TY - JOUR
T1 - Pyridylamido Bi-Hafnium Olefin Polymerization Catalysis
T2 - Conformationally Supported Hf⋯Hf Enchainment Cooperativity
AU - Gao, Yanshan
AU - Mouat, Aidan R.
AU - Motta, Alessandro
AU - Macchioni, Alceo
AU - Zuccaccia, Cristiano
AU - Delferro, Massimiliano
AU - Marks, Tobin J.
N1 - Publisher Copyright:
© 2015 American Chemical Society.
PY - 2015/7/27
Y1 - 2015/7/27
N2 - Homobimetallic Hf(IV) complexes, L2-Hf2Me5 (3) and L2-Hf2Me4 (4) (L2 = N,N′-{[naphthalene-1,4-diylbis(pyridine-6,2-diyl)]bis[(2-isopropylphenyl)methylene)]bis(2,6-diisopropylaniline}), were synthesized by reaction of the free ligand L2 with the appropriate Hf precursor and were characterized in solution (NMR) and in the solid state (X-ray diffraction). In 3, L2 acts as a dianionic tridentate ligand for one Hf metal center and as a monoanionic bidentate ligand for the other, whereas in 4, both Hf units are tricoordinated to opposite sides of L2. In the solid state, the Hf···Hf distance is significantly different in 3 vs 4 (6.16 vs 8.06 Å, respectively), but in solution, the structural dynamics of the two linked metallic units in bis-activated complex 3 accesses conformers with far closer Hf···Hf distances (∼3.2 Å). Once activated with Ph3C+B(C6F5)4- (B1) or PhNMe2H+B(C6F5)4- (NB), 3 exhibits pronounced bimetallic cooperative effects in ethylene homopolymerization and ethylene +1-octene copolymerization vs the monometallic analogue L1-HfMe2 (1, L1 = 2,6-diisopropyl-N-{(2-isopropylphenyl)[6-(naphthalen-1-yl)pyridin-2-yl]methyl}aniline) and bimetallic 4, producing polyethylene with 5.7 times higher Mw and poly(ethylene-co-1-octene) with 2.4 times higher Mw and 1.9 times greater 1-octene enchainment densities than 1. The activation chemistry of 3 and 4 with 1 or 2 equiv of B1 and NB is characterized in detail by NMR spectroscopy. In sharp contrast to 1, which undergoes Hf-Cnaph protonolysis followed by naphthyl remetalation with NB as the cocatalyst, activation of 3 with B1 or NB proceeds by consecutive -CH3 protonolysis/abstractions at each Hf center, explaining the higher polymerization activity of 3/NB versus 1/NB. All product polymers have narrow (2-3) PDIs, and this is explained by NMR evidence for very fast exchange of alkyl moieties between the two active Hf metal centers. Key experimental findings are supported by DFT analysis.
AB - Homobimetallic Hf(IV) complexes, L2-Hf2Me5 (3) and L2-Hf2Me4 (4) (L2 = N,N′-{[naphthalene-1,4-diylbis(pyridine-6,2-diyl)]bis[(2-isopropylphenyl)methylene)]bis(2,6-diisopropylaniline}), were synthesized by reaction of the free ligand L2 with the appropriate Hf precursor and were characterized in solution (NMR) and in the solid state (X-ray diffraction). In 3, L2 acts as a dianionic tridentate ligand for one Hf metal center and as a monoanionic bidentate ligand for the other, whereas in 4, both Hf units are tricoordinated to opposite sides of L2. In the solid state, the Hf···Hf distance is significantly different in 3 vs 4 (6.16 vs 8.06 Å, respectively), but in solution, the structural dynamics of the two linked metallic units in bis-activated complex 3 accesses conformers with far closer Hf···Hf distances (∼3.2 Å). Once activated with Ph3C+B(C6F5)4- (B1) or PhNMe2H+B(C6F5)4- (NB), 3 exhibits pronounced bimetallic cooperative effects in ethylene homopolymerization and ethylene +1-octene copolymerization vs the monometallic analogue L1-HfMe2 (1, L1 = 2,6-diisopropyl-N-{(2-isopropylphenyl)[6-(naphthalen-1-yl)pyridin-2-yl]methyl}aniline) and bimetallic 4, producing polyethylene with 5.7 times higher Mw and poly(ethylene-co-1-octene) with 2.4 times higher Mw and 1.9 times greater 1-octene enchainment densities than 1. The activation chemistry of 3 and 4 with 1 or 2 equiv of B1 and NB is characterized in detail by NMR spectroscopy. In sharp contrast to 1, which undergoes Hf-Cnaph protonolysis followed by naphthyl remetalation with NB as the cocatalyst, activation of 3 with B1 or NB proceeds by consecutive -CH3 protonolysis/abstractions at each Hf center, explaining the higher polymerization activity of 3/NB versus 1/NB. All product polymers have narrow (2-3) PDIs, and this is explained by NMR evidence for very fast exchange of alkyl moieties between the two active Hf metal centers. Key experimental findings are supported by DFT analysis.
KW - NMR spectroscopy
KW - bimetallic
KW - cooperativity effects
KW - hafnium
KW - olefin polymerization
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U2 - 10.1021/acscatal.5b00788
DO - 10.1021/acscatal.5b00788
M3 - Article
AN - SCOPUS:84940976694
SN - 2155-5435
VL - 5
SP - 5272
EP - 5282
JO - ACS Catalysis
JF - ACS Catalysis
IS - 9
ER -