[Li(tmeda)2][cyclo-(P5But4)]: An unusual ion-separated lithium oligophosphanide

The reaction of lithium with Bu^tPCl₂ and PCl₃ in the ratio 12:4:1 in THF gave a product mixture comprising cyclo-(P₄Bu^t₄), Li₂(P₄Bu^t₄), and lithium tetra-tert-butylcyclopentaphosphanide Li[cyclo-(P₅Bu^t₄)] (1) among other phosphanides and phosphanes. Optimization of the reaction conditions and recrystallization from THF/TMEDA (TMEDA: Me₂NCH₂CH₂NMe₂) gave [Li(tmeda)₂][cyclo-(P₅Bu^t₄)] (1b) which was characterized by multinuclear NMR spectroscopy, mass spectrometry, IR spectroscopy, and elemental analysis. Single-crystal X-ray diffraction studies showed the presence of separated [Li(tmeda)₂]⁺ cations and [cyclo-(P₅Bu^t₄)]^? anions. 1b represents the first structure of a “naked” [cyclo-(P₅Bu^t₄)]^? anion.