Phosphinomethanides and group 15 element halides: Redox reactions, rearrangements and novel heterocycles

Article abstract of DOI:10.1016/S0022-328X(96)06578-3

The reactions of ECl₃ (E = P, As, Sb, Bi), RPCl₂ (R = Me, Ph, ¹Bu, Cy₂N) and Ph₂PCl, respectively, with ambident lithium phosphinomethanides are described. The reaction with LiCH₂PMe₂, 1, by E-C bond formation, leads to the substitution products E(CH₂PMe₂)₃, 2a-d, (E = P, As, Sb, Bi) and R-P(CH₂PMe₂)₂ (R = Me, Ph, ¹Bu, Cy₂N) 5a-d. In contrast, LiC(PMe₂)(SiMe₃)₂ -0.5TMEDA, 6, gives substitution products with ECl₃ (E = P, As, Sb), by E-P bond formation. Thus, the first element-tris(P-ylide)derivatives E(PMe₂=C(SiMe₃)₂)₃, 7a-c, are obtained. 7b is characterized by X-ray structure determination. In these reactions, oxidative P-P coupling to give [(Me₃Si)₂C=PMe₂]₂, 8, is also observed, and exclusively in the reaction of BiCl₃ with 6. The reaction of RPCl₂ (R = Me, Ph, ¹Bu, Cy₂N) with 6 strongly is dependent on the nature of R. For R = Me, only substitution is observed, yielding Me-P(PMe₂=C(SiMe₃)₂)₂, 10, while for R = Ph, both substitution and Li/Cl exchange with subsequent formation of 8 and the diphosphane [(Me₃Si)₂C=PMe₂-PPh]₂, 12, are found. The latter has been characterized structurally. In contrast, for R = ¹Bu, only (¹BuP)₃, 13, and (¹BuP)₄, 14, are obtained. An analogous result is observed in the reaction of ¹BuPCl₂ with LiC(PMe₂)₂(SiMe₃), 17. The reaction of Cy₂NPCl₂ with two equivalents of LiC(PMe₂)(SiMe₃)₂ · 0.5TMEDA, 6, gives a phospha-alkene Cy₂N-P=C(SiMe₃)₂, 16, and the substitution product Cy₂N-P(PMe₂=C(SiMe₃)₂)₂, 15. Likewise, LiC(PMe₂)₂(SiMe₃), 17, reacts with PhPCl₂ to give the substitution product Ph-P(PMe₂=C(PMe₂)(SiMe₃))₂, 18, which is characterized by X-ray structure determination, whereas with MePCl₂ only the P-ylide Me₂P-PMe₂=C(PMe₂)(SiMe₃), 20, and the coupling product [(Me₂P)(Me₃Si)C=PMe₂]₂, 19, are formed. The latter is also obtained in the reactions of BiCl₃ or SbCl₃ with LiC(PMe₂)₂(SiMe₃), 17. Analogous redox reactions with AsCl₃ and PCl₃, respectively, lead to the bis-pentacyclic {μ-[C(PMe₂)₂(SiMe₃)]As₂}₂, 21, and the hexacycle P-PMe₂-C(SiMe₃)-PMe₂-C(SiMe₃)-PMe₂, 22, which were structurally characterized by X-ray analyses. Depending on the reaction conditions, the reaction of PCl₃ with LiC(PMe₂)₂(SiMe₃), 17, alternatively may lead to the triphosphete P-PMe₂-C(SiMe₃)-PMe₂, 24. By using P-phenyl-substituents instead of P-methyl-substituents, i.e. in the reaction of LiC(PPh₂)₂(SiMe₃), 25, with PCl₃ or AsCl₃, the triphosphete P-PPh₂-C(SiMe₃)-PPh₂, 26a, or its arsenic analogue As-PPh₂-C(SiMe₃)-PPh₂, 26b, are respectively formed, along with the chlorine substituted ylide (Cl)(Ph)₂P=C(PPh₂)(SiMe₃), 27. 26a,b are characterized by X-ray structure determinations. The synthesis of the first ten-electron phosphorus cation P[C(PPh₂)₂(SiMe₃)]⁺₂, 30, with a homonuclear, spirocyclic PP₄-framework was achieved by reacting the triphosphete 26a with the ylide 27 in the presence of NaBPh₄. The crystal structure of the cation of 30, which adopts a Ψ-tbp geometry, was determined.