Synthesis and Unusual Reactivity of Compounds Containing Silicon−Phosphorus and Silicon−Arsenic Double Bonds: New Silylidenephosphanes and -arsanes of the Type R 2 SiE(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 = Si i Pr 3 ( a ), SiMe 3 ( b ), Si t BuMe 2 ( c ), SiPh 2 Me ( d ), SiPh 3 ( e ), Si(Naph) 3 ( f ), Si t Bu 2 H ( g ), Ge t Bu 2 H ( h, L = DME, n = 1)) and the related lithium (fluorosilyl)arsanides Is 2 Si(F)As[Li(THF) 2 ]R ( 3 ) (R = Si i Pr 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-arsa-2,3-diphospha-4-silabicyclo[1.1.0]butane ( 13 ) and 3-(triisopropylsilyl)-4,4-diisityl-1-arsa-2,3-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(Si i Pr 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( t Bu) ( 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(Si i Pr 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(Si i Pr 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(Si i Pr 3 )NN CPh 2 ( 29 ). The structures of 1h, 20, 23, and 29 were determined by X-ray crystallography.