Microwave-assisted synthesis of cyclopentadienyl-cobalt sandwich complexes from diaryl acetylenes

Sealed tube microwave dielectric heating of diaryl acetylenes with cyclopentadienyl cobalt dicarbonyl at elevated temperature in p-xylene provides access to metallocenes in both the cyclobutadiene (Ar(4)C(4)CoCp) and cyclopentadienone (Ar(4)C(4)(C=O)CoCp) families. When compared with the traditional thermal approach, the current method offers dramatically reduced reaction times and, especially with respect to cyclopentadienone complexes, increased yields. In the case of an especially bulky diarylacetylene the microwave approach allows access to a complex that cannot be readily obtained under traditional thermal conditions. An initial microwave-promoted Sonogashira coupling may be employed for in situ generation of the diarylacetylene, although lower yields of the metallocene complexes are ultimately obtained.