Density functional theory calculations have been performed for the dimethylgallyl complexes of iron, ruthenium, and osmium [(eta(5)-C5H5)(L)(2)M(GaMe2] (M = Fe, Ru, Os; L = CO, PMe3) at the DFT/BP86/TZ2P/ZORA level of theory. The calculated geometry of the iron complex [(eta(5)-C5H5)(CO)(2)Fe(GaMe2)] is in excellent agreement with structurally characterized complex [(eta(5)-C5H5)(CO)(2)Fe((GaBu2)-Bu-t)]. The Pauling bond order of the optimized structures shows that the M-Ga bonds in these complexes are nearly M-Ga single bond. Upon going from M = Fe to M = Os, the calculated M-Ga bond distance increases, while on substitution of the CO ligand by PMe3, the calculated M-Ga bond distances decrease. The pi-bonding component of the total orbital contribution is significantly smaller than that of a-bonding. Thus, in these complexes the GaX2 ligand behaves predominantly as a sigma-donor. The contributions of the electrostatic interaction terms Delta E-elstat, are significantly smaller in all gallyl complexes than the covalent bonding Delta E-orb term. The absolute values of the Delta E-pauli, Delta E-int, and Delta E-elstat at contributions to the M-Ga bonds increases in both sets of complexes via the order Fe < Ru < Os. The Ga-C(CO) and Ga P bond distances are smaller than the sum of van der Waal radii and, thus, suggest the presence of weak intermolecular Ga-C(CO) and Ga-P interactions.