Hydride–Rhodium(III)-N-Heterocyclic Carbene Catalyst for Tandem Alkylation/Alkenylation via C–H Activation

Abstract

The unsaturated hydride complex RhClH{κ2-N,C-(C11H8N)}(IPr) {IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazolin-2-carbene} (2) has been prepared via C–H activation of 2-phenylpyridine and fully characterized by spectroscopic methods and X-ray diffraction analysis. Complex 2 efficiently catalyzes the isomerization of terminal and internal olefins under mild conditions to give preferentially the E regioisomers. Complex 2 also catalyzes the hydroarylation of terminal olefins with 2-phenylpyridine to yield selectively mono-ortho-alkylated derivatives. Tandem isomerization–alkylation processes were observed for internal olefins. In contrast to olefins, double alkenylation is operative for internal alkynes. The marked complementary reactivity of olefins and alkynes allows for a tandem alkylation/alkenylation of 2-phenylpyridine to yield substituted styrenes. These heterobiaryl compounds exhibit axial chirality. The rotational barrier has been experimentally calculated and corroborated by density functional theory ...