Rr-arene complexes

Refer to 5.8.2.9.3 for a discussion of the formation of rr-arene complexes subsequent to oxidative addition-disproportionation-metal-atom reactions, e.g. ... 

Hydrocarbon-Metal rr-Complexes, Other than rr-Cyclopentadienyl rr-Arene Complexes 331... 

Hydrocarbon-Metal TT-Complexes, Other than TT-Cyclopentadienyl rr-Arene Complexes 361... 

Hydrocarbon-Metal ir-Complexes, Other than Tr-Cyclopentadienyl rr-Arene Complexes 369... 

There are two different general classes of rr-bound arene-containing complexes of molybdenum the monoarene complexes [() -arene)Mo(CO)3] or the h/i-arene complexes [()] -arene)2Mo]. The solid-state structures of both classes of compound show that the bond lengths around the arene ligand are equivalent. This clearly means that the arene does not bond as a friene through localized electron pairs. 

The electronic difference between benzene and borazine is further supported by the properties of compounds of the type (R<,BjN j)Cr(CO)j. Although the.se are formally analogous to (rj< -QRf,)Cr(CO)j. the bonding is not nearly so strong in the borazine complex—its ring-metal dissociation energy appears to be about one-half that of the arene complex. In addition, there is considerable evidence that the borazine molecule is puckered in the.sc complexes. The actual structure appears to be intermediate between a true tt complex and the extreme rr-only model ... 

Arene complexes with mint metals are rather rare. The arene metal bond is weaker compared to the other transition metals and hapticity is lower. For this reason the stronger rr-donor properties of the cyclophanes compared to open chained arenes [109c] make the preparation in benzene solution possible. The cyclophane is simply heated with silver-I (Fig. 29a) [109a] or copper-I (Fig. 29b) [109b] and yields the respective complex formed in almost quantitative yield. It is noteworthy that the silver ion in 128 shows no interaction with the benzene ring at all the naphthalene unit acts as 7t-donor only [109a]. 

Organoaluminum /7-t< rr-butylcalix[4]arene complexes are formed in reactions... 

This survey of the 2000 literature relating to rr-hydrocarbon complexes of the transition elements other than p-CsHs and r -arene complexes is similar in nature to previous reports. This chapter is sub-divided into the following sections dealing with reviews complexes containing allyls or monoalkenes unconjugated alkenes conjugated alkenes acyclic alkenes alkynes and polymetallic complexes. 

Yosida et al. [41] found that p-t< rr-butylcalix[6]ar-ene can extract Cu from the alkaline-ammonia solution to the organic solvent. Nagasaki and Shinkai [42] described the synthesis of carboxyl, derivatives of calix-[n]arenes ( = 4 and 6) and their selective extraction capacity of transition metal cations from aqueous phase to the organic phase. Gutsche and Nam [43] have synthesized various substituted calix[n]arenes and examined the complexes of the p-bromo benzene sulfonate of p-(2-aminoethyl)calix[4]arene with Ni, Cu , Co-, and Fe. ... 

Labelling experiments provided the evidence that the Fe1- and Co1-mediated losses of H2 and 2H2 from tetralin are extremely specific. Both reactions follow a clear syn- 1,2-elimination involving C(i)/C(2) and C(3)/C(4), respectively. In the course of the multistep reaction the metal ions do not move from one side of the rr-surface to the other. The kinetic isotope effect associated with the loss of the first H2 molecule, k( 2)/k(Y)2) = 3.4 0.2, is larger than the KIE, WFLj/ATHD) = 1.5 0.2, for the elimination of the second H2 molecule. A mechanism of interaction of the metal ion with the hydrocarbon n-surface, ending with arene-M+ complex 246 formation in the final step of the reaction, outlined in equation 100, has been proposed241 to rationalize the tandem MS studies of the unimolecular single and double dehydrogenation by Fe+ and Co+ complexes of tetraline and its isotopomers 247-251. 

Alkylation and Vinylation via Intermediary Transition Metal rr-Complexes of Arenes... 

Complexes with alkenes and arenes are formed when the hydrocarbons are shaken with aqueous solutions of silver(I) salts. Di- or polyalkenes often give crystalline compounds with Ag+ bound to one to three double bonds. The formation of alkene complexes of varying stability may be used for the purification of alkenes, or for the separation of isomeric mixtures (e.g., 1,3-, 1,4-, and 1,5-cyclooctadienes), or of the optical isomers of a- and /3-pinene. There is very little back-bonding contribution in the formation of Ag1 rr-complexes. For example, the planar complex (hfa)Ag(Ph-C= C-Ph) contains an almost linear acetylene ligand with a C=C... 

Chiefly through the work of Jonas and co-workers (55) mixed-metal organometallic complexes also are known that involve interactions of lithium atoms with unsaturated rr-bonded hydrocarbon ligands (olefin, cyclopentadienyl, arene, etc.). While reviews already are available (55, 89), we include examples for comparison purposes. The lithium complexes in this section show increasing complexity and diversity both in the geometries around the lithium atoms and in the degree and type of interactions involved. The common feature in these compounds is the interaction of a lithium atom with a hydrocarbon ligand which is tt... 

The classic SsAi substitution of activated aryl halides by protected cyanohydrin anions provides substituted benzophenones. Another procedure for the arylation of protected cyanohydrin anions involves the use of aromatic substrates activated as their rr-chromium tricarbonyl complexes. - Addition of the anion of (32) to the 1,3-dimethoxybenzene complex, for example, leads principally to the meta-suh-stituted isomer (33 equation 20). Preferential meta regioselectivity is also noted with other -rr-chromium tricarbonyl complexes of arenes. Other arylations of cyanohydrin anions include interesting but synthetically limited additions at the a-position of quinoline N-oxides. In a similar manner, cyanohydrin carbonates of aromatic aldehydes react with A -oxides of quinoline and isoquinoline. ... 

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