Direct Syntheses of 1-Phenylphosphetane and 1-Phenylphosphirane. Crystal and Molecular Structures of Neutral and Cationic Cyclotrimerization Precursor Complexes

Dilithium phenylphosphide reacts with 1,3-dichloropropane or 1,2-dichloroethane to give 1-phenylphosphetane ( 1 ) or 1-phenylphosphirane ( 2 ), respectively, both of which can be isolated by distillation in vacuo. The phosphetane rapidly polymerizes when neat but is stable in benzene wherefrom the polymer can be selectively and quantitatively separated from 1 by the addition of trans -dichlorobis(diethyl sulfide)palladium(II). Four-membered 1 has a remarkably low-field 31 P NMR chemical shift (13.9 ppm), and 2, a remarkably high-field shift (−236 ppm). The crystal and molecular structures of the potential cyclotrimerization precursor complexes fac -[Mo(CO) 3 ( 1 ) 3 ] ( 7 ), fac -[Mo(CO) 3 ( 2 ) 3 ] ( 8 ), and [(η 5 -C 5 H 5 )Fe( 2 ) 3 ]PF 6 ( 9 ) have been determined. Both molybdenum complexes have C 3 symmetry in the solid state, and the iron complex has C 1 symmetry. An interesting feature of the three structures is that the phenyl groups of the small phosphorus heterocycles in each case are arranged in groups of three syn or anti to the auxiliary ligands.