[3,5-Bis(trimethylsilyl)-1-methyl-4(1H)-pyridinylidene]-dicyanomethane

3,5-Bis(trimethylsilyl)-1-methyl-4-thiophenoxypyridinium iodide reacts with the anion of malononitrile to give the corresponding dicyanomethylidene-1,4-dihydropyridine. The product was evaluated for its potential as a material for use in non-linear optics.

To a solution of ethanolic sodium ethoxide [prepared from sodium metal (33 mg, 1.43 mmol) and ethanol (10 mL)] was added malononitrile (94 mg, 1.42 mmol), the mixture stirred for 30 min and then 3,5-bis(trimethylsilyl)-1-methyl-4-thiophenoxypyridinium iodide [1] (670 mg, 1.42 mmol) added. The solution was refluxed for 1 h, cooled and the resulting precipitate recovered by filtration, and washed, firstly with water (10 mL), and then with isopropanol (10 mL) to give a pale yellow solid (308 mg, 72%). Recrystallisation from ethanol afforded pale yellow microcrystals.

M.p. 230-232 °C.

MS: Found: MH⁺ m/z 302.15185 C15H23N3Si2 requires MH⁺ m/z 302.15033 D = 1.5 p.p.m

¹H NMR (300 MHz, d₆-DMSO): d 0.20, s, 18H; 3.62, s, 3H; 7.51, s, 2H.

¹³C NMR (75 MHz, d₆-DMSO): d 0.0 (CH₃), 41.7 (CH₃), 50.6 (C_Q), 118.6 (C_Q), 120.3 (C_Q), 143.7 (CH), 162.7 (C_Q).

Anal. Calc for C₁₅H₂₃N₃Si₂ C 59.75, H 7.69, N 13.94. Found C 59.61, H 7.47, N 14.01.

IR (nujol): 2189, 1609, 1439, 1250, 1224, 847.

l_max 374 (methanol) log10_e4.49; 380 (pyridine) log10_e4.47.