Polymer-Bound Tetraruthenium and Tetrairidium Carbonyl Catalysts for Olefin Hydrogenation

J. BOURDON (Editor)

Growth and Properties of Metal Clusters, p. 535

535

© 1980 Elsevier Scientific Publishing Company - Printed in The Netherlands

POLYMER-BOUND TETRARUTHENIUM AND TETRAIRIDIUM CARBONYL CATALYSTS FOR OLEFIN HYDROGENATION Z. Otero-Schipper, J. Lieto, J. J. Rafa1ko and B. C. Gates Center for Catalytic Science and Technology Department of Chemical Engineering University of Delaware Newark, Delaware 19711, U.S.A.

Tetraruthenium clusters with unique structures have been attached to solid polymeric supports and used to catalyze ethylene hydrogenation at 1 atm and 50-90°C.

Polymer-bound ana-

logs of [H4Ru4(CO)lZ_x(PPh3)x) (with x = 1,3, or 4) were synthesized by ligand exchange between [H4Ru4(CO)lZ) and po1y(styrene-divinylbenzene) membranes functiona1ized with phosphine ligands.

Rates of ethylene hydrogenation were measured with a flow reactor allowing

simultaneous recording of the infrared spectra of the functioning catalyst.

Each catalyst

was stable, exhibiting undiminished activity after thousands of turnovers and presenting a carbonyl spectrum unchanged during catalysis and indistinguishable from that of the membrane incorporating the originally bound tetraruthenium cluster.

The catalysts incorporat-

ing tri- and tetra-substituted clusters exhibited the same form of kinetics, indicating saturation in ethylene and a reaction order in HZ of 0.8.

The catalytic activity increased,

the activation energy decreased, and the strength of bonding of ethylene to the catalyst increased with increasing substitution by electron-donor phosphine ligands on the cluster. framework provided the catalytic sites, perhaps by revers4 ible Ru-Ru bond breaking to form coordinative1y unsaturated metal centers.

The results suggest that the RU

Unique tetrairidium carbonyl clusters were also anchored to phosphine-functiona1ized poly (styrene-diviny1benzene), the metal species being identified by carbonyl infrared spec-

tra as the clusters analogous to .[Ir (x = 1, Z, or 3). The synthesis 4(CO)lZ_x(PPh3)x) method was developed from that reported by J. J. Rafa1ko, J. Lieto, B. C. Gates, and G. L. Schrader, Jr.,

~

Chern. Soc. Chern. Commun. 540 (1978).

Infrared spectra of polymer mem-

branes functioning as catalysts for ethylene and cyclohexene hydrogenation in a flow reactor at 1 atm and 40-80°C indicated that the predominant metal species in each catalyst was the originally prepared tetrairidium cluster.

The catalysts were stable, exhibiting unchanged

spectra and undiminished activity for as many as 5000 turnovers at temperatures <90°C, but at temperatures >lZ0°C, the iridium clusters aggregated to form crystallites.

Catalytic

kinetics measured at <90°C showed that for each olefin, the rate of hydrogenation decreased with an increasing number of phosphine substituents on the tetrairidium cluster (in contrast to the results observed with tetraruthenium clusters).

The results suggest that the

metal clusters provided the catalytic sites, possibly formed by reversible cleavage of Ir-Ir or Ir-P bonds- to generate coordinative unsaturation.