New rearrangement and fragmentation processes of group 6 alkoxyalkynyl (fischer) carbene complexes induced by aromatic diamines

Article abstract of DOI:10.1021/om020827x

The rearrangement of chromium(0) carbene complexes 4 to isocyanides 5 occurs either thermally or by SiO₂ catalysis through 1,2-diaminobenzene addition followed by breakage of the bicyclic carbene intermediate 11. Complexes 4 with 1,8-diaminonaphthalene lead in very smooth conditions to 2-substituted perimidines 9 with good yields through an unprecedented cleavage of the carbon skeleton of the metal complex in a formal retro-Aumann reaction.

Full text of DOI:10.1021/om020827x

384
Organometallics 2003, 22, 384-386
New Rea r r a n gem en t a n d F r a gm en ta tion P r ocesses of
Gr ou p 6 Alk oxya lk yn yl (F isch er ) Ca r ben e Com p lexes
In d u ced by Ar om a tic Dia m in es
Miguel A. Sierra,*,† Mar´ıa J . Manchen˜o,† J uan C. del Amo,† Israel Ferna´ndez,†
Mar Go´mez-Gallego,† and M. Rosario Torres‡,§
Departamento de Quı´mica Orga´nica and Laboratorio de Difraccio´n de Rayos X,
Facultad de Quı´mica, Universidad Complutense, 28040-Madrid, Spain
Received October 3, 2002
Sch em e 1
Summary: The rearrangement of chromium(0) carbene
complexes 4 to isocyanides 5 occurs either thermally or
by SiO2 catalysis through 1,2-diaminobenzene addition
followed by breakage of the bicyclic carbene intermediate
11. Complexes 4 with 1,8-diaminonaphthalene lead in
very smooth conditions to 2-substituted perimidines 9
with good yields through an unprecedented cleavage of
the carbon skeleton of the metal complex in a formal
retro-Aumann reaction.
2 (Scheme 1).5,6 During our ongoing research directed
toward the synthesis of cyclophanic bi- and polynuclear
group 6 metal carbene complexes,7 we observed that 1,4-
adducts such as 3 derived from the addition of 1,2-
diaminobenzene to different alkoxyalkynyl group 6
carbene complexes 4 were reactive either by gently
heating or in the presence of SiO2 (Scheme 2). Reported
herein is this novel alkoxyalkynylchromium(0) carbene
to chromium(0) isocyanide rearrangement in the Michael
adducts 3 derived from the reaction of those complexes
with 1,2-diaminobenzene,6 as well as an unprecedented
“retro-Aumann” process8 in the reaction of alkynyl-
alkoxy group 6 carbene complexes with 1,8-diamino-
naphthalene.
Many reactions of R,â-unsaturated group 6 Fischer
carbene complexes and nucleophiles are analogous to
those experienced by organic esters and amides.1 How-
ever, in many cases, the presence of the metal fragment
results in the formation of more sophisticated products
than those expected from the standard 1,4- or 1,2-
addition of the nucleophile.2 The chemistry developed
therefrom has produced an impressive array of syn-
thetically useful processes.3 Recently, we and others
have demonstrated that the metal fragment of R,â-
unsaturated chromium(0) carbene complexes also par-
ticipates in the addition reactions of simple nucleophiles
such as the hydride anion.4 Despite the number of
reactions reported for R,â-unsaturated group 6 metal
carbenes, reactions in which the carbon skeleton of the
complex is broken are rare. The first example of this
class of processes was reported by Do¨tz in the spontane-
ous retro-Fischer fragmentation of complex 1 to enyne
Sch em e 2
* To whom correspondence should be addressed. E-mail: sierraor@
quim.ucm.es.
† Departamento de Qu´ımica Orga´nica.
‡ Laboratorio de Difraccio´n de Rayos X.
§ To whom inquiries regarding the determination of the structure
of compound 5b should be addressed.
(1) This is in agreement with the statement of the isolobal analogy
principle. See: (a) Hoffmann, R. Science, 1981, 211, 995. (b) Hoffmann,
R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711.
(2) Reviews: (a) Barluenga, J .; Flo´rez, F.; Fan˜ana´s, J . J . Organomet.
Chem. 2001, 624, 5. (b) de Meijere, A.; Schirmer, H.; Duetsch, M.
Angew. Chem., Int. Ed. 2000, 39, 3964. (c) Aumann, R.; Nienaber, H.
Adv. Organomet. Chem. 1997, 41, 163.
(3) Selected reviews in the chemistry and synthetic applications of
Fischer-carbene complexes: (a) Do¨tz, K. H.; Fischer, H.; Hoffmann,
P.; Kreissel, F. R.; Schubert, U.; Weiss, K. Transition Metal Carbene
Complexes; Verlag Chemie: Deerfield Beach, FL, 1983. (b) Do¨tz, K.
H. Angew. Chem., Int. Ed. Engl. 1984, 23, 587. (c) Wulff W. D. In
Comprenhesive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon: Oxford 1995; Vol. 12, p 470. (d)
Harvey, D. F.; Sigano, D. M. Chem. Rev. 1996, 96, 271. (e) Hegedus,
L. S. Tetrahedron 1997, 53, 4105. (f) Sierra, M. A. Chem. Rev. 2000,
100, 3591.
(4) (a) Go´mez-Gallego, M.; Manchen˜o, M. J .; Ram´ırez, P.; Pin˜ar, C.;
Sierra, M. A. Tetrahedron 2000, 56, 4893. (b) Manchen˜o, M. J .; Sierra,
M. A.; Go´mez-Gallego, M.; Ram´ırez, P. Organometallics 1999, 18, 3252.
(c) Barluenga, J .; Rubio, E.; Lo´pez-Pelegr´ın, J . A.; Toma´s, M. Angew.
Chem., Int. Ed. 1999, 38, 1091.
Complexes 3a -c, obtained from the standard addition
of 1,2-diaminobenzene to alkoxyalkynylchromium(0)
carbene complexes 4a -c, evolve to new chromium-
(5) (a) Christoffers, J .; Do¨tz, K. H. Organometallics 1994, 13, 4189.
The retro-Fischer reaction of (alkylethoxy)carbene complexes (M ) Cr,
W) induced by a â-imino functionality has been reported while this
paper was being considered for publication: (b) Aumann, R.; Fu, X.;
Vogt, D.; Fro¨hlich, R.; Kataeva, O. Organometallics 2002, 21, 2736.
10.1021/om020827x CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/24/2002

Communications
Organometallics, Vol. 22, No. 3, 2003 385
containing products by gently heating in THF solution
(Scheme 2).9 These new products lacked the carbene
ligand, and their outstanding NMR characteristics were
the presence of a signal attributable to a methyl group
1
(δ ) 1.77-2.23 ppm and δ ) 18.0-20.4 ppm in H and
13C NMR, respectively), as well as a signal assignable
to a quaternary carbon at 214.5 ppm in their 13C NMR
spectra. A single monocrystal of the product derived
from complex 3b was analyzed by X-ray diffraction.10
The structure of isocyanide complex 5b was thus
established for this compound (Figure 1) and, hence, for
compounds 5a and 5c obtained from complexes 3a and
3c, respectively.11 The rearrangement alkoxychromium-
(0) carbene f pentacarbonylchromium(0) isocyanide
also occurred in the presence of silica gel, and com-
pounds 5 could be obtained by column chromatography
or by stirring a hexane/AcOEt (10:1) solution of com-
plexes 3 in the presence of SiO2. Under these conditions
compound 3c produced complex 6 resulting from the
hydrolysis of the imine group in the initially formed
isocyanide complex 5c. This is an expected result since
aliphatic imines are considerably more prone to hy-
drolysis than aromatic imines.
F igu r e 1. ORTEP view of the structure of 3b showing the
atomic numbering with 30% probability ellipsoids. Selected
bond lengths [Å] and angles [deg]: Cr1-C24 (COtrans
)
1.867(3) Cr1-(COcis) (average) 1.893(3), Cr1-C1 1.988(3),
C1-N2 1.154(3), N2-C3 1.394(3), N9-C10 1.289(3), Cr1-
C1-N2 177.2(2), C24-Cr1-C1 179.0(1).
The reaction of compound 4d with 1,2-diaminoben-
zene produced a new chromium carbene complex that
quickly evolved after SiO2 flash chromatography to the
isocyanide complex 5d and complex 6. Although this
new carbene complex was thermally stable at room
temperature, it quickly decomposed to a mixture of
unidentified products when heated in THF. The spec-
troscopic data for this new complex were consistent with
the hemiaminal 7. The hemiaminal structure also
explains the thermal stability of 7 and its evolution to
5d in the presence of acid silica gel, since hemiaminals
are not stable in acid media (Scheme 3).
(6) The identification in very low yields of pentacarbonyltungsten-
(0) allylisocyanide in the decomposition mixtures obtained during the
reaction of pentacarbonyl[(allylamino)(phenylethynyl)carbene]tungsten-
(0) and allylamine has been also reported. Moreto´, J . M.; Ricart, S. J .
Organomet. Chem. 2001, 617-618, 334.
(7) Ferna´ndez, I.; Sierra, M. A.; Manchen˜o, M. J .; Go´mez-Gallego,
M.; Ricart, S. Organometallics 2001, 20, 4304.
(8) The Aumann reaction, namely, the reaction of an alkoxyalkyl
group 6 carbene complex with an aldehyde lacking an R-hydrogen,
TMSCl, and Et3N to yield an R,â-unsaturated complex, is the standard
method to prepare this kind of compound. Aumann, R.; Heinen, H.
Chem. Ber. 1987, 120, 537.
(9) The experimental procedure for the reaction of complex 3b to
form isocyanide complex 5b is representative of the methodology
followed through this work: In a flame-dried, airless flask containing
a magnetic stirring bar, degassed by evacuation/back-filled with argon
(3 times), 100 mg (0.18 mmol) of carbene complex 3b was dissolved in
THF (3 mL). The reaction was heated at 50 °C under an argon
atmosphere until the disappearance of the starting material (10 h,
checked by TLC). The solvent was removed under reduced pressure,
and the reaction crude was dissolved into a mixture of hexane/Et2O
(2:1) and filtered through a double pad of Celite and SiO2 to yield, after
removing the solvent, 80 mg (87%) of isocyanide complex 5b as an
orange solid. When carbene complex 3b (1.13 g, 2 mmol) was submitted
to flash column chromatography on silica gel under argon pressure
935 mg (90%) of the isocyanide complex 5b was also obtained. 1H NMR
(300 MHz): δ 7.32-7.24 (m, 2H, ArH), 7.01 (t, J ) 7.3 Hz, 1H, ArH),
6.79 (d, J ) 7.8 Hz, 1H, ArH), 4.77 (s, 2H, CH), 4.40 (s, 2H, CH), 4.16
(s, 5H, Cp), 2.08 (s, 3H, CH3). 13C NMR (75 MHz): δ 216.7 (CO trans),
214.5 (Cr-CN), 214.3 (CO cis), 171.2 (CdN), 148.8, 129.5, 126.2, 123.4,
120.7 (aromatic C), 82.0 (Cq), 71.2 (CH), 69.5 (Cp), 68.8 (CH), 18.6
Sch em e 3
(CH3). IR (CCl4): ν 2141 (CN), 2056, 1998, 1954, 1626, 1464, 1215 cm-1
.
MS (ESI), [M + H]+: 521.1. Anal. Calcd C24H16CrFeN2O5: C 55.41, H
3.10, N 5.38. Found: C 55.64, H 3.27, N 5.55.
(10) Crystal was monoclinic, space group ) P2(1)/c; a ) 9.972(2) Å,
b ) 18.104(4) Å, c ) 12.532(3) Å, â ) 94.262(4)°; V ) 2257.0(8) Å3; Z
) 4; cd ) 1.531 mg‚m-3; µ ) 1.162 mm-1; F(000) ) 1056. 11 550
measured reflections were collected on a SMART CCD-Bruker diffrac-
tometer, 3967 reflections observed (I > 3σ(I)), 298 refined parameters,
R ) 0.033, (Rw ) 0.0709). The structure was solved by direct methods
and Fourier synthesis. The refinement was done by full matrix least-
squares procedures on F2 (SHELXTL version 5.1). The non-hydrogen
atoms were refined anisotropically. The hydrogen atoms were included
in calculated positions. Further crystallographic details for the struc-
ture reported in this paper may be obtained from the Cambridge
Crystallographic Data Center, on quoting the depository number CCDC
180603.
(11) Some examples of group 6 isocyanide complexes: (a) Balbo-
Block, M.; Bartel, C.; Lentz, D.; Preugschat, D. Chem. Eur. J . 2001, 7,
881. (b) Lentz, D.; Willemsen, S. J . Organomet. Chem. 2000, 612, 96.
(c) Liu, C.-Y.; Chen, D.-Y.; Lee, G.-H.; Peng, S.-M.; Liu, S.-T. Organo-
metallics 1996, 15, 1055. (d) Hahn, F. E.; Tamm, M.; Lu¨gger, T. Angew.
Chem., Int. Ed. Engl. 1994, 33, 1356. (e) Kunz, R.; Fehlhammer, W.
P. Angew. Chem., Int. Ed. Engl. 1994, 33, 330. Review: (f) Lentz, D.
Angew. Chem., Int. Ed. Engl. 1994, 33, 1315.
The scenario was totally different when 1,8-diami-
nonaphthalene was used as the nucleophile. Thus, the
reaction of alkynyl alkoxy chromium carbene complexes
4a and 4d with 1,8-diaminonaphthalene in Cl2CH2 at
room temperature produced a new complex identified
as pentacarbonyl[(ethoxy)(methyl)carbene]chromium(0),
8a , together with a new organic material lacking any
metal moiety. The spectroscopic and analytical data of
these organic compounds were fully consistent with a
perimidine structure 9.12 The reaction is independent
of the substituent attached to the triple bond. Thus,
phenyl and alkyl substituents are compatible with the
fragmentation, producing the heterocyclic compounds
9a ,b in goods yields (Scheme 4). Tungsten carbene
complex 4e also reacted with 1,8-naphthalenediamine,

386 Organometallics, Vol. 22, No. 3, 2003
Communications
yielding perimidine 9a and pentacarbonyl[(ethoxy)-
(methyl)carbene]tungsten(0), 8b, in 97% and 91% yields,
respectively. Therefore, the use of tungsten instead of
chromium carbene complexes exerts no influence on the
reactivity observed (Scheme 4).
perimidines 9 together with enolates 16, which after
protonation would yield carbene complexes 8 (Scheme
6). A similar 1,4-addition of a dinucleophile to an
alkynylcarbene complex was earlier reported in the
reaction of cathecol with pentacarbonyl[ethoxy(2-phe-
nylethenyl)]tungsten(0) carbene complex.14 In this case
the oxygenated Michael adduct was stable. Evidently,
in our case the bond breakage is favored by the strong
peri-interaction present in intermediate 15.
Sch em e 4
Sch em e 6
The results obtained in the reactions of complexes 4
with 1,2-diaminobenzene may be rationalized through
an initial intramolecular addition of the amino group
to the carbene carbon of complexes 3 to form zwitterionic
complexes 10.13 Compounds 10 should evolve by elimi-
nation of EtOH to form intermediates 11, which produce
the final products through their imine tautomers 12 by
breakage of the bond R to the chromium center (Scheme
5). Support for this proposal is found in the isolation of
hemiaminal complex 7, which should be formed by
EtOH addition to intermediate 12 (R ) t-Bu) (Scheme
3).
In conclusion, we have reported two new fragmenta-
tion reactions of alkynyl group 6 carbene complexes: the
thermal or SiO2-promoted rearrangement of complexes
3 to isocyanides 5 and the unprecedented “retro-
Aumann” cleavage of R,â-unsaturated group 6 Fischer
carbene complexes 4 by reaction with 1,8-diamino-
naphthalene. This latter process leads to 2-substituted
perimidines 9 with good yields under smooth conditions.
These kind of compounds have great potential as DNA-
intercalating agents and play an important role in
organic molecule-based magnets and conducting materi-
als.12 Further work directed toward the application of
these new processes to other complexes and dinucleo-
philes is actively underway in our laboratories.
Sch em e 5
Ack n ow led gm en t. Financial support by the Span-
ish Ministerio de Ciencia y Tecnolog´ıa (Grant BQU2001-
1283) is gratefully acknowledged. J .C.d.A. and I.F.
thank the MEC (Spain) for predoctoral fellowships. We
thank Dr. Susagna Ricart (CSIC-Barcelona-Spain) for
fruitful discussions.
Su p p or tin g In for m a tion Ava ila ble: Text describing the
full experimental procedure and characterization of compounds
3a -c, 4b, 5a -d , 6, 7, and 9a ,b, as well as crystallographic
information for compound 3b. This material is available free
of charge via the Internet at http://pubs.acs.org.
The particular peri-position of the two amino groups
in 1,8-diaminonaphthalene enables the double Michael
addition of this reagent to the alkynyl carbene com-
plexes 4 to form the intermediate complexes 15, through
the first 1,4-adducts 14. Cleavage of 15 would form
OM020827X
(13) Zwitterionic complexes related to 10 have been isolated in the
reactions of alkoxypentacarbonylchromium(0) carbene complexes and
different amines. See: (a) Rudler, H.; Durand-Reville´, T. J . Organomet.
Chem. 2001, 617-618, 571, and references therein. Other nucleophiles
such as tertiary phosphines and hydride anions formed structurally
related zwitterionic complexes. See: (b) Aumann, R.; J aspe, B.; La¨ge,
M.; Krebs, B. Chem. Ber. 1994, 127, 2475.
(14) (a) Camps, F.; Llebaria, A.; Moreto´, J . M.; Ricart, S.; Vin˜as, J .
M. J . Organomet. Chem. 1991, 35, C-17. (b) Camps, F.; Llebaria, A.;
Moreto´, J . M.; Ricart, S.; Vin˜as, J . M.; Ros, J .; Ya´n˜ez, R. J . Organomet.
Chem. 1992, 440, 79.
(12) For recent articles about the properties of these compounds,
see: (a) Bu, X.; Deady, L. W.; Finlay, G. J .; Baguley, B. C.; Denny, W.
A. J . Med. Chem. 2001, 44, 2004. (b) Tkacyk, K.; Tarasiuk, J .; Seksek,
O.; Borowski, E.; Garnier-Suillerot, A. Eur. J . Pharmacol. 2001, 413,
131. (c) Citterio, D.; Minamihashi, T. K.; Kuniyoshi, Y.; Hisamoto, H.;
Sasaki, S.; Suzuki, K. Anal. Chem. 2001, 73, 5339. (d) Morita, Y.; Aoki,
T.; Fukui, K.; Nakawaza, S.; Tamaki, K.; Suzuki, S.; Fuyuhiro, A.;
Yamamoto, K.; Sato, K.; Shiomi, D.; Naito, A.; Takui, T.; Nakasuji, K.
Angew. Chem., Int. Ed. 2002, 41, 1793.