Characterization of Rh(I) complexes bearing N-2-nitrobenzenesulfonyl substituted, N-heterocyclic carbenes

Article abstract of DOI:10.1016/j.jorganchem.2013.12.024

Synthesis and structural characterization of novel Rh(I) complexes bearing 1,2,4-triazol-3-ylidene or imidazol-2-ylidene substituted with an N-2-nitrobenzenesulfonyl (N-nosyl) group are described. The complexes were characterized by infrared (IR), NMR, an

Full text of DOI:10.1016/j.jorganchem.2013.12.024

Journal of Organometallic Chemistry 753 (2014) 20e26
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Characterization of Rh(I) complexes bearing N-2-nitrobenzenesulfonyl
substituted, N-heterocyclic carbenes
,
b
,
a
a
a,b,
Tetsuo Sato a , Daisuke Yoshioka , Yoichi Hirose , Shuichi Oi
*
**
a Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, 6-6-11 Aramaki-Aoba, Aoba-ku, Sendai 980-8579, Japan
b Environment Conservation Research Institute, Tohoku University, 6-6-11 Aramaki-Aoba, Aoba-ku, Sendai 980-8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis and structural characterization of novel Rh(I) complexes bearing 1,2,4-triazol-3-ylidene or
imidazol-2-ylidene substituted with an N-2-nitrobenzenesulfonyl (N-nosyl) group are described. The
complexes were characterized by infrared (IR), NMR, and single-crystal X-ray diffraction analyses. The
Tolman electronic parameter (TEP) values of both of the 1,2,4-triazol-3-ylidene (2064 cmꢀ1) and imi-
dazol-2-ylidene (2059 cmꢀ1), as determined from the average carbonyl (CO) stretching frequencies for
the corresponding RhCl(NHC)(CO)2 (NHC ¼ N-heterocyclic carbene) complexes, were higher than that of
RhCl(IMes)(CO)2 (IMes ¼ 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (2050 cmꢀ1). As the TEP
values of the NHCs increased, the 13C NMR signal of the carbenic carbon in the corresponding
RhCl(NHC)(cod) (cod ¼ 1,5-cyclooctadiene) and RhCl(NHC)(CO)2 complexes shifted downfield. Moreover,
the crystallographic analysis of the RhCl(NHC)(cod) complexes revealed that one of the S]O bonds in the
sulfonyl group could be conjugated with the NHC frameworks, while the remaining S]O bond conju-
gated with the 2-nitrophenyl groups of the N-nosyl substituent.
Received 22 October 2013
Received in revised form
4 December 2013
Accepted 10 December 2013
Keywords:
N-Heterocyclic carbene
2-Nitrobenzenesulfonyl group
Electronic property
Rhodium complex
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
p-overlaps of the lone pairs of the adjacent N atoms with the
vacant p orbital of the carbene carbon atom, have also been re-
ported in the last decade [5]. The structural modification of the
electron-deficient NHCs can be classified as follows: (i) the ex-
change of NHC backbone; (ii) the incorporation of electronegative
heteroelements to the framework of basic imidazol-2-ylidenes;
and (iii) the substitution of electron-withdrawing groups on the
adjacent N atoms to the carbene carbon atom. A few types of
electron-deficient NHCs bearing N-electron-withdrawing sub-
stituents, such as fluorinated phenyl groups A and nitrated phenyl
groups B, have been reported (Fig. 1) [5p,6]. In the metal-
complexes of these NHCs, the dihedral angles between the N-
substituent and NHC frameworks were in the range 45e90ꢁ in the
solid-state, suggesting that the N-substituents can almost never
conjugate with the NHC frameworks, i.e., they act as an electron-
withdrawing groups because of the inductive effect. Recently, we
synthesized N-2,4-dinitrophenyl (N-DNP)-substituted 1,2,4-
triazol-3-yledene (C) [7] and imidazol-2-ylidene (D) [8], and clar-
Until now, numerous N-heterocyclic carbenes (NHCs) have been
developed [1], because of their important roles in organic chem-
istry as ligands for metal-complex catalysts [2] and organocatalysts
[3]. The typical NHCs, such as 1,3-bis(2,4,6-trimethylphenyl)imi-
dazol-2-ylidene (IMes), have strong
s-donating property that
promotes the oxidative addition of the metal atoms in the metal-
complex catalysts [2,4]. One of the primary factors supporting
the evolution of the NHC chemistry is the high flexibility of the
NHC molecules in designing their electronic and structural prop-
erties [1]. Along with the development of strong
poor -accepting electron-rich NHCs, electron-deficient NHCs with
improved -accepting ability, which involves the decrease in the
s-donating and
p
p
* Corresponding author. Environment Conservation Research Institute, Tohoku
University, 6-6-11 Aramaki-Aoba, Aoba-ku, Sendai 980-8579, Japan. Tel.: þ81 22
795 5874.
ified that the N-DNP group enhanced the p-accepting ability of the
carbenes because of its inductive electron-withdrawing effect.
However, N-electron-withdrawing groups, which can conjugate to
the NHC framework, are expected to decrease the N-to-carbene
** Corresponding author. Department of Applied Chemistry, Graduate School of
Engineering, Tohoku University, 6-6-11 Aramaki-Aoba, Aoba-ku, Sendai 980-8579,
Japan. Tel.: þ81 22 795 5873.
carbon
p-overlaps more efficiently, and therefore, a sulfonyl group
E-mail addresses: tetsuo@aporg.che.tohoku.ac.jp (T. Sato), oishu@aporg.che.
tohoku.ac.jp (S. Oi).
seems to be suitable as the N-electron-withdrawing substituent.
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.12.024

T. Sato et al. / Journal of Organometallic Chemistry 753 (2014) 20e26
21
Scheme 2. Syntheses of Rh(I)eNHC complexes.
Fig. 1. Electron-deficient N-heterocyclic carbenes (NHCs) substituted N-electron-
withdrawing groups.
CO gas through their solutions in CH2Cl2 for the IR or in CDCl3
for the NMR analyses.
2.2. Characterization of Rh(I) complexes
2.2.1. IR analysis
Herein, we evaluate the electronic properties of N-nosyl
substituted 1,2,4-triazol-3-ylidene and imidazol-2-ylidene Rh(I)
complexes by spectroscopic and crystallographic analyses.
First, we evaluated the
s-donor properties of NHC ligands 3a
and 3b by performing the IR spectral analysis of Rh(I)ecarbonyl
complexes 5a and 5b in CH2Cl2. The results were compared to the
corresponding Rh(I)ecarbonyl complexes, 5c and 5d, as well as 5e,
bearing N-DNP-substituted NHC C and D, as well as a common NHC
IMes, respectively. The resulting symmetric and antisymmetric CO
2. Results and discussion
2.1. Syntheses of Rh(I) complexes
We chose two starting materials, 1,2,4-triazole (1a) and imid-
azole (1b), to compare the electronic properties of the NHCs in this
study. N-Nosyl substituted 1,2,4-triazole 2a and imidazole 2b were
obtained by the reactions of 1a and 1b with 2-nitrobenzenesulfonyl
chloride in 61% and 21% yields, respectively (Scheme 1) [9,10]. The
N-nosyl substituted azoles 2a and 2b were methylated with
1.00 equiv. of methyl triflate in CH2Cl2 at room temperature to
afford imidazolium salts 3a$HOTf and 3b$HOTf in 58% and 71%
yields, respectively (Scheme 2).
Two types of Rh(I) complexes were synthesized to evaluate
the electronic properties of the NHCs. The reaction of a mixture
of [RhCl(cod)]2 (cod ¼ 1,5-cyclooctadiene) and 1.00 equiv. of
3a$HOTf or 3b$HOTf with 1.05 equiv. NaHMDS in THF, which
generated NHC 3a or 3b in situ, afforded Rh(I)ecod complexes
RhCl(3a)(cod) (4a) and RhCl(3b)(cod) (4b) in 18% and 69%
yields, respectively. Finally, the Rh(I)ecod complexes 4a and 4b
were converted into Rh(I)ecarbonyl complexes, RhCl(3a)(CO)2
(4a) and RhCl(3b)(CO)2 (4b), in quantitative yields by bubbling
stretching frequencies (
are listed in Table 1. The nav (CO) values of 5a and 5b were 2054.8
and 2049.0 cmꢀ1, i.e., the
-donating ability of 1,2,4-triazol-3-
n (CO)) and the averages of n (CO) (nav (CO))
s
ylidene 3a was weaker than that of imidazol-2-ylidene 3b
(Fig. 2). Furthermore, the nav (CO) values of 5c and 5d were slightly
higher than those of the corresponding complexes, 5c
(2054.4 cmꢀ1) [7] and 5d (2047.1 cmꢀ1) [8], respectively, indicating
that the N-nosyl group decreased the
NHCs more effectively than the N-DNP group. The IR spectra of
Rh(I)eIMes complex 5e was measured in CH2Cl2. The -donating
s-donating ability of the
s
ability of NHCs 3a and 3b were significantly weaker compared to
that of IMes, because the nav (CO) value of 5e (2037.0 cmꢀ1) was
remarkably lower than those of 5a and 5b.
2.2.2. 13C NMR analysis
The 13C NMR chemical shift of the carbenic carbon in the NHC
ligand of Rh(I)eNHC complexes has also been used as an index for
the
s
-donating ability of the NHC ligand [5c,11]. The 13C NMR
chemical shifts of the carbenic carbons in 4aee and 5aee are listed
in Table 2. As the TEP values of the NHCs increased, the carbenic
carbon signals were shifted downfield in the order (d ppm): 4e
Table 1
IR
n (CO) stretching frequencies and TEP values of RhCl(L)(CO)2 5aee in CH2Cl2.
Complex
n
(CO)a
nav (CO)b
TEPc
5a (L ¼ 3a)
2092.4, 2017.2
2086.6, 2011.4
2093.4, 2015.3
2086.6, 2007.5
2078.9, 1995.0
2054.8
2049.0
2054.4
2047.1
2037.0
2064
2059
2064
2058
2050
5b (L ¼ 3b)
5c (L ¼ C) [7]
5d (L ¼ D) [8]
5e (L ¼ IMes)
a
IR CO stretching frequencies in cmꢀ1 (CH2Cl2).
b
The average of
n .
(CO) in cmꢀ1
c
Scheme 1. Preparations of N-2-nitrobenzenesulfonylated 1,2,4-triazole 2a and imid-
azole 2b.
Tolman electronic parameter (TEP) in cmꢀ1 calculated using the equation TEP
(cmꢀ1) ¼ 0.8001 nav (CO) (cmꢀ1) þ 420.0 (cmꢀ1) [1b].

22
T. Sato et al. / Journal of Organometallic Chemistry 753 (2014) 20e26
nitrophenyl groups conjugated with the remaining S]O bond
in the solid state; the dihedral angles C(1)eN(1)eS(1)eO(1) and
C(8)eC(3)eS(1)eO(2) for 4a are ꢀ172.23(13)ꢁ and ꢀ10.24(14)ꢁ,
respectively, and the dihedral angles O(1)eS(1)eN(1)eC(1) and
O(2)eS(1)eC(4)eC(9) for 4b are ꢀ174.84(12)ꢁ and 16.47(15)ꢁ,
respectively, even though most N-aryl substituents bearing
electron-withdrawing group could hardly be conjugated with
their NHC frameworks in solid state [5p,6b,deh,j,k]. These facts
suggested that N-nosyl substituent, because of its mesomeric
and electron-withdrawing effects, effectively decreased the
electron densities of the carbenic carbons. In the
RhCl(NHC)(cod) complexes, because of increase in the
p-back-
donation ability of the NHC ligands, the RheCcarbene bond dis-
tances shortened and the RheCtrans-COD bond distances, between
the Rh atom and the alkene moiety of the cod trans to the NHC
ligand, elongated [5c]. The RheCcarbene bond distances in com-
Fig. 2. Comparison of the nav (CO) values of RhCl(NHC)(CO)2 5aee.
ꢀ
plexes 4aee shortened in the order: 4e (2.0494(16) A) [12] > 4b
(183.6) [5f] < 4d (187.2) [8] < 4b (189.7) < 4c (190.3) [7] < 4a
(197.7), and 5e (177.6) [5f] < 5d (177.9) [8] < 5b (179.9) < 5c (182.7)
ꢀ
ꢀ
ꢀ
(2.0262(2) A) > 4d (2.017(2) A) [8] > 4a (2.0080(15) A) > 4c
ꢀ
(2.003(3) A) [7]; however, this order did not agree with that of
[7] < 5a (186.8). Because the increase in the p-accepting ability of
the TEP values of the corresponding NHCs, which increased in
the order: IMes < D < 3b < C < 3a, i.e., the orders of 4a and 4b
were reversed to 4c and 4d, respectively. The percent buried
volume (%Vbur) values of the NHCs [13], which are indexes of the
steric bulk of ligands calculated by the SambVca program [14]
using the crystallographic data for 4aee, are listed in Table 3.
Because the %Vbur values of 3a (36.0) and 3b (35.2) are 1.20e1.24
times as large as that of C (29.0) [7] and D (29.4) [8], it is assumed
that the steric bulk of the NHC ligands affect the RheCcarbene
bond distances. In contrast, as the TEP values of the ligands
increased, the averages of the RheCtrans-COD bond distances
the NHC ligands in the Rh(I)eNHC complexes shift the 13C NMR
signals of the carbenic carbons to downfield [5c], these results
indicate that the N-substituent increased the
p-accepting ability of
the carbenic carbon in the order: Mes < DNP < nosyl, and the
p
-
accepting ability of 1,2,4-triazol-3-ylidenes are stronger than that
of imidazol-2-ylidenes. Unlike the 13C NMR signals of the carbenic
carbons, the 13C chemical shifts of the alkene moiety of cod trans to
the NHC ligands in 4aee and both carbons of the carbonyls cis and
trans to the NHC ligands in 5aee did not correlate with the
p-
accepting ability of the NHC ligands. The N-nosyl substituent
strongly deshields the carbenic carbon atom compared to N-DNP
and N-mesityl substituents.
ꢀ
ꢀ
lengthened in the order: 4e (2.1971 A) < 4d (2.207 A) < 4b
ꢀ
ꢀ
ꢀ
(2.211 A) < 4c (2.214 A) < 4a (2.2194 A) (Table 3). These changes
in the bond distances with the corresponding changes in the TEP
values of the ligands agree well with the results of NMR analyses.
2.2.3. X-ray diffraction analysis
Single crystals of 4a and 4b suitable for X-ray diffraction
analysis were obtained by the slow diffusion of hexane to their
acetone solution. The ORTEP representations of 4a and 4b are
shown in Figs. 3 and 4, respectively. The selected bond distances
and bond angles of both complexes are listed in the footnotes to
Figs. 3 and 4. In both the complexes, the Rh(I) atoms showed
pseudo-square-planar geometries coordinated to NHC ligand 3a
or 3b, a chloride ligand, and a cod ligand. The dihedral angles
between the NHC framework and the metal-ligand plane were
approximately orthogonal; the dihedral angles Cl(1)eRh(1)e
C(1)eN(1) are 89.21(14)ꢁ and ꢀ86.78(15)ꢁ for 4a and 4b,
respectively. Both the 2-nitrophenyl groups project into the
chloride ligand sides. Moreover, the NHC frameworks could be
conjugated with the S]O bond in the sulfonyl group, and 2-
3. Conclusions
We synthesized and characterized novel Rh(I) complexes
bearing N-nosyl substituted 1,2,4-triazol-3-ylidene 3a and imida-
zol-2-ylidene 3b. The IR analysis of RhCl(NHC)(cod) 4 revealed that
the
s-donating ability of the NHCs decreased in the order:
IMes > N-DNP-substituted imidazol-2-ylidene D > 3b > N-DNP-
substituted 1,2,4-triazol-3-ylidene C > 3a. This result indicates that
the N-nosyl substituent, compared to the N-DNP substituent,
strongly decreases the
analysis supported the IR analysis. The carbenic carbons in 4aee
and RhCl(NHC)(CO)2 5aee were strongly deshielded in the order:
s-donating ability of carbenes. The NMR
Table 2
13C NMR chemical shifts of carbenic carbons and carbonyls in the RhCl(L)(cod) 4aee and the RhCl(L)(CO)2 5aee in CDCl3.
Complex
trans-CHCOD (ppm)
CN2 (ppm)
CO (ppm)
CO (ppm)
4a (L ¼ 3a)
101.3 (1J(Rh,C) ¼ 7.4 Hz)
100.1 (1J(Rh,C) ¼ 6.8 Hz)
99.7 (1J(Rh,C) ¼ 7.6 Hz)
97.8 (1J(Rh,C) ¼ 7.4 Hz)
99.5 (1J(Rh,C) ¼ 7.3 Hz)
99.3 (1J(Rh,C) ¼ 6.2 Hz)
100.4 (1J(Rh,C) ¼ 6.3 Hz)
99.9 (1J(Rh,C) ¼ 7.3 Hz)
96.3
197.7 (1J(Rh,C) ¼ 51.4 Hz)
4b (L ¼ 3b)
189.7 (1J(Rh,C) ¼ 51.3 Hz)
190.3 (1J(Rh,C) ¼ 50.4 Hz)
187.2 (1J(Rh,C) ¼ 52.4 Hz)
4c (L ¼ C) [7]
4d (L ¼ D) [8]
4e (L ¼ IMes) [5f]
5a (L ¼ 3a)
183.6 (1J(Rh,C) ¼ 53 Hz)
186.8 (1J(Rh,C) ¼ 44.0 Hz)
179.9 (1J(Rh,C) ¼ 44.0 Hz)
182.7 (1J(Rh,C) ¼ 44.2 Hz)
177.9 (1J(Rh,C) ¼ 44.0 Hz)
177.6 (1J(Rh,C) ¼ 45 Hz)
184.2 (1J(Rh,C) ¼ 56.6 Hz)
185.0 (1J(Rh,C) ¼ 55.3 Hz)
186.2 (1J(Rh,C) ¼ 55.6 Hz)
184.7 (1J(Rh,C) ¼ 54.7 Hz)
184.7 (1J(Rh,C) ¼ 54 Hz)
181.2 (1J(Rh,C) ¼ 72.9 Hz)
181.8 (1J(Rh,C) ¼ 72.9 Hz)
182.2 (1J(Rh,C) ¼ 76.0 Hz)
181.4 (1J(Rh,C) ¼ 70.4 Hz)
182.7 (1J(Rh,C) ¼ 74 Hz)
5b (L ¼ 3b)
5c (L ¼ C) [7]
5d (L ¼ D) [8]
5e (L ¼ IMes) [5f]

T. Sato et al. / Journal of Organometallic Chemistry 753 (2014) 20e26
23
Table 3
ꢀ
Selected bond lengths (A) and percent buried volume (%Vbur) values in 4aed.
a
Complex
RheCcarbene
RheCtrans-COD
%Vbur
4a
2.0080(15)
2.2197(16)
2.2192(16)
2.221(3)
2.201(2)
2.218(2)
2.209(2)
2.217(2)
2.197(2)
2.2241(18)
2.1701(17)
36.0
4b
2.026(2)
2.003(3)
35.2
29.0
29.4
33.5
4c [7]
4d [8]
4e [17]
2.017(2)
2.0494(16)
a
%Vbur values were calculated with the Bondi radii scaled by 1.17, a sphere of
ꢀ
ꢀ
ꢀ
radius 3.5 A, a mesh size of 0.05 A, and a RheNHC length 2.00 A, and omission of all
hydrogen atoms.
Fig. 3. ORTEP representation of 4a with thermal ellipsoids at 50% probabiliꢁty.
anhydrous and deoxygenated solvents. The 1H (400.03 MHz) and
13C (100.60 MHz) nuclear magnetic resonance (NMR) spectra were
recorded using a Bruker BioSpin AV400 NMR spectrometer. The 1H
ꢀ
Hydrogen atoms have been omitted for clarity. Selected distances (A) and angles ( ):
Rh(1)eC(1) 2.0080(15), Rh(1)eC(10) 2.1227(16), Rh(1)eC(11) 2.1080(16), Rh(1)eC(14)
2.2197(16), Rh(1)eC(15) 2.2192(16), Rh(1)eCl(1) 2.3899(5), C(1)eN(1) 1.3620(19),
C(1)eN(3) 1.3580(19), N(3)eC(1)eN(1) 101.51(12), C(1)eRh(1)eCl(1) 86.07(4), Cl(1)e
Rh(1)eC(1)eN(1) 89.21(14), C(1)eN(1)eS(1)eO(1) ꢀ172.23(13), C(1)eN(1)eS(1)eO(2)
58.51(14), C(1)eN(1)eS(1)eC(3) ꢀ55.81(14), C(4)eC(3)eS(1)eO(1) 28.71(15), C(8)e
C(3)eS(1)eO(2) ꢀ10.24(14).
NMR chemical shift (d) values in ppm are relative to that of tetra-
methylsilane at 0.00 ppm; multiplicities are represented as s
(singlet), d (doublet), t (triplet), q (quartet), quint (quintet), m
(multiplet), and br (broad); coupling constants are represented as
Hz. The 13C{1H} NMR chemical shift (
d
) values in ppm are relative to
that of solvent residual signals for CDCl3 at 77.00 ppm and DMSO-d6
at 39.52 ppm. The 19F{1H} NMR chemical shift (
) values in ppm are
4e, 4d, 4b, 4c, and 4a, and 5e, 5d, 5b, 5c, and 5a, which were the
Rh(I) complexes including IMes, D, 3b, C, and 3a, respectively.
Furthermore, the crystallographic analysis elucidated that one of
the S]O bond in the sulfonyl group conjugated with the NHC
framework, while the remaining S]O bond conjugated with the 2-
nitrophenyl group. Therefore, it is assumed that the N-nosyl sub-
stituent, because of its mesomeric and inductive effects, acts as a
strong electron-withdrawing group.
d
relative to that of fluorotrichloromethane at 0.00 ppm. The high-
resolution mass spectra were obtained using a JEOL JMS-700
spectrometer at the Department of Instrumental Analysis, Tech-
nical Division, School of Engineering, Tohoku University, Japan. The
IR spectra were recorded using a Jasco FT/IR-350 Fourier-transform
infrared spectrophotometer; the absorptions are reported in cmꢀ1
.
The single-crystal X-ray diffraction analyses were carried out using
a Bruker AXS APEX II CCD diffractometer.
4. Experimental
4.1. General information
4.2. Materials
All reactions were carried out under nitrogen atmosphere using
a standard vacuum line, and Schlenk tube techniques, as well as
Dichloromethane (CH2Cl2, anhydrous grade), tetrahydrofuran
(THF, anhydrous grade), sodium bis(trimethylsilyl)amide (NaHMDS,
1.09 M THF solution, Kanto Chemical), N,N-dimethylformamide
(DMF, anhydrous grade), diethyl ether (anhydrous grade), acetone
(anhydrous grade), hexane (anhydrous grade, Wako Pure Chemical),
1,2,4-tiazole (1a), imidazole (1b), 2-nitrobenzenesulfonyl chloride,
triethylamine, methyl triflate (TCI), NaH (55e65%, oil suspension,
Nacalai Tesque) were purchased and used as received without
further purification. [RhCl(cod)]2 was prepared as described in the
literature [15].
4.3. Synthesis of azoles
4.3.1. 1-(2-Nitrobenzenesulfonyl)-1,2,4-triazole (2a)
Following the known procedure [9], in a Schlenk flask (50 mL),
triethylamine (1.52 g, 15.0 mmol) was added to a solution of
1,2,4-triazole (1a) (1.04 g, 15.0 mmol) and 2-nitrobenzenesulfonyl
chloride (3.32 g, 15.0 mmol) in anhydrous CH2Cl2 (30 mL) at 0 ꢁC
and stirred for 12 h at room temperature. Next, the resulting
mixture was added to CH2Cl2 (30 mL) and washed with water
(3 ꢂ 10 mL). The organic layer was dried over anhydrous Na2SO4
and concentrated in vacuo. The crude solid was purified by
recrystallization from acetone/hexane to afford 2a as a colorless
needle (2.34 g, 9.20 mmol, 61%). 1H NMR (400.03 MHz, CDCl3):
Fig. 4. ORTEP representation of 4b with thermal ellipsoids at 50% probabiliꢁty.
ꢀ
Hydrogen atoms have been omitted for clarity. Selected distances (A) and angles ( ):
Rh(1)eC(1) 2.026(2), Rh(1)eC(11) 2.115(2), Rh(1)eC(12) 2.138(3), Rh(1)eC(15)
2.201(2), Rh(1)eC(16) 2.221(3), Rh(1)eCl(1) 2.393(2), C(1)eN(1) 1.390(2), C(1)eN(2)
1.340(2), N(2)eC(1)eN(1) 103.07(14), C(1)eRh(1)eCl(1) 85.23(5), Cl(1)eRh(1)eC(1)e
N(1)
ꢀ86.78(15),
O(1)eS(1)eN(1)eC(1)
ꢀ174.84(12),
O(2)eS(1)eN(1)e
d
8.88 (s, 1H, ArSO2NCHN), 8.51 (dd, 1H, 3J ¼ 7.5 Hz, 4J ¼ 1.8 Hz,
C(1) ꢀ45.80(14), C(4)eS(1)eN(1)eC(1) 68.96(15), O(1)eS(1)eC(4)eC(5) ꢀ24.58(17),
O(2)eS(1)eC(4)eC(9) 16.47(15).
CH3-Ar), 8.08 (s, 1H, NNCHN), 7.99e7.83 (m, 3H, CH4-Ar, CH5-Ar
,

24
T. Sato et al. / Journal of Organometallic Chemistry 753 (2014) 20e26
CH6-Ar). 13C{1H} NMR (100.60 MHz, CDCl3):
137.0, 133.6, 133.2, 128.8, 125.6.
d
154.5, 148.3, 146.4,
4.5. Synthesis of Rh(I)e1,5-cyclooctadiene complexes
4-cycloocta-1,5-diene)[4-methyl-2-(2-
4.5.1. Chloro(
h
4.3.2. 1-(2-Nitrobenzenesulfonyl)imidazole (2b)
nitrobenzenesulfonyl)-1,2,4-triazol-3-ylidene]rhodium(I) (4a)
In a Schlenk flask (50 mL), NaH (360 mg, 15.0 mmol) was added
to a solution of imidazole (1b) (1.02 g, 15.0 mmol) in anhydrous
DMF (15 mL) at 0 ꢁC and stirred for 15 min at same temperature.
Next, 2-nitrobenzenesulfonyl chloride (3.32 g, 15.0 mmol) was
added to the reaction mixture and stirred at room temperature for
1 h. The resulting mixture was poured into ice water (150 mL) and
extracted with toluene (3 ꢂ 45 mL). The combined organic layer
was dried over anhydrous Na2SO4 and concentrated in vacuo. The
crude product was purified by recrystallization from EtOAc/hexane
to afford 2b as a colorless needle (779 mg, 3.08 mmol, 21%). The
characterization of 2b is described in the literature [10]. 1H NMR
In a Schlenk tube (10 mL), NaHMDS (1.09 M in THF, 0.525 mmol,
0.48 mL) was added to a mixture of 3a$HOTf (209 mg, 0.500 mmol)
and [RhCl(cod)]2 (123 mg, 0.250 mmol) in anhydrous THF (7 mL)
at ꢀ78 ꢁC. The reaction mixture was warmed to room temperature
slowly and stirred for 12 h. The resulting salt was filtered off, and
the filtrate was concentrated under reduced pressure. The resulting
crude product was purified by column chromatography (SiO2, first
eluted with CH2Cl2 to remove the impurities followed by CH2Cl2/
acetone
¼
15/1) to afford 4a as a red powder (45.1 mg,
0.0876 mmol, 18%). The single crystals suitable for X-ray diffraction
analysis were obtained by the slow diffusion of hexane to the
(400.03 MHz, CDCl3):
d
(s, NCHN), 8.12 (dd, 1H, 3J ¼ 7.9 Hz,
acetone solution of 4a. 1H NMR (400.03 MHz, CDCl3):
d
8.95e8.87
4J ¼ 1.5 Hz, CH3-Ar), 7.89 (td, 1H, 3J ¼ 7.3 Hz, 4J ¼ 1.5 Hz, CH5-Ar),
7.86e7.79 (m, 2H, CH4-Ar, CH6-Ar), 7.43 (t, 1H, 3J ¼ 1.6 Hz, 4J ¼ 1.6 Hz,
NCHCHN), 7.15 (dd, 1H, 3J ¼ 1.6 Hz, 4J ¼ 0.8 Hz, NCHCHN). 13C{1H}
(m, 1H, CH3-Ar), 8.08 (s, 1H, NCHN), 7.95e7.81 (m, 3H, CH4-Ar, CH5-Ar
,
CH6-Ar), 5.12e4.98 (m,1H, CHCOD), 4.88e4.76 (m, 1H, CHCOD), 4.31 (s,
3H, CH3), 3.96e3.85 (m, 1H, CHCOD), 3.53e3.41 (m, 1H, CHCOD),
2.68e2.40 (m, 3H, CH2COD), 2.36e2.20 (m, 1H, CH2COD), 2.17e2.05
(m, 2H, CH2COD), 2.04e1.84 (m, 2H, CH2COD). 13C{1H} NMR
NMR (100.60 MHz, CDCl3):
131.0, 125.4, 118.2.
d 148.2, 137.6, 136.3, 133.1, 131.4, 131.1,
(100.60 MHz, CDCl3):
d
197.7 (d, 1JRhC ¼ 51.4 Hz, NCN), 148.5, 143.2,
4.4. Synthesis of azolium salts
136.8, 134.0, 132.6, 130.1, 125.8, 101.3 (d, 1JRhC ¼ 7.4 Hz, CHCOD), 100.1
(d, 1JRhC ¼ 6.8 Hz, CHCOD), 71.2 (d, 1JRhC ¼ 14.3 Hz, CHCOD), 71.1 (d,
1JRhC ¼ 13.6 Hz, CHCOD), 37.1, 33.8, 31.9, 29.5, 28.2. IR (KBr): 3067,
2927, 2830, 1543, 1467, 1396, 1360, 1198 cmꢀ1. HRMS (FAB):
[M ꢀ Cl]þ calcd for C17H20N4O4RhS 479.0260; found 479.0255. Anal.
Calcd (%) for C17H20ClN4O4RhS: C 39.66, H 3.92, N 10.88. Found: C
39.42, H 4.07, N 10.74. Mp. 155 ꢁC (dec).
4.4.1. 4-Methyl-1-(2-nitrobenzenesulfonyl)-1,2,4-triazol-4-ium
triflate (3a$HOTf)
In a Schlenk flask (20 mL), MeOTf (197 mg, 1.2 mmol) was added
to
a solution of 1-[(2-nitrobenzene)sulfonyl]imidazole (2a)
(305 mg, 1.20 mmol) in anhydrous CH2Cl2 (15 mL), and the reaction
mixture was stirred at room temperature for 4 h. Next, diethyl ether
(2 mL) was added to the reaction mixture, and the resulting pre-
cipitate was collected and purified by washing with diethyl ether
(2 ꢂ 5 mL). The solid was dried under vacuum to afford 3a$HOTf as
a white powder (479 mg, 1.15 mmol, 58%). 1H NMR (400.03 MHz,
4.5.2. Chloro(h
4-cycloocta-1,5-diene)[1-methyl-3-(2-
nitrobenzenesulfonyl)imidazol-2-ylidene]rhodium(I) (4b)
In a Schlenk tube (10 mL), NaHMDS (1.09 M in THF, 0.315 mmol,
0.29 mL) was added to a mixture of 3b$HOTf (125 mg, 0.300 mmol)
and [RhCl(cod)]2 (74.0 mg, 0.150 mmol) in anhydrous THF (5 mL)
at ꢀ78 ꢁC. The reaction mixture was warmed to room temperature
slowly and stirred for 12 h. The resulting salt was filtered off, and the
filtrate was concentrated under reduced pressure. The resulting
crude product was purified by column chromatography (SiO2, first
eluted with CH2Cl2 to remove the impurities followed by CH2Cl2/
acetone ¼ 15/1) to afford 4b as a red powder (107 mg, 0.208 mmol,
69%). The single crystals suitable for X-ray diffraction analysis were
obtained by the slow diffusion of hexane in an acetone solution of
acetone-d6):
d 10.94 (s, 1H, ArSO2NCHN), 9.42 (s, 1H, NCHNCH3),
8.63 (dd, 1H, 3J ¼ 7.9 Hz, 4J ¼ 1.3 Hz, CH3-Ar), 8.35 (ddd, 1H,
3J ¼ 8.0 Hz, 3J ¼ 7.2 Hz, 4J ¼ 1.3 Hz, CH5-Ar), 8.32 (dd, 1H, 3J ¼ 8.0 Hz,
4J ¼ 1.8 Hz, CH6-Ar), 8.23 (ddd, 1H, 3J ¼ 7.9 Hz, 3J ¼ 7.2 Hz, 4J ¼ 1.8 Hz,
CH4-Ar), 4.36 (s, 3H, CH3). 13C{1H} NMR (100.60 MHz, DMSO-d6):
d
149.2, 148.6, 148.0, 140.6, 138.8, 135.3, 135.3, 127.6, 126.4, 122.1 (q,
1JCF ¼ 320.7 Hz, CF3SO3), 36.3. 19F{1H} NMR (376.37 MHz, DMSO-
d6):
d
ꢀ77.27 (CF3SO3). IR (KBr): 3140, 3106, 1589, 1543, 1355, 1284,
1033 cmꢀ1. HRMS (FAB): [M ꢀ CF3SO3]þ calcd for C9H9N4O4S
269.0345; found 269.0344. Mp: 108 ꢁC.
4b. 1H NMR (400.03 MHz, CDCl3):
d
9.33 (dd, 1H, 3J ¼ 7.8 Hz,
4J ¼ 1.3 Hz, CH3-Ar), 7.96e7.88 (m, 3H, CH4-Ar, CH5-Ar, CH6-Ar), 7.65 (d,
1H, 3J ¼ 2.2 Hz, ArSO2NCHCHNCH3), 6.95 (d, 1H, 3J ¼ 2.2 Hz,
ArSO2NCHCHNCH3), 4.96e4.85 (m, 1H, CHCOD), 4.67e4.56 (m, 1H,
CHCOD), 4.28 (s, 3H, CH3), 4.04e3.91 (m, 1H, CHCOD), 3.57e3.45 (m,
1H, CHCOD), 2.68e2.42 (m, 3H, CH2COD), 2.30e2.16 (m, 1H, CH2COD),
2.16e2.02 (m, 2H, CH2COD), 2.00e1.85 (m, 1H, CH2COD), 1.85e1.72 (m,
4.4.2. 1-Methyl-3-(2-nitrobenzenesulfonyl)imidazol-1-ium triflate
(3b$HOTf)
In a Schlenk flask (20 mL), MeOTf (197 mg, 1.2 mmol) was added
to a solution of 1-[(2-nitrobenzene)sulfonyl]imidazole (2b) (304 mg,
1.20 mmol) in anhydrous CH2Cl2 (10 mL), and the reaction mixture
was stirred at room temperature for 30 min. Next, diethyl ether
(2 mL) was added to the reaction mixture, and the resulting pre-
cipitate was collected and purified by washing with diethyl ether
(2 ꢂ 5 mL). The solid was dried under vacuum to afford 3b$HOTf as a
1H, CH2COD). 13C{1H} NMR (100.60 MHz, CDCl3):
d 189.7 (d,
1JRhC ¼ 51.3 Hz, NCN), 148.1, 136.8, 135.0, 132.4, 130.6, 126.1, 122.9,
121.7, 99.7 (d, 1JRhC ¼ 7.6 Hz, CHCOD), 97.8 (d, 1JRhC ¼ 7.4 Hz, CHCOD),
71.7 (d, 1JRhC ¼ 14.4 Hz, CHCOD), 69.6 (d, 1JRhC ¼ 14.0 Hz, CHCOD), 39.8,
34.0, 31.8, 29.8, 27.8. IR (KBr): 3175, 3109, 2945, 1592, 1381, 1238,
1183, 1150, 1085 cmꢀ1. HRMS (FAB): [M]þ calcd for C18H21ClN3O4RhS
512.9996; found 512.9990. Anal. Calcd (%) for C18H21ClN3O4RhS: C
42.08, H 4.12, N 8.18. Found: C 41.89, H 4.01, N 8.02. Mp. 163 ꢁC (dec).
1
white powder (356 mg, 0.853 mmol, 71%). H NMR (400.03 MHz,
DMSO-d6):
d
9.05 (s, 1H, NCHN), 7.84 (dd, 1H, 3J ¼ 7.8 Hz, 4J ¼ 1.5 Hz,
CH3-Ar), 7.70 (t, 1H, 3J ¼ 1.6 Hz, 4J ¼ 1.6 Hz, NCHCHN), 7.67 (t, 1H,
3J ¼ 1.6 Hz, 4J ¼ 1.6 Hz, NCHCHN), 7.58 (td,1H, 3J ¼ 7.8 Hz, 4J ¼ 1.5 Hz,
CH5-Ar), 7.57 (dd, 1H, 3J ¼ 7.8 Hz, 4J ¼ 1.5 Hz, CH6-Ar), 7.51 (td, 1H,
3J ¼ 7.8 Hz, 4J ¼ 1.5 Hz, CH4-Ar), 3.86 (s, 3H, CH3). 13C{1H} NMR
4.6. Synthesis of Rh(I)ecarbonyl complexes
(100.60 MHz, DMSO-d6):
d 147.8, 139.3, 135.8, 130.8, 130.1, 129.0,
123.2, 122.4, 120.4 (q, JCF ¼ 321.1 Hz, CF3SO3), 119.8, 36.3. 19F{1H}
4.6.1. Chlorodicarbonyl[4-methyl-2-(2-nitrobenzenesulfonyl)-1,2,4-
triazol-3-ylidene]rhodium(I) (5a)
CO gas was bubbled through a solution of 4a (25.7 mg,
0.0500 mmol) in anhydrous CH2Cl2 (2 mL) for the IR or in CDCl3
1
NMR (376.37 MHz, DMSO-d6):
d
ꢀ77.26 (CF3SO3). IR (KBr): 3163,
3085,1594,1549,1413,1260 cmꢀ1. HRMS (FAB): [M ꢀ CF3SO3]þ calcd
for C10H10N3O4S 268.0392; found 268.0394. Mp: 94 ꢁC.

T. Sato et al. / Journal of Organometallic Chemistry 753 (2014) 20e26
25
(2 mL) for the NMR analyses at room temperature for 30 min. The
initial red solution of 5a became a yellow solution (quantitative
yield). The reaction yield was determined by 1H NMR based on COD.
When the solution of 5a was concentrated, 5a decomposed. 1H
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Appendix B. Supplementary data
NMR (400.03 MHz, CDCl3):
d
8.82 (dd, 1H, 3J ¼ 7.9 Hz, 4J ¼ 1.5 Hz,
CH3-Ar), 8.23 (s, 1H, NCHN), 8.01 (dd, 1H, 3J ¼ 7.9 Hz, 4J ¼ 1.6 Hz, CH6-
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.12.024.
Ar), 7.97 (td, 1H, 3J ¼ 7.9 Hz, 4J ¼ 1.5 Hz, CH4-Ar), 7.91 (dd, 1H,
3J ¼ 7.9 Hz, 4J ¼ 1.6 Hz, CH5-Ar), 4.08 (s, 3H, CH3). 13C{1H} NMR
1
(100.60 MHz, CDCl3):
d
186.8 (d, JRhC ¼ 44.0 Hz, NCN), 184.2 (d,
References
1JRhC ¼ 56.6 Hz, CO),181.2 (d, 1JRhC ¼ 72.9 Hz, CO),148.2,143.5,137.6,
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426.9220; found 426.9227.
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0.0500 mmol) inanhydrous CH2Cl2 (2 mL) forthe IRorin CDCl3 (2 mL)
for NMR analyses at room temperature for 30 min. The initial red
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solution of 5b was concentrated, 5b decomposed. 1H NMR
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d
9.04 (dd, 1H, 3J ¼ 7.1 Hz, 4J ¼ 2.3 Hz, CH3-Ar),
8.02e7.88 (m, 3H, CH4-Ar, CH5-Ar, CH6-Ar), 7.82 (d, 1H, 3J ¼ 2.3 Hz,
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ArSO2NCHCHNCH3), 7.07 (d, 1H, d, 1H, 3J
¼
2.3 Hz,
ArSO2NCHCHNCH3), 4.01 (s, 3H, CH3). 13C{1H} NMR (100.60 MHz,
185.0 (d, 1JRhC ¼ 55.3 Hz, CO), 181.8 (d, 1JRhC ¼ 72.9 Hz, CO),
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179.9 (d, 1JRhC ¼ 44.0 Hz, NCN), 147.9, 137.3, 135.0, 133.0, 130.3, 126.3,
123.1, 122.5, 40.4. IR (CH2Cl2): 2086.6 (n (CO)), 2011.4 (n .
(CO)) cmꢀ1
HRMS (FAB): [M ꢀ Cl]þ calcd for C12H9N3O6RhS 425.9267; found
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a
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l
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Acknowledgments
This work was supported in part by a Grant-in-Aid for Scientific
Research on Innovative Areas “Molecular Activation Directed to-
ward Straightforward Synthesis” from MEXT, Japan and by a
commissioned project conducted by New Energy and Industrial
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crystallographic data for this paper. These data can be obtained free

26
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