Protonating metal-metal bonds: Changing the metal-metal interaction from bonding, to nonbonding, and to antibonding

Abstract

Density functional theory (DFT) has been used to determine the geometric and electronic structure of the series [cis-{(η5-C5H3)2(CMe2)2}-Ru2(CO)4(μ-H)n]n+ (n = 0, 1, 2) and their di-tert-butyl-bipyridine (bipy) analogs ((CO)2 = bipy). The results have been analyzed by using natural bond orbitals (NBO) and quantum theory of atoms in molecules (QTAIM). This series provide a thorough description of the changes in the bonding that occur as the Ru-Ru bond in the n = 0 complexes is first protonated to form the 18-electron hydrogen bridged complexes, which each has a 3-center/2-electron Ru-H-Ru bond but not a direct Ru-Ru bond, and then protonated again to form dibridged complexes, which have two 3-center/2-electron Ru-H-Ru bonds and even without a direct Ru-Ru bond have an electron count of 19 electrons, which is compensated by having one more antibonding than bonding Ru-Ru molecular orbitals.