Benzene, metallation

Although catalytic preparations of cyclopentadienones with other metal systems are known, chemose-lectivity is often a problem. For example, the reactions of 2-butyne, 3-hexyne and diphenylacetylene with [(CO)2RhCl]2 at 80 °C give mixtures of hexasubstituted benzenes, metal-complexed, tetrasub-stituted cyclopentadienones and quinones. An exception is the preparation of the stable tetrakis(trifluo-romethyl)cyclopentadienone from the alkyne the unusual electronic properties of the product make this result lack generality. 

Table 7.14 Calculated benzene force constants and benzene-metal separations (a).

System fed mdyn A mdyn A" fc-meXaJ mdyn A AlCmetal mdyn A rad Benzene metal / A... 

Optimum Conditions for Preparing Benzyllithium from Toluene. Both the TMEDA and TED complexes of benzyllithium were investigated. Toluene metalation proceeds much faster than does benzene metalation under similar conditions. The benzyllithium complexes were more soluble in hydrocarbon solvents than were the corresponding phenyllithium complexes. This method of preparation of benzyllithium is the most convenient of the few literature procedures available. Other procedures described are the cleavage of benzyl methyl ether with lithium... 

Only a brief study was made of the metalation rate of toluene by n-butyllithium because the reaction proceeded readily with TMEDA under most conditions. The runs listed in Table IV indicate just how much faster toluene metalation proceeded compared with benzene metalation. This rate was about 6.5 times faster with hexane as the solvent and at least 10 times faster when the corresponding aromatics (toluene and benzene) were used as the solvents. 

Using the optimum conditions for benzene metalation as indicated by the carbonation studies, we found that other reactions typical of phenyllithium proceed in very high yield when phenyllithium-TMEDA is prepared this way. Some typical reactions are outlined below. 

The first example of a fluxional benzene-metal compound has been reported, the l,2,3,4-/e/ru/r / robenzenerhodium(i) compound (50). The... 

CFR 212.18 authorizes the jse ol one-half gallon mbber hydrocarbon solvent or toluene n heu of benzene. Metallic sodium m excess of 33 pounds is also authorized. SOA 2C IS only supplied m the anhydrous k>nnuiatK>n It must be used m a closed arxl conimuous system unless it is shown tttat it is not practical to do so... 

Ferrocene was the first organometallic guest incorporated and numerous spectroscopic and electrochemical studies have been performed on ferrocene, substituted ferrocene, and related metallocene (e.g. cobaltocene) inclusion complexes (444-469]. Half-sandwich cyclopentadienyl- and benzene-metal carbonyl complexes have also been studied quite extensively [470-479] as have // -allyl metal (palladium) complexes [480], diene metal (rhodium) complexes [481-484], acetylene cobalt carbonyl cluster complexes [485], and complexes with metal carbonyls, e.g. Fe(CO)5, Mn2(CO)io, and CoNO(CO)3 [485a]. 

For the current discussion, RVS analysis has been carried out on cation-jt complexes of benzene-metal complexes. An overview of the results obtained for the RVS analysis carried out at the HF/6-31G level on the cation-jt complexes of benzene with monovalent and bivalent metal ions such as LP, Na, K, Mg and Ca + is presented in Figure 15.5. Generally, cation- t complexes are held by pure electrostatic effects due to strong attraction between opposite charges. Hence, bivalent metal ions show stronger interaction than the monovalent metal ions. However, the contribution of ion-quadrupole interactions in complex stabilization is still being... 

FIGURE 15.5 RVS decomposition carried out on various benzene-metal ion complexes at the HF/6-31G level. 

R ligands which may effectively prevent solvent molecules from entering the yttrium coordination sphere. It is relevant to mention here the compounds CpJTiR (R = H, CH ) which don t show benzene metallation not even when solutions of CpJTiR are heated for prolonged periods in at 90 C (vide supra). This clearly demonstrates the difference between Ti on one side and Group IIIB metals and lanthanides on the other. 

Studies of General Interest.- Dicationic benzene-metal complexes such as [Cp M(n-PhH) ] (M = Rh, Ir) and [ (hmb) Ru (n-PhH) ] add two hydride ions (from NaBH ) successively to give finally neutral products from which cyclohexene can be liberated by treatment with protlc acid (i.e., overall benzene + 2h + 2H - cyclohexene) j similar reactions occur with HeLl and MeONa in place of NaBH, Vanadium.- MO calculations on the triple-decker sandwich complexes... 

Table 4-15. Infrared Active Vibrations of in Benzene-Metal...

List the characteristic absorption bands of 7r-benzene metal complexes. 4-17. What kind of information can be obtained from the electronic (ultraviolet and visible) spectra of 7c-complexes ... 

Infrared-Active Normal Vibrations of w-CeHe in Benzene-Metal Complexes"... 

Table XXXV lists the seven infrared-active n.v. assuming metal-ring local symmetry. In addition to these bands in the chromium and molybdenum complexes eight other n.v. can be assigned according to C3 local symmetry of the ligand rings. The other benzene-metal carbonyls have yet to be studied more thoroughly in order to decide on the exact symmetry of the rings.

Substituted-benzene-metal tricarbonyls of chromium, molybdenum, and tungsten do not have any intense band in the 900 to 980 cm range, while the parent compounds absorb at 902 and 978 cm, respectively 131). The IR spectra of hexamethyl-, hexaethyl-, and iefa-diisopropylbenzene(Mo, W) tricarbonyls show weak to medium intensity bands, probably due to some... 

Hobza and coworkers performed a comparative study of Ag, Au, and Pd atoms binding to graphene [114] with electron correlation (CCSD(T) and MP2 with Douglas-Kroll Hamiltonians), conventional (i.e., LDA and GGA) and dispersionaccounting DFT methods (PBE-D3, M06-2X, vdW-DF, and EE -I- vdW). Binding of these metals to graphene is of varied nature, but it is due to electron correlation, as ROHF/ANO-RCC-VTZP benzene-metal potential energy curves have no minima. 

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