C-S and C-Se Bond Formation at Bridging Vinyliminium Ligands in Diiron Complexes

The vinyliminium complexes [Fe-2{-(1):(3)-C(R)C(R)CN(Me)(2)}(-CO)(CO)(Cp)(2)][SO3CF3] (R = Me, 3a; R = CO2Me, 3b; R = Ph, 3c) were treated with S-8 in the presence of tBuLi, undergoing fragmentation and affording the corresponding six-membered metallacyclic complexes [Fe(Cp)(CO){SC(R)=C(R)C(NMe2)S}] (5a-c). Complexes 5a-c result from cleavage of the diiron precursor and addition of S to the vinyliminium ligand to generate a dithiochelating ligand. Analogous reactions of the vinyliminium complexes [Fe-2{-(1):(3)-C(R)C(R)CN(Me)(Xyl)}(-CO)(CO)(Cp)(2)][SO3CF3] (R = Me, 3d; R = CO2Me, 3e), which contain a Xyl group (Xyl = 2,6-Me2C6H3) in place of a methyl, displayed a different outcome. Complex 3d afforded the diiron complex [Fe-2{-(1):(3)-C(Me)=C(CS2)C=N(Me)(Xyl)}(-CO)(CO)(Cp)(2)] (10), whereas 3e led to the formation of the five-membered metallacycle [Fe(Cp)(CO){C{N(Me)(Xyl)}C(CO2Me)C(CO2Me)S}] (11) together with the diiron complex [Fe-2{-(1):(3)-C(CO2Me)=C(S)C=N(Me)(Xyl)}(-CO)(CO)(Cp)(2)] (12). The formation of 10 and 12 implies C-H and C-C cleavage, respectively, and C-S bond formation without rupture of the diiron framework. The vinyliminium complexes 3a-d and also [Fe-2{-(1):(3)-C(Et)C(Et)CN(Me)(CH2Ph)}(-CO)(CO)(Cp)(2)][SO3CF3] (3f) reacted with gray selenium in the presence of tBuLi to afford the five-membered metallacycles [Fe(Cp)(CO){C{N(Me)R}C(R)C(R)Se}] (R = R = Me, 13a; R = Me, R = CO2Me, 13b; R = Me, R = Ph, 13c; R = Xyl, R = Me, 13d; R = CH2Ph, R = Et, 13f) in which one Se atom has been incorporated into the chelating ligand. The X-ray molecular structures of 5a and 13a have been determined.