|
Organozinc compounds in organic chemistry contain carbon to zinc chemical bonds. Organozinc chemistry is the science of organozinc compounds describing their physical properties, synthesis and reactions.〔''(The Chemistry of Organozinc Compounds )'' (Patai Series: (The Chemistry of Functional Groups )), (Eds. Z. Rappoport and I. Marek), John Wiley & Sons: Chichester, UK, 2006, ISBN 0-470-09337-4.〕〔''Organozinc reagents – A Practical Approach'', (Eds. P. Knochel and P. Jones), Oxford Medical Publications, Oxford, 1999, ISBN 0-19-850121-8.〕〔''Synthetic Methods of Organometallic and Inorganic Chemistry Vol 5, Copper, Silver, Gold, Zinc, Cadmium, and Mercury'', W.A. Herrmann Ed., ISBN 3-13-103061-5〕 Organozinc compounds were among the first organometallic compounds made. They are less reactive than many other analogous organometallic reagents, such as Grignard and organolithium reagents. In 1848 Edward Frankland prepared the first organozinc compound, diethylzinc, by heating ethyl iodide in the presence of zinc metal.〔E. Frankland, Liebigs Ann. Chem.,1849, 71, 171〕 This reaction produced a volatile colorless liquid that spontaneous combusted upon contact with air. Due to their pyrophoric nature, organozinc compounds are generally prepared using air-free techniques. They are unstable toward protic solvents. For many purposes they are prepared in situ, not isolated, but many have been isolated as pure substances and thoroughly characterized.〔Elschenbroich, C. ”Organometallics” (2006) Wiley-VCH: Weinheim. ISBN 978-3-527-29390-2〕 Organozinc can be categorized according to the number of carbon substituents that are bound to the metal.〔〔''Organozinc reagents – A Practical Approach'', (Eds. P. Knochel and P. Jones), Oxford Medical Publications, Oxford, 1999, ISBN 0-19-850121-8.〕 # Diorganozinc (R2Zn): A class of organozinc compounds in which two alkyl ligands. These may be further divided into subclasses depending on the other ligands attached # Heteroleptic (RZnX): Compounds which an electronegative or monoanionic ligand (X), such as a halide, is attached to the zinc center with another alkyl or aryl substituent (R). # Ionic organozinc compounds: This class is divided in to organozincates (RnZn−) and organozinc cations (RZnLn+). ==Bonding== In its coordination complexes zinc(II) adopts several coordination geometries, commonly octahedral, tetrahedral, and various pentacoordinate geometries. These structural flexibility can be attributed to zinc’s electronic configuration ()3d104s2. The 3d orbital is filled. therefore, ligand field effects are nonexistent.Coordination geometry is thus determined largely by electrostatic and steric interactions.〔 Organozinc compounds usually are two- or three-coordinate, reflecting the strongly donating property of the carbanionic ligands. Typical diorganozinc complexes have the formula R2Zn. A polar covalent bond exists between carbon and zinc, being polarized toward carbon due to the differences in electronegativity values (carbon: 2.5 & zinc: 1.65). The dipole moment of symmetric diorganozinc reagents can be seen as zero in these linear complexes, which explains their solubility in nonpolar solvents like cyclohexane. Unlike other binary metal alkyls, the diorganozinc species show a low affinity for complexation with ethereal solvent. Bonding in R2Zn is described as employing sp-hybridized orbitals on Zn.〔 These structures cause zinc to have two bonding d-orbitals and four low-lying non-bonding d-orbitals (see non-bonding orbital), which are available for binding. When zinc lacks electron donating ligands it is unable to obtain coordination saturation, which is a consequence of the large atomic radius and low electron deficiency of zinc. Therefore it is rare for bridging alkyl or aryl groups to occur due to the weak electron deficiency of the zinc atom. Although, it does occur in some cases such as Ph2Zn (Shown below) and which halogens are the organozinc can form metal clusters (see cluster chemistry). When a halogen ligand is added to the zinc atom both the acceptor and donor character of zinc is enhanced allowing for aggregation.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Organozinc compound」の詳細全文を読む スポンサード リンク
|