Journal
ACS CATALYSIS
Volume 6, Issue 3, Pages 1793-1798Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.5b02896
Keywords
frustrated Lewis pairs; water tolerance; reductive amination; metal-free; amines
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Funding
- University of Manchester
- EPSRC [EP/M023346/1, EP/K03099X/1]
- Royal Society
- EPSRC [EP/M023346/1, EP/K03099X/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [1537618, EP/M023346/1, EP/K03099X/1] Funding Source: researchfish
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In contrast to the established dogma that B(C6F5)(3) is irreversibly poisoned by excess H2O/amine (or imine) bases, B(C6F5)(3) is actually a water-tolerant catalyst for the reductive amination of primary and secondary arylamines with aldehydes and ketones in wet solvents at raised temperatures and using only 1.2 equiv of Me2PhSiH as reductant. Arylamines/N-arylimines do not result in the irreversible deprotonation of H2O-B(C6F5)(3), allowing sufficient B(C6F5)(3) to be evolved at raised temperatures to effect catalytic reductions. Stronger Brensted basic amines such as (BuNH2)-Bu-t (and derived imines) result in irreversible formation of [HO-B(C6F5)(3)](-) from H2O-B(C6F5)(3), precluding the formation of B(C6F5)(3) at raised temperatures and thus preventing any imine reduction. A substrate scope exploration using 1 mol % nonpurified B(C6F5)(3) and wet solvents demonstrates that this is an operationally simple and effective methodology for the production of secondary and tertiary arylamines in high yield, with imine reduction proceeding in preference to other possible reactions catalyzed by B(C6F5)(3), including the dehydrosilylation of H2O and the reduction of carbonyl moieties (e.g., esters).
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