Radical metalloids with N-heterocyclic carbene and phenanthroline ligands: Synthesis, properties, and cross-coupling reaction of [(nitronyl nitroxide)-2-ido]metal complexes with aryl halides

Article abstract of DOI:10.1246/bcsj.20180033

New radical metalloids, NN-AuSIMes and NNCu( bdmpphen), were prepared and their properties were investigated. They were applied to Pd(0)-mediated crosscoupling reactions with aryl halides (ArX) to produce 2-aryl (nitronyl nitroxide) s in moderate to high

Full text of DOI:10.1246/bcsj.20180033

Advance Publication Cover Page
Radical Metalloids with N-Heterocyclic Carbene and Phenanthroline Ligands: Synthesis, Properties,
and Cross-Coupling Reaction of [(Nitronyl Nitroxide)-2-ido]metal Complexes with Aryl Halides
Kiyomi Yamada, Xun Zhang, Ryu Tanimoto, Shuichi Suzuki, Masatoshi Kozaki,
Rika Tanaka, and Keiji Okada*
Advance Publication on the web April 14, 2018
doi:10.1246/bcsj.20180033
© 2018 The Chemical Society of Japan
Advance Publication is a service for online publication of manuscripts prior to releasing fully edited, printed versions. Entire
manuscripts and a portion of the graphical abstract can be released on the web as soon as the submission is accepted. Note that the
Chemical Society of Japan bears no responsibility for issues resulting from the use of information taken from unedited, Advance
Publication manuscripts.

Radical Metalloids with N-Heterocyclic Carbene and Phenanthroline Ligands:
Synthesis, Properties, and Cross-Coupling Reaction of [(Nitronyl
Nitroxide)-2-ido]metal Complexes with Aryl Halides
Kiyomi Yamada,1 Xun Zhang,1 Ryu Tanimoto,1 Shuichi Suzuki,1,2 Masatoshi Kozaki,1 Rika Tanaka,3 and Keiji
Okada*1,4
1Department of Chemistry, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585.
2Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531.
3Graduate School of Engineering, Osaka City University and Analytical Center of Osaka City University, Sugimoto, Osaka 558-8585.
4Osaka City University Advanced Research Institute for Natural Science and Technology (OCARINA), Sugimoto, Osaka 558-8585.
okadak@sci.osaka-cu.ac.jp
Keiji Okada retired on March 31, 2017 and is now Professor Emeritus of Chemistry at Osaka City University
(OCU). He is currently enjoying new findings in spin chemistry. His career is summarized as follows: D.Sc. in
1979 from Tohoku University (Prof. Toshio Mukai), Post-doctoral Fellow (UWO, Canada 1980-1982, Prof.
Paul de Mayo), Assistant Professor (19821990) and Associate Professor (19911995) in Faculty of Science,
Osaka University with Prof. Masaji Oda, and Full Professor (1996-2017) at Faculty of Science, OCU.
Abstract
New
radical
metalloids,
NN-AuSIMes
and
NN-Cu(bdmpphen), were prepared and their properties were
investigated. They were applied to Pd(0)-mediated cross-
coupling reactions with aryl halides (ArX) to produce 2-aryl
(nitronyl nitroxide)s in moderate to high yields.
1. Introduction
Stable open-shell compounds with
a redox-active
Scheme 1. Synthetic routes to NN-Ar.
-conjugated system exhibit unique electronic and magnetic
properties.1 In particular, nitronyl nitroxide radicals (NN-R: R
= alkyl, aryl (Ar), H, etc., at the C2 position) have been widely
utilized as stable spin sources. Various redox-active functional
-conjugated R groups can be introduced to produce new
magnetic materials.2 NN-H is also useful compound;
deprotonation from NN-H by a base produces an unstable
NN-C2-ide radical anion ( < 30 min at room temperature);3
this unique radical-nucleophile reacts with various electrophiles
to give rise to interesting open-shell species.4,5,6 As an
extension, we recently developed new transition metal
complexes (radical metalloids) NN-MLn (M: metal such as
Pt(II), Au(I), L: ligand), in which the NN-C2-ide radical anion
coordinates to M.2c,7 These radical metalloids have an NN
NN-skeleton onto aromatic rings. To date, the cross-coupling
of NN-C6H4-X (X = Br or I) at a remote position of NN with a
terminal acetylene (Sonogashira coupling)11 or an arylboronic
acid (Suzuki coupling)12 has been reported. More recently,
Suzuki and Naota et al. reported a Negishi type cross-coupling
reaction of NN-C2-ide in the presence of zinc(II) chloride.13
We recently found that radical metalloid NN-AuPPh3 can
be utilized as an effective agent in the Pd(0)-mediated
cross-coupling14 with ArX (X = I, Br) to produce NN-Ar in
high yields (eq. 2 in Scheme 1).15 The developed reaction can
moiety with
a
low oxidation potential7a,c owing to the
contribution of resonance structure of NN-C2-ide radical
anion;7c however, they are very stable in solid and solution
states under aerated conditions at room temperature. Because of
these unique characteristics of radical metalloids, they are
applicable as useful organometallic synthetic reagents.
NN-Ar derivatives are generally prepared by the
condensation reaction of N,N'-dihydroxy-2,3-dimethylbutane-
2,3-diamine with various Ar-CHO followed by oxidation (eq. 1
in Scheme 1). However, the reaction is occasionally
unsuccessful, particularly when electron-donating2b,8,9 or
deficient8,10 aromatic aldehydes are used. In addition to the
condensation method, the cross-coupling of NN derivatives
with aryl halides is an attractive route to directly introduce the
Scheme 2. Structures of some NN-deivatives.

be applied to various ArX; this method clearly complements the
aforementioned condensation procedure. In order to find out
general and wider applicability of radical metalloids, we herein
investigate syntheses, properties, and reactivity of new radical
metalloids, NN-AuSIMes and NN-Cu(bdmpphen) (Scheme
2).
yield by basic treatment (NaOH in MeOH) of a CH2Cl2
solution containing an equimolar mixture of NN-H and
Cl-Cu(bdmpphen). Cl-Cu(bdmpphen) was readily prepared
from the reaction of bdmpphen with copper (I) chloride.
NN-Cu(bdmpphen) was stable in the solid state under
aerated conditions and in solution under an inert atmosphere.
This complex had an extremely low oxidation potential (vide
infra) and slowly decomposed under aerated conditions in
solution. Under chromatographic conditions, this compound
instantaneously decomposed.
Recrystallization of NN-Cu(bdmpphen) from i-PrOH
n-hexane provided single crystals suitable for X-ray crystal
structure. The molecular structure is shown in Figure 2, in
which large disorder in the OMe groups on phenanthroline,
the(CH3)2CC(CH3)2 moiety in NN, and incorporated
solvents was observed; i-PrOH was treated as usual disorder,
however, n-hexane could not be modeled and treated according
to the PLATON/SQUEEZE method as described in Table S2.
The bond angle, N1Cu°, and the CuN bond
lengths (2.037(3), 2.048(3) Å) are similar to those
(N1Cu°, CuN bond lengths = 2.024(8),
2.096(8) Å) of (4,7-diphenylphenanthroline)Cu(I)CF3.20 The
CuC2 bond length (1.868(4) Å) is shorter than Cu(I)-CF3
bond length (1.907(9) Å) or Cu(I)C(aryl sp2 carbon atom)
bond length (1.947(2) Å).21
2. Results and Discussion
Syntheses and Structures of NN-AuSIMes and
NN-Cu(bdmpphen): NN-AuSIMes (NN-AuLn complex with
a N-heterocyclic carbene ligand, Ln = SIMes (1,3-dimesityl-
imidazolidin-2-ylidene)) was prepared by basic treatment
(NaOH in MeOH) of a CH2Cl2 solution containing an
equimolar mixture of NN-H and Cl-AuSIMes16 in 71% yield.
NN-AuSIMes was stable in solid and solution states under
aerated conditions and even under usual silica gel
chromatographic conditions; on the other hand, NN-AuPPh3
could be purified on deactivated alumina containing 10% water.
Furthermore, slight decomposition of NN-AuPPh3 occurred in
aerated toluene after 3 days at room temperature, whereas no
decomposition was observed in the same solvent after a week
for NN-AuSIMes.
Recrystallization of NN-AuSIMes from toluenen-hexane
gave single crystals suitable for X-ray structure analysis.17 Two
independent structures were observed in a unit cell. They are
very similar and one of them is shown in Figure 1.
Crystallographic data are shown in Table S1. This complex has
an almost linear form (C1AuC2 = 175.9(3)° and 177.9(3)o
for the independent two molecules) based on 14 electrons as
the total valence electrons around Au(I) and a large twisted
dihedral angle (77.8° and 73.2°) between the NN
(O-N=C-N-O) and NHC (N-C1-N) planes. The AuC2
(2.019(7) and 2.036(7) Å), NO (1.285(9)1.287(9), and
1.300(8)1.312(8) Å), and C2N (1.344(9)1.357(10) and
1.350(9), 1.350(10) Å) bond lengths are similar to those of
NN-AuPPh3 (AuC2: 2.032 Å, NO: 1.2861.287 Å, C2N:
1.3511.357 Å). The AuC1 bond lengths (2.026(7) and
2.045(8) Å) are close to that (1.998(5) Å) of Cl-AuSIMes.16a
Figure 2.
Molecular structure of NN-Cu(bdmpphen).
Top view (a) and side view (b) at the 50% ellipsoid level.
Incorporated solvents and hydrogen atoms are omitted for
clarity.
ESR spectra of NN-AuSIMes and NN-Cu(bdmpphen):
The ESR spectrum of NN-AuSIMes in toluene at room
temperature is shown in Figure 3a. The ESR signal splits into
five lines with g = 2.0071, |aN| = 0.781 mT in a ratio of
1:2:3:2:1 due to the two equivalent 14N nuclei (I = 1).
Hyperfine coupling |aAu| due to 197Au (I = 3/2, natural
abundance (NA) = 100%) was not observed, suggesting a small
spin density on the Au atom. However, the small negative spin
density (0.0066) on the Au(I) dxy orbital was observed in the
spin density map calculated using a DFT method at the
UB3PW91/6-31G(d,p) level (Figure 3b).22
a
b
O1
N1
N2
C2
C2
Au
C1
O2
Figure 1. Molecular structure of NN-AuSIMes (one of
two independent molecules is shown). Top view (a) and
side view (b) at the 50% ellipsoid level. Hydrogen atoms
are omitted for clarity.
Although NN-AuSIMes was stable, the corresponding
Cu(I) complex was unstable and could not be isolated. Only a
few isolable Cu (I) reagents for the Pd(0)-mediated
cross-coupling have been reported in the case of
trifluoromethylation.18 After several unsuccessful trials, we
found that NN-Cu(bdmpphen) is an isolable complex and
works as a Pd(0)-mediated cross-coupling reagent with ArX to
Figure 3. Observed and simulated ESR spectra of
give NN-Ar. NN-Cu(bdmpphen) (NN-CuLn, Ln
bdmpphen19
[2,9-bis(2,6-
dimethoxyphenyl-1,10-phenanthroline]) was prepared in 89%
=
NN-AuSIMes [0
= 9.305459 GHz, [NN-AuSIMes] = 
2×104 M in toluene at room temperature] (a); calculated
=
spin density drawn at isovalue = 0.0007) (b).

NN-Cu(bdmpphen) showed a considerably different ESR
Table 1. Oxidation potentials of radical metalloids and NN-H.
pattern (Figure 4a) in the same solvent. The spectrum can be
ox, b
Compound
E1/2ox V (vs Fc/Fc+)a
E1/2
simulated with g = 2.0059, |aN| = 0.821 mT (14N×2, I = 1), |aCu
|
= 0.890 mT (63Cu, I = 3/2, NA = 69.2%), and 0.952 mT (65Cu, I
= 3/2, NA = 30.8%); hyperfine coupling due to the Cu(I) atom
was clearly observed in this case. The larger spin density
(0.0139) on the Cu(I) dxy-orbital was calculated (Figure 4b).
NN-H
+0.38
0.19
0.56
0.07
0.19
0
NN-AuSIMes
NN-Cu(bdmpphen)
NN-AuPPh3
0.57
0.95
0.45
0.57
NN-Pt(NCN)
aConditions: in CH2Cl2 in the presence of 0.1
M
n-Bu4NClO4: V vs Fc/Fc+ = 0 V (+0.48 V vs SCE), working
electrode: glassy carbon, counter electrode: platinum, reference
ox
ox
electrode: SCE, scan rate: 100 mV/s. bE1/2
(Compound) E1/2ox(NN-H).
= E1/2
Table 2. The cross-coupling reactions of NN-AuSIMes
with PhX.
Figure 4. Observed and simulated ESR spectra of
NN-Cu(bdmpphen)
[0
=
9.332783
GHz,
[NN-Cu(bdmpphen)] =  2×104 M in toluene at room
temperature] (a); calculated spin density drawn at isovalue =
0.0007 (b).
Reaction
Time
#
1
2
PhX
1a
Pd-catalyst
Solvent
THF
Yield
94
Pd(PPh3)4
10 mol%
Pd2(dba)3·CHCl3
5 mol%
3 h
The spin density on the group 11 metal(I) can be induced
by spin delocalization through a back-donation type orbital
interaction between the dxy (metal) and * (NN)-orbitals
(Figure 5). Judging from the spin density on the Cu(I) atom,
approximate contribution of the back-donation is  1%
assuming spin density = 1.0 on Cu(I) at the hypothetical 100%
back-donation.
1a
THF
1.5 h
6 h
92
Pd(PPh3)4
10 mol%
3
4
1b
1a
THF
57b
a
Pd(PPh3)2Cl2
10 mol%
DMF
3 h
19
aIn the presence of Cs2CO3 (1.5 equiv). bYield and
approximate conversion.
Figure 5. Spin delocalization scheme (a) and back-donation
through the orbital interaction between the dxy (metal) and
* (NN)-orbitals (b).
Scheme 3. Various Ar-X (2a,b14a,b, a: X = I, b: X = Br)
examined for cross-coupling reactions of radical metalloids.
Electrochemical Properties of NN-AuSIMes and
NN-Cu(bdmpphen): We previously reported that radical
metalloid NNPt(NCN) had a considerably lower oxidation
Pd(0)-Mediated
Cross-Coupling
Reactions
of
NN-AuSIMes: Cross-coupling reactions with PhX (1a: X = I,
1b: X = Br) were examined under the conditions described in
the general procedure (see experimental section). PhX (1.1
equiv), NN-AuSIMes (1.0 equiv), and a Pd catalyst (Pd(PPh3)4
(10 mol%) or Pd2(dba)3·CHCl3 (5 mol%)) were dissolved in a
dry solvent (typically THF) under nitrogen. Catalysts Pd(PPh3)4
and Pd2(dba)3·CHCl3 were equally effective; the reactions
proceeded more rapidly in the latter catalyst. Pd(PPh3)2Cl2 with
ox
potential of the NN-moiety (E1/2 = 0.19 V vs Fc/Fc+) than
NN-H.7a This low oxidation potential is considered to be due to
the contribution of the NN-C2-ide radical anion and is metal
dependent. NN-AuSIMes has the same oxidation potential as
NN-Pt(NCN). NN-Cu(bdmpphen) has an extremely low
oxidation potential (0.56 V) of the NN-moiety, which is 1 V
more negative compared to that of NN-H (Table 1 and Figure
S1).
Cs2CO3 was not
bromobenzene was slow and inefficient (entry 3 in Table 2;
57% conversion after 6 h).
a good catalyst. The reaction with

The reactions could be applied to various Ar-X (214)
(Scheme 3 and Table 3). Substrates with an ortho-substituent (4,
8) required longer reaction times and exhibited low yields
because of the steric interference or coordination of the
Pd-complex to the ortho-substituted Ar-NN product. The latter
possibility was supported by the slow reaction for the 2-thienyl
compound (11) and no reaction for the 2-pyridyl substrate (14).
The reaction with arylbromide, especially when an
electron-donating group was incorporated such as in 6b, was
extremely slow (entry 10 in Table 3; 34% conversion after 41
h). However, the arylbromides with an electron-deficient
substituent provided good yields within moderate reaction
times (entry 3, 7 in Table 3; 2b: 73%, 5b: 85% after 7 h).
decomposed in the Pd(PPh3)4-catalyzed reaction (entry 1 in
Table 4). The best yield was 76% (entry 3 in Table 4) in the
presence of 1,1'-bis(diphenylphosphino)ferrocene (DPPF, 10
mol%) using Pd2(dba)3·CHCl3 (5 mol%).
Table
4.
The
cross-coupling
reactions
of
NN-Cu(bdmpphen) with PhX.
Reaction
Time
#
PhX
Pd-catalyst
Yield
Table 3. The cross-coupling reactions of NN-AuSIMes
with various ArX.
1
2
1a
1a
Pd(PPh3)4, 10 mol%
30 min
30 min
25a
69
Pd2(dba)3·CHCl3, 5 mol%
Pd2(dba)3·CHCl3, 5 mol%/
3
1a
30 min
3 h
76
6a
DPPF, 10 mol%
Pd2(dba)3·CHCl3, 5 mol%/
4
1b
DPPF, 10 mol％
aA considerable
decomposed.
amount
of
NN-Cu(bdmpphen)
Reaction
Time
#
ArX
Pd-catalyst
Yield
1
2
3
4
2a
2a
2b
3a
Pd(PPh3)4, 10 mol%
Pd2(dba)3·CHCl3, 5 mol%
Pd(PPh3)4, 10 mol%
3 h
95
82
The coupling reactions of NN-Cu(bdmpphen) could be
applied to various ArX with short reaction times to obtain the
products in good yields (Table 5). The reactions with
electron-deficient ArBr gave moderate yields within reasonable
reaction times in contrast to that with electron-donating ArBr
(entry 2 and 6 vs 8 in Table 5). This feature is similar to that of
NN-AuSIMes system, although yields are higher in the
reactions with NN-AuSIMes.
30 min
7 h
73a
Pd(PPh3)4, 10 mol%
2 h
68
5
6
4a
5a
Pd(PPh3)4, 10 mol%
Pd(PPh3)4, 10 mol%
Pd(PPh3)4, 10 mol%
56 h
45
92
1.5 h
Table
5.
The
cross-coupling
reactions
of
7
8
5b
6a
6a
6b
7 h
3 h
85
73
NN-Cu(bdmpphen) with various ArX.
Pd(PPh3)4, 10 mol%
Pd2(dba)3·CHCl3, 5 mol%
Pd(PPh3)4, 10 mol%
9
40 min
41 h
72
10
34a
#
1
Ar-X
Reaction Time
15 min
Yield
71
11
12
13
14
7a
8a
9a
9a
Pd(PPh3)4, 10 mol%
Pd(PPh3)4, 10 mol%
Pd(PPh3)4, 10 mol%
Pd2(dba)3·CHCl3, 5 mol%
Pd(PPh3)4, 10 mol%
Pd(PPh3)4, 10 mol%
Pd(PPh3)4, 10 mol%
2.5 h
5 h
79
53a
91
88
87
89
84
79
0
2a
2
3
2b
3a
30 min
30 min
30 min
20 min
30 min
15 min
5 h
49a
62
67
74
63
73
5b
2 h
4
4a
40 min
3 h
5
5a
15 10a
16 11a
6
5b
7 h
7
6a
17 12a
18 13a
19 14a
1.5 h
2 h
8
6b
Pd(PPh3)4, 10 mol%
Pd(PPh3)4, 10 mol%
9
7a
40 min
30 min
15 min
20 min
30 min
20 min
20 min
2 h
48
62
64
66
75
65
82
0
72 h
10
11
12
13
14
15
16
8a
a Yield and approximate conversion.
9a
10a
11a
12a
13a
14a
Pd(0)-Mediated
Cross-Coupling
Cross-coupling
Reaction
reactions
of
of
NN-Cu(bdmpphen):
Cu(I)-phenanthroline complex NN-Cu(bdmpphen) with PhX
(1a,b) were carried out according to the general procedures
(see
experimental
section):
PhX
(1.2
equiv),
NN-Cu(bdmpphen) (1.0 equiv), and Pd catalyst
(Pd2(dba)3·CHCl3 (5 mol%) or Pd(PPh3)4 (10 mol%)) were
dissolved in dry THF under nitrogen. The results are shown in
Table 4. A considerable amount of NN-Cu(bdmpphen)
aYield and approximate conversion. bA considerable amount
of NN-Cu(bdmpphen) decomposed.

Additional Features of the Cross-Coupling Reactions of
NN-AuSIMes and NN-Cu(bdmpphen): The reactions could
be extended to introduce multiple NN groups on m- and
p-diiodobenzene in good yields with NN-AuSIMes and in
moderate yields with NN-Cu(bdmpphen) as shown in eq. 3
(Scheme 4), where the mono-adducts were formed in negligibly
small amount. The selective formation of bis-adducts is
probably due to the higher reactivity of the mono-adducts, in
which the NN group behaves as an electron-withdrawing group.
This result is consistent with the higher reactivity of
electron-deficient ArX in Tables 3, 5 (cf. compounds 2 and 5 vs
6). o-Diiodobenzene 17a only produced mono-adduct 17-NN
(eq. 4 in Scheme 4) because of the steric hindrance.
After stirring for 3 h at room temperature, further 300 mL of
CH2Cl2 was added to the copper(I) chloride suspension and the
mixture was stirred for 30 min and finally passed through a
Celite pad. The filtrate was concentrated under reduced
pressure to give Cl-Cu(bdmpphen) as a beige solid (1.95 g,
3.5 mmol, 95%). Cl-Cu(bdmpphen): C28H24ClCuN2O4, beige
1
solid; MW 551.51; H NMR (400 MHz, CDCl3) ppm) 8.38
(d, J = 8.2 Hz, 2H), 7.91 (s, 2H), 7.85 (d, J = 8.2 Hz, 2H), 7.39
(t, J = 8.4 Hz, 2H), 6.69 (d, J = 8.4 Hz, 4H), 3.76 (s, 12H); mp
o
> 300 C; MS (DART+) m/z 551 [(M+H)+], 550 [M+]; HRMS
(DART+): found m/z 550.07505; calcd for C28H24ClCuN2O4
m/z 550.07206; IR (KBr, cm–1) 2939, 2835, 2360, 2341, 1623,
1599, 1589, 1509, 1499, 1472, 1427, 1358, 1288, 1251, 1107,
1025, 849, 777, 734. 13C NMR could not be measured due to
the low solubility.
Interestingly, iodoethene 18a was also reactive (eq. 5 in
Scheme 4), although the 1,1-diiodoethene analogue was
entirely unreactive and even the mono-adduct was not formed
because of steric hindrance.
Synthesis of NN-Cu(bdmpphen): NN-H (534 mg, 3.4
mmol, 1.1 equiv) and Cl-Cu(bdmpphen) (1.70 g, 3.1 mmol,
1.0 equiv) were dissolved in CH2Cl2 (100 mL) under nitrogen.
Then, a MeOH solution of sodium hydroxide (0.65 M, 5.25 mL,
3.4 mmol, 1.0 equiv) was added to the CH2Cl2 solution. After
stirring for 4 h at room temperature, the solution was
concentrated to ca. 50 mL under reduced pressure, and then,
washed with water and brine. The organic layer was dried over
sodium sulfate and filtered. The filtrate was concentrated to ca.
15 mL under reduced pressure. Then, Et2O (90 mL) was added
to the concentrated mixture. The generated precipitate was
collected and washed with Et2O to give NN-Cu(bdmpphen) as
a
bluish purple solid (1.85 g, 2.7 mmol, 89%).
NN-Cu(bdmpphen): C35H36CuN4O6, bluish purple solid; MW
672.24; mp 218219 oC (decomp); MS (ESI+) m/z 672
[(M+H)+], 671 [M+]; HRMS (ESI+): found m/z 671.19176;
calcd for C35H36CuN4O6 m/z 671.19308; IR (KBr, cm–1) 2996,
2935, 2837, 2360, 2341, 1623, 1599, 1553, 1510, 1497, 1474,
1433, 1362, 1309, 1253, 1204, 1137, 1107, 1023, 858, 777;
ESR g = 2.0059 (v0 = 9.332783 GHz, |aN| (14N) = 0.821 mT,
|aCu| (63Cu) = 0.890 mT, |aCu| (65Cu) = 0.952 mT in toluene at
room temperature); Anal. Calcd. for C35H36CuN4O6·2H2O
recrystallized from 2-propanoln-hexane: C, 59.35; H, 5.69; N,
7.91; Found: C, 58.96; H, 5.55; N, 7.78. NN-Cu(bdmpphen) is
hygroscopic.
Scheme 4. Some useful cross-coupling reactions with radical
metalloids; condition A: NN-AuSIMes, Pd(PPh3)4 (20
mol%), condition B: NN-Cu(bdmpphen), Pd2(dba)3·CHCl3
(10 mol%), DPPF (20 mol%).
General Procedure for the Palladium-catalyzed
Cross-coupling Reactions of NN-AuSIMes: Aryl halide
(1a,b18a,b, 1.1 equiv, typically ca. 50 mg), NN-AuSIMes
(1.0 equiv) and a Pd catalyst [Pd(PPh3)4 (10 mol% in most
cases), or Pd2(dba)3·CHCl3 (5 mol% in most cases)] were
dissolved in a dry solvent (typically THF) under nitrogen. The
mixture was heated at THF reflux temperature (66 °C) until the
starting Au-complex was consumed (monitored by TLC,
usually 3 h for ArI but longer time for ArBr). After the reaction
mixture was concentrated under reduced pressure, toluene (ca.
3 mL) was added to the residue. The filtrate was concentrated.
The residue was separated and purified by chromatography, to
afford the cross-coupling product.
3. Experimental
Synthesis of NN-AuSIMes: NN-H (439 mg, 2.8 mmol, 1.0
equiv) and Cl-AuSIMes16 (1.50 g, 2.8 mmol, 1.0 equiv) were
dissolved in CH2Cl2 (150 mL) under nitrogen. Then, a MeOH
solution of sodium hydroxide (0.64 M, 4.4 mL, 2.8 mmol, 1.0
equiv) was added to the CH2Cl2 solution. After stirring for 4 h
at room temperature, the solution was concentrated under
reduced pressure. The residue was separated and purified by
silica gel column chromatography using AcOEt as eluent, to
give NN-AuSIMes as a purple solid (1.30 g, 2.0 mmol, 71%).
Single crystals suitable for X-ray crystal analysis were obtained
by recrystallization from toluenen-hexane. NN-AuSIMes:
C28H38AuN4O2, purple solid; MW 659.60; mp 220 oC
(decomp); MS (ESI+) m/z 682 [(M+Na)+], 660 [(M+H)+], 659
[M+]; HRMS (ESI+): found m/z 659.26573; calcd for
C28H38AuN4O2 m/z 659.26603; IR (KBr, cm–1) 2989, 2947,
1609, 1495, 1448, 1378, 1363, 1317, 1272, 1209, 1154, 1138,
1015, 855, 742, 621, 575, 538; ESR g = 2.0071 (v0 = 9.305459
GHz), |aN| (14N×2) = 0.781 mT in toluene at room temperature.
Synthesis of Cl-Cu(bdmpphen): Copper(I) chloride (386
mg, 3.9 mmol, 1.1 equiv) was added as a solid in one portion to
General Procedure for the Palladium-catalyzed
Cross-coupling Reactions of NN-Cu(bdmpphen): Aryl halide
(1a,b18a,b,
1.2
equiv,
typically
ca.
50
mg),
NN-Cu(bdmpphen) (1.0 equiv, typically ca. 50 mg),
Pd2(dba)3·CHCl3 (5 mol% in most cases), and DPPF (10 mol%
in most cases) were dissolved in dry THF under nitrogen. The
mixture was refluxed until the starting Cu-complex was
consumed (monitored by TLC, typically 30 min in most cases
for ArI). After the reaction mixture was concentrated under
reduced pressure, toluene (3 mL) was added into the residue.
The residual mixture was separated and purified by
chromatography, to afford the corresponding cross-coupling
product.
a
CH2Cl2
2,9-bis(2,6-dimethoxyphenyl)-1,10-phenanthroline
(bdmpphen)19 (1.67 g, 3.7 mmol, 1.0 equiv) under nitrogen.
solution
(100
mL)
containing

1-NN:23 C13H17N2O2, bluish crystals; MW 233.29; mp
85–86 °C; TLC Rf 0.68 (CH2Cl2AcOEt = 5:1 (v/v)); MS
(ESI+) m/z 234 [(M+H)+], 233 [M+].
molecular orbital interaction (dxy orbital * orbital
of NN moiety). Similar spin distribution was obtained
in the calculated spin density map for NN-AuSIMes.
ii) The oxidation potentials of the NN moieties of these
2-NN:24 C15H19N2O3, bluish green crystals; MW 275.32; mp
134–135 °C; TLC Rf 0.39 (CH2Cl2–AcOEt = 5:1 (v/v)); MS
(ESI+) m/z 276 [(M+H)+], 275 [M+].
radical metalloids were 0.19
NN-AuSIMes and 0.56
V
Fc/Fc+ for
Fc/Fc+
for
V
3-NN:24 C15H19N2O3, bluish green crystals; MW 275.32; mp
97–98 °C; TLC Rf 0.49 (CH2Cl2–AcOEt = 5:1); MS (ESI+)
m/z 275 [M+].
NN-Cu(bdmpphen); they are 0.57 V and 0.95 V
more negative than that of NN-H.
iii) These radical metalloids were applied to the
Pd(0)-mediated cross-coupling reagents with ArX (X =
Br, I) to give NN-Ar in moderate to high yields.
Multiple introduction of the NN-groups was possible.
This paper demonstrates the first copper reagent for
introduction of the NN radical in the cross-coupling
reactions with ArX.
4-NN:24 C15H19N2O3, purple crystals; MW 275.32; mp
134–135 °C; TLC Rf 0.41 (Et2O); MS (ESI+) m/z 276 [(M+H)+],
275 [M+].
5-NN:25 C13H16N3O4, green crystals; MW 278.28; mp
176177 °C; TLC Rf 0.28 (CH2Cl2); MS (ESI+) m/z 279
[(M+H)+], 278 [M+].
6-NN:26 C14H19N2O3, blue crystals; MW 263.31; mp 97–98 °C;
TLC Rf 0.45 (CH2Cl2–AcOEt = 5:1 (v/v)); MS (ESI+) m/z 264
[(M+H)+], 263 [M+].
Acknowledgement
The study was supported by Grant-in-Aid for Scientific
Research from JSPS KAKENHI (Grant Number JP17K05790
for M.K. and K.O. and JP26102005 for S.S.).
7-NN:26 C14H19N2O3, blue crystals; MW 263.31; mp 8384 °C;
TLC Rf 0.40 (CH2Cl2); MS (ESI+) m/z 264 [(M+H)+], 263 [M+].
8-NN:26 C14H19N2O3, purple crystals; MW 263.31; mp
118119 °C; TLC Rf 0.32 (Et2O); MS (ESI+) m/z 264 [(M+H)+],
263 [M+].
9-NN:27 C19H21N2O2, blue crystals; MW 309.38; mp
159–160 °C; TLC Rf 0.74 (CH2Cl2–AcOEt=5:1 (v/v)); MS
(ESI+) m/z 310 [(M+H)+], 309 [M+].
10-NN:28 C17H19N2O2, purple crystals; MW 283.34; mp
184185 °C; TLC Rf 0.47 (CH2Cl2AcOEt)=5:1 (v/v)); MS
(ESI+) m/z 284 [(M+H)+], 283 [M+].
11-NN:27 C11H15N2O2S, blue crystals; MW 239.31; mp
107108 °C; TLC Rf 0.31 (CH2Cl2); MS (ESI+) m/z 239 [M+].
12-NN:29 C12H16N3O2, blue crystals; MW 234.28; mp
127128 °C; TLC Rf 0.45 (Et2O); MS (ESI+) m/z 235 [(M+H)+],
234 [M+].
13-NN:29 C12H16N3O2, blue crystals; MW 234.28; mp
109110 °C; TLC (alumina) Rf 0.35 (CH2Cl2); MS (ESI+) m/z
235 [(M+H)+], 234 [M+].
15-NN:23 C20H28N4O4, purple crystals; MW 388.44; mp
231232 °C; TLC Rf 0.23 (CH2Cl2–AcOEt = 5:1 (v/v)); MS
(ESI+) m/z 389 [(M+H)+], 388 [M+].
Supporting Information available
Tables S1, S2 and Figure S1 are available as Supporting
Information.
16-NN:23 C20H28N4O4, purple crystals; MW 388.44; mp
214215 °C; TLC Rf 0.26 (Et2O); MS (ESI+) m/z 389 [(M+H)+],
388 [M+].
17-NN:30 C13H16IN2O2, purple crystals; MW 359.19; mp
163164 °C; TLC Rf 0.60 (CH2Cl2–AcOEt=5:1 (v/v)); MS
(ESI+) m/z 360 [(M+H)+], 359 [M+].
18-NN: C21H23N2O2, green crystals; MW 335.43; mp 150 °C;
TLC Rf 0.28 (CH2Cl2–AcOEt = 10:1 (v/v)); MS (DART+) m/z
336 [(M+H)+], 335 [M+]; HRMS (DART+): found m/z
335.17509; calcd for C21H23N2O2, m/z 335.17595; IR (KBr,
cm–1) 2993, 2924, 2853, 2360, 2342, 1604, 1574, 1494, 1466,
1444, 1405, 1388, 1371, 1261, 1215, 1170, 1136, 876, 776,
701.; ESR g=2.0068 (v0=9.340526 GHz, a(14N×2)=0.731 mT,
a(1H×1) = 0.289 mT in toluene at room temperature.
References
1.
(a) (a) Magnetic Properties of Organic Materials, ed. by
P. M. Lahti, Marcel Dekker, New York, 1999; (b) Stable
Radicals: Fundamentals and Applied Aspects of
Odd-Electro Compounds, ed. by R. G. Hicks, Wiley,
Chichester, UK, 2010.
2.
(a) S. Suzuki, K. Okada, Magnetic Properties of
Multiradicals Based on Triarylamine Radical Cations
(Chapter 8, pp. 269285) in Organic Redox Systems, ed
by T. Nishinaga, Wiley, New Jersey, 2016; (b) M. Kuratsu,
S. Suzuki, M. Kozaki, D. Shiomi, K. Sato, T. Takui, T.
Kanzawa, Y. Hosokoshi, X.-Z. Lan, Y. Miyazaki, A.
Inaba, and K. Okada, Chem.Asian. J. 2012, 7, 1604; (c)
S. Suzuki, T. Wada, R. Tanimoto, M. Kozaki, D. Shiomi,
K. Sugisaki, K. Sato, T. Takui, Y. Miyake, Y. Hosokoahi,
K. Okada, Angew. Chem. Int. Ed. 2016, 55, 10791; (d) S.
Suzuki, N. Tanaka, M. Kozaki, D. Shiomi, K. Sato, T.
Takui, K. Okada, Chem. Eur. J. 2017, 23, 16014.
4. Conclusion
We have newly synthesized two radical matalloids,
NN-AuSIMes and NN-Cu(bdmpphen) (NN: nitronyl
nitroxide) and investigated their physicochemical properties
and chemical reactivity as Pd(0)-mediated cross-coupling
reagents. The results are briefly summarized as follows:
3.
4.
D. G. B. Boocock, R. Darcy, E. F. Ullman, J. Am. Chem.
Soc. 1968, 90, 5945.
S. Suzuki, T. Furui, M. Kuratsu, M. Kozaki, D. Shiomi, K.
Sato, T. Takui, K. Okada, J. Am. Chem. Soc. 2010, 132,
i) The ESR spectra showed a small but clear spin density
on the Cu(I) atom for NN-Cu(bdmpphen), indicating
spin delocalization through
a back-donation type

20. Z. Weng, R. Lee, W. Jia, Y. Yuan, W. Wang, X. Feng,
K.-W. Huang, Organometallics 2011, 30. 3229.
21. M. D. Janssen, K. Ko1hler, M. Herres, A. Dedieu, W. J. J.
Smeets, A. L. Spek, D. M. Grove, H. Lang, G. van Koten,
J. Am. Chem. Soc. 1996, 118, 4817.
15908.
5.
6.
R. Weiss, N. Kraut and F. Hampel, J. Organomet. Chem.
2001, 617–618, 473.
(a) E. V. Tretyakov, S. E. Tolstikov, G. V. Romanenko, A.
S. Bogomyakov, D. V. Stass, A. G. Maryasov, N. P.
Gristan, V. I. Ovcharenko, Russ. Chem. Bull. 2011, 60,
2608; (b) O. N. Chupakhin, I. A. Utepova, M. V. Varaksin,
E. V. Tretyakov, G. V. Romanenko, D. V. Stass, V. I.
Ovcharenko, J. Org. Chem. 2009, 74, 2870; (c) V. I
Ovcharenko, O. N. Chupakhin, I. S. Kovalev, E. V.
Tretyakov, G. V. Romanenko, D. V. Stass, Russ. Chem.
Bull. 2008, 57, 2227; (d) M. V. Varaksin, E. V. Tretyakov,
I. A. Utepova, G. V. Romanenko, A. S. Bogomyakov, D. V.
Stass, R. Z. Sagdeev, V. I. Ovcharenko, O. N. Chupakhin,
Russ. Chem. Bull. 2012, 61, 1469; (e) S. Tolstikov, E.
Tretyakov, S. Fokin, E. Suturina, G. Romanenko, A.
Bogomyakov, D. Stass, A. Maryasov, M. Fedin, N.
Gritsan, V. Ovcharenko, Chem. Eur. J. 2014, 20, 2793; (f)
E. V. Tretyakov, P. A. Fedyushim, E. V. Panteleeva, D. V.
Stass, I. Y. Bagryanskaya, I. V. Beregovaya, A. S.
Bogomyakov, J. Org. Chem., 2017, 82, 4179.
(a) Xun Zhang, S. Suzuki, M. Kozaki, K. Okada, J. Am.
Chem. Soc. 2012, 134, 17866; (b) S. Suzuki, H. Yokoi, M.
Kozaki, Y. Kanzaki, D. Shiomi, K. Sato, T. Takui, K.
Okada, Eur. J. Inorg. Chem. 2014, 4740. (c) R. Tanimoto,
K. Yamada, S. Suzuki, M. Kozaki, K. Okada, Eur J. Inorg.
Chem. 2018, 1198.
E. F. Ullman, J. H. Osiecki, D. G. B. Boocock, R. Darcy,
J. Am. Chem. Soc. 1972, 94, 7049.
S. Hiraoka, T. Okamoto, M. Kozaki, D. Shiomi, K. Sato,
22. Gaussian 09, Revision C.01, M. J. Frisch, G. W. Trucks,
H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H.
Nakatsuji, X. Li, M. Caricato, A. Marenich, J. Bloino, B.
G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian,
J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D.
Williams-Young, F. Ding, F. Lipparini, F. Egidi, J.
Goings, B. Peng, A. Petrone, T. Henderson, D.
Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G.
Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R.
Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A.
Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J.
J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T.
Keith, R. Kobayashi, J. Normand, K. Raghavachari, A.
Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi,
J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W.
Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B.
Foresman, and D. J. Fox, Gaussian, Inc., Wallingford CT,
2016.
7.
23. J. H. Osiecki, E. F. Ullman, J. Am. Chem. Soc. 1968, 90,
1078.
24. R. Tanimoto, S. Suzuki, M. Kozaki, K. Okada, Chem.
Lett. 2014, 43, 678.
8.
9.
25. E. F. Ullman, J. H. Osiecki, D. G. B. Boocock, R. Darcy,
J. Am. Chem. Soc. 1972, 94, 7049.
26. O. Shimomura, K. Abe, M. Hirota, J. Chem. Soc., Perkin
Trans. 2, 1988, 795.
T. Takui, K. Okada, J. Am. Chem. Soc. 2004, 126, 58.
10. a) Y. Hosokoshi, M. Tamura, H. Sawa, R. Kato, M.
Kinoshita, J. Mater. Chem. 1995, 5, 41. b) O. V.
Koreneva, G. V. Romanenko, Y. G. Shvedenkov, V. N.
Ikorskii, V. I. Ovcharenko, Polyhedron 2003, 22, 2487.
11. a) Y. Miura, T. Issiki, Y. Ushitani, Y. Teki, K. Itoh, J.
Mater. Chem. 1996, 6, 1745. b) S. V. Klyatskaya, E. V.
Tretyakov, S. F. Vasilevsky, Russ. Chem. Bull. 2002, 51,
128. c) C. Stroh, M. Mayor, C. von Hänisch, Tetrahedron
Lett. 2004, 45, 9623. 9. Stroh.
27. Nozawa, K. ; Hosokoshi, Y.; Shiomi, D.; Tamura, M.;
Iwasawa, N.; Saswa, H.; Kato, R.; Kinoshita, M. Synth.
Met. 1993, 56, 3323.
28. (a) T. Sugano, M. Kurmoo, P. Day, F. L. Pratt, S. J.
Blundell, W. Hayes, M. Ishikawa, M. Kinoshita, Y.
Ohashi, Mol. Cryst. Liq. Cryst. Sci. 1995, 271, 107; (b) A.
G. Matveeva, E. M. Glebov, V. V. Korolev, I. P.
Pozdnyakov, V. F. Plyusnin, D. V. Stass, V. A. Reznikov,
High Energy Chemistry 2011, 45, 416.
12. C. Stroh, M. Mayor, C. von Hänisch, Eur. J. Org. Chem.
2005, 3697.
13. S. Suzuki, F. Nakamura, T. Naota, Mater. Chem. Front.
2018, 2, 591.
29. M. S. Davis, K. Morokuma, R. W. Kreilick, J. Am. Chem.
Soc. 1972, 94, 5588.
14. The Pd(0) mediated cross-coupling reactions using
organogold(I) (not involving a radical) reagent has been
well reported by Sarandeses, Sestelo, and co-workers: a)
M. Peña-López, M. Ayán-Varela, L. A. Sarandeses, J. P.
Sestelo, Chem.Eur. J. 2010, 16, 9905. b) M. Peña-López,
L. A. Sarandeses, J. P. Sestelo, Eur. J. Org. Chem. 2013,
2545.
30. S. Nakatsuji, M. Saiga, N. Haga, A. Naito, T. Hirayama,
M. Nakagawa, Y. Oda, H. Anzai, K. Suzuki, T. Enoki, M.
Mito, K. Takeda, New. J. Chem. 1998, 22, 275.
15. R. Tanimoto, S. Suzuki, M. Kozaki, K. Okada, Chem.
Lett. 2014, 43, 678.
16. (a) P. de Fre´mont, N. M. Scott, E. D. Stevens, S. P.
Nolan, Organometallics 2005, 24. 2411; (b) R. Visbal, A.
Laguna, M. C. Gimeno, Chem. Commun. 2013, 49, 5642.
17. The crystallographic data have been deposited to the
Cambridge Crystallographic Data Centre (NN-AuSIMes:
CCDC 1819870, NN-Cu(bdmpphen): CCDC 1819871.
18. (a) G. G. Dubinina, H. Furutachi, D. A. Vicic, J. Am.
Chem. Soc. 130, 8600. (b) M. Oishi, H. Kondo, H. Amii,
Chem. Comm. 2009, 1909. (c) H. Morimoto, T. Tsubogo,
N. D. Litvinas, J. F. Hartwig, Angew. Chem. Int. Ed. 2011,
50, 3793.
19. U. Lüning, M.Abbass, F. Fahrenkrug, Eur. J. Org. Chem.
2002, 3294.