The Regulatory Role Of Ligands In The Activation Of C-H Catalyzed By Metal Complexes

Selective transformations serve as a powerful tool to get pure isomer have attracted much attention from organic chemists.Reactions catalyzed by transition-metal-complex can provide more possible reaction diversity.As is known to us all,reaction selectivity includes chemoselectivity,regioselectivity,diastereoselectivity,and enantioselectivity.Although many challenges still exist in highly selective transformations,remarkable success has been achieved in the past years.In particular,the great development made by transition metal catalyzed reactions which assisted by the discovery of many ligands.It is now widely accepted that the properties of metal center on the metallic complex can be changed by the ligand,and thus can change the selectivity of the reactions.The activity and selectivity quality of the catalyst are mainly affected by the steric and electronic properties of the ligands.During the last several years,many new ligands have been invented and applied to improve reaction outcomes.In this dissertation,we performed a detailed theoretical study of four kinds of reactions such as B?C₆F₅?₃ promoted Cp^*Co^III-catalyzed C-H/N-H activations.We discussed the influences of ligands on reaction selectivity and elucidated the origins.The main research contributions and valuable innovations are highlighted as follows:?1?The reaction mechanism and the origins of regio-and enantioselectivities for Pd-catalyzed the asymmetric arylation of aliphatic?-amino anion equivalents were investigated computationally.The results indicate that the reaction proceeds via mainly six sequential steps:deprotonation at?'-site of imine,coordination of?-amino anion to Pd-catalyst,oxidative addition,transmetalation,reductive elimination,as well as the final dissociation to release the product and regenerate the catalyst.The transmetalation is a key step on which both enantioselectivity and regioselectivity depend.The charge inversions of?-and?'-C atoms and the orbital interaction between Pd center and?-C in transmetalation step are responsible for the regioselectivity.Additionally,the intermediates before the dissociation step are critical in controlling the enantioselectivity.Noncovalent interactions analyses indicate that the enantioselectivity primarily arises from the CH…?interactions of isopropyl?iPr?groups with the fluorene and the benzene rings for PdL₁ catalyzed reaction.?2?The mechanism of B?C₆F₅?₃ promoted Cp^*Co^III-catalyzed C-H functionalization was investigated in detail employing density functional theory?DFT?.The formation free energy of every possible species in the multicomponent complex system was explored and the optimal active catalyst was screened out.The results uncover the role of B?C₆F₅?₃ played in forming active catalyst is from the coordination with OAc^-,but not from the formation of[I?C₆F₅?₃B]^-,and no acceleration effect is found in C-H activation as well as the formation of Co^III-carbene intermediate.Moreover,present theoretical results elucidate the Cp^*Co^III-catalyzed C-H activation is mediated by imine N-coordination other than general proposed the sequence of N-deprotonation directed C-H activation.The metal-controlled C-H/N-H selectivity was then elucidated by insighting into[Cp^*Co^IIIOAc]⁺/[Cp^*Rh^IIIOAc]⁺-catalyzed C-H and N-H activations respectively.?3?Mechanistic details and the origins of stereodivergent for Co-catalyzed the transfer semihydrogenation of alkynes to Z-and E-alkenes were investigated by DFT calculations.The calculated results indicate that Z-alkene is first generated from the hydrogenation of alkyne which is followed by Z/E isomerization.Insertions of alkyne and Z-alkene into Co-H bonds are critical on the Z/E stereoselectivity.Moreover,for PNPCoH and NNPCoH,the geometry optimizations indicate that one pyridine or PtBu₂ is dissociated from Co center in both alkyne and alkene insertion steps,so that BH₃ pop up from ammonia borane to bond the free PtBu₂ arm,as well as unsaturated-coordinate Co center is further bound to BH₃,which makes the PNP-catalyst deactivation.Thus,chelating PN ligand is proposed to be a potential ligand for Co?I?catalyst in Z/E selective alkynes semihydrogenation which is also verified computationally by us.In addition,the role of chelating bidentate framework and ligand size played in stereodivergent for NNP/PNP-mediated semihydrogenation of alkyne were analyzed.The substituent effect study of PN ligands indicate that ligands NHR-PMe₂ are much favorable in the modulation of Z/E stereoselectivity of alkyne semihydrogenation.?4?The mechanisms of aminocarbonylations and alkoxycarbonylations in coupling of aminophenols with iodoarenes catalyzed by the bidentate phosphorus ligand Pd complexes were explored with theoretical calculations.The origins of chemoselective carbonylation mediated by ligands and bases were disclosed.According to our calculations,the bifurcation points of reaction pathways caused by differentligandsandbasescombinationsare^L1/L2INT5,a[DPPP/DIBPP]benzoylpalladium?II?iodide complex.The affinity of ^L1/L2INT5 and adducts?K₂CO₃ and DBU?,as well as substrate itself are the predominant factors of switching from the aminocarbonylation to alkoxycarbonylation.The results reveal that K₂CO₃ directly exchanges iodine with ^L1INT5 and assisted in hydrogen transfer in DPPP-K₂CO₃ combination,in which the alkoxycarbonylation is more favorable than the aminocarbonylation.While for DIBPP-DBU combination,iodine exchange is achieved by means of the hydrogen bond formed between the carbonyl group on ^L2INT5 and the substrate amino H due to the influence of ligand,and then occurs iodine exchange;subsequently DBU assisted amino H transfers to complete the aminocarbonylation.The proton transfer is the step that determines the chemoselectivity in DPPP-K₂CO₃ combination.The iodine exchange determines the chemoselectivity between aminocarbonylation and alkoxycarbonylation in DIBPP-DBU one.These results would be helpful to deeply understand the roles of each component in chemoselective reaction in a multicomponent complex system.