Monatsh Chem 139, 1163–1167 (2008) DOI 10.1007/s00706-008-0856-x Printed in The Netherlands Tetrapyrrole bizirconium complexes as active catalysts for ethylene polymerization Sajjad Mohebbi 1 , Jalil Assoud 2 1 Chemistry Department, University of Kurdistan, Sanandaj, Iran 2 Chemistry Department, University of Waterloo, Ontario, Canada Received 15 October 2007; Accepted 17 November 2007; Published online 31 July 2008 # Springer-Verlag 2008 Abstract Ethylene polymerization was carried out by using a group of new dizirconium(IV) tetrapyrrole complexes as catalysts and MAO as co-catalyst under 1 atmosphere pressure of ethylene gas at 25 and 40  C. The highest value of catalyst activity was obtained at 40  C by using bizirconium complexes including one calix[4]pyrrole between two zirconium centers and two terminal chlorines, while zirconium(IV) complexes with coordinated THF , almost have not catalytic activity. The maximum catalytic activity mounted to 830 kg=mol  bar  h by Zr 2 (Cy 4 Pyr 4 )Cl 4 . The results show that the structure of the coordination sphere of zirconium(IV) has great influence on the rate of polymerization, molar masses of forming poly- mer, and its molecular mass distribution. Keywords Ethylene; Polymerizations catalysts; Zirconium coordination; Calix[4]pyrrole complexes. Introduction An active area of research in the field of metal complexes containing chelating amido ligands has focused on the development of well-defined metal complexes as catalysts for olefin polymerization [1]. Chelating and multidentate amido ligands have emerged as a viable alternative to the traditionally used cyclopentadienide ligands in the chemistry of early transition metals [2]. Literature reviews on the catalytic polymeri- zation of olefins show that catalytic performance improvement of high valance d 0 early transition metals [3] and more particularly, amido complexes of fourth group elements are still on important sub- ject [4, 5]. Commonly, metal chloride derivatives are used as polymerization catalysts with the co-catalyst methylaluminoxane (MAO) [6]. Actually, high olefin polymerization activity of dichloro-diamido zirco- nium(IV) complexes [7] and dibenzyl derivatives [5] are valuable evidence for this opinion. But low stability of the coordination sphere has limited their application as robust catalyst. Although the elucida- tion of the structure of the active site and the poly- merization mechanism are not completely understood yet but using of high valances early transition metals as strong Lewis acids and specific ligands including hard donor atoms as strong - and -donors are appropriate. Our goal is the development of hydro- carbon polymerization under controlled and mild condition. For this purpose, we discuss the use of a group of new tetraamido pyrrole complexes (Fig. 1) of bizirconium(IV) and their use as ethylene polymerization catalysts when activated in the stan- dard fashion with methylaluminoxane (MAO). Correspondence: Sajjad Mohebbi, Chemistry Department, University of Kurdistan, P.O. Box 66176-416, Sanandaj, Iran. E-mail: smohebbi@uok.ac.ir