Structure and bonding analysis of dihalogallyl and dimethylgallyl complexes of molybdenum and tungsten [(η5-C5H5)(CO)3M(GaX2)] (M = Mo, W; X = Cl, Br, I, Me): A theoretical study

The electronic, molecular structures and bonding of the terminal neutral dihalogallyl and dimethylgallyl complexes of molybdenum and tungsten [(eta(5)-C5H5)(CO)(3)M(GaX2)] (M = Mo, W; X = Cl, Br, I, Me) were investigated at the DFT/BP86/TZ2P/ZORA level of theory. The calculated geometry of molybdenum complex [(eta(5)-C5H5)(CO)(3)Mo(GaMe2)] is in excellent agreement with structurally characterized complex [(eta(5)-C5H5)(CO)(3)Mo((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. The gallium bound substituent exerts an influence on the length of the M-Ga bonds. The M-Ga bond distances are longer for dimethylgallyl complexes than the dihalogallyl complexes. The Mayer bond order of the M-Ga bonds decrease on going from X = Cl to Me, indicating progressive weakening of the M-Ga bond. The M-Ga sigma bonding orbitals are significantly polarized towards the metal atom. The pi-bonding component of the total orbital contributions is significantly smaller than that of sigma-bonding. Thus, in these complexes the GaX2 ligand behaves predominantly as a sigma-donor. Orbital contributions for the interactions between neutral fragments [(eta(5)-C5H5)(CO)(3)M] and [GaX2] are larger while the electrostatic interactions, interaction energies and bond dissociation energies are significantly smaller than the values obtained for the interactions between ionic fragments [(eta(5)-C5H5)(CO)(3)M](+) and [GaX2](-). The Ga-C(CO) bond distances are smaller than the sum of van der Waal radii (Ga-C(CO) = 2.60 angstrom) and thus, suggest the presence of weak inter-molecular Ga-C(CO) interactions. (C) 2011 Elsevier B.V. All rights reserved.