Rhodium catalyzed arene alkenylation reactions with arenes
and
olefins using dioxygen as the direct oxidant (e.g., ACS Catal.
2020, 10, 11519), Cu(II) carboxylates
(e.g., Science
2015, 348, 421; J. Am. Chem. Soc.
2017, 139, 5474) or Fe(III) carboxylate clusters (e.g., ACS Catal.
2024,
14, 10295),
in the presence or absence of dioxygen, have been reported. These
processes involve heating catalyst precursor [(η2-C2H4)2Rh(μ-OAc)]2, olefin, arene, and oxidant at temperatures between 120 and 200
°C. Herein, we report comparative studies of Rh-catalyzed arene
alkenylation as a function of oxidant identity. This work includes
comparisons of catalysis using Cu(II) carboxylates in the presence
and absence of dioxygen, catalysis with only dioxygen as the oxidant,
and Fe(III) carboxylates in the presence and absence of dioxygen.
We report studies of catalysis with each oxidant including reagent
concentration dependencies and kinetic isotope effect experiments
using C6H6 or C6D6 and
protio- or deutero carboxylic acid. Additionally, we probe ortho/meta/para
regioselectivity for reactions of ethylene with monosubstituted arenes
and Markovnikov/anti-Markovnikov selectivity with monosubstituted
olefins. These studies indicate that the variation of oxidant identity
impacts catalyst speciation, the reaction mechanism, and the reaction
rate. Consequently, distinct Markovnikov/anti-Markovnikov and ortho/meta/para
selectivities are observed for catalysis with each oxidant.