Hydrosilylation of (hetero)aromatic aldimines in the presence of a Pd(I) complex

Article abstract of DOI:10.1023/B:COHC.0000040765.61681.f0

The reaction of triethylsilane with heterocyclic and aromatic azomethines, catalyzed by the [Pd(allyl)Cl]₂ complex, was studied. It was found that the reaction is affected by the nature of the functional groups in the aza and methine parts of the aldimine molecules, which were produced by the condensation of furan, thiophene, and benzene aldehydes with aniline and its derivatives. The reactivity of a series of imines is compared with their electronic and structural characteristics, determined by quantum-chemical methods. The corresponding furan, thiophene, and aromatic amines and also certain silylamines were synthesized.

Full text of DOI:10.1023/B:COHC.0000040765.61681.f0

Chemistry of Heterocyclic Compounds, Vol. 40, No. 6, 2004
HYDROSILYLATION OF (HETERO)-
AROMATIC ALDIMINES IN THE
PRESENCE OF A Pd(I) COMPLEX
I. Iovel, L. Golomba, M. Fleisher, J. Popelis, S. Grinberga, and E. Lukevics
The reaction of triethylsilane with heterocyclic and aromatic azomethines, catalyzed by the
[Pd(allyl)Cl]2 complex, was studied. It was found that the reaction is affected by the nature of the
functional groups in the aza and methine parts of the aldimine molecules, which were produced by the
condensation of furan, thiophene, and benzene aldehydes with aniline and its derivatives. The reactivity
of a series of imines is compared with their electronic and structural characteristics, determined by
quantum-chemical methods. The corresponding furan, thiophene, and aromatic amines and also certain
silylamines were synthesized.
Keywords: transition metal complexes, Schiff bases, hydrosilylation, catalysis.
Investigations into catalytic hydrosilylation of the C=N bond are of both practical significance (for the
production of useful items) and theoretical interest (to determine the relationships governing the processes). As
known (see the reviews [1-3] and also the papers [4-6]), hydrosilylation of the CH=N double bond leads mainly
to the formation of products silylated at the nitrogen atom. Recently, we found for the first time [7] in the
reaction of alkylhydrosilanes with furan, thiophene, and pyridine aldimines containing a trifluoromethyl group at
the ortho position of the aza part of the molecules that addition of the silyl group at the carbon atom of the imine
CH=N bond takes place alongside N-silylation. It is possible that the last process takes place by a carbene
mechanism [8]. In this connection it seemed of interest to determine the dependence of the direction of
hydrosilylation on the structure of the initial amines and also the effect of electron-donating and accepting
functional groups in the aza and methine parts of the molecules on this process.
In the present work the method that we developed previously [9-14] with molecular sieves as effective
agents for the condensation of aromatic and heterocyclic aldehydes with various amines was used for the
production of the aldimines. A series of syntheses were realized, and the corresponding N-(hetarylmethylidene)-
and N-(arylmethylidene)anilines were obtained.
As we discovered earlier [5, 7], one of the most active catalysts for the hydrosilylation of imines is the
dimeric complex of monovalent palladium bis{[µ-chloroallyl]palladium} – [Pd(allyl)Cl]2. In the present work
we studied the reaction of the above-mentioned previously synthesized aldimines with trimethylsilane in the
presence of this complex. The reactions were conducted in benzene at 65°C with the substrate and silane in a
molar ratio of 1:1.2 and a catalyst concentration of 2 mol %. The reactions were monitored by TLC and
GLC-MS. At the end of silylation (the reaction times are given in Table 2) the reaction mixture was treated (as
1
indicated in the experimental section) and was analyzed by H NMR. The spectra of the reaction mixture
__________________________________________________________________________________________
Latvian Institute of Organic Synthesis, Riga LV-1006; e-mail: iovel@osi.lv. Translated from Khimiya
Geterotsiklicheskikh Soedinenii, No. 6, pp. 825-838, June, 2004. Original article submitted February 16, 2004.
0009-3122/04/4006-0701©2004 Plenum Publishing Corporation
701

Scheme 1
R'
R'
MS 4A
H2N
+
N
R
C
H
CHO
R
X
X
PhH,
20–80 oC
R''
1a–l
R''
R'
X = O, S; R = H, Me; R' = Me, Br; R'' = H, Me
R'
MS 4A
H N
R"'
C
H
N
R"'
CHO
+
2
PhH,
20–80 oC
R''
R''
1m–y
R' = H, Me, CF3, Br, F, NO2; R'' = H, Me; R"' = H, Me, OMe, Br, NO2
contain three sets of signals, indicating the formation of three types of products – structures 2, 3, and 4
(Scheme 2) containing Et3SiCH–NH, CH2–NSiEt3, and CH2–NH groups. These compounds are characterized
respectively by two doublets for the protons of the CH–NH group (1H–1H), a singlet for CH2 (2H), and for the
amines 4 by a signal for CH2 and a broad singlet for NH (2H and 1H) (Table 2). The mass spectra of the
obtained compounds (Table 3) also correspond to the three indicated types of products.
Scheme 2
R'
(Het)Ar
N
C
H
R''
1a–w
HSiEt3, PhH
[Pd(allyl)Cl]2,
65 oC
R'
R'
H
C
(Het)Ar
(Het)Ar
OH
NH
N
C
H2
SiEt3
SiEt3
R''
R''
3
_
_
2
OH
R'
(Het)Ar
NH
C
H2
R''
4
By preparative column chromatography it was possible to isolate nearly all the synthesized amines with
structure 4 and also certain other silyl derivatives with structures 2 and 3 (Table 2). The signals of the ring
protons in all the obtained compounds were in the characteristic regions of the spectrum. In the 1H NMR spectra
of the synthesized silyl compounds the SiEt3 group appears in the form of two groups of signals for the CH2 (6H,
q) and CH3 (9H, m) in the region of δ 0.5-1.6 ppm.
702

TABLE 1. The Characteristics of the Synthesized Aldimines
Found, %
Calculated, %
——————
Empirical
formula
Imine*
1
X
2
R
3
R'
4
R''
5
R'''
6
Т, °С
Time, h
8
mp, °С*2 Yield, %
C
H
N
S
7
9
10
11
12
13
14
15
1a
1b
O
O
H
Me
Me
H
H
—
—
20
20
22
24
C12H11NO
C13H13NO
76
76
Me
1c
1d
1e
O
O
O
H
Me
H
Br
Br
H
H
—
—
—
20
20
21
26
C11H8BrNO
C12H10BrNO
C13H13NO
64
64
60
Me
Me
20
80
24
1
1f
O
Me
Me
Me
—
20
80
24
1
C14H15NO
66
1g
1h
1i
S
S
S
H
Me
H
Me
Me
Br
H
H
H
—
—
—
20
24
C12H11NS
C13H13NS
C11H8BrNS
76
56
52
20
24
72.23
72.52
49.70
49.64
5.98
6.09
2.84
3.03
6.41
6.50
4.98
5.26
14.75
14.89
12.02
12.05
46-47
49-50
20
80
24
2
1j
S
Me
Br
H
—
20
80
24
2
C12H10BrNS
51.14
51.44
3.43
3.60
4.82
4.99
11.55
11.44
45-46
50
1k
1l
S
S
H
Me
Me
Me
Me
—
—
20
24
C13H13NS
C14H15NS
74
77
Me
20
80
24
8

TABLE 1 (continued)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1m
1n
—
—
—
—
Me
H
H
H
H
20
20
23
22
C14H13N
76
56
CF3
C14H10F3N
1o
1p
1q
—
—
—
—
—
—
Br
F
H
H
H
H
H
H
20
20
23
22
C13H10BrN
C13H10FN
74
64
72
77.68
78.37
68.36
69.02
4.81
5.06
4.36
4.46
6.77
7.03
12.69
12.38
28-29
71-72
NO2
20
80
19
8
C13H10N2O2
1r
—
—
Me
Me
H
20
80
20
2
C15H15N
83
1s
1t
—
—
—
—
—
—
—
—
—
—
H
H
H
H
H
H
H
Me
OMe
Br
20
20
20
20
24
21
21
24
C14H13N
65
66
69
74
64
C14H13NO
C13H10BrN
C13H10N2O2
C15H12F3NO
79.47
79.59
60.06
60.02
69.03
69.02
6.16
6.20
3.82
3.87
4.44
4.46
6.61
6.63
5.28
5.38
12.28
12.38
49-50
71-72
86-87
1u
1v
1w
H
H
NO2
OMe
CF3
20
80
22
3
1x
1y
—
—
—
—
CF3
H
H
Br
Br
20
20
C14H9BrF3N
C13H9BrN2O2
51.40
51.25
51.21
51.17
2.72
2.76
2.85
2.97
4.17
4.27
9.08
9.18
59-60
96-97
87
64
NO2
20
80
24
6
_______
* The imines 1a-g,k-o,r,s,w were oily substances, 1p was not recrystallized.
*2 Solvent for recrystallization: hexane (1h,i,t,u,x) or 1:1 hexane–ethyl acetate (1j,q,v,y).

TABLE 2. The Characteristics of the Hydrosilylation Reactions and Their Products
Product
1Н NMR (in CDCl3), δ, ppm, (J, Hz)
SiСH–NH
Reaction
time, h
(Т 65°С)
Conversion
of imine,
% (GLC)
CH2–NH
(structure 4)
Initial
imine
CH2–NSi
after
(structure 3)
(structure 2)
in reaction mixture*
4
СH3 (3Н, s)
isolation*2
CH2 (2H, s)
CH (d)
NH (d)
9
CH2 (s)
NH br. s)
11
1
2
3
5
6
7
8
10
1a
1b
1c
6
6
4
68
86
53
4а
4b
3c
4а
4b
3c
2.09
4.29
4.22
3.8
3.8
2.04, 2.20
4.33
4.6
4.6
J = 5.0
J = 5.0
4c
C4H3OCH2NHPh (9%)
3d
4c
3d
4d
2e
4.29
4.0
1d
1e
4
68
86
2.20
2.22
4.27
4d
4.20
4.07
3.9
4.0
MeC4H2OCH2NHPh (18%)
24
2e
4e
2.00 (6H)
2.15 (6H)
4.07
1f
1g
1h
1i
24
15
20
4
0
41
100
51
90
4g
4h
4i
4g
4h
4i
2.11
2.07, 2.36
4.51
4.38
4.51
3.8
3.8
4.0
1j
20
3j
3j
2.40
2.40
4.44
4.6
J = 5.0
4j
4j
4.40
4.27
3.9
MeC4H2SCH2NHPh (21%)
1k
35
42
2k
2k
4k
2.11 (6H)
2.9 (6H)
4.31
~3.0

TABLE 2 (continued)
1
2
3
4
5
6
7
8
9
10
11
1l
35
60
2l
2l
2.04 (6H),
2.33 (3H)
4.22
4l
4l
2.27 (6H),
2.38 (3H)
2.11
4.18
4.33
4.38
4.31
3.2
—
1m
1n
4
100
59
4m
4m*3
20
2n
4n
4n
2o
4.8
1o
11
72
2o
4.36
4o
PhCH2NHPh (31%)
4p
~ 4.8
1p
8
100
4.24
4.55
4.1
—
1q
1r
20
8
100
86
4q, q*4
4q
4r
2r
4r
2.18 (6H)
2.27
2.33
4.04
4.27
4.18
2.9
3.9
4.0
1s
1t
7
100
81
2s
4s
4.51
4.22
15
2t
2t
4t
3.73 (OCH3)
3.73 (OCH3)
4t
4u, PhCH2NHPh (82%), u*4
4u, PhCHNPh (12%)
H2NC6H4CHNPh
2w
1u
1u*5
1v
8
100
24
26
17
21
25
1w
63
2w
3.47 (OCH3)
4.31
4w
_______
* According to the data from the 1H NMR spectra and GLC-MS of the mixture of products.
*2 The products were isolated by column chromatography. Eluants: 10:0.05 benzene–ethyl acetate (4a-d,g,h,j,t, 3c,d,j,
2t), 3:1 hexane–ethyl acetate (2e, 4i), 9:1 benzene–ethyl acetate (2k,l, 4k,l,q,r), benzene (4n), 9:1 hexane–ethyl acetate
(2o).
*3 The product was isolated by recrystallization from hexane (mp 54°C).
*4 Unidentified side products were formed.
*5 Catalyst: RhCl(PPh3)3.

TABLE 3. The Mass Spectra of the Hydrosilylation Products
m/z (Irel, %)*2
Compound*
1
2
4a
4b
3c
187 [M]+ (34), 186 [M – H]+ (25), 118 (7), 106 [M – C4H3OСH2]+ (6),
91 (11), 81 [C4H3OCH2]+ (100), 77 (15), 65 (11), 53 (37)
201 [ M]+ (18), 216 (2), 118 (2), 107 (12), 95 [H3CC4H2OCH2]+ (100),
91 (8), 77 (8), 65 (11), 57 (7), 43 (13)
252/250 [M – SiEt3]+ (100/100), 184/182 (7/8), 171 (11), 170 [M – HSiEt3 – Br]+ (9),
157/155 [C6H4Br]+ (5/9), 143 (8), 131 (6), 115 [SiEt3]+ (25), 103 (9), 91 (5),
87 (18), 75 (9), 59 (14), 39 (7)
4c
A
253/251 [M]+ (100/100), 184 (2), 172 (4), 157/155 [C6H4Br]+ (2/3),
143 (4), 117/115 (3/5), 104 (3), 91 (10), 81 [C4H3OCH2]+ (100), 63 (10), 53 (30),
39 (10), 32 (25)
173 [M]+ (42), 172 [M – H]+ (32), 144 [M – HCO]+ (10), 115 (12),
106 [M – C4H3OСH2]+ (5), 91 (5), 81 [C4H3OCH2]+ (100), 77 [Ph]+ (26), 65 (15),
53 (31), 51 (21), 39 (23), 32 (89)
4d
267/265 [M]+ (8/8), 186 [M – Br]+ (4), 173/171 (4/4), 157 [C6H4Br]+ (2),
143 (2), 130 (1), 115 (2), 104 (2), 95 [H3CC4H2OCH2]+ (100), 91 (7), 77 (6),
65 (7), 51 (7), 43 (14)
187 [M]+ (16), 172 [M – H]+ (2), 95 [H3CC4H2OCH2]+ (100), 77 [Ph]+ (10),
65 (12), 51 (11), 43 (15), 32 (39)
B
2e
315 [ M]+ (15), 287 (24), 286 [M – Et]+ (100), 205 (22), 184 (18), 176 (17),
153 (35), 148 (35), 146 (29), 125 (13), 115 (5), 105 (13), 91 (8), 87 (14),
81 [C4H3OCH2]+ (38), 77 (7), 59 (29), 53 (24)
4e
4g
4h
4i
201 [M]+ (38), 200 [M – H]+ (32), 184 (3), 172 (2), 158 (4), 144 (3), 132 (8),
120 (12), 103 (5), 91 (20), 81 [C4H3OCH2]+ (100), 77 (24), 65 (10), 53 (42), 39 (15)
203 [M]+ (28), 106 (3), 97 [C4H3SCH2]+ (100), 91 (10), 77 (11), 65 (11),
53 (37), 45 (13), 39 (15)
217 [M]+ (18), 182 (2), 118 (3), 111 [H3CC4H2SCH2]+ (100), 91 (11), 77 (21),
65 (14), 51 (12), 45 (10), 39 (13)
269/267 [M]+ (13/12), 186 (3), 172 (1), 157/155 [C6H4Br]+ (2/3),143 (2), 115 (2),
105 (2), 97 [C4H3SCH2]+ (100), 91 (11), 63 (10), 77 (8), 63 (10), 53 (11),
45 (15), 39 (11)
4j
283/281 [M]+ (9/9), 200 (1), 184 (2), 168 (2), 155 [C6H4Br]+ (2), 143 (2),
104 (2), 111 [H3CC4H2SCH2]+ (100), 91 (12), 77 (18), 63 (9), 51 (11),
45 (11), 39 (10)
203 [M]+ (21), 111 [H3CC4H2SCH2]+ (100), 77 [Ph]+ (31), 65 (15), 51 (20), 45 (9),
39 (19)
C
2k
331 [M]+ (23), 300 (13), 301 (27), 302 [M – Et]+ (100), 274 (2), 234 (4),
216 [M – SiEt]+ (3), 205 (19), 184 (2), 176 (21), 169 (34), 148 (40), 146 (35),
141 (24), 132 (13), 119 (7), 115 (17), 97 [C4H3SCH2]+ (38), 87 (21), 77 (8),
59 (38), 53 (14), 45 (16)
2l
345 [M]+ (22), 314 (6), 315 (14), 316 [M – Et]+ (100), 288 (2), 234 (2), 205 (9),
183 (43), 176 (12), 159 (17), 148 (27), 146 (25), 132 (10), 115 (12),
111 [H3CC4H2SCH2]+ (100), 105 (7), 87 (18), 77 (15), 59 (38), 45 (10)
4l
231 [M]+ (14), 134 [M – H3CC4H2SCH2]+ (2), 121 (8), 111 [H3CC4H2SCH2]+ (100),
105 (7), 87 (18), 77 (15), 59 (38), 45 (10)
4m
2n
197 [M]+ (40), 196 [M – H]+ (13), 120 [M – Ph]+ (11), 118 (7),
106 [PhCH2NH]+ (13), 91 [PhCH2]+ (100), 77 [Ph]+ (13), 65 (26), 51 (11), 39 (13)
365 [M]+ (2), 230 (3), 213 (15), 214 [M – SiEt3 – 2F]+ (100),
192 [M – SiEt3 – 2F – HF]+ (7), 165 (7), 145 [C6H4CF3]+ (2), 134 (6), 109 (11),
91 [PhCH2]+ (81), 77 [Ph]+ (23), 65 (10), 59 (9), 49 (6)
4n
4o
D
251 [M]+ (27), 230 (4), 212 (3), 165 (1), 154 (3), 145 [C6H4CF3]+ (2),
91 [PhCH2]+ (100), 77 (4), 69 (12), 51 (5), 39 (4), 32 (7)
263/261 [M]+ (18/19), 180 [M – Br]+ (9), 152 (3), 143 (1), 104 (4),
91 [PhCH2]+ (100), 77 [Ph]+ (9), 65 (14), 51 (7), 39 (6)
183 [M]+ (55), 182 [M – H]+ (22), 106 [PhСH2NH]+ (20), 91 [PhCH2]+ (100),
77 [Ph]+ (26), 65 (22), 51 (15), 39 (10)
4p
201 [M]+ (35), 200 [M – H]+ (8), 124 [M – Ph+] (8), 122 (7), 91 [PhCH2]+ (100),
77 [Ph]+ (9), 65 (15), 51 (8), 39 (7)
707

TABLE 3 (continued)
1
2
4q
2r
228 [M]+ (11), 210 (3), 195 (5), 181 (13), 190 (17), 168 (3), 152 (4), 105 (61),
91 [PhCH2]+ (100), 77 [Ph]+ (14), 65 (24), 51 (11), 39 (10)
325 [M]+ (10), 297 (25), 296 [M – Et]+ (100), 281 (6), 266 (3), 234 (2), 207 (16),
205 (10), 176 (13), 163 (8), 148 (29), 146 (14), 135 (10), 115 (4), 105 (8),
91 [PhCH2]+ (30), 87 (14), 73 (6), 59 (21)
4r
211 [M]+ (40), 210 [M – H]+ (8), 196 [M – Me]+ (2), 134 [M – Ph]+ (6),
120 [M – PhCH2]+ (42), 103 (3), 91 [PhCH2]+ (100), 77 [Ph]+ (14), 65 (15),
51 (6), 39 (8)
2s
4s
2t
311 [M]+ (15), 283 (26), 282 [M – Et]+ (100), 254 (4), 194 (6), 177 (34), 149 (63),
121 (41), 120 (40), 115 (5), 105 [C6H4CH3]+ (56), 87 (23), 77 [ Ph]+ (35), 59 (47)
197 [M]+ (26), 182 (2), 105 [C6H4CH3]+ (100), 91 (4), 79 (10), 77 [ Ph]+ (26), 65 (7),
51 (8)
327 [M]+ (23), 299 (11), 298 [M – Et]+ (100), 254 (2), 193 (19), 165 (29), 149 (4),
137 (13), 121 [M – SiEt3 – PhN]+ (100), 120 (14), 104 (4), 87 (13), 78 (15),
77 [Ph]+ (20), 59 (23)
4t
213 [M]+ (15), 196 (2), 168 (2), 121 [M – PhNH]+ (100), 91 (6), 78 (12),
77 [Ph]+ (18), 65 (8), 51 (8)
4u
263/261 [M]+ (40/41), 262/260 [M – H]+ (15/9), 182 [M – Br]+ (18),
171/169 [CH2C6H4Br]+ (98/100), 106 [PhNHСH2]+ (20), 104 (12),
90 [M – Br – PhNH]+ (54), 91 (46), 77 [Ph]+(41), 65 (15), 63 (21), 51 (24), 39 (15)
E
181 [M]+ (82), 180 [M – H]+ (100), 104 [M – Ph]+ (17), 77 [ Ph]+ (85), 63 (7),
51 (37), 39 (8)
F
196 [M]+ (52), 195 [M – H]+ (63), 178 (3), 167 (2), 118 (3), 104 [PhNCH]+ (4),
98 (5), 92 [M – PhNCH]+ (9), 77 [ Ph]+ (29), 65 (9), 51 (13), 40 (9), 32 (100)
2w
4w
395 [M]+ (3), 280 [M – SiEt3]+ (2), 242 [M – SiEt3 – 2F]+ (100), 222 (7),
172 (2), 134 (5), 121 [CH3OC6H4CH2]+ (56), 109 (3), 91 (9), 77 (23), 59 (9)
281 [M]+ (10), 242 (2), 145 [C6H4CF3]+ (2), 121 [CH3OC6H4CH2]+ (100), 106 (1),
91 (6), 78 (9), 77 (10), 63 (4), 51 (5), 39 (3)
_______
* А-C4H3OCH2NHPh, B-H3CC4H2OCH2NHPh, C-H3CC4H2SCH2NHPh,
D-PhCH2NHPh, E-PhCHNPh, F-H2NC6H4CHNPh
*2 The signals of the characteristic ions are given.
The hydrosilylation of many of the investigated substrates (1a-e,g-p,r-t) mostly leads to the formation of
the desired products having structures 2-4. In most cases the respective amines were isolated. Of the initial
heterocyclic compounds only the imine 1f did not react with triethylsilane under the investigated conditions.
Nearly all the bromine derivatives undergo debromination with the formation of the corresponding saturated
compounds or the debromoimine (Tables 2 and 3). This applies particularly to the imine 1u. An attempt to
silylate the latter in the presence of the complex RhCl(PPh3)3 did not give positive results. N-Silylation products
are hardly formed at all during the hydrosilylation of the two investigated nitro compounds 1q and 1v. Thus, the
imine 1q reacts with the formation mainly of unidentified side products, while in the reaction of the aldimine 1v
its nitro group is reduced to an NH2 group. The last imine does not react with triethylsilane in the presence of
RhCl(PPh3)3 (65°C, 26 h) or with dimethylphenylsilane in the presence of [Pd(allyl)Cl]2 and RhCl(PPh3)3 (65°C,
13-14 h). Since the nitro- and bromine-containing aromatic imines 1q and 1u hardly gave the desired products at
all, we did not investigate their analogs 1x,y.
Of all the investigated compounds only the bromine-substituted heterocyclic imines are transformed into
the C-silylation products 3c,d,j, which were successfully isolated by column chromatography, demonstrating
their adequate stability. The N-silylation products were recorded in the reactions of many imines:
1e,k,l,n,o,r-t,w). Nearly all were isolated by chromatography (with the exception of the products 2n,r that are
probably hydrolyzed in the column to the corresponding amines 4n,r, which were isolated (Table 2)).
708

Thus, the unusual direction of transformation leading to the formation of the C-silylated products is only
observed in the reactions of the O- and S-heterocyclic imines. Here the presence of the bromine atom at the
ortho position of the aza part of the molecules of the reacting imines promotes C-silylation. The obtained data
agree with our previous results [7, 8]. Probably, the presence of the heterocycles in the molecules of the reacting
imines leads to the appearance of intermediate carbene structures (type I, scheme 3), which are formed during
complexation of the substrates with the catalyst (by analogy with the mechanism proposed in [15]) and lead to
C-silylation. In addition, the bulky bromine atom at the ortho position to the carbon atom of the aromatic ring
attached to the nitrogen atom of the reacting imine group N=C prevents N-silylation sterically (like the CF3
group in [7]).
Scheme 3
H
Pd
Pd
Pd
Ar
Ar
Ar
Het
Het
Het
HSiEt3
N
N
N
H
I
H
Pd
H
Het
H
_
Ar
Ar
Het
Pd
N
N
Et3Si
H
H
Et3Si
The structure and electronic characteristics of the aldimines 1m-r, containing various substituents at the
ortho position of the aza part of the molecule, were calculated by the quantum-chemical AM1 method in order to
determine the effect of the functional groups on the characteristics of the molecules (Table 4 and Fig. 1).
By comparing the obtaining data it can be seen that the greatest differences in all the values of the
parameters (Table 4) are, as expected, characteristic of the molecules 1q,r, which contain the most
electronegative NO2 group and two donating CH3 groups respectively. However, the molecules containing CF3
and Br substituents, which have a special effect on hydrosilylation, are characterized by average values of all the
calculated electronic parameters. It can, consequently, be supposed that steric and not electronic factors play the
major role in the investigated reaction. In fact, as seen from the molecular structures of 1m and 1n (Fig. 1), the
CF3 group creates steric hindrances for the addition of the reagent to the nitrogen atom of the imine group,
whereas the methyl substituent does not prevent such a reaction.
TABLE 4. The Characteristics of the Compounds, Obtained by the AM1
Quantum-chemical Method
Compound
qN
qC
HOMO, eV
LUMO, eV
1m
1n
1o
1p
1q
1r
-0.148
-0.163
-0.158
-0.157
-0.194
-0.145
-0.001
-0.020
-0.019
-0.004
-0.064
-0.004
-8.91
-9.27
-9.09
-8.95
-9.51
-8.84
-0.28
-0.85
-0.42
-0.61
-0.91
-0.26
709

a
b
Fig. 1. The optimized structures of the molecules of the imines 1m (a) and 1n (b)
obtained by the quantum-chemical AM1 method.
EXPERIMENTAL
1
The H NMR spectra were recorded on Varian Mercury-200 (200 MHz) and Bruker WH-90/DS
(90 MHz) spectrometers for solutions in deuterochloroform with TMS as internal standard. The mass spectra
were obtained on an HP6890 GC/MS chromato-mass spectrometer with an HP-5 MS capillary column
(30.0 m × 250 µm × 0.25 µm) at programmed temperature from 70 to 260°C (10 deg/min). Before use the
benzene was distilled over calcium hydride. Aldehydes, amines, hydrosilanes, and Pd complex produced by
Acros, Aldrich, and Fluka were used. The molecular sieves were 4A (VEB Laborchemie Apolda).
General Procedure for the Synthesis of the Aldimines. In a round-bottom flask with a reflux
condenser we placed 10 ml of dry benzene and 5 mmol each of the initial aldehyde and amine and then 5 g of the
freshly baked molecular sieves. The reaction was conducted at room temperature or with heating on a water bath
at 80°C in an atmosphere of argon. Samples were taken periodically and analyzed by TLC and GLC-MS. After a
specific time interval, depending on the substrates (Table 1), they were almost completely converted into the
respective products. At the end of the reaction the sieves were filtered off and washed with benzene. The filtrate
was evaporated at reduced pressure (40°C/15 mm Hg), and the small residues of the initial substances
710

were removed under vacuum (45-50°C/0.1 mm Hg). The products were yellow oily or crystalline substances.
The solid compounds were purified by recrystallization from hexane or its mixture with ethyl acetate, and the
1H NMR spectra were recorded.
General Procedure for Hydrosilylation. A 5-cm3 Pierce reaction tube was blown with argon, and 2 ml
of dry benzene, 0.01 mmol of the catalyst, and 0.5 mmol of the initial imine were placed in it, after which the
mixture was stirred at room temperature for 30 min. The solution was then cooled to 0°C with ice, and 0.6 mmol
of hydrosilane was added with a syringe. The reaction was carried out at 65°C, and samples were taken
periodically and analyzed by TLC and GLC-MS. At the end of silylation the reaction mixture was evaporated at
reduced pressure (30°C/15 mm Hg), and the 1H NMR spectra were recorded. The mixture was then separated by
liquid chromatography on a column of silica gel (Kieselgel 60, 0.063-0.200 mesh, Merck) with various eluants.
All the obtained products were yellow oily substances,
Quantum-chemical Calculations. All the calculations were carried out by the semiempirical AM1
method [16], included in the MOPAC 6 software package [17]. The equilibrium geometric structures of the
molecules were calculated with full optimization of the parameters using the PRECISE enhanced accuracy
criterion [18]. Analysis of the obtained frequencies of the molecular vibrations showed that all the optimized
structures correspond to minima on the potential energy surface of the system. Computer design was realized by
means of the JMol software [19].
N-(2-Furylmethylidene)-2-methylaniline (1a). Mass spectrum, m/z (Irel, %): 186 [M + H]+ (9), 185
[M]+ (69), 184 [M - H]+ (29), 168 (14), 157 (14), 156 [M - HCO]+ (100), 154 (16), 130 (53), 129 (24), 128 (26),
117 (20), 91 [C6H4CH3]+ (35), 90 (9), 89 (20), 77 (18), 65 (54), 63 (24), 52 (29), 51 (45), 50 (21), 39 (53).
1H NMR spectrum, δ, ppm: 2.33 (3H, s, CH3); 6.3-7.8 (7H, m, Ar, Fur); 8.13 (1H, s, CH=N).
N-(5-Methyl-2-furylmethylidene)-2-methylaniline (1b). Mass spectrum, m/z, (Irel, %): 200 [M + H]+
(10), 199 [M]+ (68), 198 [M - H]+ (22), 184 [M - Mе]+ (25), 170 (8), 157 (14), 156 [M - MеCO]+ (100), 154
(14), 130 (21), 129 (24), 128 (20), 117 (30), 91 [C6H4CH3]+ (32), 90 (8), 89 (15), 79 (13), 77 [Ph]+ (12), 65 (52),
63 (17), 53 (19), 52 (16), 51 (34), 50 (14), 43 (30), 39 (32). 1H NMR spectrum, δ, ppm: 2.27 (3H, s, CH3); 2.33
(3H, s, CH3); 6.0-7.3 (6H, m, Ar, Fur); 7.98 (1H, s, CH=N).
N-(2-Furylmethylidene)-2-bromoaniline (1c). Mass spectrum, m/z (Irel, %): 251/249 [M]+ (96/100),
250/248 [M - H]+ (57/45), 222 [M - HCO]+ (4), 195 (5), 184/182 (5/6), 171 (11), 170 [M - Br]+ (91), 157/155
[C6H4Br]+ (38/39), 142 (29), 141 (15), 140 (16), 115 (78), 102 (9), 89 (18), 77 (26), 76 (55), 75 (59), 74 (23), 64
(21), 63 (32), 52 (42), 51 (69), 50 (71), 39 (77). 1H NMR spectrum, δ, ppm: 6.4-7.8 (7H, m, Ar, Fur); 8.09 (1H,
s, CH=N).
N-(5-Methyl-2-furylmethylidene)-2-bromoaniline (1d). Mass spectrum, m/z (Irel, %): 265/263 [M]+
(99/100) , 264/262 [M - H]+ (48/32), 222 [M - MeCO]+ (7), 195 (3), 184 [M - Br]+ (92), 169 (14), 157/155
[C6H4Br]+ (29/34), 141 (9), 140 (8), 129 (12), 128 (15), 114 (6), 79 (14), 77 (14), 76 (24), 75 (25), 74 (8), 64 (7),
63 (9), 53 (21), 52 (12), 51 (25), 50 (23), 43 (19), 39 (14). 1H NMR spectrum, δ, ppm: 2.38 (3H, s, CH3); 6.0-7.7
(6H, m, Ar, Fur); 7.98 (1H, s, CH=N).
N-(2-Furylmethylidene)-2,6-dimethylaniline (1e). Mass spectrum, m/z (Irel, %): 200 [M + H]+
(10), 199 [M]+ (71), 198 [M - H]+ (33), 183 [M - H- Me]+ (12), 171 (14), 170 [M - HCO]+ (100), 168 (15), 156
(14), 155 (14), 154 (21), 144 (43), 143 (16), 142 (13), 130 (25), 129 (8), 128 (16), 117 (11), 115 (13), 103 (19),
91 (14), 89 (9), 79 (19), 78 (19), 77 (55), 65 (19), 63 (17), 52 (33), 51 (46), 50 (18), 39 (54). 1H NMR spectrum,
δ, ppm: 2.09 (6H, s, CH3); 6.4-7.6 (6H, m, Ar, Fur); 7.91 (1H, s, CH=N).
N-(5-Methyl-2-furylmethylidene)-2,6-dimethylaniline (1f). Mass spectrum, m/z (Irel, %): 214 [M + H]+
(10), 213 [M]+ (77), 212 [M - H]+ (22), 198 [M - Me]+ (8), 183 (6), 170 [M - MeCO]+ (100), 168 (9), 155 (14),
154 (15), 144 (15), 143 (9), 142 (7), 130 (14), 128 (8), 117 (7), 115 (7), 103 (13), 91 (10), 79 (24), 78 (13), 77
(36), 65 (15), 53 (14), 51 (29), 50 (18), 43 (28), 39 (26). 1H NMR spectrum, δ, ppm: 2.11 (6H, s, CH3); 2.38 (3H,
s, CH3); 6.0-7.3 (6H, m, Ar, Fur); 7.82 (1H, s, CH=N).
711

N-(2-Thienylmethylidene)-2-methylaniline (1g). Mass spectrum, m/z (Irel, %): 202 [M + H]+ (15), 201
[M]+ (100), 200 [M - H]+ (64), 186 [M - Me]+ (12), 169 (11), 168 [M - HS]+ (78), 167 (41), 156 [M - HCS]+ (12),
154 (6), 129 (7), 118 [M - Th]+ (22), 117 [M - H - Th]+ (28), 110 (6), 91 [C6H4CH3]+ (42), 90 (9), 89 (14), 77 (9),
70 (10), 65 (51), 63 (18), 58 (8), 52 (9), 51 (20), 50 (10), 45 (19), 39 (41). 1H NMR spectrum, δ, ppm: 2.29 (3H,
s, CH3); 6.8-7.6 (7H, m, Ar, Th); 8.38 (1H, s, CH=N).
N-(5-Methyl-2-thienylmethylidene)-2-methylaniline (1h). Mass spectrum, m/z (Irel, %): 216 [M + H]+
(5), 215 [M]+ (100), 214 [M - H]+ (33), 200 [M - Me]+ (28), 199 (22), 183 (11), 182 [M - HS]+ (68), 181 (16),
180 (17), 167 (51), 156 [M - MeCS]+ (15), 154 (11), 129 (8), 118 (19), 117 [M - H - MeTh]+ (43), 109 (8), 97
[MeTh]+ (29), 91 [C6H4CH3]+ (52), 90 (13), 89 (21), 77 (15), 69 (9), 65 (65), 63 (24), 59 (12), 53 (20), 52 (13),
51 (37), 50 (17), 45 (24), 39 (48). 1H NMR spectrum, δ, ppm: 2.27 (3H, s, CH3); 2.47 (3H, s, CH3); 6.6-7.3 (6H,
m, Ar, Th); 8.29 (1H, s, CH=N).
N-(2-Thienylmethylidene)-2-bromoaniline (1i). Mass spectrum, m/z (Irel, %): 267/265 [M]+ (76/78),
266/264 [M - H]+ (57/45), 187 (14), 186 [M - Br]+(100), 157/155 [C6H4Br]+ (38/39), 140 (7), 115 (16), 93 (15),
84 (13), 77 (14), 76 (32), 75 (35), 74 (10), 63 (14), 52 (7), 51 (99), 50 (30), 45 (25), 39 (32). 1H NMR spectrum,
δ, ppm: 6.8-7.7 (7H, m, Ar, Th); 8.39 (1H, s, CH=N).
N-(5-Methyl-2-thienylmethylidene)-2-bromoaniline (1j). Mass spectrum, m/z (Irel, %): 281/279 [M]+
(62/63), 280/278 [M - H]+ (51/43), 201 (14), 200 [M - Br]+ (100), 157/155 [C6H4Br]+ (23/24), 140 (3), 122 (12),
97 (29), 95 (12), 77 (19), 76 (33), 75 (33), 74 (11), 63 (14), 53 (15), 51 (24), 50 (29), 45 (25), 39 (21). 1H NMR
spectrum, δ, ppm: 2.51 (3H, s, CH3); 6.6-7.7 (6H, m, Ar, Th); 8.29 (1H, s, CH=N).
N-(2-Thienylmethylidene)-2,6-dimethylaniline (1k). Mass spectrum, m/z (Irel, %): 216 [M + H]+ (18),
215 [M]+ (100), 214 [M - H]+ (59), 199 [M - H - Me]+ (12 ), 182 [M - HS]+ (55), 181 (16), 170 [M - HCS]+
(13), 167 [M - HS - Me]+ (39), 132 (24), 131 (24), 130 (32), 117 (13), 110 (5), 103 (22), 91 (13), 79 (23), 78
1
(19), 77 (60), 70 (6), 65 (18), 63 (19), 58 (9), 53 (13), 52 (15), 51 (30), 50 (12), 45 (25), 39 (36). H NMR
spectrum, δ, ppm: 2.04 (6H, s, CH3); 6.8-7.6 (6H, m, Ar, Th); 8.20 (1H, s, CH=N).
N-(5-Methyl-2-thienylmethylidene)-2,6-dimethylaniline (1l). Mass spectrum, m/z (Irel, %): 230
[M + H]+ (18), 229 [M]+ (100), 214 (17), 213 [M - H - Me]+ (23), 196 [M - HS]+ (51), 181 (37), 170
[M - MeCS]+ (16), 132 (16), 131 (25), 130 (27), 117 (9), 105 (8), 103 (16), 97 (18), 79 (18), 78 (12), 77 (44), 65
1
(15), 63 (10), 53 (16), 52 (7), 51 (18), 50 (6), 45 (13), 39 (26). H NMR spectrum, δ, ppm: 2.04 (6H, s, CH3);
2.44 (3H, s, CH3); 6.6-7.2 (5H, m, Ar, Th); 8.09 (1H, s, CH=N).
N-(Benzylidene)-2-methylaniline (1m). Mass spectrum, m/z (Irel, %): 196 [M + H]+ (10), 195 [M]+ (73),
194 [M - H]+ (66), 180 (4), 167 (6), 152 (5), 119 (9), 118 [M - Ph]+ (100), 117 (24), 91 [C6H4CH3]+ (47), 90 (10),
89 (23), 77 [Ph]+ (13), 65 (44), 63 (19), 51 (24), 50 (11). 1H NMR spectrum, δ, ppm: 2.31 (3H, s, CH3); 6.7-8.0
(9H, m, Ar); 8.33 (1H, s, CH=N).
N-(Benzylidene)-2-trifluoromethylaniline (1n). Mass spectrum, m/z (Irel, %): 250 [M + H]+ (11), 249
[M]+ (79), 248 [M - H]+ (100), 230 [M - F]+ (6), 208 (4), 180 (5), 172 (10), 152 (6), 145 [PhCF3 - H]+ (53), 125
(11), 95 (16), 89 (7), 76 (14), 77 [Ph]+ (16), 63 (9), 51 (18), 50 (11). 1H NMR spectrum, δ, ppm: 6.9-8.0 (9H, m,
Ar); 8.33 (1H, s, CH=N).
N-(Benzylidene)-2-bromoaniline (1o). Mass spectrum, m/z (Irel, %): 261/259 [M]+ (96/100), 260/258
[M - H]+ (96/87), 180 [M - Br]+ (60), 157/155 [C6H4Br]+ (41/42), 152 (24), 102 (9), 90 (25), 89 (32), 76 (26), 77
[Ph]+ (51), 76 (66), 75 (32), 74 (17), 64 (13), 63 (34), 52 (12), 51 (55) 50 (50). 1H NMR spectrum, δ, ppm: 6.8-
8.0 (9H, m, Ar); 8.31 (1H, s, CH=N).
N-(Benzylidene)-2-fluoroaniline (1p). Mass spectrum, m/z (Irel, %): 200 [M + H]+ (11), 199 [M]+ (84),
1
198 [M - H]+ (100), 122 [M - Ph]+ (12), 95 (15), 78 (8), 77 [Ph]+ (16), 74 (13), 51 (8). H NMR spectrum,
δ, ppm: 7.0-8.0 (9H, m, Ar); 8.49 (1H, s, CH=N).
N-(Benzylidene)-2-nitroaniline (1q). Mass spectrum, m/z (Irel, %): 226 [M]+ (13), 178 (7), 152 (12),
1
105 [PhCHNH]+ (100), 89 (10), 78 (5), 77 [Ph]+ (32), 76 (12), 63 (11), 51 (14). H NMR spectrum, δ, ppm:
6.9-8.1 (9H, m, Ar); 8.38 (1H, s, CH=N).
712

N-(Benzylidene)-2,6-dimethylaniline (1r). Mass spectrum, m/z (Irel, %): 210 [M + H]+ (13), 209 [M]+
(82), 208 [M - H]+ (33), 193 [M - H- Me]+ (23), 165 (6), 132 [M - Ph]+ (100), 131 (14), 130 (15), 117 (21), 103
1
(18), 91 (9), 89 (15), 79 (17), 78 (13), 77 [Ph]+ (39), 65 (10), 63 (12), 51 (19), 39 (15). H NMR spectrum,
δ, ppm: 2.09 (6H, s, CH3); 6.9-8.0 (6H, m, Ar); 8.18 (1H, s, CH=N).
N-(4-Methylbenzylidene)aniline (1s). Mass spectrum, m/z (Irel, %): 196 [M + H]+ (11), 195 [M]+ (81),
194 [M - H]+ (100), 180 (5), 165 (3), 152 (3), 104 (7), 91 [C6H4CH3]+ (15), 77 [Ph]+ (13), 65 (9), 51 (25).
1H NMR spectrum, δ, ppm: 2.36 (3H, s, CH3); 6.9-7.9 (9H, m, Ar); 8.39 (1H, s, CH=N).
N-(4-Methoxybenzylidene)aniline (1t). Mass spectrum, m/z (Irel, %): 212 [M + H]+ (13), 211 [M]+ (88),
1
210 [M - H]+ (100), 196 (6), 167 (22), 104 (6), 91 (5), 77 [Ph]+ (69), 65 (13), 51 (38), 39 (12). H NMR
spectrum, δ, ppm: 3.76 (3H, s, OCH3); 6.9-8.0 (9H, m, Ar); 8.36 (1H, s, CH=N).
N-(4-Bromobenzylidene)aniline (1u). Mass spectrum, m/z (Irel, %): 261/259 [M]+ (50/54), 260/258 [M -
H]+ (49/44), 179 [M - Br]+ (13), 152 (8), 104 [PhNCH]+ (19), 89 (11), 78 (9), 77 [Ph]+ (100), 76 (20), 63 (14),
51 (47), 50 (24), 39 (13). 1H NMR spectrum, δ, ppm: 7.1-7.9 (9H, m, Ar); 8.40 (1H, s, CH=N).
N-(4-Nitrobenzylidene)aniline (1v). Mass spectrum, m/z (Irel, %): 227 [M + H]+ (14), 226 [M]+ (100),
225 [M - H]+ (45), 179 (53), 167 (11), 152 (18), ), 104 [PhNCH]+ (30), 89 (3), 78 (9), 77 [Ph]+ (96), 76 (16), 63
(13), 51 (45), 50 (20). 1H NMR spectrum, δ, ppm: 7.1-8.4 (9H, m, Ar); 8.51 (1H, s, CH=N).
N-(4-Methoxybenzylidene)-2-trifluoromethylaniline (1w). Mass spectrum, m/z (Irel, %): 280 [M + H]+
(13), 279 [M]+ (85), 278 [M - H]+ (100), 260 [M - F]+ (5), 235 (11), 145 [PhCF3 - H]+ (34), 134 (5), 125 (8), 108
1
(5), 95 (10), 77 (13), 65 (11), 51 (10), 39 (5). H NMR spectrum, δ, ppm: 3.87 (3H, s, OCH3); 6.9-8.0 (8H, m,
Ar); 8.28 (1H, s, CH=N).
N-(4-Bromobenzylidene)-2-trifluoromethylaniline (1x). Mass spectrum, m/z (Irel, %): 329/327 [M]+
(79/85), 328/326 [M - H]+ (89/78), 308 [M - F]+ (5), 247 [M - Br]+ (5), 227 (6), 201 (5), 179 (13), 172 (19), 145
[PhCF3 - H]+ (34), 125 (20), 102 (15), 95 (30), 89 (13), 77 (18), 76 (28), 75 (44), 63 (18), 51 (20), 50 (31), 39
(10). 1H NMR spectrum, δ, ppm: 7.0-7.9 (8H, m, Ar); 8.32 (1H, s, CH=N).
N-(4-Bromobenzylidene)-2-nitroaniline (1y). Mass spectrum, m/z (Irel, %): 306/304 [M]+ (10/10), 259
[M - NO2]+ (2), 208 (7), 185/183 [BrC6H4CHNH]+ (96/100), 178 (17), 167 (5), 157/155 [C6H4Br]+ (15/16), 102
1
(10), 89 (26), 77 (23), 76 (30), 75 (19), 63 (31), 51 (26) 50 (30), 39 (20). H NMR spectrum, δ, ppm: 7.0-8.1
(8H, m, Ar), 8.33 (1H, s, CH=N).
The authors thank the Latvian Council of Science for financing the work (Grant No. 181).
REFERENCES
1.
2.
B. Marciniec (editor), Comprehensive Handbook of Hydrosilylation, Pergamon, Oxford (1992).
V. B. Pukhnarevich, E. Lukevics, L. I. Kopylova, and M. G. Voronkov, Prospects of Hydrosilylation
[in Russian], Inst. Organ. Sinteza Latv. Akad. Nauk, Riga (1992).
3.
4.
5.
6.
K. A. Horn, Chem. Rev., 95, 1317 (1995).
J.-F. Carpentier and V. Bette, Current Org. Chem., 6, 913 (2002).
I. Iovel, L. Golomba, J. Popelis, and E. Lukevics, Khim. Geterotsikl. Soedin., 51 (2002).
V. V. Zuev, O. P. Kovaleva, and N. K. Skvortsov, Phosphorus, Sulfur, and Silicon and the Related
Elements, 179, 83 (2004).
7.
8.
I. Iovel, L. Golomba, J. Popelis, S. Grinberga, and E. Lukevics, Khim. Geterotsikl. Soedin., 52 (2003).
E. Lukevics, I. Jovel, and L. Golomba, in: Abstracts of XVth FECHEM Conference on Organometallic
Chemistry, Zurich, Switzerland (2003], PO104.
9.
10.
11.
I. Iovel, L. Golomba, J. Popelis, A. Gaukhman, and E. Lukevics, Khim. Geterotsikl. Soedin., 324 (2000).
I. Iovel, L. Golomba, S. Belyakov, and E. Lukevics, Khim. Geterotsikl. Soedin., 778 (2000).
I. Iovel, L. Golomba, J. Popelis, S. Grinberga, and E. Lukevics, Khim. Geterotsikl. Soedin., 890 (2000).
713

12.
I. Iovel, L. Golomba, S. Belyakov, A. Kemme, and E. Lukevics, Appl. Organometal. Chem., 15, 733
(2001).
13.
14.
I. Iovel, L. Golomba, J. Popelis, S. Grinberga, and E. Lukevics, Khim. Geterotsikl. Soedin., 1375 (2002).
I. Iovel, L. Golomba, S. Belyakov, J. Popelis, A. Gaukhman, and E. Lukevits, Khim. Geterotsikl.
Soedin., 361 (2003).
15.
16.
17.
Ch. M. Standfest-Hauser, K. Mereiter, R. Schmid, and K. Kirchner, Organometallics, 21, 4891 (2002).
M. J. S. Dewar, E. G. Zoebisch, E. F. Healy, and J. J. P. Stewart, J. Am. Chem. Soc., 107, 3902 (1985).
J. J. P. Stewart, MOPAC, Version 6.0, Quantum Chemical Program Exchange (QCPE), Program
No. 455, Bloomington, IN (1984).
18.
19.
J. J. P. Stewart, MOPAC, Version 6.0, Manual Program No. 455, Bloomington, IN (1984).
JMol: http://www.chem.columbia.edu/~gezelter.
714