Alkyne Substitution on Cobaltocenium Triflates

Cobaltocenium triflates consisting of a CpCo‐capped η 5 ‐1‐trifluoromethylsulfonyloxy‐2,3,4,5‐tetrapropylcyclopentadienyl ring were substituted at the Cp ring by a trialkylsilylethynyl group to yield the R–CpCo capped tetra‐ n ‐propylcyclopentadienone with R = C 2 SiMe 3 ( 11a ) and R = C 2 SiEt 3 ( 11b ). The parent system with R = C 2 H ( 11c ) was generated by hydrolyzing the SiR 3 groups of 11a and 11b . The trialkylsilyl‐1,3‐butadiyne derivatives with alkyl = CH 3 ( 11d ) and alkyl = C 2 H 5 ( 11e ) were derived from 11c by using a Cadiot–Chodkiewicz coupling with bromo(triethylsilyl)acetylene. Removal of the SiEt 3 protecting group led to 11f . The alkynes 11c and 11f could be dimerized to 13a and 13b by a Hay coupling. These results were confirmed by X‐ray diffraction studies on the starting materials 7 , 8 , and 12 as well as the derivatives 11c , 11f , and 13a .(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)