Photoinduced coupling of CO and vinylidene ligands-formation of cyclobutane-1,3-diones

Article abstract of DOI:10.1021/om049188b

Photolysis of pentacarbonyl vinylidene complexes of chromium and tungsten affords cyclobutane-1,3-dione derivatives, whereas thermolysis yields binuclear vinylidene nonacarbonyl complexes. In contrast to vinylidene complexes, photolysis of the diphenylall

Full text of DOI:10.1021/om049188b

1050
Organometallics 2005, 24, 1050-1052
Communications
Photoinduced Coupling of CO and Vinylidene
LigandssFormation of Cyclobutane-1,3-diones
Mokhles M. Abd-Elzaher,† Bernhard Weibert, and Helmut Fischer*
Fachbereich Chemie, Universita¨t Konstanz, Fach M727, 78457 Konstanz, Germany
Received October 20, 2004
Summary: Photolysis of pentacarbonyl vinylidene com-
plexes of chromium and tungsten affords cyclobutane-
1,3-dione derivatives, whereas thermolysis yields binu-
clear vinylidene nonacarbonyl complexes. In contrast to
vinylidene complexes, photolysis of the diphenylalle-
nylidene chromium complex gives, without incorporation
of CO, the dimer of the allenylidene ligand, tetraphen-
ylhexapentaene.
derivatives,9 and various other products.10 These reac-
tions are assumed to be initiated by a photolytically
induced coupling of a CO ligand with the carbene ligand
to generate metal-coordinated ketenes. These are then
trapped by the substrate.1 Despite several attempts,11
it has not been possible to isolate or spectroscopically
detect the presumed ketene complexes. However, there
is considerable indirect evidence for the formation of
short-lived metal-coordinated ketenes.12
In contrast to the photochemically induced coupling,
the thermal intramolecular coupling of a CO and a CPh2
ligand to form diphenylketene has been observed in the
coordinatively unsaturated carbene complexes “(CO)4Md
CPh2” (M ) Cr, W).13 The intermolecular carbonylations
of a carbene ligand to form a ketene ligand at manga-
nese and iron centers14 and of the very electrophilic
phenylcarbene complex [(CO)5WdC(C6H4R-p)H] (R ) H,
Me)15 have likewise been reported.
The photolysis of heteroatom-stabilized carbene com-
plexes of chromium and molybdenum (Fischer carbene
complexes) in the presence of various substrates1 such
as imines, olefins, aldehydes, amines, alcohols, CO, and
isocyanides provides a convenient route to, for instance,
â-lactams,2 imidazolines, azapenams, dioxocyclams,3
cyclobutanones,4 butenolides,5 â-lactones,6 2-aminobu-
tyrolactones,7 amino acid derivatives,8 R-hydroxy acid
* To whom correspondence should be addressed. Fax: +49-7531-
883136. E-mail: helmut.fischer@uni-konstanz.de.
Recently, the controlled, reversible conversion of a
ketene ligand to carbene and CO ligands on a iridium
center has been observed16 and then studied by theo-
retical means.17 Furthermore, the rapid exchange of the
† Present address: Inorganic Chemistry Department, National
Research Centre, P.O. 12622 Dokki, Cairo, Egypt.
(1) Review: (a) Hegedus, L. S. Acc. Chem. Res. 1995, 28, 299. (b)
Hegedus, L. S. Tetrahedron 1997, 53, 4105.
(2) See e.g.: (a) McGuire, M. A.; Hegedus, L. S. J. Am. Chem. Soc.
1982, 104, 5538. (b) Hegedus, L. S.; McGuire, M. A.; Schultze, L. M.;
Yijun, C.; Anderson, O. P. J. Am. Chem. Soc. 1984, 106, 2680. (c) Borel,
C.; Hegedus, L. S.; Krebs, J.; Satoh, Y. J. Am. Chem. Soc. 1987, 109,
1101. (d) Hegedus, L. S.; Imwinkelried, R.; Alarid-Sargent, M.; Dvorak,
D.; Satoh, Y. J. Am. Chem. Soc. 1990, 112, 1109. (e) Hegedus, L. S.;
Montgomery, J.; Narukawa, Y.; Snustad, D. J. Am. Chem. Soc. 1991,
113, 5784. (f) Hegedus, L. S.; Lastra, E.; Narukawa, Y.; Snustad, D.
C. J. Am. Chem. Soc. 1992, 114, 2991. (g) Betschart, C.; Hegedus, L.
S. J. Am. Chem. Soc. 1992, 114, 5010. (h) Dumas, S.; Hegedus, L. S.
J. Org. Chem. 1994, 59, 4967. (i) Alcaide, B.; Casarrubios, L.;
Dom´ınguez, G.; Sierra, M. A. J. Org. Chem. 1994, 59, 7934. (j) Merino,
I.; Hegedus, L. S. Organometallics 1995, 14, 2522. (k) Arrieta, A.;
Cossio, F. P.; Ferna´ndez, I.; Go´mez-Gallego, M.; Lecea, B.; Manchen˜o,
Sierra, M. A. J. Am. Chem. Soc. 2000, 122, 11509.
(3) Hsiao, Y.; Hegedus, L. S. J. Org. Chem. 1998, 62, 33586.
(4) See e.g.: (a) Sierra, M. A.; Hegedus, L. S. J. Am. Chem. Soc.
1989, 111, 2335. (b) So¨derberg, B. C.; Hegedus, L. S.; Sierra, M. A. J.
Am. Chem. Soc. 1990, 112, 4364. (c) So¨derberg, B. C.; Hegedus, L. S.
J. Org. Chem. 1991, 56, 2209. (d) So¨derberg, B. C.; Bates, R. W.;
Hegedus, L. S. J. Am. Chem. Soc. 1991, 113, 923. (e) Ko¨bbing, S.;
Mattay, J.; Raabe, G. Chem. Ber. 1993, 126, 1849.
(5) (a) Miller, M.; Hegedus, L. S. J. Org. Chem. 1993, 58, 6779. (b)
Reed, A. D.; Hegedus, L. S. J. Org. Chem. 1995, 60, 3787. (c) Bueno,
A. B.; Hegedus, L. S. J. Org. Chem. 1998, 63, 684.
(6) (a) Colson, P.-H.; Hegedus, L. S. J. Org. Chem. 1994, 59, 4972.
(b) Merlic, C. A.; Doroh, B. C. J. Org. Chem. 2003, 68, 6056.
(7) Schmeck, C.; Hegedus, L. S. J. Am. Chem. Soc. 1994, 116, 9927.
(8) See e.g.: (a) Hegedus, L. S.; Schwindt, M. A.; De Lombaert, S.;
Imwinkelried, R. J. Am. Chem. Soc. 1990, 112, 2264. (b) Vernier, J.-
M.; Hegedus, L. S.; Miller, D. B. J. Org. Chem. 1992, 57, 6914. (c) Zhu,
J.; Hegedus, L. S. J. Org. Chem. 1995, 60, 5831. (d) Dubuisson, C.;
Fukumoto, Y.; Hegedus, L. S. J. Am. Chem. Soc. 1995, 117, 3697. (e)
Zhu, J.; Deur, C.; Hegedus, L. S. J. Org. Chem. 1997, 62, 7704. (f)
Klumpe, M.; Do¨tz, K. H. Tetrahedron Lett. 1998, 39, 3683.
(9) (a) Alcaide, B.; Casarrubios, L.; Dom´ınguez, G.; Sierra, M. A.
Inorg. Chim. Acta 1994, 222, 261. (b) So¨derberg, B. C.; Odens, H. H.
Organometallics 1996, 15, 5080.
(10) See e.g.: (a) Merlic, C. A.; Roberts, W. M. Tetrahedron Lett.
1993, 34, 7379. (b) Merlic, C. A.; Xu, Y.; Gladstone, B. G. J. Org. Chem.
1993, 58, 538. (c) Alcaide, B.; Casarrubios, L.; Dom´ınguez, G.; Sierra,
M. A.; Monge, A. J. Am. Chem. Soc. 1995, 117, 5604. (d) Deur, C.;
Miller, M. W.; Hegedus, L. S. J. Org. Chem. 1996, 61, 2871. (e) Merlic,
C. A.; McInnes, D. M.; You, Y. Tetrahedron Lett. 1997, 38, 6787.
(11) See e.g.: (a) Gallagher, M. L.; Greene, J. B.; Rooney, A. D.
Organometallics 1997, 16, 5260. (b) Arrieta, A.; Coss´ıo, F. P.; Ferna´n-
dez, I.; Go´mez-Gallego, M.; Lecea, B.; Manchen˜o, M. J.; Sierra, M. A.
J. Am. Chem. Soc. 2000, 122, 11509. (c) Gut, H.-P.; Welte, N.; Link,
U.; Fischer, H.; Steiner, U. E. Organometallics 2000, 19, 2354. (d)
Doyle, K. O.; Gallagher, M. L.; Pryce, M. T.; Rooney, A. D. J.
Organomet. Chem. 2001, 617-618, 269.
(12) Hegedus, L. S.; de Weck, G.; D’Andrea, S. J. Am. Chem. Soc.
1988, 110, 2122.
(13) Fischer, H. Angew. Chem. 1983, 95, 913; Angew. Chem., Int.
Ed. Engl. 1983, 22, 874.
(14) (a) Herrmann, W. A.; Plank, J. Angew. Chem. 1978, 90, 555;
Angew. Chem., Int. Ed. Engl. 1978, 17, 525. (b) Bodnar, T. W.; Cutler,
A. R. J. Am. Chem. Soc. 1983, 105, 5926. (c) Herrmann, W. A.; Plank,
J.; Kriechbaum, G. W. J. Organomet. Chem. 1984, 264, 327. (d)
Mitsudo, T.-A.; Watanabe, H.; Sasaki, T.; Watanabe, Y. T. Y.; Kafuku,
K.; Nakatsu, K. Organometallics 1989, 8, 368. (e) Gibson (nee Thomas),
S. E. G.; Ward, M. F.; Kipps, M.; Stanley, P. D.; Worthington, P. A.
Chem. Commun. 1996, 263.
(15) Fischer, H.; Jungklaus, H.; Schmid, J. J. Organomet. Chem.
1989, 368, 193.
(16) Grotjahn, D. B.; Bikzhanova, G. A.; Collins, L. S. B.; Concolino,
T.; Lam, K.-C.; Rheingold, A. L. J. Am. Chem. Soc. 2000, 122, 5222.
(17) Urtel, H.; Bikzhanova, G. A.; Grotjahn, D. B.; Hofmann, P.
Organometallics 2001, 20, 3938.
10.1021/om049188b CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/12/2005

Communications
Organometallics, Vol. 24, No. 6, 2005 1051
Scheme 1
Figure 1. Molecular structure of cyclobutanedione 3a in
the crystal state (hydrogen atoms omitted). Selected bond
lengths (Å) and angles (deg): C1-C2 ) 1.505(2), O1-C1
) 1.2211(16), C3-C2 ) 1.365(2), C3-C4 ) 1.500(2), C3-
C5 ) 1.534(2); C1-C2-C1A ) 88.6(1), C2-C1-C2A )
91.4(1), O1-C1-C2 ) 133.6(1), C1-C2-C3 ) 132.0(1).
C2-C3-C4 ) 118.0(1), C2-C3-C5 ) 123.2(1).
Scheme 2
carbonyl of the ketene ligand with CO ligands in
manganese complexes of the type [(η5-C5H4R)(CO)2Mn-
(η2-R′(Ph)CdCdO)] may also involve a carbene carbonyl
complex intermediate.18
The coupling of CO ligands with a metal-coordinated
higher homologue of carbene ligands such as vinylidene
or allenylidene ligands, however, has not been observed
until now. We now report on the first photochemically
induced coupling of a CO and a “CdC(Me)R” ligand at
chromium and tungsten and on the formation of cy-
clobutane-1,3-diones.
The cyclobutane-1,3-diones are the products of cou-
pling of CO with the vinylidene ligand followed by
dimerization of the resulting propadienone. The cou-
pling must be photolytically induced, since on thermoly-
sis of 1a,b cyclobutane-1,3-diones are not formed. The
yields considerably drop when the chromium complexes
1a,b are replaced by the tungsten complexes 2a,b. From
the photolysis of 2a,b, the cyclobutane-1,3-diones 3a,b
are obtained in only 27 and 19% yields, respectively.
The metal-carbonyl fragment can be trapped by
nucleophiles. When the photolysis of 1a or 2a is carried
out in the presence of triphenylphosphine or thiethane,
the pentacarbonyl complexes [(CO)5ML] (M ) Cr, W; L
) PPh3, S(CH2)3) are isolated from the reaction mixture
in addition to 3a (Scheme 2). The time required for
complete conversion of 1a and 2a decreases from 1 h to
about 25 to 30 min, suggesting that the coupling is
reversible. However, the yield of 3a likewise drops to
20-27%.
Presumably the coupling of CO and the vinylidene
ligand to give a propadienone proceeds by an intramo-
lecular pathway. Whether the formation of the cyclobu-
tane-1,3-diones by “dimerization” of propadienones in-
volves free propadienones or proceeds in a metal-
centered fashion is at present unknown. A metal-
centered mechanism seems more likely, since the
cyclobutane-1,3-dione 3a is also formed when the pho-
tolysis of 1a is carried out in the presence of olefins or
carbonyl compounds such as 2-methylpropene, ethyl
vinyl ether, or acetone. Products derived from cycload-
dition of the olefin or of acetone to propadienone could
not be detected. Nevertheless, the intermediacy of free
propadienones cannot completely be excluded.
The chromium vinylidene complexes 1a,b, obtained
as described previously19 by the sequential reaction of
[Cr(CO)6] with KC8, the corresponding alkynyllithium
compound, and trimethyloxonium tetrafluoroborate, are
thermally unstable and decompose in solution at room
temperature to form binuclear vinylidene-bridged nona-
carbonyl chromium complexes (see Scheme 1, complexes
4a,b).19 In contrast, photolysis of 1a,b in pentane-
dichloromethane (1:1) at -30 °C for about 1 h20 affords
reaction mixtures, from which the cyclobutane-1,3-
diones 3a,b are isolated in 62 and 58% yield in addition
to hexacarbonyl chromium (Scheme 1).
1
The H and 13C NMR spectra of 3a,b show only one
signal each for the C(sp2)-bound methyl groups, indicat-
ing the presence of a single isomer. Only two resonances
are observed for the four ring carbon atoms in the 13C
NMR spectra. Therefore, the methyl groups are trans
oriented. These conclusions are supported by the X-ray
structural analysis of 3a (Figure 1).21 The CdC and
CdO distances and the distances within the four-
membered ring are similar to those reported for related
cyclobutane-1,3-diones.23
(18) Ortin, Y.; Coppel, Y.; Lugan, N.; Mathieu, R.; McGlinchey, M.
J. Chem. Commun. 2001, 2636.
(19) Karl, C. C.; Joneleit, S.; Abd-Elzaher, M. M.; Weibert, B.;
Fischer, H. J. Organomet. Chem. 2003, 677, 46.
(20) For details on the syntheses and the spectroscopic data see the
Supporting Information.
(21) Crystal data for 3a: C8H12O, Mr ) 124.18, monoclinic, P21/n, a
) 6.829(2) Å, b ) 10.524(3) Å, c ) 10.179(3) Å, â ) 96.11(2)°, V )
727.4(4) Å3, T ) 188(2) K, Z ) 4, D ) 1.134 g/cm3, 3618 reflections
collected, 1586 unique reflections (Rint ) 0.0869), which were used in
the calculations. The final R1 and wR2 values (all data) were 0.0632
and 0.1129, respectively. The structure was solved by direct methods
using the SHELXTL-97 program package.22 The positions of the
hydrogen atoms were found and refined isotropically. All other atoms
were refined anisotropically.
Thermolysis of 1a at room temperature affords the
binuclear complex 4a in high yield. Irradiation of 4a in
(22) Sheldrick, G. M., SHELX-97, Programs for Crystal Structure
Analysis; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(23) (a) Gatehouse, B. M. Cryst. Struct. Commun. 1982, 11, 365. (b)
Gatehouse, B. M. Cryst. Struct. Commun. 1982, 11, 369.

1052 Organometallics, Vol. 24, No. 6, 2005
Communications
ligand in [(η5-C5H5)(CO)2MndCdCdC(t-Bu)2] at 100 °C
to form tetra-tert-butylhexapentaene has been re-
ported.25
Scheme 3
As has already been observed with vinylidene com-
plexes, the thermal and the photolytic reactions of 5
differ. At room temperature complex 5 in pentane-
dichloromethane slowly decomposes within about 2 days
to give hexacarbonyl chromium. The formation of 6
cannot be detected. Addition of thiethane accelerates the
decomposition process, and [(CO)5Cr{S(CH2)3}] is iso-
lated from the reaction mixture instead of hexacarbonyl
chromium. Again, hexapentaene 6 is not formed.
In carbonyl complex chemistry photolysis is often used
instead of heating to initiate substitution reactions
under mild conditions.26 Our observations show that,
when chromium and tungsten metallacumulenes are
employed, thermally and photolytically initiated reac-
tions can differ considerably. Instead of substitution
reactions the photolysis induces coupling processes in
pentacarbonyl vinylidene and allenylidene complexes
(CO/vinylidene and allenylidene/allenylidene coupling).
pentane-dichloromethane at -30 °C again yields the
cyclobutane-1,3-dione 3a. The formation of 3a from 4a
is faster (20-30 min versus 1 h) than from 1a. Whether
4a is an intermediate in the formation of 3a from 1a is
at present unknown.
In contrast to vinylidene complexes, photolysis of the
diphenylallenylidene chromium complex 5 does not give
rise to the formation of any CO-allenylidene coupling
product. Instead, irradiation of 5 in pentane-dichlo-
romethane at -30 °C affords tetraphenylhexapentaene
(6) in 83% yield,20 formed by dimerization of the
allenylidene ligand without incorporation of CO (Scheme
3).
Presumably loss of a CO ligand from 5 is much faster
than CO/allenylidene coupling. Loss of CO from 5 would
yield a coordinatively unsaturated complex that then
could react with another complex 5 to form 6. A similar
mechanism has been proposed by Casey and Anderson
to account for the observation that on thermolysis of the
carbene complex (2-oxacyclopentylidene)pentacarbonyl-
chromium mainly the dimer of the carbene ligand is
formed and no cyclobutanone.24
Acknowledgment. M.M.A.-E. thanks the Alexander
von Humboldt Foundation for a research fellowship.
Supporting Information Available: Text describing the
synthesis and characterization of the new compounds and
details of the experimental procedures and figures and tables
giving crystallographic data for 3a. This material is available
free of charge via the Internet at http://pubs.acs.org.
The photoinduced dimerization of an allenylidene
ligand has not been observed before, although the
thermal dimerization of the di-tert-butylallenylidene
OM049188B
(25) Berke, H. Angew. Chem. 1976, 88, 684; Angew. Chem., Int. Ed.
Engl. 1976, 15, 624.
(26) Review: Strohmeier, W. Angew. Chem. 1964, 76, 873; Angew.
Chem., Int. Ed. Engl. 1964, 3, 730.
(24) Casey, C. P.; Anderson, R. L. J. Chem. Soc., Chem. Commun.
1975, 895.