Synthesis, Molecular Structure, Fluxional Behavior, and Tricarbonyliron Transfer Reactions of (η4-1-Azabuta-1,3-diene)tricarbonyliron Complexes

Article abstract of DOI:10.1002/(SICI)1099-0682(199807)1998:7<993::AID-EJIC993>3.0.CO;2-6

The η⁴-1-azabuta-1,3-diene)tricarbonyliron complexes 10 are easily prepared in high yield by condensation of the corresponding arylamines 7 with the cinnamaldehydes 8 and subsequent ultrasound-promoted complexation of the resulting 1-azabuta-1,3-dienes 9 with nonacarbonyldiiron. The complexes 10 are shown to represent excellent reagents for the transfer of the tricarbonyliron fragment onto cyclohexa-1,3-diene (1a). The structural characterization for the complexes 10 is achieved by IR, ¹H-NMR, and ¹³C-NMR spectroscopy, as well as X-ray crystallography of 10b, 10c, and 101. Using variable temperature ¹³C-NMR spectroscopy the fluxionality of the complexes 10a, 10b, 10c, 10e, and 2 is investigated and the activation barrier for the turnstile rotation of the tricarbonyliron fragment is determined. The transfer reaction and the structural factors influencing the transfer of the tricarbonyliron fragment are extensively investigated.

Full text of DOI:10.1002/(SICI)1099-0682(199807)1998:7<993::AID-EJIC993>3.0.CO;2-6

FULL PAPER
Transition Metal Complexes in Organic Synthesis, 41[᭛]
Synthesis, Molecular Structure, Fluxional Behavior, and Tricarbonyliron
Transfer Reactions of (η4-1-Azabuta-1,3-diene)tricarbonyliron Complexes
Hans-Joachim Knölker*a, Gerhard Baumb, Norbert Foitzika, Helmut Goesmannb, Peter Gonsera, Peter G. Jonesc,
and Herbert Röttelea
Institut für Organische Chemie der Universität Karlsruhea,
Richard-Willstätter-Allee, D-76131 Karlsruhe, Germany
Fax: ϩ49 (0) 721/698529
E-mail: knoe@ochhades.chemie.uni-karlsruhe.de
Institut für Anorganische Chemie der Universität Karlsruheb,
Engesserstraße, D-76128 Karlsruhe, Germany
Institut für Anorganische und Analytische Chemie der Technischen Universität Braunschweigc,
Hagenring 30, D-38106 Braunschweig, Germany
Received February 27, 1998
Keywords: Azabutadienes / Tricarbonyliron complexes / Transfer reagents / Molecular structure / Fluxionality
The (η4-1-azabuta-1,3-diene)tricarbonyliron complexes 10
are easily prepared in high yield by condensation of the and 10l. Using variable temperature 13C-NMR spectroscopy
corresponding arylamines 7 with the cinnamaldehydes 8 and the fluxionality of the complexes 10a, 10b, 10c, 10e, and 2 is
subsequent ultrasound-promoted complexation of the investigated and the activation barrier for the turnstile
spectroscopy, as well as X-ray crystallography of 10b, 10c,
resulting 1-azabuta-1,3-dienes 9 with nonacarbonyldiiron.
The complexes 10 are shown to represent excellent reagents
for the transfer of the tricarbonyliron fragment onto
cyclohexa-1,3-diene (1a). The structural characterization for
rotation of the tricarbonyliron fragment is determined. The
transfer reaction and the structural factors influencing the
transfer of the tricarbonyliron fragment are extensively
investigated.
1
the complexes 10 is achieved by IR, H-NMR, and 13C-NMR
Introduction
Scheme 1. Complexation of cyclohexa-1,3-diene (1a) and cyclo-
hexa-1,4-diene (1b) with Fe(CO)5 or Fe2(CO)9 and prep-
aration of the complex salt 3
Tricarbonyl(η4-cyclohexa-1,3-diene)iron complexes have
found many useful applications in synthetic organic chemis-
try and have been shown to represent excellent starting ma-
terials for the stereoselective synthesis of natural prod-
ucts.[1] The parent complex, tricarbonyl(η4-cyclohexa-1,3-
diene)iron (2), was prepared first in 1958 by Pauson via
complexation of cyclohexa-1,3-diene (1a) with pentacar-
bonyliron under thermal reaction conditions (yield: 21%).[2]
The yield of this complexation was later improved by
photolytic reaction of cyclohexa-1,4-diene (1b) with penta-
carbonyliron in benzene (yield: 56%),[3] by reaction of
cyclohexa-1,4-diene (1b) with pentacarbonyliron in di-n-bu-
tyl ether at reflux (yield: 46%),[4] by reaction of cyclohexa-
1,3-diene (1a) with nonacarbonyldiiron in tetrahydrofuran
at reflux (yield: 43%),[5] and by photolytic reaction of cyclo-
hexa-1,3-diene (1a) with pentacarbonyliron in hexane
(yield: 77%)[5] (Scheme 1).
resulting tricarbonyl(η5-cyclohexadienylium)iron tetra-
fluoroborate (3) can be utilized for regio- and stereoselec-
tive bond formation with a broad range of nucleophiles.[1]
Projected synthetic applications of the complex salt 3 re-
quire an access to the iron complex 2 in large scale and high
yield. However, the methods described above, involving
either thermally or photochemically induced direct com-
plexation of the cyclohexadienes 1a or 1b with pentacar-
bonyliron or nonacarbonyldiiron, afford complex 2 in only
21Ϫ77% yield. Moreover, these procedures lead to the for-
mation of pyrophoric iron which is hazardous during
The high synthetic potential of tricarbonyl(η4-cyclohexa-
1,3-diene)iron (2) became evident in 1960, when E. O.
Fischer found the possibility of hydride abstraction using
triphenylmethyl tetrafluoroborate.[6] The reactivity of the
[᭛] Part 40: H.-J. Knölker, E. Baum, M. Heininger, Tetrahedron
Lett. 1997, 38, 8021.
Eur. J. Inorg. Chem. 1998, 993Ϫ1007
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1434Ϫ1948/98/0707Ϫ0993 $ 17.50ϩ.50/0
993

H.-J. Knölker et al.
FULL PAPER
workup, especially on large scale complexations. This prob-
A further tricarbonyliron transfer reagent was developed
lem can be circumvented by using labile tricarbonyliron by Grevels in 1984. Photolytic reaction of pentacar-
complexes in order to transfer the tricarbonyliron fragment bonyliron with an excess of cis-cyclooctene (5) in hexane at
from the weakly bound ligand to cyclohexa-1,3-dienes or Ϫ40°C afforded tricarbonylbis(η2-cis-cyclooctene)iron
buta-1,3-dienes under mild reaction conditions. The devel- (GrevelsЈ reagent) (6), which can be isolated as yellow crys-
opment of such tricarbonyliron transfer reagents for the ef- tals in 85Ϫ90% yield (Scheme 3).[11] While the solid com-
ficient complexation of 1,3-dienes has been extensively in- pound can be handled at room temperature, complex 6 is
vestigated over the last 25 years.[7]
labile in solution at temperatures above Ϫ35°C. The advan-
The ability of tricarbonyl(η4-1-oxabuta-1,3-diene)iron tage of GrevelsЈ reagent is that the transfer of the tricarbon-
complexes to serve as a mild source of the tricarbonyliron yliron fragment to 1,3-dienes occurs under extremely mild
fragment was first described by Lewis in 1972.[8] The reaction conditions at temperatures below 0°C. Moreover,
(η4-benzylideneacetone)tricarbonyliron (4) was found to re- using GrevelsЈ reagent 6 also non-conjugated 1,4-dienes can
present an especially efficient transfer reagent. Brookhart be complexed with concomitant migration of the double
reported the transfer of the tricarbonyliron fragment of 4 bond, e.g. the transfer of the tricarbonyliron fragment of
to cyclohexa-1,3-diene (1a) in a thermal reaction that af- GrevelsЈ reagent 6 to cyclohexa-1,4-diene (1b) provides
fords the iron complex 2 in over 95% yield (Scheme 2).[9]
Scheme 2. Complexation of benzylideneacetone to 4 and tricarbo-
nyliron transfer to cyclohexa-1,3-diene (1a) using the
complex 4
tricarbonyl(η4-cyclohexa-1,3-diene)iron (2) in 78% yield
(Scheme 3).
The high lability of the tricarbonyl(η4-1-oxabuta-1,3-di-
ene)iron complex 4 and the GrevelsЈ reagent 6 in solution
at room temperature and in the air induced our search for
alternative tricarbonyliron transfer reagents, whose higher
stability should make them useful for a wider range of ap-
plications in synthetic organometallic chemistry.
Results and Discussion
Our investigations led us to the (η4-1-azabuta-1,3-diene)-
tricarbonyliron complexes 10 as efficient and selective
tricarbonyliron transfer reagents of high stability (Scheme
4).[12][13] (η4-1-Azabuta-1,3-diene)tricarbonyliron com-
plexes were first described by Otsuka[14] and Lewis[15] and
have been applied to the synthesis of dicarbonyl(η4-styr-
ene)iron carbene complexes,[16] substituted pyrroles,[17] and
to the preparation of labile Schiff bases in the form of their
metal complexes.[18] The following methods were previously
used for the preparation of the complexes 10: 1. conden-
sation of amines with tetracarbonyl(η2-1-oxabuta-1,3-diene)-
iron complexes;[14a][18] 2. thermal reaction of the 1-azabuta-
1,3-dienes 9 with nonacarbonyldiiron;[14][17] and 3. aza-Wit-
tig reaction of tetracarbonyl(η2-1-oxabuta-1,3-diene)iron
complexes.[19] We found that the yields of the (η4-1-aza-
buta-1,3-diene)tricarbonyliron complexes 10 are consider-
ably improved by an ultrasound-promoted complexation[20]
of 1-azabuta-1,3-dienes 9 with nonacarbonyldiiron at room
temperature.[12][13] In the present paper we describe an
extensive investigation of the transfer reaction of the tricar-
bonyliron fragment from the complexes 10 to cyclohexa-
1,3-diene (1a) as well as the structural factors influencing
the transfer of the metal fragment.
However, the problematic step of this reaction sequence
is the preparation of the transfer reagent 4. The original
procedure described by Lewis involved complexation of
benzylideneacetone with 1 equivalent of nonacarbonyldi-
iron in toluene at 60°C and afforded complex 4 in only 32%
yield.[8] Brookhart improved this yield to 60% by a photo-
lytic and subsequent thermal reaction of benzylideneace-
tone with pentacarbonyliron.[9] Only by heating a solution
of benzylideneacetone with an excess of nonacarbonyldi-
iron in diethyl ether at reflux, as reported by Thomas, the
tricarbonyliron complex 4 was obtained in reasonable
yields (74Ϫ81%).[10]
Scheme 3. Complexation of cyclohexa-1,4-diene (1b) to 2 using
GrevelsЈ reagent 6
The synthesis of the 1-azabuta-1,3-dienes 9 was achieved
by adaptation of standard literature procedures for the im-
ine condensation of the arylamines 7 with the cinnamal-
dehydes 8. Reaction of 1 equivalent of the freshly distilled
or sublimated arylamine 7 and 1 equivalent of the cinnam-
aldehyde 8 in an inert solvent, generally with addition of a
drying agent, afforded the 1-azabuta-1,3-dienes 9 in high
yields (Scheme 4, Table 1). Most of the arylamines 7 and
the cinnamaldehydes 8 are commercially available. 2,4,6-Tri-
methoxyaniline (7i) was prepared in 88% yield by hydrogen-
994
Eur. J. Inorg. Chem. 1998, 993Ϫ1007

Transition Metal Complexes in Organic Synthesis, 41
FULL PAPER
Scheme 4. Synthesis of the azadienes 9, complexation of 9 to the iron complexes 10 with nonacarbonyldiiron, and the tricarbonyliron
transfer to cyclohexa-1,3-diene (1a)
Table 1. Synthesis and characteristic 1H-NMR data of the 1-azabuta-1,3-dienes 9 and their iron complexes 10 and transfer of the
tricarbonyliron fragment to cyclohexa-1,3-diene (1a)
R1
R2
R3
R4
R5
R6
R7
9, Yield [%]δ [ppm][a] 10, Yield [%]δ [ppm][a]
2, Yield [%]
a
b
c
d
e
f
H
H
H
H
H
H
H
H
H
H
OMe
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
OMe
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
OMe
H
H
H
H
82
100
87
40
72
56
81
79
73
88
95
79
59
80
86
78
99
85
75
8.27
8.30
8.28
8.35
8.24
8.30
8.31
8.30
8.51
8.21
8.26
8.24
8.20
8.26
8.31
8.47
8.36
8.24
8.34
82
88
80
55
59
0
43
40
56
73
41
82
64
79
81
57
61
62
0
6.95
6.99
7.10
7.06
6.84
Ϫ
7.15
6.97
7.94
Ϫ[b]
6.95
Ϫ[b]
6.83
7.10
6.95
7.04
7.23
6.89
Ϫ
88
95
74
45
78
Ϫ
80
87
74
93
90
83
88
78
92
69
60
74
Ϫ
H
H
OMe
H
H
OMe
H
H
H
H
NMe2
CF3
H
OMe
OMe
OMe
H
OMe
H
CF3
OMe
OMe
H
OMe
OMe
OMe
H
H
H
H
H
NO2
H
H
g
h
i
OMe
H
H
OMe
H
H
OMe
H
H
j
k
l
H
OMe
OMe
OMe
OMe
OMe
H
H
H
OMe
H
H
m
n
o
p
q
r
H
OMe
H
H
H
H
H
CN
CN
NMe2
NO2
OMe
H
H
H
s
H
H
[a]
1
[b]
Chemical shift of the H-C2 signal in the H-NMR spectrum. Ϫ No assignment possible, due to coincidental overlap of signals.
ation of 2,4,6-trimethoxynitrobenzene.[21] The synthesis of and para positions of the 1-aryl ring (R1, R3, R5) cause a
4-cyanocinnamaldehyde (8p ϭ 8q; R6 ϭ CN, R7 ϭ H) was downfield shift of the signal of the imine proton relative to
achieved in 78% yield by Wittig reaction of 4-cyanobenzal- the value obtained for the parent compound 9a (δ ϭ 8.27).
dehyde and (formylmethylene)triphenylphosphorane in The maximum is observed for the 2,4,6-trimethoxy deriva-
toluene at reflux.
tive 9i with a chemical shift of δ ϭ 8.51, which can be at
As shown below, the electron density at the nitrogen of least partly ascribed to the influence of the anisotropy of
the 1-azabuta-1,3-dienes 9 is crucial for the efficiency of the the oxygen atoms. In contrast, a highfield shift is found with
tricarbonyliron transfer from the corresponding complexes donor substituents in the para position of the 4-aryl ring
10 and for the catalytic complexation[12][13] of cyclohexa- (R6). Exactly the opposite effects on the chemical shift of
1,3-diene (1a) using 9 and nonacarbonyldiiron or pentacar- H-C2 are observed with acceptor substituents in these posi-
bonyliron. The chemical shift of the imine proton (H-C2) tions. In a few cases steric effects are overriding, since sub-
1
in the H-NMR spectra of the 1-azabuta-1,3-dienes 9 is a stituents in the ortho positions of the aryl ring cause larger
measure of the electron density at the imine nitrogen atom. torsion angles between the aryl ring and the 1-azabuta-1,3-
A larger downfield shift of H-C2 correlates with a higher diene plane, resulting in decreased π-overlap.
electron density at the nitrogen. Thus, this value can be used
The complexation of the 1-azabuta-1,3-dienes 9 to the
to estimate the activity of the 1-azabuta-1,3-dienes 9 for (η4-1-azabuta-1,3-diene)tricarbonyliron complexes 10 was
catalytic complexations and the transfer ability of the corre- conveniently achieved by reaction with nonacarbonyldiiron
sponding complexes 10. Donor substituents in the ortho under sonication in tetrahydrofuran at room temperature
Eur. J. Inorg. Chem. 1998, 993Ϫ1007
995

H.-J. Knölker et al.
FULL PAPER
(Scheme 4, Table 1). The ultrasound-promoted tricarbonyl- ity of these complexes leading to equivalency of the three
iron complexation, previously applied by Ley and coworkers carbonyl ligands is caused by the turnstile rotation of the
to buta-1,3-dienes and cyclohexa-1,3-dienes,[20] was found tricarbonyliron fragment. This dynamic process is suffic-
to be superior to the thermal complexation of the 1-aza- iently slow on the NMR time scale at low temperatures to
buta-1,3-dienes 9. With respect to the diastereoselectivity allow the observation of two peaks for the three carbonyl
of the complexation of chiral 1-azabuta-1,3-dienes,[22] the ligands with an intensity ratio of 2:1 in the case of sym-
ultrasound procedure also provides better results than the metrical diene ligands or three peaks of equal height for
thermal reaction, since it does not require elevated tempera- unsymmetrical diene ligands.[24] Previous investigations of
tures, which were shown to cause epimerization of the the fluxional behavior of tricarbonyliron-diene complexes
planar chirality.[23]
have demonstrated that the activation barriers for this intra-
The red crystalline (η4-1-azabuta-1,3-diene)tricarbonyl- molecular basal-apical exchange of the carbonyl groups for
iron complexes 10 are stable in the air for months and there- complexes with carbadiene ligands are significantly lower
fore appeared to represent appropriate potential transfer re- than those of 1-heterodiene ligands.[25] Takats concluded
agents for our purposes. The IR spectra of the iron com- that the variations in the activation barrier for the turnstile
plexes 10 in KBr exhibit intense broad bands in the region rotation of the tricarbonyliron fragment can be rationalized
of 1960Ϫ2060 cmϪ1, which are typical of carbonyl ligands by the metal-carbonyl back bonding, however steric factors
of tricarbonylironϪdiene complexes (Table 2). The wave also contribute to this value.[25c]
number of the CO stretching vibration represents an in-
We determined precisely the activation barrier for the in-
direct measure of the strength of the bonding between the tramolecular carbonyl ligand exchange of four (η4-1-aza-
metal and the organic ligand. A shift to lower wave num- buta-1,3-diene)tricarbonyliron complexes (10a؊c and 10e)
bers relative to the value for the parent compound 10a is and for tricarbonyl(η4-cyclohexa-1,3-diene)iron (2) by dy-
observed by donor substituents in the para position of the namic 13C-NMR spectroscopy at 125 MHz in deuterated
1-aryl ring (e.g. 10b: R3 ϭ OMe, 10d: R3 ϭ NMe2) indicat- toluene (Figure 1aϪe, Table 2). The stepwise increase of the
ing a reduced back bonding from the iron atom to the aza- temperature up to 373 K during the measurement of the
diene ligand in these complexes, which is explained by an 13C-NMR spectra of the complexes 10 provided a single
increase in energy of the π* orbitals of the 1-azabutadiene. signal for the three carbonyl ligands, which still showed
The 1H-NMR spectra of the η4-tricarbonyliron-com- some line broadening. As expected the low temperature
plexed 1-azabuta-1,3-dienes 10 exhibit the characteristic spectra of the 1-azadiene complexes 10 at 233 K exhibited
high field shifts for the protons at the carbon atoms which three sharp singlets for the carbonyl ligands. The coales-
are coordinated to the metal (C2 to C4). A closer inspection cence temperature TC of the dynamic process was clearly
of the chemical shifts which are found for the signals of above room temperature for all four cases investigated. This
the imine protons (H-C2) of the complexes 10 reveals that was already indicated by the fact that the signals for the
generally a highfield shift of about 1.3Ϫ1.4 ppm relative to carbonyl ligands were missing in the 13C-NMR spectra in
the value for the corresponding free ligand 9 is observed deuterochloroform at room temperature for most of the
(Table 1). For those derivatives of 10 having one methoxy 1-azadiene complexes 10 prepared in the present work. For
substituent in the ortho position of the 1-aryl ring (R1 ϭ the cyclohexadiene complex 2 one sharp singlet for the
OMe; 10c, 10g, 10n, and 10q) this highfield shift relative to three carbonyl ligands is observed at room temperature,
9 is decreased to 1.13Ϫ1.18 ppm, which is ascribed partly while the 13C-NMR spectrum at 185 K exhibits two singlets
to a steric effect of the ortho substituent (increase of the at δ ϭ 211.32 and 216.05 in a ratio of 2:1. The coalescence
torsion angle) leading to reduced π-overlap and partly to temperatures could be determined with a tolerance of ±5
the anisotropy of the oxygen atom. For complex 10i with K. With the value for δν taken from the low temperature
two ortho methoxy substituents in the 1-aryl ring (R1 ϭ spectrum, the free enthalpy of activation for the intramol-
R5 ϭ OMe) the highfield shift of the imine proton relative ecular exchange of carbonyl ligands could be calculated in
to the value observed for 9i drops to 0.57 ppm.
good approximation by using the formula ∆G° ϭ R·TC
Almost all of the (η4-1-azabuta-1,3-diene)tricarbonyliron [22.96 ϩ ln(TC/δν)].[26] The activation barrier for this turn-
complexes 10 described in this paper show no or at best stile rotation of the tricarbonyliron fragment in the 1-p-ani-
three very broad signals for the carbon atoms of the car- syl-substituted 1-azadiene complex 10b is 13.5 ± 0.3 kcal/
bonyl ligands in their 13C-NMR spectra when taken in deu- mol. For the other 1-azadiene complexes that were investi-
terochloroform at room temperature, although the IR spec- gated by dynamic 13C-NMR spectroscopy (10a, 10c, and
tra in KBr exhibit the typical three bands for the carbonyl 10e), the value was found to be increased by about 1 kcal/
ligands at 1960Ϫ2060 cmϪ1. The trifluoromethyl-substi- mol (Table 2). Thus the intramolecular ligand exchange of
tuted compounds 10e and 10m are exceptions and exhibit the carbonyl groups is facilitated by a donor substituent in
three only slightly broadened signals in their 13C-NMR the para position of the 1-aryl ring (complex 10b) as com-
spectra under these conditions (10e: δ ϭ 204.77, 208.30, pared to the parent compound 10a. This finding is again in
211.49; 10m: δ ϭ 205.07, 208.94, 211.97). The 13C-NMR agreement with the assumption of reduced back bonding
spectra of (η4-carba-1,3-diene)tricarbonyliron complexes from the iron atom to the 1-azadiene ligand in complex
show in most cases only one singlet at δ ϭ 210Ϫ213 for the 10b relative to 10a. The opposite effect is observed with an
three carbonyl ligands at room temperature. The fluxional- acceptor group in this position (complex 10e) and also with
996
Eur. J. Inorg. Chem. 1998, 993Ϫ1007

Transition Metal Complexes in Organic Synthesis, 41
FULL PAPER
Figure 1a. Dynamic 13C-NMR spectra of complex 10a in the metal
Figure 1b. Dynamic 13C-NMR spectra of complex 10b in the metal
carbonyl region (125 MHz, [D8]toluene)
carbonyl region (125 MHz, [D8]toluene)
Figure 1c. Dynamic 13C-NMR spectra of complex 10c in the metal
Figure 1d. Dynamic 13C-NMR spectra of complex 10e in the metal
carbonyl region (125 MHz, [D8]toluene)
carbonyl region (125 MHz, [D8]toluene)
Figure 1e. Dynamic 13C-NMR spectra of complex 2 in the metal
a donor group in the ortho position of the 1-aryl ring, be-
cause of the increased torsion angle (compound 10c). For
the cyclohexa-1,3-diene complex 2 the activation barrier for
the rotation of the tricarbonyliron fragment has been deter-
mined as 8.7 ± 0.3 kcal/mol, which is in good agreement
with the value of 8.8 ± 0.5 kcal/mol obtained earlier by
Takats et al. in [D6]DMSO/CS2.[25c] For the related (η4-
buta-1,3-diene)tricarbonyliron complex activation barriers
of 9.5 kcal/mol[24] and 10.5 ± 0.5 kcal/mol[25c] have been
reported. These findings emphasize that the free enthalpy
of activation for the turnstile rotation of the tricarbonyliron
fragment for the complexes of 1-hetero-1,3-dienes is gener-
ally about 4Ϫ5 kcal/mol higher than for the corresponding
complexes of carba-1,3-dienes, no matter whether they are
cyclic or acyclic. The data are in agreement with decreased
back donation of electrons from filled iron d-orbitals into
the LUMO of the carbonyl group for the tricarbonyliron
carbonyl region (125 MHz, [D8]toluene)
Table 2. Characteristic IR and 13C-NMR data for the carbonyl ligands of selected tricarbonyliron complexes[a]
˜
νCO [cmϪ1
]
δCO (233 K) [ppm]
δCO (373 K) [ppm]
TC [K]
δν [Hz]
∆G° [kcal/mol]
10a
10b
10c
10e
2
2055, 1988, 1977
2049, 1987, 1963
2058, 2000, 1970
2059, 2002, 1983
2042, 1957
206.02, 209.49, 212.70 209.53
206.60, 209.71, 213.03 209.81
206.41, 210.06, 213.84 210.02
205.19, 208.90, 212.16 208.79
328 ± 5
308 ± 5
338 ± 5
335 ± 5
201 ± 5
840.79
809.65
934.21
876.08
594.79
14.3 ± 0.3
13.5 ± 0.3
14.7 ± 0.3
14.6 ± 0.3
8.7 ± 0.3
211.32, 216.05[b]
212.56[c]
[a]
[b]
[c]
IR spectra: Drift at room temp.; 13C-NMR spectra: 125 MHz in [D8]toluene. Ϫ
This spectrum was recorded at 185 K. Ϫ This
spectrum was recorded at 298 K.
Eur. J. Inorg. Chem. 1998, 993Ϫ1007
997

H.-J. Knölker et al.
FULL PAPER
complexes of 1-hetero-1,3-dienes, as compared to 1-carba- cyclohexa-1,3-dienes and buta-1,3-dienes, correlate very
1,3-dienes. This is confirmed by the higher stretching fre- well with the concept of increased back bonding from the
quencies for the carbonyl bands in the IR spectra of 1-het- filled iron d-orbitals into the π* orbitals of the organic li-
ero-1,3-diene complexes. In consequence the averaged gand for the heterodiene complexes. This is emphasized by
chemical shifts in the 13C-NMR spectra observed at high the IR, 1H-NMR, and 13C-NMR data described above.
temperatures are shifted to higher field and the activation Some anomalies in the spectral data of the 1-azabuta-1,3-
barrier for the rotation of the tricarbonyliron fragment is diene complexes presented above were ascribed to steric fac-
higher for the 1-heterodiene complexes.
tors, especially for those cases of 1-azabuta-1,3-dienes re-
sulting from an ortho-substituted arylamine. The X-ray
crystal structures reveal an increased torsion angle for the
complexes with an ortho-methoxy substituent. It is note-
worthy that the out-of-plane arrangement of the 1-aryl ring
relative to the 1-azabuta-1,3-diene plane in these complexes
proceeds in a way that the oxygen atom of the methoxy
group is oriented towards the iron atom. For electronic rea-
sons this arrangement becomes most evident for complex
10l with an ortho-methoxy substituent in the 1-aryl ring and
a para-methoxy substituent in the 4-aryl ring. The torsional
Figure 2. Molecular structure of 10b in the crystal (SCHAKAL
˚
representation; arbitrary numbering). Selected bond lengths [A]:
FeϪN 2.075(3), FeϪC2 2.074(4), FeϪC3 2.068(4), FeϪC4
2.167(4). Torsion angle: C2,NϪC11,C16: 10.8°
angle between the 1-aryl ring and the 1-azabuta-1,3-diene
˚
plane of 10l is 37.4° and the distance FeϪO4 is only 3.35 A,
suggesting the possibility of chelation of the tricarbonyliron
fragment by coordination of the oxygen to the iron atom
on haptotropic η4 Ǟ η1 migration during the transfer of
the metal fragment (see below).
Figure 3. Molecular structure of 10c in the crystal (SCHAKAL
˚
representation; arbitrary numbering). Selected bond lengths [A]:
FeϪN 2.074(2), FeϪC2 2.064(2), FeϪC3 2.050(2), FeϪC4
2.132(3). Torsion angle: C2,NϪC11,C16: 13.4°. Distance FeϪO4:
˚
3.62 A
The transfer of the tricarbonyliron fragment from the
(1-azabuta-1,3-diene)tricarbonyliron complexes 10 to cyclo-
hexa-1,3-diene (1a) was extensively investigated. It was
shown that a smooth transfer of the metal fragment from
all 1-azabuta-1,3-diene complexes described in this study
was achieved simply by heating the reaction mixture of
complex 10 and 1a in tetrahydrofuran at reflux (Scheme 4,
Table 1). The variation of the reaction time for the transfer
of the tricarbonyliron fragment to cyclohexa-1,3-diene (1a)
was investigated for the complexes 10b, 10c, and 10g (Table
3). At all three different reaction times the transfer reagent
10b was superior. Complex 10b transfers the metal fragment
faster and provides the best yield after 2 h. With increasing
turnover, the transfer of the tricarbonyliron fragment from
complex 10 to already generated corresponding free 1-aza-
buta-1,3-diene ligand 9 can compete with the desired trans-
fer to 1a and finally becomes dominant if only a 1:1 ratio
Figure 4. Molecular structure of 10l in the crystal (SCHAKAL
˚
representation; arbitrary numbering). Selected bond lengths [A]:
FeϪN 2.070(2), FeϪC2 2.068(2), FeϪC3 2.062(2), FeϪC4
2.155(2). Torsion angle: C2,NϪC11,C16: 37.4°. Distance FeϪO4:
˚
3.35 A
Table 3. Variation of the reaction time for the tricarbonyliron trans-
fer to 1a using the complexes 10b, c, g
The X-ray crystal structure determinations of the (η4-1-
azabuta-1,3-diene)tricarbonyliron complexes 10b, 10c, and
10l confirm the tetragonal pyramidal coordination of the
iron atom (Figure 2Ϫ4, Table 4). Two basal positions are
occupied by the two π bonds, the two others by carbonyl
ligands. The third carbonyl ligand adopts the apical posi-
tion of these complexes. Similar arrangements were pre-
viously found for tricarbonyliron complexes of buta-1,3-di-
enes and cyclohexa-1,3-dienes and also for the parent com-
plex 10a.[14b] The bond lengths found in the tricarbonyliron
complexes of 1-azabuta-1,3-dienes, compared to those of
998
Eur. J. Inorg. Chem. 1998, 993Ϫ1007

Transition Metal Complexes in Organic Synthesis, 41
FULL PAPER
of complex 10 and 1a is employed. Therefore, an excess of forded the iron complex 2 after 20 min in 85% yield
cyclohexa-1,3-diene (1a) is used in order to bring the reac- (Scheme 5). Thus, the required reaction time for compar-
tion to completion.
able yields of 2 with the 1-oxabuta-1,3-diene complex 11
Using a standard set of reaction conditions, the transfer as transfer reagent is significantly shorter than with the 1-
of the metal fragment to cyclohexa-1,3-diene (1a) was com- azabuta-1,3-diene complexes 10 (cf. Table 3). On direct
pared for the various (1-azabuta-1,3-diene)tricarbonyliron comparison of the transfer reagents 11 and 10b this differ-
complexes 10 (Table 1, Scheme 4). By far the best overall ence in reactivity becomes even more evident (Scheme 6).
result was achieved using tricarbonyl[(1-4-η)-1-(4-meth- The transfer of the tricarbonyliron fragment from the
oxyphenyl)-4-phenyl-1-azabuta-1,3-diene]iron (10b) as tricarbonyl(4-methoxybenzylideneacetone)iron complex 11
transfer reagent. First, the free 1-azabuta-1,3-diene 9b can to the free 1-azadiene 9b by heating in benzene at reflux for
be prepared quantitatively and crystallizes very easily. Sec- 20 min afforded exclusively the (1-azabuta-1,3-diene)tricar-
ondly, the complexation of 9b with nonacarbonyldiiron pro- bonyliron complex 10b along with the free 1-oxabuta-1,3-
moted by ultrasound provided the tricarbonyliron complex diene 12. However, a transfer of the metal fragment from
10b in a yield of 88%. Thirdly, the reaction of 10b with complex 10b to the free ligand 12 could not be achieved.
cyclohexa-1,3-diene (1a) afforded tricarbonyl(η4-cyclohexa- This result confirmed the higher reactivity of the 1-oxabuta-
1,3-diene)iron (2) in 95% yield. Thus, the complexation of 1,3-diene complexes for the transfer of the tricarbonyliron
1a using this 3-step sequence could be realized in an overall fragment.
A direct comparison of the (η4-1-azabuta-1,3-diene)-
tricarbonyliron complexes 10a and 10b demonstrated the
higher transfer reactivity of the latter reagent. Reaction of
either equimolar amounts of the free 1-azabuta-1,3-diene
9a with the iron complex 10b of the free ligand 9b with the
iron complex 10a in tetrahydrofuran at reflux led within 4
h to an equilibrium with a 2:1 ratio of the iron complexes
10a and 10b. This result confirms again that the transfer
of the tricarbonyliron fragment is facilitated by the donor
substituent in the para position of the 1-aryl ring.
yield of 84%. Moreover, the free 1-azadiene 9b can be reco-
vered from the reaction mixture by simple crystallization in
more than 95% yield.
Scheme 5. Transfer of the tricarbonyliron fragment from the 4-me-
thoxybenzylideneacetone complex 11 to cyclohexa-1,3-
diene (1a)
Based on previous kinetic studies on ligand exchange re-
actions at complex 10a[28] and our own mechanistic investi-
gations,[23][29] the following mechanism is proposed for the
Some information on the relative reactivities of various transfer of the tricarbonyliron fragment using (η4-1-aza-
tricarbonyliron transfer reagents was provided by compe- buta-1,3-diene)tricarbonyliron complexes 10 (Scheme 7).
tition experiments. For this purpose we prepared the tricar- Complex 10 generates, by a thermally induced haptotropic
bonyliron complex 11 containing the more electron-rich 4- migration, the 16-electron tricarbonyl(η1-imine)iron com-
methoxybenzylideneacetone ligand. Complex 11 was re- plex 13. This type of 16-electron η1-imine complex is also
ported to be more reactive in transfer reactions than the considered as the intermediate in the thermal epimerization
tricarbonyliron complex 4 with unsubstituted benzylidenea- of tricarbonyliron complexes of chiral 1-azabuta-1,3-di-
cetone as ligand.[27] A smooth transfer of the metal frag- enes[23] and was obtained on matrix photolysis studies of
ment was observed on reaction of complex 11 with cyclo- (η4-1-azabuta-1,3-diene)tricarbonyliron complexes.[30] The
hexa-1,3-diene (1a) in tetrahydrofuran at reflux and af- vacant coordination site of complex 13 is filled by η2-coor-
Scheme 6. Competition experiments between various tricarbonyliron transfer reagents
Eur. J. Inorg. Chem. 1998, 993Ϫ1007
999

H.-J. Knölker et al.
FULL PAPER
phy: Baker or Merck silica gel (0.03Ϫ0.06 mm). Ϫ Ultrasound:
Bandelin Sonorex-TK52H cleaning bath; frequency: 35 kHz, used
at 50% power. Ϫ Melting points: Leitz hot stage and Büchi 535. Ϫ
IR spectra: Bruker IFS-88, Perkin-Elmer 882 and 1710. Ϫ 1H-
NMR and 13C-NMR spectra: Bruker WP-200, AC-250, AM-400,
and DRX-500; internal standard: tetramethylsilane or the signal of
the deuterated solvent; coupling constants in Hz. Ϫ Mass spectra:
Finnigan MAT-312 and MAT-90: ionization potential: 70 eV. Ϫ
Elemental analysis: Heraeus CHN-Rapid. Bulb-to-bulb distillation:
Büchi glass tube oven GKR-51. Ϫ X-ray analyses: The data were
collected on a STOE STADI-4 diffractometer using Mo-Kα radi-
ation. The structures were solved by direct methods (SHELXS-86)
and refined anisotropically by full-matrix least squares based on all
unique F2 (SHELXL-93); the program SCHAKAL-92 was used for
the graphical representation of the crystal structures (E. Keller, a
computer program for the graphic representation of molecular and
crystallographic models, Universität Freiburg, Germany, 1992).
Scheme 7. Proposed mechanism of the tricarbonyliron transfer
from 1,4-diaryl-1-azabuta-1,3-diene complexes 10 to
cyclohexa-1,3-diene (1a)
2,4,6-Trimethoxyaniline (7i): A mixture of 2,4,6-trimethoxynitro-
benzene[21] (500 mg, 2.35 mmol) and Pd/C (100 mg) in EtOH (30
ml) was stirred under a hydrogen atmosphere (1.1 bar) for 20 h.
The reaction mixture was filtered through a short path of Celite/
Alox B and the solvent was removed under reduced pressure. Bulb-
to-bulb distillation (120°C, 0.1 mbar) of the residue afforded 7i
˜
(380 mg, 88%). Pale yellow solid. M.p. 33Ϫ35°C. Ϫ IR (drift): ν ϭ
dination of cyclohexa-1,3-diene (1a) to provide complex 14.
This 18-electron complex, which could not be isolated, re-
presents the crucial intermediate of the transfer reaction.
Based on X-ray crystal structure determinations of (η1-1-
azabuta-1,3-diene)tetracarbonyliron complexes[29][31] and
additional experimental evidence,[29][32] complex 14 is pro-
posed to have a trigonal-bipyramidal structure with the η2-
coordinated 1,3-diene in equatorial and the η1-coordinated
α,β-unsaturated imine in an axial position. Disengagement
of the 1-azabuta-1,3-diene 9 from complex 14 leads to the
16-electron complex 15, which affords the tricarbonyliron
complex 2 by haptotropic (η2 Ǟ η4) migration of the
metal fragment.
3449, 3362, 2939, 2837, 1611, 1512, 1164 cmϪ1. Ϫ H NMR (400
1
MHz, CDCl3): δ ϭ 3.48 (br s, 2 H), 3.74 (s, 3 H), 3.81 (s, 6 H),
6.15 (s, 2 H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3): δ ϭ
55.91 (3 CH3), 91.40 (2 CH), 118.97 (C), 148.13 (2 C), 152.62 (C).
Ϫ MS (30°C): m/z (%) ϭ 183 (100) [Mϩ], 168 (87), 140 (39), 125
(28); HRMS: 183.0910 (C9H13NO3, calcd. 183.0895).
4-Cyanocinnamaldehyde (8; R6 ϭ CN, R7 ϭ H): A solution of 4-
cyanobenzaldehyde (823 mg, 6.28 mmol) and (formylmethylene)tri-
phenylphosphorane (2.10 g, 6.90 mmol) in toluene (40 ml) was
stirred at 80°C for 24 h. The solvent was evaporated in vacuo and
the residue was subjected to flash chromatography (gradient elu-
tion, first with Et2O/pentane, 1:3 and then elution with Et2O) on
silica gel. Evaporation of the solvent afforded a crude product,
which was dissolved in Et2O (30 ml). Recrystallization at Ϫ30°C
provided the aldehyde 8 (R6 ϭ CN, R7 ϭ H) as a mixture of dia-
Conclusion
stereoisomers (771 mg, 78%, (E)/(Z) Ն 10:1). Yellow solid. M.p.
We have shown that the tricarbonyliron complexes of 1,4-
diaryl-substituted 1-azabuta-1,3-dienes serve as highly ef-
ficient tricarbonyliron transfer reagents for the com-
plexation of cyclohexa-1,3-diene. Complexation using these
transfer reagents can also be applied to a broad range of
other 1,3-dienes.[12] After the transfer of the metal fragment
the 1-azabuta-1,3-dienes 9 are recovered almost quantita-
tively by simple crystallization. This fact has been exploited
for the development of a complexation of 1,3-dienes using
only catalytic amounts of the 1-azabuta-1,3-dienes 9.[12][13]
Most importantly, it has been demonstrated that high
asymmetric inductions are achieved on the catalytic com-
plexation of prochiral 1,3-dienes using chiral 1-azabuta-
1,3-dienes.[32]
˜
132°C. Ϫ IR (drift): ν ϭ 2228, 1685, 1627, 1420, 1293, 1129, 987,
1
817 cmϪ1. Ϫ H NMR (250 MHz, CDCl3) [(E)-isomer]: δ ϭ 6.78
(dd, J ϭ 16.1, 7.5 Hz, 1 H), 7.49 (d, J ϭ 16.1 Hz, 1 H), 7.67 (d,
J ϭ 8.5 Hz, 2 H), 7.74 (d, J ϭ 8.5 Hz, 2 H), 9.78 (d, J ϭ 7.5 Hz,
1 H). Ϫ MS (25°C): m/z (%) ϭ 157 (100) [Mϩ], 156 (92), 129 (57),
128 (46), 103 (14), 102 (20), 101 (17); HRMS: 157.0516 (C10H7NO,
calcd. 157.0528).
1,4-Diphenyl-1-azabuta-1,3-diene (9a): Na2SO4 (3 g) was added
to a solution of cinnamaldehyde (8; R6 ϭ R7 ϭ H) (1.91 ml, 2.00
g, 15.1 mmol) and freshly distilled aniline (7a) (1.38 ml, 1.41 g,
15.1 mmol) in Et2O (30 ml). The reaction mixture was stirred at
room temp. for 1 h, then filtered, and the residue was washed with
Et2O (20 ml). Crystallization from the filtrate at Ϫ20°C afforded
˜
the product 9a (2.56 g, 82%). Pale yellow needles. Ϫ IR (drift): ν ϭ
2958, 2839, 1630, 1605, 1505, 1295, 1251, 1032, 986, 720 cmϪ1. Ϫ
1H NMR (400 MHz, CDCl3): δ ϭ 7.17 (m, 5 H), 7.38 (m, 5 H),
7.54 (m, 2 H), 8.27 (dd, J ϭ 7.2, 1.0 Hz, 1 H). Ϫ 13C NMR and
DEPT (63 MHz, CDCl3): δ ϭ 120.87 (2 CH), 126.07 (CH), 127.44
(2 CH), 128.52 (CH), 128.87 (2 CH), 129.13 (2 CH), 129.55 (CH),
135.50 (C), 143.98 (CH), 151.64 (C), 161.60 (CH). Ϫ MS (35°C):
m/z (%) ϭ 207 (40) [Mϩ], 206 (100), 130 (3), 115 (7), 77 (22);
HRMS: 207.1062 (C15H13N, calcd. 207.1048).
This work was supported by the Deutsche Forschungsgemein-
schaft (Gerhard-Hess award) and the Fonds der Chemischen Indus-
trie.
Experimental Section
General: All reactions were carried out using anhydrous and de-
gassed solvents under an argon atmosphere. Ϫ Flash chromatogra-
1000
Eur. J. Inorg. Chem. 1998, 993Ϫ1007

Transition Metal Complexes in Organic Synthesis, 41
Table 4. Crystallographic data, summary of data collection, and refinement of 10b, 10c, and 10l
FULL PAPER
10b
10c
10l
empirical formula
formula weight
crystal color
C19H15FeNO4
377.17
C19H15FeNO4
377.17
C20H17FeNO5
407.20
red
red
red
crystal size [mm]
crystal system
0.54 x 0.12 x 0.12
monoclinic
P21/c
11.975(5)
15.735(8)
9.439(4)
90
101.07(3)
90
0.4 ϫ 0.3 ϫ 0.3
orthorhombic
Pbca
18.5970(10)
7.938(3)
0.80 ϫ 0.60 ϫ 0.55
triclinic
¯
space group
P1
˚
a [A]
6.549(3)
10.400(5)
˚
b [A]
˚
c [A]
α [°]
β [°]
23.483(3)
14.618(6)
106.71(3)
96.30(3)
90
90
90
γ [°]
103.07(3)
˚
V [A3]
1745.5(14)
3466.6(14)
912.4(7)
Z
4
8
2
ρ
[g cmϪ3
]
1.435
1.445
1.482
acbaslcodr. ption coefficient [mmϪ1
]
0.862
0.893
0.858
F (000)
776
1552
420
˚
λ [A]
0.71073
0.71073
0.71073
T [K]
293(2)
200(2)
173(2)
θ range [°]
5.20Ϫ28.15
1.73Ϫ25.03
3.04Ϫ25.00
reflections collected
independent reflections
refinement method
data / restraints / parameters
final R indices [I>2σ (I)]
9737
6121
3202
4111
3063
3202
full-matrix least squares on F2
4106 / 0 / 251
full-matrix least squares on F2
3062 / 0 / 286
full-matrix least squares on F2
3200 / 3 / 255
R1 ϭ 0.0583; wR2 ϭ 0.1376
0.467
R1 ϭ 0.0317; wR2 ϭ 0.0772
0.274
R1 ϭ 0.0317; wR2 ϭ 0.0805
0.395
max. residual electron density
˚
[e AϪ3
]
CSD number[a]
59410
408182
58301
[a]
Further details of the crystal structure investigations may be obtained from the Fachinformationszentrum Karlsruhe D-76344 Eggen-
stein-Leopoldshafen on quoting the CSD numbers given.
1-(4-Methoxyphenyl)-4-phenyl-1-azabuta-1,3-diene (9b): Cinna-
H), 7.19 (m, 1 H), 7.23 (dd, J ϭ 16.0, 8.7 Hz, 1 H), 7.33Ϫ7.41 (m,
maldehyde (8; R6 ϭ R7 ϭ H) (10 ml, 10.5 g, 79.3 mmol) was added 3 H), 7.53 (m, 2 H), 8.28 (d, J ϭ 8.7 Hz, 1 H). Ϫ 13C NMR and
to a solution of freshly sublimated p-anisidine (7b) (9.77 g, 79.3 DEPT (100 MHz, CDCl3): δ ϭ 55.75 (CH3), 111.22 (CH), 119.41
mmol) in EtOAc (150 ml). MgSO4 (4 g) was added and the mixture (CH), 120.93 (CH), 126.99 (CH), 127.47 (2 CH), 128.89 (2 CH),
was stirred for 1 h at room temp. The solution was separated and
129.06 (CH), 129.47 (CH), 135.66 (C), 141.21 (C), 143.66 (CH),
the residue was washed with EtOAc. The solutions were combined 152.73 (C), 162.01 (CH). Ϫ MS (45°C): m/z (%) ϭ 237 (100) [Mϩ],
and the solvent was evaporated slowly at 40°C until crystallization 236 (81), 220 (21), 130 (12), 115 (17); HRMS: 237.1140 (C16H15NO,
could be observed. Then pentane (100 ml) was added to the warm calcd. 237.1154). ϪC16H15NO: C 80.98, H 6.37, N 5.90; found: C
solution. Recrystallization at Ϫ20°C afforded the azadiene 9b (18.8
g, 100%). Yellow-green crystals. M.p. 122°C. Ϫ IR (drift): ν ϭ
80.46, H 6.37, N 6.30.
˜
1-(4-N,N-Dimethylaminophenyl)-4-phenyl-1-azabuta-1,3-diene
(9d): A solution of cinnamaldehyde (8; R6 ϭ R7 ϭ H) (0.95 ml,
1.00 g, 7.57 mmol) and freshly sublimated 4-N,N-dimethylami-
noaniline (7d) (1.03 g, 7.57 mmol) in Et2O (30 ml) was stirred at
room temp. for 1 h. Na2SO4 (2 g) was added and the reaction mix-
ture was stirred at room temp. for additionally 2 h. The solution
was separated and evaporated in vacuo to a volume of 15 ml. Crys-
3060, 1625, 1600, 1576, 1150, 999, 994, 753 cmϪ1. Ϫ 1H NMR (400
MHz, CDCl3): δ ϭ 3.83 (s, 3 H), 6.92 (br d, J ϭ 9.0 Hz, 2 H), 7.11
(m, 2 H), 7.21 (br d, J ϭ 9.0 Hz, 2 H), 7.38 (m, 3 H), 7.53 (m, 2
H), 8.30 (dd, J ϭ 4.5, 3.8 Hz, 1 H). Ϫ 13C NMR and DEPT (63
MHz, CDCl3): δ ϭ 55.29 (CH3), 114.27 (2 CH), 122.11 (2 CH),
127.24 (2 CH), 128.61 (CH), 128.75 (2 CH), 129.23 (CH), 135.60
(C), 142.85 (CH), 144.37 (C), 158.25 (C), 159.29 (CH). Ϫ MS
(55°C): m/z (%) ϭ 237 (63) [Mϩ], 236 (100), 115 (17); HRMS:
237.1137 (C16H15NO, calcd. 237.1154). Ϫ C16H15NO: C 80.98, H
6.37, N 5.90; found: C 81.14, H 6.35, N 6.35.
tallization at Ϫ20°C provided the product 9d (760 mg, 40%). Yel-
˜
low crystals. M.p. 146°C. Ϫ IR (drift): ν ϭ 1625, 1605, 1512, 1448,
1349, 1220, 1169, 955, 821, 752, 693 cmϪ1. Ϫ 1H NMR (400 MHz,
CDCl3): δ ϭ 2.99 (s, 6 H), 6.75 (br d, J ϭ 9.0 Hz, 2 H), 7.07 (d,
J ϭ 15.9 Hz, 1 H), 7.14 (dd, J ϭ 15.9, 8.2 Hz, 1 H), 7.25 (br d,
J ϭ 9.0 Hz, 2 H), 7.33 (m, 1 H), 7.39 (m, 2 H), 7.53 (m, 2 H), 8.35
(d, J ϭ 8.2 Hz, 1 H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3):
δ ϭ 40.68 (2 CH3), 112.76 (2 CH), 122.33 (2 CH), 127.25 (2 CH),
128.86 (2 CH), 129.07 (CH), 129.15 (CH), 136.03 (C), 140.31 (C),
141.63 (CH), 149.58 (C), 156.94 (CH). Ϫ MS (65°C): m/z (%) ϭ
250 (84) [Mϩ], 249 (100), 233 (12), 124 (4); HRMS: 250.1450
(C17H18N2, calcd. 250.1470).
1-(2-Methoxyphenyl)-4-phenyl-1-azabuta-1,3-diene (9c): Na2SO4
(1.5 g) was added to a solution of cinnamaldehyde (8; R6 ϭ R7 ϭ
H) (1.91 ml, 2.00 g, 15.1 mmol) and freshly distilled o-anisidine
(7c) (1.70 ml, 1.86 g, 15.1 mmol) in Et2O (30 ml). The reaction
mixture was stirred at room temp. for 3 h. The solution was sepa-
rated and the residue was washed with Et2O. The solution of the
combined organic layers was evaporated in vacuo to a volume of 5
ml. Crystallization from the filtrate at Ϫ20°C provided the product
˜
9c (3.11 g, 87%). Yellow crystals. M.p. 67°C. Ϫ IR (drift): ν ϭ
1627, 1602, 1581, 1493, 1447, 1296, 1247, 1115, 1027, 1001, 754,
1-(4-Trifluoromethylphenyl)-4-phenyl-1-azabuta-1,3-diene (9e): A
1
747 cmϪ1. Ϫ H NMR (400 MHz, CDCl3): δ ϭ 3.90 (s, 3 H), 6.95 solution of cinnamaldehyde (8; R6 ϭ R7 ϭ H) (1.26 ml, 1.32 g, 10.0
(m, 2 H), 7.00 (dd, J ϭ 7.7, 2.0 Hz, 1 H), 7.12 (d, J ϭ 16.0 Hz, 1 mmol) and freshly sublimated 4-trifluoromethylaniline (7e) (1.61 g,
Eur. J. Inorg. Chem. 1998, 993Ϫ1007
1001

H.-J. Knölker et al.
FULL PAPER
10.0 mmol) in Et2O (30 ml) was stirred at room temp. for 2 h. The
mixture was subsequently dried over Na2SO4. The solution was
15.9 Hz, 1 H), 7.39 (m, 3 H), 7.55 (m, 2 H), 8.30 (d, J ϭ 7.9 Hz,
1 H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3): δ ϭ 56.09 (2
separated and the residue was washed with Et2O. The solution of CH3), 60.97 (CH3), 98.29 (2 CH), 127.46 (2 CH), 128.41 (CH),
the combined organic layers was evaporated to a volume of 20 ml. 128.93 (2 CH), 129.60 (CH), 135.57 (C), 136.67 (C), 143.97 (CH),
Crystallization at Ϫ20°C provided a crude product, which was 147.42 (C), 153.58 (2 C), 160.70 (CH). Ϫ MS (70°C): m/z (%) ϭ
washed with a mixture of cold Et2O/pentane (1:7) to afford 9e (1.97 297 (100) [Mϩ], 296 (84), 282 (52), 115 (19), 74 (68), 59 (91);
˜
g, 72%). Yellow crystals. Ϫ IR (drift): ν ϭ 1628, 1611, 1586, 1333, HRMS: 297.1347 (C18H19NO3, calcd. 297.1365).
1313, 1156, 1109, 1073, 841, 753 cmϪ1. Ϫ 1H NMR (400 MHz,
1-(2,4,6-Trimethoxyphenyl)-4-phenyl-1-azabuta-1,3-diene (9i): A
CDCl3): δ ϭ 7.11 (dd, J ϭ 15.9, 8.7 Hz, 1 H), 7.22 (d, J ϭ 15.9
solution of cinnamaldehyde (8; R6 ϭ R7 ϭ H) (195 µl, 204 mg,
Hz, 1 H), 7.22 (d, J ϭ 8.2 Hz, 2 H), 7.40 (m, 3 H), 7.56 (m, 2 H),
1.54 mmol) and freshly sublimated 2,4,6-trimethoxyaniline (7i) (282
7.64 (d, J ϭ 8.2 Hz, 2 H), 8.24 (d, J ϭ 8.7 Hz, 1 H). Ϫ 13C NMR
mg, 1.54 mmol) in Et2O (20 ml) was stirred at room temp. for 2 h.
and DEPT (100 MHz, CDCl3): δ ϭ 121.03 (2 CH), 124.51 (CF3,
The solvent was evaporated and the residue was dissolved in Et2O
1
3
q, JCF ϭ 276 Hz), 126.38 (2 CH, q, JCF ϭ 3.4 Hz), 127.67 (2
CH), 128.08 (CH), 129.00 (2 CH), 129.99 (CH), 135.25 (C), 145.51
(CH), 154.87 (C), 163.30 (CH), the signal of one carbon atom is
missing. Ϫ MS (35°C): m/z (%) ϭ 275 (34) [Mϩ], 274 (100), 145
(7), 115 (4); HRMS: 275.0907 (C16H12F3N, calcd. 275.0922).
(5 ml). Crystallization at Ϫ20°C provided the product 9i (336 mg,
73%). Yellow crystals. M.p. 114°C. Ϫ IR (drift): ν ϭ 1628, 1607,
˜
1579, 1468, 1449, 1334, 1228, 1201, 1149, 1121, 812 cmϪ1. Ϫ 1H
NMR (400 MHz, CDCl3): δ ϭ 3.82 (s, 3 H), 3.83 (s, 6 H), 6.21 (s,
2 H), 7.02 (d, J ϭ 16.0 Hz, 1 H), 7.20 (dd, J ϭ 16.0, 8.9 Hz, 1 H),
7.35 (m, 3 H), 7.51 (m, 2 H), 8.51 (d, J ϭ 8.9 Hz, 1 H). Ϫ 13C
NMR and DEPT (100 MHz, CDCl3): δ ϭ 55.45 (CH3), 56.12 (2
CH3), 91.43 (2 CH), 123.64 (C), 127.34 (2 CH), 128.81 (2 CH),
129.02 (CH), 130.19 (CH), 136.15 (C), 142.04 (CH), 153.22 (2 C),
158.09 (C), 165.18 (CH). Ϫ MS (75°C): m/z (%) ϭ 297 (100) [Mϩ],
296 (99.7), 266 (9), 130 (12), 115 (17); HRMS: 297.1351
(C18H19NO3, calcd. 297.1365).
1-(3-Nitrophenyl)-4-phenyl-1-azabuta-1,3-diene (9f): A solution
of cinnamaldehyde (8; R6 ϭ R7 ϭ H) (0.95 ml, 1.00 g, 7.57 mmol)
and freshly sublimated 3-nitroaniline (7f) (1.05 g, 7.57 mmol) in
˚
C6H6 (30 ml) was stirred with activated molecular sieves (4 A, 5 g)
at room temp. for 17 h. The reaction mixture was filtered over a
short path of Celite. The solvent was evaporated and the residue
dissolved in EtOAc (15 ml). The crude product was crystallized by
addition of pentane (80 ml). The solid was recrystallized twice from
EtOAc/pentane (1:10) to afford the product 9f (1.07 g, 56%). Yel-
low needles. Ϫ 1H NMR (200 MHz, CDCl3): δ ϭ 7.11 (dd, J ϭ
16.0, 8.4 Hz, 1 H), 7.27 (d, J ϭ 16.0 Hz, 1 H), 7.38Ϫ7.59 (m, 7
H), 8.00 (m, 1 H), 8.07 (dt, J ϭ 7.2, 2.1 Hz, 1 H), 8.30 (d, J ϭ 8.4
Hz, 1 H).
4-(4-Methoxyphenyl)-1-phenyl-1-azabuta-1,3-diene (9j): Na2SO4
(3 g) was added to a solution of 4-methoxycinnamaldehyde (8;
R6 ϭ OMe, R7 ϭ H) (2.00 g, 12.3 mmol) and freshly distilled ani-
line (7j) (1.12 ml, 1.15 g, 12.3 mmol) in Et2O (30 ml). The mixture
was stirred for 3 h at room temp. and then filtered. The residue
was washed with Et2O and the solvent of the combined organic
layers was evaporated. The crude product was dissolved in a mix-
ture of Et2O (80 ml) and EtOAc (10 ml). Recrystallization afforded
the azadiene 9j (2.58 g, 88%). Light yellow crystals. Ϫ 1H NMR
(400 MHz, CDCl3): δ ϭ 3.80 (s, 3 H), 6.90 (d, J ϭ 8.4 Hz, 2 H),
6.98 (dd, J ϭ 15.9, 8.5 Hz, 1 H), 7.07 (d, J ϭ 15.9 Hz, 1 H), 7.18
(m, 3 H), 7.36 (t, J ϭ 7.5 Hz, 2 H), 7.46 (d, J ϭ 8.4 Hz, 2 H), 8.21
(d, J ϭ 8.5 Hz, 1 H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3):
δ ϭ 55.37 (CH3), 114.40 (2 CH), 120.95 (2 CH), 125.91 (CH),
126.46 (CH), 128.40 (C), 129.07 (2 CH), 129.18 (2 CH), 143.85
(CH), 151.90 (C), 160.86 (C), 161.92 (CH).
1-(2,4-Dimethoxyphenyl)-4-phenyl-1-azabuta-1,3-diene
(9g):
Na2SO4 (5 g) was added to a solution of cinnamaldehyde (8; R6 ϭ
R7 ϭ H) (2.86 ml, 3.00 g, 22.7 mmol) and freshly distilled 2,4-
dimethoxyaniline (7g) (3.24 ml, 3.48 g, 22.7 mmol) in Et2O (50 ml)
and the reaction mixture was stirred at room temp. for 2 h. The
mixture was filtered and the residue was washed with Et2O. The
solution of the combined ethereal layers was evaporated in vacuo
to a volume of 25 ml. Crystallization at Ϫ20°C provided the prod-
˜
uct 9g (4.91 g, 81%). Yellow crystals. M.p. 75°C. Ϫ IR (drift): ν ϭ
1628, 1602, 1588, 1497, 1280, 1259, 1206, 1157, 966, 824, 754 cmϪ1
.
1
Ϫ H NMR (250 MHz, CDCl3): δ ϭ 3.82 (s, 3 H), 3.89 (s, 3 H),
6.48 (dd, J ϭ 8.5, 2.6 Hz, 1 H), 6.53 (d, J ϭ 2.6 Hz, 1 H), 7.01 (d,
J ϭ 8.5 Hz, 1 H), 7.07 (d, J ϭ 16.0 Hz, 1 H), 7.22 (dd, J ϭ 16.0,
8.6 Hz, 1 H), 7.35 (m, 3 H), 7.50 (m, 2 H), 8.31 (d, J ϭ 8.6 Hz, 1
H). Ϫ 13C NMR and DEPT (63 MHz, CDCl3): δ ϭ 55.50 (CH3),
55.82 (CH3), 99.24 (CH), 104.33 (CH), 119.53 (CH), 127.36 (2 CH),
128.87 (2 CH), 129.25 (CH), 129.39 (CH), 134.50 (C), 135.90 (C),
142.59 (CH), 154.21 (C), 159.37 (C), 159.90 (CH). Ϫ MS (50°C):
m/z (%) ϭ 267 (93) [Mϩ], 266 (100), 130 (6), 115 (13); HRMS:
267.1254 (C17H17NO2, calcd. 267.1259).
1,4-Di-(4-methoxyphenyl)-1-azabuta-1,3-diene (9k): 4-Meth-
oxycinnamaldehyde (8; R6 ϭ OMe, R7 ϭ H) (1.62 g, 10.0 mmol)
and freshly sublimated p-anisidine (7k) (1.23 g, 10.0 mmol) were
dissolved in a mixture of Et2O (30 ml) and THF (15 ml). On cool-
ing the reaction mixture to 5°C for 15 h, the azadiene 9k crys-
tallized (1.03 g, 39%). The solvent of the mother liquor was evapo-
rated and the residue was dissolved in EtOAc (200 ml) at 65°C.
Recrystallization at Ϫ20°C afforded 9k (1.50 g, 56%). Total yield
of the azadiene 9k: 2.53 g (95%). Light yellow crystals. M.p. 182°C.
˜
Ϫ IR (drift): ν ϭ 1900, 1627, 1602, 1576, 1504, 1441, 1307, 1290,
1
1245, 1178, 1031, 864, 816 cmϪ1. Ϫ H NMR (400 MHz, CDCl3):
1-(3,4,5-Trimethoxyphenyl)-4-phenyl-1-azabuta-1,3-diene (9h):
Na2SO4 (5 g) was added to a solution of cinnamaldehyde (8; R6 ϭ
R7 ϭ H) (2.86 ml, 3.00 g, 22.7 mmol) and freshly sublimated 3,4,5-
trimethoxyaniline (7h) (4.16 g, 22.7 mmol) in Et2O (50 ml) and the
reaction mixture was stirred at room temp. for 2 h. The mixture
was filtered and the residue was washed with Et2O. The solution
of the combined organic layers was evaporated in vacuo to a vol-
δ ϭ 3.82 (s, 3 H), 3.84 (s, 3 H), 6.91 (br d, J ϭ 8.8 Hz, 4 H), 6.98
(dd, J ϭ 15.9, 8.4 Hz, 1 H), 7.07 (d, J ϭ 15.9 Hz, 1 H), 7.19 (br
d, J ϭ 8.8 Hz, 2 H), 7.47 (br d, J ϭ 8.8 Hz, 2 H), 8.26 (d, J ϭ 8.4
Hz, 1 H). Ϫ 13C NMR and DEPT (63 MHz, CDCl3): δ ϭ 55.74
(CH3), 55.86 (CH3), 114.75 (2 CH), 114.78 (2 CH), 122.53 (2 CH),
127.08 (CH), 128.99 (C), 129.28 (2 CH), 143.19 (CH), 145.17 (C),
158.59 (C), 160.24 (CH), 161.07 (C). Ϫ MS (80°C): m/z (%) ϭ 267
(34) [Mϩ], 266 (100), 252 (12), 145 (6); HRMS: 267.1264
(C17H17NO2, calcd. 267.1259).
ume of 25 ml. Crystallization at Ϫ20°C provided the product 9h
˜
(5.33 g, 79%). Yellow needles. M.p. 88Ϫ91°C. Ϫ IR (drift): ν ϭ
1627, 1584, 1503, 1446, 1417, 1243, 1232, 1008, 991, 838, 753, 693
1
cmϪ1. Ϫ H NMR (250 MHz, CDCl3): δ ϭ 3.87 (s, 3 H), 3.90 (s,
1-(2-Methoxyphenyl)-4-(4-methoxyphenyl)-1-azabuta-1,3-diene
6 H), 6.48 (s, 2 H), 7.09 (dd, J ϭ 15.9, 7.9 Hz, 1 H), 7.19 (d, J ϭ
(9l): A solution of 4-methoxycinnamaldehyde (8; R6 ϭ OMe, R7 ϭ
1002
Eur. J. Inorg. Chem. 1998, 993Ϫ1007

Transition Metal Complexes in Organic Synthesis, 41
FULL PAPER
H) (1.62 g, 10.0 mmol) and freshly distilled o-anisidine (7l) (1.13
solvent of the combined organic solutions was evaporated and the
ml, 1.23 g, 10.0 mmol) in Et2O (30 ml) was stirred at room temp. residue was dissolved in Et2O/pentane (2:1, 100 ml). Precipitation
for 2 h. Subsequently, the reaction mixture was dried over Na2SO4.
The solution was separated and the residue was washed with Et2O.
The solution of the combined organic layers was evaporated in va-
of the product was completed by cooling this solution to Ϫ78°C
and subsequent warming to 40°C. Repetition of this procedure sev-
eral times afforded the product 9o (2.82 g, 86%). Yellow solid. M.p.
˜
cuo to a volume of 20 ml. Crystallization at Ϫ30°C afforded 9l 62°C. Ϫ IR (drift): ν ϭ 2839, 1620, 1596, 1504, 1484, 1467, 1244,
˜
(2.11 g, 79%). Light yellow needles. M.p. 105°C. Ϫ IR (drift): ν ϭ 1028, 990, 956, 756 cmϪ1. Ϫ 1H NMR (250 MHz, CDCl3): δ ϭ
1626, 1580, 1492, 1307, 1246, 1025, 810, 754 cmϪ1. Ϫ 1H NMR
3.82 (s, 3 H), 3.89 (s, 3 H), 6.88Ϫ7.01 (m, 2 H), 6.91 (br d, J ϭ 8.9
(400 MHz, CDCl3): δ ϭ 3.82 (s, 3 H), 3.90 (s, 3 H), 6.90Ϫ7.00 (m, Hz, 2 H), 7.11Ϫ7.23 (m, 2 H), 7.17 (dd, J ϭ 16.1, 9.0 Hz, 1 H),
5 H), 7.04Ϫ7.20 (m, 3 H), 7.47 (br d, J ϭ 8.8 Hz, 2 H), 8.24 (dd, 7.32 (m, 1 H), 7.48 (d, J ϭ 16.1 Hz, 1 H), 7.57 (dd, J ϭ 7.7, 1.6
J ϭ 7.5, 0.8 Hz, 1 H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3): Hz, 1 H), 8.31 (d, J ϭ 9.0 Hz, 1 H). Ϫ 13C NMR and DEPT (63
δ ϭ 55.30 (CH3), 55.70 (CH3), 111.12 (CH), 114.30 (2 CH), 119.34 MHz, CDCl3): δ ϭ 56.13 (2 CH3), 111.72 (CH), 115.04 (2 CH),
(CH), 120.88 (CH), 126.69 (CH), 126.95 (CH), 128.46 (C), 128.96 121.51 (CH), 122.85 (2 CH), 125.38 (C), 128.30 (CH), 129.90 (CH),
(2 CH), 141.38 (C), 143.40 (CH), 152.69 (C), 160.69 (C), 162.21 131.24 (CH), 138.96 (CH), 145.43 (C), 158.12 (C), 158.90 (C),
(CH). Ϫ MS (50°C): m/z (%) ϭ 267 (40) [Mϩ], 266 (100), 252 (24), 161.24 (CH). Ϫ MS (70°C): m/z (%) ϭ 267 (32) [Mϩ], 266 (24),
250 (8), 236 (6); HRMS: 267.1249 (C17H17NO2, calcd. 267.1259).
252 (16), 237 (16), 236 (100), 115 (6); HRMS: 267.1237
(C17H17NO2, calcd. 267.1259).
1-(4-Trifluoromethylphenyl)-4-(4-methoxyphenyl)-1-azabuta-
1,3-diene (9m): 4-Methoxycinnamaldehyde (8; R6 ϭ OMe, R7 ϭ H)
4-(4-Cyanophenyl)-1-phenyl-1-azabuta-1,3-diene (9p): A solution
(1.62 g, 10.0 mmol) and freshly distilled 4-trifluoromethylaniline of 4-cyanocinnamaldehyde (8; R6 ϭ CN, R7 ϭ H) (157 mg, 1.00
(7m) (1.25 ml, 1.61 g, 10.0 mmol) were dissolved in a mixture of
mmol) and freshly distilled aniline (7p) (182 µl, 186 mg, 2.00 mmol)
Et2O (50 ml) and THF (15 ml). The reaction mixture was cooled in THF (10 ml) was stirred at room temp. for 1.5 h. After addition
to 5°C for 15 h and was dried over Na2SO4. After filtration the of pentane (30 ml) the product was crystallized at Ϫ30°C to afford
solvent was evaporated and the residue was crystallized from Et2O/
the azadiene 9p (181 mg, 78%). Yellow crystals. M.p. 104°C. Ϫ IR
˜
EtOAc (3:1, 80 ml) to afford the azadiene 9m (1.81 g, 59%). Yellow (drift): ν ϭ 3049, 2221, 1627, 1608, 1583, 1488, 1413, 1156, 983,
˜
crystals. M.p. 121°C. Ϫ IR (drift): ν ϭ 1628, 1588, 1513, 1330,
954, 816, 764 cmϪ1. Ϫ 1H NMR (250 MHz, CDCl3): δ ϭ
1
1270, 1130, 1011, 850 cmϪ1. Ϫ H NMR (400 MHz, CDCl3): δ ϭ 7.32Ϫ7.47 (m, 5 H), 7.58 (m, 2 H), 7.77 (d, J ϭ 7.9 Hz, 2 H), 7.83
3.85 (s, 3 H), 6.94 (br d, J ϭ 8.8 Hz, 2 H), 6.99 (dd, J ϭ 15.9, 8.9 (d, J ϭ 7.9 Hz, 2 H), 8.47 (d, J ϭ 7.0 Hz, 1 H). Ϫ 13C NMR and
Hz, 1 H), 7.16 (d, J ϭ 15.9 Hz, 1 H), 7.21 (d, J ϭ 8.4 Hz, 2 H), DEPT (63 MHz, CDCl3): δ ϭ 112.93 (C), 119.11 (CϵN), 121.48
7.50 (br d, J ϭ 8.8 Hz, 2 H), 7.62 (d, J ϭ 8.4 Hz, 2 H), 8.20 (d,
(2 CH), 127.22 (CH), 128.27 (2 CH), 129.79 (2 CH), 132.27 (CH),
J ϭ 8.9 Hz, 1 H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3): 133.14 (2 CH), 140.35 (C), 141.68 (CH), 151.70 (C), 161.00 (CH).
δ ϭ 55.39 (CH3), 114.44 (2 CH), 121.02 (2 CH), 124.30 (CF3, q, Ϫ MS (60°C): m/z (%) ϭ 232 (53) [Mϩ], 231 (100), 77 (21); HRMS:
3
1JCF ϭ 272 Hz), 125.93 (CH), 126.35 (2 CH, q, JCF ϭ 3.5 Hz), 232.1015 (C16H12N2, calcd. 232.1000).
2
127.53 (C, q, JCF ϭ 32.5 Hz), 128.06 (C), 129.27 (2 CH), 145.33
4-(4-Cyanophenyl)-1-(2,4-dimethoxyphenyl)-1-azabuta-1,3-diene
(CH), 155.04 (C), 161.15 (C), 163.54 (CH). Ϫ MS (40°C): m/z
(9q): A solution of freshly distilled 2,4-dimethoxyaniline (7q) (141
(%) ϭ 305 (25) [Mϩ], 304 (100), 290 (13), 261 (7), 145 (7); HRMS:
µl, 153 mg, 1.00 mmol) in Et2O (14 ml) was added to a solution of
305.1006 (C17H14F3NO, calcd. 305.1027).
4-cyanocinnamaldehyde (8; R6 ϭ CN, R7 ϭ H) (157 mg, 1.00
1-(2,4-Dimethoxyphenyl)-4-(4-methoxyphenyl)-1-azabuta-1,3- mmol) in Et2O (20 ml). The reaction mixture was stirred for 10
diene (9n): A solution of 4-methoxycinnamaldehyde (8; R6 ϭ OMe,
min at room temp. and then cooled to Ϫ20°C for 15 h without
R7 ϭ H) (1.00 g, 6.17 mmol) and freshly distilled 2,4-dimethoxyani-
stirring. Evaporation of the solvent afforded the product 9q (289
˜
line (7n) (0.88 ml, 945 mg, 6.17 mmol) in THF (30 ml) was stirred mg, 99%). Orange solid. M.p. 121°C. Ϫ IR (drift): ν ϭ 2223, 1623,
at 40°C for 1 h. The solvent was evaporated and the residue was 1604, 1585, 1498, 1311, 1258, 1210, 1161, 1130, 1047, 843, 827
crystallized from a mixture of Et2O (200 ml) and EtOAc (30 ml) at cmϪ1. Ϫ H NMR (400 MHz, CDCl3): δ ϭ 3.83 (s, 3 H), 3.90 (s,
1
Ϫ20°C to provide the product 9n (1.46 g, 80%). Yellow solid. M.p. 3 H), 6.49 (dd, J ϭ 8.6, 2.6 Hz, 1 H), 6.54 (d, J ϭ 2.6 Hz, 1 H),
˜
123°C. Ϫ IR (drift): ν ϭ 1625, 1603, 1587, 1509, 1497, 1259, 1246, 7.05 (d, J ϭ 8.6 Hz, 1 H), 7.06 (d, J ϭ 16.0 Hz, 1 H), 7.28 (dd,
1
1206, 1176, 1157, 1128, 1025, 824 cmϪ1. Ϫ H NMR (400 MHz, J ϭ 16.0, 8.9 Hz, 1 H), 7.58 (br d, J ϭ 8.4 Hz, 2 H), 7.65 (br d,
CDCl3): δ ϭ 3.80 (s, 3 H), 3.81 (s, 3 H), 3.88 (s, 3 H), 6.46 (dd, J ϭ 8.4 Hz, 2 H), 8.36 (d, J ϭ 8.9 Hz, 1 H). Ϫ 13C NMR and
J ϭ 8.6, 2.5 Hz, 1 H), 6.52 (d, J ϭ 2.5 Hz, 1 H), 6.89 (d, J ϭ 8.7 DEPT (100 MHz, CDCl3): δ ϭ 55.54 (CH3), 55.86 (CH3), 99.23
Hz, 2 H), 6.98 (d, J ϭ 8.6 Hz, 1 H), 7.02 (d, J ϭ 15.9 Hz, 1 H), (CH), 104.49 (CH), 112.06 (C), 118.69 (CϵN), 119.73 (CH), 127.59
7.09 (dd, J ϭ 15.9, 8.3 Hz, 1 H), 7.45 (d, J ϭ 8.7 Hz, 2 H), 8.26 (2 CH), 132.63 (2 CH), 132.69 (CH), 133.80 (C), 139.62 (CH),
(d, J ϭ 8.3 Hz, 1 H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3): 140.27 (C), 154.45 (C), 158.43 (CH), 159.92 (C). Ϫ MS (85°C):
δ ϭ 55.33 (CH3), 55.49 (CH3), 55.80 (CH3), 99.20 (CH), 104.26
m/z (%) ϭ 292 (43) [Mϩ], 291 (42), 157 (100), 156 (82), 153 (25),
(CH), 114.33 (2 CH), 119.41 (CH), 127.30 (CH), 128.72 (C), 128.85 138 (28), 129 (51), 128 (43); HRMS: 292.1203 (C18H16N2, calcd.
(2 CH), 134.72 (C), 142.40 (CH), 154.13 (C), 159.14 (C), 160.22 292.1212).
(CH), 160.57 (C). Ϫ MS (85°C): m/z (%) ϭ 297 (56) [Mϩ], 296
(100), 282 (22), 145 (5); HRMS: 297.1354 (C18H19NO3, calcd.
297.1365).
1-(4-Methoxyphenyl)-4-(4-N,N-dimethylaminophenyl)-1-aza-
buta-1,3-diene (9r): A solution of 4-N,N-dimethylaminocinnamal-
dehyde (8; R6 ϭ NMe2, R7 ϭ H) (1.00 g, 5.71 mmol) and freshly
1-(4-Methoxyphenyl)-4-(2-methoxyphenyl)-1-azabuta-1,3-diene sublimated p-anisidine (7r) (703 mg, 5.71 mmol) in CH2Cl2 (30 ml)
(9o): Na2SO4 (5 g) was added to a solution of 2-methoxycinnamal-
was stirred at room temp. for 1 h. Na2SO4 (2 g) was added and the
dehyde (8; R6 ϭ H, R7 ϭ OMe) (2.00 g, 12.3 mmol) and freshly reaction mixture was stirred at room temp. for an additional 2 h.
sublimated p-anisidine (7o) (1.52 g, 12.3 mmol) in Et2O (100 ml).
The reaction mixture was stirred at room temp. for 2 h. The solu-
tion was separated and the residue was washed with Et2O. The
The solution was separated and by addition of Et2O/pentane (1:7,
50 ml) the product 9r was precipitated (1.36 g, 85%). Green crys-
˜
tals. M.p. 146Ϫ150°C. Ϫ IR (drift): ν ϭ 2540, 2057, 2006, 1887,
Eur. J. Inorg. Chem. 1998, 993Ϫ1007
1003

H.-J. Knölker et al.
FULL PAPER
1
1609, 1575, 1503, 1248, 1156, 836, 810 cmϪ1. Ϫ 1H NMR (250 1450, 1290, 1155, 761 cmϪ1. Ϫ H NMR (400 MHz, CDCl3): δ ϭ
MHz, CDCl3): δ ϭ 3.01 (s, 6 H), 3.82 (s, 3 H), 6.63Ϫ6.76 (m, 2 3.38 (d, J ϭ 9.4 Hz, 1 H), 5.72 (dd, J ϭ 9.4, 2.8 Hz, 1 H), 6.92 (m,
H), 6.87Ϫ6.94 (m, 2 H), 6.92 (dd, J ϭ 15.7, 8.5 Hz, 1 H), 7.05 (d, 3 H), 6.95 (d, J ϭ 2.8 Hz, 1 H), 7.19 (m, 3 H), 7.30 (m, 4 H). Ϫ
J ϭ 15.7 Hz, 1 H), 7.18 (br d, J ϭ 8.9 Hz, 2 H), 7.42 (br d, J ϭ
8.9 Hz, 2 H), 8.24 (d, J ϭ 8.5 Hz, 1 H). Ϫ 13C NMR and DEPT (CH), 74.45 (CH), 103.86 (CH), 121.86 (2 CH), 122.56 (CH),
(125 MHz, CDCl3): δ ϭ 40.11 (2 CH3), 55.40 (CH3), 111.96 (2 126.61 (2 CH), 126.93 (CH), 128.80 (2 CH), 128.99 (2 CH), 138.81
13C NMR and DEPT (100 MHz, CDCl3): δ (T ϭ 298 K) ϭ 62.17
CH), 114.30 (2 CH), 122.02 (2 CH), 123.74 (C), 124.08 (CH), (C), 153.38 (C), 205.79 (CO, very br), 208.77 (CO, very br), 211.90
128.87 (2 CH), 143.90 (CH), 145.05 (C), 151.11 (C), 157.86 (C), (CO, very br); 13C NMR (125 MHz, [D8]toluene): δ (T ϭ 233 K) ϭ
160.35 (CH). Ϫ MS (110°C): m/z (%) ϭ 280 (45) [Mϩ], 279 (100), 62.31 (CH), 74.20 (CH), 104.37 (CH), 122.09 (2 CH), 122.63 (CH),
265 (3), 158 (7); HRMS: 280.1563 (C18H20N2O, calcd. 280.1576).
126.67 (2 CH), 127.08 (CH), 128.93 (2 CH), 129.16 (2 CH), 138.91
(C), 153.90 (C), 206.02 (CO), 209.49 (CO), 212.70 (CO); δ (T ϭ
292 K) ϭ 62.63 (CH), 74.29 (CH), 104.43 (CH), 122.16 (2 CH),
122.79 (CH), 126.81 (2 CH), 127.12 (CH), 128.96 (2 CH), 129.19
(2 CH), 138.13 (C), 153.96 (C), 206.04 (CO, br), 209.42 (CO, br),
212.66 (CO, br); δ (T ϭ 373 K) ϭ 63.21 (CH), 74.51 (CH), 104.75
(CH), 122.37 (2 CH), 123.13 (CH), 127.15 (2 CH), 127.30 (CH),
129.11 (2 CH), 129.34 (2 CH), 139.61 (C), 154.15 (C), 209.53 (3
CO, br). Ϫ MS (75°C): m/z (%) ϭ 347 (3) [Mϩ], 319 (8), 291 (12),
263 (100), 207 (10), 206 (31), 56 (18); HRMS: 347.0217
(C18H13FeNO3, calcd. 347.0245). Ϫ C18H13FeNO3: C 62.28, H
3.77, N 4.03; found: C 62.33, H 4.08, N 4.22.
1-(4-Methoxyphenyl)-4-(4-nitrophenyl)-1-azabuta-1,3-diene (9s):
A solution of 4-nitrocinnamaldehyde (8; R6 ϭ NO2, R7 ϭ H) (713
mg, 4.02 mmol) in THF (20 ml) was added to a solution of freshly
sublimated p-anisidine (7s) (495 mg, 4.02 mmol) in THF (20 ml).
The reaction mixture was stirred at room temp. for 1 h. The solvent
was evaporated and the residue was recrystallized from EtOAc (60
ml) to afford the azadiene 9s (848 mg, 75%). Yellow needles. M.p.
˜
164°C. Ϫ IR (drift): ν ϭ 1622, 1608, 1595, 1441, 1415, 1300, 953,
1
758 cmϪ1. Ϫ H NMR (250 MHz, CDCl3): δ ϭ 3.84 (s, 3 H), 6.94
(br d, J ϭ 8.9 Hz, 2 H), 7.14 (d, J ϭ 16.1 Hz, 1 H), 7.23 (dd, J ϭ
16.1, 8.3 Hz, 1 H), 7.24 (br d, J ϭ 8.9 Hz, 2 H), 7.66 (br d, J ϭ
8.8 Hz, 2 H), 8.25 (br d, J ϭ 8.8 Hz, 2 H), 8.34 (d, J ϭ 8.3 Hz, 1
Tricarbonyl[(1-4-η)-1-(4-methoxyphenyl)-4-phenyl-1-azabuta-
˜
H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3): δ ϭ 55.51 (CH3), 1,3-diene]iron (10b): Mp Ն 140°C (dec). Ϫ IR (drift): ν ϭ 2049,
114.52 (2 CH), 122.46 (2 CH), 124.25 (2 CH), 127.78 (2 CH), 1987, 1963, 1507, 1250, 1040, 832 cmϪ1. Ϫ H NMR (200 MHz,
1
132.86 (CH), 139.45 (CH), 142.02 (C), 143.95 (C), 147.76 (C),
CDCl3): δ ϭ 3.37 (d, J ϭ 9.4 Hz, 1 H), 3.75 (s, 3 H), 5.68 (dd, J ϭ
157.90 (CH), 158.98 (C). Ϫ MS (100°C): m/z (%) ϭ 282 (100) [Mϩ], 9.4, 2.9 Hz, 1 H), 6.73 (d, J ϭ 8.9 Hz, 2 H), 6.91 (d, J ϭ 8.9 Hz,
281 (74), 235 (65), 192 (9); HRMS: 282.0998 (C16H14N2O3, calcd.
282.1004).
2 H), 6.99 (d, J ϭ 2.9 Hz, 1 H), 7.19Ϫ7.34 (m, 5 H). Ϫ 13C NMR
and DEPT (100 MHz, CDCl3): δ (T ϭ 298 K) ϭ 55.42 (CH3),
61.89 (CH), 73.95 (CH), 104.28 (CH), 114.28 (2 CH), 122.55 (2
CH), 126.59 (2 CH), 126.84 (CH), 128.77 (2 CH), 138.97 (C),
146.55 (C), 155.37 (C); 13C NMR (125 MHz, [D8]toluene): δ (T ϭ
233 K) ϭ 54.44 (CH3), 62.10 (CH), 73.71 (CH), 104.82 (CH),
114.20 (2 CH), 122.76 (2 CH), 126.69 (2 CH), 127.00 (CH), 128.93
(2 CH), 139.12 (C), 146.74 (C), 155.59 (C), 206.60 (CO), 209.71
(CO), 213.03 (CO); δ (T ϭ 298 K) ϭ 54.85 (CH3), 62.48 (CH),
73.81 (CH), 105.03 (CH), 114.65 (2 CH), 122.94 (2 CH), 126.92 (2
CH), 127.12 (CH), 129.03 (2 CH), 139.46 (C), 147.00 (C), 156.17
(C), 206.91 (CO, very br), 209.80 (CO, very br), 212.84 (CO, very
br); δ (T ϭ 373 K) ϭ 55.31 (CH3), 62.89 (CH), 73.90 (CH), 105.32
(CH), 115.17 (2 CH), 123.09 (2 CH), 127.15 (2 CH), 127.19 (CH),
129.08 (2 CH), 139.80 (C), 147.27 (C), 156.75 (C), 209.81 (3 CO).
Ϫ MS (90°C): m/z (%) ϭ 377 (3) [Mϩ], 349 (6), 321 (8), 293 (100),
237 (29), 236 (54), 115 (16); HRMS: 377.0339 (C19H15FeNO4,
calcd. 377.0350). Ϫ C19H15FeNO4: C 60.50, H 4.01, N 3.71; found:
C 60.51, H 4.05, N 3.94.
Preparation of the (η4-1-Azabuta-1,3-diene)tricarbonyliron Com-
plexes 10 by Sonochemical Reaction of the 1-Azabuta-1,3-dienes 9
with Nonacarbonyldiiron at Room Temperature Ϫ General Pro-
cedure: A solution of the 1-azabuta-1,3-dienes 9 (1 eq.) and
Fe2(CO)9 (1.5 eq.) in THF (15 ml) was sonicated at room temp. for
16 h. Removal of the solvent by evaporation and flash chromatog-
raphy (Et2O/pentane) of the residue on silica gel afforded the tricar-
bonyliron complexes 10 as red crystals (Table 5).
Table 5. Sonochemical complexation of the 1-azabuta-1,3-dienes 9
and yield of the iron complexes 10
Entry
9
[g]
Fe2(CO)9
Eluent[b]
Et2O/pentane [g]
Yield 10
[%]
[mmol]
[g]
[mmol]
a
b
c
0.500 2.41
0.500 2.11
1.78 7.50
0.500 2.00
1.00 3.63
1.50 5.61
1.50 5.04
1.00 3.36
1.00 4.21
1.00 3.74
1.50 5.61
1.00 3.28
0.500 1.68
1.00 3.74
0.450 1.94
0.846 2.89
0.500 1.78
1.10 3.03[a]
0.960 2.64[a]
4.11 11.3
1.09 3.00
1.98 5.45
3.06 8.42
2.75 7.56
1.83 5.04
2.30 6.32
2.04 5.61
3.06 8.42
1.79 4.92
0.917 2.52
2.04 5.61
1.06 2.91
1.58 4.34
0.971 2.67
1:10
0.682 82
0.701 88
2.25 80
0.428 55
0.882 59
0.990 43
0.890 40
1:10
1:10
d
e[c]
g
h
i
1:7 to 1:3
1:10
Tricarbonyl[(1-4-η)-1-(2-methoxyphenyl)-4-phenyl-1-azabuta-
˜
1,3-diene]iron (10c): Mp Ն 123°C (dec). Ϫ IR (drift): ν ϭ 2058,
1:10
1:10
2000, 1970, 1497, 1455, 1297, 1245, 1031, 749, 695 cmϪ1. Ϫ 1H
NMR (400 MHz, CDCl3): δ ϭ 3.33 (d, J ϭ 9.5 Hz, 1 H), 3.97 (s,
3 H), 5.80 (dd, J ϭ 9.5, 3.0 Hz, 1 H), 6.81 (m, 2 H), 6.98 (br dt,
J ϭ 1.5, 7.8 Hz, 1 H), 7.04 (m, 1 H), 7.10 (br d, J ϭ 3.0 Hz, 1 H),
7.19 (m, 1 H), 7.28 (m, 2 H), 7.34 (m, 2 H). Ϫ 13C NMR and
DEPT (100 MHz, CDCl3): δ (T ϭ 298 K) ϭ 54.79 (CH3), 62.08
(CH), 76.09 (CH), 101.99 (CH), 110.99 (CH), 118.96 (CH), 120.51
(CH), 123.57 (CH), 126.53 (2 CH), 126.75 (CH), 128.76 (2 CH),
139.11 (C), 141.38 (C), 150.88 (C), 205.70 (CO, very br), 209.33
(CO, very br), 212.82 (CO, very br); 13C NMR (125 MHz, [D8]tol-
uene): δ (T ϭ 233 K) ϭ 53.90 (CH3), 62.58 (CH), 76.24 (CH),
101.97 (CH), 110.90 (CH), 118.41 (CH), 120.39 (CH), 123.59 (CH),
126.61 (2 CH), 126.86 (CH), 128.91 (2 CH), 139.33 (C), 141.70 (C),
150.86 (C), 206.41 (CO), 210.06 (CO), 213.84 (CO); δ (T ϭ 298
10:1 to 5:1 0.819 56
j[c]
k
l
0:1 to 1:4
1.16 73
1:10 to 1:2 0.626 41
1:7
1.88 82
0.935 64
m
n
o
p
q
r
0:1 to 1:3
1:10 to 1:5 0.578 79
1:10
1.24 81
0.410 57
1:7 to 1:1
1:10 to 2:1 0.760 61
1:7 to 1:0
0.463 62
[a]
[b]
1.25 Equivalents of Fe2(CO)9. Ϫ Gradient elution by entry d,
[c]
i, j, k, m, n, p, and q. Ϫ
was 18 h and of entry j 17 h.
Reaction time (sonication) of entry e
Tricarbonyl[(1-4-η)-1,4-diphenyl-1-azabuta-1,3-diene]iron (10a): K) ϭ 54.33 (CH3), 62.85 (CH), 76.00 (CH), 102.71 (CH), 111.47
˜
Mp Ն 132°C (dec). Ϫ IR (drift): ν ϭ 2055, 1988, 1977, 1593, 1486,
(CH), 119.17 (CH), 120.73 (CH), 123.64 (CH), 126.79 (2 CH),
1004
Eur. J. Inorg. Chem. 1998, 993Ϫ1007

Transition Metal Complexes in Organic Synthesis, 41
FULL PAPER
126.93 (CH), 128.93 (2 CH), 139.54 (C), 142.14 (C), 151.44 (C), 2054, 1995, 1980, 1580, 1501, 1451, 1251, 1128, 1011, 770 cmϪ1. Ϫ
206.46 (CO, br), 210.04 (CO, br), 213.75 (CO, br); δ (T ϭ 373 K) ϭ 1H NMR (250 MHz, CDCl3): δ ϭ 3.38 (d, J ϭ 9.4 Hz, 1 H), 3.78
55.01 (CH3), 63.27 (CH), 75.85 (CH), 103.64 (CH), 112.50 (CH), (s, 3 H), 3.86 (s, 6 H), 5.70 (dd, J ϭ 9.4, 2.9 Hz, 1 H), 6.18 (s, 2
120.21 (CH), 121.27 (CH), 123.82 (CH), 127.10 (3 CH), 129.05 (2 H), 6.97 (dd, J ϭ 2.9, 0.8 Hz, 1 H), 7.17Ϫ7.35 (m, 5 H). Ϫ 13C
CH), 139.93 (C), 142.73 (C), 152.26 (C), 210.02 (3 CO, br). Ϫ MS
NMR and DEPT (100 MHz, CDCl3): δ ϭ 56.00 (2 CH3), 60.92
(75°C): m/z (%) ϭ 377 (3) [Mϩ], 349 (12), 321 (23), 293 (58), 278 (CH3), 62.30 (CH), 74.11 (CH), 99.26 (2 CH), 103.91 (CH), 126.61
(100), 237 (11), 236 (11), 139 (12), 56 (6).
(2 CH), 126.99 (CH), 128.81 (2 CH), 134.03 (C), 138.74 (C), 149.43
(C), 153.22 (2 C). Ϫ MS (90°C): m/z (%) ϭ 437 (3) [Mϩ], 409 (9),
381 (6), 353 (100), 297 (51), 296 (45), 282 (28), 177 (8); HRMS:
437.0575 (C21H19FeNO6, calcd. 437.0562).
Tricarbonyl[(1-4-η)-1-(4-N,N-dimethylaminophenyl)-4-phenyl-1-
azabuta-1,3-diene]iron (10d): Mp Ն 136°C (dec). Ϫ IR (drift): ν ϭ
˜
2047, 1987, 1965, 1607, 1515, 1283, 1154, 822, 765, 698 cmϪ1. Ϫ
1H NMR (250 MHz, CDCl3): δ ϭ 2.88 (s, 6 H), 3.37 (d, J ϭ 9.3
Hz, 1 H), 5.63 (dd, J ϭ 9.3, 2.9 Hz, 1 H), 6.58 (br d, J ϭ 9.0 Hz,
2 H), 6.93 (br d, J ϭ 9.0 Hz, 2 H), 7.06 (dd, J ϭ 2.9, 0.8 Hz, 1 H),
7.17Ϫ7.34 (m, 5 H). Ϫ 13C NMR and DEPT (63 MHz, CDCl3):
δ ϭ 40.91 (2 CH3), 61.34 (CH), 73.43 (CH), 104.40 (CH), 113.28
(2 CH), 122.45 (2 CH), 126.56 (2 CH), 126.64 (CH), 128.69 (2 CH),
139.29 (C), 143.14 (C), 146.96 (C). Ϫ MS (105°C): m/z (%) ϭ 390
(5) [Mϩ], 362 (1), 334 (7), 306 (100), 250 (69), 249 (89), 233 (15);
HRMS: 390.0671 (C20H18FeN2O3, calcd. 390.0667).
Tricarbonyl[(1-4-η)-1-(2,4,6-trimethoxyphenyl)-4-phenyl-1-aza-
˜
buta-1,3-diene]iron (10i): Mp Ն103°C (dec). Ϫ IR (drift): ν ϭ 2052,
2038, 1992, 1978, 1968, 1597, 1578, 1465, 1337, 1205, 1131 cmϪ1
.
1
Ϫ H NMR (250 MHz, CDCl3): δ ϭ 3.23 (d, J ϭ 9.4 Hz, 1 H),
3.77 (s, 3 H), 3.91 (s, 6 H), 5.65 (dd, J ϭ 9.4, 3.0 Hz, 1 H), 6.09 (s,
2 H), 7.17 (m, 1 H), 7.30 (m, 4 H), 7.94 (dd, J ϭ 3.0, 0.8 Hz, 1 H).
Ϫ
13C NMR and DEPT (63 MHz, CDCl3): δ ϭ 55.25 (CH3), 55.44
(2 CH3), 60.79 (CH), 74.06 (CH), 91.18 (2 CH), 106.17 (CH),
122.93 (C), 126.33 (CH), 126.43 (2 CH), 128.56 (2 CH), 139.62 (C),
153.60 (2 C), 156.00 (C). Ϫ MS (120°C): m/z (%) ϭ 437 (0.2) [Mϩ],
409 (2), 381 (9), 353 (72), 338 (100), 297 (43), 296 (31), 115 (20);
HRMS: 437.0546 (C21H19FeNO6, calcd. 437.0562).
Tricarbonyl[(1-4-η)-1-(4-trifluoromethylphenyl)-4-phenyl-1-
azabuta-1,3-diene]iron (10e): Mp Ն 151°C (dec). Ϫ IR (drift): ν ϭ
˜
3061, 2059, 2002, 1983, 1611, 1329, 1288, 1166, 1123, 1110, 842,
1
768, 698 cmϪ1. Ϫ H NMR (400 MHz, CDCl3): δ ϭ 3.41 (d, J ϭ
9.5 Hz, 1 H), 5.75 (dd, J ϭ 9.5, 2.9 Hz, 1 H), 6.84 (dd, J ϭ 2.9,
Tricarbonyl[(1-4-η)-4-(4-methoxyphenyl)-1-phenyl-1-azabuta-
˜
0.7 Hz, 1 H), 6.92 (d, J ϭ 8.3 Hz, 2 H), 7.22 (m, 1 H), 7.31 (m, 4 1,3-diene]iron (10j): Mp Ն136°C (dec). Ϫ IR (drift): ν ϭ 2054,
H), 7.41 (d, J ϭ 8.3 Hz, 2 H). Ϫ 13C NMR and DEPT (100 MHz,
1981, 1607, 1515, 1485, 1475, 1278, 1249, 1032, 835, 762 cmϪ1. Ϫ
CDCl3): δ (T ϭ 298 K) ϭ 63.04 (CH), 75.65 (CH), 102.01 (CH), 1H NMR (400 MHz, CDCl3): δ ϭ 3.43 (d, J ϭ 9.5 Hz, 1 H), 3.80
2
121.77 (2 CH), 123.98 (C, q, JCF ϭ 32.6 Hz), 124.45 (CF3, q, (s, 3 H), 5.65 (dd , J ϭ 9.5, 2.9 Hz, 1 H), 6.84 (br d, J ϭ 8.8 Hz,
3
1JCF ϭ 271 Hz), 126.24 (2 CH, q, JCF ϭ 3.5 Hz), 126.67 (2 CH), 2 H), 6.92 (m, 4 H), 7.17 (m, 2 H), 7.27 (br d, J ϭ 8.8 Hz, 2 H).
127.26 (CH), 128.93 (2 CH), 138.34 (C), 156.70 (C), 204.77 (CO,
Ϫ
13C NMR and DEPT (100 MHz, CDCl3): δ ϭ 55.27 (CH3),
63.15 (CH), 74.28 (CH), 103.03 (CH), 114.31 (2 CH), 121.86 (2
br), 208.30 (CO, br), 211.49 (CO, br); 13C NMR (125 MHz,
[D8]toluene): δ (T ϭ 233 K) ϭ 62.95 (CH), 75.33 (CH), 102.36 CH), 122.44 (CH), 127.83 (2 CH), 128.96 (2 CH), 130.89 (C),
2
(CH), 121.94 (2 CH), 123.56 (C, q, JCF ϭ 32.2 Hz), 125.22 (CF3,
153.51 (C), 158.71 (C). Ϫ MS (85°C): m/z (%) ϭ 377 (2) [Mϩ], 349
q, 1JCF ϭ 271 Hz), 126.32 (2 CH, br), 126.68 (2 CH), 127.41 (CH), (7), 321 (11), 293 (100), 237 (19), 236 (73), 222 (12); HRMS:
129.04 (2 CH), 138.38 (C), 156.97 (C), 205.19 (CO), 208.90 (CO), 377.0360 (C19H15FeNO4, calcd. 377.0350).
212.16 (CO); δ (T ϭ 307 K) ϭ 63.49 (CH), 75.54 (CH), 102.50
Tricarbonyl[(1-4-η)-1,4-di-(4-methoxyphenyl)-1-azabuta-1,3-
2
(CH), 122.05 (2 CH), 124.31 (C, q, JCF ϭ 33 Hz), 126.46 (2 CH,
˜
diene]iron (10k): Mp Ն132°C (dec). Ϫ IR (drift): ν ϭ 2049, 1985,
br), 126.89 (2 CH), 127.51 (CH), 129.08 (2 CH), 138.66 (C), 157.10
(C), 205.44 (CO, br), 208.89 (CO, br), 212.16 (CO, br), the signal
1974, 1607, 1518, 1506, 1274, 1252, 1179, 1031, 839 cmϪ1. Ϫ 1H
NMR (400 MHz, CDCl3): δ ϭ 3.41 (d, J ϭ 9.5 Hz, 1 H), 3.75 (s,
of the CF3 carbon atom is missing due to overlapping; δ (T ϭ 373
3 H), 3.79 (s, 3 H), 5.61 (dd, J ϭ 9.5, 2.9 Hz, 1 H), 6.72 (br d, J ϭ
K) ϭ 64.02 (CH), 75.80 (CH), 102.74 (CH), 122.22 (2 CH), 125.35
8.9 Hz, 2 H), 6.83 (br d, J ϭ 8.8 Hz, 2 H), 6.90 (br d, J ϭ 8.9 Hz,
2 H), 6.95 (br d, J ϭ 2.9 Hz, 1 H), 7.26 (br d, J ϭ 8.8 Hz, 2 H).
(CF3, q, 1JCF ϭ 273 Hz), 126.63 (2 CH, br), 127.16 (2 CH), 127.66
(CH), 129.20 (2 CH), 139.01 (C), 157.25 (C), 208.79 (3 CO, br),
the signal of the aromatic carbon atom α to the CF3 group is mis-
sing due to overlapping. Ϫ MS (90°C): m/z (%) ϭ 415 (1) [Mϩ],
387 (6), 359 (7), 331 (73), 275 (24), 274 (100), 256 (17), 145 (13),
115 (29); HRMS: 415.0085 (C19H12F3FeNO3, calcd. 415.0119).
Ϫ
13C NMR and DEPT (100 MHz, CDCl3): δ ϭ 55.27 (CH3),
55.42 (CH3), 62.83 (CH), 73.77 (CH), 103.48 (CH), 114.23 (2 CH),
114.27 (2 CH), 122.52 (2 CH), 127.79 (2 CH), 131.05 (C), 146.68
(C), 155.27 (C), 158.64 (C). Ϫ MS (115°C): m/z (%) ϭ 407 (0.4)
[Mϩ], 379 (1), 351 (2), 323 (32), 267 (20), 266 (100), 252 (14), 145
(10); HRMS: 407.0473 (C20H17FeNO5, calcd. 407.0456).
Tricarbonyl[(1-4-η)-1-(2,4-dimethoxyphenyl)-4-phenyl-1-
azabuta-1,3-diene]iron (10g): Mp Ն95°C (dec). Ϫ IR (drift): ν ϭ
˜
2048, 1994, 1970, 1503, 1456, 1285, 1259, 1205, 1030, 823 cmϪ1. Ϫ
1H NMR (400 MHz, CDCl3): δ ϭ 3.30 (d, J ϭ 9.4 Hz, 1 H), 3.77
(s, 3 H), 3.96 (s, 3 H), 5.77 (dd, J ϭ 9.4, 2.9 Hz, 1 H), 6.34 (dd,
J ϭ 8.7, 2.6 Hz, 1 H), 6.41 (d, J ϭ 2.6 Hz, 1 H), 6.99 (d, J ϭ 8.7
Hz, 1 H), 7.15 (d, J ϭ 2.9 Hz, 1 H), 7.19 (m, 1 H), 7.28 (t, J ϭ 7.4
Hz, 2 H), 7.34 (m, 2 H). Ϫ 13C NMR and DEPT (100 MHz,
CDCl3): δ ϭ 54.93 (CH3), 55.43 (CH3), 61.66 (CH), 75.59 (CH),
99.25 (CH), 102.30 (CH), 103.60 (CH), 118.53 (CH), 126.53 (2
CH), 126.66 (CH), 128.74 (2 CH), 135.03 (C), 139.29 (C), 152.27
(C), 156.67 (C). Ϫ MS (70°C): m/z (%) ϭ 407 (1) [Mϩ], 379 (5),
351 (18), 323 (78), 308 (100), 267 (74), 266 (82), 154 (15), 115 (16);
HRMS: 407.0447 (C20H17FeNO5, calcd. 407.0456).
Tricarbonyl[(1-4-η)-1-(2-methoxyphenyl)-4-(4-methoxyphenyl)-
1-azabuta-1,3-diene]iron (10l): Mp Ն 134Ϫ136°C (dec). Ϫ IR
˜
(drift): ν ϭ 2054, 1989, 1972, 1516, 1495, 1274, 1253, 1023, 831
1
cmϪ1. Ϫ H NMR (250 MHz, CDCl3): δ ϭ 3.38 (d, J ϭ 9.5 Hz, 1
H), 3.80 (s, 3 H), 3.98 (s, 3 H), 5.74 (dd, J ϭ 9.5, 3.0 Hz, 1 H),
6.78Ϫ6.87 (m, 2 H), 6.84 (br d, J ϭ 8.8 Hz, 2 H), 6.95Ϫ7.07 (m,
3 H), 7.29 (br d, J ϭ 8.8 Hz, 2 H). Ϫ 13C NMR and DEPT (100
MHz, CDCl3): δ ϭ 54.80 (CH3), 55.28 (CH3), 63.00 (CH), 75.88
(CH), 101.18 (CH), 110.92 (CH), 114.27 (2 CH), 118.94 (CH),
120.48 (CH), 123.44 (CH), 127.72 (2 CH), 131.21 (C), 141.50 (C),
150.86 (C), 158.57 (C). Ϫ MS (110°C): m/z (%) ϭ 379 (2) [Mϩ
Ϫ
28), 351 (13), 323 (42), 308 (100), 267 (11), 266 (28), 252 (10), 56
Tricarbonyl[(1-4-η)-1-(3,4,5-trimethoxyphenyl)-4-phenyl-1- (11); HRMS: 379.0484 (C19H17FeNO4 [Mϩ
Ϫ
CO]), calcd.
1005
˜
azabuta-1,3-diene]iron (10h): Mp Ն 147°C (dec). Ϫ IR (drift): ν ϭ 379.0507).
Eur. J. Inorg. Chem. 1998, 993Ϫ1007

H.-J. Knölker et al.
FULL PAPER
Tricarbonyl[(1-4-η)-1-(4-trifluoromethylphenyl)-4-(4-methoxy- 1 H), 6.35 (dd, J ϭ 8.7, 2.6 Hz, 1 H), 6.43 (d, J ϭ 2.6 Hz, 1 H),
phenyl)-1-azabuta-1,3-diene]iron (10m): Mp 124°C. Ϫ IR (drift): 7.01 (d, J ϭ 8.7 Hz, 1 H), 7.23 (br d, J ϭ 3.0 Hz, 1 H), 7.37 (d,
˜
ν ϭ 2066, 2001, 1982, 1610, 1517, 1443, 1325, 1312, 1172, 1129, J ϭ 8.4 Hz, 2 H), 7.55 (d, J ϭ 8.4 Hz, 2 H). Ϫ 13C NMR and
1
831 cmϪ1. Ϫ H NMR (400 MHz, CDCl3): δ ϭ 3.46 (d, J ϭ 9.6
DEPT (100 MHz, CDCl3): δ ϭ 54.91 (CH3), 55.43 (CH3), 58.19
Hz, 1 H), 3.81 (s, 3 H), 5.71 (dd, J ϭ 9.6, 2.9 Hz, 1 H), 6.83 (dd, (CH), 74.87 (CH), 99.27 (CH), 103.70 (CH), 103.93 (CH), 109.43
J ϭ 2.9, 0.8 Hz, 1 H), 6.85 (br d, J ϭ 8.8 Hz, 2 H), 6.93 (d, J ϭ (C), 118.54 (CH), 119.10 (CϵN), 126.72 (2 CH), 132.51 (2 CH),
8.4 Hz, 2 H), 7.29 (br d, J ϭ 8.8 Hz, 2 H), 7.42 (d, J ϭ 8.4 Hz, 2
H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3): δ ϭ 55.33 (CH3),
64.14 (CH), 75.49 (CH), 101.19 (CH), 114.48 (2 CH), 121.80 (2
134.37 (C), 145.36 (C), 152.30 (C), 157.04 (C).
Tricarbonyl[(1-4-η)-1-(4-methoxyphenyl)-4-(4-N,N-dimethyl-
aminophenyl)-1-azabuta-1,3-diene]iron (10r): Mp Ն125°C (dec). Ϫ
2
1
˜
CH), 123.86 (C, q, JCF ϭ 32.6 Hz), 124.49 (CF3, q, JCF ϭ 271
IR (drift): ν ϭ 2045, 2041, 1989, 1971, 1964, 1605, 1502, 1243,
3
Hz), 126.24 (2 CH, q, JCF ϭ 3.8 Hz), 127.97 (2 CH), 130.42 (C),
1
1035, 836, 823 cmϪ1. Ϫ H NMR (250 MHz, CDCl3): δ ϭ 2.95 (s,
156.87 (C), 159.01 (C), 205.07 (CO, br), 208.94 (CO, br), 211.97
(CO, br). Ϫ MS (90°C): m/z (%) ϭ 445 (2) [Mϩ], 417 (6), 389 (11),
361 (100), 304 (52), 286 (16), 145 (17); HRMS: 445.0214
(C20H14F3FeNO4, calcd. 445.0224).
6 H), 3.50 (d, J ϭ 9.6 Hz, 1 H), 3.75 (s, 3 H), 5.61 (dd, J ϭ 9.6,
2.9 Hz, 1 H), 6.63 (d, J ϭ 8.8 Hz, 2 H), 6.71 (d, J ϭ 8.8 Hz, 2 H),
6.89 (br d, J ϭ 2.9 Hz, 1 H), 6.89 (d, J ϭ 8.8 Hz, 2 H), 7.22 (d,
J ϭ 8.8 Hz, 2 H). Ϫ 13C NMR and DEPT (63 MHz, CDCl3): δ ϭ
40.36 (2 CH3), 55.44 (CH3), 65.36 (CH), 73.60 (CH), 102.53 (CH),
112.46 (2 CH), 114.22 (2 CH), 122.53 (2 CH), 126.06 (C), 127.80
(2 CH), 147.01 (C), 149.52 (C), 155.15 (C). Ϫ MS (130°C): m/z
(%) ϭ 420 (0.1) [Mϩ], 392 (0.2), 364 (1), 336 (9), 280 (43), 279
(100), 158 (10); HRMS: 420.0795 (C21H20FeN2O4, calcd.
420.0772).
Preparation of Tricarbonyl(η4-cyclohexa-1,3-diene)iron (2) by
Transfer of the Fe(CO)3-Fragment of the (η4-1-Azabuta-1,3-diene)-
tricarbonyliron Complexes 10 to Cyclohexa-1,3-diene (1a) Ϫ General
Procedure: Dry THF (10 ml) and cyclohexa-1,3-diene (1a) (0.37
ml, 3.88 mmol) were added to the azadiene complex 10 (1.00 mmol)
and the reaction mixture was stirred at reflux (reaction time, see
Table 6). The mixture was cooled to room temp. and the solvent
was evaporated in vacuo to a volume of 1 ml. The residue was
subjected to flash chromatography (pentane) on silica gel and af-
forded the iron complex 2 as a yellow oil (Table 6).
Tricarbonyl[(1-4-η)-1-(2,4-dimethoxyphenyl)-4-(4-methoxy-
phenyl)-1-azabuta-1,3-diene]iron (10n): Mp Ն116°C (dec). Ϫ IR
˜
(drift): ν ϭ 2051, 2043, 1992, 1984, 1964, 1518, 1443, 1285, 1255,
1
1034, 837 cmϪ1. Ϫ H NMR (400 MHz, CDCl3): δ ϭ 3.34 (d, J ϭ
9.5 Hz, 1 H), 3.76 (s, 3 H), 3.79 (s, 3 H), 3.96 (s, 3 H), 5.70 (dd,
J ϭ 9.5, 2.8 Hz, 1 H), 6.33 (dd, J ϭ 8.6, 2.5 Hz, 1 H), 6.41 (d, J ϭ
2.5 Hz, 1 H), 6.83 (d, J ϭ 8.7 Hz, 2 H), 6.99 (d, J ϭ 8.6 Hz, 1 H),
7.10 (d, J ϭ 2.8 Hz, 1 H), 7.28 (d, J ϭ 8.7 Hz, 2 H). Ϫ 13C NMR
and DEPT (100 MHz, CDCl3): δ ϭ 54.91 (CH3), 55.28 (CH3),
55.40 (CH3), 62.52 (CH), 75.40 (CH), 99.14 (CH), 101.42 (CH),
103.44 (CH), 114.22 (2 CH), 118.39 (CH), 127.69 (2 CH), 131.35
(C), 135.10 (C), 152.18 (C), 156.52 (C), 158.48 (C). Ϫ MS (135°C):
m/z (%) ϭ 437 (0.2) [Mϩ], 409 (2), 381 (13), 353 (49), 338 (81), 310
(11), 299 (16), 297 (59), 296 (100), 282 (28), 153 (35), 138 (40), 84
(30), 56 (28); HRMS: 437.0583 (C21H19FeNO6, calcd. 437.0562).
Tricarbonyl[(1-4-η)-1-(4-methoxyphenyl)-4-(2-methoxyphenyl)-
˜
1-azabuta-1,3-diene]iron (10o): Mp Ն121°C (dec). Ϫ IR (drift): ν ϭ
2049, 1994, 1975, 1604, 1595, 1503, 1441, 1293, 1242, 1100, 1031,
1024, 836, 754 cmϪ1. Ϫ 1H NMR (250 MHz, CDCl3): δ ϭ 3.71 (d,
J ϭ 9.8 Hz, 1 H), 3.75 (s, 3 H), 3.92 (s, 3 H), 5.81 (dd, J ϭ 9.8,
3.0 Hz, 1 H), 6.72 (br d, J ϭ 8.9 Hz, 2 H), 6.85 (d, J ϭ 7.9 Hz, 2
H), 6.92 (br d, J ϭ 8.9 Hz, 2 H), 6.95 (br d, J ϭ 3.0 Hz, 1 H),
7.15Ϫ7.24 (m, 2 H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3):
δ ϭ 55.11 (CH3), 55.44 (CH3), 56.33 (CH), 73.73 (CH), 104.51
(CH), 110.46 (CH), 114.18 (2 CH), 120.30 (CH), 122.57 (2 CH),
125.27 (CH), 127.37 (C), 127.81 (CH), 147.01 (C), 155.14 (C),
157.14 (C). Ϫ MS (100°C): m/z (%) ϭ 407 (1) [Mϩ], 379 (1), 351
(5), 323 (32), 267 (21), 266 (16), 252 (11), 236 (100); HRMS:
407.0455 (C20H17FeNO5, calcd. 407.0456). Ϫ C20H17FeNO5: C
58.99, H 4.21, N 3.44; found: C 58.80, H 4.26, N 3.65.
Table 6. Transfer reagent 10, reaction time, and yield of the iron
complex 2
Iron Complex 10
Reaction time
[min]
2, Yield
[mg]
Entry
[mg]
[%]
a[a]
b
250
377
377
200
377
377
377
200
415
407
407
407
437
437
377
407
407
445
437
407
372
432
420
180
30
140
134
183
111
68
103
163
98
171
109
148
177
192
163
205
199
183
194
172
203
152
131
162
88
61
83
95
31
47
74
45
78
50
67
80
87
74
93
90
83
88
78
92
69
60
74
60
[b]
120
30
60
c
120
120
120
30
d[c]
e
g
Tricarbonyl[(1-4-η)-4-(4-cyanophenyl)-1-phenyl-1-azabuta-1,3-
˜
60
diene]iron (10p): Mp Ն143°C (dec). Ϫ IR (drift): ν ϭ 2224, 2057,
120
120
120
120
120
120
120
120
120
120
120
120
1997, 1991, 1485, 1439, 1295, 836, 764 cmϪ1. Ϫ 1H NMR (400
MHz, CDCl3): δ ϭ 3.24 (d, J ϭ 9.2 Hz, 1 H), 5.70 (dd, J ϭ 9.2,
2.9 Hz, 1 H), 6.94 (m, 3 H), 7.04 (dd, J ϭ 2.9, 0.8 Hz, 1 H), 7.20
(m, 2 H), 7.37 (br d, J ϭ 8.4 Hz, 2 H), 7.56 (br d, J ϭ 8.4 Hz, 2
H). Ϫ 13C NMR and DEPT (100 MHz, CDCl3): δ ϭ 58.69 (CH),
73.70 (CH), 105.71 (CH), 109.80 (C), 118.95 (CϵN), 121.82 (2
CH), 123.04 (CH), 126.85 (2 CH), 129.12 (2 CH), 132.57 (2 CH),
144.86 (C), 152.81 (C). Ϫ MS (95°C): m/z (%) ϭ 372 (1) [Mϩ], 344
(2), 316 (5), 288 (32), 232 (51), 231 (100), 77 (24); HRMS: 372.0204
(C19H12FeN2O3, calcd. 372.0197).
h
i
j
k
l
m
n
o
p
q
r
Tricarbonyl[(1-4-η)-4-(4-cyanophenyl)-1-(2,4-dimethoxy- The following reactions were run on a different scale: [a] Cyclohexa-
1,3-diene 1a (0.20 ml, 168 mg, 2.10 mmol) and azadiene complex
phenyl)-1-azabuta-1,3-diene]iron (10q): Mp Ն118°C (dec). Ϫ IR
[b]
˜
10a (250 mg, 0.720 mmol). Ϫ
Cyclohexa-1,3-diene 1a (0.20 ml,
(drift): ν ϭ 2226, 2057, 2004, 1995, 1970, 1602, 1503, 1311, 1214,
168 mg, 2.10 mmol) and azadiene complex 10b (200 mg, 0.531
1
843, 791 cmϪ1. Ϫ H NMR (400 MHz, CDCl3): δ ϭ 3.15 (d, J ϭ
[c]
mmol). Ϫ Cyclohexa-1,3-diene 1a (0.25 ml, 210 mg, 2.62 mmol)
9.2 Hz, 1 H), 3.77 (s, 3 H), 3.97 (s, 3 H), 5.74 (dd, J ϭ 9.2, 3.0 Hz,
and azadiene complex 10d (200 mg, 0.513 mmol).
1006
Eur. J. Inorg. Chem. 1998, 993Ϫ1007

Transition Metal Complexes in Organic Synthesis, 41
FULL PAPER
Preparation of Tricarbonyl(η4-cyclohexa-1,3-diene)iron (2) by Di-
rect Complexation of Cyclohexa-1,3-diene (1a) with Nonacarbonyl-
diiron: Cyclohexa-1,3-diene (1a) (13.9 ml, 146 mmol) was added to
a suspension of nonacarbonyldiiron (44.2 g, 121.5 mmol) in THF
(250 ml) and the heterogeneous mixture was stirred at reflux for 6
h. The mixture was cooled to room temp., filtered through a short
path of Celite, and the solvent was removed. The residue was dis-
solved in light petroleum and filtered through a short path of Alox
B. Evaporation of the solvent in vacuo afforded the iron complex
p. 59; H. Hermann, Diplomarbeit, Universität Karlsruhe, 1994,
p. 28.
[6]
[7]
E. O. Fischer, R. D. Fischer, Angew. Chem. 1960, 72, 919.
For a brief review on tricarbonyliron transfer reagents, see: H.-
J. Knölker, in Encyclopedia of Reagents for Organic Synthesis,
Vol. 1 (Ed.: L. A. Paquette), Wiley, Chichester, 1995, p. 333.
J. A. S. Howell, B. F. G. Johnson, P. L. Josty, J. Lewis, J. Or-
ganomet. Chem. 1972, 39, 329; A. J. P. Domingos, J. A. S. How-
ell, B. F. G. Johnson, J. Lewis, Inorg. Synth. 1976, 16, 103.
C. R. Graham, G. Scholes, M. Brookhart, J. Am. Chem. Soc.
1977, 99, 1180; M. Brookhart, G. O. Nelson, J. Organomet.
Chem. 1979, 164, 193.
[8]
[9]
2 (11.5 g, 43%), which could be subjected directly to hydride ab-
[10]
[11]
S. E. Thomas, T. N. Danks, D. Rakshit, Philos. Trans. R. Soc.
London A 1988, 326, 611; N. W. Alcock, C. J. Richards, S. E.
Thomas, Organometallics 1991, 10, 231.
˜
straction. Yellow oil. Ϫ IR (film): ν ϭ 3009, 2926, 2907, 2887, 2850,
2042, 1957, 1467, 1333, 1180, 1029, 1007, 938, 879, 865, 642, 623
1
cmϪ1. Ϫ H NMR (400 MHz, C6D6): δ ϭ 1.18 (br d, J ϭ 12 Hz,
H. Fleckner, F.-W. Grevels, D. Hess, J. Am. Chem. Soc. 1984,
106, 2027.
2 H), 1.45 (br dt, J ϭ 12, 2 Hz, 2 H), 2.74 (dd, J ϭ 5, 2 Hz, 2 H),
4.63 (dd, J ϭ 5, 3 Hz, 2 H). Ϫ 13C NMR and DEPT (100 MHz,
C6D6): δ (T ϭ 298 K) ϭ 23.82 (2 CH2), 62.52 (2 CH), 85.37 (2
CH), 212.63 (3 CO); 13C NMR (125 MHz, [D8]toluene): δ (T ϭ
185 K) ϭ 23.45 (2 CH2), 62.30 (2 CH), 85.09 (2 CH), 211.32 (2
CO), 216.05 (CO); δ (T ϭ 298 K) ϭ 23.89 (2 CH2), 62.47 (2 CH),
85.41 (2 CH), 212.56 (3 CO). Ϫ MS (20°C): m/z (%) ϭ 220 (9)
[Mϩ], 192 (32), 164 (5), 162 (10), 134 (100), 56 (33); HRMS:
219.9834 (C9H8FeO3, calcd. 219.9823).
[12]
[13]
H.-J. Knölker, P. Gonser, Synlett 1992, 517.
H.-J. Knölker, P. Gonser, P. G. Jones, Synlett 1994, 405.
[14] [14a]
S. Otsuka, T. Yoshida, A. Nakamura, Inorg. Chem. 1967,
[14b]
6, 20. Ϫ
A. De Cian, R. Weiss, J. Chem. Soc. Chem. Com-
mun. 1968, 348; A. De Cian, R. Weiss, Acta Cryst. B 1972,
28, 3264.
[15]
[16]
[17]
A. M. Brodie, B. F. G. Johnson, P. L. Josty, J. Lewis, J. Chem.
Soc. Dalton Trans. 1972, 2031.
J. Yin, J. Chen, W. Xu, Z. Zhang, Y. Tang, Organometallics
1988, 7, 21.
T. N. Danks, S. E. Thomas, Tetrahedron Lett. 1988, 29, 1425;
T. N. Danks, S. E. Thomas, J. Chem. Soc. Perkin Trans. 1
1990, 761.
Synthesis of the Tricarbonyl(η5-cyclohexadienylium)iron Tetra-
fluoroborate (3) by Hydride Abstraction of the Iron Complex 2: A
solution of tricarbonyl(η4-cyclohexa-1,3-diene)iron (2) (11.5 g, 52.4
mmol) in CH2Cl2 (70 ml) was added to a solution of tri-
phenylmethyl tetrafluoroborate (20.8 g, 62.9 mmol) in CH2Cl2 (70
ml). The reaction mixture was stirred for 40 min at room temp. and
then poured into wet Et2O (700 ml). The resulting yellow precipi-
tate was washed twice with Et2O (150 ml) and dried in vacuo to
[18]
[19]
[20]
M. F. Semmelhack, C. H. Cheng, J. Organomet. Chem. 1990,
393, 237.
´
H. Cherkaoui, J. Martelli, R. Gree, Tetrahedron Lett. 1994,
35, 4781.
S. V. Ley, C. M. R. Low, A. D. White, J. Organomet. Chem.
1986, 302, C13; S. V. Ley, C. M. R. Low, Ultrasound in Organic
Synthesis, Springer Verlag, Berlin, 1989, chap. 14.
M. Geisert, H. Oelschläger, J. Prakt. Chem. 1967, 35, 110.
K. G. Morris, S. E. Thomas, J. Chem. Soc. Perkin Trans. 1 1991,
97; A. J. Pearson, K. Chang, D. B. McConville, W. J. Youngs,
Organometallics 1994, 13, 4.
[21]
[22]
provide pure tricarbonyl(η5-cyclohexadienylium)iron tetrafluoro-
˜
borate (3) (15.7 g, 98%). Yellow crystals. Ϫ IR (KBr): ν ϭ 2118,
[23]
[24]
2060, 1455, 1410, 1311, 1062, 603, 589, 558 cmϪ1. Ϫ 1H NMR (200
MHz, CD3CN): δ ϭ 1.91 (d, J ϭ 15.7 Hz, 1 H), 2.92 (dt, J ϭ 15.7,
6.3 Hz, 1 H), 4.24 (t, J ϭ 6.3 Hz, 2 H), 5.83 (t, J ϭ 6.3 Hz, 2 H),
7.16 (t, J ϭ 6.3 Hz, 1 H).
H.-J. Knölker, G. Baum, P. Gonser, Tetrahedron Lett. 1995,
36, 8191.
A. J. Pearson, Metallo-organic Chemistry, Wiley, Chichester,
1985, chap. 2.
[25] [25a]
J.-Y. Lallemand, P. Laszlo, C. Muzette, A. Stockis, J. Or-
ganomet. Chem. 1975, 91, 71. Ϫ [25b] D. Leibfritz, H. tom Dieck,
[25c]
J. Organomet. Chem. 1976, 105, 255. Ϫ
Takats, Inorg. Chem. 1976, 15, 3140.
L. Kruczynski, J.
[1]
[26]
[27]
For reviews, see: A. J. Pearson, Acc. Chem. Res. 1980, 13, 463;
H. Günther, NMR-Spektroskopie, 3rd ed., Thieme Verlag,
Stuttgart, 1992, p. 310.
A. J. Pearson, in Comprehensive Organometallic Chemistry, Vol.
8 (Eds.: G. Wilkinson, F. G. A. Stone, E. W. Abel), Pergamon
Press, Oxford, 1982, chap. 58; A. J. Pearson, Metallo-organic
Chemistry, Wiley, Chichester, 1985, chap. 7 and 8; H.-J.
Knölker, in Organic Synthesis via Organometallics (Eds.: K. H.
Dötz, R. W. Hoffmann), Vieweg, Braunschweig, 1991, p. 119;
H.-J. Knölker, Synlett 1992, 371; A. J. Pearson, Iron Compounds
in Organic Synthesis, Academic Press, London, 1994, chap. 4
and 5; H.-J. Knölker, in Advances in Nitrogen Heterocycles, Vol.
1 (Ed.: C. J. Moody), JAI Press, Greenwich, CT, 1995, p. 173.
D. H. R. Barton, A. A. L. Gunatilaka, T. Nakanishi, H. Patin,
D. A. Widdowson, B. R. Worth, J. Chem. Soc. Perkin Trans. 1
1976, 821.
[28]
G. Bellachioma, G. Cardaci, J. Chem. Soc. Dalton Trans. 1977,
909; G. Bellachioma, G. Cardaci, J. Chem. Soc. Dalton Trans.
1977, 2181; G. Bellachioma, G. Reichenbach, G. Cardaci, J.
Chem. Soc. Dalton Trans. 1980, 634.
[29]
[30]
[31]
H.-J. Knölker, P. Gonser, H. Hermann, P. G. Jones, G. Rohde,
unpublished results.
[2]
B. F. Hallam, P. L. Pauson, J. Chem. Soc. 1958, 642.
M. W. Kokkes, P. C. J. Beentjes, D. J. Stufkens, A. Oskam, J.
Organomet. Chem. 1986, 306, 77.
[3]
A. J. Birch, P. E. Cross, J. Lewis, D. A. White, S. B. Wild, J.
Chem. Soc. A 1968, 332.
A. N. Nesmeyanov, L. V. Rybin, N. A. Stelzer, Y. T. Struchkov,
A. S. Batsanov, M. I. Rybinskaya, J. Organomet. Chem. 1979,
182, 399.
[4]
A. J. Birch, K. B. Chamberlain, M. A. Haas, D. J. Thompson,
J. Chem. Soc., Perkin Trans. 1 1973, 1882.
[5]
[32]
H.-J. Knölker, H. Hermann, J.-B. Pannek, unpublished results;
H.-J. Knölker, H. Hermann, Angew. Chem. 1996, 108, 363; An-
gew. Chem. Int. Ed. Engl. 1996, 35, 341.
J.-B. Pannek, Diplomarbeit, Universität Hannover, 1989, p. 46;
H.-J. Knölker, Habilitationsschrift, Universität Hannover, 1989,
[98045]
Eur. J. Inorg. Chem. 1998, 993Ϫ1007
1007