Reaction of Pentadienyl Complexes with Metal Carbonyls:  Synthetic, Structural, and Theoretical Studies of Metallabenzene π-Complexes

Abstract

The reaction of open and half-open sandwich complexes of iron and ruthenium with metal carbonyls was studied. Three types of complexes could be isolated: Carbonyl-bridged iron−ruthenium dimers with cyclopentadienyl and pentadienyl terminal ligands, dimetallic iron carbonyl complexes with a bridging σ,π-coordinated pentadienyl ligand, and ruthenium complexes with one or two π-coordinated ruthenabenzene ligands. The latter are the first ever isolated bis(metallabenzene) π-complexes. The X-ray structures of C 5 Me 5 Ru(CO) 4 Fe(C 7 H 11 ), (μ-C 7 H 10 )Fe 2 (CO) 6, and [(C 8 H 11 )Ru(CO) 3 ] 2 Ru are reported. Density functional calculations have been used to better understand the bonding in metallabenzene complexes. The electron localization function (ELF) clearly confirms metal−metal bonding interactions in the complexes studied. In particular, the bis(metallabenzene) complex 13 is found to exhibit a three-center bonding attractor in the ELF in its stable syn-eclipsed conformation but two two-center attractors in the ca. 30 kJ mol -1 less stable anti-eclipsed arrangement. The frontier orbitals of metallabenzenes exhibit very large participation of the ring metal. When metallabenzenes act as ligands to other metal fragments, direct metal−metal interactions are thus expected to be a general feature of the complexes, unless they are replaced by other interactions, e.g. by protonation. Natural population analyses suggest that the σ-donor abilities of the electron-rich d 8 metallabenzene fragments predominate over their π-acceptor character.