Novel synthesis of acyloxyferrole complexes from alkynes and their conversion to cyclobutenediones

Article abstract of DOI:10.1021/om0341395

Acyloxyferrole complexes are easily prepared by the reaction of alkynes and Fe₃(CO)₁₂/Et₃N in THF, which upon reaction with Br₂ in dichloromethane at -78°C give the corresponding cyclobutenediones in 60-90% yiel

Full text of DOI:10.1021/om0341395

Organometallics 2004, 23, 619-621
619
Novel Syn th esis of Acyloxyfer r ole Com p lexes fr om
Alk yn es a n d Th eir Con ver sion to Cyclobu ten ed ion es
Mariappan Periasamy,* Amere Mukkanti, and D. Shyam Raj
School of Chemistry, University of Hyderabad, Central University P.O.,
Hyderabad-500 046, India
Received August 28, 2003
Sch em e 1
Summary: Acyloxyferrole complexes are easily prepared
by the reaction of alkynes and Fe3(CO)12/ Et3N in THF,
which upon reaction with Br2 in dichloromethane at
-78 °C give the corresponding cyclobutenediones in
60-90% yields. The acyloxyferrole complex prepared
using diphenylacetylene and acetyl chloride was char-
acterized by single-crystal X-ray analysis.
In r od u ction
Since the early reports on the reaction of iron carbon-
yls with alkynes,1 organometallic complexes of different
structural types derived from alkynes have been pre-
pared.2,3 Among these complexes the hydroxyferrole
complexes have good synthetic potential. The simple
ferrole complex using acetylene can be readily prepared
by the reactions with iron carbonyls in water.4 Such
ferrole complexes were also prepared exploiting the
reaction of alkynes with an aqueous alkaline solution
Sch em e 2
5a
of Fe(CO)5 and by refluxing a mixture of alkynes and
Fe3(CO)12 in hydrocarbon solvents.5b However, the yields
reported in the above methods are around 5% and never
more than 18% even after 3 weeks of reaction. Hence,
such ferrole complexes are not well exploited in organic
synthesis due to the lack of a practically viable method
to prepare them in good amounts. In continuation of
studies on the development of metal cabonyl reagents
for synthetic applications,6 we wish to report here that
the Et3N-promoted reaction of Fe3(CO)12 with alkynes
and acid chlorides gives the corresponding acyloxy-
ferrole complexes (65-76% yields), which upon further
reaction with Br2 in dichloromethane at -78 °C produce
the corresponding cyclobutenediones.
Resu lts a n d Discu ssion
We have observed that the addition of Et3N and CH3-
COCl to the iron carbonyl formed using Fe3(CO)12, Et3N,
and alkyne in THF gives the corresponding acyloxy
ferrole complexes (Scheme 1). This transformation was
found to be general for various alkynes and acid
chlorides (Table 1).
* Corresponding author. E-mail: mpsc@uohyd.ernet.in.
(1) Wender, I.; Friedel, R. A.; Markby, R.; Sternberg, H. W. J . Am.
Chem. Soc. 1955, 77, 4946.
(2) (a) Hubel, W. In Organic Synthesis via Metal Carbonyls; Wender,
I., Pino, P., Eds.; Wiley-Interscience: New York, 1968; Vol. 1, p 273,
and references therein. (b) Fehlhammer, W. R.; Stolzenberg, H. In
Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G.
A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1983; Vol. 4, p 545. (c)
Sternberg, H. W.; Markby, R.; Wender, I. J . Am. Chem. Soc. 1958, 80,
1009. (d) Clarkson, V R.; J ones, E. R.; Wailes, P. C.; Whiting, M. C. J .
Am. Chem. Soc. 1956, 78, 6206.
(3) (a) Pearson, A. J .; Shively, R. J ., J r.; Dubbert, R. A. Organo-
metallics 1992, 11, 4096. (b) Pearson, A. J .; Shively, R. J ., J r.
Organometallics 1994, 13, 578. (c) Pearson, A. J .; Perosa, A. Organo-
metallics 1995, 14, 5178.
(4) Hock, A. A.; Mills, O. S. Acta Crystallogr. 1961, 14, 139.
(5) (a) Sternberg, H. W.; Friedel, R. A.; Markby, R.; Wender, I. J .
Am. Chem. Soc. 1956, 78, 3621. (b) Aime, S.; Milone, L.; Sappa, E.;
Tiripicchio, A.; Lanfredi, A. M. M. J . Chem. Soc., Dalton Trans. 1979,
1664.
The effect of other trialkylamines on the conversion
of diphenylacetylene to the corresponding acyloxyferrole
complex was examined. The ferrole complexes were
obtained in 35% and 50% yields, respectively, using
Bu3N and pyridine (entries 2 and 3).
The structural assignment of the hydroxyferrole
complex 1a was confirmed by single-crystal X-ray
analysis (Figure 1). It contains the semibridged carbonyl
group between Fe(1)-Fe(2), which was considered as a
stabilizing factor.7
(6) (a) Periasamy, M.; Radhakrihnan, U.; Brunet, J . J .; Chauvin,
R.; Elzaizi, A. Chem. Commun. 1996, 1499. (b) Rajesh, T.; Periasamy,
M. Organometallics 1999, 18, 5709.
(7) (a) Cotton, F. A.; Troup, J . M. J . Am. Chem. Soc. 1974, 96, 1233.
(b) Casarin, M.; Ajo, D.; Granozzi, G.; Tondello, E.; Aime, S. Inorg.
Chem. 1985, 24, 1241.
10.1021/om0341395 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 12/25/2003

620 Organometallics, Vol. 23, No. 3, 2004
Notes
Ta ble 1. Rea ction of Alk yn es w ith F e3(CO)12/R3N
Ta ble 2. F or m a tion of Cyclobu ten ed ion es u p on
in th e P r esen ce of R′′COCl/R3Na
Br 2 Oxid a tion a
entry
R
R′
R′′
amine complex yield (%)
acyloxyferrole complex 1
1
2
3
4
5
6
7
8
9
C6H5
C6H5
C6H5
C6H5
C6H5
C5H11
C5H11
C6H13
C6H5 CH3
C6H5 CH3
C6H5 CH3
Et3N
Bu3N
Py
1a
1a
1a
1b
1c
1d
1e
1f
76
35
50
68
72
70
72
65
68
entry
R
R′
R′′
dione
yield (%)
1
2
3
4
5
C6H5
C6H5
C5H11
C6H13
C6H5
H
H
H
H
CH3
CH3
4a
4b
4c
4d
4e
90
62
60
65
63
C6H5 p-NO2C6H4 Et3N
p-NO2C6H4
C6H5
C6H5
H
H
H
H
H
CH3
C6H5
p-NO2C6H4 Et3N
C6H5
C6H5
Et3N
Et3N
C
10H21
a
Products were identified by spectral data (IR, 1H, 13C NMR,
and comparison with reported data10). Yields are of the isolated
products and based on the amount of ferrole complexes 1 used.
Et3N
Et3N
C
10H21
1g
a
Products were identified by spectral data (IR, 1H, 13C NMR,
and single-crystal X-ray analysis for 1a ). Yields are of the isolated
products and based on the amount of alkynes used.
The use of I2 at 25 °C in the place of Br2 for the
oxidation of complex 1a gave the corresponding cy-
clobutenedione in low yield (15%) besides a mixture of
unidentified iron carbonyl complexes. In the case of the
benzoyl derivative of 1 (R′′ ) Ph), benzoic acid (65%)
was isolated besides the cyclobutenedione 4a in the
reaction with bromine. Previously, bromine and iodine
have been used in the oxidative decomplexation of
organometallic complexes.8 Further, the enolic com-
plexes of the type 5 were reported9a to give the corre-
sponding cyclobutenedione upon oxidative decomplex-
ation using FeCl3. Also, the maleoyl complexes of nickel
6 were readily decomplexed to obtain the corresponding
cyclobutenediones using maleic anhydride.9b Moreover,
some Fe, Rh, and Co complexes were reported to react
with benzocyclobutenedione to give phthaloyl complexes
of the type 6 and 7.9c
F igu r e 1. ORTEP diagram of acyloxyferrole complex 1a .
The transformation of alkynes to the complexes 1 can
be explained by a tentative mechanism outlined in
Scheme 1. Initial decomposition of the Fe3(CO)12 in the
presence of R3N would give a coordinatively unsaturated
reactive species.10c These species may further split into
other coordinatively unsaturated species before reaction
with alkynes. The resulting species would then react
with the alkyne and CO to give the maleoyl iron
complexes 2 and 3, which could undergo acylation in
the presence of R′′COCl.
Accordingly, it is reasonable to assume that the
decomplexation of the acyl complexes 1 by bromine to
the corresponding cyclobutenediones may go through
intermediates similar to 5 and 7. However, we do not
have evidence in support of such intermediates in this
transformation.
We have observed that the ferrole complexes 1 are
relatively stable under nitrogen but decompose upon
exposure to air. Whereas the ferrole 1a in alcoholic
solvents gave unclean reaction on ceric ammonium
nitrate oxidation, it remained unaffected by CuCl2 in
acetone solvent at 25 °C. Interestingly, the reaction of
1 with Br2 in dichloromethane at -78 °C produced the
corresponding cyclobutenediones in moderate to good
yields (Table 2).
In conclusion, although the mechanism and the
intermediates involved in the transformations reported
here are not clearly understood, the simple and conve-
nient methods for the conversion of alkynes to the
acyloxy ferrole complexes and cyclobutenediones have
good synthetic potential. Since certain cyclobutenedione
derivatives have potential for applications as NLO
materials, growth regulators, herbicides, and antitumor
agents11 and as versatile starting materials for the
synthesis of several functionalzed carbocycles,12 easy
accessibility of these derivatives via the methods de-
scribed here should facilitate further exploitation of such
iron carbonyl complexes in organic synthesis.
(8) (a) Ingham, W. L.; Coville, N. J . Inorg. Chem. 1992, 31, 4084.
(b) Liebeskind, L. S.; Welker, M. E.; Fengl, R. W. J . Am. Chem. Soc.
1986, 108, 6328. (c) Beckett, R. P.; Davies, S. G. Chem. Commun. 1988,
160.
(9) (a) Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds. Comprehen-
sive Organometallic Chemistry; Pergamon Press: Oxford, 1982; Vol.
4, p 554. (b) Hoberg, H.; Herrera, A. Angew. Chem., Int. Ed. Engl. 1980,
29, 927. (c) Liebeskind, L. S.; Baysdon, S. L.; South, M. S.; Iyer, S.;
Leeds, J . P.; Tetrahedron 1985, 41, 5839.
(11) (a) Cole, R. J .; Kirksey, I. W.; Cutler, H. G.; Doupkin, B. L.;
Peckhan, J . C. Science 1973, 179. (b) K. Y.; Bailey, F. C. J . Org. Chem.
1992, 52, 3278.
(10) (a) Liebeskind, L. S.; Baysdon, S. L. Tetrahedron Lett. 1984,
25, 1747. (b) Parker, M. S. A.; Rizzo, C. J . Synth. Commun. 1995, 25,
2781. (c) Periasamy, M.; Rameshkumar, C.; Radhakrihnan, U.; Brunet,
J . J . J . Org. Chem. 1998, 63, 4930. (d) Rameshkumar, C.; Periasamy,
M. Organometallics 2000, 19, 2400.
(12) (a) Zhang, S.; Liebeskind, L. S. J . Org. Chem. 1999, 64, 4042.
(b) Mingo, P.; Zhang, S.; Liebeskind, L. S. J . Org. Chem. 1999, 64,
2145. (c) Wipf, P.; Hopkins, C. R. J . Org. Chem. 1999, 64, 6881. (d)
Tiedemann, R.; Turnbull, P.; Moore, H. W. J . Org. Chem. 1999, 64,
4030.

Notes
Organometallics, Vol. 23, No. 3, 2004 621
1e: Yield: 72% (1.582 g); mp 122-125 °C (dec). IR (neat): ν
Exp er im en ta l Section
1
(cm-1) 2091, 2040, 1994, 1965, 1730. H NMR: δ 8.1-8.5 (m,
Gen er a l P r oced u r es. The X-ray diffraction measurements
were carried out at 293 K on an automated Enraf-Nonious
MACH 3 diffractometer using graphite-monochromated Mo KR
(λ ) 0.71073 cm-1) radiation. Intensity data were collected by
the ω-scan mode. The data were reduced using the XTAL
program. No absorption correction was applied. The refine-
ment for structure 1a was made by full matrix least squares
on F2 (SHELX 97). 1H NMR (200 MHz) and 13C NMR (50 MHz)
spectra were recorded in CDCl3, and TMS was used as
reference (δ ) 0 ppm). Melting points are uncorrected. IR
spectra were recorded on a J ASCO FT-5300 instrument with
polystyrene as reference. Mass spectral analyses were carried
out on a VG 7070H mass spectrometer using EI techniques at
70 eV. Fe3(CO)12 was prepared following a reported procedure
using Fe(CO)5 supplied by Fluka.13 THF was distilled over
sodium-benzophenone ketyl. Dichloromethane (DCM) was
distilled over calcium hydride and stored over molecular sieves.
Chromatographic purification was conducted by column chro-
matography using 100-200 mesh silica gel obtained from
Acme Synthetic Chemicals, India. All reactions and manipula-
tions were carried out under nitrogen atmosphere. All the
yields reported are isolated yields of materials, judged homo-
geneous by TLC analysis.
P r ep a r a tion of Acyloxyfer r ole Com p lexes 1. A mixture
of Fe3(CO)12 (4 mmol) and Et3N (10 mmol) in THF (40 mL)
was stirred for 5 min under dry nitrogen at 25 °C. Diphenyl-
acetylene (3 mmol) was added and stirred for 30 min. Then
Et3N (10 mmol) and CH3COCl (15 mmol) were added, and the
contents were further stirred at the same temperature for 12
h. Ether (100 mL) was added, and the reaction mixture was
washed successively with H2O (40 mL) and brine (2 × 50 mL),
dried over Na2SO4, and concentrated under reduced pressure.
The residue was subjected to column chromatography (silica
gel, hexane-EtOAc). Ethyl acetate (1%) in hexane eluted the
ferrole complex 1a . Crystals suitable for single-crystal X-ray
analysis were grown as follows: Complex 1a (100 mg) was
dissolved in a minimum amount of hot methanol (4 mL) and
allowed to cool to room temperature under N2 atmosphere.
1a : Yield: 76% (1.369 g); mp 152-155 °C (dec). IR (KBr):
ν (cm-1) 2083, 2042, 2005, 1956, 1749. 1H NMR: δ 1.9 (s, 6
H), 7.18-7.25 (m, 10 H). 13C NMR: δ 211.8, 207.7, 205.3, 185.5,
168.4, 130.7, 130.5, 128.5, 127.9, 125.6, 20.6.
8H), 6.15 (s, 1H), 0.8-2.8 (m, 11H). 13C NMR: δ 210.6, 207.8,
205.5, 190.6, 185.4, 162.4, 151.0, 134.2, 130.9, 123.8, 121.8,
99.2, 31.5, 29.1, 27.1, 22.1, 13.7.
1f: Yield: 65% (1.279 g). IR (neat): ν (cm-1) 2081, 2040, 2003,
1957, 1732. 1H NMR: δ 8.1-8.4 (m, 4H), 7.4-7.7(mm, 6H),
6.1 (s, 1H), 0.8-2.5 (m, 13H). 13C NMR: δ 211.4, 208.5, 205.7,
191.7, 186.5, 164.2, 134.4, 133.7, 130.5, 129.9, 129.8, 129.1,
128.8, 128.7, 122.0, 99.5, 31.3, 29.6, 29.1, 27.2, 22.4, 13.8.
1g: Yield: 68% (1.453 g). IR (neat): ν (cm-1) 2081, 2040,
2005, 1957, 1732. 1H NMR: δ 8.0-8.2, (m, 4H), 7.4-7.7 (m,
6H), 6.1 (s, 1H), 0.8-2.2 (m, 21H). 13C NMR: δ 211.3, 208.4,
205.6, 191.6, 186.5, 164.1, 133.6, 129.8, 129.1, 128.6, 122.0,
99.4, 31.8, 29.6, 29.5, 29.4, 29.3, 29.2, 29.1, 27.2, 22.6, 14.0.
P r ep a r a tion of Cyclobu ten ed ion e. To a solution of
ferrole complex 1a (1 mmol) in dichloromethane (10 mL) was
added Br2 (3 mmol) at -78 °C under nitrogen atmosphere, and
the reaction mixture was stirred at the same temperature for
1 h. The contents were brought to 25 °C, and the excess
bromine was destroyed using aqueous NaHSO3. DCM (100 mL)
was added, and the combined organic mixture was washed
with H2O (40 mL) and brine (2 × 50 mL), dried over Na2SO4,
and concentrated. The residue was subjected to column chro-
matography (silica gel, hexane-EtOAc). Ethyl acetate (1.5%)
in hexane eluted the 3,4-diphenylcyclcobutene-1,2-dione 4a .
4a : Yield: 90% (0.212 g); mp 95-96 °C (lit.10 mp 97 °C). IR
(KBr): ν (cm-1) 1780. 1H NMR: δ 7.45-7.68 (m, 6 H), 8.14
(m, 4 H). 13C NMR: δ 196.1, 187.4, 134.6, 131.2, 129.7, 128.7.
MS (EI): 235 (M+, 12%), 179 [(M+1) - (Ph2C2+1), 100%].
4b: Yield: 62% (0.099 g); mp 152-153 °C (lit.10 mp 152-
153 °C). IR (KBr): ν (cm-1) 1768. 1H NMR: δ 9.5 (s, 1H), 7.3-
8.0 (m, 5H). 13C NMR: δ 197.7, 196.0, 195.5, 178.3, 134.6,
129.5, 129.4, 128.6.
4c: Yield: 60% (0.091 g). IR (neat): ν (cm-1) 1778. 1H
NMR: δ 9.20 (s, 1H) 2.81 (t, J ) 7.3 Hz, 2H) 1.70-1.83 (m,
2H) 1.27-1.40 (m, 4H), 0.82 (t, J ) 7.3 Hz, 3H). 13C NMR: δ
208.3, 199.9, 196.6, 184.8, 31.2, 27.1, 25.6, 22.1, 13.7. MS
(EI): m/z 152 (M+, 13%), 81 [M+ - C5H11, 20%].
4d : Yield: 65% (0.108 g). IR (neat): ν (cm-1) 1786. 1H
NMR: δ 9.1 (s, 1H), 2.81 (t, J ) 7.2 Hz, 2H), 2.7-1.2 (m, 8H),
0.89 (t, J ) 7.3 Hz, 3H). 13C NMR: δ 208.3, 199.9, 196.7, 184.9,
31.8, 29.6, 28.9, 26.8, 25.9, 13.9.
4e: Yield: 63% (0.139 g). IR (neat): ν (cm-1) 1774. 1H
NMR: δ 9.21 (s, 1H), 2.75 (t, J ) 7.4 Hz, 2H), 2.42-1.23 (m,
16H), 0.81 (t, J ) 7.2 Hz, 3H). 13C NMR: δ 203.4, 199.4, 199.1,
198.7, 31.9, 31.8, 29.6, 29.5, 29.2, 29.1, 26.3, 25.9, 22.6, 13.9.
MS (EI): m/z 222 (M+, 25%), 81 [M+ - C10H21, 60%].
1b: Yield: 68% (1.662 g); mp 158-160 °C (dec). IR (KBr):
1
ν (cm-1) 2081, 2044, 2027, 1988, 1726. H NMR: δ 9.9-10 (d,
J ) 8.6 Hz, 4H), 9.6-9.7 (d, J ) 8.6 Hz, 4H), 8.8-9.0 (m, 10H).
13C NMR: δ 211.3, 208.4, 204.9, 184.7, 162.7, 150.8, 134.2,
131.5, 130.6, 130, 128.9, 128.1, 125.9, 123.7.
1c: Yield: 72% (1.132 g); mp 150-152 °C (dec). IR (neat): ν
(cm-1) 2083, 2007, 1953, 1759. 1H NMR: δ 7.3 (m, 5H), 6.1 (s,
1H), 2.1(s, 3H), 2.0 (s, 3H). 13C NMR: δ 210.6, 208.2, 206.1,
190.7, 188.1, 168.1, 168, 131.2, 129.3, 129.0, 128.6, 118.7, 99.7,
21.0, 20.8.
1d : Yield: 70% 1.348 g). IR (neat): ν (cm-1) 2081, 2040, 2000,
1957, 1732. 1H NMR: δ 7.5-8.0 (m, 10H), 6.1 (s, 1H), 0.7-2.5
(m, 11H). 13C NMR: δ 211.3, 208.4, 205.6, 191.5, 186.5, 164.1,
133.6, 129.8, 129.1, 128.6, 122.0, 99.4, 31.6, 29.2, 27.1, 22.2,
13.7.
Ack n ow led gm en t. We are thankful to the CSIR
(New Delhi) for financial support. Support of the UGC
under the “University of Potential for Excellence”
program is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: 13C NMR spectra of
the compounds 1a -1g and 4a -4e, and crystal data and
structure refinement details for 1a and CIF. This material is
available free of charge via the Internet at http://pubs.acs.org.
(13) King, R. B.; Stone, F. G. A. Inorg. Synth. 1963, 7, 193.
OM0341395