A Localized Molecular Orbital Study of the Halogen Substitution Effect on 103Rh NMR Shielding in [CpRhX2]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.