Clusters containing P-donor ligands

The catalytic hydrogenation of 1-pentyne and 2-pentyne in the presence of phosphine- and phosphite-substituted derivatives of compound 2 has been studied under mild conditions by Valle and coworkers (Table 1, entries 11-14). As occurs 

3-dimethyl-1-butene after 90 min. Small amounts (3-7%) of 2,2-dimethylbutane are also formed. The rather similar activities and selectivities observed for these complexes suggest that a common catalytic species is probably formed in solution. When treated with the alkyne at high temperature, all these clusters form a similar product mixture which contains variable amounts of 23 and 24 accompanied by the phosphalkyne derivatives 25 and 26. The fact that compounds 25 and 26 give 3,3-dimethy 1-1-butene when treated with hydrogen and that the activity of the catalytic solutions decreases when the amounts of 25 and 26 are progressively reduced, induced the authors to propose 25 and 26 as catalytic intermediates.  

Clusters 19 22 and 24 have also been tested as catalyst precursors for the hydrogenation of diphenylacetylene (Table 1, entries 16, 18, 20). Z-Stilbene (kinetic product) and f-stilbene (thermodynamic product) are formed with higher conversions (70-100% after 90 min) than in the case of terminal alkynes. As with tert-butylacetylene, similar activities and selectivities are observed for the five cluster complexes, suggesting the intermediacy of common catalytic species in solution. Compound 27 (which arises from the reactions of 21 or 22 with diphenylacetylene) and compound 28 (which arises from the reaction of 24 with the same alkyne) (Fig. 4) have been proposed as catalytic intermediates in these hydrogenation reactions.  

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F, 1 NMR studies on the dynamic behaviour in solution of rhenium-platinum mixed metal clusters containing P-donor ligands... 

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