Versatile Access to Very Short P═P Double Bonds in Mixed-Valent 1λ5-Diphosphenes via 1,3-Silyl Migration

Formation, Reactivity and Decomposition of Aryl Phospha-Enolates

Two lithium phospha-enolates [RP=C(Siⁱ Pr₃ )OLi]₂ were prepared by reaction of triisopropyl silyl phosphaethynolate, ⁱ Pr₃ SiPCO, with aryl lithium reagents LiR (R=Mes: 1,3,5-trimethyl phenyl; or Mes*: 1,3,5,-tri-tertbutyl phenyl). Monomer/dimer aggregation of the enolates can be modulated by addition of 12-crown-4. Substitution of lithium for a heavier alkali metal was achieved through initial formation of a silyl enol ether, followed by reaction with KO^t Bu to form the corresponding potassium phospha-enolate [MesP=C(Siⁱ Pr₃ )OK]₂ . On addition of water, the enolates are protonated to afford RP=C(Siⁱ Pr₃ )(OH). For the sterically less demanding system (R=Mes), this phospha-enol rapidly tautomerises to the corresponding acyl phosphine MesP(H)C(Siⁱ Pr₃ )(O), which on heating extrudes CO. In contrast, bulkier phospha-enol (R=Mes*) is stable to rearrangement at room temperature and thermally decomposes to RH and ⁱ Pr₃ SiPCO.

Reductive Elimination at Pb(II) Center of an (Amino)plumbylene-Substituted Phosphaketene: New Pathway for Phosphinidene Synthesis

A stable (amino)plumbylene‐substituted phosphaketene 3 was synthesized by the successive reactions of PbCl₂ with two anionic reagents (lithium amidophosphine and NaPCO). Of particular interest, the thermal evolution of 3, at 80 °C, leads to the transient formation of corresponding amino‐ and phosphanylidene‐phosphaketenes (6 and 7), via a reductive elimination at the Pb^II center forming new N−P and P−P bonds. Further evolution of 6 gives a new cyclic (amino)phosphanylidene phosphorane 4, which shows a unique reactivity as a phosphinidene. This result provides a new synthetic route to phosphinidenes, extending and facilitating further their access.