Metallocene-catalyzed olefin polymerizations using triphenylcyclopropenium tetrakis(pentafluorophenyl)borate as the activator

Triphenylcyclopropenium (TPCP) tetrakis(pentafluorophenyl)borate activates bis(cyclopentadienyl)dimethyl titanium resulting in a highly reactive initiating system for the polymerization of styrene. In contrast to triphenylmethyl tetrakis(pentafluorophenyl)borate which is quite active in the absence of the metallocene, TPCP borate shows no activity for styrene polymerization in the absence of bis(cyclopentadienyl)dimethyl titanium. TPCP is the most efficient activator in the carbonium ion – borate class. We propose, based on 1H NMR evidence that reaction of Cp2TiMe2 and TPCP borate leads to the formation of the cationic Ti complex [Cp2TiMe]+B(C6F5)4–. Evidence for the latter is also provided by UV–vis spectroscopy in that we found a bathochromic shift of the Cp2TiMe2 LMCT absorption band from 361 to 482 nm in CH2Cl2 and 487 nm in toluene, respectively. Thermal decomposition of the cationic complex [Cp2TiMe]+B(C6F5)4– leads to less activity. The systems are good catalysts for ethylene polymerization as well, but are less active when using propylene. A conventional Ziegler–Natta coordination polymerization mechanism accounts for ethylene and propylene polymerization while a carbocationic polymerization mechanism is proposed for styrene.Key words: triphenylcyclopropenium tetrakis(pentafluorophenyl)borate, bis(cyclopentadienyl)dimethyl titanium, activator, olefin polymerization.

Characterization of iodonium salts differing in the anion

The properties and reactivity of a series of iodonium salts with different anions were compared. The nucleophilicity of the anions in such compounds can be characterized by their melting points and NMR spectra. When using Quinaldine Red as indicator and CH3CN as solvent, the acid release rate of the iodonium salts correlated very well with their polymerization results in acid-sensitive epoxides.

Photolysis of ((3-(Trimethylsilyl)propoxy)phenyl)phenyliodonium salts in the presence of 1-naphthol and 1-methoxynaphthalene

Direct photolysis of ((3-trimethylsilylpropoxy)phenyl)phenyliodonium salts with different counteranions (Cl(-), SbF(6)(-), and B(C(6)F(5))(4)(-)) in methanol leads to products by both heterolytic and homolytic processes. In the presence of 1-naphthol and 1-methoxynaphthalene, products formed by a heterolytic reaction disappear, suggesting an electron-transfer process occurs between excited 1-naphthol/1-methoxynaphthalene and the iodonium salts. In the case of 1-methoxynaphthalene, three phenylated methoxynaphthalene isomers are produced. These are produced as radical coupling products from the phenyl radical and 1-methoxynaphthalene radical cation.