Synthesis and characterization of amino-NHC coinage metal complexes and application for C-H activation of caffeine

Article abstract of DOI:10.1016/j.jorganchem.2014.02.024

This paper describes the synthesis and characterization of silver, copper and gold complexes supported by several amino-NHC ligands with different amino side arms. The transmetallation process using silver-NHC complexes can be used to prepare amino-NHC copper and gold complexes easily in high yield. In addition, the catalytic activities of copper complexes are examined for arylation of caffeine via C-H bond activation.

Full text of DOI:10.1016/j.jorganchem.2014.02.024

Journal of Organometallic Chemistry 761 (2014) 64e73
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of amino-NHC coinage metal
complexes and application for CeH activation of caffeine
,
,
Hsuan-Jui Huang a b, Wei-Chih Lee a, Glenn P.A. Yap c, Tiow-Gan Ong a
*
a Institute of Chemistry, Academia Sinica, Nangang, Taipei 115, Taiwan, ROC
b Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan, ROC
c Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
This paper describes the synthesis and characterization of silver, copper and gold complexes supported
by several amino-NHC ligands with different amino side arms. The transmetallation process using silver-
NHC complexes can be used to prepare amino-NHC copper and gold complexes easily in high yield. In
addition, the catalytic activities of copper complexes are examined for arylation of caffeine via CeH bond
activation.
Received 13 January 2014
Received in revised form
22 February 2014
Accepted 26 February 2014
Ó 2014 Elsevier B.V. All rights reserved.
Keywords:
Copper
Caffeine
Carbene
CeH activation
Introduction
Previously, we reported the intrinsic reactivities of main group
metal complexes supported by amino linked NHC framework [9] as
A quarter-century ago, the curiosity-driven efforts by many
pioneers eventually led to isolation of a stable free six-electron
carbon species, namely phosphino-silyl carbenes [1] and N-het-
erocyclic carbenes (NHC) [2]. Today, the judicious employment of
N-heterocyclic carbenes (NHCs) as a supporting ligand platform for
metal complexes has resulted in significant advances in catalysis
sector [3], thanks to their strong coordination ability and synthetic
simplicity with tunable steric and electronic features. In this
context, development of a new NHC framework tethered with an
additional functional pendant arm would have distinct implication
in the field. For example, a functionalized NHC bearing a hemilabile
donor group would offer possibility of dynamic “on and off” ligation
to protect and create a vacant coordination site for the active spe-
cies in the catalytic cycle [4]. More importantly, the secondary in-
teractions invoked between the dangling functional component of
ligand and the substrate may help to enhance the reaction rate and
selectivity. Despite featuring all these promising potentials, reports
concerning the anionic functionally-linked NHCs in the form of
amino [5], amido [6], alcohol [7], and phenoxide [8] appear to be
less common at this stage.
well as the catalytic CeH activation mediated by amino-NHC nickel
complexes [9b]. Delving into group coinage metal chemistry, we are
interested in the influence of amino functional-NHC on the struc-
tural motif of metal complexes as well as their possible roles in the
catalytic CeH bond activation. Herein, we report the synthesis and
characterization of silver, copper and gold complexes supported by
this ligand framework, and the use of their copper complexes in the
catalytic arylation of caffeine with aryl halide via CeH bond
activation.
Results and discussion
Synthesis and characterization of Amino-NHC silver complexes
We have previously reported synthetic methods for NHC
precursors, functionally-linked imidazoliums containing a tert-
butyl (1a) or 2,6-diisopropylphenylamine (1b) pendant arm [10].
Amino-linked imidazoliums bearing methylamino (1c) and
dimethylamino (1d) [11] groups,
a newly addition to our
library’s collection, can be prepared in a similar manner. Treat-
ment of imidazolium salt 1 with Ag2O in a dichloromethane
solution led to the expected silver adducts 2 in high yield
(Scheme 1). The proton NMR analysis of 2 displayed disap-
pearance of the C(2)-H signature peak related to the
* Corresponding author.
E-mail address: tgong@gate.sinica.edu.tw (T.-G. Ong).
http://dx.doi.org/10.1016/j.jorganchem.2014.02.024
0022-328X/Ó 2014 Elsevier B.V. All rights reserved.

H.-J. Huang et al. / Journal of Organometallic Chemistry 761 (2014) 64e73
65
Scheme 1. Synthesis of amino-NHC Ag complexes.
corresponding imidazolium salt 1 at w
formation of a AgeNHC complex with a carbenic 13C NMR signal
around w 180e185 ppm.
d
9.00 ppm, indicating
Synthesis and characterization of amino-NHC copper complexes
d
With amino-NHC silver complexes in hands, we began to
examine the viability of 2 acting as NHC transfer agents to a variety
of other coinage metals. First, synthesis of amino-NHC copper
complexes 3aed can be achieved by reacting copper (I) chloride in
dichloromethane at room temperature with the corresponding
silver compounds 2aed (Scheme 2). After removal of insoluble
silver salts from the reaction mixture, copper complexes 3aeb and
3d can be purified in good yields by recrystallization. Similarly, high
yield synthesis (88%) of 3e, a copper iodide counterpart is also
conceivable through transmetallation method using the silver
transfer agent.
Crystals of 2a-Br suitable for X-ray diffraction analysis were
obtained by cooling a saturated THF solution at ꢀ10 ꢁC. Complex
2a-Br crystallized in a triclinic space group of P-1 (Fig. 1), in which
the cationic silver complex contained a distorted linear geometry
(C(28)eAg(1)eC(10) 175ꢁ) with two amino-NHCs orientating in an
ꢀ
anti-like manner. The Agecarbene bond length is 2.064(5) A, in line
with those of bis-NHC Ag(I) complexes in the literature [11,12]. The
two imidazole rings in 2a-Br are not coplanar and twisted by 54ꢁ,
which appears to be necessary to avoid any steric clash within the
molecule itself. Finally, the counterion is composed of a silver dimer
bridged by two bromides, showing no any visible coordinating
interaction with cation complex.
Consistent with NMR and mass analyses, molecular structures of
3a, 3b and 3d were confirmed by single crystal X-ray diffraction, as
Fig. 1. The molecular structure of 2a-Br with thermal ellipsoids drawn at the 50% probability level. All hydrogen atoms were omitted for clarity except the hydrogen atom resided
ꢀ
on N3 and N6. Selected bond lengths (A) and angles (deg): Ag(1)eC(10) ¼ 2.0644(56), Ag(1)eC(28) ¼ 2.0646(57), N(1)-C(10) ¼ 1.3518(69), N(2)-C(10) ¼ 1.3488(59), N(4)-
C(28) ¼ 1.3471(66), N(5)-C(28) ¼ 1.3586(64), C(10)eAg(1)eC(28) ¼ 174.87(19), N(1)eC(10)eAg(1) ¼ 130.30(87), N(2)eC(10)eAg(1) ¼ 125.36(35), N(4)eC(28)eAg(1) ¼ 126.46(37),
N(5)eC(28)eAg(1) ¼ 129.20(35).

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H.-J. Huang et al. / Journal of Organometallic Chemistry 761 (2014) 64e73
Scheme 2. Synthesis of amino-NHC Cu complexes.
illustrated in Figs. 2e4, respectively. As projected, all copper chlo-
ride complexes coordinated linearly to NHC (CleCueC w 178ꢁ) in a
k
In contrast to other copper monomers as mentioned earlier, the
synthesis of amino-NHC copper complexes 3c seemed less effective
in this transmellation process, plagued by various side products
which could not be removed easily through any mean of purifica-
tion steps. As a result, we are not able to fully characterize 3c.
Nevertheless, we obtained a single crystal of 3c suitable for X-ray
diffraction analysis as shown in Fig. 5, which is uniquely different
from other amino-NHC monomeric analogs. The structure of 3c
with less steric hindrance at amino side-arm comprises an organ-
1 style with a dangling amine pendant arm. In spite of higher steric
demand in 3a and 3b compared to 3d, all copper-carbene distances
ꢀ
are statistically equal with 1.8768(15), 1.8938 (14) and 1.8784 (17) A
for 3a, 3b and 3d, respectively, illustrating the lack of steric influ-
ence by remote amine pendant arm, as well as any electronic
perturbation within NHC ring onto the metal center.
ometallic polymer with a repeating unit of [Cu(
[CuCl]2. The repeating unit consists of two types of binuclear copper
clusters of [Cu(2)( -NC)2Cu(2)] and [Cu(2)Cl]2, at which each of
cluster units are directly connected asymmetrically by a bridging
m-NC)2Cu]-m-Cl-
m
ꢀ
ꢀ
chlorine atom (Cu(1)eCl(1) 2.5367(5) A, Cu(2)eCu(1) 2.1926(5) A).
The [Cu(1)( -NC)2Cu(1)] component crystallizes as centrosym-
m
metric dimer with two amino-NHC ligands bridging the two copper
centers. The geometry around the copper is best described as a
distorted trigonal planar with a copper atom slightly sitting above
ꢀ
the plane of C(10)eN(3)eCl(1) by 0.16 A. The Cuecarbene bond
ꢀ
distance of 1.8808(17) A is within the characteristic range for Cue
ꢀ
carbene single bonds. The CueCu distance of 3.50 A gives no further
evidence for a weak metalemetal interaction. Lastly, the other
cluster has two Cu(2) cluster lying on the same plane in a rhom-
boidal arrangement bridged symmetrically by Cl(2).
To determine if the transmellation reaction from amino-NHC Ag
complexes (Scheme 3) is also general for the other coinage metal,
the gold complexes are used for the comparison purpose. To our
delight, the direct reaction of 2a or 2b with AuCl(SMe2) in
Fig. 2. The molecular structure of 3a with thermal ellipsoids drawn at the 50% prob-
ability level. Hydrogen atoms were omitted for clarity except the hydrogen atom
ꢀ
resided on N3. Selected bond lengths (A) and angles (deg): Cu(1)eC(1) ¼ 1.8768(15),
Cu(1)eCl(1) ¼ 2.1094(4), N(1)eC(1) ¼ 1.3550(19), N(2)eC(1) ¼ 1.354(2), C(1)eCu(1)e
Cl(1) ¼ 175.85(5), N(1)eC(1)eCu(1) ¼ 130.90(11), N(2)eC(1)eCu(1) ¼ 125.20(13),
C(1)eN(1)eC(9) ¼ 125.89(13), C(1)eN(2)eC(13) ¼ 124.35(13).

H.-J. Huang et al. / Journal of Organometallic Chemistry 761 (2014) 64e73
67
Fig. 3. The molecular structure of 3b with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms were omitted for clarity except the hydrogen atom resided on N3.
ꢀ
Selected bond lengths (A) and angles (deg): CueC(10) ¼ 1.8938(16), CueCl ¼ 2.1247(4), N(1)eC(10) ¼ 1.3600(2), N(2)eC(10) ¼ 1.3559(19), C(10)eCueCl ¼ 178.44(4), N(1)eC(10)e
Cu ¼ 127.39(10), N(2)eC(10)eCu ¼ 128.86(11), C(10)eN(1)eC(6) ¼ 124.77(11), C(10)eN(2)eC(13) ¼ 125.01(12).
dichloromethane resulted in the desired gold complex 4a or 4b in
excellent yield. Previously, we prepared compounds similar to 4a
(Fig. 6) via free NHC route, albeit lower yield [13]. Single crystals
suitable for X-ray diffraction study were grown by slowly cooling a
concentrated dichloromethane solution of 4b to furnish a mono-
clinic crystal with P21/c space group, demonstrating that gold
complex 4b contains an essentially linear two-coordinated gold (I)
C(10)eAueCl(1) arrangement with 179.3ꢁ (Fig. 7). Both gold-
experiments examined the CeH bond functionalization of caffeine
10 with phenyl iodide 11a involving various catalytic amounts of
amino-NHC copper complexes 3 with t-BuONa in DMF at 140 ꢁC as
listed in Table 1 (Entries 1e4). To our delight, addition of 10 mol % of
3e furnished a coupling product 12a in a yield of 56%. Subsequently,
we turned our attention to finding an appropriate base for opti-
mizing the CeH activation process. A number of bases were
screened (Entries 5e9), in which t-BuOLi gave the highest yield
(83%) in 8 h (Entry 11). Prolonging the reaction to 48 h did not seem
to have any beneficial effect on the reaction yield (Entry 10).
Under the optimal reaction condition, a series of aryl iodide (11)
with caffeine (10) were investigated to evaluate the generality of
the reaction. The results are listed in Table 2. High yield of coupling
was observed for iodo-methylbenzenes like ortho-substituents
(12b, 80%), meta-substituents (12c, 92%) and para-substituents
(12d, 90%), illustrating the non-sensitivity of the reaction toward
methyl substituents at different positions. Likewise, methoxy
groups at ortho (12e, 95%) and para (12g, 97%) positions still retain
high conversion except substrate bearing meta-methoxy (12f)
group with a moderate yield of 50%. A moderate yield was wit-
nessed using substrates with more electron-withdrawing groups
(12hek) such as chloride, bromide, fluoride and nitrile. The chloro-
and bromo-substituents may be subject to further synthetic
transformations. Again, such method can be extended effectively to
other more exotic species as such 2-iodonapthelene (12l), 2-
iodopyridine (12m) and 2-methylenebromide (12n).
ꢀ
ꢀ
carbene bond distances in 4a (1.978(6) A) and 4b (1.9847(41) A)
are essentially identical Scheme 3
Copper-mediated arylation of caffeine
Caffeine is one of the most important biologically active alka-
loids with an imidazole motif. In addition, 8-heteroaryl-substituted
caffeine and derivatives are also of great interest and importance
since such structural motifs are usually found in many biologically
active compounds, natural products, pharmaceuticals, and func-
tional materials [14]. Direct C-arylation of heterocycles has received
great attention and been developed as an efficient synthetic route
for the formation of aryl-heteroaryl bonds [15]. Therefore, we are
intrigued by the use of our copper complexes supported by amino-
NHC ligands in arylation of caffeine. Our initial screening
To further demonstrate its catalytic utility, we expanded the
scope of this protocol to numerous caffeine derivatives (Table 3).
High levels of coupling product (w80%) were consistently observed
with caffeine bearing ethyl (12ba) or isopropyl side arm (12ca). The
slightly low yield was observed for 12ca, which is attributed to
steric hindrance invoked by isopropyl side arm. Remarkably, high
level of yield was consistently witnessed for the benzyl derivatives
without (12da) or with substituents (methyl (12ea), chloride (12fa)
fluoride (12ga)). In addition, we also attempted other heteroarenes
coupling with aryl iodide. Average yields are witnessed for ben-
zoxazole (12ha) and N-methylbenzimidazole (12ja), but lower
yield for benzothiozole (12ia).
Fig. 4. The molecular structure of 3d with thermal ellipsoids drawn at the 50%
ꢀ
probability level. Hydrogen atoms were omitted for clarity. Selected bond lengths (A)
Conclusion
and angles (deg): Cu(1)eC(10)
C(10) ¼ 1.3582(21), N(2)eC(10) ¼ 1.3586(23), C(10)eCu(1)eCl(1) ¼ 177.54(6), N(1)e
C(10)eCu(1) 129.85(13), N(2)eC(10)eCu(1) 126.08(13), C(10)eN(1)e
C(6) ¼ 124.77(14), C(10)eN(2)eC(13) ¼ 124.62(14).
¼
1.8785(17), Cu(1)eCl(1)
¼
2.1113(5), N(1)e
In conclusion, this paper describes the synthesis and charac-
terization of silver, copper and gold complexes supported by
¼
¼

68
H.-J. Huang et al. / Journal of Organometallic Chemistry 761 (2014) 64e73
ꢀ
Fig. 5. The molecular structure of 3c. Hydrogen atoms were omitted for clarity. Selected bond lengths (A) and angles (deg): Cu(1)eC(10) ¼ 1.881(2), Cu(1)eCl(1) ¼ 2.5367(5),
Cu(1)eN(3) ¼ 1.980(2), Cu(2)eCl(1) ¼ 2.1926(5), Cu(2)eCl(2) ¼ 2.2785(4), Cu(2)eCl(2) ¼ 2.3729(6), C(10)eCu(1)eCl(1) ¼ 117.9(6), C(10)eCu(1)eN(3) ¼ 150.80(7), N(3)eCu(1)e
Cl(1) ¼ 88.83(5), Cl(1)eCu(2)eCl(2) ¼ 134.99(2), Cl(1)eCu(2)eCl(2) ¼ 125.60(2), Cl(2)eCu(2)eCl(2i) ¼ 99.39(2), Cu(1)eCl(1)eCu(2) ¼ 115.58(2), Cu(2)eCl(2)eCu(2) ¼ 80.61(2).
amino-NHC ligands. In addition, our results show that catalytic
arylation of caffeine via CeH bond activation is also feasible for
copper complexes supported by amino-NHC ligands.
Synthesis of bis(1-(2-((2,6-diisopropylphenyl)amino)ethyl)-3-mesityl-
2,3-dihydro-1H- imidazol-2-yl)silver dibromoargentate(I) (2b)
Compound 1b (500 mg, 1.06 mmol) and Ag2O (123 mg,
0.53 mmol) were mixed in dichloromethane (3 mL) in darkness at
room temperature. After stirring for 18 h, the insoluble salt was
removed from the reaction mixture by using filtered frit filled with
Celite, All volatiles were removed under vacuum to afford the yel-
Experimental section
Synthesis of bis(1-(2-(tert-butylamino)ethyl)-3-mesityl-2,3-
dihydro-1H-imidazol-2-yl) silver(III) silver(I) bromide (2a-Br)
low solid. Yield: 80.0% (491 mg). 1H NMR (400 MHz, CDCl3):
d 7.35
(d, 3JHH ¼ 1.2 Hz, 1H), 7.07 (s, 3H), 6.97 (d, 3JHH ¼ 1.6 Hz, 1H), 6.95 (s,
2H), 4.48 (t, 3JHH ¼ 5.8 Hz, 2H, CH2), 3.29 (m, 2H, CH2), 3.08 (m, 2H,
CH), 2.93 (s, 1H, NH), 2.31 (s, 3H, CH3), 1.98 (s, 6H, CH3), 1.19 (d,
Compound 1a-Br (500 mg, 1.55 mmol) and Ag2O (179 mg,
0.77 mmol) were mixed in dichloromethane (3 mL) in darkness at
room temperature. After stirring for 18 h, the insoluble salt was
removed from the reaction mixture by using filtered frit filled with
Celite, All volatiles were removed under vacuum and the residue
was purified by recrystallization from THF/diethyl ether. Yield:
3JHH ¼ 6.8 Hz, 12H, CH3). 13C{1H} NMR (75 MHz, CDCl3):
d 184.13,
143.15, 141.83, 139.75, 135.62, 134.86, 129.64, 124.91, 123.91, 122.69,
121.91, 53.01, 52.56, 27.86, 24.58, 21.25, 17.88.
96.7% (634 mg). 1H NMR (400 MHz, CDCl3):
d
7.30 (d, 3JHH ¼ 1.2 Hz,
1H), 6.90 (s, 2H), 6.86 (d, 3JHH ¼ 1.6 Hz,1H), 4.19 (t, 3JHH ¼ 5.8 Hz, 2H,
CH2), 2.97e2.95 (m, 2H, CH2), 2.29 (s, 3H, CH3), 1.29 (s, 6H, CH3),
Synthesis of (1-mesityl-3-(2-(methylamino)ethyl)-2,3-dihydro-1H-
imidazol-2-yl)silver chloride (2c)
1.00 (s, 9H, CH3). 13C{1H} NMR (75 MHz, CDCl3):
d 181.7, 139.1, 135.5,
134.6, 129.2, 122.4, 122.0, 53.1, 50.2, 43.5, 29.0, 21.0, 17.5. The NMR
spectra were consistent with those reported in the literature [13].
Compound 1c (500 mg, 1.78 mmol) and Ag2O (413 mg,
1.78 mmol) were mixed in dichloromethane (3 mL) in darkness at
Scheme 3. Synthesis of amino-NHC Au complexes.

H.-J. Huang et al. / Journal of Organometallic Chemistry 761 (2014) 64e73
69
(d, 3JHH ¼ 1.6 Hz, 1H), 6.93 (s, 2H), 6.88 (d, 3JHH ¼ 1.6 Hz, 1H), 4.25 (t,
3JHH ¼ 6.0 Hz, 2H, CH2), 2.71 (t, 3JHH ¼ 6.0 Hz, 2H, CH2), 2.31 (s, 3H,
CH3), 2.28 (s, 6H, CH3), 1.95 (s, 6H, CH3). 13C{1H} NMR (75 MHz,
CDCl3):
d 180.79, 139.37, 135.50, 134.74, 129.37, 122.31, 122.02,
60.25, 50.00, 45.64, 21.08, 17.63. HR-MS (FAB): m/z calcd. for
C
16H23N3Ag ([M þ H]þ) 364.0943, found 364.0941.
Synthesis of bis(1-(2-(tert-butylamino)ethyl)-3-mesityl-2,3-
dihydro-1H-imidazol-2-yl) silver chloride (2a-Cl)
Compound 1a-Cl (500 mg, 1.55 mmol) and Ag2O (359 mg,
1.55 mmol) were mixed in dichloromethane (3 mL) in darkness at
room temperature. After stirring for 18 h, the insoluble salt was
removed from the reaction mixture by using filtered frit filled with
Celite, All volatiles were removed under vacuum and the residue
was purified by recrystallization from THF/diethyl ether. Yield: 92%
Fig. 6. The molecular structure of 4a with thermal ellipsoids drawn at the 50% prob-
ability level. Hydrogen atoms were omitted for clarity. Selected bond lengths (A) and
angles (deg): Au(1)eC(7) ¼ 1.978(6), Au(1)eCl(1) ¼ 2.293(1), N(2)eC(7) ¼ 1.350(6),
N(3)eC(7) ¼ 1.349(7), C(7)eAu(1)eCl(1) ¼ 177.42(2), N(2)eC(7)eAu(1) ¼ 125.4(4),
N(3)eC(7)eAu(1) ¼ 129.4(4), C(6)eN(2)eC(7) ¼ 125.5(4), C(7)eN(3)eC(15) ¼ 126.7(4).
ꢀ
(613 mg). 1H NMR (400 MHz, CDCl3) :
d
7.30 (d, 3JHH ¼ 1.2 Hz, 1H),
3
3
6.90 (s, 2H), 6.86 (d, JHH ¼ 1.6 Hz, 1H), 4.19 (t, JHH ¼ 5.8 Hz, 2H,
CH2), 2.94 (m, 2H, CH2), 2.29 (s, 3H, CH3), 1.29 (s, 6H, CH3), 1.00 (s,
9H, CH3). 13C{1H} NMR (75 MHz, CDCl3):
d 180.47, 139.01, 135.35,
room temperature. After stirring for 18 h, the insoluble salt was
removed from the reaction mixture by using filtered frit filled with
Celite, All volatiles were removed under vacuum to afford the yel-
134.52, 129.09, 122.26, 122.00, 53.01, 50.08, 43.45, 28.83, 21.88,
17.42. HR-MS (FAB): m/z calcd. for C18H27N3ClAg ([M þ H]þ)
388.6731, found 383.6727.
low solid. Yield: 63% (435 mg). 1H NMR (400 MHz, CDCl3):
d
7.27 (d,
3
3JHH ¼ 2.0 Hz, 1H), 6.93 (s, 2H), 6.91 (d, JHH ¼ 1.6 Hz, 1H), 4.27 (t,
3JHH ¼ 6.0 Hz, 2H, CH2), 3.05 (m, 2H, CH2), 2.46 (d, JHH ¼ 6.4 Hz,
3
Synthesis of (1-(2-(tert-butylamino)ethyl)-3-mesityl-2,3-dihydro-
1H-imidazol-2-yl)copper(I) chloride (3a)
3H), 2.31 (s, 3H, CH2), 1.95 (s, 6H, CH3). 13C{1H} NMR (75 MHz,
CDCl3): d 180.68, 139.19, 135.37, 134.61, 129.19, 122.36, 122.02, 52.41,
Compound 2a-Cl (585 mg, 1.36 mmol) and copper (I) chloride
(135 mg, 1.36 mmol) were mixed in dichloromethane (3 mL) in
darkness at room temperature. After stirring for 18 h, the insoluble
salt was removed from the reaction mixture by using filtered frit
filled with Celite, All volatiles were removed under vacuum and the
residue was purified by recrystallization from THF/diethyl ether.
51.59, 36.29, 20.97, 17.54. HR-MS (FAB): m/z calcd. for C15H21N3Ag
([M þ H]þ) 350.0786, found 350.0785.
Synthesis of (1-(2-(dimethylamino)ethyl)-3-mesityl-2,3-dihydro-
1H-imidazol-2-yl)silver chloride (2d)
Yield: 96.8% (508 mg). 1H NMR (400 MHz, CDCl3):
d 7.23 (d,
3
Compound 1d (500 mg, 1.70 mmol) and Ag2O (394 mg,
1.70 mmol) were mixed in dichloromethane (3 mL) in darkness at
room temperature. After stirring for 18 h, the insoluble salt was
removed from the reaction mixture by using filtered frit filled with
Celite, All volatiles were removed under vacuum to afford the yel-
3JHH ¼ 1.6 Hz, 1H), 6.93 (s, 2H), 6.81 (d, JHH ¼ 1.6 Hz, 1H), 4.24 (t,
3JHH ¼ 5.8 Hz, 2H, CH2), 3.03 (m, 2H, CH2), 2.30 (s, 3H, CH3), 1.97 (s,
6H, CH3), 1.03 (s, 9H, CH3). 13C{1H} NMR (75 MHz, CDCl3):
d 177.53,
139.20, 135.42, 134.69, 129.35, 121.82, 121.64, 52.82, 50.54, 43.91,
29.08, 21.09, 17.76. HR-MS (FAB): m/z calcd. for C18H27N3ClCu
([M þ H]þ) 383.1189, found 383.1183.
low solid. Yield: 91.6% (625 mg). 1H NMR (400 MHz, CDCl3) :
d 7.29
ꢀ
Fig. 7. The molecular structure of 4b with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms were omitted for clarity. Selected bond lengths (A) and angles
(deg): Au(1)eC(10) ¼ 1.9847(41), Au(1)eCl(1) ¼ 2.2952(11), N(1)eC(10) ¼ 1.3493(51), N(2)eC(10) ¼ 1.3522(49), C(10)eAu(1)eCl(1) ¼ 179.29(12), N(1)eC(10)eAu(1) ¼ 126.82(28),
N(2)eC(10)eAu(1) ¼ 127.81(29), C(10)eN(1)eC(6) ¼ 125.99(33), C(10)eN(2)eC(13) ¼ 125.74(32).

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H.-J. Huang et al. / Journal of Organometallic Chemistry 761 (2014) 64e73
Table 1
Optimization of CeH activation of caffeine 10 with aryl iodide 11a.a
Entry
1
[Cu]
Base
Temp (ꢁC)
140
Time (h)
24
Yieldb (%)
48
3a
tBuONa
2
3
4
5
6
7
8
9
10
11
12
13
3b
3d
3e
3e
3e
3e
3e
3e
3e
3e
3e
3e
tBuONa
tBuONa
tBuONa
tBuOK
tBuOLi
K2CO3
Na2CO3
Cs2CO3
tBuOLi
tBuOLi
tBuOLi
tBuOLi
140
140
140
140
140
140
140
140
140
140
140
140
24
24
24
24
24
24
24
24
48
8
42
32
56
54
83
11
0
0
84
83
42
3
3
0.5
a
Conditions: 10 (0.5 mmol), 11a (1 mmol), [Cu] (10 mol%), and base (1 mmol) in DMF (1 mL) at 140 ꢁC.
GC yield (%).
b
Synthesis of (1-(2-((2,6-diisopropylphenyl)amino)ethyl)-3-mesityl-
2,3-dihydro-1H-imidazol- 2-yl)copper(I) chloride (3b)
129.30, 121.68, 121.54, 60.31, 49.33, 45.62, 21.07, 17.76. HR-MS
(FAB): m/z calcd. for C16H23N3ClCu ([M þ H]þ) 355.0876, found
355.0874.
Compound 2b (360 mg, 0.31 mmol) and copper (I) chloride
(62 mg, 0.62 mmol) were mixed in dichloromethane (3 mL) in
darkness at room temperature. After stirring for 18 h, the insoluble
salt was removed from the reaction mixture by using filtered frit
filled with Celite, All volatiles were removed under vacuum and the
residue was purified by recrystallization from dichloromethane.
Synthesis of (1-(2-(tert-butylamino)ethyl)-3-mesityl-2,3-dihydro-
1H-imidazol-2-yl) copper(I) iodide (3e)
Compound 2a-Cl (400 mg, 0.92 mmol) and copper (I) iodide
(177 mg, 0.92 mmol) were mixed in dichloromethane (3 mL) in
darkness at room temperature. After stirring for 18 h, the insoluble
salt was removed from the reaction mixture by using filtered frit
filled with Celite, All volatiles were removed under vacuum to
afford the yellow solid. Yield: 88.1% (391 mg). 1H NMR (400 MHz,
Yield: 82.0% (250 mg). 1H NMR (300 MHz, CDCl3):
d 7.29 (s,1H), 7.07
(s, 3H), 6.95 (s, 2H), 6.90 (s, 1H), 4.48 (t, 3JHH ¼ 5.7 Hz, 2H, CH2), 3.31
(m, 2H, CH2), 3.08 (m, 2H, CH), 2.95 (t, 3JHH ¼ 8.1 Hz,1H, NH), 2.31 (s,
3H, CH3), 2.02 (s, 6H, CH3), 1.19 (d, 3JHH ¼ 6.9 Hz, 12H, CH3). 13C{1H}
NMR (75 MHz, CDCl3):
d 177.53, 142.95, 141.69, 139.26, 135.21,
CDCl3):
d
7.24 (s, 1H), 6.90 (s, 2H), 6.79 (d, 3JHH ¼ 1.5 Hz, 1H), 4.18 (t,
134.51, 129.33, 124.58, 123.59, 122.11, 121.67, 52.37, 52.17, 27.54,
3JHH ¼ 5.4 Hz, 2H, CH2), 2.96 (m, 2H, CH2), 2.28 (s, 3H, CH3), 1.94 (s,
24.35, 21.03, 17.73. HR-MS (FAB): m/z calcd. for C26H35N3ClCu
6H, CH3), 1.00 (s, 9H, CH3). 13C{1H} NMR (75 MHz, CDCl3):
d 178.16,
([M
þ
H]þ) 487.1816, found 487.1819. Anal. Calcd for for
139.37, 135.55, 134.82, 129.47, 121.88, 121.74, 53.03, 50.59, 43.96,
C
26H36ClCuN3: C, 63.78; H, 7.41; N, 8.58. Found: C, 63.94; H, 7.26; N,
29.19, 21.17, 17.84. HR-MS (FAB): m/z calcd. for
C18H27N3Cu
8.63.
([M þ H]þ) 348.1501, found 348.1496.
Synthesis of (1-(2-(dimethylamino)ethyl)-3-mesityl-2,3-dihydro-
Synthesis of (1-(2-(tert-butylamino)ethyl)-3-mesityl-2,3-dihydro-
1H-imidazol-2-yl) copper(I) chloride (3d)
1H-imidazol-2-yl) gold(I) chloride (4a)
Compound 2d (342 mg, 0.85 mmol) and copper (I) chloride
(84 mg, 0.85 mmol) were mixed in dichloromethane (3 mL) in
darkness at room temperature. After stirring for 18 h, the insoluble
salt was removed from the reaction mixture by using filtered frit
filled with Celite, All volatiles were removed under vacuum and the
residue was purified by recrystallization from THF/Hexane. Yield:
Compound 2a-Cl (146 mg, 0.34 mmol) and chloro(dimethyl-
sulfide)-gold(I) (100 mg, 0.34 mmol) were mixed in dichloro-
methane (3 mL) in darkness at room temperature. After stirring for
18 h, the insoluble salt was removed from the reaction mixture by
using filtered frit filled with Celite, All volatiles were removed under
vacuum and the residue was purified by recrystallization from THF/
diethyl ether. Yield: 82.0% (145 mg). 1H NMR (300 MHz, CDCl3):
92.4% (281 mg). 1H NMR (400 MHz, CDCl3):
d
7.19 (d, 3JHH ¼ 2.0 Hz,
3
3
1H), 6.93 (s, 2H), 6.81 (d, JHH ¼ 1.6 Hz, 1H), 4.27 (t, JHH ¼ 6.0 Hz,
d
7.31 (d, 3JHH ¼ 1.8 Hz, 1H), 6.91 (s, 2H), 6.81 (d, 3JHH ¼ 1.8 Hz, 1H),
3
2H, CH2), 2.74 (t, JHH ¼ 6.0 Hz, 2H, CH2), 2.30 (s, 9H), 1.98 (s, 6H,
4.28 (t, 3JHH ¼ 5.9 Hz, 2H, CH2), 3.04 (t, 3JHH ¼ 5.9 Hz, 2H, CH2), 2.29
CH3). 13C{1H} NMR (75 MHz, CDCl3):
d
177.91, 139.09, 135.45, 134.67,
(s, 3H, CH3), 1.97 (s, 6H, CH3), 1.02 (s, 9H, CH3). 13C{1H} NMR

H.-J. Huang et al. / Journal of Organometallic Chemistry 761 (2014) 64e73
71
Table 2
Scope of copper mediated CH activation: various aryl iodide.
a Conditions: 10 (0.5 mmol), 11 (1.0 mmol), t-BuOLi (1 mmol), 3e (10 mol%) in DMF (1 mL) at
140 o C for 8 hours unless otherwise noted. b Isolated yield (%).
(100 MHz, CDCl3):
d
171.45, 139.55, 135.03, 134.88, 129.43, 122.18,
1H), 4.53 (t, 3JHH ¼ 5.9 Hz, 2H, CH2), 3.35 (t, 3JHH ¼ 5.9 Hz, 2H, CH2),
121.46, 52.79, 50.58, 43.43, 29.11, 21.18, 17.84. HR-MS (FAB): m/z
calcd. for C18H28N3ClAu ([M þ H]þ) 518.1637, found 518.1638. The
NMR spectra were consistent with those reported in the literature
[13].
3.08 (m, 3H, CH), 2.31 (s, 3H, CH3), 2.02 (s, 6H, CH3), 1.20 (d,
3JHH ¼ 6.6 Hz, 12H, CH3). 13C{1H} NMR (75 MHz, CDCl3):
d 172.56,
143.13, 141.78, 139.91, 134.93, 134.88, 129.61, 124.90, 123.88, 122.19,
121.55, 52.27, 51.99, 27.86, 24.52, 21.29, 17.97. HR-MS (FAB): m/z
calcd. for C26H35N3ClAu ([M þ H]þ) 621.2185, found 621.2188.
Synthesis of (1-(2-((2,6-diisopropylphenyl)amino)ethyl)-3-mesityl-
2,3-dihydro-1H-imidazol- 2-yl) gold(I) chloride (4b)
Synthesis of (1-(2-(dimethylamino)ethyl)-3-mesityl-2,3-dihydro-
1H-imidazol-2-yl) gold(I) chloride (4d)
Compound 2b (98 mg, 0.08 mmol) and chloro(dimethyl-
sulfide)- gold(I) (50 mg, 0.02 mmol) were mixed in dichloro-
methane (3 mL) in darkness at room temperature. After stirring for
18 h, the insoluble salt was removed from the reaction mixture by
using filtered frit filled with Celite, All volatiles were removed under
vacuum and the residue was purified by recrystallization from THF/
Compound 2d (68 mg, 0.17 mmol) and chloro(dimethyl-
sulfide)-gold(I) (50 mg, 0.17 mmol) were mixed in dichloro-
methane (3 mL) in darkness at room temperature. After stirring for
18 h, the insoluble salt was removed from the reaction mixture by
using filtered frit filled with Celite, All volatiles were removed under
vacuum to afford the yellow solid. Yield: 85.2% (71 mg). 1H NMR
diethyl ether. Yield: 81.1% (86 mg). 1H NMR (300 MHz, CDCl3):
d 7.33
(d, 3JHH ¼ 1.8 Hz, 1H), 7.08 (s, 3H), 6.95 (s, 2H), 6.90 (d, 3JHH ¼ 1.8 Hz,
(400 MHz, CDCl3):
d
7.28 (d, 3JHH ¼ 2.0 Hz, 1H), 6.93 (s, 2H), 6.82 (d,

72
H.-J. Huang et al. / Journal of Organometallic Chemistry 761 (2014) 64e73
Table 3
Scope of copper mediated CH activation: various caffeine derivatives.
a
Conditions: caffeine derivative (0.5 mmol), 11a (1.0 mmol), t-BuOLi (1 mmol), 3e (10
mol%) in DMF (1 mL) at 140 oC for 8 hours unless otherwise noted. b Isolated yield (%).
3
3JHH ¼ 1.6 Hz, 1H), 4.33 (t, JHH ¼ 6.2 Hz, 2H, CH2), 2.77 (t,
Single-crystal X-ray characterization
3JHH ¼ 6.2 Hz, 2H, CH2), 2.30 (s, 3H, CH3), 2.29 (s, 6H, CH3), 1.98
(s, 6H, CH3). 13C{1H} NMR (75 MHz, CDCl3):
d
171.29, 139.43, 135.45,
X-ray structural analysis for 2a, 3a, 3b, 3c, 3d, 4a, and 4b: Unit
134.88, 134.79, 129.31, 121.78, 121.67, 59.69, 49.17, 45.57, 21.13, 17.77.
HR-MS (FAB): m/z calcd. for C16H24N3ClAu ([M þ H]þ) 490.1324,
found 490.1324.
cell parameters were obtained from 36 data frames, 0.5ꢁ
u, from
three different sections of the Ewald sphere. No symmetry higher
than triclinic was observed for 2a, 3c and 4b, and solution in the
centrosymmetric space group option yielded chemically reasonable
and computationally stable results of refinement. For the other
data-sets, the systematic absences in the diffraction data are
uniquely consistent with P21/n or P21/c. The data-sets were treated
with multi-scan absorption corrections (Apex2 software suite,
Madison, WI, 2005). The structures were solved using direct
methods or by intrinsic phasing and refined with full-matrix, least-
squares procedures on F [2,16]. The anion in 2a is located on an
inversion center. The structure in 3c is a polymer propagated by
inversion symmetry on the monomeric unit along the c-plane. All
non-hydrogen atoms were refined with anisotropic displacement
parameters. Hydrogen atoms attached to nitrogen atoms were
located from the difference map and refined with 1.2 Ueq of the
attached atom. All hydrogen atoms attached to carbon atoms were
General procedure for copper-mediated CeH bond activation of
caffeine
The product 12a is a representative reaction. To a vial (5 mL)
containing caffeine (0.5 mmol), iodobenzene (1.0 mmol), catalyst
3e (0.05 mmol), and LiOtBu (1.0 mmol) was added DMF (1.0 mL)
solvent under a glovebox atmosphere. After the substances were
completely dissolved, the vial was screw-capped, taken outside the
glovebox and heated at 140 ꢁC for 8 h. The resulting mixture was
filtered through Celite and washed with dichloromethane. The
filtrate solution was concentrated in vacuo to afford the crude
product, which was further purified by column chromatography
using hexane/ethyl acetate as eluent to furnish 12a in 80% yield.

H.-J. Huang et al. / Journal of Organometallic Chemistry 761 (2014) 64e73
73
(c) J.-Y. Lee, P.-Y. Cheng, Y.-H. Tsai, G.-R. Lin, S.-P. Liu, M.-H. Sie, H.M. Lee,
Organometallics 29 (2010) 3901e3911;
(e) M.-H. Sie, Y.-H. Hsieh, Y.-H. Tsai, J.-R. Wu, S.-J. Chen, P.V. Kumar, J.-H. Lii,
H.M. Lee, Organometallics 29 (2010) 6473e6481.
treated as idealized contributions. Atomic scattering factors are
contained in the SHELXTL 6.12 program library (Sheldrick, G., op.
cit.).
[7] (a) I. Peñafiel, I.M. Pastor, M. Yus, M.A. Esteruelas, M. Oliván, E. Oñate, Eur. J.
Org. Chem. 2011 (2011) 7174e7181;
Acknowledgment
(b) C. Costabile, C. Bocchino, M. Napoli, P. Longo, J. Polym. Sci. A Polym. Chem.
50 (2012) 3728e3735;
(c) A. Bartoszewicz, R. Marcos, S. Sahoo, A.K. Inge, X. Zou, B. Martín-Matute,
Chem. Eur. J. 18 (2012) 14510e14519;
(d) L. Ray, V. Katiyar, M. Raihan, H. Nanavati, M.M. Shaikh, P. Ghosh, Eur. J.
Inorg. Chem. 45 (2006) 3724e3730;
(e) A. John, P. Ghosh, Dalton Trans. 39 (2010) 7183e7286;
(f) M. Benítez, E. Mas-Marzá, J.A. Mata, E. Peris, Chem. Eur. J. 17 (2011) 10453e
10461;
(g) S. Kumar, A. Narayanan, M.N. Rao, M.M. Shaikh, P. Ghosh, J. Organomet.
Chem. 696 (2012) 4159e4165.
This work is financially supported by National Science Council of
Taiwan (NSC-101-2628-M-001-002-MY3 grant) and Academia
Sinica Funding. We also thank Dr. Mei-Chin Tseng for generous
technical support for using the Mass Analysis facility.
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