Steering On-Surface Synthesis Of Covalent Nanostructures Via Metal-Organic Interaction

On-surface synthesis(OSS),defined as a novel synthetic strategy that proceeds chemical reactions catalyzed by confined solid surfaces.With the advantages of the extraordinary mechanisms,the atomically precise structures,the in-situ synthesis and characterization,it has reproduced sets of classical reactions in solution-based synthesis and has become an important approach to construct the low-dimensional covalent nanostructures.In contrast to the traditional synthesis in bulk phases,however,solventfree environment of OSS has limited the rich utilization of reaction parameters.Therefore,it has become one of the core issues gradually to develop appropriate controlled strategies and tools to steer the reactivity and chemoselectivity in the procedure of OSS.The interaction between metal and organics is a staple in OSS.It has been revealed by a quantities of documents that the metal-organic interaction has a positive impact on the select of reactivity and reaction pathways,utilizing either the intrinsic metallic substrates or the extrinsic metal adatoms.Whereas,the employment of this strategy is limited only to Ullmann-type dehalogenation coupling,with other classical on-surface reactions that are also capable of constructing the novel covalent nanostructures rarely involved.Hence,with the interplay of scanning probe microscopy and density functional theory,this thesis will investigate systematically the steering of metal-organic interaction brought to three types of reactions with different functional groups.The included contents are as follows:(1)[2+2]cycloaddition:Steering the chemoselectivity of 2,3-dibromophenazine via the silver-aryl intermediates formed by the hybridization between metal atoms(adatoms)of substrates and aromatic radicals,leading to the uniform[2+2]cycloaddition products on Ag(111).Through the comparative studies on Au(111),we have revealed that the highly selectivity originates from the preorganization of bonding motifs among momers,which is induced by the hierarchical evolution of the silver-aryl intermediates.In addition,we have characterized the chemical and electronic properties at the singlemolecule level,with the assistance of bond length measurements and scanning tunneling spectroscopy,respectively.(2)Terminal alkynes coupling:Steering the product structures in the reactions of 4,4’-diethynyl-2,2’-bipyridine and 3,8-diethynyl-1,10-phenanthroline onAu(111)via the metal-organic coordination templates formed by the coordination between the extrinsic Fe and Cu adatoms and the pyridinic nitrogen,leading to the high stereoselectivity of final coupling.It has been revealed that the coordination templates preorganize the adsorption configurations of unreacted monomers,thus providing the normalized geometries for the final covalent coupling.(3)Alkane dehydrogenation:Steering the dehydrogenation reaction of 1,4,7,10,13,16-hexaazacyclooctadecane on Au(111)via the metal-organic coordination formed by the coordination between the extrinsic Fe and Cu adatoms and the alkyl nitrogen,leading to the reactivity which is absent on bare Au(111)due to the over-high adsorption energy.The anchoring effect of the metal-organic coordination on the weakly adsorbed monomers and the different catalytic properties of iron and copper coordination atoms have been revealed.