Generation and Trapping of a 1,1‘-Diphosphazirconocene

The reduction of [(η 5 -C 4 Me 4 P) 2 ZrCl 2 ] ( 1 ) by magnesium in THF affords a transient octamethyl-1,1‘-diphosphazirconocene which can be trapped by CO, bis(trimethylsilyl)acetylene, and 2-butyne to give the corresponding dicarbonyl 2, zirconacyclopropene 3, and zirconacyclopentadiene 4; all of these products have been characterized by X-ray analyses. An assessment of the π-basicity of the η 5 -C 4 Me 4 P ligand has been made by several methods: (a) a comparison of the IR carbonyl stretching frequencies of 2 and of other dicarbonylzirconocene complexes, (b) a correlation of the 13 C NMR and IR data in 3 and in similar zirconacyclopropenes, and (c) an electrochemical study on 1 . All these experiments confirm that the η 5 -C 4 Me 4 P ligand is a poorer π-base than the Cp ligand.