Oxophilicity is the tendency of certain chemical compounds to form oxides by hydrolysis or abstraction of an oxygen atom from another molecule, often from organic compounds. The term is often used to describe metal centers, commonly the early transition metals such as titanium, niobium, and tungsten. Oxophilicity is often stated to be related to the hardness of the element, within the HSAB theory (hard and soft (Lewis) acids and bases), but it has been shown that oxophilicity depends more on the electronegativity and effective nuclear charge of the element than on its hardness.[1] This explains why the early transition metals, whose electronegativities and effective nuclear charges are low, are very oxophilic. Many main group compounds are also oxophilic, such as derivatives of aluminium, silicon, and phosphorus(III). The handling of oxophilic compounds often requires air-free techniques.
Examples
Complexes of oxophilic metals typically are prone to hydrolysis. For example, the high valent chlorides hydrolyze rapidly to give oxides:
These reactions proceed via oxychloride intermediates. For example, WOCl4 results from the partial hydrolysis of tungsten hexachloride. Hydroxide-containing intermediates are rarely observed for oxophilic metals. In contrast, the anhydrous halides of the later metals tend to hydrate, not hydrolyze, and they often form hydroxides.
Reduced complexes of oxophilic metals tend to generate oxides by reaction with oxygen. Typically the oxide-ligand is bridging, e.g.
2 (C5H5)2TiCl + 1/2 O2 → {(C5H5)2TiCl}2O
Only in rare cases do the products of oxygenation feature terminal oxo ligands.[2]
Applications of oxophilicity in synthesis
Oxophilic reagents are often used to extract or exchange oxygen centers in organic substrates, especially carbonyls (esters, ketones, amides) and epoxides. The highly oxophilic reagent generated from tungsten hexachloride and butyl lithium is useful for the deoxygenation of epoxides.[3] Such conversions are sometimes valuable in organic synthesis. In the McMurry reaction, ketones are converted into alkenes using oxophilic reagents:
Oxophilic main group compounds are also well known and useful. The highly oxophilic reagent Si2Cl6 stereospecifically deoxygenates phosphine oxides.[5]Phosphorus pentasulfide and the related Lawesson's reagent convert certain organic carbonyls to the corresponding sulfur derivatives:
^Kepp, Kasper P. (2016-09-19). "A Quantitative Scale of Oxophilicity and Thiophilicity". Inorganic Chemistry. 55 (18): 9461–9470. doi:10.1021/acs.inorgchem.6b01702. ISSN 0020-1669. PMID 27580183.
^Nugent, W. A.; Mayer, J. M. "Metal-Ligand Multiple Bonds" J. Wiley: New York, 1988. ISBN0-471-85440-9.
^M. A. Umbreit; K. B. Sharpless (1990). "Deoxygenation of Epoxides with Lower Valent Tungsten Halides: trans-Cyclododecene". Organic Syntheses.; Collective Volume, vol. 7, p. 121
^Pine, S. H.; Kim, G.; Lee, V. (1993). "Enol Ethers by Methylenation of Esters: 1-Phenoxy-1-phenylethene and 3,4-Dihydro-2-methylene-2H-1-benzopyran". Organic Syntheses.; Collective Volume, vol. 8, p. 512
^David P. Sebesta "Hexachlorodisilane" in Encyclopedia of Reagents for Organic Synthesis John Wiley, London, 2001. doi:10.1002/047084289X.rh007 Article Online Posting Date: April 15, 2001.
^van Kalkeren, H. A.; van Delft, F. L.; Rutjes, F. P. J. T. (2013). "Organophosphorus Catalysis to Bypass Phosphine Oxide Waste". ChemSusChem. 6 (9): 1615–1624. doi:10.1002/cssc.201300368. hdl:2066/117145. PMID 24039197.
April 12, 2023
oxophilicity, tendency, certain, chemical, compounds, form, oxides, hydrolysis, abstraction, oxygen, atom, from, another, molecule, often, from, organic, compounds, term, often, used, describe, metal, centers, commonly, early, transition, metals, such, titaniu. Oxophilicity is the tendency of certain chemical compounds to form oxides by hydrolysis or abstraction of an oxygen atom from another molecule often from organic compounds The term is often used to describe metal centers commonly the early transition metals such as titanium niobium and tungsten Oxophilicity is often stated to be related to the hardness of the element within the HSAB theory hard and soft Lewis acids and bases but it has been shown that oxophilicity depends more on the electronegativity and effective nuclear charge of the element than on its hardness 1 This explains why the early transition metals whose electronegativities and effective nuclear charges are low are very oxophilic Many main group compounds are also oxophilic such as derivatives of aluminium silicon and phosphorus III The handling of oxophilic compounds often requires air free techniques Examples EditComplexes of oxophilic metals typically are prone to hydrolysis For example the high valent chlorides hydrolyze rapidly to give oxides TiCl4 2 H2O TiO2 4 HClThese reactions proceed via oxychloride intermediates For example WOCl4 results from the partial hydrolysis of tungsten hexachloride Hydroxide containing intermediates are rarely observed for oxophilic metals In contrast the anhydrous halides of the later metals tend to hydrate not hydrolyze and they often form hydroxides Reduced complexes of oxophilic metals tend to generate oxides by reaction with oxygen Typically the oxide ligand is bridging e g 2 C5H5 2TiCl 1 2 O2 C5H5 2TiCl 2OOnly in rare cases do the products of oxygenation feature terminal oxo ligands 2 Applications of oxophilicity in synthesis EditOxophilic reagents are often used to extract or exchange oxygen centers in organic substrates especially carbonyls esters ketones amides and epoxides The highly oxophilic reagent generated from tungsten hexachloride and butyl lithium is useful for the deoxygenation of epoxides 3 Such conversions are sometimes valuable in organic synthesis In the McMurry reaction ketones are converted into alkenes using oxophilic reagents 2 R2CO Ti R2C CR2 TiO2Similarly Tebbe s reagent is used in olefination reactions 4 Cp2TiCH2AlCl CH3 2 R2C O Cp2TiO 0 5 AlCl CH3 2 2 R2C CH2Oxophilic main group compounds are also well known and useful The highly oxophilic reagent Si2Cl6 stereospecifically deoxygenates phosphine oxides 5 Phosphorus pentasulfide and the related Lawesson s reagent convert certain organic carbonyls to the corresponding sulfur derivatives P4S10 n R2C O P4S10 nOn n R2C SOwing to the high stability of carbon dioxide many carbon compounds such as phosgene are oxophilic This reactivity is used for recycling of triphenylphosphine oxide 6 OPPh3 COCl2 Cl2PPh3 CO2References Edit Kepp Kasper P 2016 09 19 A Quantitative Scale of Oxophilicity and Thiophilicity Inorganic Chemistry 55 18 9461 9470 doi 10 1021 acs inorgchem 6b01702 ISSN 0020 1669 PMID 27580183 Nugent W A Mayer J M Metal Ligand Multiple Bonds J Wiley New York 1988 ISBN 0 471 85440 9 M A Umbreit K B Sharpless 1990 Deoxygenation of Epoxides with Lower Valent Tungsten Halides trans Cyclododecene Organic Syntheses Collective Volume vol 7 p 121 Pine S H Kim G Lee V 1993 Enol Ethers by Methylenation of Esters 1 Phenoxy 1 phenylethene and 3 4 Dihydro 2 methylene 2H 1 benzopyran Organic Syntheses Collective Volume vol 8 p 512 David P Sebesta Hexachlorodisilane in Encyclopedia of Reagents for Organic Synthesis John Wiley London 2001 doi 10 1002 047084289X rh007 Article Online Posting Date April 15 2001 van Kalkeren H A van Delft F L Rutjes F P J T 2013 Organophosphorus Catalysis to Bypass Phosphine Oxide Waste ChemSusChem 6 9 1615 1624 doi 10 1002 cssc 201300368 hdl 2066 117145 PMID 24039197 Retrieved from https en wikipedia org w index php title Oxophilicity amp oldid 1136399323, wikipedia, wiki, book, books, library,
