The trimetallic clusters [Ru3(CO)10(dppm)], [Ru3(CO)12] and [RuCo2(CO)11] react with a number of multifunctional secondary phosphine and tertiary arsine ligands to give products consequent on carbonyl substitution and, in the case of the secondary phosphines, PH activation. The reaction with the unresolved mixed P/S donor, 1-phenylphosphino-2-thio(ethane), HSCH2CH2PHPh ( LH2), gave two products under various conditions which have been characterised by spectroscopic and crystallographic means. These two complexes [Ru3(μ-dppm)(H)(CO)7(LH)] and [Ru3(μ-dppm)(H)(CO)8(LH)Ru3(μ-dppm)(CO)9], show the versatility of the ligand, with it chelating in the former and bridging two Ru3 units in the latter. The stereogenic centres in the molecules gave rise to complicated spectroscopic data which are consistent with the presence of diastereoisomers. In the case of [Ru3(CO)12] the reaction with LH2 gave a poor yield of a tetranuclear butterfly cluster, [Ru4(CO)10(L)2], in which two of the ligands bridge opposite hinge wingtip bonds of the cluster. A related ligand, HSCH2CH2AsMe(C6H4CH2OMe), reacted with [RuCo2(CO)11] to give a low yield of the heterobimetallic Ru–Co adduct, [RuCo(CO)6(SCH2CH2AsMe(C6H4CH2OMe))], which appears to be the only one of its type so far structurally characterised.The secondary phosphine, HPMe(C6H4(CH2OMe)) and its oxide HP(O)Me(C6H4(CH2OMe)) also react with the cluster [Ru3(CO)10(dppm)] to give carbonyl substitution products, [Ru3(CO)5(dppm)(μ2-PMe(C6H4CH2OMe))4], and [Ru3H(CO)7(dppm)(μ2,η1-P(O)Me(C6H4CH2OMe))]. The former consists of an open Ru3 triangle with four phosphide ligands bridging the metal–metal bonds; the latter has the O atom symmetrically bridging one Ru–Ru bond, the P atom being attached to a non-bridged Ru atom.