Preparation of Pyridylamido Hafnium Complexes for Coordinative Chain Transfer Polymerization

Abstract

The pyridylamido hafnium complex (I) discovered at Dow is a flagship catalyst among postmetallocenes, which are used in the polyolefin industry for PO-chain growth from a chain transfer agent, dialkylzinc. In the present work, with the aim to block a possible deactivation process in prototype compound I, the corresponding derivatives were prepared. A series of pyridylamido Hf complexes were prepared by replacing the 2,6-diisopropylphenylamido part in I with various 2,6-R2C6H3N-moieties (R = cycloheptyl, cyclohexyl, cyclopentyl, 3-pentyl, ethyl, or Ph) or by replacing 2-iPrC6H4C(H)- in I with the simple PhC(H)-moiety. The isopropyl substituent in the 2-iPrC6H4C(H)-moiety influences not only the geometry of the structures (revealed by X-ray crystallography), but also catalytic performance. In the complexes bearing the 2-iPrC6H4C(H)-moiety, the chelation framework forms a plane; however, this framework is distorted in the complexes containing the PhC(H)-moiety. The ability to incorporate α-olefin decreased upon replacing 2-iPrC6H4C(H)-with the PhC(H)-moiety. The complexes carrying the 2,6-di(cycloheptyl)phenylamido or 2,6-di(cyclohexyl)phenylamido moiety (replacing the 2,6-diisopropylphenylamido part in I) showed somewhat higher activity with greater longevity than did prototype catalyst I.

Coordinative Chain Transfer and Chain Shuttling Polymerization

“…77 Similarly, the Hf pyridyl amide catalyst 4, well-known for chain shuttling copolymerization, 5 was reported for ethene/propene CCG with dihexylzinc. 15 In a similar way, the Ni α-diimine complex 11c was already reported for ethene CSP. 73 Even if the transfer efficiency with Ni α-diimine complexes is low, the study showed that among this family, the less sterically hindered complexes lead to higher chain transfer efficiencies with Et 2 Zn.…”

“…14 The classical Dow's hafnium pyridylamido CCTP catalyst bearing i-Pr substituents (3, Figure 2) was structurally modified (4, substituents R and R 1 , Figure 2) and tested for ethene CCTP and its CCTcoP with propene in order to avoid the deactivation of the original catalyst that may occur during the CCTP process. 15 The R 1 isopropyl moiety affected not only the geometry (distorted vs planar for i-Pr) of complexes but also its catalytic behavior. When using H as a R 1 substituent, the polymerization activity was reduced together with a lower preference for propene addition.…”

“…Using dihexylzinc as a CTA with these modified catalysts allowed the formation of polyolefin chains with narrow dispersities. 15 It was described, that diethylzinc (Et 2 Zn) does not only serve as the efficient CTA but can also affect the overall catalytic activity. 16 Addition of its proper amount significantly increased the activity of ethene (co)polymerization catalyzed by rac-EtInd 2 ZrCl 2 (5, Figure 3)/MAO (70 °C, toluene).…”

“…The opposite trend was observed upon the replacement of R substituent i -Pr in original complex 3 with a cycloheptyl or cyclohexyl ( 4 , Figure ), along with the longer vivacity of the activated catalyst. Using dihexylzinc as a CTA with these modified catalysts allowed the formation of polyolefin chains with narrow dispersities …”

“…The classical Dow’s hafnium pyridylamido CCTP catalyst bearing i -Pr substituents ( 3 , Figure ) was structurally modified ( 4 , substituents R and R 1 , Figure ) and tested for ethene CCTP and its CCTcoP with propene in order to avoid the deactivation of the original catalyst that may occur during the CCTP process …”