An osmium complex bearing a terminal hydrogen-substituted stannylene ligand, Cp-star((Pr3P)-Pr-i)(H)Os=SnH(trip) (1) (trip = 2,4,6-triisopropylphenyl), has been prepared by stannylene extrusion, and the complex has been structuratly characterized. Complex 1 coordinates Lewis bases and activates the O-H bonds of water and methanol. Most interestingly, 1 converts to the metallostannylene complex Cp-star((Pr3P)-Pr-i)(H)(2)OsSn(trip) (2) thermally or photochemically by what appears to be a radical process.