5
86
Y. Tomisaka et al. / Tetrahedron Letters 50 (2009) 584–586
conducted at 67 °C for 20 h in the dark [yield of dodecane; Tb: 70%
dark), 74% (h ), Dy: 68% (dark), 75% (h )]. However, the decrease
in the reaction time (8 h) clearly indicates that the influence of
the photoirradiation was recognized more definitely: the yields
of n-C12H26 were 2% (dark), 33% (hm) [Tb]; 3% (dark), 46% (hm) [Dy].
In summary, we have investigated the generation and reducing
ability of a series of low-valent rare earths systematically. In the
case of light rare earths as La, Ce, Pr, Nd, Sm, Eu, and Yb, it has been
6. (a) Bochkarev, M. N.; Fedushkin, I. L.; Fagin, A. A.; Petrovskaya, T. V.; Ziller, J.
W.; Broomhall-Dillard, R. N. R.; Evans, W. J. Angew. Chem., Int. Ed. Engl. 1997, 36,
(
m
m
133; (b) Bochkarev, M. N.; Fagin, A. A. Chem. Eur. J. 1999, 5, 2990; (c) Evans, W.
J.; Allen, N. T. J. Am. Chem. Soc. 2000, 122, 2118; (d) Evans, W. J.; Allen, N. T.;
Ziller, J. W. J. Am. Chem. Soc. 2000, 122, 11749; (e) Zhu, Z. Y.; Wang, J. L.; Zhang,
Z. X.; Xiang, X.; Zhou, X. G. Organometallics 2007, 26, 2499; (f) Xiang, X.; Shen,
Q. S.; Wang, J. L.; Zhu, Z. Y.; Haung, W.; Zhou, X. Organometallics 2008, 27, 1959.
0
3+
2+
2+
7
.
.
Standard oxidation potentials (E Ln /Ln ), ionic radii of Ln
(R),
2+
thermodynamic functions for the formation of the aquo-ions of Ln , and the
enthalpies of hydration of the gaseous Ln2 ions are known. See: Mikheev, N. B.
Russ. J. Inorg. Chem. 1984, 2, 251.
+
shown that the mixed-valent rare earths (‘Ln/LnI
tially higher reducing ability compared with Ln or LnI
2
’) indicate poten-
single sys-
8
Girard, P.; Namy, J. L.; Kagan, H. B. J. Am. Chem. Soc. 1980, 102, 2693.
2
9. ‘Ln/LnI
2
’ Systems: In a three-necked flask equipped with a reflux condenser and
a
dropping funnel were placed rare earth (Ln) powder (1.0 mmol), 1,2-
tem. More importantly, it has been revealed that photoirradiation
can induce excellent reducing ability of low-valent rare earths in
the cases of most of rare earths species. As shown in the cases of
diiodoethane (0.2 mmol), and freshly distilled (sodium/benzophenone ketyl)
THF (2 mL) under a nitrogen atmosphere. The mixture was stirred for 1.5 h at
room temperature. In all cases of rare earths, the color of the solution was
changed, and unreacted Ln metal was insoluble in THF. To the resulting
2 2
SmI and YbI typically, divalent lanthanoid diiodides have their
suspension of ‘Ln/LnI
2
’ in THF were added dropwise a solution of 1-
absorption in near UV and/or visible region based on the 4f–5d
excitation. Accordingly, it is expected that ‘the photoinduced diva-
lent rare earth species in the excited state’ exhibits higher reducing
iodododecane (0.5 mmol), 2-propanol (2.0 mmol), and tetradecane (n-C14
30
H ,
an internal standard for GC analysis) in THF (2 mL) for 1 h, and the reaction was
continued for additional 2 h. To quench the reaction, the flask was exposed to
1
9
4
f,18
air. Aqueous saturated NaHCO
3
(40 mL) was added to the reaction mixture,
O (20 mL Â 3). The combined extracts
4
, and filtered off. The resulting solution was
ability than ‘the divalent rare earth species in the ground state’.
and the products were extracted with Et
were dried over anhydrous MgSO
analyzed by GC.2
2
We believe that this finding will open up a new field of rare earth
chemistry.
0
1
1
0. In the case of Yb, the reductive dimerization product (n-C24H50) was obtained
in the similar yield as that of the reduction product (n-C12
H
26). Relatively lower
Acknowledgments
Å
solubility of YbI
2
in THF may contribute to the dimerization of n-C12
H
5.
2
1. In general, high-grade lanthanoide powders (40 mesh) are commercially
available and can be used without further activation. However, Eu powder is
not commercially available as high-grade powder. Thus, we filed Eu ingot to
powder in a grove box under nitrogen atmosphere and used directly for the
reduction of 1-iodododecane. See: Tomisaka, Y.; Tsuchii, K.; Ogawa, A. J. Alloys
Compd. 2006, 408–412, 427.
This work is supported by Grant-in-Aid for Scientific Research
on Priority Areas (Area 444, No. 19020061) and Scientific Research
(
B, 19350095), from the Ministry of Education, Culture, Sports, Sci-
ence and Technology, Japan.
1
2. The reduction of 1-iodododecane with Ln metal can proceed at the THF
refluxing temperature for 2 h. See: (a) Nishino, T.; Watanabe, T.; Okada, M.;
Nishiyama, Y.; Sonoda, N. J. Org. Chem. 2002, 67, 966; (b) Nishino, T.; Okada, M.;
Kuroki, T.; Watanabe, T.; Nishiyama, Y.; Sonoda, N. J. Org. Chem. 2002, 67, 8696.
References and notes
1
.
For recent reviews concerning the chemistry of rare earth compounds, see for
example: (a) Imamoto, T. In Lanthanides in Organic Synthesis; Katrizky, A. R.,
Meth-cohn, O., Ress, C. W., Eds.; Academic Press: London, 1994; (b) Anwander,
R.; Edelmann, F. T.; Herrmann, W. A.. In Topics in Current Chemistry; Herrmann,
W. A., Ed.; Springer: Berlin, 1996; Vol. 179, (c) Herrmann, W. A.. In Synthetic
Methods of Organometallic and Inorganic Chemistry; Edelmann, F. T., Ed.;
Thieme: Stuttgart, 1997; Vol. 6, (d) Kobayashi, S.. In Topics in Organometallic
Chemistry; Springer: Berlin, 1999; Vol. 2; (e) Molander, G. A.; Antoinette, J.;
Romero, C. Chem. Rev. 2002, 102, 2161; (f) Shibasaki, M.; Yoshikawa, N. Chem.
Rev. 2002, 102, 2187; (g) Inanaga, J.; Furuno, H.; Hayano, T. Chem. Rev. 2002,
13. Ln Systems: In a three-necked flask equipped with a reflux condenser and a
dropping funnel were placed rare earth (Ln) powder (1.0 mmol) and freshly
distilled (sodium/benzophenone ketyl) THF (2 mL) under
a nitrogen
atmosphere. The mixture was stirred for 1.5 h at room temperature (to
attain the identical conditions). In all cases of rare earths, the color of the
solution was not changed, and unreacted Ln metal was insoluble in THF. To the
resulting suspension of Ln metal in THF were added dropwise a solution of 1-
iodododecane (0.5 mmol), 2-propanol (2.0 mmol), and tetradecane in THF
(2 mL) for 1 h, and the reaction was continued for additional 2 h. To quench the
reaction, the flask was exposed to air. After similar workups, the resulting
ethereal solution was analyzed by GC.
102, 2211; (h) Mikami, K.; Terada, M.; Matsuzawa, H. Angew. Chem., Int. Ed.
2
002, 41, 3554; (i) Sumino, Y.; Ogawa, A. J. Synth. Org. Chem. Jpn. 2003, 61, 201.
14. The color of solutions changed similarly as described about the Ln(0)/Ln(II)
binary system. In the cases of Gd, Tb, Dy, Ho, Er, Tm, and Lu, however, most of
metals were observed to remain unchanged.
2
.
.
(a) Ogawa, A.; Takami, N.; Sekiguchi, M.; Ryu, I.; Kambe, N.; Sonoda, N. J. Am.
Chem. Soc. 1992, 114, 8729; (b) Ogawa, A.; Nanke, T.; Takami, N.; Sumino, Y.;
Ryu, I.; Sonoda, N. Chem. Lett. 1994, 379; (c) Ogawa, A.; Takami, N.; Nanke, T.;
Sekiguchi, M.; Kambe, N.; Sonoda, N. Appl. Organomet. Chem. 1995, 9, 461; (d)
Ogawa, A.; Takami, N.; Nanke, T.; Ohya, S.; Hirao, T.; Sonoda, N. Tetrahedron
15. LnI
2
systems: In a three-necked flask equipped with a reflux condenser and a
dropping funnel were placed rare earth (Ln) powder (1.0 mmol), 1,2-
diiodoethane (1.0 mmol), and freshly distilled (sodium/benzophenone ketyl)
THF (2 mL) under a nitrogen atmosphere. The mixture was stirred for 1.5 h at
room temperature. In the cases of Ce, Pr, Nd and Sm, the color of the solution
was changed and homogeneous solution was formed. In other rare earths, the
color of the solution was not changed, and unreacted Ln metal existed. To the
1
997, 53, 12895.
3
(a) Murakami, M.; Hayashi, M.; Ito, Y. Synlett 1994, 179; (b) Yanada, R.; Negoro,
N.; Bessho, K.; Yanada, K. Synlett 1995, 1261; (c) Agarwal, S.; Brandukova-
Szmikowski, N. E.; Greiner, A. Macromol. Rapid Commun. 1999, 20, 274; (d)
Clausen, C.; Weidner, I.; Butenschön, H. Eur. J. Org. Chem. 2000, 3799; (e)
Yoshida, A.; Takayama, H. Tetrahedron Lett. 2001, 42, 3603; (f) Ma, Y. M.; Zhang,
Y. M.; Chen, J. Synthesis 2001, 1004; (g) Xu, X. L.; Zhang, Y. M. Tetrahedron 2002,
2
resulting THF solution or suspension of ‘LnI ’ were added dropwise a solution
of 1-iodododecane (0.5 mmol), 2-propanol (2.0 mmol), and tetradecane in THF
(2 mL) for 1 h, and the reaction was continued for additional 2 h. To quench the
reaction, the flask was exposed to air. After similar workups, the resulting
ethereal solution was analyzed by GC.
5
8, 503; (h) Matsukawa, S.; Hinakubo, Y. Org. Lett. 2003, 5, 1221; (i) Shinohara,
I.; Okue, M.; Yamada, Y.; Nagaoka, H. Tetrahedron Lett. 2003, 44, 4649; (j) Zhu,
W. M.; Qian, W. X.; Zhang, Y. M. J. Chem. Res. (S) 2005, 164; (k) Zhu, W. M.; Qian,
W. X.; Zhang, Y. M. J. Chem. Res. (S) 2005, 410; (l) Inui, M.; Nakazaki, A.;
Kobayashi, S. Org. Lett. 2007, 9, 469; (m) Li, Z. F.; Iida, K.; Tomisaka, Y.;
Yoshimura, A.; Hirao, T.; Nomoto, A.; Ogawa, A. Organometallics 2007, 26, 1212.
(a) Ogawa, A.; Sumino, Y.; Nanke, T.; Ohya, S.; Sonoda, N.; Hirao, T. J. Am. Chem.
Soc. 1997, 119, 2745; (b) Ogawa, A.; Ohya, S.; Hirao, T. Chem. Lett. 1997, 275; (c)
Ogawa, A.; Sumino, Y.; Nanke, T.; Ryu, I.; Kambe, N.; Sonode, N. Rare Earths
16. ‘Ln/LnI
2
/h
m
’ systems: To the THF solution of ‘Ln/LnI
2
’ prepared in a similar
solution of 1-
manner as mentioned above were added dropwise
a
iodododecane (0.5 mmol), 2-propanol (2.0 mmol), and tetradecane (an
internal standard for GC analysis) in THF (2 mL) for 1 h, and the reaction was
continued for additional 2 h. Irradiation through Pyrex with a xenon lamp
(500 W) was performed during the reaction. To quench the reaction, the flask
was exposed to air. After similar workups, the resulting ethereal solution was
analyzed by GC.
4
.
.
1
2
995, 338; (d) Ogawa, A.; Hirao, T.; Sumino, Y.; Sonoda, N. Rare Earths 1996,
98; (e) Imamoto, T.; Tawarayama, Y.; Kusumoto, T.; Yokoyama, M. J. Synth.
2 2
17. In the cases of SmI and YbI , similar reduction of the corresponding chloride
Org. Chem. Jpn. 1984, 42, 143; (f) Skene, W. G.; Scaiano, J. C.; Cozens, F. L. J. Org.
Chem. 1996, 61, 7918.
(a) Molander, G. A.; Alonso-Alija, C. J. Org. Chem. 1998, 63, 4366; (b) Ogawa, A.;
Ohya, S.; Doi, M.; Sumino, Y.; Sonoda, N.; Hirao, T. Tetrahedron Lett. 1998, 39,
and bromide took place successfully upon photoirradiation. See Refs. 4a and b:
Ogawa, A.; Ohya, S.; Sumino, Y.; Sonoda, N.; Hirao, T. Tetrahedron Lett. 1997, 38,
9017.
5
18. (a) Bray, K. L. Trans. Met. Rare Earth Compd. 2001, 213, 1; (b) Namy, J. L.; Girard,
P.; Kagan, H. B.; Caro, P. E. New J. Chem. 1981, 5, 479.
19. Hasegawa, E.; Curran, D. P. J. Org. Chem. 1993, 58, 5006.
6
341; (c) Molander, G. A.; Wolfe, C. N. J. Org. Chem. 1998, 63, 9031; (d)
Molander, G. A.; Machrouhi, F. J. Org. Chem. 1999, 64, 4119; (e) Sumino, Y.;
Harato, N.; Tomisaka, Y.; Ogawa, A. Tetrahedron 2003, 59, 10499; (f) Prasad, E.;
Knettle, B. W.; Flowers, R. A. Chem. Eur. J. 2005, 11, 3105; (g) Concellón, J. M.;
Rodríguez-Solla, H.; Simal, C.; Huerta, M. Org. Lett. 2005, 7, 5833; (h)
Dichiarante, V.; Fagnoni, M.; Mella, M.; Albini, A. Chem. Eur. J. 2006, 12, 3905;
2 2
20. We attempted the preparation of LnI by the reaction of Ln (1.0 mmol) with I
(0.2 mmol) in freshly distilled (sodium/benzophenone ketyl) THF (2 mL) under
a nitrogen atmosphere, and then examined the reduction of 1-iodododecane.
The yields of dodecane were 4% (Sm and Yb); trace (Pr, Nd, Gd, Dy, Ho, Er and
Tm). Therefore, 1,2-diiodoethane is more suitable additive for the preparation
of divalent rare earth species.
(
2
i) Tomisaka, Y.; Harato, N.; Sato, M.; Nomoto, A.; Ogawa, A. Bull. Chem. Soc. Jpn.
006, 79, 1444.