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The synthesis, structural characterization, and ethylene polymerization performance of heterobimetallic aluminum-pyrrolyl complexes of group IV metals are described. The combination of MCl 4 (M = Ti, Zr, Hf), aluminum alkyls and pyrroles leads, depending on stoichiometry, to mono-and bis(aluminum-pyrrolyl) complexes that are remiscent of the corresponding mono-and bis-cyclopentadienyl systems. The bis(aluminum-pyrrolyl) complexes (η 5 -2,5-2 (7), obtained by treatment of TiCl 4 with equimolar amounts of trimethyl aluminum and the corresponding pyrrole ligands, were found to be moderately active for ethylene polymerization with MAO or [Ph 3 C] + [B(C 6 F 5 ) 4 ] − , in all cases producing UHMWPE. The NMR scale reaction of 5 with B(C 6 F 5 ) 3 showed the formation of a solvent-separated ion pair, formed by the abstraction by B(C 6 F 5 ) 3 of a methyl group from Al-CH 3 rather than from Ti-CH 3 . 1 H and 13 C NMR analysis of 6 and 7 revealed that several stable structural isomers exist in solution, with a slow interconversion on the NMR time scale. The dimeric zirconium complexes [(η 5 ,κ 1 -2,5-Me 2 C 4 H 2 NAlClMe 2 )ZrMeCl(μ-Cl)] 2 (8) and [(η 5 ,κ 1 -2,5-Me 2 C 4 H 2 NAlCl 2 Et)ZrCl 2 (μ-Cl)] 2 (9), prepared by the reaction of 2 equivalents of ZrCl 4 , 1 equivalent of 2,5-dimethylpyrrole, and 1 equivalent of aluminum alkyl, showed structures containing a bridging chloride between aluminum and zirconium, thereby giving structural evidence for the lack of catalytic behavior of these complexes. A possible explanation for the moderate or absence of catalytic activity of the aluminum-pyrrolyl complexes was proposed based on DFT calculations.

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