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Ligand Effects and Kinetic Investigations of Sterically Accessible 2‑Pyridonate Tantalum Complexes for Hydroaminoalkylation

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posted on 22.08.2017, 19:48 by Jason W. Brandt, Eugene Chong, Laurel L. Schafer
The synthesis of a series of structurally varied pyridonate-supported tantalum amido complexes and their catalytic reactivity in the intermolecular α-alkylation of unprotected secondary amines are described. Both terminal and internal alkenes can undergo this hydroaminoalkylation reaction to give selectively substituted secondary amine products. The reactivity profiles of 3- and 6-substituted pyridonate tantalum complexes, [(2-pyridonate)­Ta­(NMe2)3Cl], and a triflato pyridonate tantalum complex, [(2-pyridonate)­Ta­(NMe2)3OTf], were evaluated to analyze ligand effects. The deprotonation and complexation of commercially available 3-methyl-2-pyridone and 2-pyridone readily yielded effective, catalytically active tantalum complexes, displaying reactivity with both terminal and internal alkene substrates. Kinetic studies and deuterium labeling experiments reveal a complex kinetic profile and provide evidence for off-cycle equilibria that dominate catalytic activity and provide guidance for future catalyst development.