Reactivity of Bridged and Nonbridged Zirconocenes toward Biorenewable Itaconic Esters and Anhydride

Abstract

This work investigates the reactivity of neutral and cationic complexes of both bridged ansa-zirconocenes, rac-[C2H4(Ind)2]ZrMe[OC(OiPr)═CMe2] (1) and rac-[C2H4(Ind)2]Zr+(THF)[OC(OiPr)═CMe2][MeB(C6F5)3]− (1+), and nonbridged zirconocenes, Cp*(nPrCp)ZrMe[OC(OiPr)═CMe2] (13) and Cp*(nPrCp)Zr(THF)[OC(OiPr)═CMe2]+[MeB(C6F5)3]− (13+), toward biorenewable itaconic dialkyl esters (itaconates) and anhydride (IA). Behaving similarly, both cationic complexes 1+ and 13+ react readily with itaconates to form cleanly single monomer addition products, eight-membered-ring metallacycles 2 and 15, respectively, and neutral enolate complexes 1 and 13 insert 1 equiv of IA to afford single-IA-addition products 5 and 17. Behaving differently, eight-membered-ring chelates 2 derived from the bridged metallocene framework undergo slow isomerization at room temperature via ligand exchange between the coordinated and uncoordinated ester groups to form thermodynamically favored seven-membered-ring chelates 4, while eight-membered c...