Chiral diazadiene and β-ketoimine ligands from the reaction of N,N′-bis-aryl-oxalimidoylchlorides with (S)-prolinol and their reactivity towards iron carbonyls

Article abstract of DOI:10.1016/S0022-328X(99)00439-8

N,N′-Bis-aryl-oxalimidoylchlorides react with (S)-prolinol to give chiral N,N′-bis-aryl-tetrahydropyrrolo-[2,1-c][1,4]oxazine-3,4-diylidenediamines. These compounds exhibit a 1,3-diazadiene subunit which may be reacted either with Fe(CO)₅ under photochemical or with Fe₂(CO)₉ under thermal reaction conditions to yield dinuclear complexes of the general formula (ligand)Fe₂(CO)₆. In these complexes an unsymmetrical binding mode of the Fe₂(CO)₆ moiety is realized. One of the iron atoms is coordinating both imine nitrogen atoms, whereas the second iron atom is connected to one of the C-N double bonds in a side-on fashion. If the aromatic substituent of the oxalimidoylchloride is p-OCH₃-C₆H₄ the reaction with Fe(CO)₅ or Fe₂(CO)₉ produces a mixture of diastereomers. In all other cases the (S)-configuration of the starting material is retained. If the aromatic substituent is p-Br-C₆H₄ the corresponding tetrahydropyrrolo-[2,1-c][1,4]oxazine derivative undergoes a quantitative rearrangement reaction to produce the isomeric 2-(4-bromphenyl)-3-(4-bromphenylimino)-tetrahydropyrrolo[1,2-a]pyrazine-4-one. The reaction of this ligand with Fe(CO)₅ or Fe₂(CO)₉ ends up in the formation of a complex of the general formula [(ligand)₃Fe][(μ₂-H)Fe₃(CO) ₁₁]₂ consisting of an octahedrally coordinated Fe²⁺ and two triangular [(μ₂-H)Fe₃(CO)₁₁] anions.

Full text of DOI:10.1016/S0022-328X(99)00439-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 590 (1999) 104–114
Chiral diazadiene and b-ketoimine ligands from the reaction of
N,N%-bis-aryl-oxalimidoylchlorides with (S)-prolinol and their
reactivity towards iron carbonyls
Wolfgang Imhof a,*, Angela Go¨bel a, Rainer Beckert b, Thomas Billert b, Helmar Go¨rls a
a Institut fu¨r Anorganische und Analytische Chemie, August-Bebel-Strasse 2, D-07743 Jena, Germany
b Institut fu¨r Organische und Makromolekulare Chemie, Humboldtstrasse 10, D-07743 Jena, Germany
Received 25 June 1999
Abstract
N,N%-Bis-aryl-oxalimidoylchlorides react with (S)-prolinol to give chiral N,N%-bis-aryl-tetrahydropyrrolo-[2,1-c][1,4]oxazine-3,4-
diylidenediamines. These compounds exhibit a 1,3-diazadiene subunit which may be reacted either with Fe(CO)5 under
photochemical or with Fe2(CO)9 under thermal reaction conditions to yield dinuclear complexes of the general formula
(ligand)Fe2(CO)6. In these complexes an unsymmetrical binding mode of the Fe2(CO)6 moiety is realized. One of the iron atoms
is coordinating both imine nitrogen atoms, whereas the second iron atom is connected to one of the CꢀN double bonds in a
side-on fashion. If the aromatic substituent of the oxalimidoylchloride is p-OCH3ꢀC6H4 the reaction with Fe(CO)5 or Fe2(CO)9
produces a mixture of diastereomers. In all other cases the (S)-configuration of the starting material is retained. If the aromatic
substituent is p-BrꢀC6H4 the corresponding tetrahydropyrrolo-[2,1-c][1,4]oxazine derivative undergoes a quantitative rearrange-
ment reaction to produce the isomeric 2-(4-bromphenyl)-3-(4-bromphenylimino)-tetrahydropyrrolo[1,2-a]pyrazine-4-one. The
reaction of this ligand with Fe(CO)5 or Fe2(CO)9 ends up in the formation of a complex of the general formula [(ligand)3Fe][(m2-
H)Fe3(CO)11]2 consisting of an octahedrally coordinated Fe2+ and two triangular [(m2-H)Fe3(CO)11] anions. © 1999 Elsevier
Science S.A. All rights reserved.
Keywords: Diazadiene; b-Ketoimine; Bis-aryl-oxalimidoylchloride; (S)-Prolinol; Iron carbonyls
These reactions always proceed via the attack of the
organolithium reagent at one of the CO ligands. Depend-
1. Introduction
ing on the organic residue of the organolithium reagent
(Butadiene)Fe(CO)3 complexes are widely used as
either pyrrole derivatives [2] or the intramolecular forma-
starting materials in organic synthesis [1]. In these
tion of Fischer type carbene complexes is observed [3].
compounds the organometallic moiety may act as an
Complexes of the form (1-azadiene)Fe(CO)3 have also
activating as well as a stereodirecting group, since it
efficiently shields one side of the conjugated system. So
been used as reagents that allow the transfer of Fe(CO)3
groups to butadiene ligands in a very effective way under
if a prochiral diene is used, stereoselective reactions at the
mild reaction conditions [4]. In addition, only a few
coordinated substrate may be achieved. In contrast, not
compounds have been structurally characterized [5]. Very
much information is available on the chemistry of the
nitrogen analogs of (butadiene)Fe(CO)3 complexes. Al-
though a lot of (1-azadiene)Fe(CO)3 compounds are
described in the literature, up to now only their reactivity
towards organolithium reagents has been investigated.
recently it was shown that 1-azadienes may be catalyti-
cally activated by Ru3(CO)12 to insert CO into the CꢀH
bond in the b-position with respect to the imine bond
which after a subsequent nucleophilic attack of the imine
nitrogen at the carbonyl carbon produces 1,5-dihydropy-
rrol-2-one derivatives [6]. If at the same time ethylene is
also present in the reaction mixture the thermodynami-
cally less stable 1,3-dihydropyrrol-2-one derivatives may
be obtained [7].
* Corresponding author: Tel.: +49-3641-948-128; fax: +49-3641-
948-102.
E-mail address: cwi@rz.uni-jena.de (W. Imhof)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00439-8

W. Imhof et al. / Journal of Organometallic Chemistry 590 (1999) 104–114
105
complexes are also determined by spectroscopic meth-
ods as well as by X-ray structure analysis.
Scheme 1. Binding modes of 1,4-diazadiene ligands in mono- and
dinuclear transition metal complexes (M=Group 8 metal).
2. Results and discussion
2.1. Synthesis and characterization of the ligands
Since the preparation of the first (1,4-diazadi-
ene)Fe(CO)3 complex in 1967, a number of derivatives
have been synthesized and structurally characterized [8].
In contrast to the above-mentioned butadiene and 1-
azadiene complexes in which the iron atom coordinates
the conjugated p-system of the ligand and thus is
situated beneath the plane of the ligand, in (diazadi-
ene)Fe(CO)3 compounds the iron atom interacts with
the imine nitrogen lone pairs thus building up a planar
five-membered FeC2N2 ring. In transition metal com-
plexes of higher nuclearity containing diazadiene lig-
ands, three different binding modes have been
observed. In all compounds one of the metal atoms is
again coordinated by the two imine nitrogen lone pairs
in analogy to the mononuclear complexes. The second
metal atom is either not coordinated to the ligand at all
[9] or it interacts with both the CꢀN double bonds in
terms of an h4-coordination [10] or it just interacts with
one of the imine subunits thus producing an unsymmet-
rical binding mode of the dinuclear transition metal
fragment [9a,b,10k,11] (Scheme 1).
Scheme 2 shows the synthesis of the ligands 1a–c and
3. The reaction of N,N%-bis-aryl-oxalimidoylchlorides
with (S)-prolinol leads to the formation of chiral N,N%-
bis-aryl-tetrahydropyrrolo-[2,1-c][1,4]oxazine-3,4-diyli-
denediamines 1a–c in acceptable yields. The synthesis
of 1a has already been published [13]. Surprisingly
variation of the aryl group to p-BrꢀC6H4 changes the
reaction pathway dramatically. The formation of the
ligands 1a–c required 2 days of stirring in toluene at
room temperature, whereas the reaction of the corre-
sponding p-BrꢀC6H4 derivative with prolinol made it
necessary to keep the reaction mixture at reflux temper-
ature for 4 days to obtain 3 in quite moderate yield.
Compound 3 is an isomer of the expected tetrahydropyr-
rolo-[2,1-c][1,4]oxazine derivative and is best described
as a 2-(4-bromphenyl)-3-(4-bromphenylimino)-tetrahy-
dropyrrolo[1,2-a]pyrazine-4-one. The formation of this
product may be explained by the assumption that first
the expected product of type 1 is formed. A subsequent
Chapman-like rearrangement then may lead to the
pyrazine system which finally undergoes a transacyla-
tion reaction leading to 3. So in general the reaction of
the p-BrꢀC6H4 derivative with prolinol yields a 1-oxa-4-
azadiene in contrast to the other oxalimidoylchlorides
which produce 1,4-diazadiene systems.
Both mono- and dinuclear diazadiene iron carbonyl
complexes may be reacted with alkynes to produce
various nitrogen containing heterocycles by cycloaddi-
tion reactions [12].
To our knowledge there are no reactions of iron
carbonyls with chiral diazadiene ligands published up
to now. Some of us recently showed that starting from
(S)-prolinol chiral ligands with diazadiene substruc-
tures may be obtained in only a few synthetic steps [13].
In this paper we wish to report the synthesis and
spectroscopical as well as the structural characterization
of a number of new chiral diazadiene and b-ketoimine
ligands derived from (S)-prolinol and various N,N%-bis-
aryl-oxalimidoylchlorides and their reactivity towards
iron carbonyls. The molecular structures of the new
The tetrahydropyrrolo-[2,1-c][1,4]oxazine core of 1a–
c shows characteristic signals in the 13C-NMR spectra
which are nearly not affected by the nature of the
aromatic groups attached to the imine nitrogen atoms.
So for the methylene groups resonances at about l=
24, 28, 47 and 71 are observed with the signals at lower
field representing the methylene groups ortho to the
pyrrole nitrogen and the oxazine oxygen atom, respec-
tively. The tertiary carbon atom of the pyrrole ring
gives rise to a signal at l=56 and the two quaternary
Scheme 2. Synthesis of the ligands 1a–c and 3.

106
W. Imhof et al. / Journal of Organometallic Chemistry 590 (1999) 104–114
Fig. 1. Molecular structure of 1a.
imine carbon atoms show two signals at about l=
142–145. The 13C-NMR spectrum of 3 is quite similar
concerning the carbon atoms which form the tetrahy-
dropyrrolo[1,2-a]pyrazine-4-one ring system. The only
difference being the signal representing the methylene
moiety ortho to the pyrazine nitrogen atom at l=54.6
and of course the quaternary carbonyl carbon atom at
l=154.4.
the imine carbon atoms being quite short due to the
same facts that were already mentioned above. The
most interesting fact in the structural analysis of 3 is
that the intensity data clearly show that the crystal was
a racemic twin. So obviously during one of the rear-
Table 1
Selected bond lengths (pm) and angles (°) of 1a–c
By recrystallization from diethylether (1a–c) or
toluene–CHCl3 (3) it was possible to obtain crystals
suitable for X-ray structure determination. The molecu-
lar structure of 1a is shown in Fig. 1; the numbering
scheme has been adopted for the molecular structures
of 1b and 1c. Selected bond lengths and angles of 1a–c
are depicted in Table 1. As expected, the variation of
aromatic substituents at the imine nitrogen atoms does
not affect the bond lengths and angles inside the te-
trahydropyrrolo-[2,1-c][1,4]oxazine core. The single
bond between the pyrrole nitrogen atom N1 and the
imine carbon atom C1 is quite short corresponding to
the sp2 hybridization of C1 and the electronic effect of
the imine moiety itself. Both nitrogen carbon bonds of
the imine groups clearly are double bonds with that of
C1 to N2 being about 3 pm longer than C2ꢀN3 for all
compounds 1a–c.
1a
1b
1c
Bond lengths
N1ꢀC1
C1ꢀC2
C2ꢀO1
O1ꢀC3
C3ꢀC4
C4ꢀN1
C1ꢀN2
C2ꢀN3
136.2(3)
151.2(3)
136.6(2)
145.7(3)
150.3(3)
147.4(3)
129.9(2)
126.7(3)
133.6(9)
150(1)
135.9(7)
144.1(8)
151(1)
147.5(8)
129.8(8)
126.4(8)
134.1(5)
152.8(5)
135.3(5)
145.1(5)
149.5(6)
146.2(5)
128.5(5)
125.9(5)
Bond angles
N1ꢀC1ꢀC2
C1ꢀC2ꢀO1
C2ꢀO1ꢀC3
O1ꢀC3ꢀC4
C3ꢀC4ꢀN1
C4ꢀN1ꢀC1
N1ꢀC1ꢀN2
C2ꢀC1ꢀN2
C1ꢀN2ꢀC8
C1ꢀC2ꢀN3
O1ꢀC2ꢀN3
C2ꢀN3ꢀC15
114.6(2)
118.0(2)
117.1(2)
110.4(2)
109.0(2)
122.2(2)
118.7(2)
126.6(2)
124.6(2)
119.1(2)
122.8(2)
123.1(2)
113.0(6)
118.6(6)
115.8(6)
111.2(5)
107.6(6)
122.4(6)
119.0(7)
127.8(7)
121.3(6)
119.7(6)
121.7(7)
123.2(5)
115.2(3)
118.4(3)
117.3(3)
109.9(4)
108.7(3)
122.4(3)
120.3(3)
124.5(3)
123.1(3)
117.3(3)
124.3(3)
126.8(3)
The molecular structure of (S)-3 is shown in Fig. 2;
selected bond lengths and angles are summarized in
Table 2. The bond lengths and angles are all of ex-
pected values again with the carbon nitrogen bonds of
the pyrrole as well as of the pyrazine nitrogen atoms to

W. Imhof et al. / Journal of Organometallic Chemistry 590 (1999) 104–114
107
ene ligand is coordinated by metal atoms, since one of
the imine carbon atoms shows a signal at about l=93
whereas the other quaternary imine carbon atom still
gives a resonance at very low field at l=161. The
chemical shift of the carbon atoms of the tetrahydropyr-
rolo-[2,1-c][1,4]oxazine core does not change signifi-
cantly upon coordination of the ligand. The CO ligands
of 2a–c show more than one signal, meaning that the
structure is not flexible enough to exchange all iron and
CO positions fast enough to make them equivalent on
the NMR time-scale. In contrast to the 13C-NMR
spectra of 2a and 2c, the spectrum of 2b shows the
presence of two diastereomers in solution. Together
with the result of the X-ray structure analysis (see
below) this proves that racemisation at the asymmetric
carbon atom of the pyrrole ring has occurred. Since
1H-NMR measurements of the ligand 1b together with
various shift reagents gave no evidence for racemisation
during the synthesis of the ligand, this process must
have taken place during the formation of the complex.
Although there are quite a lot of reactions reported in
the literature where Fe2(CO)9 might induce CꢀH activa-
tion reactions at imine ligands, these reactions normally
take place at aromatic carbon atoms [14]. So it is
reasonable that in the case of 1b the effect of the
neighboring pyrrole nitrogen atom as well as the elec-
tronic effect of the p-OMe groups may increase the
acidity of the hydrogen at the asymmetric carbon atom
to the extent that an iron carbonyl fragment may
activate this bond and thus induce racemisation.
Fig. 2. Molecular structure of (S)-3.
rangement processes in the formation of 3 racemisation
of the prolinol substructure must have taken place.
2.2. Synthesis and characterization of the iron carbonyl
complexes
By recrystallization of 2a and 2b from mixtures of
light petroleum–CH2Cl2 it was possible to obtain crys-
tals suitable for X-ray structure determination. Fig. 3
shows the result of the structural analysis of 2a; the
numbering scheme has also been adopted for 2b. The
most important bond lengths and angles are summa-
rized in Table 3, which clearly shows that the variation
of the aromatic groups does not have a drastic effect on
the bonding parameters. The iron–iron bond lengths
are in the range typical for single bonds. One of the
iron tricarbonyl fragments (Fe1) is coordinated by the
two lone pairs of the imine nitrogen atoms. The other
Fe(CO)3 group (Fe2) interacts with one of the imine
CꢁN double bonds in a side-on binding mode. This is
one of the three types of binding modes in dinuclear
transition metal complexes of diazadiene ligands, other
examples were reported in [9a,9b,10k,11]. The iron
nitrogen bond of Fe1 to the nitrogen atom of the imine
group being noncoordinated (N2) is about 6 pm longer
than the other one (Fe1ꢀN3). The bond lengths inside
the ligand do not differ very much compared to those
of the free ligand, with the exception of the imine
double bond C2ꢁN3, which is elongated due to the
side-on coordination of one of the Fe(CO)3 moieties for
about 13 pm. The structure analysis of 2b in accordance
with the observations made in the 13C-NMR spectrum
Scheme 3 shows the reactions of 1a–c and 3 with
iron carbonyls. Both Fe2(CO)9 and Fe(CO)5 may be
used in these complexation reactions. Thermal activa-
tion of Fe2(CO)9 and photochemical activation of
Fe(CO)5 give the same products with the yields being
much better in the latter case.
The reaction of the chiral diazadiene ligands 1a–c
with iron carbonyls produces the dinuclear complexes
2a–c. The 13C-NMR spectra of 2a–c clearly indicate
that only one of the CꢀN double bonds of the diazadi-
Table 2
Selected bond lengths (pm) and angles (°) of 3
Bond lengths
N1ꢀC1
C2ꢀN2
C3ꢀC4
C1ꢀO1
N3ꢀC14
136.2(7)
137.9(7)
149.6(7)
121.1(7)
140.9(7)
C1ꢀC2
N2ꢀC3
C4ꢀN1
C2ꢀN3
N2ꢀC8
152.7(8)
149.3(6)
148.1(7)
128.7(7)
142.4(7)
Bond angles
N1ꢀC1ꢀC2
C2ꢀN2ꢀC3
C3ꢀC4ꢀN1
C1ꢀC2ꢀN3
C2ꢀN3ꢀC14
C3ꢀN2ꢀC8
115.6(5)
117.6(5)
108.9(4)
123.2(5)
125.2(5)
118.6(4)
C1ꢀC2ꢀN2
N2ꢀC3ꢀC4
C4ꢀN1ꢀC1
N3ꢀC2ꢀN2
C2ꢀN2ꢀC8
117.3(4)
108.6(4)
124.2(4)
119.5(5)
123.7(4)

108
W. Imhof et al. / Journal of Organometallic Chemistry 590 (1999) 104–114
Scheme 3. Synthesis of the complexes 2a–c and 4.
configurated since no racemisation processes occurred
in the formation of this derivative.
In contrast to 1a–c, which show a diazadiene sub-
structure, in 3 a b-ketoimine substructure is present. In
principle this a, b-unsaturated ligand should be able to
interact with iron carbonyl fragments the same way
shows the presence of two diastereomers that are statis-
tically disordered in the packing of the crystal. The
bond lengths and angles given in Table 3 correspond to
the diastereomer with (S)-configuration at the asym-
metric carbon atom of the pyrrole ring in order to
allow a comparison with 2a which is exclusively (S)-
Fig. 3. Molecular structure of (S)-2a.

W. Imhof et al. / Journal of Organometallic Chemistry 590 (1999) 104–114
109
1a–c do. In Scheme 3 the reaction of 3 with Fe(CO)5
under photochemical and with Fe2(CO)9 under thermal
reaction conditions is shown. Again the photochemical
reaction gives an improved yield compared with the
thermal reaction. The only product that may be
obtained by column chromatography of the crude
reaction mixture is the ionic compound 4. This
compound consists of a cation of the general formula
[Fe(ligand)3]2+ with an iron atom octahedrally
surrounded by three ligand molecules in a meridional
arrangement. To our knowledge there is no structurally
characterized transition metal complex of a b-ketoimine
reported in the literature. The anions are two
[(m2-H)Fe3(CO)11]− moieties of triangular shape. The
those of 1a, 1b, 2b, 3 and 4 were carried out on an
Enraf–Nonius Kappa CCD diffractometer, crystal de-
tector distance 25 mm, 180 frames. Both diffractome-
ters used graphite monochromated MoꢀKa radiation.
The crystals were mounted in a stream of cold nitrogen.
Data were corrected for Lorentz and polarization ef-
fects but not for absorption. The structures were solved
by direct methods and refined by full-matrix least-
squares techniques against F2 using the programs
SHELXS-86 and SHELXL-93 [17]. Computations of the
structures were carried out with the XPMA program
[18] and the molecular illustrations were drawn using
the XP program [19]. The crystal and intensity data are
given in Table 4.
1
hydride signal in the H-NMR spectrum of 4 is in the
typical range at l= −13.9. Carbonylate anions of this
type are well known from the reaction of the metal
carbonyls with sodium or potassium hydroxide [15].
Fig. 4 shows the molecular structure of the cation in 4.
Since the anions are highly disordered in the crystal the
R-values are not satisfactory and thus no discussion of
bond lengths and angles is possible and Fig. 4 only
gives the motif of the cation.
3.3. Preparation of the ligands 1a–c
The synthesis of 1a has been reported in Ref. [13].
The identity and purity of the ligand used in this work
was ensured by comparison of the melting point as well
as the spectroscopic data with those reported in the
literature. In analogy, 1b and 1c were prepared by
adding a total of 40 mmol triethylamine (3.99 g, 5.50
ml) and 20 mmol (S)-prolinol (2.02 g) to a solution of
20 mmol of the corresponding N,N%-bis-aryl-oxalimi-
doylchloride (1b: aryl=p-OCH3ꢀC6H4, 6.77 g; 1c:
aryl=m-CF3ꢀC6H4, 8.26 g) in 150 ml of toluene. After
stirring at room temperature (r.t.) for 2 days the solu-
tion was filtered, the solvent evaporated in vacuo and
the residue was recrystallized from diethylether. This
procedure gave 1b and 1c as yellow crystalline solids.
Yields: 3.00 g (41.0%) 1b, 6.01 g (68.1%) 1c. Melting
points: 1b 141–144°C; 1c 100–102°C. Analyses Found
(Calc.): 1b C21H23N3O3 C 68.17 (69.02), H 6.62 (6.34),
N 11.55 (11.50); 1c C21H17F6N3O C 57.14 (57.15), H
4.09 (3.88), N 9.55 (9.52).
3. Experimental
3.1. General
All procedures were carried out under an argon
atmosphere in anhydrous, freshly distilled solvents.
Chromatography was carried out using silica gel 60 and
silanized silica gel 60, 70–230 mesh ASTM (Merck),
which were dried at 10−2 bar (103 Pa) for 2 days before
use. Fe2(CO)9 was prepared from Fe(CO)5 (Aldrich) by
irradiation in acetic acid [16]. N,N%-Bis-aryl-oxalimi-
doylchlorides were prepared from the corresponding
aromatic amines and oxalylchloride to give the N,N%-
bis-aryl-oxamides, which were then treated with PCl5
according to Ref. [13]. IR 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 with SiMe4 as internal
standard; 13C, 50.32 MHz with CDCl3 as internal stan-
dard). Mass spectra were recorded on a Finnigan MAT
SSQ 710 instrument. Elemental analyses were carried
out at the laboratory of the Institute of Organic and
Macromolecular Chemistry, Friedrich Schiller Univer-
sity Jena.
3.4. MS and spectroscopic data for 1b
MS (CI, H2O) (m/z): 366 [M+]. IR (CH2Cl2, 298 K)
(cm−1): 1674 (vs, CꢁN), 1615 (vs, br, CꢁN). H-NMR
1
(CDCl3, 298 K) (ppm): 1.36–1.62 (m, 1H, CH2), 1.84–
2.24 (m, 3H, CH2), 3.49–3.83 (m, 2H, CH2), 3.70 (s,
3H, CH3), 3.73 (s, 3H, CH3), 3.83–4.16 (m, 2H, CH,
CH2), 4.22–4.48 (m, 1H, CH2), 6.40–7.30 (m, 8H, CH).
13C-NMR (CDCl3, 298 K) (ppm): 24.0 (CH2), 28.4
(CH2), 47.0 (CH2), 55.3 (CH3), 55.5 (CH3), 56.3 (CH),
71.3 (CH2), 113.5 (CH), 113.6 (CH), 122.3 (CH), 124.6
(CH), 137.6 (C), 142.3 (C), 144.4 (C), 144.9 (C), 154.7
(C), 157.7 (C).
3.5. MS and spectroscopic data for 1c
3.2. X-ray crystallographic studies
MS (CI, H2O) (m/z): 442 [MH+], 422 [M+−F]. IR
(CH2Cl2, 298 K) (cm−1): 1679 (vs, CꢁN), 1631 (vs, br,
The structure determinations of 1c and 2a were car-
ried out on an Enraf–Nonius CAD4 diffractometer,
1
CꢁN). H-NMR (CDCl3, 298 K) (ppm): 1.40–1.82 (m,

110
W. Imhof et al. / Journal of Organometallic Chemistry 590 (1999) 104–114
Table 3
Selected bond lengths (pm) and angles (°) of 2a and 2b
2a
2b
2a
2b
2a
2b
Bond angles
Fe1ꢀFe2
Fe1ꢀN2
Fe1ꢀN3
Fe2ꢀN3
Fe2ꢀC2
256.5(1)
201.5(6)
195.9(6)
192.6(6)
202.1(6)
259.2(9)
201.5(4)
196.8(4)
192.9(4)
204.5(5)
N1ꢀC1
C1ꢀC2
C2ꢀO1
O1ꢀC3
C3ꢀC4
132.9(8)
149.7(9)
138.4(8)
143.0(7)
149.8(9)
133.6(6)
149.5(6)
140.0(5)
143(1)
C4ꢀN1
C1ꢀN2
C2ꢀN3
148.6(8)
130.4(8)
139.4(8)
148.6(6)
131.3(6)
139.7(6)
146(1)
Bond lengths
N2ꢀFe1ꢀN3
Fe1ꢀN2ꢀC1
Fe1ꢀN3ꢀC2
N2ꢀFe1ꢀFe2
C2ꢀN3ꢀFe2
C2ꢀFe2ꢀFe1
N3ꢀFe1ꢀFe2
83.3(2)
113.7(4)
107.3(4)
87.2(2)
73.0(4)
71.7(2)
48.1(2)
83.7(2)
113.4(3)
107.6(3)
86.5(1)
73.9(3)
71.2(1)
47.7(1)
Fe1ꢀFe2ꢀN3
Fe2ꢀN3ꢀFe1
N1ꢀC1ꢀC2
C1ꢀC2ꢀO1
C2ꢀO1ꢀC3
O1ꢀC3ꢀC4
C3ꢀC4ꢀN1
49.3(2)
82.6(2)
49.0(1)
83.3(2)
C4ꢀN1ꢀC1
N1ꢀC1ꢀN2
C2ꢀC1ꢀN2
C1ꢀN2ꢀC8
C1ꢀC2ꢀN3
O1ꢀC2ꢀN3
C2ꢀN3ꢀC15
122.4(5)
129.9(6)
112.3(6)
123.1(6)
116.0(6)
115.8(6)
121.0(5)
120.2(4)
128.9(4)
112.9(4)
123.8(4)
116.4(4)
115.5(4)
121.6(4)
117.8(6)
116.9(5)
110.4(5)
109.9(5)
109.1(6)
118.2(4)
118.1(4)
116.2(5)
112.4(8)
110.8(5)
Fig. 4. Molecular structure of the cation of complex 4.
1H, CH2), 1.82–2.51 (m, 3H, CH2), 3.39–3.87 (m, 2H,
CH2), 3.87–4.26 (m, 2H, CH2, CH), 4.26–4.67 (m, 1H,
CH2), 6.54–7.79 (m, 8H, CH). 13C-NMR (CDCl3, 298
K) (ppm): 23.9 (CH2), 28.5 (CH2), 47.2 (CH2), 56.1
3.6. Preparation of the complexes 2a–c
3.6.1. Synthesis 6ia thermal acti6ation
A 1.37 mmol (0.5 g) sample of Fe2(CO)9 was stirred
together with 1.65 mmol of the corresponding ligand
(1a 0.55 g; 1b 0.60 g; 1c 0.73 g) in 40 ml of n-heptane
at 50°C for 1.5 h. The yellow suspension turned deep
red and a small amount of a red precipitate was
formed. After the solvent was evaporated in vacuo the
oily residue was dissolved in 10 ml of CH2Cl2, 1 g
3
(CH), 71.4 (CH2), 118.1 (CH, JCF=3 Hz), 118.9 (CH,
3JCF=4 Hz), 120.9 (CH, 3JCF=4 Hz), 123.9 (CF3,
1JCF=273 Hz), 124.4 (CF3, 1JCF=272 Hz), 125.1
(CH), 125.4 (CH), 128.7 (CH), 128.8 (CH), 130.5 (C,
2
2JCF=32 Hz), 130.7 (C, JCF=32 Hz), 143.4 (CꢁN),
145.1 (CꢁN), 151.9 (C).

W. Imhof et al. / Journal of Organometallic Chemistry 590 (1999) 104–114
111
silanized silica gel was added and the solvent was again
evaporated. Chromatography using a mixture of light
petroleum (b.p. 40–60°C) and CH2Cl2 (2a 5:1; 2b 4:1;
2c 6:1) as the eluent yielded 2a–c as deep red solutions.
After the solvents were evaporated the crude products
were recrystallized from mixture of light petroleum
(b.p. 40–60°C) and CH2Cl2 at −20°C. Yields: 200 mg
(23.7%) 2a, 180 mg (20.0%) 2b, 170 mg (17.5%) 2c.
2a–c decomposed before their melting points could
be determined. Analyses Found (Calc.): 2a
C27H23N3O7Fe2 C 53.06 (52.89), H 3.92 (3.78), N 6.92
(6.85); 2b C27H23N3O9Fe2 C 49.85 (50.26), H 4.17
(3.59), N 5.84 (6.51); 2c C27H17F6N3O7Fe2 C 45.34
(44.97), H 2.85 (2.38), N 5.01 (5.83).
3.7. MS and spectroscopic data for 2a
3.6.2. Synthesis 6ia photochemical acti6ation
MS (FAB) (m/z): 614 [MH+], 598 [M+−Me], 585
[M+−CO], 557 [M+−2CO], 529 [M+−3CO], 501
[M+−4CO], 473 [M+−5CO], 445 [M+−6CO], 417
[C19H19N3OFe+2 ], 406 [C18H20N3OFe2+], 389 [M+−
6CO−Fe], 334 [MH+−6CO−2Fe], 307 [C19H21-
N3O+], 289 [C19H19N3+]. IR (CH2Cl2, 298 K) (cm−1):
2049 (vs, CO), 1937 (vs, br, CO). 1H-NMR (CDCl3, 298
K) (ppm): 1.20–1.46 (m, 1H, CH2), 1.46–1.65 (m, 1H,
CH2), 1.65–1.94 (m, 2H, CH2), 2.19–2.50 (m, 7H,
CH2, CH3), 2.56–2.79 (m, 1H, CH2), 3.50–3.74 (m, 2H,
CH, CH2), 4.08–4.25 (m, 1H, CH2), 6.60–7.46 (m,
8H, CH). 13C-NMR (CDCl3, 298 K) (ppm): 20.8
In a typical experiment a total of 1 mmol Fe(CO)5
(196 mg) was irradiated together with an equimolar
amount of the corresponding ligand (1a 333 mg; 1b 365
mg; 1c 441 mg) in 85 ml of THF for 20 min at 0°C. The
color of the solution immediately turned deep blue and
then changed to deep red. After the solvent was evapo-
rated the residue was dissolved in CH2Cl2, 1 g silanized
silica gel was added and the solvent was again evapo-
rated. Chromatography with the eluents mentioned
above again yielded the compounds 2a–c. Yields: 410
mg (67.0%) 2a, 500 mg (77.5%) 2b, 687 mg (95.3%) 2c.
Table 4
Crystal and intensity data for the compounds 1a–c, 2a, 2b and 3
1a
1b
1c
2a
2b
3
Formula
C21H23N3O
333.42
MoꢀKa
Graphite
183
Yellow
0.4×0.3×0.2
6.0051(3)
11.9454(6)
25.816(2)
90
C21H23N3O3
365.42
MoꢀKa
Graphite
183
Yellow
0.3×0.3×0.1
8.225(2)
9.515(2)
23.717(4)
90
C21H17F6N3O
441.38
MoꢀKa
Graphite
213
Yellow
0.6×0.3×0.2
8.124(2)
9.889(2)
24.720(6)
90
C27H23N3O7Fe2 C27H23N3O9Fe2 C19H17N3OBr2
Molecular weight (g mol−1
Radiation
)
613.18
MoꢀKa
Graphite
213
645.18
463.18
MoꢀKa
Graphite
183
MoꢀKa
Graphite
183
Monochromator
Temperature (K)
Crystal color
Red
Red
Yellow
0.4×0.1×0.1
11.5415(3)
12.5793(3)
12.7361(3)
90
Crystal size
0.6×0.2×0.2
8.707(2)
13.233(3)
23.813(5)
90
90
90
2744(1)
4
0.4×0.2×0.1
8.4501(3)
12.4030(5)
14.1358(4)
73.511(2)
83.830(2)
81.529(2)
1401.73(9)
2
,
a (A)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
Volume (A )
Z
90
90
1851.9(2)
4
90
90
1856.1(7)
4
90
90
1986.0(8)
4
90
90
3
,
1849.08(8)
4
F(000)
712
1.196
776
1.308
904
1.476
1256
1.484
660
1.529
920
1.664
zcalc (g cm−3
)
Crystal system
Space group
Orthorhombic
P212121
0.075
3.41–23.25
€
Orthorhombic
P212121
0.089
2.31–23.30
€
Orthorhombic
P212121
0.131
1.65–30.00
q−2q
3–60
Orthorhombic
P212121
1.110
1.71–29.99
q−2q
3–60
Triclinic
Orthorhombic
P212121
4.396
4.89–23.27
€
(
P1
Absorption coefficient (mm−1
q limit
)
1.095
2.44–23.28
€
Scan mode
Scan speed (° min−1
)
Reflections measured
Independent reflections
Rint
4932
2644
0.0326
2339
4750
2623
0.1294
1429
3450
3437
0.0170
2388
3144
3132
0.0201
2321
3819
3819
0.0000
3539
4922
2619
0.0668
2544
Reflections observed F2o\2|(Fo2)
No. of parameters
319
238
301
358
405
229
Goodness-of-fit
R1
wR2
0.854
0.0352
0.0842
0.171
0.851
0.0752
0.1731
0.208
1.026
0.978
1.262
0.0453
0.1224
0.387
1.057
0.0451
0.1159
0.428
0.0672
0.1641
0.501
0.0474
0.1062
0.744
Final diffraction map electron
−3
,
density (e A
)

112
W. Imhof et al. / Journal of Organometallic Chemistry 590 (1999) 104–114
(CH3), 20.9 (CH3), 23.9 (CH2), 27.0 (CH2), 49.6 (CH2),
57.2 (CH), 68.6 (CH2), 93.9 (CꢁN), 124.2 (C), 125.5 (C),
125.9 (CH), 129.4 (CH), 135.4 (CH), 135.6 (CH), 146.9
(C), 150.6 (C), 161.5 (CꢁN), 202.2 (CO), 210.0 (CO),
214.3 (CO), 217.6 (CO).
showed that no reaction had taken place up to then, so
the solution was refluxed for 4 days. After being cooled
down the solution was filtered and the solvent removed
stepwise. By this procedure yellow crystals which still
contain triethylammoniumhydrochloride precipitated.
The crude product was purified by recrystallisation from
toluene/chloroform. Yield: 1.81 g (19.6%) 3. M.p.: 275–
278°C. Analysis Found (Calc.): C19H17N3OBr2 C 49.17
(49.27), H 3.88 (3.70), N 8.84 (9.07).
3.8. MS and spectroscopic data for 2b
MS (FAB) (m/z): 664 [MH3O+], 646 [MH+], 630
[M+−Me], 617 [M+−CO], 589 [M+−2CO], 561 [M+
−3CO], 533 [M+−4CO], 505 [M+−5CO], 477 [M+−
6CO], 438 [C18H20N3O3Fe+2 ], 421 [M+−6CO−Fe], 391
[C20H21N3O2Fe+], 366 [MH+−6 CO−2Fe], 307
[C18H17N3O+2 ], 289 [C18H15N3O+]. IR (CH2Cl2, 298 K)
(cm−1): 2054 (vs, CO), 1999 (vs, CO), 1979 (vs, br, CO),
3.11. MS and spectroscopic data of 3
MS (CI, H20) (m/z): 466 [MH+], 401 [C14H14N3OBr2+],
102 [C7H4N+], 93 [C6H7N+]. IR (CH2Cl2, 298 K)
1
(cm−1): 1675 (vs, CO), 1635 (vs, br, CꢁN). H-NMR
1
1928 (vs, CO). H-NMR (CDCl3, 298 K) (ppm): 1.07–
(CDCl3, 298 K) (ppm): 1.46–1.70 (m, 1H, CH2), 1.76–
2.28 (m, 3H, CH2), 3.37–3.93 (m, 3H, CH, CH2),
3.98–4.22 (m, 2H, CH2), 6.43–6.72 (m, 2H, CH), 7.05–
7.19 (m, 4H, CH), 7.35–7.69 (m, 2H, CH). 13C-NMR
(CDCl3, 298 K) (ppm): 23.2 (CH2), 30.2 (CH2), 45.6
(CH2), 54.6 (CH), 56.0 (CH2), 114.3 (C), 119.3 (C),121.2
(CH), 127.1 (CH), 131.1 (CH), 132.1 (CH), 142.9 (C),
143.8 (C), 149.8 (CꢁN), 154.4 (CꢁO).
1.45 (m, 1H, CH2), 1.45–2.19 (m, 3H, CH2), 2.32–2.61
(m, 1H, CH2), 2.61–2.85 (m, 1H, CH2), 3.41–3.96 (m,
8H, CH, CH2, CH3), 3.96–4.40 (m, 1H, CH2), 6.54–7.64
(m, 8H, CH). 13C-NMR (CDCl3, 298 K) (ppm): 23.9
(CH2), 26.5 (CH2), 26.9 (CH2), 49.5 (CH2), 55.3 (CH3),
57.1 (CH), 57.6 (CH), 68.5 (CH2), 69.5 (CH2), 92.2
(CꢁN), 94.0 (CꢁN), 113.2 (CH), 113.7 (CH), 125.2 (CH),
125.9 (CH), 126.5 (CH), 126.9 (CH), 127.0 (CH), 142.2
(C), 142.5 (C), 146.0/146.7 (C), 157.0 (C), 157.1 (C), 157.4
(C) 157.5 (C), 161.2 (CꢁN), 161.4 (CꢁN), 210.2 (CO),
214.2 (CO), 217.4 (CO).
3.12. Preparation of the complex 4
3.12.1. Synthesis 6ia thermal acti6ation
A 0.5 g sample of Fe2(CO)9 (1.37 mmol) together with
0.76 g 3 (1.65 mmol) was stirred in 40 ml of n-heptane
at 50°C for 3 h. The color of the solution turned reddish
brown with a small amount of a light brown solid
precipitating. After evaporation of the solvent the residue
was dissolved in 10 ml of CH2Cl2 and 1 g silanized silica
gel was added. Chromatography using a mixture of light
petroleum (b.p. 40–60°C) and THF (5:2) yielded 240 mg
of 3. Using a mixture of THF and ethanol (2:1) 4 could
be eluted as a deep red solution. Yield: 90 mg (14.2%)
4.
3.9. MS and spectroscopic data for 2c
MS (FAB) (m/z): 722 [MH+], 693 [M+−CO], 665
[M+−2CO], 637 [M+−3CO], 609 [M+−4CO], 581
[M+−5CO], 553 [M+−6CO], 514 [C18H14F6N3OFe+2 ],
497 [M+−6CO−Fe], 459 [C18H15F6N3OFe+], 442
[MH+−6CO−2Fe], 422 [C21H17F5N3OFe+], 391 [C20–
H17F4N3O+]. IR (CH2Cl2, 298 K) (cm−1): 2059 (vs, CO),
1
2010 (vs, br, CO), 1937 (vs, br, CO). H-NMR (CDCl3,
298 K) (ppm): 1.03–1.52 (m, 2H, CH2), 1.72–2.07 (m,
2H, CH2), 2.30–2.56 (m, 1H, CH2), 2.56–2.78 (m, 1H,
CH2), 3.52–3.88 (m, 2H, CH, CH2), 3.88–4.31 (m, 1H,
CH2), 6.84–7.77 (m, 8H, CH). 13C-NMR (CDCl3, 298 K)
(ppm): 23.9 (CH2), 26.8 (CH2), 50.0 (CH2), 57.5 (CH),
68.4 (CH2), 93.3 (CꢁN), 121.4 (CH), 122.5 (CH, 3JCF=4
Hz), 123.3 (CF3, 1JCF=273 Hz), 123.6 (CF3, 1JCF=271
Hz), 127.9 (CH), 128.0 (CH), 129.1 (CH), 129.2 (CH),
3.12.2. Synthesis 6ia photochemical acti6ation
A total of 0.59 mmol of Fe(CO)5 (0.12 g) together with
0.59 mmol 3 (0.27 g) was irradiated in 85 ml of THF at
0°C for 20 min. The color of the solution changed from
yellow to deep red. After evaporation of the solvent the
product mixture was chromatographed. Using a mixture
of light petroleum (b.p. 40–60°C) and THF (5:2) yielded
30 mg of 3. Again using a mixture of THF and ethanol
(2:1) 4 could be eluted as a deep red solution. Yield: 130
mg (80.1%) 4. Complex 4 decomposes before melting.
Analysis Found (Calc.): C79H53N9O25Br6Fe7 C 39.46
(39.56), H 2.46 (2.23), N 4.39 (5.26).
2
129.4 (CH), 129.6 (CH), 131.2 (C, JCF=34 Hz), 131.4
2
(C, JCF=33 Hz), 149.6 (C), 153.6 (C), 161.5 (CꢁN),
209.3 (CO), 213.4 (CO).
3.10. Preparation of the ligand 3
In analogy to the synthesis of 1a–c, a total of 20 mmol
(8.70 g) N,N%-bis-(4-bromphenyl)-oxalimidoylchloride
together with 40 mmol (3.99 g, 5.5 ml) triethylamine and
20 mmol (2.02 g) (S)-prolinol in 150 ml of toluene was
stirred at r.t. overnight. Thin-layer chromatography
3.13. MS and spectroscopic data for 4
IR (KBr, 298 K) (cm−1): 2065 (w, CO), 2040 (m, CO),
1997 (vs, CO), 1971 (vs, CO), 1722 (m, br, m2-CO), 1658

W. Imhof et al. / Journal of Organometallic Chemistry 590 (1999) 104–114
113
1
[6] T. Morimoto, N. Chatani, S. Murai, J. Am. Chem. Soc. 121
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[7] W. Imhof, D. Berger, Chem. Commun. (Cambridge) (1999)
1457.
(s, CꢁO), 1608 (s, br, CꢁN). H-NMR (CDCl3, 298 K)
(ppm):−13.9 (s, 3H, m2-H), 1.00–1.27 (m, 6H, CH2),
1.33–2.09 (m, 6H, CH2), 2.35–2.65 (m, 9H, CH2, CH),
3.84–4.52 (m, 6H, CH2), 6.38–6.56 (m, 6H, CH), 6.80–
6.97 (m, 6H, CH), 7.09–7.57 (m, 12H, CH).
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Chim. Acta, 158 (1989) 69. (j) F. Muller, G. van Koten, M.J.A.
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4. Supplementary material
Additional material on the structure analysis is avail-
able from the Cambridge Crystallographic Data Centre
by mentioning the deposition numbers 127809 (1a),
127810 (1b), 127811 (1c), 127812 (2a), 127813 (2b),
127814 (3). Copies of this information may be obtained
free of charge from: The Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (Fax: +44-1223-336-
033; email: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
Acknowledgements
The authors gratefully acknowledge financial support
from the Deutsche Forschungsgemeinschaft (SFB 436).
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