Chemistry of acetylenic ethers LXII: Tertiary phosphines with an acetylene‐phosphorus bond

A number of dialkylphosphinoethynes R2PC≡CH were prepared from chlorodialkylphosphines and ethynylmagnesium bromide. With di‐n‐butylphosphinoethyne the following experiments were performed. From the lithium compound LiC≡CP(n•C4H9)2 it was possible to obtain 1‐dibutylphosphinoalkynes (n•C4H9)2PC≡CR and dibutylphosphinoethynylcarbinols (n•C4H9)2PC≡CC(OH)R′R″ in liquid ammonia. With diethylamine and paraformaldehyde, dibutylphosphinoethyne gave no normal Mannich reaction, since acetylene separated off and the phosphine oxide (n•C4H9)2P(=O)CH2N(C2H5)2 was formed. By free‐radical addition of ethanethiol, (n•C4H9)2PCH = CHSC2H5 was obtained. During the reaction of organometallic compounds with dibutylphosphinoethyne we observed breaking of the P‐C ≡ bond. Further investigation proved that a nucleophilic substitution on phosphorus took place. On the strength of the reactions which are involved in this (see the scheme on p. 6) new methods could be developed for the replacement of acetylene‐hydrogen atoms by a dialkylphosphino group. These are based on reactions of the acetylene anion with RSPR2 or ROPR2. From phenyllithium and bis‐(dibutylphosphino)ethyne, mono(dibutylphosphino)ethyne and dibutyl‐phenylphosphine were obtained.