Design And Synthesis Of Benzimidazole,Pyridine And 1,3,5-triazine Ligands And Their Application In Cobalt Catalyzed Sem Ihydrogenation Of Terminal Alkynes

The importance of metal catalysis in both material sciences and industry can never be overemphasized.Searching for new catalysts with improved efficiency and/or novel functions constitutes one of the central themes of modern chemistry and is considered as a vital approach to solve many global issues.As the property and activity of a given metal complex is defined largely by its supporting ligands,design and synthesis of novel ligands and their metal complexes keep contributing to the most important means for discovery of new metal catalysts.In this thesis,three types of novel PNP pincer ligands are designed and synthesized,（1）Six kinds of ligands based on the benzimidazole skeleton are synthesized from o-phenylenediamine,which through cyclization,oxidation,condensation,reduction and other functional groups;（2）Four kinds of ligands based on pyridine skeleton were synthesized by substitution reactions of pyridine derivatives,CO₂Et activated analogue 2,6-dibromopyridine reaction with 2-aminophosphanes to give PNNNP ligand in 26%yield.Moreover,3-nitro-2,6-dichloropyridine demonstrated improved reactivity in similar transformation,delivering PNNNP ligand in a high yield of 84%.Reduction of Nitro with Zn in acetic acid followed by acylation of the amino group with pivaloyl chloride afforded PNNNP ligand with a total yield of 46%in two steps.Among them,2-aminophosphanes is prepared from L-（+）-prolinol as a raw material through a series of functional group conversions such as amino protection,mesylation,substitution,and deprotection;（3）Two new PNNNP ligands based on 1,3,5-triazine skeleton synthesized by Mono-arylation of trichloro-1,2,3-triazine then through subsequent diamination with 2-aminophosphanes.These ligands possess unprecedented structural characteristics.With these PNNNP pincer ligands in hand,our group set out to test their activity as catalyst ligand.Quickly,it was found that can these ligands impact the cobalt dichloride catalyzed hydrogenation of terminal alkyne with triethoxylsilane.Through condition screening,we determined the optimal reaction conditions:cobalt chloride as the metal catalyst,trimethoxysilane as the reducing agent,tetrahydrofuran as the solvent,and the reaction temperature was 80 ^oC.After our group determined the optimal reaction conditions,we proceeded to expand the substrate.During this period,our group discovered more interesting reaction phenomena.When extending the carbon chain of terminal alkynes,we find out that PNNNP pincer ligands can promote semihydrogenation of terminal alkynes with concomitant shift of double bond.In order to further study the applicability of the new ligand in this reaction system,we prepared15 compounds to explore its scope of application.