Rhodium-Catalyzed\nArene Alkenylation: Selectivity\nand Reaction Mechanism as a Function of In Situ Oxidant Identity

Rhodium catalyzed arene alkenylation reactions with arenes\nand\nolefins using dioxygen as the direct oxidant (e.g., <i>ACS Catal.</i> <b>2020</b>, <i>10</i>, 11519), Cu(II) carboxylates\n(e.g., <i>Science</i> <b>2015</b>, <i>348</i>, 421; <i>J. Am. Chem. Soc.</i> <b>2017</b>, <i>139</i>, 5474) or Fe(III) carboxylate clusters (e.g., <i>ACS Catal.</i> <b>2024,</b> <i>14</i>, 10295),\nin the presence or absence of dioxygen, have been reported. These\nprocesses involve heating catalyst precursor [(η<sup>2</sup>-C<sub>2</sub>H<sub>4</sub>)<sub>2</sub>Rh(μ-OAc)]<sub>2</sub>, olefin, arene, and oxidant at temperatures between 120 and 200\n°C. Herein, we report comparative studies of Rh-catalyzed arene\nalkenylation as a function of oxidant identity. This work includes\ncomparisons of catalysis using Cu(II) carboxylates in the presence\nand absence of dioxygen, catalysis with only dioxygen as the oxidant,\nand Fe(III) carboxylates in the presence and absence of dioxygen.\nWe report studies of catalysis with each oxidant including reagent\nconcentration dependencies and kinetic isotope effect experiments\nusing C<sub>6</sub>H<sub>6</sub> or C<sub>6</sub>D<sub>6</sub> and\nprotio- or deutero carboxylic acid. Additionally, we probe ortho/meta/para\nregioselectivity for reactions of ethylene with monosubstituted arenes\nand Markovnikov/anti-Markovnikov selectivity with monosubstituted\nolefins. These studies indicate that the variation of oxidant identity\nimpacts catalyst speciation, the reaction mechanism, and the reaction\nrate. Consequently, distinct Markovnikov/anti-Markovnikov and ortho/meta/para\nselectivities are observed for catalysis with each oxidant.