Aryloxy Alkyl Magnesium versus Dialkyl Magnesium in the Lanthanidocene-Catalyzed Coordinative Chain Transfer Polymerization of Ethylene

Complexes [(1,2,4-Ph3C5H2)(2)NdCl2K(THF)(2)](2) (Nd1), {[1,2-Ph-2-4-(4-MeOC6H4)C5H2](2)NdCl2K(THF)(2)}(2) (Nd2), {[1,2-Ph-2-4-(2-MeO-C6H4)C5H2](2)NdCl2[K(THF)(4)]}-(THF)(0.5) (Nd3), and [(1,2,4-Ph3C5H2)(2)TbCl2K](2) (Tb1) have been synthesized, studied by X-ray diffraction analysis, and used in coordinative chain transfer polymerization (CCTP) of ethylene upon activation by alkyl magnesium derivatives. The complexes Ndl and Tbl exhibiting similar molecular structures and the same core type have demonstrated similar catalytic activities. Two types of alkylating/chain transfer agents, namely, di-n-butyl magnesium and heteroleptic complex (BHT)Mg(THF)(2)Bu-n Mg1 (BHT = 2,6-di-tert-butyl-4-methylphenoxide), have been studied in this reaction. We have found that (BHT)Mg(PE) products (PE is an oligoethylene chain) are being formed at a relatively high rate while using Mgl at 40 degrees C in the solution polymerization of ethylene; the oligomeric products comprise more than 40 ethylene fragments, unlike Mg(PE)(2) derivatives, which are obtained from (MgBu2)-Bu-n and contain about 20 ethylene fragments. Luminescence spectroscopy study of the reaction mixtures, while initiating the complex Tb 1 by (MgBu2)-Bu-n or Mg1, confirmed the structural proximity and high symmetry of the catalytic complexes for both types of Mg reagents. These experimental results reaffirmed the hypothesis about the CCTP mechanism, suggesting the formation of trinuclear LnMg(2) catalytic species. Within this mechanism, we can explain the increase in the polymerization degree (P-n) when Mg1 is used by growing a single oligoethylene chain (PE) per a Mg atom to form (mu-BHT)(2)Mg-2(PE)(2) species, whereas application of (MgBu2)-Bu-n provides the growth of two PE chains to form the Mg-2(PE)(4) product with lower solubility.