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Title: Reduction of a Redox-Active Ligand Drives Switching in a Cu(I) Pseudorotaxane by a Bimolecular Mechanism

Abstract

The reduction of a redox-active ligand is shown to drive reversible switching of a Cu(I) [2]pseudorotaxane ([2]PR{sup 2+}) into the reduced [3]pseudorotaxane ([3]PR{sup 2+}) by a bimolecular mechanism. The unreduced pseudorotaxanes [2]PR{sup 2+} and [3]PR{sup 2+} are initially self-assembled from the binucleating ligand, 3,6-bis(5-methyl-2-pyridine)-1,2,4,5-tetrazine (Me2BPTZ), and a preformed copper-macrocycle moiety (Cu-M{sup 2+}) based on 1,10-phenanthroline. X-ray crystallography revealed a syn geometry of the [3]PR{sup 2+}. The UV-vis-NIR spectra show low-energy metal-to-ligand charge-transfer transitions that red shift from 808 nm for [2]PR{sup 2+} to 1088 nm for [3]PR{sup 2+}. Quantitative analysis of the UV-vis-NIR titration shows the stepwise formation constants to be K{sub 1} = 8.9 x 10{sup 8} M{sup -1} and K{sub 2} = 3.1 x 10{sup 6} M{sup -1}, indicative of negative cooperativity. The cyclic voltammetry (CV) and coulometry of Me{sub 2}BPTZ, [2]PR{sup 2+}, and [3]PR{sup 2+} shows the one-electron reductions at E{sub 1/2} = -0.96, -0.65, and -0.285 V, respectively, to be stabilized in a stepwise manner by each Cu{sup 2+} ion. CVs of [2]PR{sup 2+} show changes with scan rate consistent with an EC mechanism of supramolecular disproportionation after reduction: [2]PR{sup 0} + [2]PR{sup 2+} = [3]PR{sup 2+} + Me{sub 2}BPTZ{sup 0} (K*{sub D}, k{sub d}). UV-vis-NIRmore » spectroelectrochemistry was used to confirm the 1:1 product stoichiometry for [3]PR{sup 2+}:Me{sub 2}BPTZ. The driving force ({Delta}G*{sub D} = -5.1 kcal mol{sup -1}) for the reaction is based on the enhanced stability of the reduced [3]PR{sup 2+} over reduced [2]PR{sup 0} by 365 mV (8.4 kcal mol{sup -1}). Digital simulations of the CVs are consistent with a bimolecular pathway (k{sub d} = 12,000 s{sup -1} M{sup -1}). Confirmation of the mechanism provides a basis to extend this new switching modality to molecular machines.« less

Authors:
; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1005517
Resource Type:
Journal Article
Journal Name:
J. Am. Chem. Soc.
Additional Journal Information:
Journal Volume: 131; Journal Issue: (3) ; 01, 2009; Journal ID: ISSN 0002-7863
Country of Publication:
United States
Language:
ENGLISH
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CRYSTALLOGRAPHY; GEOMETRY; OXIDATION; RED SHIFT; REDUCTION; SPECTRA; STABILITY; STOICHIOMETRY; TITRATION; VOLTAMETRY

Citation Formats

McNitt, Kristy A, Parimal, Kumar, Share, Andrew I, Fahrenbach, Albert C, Witlicki, Edward H, Pink, Maren, Bediako, D Kwabena, Plaisier, Christina L, Le, Nga, Heeringa, Lee P, Vander Griend, Douglas A, Flood, Amar H, Calvin), and Indiana). Reduction of a Redox-Active Ligand Drives Switching in a Cu(I) Pseudorotaxane by a Bimolecular Mechanism. United States: N. p., 2009. Web. doi:10.1021/ja8085593.
McNitt, Kristy A, Parimal, Kumar, Share, Andrew I, Fahrenbach, Albert C, Witlicki, Edward H, Pink, Maren, Bediako, D Kwabena, Plaisier, Christina L, Le, Nga, Heeringa, Lee P, Vander Griend, Douglas A, Flood, Amar H, Calvin), & Indiana). Reduction of a Redox-Active Ligand Drives Switching in a Cu(I) Pseudorotaxane by a Bimolecular Mechanism. United States. https://doi.org/10.1021/ja8085593
McNitt, Kristy A, Parimal, Kumar, Share, Andrew I, Fahrenbach, Albert C, Witlicki, Edward H, Pink, Maren, Bediako, D Kwabena, Plaisier, Christina L, Le, Nga, Heeringa, Lee P, Vander Griend, Douglas A, Flood, Amar H, Calvin), and Indiana). 2009. "Reduction of a Redox-Active Ligand Drives Switching in a Cu(I) Pseudorotaxane by a Bimolecular Mechanism". United States. https://doi.org/10.1021/ja8085593.
@article{osti_1005517,
title = {Reduction of a Redox-Active Ligand Drives Switching in a Cu(I) Pseudorotaxane by a Bimolecular Mechanism},
author = {McNitt, Kristy A and Parimal, Kumar and Share, Andrew I and Fahrenbach, Albert C and Witlicki, Edward H and Pink, Maren and Bediako, D Kwabena and Plaisier, Christina L and Le, Nga and Heeringa, Lee P and Vander Griend, Douglas A and Flood, Amar H and Calvin) and Indiana)},
abstractNote = {The reduction of a redox-active ligand is shown to drive reversible switching of a Cu(I) [2]pseudorotaxane ([2]PR{sup 2+}) into the reduced [3]pseudorotaxane ([3]PR{sup 2+}) by a bimolecular mechanism. The unreduced pseudorotaxanes [2]PR{sup 2+} and [3]PR{sup 2+} are initially self-assembled from the binucleating ligand, 3,6-bis(5-methyl-2-pyridine)-1,2,4,5-tetrazine (Me2BPTZ), and a preformed copper-macrocycle moiety (Cu-M{sup 2+}) based on 1,10-phenanthroline. X-ray crystallography revealed a syn geometry of the [3]PR{sup 2+}. The UV-vis-NIR spectra show low-energy metal-to-ligand charge-transfer transitions that red shift from 808 nm for [2]PR{sup 2+} to 1088 nm for [3]PR{sup 2+}. Quantitative analysis of the UV-vis-NIR titration shows the stepwise formation constants to be K{sub 1} = 8.9 x 10{sup 8} M{sup -1} and K{sub 2} = 3.1 x 10{sup 6} M{sup -1}, indicative of negative cooperativity. The cyclic voltammetry (CV) and coulometry of Me{sub 2}BPTZ, [2]PR{sup 2+}, and [3]PR{sup 2+} shows the one-electron reductions at E{sub 1/2} = -0.96, -0.65, and -0.285 V, respectively, to be stabilized in a stepwise manner by each Cu{sup 2+} ion. CVs of [2]PR{sup 2+} show changes with scan rate consistent with an EC mechanism of supramolecular disproportionation after reduction: [2]PR{sup 0} + [2]PR{sup 2+} = [3]PR{sup 2+} + Me{sub 2}BPTZ{sup 0} (K*{sub D}, k{sub d}). UV-vis-NIR spectroelectrochemistry was used to confirm the 1:1 product stoichiometry for [3]PR{sup 2+}:Me{sub 2}BPTZ. The driving force ({Delta}G*{sub D} = -5.1 kcal mol{sup -1}) for the reaction is based on the enhanced stability of the reduced [3]PR{sup 2+} over reduced [2]PR{sup 0} by 365 mV (8.4 kcal mol{sup -1}). Digital simulations of the CVs are consistent with a bimolecular pathway (k{sub d} = 12,000 s{sup -1} M{sup -1}). Confirmation of the mechanism provides a basis to extend this new switching modality to molecular machines.},
doi = {10.1021/ja8085593},
url = {https://www.osti.gov/biblio/1005517}, journal = {J. Am. Chem. Soc.},
issn = {0002-7863},
number = (3) ; 01, 2009,
volume = 131,
place = {United States},
year = {Thu Apr 02 00:00:00 EDT 2009},
month = {Thu Apr 02 00:00:00 EDT 2009}
}