Facile activation of hydrogen by an unsaturated platinum-osmium cluster complex

The electronically unsaturated platinum-osmium complex Pt2Os3(CO)(10)((PBu3)-Bu-t)(2), 3, has been obtained from the reaction of Os-3(CO)(10)(NCMe)(2) with Pt((PBu3)-Bu-t)(2). Compound 3 adds hydrogen at 0 degrees C to yield the dihydrido complex Pt2Os3(CO)(10)(PtBu3)(2)((mu)- H)(2), 4 (93% yield) within 10 min and subsequently the tetrahydrido complex Pt2Os3(CO)(10)((PBu3)-Bu-t)(2)((mu)-H)(4), 5, in 70% yield within 60 min. Compound 3 contains a trigonal bipyramidal cluster of five metal atoms having the two platinum atoms in the apical sites. With the addition of each equivalent of hydrogen, the trigonal bipyramidal cluster opens by series of Pt-Os bond cleavages that result in sequential shifts of the Pt groups to edges of the Os-3 triangle. The hydrogen addition process can be reversed partially at 25 degrees C by purging solutions of 5 with nitrogen.