Polyoxometalates in Catalytic Photochemical Hydrocarbon Functionalization and Photomicrolithography

Hill, Craig L.; Kozik, Mariusz; Winkler, Jay R.; Hou, Yuqi; Prosser-McCartha, Christina M.

doi:10.1021/ba-1993-0238.ch013

Cited by 20 publications

(16 citation statements)

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“…Not unsurprisingly, neither the excited state nor wO reacts with molecular oxygen to produce singlet molecular oxygen but extremely weak emission has been reported for the excited state. 7 Reaction with certain substrates, such as hydrocarbons, alcohols, alkyl halides, and ketones, is known to result in formation of the one-electronreduced form of decatungstate. 2,6,8 This latter species, which is readily detected from its characteristic absorption spectrum, [9][10][11] is quite stable in the absence of an oxidizing agent.…”

Section: Introductionmentioning

confidence: 99%

Kinetic and Mechanistic Aspects of Photocatalysis by Polyoxotungstates: A Laser Flash Photolysis, Pulse Radiolysis, and Continuous Photolysis Study

Taniélian¹,

Duffy²,

Jones³

1997

J. Phys. Chem. B

106

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Illumination of polyoxotungstates generates a short-lived excited state which decays to form the reactive intermediate wO that is responsible for subsequent transformation of organic substrates. It is shown by laser flash photolysis that wO is formed with a quantum yield of 0.6 and that it survives for ca. 55 ns in deoxygenated acetonitrile. In the presence of a substrate such as propan-2-ol wO reacts to produce the one-electron-reduced species, as characterized by transient spectroscopy and as confirmed by pulse radiolysis. Oxygen intercepts the initially-formed radicals so that this methodology may be used to follow the course of the reaction. Under continuous photolysis, propan-2-ol is converted into acetone and hydrogen peroxide but with adamantane as substrate the corresponding hydroperoxides are formed. Quantum yields of oxygen consumption have been measured for a variety of other substrates and range from ca. 0.05 for pure acetonitrile to ca. 0.5 for propan-2-ol. In the absence of other substrates, reaction of organic counterions may be observed. All these observations are consistent with hydrogen-atom abstraction from an organic substrate by wO, followed by rapid deprotonation of • wOH and/or trapping by O 2 . A concise reaction scheme involving coupling between oxyradicals is proposed that adequately describes the overall chemistry.

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Section: Introductionmentioning

confidence: 99%

Kinetic and Mechanistic Aspects of Photocatalysis by Polyoxotungstates: A Laser Flash Photolysis, Pulse Radiolysis, and Continuous Photolysis Study

Taniélian¹,

Duffy²,

Jones³

1997

J. Phys. Chem. B

106

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“…The applications of polyoxometalates in catalytic dehalogenation of halocarbons have been succinctly reviewed by Hill and coworkers [188]. This reaction involves the photocatalytic transformation of organic halides coupled with the oxidation of sacrificial organic reductants (secondary alcohols or tertiary amides) (Eq.…”

Section: Miscellaneous Reducing Methodsmentioning

confidence: 99%

Dehalogenation Reactions

and¹,

Simon²

2006

The Handbook of Homogeneous Hydrogenation

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Reductive dehalogenation -one of the earliest reactions described in the organic chemical literature -has achieved special significance since the 1980s when the harmful properties of numerous halogenated (chiefly chlorinated) hydrocarbons became clear. The identification of methods capable of neutralizing or, at least, diminishing these dangers, remains a major challenge for chemistry. It is reasonable to convert stocks of the prohibited chemicals (e.g., polychlorobiphenyls, PCBs; chlorofluorocarbons, CFCs) to valuable products as far as possible. At the same time, the halogen-containing wastes should be detoxified by degradation. During the past two decades, the mainly heterogeneous (but also homogeneous) catalytic dehalogenation provided a major share towards solving these problems. Within this period, substantial progress was also made in the application of these reactions in organic syntheses.Hydrodehalogenation -that is, hydrogenolysis of the carbon-halogen bondinvolves the displacement of a halogen bound to carbon by a hydrogen atom. This chapter is devoted to dehalogenations mediated by transition-metal complexes (Eq. (1)): ÀC j j ÀX reducing agent L n Mj 3 ÀC j j ÀH Y 1 where X = F, Cl, Br, I, and [L n M] = a transition metal complex. The use of a wide variety of reducing agents (H 2 , hydrides of metals and metalloids, organic reductants, etc.) under the most diverse reaction conditions (e.g., one-or two-phase systems) has been reported. Organic halides have also been reduced by electrochemical and photochemical methods in the presence of compounds of the type [L n M]. Reductive transformations of organic halides not relevant to Eq.(1) (e.g., coupling reactions) and dehalogenation of acyl halides will not be included here. 513The Handbook of Homogeneous Hydrogenation. Edited by J. G. de Vries and C. J. ElsevierThe reactivity of the carbon-halogen bond in Eq. (1) depends on several factors: · the nature of the halogen atom; · the environment of the halogen atom in the molecule; and · the reagents and conditions used in Eq. (1) [1].The order of reactivity of the C-X bond (generally: I > Br > Cl > F) is consistent with its strength. For instance, the experimentally found dissociation energies for phenyl halides (D Ph-X ) are 528, 402, 339, and 272 kJ mol -1 at 298 K for X = F, Cl, Br, and I, respectively [2]. Consequently, catalytic defluorination in the literature is comparatively rare. The different reactivity of the C-X bonds renders possible the selective dehalogenation of compounds containing two dissimilar halides, leaving intact the stronger C-X bond.

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“…ii. β. Μέσω εκπομπής φωτός στις ελάχιστες εξαιρέσεις όπου έχει παρατηρηθεί ασθενής ένταση φθορισμού από διεγερμένα πολυοξομεταλλικά ανιόντα (216,223,224) .…”

Section: φωτοκατάλυση με πομunclassified

“…παρουσία ΠΟΜ, καθιστά επιβεβλημένη την απλοποίηση των παραγόντων που πρέπει να ελεγχθούν. Για το λόγο αυτό, έγινε η επιλογή της 2-προπανόλης που αποτελεί ένα πολύ καλά μελετημένο υπόστρωμα ως προς το μηχανισμό δράσης της (179,224) .…”

Section: επίδραση της φύσης του οργανικού υποστρώματοςunclassified

“…Γενικά, το οργανικό υπόστρωμα δεν φαίνεται να παίζει άλλο ρόλο εκτός από αυτόν του δότη ηλεκτρονίων στη ΠΟΜ όπως προκύπτει από τα αποτελέσματα που λαμβάνονται κατά τη φωτόλυση 2-προπανόλης/Μ n+ ή χρωστικής. Η 2-προπανόλη προσκολλάται στην ΠΟΜ και παράγει φωτοχημικά τη ρίζα MeCOH (με δυναμικό αναγωγής -1.3 V, ως προς ΚΗΥ) (179,224) .…”

Section: επίδραση της φύσης του οργανικού υποστρώματοςunclassified

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Φωτοκαταλυτική Διάσπαση Οργανικών Ρύπων Και Αναγωγή Μετάλλων Σε Υδατικά Διαλύματα Παρουσία Πολυοξομεταλλικών Ενώσεων

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Polyoxometalates in Catalytic Photochemical Hydrocarbon Functionalization and Photomicrolithography

Cited by 20 publications

References 0 publications

Kinetic and Mechanistic Aspects of Photocatalysis by Polyoxotungstates: A Laser Flash Photolysis, Pulse Radiolysis, and Continuous Photolysis Study

Kinetic and Mechanistic Aspects of Photocatalysis by Polyoxotungstates: A Laser Flash Photolysis, Pulse Radiolysis, and Continuous Photolysis Study

Dehalogenation Reactions

Φωτοκαταλυτική Διάσπαση Οργανικών Ρύπων Και Αναγωγή Μετάλλων Σε Υδατικά Διαλύματα Παρουσία Πολυοξομεταλλικών Ενώσεων

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