A designed, enantiomerically pure, fused cyclopentadienyl ligand with C2 symmetry. Synthesis and use in enantioselective titanocene-catalyzed hydrogenations of alkenes.
The synthesis of title cyclopentadienyl ligand I with C2 symmetry is described. I was designed to maximize the steric encumbrance of both diastereotopic faces, an effect achieved by annelation involving a stereospecifically 1,5-disubstituted bicyclo[2.2.2]octane frame. The system has been complexed to cobalt, titanium, and zirconium as model transition metals to demonstrate its effective function as a ligand in the formation of potentially catalytic organometallic complexes. As an example of this potential, the resulting titanocene dichloride was a catalyst precursor in the enantioselective hydrogenation of 2-phenyl-1-butene and 2-ethyl-1-hexene with unprecedented stereoselectivity.
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