Theoretical Study On Copper-catalyzed Desulfurization Reaction And Dehydration And Dehydration Reaction Of Diol

In this thesis, two projects have been investigated theoretically by means ofdensity functional theory ?DFT? calculations at the B3LYP level of theory. Thefirst project is related to the mechaistic study on the copper-mediated desulfitativereactions, and the second one is related to the mechaistic study on thedeoxydehydration of diols to alkenes catalyzed by Cp ReO3.?1? Liebeskind and co-workers have extensively studied the desulfitativecarbon-carbon bond forming processes that take place between thioorganicsubstrates and organotin reagents or boronic acids. The “firstgeneration” systemproceeds under anaerobic conditions, and is catalyzed by Pd and enabled bystoichiometric quantities of a Cu?I? carboxylate. The second-generation systemtakes place under aerobic reaction conditions, is palladium-free, and uses onlycatalytic quantities of Cu. But this system requires a sacrificial second equivalentof the organotin reagents or boronic acid. In2011, they reported a new class ofreactions that can take place catalyzed only by Cu?I? under anaerobic conditions.Also, this system is palladium-free and without squandering an extra equivalent ofthe boronic acid. In view of the system having so many advantages, this systemwas chosen in this work for the perpose of understanding its reaction mechaismswith the help of DFT calculations. In our study, CuCl is chosen as the catalyst thathas been experimentally confirmed catalytically effective. The first reactionstudied is the reaction of the thiolate ?R1? with the organotin reagent ?R2?. It isfound that this reaction proceeds by mainly the following steps: Cu?Ncoordination,[Cu-Cl+C-Sn] ?-bond metathesis,[OC-S oxidative addition+C-Creductive elimination]?in one step?, S-N bond formation. The overall activationenergy for formation of the intermediate product ?8? is calculated to be26.0kcal/mol, in agreement with the reaction condition ?60°C?. However, our studyfound that an equilibrium is involved between the intermediate product ?8? andthe proposed intermediate ?9?. The overall activation energy for formation of thefinal product ?10? is calculated to be35.8kcal/mol, in accordance with thereaction condition ?150°C?.For deeply understanding the reaction mentioned above, we comparativelystudied the following three model reactions. The first model reaction is that thegroup containing C?sp²? attached to S is replaced by a methyl ontaining C?sp³?.Our conclusion is that such a reaction is kinetically inavailable ?the overall ?H^#=44.6kcal/mol?. This is due to the very unfavorable S-C?sp³? oxidativeaddition to Cu?I? The reason is that the S-C?sp³? has a high ?-antibonding energy,making the backbonding M??*less effective. The sceond model reaction is thereaction of R1with Me3Sn-Me, which means the C?sp²? attached to Sn in R2isreplaced by C?sp³?. Our calculation suggests that such a reaction is favorablekinetically, indicating hybridization of the carbon attached to Sn does not blockthe reaction. The third model reaction is the one between the thiolate with anamide group and R2. Our calculation also suggests such a reaction can still takeplace. In summary, the hybridization of the carbon attached to S has largeinfluence on desulfitative carbon-carbon bond forming processes, while the oneattached to Sn has not.?2? Andrews's group reported the deoxydehydration of diols by PPh3in thepresence of Cp ReO3. The reasonable mechanism for the catalytic model reaction?CpReO3+PMe₃? has been presented based on our calculations. The first processis an O-transfer process from CpReO3to PMe₃. The second process is the reactionof the formed CpReO2with diol to give a five-membered metal diolate. The lastprocess is the extrusion of styrene from the diolate via a3+2process. Theextrusion of styrene from the metallaoxetane, which is generated from the metalldiolate, is suggested to be inaccessible ?a2+2process?.