Scandium-Mediated Formation of a Bis(tetrahydropentalene).

The reactivity of Li[Sc(COT'') ] (1; COT''=1,4-bis(trimethylsilyl)cyclooctatetraenyl) towards CoCl is considerably different from that of related lanthanide triple-decker sandwich complexes. In addition to the expected triple-decker complex Sc (COT'') (2), the complex Sc {μ-BTHP}(COT'') (3) is formed, which comprises the novel BTHP ligand (BTHP =bis(3,5-bis(trimethylsilyl)-1,3a,6,6a-tetrahydropentalene-1-yl)diide or bis(2,7-bis(trimethylsilyl)bicyclo[3.3.0]octa-2,7-dien-4-yl)diide, C H (SiMe ) ). The formation of 3 is likely facilitated by the fact that scandium prefers η ,η  coordination rather than highly symmetric η ,η  coordination, and the η -coordinated COT'' ligand in 1 is activated owing to a loss of aromaticity. Acid hydrolysis of 3 leads to air-stable H BTHP (4).