(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)₂Cl ₂] (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.