Dinuclear (Arene)ruthenium Hydrido Complexes: Synthesis, Structure, and Fluxionality of (C6Me6)2Ru2H3(BH4)

Abstract

In aqueous solution, the cationic complex [(C6Me6)Ru(H2O)3]2+ reacts with sodium borohydride to give the known dinuclear cation [(C6Me6)2Ru2H3]+ (1+), which can be isolated as the hexafluorophosphate salt. Under biphasic conditions (water/diethyl ether), 1+ reacts with additional sodium borohydride to afford the neutral dinuclear hydrido complexes (C6Me6)2Ru2H4 (2) and (C6Me6)2Ru2H3(BH4) (3), which are extracted into the organic phase. The solid-state structure of 3 has been solved by a single-crystal X-ray structure analysis. It contains a single-bonded ruthenium−ruthenium backbone with one μ-hydride and two terminal hydrides; the BH4 bridge is bonded through two H atoms to the two ruthenium atoms. In solution, two independent fluxional processes can be distinguished by variable-temperature 1H NMR spectroscopy, one of which involves the bridging and the terminal hydrido ligands and the other the coordinated and the noncoordinated H atoms of the BH4 bridge. In addition, deuteration experiments reveal that the terminal hydrides and the μ-hydrides at the Ru atoms as well as the boron-bound hydrides of the BH4 ligand undergo complete hydride scrambling, a process that is slow with respect to the NMR time scale.