The reaction of 1,4,8,11-tetrathiacyclotetradeca-2,9-diyne (7) with C 5 H 4 (CO 2 Me)Co(CO) 2 (8) and C 5 H 4 (SiMe 3 )Co(CO) 2 (10) led to the tricyclic cyclopentadienone complexes 9 and 11. In both species the CO was inserted into a former triple bond. This observation led to the preparation of the tetrathiaalkyl-and tetrathiaaryl-substituted C 5 H 4 (CO 2 Me)Co-capped cyclobutadiene complexes 23 and 27-30. When these compounds were heated under a pressurized CO atmosphere at 170 °C, the corresponding cyclopentadienone complexes 9, 15, and 31-33 were formed. Model calculations at the B3LYP level of theory on tetrasubstituted (R ) CH 3 , SH, (CH 2 ) 3 , S-CH 2 -S) CpCo-capped cyclobutadiene complexes showed that the substitution, especially by SH and S-CH 2 -S, considerably lowered the energy of the assumed intermediate metallacycles 35 and 36, which opens the possibility of reaction.

With a little help from the ferrocenyl catalyst ((−)‐1), a wide array of α‐arylalkanoic acid derivatives can be produced from the catalytic asymmetric coupling of ketenes with aldehydes (see scheme). The enol esters are readily transformed into other useful families of compounds such as carboxylic acids and alcohols.

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CpCo-capped tetra-n-propylcyclopentadienone complexes were O-alkylated and O-acylated. Reactions of the O-triflated product with organolithium compounds afford a substitution of the Cp ring in 40-80% yield; as products the RCpCo-capped tetra-n-propyl-cyclopentadienone complexes were isolated.