Chromocene–Cyclopentadienyltitanium Trichloride Ion Pairs and Their Rearrangement to Titanocene Chloride–Cyclopentadienylchromium Dichlorides – Ethylene Polymerization Tests

Abstract

Reactions of chromocene [CrCp2] (Cp = η5‐C5H5) with cyclopentadienyltitanium trichlorides [Ti(η5‐C5H5–nMen)Cl3] (n = 0–5) and [Ti(C5Me4Et)TiCl3] in toluene resulted in precipitation of ion pairs of [CrCp2]+[Ti(η5‐C5H5–nMen)Cl3]– (1–6) and [CrCp2]+[Ti(η5‐C5Me4Et)Cl3]– (7). Heating their toluene solutions to 100 °C yielded the titanocene chloride – cyclopentadienylchromium dichloride complexes with the metals linked by bridging chloride ligands. For n = 0–3, the purple‐violet complexes [CpCp′Ti(µ‐Cl)2Cr(Cp)Cl] (Cp′ – cyclopentadienyl ligand of the titanium component) (8–11) were stable at 100 °C, and the single‐crystal structure of [Cp2Ti(µ‐Cl)2Cr(Cp)Cl] (8) was determined. The bridging complexes of the same type for n = 4, 5 and the C5Me4Et ligand (12–14) were contaminated with titanocene dichlorides containing mixed auxiliary ligands [TiCp(C5HMe4)Cl2] (15), [TiCp(C5Me5)Cl2] (16), and [TiCp(C5Me4Et)Cl2] (17), respectively. In addition, they contained the hitherto unknown (CpCrCl)n (18). Heating of 12–14 to 100 °C resulted in their decomposition to 15–17, accompanied with 18 in all cases. The molecular and electronic properties of 1, 4, 5, 8 and both isomers of 13 were investigated by DFT. Complexes 8, 9, and 11 activated with MMAO polymerized ethylene in toluene to very high molecular weights polyethylene (Mn ≥ 500 kg mol–1); upon activation with B(C6F5)3/Et3SiH in dichloromethane they produced Mn = 9–23 kg mol–1. The titanium species was the catalytically dominant one in both cases.