Synthesis of rhenium carbonyl complexes bearing substituted pyrrolyl ligands

Article abstract of DOI:10.1021/om800348a

The formation of rhenium carbonyl complexes incorporating substituted pyrrolyl ligands was studied: the η⁵ coordination mode of the pyrrolyl motif was not favored, while several bidentate monosubstituted pyrrolyl rhenium complexes were synthesi

Full text of DOI:10.1021/om800348a

Organometallics 2008, 27, 2911–2914
2911
Synthesis of Rhenium Carbonyl Complexes Bearing Substituted
Pyrrolyl Ligands
Jean-Hugues Mirebeau,† Franck Le Bideau,*,† Je´roˆme Marrot,‡ and Ge´rard Jaouen†
Laboratoire de Chimie et Biochimie des Complexes Mole´culaires, UMR 7576, Ecole Nationale Supe´rieure
de Chimie de Paris, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France, and Institut LaVoisier
de Versailles, UMR 8180, UniVersite´ de Versailles-Saint-Quentin-en-YVelines, 45 aVenue des Etats-Unis,
78035 Versailles Cedex, France
ReceiVed April 18, 2008
Scheme 1. Design of Potential Radiopharmaceuticals
Incorporating the Cyclopentadienyltricarbonylrhenium Group
Summary: The formation of rhenium carbonyl complexes in-
corporating substituted pyrrolyl ligands was studied: the η5
coordination mode of the pyrrolyl motif was not faVored, while
seVeral bidentate monosubstituted pyrrolyl rhenium complexes
were synthesized. It was shown that these species easily lose
onecarbonylinrefluxingTHForinthepresenceoftriphenylphosphine.
Our interest in bioorganometallic chemistry,1 and in particular
in the design of new potential radiopharmaceuticals incorporat-
ing rhenium,2 led us and others to the synthesis of complexes
based on the association of a robust, low-valent, and relatively
unhindered cyclopentadienyltricarbonylrhenium unit with bio-
molecules (Scheme 1) known for their capability for binding
to estrogen receptors (ERR and ERꢀ).3
Scheme 2. Examples of Organometallic Complexes of
Rhenium Bearing Pyrrolyl or Substituted Pyrrolyl Ligands
In order to find new species of biological interest, and to
explore new synthetic routes in the field of organometallic
chemistry, we envisaged a modification of the nature of the
cyclopentadienyl link between the biomolecule and the metal.
For that purpose, the corresponding isoelectronic pyrrolyl group
has emerged as a good candidate, principally due to the large
occurrence of the pyrrole motif in natural products4 but also
because of the interest in its use in the field of organometallic
* To whom correspondence should be addressed. E-mail: franck-
lebideau@enscp.fr.
† Ecole Nationale Supe´rieure de Chimie de Paris.
‡ Universite´ de Versailles-Saint-Quentin-en-Yvelines.
(1) Jaouen, G. Bioorganometallics. Biomolecules, Labelling, Medicine;
Wiley-VCH: Weinheim, Germany, 2005.
(2) (a) Alberto, R. In Radiopharmaceuticals: Bioorganometallics. Bio-
molecules, Labelling, Medicine; Jaouen, G., Ed.; Wiley-VCH: Weinheim,
Germany, 2005. (b) Le Bideau, F.; Salmain, M.; Top, S.; Jaouen, G. Chem.
Eur. J. 2001, 7, 2289.
chemistry.5 The use of this ligand for the synthesis of organo-
metallic species of rhenium has not been widely studied (Scheme
2). Gladysz et al. reported6 the first η1-pyrrolyl-C complex 1,
prepared from the corresponding η1-pyrrolyl-N species. A few
other examples, such as compounds 2 and 3, were respectively
described by the groups of Bergman7 and Harman.8 The η5
coordination mode between the pyrrolyl ring and the rhenium
atom has been rarely encountered in the literature. Felkin and
Zakrzewski9 were pioneers in this field with the synthesis of 4,
while compound 5, reported by Ziegler et al.,10 is the only
example of a rhenium complex incorporating both carbonyl
ligands and an η5-pyrrolyl ring.
(3) (a) Ferber, B.; Top, S.; Vessie`res, A.; Welter, R.; Jaouen, G.
Organometallics 2006, 25, 5730. (b) Top, S.; Vessie`res, A.; Pigeon, P.;
Rager, M.-N.; Huche´, M.; Salomon, E.; Cabestaing, C.; Vaissermann, J.;
Jaouen, G. ChemBioChem. 2004, 5, 1104. (c) Masi, S.; Top, S.; Boubekeur,
L.; Jaouen, G.; Mundwiler, S.; Spingler, B.; Alberto, R. Eur. J. Inorg. Chem.
2004, 17, 2013. (d) Le Bideau, F.; Pe´rez-Luna, A.; Marrot, J.; Rager, M.-
N.; Ste´phan, E.; Top, S.; Vessières, A.; Jaouen, G. Tetrahedron 2001, 57,
3939. (e) Le Bideau, F.; Kaloum, E.-B.; Haquette, P.; Kernbach, U.; Marrot,
J.; Ste´phan, E.; Top, S.; Vessie`res, A.; Jaouen, G. Chem. Commun. 2000,
211. (f) Bigott, H. M.; Parent, E.; Luyt, L. G.; Katzenellenbogen, J. A.;
Welch, M. J. Bioconjugate Chem. 2005, 16, 255. (g) Cesati, R. R., III;
Tamagnan, G.; Baldwin, R. M.; Zoghbi, S. S.; Innis, R. B.; Kula, N. S.;
Baldessarini, R. J.; Katzenellenbogen, J. A. Bioconjugate Chem. 2002, 13,
29. (h) Mull, E. S.; Sattigeri, V. J.; Rodriguez, A. L.; Katzenellenbogen,
J. A. Bioorg. Med. Chem. 2002, 10, 1381. (I) Spradau, T. W.; Katzenel-
lenbogen, J. A. Bioorg. Med. Chem. Lett. 1998, 8, 3235. (j) Liu, Y.; Spingler,
B.; Schmutz, P.; Alberto, R. J. Am. Chem. Soc. 2008, 130, 1554. (k) Schibli,
R.; Schwarzbach, R.; Alberto, R.; Ortner, K.; Schmalle, H.; Dumas, C.;
Egli, A.; Schubiger, P. A. Bioconjugate Chem. 2002, 13, 750. (l) Wald, J.;
Alberto, R.; Ortner, K.; Candreia, L. Angew. Chem., Int. Ed. 2001, 40, 3152.
(4) (a) Fan, H.; Peng, J.; Hamann, M. T.; Hu, J.-F. Chem. ReV. 2008,
108, 264. (b) Walsh, C. T.; Garneau-Tsodikova, S.; Howard-Jones, A. R.
Nat. Prod. Rep. 2006, 23, 517. (c) Fu¨rstner, A. Angew. Chem., Int. Ed.
2003, 42, 3582. (d) Bellina, F.; Rossi, R. Tetrahedron 2006, 62, 7213.
The presence of voluminous ligands such as phosphines,
tetramethylpyrrolyl, and tris(pyrazolyl)borate (Tp) in these
examples is a handicap for the design of species as potential
(5) Rakowski DuBois, M. Coord. Chem. ReV. 1998, 174, 191.
(6) Johnson, T. J.; Arif, A. M.; Gladysz, J. A. Organometallics 1993,
12, 4728.
(7) Simpson, R. D.; Bergman, R. G. Organometallics 1992, 11, 3980.
(8) Myers, W. H.; Welch, K. D.; Graham, P. M.; Keller, A.; Sabat, M.;
Trindle, C. O.; Harman, W. D. Organometallics 2005, 24, 5267.
(9) Felkin, H.; Zakrzewski, J. J. Am. Chem. Soc. 1985, 107, 3374.
(10) Joachim, J. E.; Apostolidis, C.; Kanellakopulos, B.; Meyer, D.;
Raptis, K.; Rebizant, J.; Ziegler, M. J. Organomet. Chem. 1994, 476, 77.
10.1021/om800348a CCC: $40.75
2008 American Chemical Society
Publication on Web 05/28/2008

2912 Organometallics, Vol. 27, No. 13, 2008
Communications
Scheme 4. Toward the η5 Coordination Mode
Scheme 3. Design of Potential Radiopharmaceuticals
Incorporating a Substituted Pyrrolyl Tricarbonylrhenium or
Tetracarbonylrhenium Group
radiopharmaceuticals when one has to consider the necessity
of strong binding to the receptor studied. The less hindered
carbonyl ligands are thus much more appropriate for such a
purpose, as previously demonstrated in the cyclopentadienyl
series.2,3 The first target which comes to mind is the corre-
sponding η5 species 6 (Scheme 3), incorporating a biomolecule
(B) on the pyrrolyl ring. As mentioned above, such a complex
has been synthesized just once in the tetramethyl-substituted
form 5 (Scheme 2), which forbids any extra substitution or link
with a biomolecule. Furthermore, the presence of both the
nitrogen atom and the substituent B on the ring introduces planar
chirality and an exciting challenge in separating the resulting
enantio- or diastereomers. On the other hand, the tetracarbonyl
η1 complex 7, built on a strong bidentate pyrrolyl group, offers
more possibilities for the attachment of the biomolecule part
on the ring as well as on the chelating arm (Scheme 3). This
type of ligand was used once, in a pyrrolylthione form for the
synthesis of an inorganic species of rhenium.11
Scheme 5. Synthesis of Bidentate 2-Substituted Pyrrolyltetra-
carbonylrhenium Complexes
8 in 46% yield (Scheme 4), according to a procedure reported
in the literature for the trimethylsilyl-substituted pyrrole.16
This compound was deprotonated in the presence of potas-
sium hydride, and the resulting salt was reacted with bromorhe-
nium pentacarbonyl in refluxing toluene (Scheme 4) for 30 min.
The 1H NMR spectra of the crude reaction mixture showed the
presence of a new compound, characterized by a pronounced
magnetic shielding of its pyrrolyl protons (dd at 5.94, 4.92, and
4.60 ppm in C6D6; see the Supporting Information) in com-
parison with the free corresponding pyrrole (ddd at 6.64, 6.54,
and 6.39 ppm in C6D6) and consistent with an η5 coordination
mode with loss of the double -bond character in the ring, as
encountered in the manganese series.17 Unfortunately, any
atempts to isolate this supposed complex 10 were unsuccessful.
For the study concerning the bidentate pyrrolyl ligands
(compound 7 in Scheme 3), the four monosubstituted com-
mercially available pyrroles 11a-d were reacted in refluxing
toluene for 1 h in the presence of bromorhenium pentacarbonyl
and potassium tert-butoxide to give the corresponding com-
plexes 12a-d in medium to good yields (43-75%) (Scheme
In this preliminary study, we will focus on obtaining simple
η5 or bidentate pyrrolyl organometallic compounds, while the
tethering of a biomolecule will be the subject of future research.
The η5 complexation mode (compound 6 in Scheme 3) was
first investigated in this study. Thus, pyrrole and simple mono-
or dicoordinating alkyl- or phenyl-substituted pyrroles were
reacted according to the reaction conditions encountered in the
cyclopentadienyl series, with dirhenium decacarbonyl under
neutral conditions12 or bromorhenium pentacarbonyl and its
derivatives (BrRe(CO)3(CH3CN)2, [BrRe(CO)3(THF)]2) under
basic conditions.13 Despite great effort and a thorough screening
of reaction conditions (nature of the solvents and bases,
modification of concentrations and temperatures), we were not
able to isolate any desired products. The reason for this failure
could be explained by a poorer σ-donor character of the pyrrolyl
ring compared to that of the cyclopentadienyl ring which was
studied in the manganese series.14 It was thus shown15 that in
comparison with the cyclopentadienyltricarbonylmanganese
compounds, the higher ν(CO) frequencies encountered in the
corresponding pyrrolyl species reflected a greater instability of
the metal-CO bond as well as the metal-pyrrolyl bond in these
molecules. To overcome this lack of electron density on the
metal, the pyrrole 9 containing a dimethylphenylsilyl donor
substituent was synthesized in two steps from the N-Boc pyrrole
1
5). In contrast to the H NMR spectra of compound 10, these
derivatives show a pronounced magnetic deshielding of the
pyrrolyl protons in comparison with the case for the free
corresponding pyrrole ligands, reflecting the lower π-electron
density of the aromatic ring and consistent with an η1 coordina-
tion mode (see the Experimental Section). The four carbonyl
stretches of these complexes in the IR spectra, ranging from
1943 to 2012 cm-1, are consistent with C2V symmetry.
These compounds may be placed in the order R ) CCl3 ≈
OMe < H, Me in terms of increasing stability. The trichloro-
acetyl derivative 12a, in particular, was not fully characterized
due to its fast decomposition (see the Experimental Section).
This can be attributed to the strong electron-withdrawing effect
of the chlorine atoms, which weakens the corresponding
(11) Selivanova, S.; Dolphin, D.; Van Lier, J. E.; Kudrevich, S. V. Inorg.
Chim. Acta 2003, 349, 58.
(12) Le Bideau, F.; He´nique, J.; Pigeon, P.; Joerger, J.-M.; Top, S.;
Jaouen, G. J. Organomet. Chem. 2003, 668, 140.
(13) Plazuk, D.; Le Bideau, F.; Perez-Luna, A.; Ste´phan, E.; Vessie`res,
A.; Zakrzewski, J.; Jaouen, G. Appl. Organomet. Chem. 2006, 20, 168.
(14) (a) Joshi, K. K.; Pauson, P. L.; Qazi, A. R.; Stubbs, W. H. J.
Organomet. Chem. 1964, 1, 471. (b) Ji, L.-N.; Kershner, D. L.; Rerek, M. E.;
Basolo, F. J. Organomet. Chem. 1985, 296, 83. (c) Kershner, D. L.;
Rheingold, A. L.; Basolo, F. Organometallics 1987, 6, 196.
(15) King, R. B.; Efraty, A. J. Organomet. Chem. 1969, 20, 264.
(16) Hasan, I.; Marinelli, E. R.; Chang Lin, L.-C.; Fowler, F. W.; Levy,
A. B. J. Org. Chem. 1981, 46, 157.
(17) Kershner, D. L.; Basolo, F. J. Am. Chem. Soc. 1987, 109, 7396.

Communications
Organometallics, Vol. 27, No. 13, 2008 2913
Figure 1. Molecular structure of 12c. Selected bond lengths (Å)
and angles (deg): Re-C(1) ) 2.005(5), Re-C(2) ) 1.950(5),
Re-C(3) ) 1.917(5), Re-C(4) ) 2.020(5); O(6)-Re-N(5) )
75.96,C(2)-Re-C(3))91.65,C(1)-Re-C(2))90.26,C(1)-Re-C(3)
) 86.74, C(3)-Re-C(4) ) 87.52, C(2)-Re-C(4) ) 91.52.
Figure 2. Molecular structure of 14. Selected bond lengths (Å)
and angles (deg): Re-C(1) ) 1.955(9), Re-C(2) ) 1.941(8),
Re-C(3) ) 1.904(9), Re-P ) 2.496(2); O(4)-Re-N ) 75.1,
C(2)-Re-C(3) ) 92.2, C(1)-Re-C(2) ) 91.5, C(1)-Re-C(3)
) 88.4, N-Re-P ) 90.5, O(4)-Re-P ) 89.70.
Scheme 6. Transformation of 12c in Refluxing THF
Scheme 8. Synthesis of Tetracarbonyl- and Tricarbonyl-
rhenium Compounds from the Substituted Pyrrole 15
Scheme 7. Substitution of One Carbonyl Group in 12d by
Triphenylphosphine
of a doublet (JC-P ) 28.5 Hz) for the CO anti to the phosphine
and confirmed by an X-ray diffraction study (Figure 2).
As previously mentioned, the binding arm in our model
(Scheme 3) could include the bioligand through its attachment
to the L atom. To test this idea, the imine 15 was reacted with
bromorhenium pentacarbonyl under the same reaction conditions
as for the corresponding pyrrole carboxaldehyde 11c (Scheme
8). Complex 16 was thus isolated in 85% yield and fully
characterized. This compound reacted with triphenylphosphine
at THF reflux for 1 h to give 17 in 22% yield, which presents
once again a cis substitution of one carbonyl by the phosphine
group.
We have studied in this work the access to tricarbonyl- or
tetracarbonylrhenium complexes bearing 2-substituted pyrrolyl
ligands. We have shown that the η5 coordination mode of the
pyrrolyl ring was not easy to reach, since only one example of
such a product type incorporating a silyl substituent was detected
in the crude reaction mixture without being isolated. On the
other hand, and despite the low affinity of a low-valent rhenium
metal center for hard nitrogen and oxygen donor ligands, we
have synthesized a series of stable bidentate O,N and N,N
pyrrolyl complexes. Most of them are stable enough to be flash
chromatographed and kept neat at room temperature for at least
1 month without noticeable decomposition. Their reactivity
toward substitution was studied and showed that these species
easily lose one carbonyl ligand in the presence of triphenylphos-
phine or in a coordinating solvent like THF to give the
corresponding tricarbonyl compounds, even at room tempera-
ture. In addition to the synthesis of potential radiopharmaceu-
ticals, which is currently under investigation with the incorpo-
ration of the B part, this CO lability is very promising in the
new field of CO-releasing molecules.19
oxygen-rhenium link. On the other hand, the relative instability
of the more donating methoxy group in compound 12b could
be the result of a greater cis labilization of one carbonyl group.
Crystals of compound 12c were grown in pentane at low
temperature (-15 °C), and its structure was confirmed by an
X-ray diffraction study (Figure 1). The average rhenium-carbonyl
bond length for the terminal carbonyl groups trans to the pyrrolyl
bidentateligand(1.93Å)isshorterthantheaveragerhenium-carbonyl
bond length in the cis position (2.01 Å). This is in accordance
with the mutual trans influence of these latter carbonyl groups
and their greater lability under substitution conditions in the
presence of L type ligands, as previously reported in the
literature for other tetracarbonylrhenium complexes.18
Refluxing compound 12d in THF for 2 h gave the new
complex 13 (Scheme 6). The position of the THF ligand was
1
ascribed on the basis of the H NMR spectrum of the crude
reaction mixture, which shows, for this substitution, a diaste-
reotopic relationship of the CH2O protons (Ha and Hb as two
sets of signals at 3.69 and 3.48 ppm in CDCl3; see the
Supporting Information). Such a relationship does not exist in
the complexes arising from the substitution of the carbonyl
groups trans to the pyrrolyl unit, where the metal is no longer
a stereogenic center.
This cis substitution was confirmed by a treatment of
compound 12d with triphenylphosphine in refluxing THF for
30 min or at room temperature for 70 h, which gave the complex
14 in quantitative yield (Scheme 7). The fac configuration of
this species was assigned, in the 13C NMR, from the existence
Experimental Section Reactions were carried out under
argon. Toluene and THF were distilled over sodium benzophe-
none ketyl. Pyrroles and BrRe(CO)5 were purchased from
Aldrich and used as received. Pyrrol-2-ylmethyleneaniline was
(18) Atwood, J. D.; Brown, T. L. J. Am. Chem. Soc. 1976, 98, 3160.

2914 Organometallics, Vol. 27, No. 13, 2008
Communications
synthesized by condensation of aniline on pyrrolecarboxalde-
hyde in refluxing toluene in the presence of molecular sieves.
Thin-layer chromatography (TLC) was performed on Merck 60
F254 silica gel. Merck Gerudan SI 60 Å silica gel (35-70 µm)
was used for column chromatography. Chromatography solvents
δ 193.7, 189.4, 189.2, 184.4, 144.9, 142.8, 123.6, 117.2, 21.8.
IR (KBr): 2106, 1989, 1912, 1545 cm-1. Anal. Calcd for
C10H6NO5Re: C, 29.56; H, 1.49. Found: C, 29.50; H, 1.14.
{2-(CHNPh)-C4H3N}Re(CO)4 (16): 81% yield, pentane/
CH2Cl2 8/2, yellow solid, mp 90 °C. 1H NMR (CDCl3): δ 8.06
(d, J ) 0.9 Hz, 1H), 7.5-7.3 (m, 2H), 7.3-7.2 (m, 4H), 7.06
(dd, J ) 1.0, 3.9 Hz, 1H), 6.42 (dd, J ) 1.7, 3.9 Hz, 1H). 13C
NMR (CDCl3): δ 189.5, 189.2, 183.9, 160.8, 152.6, 143.9,
141.8, 129.5, 126.6, 122.5, 120.9, 11.6. IR (KBr): 2108, 2002,
1
were used as received. H, 13C, and 31P NMR spectra were
recorded at 20 °C at 300, 75, and 121.5 MHz, respectively, on
a Bruker AVANCE300 spectrometer. Chemical shifts (δ) are
given in ppm, referenced to the residual proton resonance of
the solvents (7.26 ppm for CDCl3; 7.16 ppm for C6D6) or to
the residual carbon resonance of the solvent (77.16 ppm for
CDCl3; 128.06 ppm for C6D6). Melting points (Kofler hot stage)
are uncorrected. Elemental analyses were performed by the
ICSN.
General Procedure for the Synthesis of the
Tetracarbonyl Complexes 12a-d and 16. A solution of
BrRe(CO)5 (1 equiv), t-BuOK (1.1 equiv), and the appropriate
pyrrole (1 equiv) in toluene (8 × 10-2 M) was heated at reflux
and stirred for 1 h. The reaction mixture was then cooled to
room temperature and purified by flash chromatography using
the appropriate eluting system.
1981, 1566 cm-1
.
General Procedure for Carbonyl Exchange. A solution of
the appropriate complex (1 equiv) with triphenylphosphine (1.1
equiv) in dry THF (1.65 × 10-2 M) was heated to reflux and
stirred for 2 h. The reaction mixture was then cooled to room
temperature and purified by flash chromatography using an
appropriate eluting system.
{2-(CH3CO)-C4H3N}Re(PPh3)(CO)3 (14): 95% yield, pe-
troleum ether/CH2Cl2 95/5, yellow solid, mp 164 °C. 1H NMR
(CDCl3): δ 7.4-7.2 (m, 9H), 7.2-7.1 (m, 7H), 6.81 (d, J )
4.1 Hz, 1H), 6.25 (dd, J ) 1.3, 4.1 Hz, 1H), 1.92 (s, 3H). 13C
NMR (CDCl3): δ 194.5 (d, 1C, J ) 55.5 Hz), 189.4, 187.2,
186.2, 141.8, 140.5, 131.9, 131.7, 128.4, 128 (d, 3C, J ) 42.8
Hz), 126.6, 126.5, 120.2, 114.5, 19.5. 31P NMR (CDCl3): δ
20.31. IR (KBr): 2022, 1923, 1892 cm-1. Anal. Calcd for
C27H21NO4PRe: C, 50.62; H, 3.30. Found: C, 50.76; H, 3.41.
{2-(CCl3CO)-C4H3N}Re(CO)4 (12a): 43% yield, pentane/
1
ether 5/5, yellow oil. H NMR (CDCl3): δ 7.68 (dd, J ) 0.9,
4.6 Hz, 1H), 7.58 (dd, J ) 1.2, 1.2 Hz, 1H), 6.56 (dd, J ) 1.3,
4.6 Hz, 1H). 13C NMR (CDCl3): δ 188.9, 188.7, 183.7, 181.3,
149.7, 136.1, 128.3, 120, 9.
{2-(CH3OCO)-C4H3N}Re(CO)4 (12b): 53% yield, CH2Cl2,
{2-(CHNPh)-C4H3N}Re(CO)4 (17): 99% yield, petroleum
ether/CH2Cl2 6/4, orange crystalline solid, mp 166 °C. 1H NMR
(CDCl3): δ 7.66 (dd, J ) 0.9, 1.9 Hz, 1H), 7.3-7.2 (m, 5H),
7.2-7.1 (m, 7H), 7.0-6.9 (m, 9H), 6.77 (ddd, J ) 0.9, 1.7, 3.7
Hz, 1H), 6.21 (dd, J ) 1.5, 3.8 Hz, 1H). 13C NMR (CDCl3): δ
196.4 (d, 1C, J ) 24 Hz), 188.8, 187.9, 159.2, 152.4, 143.6,
140.6, 133.6, 133.4, 130.6 (d, 3C, J ) 42 Hz), 129.9, 128.9,
128.2, 128.1, 125.6, 123.1, 119.9, 115.1. 31P NMR (CDCl3): δ
15.3. IR (KBr): 2019, 1919, 1567 cm-1. Anal. Calcd for
C32H24N2O3Pre: C, 54.77; H, 3.45. Found: C, 54.45; H, 3.18.
1
yellow oil. H NMR (CDCl3): δ 7.12 (dd, J ) 1.5, 1.5 Hz,
1H), 6.95 (dd, J ) 0.9, 3.9 Hz, 1H), 6.29 (dd, J ) 1.5, 3.9 Hz,
1H). 13C NMR (CDCl3): δ 187.5, 187.1, 173.3, 182.9, 138.7,
125.6, 116.7, 113.3, 52.2.
{2-(CHO)-C4H3N}Re(CO)4 (12c): 75% yield, pentane/
CH2Cl2 9/1, yellow crystalline solid, mp 72 °C. 1H NMR
(CDCl3): δ 8.73 (d, J ) 0.6 Hz, 1H), 7.49 (dd, J ) 1.7, 0.9 Hz,
1H), 7.30 (dd, J ) 3.2, 0.6 Hz, 1H), 6.51 (dd, J ) 3.2, 0.9 Hz,
1H). 13C NMR (CDCl3): δ 189.1, 184.4, 181.9, 147.3, 145.0,
125.5, 119.2. IR (CDCl3): 2112, 2012, 1991, 1943, 1571 cm-1
.
Anal. Calcd for C9H4NO5Re: C, 27.55; H, 1.03. Found: C,
27.91; H, 1.06.
{2-(CH3CO)-C4H3N}Re(CO)4 (12d): 73% yield, pentane/
CH2Cl2 9/1, yellow crystalline solid, mp 88 °C. 1H NMR
(CDCl3): δ 7.39 (br s, 1H), 7.18 (dd, J ) 0.9, 1.2 Hz, 1H),
6.43 (dd, J ) 1.5, 4.2 Hz, 1H), 2.45 (s, 3H). 13C NMR (CDCl3):
Acknowledgment. Financial support from the Ministe`re
de la Recherche (S. M. grant) and the Centre National de la
Recherche Scientifique are gratefully acknowledged.
Supporting Information Available: Figures giving NMR
spectra of the crude reaction mixture containing compounds 10 and
13 and CIF files giving crystal data for 12c and 14.This material is
available free of charge via the Internet at http://pubs.acs.org.
(19) (a) Alberto, R.; Motterlini, R. Dalton Trans. 2007, 1651. (b)
Johnson, T. R.; Mann, B. E.; Clark, J. E.; Foresti, R.; Green, C. J.; Motterlini,
R. Angew. Chem., Int. Ed. 2003, 42, 3722.
OM800348A