Metallated benzene

Metalation. Benzene reacts with alkaH metal derivatives such as methyl or ethyUithium ia hydrocarbon solvents to produce phenyUithium [591 -51 -5], CgH Li, and methane or ethane. Chloro-, bromo-, or iodobenzene will react with magnesium metal ia ethereal solvents to produce phenyHnagnesium chloride [100-59-4], C H MgCl, bromide, oriodide (Grignard reagents) (32). 

Metalated benzene derivatives can also be prepared by the reaction of alkynyl lithium reagents with zirconacyclopentadienes (Eq. 2.55) [39]. 

Metalation, benzene, 3 603-604 Metal-based fuel additives, 10 54 Metal-bearing wastes, 21 388-389, 406-407... 

Fig. 20. (a) One component of the bonding et metal-benzene molecular orbital set. Diagrams (b) and (c) illustrate the effect of tilting the p orbitals of the benzene and cyclopropenyl rings. 

The metal-benzene ring centroid distances of approximately 3.5 A indicate weak bonding. In organotin chemistry both metal-cyclopentadienyl complexes, e.g. [p -CsHsSnCl] and metal-7r-arene com-... 

Reactions of lithium alkyls are generally considered to be carbanionic in nature, but in reactions with alkyl halides free radicals have been detected by electron spin resonance.32 Lithium alkyls are widely employed as stereospecific catalysts for the polymerization of alkenes, notably isoprene, which gives up to 90% of 1,4-cA-polyisoprene numerous other reactions with alkenes have been studied.33 The TMED complexes again are especially active not only will they polymerize ethylene but they will even metallate benzene and aromatic compounds, as well as reacting with hydrogen at 1 atm to give LiH and alkane. 

Unpaired electrons can be present in ions as well as in the neutral systems that have been considered up to this point. There are many such radical cations and radical anions, and we consider some representative examples in this section. Various aromatic and conjugated polyunsaturated hydrocarbons undergo one-electron reduction by alkali metals. Benzene and naphthalene are examples. The ESR spectrum of the benzene radical anion was shown earlier in Figure 11.2a. These reductions must be carried out in aprotic solvents, and ethers are usually used for that purpose. The ease of formation of the radical anion increases as the number of fused rings increases. The electrochemical reduction potentials of some representative compounds are given in... 

In the reaction between a tantalum complex and benzene, thermolysis of the initial complex produces an electrophilic three-coordinate imido intermediate which is capable of metalating benzene (R f-BusSi) [35a] ... 

Figure 19. A hypothetical fully metallated benzene in a Mi C6 system.

Not all ligands use just two electrons to bond to transition metals. Benzene uses its six TT electrons in organometallic compounds such as (benzene)tricarbonylchromium. 

Osmocene is a photoactive compound. Photolysis of osmocene in n-hexane led to metallic osmium by reductive elimination. In the LF excited triplet state, osmocene undergoes a distortion by bending, which facilitates the transfer of a CH group between the cyclopentadienyl ligands. The resulting intermediate is an osmium complex with benzene and cyclobutadiene ligands, that decomposes to osmium metal, benzene and cyclobutadiene. ... 

Table 1.2 Ionization potentials of metal-benzene jt-complexes...

Pauling L (1960) The nature of the chemical bond, 3rd edn. Cornell Univ Press, Ithaca Liu Y, Guo Y, Lin 1 et al (2001) Measurement of the electric dipole moment of NO by mid-infrared laser magnetic resonance spectroscopy. Mol Phys 99 1457-1461 Coulson CA (1942) The dipole moment of the C-H bond. Trans Faraday Soc 38 433-444 Rayane D, Allouche A-R, Antoine R et al (2003) Electric dipole of metal-benzene sandwiches. Chem Phys Lett 375 506-510... 

S 6°4 Metal Benzene-1,3-dicarboxylic acid (isophthalic acid) H.L... 

Other important reactive metal-containing intermediates (e.g. metal-benzene complexes) and processes (e.g. decarboxylation of ketones by metal ions) of practical interest have been characterized using various mass special methods and provide insight into the mechanisms of organometallic reactions. 

Thallic salts metallate benzene and thiophene similarly, e.g. 

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