Probing β-alkyl elimination and selectivity in polyolefin hydrogenolysis through DFT

Abstract

Polyolefin waste is constantly growing, and the few existing solutions for recycling, reuse, and degradation are not viable long term. Carbon–carbon bond scission is a highly sought-after technology to assist in reclaiming polymers. This work compiles and advances the understanding of β-alkyl elimination, a method of C–C cleavage, through DFT characterization on a model substrate, (S)-2,8-dimethyldecane, and silica-supported Zr–H catalyst, [(SiO)₃ZrH]. The primary goal is to examine selectivity in C–C bond cleavage events. σ-Bond metathesis favors C–H activation at methyl branches by ∼2 kcal mol⁻¹. Chain walking via β-H elimination and insertion occurs readily and prefers E-alkene eliminations. β-Alkyl elimination also favors formation of E-alkene elimination products (∼2 kcal mol⁻¹), β-Me elimination (∼1 kcal mol⁻¹), and primary Zr–C cleavage (∼2 kcal mol⁻¹) over Z-alkenes, β-R (R > CH₃) elimination, and secondary Zr–C cleavage, respectively. These selectivity rules will help guide future experimental work and catalyst design.