CpCo-Stabilized Cyclopentadienones from Cyclobutadiene Complexes: Experimental and Theoretical Investigations

The reaction of 1,4,8,11-tetrathiacyclotetradeca-2,9-diyne (7) with C5H4(CO2Me)Co(CO)2
(8) and C5H4(SiMe3)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 C5H4(CO2Me)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 = CH3, SH, (CH2)3, S−CH2−S) CpCo-capped cyclobutadiene complexes showed
that the substitution, especially by SH and S−CH2−S, considerably lowered the energy of
the assumed intermediate metallacycles 35 and 36, which opens the possibility of reaction.