Theoretical Study On C-H And O-H Bond Activation By Transition-metal Iron, Molybdenum And Platium

Theoretical study of the reaction mechanism is very significant. Activation of the C-H bond and O-H bond have been attracted much attentionin chemistry.In this work, C-H and O-H bond activationby several kinds of transitionmetalswere studied systematicallyand detailly by the quantum chemical method. This work may provide valuable theoretical guidance and clues for the development of transition metal catalyst,and enrich the C-H and O-H bond activation reactions.The main contents are summarized as follows:1) Density functional theory (DFT) calculations were carried out to investigate the methanol oxidation mediated by [(bpg)FeⅣO]+(A). Two models (CH3CN-bound ferryl model B and CH3OH-bound ferryl model C) were also studied in this work. Mechanistically, both direct and concerted hydrogen transfer (DHT and CHT) pathways were explored. It is found that the initial step of the methanol oxidation by A is the C-H bond activation via a DHT pathway. Adding different equatorial ligands has considerable influence on the reaction mechanisms. The methanol oxidation mediated by B commences via O-H bond activation. In sharp contrast, the oxidation mediated by C stems from C-H bond activation. Frontier molecular orbital analysis showed that the initial C-H bond activation by all these model complexes follows a hydrogen atom transfer (HAT) mechanism, while O-H bond activation proceeds via a hydrogen atom transfer or proton transfer (PT).2) PtRuelectrocatalyst is themosteffectiveanodecatalystfordirectmethanolfuel cell(DMFC)by far.Density functional theory calculations were performed to study the mechanism and reactivity ofmethanol oxidation mediated by PtnRum (n+m=3,n≠0) clusters. The potential energy surfaces and pathwaysof the initial O-H and C-H bond activations were predicted. The results show that the activation of methanolproceeds preferentially along the C-H bond activation pathway. The calculated reactivity order was Pt2Ru>Pt3>PtRu2. Frontier molecular orbital analysis showed that the initial C/O-H bond activation is a proton transferprocess. The solvent effect was also investigated. This study will enable a deeper understanding of C/O-Hbond activation and provide new ideas for catalyst selection and optimizing conditions for methanol activation.3) Density functional theory (DFT) calculations were carried out to explore the mechanistic insight of methanol C-H and O-H bonds activation mediated by ruthenium doped platinum cationic clusters [PtnRum]+(m+n=3, n≥1). The charge effect on the reactivity has been elucidated; calculations show that positive charge is evenly distributed on the three Pt atoms of the[Pt3]+cluster; while for Ru doped clusters, positive charge is mainly distributed on the Ru atom(s). The reactivity of [PtnRum]+is significantly greater than neutral [PtnRum] in the process of the initialC-H bond cleavage; while only [Pt3]+isgreater than [Pt3] in course of O-H bond cleavage. This study may be valuable for deeper understanding of C-H/O-H bonds activation mediated by metal cluters.4) Activation of the O-H bond of water by transition-metal compoundshas been attracted much attentionto academics.Density functional theory calculations were carried out toinvestigated the reaction of water O-H bond activation by[(PY5Me2)MoX]0/+/2+(MoX0/+/2+)(X= O or S). It isfound that for the O-H bond activationreaction by MoO the reactivity order wasMoO+>Mo00>Mo02+, and for MoS, the reactivity order wasMoS+>MoS2+>MoS0. From calculation results that the reactivityof MoO0/+are higher thanMoS0/+, MoS2+ is more favorable than MoO2+for O-H bond activation. Solvent effectwas also investigated.