Combined Experimental and Theoretical Approach for Living and Isoselective Propylene Polymerization

Abstract

The controlled polymerization of propylene with living catalysts in an isoselective fashion with high activities is a continuing challenge for catalysis, with at least one of these properties suffering in most existing systems. Through experimental and theoretical studies, the pyridylamidohafnium olefin polymerization catalysts have been optimized for living behavior, isoselectivity, and activity of propylene polymerization (Đ = 1.2, [m4] = 91%, TOF = 25 000 h–1). Substitution of the bridgehead position with geminal dimethyl substituents forces the stereoselective elements of the catalyst into closer proximity with the active site through a “buttressing effect” while simultaneously preserving symmetry in the catalyst after activation and the first monomer insertion into the Hf–Caryl bond of the ligand. Propagation was shown to be favored over termination through beta-hydrogen transfer to the monomer through a combination of theoretical modeling and experimental monitoring of the reaction which showed a linear increase in molecular weight as a function of polymer yield. Furthermore, through computational and 13C labeling NMR studies, a different mechanism of stereocontrol involving a direct ligand–monomer interaction was confirmed

Polystyrene Chain Growth Initiated from Dialkylzinc for Synthesis of Polyolefin-Polystyrene Block Copolymers

“…It undergoes fast alkyl exchange with Zn sites to generate PO chains with a narrow molecular weight distribution [21,44]. The β-elimination process can be avoided with 1, preventing the generation of PO chains that are not attached to Zn sites [18,45,46]. Moreover, 1 is capable of incorporating a significant amount of α-olefins in an ethylene/α-olefin copolymerization [47].…”

Preparation of Pyridylamido Hafnium Complexes for Coordinative Chain Transfer Polymerization

“…α-Olefin content in the copolymer generated with I is comparable with that in the copolymer generated with a constrained geometry complex, [Me 2 Si(η 5 -C 5 Me 4 )NtBu]TiMe 2 , though its activity is significantly lower than that of the constrained geometry complex (~1/ 15 ). Besides this, it can polymerize a propylene monomer with high isoselectivity [10][11][12]. The most surprising feature is that the β-elimination process (or a β-hydrogen…”

Reactivity of C1‐Symmetric Heteroarylamido Hafnium Complexes towards Unsaturated Electrophilic Molecules: Development of New Families of Olefin Polymerization Catalysts

“…demonstrated that bridgehead substituents in pyridylamidohafnium complexes influence the stereoselectivity of the respective catalysts in propylene polymerization through aT horpe-Ingold-like "buttressing effect", which brings together ortho substituentso ft he aniline group and coordinations ites on the hafniumc enter. [27] We believe that, in our case, the described interaction of ortho substituents of the aniline and coordination sites on the hafnium center can also have an impact. Perhaps, ar otationo ft he 2isopropylphenylo rm esityl group about the ArÀC(bridge) bond [17] arranges the 2,6-diisopropylaniline fragment so that one of the isopropyl groups is pushed under the hafnium atom, displaces the chloride or methyl group, and turns the trigonal bipyramid into the square pyramid geometry around the hafnium center( Figure 5).…”