Ruthenium Complex-Catalyzed Formation and Cleavage of Carbon-Carbon σ-Bonds. On the Requirement of Highly Qualified Tuning of the Reaction Conditions

Characteristic aspects of ruthenium complex-catalyzed carbon-carbon bond forming reactions and carbon-carbon σ-bond cleavage reactions are discussed. It is pointed out that these ruthenium complex-catalyzed reactions require highly qualified tuning of reaction conditions with substrates to attain high yields and selectivities of the products. In the [2 + 2] cycloaddition of alkynes and norbornenes catalyzed by RuH₂(CO)(PPh₃)₃, Ru(cod)(cot)/PBu₃ [cod: 1,5-cyclooctadiene, cot: 1,3,5-cyclooctatriene] and Cp*RuCl(cod) [Cp*: pentamethylcyclopentadienyl] giving cyclobutenes, matching of the alkyne derivative with the catalyst is essential. In the Ru₃(CO)₁₂-catalyzed intramolecular carbonylative cyclization of 1,6-enynes giving bicyclic cyclopentenones, remarkable solvent effects are observed. Linear codimerization of diphenylacetylene and methyl acrylate by Ru(cod)(cot)/pyridine; however, for the reaction of diphenylacetylene with N,N-dimethylacrylamide, pyridine is not required. N,N-Dimethylacrylamide works as a ligand as well as the substrate. Ru(cod)(cot)/dimethyl fumarate catalyzed novel dimerization of 2,5-norbornadiene in THF to give pentacyclo[6.6.0.0^2,6.0^3,13.O^10,14]tetradeca-4,11-diene (PCTD) via carbon-carbon bond cleavage. In DMSO, the major product is heptacyclo[6.6.0.0^2,6.0^3,13.0^4,11.0^5,9.0^10,14]tetradecane (HCTD) in place of PCTD, and no cleavage of the carbon-carbon bond occurs. The first catalytic deallylation of tert-homoallyl alcohols is achieved. The presence of an excess of allyl acetate is essential. The reaction can be applied to a ring-opening reaction of cyclic homoallyl alcohols. The reasons for the requirement of highly qualified tuning of the reaction conditions for the ruthenium catalysts are discussed comparing with the catalytic activities of palladium complexes.

ruthenium - catalysis - alkenes - alkynes - cleavage