5,17-Bis arene

Bis ( -arene) metal complexes have been made for many transition metals by the AI/AICI3 reduction method and cationic species [M( j -Ar)2]"" " are also well established for n = 1, 2, and 3. Numerous arenas besides benzene have been used, the next most common being l,3,5-Mc3C6H3 (mesitylene) and CeMce. Reaction of arenas with metal carbonyls in high-boiling solvents or under the influence of ultraviolet light results in the displacement of 3CO and the formation of arena-metal carbonyls ... 

Although the cyclopentadienyls dominate the aromatic chemistry of this group, bis(arene) compounds are also well established. They are able to satisfy the 18-electron rule as the dications, [M(arene)2] " or by the two rings adopting different bonding modes one tj the other tj". ... 

Bis-arene iron dications [20] are easily accessible from arenes, A1C13 and FeCl3 (for C6Me6, FeCl2 must be used). It is advisable to use tris-sublimated A1C13 to avoid problems of isomerization [23], With toluene, this isomerization due to the re/ro-Friedel-Crafts mechanism [24] is too extensive to give any clean complex. 

Although the o-xylylene complex is thermally unstable, it was characterized at — 50 °C by its 1H- and 13C-NMR spectra showing the exocyclic methylene at 5 = 5.04,4.42 ppm (JH) and 5 = 144.8 ppm (13C) using C6D5CD3 as the solvent. Its reaction with benzoyl chloride on the exocyclic carbon leaves a very acidic methylene group which transfers a proton onto the adjacent methylene unit. The double bond is benzoylated again in in situ and a di-cation of the [bis(arene)Fe]2+ type is obtained [47] Scheme VIII. 

In all the working strategies with the [bis(arene)Fe]2+ series, only one ring must be functionalized several times, although the starting product is symmetric. 

Maury, F., Oquab, D., Morancho, R., Nowak, J., and Gauthier, J., Low Temperature Deposition of Chromium Carbide by LPC VD Process using Bis-Arene Chromium as Single Source, Croc. 10th Int. Conf. on CVD, (G. Cullen, ed.), pp. 1213-1219, Electrochem Soc., Pennington, NJ 08534 (1987)... 

Lagowski et al. (79) synthesized a very large series of bis(arene) Cr(0) compounds, thereby providing a good example of the use of metal-atom chemistry in synthesizing homologous series of compounds... 

Mixed arene-2,5-dihydro-l,2,5-thiadiborole-iron complexes have been synthesized by a novel route thermally unstable bis(arene)iron sandwich complexes, prepared by cocondensation of iron atoms with arene, react in the temperature range of -100 to -60°C with free Et2C2B2Mc2S to form reactive intermediates that decom-... 

Tullock C.W. et al.. Polyethylene and elastomeric polypropylene using alumina-supported bis(arene) titanium, zirconium, and hafnium catalysts, J. Polym. Sci, Part A, Polym. Chem., 27, 3063, 1989. Mueller G. and Rieger R., Propene based thermoplastic elastomers by early and late transition metal catalysis. Prog. Polym. Sci., 27, 815, 2002. 

Co-condensation of transition metal atoms with arenes such as benzene and toluene is well known to yield bis-arene-metal compounds. However, in many cases the yields based on the metal atoms are less than 40%. Evidence that competing reactions such as carbon-hydrogen activation can occur is provided by the isolation of non-metal-containing products such as biaryl derivatives (2JL). ... 

Consequently, in Figures 5-11 are shown the appropriate Tanabe-Sugano type diagrams for dx systems (x = 2 — 8) in pseudo-axial, CmV, symmetry, the parameters DtjDs = 0.55 and C/B = 4.0 being adopted throughout. As indicated above this parameteri-sation is most appropriate for the metallocenes, for which the d-d spectra are now considered in more detail. Thereafter a brief survey is made of the limited data relating to bis-arene species, and to various mixed sandwich complexes. 

The best known bis-arene system, bis-benzenechromium, Cr(Bz)2, has been studied by a number of authors (94, 95, 96), but the results of Feltham, in cyclohexane solution, are typical a broad band with a maximum (e = 25) at 15.6 kK. is the only feature at lower energies, a stronger peak (e = 8000) being found at 31.25 kK. with a rising absorption... 

The overall picture for the bis-arene systems is therefore not at all satisfactory, and much more experimental work is required on these compounds, especially for complexes representing d 6 and <2 8 configurations. 

Of these there are no established examples of the first two cases, but for the d3 and ds systems the metallocenes V(Cp)2 and Ni(Cp)2 respectively have been shown to have the appropriate ground states, and in the latter case a number of bis-arene species are also known. For d5 complexes Mn(Cp)2 is known to be able to exist in the high-spin 62+ form, but the bis-arenes all possess the low-spin 2E+(a S4) ground state which yields little information from susceptibility measurements since it consists only of a single Kramers doublet. 

For the odd electron systems, tf3 4Z andc 5 6Z+, measurements of the average susceptibility at very low temperatures are not likely to prove as informative as for the even electron, d 32 species. This is because whereas the latter yield a limiting value of 1 as T -+ 0, from which D/g2 can be directly estimated, the former lead only to a limiting value of the (x)-1 vs. T slope, which except for large values of D will be difficult to determine. Nevertheless calculation shows that even in cases for which only very small deviations from the spin-only behaviour are to be expected, e.g. V(Cp)2, the susceptibility may yet show very considerable anisotropy. Thus, with the parameters of Prim and Van Voorst (47), V(Cp)2 is predicted to show an anisotropy, (x — X )Kx of some 5% at liquid nitrogen temperatures, whilst Ni(Cp)2, with the much larger/) value, should show an anisotropy of about 30% at 77K, which is reduced only to some 12% even at room temperature. There is thus considerable scope for the measurement of anisotropic susceptibilities, and although this technique would probably not be applicable to the d8 bis-arenes (97,... 

For the orbital doublet ground states of the bis-arene series there is virtually no information the d9, 2II complex, Co (HMBz)2, has been reported to show three different g values (but no numerical details were given) (122), whilst for Fe(HMBz)2+ in 50%aqueous ethanol at 25 K the valuesgz = 2.086, gx = 1.865, andg = 1.996 were recorded (121). From these resalts Ammeter etal. (142) calculate k V4S = 0.40 and /A = 0.17, which corresponds to a substantial A of almost 2060 cm-1, if g is taken as 350 cm-1. 

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