derived from pentamethylcyclopentadiene can undergo reactions involving the methyl groups. For example, decamethyltungstocene dihydride undergoes dehydrogenation to give the tuck-in complex. The original example proceeded via sequential loss of two equivalents of H2 from decamethyltungstocene dihydride, Cp*2WH2. The first dehydrogenation step affords a simple tuck-in complex: (C5Me5)2WH2 → (C5Me5)(C5Me3(CH2)2)W + 2 H2 Redox When the non-Cp ligands are halides, these complexes undergo reduction to give carbonyl, alkene, and alkyne complexes that are useful reagents. A well-known example is titanocene dicarbonyl: Cp2TiCl2 + Mg + 2 CO → Cp2Ti(CO)2 + MgCl2 Reduction of vanadocene dichloride gives vanadocene. Olefin polymerization catalysis Although bent metallocenes are of no commercial value as olefin polymerization catalysts, studies on these compounds were highly influential on the industrial processes. Already in 1957 there were reports on the polymerization of ethylene using a catalyst prepared from Cp2TiCl2 and trimethyl aluminium. Reactions involving the related Cp2Zr2Cl2/Al(CH3)3 system revealed the beneficial effects of trace amounts of water for ethylene polymerization. It is now known that the partially hydrolyzed organoaluminium reagent methylaluminoxane ("MAO") gives rise to families of highly active catalysts. Work in this are led to constrained geometry complexes, which are not bent metallocenes, but exhibit related structural features. References Further reading , . Metallocenes Catalysts