Cp-Functionalized Building Blocks for Polymetallacarborane Assemblies. Multinuclear Cobaltacarborane Complexes on Fulvalene and 1,3,5-Tris(cyclopentadienyl)benzene Scaffolds1

The introduction of organic and inorganic substituents onto η 5 -C 5 H 5 (Cp) ligands in the small cobaltacarboranes CpCo(Et 2 C 2 B 4 H 4 ) and nido -CpCo(Et 2 C 2 B 3 H 5 ) and their derivatives has been explored, together with metal-promoted C−C coupling to generate polycluster species featuring Cp−Cp and Cp−benzene linkages. This approach supplements alternative synthetic strategies based on functionalization of boron vertexes via metal-promoted B−C coupling, as described in a series of recent papers from our group, 4,5 and affords complexes of novel architecture as well as improved routes to previously known types. Among the new compounds are triple-sandwich trinuclear and hexanuclear benzene-centered complexes in which three cobaltacarborane units are anchored to a central 1,3,5-(η 5 -C 5 H 4 ) 3 C 6 H 3 hydrocarbon scaffold. The fulvalene-bridged dinuclear species [(2,3-Et 2 C 2 B 4 H 4 )Co(η 5 -C 5 H 4 )] 2 ( 7 ) and ( closo -2,3-Et 2 C 2 B 4 H 4 )( nido -2,3-Et 2 C 2 B 3 H 5 )Co 2 (η 5 -C 5 H 4 ) 2 ( 8 ), previously obtained by Davis et al. 7 from the fulvalenide dianion, were prepared in this work directly from the CpCo(Et 2 C 2 B 4 H 4 ) and nido -CpCo(Et 2 C 2 B 3 H 5 ) monomers. Apically substituted B(7)-trimethylsilylethynyl derivatives of 7 were also synthesized. New compounds were characterized via multinuclear NMR, IR, UV−visible (in some cases), and mass spectroscopy.