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)2AliBu2 are formed by reduction of [(SBI)Zr(μ-Me)2AlMe2]+ B(C6F5)4– and [(SBI)Zr(μ-H)3(AliBu2)2]+ B(C6F5)4–, respectively. These products can also be accessed, along with (SBI)ZrIII-iBu and [(SBI)ZrIII]+ AlR4–, when (SBI)ZrMe2 is allowed to react with HAliBu2, 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.