van't Hoff-Le Bel Stranger: Formation of a Phosphonium Cation with a Planar Tetracoordinate Phosphorus Atom.

A novel intriguing type of coordination mode in phosphorus chemistry has been established that is of fundamental interest in the understanding of chemical bonding. Besides the synthesis of the first planar phosphonium cation PR(4)(+) 1 by a surprisingly simple metathesis reaction, a potentially general experimental method that reaches the seemingly impossible high-energy region of basic molecular and isoelectronic ER(4) systems (E=B(-), C, N(+), Al(-), Si, P(+)) is provided.