A Localized Molecular Orbital Study of the Halogen Substitution Effect on 103Rh NMR Shielding in [Cp*RhX2]2, Where X = Cl, Br, or I.

103Rh NMR parameters and the bonding structure of three complexes of [Cp*RhX2]2, where X = Cl, Br, or I, have been studied with the help of natural bond orbitals (NBOs) and natural localized molecular orbitals (NLMOs). The complexes of [Cp*RhX2]2, where X = Cl, Br, or I, have similar bonding structures, with the major difference being in the degree of covalency of the Rh-X bonds. The decomposition of 103Rh NMR shielding into diamagnetic, paramagnetic, and spin-orbit terms shows that normal halogen dependence (NHD) of the 103Rh NMR shift is defined mostly by the paramagnetic term, with the spin-orbit term being significantly smaller. The decomposition of 103Rh shielding into spin-free NBO and NLMO contributions shows that 103Rh shielding is dominated by Rh d-orbital deshielding contributions. We explain the NHD of the 103Rh NMR shift with the increase in the energies of the virtual antibonding Rh-X orbitals along the X = Cl, Br, and I series. [ABSTRACT FROM AUTHOR]