Synthesis Of High-Valent Tantalum And Niobium Phosphoniomethylidyne Complexes

The discovery of ferrocene in the 1950s is a milestone in the development of Organometallic Chemistry.During these 50 years,the research of transition metal organic compounds has made great achievements.The application of these compounds in organic synthesis, Catalytic fields, promote the development of organic chemistry greatly. Currently, transition metal organic compounds have been used for hydrogenation, dehydrogenation,oxidation, reduction, isomerization, carbonylation, hydroformylation, carboxylation, polymerization reaction.The synthesis and properties of metal-carbyne complexes is always a hot topic in the research field of organometallic chemistry since the first synthesis of transition metal complexes with a formal metal-carbon triple bond reported by E. O. Fischer et al. in 1973.Since these compounds have various particular reaction in organic synthesis, especially in vitamins, peptides, synthesis of anti-cancer drugs and natural products, and as olefins, alkyne polymerization catalysts demonstrated its unique advantages and broad application prospects.However,because it is very difficult to synthesize the metal-carbyne complexes and the reaction is complicated,the development of metal-carbyne is not perfect until now.The functional group linked with carbyne carbon has a strong effect on the reactivity and strength of metal-carbon triple bond. The phosphorous ylide carbyne complexes as a kind of special carbyne complexes (M≡C—PR₃(?)M = C = PR₃) could be regarded as a double-metal substituted complex of phosphorous ylide and they have special chemical properties with application potential in organic synthesis and catalysis. Very few examples of high-valent transition metal phosphonio methylidyne complexes with d⁰ electron configurationare known so far.In this paper, Two novel high-valent tantalum phosphonio methylidyne complexes and two novel high-valent niobium ylideaddict complexes have been synthesized through ylide translation reaction from the reaction of two phosphorus ylides ( H₂C=PPh₃ , H₂C=P(Net₂)₃ ) with cyclopentadienyl tantalumchloride, cyclopentadienyl niobium chloride and pentamethylcyclopentadienyl niobium chloride.Four novel complexes were obtained and these complexes were characterized with ¹H NMR, ¹³C NMR, ³¹P NMR and elemental analyses. The crystal structure was determined with X-ray diffraction.And the reaction mechanism was discussed.