(Diazomethyl)silyl-functionalized Fischer-type carbene complexes

Article abstract of DOI:10.1016/S0022-328X(00)00616-1

The synthesis of two types of so far unknown title compounds is described. Carbene complexes L_nM=C(R)O-SiR₂-C(N₂)COOMe [L_nM=(OC)₅W (3), (OC)₅Cr (4), (OC)₅Mo (5), (MeCp)(OC)₂Mn (6)] were obtained from the corresponding acyl metalates by electrophilic (diazomethyl)silylation. Similarly, (diazomethyl)silylation of lithiated dicarbonyl(η ⁵-methylcyclopentadienyl)(1-ethoxyethylidene)manganese yielded a manganese carbene complex (8a) with CH₂-SiR₂-C(N₂)COOMe substitution.

Full text of DOI:10.1016/S0022-328X(00)00616-1

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 617–618 (2001) 339–345
(Diazomethyl)silyl-functionalized Fischer-type carbene complexes
Gerhard Maas *, Dieter Mayer 1
Abteilung Organische Chemie I, Uni6ersita¨t Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
Received 17 July 2000
Abstract
The synthesis of two types of so far unknown title compounds is described. Carbene complexes LnMꢀC(R)OꢁSiR2ꢁ
C(N2)COOMe [LnMꢀ(OC)5W (3), (OC)5Cr (4), (OC)5Mo (5), (MeCp)(OC)2Mn (6)] were obtained from the corresponding acyl
metalates by electrophilic (diazomethyl)silylation. Similarly, (diazomethyl)silylation of lithiated dicarbonyl(h5-methylcyclopentadi-
enyl)(1-ethoxyethylidene)manganese yielded a manganese carbene complex (8a) with CH2ꢁSiR2ꢁC(N2)COOMe substitution.
© 2001 Elsevier Science B.V. All rights reserved.
Keywords: Fischer-type carbene complexes; Diazo compounds; Silyl triflates
1. Introduction
2. Results and discussion
Aliphatic diazo compounds are undoubtedly the
most important and versatile carbene transfer reagents
[1]. While their photochemical and thermal dediazonia-
tion provide access to free carbenes, N2 extrusion by
transition-metal catalysts [2] (especially based on Cu,
Rh, Pd, and Ru) generates short-lived metal–carbene
complexes which may also be considered as metal-stabi-
lized carbenium ions and which represent the proper
carbene-transfer reagents. The analogy, both in elec-
tronic structure and reactivity, between these intermedi-
ate metal–carbene complexes and the stable carbene
complexes of the Fischer type [3] is undeniable. Perhaps
the most obvious manifestation of Fischer-type carbene
complexes to act as carbene transfer reagents is their
ability to cyclopropanate olefinic substrates [4].
2.1. (Diazomethyl)silyloxy-substituted carbene
complexes
Complexes of this type were prepared according to
the classical recipe to prepare alkoxycarbene [3,6] and
siloxycarbene [7] complexes of chromium, molybde-
num, and tungsten, namely nucleophilic alkylation of
M(CO)6 followed by electrophilic O-alkylation (O-silyl-
ation) of the acyl metalate intermediate. For our pur-
pose, we used silyl triflate (1) [8] as an electrophilic
(diazomethyl)silylation reagent.
Previous to our work [5], the synthesis of diazo-func-
tionalized Fischer-type carbene complexes, featuring
the combination of two familiar carbene transfer func-
tions in one molecule, has not been reported. We
present here the synthesis of Fischer-type carbene com-
plexes in which a diazomethyl function is separated
from the carbenic carbon atom by either an OSiR2 or a
CH2SiR2 unit.
Silyl triflate (1) was added at −40°C to a suspension
of the yellow acetyl tungstate (2a), obtained from hexa-
carbonyltungsten and methyl lithium (Scheme 1). When
this mixture was allowed to assume 0°C, a deep-
red color indicative of the tungsten carbene complex
(3a) developed which was isolated as a solid in 12%
yield by evaporation of the volatiles and extraction into
pentane at −20°C. The IR spectrum of 3a confirmed
the presence of a diazo function (w(N2)=2080 cm−1
)
* Corresponding author. Tel./fax: +49-731-5022790.
and a W(CO)5 moiety (w(CO)=2060, 1974, 1941
E-mail address: gerhard.maas@chemie.uni-ulm.de (G. Maas).
1 New address: Merck KGaA, D-64271 Darmstadt, Germany.
cm−1). The 13C-NMR chemical shifts of WꢀC (l=
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00616-1

340
G. Maas, D. Mayer / Journal of Organometallic Chemistry 617–618 (2001) 339–345
bon atom enhances the thermodynamic stability of the
latter considerably [9]. Therefore, we chose to prepare
4-anisyl-substituted chromium (4) and molybdenum (5)
carbene complexes as shown in Scheme 2. In both
cases, however, this procedure was disappointingly inef-
fective. Complex 4 could be extracted in low yield from
the reaction mixture with pentane at −10°C, but not in
pure form. The presence of 4 was established by the
13C-NMR signal at l=348.4 ppm (CrꢀC) and the
molecular ion peak in the EI mass spectrum (m/z=
540). Complex 5 was obtained in low yield (5%) as a
dark-red oil after column chromatography on silica gel
at −30°C; a sample that was stored at −78°C under-
went decomposition already after a few days as indi-
cated by a color change from red to black. The
13C-NMR spectrum at −20°C showed, besides some
impurities (signals in the aliphatic and aromatic region),
the presence of two metal carbene species, most likely
again the s-trans- and s-cis-isomers with respect to the
CcarbeneꢁO bond, characterized by chemical shifts at
l=323.0/327.0 (MoꢀC), 213.8/215.7 (trans-CO) and
207.0/206.8 ppm (cis-CO).
Scheme 1.
Scheme 2.
345.6 ppm), cis-CO (198.1 ppm) and trans-CO (206.1
ppm) are in close agreement with the values reported
for the related carbene complex (OC)5WꢀC(Me)OSiMe3
[7]. In the 13C-NMR spectrum, recorded at −10°C in
toluene-d8, a second, less intense set of signals was
present (l=344.2, 204.8, 198.8 ppm for the carbon
atoms mentioned before). As for other carbene com-
plexes [9], this points to the presence of s-trans- and
s-cis-isomers with respect to the CcarbeneꢁO bond, and
similar to complexes of the type (OC)5CrꢀC-
(Ph)OSi(iPr2)OR [10] it may be assumed that the s-
trans-isomer prevails. Line broadening of the signals of
the diazo and ester carbon atoms indicates that another
dynamic process, namely rotation around the
C(N2)ꢁC(ꢀO) bond, is also slowed down at this temper-
ature.
The difficulty in isolating carbene complexes 3–5 and
their thermolability is not totally unexpected. Since
complexes of the type (OC)5WꢀC(Ar)OSiMe3 are
known to undergo readily a nucleophile-assisted cleav-
age of the OꢁSi bond [7,11], it cannot be excluded that
3–5 behave similarly, in spite of the presence of the
i
bulkier Pr substituents at silicon, under the conditions
of chromatographic workup and in the presence of
traces of water in general. The thermolability may have
several causes, one of them being the intrinsic incom-
patibility of the metal carbene and the diazo functional-
ities. The MꢀC bond in carbene complexes of Cr, Mo,
and W is strongly polarized, and the electrophilic car-
bon may induce diazo decomposition by interaction
with the nucleophilic diazo carbon atom. In fact, it is
known that the stable tungsten carbene complex
(OC)5WꢀC(OMe)Ph is able to eliminate N2 from di-
azoalkanes and ethyl diazoacetate [12]. Therefore, our
attention was drawn to dicarbonyl(cyclopentadienyl)-
manganese carbene complexes. Since the Cp(CO)2Mn
fragment is a stronger p donor than the pentacarbonyl
metal moiety, the bond order of the MnꢀC bond
is higher and the carbon atom is less electrophilic
[13]. Consequently, manganese complexes are far less
reactive across the metal–carbene bond than the
M(CO)5 carbene complexes of Cr, Mo, and W [14]. In
the literature, a few siloxy-substituted manganese car-
bene complexes have been described as viscous red oils
of limited stability [14b,15].
According to the 13C-NMR spectrum, complex 3a
contained small amounts of impurities. However,
purification was not possible since 3a did not survive
column chromatography at −30°C on silica gel or
alumina and since it rapidly underwent unspecific de-
composition above 0°C. The related benzylidenetung-
sten complex (3b), prepared similarly to 3a, is also
thermolabile above 0°C. In contrast to 3a, it could be
recovered partially after passing a silica gel column at
−30°C, but this method did not allow a complete
separation from impurities. In the 13C-NMR spectrum,
the signals at l=322.9 (WꢀC), 197.1 (cis-CO), and
203.4 ppm (trans-CO) confirm the presence of the metal
carbene functionality.
Reaction of tricarbonyl(methylcyclopentadienyl)-
manganese with an organolithium compound followed
by silylation with 1 afforded manganese carbene com-
plexes (6a–f) as viscous deep-red oils (Scheme 3, Table
1) which could by handled indeed more easily
Tungsten carbene complexes typically have a higher
thermal stability than the related complexes of
chromium and molybdenum [4,9]; however, an elec-
tron-donating aromatic substituent at the carbenic car-

G. Maas, D. Mayer / Journal of Organometallic Chemistry 617–618 (2001) 339–345
341
The constitution of 6a–f is fully supported by their
IR, NMR, and mass spectra. The IR spectra show
intense absorptions caused by the stretching vibrations
of the diazo group (w=2080–2100 cm−1) and the
carbonyl ligands (1940–1970 and 1880–1900 cm−1).
The 13C-NMR spectra could be recorded in CDCl3 at
25°C, and their diagnostic signals are given in Table 1.
Other than in the case of 3a and 5, a second isomer
(due to slow rotation around the CcarbeneꢁO bond) was
not observed when the 13C-NMR spectra were recorded
at −2595°C; only dynamic line broadening of the
CN2 and COOMe signals was noted in some cases. The
occurrence of separate signals for each of the two
carbonyl ligands in the case of 6e and f is unusual; it
indicates that the mirror plane of the (MeCp)Mn(CO)2
fragment does not extend to the carbene ligand. It is
known that complexes of the types CpMn(CO)2ꢀC-
(OR1)R2 (R2ꢀPh [13a,14b], vinyl [16]) and (h5-cyclo-
hexadienyl)Mn(CO)2ꢀC(OEt)aryl [17]) in the solid state
exhibit a variety of different conformations around the
three bonds involving the Ccarbene atom. In the case of
aryl and hetaryl-substituted complexes 6c–f, steric in-
teractions between the bulky SiiPr2 group and neigh-
boring groups are minimized when an s-trans
conformation at the CcarbeneꢁO bond is given and when
at the same time the (het)aryl ring is approximately
perpendicular to the OꢁCcarbeneꢁC(het)aryl plane. In this
conformation, the two isopropyl substituents at Si may
still prevent the 2-furyl and 2-pyrrolyl ring from rotat-
ing, thus rendering the two carbonyl groups
diastereotopic even when the conformation around the
MnꢁCcarbene bond is the most common one in such
manganese carbene complexes [13a], namely with the
ChetarylꢁCcarbeneꢁO plane bisecting the OCꢁMnꢁCO an-
gle. It should be added that temperature-dependent
13C-NMR spectra between −25 and+30°C did not
reveal a dynamic exchange for the two CO signals.
Mass spectra (CI mode) of 6c and e showed the
molecular ion as the base peak. Similar to other siloxy-
carbene complexes with the (MeCp)(CO)2Mn moiety
[15], it appears that the two carbonyl ligands are lost in
one step, and a fragment formed by loss of 2CO and N2
was also observed.
than complexes 3–5. Purification by column chro-
matography on silica gel at −30°C should be possible
in principle, but we found it necessary to make a
compromise between keeping the loss of product (by
decomposition on the column) low and achieving a
complete separation of 6 from residual (MeCp)Mn-
(CO)3. Therefore, in almost all cases no satisfactory
elemental analyses could be obtained. Complexes
6 are rather thermally stable at 25°C, but must be
handled with rigorous exclusion of moisture and air.
On prolonged storing, paramagnetic impurities are
formed which cause considerable line broadening in the
NMR spectra of such samples but can be removed by
filtering their solutions over a pad of kieselguhr.
Scheme 3.
Table 1
Diagnostic 13C-NMR signals of manganese carbene complexes 6
(CDCl3, l/ppm)
6
R
MnꢀC MnꢁCO CN2 COOMe
a
b
c
d
e
Me
Bu
Ph
339.6
346.6
334.0
327.9
348.3
232.8
232.8
231.9
232.2
232.5
234.4
232.0
232.2
44.0 168.5
44.6 168.5
44.2 168.5
44.8 167.9
45.0 164.0
4-Methoxyphenyl
2-Furyl
f
1-Methylpyrrol-2-yl
324.3
44.5 169.4
2.2. (Diazomethyl)silylmethyl-substituted carbene
complexes
The approach to these complexes takes advantage of
the CꢁH acidity of alkyl-substituted Fischer carbene
complexes [16,18]. Deprotonation of 7a with butyl
lithium followed by C-silylation with (trifloxysilyl)-
diazoacetate (1) provided the organometallic diazoac-
etate (8a) (Scheme 4) which was obtained as a deep-red
oil after chromatographic purification on silica gel at
−30°C. The compound is stable in substance and in
dry non-protic solvents at least for several weeks. The
Scheme 4.

342
G. Maas, D. Mayer / Journal of Organometallic Chemistry 617–618 (2001) 339–345
composition of 8a follows from the analytical and
spectroscopic data. The IR spectrum showed the ex-
pected absorptions for the stretching vibrations of the
diazo group (2080 cm−1) and the two carbonyl ligands
(1940, 1875 cm−1). In the 13C-NMR spectrum, the
resonance of the carbenic carbon atom (l=337.9 ppm)
appeared at slightly lower field (ca. 2 ppm) than in 7a.
4.1. Preparation of silyl triflate (1)
The literature procedure [8] was modified as follows:
a
stirred solution of diisopropylsilyl bis(trifluoro-
methanesulfonate) (2.04 g, 1.46 ml, 5.0 mmol) in pen-
tane (20 ml) was cooled at 0°C, and a solution of
diisopropylethylamine (0.74 g, 1.0 ml, 5.7 mmol) and
methyl diazoacetate (0.50 g, 5.0 mmol) in ether (5 ml)
was gradually added. The mixture was brought to room
temperature (r.t.) and stirring continued for 3 h. The
precipitated ammonium triflate was separated by filtra-
tion (sintered glass filter funnel) and rinsed with pen-
tane (2×10 ml). The solution was concentrated to a
volume of 10 ml and used directly for the silylation
reactions.
1
The value of the J(13C,1H) coupling constant of the
a-CH2 carbon (l=48.6 ppm, J=122 Hz) was lower by
6 Hz than in 7a, in agreement with the expected [19]
inductive effect of the silyl group.
Efforts to prepare diazoacetate (8b) from 7b by de-
protonation with BuLi and subsequent addition of 1
were unsuccessful, probably because the SN reaction at
silicon failed due to steric hindrance. Analogous
workup as for 8a gave only unchanged 7b besides small
amounts of an unidentified product.
4.2. Pentacarbonyl{[1-[diazo(methoxycarbonyl)methyl]-
diisopropylsilyloxy]ethylidene}tungsten (3a)
3. Conclusions
MeLi in ether (1.6 M, 2.50 ml, 4.0 mmol) was added
to a suspension of W(CO)6 (1.45 g, 4.1 mmol) in
pentane (100 ml) at r.t. A yellow precipitate formed.
The mixture was refluxed for 90 min, then cooled at
−40°C. A freshly prepared solution of silyl triflate (1)
(4.0 mmol) in pentane–ether (4.0 mmol) was gradually
added. The mixture was then allowed to warm up to
0°C within 6 h, thereby developing a deep-red color.
The solvent was evaporated at −20°C/0.002 mbar, and
the semi-solid residue was extracted with pentane (2×
40 ml). The extracts furnished 3a as a red solid (280 mg,
12%) which is both moisture-sensitive and thermolabile.
Unspecific decomposition started above 0°C after a few
min and was indicated by a color change from red to
black. IR (pentane solution): w=2080 (s), 2060 (s),
We have presented here the synthesis of two types of
novel diazo-functionalized Fischer-type carbene com-
plexes, in which a diazomethyl function is separated
from the metal–carbene either by a OCH2SiR2 or by a
CH2SiR2 moiety. It is worth noting that the metal–car-
bene function (with an electrophilic carbon atom) and
the diazo functionality (with a nucleophilic carbon
atom) tolerate each other in the same molecule, but the
low thermal stability of the M(CO)5 complexes 3–5
suggests that the compatibility is limited. The synthetic
potential of these diazo-functionalized carbene com-
plexes is still to be evaluated.
1974 (vs), 1941 (vs), 1685 (m) cm−1 13C-NMR (tolu-
.
4. Experimental
ene-d8, −10°C): signals for two isomers (major/minor),
see text; l=13.4 and 13.9 (SiCH), 16.5–16.8 (4 signals,
CHMe2), 44.0 (broad, CꢀN2), 52.8 (OMe), 55.0/55.6
(WꢀCMe), 169.0 (broad, ester CꢀO), 191.1/191.8 (cis-
CO), 206.1/204.8 (trans-CO), 345.6/344.2 (WꢀC).
All reactions were carried out under argon in glass-
ware that had been evacuated, heated with a heat gun,
and filled with argon prior to use. Solvents were dried
by standard procedures and stored under argon.
Column chromatography was performed on silica gel
(Macherey&Nagel, 0.063–0.2 mm) which had been
dried during 2 days at 220°C/0.002 mbar and then
deactivated by treatment with 3% (w/w) of water. For
low-temperature column chromatography, a cooling
liquid was circulated through the outer chamber of a
two-walled glass column. NMR spectra were recorded
on Bruker AC 200 (1H: 200.1 MHz) and AMX 400
instruments (1H: 400.1 MHz; 13C: 100.6 MHz). The
4.3. Pentacarbonyl{1-[[diazo(methoxycarbonyl)methyl]-
diisopropylsilyloxy]benzylidene}tungsten (3b)
A solution of phenyl lithium in cyclohexane–ether (2
M, 2.50 ml, 5.0 mmol) was added to a suspension of
W(CO)6 (1.80 g, 5.1 mmol) in ether (50 ml). The
mixture was stirred for 3 h, cooled at −30°C, and a
solution of 1 (5.0 mmol) in pentane–ether (10 ml) was
added gradually. After a further 6 h between −30 and
−10°C, the volatiles were evaporated at −10°C/0.003
mbar. The remaining red–brown solid was extracted
with pentane (3×30 ml) and cooled at −30°C. The
combined extracts were concentrated and subjected to
column chromatography on silica gel (60 g) at −30°C.
Elution with pentane–ether (2:1) furnished a dark-red
,
solvents used were stored over molecular sieves (4 A)
and saturated with argon before use. Internal standards
were used (1H: TMS; 13C: CDCl3, l=77.0; toluene-d8,
l=20.4). IR spectra were recorded on Perkin–Elmer
1310 and 397 spectrophotometers. Mass spectra were
obtained with a Varian MAT 311A instrument.

G. Maas, D. Mayer / Journal of Organometallic Chemistry 617–618 (2001) 339–345
343
oil (180 mg) which contained 3b and some impurities.
Further purification was not possible due to the ther-
molability of the complex as described for 3a. IR
(pentane solution): w=2080 (s), 1975 (vs), 1950 (m),
CꢀO), 207.0/206.8 (cis-CO), 213.8/215.7 (trans-CO),
323.0/327.0 (MoꢀC).
4.6. {1-[[Diazo(methoxycarbonyl)methyl]diisopropyl-
silyloxy]ethylidene}dicarbonyl(methylcyclopentadienyl)-
manganese (6a)
1940 (s), 1920 (s), 1670 (m) cm−1 13C-NMR (toluene-
.
d8, −20°C): l=13.8 (SiCH), 16.8 and 17.1 (CHMe2),
41.9 (CꢀN2), 51.5 (OMe), 126.3 (m-C), 128.3 (o-C),
130.7 (p-C), 156.2 (i-C), 169.8 (CꢀO), 197.1 (cis-CO),
203.4 (trans-CO), 322.9 (WꢀC).
A solution of MeLi in ether (1.6 M, 6.25 ml, 10.0
mmol) was added at r.t. to
a
solution of
(C5H4Me)(CO)3Mn (2.18 g, 1.58 ml, 10.0 mmol) in
ether (20 ml). An orange-colored precipitate formed
while the solution assumed an olive-green color. After
12 h, the mixture was cooled at 0°C and a solution of
1 (10.0 mmol) in pentane (10 ml) was added, causing an
immediate color change to dark-red. The mixture was
brought to r.t., and the solvent was evaporated. The
residue was extracted with 20 ml portions of pentane
until the extract remained colorless (4 portions), and
the combined extracts were concentrated. Column chro-
matography on silica gel (155 g) at −30°C with ether–
pentane (3:1) furnished 6a as a dark-red viscous oil
(2.72 g, 61%). IR (film): w=2080 (s), 1960 (s), 1900 (s),
4.4. Pentacarbonyl{1-[[diazo(methoxycarbonyl)methyl]-
diisopropylsilyloxy](4-methoxyphenyl)methylene}-
chromium (4)
A solution of 4-methoxyphenyl lithium in ether (10
ml), prepared from 1-bromo-4-methoxybenzene (1.05 g,
5.6 mmol) and BuLi (1.6 M in ether, 5.5 mmol) at
−25°C, was added to a stirred suspension of Cr(CO)6
(1.32 g, 6.0 mmol) in ether (25 ml). The red mixture was
stirred for another 90 min at 0°C, then cooled at
−20°C, and silyl triflate 1 (5.0 mmol) in pentane (10
ml) was gradually added. The color changed immedi-
ately from red to dark-red. When the addition was
complete, stirring was continued for 30 min, the solvent
was evaporated at −10°C/0.003 mbar, and the residue
was extracted with pentane (4×10 ml) cooled at
−10°C. The combined extracts were concentrated to
leave a dark-red residue (130 mg) which consisted of 4
and some unidentified impurities. 13C-NMR (toluene-
d8, −10°C): l=13.6 (SiCH), 16.7 and 16.9 (CHMe2),
43.0 (br, CꢀN2), 50.9 (COOMe), 51.7 (ArꢁOMe), 112.8
(m-C), 129.4 (o-C), 160.2 (CarylꢁOMe), 169.5 (br, CꢀO),
214.2 (cis-CO), 348.4 (CrꢀC); identification of i-Caryl
and trans-CO not possible due to impurities. MS (EI,
70 eV): m/z=540 (1%) [M+], 375 (13), 361 (17), 287
(9), 264 (19), 263 (100).
1
1660 (m) cm−1. H-NMR(toluene-d8, 400.1 MHz): l=
0.75–1.45 (m, 14H, CHMe2), 1.65 (s, 3H, CpꢁMe), 2.50
(s, 3H, ꢀCMe), 3.35 (br s, 3H, OMe), 4.25 and 4.40 (2s,
4H, C5H4). 13C-NMR (CDCl3): l=13.6 (CpMe), 13.9
(SiCH), 17.0 and 17.1 (CHMe2), 44.0 (CꢀN2), 48.9
(ꢀCMe), 52.0 (OMe), 87.0 and 88.0 (C-2,3,4,5, Cp),
104.2 (C-1, Cp), 168.5 (CꢀO, ester), 232.8 (CO, ligand),
339.6 (MnꢀC). Anal. Calc. for C19H27MnN2O5Si
(446.46): C, 51.12; H, 6.10. Found: C, 51.9; H, 6.30%.
Complexes 6b–d were prepared analogously.
4.6.1. Complex 6b
BuLi in hexane was used; red–brown oil (2.30 g,
47%). IR (pentane): w=2080 (s), 1970 (s), 1900 (s),
1
1685 (s) cm−1. H-NMR(toluene-d8, 400.1 MHz): l=
0.80–1.30 (m, 19H, CHMe2, CH2CH3), 1.50 (t, 2H,
CH2), 1.65 (s, 3H, CpꢁMe), 2.90 (t, 2H,ꢀCCH2), 3.35
(s, 3H, OMe), 4.30 and 4.47 (2 s, 4H, C5H4). 13C-NMR
(CDCl3): l=12.6 (CpMe), 13.8 (SiCH), 16.8 (CH2Me),
17.0 and 17.1 (CHMe2), 22.7 (CH2), 31.0 (CH2), 44.6
(CꢀN2), 51.9 (OMe), 62.8 (ꢀCCH2), 86.9 and 87.8 (C-
2,3,4,5, Cp), 104.5 (C-1, Cp), 168.5 (br, CꢀO, ester),
232.8 (CO, ligand), 346.6 (MnꢀC).
4.5. Pentacarbonyl{1-[[diazo(methoxycarbonyl)methyl]-
diisopropylsilyloxy](4-methoxyphenyl)methylene}-
molybdenum (5)
Preparation
from
4-methoxyphenyl
lithium,
Mo(CO)6, and 1 as described for 4, and column chro-
matography as described for 3b (all manipulations at
−25 to −30°C) afforded a dark-red oil (150 mg) of 5
and some impurities. Further purification was not pos-
sible due to the thermolability of the complex; even on
storing at −78°C, a color change from red to black
occurred after a few days. IR (pentane solution): w=
2090 (s), 2010 (sh), 1975 (s, br), 1880 (sh), 1685 (s)
4.6.2. Complex 6c
Phenyl lithium (2 M in cyclohexane–ether) was used;
dark-red viscous oil (4.05 g, 80%). IR (film): w=2080
(s), 1960 (s), 1880 (s), 1690 (s) cm−1. 1H-NMR (CDCl3,
400.1 MHz, −20°C): l=0.97–1.16 (m, 14H, CHMe2),
1.88 (s, 3H, CpMe), 3.67 (s, 3H, OMe), 4.52 and 4.58 (2
s, 4H, C5H4), 6.87–6.93 (m, 2H), 7.18–7.24 (mc, 1H),
7.25–7.30 (mc, 2H). 13C-NMR (CDCl3, −20°C): l=
13.2 (SiCH), 13.6 (CpMe), 16.7 and 17.5 (CHMe2), 44.2
(br, CꢀN2), 51.6 (OMe), 87.1 and 88.5 (Cꢁ2,3,4,5, Cp),
cm−1 13C-NMR (toluene-d8, −20°C): Signals for two
.
isomers (major/minor), see text; l=13.5 and 14.6
(SiCH); 15.5, 16.8, 17.0, 17.6 (CHMe2); 41.0 (br,
CꢀN2), 52.3 (COOMe), 54.4 (ArꢁOMe), 114.1 (m-C),
132.5 (o-C), 142.1 (i-C), 165.8 (CarylꢁOMe), 171.0 (br,

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1
104.4 (C-1, Cp); 121.1, 126.8, 127.2, 156.2 (Ph); 168.5
(br, CꢀO, ester), 231.9 (CO, ligand), 334.0 (MnꢀC). MS
(CI, isobutane, 120 eV): m/z=509 (47%) [MH+], 508
(100) [M+], 452 (45) [M+−2CO], 424 (17)
[M+−2CO−N2]. Anal. Calc. for C24H29MnN2O5Si
(508.53): C, 56.69, H, 5.75; N, 5.51. Found: C, 55.8; H,
5.80; N, 4.50%.
1875 (s), 1675 (s) cm−1. H-NMR (toluene-d8, 400.1
MHz): l=0.80–1.30 (m, 14H, CHMe2), 1.55 (mc, 3H,
OCH2Me), 1.70 (s, 3H, MeCp), 3.10 (s, 2H, =CCH2),
3.36 (s, 3H, OMe), 4.30 (m, 2H, OCH2), 4.27 and 4.55
(2 s, 2×2H, C5H4). 13C-NMR (toluene-d8): l=12.8
(CHMe2), 13.6 (MeCp), 14.9 (OCH2Me), 18.2
(CHMe2), 41.9 (CN2), 48.6 (ꢀCCH2), 51.4 (OMe), 72.2
(OCH2), 86.5 and 88.3 (C-2,5 and C-3,4 of MeCp),
103.7 (C-1 of MeCp), 168.8 (COO), 234.0 (CO), 337.9
(MnꢀC). Anal. Calc. for C21H31MnN2O5Si (474.53): C,
53.15; H, 6.58; N, 5.90. Found: C, 54.7, H, 6.5; N,
4.0%.
4.6.3. Complex 6d
4-Methoxyphenyl lithium, prepared from 1-bromo-4-
methoxybenzene and BuLi (see above), was used; red
oil (3.72 g, 69%). IR (pentane): w=2100 (s), 1960 (s),
1900 (s), 1680 (s) cm−1 13C-NMR (CDCl3): l=13.6
.
(SiCH), 13.6 (CpMe), 17.0 (CHMe2), 44.8 (CꢀN2), 51.7
(OMe), 55.1 (ArOMe), 87.4 and 88.3 (C-2,3,4,5, Cp),
104.2 (C-1, Cp); 111.8, 128.2, 149.9, 158.6 (Ph); 167.9
(CꢀO, ester), 232.2 (CO, ligand), 327.9 (MnꢀC).
4.8. Dicarbonyl(methylcyclopentadienyl)-
(1-ethoxy-1-butylidene)manganese (7b)
This compound was prepared from tricarbonyl-
(methylcyclopentadienyl)manganese and BuLi by an-
alogy to literature [6]; red oil, yield: 60%. 1H-NMR
(CDCl3, 400.1 MHz): l=0.90 (t, 3H, CH2CH2Me),
1.30 (mc, 2H, CH2), 1.42 (mc, 2H, CH2), 1.47 (t, 3H,
OCH2Me), 1.93 (s, 3H, CpMe), 2.92 (t, 2H,ꢀCCH2),
4.62 (q, 2 H, OCH2), 4.53 and 4.71 (2 s, 2×2H, C5H4).
13C-NMR (CDCl3): l=13.6, 14.1, 14.5, 22.8, 31.7,
59.6, 72.2, 85.9, 86.8, 103.0, 233.4, 342.5.
4.6.4. Complex 6e
2-Furyl lithium, prepared from furan and BuLi (1.6
M in ether) was used; deep-red oil (1.15 g, 23%). IR
(film): w=2080 (s), 1940 (s), 1880 (sh), 1670 (m) cm−1
.
13C-NMR (CDCl3): l=12.8 (SiCH), 13.6 (CpMe), 16.9
(CHMe2), 45.0 (br, CꢀN2), 51.9 (OMe), 87.7 and 89.5
(C-2,3,4,5, Cp), 105.0 (C-1, Cp); 113.7, 119.7, 140.5,
164.0 (C-furyl); 169.0 (CꢀO, ester), 232.5 and 234.4
(CO, ligand), 348.3 (br, MnꢀC). MS (CI, isobutane, 120
eV): m/z=499 (100%) [MH+], 498 (100) [M+], 443 (26)
[MH+−2CO], 442 (45) [M+−2CO], 415 (19) [MH+
−2CO−N2], 414 (15) [M+−2CO−N2].
Acknowledgements
We thank the Volkswagen Foundation for generous
support.
4.6.5. Complex 6f
1-Methylpyrrol-2-yl lithium, prepared from 1-
methylpyrrole and BuLi (1.6 M in ether) was used;
deep-red oil (3.68 g, 72%). IR (film): w=2080 (s), 1960
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