Stereochemical factors associated with the rearrangement of (2-ethyl-1-azabuta-1,3-diene)tricarbonyliron(0) complexes

Article abstract of DOI:10.1016/S0022-328X(98)01208-X

Reaction of (2-ethyl-1,4-diphenyl-1-azabuta-1,3-diene)tricarbonyliron(0) 4 and (2-ethyl-1-benzyl-4-phenyl-1-azabuta-1,3-diene)tricarbonyliron(0) 7 with lithium diethylamide leads to selective formation of the corresponding endo (1-methyl-2-amino buta-1,3-

Full text of DOI:10.1016/S0022-328X(98)01208-X

Journal of Organometallic Chemistry 579 (1999) 53–58
Stereochemical factors associated with the rearrangement of
(2-ethyl-1-azabuta-1,3-diene)tricarbonyliron(0) complexes
Timothy N. Danks a,*, Mark E. Howells a, Mark J. Ackland b
a Department of Chemistry, Uni6ersity of Surrey, Guildford, Surrey GU2 5XH, UK
b Pharmacia and Upjohn, Flemming Way, Crawley, West Sussex, UK
Received 4 November 1998
Abstract
Reaction of (2-ethyl-1,4-diphenyl-1-azabuta-1,3-diene)tricarbonyliron(0) 4 and (2-ethyl-1-benzyl-4-phenyl-1-azabuta-1,3-di-
ene)tricarbonyliron(0) 7 with lithium diethylamide leads to selective formation of the corresponding endo (1-methyl-2-amino
buta-1,3-diene)tricarbonyliron(0) complexes 5 and 8, respectively. In each case there is no evidence for the exo complexes 6 and
9. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Lithium amide; Rearrangement; Endo enamine complexes
ene from a methyl to an ethyl group. In principle,
rearrangement of complexes 4 and 7 should lead to
formation of 2-amino homo-1,3-diene complexes 5 and
6 or 8 and 9, respectively (Scheme 2).
1. Introduction
During our investigation of the reaction between (2-
methyl-1-azabuta-1,3-diene)tricarbonyliron(0) 1 com-
plexes with lithiated amines we demonstrated that when
these contain a methyl group at C-2, the reaction leads
to deprotonation, followed by rearrangement of the
intermediate anion and re-protonation to yield sec-
ondary (2-amino homo-1,3-diene)tricarbonyliron(0)
complex 2 in good yield [1,2]. Although tertiary enam-
ine complexes in the cyclohexa-1,3-diene series have
previously been reported [3], our deprotonation strat-
egy represented the first synthesis of secondary (enam-
ine)tricarbonyliron(0) complexes.
In cases where the substituent at C-2 of complex 1 is
a hydrogen, the lithiated amine reacts by nucleophilic
addition at a coordinated carbonyl group, resulting in
formation of a formamide 3 after addition of a proton
source [2] (Scheme 1).
2. Results and discussion
Initially, the reaction between (2-ethyl-1,4-diphenyl-
1-azabuta-1,3-diene)tricarbonyliron(0) 4 and lithium di-
ethylamide was studied. Complex 4 was synthesised as
follows. Condensation of aniline with 2-ethyl-4-phenyl-
1-oxabuta-1,3-diene 10 in dichloromethane under tita-
nium tetrachloride catalysis led to formation of a
yellow gum after filtration and removal of the solvent
1
under reduced pressure. Examination of the H-NMR
spectrum of the crude product mixture indicated that
1-azabuta-1,3-diene 11 was present as the major com-
In this paper we describe the effect of changing the
substituent at C-2 of the coordinated 1-azabuta-1,3-di-
* Corresponding author. Fax: +44-1483-259-514.
E-mail address: t.danks@surrey.ac.uk (T.N. Danks)
Scheme 1.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01208-X

54
T.N. Danks et al. / Journal of Organometallic Chemistry 579 (1999) 53–58
Scheme 4.
Scheme 2.
the ortho protons of the N-phenyl group of complex 5
or the methylene or ortho protons of the N-benzyl
groups of complex 8. These results indicate that the
methyl group of complexes 5 and 8 are in the proximity
of the protons at C-4. Such enhancements are only
possible if the E,E-isomer 2-amino homo-1,3-diene lig-
ands are complexed to the tricarbonyliron(0) moiety
(Fig. 1).
1
ponent (\80% by 300 MHz H-NMR spectroscopy).
All attempts to purify 11 either by chromatography or
crystallisation were unsuccessful and resulted in hydrol-
ysis and formation of the 2-ethyl-4-phenyl-1-oxabuta-
1,3-diene 10 and aniline. In view of the high yield of 11
and the difficulty encountered during its purification,
the crude mixture was used directly in the complexation
step. Formation of complex 4 was therefore achieved
by stirring a mixture of crude 1-azabuta-1,3-diene 11
and enneacarbonyldiiron(0) in toluene at 40°C for 3 h
in accordance with procedures described in the litera-
ture [4,5] to yield red crystals identified as complex 4 on
the basis of their spectroscopic and analytical data
(Scheme 3).
Additional information regarding the geometry of
the 2-amino homo-1,3-diene ligands of complexes 5 and
8 was obtained by consideration of the chemical shift of
the signal due to the proton at C-1. The signal due to
this proton appeared as a doublet of quartets at 3.19
(J=1.7 and 7.2 Hz) and 2.84 (J=1.9 and 7.2 Hz). This
result confirms the nOe observations that the proton at
C-1 is in the exo position since an endo proton will be
situated over and highly shielded by the tricar-
Treatment of a solution of complex 4 in tetrahydro-
furan with lithium diethylamide (synthesised by stirring
a solution of diethylamine in tetrahydrofuran with
butyl-lithium at 0°C for 0.25 h) for 3 h at 0°C followed
by a methanol quench and chromatography lead to
isolation of yellow crystals identified as 2-amino homo-
1,3-diene complex 5 from their spectroscopic and ana-
lytical data. There was no evidence for formation of
1
bonyliron(0) moiety [6] and its signal in the H-NMR
spectrum is expected to appear between 0 and 1.00
ppm.
In an attempt to understand the reasons for the
stereochemistry of this rearrangement reaction, the na-
ture of the starting complexes 4 and 7 was also studied
by nOe difference spectroscopy. Irradiation of the sig-
nals at 1.55 and 1.47 ppm due to the methyl group of
the ethyl fragment at C-2 of complexes 4 and 7 lead to
enhancements of the signals at 5.63 and 5.46 ppm due
to the protons at C-3, respectively. There was no evi-
dence for any enhancement of the signals due to the
ortho protons of the N-phenyl fragment of complex 4
or the methylene or ortho protons of the N-benzyl
group of complex 7. From these results it can be
assumed that the methyl group at C-1 of complexes 4
and 7 are in the proximity of the protons at C-3 (Fig.
2).
1
E,Z-complex 6 (by 300 MHz H-NMR spectroscopy).
Similarly, complex 7 was synthesised by reaction of
2-ethyl-4-phenyl-1-oxabuta-1,3-diene with benzylamine
followed by warming the crude reaction mixture with
enneacarbonyldiiron(0). Treatment of 7 with lithium
diethylamide lead to formation of the corresponding
rearrangement complex 8. There was again no evidence
1
(by 300 MHz H-NMR spectroscopy) for E,Z-complex
9 in the product mixture (Scheme 4).
The geometry of the 2-amino homo-1,3-diene ligands
of complexes 5 and 8 were confirmed as E,E on the
basis of nOe difference and 1H-NMR spectroscopy.
Irradiation of the signals due to the methyl groups at
1.44 and 1.32 ppm lead to an enhancement of the
signals at 2.99 and 3.07 ppm due to the protons at C-4
of complexes 5 (5%) and 8 (4%), respectively. There was
no evidence for any enhancement of the signal due to
Examination of the molecular models of complexes 4
and 7 indicates that rotation of the bond between the
C-2 and the ethyl fragment leads to a significant inter-
action between the methyl group and the substituents at
nitrogen. Such a conformational constraint may be
Scheme 3.

T.N. Danks et al. / Journal of Organometallic Chemistry 579 (1999) 53–58
55
Fig. 1. Complexes 5 and 8.
Scheme 5.
used to rationalise the stereochemistry of the rearrange-
ment of complexes 4 and 7.
spectra of the reaction mixture even when the samples
were prepared under an inert atmosphere. Conse-
quently, the effect of changing the substituent at nitro-
gen to 2-phenylethyl could not be studied.
The rearrangement of complexes 4 and 7 may there-
fore be described by deprotonation of the methylene of
the conformationally constrained ethyl substituent at
C-2. This results in formation of the carbon centred
anionic complexes 12 and 13. Complexes 12 and 13
rapidly convert to the h3-azaallyl complexes 14 and 15,
in which the negative charges are centred on the tricar-
bonyliron(0) moiety. Rotation of the bond between C-2
and C-3 will lead to h3-azaallyl complex 16 and 17,
which upon recoordination of the double bond between
carbons 3 and 4 of the 1-homo-1,3-diene leads to the
anionic complexes 18 and 19, in which the negative
charge is isolated on nitrogen. Protonation of 18 and 19
will lead to 2-amino-1,3-diene complexes 5 and 8 in
which the methyl substituent at C-1 is exclusively in the
endo position (Scheme 5).
In an attempt to reduce the steric interaction between
the substituent at nitrogen and the ethyl substituent at
C-2 of complexes 4 and 7, the complex derived from
2-phenyl ethylamine and 2-ethyl-4-phenyl-1-oxabuta-
1,3-diene was prepared. 1-Azabuta-1,3-diene 16 was
synthesised by condensation of 2-phenylethylamine
with 2-ethyl-4-phenyl-1-oxabuta-1,3-diene under tita-
nium tetrachloride catalysis. Reaction of the crude reac-
tion mixture with enneacarbonyldiiron(0) at 40°C for 3
h lead to isolation of red crystals identified as complex
17 from their spectroscopic and analytical data (Scheme
6).
Synthesis of complexes bearing a propyl substituent
at C-2 was also attempted. In accordance with previous
procedures, 2-propyl-4-phenyl-1-oxabuta-1,3-diene was
reacted with aniline and benzylamine. In each case the
reactions yielded Michael addition products; there was
no evidence for the formation of 1-azabuta-1,3-dienes
20 and 21. Even when the crude reaction mixture was
heated with enneacarbonyldiiron(0), formation of 1-
azabuta-1,3-diene complexes 22 and 23 was not ob-
served. An alternative approach to complexes 22 and
23, where the (2-propyl-4-phenyl-1-oxabuta-1,3-di-
ene)tetracarbo-nyliron(0) 24 was heated with aniline or
benzylamine, also failed to yield complexes 22 and 23
[7]. Consequently, the effect of changing the substituent
at C-2 from ethyl to propyl on this reaarangement
reaction was not possible.
The work in this paper illustrates that for rearrange-
ment of (1-azabuta-1,3-diene)tricarbonyliron(0) com-
plexes 4 and 7 that contain an ethyl group at C-2, the
relative conformation of the ethyl group with respect to
the 1-azabuta-1,3-diene appears to play an important
role in determining the stereochemical course of the
reaction and hence the reaction products. In the cases
of complexes 4 and 7, the ethyl group is orientated
away from the substituents at nitrogen and results in
formation of endo complexes 5 and 8. In the case of
complex 17, the conformational constraints associated
with the ethyl group at C-2 appear to be absent.
Although reaction of this complex with lithium diethy-
lamide leads to unstable reaction products, these failed
Although complex 17 was stable and could be fully
characterised, reaction with lithium diethylamide at 0°C
lead to the formation of an unstable reaction product.
It was not possible to obtain satisfactory 1H-NMR
to give satisfactory H- and 13C-NMR spectra.
1
3. Experimental
All reactions under an atmosphere of nitrogen were
performed using standard vacuum and Schlenk line
techniques [8]. Dichloromethane was dried over calcium
hydride and was distilled, toluene was dried over
Fig. 2. Complexes 4 and 7.

56
T.N. Danks et al. / Journal of Organometallic Chemistry 579 (1999) 53–58
Scheme 6.
matographed on silica gel using diethyl ether:hexane
(1:5) as the eluent to yield complex 4 as red crystals
(0.16 g, 50% with respect to 11). M.p. (dec.) 123–
125°C; (found: C, 64.02; H, 4.43; N, 3.65%
C20H17NFeO3 requires C, 64.02; H, 4.57; N, 3.73%);
wmax. (C4Cl6) 2 053vs (CꢁO), 1 991vs (CꢁO) and 1 976vs
cm−1 (CꢁO); lH (300 MHz; CDCl3) 1.55 (3H, m,
CH2CH3), 2.46–2.80 (2H, m, CH2CH3), 3.21 (1H, d,
J=8.9 Hz, PhCHꢀCH), 5.63 (1H, d, J=8.9 Hz,
PhCHꢀCH and 6.72–7.40 (10H, m, 2×Ph); lC (75
MHz; CDCl3) 13.20 (CH2CH3), 22.20 (CH2CH3), 60.21
(C4), 68.28 (C3), 121.26, 123.30, 126.62, 126.73, 128.68,
129.09, 139.46 and 149.82 (2×Ph and C2).
sodium metal and was distilled and tetrahydrofuran
was dried over potassium benzophenone ketyl and was
distilled. Diethylamine was redistilled and butyl-lithium
was used as a 1.6 M solution in hexanes. Melting points
were recorded on a Kofler hot-stage micromelting point
apparatus and are uncorrected. 1H- and 13C-NMR
spectra were recorded on a Bruker AC 300 instrument
at 300 and 75.4 MHz, respectively. All chemical shifts
are quoted in ppm relative to a tetramethylsilane stan-
dard. Chromatography was performed on Merck (40–
63 mm) silica. Filtrations through alumina were
performed using deactivated Brockmann grade IV
alumina.
3.1. Synthesis of (2-ethyl-1,4-diphenyl-1-
azabuta-1,3-diene)tricarbonyliron(0) 4
3.2. Reaction of (2-ethyl-1,4-diphenyl-1-azabuta-
1,3-diene)tricarbonyliron(0) 4 with lithium diethylamide
2-Ethyl-4-phenyl-1-oxabuta-1,3-diene 10 (0.18 g, 1.14
mmol) was dissolved in dry dichloromethane (30 ml)
and stirred at 0°C under an atmosphere of nitrogen.
Aniline (0.10 ml, 1.14 mmol) and triethylamine (0.49
ml, 3.50 mmol) were added and the resulting solution
was stirred for 0.25 h. Titanium tetrachloride (0.091 g,
0.63 mmol) was added dropwise over a period of 10
min and the dark brown mixture produced was stirred
for 0.5 h. The ice-bath was removed and stirring was
continued for a further 4 h. The resulting mixture was
filtered through celite to remove titanium oxide and the
solvent was removed under reduced pressure to give a
yellow solid. Dry toluene (30 ml) was added and the
mixture was stirred for 0.25 h before being filtered to
remove the precipitated amine hydrochloride and the
solvent was removed under reduced pressure to yield a
yellow gum. The 1H-NMR spectrum of this gum
showed a \65% conversion to E,E and E,Z 2-ethyl-4-
phenyl-1-azabuta-1,3-diene 11. lH (300 MHz; CDCl3)
1.12 and 1.33 (3H, m, CH2CH3), 2.47 and 2.80 (2H, m,
CH2CH3) and 6.61–7.56 (12H, m, 2×Ph and
PhCHꢀCH). The crude gum containing 11 was redis-
solved in toluene (10 ml) and enneacarbonyldiiron(0)
(0.83 g, 2.28 mmol) was added. The mixture was heated
at 40°C for 3 h under an atmosphere of nitrogen. The
reaction mixture was cooled to room temperature and
filtered through a plug of alumina to remove the solid
residues. The solvent was removed under reduced pres-
Butyl-lithium (1.6 M; 0.84 ml, 1.35 mmol) was added
to a solution of diethylamine (0.10 g, 1.33 mmol) in
tetrahydrofuran (5 ml) and the solution was cooled to
0°C and the resulting solution was stirred for 0.25 h. A
solution of (2-ethyl-1,4-diphenyl-1-azabuta-1,3-diene)-
tricarbonyliron(0) 4 (0.10 g, 0.27 mmol) in tetrahydro-
furan (5 ml) was added and the reaction was stirred at
0°C for 3 h under an atmosphere of nitrogen before
being quenched with methanol (1 ml). The resulting
solution was allowed to warm to room temperature for
0.5 h and was filtered through alumina to remove the
solid residues and the solvent was removed under re-
duced pressure to yield an orange gum. This gum was
chromatographed on silica gel using diethyl
ether:hexane (1:20) as the eluent to yield complex 5 as
a yellow gum that crystallised on standing and was
recrystallised from hexane at −20°C (0.072 g, 72%).
M.p. 126–128°C; (found: C, 63.91; H, 4.39; N, 3.74%,
C20H17NFeO3 requires C, 64.02; H, 4.57; N, 3.73%);
wmax. (thin film) 2 039vs (CꢁO) and 1 973vs, br cm−1
(CꢁO); lH (300 MHz; CDCl3) 1.44 (3H, d, J=7.2 Hz,
CꢀCHaCH3), 2.99 (1H, d, J=8.6 Hz, PhCHꢀCH), 3.19
(1H, dq, J=1.7 Hz and 7.2 Hz, CꢀCHaCH3), 5.38
(1H, br, NH), 5.76 (1H, dd, J=1.7 Hz and J=8.6 Hz,
PhCHꢀCH) and 7.00–7.42 (10H, m, 2×Ph); lC (75
MHz;
CDCl3)
14.33
(CꢀCHaCH3),
(CꢀCHaCH3), 50.49 (C4), 71.19 (C3), 119.52, 122.40,
125.97, 126.16, 128.51 and 129.53 (2×Ph and C-2).
48.48
sure to give
a red/brown gum that was chro-

T.N. Danks et al. / Journal of Organometallic Chemistry 579 (1999) 53–58
57
3.3. Synthesis of (1-benzyl-2-ethyl-4-phenyl-1-azabuta-
1,3-diene)tricarbonyliron(0) 7
was added and the resulting mixture was stirred at 0°C
for 1.5 h under an atmosphere of nitrogen. The reaction
was quenched with methanol (1 ml) and was allowed to
warm to room temperature for 0.5 h. The dark solution
produced was filtered through alumina and the solvent
was removed under reduced pressure to give a dark
yellow gum. This gum was chromatographed on silica
gel using diethyl ether:hexane (1:20) as the eluent to
yield a yellow oil identified as enamine complex 8,
(0.078 g, 78%). B.p. (dec.) \100°C; (found: C, 64.56;
H, 4.70; N, 3.75; C21H19FeNO3 requires C, 64.77; H,
4.92; N, 3.60); wmax. (hexane) 1 974 (CꢁO) 1 992 (CꢁO),
2 053 cm−1 (CꢁO); lH (300 MHz; CDCl3) 1.32 (3H, d,
J=7.2 Hz, CꢀCHaCH3), 2.84 (1H, dq, J=1.8 Hz and
7.2 Hz CꢀCHaCH3), 3.07 (1H, d, J=8.4 Hz,
PhCHꢀCH), 3.42 (1H, br, NH), 4.13–4.31 (2H, m,
PhCH2N), 5.27 (1H, dd, J=1.8 Hz and 8.4 Hz,
PhCHꢀCH) and 7.11–7.44 (10H, m, 2×Ph); lC (75
MHz; CDCl3) 14.43 (ꢀCHaCH3), 49.15 (NCH2Ph),
49.66 (ꢀCHaCH3), 51.38 (C-4) 61.97 (C-3) 125.96,
126.10, 126.29, 127.13, 128.09, 128.32, 128.65, 129.47
and 129.15 (2×Ph and C-2).
4-Phenyl-2-ethyl-1-oxabuta-1,3-diene 10 (1.0 g, 6.25
mmol) was dissolved in dry dichloromethane (30 ml)
and cooled to 0°C under an atmosphere of nitrogen. To
this solution was added benzylamine (0.68 ml, 6.25
mmol), dry triethylamine (2.7 ml, 19.3 mmol) and
titanium tetrachloride (0.38 ml, 3.47 mmol) was added
dropwise over a period of 10 min. The mixture was
stirred for 30 min before the ice-bath was removed and
stirring was continued for 15 h. The dark brown solu-
tion produced was filtered through celite and the sol-
vent removed under reduced pressure to give a yellow
gum that was dissolved in dry toluene and stirred for 20
min in order to precipitate the amine hydrochloride.
The salt was removed by filtration, which afforded a 2:1
mixture of crude E,E and E,Z 2-ethyl-1-benzyl-4-
phenyl-1-azabuta-1,3-diene 16 as a yellow gum after
removal of the solvent. lH (300 MHz; CDCl3) 1.22 (3H,
m, CH2CH3), 2.18 (2H, m, CH2CH3), 4.20 (2H, m,
CH2Ph) and 7.00–7.50 (12H, m, 2×Ph and
PhCHꢀCH). Crude 16 was redissolved in toluene (10
ml) and enneacarbonyldiiron(0) (4.55 g, 12.5 mmol)
was added and the mixture was heated at 40°C for 3 h
under an atmosphere of nitrogen. The resulting dark
brown mixture produced was filtered through alumina
to remove the solid residues and the solvent was re-
moved under reduced pressure to yield a brown gum.
Chromatography of this gum on silica using diethyl
ether:light petroleum (1:20) as the eluent gave complex
7 as red crystals, (0.88 g, 36%). M.p. (dec.) \60°C;
(found: C, 64.66; H, 4.89; N, 3.68; C21H19FeNO3 re-
quires C, 64.77; H, 4.92; N, 3.60); wmax. (C4Cl6) 2 050vs
(CꢁO), 1 987vs (CꢁO) and 1 963vs cm−1 (CꢁO); lH
(300 MHz; CDCl3) 1.47 (3H, m, CH2CH3), 2.67–2.94
(2H, m, CH2CH3), 2.93 (1H, d, J=8.8 Hz,
PhCHꢀCH), 3.40 (1H, d, J=15.4 Hz, PhCHHN), 4.07
(1H, d, J=15.4 Hz, PhCHHN), 5.46 (1H, d, J=8.8
Hz, PhCHꢀCH) and 7.12–7.37 (10H, m, 2×Ph); lC
(75 MHz; CDCl3) 12.46 (CH2CH3), 21.64 (CH2CH3),
57.81 (PhCH2N), 58.87 (C4), 67.90 (C3), 126.58,
127.07, 127.91, 128.27, 128.48, 133.51, 140.06 and
140.41(2×Ph and C2).
3.5. Synthesis of (2-ethyl-1-(2-phenylethyl)-4-phenyl-
1-azabuta-1,3-diene)tricarbonyliron(O) 17
2-Ethyl-4-phenyl-1-oxabuta-1,3-diene 10 (1.00 g, 6.25
mmol) and 2-phenylethylamine (0.76 g, 6.25 mmol)
were dissolved in toluene (10 ml) and the mixture was
stirred for 60 h. A small aliquot was taken for 1H-
NMR analysis. Owing to the complexity of the spec-
trum, it was not possible to confirm formation of
2-ethyl-1-(2-phenylethyl)-4-phenyl-1-azabuta-1,3-diene
16. Enneacarbonyldiiron(0) (4.55 g, 12.5 mmol) was
added to crude 1-azabuta-1,3-diene 16 and the mixture
was stirred at 40°C for 1 h under an atmosphere of
nitrogen. The product mixture was filtered through
alumina and the solvent was removed under reduced
pressure to yield a brown gum. Chromatography of this
gum on silica gel using diethyl ether:hexane (1:20) as
the eluent, followed by removal of the solvent gave
(2-ethyl-1-(2-phenylethyl)-4-phenyl-1-azabuta-1,3-diene)
tricarbonyliron(0) 17 as a red gum, (0.026 g, 10%). B.p.
(dec.) \100°C; (found: C, 65.44 H, 5.22 N, 3.30;
C22H21NFeO3 requires C, 65.49; H, 5.25; N, 3.47); wmax.
(hexane) 2 049vs (CꢁO), 1 986vs (CꢁO) and 1 968vs
cm−1 (CꢁO); lH (300 MHz; CDCl3) 1.43 (3H, m,
CH2CH3), 2.33–3.03 (7H, m, PhCH2CH2N, PhCHꢀCH
and CH2CH3), 5.45 (1H, d, J=8.8 Hz, PhCHꢀCH)
and 7.12–7.32 (10H, m, 2×Ph); lC (75 MHz; CDCI3)
12.43 (CH2CH3), 21.48 (CH2CH3), 38.51 and 56.04
(PhCH2CH2N), 59.14 (C-4), 67.55 (C-3), 126.16,
126.28, 126.58, 128.36, 128.53, 128.76, 133.47, 139.90
and 140.01 (2×Ph and C-2).
3.4. Reaction of (1-benzyl-2-ethyl-4-phenyl-1-
azabuta-1,3-diene)tricarbonyliron(0) 7 with lithium
diethylamide
n-Butyl-lithium (1.6 M; 0.81 ml, 1.30 mmol) was
added to a solution of diethylamine (0.09 ml, 1.28
mmol) in tetrahydrofuran (5 ml) at 0°C and the result-
ing solution was stirred at this temperature for 0.25 h
under an atmosphere of nitrogen. A solution of com-
plex 7 (0.10 g, 0.26 mmol) in tetrahydrofuran (5 ml)

58
T.N. Danks et al. / Journal of Organometallic Chemistry 579 (1999) 53–58
[2] M.J. Ackland, T.N. Danks, M.E. Howells, Tetrahedron Letts. 37
Acknowledgements
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The authors thank the EPSRC and Pharmacia and
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