Diaminostannylenes react with [Ru-3(CO)(12)] without cluster fragmentation to give carbonyl substitution products regardless of the steric demand of the diaminostannylene reagent. Thus, the Sn3Ru3 clusters [Ru-3{mu-Sn((NCH2Bu)-Bu-t)(2)C6H4}(3)(CO)(9)] (4) and [Ru-3{mu-Sn(HMDS)(2)}(3)(CO)(9)] (6) [HMDS = N(SiMe3)(2)] have been prepared in good yields by treating [Ru-3(CO)(12)] with an excess of the cyclic 1,3-bis(neo-pentyl)-2-stannabenzimidazol-2-ylidene and the acyclic and bulkier Sn(HMDS)(2), respectively, in toluene at 110 degrees C. The use of smaller amounts of Sn(HMDS)(2) (Sn/Ru-3 ratio = 2.5) in toluene at 80 degrees C afforded the Sn2Ru3 derivative [Ru-3{mu-Sn(HMDS)(2)}(2)(mu-CO)(CO)(9)] (5). Compounds 5 and 6 represent the first structurally characterized diaminostannylene-ruthenium complexes. While a further treatment of 5 with Ge(HMDS)(2) led to a mixture of uncharacterized compounds, a similar treatment with the sterically alleviated diaminogermylene Ge((NCH2Bu)-Bu-t)(2)C6H4 provided [Ru-3{mu-Sn(HMDS)(2)}(2){mu-Ge((NCH2Bu)-Bu-t)(2)C6H4}(CO)(9)] (7), which is a unique example of Sn2GeRu3 cluster. All these reactions, coupled to a previous observation that [Ru-3(CO)(12)] reacts with excess of Ge(HMDS)(2) to give the mononuclear complex [Ru{Ge(HMDS)(2)}(2)(CO)(3)] but triruthenium products with less bulky diaminogermylenes, indicate that, for reactions of [Ru-3(CO)(12)] with diaminometalenes, both the volume of the diaminometalene and the size of its donor atom (Ge or Sn) are of key importance in determining the nuclearity of the final products.