Intervention by an η6-organochromium moiety switches chemoselectivity in palladium-catalyzed reactions with trialkyltin compounds

Article abstract of DOI:10.1021/om010004s

The reaction of (chloroarene)tricarbonylchromium with hexaalkylditin under palladium catalysis does not proceed by the expected Stille reaction with addition of an SnR₃ group but, instead, affords alkylarene complexes via a postulated chromium-assisted alkyl migration.

Full text of DOI:10.1021/om010004s

Organometallics 2001, 20, 1279-1281
1279
6
In ter ven tion by a n η -Or ga n och r om iu m Moiety Sw itch es
Ch em oselectivity in P a lla d iu m -Ca ta lyzed Rea ction s w ith
Tr ia lk yltin Com p ou n d s
Damien Prim, J ean-Philippe Tranchier, Ren e´ Chavignon,
Fran c¸ oise Rose-Munch, and Eric Rose*
Laboratoire de Synth e` se Organique et Organom e´ tallique, UMR CNRS 7611, Universit e´ Pierre
et Marie Curie, Tour 44-1er e´ tage, 4, Place J ussieu, 75252 Paris Cedex 05, France
Received J anuary 2, 2001
Summary: The reaction of (chloroarene)tricarbonylchro-
mium with hexaalkylditin under palladium catalysis
does not proceed by the expected Stille reaction with
addition of an SnR3 group but, instead, affords alkyl-
arene complexes via a postulated chromium-assisted
alkyl migration.
Sch em e 1
Trialkylaryltin derivatives have found widespread
applications in organic synthesis in the last two de-
cades, and palladium-catalyzed coupling reactions us-
Sch em e 2
1
ing such compounds constitute the popular and general
2
Stille coupling procedure. The combination of the
organotin coupling procedure with chromium-bound
π-systems is, however, far less fully explored. In an
6
attempt to prepare (η -phenyl)trialkyltin compounds for
use in our continuing studies of tricarbonylchromium
3
arene complexes in palladium-catalyzed cross-coupling
4
reactions, we have examined the transfer of trialkyltin
6
to (η -chlorobenzene)tricarbonylchromium derivatives.
6
Attempts to prepare the tributyltin(η -benzene)tri-
are aware, unprecedented, whereas alkyl transfer from
tetraalkyltin to arylhalides (or triflates) under pal-
ladium catalysis is well-known. We wish to report here
the initial study of this unexpected palladium-catalyzed
reaction.
6
carbonylchromium complex 2 from the (η -chloroben-
5
zene)tricarbonylchromium complex 1, using hexabu-
tylditin together with Pd2(dba)3 and AsPh3 as catalyst
in refluxing THF, failed. The expected product of the
Stille reaction complex 2, which corresponds to the
stannylation of the arene, was not formed (Scheme 1).
Results of our investigations are listed in Table 1. (η6-
Chlorobenzene)tricarbonylchromium (1a ) reacted with
Sn2Bu6, AsPh3, and Pd2(dba)3, giving rise to the forma-
tion of butyl derivative 3a in 88% yield (entry 1). When
the above reaction conditions were applied to the free
bromobenzene, no alkyl transfer product 3a was de-
tected (entry 2), but in contrast, 1,1′-biphenyl resulting
6
Instead, (η -butylbenzene)Cr(CO)3 (3a ) was isolated in
high yield as the sole product, indicating an overall
displacement of the chloride by the butyl group (Scheme
2
). Alkyl transfer from hexaalkylditin is, as far as we
6
*
To whom correspondence should be addressed. E-mail: rose@
from a homocoupling reaction could be isolated in 34%
ccr.jussieu.fr.
yield together with 10% of unreacted starting material.
The noncomplexed p-nitrochlorobenzene gave no reac-
tion, and it was recovered unchanged (entry 3). This
result demonstrated that the electron deficiency in the
nitroarene ring (which is comparable to the arene Cr-
(
1) See for example: (a) Corsico, E. F.; Rossi, R. A. Synlett 2000, 2,
2
2
1
30. (b) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. Engl. 1999, 38,
411. (c) Borzilleri, R. M.; Weinreb, S. M. J . Am. Chem. Soc. 1994,
16, 9789. (d) Nicolaou, K. C.; Chakraborty, T. K.; Piscopo, A. D.;
Minowa, N.; Bertinato, P. J . Am. Chem. Soc. 1993, 115, 4419. (e)
Pattenden, G.; Thom, S. M. Synlett 1993, 215.
(
2) (a) Han, X.; Stoltz, B. M.; Corey, E. J . J . Am. Chem. Soc. 1999,
(CO)3 ring) was not alone sufficient to promote the
1
8
21, 7600. (b) Casado, A. L.; Espinet, P. J . Am. Chem. Soc. 1998, 120,
978. (c) Casado, A. L.; Espinet, P. Organometallics 1998, 17, 954. (d)
unusual alkyl transfer reaction, suggesting that the
chromium entity could be directly involved in the alkyl
migration.
Farina, V.; Krishnarmurthy, V.; Scott, J . The Stille Reaction. In
Organic Reactions; Paquette, L. A., Ed.; Wiley: Chichester, U.K., 1997;
Vol. 50, pp 1-633. (e) Farina, V.; Kapadia, S.; Krishnan, B.; Wang,
C.; Liebeskind, L. S. J . Org. Chem. 1994, 59, 5905. (f) Stille, J . K.
Angew. Chem., Int. Ed. Engl. 1986, 25, 508.
The generality of the alkyl transfer reaction was
6
examined with disubstituted chloroarene complexes. (η -
(3) (a) Rose-Munch, F.; Rose, E.; Djukic, J . P.; Vaissermann, J . Eur.
p-Chlorotoluene)tricarbonylchromium (1b) reacted with
J . Inorg. Chem. 2000, 1295. (b) Rose-Munch, F.; Rose, E. Curr. Org.
Chem. 1999, 3, 445. (c) Rose-Munch, F.; Gagliardini, V.; Renard, C.;
Rose, E. Coord. Chem. Rev. 1998, 178-180, 249.
(5) (a) Farina, V.; Krishnan, B.; Marshall, D. R.; Roth, R. P. J . Org.
Chem. 1993, 58, 5434. (b) Farina, V.; Krishnan, B. J . Am. Chem. Soc.
1991, 113, 9585. (c) Echavarren, A. M.; Stille, J . K. J . Am. Chem. Soc.
1987, 109, 5478.
(6) Homocoupling was already observed in high yield using Stille
conditions. See for example ref 5c.
(4) (a) Prim, D.; Tranchier, J .-P.; Rose-Munch, F.; Rose, E.; Vais-
sermann, J . Eur. J . Inorg. Chem. 2000, 5, 901. (b) Tranchier, J -P.;
Chavignon, R.; Prim, D.; Auffrant, A.; Plyta, Z. F.; Rose-Munch, F.;
Rose, E. Tetrahedron Lett. 2000, 41, 3607. (c) Prim, D.; Kirsch, G. J .
Chem. Soc., Perkin Trans. 1 1994, 2603.
1
0.1021/om010004s CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/09/2001

1
280 Organometallics, Vol. 20, No. 7, 2001
Ta ble 1. Stille Cou p lin g Rea ction s of Com p lexes 1
Communications
R1
M
X
2
R SnR33 (1 equiv)
catalyst (0.05 equiv, 0.2 equiv)
conditions
1
3
entry
1
2
3
4
5
6
7
8
9
H
H
Cr(CO)3
Cl
Br
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
F
(Bu3Sn)2
(Bu3Sn)2
(Bu3Sn)2
(Bu3Sn)2
Bu3SnCl
(Bu3Sn)2
(Bu3Sn)2
(Bu3Sn)2
Bu4Sn
Pd2dba3, AsPh3
Pd2dba3, AsPh3
Pd2dba3, AsPh3
Pd2dba3, AsPh3
Pd2dba3, AsPh3
THF, reflux, 3 h
THF, reflux, 2 h
THF, reflux, 2 h
THF, reflux, 2 h
THF, reflux, 2 h
THF, reflux, 2 h
THF, reflux, 5 h
THF, reflux, 5 h
THF, reflux, 2 h
THF, reflux, 3 h
THF, reflux, 3 h
THF, reflux, 18 h
88
10a
100
NO2
Me
Me
Me
Me
Me
Me
Me
Me
H
Cr(CO)3
Cr(CO)3
Cr(CO)3
Cr(CO)3
Cr(CO)3
Cr(CO)3
Cr(CO)3
Cr(CO)3
Cr(CO)3
75
85
100
100
100
Pd(TPP)4
Pd2dba3, dppf
Pd2dba3, AsPh3
Pd2dba3, AsPh3
Pd2dba3, AsPh3
Pd2dba3, AsPh3
81
68
1
1
1
0
1
2
(Me3Sn)2
(Bu3Sn)2
2
22
100
100
Cl
a
3
4% homocoupling product.
Sch em e 3
hexabutylditin to afford the corresponding butyl-sub-
stituted complex 3b in 75% yield (entry 4). The forma-
tion of p-n-butyltoluene complex confirmed the regiose-
lectivity of this reaction. The butyl transfer resulted
from an overall ipso substitution of the chlorine atom.
In the same way, the butyl transfer occurred in 85%
yield by using Bu3SnCl as the reactant (entry 5). An
attempted reaction without the catalytic system under
the same conditions (THF, reflux) gave no coupling
product, and the starting complex was recovered un-
changed (entry 6). This clearly confirmed that butyl
transfer is a result of a Pd-catalyzed process.
6
this η -tributyltin benzene complex 2 with the chloro
derivative 1a under the alkyl transfer reaction condi-
tions mentioned above, at room temperature for 24 h
or at reflux for 18 h (entry 12), but we did not observe
the formation of either the complex 3a or the binuclear
biphenyl complex [C6H5Cr(CO)3]2 which could also be
expected; complex 2 was recovered unchanged. From
this result it is clear that a trialkyltin arene complex
such as 2 cannot be an intermediate in the alkyl transfer
Moreover, the use of neither triphenylphosphine
(TPP; entry 7) nor bidentate diphenylphosphinofer-
rocene (dppf; entry 8) in refluxing THF for 5 h afforded
coupling products. Thus, we observed this reaction only
in the presence of AsPh3 as ligand. The role of AsPh3
5
has been studied by Farina, and the compound has
been introduced in Stille coupling reactions because of
its high nucleophilicity, which allows fast transmeta-
lation steps. We recently stressed its high potentiality
10
process.
6
in cross-coupling reactions involving (η -arene)tricar-
When these data are taken into account, it is obvious
that, besides the activation of a C-Cl bond, the Cr-
CO)3 tripod plays another role in the alkyl transfer
bonylchromium complexes by allowing milder reaction
conditions and by avoiding side reactions,4 but no
satisfying explanation for the exact role of this ligand
has been yet found.
11
a
(
process. Among the possible explanations, we think that
the peculiar ability of the chromium entity to form a
Sn-Cr metal-metal bond in (arene)tricarbonylchro-
mium complex chemistry would be one of the reasons
for our unexpected results. Indeed, it is well-precedented
that unstable anionic chromium complexes such as 4
can be trapped with ClSnPh3, leading to the formation
The known alkyl transfer using tetrabutyltin7 af-
forded similar yields (81%) under the aforementioned
conditions (entry 9). The alkyl transfer process was then
extended to a methyl migration in the case of hexam-
ethylditin (entry 10). Although the p-xylene complex 3c
was obtained in 68% yield, hexamethylditin appeared
less reactive than the butyl analogue at comparable
reaction times. It is noteworthy that only chloroarene
complexes undergo alkyl transfer; indeed in the case of
12
of dinuclear complex 5. The propensity of establishing
a Cr-Sn bond can only occur if a partial negative charge
is formed due to the exo addition of a nucleophile (a
hydride, for example, in Scheme 3).
8
fluoro derivatives no alkyl migration was observed and
According to literature data, we propose intermediate
starting material was recovered unchanged (entry 11).
Trialkyltin arenes are the expected products of pal-
ladium-catalyzed reactions of hexaalkylditin and aryl
6
(Scheme 4), which might highlight the role of the
5
chromium entity. This “pseudo” η -cyclohexadienyl in-
termediate would be formed in the alkyl transfer process
9
halides; thus, one could expect the formation of such
an intermediate in the first step and subsequent metal-
catalyzed rearrangement of the latter to afford the
butylarene complex 3. For this purpose, we prepared
tributyltinarene complex 2 by trapping the lithio de-
rivative C6H5LiCr(CO)3 with ClSnBu3. We then reacted
(10) (a) These results are consistent with those obtained by Wright
et al., who did not observe a Stille coupling reaction in the case of
1
0c
complexed aryltributylstannane derivatives. In contrast, J ohansson et
al.10b described the formation of coupling products, using phosphines
as catalyst ligands. (b) Caldirola, P.; Chowdhury, R.; J ohansson, A.
M.; Hacksell, U. Organometallics 1995, 14, 3897. (c) Wright, M. E. J .
Organomet. Chem. 1989, 376, 353.
(
11) Kamikawa, K.; Watanabe, T.; Daimon, A.; Uemura, M. Tetra-
(7) Scott, W. J . Chem. Soc., Chem. Commun. 1987, 1755.
hedron 2000, 56, 2325.
(
8) (Fluoroarene)tricarbonylchromium complexes were found to
(12) (a) Djukic, J .-P.; Rose-Munch, F.; Rose, E.; Simon, F.; Dromzee,
Y. Organometallics 1995, 14, 2027. (b) Djukic, J .-P.; Rose-Munch, F.;
Rose, E. J . Am. Chem. Soc. 1993, 115, 6434. (c) K u¨ ndig, E. P.;
Cunningham, A. F.; Paglia, P.; Simmons, D. P.; Bernardinelli, G. Helv.
Chim. Acta 1990, 73, 386.
undergo Suzuki reactions using another catalytic system: Widdowson,
D. A.; Wilhelm, R. J . Chem. Soc., Chem. Commun. 1999, 2211.
(9) Azizian, H.; Eaborn, C.; Pidcock, A. J . Organomet. Chem. 1981,
2
15, 49.

Communications
Organometallics, Vol. 20, No. 7, 2001 1281
Sch em e 4
edented product arising from alkyl migration to the
aromatic carbon, yielding the (alkylarene)tricarbonyl-
chromium complex 3. A plausible mechanism is sug-
gested which involves a chromium-assisted ipso addition
to the aromatic carbon, shedding light on the crucial role
of the Cr(CO)3 tripod, which can interact with the tin
moiety. Work is currently in progress to confirm this
hypothesis.
via a partial coordination of the Cr atom to the tin atom,
which would weaken the Sn-R bond by increasing its
Ack n ow led gm en t. We thank CNRS and the Euro-
pean Community (TMR program: Grant No. FMRX-
CT98-0166) for financial support.
1
3
polarity. This might be the driving force of this
unexpected alkyl transfer. Moreover, our hypothesis
would be consistent with a relevant example of pal-
ladium-linked Meisenheimer type species 7 (Scheme 4),
which has been recently suggested by Buchwald et al.
Su p p or tin g In for m a tion Ava ila ble: Text giving ad-
ditional details of the syntheses of compounds reported in this
paper. This material is available free of charge via the Internet
at http://pubs.acs.org.
1
4
as one possible intermediate in aryl ether formation.
These results raise new mechanistic questions,
1
5,16
which we continue to address and add further possibili-
ties for the use of arenetricarbonylchromium complexes
in addition to their already well-established role in
organic synthesis.
In conclusion, reactions of (chloroarene)tricarbonyl-
chromium complexes with hexaalkylditin (or trialkyltin
chloride) under palladium catalysis do not proceed by
the usual Stille coupling but, instead, give an unprec-
OM010004S
(
15) Other pathways are not excluded. Indeed, one of the reviewers
suggested the following plausible mechanism. Because of steric reasons
due to the bulky Cr(CO) group, the expected stannane product
ArPdSnBu would not have formed. Instead, the ready dissociation of
the arsine would create a vacant binding site on Pd and would allow
competitive R-elimination of Bu Sn16 to give ArPd(AsPh ) Bu.
3
3
a
2
3 2
Reductive elimination would produce the observed compound. How-
ever, our first preliminary results of a NMR study performed with
complex 1b, in perdeuterated THF, showed that, depending on reaction
time, doublets appeared at high field that could not be attributed to
6
5
(13) Pentacoordinate tin species may form; see for example: J a¨ kle,
η -arene intermediates but, rather, to labile η -cyclohexadienyl
12b
F.; Rulkens, R.; Zech, G.; Massey, J . A.; Manners, I. J . Am. Chem.
Soc. 2000, 122, 4232.
complexes. A complete spectroscopic study is underway and will be
reported in due time.
(
14) Widenhoefer, R. A.; Zhong, H. A.; Buchwald, S. L. J . Am. Chem.
(16) Clark, G. R.; Flower, K. R.; Roper, W. R.; Wright, L. J .
Organometallics 1993, 12, 259.
Soc. 1997, 119, 6787.