Cationic copper (I) complexes with bulky 1,4-diaza-1,3-butadiene ligands - Synthesis, solid state structure and catalysis

Article abstract of DOI:10.1016/j.molstruc.2013.02.037

We report the full characterization of two glyoxal-based ligands N,N bis(diphenylmethyl)-1,4-diaza-1,3-butadiene ligand (DAD^Ph2, 1) and more bulky N,N bis(triphenylmethyl)-1,4-diaza-1,3-butadiene ligand (DAD ^Ph3, 2) by the condensation reaction of glyoxal and diphenylmethanamine and triphenyl-methanamine respectively. The copper (I) complex of composition [Cu(DAD^Ph2)₂]PF₆ (3) having two neutral bidentate N,N bis(diphenyl-methyl)-1,4-diaza-1,3-butadiene ligand was prepared by the reaction of [Cu(CH₃CN)₄]PF ₆ and 1 in 1:2 ratio in dichloromethane. In a similar reaction with N,N bis(triphenylmethyl)-1,4-diaza-1,3-butadiene ligand (2) and [Cu(CH ₃CN)₄]PF₆ in dichloromethane yielded corresponding heteroleptic copper (I) complex [Cu(DAD^Ph3)(CH ₃CN)₂]PF₆ (4). Another copper (I) complex [Cu(DAD^Ph2)(PPh₃)]PF₆ (5) can also be obtained by the one pot reaction involving ligand 1, [Cu(CH₃CN) ₄]PF₆ and triphenylphosphine. Solid state structures of all the five compounds were established by single crystal X-ray diffraction analysis. The solid state structures of the copper complexes 3-5 reveal a distorted tetrahedral geometry around the copper (I) centers. The copper complexes 3-5 were tested as catalysts for the coupling reaction of o-iodophenol and phenyl acetylene and it was observed that complex 4 exhibits the highest catalytic activity.

Full text of DOI:10.1016/j.molstruc.2013.02.037

Accepted Manuscript
Cationic Copper (I) Complexes with Bulky 1,4-Diaza-1,3-Butadiene Ligands -
Synthesis, Solid State Structure and Catalysis
Srinivas Anga, Ravi K. Kottalanka, Tigmansu Pal, Tarun K. Panda
PII:
S0022-2860(13)00193-2
DOI:
http://dx.doi.org/10.1016/j.molstruc.2013.02.037
MOLSTR 19586
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
20 December 2012
26 February 2013
26 February 2013
Please cite this article as: S. Anga, R.K. Kottalanka, T. Pal, T.K. Panda, Cationic Copper (I) Complexes with Bulky
1,4-Diaza-1,3-Butadiene Ligands - Synthesis, Solid State Structure and Catalysis, Journal of Molecular Structure
(2013), doi: http://dx.doi.org/10.1016/j.molstruc.2013.02.037
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Cationic Copper (I) Complexes with Bulky 1,4-Diaza-1,3-Butadiene Ligands -
Synthesis, Solid State Structure and Catalysis
Srinivas Anga, Ravi K. Kottalanka, Tigmansu Pal and Tarun K. Panda*
Department of Chemistry, Indian Institute of Technology Hyderabad, Ordnance Factory Estate,
Yeddumailaram 502205, Andhra Pradesh, India. Fax: + 91(40) 2301 6032; Tel: + 91(40) 2301 6036;
E-mail: tpanda@iith.ac.in
Received th December, 2012

Abstract:
We report the full characterization of two glyoxal-based ligands N,N bis(diphenylmethyl)-1,4-diaza-1,3-
butadiene ligand (DADPh2, 1) and more bulky N,N bis(triphenylmethyl)-1,4-diaza-1,3-butadiene ligand
(DADPh3, 2) by the condensation reaction of glyoxal and diphenylmethanamine and triphenyl-
methanamine respectively. The copper (I) complex of composition [Cu(DADPh2)2]PF6 (3) having two
neutral bidentate N,N bis(diphenyl-methyl)-1,4-diaza-1,3-butadiene ligand was prepared by the reaction
of [Cu(CH3CN)4]PF6 and 1 in 1:2 ratio in dichloromethane. In a similar reaction with N,N
bis(triphenylmethyl)-1,4-diaza-1,3-butadiene ligand (2) and [Cu(CH3CN)4]PF6 in dichloromethane
yielded corresoinding heteroleptic copper (I) complex [Cu(DADPh3)(CH3CN)2]PF6 (4). Another copper (I)
[Cu(DADPh2)(PPh3)]PF6 (5) can also be obtained by the one pot reaction involving ligand 1,
[Cu(CH3CN)4]PF6 and triphenylphosphine. Solid state structures of all the five compounds were
established by single crystal X-ray diffraction analysis. The solid state structures of the copper complex 3-
5 reveal a distorted tetrahedral geometry around the copper (I) centers. The copper complexes 3-5 were
tested as catalysts for the coupling reaction of o-iodophenol and phenyl acetylene and it is observed that
complex 4 exhibits the highest catalytic activity.
Highlights:
ꢀ N,N bis(diphenylmethyl)-1,4-diaza-1,3-butadiene more bulky N,N bis(triphenyl-methyl)-1,4-
diaza-1,3-butadiene ligand 1,4-diaza-1,3-butadiene ligands were synthesized.
ꢀ All the ligands and copper (I) complexes were structurally characterized.
ꢀ Less bulky DAD ligand 2 form homoleptic complex [Cu(DADPh2)2]PF6 (3) whereas more bulky
ligand 2 forms heteroleptic copper (I) complex [Cu(DADPh3)(CH3CN)2]PF6 (4). When the
corresponding ligands were treated with [Cu(CH3CN)4]PF6.
ꢀ One pot reaction involving 1, [Cu(CH3CN)4]PF6 and PPh3 produces another copper complex
[Cu(DADPh2)(PPh3)]PF6 (5).
ꢀ Complexes 3-5 were tested as catalysts for the coupling reaction of o-iodophenol and phenyl
acetylene.
Keywords: 1,4 diaza-1,3-butadiene / copper(I) / metallacycle / homoleptic complex /coupling reaction.
2

1. Introduction
The use of bidentate and tridentate ligands received significant attention by many research groups due to
their wide application as ancillary ligands in catalysis.1-5 To improve the catalytic activity of the metal
complexes, proper ligand design is most important. In the post metallocene era, chelating nitrogen ligands
with bulky substituent are being explored as alternatives to η5-cyclopentadienyl ligands for the design of
olefin polymerization catalysts based on early and late transition metal complexes.6-11The 1, 4-diaza-1, 3-
butadiene (DAD) ligands are an important class of redox-active ligands that are able to tune the electronic
behavior of coordination compounds throughout the periodic table.12 The coordination modes of DAD
ligands are flexible, and all possible modes (A-E) are described in Scheme 1, showing that the ligands
coordinate to metals in neutral, monoanionic, and dianionic modes. Although the dianionic DAD ligands
preferentially coordinate to early transition metals and alkaline metals in σ2- and σ2,π-coordination
modes13-15 in many cases the DAD ligands coordinate to group 3 metal atoms as a σ2-monoanion,16 and,
in addition, both monoanionic and dianionic coordination modes were observed for alkaline-earth metal,
group 12, and group 13 metal complexes.17,18 Recently, Mashima group with other research groups
reported the preparation of group 3 metal complexes with DAD ligands, in which the ligands coordinated
to the central metals as σ2,π-dianions.19,20 The same working group also reported the synthesis of 1,4-
diaza-1,3-butadiene complexes of barium, strontium and calcium using two synthetic methods, a salt
metathesis reaction and a direct metallation.21 Inspired by these results we were interested to prepare
more bulky DAD ligands which can provide steric control onto the metal center. This can be done by
employing bulky substituent on the imino nitrogen atoms. Very recently Murakami et.al reported the
synthesis of N,N bis(diphenyl-methyl)-1,4-diaza-1,3-butadiene ligand as an intermediate for the
preparation of chiral N-heterocyclic carbene ligand, however structural characterization or any further
chemistry with this ligand to form any metal complex are not explored yet.22
3

Scheme1. Coordination Modes of 1, 4-Diaza-1, 3-butadiene Ligands to Transition Metals
In this contribution, we would like to report full structural characterization of bulky N,N
bis(diphenyl-methyl)-1,4 diaza-1,3-butadiene ligand (DADPh2, 1) and synthesis and structural aspects of
more bulky N,N bis(triphenylmethyl)-1,4diaza-1,3-butadiene (DADPh3, 2) and their three different
copper(I) complex of 3, 4 and 5. The results of catalytic coupling reaction of o-iodophenols and phenyl
acetylene using copper complexes 3-5 as catalyst is also presented
2. Experimental:
2.1 General: All manipulations involving air- and moisture-sensitive organometallic compounds were
carried out under argon using the standard Schlenk technique or argon-filled glove box. Hydrocarbon
solvents (n-pentane, toluene) were distilled under nitrogen from LiAlH4 and stored in the glove box.
Dichloromethane was dried over P2O5 followed by distillation and kept under molecular sieves prior
13
to use. 1H NMR (400 MHz) and C {1H} NMR (100 MHz) spectra were recorded on a BRUKER
AVANCE III-400 spectrometer. BRUKER ALPHA FT-IR was used for FT-IR measurement.
Elemental analyses were performed on a BRUKER EURO EA at the Indian Institute of Technology
Hyderabad. [Cu(MeCN)4]PF6, diphenylmethanamine, triphenylmethanamine, iodophenol,
phenylacetylene were purchased from Sigma Aldrich and used as such.
2.2 Synthesis of N,N bis(diphenyl-methyl)-1,4-diaza-1,3-butadiene22 (1):
To a stirred solution of diphenylmethanamine (3 g, 16 mmol) in methanol (15 mL) at ambient
temperature was added glyoxal (40 wt. % solution in water, 1mL, 8 mmol). The resulted solution stirred
at ambient temperature for overnight, the white precipitate generated was collected by filtration, washed
with hexane (5 mL x 2) and dried under vacuum to give a white solid. M.p.144oC. Yield 2.7 g, 85%. FT-
1
IR (selective frequency): 3027 (ν, Ar-H), 2861 (sp3C-H), 1628(ν, C=N), 1492(δ, C-H) cm-1. H NMR
(400 MHz, CDCl3) δ 8.13 (s, 2H, N=CH), 7.14-7.24 (m, 20H, Ph), 5.50 (s, 2H, CH) ppm; 13C{1H} NMR
(100 MHz, CDCl3) δ 162.1(imine -C), 142.5 (quaternary-C), 128.6 (aromatic-C), 127.6 (aromatic-C),
127.3 (aromatic -C), 78.1(C=N-C).; C28H24N2 (388.49): calcd C, 86.56, H, 6.23, N, 7.21 ; found C, 85.97,
H, 6.04, N, 7.02.
2.3 Synthesis of N, N bis(triphenylmethyl)-1,4-diaza-1,3-butadiene (2):
4

To a stirred solution of triphenylmethanamine (1 g, 3.8 mmol) in methanol (15 mL) at ambient
temperature was added glyoxal (40 wt. % solution in water, 0.5mL, 4 mmol). After being stirred at
ambient temperature for overnight, the white precipitate generated was collected by filtration, washed
with hexane (5 mL x 2) and dried under vacuum to give 2 as white solid (770 mg, 77 % yield). M.p. 256
oC. FT- IR (selective stretching frequency): 3021(ν, Ar-H), 1622(ν, C=N), 1489 (δ, C-H), cm-1. 1H NMR
(400 MHz, CDCl3) δ 7.80 (s, 2H, N=CH), 7.18-7.24(m, 20H, Ph), 7.08-7.17(m, 10H, Ph); 13C NMR (100
MHz, CDCl3) δ 161.7(Imine -C), 144.7(Quaternary-C), 129.8(aromatic-C), 127.9(aromatic-C),
127.1(aromatic-C), 79.4 ((C=N-C); C40H32N2 (540.68): calcd C, 88.85, H, 5.97, N, 5.18; found C, 88.24,
H, 5.73, N, 5.10.
2.4 Synthesis of [Cu(DADPh2)2]PF6 (3):
To a colorless solution of [Cu(CH3CN)4]PF6 (68 mg, 0.18 mmol) in CH2Cl2 (2 mL) was treated with 1
(142 mg, 0.36 mmol) in CH2Cl2 (3 mL), at ambient temperature. The color of solution turned to brown
and left stirring for overnight. After filtration, the solution was concentrated and doubled-layered with
pentane. The brown color solution was placed in refrigerator for crystallization. Brown color crystals
were isolated. Yield 153 mg (85%). FT- IR (selective frequency): 3029 (ν, Ar-H), 2962 (ν, sp3C-H),
1
1600(ν, C=N), 1494 (δ, C-H) cm-1. H NMR (400 MHz, CDCl3) δ 7.93 (s, 4H, N=CH), 7.15-7.28 (m,
13
40H, Ph), 5.28 (s, 4H, CH) ppm. C{1H} NMR (100 MHz, CDCl3) δ =160.8(C=N), 143.5 (quaternary -
C), 129.6 (aromatic-C), 127.9 (aromatic-C), 127.8 (aromatic-C), 77.1(C=N-C) ppm. C59H54Cl6CuF6N4P
(1240.28): calcd C, 57.13, H, 4.39, N, 4.52 ; found C, 56.83, H, 4.21, N, 4.29.
2.5 Synthesis of [Cu(DADPh3)(CH3CN)2]PF6 (4):
The Complex 4 was prepared in an analogous procedure as described for the preparation of complex 3.
Yield 124 mg (88%). FT- IR (selective): 2963(ν, Ar-H), 2369 (ν, CH3CN), 2351(ν, CH3CN), 1623(ν,
1
C=N) cm-1; H NMR (400 MHz, CDCl3) δ 8.19 (s, 2H, N=CH), 7.28-7.30(m, 12H, Ph), 7.00-7.07(m,
16H, Ph), 2.13(s, 6H, CH3CN) ppm. 13C{1H} NMR (100 MHz, CDCl3) δ 160.2(C=N), 143.6 (quaternary-
C), 128.8 (aromatic-C), 125.9 (aromatic-C), 116.7(CN-CH3), 78.8(C=N-C), 28.8(CN-CH3) ppm.
C90H78Cl4Cu2F12N8P2 (1830.44): calcd C, 59.05, H, 4.30, N, 6.12 ; found C, 58.79, H, 4.10, N, 5.92.
2.6 Synthesis of [Cu(DADPh2)(PPh3)]PF6 (5):
A colorless solution of [Cu(CNCH3)4]PF6 (50 mg, 0.13mmol) and PPh3 (70.3 mg, 0.26 mmol) in CH2Cl2
(5 mL) was stirred for 15 minutes then the reaction mixture were added to a dichloromethane solution (3
mL) of 1 (52 mg, 13 mmol). The resulting orange color solution stirred for overnight. After filtration, the
solution was concentrated and doubled-layered with pentane. The orange color solution was placed in
5

refrigerator for crystallization. After two days, orange color crystals were isolated. Yield 98 mg (67%).
1
FT- IR: 3059 (ν, Ar-H), 2943 (ν, sp3C-H), 1619(ν, C=N); H NMR (400 MHz, CDCl3) δ 8.09(s, 2H,
13
N=CH), 7.01-7.73(m, 50H, Ph), 5.83(s, 2H, CH) ppm. C{1H} NMR (100 MHz, CDCl3) δ 159.5(C=N),
132.3(quaternary-C), 129.5(aromatic-C), 128.0 (aromatic-C), 127.9 (aromatic-C), 127.8(aromatic-C),
74.2(C=N-C) ppm; 31P{1H} NMR (161.7 MHz CDCl3) δ 12.0 (PPh3), -129.5 (PF6) ppm.
C65H56Cl2CuF6N2P3 (1206.08): calcd C, 64.71, H, 4.68, N, 2.32 ; found C, 64.16, H, 4.19, N, 2.01.
2.11 X-ray Crystallographic Studies
Single crystals of compound 1 and 2 were grown from hot methanol and 3-5 were grown from a solution
of dichloromethane and pentane under inert atmosphere at a temperature of -4°C. In each case a crystal
of suitable dimensions was mounted on a CryoLoop (Hampton Research Corp.) with a layer of light
mineral oil and placed in a nitrogen stream at 150(2) K. All measurements were made on a Oxford
Supernova X-Calibur Eos CCD detector with graphite-monochromatic Cu Kα (1.54184 Å) (for 1, 3, 4 and
5) and MoKα (0.71069 Å) (for 2) radiation. Crystal data and structure refinement parameters are
summarized in the Table 1. The structures were solved by direct methods (SIR92)23 and refined on F2 by
full-matrix least-squares methods; using SHELXL-97.24 Non-hydrogen atoms were anisotropically
refined. H-atoms were included in the refinement on calculated positions riding on their carrier atoms.
The function minimized was [∑w(Fo2- Fc2)2] (w = 1 / [σ2 (Fo2) + (aP)2 + bP]), where P = (Max(Fo2,0) +
2Fc2) / 3 with σ2(Fo2) from counting statistics. The function R1 and wR2 were (Σ||Fo| - |Fc||) / Σ|Fo| and
[Σw(Fo2 - Fc2)2 / Σ(wFo4)]1/2, respectively. The ORTEP-3 program was used to draw the molecule.
Crystallographic data (excluding structure factors) for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as a supplementary publication no. CCDC
914540 (1), 914541 (2), 914537 (3), 914538 (4) and 914539 (5) Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax: + (44)1223-336-033;
email: deposit@ccdc.cam.ac.uk).
(Table 1 here)
3. Results and discussion
The glyoxal based ligands N,N bis(diphenyl-methyl)-1,4 diaza-1,3-butadiene ligand (1) was prepared by
the reaction of glyoxal and diphenylmethanamine in 1:2 molar ratio in methanol.22, 25 The other ligand
N,N bis(triphenylmethyl)-1,4 diaza-1,3-butadiene ligand (2) was also prepared by similar fashion
6

involving the reaction of glyoxal and triphenylmethanamine (Scheme 2). The compound 2 was
characterized by spectroscopic/analytical method and solid state structures of both the compounds were
determined by single crystal X-ray diffraction analysis.
MeOH
2
R
NH2
R
N
+
N
R
O
O
- 2 H2O
1
2
R = H ( ); Ph ( )
Scheme2. Synthesis of DAD ligands 1 and 2.
(Figure 1 here)
The compound 1 crystallizes in monoclinic space group P21/n having two molecules of compound 1 in
the unit cell. The molecular structure of compound 1 is shown in Fig 1 and the structural parameters and
selected bond lengths and bond angles are shown in Table 1 and Table 2 respectively. In the compound 1
two C-N double bonds (C1-N1 and C1i-N1i) are trans to each other and have a distance of 1.2613(2) Å
which is well agreement with C-N doubles bond in analogius compounds in literature. The atoms C1, C2,
N1, C1i, N1i and C2i are coplanar and makes a dihedral angle of 67.44o with phenyl ring plane containing
C9, C14, C13, C12, C11, C10 atoms and 46.89o with the phenyl plane formed by C4, C5, C6, C7 and C8
atoms. The N1-C2 and N1i -C2i distances (1.4757(2) Å) are also expected as the nitrogen carbon single
bond. The C1-N1-C2 bond angle is 117.51(13)o. The more bulky compound 2 crystallizes in triclinic
space group P -1 having two independent molecules in the asymmetric unit. The molecular structure of
compound 2 is shown in Fig 2 and the structural parameters and selected bond lengths and bond angles
are shown in Table 1 and Table 2 respectively. Due to presence of three phenyl groups a steric crowding
has been observed around the C3 center (N1-C3-C10 106.07(14)o, N1-C3-C4 114.09(15)o, N1-C3-C16
106.03(14)o, C10-C3-C16 109.40(15)o The plane containing C3, N1, C1 makes a dihedral angle of 81.15o
.
with the plane of the phenyl ring containing C16, C17, C19, C20, C18, 37.88o with second phenyl plane
containing C10, C15, C14, C13, C12, C11atoms and 70.93o with third phenyl plane having C9, C8, C7,
C6, C4 planes.
(Figure 2 here)
Copper complexes: The homoleptic copper (I) complex with N, N bis(diphenyl-methyl)-1,4 diaza-1,3-
butadiene ligand (1) was prepared by the reaction of [Cu(CH3CN)4]PF6 with ligand 1 in 1:2 molar ratio in
dichloromethane at ambient temperature (Scheme 3). Brown colored crystals of [Cu(DADPh2)2]PF6 (3)
were obtained from CH2Cl2/pentane mixture at -4oC. However, attempt to isolate the copper(I)
7

heteroleptic complex [Cu(DADPh2)(CH3CN)2]PF6] by employing the reaction of [Cu(CH3CN)4]PF6 with
ligand 1 in 1:1 molar ratio in dichloromethane at ambient temperature resulted only the complex 3 in
lower yield. In contrast, in a similar reaction when the more bulky ligand N,N bis(triphenylmethyl)-1,4
diaza-1,3-butadiene (2) was treated with [Cu(CH3CN)4]PF6 in 1:1 molar ratio in dichloromethane,
heteroleptic copper complex [Cu(DADph3)(CH3CN)2]PF6 (4) was obtained which was re-crystallized from
CH2Cl2/pentane mixture at - 4oC (Scheme 3). Both the copper complexes 3 and 4 were characterized by
standard spectroscopic/analytic method and the solid state structure of these complexes was established
by single crystal X-ray analysis.
(Table 2)
Scheme3. Synthesis of copper complexes 3 and 4.
The homoleptic copper complex 3 shows a sharp singlet in 1H NMR spectra at δ = 7.93 ppm corresponds
to the imine protons of the DAD ligand backbone which is slightly up-field shifted compare to the free
ligand 1 (δ = 8.13 ppm). However the resonance for the methine protons (δ = 5.28 ppm) also slightly high
field shifted compare to that of the free ligand 1 (δ = 5.49 ppm) upon coordination with copper (I) atom.
1
In contrast to the complex 3, in H NMR spectra, the signal for the imine protons of the heterpleptic
copper (I) complex 4, significantly low field shifted (δ = 8.19 ppm) compare to that of free ligand 2 (δ =
7.80 ppm). The resonance for the methyl protons of the coordinated acetonitrile groups show a singlet at δ
= 2.13 ppm.
8

(Figure 3 here)
The solid state structure of the compound 3 was established by single crystal X-ray diffraction analysis
and the structural parameters and selected bond lengths and bond angles are given in the Table 1 and
Table 2 respectively. The molecular structure of compound 3 is shown in Fig 3. The compound 3
crystallizes in triclinic space group P-1 having two independent molecules of 3 and three molecules of
dichloromethane in the unit cell. The molecular structure of 3 consists of an zwitter-ionic pair composed
of a [PF6]- anion and an [Cu(I)(η2-DADPh2)2]+ cation. In the cationic part of the molecule, the centre metal
copper is coordinated by two bidentate N, N bis(diphenylmethyl)-1,4-diaza-1,3-butadiene ligand moieties
through the chelation of two iminium nitrogen atoms of the each ligand. Thus two five membered rings
Cu1-N1-C1-C2-N2 and Cu1-N3-C30-C29-N4 are formed and gives a distorted tetrahedral geometry for
the central copper (1) atom. The Cu1, N1, C1, C2, N2 atoms are almost coplanar and makes a dihedral
angle of 76.63o with plane containing Cu1, N3, C30, C29, N4 atoms. The Cu-N distances are almost
equal (Cu1-N1 2.058(4), Cu1-N2 2.010(4), Cu1-N3 2.026, Cu1-N4 2.055 Å) and within the same range
to the reported copper (I)-nitrogen bond distances (2.06 Å) for [{CH(PPh2NSiMe3)2}Cu(PPh3)].26
(Figure 4 here)
In the solid state the heteroleptic copper complex 4 crystallizes in the orthorhombic space group P na21
having four independent molecules of compound 4 and one CH2Cl2 molecule in the unit cell. The
structural parameters and selected bond lengths and bond angles for the complex 4 are given in the Table
1 and Table 2 respectively. The molecular structure of compound 4 is shown in Fig 4. Like complex 3, the
molecular structure of 4 consists of an ion pair composed of a [PF6]- anion and an [Cu(I)(η2-DADPh3)2]+.
The metalla-polyhedron in the cationic part is formed by the chelation of two iminium nitrogen atoms of
the N,N bis(triphenyl-methyl)-1,4-diaza-1,3-butadiene ligand and two nitrogen from two acetonitrile
groups. Thus a five membered metallacycle Cu1-N1-C1-C2-N2 (Cu2-N5-C47-C48-N6 for molecule 2) is
formed and the central copper atom adopts a distorted tetrahedral geometry. The Cu1-N3 and Cu1-N4
distances (1.957(4) and 1.986(4) Å respectively and Cu2-N7 1.972(4) and Cu2-N8 1.948(4)Å for
molecule 2) are slightly shortened compare to Cu-N1 and Cu1-N2 (2.107(4) and 2.137(4) Å respectively
and Cu2-N5 2.107(4) and Cu2-N6 2.117(4) Å for molecule 2) indicating that the iminium nitrogen’s are
weakly coordinated to the copper atom compare to acetonitrile nitrogen atoms. The Cu1, N1, C1, C2 and
N2 atoms are almost coplanar and the plane forms a dihedral angle of 67.29o (81.44o between the plane
containing Cu2, N5, C47, C48, N6 vs plane containing N7, C87, C88 atoms of molecule 2) with the plane
containing N4, C43, C44 atoms where as a dihedral angle of 66.66o (85.27o between the plane containing
Cu2, N5, C47, C48, N6 vs plane containing N8, C89, C90 atoms of molecule 2) is formed with the plane
9

having N3, C41, C42 atoms. A significant steric congestion is observed due to presence of three phenyl
groups which prevent the formation of homoleptic copper complex like compound 3 with bulky N,N
bis(triphenylmethyl)-1,4-diaza-1,3-butadiene ligand.
Scheme 4.
As it is evident from the structural point of view of the copper(I) complex 3 and 4 that presence of
triphenyl moiety prevents the approach of second DADPh3 ligand to form homoleptic complex, we made
an one pot reaction involving ligand 1, [Cu(CH3CN)4]PF6 and triphenylphosphine (PPh3) in
dichloromethane at ambient temperature. A heteroleptic copper complex 5 of composition
[Cu(DADPh2)(PPh3)2]PF6, where only one ligand moiety attach to the copper centre, was isolated in good
yield (Scheme 4). The compound 5 was characterized by standard spectroscopic/analytic method and the
solid state structure was established by single crystal X-ray analysis.
(Figure 5 here)
The complex 5 crystallizes in the orthorhombic space group P bc21 having four molecules of 5 and one
dichloromethane molecule in the unit cell. The structural parameters and selected bond lengths and bond
angles for the complex 5 are given in the Table 1. The molecular structure of compound 5 is shown in Fig
5. Like previous complexes 3 and 4, the solid state structure of 5 is ionic and the coordination polyhedron
in the cationic part is formed by the chelation of two iminium nitrogen atoms of the bidentate N, N
bis(diphenylmethyl)-1,4-diaza-1,3-butadiene ligand (DADPh2) and two phosphorus atoms from two
phosphine moieties. Phosphine groups being better donor capabilities replace the poor coordinating
acetonitrile groups from the copper atom. It is also noteworthy that the approach of second DADPh2 ligand
towards copper atom is preventer by the phosphine groups which are the soft donors and prefer soft
copper (I) center more effectively. Thus a five membered metallacycle Cu1-N1-C1-C2-N2 is formed by
the coordination of two nitrogen atoms. And the central copper atom adopts a tetrahedral geometry
around it. The Cu-N bond distances (Cu1-N1 2.086(4) Å, Cu1-N2 2.096(4) Å) are similar with the other
two copper complexes 3 and 4 (Table 2). The Cu-P distances (Cu1-P1 2.2678(15) Å and 2.2704(14)) Å
are slightly elongated compare to Cu(I)-phosphorus bond distance (2.176 Å) reported in reported
[{CH(PPh2NSiMe3)2}Cu(PPh3)].26
10

(Table 2 here)
10 mol % Cat
2 eq. K3PO4
I
+
R
R
O
HO
Toluene 110 oC, 24 h
Scheme 5.
Catalysis: Benzo[b]furans are important class of compounds and present in many compounds and natural
products having various biological properties like inhibition of protein phosphatase1B,27 5-HT2 and 5-HT3
antagonist activity,28 inhibition of 5-Lipoxygenase (5-LO),28 and anti-fungal properties.29 In contrast to
the multi-step synthesis of benzo[b]furans, recently Venkataraman and co-worker,30 Buchwald and
coworker31 and others32 employed copper-catalyzed cross-coupling reactions to develop the synthesis of
benzo[b]furans. It was proved that copper-based methods have an economic attractiveness and hence can
be the choice in large and industrial scale reactions. We employed our newly synthesized three copper
complexes 3-5 as catalysts for the synthesis of 2-phenylbenzo[b]furan by using o-iodophenols and phenyl
acetylene as the coupling reagents and potassium phosphate (K3PO4) as base in toluene (Scheme 5). The
results are given Table 3. It is observed that compound 4 is the most effective catalyst to produce 2-
phenylbenzo[b]furan which was obtained in 86% yield (entry 2) compare to compound 3 and 5 under
identical conditions (entry 1 and 3). In each case we loaded only 10 mol% copper catalyst with respect
substrate phenyl acetylene. We also screened the catalytic activity of the complexes 4 and 5 using another
substrate 2-bromo 4,6-di-tert-butylphenol and phenyl acetylene as the coupling reagents with potassium
phosphate (K3PO4) as base in toluene, however no coupling product was detected in each case under
similar condition (entry 4 and entry 5).
(Table 3 here)
Conclusions
In conclusion, we have prepared two glyoxal based bulky ligands N,N’ Bis(diphenyl-methyl)-1,4-diaza-
1,3-butadiene and N,N bis(triphenylmethyl)-1,4-diaza-1,3-butadiene and they were introduced in
copper(I) chemistry. Due to the more steric influence of two phenyl groups in ligand 2, homeleptic
complex of copper was observed whereas the triphenyl analogue 3 formed heteroleptic copper complex
11

under similar condition. In the molecular structures, all the copper complexes form distorted tetrahedral
geometry. The copper complexes are also proved to be potent catalyst for the synthesis of 2-
phenylbenzo[b]furan from o-iodophenols and phenyl acetylene. Further details of the ligands towards d-
block and f-block elements are in progress in our laboratory and will be published in due course of time.
Acknowledgments
This work was supported by the Council of Scientific and Industrial Research (CSIR) scheme ((No.
01(2530)/11/EMRII)) and start-up grant from IIT Hyderabad. S.A. thanks CSIR, India and R. K. thanks
UGC, India for their PhD fellowship. Generous support from K. Mashima, Osaka University, Japan is
gratefully acknowledged.
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16

Figure 1. Solid state structure of compound 1. Selected bond lengths (Å) and bond angles (o) are given.
C1-N1 1.2613(19), N1-C2 1.4757(17), C2-C9 1.520(2), C2-C3 1.519(2), C1-N1-C2 117.51(13), C1i-C1-
N1 120.15(18), N1-C2-C9 108.22(11), N1-C2-C3110.32(12) .
Figure 2. Solid-state structure of 2 (molecule 1) showing the atom labeling scheme. Selected distances
[Å] and angles [o] Selected bond lengths (Å) are given. C1-N1 1.269(2), N1-C2 1.272(2), C3-C4
1.547(2), C3-C10 1.547(2), C3-C16 1.540(3), C1-N1-C3 121.40(16), C1i-C1-N1 119.2(2), N1-C3-C4
114.09(15). N1-C3-C10 106.07(14), N1-C3-C16 106.03(14).
Figure 3. Solid-state structure of the cationic part of 3 showing the atom labeling scheme, omitting
hydrogen atoms for clarity. Selected distances [Å] and angles [o] are given. Cu1-N1 2.058(4), Cu1-N2
2.010(4), Cu1-N3 2.026(4), Cu1-N4 2.055(4), N1-C1 1.276(7), C1-C2 1.474(8), C2-N2 1.280(7), N3-C30
1.278(7), C30-C29 1.456(8), C29-N4 1.289(7) , N1-Cu1-N2 81.26(17), N1-Cu1-N3 113.82(17), N1-Cu1-
N4 120.17(18), N2-Cu1-N3 148.01(18), N2-Cu1-N4 116.56(18), N3-Cu1-N4 81.35(18), Cu1-N1-C1
111.1(4), Cu1-N2-C2 112.2(4), Cu1-N3-C30 110.7(4), Cu1-N4-C29 110.6(4).
Figure 4. Solid-state structure of 4 showing the atom labeling scheme, omitting hydrogen atoms for
clarity. Selected distances [Å] and angles [o] are given.
Molecule 1; Cu1-N1 2.107(4), Cu1-N2 2.137(4), Cu1-N3 1.957(4), Cu1-N4 1.986(4), N1-C1 1.288(7),
C1-C2 1.483(7), C2-N2 1.280(6), N1-Cu1-N2 81.73(16), N1-Cu1-N3 126.08(16), N1-Cu1-N4
111.20(16), N2-Cu1-N3 119.52(16), N2-Cu1-N4 115.69(17), N3-Cu1-N4 102.60(18), Cu1-N1-C1
108.6(3), Cu1-N2-C2 108.4(3) , Cu1-N3-C41 173.6(4) , Cu1-N4-C43 168.5(4).
Molecule 2; Cu2-N5 2.107(4), Cu2-N6 2.117(4), Cu2-N8 1.948(4), Cu2-N7 1.972(4), N5-C47 1.270(7),
N6-C48 1.279(7), C47-C48 1.469(7), N5-Cu2-N6 81.50(16), N5-Cu2-N7 118.58(16), N5-Cu2-N8
119.83(16), N6-Cu2-N7 104.96(16), N6-Cu2-N8 130.21(16), N7-Cu2-N8 101.93(18), Cu2-N5-C47
108.8(3), Cu2-N6-C48 108.3(3), Cu2-N7-C87 170.2(5), Cu2-N8-C89 171.3(4).
Figure 5. Solid-state structure of the cationic part of 5 showing the atom labeling scheme, omitting
hydrogen atoms for clarity. Selected distances [Å] and angles [o] are given.
Cu1-N1 2.086(4), Cu1-N2 2.096(4), Cu1-P1 2.2678(15), Cu1-P2 2.2704(14), C1-N1 1.281(5), C2-N2
1.280(6), C1-C2 1.467(5), N1-Cu1-N2 78.34(11), Cu1-N1-C1 113.5(3), Cu1-N2-C2 113.3(3), N1-Cu1-
P1 120.87(11) , N1-Cu1-P2 103.56(12), N2-Cu1-P1 105.23(12), N2-Cu1-P2 119.53(12), P1-Cu-P2
122.00(4).

Figures 1

Figure 2

Figure 3

Figure 4

Figure 5

Table 1. Crystallographic details and structural parameters of compounds 1-5.
Crystal
CCDC No.
3(CH2Cl2)
914537
4(CH2Cl2)
914538
1
2
914540
914541
Empirical formula
C28H24N2
C40H32N2
C59H54Cl6 CuF6
N4P
C90H78Cl4Cu2F12N8P2
Formula weight
T (K)
λ (Å)
Crystal system
Space group
a (Å)
388.49
150(2)
1.54184
Monoclinic,
P 21/n
12.6098(16)
5.5803(7)
15.513(2)
90
101.385
90
540.68
150(2)
1240.28
150(2) K
1.54184
Triclinic
P-1
9.9004(9)
13.8731(9)
21.467(2)
86.027(7)
78.923
1830.44
150(2) K
1.54184
Orthorhombic
P n a 21
25.4177(7)
11.4473(2)
29.0063(7)
90
0.71069
Triclinic
P -1
9.435(5)
11.370(5)
14.164(5)
91.307(5)
91.403(5)
107.631
b (Å)
c (Å)
 ( o)
 ( o)
90
90
 ( o)
85.454(7)
V ( Å3)
Z
1070.1(2)
2
1.206
0.538
412
1446.9(11)
2
1.241
0.072
572
2880.0(4)
2
1.430
3.876
1272
8439.8(3)
4
1.441
2.804
3752
Dcalc mg/cm-3
µ (mm-1)
F (000)
Theta range for data 4.14 to 70.59 deg.
collection
3.36 to 27.47 deg. 3.20 to 59.99 deg. 3.48 to 70.69 deg.
Limiting indices
-
-15<=h<=15,
-6<=k<=4,
-15<=l<=18
3672 / 2006
[R(int) = 0.0235]
97.9 %
-11<=h<=12,
-14<=k<=14,
-18<=l<=18
13787 /6395
[R(int) = 0.0401]
96.5 %
-11<=h<=10,
-15<=k<=11,
-24<=l<=13
17720 / 8440
[R(int) = 0.0303]
98.8 %
-30<=h<=29,
-14<=k<=13,
-21<=l<=35
22272 / 10935
[R(int) = 0.0303]
96.2 %
Reflections
collected / unique
Completeness to
theta = 71.25
Absorption
Empirical
Empirical
Empirical
Empirical
correction
Max. and min.
transmission
Refinement method Full-matrix
0.943 and 0.908
0.989 and 0.983
Full-matrix
0.561 and 0.484
Full-matrix
0.659 and 0.573
Full-matrix
least-squares on F2 least-squares on F2 least-squares on F2 least-squares on F2
Data / restraints /
parameters
2006 / 0 / 136
6395 / 0 / 379
1.050
8440 / 0 / 694
1.035
10935 / 1 / 1067
1.028
Goodness-of-fit on 0.853
F2
Final R indices
[I>2sigma(I)]
R indices (all data) R1 = 0.0539,
wR2 = 0.1435
R1 = 0.0467,
wR2 = 0.1273
R1 = 0.0622,
wR2 = 0.1510
R1 = 0.0977,
wR2 = 0.1782
R1 = 0.0912,
wR2 = 0.2569
R1 = 0.1031,
wR2 = 0.2695
R1 = 0.0590,
wR2 = 0.1653
R1 = 0.0628,
wR2 = 0.1715
Absolute structure
parameter
Largest diff. peak
and hole
0.152 and -0.232
e.A-3
0.280 and -0.280
e.A-3
2.771 and -1.137
e.A-3
1.286 and -0.994
e.A-3

Crystal
5(CH2Cl2)
CCDC No.
914539
Empirical formula
Formula weight
T (K)
C65H56Cl2CuF6N2P3
1206.48
150(2)
λ (Å)
1.54184
Orthorhombic
P b c 21
15.3393(3)
21.5491(7)
17.6880(3)
90
Crystal system
Space group
a (Å)
b (Å)
c (Å)
 ( o)
 ( o)
90
90
 ( o)
V ( Å3)
5846.7(2)
4
1.371
2.655
2488
Z
Dcalc g cm-3
µ (mm-1)
F (000)
Theta range for data collection 3.54to 70.88 deg.
Limiting indices
-
-11<=h<=18,
-23<=k<=26,
-13<=l<=21
Reflections collected / unique
15761 / 8277
[R(int) = 0.0396]
Completeness to theta = 71.25 98.6 %
Absorption correction
Max. and min. transmission
Refinement method
Empirical
0.710 and 0.573
Full-matrix
least-squares on F2
5
Data / restraints / parameters
8277 / 1 / 713
1.043
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R1 a = 0.0509,
wR2b = 0.1371
R1a = 0.0601,
wR2 b = 0.1492
R indices (all data)
Absolute structure parameter
Largest diff. peak and hole
0.402 and -0.653 e.A-3
a
R1(F) = ||Fo| - |Fc|| / |Fo|.
b
wR2(F2) = [w(Fo2 - Fc2)2 / (wFo4)]1/2.

Table 2: Selected bond lengths and bond angles for compound 1, 2, 3, 4 and 5.
Bond Length (A0)
1
2
3
4
5
C(1)-N(1)
N(1)-C(2)
C(1)-C(1)i
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-N(3)
Cu(1)-N(4)
Cu(1)-P(1)
Cu(1)-P(2)
C(1)-C(2)
C(2)-N(2)
N(1)-C(3)
1.2613(19)
1.4757(17)
1.467(3)
1.269(2)
1.276(7)
1.281(5)
1.288(7)
1.472(4)
2.058(4)
2.010(4)
2.026(4)
2.055(4)
2.107(4)
2.137(4)
1.957(4)
1.986(4)
2.086(4)
2.096(4)
2.2678(15)
2.2704(14)
1.467(5)
1.280(6)
1.484(5)
5
1.474(8)
1.280(7)
1.483(7)
1.280(6)
1.508(6)
4
1.272(2)
Bond angle (O)
1
2
3
C(1)-N(1)-C(2)
C(1)i-C(1)-N(1)
N(1)-C(2)-C(9)
N(1)-C(2)-C(3)
N(1)-Cu(1)-N(2)
N(1)-Cu(1)-N(3)
N(1)-Cu(1)-N(4)
N(2)-Cu(1)-N(3)
N(2)-Cu(1)-N(4)
N(3)-Cu(1)-N(4)
Cu(1)-N(1)-C(1)
Cu(1)-N(2)-C(2)
N(1)-Cu(1)-P(1)
N(1)-Cu(1)-P(2)
N(2)-Cu(1)-P(1)
N(2)-Cu1-P(2)
117.51(13)
120.15(18)
108.22(11)
110.32(12)
119.2(2)
81.26(17)
113.82(17)
120.17(18)
148.01(18)
116.56(18)
81.35(18)
111.1(4)
81.73(16)
126.08(16)
111.20(16)
119.52(16)
115.69(17)
102.60(18)
108.6(3)
78.34(11)
113.5(3)
113.3(3)
112.2(4)
108.4(3)
120.87(11)
103.56(12)
105.23(12)
119.53(12)
122.00(4)
P(1)-Cu(1)-P(2)

Table 3: Copper(I)-catalyzed synthesis of 2-pheylbenzo[b]furans
Entry
Catalyst
Time (h)
Temperature(oC)
Yield (isolated)
52%
1
2
3
4
24
24
24
24
110
110
110
110
3
4
5
4
86%
66%
No reaction
5
24
110
No reaction
5
Conditions: 1.0 mmol of iodophenol (or 2-bromo 4,6-di-tertbutylphenol for entry 5), 1.00 mmol of phenyl
acetylene, 0.10 mmol Cu complexes (10 mol% with respect to iodophenol) and K3PO4 (2 equivalents) in
toluene at 110 oC under nitrogen atmosphere.

Cationic Copper (I) Complexes with Bulky 1,4-Diaza-1,3-Butadiene Ligands -
Synthesis, Solid State Structure and Catalysis
Srinivas Anga, Ravi K. Kottalanka, Tigmansu Pal and Tarun K. Panda*
Department of Chemistry, Indian Institute of Technology Hyderabad, Ordnance Factory Estate,
Yeddumailaram 502205, Andhra Pradesh, India. Fax: + 91(40) 2301 6032; Tel: + 91(40) 2301 6036;
E-mail: tpanda@iith.ac.in
Highlights:
 N,N bis(diphenylmethyl)-1,4-diaza-1,3-butadiene more bulky N,N bis(triphenyl-methyl)-1,4-
diaza-1,3-butadiene ligand 1,4-diaza-1,3-butadiene ligands were synthesized.
 All the ligands and copper (I) complexes were structurally characterized.
 Less bulky DAD ligand 2 form homoleptic complex [Cu(DADPh2)2]PF6 (3) whereas more bulky
ligand 2 forms heteroleptic copper (I) complex [Cu(DADPh3)(CH3CN)2]PF6 (4). When the
corresponding ligands were treated with [Cu(CH3CN)4]PF6.
 One pot reaction involving 1, [Cu(CH3CN)4]PF6 and PPh3 produces another copper complex
[Cu(DADPh2)(PPh3)]PF6 (5).
 Complexes 3-5 were tested as catalysts for the coupling reaction of o-iodophenol and phenyl
acetylene.