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

The CpCo-stabilized tricyclic cyclopentadienone complexes 4 and 6 as well a s the cyclopentadienonophane 8 were treated with an excess of triethyloxoni um tetrafluoroborate. This yields, in case of 4 and 6, to the yellow colore d O-ethylcobalticinium salts 5 and 7. In the case of 8 the alkylation yield ed the mono- and bis-O-ethylcobalticinium salts 9 and 10, respectively. Pro tonation of the superphane 8 yields to the diprotonated superphane 11. X-ra y investigations allowed a comparison of 5 and 11 with 4 and 8. This compar ison shows that the CpCo units in 4 and 8 are more tightly bound to the but adiene units of the cyclopentadienone rings than to the CO groups. In the c ase of 5 and 11 the distances to all five carbons of the alkoxycyclopentadi enyl units are approximately equal. This difference in the bonding was subs tantiated by model calculations on (eta (5)-cyclopentadienone)(eta (5)-cycl opentadienyl)cobalt (2) and its O-protonated form 12 as well as (eta (4)-bu tadiene)(eta (5)-cyclopentadienyl)cob (13) and the cobalticinium ion (14). The results show similarities between 2 and 13 as well as 12 and 14. (C) 20 00 Elsevier Science S.A. All rights reserved.