First synthesis of cationic [(η6-arene)Mn(CO)3] complexes substituted by resonance electron withdrawing groups

Article abstract of DOI:10.1021/om010162j

An unprecedented class of cationic [(η⁶-RCO-arene)Mn(CO)₃] complexes bearing resonance electron withdrawing groups have been synthesized by a high-yield two-step methodology starting from the neutral (η⁵-1-chlorocyclohexadienyl)Mn(CO)₃ complex, employing a facile and selective transition-metal-catalyzed carbonylation followed by rearomatization. Definitive spectroscopic details of the novel [(η⁶-RCO-arene)Mn(CO)₃]⁺ products are discussed, and in one case (R = PhO), the structure has been confirmed by X-ray crystallography.

Full text of DOI:10.1021/om010162j

3214
Organometallics 2001, 20, 3214-3216
F ir st Syn th esis of Ca tion ic [(η6-a r en e)Mn (CO)3]
Com p lexes Su bstitu ted by Reson a n ce Electr on
With d r a w in g Gr ou p s
Audrey Auffrant,† Damien Prim,† Franc¸oise Rose-Munch,† Eric Rose,*,† and
J acqueline Vaissermann‡
Laboratoire de Synthe`se Organique et Organome´tallique, UMR CNRS 7611, Universite´ Pierre
et Marie Curie, Tour 44, 1er e´tage, 4 Place J ussieu, 75252 Paris Cedex 05, France, and
Laboratoire de Chimie Inorganique et Mate´riaux Mole´culaires, ESA CNRS 7071, Universite´
Pierre et Marie Curie, Batiment F, 4 Place J ussieu, 75252 Paris Cedex 05, France
Received February 28, 2001
Summary: An unprecedented class of cationic [(η6-RCO-
arene)Mn(CO)3] complexes bearing resonance electron
withdrawing groups have been synthesized by a high-
yield two-step methodology starting from the neutral
(η5-1-chlorocyclohexadienyl)Mn(CO)3 complex, employing
a facile and selective transition-metal-catalyzed car-
bonylation followed by rearomatization. Definitive spec-
troscopic details of the novel [(η6-RCO-arene)Mn(CO)3]+
products are discussed, and in one case (R ) PhO), the
structure has been confirmed by X-ray crystallography.
tion of Mn complexes of arenes substituted by strongly
electron withdrawing groups that accept electron den-
sity through resonance effects.
The failure of the complexation of such arenes has to
be attributed to electron deficiency of the ring. Further-
more, unlike the corresponding Cr complexes,4 even
when the resonance electron withdrawal of the keto
group is disrupted by the formation of a ketal, for
example, no coordination occurred.3a
Consequently, we have tried to develop a strategy for
the synthesis of such complexes. The approach adopted
takes advantage of the particular property of η5-cyclo-
hexadienyl complexes 15 that easily undergo exo hydride
abstraction at the sp3 carbon, thus forming the corre-
sponding cationic η6 complexes 2 (eq 1).6
Complexation of arenes alters their chemical reactiv-
ity and provides a useful synthetic methodology to
prepare functionalized arenes and cyclohexadienes.1,2 In
particular, η6 coordination of aromatic molecules to the
+
cationic Mn(CO)3 moiety activates the arene ring
toward nucleophilic addition, affording neutral η5-
cyclohexadienyl complexes which can release the free
arenes upon oxidative removal of the metal.2
The main synthetic methods reported for the prepa-
ration of such cationic complexes involve the direct
coordination of arenes to the Mn(CO)3 residue by using
Thus, our aim was, first, the preparation of η5 neutral
complexes substituted by electron-withdrawing groups
such as a keto, an ester, an amide, or a cyano group
and, second, their rearomatization. This communication
describes a successful two-step methodology that gives
access to unprecedented (η6-arene)Mn+(CO)3 complexes
substituted by resonance electron withdrawing groups
and characterization details of the products. Our ap-
proach is based on palladium-catalyzed carbonylation
reactions at C-Cl positions π-bound to manganese.
Recently the unique behavior of the Pd2(dba)3/AsPh3
catalytic system has been applied successfully in organo-
metallic compounds. Indeed, it allows new synthetic
transformations which failed or were much less effective
when phosphine-based ligands were used. Examples
include the preparation of new (η6-RCO-arene)Cr(CO)3
complexes under mild conditions7 and selective substi-
tution of halogens in (η5-chlorocyclohexadienyl)Mn(CO)3
complexes.8 Unfortunately, all our attempts to extend
3a
Mn(CO)5Br3a or Mn2(CO)10 or by transferring Mn-
(CO)3+ from cationic (polyarene)Mn(CO)3+ complexes.3b,c
Thus, arenes bearing electron donating substituents
such as alkyl, alkoxy, and hydroxy may be coordinated
in high yield. Even arenes with only moderately accept-
ing groups such as aryl, chloride, or nonconjugated
carbonyl groups can be coordinated as well,3a but, to the
best of our knowledge, there is no report of the prepara-
* To whom correspondence should be addressed. E-mail:
rose@ccr.jussieu.fr.
† Laboratoire de Synthe`se Organique et Organometallique.
‡ Laboratoire de Chimie Inorganique et Mate´riaux Mole´culaires.
(1) See for example: (a) Astruc, D. In Chimie Organome´tallique;
EDP Sciences: Les Ulis, France, 2000; Chapter 3-6, p 87. (b) Rose-
Munch, F.; Rose, E. Current Org. Chem. 1999, 3, 445 and references
therein. (c) Rose-Munch, F.; Gagliardini, V.; Renard, C.; Rose, E. Coord.
Chem. Rev. 1998, 178-180, 249. (d) Semmelhack, M. F. In Compre-
hensive Organometallic Chemistry II; Abel, E. W., Stone, F. G. A.,
Wilkinson, G., Eds.; Pergamon: Oxford, U.K., 1995; Vol. 12, p 979.
(2) McDaniel, K. F. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford,
U.K., 1995; Vol. 6, p 93.
(4) (a) Mahaffy, C. A. L.; Pauson, P. L. Inorg. Synth. 1979, 19, 154.
(b) Kondo, Y.; Green, J . R.; Ho, J . J . Organomet. Chem. 1993, 58, 6182.
(5) Pauson, P. L.; Segal, J . A. J . Chem. Soc., Dalton Trans. 1975,
1677.
(6) Woo, K.; Williard, P. G.; Sweigart, D. A.; Duffy, N. W.; Robinson,
B. H.; Simpson, J . J . Organomet. Chem. 1995, 487, 111.
(7) Prim, D.; Tranchier, J . P.; Rose-Munch, F.; Rose, E.; Vaisser-
mann, J . Eur. J . Inorg. Chem. 2000, 5, 901.
(3) (a) For the scope of (η6-arene)Mn(CO)3 synthesis, see for ex-
ample: J ackson, J . D.; Villa, S. J .; Bacon, D. S.; Pike, R. D.; Carpenter,
G. B. Organometallics 1994, 13, 3972 and references therein. (b) Lee,
S. S.; Lee, T. Y.; Lee, I. S.; Chung, Y. K.; Lah, M. Soo. Organometallics
1996, 15, 3664. (c) Sun, S.; Yeung, L. K.; Sweigart, D. A.; Lee, T. Y.;
Lee, S. S.; Chung, Y. K.; Switzer, S. R.; Pike, R. D. Organometallics
1995, 14, 2613.
10.1021/om010162j CCC: $20.00 © 2001 American Chemical Society
Publication on Web 07/16/2001

Communications
Organometallics, Vol. 20, No. 15, 2001 3215
Ta ble 1. Su bstitu tion of Ch lor id e Atom by a n
Electr on -With d r a w in g Gr ou p
Ta ble 2. Ar om a tiza tion of η5-Cycloh exa d ien yl
Com p lexes
entry
R′
6
EWG
yield (%)
7
yield
(%)
1
2
3
4
4-Me
6a
6b
6f
COTh
COTh
CO2Ph
95a
85b
70a
85a
7a
7b
7f
entry
R′
3
RX
6
EWG
4-MeO
4-MeO
4-MeO
1
2
3
4
5
6
7
4-Me
3a thienyl-2-SnBu3 90a 6a COTh
4-MeO 3b thienyl-2-SnBu3 90b 6b COTh
6g
CON(CH2CH2)2O
7g
4-Me
4-MeO 3b Bu4Sn
4-Me 3a Bu3SnH
4-MeO 3b PhONa
4-MeO 3b HN(CH2CH2)2O
3a Bu4Sn
56a 6c COBu
45a 6d COBu
6e CHO
a
b
Reaction time 3 h. Reaction time 15 h.
Ta ble 3. Selected 1H NMRa Da ta of Com p lexes
6 a n d 7
71a 6f CO2Ph
48a 6g CON(CH2CH2)2O
complex δ(H2) δ(H3) ∆δb complex δ(H2) δ(H3) ∆δb
a
b
Reaction time 2 h. Reaction time 6 h.
6a
6b
6f
6g
6h
6.01c 6.01c 0.00
7a
7b
7f
7g
7h
7.52
6.83
0.69
such catalytic transformations to cationic tricarbonyl-
(η6-chloroarene)manganese complexes have failed up to
now;9 therefore, we turned instead to investigate first
the transition-metal-catalyzed carbonylation of a series
of (η5-chlorocyclohexadienyl)Mn(CO)3 complexes 3 under
a CO atmosphere in the presence of Pd2(dba)3, AsPh3,10
and stannous derivatives as a source of the second
substituent (Nu, eq 2) on the electron withdrawing end
group (EWG) of the products.
6.03
6.03
5.43
5.08
6.14
6.12
5.81
6.07
0.11
0.08
0.38
0.99
7.66d 6.57e 1.09f
7.69
7.43
7.90
6.49
6.40
7.74
1.20
1.03
0.14
a
b
d
CDCl3. ∆δ ) δ(H2) - δ(H3). c Broad. δ 7.89 for the free
arene. e δ 6.97 for the free arene. f In the case of the corresponding
chromium complex7 this difference was found to be 1.13.
We propose that these ketones 6a -d are most prob-
ably formed via the postulated intermediate 4, which
can undergo CO insertion to give the acylpalladate
complex 5. This mechanistic postulate provides a pos-
sibility to extend the reaction to the preparation of
carboxylic acid derivatives. For this purpose, we tried
to trap the intermediate 5 with classical nucleophiles12
in order to have an access to esters and amides. PhONa
as well as morpholine reacted with complex 3b, giving
the corresponding ester 6f and amide 6g in 71% and
48% yields, respectively (Table 1, entries 6 and 7).
At this point it was crucial to know if it was possible
to perform the aromatization of these η5 derivatives.13
This was achieved by reaction with CPh3BF4 in CH2-
Cl2, and the required cationic complexes 6a ,b,f,g were
obtained in 95, 85, 70, and 85% yields, respectively
(Table 2).
In the case of 2-(tributylstannyl)thiophene (RX )
SC4H3SnBu3), after the reaction mixture was refluxed
for 2 h, the thienyl ketone 6a was obtained in 90% yield
(Table 1, entry 1). The reaction has to be undertaken
carefully under a CO atmosphere during the entire
process. Indeed, if CO is introduced only after the
addition of RX, a direct coupling compound may
be isolated as a byproduct in yields ranging from 5%
to 20%. The same reaction performed with the η5-1-
chloro-4-methoxycyclohexadienyl complex 3b afforded
the thienyl ketones 6b in 90% yield (Table 1, entry 2).11
This reaction has been extended to another stannous
derivative, SnBu4. Under the same conditions, com-
plexes 3a and 3b afforded alkyl ketones 6c and 6d in
56 and 45% yields, respectively (Table 1, entries 3 and
4). In the case of 3a and Bu3SnH, however, we never
observed the expected formation of the aldehyde 6e
(Table 1, entry 5) even by changing the experimental
conditions.
1
Selected H NMR data of η5 and η6 complexes (Table
3) show that the differences of chemical shifts ∆δ )
δ(Η2) - δ(Η3) of these complexes are small in the case
of the η5 derivatives and positive and very large in the
case of the η6 complexes (up to 1.20 ppm; Table 3). This
suggests a synergistic effect of the electron withdrawing
group favoring an anti-eclipsed conformation of the
tripod Mn(CO)3, whereas the electron-donating MeO
group favors the eclipsed conformation, as is already
known for analogous Cr complexes.1
Cationic arene-Mn complexes are usually described
as amorphous powders14 which are difficult to crystal-
(11) In the case of the more crowded (η5-1-chloro-2-methyl)cyclo-
hexadienyl complex, no coupling reaction occurred.
(12) See for example: (a) Wolfe, J . P.; Tomori, H.; Sadighi, J . P.; Yin,
J .; Buchwald, S. L. J . Org. Chem. 2000, 65, 1158. (b) Torraca, K. E.;
Kuwabe, S.-I.; Buchwald, S. L. J . Am. Chem. Soc. 2000, 122, 12907.
(c) Shelby, Q.; Kataoka, N.; Mann, G.; Hartwig, J . J . Am. Chem. Soc.
2000, 122, 10718.
(8) Prim, D.; Auffrant, A.; Rose-Munch, F.; Rose, E.; Vaissermann,
J . Organometallics 2001, 20, 901.
(9) Carpentier, J . F.; Castanet, Y.; Brocard, J .; Mortreux, A.; Rose-
Munch, F.; Susanne, C.; Rose, E. J . Organomet. Chem. 1995, 493, C22.
(10) Farina, V.; Krishnan, B.; Marshall, D. R.; Roth, G. P. J . Org.
Chem. 1993, 58, 5434.
(13) Reaction of complex 3b with KCN in DMF at 60 °C for 8 h
afforded the corresponding nitrile 6h (R′ ) 4-OMe, EWG ) CN), which
was very difficult to purify from the crude mixture. However, treating
directly the reaction mixture with CPh3BF4 in CH2Cl2, we succeeded
in isolating the pure complex 7h (R′ ) 4-OMe, EWG ) CN) in an
overall yield of 35% (from 3b).

3216 Organometallics, Vol. 20, No. 15, 2001
Communications
F igu r e 1. Molecular structure of 7f (molecule a). Selected
bond lengths (Å) and angles (deg): C1-C7 ) 1.494(7),
Mn1-C1 ) 2.154(4), Mn1-C4 2.273(5), C7-O7 ) 1.191(6);
C1-C7-O7 ) 123.7(4), O7-C7-O8 ) 125.2(4).
F igu r e 2. Molecular structure of 7f (molecule b). Selected
bond lengths (Å) and angles (deg): C101-C107 ) 1.486(7),
C107-O107 ) 1.180(6), Mn101-C101 ) 2.161(4), Mn101-
C104 ) 2.266(5); C101-C107-O107 ) 111.1(4), O107-
C107-O108 ) 124.5(5).
lize, but after many attempts, we finally succeeded in
obtaining well-formed, very stable yellow crystals of
complex 7f whose structure was determined by an X-ray
study.15
points out in the direction opposite to the Mn(CO)3
entity with dihedral angles of 28 and 15° in molecules
a and b, respectively.
In this structure, the asymmetric unit consists of two
independent molecular cations (labeled a and b) and two
independent BF4 anions (Figures 1 and 2). The confor-
mations of the two Mn(CO)3 tripods are not identical.
In molecule a, the structure shows an eclipsed Mn(CO)3
conformation with respect to the methoxy group (Figure
1), whereas a slightly more deviated conformation is
observed in molecule b (Figure 2), the Mn-CO bond
being rotated by 5 and 17° from carbons C4 and C104,
respectively.16
In conclusion, we were able to prepare unprecedented
[(η6-arene)Mn(CO)3]+ complexes substituted by reso-
nance electron withdrawing groups using a two-step
methodology to overcome the impossibility of direct
complexation. These compounds should have excep-
tional reactivity, as they possess three highly electro-
philic sites: the Mn(CO)3 entity, the complexed arene
ring, and, finally, the acyl group. Our results open the
way to explore new perspectives in the reactivity of such
complexes, and their potential applications in organic
synthesis as well as in material science are being
actively studied.
It is interesting to note that the CdO double bond is
not parallel to the plane of the Mn-bound arene but
(14) Pearson, A. J .; Zhu, P. Y.; Youngs, W. J .; Bradshaw, J . D.;
McConville, D. B.; J . Am. Chem. Soc. 1993, 115, 10376.
(15) Crystal data: C17H12BF4MnO6, Mr ) 454, triclinic, space group
P1h, a ) 10.227(7) Å, b ) 10.284(6) Å, c ) 18.704(6) Å, R ) 77.90(5)°,
â ) 78.84(6)°, γ ) 84.49(5)°, Dc ) 1.60 g cm-3, Z ) 4, crystal size
0.06 × 0.40 × 1.00 mm, µ ) 7.40 cm-1, 7014 data collected at 266 K
on an Enraf-Nonius MACH3 diffractometer. An absorption correction
using DIFABS (Tmin ) 0.72, Tmax ) 1) was applied. Anomalous
dispersion terms and no correction of secondary extinction were
applied. The structure was solved by direct methods (SHELXS) and
refined (CRYSTALS) by least-squares analysis using anisotropic
Ack n ow led gm en t . We thank the CNRS and the
EU Training and Mobility of Researchers Program,
(Contract No. ERBFMRXCT-CT98-0166) for financial
support and the Ministe`re de l’Education Nationale for
a MENRT grant to A.A.
Su p p or tin g In for m a tion Ava ila ble: Text giving spectral
data for the new compounds and tables of crystal data, atomic
coordinates, and bond distances and angles for compound 7f.
This material is available free of charge via the Internet at
http://pubs.acs.org.
thermal parameters for all non-hydrogen atoms.
H atoms were
introduced in calculated positions and were allocated an overall
isotropic thermal parameter. A total of 4329 reflections with I > 3σ(I)
were used to solve and refine the structure to R ) 0.0556 and Rw
0.0678: 525 least-squares parameters, GOF ) 1.10.
)
(16) This value is very close to the value of the corresponding angle
in the CH3CO2-C6H5Cr(CO)3 complex: Saillard, J . Y.; Grandjean, D.
Acta Crystallogr. 1976, B32, 2285.
OM010162J