NOVEL SYNTHESES AND REACTIONS OF PHOSPHETANIUM SALTS WITH A PLANAR C-C-C-P SKELETON

Cleavage 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 [R2P - [CH2]3]+X- (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 [tBu2P - [CH]3]+I- (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.