Novel Ncn Metal Complexes: Synthesis, Characterization And Their Catalysis Behavior

In the literatures, PCP, SCS, and diaminoaryl NCNpincer ligands were widelyused in nickel and platinum complexes. Recently, the bis(imino)aryl NCN pincerligands with more rigid and conjugated framework have received considerableattention. Ir, Pt, and Pd pincer complexes with the bis-(imino)aryl NCN ligands havebeen developed and investigated as catalysts for transfer hydrogenation of ketones,Heck coupling and C-C bond formation reactions. More recently, bis(imino)arylNCN pincer lanthanide complexes were found to exhibit high catalytic activity andcis-1,4selectivity for butadiene and isoprene polymerization.In summary, we have synthesized and characterized a series of new chromium(II)and chromium(III) complexes supported by bis(imino)aryl pincer ligands via lithiumsalt elimination reaction. Upon activation with trialkylaluminum and boratecocatalyst, the Cr(III) complexes show high catalytic activity for isoprenepolymerization and afford polyisoprene with predominately trans-1,4units, whereasthe Cr(II) complexes are inert under the same conditions. The catalytic performanceof these Cr(III) complexes were found to be influenced by the ortho-substituent ofthe N-aryl ring, trialkylaluminum, and the type of the borate/borane cocatalyst.A series of aluminum and zinc complexes1-8chelated by bis(imino)aryl NCNligands have been synthesized and structurally characterized. All aluminumcomplexes1-4were obtained in a monoligated form in which the Al atom is chelatedby a κ3N,C,N’-NCN pincer ligand. The zinc complexes5,6, and7were proved to bebisligated with the zinc being chelated by two κ2N,C-NCN ligands, while complex8possesses a structure similar to those of complexes1-4, with the central zinc atombeing chelated by a κ3N,C, N’-NCN pincer ligand. All these Al and Zn complexesare efficient initiators for L-lactide ring-opening polymerization in the presence ofbenzyl alcohol, and the polymerization reaction takes place in an immortal manner.The productivity of the Zn complexes is generally higher than that of the Al complexes under similar conditions.