Two novel stable silenes (t-BuMe2Si)(Me3Si)Si:Ad (5b) and (t-BuMe2Si)2Si:Ad (5c), where Ad = 2-adamantyl, were synthesized by a sila-Peterson-type reaction in which a ketone is reacted with a silyllithium reagent; e.g., reaction of adamantanone with (t-BuMe2Si)(Me3Si)2SiLi.3THF gives 5b. 5B and 5c are stable at room temp. for several months in the absence of nucleophiles, in contrast to (Me3Si)2Si:Ad (5a) which dimerizes instantaneously. However, they react instantaneously with H2O, alcs. and 1-methoxybutadiene to give the expected addn. products. Spectroscopic data for 5b and 5c as well as the x-ray mol. structure for 5b are reported. The C:Si bond length in 5b is 1.741 .ANG., significantly longer than in Me2Si:CH2, and in good agreement with ab initio calcns.