化学专业英语之有机金属化合物——金属配合物.doc

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1、化学专业英语之有机金属化合物金属配合物化学专业英语之有机金属化合物金属配合物ORGANOMETALLICSMETAL COMPLEXESMetal complexes are characterized by a type of direct carbonto-metal bonding that is not a classical ionic， , or bond 。 Numerous molecules and ions， e.g。， mono- and diolefins， polyenes, arenes, cyclopentadienyl ions， tropylium ions，

2、 andallylic ions, can form metal complexes with transitionmetal atoms or ions. These are classified as organ metallic complexes， because of their direct carbonmetal bond, and as coordination complexes， because the nature and characteristics of the tt ligands are similar to those in coordination comp

3、lexes。 In 1827, Zeise reported that ethylene reacts with platinum (II ） chloride to form a salt K （C2H4）PtCl3(l）, but it was not until after the elucidation of the structure of ferrocene (2） in 1953 that attention was redirected to Zieses salt， which was the first reported metal complex。Generally， m

4、etal tt complexes can be classified into three main groups; olefin-， cyclopentadienyl-, and arenemetal complexes； mixed complexes are categorized according to structural or chemical analogies within these groups. Allyl complexes are designated as olefin complexes in this review. Study of metal compl

5、exes has contributed to the elucidation of the mechanisms of ZieglerNatta polymerization， the oxo reaction， and catalytic hydrogenation, and to the development of the Wacker process which is used for the oxidation of olefins1。The following nomenclature for metal it complexes is used ： (1） Organic li

6、gands precede the metal atom. （2)Organic ligands precede inorganic 7t ligands. (3)Inorganic ligands, e.g。， carbonyl or nitrosyls, generally follow the metal atom； halides also follow the metal but precede carbonyls or nitrosyls。 (4）A prefix， e。g.， di， is preferred rather than bis in describing sandw

7、ich-type complexes， e。g., dibenzenechromium。 (5） The symbol can be used preceding a ligand in order to distinguish complex bonding from a， ionic， or other bonding。 The symbol (eta or hapto）precedes a ligand and indicates the number of C-M bonds in the ligand.Monoolefins , dienes, polyolefins， and ac

8、etylenes serve as ligands to transition metals and form olefin complexes。 Typical examples of olefin complexes are monoolefin ligands， e.g.， potassium 2-ethyleneplatinum trichloride (1）； and cyclopentadienylium. 3-cycloheptatrienylium molybdenum dicarbonyl （3); diene ligands, eg， 4butadieneiron tric

9、arbonyl（4 )。Certain of the delocalized -electron ring systems of aromatic molecules overlap with dxy and dy3 metal orbitals as do the electrons of alkenes with metal d orbitals2. The following aromatic rings can form complexes；The C5H5- ,C6H6，and C8HS arenes are the most common in arene k complexes

10、that are characterized by -bonded rings alone or -bonded rings that are associated with one ring and other ligands, eg, halogens, CO, RNC， and R3P. Typical examples are the di-5-cyclopentadienyl complexes ， ie, metallocenes , eg ， di5cyclopentadienyliron （2 )。 In di-4-5-cyclopentadienyliron ,ie， fer

11、rocene, the 6electron system of the C5H5 ion is bonded to the metal. Other aromatic ring systems are mono-5-cyclopentadienylmetal nitrosyl and carbonyl complexes.PropertiesThe Complex Bond。 Metal complexes are among those that are least satisfactorily described by crystalfield theory (CFT) or valenc

12、e-bond theory (VBT）。 The nature of the bonding can be treated more completely and quantitatively by molecular-orbital theory (MOT) or ligandfield theory （LFT）。 The ligandfield theory originally was advanced as a corrected CFT. The LFT relies on the use of molecular orbitals and often is used interch

13、angeably with the MOT。 The usual approach is to use the linear combination of atomic orbitals (LCAO） method。 It is assumed that when an electron in a molecule is near a particular nucleus， the molecular wave function is approximately an atomic orbital that is centered at the nucleus. The molecular o

14、rbitals are formed by adding or subtracting the appropriate atomic orbitals。 For transition metals 。the ”3d， 4s， and 4p orbitals are the atomic orbitals of interest。 The ligands may have and -valence orbitals. Once the appropriate atomic orbitals have been selected for the metal and ligands， the pro

15、per linear combination of valence atomic orbitals is determined for the molecular orbitals. The determination of orbital overlaps that are possible， ie， meet inherent symmetry requirements， is done by application of the principles of group theory. At this point, the procedure becomes arbitrary in th

16、at approximate wave functions must be selected for use in the calculations of the overlap integrals and coulomb integrals3. Finally， an arbitrary charge distribution is chosen and the orbital energies and interaction energies are calculated, and a solution of the secular equation for the energies an

17、d coefficients of the atomic wave functions can be determined。 A new initial charge distribution is repeated until consistent values are obtained。ReactionsMetal complexes react with a wide range of chemical reagents. However, the reactions of the olefin, cyclopentadienyl-， and it-arene-metal complex

18、es are distinctly characteristic of each group， Cyclopentadienyl complexes， ie， metallocenes ，exhibit a high degree of aromaticity and undergo many typical aromatic substitution reactions。 However， the arene complexes do not exhibit a discernible degree of aromaticity。Although most physical properti

19、es, particularly the structure of metal tt complexes， are interpreted by use of the basic principles of coordination chemistry， these established principles do not explain suitably some reaction anomalies of the different groups of metal complexes。Olefin Complexes。 Reactions involving olefin x。 comp

20、lexes similarly are characteristic of uncomplexed and complexed olefinic functions。 Generally， reactions involving the former are not very different from those observed for free olefins。 However， reactions of the latter are altered significantly by complex formation。 Among the reactions of interest

21、are addition, elimination， and substitution.Cyclopentadienyl Complexes. The most significant feature of the reactions of -cyclopentadienyl complexes in general and ferrocene in particular involves their aromatic nature。 The resonance stabilization energy for ferrocene is 210 kj/mol（50 kcal/mol）. Fer

22、rocene undergoes a large number of typical ionic aromatic substitution reactions， eg, FriedelCrafts acylation, alkylation, metalation， sulfonation, and aminomethylation。Friedel-Crafts Acylation. The acylation of metallocenes proceeds easily。 The equimolar reaction of ferrocene and acetyl chloride in

23、 the presence of aluminum chloride yields monoacetylferrocene almost exclusively. When an excess of acetyl chloride and aluminum chloride is used， a mixture of two isomeric diacetylferrocenes is produced。 The heteroannular disubstituted derivative 1,1-diacetylferrocene and the homoannular isomer 1,2

24、diacetylferrocene are obtained in a ratio of 60:1. The first acetyl group deactivates the cyclopentadienyl ligand toward further electrophilic substitution。 Thus， the second acetyl group enters the other ring。Sulfonation. Ferrocene can be sulfonated readily by sulfuric acid or cholrosulfonic acid in

25、 acetic anhydride to form ferrocenesulfonic acid and heteroannular disulfonic acid， -Cyclopentadienylrhenium tricarbonyl can be sulfonated with concentrated sulfuric acid in acetic anhydride; the product is isolated as the p-toluidine salt.Formylation. Ferrocene is formylated with Nmethylformanilide

26、 in the presence of phosphorus oxychloride。 This reaction also is characteristic of highly reactive aromatic rings.Arylation. The most significant radical substitution reaction of ferrocene is its reaction with aryl diazonium salts giving an arylation product.Arene-Metal Complexes. Generally, arene

27、complexes do not undergo the reactions that are characteristic of benzene and its derivatives. However， arene complexes do undergo a limited number of substitution 。addition .expansion, and condensation reactions。UsesCatalysis Involving Metal 7tComplex Intermediates。 Many metal-catalyzed reactions p

28、roceed by way of a substrate metal complex intermediate. Commercially， the mostsignificant of these include the polymerization of ethylene,the hydroformylation of olefins yielding aldehydes ， ie , the oxo process (qv ）, and the air oxidation of ethyleneproducing acetaldehyde(qv) ,ie ，the Wacker proc

29、ess.Polymerization of Olefins. ZieglerNatta Process。 During the 1950s, ethylene was polymerized using a ZieglerNatta catalyst， ie, a mixture of transition metal halides, eg， titanium halides, and trialkylaluminum (triethylaluminum commonly is used)。 The use of trialkylaluminum stimulated research in

30、to the use of organ metallic compounds in general. It has been determined that the ZieglerNatta process involves a metal -complex intermediate. A plausible mechanism for the polymerization can be formulated by applying typical organometallic and coordination reactions.Oxidation of Olefins。 Wacker Pr

31、ocess。 The oxidation of ethylene exclusively to ace-taldehyde and of other straightchain olefins to ketones is achieved by the catalytic reaction of ethylene in an aqueous solution by palladium (II） or by oxygen in the presence of palladium( II ） chloride， copper （II）chloride，or iron（III)chloride. G

32、enerally, the oxidation of olefins by other metal ions ，eg ,Hg（II) ,Th(III） ,and Pb（ IV ) ，yields glycol derivatives as well as carbonyl products。 The mechanism for the oxidation is postulated to include n-o rearrangements.Addition of Carbon Monoxide。 Oxo Reaction. The oxo process has been developed

33、 extensively to produce primary alcohols by the reduction of the aldehydes which are formed in the process.Health and Safety FactorsSome metal complexes are airsensitive and， therefore, their preparation requires an air-free reaction system. Their toxicity usually is based on the metal； however， organometallic compounds generally exhibit greater toxicities than their corresponding inorganic salts. The alkyl derivatives tend to be more toxic than the aryl complexes， which exhibit toxicities similar to those of the corresponding inorganic compounds.