Beyond the Active Site. Cp*ZrMe₃/Sulfated Alumina‐Catalyzed Olefin Polymerization Tacticity via Catalyst⋅⋅⋅Surface Ion‐Pairing

Abstract

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.

Rapid atom-efficient polyolefin plastics hydrogenolysis mediated by a well-defined single-site electrophilic/cationic organo-zirconium catalyst

“…g Control experiment without Zr. h Hydrogenolysis reaction catalyzed by Cp*Zr(CH 3 ) 3 supported on AlS 38 . i Trace C13–C15 hydrocarbons not attributable to starting C16 detected in GC–MS.…”

“…Note that the AlS/ZrNp 2 and AlS/ZrH(Np) Zr–O bonds are significantly elongated vs. those in neutrally charged 2,6- t Bu 2 PhOZr(benzyl) 3 (Zr–O = 1.94 Å) 35 and (L(Me)AlO) 2 Zr(benzyl) 2 (L = (2,6- i Pr 2 C 6 H 3 NC(Me)) 2 CH) (Zr–O = 1.91 Å; Fig. 5d , Table 2 , entries 3, 4) 36 , and for formally neutrally charged SiO 2 /Zr–H (1.95 Å; Table 2 , entry 5) 37 , with shorter Zr–O bonds suggesting more covalent σ-bonding, and longer Zr–O bonds greater electrostatic character between the electron-deficient Zr centers and weakly basic AlS oxide ligands 23 , 38 , 39 . Also, the XANES Zr K-edge energies for AlS/ZrNp 2 (18.005 keV), AlS/ZrH(Np) (18.008 keV), and AlS/Zr(alkyl) 2 (18.006 keV) lie in the range of cationic complexes vs. neutrally charged t Bu 2 PhOZr(benzyl) 3 (17.998 keV) and Zr(benzyl) 4 (17.999 keV) (Fig.…”

Facile Polyolefin Plastics Hydrogenolysis Catalyzed by a Surface Electrophilic d0 Hydride

“…2C, Table 1, entries 3, 4) (31), and formally neutrally charged SiO2/Zr-H (1.95Å; Fig. 1A, Table 1, entry 5) (32), with shorter Zr-O bonds suggesting more covalent σ-bonding, and longer Zr-O bonds greater electrostatic character between the electron-deficient Zr centers and weakly basic AlS oxide ligands (21,33,34). Also, the XANES Zr K-edge energies for AlS/ZrNp2 (18.005 KeV), AlS/ZrH(Np) (18.008 KeV), and AlS/Zr(alkyl)2 (18.006 KeV) lie in the range of cationic complexes vs neutrally charged t Bu2PhOZr(benzyl)3 (17.998 KeV) and Zr(benzyl)4 (17.999 KeV) (Fig.…”

Rapid Polyolefin Hydrogenolysis by a Single‐Site Organo‐Tantalum Catalyst on a Super‐Acidic Support: Structure and Mechanism

“…According to the Cambridge Structural Database, the average Ta(V)−O bond length lies at ≈1.9 Å (Figure S33), in the range of the short 1.83(1) Å bond in 1 . The two significantly elongated Ta−O bonds in 1 vs. those in similar neutrally charged complexes (Figure S33) [16a,27] suggest a significant electrostatic bonding character, typical of supported d 0 cationic species [24,28] . The Ta−C bond length of 2.02(2) Å is in the expected range of organo‐tantalum complexes (Figure S34).…”