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Selective Oxidation by H(5)[PV(2)Mo(10)O(40)] in a Highly Acidic Medium

[Image: see text] Dissolution of the polyoxometalate (POM) cluster anion H(5)[PV(2)Mo(10)O(40)] (1; a mixture of positional isomers) in 50% aq H(2)SO(4) dramatically enhances its ability to oxidize methylarenes, while fully retaining the high selectivities typical of this versatile oxidant. To bette...

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Autores principales: Tiwari, Chandan Kumar, Baranov, Mark, Neyman, Alevtina, Neumann, Ronny, Weinstock, Ira A.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2020
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7482320/
https://www.ncbi.nlm.nih.gov/pubmed/32134633
http://dx.doi.org/10.1021/acs.inorgchem.9b03747
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author Tiwari, Chandan Kumar
Baranov, Mark
Neyman, Alevtina
Neumann, Ronny
Weinstock, Ira A.
author_facet Tiwari, Chandan Kumar
Baranov, Mark
Neyman, Alevtina
Neumann, Ronny
Weinstock, Ira A.
author_sort Tiwari, Chandan Kumar
collection PubMed
description [Image: see text] Dissolution of the polyoxometalate (POM) cluster anion H(5)[PV(2)Mo(10)O(40)] (1; a mixture of positional isomers) in 50% aq H(2)SO(4) dramatically enhances its ability to oxidize methylarenes, while fully retaining the high selectivities typical of this versatile oxidant. To better understand this impressive reactivity, we now provide new information regarding the nature of 1 (115 mM) in 50% (9.4 M) H(2)SO(4). Data from (51)V NMR spectroscopy and cyclic voltammetry reveal that as the volume of H(2)SO(4) in water is incrementally increased to 50%, V(V) ions are stoichiometrically released from 1, generating two reactive pervanadyl, VO(2)(+), ions, each with a one-electron reduction potential of ca. 0.95 V (versus Ag/AgCl), compared to 0.46 V for 1 in 1.0 M aq H(2)SO(4). Phosphorus-31 NMR spectra obtained in parallel reveal the presence of PO(4)(3–), which at 50% H(2)SO(4) accounts for all the P(V) initially present in 1. Addition of (NH(4))(2)SO(4) leads to the formation of crystalline [NH(4)](6)[Mo(2)O(5)(SO(4))(4)] (34% yield based on Mo), whose structure (from single-crystal X-ray diffraction) features a corner-shared, permolybdenyl [Mo(2)O(5)](2+) core, conceptually derived by acid condensation of two MoO(3) moieties. While 1 in 50% aq H(2)SO(4) oxidizes p-xylene to p-methylbenzaldehyde with conversion and selectivity both greater than 90%, reaction with VO(2)(+) alone gives the same high conversion, but at a significantly lower selectivity. Importantly, selectivity is fully restored by adding [NH(4)](6)[Mo(2)O(5)(SO(4))(4)], suggesting a central role for Mo(VI) in attenuating the (generally) poor selectivity achievable using VO(2)(+) alone. Finally, (31)P and (51)V NMR spectra show that intact 1 is fully restored upon dilution to 1 M H(2)SO(4).
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spelling pubmed-74823202020-09-11 Selective Oxidation by H(5)[PV(2)Mo(10)O(40)] in a Highly Acidic Medium Tiwari, Chandan Kumar Baranov, Mark Neyman, Alevtina Neumann, Ronny Weinstock, Ira A. Inorg Chem [Image: see text] Dissolution of the polyoxometalate (POM) cluster anion H(5)[PV(2)Mo(10)O(40)] (1; a mixture of positional isomers) in 50% aq H(2)SO(4) dramatically enhances its ability to oxidize methylarenes, while fully retaining the high selectivities typical of this versatile oxidant. To better understand this impressive reactivity, we now provide new information regarding the nature of 1 (115 mM) in 50% (9.4 M) H(2)SO(4). Data from (51)V NMR spectroscopy and cyclic voltammetry reveal that as the volume of H(2)SO(4) in water is incrementally increased to 50%, V(V) ions are stoichiometrically released from 1, generating two reactive pervanadyl, VO(2)(+), ions, each with a one-electron reduction potential of ca. 0.95 V (versus Ag/AgCl), compared to 0.46 V for 1 in 1.0 M aq H(2)SO(4). Phosphorus-31 NMR spectra obtained in parallel reveal the presence of PO(4)(3–), which at 50% H(2)SO(4) accounts for all the P(V) initially present in 1. Addition of (NH(4))(2)SO(4) leads to the formation of crystalline [NH(4)](6)[Mo(2)O(5)(SO(4))(4)] (34% yield based on Mo), whose structure (from single-crystal X-ray diffraction) features a corner-shared, permolybdenyl [Mo(2)O(5)](2+) core, conceptually derived by acid condensation of two MoO(3) moieties. While 1 in 50% aq H(2)SO(4) oxidizes p-xylene to p-methylbenzaldehyde with conversion and selectivity both greater than 90%, reaction with VO(2)(+) alone gives the same high conversion, but at a significantly lower selectivity. Importantly, selectivity is fully restored by adding [NH(4)](6)[Mo(2)O(5)(SO(4))(4)], suggesting a central role for Mo(VI) in attenuating the (generally) poor selectivity achievable using VO(2)(+) alone. Finally, (31)P and (51)V NMR spectra show that intact 1 is fully restored upon dilution to 1 M H(2)SO(4). American Chemical Society 2020-03-05 2020-09-08 /pmc/articles/PMC7482320/ /pubmed/32134633 http://dx.doi.org/10.1021/acs.inorgchem.9b03747 Text en Copyright © 2020 American Chemical Society This is an open access article published under a Creative Commons Attribution (CC-BY) License (http://pubs.acs.org/page/policy/authorchoice_ccby_termsofuse.html) , which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
spellingShingle Tiwari, Chandan Kumar
Baranov, Mark
Neyman, Alevtina
Neumann, Ronny
Weinstock, Ira A.
Selective Oxidation by H(5)[PV(2)Mo(10)O(40)] in a Highly Acidic Medium
title Selective Oxidation by H(5)[PV(2)Mo(10)O(40)] in a Highly Acidic Medium
title_full Selective Oxidation by H(5)[PV(2)Mo(10)O(40)] in a Highly Acidic Medium
title_fullStr Selective Oxidation by H(5)[PV(2)Mo(10)O(40)] in a Highly Acidic Medium
title_full_unstemmed Selective Oxidation by H(5)[PV(2)Mo(10)O(40)] in a Highly Acidic Medium
title_short Selective Oxidation by H(5)[PV(2)Mo(10)O(40)] in a Highly Acidic Medium
title_sort selective oxidation by h(5)[pv(2)mo(10)o(40)] in a highly acidic medium
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7482320/
https://www.ncbi.nlm.nih.gov/pubmed/32134633
http://dx.doi.org/10.1021/acs.inorgchem.9b03747
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