Ruthenium-to-platinum interactions in η6,η1 NCN-pincer arene heterobimetallic complexes: An experimental and theoretical study

A series of η6,η1-heterobimetallic complexes have been prepared in which a [Ru(η6-arene)(C5R5)]+ fragment (R = H or Me) and an η1-NCN-pincer platinum fragment are combined within the same molecule. In complexes [2]+ and [3]+, the ruthenium and platinum centers are η6 and η1 coordinated, respectively, to the same arene ring, whereas in [4A]+ and [5A]+ they are coordinated to two different arene rings that are linked with a covalent bond ([4A]+) or an ethyl bridge ([5A]+). Upon changing the organic manifold between both metal centers, very strong ([2]+) to very weak ([5A]+) ruthenium- to-platinum interactions are obtained. Experimentally, X-ray crystal structures show an increaing steric hindrance when the Ru–Pt distance diminishes, and electrochemical and 195Pt NMR spectroscopic studies show a decreasing electron density on platinum from [5A]+ to [2]+. Theoretical DFT calculations were undertaken, which show an increasing charge on platinum from [5A]+ to [2]+. Our theoretical analysis shows that the particularly strong ruthenium-to-platinum electronic interactions in [2]+ and [3]+ do not come from binding of ruthenium to platinum, but from the pincer Cipso sharing its electron density between both metal centers, which decreases the σ donation to platinum, and from increased backdonation of the platinum d electrons into the π system of the arene ring.