Quantum Chemical Studies Of Mechanisms For The Hydrothiolation Reactions Catalyzed By The Transition Metal Rh And Ionic Liquid [Hmim]Br

The hydrothiolation reaction is the addition of thiols to unsaturated C-C bonds.With the advantages of 100%atom economy,simple synthetic procedures and friendly to enviroment,hydrothiolation reaction has become one of the most powerful strategies for constructing C-S bond.Transition-metal-catalyzed hydrothiolation reactions have played an increasingly important role in the synthesis of organosulfur compounds because of the benefits like high regioselectivity,high yield and high reaction rate.Hydrothiolation reaction catalyzed by ionic liquids features the simple synthesis and separation processes,high catalyst recyclability and inexpensive nature,and has drawn more and more research attentions.Mechanistic studies on these two types of hydrothiolation reactions have important industrial and academic values.In this thesis,we present theoretical investigatations on the mechanisms of hydrothiolations of alkenes catalyzed by the transition metal and ionic liquid.In the first part of thesis,the reaction mechanisms of Rh-catalyzed regioselective hydrothiolation of the allyl amine employing four bidentate phosphine ligands are investigated by DFT calculations.The free energy profiles of anti-Markovnikov and Markovnikov pathways arising from different alkene insertion types are computed to elucidate the ligand-controlled regioselectivity.For dppbz and dppp ligands with small nature bite angle(β_n≤86°),the anti-Markovnikov pathway that features the 1,2-alkene insertion into Rh-H bond is favored.While for dppb and DPEphos ligands with large nature bite angle(β_n≥99°),the Markovnikov pathway with 1,2-alkene insertion into Rh-S bond is preferential.The P-Rh-P bite angle is a reliable predictor and regulator of the regioselectivity of reaction as evidenced by good correlations between reaction barrier and P-Rh-P bite angle.Smaller P-Rh-P bite angle in TSs is generally found for small nature bite angle ligand dppbz and dppp in preferential anti-Markovnikov pathway,while TSs with larger P-Rh-P bite angle are favored by large nature bite angle ligand DPEphos and dppb.Larger difference in P-Rh-P bite angles of TSs between Markovnikov and anti-Markovnikov pathway generally leads to the greater disparity in barrier heights of two pathways,and hence greater regiodivergency of reaction.In the second part of thesis,a concerted one-step addition mechanism for[hmim]Br-catalyzed hydrothiolation of styrene by thiophenol is revealed by a combined DFT and experimental study.This special mechanism is driven by the directional hydrogen bond andπ~+-πinteractions that conjoin the substrates and[hmim]Br to a prereactive complex.The transition state is characterized by a planar 6-membered ring containing HBr and four substrate atoms at the reaction site.The concerted addition mechanism and the special structural feature of the TS renders the reaction regioselective,i.e.only the anti-Markovnikov product is yieled.When the styrene is replaced by aliphatic alkene,the substrates are loosely bound with the ionic liquid.As a result,the prereactive complex is destabilized and the reactivity drops significantly.