Highly Efficient and Regioselective Synthesis of 1,1-Bis(alkoxy­dimethylsilyl)ethenes

Abstract

New 1,1-bis(alkoxydimethylsilyl)ethenes have been readily synthesized via ruthenium-hydride complex catalyzed selective silylative coupling cyclization of N,N′-dimethyl-N,N′-bis(dimethylvinylsilyl)ethane-1,2-diamine to yield 1,2,2,4,4,5-hexamethyl-3-methylene-1,5-diaza-2,4-disilacycloheptane, which then undergoes reaction with various alcohols.

1,1-bis(silyl)ethenes - silylative coupling - ruthenium-hydride complexes - silylamines - cyclic silaalkenes

References

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9

Synthesis and characterization of N , N ′-dimethyl- N , N ′-bis(dimethylvinylsilyl)ethane-1,2-diamine (1): Anhydrous triethylamine (20.8 mL, 0.15 mol) in anhydrous pentane (200 mL) was introduced into a flame-dried three-necked, 500 mL round-bottomed flask equipped with a magnetic stirring bar, rubber septum cap, and argon bubbling tube. To the resulting solution N,N′-dimethylethane-1,2-diamine (7.32 mL, 0.068 mol) was added. Chlorodimethylvinylsilane (18.1 mL, 0.132 mol) was subsequently added over 1 h and the reaction mixture was stirred under the flow of argon for 2 h at room temperature. After the substrate disappearance was confirmed by GC, the resulting salt was filtered off and the volatiles were removed by evaporation. Distillation under reduced pressure (51-53 °C/0.5 mmHg) afforded 16.2 g of compound 1 in 93% yield as a colorless liquid. ¹H NMR (300 MHz, CDCl₃):
δ (ppm) = 0.12 (s, 12 H, SiCH₃), 2.48 (s, 6 H, NCH₃), 2.72 (s, 4 H, CH₂), 5.65-5.72 (dd, J = 4.4, 19.8 Hz, 2 H, CH=CH ₂), 5.91-5.97 (dd, J = 4.4, 14.8 Hz, 2 H, CH=CH ₂), 6.05-6.16 (dd, J = 14.8, 19.8 Hz, 2 H, CH=CH₂). ¹³C NMR (75 MHz, CDCl₃): δ (ppm) = -2.32 (SiCH₃), 35.23 (NCH₃), 50.06 (CH₂), 131.55 (CH=CH₂), 139.16 (CH=CH₂). HRMS (EI): m/z calcd for C₁₂H₂₈N₂Si₂: 256.1791; found: 256.1801.

10

Synthesis and characterization of 1,2,2,4,4,5-hexamethyl-3-methylene-1,5-diaza-2,4-disilacycloheptane (2): Compound 1 (10.0g, 0.039mol) was added to a solution of 0.283 g [RuHCl(CO)(PCy₃)₂] (3.9 × 10^-4 mol) and toluene (50 mL) in a two-necked, 100 mL flask equipped with a magnetic stirring bar and a reflux condenser. The reaction mixture was heated under a flow of argon for 24 h at 110 °C with stirring. The cyclic product was isolated by bulb-to-bulb distillation to give 8.19 g of compound 2 in 92% yield as a colorless liquid. ¹H NMR (300 MHz, CDCl₃): δ (ppm) = 0.12 (s, 12 H, SiCH₃), 2.47 (s, 6 H, NCH₃), 2.83 (s, 4 H, CH₂), 6.11 (s, 2 H, C=CH₂). ¹³C NMR (75 MHz, CDCl₃): δ (ppm) = -2.28 (SiCH₃), 35.67 (NCH₃), 49.92 (CH₂), 137.87 (C=CH₂) 159.29 (C=CH₂). Anal. calcd for C₁₀H₂₄N₂Si₂: C, 52.57; H, 10.59; N, 12.26; Found: C, 51.75; H, 10.56; N, 12.25.

11

Representative procedure for the synthesis of 1,1-bis(alkoxydimethylsilyl)ethenes and spectroscopic data of selected new products: The glass reactor (50 mL, two-necked, round-bottomed flask equipped with a magnetic stirring bar, reflux condenser, and argon bubbling tube) was evacuated and flushed with argon. 1,2,2,4,4,5-Hexamethyl-3-methylene-1,5-diaza-2,4-disilacycloheptane (2) and THF were added to the reactor. At room temperature the corresponding alcohol (2/alcohol = 1:2.5) was added dropwise. The reaction mixture was stirred under the conditions shown in Table [1] . After the reaction was complete the excess amount of the alcohol and the solvent were evaporated in vacuo. After evaporation the crude product was distilled under reduced pressure to afford the analytically pure product.
1,1-Bis(methoxydimethylsilyl)ethene (I): ¹H NMR (300 MHz, CDCl₃): δ (ppm) = 0.18 (s, 12 H, SiCH₃), 3.38 (s, 6 H, OCH₃), 6.44 (s, 2H, C=CH₂). ¹³C NMR (75 MHz, CDCl₃): δ (ppm) = -1.92 (SiCH₃), 50.25 (OCH₃), 143.52 (C=CH₂), 150.88 (C=CH₂). Anal. calcd for C₈H₂₀O₂Si₂: C, 47.01; H, 9.86. Found: C, 47.16; H, 9.63.
1,1-Bis(benzyloxydimethylsilyl)ethene (VII): ¹H NMR (300 MHz, CDCl₃): δ (ppm) = 0.30 (s, 12 H, SiCH₃), 4.73 (s, 4 H, OCH₂C<), 6.57 (s, 2 H, C=CH₂), 7.34-7.39 (m, 10 H, Ph). ¹³C NMR (75 MHz, CDCl₃): δ (ppm) = -1.20 (SiCH₃), 64.67 (OCH₂C<), 126.44, 126.97, 128.20 (o-, m-, p-Ph), 140.94 (C=CH₂), 143.79 (OCH₂ C<), 151.17 (C=CH₂). Anal. calcd for C₂₀H₂₈O₂Si₂: C, 67.36; H, 7.91. Found: C, 67.57; H, 7.94.

12

Representative procedure for the one-pot synthesis of 1,1-bis(alkoxydimethylsilyl)ethenes: The glass reactor (50 mL, two-necked, round-bottomed flask equipped with a magnetic stirring bar, reflux condenser, and argon bubbling tube) was evacuated and flushed with argon. Compound 1 and [RuHCl(CO)(PCy₃)₂] were added to the reactor ( 1/catalyst = 1:10^-2). The reaction mixture was heated under the flow of argon for 24 h at 120 °C with stirring. After cooling to room temperature 1 M solution of the corresponding alcohol in THF was added dropwise (1/alcohol = 1:2.5) The reaction mixture was stirred under the conditions shown in Table [2] . After the reaction was complete, the excess alcohol and the solvent were evaporated in vacuo. After evaporation, the crude product was distilled under reduced pressure to afford the analytically pure product.