Chemistry Letters Vol.35, No.8 (2006)
871
Cl
Cl
Rh
Rh
´
Me
Me
Me
Me
N
N
N
N
5
6
S. Ohta, T. Yamamoto, I. Kawasaki, M. Yamashita, H. Katsuma,
R. Nasako, K. Kobayashi, K. Ogawa, Chem. Pharm. Bull. 1992,
40, 2681.
Me
Me
9
9
S
S
7
The Ph3CS-terminated alkyl bromide Br(CH2)10SCPh3 was pre-
pared from Ph3CSH, 1,10-dibromodecane (4.4 equiv.), and NaH
(6.9 equiv.) in refluxing THF for 28 h (49% yield): 1H NMR
(300 MHz, CDCl3) ꢁ 7.43–7.40 (m, 6H, phenyl), 7.30–7.17 (m,
9H, phenyl), 3.40 (t, J ¼ 6:9 Hz, 2H, BrCH2), 2.13 (t, J ¼ 7:2 Hz,
2H, SCH2), 1.84 (qn, J ¼ 6:9 Hz, 2H, BrCH2CH2), 1.39–1.18 (m,
14H, SCH2(CH2)7).
Reductive deprotection of the phenylthio group in imidazole 4 with
Bu3SnH in the presence of AIBN (2,20-azobisisobutyronitrile) as a
radical initiator gave 47% yield of the deprotected imidazole, albeit
with Bu3Sn-derived impurities. The tin impurities could not be
separated by several column chromatographies nor several reported
procedures.
Au
Figure 1. Expected gold surface modified with complex 1.
(evaporated onto a Ti-coated glass plate) in a 1.0 mM THF
solution of 1 at rt for 20 h. The XPS (X-ray photoelectron
spectroscopy) analysis of the modified gold surface indicated
the existence of Rh (3d at 308.9 eV), N (1s at 400.9 eV), Cl
(2p at 198.5 eV), and S (2p at 162.9 eV) atoms, confirming the
successful anchoring of the NHC–Rh(I) complex on the surface.
The relative peak intensities are well consistent with the mono-
layer structure as shown in Figure 1.16 Notably, it seems that the
terminal thiolate group forms a stable covalent bond with the
surface Au atoms without coordinating to the rhodium center.
This is the first incorporation of N-heterocyclic carbene metal
complexes into the alkane thiolate monolayer on a gold surface.
In summary, a dimeric N-heterocyclic carbene (NHC)–
rhodium(I) complex connected with a long chain dialkyl disul-
fide linker was synthesized, and used for the preparation of a
Rh-modified alkane thiolate monolayer on a gold surface. Efforts
aimed at catalytic applications of the NHC–rhodium monolayer
are ongoing in our laboratory.
8
9
10 The spectral data for 7: 1H NMR (300 MHz, CDCl3) ꢁ 10.08 (s, 2H,
NCHN), 3.915 (s, 6H, NCH3), 3.925 (s, 6H, NCH3), 2.68 (t, J ¼
7:2 Hz, 4H, CH2S), 2.61 (t, J ¼ 7:2 Hz, 4H, NCCH2), 2.27 (s, 6H,
NCCH3), 1.67 (qn, J ¼ 7:2 Hz, 4H, CH2CH2S), 1.53 (qn, J ¼ 7:2
Hz, 4H, NCCH2CH2), 1.38–1.26 (m, 24H, alkyl CH2); 13C NMR
(75 MHz, CDCl3) ꢁ 136.3 (2C, NCHN), 131.1 (2C, NCCH2),
127.1 (2C, NCCH3), 74.1 (2C, NCCH2), 39.1 (2C, CH2S), 34.1
(2C, NCH3), 34.1 (2C, NCH3), 29.2 (2C), 29.2 (2C), 29.1 (2C),
29.0 (2C), 29.0 (2C), 29.0 (2C), 28.6 (2C), 28.3 (2C), 22.5 (2C,
NCCH3); IR (neat) ꢂ/cmꢁ1 3150 (w), 3017 (w), 2926 (s), 2854
(s), 1630 (m), 1576 (s), 1452 (m), 1415 (m), 1201 (m), 1124 (w),
1088 (w), 807 (s).
b) A. R. Chianese, X. Li, M. C. Janzen, J. W. Faller, R. H. Crabtree,
We thank Prof. K. Shimazu, Dr. Y. Yoshinaga, and Prof.
W. J. Chun, Hokkaido University for the help in XPS measure-
ments. This work was supported by a PRESTO program,
JST (for M.S.) and a Grant-in-Aid for Scientific Research in
the Priority Area ‘‘Conductance of Nano-link Molecules’’
(No. 18041002), the Ministry of Education, Culture, Sports,
Science and Technology (for K.H.).
12 The spectral data for 1: 1H NMR (300 MHz, CDCl3) ꢁ 4.98 (m, 4H,
COD CH), 3.98 (s, 6H, NCH3), 3.96 (s, 6H, NCH3), 3.27 (m, 4H,
COD CH), 2.68 (t, J ¼ 7:2 Hz, 4H, CH2S), 2.50–2.30 (m, 8H,
COD CH2), 2.38 (t, J ¼ 7:2 Hz, 4H, NCCH2), 2.03 (s, 6H, NCCH3),
2.02–1.84 (m, 8H, COD CH2), 1.67 (qn, J ¼ 7:2 Hz, 4H,
CH2CH2S), 1.52–1.16 (m, 28H, alkyl CH2); 13C NMR (75 MHz,
1
References and Notes
CD2Cl2): ꢁ 178.9 (d, JRh{C ¼ 52:1 Hz, 2C, NCRh), 129.1 (2C,
1
1
For reviews, see: a) A. Ulman, in An Introduction To Ultrathin
Organic Films: From Langmuir-Blodgett To Self-Assembly, Aca-
1533. c) A. Ulman, in Thin Films: Self-assembled Monolayers of
Thiols, Academic Press, San Diego, 1998.
NCCH2), 124.9 (2C, CCH3), 97.2 (d, JRh{C ¼ 7:4 Hz, 2C, COD
1
1
CH), 97.2 (d, JRh{C ¼ 6:9 Hz, 2C, COD CH), 67.2 (d, JRh{C
¼
14:9 Hz, 4C, COD CH), 38.7 (2C, CH2S), 34.4 (2C, COD CH2),
34.4 (2C, COD CH2), 32.6 (2C, COD CH2), 32.5 (2C, COD
CH2), 29.1 (4C), 28.9 (2C), 28.8 (2C), 28.8 (6C), 28.5 (2C), 28.5
(2C), 28.1 (2C), 23.1 (2C, NCCH2), 8.4 (2C, NCCH3); HRMS
(ESI, MeOH) Found: 1019.3685. Calcd for C48H82ClN4Rh2S2
(M ꢁ Cl): 1019.3780.
2
For applications to catalysis, see: a) M. Bartz, J. Kuther, R. Seshadri,
¨
13 For the catalytic activities of palladium species toward disulfides,
see: a) H. Kuniyasu, A. Ogawa, S.-I. Miyazaki, I. Ryu, N. Kambe,
c) Y. Gareau, A. Orellana, Synlett 1997, 803.
¨
7623. For studies on other subjects, see: f) M. Maskus, H. D.
M. S. Ennis, T. A. Eberspacher, J. H. Griffin, C. E. D. Chidsey,
i) M. Abe, A. Sato, T. Inomata, T. Kondo, K. Uosaki, Y. Sasaki,
14 For the stoichiometric reactions of rhodium(I) species with diaryl
disulfides, see: H. Seino, T. Yoshikawa, M. Hidai, Y. Mizobe,
15 For the catalytic activities of rhodium species toward dialkyl disul-
16 The XPS characterization is based on the comparison with monolay-
ers consisting of a related structure and with the data for complex 1
deposited on oxidized silicon. Details of surface characterization
will be reported elsewhere.
3
4
W. A. Herrmann, M. Elison, J. Fischer, C. Kocher, G. R. J. Artus,
¨
¨