NEUTRALIZATION OF PALLADIUM HYDROXIDES, [L(2)PD(2)(R)(2)(MU-OH)(2)], BY M-H ACIDS, [CPM(CO)(3)H] (M=W, MO, CR)

The reaction of [L(2)Pd(2)(Ph)(2)(mu-OH)(2)] (L Ph(3)P, Cy(3)P) with a n equimolar amount of [CpM(CO)(3)H] (M = W, Mo, Cr) afforded the organ ometallic hydroxo clusters [L(2)Pd(2)(Ph)(2)(mu-OH)(mu-CO)(2)(mu(3)-CO )MCp) (1-3) in high yield. These reactions can be regarded as the ''ne utralization'' of an acidic transition-metal hydride by a basic transi tion-metal hydroxide. The structure of the Pd2Cr cluster 3 was establi shed by a single-crystal X-ray diffraction study. The trinuclear hydro xo clusters are stable in the solid state but slowly decompose in solu tion, the decomposition path being strongly dependent on the nature of M. Facile and selective decomposition: of 1 (M = W) resulted in the f ormation of [(Ph(3)P)(2)Pd-2(Ph)(2)(mu-OH)(2)], biphenyl, and the tetr anuclear Pd2W2 cluster 4. Similar tetranuclear clusters 4-8 were obtai ned in high yield when the palladium hydroxo dimers were neutralized w ith excess [CpM(CO)(3)H] or [CpW(CO)(3)H]. However, these reactions p roceed by a different pathway involving Ph/H exchange processes, and r esulted in the formation of benzene and [CpM(CO)(3)Ph] or [CpW(CO)(3) Ph], respectively. Labeling experiments suggested that H atoms of the hydride and hydroxo ligands underwent an exchange which was faster tha n the neutralization and the concomitant formation of the metal-metal bond. Infrared and NMR studies show that the structures of the trinucl ear hydroxo clusters were more rigid than those of the tetranuclear sp ecies. Tetranuclear systems containing three different metals, Pd2WMo (9) and Pd2WCr (10), were prepared and characterized.