center in
7 is coordinated by two monoanionic tridentate
indicative of π-π interaction. This interaction results in
shortening of Ca-OMe coordination bonds compared to 7 (8:
phenolato ligands. Despite identical denticity of L1 and L4 the
smaller bulkiness of the latter allows for additional
coordination of DME molecule to the metal center thus
resulting in coordination number of 8. The Ca-OPhenolate and Ca-
Ca(1)−O(4) 2.5043(9), Ca(1)−O(2) 2.5491(9));
2.658(2), Ca(1)−O(2) 2.615(2) Å).
7: Ca(1)−O(4)
N bond distances in 7 are slightly longer than those in 5 due to
higher coordination number of Ca(II) ion.
Figure 5. Molecular structure of
8. Hydrogen atoms,
methylene fragments of the THF molecule, and methyl
substituents of tBu groups are omitted for clarity; thermal
ellipsoids drawn at the 30% probability level. Bond lengths (Å)
and angles (deg): Ca(1)−O(3) 2.2315(8), Ca(1)−O(1) 2.2471(8),
Ca(1)−O(4) 2.5043(9), Ca(1)−N(1) 2.5373(9), Ca(1)−N(2)
2.540(2), Ca(1)−O(2) 2.5491(9), Ca(1)−O(6) 2.5517(9),
Figure 4. Molecular structure of 7. Hydrogen atoms, methyl
and methylene fragments of the DME molecule, and methyl
substituents of tBu groups are omitted for clarity; thermal
ellipsoids drawn at the 30% probability level. Bond lengths (Å)
and angles (deg): Ca(1)−O(1) 2.253(2), Ca(1)−O(3) 2.264(2),
Ca(1)−O(6) 2.520(2), Ca(1)−N(2) 2.535(2), Ca(1)−O(5) 2.530(2),
Ca(1)−N(1) 2.540(2), Ca(1)−O(2) 2.615(2), Ca(1)−O(4) 2.658(2);
O(1)−Ca(1)−O(3) 158.87(6), O(1)−Ca(1)−N(2) 114.00(6),
Ca(1)−O(5)
O(1)−Ca(1)−N(2)
N(1)−Ca(1)−N(2)
2.567(2);
145.70(3),
112.40(3),
O(3)−Ca(1)−O(1)
O(4)−Ca(1)−N(1)
O(1)−Ca(1)−O(4)
123.45(3),
71.67(3),
88.98(3),
O(4)−Ca(1)−O(2) 89.88(3).
Cross-dehydrogenative coupling of silanes with amines
catalyzed by complexes 1-4. Complexes 1-4 were evaluated as
precatalysts for cross-dehydrogenative coupling of silanes with
amines. The catalytic tests were performed either in neat
substrates ([silane]:[amine] = 1:1) or in C6D6 solution in the
presence of 2 mol % of precatalyst. The representative results
are listed in Table 1-2.
N(2)−Ca(1)−N(1)
139.58(6),
N(1)−Ca(1)−O(4)
85.23(5),
O(2)−Ca(1)−O(4) 69.46(5), O(1)−Ca(1)−O(4) 76.78(6).
The analogue of
7
containing 2 coordinated THF molecules
) was synthesized via amine elimination
instead of DME (
reaction of Ca[N(SiMe3)2]2(THF)2 with 2 equivalents of L4H
8
(Scheme 5). After recrystallization from THF-hexane mixture
was isolated in 89% yield.
8
4 | J. Name., 2012, 00, 1-3
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Journal Name
Table Cross-dehydrogenative coupling of PhSiH3 with
ARTICLE
49b
50b
51b
52b
53b
54b
55b
56b
57b
58b
59b
60b
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
92
76
1
.
primary and secondary amines catalyzed by complexes 1-4.
Et2NH
Cy2NH
Ph2NH
PhSiH2NEt2
83
90
70
34
45
62
0
PhSiH2NCy2
PhSiH2NPh2
a
№
Cat.
Amine
Product
Conversion
1
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
100 (67:33)
PhSiH2NHPr
+
0
2
100 (61:39)
nPrNH2
0
3
100 (75:25)
PhSiH(NHPr2)2
0
4
100 (80:20)
91
20
83
100
0
61
62
5
92
6
68
iPrNH2
CyNH2
PhSiH2NHiPr
PhSiH2NHCy
63
7
66
64
8
87
65b
66b
67b
68b
69b
70b
71b
72b
73b
74b
75b
76b
9
100
0
10
11
12
13b
14b
15b
16b
17b
18b
19b
20b
21
22
23
24
25
26
27
28
29b
30b
31b
32b
33b
34b
35b
36b
37
38
39
40
41
42
43
44
45
46
47
48
94
0
NH
NSiH2Ph
96
0
100
48
14
28
33
50
70
91
46
99
74
sec-BuNH2
tBuNH2
PhSiH2NHsec-Bu
PhSiH2NHtBu
68
100
39
28
25
40
a[precatalyst]0/[silane]0/[amine]0 = 1:50:50, neat substrates,
b
100(65:35)
100(79:21)
100(75:25)
100(70:30)
100
precatalyst: 10.0
[precatalyst]0/[silane]0/[amine]0
µmol,
RT,
5
min.
1:50:50, no solvent,
PhSiH2NHCH2Ph
+
=
PhCH2NH2
precatalyst: 10.0 µmol, 60oC, 5h. cSilane conversion
determined by 1H NMR spectroscopy.
PhSiH2(NHCH2Ph)2
Complexes
1-4 proved to be catalytically active in cross-
NH2
Intractable
mixture
100
dehydrogenative coupling of phenylsilane with primary and
secondary amines under mild reaction conditions. The reaction
rates and selectivity were found to be strongly affected by
steric and electronic properties of amine substrate. Thus, for
primary aliphatic (nPrNH2, iPrNH2, CyNH2, sec-BuNH2,
PhCH2NH2, (CH3)2N(CH2)2NH2) and secondary cyclic amines
(pyrrolidine and morpholine) quantitative conversions were
reached in 5 minutes at room temperature. Interestingly
primary aromatic PhNH2 turned out much less reactive
compared to primary aliphatic CyNH2 featuring similar steric
demand. For PhNH2 quantitative conversions were provided by
all catalysts only in 5 h at 60oC, while in the case of CyNH2 for
all catalysts the reactions were complexed in 5 min at 20°C.
Anilines containing donor (OMe, OPh) or bulky (tBu)
substituents in ortho position are completely inactive in that
transformation even at 80oC for 24 h. However, for a sterically
demanding 2,6-iPr2C6H3NH2 32-84% conversions were reached
in 5 min at 20°C. Reaction rates of dehydro-coupling of PhSiH3
with primary aliphatic amines decrease with increase of steric
demand of amine substituent in line nPr - Cy - tBu. For most
OMe
100
100
99
95
PhNH2
PhSiH2NHPh
97
100
83
32
PhSiH2NHC6H3
iPr2-2,6
2,6-iPr2C6H3NH2
40
84
100
(CH3)2N-
Intractable
mixture
100
(CH2)2NH2
100
100
88 (100:0)
75 (83:17)
91 (100:0)
87 (100:0)
95
PhSiH2N(CH2)4
+
(CH2)4NH
PhSiH(N(CH2)4)2
93
(CH2)4NH
2equiv.
sterically demanding tBuNH2 complexes 1-4 performed lowest
activities: even in 5 h at 60oC the conversion did not overpass
PhSiH(N(CH2)4)2
92
95
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Journal Name
0
0
0
40%. Expectedly for the same
R
secondary amines 22
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
demonstrated lower reactivity compared to that of primary 23
ones (compare CyNH2 vs Cy2NH). It takes at least 5 h at 60oC to 24
reach high conversion. In the case of pyrrolidine complexes 1-4
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
64
45
enable the formation of the tertiary silane PhSiH(N(CH2)4)2 in
quantitative yields and excellent chemoselectivity (Table 1,
(CH2)4NH
PhMeSiHN(CH2)4
43
75
70
67
64
89
0
entry 45-48), however
activity. The results of silane-amine coupling catalyzed by
complexes do not demonstrate a dramatic effect of the
1 and 4 perform slightly higher catalytic
NH2
OMe
1-4
ancillary ligand on both catalytic activity and selectivity of
metal promoted reactions obviously due to their similar
structure and steric demand. For highly reactive primary
aliphatic amines nPrNH2, CyNH2, (CH3)2N(CH2)2NH2 as well as
for secondary Et2NH and pyrrolidine (Figure 6) no noticeable
0
0
difference of catalytic activity for 4 was observed. Similarly in
1-
0
the case of PhNH2 complexes 1-4 displayed close catalytic
activities at 60oC. However, in the reactions of 2,6-iPr2C6H3NH2
44
3
and Cy2NH complexes 2 and 3 were less catalytically active. For
18
35
NH
NSiHMePh
most amines the reactions were found to be highly selective
affording exclusively mono-addition products with no
indication for the formation of other products. However, in
0
0
0
0
0
0
0
0
coupling of PhSiH3 with nPrNH2 and PhCH2NH2 complexes
turned out to be less chemoselective: the formation of both
secondary and tertiary silanes was detected (in 67:33 ( ) ,
61:39 ( ) 75:25 ( ) and 80:20 ( ) ratios for nPrNH2, and 65:35
) , 79:21 ( ) 75:25 ( ) and 70:30 ( ) ratios for PhCH2NH2).
1-4
1
2
3
4
(
1
2
3
4
a[precatalyst]0/[silane]0/[amine]0 = 1:50:50, neat substrates,
precatalyst: 10.0 µmol, 60oC, 5h. cSilane conversion
determined by 1H NMR spectroscopy.
Table 2. Cross-dehydrogenative coupling of PhMeSiH2 with
primary and secondary amines catalyzed by complexes 1-4.
To have better insight into the effect of nature of silane on the
reaction rate, complexes 1-4 were evaluated as catalysts for
cross-dehydrogenative coupling of PhMeSiH2 with primary and
secondary amines. As it could be expected the reactions of
PhMeSiH2 proved to be much slower compared to those of
PhSiH3 and to enable the reaction it was necessary to carry out
the catalytic tests at 60oC. The reactions were found to be
extremely selective affording exclusively mono-addition
products. Morpholine, tBuNH2, Cy2NH, carbazole, bis(2-
methoxyethyl)amine were found to be inactive in coupling
a
№
Cat.
Amine
nPrNH2
Product
Conversion
1
2
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
85
65
67
88
56
45
44
60
0
PhMeSiHNHPr
3
4
5
with PhMeSiH2 in presence of
with PhMeSiH2 reaching highest conversion of 44% in the case
of complex , while it turned out completely inert with PhSiH3.
1-4. Surprisingly indole reacts
6
CyNH2
tBuNH2
PhNH2
PhMeSiHNHCy
PPhMeSiHtBu
PhMeSiHNHPh
7
1
8
Similarly the reaction of (2-methoxyphenyl)methylamine with
PhMeSiH2 leads to the formation of the appropriate tertiary
silane, while for PhSiH3 only intractable mixture of silanes and
9
10
11
12
13
14
15
16
17
18
19
20
21
0
oligomeric silazanes was obtained. Unfortunately complexes
4
1-
were unable to promote catalytic reactions of tertiary silanes
0
0
(Ph3SiH and Ph2MeSiH) with any primary and secondary
amines.
93
10
75
91
65
46
50
70
0
DippNH2
Cy2NH
PhSiH2NHDipp
PhMeSiHNCy2
6 | J. Name., 2012, 00, 1-3
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ARTICLE
leaving no chance for the slower disproportionation reaction
to proceed.
As it was mentioned above a number of Ca(II) catalysts for
cross-dehydrogenative coupling of silanes with amines still
remains very limited. Compared to the previously published
Ca(II)
catalysts
Ph2CNPh)(hmpa)3
of
azametallacyclopropane
and amidoiminoanilido48,49 types
Ca(η2-
52, 53
complexes
unable to promote coupling of tertiary silanes. On the other
hand, high chemoselectivity of complexes in coupling of
1-4 performed moderate activity and turned out
1-4
PhSiH3 and tBuNH2, EtNH2, DippNH2 and pirrolidine is the
undoubted merit of these compounds. In these reactions
complexes
1-
4
enable the formation of exclusively mono-
addition products while complex Ca(η2-Ph2CNPh)(hmpa)3
affords a mixture of mono-, doubly dehydrocoupled products
and higher oligomers.53
Figure 6. Plot of PhSiH3 consumption vs reaction time for the
cross-dehydrogenative coupling of PhSiH3 with pyrrolidine
catalyzed by complexes 1-4 and Ca[N(SiMe3)2]2(THF)2
benzene-d6 at 25 °C. Reaction conditions:
(5) in
[precatalyst]0/[silane]0/[amine]0 = 1:50:50, neat substrates,
precatalyst: 4.7 mmol, RT; total volume 0.7 mL.
Conclusions
In order to get a deeper insight into the effect of the
supporting ligand on catalytic activity a comparative study of
the reaction rates of cross-dehydrogenative coupling of PhSiH3
The reactions of bis(amido) complex Ca[N(SiMe3)2]2(THF)2 and
iminophenols L1−4H cleanly occur in toluene under mild
conditions and allow for the preparation of a series of related
with pyrrolidine catalysed by complexes
Ca[N(SiMe3)2]2(THF)2 was performed. No noticeable
difference in the rates of the reactions catalyzed by was
detected. Surprisingly under the similar conditions bis(amido)
complex proved to be the most active catalyst however less
chemoselective for this transformation (Table 3).
1-
4
and
heteroleptic amidophenolates LCa[N(SiMe3)2](THF) (1−4) in
(5)
good yields. Herein once again we clearly demonstrated that
similarity of Ca(II) and Yb(II) chemistries disappears when
redox active ligands are applied. Due to redox character of
Schiff base ligands and Yb(II) center unlike Ca(II) species the
amine elimination reaction is accompanied by metal-to-ligand
electron transfer resulting in C−H bond activation and C-C
1-4
5
Table
3. Cross-dehydrogenative coupling of PhSiH3 with
bond formation. Amido Ca(II) complexes
1−4 supported by
pyrrolidine catalyzed by complexes 1-5.
Schiff base ligands proved to be stable in solution and are not
prone to Schlenk equilibrium. However the related
heteroleptic hydrido species generated in the reactions of
LCa[N(SiMe3)2](THF)n and PhSiH3 immediately undergo the
ligand redistribution reaction affording homoleptic
Time,
min
15
a
№
Cat.
Product
Conversion, %
100 (100:0)
100 (100:0)
100 (100:0)
100 (100:0)
100 (82:18)
1
2
3
4
5
1
2
3
4
5
22
PhSiH2N(CH2)4
+
19
bis(phenolate) species. Complexes
1-4 demonstrated high
16
PhSiH(N(CH2)4)2
catalytic activity towards cross-dehydrogenative coupling of
amines and organosilanes under mild conditions. Despite of
10
a[precatalyst]0/[silane]0/[amine]0 = 1:500:500, neat substrates,
c
precatalyst: 1.0 µmol, RT, C6D6, Total volume 0.7 mL.
Conversion determined by 1H NMR spectroscopy.
lower catalytic activity of 1-4 compared to some of previously
published alkaline-earth metals48,49,52,53 they provide very high
chemo-selectivity in coupling of primary silanes with primary
amines.
The fact that hydrido complexes [LCaH] which are expected
intermediates in the reactions of complexes 1 and 4 with
PhSiH3 are prone to ligand redistribution raises the question of
nature of the real catalytic species that form in the reaction
mixtures and are responsible for the realization of the catalytic
cycle. In order to clarify the situation a series of experiments
was carried out. The isolated products of symmetrization of
Experimental
General considerations and materials characterization. All
experiments were performed in evacuated tubes or in inert
atmosphere, using standard Schlenk or glove-box techniques,
with rigorous exclusion of traces of moisture and air. After
drying over KOH, THF and DME were purified by distillation
from sodium/benzophenone ketyl, hexane and toluene by
distillation from sodium/triglyme benzophenone ketyl prior to
use. Benzene-d6 was dried with sodium/benzophenone ketyl
and condensed in vacuum prior to use. [(Me3Si)2N]2M(THF)2
(M = Yb69, Ca70), L1-3H55 were prepared according to literature
procedures. PhSiH3, PhMeSiH2, Ph3SiH, pirrolidine, DippNH2,
[LCaH]: bis(phenolate) complexes
1,4
5, 7, 8 and CaH2 as well as
crude reaction mixtures and PhSiH3 (in 1h) proved to be
inert even in promoting cross-dehydrogenative coupling of the
most active substrates pyrrolidine and PhSiH3. Thus, it seems
appropriate to assume that the reactions catalyzed by 1-4
proceed according to the mechanism previously established
for the related Ba complexes involving amido [LMNR] and
hydrido [LMH] intermediates.48 Most likely the transient
hydrido species being highly reactive rapidly react with amine
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pirrole, iPr2NH, nPrNH2, morpholine, CyNH2, Cy2NH, Et2NH, Synthesis of L2Ca[N(SiMe3)2] (2). A solution of L2H (0.150 g,
BnNH2, tBuNH2, (MeOCH2CH2)2NH were vacuum-distilled over 0.373 mmol) in toluene (15 mL) was added to a solution of
CaH2 and then were degassed by freeze-pump-thaw methods. Ca[N(SiMe3)2]2(THF)2 (0.188 g, 0.373 mmol) in toluene (10 mL)
NMR spectra were recorded on a Bruker DPX 200 or Bruker at room temperature. The color of the reaction mixture
1
Avance DRX-400 spectrometer. Chemical shifts for H, 13C and changed immediately from pale-yellow to bright-orange. The
29Si spectra were referenced internally using the residual reaction mixture was stirred for 1 h at room temperature. The
solvent resonances and are reported relative to TMS. C,H,N volatiles were then removed under reduced pressure and the
elemental combustion analysis was performed in the solid residue was dissolved in THF/hexane mixture (1:1). Slow
microanalytical laboratory of IOMC.
concentration of the solution at room temperature resulted in
the formation of as bright-yellow microcrystalline powder.
2
Synthesis of L4H 2-Methoxy-5-methylaniline (0.54 g, 4.30
mmol) and 2 drops of formic acid were added to a solution of
3,5-di-tert-butyl-2-hydroxybenzaldehyde (1.00 g, 4.30 mmol) in
methanol (100 mL). Resulted solution was refluxed for 10 h
and then cooled to −20оС. The mother liquid was decanted
from yellow crystals, and the crystals were washed with cold
hexane and dried in vacuum for 30 min. L4H was isolated in
The mother liquid was decanted and the solid residue was
washed with cold hexane and dried in vacuum for 30 min.
Complex
2
was isolated in 91% yield (0.204 g). 1H NMR (400
MHz, C6D6) δ = 0.09, 0.29 (s, together 18H, Si(CH3)3), 1.45 (s,
3
18H, C(CH3)3), 6.31 (d, JHH =8.1 Hz, 1Н, Ar), 6.68 (m, 6Н, Ar),
6.79 (d, 3JHH =7.2 Hz, 1Н, Ar), 6.94 (d, 3JHH =7.5 Hz, 1Н, Ar), 7.23
(s, 1Н, Ar), 7.67 (s, 1Н, Ar), 8.42 (s, 1H, CH=N). 13C NMR (101
MHz, C6D6) δ= 1.1, 2.3 (SiCH3), 29.5 (C(CH3)3), 31.6 (C(CH3)3),
33.8 (C(СH3)3), 35.3 (C(СH3)3), 114.5, 118.8, 121.9, 124.0, 125.2,
125.5, 129.7, 129.9, 130.4, 133.4, 140.8, 140.9, 152.3, 152.6,
166.5, 167.8, 168.7 (Ar), 170.1 (CH=N). IR (Nujol, KBr, ν/cm−1):
1615 (s), 1585 (s), 1525 (s), 1485 (s), 1410 (s), 1260 (s), 1200
(s), 1150 (m), 1100 (m), 1020 (m), 870 (s), 760 (m), 700 (w),
640 (w), 520 (m). Elem. anal. calc. for C33H48CaN2O2Si2 (601.01
g/mol): C 65.95; H 8.05; N 4.66. Found: C 65.60; H 8.17; N 4.32.
1
88% yield (1.34 g). H NMR (400 MHz, CDCl3) δ = 1.34 (s, 9H,
C(CH3)3), 1.49 (s, 9H, C(CH3)3), 2.33 (s, 3H, CH3), 3.87 (s, 3H,
3
OCH3), 6.87 (d, 3JHH = 8.9 Hz, 1H, Ar), 7.01 (d, JHH = 6.4 Hz, 2Н,
Ar), 7.21 (s, 1H, Ar), 7.43 (s, 1H, Ar), 8.70 (s, 1H, CH=N), 14.05
(s, 1H, OH). 13C NMR (101 MHz, CDCl3) δ = 20.5 (CH3), 29.5
(C(CH3)3), 31.5 (C(CH3)3), 34.2 (C(CH3)3), 35.1(C(CH3)3), 56.1
(OCH3), 112.0, 118.6, 121.1, 126.6, 127.6, 127.7, 130.4, 137.0,
137.5, 140.2, 150.8, 158.7 (Ar), 163.8 (CH=N). IR (Nujol, KBr,
ν/cm−1): 1615 (s), 1580 (s), 1510 (s), 1460 (s), 1380 (s), 1300
(w), 1270 (m), 1250 (s), 1230 (m), 1170 (w), 1130 (s), 1030 (m), Synthesis of L3CaN[(SiMe3)2](THF) (3). A solution of L3H (0.140
990 (w), 950 (w), 890 (w), 870 (w), 830 (w), 810 (s), 770 (m), g, 0.431 mmol) in toluene (15 mL) was added to a solution of
720 (w). Elem. anal. calc. for C23H31NO2 (353,24 g/mol): C, Ca[N(SiMe3)2]2(THF)2 (0.218 g, 0.431 mmol) in toluene (10 mL)
78.15; H, 8.84; N, 3.96. Found: C, 78.25; H, 8.80; N, 3.86.
at room temperature. The color of the reaction mixture
changed immediately from pale-yellow to bright-purple.
Reaction mixture was stirred for 1 h at room temperature. The
volatiles were then removed under reduced pressure and the
solid residue was dissolved in toluene. Slow concentration of
the solution at room temperature resulted in the formation of
Synthesis of L1Ca[N(SiMe3)2](THF)2 (1). A solution of L1H (0.161
g, 0.447 mmol) in toluene (15 mL) was added to a solution of
Ca[N(SiMe3)2]2(THF)2 (0.226 g, 0.447 mmol) in toluene (10 mL)
at room temperature. The color of the reaction mixture
changed immediately from pale-yellow to bright-orange.
Reaction mixture was stirred for 1 h at room temperature. The
volatiles were then removed under reduced pressure and the
solid residue was dissolved in THF/hexane mixture (1:1). Slow
concentration of the solution at room temperature resulted in
3
as dark-purple microcrystalline powder. The mother liquid
was decanted and the solids were washed with cold hexane
and dried in vacuum for 30 min. Complex was isolated in 86%
3
yield (0.221 g). 1H NMR (400 MHz, C6D6) δ = 0.29 (s, 18H,
Si(CH3)3), 1.41 (m, 4H, β-CH2 THF), 1.51 (s, 9H, C(CH3)3), 1.74 (s,
9H, C(CH3)3), 3.57 (m, 4H, α-CH2 THF), 4.29 (s, 2H, CH2), 6.24 (t,
the formation of
decanted and the crystals were washed with cold hexane and
dried in vacuum for 30 min. Complex was isolated in 90%
1 as dark-red crystals. The mother liquid was
3
3
3JHH =8.2 Hz, 1Н, Ar), 6.37 (d, JHH =8.1 Hz, 1Н, Ar), 6.79 (d, JHH
=7.7 Hz, 1Н, Ar), 7.20 (d, 3JHH =2.1 Hz, 1 H, Ar), 7.73 (d, 3JHH =2.5
Hz, 1Н, Ar), 8.02 (s, 1Н, Ar), 8.31 (s, 1H, CH=N). 13CNMR (101
MHz, C6D6) δ = 1.1 (SiCH3), 25.5 (β-CH2 THF), 29.7 (C(CH3)3),
31.8 (C(CH3)3), 33.8 (C(СH3)3), 35.6 (C(СH3)3), 65.3 (CH2), 67.5
(α-CH2 THF), 121.0, 121.1, 121.7, 129.0, 129.8, 132.0, 137.2,
140.5, 149.3, 160.2, 169.2, (Ar), 170.2 (CH=N). IR (Nujol, KBr,
ν/cm−1): 1610 (s), 1550 (s), 1510 (s), 1310 (s), 1260 (s), 1210 (s),
1170 (s), 1140 (s), 990 (m), 970 (s), 940 (m), 880 (m), 830 (s),
780 (m), 660 (w), 640 (w), 610 (m), 520 (s). Elem. anal. calc. for
C31H53CaN3O2Si2 (596.03 g/mol): C 62.47; H 8.96; N 7.05.
Found: C 62.70; H 8.67; N 6.98.
1
yield (0.284 g). 1H NMR (400 MHz, C6D6) δ = 0.29 (s, 18H,
Si(CH3)3), 1.42 (m, 8H, β-CH2 THF), 1.48 (s, 9H, C(CH3)3), 1.57 (s,
9H, C(CH3)3), 3.57 (m, 8H, α-CH2 THF), 6.36 (d, 3JHH =8.2 Hz, 1Н,
3
Ar), 6.98 (d, JHH =7.4 Hz, 1Н, Ar), 7.07 (d, 3JHH =7.6 Hz, 1Н, Ar),
3
7.13 (s, 1Н, Ar), 7.24 (d, JHH =8.1 Hz, 1Н, Ar), 7.33 (s, 1Н, Ar),
7.71 (s, 1Н, Ar), 8.52 (s, 1Н, Ar), 8.61 (s, 1H, CH=N). 13CNMR
(101 MHz, C6D6) δ= 1.1 (SiCH3), 25.5 (β-CH2 THF), 29.5
(C(CH3)3), 31.6 (C(CH3)3), 33.8 (C(СH3)3), 35.5 (C(СH3)3), 67.5 (α-
CH2 THF), 115.9, 121.2, 121.9, 123.4, 127.5, 128.0, 129.1,
129.9, 130.6, 132.9, 137.2, 141.4, 149.1, 149.5, 167.3 (Ar),
171.4 (CH=N). IR (Nujol, KBr, ν/cm−1): 1600 (s), 1590 (s), 1525
(s), 1500 (w), 1410 (m), 1315 (s), 1270 (m), 1260 (w), 1225 (m), Synthesis of L4CaN[(SiMe3)2] (4). A solution of L1H (0.083 g,
1160 (s), 1080 (m), 1060 (s), 1020 (w), 960 (s), 890 (w), 830 0.235 mmol) in toluene (15 mL) was added to a solution of
(w), 790 (m). Elem. anal. calc. for C38H61CaN3O3Si2 (704.15 Ca[N(SiMe3)2]2(THF)2 (0.119 g, 0.235 mmol) in toluene (10 mL)
g/mol): C 64.81; H 8.75; N 5.97. Found: C 64.50; H 8.47; N 5.68. at room temperature. The color of the reaction mixture
8 | J. Name., 2012, 00, 1-3
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changed immediately from pale-yellow to bright-yellow. mixture was stirred for 1 h at room temperature. The volatiles
Reaction mixture was stirred for 1 h at room temperature. The were then removed under reduced pressure and the solid
volatiles were then removed under reduced pressure and the residue was dissolved in DME/hexane mixture (1:1). Slow
solid residue was dissolved in THF/hexane mixture (1:1). Slow concentration of the solution at room temperature resulted in
concentration of the solution at room temperature resulted in the formation of
the formation of as bright-yellow crystals. The mother liquid was decanted and the crystals were washed with cold hexane
was decanted and the crystals were washed with cold hexane and dried in vacuum for 30 min. Complex was isolated in 20%
and dried in vacuum for 30 min. Complex
was isolated in 95% yield (0.032 g). IR (Nujol, KBr, ν/cm−1): 1600 (s), 1590 (s), 1525
6 as dark-brown crystals. The mother liquid
4
6
4
yield (0.140 g). 1H NMR (400 MHz, C6D6) δ = 0.09, 0.29 (s, (s), 1500 (w), 1410 (m), 1315 (s), 1270 (m), 1260 (w), 1225 (m),
together 18H, Si(CH3)3), 1.44 (s, 9H, C(CH3)3), 1.69 (s, 9H, 1160 (s), 1080 (m), 1060 (s), 1020 (w), 960 (s), 890 (w), 830
C(CH3)3), 2.06 (s, 3H, CH3), 3.32 (s, 3H, OCH3), 6.17 (d, 3JHH = 8.4 (w), 790 (m). Elem. anal. calc. for C54H66YbN4O4 (1008.14
Hz, 1Н, Ar), 6.57 (d, 3JHH = 9.3 Hz, 1Н, Ar), 6.88 (s, 1Н, Ar), 7.26 g/mol): C 64.33; H 6.61; N 5.56; Yb 17.16. Found: C 64.60; H
(s, 1Н, Ar), 7.72 (d, 3JHH = 2.6 Hz, 1Н, Ar), 8.45 (s, 1H, CH=N). 13
C
6.90; N 5.61; Yb 17.02.
NMR (101 MHz, C6D6) δ = 1.1, 2.9 (SiCH3), 20.4 (CH3),
29.7(C(CH3)3), 31.6 (C(CH3)3), 33.8 (C(СH3)3), 35.5 (C(СH3)3),
55.6 (OCH3), 110.6, 118.4, 121.8, 125.8, 129.7, 130.5, 131.9,
133.3, 140.2, 141.0, 149.7, 166.1 (Ar), 170.2 (CH=N). IR (Nujol,
KBr, ν/cm−1): 1615 (s), 1585 (s), 1540 (m), 1525 (m), 1500(s),
1410 (m), 1360 (m), 1270 (s), 1230 (s), 1160 (s), 1120 (s), 1020
(s), 880 (s), 770 (m), 660 (s), 590 (m), 520 (w). Elem. anal. calc.
for C33H55CaN2O3Si2 (623.34 g/mol): C 63.51; H 8.88; N 4.49.
Found: C 63.70; H 8.97; N 4.38.
Reaction of complex 4 with PhSiH3. PhSiH3 (0.021 g, 0.194
mmol) was added to a solution of
4 (0.093 g, 0.149 mmol) in
toluene (15 mL) at room temperature. The color of the
reaction mixture within 0.5 h changed from pale-yellow to
bright-purple. The reaction mixture was stirred for 1 h at room
temperature, centrifuged and the solution was decanted from
the off-white precipitate. The volatiles were then removed
under reduced pressure and the solid residue was redissolved
in DME/hexane mixture (1:1). Slow concentration of the
Reaction of complex 1 with PhSiH3. To a solution of 1 (0.075 g, solution at room temperature resulted in the formation of 7 as
0.106 mmol) in toluene (15 mL) PhSiH3 (0.015 g, 0.138 mmol) lemon-yellow crystals. The mother liquid was decanted and
was added at room temperature. The color of the reaction the crystals were washed with cold hexane and dried in
mixture changed from red to dark-red. The reaction mixture vacuum for 30 min. Complex 7 was isolated in 38% yield (0.047
1
was stirred at room temperature overnight, centrifuged and g). H NMR (400 MHz, C6D6) δ = 1.43 (s, 18H, C(CH3)3), 1.56 (s,
the solution was decanted from the off-white precipitate. The 18H, C(CH3)3)), 2.15 (s, 6H, CH3), 3.04 (s, 6H, OCH3 DME), 3.19
3
volatiles were then removed under reduced pressure and the (s, 4H, CH2 DME), 3.34 (s, 6H, OCH3), 6.33 (d, JHH =8.2 Hz, 2Н,
3
solid residue was dissolved in toluene. Slow concentration of Ar), 6.70 (d, JHH =8.0 Hz, 2Н, Ar), 6.95 (s, 2Н, Ar), 7.28 (s, 2Н,
3
the solution at room temperature resulted in the formation of Ar), 7.69 (d, JHH =2.2 Hz, 2Н, Ar), 8.44 (s, 2H, CH=N). 13C NMR
5
as dark-red crystals. The mother liquid was decanted and the (101 MHz, C6D6) δ = 20.4 (CH3), 29.6 (C(CH3)3), 31.6 (C(CH3)3),
crystals were washed with cold hexane and dried in vacuum 33.8 (C(СH3)3), 35.4 (C(СH3)3), 55.3 (OCH3), 58.6 (OCH3 DME),
1
5 was isolated in 20% yield (0.018 g). H 71.5 (CH2 DME), 110.6, 118.9, 121.5, 125.7, 129.1, 130.4,
for 30 min. Complex
NMR (400 MHz, C6D6) δ = 1.48 (s, 9H, C(CH3)3), 1.57 (s, 9H, 131.1, 132.0, 140.8, 141.5, 150.2, 166.4 (Ar), 170.3 (CH=N). IR
3
3
C(CH3)3), 6.37 (dd, JHH = 8.2, 4.4 Hz, 1Н, Ar), 7.01 (t, JHH = 8.9 (Nujol, KBr, ν/cm−1): 1615 (s), 1585 (s), 1540 (m), 1525 (m),
Hz, 2Н, Ar), 7.12 (d, 3JHH = 7.6 Hz, 1Н, Ar), 7.25 (d, 3JHH = 8.3 Hz, 1500(s), 1410 (m), 1360 (m), 1270 (s), 1230 (s), 1160 (s), 1120
1Н, Ar), 7.33 (s, 1Н, Ar), 7.70 (s, 1Н, Ar), 8.53 (s, 1Н, Ar), 8.62 (s), 1060(s), 1020 (s), 880 (s), 820 (m), 780 (m), 660 (s), 620
(s, 1H, CH=N). 13C NMR (101 MHz, C6D6) δ = 29.5 (C(CH3)3), 31.6 (m), 570 (m), 540 (w). Elem. anal. calc. for C50H70CaN2O6
(C(CH3)3), 33.8 (C(СH3)3), 35.5 (C(СH3)3), 115.9, 121.1, 121.9, (835.16 g/mol): C 71.90; H 8.46; N 3.35. Found: C 71.69; H
123.4, 125.3, 129.0, 129.1, 129.9, 130.6, 132.9, 137.2, 141.4, 8.11; N 3.18. The precipitate of CaH2 was washed with hexane
143.4, 149.1, 167.3 (Ar), 171.4 (CH=N). IR (Nujol, KBr, ν/cm−1): and dried in vacuum at 20°C to give 0.005 g (65%) of off-white
1610 (s), 1590 (s), 1525 (s), 1510 (w), 1400 (m), 1315 (s), 1270 powder. IR (Nujol, KBr, ν/cm−1): 3640 (s), 2925 (s), 2855 (s),
(m), 1225 (m), 1160 (s), 1080 (m), 1020 (w), 980 (s), 860 (m), 2670 (s), 1455(s), 1380 (s), 720 (s).
810 (w), 750 (m). Elem. anal. calc. for C55H62CaN4O2(851.16
Synthesis of 8. A solution of L4H (0.169 g, 0.479 mmol) in
g/mol): C 77.60; H 7.35; N 6.58. Found: C 77.90; H 7.53; N 6.47.
toluene (15 mL) was added to
a
solution of
The precipitate of CaH2 was washed with hexane and dried in
vacuum at 20°C to give 0.003 g (75%) of off-white powder. IR
(Nujol, KBr, ν/cm−1): 3640 (s), 2925 (s), 2855 (s), 2670 (s),
1455(s), 1380 (s), 720 (s). Elem. anal. calc. for CaH2(42.096
g/mol): Ca 95.21. Found: Ca 95.00.
Ca[N(SiMe3)2]2(THF)2 (0.121 g, 0.239 mmol) in toluene (10 mL)
at room temperature. The color of the reaction mixture
changed immediately from pale-yellow to bright-yellow.
Reaction mixture was stirred for 1 h at room temperature. The
volatiles were then removed under reduced pressure and the
Synthesis of 6. A solution of L1H (0.057 g, 0.160 mmol) in solid residue was dissolved in THF/hexane mixture (1:1). Slow
toluene (15 mL) was added to solution of concentration of the solution at room temperature resulted in
Yb[N(SiMe3)2]2(THF)2 (0.102 g, 0.160 mmol) in toluene (10 mL) the formation of as bright-yellow crystals. The mother liquid
at room temperature. The color of the reaction mixture was decanted and the crystals were washed with cold hexane
changed immediately from orange to dark-brown. Reaction and dried in vacuum for 30 min. Complex was isolated in 89%
a
8
8
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yield (0.189 g). 1H NMR (400 MHz, C6D6) δ = 1.38 (m, 8H, β-CH2 38.4 (CH2, Cy), 50.4 (C, Cy), 127.7 (m-CH, Ph), 129.4 (p-CH, Ph),
THF), 1.44 (s, 18H, C(CH3)3), 1.69 (s, 18H, C(CH3)3), 2.07 (s, 6H, 134.1 (o-CH, Ph), 138.4 (i-C, Ph). 29Si NMR (79 MHz, CDCl3) δ = -
3
CH3), 3.32 (s, 6H, OCH3), 3.57 (m, 8H, α-CH2 THF), 6.16 (d, JHH 36.0. Elem. anal. calc. for C18H29NSi (287.52 g/mol): C 75.19; H
3
=8.3 Hz, 2Н, Ar), 6.57 (d, JHH = 8.6 Hz, 2Н, Ar), 6.88 (s, 2Н, Ar), 10.17; N 4.87. Found: C 75.33; H 10.00; N 4.65.
7.25 (s, 2Н, Ar), 7.73 (s, 2Н, Ar), 8.45 (s, 2H, CH=N). 13C NMR
N-cyclohexyl-1-phenylsilanamine. 1H NMR (400 MHz, CDCl3) δ
(101 MHz, C6D6) δ= 20.3 (CH3), 25.4 (β-CH2 THF), 29.7 (C(CH3)3),
= 1.15 (m, 4H, CH2 Cy), 1.64 (m, 4H, CH2 Cy), 2.88 (m, 2H, CH2
31.6 (C(CH3)3), 33.8 (C(СH3)3), 35.6 (C(СH3)3), 55.6 (OCH3), 67.5
Cy), 5.02 (s, 2H, SiH), 7.39 (m, 3Н, Ar), 7.62 (m, 2Н, Ar). 13C
(α -CH2 THF), 108.6, 110.6, 118.4, 121.8, 125.8, 129.6, 130.5,
NMR (101 MHz, CDCl3)δ = 25.6 (CH2, Cy), 26.3 (CH2, Cy), 35.9
131.8, 133.2, 141.0, 149.7, 166.0 (Ar), 170.2 (CH=N). IR (Nujol,
(CH2, Cy), 58.0 (C, Cy), 127.9 (m-CH, Ph), 129.8 (p-CH, Ph),
KBr, ν/cm−1): 1610 (s), 1585 (s), 1545 (m), 1525 (m), 1505(s),
134.6 (o-CH, Ph), 135.7 (i-C, Ph). 29Si NMR (79 MHz, CDCl3) δ = -
1410 (m), 1360 (m), 1270 (s), 1230 (s), 1170 (s), 1120 (s), 1050
28.6 Elem. anal. calc. for C12H19NSi (205.38 g/mol): C 70.18; H
(s), 960 (s), 870 (m), 660 (s), 590 (m), 510 (w). Elem. anal. calc.
9.33; N 6.82. Found: C 70.41; H 9.56; N 6.78.
for C54H76CaN2O6 (889.24 g/mol): C 72.93; H 8.63; N 3.15.
Found: C 73.20; H 8.99; N 3.18.
N,N-bis(2-methoxyethyl)-1-phenylsilanamine. 1H NMR (400
3
MHz, CDCl3) δ = 3.08 (t, JHH = 6.4 Hz, 4Н, CH2), 3.29 (s, 12H,
Typical catalytic experiments: In a typical reaction with neat
substrates the catalyst (10 µmol) was loaded into NMR tube,
then substrates (silane (500 µmol) and amine (500 µmol))
were added to the NMR tube using microsyringes in the glove-
box. The NMR tube was sealed and shaken vigorously, and the
reaction time started after quickly placing the NMR tube in an
oil bath preheated at the desired temperature. After the
OCH3), 3.40 (t, 3JHH = 6.4 Hz, 4Н, CH2), 4.85 (s, 2H, SiH), 7.37 (m,
3Н, Ar), 7.71 (m, 2Н, Ar). 13C NMR (101 MHz, CDCl3) δ = 46.8
(CH2), 58.6 (OCH3), 72.7 (CH2), 127.8, 129.5, 134.7 (Ar). 29Si
NMR (79 MHz, CDCl3) δ = -42.6. Elem. anal. calc. for C10H11NSi
(239.39g/mol): C 60.21; H 8.84; N 5.85. Found: C 60.05; H 8.50;
N 5.53.
desired reaction time, the NMR tube was removed from the oil N-(2-methoxybenzyl)-1-methyl-1-phenylsilanamine. 1H NMR
bath, benzene-d6 (0.5 mL) was added and the 1H, 29Si NMR (400 MHz, CDCl3) δ = 0.53 (d, 3JHH =3.2 Hz, 3Н, SiCH3), 3.90 (s,
3
spectra of the reaction mixture were recorded. Conversion 3Н, OCH3), 4.13(d, JHH = 8.2 Hz, 2Н, CH2), 5.10 (m, 1H, SiH),
3
was determined by integrating the remaining silane and amine 6.94 (d, JHH = 8.2 Hz, 1H, Ar), 7.07 (d, JHH = 7.2 Hz, 1H, Ar),
3
3
3
and the newly formed addition product. Reactions in dry 7.33 (d, JHH = 7.2 Hz, 1H, Ar), 7.42 (d, JHH = 7.4 Hz, 1H, Ar),
benzene-d6 were carried out in a similar manner, but the 7.50 (m, 3H, Ar), 7.76 (m, 2H, Ar). 13C NMR (101 MHz, CDCl3) δ
solvent was added at the same time as the substrates to the = -2.7 (SiCH3), 42.3 (CH2), 55.2 (OCH3), 110.1, 120.6, 127.5,
NMR tube.
127.8, 128.0, 128.3, 129.7, 132.0, 132.6, 134.6, 134.3, 137.9,
157.3 (Ar). 29Si NMR (79 MHz, CDCl3)δ = -12.9. Elem. anal. calc.
for C10H11NSi (239.39 g/mol): C 69.99; H 7.44; N 5.44. Found: C
70.11; H 7.30; N 5.22.
Product characterization. NMR spectroscopic data for
PhSiH2N(CH2)4,48
iPrNHSiH2Ph,27
PhSiH2NHDIPP,53
PhSiH2NEt2,53
PhSiH(N(CH2)4)2,48
(nPrNH)3SiPh,27
tBuNHSiH2Ph,27
nPrNHSiHMePh,27
PhSiH2NHPh,53
PhSiH(NHDIPP)2,53
PhSiH(NEt2)2,53
1-(methyl(phenyl)silyl)-1H-indole. 1H NMR (400 MHz, CDCl3) δ
= 0.37 (d, 3JHH = 3.5 Hz, 3Н, CH3), 5.51 (q, 3JHH = 3.4 Hz, 1Н, SiH),
PhMeSiHNHtBu,71
PhMeSiHNHBn,71 PhMeSiHNHiPr,71 PhMeSiHNEt2,71 4-
(methyl(phenyl)silyl)morpholine71 match those previously
3
6.46 (s, 1Н, Ar), 6.54 (s, 1Н, Ar), 6.64 (d, JHH = 3.2 Hz, 1Н, Ar),
3
6.96 (d, JHH = 3.2 Hz, 1Н, Ar), 7.02 (d, JHH = 7.2 Hz, 1Н, Ar),
3
reported.
phenylsilanamine, N-cyclohexyl-1-phenylsilanamine, N,N-bis(2-
methoxyethyl)-1-phenylsilanamine, N-(2-methoxybenzyl)-1-
9-(phenylsilyl)-9H-carbazole,
N,N-dicyclohexyl-1-
3
3
7.28 (d, JHH = 6.8 Hz, 1Н, Ar), 7.44 (d, JHH = 7.4 Hz, 1Н, Ar),
3
7.69 (d, JHH = 15.6, 7.2 Hz, 1Н, Ar). 13C NMR (101 MHz, CDCl3)
δ = -8.0 (SiHCH3), 102.3, 106.0, 111.0, 112.8, 119.8, 120.8,
121.8, 123.9, 128.2, 129.5, 130.0, 133.5, 134.2, 134.9 (Ar). 29Si
NMR (79 MHz, CDCl3) δ = -36.0. Elem. anal. calc. for C15H15NSi
(237.38 g/mol): C 75.90; H 6.37; N 5.90. Found: C 75.75; H
6.52; N 5.62.
methyl-1-phenylsilanamine, N-(2-methoxybenzyl)-1-methyl-1-
phenylsilanamine, 1-(methyl(phenyl)silyl)-1H-indole were
purified by vaccum distillation and characterized according to
the standard analytic procedure.
9-(phenylsilyl)-9H-carbazole. 1H NMR (400 MHz, CDCl3) δ =
5.68 (s, 2H, SiH), 7.09 (d, 3JHH =7.7 Hz, 4Н, Ar), 7.17 (d, 3JHH =7.2
Hz, 3Н, Ar), 7.23 (s, 2Н, Ar), 7.50 (dd, 3JHH = 20, 8.6 Hz, 3Н, Ar),
X-Ray crystallography. The X-ray data for 1, 5, 7, 8 were collected
on Bruker Smart Apex (1) and Bruker D8 Quest (5, 7, 8)
diffractometers (MoKα-radiation, ω-scans technique, λ = 0.71073 Å)
using SMART and APEX272 software packages. The structures were
solved by direct and dual-space methods73 and were refined by full-
matrix least squares on F2 for all data using SHELX74. SADABS75 were
used to perform area-detector scaling and absorption corrections.
All non-hydrogen atoms in 1, 5, 7, 8 were found from Fourier
syntheses of electron density and were refined anisotropically.
Hydrogen atoms were placed in calculated positions and were
refined in the “riding” model with U(H)iso = 1.2Ueq of their parent
atoms (U(H)iso = 1.5Ueq for methyl groups). CCDC–1821218 (1),
3
8.00 (d, JHH =7.7 Hz, 1Н, Ar). 13C NMR (101 MHz, CDCl3) δ =
112.7, 120.7, 120.9, 125.8, 126.4, 128.6, 128.7, 128.9, 129.5,
130.2, 131.4, 135.0, 136.3, 138.2, 144.6 (Ar). 29Si NMR (79
MHz, CDCl3) δ = -38.3. Elem. anal. calc. for C18H15NSi (273.41
g/mol): C 79.07; H 5.53; N 5.12. Found: C 79.25; H 5.31; N 5.38.
N,N-dicyclohexyl-1-phenylsilanamine. 1H NMR (400 MHz,
CDCl3) δ = 1.20 (m, 8H, CH2 Cy), 1.76 (m, 8H, CH2 Cy), 2.85 (m,
4H, CH2 Cy), 4.99 (s, 2H, SiH), 7.40 (m, 3Н, Ar), 7.68 (m, 2Н, Ar).
13C NMR (101 MHz, CDCl3) δ =25.6 (CH2, Cy), 25.9 (CH2, Cy),
10 | J. Name., 2012, 00, 1-3
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1821219 (5), 1831220 (7), and 1831221 (8) contains the 18.
supplementary crystallographic data for this paper. These data are
provided free of charge by The Cambridge Crystallographic Data 19.
Centre: ccdc.cam.ac.uk/structures. The crystallographic data and
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structure refinement details for 1, 5, 7, 8 are given in Table S1.
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Conflicts of interest
There are no conflicts to declare.
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Acknowledgements
The authors thank Russian Foundation for Basic Research
(Grant No. 17-33-50014-mol_nr) and Russian Academy of
Sciences (Program 44, Theme No. 44.4, Project No. 0094-2016-
0008) for financial support. The X-ray studies have been
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DOI: 10.1039/C8DT01130C
Dalton Transactions
ARTICLE
TOC
X
N
tBu
Ca
O
(Me3Si)2N
THFn
tBu
R1
Si
n=0,1,2
R1
Si
R3
N
R3
H
H
+
+
H
N
H
Ph
Ph
R4
R2
R2
R4
Heteroleptic Ca(II) amides coordinated by multidentate phenolato ligands proved to be efficient catalysts for catalytic
cross-dehydrogenative coupling of amines with silanes.
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