Neutral Dimethylzirconocene Complexes as Initiators for the Ring‐Opening Polymerization of ϵ‐Caprolactone

Abstract

AbstractThe synthesis, structures, and ring‐opening polymerization (ROP) activity of new dimethyl‐ansa‐ and ‐non‐ansa‐zirconocene complexes are reported. The substituted indene precursors 1‐C9H7R [R = CH3 (1), CH2Ph (2) and C2H4(C4H7O2) (3)] were synthesised by treating RBr [R = CH2Ph and C2H4(C4H7O2)] or MeI with indenyllithium. Likewise, bridged indenyl/cyclopentadiene compounds [Me2Si(3‐C9H6R)(C5Me4H)] [R = H (4), CH3 (5), CH2Ph (6) and C2H4(C4H7O2) (7)] were obtained by treating the lithium salt of the appropriately substituted indene with ClSiMe2(C5Me4H). ansa‐Indenyl–cyclopentadienylmetallocenes [Zr{Me2Si(3‐η5‐C9H5R)(η5‐C5Me4)}Cl2] [R = H (8), CH3 (9), CH2Ph (10), C2H4(C4H7O2) (11)] were subsequently obtained by treating the dilithium salts of the corresponding ligands with ZrCl4 in toluene. The dimethyl derivatives [Zr{Me2Si(3‐η5‐C9H5R)(η5‐C5Me4)}Me2] [R = H (12), CH3 (13), CH2Ph (14), C2H4(C4H7O2) (15)] were prepared by treating the corresponding ansa‐zirconocene dichloride complex with MgMeBr. Dialkyl derivative [Zr{Me2Si{3‐η5‐C9H5(CH2Ph)}(η5‐C5Me4)}(CH2SiMe3)2] (16) was prepared by adding 2 equiv. of LiCH2SiMe3 to complex 10. Mixed indenyl/cyclopentadienylzirconocene complexes [Zr(η5‐C9H6R)(η5‐C5H5)Cl2] [R = H (17), C2H4(C4H7O2) (18)] were prepared by treating the lithium salt of the appropriately substituted indene with [Zr(η5‐C5H5)Cl3]. Likewise, dimethyl derivatives [Zr(η5‐C9H6R)(η5‐C5H5)Me2] [R = H (19), C2H4(C4H7O2) (20)] were prepared by treating the corresponding mixed indenyl/cyclopentadienyl dichloride complex with 2 equiv. of MgMeBr. The X‐ray crystal structures of 7, 12, and 13 were also established. Finally, comparative catalytic studies of zirconium complexes 12–16, 19 and 20 in ROP reactions of ϵ‐caprolactone are described.