CARBON-CARBON BOND FORMATION IN THE REACTIONS OF DIIRON MU-CARBYNE COMPLEXES WITH 2-THIENYLLITHIUM, SYNTHESIS AND STRUCTURAL CHARACTERIZATION

The reactions of 2-thienyllithium (Lith) with a variety of carbyne com plexes result in C-C bond formation at different sites of the molecule s. The thiocarbyne cis-[Fe-2(mu-CSMe)(mu-CS)(CO)(2)(Cp)(2)](+) 1 (Cp=e ta-C5H5) underwent Cp addition forming e-2(mu-CSMe)(mu-CS)(CO)(2)(Cp)( eta(4)-C(5)H(5)th)] 3 and trace amounts of [Fe-2(mu-CSMe)(mu-CS)-{C(O) th}(CO)(Cp)(2)] 4. By contrast all the aminocarbynes [Fe-2(mu-CNRR')(m u-CO)(CO)(2)(Cp)(2)](+) (R=R'=Me 2a; R=Me, R'=PhCH2 2b) and [Ru-2(mu-C NMe2)(mu-CO)(CO)(2)(Cp)(2)](+) 6 gave the corresponding acyl derivativ es [M-2(mu-CNRR')(mu-CO)(CO){C(O)th}(Cp)(2)] (M=Fe 5a and 5b; R=R'=Me, M=Ru 7). When R not equal R', the NMR spectra of these neutral specie s show the presence of two isomers alpha and beta arising from hindere d rotation around the mu-C=N bond. The relevance of these reactions is discussed in terms of selective C-C bond formation in comparison with analogous carbon nucleophile addition at [Fe-2(mu-CSMe)(mu-CO)(CO)(2) (Cp)(2)](+). The crystal structures of 3 and [Fe-2{mu-CN(ME)CH2Ph}(mu- CO)(CO){C(O)th}(Cp)(2)] 5b are reported and discussed. The conformatio n of the Fe2C2 diamond is shown to depend on the nature of the bridgin g ligands. Simple models of electronic structure are outlined on the b asis of the geometric evidence.