Synthesis of triisocyanomesitylene β?diketiminato copper(I) complexes and evaluation of isocyanide π-back bonding

Article abstract of DOI:10.1016/j.poly.2020.114828

A new 2,4,6-triisocyanomesitylene ligand was synthesized and along with 1,4-isocyanobenzene utilized to prepare unique N-aryl-N′-alkylpyridyl β-diketiminato copper(I) complexes. Crystallographic characterization of 2,4,6-triisocyanomesitylene, dinuclear a

Full text of DOI:10.1016/j.poly.2020.114828

Polyhedron 192 (2020) 114828
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis of triisocyanomesitylene b diketiminato copper(I) complexes
and evaluation of isocyanide
p-back bonding
Yen-Chung Huang a, Hsing-Yin Chen a, Yu-Lun Chang a,d, Punitharaj Vasanthakumar b, Shih-Yun Chen a,
Chai-Lin Kao a,c, Carol Hsin-Yi Wu c, Sodio C.N. Hsu a,c,d,
⇑
a Department of Medicinal and Applied Chemistry, Drug Development and Value Creation Research Center, Kaohsiung Medical University, Kaohsiung 807, Taiwan
b Department of Chemistry, National Institute of Technology, Tiruchirappalli 620 015, India
c Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 807, Taiwan
d Department of Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
A new 2,4,6-triisocyanomesitylene ligand was synthesized and along with 1,4-isocyanobenzene utilized
to prepare unique N-aryl-N0-alkylpyridyl b-diketiminato copper(I) complexes. Crystallographic character-
ization of 2,4,6-triisocyanomesitylene, dinuclear and trinuclear copper isocyanide complexes were car-
ried out to elucidate their structural features. The FT-IR spectroscopic analysis of the prepared copper
(I) isocyanide complexes show the CN stretching frequencies experience a significant red shift relative
Received 15 August 2020
Accepted 2 October 2020
Available online 12 October 2020
Keywords:
Isocyanide ligand
b-Diketiminato copper complex
to those of the free ligands, indicating that
p-back bonding interaction exist between copper(I) centers
and isocyanide moieties. DFT based frontier molecular orbital analysis demonstrated that the enhanced
p-back bonding is a consequence of the
p
-accepting abilities of the 1,4-diisocyanobenzene and 2,4,6-tri-
p-Back bonding interaction
isocyanomesitylene ligands.
Ó 2020 Elsevier Ltd. All rights reserved.
1. Introduction
to probe the combined electronic and structural features of Cu(I)
complexes. Most of b-diketiminato copper(I)–CO adducts display
The b-diketiminates with differing electronic and steric proper-
ties have been utilized as spectator chelating ligands [1–3] in a
variety of alkaline earth, main group, lanthanide, actinide and tran-
sition metal complexes [4,5]. Moreover, many studies have been
conducted to elucidate the effects of functional groups on the
b-diketiminate ligands [6–15], but only few have focused on unsym-
metrical b-diketiminates [16–20]. b-Diketiminato copper(I) com-
plexes containing CO, isocyanides (CNRs), and phosphine ligands
have been widely studied [6–8,10–12,15,18,21,22], and nearly a
dozen of investigations have concentrated on complexes where the
metal is coordinated with mono-isocyanides [6,7,10–12,15,18].
An understanding of the electron-donating characteristics of
copper(I) complexes has come from studies of the CO binding abil-
ity in terms of the formation of copper(I)–CO adducts [18,21,22].
However, the reversible nature of CO binding usually causes isola-
tion of copper(I)–CO adducts to be difficult and this issue limits
structural characterization of the complexes. In contrast, b-dike-
timinato copper(I) isocyanide complexes are much more thermo-
dynamically stable and, as a result, they serve as better systems
CO stretching frequencies (
that of uncoordinated CO (2143 cmꢀ1), indicating that the CO
ligand participates in a strong -accepter interaction with the cop-
per(I) center. In contrast, isocyanides are stronger -donors and
weaker -accepters than CO [6,7,10–12,15,18]. Therefore, the b-
mCO) that are lower (red shifted) than
p
r
p
diketiminato copper(I)-isocyanide adducts usually show blue shift
on the CNRs stretching frequencies, indicating isocyanide ligand
predominantly as
[6,7,10,12,18].
r donors and p acceptor interactions are minor
In a previous investigation, we found that the mono-isocyanide
(2,6-xylylisocyanide) induces de-coordination of the chelating pyr-
idyl arm of the unsymmetrical N-aryl-N0-alkylpyridyl b-diketimi-
nato ligand in the copper(I) complexes CuL1 (1) and CuL2 (2)
(Scheme 1) while the Cu(I) center remains three coordinated
[18]. However, no reports exist describing b-diketiminato copper
(I) complexes that contain poly-isocyanides as bridging ligands.
In the study described below, we prepared b-diketiminato copper
(I) complexes that contain 1,4-diisocyanobenzene and new 2,4,6-
triisocyanomesitylene as bridging ligands, and assessed their
structural and electronic properties by using NMR and FT-IR spec-
troscopy as well as X-ray crystallography. Importantly, an analysis
the CN vibrational frequencies in the isocyanide ligands in these
⇑
Corresponding author.
E-mail address: sodiohsu@kmu.edu.tw (S.C.N. Hsu).
https://doi.org/10.1016/j.poly.2020.114828
0277-5387/Ó 2020 Elsevier Ltd. All rights reserved.

Yen-Chung Huang, Hsing-Yin Chen, Yu-Lun Chang et al.
Polyhedron 192 (2020) 114828
N-aryl-N0-alkylpyridyl b-diketiminato copper(I) complexes 1 and 2
[18]. For this purpose, toluene solutions of 1 or 2 containing stoi-
chiometric amounts of either 1,4-diisocyanobenzene or 2,4,6-tri-
isocyanomesitylene were stirred under a N2 atmosphere at room
temperature (Scheme 3). The progress of each reaction was moni-
tored using FT-IR spectroscopy and by following a color change of
the solution from clear red–orange to a yellow-orange suspension.
The pure orange, air-sensitive copper complexes, obtained by using
filtration, were characterized by using 1H NMR, 13C NMR and FT-IR
spectroscopy, and elemental analysis.
As expected, the 1H NMR spectrum of 2,4,6-triisocyanome-
sitylene in CDCl3 (Figs. S1-S2) contains a methyl singlet at
2.57 ppm, and its 13C NMR spectrum of contains a peak at
171.68 ppm, assigned to the isocyanide carbon, at 133.61 and
125.98 ppm for the arene ring carbons, and at 16.43 ppm for the
methyl groups. The NMR spectra of N-aryl-N0-alkylpyridyl b-dike-
timinato copper(I) complexes 1 and 2 have been described in pre-
vious studies[18]. The 1H NMR and 13C NMR spectra of complexes
3–6 (Figs. S3-S10) contain signals associated with both b-diketim-
inate and isocyanide ligands. Moreover, in a manner that is consis-
tent with previous findings[18], the 1H NMR signals for H-6 of the
pyridine ring in the uncoordinated pyridyl arm of complexes 3–6
(8.47, 8.47, 8.57 and 8.53 ppm, respectively) are shifted downfield
with respect to the analogous proton resonances in the corre-
sponding copper(I) complexes 1–2 (7.86 and 7.95 ppm, respec-
tively[18].
Scheme 1. Synthesis of copper(I) complexes CuL1 (1) and CuL2 (2).
complexes has contributed to an understanding of bonding inter-
actions occurring between metal fragment and new isocyanide
ligands.
2. Results and discussion
2.1. Synthesis of new 2,4,6-triisocyanomesitylene
Isocyanides are typically synthesized by using dehydration
reactions of N-substituted formamides or by the carbylamine reac-
tion of amines with chloroform under basic conditions [23–25]. We
have employed the earlier procedure used to produce 1,4-diiso-
cyanobenzene [24] to prepare the previously unknown 2,4,6-triiso-
cyanoomesitylene
starting
with
2,4,6-triaminomesitylene,
´
generated by a modification of the route used by Havlık et al.
[26]. Specifically, 2,4,6-trinitromesitylene was produced by nitra-
tion of mesitylene using fuming nitric acid and sulfuric acid
(Scheme 2) and then reduced employing SnCl2 and conc.
hydrochloric acid to give 2,4,6-triaminomesitylene. The 2,4,6-tri-
aminomesitylene was transformed to 2,4,6-triformamidome-
sitylene by reaction with formic acid in refluxing toluene for 4 h.
Finally, dehydration of the 2,4,6-triformamidomesitylene was car-
ried out by treatment with POCl3 and triethylamine. Column chro-
matographic purification gave 2,4,6-triisocyanomesitylene as a
disagreeable smelling, air stable, non-hygroscopic and highly
organic soluble white solid in 25% yield.
2.3. X-ray crystallographic results
X-ray quality single crystals of 2,4,6-triisocyanomesitylene and
Cu(I) complexes 3–6 were obtained from concentrated hexane
solutions at ꢀ20 ℃. Representations of the molecular structures
of 2,4,6-triisocyanomesitylene and complexes 3–6 are shown in
Figs. 1-3 and supporting information (Figs. S11-S13), and selected
bond distances and angles are listed in Table 1. In its molecular
structure, the three isocyanide groups of the 2,4,6-triisocyanome-
sitylene ligand are oriented in a 120° manner with each CANAR
angle lying in the range of 178-179°. In addition, the CN bond dis-
tances in fall in the range of 1.157–1.161 Å, which is expected for
isocyanide CN triple bonds[27–30]. Furthermore, analysis of the
structures of complexes 3–6 shows that the de-coordinated pyri-
dine moiety is replaced by an isocyanide ligand and that all related
bond distances and angles are similar to those reported for other
b-diketiminato copper isocyanide complexes[6,10–12,18]. The
2.2. Synthesis and characterizations of copper(I) isocyanide complexes
The respective di- (3 and 4) and tri- (5 and 6) nuclear copper
complexes were prepared starting with the previously synthesized
Scheme 2. Synthesis of triisocyanomesitylene.
2

Yen-Chung Huang, Hsing-Yin Chen, Yu-Lun Chang et al.
Polyhedron 192 (2020) 114828
Scheme 3. Synthesis of N-aryl-N0-alkylpyridyl b-diketiminato copper(I) complexes 3–6 containing isocyanide bridging ligands.
Fig. 2. ORTEP representation of the crystal structure of 3. (50% ellipsoid; all H atoms
are omitted for clarity).
2.4. FT-IR investigations of copper(I) isocyanide adducts
Fig. 1. ORTEP representation of the crystal structure of 2,4,6-triisocyanomesitylene.
(50% ellipsoid; all H atoms are omitted for clarity).
FT-IR is a superior method for characterizing the nature of elec-
tronic interactions occurring between metals and CNR ligands.
Typically in higher-valent metal or Group 11 triad metal (formal + 1
oxidation state) complexes, the stretching frequencies of the CN
triple bond in metal bonded CNRs are higher than that of the free
ligand (blue shift), indicating that the ligands interact with the
copper(I) centers in the complexes all display three coordination
geometries arising from bonding with two N donors from b-dike-
timinate backbone and one C donor from isocyanide ligand. The
CN triple bond distances in 3–6 are in the 1.146–1.175 Å range,
which are similar to those of related complexes [6,10–12,18]. In
3–6, the CN bonds are slightly longer and the CANAR bond angles
are slightly distorted away from 180° than the those of the free
metal ion predominantly as
r donors and that their p acceptor
interactions are minor [11,15,31–40]. However, some examples
of isocyanide complexes (especial on the electron rich low-valent
metal center) do exist in which CAN stretching frequencies are
2,4,6-triisocyanomesitylene ligand as a consequence of
p-back
bonding interactions with the copper(I) center (see below).
red shifted, indicating significant
p-interactions occur in these
3

Yen-Chung Huang, Hsing-Yin Chen, Yu-Lun Chang et al.
Polyhedron 192 (2020) 114828
Table 2
CAN Vibrational Frequency Data for Selected b-Diketiminato Copper(I)
Complexes
ꢀ
CNR
CNR, cmꢀ1
D
mCNR cmꢀ1
ref
a,
compound
m
2,6-xylyl isocyanide
1,4-diisocyanobenzene
2,4,6-triisocyanomesitylene
2119
2121
2115
2111
2109
2101
2100
2121
2123
2128
2126
2122
2122
2114
2114
–
–
–
ꢀ10
ꢀ12
ꢀ14
ꢀ15
+2
+4
+9
+7
+3
[18]
[24]
this work
this work
this work
this work
this work
[10]
[12]
[7]
[6]
[18]
3
4
5
6
A
B
C
D
E
F
Fig. 3. ORTEP representation of the crystal structure of 5. (50% ellipsoid; all H atoms
are omitted for clarity).
+3
[18]
[15]
[11]
systems between the metal and isocyanide ligand [41–46]. It is
clear that a systematic study analysing factors for b-diketiminato
G
H
ꢀ5
ꢀ5
copper(I) complexes that govern the degree of
p-interactions by
a
D
mCNR = the difference of wavenumber between complexes and the corre-
using CNR stretching frequencies is required in order to gain
understanding of the electronic features of bonding between
b-diketiminato copper(I) moieties and CNRs [6,7,10–12,15,18].
In order to explore relationships that exist between the struc-
tures and the isocyanide ligand electronic interactions with b-dike-
timinato copper(I) fragment, we compared differences of CN
sponding free ligand.
occurs at a higher wavenumber (larger blue shift) than that of B,
where as those of complexes G and H, containing N, N0-isopropyl
and N, N0-benzyl groups have negative
D
mCNR values (red shifted).
The red shift of the CN stretching frequency in these cases indicates
that stronger -back bonding interactions take place between the
stretching frequencies (DmCNR) between complexes and the corre-
sponding free ligand of the previously prepared b-diketiminato
copper(I) isocyanide adducts A-H with those of the new isocyanide
copper(I) complexes 3–6 (Table 2). The data show that differences
p
isocyanide ligand and copper center as a result of the stronger elec-
tron donating ability of N, N0-alkyl substituents in comparison to N,
N0-aryl substituents on the b-diketiminate backbone. The positive
in the
DmCNR values of complexes A, B and D, which contain the
same 2,6-xylyl isocyanide ligand, are a consequence of the nature
of functional groups present on the N-aryl substituents. Specifi-
cally, the mesityl, dimethylphenyl, and diisopropylphenyl groups
DmCNR values displayed by complexes E and F suggest that the elec-
tron donation abilities of the unsymmetrical b-diketiminate
ligands are similar to those of the N, N0-aryl substituted analogs.
Inspection of the CN stretching regions of the FT-IR spectra of
complexes 3–6 displayed in Figs. 4 and 5 shows that the stretching
in these substances increasingly enhance
r donation from the iso-
cyanide ligand to the copper(I) core. The stretching frequency of
complex C, which possess Cl groups on b-diketiminate backbone,
Table 1
Selected Bond Lengths and Angles for b-Diketiminato Copper(I) ꢀ CNR Complexes.
C„N (Å)
Cu—C (Å)
–
Cu–N (Å)
–
C„N—C (o)
N—Cu–N(o)
–
ref
2,4,6-triisocyanomesitylene 1.157(4) 1.157(4)
1.161(4)
178.0(3) 178.8(3)
178.7(3)
174.5(3)
This
work
This
work
This
work
This
work
This
work
[10]
[12]
[6]
3
4
5
6
1.163(3)
1.804(3)
1.9298(19)a, 1.924(2)b
99.41(8)
1.150(11), 1.146
(10)
1.156(6), 1.175(6),
1.152(6)
1.159(12), 1.159
(14) 1.174(14)
1.159(2)
1.157(3)
1.158(3)
1.159(4)
1.159(2)
1.829(10)1.822
(10)
1.804(6)1.775(6)
1.800(5)
1.802(11)1.798
(13)1.808(15)
1.814(2)
1.822(2)
1.817(2)
1.808(4)
1.816(2)
1.940(7)a, 1.920(7)b,1.942(7)a, 1.894(8)b
177.7(10)177.8
(10)
167.7(5)175.9(5)
176.4(5)
175.7(12)172.8
(13)171.9(11)
177.01(16)
173.8(2)
100.4(3)99.3(3)
1.927(4)a, 1.909(4)b,1.918(4)a, 1.931
(4)b,1.939(4)a, 1.918(4)b
1.934(9)a, 1.930(8)b,1.967(11)a, 1.903
(11)b,1.956(8)a, 1.921(9)b
1.945(1)a, 1.926(2)a
99.40(17)98.92
(17)99.03(17)
101.7(4)99.6(5)
100.1(4)
97.85(6)
98.08(6)
98.20(7)
98.55(11)
98.4(1)
A
B
D
E
1.933(2)a, 1.946(2)a
1.928(2)a, 1.962(2)a
171.4(2)
176.6(3)
172.49(16)
1.937(3)a, 1.921(3)b
[18]
[11]
H
1.941(1)b, 1.941(1)b
a
Cu ꢀ N[amide(aryl)]. bCu ꢀ N[amide(alkyl)].
4

Yen-Chung Huang, Hsing-Yin Chen, Yu-Lun Chang et al.
Polyhedron 192 (2020) 114828
a consequence, in most 2,6-xylyl isocyanide complexes with Cu
(I), the inductive effect of the positively charged metal dominates
over p
-back donation by the isocyanide ligand,44 resulting in blue
shifts of mCNR (A-F in Table 1). However, the presence of a second
and third CN group on the aryl ring significantly lowers the LUMO
energy and, therefore, enhances the
p -accepting capability of
ligand (-2.326 eV for 1,4-diisocyanobenzene and ꢀ2.149,
ꢀ2.131 eV for 1,3,5-triisocyanomesitylene vs. ꢀ1.240 eV for
2,6-xylyl isocyanide). Thus,
p-back donation by the 1,4-diiso-
cyanobenzene and 2,4,6-triisocyanomesitylene ligands overwhelms
the Cu(I) inductive effect in the newly prepared complexes 3–6.
3. Conclusion
In the effort described above, the new isocyanide ligand, 2,4,6-
triisocyanomesitylene, was synthesized and its structural features
were characterized by using X-ray diffraction analysis. This ligand
and its 1,4-diisocyanobenzene analog, where the respective
isocyanides are 120° and 180° disposed, were utilized to prepare
N-aryl-N0-alkylpyridyl b-diketiminato copper(I) dinuclear and trin-
uclear complexes 3–6. The NMR, FT-IR, and X-ray structures of the
complexes indicate that the pyridine ring nitrogen in the pyridyl
arm is not coordinated with the copper(I) center and isocyanide
binds in its place. A comparison of CN stretching frequencies shows
Fig. 4. CNR regions of FT-IR spectra of toluene solutions of (a) 1,4-diisocyanoben-
zene, (b) 3, and (c) 4.
that
p-back bonding from the copper(I) center to the isocyanide
group in 2,6-xylylisocyanide containing N-aryl-N0-alkylpyridyl
b-diketiminate complexes is enhanced by more strongly electron
donating substituents on the b-diketiminate. Moreover, a
p-back
bonding from Cu(I) to the isocyanide moieties take place in 3–6
relative to complexes of 2,6-xylylisocyanide. DFT analysis indicates
that 1,4-diisocyanobenzene and 2,4,6-triisocyanomesitylene
ligands have enhanced
p-accepting abilities relative to that of
2,6-xylylisocyanide as a result of their lower LUMO energies.
Furthermore, the results show that 1,4-diisocyanobenzene and
2,4,6-triisocyanomesitylene ligands act as bridging units in metal
complexes with unique linear and triangular coordination sites.
4. Experimental section
Fig. 5. CNR regions of FT-IR spectra of toluene solutions of (a) 2,4,6-triisocyanome-
sitylene, (b) 5, and (c) 6.
All manipulations carried out under an atmosphere of purified
dinitrogen using standard Schlenk techniques. Chemical reagents
were purchased from Aldrich Chemical Co. Ltd., Lancaster Chemi-
cals Ltd. or Fluka Ltd. IR spectra were recorded on a Bruker Optics
FTIR Alpha OPUS. 1H NMR and 13C NMR spectra were acquired on
JEOL-400 NMR. Elemental analyses were performed on a Heraeus
CHN-OS Rapid Elemental Analyzer. CuL1 and CuL2 were synthe-
sized by using a previously reported method [18]. 1,4-Diiso-
cyanobenzene was synthesized by using a previously reported
method[24]. 2,4,6-Triaminomesitylene was synthesized using a
slight modification of a previously reported method[26].
frequencies (
mCNR) of free 1,4-diisocyanobenzene and 1,3,5-triiso-
cyanomestylene ligands are 2121 and 2115 cmꢀ1, respectively.
The mCNR values of the Cu(I) complexes
3 4
(2111 cmꢀ1),
(2109 cmꢀ1), 5 (2101 cmꢀ1), and 6 (2100 cmꢀ1) are red-shifted rel-
ative to the corresponding free isocyanide ligands (significant neg-
ative
DmCNR), indicating that the isocyanide ligands in all
complexes participate in strong
p-back bonding. Significantly, the
respective mCNR values of 5 and 6 of 2101 and 2100 cmꢀ1 are the
lowest observed thus far for copper(I) isocyanide complexes. It is
interesting to speculate that the abnormally strong back bonding
taking place between Cu(I) and the isocyanide groups in these
4.1. Preparation of 2,4,6-Triisocyanomesitylene
complexes is a result of the stronger
p-accepting abilities of
1,4-diisocyanobenzene and 2,4,6-triisocyanomesitylene.
Mesitylene (10 mL, 71.6 mmol) was slowly added to a mixture
of 42 mL sulfuric acid and 21 mL fuming nitric acid at 0 ℃. The mix-
ture was stirred at 0 ℃ for 2 h and poured onto ice. Precipitated
solid was separated by filtration, and washed with water and
methanol. A solution of the solid in ethanol was stirred at reflux
overnight, and filtered to give a solid that was dried in vacuum,
giving 10.4 g (57%) of 2,4,6-trinitromesitylene as a white solid.
2,4,6-Trinitromesitylene (3.0 g, 11.8 mmol) was stirred with
SnCl2ꢁ2H2O (31.8 g, 140.9 mmol) in concentrated HCl (300 mL) at
110 ℃ for 5 h. The solution was carefully made basic at 0 ℃ by
addition of concentrated aqꢁNH3 and extracted with dichloro-
methane. The extracts were dried over by MgSO4 and concentrated
2.5. Computational results
DFT calculations were carried out to gain insight into the
p-accepting ability of arylisocyanide ligands. The energies and
population analysis of LUMOs of arylisocyanide ligands, obtained
using wave function analysis performed at B3LYP/Def2-TZVP level
and X-ray structural data for the isocyanide ligands are given in
Fig. 6. Results of the current DFT calculations show that the LUMO
populations on carbon sites of isocyanide ligands are relatively
small (<20%), leading to a relatively weaker
p-acceptor ability. As
5

Yen-Chung Huang, Hsing-Yin Chen, Yu-Lun Chang et al.
Polyhedron 192 (2020) 114828
Fig. 6. Calculated LUMO energies and populations of isocyanide ligands.
in vacuum to give 1.2 g (50%) of 2,4,6-triaminomesitylene as a
pale-yellow solid. A solution of 2,4,6-triaminomesitylene (1.2 g,
7 mmol) and formic acid 3 mL in toluene (100 mL) was stirred at
refluxed for 4 h, cooled to room temperature, and filtered. The pre-
cipitate was washed with ether giving a resulting brown solid con-
4: Yield: 32.6%. 1H NMR (C6D6, 400 Hz, 298 K, d): 8.47 (d, 2H,
J = 4 Hz, Py1), 7.06–7.20 (m, 6H, Py + Ph), 6.91 (d, 2H, J = 8 Hz,
Py4), 6.63 (td, 2H, J = 8 Hz, Py3), 6.15 (s, 4H, Ph(C„N)), 4.90 (s,
2H, CH(C@N)2), 4.2 (t, 4H, CH2CH2Py), 3.54 (m, 4H, J = 8 Hz,
PhCH(Me)2), 3.42 (t, 4H, J = 8 Hz, CH2CH2Py), 2.00 (s, 6H,
CH3(C@N)), 1.82 (s, 6H, CH3(C@N)), 1.34 (d, 12H, J = 8 Hz, PhCH
taining 2,4,6-triformamidomesitylene. To
a solution of 2,4,6-
triformamidomesitylene and triethylamine (12 mL) in CH2Cl2
(100 mL) was slowly added POCl3 (3 mL) at 0 ℃. The mixture
was stirred at 0℃ for 1 h and at room temperature for 14 h, fol-
lowed by slow addition of 10% Na2CO3(aq) at 0 ℃. Extraction with
dichloromethane gave an the organic layer that was dried over
MgSO4 and concentrated in vacuum to give a residue that was sub-
jected to silica gel column chromatography (EA:Hexane = 5:100) to
give 2,4,6-triisocyanomesitylene as a white solid. Yield: 512 mg
(25%). 1H NMR (CDCl3, 400 Hz, 298 K, d): 2.56 (s, 9H, Ph(CH3)).
13C NMR (CDCl3, 400 Hz, 298 K, d): 171.68(C„N), 133.61(C6H6),
125.98(C6H6), 16.43(CH3). IR(Hexane): mCNR = 2115 cmꢀ1. Anal.
Calcd for C12H9N3: C, 73.83; H, 4.65; N, 21.52. Found: C, 73.89; H,
4.72; N, 21.34.
(Me)2), 1.29 (d, 12H, J = 8
Hz, PhCH(Me)2). 13C NMR
(C6D6, 100 Hz, 298 K, d): 165.70 (C@N), 162.79(C@N), 161.79
(Py5), 153.34 (C„N), 150.88 (ipso Ph), 150.34 (Py1), 141.54 (ortho
Ph), 136.15 (Py3), 127.47 (Ph(C N)), 124.53 (Py4), 124.06 (para Ph),
123.98 (meta Ph), 121.62 (Py2), 96.03 (CH(C@N)2), 55.83 (CH2CH2-
Py), 44.47 (CH2CH2Py), 28.70 (PhCH(Me)2), 25.48 (CH3(C@N)),
24.11 (PhCH(Me)2), 23.85 (CH3(C@N)), 22.75 (CH3(C@N)).
IR(toluene): mCNR
= . Anal. Calcd for C56H68N8:
2109 cmꢀ1
C, 68.61; H, 6.94; N, 11.43. Found: C, 68.49; H, 7.17; N, 11.24.
5: Yield: 82.7%. 1H NMR (C6D6, 400 Hz, 298 K, d): 8.57 (d, 3H,
J
J
=
=
4.8 Hz, Py1), 7.44(d, 3H,
2,7.6 Hz, Py2), 7.13–7.21 (m, 9H, Ph), 6.73 (dd, 3H,
J = 4 Hz, Py3), 7.26 (td,3H,
J = 5.2,6.8 Hz, Py4), 5.34 (s, 6H, CH2Py), 4.93 (s, 3H, CH(C@N)2),
3.52 (m, 6H, J = 6.8 Hz, PhCH(Me)2), 1.97 (s, 9H, CH3(C@N)), 1.83
(s, 9H, CH3(C@N)), 1.32 (m, 18H, PhCH(Me)2), 1.229 (s, 9H,
PhCH3(C„N)).13C NMR (C6D6, 100 Hz, 298 K, d): 165.89, 164.48,
162.94, 150.13 ,149.36 ,140.45, 135.93, 131.29, 125.97, 124.16,
123.42, 121.34, 124.02, 122.16, 121.92, 96.28, 62.59, 28.77, 25.37,
24.03, 23.86, 22.66. IR(toluene): mCNR = 2101 cmꢀ1. Anal. Calcd
for C81H108Cu3N12: C, 67.54; H, 7.56; N, 11.67. Found: C, 67.48;
H, 7.67; N, 11.54.
Caution: Polynitroaromatic compounds are explosive; proper
precautions and protective equipment (shields, glasses) should
be used during even small-scale experiments.
4.2. General procedures for Synthesis of Di- and Tri-Isocyanide Cu(I)
complexes
Under an inert atmosphere, the appropriate complex (CuL1 or
CuL2) (0.36 mmol) in toluene (20 mL) was added to a half equiva-
lent amount of 1,4-diisocyanobenzene or a one-third equivalent
amount of 2,4,6-triisocyanomesitylene in toluene (10 mL). The
resulting solution was stirred for 1 h, while the color changed from
clear red–orange solution to a yellow-orange suspension solution.
The product was collected by using filtration and dried by vacuum.
All complexes were recrystallized from hexane at ꢀ20 ℃ to form
yellow crystal.
6: Yield: 40.49%. 1H NMR (C6D6, 400 Hz, 298 K, d): 8.53(dq, 3H,
J = 4.8,0.8 Hz, Py1), 7.11–7.19 (m, 12H, Ph + Py3), 6.96 (td,3H,
J = 7.6,0.8 Hz, Py4), 6.67 (ddd, 3H, J = 7.6,4.8,1.2 Hz, Py2), 4.90 (s,
3H, CH(C@N)2), 4.16 (t, 6H, J = 8, CH2CH2Py), 3.50 (m, 12H, PhCH
(Me)2 + CH2CH2Py), 2.00 (s, 9H, CH3(C@N)), 1.83 (s, 9H, CH3(C@N))
, 1.65 (s, 9H, PhCH3(C„N)), 1.34 (m, 18H, J = 6.8 Hz, PhCH(Me)2) ,
1.29 (m, 18H, J = 7.2 Hz, PhCH(Me)2). 13C NMR (C6D6, 400 Hz, 298 K,
d): 165.18, 162.17, 161.09, 154.89(C„N), 150.39, 149.85, 140.59,
135.79, 132.05, 128.06, 126.31, 124.06, 123.38, 123.17, 121.15,
95.35, 55.04, 44.11, 28.07, 25.04, 23.45, 23.10, 22.31, 15.37.
IR(toluene): mCNR = 2100 cmꢀ1. Anal. Calcd for C84H114Cu3N12: C,
68.05; H, 7.75; N, 11.34. Found: C, 68.19; H, 7.87; N, 11.26.
X-ray Crystal Structure Determination. Single crystals of
2,4,6-triisocyanomesitylene and complexes 3–6 suitable for X-ray
diffraction analysis were grown from a concentrated hexane solu-
tion at ꢀ20 ℃. All single-crystal X-ray diffraction data were
recorded on a Bruker Nonius Kappa CCD diffractometer using k
3: Yield: 51.8%. 1H NMR (C6D6, 400 Hz, 298 K, d): 8.47 (d, 2H,
J = 4 Hz, Py1), 7.44 (d, 2H, J = 8 Hz, Py4), 7.00–7.19 (m, 6H,
Py + Ph), 6.57 (d, 4H, J = 8 Hz, Py2), 5.79 (s, 4H, Ph(C„N)), 5.34
(s, 4H, CH2Py), 4.92 (s, 2H, CH(C@N)2), 3.53 (m, 4H, J = 8 Hz,
PhCH(Me)2), 1.95 (s, 6H, CH3(C@N)), 1.81 (s, 6H, CH3(C@N)), 1.33
(d, 12H, J = 8 Hz, PhCH(Me)2), 1.28 (d, 12H, J = 8 Hz, PhCH(Me)2).
13C NMR (C6D6, 100 Hz, 298 K, d): 166.7 (C@N), 164.90 (Py5),
163.53 (C@N), 152.42 (C„N), 150.66 (Py1), 149.94 (ipso Ph),
141.30 (ortho Ph), 136.60 (Py3), 127.09 (para Ph), 124.68 (meta
Ph), 124.02 (Ph(C„N)), 122.16 (Py4), 121.92 (Py2), 96.28 (CH
(C@N)2), 62.59 (CH2Py), 28.77 (PhCH(Me)2), 25.37 (PhCH(Me)2),
24.03 (CH3(C@N)), 23.86 (PhCH(Me)2), 22.66 (CH3(C@N)). IR(-
toluene): mCNR = 2111 cmꢀ1. Anal. Calcd for C54H64N8: C,68.11; H,
6.72; N, 11.77. Found: C, 68.09; H, 6.89; N, 11.68.
(Mo K ) radiation (k = 0.71073 Å). The data collection was executed
a
using the SMART program[47]. Cell refinement and data reduction
were made with the SAINT program[48]. The structures were deter-
mined using the SHELXTL/PC program[47] and refined using full-
matrix least squares. All non-H atoms were refined anisotropically,
whereas H atoms were placed at calculated positions and included
6

Yen-Chung Huang, Hsing-Yin Chen, Yu-Lun Chang et al.
Polyhedron 192 (2020) 114828
[5] R.L. Webster, Dalton Trans. 46 (2017) 4483–4498.
[6] B.A. Jazdzewski, P.L. Holland, M. Pink, V.G. Young, D.J.E. Spencer, W.B. Tolman,
Inorg. Chem. 40 (2001) 6097–6107.
[7] D.J.E. Spencer, A.M. Reynolds, P.L. Holland, B.A. Jazdzewski, C. Duboc-Toia, L. Le
Pape, S. Yokota, Y. Tachi, S. Itoh, W.B. Tolman, Inorg. Chem. 41 (2002) 6307–
6321.
[8] D.S. Laitar, C.J.N. Mathison, W.M. Davis, J.P. Sadighi, Inorg. Chem. 42 (2003)
7354–7356.
in the final stage of refinement with fixed parameters. A summary
of the relevant crystallographic data for 2,4,6-triisocyanome-
sitylene and complexes 3–6 is provided in Table S2. The B-level
alert message for 2,4,6-triisocyanomesitylene and complexes 4–6
is addressed in supporting information.
[9] X. Dai, T.H. Warren, J. Am. Chem. Soc. 126 (2004) 10085–10094.
[10] Y.M. Badiei, T.H. Warren, J. Organomet. Chem. 690 (2005) 5989–6000.
[11] P.O. Oguadinma, F. Schaper, Organometallics 28 (2009) 6721–6731.
[12] P.O. Oguadinma, F. Schaper, Inorg. Chim. Acta 362 (2009) 570–574.
[13] S. Wiese, P. Kapoor, K.D. Williams, T.H. Warren, J. Am. Chem. Soc. 131 (2009)
18105–18111.
4.3. Computational methods
DFT wave function analysis was performed at B3LYP/Def2-TZVP
level. Crystal structures of isocyanide ligands were adopted in the
analysis.
[14] M.M. Melzer, S. Mossin, X. Dai, A.M. Bartell, P. Kapoor, K. Meyer, T.H. Warren,
Angew. Chem. Int. Ed. 49 (2010) 904–907.
[15] P.O. Oguadinma, F. Schaper, Can. J. Chem. 88 (2010) 472–477.
[16] D.V. Vitanova, F. Hampel, K.C. Hultzsch, Dalton Trans. (2005) 1565–1566.
[17] K.-H. Park, W.J. Marshall, J. Am. Chem. Soc. 127 (2005) 9330–9331.
[18] W.-J. Chuang, S.-P. Hsu, K. Chand, F.-L. Yu, C.-L. Tsai, Y.-H. Tseng, Y.-H. Lu, J.-Y.
Kuo, J.R. Carey, H.-Y. Chen, H.-Y. Chen, M.Y. Chiang, S.C.N. Hsu, Inorg. Chem. 56
(2017) 2722–2735.
[19] K. Chand, C.-L. Tsai, H.-Y. Chen, W.-M. Ching, S.-P. Hsu, J.R. Carey, S.C.N. Hsu,
Eur. J. Inorg. Chem. 2018 (2018) 1093–1098.
[20] D.V. Vitanova, F. Hampel, K.C. Hultzsch, J. Organomet. Chem. 696 (2011) 321–
330.
CRediT authorship contribution statement
Yen-Chung Huang: Investigation, Data curation, Visualization,
Writing - original draft. Hsing-Yin Chen: Methodology, Resources.
Yu-Lun Chang: Methodology, Resources. Punitharaj Vasanthaku-
mar: Writing - original draft. Shih-Yun Chen: Investigation, Data
curation. Chai-Lin Kao: Project administration, Funding acquisi-
tion. Carol Hsin-Yi Wu: Funding acquisition. Sodio C.N. Hsu: Con-
ceptualization, Project administration.
[21] L.M.R. Hill, B.F. Gherman, N.W. Aboelella, C.J. Cramer, W.B. Tolman, Dalton
Trans. (2006) 4944–4953.
[22] S. Hong, L.M.R. Hill, A.K. Gupta, B.D. Naab, J.B. Gilroy, R.G. Hicks, C.J. Cramer, W.
B. Tolman, Inorg. Chem. 48 (2009) 4514–4523.
[23] K. Heinze, V. Jacob, Eur. J. Inorg. Chem. 2003 (2003) 3918–3923.
[24] N.L.M. Wagner, Kristen L.; Haworth, Daniel T.; Bennett, Dennis W.; Zeller,
Matthias; Takas, Nathan; di Muzio, Steven; Hunter, Allen D., Inorg. Synth., 34
(2004) 24-29.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
[25] X. Wang, Q.-G. Wang, Q.-L. Luo, Synthesis 47 (2015) 49–54.
´
ˇ
[26] B. Dolensky, J. Kessler, I. Císarová, V. Král, Supramol. Chem. 24 (2012) 127–134.
[27] M. Colapietro, A. Domenicano, G. Portalone, I. Torrini, I. Hargittai, G. Schultz, J.
Mol. Struct. 125 (1984) 19–32.
Acknowledgments
[28] T. Mathieson, A. Schier, H. Schmidbaur, J. Chem. Soc., Dalton Trans. (2001)
1196–1200.
We gratefully acknowledge financial support from Kaohsiung
Medical University (grant No. KMU-DK109006), the NSYSU-KMU
Joint Research Project (NSYSUKMU 108-I002), and the Ministry of
Science and Technology, Taiwan (MOST108-2113-M-037-016).
We thank Ting-Shen Kuo, National Taiwan Normal University, for
X-ray structural determinations, Mr. Min-Yuan Hung, Center for
Research Resources and Development of KMU, for use of their
facilities.
[29] M.A. Fernandes, M. Layh, B. Omondi, Acta Crystallogr. Sect. C: Cryst. Struct.
Commun. 58 (2002) o384–o385.
[30] P.J. Shapiro, R. Zehnder, D.M. Foo, P. Perrotin, P.H.M. Budzelaar, S. Leitch, B.
Twamley, Organometallics 25 (2006) 719–732.
[31] F.A. Cotton, F. Zingales, J. Am. Chem. Soc. 83 (1961) 351–355.
[32] L. Malatesta, Prog. Inorg. Chem. (1959) 283–379.
[33] W.W. Brennessel, J.E. Ellis, Angew. Chem. Int. Ed. 46 (2007) 598–600.
[34] C.B. Gilley, Y. Kobayashi, J. Org. Chem. 73 (2008) 4198–4204.
[35] B.R. Barnett, J.S. Figueroa, Chem. Commun. 52 (2016) 13829–13839.
[36] H. Suzuki, N. Tajima, K. Tatsumi, Y. Yamamoto, Chem. Commun. (2000) 1801–
1802.
[37] Y. Yamamotoa, H. Suzuki, N. Tajima, K. Tatsumi, Chem. Eur. J. 8 (2002) 372–
379.
Appendix A. Supplementary data
[38] S.C.N. Hsu, H.H.Z. Chen, I.J. Lin, J.-J. Liu, P.-Y. Chen, J. Organomet. Chem. 692
(2007) 3676–3684.
[39] S.C.N. Hsu, S.S.C. Chien, H.H.Z. Chen, M.Y. Chiang, J. Chin. Chem. Soc. 54 (2007)
685–692.
[40] P.-C. Lin, H.-Y. Chen, P.-Y. Chen, M.-H. Chiang, M.Y. Chiang, T.-S. Kuo, S.C.N.
Hsu, Inorg. Chem. 50 (2011) 10825–10834.
[41] F.E. Hahn, Angew. Chem. Int. Ed. Engl. 32 (1993) 650–665.
[42] U. Siemeling, L.R.R. Klapp, C. Bruhn, Z. Anorg, Allg. Chem. 636 (2010) 539–542.
[43] A.E. Carpenter, C.C. Mokhtarzadeh, D.S. Ripatti, I. Havrylyuk, R. Kamezawa, C.E.
Moore, A.L. Rheingold, J.S. Figueroa, Inorg. Chem. 54 (2015) 2936–2944.
[44] B.R. Barnett, C.E. Moore, P. Chandrasekaran, S. Sproules, A.L. Rheingold, S.
DeBeer, J.S. Figueroa, Chem. Sci. 6 (2015) 7169–7178.
[45] A.E. Carpenter, C. Chan, A.L. Rheingold, J.S. Figueroa, Organometallics 35 (2016)
2319–2326.
[46] J. Huang, R. Lin, L. Wu, Q. Zhao, C. Zhu, T.B. Wen, H. Xia, Organometallics 29
(2010) 2916–2925.
CCDC 2007072, 2007051, 2007064, 2007071, and 2007106 con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Additional fig-
ures (Figures S1–S13), Table S1 - S2, and crystallographic data in
CIF format for the structure determinations have been presented.
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.poly.2020.114828.
References
[47] G. M. Sheldrick; SHELXL-2014/7: Program for the Solution of Crystal
Structures. University of Gottingen, Gottingen, Germany, 2014.
[48] SAINT, Bruker Analytical X-ray Systems Inc., Madison, WI, Manual Version 5/
6.0, 1997; SHELXTL-PC, Bruker Analytical X-ray Systems Inc., Madison, WI,
Manual Version 5.1, 1997.
[1] L. Bourget-Merle, M.F. Lappert, J.R. Severn, Chem. Rev. 102 (2002) 3031–3066.
[2] D.J. Mindiola, Acc. Chem. Res. 39 (2006) 813–821.
[3] P.L. Holland, Acc. Chem. Res. 41 (2008) 905–914.
[4] Y.-C. Tsai, Coord. Chem. Rev. 256 (2012) 722–758.
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