Synthesis of oxygen- and sulfur-bridged dirhodium complexes and their use as catalysts in the chemoselective hydrogenation of alkenes

Article abstract of DOI:10.1021/om100067r

Oxygen-bridged and sulfur-bridged rhodium homobimetallic complexes were synthesized as air-stable crystals by using 2,6-bis(phosphanylmethyl)phenolate and -thiophenolate as the ligands, respectively. The oxygen-bridged dirhodium complex has a symmetrical structure where the carbon atom at the ipso position, oxygen, and two rhodium atoms are located in the same plane. It is thermally stable compared to the sulfur-bridged dirhodium complex and shows catalytic activity for hydrogenation of alkenes with high chemoselectivity.

Full text of DOI:10.1021/om100067r

2098 Organometallics 2010, 29, 2098–2103
DOI: 10.1021/om100067r
Synthesis of Oxygen- and Sulfur-Bridged Dirhodium Complexes and
Their Use As Catalysts in the Chemoselective Hydrogenation of Alkenes
Chuan Zhu, Noriaki Yukimura,† and Motoki Yamane*
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences,
Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore. †Current address:
Tire Material Development, Bridgestone Corporation, Tokyo 187-8531, Japan.
Received January 27, 2010
Oxygen-bridged and sulfur-bridged rhodium homobimetallic complexes were synthesized as air-
stable crystals by using 2,6-bis(phosphanylmethyl)phenolate and -thiophenolate as the ligands,
respectively. The oxygen-bridged dirhodium complex has a symmetrical structure where the carbon
atom at the ipso position, oxygen, and two rhodium atoms are located in the same plane. It is
thermally stable compared to the sulfur-bridged dirhodium complex and shows catalytic activity for
hydrogenation of alkenes with high chemoselectivity.
Scheme 1. Heteroatom-Bridged Bimetallic Complex
Introduction
Bimetallic catalysts have attracted synthetic organic che-
mists because it is expected that two metal centers in the same
molecule cooperatively take part in a reaction and achieve an
efficient or novel chemical transformation.1 Many reactions
involving bimetallic catalysis have been reported; however,
bimetallic catalysis that surpasses conventional monometal-
lic catalysis is still rare, and we need more efficient reactions
that are applicable for practical organic synthesis. We have
studied heteroatom-bridged bimetallic catalysts2,3 because it
is supposed that the heteroatom captures and brings the two
metal atoms close to each other, and the electronic properties
of one of the metal centers can be controlled by the other
metal center by donating or accepting electrons through
the heteroatom (Scheme 1).4 For the metal center, we
have been interested in rhodium because many unique
reactions including activation of inert bonds were recently
reported.5 In this paper, we describe the design and pre-
paration of oxygen- or sulfur-bridged dirhodium com-
plexes and their application for chemoselective hydrogena-
tion of alkenes.
*Corresponding author. Tel: (þ65) 6513 8014. Fax: (þ65) 6791 1961.
E-mail: yamane@ntu.edu.sg.
Results and Discussion
(1) For the review of bimetallic catalysis, see: (a) Multimetallic
Catalysts in Organic Synthesis; Shibasaki, M.; Yamamoto, Y., Eds.; Wiely-
VCH Verlag GmbH & Co. KGaA: Weinheim, 2004. Braunstein, P.; Rose, J.
Catalysis and Related Reactions with Compounds Containing Heteronuclear
Metal-Metal Bonds. In Comprehensive Organometallic Chemistry II; Abel, E.
W.; Willkinson, G.; Stone, F. G. A., Eds.; Elsevier: Oxford, U.K., 1995, Vol. 10, p
351. (b) Wheatley, N.; Kalck, P. Chem. Rev. 1999, 99, 3379. For a recent article,
see: (c) Tsukada, N.; Mitsuboshi, T.; Setoguchi, H.; Inoue, Y. J. Am. Chem. Soc.
2003, 125, 12102. (d) Parimala, S.; Kandaswamy, M. Inorg. Chem. Commun.
2003,6, 1252. (e) Tsukada, N.; Setoguchi, H.; Mitsuboshi, T.; Inoue, Y. Chem. Lett.
2006, 35, 1164. (f)Man, M. L.;Lam, K. C.;Sit, W. N.;Ng, S. M.;Zhou, Z.;Lin, Z.;
Lau, C. P. Chem.;Eur. J. 2006, 12, 1004. (g) Chen, Q.; Yu, J.; Huang, J.
Organometallics 2007, 26, 617. (h) Biffis, A.; Lobbia, G. G.; Papini, G.; Pellei, M.;
Santini, C.; Scattolin, E.; Tubaro, C. J. Organomet. Chem. 2008, 693, 3760.
(i) Rodriguez, B. A.; Delferro, M.; Marks, T. J. Organometallics 2008, 27, 2166.
(j) Singh, A. K.; Dwivedi, S. D.; Dubey, S. K.; Singh, S. K.; Sharma, S.; Pandey,
D. S.; Zou, R.-K.; Xu, Q. J. Organomet. Chem. 2009, 694, 3084. (k) Fang, F.; Xie,
F.; Yu, H.; Zhang, H.; Yang, B.; Zhang, W. Tetrahedron Lett. 2009, 50, 6672.
(2) (a) Loose, C.; Ruiz, E.; Kersting, B.; Kortus, J. Chem. Phys. Lett.
2008, 452, 38. (b) Punji, B.; Mague, J. T.; Balakrishna, M. S. Inorg. Chem. 2007,
46, 11316. (c) Sarkar, S.; Mondal, A.; Banerjee, A.; Chopra, D.; Ribas, J.; Rajak,
K. K. Polyhedron 2006, 25, 2284. (d) Konno, T.; Usami, M.; Toyota, A.; Hirotsu,
M.; Kawamoto, T. Chem. Lett. 2005, 34, 1046. (e) Xie, Y.; Jiang, H.; Chan, A.
S.-C.; Liu, Q.; Xu, X.; Du, C.; Zhu, Y. Inorg. Chim. Acta 2002, 333, 138.
(f) Palmer, M. S.; Harris, S. Organometallics 2000, 19, 2114.
Design and Preparation of Heteroatom-Bridged Dirhodium
Complexes. We chose 2,6-bis(phosphanylmethyl)phenol 2
and -thiophenol 3 as the ligands and designed dirhodium
complexes as depicted in Figure 1.6 The tridentate ligands are
expected to coordinate to rhodium centers strongly from one
side, making the structure of the complex rigid and leaving
the opposite side free for reactions.
Bis[(diphenylphosphanyl)methyl]phenol (2) was prepared
from commercially available 2,6-dimethylphenol (4) in four
steps (Scheme 2). The hydroxy group was protected by silylation
(5) For the review of rhodium-catalyzed reactions, see: (a) Fagnou, K.;
Lautens, M. Chem. Rev. 2003, 103, 169. (b) Lewis, J. C.; Bergman, R. G.;
Ellman, J. A. Acc. Chem. Res. 2008,41, 1013. For recent articles, see: (c) Yamane,
M.; Uera, K.; Narasaka, K. Chem. Lett. 2004, 33, 424. (d) Yamane, M.; Uera, K.;
Narasaka, K. Bull. Chem. Soc. Jpn. 2005, 78, 477. (e) Joo, J. M.; Yuan, Y.; Lee, C.
J. Am. Chem. Soc. 2006, 128, 14818. (f) Cook, M. J.; Rovis, T. J. Am. Chem.
Soc. 2007, 129, 9302. (g) Osborne, J. D.; Randell-Sly, H. E.; Currie, G. S.; Cowley,
A. R.; Willis, M. C. J. Am. Chem. Soc. 2008, 130, 17232. (h) Phan, D. H. T.; Kim,
B.; Dong, V. M. J. Am. Chem. Soc. 2009, 131, 15608. (i) Hojo, D.; Noguchi, K.;
Tanaka, K. Angew. Chem., Int. Ed. 2009, 48, 8129. (j) Shibata, Y.; Tanaka, K.
J. Am. Chem. Soc. 2009, 131, 12552.
(3) Yamane, M.; Yukimura, N.; Ishiai, H.; Narasaka, K. Chem. Lett.
2006, 35, 540.
(4) (a) Nakamura, E.; Yoshikai, N; Yamanaka, M. J. Am. Chem. Soc.
2002, 124, 7181. (b) Nishibayashi, Y.; Milton, M. D.; Inada, Y.; Yoshikawa,
M.; Wakiji, I.; Hidai, M.; Uemura, S. Chem.;Eur. J. 2005, 11, 1433.
(6) For sulfur-bridged dirhodium complexes with the same ligand,
see: Dilworth, J. R.; Zheng, Y.; Griffths, D. V. J. Chem. Soc., Dalton.
Trans. 1999, 1877.
r
pubs.acs.org/Organometallics
Published on Web 04/09/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 9, 2010 2099
Scheme 4. Preparation of O- and S-Bridged Dirhodium Com-
plexes
Figure 1. Designed O- and S-bridged dirhodium complexes.
Scheme 2. Preparation of O-Ligand 2a
almost planar (359.9°), which means the structure around oxygen
is distorted trigonal planar. Rh(1)-O(1) and Rh(2)-O(1) bond
distances of 2.1237(19) and 2.1191 A are almost identical and simi-
lar to data of reported μ-O dirhodium complexes.11 On the con-
trary, the X-ray diffraction of complex μ-S-1 reveals its less sym-
metrical structure. The sum of three angles, Rh(1)-S(1)-Rh(2)
123.7°, C(1)-S(1)-Rh(1) 98.4°, and C(1)-S(1)-Rh(2) 118.0°,
is 340.1°, and the structure around sulfur is distorted tetrahedral.
Application for Chemoselective Hydrogenation of Alkenes.
We examined the catalytic ability of the synthesized bime-
tallic complexes μ-O-1 and μ-S-1 by analyzing its catalytic
effects on the hydrogenation of alkenes.12 We found that both
complexes μ-O-1 and μ-S-1 had good catalytic activity for the
hydrogenation of monosubstituted alkenes. When 1-(3-butenyl)-
naphthalene 12a was treated with a catalytic amount of μ-O-1
under the atmospheric pressure of H2, reduced product 13a was
obtained in 96% yield (eq 1). To confirm whether the μ-O-
bimetallic structure was maintained during the reaction, mon-
itoring by 31P NMR analysis was conducted. For both analyses
during the reaction (2 h) and after the reaction (6 h), only the
doublet peak corresponding to the phosphorus atom in μ-O-1
was observed (δ (ppm) = 46 (d, 1J31P-103Rh = 165 Hz)). This
observation suggests that the bimetallic structure is rigid and
would not release monometallic complexes. Compared to
complex μ-O-1, complex μ-S-1 shows less stability under the
hydrogenation conditions. Although the reduction proceeded
and alkane 13a was obtained in good yield, precipitation of
rhodium black was observed during the reaction (eq 1). For-
mation of cyclooctane and cyclooctene was confirmed by 1H
NMR analysis when μ-S-1 was dissolved in CDCl3 under an
atmospheric pressure of H2. This hydrogenation of the ligand
cyclooctadiene (COD) generated unstable dirhodium inter-
mediates that gradually decomposed to form rhodium black.
Meanwhile, μ-O-1 was found stable even in solution in the
presence of H2, and no hydrogenation of ligand was observed.
a (a) Me2 BuSiCl, imidazole, DMF, 50 °C, 4 h, 5 86%, (b) cat. AIBN,
t
n
NBS, CCl4, reflux, 8 h, 6 48%, (c) Ph2PH BH3, cat. Bu4NBr, KOH,
toluene-H2O, 50 °C, 7 h, 7 81%, (d) DABCO, 50 °C, 12 h, 2 78%.
3
Scheme 3. Preparation of S-Ligand 3a
a (a) Ph2PH BH3, cat. nBu4NBr, KOH, toluene-H2O, rt, 16 h, 9
3
81%, (b) Et2NH, 50 °C, 4 h, 10 95%, (c) nBuLi then S8, THF, -78 °C,
12 h, 11 80%, (d) nBu3P, 195 °C, 3 h, 3 39%.
to give silyl ether 5. Radical dibromination afforded dibromide 6
in 41% yield in two steps. Introduction of a phosphanyl group
was performed by using Ph2PH BH3 with a base,7 and borane
3
parts were removed by heating with DABCO,8 to give phenol 2
in 63% yield in two steps.
Bis[(diphenylphosphanyl)methyl]thiophenol (3) is a known
compound and was prepared according to the literature6 with
modification (Scheme 3). Two phosphanyl groups were intro-
duced by using Ph2PH BH3, and borane parts were removed
3
by heating with diethylamine9 to give bisphosphane 2 in 77%
yield in two steps. Lithium-bromine exchange and successive
treatment with S8 gave bis(phosphane sulfide), and successive
desulfurization10 by nBu3P afforded tridentateligand 3in31%
yield in two steps.
With tridentate ligands in hand, we tried complexation with
[RhCl(cod)2] (Scheme 4). To a solution of O-tridentate ligand 2
in THF, NaH and [RhCl(cod)2] were added at 0 °C. After
stirring for 4 h at room temperature, AgClO4 was added for
counteranion exchange. The crude material was purified by
column chromatography on silica gel to afford the desired
O-bridged dirhodium complex μ-O-1 in 70% yield. The same
procedure was applied with tridentate ligand 3and gave μ-S-1 in
43% yield. Both complexes were obtained as yellow air-stable
crystals that were suitable for X-ray crystallographic analysis.
The ORTEP diagrams of O- and S-bridged dirhodium com-
plexes μ-O-1 and μ-S-1 are shown in Figures 2 and 3, respectively.
X-ray diffraction of complex μ-O-1 shows a quite symmetrical
structure. The sum of three angles, Rh(1)-O(1)-Rh(2) 126.1°,
C(1)-O(1)-Rh(1) 116.4°, and C(1)-O(1)-Rh(2) 117.4°, is
Complex μ-O-1 was also active for hydrosilylation
of a terminal alkene.13 The reaction of alkene 12a and
(11) Fryzuk, M. D.; Jang, M.-L. Can. J. Chem. 1986, 64, 174.
(12) For reviews of transition metal-catalyzed hydrogenation of alkenes,
see: (a) Chessum, N.; Couty, S.; Jones, K. Reduction by Heterogeneous
Catalysis. In Science of Synthsis; Hiemstra, H., Ed.; Georg Thieme Verlag:
Stuttgart, NY, 2002; Vol. 48, p 275. (b) Tsukamoto, M.; M. Kitamura, M.
Reduction by Homogeneous Catalysis or Biocatalysis. In Science of Synthsis;
Hiemstra, H., Ed.; Georg Thieme Verlag: Stuttgart, NY, 2002; Vol. 48, p 341.
(c) Diesen, J. S.; Andersson, P. G. Hydrogenation of Unfunctionalized Alkenes. In
Modern Reduction Methods; Andersson, P. G.; Munslow, I. J., Eds.; Wiely-VCH
Verlag GmbH & Co. KGaA: Weinheim, 2008; p 39.
(7) (a) Imamoto, T.; Oshiki, T.; Onozawa, T.; Kusumoto, T.; Sato, K.
J. Am. Chem. Soc. 1990, 112, 5244. (b) Wyatt, P.; Eley, H.; Charmant, J.;
Daniel, B. J.; Kantacha, A. Eur. J. Org. Chem. 2003, 4216. (c) Clark, T. J.;
Rodezno, J. M.; Clendenning, S. B.; Aouba, S.; Brodersen, P. M.; Lough, A.
J.; Ruda, H. E.; Manners, I. Chem.;Eur. J. 2005, 11, 4526.
(8) Anderson, B. J.; Glueck, D. S.; DiPasquale, A. G.; Rheingold, A.
L. Organometallics 2008, 27, 4992.
(9) Speiser, F.; Braunstein, P. Organometallics 2004, 23, 2625.
(10) Gorla, F.; Venanzil, L. M. Organometallics 1994, 13, 43.
(13) For review of hydrosilylation, see: Mayes, P. A.; Perlmutter, P.
Alkene Reduction: Hydrosilylation. In Modern Reduction Methods;
Andersson, P. G.; Munslow, I. J., Eds.; Wiely-VCH Verlag GmbH & Co.
KGaA: Weinheim, 2008; p 87.

2100 Organometallics, Vol. 29, No. 9, 2010
Zhu et al.
Figure 2. ORTEP drawing of μ-O-1. All hydrogen atoms, solvent molecule, and counteranion are omitted for clarity. Key atoms are
labeled. Selected bond lengths (A) and angles (deg): P(1)-Rh(1) 2.2743(9), P(2)-Rh(2) 2.2791(9), O(1)-Rh(1) 2.1237(19), O(1)-Rh(2)
2.1191(19), C(1)-O(1) 1.370(3); Rh(1)-O(1)-Rh(2) 126.14(9), C(1)-O(1)-Rh(1) 116.47(16), C(1)-O(1)-Rh(2) 117.39(15),
P(1)-Rh(1)-O(1) 88.34(6), P(2)-Rh(2)-O(1) 88.62(6), C(6)-C(7)-P(1) 106.83(19), C(2)-C(8)-P(2) 108.14(19).
Figure 3. ORTEP drawing of μ-S-1. All hydrogen atoms, solvent molecule, and counteranion are omitted for clarity. Key atoms are
labeled. Selected bond lengths (A) and angles (deg): P(1)-Rh(1) 2.3315(14), P(2)-Rh(2) 2.2851(14), S(1)-Rh(1) 2.3549(13),
S(1)-Rh(2) 2.3178(13), C(1)-S(1) 1.780(4); Rh(1)-S(1)-Rh(2) 123.79(5), C(1)-S(1)-Rh(1) 98.43(14), C(1)-S(1)-Rh(2)
118.01(14), P(1)-Rh(1)-S(1) 83.34(5), P(2)-Rh(2)-S(1) 91.65(5), C(6)-C(7)-P(1) 111.6(3), C(2)-C(8)-P(2) 115.3(3).
dimethyl(phenyl)silane gave silane 14 in 39% yield along
with internal alkenes that were obtained by the alkene
isomerization of 12a (34%) (eq 2).
μ-O-1 did not show any reactivity toward them. In conclu-
sion, complex μ-O-1 seemed to be reactive only to com-
pounds that had a simple chemical bond involving a
hydrogen atom: H-H, Si-H, sp-C-H.
The above trials and failures led us to think of chemose-
lective hydrogenation.15 If the catalyst μ-O-1 does not affect
any other functional groups but H2, chemoselective hydro-
genation of functionalized alkenes is possible. With such an
idea, we examined μ-O-1-catalyzed hydrogenation of styr-
enes with a functional group that is normally affected in the
conventional hydrogenation conditions. The results of the
reaction are summarized in Table 1.
When we mixed μ-O-1 with phenylacetylene, the terminal
sp-C-H bond was activated and polymerization proceeded
to give all-trans polyacetylene as the whole product (eq 3).14
Oxidative addition of aryl bromide to a low-valent transi-
tion metal is an important key step for many kinds of
We tried the reactions with a variety of compounds, such
as aryl iodide and acid anhydride; unfortunately, complex
(14) Yashima, E.; Matsushima, T.; Okamoto, Y. J. Am. Chem. Soc.
1997, 119, 6345.

Article
Organometallics, Vol. 29, No. 9, 2010 2101
Table 1. Chemoselective Hydrogenation of Substituted Styrene
so specific to alkenes that the allyl group was reduced without
cleavage of the C-O bond.15a,b,j,n,u,v,x For example, benzyl allyl
carbonate 12g was subjected to the hydrogenation conditions,
and benzyl propyl carbonate 13g was obtained in 98% yield
(eq 4). The carbonyl group of aldehyde 12h was also tolerant of
chemoselective hydrogenation, giving propyloxybenzaldehyde
13h in 97% yield (eq 5).
entry
R
temp
time (h)
yield (%)
1
2
3
4
5
Br
I
NO2
OCH2Ph
12b
12c
12d
12e
12f
rt
50 °C
rt
rt
rt
20
60
22
27
22
98
97
98
99
83
-CtC-SiMe3
transition metal-catalyzed reactions such as cross-coupling
reactions.16 Interestingly, μ-O-1-catalyzed hydrogenation
of alkene did not affect the aryl bromide functionality
(entry 1).15a-d Surprisingly, aryl iodide functionality was
also found to be tolerant in the reaction conditions. This is a very
rare example of chemoselective hydrogenation of alkenes that
possess an sp2-C-I bond in the molecule (entry 2).15f Chemo-
selective hydrogenation was also achieved for styrenes that have
a nitro,15d-f,17 benzyloxy,15f-j,18 or alkynyl group and gave the
corresponding alkanes in satisfactory yields (entries 3-5).
The allyl group is used for protecting hydroxy compounds
such as alcohol and carboxylic acid.19 Deprotection by a
transition metal catalyst is one of the convenient ways to remove
the allyl moiety. However, μ-O-1-catalyzed hydrogenation was
Conclusion
Air-stable O- and S-bridged dirhodium complexes μ-X-1
(X = O, S) were designed and synthesized by using bis[(diphe-
nylphosphanyl)methyl]phenol and -thiophenol, respectively.
Complex μ-O-1 has a symmetrical structure and shows catalytic
activity for chemoselective hydrogenation of alkenes.
(15) For chemoselective hydrogenation, see: (a) Ikawa, T.; Sajiki, H.;
Hirota, K. Tetrahedron 2005, 61, 2217. (b) Sajiki, H.; Ikawa, T.; Yamada, H.;
Tsubouchi, K.; Hirota, K. Tetrahedron Lett. 2003, 44, 171. (c) Kitamura, Y.;
Tanaka, A.; Sato, M.; Oono, K.; Ikawa, T.; Maegawa, T.; Monguchi, Y.; Sajiki, H.
Synth. Commun. 2007, 37, 4381. (d) Burk, M. J.; Gerlach, A.; Semmeril, D.
J. Org. Chem. 2000, 65, 8933. (e) Amer, I.; Bravdo, T.; Blum, J. Tetrahedron
Experimental Section
General Methods. All reactions were performed under a
nitrogen or argon atmosphere. Solvents (toluene, tetrahydro-
furan, Et2O) were purified with a PS-MD-5 slovent purification
system (Innovative Technology, Inc.) prior to use. The compounds
[RhCl(cod)]2,20 3,6 5,21 6,21 9,6 10,6 and 116 were prepared by
literature methods. 1H, 13C, and 31P NMR spectra were
recorded on 400 and 500 MHz spectrometers. The NMR spectra
were recorded in CDCl3. The chemical shift are reported in ppm
ꢀ
Lett. 1987, 28, 1321. (f) Jourdant, A.; Gonzalez-Zamora, E.; Zhu, J. J. Org. Chem.
2002, 67, 3163. (g) Sajiki, H.; Hirota, K. Tetrahedron 1998, 54, 13981. (h) Sajiki,
H.; Hattori, K.; Hirota, K. J. Org. Chem. 1998, 63, 7990. (i) Maki, S.; Okawa, M.;
Matsui, R.; Hirano, T.; Niwa, H. Synlett 2001, 1590. (j) Callis, N. M.; Thiery, E.;
Bras, J. L.; Muzart, J. Tetrahedron Lett. 2007, 48, 8128. (k) Ghosh, A. K.;
Krishnan, K. Tetrahedron Lett. 1998, 39, 947. (l) Misiti, D.; Zappia, G.; Monache,
G. D. Synthesis 1999, 873. (m) Maki, S.; Harada, Y.; Hirano, T.; Niwa, H.; Yoshida,
Y.; Ogata, S.; Nakamatsu, S.; Inoue, H.; Iwakura, C. Synth. Commun. 2000, 30,
3575. (n) Shinada, T.; Hayashi, K.; Yoshida, Y.; Ohfune, Y. Synlett 2000, 1506. (o)
Hattori, K.; Sajiki, H.; Hirota, K. Tetrahedron 2000,56, 8433. (p) Maki, S.; Harada,
Y.; Matsui, R.; Okawa, M.; Hirano, T.; Niwa, H.; Koizumi, M.; Nishiki, Y.; Furuta,
T.; Inouec, H.; Iwakura, C. Tetrahedron Lett. 2001,42, 8323. (q) Maki, S.; Okawa,
M.; Makii, T.; Hirano, T.; Niwa, H. Tetrahedron Lett. 2003,44, 3717. (r) Sajiki, H.;
Ikawa, T.; Hirota, K. Tetrahedron Lett. 2003, 44, 8437. (s) Bras, J. L.; Mukherjee,
1
against TMS (δ = 0) for H and the residual solvent signal
(using CDCl3, δ = 77) for 13C as internal standard, and 85%
H3PO4 (δ = 0) for 31P as external standard. Melting points were
measured in sealed glass tubes without correction.
tert-Butyl(2,6-dimethylphenoxy)dimethylsilane (5).21 To a so-
lution of 2,6-dimethylphenol (7.50 g, 61.4 mol) and imidazole
(5.81 g, 85.4 mmol) in DMF (250 mL) at 0 °C was added
tBuMe2SiCl (11.7 g, 77.7 mmol). The solution was stirred for
12 h at 50 °C. Then the solution was quenched with saturated
aqueous NH4Cl, and the organic layer was extracted with Et2O.
The combined organic extracts were washed with water and dried
over MgSO4. The solvent was removed under reduced pressure,
and the residue was purified by column chromatography on silica
gel (hexane-ethyl acetate, 24:1) to afford tert-butyl(2,6-dimethyl-
phenoxy)dimethylsilane as colorless oil (13.6 g, 57.4 mmol) in
93% yield.: 1H NMR (400 MHz, CDCl3) δ 0.19 (6H, s), 1.03 (9H,
s), 2.12 (6H, s), 6.79 (1H, t, J = 7.6 Hz), 6.96 (2H, d, J = 7.6 Hz).
[2,6-Bis(bromomethyl)phenoxy](tert-butyl)dimethylsilane (6).21
To a CCl4 solution (90 mL) of tert-butyl(2,6-dimethylphenoxy)-
dimethylsilane (13.6 g, 57.4 mol) were added NBS (20.8 g, 114.9
mmol) and a catalytic amount of AIBN (0.94 g, 5.7 mmol), and the
mixture was refluxed for 6 h. Then the solution was filtered by
Celite and the solvent was removed under reduced pressure. The
residue was purified by column chromatography on silica gel
(hexane-ethyl acetate, 19:1) to afford [2,6-bis(bromomethyl)phe-
noxy](tert-butyl)dimethylsilane as colorless oil (10.9 g, 27.6 mol) in
ꢀ
~
D. K.; Gonzalez, S.; Tristany, M.; Ganchegui, B.; Moreno-Manas, M.; Pleixats, R.;
ꢀ
Henin, F.; Muzart, J. New J. Chem. 2004, 28, 1550. (t) Miyazaki, Y.; Hagio, H.;
Kobayashi, S. Org. Biomol. Chem. 2006, 4, 2529. (u) Mori, A.; Miyakawa, Y.;
Ohashi, E.; Haga, T.; Maegawa, T.; Sajiki, H. Org. Lett. 2006,8, 3279. (v) Mori, A.;
Mizusaki, T.; Miyakawa, Y.; Ohashi, E.; Haga, T.; Maegawa, T.; Monguchi, Y.;
Sajiki, H. Tetrahedron 2006, 62, 11925. (w) Sajiki, H.; Hattori, K.; Hirota, K.
Chem.;Eur. J. 2006, 6, 2200. (x) Erathodiyil, N.; Ooi, S.; Seayad, A. M.; Han, Y.;
Lee, S. S.; Ying, J. Y. Chem.;Eur. J. 2008, 14, 3118. (y) Akao, A.; Sato, K.;
Nonoyama, N.; Mase, T.; Yasuda, N. Tetrahedron. Lett. 2006, 47, 969. (z) Corma,
ꢀ
ꢀ
A.; Gonza-Arellano, G.; Iglesias, M.; Sanchez, F. Appl. Catal., A 2009, 356, 99.
(16) (a) Metal-Catalyzed Cross-Coupling Reactions; De Meijere, A.;
Diederich, F., Eds.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim,
2004. (b) Buchwald, S. L. Acc. Chem. Res. 2008, 41, 1439.
(17) The nitro group is reduced in the normal hydrogenation condi-
tions using palladium complexes as the catalysts; see: (a) Erion, M. D.;
Dang, Q.; Reddy, M. R.; Kasibhatla, S. R.; Huang, J.; Lipscomb, W. N.;
Van Poelje, P. D. J. Am. Chem. Soc. 2007, 129, 15480. (b) Takasaki, M.;
Motoyama, Y.; Higashi, K.; Yoon, S.-H.; Mochida, I.; Nagashima, H. Org.
Lett. 2008, 10, 1601.
(18) The benzyl group is used as the protecting group for hydroxy
compounds and easily removed in hydrogenation conditions; see: (a) Buchi,
G.;Weinreb, S. M. J. Am. Chem. Soc. 1971, 93, 746. (b)Barrero, A. F.;Alvarez-
Manzaneda, E. J.; Chahboun, R. Tetrahedron Lett. 1997, 38, 8101.
(19) (a) Dufour, M.; Gramain, J.-C.; Husson, H.-P.; Sinibaldi, M.-E.;
Troin, Y. Tetrahedron Lett. 1989, 30, 3429. (b) Ziegler, F. E.; Brown, E. G.;
Sobolov, S. B. J. Org. Chem. 1990, 55, 3961. (c) Mereyala, H. B.; Guntha, S.
Tetrahedron Lett. 1993, 34, 6929.
(20) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1979, 19, 218.
(21) Weng, X.; Ren, L.; Weng, L.; Huang, J.; Zhu, S.; Zhou, X.;
Weng, L. Angew. Chem., Int. Ed. 2007, 46, 8020.

2102 Organometallics, Vol. 29, No. 9, 2010
Zhu et al.
48% yield: 1H NMR (500 MHz, CDCl3) δ 0.29 (6H, s), 1.09 (9H,
s), 4.52 (4H, s), 6.99 (1H, t, J = 7.6 Hz), 7.37 (2H, d, J = 7.6 Hz);
13C NMR (125 MHz, CDCl3) δ -3.4, 18.9, 26.0, 29.2, 122.5, 129.2,
132.3, 150.8. Anal. Found: C, 42.72; H, 5.63. Calcd for C14H22-
Br2OSi: C, 42.65; H, 5.62.
(202 MHz, CDCl3) δ 46.2 (2P, d, J = 165 Hz, CH2PPh2). For μ-O-
1 AcOEt, Anal. Found: C, 56.61; H, 5.28. Calcd for C52H59O7-
ClRh2P2: C, 56.82; H, 5.41. Crystal data for μ-O-1 2CHCl3:
3
3
C50H53Cl7O5P2Rh2, fw = 1249.83, triclinic, space group P1, a=
13.389(4) A, b= 13.783(4) A, c= 14.458(4) A, β = 79.395(8)°,
V = 2564.1(14) A3, Z = 2, Dcalcd = 1.619 g/cm3, temperature
-153 °C, μ(Mo KR) = 1.117 mm-1, R1=0.0308, wR2=0.0751
for 8705 reflections with I >2σ(I).
2,6-Bis[(boronatediphenylphosphanyl)methyl]phenol (7). To a
stirred solution of [2,6-bis(bromomethyl)phenoxy](tert-butyl)-
dimethylsilane (4.14 g, 10.5 mmol) in toulene-H2O (200 mL,
1:1) were added diphenylphosphine-borane (4.46 g, 22.3 mmol),
KOH (100 g, 1.53 mol), and a catalytic amount of tetrabutyl-
ammonium bromide (338 mg, 1.05 mmol). The solution was
stirred for 7 h at 50 °C. Then the solution was quenched with
saturated aqueous NH4Cl, and the organic layer was extracted
with Et2O. The combined organic extracts were washed with
water and dried over MgSO4. The solvent was removed under
reduced pressure, and the residue was purified by column
chromatography on silica gel (hexane-ethyl acetate, 7:1) to
afford 2,6-bis[(boronatediphenylphosphanyl)methyl]phenol as
white crystals (4.68 g, 9.0 mmol) in 86% yield: mp 148-150 °C
(dec); IR (ZnSe) 3419, 2382, 1589, 1464, 1437, 1107, 1057, 904,
860, 723 cm-1; 1H NMR (500 MHz, CDCl3) δ 1.00 (6H, br), 3.65
(4H, d, J = 12.1 Hz), 5.82 (1H, brs), 6.49 (1H, t, J = 7.6 Hz),
6.65 (2H, dt, J = 1.9, 7.6 Hz), 7.38-7.41 (8H, m), 7.45-7.48
(4H, m), 7.61-7.65 (8H, m); 13C NMR (125 MHz, CDCl3) δ =
28.1 (d, J = 34.1 Hz), 121.0 (t, J = 2.3 Hz), 122.3 (dd, J = 2.6, 4.2
Hz), 128.3 (d, J = 55.2 Hz), 128.6 (t, J = 9.8 Hz), 130.6 (t,
J = 3.4 Hz), 131.3 (d, J = 1.9 Hz), 132.5 (d, J = 8.8 Hz), 152.4 (t,
J = 4.7 Hz); 31P NMR (202 MHz, CDCl3) δ 17.5. Anal. Found: C,
74.12; H, 6.85. Calcd for C32H34B2OP2: C, 74.17; H, 6.61.
2,6-Bis[(diphenylphosphanyl)methyl]phenol (2). To a solution
of 2,6-bis[(boronatediphenylphosphanyl)methyl]phenol (1.31 g,
2.5 mmol) in CH2Cl2 (10 mL) at 0 °C was added [2.2.2]-diazabi-
cyclooctane (1.10 g, 9.8 mmol). The solution was stirred for 12 h at
50 °C. The solvent was removed under reduced pressure, and the
residue was purified by column chromatography on silica gel
(hexane-ethyl acetate, 7:1) under an Ar atmosphere at 0 °C to
afford 2,6-bis[(diphenylphosphanyl)methyl]phenol as a white solid
(966 mg, 1.97 mmol) in 78% yield: IR (NaCl) 3361, 3016, 1461,
2,6-Bis[(boronatediphenylphosphanyl)methyl]bormobenzene (9).6
To a stirred solution of 2-bromo-1,3-bis(bromomethyl)benzene
(2.06 g, 6.0 mmol) in toulene-H2O (60 mL, 5:1) were added
phosphineborane (2.64 g, 13.2 mmol), KOH (20.0 g, 30.6 mmol),
and a catalytic amount of terabutylammonium bromide (193 mg,
0.60 mmol). The solution was stirred for 20 h at room temperature.
Then the organic phase was separated, and the aqueous layer was
extracted with Et2O. The combined organic extracts were washed
with water and dried over MgSO4. The solvent was removed under
reduced pressure, and the residue was purified by column chroma-
tography on silica gel (hexane-ethyl acetate, 8:1) to afford 2,6-
bis[(boronatediphenylphosphanyl)methyl]bromobenzene (2.64 g,
1
4.3 mmol) as white crystals in 72% yield: H NMR (500 MHz,
CDCl3) δ 0.60-1.40 (6H, br), 3.82 (4H, d, J = 12.0 Hz), 6.96-7.02
(3H, m), 7.37-7.41 (8H, m), 7.46-7.49 (4H, m), 7.51-7.61 (8H,
m); 13C NMR (125 MHz, CDCl3) δ 34.4 (d, J = 17.0 Hz), 126.2 (d,
J = 2.6 Hz), 128.3 (d, J = 54.1 Hz), 128.6 (d, J = 9.7 Hz), 128.9 (t,
J = 6.0 Hz), 130.6 (t, J = 3.5 Hz), 131.3 (d, J = 2.4 Hz), 132.7 (d,
J = 8.9 Hz), 133.3 (dd, J = 1.9, 3.5 Hz); 31P NMR (202 MHz,
CDCl3) δ 17.1. Anal. Found: C, 66.26; H, 5.94. Calcd for
C32H33B2BrP2: C, 66.14; H, 5.72.
2,6-Bis[(diphenylphosphanyl)methyl]bromobenzene (10).6
A
solution of 2,6-bis[(boronatediphenylphosphanyl)methyl]bro-
mobenzene (2.11 g, 3.6 mmol) in degassed Et2NH (30 mL) was
stirred for 2 h at 50 °C. The solvent was removed under reduced
pressure, and to the residue was added hexane. The resulting white
solid was filtered off under Ar and dried to afford 2,6-bis[(di-
phenylphosphanyl)methyl]bromobenzene as a colorless oil (1.81 g,
3.3 mmol) in 91% yield: 1H NMR (500 MHz, CDCl3) δ 3.60 (4H,
s), 6.55 (2H, d, J = 7.5 Hz), 6.72 (1H, t, J = 7.5 Hz), 7.31-7.45
(20H, m); 31P NMR (202 MHz, CDCl3) δ -16.0.
1
1434, 1216, 908, 747 cm-1; H NMR (500 MHz, CDCl3) δ 3.44
(4H, s), 6.51 (1H, t, 7.5 Hz), 6.64 (2H, d, J = 7.5 Hz), 7.30-7.35
(12H, m), 7.38-7.42 (8H, m); 13C (125 MHz, CDCl3) δ 31.1 (d,
J = 12.5 Hz), 120.6 (s, J = 2.6 Hz), 124.5 (d, J = 5.0 Hz), 128.4 (d,
J = 6.8 Hz), 128.8 (t, J = 6.0 Hz), 129.1 (dd, J = 2.0 Hz, 6.3 Hz),
132.9 (d, J = 2.4 Hz), 137.6 (d, J = 12.4 Hz), 152.1 (t, J = 3.5 Hz);
31P (202 MHz, CDCl3) δ -17.5; HRMS (ESI) m/z calcd for
C32H28OP2 (M þ H) 491.1694, found 491.1689.
2,6-Bis[(diphenylthioxophosphanyl)methyl]benzenethiol (11).6
To a stirred solution of 2,6-bis[(diphenylphosphanyl)methyl]-
bromobenzene (1.81 g, 3.3 mmol) in THF (10 mL) was added
nBuLi (2.5 mL, 1.6 M in hexane) at -78 °C. The solution was
stirred for 6 h at -78 °C. To the solution was added S8 (839 mg,
3.3 mmol), and the mixture was warmed to room temperature
and stirred overnight. The solution was added to a suspension
of LiAlH4 (1.74 g, 46.0 mmol) in Et2O (5 mL). The suspension
was stirred 4 h, and any excess LiAlH4 was filtered off. To the
filtrate were added water and concentrated aqueous HCl at
0 °C, the organic phase was separated, and the aqueous layer
was extracted with Et2O. The combined organic extracts were
washed with water and dried over MgSO4. The solvent was
removed under reduced pressure to afford 2,6-bis[(diphenyl-
thioxophosphanyl)methyl]benzenethiol (1.53 g, 2.7 mmol) in 82%
yield: 1H NMR (500 MHz, CDCl3) δ 4.35 (4H, d, J = 13.6 Hz),
6.72-6.76 (3H, m), 7.43-7.48 (8H, m), 7.51-7.54 (4H, m),
7.34-7.82 (8H, m); 31P NMR (202 MHz, CDCl3) δ 39.2.
{Rh2(1,5-cyclooctadiene)2[2,6-(Ph2PCH2)2C6H3O]}(ClO4)
(μ-O-1). To a solution of 2,6-bis[(diphenylphosphanyl)me-
thyl]phenol (929 mg, 1.89 mmol) in THF (20 mL) at 0 °C were
added sodium hydride (54 mg, 2.27 mmol) and [RhCl(cod)]2 (932
mg, 1.89 mmol). The solution was stirred for 4 h at room tempera-
ture. To the solution was added AgClO4 (431 mg, 2.08 mmol), and
the reaction mixture was stirred for 1 h. Then the solution was
filtered by Celite and washed with CH2Cl2 (40 mL), and the solvent
was removed under reduced pressure. The residue was purified by
column chromatography on silica gel (hexane-ethyl acetate, 3:1, to
ethyl acetate only) to afford {Rh2(1,5-cyclooctadiene)2[2,6-(Ph2P-
CH2)2C6H3O]}(ClO4) as a yellow crystals in 70% yield (1.34 g, 1.3
mol): mp 201-202 °C (dec); IR (NaCl) 3019, 2401, 1445, 1437,
1212, 1102757, 669 cm-1;1H NMR (500 MHz, CDCl3) δ1.98-2.65
(16H, m, CH2 (cod)), 3.11 (2H, dd, J = 12.9, 15.7 Hz, CHHPPh2),
3.26 (2H, br, dCH (cod)), 3.31 (2H, br, dCH (cod)), 3.44 (2H, dd,
J=4.1, 12.9Hz, CHHPPh2),5.67(2H,br,dCH(cod)), 6.22(1H, t,
J=7.5Hz, OC6H3), 6.32 (2H, d, J=7.5Hz, OC6H3), 6.62(2H, br,
dCH (cod)), 7.29-7.56 (20H, m, P(C6H5)2); 13C NMR (125 MHz,
CDCl3, selected) δ 27.9 (2C, s, CH2 (cod)), 29.0 (2C, s, CH2 (cod)),
30.5 (2C, d, J=21Hz, CH2PPh2), 32.4 (2C, s, CH2 (cod)),32.4(2C,
s, CH2 (cod)), 67.5 (2C, d, J = 13.5 Hz, dCH (cod)), 73.1 (2C, d,
J = 14.1 Hz, dCH (cod)), 107.1 (2C, dd, J = 12.8, 21.6 Hz, dCH
(cod)), 109.6 (2C, dd, J = 15.5, 15.5 Hz, dCH (cod)); 31P NMR
2,6-Bis[(diphenylphosphanyl)methyl]benzenethiol (3). 6 To 2,6-
bis[(diphenylthioxophosphanyl)methyl]benzenethiol (640 mg,
1.12 mmol) was added nBu3P (2 mL) under Ar, and the solution
n
was stirred for 3 h at 195 °C. The excess Bu3P was removed
under reducedpressure, andtothe residuewasaddeddrydegassed
methanol. The resulting white solid was filtered off under Ar to
afford 2,6-bis[(diphenylphosphanyl)methyl]benzenethiol (230 mg,
0.45 mmol) in 40% yield: 1H NMR (500 MHz, CDCl3) δ 3.65 (4H,
s), 6.50 (2H, d, J = 7.55 Hz), 6.64 (1H, t, J = 7.55 Hz), 7.31-7.41
(20H, m); 31P NMR (202 MHz, CDCl3) δ -15.8.
{Rh2(1,5-cyclooctadiene)2[2,6-(Ph2PCH2)2C6H3S]}(ClO4) (μ-S-1).
To a solution of 2,6-bis[(diphenylphosphanyl)methyl]benzene-
thiol (77.0 mg, 0.15 mmol) in THF (5 mL) at 0 °C were added

Article
Organometallics, Vol. 29, No. 9, 2010 2103
sodium hydride (4.4 mg, 0.18 mmol) and [RhCl(cod)]2 (75.0 mg,
0.15 mmol). The solution was stirred for 4 h at room tempera-
ture. To the solution was added AgClO4 (35.0 mg, 0.17 mmol),
and the mixture was stirred for 1 h. Then the solution was
filtered by Celite and washed with THF, and the solvent was
removed under reduced pressure. The residue was purified by
column chromatography on silica gel (hexane-ethyl acetate,
3:1, to ethyl acetate only) to afford {Rh2(1,5-cyclooctadiene)2-
[2,6-(Ph2PCH2)2C6H3S]}(ClO4) (57.3 mg, 0.06 mol) in 43%
yield as a yellow crystal: mp 211 °C (dec); IR (ZnSe) 3055,
oxide (dichloromethane only) to afford polyphenylacetylene as
a sticky brown oil (9.5 mg) in 93% yield: IR (NaCl) 3019, 1598,
1492, 1216, 1027, 756, 699 cm-1; 1H NMR (400 MHz, CDCl3) δ
5.85 (1H, s), 6.63-6.65 (2H, m), 6.94-7.01 (3H, m); 13C NMR
(100 MHz, CDCl3) δ 126.7, 127.5, 127.8, 131.8, 139.3, 142.9.
General Procedure of {Rh2(1,5-cyclooctadiene)2[2,6-(Ph2P-
CH2)2C6H3O]}(ClO4)-Catalyzed Hydrogenation. Under 1 atm of
H2, to a THF solution (3 mL) of 4-bromostyrene (54.9 mg, 0.30
mmol) was added {Rh2(1,5-cyclooctadiene)2[2,6-(Ph2PCH2)2C6-
H3O]}(ClO4) (30.3 mg, 0.03 mmol), and the mixture was stirred
at room temperature for 20 h. After evaporation of the solvent, the
crude products were purified by column chromatography on silica
gel (hexane only) to afford 1-bromo-4-ethylbenzene (54.4 mg,
0.29 mmol) in 98% yield.
1
2881, 1571, 1481, 1432, 1087, 694 cm-1; H NMR (500 MHz,
CDCl3) δ 2.10-2.51 (16H, m, CH2 (cod)), 3.41 (2H, br, dCH
(cod)), 3.46-3.53 (2H, m, CHHPPh2), 3.72-3.77 (2H, m,
CHHPPh2), 3.72-3.77 (2H, br, dCH (cod)), 5.35 (2H, br,
dCH (cod)), 5.70 (2H, br, dCH (cod)), 6.69-6.72 (3H, m,
SC6H3), 7.28-7.68 (20H, m, P(C6H5)2); 13C NMR (125 MHz,
CDCl3, selected) δ 28.7 (2C, s, CH2 (cod)), 30.1 (2C, s, CH2 (cod)),
31.8 (2C, s, CH2 (cod)),32.4(2C,s,CH2 (cod)),35.9(2C,d,J=27.2
Hz, CH2PPh2), 78.8 (2C, d, J = 11.3 Hz, dCH (cod)), 83.3 (2C, d,
J = 12.1 Hz, dCH (cod)), 103.6 (2C, dd, J = 6.8, 12.2 Hz, dCH
(cod)), 107.7 (2C, dd, J = 6.7, 10.6 Hz, dCH (cod)); 31P NMR (202
MHz, CDCl3) δ 51.0 (2P, d, J = 155 Hz, CH2PPh2). Crystal data
1-Bromo-4-ethylbenzene (13b):15c colorless oil; IR (ZnSe)
2966, 1487, 1072, 1011, 820, cm-1; 1H NMR (500 MHz, CDCl3)
δ 1.22 (3H, t, J = 7.6 Hz), 2.60 (2H, q, J = 7.6 Hz), 7.07 (2H, d,
J = 8.3 Hz), 7.39 (2H, d, J = 8.3 Hz); 13C NMR (125 MHz,
CDCl3) δ 15.5, 28.3, 119.2, 129.6, 131.3, 143.1.
1-Ethyl-4-iodobenzene (13c):24 colorless oil; IR (ZnSe) 2964,
1646, 1483, 1400, 1061, 1007, 817, cm-1; 1H NMR (500 MHz,
CDCl3) δ 1.21 (3H, t, J = 7.6 Hz), 2.59 (2H, d, J = 7.6 Hz), 6.95
(2H, d, J = 7.1 Hz), 7.59 (2H, d, J = 7.1 Hz); 13C NMR (125
MHz, CDCl3) δ 15.4, 28.4, 90.5, 130.0, 137.3, 143.8.
for μ-S-1 CH2Cl2:C49H53Cl3O4P2Rh2S, fw =1112.08, monoclinic,
3
space group P21/n, a = 13.427(6) A, b = 24.331(10) A, c =
=
14.036(6) A, β = 99.584(2)°, V = 4522(3) A3, Z = 4, Dcalcd
1-(Benzyloxy)-4-ethylbenzene (13d):25 colorless oil; IR
1.634 g/cm3, temperature -153 °C, μ(Mo KR) = 1.070 mm-1
,
(ZnSe) 2962, 1610, 1508, 1234, 1174, 1024, 827, 694 cm-1; H
1
R1 = 0.0450, wR2 = 0.1076 for 26 570 reflections with I >2σ(I).
1-Butylnapthalene (13a).22 Under 1 atm of H2, to a toluene
solution (1.5 mL) of 1-(but-3-en-1-yl)naphthalene (18.2 mg, 0.10
mmol) was added {Rh2(1,5-cyclooctadiene)2[2,6-Ph2PCH2)2-
C6H3O]} (ClO4) (10.1 mg, 0.01 mmol), and the mixture was
stirred at room temperature for 5 h. After evaporation of the
solvent, the crude products were purified by column chroma-
tography on silica gel (hexane only) to afford 1-butylnapthalene
(17.6 mg, 0.095 mmol) as a colorless oil in 96% yield: IR (NaCl)
2956, 2870, 1596, 1510, 1466, 1396, 1165, 1013 cm-1; 1H NMR
(400 MHz, CDCl3) δ 0.99 (3H, t, J = 7.6 Hz), 1.48 (2H, m), 1.75
(2H, m), 3.09 (2H, t, J = 7.6 Hz), 7.34 (1H, d, J = 6.8 Hz), 7.41
(1H, t, J = 8 Hz), 7.51 (2H, m), 7.72 (1H, d, J = 8.4 Hz), 7.86
(1H, t, J = 1.2 Hz), 8.07 (1H, d, J = 8.4 Hz); 13C NMR (100
MHz, CDCl3) δ 14.0, 22.9, 33.0, 123.9, 125.3, 125.5, 125.6,
125.8, 126.4, 128.7, 131.9, 133.9, 139.0.
NMR (500 MHz, CDCl3) δ 1.21 (3H, t, J = 7.6 Hz), 2.59 (2H, d,
J = 7.6 Hz), 5.04 (1H, s), 6.90 (2H, d, J = 8.7 Hz), 7.11 (2H, d, J =
8.7 Hz), 7.30-7.33 (1H, m), 6.95 (2H, d, J = 7.1 Hz), 7.59 (2H, d,
J = 7.1 Hz); 13C NMR (125 MHz, CDCl3) δ 15.9, 28.0, 70.0, 114.7,
127.5, 127.9, 128.5, 128.7, 136.7, 137.2, 156.8.
1-Ethyl-4-nitrobenzene (13e):26 colorless oil; IR (ZnSe) 2970,
1
2360, 1599, 1512, 1340, 1109, 849, 694 cm-1; H NMR (500
MHz, CDCl3) δ 1.28 (3H, t, J=7.6 Hz), 2.76 (2H, q, J=7.6 Hz),
7.35 (2H, d, J = 8.8 Hz), 8.15 (2H, d, J = 8.8 Hz); 13C NMR
(125 MHz, CDCl3) δ 15.0, 28.8, 123.6, 128.6, 146.2, 152.0.
1-Ethyl-4-trimethylsilylethynylbenzene (13f):27 colorless oil;
IR (NaCl) 2963, 2156, 1607, 1504, 1250, 760, 689 cm-1; 1H NMR
(400 MHz, CDCl3) δ0.26 (9H, s), 1.23 (3H, t, J=7.6Hz), 2.64(2H,
q, J = 7.6 Hz), 7.13 (2H, d, J = 8.0 Hz), 7.39 (2H, d, J = 8.0 Hz);
13C NMR (100 MHz, CDCl3) δ 0.0, 15.3, 28.8, 93.2, 105.4, 120.3,
127.7, 131.9, 144.9.
Dimethyl[4-(naphthalen-1-yl)butyl]phenylsilane (14). To a to-
luene solution (1.5 mL) of 1-(but-3-en-1-yl)naphthalene (18.2 mg,
0.10 mmol) was added {Rh2(1,5-cyclooctadiene)2[2,6-(Ph2PCH2)2-
C6H3O]}(ClO4) (10.1 mg, 0.01 mmol) and dimethyphenylsilane
(15.0 mg, 0.11 mmol), and the mixture was stirred at room tempe-
rature for 3 days. After evaporation of the solvent, the crude pro-
ducts were purified by colummn chromatography on silica gel
(hexane only) to afford dimethyl(4-(naphthalen-1-yl)butyl)(phenyl)-
silane (13.0 mg, 0.04 mmol) as a colorless oil in 43% yield: IR
(NaCl) 3018, 2931, 1249, 1216, 1113, 750, 668 cm-1; 1H NMR (400
MHz, CDCl3) δ 0.99 (3H, t, J = 7.6 Hz), 1.48 (2H, m), 1.75 (2H,
m), 3.09 (2H, t, J = 7.6 Hz), 7.34 (1H, d, J = 6.8), 7.41 (1H, t, J=
8.0 Hz), 7.52 (2H, m), 7.72 (1H, d, J = 8.4 Hz), 7.86 (1H, d,
J=7.6Hz), 8.07 (1H, d, J = 8.4 Hz);13C NMR (100 MHz, CDCl3)
δ -3.0, 15.6, 24.1, 32.8, 34.6, 123.9, 125.3, 125.5, 125.6, 125.8,
126.3, 127.7, 128.7, 128.8, 131.9, 133.6, 133.8, 138.9, 139.5; HRMS
(ESI) m/z calcd for C22H26Si (M þ H) 305.1726, found 305.1726.
Benzyl propyl carbonate (13g):28 colorless oil; IR (ZnSe) 2970,
2360, 1739, 1238, cm-1;1H NMR (500 MHz, CDCl3) δ0.96 (3H, t,
J =7.4 Hz), 1.70(2H, tq, J= 6.7, 7.4 Hz), 4.11 (2H, t, J =6.7 Hz),
5.16 (2H, s), 7.26-7.40 (5H, m); 13C NMR (125 MHz, CDCl3) δ
10.2, 22.0, 69.4, 69.7, 128.3, 128.5, 128.6, 135.3, 155.2.
4-Propoxybenzaldehyde (13h):29 colorless oil; IR (ZnSe) 2966,
2360, 1685, 1597, 1577, 1508, 1254, 1213, 1155, 972, 829 cm-1
;
1H NMR (500 MHz, CDCl3) δ 1.58 (3H, t, J = 7.4 Hz), 1.84 (2H,
tq, J = 6.6, 7.4 Hz), 4.01 (2H, t, J = 6.6 Hz), 7.00 (2H, d, J = 8.8
Hz), 7.83 (2H, d, J = 8.8 Hz), 9.88 (1H, s); 13C NMR (125 MHz,
CDCl3) δ 10.4, 22.4, 69.8, 114.7, 129.7, 132.0, 164.2, 190.8.
Acknowledgment. We thank Nanyang Technological
University for their generous financial support.
Supporting Information Available: Representative NMR
spectra and crystallographic data are available free of charge
via the Internet at http://pubs.acs.org.
23
Polyphenylacetylene (15). To a CDCl3 solution (0.5 mL)
of {Rh2(1,5-cyclooctadiene)2[2,6-(Ph2PCH2)2C6H3O]}(ClO4)
(10.1 mg, 0.01 mmol) was added phenylacetylene (10.2 mg,
0.10 mmol), and the mixture was stirred at room temperature
for 3 h. After evaporation of the solvent, the crude products
were purified by column chromatography on neutral aluminum
(24) Abe, T.; Yamaji, T.; Kitamura, T. Bull. Chem. Soc. Jpn. 2003, 76,
2175.
(25) Baggaley, K. H.; Fears, R.; Hindley, R. M.; Morgan, B.;
Murrell, E.; Thorne, D. E. J. Med. Chem. 1977, 20, 1388.
(26) Shi, M.; Cui, S.-C. Adv. Synth. Catal. 2003, 345, 1329.
(27) Gottardo, C.; Kraft, T. M.; Hossain, M. S.; Zawada, P. V.;
Muchall, H. M. Can. J. Chem. 2008, 86, 410.
(22) Xu, H.; Ekoue-Kovi, K.; Wolf, C. J. Org. Chem. 2008, 73, 7638.
(23) Falcon, M.; Farnetti, E.; Marsich, N. J. Organomet. Chem. 2001,
629, 187.
(28) Bratt, M. O.; Taylor, P. C. J. Org. Chem. 2003, 68, 5439.
ꢀ
(29) Bertran, J. F.; Rodrıguez, M. Org. Magn. Reson. 1983, 21, 2.
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