DINUCLEAR (ARENE)RUTHENIUM HYDRIDO COMPLEXES - SYNTHESIS, STRUCTURE, AND FLUXIONALITY OF (C(6)ME(6))(2)RU2H3(BH4)

In aqueous solution, the cationic complex [(C(6)Me(6))Ru(H2O)(3)](2+) reacts with sodium borohydride to give the known dinuclear cation [(C( 6)Me(6))(2)Ru2H3](+) (1(+)), which can be isolated as the hexafluoroph osphate salt. Under biphasic conditions (water/diethyl ether), 1(+) re acts with; additional sodium borohydride to afford the neutral dinucle ar hydride complexes (C(6)Me(6))(2)Ru2H4 (2) and (C(6)Me(6))(2)Ru2H3(B H4) (3), which are extracted into the organic phase. The solid-state s tructure of 3 has been solved by a single-crystal X-ray structure anal ysis. It contains a single-bonded ruthenium-ruthenium backbone with on e mu-hydride and two terminal hydrides; the BH4 bridge is bonded throu gh two H atoms to the two ruthenium atoms. In solution, two independen t fluxional processes can be distinguished by variable-temperature H-1 NMR spectroscopy, one of which involves the bridging and the terminal hydride 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 mu-hydrides at the Ru atoms as wel l as the boron-bound hydrides of the BH4 ligand undergo complete hydri de scrambling, a process that is slow with respect to the NMR time sca le.