Synthesis of azetidinylidene complexes from [(CO)5M(CH2Cl2)], phenylacetylene and imines and oxidative decomplexation to give β-lactams

Article abstract of DOI:10.1016/S0022-328X(99)00381-2

Photolysis of [M(CO)₆] in CH₂Cl₂ gives [(CO)₅M(CH₂Cl₂)]. Substitution of phenylacetylene for CH₂Cl₂ produces the thermolabile phenylacetylene complexes [(CO)₅

Full text of DOI:10.1016/S0022-328X(99)00381-2

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Journal of Organometallic Chemistry 588 (1999) 235–241
Synthesis of azetidinylidene complexes from [(CO)5M(CH2Cl2)],
phenylacetylene and imines and oxidative decomplexation to give
b-lactams
Mokhles M. Abd-Elzaher 1, Helmut Fischer *
Fakulta¨t fu¨r Chemie, Uni6ersita¨t Konstanz, Fach M727, D-78457 Konstanz, Germany
Received 28 April 1999
Abstract
Photolysis of [M(CO)6] in CH2Cl2 gives [(CO)5M(CH2Cl2)]. Substitution of phenylacetylene for CH2Cl2 produces the
thermolabile phenylacetylene complexes [(CO)5M(HCꢀCPh)] [M=Cr (1), Mo (2), W (3)]. Addition of N-alkyl benzylideneimines,
¸¹¹¹¹¹¹¹¹º
RNꢁC(Ph)H, to solutions of 1–3 affords the 2-azetidin-1-ylidene complexes [(CO)5MꢁCꢂNRꢂC(Ph)HꢂC(Ph)H] [M=Cr, Mo, W;
R=Et, i-Pr]. The reaction presumably proceeds by cycloaddition of the imines to the CꢁC bond of vinylidene complexes resulting
from tautomerization of the alkyne complexes. The cycloaddition is highly stereoselective. Predominantly, the syn isomer
is obtained (syn/anti]9). The reaction of 3 with dialkylcarbodimides, RNꢁCꢁNR (R=c-Hex, i-Pr), yields 3-imino-2-azetidin-
¸¹¹¹¹¹¹¹¹º
1-ylidene
complexes,
[(CO)5WꢁCꢂNRꢂC(ꢁNR)ꢂC(Ph)H].
By
oxidative
cleavage
of
the
CrꢁC
bond
in
¸¹¹¹¹¹¹¹¹º
[(CO)5CrꢁCꢂNRꢂC(Ph)HꢂC(Ph)H] the corresponding b-lactams are obtained in high yields. © 1999 Elsevier Science S.A. All
rights reserved.
Keywords: Azetidinylidene complexes; Oxidative decomplexation; b-lactams
posed as an intermediate in the reactions of pentacar-
bonyl[hydroxy(methyl)carbene]chromium with dicyclo-
1. Introduction
hexyl carbodiimide [3] and of tetramethylammonium
Vinylidene complexes may be regarded as
acetyl(pentacarbonyl)chromate toluene-4-sulfonyl chlo-
organometallic analogues of ketenes. Ketenes react with
ride/imines [4,5], to give azetidinylidene complexes
imines by cycloaddition to afford b-lactams [1]. The
reaction is generally carried out with ketenes of the
form R2CꢁCꢁO. It has not been successfully applied to
R(H)CꢁCꢁO, except when these are generated in situ by
decomposition of a diazo ketone [1a].
(Scheme 1).
The formation of azetidinylidene complexes by cy-
cloaddition of imines to the CꢁC bond of isolable or at
least spectroscopically detectable vinylidene complexes
has also been observed. [Cp(CO)(L)FeꢁCꢁCR2]+ [L=
Ketene complexes have been proposed as key inter-
mediates in the synthesis of b-lactams by photolysis of
carbene complexes in the presence of imines [2]. It has
been suggested that these ketene complexes arise from
photoinduced coupling of a carbonyl and the carbene
ligand in [(CO)5MꢁC(R1)R2] complexes.
The vinylidene complex [(CO)5CrꢁCꢁCH2] was pro-
* Corresponding author. Tel.: +49-7531-88-2783; fax: +49-7531-
88-3136.
E-mail address: hfischer@dg6.chemie.uni-konstanz.de (H. Fischer)
1 Present address: Inorganic Chemistry Department, National Re-
search Centre, PO 12622 Dokki, Cairo, Egypt.
Scheme 1.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00381-2

236
M.M. Abd-Elzaher, H. Fischer / Journal of Organometallic Chemistry 588 (1999) 235–241
P(OMe)3, PPh3; R=H, Me] adds MeNꢁC(H)Aryl and
thiazolines to give azetidinylidene complexes [5,6].
Analogously, azetidinylidene complexes of manganese
and rhenium have been prepared by cycloaddition of
imines to vinylidene complexes [7]. Usually, oxidative
decoordination of the four-membered ring yields b-lac-
tams in moderate to good yields. In addition to
chromium, manganese and rhenium vinylidene com-
plexes, the tungsten complex [(CO)5WꢁCꢁCPh2] has
also been shown to add imines and to afford aze-
tidinylidene complexes [8]. All organometallic routes
are either restricted with respect to the imine and the
vinylidene substituents (as in the case of the chromium
complex) or require multi-step procedures for the syn-
thesis of the starting vinylidene complexes.
Scheme 2.
NMR spectroscopy. However, the presence of the
vinylidene complex tautomers in solution is plausible
on the basis of trapping experiments with alcohols,
ynamines and alkoxyalkynes to give alkoxycarbene [10]
and cyclobutenylidene complexes [9], respectively.
The alkyne complexes/vinylidene complexes quickly
decompose in solution at temperatures above −20°C
(Cr, Mo) and 0°C (W). Therefore, they were not iso-
lated but only characterized by their IR and NMR
spectra. For the subsequent reactions with imines, the
solutions of the alkyne complexes were immediately
used after their volume had been reduced to a few
milliliters. The complex [(CO)5W(h2-HCꢀCPh)] has al-
ready earlier been isolated and fully characterized in-
cluding an X-ray structural analysis [9].
Recently we observed that [(CO)5W(HCꢀCR)] com-
plexes [readily obtained by reaction of alkynes with
photolytically generated [(CO)5W(CH2Cl2)] rapidly re-
act with ynamines, R1CꢀCNR22, to give cyclobutenyli-
¸¹¹¹¹¹¹¹¹¹º
dene complexes, [(CO)5WꢁCꢂCR1ꢁC(NR22)ꢂC(H)R] [9].
We proposed that the cyclobutenylidene complex was
formed by addition of the CꢀC bond of the alkyne to
the CaꢁCb bond of the vinylidene complexes
[(CO)5WꢁCꢁC(R)H] which are in equilibrium with their
alkyne complexes tautomers. Apart from their reactions
with ynamines, these vinylidene complexes have also
been trapped with alcohols to give alkoxycarbene com-
plexes [10]. The facile availability of such monosubsti-
tuted vinylidene complexes from the tautomerization of
terminal alkyne complexes should offer a convenient
route to azetidinylidene complexes.
2.2. Reactions with N-alkyl imines
Addition of two equivalents (relative to the starting
metal hexacarbonyls) of N-ethyl or N-isopropyl ben-
zylideneimine to concentrated solutions of 1/1%, 2/2% and
3/3%, respectively, afforded the 2-azetidin-1-ylidene com-
plexes 4a–6a, 4b and 6b by a formal [2+2] cycloaddi-
tion of the NꢁC bond of the imine to the CꢁC bond of
the vinylidene complex tautomers 1%, 2% and 3% (Scheme
3).
We now report on a novel approach to 2-azetidin-1-
ylidene complexes starting from [M(CO)6], phenyl-
acetylene and N-alkyl benzylideneimines and on the
oxidative decomplexation of the azetidinylidene ligand
of some representative examples to give b-lactams.
2. Results and discussion
2.1. Generation of pentacarbonyl(phenyl6inylidene)
complexes
Irradiation of the metal hexacarbonyls [M(CO)6] in
dichloromethane
at
−85°C
gives
pentacar-
bonyl(dichloromethane) complexes. Although, these are
unstable and cannot be isolated, solutions of
[(CO)5M(CH2Cl2)] can be handled at −80°C for short
periods of time. Addition of phenylacetylene affords the
phenylacetylene(pentacarbonyl) complexes 1–3 by sub-
stitution of the alkyne for coordinated dichloromethane
(Scheme 2). Presumably, in solution the alkyne com-
plexes are in equilibrium with their vinylidene complex
tautomers 1%–3% [9] (Scheme 2). The equilibrium is far
on the side of the alkyne complexes since it was not
possible to detect the vinylidene complexes by IR or
Scheme 3.

M.M. Abd-Elzaher, H. Fischer / Journal of Organometallic Chemistry 588 (1999) 235–241
237
The cycloaddition is regiospecific. The formation of
the regioisomeric 3-azetidinylidene complexes has not
1
been observed. The H-NMR data indicated that the
azetidinylidene complexes were obtained as mixtures of
two stereoisomers which could not be separated by
column chromatography. The ratio of isomers was
]9:1 and was almost independent of the metal and the
alkyl substituent on nitrogen. The resonances of the
protons bonded to the ring C(Ph) atoms of the major
isomer appeared as doublets at l=5.98–6.08 ppm and
4.37–4.42 ppm (3JH,H=4.2–4.6 Hz, each) suggesting a
syn arrangement of these protons. The coupling con-
stants for the corresponding signals of the minor isomer
3
were JH,H=1.2–1.6 Hz establishing that these protons
are anti to each other. Therefore, predominantly the
thermodynamically less stable syn isomers were formed.
An analogous preference for the formation of the syn
isomers was also observed in the reactions of imines
with ketenes to give b-lactams [11]. This suggests that
both reactions, the cycloaddition of imines to vinyli-
dene ligands and to ketenes, proceed by a similar
mechanism.
The reaction of the imines with the alkyne complexes
is very likely initiated by a nucleophilic addition of the
imine via the nitrogen lone electron pair to the Ca atom
of the vinylidene ligand to give a dipolar adduct A.
Adduct formation is followed by ring closure to form
the final product (Scheme 4). The synthesis of the
azetidinylidene complexes of iron [4–6], manganese [7],
rhenium [7], and tungsten [8] has also been suggested to
proceed by a similar stepwise mechanism. Two com-
plexes related to the proposed intermediate A (Scheme
2) have been isolated [5,6,8].
Scheme 5.
In contrast, no reaction was observed between 3/3% and
diarylcarbodiimides. This may be attributed to
mesomeric effects in these carbodiimides which reduce
the nucleophilicity of the nitrogen atom.
Again, the reaction is highly selective, regioisomers of
7 and 8 could not be detected. The H-NMR spectrum
of 8 shows one singlet for the hydrogen atom bonded to
the ring-C(sp2) atom and two septets and four well-sep-
arated doublets for the two isopropyl groups.
Analogously, complex 7 exhibits only one singlet for
the C(Ph)H atom. These data indicate that in solution
there is either only one isomer (with respect to the CꢁN
bond) present or there is a rapid interconversion of the
isomers.
1
2.4. Oxidati6e clea6age of the MꢁC bond
The oxidative cleavage of the metal–carbon bond
and the formation of b-lactams was investigated with
the examples of syn/anti-4a and syn/anti-4b. The reac-
tion of syn/anti-4a and syn/anti-4b with ammonium
ceric(IV) nitrate in acetone at room temperature af-
forded the b-lactams syn/anti-9a and syn/anti-9b in 83
and 84% yield (Scheme 6). The progress of the reaction
could be followed by IR spectroscopy. The NMR spec-
tra indicated that the decomplexation proceeded with-
out structural changes at the ring. The syn/anti ratio
was at least 9:1.
2.3. Reactions with carbodiimides
Substitution of dialkylcarbodimides for N-alkyl ben-
zylideneimines in the reaction with 3/3% afforded the
3-imino-2-azetidin-1-ylidene complexes 7 and 8 (Scheme
5), although in rather low yield [21% (7) and 10% (8)].
Scheme 6.
Scheme 4.

238
M.M. Abd-Elzaher, H. Fischer / Journal of Organometallic Chemistry 588 (1999) 235–241
3. Discussion
tams. The oxidative decomplexation proceeds with high
yield. Thus, the reaction sequence offers an interesting
These results demonstrate that azetidinylidene com-
plexes of chromium, molybdenum and tungsten are
readily obtained from commercially available [M(CO)6],
terminal alkynes and imines by a simple reaction se-
quence. Presumably, the key intermediate is a mono-
alternative route to b-lactams.
4. Experimental
substituted
vinylidene
complex
formed
by
4.1. General
tautomerization of [(CO)5M(HCꢀCPh)]. In earlier in-
vestigations, hydroxycarbene complexes (M=Cr) [2],
acetylchromate [4,5], carbyne complexes (M=Mn, Re)
[7], or benzylidene complexes [8] were employed as the
starting compounds for the generation of vinylidene
intermediates. Subsequent addition of the NꢁC bond of
the imine to the CꢁC bond of the vinylidene complex in
a stepwise fashion affords then the azetidinylidene com-
plexes. A two-step mechanism has also been proposed
for the addition of imines to ketenes to give b-lactams.
The proposal agrees well with the results of calculations
on the ketene/imine system [11]. A two-step mechanism
for the reaction of imines and carbodiimides with
vinylidene complexes is supported by the isolation of
dipolar vinylidene complex/imine adducts in the reac-
tion of [Cp(CO){P(OMe)3}FeꢁCꢁCMe2]+ with MeNꢁ
C(Ph)H [5] and of (CO)5WꢁCꢁCPh2 with PhNꢁC(Ph)H
[8]. On standing in solution, the adducts undergo cy-
clization.
In former studies usually symmetrically disubstituted
vinylidene complexes were employed giving 4-disubsti-
tuted complexes. An exception are the reactions of
N-phenyl benzylideneimine with the manganese com-
plexes [Cp(CO)2MnꢁCꢁC(R)H] (R=Me, Ph) derived
from carbyne complexes [7]. For R=Me, the
diastereoelectivity has been reported to range from 4:1
to 9:1 in favor of the anti isomer, the ratio depending
on the reaction conditions. For R=Ph, the formation
of a single diastereomer (anti ) was observed. Its
configuration was established by an X-ray structural
analysis. In contrast, the addition of imines to the
complexes 1–3 proceeds with a strong preference for
the formation of the thermodynamically less stable syn
isomer.
All operations were performed under an inert atmo-
sphere (nitrogen or argon) by using standard Schlenk
techniques. Solvents were dried by refluxing over CaH2
(CH2Cl2, pentane) or sodium–benzophenone ketyl
(Et2O) and were freshly distilled prior to use. The silica
gel used for chromatography (Baker, silica gel for flash
chromatography) was nitrogen saturated. The yields
refer to analytically pure compounds and were not
optimized. Instrumentation: 1H-NMR and 13C-NMR
spectra were recorded with a Bruker AC 250 or a
1
Bruker WM 250 spectrometer. H-NMR resonances of
solutions in CDCl3 are reported relative to TMS, those
of solutions in acetone-d6 and the 13C-NMR resonances
relative to the residual solvent peaks of acetone-d6 and
CDCl3. If not specifically mentioned, IR and NMR
spectra are recorded at room temperature (r.t.). IR:
Biorad FTS 60 spectrophotometer; MS: Finnigan MAT
312 (EI, 70 eV or FAB, NBOH). The peaks of the
tungsten complexes are listed with respect to 184W.
Elemental analyses: Heraeus CHN-O-RAPID. Photoly-
sis reactions were carried out in a duran glass apparatus
by using a mercury high pressure lamp (TQ 150, Fa.
Heraeus). The imines [12,13] were prepared according
to literature procedures.
4.2. General procedure for the synthesis of the
(phenylacetylene)metal complexes (1–3)
A solution of the hexacarbonyl metals [M(CO)6]
{2.84 mmol of [W(CO)6], 2.73 mmol of [Cr(CO)6], 3.79
mmol of [Mo(CO)6]} in ca. 300 ml of dichloromethane
was irradiated at −85°C while passing a slight stream
of nitrogen through the solution. The progress of the
reaction was controlled by IR spectroscopy. After ca.
90 min [M(CO)6] was converted to pentacar-
bonyl(dichloromethane)metal complexes as evidenced
by the disappearance of the characteristic w(CO) ab-
sorption of [M(CO)6] at ca. 1980 cm−1 and the appear-
ance of those of [(CO)5M(CH2Cl2)] (IR (CH2Cl2, 230
K): [(CO)5Cr(CH2Cl2)]: w(CO)=1885 m, 1936 vs, 2073
w cm−1; [(CO)5Mo(CH2Cl2)]: w(CO)=1885 m, 1942
vs, 2079 w cm−1; [(CO)5W(CH2Cl2]: wCO)=2076 w,
1934 vs, 1880 m cm−1). The resulting solutions were
immediately used for the subsequent reactions with
alkynes.
Analogously to N-alkyl benzylideneimines, carbodi-
imides also add to 3 giving the 3-imino-2-azetidin-1-yli-
dene complexes 7 and 8. These results contrast with
those obtained with [Cp(CO)2MnꢁCꢁC(Ph)H] and
[Cp(CO)2ReꢁCꢁCH2]. The rhenium complex was found
to react with RNꢁCꢁNR (R=i-Pr, t-Bu) by CꢁC/CꢁN
metathesis to give ketenimines, H2CꢁCꢁNR, and the
isocyanide complexes [Cp(CO)2ReꢂCꢀNR]. The reac-
tion of [Cp(CO)2MnꢁCꢁC(Ph)H] with (i-Pr)NꢁCꢁN(i-
Pr) did neither give an azetidin-1-ylidene complex nor
an isocyanide complex but rather an ansa-carbene com-
plex [9].
The CrꢁC bond in 4a,b can be cleaved oxidatively by
ammonium ceric(IV) nitrate in acetone to give b-lac-
Two equivalents (relative to the starting metal hex-
acarbonyls) of phenylacetylene were added at −80°C

M.M. Abd-Elzaher, H. Fischer / Journal of Organometallic Chemistry 588 (1999) 235–241
239
3
to the freshly prepared solution of [(CO)5M(CH2Cl2)]
(M=Cr, Mo, W). The solution was stirred for 10 min
at −80°C. Then the temperature was gradually raised
from −80 to −40°C [10°C/10 min]. The resulting
brown solution was concentrated at −30°C in vacuo to
a volume of ca. 5 ml. These highly concentrated solu-
tions containing the (phenylacetylene)pentacarbonyl
complexes 1–3 were used for the subsequent reactions
with imines. These (phenylacetylene)pentacarbonyl
complexes are unstable and quickly decompose at tem-
perature above −20°C (M=Cr, Mo) or 0°C (M=Cr).
2J=14.6 Hz, J=7.3 Hz, 1H, CHHMe), 1.33 (t, J=
7.3 Hz, Me); anti isomer: l=7.20–6.90 (m, 2 Ph), 5.35
(d, 3-CH), 4.10 (m, CHHMe), 3.84 (d, 4-CH), 3.45 (m,
CHHMe), 1.33 (t, Me). 13C-NMR (CDCl3): l=289.0
(C1), 222.9 (trans-CO), 217.4 (cis-CO, syn), 217.2 (cis-
CO, anti ), 133.6, 132.6, 130.0, 128.1, 127.7, 127.3, 126.4
(Ph), 79. 5 (C3, anti ), 77.5 (C3, syn), 67.3 (C4, anti ),
65.5 (C4, syn), 45.0 (NCH2, syn), 44.5 (NCH2, anti ),
13.5 (CH3, anti ), 12.6 (CH3, syn). MS: m/z (%)=427
(5) [M+], 343 (5) [M+-3CO], 287 (76) [M+ꢂ5CO]; 232
(13) [M+ꢂ5COꢂCNEt]. Anal. Found: C, 61.82; H, 4.21;
N, 3.60. C22H17CrNO5 (427.4) Calc.: C, 61.83; H, 4.01;
N, 3.28%.
4.2.1. Pentacarbonyl(phenylacetylene)chromium (1)
IR (CH2Cl2, 243 K): w(CO)=2010 m, 2075 m, 1956
vs, 1889 sh cm−1
.
4.3.2. Pentacarbonyl(N-isopropyl-3,4-diphenyl-2-aze-
tidin-1-ylidene)chromium (4b)
Yield 0.66 g (33% relative to [Cr(CO)6]), two isomers:
4.2.2. Pentacarbonyl(phenylacetylene)molybdenum (2)
IR (CH2Cl2, 243 K): w(CO)=2084 s, 1959 sh, 1939
syn/anti \9:1. IR (CH2Cl2): w(CO)=2056 m, 1936 vs
vs cm−1
.
cm−1 1H-NMR (CDCl3): syn isomer: l=7.56–7.06
.
(m, 10 H, 2 Ph), 6.07 (d, J=4.6 Hz, 1H, 3-CH), 4.73
(sept, J=6.8 Hz, 1H, CHMe2), 4.41 (d, J=4.6 Hz, 1H,
4-CH), 1.41 (d, J=6.7 Hz, Me), 1.36 (d, J=6.8 Hz,
3H, Me); anti isomer: l=7.56–7.06 (m, 2 Ph), 5.38 (d,
J ca. 1.5 Hz, 3-CH), 4.5 (sept, CHMe2), 3.92 (d, J ca.
1.5 Hz, 4-CH), 1.52 (d, J=6.7 Hz, Me), 1.00 (d, J=6.8
Hz, Me);. 13C-NMR (CDCl3): syn isomer: l=290.5
(C1), 222.9 (trans-CO), 217.6 (cis-CO), 134.1, 133.4,
130.3, 128.4, 128.0, 127.8, 127.5, 127.3 (2 aryl), 77.5
(C3), 65.5 (C4), 54.8 (N-CHMe2), 22.7, 20.5 (2 Me).
MS: m/z (%)=441 (2) [M+], 357 (2) [M+ꢂ3CO], 301
(41) [M+ꢂ5CO], 259 (45) [M+ꢂ5COꢂCMe2], 206 (48)
[M+ꢂCr(CO)5ꢂCMe2H]. Anal. Found: C, 62.55; H,
4.64; N, 3.23. C23H19CrNO5 (441.4) Calc.: C, 62.59; H,
4.34; N, 3.17%.
4.2.3. Pentacarbonyl(phenylacetylene)tungsten (3)
IR (CH2Cl2, 243 K): w(CO)=2085 m, 1955 vs, 1933
1
sh cm−1. H-NMR (CDCl3, 243 K): l=7.52–6.73 (m,
5H, aryl), 6.15 (s, 1H, ꢀCH). 13C-NMR ( CDCl3, 243
K): l=203.4 (trans-CO), 195.8 (cis-CO), 131.3, 128.9,
128.2, 125.7 (aryl), 64.6 (ꢀCꢂPh), 57.5 (ꢀCꢂH)
4.3. Reactions of [(CO)5M(HCꢀCPh)] with N-alkyl
imines
At −30°C N-ethyl benzylideneimine or N-isopropyl
benzylideneimine [two equivalents relative to the start-
ing M(CO)6] was added to the highly concentrated
solutions of the alkyne complexes 1, 2, or 3. The
solution was stirred and gradually warmed to r.t. The
reaction was followed by IR spectroscopy. When the
w(CO) absorptions due to the alkyne complexes had
disappeared the solvent was removed in vacuo to give a
brown oil. The reaction products were chro-
matographed at −30°C on neutral Al2O3 or silica gel.
First, unreacted [M(CO)6] and imine were eluted with
pentane. Next, with pentane–dichloromethane (10:3) a
yellow band containing the azetidinylidene complexes
was eluted. Removal of the solvent in vacuo gave the
complexes 4a–6a, 4b, and 6b which were characterized
4.3.3. Pentacarbonyl(N-ethyl-3,4-diphenyl-2-azetidin-1-
ylidene)molybdenum (5a)
Yield 0.25 g (14% relative to [Mo(CO)6]), two iso-
mers: 90% syn, 10% anti. IR (CH2Cl2): w(CO)=2064
1
m, 1934 vs cm−1. H-NMR (CDCl3): syn isomer: l=
7.70–6.94 (m, 10H, 2 Ph), 6.08 (d, J=4.4 Hz, 1H,
2
3-CH), 4.38 (d, J=4.2 Hz, 1H, 4-CH), 4.15 (dq, J=
3
2
14.6 Hz, J=7.3 Hz, 1H, CHHMe), 3.77 (dq, J=14.6
3
Hz, J=7.3 Hz, 1H, CHHMe), 1.38 (t, J=7.3 Hz, 3H,
Me). H-NMR (CDCl3): anti isomer: l=7.70–6.94 (m,
1
1
by their IR, MS, H-NMR and 13C-NMR spectra, and
by elemental analysis.
10H, 2 Ph), 5.41 (d, J=1.5 Hz, 3-CH), 4.00 (dq,
3
2J=14.6 Hz, J=7.3 Hz, CHHMe), 3.97 (d, J=1.5
4.3.1. Pentacarbonyl(N-ethyl-3,4-diphenyl-2-
azetidin-1-ylidene)chromium (4a)
Yield 0.59 g (30% relative to [Cr(CO)6]), two isomers:
Hz, 4-CH), 3.47 (dq, 2J=14.6 Hz, 3J=7.3 Hz,
CHHMe), 1.36 (t, J=7.3 Hz, Me). 13C-NMR (CDCl3):
l=281.5 (C1), 212.8, (trans-CO), 206.5 (cis-CO, syn),
206.4 (cis-CO, anti ), 133.9, 132.6, 132.1, 130.0, 129.8,
129.5, 129.4, 129.0, 128.8, 128.3, 127.8, 127.3, 127.1,
126.6 (4 Ph), 83.6 (C3, syn), 77.5 (C3, anti ), 66.6 (C4,
anti ), 65.0 (C4, syn), 45.9 (NCH2, syn), 45.4 (NCH2,
anti ), 13.2 (Me, anti ), 12.9 (Me, syn). MS: m/z (%)=
syn/anti ratio \95:5. M.p. 123°C. IR (CH2Cl2):
1
w(CO)=2056 m, 1936 vs cm−1. H-NMR (CDCl3): syn
isomer: l=7.20–6.90 (m, 10 H, 2 Ph), 6.04 (d, J=4.6
Hz, 1H, 3-CH), 4.42 (d, J=4.5 Hz, 1H, 4-CH), 4.24
2
3
(dq, J=14.6 Hz, J=7.3 Hz, 1H, CHHMe), 3.80 (dq,

240
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473 (6) [M+], 389 (12) [M+ꢂ3CO], 333 (9) [M+ꢂ5CO],
278 (100) [M+ꢂ5COꢂCNEt]. Correct elemental analysis
could not be obtained probably due to unseparable
impurities.
products were carried out analogously to those with
imines. The resulting complexes 7 and 8 were character-
1
ized by IR, MS, H-NMR and 13C-NMR spectroscopy
and by elemental analysis.
4.3.4. Pentacarbonyl(N-ethyl-3,4-diphenyl-2-azetidin-1-
ylidene)tungsten (6a)
Yield 0.49 g (31% relative to [W(CO)6]), two isomers:
4.4.1. Pentacarbonyl(N-cyclohexyl-3-cyclohexylimino-
4-phenyl-2-azetidin-1-ylidene)tungsten (7)
Yield 0.38 g (21% relative to [W(CO)6]). M.p. 132°C.
IR (CH2Cl2): w(CO)=2066 m, 1933 vs cm−1. 1H-NMR
(CDCl3): d=7.68–7.10 (m, 5H, aryl), 4.58 (s, 1H,
4-CH), 4.00 (m, br, 1H, NCH), 2.90 (m, br, 1H, NCH),
2.28–0.84 (m, br, 20H, 2 cyclohexyl). 13C-NMR
(CDCl3): l=270.5 (C1), 203.7 (trans-CO), 196.4 (cis-
CO), 153.5 (C3), 133.4, 129.2, 128.4, 128.1 (Ph), 72.2
(C4), 62.7, 57.2 (NCH), 34.2, 33.0, 30.4, 29.8, 25.5,
25.4, 25.3, 24.9, 24.0, 23.8 (CH2). MS: m/z (%)=632
(0.6) [M+], 548 (2) [M+ꢂ3CO], 492 (1) [M+ꢂ5CO], 327
(3) [M+ꢂ5CO-2 cyclohexyl], 117 (100) [M+ꢂW(CO)5ꢂ2
cyclohexyl]. Anal. Found: C, 48.91; H, 4.78; N, 4.16.
C26H28N2O5W (632.4) Calc.: C, 49.38; H, 4.46; N,
4.43%.
90% syn, 10% anti. M.p. 124°C, IR (CH2Cl2): w(CO)=
1
2064 m, 1927 vs cm−1. H-NMR (CDCl3): syn isomer:
l=7.43–6.95 (m, 10H, 2 Ph), 6.03 (d, J=4.5 Hz, 1H,
2
3-CH), 4.41 (d, J=4.4 Hz, 1H, 4-CH), 4.14 (dq, J=
3
2
14.6 Hz, J=7.3 Hz 1H, CHHMe), 3.74 (dq, J=14.0
3
Hz, J=7.0 Hz 1H, CHHMe), 1.39 (t, J=7.3 Hz, 3H,
Me). H-NMR (CDCl3) anti isomer: l=7.43–6.95 (m,
1
2 Ph), 5.42 (d, J=1.2 Hz, 3-CH), 3.95 (m, CHHMe),
3.80 (d, 4-CH), 3.40 (m, CHHMe), 1.34 (t, J=7.3 Hz,
Me). 13C-NMR (CDCl3): l=267.2 (C1), 202.9 (trans-
CO), 197.6 (cis-CO, JWC=80.4 Hz, syn), 197.3 (cis-
CO, anti ), 133.7, 132.7, 130.0, 128.5, 128.3, 127.9,
127.4, 126.5 (2 Ph), 77.5 (C3), 68.4 (C4, anti ), 65.9 (C4,
syn), 46.2 (CH2, syn), 45.5 (CH2, anti ), 13.1 (Me, anti ),
12.8 (Me, syn). MS: m/z (%)=559 (7) [M+], 475 (15)
[M+ꢂ3CO], 419 (18) [M+ꢂ5CO], 364 (100)
[M+ꢂ5COꢂCNEt], 178 (40) [M+ꢂ5COꢂCNEtꢂWꢂ2H].
Anal. Found: C, 47.25; H, 3.06; N, 2.50. C22H17NO5W
(559.2) Calc.: C, 7.12; H, 3.19; N, 2.56%.
4.4.2.
Pentacarbonyl(N-isopropyl-3-isopropylimino-
4-phenyl-2-azetidin-1-ylidene)tungsten (8)
Yield 0.16 g (10% relative to [W(CO)6]). IR (CH2Cl2):
w(CO)=2069 m, 1928 vs cm−1 1H-NMR (CDCl3):
.
l=7.51–7.14 (m, 5H, aryl), 4.64 (s, 1H, 4-C), 4.45
(sept, J=6.8 Hz, 1H, CHMe2), 3.29 (sept, J=6.3 Hz,
1H, CHMe2), 1.71 (d, 3H, J=6.5 Hz, Me), 1.65 (d, 3H,
J=6.5 Hz, Me), 1.09 (d, 3H, J=5.8 Hz, Me) 0.84 (d,
3H, J=6.0 Hz, Me). 13C-NMR (CDCl3): l=270.6
(C1), 204.8 (trans-CO), 196.3 (cis-CO), 153.3 (C3),
133.7, 129.3, 128.5, 128.2 (aryl), 72.4 (C4), 55.0, 49.9
(CHMe2), 29.7, 24.2, 23.1, 20.4 (Me). MS: m/z (%)=
552 (2) [M+], 468 (4) [M+ꢂ3CO], 412 (7) [M+ꢂ5CO],
367 (10) [M+ꢂ5COꢂHꢂPr], 300 (10) [M+ꢂ5COꢂHꢂiPr],
300 (10) [M+ꢂ5COꢂHꢂiPrꢂCꢁNꢂiPr]. Correct elemental
analysis could not be obtained probably due to the
unseparable impurities.
4.3.5.
Pentacarbonyl(N-isopropyl-3,4-diphenyl-2-aze-
tidin-1-ylidene)tungsten (6b)
Yield 0.62 g (38% relative to [W(CO)6]), two isomers:
90% syn, 10% anti. M.p. 158°C. IR (CH2Cl2): w(CO)=
1
2068 m, 1925 vs cm−1. H-NMR (CDCl3): syn isomer:
l=7.40–7.02 (m, 10H, 2 Ph), 5.98 (d, J=4.6 Hz, 1H,
3-CH), 4.57 (sept, 1H, J=6.7 Hz, CHMe2), 4.37 (d,
J=4.6 Hz, 1H, 4-CH), 1.41 (d, J=6.7 Hz, 3H, Me),
1
1.33 (d, J=6.8 Hz, 3H, Me). H-NMR (CDCl3) anti
isomer: l=7.40–7.02 (m, 2 Ph), 5.39 (d, J=1.6 Hz,
3-CH), 4.42 (sept, CHMe2), 3.87 (d, J=1.6 Hz, 4-CH),
1.47 (d, J=6.7 Hz, Me), 1.01 (d, J=6.8 Hz, Me).
13C-NMR (CDCl3): l=267.7 (C1), 202.9 (trans-CO),
197.8 (JWC=128.1 Hz, cis-CO, syn), 197.4 (cis-CO,
anti ), 134.1, 133.4, 130.2, 129.2,129.0, 128.0, 127.6,
127.3 (2 Ph), 77.5 (C3), 67.4 (C4, anti ), 65.5 (C4, syn),
55.9 (CHMe2, syn), 53.0 (CHMe2, anti ), 22.4, 20.4 (2
Me, syn), 21.3, 21.0 (2 Me, anti ). MS: m/z (%)=573
(3) [(M+], 489 (10) [M+ꢂ3CO], 364 (100)
[M+ꢂ5COꢂCNPr], 179 (19) [M+ꢂW(CO)5ꢂCNPrꢂH].
Anal. Found: C, 48.19; H, 3.36; N, 2.44. C23H19NO5W
(573.3) Calc.: C, 48.20; H, 3.26; N, 2.42%.
4.5. Oxidation of 4a,b to form the i-Lactams 9a,b
Ca. 4.0 g of silica gel was added to a solution of 0.30
g syn/anti-4a [0.70 mmol] or syn/anti-4b [0.68 mmol] in
100 ml of acetone. The slurry was vigorously stirred
and 0.60 g of ammonium ceric(IV) nitrate was added.
The mixture was stirred for 2–3 days at r.t. until the IR
spectrum indicated that the complexes 4a and 4b, re-
spectively, were completely consumed. The mixture was
filtered. The solvent of the filtrate was removed in
vacuo to give the b-lactams as colorless oils.
4.4. Reactions of complex 3 with carbodiimides
4.5.1. syn/anti-N-Ethyl-3,4-diphenylazetidin-1-one (9a)
Yield 0.24 g (81% relative to complex 4a). IR
The reactions of complex 3 with carbodiimides
[RNꢁCꢁNR; R, R=cyclohexyl, isopropyl] in 3–4 ml of
CH2Cl2 and the subsequent purification of the reaction
1
(CH2Cl2): w(CO)=1746 vs cm−1. H-NMR (CDCl3):
l=7.47–6.91 (m, 10H, 2 aryl), 4.96 (d, 1H, J=5.6 Hz,

M.M. Abd-Elzaher, H. Fischer / Journal of Organometallic Chemistry 588 (1999) 235–241
241
2
Chemistry of Ketenes, Allenes, and Related Compounds, Wiley,
New York, 1980, p. 279ff. (c) T.T. Tidwell, Ketenes, Wiley, New
York, 1995.
3-CH), 4.74 (d, 1H, J=7.6 Hz, 4-CH), 3.60 (dq, J=
3
2
15.2 Hz, J=5.6 Hz, 1H, CH2), 3.00 (dq, J=15.2 Hz,
3J=7.6 Hz, 1H, CH2), 1.09 (t, J=7.6 Hz, 3H, Me).
13C-NMR (CDCl3): l=167.9 (CꢁO), 135.2, 132.8,
128.6, 128.0, 127.9, 127.8, 127.4, 126.7 (2 aryl), 60.5
(C3), 59.8 (NCH2), 35.5 (C4), 12.7 (Me). MS: m/z
(%)=251 (7) [M+], 180 (100) [M+ꢂC(O)NEt], 90 (31)
[M+ꢂC(O)NEtꢂC(H)Ph].
[2] (a) L.S. Hegedus, Pure Appl. Chem. 62 (1990) 691. (b) L.S.
Hegedus, R. Imwinkelried, M. Alarid-Sargent, D. Dvorak, Y.
Satoh, J. Am. Chem. Soc. 112 (1990) 1109 and literature cited
therein. (c) L.S. Hegedus, Transition Metals in the Synthesis of
Complex Organic Molecules, University Science Book, Mill Val-
ley, 1994, p. 174ff.
[3] K. Weiss, E.O. Fischer, J. Mu¨ller, Chem. Ber. 107 (1974) 3548.
[4] A.M.G. Barrett, C.P. Brock, M.A. Sturgess, Organometallics 4
(1985) 1903.
[5] A.M.G. Barrett, J. Mortier, M. Sabat, M.A. Sturgess,
Organometallics 7 (1988) 2553.
[6] (a) A.M.G. Barrett, M.A. Sturgess, Tetrahedron Lett. 27 (1986)
3811. (b) A.G.M. Barrett, M.A. Sturgess, J. Org. Chem. 52
(1987) 3940.
4.5.2. syn/anti-N-Isopropyl-3,4-diphenylazetidin-1-one
(9b)
Yield 0.25 g (84% relative to complex 4b). IR
(CH2Cl2): w(CO)=1742 vs cm−1. H-NMR (CDCl3):
1
l=7.47–6.91 (m, 10H, 2 aryl), 5.02 (d, 1H, J=5.6 Hz,
3-CH), 4.76 (d, 1H, J=5.6 Hz, 4-CH), 3.87 (s, J=6.7
Hz, 1H, CHMe2), 1.36, 1.15 (2 t, J=6.7 Hz, 3H, Me).
13C-NMR (CDCl3): l=167.9 (CꢁO), 135.2, 132.8,
128.6, 128.0, 127.9, 127.8, 127.4, 126.7 (2 Ph), 60.5
(C3), 59.8 (CHMe2), 35.5 (C4), 12.7 (Me). MS: m/z
(%)=265 (3) [M+], 180 (100) [M+ꢂC(O)NiPr].
[7] M.R. Terry, L.A. Mercando, C. Kelley, G.L. Geoffroy, P.
Nombel, N. Lugan, R. Mathieu, R.L. Ostrander, B.E. Owens-
Waltermire, A.L. Rheingold, Organometallics 13 (1994) 843.
[8] H. Fischer, A. Schlageter, W. Bidell, A. Fru¨h, Organometallics
10 (1991) 389.
[9] H. Fischer, H.-P. Volkland, A. Fru¨h, R. Stumpf, J. Organomet.
Chem. 491 (1995) 267.
[10] (a) A. Parlier, H. Rudler, J. Chem. Soc. Chem. Commun. (1986)
514. (b) H. Le Bozec, C. Cosset, P.H. Dixneuf, J. Chem. Soc.
Chem. Commun. (1991) 881.
Acknowledgements
Support of these investigations by the Deutscher
Akademischer Austauschdienst (grant for M.M.A.-E.),
the Volkswagen-Stiftung and the Fonds der Chemis-
chen Industrie is gratefully acknowledged.
[11] (a) L.S. Hegedus, J. Montgomery, Y. Narukawa, D.C. Snustad,
J. Am. Chem. Soc. 113 (1991) 5784. (b) C. Palomo, F.P. Coss´ıo,
C. Cuevas, B. Lecea, A. Mielgo, P. Roma´n, A. Luque, M.
Martinez-Ripoll, J. Am. Chem. Soc. 114 (1992) 9360. (c) F.P.
Coss´ıo, J.M. Ugalde, X. Lopez, B. Lecea, C. Palomo, J. Am.
Chem. Soc. 115 (1993) 995. (d) F.P. Coss´ıo, A. Arrieta, B. Lecea,
J.M. Ugalde, J. Am. Chem. Soc. 116 (1994) 2085 and literature
cited therein.
References
[12] R.W. Layer, Chem. Rev. 63 (1963) 489.
[13] F. Texier-Boullet, Synthesis (1985) 679.
[1] (a) J. March, Advanced Organic Chemistry, 3rd edition, Wiley,
New York, 1985, p. 869. (b) W.T. Brady, in: S. Patai (Ed.), The
.