Article Cite This: J. Am. Chem. Soc. 2018, 140, 2260−2264
pubs.acs.org/JACS
Selective Dehydrogenative Coupling of Ethylene to Butadiene via an Iridacyclopentane Complex Yang Gao, Thomas J. Emge, Karsten Krogh-Jespersen,* and Alan S. Goldman* Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States S Supporting Information *
ABSTRACT: An iridium complex is found to catalyze the selective dehydrogenative coupling of ethylene to 1,3-butadiene. The key intermediate, and a major resting state, is an iridacyclopentane that undergoes a surprisingly facile β-H elimination, enabled by a partial dechelation (κ3−κ2) of the supporting 3,5-dimethylphenyl-2,6-bis(oxazolinyl) ligand.
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mM) and ethane (3.0 mM) were observed in solution by 1H NMR spectroscopy (eq 1). Surprisingly, only a minimal
INTRODUCTION 1,3-Butadiene is a “platform chemical”, with ca. 10 M tons per annum produced for the manufacture of rubbers, polymers, and chemicals.1 Until recently demand for butadiene was largely met through its production as a side product from the cracking of naphtha, driven primarily by demand for ethylene.2 The recent abundance of ethane-rich shale gas, however, has shifted the production of ethylene toward the cracking of ethane; this has led to tightening supplies of butadiene while demand continues to increase with growth of the global economy. As a result, there is renewed interest in the development of methods for the on-purpose production of butadiene from inexpensive feedstock.3 On the supply side of this calculus, the same abundance of ethane that has led to decreased butadiene production from naphtha makes ethylene an attractive potential feedstock for butadiene. Herein we report the discovery of a catalyst for the selective formation of butadiene from ethylene, a reaction with little if any precedent. We show that this dehydrogenative coupling proceeds via an iridacyclopentane intermediate that undergoes β-H elimination, a reaction step which also has limited precedent.
concentration of butenes (
