Palladium-Catalyzed Ethylene/Methyl Acrylate Copolymerization:Moving from the Acenaphthene to the Phenanthrene Skeleton of α‑DiimineLigands

The development of efficient homogeneous catalysts for the synthesis of functionalized polyolefins is a challenging topic. Palladium(II) complexes with α-diimine ligands having a phenanthrene skeleton and 2,6-disubstituted aryl rings (Ar-BIP) were synthesized, characterized, and tested as precatalysts in the copolymerization of ethylene with methyl acrylate. The direct comparison with analogous complexes having the corresponding α-diimines with an acenaphthene skeleton (Ar-BIAN) was performed. X-ray characterization in the solid state and NMR analysis in solution of both neutral [Pd(Ar-BIP)(CH3)Cl] and monocationic [Pd(Ar-BIP)(CH3)(NCCH3)][PF6] complexes indicate that the Ar-BIP ligands have a higher Lewis basicity and are more strongly coordinated to the metal center in comparison to the Ar-BIAN counterparts. Therefore, the Pd(Ar-BIP) cationic complexes can be regarded as electron-rich metal cations. In addition, they create a higher steric congestion around palladium in comparison to Ar-BIAN, regardless...