P-N/P-P bond metathesis for the synthesis of complex polyphosphanes

A unique hexaphosphane featuring a 2,2'-bi(1,2,3-triphosphacyclopentane) moiety (19) and an ethylene-bridged bis-isotetraphosphane (27(c,m)) were both selectively prepared in efficient one-pot syntheses from easily accessible tris(3,5-dimethyl-1-pyrazolyl)phosphane (14) and 1,2-bis(phenylphosphanyl)ethane (18(c,m)). The formation of 27(c,m) is an example of a highly efficient P-P bond formation via protolysis. In contrast, the formation of 19 comprises P-N/P-P bond metathesis steps. This constitutes a novel synthetic approach toward the preparation of complex polyphosphanes. Detailed spectroscopic investigations form the basis for a mechanistic understanding of this unprecedented methodology. Furthermore, the preparation of a unique dinuclear iron-carbonyl complex which features hexaphosphane 19 as a bridging ligand illustrates the potential use of complex polyphosphanes such as 19 as ligands in transition metal chemistry.