The reaction of 1 equiv of primary silanes, SiH3R (R = Ph, Mes), with [RhIr(CO)(3)(dppm)(2)] yields mono(silylene)-bridged complexes of the type [RhIr(H)(2)(CO)(2)(mu-SiHR)(dppm)(2)] (R = Ph or Mes), while for R = Ph the addition of 2 equiv yields the bis(silylene)-bridged complexes, [RhIr(CO)(2)(mu-SiHPh)(2)(dppm)(2)]. The kinetic isomer of this bis(silylene)-bridged product has the phenyl substituent axial on one silylene unit and equatorial on the other, and in the presence of excess silane this rearranges to the thermodynamically preferred "axial-axial" isomer, in which the phenyl substituents on each bridging silylene unit are axial and parallel to one another. The reaction of 1 equiv of diphenylsilane with [RhIr(CO)(3)(dppm)(2)] produces the mono(silylene)-bridged product, [RhIr(H)(2)(CO)(2)(mu-SiPh2)(dppm)(2)], and the subsequent addition of silane in the presence of CO yields the silyl/silylene product [RhIr(H)(SiPh2H)(CO)(3)(kappa(1)-dppm)(mu-SiPh2)(dppm)]. The reaction of [RhIr(CO)(3)(dppm)(2)] with 2 equiv of SiH2Me2 yields the analogous product [RhIr(H)(SiMe2H)(CO)(3)(kappa(1)-dppm)(mu-SiMe2)(dppm)]. Low-temperature NMR spectroscopic observation of some key intermediates, such as [RhIr(H)(SiH2Ph)(CO)(2)(mu-CO)(dppm)(2)], formed during the formation of the mono(silylene)-bridged species provides evidence for a mechanism involving initial Si-H bond activation at Rh, followed by the subsequent Si-H bond activation at Ir. The Si-H bond activation of a second equivalent of silane seems to be initiated by dissociation of the Rh-bound end of one diphosphine. The reaction of diphenylsilane with the cationic complex [RhIr(CH3)(CO)(2)(dppm)(2)][CF3SO3] gives rise to a different reactivity pattern in which Si-H bond activation is initiated at Ir. In this case, the cationic silyl-bridged species, [RhIr(CH3)(CO)(2)(kappa(1):eta(2)-SiHPh2)(dppm)(2)][CF3SO3], contains an agostic Si-H interaction with Rh. In solution, at ambient temperature, this complex converts to two species, [RhIr(H)(COCH3)(CO)(mu-H)(mu-SiPh2)(dppm)(2)][CF3SO3] and [RhIr(CO)(2)(mu-H)(mu-SiPh2)(dppm)(2)] [CF3SO3], formed by the competing methyl migration to CO and reductive elimination of methane, respectively. In the diphenylsilylene dihydride product, a weak interaction between the bridging silicon and the terminal Ir-bound hydride is proposed on the basis of NMR evidence.