TRI(1-CYCLOHEPTA-2,4,6-TRIENYL)PHOSPHANE, P(C7H7)(3), AND TETRA(1-CYCLOHEPTA-2,4-6-TRIENYL)PHOSPHONIUM TETRAFLUOROBORATE, [P(C7H7)(4)]BF4

The reaction of tris(trimethylsilyl)phosphane, P(SiMe(3))(3), with tropylium bromide, C7H7+Br-, in polar solvents such as dichloromethane or tetrahydrofuran gives P(C7H7)(3) (1) and [P(C7H7)(4)]Br (2a). According to the X-ray crystallographic structure determinations, all 1-cyclohepta-2,4,6-trienyl substituents are present in the boat conformation in both P(C7H7)(3) (1) and the phosphonium salt, [P(C7H7)(4)]BF4 (2b). The boat-shaped C7H7 rings are significantly more flattened if the phosphorus occupies the axial rather than the equatorial position at the ring substituent. Addition of a chalcogen to the lone pair at the central phosphorus atom of 1 leads to the chalcogena-phosphoranes EP(C7H7)(3) (E = O (3a), S (3b), Se (3c)). The new 1-cyclo-hepta-2,4,6-trienyl-phosphorus compounds 1, 2b and 3a-c were characterized by their H-1, C-13, and P-31 NMR spectra in C6D6 solution.