Synthesis and reactivity of sterically hindered iminopyrrolato complexes of zirconium, iron, cobalt and nickel

Abstract

The new bis(imino)pyrrole ligand 2,5-C₄H₂NH(CHNC₆H₃Prⁱ₂)₂ (HL¹1111) reacts with Zr(NMe₂)₄ to give the 1∶1 complex (L¹1111)Zr(NMe₂)₃ (1), whereas the mono(imino)pyrrole 2-C₄H₃NH(CHNC₆H₃Prⁱ₂) (HL²2222) substitutes two amido ligands to give (L²2222)₂Zr(NMe₂)₂ (2). The lithium salt LiL¹1111 reacts with ZrCl₄ to give (L¹1111)ZrCl₂(μ-Cl)₂Li(OEt₂)₂ (3), while the reaction of LiL²2222 with ZrCl₄ or treating 2 with Me₃SiCl gives (L²2222)₂ZrCl₂. Iron(II) chloride reacts with LiL¹1111 to afford the bis(ligand) complex Fe(L¹1111)₂ (5), while only one pyrrolato ligand is incorporated on reacting LiL¹1111 with CoCl₂(thf) to give [Li(thf)₄][CoCl₂L¹1111] (6a). On warming, 6a readily loses thf to give [Li(thf)₂][CoCl₂L¹1111] (6b). By contrast, LiL²2222 reacts with CoCl₂ and NiCl₂ to give the halide-free complexes Co(L²2222)₂ and Ni(L²2222)₂, respectively. The crystal structures of HL¹1111 and complexes 1, 2 and 5 are reported. In all cases the potentially tridentate ligand L¹1111 is two-coordinate. Mixtures of the halide-free bis(ligand) complexes with methylaluminoxane do not show any activity for ethene polymerisation; however, 3 and 4 catalyse the polymerisation of ethene, while 6 has moderate activity for the oligomerisation of ethene and propene to linear and branched products.