Synthesis and Thermolysis of an Overcrowded 1,3-Dihydrotriphosphane

Abstract

Treatment of dichloroferrocenylphosphine with two molar amounts of a lithium phosphide bearing 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (denoted as Tbt) group afforded the corresponding 1,3-dihydro-2-ferrocenyltriphosphane [1; (TbtHP)₂PFc, Fc = ferrocenyl] in 73% yield. The structural characterization of 1 was achieved by the NMR spectra and X-ray crystallographic analysis. In the ³¹P{¹H} NMR spectrum of the mixture of three diastereomers of 1, the characteristic two A₂B and one ABX systems were observed as signals assignable to two meso and one dl isomers, respectively. Thermolysis of 1 in toluene led to the quantitative formation of TbtPH₂ and (E)-TbtP=PFc. Kinetic studies indicated that the thermolysis of 1 is the first-order reaction including a unimolecular dissociative process, which was reasonablely supported by theoretical calculations.