Reactions of two-coordinate phosphines with acetylenes: synthesis of new allenic and acetylenic phosphines

The two-coordinate phosphines (Me[sub 3]Si)[sub 2]NP[double bond]ESiMe[sub 3] (1, E = N; 2, E = CH) reacted smoothly with 2-butyne via an ene process (instead of the expected cycloaddition reaction) to give the novel allenic phosphines H[sub 2]C[double bond]C[double bond]C(CH[sub 3])P[E(H)SiMe[sub 3]]N(SiMe[sub 3])[sub 2] (3, E = N; 4, E = CH). Similarly, treatment of the iminophosphine 1 with 1-hexyne (in benezene solution at 80[degrees]C) afforded the analogous allene derivative CH[sub 3]CH[sub 2]CH[sub 2]CH[double bond]C[double bond]CHP[N(H)SiMe[sub 3]]N(SiMe[sub 3])[sub 2] (5). Under different conditions (no solvent, 25[degrees]C), however, the reaction of 1 with 1-hexyne occurred via a unique 1,2-addition of the terminal H-C bond to the P[double bond]N linkage, thus affording the acetylene isomer CH[sub 3]CH[sub 2]CH[sub 2]CH[sub 2]C[triple bond]CP[N(H)SiMe[sub 3]]N(SiMe[sub 3])[sub 2] (6). Other terminal acetylenes, PhC[triple bond]CH and Me[sub 3]SiC[triple bond]CH, reacted with 1 via this 1,2-addition pathway to give the acetylenic phosphines RC[triple bond]CP[N(H)SiMe[sub 3]]N(SiMe[sub 3])[sub 2] (7, R = Ph; 8, R = SiMe[sub 3]). These new allenic (3-5) and acetylenic (6-8) phosphines were obtained in good yields (50-82%) as thermally stable liquids and were fully characterized by NMR ([sup 1]H, [sup 13]C, [sup 31]P) spectroscopy and elemental analysis. 11 refs., 2 tabs.