Ruthenium-to-Platinum Interactions in η6,η1 NCN-Pincer Arene Heterobimetallic Complexes: An Experimental and Theoretical Study

A series of eta(6),eta(1)-heterobimetallic complexes have been prepared in which a [Ru(eta(6)-arene)(C5R5)](+) fragment (R = H or Me) and an eta(1)-NCN-pincer platinum fragment are combined within the same molecule. In complexes [2](+) and [3](+), the ruthenium and platinum centers are eta(6) and eta(1) coordinated, respectively, to the same arene ring, whereas in [4(A)](+) and [5(A)](+) they are coordinated to two different arene rings that are linked with a covalent bond ([4(A)](+)) or an ethyl bridge ([5(A)](+)). Upon changing the organic manifold between both metal centers, very strong ([2](+)) to very weak ([5(A)](+)) 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 Pt-195 NMR spectroscopic studies show a decreasing electron density on platinum from [5(A)](+) to [2](+). Theoretical DFT calculations were undertaken, which show an increasing charge on platinum from [5(A)](+) 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 C-ipso sharing its electron density between both metal centers, which decreases the a donation to platinum, and from increased backdonation of the platinum d electrons into the pi system of the arene ring.