HOMOGENEOUS TUNGSTEN, RHENIUM, AND IRIDIUM CATALYSTS IN ALKANE DEHYDROGENATION DRIVEN BY REFLUX OF SUBSTRATE OR OF COSOLVENT OR BY INERT-GAS FLOW

A variety of catalysts have been studied for alkane dehydrogenation activity. The activities have been assayed by using the reflux method of Fujii and Saito, in which the endoergonic alkane dehydrogenation reactions can be driven by continuous removal of H-2 in the reflux process, which displaces the equilibrium of eq 1 toward alkene. 1b ([IrH2(O2CR)(PCY3)2]; CY = cyclohexyl, R = C2F5) is interesting in that initial deactivation leads to a less active catalyst, but one which is stable to further deactivation. [(triphos)WH6] (6; triphos = PhP(CH2CH2-PPh2)2) is also notable in that, for the first time, base-metal homogeneous catalysts are shown to be effective in alkane dehydrogenation. [(triphos)ReH5] is also active. Using the substrate as reflux fluid limits the temperature at which the reaction can conveniently be run, but if the medium that removes the H-2 is other than the refluxing substrate, this limitation is lifted. We find that refluxing perfluorodecane is effective. Removal of the H-2 Can also be effected by bubbling argon.