Theoretical Study Based On Manganese/rhodium Catalyzed Hydrosilylation Of Unsaturated Hydrocarbons

Organosilicon compounds,with their specific physical and chemical characters,have been widely used in the area of modern industries,pharmaceuticals and high-performance material fields,and have received extensive attention from chemists.Transition metal-catalyzed hydrosilylation of unsaturated hydrocarbons can rapidly construct organosilicon compounds from simple and readily available starting materials,which is one of the most fundamental methods for the laboratory and industrial synthesis of organosilicon compounds,and other related silicon compounds.For a long time,platinum catalysts are widely used in the silicone industrial production.But it has the disadvantages of high cost and the relatively narrow substrates scope.Therefore,the replacement of traditional platinum-based catalysts in unsaturated hydrocarbons hydrosilylation by more sustainable and economic transition metal catalysts is a research hotspot in recent years.In this paper,we use the density functional theory（DFT）method to study the hydridesilylation of unsaturated hydrocarbons catalyzed by manganese and rhodium.We elucidate the detailed reaction mechanism of the ligand and adding order regulating reaction selectivity.And the influence of electronic effects and steric hindrance on reaction selectivity is analyzed.The research contents of this paper are divided into the following two parts.（1）Theoretical study of the ligand-controlled binuclear manganese-catalyzed olefin hydrosilylation and dishydrosilylation reaction mechanism and the origins of selectivity.The reaction pathway is consisting of four processes:（1）breaking the Mn-Mn bond to produce the manganese radical（LMn·）;（2）the LMn·undergoes a hydrogen atom transfer（HAT）process with silane to generate the corresponding silyl radical;（3）the silyl radical rapidly undergoes radical addition to olefins to generate a secondary alkyl radical;（4）this alkyl radical can evolve according to two different ways:（a）via HAT with LMn H to afford the hydrosilylation products;or（b）viaβ-H elimination with LMn·to afford the dehydrosilylation products.Through the study of bidentate ⁱPr PNP ligand（L12）and monodentate jackiephos ligand（L22）,we can find that:the relatively electron-rich L12 ligand can enhance orbital interaction to activate the C_（β）-H bond,which favors theβ-H elimination,and provides the dehydrosilylation products.Moreover,the severe steric crowding is unfavorable for the HAT process.The Mn-H bond in LMn H complexes is weakened by relatively electron-deficient L22 ligand,which is a favor to HAT process,and provides the hydrosilylation products.The mechanism revealed in this study will provide ideas for design new organic synthesis reactions.（2）Theoretical study of the reaction mechanism and the origins of selectivity of adding-order-regulated rhodium-catalyzed hydrosilylation of terminal alkyne.When addition of the silane and the alkyne to the rhodium catalyst（RhI（PPh₃）₃）in one portion,the reaction is following the m CH mechanism.The m CH mechanism commences with silane oxidative addition,followed by hydrogen migration and silicon migration to giving the syn-addition products.However,when Rh I（PPh₃）₃ was pretreated with silane reagent before adding alkynes,the reaction is following the Haszeldine’s mechanism.The silyl-Rh（Ⅲ）active species will be generated in the pretreatment process,which then through hydrogen migration and silyl migration to form three-coordinate Rh（Ⅰ）intermediate.This Rh（Ⅰ）intermediate undergoes second oxidative addition,C-C rotation and reductive elimination to give trans-addition products and regenerates the active catalyst.In the m CH mechanism,the hydride migration process is the rate-determining step;in the Haszeldine’s mechanism,the silyl migration process is the rate-determining step.In terms of regiochemistry,hydride-migratory to C_αis much favorable,which have a minimum steric interference and coplanarity.Such a hydride migratory nicely reproduces the observed regioselectivity.The mechanistic revealed in the present study will to provide important implications for better understanding of the adding order controlled hydrosilylation reactions and for the design of new catalytic systems.