TY - JOUR
T1 - Propene polymerization using ansa-metallocenium ions
T2 - Catalyst deactivation processes during monomer consumption and molecular structures of the products formed
AU - Al-Humydi, Abdulaziz
AU - Garrison, Jered C.
AU - Mohammed, Muqtar
AU - Youngs, Wiley J.
AU - Collins, Scott
N1 - Funding Information:
The authors thank the Natural Sciences and Engineering Research Council of Canada, Nova Chemicals Ltd. of Calgary, Alberta, The University of Akron and the National Science Foundation for financial support of this work.
PY - 2005/8/4
Y1 - 2005/8/4
N2 - Propene polymerization using ansa-metallocene dialkyl complexes [Me 2C(Cp)IndMMe2] (1a; M = Zr) and (1b; M = Hf) was studied using B(C6F5)3 as a stoichometric activator. The initial rates of propene uptake as well as the steady-state rates of propene consumption are dramatically increased in the presence of excess borane using 1a and to a lesser extent 1b. 1H and 19F NMR experiments at B:Zr ratios of 1:1 and 1.2:1 reveal that the by-products produced following consumption of monomer are also sensitive to B:Zr stoichiometry. Under the former conditions, initiation is inefficient and unreacted ion-pairs [Me 2C(Cp)IndZrMe][MeB(C6F5)3] (2a-b) effect C-H activation of the unsaturated oligomers that form to produce π-allyl complexes [Me2C(Cp)IndZr(η3-2-R-C 3H4)][MeB(C6F5)3] (4a) [R = -(CH2CHMe)nCH2CH2CH3] and methane; these oligomeric complexes were identified by comparison to π-allyl complexes 4b (R = Me) and 4c (R = CH2CMe3) prepared from ion-pairs 2a-b and either isobutene or 2,4,4-trimethylpentene. Complex 4b was structurally characterized and presents a highly distorted π-methallyl ligand. In the presence of excess borane, initiation is efficient, and the principal by-products formed are Zr-borohydride complexes Me2C(Cp)IndZrMe(μ-H)B(C6F5)3 (5a-b). The major isomer present was identified by comparison to the spectroscopic data observed for its Hf-analog 6 with could be isolated from these reactions and was structurally characterized. Complexes 5 are detected after consumption of monomer is complete whereas complex 6 was formed competitively during consumption of monomer and both are relatively unreactive towards subsequent monomer insertion. Thus, the formation of these μ-borohydride complexes is a reversible deactivation pathway for some ansa-metallocenium ions, and that excess borane may serve to reactivate them towards further insertion.
AB - Propene polymerization using ansa-metallocene dialkyl complexes [Me 2C(Cp)IndMMe2] (1a; M = Zr) and (1b; M = Hf) was studied using B(C6F5)3 as a stoichometric activator. The initial rates of propene uptake as well as the steady-state rates of propene consumption are dramatically increased in the presence of excess borane using 1a and to a lesser extent 1b. 1H and 19F NMR experiments at B:Zr ratios of 1:1 and 1.2:1 reveal that the by-products produced following consumption of monomer are also sensitive to B:Zr stoichiometry. Under the former conditions, initiation is inefficient and unreacted ion-pairs [Me 2C(Cp)IndZrMe][MeB(C6F5)3] (2a-b) effect C-H activation of the unsaturated oligomers that form to produce π-allyl complexes [Me2C(Cp)IndZr(η3-2-R-C 3H4)][MeB(C6F5)3] (4a) [R = -(CH2CHMe)nCH2CH2CH3] and methane; these oligomeric complexes were identified by comparison to π-allyl complexes 4b (R = Me) and 4c (R = CH2CMe3) prepared from ion-pairs 2a-b and either isobutene or 2,4,4-trimethylpentene. Complex 4b was structurally characterized and presents a highly distorted π-methallyl ligand. In the presence of excess borane, initiation is efficient, and the principal by-products formed are Zr-borohydride complexes Me2C(Cp)IndZrMe(μ-H)B(C6F5)3 (5a-b). The major isomer present was identified by comparison to the spectroscopic data observed for its Hf-analog 6 with could be isolated from these reactions and was structurally characterized. Complexes 5 are detected after consumption of monomer is complete whereas complex 6 was formed competitively during consumption of monomer and both are relatively unreactive towards subsequent monomer insertion. Thus, the formation of these μ-borohydride complexes is a reversible deactivation pathway for some ansa-metallocenium ions, and that excess borane may serve to reactivate them towards further insertion.
KW - Borohydride complexes
KW - C-H activation
KW - Metallocene
KW - Polymerization
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U2 - 10.1016/j.poly.2005.02.005
DO - 10.1016/j.poly.2005.02.005
M3 - Article
AN - SCOPUS:22744458923
VL - 24
SP - 1234
EP - 1249
JO - Polyhedron
JF - Polyhedron
SN - 0277-5387
IS - 11
ER -