Synthesis of trinuclear osmium polyhydrido clusters [{(C5Me5)Os}3(μ-H)6]+ and {(C5Me5)Os}3(μ-H)3(μ3-H)2 and comparison with the ruthenium analogues

In this study, novel trinuclear polyhydrido complexes of osmium were synthesized. The protonation of the dinuclear tetrahydride complex (C5Me5)Os(mu-H)(4)Os(C5Me5) (4) with tetrafluoroboric acid selectively afforded the novel monocationic pentahydrido species [(C5Me5)Os(H)(5)Os(C5Me5)](+) (5), whereas the protonation of the corresponding ruthenium tetrahydride, (C5Me5)Ru(mu-H)(4)Ru(C5Me5) (3), resulted in the formation of monocationic triruthenium hexahydride [{(C5Me5)Ru)(3)(mu-H)(6)](+) (1) via the formation of intermediary dicationic diruthenium hexahydride [(C5Me5)Ru(H)(6)Ru(C5Me5)](2+). The dinuclear monocationic complex 5 functioned as a starting material for the synthesis of the trinuclear polyhydrido complexes of osmium. The reaction of 5 with (C5Me5)OsH5 in dichloromethane led to the formation of trinuclear cation [{C5Me5)Os}(3)(mu-H)(6)](+) (6), which was converted into {(C5Me5)Os}(3)(mu-H)(3)(mu(3)-H)(2) (7) by the treatment with n-butyllithium. The molecular structures of 6 and 7 were determined by X-ray diffraction studies. A proton transfer between 1 and 7 yielded {(C5Me5)Ru}(3)(mu-H)(3)(mu(3)-H)(2) (2) and 6. In addition, it was concluded that the triosmium pentahydride 7 is more basic than the ruthenium analogue 2 on the basis of the reaction of the trinuclear pentahydrido clusters 7 and 2 with NEt3HBF4.