A comparison between CpCo-stabilized cyclopentadienone complexes and their O-alkylated or protonated congeners

The CpCo-stabilized tricyclic cyclopentadienone complexes 4 and 6 as well as the cyclopentadienonophane 8 were treated with an excess of triethyloxonium tetrafluoroborate. This yields, in case of 4 and 6, to the yellow colored O-ethylcobalticinium salts 5 and 7. In the case of 8 the alkylation yielded the mono- and bis-O-ethylcobalticinium salts 9 and 10, respectively. Protonation of the superphane 8 yields to the diprotonated superphane 11. X-ray investigations allowed a comparison of 5 and 11 with 4 and 8. This comparison shows that the CpCo units in 4 and 8 are more tightly bound to the butadiene units of the cyclopentadienone rings than to the CO groups. In the case of 5 and 11 the distances to all five carbons of the alkoxycyclopentadienyl units are approximately equal. This difference in the bonding was substantiated by model calculations on (η5-cyclopentadienone)(η5-cyclopentadienyl)cobalt (2) and its O-protonated form 12 as well as (η4-butadiene)(η5-cyclopentadienyl)cobalt (13) and the cobalticinium ion (14). The results show similarities between 2 and 13 as well as 12 and 14.