Beyond the active site. Cp*ZrMe3/sulfated alumina-catalyzed olefin polymerization tacticity via catalyst...surface ion-pairing

Surface-bound organometallic molecules have recently enabled the development of single-site heterogeneous catalysts, advancing the atomic scale understanding and diversity of heterogeneous catalysis. Here we report that supporting Cp*ZrMe3 (Cat1) on acidic sulfated-alumina (AlS) affords the surface catalyst Cat1/AlS, which was characterized by multi-dimensional solid-state NMR spectroscopies, and is active in ethylene homo- and copolymerizations, as well as propylene and 1-hexene homopolymerizations. In contrast to propylene (or 1-hexene) polymerization by homogeneous Cp*ZrMe2+ B(C6F5)4− which yields atactic polyolefins, Cat1/AlS promotes remarkable isotacticity with mmmm >95 %. Complementary DFT analysis argues that the restrictive local Cat1/AlS C1-symmetry favors activation and enchainment at the propylene re enantioface, promoting isotactic polymerization via a “back-skip-like” mechanism