Periodinane 2182805 178918414 2007-12-19T09:03:43Z 68.227.84.67 add pointer to antenna article {{Redirect|PIFA|PIFA (Planar Inverted F Antenna)|Microstrip antenna}} [[Image:Dess-Martin Periodinane Structure.png|thumb|150px|right|The Dess-Martin Periodinane]]'''Periodinanes''' are [[chemical compound]]s containing '''hypervalent iodine'''. These [[iodine]] compounds are [[hypervalency|hypervalent]] because the iodine atom in it contains more than the 8 electrons in the [[valence shell]] required for the [[octet rule]]. When iodine is complexed with a [[monodentate]] [[electronegative]] [[ligand]] such as [[chlorine]], iodine compounds occur with a +3 [[oxidation number]] as iodine(III) or '''[[lambda|&lambda;]]<sup>3</sup>-iodanes''' or as a +5 [[oxidation number]] as iodine(V) or '''[[lambda|&lambda;]]<sup>5</sup>-iodanes'''. Iodine itself contains 7 valence electrons and in a &lambda;<sup>3</sup>-iodane three more are donated by the ligands making it a '''decet''' structure. &lambda;<sup>5</sup>-iodanes are '''dodecet''' molecules. In an ordinary iodine compound such as iodobenzene the number of valence electrons is eight as expected. In order to get from iodine to a hypervalent iodine compound it gets oxidized with removal of first 3 electrons and then 5 electrons. The ligands in turn contribute electrons pairs and form [[coordinate covalent bond]]s by adding a total of 6 or 10 electrons back to iodine. In the '''L-I-N notation''' L stand for the number of electrons donated by ligands and N the number of ligands. ==Periodinane compounds== The concept of hypervalent iodine was developed by J.J. Musher in 1969. In order to accommodate the excess of electrons in hypervalent compounds the [[3-center-4-electron bond]] was introduced in analogy with the [[3-center-2-electron bond]] observed in electron deficient compounds. One such bond exists in iodine(III) compounds and two such bonds reside in iodine(V) compounds. The first hypervalent iodine compound, dichloroiodobenzene (C<sub>6</sub>H<sub>5</sub>Cl<sub>2</sub>I) was prepared in 1886 by the German chemist [[C. Willgerodt]] <ref>C. Willgerodt, Tageblatt der 58. Vers. deutscher Naturforscher u. Aertzte, Strassburg '''1885'''.</ref> by passing [[chlorine]] gas through [[iodobenzene]] in a cooled solution of [[chloroform]]. :C<sub>6</sub>H<sub>5</sub>I + ICl<sub>3</sub> &rarr; C<sub>6</sub>H<sub>5</sub>ICl<sub>2</sub> + ICl &lambda;<sup>3</sup>-iodanes such as diarylchloroiodanes have a [[Trigonal bipyramid molecular geometry|pseudotrigonal bipyramidal]] geometry displaying [[apicophilicity]] with a [[phenyl]] group and a chlorine group at the apical positions and other phenyl group with two [[lone pair]] electrons in the equatorial positions. The &lambda;<sup>5</sup>-iodanes such as the [[Dess-Martin periodinane]] have [[Square pyramidal molecular geometry|square pyramidal]] geometries with 4 heteroatoms in basal positions and one apical phenyl group. Classical organic procedures exist for the preparation of '''iodosobenzene diacetate''' from [[peracetic acid]] and [[acetic acid]] <ref>{{OrgSynth | title = Benzene, iodoso-, diacetate | author = J. G. Sharefkin and H. Saltzman | collvol = 5 | collvolpages = 660 | prep = cv5p0660}}</ref>. :C<sub>6</sub>H<sub>5</sub>I + CH<sub>3</sub>COOOH &rarr; C<sub>6</sub>H<sub>5</sub>I(OOCCH<sub>3</sub>)<sub>2</sub> '''Phenyliodine bis(trifluoroacetate)''', '''PIFA''', or [[(bis(trifluoroacetoxy)iodo)benzene]] is a related compound based on [[trifluoroacetic acid]] The acetate can be hydrolysed with water to '''iodoxybenzene''' or '''iodylbenzene''' C<sub>6</sub>H<sub>5</sub>O<sub>2</sub>I <ref>{{OrgSynth | title = Benzene, iodoxy- | author = J. G. Sharefkin and H. Saltzman| collvol = 5 | collvolpages = 665 | prep = cv5p0665}}</ref> This compound was first prepared by Willgerodt by [[disproportionation]] of iodosylbenzene under [[steam distillation]] to iodylbenzene and iodobenzene :2 PhIO &rarr; PhIO<sub>2</sub> + PhI is a known [[oxidizing agent]]. Iodosobenzene diacetate can also be hydrolyzed to '''iodosylbenzene''' with [[sodium hydroxide]] which is actually a [[polymer]] with the [[molecular formula]] (C<sub>6</sub>H<sub>5</sub>O<sub></sub>I)<sub>n</sub> <ref>{{OrgSynth | title = Benzene, iodoso- | author = H. Saltzman and J. G. Sharefkin | collvol = 5 | collvolpages = 658 | prep = cv5p0658}}</ref>. Iodosylbenzene is used in [[organic oxidation]]s. [[Dess-Martin periodinane]] (1983) is another powerful oxidant and an improvement of the [[IBX acid]] already in existence in 1893. The IBX acid is prepared from 2-iodobenzoic acid and potassium [[bromate]] and [[sulfuric acid]] <ref>{{OrgSynth | title = 1,2-Benziodoxol-3(1H)-one, 1,1,1-tris(acetyloxy)-1,1-dihydro- | author = Robert K. Boeckman, Jr., Pengcheng Shao, and Joseph J. Mullins| collvol = 10 | collvolpages = 696 | prep = v77p0141}}</ref> and is insoluble in most solvents whereas the Dess-Martin reagent prepared from reaction of the IBX acid with [[acetic anhydride]] is very soluble. The oxidation mechanism ordinarily consists of a [[ligand exchange reaction]] followed by a [[reductive elimination]]. ==Periodinane uses== The predominant use of hypervalent iodine compounds is that of oxidizing reagent replacing many toxic reagents based on heavy metals <ref>''Hypervalent iodine(V) reagents in organic synthesis'' Uladzimir Ladziata and Viktor V. Zhdankin [[Arkivoc]] 05-1784CR pp 26-58 '''2006''' [http://www.arkat-usa.org/ark/journal/2006/I09_General/1784/06-1784CR%20as%20published%20mainmanuscript.pdf Article]</ref>. Current research focuses on their use in [[Carbon-carbon bond|carbon-carbon]] and carbon-heteroatom bond forming reactions. In one study such reaction, an [[intramolecular]] C-N coupling of an [[alkoxyhydroxylamine]] to its [[anisole]] group is accomplished with a catalytic amount of aryliodide in [[trifluoroethanol]] <ref>''First hypervalent iodine(III)-catalyzed C–N bond forming reaction: catalytic spirocyclization of amides to N-fused spirolactams'' Toshifumi Dohi, Akinobu Maruyama, Yutaka Minamitsuji, Naoko Takenaga and Yasuyuki Kita [[Chem. Commun.]], '''2007''', 1224 - 1226, {{DOI|10.1039/b616510a}}</ref>: :[[Image:HypervalentIodineCNbondFormation.png|400px|hypervalent iodine(III)-catalyzed C–N bond forming reaction]] In this reaction the periodinane (depicted as intermediate A) is formed by oxidation of the aryliodide with the [[sacrificial catalyst]] [[mCPBA]] which in turn converts the hydroxylamine group to a [[nitrenium ion]] '''B'''. This ion is the [[electrophile]] in [[ipso]] addition to the aromatic ring forming a [[lactam]] with a [[enone]] group. == References == {{reflist}} == External links == *[http://www.organic-chemistry.org/Highlights/2005/25May.shtm Hypervalent Iodine Chemistry] [[Category:Periodinanes|*]]