Magnesium-catalysed hydroboration of pyridines : kinetic analysis and poly-pyridine dearomatisation

Weetman, Catherine and Hill, Michael S. and Mahon, Mary F. (2016) Magnesium-catalysed hydroboration of pyridines : kinetic analysis and poly-pyridine dearomatisation. Polyhedron, 103 (Part A). pp. 115-120. ISSN 0277-5387

[img]
Preview
Text (Weetman-etal-P2016-Magnesium-catalysed-hydroboration-pyridines-kinetic-analysis-poly-pyridine-dearomatisation)
Weetman_etal_P2016_Magnesium_catalysed_hydroboration_pyridines_kinetic_analysis_poly_pyridine_dearomatisation.pdf
Accepted Author Manuscript
License: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 logo

Download (736kB)| Preview

    Abstract

    A kinetic analysis of the hydroboration of iso-quinoline with pinacol borane (HBpin) and catalysed by a β-diketiminato magnesium n-butyl pre-catalyst has provided evidence that the reaction proceeds via rate determining Mg–N/H–B metathesis of a dearomatised iso-quinolide anion. The reaction rate is suppressed by increasing [iso-quinoline] leading to the suggestion that catalytic turnover is also dependent on a pre-equilibrium involving dissociation of donor substrate molecules from the coordination sphere of the catalytic Mg centre. Stoichiometric reactions with a variety of poly-pyridine heterocycles have provided a range of magnesium derivatives of the dearomatised poly-pyridides either by alkyl or hydride transfer. The resistance of these latter species toward hydroboration is rationalised as a consequence of their additional coordinative stability providing corroborative evidence for the dissociative mechanism inferred from the kinetic analysis.