Several groups, including our own, have reported that PCP-pincer iridium(I) complexes are highly effective as catalysts for the dehydrogenation of alkanes. We considered that isoelectronic ruthenium(0) complexes might show comparable or perhaps even greater reactivity, and we have accordingly designed and synthesized a neutral 2,7-di-tert-butyl-4,5-bis(diisopropylphosphino)-9,9-dimethylthioxanthene (PSP) ligand, and several (PSP)Ru complexes. The (PSP)Ru complexes catalyze transfer dehydrogenation of cyclooctane with turnover frequencies up to 3600/h at 180oC. However, transfer dehydrogenation of n-octane is much less effective with only ca. 32 TO obtained after 40 h. We have found that ruthenium allyl complexes are the resting states in the transfer dehydrogenation of n-octane; in the case of cyclooctane transfer dehydrogenation the much less stable ruthenium cyclooctene complex is the resting state. This illustrates the danger of extrapolating from COA to n-alkanes for alkane dehydrogenation studies. Other reactions catalyzed by (PSP)Ru will be discussed.

Synthesis, characterization, and reactivity of a ruthenium complex of a new PSP pincer ligand

254th National Meeting (2017)

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