Silica may be employed as a bidentate ligand to bis(neopentyl) fragments of titanium(IV) and zirconium(IV). The resulting supported organometallic complexes ( SiO) 2 M(CHCMe 3 ) 2 undergo thermolysis corresponding to their transformation to isolated neopentylidene complexes by extrusion of neopentane. The reactions are kinetically first-order and therefore deemed to be intramolecular. The products have the empirical formula ( SiO) 2 M CHCMe 3 , retaining two covalent interactions with oxygens of the silica surface which serve to immobilize and stabilize the neopentylidene complexes. For M=Zr, reaction with styrene results in formation of neohexene via metathesis; for M=Ti, styrene appears to undergo [2+2] addition to yield a stable titanacyclobutane. The neopentylidene complexes also react with ethylene, producing C 2 n oligomers.