Crowded organometallic compounds of the alkali metals with diphenylphosphino substituents in the organic group

The lithium compound [LiC(SiMe2CH2PPh2)(3)] 1, obtained by metallation of the precursor HC(SiMe2CH2PPh2)(3) I with LiMe, crystallised from benzene as a solvate 1 . 1.5C(6)H(6) that both in solution and in the solid state has an unusual tricyclic structure, with lithium bound to the carbanionic centre and the three phosphorus atoms. Lithiation of the related precursor HC(SiMe3)(2)(SiMe2CH2PPh2) II under similar conditions gave the dilithium compound [Li(thf)C(SiMe3)(2){SiMe2CH[Li(thf)(2)]PPh2}] 2, which has a fluxional structure in solution. Metallation of the precursor HC(SiMe3)(2)(SiMe2PPh2) III gave the compounds MC(SiMe3)(2)(SiMe2PPh2) (M=Li 3 or Na 4). Compound 3 is fluxional in benzene with interchange of methyl groups between SiMe2 and SiMe3 fragments. Compound 4, in contrast, has a non-fluxional molecular structure. In the solid the molecules of 4 form chains in which the sodium is bound intramolecularly to the carbanionic centre and to phenyl and intermolecularly to phenyl and phosphorus. Attempts to make the potassium analogue of 3 or 4 led to cleavage of the P-Si bond and formation of KPPh2. This has a complicated polymeric crystal structure in which molecules are linked by potassium-phenyl interactions.