Pentafluorophenyl derivatives lithium

Trifluorovinyl and pentafluorophenyl derivatives of tin [11, 15] can be obtained readily via magnesium or lithium derivatives. It is interesting that the stability of (CH3)3SnCgF5 to hydrolysis is very dependent on purity in the presence of fluoride ion, rapid hydrolysis occurs and a process involving initial co-ordination of fluoride ion, and other halide ions, to tin has been suggested [111] (Figure 10.53). 

Pentafluorophenyllithium in ether reacts slowly with mercury at 15° C to afford bis(pentafluorophenyl)mercury, a compound recently prepared by another route (Section VII, B). The lithium reagent has very recently been used to prepare pentafluorophenyl derivatives of boron (79a), tin 19b), lead 19b), and several transition metals 19c). 

The organolithium-reagent (5) is itself capable of forming the aryne (9) which can add pentafluorophenyl-lithium. This was found to occur and gave the terphenyl derivatives (10) and (11) in the ratio of 1 9 26>. 

When we allowed pentafluorophenyl-lithium to decompose in ether in the presence of an excess of N, ZV-dimethy laniline we obtained the compounds (92) 70, X = F), (94), the latter as the major compound, and a product which was shown to be (97). That this latter compound did not arise by metallation of 2V,lV-dimethylaniline followed by addition to tetrafluorobenzyne was shown by quenching the reaction mixture with deuterium oxide. No deuterium incorporation was detected. The compound (97) provides a rare example of a product derived by a Stevens rearrangement in which aryl migration has occurred b>. 

Not only lithium-derived organometallic compounds have proved to be suitable reagents for generating a new C —P bond Grignard and cadmium compounds have also found some applications, but they are not so widespread. For example, tris(pentafluorophenyl)phosphane... 

In addition to these cycloaddition reactions with nucleophilic Tr-donors, tetrafluoro-benzyne is very susceptible to more general nucleophilic attack. Biphenyl derivatives often occur as by-products in reactions of pentafluorophenyl-lithium, formed by addition to the benzyne [204, 229] (Figure 9.89). 

Tris(pentafluorophenyl)aluminium is obtained as the etherate from either the Grignard reagent in ether or the lithium derivative in ether/hexane [81, 85], whereas only complex materials are obtained from pentafluorophenyl-lithium in hexane (Figure 10.34). Attempts to remove the ether from the etherate, 10.34A, inevitably led to explosions. 

Reaction of pentafluorophenyl-lithium with tungsten pentachloride in diethyl ether yields the bright-green complex LiW(C,F5)5,2Et,0, which is stable for several months at -10 °C, and decomposes only slowly at room temperature. It yields (C F5)2Hg with mercuric chloride, CeFsI with iodine, and is hydrolysed to pentafluorobenzene. When heated to 100 °C it gives pentakis(pentafluorophenyl)tungsten as an orange-red solid in low yield and a tungsten(iv) derivative, (C,F5)iW, may be formed, but is too unstable to isolate. ... 

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