Lithium, magnesium, zinc complexes supported by tridentate pincer type pyrrolyl ligands: Synthesis, crystal structures and catalytic activities for the cyclotrimerization of isocyanates

Abstract

Lithium, magnesium, zinc complexes incorporating substituted symmetrical tridentate pyrrolyl ligands were synthesized conveniently and their application for the cyclotrimerization of isocyanate to corresponding isocyanurate has been investigated. The reaction of 1 equivalent of 2,5-bis(pyrrolidinomethyl)pyrrole {C4H2NH(2,5-CH2NC4H8)2} with n-BuLi generated [Li{C4H2N(2,5-CH2NC4H8)2}]2 (1) in diethyl ether. Treatment of 2 equivalents of C4H2NH(2,5-CH2NC4H8)2 with MgBu2 or ZnEt2 in THF afforded [Mg(THF){C4H2N(2,5-CH2NC4H8)2}2] (2) or [Zn{C4H2N(2,5-CH2NC4H8)2}2] (3) in high yield, respectively. Compounds 1, 2 and 3 were characterized by 1H and 13C NMR spectra and their molecular structures were determined by single crystal X-ray diffraction. Furthermore, compounds 1, 2 and 3 were proved to be moderate to good initiators for cyclotrimerization of isocyanate to the corresponding isocyanurate in diethyl ether.