Comparative DFT analysis of ligand and solvent effects on the mechanism of H2 activation in water mediated by half-sandwich complexes [Cp Ru(PTA)2Cl] (Cp = C5H5, C5Me5; PTA = 1,3,5-triaza-7-phosphaadamantane)

The activation of hydrogen by complexes [Cp0Ru(PTA)2Cl] (Cp0 =C5H5, C5Me5; PTA = 1,3,5-triaza-7-phosphaadamantane) in water was investigated in a comparative DFT study carried out using a discrete þ continuum model based on a four-water-molecule cluster. As a starting point were chosen the ?2-H2 dihydrogen complexes [Cp0Ru(PTA)2(?2-H2)]þ (1H2), which are formed initially upon reaction of the chloride precursors with hydrogen gas. A rationale for the experimental data, showing that the monohydrido complex [CpRu(PTA){PTA(H)}H]+ (4a) and the dihydrido complex [Cp*Ru(PTA)2(H)2]Cl (3b) are the stable products for the two systems, is proposed, together with an in-depth analysis of both ligand and solvent effects in the stability of the different species, leading to more general mechanistic implications for metal-mediated hydrogen activation in water.