Studies On Acylruthenium Complexes From Reactions Of RuCl₂?PPh₃?₃ With Terminal Alkynes

The activation and functionalization of C-C triple bond in alkynes by ruthenium complexes has been widely used in organic synthesis.It has attracted the interest of many researchers recent years.Ruthenium complexes can catalyze the hydration of terminal alkynes,producing some important organic compounds.With different structures of metal catalysts,the reaction mechanisms are different.Ruthenium complexes with a strongly coordinated?⁵-cyclopentadienyl ring have high activity for anti-Markovnikov hydration of terminal alkynes,giving aldehydes as products.Replacing?⁵-cyclopentadienyl ring with?⁶-arene ring,Ru complexes can catalyze Markovnikov hydration of terminal alkynes.Both the Markovnikov and anti-Markovnikov products are useful to synthesize some antimicrobial agents,macromonomer,and drug molecules.Moreover,ruthenium complexes can react with alkyne under nitrogen to produce new complexes.Terminal alkynes can coordinate with Ru metal center and form vinylidene complexes.In solution,water molecules can be nucleophile to attack those structures,so hydration will occur.Different reaction conditions and complex structures lead to different products,in other words,the hydration can be carried out in Markovnikov rule or anti-Markovnikov rule.Metal-vinylidene complexes play an important role in the development of organometallic chemistry.In this work,the reactions of RuCl₂?PPh₃?₃?compound 1?with different terminal alkynes were studied.Reaction conditions were investigated.The experimental results showed that when n?RuCl₂?PPh₃?₃?:n?terminal alkyne?=1:5,in the presence of dichloromethane and concentrated hydrochloric acid,heating at 40?for two hours,the reaction produced Ru?=C=CHPh??-C?=O?CH₂Ph?Cl?PPh₃?₂?compound 2?in 54.3%yield.This structure was confirmed by NMR and single crystal diffraction,with a vinylidene?=C=CPh?ligand and an acyl?-C?=O?CH₂Ph?ligand.Under the same condition,the reaction of RuCl₂?PPh₃?₃ with1-octyne obtained Ru?-C?=O??CH₂?₆CH₃?Cl?CO??PPh₃?₂?compound 3?in 80.0%yield.It was confirmed by NMR and IR.These complexes are proposed from nucleophilic addition of water onto Ru vinylidene intermediates,i.e.anti-Markovnikov hydration.Further decarbonylation of the acyl complexes under heating condition was studied.Decarbonylation and migration of ligands in compound 2 occurred while it was heated at80?for four hours in toluene,with Ru?-C?CH₂Ph?=CHPh?Cl?CO??PPh₃?₂?compound 4?as product.After decarbonylation of compound 3,a mixture of RuHCl?CO?₂?PPh₃?₂?compound5?and RuCl₂?CO?₂?PPh₃?₂?compound 6?was formed,with a ratio of 5:1.