Cu+ association to some Ph-X (X = OH, NH2, CHO, COOH, CF3) phenyl derivatives.: A comparison with Li+ complexes

The complexes of Cu+ with phenol, aniline, benzaldehyde, benzoic acid, and trifluromethyl-benzene were investigated through the use of MP2 and density functional theory (DFT) methods. Both harmonic vibrational frequencies and optimized geometries were obtained at the B3LYP/6-311G(d,p) and MP2(full)/6-311G(d,p) levels of theory. Final energies were obtained through single point B3LYP/6-311+G(3df,2p)//B3LYP/6-311G(d,p) calculations. The interactions of Cu+ with these aromatic compounds have a non-negligible covalent character, which clearly differentiate Cu+-complexes from the corresponding Li+-complexes. These dissimilarities are reflected in the geometries, binding energies and infrared spectra of the most stable adducts. For Li+ only conventional pi-complexes should be expected when interacting with aniline, while Cu+ attaches preferentially to the para carbon atom. For phenol, besides the conventional pi-complexes, a 12% of oxygen attached species are expected to be found upon Li+ association. Conversely, no oxygen attached species should be formed in reactions of phenol with Cu+. For benzoic acid and benzaldehyde, Li+ aligns with the dipole moment of the base, interacting exclusively with the carbonyl oxygen in the plane of the molecule. This is also the case in Cu+-benzoic acid complex, while in the Cu+-benzaldehyde complex the metal ion also interacts with the aromatic pi-system. Cu+ binding enthalpies (BEs) are systematically larger (about 1.3 times) than Li+ BEs. The covalent character of Cu+ interactions is associated with electron donations from bonding (pi) orbitals or lone-pairs of the base toward the 4s empty orbital of the metal and with back-donations from the occupied d orbitals of the metal toward antibonding (pi*) empty orbitals of the base. This non-negligible covalent character is also reflected in a rough correlation between the calculated Cu+ BEs and the available experimental proton affinities that does not exist for Li+ BEs. (C) 2005 Elsevier B.V. All rights reserved.