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 t he 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 centr e and the three phosphorus atoms. Lithiation of the related precursor HC(Si Me3)(2)(SiMe2CH2PPh2) II under similar conditions gave the dilithium compou nd [Li(thf)C(SiMe3)(2){SiMe2CH[Li(thf)(2)]PPh2}] 2, which has a fluxional s tructure 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 an d SiMe3 fragments. Compound 4, in contrast, has a non-fluxional molecular s tructure. In the solid the molecules of 4 form chains in which the sodium i s bound intramolecularly to the carbanionic centre and to phenyl and interm olecularly to phenyl and phosphorus. Attempts to make the potassium analogu e of 3 or 4 led to cleavage of the P-Si bond and formation of KPPh2. This h as a complicated polymeric crystal structure in which molecules are linked by potassium-phenyl interactions.