Reactions of Ruthenium Allenylidene Complex Containing a Cyclopropyl Group and Ring Opening Reaction Catalyzed by Ruthenium Chloride

The allenylidene complex 3 was prepared by the treatment of a CH2Cl¬¬¬¬2 solution of Cp(PPh3)2RuCl with 1-cyclopropyl-1-phenylprop-2-yn-1-ol, 1a in the presence of NH4PF6. The reaction of 2 with Cp(PPh3)2RuCl and NH4PF6 in CH2Cl2 proceeded via an intramolecular cyclization to afford the carbene complex 4. Reactions of 3 with a variety of nucleophiles, like NaBH4 and pyrrole formed 5, 6 and 8 respectively. Besides, Grignard reagents could attack on C¬γ of 3 to acquire the neutral acetylide complexes 10a-b. Complexes 10a-b underwent protonation reactions affording the corresponding vinylidene complexes 11a-b. When the allenylidene complex 3 was dissolved in CH2Cl¬2 or CHCl3 in the presence of amine, ring-opening of the cyclopropane group occurred. For instances, a CH2Cl2 solution of 3 was treated with triethylamine, and the acetylide complex 12a was obtained. It is noteworthy that the reaction of 3 with propargyl amine in the presence of methanol proceeds via a retro-ene process to give 17a. Furthermore, iodide could attack the cyclopropyl group of 3, which was followed by a subsequent C-C bond formation with the halides serving as a leaving group to yield complex 15. Complex 3 could also react with acid to yield a carbyne intermediate, and then water could act as a nucleophile to induce ring opening to give the final carbene product 16. The reaction of 18a with Cp(PPh3)2RuCl leads to the formation of 19a. The cyclization may proceed via an allenylidene intermediate which was not observed in this system. Interestingly, treatment of 1a with water in the presence of catalytic amount of ruthenium chloride complex Cp(PPh3)RuCl afforded (E)-1,3-enynes 21a with high selectivity.