Synthesis and Characterization of Dimethylbis(2-pyridyl)borate Nickel(II) Complexes: Unimolecular Square-Planar to Square-Planar Rotation around Nickel(II)

The syntheses of novel dimethylbis­(2-pyridyl)­borate nickel­(II) complexes <b>4</b> and <b>6</b> are reported. These complexes were unambiguously characterized by X-ray analysis. In dichloromethane solvent, complex <b>4</b> undergoes a unique square-planar to square-planar rotation around the nickel­(II) center, for which activation parameters of Δ<i>H</i>^⧧ = 12.2(1) kcal mol^–1 and Δ<i>S</i>^⧧ = 0.8(5) eu were measured via NMR inversion recovery experiments. Complex <b>4</b> was also observed to isomerize via a relatively slow ring flip: Δ<i>H</i>^⧧ = 15.0(2) kcal mol^–1; and Δ<i>S</i>^⧧ = −4.2(7) eu. DFT studies support the experimentally measured rotation activation energy (cf. calculated Δ<i>H</i>^⧧ = 11.1 kcal mol^–1) as well as the presence of a high-energy triplet intermediate (Δ<i>H</i> = 8.8 kcal mol^–1)

A Base and Solvent-Free Ruthenium-Catalyzed Alkylation of Amines

A (pyridyl)­phosphine-ligated ruthenium­(II) catalyst is reported for the chemoselective benzylic N-alkylation of amines, via a hydrogen-borrowing mechanism. The catalyst operates under mild conditions, neat, and without a base or other additive. These conditions offer remarkable functional group compatibility for applications in organic synthesis, including reactions involving phenols and anilines, which are very difficult to achieve. Mechanistic studies suggest that, unlike other catalysts for this reaction, the redox steps are fast and reversible while imine formation is slow. We perceive that this is the origin of the selectivity realized with these reaction conditions

A Base and Solvent-Free Ruthenium-Catalyzed Alkylation of Amines

A (pyridyl)­phosphine-ligated ruthenium­(II) catalyst is reported for the chemoselective benzylic N-alkylation of amines, via a hydrogen-borrowing mechanism. The catalyst operates under mild conditions, neat, and without a base or other additive. These conditions offer remarkable functional group compatibility for applications in organic synthesis, including reactions involving phenols and anilines, which are very difficult to achieve. Mechanistic studies suggest that, unlike other catalysts for this reaction, the redox steps are fast and reversible while imine formation is slow. We perceive that this is the origin of the selectivity realized with these reaction conditions