Research on the cyanosilylation of prochiral aldehydes catalyzed by alkyldimethoxyl silylene-bridged lanthanide complexes

Article abstract of DOI:10.1080/00397910600781257

A series of novel silylene-bridged Ln-O rare earth complexes are very efficient Lewis acidic catalysts in cyanosilylation of aldehydes, giving some cyano trimethylsilyl ethers of aldehydes in >99% yields. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910600781257

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Research on the Cyanosilylation of Prochiral
Aldehydes Catalyzed by Alkyldimethoxyl
Silylene–Bridged Lanthanide Complexes
Luo Mei a , Ke Yu Ping b , Li Xiao Xuan a , Yin Hao c , Hu Ke Liang c & Jiang
Ying a
a Department of Chemical Engineering , Hefei University of Technology ,
Hefei, China
b Department of Chemistry , University of Science and Technology , Hefei,
China
c Structure Research Laboratory , University of Science and Technology ,
Hefei, China
Published online: 27 Oct 2006.
To cite this article: Luo Mei , Ke Yu Ping , Li Xiao Xuan , Yin Hao , Hu Ke Liang & Jiang Ying (2006) Research
on the Cyanosilylation of Prochiral Aldehydes Catalyzed by Alkyldimethoxyl Silylene–Bridged Lanthanide
Complexes, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 36:17, 2483-2490, DOI: 10.1080/00397910600781257
To link to this article: http://dx.doi.org/10.1080/00397910600781257
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Synthetic Communicationsw, 36: 2483–2490, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600781257
Research on the Cyanosilylation of
Prochiral Aldehydes Catalyzed by
Alkyldimethoxyl Silylene–Bridged
Lanthanide Complexes
Luo Mei
Department of Chemical Engineering, Hefei University of Technology,
Hefei, China
Ke Yu Ping
Department of Chemistry, University of Science and Technology,
Hefei, China
Li Xiao Xuan
Department of Chemical Engineering, Hefei University of Technology,
Hefei, China
Yin Hao and Hu Ke Liang
Structure Research Laboratory, University of Science and Technology,
Hefei, China
Jiang Ying
Department of Chemical Engineering, Hefei University of Technology,
Hefei, China
Abstract: A series of novel silylene-bridged Ln-O rare earth complexes are very
efficient Lewis acidic catalysts in cyanosilylation of aldehydes, giving some cyano
trimethylsilyl ethers of aldehydes in .99% yields.
Keywords: Cyanosilylation of aldehydes, cyano trimethylsilyl ethers, Lewis acidic
catalysts, novel silylene-bridged Ln-O rare earth complexes
Received in Japan December 19, 2005
Address correspondence to Luo Mei, Department of Chemical Engineering, Hefei
University of Technology, Hefei 230009, China. E-mail: luomei@pku.edu.cn
2483

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L. Mei et al.
With the development of chemistry, rare earth organometallic complexes
are becoming more important in polymerization and organic reactions.[1–4]
Chiral cyanohydrins are important synthetic intermediates including chiral
a-hydroxyacids, a-amino acids, and b-amino alcohols, and they are also
applied in natural products such as (S)-oxybutynin,[5] (20S)-camptothecin[6]
synthesis, and so forth. Many chemists such as Corey,[7] Jacobsen,[8]
Shibasaki,[9–12] Garcia,[13–15] and Nakai[16] have made great contributions
to this field.
Alkyldimethoxyl silane, the electronic donors in Ln-O complexes, have
been widely used as the catalysts in industry. We have tried the cyanosilyla-
tion of aldehydes using the rare earth complexes involving cyclopropenyl and
got satisfactory results. To enrich the pool of catalysts, we employed these six
ligands[17] and lanthanide complexes (Fig. 1) for further research.
The first step is screening the ligand-Dy complexes with dichloromethane
solvent at room temperature; after 1 h, it was found that 4a had achieved the
product formation in 94.1% yield (Table 1). From this table, we can see that
the alkyl groups have some effects on the reaction, and the steric factor may be
the reason. No catalysts and ligands lead to a low reaction. With the rare earth
ion optimization, Dy3þ . Sm3þ . Nd3þ . La3þ . Pr3þ, 4a in 2 h .99%,
but thus can properly reduce the reaction time to 1 h, and still result in 94%
yield (Table 2).
We propose that the mechanism of cyanosilylation of aldehydes is that
Ln3þ could complex with the one pair of isolated electrons in the oxygen
atom of C55O bond and the reactivities of the substrates are greatly actived
by the complexes, leading to the smooth reaction.
Catalyst 4a proved to be general for the high activity including electron-
deficient and electron-rich substrates. The results are in entries 1–10, Table 3.
From Table 3, as to the 4-position aromatic aldehydes, the electron-
deficient substrates are proved to have poor reactivity after 2.5 h.
Their electron-rich counterparts are better in reactivity. The conversion
of 2-position substitution substrates are better than that of 4-position
substitution substrates, even through the 2-position are electron deficient.
Figure 1. Lanthanide complexes.

Cyanosilylation of Prochiral Aldehydes
2485
Table 1. Ligand-complexes optimizationa
Catalyst
Time (h)
Yield (%)b
1a
2a
1
1
1
1
1
2
2
2
2
2
2
1
80.0
46.9
60.2
94.1
71.9
80.1
5.57
59.6
0.30
0.48
.99
94.1
3a
4a
5a
6a
LaCl3
DyCl3
No catalyst
Ligand 4
4a
4a
aThe temperature is 308C, CH2Cl2 solvent.
1
bThe yield (%) was given by H NMR (300 MHz, CDCl3).
This follows the chemical theory and fully shows the results of P-p conjugate
effects (entries 2–5), electron effects (entries 2–9), and steric effects (entry 2).
In conclusion, the highly Ln-O complexes as the catalysts in cyanosi-
lylation of aldehydes give stable cyano trimethylsilyl ethers in excellent
yields at room temperature and with broad substrate generality. Further
efforts are being developed toward the determination of the structure of
complexes (cultivating the single crystals of the complexes), application
to cyanosilylation of prochiral ketones, and some other alkene polymeriz-
ation reactions.
Table 2. Rare earth opatimizationa
Catalyst
Time (h)
Yield (%)b
4a
4a
4b
4c
4d
4e
2h
1h
2h
2h
2h
2h
.99
94.1
46.2
73.5
83.0
89.9
aThe temperature is 308C, CH2Cl2 solvent.
bThe yield (%) was given by 1H NMR
(300 MHz, CDCl3).

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L. Mei et al.
Table 3. Cyanosilylation of aldehydes catalyzed by rare earth complex 4aa
Entry
R1
Time (h)
Yield (%)b
1
2
C6H5
1
94.1
93.0
.99
.99
.99
.99
79.4
83.6
83.8
91.3
65.9
90.5
2-OCH3C6C4
2-BrCH3C6H4
2-FC6H4
2.5
2.5
2.5
2.5
2.5
1
3
4
5
2-NO2C6H4
4- OCH3C6H4
4- BrC6H4
6
7
7
4- BrC6H4
4-ClCH3C6H4
4-ClC6H4
2.5
1
8
8
2.5
2.5
2.5
9
10
4- NO2C6H4
Naphthyl
aThe temperature is 308C, CH2Cl2 solvent.
bThe yield (%) was given by 1H NMR (300 MHz, CDCl3).
EXPERIMENTAL
General Procedures
All cyanosilylation reactions were performed using chloroform as solvent;
ligands and lanthanum complexes were synthesized. Reactions were
monitored by thin layer chromatography using 0.25-mm E. Merck silica
gel–coated glass plates (60F-254) with UV light to visualize the course of
reaction. Flash column chromatography was performed using E. Merck
silica gel (60, particle size 0.02–0.03 mm). Chemical conversion were
1
1
obtained by H NMR,13C NMR. H and 13C NMR spectra were obtained
using a Bruker AM-300 spectrometer. The following abbreviations were
used to designate chemical shift mutiplicities: s ¼ singlet, d ¼ doublet,
t ¼ triplet, and m ¼ multiplet. Infrared spectra were recorded on a Mattson
Galaxy Series FTIR 3000 spectrometer. High-resolution mass spectra were
obtained on a MASPEC.
Preparation of Diphenyl Dimethoxyl Silane (Method A)
A 250-mL Schlenk flask, equipped with a pressure-equalizing dropping
funnel, was charged with a solution of dichlorine silane (10 mL, 50 mmol)
of dry methanol (30 mL) in 20 ml of benzene. The dropping funnel was
charged with 25 mL of benzene and 8 mL of pyridine, and this was added

Cyanosilylation of Prochiral Aldehydes
2487
dropwise to the flask at about 2520 8C while stirring; after 20 min, white
pyridine hydrochloric acid was obtained. The mixture was allowed to warm
up to room temperature and was refuxed at 70–808C for 5 h. The mixture
was carefully filtered at room temperature, and the solvent was evaporated
in vacuo using a rotary evaporator, then washed with 10 mL of H2O,
extracted with 2 ꢀ 30 mL CH2Cl2, and dried with NaSO4 to yield 9.0 g
1
(36.8 mmol, 71%). H NMR (300 MHz,CDCl3, 278C), d(ppm) ¼ 7.66–7.69
(m, 5H, aromH), 7.31–7.66 (m, 5H, aromH), 3.59 (s,6H). 13C NMR 50.93,
51.00, 127.81, 127.93, 127.98, 130.20, 130.28, 130.35, 130.45, 134.076,
134.45, 134.64, 134.70, 134.88.
Preparation of Diisobutyl Dimethoxyl Silane
We followed the procedure previously described (method A). Bp: 728C
(10 mm Hg),1H NMR (300 MHz, CDCl3, 278C), d (ppm) ¼ 3.51 (m, 6H),
1.81–1.90 (m, 2H), 0.96–0.98 (d, 6.58 Hz, 2H), 0.61–0.64 (7.05 Hz, 4H).
13C NMR 23.06 (ꢀ2), 23.96 (ꢀ2), 26.17 (ꢀ4), 50.16 (ꢀ2).
Cyclohexyl Methyl Dimethoxyl Silane
Method A. Bp:196–1988C 1H NMR (300 MHz, CDCl3, 278C), d (ppm) ¼ 3.45
(s, 6H), 1.66–1.68 (m, 5H), 1.10–1.19 (m,5H), 20.004 to 20.0021 (s,3H). 13
NMR 27.89, 24.78, 26.70, 26.90, 27.61, 27.79, 50.39 (ꢀ2).
C
Diisopropyl Dimethoxyl Silane
1
Method A. Bp:1648C (740 mm Hg), H NMR (300 MHz, CDCl3, 278C), d
(ppm) ¼ 3.56 (s, 6H), 1.48–1.83 (m, 2H), 1.05–1.06 (d, 2.53 Hz, 12H), 13C
NMR 11.91 (ꢀ2), 17.38 (ꢀ4), 50.99 (ꢀ2).
Dicyclopentyl Dimethoxy Silane
Method A. Bp:1208C (6 mmHg), 1H NMR (300MHz,CDCl3, 278C), d (ppm) ¼
3.61 (s, 6H), 1.82–1.84 (m, 2H), 1.65–1.66 (m, 2H), 1.52–1.58 (m, 4H), 1.08–
1.12 (m, 2H). 13C NMR 23.55 (ꢀ2), 26.99 (ꢀ4), 27.70 (ꢀ4), 50.99 (ꢀ2).
Methyl, Phenyl Dimethoxy Silane
Method A. Bp: 106–1088C (10 mm Hg), 1H NMR (300 MHz, CDCl3, 278C), d
(ppm) ¼ 7.61–7.64 (m, 2H, aromH), 7.35–7.41 (m, 3H, aromH), 3.56 (s,6H),
0.36 (s, 3H). 13C NMR 25.13, 127.99 (ꢀ2), 130.23, 133.94, 134.05.

2488
L. Mei et al.
Preparation of a-(Trimethylsilyoxyl)-phenylacetonitrile (Method B)
To a solution of rare earth trichlorine (11.2 mg), ligand diisopropyl
dimethoxyl silane (7.8 mg) was added dropwise under argon. The resulting
white mixture was stirred for 2 h at room temperature. The resulting
solution was concentrated in vacuum and dried to give complex 4a, which
was dissolved in 1 mL of CH2Cl2. Phenyl aldehyde (1 mmol) and TMSCN
(0.2 ml, 2.2 mmol) were successively added at room temperature. After
2.5 h, the reaction was quenched. Further purification was performed by
1
silica gel. H NMR (300 MHz, CDCl3) 7.39–7.39 (t, 0.9 Hz, 2H), 7.31–
7.34 (m, 3H), 5.43 (s, 1H), 0.16 (s, 9H). 13C NMR (75 MHz, CDCl3) 148.0,
129.4, 128.9,124.3, 115.8, 62.9, 20.26.
a-(Trimethylsilyoxyl)-o-methyloxylphenylacetonitrile
We followed the procedure described in the previous paragraph (method
B).1H NMR (300 MHz, CDCl3) 7.57–7.61 (d, 11.4 Hz, 1H), 7.28–7.36
(t, 5.8 Hz, 1H), 6.99–7.07 (t, 0.9 Hz, 1H), 6.89–6.92 (d, 11.7 Hz, 1H), 5.80
(s, 1H), 3.75 (s, 3H), 0.158 (s, 9H). 13C NMR (75 MHz, CDCl3), 13C NMR
(75 MHz, CDCl3) 162.5, 130.2, 126.9, 126.7, 124.6, 120.5, 110.3, 57.9,
55.2, 22.18.
a(Trimethylsilyoxyl)-o-fluorophenylacetonitrile
1
Method B. H NMR (300 MHz, CDCl3) 7.17–7.20 (d, 9 Hz, 2H) 7.04–7.08
(d, 12 Hz, 2H), 5.70 (s, 1H), 0.098 (s, 9H). 13C NMR (75 MHz, 6CDCl3)
162.6, 131.3, 128.3, 127.1, 124.7, 115.7,115.2, 57.5, 21.95.
a-(Trimethylsilyoxyl)-o-nitrophenylacetonitrile
1
Method B. H NMR (300 MHz, CDCl3) 8.03–8.16 (d, 10.5 Hz, 1H), 7.94–
7.98 (d, 12 Hz, 1H), 7.62–7.71 (t, 2.7 Hz, 1H), 7.54–7.58 (t, 5.4 Hz, 1H),
6.15 (s, 1H), 0.31 (s, 9H). 13C NMR (75 MHz, CDCl3): 134.9, 132.4, 130.6,
128.8, 127.6, 125.7, 118.2, 60.5, 21.54.
a-(Trimethylsilyoxyl)-p-methyloxylphenylacetonitrile
Method B. 1H NMR (300 MHz, CDCl3) 7.38–7.42 (d, 12 Hz, 2H), 6.94–6.96
(d, 8 Hz, 2H), 5.45 (s, 1H), 3.83 (s, 3H), 0.23 (s, 9H). 13C NMR (75 MHz,
CDCl3) 161.3, 129.8, 128.4, 127.8, 119.2, 114.4, 114.1, 113.7, 63.2, 55.2,
20.40.

Cyanosilylation of Prochiral Aldehydes
2489
a-(Trimethylsilyoxyl)-p-fluorophenylacetonitrile
1
Method B. H NMR (300 MHz, CDCl3) 8.09–8.12 (d, 10.5 Hz, 1H), 7.94–
7.98 (d, 11.7 Hz, 1H), 7.71–7.73 (t, 3.3 Hz, 1H), 7.54–7.58 (t, 9 Hz, 1H),
6.16 (s, 1H), 0.31 (s, 9H). 13C NMR (75 MHz, CDCl3) 161.4, 130.8, 128.4,
128.3, 118.9, 116.2, 115.9, 63.3, 20.33.
a-(Trimethylsilyoxyl)-p-chlorophenylacetonitrile
1
Method B. H NMR (300 MHz, CDCl3) 7.38–7.40 (d, 6 Hz, 2H), 7.21–7.27
(d, 3 Hz, 2H), 5.48 (s, 1H), 0.245 (s, 9H). 13C NMR (75 MHz, CDCl3)
134.9, 131.8, 128.7, 128.4, 127.4, 126.6, 118.7, 62.5, 22.67.
a-(Trimethylsilyoxyl)-p-nitrophenylacetonitrile
Method B. 1H NMR (300 MHz, CDCl3) 8.28–8.38 (d, 2H), 7.67–7.77 (d, 2H),
5.62 (s, 1H), 0.38 (s, 9H). 13C NMR (75 MHz, CDCl3) 143.8, 130.8, 127.3,
126.9, 123.8, 123.3, 117.9, 62.3, 22.16.
a-(Trimethylsilyoxyl)-1-naphthylacetonitrile
Method B. 1H NMR (300 MHz, CDCl3) 7.84–7.88 (d, 12 Hz, 2H), 7.18–7.54
(m, 5H), 6.09 (s, 1H), 0.32 (s, 9H). 13C NMR (75 MHz, CDCl3) 133.7,
130.4, 129.6, 128.8, 126.9, 126.2, 125.5, 124.9, 122.9, 122.1, 118.9, 62.8,
20.36.
a-(Trimethylsilyoxyl)-1-p-bromophenylacetonitrile
Method B. 1H NMR(300 MHz, CDCl3) 7.49–7.50 (m, 2H), 7. 29–7.34
(m, 2H), 5.41 (s, 1H), 0.093 (s, 9H).13C NMR (75 MHz, CDCl3) 135.4,
132.2, 128.3, 128.0, 124.0, 123.6, 118.8, 20.19. HRMS: calcd. for
C11H14SiNO81Br: 85.0008, found: 284.9986.
a-(Trimethylsilyoxyl)-1-o-bromophenylacetonitrile
Method B. 1H NMR (300 MHz, CDCl3) 7.64–7.66 (m, 1H), 7.48–7.51
(m, 1H), 7. 31–7.35 (m,1H), 7.18–7.20 (m, 1H), 0.060 (s, 9H). 13C
NMR (75 MHz, CDCl3) 135.5, 133.1, 130.9, 128.6, 128.2, 121.8, 118.4,
20.21.

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L. Mei et al.
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