Binuclear Pd-methyl complexes of N,N′-{1, n}-alkanediyl-bis(pyridinyl-2-methanimine) ligands (n = 5, 8, 9, 10 and 12): Evaluation as catalysts precursors for phenylacetylene polymerization

A series of bifunctional ligands of the type N,N′-{1, n}-alkanediyl-bis(pyridinyl-2-methanimine) {n = 5, 8, 9, 10, 12}(L1–L5) were synthesized and fully characterized by IR, 1H NMR, and 13C NMR spectroscopy. Binuclear palladium-methylchloride complexes C1–C5 were formed by reacting the ligands with [(COD)Pd(CH3)Cl]. The formed complexes were fully characterized by IR, 1H NMR, 13C NMR, spectroscopy, electrospray ionization mass spectrometry and elemental analysis. The synthesized complexes were evaluated as catalyst precursors for phenylacetylene polymerization after activation with AgBF4, AgBPh4 and NaB(Arf)4 (Sodium tetrakis[(3.5-trifluoromethyl)phenyl]borate) under various reaction conditions (solvent ratio, catalyst type, monomer/catalyst ratio, reaction time and nature of counterion). The cationic palladium-methyl catalyst precursors C1a–C5a were found to be active catalysts for phenylacetylene polymerization. The obtained polyphenylacetylene were analyzed by IR, 1H NMR and 13C NMR spectroscopy and gel permeation chromatography (GPC) and found to be largely cis-transoidal in nature.

Graphical abstractNovel binuclear methyl chloride complexes of N,N′-{1,n}-alkanediyl-bis(pyridinyl-2-methanimine) ligands were employed as catalyst precursors in the polymerization of phenylacetylene. The polymerization process was controlled by the nature of the activator and the solvent employed.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► New binuclear palladium diimine complexes were prepared and fully characterized using a range of analytical techniques. ► Activation of these binuclear complexes with AgBF4 or AgBPh4 gave active catalysts for phenylacetylene polymerization. ► The nature of the activator as well as the solvent mixtures employed impacts on the type of product isolated. ► In all cases cis-transoidal polyphenylacetylenes with narrow molecular weight distributions were obtained.