''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 an equimolar amount of [CpM(CO)(3)H] (M = W, Mo, Cr) afforded the organometallic 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 ''neutralization'' of an acidic transition-metal hydride by a basic transition-metal hydroxide. The structure of the Pd2Cr cluster 3 was established by a single-crystal X-ray diffraction study. The trinuclear hydroxo clusters are stable in the solid state but slowly decompose in solution, the decomposition path being strongly dependent on the nature of M. Facile and selective decomposition: of 1 (M = W) resulted in the formation of [(Ph(3)P)(2)Pd-2(Ph)(2)(mu-OH)(2)], biphenyl, and the tetranuclear Pd2W2 cluster 4. Similar tetranuclear clusters 4-8 were obtained in high yield when the palladium hydroxo dimers were neutralized with excess [CpM(CO)(3)H] or [Cp*W(CO)(3)H]. However, these reactions proceed by a different pathway involving Ph/H exchange processes, and resulted in the formation of benzene and [CpM(CO)(3)Ph] or [Cp*W(CO)(3)Ph], respectively. Labeling experiments suggested that H atoms of the hydride and hydroxo ligands underwent an exchange which was faster than the neutralization and the concomitant formation of the metal-metal bond. Infrared and NMR studies show that the structures of the trinuclear hydroxo clusters were more rigid than those of the tetranuclear species. Tetranuclear systems containing three different metals, Pd2WMo (9) and Pd2WCr (10), were prepared and characterized.