A stoichiometric reaction of [Ru(eta(4)-2,3-dimethyl-1,3-butadiene)(eta(4)-1,5-COD)(NCMe)] (1a) with diphenylketene at room temperature produces a new zero-vatent complex [Ru(eta(4)-4,5-dimethyl-1,1-diphenylhexa-3,5-diene-2-one)(eta(4)-1,5-COD)(NCMe)] (2aa) in 92% yield. This is the first example of conjugated dienyl ketone formation from 1,3-dienes and ketene. Similarly, the treatment of la with ethylphenylketene produces the decarbonylated coupling product (Z)-5-alkyl-2,3-dimethyl-5-phenylhepta-1,4-diene (5) in 77% yields.