An endohedrally functionalized self‐assembled Fe4L6cage complex can catalyze oxa‐Pictet—Spengler cyclizations of tryptophols and various aldehyde derivatives, showing strong rate accelerations and size‐selectivity. Selective molecular recognition of substrates controls the reactivity, and the cage is capable of binding and activating multiple different species along the multistep reaction pathway. The combination of a functionalized active site, size‐selective reactivity, and multistep activation, all from a single host molecule, illustrates the biomimetic nature of the catalysis.
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Catalytic Inhibition of Base‐Mediated Reactivity by a Self‐Assembled Metal‐Ligand Host
Spacious M4L6tetrahedra can act as catalytic inhibitors for base‐mediated reactions. Upon adding only 5 % of a self‐assembled Fe4L6cage complex, the conversion of the conjugate addition between ethylcyanoacetate and β‐nitrostyrene catalyzed by proton sponge can be reduced from 83 % after 75 mins at ambient temperature to <1 % under identical conditions. The mechanism of the catalytic inhibition is unusual: the octacationic Fe4L6cage increases the acidity of exogenous water in the acetonitrile reaction solvent by favorably binding the conjugate acid of the basic catalyst. The inhibition only occurs for Fe4L6hosts with spacious internal cavities: minimal inhibition is seen with smaller tetrahedra or Fe2L3helicates. The surprising tendency of the cationic cage to preferentially bind protonated, cationic ammonium guests is quantified via the comprehensive modeling of spectrophotometric titration datasets.
more » « less- Award ID(s):
- 2002619
- NSF-PAR ID:
- 10468073
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 29
- Issue:
- 63
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract An endohedrally functionalized self‐assembled Fe4L6cage complex can catalyze oxa‐Pictet—Spengler cyclizations of tryptophols and various aldehyde derivatives, showing strong rate accelerations and size‐selectivity. Selective molecular recognition of substrates controls the reactivity, and the cage is capable of binding and activating multiple different species along the multistep reaction pathway. The combination of a functionalized active site, size‐selective reactivity, and multistep activation, all from a single host molecule, illustrates the biomimetic nature of the catalysis.
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K aunit difference between the first and last protons to be removed. This moderation of side‐chain basicity in an active site is a hallmark of enzymatic catalysis. -
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Abstract A self‐assembled FeII4L6cage was synthesized with 12 internal amines in the cavity. The cage forms as the dodeca‐ammonium salt, despite the cage carrying an overall 8+ charge at the metal centers, extracting protons from displaced water in the reaction. Despite this, the basicity of the internal amines is lower than their counterparts in free solution. The 12 amines have a sliding scale of basicity, with a ≈6 p
K aunit difference between the first and last protons to be removed. This moderation of side‐chain basicity in an active site is a hallmark of enzymatic catalysis. -
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Abstract Recently, CuI‐ and AgI‐based halide double perovskites have been proposed as promising candidates for overcoming the toxicity and instability issues inherent within the emerging Pb‐based halide perovskite absorbers. However, up to date, only AgI‐based halide double perovskites have been experimentally synthesized; there are no reports on successful synthesis of CuI‐based analogues. Here we show that, owing to the much higher energy level for the Cu 3d10orbitals than for the Ag 4d10orbitals, CuIatoms energetically favor 4‐fold coordination, forming [CuX4] tetrahedra (X=halogen), but not 6‐fold coordination as required for [CuX6] octahedra. In contrast, AgIatoms can have both 6‐ and 4‐fold coordinations. Our density functional theory calculations reveal that the synthesis of CuIhalide double perovskites may instead lead to non‐perovskites containing [CuX4] tetrahedra, as confirmed by our material synthesis efforts.
