Organolanthanide complexes of the type Cp'2LnR (Cp' = eta-5-Me5C5; Ln = La, Nd, Sm, Y, Lu; R = Nd; R = CH(SiMe3)2), Cp'2Sm, and Cp'2Sm(THF)2 catalyze the rapid dehydrogenative oligomerization of PhSiH3. Kinetic and mechanistic arguments exclude the importance of metal-centered redox processes in the catalytic cycle and support instead ''four-center'' ''heterolytic'' bond-scission/bond-forming sequences.