Reductive coupling of six carbon monoxides by a ditantalum hydride complex.

A ditantalum hydride complex undergoes head-to-head C-C coupling of six CO molecules under mild conditions to produce an octaanionic C(6)O(6) unit. During the reaction, eight-electron reduction of six CO molecules takes place. In the product, the C(6)O(6) unit is coordinated to four tantalum metals through six oxygen and two carbon atoms. The geometrical parameters within the Ta(4)C(6)O(6) core indicate significant contribution from a hexatriene-hexaolate form.