FECP(+) INDUCED HETEROLYTIC CLEAVAGE OF PHENYL ETHERS AND TRANSETHERIFICATION

The aryl ether complexes [FeCp(eta(6)-PhOR)](PF6-)-P-+, 1, (R = alkyl or phenyl) and [Fe(C(5)Me(5))(eta(6)-PhOEt)](PF6-)-P-+ 6, react with o ne equiv. KO-t-Bu and one equiv. n-Bu(4)NPF(6) in THF to give the clea ved complexes [Fe(+)Cp(eta(6)-PhO(-))], 3, and [Fe+(C(5)Me(5))(eta(6)- PhO(-))], 7. The X-ray crystal structure of 7, H2O, reported in a prel iminary communication, showed a phenate zwitterionic structure. The in frared and H-1 and C-13 NMR spectra indicate that the structures of 3 and 7 are intermediate between those of the hexahapto phenate complexe s and the pentahapto oxo-cyclohexadienyl complexes. The interaction wi th weak (H2O, Na+) or strong (H+PF6-) electrophiles shifts the haptici ty to fully hexahapto. The heterolytic C-O cleavage reaction is best v iewed as a simple nucleophilic substitution of the phenate complex by the nucleophile (KOt-Bu or KOH). The requirement of n-Bu(4)NPF(6) emph asizes the need to develop a polar transition state. In the absence of this salt, the same reaction carried out under identical conditions l eads to electron-transfer between KOt-Bu and 1 in the deeply-colored c harge-transfer complex [Fe(+)Cp(arene) Ot-Bu(-)], giving the Fe-l comp lex, which slowly decomposes without C-O cleavage. When the reaction b etween [FeCp(PhOR)](PF6-)-P-+ and KOt-Bu or KOH is carried out in the presence of R'X at room temperature for one to three days, transetheri fication proceeds, giving [FeCp(eta(6)-PhOR')](PF6-)-P-+. The KBr salt , formed in situ, inhibits the decomplexation side reaction. Alkylatio n of 3 in DMF with pentyl iodide (under ambient conditions) only proce eds in the presence of K2CO3. This feature is consistent with the need to form an alkali-coordinated phenate complex that is more reactive t han 3.