Samarium(III) tris(2,6-di-tert-butyl-4-methylphenoxide): Preparation, properties, and catalytic activity in the Michael type reaction

Article abstract of DOI:10.1246/cl.2002.426

Samarium(III) tris(2,6-di-tert-butyl-4-methylphenoxide) (1), which is a highly coordinatively unsaturated complex, was prepared by the reaction of samarium(III) iodide with sodium 2,6-di-tert-butyl-4-methylphenoxide, and the crystal structure of its aceto

Full text of DOI:10.1246/cl.2002.426

426
Chemistry Letters 2002
Samarium(III) Tris(2,6-di-tert-butyl-4-methylphenoxide): Preparation, Properties,
and Catalytic Activity in the Michael Type Reaction
Kosuke Katagiri, Miyuki Kameoka, Masayoshi Nishiura, and Tsuneo Imamotoꢀ
Department of Chemistry, Faculty of Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522
(Received December 26, 2001;CL-011300)
Samarium(III) tris(2,6-di-tert-butyl-4-methylphenoxide) (1),
analysis.10 Its molecular structure and selected coordination lengths
and angles are shown in Figure 1. It is clear that this complex 2
contains three aryloxide ligands and two acetonitrile molecules to
form a penta-coordinate structure. A characteristic feature of this
molecular structure is manifested in the N1–Sm1–N2 bond angle
(67.2 ꢁ). The extremely small bond angle in comparison with others
in the same complex is ascribed to the limited coordination sphere
for the acetonitrile molecules. It is noted that complex 2 liberated
the coordinated acetonitriles on standing in vacuum at room
temperature for a few hours to form complex 1. This fact strongly
supports that the initially formed complex 1 is a tri-coordinated
complex without any solvent ligands.
which is a highly coordinatively unsaturated complex, was prepared
by the reaction of samarium(III) iodide with sodium 2,6-di-tert-
butyl-4-methylphenoxide, and the crystal structure of its aceto-
nitrile complex was determined by X-ray analysis. Complex 1
catalyzed the sequential Michael-Michael-aldol reaction of 3,3-
dimethyl-2-butanone with benzalacetophenone.
Lanthanide elements are capable of forming complexes with
high coordination numbers, and this property is one of the origins of
the unique reactivity of lanthanide reagents in organic trans-
formations.1 Trivalent samarium ion can function as Lewis acid to
promote a variety of reactions such as aldol reaction,2 Diels–Alder
reaction,3 Meerwein reduction,4 Tishchenko reaction,5 and tandem
Michael–aldol reaction.6 Shibasaki et al. reported that optically
active LaLi3tris(binaphthoxide) (LLB) and related complexes
effectively catalyzed asymmetric reactions such as nitroaldol
reaction and Michael addition reaction. Furthermore, they recently
found that the similar complexes promoted the asymmetric direct
aldol reaction of unmodified ketones with aldehydes.7 The highly
sophisticated catalysts used in those reactions involve the metal
centers coordinated with six phenoxide moieties. On the other hand,
tri-coordinate lanthanide–phenoxide complexes8 have been rarely
used in organic synthesis, despite their anticipated high catalytic
activity. Here we wish to report some preliminary results of the
preparation of a samarium(III) triphenoxide complex and its use in
the Michael type reaction of carbonyl compounds with benzalace-
tophenone.
For the preparation of the desired highly coordinatively
unsaturated phenoxide complexes, we chose 2,6-di-tert-butyl-4-
methylphenol as a sterically hindered phenoxide component. At
first, samarium(III) tris(2,6-di-tert-butyl-4-methylphenoxide) (1)
was prepared by the reaction of anhydrous samarium(III) iodide
with three molar equivalents of sodium 2,6-di-tert-butyl-4-
methylphenoxide in dry THF (Scheme 1).
Figure 1. ORTEP drawing of complex 2 with 30% probability thermal
ellipsolds.
The catalytic activity of complex 1 was tested for the direct
Michael addition of several representative carbonyl compounds
having methyl group or methylene component to benzalacetophe-
none. The reactions were carried out by employing exactly 1 : 1
ratio of the carbonyl compounds and benzalacetophenone except a
few cases. The results are summarized in Table 1. The addition
reaction of 3,3-dimethyl-2-butanone to benzalacetophenoe pro-
ceeded in THF, toluene, hexane, or dichloromethane to give 6,6-
dimethyl-1,3-diphenyl-1,5-heptanedione (3) and 2,4-dibenzoyl-
3,5-diphenyl-1-tert-butylcyclo-hexanol (4)11 (entries 1, 2, 6, and
7). It is reasonable to consider that the latter compound 4 isproduced
via sequential Michael– Michael–aldol reaction. Thus, the initially
formed Michael adduct 3 reacts with another molecule of
benzalacetophenone, followed by intramolecular aldol reaction, to
afford compound 4. This compound was obtained as major product
when the reaction was carried out at 0 ꢁC using 3,3-dimethyl-2-
butanone and benzalacetophenone in 1 : 2 ratio (entry 5).
Scheme 1.
The NMR analysis of this product indicates that the complex
contains no coordinated THF or water.9 Analysis of samarium
content by chelatometric titration suggests that the ratio of the
phenoxide ligand to samarium metal is three. Attempted recrys-
tallization from THF to obtain single crystals for X-ray analysis was
unsuccessful. Recrystallization from a mixed solvent of THF and
acetonitrile gave yellow cubes, which were subjected to X-ray
On the other hand, the reaction in acetonitlrile or nitromethane
resulted in the formation of complex mixture (entries 8 and 9).
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
427
Table 1. Reactions of Michael donors with benzalacetophenone in the presence of catalyst 1a
Collin, Tetrahedron Lett., 39, 7845 (1998). e) C. M. Mascarenhas, M. O. Duffey,
S.-Y. Liu, and J. P. Morken, Org. Lett., 1, 1427 (1999). f) L. Lu, H.-Y. Chang, and
J.-M. Fang, J. Org. Chem., 64, 843 (1999). g) C. M. Mascarenhas, S. P. Miller, P. S.
White, and J. P. Morken, Angew. Chem., Int. Ed., 40, 601 (2001).
These results are ascribed to that the used solvent CH3CN or
CH3NO2 also reacted with benzalacetophenone.12 Other carbonyl
compounds including active methylene compounds reacted with
benzal-acetophenone to give the corresponding Michael adduct in
good to high yield. It is noted that the Michael reaction of ꢀ-
naphthylmethyl ketone and thioacetic acid S-phenyl ester pro-
ceeded smoothly to give 1-ꢀ-naphthyl-3,5-diphenyl-1,5-pentane-
dione and 1,3-diphenyl-5-thiophenyl-1,5-pentanedione (entries 10
and 14).
In summary, we prepared samarium(III) tris(2,6-di-tert-butyl-
4-methylphenoxide) (1) and found that the complex catalyzed the
Michael type reaction of some representative carbonyl compounds
to benzalacetophenone.
6
7
a) G. H. Posner, S.-B. Lu, E. Asirvatham, E. F. Silversmith, and E. M. Shulman, J.
Am. Chem. Soc., 108, 511 (1986). b) M. Ihara, M. Ohnishi, M. Takano, K. Makita,
N. Taniguchi, and K. Fukumoto, J. Am. Chem. Soc., 114, 4408 (1992). c) M. Ihara,
K. Makita, Y. Tokunaga, and K. Fukumoto, J. Org. Chem., 59, 6008 (1994). d) H.
Paulsen, S. Antons, A. Brandes, M. Logers, S. N. Muller, P. Naab, C. Schmeck, S.
Schneider, and J. Stoltefuss., Angew. Chem., Int. Ed., 38, 3373 (1999).
a) H. Sasai, T. Arai, and M. Shibasaki, J. Am. Chem. Soc., 116, 1571 (1994). b) H.
Sasai, T. Arai, Y. Satow, K. N. Houk, and M. Shibasaki, J. Am. Chem. Soc., 117,
6194 (1995). c) Y. M. A. Yamada, N. Yoshikawa, H. Sasaki, and M. Shibasaki,
Angew. Chem., Int. Ed. Engl., 36, 1871 (1997). d) M. Shibasaki, H. Sasai, and T.
Arai, Angew. Chem., Int. Ed. Engl., 36, 1236 (1997). e) N. Yoshikawa, Y. M. A.
Yamada, J. Das, H. Sasai, and M. Shibasaki, J. Am. Chem. Soc., 121, 4168 (1999).
a) P. B. Hitchcock, M. F. Lappert, and A. Singh, J. Chem. Soc., Chem. Commun.,
1983, 1499. b) H. A. Stecher, A. Sen, and A. L. Rheingold, Inorg. Chem., 27, 1132
(1988). c) W. J. Evans, R. Anwander, M. A. Ansari, and J. W. Ziller, Inorg. Chem.,
34, 5 (1995).
8
9
Dedicated to Prof. Teruaki Mukaiyama on the occasion of his
75th birthday.
1H NMR (C6D6, 400 MHz, 25 ꢁC) ꢁ 0.86 (s, tBu, 54H), ꢁ 2.84 (s, Me, 9H), ꢁ 8.17
(s, Ar-H, 6H).
10 Crystal data of 2: C53H81O3N4Sm, M ¼ 972:65, triclinic, space group P1 (#2),
References and Notes
a ¼ 12:627ð9Þ A, b ¼ 21:20ð1Þ A, c ¼ 11:230ð4Þ A, ꢂ ¼ 91:02ð3Þ ꢁ, ꢀ ¼
ꢀ
ꢀ
ꢀ
1
a) G. A. Molander, in ‘‘Comprehensive Organic Synthesis,’’ ed. by B. M. Trost and
I. Fleming, Pergamon Press, Oxford (1991), Vol. 1, p 251. b) G. A. Molander,
Chem. Rev., 92, 29 (1992). c) T. Imamoto, ‘‘Lanthanide in Organic Synthesis,’’
Academic Press, London (1994). d) S. Kobayashi, Eur. J. Org. Chem., 1999, 15.
a) A. E. Vougioukas and H. B. Kagan, Tetrahedron Lett., 28, 5513 (1987). b) P.
Van de Weghe and J. Collin, Tetrahedron Lett., 34, 3881 (1993). c) T.-H. Chuang,
J.-M. Fang, W.-T. Jiaang, and Y.-M. Tsai, J. Org. Chem., 61, 1794 (1996). d) L.
Lu, H.-Y. Chang, and J.-M. Fang, J. Org. Chem., 64, 843 (1999).
109:84ð3Þ ꢁ, ꢃ ¼ 76:00ð3Þ ꢁ V ¼ 2736ð2Þ cm3, Z ¼ 2, Dcala ¼ 1:180 g/cmꢂ3
,
ꢄðMoKꢂÞ ¼ 11:16 cmꢂ1, T ¼ 278 K, R ¼ 0:085, Rw ¼ 0:142.
11 4-Dibenzoyl-3,5-diphenyl-1-tert-butylcyclohexanol (4);mp 222–223 ꢁC
(AcOEt/hexane (1 : 5)). 1H NMR (CDCl3, 400 MHz, 25 ꢁC) ꢁ 0.15 (s, tBu, 9H),
ꢁ 2.17 (dd, J ¼ 3:42, 13.90 ,Hz, 1H), ꢁ 2.48 (dd, J ¼ 13:90, 13.40 Hz, 1H), ꢁ 3.94
(dd, J ¼ 11:24, 11.44 Hz, 1H), ꢁ3.97 (ddd, J ¼ 3:42, 11.44, 13.40 Hz, 1H), ꢁ4.07
(d, J ¼ 11:72 Hz, 1H), ꢁ 4.15 (dd, J ¼ 11:24, 11.72 Hz, 1H), ꢁ 5.35 (s, OH, 1H), ꢁ
6.89–7.56 (m, 20H). IR (KBr) 3460 (s), 1670 (s).
2
3
4
a) P. Van de Weghe and J. Collin, Tetrahedron Lett., 35, 2545 (1994).
D. A. Evans, S. G. Nelson, M. R. Gagne, and A. R. Muci, J. Am. Chem. Soc., 115,
9800 (1993).
12 In a separate experiment, we found that benzalacetophenone on treatment with 1
equivalent of complex 1 in CH3CN at room temperature for 24 h lead to 1-
cyanomethyl-1,3-diphenyl-2-propen-1-ol in 60% yield. The reaction of benzal-
acetophenone in CH3NO2 under similar conditions afforded 4-nitro-1,3-diphenyl-
1-butanone in 98% yield.
5
a) D. A. Evans and A. H. Hoveyda, J. Am. Chem. Soc., 112, 6447 (1990). b) D. P.
Curran and R. L. Wolin, Synlett, 1991, 317. c) H. Berberich and P. W. Roesky,
Angew. Chem., Int. Ed., 37, 1569 (1998). d) N. Giuseppone, Y. Courtaux, and J.