Synthesis and characterization of cationic cyclopalladated complexes derived from p-tert-butyl-calix[4]arene bisphosphite with nitrogen donors

Article abstract of DOI:10.1016/j.ica.2011.01.085

A series of new cationic cyclopalladated complexes 2-6 have been synthesized from neutral cyclopalladated complex 1 of p-tert-butyl-calix[4]arene bisphosphite with various nitrogen donor ligands (acetonitrile, pyridine, aniline, (R)-(+)-1-phenylethylamine

Full text of DOI:10.1016/j.ica.2011.01.085

Inorganica Chimica Acta 372 (2011) 120–125
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and characterization of cationic cyclopalladated complexes derived
from p-tert-butyl-calix[4]arene bisphosphite with nitrogen donors
Pathik Maji
Dept. of Inorganic and Physical Chemistry, IISc, Bangalore, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 3 February 2011
A series of new cationic cyclopalladated complexes 2–6 have been synthesized from neutral cyclopalla-
dated complex 1 of p-tert-butyl-calix[4]arene bisphosphite with various nitrogen donor ligands (acetoni-
trile, pyridine, aniline, (R)-(+)-1-phenylethylamine and 4,40-bipyridine) in presence of Ag(OSO2CF3) as a
chloride scavenger. These cationic cyclopalladated complexes have been characterized by NMR spectros-
copy. Single crystal X-ray diffraction studies performed on cationic cyclopalladated complexes 3 and 6 in
solid state reveal nearly square planar geometry around the metal and distorted cone conformation of the
calix[4]arene framework. These cationic cyclopalladated complexes based on hetero ligands having var-
iable steric and electronic properties could be efficient catalysts for important organic transformation
reactions.
Dedicated to Professor. S.S. Krishnamurthy
on his 70th birthday
Keywords:
Calix[4]arene
Cationic cyclopalladated complex
Nitrogen donor ligands
X-ray crystal structures
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Calixarenes are phenolic macrocycles which display signifi-
cant features such as structural versatility, conformational flexi-
bility, tunable molecular shape in both upper and lower rims
and presence of well-defined cavities [1,2]. The chemistry of cal-
ixarene has been grown up along several directions during last
two decades. Particularly the transition metal chemistry of phos-
phorus functionalized calixarenes and their use in catalysis are
significantly interesting and have been studied from a variety
of perspectives by many research groups [3–13]. Previous studies
in our laboratory have shown that transition metals (Pd, Pt)
dichloride complexes of p-tert-butyl calix[4]arene bisphosphites
readily undergo cyclometalation by C–C, C–H bond activation
to give metallacycle at higher temperature [14,15]. In continua-
tion with our ongoing studies on phosphorus functionalized
calixarenes and their coordination chemistry [16], in this paper
the synthesis of a series of new cationic cyclopalladated com-
plexes derived from p-tert-butyl calix[4]arene bisphosphite with
various nitrogen donor ligands such as acetonitrile, pyridine, ani-
line, (R)-(+)-1-phenylethylamine and 4,40-bipyridine in presence
of Ag(OSO2CF3) as a chloride scavenger is reported. The charac-
terization of these cationic cyclopalladated complexes 2–6 by
NMR spectroscopy and X-ray crystallography is also discussed
here.
2.1. General
All the reactions were carried out under an atmosphere of dry
nitrogen or argon by using Schlenk tube techniques. The solvents
were dried and distilled by conventional methods and deoxy-
genated before use. The starting neutral cyclopalladated complex
1 was prepared from p-tert-butyl calix[4]arene bisphosphite as
reported [14]. Specific rotation of complex 5 was measured on a
JASCO DIP-370 digital polarimeter. The NMR spectra were recorded
in CDCl3 using a Bruker Avance-400 spectrometer with Me4Si as an
internal standard for 1H NMR measurements and 85% H3PO4 as an
external standard for 31P NMR measurements. Elemental analysis
was carried out using a Perkin–Elmer 2400 CHN analyzer.
2.2. Synthesis
Complex 2: The neutral cyclopalladated complex 1 (30 mg,
2.44 ꢀ 10ꢁ5 mol) was dissolved in chloroform (15 ml) with Ag
(OSO2CF3) (6 mg, 2.44 ꢀ 10ꢁ5 mol) and treated with few drops of
acetonitrile. The reaction mixture was stirred at 25 °C for 2 h. The
precipitate of AgCl was filtered off and the filtrate was evaporated
to dryness. Pure complex 2 was obtained by precipitation of using
chloroform and petroleum ether (1:2). Yield: 21 mg (64%); Anal.
Calc. for C73H92O9P2F3N1S1Pd1 (mol. wt.: 1384.94): C, 63.31; H,
6.70; N, 1.01. Found: C, 63.36; H, 6.68; N, 0.98%; 31P NMR
(162 MHz, CDCl3), AX spectra d = 114.4 ppm (d), 103.7 ppm (d),
E-mail addresses: pathikm.iisc@gmail.com, pathik.maji@ucd.ie
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.085

P. Maji / Inorganica Chimica Acta 372 (2011) 120–125
121
2JP–P = 82.1 Hz; 1H NMR d = 1.13 (s, 9H, But), 1.14 (s, 18H, But), 1.16
(s, 18H, But), 1.40 (s, 18H, But of aryl substituent), 2.29 (s, 3H, Me),
2.37 (s, 3H, Me), 3.12 (bs, 3H, Me of acetonitrile), 3.66 (d, H, Hb2,
J = 13.2 Hz), 3.73 (d, 2H, Hb3, J = 14.8 Hz), 3.85 (d, H, Hb1,
J = 15.6 Hz), 4.78 (d, H, Ha2, J = 15.2 Hz), 4.83 (d, 2H, Ha3,
J = 15.6 Hz), 5.11 (d, H, Ha1, J = 15.2 Hz), 6.66(s), 6.78(s), 6.82(s),
6.94(s), 7.08(s), 7.17(s), 7.19(s), 7.20(s) (12H, aromatic protons
from phenyl and calixarene).
refinement and data acquisition and the SAINT [18] software was
used for data reduction. An absorption correction was made on
the intensity data using SADABS [19] program. The structures were
solved using SHELXS [20] and the WinGX graphical user interface.
Least square refinements were performed by the full-matrix method
with SHELXL [21]. The PLATON/SQUEEZE routine was used to
remove the contributions of any disordered solvent molecules.
The CIF format output from PLATON is appended to the CIF. Some
of the tert-butyl groups were disordered and hydrogen atoms of
these disordered groups were neither located nor fixed during
the refinement.
The complexes 3, 4, 5 and 6 were synthesized from neutral
complex 1 on employing a procedure similar to that for complex
2 (for details see the Supplementary information).
Complex 3: Yield: 24 mg (66%); Anal. Calc. for
C76H94O9P2F3N1S1Pd1(3H2O) (mol. wt.: 1477.03): C, 61.80; H,
3. Results and discussion
6.82; N, 0.95. Found: C, 61.83; H, 6.79; N, 0.94%; 31P NMR
(162 MHz, CDCl3), AX spectra d = 117.7 ppm (d), 104.1 ppm (d),
2JP–P = 83.7 Hz; 1H NMR d = 1.08 (s, 9H, But), 1.16 (s, 18H, But),
1.19 (s, 18H, But), 1.32 (s, 18H, But of aryl substituent), 2.21(s,
3H, Me), 2.28 (s, 3H, Me), 3.50(d, H, Hb2, J = 12.2 Hz), 3.55 (d, 2H,
Hb3, J = 12.4 Hz), 3.64 (d, H, Hb1, J = 13.0 Hz), 4.72 (d, H, Ha2,
J = 13.6 Hz), 4.76(d, 2H, Ha3, J = 14.0 Hz), 5.09 (d, H, Ha1,
J = 14.2 Hz), 6.81(s), 6.82(s), 6.91(s), 6.93(s), 6.96(s), 7.01(s),
7.16(s), 7.24(s) (12H, aromatic protons of phenyl and calixarene),
7.42(bs), 8.14(bs), 8.81(bs), (5H, aromatic protons of pyridine).
Complex 4: Yield: 22 mg (62%); Anal. Calc. for
3.1. Synthesis of cationic cyclopalladated complexes and their NMR
spectra
A series of cationic cyclopalladated complexes 2–6 have been
synthesized from neutral cyclopalladated complex 1 of p-tert-butyl-
calix[4]arene bisphosphite with various nitrogen donor ligands
(acetonitrile, aniline, (R)-(+)-1-phenylethylamine, pyridine and
4,40-bipyridine) in presence of Ag(OSO2CF3) as a chloride scaven-
ger. These reactions are shown in Scheme 1. Ligand such as
4,40-bipyridine plays an important role for the synthesis of cationic
dinuclear palladium complex 6 due to its length which renders less
steric strain between the two metal centre.
C
77H96O9P2F3N1S1Pd1(mol. wt.: 1437.02): C, 64.36; H, 6.73, N,
0.97. Found: C, 64.38; H, 6.69; N, 0.96%; 31P NMR (162 MHz, CDCl3),
AX spectra d = 119.3 ppm (d), 107.5 ppm (d), JP–P = 90.2 Hz; 1H
The 31P NMR spectra of the cationic cyclopalladated complexes
2–6 show an AX pattern as it is in the neutral cyclopalladated com-
plex 1 (see the ESI, Figs. S1–S3). The chemical shifts and coupling
constants are in the same range as those observed for neutral
cyclopalladated complex 1 and are listed in Table 1. The chemical
shift value of the phosphorus atom Px moves to an upfield region
for all the cationic complexes 2–6 in comparison with the neutral
cyclopalladated complex 1. The chemical shift value of the phos-
phorus atom PA is almost unchanged for all cationic cyclopalladated
complexes except for complexes 4 and 5. For cationic complex 5
the chemical shift value of PA moves down field to a significant
extent. The chemical shift value of the phosphorus atom Px in
cyclopalladated complex 2 is in more upfield region (114.4 ppm)
with respect to other cationic cyclopalladated complexes 3–6.
The 1H NMR spectrum of cationic cyclopalladated complexes
2–4, 6 show six doublets (three doublets are in the downfield region
and three doublets are in the upfield region) with a coupling con-
stant typical of geminal protons. The intensity ratio of the three
doublets in both upfield and downfield region is 1:1:2 which is
same in neutral cyclopalladated complex 1. For cationic cyclopalla-
dated complex 5 which contains a chiral CH(Me)(Ph) group, all the
methylene protons are magnetically nonequivalent and the inten-
sity ratio of the four doublets in both upfield and downfield region
is 1:1:1:1.
2
NMR d = 1.11 (s, 9H, But), 1.12 (s, 18H, But), 1.14 (s, 18H, But),
1.38 (s, 18H, But of aryl substituent), 2.26 (s, 3H, Me), 2.34 (s, 3H,
Me), 3.37 (bs, 2H, –NH2), 3.67 (d, H, Hb2, J = 11.6 Hz), 3.76 (d, 2H,
Hb3, J = 11.8 Hz), 3.82 (d, H, Hb1, J = 13.6 Hz), 4.88 (d, H, Ha2,
J = 14.4 Hz), 4.91 (d, 2H, Ha3, J = 12.8 Hz), 5.32 (d, H, Ha1,
J = 13.4 Hz), 6.76(s), 6.80(d), 6.83(s), 6.92 (s), 7.12(s), 7.13(s),
7.17(s), 7.18(s), 7.21(d), 7.22(d), 7.25(s) (17H, aromatic protons
of phenyl, calixarene and aniline).
Complex 5: Yield: 23 mg (64%); ½a D25
ꢂ
= 38.5 (1.0, CHCl3); Anal.
Calc. for C79H100O9P2F3N1S1Pd1(mol. wt.: 1465.07): C, 64.76; H,
6.88; N, 0.96. Found: C, 64.78; H, 6.85; N, 0.94%; 31P NMR
(162 MHz, CDCl3), AX spectra d = 117.3 ppm (d), 110.2 ppm (d),
2JP–P = 77.3 Hz; 1H NMR d = 0.95 (d, Me, phenylethylamine), 1.03
(s, 9H, But), 1.10 (s, 18H, But), 1.12 (s, 18H, But), 1.18 (s, 9H, But
of aryl substituent), 1.20 (s, 9H, But of aryl substituent), 2.06 (s,
3H, Me), 2.24 (s, 3H, Me), 2.84 (bs, H, phenylethyl-amine), 3.37(d,
H, Hb4, J = 13.6 Hz), 3.46 (d, H, Hb2, J = 14.0 Hz), 3.61 (d, H, Hb3,
J = 14.4 Hz), 3.66 (d, H, Hb1, J = 14.6 Hz), 4.10 (bs, 2H, –NH2 of
phenylethylamine), 4.46 (d, H, Ha4, J = 14.2 Hz), 4.60 (d, H, Ha2, J
= 13.6 Hz), 4.65 (d, H, Ha3, J = 15.6 Hz), 5.16 (d, H, Ha1,
J = 13.8 Hz), 6.89(s), 6.96(s), 6.98(s), 7.01(s), 7.05(s), 7.11(s),
7.25(s), 7.28(s), 7.37(s), 7.38(s) (17H, aromatic protons of phenyl,
calixarene and (R)-(+)-1-phenylethyl).
Complex 6: Yield: 44 mg (63%); Anal. Calc. for
C
152H186O18P4F6N2S2Pd2 (mol. wt.: 2843.96): C, 64.19; H, 6.59; N,
3.2. X-ray crystallographic studies
0.99. Found: C, 64.21; H, 6.58; N, 0.97%; 31P NMR (162 MHz, CDCl3),
AX spectra d = 118.1 ppm (d), 104.4 ppm (d), JP–P = 85.3 Hz; 1H
The solid-state structures of complexes 3 and 6 have been
determined by single crystal X-ray diffraction analysis. Details per-
tinent to data collection, structure solution and refinement are
summarized in Table 2. Selected bond lengths and angles are given
respectively in Tables 3 and 4. The data are comparable with neu-
tral cyclopalladated calix[4]arene bisphosphite complex 1 reported
by Mahalakshmi et al. [14].
The ORTEP plots of the molecular structures of cationic cyclo-
palladated complexes 3 and 6 are presented in Figs. 1 and 2,
respectively. The cyclopalladated complex 3 crystallizes in the
monoclinic system of P2/c space group with three water molecules.
The geometry around the palladium is nearly square planar and
that around the two phosphorus atoms is nearly tetrahedral. The
2
NMR d = 1.15 (s, 9H, But), 1.17 (s, 18H, But), 1.20 (s, 18H, But),
1.33 (s, 18H, But of aryl substituent), 2.09 (s, 3H, Me), 2.16 (s, 3H,
Me), 3.52 (d, H, Hb2, J = 12.4 Hz), 3.58 (d, H, Hb3, J = 12.8 Hz), 3.66
(d, H, Hb1, J = 13.2 Hz), 4.72 (d, H, Ha2, J = 13.8 Hz), 4.78(d, 2H,
Ha3, J = 14.2 Hz), 5.08 (d, H, Ha1, J = 14.4 Hz), 6.81(s), 6.92(s),
6.94(s), 6.97(s), 6.99(s), 7.04(s), 7.11(d), 7.25(s) (12H, aromatic pro-
tons), 8.57(bs), 8.30(bs), (8H, aromatic protons of 4,40-bipyridine).
2.3. X-Ray crystallography
X-ray diffraction data were collected on a Bruker SMART APEX
CCD diffractometer. The SMART [17] software was used for cell

122
P. Maji / Inorganica Chimica Acta 372 (2011) 120–125
+
But But
But
But
OTf
O
O
O
O
But
Px
PA
O
Pd
O
But
N
But
Me
C
Me
+
2
But But
2
But
But
Me
+
OTf
But But
But
But
2OTf
(i)
O
O
O
O
But But
But
But
O
O
O
O
But
(ii)
PA
Px
But
PA
Px
O
Pd
O
O
Pd
But
O
But
N
N
Me
But
O
Me
O
O
(v)
O
But
Me
But
Me
But
Px
PA
Me
But
O
Me
3
Pd
O
N
But
But
Cl
O
Pd
Me
But
O
But
1
Px
PA
Me
+
OTf
But
O
But
But
O
O
O
O
O
(iii)
(iv)
But
But
But
+
But
But
But
O
Px
But
O
But
But
PA
OTf
O
6
Pd
O
But
NH2
Ph
4
Me
O
But
O
O
O
But
PA
Me
Px
O
Pd
O
But
NH2
Me
But
(Me)CH
Me
5
Ph
Scheme 1. (i) CHCl3, AgOSO2CF3, CH3CN, 25 °C, 2 h; (ii) CHCl3, AgOSO2CF3, pyridine, 25 °C, 2 h; (iii) CHCl3, AgOSO2CF3, aniline, 25 °C, 2 h; (iv) CHCl3, AgOSO2CF3, (R)-(+)-1-
phenylethylamine, 25 °C, 2 h; (v) CHCl3, AgOSO2CF3, 4,40-bipyridine, 25 °C, 2 h.
Table 1
almost parallel with the 2,6-di-tert-butyl-4-Me-phenyl ring to
The 31P NMR chemical shifts for cationic cyclopalladated complexes 2–6 and the
minimize steric strain. Similarly, the 4,40-bipyridine ring in com-
neutral cyclopalladated complex 1.a
plex 6 is also parallel with the 2,6-di-tert-butyl-4-Me-phenyl ring
Complex
31P NMR (ppm)
Px
2JP–P (Hz)
which is not bonded with the palladium. In comparison with the
bond angle [C(36)-Pd(1)-Cl(1) = 92.5(3)°] of the neutral cyclopalla-
dated palladium complex 1 [14], the bond angle [C(36)–Pd(1)–
N(1)] of the cationic cyclopalladated complexes 3 and 6 is slightly
lower. This result suggests that the distortion towards the cone
conformation is more in the cationic cyclopalladated complex 6
and 3 as compared with the neutral complex 1. The average P–O
bond distance in the cationic cyclopalladated complexes 3 and 6
is close to the average P–O distance in the neutral cyclopalladated
complex 1. The distance between palladium metal and the carbon
atom of the phenyl ring [Pd(1)–C(36)] in cationic cyclopalladated
complexes 3 [2.078(6) Å] and 6 [2.086(5) Å] is slightly higher than
PA
2
3
4
5
6
1
114.4(d)
117.7(d)
119.3(d)
117.3(d)
118.1(d)
120.6(d)
103.7(d)
104.1(d)
107.5(d)
110.2(d)
104.4(d)
103.4(d)
82.1
83.7
90.2
77.3
85.3
77.3
a
Recorded in CDCl3 at 25 °C and at 161.9 MHz, d in ppm.
cationic cyclopalladated dinuclear complex 6 crystallizes in the tri-
clinic system of P1 space group. The pyridine ring in complex 3 is
ꢀ

P. Maji / Inorganica Chimica Acta 372 (2011) 120–125
123
Table 2
Details of X-ray data collection and refinement for cationic cycloplladated complexes 3 and 6.
Empirical formula
C76 H100 F3 N O12 P2 Pd S (3)
C152 H186 F6 N2 O18 P4 Pd2 S2 (6)
Formula weight
Temperature
Wavelength
1477.03
293(2) K
0.7107
2843.96
293(2) K
0.7107
Crystal system
Space group
Monoclinic
P21/c
Triclinic
P1
ꢀ
Unit cell dimensions
a = 16.041(5) Å,
a
= 90°
a = 16.970(2) Å, a = 112.068(2)°
b = 30.972(9) Å, b = 114.346(4)°
b = 17.643(2) Å, b = 108.452(2)°
c = 18.857(5) Å,
8535(4) Å3
4
c
= 90°
c = 17.727(2) Å,
4435(8) Å3
1
c = 98.874(2)°
Volume
Z
Density (calculated)
Absorption coefficient
F(0 0 0)
1.149 Mg/m3
0.338 mmꢁ1
3112
1.052 Mg/m3
0.320 mmꢁ1
1460
Crystal size
Theta range for data collection
Index ranges
0.42 ꢀ 0.34 ꢀ 0.24 mm
0.48 ꢀ 0.38 ꢀ 0.32 mm
1.36–25.00°
1.33–27.85°
ꢁ21 ꢃ h ꢃ 19, ꢁ33 ꢃ k ꢃ 36,
ꢁ22 ꢃ l ꢃ 22
ꢁ21 ꢃ h ꢃ 21, ꢁ23 ꢃ k ꢃ 22,
ꢁ22 ꢃ l ꢃ 23
Reflections collected
60,107
42,057
Independent reflections
Completeness to theta
Absorption correction
14,994 [R(int) = 0.0936]
99.8%
Empirical
15,522 [R(int) = 0.0599]
90.1%
Empirical
Maximum and minimum transmission
Refinement method
0.911 and 0.877
Full-matrix-least-squares on F2
4994/0/883
0.905 and 0.862
Full-matrix-least-squares on F2
15522/0/859
Data/restraints/parameters
Goodness-of-fit on F2
0.904
0.974
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole
R1 = 0.0936, wR2 = 0.2520
R1 = 0.1484, wR2 = 0.2823
1.347 and ꢁ0.410 e Åꢁ3
R1 = 0.0802, wR2 = 0.2423
R1 = 0.1113, wR2 = 0.2636
1.390 and ꢁ0.501 e Åꢁ3
Table 3
Selected bond lengths (Å) for the cationic cyclopalladated complexes 3 and 6.
Bond distance
Complex 3
Complex 6
Bond distance
Complex 3
Complex 6
P(1)–Pd(1)
P(2)–Pd(1)
N(1)–Pd(1)
C(36)–Pd(1)
P(1)–O(1)
2.371(2)
2.194(2)
2.101(8)
2.078(8)
1.603(5)
2.394(2)
2.197(3)
2.165(4)
2.086(5)
1.596(4)
P(1)–O(2)
P(1)–O(3)
P(2)–O(4)
P(2)–O(5)
P(2)–O(6)
1.593(5)
1.595(5)
1.584(5)
1.577(5)
1.607(5)
1.598(4)
1.602(4)
1.576(4)
1.587(4)
1.595(4)
Table 4
Selected bond angles (°) for the cationic cyclopalladated complexes 3 and 6.
Bond angle
Complex 3
Complex 6
Bond angle
Complex 3
Complex 6
P(2)–Pd(1)–P(1)
P(2)–Pd(1)–N(1)
P(1)–Pd(1)–N(1)
P(2)–Pd(1)–C(36)
P(1)–Pd(1)–C(36)
C(36)–Pd(1)–N(1)
O(3)–P(1)–O(1)
O(3)–P(1)–O(2)
O(1)–P(1)–O(2)
91.5(7)
168.5(2)
99.6(2)
79.5(2)
167.4(2)
89.0(3)
102.8(3)
106.5(3)
103.0(2)
88.8(5)
169.8(1)
101.4(1)
79.3(2)
164.9(2)
90.8(2)
104.8(2)
103.1(2)
102.1(2)
O(3)–P(1)–Pd(1)
O(1)–P(1)–Pd(1)
O(2)–P(1)–Pd(1)
O(6)–P(2)–O(5)
O(6)–P(2)–O(4)
O(5)–P(2)–O(4)
O(6)–P(2)–Pd(1)
O(5)–P(2)–Pd(1)
O(4)–P(2)–Pd(1)
124.1(2)
110.5(2)
107.9(2)
105.2(3)
104.9(3)
103.7(3)
107.8(2)
114.9(2)
119.1(2)
125.2(2)
108.3(1)
110.9(2)
105.7(2)
103.5(2)
103.8(2)
108.0(1)
117.1(1)
117.3(1)
the distance in neutral cyclopalladated complex 1 [2.064(8) Å] [14]
because of the electronic property of pyridine and 4,40-bipyridine.
The conformation of the calix[4]arene backbone can be dis-
cussed in terms of either dihedral angles or torsion angles. The
dihedral angles of the calix[4]arene aryl rings (A, B, C, and D) with
the least square plane X of the four methylene carbons (C2, C8, C14
and C20) for cationic cyclopalladated complexes 3, 6 are listed in
Table 5. These data indicate that the calixarene framework in the
cationic cyclopalladated complexes 3 and 6 adopts distorted cone
conformation as it is in the neutral cyclopalladated complex 1
[14]. But the distorsion in the cationic cyclopalladated complexes
3 and 6 is higher than that of the neutral cyclopalladated complex
1.
The torsion angles involving the bridging methylene carbon
atoms and aryl ring carbon atoms for the cationic cyclopalladated
complexes 3 and 6 are listed in Table 6. The sequence of signs for
the two torsion angles / and
(or reverse) and confirms the cone conformation for both the com-
plexes. A comparison of the observed torsion angles / and for the
v
is found to be + ꢁ, + ꢁ, + ꢁ, + ꢁ
v
two cationic complexes 3 and 6 with those expected for an ideal
cone conformation [90° and ꢁ90°, respectively] shows that there
is a larger deviation for two aryl rings (larger torsion angles) and

124
P. Maji / Inorganica Chimica Acta 372 (2011) 120–125
Table 6
Torsion angles / and
v
of cationic cyclopalladated complexes 3 and 6.
Complex 3
Molecular fragment
Complex 6
C(24)–C(1)–C(2)–C(3)
C(1)–C(2)–C(3)–C(4)
C(6)–C(7)–C(8)–C(9)
C(7)–C(8)–C(9)–C(10)
C(12)–C(13)–C(14)–C(15)
C(13)–C(14)–C(15)–C(16)
C(18)–C(19)–C(20)–C(21)
C(19)–C(20)–C(21)–C(22)
[/]
[v]
[/]
85.8(8)
ꢁ116.1(7)
93.9(8)
ꢁ118.8(6)
84.2(7)
ꢁ56.1(8)
106.3(7)
ꢁ128.0(7)
84.6(2)
[
v]
ꢁ56.0(9)
[/]
85.0(8)
[v]
ꢁ125.8(8)
103.6(3)
ꢁ56.7(1)
[/]
[v]
ꢁ55.8(7)
96.9(7)
torsion angles are tilted from the mean plane X of the methylene
carbon atoms. This type of conformation is known as ‘‘flattened
cone conformation’’ [22]. These values indicate that the cone
conformation is more flattened in complexes 3 and 6 than in
neutral cyclopalladated complex 1 [14].
4. Conclusions
Fig. 1. ORTEP plot of cationic cyclopalladated complex 3. Only selected atoms are
labelled and hydrogen atoms and solvent atoms are omitted for clarity.
The synthesis of new cationic cyclopalladated mono and dinu-
clear bisphosphite complexes anchored to p-tert-butyl-calix[4]
Fig. 2. ORTEP plot of cationic cyclopalladated dinuclear complex 6. Only selected atoms are labelled and hydrogen atoms are omitted for clarity.
arene framework was described. Ligand such as 4,40-bipyridine
Table 5
plays an important role for the synthesis of cationic dinuclear pal-
ladium complex because of its length which renders less steric
strain between the two metal centre. Single crystal X-ray diffrac-
tion studies of cationic cyclopalladated complexes 3 and 6 in solid
state reveal nearly square planar geometry around the metal and
distorted cone conformation of the calix[4]arene framework. These
cationic cyclopalladated complexes based on hetero ligands having
variable steric and electronic properties could be efficient catalysts
for important organic transformation reactions.
Dihedral angles between the different planes of cationic cyclopalladated complexes 3
and 6.
Dihedral angles (°)
Plane–Plane
Complex 3
Complex 6
A–X
B–X
C–X
D–X
80.7(1)
42.5(0)
82.0(0)
31.6(1)
40.0(0)
83.1(0)
31.2(1)
83.6(0)
X refers to the least square plane defined by the methylene bridged carbons of the
calix[4]arene frame work C2, C8, C14 and C20. A, B, C and D denote to the plane of
the aromatic rings bonded to the calix[4]arene oxygens defined by C1–C24–C23–
C22–C21–C25, C3–C4–C5–C6–C7–C26, C9–C10–C11–C12–C13–C27, C15–C16–
C17–C18–C19–C28, respectively.
Acknowledgements
PM thanks the Department of Science and Technology, New
Delhi, India for financial support and also for data collection using
the CCD X-ray facility at IISc, Bangalore set up under IRHPA pro-
gram. PM also thanks Prof. S.S. Krishnamurthy for the discussion
and support to write this paper.
smaller deviation for other two aryl rings (smaller torsion angles).
The two aryl rings with larger torsion angles are parallel with
respect to each other and the other two aryl rings with smaller

P. Maji / Inorganica Chimica Acta 372 (2011) 120–125
125
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Appendix A. Supplementary material
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CCDC 790438 and 790439 contains the supplementary crystal-
lographic 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. Supplementary data associ-
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