A DFT Study On The Conversion Of Chlorobenzenes To Parachlorophenols Promoted By Transition Metal Monoxide

In this paper, density functional theory are carried out to study the reaction of thefirst period transition metal monoxides (MO) and chlorobenzene, the ground stategeometry configurations of reactants, products, intermediates and transition states areoptimized, and the reaction mechanism is presented. TS, QST2, QST3method isapplied to search the transition state of each step reaction, observing the frequency oftransition state, ensure the transition state only exists one imaginary frequency.Intrinsic reaction coordinate (IRC) ensure the correctness of the reaction of the firstperiod transition metal monoxides (MO) and C6H5Cl, and the detailed analyses of thereaction mechanism are presented. The reaction mechanism of the first periodtransition metal monoxides and chlorobenzene could be summarized as follow:We found the the first period transition metal monoxides catalyzed directchlorobenzene-parachlorophenol reaction is a two-step concerted reaction. Thisreaction is initiated by the formation of the reactant complex, OM(C6H5Cl),chlorobenzene C-H bonds are activated on this complex due to significant electrontransfer from the chlorobenzene to the transition metal species. The reaction shouldproceed in a concerted manner, the first one is a nonradical mechanism to form ahydroxo intermediate via a transition state, HO-M-C6H5, via H atom abstraction witha coordinatively unsaturated four-centered transition state. The second one occurs in aconcerted manner via a1,2-parachlorphenyl migration on the hydroxy intermediate,via the dissociation of transition metal carbon bond and the formation of carbon oxygen bond to form product. We consider the reaction may exist spin inversion, butthe reaction of first period transition metal monoxides and chlorobenzene doesn’texist any spin inversion, high-spin potential energy surface affords a low-cost reactionpathway. Sc, Ti, V, Cr, Fe complexes are endothermic reactions, Mn, Co, Ni, Cu, Zncomplexes are exothermic reactions. The second step reaction activation barrier(60-90kcal/mol) siginificantly greater than the first one (20-30kcal/mol). Theintrinsic reaction coordinate (IRC) approach are important in order to betterunderstand the mechanism of the direct chlorobenzene-parachlorophenol conversionand detailed analyses of the low-spin and the high-spin potential energy surfaces.