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 (27c,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 (18c,m). The formation of 27c,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.