Models for the Anionic Polymerization of P═C Bonds: Cyclization of n-BuLi-Initiated MesP═CPh and Related Phosphaalkenes with HC═CPh.

To model the first propagation step in the anionic polymerization of MesP═CPh we studied the addition of Li[MesP(Bu)-CPh] (and related species) to nonpolymerizable HC═CPh. Addition proceeds via the o-CH of the P-Mes followed by unprecedented cyclization to CP-rings with release of Li[CHPh]. Further investigation of the aforementioned reaction using phosphaalkenes, RP═CAr (R ═ Mes, m-Xyl; R' ═ Ph, 4-FCH, 4-MeCH, 4-MeOCH), resulted in the observation of a relatively long-lived intermediate in two instances (R ═ Mes, R' = 4-MeCH, 4-MeOCH). For the latter, the intermediate was identified as n-BuP(CH(4-MeOCH))[C(4,6-Me)H-(2-CHCHCPhLi) by isolation of the oxidized, H-quenched product. These observations provide intriguing clues into the complex mechanism of polymerization of P-Mes phosphaalkenes and the chiral cyclophosphane products are of interest as ligands for catalytic applications.