The reaction of carboxylic acids RCOOH (R = tBu, Ph, Fc) with [Ru3(CO)12] in refluxing acetonitrile afforded dark purple/red solids. These reacted with phosphines in a 2:1 (Ru:P) ratio to form phosphine-substitued derivatives of the electron-deficient tetraruthenium chains, viz., [Ru4(CO)8(μ-OOCR)4(PR′3)2] (where R′ = Ph or OMe). © 2015 Elsevier B.V.