[59873-73-3]  · Pd  · Palladium-Graphite  · (MW 106.42)

(hydrogenation catalyst for aromatic nitro compounds, alkenes, and alkynes;1 catalyzes arylation and vinylation of activated double bonds2,3)

Physical Data: 31-33% Pd by weight.

Form Supplied in: not commercially available.

Preparative Method: by reduction of Palladium(II) Chloride by Potassium-Graphite in 1,2-dimethoxyethane at 100 °C.1

Handling, Storage, and Precautions: no special handling or storage necessary; the catalyst is stable in air and can be stored for a long time without loss of activity.

Hydrogenation Catalyst.

Palladium-graphite is an effective catalyst for hydrogenation of aromatic nitro compounds to anilines (eq 1) and alkenes to alkanes (eq 2).1 The results of these investigations indicated that palladium-graphite is an alternative to the more commonly used Palladium on Carbon catalyst.

The catalyst has also been found to be effective in the stereospecific semihydrogenation of mono- and disubstituted alkynes to (Z)-alkenes (eqs 3 and 4).1 Addition of 1,2-Diaminoethane (EDA) is required for this stereospecificity to be achieved. Full hydrogenation is almost completely suppressed and results are comparable to those obtained by Lindlar or P-2 nickel catalysts. In fact, higher specificity is achieved with palladium-graphite compared to palladium on carbon in the presence of ethylenediamine although the rate of hydrogenation is slower.

Arylation and Vinylation of Activated Double Bonds.

Palladium-graphite undergoes oxidative addition into the carbon-halogen bond of aryl and vinyl iodides, which, after reductive elimination, yield the corresponding arylated or allylated compounds.2 Aryl bromides should not be used as they are not as reactive under these reaction conditions. By using a stoichiometric amount of a tertiary amine to trap the HI, the reaction can be carried out with a catalytic amount of palladium. When monosubstituted alkenes are used, high stereospecificity is achieved, thereby affording substituted (E)-alkenes (eqs 5 and 6). The yields are comparable with those reported using other palladium catalysts such as Palladium(II) Acetate.

Substitution reactions of allylic esters are also catalyzed by palladium-graphite.3 The reaction between allyl acetate and Sodium Benzenesulfinate in the presence of catalytic amounts of Pd-Gr and Triphenylphosphine afforded the allyl phenyl sulfone in quantitative yield (eq 7). In fact, the catalyst can be recovered and after ten runs the yield was 93%, showing that the catalyst retains its activity.

1. Savoia, D.; Trombini, C.; Umani-Ronchi, A.; Verardo, G. CC 1981, 540.
2. Savoia, D.; Trombini, C.; Umani-Ronchi, A.; Verardo, G. CC 1981, 541.
3. Boldrini, G. P.; Savoia, D.; Tagliavini, E.; Trombini, C.; Umani-Ronchi, A. JOM 1984, 268, 97.

Ellen M. Leahy

Affymax Research Institute, Palo Alto, CA, USA

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