Addition of diazoalkanes to alkyne(pentacarbonyl)-chromium and -tungsten - Formation of 3H-pyrazole complexes

Article abstract of DOI:10.1016/S0022-328X(02)02163-0

Photolysis of [M(CO)₆] (M=Cr, W) in CH₂Cl₂ at -78 °C generates [(CO)₅M(CH₂Cl₂)]. Subsequent sequential reaction of [(CO)₅M(CH₂Cl₂)] with terminal alkynes, H

Full text of DOI:10.1016/S0022-328X(02)02163-0

Journal of Organometallic Chemistry 669 (2003) 6ꢀ13
/
www.elsevier.com/locate/jorganchem
Addition of diazoalkanes to alkyne(pentacarbonyl)ꢀ
/
chromium
and ꢀtungsten * formation of 3H-pyrazole complexes
/
/
Mokhles M. Abd-Elzaher 1, Bernhard Weibert, Helmut Fischer *
Fachbereich Chemie, Universitat Konstanz, Fach M727, 78457 Konstanz, Germany
¨
Received 7 October 2002; accepted 2 December 2002
Abstract
Photolysis of [M(CO)6] (Mꢁ
[(CO)5M(CH2Cl2)] with terminal alkynes, HCÅ
R2ꢁMe, Et) affords 3H-pyrazole complexes, [(CO)5Mꢀ
of diazoalkanes to alkyne complex intermediates, [(CO)5M(HCÅ
/
Cr, W) in CH2Cl2 at ꢂ
/
78 8C generates [(CO)5M(CH2Cl2)]. Subsequent sequential reaction of
Me, Et, Ph;
(R1)(R2)]. These complexes are derived from addition
CR)]. Their vinylidene tautomers, [(CO)5MÄCÄC(R)H], present in
CÄ
/
CR (Rꢁ
/
COOMe, Ph, p-Tol), and diazoalkanes, R1(R2)CN2 (R1ꢁ
/
ꢀ
ꢁ
/
/
/
NÄNꢀC(R)ÄC(H)ꢀC
/
/
/
solution in equilibrium with the alkyne complexes, do not react. Likewise, isolable disubstituted vinylidene complexes, [(CO)5MÄ
/
/
C(R‘)R*], do not add diazoalkanes.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Alkyne complexes; 3H-Pyrazole complex; Addition; Tungsten; Chromium
1. Introduction
[(CO)5W(HCÅ
for the polymerization of terminal alkynes in hydro-
carbon solutions. The polymerization of acetylene, HCÅ
CH, requires irradiation of the solutions to only initiate
the reaction whereas for terminal alkynes continued
irradiation is necessary [7]. The reaction of
/
CR)] can also be used as a pre-catalyst
Until now only very few alkyne(pentacarbonyl) com-
plexes have been isolated having terminal alkyne
/
ligands. Only one complex, [(CO)5W(HCÅ
/CPh)], has
been characterized by an X-ray structural analysis [1].
However, such complexes can easily be generated and
subsequently be used for a series of transformations. In
solutions these complexes are present in a rapid
equilibrium with their vinylidene tautomer. The equili-
brium is far to the side of the alkyne form. Usually it is
not possible to detect the vinylidene tautomer by
spectroscopic means. Theoretical studies indicate that
the alkyne/vinylidene isomerization proceeds in these d6
complexes by an intramolecular process [2].
[(CO)5Cr(Et2O)] with a stoichiometric amount of HCÅ
CꢀCOOMe, however, afforded in addition to the alkyne
complex [(CO)5Cr(HCÅCꢀCOOMe)] two products de-
/
/
/
/
rived from addition of the alkyne to the vinylidene
complex tautomer, a cyclobutenylidene complex and a
vinylvinylidene complex [8].
All of these reactions are best explained by assuming
that the vinylidene tautomer is trapped by the substrate.
We now report on reactions that proceed by addition of
the substrate to the alkyne tautomer.
These complexes readily react for example (a) with
alcohols to give carbene complexes [3], with (b) yna-
mines to form cyclobutenylidene complexes [1,4], and (c)
with imines and carbodimides to form 2-azetidinylidene
complexes [5,6] (Scheme 1).
2. Results and discussion
The starting alkyne complexes were generated from
the corresponding hexacarbonyl compounds. Irradia-
* Corresponding author. Tel.: ꢃ
883-136.
/
49-7531-882-783; fax: ꢃ49-7531-
/
tion of solutions of [M(CO)6] in CH2Cl2 at ꢂ78 8C
/
E-mail address: helmut.fischer@uni-konstanz.de (H. Fischer).
1
Present address: Inorganic Chemistry Department, National
Research Centre, PO Box 12622 Dokki, Cairo, Egypt.
afforded, through loss of one CO ligand, the pentacar-
bonyl complexes [(CO)5M(CH2Cl2)]. Their formation
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(02)02163-0

M.M. Abd-Elzaher et al. / Journal of Organometallic Chemistry 669 (2003) 6ꢀ
/13
7
Fig. 1. Molecular structure of complex 3 in the crystal (hydrogen
atoms omitted for clarity).
Table 1
˚
Selected bond lengths (A), bond and torsion angles (8) of complex 3
Bond lengths
Cr(1)ꢀ
N(1)ꢀ
N(1)ꢀ
N(2)ꢀ
C(6)ꢀ
/
N(1)
2.138(2) C(7)ꢀ
1.272(2) C(8)ꢀ
1.509(2) O(6)ꢀ
1.438(3) O(7)ꢀ
/
C(8)
1.334(3)
1.489(3)
1.204(3)
1.342(2)
1.450(3)
/
N(2)
C(6)
C(8)
/C(9)
/
/
C(9)
C(9)
C(10)
Scheme 1.
/
/
/
C(7)
1.485(3) O(7)ꢀ
/
could easily be followed by the changes of the n(CO)
absorptions in the IR spectra. Subsequent addition of
two equivalents (relative to [M(CO)6]) of terminal
Bond angles
N(2)ꢀN(1)ꢀ
N(2)ꢀN(1)ꢀ
C(6)ꢀN(1)ꢀ
N(1)ꢀN(2)ꢀ
C(7)ꢀC(6)ꢀN(1)
/
/
C(6)
110.81(16) N(2)ꢀ
/
C(8)ꢀ
C(8)ꢀ
C(8)ꢀ
C(9)ꢀ
C(7)ꢀ
/
C(9)
N(2)
C(9)
119.08(17)
110.26(18)
130.63(19)
125.18(19)
108.10(18)
/
/Cr(1)
119.13(12) C(7)ꢀ
130.05(13) C(7)ꢀ
109.26(16) O(6)ꢀ
101.57(16) C(8)ꢀ
/
/
/
/
Cr(1)
C(8)
/
/
alkynes at ꢂ40 8C produced alkyne complexes generally
/
/
/
/
/
C(8)
in good yield. The formation of the alkyne complexes
was verified by IR spectroscopy. Most of these com-
plexes are thermally labile and readily decompose at
room temperature. Therefore, they were not isolated but
immediately used for the subsequent reactions after the
volume of the solutions had been reduced in vacuo to a
few milliliters. Two to three equivalents of diazoalkane,
/
/
/
/C(6)
Torsion angles
C(2)ꢀCrꢀN(1)ꢀ
CrꢀN(1)ꢀN(2)ꢀ
/
/
/
N(2)
33.6(2) Crꢀ/N(1)ꢀ
/C(6)ꢀ
/
C(7)
C(7)
179.9(1)
0.8(2)
/
/
/
C(8) 179.8(1) N(1)ꢀ
/
N(2)ꢀ
/
C(8)ꢀ
/
observed for other [(CO)5CrL] complexes with an
N(sp2)-bonded N-heterocyclic ligand (L, e.g. 4-methyl-
˚
1,2,4-triazole-N1: 2.111(2) A [9], 3-ethoxy-1H-isoindole-
R1(R2)Cꢀ
/
N2, were added at ꢂ40 8C to the concentrated
/
solutions. The reactions proceeded quickly and were
complete within a few minutes. Chromatographic
workup of the reaction mixture afforded the 3H-
˚
N: 2.134(3) A [10], 4-methyl-1,2,3-selenadiazole-N:
2.114(6) A [11]). (CO)5Crꢀ
/
N(sp3) distances are usually
˚
pyrazole complexes 1ꢀ
from 56 to 74%.
The reaction of [(CO)5Mo(CH2Cl2)] with HCÅ
COOMe and Et2CꢀN2 proceeded similarly, however,
/
6 (Scheme 2) in yields ranging
/
Cꢀ
/
/
the resulting complex was very unstable. Therefore, it
was not possible to isolate it in a pure form.
The compounds 1ꢀ6 are readily soluble in polar
/
solvents such as dichloromethane or diethyl ether, but
only poorly soluble in non-polar solvents. The com-
1
plexes were characterized by their IR, H-NMR, and
13C-NMR spectra. The structure of 3 and 5 was
additionally established by X-ray structural analyses.
The results of the X-ray analysis of 3 (Fig. 1, Table 1)
shows that a 3H-pyrazole complex has been formed.
The five-membered ring is bonded to chromium via the
nitrogen atom adjacent to the sp3 carbon atom. The
pyrazole ring is planar. To avoid steric congestion, the
ring is staggered with respect to the cis carbonyl ligands
(torsion angle C(2)ꢀ
/
Crꢀ
/
N(1)ꢀ
/
N(2) 33.6(2)8). The Crꢀ
/
˚
N(1) bond length (2.1384(18) A) is similar to that
Scheme 2.

8
M.M. Abd-Elzaher et al. / Journal of Organometallic Chemistry 669 (2003) 6ꢀ
/13
˚
longer and are observed in the range 2.19 ꢀ
/
2.25 A [12].
N(2) distance (1.272(2) A) agrees very well
the N(sp2)ÄN(sp2) bond length in (CO)5Cr-coordinated
b) displacement of the coordinated alkyne by the
solvent, 1,3-dipolar cycloaddition of the diazo
compound to the non-coordinated alkyne to give
the 3H-pyrazole followed by displacement of the
coordinated solvent by 3H-pyrazole.
˚
The N(1)ꢀ
/
/
˚
4-methyl-1,2,3-selenadiazole (1.272(1) A [11]) and in 6-
chloro 9,9-dimethyl 9H-imidazo(1,2-b)pyrazolo(4,3-
˚
d)pyridazine (1.265(8) A [13]), but is significantly
N(sp2) bond in [(CO)5Cr(4-
˚
shorter than the N(sp2)ꢀ
/
To distinguish between these two likely mechanisms
several experiments with the system [(CO)5Cr(CH2Cl2)]/
methyl-1,2,4-triazole)] (1.380(3) A [9]). Bond lengths
and angles in 5 deviate only sightly from those in 3.
Therefore, they are not discussed here.
HCÅ
/
Cꢀ
/
COOMe/Et2CꢀN2 were carried out:
/
ꢀ
/
The cycloaddition of Et2Cꢀ
HCÅCꢀCOOMe to form the 3H-pyrazole (step b2)
was faster than the overall reaction of Et2CꢀN2 with
CꢀCOOMe)].
The rate of displacement of coordinated CH2Cl2 by
3H-pyrazole (step b3) was faster than the reaction of
/
N2 to non-coordinated
The X-ray structural analyses of 3 and 5 and the
/
/
spectroscopic data of 1ꢀ6 confirm that the new hetero-
/
/
cyclic ligand is derived from the alkyne tautomer. From
addition of diazoalkane to the vinylidene tautomer (as
has been observed in all reactions with nucleophiles
summarized in Scheme 1) the formation of isomeric 2-
dihydropyrazolylidene complexes was to be expected.
However, there is no spectroscopic indication for the
formation of 2-dihydropyrazolylidene complexes. In
accord with the conclusion is the observation that
disubstituted pentacarbonyl(vinylidene) complexes did
not react with diazoalkanes to give 2-dihydropyrazo-
[(CO)5Cr(HCÅ
/
/
ꢀ
/
Et2Cꢀ
3H-pyrazole complex.
The rate of displacement of coordinated HCÅ
/
N2 with [(CO)5Cr(HCÅ
/
CꢀCOOMe)] to form
/
ꢀ
/
/
Cꢀ
/
COOMe by nucleophiles, however, was considerably
slower than the rate of formation of 3H-pyrazole
complexes. P(C6H4Me-p)3 (as a typical nucleophile)
reacted only very slowly with [(CO)5Cr(HCÅ
/
Cꢀ
/
lylidene complexes. When solutions of [(CO)5MÄ
/
CÄ
/
COOMe)]. From the reaction mixture only small
amounts of stable [(CO)5Cr(P(C6H4Me-p)3)] were
isolated. The major products were [Cr(CO)6] and
several organic products presumably derived from
nucleophilic addition of P(C6H4Me-p)3 to the co-
ordinated alkyne and subsequent decomposition of
the adduct.
C(CMe3)R] (MꢁCr, W; RꢁMe, Et) were treated
/
/
with phenyl diazomethane, phenyl diazoethane, diphe-
nyl diazomethane, 4-methoxyphenyl diazomethane, or
diazopentane using the same reaction conditions as
previously applied (Scheme 2), after three hours the
vinylidene complex was recovered unchanged. In addi-
tion, small amounts of its decomposition product,
[M(CO)6], and products derived from the thermal
decomposition of the diazoalkane were isolated. 2-
Dihydropyrazolylidene complexes could not be de-
tected.
From the significantly slower rate of step b1 com-
pared to the overall reactions of Scheme 2 it follows that
path b can be excluded and that the 3H-pyrazole
complexes are formed within the coordination sphere
of the metal.
The formation of 3H-pyrazole complexes can be
explained by two pathways (Scheme 3):
An alternative route involves reaction of excess alkyne
with excess diazoalkane to form the 3H-pyrazole
followed by displacement of coordinated alkyne by the
3H-pyrazole. This route, at least as the major pathway,
is unlikely since displacement of coordinated alkynes by
3H-pyrazoles is considerably slower than the overall
reaction (Scheme 2). Nevertheless, the formation of
small amounts of the 3H-pyrazole complexes by this
route cannot completely be excluded.
a) addition of the diazo compound to the coordinated
alkyne followed by rearrangement or
The rate of addition of diazoalkanes to the alkyne of
the complexes [(CO)5M(HCÅ
substituent R. When HCÅCꢀCOOMe was replaced by
aryl-substituted alkynes the stability and also the
reactivity towards nucleophiles decreased. When HCÅ
/
Cꢀ/R)] depended on the
/
/
/
CPh was employed the displacement of the alkyne by
nucleophiles already competed with 3H-pyrazole for-
mation. Therefore, from the slow reaction of
[(CO)5Cr(HCÅ
/
Cꢀ
/
Ph)] with Et2CꢀN2 three compounds
/
Scheme 3.
were isolated (Scheme 4); the pyrazole complex 7, small

M.M. Abd-Elzaher et al. / Journal of Organometallic Chemistry 669 (2003) 6ꢀ
/13
9
Scheme 5.
group (dꢁ
/
154.8), three resonances at dꢁ/147.4, 71.8,
Scheme 4.
and 67.3. Based on these spectroscopic data we assign
the structure shown in Scheme 5 to compound 11. It is
presumably formed by addition of 3-pentanone hydra-
zone present in solution as a by-product from the
synthesis of 3-diazopentane to the 3H-pyrazole.
amounts of an azine complex (8), and the hydrazone
complex (9).
The complexes 8 and 9 are formed by substitution of
tetraethyl azine and 3-pentanone hydrazone, respec-
tively, for coordinated phenylethyne. 3-Pentanone hy-
dazone is an intermediate in the synthesis of 3-
diazopentane from 3-pentanone, hydrazone, and HgO.
Due to the modest stability of 3-diazopentane its
purification is difficult and, therefore, it is usually
accompanied by its precursor 3-pentanone hydrazone.
Tetraethyl azine in turn is a well-known by-product in
the synthesis of 3-diazopentane by oxidation of 3-
pentanone hydrazone with HgO [14].
Decomplexation of the 3H-pyrazole in 1ꢀ6 could be
/
achieved by addition of nucleophiles. For instance
addition of [NBu4]Br to solutions of 3 in CH2Cl2 and
stirring the solutions for 48 h at ambient temperature
afforded the 3H-pyrazole after purification in 66% yield.
In summary, the reactions of the equilibrium alky-
ne(pentacarbonyl) complex/pentacarbonyl(vinylidene)
complex strongly depends on the type of substrate.
Whereas imines, ynamines, and alcohols preferentially
react quickly with the vinylidene complex tautomer in
the equilibrium, the products (3H-pyrazole complexes)
of the reactions with diazoalkanes as typical 1,3-dipoles
are derived from the alkyne complex tautomer.
In contrast to the reaction of [(CO)5Cr(HCÅ
/
CꢀPh)]
/
with Et2Cꢀ CꢀC(O)Ph)] was
/
N2 that of [(CO)5Cr(HCÅ
/
/
fast. However, the resulting 3H-pyrazole complex 10
(Scheme 5) turned out to be too unstable for isolation. It
quickly decomposed in solution even at ꢂ30 8C pre-
/
dominantly by decomplexation of the 3H-pyrazole. The
major product isolated from the reaction mixture by
column chromatography was a green oil. From the
molecular peak in its mass spectrum a combined mass of
that of the 3H-pyrazole and that of 3-pentanone
3. Experimental
3.1. General
1
hydrazone could be deduced. The H-NMR spectrum
exhibited in CDCl3, in addition to resonances for one
C6H5 substituent and four C2H5 groups, two doublets at
All operations were carried out under either nitrogen
or argon by using conventional Schlenk techniques.
Solvents were dried by refluxing over sodiumꢀbenzo-
/
dꢁ
singulet at dꢁ
concentration- and solvent-dependent. Its position in
CDCl3 varied between dꢁ6.83 and 7.16 depending on
the concentration of the compound. In acetone-d6 the
singulet appeared at dꢁ
8.05. The 13C-NMR spectrum
showed, in addition to peaks for the ethyl groups, the
phenyl substituent, a CÄO (dꢁ188.8) and a Cꢁ
/
4.55 (Jꢁ
/
3.0 Hz) and 5.53 (Jꢁ/2.8 Hz) and a
phenone ketyl (THF, diethyl ether) or CaH2 (pentane,
dichloromethane) and were freshly distilled prior to use.
The silica gel used for chromatography (J.T. Baker,
silica gel for flash chromatography) was argon satu-
rated. The yields refer to analytically pure compounds
and were not optimized. 2-Acetone hydrazone [15], 2-
diazopropane [16], 3-diazopentane [17], 1-phenyl di-
azoethane [18], bis-(p-dimethylaminophenyl) diazo-
/
6.83. The position of the singulet was
/
/
/
/
/
N

10
M.M. Abd-Elzaher et al. / Journal of Organometallic Chemistry 669 (2003) 6ꢀ13
/
methane [19] and benzoylacetylene [20] were prepared
according to the literature procedures. Metal hexacar-
bonyls (Aldrich) and HgO, yellow (ACROS), and all
other chemicals (Merck) were commercial products and
were used without further purification. IR: FT-IR
spectrophotometer (FTS70), Bio-Rad. All IR measure-
3.3.1. Pentacarbonyl(3,3-dimethyl-5-methoxycarbonyl-
3H-pyrazole-N2)chromium(0) (1)
Elution of the complex with pentaneꢃ
Yield: 0.75 g (72% relative to [Cr(CO)6]). M.p. 76 8C. IR
(pentane, 298 K, cmꢂ1) n(CO)ꢁ
2071 m, 1954 vs, 1943
s, 1921 s, 1742 m. 1H-NMR (CD3C(O)CD3): dꢁ
8.32 (s,
1H, C7-H), 3.87 (s, 3H, OMe), 1.62 (s, 6H, C6ꢀCH3).
13C-NMR (CD3C(O)CD3): dꢁ
222.2 (trans CO), 214.9
/CH2Cl2 (1:1).
/
/
1
ments were carried out at 298 K. H- and 13C-NMR
/
spectra were recorded at room temperature on a Bruker
AC 250. Chemical shifts are reported in ppm relative to
internal TMS. For the numbering scheme see Fig. 1.
MS: Finnigan MAT 312 (EI). Elemental analysis: CHN-
analyser (CHN-O-RAPID) Heraeus. Photolysis reac-
tions were carried out in a duran glass apparatus using a
mercury high pressure lamp (TQ 150, Fa. Heraeus).
/
(cis CO), 160.5 (C9), 158.3 (C7), 147.8 (C8), 99.4 (C6),
52.7 (OCH3), 22.4 (CCH3). MS, m/z (%): 346 (1.0)
[Mꢃ], 318 (3) [Mꢃꢂ
/
CO], 234 (6) [Mꢃꢂ
5COꢀ
/
4CO], 206 (29)
[Mꢃꢂ
/
5CO], 147 (27.3) [Mꢃꢂ
/
/
C(O)OMe]. Anal.
Found: C, 41.95; H, 2.99; N, 7.84. Calc. for
C12H10N2O7Cr (346.2): C, 41.63; H, 2.91; N, 8.09%.
3.2. General procedure for the generation of the h2-alkyne
metal complexes
3.3.2. Pentacarbonyl(3-methyl-3-phenyl-5-
methoxycarbonyl-3H-pyrazole-N2)chromium(0) (2)
Elution of the complex with pentaneꢃ
/
CH2Cl2 (1:1).
At ꢂ78 8C, a solution of the metal hexacarbonyls,
/
Yield: 0.69 g (56% relative to [Cr(CO)6]), two isomers,
[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 with a UV lamp while
stirring. The progress of the photolysis was followed by
IR-spectroscopy. After ca. 90 min the metal hexacarbo-
nyls were converted into pentacarbonyl(dichlorometha-
ne)metal complexes. Two equivalents (based on the
metal hexacarbonyls used) of the corresponding alkyne
2a and 2b (ratio 2a:2bꢁ
/
1:1.6). M.p. 70 8C. IR (pentane,
298 K, cmꢂ1) n(CO)ꢁ
vs, 1950 s, 1932 s, 1743 m. H-NMR (CD3C(O)CD3):
/
2070 m, 2066 m, 1995 m, 1955
1
dꢁ
aryl), 3.78 (s, OMe, 2b), 3.69 (s, OMe, 2a), 2.14 (s, Me,
2a), 1.98 (s, Me, 2b). 13C-NMR (CD3C(O)CD3): dꢁ
/
8.33 (s, C7ꢀ
/
H, 2a), 8.22 (s, C7ꢀ
/
H, 2b), 7.5ꢀ7.2 (m,
/
/
222.3 (trans CO, 2a), 221.7 (trans CO, 2b), 214.0 (cis
CO, 2b), 213.8 (cis CO, 2a), 160.5 (C9, 2b), 159.8 (C9,
2a), 152.2 (C7), 150.0 (C8), 146.5, 131.1, 129.4, 129.2,
128.9, 128.7, 128.4, 126.1 (m, aryl), 98.4 (C6), 52.0
(OCH3, 2b), 51.8 (OCH3, 2a), 22.7 (CCH3, 2a), 19.9
(CCH3, 2b). MS, m/z (%): 408 (13) [Mꢃ], 352 (5.6)
(RCÅ
/
CH; Rꢁ
/
COOMe, Ph, p-tolyl, C(O)Ph) were
added at ꢂ
/
78 8C with stirring to the freshly prepared
solution of the [(CO)5M(CH2Cl2)] complexes. Stirring
was continued for 10 min. The temperature was allowed
to rise gradually from ꢂ
concentrated at ꢂ30 8C to a volume of ca. 10 ml. The
h2-alkyne(pentacarbonyl)metal
[(CO)5M(HCÅCR)] (MꢁCr: Rꢁ
Ph, p-Tol; MꢁMo: Rꢁ
/
78 to ꢂ
/
30 8C. The solution was
[Mꢃꢂ
4CO], 268 (100) [Mꢃꢂ
50.95; H, 3.58; N, 6.88. Calc. for C17H12N2O7Crꢄ
0.15 pentane (408.3ꢃ10.8): C, 50.82; H, 3.29; N, 6.68%.
/
2CO], 324 (8.1) [Mꢃꢂ
/
3CO], 296 (4.3) [Mꢃ
/
ꢂ
/
/
5CO]. Anal. Found: C,
complexes
/
/
/
/COOMe, C(O)Me,
/
/
/
COOMe; Mꢁ
/
W: Rꢁ
/
COOMe, Ph) were identified by comparison of their
IR spectra with published data [1,5,6]. The solutions
containing the h2-alkyne(pentacarbonyl)metal com-
plexes were immediately used for the subsequent reac-
tions.
3.3.3. Pentacarbonyl(3,3-diethyl-5-methoxycarbonyl-
3H-pyrazole-N2)chromium(0) (3)
Elution of the complex with pentaneꢃ
Yield: 0.85 g (76% relative to [Cr(CO)6]). M.p. 73 8C. IR
(pentane, 298 K, cmꢂ1) n(CO)ꢁ
2069 m, 1997 m, 1950
vs, 1942 s, 1922 s, 1745 m. H-NMR (CD3C(O)CD3):
dꢁ8.23 (s, 1H, C7), 3.91 (s, 3H, OMe), 2.45 (m, 2H,
CH2), 2.28 (m, 2H, CH2), 0.56 (t, Jꢁ7.4 Hz, 6H, CH3).
13C-NMR (CD3C(O)CD3): dꢁ
222.2 (trans CO), 214.9
/CH2Cl2 (1:9).
/
1
3.3. Reaction of h2-alkyne(pentacarbonyl)metal
/
complexes with diazo compounds
/
/
At ꢂ
/
30 8C, the diazo compound (two equivalents,
(cis CO), 160.3 (C9), 156.6 (C7), 150.2 (C8), 108.3 (C6),
52.8 (OCH3), 31.0 (CH2), 9.0 (CCH3). MS, m/z (%): 374
relative to [M(CO)6]) was added to the concentrated
solutions of the alkyne complexes. The progress of the
reaction was monitored by IR spectroscopy. When the
starting alkyne complexes could not be detected any
more, the solvent was removed in vacuo. A brown oily
product was obtained. Then, the reaction products were
(2.3) [Mꢃ], 262 (21.4) [Mꢃꢂ
/
4CO], 234 (100)
5CO], 175 (27.3) [Mꢃꢂ
5COꢀC(O)OMe].
C14H14N2O7Cr (374.3).
[Mꢃꢂ
/
/
/
3.3.4. Pentacarbonyl(3,3-diethyl-5-p-tolyl-3H-pyrazole-
N2)chromium(0) (4)
chromatographed at ꢂ
/
50 8C on silica gel or neutral
Al2O3. Elution with pentane gave first [M(CO)6] and
subsequently with pentane/dichloromethane a red band
containing 3H-pyrazole complexes.
Elution of the complex with pentaneꢃ
Yield: 0.54 g (44% relative to [Cr(CO)6]). M.p. 96 8C. IR
(pentane, 298 K, cmꢂ1) n(CO)ꢁ
2068 m, 1947 vs, 1940
/
CH2Cl2 (1:9).
/

M.M. Abd-Elzaher et al. / Journal of Organometallic Chemistry 669 (2003) 6ꢀ
/13
11
1
s, 1920 s. H-NMR (CDCl3): dꢁ
2H, aryl), 7.28 (d, Jꢁ7.6 Hz, 2H, aryl), 6.99 (s, 1H, C7ꢀ
H), 2.41 (s, 3H, arylꢀCH3), 2.21 (m, 4H, CH2), 0.60 (t,
Jꢁ 221.6
6.8 Hz, 6H, CH3). 13C-NMR (CDCl3): dꢁ
/
7.85 (d, Jꢁ
/
7.6 Hz,
pyrazole complexes (7). Next, with pentaneꢃ
(7:3) a violetꢀ
hydrazone complex 8. Finally, the azine complex 9 was
eluted with pentaneꢃCH2Cl2 (1:1) as a slight green
band.
7: yield: 0.49 g (42% relative to [Cr(CO)6]). M.p.
78 8C. IR (pentane, 298 K, cmꢂ1) n(CO)ꢁ
2068 m,
1993 m, 1948 vs, 1940 s, 1921 s. 1H-NMR (CDCl3): dꢁ
7.96 (m, 2H, aryl), 7.48 (m, 3H, aryl), 7.07 (s, 1H, C7ꢀ
H), 2.22 (m, 4H, CH2), 0.62 (t, Jꢁ6.4 Hz, 6H, CH3).
13C-NMR (CDCl3): dꢁ
221.6 (trans CO), 214.3 (cis
/
CH2Cl2
/
/
/
green band was eluted containing the
/
/
/
/
(trans CO), 214.3 (cis CO), 156.6 (C8), 136.2 (C7),
140.0, 130.1, 129.8, 126.6 (aryl), 106.2 (C6), 30.7 (CH2),
21.4 (aryl-CH3), 8.9 (CH3). MS, m/z (%): 406 (7.2)
[Mꢃ], 350 (3.5) [Mꢃꢂ
Anal. Found: C, 56.14; H, 4.70; N, 6.77. Calc. for
C19H18N2O5Cr (406.4): C, 56.16; H, 4.46; N, 6.89%.
/
/
2CO], 266 (73) [Mꢃꢂ
/5CO].
/
/
/
/
3.3.5. Pentacarbonyl(3,3-dimethyl-5-methoxycarbonyl-
3H-pyrazole-N2)tungsten(0) (5)
CO), 156.5 (C8), 137.2 (C7), 129.8, 129.4, 129.1, 126.7
(aryl), 106.4 (C6), 30.8 (CH2), 9.0 (CH3). MS, m/z (%):
Elution of the complex with pentaneꢃ
Yield: 0.87 g (64% relative to [W(CO)6]). M.p. 82 8C. IR
(pentane, 298 K, cmꢂ1) n(CO)ꢁ
2075 m, 1990 m, 1948
vs, 1943 s, 1922 s, 1741 m. H-NMR (CD3C(O)CD3):
dꢁ8.39 (s, 1H, C7), 3.90 (s, 3H, OꢀCH3), 1.64 (s, 6H,
CH3). MS, m/z (%): 478 (6) [Mꢃ], 394 (9) [Mꢃꢂ
3CO],
338 (20) [Mꢃꢂ5CO], 279 (18) [Mꢃꢂ
5COꢀC(O)OMe].
Anal. Found: C, 31.12; H, 2.42; N, 6.17. Calc. for
C12H10N2O7Wꢄ0.1 pentane (478.1ꢃ7.2): C, 30.91; H,
2.31; N, 5.77%.
/CH2Cl2 (1:9).
392 (7.1) [Mꢃ], 364 (3.4) [Mꢃꢂ
/
CO], 336 (8.7)
3CO], 280 (19.4)
5CO]. Anal. Found: C,
[Mꢃꢂ
/
2CO], 308 (4.5) [Mꢃꢂ
/
/
Mꢃꢂ4CO], 252 (59.8) [Mꢃꢂ
/
/
1
55.38; H, 4.09; N; 6.98. Calc. for C18H16CrN2O5
(392.3):C, 55.11; H, 4.11; N 7.14%.
8: yield: 0.10 g (9.0% relative to [Cr(CO)6]). Green oil
/
/
/
/
/
/
at room temperature (r.t.). IR (pentane, 298 K, cmꢂ1
)
1
n(CO)ꢁ
dꢁ2.31 (q, 4H, Jꢁ
Hz, CH2), 1.14 (t, 4H, Jꢁ
7.5 Hz, CH3). 13C-NMR (CDCl3): dꢁ
214.2 (cis CO), 166.1 (2 CꢁN), 28.9, 23.4 (CH2), 10.5,
10.1(CH3). MS, m/z (%): 360 (8.3) [Mꢃ], 248 (22.4)
[Mꢃꢂ4CO], 220 (100) [Mꢃꢂ
5CO], 163 (37.7)
[Mꢃꢂ
5COꢀ2Et]. C15H20CrN2O5 (360.1).
9: yield: 0.25 g (21% relative to [Cr(CO)6]). M.p.
106 8C. IR (pentane, 298 K, cmꢂ1) n(CO)ꢁ
2070 m,
1937 vs, 1916sh. H-NMR (CD3C(O)CD3): dꢁ6.26 (s,
2H, NH2), 2.41 (q, Jꢁ7.6 Hz, CH2), 2.27 (q, Jꢁ7.3 Hz,
CH2), 1.13 (t, Jꢁ7.6 Hz, CH3), 1.07 (t, Jꢁ7.6 Hz,
CH3). 13C-NMR (CD3C(O)CD3): dꢁ
221.8 (trans CO),
215.7 (cis CO), 166.2 (CÄN), 21.4 (CH2), 10.8, 10.6
(CH3). MS, m/z (%): 292 (5.27) [Mꢃ], 264 (16.8)
[MꢃꢂCO], 208 (4.8) [Mꢃꢂ
3CO], 180 (36.3)
[Mꢃꢂ4CO], 152 (75.0) [Mꢃꢂ
5CO], 123 (100)
[Mꢃꢂ
5COꢀEt]. Anal. Found: C, 40.86; H, 4.18; N,
/
2069 m, 1934 vs, 1900 s. H-NMR (CDCl3):
/
/
/
/
7.2 Hz, CH2), 2.27 (q, 4H, Jꢁ
7.3 Hz, CH3), 0.99 (t, 4H, Jꢁ
221.8 (trans CO),
/
7.4
/
/
/
3.3.6. Pentacarbonyl(3,3-diethyl-5-methoxycarbonyl-
3H-pyrazole-N2)tungsten(0) (6)
/
Elution of the complex with pentaneꢃ
Yield: 0.74 g (52% relative to [W(CO)6]). M.p. 86 8C
(dec.). IR (pentane, 298 K, cmꢂ1) n(CO)ꢁ
2074 m,
/CH2Cl2 (1:9).
/
/
/
/
/
1
1990 w, 1945 vs, 1941 vs, 1921 m, 1747 m. H-NMR
(CD3C(O)CD3): dꢁ8.36 (s, 1H, C7ꢀH), 3.94 (s, 3H,
OꢀCH3), 2.5ꢀ2.2 (m, 4H, CH2), 0.58 (t, Jꢁ7.4 Hz, 6H,
CH3). 13C-NMR (CD3C(O)CD3): dꢁ
201.9 (trans CO),
/
1
/
/
/
/
/
/
/
/
/
/
/
197.5 (cis CO), 158.4 (C9), 154.4 (C7), 152.8 (C8), 107.0
/
(C6), 52.0 (OCH3), 31.0 (CH2), 8.1 (CCH3). MS: m/z
/
(%): 506 (28.5) [Mꢃ], 450 (56.4) [Mꢃꢂ
/
2CO], 422 (45)
5CO], 337 (36) [Mꢃꢂ
Et]. Anal. Found: C, 34.74; H, 3.46; N, 5.30.
Calc. for C14H14N2O7Wꢄ0.25 pentane (506.1ꢃ18.0):
C, 34.91; H, 3.25; N, 5.34%.
[Mꢃꢂ
/
3CO], 366 (100) [Mꢃꢂ
/
/
/
/
5COꢀ
/
/
/
/
/
/
/
9.50. Calc. for C10H12CrN2O5 (292.2): C, 41.10; H, 4.14;
N, 9.59%.
3.4. Reaction of h2-pentacarbonyl(phenylethyne)-
chromium with 3-diazopentane: pentacarbonyl(3,3-
3.5. Reaction of h2-benzoylethyne(pentacarbonyl)-
chromium with 3-diazopentane: pentacarbonyl(3,3-
diethyl-5(benzoyl-3H-pyrazole-N2)chromium(0) (10)
and 3,3-diethyl-4-(N-pentane hydrazone)-5-
benzoylpyrazoline (11)
diethyl-5-phenyl-3H-pyrazole-N2)chromium(0) (7),
pentacarbonyl(tetraethyl azine)chromium(0) (8), and
pentacarbonyl(diethyl ketonehydrazone)chromium(0)
(9)
At ꢂ
lative to [Cr(CO)6]) was added to the concentrated
CꢀPh)]. The progress of
the reaction was monitored by IR spectroscopy. After
ca. 45 min, the solvent was removed in vacuo and the
/
30 8C, two equivalents of 3-diazopentane (re-
At ꢂ
lative to [Cr(CO)6]) were added to the concentrated
solutions of [(CO)5Cr(HCÅCꢀC(O)Ph)]. After ca. 15
min, the solvent was removed in vacuo and the residue
was chromatographed at ꢂ50 8C on silica gel. Elution
with pentane gave first [Cr(CO)6], and then with
pentaneꢃCH2Cl2 (9:1) a red band containing the 3H-
pyrazole complexes 10. Finally, with pentaneꢃCH2Cl2
/
30 8C, two equivalents of 3-diazopentane (re-
solutions of [(CO)5Cr(HCÅ
/
/
/
/
/
residue was chromatographed at ꢂ
Elution with pentane gave first [Cr(CO)6] and then with
pentaneꢃCH2Cl2 (9:1) a red band containing the 3H-
/
50 8C on silica gel.
/
/
/

12
M.M. Abd-Elzaher et al. / Journal of Organometallic Chemistry 669 (2003) 6ꢀ13
/
(7:3) a olive-green band was eluted containing com-
pound 11. Complex 10 was unstable and rapidly
decomposed at room temp. It was therefore identified
by the similarity of its IR spectrum (pentane, 298 K,
[Mꢃꢂ
/
Me], 138 (57.5) [Mꢃꢂ
2Et], 94 (100) [Mꢃꢂ
/
Meꢀ
/
Et], 110 (22.9)
[Mꢃꢂ
Found: C, 59.20; H, 7.70; N, 15.30. Calc. For
C9H14N2O2 (182.2): C, 59.32; H, 7.74; N, 15.37%.
/
Meꢀ
/
/
Meꢀ
/
2 EtꢀO]. Anal.
/
cmꢂ1: n(CO)ꢁ
2065 m, 1987 m, 1942 vs, 1937 s, 1913 s,
/
1723 m) with that of the other 3H-pyrazole complexes.
11: yield: 0.53 g (54% relative to [Cr(CO)6]). Green oil
3.7. X-ray structural analyses of 3
1
at r.t. H-NMR (CDCl3): dꢁ
/
8.01 (d, Jꢁ7.2 Hz, 2H,
/
C14H14CrN2O7, molecular mass (374.27), crystal size
0.4ꢄ
dichloromethaneꢃ
clinic, space group P21/c, aꢁ
/
0.4ꢄ
0.4 mm3 (obtained by recrystallization from
/
aryl), 7.42 (m, 3H, aryl), 6.83 (s, 1H, NH), 5.53 (d, Jꢁ
2.8 Hz, 1H, C5H), 4.55 (d, Jꢁ3.0 Hz, 1H, C4H), 2.09 (q,
Jꢁ7.5 Hz, 4H, CH2), 1.78 (q, Jꢁ7.4 Hz, 2H, CH2),
1.59 (q, Jꢁ7.7 Hz, 2H, CH2), 1.02 (t, Jꢁ7.6 Hz, 3H,
Me), 0.95 (t, Jꢁ7.6 Hz, 6H, Me), 0.90 (t, 6 Jꢁ7.4 Hz,
3H, Me). 13C-NMR (CDCl3): dꢁ
188.8 (CÄO), 154.8
C(sp2)), 147.4 (CEt2), 137.8, 131.6, 129.6, 127.7
/
/
/
pentane (1:9)); crystal system mono-
˚
/
/
/
7.224(2) A, bꢁ
/
13.436(4)
3
˚
˚
˚
/
/
A, cꢁ
Zꢁ4, Dcalc
0.715 mmꢂ1, F(000) 768; scan type: adaptive v, U
range 2.34ꢀ27.08, 4943 independent reflections, 3691
reflection with I ꢀ2s(I); 217 refined parameters; R1ꢁ
0.0390, wR2ꢁ0.0941. Largest difference peak (hole): ꢃ
/
17.514(5) A, bꢁ
/
97.04(2)8; Vꢁ
/
1687.2(9) A ,
/
ꢁ
1.473 g cmꢂ3, absorption coefficient
/
/
/
/
/
(NÄ
/
/
(aryl), 71.8 (C5), 67.3 (C4), 29.2, (2 CH2), 24.0 (CH2),
21.4 (CH2), 10.7, 9.3, 8.6, 7.6 (CH3). MS, m/z (%): 328
/
/
/
/
(13.7) [Mꢃ], 244 (22.5) [Mꢃꢂ
/
2Etꢀ
2N], 172 (13.5) [Mꢃꢂ
Anal. Found: C, 68.06; H, 8.44; N, 16.43. Calc. for
C19H28N4Oꢄ0.1 CH2Cl2: (328.5ꢃ9.7): C, 68.02; H,
8.37; N, 16.62%.
/
Cꢀ
/
N], 201 (36)
ꢂ3
0.315 e A
performed at ꢂ
fibre on a Bruker P4 diffractometer (graphite mono-
(ꢂ
/
0.487 e Aꢂ3). The measurements were
˚
˚
[Mꢃꢂ
/
3Etꢀ
/
Cꢀ
/
/
4EtꢀCꢀ2N].
/
/
/
85 8C with a crystal mounted on a glass
˚
/
/
chromator, Moꢀ
/
Ka radiation, lꢁ0.71073 A). The
/
structures was solved by direct methods using the
SHELXTL-97 program package [21]. The positions of
the hydrogen atoms were calculated in ideal geometry
and refined in the ‘riding model’. All other atoms were
refined anisotropically.
3.6. Decomplexation of the 3H-pyrazole ligand in
pentacarbonyl(3,3-diethyl-5-methoxycarbonyl-3H-
pyrazole-N2)chromium(0) (3)
[Bu4N]Br (1.4 g, 4.3 mmol) was added to a solution of
3 (0.70 g). The solution was stirred for 48 h at r.t.
Gradually, the red color and the n(CO) absorptions in
the IR spectrum disappeared. The precipitate was
filtered over kieselgur and washed with cold pentane.
The solvent was evaporated to afford the 3H-pyrazole.
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 194293 and 194294 for
compounds 3 and 5, respectively. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
Yield: 0.46 g (66%). M.p. 95 8C. IR (pentane, 298 K,
1
cmꢂ1) n(CO)ꢁ
/
1758 m. H-NMR (CDCl3): dꢁ
/
7.68 (s,
2.0 (m, 4H, CH2),
0.68 (t, 6H, CH3). 13C-NMR (CDCl3): dꢁ
152.8 (CO),
1H, CH), 4.02 (s, 3H, OCH3), 2.2ꢀ
/
/
UK (Fax: ꢃ44-1223-336033; e-mail: deposit@ccdc.cam.
/
148.4 (C6), 133.9 (C7), 107.2 (C8), 52.5 (OCH3), 27.0
(CH2), 10.4 (CCH3). MS (FAB), m/z (%): 183 (100)
ac.uk or www: http://www.ccdc.cam.ac.uk).
[Mꢃꢃ
/
H], 152 (70) [Mꢃꢃ
/
HꢀOMe]. Anal. Found: C,
/
59.11; H, 7.72; N, 15.15. Calc. for C9H14N2O2 (182.2):
C, 59.32; H, 7.74; N, 15.37%.
Acknowledgements
The compound 3,3-diethyl-5-methoxycarbonyl-3H-
pyrazole was independently prepared from 2.0 g (24
mmol) of methyl propynoate in 5 ml of CH2Cl2 and one
equivalent of 3-diazopentane in 15 ml of diethyl ether.
Mokhles M. Abd-Elzaher thanks the Alexander von
Humboldt Foundation for a research fellowship. Sup-
port of these investigations by the Fonds der Che-
mischen Industrie is gratefully acknowledged.
After mixing the solutions at ꢂ30 8C, the red color of 3-
/
diazopentane disappeared within 1 min. The reaction
mixture was warmed to r.t. The solvent was removed in
vacuo and the residue was recrystallized from diethyl
ether. Yield: 3.42 g (79%). M.p. 95 8C. IR (pentane, 298
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152.8 (CO), 148.4
/
1758m. 1H-NMR (CDCl3): dꢁ
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