ALKYLIDYNEPHOSPHANES AND ALKYLIDYNEARSANE S .1. [P-EQUIVALENT-TO-C-S]-[LI(DME)3]- SYNTHESIS AND STRUCTURE( )

O,O'-Diethyl thiocarbonate and bis(tetrahydrofuran)lithium bis(trimeth ylsilyl)phosphanide dissolved in 1,2-dimethoxyethane, react below 0-de grees-C to give ethoxy trimethylsilane and tris(1,2-dimethoxyethane-O, O')lithium 2lambda3-phosphaethynylsulfanide -[P=C-S]-[Li(dme)3]+ - (1a ). Apart from bis(trimethylsilyl)sulfane or carbon oxide sulfide, dark red concentrated solutions of lambda3-phosphaalkyne 1 are also obtain ed from reactions of carbon disulfide with bis(tetrahydrofuran)lithium bis(trimethylsilyl)phosphanide or with the homologous lithoxy-methyli dynephosphane (2) [1]. The ir spectrum shows two absorptions at 1762 a nd 747 cm-1 characteristic for the P=C and C-S stretching vibrations. The nmr parameters {delta(P-31) - 121.3; delta(C-13) 190.8 ppm; 1J(CP) 18.2 Hz} resemble much more values of diorganylamino-2lambda3-phospha alkynes than those of -dimethoxyethane-O,O')lithoxy-methylidynephospha ne (2a). As found by an X-ray structure analysis (P2(1))/c; a = 1192.6 (16); b = 1239.1(19); c = 1414.8(26) pm; beta = 105.91(13)degrees at - 100 +/- 3-degrees-C; Z = 4 formula units; wR = 0.064) of pale yellow c rystals (mp. + 16-degrees-C) isolated from the reaction with O,O'-diet hyl thiocarbonate, the solid is built up of separate [P=C-S] - and [Li (dme)3]+ ions. Typical bond lengths and angles are: P=C 155.5(11); C-S 162.0(11); Li-O 206.4(17) to 220.3(20) pm; P=C-S 178.9(7)degrees.