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Y.-C. Shi et al. / Polyhedron 23 (2004) 749–754
ethanol
RT
density resulting from deprotonation and nickel-
to-ligand feedback after forming the complex [12,23].
In the IR spectrum of the ligand, the band at ca. 3100
H L + M(OAc)2
2
LM + 2HOAc
M = Cu,Ni
ꢀ
1
cm due to m(NH) appears. However, no band assign-
able to m(NH) is present in the spectra of the complexes.
This fact indicates that the ligand is bonded to copper
and nickel ions in the dianionic form. Moreover, the
strong bands attributed to the stretching vibrations of
the skeleton C@O and C@C groups, which are observed
Scheme 2. Syntheses of complexes.
is a mixture of two isomers whereas the latter is a single
isomer. However attempts to isolate any isomer of
complex I have proven to be unsuccessful. In contrast,
the same reaction of ferrocenoylacetone and 1,2-diami-
noethane in refluxing methanol for 1.5 h furnished a li-
gand (H2bfe) in a yield of 84% [11,12]. An analytical data
ꢀ
1
at 1601, 1557 and 1520 cm in the ligand, are red-
ꢀ
1
shifted to the region 1576–1578 and 1511–1513 cm in
the complexes [3,13,19]. This is because the doubly de-
protonated ligand (L ) has a stronger conjugate effect
which results in the decrease of the double bond char-
1
2ꢀ
comparison of the three isolated isomers H2L, H2L and
2
H2L with H2bfe reveals that H2L seems to be H2bfe [11].
However, none of the three isomers is fully consistent
with H2bfe. Therefore, perhaps H2bfe is a mixture of the
above isomers [13]. Complexes I and II were prepared in
refluxing methanol and dichloromethane for 17 h [12]. In
acter of C@O and C@C groups [13]. It is noted that
H2L and H2L display the following absorptions at
1
2
3429, 3096, 1600, 1557, 1520 and 3417, 3090, 1599, 1561,
1523 cm 1, respectively. Among the three isomers, the
most marked differences result from the relative inten-
sities of the four last characteristic absorptions.
ꢀ
fact, at room temperature, H L can react with copper(II)
2
and nickel(II) ions in ethanol and dichloromethane for
1
2 h to produce complexes I and II.
The UV spectrum of the ligand shows three absorp-
tions at 271, 342 and 450 nm, which are attributable to
the B-band of the cyclopentadienyl ring, K-band of the
skeleton and an intraligand charge transfer transition
3
.2. Spectra
1
1
2
The H NMR spectrum of the free ligand (H L) shows
2
2 2
band [13,23]. Similarly, H L and H L display three
clearly that it exists entirely in the bis(ketoenamine) form
both acidic protons on enamine nitrogen atoms),
namely [C5H5FeC5H4COCH@C(CH3)NHCH2]2 [13,19–
1]. The protons of the substituted cyclopentadienyl
rings display two singlets at d4.37 and 4.72 ppm, whereas
a singlet at d4.17 ppm is due to protons on the unsub-
stituted cyclopentadienyl rings. Moreover, methylene
absorptions at 265, 346, 453 and 271, 347, 446 nm, re-
spectively. Because the three isomers have similar curves
of UV absorptions, they should have similar conjugated
systems. This further supports the proposed structures
for the three isomers as described in Scheme 1. For
complex I, the shortest wavelength absorption which is
assigned as the B-band of the cyclopentadienyl ring
displays a hypsochromic shift compared with that of the
ligand [12,23]. However, the K-band at 344 nm shows a
red shift. In addition, complex I exhibits an intense
absorption band at 446 nm which may be due to a li-
gand-to-metal charge transfer transition. For complex
II, interestingly, compared with those absorptions of the
ligand, the B-band and K-band show hypsochromic
shifts. It is noteworthy that as expected, tetrahedral
complex I does not show a d–d absorption, however, the
theoretically planar nickel complex II should exhibit a
d–d absorption, in fact, the ligand field band of complex
II is not observed because the weak d–d transition is
obscured by other intense absorptions [13,23].
(
2
protons of the NCH moiety exhibit a triplet at d3.50
2
ppm. In contrast, the methyl protons show a singlet at
d2.02 ppm. A singlet at d5.30 ppm may be assigned to
two methine protons. A singlet signal attributed to the
enamino NH appears at d11.10 ppm and disappears in
the presence of D2O. The very downfield position of this
signal may be mainly resulted from the intramolecular
hydrogen bonding [13,22]. It is obvious that the above
evidence is consistent with the proposed structure of the
1
ligand [13,22]. Similarly, two other isomers H L and
2
2
H L display corresponding absorptions [13,22]. For
2
example, those of methyl, methylene, methine, unsub-
stituted cyclopentadienyl and substituted cyclopenta-
dienyl (two triplets) groups appear at d2.01, 2.03; 3.49,
3
4
.50; 5.30, 5.30; 4.17, 4.19 and 4.36, 4.37 as well as 4.72,
.72 ppm whereas signals of labile hydrogens are ob-
3.3. Crystal structures
served at d11.1 and 11.11 ppm. For complex II, the signal
corresponding to the enamino NH at ca. 11.1 ppm dis-
appears and the absorption of methylene protons is
present as a singlet, indicating that the ligand is deprot-
onated and bonded to the nickel ion which is also sup-
ported by the crystal structure as described below. In
addition, all the signals of protons shift highfield in
complex II, which may be due to the increase of electron
In principle, in view of the planar or tetrahedral co-
ordination geometry of the central metal ion (copper or
nickel) and anti or syn arrangement of the ferrocenyl
groups with respect to the mean plane with the central
metal ion (copper or nickel) and donor atoms, four-
coordinate copper or nickel complexes may have four
stereoisomers: planar-anti, planar-syn, tetrahedral-anti
and tetrahedral-syn [13].
Shi, Yao-Cheng
