Neue Synthesen und Reaktionen von Phosphetaniumsalzen mit planarem Gerüst

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Abstract
Novel Syntheses and Reactions of Phosphetanium Salts with a Planar magnified image SkeletonCleavage of the P–Si bond of silylphosphanes R2P‐SiMe3 (R = iPr, tBu, 2,4,6‐Me3C6H2) with excess 1,3‐dihalogenpropanes X–[CH2]3–X (X = Br, I) affords phosphetanium salts magnified image (3) in good yields. These strained four‐membered ring systems are also obtained by alkylation of secondary phosphanes R2PH with X–[CH2]3–X followed by deprotonation of the intermediate phosphonium salts [R2P(H)—[CH2]3–X]+ X‐ (R e.g. tBu; X = Br, 7b). Silylphosphanes and secondary phosphanes with less bulky substituents preferably form open‐chain phosphonium salts with [CH2]3–X or allyl substituents in these reactions. X‐ray structural analysis of magnified image (3h) reveals planar geometries for the PC3 skeletons of the cations. The reactivity of 3b towards different types of nucleophiles [F‐, NH2‐, OH‐, OR‐, Fe(CO)2Cp‐, NaN(SiMe3)2, RR′PLi] has been studied. Reaction with CsF or NaNH2, leads to a stable monofluoro or monoamino phosphorane, respectively, with cyclic four‐membered PC3 skeletons. In all other cases opening of the phosphetanium ring system occurs leading to derivatives with R2P—[CH2]3 terminal groups. Bidentate and polydentate ligands, e.g. 19–25, with bulky substituents in terminal position have been synthesized in high yields by cleavage of 3b with mono‐ and bifunctional lithium phosphides. By deprotonation of 3b with MeLi the cyclic ylide 14 is formed. Treatment with acetone or benzaldehyde leads to the unsaturated open‐chain phosphane oxides 15a or 15b in a Wittig‐type reaction.

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