Reversible C–N Bond Formation in the Zirconium-Catalyzed Intermolecular Hydroamination of 2‑Vinylpyridine

The intermolecular hydroamination of alkenes with alkylamines has been a long-standing challenge in catalysis, partially due to the near-thermoneutral nature of this transformation. Consistent with this understanding, we report the direct observation of reversible C–N bond formation in hydroamination. A bis­(ureate) zirconium complex catalyzed the intermolecular hydroamination of 2-vinylpyridine. Reversible C–N bond formation was characterized by variable-temperature NMR spectroscopy, and thermodynamic parameters were determined using van’t Hoff plots. Isolated intermediates support an aza-Michael-addition mechanism. Sensitivity to steric bulk in the C–N bond forming step provided further evidence for the kinetically accessible but limited thermodynamic driving force for this transformation.