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

The 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-eta(5)-C9H5R)(eta(5)-C5Me4)}Cl-2] [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-eta(5)-C9H5R)(eta(5)-C5Me4)}Me-2] [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-eta(5)-C9H5(CH2Ph)}-(eta(5)-C5Me4)}(CH2SiMe3)(2)] (16) was prepared by adding 2 equiv. of LiCH(2)SiMe3 to complex 10. Mixed indenyl/cyclopentadienylzirconocene complexes [Zr(eta(5)-C9H6R)(eta(5)-C5H5)-Cl-2] [R = H (17), C2H4(C4H7O2) (18)] were prepared by treating the lithium salt of the appropriately substituted indene with [Zr(eta(5)-C5H5)Cl-3]. Likewise, dimethyl derivatives [Zr(eta(C9H6R)-C-5)(eta(5)-C5H5)Me-2] [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 epsilon-caprolactone are described.