Details

Autor(en) / Beteiligte

• Feng, Shaoguang
• Roof, Gordon R
• Chen, Eugene Y.-X

Titel

Tantalum(V)-Based Metallocene, Half-Metallocene, and Non-Metallocene Complexes as Ethylene−1-Octene Copolymerization and Methyl Methacrylate Polymerization Catalysts

Ist Teil von

• Organometallics, 2002-03, Vol.21 (5), p.832-839

Ort / Verlag

American Chemical Society

Erscheinungsjahr

2002

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The half-sandwich imido tantalum dichloride (η5-C5Me4H)Ta(NtBu)Cl2 is prepared directly from the reaction of the neutral constrained-geometry ligand Me2Si(C5Me4H)(tBuNH) and TaCl5 in refluxing toluene. The dichloride is cleanly converted to the corresponding imido tantalum dimethyl complex (η5-C5Me4H)Ta(NtBu)Me2 (2). Using the same synthetic strategy, the neutral bulky chelating diamine ligand ArNH(CH2)3NHAr (Ar = 2,6-iPr2C6H3) is reacted with TaCl5 in toluene under mild reflux conditions, affording the six-coordinate tantalum complex [ArN(CH2)3NHAr]TaCl4, which is conveniently converted to the corresponding non-metallocene tantalum trimethyl complex [ArN(CH2)3NAr]TaMe3 (4) on treatment with an excess of MeMgBr. Alternatively, 4 can be prepared in better than 70% overall yield based on the diamine ligand from a one-pot synthesis by mixing the neutral diamine ligand with TaCl5 followed by addition of an excess of MeMgBr. Reaction of Cp2TaMe3 with 1 equiv of B(C6F5)3 in benzene or toluene produces an oily mixture containing both Cp2TaMe2 +CH3B(C6F5)3 - and Cp2TaMe2 +[(C6F5)3B−CH3−B(C6F5)3]- in the solution phase. Subsequently, the reaction of Cp2TaMe3 with 2 equiv of Al(C6F5)3 cleanly generates the tantalocene cation−binuclear anion ion pair Cp2TaMe2 +[(C6F5)3Al−CH3−Al(C6F5)3]- (5) as colorless crystals. In bromobenzene-d 5, reactions of Cp2TaMe3 with Lewis acids M(C6F5)3 (M = B, Al) in a 1:1 ratio afford the expected cationic species Cp2TaMe2 +CH3M(C6F5)3 - as clean products. Reaction of the non-metallocene 4 with M(C6F5)3 is similar to that of Cp2TaMe3. When it is activated with 2 equiv of Al(C6F5)3, Cp2TaMe3 is active for syndiospecific MMA polymerization but inactive for olefin polymerization. In contrast, the non-metallocene 4 has no activity for MMA polymerization but is active for olefin polymerization. Most interestingly, the half-metallocene 2, when activated with a suitable activator, is very active (with a catalytic efficiency of 1.2 × 106 g of polymer/((mol of metal) atm h)) for high-temperature (140 °C) olefin copolymerizations, producing low-density poly(ethylene-co-1-octene) copolymers with high molecular weight.