Oxidative carbonylation of alkynyltungsten compounds via protonation with triflic acid

Article abstract of DOI:10.1021/om980093h

Treatment of several alkynyltungsten(II) compounds with 4.0 mol equiv of CF₃SO₃H led to oxidative carbonylation to yield acyltungsten(IV) compounds; this reaction can be applied to syntheses of indanones and unsaturated carbonyl comp

Full text of DOI:10.1021/om980093h

Organometallics 1998, 17, 2683-2685
2683
Oxid a tive Ca r bon yla tion of Alk yn yltu n gsten Com p ou n d s
via P r oton a tion w ith Tr iflic Acid
Kwei-Wen Liang, M. Chandrasekharam, Chien-Le Li, and Rai-Shung Liu*
Department of Chemistry, National Tsing-Hua University,
Hsinchu 30043, Taiwan, Republic of China
Received February 12, 1998
Sch em e 1
Summary: Treatment of several alkynyltungsten(II) com-
pounds with 4.0 mol equiv of CF3SO3H led to oxidative
carbonylation to yield acyltungsten(IV) compounds; this
reaction can be applied to syntheses of indanones and
unsaturated carbonyl compounds.
The actions of organic molecules with superacids such
as triflic acid, CF3SO3H, often give rise to organic reac-
tions of unusual types.1-3 CF3SO3H can easily ionize
organic olefins, alkynes, alcohols, epoxides, acetals,
aryls, acyl halides and organic carbonyls to form reactive
carbocations, further leading to formation or scission of
carbon-carbon bonds.1-4 This principle is widely ap-
plicable to cycloaddition reaction, intramolecular cycli-
zation, electrophilic substitution of olefins and aroma-
tic compounds, addition of organic carbonyls to enol
ethers, Beckman rearrangement, and rearrangement of
phenols.1-4 Although CF3SO3H is also often used in
organometallic reactions, its scope is limited to two
major uses: generations of (1) metal hydrides5 and (2)
metal-bound carbocations.6 Scheme 1 (parts 1-3) lists
three important representatives for generation of metal
carbocations such as η2-alkene (A), η2-allene (B), and
η1-vinylidene species (C) via protonation of their cor-
responding allyl, propargyl, and alkynyl complexes.6
The significance of these three carbocations is well-
known because of their roles in many metal-mediated
or -catalyzed organic syntheses.7-9 Although numerous
studies have focused on the reactivity of these metal
carbocations, there has been no report that a Brønsted
Sch em e 2
(1) Stang, P. J .; White, M. R. Aldrichim. Acta. 1983, 16, 15.
(2) Howells, R. D.; Cown, J . D. Chem. Rev. 1977, 69.
(3) Subramanian, L. S.; Garcia, A.; Hanack, M. In Encyclopedia of
Reagents for Organic Synthesis; Paquette, L. A., Ed.; Wiley: London,
1995; Vol. 7, p 5143.
(4) For representative reactions, see: (a) Sagl, D.; Martin, J . C. J .
Am. Chem. Soc. 1988, 110, 5827. (b) Gassman, P. G.; Singleton, D. A.;
Wilwerding, J . J .; Chavan, S. P. J . Am. Chem. Soc. 1987, 109, 2182.
(c) Gassman, P. G.; Singleton, D. A. J . Org. Chem. 1986, 51, 3075. (d)
Olah, G. A.; Wu, A. J . Org. Chem. 1991, 56, 2531. (e) Olah, G. A.; Ernst,
T. D. J . Org. Chem. 1989, 54, 1203. (f) Kawai, M.; Onaka, M.; Izumi,
Y. Bull. Chem. Soc. J pn. 1988, 61, 1237. (g) Hulin, B.; Koreeda, M. J .
Org. Chem. 1984, 49, 207. (h) Childs, R. F.; Shaw, G. S.; Varadarajan,
A. S. Synthesis 1982, 198.
(5) Review papers: (a) Norton, J . R. In Inorganic Reactions and
Methods; Verlag Chemie: Weinheim, Germany, 1987. (b) Pearson, R.
G. Chem. Rev. 1985, 85, 41.
(6) (a) 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 8, p 619.
(b) Hegedus, L. S., Transition Metals in the Synthesis of Complex
Organic Molecules; University Science Books: Mill Valley, CA 1994;
Chapter 8, p 433.
(7) For organic syntheses via metal-η2-alkene cations, see the
following representative papers: (a) Welker, M. E. Chem. Rev. 1992,
92, 97. (b) J iang, S.; Turos, E. Organometallics 1993, 12, 4280. (c) J iang,
S.; Turos, E. Tetrahedron Lett. 1991, 4639. (d) Rosenblum, M.; Watkins,
J . C. J . Am. Chem. Soc. 1990, 112, 6316.
acid can oxidize a metal center via protonation of these
unsaturated metal hydrocarbonyl complexes. In this
communication, we report the new discovery that CF3-
SO3H can induce oxidative carbonylation of tungsten-
S0276-7333(98)00093-4 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 06/05/1998

2684 Organometallics, Vol. 17, No. 13, 1998
Communications
Sch em e 3
Sch em e 4
alkynyl compounds over a prolonged reaction period;
application of this reaction to organic syntheses is also
reported.
As a continuation of our interest in alkynyltungsten
compounds,10 we have studied the protonation of alky-
nyltungsten complexes 1-4 tethered with an electron-
rich phenyl or thiophene group. We envision that the
resulting metal-η1-vinylidene cations (C) may form a
vinyltungsten species via arylation at its WdC carbon9a
as shown in Scheme 2 (part 1). In a typical reaction,
compounds 1-3 were treated with CF3SO3H (2.0 equiv)
in cold CH2Cl2 (-78 °C) and stirred for 2 h before the
temperature was slowly brought to 23 °C over a period
of 12 h. For compound 1, monitoring its CH2Cl2 solution
by proton NMR spectra reveals that indanone 5 is the
only detectable species together with a single cyclopen-
tadienyl signal at δ 6.10 ppm due to an unidentified
tungsten complex. Workup of this solution delivered
5-7 in good yields (81-86%). Similarly, the reaction
of alkynyltungsten complex 4 with CF3SO3H (2.0 equiv)
under the same experimental conditions gave cyclopen-
tanone 8 and several unknown tungsten species. Fil-
tration of this CH2Cl2 solution through a short silica
bed at 23 °C afforded 8 and 9 in 32% and 28% yields,
respectively. In this transformation, we are aware that
2.0 mol equiv of CF3SO3H is insufficient to furnish the
hydrogen content of indanones 5-8; additional hydrogen
sources may be available from the small water content
in CF3SO3H.
cording to in situ NMR studies. We therefore pre-
pared11 alkynyltungsten compounds 10 and 11 in order
to obtain kinetically stable intermediates with the use
of a suitable amount of CF3SO3H; the best result is the
use of 4.0 mol equiv of CF3SO3H. Notably, the proto-
nation reaction of alkynyltungsten compounds was pre-
viously reported.12 Treatment of CpW(CO)3(η1-phenyl-
ethynyl) with excess HBF4 (5.0 equiv) in CH2Cl2 gave
the binuclear species cation D12 in 52% yield:
Formation of synthetically useful indanones 5-9 from
1-4 represents an unusual carbonylation reaction. It
is difficult to deduce the formation mechanism of 5-9
without isolation of organometallic reaction intermedi-
ates. The alkynyl compounds 1-4 are not suitable for
this study because the observed tungsten intermediates
are kinetically unstable, easily forming indanones ac-
CF3SO3H acidification of 10 and 11, however, proceeded
in a distinct reaction pathway outlined in Scheme 3.
Treatment of compound 10 with CF3SO3H (4.0 equiv)
in cold CH2Cl2 (-78 °C) led to its disappearance after a
short reaction period (ca. 1.0 h). Subsequent treatment
of this solution with water at -78 °C led to formation
of 12 in 75% yield, indicating that the vinylidenetung-
sten cation C was first formed9a in the CF3SO3H
acidification of 10. As shown in Scheme 3, slow warm-
ing of this acidic solution to 23 °C (ca. 12 h) produced
the stable acyltungsten(IV) complex 13 in 86% yield. If
2.0 equiv of CF3SO3H was used in the same reaction
sequence, five unknown species were formed without
(8) For organic syntheses via metal-η2-allene cations, see the
representative papers: (a) Bell, P. B.; Wojcicki, A. Inorg. Chem. 1981,
20, 1585. (b) Raghu, S.; Rosenblum, M. J . Am. Chem. Soc. 1973, 95,
3060. (c) Blosser, P. W.; Shimpff, D. G.; Gallucci, J . C.; Wojcicki, A.
Organometallics 1993, 12, 1393. (d) Chen, C.-C.; Fan, J .-S.; Shieh, S.-
J .; Lee, G.-H.; Peng, S.-M.; Wang, S.-L.; Liu, R.-S. J . Am. Chem. Soc.
1996, 118, 9279.
(9) For organic syntheses via metal-η1-vinylidene cations, see the
following representative papers: (a) Bruce, M. I. Chem. Rev. 1991, 91,
257. (b) Trost, B. M.; Dyker, G.; Kulawiec, R. J . J . Am. Chem. Soc.
1990, 112, 7809. (c) Trost, B. M.; Martinez, J . A.; Indolese, A. F. J .
Am. Chem. Soc. 1993, 115, 10402. (d) Trost, B. M.; Flygare, J . A. J .
Am. Chem. Soc. 1992, 114, 5467. (e) McDonald, F. E.; Bowman, J . L.
Tetrahedron Lett. 1996, 4675.
(11) Bruce, M. I.; Humphrey, M. G.; Mattisons, J . G.; Roy, S. K.;
Swincer, A. G. Aust. J . Chem. 1984, 1041.
(12) Kolobova, N. E.; Skripkin, V. V.; Rozantseva, T. V.; Struchkov,
Yu. T.; Aleksandrov, G. G.; Andriannov, V. G. J . Organomet. Chem.
1981, 218, 351.
(10) Liang, K.-W.; Li, W.-T.; Peng, S.-M.; Wang, S.-L.; Liu, R.-S. J .
Am. Chem. Soc. 1997, 119, 4404.

Communications
Organometallics, Vol. 17, No. 13, 1998 2685
Sch em e 5
formation of acyltungsten species 13. Acidification of
11 with CF3SO3H (4.0 equiv) afforded the acyl com-
pound 14 (82%) after a prolonged reaction period.
Compounds 13 and 14 were present as oils and were
thus not suitable for X-ray diffraction studies. It is
difficult to deduce the structure on the basis of spectral
data alone. Fortunately, compounds of this type have
been previously prepared13 from the reaction of HX (X
) CF3CO2, Cl, Br, I) with carbynyltungsten compounds
Cp(CO)2WtR:
Scheme 5 shows a plausible mechanism to account
for formation of 13 from alkynyltungsten species 10. We
propose that the initial vinylidene intermediate C
undergoes a tungsten η1-vinylidenehη2-alkyne rear-
rangement14 to yield species E. In the presence of free
OTf- anion, species E is envisaged to undergo ligand
substitution to yield the neutral intermediate W(II)
intermediate F . Further protonation at the η2-alkyne
ligand of F leads to oxidation, yielding the vinyltung-
sten(IV) cation G. This high-valent 16-electron species
G is readily captured by an OTf anion to yield the 16-
electron species H, which subsequently undergoes CO
insertion to yield the η2-acyl species 13. If a highly nu-
cleophilic phenyl or thione group is present, orthoaryla-
tion will occur to yield the unsaturated indanone I, the
precursor for 5-8, accompanied by release of a hydrido-
tungsten(IV) species. Unsaturated indanone is further
reduced with this hydridotungsten(IV) species to yield
compounds 5-8; in this case, 2 mol equiv of CF3SO3H
suffices this intramolecular arylation reaction.
In summary, we report that alkynyltungsten com-
pounds can be oxidized by CF3SO3H over a prolonged
reaction period, leading to a rearrangement and carbo-
nylation reaction. We elucidate the reaction mechanism
with isolation and characterization of the two acyltung-
sten(IV) species 13 and 14. This oxidation is useful for
syntheses of different classes of indanones or unsatur-
ated esters and acids; in most cases, the yields are
reasonable. Further expansion of this reaction scope
is under investigation.
A good match has been found to compare the IR and
NMR spectral data of 13 and 14 to these of the known
compounds. For compound 13, the single W-CO group
is characterized by the IR absorption band at 2060 cm-1
and also by the 13C NMR signal at 197.9 ppm in CD2-
Cl2. The η2-acyl group is indicated by both the IR band
at 1580 cm-1 and the 13C NMR signal at 263.2 ppm.
The two coordinated CF3SO3 ligands are nonequivalent,
as shown by their 13C NMR signals in CD2Cl2 as two
quartets at δ 119.0 ppm (J CF ) 315.6 Hz) and δ 118.5
ppm (J CF ) 315.4 Hz), respectively. The free vinyl
1
group of 13 has the H NMR signals at δ 6.37 and 6.35
ppm, respectively, and the corresponding carbons have
the signals at 145.8 and 143.1 ppm, respectively.
The acyltungsten compounds 13 and 14 are useful for
production of unsaturated acids and esters. Treatment
of a CH2Cl2 solution of 14 with a mixture of MeOH and
Et3N afforded the unsaturated ester 15 in 72% yield
(Scheme 4). Filtration of a CH2Cl2 solution of 14
through a silica bed afforded a mixture of acids 16 and
17 in a combined yield of 72% (16/17 ) 4/1). Reduction
of this acyl species with Bu3SnH (5.0 equiv) in CH2Cl2
delivered the alcohol 18 in 46% yield.
Ack n ow led gm en t. We gratefully acknowledge fi-
nancial support from the National Science Council for
financial support of this work.
Su p p or tin g In for m a tion Ava ila ble: Text giving ad-
ditional information on synthetic procedures and spectral data
for compounds 1-18 (11 pages). Ordering information is given
on any current masthead page.
OM980093H
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