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

The new bis(imino)pyrrole ligand 2,5-C4H2NH(CH=NC6H3Pr2i)(2) (HL1) reacts with Zr(NMe2)(4) to give the 1:1 complex (L-1)Zr(NMe2)(3) (1), whereas the mono(imino)pyrrole 2-C4H3NH(CH=NC6H3Pr2i) (HL2) substitutes two amido ligands to give (L-2)(2)Zr(NMe2)(2) (2). The lithium salt LiL1 reacts with ZrCl4 to give (L-1)ZrCl2(mu-Cl)(2)Li(OEt2)(2) (3), while the reaction of LiL2 with ZrCl4 or treating 2 with Me3SiCl gives (L-2)(2)ZrCl2. Iron(II) chloride reacts with LiL1 to afford the bis(ligand) complex Fe(L-1)(2) (5), while only one pyrrolato ligand is incorporated on reacting LiL1 with CoCl2(thf) to give [Li(thf)(4)][CoCl2L1] (6a). On warming, 6a readily loses thf to give [Li(thf)(2)][CoCl2L1] (6b). By contrast, LiL2 reacts with CoCl2 and NiCl2 to give the halide-free complexes Co(L-2)(2) and Ni(L-2)(2), respectively. The crystal structures of HL1 and complexes 1, 2 and 5 are reported. In all cases the potentially tridentate ligand L-1 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.