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And organozincique is an organometallic compound containing a carbon – zinc link [ first ] . These are reactive compounds that are sensitive to air and water. They are involved in various important chemical reactions such as the Reformski reaction and the coupling of Negishi.
The organozincics were among the first organomotallic compounds known with an σ bond between a carbon atom and a metal atom. They are less reactive than similar organomietallic, such as organomagnesians and Grignard reagents. Diéthylzinc zn (ch 2 CH 3 ) 2 fut le premier organozincique synthétisé, en 1848 par le chimiste britannique Edward Frankland, en chauffant de l’iodoéthane CH3CH2I en présence de zinc élémentaire[2] : la réaction produisit un liquide incolore volatil qui s’enflamma spontanément au contact de l’air ; auparavant, on ne connaissait que des complexes organiques de l’arsenic et du sel de Zeise ayant des ligands organiques sur un atome métallique.
Due to their pyrophic nature, organozincics are generally prepared for air. They are unstable in the pro -solvents. They are mostly prepared on-site To be immediately used without being isolated specifically, but some were isolated as pure substances and were characterized in detail [ 3 ] .
Among the organozincics, we can distinguish the following categories according to the number of Zn – C connections [ 4 ] :
- Diorganozincics r 2 Zn , dans lesquels deux ligands alkyle sont liés à l’atome de zinc ;
- The heteroleptics, in which an electronegative or monoanionic ligand, for example an X halogenure, is linked to the zinc atom, itself linked to an alkyl or aryl ligand;
- Ionic organozincics, which include organozincates R n Zn −and organozincic cations RZnL n +, where he is a ligand.
In its complexes, zinc ( II ) Adopt several geometries, generally Octaédrique, Tetrahedral, as well as several Pentacorian geometries. This structural flexibility can be attributed to the electronic zinc configuration, which can be written [AR] 3D ten 4s 2 . The 3D orbital is complete, so that there is no ligand field effect. Coordination geometry is therefore largely determined by electrostatic and steric interactions [ 4 ] . The organozincics are generally bi- or knitted, which reflects the fact that the carbanions are strongly electron donors.
Diorganozincic complexes are typically in form R 2 Zn . Les composés de type dialkylzinc sont monomériques avec une coordination linéaire sur l’atome de zinc[5]. La liaison covalente entre les atomes de carbone et de zinc est polarisée vers l’atome de carbone en raison de la différence d’électronégativité entre les deux (2,55 pour le carbone contre 1,65 pour le zinc sur l’échelle de Pauling). Le moment dipolaire des réactifs diorganozinciques symétriques peut être considéré comme nul dans ces complexes linéaires, ce qui explique leur solubilité dans les solvants apolaires comme le cyclohexane. Contrairement à d’autres alkyles binaires métalliques, les espèces diorganozinciques ont une faible affinité pour la complexation avec les solvants de type éther. Les liaisons dans les composés R2Zn sont décrites comme mettant en œuvre des hybridations sp sur l’atome de zinc[4].
The zinc atom therefore has two binding orbitals and three non -binding orbitals available to establish links. In the absence of electrons donor ligands, the zinc atom cannot complete its orbitals, so that it binds to a relatively small number of alkyl and Aryle groups. The binding of a halogen to the zinc atom accentuates the donor and acceptor of these orbitals, which allows the formation of clusters , for example by involving ligands pontants [ 4 ] .
There are several methods for obtaining organozincics. Diorganozinc type compounds available are the dimethylzinc zn (CH 3 ) 2 , le diéthylzinc Zn(CH2CH3)2 et le diphénylzinc Zn(C6H5)2. Ce sont des réactifs chers et difficiles à manipuler. Il est également possible de produire ses organozinciques in situ à partir de précurseurs organobromés qui sont meilleur marché[6] :
In the example above, the Bromobenzene C 6 H 5 Br est converti en phényllithium C6H5Li par réaction avec quatre équivalents de n-butyllithium CH3CH2CH2CH2Li. Une transmétallation avec le chlorure de zinc ZnCl2 donne ensuite le diphénylzinc Zn(C6H5)2.
From elementary zinc [ modifier | Modifier and code ]
The Diethylzinc Zn (CH 2 CH 3 ) 2 par Edward Frankland mettait en œuvre de l’iodoéthane CH3CH2I avec du zinc. Ce dernier doit être activé pour faciliter la réaction d’oxydoréduction. L’une des formes activées du zinc utilisées par Frankland était le couple zinc-cuivre[2] :
- 2 CH 3 CH 2 I + 2 Zn0 ⟶ Zn(CH2CH3)2 + ZnI2.
Zinc can also be activated in the form of rieke metal by reducing zinc chloride ZNCL 2 avec du potassium. Cette forme s’est révélée utile pour des réactions telles que le couplage de Negishi et le couplage de Fukuyama. La formations de réactifs organozinciques est facilitée lorsque les halogénoalcanes ou les halogénures d’aryle portent des substituants attirant les électrons, comme les nitriles et les esters[7],[8].
The two most common interconversions of zinc functional groups are with halogenures and boron, which are catalyzed with copper iodide (i) copper and bases. The Boré intermediary is produced by a hydroboration followed by a diethylzinc treatment. This synthesis highlights the interest of organozincics by emphasizing their selectivity for the most reactive site of the molecule while forming useful coupling agents [ 9 ] .
This functional group transfer reaction can be used for allylations, or other coupling reactions, such as that of Negishi [ ten ] .
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(in) Examples of transfers of functional groups.
- (in) Paul Knochel, Nicolas Millot, Alain L. Rodriguez and Charles E. Tucker , ‘ Preparation and Applications of Functionalized Organozinc Compounds » , Organic Reactions , (DOI 10.1002/0471264180.or058.02 , read online )
- (of) Edward from Frankland , ‘ About the isolation of the organic radicals » , Justus Liebigs Annals of Chemistry , vol. 71, n O 2, , p. 171-213 (DOI 10.1002/JLAC.18490710205 , read online )
- (in) Christoph Elschenbroich, Organometallics , 3 It is Éd., Wiley-Vch, Weinheim, 2006. (ISBN 978-3-527-29390-2 )
- (in) The Chemistry of Organozinc Compounds , John Wiley & Sons, 2006. (ISBN 978-0-470-09337-5 )
- (in) John Bacsa, Felix Hanke, Sarah Hindley, Rajesh Odedra, George R. Darling, Anthony C. Jones et Alexander Steiner , ‘ The Solid‐State Structures of Dimethylzinc and Diethylzinc » , Applied Chemistry International Edition , vol. 50, n O 49, , p. 11685-11687 (PMID 21919175 , PMCID 3326375 , DOI 10.1002 / note.201109999 , read online )
- (in) And Gon Kim et Patrick J. Walsh , ‘ From Aryl Bromides to Enantioenriched Benzylic Alcohols in a Single Flask: Catalytic Asymmetric Arylation of Aldehydes » , Applied Chemistry International Edition , vol. 45, n O 25, , p. 4175-4178 (PMID 16721894 , DOI 10.1002 / may.200600741 , read online )
- (in) Reuben D. Rieke , ‘ Preparation of Organometallic Compounds from Highly Reactive Metal Powders » , Science , vol. 246, n O 4935, , p. 1260-1264 (PMID 17832221 , DOI 10.1126/science.246.4935.1260 , Bibcode 1989Sci…246.1260R , read online )
- (in) EI-Ichi Negishi , ‘ A genealogy of Pd-catalyzed cross-coupling » , Journal of Organometallic Chemistry , vol. 653, n you 1-2, , p. 34-40 (DOI 10.1016/S0022-328X(02)01273-1 , read online )
- (in) Falk Langer, Lothar Schwink, Arokiasamy Devasagayaraj, Pierre-Yoves Chavant et Paul Knochel , ‘ Preparation of Functionalized Dialkylzincs via a Boron−Zinc Exchange. Reactivity and Catalytic Asymmetric Addition to Aldehydes » , The Journal of Organic Chemistry , vol. sixty one, n O 23, , p. 8229-8243 (PMID 11667810 , DOI 10.1021/jo961129n , read online )
- (in) HIROSHI NAKA, KEISUKE ITO, MASAHIRO UENO, KOBAYASHIA et YOSHINORI KONDO , ‘ Generation of arylzinc reagents through an iodine–zinc exchange reaction promoted by a non-metallic organic superbase » , New Journal of Chemistry , vol. 34, n O 8, , p. 1700-1706 (DOI 10.1039/C0NJ00202J , read online )
Basic bond in organic chemistry | Many uses in chemistry |
Academic research, few current uses | Unknown / unrespoted link |
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