Synthesis of N,N′,X‐tridentate 2‐iminomethylpyrrole‐coordinated palladium(II) complexes via N─H bond activation of pyrrole moiety

Abstract

The reaction of [Pd(CH3CN)2Cl2] with N‐functional group‐substituted 2‐iminomethylpyrrole‐based ligands, namely N1‐((1H‐pyrrol‐2‐yl)methylene)‐N3,N3‐dimethylpropane‐1,3‐diamine (LA), N1‐((1H‐pyrrol‐2‐yl)methylene)‐N3‐methyl‐N3‐phenylpropane‐1,3‐diamine (LB), N‐((1H‐pyrrol‐2‐yl)methylene)‐3‐(methylthio)propan‐1‐amine (LC) and N‐((1H‐pyrrol‐2‐yl)methylene)‐3‐methoxypropan‐1‐amine (LD), resulted in [LnPdCl] (Ln = LA–LD) complexes in high yield via N─H bond activation of pyrrole moiety without use of base. [LnPdCl] existed as monomeric four‐coordinated complexes with slightly distorted square planar geometries around the palladium metal center. The ligands show N,N′,X‐tridentate binding mode to the palladium metal center to give two fused ring metallacycles. [LBPdCl] gave the highest activity (3.29 × 105 g PMMA (mol Pd)−1 h−1) for a methyl methacrylate (MMA) polymerization in the presence of modified methylaluminoxane at 60 °C compared to the other Pd(II) analogues, and resulted in PMMA with higher molecular weight (Mw = 7.16 × 105 g mol−1) and narrower polydispersity index. Syndiotactic‐enriched PMMA resulted in all cases.