The variation of coordination modes of aromatic imines in iron carbonyl complexes: Is there a correlation between bond lengths in organometallic model compounds and the reactivity of the ligands in catalytic C-C bond formation reactions?

Article abstract of DOI:10.1016/j.jorganchem.2005.04.056

The reaction of aromatic imines with Fe₂(CO)₉ proceeds via a two-step reaction sequence. A C-H activation reaction in ortho-position with respect to the exocyclic imine function is followed by an intramolecular hydrogen transfer reac

Full text of DOI:10.1016/j.jorganchem.2005.04.056

Journal of Organometallic Chemistry 690 (2005) 3886–3897
www.elsevier.com/locate/jorganchem
The variation of coordination modes of aromatic imines
in iron carbonyl complexes: Is there a correlation between bond
lengths in organometallic model compounds and the reactivity
of the ligands in catalytic C–C bond formation reactions?
*
W. Imhof , A. Go¨bel, L. Schweda, D. Do¨nnecke, K. Halbauer
Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-University, August-Bebel-Str. 2, 07743 Jena, Germany
Received 1 April 2005; received in revised form 18 April 2005; accepted 18 April 2005
Available online 28 June 2005
Abstract
The reaction of aromatic imines with Fe2(CO)9 proceeds via a two-step reaction sequence. A C–H activation reaction in ortho-
position with respect to the exocyclic imine function is followed by an intramolecular hydrogen transfer reaction towards the former
imine carbon atom. The resulting dinuclear iron carbonyl complexes show an aza-ferra-cyclopentadiene ligand which is apically
coordinated by the second iron tricarbonyl moiety. Comparing the bond lengths of 43 different compounds, which were synthesized
and structurally characterized in our group shows that the iron iron bond length correlates with one of the iron carbon bond lengths.
The longer the iron carbon bond between the apically coordinated iron atom and the carbon atom next to the former imine carbon
atom is, the shorter is the iron iron bond. The same ligands may be used as the substrates in ruthenium catalyzed C–C bond for-
mation reactions. Whereas most of the imines react via the formal insertion of CO and/or ethylene into the C–H bond in ortho-posi-
tion to the imine function, the ligands that show the longest iron carbon bond lengths in the model compounds under the same
reaction conditions produce different types of isoindolones.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Iron; Carbonyls; C–H activation; Catalysis; X-ray
1. Introduction
[1–14]. This reaction sequence has been shown to be
the major reaction pathway for a wide variety of carbo-
cyclic and heterocyclic imine ligands.
The reaction of aromatic imines with Fe2(CO)9 or
Fe3(CO)12, respectively, leads to the formation of dinu-
clear iron carbonyl complexes via the activation of a C–
H bond in ortho-position with respect to the exocyclic
imine function followed by an intramolecular hydrogen
shift reaction towards the former imine carbon atom.
The resulting organometallic compounds therefore con-
sist of an formally six electron donating enyl-amido li-
gand adopting a l2-g3-coordination mode (Scheme 1)
The iron carbonyl complexes mentioned above may
well serve as model compounds for the initial steps in
ruthenium catalyzed C–H activation reactions of aro-
matic compounds taking place in ortho-position with re-
spect to exocyclic functional groups with potential metal
coordinating donor sites. These catalytic C–H activation
reactions are used to introduce new carbon carbon
bonds instead and due to the initial cyclometallation
step show the same regioselectivity as the stoichiometric
reactions with iron carbonyls [15–31].
*
Corresponding author. Tel.: +49 3641 94 8129; fax: +49 3641 94
The results presented herein show that the coordina-
tion mode of the ligand represented by the various bond
8102.
E-mail address: Wolfgang.Imhof@uni-jena.de (W. Imhof).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.04.056

W. Imhof et al. / Journal of Organometallic Chemistry 690 (2005) 3886–3897
3887
ligands in organometallic compounds with the reaction
pathways observed in catalytic C–C coupling reactions.
2. Results and discussion
Scheme 1.
During the last years, we have published a number of
diironhexacarbonyl complexes of various aromatic imi-
nes which are produced via the reaction depicted in
Scheme 1 [5,6,9–12]. The imine ligands are easily pre-
pared by condensation of the corresponding aromatic
aldehyde with a primary amine (cf. Section 3).
lengths may change dramatically depending on the aro-
matic system the imine ligands are based upon. In addi-
tion, these findings are used to attempt a correlation
between the properties of the coordination of the imine
Scheme 2.

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W. Imhof et al. / Journal of Organometallic Chemistry 690 (2005) 3886–3897
Scheme 2 shows the different classes of aromatic
imines used in this investigation. The ligands 1–9 are
based on heteroaromatic aledehydes like 3-indole-
carbaldehyde, thiophene-2-carbaldehyde, N-methyl-
pyrrole-2-carbaldehyde, furan-2-carbaldehyde
and
thiophene-3-carbaldehyde. 10–23 are benzaldehyde or
a- or b-naphthylcarbaldehyde derivatives whereas 24–
31 are bifunctional imines produced from terephthalic
aldehyde (24, 25) or from various diamines (26–31).
The synthesis and X-ray structures of the dinuclear
iron carbonyl compounds prepared from these imines
have been published before with the exception of the
molecular structures of the iron carbonyl complexes syn-
thesized from 7, 8, 14 and 30. The synthesis of the cor-
responding iron carbonyl compounds 32–35 as well as
the synthesis of the new but not structurally character-
ized di- and tetranuclear compounds 36–38 is shown in
Scheme 3.
The molecular structures of 32–35 are presented in
Figs. 1, 3, 5 and 7, respectively. They all show the coor-
dination mode which is typical for this class of com-
pounds, in which a diironhexacarbonyl fragment is
bound to an enyl-amido ligand in a l2-g3-fashion. The
molecular structures of these four iron carbonyl com-
pounds already show, that most of the bond lengths in
the coordination polyhedra of the iron atoms are very
similar in 32–35. The most important exception from
Fig. 1. Molecular structure of 32, selected bond lengths (pm) and bond
angles (ꢁ): Fe1–Fe2 241.6(1), Fe1–N2 195.6(3), Fe1–C3 214.2(4), Fe1–
C4 243.8(4), Fe2–N2 199.2(3), Fe2–C3 197.4(4), C3–C4 140.6(5), C4–C5
147.6(5), C5–N2 148.3(5); N2–Fe1–Fe2 52.94(9), N2–Fe1–C3 74.5(1),
N2–Fe1–C4 61.0(1), Fe2–Fe1–C3 50.9(1), Fe2–Fe1–C4 71.1(1), C3–
Fe1–C4 35.0(1), N2–Fe2–C3 77.6(1), Fe2–C3–C4 112.2(2), C3–C4–C5
118.6(3), C4–C5–N2 100.0(3), C5–N2–Fe2 112.9(2).
this finding is the bond length between the apical iron
atom Feap and the carbon atom (Cb in Scheme 1) next
to the methylene group which was formed by the hydro-
gen transfer reaction. This iron carbon bond length
Scheme 3.

W. Imhof et al. / Journal of Organometallic Chemistry 690 (2005) 3886–3897
3889
Fig. 2. Supramolecular structure of 32, H11ꢀ ꢀ ꢀO1x 258(1) pm, C11–H11ꢀ ꢀ ꢀO1x 161.5(8)ꢁ, H6aꢀ ꢀ ꢀO4x 251(1), C6-H6aꢀ ꢀ ꢀO4x 172.2(8)ꢁ.
ranges from 228.1(2) pm (33) to 246.7(2) pm (35). In
addition, the iron iron bond lengths also shows different
values ranging from 241.24(4) pm (35) to 245.51(4) pm
(34). Compared to the standard deviations these differ-
ences are unequivocally significant. These findings will
be discussed in detail together with the structural data
of another 39 compounds showing the same coordina-
tion mode as 32–35.
The supramolecular arrangement of 32–35 is depicted
in Figs. 2, 4, 6 and 8. The architecture of the crystal
structures is determined by weak C–Hꢀ ꢀ ꢀO interactions
[32], which of course are highly dependent on the nature
of the organic substituents attached to the ligand. If
these substituents are hydrocarbon groups, the most
effective hydrogen bond acceptors are the terminal CO
ligands. In the case of the crystal structure of 32 the fur-
an system in the side chain acts as an additional hydro-
gen bond acceptor site leading to the formation of
dimers linked by a C–Hꢀ ꢀ ꢀO interaction between the fur-
an oxygen and a hydrogen atom of the furan moiety of a
neighboring molecule and vice versa. These dimers are
connected to infinite chains by a C–Hꢀ ꢀ ꢀO interaction
between a CO ligand and one of the hydrogen atoms
of the NMe group (Fig. 2). The supramolecular struc-
tures of 33 and 34 are quite similar in that the shortest
intermolecular distances correspond to C–Hꢀ ꢀ ꢀO inter-
actions between a terminal CO and a proton of the
methylene group (33) or the cyclohexyl substituent (34)
building up infinite chains (Figs. 4 and 6). In the crystal
structure of 35 three short C–Hꢀ ꢀ ꢀO interactions are rec-
ognized, the imine nitrogen atom N2 is not involved in
any hydrogen bond network. Fig. 8 shows the infinite
two dimensional plain built up by the shortest intermo-
lecular hydrogen bonds between terminal CO ligands
and an aromatic hydrogen atom and one of the hydro-
gen atoms of the central cyclohexyl moiety. The third
interaction, that has been omitted for the sake of clarity,
leads to an three dimensional network by another C–
Hꢀ ꢀ ꢀO bond between a CO ligand and another hydrogen
atom of the cyclohexyl ring.
The iron iron bond lengths as well as the iron carbon
bond lengths between the apical iron atom and Cb
(Scheme 1) of 43 molecular structures that have been ob-
tained in our group during the last years are summarized
in Table 1. Fig. 9 shows the correlation between the two
bond lengths. The iron carbon distances in particular
show a very broad range from ꢁ220 up to ꢁ268 pm,
which is already above the sum of the van der Waals ra-
dii of iron and carbon. Scheme 4 shows three mesomeric
Fig. 3. Molecular structure of 33, selected bond lengths (pm) and
bond angles (ꢁ): Fe1–Fe2 244.93(5), Fe1–N1 196.8(2), Fe1–C3
216.8(2), Fe1–C4 228.1(2), Fe2–N1 200.5(2), Fe2–C3 194.8(2), C3–
C4 138.4(3), C4–C5 148.5(3), C5–N1 149.0(2); N1–Fe1–Fe2 51.25(5),
N1–Fe1–C3 74.62(7), N1–Fe1–C4 63.00(7), Fe2–Fe1–C3 49.45(6),
Fe2–Fe1–C4 71.95(5), C3–Fe1–C4 36.15(8), N1–Fe2–C3 78.87(8),
Fe2–C3–C4 112.1(2), C3–C4–C5 120.1(2), C4–C5–N1 97.4(2), C5–
N1–Fe2 112.2(1).
Scheme 4.

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W. Imhof et al. / Journal of Organometallic Chemistry 690 (2005) 3886–3897
Fig. 4. Supramolecular structure of 33, H5bꢀ ꢀ ꢀO5x 267.5(7) pm, C5-H5bꢀ ꢀ ꢀO5x 157.5(4)ꢁ.
forms of the coordination mode in the corresponding
dinuclear cluster compounds that reflect the observed
bonding situation on the basis of simple localized Lewis
formulae. It is obvious from Scheme 4 that the longer
the iron carbon bond length Feap–Cb gets, the shorter
becomes the iron iron bond.
The compounds with the longest iron carbon distances
are the dinuclear iron carbonyl clusters derived from the
ligands 22 and 23 based on b-naphthylcarbaldehyde.
If the second aromatic ring of the naphthaline system
is coordinated by another Fe(CO)3 moiety in a g4-fash-
ion, the Feap–Cb bond is shortened by ꢁ20 pm whereas
the iron iron bond is elongated by ꢁ2 pm [10]. This
example shows that the electronic properties of the cor-
responding aromatic system the ligands are based upon
play the most important role in the observed reciprocal
dependency of the bond lengths in dinuclear iron car-
bonyl compounds of this kind.
Fig. 5. Molecular structure of 34, selected bond lengths (pm) and bond angles (ꢁ): Fe1–Fe2 245.51(4), Fe2–N1 198.8(2), Fe2–C1 218.7(2), Fe2–C6
231.5(2), Fe1–N1 200.2(2), Fe1–C1 199.2(2), C1–C6 142.5(3), C6–C7 151.8(3), C7–N1 150.4(3); N1–Fe2–Fe1 52.29(5), N1–Fe2–C1 74.47(8), N1–
Fe2–C6 64.71(8), Fe1–Fe2–C1 50.41(6), Fe1–Fe2–C6 74.53(6), C1–Fe2–C6 36.76(8), N1–Fe1–C1 78.65(8), Fe1–C1–C6 114.6(2), C1–C6–C7 115.5(2),
C6–C7–N1 100.3(2), C7–N1–Fe1 113.8(1).
Fig. 6. Supramolecular structure of 34, H14aꢀ ꢀ ꢀO4x 261.7(8) pm, C14–H14aꢀ ꢀ ꢀO4x 126.1(5)ꢁ.

W. Imhof et al. / Journal of Organometallic Chemistry 690 (2005) 3886–3897
3891
Fig. 7. Molecular structure of 35, selected bond lengths (pm) and bond angles (ꢁ): Fe1–Fe2 241.24(4), Fe2–N1 196.3(2), Fe2–C1 217.6(2), Fe2–C6
246.7(2), Fe1–N1 198.0(2), Fe1–C1 200.6(2), C1–C6 141.3(3), C6–C7 149.8(3), C7–N1 148.3(2), C14-N2 125.3(3); N1–Fe2–Fe1 52.61(5), N1–Fe2–C1
74.52(7), N1–Fe2–C6 61.95(6), Fe1–Fe2–C1 51.55(5), Fe1–Fe2–C6 72.05(5), C1–Fe2–C6 34.74(7), N1–Fe1–C1 78.08(7), Fe1–C1–C6 113.0(1), C1–
C6–C7 115.1(2), C6–C7–N1 102.2(2), C7–N1–Fe1 111.3(1), C11–N2–C14 118.3(2), N2–C14–C15 123.4(2).
Fig. 8. Supramolecular structure of 35, H4ꢀ ꢀ ꢀO6 259.8(8) pm, C4-H4ꢀ ꢀ ꢀO6x 136.6(4)ꢁ, H14ꢀ ꢀ ꢀO4x 262.9(8) pm, C14–H14ꢀ ꢀ ꢀO6x 173.8(5)ꢁ, the third
C–Hꢀ ꢀ ꢀO interaction (H11ꢀ ꢀ ꢀO5x 263.5(8) pm, C11–H11ꢀ ꢀ ꢀO5x 135.5(5)ꢁ) has been omitted for the sake of clarity.
Another interesting feature is the reaction pathway
being observed in ruthenium catalyzed C–H activation
reactions in the presence of alkenes and/or carbon
monoxide if the imine ligands 1–31 are used as the sub-
strates. In all cases we investigated up to now the C–H
activation reaction takes place at the same position
that was observed in the formation of the iron car-
bonyl model compounds. But it is remarkable that
the imines showing very long Feap–Cb interactions in
their iron carbonyl complexes produce heterocyclic
products if reacted with carbon monoxide and ethylene
(Scheme 5, Fig. 9) [16], whereas the ligands derived
from benzaldimines 10–16 or a-naphthylcarbaldimines
18, 19 and 21 either yield the alkene insertion products
or acylated compounds by the subsequent insertion of
CO and an alkene under similar reaction conditions
[16,25,26,36]. The diironhexacarbonyl complexes pro-
duced from the latter ligands show Feap–Cb bond
lengths in the range of 228–240 pm. The only exception
to this rule is the iron complex of 17 with a Feap–Cb
bond length of 247.4 pm but a iron iron bond which
is shorter compared to the model compounds of
ligands which in catalytic reactions produce
heterocycles.
In Scheme 5, the isoindolone derivatives that are ob-
served as the products of catalytic three component
reactions of the imines 22, 23, 30 and 31 are presented.
The b-naphthyl-carbaldimines 22 and 23 show the
typical reaction pathway of producing an acyl substitu-
ent by the subsequent insertion of carbon monoxide and
ethylene at C-3. In addition, the insertion of another
equivalent of CO into the C–H bond at C-1 is followed
by the formation of a 2,9-dihydro-benzoisoindol-1-one
system. One molecule of ethylene is then catalytically
attached to the same naphthalene carbon atom [16].
This incorporation of two equivalents of carbon monox-
ide and two equivalents of ethylene takes place regiose-
lectively meaning that the propionyl group is never
observed at C-1 of the naphthalene system and the het-
erocycle is always formed between the positions C-1 and
C-2 of the naphthalene ring. The diimines 30 and 31 also
produce isoindolone derivatives under the same reaction
condidtions. But in contrast to the formation of 39 and
40, 41–43 are 2,3-dihydroisoindol-1-one derivatives.
This means that after the insertion of CO into the C–
H bond in ortho-position with respect to the imine sub-
stituent and the formation of the heterocyclic system,
ethylene is catalytically attached to the former imine car-

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W. Imhof et al. / Journal of Organometallic Chemistry 690 (2005) 3886–3897
Table 1
Comparison of the bond lengths Fe–Fe and Feap–Cb (pm) in diironhexacarbonyl complexes showing an l2-g3-enylamido ligand
Ligand
Fe–Fe
Feap–Cb
Reference
Remarks
1
2
3
4
5
6
7
8
9
245.9
243.4
245.0
242.1
242.1
244.0
241.6
244.9
245.4
245.7
246.1
244.1
243.5
244.6
245.5
245.8
246.0
243.4
245.3
245.3
244.7
245.7
243.7
238.9
242.3
240.5
242.9
246.1
244.0
242.5
245.1
245.4
246.7
245.4
244.9
243.3
244.7
246.4
246.6
246.4
246.9
244.5
241.2
219.9
227.9
228.0
247.5
241.4
236.4
243.8
228.1
232.1
227.0
231.0
233.6
234.7
237.0
231.5
232.9
231.1
247.4
230.3
229.7
230.2
228.9
227.4
268.0
245.4
258.6
244.6
229.5
241.4
236.4
220.5
234.2
231.6
238.2
238.5
236.3
233.5
229.7
232.5
231.0
229.9
235.5
246.7
[5]
[5]
[5]
[5]
[5]
[6]
–
This paper, 32
This paper, 33
Two molecules per asymmetric unit
–
[33]
10
11
12
13
14
15
16
17
18
[9]
[9]
[9]
[9]
–
This paper, 34
[34]
[34]
[35]
[10]
Coordination of sulfur at Feap
Two molecules per asymmetric unit
19
20
21
22
22
23
23
24
24
25
25
26
[10]
[36]
[36]
[10]
[10]
[10]
[10]
[11]
[11]
[11]
[11]
[12]
Naphthaline system g4-coordinated by another Fe(CO)3 moiety
Naphthaline system g4-coordinated by another Fe(CO)3 moiety
Only one imine function coordinated
Both imine functions coordinated, centrosymmetric molecular structure
Only one imine function coordinated
Second imine function coordinated differently
Only one imine function coordinated, 2 molecules per asymmetric unit
26
27
[12]
[12]
Both imine functions coordinated, centrosymmetric molecular structure
Both imine functions coordinated
28
28
[12]
[12]
Only one imine function coordinated
Both imine functions coordinated, 2 molecules per asymmetric unit
29
30
[12]
–
Only one imine function coordinated
This paper, 35
bon atom. Complex 43 is obtained in more than 90%
yield and could therefore be fully characterized by
means of several spectroscopic techniques. NMR exper-
iments unequivocally showed that first of all there is one
more aliphatic CH moiety present than it would be ex-
pected if the reaction sequence was analogous to the
one producing 39 and 40. In addition, the methylene
protons of the new ethyl substituent show a coupling
with this CH group. Both facts are only consistent with
a structural formula of 43 as depicted in Scheme 5.
Compounds 41 and 42 were observed in much lower
yield, but by GC-MS measurements as well as from typ-
ical resonances in the 13C NMR of the crude reaction
mixture, their identity as 2,3-dihydroisoindolone deriva-
tives could be demonstrated. The signals of the carbonyl
carbon atoms are observed at d = 167.4 and 168.8 ppm
being in good agreement with the corresponding chemi-
cal shift in the spectrum of 43 (168.5 ppm) and related
1,5-dihydropyrrol-2-one derivatives (170–172 ppm)
[37]. In contrast, 39 and 40 as well as related 1,3-dihy-
dropyrrol-2-ones show the carbon resonance of the car-
bonyl function at ꢁ182 ppm [16,33,37–40].
In the near future, we will investigate the reaction
pathways of 4, 5 and 7 in catalytic reactions as well as
the corresponding properties of 1 showing the shortest
Feap–Cb interaction at all. One of the iron carbonyl
compounds derived from 25 also exhibits a very short
Feap–Cb bond length which in this case is caused by
the second imine function which is also coordinated to
another Fe2(CO)6 moiety [11].

W. Imhof et al. / Journal of Organometallic Chemistry 690 (2005) 3886–3897
3893
248,0
247,0
1
246,0
25
245,0
R
O
17
244,0
N
Et
23
Fe-Fe
243,0
242,0
241,0
240,0
239,0
238,0
Et
22
7
O
4
5
30
O
23
H
Et
N
N
22
Et
H
O
210,
220,
230,
240,
250,
260,
270,
280,
Feap-Cβ
Fig. 9. Reciprocal correlation between the Fe–Fe and Feap–Cb bond lengths in dinuclear iron carbonyl complexes; the isoindolone derivatives
produced by subsequent insertion of carbon monoxide and ethylene into C–H bonds of 22, 23 and 30 are also depicted.
Scheme 5.
3. Experimental
dard). Mass spectra were recorded on a Finnigan MAT
SSQ 710 instrument. Elemental analyses were carried
out at the laboratory of the Institute of Oraganic Chem-
istry and Macromolecular Chemistry of the Friedrich-
Schille-University Jena.
3.1. General
All procedures were carried out under an argon
atmosphere in anhydrous, freshly distilled solvents.
Infrared spectra were recorded on a Perkin–Elmer
FT-IR System 2000 using 0.2 mm KBr cuvettes. NMR
spectra were recorded on a Bruker AC 200 spectrometer
(1H: 200 MHz, 13C: 50.32 MHz, CDCl3 as internal stan-
3.2. X-ray crystallographic studies
The structure determinations of 32 and 33 were carried
out on an Enraf Nonius CAD4 diffractometer, the struc-

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W. Imhof et al. / Journal of Organometallic Chemistry 690 (2005) 3886–3897
ture determinations of 34 and 35 were carried out on a En-
raf Nonius Kappa CCD diffractometer, in all cases using
graphite monochromated Mo Ka radiation. The crystal
was mounted in a stream of cold nitrogen. Data were cor-
rected for Lorentz and polarization effects but not for
absorption. The structure was solved by direct methods
and refined by full-matrix least-squares techniques
against F2 using the programs SHELXS-86 and SHELXL-97
[41,42]. Computation of the structures and the molecular
illustrations were drawn using the program XP [43]. The
crystal and intensity data are given in Table 2.
are added. After stirring at room temperature for 20 h the
resulting precipitate is collected and washed twice with
cold anhydrous ethanol and cold diethylether. The melt-
ing point of 30 was identical to the one reported in the lit-
erature [47]. Yield: 5.528 g 30 (76.1%), 2.608 31 (27.0%).
3.5. Analytical data for 31
MS (CI, H2O): 387 (MH+), 299 ðC20H31NþÞ, 201
2
(C14H19N+), 123 (C8H13N+), 105 (C7H7N+); IR (Nujol,
1
cmꢂ1): 1643 s; H NMR (200 MHz, CDCl3, 298 K):
0.60–2.22 (m, 20H, CH, CH2), 3.04–3.29 (m, 2H, CH),
7.28–7.50 (m, 6H, @CH), 7.64–7.82 (m, 4H, @CH),
8.32 (s, 2H, N@CH); 13C NMR (200 MHz, CDCl3,
298 K): 31.8 (CH2), 33.6 (CH), 34.0 (CH2), 44.7 (CH2),
70.2 (CH), 127.9 (@CH), 128.3 (@CH), 130.1 (@CH),
136.4 (@C), 158.6 (N@CH). Anal. Calc. for C27H34N2
(found) (%): C 83.89 (84.01), H 8.86 (9.04), N 7.25 (7.26).
3.3. Synthesis of 7, 8 and 14
The ligands were synthesized by literature procedures
and characterized by comparison of melting points and
NMR spectroscopical data with the data reported in the
literature [44–46].
3.4. Synthesis of 30 and 31
3.6. Synthesis of 32–38
A sample of 25 mmol of the corresponding diamine
(2.855 g trans-cyclohexane-1,4-diamine, 5.259 g 4,40-dia-
mino-dicyclohexylmethane) is dissolved in 100 mL of
anhydrous ethanol and 5.306 g (50 mmol) benzaldehyde
A 360 mg portion Fe2(CO)9 (1 mmol) together with
an equimolar amount of the corresponding imines with
only one imine function (188 mg 7, 177 mg 8, 201 mg 14)
or half an equivalent of the diimines (146 mg 30, 193 mg
Table 2
Crystal and intensity data for 32, 33, 34 and 35
32
33
34
35
Formula
Molecular weight (g molꢂ1
Radiation
C
17H12N2O7Fe2
C17H15NO7Fe2
457.00
Mo Ka
Graphite
183
C20H19NO6Fe2
481.06
Mo Ka
Graphite
183
C26H22N2O6Fe2
570.16
Mo Ka
Graphite
183
)
467.99
Mo Ka
Graphite
183
Monochromator
T (K)
Crystal color
Crystal size
Red
Red
Red
Red
0.4 · 0.3 · 0.3
7.853(4)
11.468(6)
20.33(2)
90
0.2 · 0.1 · 0.1
17.426(3)
8.802(1)
12.175(2)
90
0.2 · 0.2 · 0.1
8.5901(3)
16.6276(5)
14.6971(5)
90
0.5 · 0.2 · 0.1
9.8896(2)
24.201(1)
10.9304(4)
90
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
93.07(6)
90
100.27(1)
90
99.327(2)
90
104.966(2)
90
3
˚
V (A )
1828(2)
4
944
1837.5(5)
4
928
2071.5(1)
4
984
2527.3(2)
4
1168
Z
F(000)
qcalc (g cmꢂ3
)
1.700
1.652
1.543
1.498
Crystal system
Space group
Absorption coefficient (mmꢂ1
Monoclinic
P21/c
1.635
Monoclinic
P21/c
1.622
Monoclinic
P21/c
1.436
Monoclinic
P21/n
1.191
)
h Limit (ꢁ)
2.60 < h < 25.07
3324
3227
1.19 < h < 25.00
4255
3247
2.40 < h < 23.27
5529
2984
1.68 < h < 27.48
9530
5735
Reflections measured
Independent reflections
Rint
0.1353
2590
301
0.0179
2955
304
0.0227
2623
338
0.0312
4090
413
Reflections observed (F 2o > 2rðF o2Þ)
Number of parameters
Goodness-of-fit
R1
1.085
1.046
1.026
0.970
0.0336
0.0889
0.472
0.0274
0.0727
0.389
0.0245
0.0585
0.239
0.0354
0.0688
0.326
wR2
Final diffraction map electron density peak (e A
ꢂ3
˚
)

W. Imhof et al. / Journal of Organometallic Chemistry 690 (2005) 3886–3897
3895
31) and 20 mL n-heptane are stirred together at 50 ꢁC
for 45 min. In the course of the reaction the pale yellow
suspension slowly changes to a deep red solution as the
ligand and Fe2(CO)9 dissolve. After the reaction is com-
pleted all volatile materials are removed in vacuo. The
residue is dissolved in CH2Cl2, 1 g silanized silica gel
is added and the solvent is again removed under reduced
pressure. Chromatography on silica gel using light
petroleum (b.p. 40–60 ꢁC) as the eluent first yields a
small green band containing Fe3(CO)12 followed by a
deep red band of 32, 33 or 34, respectively. Chromato-
graphic workup of the crude reaction mixture from the
reaction of 30 with Fe2(CO)9 first yields a band contain-
ing the tetranuclear iron carbonyl cluster compound 36
using a mixture of light petroleum (b.p. 40–60 ꢁC) and
CH2Cl2 in a 2:1 ratio. Using a mixture of light petro-
leum (b.p. 40–60 ꢁC) and THF in a 10:1 ratio leads to
the elution of 34 as the main product of the reaction.
Similarily, the chromatographic workup of the crude
reaction mixture of the reaction of 31 with Fe2(CO)9
first elutes the tetranuclear cluster compound 38 (light
petroleum (b.p. 40–60 ꢁC)/CH2Cl2 2:1), whereas the sec-
ond fraction eluted with a mixture of light petroleum
(b.p. 40–60 ꢁC) and THF in a 10:2 ratio contains the
dinuclear compound 37. Yield: 152 mg 32 (32.5%), 86
mg 33 (18.8%), 180 mg 34 (37.4%), 104 mg 35 (36.5%),
88 mg 36 (20.7%), 91 mg 37 (27.3%), 31 mg 38 (6.6%).
Recrystallization of the complexes was performed from
mixtures of light petroleum (b.p. 40–60 ꢁC) and CH2Cl2
at ꢂ20 ꢁC.
(CO). Anal. Calc. for C17H15NO7Fe2 (found): C 44.68
(45.04), H 3.31 (3.59), N 3.06 (2.95).
3.9. Analytical data for 34
MS (EI): 481 (M+), loss of six CO and two Fe; IR
(CH2Cl2, cmꢂ1): 2060 m, 2022 vs, 1982 vs (br); 1H
3
NMR (200 MHz, CDCl3, 298 K): 0.78 (d, JHH = 6.1
Hz, 3H, CH3), 0.88–2.32 (m, 11H, CH2, CH), 4.58 (q,
3
3JHH = 6.1 Hz, 1H, CH), 6.98 (dd, JHH = 8.2 Hz,
3
3JHH = 8.2 Hz, 1H, @CH), 7.23 (dd, JHH = 8.2 Hz,
3
3JHH = 8.2 Hz, 1H, @CH), 7.51 (d, JHH = 8.2 Hz, 1H,
3
@CH), 8.02 (d, JHH = 8.2 Hz, 1H, @CH); 13C NMR
(200 MHz, CDCl3, 298 K): 26.4 (CH2), 26.8 (CH3),
27.1 (CH2), 28.6 (CH2), 36.9 (CH2), 41.1 (CH2), 72.3
(CH), 76.6 (CH), 118.9 (@C), 120.9 (@C), 125.7
(@CH), 129.9 (@CH), 130.2 (@CH), 149.2 (@CH),
210.4 (CO). Anal. Calc. for C20H19NO6Fe2 (found): C
49.93 (50.05), H 3.98 (4.32), N 2.91 (2.89).
3.10. Analytical data for 35
MS (FAB in NBA): 571 (MH+), loss of six CO;
HRMS (FAB in NBA) calcd. for C26H23N2O6Fe2
(MH+) 571.0292, found 571.0273, D = 1.90 mmu. IR
(CH2Cl2, cmꢂ1): 2060 s, 2055 s, 2023 vs, 1984 vs, 1977
1
vs, 1971 sh, 1961 vs, 1948 vs (br), 1644 m; H NMR
(200 MHz, CDCl3, 298 K): 1.55–2.13 (m, 8H, CH2),
2.30–2.63 (m, 1H, CH), 2.94–3.35 (m, 1H CH), 3.95 (s,
3
2H, CH2), 7.04 (dd, JHH = 7.0 Hz, JHH = 7.0 Hz,
3
3
3
3.7. Analytical data for 32
1H, @CH), 7.30 (dd, JHH = 7.5 Hz, JHH = 7.5 Hz,
1H, @CH), 7.34–7.60 (m, 4H, @CH), 7.60–7.83 (m,
MS (EI): 468 (M+), loss of six CO and two Fe; IR
(CH2Cl2, cmꢂ1): 2057 s, 2019 vs, 1972 vs (br); 1H
NMR (200 MHz, CDCl3, 298 K): 3.61 (s, 3H, CH3),
3.79 (s, 2H, CH2), 3.87 (s, 2H, CH2), 6.27 (m, 1H,
3
2H, @CH), 8.10 (d, JHH = 8.0 Hz, 1H, @CH), 8.29 (s,
1H, N@CH); 13C NMR (200 MHz, CDCl3, 298 K):
33.1 (CH2), 33.5 (CH2), 64.9 (CH), 69.3 (CH), 73.3
(CH2), 125.2 (@C), 125.7 (@CH), 128.1 (@CH), 128.6
(@CH), 130.6 (@CH), 136.3 (@C), 145.5 (@CH), 151.0
(@C), 159.5 (N@CH), 210.5 (CO).
3
@CH), 6.34 (m, 1H, @CH), 6.52 (d, JHH = 2.9 Hz,
3
1H, @CH), 6.86 (d, JHH = 2.9 Hz, 1H, @CH), 7.40 (s,
1H, @CH); 13C NMR (200 MHz, CDCl3, 298 K):35.3
(CH3), 63.2 (CH2), 63.5 (CH2), 109.4 (@CH), 110.3
(@CH), 114.7 (@C), 126.7 (@CH), 131.0 (@CH), 141.7
(@C), 142.2 (@CH), 152.7 (@C), 211.5 (CO). Anal. Calc.
for C17H12N2O7Fe2 (found): C 43.63 (43.91), H 2.58
(2.89), N 5.99 (5.92).
3.11. Analytical data for 36
MS (FAB in NBA): 850 (M+), loss of 12 CO; HRMS
(FAB in NBA) calcd. for C32H22N2O12Fe4 (M+)
849.9200, found 849.9231, D = 3.10 mmu. IR (nujol,
cmꢂ1): 2059 vs, 2020 vs, 1990 vs, 1975 vs, 1962 vs,
3.8. Analytical data for 33
1
1957 vs (br), 1925 vs (br); H NMR (200 MHz, CDCl3,
298 K): 1.44–2.08 (m, 8H, CH2), 2.12–2.42 (m, 2H, CH),
MS (EI): 457 (M+), loss of six CO and two Fe; IR
(CH2Cl2, cmꢂ1): 2065 m, 2026 vs, 1983 vs (br); 1H
NMR (200 MHz, CDCl3, 298 K): 0.83–2.10 (m, 11H,
3
3
3.89 (s, 4H, CH2), 7.04 (dd, JHH = 7.5 Hz, JHH = 7.5
3
3
Hz, 2H, @CH), 7.30 (dd, JHH = 7.4 Hz, JHH = 7.4
3
3
Hz, 2H, @CH), 7.47 (d, JHH = 7.9 Hz, 2H, @CH),
CH2, CH), 3.74 (s, 2H, CH2), 6.71 (d, JHH = 1.9 Hz,
3
8.08 (d, JHH = 8.1 Hz, 2H, @CH); 13C NMR (200
3
1H, @CH), 7.41 (d, JHH = 1.9 Hz, 1H, @CH); 13C
MHz, CDCl3, 298 K): 33.7 (CH2), 64.8 (CH), 73.4
(CH2), 125.6 (@C), 125.8 (@CH), 128.1 (@CH), 130.9
(@CH), 145.2 (@CH), 151.0 (@C), 210.4 (CO).
NMR (200 MHz, CDCl3, 298 K): 25.9 (CH2), 26.1
(CH2), 35.8 (CH2), 57.5 (CH2), 74.3 (CH), 122.1
(@CH), 131.2 (@C), 138.7 (@C), 148.0 (@CH), 210.3

3896
W. Imhof et al. / Journal of Organometallic Chemistry 690 (2005) 3886–3897
3.12. Analytical data for 37
(C9H10N+), 117 ðC9HþÞ, 104 (C7H6N+), 91 ðC7HþÞ, 81
9
7
ðC6Hþ9 Þ; HRMS (ESI in CHCl3/methanol): calcd. for
C23H26N2ONa (MNa+) 369.4610, found 369.4608,
D = ꢂ0.23 mmu.
MS (FAB in NBA): 667 (MH+), loss of six CO;
HRMS (FAB in NBA) calcd. for C33H35N2O6Fe2
(MH+) 667.3433, found 667.3418, D = ꢂ1.54 mmu. IR
(nujol, cmꢂ1): 2060 vs, 2022 vs, 1977 vs (br), 1644 w;
1H NMR (200 MHz, CDCl3, 298 K): 0.70–2.16 (m,
20H, CH, CH2), 2.16–2.53 (m, 1H, CH), 3.00–3.34 (m,
3.16. Analytical data for 42
MS (EI): 402 (M+), 297 ðC20H29NþÞ, 282 ðC19H26NþÞ,
2
2
3
1H, CH), 3.91 (s, 2H, CH2), 7.02 (dd, JHH = 7.5 Hz,
3JHH = 7.5 Hz, 1H, @CH), 7.27 (dd, JHH = 7.0 Hz,
270 ðC18H26NþÞ, 242 (C17H24N+), 218 (C15H24N+), 202
2
(C14H20N+), 185 (C13H15N+), 172 (C12H14N+), 156
3
3JHH = 7.0 Hz, 1H, @CH), 7.33–7.58 (m, 4H, @CH),
(C11H10N+), 132 (C9H10N+), 117 ðC9HþÞ, 104 ðC8HþÞ,
9
8
3
7.61–7.80 (m, 2H, @CH), 8.08 (d, JHH = 8.1 Hz, 1H,
91 ðC7Hþ7 Þ, 81 ðC6H9þÞ, 51 ðC4Hþ3 Þ; HRMS (ESI in
CHCl3/methanol) calcd. for C26H30N2O2Na (MNa+)
425.5250, found 425.5242, D = ꢂ0.79 mmu.
@CH), 8.30 (s, 1H, N@CH); 13C NMR (200 MHz,
CDCl3, 298 K): 31.9 (CH2), 32.9 (CH2), 33.9 (CH),
34.1 (CH2), 34.5 (CH2), 34.9 (CH2), 44.1 (CH2), 64.8
(CH), 70.4 (CH), 74.4 (CH2), 125.0 (@C), 125.6
(@CH), 128.0 (@CH), 128.1 (@CH), 128.5 (@CH),
130.3 (@CH), 130.5 (@CH), 136.6 (@C), 145.7 (@CH),
150.9 (@C), 158.8 (N@CH), 210.6 (CO).
3.17. Analytical data for 43
MS (CI, H2O): 499 (MH+), 483 ðC32H39N2OþÞ, 469
2
ðC31H37N2OþÞ, 443 (C30H39N2O+), 355 ðC25H27NþÞ,
2
2
338 (C25H24N+), 267 (C19H25N+), 243 (C17H25N+), 189
(C13H19N+), 175 (C12H17N+), 161 (C11H15N+), 147
(C10H13N+), 145 (C10H11N+), 123 (C8H13N+), 105
(C7H7N+); HRMS (ESI in CHCl3/methanol) calcd. for
C33H42N2O2Na (MNa+) 521.6968, found 521.6975,
3.13. Analytical data for 38
MS (FAB in NBA): 946 (MH+), loss of 12 CO;
HRMS (FAB in NBA) calcd. for C34H35N2O7Fe4
(MH+ ꢂ 5CO) 807.0477, found 807.0441, D = ꢂ3.58
mmu. IR (nujol, cmꢂ1): 2065 vs, 2024 vs, 2006 vs,
1988 vs (br), 1975 vs (br), 1959 vs (br), 1953 vs (sh),
1940 vs (br); 1H NMR (200 MHz, CDCl3, 298 K):
1.65–2.06 (m, 20H, CH, CH2), 2.06–2.50 (m, 2H, CH),
1
D = 0,69 mmu; H NMR (CDCl3, 298 K) (ppm): 0.52
(t, JHH = 7,0 Hz, 6H, CH3), 0.68–2.19 (m, 24H, CH,
3
CH2), 3.63–3.97 (m, 2H, CH), 4.53–4.72 (m, 2H, CH–
N), 7.22–7.85 (m, 8H, CHar); 13C NMR (CDCl3, 298
K) (ppm): 6.0 (CH3), 24.7 (CH2), 29.9 (CH2), 30.5
(CH2), 32.4 (CH2), 32.5 (CH2), 32.6 (CH2), 32.7
(CH2), 33.6 (CH), 44.0 (CH2), 53.1 (CH), 59.8 (CH–
N), 121.4 (@CH), 122.9 (@CH), 127.5 (@CH), 130.8
(@CH), 133.0 (@C), 144.8 (@C), 168.5 (CO).
3
3
3.91 (s, 4H, CH2), 7.03 (dd, JHH = 6.9 Hz, JHH = 6.9
3
3
Hz, 2H, @CH), 7.28 (dd, JHH = 6.9 Hz, JHH = 6.9
3
Hz, 2H, @CH), 7.46 (d, JHH = 7.9 Hz, 2H, @CH),
3
8.08 (d, JHH = 8.1 Hz, 2H, @CH); 13C NMR (200
MHz, CDCl3, 298 K): 32.8 (CH2), 34.6 (CH), 34.9
(CH2), 43.4 (CH2), 64.8 (CH), 74.3 (CH2), 125.1 (@C),
125.6 (@CH), 128.1 (@CH), 130.5 (@CH), 145.7
(@CH), 150.9 (@C), 210.6 (CO).
4. Supplementary material
Additional material on the structure analyses is avail-
able from the Cambridge Crystallographic Data Centre
by mentioning the deposition number CCDC-243098
(32), CCDC-243099 (33), CCDC-243100 (34), CCD-
243101 (35).
3.14. Synthesis of 41–43
In a typical reaction a 50 mL autoclave charged with
1 mmol of the corresponding diimine (290 mg 30, 386
mg 31), Ru3(CO)12 (0.03 mmol) and toluene (5 mL)
was pressurized with carbon monoxide (12 bar) and eth-
ylene (8 bar) and heated at 145 ꢁC overnight. After the
reaction mixture was cooled to room temperature it
was transferred to a Schlenk tube and all volatile mate-
rial was removed under reduced pressure. The remaining
oily residue was used for NMR and IR spectroscopy
and GC-MS measurements.
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