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

The reaction of lithium with ButPCl2 and PCl3 in the ratio 12:4:1 in THF gave a product mixture comprising cyclo-(P4But4), Li2(P4But4), and lithium tetra-tert-butylcyclopentaphosphanide Li[cyclo-(P5But4)] (1) among other phosphanides and phosphanes. Optimization of the reaction conditions and recrystallization from THF/TMEDA (TMEDA: Me2NCH2CH2NMe2) gave [Li(tmeda)2][cyclo-(P5But4)] (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-(P5But4)]− anions. 1b represents the first structure of a “naked” [cyclo-(P5But4)]− anion.