Ligand Electrochemical Parameter Approach to Molecular Design. σ-Donation, π-Back Donation, and Other Metrics in Ruthenium(II) Dinitrogen Complexes.

Using the density functional theory, [(N)RuL] species are studied . The properties of the Ru-N bond are derived, including σ-donation, π-back donation, Ru-N and N-N bond lengths and bond orders, net charges and NN stretching frequencies, and so forth. These data are correlated using the ligand electrochemical parameter (E) theory, whereby the availability of electrons in the [RuL] fragment is defined by its electron richness, which is the sum of the E parameters, ΣE(L). The objective is to better understand the binding of the N ligand, leading to a molecular design whereby a specific species is constructed to have a desired property, for example, a particular bond length or charge. We supply cubic expressions linking ΣE(L) with these many metrics, allowing researchers to predict metric values of their own systems. The extended charge decomposition analysis is used. For the given target, N, σ-bonding does not vary greatly with the nature of ligand L, and π-back donation is the dominant property deciding the magnitudes of the various metrics. The E parameter provides the path to design the desired species. This contribution is devoted to dinitrogen, but the method is expected to be general for any ligand, including polydentate ligands.