Ene/Diene Copolymerization Catalyzed by Cationic Sc and Gd d⁰ Metal Complexes: Speciation, Ion Pairing, and Selectivity from a Computational Perspective

Abstract

metallocene • d 0 metal complexes • butadiene • polymerization • speciation • ion pairing • reactivity • DFT ABSTRACT A computational mechanistic study of the butadiene homopolymerization reaction performed with scandium and gadolinium catalysts [(2-Me-Ind)2(N(TMS)2)]M (M = Sc, Gd) in presence of [Ph3C][B(C6F5)4] or [PhNMe2H][B(C6F5)4] and Al2Et6 has been performed at the DFT level. The speciation of mono-and poly-metallic complexes involving alkylaluminum and the cationizing agent has been achieved. Their dormant or active character has been revealed. This speciation shows a thermodynamically favorable transmetalation reaction between the aryl group of [B(C6F5)4]and the alkyl group of AlR3. The reactivity of [(2-Me-Ind)(Et)M] + (M = Gd, Sc)toward monomer insertions is detailed. Computed energy profiles demonstrate the preference for cis-1,4 over trans-1,4 insertion. The influence of the counter-ion on the reactivity and selectivity of the catalyst has been investigated. For Gd-based system, the counter-ion has an impact on the reactivity and selectivity of the catalyst and cannot be omitted in the chemical model. Finally, the ability of these cationic complexes to copolymerize ethylene with butadiene is assessed and compared to neutral and efficient Nd based catalytic systems.

Thermodynamics of metallocene catalyst activation: alignment of theory and experiment

“…However, the experimental estimates are not based on the T dependence of K d so we cannot attach too much significance to these discrepancies, except to state that we did not consider more than one conformer when calculating thermodynamic properties. 26…”

Polymerization via Insertion of Ethylene into Al−C bond under Mild Conditions: Mechanistic Studies on the Promotion Exerted by a Catalytic Amount of Cationic Gadolinium Metallocene

“…We first examine the structure of active species and the possibility of a Gd‐alkyl species by DFT calculations, and next investigate the mechanism of ethylene polymerization reaction. Recent experimental and computational studies showed that various ion pairs can be generated in an activation process for polymerization reaction with boron‐C 6 F 5 compounds such as B(C 6 F 5 ) 3 and [Ph 3 C][B(C 6 F 5 ) 4 ] and aluminum alkyl species through Al/B transmetalation [18,19] . Perrin et al., however, adopted B(C 6 F 5 ) 4 − in their DFT calculations for polymerization reactions, to avoid considering various possibilities, although they found stable ion pairs with Et 2 B(C 6 F 5 ) 2 − or AlEt 4 − [19] .…”

Design of selective divalent chain transfer agents for coordinative chain transfer polymerization of ethylene and its copolymerization with butadiene

“…The copolymerization of olefins, including ethylene, with conjugated dienes has been one illustration of this challenging objective. This has been achieved by identifying the adequate catalysts [3][4][5][6][7][8][9][10][11][12] that produced copolymers combining the advantageous properties of olefins-and conjugated dienesbased homopolymers. 13 Among the catalysts reported, {(Me2Si(C13H8)2)Nd(-BH4)[(-BH4)Li(THF)]}2 (1) / BOMAG (BOMAG = n-butyl-n-octylmagnesium) (Scheme 1) enabled the copolymerization of ethylene with butadiene and gave access to a new class of rubber called ethylene butadiene rubber (EBR).…”

“…The copolymerization of olefins, including ethylene, with conjugated dienes has been one illustration of this challenging objective. This has been achieved by identifying adequate catalysts 3–12 that produced copolymers combining the advantageous properties of olefin- and conjugated diene-based homopolymers. 13…”