Formation of Trivalent Zirconocene Complexes from ansa-Zirconocene-Based Olefin-Polymerization Precatalysts: An EPR- and NMR-Spectroscopic Study

Reduction of Zr(IV) metallocenium cations with sodium amalgam (NaHg) produces EPR signals assignable to Zr(III) metallocene complexes. The chloro-bridged heterodinuclear ansa-zirconocenium cation [(SBI)Zr(μ-Cl)2AlMe2]+ (SBI = rac-dimethylsilylbis(1-indenyl)), present in toluene solution as its B(C6F5)4 – salt, thus gives rise to an EPR signal assignable to the complex (SBI)ZrIII(μ-Cl)2AlMe2, while (SBI)ZrIII-Me and (SBI)ZrIII(μ-H)2Al i Bu2 are formed by reduction of [(SBI)Zr(μ-Me)2AlMe2]+ B(C6F5)4 – and [(SBI)Zr(μ-H)3(Al i Bu2)2]+ B(C6F5)4 –, respectively. These products can also be accessed, along with (SBI)ZrIII- i Bu and [(SBI)ZrIII]+ AlR4 –, when (SBI)ZrMe2 is allowed to react with HAl i Bu2, eliminating isobutane en route to the Zr(III) complex. Further studies concern interconversion reactions between these and other (SBI)Zr(III) complexes and reaction mechanisms involved in their formation.