ZrCl 4 as Catalyst for Olefins and Styrene Polymerization: Effect of Ethereal Donors on the Activity and Stereospecificity Antonio Proto,* ,† Carmine Capacchione, † Oriana Motta, ‡ and Francesco De Carlo § Department of Chemistry, University of Salerno, via S. Allende, 84081 Baronissi (SA) Italy, Department of Educational Science, University of Salerno, via Ponte don Melillo, 84084 Fisciano (SA), Italy, and Aristea spa Company, via Bosco Fili, 84091 Battipaglia (SA) Italy Received April 4, 2003; Revised Manuscript Received June 13, 2003 ABSTRACT: Complexes of ZrCl 4 incorporating neutral donors such as THF and Et2O activated by methylaluminoxane have been found to be active homogeneous catalytic systems for the polymerization of ethylene. They also promote the propylene and styrene polymerization with high degree of iso- and syndiotacticity, respectively. The different behaviors in propylene and styrene polymerization using methylalumoxane containing different amounts of Al(CH3)3 with respect to isotactic propylene and syndiotactic styrene polymerization of these compounds suggest that the presence of neutral Lewis bases on the metal center plays a crucial role on the stereoselectivity of polymerization reaction. Introduction In the last few years, the development of non- metallocene catalysts which promote the polymerization of R-olefins has widely increased. 1 Very high active catalytic systems for ethylene and high stereoselective for propylene and 1-hexene have been discovered inside the “classical” group 4 and, more recently, also among metals belonging to different groups such as groups 8 and 10. 2 Group 4 oxygen-based ligands, in particular those having combinations of bis(phenoxide) and ad- ditional donors such as S, N or O, arrange as “high” on the Gibson scale of ethylene activity. 3 The exploration of the coordinative chemistry of many alternative organic compounds has brought forth the development of new monoanionic or dianionic ligands with additional neutral donors. Experimental and theoretical works attribute the high activity of these complexes to the stabilization of the active cationic species due to the interaction between the neutral donor and the metal center. 4 The latest and most interesting examples of these non-metallocenic complexes are no doubt zirco- nium ones bearing FI ligands, 5 extremely active toward ethylene polymerization, and zirconium complexes bear- ing tetradentate [ONNO] ligands, which reproduce the symmetric properties of C 2 ansa-metallocenes, able to induce isospecific polymerization of 1-hexene 6 and pro- pylene. 7 It is undoubtedly interesting to note that, despite the large interest and the great research en- deavors surrounding and involving these new non- metallocenic complexes, there is an almost total lack in the literature of examples of group 4 metal tetrachloride derivatives bearing only neutral donors, and only in a few cases have they been tested in polymerization routes. Zirconium homogeneous Ziegler-Natta catalysts with neutral donors such as esters, were reported in 1989 by Young 8 to promote oligomerization and poly- merization of ethylene. In 1996, Eberle 9 showed the structure of ZrCl 4 (THF) 2 anticipating its potential inter- est as soluble catalyst in nonpolar solvents. Recently we observed that the presence of an organic Lewis base, such as THF, enhances the syndio-specificity of ZrCl 4 methylaluminoxane catalytic system toward the poly- merization of styrene. 10 Here we present the results relative to the catalytic performance of ZrCl 4 , when an additional Lewis base (LB) is present in the coordination sphere of zirconium in ethylene, propylene and styrene polymerizations. Results and Discussion (A) Ethylene. In Table 1, the results of ethylene polymerization in the presence of some zirconium compounds and MAO are reported. As can be noted, ZrCl 4 (Et 2 O) 2 and ZrCl 4 (THF) 2 /MAO are only three times less active than Cp 2 ZrCl 2 (Cp ) cyclopentadienyl) (see runs 4, 9, and 11) and hundred times more than ZrCl 4 (see runs 4, 9 and 10); therefore, they could be considered of “high” rating using the Gibson scale. 1 13 C NMR analysis shows that all these polymers are linear. Calorimetric measurements have been performed in order to analyze the thermal transi- tions occurring upon heating and cooling, and they show that these polymers have high melting temperatures, whose values are higher than those of the polyethylenes obtained with zirconocenes (see run 11 and 12). 11 The lifetime of the ZrCl 4 (LB)/MAO catalytic system toward ethylene polymerization has been investigated by performing the polymerization reaction for different times: 5, 15, 30, 60, 120, and 180 min. As reported in Table 1 the yield, the melting temperature and molec- ular weight increase with the increase of polymerization time. In Figure 1, the kinetic profile has been plotted, and it shows how the yield increases with time. This behavior demonstrates that the catalyst has rather long lifetime (at least 3 h). The GPC analyses show a broad molecular weight distribution, due to the formation of more than one catalytic species in the reaction between the precatalyst and methylaluminoxane; however, the molecular weight values increase with polymerization time. (B) Propylene. ZrCl 4 (LB) 2 complexes, activated by MAO, lead to the production of isotactic polypropylene, * Corresponding author. E-mail: aproto@unisa.it. Fax: +39089- 965296. † Department of Chemistry, University of Salerno. ‡ Department of Educational Science, University of Salerno. § Aristea spa Company. 10.1021/ma034431o CCC: $25.00 © xxxx American Chemical Society PAGE EST: 4.4 Published on Web 00/00/0000