Deprotonation of organic compounds bearing acid protons promoted by metal amido complexes with chiral diamine ligands leading to new organometallic compounds

Article abstract of DOI:10.1021/om010874+

Well-defined 16-electron metal amido complexes bearing chiral Ts-diamine ligands readily react with nitromethane, acetone, or phenylacetylene to give new organometallic compounds in almost quantitative yields. For example, an Ir amido complex, Cp*Ir[(R,R)Tscydn], reacts with nitromethane at room temperature to give quantitatively a nitromethyl Ir complex, Cp*Ir(CH₂NO₂)[(R,R)-Tscydn], as a single diastereomer. The isolable organometallic compounds with chiral amine ligands are relevant to active catalysts for asymmetric C-C bond formation.

Full text of DOI:10.1021/om010874+

Organometallics 2002, 21, 253-255
253
Dep r oton a tion of Or ga n ic Com p ou n d s Bea r in g Acid
P r oton s P r om oted by Meta l Am id o Com p lexes w ith
Ch ir a l Dia m in e Liga n d s Lea d in g to New Or ga n om eta llic
Com p ou n d s
Kunihiko Murata, Hirokazu Konishi, Masato Ito, and Takao Ikariya*
Department of Applied Chemistry, Graduate School of Science and Engineering,
Tokyo Institute of Technology, and CREST, J apan Science and Technology Cooperation (J ST),
O-okayama, Meguro-ku, Tokyo 152-8552, J apan
Received October 5, 2001
Summary: Well-defined 16-electron metal amido com-
plexes bearing chiral Ts-diamine ligands readily react
with nitromethane, acetone, or phenylacetylene to give
new organometallic compounds in almost quantitative
yields. For example, an Ir amido complex, Cp*Ir[(R,R)-
Tscydn], reacts with nitromethane at room temperature
to give quantitatively a nitromethyl Ir complex, Cp*Ir-
(
CH2NO2)[(R,R)-Tscydn], as a single diastereomer. The
F igu r e 1. Possible transition state for hydrogen transfer
between alcohols and ketones.
isolable organometallic compounds with chiral amine
ligands are relevant to active catalysts for asymmetric
C-C bond formation.
hydrogen donors such as alcohols and formic acid to
produce metal amine hydrido complexes. This hydrido
complex reacts readily with carbonyl compounds, pos-
sibly through a pericyclic six-membered transition state
Chiral transition-metal complexes with a metal/NH
bifunctional synergetic effect have been recently devel-
oped as practical asymmetric transfer hydrogenation
catalysts for the synthesis of optically active alcohols,
in which both chiral metal amido and chiral metal
amine hydrido complexes are involved as catalysts and
intermediates. In particular, the coordinatively un-
saturated 16-electron metal amido complexes Ru(Ts-
diamine)(η -arene) and Cp*M(Ts-diamine)
1
d,2
as shown in Figure 1
to regenerate the amido
complex and release the reduction product. If the amido
complex could react with certain organic compounds
which have suitable acidic protons to give an amino
complex bearing a metal-bonded C-nucleophile and
could then be followed by further reactions with car-
bonyl compounds, catalytic enantioselective C-C bond
formation could be achieved. To accomplish this asym-
metric catalysis process, we first examined the reaction
of these chiral metal amido complexes with a series of
acidic organic compounds and found that a C-H bond
of these compounds readily adds across the M-N bond
of the amido complex, leading to new organometallic
1
,2
6
1
1e,3
(Cp* )
pentamethylcyclopentadienyl, Ts-diamine ) N-(p-tolu-
enesulfonyl)-1,2-diamine, M ) Rh, Ir) have suitable
Brønsted basicity on the amido group to react with
(1) (a) Hashiguchi, S.; Fujii, A.; Takehara, J .; Ikariya, T.; Noyori,
R. J . Am. Chem. Soc. 1995, 117, 7562-7563. (b) Haack, K.-J .;
Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R. Angew. Chem., Int.
Ed. Engl. 1997, 36, 285-288. (c) Matsumura, K.; Hashiguchi, S.;
Ikariya, T.; Noyori, R. J . Am. Chem. Soc. 1997, 119, 8738-8739. (d)
Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97-102. (e)
Murata, K.; Ikariya, T.; Noyori, R. J . Org. Chem. 1999, 64, 2186-2187.
4
compounds.
A 16-electron metal amido complex, Cp*Ir(Ts-di-
6
amine) or Ru(Ts-diamine)(η -arene), has now been
(
f) Murata, K.; Okano, K.; Miyagi, M.; Iwane, H.; Noyori, R.; Ikariya,
T. Org. Lett. 1999, 1, 1119-1121. (g) Okano, K.; Murata, K.; Ikariya,
T. Tetrahedron Lett. 2000, 41, 9277-9280. (h) Koike, T.; Murata, K.,
Ikariya, T. Org. Lett. 2000, 2, 3833-3836.
proven to react smoothly with nitromethane (pKa )
1
0.2) at room temperature to give a nitromethyl complex
(2) (a) Alonso, D. A.; Brandt, P.; Nordin, S. J . M.; Andersson, P. G.
(Scheme 1). Since there is a structural similarity
between these amido complexes, they exhibit similar
reactivity toward nitromethane, but the outcome of the
reaction is delicately affected by the electronic prop-
erties of the ligands and the central metal. For ex-
ample, the reaction of Cp*Ir[(R,R)-Tscydn] (1a ; (R,R)-
J . Am. Chem. Soc. 1999, 121, 9580-9588. (b) Yamakawa, M.; Ito, H.;
Noyori, R. J . Am. Chem. Soc. 2000, 122, 1466-1478. (c) Casey, C. P.;
Singer, S. W.; Powell, D. R.; Hayashi, R. K.; Kavana, M. J . Am. Chem.
Soc. 2001, 123, 1090-1100.
(3) Previously, we reported that the Ir amido complex was obtained
from the reaction of Cp*IrH[(R,R)-Tscydn] with acetone as a yellow
crystal.1e However, the structure of this isolable yellow complex was
later confirmed by X-ray crystal structural analysis to be Cp*Ir(CH
COCH )[(R,R)-Tscydn] (1c). A careful stoichiometric reaction of the Ir
hydrido species and acetone in CH Cl gave a purple complex. The
structure of the complex was determined to be Cp*Ir[(R,R)-Tscydn]
1a ) on the basis of NMR analysis and elemental analysis. The complex
a can be conveniently obtained by the reaction of Cp*IrCl[(R,R)-
2
-
TsCYDN
hexanediamine)
) (1R,2R)-N-(p-toluenesulfonyl)-1,2-cyclo-
3
1f,3
with 1 equiv of nitromethane in
2
2
CH2Cl2 gave quantitatively a pale yellow complex,
Cp*Ir(CH2NO2)[(R,R)-Tscydn] (1b ) as a single dia-
(
1
1
e
Tscydn] with 1 equiv of NaOH in CH
2
Cl
) δ 0.8-2.2 (cyclohexane ring protons, 9H), 1.77 (s,
), 2.38 (s, 3H, CH of Ts), 2.71 (m, 1H, CH-NTs), 5.64 (br
s, 1H, NH), 7.22, 7.73 (4H, aromatic ring protons). Anal. Calcd for
SIr‚H O: C, 45.15; H, 5.77; N, 4.58. Found: C, 45.06; H,
.49; N, 4.60.
2 2
-H O quantitatively. 1a :
1
H NMR (CD
5H, C (CH)
2
Cl
2
(4) During the preparation of this paper, an effective stepwise C-H
bond activation with a coordinatively saturated Ru amido complex with
diphosphane ligands, followed by subsequent Ru-C bond formation,
was reported by Bergman’s group: Fulton, J . R.; Bouwkamp, M. W.;
Bergman, R. G. J . Am. Chem. Soc. 2000, 122, 8799-8800.
1
5
3
3
C
5
23
H
33
N
2
O
2
2
1
0.1021/om010874+ CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/14/2002

2
54 Organometallics, Vol. 21, No. 2, 2002
Communications
Sch em e 1
5
F igu r e 2. ORTEP view of (η -pentamethylcyclopentadi-
enyl)(nitromethyl)[(1R,2R)-N-(p-toluenesulfonyl)-1,2-cyclo-
hexanediamine)iridium (1b) (all hydrogen atoms except for
2 2
NH , CH of the cyclohexyl group, and CH of the nitro-
methyl group have been omitted for clarity). Selected bond
lengths (Å): Ir(1)-C(24), 2.16(2); Ir(1)-N(1), 2.12(1); Ir(1)-
N(2), 2.18(1); C(24)-N(3), 1.43. Selected bond angles
Sch em e 2
(
deg): C(24)-Ir(1)-N(1), 89.2(6); C(24)-Ir(1)-N(2), 87.1(6);
N(1)-Ir(1)-N(2), 78.6(5); Ir(1)-C(24)-N(3), 113(1). Prior-
ity for the assignment of absolute configuration at Ir: Cp*
>
NTs > NH
2
2
> CH .
with 4a under otherwise identical conditions to give the
corresponding nitroethyl complex as a single dia-
stereomer in the NMR spectrum, in which 4a could
discriminate the enantiotopic hydrogen atoms of nitro-
ethane.
The single-crystal X-ray crystallographic analysis of
the nitromethyl complex (R,R)-1b, as illustrated in
Figure 2, confirmed that it has a three-legged piano-
stool coordination environment with Cp*, amino, sul-
stereomer after 0.5 h.5,6 The analogous nitromethyl Ru
complex 2b was obtained in 90% yield from the reaction
of nitromethane and the Ru complex 2a , which was in
situ generated from the reaction of RuCl[(R,R)-Tscydn]-
7
fonamino, and nitromethyl ligands. The chirality of the
(R,R)-diamine ligand determines the S configuration
around the central metal, as observed in the metal
(p-cycmene) with NaOH. In contrast, the reaction of Ir
1
f
hydrido and chlorido complexes. It should be noted that
or Ru amido complex with a less electron donating
TsDPEN ligand (TsDPEN ) N-(p-toluenesulfonyl)-1,2-
diphenylethylenediamine), 3a or 4a , with nitromethane
under otherwise identical conditions gave an equilibri-
um mixture of the amido complex 3a or 4a , nitro-
methane, and the nitromethyl complex 3b or 4b in the
1
b has a nitromethyl group with an Ir-C bond length
of 2.16 Å, and there is a short O‚‚‚NH distance of 2.06
Å, which is ascribed to an intramolecular hydrogen
bond. The H NMR spectrum of 1b at room temperature
1
displays one AB quartet due to the diastereotopic
methylene protons at δ 5.58 and 5.66 ppm. Two in-
equivalent acidic NH protons of the amino group were
observed at δ 3.57 and 4.62 ppm. The signal at the lower
field can be assigned to the proton that interacts with
the oxygen atom of the nitro group through hydrogen
1
H NMR spectra. An equilibrium constant of Keq ) 2.4
2
×
10 for the reaction of 4a and nitromethane in CD2Cl2
at 22 °C could be estimated from a linear van’t Hoff plot
obtained at several different temperatures (Scheme 2).
The use of 10 equiv of nitromethane with 4a caused an
equilibrium shift to the right, leading to the nitromethyl
Ru complex in almost quantitative yield in the solution.
These results indicate that the TsCYDN complex ex-
hibits stronger basicity than the TsDPEN complex and
that the deprotonation with the amido complexes pro-
ceeds reversibly as shown in Scheme 2. In fact, the
treatment of isolable complexes 1b with CD3NO2 re-
sulted in deuterium incorporation in the nitromethyl
group of 1b without loss of the chirality of the metal
center. Noticeably, nitroethane reacted stereoselectively
1
b
bonding.
In the addition of the C-H bond to the M-N bond of
8
the amido complex to form a nitromethyl complex, two
pathways are possible, as illustrated in Scheme 3: a
concerted σ-bond metathesis and a proton transfer4
9
(
7) An X-ray crystallographic analysis of 1b was performed. The
NO
N O SIr‚CH NO , M ) 715.89, orthorhombic, space group
structures were resolved with SHELX86 and DIRDIF94. 1b‚CH
3
2
:
C
P2
)
2
4
H
36
3
4
3
2
r
1
2
1
2
1
(No. 19), a ) 13.198(10) Å, b ) 22.501(10) Å, c ) 9.39 (1) Å, V
3
3
-1
2787(3) Å , Z ) 4, D
K, R (R
All hydrogen atoms were calculated from ideal geometries, fixed, and
included in the calculation of the structural factor.
c
) 1.706 g/cm , µ(Mo KR) ) 49.2 cm , T ) 253
w
) ) 0.050 (0.059) for 2938 observed reflections (I > 2.00σ(I)).
(5) More conveniently, the reaction of the Ir chloride complex
Cp*IrCl[(R,R)-Tscydn] with nitromethane in CH
of NaOH gave 1b, quantitatively.
2
Cl
2
containing 1 equiv
(8) Reactions of metal amido complexes with alkanes and alkynes:
(a) Bashall, A.; Collier, P. E.; Gade, L. H.; McPartlin, M.; Mountford,
P.; Tr o¨ sch, D. J . M. J . Chem. Soc., Chem. Commun. 1998, 2555-2556.
(b) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J . Am. Chem.
Soc. 1988, 110, 8731-8733.
(6) The analogous nitromethyl Cp*Rh complex was obtainable from
2 2
the reaction of Cp*RhCl[(R,R)-Tscydn] with nitromethane in CH Cl
containing 1 equiv of NaOH.

Communications
Organometallics, Vol. 21, No. 2, 2002 255
Sch em e 3
acidic organic compounds to give new organometallic
compounds of these acidic compounds. The Brønsted
basicity on the amido group in the amido complexes is
responsible for an effective C-H bond activation. Thanks
to the bifunctionality of the amido complex, the asym-
metric catalytic nitroaldol reaction with these amido
1
3,14
complexes was examined.
Preliminary experimental
results showed that although 1a , 2a , or 3a exhibited
low catalytic activity for the reaction, (S,S)-4a (2 mol
%
) effected the nitroaldol reaction of cyclohexane-
carboxaldehyde with 2 equiv of nitromethane in 2-methyl-
2
2
-butanol (0.2 M) at 30 °C for 24 h to give (S)-1-nitro-
-cyclohexyl-2-ethanol with good enantioselectivity, 75%
ee, albeit in low yield (18% yield). Further studies on
the mechanism and the scope of this new type of
enantioselective catalytic C-C bond formation are now
1
5
under way.
Ack n ow led gm en t. We thank Professor Masakatsu
Shibasaki of Tokyo University for discussions and
information about nitroaldol products. This work was
financially supported by a grant-in-aid from the Min-
istry of Education, Science, Sports and Culture of J apan
(No. 12305057).
through an ion pair intermediate, leading to the complex
bD and a mixture of isotopomers, 1bH and 1bD,
1
respectively. Monitoring the reaction of 1a with 1 equiv
of CD3NO2 revealed that the addition of the C-H bond
to the Ir-N bond of the amido complex possibly proceeds
via proton transfer from the carbon to the nitrogen
1
Su ppor tin g In for m ation Available: Tables giving single-
crystal X-ray information on the complexes 1b, 1c, and 1d and
text giving physical and NMR data of the complexes 1b, 1c,
which is bonded to the Ir metal. The H NMR spectrum
of the reaction mixture of 1a at -80 °C in CD2Cl2 shows
two signals due to NH2 protons at 3.57 and 4.62 ppm
1
d , 2b, 3b, and 4b. This material is available free of charge
(
vide infra) with a 1:3 ratio of the relative intensity,
via the Internet at http://pubs.acs.org.
indicating that the complex 1bH bearing a hydrogen-
bonded NH proton is initially formed in an anti fashion,
possibly through a proton transfer followed by Ir-C
bond formation. An increase in the temperature of this
reaction mixture to -50 °C resulted in formation of a
OM010874+
(11) The precise structures of 1c and 1d were determined by the
single-crystal X-ray analysis, indicating that they have structures
similar to that of the nitromethyl Ir complex with an S configuration
around the central metal. 1c: C26
39 2 3 6 5 3
H N O SIr‚C H CH . monoclinic,
1
:1 mixture of isotopomers, 1bH and 1bD, without loss
space group C2 (No. 5), a ) 24.426(8) Å, b ) 13.461(9) Å, c ) 9.418(6)
3
3
of the chirality of the metal center. Rapid H/D exchange
in the NH2 group with a trace amount of water impurity
in the solvent might be taking place even at low
temperatures.1b It should be noted that no detectable
formation of the O-bound isomer of 1b was observed in
these NMR studies, even with heating.10
Å, â ) 102.71(5)°, V ) 3020(2) Å , Z ) 4, D
c
) 1.636 g/cm , µ(Mo KR)
1
)
45.3 cm- , T ) 253 K, R (R
w
) ) 0.052 (0.056) for 2141 observed
reflections (I > 2.00σ(I)). All hydrogen atoms were calculated from ideal
geometries, fixed, and included in the calculation of the structural
factor. 1d : C31H39N O SIr‚C H CH , monoclinic space group P2 (No.
2
2
6
5
3
1
4
), a ) 10.705(3) Å, b ) 13.313(5) Å, c ) 13.190(3) Å, â ) 107.98(2)°,
3
3
-
1
V ) 1787.9(2) Å , Z ) 2, D
253 K, R (R ) ) 0.041 (0.035) for 2389 observed reflections (I >
.00σ(I)). All hydrogen atoms were calculated from ideal geometries,
fixed, and included in the calculation of the structural factor. 1c and
d : 1c and 1d were also obtained quantitatively by the reaction of
Cp*IrCl[(R,R)-Tscydn] with acetone or phenylacetylene in the presence
of 1.0 equiv of NaOH(aq) in CH Cl
12) (a) Matsumoto, K.; Uemura, H.; Kawano, M. Inorg. Chem. 1995,
c
) 1.464 g/cm , µ(Mo KR) 38.36 cm , T )
w
3
In a manner similar to the reaction of nitromethane,
1
a reacted with acetone (pKa ) 20) and phenylacetylene
pKa ) 18.5) to give quantitatively the corresponding
organometallic compounds 1c and 1d , respectively
1
(
2
2
.
(
1,12
(
Scheme 1).1
Complex 3a did not deprotonate acetone
34, 658-662. (b) Venturelli, A.; Rauchfuss, T. B.; Verma, A. K. Inorg.
Chem. 1997, 36, 1360-1365. (c) Lin, Y.-S.; Misawa, H.; Yamada, J .;
Matsumoto, K. J . Am. Chem. Soc. 2001, 123, 569-575.
at all under the same conditions, while the reaction of
4
4
a with acetone gave an equilibrium mixture of 4a and
c in an almost 1:1 molar ratio. Isotope labeling
(
13) For catalytic asymmetric C-C bond formation after C-H bond
activation: (a) Rodewald, S.; J ordan, R. F. J . Am. Chem. Soc. 1994,
16, 4491-4492. (b) Sawamura, M.; Hashimoto, H.; Ito, Y. J . Am.
1
experiments on the reaction of acetophenone (pKa ) 19)
with 4a revealed that an addition of the C-H bond
across the M-N bond occurred reversibly, although no
detectable amount of benzoylmethyl Ru complex was
observed in the solution.
Chem. Soc. 1992, 114, 8295-8296. (c) Kuwano, R.; Miyazawa, H.; Ito,
Y. J . Chem. Soc., Chem. Commun. 1998, 71-72. (d) Davies, H. W.;
Hansen, T.; Churchill, M. R. J . Am. Chem. Soc. 2000, 122, 3063-3070.
For reviews of C-C bond activation and transformation, see: (e) Murai,
S. Activation of Unreactive Bonds and Organic Synthesis; Springer-
Verlag: Berlin, Heidelberg, New York, 1999. (f) Dyker, G. Angew.
Chem., Int. Ed. 1999, 39, 1698-1712. (g) Shilov, A. E.; Shul’pin, G. B.
Chem. Rev. 1997, 97, 2879-2932.
In summary, the 16-electron metal amido complex
bearing the chiral Ts-diamine ligand readily reacts with
(14) Leading review paper for catalytic asymmetric nitro aldol
reaction: Shibasaki, M.; Sasai, H.; Arai, T. Angew. Chem., Int. Ed.
Engl. 1997, 36, 1236-1256 and references therein.
(
9) (a) Lee, J . C., J r.; Peris, E.; Rheingold, A. L.; Crabtree, R. H. J .
Am. Chem. Soc. 1994, 116, 11014-11019. (b) Niu, S.; Hall, M. B. J .
Am. Chem. Soc. 1998, 120, 6169-6170. (c) Musashi, Y.; Sakaki, S. J .
Am. Chem. Soc. 2000, 122, 3867-3877.
2 6 5 3 4
(15) RuH [P(C H ) ] -promoted C-C bond formation was reported
to proceed via oxidative addition followed by metal enolate formation:
Murahashi, S.-I.; Naota, T.; Taki, H.; Mizuno, M.; Takaya, H.; Komiya,
S.; Mizuno, Y.; Oyasato, N.; Hiraoka, M.; Hirano, A.; Fukuoka, A. J .
Am. Chem. Soc. 1995, 117, 12436-12451.
(10) Naota, T.; Tannna, A.; Murahashi, S.-I. J . Am. Chem. Soc. 2000,
1
22, 2960-2961.