标题：Mechanistic picture of the redox-neutral C[sbnd]C bond cleavage in 1,3-dilignol lignin model compound catalyzed by [Ru(Cl)(H)(PPh 3 ) 3 ]/triphos
作者：Zhao X.; Yang Y.; Zhu R.; Liu C.; Zhang D.
作者机构：[Zhao, X] Key Lab of Colloid and Interface Chemistry, Ministry of Education, Institute of Theoretical Chemistry, School of Chemistry and Chemical Engi 更多
通讯作者地址：[Zhang, D] Key Lab of Colloid and Interface Chemistry, Ministry of Education, Institute of Theoretical Chemistry, School of Chemistry and Chemical Eng 更多
关键词：DFT; Lignin; Retro-aldol-type C[sbnd]C bond cleavage; [Ru(Cl)(H)(PPh 3 ) 3 ]/Triphos
摘要：The cleavage mechanism of the C α [sbnd]C β bond in a 1,3-dilignol catalyzed by [Ru(Cl)(H)(PPh 3 ) 3 ]/triphos has been investigated with the aid of DFT calculations to understand the unique catalytic activity and selectivity of ruthenium complexes towards the redox-neutral deploymerization of lignin model compounds. The proposed mechanism divides the reaction into four stages: coordination of the substrate to the Ru center, dehydrogenation, retro-aldol-type C[sbnd]C bond cleavage, and product and pre-product release with catalyst regeneration. The dehydrogenation process was identified as the bottleneck of the catalytic cycle and the estimated high barrier (29.8 kcal/mol) qualitatively rationalizes the experimental observation that the reactions were carried out under elevated temperature (160 °C). The α- and γ-hydroxyl groups as well as the γ-H in the 1,3-dilignol were shown to play substantial roles and their simultaneous presence is necessary for cleavage of the C α [sbnd]C β bond. This rationalizes the experimental finding that [Ru(Cl)(H)(PPh 3 ) 3 ]/triphos complexes were inactive for cleavage of the C α ‒C β bond cleavage of 1,3-dilignols with any absence of the α-hydroxyl group, γ-hydroxyl group, or C γ [sbnd]H unit. © 2019