Reaction of CH2(Ph2PSe)(2) (dppmSe(2)) with [Ru-3(CO)(12)]. Fluxional behaviour of [Ru-3(mu(3)-Se)(2)(CO)(7)(mu-dppm)] and crystal structures of [Ru-4(mu(4)-Se)(2)(mu-CO)(CO)(8)(mu-dppm)]center dot MeOH and [Ru-6(mu(3)-Se)(4)(CO)(12)(mu-dppm)(2)]center dot CH2Cl2

The reaction of [Ru-3(CO)(12)] with dppmSe(2) afforded the open-triangular nido cluster [Ru-3(mu(3)-Se)(2)(CO)(7)(mu-dppm)] 1, the closo-octahedral sp ecies [Ru-4(mu(4)-Se)(2)(mu-CO)(CO)(8)(mu-dppm)] 2 and the cubane-like cage [Ru-4(mu(3)-Se)(4)(CO)(10)(mu-dppm)] 3. Multinuclear NMR data indicated a fluxional behaviour for 1 in solution consisting both in the reversible mig ration of a metal-metal bond in the cluster and in the oscillation of the m ethylene group of the dppm ligand. Pyrolysis of 1 gave the condensation der ivative [Ru-6(mu(3)-Se)(4)(CO)(12)(mu-dppm)(2)] containing a central 64-ele ctron butterfly core.