Theoretical Study On The B-H Activation Of O-carborane Catalyzed By Nickel And Palladium

o-Carborane is a kind of boron hydride clusters in which two adjacent B-H vertices are replaced by the C-H units,possessing unique reactivities under certain conditions.For example,o-carborane can react with transition metal reagents to generate o-carborane derivatives through B-H or C-H activation.It is of great significance to take research on transition metal-catalyzed functionalization of o-carboranes,for carborane deravatives have many applications in organic synthesis and functional material areas.In this dissertation,density functional theory?DFT?was employed to explore the B-H activations of o-carboranes catalyzed by nickel and palladium compounds.All reactants,transition states,intermediates and products were optimized at the IDSCRF-B3LYP/DGDZVP computational level in toluene solvent,accompanied by the same level frequency analysis.Possible reaction mechanism was confirmed based on geometry optimization and energy calculations.All energies reported here were corrected results under experimental temperature.1.For the reaction of carboryne,alkene,and 2-bromophenyltrimethylsilylacetylene catalyzed by nickel catalyst,possible reaction mechanism was explored based on geometric optimization and corresponding energetic results.o-Carborane would reacts with alkene to form a five-membered carboranylnickelacyclopentane intermediate firstly under the help of nickel reagent,then the nickel center in this carboranylnickelacyclopentaneintermediatecomplexeswith2-bromophenyl-trimethylsilylacetylene,leadingtotheformationofaseven-membered carboranylnickelacycloheptane intermediate through insertion of alkynyl into the metal-carbon?M-C?bond.Afterwards,a carboranylcyclopentane intermediate is formed through isomerization and ring closure processes.Finally,the B-H bond in the carboranyl group is activated with the aid of the basic reagent K₂CO₃,and produces a series of C,C,B-substituted carboranyl-fused tricyclic derivatives by getting off the nickel catalyst fragment.Three possible action styles of the basic reagent?K₂CO₃?in the activation of B-H bond were explored,including?1?the basic reagent directly involved in B-H activation?Path I?,?2?the basic reagent not involved in the reaction?Path II?and?3?the basic reagent complexes with Br group but not directly involved in B-H activation.The rate-determining step?RDS?'s free energy barriers of Path I,Path II and Path III are 26.8,35.7 and 41.6 kcal·mol^-11 respectively,suggests the basic reagent directly involved Path I is the optimal reaction path.Our computational results explain well the role of potassium carbonate basic reagent in the reaction process,and elucidate the microscopic mechanism of this reaction.In the end,comparison of computational results derived from IDSCRF-B3LYP/DGDZVP,IDSCRF-CAM-B3LYP/DGDZVP,IDSCRF-LC-?PBE/DGDZVP?IDSCRF-B3LYP+D3/DGDZVP and IDSCRF-M062X/DGDZVP calculations show smallest derivation of LC-?PBE method results from experimental data.2.For the diarylation of o-carborane with aryl iodide catalyzed by palladium catalyst,possible reaction mechanism was also explored based on geometric optimization and corresponding energetic results.The diarylation of o-carborane with phenyl iodide was found to be stepwise.The first step is corresponding to the o-carborane B?4?-H bond's activation by the palladium catalyst,and leads to the formation of B?4?-Pd bond through hydrogen migration process,accompanied by the generation and removal of one molecule of acetic acid.The second step is corresponding to the cage carbon-ajacent COOH group's hydrogen migration onto one oxygen atom in the acetate group which complexed with the palladium center,leading to the formation of a new five-membered carboranylpalladacycle intermediate by getting off a second acetic acid molecule.Afterwards,the palladium center would insert into the C-I bond in penyl iodide,forming a new intermediate based on C-I breakage.Finally,B?4?-Pd bond breaks and a new B?4?-C bond is formed through bondage between the phenyl carbon and B?4?atom on o-carborane,realizing the single arylation of o-carborane.The second phenyl group is bonded to B?5?atom of o-carborane in the same manner as the first phenyl group to B?4?atom,thus realizing the diarylation of o-carborane accordingly by reacting with a second molecule of aryl iodide.The rate-determining step of the whole process is calculated to be the B?4?-H's hydrogen migration,with a free energy barrier of 25.8 kcal.mol^-1.For investigation of the regioselectivity of this reaction,we have calculated the NBO charge distribution of some key intermediates and the Pd?OAc?₂ catalyst,which rationalizes the regioselective arylation of o-carborane on B?4?/B?5?positions.These mechanistic results about palladium catalyzed diarylation of o-carborane with aryl iodide may shed some lights on further in-depth study of other similar palladium catalyzed reaction of carboranes.