Synthesis of Trinuclear Osmium Polyhydrido Clusters [{(C<sub>5</sub>Me<sub>5</sub>)Os}<sub>3</sub>(μ-H)<sub>6</sub>]<sup>+</sup> and {(C<sub>5</sub>Me<sub>5</sub>)Os}<sub>3</sub>(μ-H)<sub>3</sub>(μ<sub>3</sub>-H)<sub>2</sub> and Comparison with the Ruthenium Analogues
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In this study, novel trinuclear polyhydrido complexes of osmium were synthesized. The protonation of the dinuclear tetrahydride complex (C5Me5)Os(μ-H)4Os(C5Me5) (4) with tetrafluoroboric acid selectively afforded the novel monocationic pentahydrido species [(C5Me5)Os(H)5Os(C5Me5)]+ (5), whereas the protonation of the corresponding ruthenium tetrahydride, (C5Me5)Ru(μ-H)4Ru(C5Me5) (3), resulted in the formation of monocationic triruthenium hexahydride [{(C5Me5)Ru}3(μ-H)6]+ (1) via the formation of intermediary dicationic diruthenium hexahydride [(C5Me5)Ru(H)6Ru(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(μ-H)6]+ (6), which was converted into {(C5Me5)Os}3(μ-H)3(μ3-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(μ-H)3(μ3-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.
