Copper(I) and silver(I) complexes of carbaphosphazene-anchored N-heterocyclic carbene ligands

Article abstract of DOI:10.1016/j.jorganchem.2012.09.005

Carbaphosphazene-anchored imidazolium salts are synthesized by treating a six-membered dichlorodiphenyldicarbaphosphazene of the formula (ClCN) ₂(Ph₂PN) with N-Me, N-tert-Bu and N-Dipp imidazoles (Dipp = 2,6-diisopropylphenyl) in tol

Full text of DOI:10.1016/j.jorganchem.2012.09.005

Journal of Organometallic Chemistry 723 (2013) 72e78
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Copper(I) and silver(I) complexes of carbaphosphazene-anchored N-heterocyclic
carbene ligands
*
R. Senkuttuvan, V. Ramakrishna, K. Bakthavachalam, N. Dastagiri Reddy
Department of Chemistry, Pondicherry University, Pondicherry 605014, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Carbaphosphazene-anchored imidazolium salts are synthesized by treating a six-membered dichlor-
odiphenyldicarbaphosphazene of the formula (ClCN)2(Ph2PN) with N-Me, N-tert-Bu and N-Dipp imid-
azoles (Dipp ¼ 2,6-diisopropylphenyl) in toluene. While Dipp and tert-Bu substituted imidazolium salts
undergo a facile reaction with Ag2O in CH2Cl2 to form carbene complexes, [DPCP-(NHC:Bu-tAgCl)2] and
[DPCP-(NHC:DippAgCl)2], no pure products are found in case of Me substituted salt. Under similar
conditions, Cu2O with the N-Dipp substituted imidazolium salt gives [(DPCP-(ImidDipp)2Cl][CuICl2],
a [CuICl2]ꢀ complex with the imidazolium ion as counter cation. However, a carbaphosphazene-anchored
NHC complex of Cu, [DPCP-(NHC:DippCuCl)2], is also synthesized by heating a mixture of Cu2O and the N-
Dipp imidazolium salt at 60 ꢁC in acetonitrile. The complexes [DPCP-(NHC:Bu-tAgCl)2], [DPCP-
(NHC:DippCuCl)2] and [(DPCP-(ImidDipp)2Cl][CuICl2] are structurally characterized. In all these
compounds the imidazole rings are coplanar with the carbaphosphazene ring.
Received 17 August 2012
Received in revised form
7 September 2012
Accepted 11 September 2012
Keywords:
Carbaphosphazene
Dicarbaphosphazene
2-phospha-1,3,5-triazine
N-heterocyclic carbene
AgeNHC
CueNHC
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
Therefore, we have chosen these ligand groups for anchoring onto
carbaphosphazenes. Herein we report the synthesis and structural
Cyclophosphazenes are one of the most extensively studied
inorganic ring systems. In addition to the polymerization reactions
leading to unique inorganic eP]Ne polymers [1], nucleophilic
substitution reactions [2] at the phosphorus center in six-membered
N3P3Cl6 and eight-membered N4P4Cl8 rings have generated rich
chemistry. Robust nature of the NP ring and high reactivity of PeCl
bonds have facilitated the installation of various coordinating
groups thereby making these inorganic heterocycles an important
class of ligands [3]. Replacement of one or two of the phosphorous
atoms in N3P3 ring by main-group elements or transition metals [4]
has resulted in several new classes of heterocycles among which
thionylphosphazenes [5] and carbaphosphazenes [6] are well
studied. Even though the nucleophilic substitution reactions at the
carbon and phosphorus centers of carbaphosphazenes have been
thoroughly investigated [7], there are only four articles reported in
the literature on the coordination chemistry of these inorganic/
organic hybrid heterocycles [8]. N-heterocyclic carbenes (NHCs) have
been the theme of interest inrecent years, which has been reflected in
number of articles being published every year. Their metal complexes
have been employed as catalysts in a wide variety of reactions [9].
characterization of novel copper(I) and silver(I) complexes of
carbaphosphazene-anchored N-heterocyclic carbene ligands.
2. Results and discussion
The imidazolium salts were prepared by treating dichlor-
odiphenyldicarbaphosphazene, [(ClCN)2(Ph2PN)], (DPCP-Cl2) [10]
with excess of appropriate imidazole in toluene at room tempera-
ture for tert-Bu and Me substituted imidazoles [11], and at reflux
temperature for 2,6-diisopropylphenyl (Dipp) substituted imid-
azole (Scheme 1). The imidazolium salts [DPCP-(ImidBu-t)2]Cl2,
[DPCP-(ImidMe)2]Cl2 and [DPCP-(ImidDipp)2]Cl2, which were
collected as precipitates, were washed with THF, dried under
vacuum and characterized by NMR. 1H NMR spectrum has been
quite useful in characterizing these salts. In all the cases, a signifi-
cant down-field shift in imidazole protons, especially NeCHeN
proton (shifted from
d w7.5 to d w12 ppm), has been observed.
The singlet resonance in 31P NMR also moved to down-field
region by w5 ppm compared to DPCP-Cl2. It is noteworthy that
N-substituted imidazoles form quaternary ammonium salts with
chlorocarbaphosphazenes in contrast to trialkyl amines, including
bicyclic compounds like quinuclidine and diazabicyclooctane
(DABCO), which undergo CeN bond cleavage [12].
* Corresponding author. Tel.: þ91 413 2654484; fax: þ91 413 2656740.
E-mail addresses: ndreddy.che@pondiuni.edu.in, ndreddy_pu@yahoo.co.in
(N.D. Reddy).
Our attempts to synthesize free carbenes (or in situ generation)
from these imidazolium salts using standard deprotonating agents
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.09.005

R. Senkuttuvan et al. / Journal of Organometallic Chemistry 723 (2013) 72e78
73
R
N
R
N
2Cl
Cl
N
P
Cl
N
N
P
N
Toluene
N
N
N
N
R
N
N
rt or reflux
DPCP-Cl2
t
[DPCP-(ImidBu- )2]Cl2
[DPCP-(ImidMe)2]Cl2
[DPCP-(ImidDipp)2]Cl2
R = tert-Bu
Me
2,6-Diisopropylphenyl
Scheme 1. Synthesis of imidazolium salts.
R
N
R
N
2Cl
R
N
N
R
N
N
P
N
N
N
P
N
Ag2O / Dichloromethane
Ag
Ag
Cl
N
N
N
N
rt / 24 h
4Å Molecular sieves
Cl
t
[DPCP-(NHC:Bu- AgCl)2]
R = tert-Bu
[DPCP-(NHC:DippAgCl)2]
2,6-Diisopropylphenyl
Scheme 2. Synthesis of Ag:NHCs.
like KN(SiMe3)2, tert-BuOK etc. were unsuccessful. Silver oxide has
been widely used to synthesize silver NHCs, which are very good
carbene transfer agents for a wide range of transition metals [13].
In view of this reaction, we treated the imidazolium salts, [DPCP-
(ImidR)2]Cl2 with excess of Ag2O in presence of molecular sieves
in dichloromethane. In case of DPCP-(ImidBu-t)2]Cl2 and [DPCP-
(ImidDipp)2]Cl2, a facile reaction took place, and the complexes
[DPCP-(NHC:Bu-tAgCl)2] and [DPCP-(NHC:DippAgCl)2] were ob-
tained in good yields. However, [DPCP-(ImidMe)2]Cl2 gave
a mixture of products (from 1H and 31P NMR data) and no pure
substances were isolated in this case. The complexes [DPCP-
(NHC:Bu-tAgCl)2] and [DPCP-(NHC:DippAgCl)2] were characterized
by multinuclear NMR. The absence of NeCHeN resonance and the
presence of other imidazole protons in 1H NMR spectra confirm
the formation of the carbene complexes. 31P NMR spectrum
showed a singlet in slightly upfiled region compared to the salts.
Solutions of complexes [DPCP-(NHC:Bu-tAgCl)2] and [DPCP-
(NHC:DippAgCl)2] are photosensitive and turned black within a few
minutes of exposure to light. However, they showed only a slow
decomposition when exposed to air in the absence of light
(Scheme 2).
Reactivity of these imidazolium salts toward Cu2O has also been
explored. Stirring [DPCP-(ImidDipp)2]Cl2 with excess of Cu2O in
dichloromethane at RT for 24 h did not give the expected NHCe
Cu(I) complex, instead, it resulted in the formation of an ionic
complex containing [DPCP-(ImidDipp)2]2þ, [CuICl2]ꢀ and Clꢀ ions
(Scheme 3).
Solid state structure of [DPCP-(NHC:Bu-tAgCl)2] was confirmed
by single crystal X-ray diffraction studies. An ORTEP diagram along
with selected bond parameters is given in Fig. 1. [DPCP-(NHC:Bu-
tAgCl)2] crystallizes in Pcnb space group. The two imidazole rings
and the carbaphosphazene ring are coplanar. CeAgeCl bond is
almost linear and Ag is weakly coordinated by skeletal N of car-
baphosphazene (AgeN distance is 2.725 Å). A thorough search on
CCDC resulted in reports of a few carbeneeAg complexes with
imido nitrogen closer to Ag [14]. All the bond parameters are as
with the AgeNHC complexes [14] and carbaphosphazenes reported
in the literature [10,12].
Fig. 1. Molecular structure of [DPCP-(NHC:Bu-tAgCl)2]. All hydrogen atoms and one set
of disordered methyl carbons from each tert-Bu group are omitted for clarity. Thermal
ellipsoids are drawn at 30% probability level. Selected bond lengths [Å]: Ag1ꢀC2
2.080(7), Ag1ꢀCl1 2.335(2), N3ꢀC2 1.371(9), N4ꢀC2 1.346(9), N3ꢀC1 1.429(8), P1ꢀN2
1.627(6), N2ꢀC1 1.284(8), C1ꢀN1 1.350(8), Ag1/N2 2.725. Selected bond angles [ꢁ]:
C2ꢀAg1ꢀCl1 171.5(2), N4ꢀC2ꢀN3 102.9(6), N4ꢀC2ꢀAg1 135.6(6), N3ꢀC2ꢀAg1
121.4(5), C2ꢀN3ꢀC1 124.4(6), C4ꢀN3ꢀC1 124.7(6), N2ꢀP1ꢀN20 110.2(4), C1ꢀN2ꢀP1
116.1(5), N2ꢀC1ꢀN1 131.2(7), N1ꢀC1ꢀN3 111.1(6), N2ꢀC1ꢀN3 117.6(6), C1ꢀN1ꢀC10
115.0(8).

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R. Senkuttuvan et al. / Journal of Organometallic Chemistry 723 (2013) 72e78
Cl
Dipp
Dipp
Dipp
Dipp
N
2Cl
N
H
H
N
N
N
Cl
Cu
Cl
N
N
N
N
P
N
Cu2O / Dichloromethane
N
N
N
N
rt / 24 h
4Å Molecular sieves
P
Scheme 3. Reaction of Dippimidazolium salt with Cu2O in CH2Cl2.
This complex is readily soluble in chloroform while the parent
imidazole rings through weak CeH/Cl interaction (Av.
H/Cl ¼ 2.488 Å) and is 1.224 Å away from the mean plane of the
imidazolium and carbaphosphazene rings.
imidazolium salt dissolves only when heated. It is colorless and
highly air sensitive. When a solution of the complex in chloroform
was exposed to air, it immediately turned green. While this
observation indicates the presence of Cu(I), the 1H, 13C and 31P NMR
spectra, which are almost the same as those of [DPCP-(ImidDipp)2]
Cl2, support the presence of [DPCP-(ImidDipp)2]2þ ion. The structure
of the complex [(DPCP-(ImidDipp)2Cl][CuICl2] was confirmed by
single crystal X-ray studies. Single crystals, suitable for X-ray
diffraction, were grown from a solution of chlorobenzene at RT. An
ORTEP diagram along with selected bond parameters is given in
Fig. 2. The two imidazole rings and the carbaphosphazene ring are
coplanar. There are three chloride ions in the molecule and two of
them coordinate to Cu in an almost linear fashion (CleCue
Cl ¼ 174ꢁ). The third chloride ion is planked between two
However, Cu(I) carbene complex, [DPCP-(NHC:DippCuCl)2], was
eventually synthesized by treating a mixture of [DPCP-(ImidDipp)2]
Cl2 and excess of Cu2O in acetonitrile at 60 ꢁC for 5 h in the
presence of 4 Å molecular sieves (Scheme 4). The complex was
characterized by NMR analysis. 1H NMR shows two singlets for
imidazole and the other peaks related to the expected structure.
The absence of NeCHeN resonance confirms the formation of
carbene. 31P NMR spectrum was compared with that of the parent
imidazolium salt and an upfield shift (by w6 ppm) of chemical
shift value was observed. The complex [DPCP-(NHC:DippCuCl)2] is
air sensitive and its solutions turn to bluish green when exposed to
air.
The crystal structure of [DPCP-(NHC:DippCuCl)2] shows copper
in an almost linear geometry (Fig. 3). Basically the molecule is iso-
structural with [DPCP-(NHC:Bu-tAgCl)2]. The imidazole rings are
coplanar with the carbaphosphazene ring. All the bond parame-
ters are as with the similar structures reported in the literature
[15].
Surprisingly, [DPCP-(ImidBu-t)2]Cl2 and [DPCP-(ImidMe)2]Cl2,
even under reflux conditions and extending the reaction time up to
24 h, did not give any pure compound in acetonitrile. Both resulted
in a mixture of compounds. 1H and 31P NMR showed that the
unreacted imidazolium salt was the major component.
3. Conclusion
In summary, dichlorodiphenylcarbaphosphazene, [(ClCN)2-
(Ph2PN)], undergoes a facile reaction with N-substituted imidazoles
to give imidazolium salts, which upon treatment with Ag2O or Cu2O,
form Ag- and Cu-NHCs respectively. The complexes [DPCP-
-
(NHC:Bu-tAgCl)2], [DPCP-(NHC:DippAgCl)2] and [DPCP-(NHC:Dipp
CuCl)2] are the first examples of carbaphosphazene-anchored
NHCs. Crystal structures of [DPCP-(NHC:Bu-tAgCl)2] and [DPCP-
(NHC:DippCuCl)2] reveal that the imidazole rings are coplanar with
the carbaphosphazene ring, though there is not much interaction
between the metal and the skeletal nitrogen. Currently, trans-
metallation reactions of these complexes with Ni and Pd reagents
are being explored.
4. Experimental section
Fig. 2. Molecular structure of [(DPCP-(ImidDipp)2Cl][CuICl2]. All hydrogen atoms,
except those connected to chloride ion, are omitted for clarity. Thermal ellipsoids are
drawn at 30% probability level. Selected bond lengths [Å]: Cu1ꢀCl1 2.1036(7), Cu1ꢀCl2
2.0979(8), P1ꢀN3 1.6349(18), P1ꢀN2 1.6356(18), N1ꢀC1 1.328(3), N1ꢀC2 1.334(3),
N3ꢀC1 1.301(2), N2ꢀC2 1.302(2), N6ꢀC1 1.426(2), N4ꢀC2 1.426(2), N4ꢀC6 1.348(2),
N5ꢀC6 1.321(3), N7ꢀC5 1.321(3), N6ꢀC5 1.345(2), Av. H/Cl 2.488. Selected bond
angles [ꢁ]: Cl2ꢀCu1ꢀCl1 174.38(3), N3ꢀP1ꢀN2 109.73(9), P1ꢀN2ꢀC2 115.28(15),
N2ꢀC2ꢀN1 132.55(19), C1ꢀN1ꢀC2 114.27(16), N3ꢀC1ꢀN1 132.47(18), C6ꢀN4ꢀC2
125.68(17), N5ꢀC6ꢀN4 107.43(17), C5ꢀN6ꢀC1 125.71(17), N7ꢀC5ꢀN6 106.81(17),
N1ꢀC2ꢀN4 112.95(16), N2ꢀC2ꢀN4 114.48(18), N3ꢀC1ꢀN6 114.18(17), N1ꢀC1ꢀN6
113.33(16).
4.1. General considerations
All manipulations, except syntheses of imidazoles, were carried
out under N2 atmosphere using a Schlenk line and a glove box. N-
substituted imidazoles were prepared by following literature
procedures [16]. 1H, 13C and 31P NMR spectra were recorded on
a Bruker 400 MHz instrument. Elemental analyses were performed
using Thermo Scientific Flash 2000 elemental analyzer.

R. Senkuttuvan et al. / Journal of Organometallic Chemistry 723 (2013) 72e78
75
2
Dipp
Dipp
N
N
Dipp
N
N Dipp
N
N
P
N
N
N
P
N
Cu2O / CH3CN
Cu
Cl
Cu
Cl
N
N
2Cl
N
N
60 oC / 5 h
4Å Molecular sieves
[DPCP-(NHC:DippCuCl)2]
Scheme 4. Synthesis of Cu:NHC.
4.2. Synthesis of dichlorodiphenylcarbaphosphazene,
[(ClCN)2(Ph2PN)], (DPCP-Cl2) [10]
analytically pure sample of [DPCP-(ImidMe)2]Cl2 (1.40 g, 91%). mp:
>200 ꢁC dec. (lit. 190e195) [11]. 1H NMR (400 MHz, CDCl3):
12.05
d
(s, 2H, imidazoleeNCHN), 8.34 (s, 2H, imidazoleeNCHCHN), 8.21 (s,
2H, imidazoleeNCHCHN), 7.72 (m, 6H, PheH), 7.60 (m, 4H, PheH),
Ph2PCl (11.60 g, 52.57 mmol) was chlorinated using dry chlorine
in chlorobenzene (30 mL) at a moderate rate till the solution turned
bright yellow. After removal of chlorobenzene in vacuo, crystalline
trichlorodiphenylphosphine was obtained, which was re-dissolved
in 1,2-dichloroethane (70 mL). Sodium dicyanamide (4.68 g,
52.56 mmol) was added to the mixture and refluxed for 20 h,
brought to room temperature (RT) and filtered using a frit. The
filtrate was concentrated to one third of its volume and kept at 0 ꢁC
overnight to obtain colorless crystals (12.20 g, 73%). mp: 103e
4.26 (s, 6H, NCH3) ppm. 13C NMR (100 MHz, CDCl3):
d
159.27,139.70,
135.11, 131.35, 129.99, 129.84, 127.46, 126.18, 125.80, 118.56,
37.53 ppm. 31P (161 MHz, CDCl3):
42.94 (s) ppm.
d
4.4. Synthesis of [DPCP-(ImidBu-t)2]Cl2
The procedure given for the synthesis of [DPCP-(ImidMe)2]Cl2
was followed. Yield: 92%. mp: 170e173 ꢁC. 1H NMR (400 MHz,
105 ꢁC. 1H NMR (400 MHz, CDCl3):
4H, pheH) ppm. 13C NMR (100 MHz, CDCl3):
131.67, 131.26, 129.40, 128.75, 127.49 ppm. 31P (161 MHz, CDCl3):
37.93 (s) ppm.
d
7.69 (m, 6H, pheH), 7.56 (m,
169.25, 134.28,
CDCl3):
d 12.00 (s, 2H, imidazoleeNCHN), 8.47 (s, 2H, imidazolee
d
NCHCHN), 8.10 (s, 2H, imidazoleeNCHCHN), 7.73 (m, 6H, PheH),
7.62 (m, 4H, PheH), 1.90 [s, 18H, C(CH3)3] ppm. 13C NMR
d
(100 MHz, CDCl3):
128.22, 127.61, 122.01, 119.29, 62.83, 30.35 ppm. 31P (161 MHz,
CDCl3): 41.89 ppm (s).
d 159.86, 137.69, 134.90, 131.27, 129.76, 129.03,
d
4.3. Synthesis of [DPCP-(ImidMe)2]Cl2
To a solution of DPCP-Cl2 (1.00 g, 3.10 mmol) in toluene (20 mL)
was added slowly 1-methylimidazole (0.65 g, 7.92 mmol) using
syringe. White precipitate was formed immediately upon addition.
The mixture was allowed to stir for 3 h at RT and filtered. The
precipitate was washed with hot THF (2 ꢂ 30 mL) to obtain
4.5. Synthesis of [DPCP-(ImidDipp)2]Cl2
It was prepared by following the procedure given for synthesis
of [DPCP-(ImidMe)2]Cl2, except that the reaction mixture was
refluxed for 3 h. Yield: 93%. mp: >270 ꢁC dec. 1H NMR (400 MHz,
Fig. 3. Molecular structure of [DPCP-(NHC:DippCuCl)2]. All hydrogen atoms and one set of disordered methyl carbons of one of the isopropyl groups are omitted for clarity. One set
of the other disordered moieties are shown with dashed bonds. Thermal ellipsoids are drawn at 30% probability level. Selected bond lengths [Å]: Cu1ꢀC3 1.870(7), Cu1ꢀCl1 2.129(2),
Cu2ꢀC4 1.845(6), Cu2ꢀCl2 2.123(4), Cu2ꢀCl3 2.176(4), P1ꢀN11.624(6), P1ꢀN2 1.642(5), N1ꢀC1 1.309(8), N2ꢀC2 1.289(8), N3ꢀC1 1.322(8), N3ꢀC2 1.355(8), N4ꢀC1 1.419(9), N4ꢀC3
1.392(8), N5ꢀC3 1.315(9), N6ꢀC2 1.394(8), C4ꢀN6 1.393(8), N7ꢀC4 1.328(7), Cu1/N1 2.537, Cu2/N2 2.566. Selected bond angles [ꢁ]: C3ꢀCu1ꢀCl1 176.1(2), C4ꢀCu2ꢀCl2 166.1(2),
C4ꢀCu2ꢀCl3, 165.7(2), N1ꢀP1ꢀN2 109.8(3), C1ꢀN1ꢀP1 116.3(5), N1ꢀC1ꢀN3 131.1(7), C1ꢀN3ꢀC2 115.6(6), N2ꢀC2ꢀN3 131.2(6), C2ꢀN2ꢀP1 115.9(5), N2ꢀC2ꢀN6 114.8(6),
N3ꢀC2ꢀN6 114.0(6), C2ꢀN6ꢀC4 123.5(6), N7ꢀC4ꢀN6 102.9(5), N7ꢀC4ꢀCu2 134.9(5), N6ꢀC4eCu2 122.1(4), N1ꢀC1ꢀN4 115.1(6), N3ꢀC1ꢀN4 113.8(6), C3ꢀN4ꢀC1 123.2(6),
N4ꢀC3ꢀN5 102.6(6), N5ꢀC3ꢀCu1 136.4(5), N4ꢀC3ꢀCu1 120.7(5).

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R. Senkuttuvan et al. / Journal of Organometallic Chemistry 723 (2013) 72e78
CDCl3):
d
12.72 (s, 2H, imidazoleeNCHN), 8.93 (s, 2H, imidazolee
4.8. Reaction of [DPCP-(ImidDipp)2]Cl2 with Cu2O in
dichloromethane
NCHCHN), 8.00 (m, 4H, imidazoleeNCHCHN & AreH), 7.15e7.78
(set of multiplets, 14H, AreH & PheH), 2.37 [m, 4H, CH(CH3)2],
1.22 [d, 12H, CH(CH3)2], 1.12 [d, 12H, CH(CH3)2] ppm. 13C NMR
A mixture of [DPCP-(ImidDipp)2]Cl2 (0.20 g, 0.25 mmol), Cu2O
(0.055 g, 0.38 mmol) and 4 Å molecular sieves (w1 g) was stirred at
RT in dichloromethane (25 mL) for 24 h. The reaction mixture was
then filtered through a pad of celite, the volatiles were removed
from the filtrate and the residue was recrystallized from dichloro-
methane/hexane mixture to obtain colorless crystals of [(DPCP-
(ImidDipp)2Cl][CuICl2] overnight at RT (0.17 g, 98% based on Cl). mp:
(100 MHz, CDCl3):
d 159.88, 144.90, 135.06, 132.00, 131.83, 131.72,
130.31, 130.01, 129.87, 129.18, 128.37, 127.74, 126.20, 125.44, 124.70,
120.29, 29.02, 24.33 ppm. 31P (161 MHz, CDCl3):
d 43.04 (s) ppm.
4.6. Synthesis of [DPCP-(NHC:Bu-tAgCl)2]
140e142 ꢁC. 1H NMR (400 MHz, CDCl3):
d 12.31 (s, 2H, imidazolee
A mixture of [DPCP-(ImidBu-t)2]Cl2 (0.24 g, 0.42 mmol), Ag2O
(0.14 g, 0.60 mmol) and 4 Å molecular sieves (w1.00 g) was stirred
at RT in dichloromethane (25 mL) for 24 h in the absence of light.
The reaction mixture was then filtered through a pad of celite, the
volatiles were removed from the filtrate and the residue was
recrystallized from dichloromethane/hexane mixture to obtain
colorless crystals overnight at RT (0.25 g, 76%). mp: >166 ꢁC dec. 1H
NMR (400 MHz, CDCl3):
4H, PheH), 7.61 (m, 6H, PheH), 7.27 (s, 2H, imidazoleeNCHCHN),
1.82 [s, 18H, C(CH3)3] ppm. 13C NMR (100 MHz, CDCl3):
162.73,
133.95, 131.38, 131.26, 129.66, 129.52, 129.19, 125.45, 119.42, 118.74,
59.06, 31.70 ppm. 31P (161 MHz, CDCl3):
38.13 (s) ppm. Anal. Calcd
NCHN), 8.70 (s, 2H, imidazoleeNCHCHN), 8.01 (m, 4H, PheH), 7.76
(m, 6H, PheH), 7.45 (t, 2H, AreH), 7.36 (s, 2H, imidazoleeNCHCHN),
7.25 (d, 4H, AreH), 2.45 [m, 4H, CH(CH3)2], 1.24 [d, 12H, CH(CH3)2],
1.12 [d, 12H, CH(CH3)2] ppm. 13C NMR (100 MHz, CDCl3):
d 159.71,
145.07, 141.02, 135.11, 132.03, 131.92, 130.25, 129.98, 129.83, 127.49,
126.82, 126.21, 125.58, 124.72, 123.97, 119.87, 28.96, 24.38 ppm. 31P
(161 MHz, CDCl3): d 43.41 (s) ppm. Anal. Calcd for C44H50Cl3CuN7P:
C, 60.20; H, 5.74; N, 11.17. Found: C, 60.23; H, 5.79; N, 11.10.
d 8.27 (s, 2H, imidazoleeNCHCHN), 8.14 (m,
d
4.9. Synthesis of [DPCP-(NHC:DippCuCl)2]
d
for C28H32Ag2Cl2N7P: C, 42.88; H, 4.11; N, 12.50. Found: C, 42.76; H,
4.20; N, 12.53.
A mixture of [DPCP-(ImidDipp)2]Cl2 (0.21 g, 0.26 mmol), Cu2O
(0.057 g, 0.39 mmol) and 4 Å molecular sieves (w1 g) in acetonitrile
(25 mL) was heated at 60 ꢁC for 5 h. It was then filtered through
a pad of celite and the yellow colored filtrate was stored at RT to
obtain pale yellow crystals, which were filtered off. Reducing the
volume of the mother liquor to half gave a further crop of yellow
crystals. Overall yield is 83% (0.20 g), mp: >246 ꢁC dec. 1H NMR
4.7. Synthesis of [DPCP-(NHC:DippAgCl)2]
It was prepared by following the procedure given for synthesis
of [DPCP-(NHC:Bu-tAgCl)2]. Yield: 89%. mp: 122e124 ꢁC. 1H NMR
(400 MHz, CDCl3):
d
8.68 (s, 2H, imidazoleeNCHCHN), 8.06 (m, 4H,
(400 MHz, CDCl3): d 8.70 (s, 2H, imidazoleeNCHCHN), 8.17 (m, 4H,
PheH), 7.60 (m, 6H, PheH), 7.45 (m, 2H, AreH), 7.23 (d, 4H, AreH),
7.06 (d, 2H, imidazoleeNCHCHN), 2.45 [m, 4H, CH(CH3)2], 1.23 [d,
12H, CH(CH3)2], 1.10 [d, 12H, CH(CH3)2] ppm. 13C NMR (100 MHz,
PheH), 7.62 (m, 6H, PheH), 7.47 (t, 2H, AreH), 7.27 (d, 4H, AreH),
7.00 (m, 2H, imidazoleeNCHCHN), 2.51 [m, 4H, CH(CH3)2], 1.29
[d, 12H, CH(CH3)2], 1.14 [d, 12H, CH(CH3)2] ppm. 13C NMR (100 MHz,
CDCl3):
131.19, 130.9, 129.73, 129.59, 129.16, 128.37, 124.54, 123.87, 120.40,
28.47, 24.69, 24.44 ppm. 31P (161 MHz, CDCl3):
38.26 (s) ppm.
d
162.87, 146.66, 145.39, 135.33, 134.06, 134.03, 131.30,
CDCl3):
130.00, 129.51, 129.37, 128.71, 124.48, 124.40, 119.48, 28.55, 24.76,
24.30 ppm. 31P (161 MHz, CDCl3):
37.67 (s) ppm. Anal. Calcd for
d 163.28, 145.39, 135.22, 133.85, 131.50, 131.39, 130.71,
d
d
Anal. Calcd for C44H48Ag2Cl2N7P: C, 53.25; H, 4.87; N, 9.88. Found:
C, 53.20; H, 4.91; N, 9.81.
C44H48Cl2Cu2N7P: C, 58.47; H, 5.35; N, 10.85. Found: C, 58.51; H,
5.40; N, 10.81.
Table 1
Crystal data for compounds [DPCP-(NHC:Bu-tAgCl)2], [(DPCP-(ImidDipp)2Cl][CuICl2] and [DPCP-(NHC:DippCuCl)2].
[DPCP-(NHC:Bu-tAgCl)2]$2CHCl3$CH2Cl2
[(DPCP-(ImidDipp)2Cl][CuICl2]$2C6H5Cl
[DPCP-(NHC:DippCuCl)2]$CH3CN
Empirical formula
Formula wt
Temp (K)
Cryst syst
Space group
a (Å)
C
31H36Ag2Cl10N7P
C56H60Cl5CuN7P
1102.87
150(2)
Monoclinic
P2/n
15.5595(2)
15.7611(3)
23.7077(4)
90
105.052(2)
90
5614.48(16)
4
1.305
0.698
C46H51Cl2Cu2N8P
944.90
150(2)
Triclinic
P
9.5478(3)
14.8445(9)
18.4794(10)
68.820(5)
79.290(4)
79.874(4)
2382.7(2)
2
1107.88
150(2)
Orthorhombic
Pbcn
13.3570(4)
19.8355(6)
17.3347(6)
90
90
90
4592.7(3)
4
1.602
1.500
b (Å)
c (Å)
a
b
g
(deg)
(deg)
(deg)
V (Å3)
Z
rcalcd (Mg mꢀ3
)
1.317
1.078
m
(mmꢀ1
)
F(000)
cryst size (mm)
range (deg)
2200
2296
980
0.30 ꢂ 0.22 ꢂ 0.12
2.80e29.42
13,432/5488 (R(int) ¼ 0.0318)
5488/23/229
0.0617, 0.2240
0.1300, 0.2529
1.004
0.40 ꢂ 0.20 ꢂ 0.19
2.73e29.37
34,377/13,173 (R(int) ¼ 0.0330)
13,173/0/639
0.0461, 0.0981
0.0714, 0.1114
1.056
0.32 ꢂ 0.24 ꢂ 0.11
2.78e29.36
17,806/10,833 (R(int) ¼ 0.0534)
10,833/0/515
0.0883, 0.2199
0.1832, 0.2439
0.936
q
No. of collected/ unique rflns
No. of data/restraints/ params
R1, wR2 (I > 2s
(I))a
R1, wR2 (all data)a
GOF
Drmax
/
Drmin (e Åꢀ3
)
1.706/ꢀ1.206
0.593/ꢀ0.664
2.613/ꢀ0.861
a
R1 ¼ SjjFoj ꢀ jFcjj/SjFoj; wR2 ¼ [Sw(F2o ꢀ F2c)2/Sw(Fo2)2]0.5
.

R. Senkuttuvan et al. / Journal of Organometallic Chemistry 723 (2013) 72e78
77
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Acknowledgement
We gratefully acknowledge the Council of Scientific and Indus-
trial Research (CSIR), New Delhi for financial support and Alexander
von Humboldt Stiftung, Germany for donation of a glove box. We
thank the Central Instrumentation Facility, Pondicherry University
for NMR spectra and DST-FIST for single crystal X-ray diffraction
facility. VR also thanks CSIR, India for a junior research fellowship.
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Appendix A. Supplementary material
CCDC 877872, 877873 and 877874 contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: þ44 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
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