Structure and bonding in haloarylgallyl complexes of iron, ruthenium and osmium [(η5-C5H5)(CO)2M{Ga(X)(Ph)}]: A theoretical study

Density Functional Theory calculations have been performed for the halophenylgallyl complexes of iron, ruthenium and osmium [(η5-C5H5)(CO)2M(Ga(X)Ph)] (M = Fe, Ru, Os; X = Cl, Br, I) at the DFT/BP86/TZ2P/ZORA level of theory. The calculated geometry of iron complexes [(η5-C5H5)(CO)2Fe(Ga(Cl)Ph)] and [(η5-C5H5)(CO)2Fe(Ga(I)Ph)] is in excellent agreement with structurally characterized complexes [(η5-C5H5)(CO)2Fe(Ga(Mes∗)Cl)], [(η5-C5Me5)(CO)2Fe(Ga(Mes∗)Cl)] and [(η5-C5Me5)(CO)2Fe(Ga(Mes)I)] (Mes = C6H2Me3-2,4,6; Mes∗ = C6H2tBu3-2,4,6). The M–Ga bond distances as well as Mayer bond order of the M–Ga bonds suggest that the M–Ga bonds in these complexes are nearly M–Ga single bond. The π-bonding component of the total orbital contribution is significantly smaller than that of σ-bonding. Thus, in these complexes the Ga(X)Ph ligand behaves predominantly as a σ-donor. The contributions of the electrostatic interaction terms ΔEelstat are significantly smaller in all gallyl complexes than the covalent bonding ΔEorb term. The absolute values of the ΔEPauli, ΔEint and ΔEelstat contributions to the M–Ga bonds increase in both sets of complexes via the order Fe < Ru < Os. In the complexes [(η5-C5H5)(Me3P)2Fe(Ga(X)Ph)] (X = Cl, Br, I), interaction energy as well as bond dissociation energy decrease upon going from X = Cl to X = I.