Zirconium complexes of cyclopentene-bridged diamidophosphine ligands for dinitrogen activation

• Main Author: Zhu, Ting
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/28114

The synthesis of two new diiminophosphine proligands, CY⁵[NPN]DMPH₂ (DMP = 2,6-Me₂C₆H₃) and CY⁵[NPN]DIPPH₂ (DIPP = 2,6-iPr2C₆H₃), is reported. These two proligands feature a cyclopentane ring linker between the phosphine and imino donors. The precursors of the proligands were prepared from cyclopentanone and the corresponding substituted aniline. After lithiation and slow addition of PhPCl₂, the diiminophosphine proligands could be obtained. It is easy to vary the bulkiness of the proligands in this synthetic strategy. The synthesis of a diamidodioxo ligand based on the scaffold of calix[4]arene was also attempted. The bis(dimethylamido)zirconium complexes of the two ligands, CY⁵[NPN]DMP and CY⁵[NPN]DIPP, were prepared via protonolysis from the proligands and Zr(NMe₂)₄. The dichlorozirconium or diiodozirconium species could be obtained from the corresponding bis(dimethylamido)zirconium complex upon addition of excess Me₃SiCl or Me₃SiI. Most of the zirconium complexes are well characterized in the solid state by single crystal X-ray diffraction. A Zr-N₂ complex, {CY⁵[NPN]DMPZr(THF)}₂(µ-η²:η²-N₂), was synthesized from CY⁵[NPN]DMPZrCl₂ and 2.2 equivalents of KC₈ in THF under 4 atm of N₂. By single crystal X-ray analysis, N₂ has been reduced to an N₂4- unit and is side-on bound to two Zr atoms. However, large number of side products was observed in the reaction. The reduction of CY⁵[NPN]DIPPZrCl₂ was also attempted. From the minor product identified from single crystal X-ray diffraction, the cyclopentene ring linker was cleaved in the reduction of CY⁵[NPN]DIPPZrCl₂.