First X-ray Crystal Study and DFT Calculations of Anionic λ4-Phosphinines

Anionic λ4-phosphinines 3 and 4 were synthesized via the reaction of the corresponding λ3-phosphinines 1 and 2 with MeLi. The X-ray structure of [3][Li(thf)2] is reported and shows the η5-coordination of the Li cation to the five carbon atoms of the phosphacyclohexadienyl moiety. Cryptated species [3][Li[2.2.2]] and [4][Li(thf)4] were also synthesized and analyzed by X-ray diffraction methods, allowing direct comparison with noncryptated species. Anion 5 was obtained by the reaction of 2 with t-BuLi. This shows that electronics and sterics can easily be modified on these highly reactive species. The crystal structure of [5][Li[2.2.2]] is presented. This study was completed by DFT calculations, which showed the negative charge to be essentially localized on the α carbon atoms of these anions.