[2]Borametallocenophanes of Zr and Hf: Synthesis, Structure, and Polymerization Activity

The first [2]borametallocenophanes of Zr and Hf are reported, which were obtained from 1,2-bis(dimethylamino)-1,2-dicyclopentadienyldiborane(4). The constitution of these complexes in solution and, for the Hf complex, in the crystalline state is discussed. The title complexes were studied as Ziegler−Natta-type catalyst precursors for the polymerization of ethylene. Both complexes produced PE of high molecular mass up to 1.6 × 106 g/mol, and very interestingly, the Hf complex proved to be as active as its Zr analogue.