Unprecedented (η5-Formylcyclohexadienyl)Mn(CO)3 complexes: Synthesis, structural and theoretical characterizations, and resolution of the planar chirality

Article abstract of DOI:10.1021/om7012666

The synthesis of the (η⁵-formylcyclohexadienyl)Mn(CO) ₃ complexes 5-8 was successfully achieved after lithiation and then electrophilic quench by DMF of variously substituted (η-cyclohexadienyl) Mn(CO)₃ complexes. Their full experimental characterization is reported, together with a theoretical study that allowed the consequences of the regiochemistry on the electronic properties of the complexes to be understood. Rearomatization of complex 6 led to the formation of the cationic [(η⁶-2-methoxybenzaldehyde)Mn(CO)₃]⁺ complex 11, first example of a benzaldehyde derivative coordinated to the Mn(CO)₃⁺ entity. The electrophilic reactivity of the formyl group of complex 5 was tested with hydrides and a Grignard reagent as the nucleophiles. The corresponding alcohols were isolated in high yields and the excellent diastereoselectivity could be explained by steric factors clearly identified thanks to the crystal structure determination of the starting aldehyde 7b. By using the enantiopure (R,R)-N,N′-dimethylcyclohexane-1,2- diamine, the corresponding aminals were obtained and their resolution afforded, after acidic treatment, the enantioenriched (η⁵- formylcyclohexadienyl)Mn(CO)₃ with very high enantiomeric excess. The X-ray analysis of two of these aminals 14 and 15 allowed the assignment of the absolute configurations of the planar chiral η⁵ moieties.

Full text of DOI:10.1021/om7012666

Organometallics 2008, 27, 2505–2517
2505
Unprecedented (η5-Formylcyclohexadienyl)Mn(CO)3 Complexes:
Synthesis, Structural and Theoretical Characterizations, and
Resolution of the Planar Chirality
Béatrice Jacques,†,‡ Antoine Eloi,†,‡ Murielle Chavarot-Kerlidou,*,†,‡
,#
Françoise Rose-Munch,*,†,‡ Eric Rose,†,‡ Hélène Gérard,§,| and Patrick Herson
UPMC UniV Paris 06, UMR 7611, Laboratoire de Chimie Organique, Institut de Chimie Moléculaire
(FR 2769), Case 181, 4 place Jussieu, F-75252 Paris Cedex 05, France, UPMC UniV Paris 06,
UMR 7616, Laboratoire de Chimie Théorique, F-75005, Paris, France, and UPMC UniV Paris 06,
UMR 7071, Laboratoire de Chimie Inorganique et Matériaux Moléculaires, F-75005, Paris, France
ReceiVed December 19, 2007
The synthesis of the (η5-formylcyclohexadienyl)Mn(CO)3 complexes 5-8 was successfully achieved
after lithiation and then electrophilic quench by DMF of variously substituted (η5-cyclohexadienyl)Mn(CO)3
complexes. Their full experimental characterization is reported, together with a theoretical study that
allowed the consequences of the regiochemistry on the electronic properties of the complexes to be
understood. Rearomatization of complex 6 led to the formation of the cationic [(η6-2-methoxybenzal-
dehyde)Mn(CO)3]+ complex 11, first example of a benzaldehyde derivative coordinated to the Mn(CO)3
+
entity. The electrophilic reactivity of the formyl group of complex 5 was tested with hydrides and a
Grignard reagent as the nucleophiles. The corresponding alcohols were isolated in high yields and the
excellent diastereoselectivity could be explained by steric factors clearly identified thanks to the crystal
structure determination of the starting aldehyde 7b. By using the enantiopure (R,R)-N,N′-dimethylcy-
clohexane-1,2-diamine, the corresponding aminals were obtained and their resolution afforded, after acidic
treatment, the enantioenriched (η5-formylcyclohexadienyl)Mn(CO)3 with very high enantiomeric excess.
The X-ray analysis of two of these aminals 14 and 15 allowed the assignment of the absolute configurations
of the planar chiral η5 moieties.
formyl-substituted derivatives have received much more atten-
tion. Thanks to the versatile reactivity of the formyl group, they
have proven to be attractive building blocks, leading to
widespread applications in asymmetric synthesis6 or in ligand
design for enantioselective catalysis.7 The (η6-arylaldehyde)-
Introduction
Aromatic activation by a tricarbonylmetal fragment M(CO)3
(M ) Cr, Mn) provides organometallic half-sandwich complexes
possessing interesting chemical properties.1 The reactivity of
the aromatic ring is greatly modified by the high electrophilicity
of the organometallic tripod, allowing a variety of transforma-
tions.2 For instance, nucleophilic aromatic substitutions3 or
additions4 become feasible, and functionalizations based on a
lithiation step are made easier by the increase in the acidity of
the aromatic hydrogens.5 Moreover, the planar chirality of
complexes bearing an unsymmetrically di- or polysubstituted
aromatic ring makes them even more attractive in modern
organometallic chemistry. Among them, the planar chiral
(2) (a) McQuillin, F. J.; Parker, D. G.; Stephenson, G. R. Transition
Metal Organometallics for Organic Synthesis; Cambridge University Press:
Cambridge, UK, 1991. (b) Pape, A. R.; Kaliappan, K. P.; Kündig, E. P.
Chem. ReV. 2000, 100, 2917. (c) Modern Arene Chemistry; Astruc, D., Ed.;
Wiley-VCH: New-York, 2002. (d) Kündig, E. P. Topics in Organometallic
Chemistry; Springer: Berlin, Germany, 2004; Vol. 7. (e) Rosillo, M.;
Dom’nguez, G.; Pérez-Castells, J. Chem. Soc. ReV. 2007, 36, 1589.
(3) (a) Rose-Munch, F.; Gagliardini, V.; Renard, C.; Rose, E. Coord.
Chem. ReV. 1998, 178, 249–180. (b) Rose-Munch, F.; Rose, E. Eur. J. Inorg.
Chem. 2002, 1269. (c) Rose-Munch, F.; Rose, E. In Modern Arene
Chemistry; Astruc, D., Ed.; Wiley-VCH, New-York, 2002, Chapter 11, p
368. (d) Semmelhack, M. F.; Chlenov, A. Top. Organomet. Chem. 2004,
7, 43.
* Corresponding author. Fax: (+33) (0)1-44-27-55-04. E-mail:
murielle.chavarot-kerlidou@upmc.fr, francoise.rose@upmc.fr.
† UPMC Univ Paris 06, UMR 7611.
(4) (a) McDaniel, K. F. In ComprehensiVe Organometallic Chemistry
II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press:
Oxford, UK, 1995; Vol. 6, p 93. (b) Kündig, E. P.; Pape, A. Top. Organomet.
Chem. 2004, 7, 71.
‡ CNRS, UMR 7611.
§ UPMC Univ Paris 06, UMR 7616.
| CNRS, UMR 7616.
UPMC Univ Paris 06, UMR 7071.
(5) (a) Semmelhack, M. F. In ComprehensiVe Organometallic Chemistry
II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press:
Oxford, UK, 1995; Vol. 12, p 1017. (b) Rose-Munch, F.; Rose, E. Curr.
Org. Chem. 1999, 3, 445. (c) Gibson, S. E.; Reddington, E. G. Chem.
Commun. 2000, 989. (d) Semmelhack, M. F.; Chlenov, A. Top. Organomet.
Chem. 2004, 7, 21.
# CNRS, UMR 7071.
(1) (a) McGlinchey, M. J.; Ortin, Y.; Seward, C. M. Chromium
Compounds with CO or Isocyanides. In ComprehensiVe Organometallic
Chemistry III; Crabtree R. H., Mingos D. M. P., Eds.; Elsevier Science
Ltd: Oxford, UK, 2006; Vol. 5, p 201. (b) Sweigart, D. A.; Reingold, J. A.;
Son, S. U. Manganese Compounds with CO Ligands. In ComprehensiVe
Organometallic Chemistry III; Crabtree R. H. Mingos, D. M. P., Eds.;
Elsevier Science Ltd: Oxford, UK, 2006; Vol. 5, p 761. (c) Kündig, E. P.;
Pache, S. H. Arene Organometallic Complexes of Chromium, Molybdenum,
and Tungsten. In Science of Synthesis; Imamoto T., Ed.;Thieme: Stuttgart,
Germany, 2002; Vol. 2, p 155. (d) Oshima, K. Organometallic Complexes
of Manganese. In Science of Synthesis;. Imamoto T., Ed.; Thieme: Stuttgart,
Germany, 2002; Vol. 2, p 13.
(6) (a) Davies, S. G.; McCarthy, T. D. In ComprehensiVe Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon
Press: Oxford, UK, 1995; Vol. 12, p 1039. (b) Uemura, M. Top. Organomet.
Chem. 2004, 7, 129.
(7) (a) Gibson, S. E.; Ibrahim, H. Chem. Commun. 2002, 2465. (b)
Delacroix, O.; Gladysz, J. A. Chem. Commun. 2003, 665. (c) Salzer, A.
Coord. Chem. ReV. 2003, 242, 59. (d) Muñiz, K. Top. Organomet. Chem.
2004, 7, 205.
10.1021/om7012666 CCC: $40.75
2008 American Chemical Society
Publication on Web 05/08/2008

2506 Organometallics, Vol. 27, No. 11, 2008
Jacques et al.
Table 1. Formylation Conditions for Complexes 1–4
Cr(CO)3 complexes are undoubtedly the best-known examples
of such chiral precursors.6–10 These developments are also found
in a weaker extent with formyl-cymantrene (CpMn(CO)3)
derivatives,7c,11 but to the best of our knowledge, they are
inexistent for their isoelectronic [(η6-arene)Mn(CO)3]+ com-
plexes. Whereas the enhanced electrophilic character of these
cationic complexes compared to neutral ones is of great
potential, a major drawback in their chemistry has been for many
years the restricted number of arenes able to coordinate the
[Mn(CO)3]+ fragment.12 [(η6-arene)Mn(CO)3]+ complexes sub-
stituted by electron-withdrawing groups such as the benzalde-
hyde derivatives were unknown, the aromatic ring being too
electron-deficient for complexation. Unlike their corresponding
isoelectronic chromium complexes, no coordination of the arene
occurs even if the resonance electron withdrawal is disrupted
by the formation of a ketal, for instance.12 Moreover, the Swern
oxidation efficiently applied to the synthesis of (η6-arylalde-
hyde)Cr(CO)3 complexes13 cannot be viewed with the corre-
sponding manganese substrates, because primary benzylic
Entry Substrate R1
R2
OMe Ph
OMe
R3
Product
Yield [%] C2:C3
1a
2
3
1b
2b
3c
4d
H
H
5
6
68
67
90
66
C3
H
C3
Cl OMe Ph 7a + 7b
H
60:40
80:20
4
H
Ph 8a + 8b
a Reference 15a. b 1.6 equiv of nBuLi, 1.6 equiv of TMEDA, 2 equiv
of DMF, reaction time ) 1 h. c 1.4 equiv of nBuLi, 1.8 equiv of DMF,
reaction time ) 15 min. d 2 equiv of nBuLi, 2 equiv of TMEDA, 2.5
equiv of DMF, reaction time ) 2 h.
and the structural characterization of the new (η5-formylcyclo-
hexadienyl)Mn(CO)3 complexes. Their reactivity toward hydride
abstraction and nucleophilic addition is also studied. Finally a
strategy for the resolution of their planar chirality is presented.
+
alcohols do not coordinate the Mn(CO)3 fragment whatever
the complexation procedure used.12 This drawback has consid-
erably slowed down the development of applications based not
only on the cationic η6-arene complexes but also on their
isoelectronic neutral analogues: the (η5-cyclohexadienyl)Mn-
(CO)3 derivatives, efficiently obtained by addition of a broad
range of nucleophiles to the arene ring.4 The first breakthrough
was realized in our group in 2001 with the development of an
efficient functionalization pathway based on palladium-catalyzed
carbonylation reactions.14 Various nucleophiles were employed
giving for the first time access to ketone, ester, or amide
derivatives. Despite that, the synthesis of a formyl derivative
by combining the carbonylative conditions with the use of a
hydride source was still unsuccessfull.14 Recently, a new route
for efficient and versatile functionalization of (η5-cyclohexadi-
enyl)Mn(CO)3 complexes based on a lithiation/electrophilic
quench sequence was developed.15 The synthesis of the first
formyl-substituted (η5-cyclohexadienyl)Mn(CO)3 complex could
then be achieved by using DMF as the electrophile.15a We
describe here an extension of this approach to other substrates
Results and Discussion
Synthesis and Characterization. Complexes 1–4 used as
starting material in this study were synthesized by complexation
of anisole, para-chloroanisole, or benzene to give the corre-
sponding [(η6-arene)Mn(CO)3]+ complexes,12 followed by nu-
cleophilic addition of either PhMgCl (R3 ) Ph; complexes 1,
3, 4)16 or LiAlH4 (R3 ) H; complex 2).17 The best experimental
conditions for the lithiation/electrophilic quench sequence of
each susbtrate were determined in a previous study,15b which
revealed that the lithiation step is highly substrate dependent.
For instance, complete conversion of 3, the most reactive
substrate of the series, is achieved by reaction with 1.4 equiv
of nBuLi for only 15 min at -78 °C, whereas 2 equiv of nBuLi
and tetramethylethylenediamine (TMEDA) for 2 h are required
to optimize the lithiation of complex 4. In the present study,
these conditions were associated with the use of DMF as the
electrophile (Table 1), in order to synthesize the first (η5-
formylcyclohexadienyl)Mn(CO)3 derivatives.15a
The expected (η5-formylcyclohexadienyl)Mn(CO)3 deriva-
tives 5–8 were isolated with yields ranging from 66% to 90%.
For the anisole derivatives 1–2, the lithiation proceeded with
complete regiocontrol thanks to the presence of the methoxy
ortho-directing group. Starting with the para-chloroanisole
derivative 3, two regioisomers were obtained in a C2:C3 ratio
of 60:40, and were separated by chromatography on silica gel
to give the pure aldehydes 7a and 7b. The formylation of
complex 4, with an unsubstituted cyclohexadienyl moiety, gave
two regioisomers functionalized at C2 and C3 in a 80:20 ratio.
This is in agreement with the regioselectivity of the silylation
of complex 4 by the lithiation/electrophilic quench sequence.15b
According to a theoretical investigation, this regioselectivity
relies mainly on the intrinsic stabilities of the deprotonated
intermediates, the species lithiated at C2, eclipsed by a Mn-CO
bond, being the most stable one.15b
(8) For the preparation of enantiopure planar chiral (η6-arylaldehyde)-
Cr(CO)3 complexes, see the selected references: (a) Solladie-Cavallo, A.;
Solladie, G.; Tsamo, E. J. Org. Chem. 1979, 44, 4189. (b) Alexakis, A.;
Mangeney, P.; Marek, I.; Rose-Munch, F.; Rose, E.; Semra, A.; Robert, F.
J. Am. Chem. Soc. 1992, 114, 8288. (c) Alexakis, A.; Kanger, T.; Mangeney,
P.; Rose-Munch, F.; Perrotey, A.; Rose, E. Tetrahedron: Asymmetry 1995,
6, 2135. (d) Ewin, R. A.; MacLeod, A. M.; Price, D. A.; Simpkins, N. S.;
Watt, A. P. J. Chem. Soc., Perkin Trans. 1 1997, 401. (e) Han, J. W.; Son,
S. U.; Chung, Y. K. J. Org. Chem. 1998, 17, 3236. (f) Pache, S.; Romanens,
P.; Kündig, E. P. HelV. Chim. Acta 2000, 83, 2436.
(9) For applications of planar chiral (η6-arylaldehyde)Cr(CO)3 derivatives
in asymmetric synthesis, see ref 6a and the following selected references: (a)
Bromley, L. A.; Davies, S. G.; Goodfellow, C. L. Tetrahedron: Asymmetry
1991, 2, 139. (b) Pache, S.; Romanens, P.; Kündig, E. P. Organometallics
2003, 22, 377. (c) Chavarot, M.; Rivard, M.; Rose-Munch, F.; Rose, E.;
Py, S. Chem. Commun. 2004, 2330.
(10) For applications of planar chiral (η6-arylaldehyde)Cr(CO)3 deriva-
tives in catalysis, see ref 7 and for instance: (a) Bolm, C.; Muñiz, K.; Ganter,
C. New J. Chem. 1998, 1371. (b) Son, S. U.; Jang, H.-Y.; Lee, I. S.; Chung,
Y. K. Organometallics 1998, 17, 3236.
NMR characterization of products 5–8 confirmed unambigu-
ously the functionalization of the cyclohexadienyl skeleton by
(11) (a) Son, S. U.; Park, K. H.; Lee, S. J.; Chung, Y. K.; Sweigart,
D. A. Chem. Commun. 2001, 1290. (b) Son, S. U.; Chung, Y. K.
Tetrahedron: Asymmetry 2003, 14, 2109. (c) Ferber, B.; Top, S.; Vessières,
A.; Welter, R.; Jaouen, G. Organometallics, 2006, 25, 5730 and references
cited therein.
(15) (a) Jacques, B.; Chavarot, M.; Rose-Munch, F.; Rose, E. Angew.
Chem., Int. Ed. 2006, 45, 3481. (b) Jacques, B.; Chanaewa, A.; Chavarot-
Kerlidou, M.; Rose-Munch, F.; Rose, E.; Gérard, H. Organometallics 2008,
27, 626.
(12) Jackson, J. D.; Villa, S. J.; Bacon, D. S.; Pike, R. D.; Carpenter,
G. B. Organometallics 1994, 13, 3972.
(13) Merlic, C. A.; Walsh, J. C. J. Org. Chem. 2001, 66, 2265.
(14) (a) Auffrant, A.; Prim, D.; Rose-Munch, F.; Rose, E.; Vaisserman,
J. Organometallics 2001, 20, 3214. (b) Auffrant, A.; Prim, D.; Rose-Munch,
F.; Rose, E.; Schouteeten, S.; Vaisserman, J. Organometallics 2003, 22,
1898.
(16) Chung, Y. K.; Williard, P. G.; Sweigart, D. A. Organometallics
1982, 1, 1053.
(17) (a) Pauson, P. L.; Segal, J. A. J. Chem. Soc., Dalton Trans. 1975,
1683. (b) Balssa, F.; Gagliardini, V.; Rose-Munch, F.; Rose, E. Organo-
metallics 1996, 15, 4373.

(η5-Formylcyclohexadienyl)Mn(CO)3 Complexes
Organometallics, Vol. 27, No. 11, 2008 2507
Table 2. Selected 1H NMR Data (CDCl3, δ in ppm) for Complexes
1–8
Entry
Complex
H2
H3
H4
CHO
5
6
7
8
1
2
3
4
5
6
7a
7b
8a
8b
5.73
5.83
5.57
5.78
5.00
4.86
5.23
4.97
4.97
5.75
5.58
9
10.62 (C3)
10.66 (C3)
10.04 (C2)
10.54 (C3)
9.31 (C2)
9.92 (C3)
10
11
12
13
14
6.07
6.30
5.97
5.58
5.13
5.58
Table 3. Selected IR Spectral Data (cm-1) for Complexes 1–8
Figure 1. Molecular structure of complex 7b with thermal ellipsoids
at the 30% probability level. Hydrogen atoms have been omitted
for clarity.
21 and 22) and the benzene derivatives 8a,b (entries 23 and
24). They are found to be higher for the C2-formylated
complexes than for the C3-formylated ones (ν˜CHO(C2) -
ν˜CHO(C3) ) 28 cm-1 for 7a,b and ν˜CHO(C2) - ν˜CHO(C3) ) 27
cm-1 for 8a,b). This difference suggests that the electronic
delocalization between the carbonyl and the π-system is better
when -CHO is linked to the C3 carbon rather than to the C2
carbon of the cyclohexadienyl.
Pleasingly, monocrystals of complex 7b were readily obtained
by slow evaporation of a diethyl ether/pentane solution of the
complex, providing the first crystal structure of a formyl-
substituted (η5-cyclohexadienyl)Mn(CO)3 complex. The ORTEP
view shown in Figure 1 indicates that the formyl group is indeed
located adjacent to the methoxy group, and does not modify
the η5-cyclohexadienyl structure, with five coplanar sp2 carbons
and the remaining sp3 carbon located 38.10° above this plane.
The conformation of the Mn(CO)3 tripod is in agreement with
what is usually observed, the sp3 carbon being eclipsed by one
Mn-CO bond. Due to steric hindrance, the aldehyde conforma-
tion is anti with respect to the methoxy group. The presence of
the aldehyde function does not modify the Mn-C bond lengths
in the range 2.2469(13) to 2.1334(12), with the Mn-C3 bond
being the shortest one (Table 7).
Finally, the formyl group is nearly coplanar with the
cyclohexadienyl moiety, the angle between the two planes being
8.3°. This might again indicate a good conjugation between the
aldehyde and the π electrons of the η5 complex. It is interesting
to compare this structure to those of benzaldehyde derivatives
coordinated to the Cr(CO)3 entity in a η6 manner. To our
knowledge, only three structures of ortho-substituted benzal-
dehyde Cr(CO)3 have been reported in the literature19 and all
of them are in line with the one of complex 7b. Indeed, the
aldehyde functions are anti to the ortho substituents (an aminal
group19a or an ether group19b,c), and in each case, the CdO
bond is almost in the same plane as the arene ring. Furthermore,
C14sO2 (1.214(2)) and C14sC3 (1.4804(18)) bond lengths of
complex 7b have values very close to the analogous bonds in
the chromium complexes of the literature: 1.101(9) and
1.56(1),19a 1.196(7) and 1.483(8),19b 1.193(10) and 1.596(11),19c
respectively.
a The Mn(CO)3 tripod is omitted for clarity.
a formyl group; the aldehydic proton signature is indeed
observed between 9.3 and 10.7 ppm (Table 2), depending on
the cyclohexadienyl substitution, together with a downfield shift
(∆δ ) +0.5 to +0.75 ppm) for the cyclohexadienyl protons
ortho to CHO. We have also recorded IR spectra for complexes
5–8 and the data are presented in Table 3. The main feature of
these spectra is the presence of two vibrational bands associated
with the carbonyl ligands of the Mn(CO)3 tripod and one with
the aldehydic function. It is well-known that the carbonyl ν˜CO
vibrations reflect π-back-bonding into the CO π* orbitals and
are therefore very sensitive to changes in electron density at
the metal.18 The observed IR frequencies are higher for
complexes 5–8 than for substrates 1–4 (∆ν˜ ) +10 to +20
cm-1), in agreement with the strong electron-withdrawing
character of the formyl group (Table 3). More interesting is the
comparison of the formyl ν˜CHO vibrations with the substitution
pattern of the cyclohexadienyl moiety. Indeed, our synthetic
methodology allows the substitution either at the C2 carbon or
at the C3 one, the regioselectivity being controlled by the
presence of ortho-directing groups (entries 15–17) or by the
intrinsic reactivity of the cyclohexadienyl ligand in the complex
(entry 18).15b
Computational Approach. Computational studies were
undertaken to get a better understanding of the electronic
properties of these (η5-formylcyclohexadienyl)Mn(CO)3 deriva-
tives and especially within the differences observed between
the regioisomers. Complexes 8a and 8b were therefore chosen
The observed ν˜CHO(C2) and ν˜CHO(C3) frequencies were
compared for the para-chloroanisole derivatives 7a,b (entries
(18) Tolman, C. A. J. Am. Chem. Soc. 1970, 92, 2952.

2508 Organometallics, Vol. 27, No. 11, 2008
Jacques et al.
Table 4. Selected Computed ν˜CHO IR Frequencies (in cm-1) for
Table 5. Selected Parameters Illustrating the Conjugation of the
CHO moietya
Structures 8–10 and Relative Energies for Structures b with Respect
to a (in kcal · mol-1 a
)
a ∆Erot is the lowest rotation barrier (in kcal · mol-1) of the CHO
moiety; ∆νrot is the corresponding increase of the νCHO vibrational
frequency (in cm-1).
structures, associated to rotation barriers of 7.8 (9a) and 12.6
kcal · mol-1 (9b). These values are perfectly in line with the
one we previously reported for the unsubstituted η5 structure
(9.9 kcal · mol-1).15b The lower energy conformations of the
tripod and of the CHO group were assumed to be the same
ones for complexes 8, differing only by the C6 substituent.
(b) CHO Vibrational Frequency and 1H NMR
Shielding Constants. The lowest energy conformers were then
used to study the spectroscopic properties of each regioisomer,
either the C2-substituted a or the C3-substituted b (Table 4).
The computed IR vibrational frequencies of the conformers
proved to be significantly larger than the experimental ones
(Table 3, entries 23 and 24), as expected from computations
carried out within the framework of the harmonic approximation.
However, correcting the computed values by applying a scaling
factor according to the standard procedure (a factor of 0.97 is
used here)21 yields ν˜CHO of 1738 cm-1 for 8a and 1706 cm-1
for 8b, in good agreement with the experimental ones (1710
and 1683 cm-1, respectively). In particular, the frequency shift
between 8a and 8b amounts to 33 cm-1, very close to the 27
cm-1 experimentally observed.
The excellent correlation between theory and experiment is
also highlighted by the computational evaluation of the NMR
shielding constants for complexes 8a and 8b (Table 4, entry
27). The aldehydic proton signature was examined by computing
the difference δ(CHO) - δ(H4) (referred as ∆δ below). For
complex 8a, a ∆δ of 4.26 ppm is obtained, very close to the
experimentally observed 4.18 ppm (Table 2). In the case of
complex 8b, due to the existence of two minimas depending
on the orientation of the CHO group, the computed H2 and H4
protons are not equivalent, in contrast with the experimental
results (Table 2). This can be correlated with the transition state
of 10.6 kcal · mol-1 reported below for the parent structure 9b
(Table 5, entry 32), associated with the rotation of the CHO
group, and corresponding to a fast interconversion at room
temperature with respect to the NMR time scale. The reported
∆δ value for 8b (Table 4, entry 27) is thus the average of the
calculated H4 and H2 shielding constants and is also in good
agreement with the experimental value (∆δexp ) 4.34 ppm). In
addition, a downfield shift for the ortho proton in the case of
8a (evaluated from δ(H3) - δ(H4)) was found within 0.18 ppm
from the experimental value.
a The computed NMR aldehydic proton signature (reported as
δ(CHO) - δ(H4), in ppm) is given for structures 8.
as model compounds. The closely related structures 9a and 9b
bearing an H instead of a Ph in the exo position were also used
to limit the computational cost.
(a) Structural Description. Geometry optimizations were
first undertaken on the model compounds 9 to determine the
lowest energy conformation of each regioisomer. In all the
cases, the CdO bond is found to lie within the plane of the
ring with a maximal deviation of 16.6°. In particular, a 9.3°
value is obtained for the OdCsC3sC2 dihedral angle in
structure 9b, a value in perfect agreement with the one
obtained by X-ray analysis of the related C3-formylated
complex 7b (8.3°). The CdO (1.220 Å) and (O)C3sC2 (1.472
Å) bond distances are found to be within 0.01 Å of the X-ray
values. For 9a, substituted at C2, two minima are obtained
depending on the orientation of the carbonyl group. The
conformer with the CdO bond pointing toward the H3 proton
(as presented in Table 4) is the lowest energy conformer by
only 0.5 kcal · mol-1 with respect to that with the CdO bond
pointing at H1. The orientation of the tripod was then
examined for species 9a and 9b. A conformation eclipsing
the C2, C4, and C6 carbons is obtained for the minima similar
to the one of all the η5 complexes described up to now. No
effect of the substitution by an electron-withdrawing group
such as CHO is thus observed, in strong contrast with the
well-known relationship between tripod conformation and
electronic properties of the substituents in the (η6-arene)-
M(CO)3 complexes (M ) Cr,20 Mn+ 14). The structures in
which C6 is anti-eclipsed with respect to the CO ligands are
found to be transition states (TS) between two eclipsed
(c) CHO Conjugation Properties. The relative energies of
the two regioisomers were then examined. The energy difference
of 9a with respect to 9b was evaluated to be 4.5 kcal · mol-1
(Table 4, entry 28). The C2-formylated structure 8a was also
found to be 4.6 kcal · mol-1 less stable than its corresponding
regioisomer 8b (Table 4, entry 25). This preference for the CHO-
substitution at the C3 position of the cyclohexadienyl is inverted
(19) (a) Rose-Munch, F.; Gagliardini, V.; Perrotey, A.; Tranchier, J.-
P.; Rose, E.; Mangeney, P.; Alexakis, A.; Kanger, T.; Vaisserman, J. Chem.
Commun. 1999, 2061. (b) Tan, Y. L.; White, A. J. P.; Widdowson, D. A.;
Wilhem, R.; Williams, D. J. J. Chem. Soc., Perkin Trans. 1 2001, 3269.
(c) Costa, M. F.; da Costa, M. R. G.; Curto, M. J. M.; Magrinho, M.; Damas,
A. M.; Gales, L. J. Organomet. Chem. 2001, 632, 27.
(20) Solladié-Cavallo, A.; Suffert, J. Org. Magn. Reson. 1980, 14, 426.
(21) Andersson, M. P.; Uvdal, P. J. Phys. Chem. A 2005, 109, 2937.

(η5-Formylcyclohexadienyl)Mn(CO)3 Complexes
Organometallics, Vol. 27, No. 11, 2008 2509
Table 6. Crystallographic Data for 7b, 11a, (R,R,6R,1pS)-12, and (R,R,6S,2pR)-1315a
7b
11a
(R,R,6R,1pS)-12
(R,R,6S,2pR)-13
empirical formula
C17H12Cl1Mn1O5
388.66
C23H19Mn1O5
430.33
C25H28Cl1Mn1N2O4
510.89
C25H29Mn1N2O4
476.44
mol wt (g cdt.mol-1
)
crystal dimensions (mm3)
a (Å)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg.)
V (Å3)
Z
0.10 × 0.12 × 0.15
0.10 × 0.12 × 0.22
8.9297(8)
10.7940(10)
11.1264(13)
72.273(8)
80.503(11)
88.397(8)
1007.23(18)
2
0.06 × 0.10 × 0.14
0.10 × 0.13 × 0.18
12.2077(13)
9.4528(12)
10.5344(14)
12.2447(11)
12.4319(14)
90
114.101(8)
90
1693.9(3)
4
12.0818(9)
21.7123(17)
90
90
90
2479.7(3)
4
13.9240(8)
16.439(2)
90
90
90
2411.3(3)
4
cryst system
space group
monoclinic
P21/c
9.60
250
1.52
3–30
-17/13, –17/15, –17/17
17431
4921
3499 (I > 3σ(I))
0.0274
0.0336
1.113
triclinic
P
6.87
200
1.42
orthorhombic
P212121
6.73
295
1.37
2–30
-13/13, –16/16, –30/30
35415
7237
5642 (I > 3σ(I))
0.0232
0.0259
1.052
orthorhombic
P212121
5.80
250
1.31
3–30
-14/14, –19/19, –22/23
21873
6866
4532 (I > 3σ(I))
0.0303
0.0321
1.100
µ (cm-1
Τ (K)
)
Fcalcd (g · cm-3
θ limits (deg)
k, k, l limits
)
3–23
-12/12, –15/15, –15/15
19938
5835
4782 (I > 2σ(I))
0.043
0.051
1.366
no. of reflns collected
no. of unique data
no. of reflns used
Ra
b
Rw
GoF
no. of variables
219
-0.37
0.26
263
-0.40
0.46
301
-0.272
0.254
292
-0.25
0.30
∆Fmin (e · Å-3
)
)
∆Fmax (e · Å-3
Flack’s x parameter
0.044(9)
0.106(14)
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo|2]1/2
.
to what is reported in the litterature for the methoxy-substituted
[(η5-cyclohexadienyl)Cr(CO)3]- species,22 as could be expected
from the opposite electronic demand of the OMe group with
respect to CHO. The comparison between the two energy
differences for 8 and 9 species (only 0.1 kcal · mol-1) shows
unambiguously that the impact of the sp3 carbon substituent is
negligible. The same trend is also observed for the computed
νCHO vibrational frequencies (Table 4, entry 26 compared to
29), validating therefore the use of the model structures 9a and
9b.
The vibrational frequencies of the aldehydic function as well
as the energy difference between structures 9a and 9b can be
put into perspective with the data obtained for the two “virtual”
cyclohexadienyl ligands 10a,b (Table 4, entries 30 and 31). Such
a comparison with an uncoordinated ligand has also proven its
usefulness in the computational studies of aryl23 or benzyl24
anions, radicals, and cations of (η6-arene)Cr(CO)3 complexes
and also in the theoretical investigation of the lithiated (η5-
cyclohexadienyl)Mn(CO)3 species.15b In the present study, it
appears that ligand 10a substituted at C2 is less stable than its
regioisomer 10b (Table 4, entry 30). The energy difference
amounts to more than 20 kcal · mol-1, which is much larger
than in the case of the corresponding complexes 9. The energy
difference between the two formylated regioisomers is thus
drastically decreased by coordination of the cyclohexadienyl
ring at the metal fragment. Moreover, when comparing the
interaction of the unsubstituted cyclohexadienyl ligand with the
metal center (242 kcal · mol-1) with that of the formyl-
substituted ones (224 kcal · mol-1 for 9a and 208 kcal · mol-1
for 9b), it appears that the functionnalization by the CHO group
diminishes significantly the binding energy to the metal center.
All the same, if considering the CHO vibrational frequencies,
the νCHO difference between 10a and 10b amounts to 75 cm-1
(Table 4, entry 31) and is also strongly reduced upon coordina-
tion to the metal center (only a 32 cm-1 difference between 9a
and 9b).
The previous results shed light on the essential role played
by the position of the CHO moiety on the electronic properties
of the complexes. This was further investigated with the
following experiment: the conjugation of the formyl group with
the cyclohexadienyl π-system was broken by rotation of the
aldehyde group about the C2/3-CHO bond. Such a rotation of
the CHO moiety can occur either clockwise or counterclockwise,
yielding transition states (TS) with the CdO bond pointing either
toward the tripod side or in the opposite direction. The two
corresponding TS structures are found to be quasi-isoenergetic,
the latter one being more stable by less than 1 kcal · mol-1. The
lowest TS localized for 9a,b and 10a,b are referred below
(Figure 2) as TS(9a), TS(9b), TS(10a), and TS(10b), respec-
tively. They correspond to structures where the CdO bond is
quasiperpendicular to the ring (OdCsCsC dihedral angle
between 87.8° and 104.6°). The associated rotation barrier ∆Erot
(in kcal · mol-1) was calculated for each structure (Table 5)
together with the corresponding variation of the IR vibrational
frequencies ∆Erot (in cm-1) between the transition states and
the lowest energy conformers.
A 10.6 kcal · mol-1 rotation barrier is obtained for the CHO
group in the case of structure 9b, whereas it is 4.1 kcal · mol-1
smaller in 9a (Table 5, entry 32). Considering that structure 9b
is also 4.5 kcal · mol-1 more stable than 9a (Table 4, entry 28),
TS(9a) and TS(9b) are thus quasi-isoenergetic (9b stabilized
by only 0.5 kcal · mol-1 as shown in Figure 2, left). All the
same, the energy difference between 10a and 10b is almost
perfectly canceled upon rotation of the CHO moiety (1.0
kcal · mol-1 in favor of 10a). The same trend is observed for
the ν˜CHO vibrational frequencies (Figure 2, right). Breaking the
(22) Pfletschinger, A.; Koch, W.; Schmalz, H.-G. New J. Chem. 2001,
25, 446.
(23) Merlic, C. A.; Miller, M. M.; Hietbrink, B. N.; Houk, K. N. J. Am.
Chem. Soc. 2001, 123, 4904.
(24) Merlic, C. A.; Walsh, J. C.; Tantillo, D. J.; Houk, K. N. J. Am.
Chem. Soc. 1999, 121, 3596.

2510 Organometallics, Vol. 27, No. 11, 2008
Jacques et al.
Figure 2. Computed νCHO vibrational frequencies and energies (relative to the most stable structure) for the lowest energy conformers and
for the lowest transition states of structures 9a and 9b.
Scheme 1. Rearomatization of Complex (η5-3-Formyl-2-me-
thoxycyclohexadienyl)Mn(CO)3 (6)
(ketones, esters, and amides) by rearomatization of the corre-
sponding (η5-cyclohexadienyl)Mn(CO)3 synthesized by carbo-
Figure 3. Highest occupied molecular orbitals for 10a (left) and
10b (right). Isodensity equal to 0.7.
nylative palladium-catalyzed cross-couplings.14 This has dem-
onstrated that the limitation was not an intrinsic instability of
+
the (η6-arene)Mn(CO)3 complexes substituted by conjugated
conjugation by rotation brings ν˜CHO for species TS(9a) and
electron-withdrawing groups but the lack of an adequate method
for their preparation.
TS(9b) only 8 cm-1 apart.
The computational results can be rationalized as follows:
The first synthetic attempts were realized following the
experimental procedure for the rearomatization of variously
functionalized η5-cyclohexadienyl complexes,14,15b using an
excess of [CPh3][BF4] in dichloromethane at room temperature.
Under these conditions, complex 11 could be isolated as an
impure sticky solid and in a relatively poor yield (20%). It was
therefore necessary to adjust the quantity of trityl salt to 1 equiv
together with a decrease of the temperature to optimize the yield
and the quality of the cationic aldehyde 11. Thus, at -15 °C,
the aromatization of the (η5-formylcyclohexadienyl)Mn(CO)3
complex 6 by hydride abstraction proceeded smoothly to give
the [(η6-2-methoxybenzaldehyde)Mn(CO)3][BF4] complex 11
in 70% yield as a yellow powder (Scheme 1).
conjugation of the CHO system with the cyclohexadienyl moiety
is larger in position 3 than in position 2, due to the presence of
a node in the C2 position of the cyclohexadienyl highest
occupied orbital (HOMO).25 Nevertheless, this conjugation, by
decreasing the energy and the coefficient of the ring carbons of
the HOMO, results in a weaker interaction of the cycle with
+
the Mn(CO)3 metal fragment.26 The resulting differences
between species 9a and 9b (either in energy or in ν˜CHO) are
thus much smaller than those in the corresponding fully organic
system 10a and 10b (Figure 3).
In conclusion, the present computational study demonstrates
that the energy and ν˜CHO differences observed between regioi-
somers 8a and 8b are fully associated with the conjugation
between the CHO moiety and the cyclohexadienyl π-system,
and that no other phenomenon (steric effects, inductive ef-
fects, . . .) needs to be proposed.
The presence of the aldehyde on the aromatic ring is
1
characterized by its signature at 10.40 ppm on the H NMR
spectrum and at 187.2 ppm in the 13C NMR spectrum of
1
Reactivity Study of the (η5-Formylcyclohexadienyl)Mn-
(CO)3 Complexes. As the functionalization by the lithiation/
electrophilic quench sequence does not affect the complexed
η5-cyclohexadienyl fragment, we decided to take advantage of
the property of (η5-cyclohexadienyl)Mn(CO)3 complexes to
undergo exo hydride abstraction at the sp3 carbon27 to achieve
the synthesis of the first (η6-arylaldehyde)Mn(CO)3+. Indeed,
the electron density of the benzaldehyde ring or of other arenes
substituted by conjugated electron-withdrawing groups is too
complex 11 in acetone-d6. Its H NMR spectrum is otherwise
characteristic of a cationic (η6-arene) manganese complex with
the most deshielded protons, H4 and H6, appearing at 7.51 and
7.56 ppm, respectively, and the less deshielded ones, H3 and
H5, at 6.82 and 6.49 ppm, respectively. Such a difference in
the chemical shifts of the aromatic protons is attributable to
the electronic distribution created by the resonance-withdrawing
group CHO located ortho to the electron-donating group OMe.
This observation is in good agreement with an anti-eclipsed
conformation in solution of the Mn(CO)3 tripod with respect to
the electron-withdrawing group. Unfortunately, an X-ray dif-
fraction analysis could not be realized to study complex 11
conformation in the solid state; several attempts were made to
grow suitable crystals, all unsuccessful because of the relative
instability of 11.
+
low to allow a direct coordination to the Mn(CO)3 moiety.12
In an earlier study, we have been able to circumvent this
+
restriction and we have prepared the first (η6-arene)Mn(CO)3
complexes with resonance electron-withdrawing substituents
(25) Eisenstein, O.; Butler, W. M.; Pearson, A. J. J. Am. Chem. Soc.
1984, 3, 1150.
This unprecedented (η6-arylaldehyde)Mn(CO)3+ complex
indeed proved to be much more reactive than the cationic
complexes substituted by keto-, ester-, or amido-groups. First,
(26) Albright, T. A.; Hofmann, P.; Hoffmann, R. J. Am. Chem. Soc.
1977, 99, 7546.
(27) Pauson, P. L.; Segal, J. A. J. Chem. Soc., Dalton Trans. 1975, 1677.

(η5-Formylcyclohexadienyl)Mn(CO)3 Complexes
Organometallics, Vol. 27, No. 11, 2008 2511
1
Figure 4. H NMR spectra (400 MHz, acetone-d6): (a) complex
[(η6-1-formyl-2-methoxybenzene)Mn(CO)3][BF4] 11 and (b) the
corresponding gem-diol 11′ after addition of D2O.
Figure 5. Molecular structure of complex 13a with thermal
ellipsoids at the 30% probability level. Hydrogen atoms have been
omitted for clarity.
the conjugation of the formyl group with the metal-complexed
aromatic ring seems to strongly increase its electrophilicity.
Indeed, the addition of D2O to an NMR sample of complex
11 in acetone-d6 resulted in the almost quantitative formation
of the corresponding gem-diol complex 11′ as indicated by
Scheme 2
1
the disappearance of the aldehydic H NMR signal at 10.40
ppm and the appearance of a singulet at 6.14 ppm for the
resonance of the benzylic proton of the gem-diol group
(Figure 4).
+
The metal center itself in the (η6-arylaldehyde)Mn(CO)3
complex appears also very electrophilic compared to the various
cationic complexes that we previously synthesized.14,15b This
was revealed by the fast appearance of 1H NMR signals
corresponding to the free aromatic ligand as a consequence of
the decoordination of the Mn(CO)3 entity by a nucleophilic
attack of acetone-d6. These observations seem to be in line with
the computational evaluation of the coordination of the anisole
ring to the Mn(CO)3+ moiety; it is indeed found to be decreased
by 8.1 kcal · mol-1 upon ortho functionalization by a formyl
group.
resulting from a nucleophilic addition on the aldehyde function
were isolated in high yields (87% for the unprecedented
hydroxymethyl derivative 12 and 91% for 13) and no side
1
products were identified in the H NMR of the crude mixture.
Specially, no addition of hydride to the π system was observed
in contrast with our previous study28 dealing with the reactivity
of keto-substituted (η5-cyclohexadienyl)Mn(CO)3 complexes
toward hydrides.
We then turned our attention toward the reactivity of the (η5-
formylcyclohexadienyl)Mn(CO)3 complexes toward nucleo-
philes. The synthesis and reactivity of (η5-cyclohexadienyl)Mn-
(CO)3 complexes functionalized by an alcohol function R to
the π system are currently under investigation in our group.
Such η5 derivatives cannot be obtained from the corresponding
η6 cationic complexes, the benzylic alcohol function being
incompatible with the complexation procedures.12 Two pathways
have already been described to prepare such functionalized
complexes. The first one relies on the reduction of a ketone
function stemming from a palladium-catalyzed carbonylative
coupling.28 The second one is based on the lithiation/electro-
philic quench procedure with use of a carbonyl electrophile,
either aldehyde or ketone.15b The easy access to the formylcy-
clohexadienyl complexes 5–8 opens a third pathway to this class
of complexes, as illustrated below by the study of their reactivity
toward a hydride source (NaBH4) and a Grignard reagent
(PhMgCl), under experimental procedures generally used for
reductions.
Second, a new stereogenic center is created during the
addition of PhMgCl on the racemic planar chiral complex 5.
Of the two possible (racemic) diastereoisomers, only one was
identified by 1H NMR analysis of the crude mixture. A
monocrystal suitable for X-ray diffraction analysis was readily
obtained by slow evaporation of a dichloromethane/pentane
solution of the purified diastereoisomer. The molecular structure
was established (ORTEP view presented in Figure 5) and
allowed the assessment of the relative configuration (R) for the
newly created sp3 carbon C14 associated with the (2pS)
configuration for the metal-coordinated cyclohexadienyl moiety,
thus corresponding to diastereoisomer 15a (Scheme 2). The
selectivity for this relative stereochemistry can be understood
according to the following two factors. For steric reasons, the
formyl group in complex 5 adopts an anti conformation with
respect to the methoxy group. This is, for instance, observed in
the crystal structure of the aldehyde 7b (Figure 1). Additionally,
the Mn(CO)3 tripod blocks one face of the cyclohexadienyl, so
that the addition of PhMgCl preferentially occurs exo with
respect to the metal. Although such a high diastereoselectivity
could be predicted,9 it represents the first example of a
diastereoselective nucleophilic addition to a formyl group
attached to a planar chiral (η5-cyclohexadienyl)Mn(CO)3 back-
bone. Diastereoisomeric complexes 13 have been previously
The first observation that can be made is the high chemose-
lectivity of these two reactions. Indeed, the starting (η5-
cyclohexadienyl)Mn(CO)3 complexes possess three electrophilic
sites, namely the cyclohexadienyl system, the Mn(CO)3 frag-
ment, and the formyl group. Nonetheless, the alcohol derivatives
(28) Eloi, A.; Rose-Munch, F.; Jonathan, D.; Tranchier, J.-P.; Rose, E.
Organometallics 2006, 25, 4554.

2512 Organometallics, Vol. 27, No. 11, 2008
Jacques et al.
obtained by the lithiation/electrophilic quench of complex 1,
using benzaldehyde as the electrophile.15b But in this synthetic
approach, a mixture of the two diastereoisomers 13a and 13b
was obtained in a 44:56 ratio. This lack of diastereoselectivity
was attributed to a very low facial stereodiscrimination of the
benzaldehyde CdO bond by the planar chiral η5-cyclohexadi-
enyl anion.
Resolution of Planar Chiral (η5-Formylcyclohexadienyl)-
Mn(CO)3 Complexes. The electrophilic reactivity of the formyl
group was also exploited to introduce a chiral auxiliary on the
η5 complex. Indeed, among the newly synthesized (η5-formyl-
cyclohexadienyl)Mn(CO)3 complexes, compounds such as 5,
6, and 7a possess a planar chirality. Up to now, to the best of
our knowledge, no general method for preparing enantiopure
(η5-cyclohexadienyl)Mn(CO)3 complexes has been developed.
However, several attempts employing different approaches
demonstrate an enduring and undoubted interest in these planar
chiral entities, especially for the enantioselective synthesis of
natural products containing polysubstituted cyclohexadienes or
cyclohexenes.2b Miles et al. reported the addition of chiral
nonracemic enolates to prochiral cationic [(η6-arene)Mn(CO)3]+
complexes to generate η5-cyclohexadienyl complexes.29 In spite
of the low stereoselectivity in the formation of the η5-
cyclohexadienyl system, subsequent separation of the diastere-
oisomeric mixture by recrystallization enabled the establishment
of a formal synthesis of (+)-juvabione.30 Using a different
approach, Pearson et al. studied the addition of various achiral
nucleophiles to η6-arene manganese complexes bearing a chiral
amino auxiliary.31 Despite good diastereoselectivities, this class
of compound has only limited applications because it is not
straightforward to remove the chiral auxiliary from the final
product. More recently, Chung and co-workers developed an
enantioselective addition of nucleophiles to prochiral (η5-
oxocyclohexadienyl)Mn(CO)3 complexes in the presence of
chiral ligands.32 This approach remains nevertheless specifically
devoted to the formation of acetoxy-subtituted enantioenriched
η5-cyclohexadienyl complexes. The development of new syn-
thetic approaches is therefore still highly demanded in view of
the chemical richness of these complexes. We have previously
described the resolution of racemic planar chiral ortho-
substituted (η6-benzaldehyde)tricarbonylchromium complexes
using an enantiopure diamine with a C2 symmetry axis.8b We
therefore decided to apply the same methodology for the
resolution of racemic (η5-formylcyclohexadienyl)Mn(CO)3
mixtures.
Figure 6. Chirality of (η5-cyclohexadienyl)Mn(CO)3 complexes.
Scheme 3
to the prochiral [(η6-arene)Mn(CO)3]+ complex I (Figure 6)
creates two stereogenic elements, a plane and a center (C6).
Thus, four stereoisomers (two pairs of enantiomers) should
theoretically be formed, but the nucleophilic addition always
being exo stereospecific,4 only a single pair of enantiomers III
and ent-III (alternatively II and ent-II for a nucleophilic ortho-
addition) is in fact obtained.
In the following study, the chirality of the various complexes
will be conventionally described by the configuration at the
chiral plane,33 together with the corresponding configuration at
the C6 center if chiral, and by the configuration of the chiral
auxiliary when present on the molecule.
Recently, we reported the first resolution of a racemic mixture
of formyl-substituted (η5-cyclohexadienyl)Mn(CO)3 complexes,
namely compound (rac)-5.15a The extension of this methodology
to complexes 6 and 7a has been studied and is presented below.
After reaction of the racemic aldehydes 5, 6, or 7a with
enantiopure (R,R)-N,N′-dimethylcyclohexane-1,2-diamine,34 two
diastereomeric aminals were obtained. Careful chromatographic
separation of the mixtures was then performed on neutralized
silica gel or on basic alumina to prevent the hydrolysis of the
chiral auxiliary.
The complete conversion of compound (rac)-7a to the
corresponding aminals was reached after 18 h of reaction at
room temperature (Scheme 3). The best separation conditions
were obtained with basic alumina and afforded diastereoisomer
(R,R,6R,1pS)-14 with g95% diastereoisomeric excess (de) and
18% yield. The diastereoisomeric purity was ascertained by
NMR analysis, the signals of the H3 protons of the diastereoi-
somers being clearly separated by 0.43 ppm (Figure 7).
Moreover, the determination of the molecular structure of
The description of the chirality of (η5-cyclohexadienyl)Mn-
(CO)3 complexes is not as straightforward as that for the closely
related planar chiral [(η6-arene)Mn(CO)3]+ precursors and
deserves some comments. All the (η5-cyclohexadienyl)Mn(CO)3
complexes unsymmetrically substituted on the cyclohexadienyl
system are chiral as, for example, the C1- or C2-substituted
complexes presented in Figure 6. But, considering for instance
a regioselective nucleophilic meta-addition to complex I (Figure
6), two different situations arise. When Nu ) H, the resulting
complexes III and ent-III contain a single stereogenic element,
the chiral plane. However if Nu * H, the nucleophilic addition
(29) Miles, W. H.; Smiley, P. M.; Brinkman, H. R. J. Chem. Soc., Chem.
Commun. 1989, 1897.
(30) Miles, W. H.; Brinkman, H. R. Tetrahedron Lett. 1992, 33, 589.
(31) (a) Pearson, A. J.; Zhu, P. Y.; Youngs, W. J.; Bradshaw, J. D.;
McConville, D. B. J. Am. Chem. Soc. 1993, 115, 10376. (b) Pearson, A. J.;
Milletti, M. C.; Zhu, P. Y. J. Chem. Soc., Chem. Commun. 1995, 853. (c)
Pearson, A. J.; Gontcharov, A. V.; Zhu, P. Y. Tetrahedron 1997, 53, 3849.
(32) Son, S. U.; Park, K. H.; Lee, S. J.; Seo, H.; Chung, Y. K. Chem.
Commun. 2002, 1230.

(η5-Formylcyclohexadienyl)Mn(CO)3 Complexes
Organometallics, Vol. 27, No. 11, 2008 2513
Scheme 4
Figure 7. Selected sections of 1H NMR spectra (200 MHz, CDCl3):
(a)crudemixtureofdiastereoisomers(R,R,6R,1pS)-14and(R,R,6S,1pR)-
14; (b) after chromatographic separation: (R,R,6R,1pS)-14 with
g95% de.
Figure 8. Molecular structure of complex (R,R,6R,1pS)-14 with
thermal ellipsoids at the 30% probability level. Hydrogen atoms
have been omitted for clarity.
Figure 9. Selected sections of 1H NMR spectra (400 MHz, CDCl3):
(a)crudemixtureofdiastereoisomers(R,R,6S,2pR)-15and(R,R,6R,2pS)-
15; after chromatographic separation, (b) (R,R,6S,2pR)-15 with
g95% de and (c) (R,R,6R,2pS)-15 with g95% de.
(R,R,6R,1pS)-14 allowed us to assign the absolute configuration
of the stereogenic center and of the planar chiral η5-cyclohexa-
dienyl moiety. Indeed, complex (R,R,6R,1pS)-14 was readily
recrystallized by slow evaporation of a diethylether/pentane
solution giving monocrystals suitable for X-ray diffraction
analysis. An ORTEP view is presented in Figure 8 and reveals
the (6R) and (1pS) configurations associated with the (R,R)
configuration of the enantiopure diamine.35
(pS)-5 in 93% and 99% yield after chromatography and with
g95% and 85% ee, respectively.
The assignment of the configurations of the chiral center and
of the planar chiral η5-cyclohexadienyl moiety was possible
through X-ray analysis of suitable crystals of one of the
diastereomeric aminals 15 (>95% de, δ(H11A) ) 4.19 ppm).15a
(6S) and (2pR) configurations connected with the (R,R) con-
figuration of the enantiopure diamine were observed for this
diastereoisomer (Figure 10).35 On this basis, the absolute
configurations of the formyl derivatives (pR)-5 and (pS)-5 could
also be unambiguously assigned.
This methodology was more successful with the anisole series.
Refluxing (rac)-5 and the enantiopure diamine with molecular
sieves in diethyl ether gave diastereoisomeric aminals 15 with
conversions up to 98% (Scheme 4). The separation of these
compounds was achieved by chromatography on neutralized
silica gel affording the two diastereoisomers in 33% and 32%
yield with g95% and 85% de, respectively. The separation could
be optimized (de g95% for both complexes; spectra presented
in Figure 9) although with lower yields (25% and 27%,
respectively). The diastereomeric composition was readily
We also considered the resolution of (rac)-6. The corre-
sponding diastereoisomeric aminals were prepared with conver-
sions ranging from 95% to 100% after 7 to 8 h of reaction in
diethyl ether at 30 °C (Scheme 5). Separation by chromatog-
raphy on neutralized silica gel provided the two diastereoisomers
in 33% and 25% yield with g95% and 92% de, respectively.
As above, 1H NMR spectroscopic analysis is a suitable method
for the determination of diastereoisomeric excesses: the signals
1
determined by H NMR spectroscopic analysis: the aminalic
protons H11A and H11B of these compounds resonate at δ 4.19
and 5.17 ppm respectively, a difference of almost 1 ppm (Figure
9). The aminals were then easily converted by acid-catalyzed
hydrolysis into the pure enantioenriched aldehydes (pR)-5 and

2514 Organometallics, Vol. 27, No. 11, 2008
Jacques et al.
Figure 10. Molecular structure of complex (R,R,6S,2pR)-1515a with
thermal ellipsoids at the 30% probability level. Hydrogen atoms
have been omitted for clarity.
Figure 11. Selected sections of 1H NMR spectra (400 MHz,
CDCl3): after chromatographic separation of the diastereoisomeric
mixture (a) (R,R,2pR)-16 (g95% de) and (b) (R,R,2pS)-16 (de )
92%).
Scheme 5
Table 7. Selected Interatomic Distances for 7b, 11a,
(R,R,6R,1pS)-12, and (R,R,6S,2pR)-13
7b
11a
(R,R,6R,1pS)-12 (R,R,6S,2pR)-13
Mn-C1 2.2347 (14) 2.2277 (14)
Mn-C2 2.1423 (12) 2.2154 (14)
Mn-C3 2.1334 (12) 2.1483 (13)
Mn-C4 2.2129 (13) 2.1482 (14)
Mn-C5 2.2469 (13) 2.2546 (15)
C2-C14
2.1589 (12)
2.1614 (12)
2.1399 (12)
2.2018 (13)
2.2262 (13)
1.5329 (18)
2.206 (2)
2.2055 (19)
2.1659 (18)
2.139 (2)
2.252 (2)
C3-C14 1.4804 (18) 1.5304 (19)
1.515 (3)
C14-O2 1.214 (2)
C14-N1
1.4455 (17)
1.4800 (19)
1.4774 (19)
1.481 (3)
1.485 (3)
C14-N2
after chromatography the enantioenriched formyl-substituted (η5-
cyclohexadienyl)Mn(CO)3 (2pR)-6 and (2pS)-6 in 98% and
quantitative yield and with g95% and 92% ee, respectively
(Tables 6 and 7).
Conclusion
Using DMF as the electrophile, we successfully applied the
lithiation/electrophilic quench sequence developed for the
functionalization of (η5-cyclohexadienyl)Mn(CO)3 complexes
to the synthesis of the first formyl derivatives in this family of
organometallic compounds. These new (η5-formylcyclohexa-
dienyl)Mn(CO)3 complexes were obtained in good yields and
were structurally characterized in solution by NMR and in the
solid state by IR spectroscopy and X-ray diffraction analysis.
Moreover, a computational study highlighted the influence of
the CHO position and of the coordination to the Mn(CO)3 tripod
on the strength of conjugation between the aldehyde and the
cyclohexadienyl ring. The method of functionalization, preserv-
ing the methylene exo fragment, allows the rearomatization of
η5 complexes by hydride abstraction and led to the first cationic
of the aminalic protons H7A (δ 4.32 ppm) and H7B (δ 5.23 ppm)
of the two diastereoisomers are clearly separated (Figure 11).
Between 4 and 6 ppm, the region corresponding to H4 and
1
aminalic protons, the H NMR spectra of diastereoisomers 16
are very similar to those of compounds 15 (see Figure 9, parts
b and c) with a strong separation of almost 1 ppm for the signals
corresponding to the aminalic protons of each diastereoisomeric
complex. Furthermore, signals at 4.32 and 5.23 ppm for the
aminalic protons of diastereoisomers 16 correlate with signals
at 4.19 and 5.17 ppm for the corresponding protons of
(R,R,2pR)-15 and (R,R,2pS)-15, respectively. The only difference
between these two complexes is the nature of the exo-substituent
at C6. Therefore, one could assume that the absolute configu-
ration of the planar chiral cyclohexadienyl moiety plays a major
role in the strong difference between the chemical shifts of the
aminalic protons of diastereoisomeric complexes. Thus, the
absolute configuration (R,R,2pR) could be assigned to one of
the diastereoisomer (g95% de, δ(H7A) ) 4.32 ppm) and the
configuration (R,R,2pS) to the other one (92% de, δ(H7B) )
5.23 ppm).
+
(η6-arylaldehyde)Mn(CO)3 complex. The reactivity of (η5-
(33) The planar chirality was assigned according to the extended Cahn-
Ingold-Prelog (CIP) rules described in ref 7a.
(34) For the preparation of the enantiopure diamine see:(a) Alexakis,
A.; Mutti, S.; Mangeney, P. J. Org. Chem. 1992, 57, 1224. (b) Alexakis,
A.; Chauvin, A.-S.; Stouvenel, R.; Vrancken, E.; Mutti, S.; Mangeney, P.
Tetrahedron: Asymmetry 2001, 12, 1171.
(35) The assignment of absolute configurations from the structures of
14 and 15 is validated by pertinent values of the Flack′s parameter (Table
6) : Flack, H. D.; Bernardinelli, G. Acta Crystallogr. 1999, A55, 908.
Once separated, the diastereoisomers (R,R,2pR)-16 and
(R,R,2pS)-16 were hydrolyzed under acidic conditions to give

(η5-Formylcyclohexadienyl)Mn(CO)3 Complexes
Organometallics, Vol. 27, No. 11, 2008 2515
Protéomique (IFR83, UPMC), for ES-MS by the Groupe de
Spectrométrie de Masse (UMR 7613, UPMC), and for the EI-MS
by the Service de Spectrométrie de Masse de l’ENS (Chemistry
Dpt, Paris). Optical rotations were measured on a Perkin-Elmer
343 polarimeter at 589 nm.
formylcyclohexadienyl)Mn(CO)3 complexes toward nucleophilic
addition was also investigated. Particularly interesting in this
matter is the reaction of planar chiral formyl derivatives with
an enantiopure diamine to give the corresponding aminals and
their subsequent resolution. This procedure led to the preparation
of novel enantiopure (η5-cyclohexadienyl)Mn(CO)3 complexes,
opening up new perspectives for the applications of η5-
manganese complexes in organometallic and organic asymmetric
syntheses.
Complexes 1,16 2,17b 3,14b and 416 were synthesized according
to procedures previously described in the literature.
Preparation of Complex (η5-3-Formyl-2-methoxy-6-phenyl-
cyclohexadienyl)Mn(CO)3 (5). A solution of complex 1 (0.404 g,
1.25 mmol, 1 equiv) and freshly distilled TMEDA (0.30 mL, 2.00
mmol, 1.6 equiv) in 12 mL of THF was cooled to -78 °C. A
solution of nBuLi (1.6 M in hexanes, 1.25 mL, 2.00 mmol, 1.6
equiv) was slowly added. The mixture was stirred for 1 h at -78
°C before the addition of DMF (0.195 mL, 2.50 mmol, 2 equiv). It
was stirred for another hour at -78 °C before being warmed to
room temperature and quenched by addition of H2O. After
extraction of the reaction mixture with Et2O, the combined organic
layers were washed with a saturated aqueous NaCl solution and
dried over MgSO4. After concentration in vacuo, the crude mixture
was purified by flash chromatography on silica gel to afford 5 as a
yellow oil (0.298 g, 0.85 mmol, 68%). 1H NMR (400 MHz, CDCl3):
Computational Details
Full geometry optimizations were systematically conducted
with no symmetry restraints by using the Gaussian 03 program36
within the framework of the Density Functional Theory (DFT),
using the hybrid B3LYP exchange-correlation functional37 and
the 6-31+G** basis set for all atoms. This level of theory has
been widely used in modeling arene-Cr(CO)3 complexes and
has proved to give good results from both geometrical38 and
energetical basis.39 Frequencies were evaluated within the
harmonic approximation and are reported, unless otherwise
mentioned, unscaled. NMR shielding constants are evaluated by
using the standard procedure implemented within the GAUSS-
IAN software. The nature of the transition states was ensured
by confirming the presence of a single imaginary frequency. The
connection between transition states and minima was ensured
by carrying out small displacements of all atoms in the two
directions along the imaginary frequency mode and carrying out
geometry optimization with these geometries as starting points.
3
4
δ 3.50 (s, 3H, OCH3), 3.59 (dd, J ) 6.2 Hz, J ) 1.5 Hz, 1H,
H1), 3.82 (m, 1H, H5), 4.08 (tapp, 3J ) 6.2 Hz, 1H, H6), 5.75 (d, 3J
3
3
) 7.6 Hz, 1H, H4), 6.93 (d, J ) 7.4 Hz, 2H, HPh), 7.19 (t, J )
3
7.4 Hz, 1H, HPh), 7.26 (tapp, J ) 7.4 Hz, 2H, HPh), 10.62 (s, 1H,
CHO). 13C NMR (100 MHz, CDCl3): δ 42.2 (C6), 45.7 (C1), 55.1
(OCH3), 65.2 (C5), 79.4 (C3), 92.0 (C4), 125.7 (CHPh), 127.5
(CHPh), 129.0 (CHPh), 145.5 (C2 or CPh), 146.8 (C2 or CPh), 189.8
(CHO), 217.3 (CO (Mn)). IR (neat): ν¯ (cm-1) 1673 (CHO), 1924
(Mn(CO)3), 2018 (Mn(CO)3). MS (ESI, positive mode): m/z 352.8
(M+). HRMS (EI, positive mode): m/z 352.0152 (M+, calcd for
C17H13MnO5: 352.0143).
Experimental Section
General Methods. All reactions were routinely performed under
a dry nitrogen atmosphere with standard Schlenk techniques. THF
and Et2O were dried over sodium benzophenone ketyl and distilled.
N,N,N′,N′-Tetramethylethylenediamine (TMEDA) was distilled over
KOH and stored under nitrogen over 4 Å molecular sieves. CH2Cl2
and DMF were distilled over CaH2. NMR spectra were recorded
on a Bruker ARX 200 MHz or Avance 400 MHz spectrometer. 1H
and 13C signals of NMR solvents were used as internal standards
respectively at δ 7.26 and 77.36 ppm in CDCl3 and at δ 2.09 and
30.60 ppm in acetone-d6. The Mn(CO)3 carbonyl signal is known
to be difficult to observe, specially when only low quantities of
complex are available. Infrared spectra were measured on a Bruker
Tensor 27 spectrometer. Elemental analyses were performed by the
Service Central d’Analyze du CNRS. Mass spectra were performed
for MALDI-TOF by the Plate-Forme Spectrométrie de Masse et
Preparation of Complex (η5-3-Formyl-2-methoxycyclohexa-
dienyl)Mn(CO)3 (6). A solution of complex 2 (0.295 g, 1.19
mmol, 1 equiv) and freshly distilled TMEDA (0.27 mL, 2.00
mmol, 1.6 equiv) in 10 mL of THF was cooled to -78 °C. A
solution of nBuLi (1.6 M in hexanes, 1.20 mL, 1.78 mmol, 1.6
equiv) was slowly added. The mixture was stirred for 1 h at
-78 °C before the addition of DMF (0.165 mL, 2.14 mmol, 2
equiv). It was stirred for another hour at -78 °C before being
warmed to room temperature and quenched by addition of H2O.
After extraction of the reaction mixture with Et2O, the combined
organic layers were washed with a saturated aqueous NaCl
solution and dried over MgSO4. After concentration in vacuo,
the crude mixture was purified by flash chromatography on silica
gel to afford 6 as a yellow powder (0.208 g, 0.75 mmol, 63%).
1H NMR (200 MHz, CDCl3): δ 2.40 (d, 2J ) 13.2 Hz, 1H,
3
H6exo), 2.85–3.06 (m, 2H, H1 and H6endo), 3.37 (tapp, J ) 6.8
Hz, 1H, H5), 3.44 (s, 3H, OCH3), 5.58 (d, 3J ) 7.7 Hz, 1H,
H4), 10.66 (s, 1H, CHO). 13C NMR (100 MHz, CDCl3): δ 26.5
(C6), 37.9 (C1), 55.0 (OCH3), 59.1 (C5), 80.1 (C3), 93.6 (C4),
(36) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; and Pople, J. A. Gaussian 03,
Revision C.02; Gaussian, Inc., Wallingford CT, 2004.
(37) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785. (b)
Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989, 157,
200. (c) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(38) Pfleschinger, A.; Dargel, T. K.; Bats, J. W.; Schmalz, H.-G.; Koch,
W. Chem. Eur. J. 1999, 5, 537 and references cited therein.
(39) Merlic, C. A.; Miller, M. M.; Hietbrink, B. N.; Houk, K. N. J. Am.
Chem. Soc. 2001, 123, 4904.
146.2 (C2), 190.3 (CHO), 217.3 (CO (Mn)). IR (neat): ν¯ (cm-1
)
1668 (CHO), 1914 (Mn(CO)3), 2014 (Mn(CO)3). HRMS (MALDI-
TOF, positive mode): m/z 274.9619 (M - H-, calcd for
C11H8MnO5: 274.9752). Anal. Calcd for C11H9MnO5: C, 47.85;
H, 3.29. Found: C, 47.69; H, 3.36.
Preparation of Complexes (η5-1-Chloro-2-formyl-4-methoxy-
6-phenylcyclohexadienyl)Mn(CO)3 (7a) and (η5-1-Chloro-3-
formyl-4-methoxy-6-phenylcyclohexadienyl)Mn(CO)3 (7b). At
-78 °C, a solution of nBuLi (1.6 M in hexanes, 0.44 mL, 0.70
mmol, 1.4 equiv) was slowly added to a solution of complex 3
(0.178 g, 0.50 mmol, 1 equiv) in 5 mL of THF. The mixture
was stirred for 15 min at -78 °C before the addition of DMF
(0.062 mL, 0.80 mmol, 1.8 equiv). It was then stirred for another
hour at -78 °C before being warmed to room temperature and
quenched by addition of H2O. After extraction of the reaction
mixture with Et2O, the combined organic layers were washed

2516 Organometallics, Vol. 27, No. 11, 2008
Jacques et al.
MHz, (CD3)2CO): δ 4.45 (s, 3H, OCH3), 6.48 (tapp,
3J ) 6.4
with a saturated aqueous NaCl solution, dried over MgSO4, and
concentrated in vacuo. Flash chromatography on silica gel then
enabled the separation of 7a (yellow oil, 0.115 g, 0.30 mmol,
60%) and 7b (yellow solid, 0.058 g, 0.15 mmol, 30%). 7a: H
NMR (400 MHz, CDCl3): δ 3.65 (s, 3H, OCH3), 3.66 (dd, J )
Hz, 1H, H5), 6.82 (d, 3J ) 7.4 Hz, 1H, H3), 7.53 (m, 2H, H4
and H6), 10.40 (s, 1H, CHO). 13C NMR (100 MHz, (CD3)2CO):
δ 60.6 (OCH3), 82.3 (C3), 90.6 (C5), 104.2 (C4 or C6), 109.5
(C4 or C6), 187.2 (CHO). IR (neat): ν¯ (cm-1) 1698 (CHO), 1999
(Mn(CO)3), 2027 (Mn(CO)3), 2071 (Mn(CO)3). HRMS (MALDI-
TOF, positive mode): m/z 274.9709 (M - BF4-, calcd for
C11H8MnO5 274.9752).
1
3
4
3
6.5 Hz, J ) 2.8 Hz, 1H, H5), 4.47 (d, J ) 6.5 Hz, 1H, H6),
4
6.07 (d, J ) 2.8 Hz, H3), 7.01–7.03 (m, 2H, HPh), 7.25–7.32
(m, 3H, HPh), 10.04 (s, 1H, CHO). 13C NMR (100 MHz, CDCl3):
δ 45.1 (C5), 53.7 (C6), 55.5 (OCH3), 61.1 (C3), 83.1 (C1), 93.1
(C2), 126.3 (CHPh), 128.3 (CHPh), 129.0 (CHPh), 141.9 (C4 or
CPh), 143.3 (C4 or CPh), 192.5 (CHO), 220.4 (CO (Mn)). IR
(neat): ν¯ (cm-1) 1704 (CHO), 1933 (Mn(CO)3), 2020 (Mn(CO)3).
MS (EI, positive mode): m/z 302 (M+ - 3CO). HRMS (EI,
positive mode): m/z 385.9751 (M+, calcd for C17H12ClMnO5:
385.9754). 7b: 1H NMR (200 MHz, CDCl3): δ 3.51 (s, 3H,
Preparation of Complex 12. At 0 °C, NaBH4 (0.026 g, 070
mmol, 1.1 equiv) was slowly added to a solution of complex 5
(0.224 g, 0.64 mmol, 1 equiv) in MeOH (10 mL). After being stirred
for 0.5 h, the reaction was quenched by addition of 1 mL of a
concentrated HCl solution then diluted with H2O. After extraction
of the reaction mixture with Et2O, the combined organic layers were
washed with H2O, then with a saturated aqueous NaCl solution,
dried over MgSO4, and concentrated in vacuo to give 12 (0.198 g,
0.55 mmol, 87%) as a yellow solid. 1H NMR (200 MHz, CDCl3):
δ 2.18 (t, 3J ) 6.4 Hz, 1H, OH), 3.32 (m, 2H, H1 and H5), 3.43 (s,
3H, OCH3), 3.92 (t, 3J ) 5.9 Hz, 1H, H6), 4.74 (dd, 2J ) 12.5 Hz,
OCH3), 3.72 (d, J ) 6.4 Hz, 1H, H5), 4.42 (dd, J ) 6.4 Hz,
3
3
4J ) 1.5 Hz, 1H, H6), 5.97 (d, J ) 1.5 Hz, 1H, H2), 6.97–7.01
4
(m, 2H, HPh), 7.26–7.34 (m, 3H, HPh), 10.54 (s, 1H, CHO). 13
C
NMR (100 MHz, CDCl3): δ 46.5 (C5), 52.1 (C6), 55.7 (OCH3),
76.0 (C3), 86.7 (C1), 90.7 (C2), 126.3 (CHPh), 128.5 (CHPh),
129.1 (CHPh), 143.4 (C4 or CPh), 144.0 (C4 or CPh), 189.0
(CHO), 216.6 (CO (Mn)). IR (neat): ν¯ (cm-1) 1676 (CHO), 1937
(Mn(CO)3), 2025 (Mn(CO)3). HRMS (EI, positive mode): m/z
385.9750 (M+, calcd for C17H12ClMnO5: 385.9754).
2
3J ) 6.3 Hz, 1H, CH2), 5.00 (dd, J ) 12.5 Hz,3J ) 5.3 Hz, 1H,
CH2), 5.16 (d, 3J ) 7.2 Hz, 1H, H4), 6.92–6.96 (m, 2H, HPh),
7.15–7.26 (m, 3H, HPh). 13C NMR (100 MHz, CDCl3): δ 42.3 (C1),
42.8 (C6), 54.8, (OCH3), 56.7 (C5), 61.0 (CH2), 88.5 (C3), 95.2
(C4), 125.7 (CHPh), 127.2 (CHPh), 128.8 (CHPh), 142.5 (C2 or CPh),
147.5 (C2 or CPh). IR (neat): ν¯ (cm-1) 1907 (Mn(CO)3), 2009
(Mn(CO)3). HRMS (ESI, positive mode): m/z 377.0187 (M + Na+,
calcd for C16H11MnNaO4 377.0192).
Preparation of Complexes (η5-2-Formyl-6-phenylcyclohexa-
dienyl)Mn(CO)3 (8a) and (η5-3-Formyl-6-phenylcyclohexadi-
enyl)Mn(CO)3 (8b). A solution of complex 4 (0.147 g, 0.50 mmol,
1 equiv) and freshly distilled TMEDA (0.15 mL, 1.00 mmol, 2
equiv) in 5 mL of THF was cooled to -78 °C. A solution of nBuLi
(1.6 M in hexanes, 0.625 mL, 1.00 mmol, 2 equiv) was slowly
added. The mixture was stirred for 2 h at -78 °C before the addition
DMF (0.100 mL, 1.25 mmol, 2.5 equiv). It was stirred for another
hour at -78 °C before being warmed to room temperature and
quenched by addition of H2O. After extraction of the reaction
mixture with Et2O, the combined organic layers were washed with
a saturated aqueous NaCl solution, dried over MgSO4, and
concentrated in vacuo. Flash chromatography on silica gel then
enabled the separation of 8a (yellow solid, 0.093 g, 0.28 mmol,
58%) and 8b (yellow solid, 0.013 g, 0.040 mmol, 8%). 8a: 1H NMR
Preparation of Complex 13a. 15b At –15 °C, PhMgCl (2 M in
THF, 0.47 mL, 1.94 mmol, 2 equiv) was slowly added to a solution
of complex 5 (0.165 g, 0.47 mmol, 1 equiv) in THF (10 mL). After
being stirred for 0.5 h, the reaction was quenched by addition of
15 mL of an aqueous HCl solution (2 M) and diluted with 30 mL
of H2O. After extraction of the reaction mixture with Et2O, the
combined organic layers were washed with H2O, then with a
saturated aqueous NaCl solution, and dried over MgSO4. After
concentration in vacuo, the crude mixture was purified by flash
chromatography on silica gel to afford 13a as a yellow powder
1
(183 mg, 0.43 mmol, 91%). H NMR (400 MHz, CDCl3): δ 2.41
3
(d, 3J ) 2.6 Hz, 1H, OH), 3.29–3.36 (m, 2H, H1 and H5), 3.39 (s,
3H, OCH3), 3,85 (tapp, 3J ) 5.8 Hz, 1H, H6), 5.36 (d, 3J ) 7.4 Hz,
1H, H4), 6.34 (d, 3J ) 2.6 Hz, 1H, CH(OH)Ph), 6.64 (d, 3J ) 7.1
Hz, 2H, HPh), 7.03–7.08 (m, 3H, HPh), 7.35–7.43 (m, 3H, HPh),
(400 MHz, CDCl3): δ 3.67 (m, 1H, H5), 3.94 (ddd, J ) 6.0 Hz,
4
3
4J ) 1.8 Hz, J ) 1.8 Hz, 1H, H1), 4.06 (tapp, J ) 6.0 Hz, 1H,
H6), 5.13 (dd, 3J ) 5.4 Hz, 3J ) 7.3 Hz, 1H, H4), 6.30 (ddd, 3J )
4
4
3
5.4 Hz, J ) 1.8 Hz, J ) 1.8 Hz, 1H, H3), 6.91 (d, J ) 7.3 Hz,
3
7.61 (d, J ) 7.3 Hz, 2H, HPh).
2H, HPh), 7.17 (t, J ) 7.3 Hz, 1H, HPh), 7.23 (tapp, J ) 7.3 Hz,
2H, HPh), 9.31 (s, 1H, CHO). 13C NMR (100 MHz, CDCl3): δ
39.5 (C6), 58.7 (C1), 60.1 (C5), 78.6 (C3), 96.4 (C4), 102.5 (C2),
125.8 (CHPh), 127.5 (CHPh), 128.9 (CHPh), 146.4 (CPh), 192.4
(CHO), 221.4 (CO (Mn)). IR (neat): ν¯ (cm-1) 1710 (CHO), 1919
(Mn(CO)3), 2013 (Mn(CO)3). HRMS (ESI, positive mode): m/z
344.9935 (M + Na+, calcd for C16H11MnNaO4: 344.9930). 8b: 1H
3
3
Preparation of Complex (R,R,6R,1pS)-14. Complex 7a (0.310
g, 0.80 mmol, 1 equiv) and (R,R)-N,N′-dimethylcyclohexane-1,2-
diamine (0.114 g, 0.80 mmol, 1 equiv) were stirred in distilled Et2O
(10 mL) in the presence of 4 Å molecular sieves for 18 h. After
filtration through Celite, the solution was concentrated in vacuo
and the mixture of the two diastereoisomers was isolated in
quantitative yield. Separation of the diastereoisomeric mixture by
chromatography on basic alumina (eluent: EP/Et2O 99/1) gave
(R,R,6R,1pS)-14 (0.075 g, 0.147 mmol) as a yellow powder in 18%
yield and with g95% de. 1H NMR (200 MHz, CDCl3): δ 1.27–1.42
(m, 4H, HCy), 1.87 (m, 3H, HCy), 2.18 (m, 1H, HCy), 2.33 (s, 3H,
NCH3), 2.47–2.54 (m, 2H, HCy), 2.73 (s, 3H, NCH3′), 3.44 (s, 3H,
OCH3), 3.71 (dd, 3J ) 6.6 Hz, 4J ) 3.0 Hz, 1H, H5), 4.25 (s, 1H,
H11), 4.37 (d, 3J ) 6.6 Hz, 1H, H6), 6.24 (d, 4J ) 3.0 Hz, 1H, H3),
7.10–7.20 (m, 5H, HPh). 13C NMR (100 MHz, CDCl3): δ 24.9
(CH2Cy), 25.4 (CH2Cy), 27.6 (CH2Cy), 31.0 (CH2Cy), 38.0 (NCH3),
42.7 (NCH3′), 47.3 (C5), 53.9 (C6 or OCH3), 54.9 (C6 or OCH3),
65.0 (CHCy), 68.0 (CHCy), 68.3 (C3), 74.0 (C1), 88.0 (C11), 112.0
(C2), 126.2 (CHPh), 127.2 (CHPh), 128.5 (CHPh), 140.2 (C4 or CPh),
144.6 (C4 or CPh), 222.2 (CO (Mn)). IR (neat): ν¯ (cm-1) 1916
(Mn(CO)3), 2013 (Mn(CO)3). HRMS (ESI, positive mode): m/z
511.1187 (M + H+, calcd for C25H29MnClN2O4 511.1191). [R]D
-112 (c 0.220, CHCl3).
NMR (200 MHz, CDCl3): δ 3.88 (t, J ) 7.4 Hz, 2H, H1,5), 4.01
3
(t, 3J ) 7.4 Hz, 1H, H6), 5.58 (d, 3J ) 5.4 Hz, 2H, H2,4), 6.89–6.95
(m, 2H, HPh), 7.18–7.30 (m, 3H, HPh), 9.92 (s, 1H, CHO). 13C
NMR (50 MHz, CDCl3): δ 40.6 (C6), 65.0 (C1,5), 88.4 (C3), 98.1
(C2,4), 125.9 (CHPh), 127.7 (CHPh), 129.0 (CHPh), 146.5 (CPh),
190.8 (CHO). IR (neat): ν¯ (cm-1) 1683 (CHO), 1928 (Mn(CO)3),
2020 (Mn(CO)3). HRMS (ESI, positive mode): m/z 344.9934
(M + Na+, calcd for C16H11MnNaO4: 344.9930).
Preparation of Complex [(η6-2-methoxybenzaldehyde)-
Mn(CO)3][BF4] (11) by Rearomatisation of 6. At -15 °C, a
solution of triphenylcarbenium tetrafluoroborate (0.165 g, 0.50
mmol, 1 equiv) in CH2Cl2 (10 mL) was added to a solution of
complex 6 (0.138 g, 0.50 mmol, 1 equiv) in CH2Cl2 (5 mL).
After being stirred at room temperature for 1.5 h, 50 mL of
freshly distilled Et2O was added to induce the precipitation of
11. The resulting yellow powder (0.126 g, 0.35 mmol, 70%)
1
was isolated by filtration and washed with Et2O. H NMR (200

(η5-Formylcyclohexadienyl)Mn(CO)3 Complexes
Organometallics, Vol. 27, No. 11, 2008 2517
Preparation of Complexes (R,R,6S,2pR)-15 and (R,R,6R,2pS)-
15. Complex 5 (0.291 g, 0.83 mmol, 1 equiv) and (R,R)-N,N′-
dimethylcyclohexane-1,2-diamine (0.141 g, 0.99 mmol, 1.2
equiv) were refluxed in distilled Et2O (6 mL) in the presence of
4 Å molecular sieves for 6.5 h. After filtration through Celite,
the solution was concentrated in vacuo and the mixture of the
two diastereoisomers was isolated in quantitative yield. Separa-
tion of the diastereoisomeric mixture by preparative TLC on
neutralized silica (eluent: EP/Et2O/Et3N 9/1/1) gave (R,R,6S,2pR)-
15 (0.129 g, 0.27 mmol, 33%) with g95% de and (R,R,6R,2pS)-
15 (0.126 g, 0.26 mmol, 32%) with 85% de. (R,R,6S,2pR)-15:
1H NMR (400 MHz, CDCl3): δ 1.21–1.30 (m, 3H, HCy),
1.48–1.54 (m, 1H, HCy), 1.81–1.87 (m, 2H, HCy), 1.97–2.00 (m,
2H, HCy), 2.08–2.13 (m, 1H, HCy), 2.42 (s, 3H, NCH3), 2.47 (s,
13C NMR (100 MHz, CDCl3): δ 24.6 (CH2Cy), 25.5 (CH2Cy), 27.0
(CH2Cy), 27.6 (C6), 29.5 (CH2Cy), 33.3 (C1), 37.9 (NCH3), 38.4
(NCH3′), 51.3 (C5), 54.3 (OCH3), 67.0 (CHCy), 69.2 (CHCy), 87.3
(C7), 91.0 (C3), 94.8 (C4), 143.6 (C2). IR (neat): ν¯ (cm-1) 1907
(Mn(CO)3), 2004 (Mn(CO)3). [R]D -166 (c 0.214, CHCl3). (R,R,2pS)-
16: 1H NMR (400 MHz, CDCl3): δ 1.19–1.35 (m, 4H, HCy),
2
1.82–1.87 (m, 2H, HCy), 1.97–2.04 (m, 2H, HCy), 2.13 (d, J )
12.6 Hz, 1H, H6exo), 2.33 (m, 1H, HCy), 2.41 (m, 1H, HCy), 2.52
(s, 3H, NCH3), 2.58 (s, 3H, NCH3′), 2.74 (m, 1H, H6endo), 2.80–2.84
(m, 2H, H1 and H5), 3.31 (s, 3H, OCH3), 5.23 (s, 1H, H7), 5.28 (d,
3J ) 7.3 Hz, 1H, H4). 13C NMR (100 MHz, CDCl3): δ 24.7
(CH2Cy), 24.8 (CH2Cy), 27.5 (C6), 28.9 (CH2Cy), 30.1 (CH2Cy), 33.9
(C1), 34.7 (NCH3), 41.1 (NCH3′), 49.1 (C5), 54.3 (OCH3), 66.4
(CHCy), 70.5 (CHCy), 81.5 (C7), 87.7 (C3), 94.1 (C4), 143.2 (C2).
IR (neat): ν¯ (cm-1) 1909 (Mn(CO)3), 2005 (Mn(CO)3). [R]D +141
(c 0.210, CHCl3).
3
4
3H, NCH3), 2.88–2.95 (m, 1H, HCy), 3.31 (dd, J ) 6.0 Hz, J
) 1.8 Hz, 1H, H1), 3.37 (s, 3H, OCH3), 3.39 (m, 1H, H5), 3.92
3
3
(tapp, J ) 6.0 Hz, 1H, H6), 4.19 (s, 1H, H11), 5.44 (d, J ) 7.3
Typical Procedure for the Hydrolysis of the Chiral Auxiliary.
A solution of the aminalic complex in Et2O (20 mL) and a 0.1 M
HCl solution (10 mL) was vigorously shaken. After decantation
and phase separation, the aqueous phase was extracted with Et2O
(10 mL). The combined organic phases were washed with water
(10 mL), a saturated NaHCO3 solution (10 mL), water (10 mL),
and finally a saturated NaCl solution (10 mL). They were dried
over MgSO4, filtered, and concentrated in vacuo. Flash chroma-
tography on silica gel then gave the pure enantioenriched formyl-
substituted complex.
(6S,2pR)-(η5-3-Formyl-2-methoxy-6-phenylcyclohexadienyl)Mn-
(CO)3 ((6S,2pR)-5). Following the above procedure, the hydrolysis
of (R,R,6S,2pR)-15 (0.129, 0.27 mmol, g95% de) gave (6S,2pR)-5
(0.089 g, 0.25 mmol, g95% ee) in 93% yield. [R]D +171 (c 0.210,
CHCl3).
Hz, 1H, H4), 6.98 (d, J ) 7.2 Hz, 2H, HPh), 7.14 (t, J ) 7.2
3
3
Hz, 1H, HPh), 7.22 (tapp, J ) 7.2 Hz, 2H, HPh). 13C NMR (100
3
MHz, CDCl3): δ 24.5 (CH2Cy), 25.5 (CH2Cy), 26.9 (CH2Cy), 29.1
(CH2Cy), 37.4 (NCH3), 37.5 (NCH3), 40.4 (C1), 43.2 (C6), 54.5
(OCH3), 58.0 (C5), 66.9 (CHCy), 69.1 (CHCy), 86.7 (C11), 90.7
(C3), 93.9 (C4), 126.0 (CHPh), 126.9 (CHPh), 128.7 (CHPh), 142.9
(C2 or CPh), 147.7 (C2 or CPh). IR (neat): ν¯ (cm-1) 1912
(Mn(CO)3), 2007 (Mn(CO)3). HRMS (ESI, positive mode): m/z
477.1576 (M + H+, calcd for C25H30MnN2O4 477.1581). [R]D
-99 (c 0.218, CHCl3). (R,R,6R,2pS)-15: 1H NMR (400 MHz,
CDCl3): δ 1.15–1.33 (m, 4H, HCy), 1.79–1.82 (m, 2H, HCy),
1.86–1.90 (m, 1H, HCy), 1.98–2.01 (m, 1H, HCy), 2.10 (s, 3H,
NCH3), 2.16–2.29 (m, 2H, HCy), 2.56 (s, 3H, NCH3′), 3.39 (m,
2H, H1 and H5), 3.44 (s, 3H, OCH3), 3.98 (tapp
,
3J ) 6.1 Hz,
3
1H, H6), 5.17 (s, 1H, H11), 5.37 (d, J ) 7.6 Hz, 1H, H4), 6.94
(6R,2pS)-(η5-3-Formyl-2-methoxy-6-phenylcyclohexadienyl)Mn-
(CO)3 ((6R,2pS)-5). Following the same procedure, the hydrolysis
of (R,R,6R,2pS)-15 (0.126 g, 0.26 mmol, 85% de) gave
(6R,2pS)-5 (0.092 g, 0.26 mmol, 85% ee) in 99% yield. [R]D
-145 (c 0.230, CHCl3).
3
3
(d, J ) 7.3 Hz, 2H, HPh), 7.11 (t, J ) 7.3 Hz, 1H, HPh), 7.21
(tapp
,
3J ) 7.3 Hz, 2H, HPh). 13C NMR (100 MHz, CDCl3): δ
24.6 (CH2Cy), 24.6 (CH2Cy), 28.9 (CH2Cy), 29.9 (CH2Cy), 34.1
(NCH3), 40.0 (C1), 41.2 (NCH3′), 41.6 (C6), 54.6 (C5 or OCH3),
55.0 (C5 or OCH3), 66.4 (CHCy), 71.2 (CHCy), 80.7 (C11), 87.9
(C3), 93.3 (C4), 125.2 (CHPh), 126.6 (CHPh), 128.5 (CHPh), 143.4
(C2 or CPh), 147.8 (C2 or CPh). IR (neat): ν¯ (cm-1) 1911
(Mn(CO)3), 2006 (Mn(CO)3). HRMS (MALDI-TOF, positive
mode): m/z 477.1489 (M + H+, calcd for C25H30MnN2O4
477.1586). [R]D +60 (c 0.217, CHCl3).
(2pR)-(η5-3-Formyl-2-methoxycyclohexadienyl)Mn(CO)3
((2pR)-6). Following the same procedure, the hydrolysis of (R,R,2pR)-
16 (0.041 g, 0.103mmol, g95% de) gave (2pR)-6 (0.028 g, 0.101
mmol, g95% ee) in 98% yield. [R]D +132 (c 0.216, CHCl3).
(2pS)-(η5-3-Formyl-2-methoxycyclohexadienyl)Mn(CO)((2pS)-
3
Preparation of Complexes (R,R,2pR)-16 and (R,R,2pS)-16.
Complex 6 (0.110 g, 0.40 mmol, 1 equiv) and (R,R)-N,N′-
dimethylcyclohexane-1,2-diamine (0.068 g, 0.48 mmol, 1.2 equiv)
were stirred in distilled Et2O (3 mL) at 30 °C in the presence of 4
Å molecular sieves for 7 h. After filtration through Celite, the
solution was concentrated in vacuo and the mixture of the two
diastereoisomers was isolated in quantitative yield. Separation of
the diastereoisomeric mixture by preparative TLC on neutralized
silica (eluent: EP/Et2O/Et3N 7/3/1) gave (R,R,2pR)-16 (0.053 g,
0.133 mmol, 33%) with g95% de and (R,R,2pS)-16 (0.040 g, 0.100
mmol, 25%) with 92% de. (R,R,2pR)-16: 1H NMR (400 MHz,
CDCl3): δ 1.22–1.35 (m, 3H, HCy), 1.53 (m, 1H, HCy), 1.81–1.88
(m, 2H, HCy), 1.97–2.06 (m, 2H, HCy), 2.18 (m, 1H, HCy), 2.19
6). Following the same procedure, the hydrolysis of (R,R,2pS)-16
(0.035 g, 0.087 mmol, 92% de) gave (2pS)-6 (0.024 g, 0.087 mmol,
92% ee). [R]D -124 (c 0.206, CHCl3).
Acknowledgment. The calculations have been per-
formed at the CCRE of the University Pierre et Marie
Curie (F. 75252, Paris, France) and at the CRIHAN (F.
76800 Saint-Etienne-du-Rouvray, France) regional super-
computing centre.
Supporting Information Available: 13C NMR spectra of
compounds 5–8, 11, 12, and 14–16 and CIF files giving crystal-
lographic data for complexes 7b, 13a, (R,R,6R,1pS)-14, and
(R,R,6S,2pR)-15. This material is available free of charge via the
Internet at http://pubs.acs.org.
2
(d, J ) 12.6 Hz, 1H, H6exo), 2.48 (s, 3H, NCH3), 2.58 (s, 3H,
NCH3′), 2.72 (m, 1H, H6endo), 2.79 (dd, 3J ) 6.0 Hz, 4J ) 1.2 Hz,
1H, H1), 2.87 (tapp, 3J ) 6.7 Hz, 1H, H5), 2.93 (m, 1H, HCy), 3.31
3
(s, 3H, OCH3), 4.32 (s, 1H, H7), 5.38 (d, J ) 7.3 Hz, 1H, H4).
OM7012666