Addition of aromatic C-H bonds to terminal metal-carbonyl groups. A new method for cyclocarbonylation of aromatic groups

Article abstract of DOI:10.1021/om990352i

Treatment of CpW(CO)₃[η¹-CH₂C≡C(CH ₂)_n-Ar] (n = 0-1) with triflic acid catalysts (25 mol %) in cold CH₂Cl₂ (-95 °C) effects a new cyclocarbonylation reaction to give CpW(CO)₂(π-cyclopentenonyl) and CpW(CO)₂(π-cyclohexenonyl) compounds; these results provide direct evidence for addition of neutral aryl C-H bonds to coordinated carbonyl groups.

Full text of DOI:10.1021/om990352i

3566
Organometallics 1999, 18, 3566-3568
Ad d ition of Ar om a tic C-H Bon d s to Ter m in a l
Meta l-Ca r bon yl Gr ou p s. A New Meth od for
Cycloca r bon yla tion of Ar om a tic Gr ou p s
Yi-Ru Wu,† Gia-Hsian Lin,† Reniguntala J . Madhushaw,† Keh-Ming Horng,‡
Chu-Chen Hu,† Chien-Le Li,† Fen-Lin Liao,† Sue-Lein Wang,† and
Rai-Shung Liu*,†
Department of Chemistry, National Tsing Hua University, Hsinchu, 30043, Taiwan,
Republic of China, and Research Center for Petroleum Refinery, China Petroleum Company,
Chia-Yi, Taiwan, Republic of China
Received May 11, 1999
Summary: Treatment of CpW(CO)3[η1-CH2CtC(CH2)n-
Ar] (n ) 0-1) with triflic acid catalysts (25 mol %) in
cold CH2Cl2 (-95 °C) effects a new cyclocarbonylation
reaction to give CpW(CO)2(π-cyclopentenonyl) and CpW-
(CO)2(π-cyclohexenonyl) compounds; these results pro-
vide direct evidence for addition of neutral aryl C-H
bonds to coordinated carbonyl groups.
pound 3a and 3b in 40% and 32% yields, respectively,
after separation from a silica column. The molecular
structure6 of 3b shows that the molecule has a cyclo-
pentenone fragment fused with a phenyl ring, and the
CpW(CO)2 fragment is bound to the ketone ring in a
metal-π-allyl fashion. This information indicates that
the aryl C-H bond of compound 2 is cleaved and
inserted by a CO group to effect a substitutive carbon-
ylation. We also examined the same operation on
alkynyltungsten complex 4 (triflic acid, 0.25 equiv, -95
°C) to give two cyclohexenonyl derivatives, 5a and 5b,
in 21% and 24% yields, respectively, after separation
on a silica column. The molecular structures of 5a and
5b7,8 are also elucidated by X-ray diffraction studies to
confirm the formation of a tungsten-π-cyclohexenonyl
complex.
We also prepared various alkynyltungsten compounds
6-11 tethered with an aromatic group to generalize the
cyclizations; the yields in Table 1 are estimated after
separation on a silica column. Cyclocarbonylation of
these alkynyl compounds 6-11 follows the same reac-
tion sequence involving the use of triflic acid catalyst
(0.25 equiv) in cold CH2Cl2 (-95 °C). Entry 1 shows an
intramolecular carbonylation of a tethered 2,5-dimeth-
oxyphenyl group to yield the tungsten-π-cyclopenten-
onyl complex 12 in 55% yield. The same reaction
sequence on compound 7 gave a 44% yield of π-cyclo-
hexenonyl complex 13, as shown in entry 2. Similarly,
treatment of alkynyltungsten species 8 and 9 with triflic
acid catalysts (0.25 equiv) gave the cyclocarbonylation
products 14 and 15 in 52% and 45% yields, respectively.
Substitutive carbonylation of the aryl C-H bond to
form an aryl ketone group is a useful reaction in organic
synthesis.1 Such syntheses are generally carried out
through treatment of aromatic compounds with car-
boxylic acid derivatives in the presence of acid catalysts
(Friedel-Crafts acylation) as shown in Scheme 1 (eq 1).1
Intramolecular Friedel-Crafts reaction is an important
tool for the syntheses of natural pericyclic ketones.2
Nucleophilic attack of a metal-coordinated carbonyl
group is an important step in metal-mediated organic
syntheses.3,4 Although this synthetic method covers a
wide range of nucleophiles,3,4 to our best knowledge,
there is no precedent for attack of a neutral aryl group
at a metal-carbonyl ligand to effect a substitutive
carbonylation (Scheme 1, eq 2). A cationic metal-
carbonyl group may serve as a good candidate to realize
this carbonylation reaction because its structure re-
sembles the intermediate in Friedel-Crafts reaction.
We report here a new cyclocarbonylation for propargyl-
tungsten compounds having a tethered aryl group.
These cyclizations show the feasibility for addition of
aryl C-H bonds at coordinated carbonyl groups.
As shown in Scheme 2, alkynyltungsten compound 2
was conveniently prepared from the corresponding
propargyl tosylate 1 and CpW(CO)3Na in 80% yield.5
Treatment of compound 2 with triflic acid (25 mol %)
in cold CH2Cl2 (-95 °C) gave tungsten-π-allyl com-
(5) (a) Bell, P. B.; Wojcicki, A. Inorg. Chem. 1981, 20, 1585. (b) Wang,
S.-H.; Shiu, L.-H.; Liao, Y.-L.; Wang, S.-L..; Lee, G.-H., Peng, S.-M.;
Liu, R.-S. J . Am. Chem. Soc. 1996, 118, 530. (c) Madhushaw, R. J .;
Lee, G.-H.; Peng, S.-M.; Liu, R.-S. Organometallics, 1999, 18, 748.
(6) Compound 3b crystallizes in the monoclinic space group C2/c,
a ) 27.2181(8) Å, b ) 8.7445(2) Å, c ) 15.1753(4) Å, â ) 121.192(2)°,
V ) 3089.7(8) Å3, Z ) 8. Data were collected on a Siemens Smart-
† National Tsing Hua University.
‡ China Petroleum Company.
(1) (a) Friedel. C.; Crafts, J . M. Compt. Rend. 1877, 84, 1392. (b)
Olah, G. A. Friedel-Crafts Chemistry; Wiley: New York, 1973; p 40.
(2) (a) Reddy, P. A.; Krishna-Rao, G. S. J . Chem Soc., Perkin Trans.
1 1974, 450. (b) Katsui, N.; Matsunaga, A.; Imaizumi, K.; Masamune,
T.; Tomiyama, K. Tetrahedron Lett. 1971, 83. (c) McCombie, S. W.;
Shankar, B. B.; Ganguly, A. K. Tetrahedron Lett. 1987, 28, 4123.
(3) Bates, R. W. In Comprehensive Organometallic Chemistry, Vol
12: Transition Metal Organometallics In Organic Synthesis; Abel, E.
W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford, 1995;
Chapter 4, p 349.
CCD diffractometer, using Mo KR radiation. Final R ) 0.0264, Rw
0.0294 for 2768 reflections > 3σ(I) out of 3346 unique reflections.
)
(7) Compound 5a crystallizes in the monoclinic space group P21/c,
a ) 7.4008(4) Å, b ) 17.8675(9) Å, c ) 12.3853(6) Å, â ) 90.591(1)°, V
) 1637.7(5) Å3, Z ) 4. Data were collected on a Siemens Smart-CCD
diffractometer, using Mo KR radiation. Final R ) 0.0262, Rw ) 0.0255
for 2586 reflections > 3.0σ(I) out of 3613 unique reflections.
(8) Compound 5b crystallizes in the triclinic space group P1h, a )
7.9912(2) Å, b ) 8.2813(2) Å, c ) 12.4342(3) Å, R ) 82.061(0)°, â )
85.265(1)°, γ ) 89.076(1)°, V ) 812.2(3) Å3, Z ) 2. Data were collected
on a Siemens Smart-CCD diffractometer, using Mo KR radiation. Final
R ) 0.0323, Rw ) 0.0304 for 2498 reflections > 3.0σ(I) out of 3496
unique reflections.
(4) Collman, J . P., Hegedus, L. S., Norton, J . R., Finke, R. G.
Principles and Application of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; Chapter 7, p 403.
10.1021/om990352i CCC: $18.00 © 1999 American Chemical Society
Publication on Web 08/08/1999

Communications
Organometallics, Vol. 18, No. 18, 1999 3567
Sch em e 1
Sch em e 2
Ta ble 1. Acid -Ca ta lyzed Cycloca r bon yla tion
Rea ction
Sch em e 3
blum reported9 that protonation of propargylmetal
compounds yielded metal-η2-cis-allene cation10 A as the
kinetically favorable intermediate. This cis-configura-
tion of A is very important because it allows intramo-
lecular attack of its tethered 2,5-dimethoxybenzene
group at the coordinated CO group to effect an electro-
philic substitution, yielding species B and C sequen-
tially. Further insertion of the η1-acyl group of C gave
the observed product 12. An alternative mechanism
involves a conventional electrophilic attack of a syn-π-
allylic acid 18 at its tethered 2,5-dimethoxy benzene as
shown in eq 2. The species 18 can be generated from
the intermediate D via attack of H2O at the tungsten-
cis-allene cation A;5c commercial triflic acid normally
contains a small amount of H2O that may furnish such
a catalytic cyclocarbonylation.
The heterocyclic thiophenes of compounds 10 and 11 can
also be carbonylated intramolecularly, as shown in
entries 5 and 6, and the yields of the cyclocarbonyltion
products 16 and 17 were 59% and 44% yields, respec-
tively. The observed products 16 and 17 are consistent
with our expectation because the thienyl C2-carbon is
generally more reactive toward electrophiles than its
C3-carbon. The conjugated effect of the sulfur atom is
responsible for this effect. For 14 and 15, the absence
of the ortho-carbonylation product is probably due to
its more congested structure compared to its para-
carbonylation product.
We therefore prepared the tungsten-π-allyl complex
18 in a separate experiment. Compound 6 was treated
with triflic acid (1.0 equiv) in anhydrous diethyl ether
The results shown in Scheme 2 and Table 1 clearly
demonstrate a substitutive carbonylation for the C-H
bonds of various aromatic compounds. Two possible
mechanisms are shown in Scheme 3. Previously, Rosen-
(9) Rosenblum, M.; Raghu, S. J . Am. Chem. Soc. 1973, 95, 3062.
(10) (a) Memour, J . Y.; Charrier, C,; Benaim, J .; Roustan, J . L. J .
Organomet. Chem. 1972, 39, 321. (b) Vinson, N. A.; Day, C. S.; Welker,
M. E.; Guzei, I.; Rheingold, A. L. Organometallics 1999, 18, 1824.

3568 Organometallics, Vol. 18, No. 18, 1999
Communications
at -95 °C for 2 h to yield a dark yellow precipitate,
presumbly the η2-allene cation A. Subsequent treatment
of this salt with an aqueous Na2CO3 solution afforded
the expected acid 18 in 61% yield. The structure of 18
was confirmed by X-ray diffraction studies.11 Treatment
of compound 18 with CF3SO3H (1.0 equiv) in CH2Cl2
over various temperatures (-95 tï 23 °C) for 24 h did
not give the desired product 12 at all, and in this case
compound 18 was recovered in significant amount (50-
71% yields). This information supports a direct attack
of the aryl C-H bond at the coordinated CO group of
species A.
this cyclization is proposed to involve addition of the
tethered aryl C-H bond of a cis-η2-allene species A at
its coordinated CO group. This cyclization is a useful
tool in organic synthesis because the resulting tungsten-
π-allyl compounds have chemical versatilities in organic
syntheses.12
Ack n ow led gm en t. We gratefully acknowledge fi-
nancial support of this work from the National Science
Council, Republic of China.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates, bond distances and angles, and
thermal parameters of compounds 3a , 5a , 5b, and 18 This
material is available free of charge via the Internet at
http://pubs.acs.org.
In a summary, we have shown a new intramolecular
cyclization via treatment of various alkynyltungsten
compounds with a triflic acid catalyst. The key step of
(11) Compound 18 crystallizes in the monoclinic space group P21/n,
a ) 12.6211(2) Å, b ) 8.9088(2) Å, c ) 17.3164(5) Å, â ) 95.180(2)°, V
) 1939.1(6) Å3, Z ) 4. Data were collected on a Siemens Smart-CCD
diffractometer, using Mo KR radiation. Final R ) 0.0429, Rw ) 0.0419
for 2148 reflections > 3.0σ(I) out of 3496 unique reflections.
OM990352I
(12) Liu, R.-S. In Advances in Metal-Organic Chemistry; Liebeskind,
L. S., Ed.; J AI Press: London, 1998; Vol 5, pp 145-187.