Tricarbonylruthenacyclopentanes were successfully synthesized by in situ reduction of RuCl3 with Zn-Cu/CO in the presence of N-vinylacetamides and electron-deficient alkenes such as ethyl acrylate, dimethyl fumarate, and dimethyl maleate. X-ray crystallography of the ruthenacyclopentanes revealed that the three carbonyl ligands occupied coordination sites facially, and the ruthenacycle moiety was stabilized by coordination with the acetamido oxygen atom. When the ruthenacyclopentanes in toluene or DMA were heated to 130 °C for 24 h, linear codimers of the alkenes were formed in moderate to good yield. Both the ruthenacyclopentane and the RuCl3/Zn-Cu/alcohol system showed catalytic activity for the linear codimerization of alkenes, affording the codimers in good yield. The results of stoichiometric and catalytic reactions revealed that the codimerization can proceed via ruthenacyclopentane intermediates.