Alkyl and alkenyl arenes are currently produced on a scale of billions of pounds per year, and the addition of aromatic C–H bonds across olefin C=C bonds, olefin hydroarylation. Current industrial catalysts (e.g., Friedel-Crafts catalysis or zeolites) for arene alkylation are based on acid-mediated olefin activation. New catalysts that operate by transition metal-mediated C–H activation followed by olefin insertion into metal-aryl bonds offer new opportunities. Studies of Pt(II) complexes supported by chelating bipyridyl ligands revealed a strategy for the direct formation of alkenyl arenes; however, catalyst decomposition to Pt(s) is problematic. New Rh catalysts that convert arenes, olefins and Cu(II) to alkenyl arenes with unique selectivity have been discovered. For example, (DAB)Rh(TFA)(C<sub>2</sub>H<sub>4</sub>) (DAB = N,N'-bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate) converts benzene, ethylene and Cu(II) salts to styrene, Cu(I) salt, and acid with high selectivity and yields ≥ 95%. We have extended these studies to new Rh(I) catalysts and demonstrated the ability to produce straight-chain alkenyl arenes when alpha-olefins are used. Also, regioselectivity for substituted benzenes is not directed by the electronic properties of the substituent but rather is catalyst directed for meta and para positions. The presentation will focus on new developments, including mechanistic studies, for these Rh-catalyzed processes.

Development of transition metal catalysts for arene alkenylation

256th National Meeting (2018)

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