Bonding in the PCP moiety. Crystal structures of [(triphenylphosphoranylidene)methyl]triphenylphosphonium bromide, and bis(diphenylphos-phinoselenoyl) methane

Abstract

In conjunction with molecular orbital studies of molecules containing the PCP moiety, the structures of the title compounds have been determined. Crystals of both compounds are monoclinic, space group P2₁/c. The unit cell of [Ph₃P·CH·PPh₅]Br is a= 9.666(3), b= 19.187(6), c= 17.116(4)Å, β= 102.675(7)°, with Z= 4; the cell for Ph₂P(Se)·CH₂·P(Se)Ph₂ is a= 9.672(1), b= 10.875(1), c= 23.067(7)Å, β= 105.14(1)°, with Z= 4. The PCP bond angles and mean P–C distances for the two compounds were found to be 128.2(3)°, 1.703(11)Å and 117.9(6)°, 1.843(14)Å, respectively. The results are compared with those observed for Ph₃P:C:PPh₃, and some preliminary molecular orbital calculations involving the PCP moiety are discussed.