Synthesis and unusual reactivity of compounds containing silicon phosphorus and silicon arsenic double bonds: New silylidenephosphanes and -arsanes of the type R(2)Si=E(SiR(3)) (E=P, As)

The monomeric lithium (fluorosilyl)phosphanides Is(2)Si(F)P[LiL(n)]R (1) (Is = 2,4,6-triisopropylphenyl; L = THF, n = 2, 3; R = SiiPr(3) (a), SiMe(3) (b), SitBuMe(2) (c), SiPh(2)Me (d), SiPh(3) (e), Si(Naph)(3) (f), SitBu(2)H (g), GetBu(2)H (h, L = DME, n = 1)) and the related lithium (fluorosilyl)arsanides Is(2)Si(F)As[Li(THF)(2)]R (3) (R = SiiPr(3) (a), SiPh(2)Me (b), SiCy(2)Me (c, Cy = cyclohexyl)) eliminate LiF and THF (DME) upon heating to give the corresponding silylidenephosphanes and -arsanes 2 and 4, respectively. The reactivity of the Si=E bonds (E = P (2a), As (4a)) toward P-4, elemental sulfur, and tellurium is very similar and leads to the corresponding 1,2,3-triphospha-4-silabicyclo[1.1.0]butane (12) and to two isomers of arsadiphosphasilabicyclo[1.1.0]butanes, namely 1-(triisopropylsilyl)-4,4-diisityl-1-ars-2,3- diphospha-4-silabicyclo[1.1.0]butane (13) and 3-(triisopropylsilyl)-4,4-diisityl-1-diphospha-4-silabicyclo[1.1.0]butane (14), respectively. The reaction of S-8 and Te with 2a gives rise to the corresponding silaphosphathia- and telluracyclopropanes 16 and 17,respectively. The reaction of 2a with phenylacetylene yields Is(2)Si(C=CPh)PH(SiiPr(3)) (18), and benzonitrile reacts with 2g and 4c to give the [2 + 2]-cycloadducts Is(2)SiE(SiR(3))C(Ph)=N (E = P (19), E = As (20)). Only 4c reacts with tert-butylphosphaacetylene to give Is(2)SiAs(SiCy(2)Me)P=C(tBu) (43). 2a reacts with cyclopentadiene to provide the expected hetero Diels-Alder product (22). The reaction of 2a with benzophenone leads to the corresponding 2,1,3-silaphosphaoxetane (23), and treatment of 2a with 1,2-diphenyl-1,2-diketone unexpectedly provides the [2 + 2]-cycloadduct Is(2)SiP(SiiPr(3))C(Ph)COPh)O (27) as the thermodynamic product. The 2,4-di-tert-butyl-o-quinone solely yields the [2 + 4]-cycloadduct Is(2)SiP(SiiPr(3))O(aryl)O (aryl = 2,4-di-tert-butylphenylene) (31). The cycloaddition reactions of 2a and 4a with diphenyldiazomethane, mesityl azide, and mesityl isocyanide were also investigated, and the respective [2 + n]-cycloadducts (n = 1, 2, 3) were characterized by means of NMR spectroscopy. For example, 4a reacts with diphenyldiazomethane to give the [2 + 1]-cycloadduct Is(2)SiAs(SiiPr(3))NN=CPh(2) (29). The structures of 1h, 20, 23, and 29 were determined by X-ray crystallography.