THE CYCLOTETRAPHOSPHANE P4[P(TERT-BU)2]4

P4[P(tBu)2]4 1 is obtained by thermal decomposition (20-degrees-C) of (tBu)2P-P = P(tBu)2Br which is formed from [(tBu)2P]2PLi and 1,2-dibromoethane. The P-31 NMR spectrum of 1 shows two complex signal patterns of the AA'A''A'''XX'X''X''' type; delta = +63 ppm (exocyclic) and delta = -43 ppm (cyclic). 1 crystallizes monoclinic in the space group C2/c, (a = 2240.8(17) pm, b = 885.6(7) pm, c = 2221.8(14) pm, beta = 101.72(5)degrees) with Z = 4 molecules in the elementary cell. The molecule has E conformation. The four-membered ring is folded (dieder angle 61-degrees) to give the P(tBu)2 groups nearly equatorial and the lone pairs nearly axial positions.