Selective formation of one or two C-C bonds promoted by carbanion addition to [Fe-2(cp)(2)(CO)(2)(mu-CO)(mu-CSMe)](+)

The reactions of [Fe-2(cp)(2)(CO)(2)(mu-CO)(mu-CSMe)]CF3SO3 (1; cp=eta-C5H5) with a variety of carbon nucleophiles results in C-C bond formation at different sites of the molecule. (allyl)-MgCl (allyl=C3H5) undergoes cp addition to form [Fe-2(cp)(eta(4)-C5H5-allyl)(CO)(2)(mu-CO)(mu-CSME)] (2) and the alkylidene complex [Fe-2(cp)(eta-C5H4-allyl)(CO)(2)(mu-CO){mu-C(SMe)H}] (3), derived from cp to mu-C hydrogen migration. Li2Cu(CN)R(2) adds at the mu-C atom to yield [Fe-2(cp)(2)(CO)(2)(mu-CO){mu-C(SMe)R}] (R=Ph, 4; R=Me, 8), [FeFe(cp)(2)(CO)(mu-CO){mu-C(SMe)R}] (R=Ph, 5; R=Me, 9), and [Fe-2(cp)(2)(CO)(mu-CO){mu-C(eta(2)-Ph)Ph}] (6) or the vinylidene derivative [Fe-2(cp)(2)(CO)(mu-CO)(mu-C=CH2)] (10) in the case of phenyl or methyl organocuprate reagents, respectively. The latter complexes are the result of C-SMe bond braking occurring, through different reaction paths, in 4 and 8. Likewise, the formation of [Fe-2(cp)(2)(CO)(mu-CO){mu-C=C(CN)(2)}] (11) from 1 and NaCH(CN)(2) occurs via a direct addition at the mu-C carbon followed by HSMe elimination. The nucleophilic attack at the terminal CO in 1 is achieved with LiC=CPh, which forms two new C-C bonds in the alkylidene complex [FeFe(cp)(2)(CO)(mu-CO){mu-C(SMe)C(O)CCPh}] (12) after C(O)CCPh migration from Fe to the bridging carbene carbon. The analogous [FeFe(cp)(2)(CO)(mu-CO){mu-C(SMe)C(O)(2-th)}] (13; 2-th=2-C4H3S) and [Fe-2(cp)(eta(4)-C5H5-(2-th)(CO)(2)(mu-CO)(mu-CSMe)] (14) are obtained from 1 and Lith via addition at the CO and cp groups, respectively. The relevance of these reactions is discussed in terms of selective C-C bond formation that, if it occurs at the cp or CO terminal ligands, favors the hydrogen migration (e.g. formation of 3) or the carbyne-carbonyl migratory coupling (e.g. formation of 12 and 13), respectively. The X-ray structures of [Fe-2(cp)(2)(CO)(mu-CO){mu-C(eta(2)-Ph)Ph}] (6) and [FeFe(cp)(2)(CO)(mu-CO){mu-C(SMe)C(O)(2-th)}] (13) have revealed the peculiarity of the Ph and SMe group coordination to the iron. Their structural features are discussed in comparison with those of analogous complexes.