The first chalcogen-bridged [1]ferrocenophanes
Fe(η-C5H3R)2E (6,
E = S, R = H; 7, E = Se, R = H;
12,
E = S, R = Me) have been synthesized and characterized both
structurally and spectroscopically. Synthesis of
sulfur- and selenium-bridged species 6 and 7 was
achieved by the reaction of dilithioferrocene·TMEDA
(TMEDA
= tetramethylethylenediamine) with bis(phenylsulfonyl) sulfide
S(O2SPh)2 and selenium
diethyldithiocarbamate
Se(S2CNEt2)2,
respectively, in 20−30% yields. Structural characterization of
both 6 and 7 revealed highly
strained
structures with tilt-angles between the cyclopentadienyl ligands of
31.05(10)° and 26.4(2)°, respectively.
Compounds
6 and 7 are purple and red-purple, respectively;
comparison of the structures of known [1]ferrocenophanes
1 showed
that when the second period (from group 14−16) is traversed, there is
a substantial increase in cyclopentadienyl
ring-tilting in main group element bridged [1]ferrocenophanes,
and the lowest energy UV/vis absorption peaks become
increasingly red-shifted. Extended Hückel MO calculations
were performed and, consistent with this observation,
predicted a decrease in the HOMO−LUMO gap as the ring-tilt increases.
Thermal ring-opening polymerization
(ROP) of both 6 and 7 afforded the insoluble
poly(ferrocenyl sulfide)
[Fe(η-C5H4)2S]
n
8 and poly(ferrocenyl selenide)
[Fe(η-C5H4)2Se]
n
9, respectively. Differential scanning calorimetry
studies of the ROP process provided estimates
of the strain energies of 6 and 7 which were ca.
130(±20) and 110(±20) kJ mol-1,
respectively. Anionic ROP of
6 also yielded the insoluble poly(ferrocenyl sulfide)
8. However, linear soluble dimeric and trimeric
trimethylsilyl-capped oligo(ferrocenyl sulfides) 10b and 11b
were synthesized by the reaction of 6 with
dilithioferrocene·TMEDA
followed by the addition of Me3SiCl and were
characterized spectroscopically, electrochemically, and, for
11b, by
X-ray diffraction, and provide useful models for the analogous high
polymer. The dimethylated sulfur-bridged species
12 was prepared as a mixture of isomers from the reaction
between dilithiodimethylferrocene·TMEDA and
S(O2SPh)2, and X-ray structural characterization of a single
isomer 12a showed the presence of a large tilt-angle
of
31.46(8)°. Thermal and anionic ROP of the isomer mixture
12 afforded the first soluble poly(ferrocenyl
sulfide)
[Fe(η-C5H3Me)2S]
n
13 which was characterized by 1H and
13C NMR, elemental analysis, thermogravimetric
analysis,
and gel permeation chromatography. Cyclic voltammetric studies of
13 showed the presence of two reversible
oxidation waves with a redox coupling ΔE = ca. 0.32 V,
which is consistent with the presence of significantly
stronger M···M interactions compared to those present in other
ring-opened poly(ferrocenes) derived from
[1]ferrocenophanes.
