Selective C-C bond formation at diiron μ-aminocarbyne complexes

The reactions of [Fe-2{mu-CN(Me)R}(mu-CO)(CO)(2)(Cp)(2)]SO3CF3, (Cp=eta-C5H5,, R=Me 2a or CH2Ph 2b) with a variety of carbon nucleophiles result in C-C bond formation at different sites of the molecules depending on the nature of the carbanions: (i) R'Li (R'=Me, Bu-n or Ph) and R'MgCl (R'=Me, CH2Ph or Pr-i) added at the Cp ligand giving eta(4)-cyclopentadiene complexes [Fe-2{mu-CN(Me)R}(mu-CO)(CO)(2)(eta(4)-C5H5R')(Cp)] 3; (ii) Li2Cu(CN)R'(2), (R'=Me or Bu-n) and LiC=CR' (R'=Ph or p-tolyl) afforded the stable acyl complexes [Fe-2 {mu-CN(Me)R}(mu-CO)(CO){C(O)R'}(Cp)(2)] 4 and [Fe-2{mu-CN(Me)R}(mu-CO)(CO){C(O)C=CR'}(Cp)(2)] 5, respectively. With R not equal Me the NMR spectra of type 3-5 derivatives show the presence of two isomers arising from the double-bond character of the mu-C=N group ascertained from the crystal structure of [Fe-2(mu-CNMe2,)(mu-CO)(CO){C(O)Bu-n}(Cp)(2)] 4b. The structural study reveals the presence of interligand interactions involving the acyl oxygen and the mu-C=NMe2, moiety which is also in accord with an extended-Huckel calculation of the charge distribution.