(η5-Cyclopentadienyl)[η2-bis(tert-butylsulfonyl)acetylene](carbonyl)cobalt: An electrophilic reagent to yield CpCo-stabilized cyclobutadiene derivatives

Various substituted (R=H, CH3, SiMe3, CO2Me, COCH3, EtMe4) (R-η5-cyclopentadienyl)[η2-bis(tert-butylsulfonyl)acetylene](carbonyl)cobalt complexes (8–13) proved to be very reactive towards alkynes under rather mild conditions. Dithiaacetylenes reacted at room temperature, dialkyl- and diarylalkynes had to be heated to 80–90 °C to yield the corresponding R-CpCo-stabilized cyclobutadiene complexes 18–37 and 39–42. X-ray investigations on 24–26, 30, 36 and 39–41 showed almost equal CC bond lengths in the cyclobutadiene rings.