A new route for the synthesis of an alkylideneamido complex

Article abstract of DOI:10.1039/b801799a

The synthesis of the new alkylideneamido complex [Re{N=C(Ph)C≡CPh} (CO)₃(bpy)] is described. Analysis of its spectroscopic and structural data reveals the absence of π-donation from the nitrogen to the metal. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b801799a

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www.rsc.org/njc | New Journal of Chemistry
A new route for the synthesis of an alkylideneamido complexw
a
a
a
b
´
Luciano Cuesta,z Dolores Morales, Julio Perez* and Daniel Miguel
Received (in Montpellier, France) 31st January 2008, Accepted 13th March 2008
First published as an Advance Article on the web 2nd April 2008
DOI: 10.1039/b801799a
The synthesis of the new alkylideneamido complex
[Re{NQC(Ph)CRCPh}(CO)3(bpy)] is described. Analysis of
its spectroscopic and structural data reveals the absence of
p-donation from the nitrogen to the metal.
Fig. 1 Generic azavinylidene (A) and alkylideneamido (B) complexes.
The vast majority of the mononuclear structurally-charac-
terized M(NQCR2) complexes display close to linear M–N–C
geometries as a result of the existence of significant p-donation
from the nitrogen atom to the empty metal orbitals. In
analogy with vinylidene complexes, they have been aptly
termed azavinylidenes (A, Fig. 1).1 Recently, we reported the
synthesis of the metalloimine [Re(NQCPh2)(CO)3(bpy)]
(1, bpy = 2,20-bipyridine).2 Complex 1 presents an angular
M–NQCR2 moiety, as in previously known alkylidene
compounds (B, Fig. 1),3 which are not azavinylidenes.
In our initial efforts toward the synthesis of alkylideneamido
complexes, we examined the reactions between Grignard or
alkyl lithium reagents and benzonitrile, using the complex
[Re(OTf)(CO)3(bpy)] as the source of the metallic fragment
in all cases. These reactions proved to be unproductive,
affording in all cases complicated mixtures of products. The
formation of these mixtures could be attributed to the opera-
tion of rearrangements, such as the one shown in the Scheme
2, which would cause the formation of amido species, in
addition to the desired alkylideneamido complexes. This kind
of hydrogen migration has been previously observed during
complexation studies of lithium imides with a-C–H units
attached to the CQN moiety.6
According to this observation, when 2-thienyllithium, which
does not have C–H units susceptible to undergo the isomeriza-
tion discussed above, was employed as a nucleophile, only one
organometallic compound was obtained, the spectroscopic data
(1H NMR and IR) of which are consistent with the formation of
alkylideneamido complex 2 (Fig. 2). Unfortunately, no satisfac-
tory elemental analysis could be obtained, a fact that we
attribute to the presence of the lithium triflate by-product. Thus,
the solubility of this salt is not sufficiently different from that of
the target rhenium complex, and this precluded the isolation of 2
as a pure sample. Based on these results, we decided to use
acetylides as nucleophiles because (a) they do not have hydro-
gens that could be transferred to the imido-N atom and (b) they
can be easily obtained as a non-lithium alkaline salts.
In contrast with azavinylidene complexes, the reactivity of
12,4 is dominated by the strong nucleophilicity of the alkyl-
ideneamido nitrogen, and by the ability of the ligand to
participate in insertion and cycloaddition processes; of parti-
cular interest are the reactions of N-rhenaimine 1 with iso-
cyanates2 and ketenes,4a which allowed us, after
demetallation, to isolate, in high yield and in a straightforward
manner, triazines and b-lactams, respectively. These results
encouraged us to seek an alternative synthesis of new alkyl-
ideneamido complexes. The strategy employed for the synth-
esis of 1, namely the reaction between [Re(OTf)(CO)3(bpy)]
and KNQCPh2 (generated in situ by deprotonation of the
benzophenone imine with K[N(SiMe3)2]), cannot be easily
extended to the synthesis of new kinds of alkylideneamido
complexes due to the fact that most N-unsubstituted Schiff
bases, HNQCRR0, particularly those derived from aldehydes,
or from ketones with non-aryl groups, are thermally unstable.
The synthesis of ketimines by the reaction of organomagne-
sium or organolithium compounds with nitriles, and with
subsequent hydrolysis, has been known since early in the last
century.5 We speculated that an analogous reaction, where
quenching with a cationic metal fragment replaces the final
protonation step (see Scheme 1), could allow us to synthesize
new alkylideneamido species.
The reaction of K[CRCPh] (prepared by a reaction be-
tween phenylacetylene and K[N(SiMe3)2]) with benzonitrile
and subsequent addition of the mixture to a solution of
[Re(OTf)(CO)3(bpy)] afforded the complex [Re{NQ-
C(Ph)CRCPh}(CO)3(bpy)] (3) (Fig. 2). The alkylideneamido
nature of this compound was initially inferred from its spectro-
scopic data. As expected for the formation of an alkylidenea-
mido ligand, which has a strong donor character, complex 3
a
´
´
´
Departamento de Quımica Organica e Inorganica-IUQOEM,
Facultad de Quımica, Universidad de Oviedo-CSIC, C/Julian
´
´
displays very low nCO band values (1999, 1899 and 1883 cmꢀ1
)
´
Claverıa no 8, Oviedo 33006, Spain. E-mail: japm@uniovi.es;
Fax: +34 985103446; Tel: +34 985103465
b IU CINQUIMA/Quı´mica Inorga´nica, Facultad de Ciencias,
Universidad de Valladolid, Valladolid 47005, Spain
w Electronic supplementary information (ESI) available: Crystallo-
graphic data in CIF or other electronic format (CCDC 675894). See
DOI: 10.1039/b801799a
in its IR spectrum, in good agreement with the values reported
z Current address: Department of Chemistry and Biochemistry, Uni-
versity of Texas, Austin, Texas 78712-0165, USA.
Scheme 1
ꢁc
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Scheme 2
for complex 1 (1999, 1898 and 1880 cmꢀ1). Attempts to
prepare 2 by the reaction of potassium phenylacetylide
(prepared from K[N(SiMe3)2] and phenylacetylene) with
7
[Re(NCPh)(CO)3(bpy)]BAr04
[Re(CCPh)(CO)3(bpy)]7 and 2.
afforded
a
mixture of
A single-crystal X-ray diffraction study confirmed the for-
mation of an alkylideneamido complex.w A graphical repre-
sentation of the results of the study is shown in Fig. 3.
Fig. 3 Thermal ellipsoid (30%) plot of 3.
freshly distilled prior to use. CH2Cl2 was dried over CaH2,
THF and diethyl ether were dried over Na-benzophenone, and
hexane was dried over sodium. Benzonitrile was dried with
CaCl2 prior to distillation over P2O5. K[N(SiMe3)2] (0.5 M in
toluene, Aldrich), 2-thienyllithium (1.0 M in THF, Aldrich)
and phenylacetylene (Aldrich) were used as supplied. [Re(OTf)-
(CO)3(bpy)] was prepared according to a literature procedure.9
1H NMR spectra were recorded in CD2Cl2 (stored in the dark
under a dinitrogen atmosphere over molecular sieves) on a
Bruker AV-400 spectrometer. IR spectra were recorded in a
Perkin-Elmer RX I FT-IR spectrometer using 0.2 mm CaF2
cells. Elemental analyses were carried out using a Fisons
EA-1108 analyzer (C, H and N) at the analytical services
section of the Universidad de Vigo (Vigo, Spain).
The solid state structure of 3 consists of an otherwise
unremarkable [Re(CO)3(bpy)] fragment bonded to the nitro-
gen atom of the alkylideneamido ligand, resulting from the
coupling between the acetylide and the nitrile. The
Re(1)–N(3)–C(4) angle (131.9(6)1) clearly indicates the ab-
sence of p-donation from the nitrogen to the metal (this kind
of interaction would cause the formation of angles close to
1801, as it occurs in the azavinylidene complexes). The
Re–N–C angle in 3 is in fact actually slightly lower that the
same angle in complex 1 (133.9(4)1).2 The Re–N distance in 3
is 2.130(6) A, similar to the distance found in complex 1
(2.113(4) A). When compared with rhenium azavinylidene
complexes
(for
example
[Re(OH)(NCQMe2)-
(Ph2PCH2CH2PPh2)2][HSO4] (1.901(5) A) and [ReCl-
{NCQ(H)(4-FC6H4)}(Ph2PCH2CH2PPh2)2][BF4] (1.831(8) A)),8
these values also reflect the lack of multiple-bond character of
the Re–N bond in complex 3.
Synthesis of 2
2-Thienyllithium (170 mL, 0.17 mmol, 1.0 M in THF) was
added to a solution of benzonitrile (1 mL) in THF (10 mL) at
ꢀ78 1C and stirred at room temperature for 15 min. The
resulting solution was transferred to a solution of [Re(OTf)-
(CO)3(bpy)] (0.100 g, 0.17 mmol) in THF (10 mL) at ꢀ78 1C.
After reaching room temperature, the solvent was evaporated
under reduced pressure to a volume of 5 mL. The addition of
hexane (20 mL) caused the precipitation of a red-orange solid,
which was washed with diethyl ether (2 ꢂ 5 mL) and dried
under vacuum. IR (THF; cmꢀ1): nCO = 1999, 1898 and 1882.
1H NMR (CD2Cl2; ppm): 8.84 [d, J = 5.5 Hz, 2H, bpy], 8.27
[m, 2H, bpy], 8.08 [m, 2H, bpy], 7.41 [m, 2H, bpy], 7.34–7.32
[m, 4H], 7.19–7.14 [m, 2H], 6.93 [m, 1H] and 6.76 [m, 1H]. No
satisfactory elemental analysis could be obtained.
In summary, we have successfully developed a new ap-
proach for the preparation of alkylideneamido complexes
based on the in situ-generation of alkaline imidates by the
reaction of appropriate carbanionic reagents and nitriles.
We thank the Ministerio de Ciencia y Tecnologı
BQU2003-08649 and CTQ2006-07036), the Ministerio de
Educacion y Ciencia (grant CTQ-2006-08924, an FPU pre-
doctoral fellowship to L. C. and a Ramo
D. Morales) and Junta de Castilla y Leo
´
a (grants
´
´
n y Cajal contract to
n (grant VA012C05)
´
for their support of this work.
Experimental
Synthesis of 3
General considerations
K[N(SiMe3)2] (0.35 mL, 0.17 mmol, 0.5 M in toluene) was
slowly added to a solution of phenylacetylene (22 mL, 0.17
mmol) in THF (10 mL) at ꢀ78 1C. Benzonitrile (70 mL, 0.68
mmol) was added to the resulting suspension, and the reaction
mixture was stirred for 6 h at room temperature. At this point,
a solution of [Re(OTf)(CO)3(bpy)] (0.100 g, 0.17 mmol) in
THF (10 mL) was transferred into the reaction mixture at
ꢀ78 1C. The resulting solution displayed a dark red color.
After reaching room temperature, allowing 15 min for stirring,
evaporating the solvent, extracting with CH2Cl2 (2 ꢂ 10 mL),
concentrating, precipitating by the addition of diethyl ether
All experiments were carried out under a dinitrogen atmo-
sphere employing Schlenk techniques. The solvents were
Fig. 2 Alkylideneamido complexes 2 and 3.
ꢁc
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918 | New J. Chem., 2008, 32, 917–919

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(15 mL) and washing with more of the same solvent (2 ꢂ 10
mL), compound 3 was obtained as a microcrystalline solid.
Crystallization from THF–hexane yielded 3 as dark red crys-
tals. Yield: 0.068 g (63%). IR (THF; cmꢀ1): nCO = 1999, 1899
Martı
´
n, E. Onate and J. Tomas, Organometallics, 2000, 19, 3100;
(b) T. Daniel, M. Muller and H. Werner, Inorg. Chem., 1991, 30,
3120; (c) S. G. Feng, P. S. White and J. L. Templeton, J. Am.
Chem. Soc., 1994, 116, 8613; (d) For examples of bridging azavi-
nylidenes, see: P. L. Andreu, J. A. Cabeza, I. del Rıo, V. Riera and
´
1
C. Bois, Organometallics, 1996, 15, 3004; (e) J. A. Cabeza, F.
Grepioni, M. Moreno and V. Riera, Organometallics, 2000, 19,
5424.
´
2 E. Hevia, J. Perez, V. Riera and D. Miguel, Angew. Chem., Int. Ed.,
2002, 41, 3858.
3 (a) M. E. Cucciolito, V. De Felice, F. Giordano, I. Orabona and F.
Ruffo, Eur. J. Inorg. Chem., 2001, 3095; (b) P. Zhao and J. F.
Hartwig, J. Am. Chem. Soc., 2005, 127, 11618.
and 1883. H NMR (CD2Cl2; ppm): 9.23 [m, 2H, bpy], 8.86
[m, 2H, bpy], 8.32–8.04 [m, 8H, Ph] and 7.58–7.14 [m, 6H, bpy
and Ph]. This compound decomposed during 13C NMR
studies. Anal. calc. for C28H18N3O3Re: C, 53.24; H, 2.87; N,
6.66. Found: C, 53.31; H, 2.67; N, 6.88%.
X-Ray diffraction study of 3
4 (a) E. Hevia, J. Pe
M. I. Menendez, T. L. Sordo and S. Garcı
Chem. Soc., 2003, 125, 3706; (b) L. Cuesta, E. Hevia, D. Morales,
J. Perez, V. Riera, M. Seitz and D. Miguel, Organometallics, 2005,
´
rez, V. Riera, D. Miguel, P. Campomanes,
´
´
a-Granda, J. Am.
Data were collected using a Bruker AXS SMART 1000
diffractometer with graphite monochromatized Mo-Ka X-
radiation and a CCD area detector. Raw frame data were
integrated using the SAINT10 program. A semi-empirical
absorption correction was applied by the program
SADABS.11 The structure was solved by direct methods and
refined against F2 using SHELXTL.12 All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were set
in calculated positions and refined as riding atoms with a
common thermal parameter. Crystal data for 3:
C28H18N3O3Re, M = 630.65, red plate (0.23 ꢂ 0.14 ꢂ 0.08
mm), monoclinic, P21/n, a = 11.039(7), b = 11.132(7), c =
´
24, 1772.
5 (a) E. E. Blaise, C. R. Hebd. Seances Acad. Sci., 1901, 132, 38; (b)
C. Moureu and G. Mignonac, C. R. Hebd. Seances Acad. Sci.,
1913, 156, 1801; (c) H. Gilman and R. H. Kirby, J. Am. Chem.
Soc., 1933, 55, 1265; (d) P. L. Pickard and D. J. Vaughan, J. Am.
Chem. Soc., 1950, 72, 876; (e) L. S. Cook and B. J. Wakefield, J.
Chem. Soc., Perkin Trans. 1, 1980, 2392; (f) F. J. Weiberth and S. S.
Hall, J. Org. Chem., 1987, 52, 3901.
6 R. E. Mulvey, Chem. Soc. Rev., 1991, 20, 167.
7 E. Hevia, J. Perez, V. Riera, D. Miguel, S. Kassel and A.
Rheingold, Inorg. Chem., 2002, 41, 4673.
8 M. F. C. Guedes da Silva, J. J. R. Frau
Pombeiro, Inorg. Chem., 2002, 41, 219.
9 E. Hevia, J. Perez, L. Riera, V. Riera, I. del Rı
and D. Miguel, Chem.–Eur. J., 2002, 8, 4510.
10 SAINT+: SAX Area Detector Integration Program, version 6.02,
Bruker AXS, Inc., Madison, WI, USA, 1999.
11 G. M. Sheldrick, SADABS: Empirical Absorption Correction Pro-
´ sto da Silva and A. J. L.
20.67(1) A, b = 102.73(1)1, V = 2478(3) A3, Z = 4, Dcalc
=
´
o, S. Garcıa-Granda
´ ´
1.62 g cmꢀ3, m(Mo-Ka) = 4.938 mmꢀ1, 3586 independent
reflections, 2429 observed (I 4 2s(I)), Rint = 0.0481, R1 =
0.0401, wR2 = 0.0836 (all data).w
gram, University of Gottingen, Gottingen, Germany, 1997.
¨
¨
12 G. M. Sheldrick, SHELXTL: An Integrated System for
Solving, Refining and Displaying Crystal Structures from
Diffraction Data, version 5.1, Bruker AXS, Inc., Madison, WI,
USA, 1998.
References
1 For a list of known azavinylidene complexes, see: (a) R. Castarle-
nas, M. A. Esteruelas, E. Gutierrez-Puebla, Y. Jean, A. Lledos, M.
´ ´
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New J. Chem., 2008, 32, 917–919 | 919