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

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.

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