The Synthesis And Reactivity Of Nickel/Palladium Complexes Supported By Mg-based Metalloligands

Transition metal complexes are widely used in the catalytic transformations of various molecules,and their catalytic performance is usually significantly influenced by the ligands.Organic ligands are mainly composed of functional groups containing nitrogen,oxygen,phosphine,carbene,etc.When an organic ligand is embedded with a metal element,it can be used as a new class of metalloligands.The Lewis acidity of metalloligands can provide unusual electronic and coordination environments for transition metals,which can broaden transition metal-coordination chemistry.This dissertation presents the synthesis and reactivity of nickel and palladium complexes supported by Mg-based metalloligands.1.The synthesis and reactivity of palladium complexes supported by Mg-metalloligand.The reaction of novel tridentate NNP ligand-supported magnesium complexes L₂Mg（L=（2,6-ⁱPr₂C₆H₃）NC（R）NCH₂CH₂PPh₂,R=^tBu,HL1;R=Ph,HL2;L=（2,6-ⁱPr₂C₆H₃）NC（^tBu）N（o-C₆H₄）PPh₂,HL3）with allyl（cyclopentadienyl）palladium（II）afforded an array of Mg-Pd heterobimetallic complexes containing Pd-Mg dative bonds.Among these complexes,the palladium atom adopted an usual T-shape geometry.Treatment of the Mg-Pd heterobimetallic complex with chalcone and its derivatives gave the corresponding coordination products.The five new complexes involved in the above study were characterized by single crystal X-ray diffraction.2.The synthesis of nickelaspiropentane complex supported by Mg-metalloligands and its application in small molecules activation.Reaction of bidentateβ-diketiminato ligand supported magnesium ethyl complex L4Mg Et（L4=（（2,6-ⁱPr₂C₆H₃）NCMe）₂CH）with bis（1,5-cyclooctadiene）nickel afforded the linear Mg-Ni-Mg heterotrimetallic complex.Experimental and theoretical results revealed that the C-Cπ-bond of ethylene is broken and the Ni-Cσ-bond formed in the complex resulted from the strongπ*-backdonation.Therefore,The Mg-Ni-Mg heterotrimetallic complex should be considered as a nickella-bis-cyclopropane,i.e.,nickelaspiropentane complex supported by Mg-metalloligands,which is difficult to achieve in late-transition metal complexes stabilized by organic ligands.The electrons in Ni-C bonds are found to be delocalized onto an empty orbital at the Mg center,which agree with the presence of a low-spin Ni（II）and Mg（II）.The reactivity of the nickelaspiropentane complex supported by Mg-metalloligands shows:（1）Coordination reactivity.Treatment of the nickelaspiropentane complex with DMAP and CO afforded the corresponding coordinative products.DMAP coordinated with magnesium atoms with the retaining of nickelaspiropentane moiety.While CO coordinated with nickel atom,accompanied by the release of ethylene.（2）The cleavage of covalent bonds.Reaction of the nickelaspiropentane complex with H₂ afforded a nickel-polyhydride complex.DFT calculations suggested that the H-H bond was activated by aσ-bond metathesis with a formal Mg-Ni bond rather than the classical two-electron oxidative addition at a single metal center.Reaction of nickelaspiropentane complex with Ph NCS resulted in the sulfur-bridged Mg-Ni-Mg heterotrimetallic complex with the cleavage of C-S bond.（3）Reductive reactivity.Treatment of the nickelaspiropentane complex with N₃Si Me₃ afforded the reductive coupling product.The seven new complexes involved in the above study were characterized by single crystal X-ray diffraction.Although numerous nickel-hydride complexes have been explored,it remained a long-standing challenge to isolate nickel-polyhydride complexes mainly due to their high propensity to lose metal-bound hydrogen in a reductive fashion.In this text,the reactivity of the nickel-polyhydride complex supported by Mg-metalloligand was carried out:（1）The coordination reactivity with CO,Michler’s ketone and diphenyldiazomethane were shown.（2）Reductive reactivity.the reaction of nickel-polyhydride complexes with cyclopropyl phenyl ketone obtained the reductive product with the insertion of Ni-H into C=O bond.while in the reaction with allene,the selective transfer-hydrogenation occurred.（3）Oxidative reactivity.Treatment of nickel-polyhydride complexes with one equivalent of silanes produced the Si-H oxidative product.While the oxidative product of secondary silane was obtained with the use of two equivalents of phenylsilane.The nine new complexes involved in the above study were characterized by single crystal X-ray diffraction.3.The catalytic applications of nickel complexes supported by Mg-metalloligand.（1）The nickelaspiropentane complex effectively catalyzed the hydrogenation of a diverse array of unsaturated substrates.Terminal aliphatic and aromatic alkenes,internal alkenes,silyl enol ether,enamine and imine were readily reduced to their corresponding alkanes in quantitative yields.Notably,the hydrogenation of silyl enol ether catalyzed by commercial nickel reagents became sluggish.hydrogenation of 8-methylquinoline and anthracene resulted in the selective reduction of the aromatic rings to generate 8-methyl tetrahydroquinoline and octahydroanthracene,respectively.（2）The nickelaspiropentane complex effectively catalyzed the hydrosilylation of unsaturated substrates to generate the linear organosilane species.In the mechanistic study,the stoichiometric reactions of the nickelaspiropentane complex with phenylsilane afforded two nickel silyl complexes,including the first example of Mgσ-Si-H complex.Such complexes were considered active intermediated in the catalytic system.Combined with control experiments,the Mg/Ni synergistic mechanism was proposed.The three new complexes involved in the above study were characterized by single crystal X-ray diffraction.（3）The catalytic application of the nickel-polyhydride complex in the H/D exchange reaction.D₂ gas as deuterated source,the nickel-polyhydride complex realized the selective H/D exchange for C（sp²）-H bond in the C2 position of pyridines.The reaction conditions are mild and highly tolerant of functional groups.In addition,the catalytic system is capable of selective H/D exchange of C（sp³）-H bonds at the benzyl position.