The serendipitous isolation of a dinuclear iron(II) complex with a bridging η2: η2-trans-butadiene reveals the stabilizing effect of benzyl-isocyanide co-ligands

The unexpected isolation and crystallographic characterization of the 1,3-butadiene complex [{FeCp (CNBn)2}2(mu-eta 2:eta 2-trans-C4H6)][CF3SO3]2, 3 (Cp = eta 5-C5H5, Bn = CH2Ph), represents a rare example of bridgingtrans coordination of the butadiene ligand between two iron(II) fragments. An extensive comparative DFT study was conducted to elucidate the bonding of butadiene in 3 and related complexes. This study unveiled the stabilizing contribution provided by intramolecular interactions involving the diene moiety and the ring electrons of the phenyl groups belonging to CNBn.