Applications of ruthenium hydride borohydride complexes containing phosphinite and diamine ligands to asymmetric catalytic reactions

Article abstract of DOI:10.1021/ol050336j

(Chemical Equation Presented) A series of novel trans-ruthenium hydride borohydride complexes with chiral phosphinite and diamine ligands were synthesized. They can be used in the asymmetric transfer hydrogenation of aryl ketones, including base-sensitive

Full text of DOI:10.1021/ol050336j

ORGANIC
LETTERS
2
005
Vol. 7, No. 9
757-1759
Applications of Ruthenium Hydride
Borohydride Complexes Containing
Phosphinite and Diamine Ligands to
Asymmetric Catalytic Reactions
1
Rongwei Guo, Xuanhua Chen, Christian Elpelt, Datong Song, and
Robert H. Morris*
Department of Chemistry, UniVersity of Toronto, 80 St. George Street,
Toronto, Ontario M5S 3H6, Canada
rmorris@chem.utoronto.ca
Received February 17, 2005
ABSTRACT
A series of novel trans-ruthenium hydride borohydride complexes with chiral phosphinite and diamine ligands were synthesized. They can be
used in the asymmetric transfer hydrogenation of aryl ketones, including base-sensitive ones, to give chiral alcohols in moderate to good
enantioselectivities (up to 94% ee). They are also efficient catalysts for the Michael addition of malonates to enones with enantioselectivities
of up to 90%. This kind of catalyst allows a one-pot tandem Michael addition/H
centers.
2
hydrogenation protocol to build structures with multiple chiral
a-2c
Combinatorial catalyst discovery is recognized as a powerful
method for the development of homogeneous enantioselec-
tive reactions. This usually involves creating a library of
high enantioselectivity.2
For example, they recently
reported that among hydride borohydride complexes of the
type RuH(BH )(diphosphine)(diamine) the combination of
1
4
catalysts by using ligands of modular design and combining
them with transition-metal precursors. This approach is
(
2) (a) Ohkuma, T.; Ooka, H.; Ikariya, T.; and Noyori, R. J. Am. Chem.
Soc. 1995, 117, 10417-10418. (b) Ohkuma, T.; Koizumi, M.; Doucet, H.;
Pham, T.; Kozawa, M.; Murata, K.; Katayama, E.; Yokozawa, T.; Ikariya,
T.; Noyori, R. J. Am. Chem. Soc. 1998, 120, 13529-13530. (c) Doucet,
H.; Ohkuma, T.; Murata, K.; Yokozawa, T.; Kozawa, M.; Katayama, E.;
F. England, A. F.; Ikariya, T.; Noyori, R. Angew. Chem., Int. Ed. 1998, 37,
readily applicable to the catalytic asymmetric hydrogenation
of prochiral ketones and olefins.2
-12
Noyori’s group used
ruthenium catalysts composed of chelating diamine and
binap-type ligand modules to discover H -hydrogenation
reactions that convert prochiral aryl ketones to alcohols with
1
3
703-1706. (d) Crepy, K. V. L.; Imamoto, T. AdV. Synth. Catal. 2003,
2
45, 79-101.
(3) (a) Pai, C. C.; Lin, C. W.; Lin, C. C.; Chen, C. C.; Chan, A. S. C. J.
Am. Chem. Soc. 2000, 122, 11513-11514. (b) Wu, J.; Chen, H.; Kwok,
W.; Guo, R.; Zhou, Z.; Yeung, C.; Chan, A. S. C. J. Org. Chem. 2002, 67,
7908-7910. (c). Wu, J.; Ji, J. X.; Guo, R.; Yeung, C. H.; Chan, A. S. C.
Chem. Eur. J. 2003, 9, 2963-2968. (d) Xie, J. H.; Wang, L. X.; Fu, Y.;
Zhu, S. F.; Fan, B. M.; Duan, H. F.; Zhou, Q. L. J. Am. Chem. Soc. 2003,
125, 4404-4405.
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Dahlenburg, L. Eur. J. Inorg. Chem. 2003, 30, 2733-2747. (d) Delacroix,
O.; Gladysz, J. A. Chem. Commun. 2003, 38, 665-675. (e) Carmona, D.;
Pilar Lamata, M.; Oro, L. A. Coord. Chem. ReV. 2000, 717-772. (f)
McMorn, P.; Hutchings, G. J. Chem. Soc. ReV. 2004, 33, 108-122. (g)
Chelucci, G.; Thummel, R. P. Chem. ReV. 2002, 102, 3129-3170. (h)
Nicolaou, K. C., Hanko, R., Hartwig, W., Eds. Handbook of Combinatorial
Chemistry; Wiley-VCH: Weinheim, 2002. (i) Hagemeyer, A., Strasser, P.,
Volpe, A. F., Jr., Eds. High Throughput Screening in Chemical Catalysis;
Wiley-VCH: Weinheim, 2004. (j) de Vries, J. G.; de Vries, A. H. M. Eur.
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1
0.1021/ol050336j CCC: $30.25
© 2005 American Chemical Society
Published on Web 04/07/2005

(
R)-xylbinap ((R)-2,2′-bis[di(3,5-xylyl)phosphino]-1,1′-bi-
naphthyl) and (R,R)-dpen ((1R,2R)-1,2-diphenylethylenedi-
amine) ligands produce catalysts for the asymmetric H
2
-
7
hydrogenation of base-sensitive ketones. Our group has
shown that combinations of binap, aminophosphine, and
diamine ligands with the precursor RuHCl(PPh
wide variety of active catalysts for the H -hydrogenation or
transfer hydrogenation of ketones and imines and for
3 3
) lead to a
2
8
8
f
Michael addition. We show here that a diverse set of
catalysts can be created by use of phosphinite ligands based
on the binol module, one of the cheapest chiral auxiliaries
currently available. These ligands are attractive and also
widely used in rhodium, iridium, and palladium complexes
for asymmetric catalytic reactions.6a,9-12
The reaction of the complexes trans-RuHCl(phosphinite)-
8
e
(
4
diamine) 1a-4a with NaBH in benzene/alcohol produces
1
the complexes trans-RuH(η -BH
4
)(phosphinite)(diamine)
b-4b in excellent yields (up to 99%), [phosphinite ) (R)-
,2′-bis(diphenylphosphinoyl)-1,1′-binaphthyl ((R)-binop) or
1
2
(
R)-2,2′-bis[bis(3,5-dimethylphenyl)phosphinoyl]-1,1′-bi-
Figure 1. Structure of complex 3b. Only hydrogen of the hydride
and borohydride ligands are shown.
naphthyl ((R)-xylbinop); diamine ) (1R,2R)-1,2-diphenyl-
ethylenediamine ((R,R)-dpen) or (1S,2S)-1,2-diphenylethyl-
enediamine ((S,S)-dpen)] (Scheme 1).
are similar to that of trans-RuHCl((R)-xylbinop)((R,R)-
8
e
dpen) with the PPNN atoms in the equatorial plane of a
slightly distorted octahedron and with the Ru-HBH bond
Scheme 1
3
leaning toward the NN side to form BH-HN hydrogen
bonds.
The complexes 1b-4b were tested in the base-free
asymmetric transfer hydrogenation of simple ketones and
showed good activities and enantioselectivities (Table 1).
2
They are less active for the H -hydrogenation of ketones.
The ruthenium complex 3b with the (R)-xylbinop and
matching diamine ligand (R,R)-dpen gives the best results
for acetophenone (compare entries 1-5).
This complex was extensively investigated with a variety
of substrates. The electronic properties of the substituent on
the phenyl ring of the ketone changed the reduction rate but
had little effect on the enantioselectivity. A para-substituted
acetophenone with an electron-donor substituent, i.e., 4′-
methyl or 4′-methoxyl, is reduced more slowly than ac-
etophenone (entries 3, 12, and 16). The ortho-substituted
acetophenone, 2′-chloroacetophenone, is reduced slowly and
The pale yellow solid products consist of two diastereo-
mers in a ratio of 3/1 for 1b and 2/1 for 2b but only one for
b and 4b. The source of the isomerism is the placement of
the trans hydride and borohydride groups relative to the
folded backbone of the diphosphinite ligand. The isomers
interconvert readily in solution and it is assumed that both
are present during catalysis.
The crystal structures of 3b and 4b were determined by
use of X-ray diffraction (Figures 1 and 2). These structures
3
(9) (a) Jerphagnon, T.; Renaud, J.-L.; Bruneau, C. Tetrahedron: Asym-
metry 2004, 15, 2101-2111. (b) Reetz, M. T.; Mehler, G. Angew. Chem.,
Int. Ed. 2000, 39, 3889-3890. (c) Reetz, M. T.; Sell, T.; Meiswinkel, A.;
Mehler, G. Angew. Chem., Int. Ed. 2003, 42, 790-793. (d) Reetz, M. T.;
Ma, J. A.; Goddard, R. Angew. Chem., Int. Ed. 2005, 44, 412-415.
(10) (a) van den Berg, M.; Minnaard, A. J.; Schudde, E. P.; van Esch,
J.; de Vries, A. H. M.; de Vries, J. G.; Feringa, B. L. J. Am. Chem. Soc.
2000, 122, 11539-11540. (b) Pena, D.; Minnaard, A. J.; de Vries, A. H.
M.; de Vries, J. G.; Feringa, B. L. Org. Lett. 2003, 5, 475-478.
(11) (a) Zhang, F. Y.; Kwok, W. H.; Chan, A. S. C. Tetrahedron:
Asymmetry 2001, 12, 2337-2342. (b) Guo, R.; Au-Yeung, T. T. L.; Wu,
J.; Choi, M. C. K.; Chan, A. S. C. Tetrahedron: Asymmetry 2002, 13, 2519.
(c) Guo, R.; Wu, J.; Kowk, W. H.; Chen, J.; Choi, M. C. K.; Zhou, Z. Y.
Acta Crystallogr. 2002, E58, o270. (d) Tietze, L. F.; Ila, H.; Bell, H. P.
Chem. ReV. 2004, 104, 3453-3516.
(
6) (a) Chen, Y.; Yekta, S.; Yudin, A. K. Chem. ReV. 2003, 103, 3155-
3
211. (b) RajanBabu, T. V.; Ayers, T. A.; Casalnuovo, A. L. J. Am. Chem.
Soc. 1994, 116, 4101-4102. (c) RajanBabu, T. V.; Radetich, B.; You, K.
K.; Ayers, T. A.; Casalnuovo, A. L.; Calabrese, J. C. J. Org. Chem. 1999,
6
4, 3429-3447.
7) (a) Ohkuma, T.; Koizumi, M.; Muniz, K.; Hilt, G.; Kabuto, C.;
(
Noyori, R. J. Am. Chem. Soc. 2002, 124, 6508-6509. (b) Sandoval, C. A.;
Ohkuma, T.; Mu n˜ iz, K.; Noyori, R. J. Am. Chem. Soc. 2003, 125, 13490-
1
3503.
(8) (a) Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Organometallics
2
001, 20, 1047-1049. (b) Rautenstrauch, V.; Hoang-Cong, X.; Churlaud,
R.; Abdur-Rashid, K.; Morris, R. H. Chem. Eur. J. 2003, 9, 4954-4967.
(
2
c) Guo, R.; Lough, A. J.; Morris, R. H.; Song, D. Organometallics 2004,
3, 5524-5529. (d) Li, T.; Churlaud, R.; Lough, A. J.; Abdur-Rashid, K.;
(12) (a) Zhou, Y. G.; Tang, W. J.; Wang, W. B.; Li, W.; Zhang, X. J.
Am. Chem. Soc. 2002, 124, 4952-4953. (b) Zhou, Y. G.; Zhang, X. Chem.
Commun. 2002, 1124-1125. (c) Tang, W. J.; Zhang, X. Chem. ReV. 2003,
103, 3029-3069.
Morris, R. H. Organometallics 2004, 23, 6239-6247. (e) Guo, R.; Elpelt,
C.; Chen, X.; Song, D.; Morris, R. H. Submitted for publication. (f) Guo,
R.; Morris, R. H.; Song, D. J. Am. Chem. Soc. 2005, 126, 516-517.
1758
Org. Lett., Vol. 7, No. 9, 2005

Scheme 2
Complexes 1b-4b are also efficient catalysts for the
enantioselective Michael addition of malonates to enones.
The complex 1b is the most enantioselective and provides
the product in 90% ee in the R-form when THF or benzene
1
3
is the solvent (Scheme 3).
Scheme 3
Figure 2. Structure of complex 4b.
shows a lower enantioselectivity (entries 6 and 7). The
enantioselectivities dropped with the extended reaction time
(entry 3 vs 4, entry 6 vs 7, entry 12 vs 13, entry 16 vs 17).
The catalyst 3b is also efficient for the hydrogenation of
7a
the base-sensitive substrate 4-acetylbenzoate ethyl ester by
transfer hydrogenation from 2-propanol. Only the ethyl ester
of alcohol is produced in 98% conversion and 92% ee (R)
in less than 20 h. No transesterification product was observed
(Scheme 2).
When the protic solvents ethanol or 2-propanol were used,
the enantioselectivity dropped sharply. The complexes 2b,
Table 1. Transfer Hydrogenation of Ketones Catalyzed by
Complexes 1b-4b
3
b, and 4b gave Michael addition products with the enantio-
meric excess of 30% in the S-form (2b), 44% in the R-form
3b), and 52% in the S-form (4b), respectively. They allow
a one-pot tandem Michael addition/H -hydrogenation proto-
col as in our previously disclosed research results with trans-
a
(
2
1
8f
4
RuH(η -BH )(binap)((R,R)-Pnor) complexes (Scheme 3).
In conclusion, we have developed a new catalytic system
for the base-free transfer hydrogenation of simple ketones
and this system is also effective for the asymmetric Michael
addition. The modular construction of these catalysts and
their flexibility toward hydrogenation, transfer hydrogenation,
Michael addition, and tandem reaction make these promising
systems to pursue.
entry
cat.
R
time (h)
conv (%)
ee (%)
1
2
3
4
5
6
7
8
9
1b
2b
3b
3b
4b
3b
3b
3b
3b
3b
3b
3b
3b
3b
3b
3b
3b
H
H
H
H
H
6
6
8
76
8
8
76
8
76
6
8
8
76
6
8
8
76
92
94
92
97
91
47
98
70
99
92
98
80
96
90
96
64
79
80 (R)
49 (R)
93 (R)
88 (R)
60 (R)
86 (R)
84 (R)
88 (R)
85 (R)
91 (R)
90 (R)
94 (R)
87 (R)
91 (R)
91 (R)
93 (R)
82 (R)
2′-Cl
2′-Cl
3′-Cl
3′-Cl
4′-Cl
4′-Cl
4′-Me
4′-Me
3′-MeO
3′-MeO
4′-MeO
4′-MeO
Acknowledgment. R.H.M. thanks NSERC and the PRF,
administrated by the American Chemical Society, for re-
search grants.
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
Supporting Information Available: Experimental pro-
cedures and characterization data of all new compounds and
crystallographic data for 3b and 4b (CIF). This material is
available free of charge via the Internet at http://pubs.acs.org.
OL050336J
a
The reactions were carried out in an Ar glovebox at room temperature.
The molar ratio of substrate/catalyst ) 100/1. The concentration of aryl
methyl ketone is 0.1 M.
(13) (a) Watanabe, M.; Murata, K.; Ikariya, T. J. Am. Chem. Soc. 2003,
125, 7508-7509. (b) Watanabe, M.; Ikagawa, A.; Wang, H.; Murata, K.;
Ikariya, T. J. Am. Chem. Soc. 2004, 126, 11148-11149.
Org. Lett., Vol. 7, No. 9, 2005
1759