(Pyrazol-1-yl)carbonyl palladium complexes as catalysts for ethylene polymerization reaction

Reactions of two equivalents of {3,5-(dimethylpyrazol-1-yl)-4-methoxy-1-carbonyl}benzene (L1), {3,5-(dimethylpyrazol-1-yl)-4-ethoxy-1-carbonyl}benzene (L2), {3,5-(dimethylpyrazol-1-yl)-4-hexyloxy-1-carbonyl}benzene (L3), and {3,5-(dimethylpyrazol-1-yl)-4-dodecycloxy-1-carbonyl}benzene (L4) with one equivalent of [Pd(NCMe)2Cl2] produced the corresponding monometallic complexes, [Pd(L1)2Cl2) (1), [Pd(L2)2Cl2) (2), [Pd(L3)2Cl2) (3) and [Pd(L4)2Cl2) (4) in good yields. Solid state structures of 2 and 4 confirmed the monodentate character of L1–L4 and trans configuration of the palladium complexes. Activation of 1–4, and the furanyl and thiophenyl carbonyl pyrazolyl palladium complexes: [Pd(MepzCOfn)2Cl2] (5), [Pd(MepzCOth)2Cl2] (6), [Pd(tBupzCOfn)2Cl2] (7) and [Pd(tBupzCOfn)2Cl2] (8) (fn = furan, th = thiophene) with MAO produced catalysts for the polymerization of ethylene with moderate activities; forming linear high density polyethylene. The structure of the complexes had a significant effect on both the activity of the catalysts and nature of the polymers obtained.

Activation of the palladium(II) complexes containing pyrazol-1-yl-4-alkoxy-1-benzene, furanyl and thiophenyl carbonyl ligands with MAO produce active catalysts for the polymerization of ethylene with moderate activities. The catalytic activities of the complexes are largely controlled by steric bulk of the ligands.Figure optionsDownload as PowerPoint slideHighlights
► A series of (pyrazol-1-yl)carbonyl Pd(II) complexes have been synthesized.
► The complexes catalyze polymerization of ethylene with moderate activities.
► High density linear polyethylene produced.
► Bulkier ligands reduced the catalytic activities of the complexes.