A concerted two-prong approach to the in situ allosteric regulation of bifunctional catalysis
Herein, we report the reversible "on-off" allosteric regulation of hydrogen-bond-donating (HBD)-Lewis base co-catalytic activity a concerted two-prong methodology entailing cooperative acid-base chemistry and a structurally addressable coordination complex. Specifically, a heteroligated Pt...
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Veröffentlicht in: | Chemical science (Cambridge) 2016-11, Vol.7 (11), p.6674-6683 |
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Sprache: | eng |
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Zusammenfassung: | Herein, we report the reversible
"on-off" allosteric regulation of hydrogen-bond-donating (HBD)-Lewis base co-catalytic activity
a concerted two-prong methodology entailing cooperative acid-base chemistry and a structurally addressable coordination complex. Specifically, a heteroligated Pt(ii) weak-link approach (WLA) tweezer complex containing both a hemilabile squaramide-piperidine-based catalytic ligand and a sodium sulfonate hydrogen-bond-accepting (HBA) ligand was synthesized. Due to the hemilabile nature of the catalyst-containing ligand, the heteroligated complex can be reversibly toggled
between a flexible, semi-open state and a rigid, fully closed state upon the addition of elemental ion cues.
H NMR spectroscopy titration studies show that in the semi-open state interligand hydrogen-bonding prevents substrate recognition by the squaramide unit, while in the fully closed state ligand-ligand interactions are prevented. This results in a catalytically active closed state, whereas in the semi-open state, when the piperidine tertiary amine is deliberately protonated, no catalytic activity is observed. Reversible interconversion between the active fully closed state and the dormant protonated semi-open state is achieved in the presence of substrate upon the concerted addition and abstraction of both a proton and a coordinating elemental anion. In this work, allosteric regulation of catalytic activity is demonstrated for both the Michael addition of nitroethane to β-nitrostyrene and the ring-opening of l-(-)-lactide. Taken together, this work details a potentially generalizable platform for the "on-off" allosteric regulation of a family of HBD-Lewis base co-catalysts capable of catalyzing a broad scope of reactions, including the living ring-opening polymerization of cyclic esters. |
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ISSN: | 2041-6520 2041-6539 |
DOI: | 10.1039/c6sc01454b |