Models for the Anionic Polymerization of P═C Bonds: Cyclization of n‐BuLi‐Initiated MesP═CPh2 and Related Phosphaalkenes with H2C═CPh2

TL;DR

This paper explores the polymerization mechanism of phosphaalkenes by studying the reaction of MesP═CPh2 with n-BuLi and H2C═CPh2, revealing new insights into cyclization and bond cleavage.

Contribution

The study identifies a novel cyclization mechanism and a long-lived intermediate in phosphaalkene reactions, offering new clues to their polymerization.

Findings

Addition of Li[MesP(Bu)–CPh2] to H2C═CPh2 leads to cyclization and release of Li[CHPh2].

A long-lived intermediate was observed in two phosphaalkene reactions.

The chiral cyclophosphane products may be useful as ligands for catalytic applications.

Abstract

To model the first propagation step in the anionic polymerization of MesP═CPh2 we studied the addition of Li[MesP(Bu)–CPh2] (and related species) to nonpolymerizable H2C═CPh2. Addition proceeds via the o‐CH3 of the P‐Mes followed by unprecedented cyclization to C5P‐rings with release of Li[CHPh2]. Further investigation of the aforementioned reaction using phosphaalkenes, RP═CAr2 (R ═ Mes, m‐Xyl; R′ ═ Ph, 4‐FC6H4, 4‐MeC6H4, 4‐MeOC6H4), resulted in the observation of a relatively long‐lived intermediate in two instances (R ═ Mes, R’ = 4‐MeC6H4, 4‐MeOC6H4). For the latter, the intermediate was identified as n‐BuP(CH(4‐MeOC6H4)2)[C6(4,6‐Me2)H2–(2‐CH2CH2CPh2Li) 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.

Noninnocence of P‐Mesityl substituent, cleavage of a P═C bond and cyclization are observed in reactions of five phosphaalkenes. The observed activation of the C─H bond of the Mesityl substituent and subsequent addition to nonpolymerizable H2C═CPh2 is examined as a potential clue to the polymerization mechanism for P‐Mesityl phosphaalkenes.

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