Jl. Fillaut et D. Astruc, POLYALKOXYBENZYLATION OF [FECP(ARENE)](+) COMPLEXES AND POLYFUNCTIONALIZATION OF THE TENTACLES WITH IRON SANDWICH REDOX CENTERS, New journal of chemistry, 20(9), 1996, pp. 945-957
The reaction of [Fe(II)Cp(C(6)Me(6))](PF6-)-P-+, 1, (Cp = eta 5-C5H5)
wih t-BuOK and para-alkoxybenzylbromides of various chain lengths in D
ME for 1 day at 40 degrees C reproducibly gives the hexa[p-alkoxybenzy
lation] complexes [Fe(II)Cp{C-6(CH(2)CH(2)PhOR)(6)}](PF6-)-P-+, 3, [R
= Me (a), Et (b), C7H15 (c), C6H12OCH3 (d), or C11H23 (e)] resulting f
rom single branching in yields around 60%. Double branching is achieve
d upon octamethoxybenzylation of [FeCp(durene)](PF6-)-P-+ 6, using KOH
and p-MeOPhCH(2)Br in DME which gives FeCp(1,2,4,5-{CH(CH(2)PhOMe)(2)
}4C6H2)](PF6-)-P-+, 7, and triple branching is achieved upon trimethox
ybenzylation of [FeCp(toluene)](PF6-)-P-+, 4, which gives [FeCp{C6H5C(
CH(2)PhOMe)(3)}](PF6-)-P-+, 5, under analogous conditions. Decomplexat
ion of the iron sandwich derivatives 3 proceeds in yields around 90% b
y photolysis with visible light in MeCN in the presence of 1 equiv. of
PPh(3) to give the ether-soluble free aromatics 10a-d and [Fe(III)Cp(
NCMe)(2)(PPh(3))](PF6-)-P-+. Reaction of the hexa[p-methoxybenzyl] der
ivatives 3a and 10a with BBr3 in CH2Cl2 gives nearly quantitative yiel
ds of the hexaphenols 11 and 12. The latter are alkylated by reaction
with BrCH2CN and K2CO3 in THF to give the hexanitriles 13 and 14. Effi
cient esterification of the hexaphenols requires prior formation of th
e hexathallium phenates, which precipitate upon reaction of the hexaph
enols with TIOEt in THF. The hexathallium phenate 12 reacts with organ
ic acyl chlorides in THF to give high yields of the hexaesters 17. The
hexaphenols 11 and 12 react in this way with Fc COCl (Fc = ferrocenyl
), giving the heptametallic hexaester [FeCp{C-6(CH(2)CH(2)PhOCOFc)(6)}
)(PF6-)-P-+, 15, and the hexaferrocene hexaester C-6(CH(2)CH(2)PhOCOFc
)(6), 16, respectively The organic hexaphenol 12 undergoes nucleophili
c substitution of the chloride by phenate in [FeCp(p-ClPhMe)](PF6-)-P-
+ to give the hexanuclear hexacationic complex C-6[CH(2)CH(2)PhO(-PhFe
(+)Cp)](6)(PF6-)(6), 18, in 65% yield. The cyclic voltammogram (CV) of
the heptanuclear complex 15, at -35 degrees C in DMF, shows two rever
sible waves with an intensity ratio of 1:6.3 +/- 0.3, indicating the p
resence of six ferocene units per [FeCp(arene)](+) in the molecule; si
milarly, the CV of the hexametallic complexes 16 and 18 show electroch
emically reversible waves; the oneness of the hexaelectron wave in 15,
16 and 18 (Delta Ep less than or equal to 80 mV) shows the independen
ce of the six redox centers located at the periphery of these molecule
s.