Chromocene-Cyclopentadienyltitanium Trichloride Ion Pairs and Their Rearrangement to Titanocene Chloride-Cyclopentadienylchromium Dichlorides - Ethylene Polymerization Tests
Abstrakt
Reactions of chromocene [CrCp2] (Cp = (5)-C5H5) with cyclopentadienyltitanium trichlorides [Ti((5)-C5H5-nMen)Cl-3] (n = 0-5) and [Ti(C5Me4Et)TiCl3] in toluene resulted in precipitation of ion pairs of [CrCp2](+)[Ti((5)-C5H5-nMen)Cl-3](-) (1-6) and [CrCp2](+)[Ti((5)-C5Me4Et)Cl-3](-) (7). Heating their toluene solutions to 100 degrees C yielded the titanocene chloride - cyclopentadienylchromium dichloride complexes with the metals linked by bridging chloride ligands.
For n = 0-3, the purple-violet complexes [CpCpTi(mu-Cl)(2)Cr(Cp)Cl] (Cp - cyclopentadienyl ligand of the titanium component) (8-11) were stable at 100 degrees C, and the single-crystal structure of [Cp2Ti(mu-Cl)(2)Cr(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)Cl-2] (15), [TiCp(C5Me5)Cl-2] (16), and [TiCp(C5Me4Et)Cl-2] (17), respectively.
In addition, they contained the hitherto unknown (CpCrCl)(n) (18). Heating of 12-14 to 100 degrees 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 (M-n 500 kg.mol(-1)); upon activation with B(C6F5)(3)/Et3SiH in dichloromethane they produced M-n = 9-23 kg.mol(-1).
The titanium species was the catalytically dominant one in both cases.