G. V. Khoroshenkov, T. V. Petrovskaya, I. L. Fedushkin, M. N. Bochkarev
reactions of Nd, Dy, and Tm with iodine [1, 2]. The forma-
tion of fusions of the metals during these processes indi-
cates that the temperatures exceed 1500 °C in the reaction
zone. Since the reaction times are very short, the hot melts
do not cause demage to the walls of the glass reactor used
for these reactions. After completion of the reactions, the
excess of metal solidifies in the shape of drops. The triiod-
ides LnI3 formed as side products partially vaporize and
deposit on the walls of the reaction vessel as white or pale
colored tight coatings. It should be noted that the reactions
of iodine with La, Ce, or Pr initiate at somewhat lower tem-
peratures, but proceed more vigorously than the reactions
with Sc, Y, Er, or Lu. These differences will be caused by
the differences in the melting temperatures of the metals.
Whereas La, Ce and Pr melt between 797Ϫ935 °C, the melt-
ing points of Sc, Y, Er, or Lu range between 1497 and
1752 °C [9]. The iodine/metal ratios of the isolated black
solids deviate from the ideal value of 2 and range from 1.8
to 2.4 what can be explained by contamination of the ex-
pected LnI2 compounds with unreacted metal and/or the
corresponding LnI3 derivatives or, perhaps, with some other
LnyIz phases. The formation of highly reduced phases like
LnI will be less probable because such phases, as demon-
strated by LaI [10], are rather unstable and can be synthe-
sized only at a definite and strictly kept temperature. The
displacement of hydrogen in the reactions of the isolated
products with phenol, alcohols, or cyclopentadiene yielding
ROLnI2 or CpLnI2 type compounds with yields up to 60 %
indicates that lanthanide diiodide will be the main compo-
nent of the starting material. The diamagnetism of the Sc,
Y, and La derivatives proving the trivalent state of the re-
spective metal causes us to suggest that all the products of
the reactions of iodine with excess Sc, Y, La, Ce, Pr, Gd,
Ho, Er or Lu under the given conditions lead to products
which, in analogy to the metallothermic method [5], must
be formulated as (Ln3ϩ)(eϪ)(IϪ)2. In the following text,
these (Ln3ϩ)(eϪ)(IϪ)2 compounds are symbolized as LnIx.
In contrast to the diiodides of divalent Sm, Eu, Nd, Dy,
Tm, and Yb, all the obtained substances do not dissolve in
THF, DME or liquid ammonia, thus confirming the differ-
ence in the nature of true LnI2 salts and the diiodides of
trivalent lanthanides, LnIx. Despite of this insolubility in
THF, these compounds readily react in this medium already
at room temperature with phenol or alcohols to give the
phenoxy- or alkoxylanthanoid diiodides [ROLnI2(THF)x]
in yields of 25 to 55 % (Table 1):
with lanthanide metall used in excess for their syntheses and
also with LnI3 formed as side product, it could be suggested
that the formation of the alkoxylanthanide diiodides would
be the result of an interaction of the alcohols with the ad-
mixed metal producing (RO)3Ln followed by dismutation
of (RO)3Ln with the side product LnI3. However, we estab-
lished qualitatively that under the given conditions alkohols
react essentially slower with lanthanide metals than with
the appropriate LnIx compounds and that a dismutation in
the supposed way does not occur at all.
Among the LnIx derivatives, ScIx shows a different reac-
tivity towards cyclopentadiene. Whereas the LnIx deriva-
tives of Y, La, Ce, Pr, and Gd react with cyclopentadiene
in THF already at room temperature yielding the complexes
CpLnI2(THF)3 with yields up to 58 % (Table 1), no reaction
takes place with ScIx not even at 60 °C. Taking into account
the close values of E0 of scandium and yttrium, such a dif-
ference in reactivity was not to expect, although it is known
that the reducing power decreases from Y to Sc.
THF
2 (Ln3ϩ)(eϪ)(IϪ)2 ϩ 2 CpH
Ln ϭ Y, Ce, Pr, Gd, Er
Ǟ 2 [CpLnI (THF) ] ϩ H
2 3 2
ᎏᎏ
In spite of the medium yields, the reactions of LnIx with
ROH and CpH can be recommended as a preparative route
for compounds of the ROLnI2(THF)x or CpLnI2(THF)x
type since the dismutation or metathesis reactions which
are generally used for their preparation, afford mixtures of
mono- and diiodocomplexes which are only hardly to sep-
arate into the components.
LaIx readily reacts with 2,2’-bipyridine to give the hetero-
leptic complex LaI2(bipy)2(THF)2 containing the 2,2’-bipy-
ridyl radical-anion. According to its IR and ESR spectra,
the complex is identical with the compound synthesized by
the reaction of the lanthanum naphthalene complex
[LaI2(THF)3]2(C10H8) with 2,2’-bipyridine [12].
Weak oxidants such as stilbene, naphthalene and anthra-
cene do not react with the LnIx compounds. However, when
a suspension of LaIx in THF was stirred with naphthalene
or anthracene for a few days, the reaction solution gets blue
(naphthalene) or violet (anthracene) colored, what may be
indicative for the formation of an organolanthanid com-
pound. Note, that the complex [LaI2(THF)3]2(C10H8) ob-
tained from LnI3 and C10H8Li has a blue color [13].
Experimental Section
THF
2 (Ln3ϩ)(eϪ)(IϪ)2 ϩ 2 ROH
Ǟ 2 [ROLnI (THF) ] ϩ H
2 x 2
ᎏᎏ
General remarks. All manipulations were carried out under vacuum
using standard Schlenk techniques. Diethyl ether, THF, toluene,
and hexane were dried with and kept over sodium benzophenone
ketyl. THF was condensed under vacuum into the reaction vessel
just before use. The IR spectra were recorded on a Specord M-75
spectrometer. The samples were prepared as Nujol mulls and
placed as films between KBr glasses. The ESR spectra were meas-
ured on a Bruker ESR 200D-SCR instrument. The 1H NMR spec-
tra were recorded on a Bruker DPX 200 spectrometer. Magnetic
measurements were carried out by the previously published pro-
Ln/R/x ϭ Sc/Ph/3; Y/Ph/3; La/Ph/2, La/i-Pr/2, La/t-Bu/2;
Pr/Ph/3; Gd/Ph/5; Er/Ph/5
No reactions take place with the less active triphenylcar-
binol. It should be noted here, that rare earth metals acti-
vated by iodine anions also can react with alcohols under
comparable conditions to give the alkoxides (RO)3Ln [11].
Since the LnIx compounds are more or less contaminated
700
Z. Anorg. Allg. Chem. 2002, 628, 699Ϫ702