Palladium and platinum complexes of chiral and achiral calix[4]arene bisphosphite ligands

Article abstract of DOI:10.1016/j.poly.2008.08.008

Chiral and achiral p-tert-butyl-calix[4]arene bisphosphites (L¹-L³) have been synthesized by the reaction of p-tert-butyl-calix[4]arene and the phosphorodichloridites, ROPCl₂ [R = (1S,2R,5R)-(+)-iso-menthyl (L¹), (1R,2S,5R)-(-)-menthyl (L²) or C₆H₄Bu^t-4 (L³)]. These bisphosphites function as chelating ligands in palladium(II) and platinum(II) complexes which are formed in good yields by the reaction of PdCl₂(PhCN)₂, MCl₂(COD) (M = Pd or Pt) or PdMeCl(COD) with the respective calix[4]arene bisphosphite. Single crystal X-ray diffraction studies performed on the complexes [PdCl₂(L¹)], [PdCl₂(L²)], [PdCl₂(L³)] and [PtCl₂(L³)] reveal a near square planar geometry around the metal with the two chloride ligands in a cis disposition. The crystal packing in the complexes [PdCl₂(L¹)] and [PdCl₂(L²)], which crystallize in the chiral (P6₁22) space group, shows different hydrophobic channels with intermolecular C-H?Cl hydrogen bonding. The complexes [PdCl₂(L³)] and [PtCl₂(L³)] are isostructural and the molecules in the crystal lattice are linked by intermolecular C-H?Cl and C-H?O hydrogen bonds.

Full text of DOI:10.1016/j.poly.2008.08.008

Polyhedron 27 (2008) 3519–3527
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Palladium and platinum complexes of chiral and achiral calix[4]arene
bisphosphite ligands
*
Pathik Maji, Setharampattu S. Krishnamurthy , Munirathinam Nethaji
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Chiral and achiral p-tert-butyl-calix[4]arene bisphosphites (L1–L3) have been synthesized by the reaction
of p-tert-butyl-calix[4]arene and the phosphorodichloridites, ROPCl2 [R = (1S,2R,5R)-(+)-iso-menthyl (L1),
(1R,2S,5R)-(ꢁ)-menthyl (L2) or C6H4But-4 (L3)]. These bisphosphites function as chelating ligands in pal-
ladium(II) and platinum(II) complexes which are formed in good yields by the reaction of PdCl2(PhCN)2,
MCl2(COD) (M = Pd or Pt) or PdMeCl(COD) with the respective calix[4]arene bisphosphite. Single crystal
X-ray diffraction studies performed on the complexes [PdCl2(L1)], [PdCl2(L2)], [PdCl2(L3)] and [PtCl2(L3)]
reveal a near square planar geometry around the metal with the two chloride ligands in a cis disposition.
The crystal packing in the complexes [PdCl2(L1)] and [PdCl2(L2)], which crystallize in the chiral (P6122)
space group, shows different hydrophobic channels with intermolecular C–Hꢀ ꢀ ꢀCl hydrogen bonding.
The complexes [PdCl2(L3)] and [PtCl2(L3)] are isostructural and the molecules in the crystal lattice are
linked by intermolecular C–Hꢀ ꢀ ꢀCl and C–Hꢀ ꢀ ꢀO hydrogen bonds.
Article history:
Received 15 July 2008
Accepted 8 August 2008
Available online 26 September 2008
Keywords:
Calix[4]arene
iso-Menthol
Menthol
Bisphosphites
Palladium
Platinum
C–Hꢀ ꢀ ꢀCl and C–Hꢀ ꢀ ꢀO hydrogen bonds
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
veal C–Hꢀ ꢀ ꢀCl and C-Hꢀ ꢀ ꢀO hydrogen bonding (inter and
intramolecular) interactions which lead to novel structural motifs.
During the last decade, there has been a growing interest in the
study of calix[n]arenes [1,2] owing to their unique molecular archi-
tecture. Among the calixarenes studied, p-tert-butyl-calix[4]arene
has proven to be a very important building block in supramolecu-
lar chemistry [3] because of its easy chemical transformability,
‘tunable’ molecular shape and conformational flexibility. It is an
attractive candidate for designing supramolecular assemblies, sen-
sors [4a], receptors [4b] and multivalent ligands with potential bio-
logical applications [5a]. Calixarenes are also gaining importance in
the field of crystal engineering [5b] which is currently experiencing
enormous growth [6,7]. Hydrogen bonds often play a dominant
role in crystal engineering [6–9] because they combine the desir-
able attributes of specificity, strength and directionality. In the last
few years, there has been a surge of interest in phosphorus func-
tionalized calixarenes and their transition metal complexes [10–
18].
Continuing our interest in the transition metal chemistry of
phosphorus functionalized calix[4]arenes [19], we report in this
paper the results of our investigations on the palladium and plati-
num complexes of chiral and achiral p-tert-butyl-calix[4]arene bis-
phosphite ligands. We have used (1S,2R,5R)-(+)-iso-menthol and
(1R,2S,5R)-(ꢁ)-menthol as chiral reagents to obtain chiral calix[4]-
arene bisphosphites. The crystal structures of these complexes re-
2. Experimental
2.1. Materials and measurements
All the reactions were carried out under an atmosphere of dry
nitrogen or argon by using Schlenk tube techniques. The solvents
{toluene, tetrahydrofuran, triethylamine, petrol (b.p. 60–80 °C)}
were dried and distilled by conventional methods and deoxygen-
ated before use. (1S,2R,5R)-(+)-iso-Menthyl and (1R,2S,5R)-(ꢁ)-
menthyl phosphorodichloridites and p-tert-butyl-phenyl phospho-
rodichloridite were synthesized by a literature procedure [20]. The
precursors PdCl2(COD) [21], PdCl2(PhCN)2 [22], PdMeCl(COD) [23]
and PtCl2(COD) [24] were prepared as reported. Specific rotations
were measured on a JASCO DIP-370 digital polarimeter. The NMR
spectra were recorded in CDCl3 using a Bruker Avance-400 spec-
trometer with Me4Si as an internal standard for 1H and 13C{1H}
NMR measurements and 85% H3PO4 as an external standard for
31P NMR measurements. Infrared spectra were recorded using a
Perkin–Elmer 580 spectrometer. Elemental analyses were carried
out using a Perkin–Elmer 2400 CHN analyzer. X-ray diffraction
data were collected on a Bruker SMART APEX CCD diffractometer.
SMART [25] software was used for cell refinement and data acquisi-
tion and SAINT [26] software was used for data reduction. An absorp-
tion correction was made on the intensity data using the SADABS [27]
program. The structures were solved using SHELXS [28] and the WINGX
* Corresponding author. Tel.: +91 80 2293 2401; fax: +91 80 2360 0683.
E-mail address: sskrish@ipc.iisc.ernet.in (S.S. Krishnamurthy).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.08.008

3520
P. Maji et al. / Polyhedron 27 (2008) 3519–3527
graphical user interface. Least square refinements were performed
by the full-matrix method with SHELXL [29]. The hydrogen atom
positions were geometrically fixed.
matic protons), 7.24 (d, 4H, J = 7.8 Hz, aromatic protons); 13C
NMR (100 MHz, CDCl3) d = 31.43, 31.89, 33.55, [33.77 and 34.18
(bridged methylene carbons)], 34.76, 38.56, 38.72 (aliphatic car-
bons), 120.44, 124.68, 126.23, 126.54, 131.60, 132.22, 144.36,
146.57, 148.06 (aromatic carbons).
2.2. Preparation of chiral p-tert-butyl-calix[4]arene bisphosphites (L1
and L2)
2.4. Preparation of chiral p-tert-butyl-calix[4]arene iso-menthyl
bisphosphite–PdCl2 complex (1) and menthyl bisphosphite–PdCl2
complex (4)
Triethylamine (2.33 g, 23 ꢂ 103 mol) was added to a stirred sus-
pension of p-tert-butyl-calix[4]arene (3.11 g, 4.8 ꢂ 103 mol) in
60 cm3 THF, and the reaction mixture was stirred at room temper-
ature for 15 min. The solution was cooled in an ice bath and
Chiral p-tert-butyl-calix[4]arene iso-menthyl bisphosphite (L1)
(107 mg, 10.5 ꢂ 105 mol) was treated with [PdCl2(COD)] (30 mg,
10.5 ꢂ 105 mol) or PdCl2(PhCN)2 (40 mg, 10.5 ꢂ 105 mol) in THF
(20 ml) and the reaction mixture was stirred for 1 h. The solvent
was evaporated and the residue was washed several times with
petrol to obtain complex (1) as a light yellow powder. The product
was crystallized from THF:petrol (1:3) to obtain pale yellow crys-
tals. Yield: 120 mg (96%); m.p. = 289–294 °C; Anal. Calc. for
C64H90O6P2PdCl2 (mol. wt.: 1194.6): C, 64.3; H, 7.5. Found C,
64.8; H, 7.8%; 1H NMR d = 0.80 (d, 6H, J = 3.4 Hz), 0.85 (d, 6H,
J = 3.8 Hz), 0.94 (d, 6H, J = 3.6 Hz), 1.06–1.69 (m, 18H, iso-menthyl
group + 18H, But +18H, But), 3.44 (d, 2H, Hb2, J = 6.4 Hz), 3.48 (d,
2H, Hb1, J = 7.6 Hz), 4.56 (d, 2H, Ha2, J = 16.4 Hz), 4.60 (d, 2H, Ha1,
J = 13.6 Hz), 5.77 (br s, 2H-methyne protons of the iso-menthyl
group), 6.90 (s), 6.96 (s) (8H, aromatic protons of calixarene); 13C
NMR (100 MHz, CDCl3) d = 18.66, 19.99, 20.35, 21.53, 26.44,
28.26, 31.24, 31.28, 32.18, [34.06 and 34.18 bridged methylene
carbons], 34.22, 37.18, 38.36, 47.29 (aliphatic carbons); 85.69
(iso-menthyl carbon), 125.48, 125.69, 126.65, 126.79, 129.38,
129.76, 132.49, 132.88 (aromatic carbons), 147.14, 147.24
148.22, 148.31 (aromatic carbons directly attached to the oxygen
atom).
The palladium dichloride complex (4) of chiral p-tert-butyl-ca-
lix[4]arene menthyl bisphosphite (L2) was prepared as described
above for complex (1): pale yellow crystals, yield: 118 mg (94%);
m.p. = 284–292 °C; Anal. Calc. for C64H90O6P2PdCl2 (mol. wt.:
1194.6): C, 64.3; H, 7.5. Found C, 64.7; H, 7.8%; 1H NMR d = 0.80
(d, 6H, J = 2.6 Hz), 0.86 (d, 6H, J = 3.4 Hz), 0.94 (d, 6H, J = 3.8 Hz),
1.03 (s, 18H, But), 1.06–1.72 (m, 18H, menthyl group + 18H, But),
3.42 (d, 2H, Hb2, J = 6.2 Hz), 3.49 (d, 2H, Hb1, J = 7.4 Hz), 4.54 (d,
2H, Ha2, J = 12.2 Hz), 4.66 (d, 2H, Ha1, J = 12.4 Hz), 5.74 (bs, 2H-
methyne protons of the menthyl group), 6.73 (s), 6.83 (s), (8H, aro-
matic protons of calixarene); 13C NMR (100 MHz, CDCl3) d = 18.61,
19.97, 20.30, 21.52, 26.41, 28.20, 31.19, 31.26, 32.09 [33.94 and
34.15 (bridged methylene carbons)], 34.21, 37.16, 38.33, 47.27 (ali-
phatic carbons), 85.68 (menthyl carbon), 125.47, 125.67, 126.63,
126.76, 129.36, 129.74, 132.47, 132.86 (aromatic carbons),
147.11, 147.28, 148.21, 148.29 (aromatic carbons directly attached
to the oxygen atoms).
(1S,2R,5R)-(+)-iso-menthyl
phosphorodichloridite
(2.47 g,
9.6 ꢂ 103 mol) was slowly added through a dropping funnel at
0 °C. The reaction mixture was allowed to attain ambient temper-
ature and stirred for 4 h. During this time, a white precipitate was
formed. The 31P NMR spectrum of the reaction mixture showed the
formation of the expected product. The precipitate was filtered off
and the filtrate was evaporated under reduced pressure to obtain a
yellowish-white foamy solid. The mixture was subjected to column
chromatographic separation over silica gel using petrol/EtOAc
(200:1 v/v) as the eluant. The initial fraction contained p-tert-bu-
tyl-calix[4]arene iso-menthyl bisphosphite (L1). Yield: 1.36 g
(28%); m.p. = 136–142 °C; ½a D25
¼ 77:7 (c 1.0, CHCl3); Anal. Calc.
ꢃ
for C64H90O6P2 (mol. wt.: 1017.5): C, 75.5; H, 8.9. Found: C, 75.9;
H, 8.4%; 1H NMR d = 0.72 (d, 6H, J = 2.8 Hz), 0.84 (d, 6H,
J = 4.2 Hz), 0.94 (d, 6H, J = 3.8 Hz), 1.01 (s, 18H, But), 1.08–1.58
(m, 18H, iso-menthyl group + 18H, But), 3.25 (d, 2H, Hb2,
J = 5.2 Hz), 3.28 (d, 2H, Hb1, J = 6.0 Hz), 4.55 (br s, 2H-methyne pro-
tons of the iso-menthyl group), 4.56 (d, 2H, Ha2, J = 13.2 Hz), 4.81
(d, 2H, Ha1, J = 14.4 Hz), 6.74 (s), 6.82 (s) (8H, aromatic protons
of the calixarene); 13C NMR (100 MHz, CDCl3) d = 15.54, 22.26,
22.88, 24.91, 27.02, 31.27, 31.29, 31.32, 31.36, 31.38, 31.64,
31.68, 31.82, [33.83 and 34.08 (bridged methylene carbons)],
34.32, 38.54, 44.61, 48.66 (aliphatic carbons), 76.42 (iso-menthyl
carbon), 124.13, 124.24, 125.81, 126.06, 131.87, 133.52 (aromatic
carbons) 145.11, 146.23, 147.59, 148.84 (aromatic carbons directly
attached to the oxygen atoms).
p-tert-Butyl-calix[4]arene menthyl bisphosphite (L2) was syn-
thesized as described above for ligand (L1): Yield: 1.41 g (29%);
m.p. = 132–138 °C;
½
a 2D5
ꢃ
¼ 93:7 (c 1.0, CHCl3); Anal. Calc. for
C64H90O6P2: (mol. wt.: 1017.5): C, 75.5; H, 8.9. Found: C, 75.8; H,
8.2%; 1H NMR d = 0.60 (d, 6H, J = 3.0 Hz), 0.63 (d, 6H, J = 3.2 Hz),
0.88 (d, 6H, J = 3.8 Hz), 0.91 (s, 18H, But), 1.09–1.62 (m, 18H, men-
thyl group + 18H, But), 3.22 (d, 2H, Hb2, J = 4.6 Hz), 3.26 (d, 2H, Hb1,
J = 8.4 Hz), 4.06 (br s, 2H-methyne protons of the menthyl group),
4.56 (d, 2H, Ha2, J = 13.2 Hz), 4.74 (d, 2H, Ha1, J = 14.4 Hz), 6.59 (s),
6.86 (s) (8H, aromatic protons of calixarene); 13C NMR (100 MHz,
CDCl3) d = 15.43, 22.14, 22.82, 24.88, 26.98, 31.18, 31.26, 31.26,
31.30, 31.37, 31.60, 31.64, 31.75, [33.77 and 34.03 (bridged meth-
ylene carbons)], 34.24 38.49, 44.45, 48.55 (aliphatic carbons),
76.09 (menthyl carbon), 123.83, 124.17, 125.73, 125.96, 131.83,
133.45 (aromatic carbons), 145.03, 146.32, 147.56, 148.78 (aro-
matic carbons directly attached to the oxygen atoms).
2.5. Preparation of chiral p-tert-butyl-calix[4]arene iso-menthyl
bisphosphite–PtCl2 complex (2) and menthyl bisphosphite–PtCl2
complex (5)
2.3. Preparation of achiral p-tert-butyl-calix[4]arene bisphosphite (L3)
The platinum dichloride complex (2) was prepared by the reac-
tion of chiral p-tert-butyl-calix[4]arene iso-menthyl bisphosphite
(L1) (107 mg, 10.5 ꢂ 105 mol) with [PtCl2(COD)] (39 mg,
10.5 ꢂ 105 mol) in 20 ml of toluene and the reaction mixture was
stirred for 1 h. The solvent was evaporated and the residue was
washed several times with petrol to obtain complex (2). The prod-
uct was crystallized from chloroform:petrol (1:3) to obtain color-
less crystals: Yield 113 mg (84%); m.p. = 291–298 °C; Anal. Calc.
for C64H90O6P2PtCl2 (mol. wt.: 1283.5): C, 59.9; H, 7.1; Found C,
60.2; H, 6.9%; 1H NMR d = 0.79 (d, 6H, J = 2.8 Hz), 0.84 (d, 6H,
J = 3.6 Hz), 0.92 (d, 6H, J = 3.2 Hz), 1.04–1.67 (m, 18H, iso-menthyl
group + 18H, But + 18H, But), 3.42 (d, 2H, Hb2, J = 6.2 Hz), 3.46 (d,
The title compound (L3) was prepared as described above for li-
gand (L1) by the reaction of p-tert-butyl-calix[4]arene (3.11 g,
4.8 ꢂ 103 mol) with 2.98 g (9.6 ꢂ 103 mol) of ROPCl2 (R = C6H4-
But-4) in toluene in the presence of triethylamine for 8 h. Yield:
1.83 g (38%); m.p. = 166–172 °C; Anal. Calc. for C64H78O6P2 (mol.
wt.: 1004.4): C, 76.5; H, 7.8. Found C, 77.1; H, 7.4%; 1H NMR
(400 MHz,CDCl3) d = 1.12 (s, 36H, But), 1.27 (s, 18H, But), 3.34 (d,
2H, Hb2, J = 8.4 Hz), 3.44 (d, 2H, Hb1, J = 12.6 Hz), 4.64 (d, 2H,
Ha2, J = 14.4 Hz), 4.88 (d, 2H, Ha1, J = 14.8 Hz), 6.80 (s), 6.90 (s),
(8H, aromatic protons of calixarene), 7.17 (d, 4H, J = 7.4 Hz, aro-

P. Maji et al. / Polyhedron 27 (2008) 3519–3527
3521
2H, Hb1, J = 7.4 Hz), 4.54 (d, 2H, Ha2, J = 16.0 Hz), 4.59 (d, 2H, Ha1,
J = 13.4 Hz), 5.76 (br s, 2H-methyne protons of the iso-menthyl
group), 6.90 (s), 6.95 (s) (8H, aromatic protons of calixarene); 13C
NMR (100 MHz, CDCl3) d = 18.66, 19.99, 20.35, 21.53, 26.44,
28.26, 31.24, 31.28, 32.18, [34.06 and 34.18, bridged methylene
carbons] 34.22, 37.18, 38.36, 47.29 (aliphatic carbons), 85.69 (iso-
menthyl carbon), 125.48, 125.69, 126.65, 126.79, 129.38, 129.76,
132.49, 132.88 (aromatic carbons), 147.14, 147.29, 148.22,
148.31 (aromatic carbons directly attached to the oxygen atoms).
The menthyl bisphosphite-platinum dichloride complex (5) was
synthesized as described above for complex (2). Yield: 115 mg
(85%); m.p. = 287–294 °C; Anal. Calc. for C64H78O6P2PtCl2: (mol.
wt.: 1283.5): C, 59.9; H, 7.1; Found C, 60.4; H 7.4%; 1H NMR
d = 0.79 (d, 6H, J = 3.4 Hz), 0.87 (d, 6H, J = 3.8 Hz), 0.96 (d, 6H,
J = 3.6 Hz), 1.06–1.54 (m, 18H, menthyl group + 18H, But + 18H,
But), 3.24 (d, 2H, Hb2, J = 3.9 Hz), 3.29 (d, 2H, Hb1, J = 4.8 Hz),
4.12 (br s, 2H-methyne protons of the menthyl group), 4.56 (d,
2H, Ha2, J = 14.2 Hz), 4.81 (d, 2H, Ha1, J = 14.4 Hz), 6.73 (s), 6.83
(s) (8H, aromatic protons of calixarene); 13C NMR (100 MHz, CDCl3)
d = 16.45, 21.11, 21.95, 22.54, 30.89, 30.93, 31.13, 31.62, 32.20
[33.85 and 33.93, bridged methylene carbons), 34.49, 37.23,
47.22, 48.62 (aliphatic carbons), 87.22 (menthyl carbon), 125.14,
125.68, 127.30, 127.80, 130.77, 131.38, 135.32 (aromatic carbons),
146.84, 146.91, 147.50, 148.77 (aromatic carbons directly attached
to the oxygen atom).
methyne protons of the menthyl group, trans to the methyl group),
6.63 (s), 6.65 (s), 7.03 (s), 7.22 (s) (8H, aromatic protons of calixa-
rene); 13C NMR (100 MHz, CDCl3) d = 16.59, 16.68, 21.12, 21.40,
21.93, 22.16, 22.50, 22.80, 25.67, 26.20, 30.89, 30.98, 31.03,
31.23, 31.43, 31.58, 31.65, 31.82, 32.03, 33.84 (Pd–Me), 34.09,
34.09, 34.33, 37.48, 37.95, 42.85, 43.78, 48.63, 48.85 (aliphatic car-
bons), 82.14, 82.46 (menthyl carbons), 124.64, 124.75, 124.95,
125.18, 125.56, 125.87, 126.62, 127.12, 127.70, 128.59, 128.92,
131.21, 131.67, 134.50, 135.10, 146.47, 146.67, 146.86, 147.02,
147.14, 147.49, 147.81 (aromatic carbons).
2.7. Preparation of achiral p-tert-butyl-calix[4]arene bisphosphite–
PdCl2 complex (7) and PtCl2 Complex (8)
The PdCl2 complex (7) was prepared by the reaction of achiral p-
tert-butyl-calix[4]arene bisphosphite (L3) (105 mg, 10.5 ꢂ 105 mol)
with [PdCl2(COD)] (30 mg, 10.5 ꢂ 105) or PdCl2(PhCN)2 (40 mg,
10.5 ꢂ 105) in 20 ml of toluene and the reaction mixture was stir-
red for 2 h. The reaction mixture was worked up as described
above for the synthesis of complex (1). The product was crystal-
lized from dichloromethane:petrol (1:3) and few drops of acetone
to obtain yellow crystals. Yield: 108 mg (87%); m.p. = 295–298 °C;
Anal. Calc. for C64H78O6P2PdCl2(CH3COCH3) (mol. wt.: 1240.6): C,
64.9; H, 6.8; Found C, 65.3; H 7.2%; 1H NMR d = 1.08 (s, 36H,
But), 1.21 (s, 18H, But), 3.45 (d, 2H, Hb2, J = 3.2 Hz), 3.49 (d, 2H,
Hb1, J = 5.2 Hz), 4.57 (d, 2H, Ha2, J = 15.2 Hz), 4.69 (d, 2H, Ha1,
J = 13.6 Hz), 6.82 (s), 6.90 (s) (8 H, aromatic protons of calixarene),
7.14 (d, J = 8.4 Hz), 7.18 (d, J = 7.8 Hz) (8H, aromatic protons); 13C
NMR (100 MHz, CDCl3) d = 31.13, 31.36, 34.18, 37.11 (aliphatic car-
bons), 118.27, 125.86, 126.25, 129.01, 132.45, 146.96, 147.59,
148.36, 148.71 (aromatic carbons).
The analogous PtCl2 complex (8) was prepared by the reaction
of ligand (L3) (105 mg, 10.5 ꢂ 105 mol) with [PtCl2(COD)] (39 mg,
10.5 ꢂ 105 mol) in 20 ml of toluene and the reaction mixture was
stirred for 2 h. The reaction mixture was worked up as described
above for the synthesis of complex (2). The product was crystal-
lized from chloroform:petrol (1:3) to obtain colorless crystals.
Yield: 112 mg (84%); m.p. = 292–295 °C; Anal. Calc. for
C64H78O6P2PtCl2(CHCl3, H2O) (mol. wt.: 1408.6): C, 55.4; H, 5.8;
Found C, 56.1; H, 5.3%; 1H NMR d = 1.07 (s, 36H, But), 1.22 (s,
18H, But), 3.44 (d, 2H, Hb2, J = 3.4 Hz), 3.51 (d, 2H, Hb1,
J = 5.4 Hz), 4.62 (d, 2H, Ha2, J = 15.4 Hz), 4.75 (d, 2H, Ha1,
J = 14.2 Hz), 6.82 (s), 6.90 (s) (8H, aromatic protons of calixarene),
7.16 (d, J = 8.2 Hz), 7.19 (d, J = 8.4 Hz) (8H, aromatic protons); 13C
NMR (100 MHz, CDCl3) d = 31.14, 31.37, 34.15, 37.09 (aliphatic car-
bons), 117.98, 125.80, 126.06, 126.70, 128.96, 132.48, 146.86,
147.25, 148.48, 148.81 (aromatic carbons).
2.6. Preparation of chiral p-tert-butyl-calix[4]arene iso-menthyl
bisphosphite PdMeCl complex (3) and menthyl bisphosphite PdMeCl
complex (6)
Chiral p-tert-butyl-calix[4]arene iso-menthyl bisphosphite (L1)
(107 mg, 10.5 ꢂ 105 mol) was treated with PdMeCl(COD) (28 mg,
10.5 ꢂ 105 mol) in 20 ml of toluene. The reaction mixture was stir-
red for 30 min. The solvent was evaporated and the residue was
washed several times with petrol to obtain complex (3) as a color-
less powder. Yield: 110 mg (82%); m.p. = 279–284 °C; Anal. Calc. for
C65H93O6P2PdCl (mol. wt.: 1174.4): C, 66.4; H, 7.9; Found C, 66.9; H
8.2%; 1H NMR d = 0.68 (d, 3H, J = 2.4 Hz), 0.72 (d, 3H, J = 2.6 Hz),
0.76 (dd, 3H, Pd–Me), 0.81 (d, 3H, J = 3.8 Hz) 0.84 (d, 3H,
J = 3.2 Hz) 0.86 (d, 3H, J = 2.6 Hz), 0.92 (d, 3H, J = 4.2 Hz), 1.04–
1.60 (m, 18H, iso-menthyl group + 18H, But + 18H, But), 3.38 (d,
0
0
2H, Hb2, Hb2 , J = 14.2 Hz), 3.44 (d, 2H, Hb1, Hb1 , J = 9.4 Hz), 4.57
0
0
(d, 2H, Ha2, Ha2 , J = 12.6 Hz), 4.70 (d, 2H, Ha1, Ha1 , J = 14.0 Hz),
4.98 (br s, H-methyne protons of the iso-menthyl group, cis to
the methyl group), 6.04 (br s, H-methyne protons of the iso-men-
thyl group, trans to the methyl group), 6.80 (s), 6.86 (s), 6.88 (s),
7.19 (s) (aromatic protons of calixarene); 13C NMR (100 MHz,
CDCl3) d = 16.62, 16.74, 21.15, 21.42, 21.95, 22.17, 22.51, 22.82,
25.69, 26.23, 30.90, 30.99, 31.04, 31.25, 31.42, 31.60, 31.66,
31.84, 32.05, 33.80 (Pd–Me), 34.10, 34.11, 34.35, 37.49, 37.96,
42.87, 43.97, 48.64, 48.87 (aliphatic carbons), 82.15, 82.48 (iso-
menthyl carbons), 124.63, 124.76, 124.97, 125.18, 125.58, 125.88,
126.66, 127.15, 127.71, 128.62, 128.94, 131.23, 131.68, 134.51,
135.11, 146.49, 146.68, 146.88, 147.11, 147.13, 147.51, 147.84
(aromatic carbons).
3. Results and discussion
3.1. Synthesis of calix[4]arene bisphosphites and their NMR spectra
Chiral p-tert-butyl-calix[4]arene iso-menthyl bisphosphite (L1)
and menthyl bisphosphite (L2) have been synthesized in moderate
yields (ꢄ30%) by the reaction of p-tert-butyl-calix[4]arene with
(1S,2R,5R)-(+)-iso-menthyl or (1R,2S,5R)-(ꢁ)-menthyl phosphoro-
dichloridites, respectively, in the presence of Et3N. Similarly, the
achiral p-tert-butyl-calix[4]arene bisphosphite (L3) has been iso-
lated from the reaction of p-tert-butyl-calix[4]arene with p-tert-
butyl-phenyl-phosphorodichloridite (Scheme 1). Bisphosphites of
the type L1–L3, in which a single phosphorus atom is bonded to
two phenolic oxygen atoms of the calixarene framework, were first
reported by Paceillo et al. [14] and Mahalakshmi et al. [19a,30].
The 31P NMR chemical shift values for ligands (L1–L3) and their
palladium and platinum complexes (1–8) are listed in Table 1. The
Complex (6) was synthesized by the same procedure as that de-
scribed above for complex (3). Yield: 106 mg (79%); m.p. = 278–
281 °C; Anal. Calc. for C65H93O6P2PdCl (mol. wt.: 1174.4): C, 66.4;
H, 7.9; Found C, 66.8; H 7.5%; 1H NMR d = 0.79 (d, 3H, J = 2.4 Hz),
0.80 (d, 3H, J = 3.2 Hz), 0.83 (d, 3H, J = 3.6 Hz), 0.84 (d, 3H,
J = 2.8 Hz), 0.86 (d, 3H, J = 3.2 Hz), 0.87 (d, 3H, J = 3.4 Hz), 0.89
(dd, 3H, Pd–Me), 0.90 (s, 9H, But), 0.92 (s, 9H, But), 1.06–1.54 (m,
18H, menthyl group + 18H, But), 3.34 (d, 2H, Hb2, Hb2 , J = 8.2 Hz),
0
0
3.40 (d, 2H, Hb1, Hb1 , J = 12.0 Hz), 4.32 (br s, H-methyne protons
of the menthyl group, cis to the methyl group), 4.57 (d, 2H, Ha2,
0
0
Ha2 , J = 16.2 Hz), 4.60 (d, 2H, Ha1, Ha1 , J = 18.2 Hz), 5.75 (br s, H-

3522
P. Maji et al. / Polyhedron 27 (2008) 3519–3527
those of the free ligands (see Table 1). The 1H NMR spectra of the
But
But
But
But
complexes display four doublets for the methylene protons of the
calix[4]arene framework. The cis stereochemistry around the palla-
dium metal centre can be inferred from the far IR spectra which
But
But
OH
But
But
(i) / (ii)
show two
m
(Pd–Cl) bands for each of the complexes. The 31P
NMR spectra of the platinum complexes (2), (5) and (8) show large
1JPt–P couplings (see Table 1), confirming the cis stereochemistry
[18a,31]. The structures of the PdCl2 complexes (1), (4) and (7)
and the PtCl2 complex (8) have been confirmed by single crystal
X-ray diffraction analysis. The exclusive formation of cis-chelate
complexes and the absence of oligomeric products (as shown by
the 31P NMR spectra of the reaction mixtures) is presumably due
to the strong ‘‘cis-preference” exhibited by phosphite ligands in
their palladium and platinum complexes, as pointed out by Pringle
and coworkers [31].
O
O
O
O
OH
OHOH
P
P
O
R
O
R
Pri
H
Pri
H
( L1 ) or
( L2 ) or
( L3 )
R =
(1R, 2S, 5R )
But
(1S, 2R, 5R )
Me
Me
The 31P NMR spectra of the PdMeCl complexes (3) and (6) show
an AB pattern because of the chemical non-equivalence of the two
phosphorus nuclei. The 31P chemical shifts lie in a region, which is
in between those for the free ligands and the dichloride complexes
Scheme 1. (i) ROPCl2, THF, Et3N, 25 °C, 4 h (L1 or L2); (ii) ROPCl2, toluene, Et3N,
25 °C, 8 h (L3).
31P NMR spectra of ligands (L1), (L2) and (L3) display singlets indi-
cating the magnetic equivalence of the two phosphorus centres.
The 1H NMR spectra show two AB patterns for the methylene pro-
tons as would be anticipated for a cone conformation of the ca-
lix[4]arene framework [1a,19a] (see Section 3.3). The 1H NMR
spectrum of ligand (L1) shows a broad singlet at 4.55 ppm for the
proton attached to the iso-menthyl carbon atom carrying the oxy-
gen atom. This signal merges with the resonances arising from the
methylene protons which exist outside the phosphite cage and
away from the calixarene cavity. However, the 1H NMR spectrum
of ligand (L2) shows a broad singlet at 4.06 ppm for the proton at-
tached to the menthyl carbon bearing the oxygen atom. This reso-
nance is flanked by the resonances arising from the two sets of
methylene protons which point towards and away from the ca-
lix[4]arene cavity. It is also noteworthy that two distinct signals
are observed for the tert-butyl (CMe3) protons of the calix[4]arene
framework in both (L1) and (L2) because of the presence of the chi-
ral iso-menthyl or menthyl group.
2
(see Table 1). The JP–P coupling constants are 113.2 and 106.4 Hz,
respectively, for the two complexes. The proton-coupled 31P NMR
spectrum of complex (6) shows a doublet of quartets for the down-
field phosphorus resonance (centered at 113.5 ppm) because of
further splitting by coupling with the protons of the methyl group
attached to palladium. Hence the downfield resonance can be as-
signed to the phosphorus which is trans to the methyl group. The
1H NMR spectra of these complexes (3) and (6) show two broad
singlets {6.04 and 4.98 ppm for complex (3); 5.75 and 4.32 ppm
for complex (6)} for the two different methyne protons of the
iso-menthyl/menthyl carbon atoms directly attached to the oxygen
atoms. Although the eight methylene protons of the calix[4]arene
framework in the complexes (3) and (6) are magnetically non-
equivalent, only four doublets are observed at room temperature.
3.3. X-ray crystallographic studies
The solid-state structures of complexes (1), (4), (7) and (8) have
been determined by single crystal X-ray diffraction analysis. De-
tails pertinent to data collection, structure solution and refinement
are summarized in Table 2. Selected bond lengths and angles are
given in Tables 3 and 4. The data are comparable to those observed
for calix[4]arene bisphosphite–PdCl2 complexes reported by Matt
and coworkers [17]. There is a slight deviation from a square planar
geometry around the metal in all these complexes, presumably be-
cause of the involvement of chlorine atom(s) in hydrogen bonding
(see below).
The ORTEP plots of the molecular structures of the palladium
dichloride complexes (1) and (4) are presented in Figs. 1 and 2,
respectively. The crystal packing diagrams are shown in Fig. S1
(see Supplementary information). When viewed down the c-axis,
one can clearly see a hexagonal shaped self-assembly of molecules
of complexes (1) or (4) resulting in a hydrophobic channel sur-
rounded by alkyl groups of the iso-menthyl and menthyl unit,
3.2. Palladium and platinum complexes of chiral and achiral p-tert-
butyl-calix[4]arene bisphosphite ligands
The reaction of bisphosphite ligands (L1), (L2) and (L3) with one
molar equivalent of PdCl2(COD) or PdCl2(PhCN)2 in THF or toluene
gives, respectively, the complexes [PdCl2(L1)] (1), PdCl2(L2) (4) and
PdCl2(L3) (7) which are isolated as pale yellow solids. The analo-
gous Pt complexes [PtCl2(L1)] (2), [PtCl2(L2)] (5) and [PtCl2(L3)]
(8) are prepared by the reaction of PtCl2(COD) with the ligands
(L1), (L2) and (L3), respectively. The methyl palladium complexes
[PdMeCl(L1)] (3) and [PdMeCl(L2)] (6) are obtained by the reaction
of [PdMeCl(COD)] with the chiral bisphosphite ligands (L1) and
(L2), respectively. These reactions are shown in Scheme 2.
The 31P NMR chemical shifts for the palladium and platinum
dichloride complexes (1), (4), (7) and (8) lie very much upfield to
Table 1
The 31P {1H} NMR data for ligands (L1–L3) and their palladium and platinum complexes (1)–(8)a
Ligand
L1
d
Pd complex
d
D
d
Pt complexc
PtCl2(L1)
d
Dd
126.7
PdCl2(L1)
80.1
46.6
46.6
37.8
54.3
72.4
73.3
61.8
PdMeCl(L1)b
PdCl2(L2)
117.4(d), 114.2 (d)
78.6
113.5(d), 107.9(d)
77.9
L2
125.2
115.7
PtCl2(L2)
PtCl2(L3)
51.9
53.9
PdMeCl(L2)b
PdCl2(L3)
L3
a
Recorded in CDCl3 at 25 °C and at 161.9 MHz, d in ppm,
D
d = (dligand ꢁ dcomplex) in ppm.
b
c
2JP–P = 113.2, 106.4 Hz for complexes (3), (6), respectively.
1JPt–P = 6056, 6045, 5345 Hz for complexes (2), (5) and (8), respectively.

P. Maji et al. / Polyhedron 27 (2008) 3519–3527
3523
But
But
But
But
O O
P
O
O
But
P
But But
But
But
O
But
O
But
O
But
R
O
R
(i), (ii), (iii),
(iv), (v), (vi)
(vii)
O O
O
O
O
O
P
P
P
P
O
R
O
M
R
O
R
O
Pd
R
Cl
Cl
Me
Cl
Pri
Pri
Pri
(4) M = Pd
(5) M = Pt
(1) M = Pd
(2) M = Pt
R =
(3) R =
R =
H
H
H
(1S, 2R, 5R)
Me
(1R, 2S, 5R)
Me
(1S, 2R, 5R)
Me
Pri
(6)
R =
(7) M = Pd
(8) M = Pt
H
R =
(1R, 2S, 5R)
Me
But
Scheme 2. (i) PdCl2 (COD) or PdCl2 (PhCN)2, THF, 25 °C, 1 h; (ii) PtCl2 (COD), toluene, 25 °C, 1 h; (iii) PdCl2 (COD) or PdCl2 (PhCN)2, THF, 25 °C, 1 h; (iv) PtCl2 (COD), toluene,
25 °C, 1 h; (v) PdCl2 (COD) or PdCl2 (PhCN)2, toluene, 25 °C, 2 h; (vi) PtCl2 (COD), toluene, 25 °C, 2 h; (vii) PdMeCl (COD), toluene, 25 °C, 30 min.
Table 2
Crystal data for complexes (1), (4), (7) and (8)
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C64H90Cl2O6P2Pd (1)
1194.60
293(2)
0.71073
hexagonal
P6122
C64H90Cl2O6P2Pd (4)
1194.60
293(2)
0.71073
hexagonal
P6122
C67H84Cl2O7P2Pd (7)
1240.58
293(2)
0.71073
monoclinic
C2/c
C65H81Cl5O7P2Pt (8)
1408.58
293(2)
0.71073
monoclinic
C2/c
19.469(3)
19.469(3)
33.857(9)
90
19.4130(14)
19.4130(14)
33.917(5)
90
37.656(10)
16.379(4)
23.670(9)
90
37.936(3)
16.3639(1)
24.0908(2)
90
b (Å)
c (Å)
a
(°)
b (°)
90
120
11114(4)
6
1.07
90
120
11070(2)
6
1.075
110.547(5)
90
13670(6)
8
1.206
0.444
111.998(1)
90
13866(2)
8
1.369
2.310
c
(°)
Volume (Å3)
Z
Dcalc. (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
)
0.406
3792
0.408
3792
5216
5760
Crystal size (mm)
Theta range for data collection
0.59 ꢂ 0.28 ꢂ 0.21
0.48 ꢂ 0.38 ꢂ 0.32
0.52 ꢂ 0.46 ꢂ 0.26
0.34 ꢂ 0.28 ꢂ 0.22
1.21–26.03
1.21–26.37
1.84–25.00
1.16–25.00
(°)
Index ranges
ꢁ24 6 h 6 21, ꢁ24 6 k 6 24,
ꢁ41 6 l 6 40
86587
ꢁ24 6 h 6 24, ꢁ24 6 k 6 24,
ꢁ42 6 l 6 42
87563
ꢁ44 6 h 6 44, ꢁ19 6 k 6 18,
ꢁ28 6 l 6 28
48476
ꢁ45 6 h 6 45, ꢁ19 6 k 6 19,
ꢁ28 6 l 6 28
66157
Reflections collected
Independent reflections (Rint
Completeness to h (%)
Absorption correction
Maximum and minimum
transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit
)
7307(0.0998)
99.9
empirical
7558(0.1606)
99.9
empirical
12035(0.0759)
99.9
empirical
12239(0.0861)
100.0
empirical
0.9196 and 0.7956
0.8806 and 0.8283
0.8925 and 0.8007
0.6303 and 0.5070
full-matrix-least-squares on F2
5416/1/348
0.787
full-matrix-least-squares on F2
7558/1/348
1.005
full-matrix-least-squares on F2
12035/0/732
0.949
full-matrix-least-squares on F2
12239/0/738
1.016
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0604, wR2 = 0.1802
R1 = 0.0825, wR2 = 0.2060
0.825 and ꢁ0.299
R1 = 0.1428, wR2 = 0.3114
R1 = 0.1761, wR2 = 0.3357
1.386 and ꢁ0.542
R1 = 0.0869, wR2 = 0.2134
R1 = 0.1029, wR2 = 0.2242
1.045 and ꢁ1.382
R1 = 0.0629, wR2 = 0.1523
R1 = 0.0883, wR2 = 0.1650
2.626 and ꢁ1.729
Largest difference in peak and
hole (e Åꢁ3
Absolute structure parameter
)
ꢁ0.04(5)
0.05(10)

3524
P. Maji et al. / Polyhedron 27 (2008) 3519–3527
Table 3
Selected structural parameters for the PdCl2 complexes (1) and (4) (distances in Å,
angles in °)
Bond distance (1)
(4)
Bond angle
(1)
91.39(6)
92.21(6)
161.69(5) 163.27(1)
(4)
91.93(2)
90.77(1)
P(1)–Pd(1)
Cl(1)–Pd(1)
P(1)–O(1)
P(1)–O(2)
P(1)–O(3)
2.227(1) 2.215(3) P(1)–Pd(1)–P(10)
2.333(2) 2.338(4) P(1)–Pd(1)–Cl(1)
1.556(4) 1.557(9) P(1)–Pd(1)–Cl(10)
1.595(3) 1.585(8) Cl(10)–Pd(1)–Cl(1)
1.585(3) 1.598(8) O(3)–P(1)–O(2)
O(3)–P(1)–Pd(1)
90.0(1)
103.8(2)
118.1(1)
115.0(1)
109.8(1)
91.4(3)
104.3(4)
117.9(3)
116.7(3)
110.1(3)
O(1)–P(1)–Pd(1)
O(2)–P(1)–Pd(1)
O(3)–P(1)–O(1)
O(1)–P(1)–O(2)
102.65(2) 100.4(4)
106.3(2) 106.1(5)
Table 4
Selected structural parameters for the complexes (7) and (8) (distances in Å, angles in
°)
Bond
distance
(7)
[M = Pd]
(8)
[M = Pt]
Bond angle
(7)
[M = Pd]
(8)
[M = Pt]
Fig. 2. ORTEP plot of calix[4]arene menthyl bisphosphite–palladium dichloride
complex (4). Only selected atoms are labelled and hydrogen atoms are omitted for
clarity.
P(1)–M(1)
P(2)–M(1)
Cl(1)–M(1)
Cl(2)–M(1)
P(1)–O(1)
P(1)–O(2)
P(1)–O(3)
P(2)–O(4)
P(2)–O(5)
P(2)–O(6)
2.224(2)
2.213(2)
2.348(2)
2.328(2)
1.584(4)
1.584(4)
1.593(5)
1.587(5)
1.599(5)
1.588(5)
2.196(2)
2.197(2)
2.328(2)
2.352(2)
1.587(6)
1.592(5)
1.585(6)
1.590(5)
1.579(5)
1.581(6)
P(2)–M(1)–P(1)
P(2)–M(1)–Cl(2)
P(1)–M(1)-Cl(1)
Cl(2)–M(1)–Cl(1)
O(3)–P(1)–O(1)
O(3)–P(1)–O(2)
O(1)–P(1)–O(2)
O(3)–P(1)–M(1)
O(1)–P(1)–M(1)
O(2)–P(1)–M(1)
O(6)–P(2)–O(5)
O(6)–P(2)–O(4)
O(5)–P(2)–O(4)
O(6)–P(2)–M(1)
O(5)–P(2)–M(1)
O(4)–P(2)–M(1)
91.37(6)
89.54(6)
88.75(6)
91.92(6)
101.9(2)
106.0(2)
105.3(2)
114.66(2)
116.23(2)
111.56(2)
106.3(3)
98.9(3)
91.58(7)
89.02(7)
91.69(7)
88.76(7)
99.0(3)
107.4(3)
103.7(3)
117.5(2)
118.2(2)
109.5(2)
106.4(3)
101.6(3)
105.0(3)
114.9(2)
112.3(2)
115.5(2)
The near perfect hexagonal shaped packing of molecules of
complexes (1) and (4) in their crystal lattices arises because of
hydrogen bonding interactions as shown in Fig. S2 (see Supple-
mentary information) and Fig. 3, respectively. The crystal lattice
of complex (1) features a bifurcated hydrogen bond involving
Cl(1) and the ortho-aryl protons of the calix[4]arene back bone
[Cl(1)–aryl proton H(24) distance = 2.936 Å, Cl(1)–aryl proton
H(13) distance = 2.954 Å]. We also observed an intramolecular
hydrogen bond between an oxygen and a methylene proton
[O(1)ꢀ ꢀ ꢀH(22B) methylene proton distance = 2.343 Å] (Fig. S2). In
the structure of complex 4, there is an intermolecular hydrogen
bond between the chlorine atom and an ortho-proton of the ca-
lix[4]arene back bone [Cl(1)ꢀ ꢀ ꢀH(1) aromatic proton dis-
tance = 2.576 Å]. In addition, two intramolecular hydrogen bonds,
one between Cl(1) and a methyne proton (H19) of the menthyl unit
and another between O(1) and the methylene proton H(13B) of the
104.7(2)
117.59(2)
109.45(2)
118.46(2)
Fig. 1. ORTEP plot of calix[4]arene iso-menthyl bisphosphite–palladium dichloride
complex (1). Only selected atoms are labelled and hydrogen atoms are omitted for
clarity.
respectively. A significant difference in the hydrophobic channels
of these two complexes is that in complex (1), the alkyl groups
of the iso-menthyl unit surround the channel without any gaps
but in complex (4), the alkyl groups of the menthyl unit surround
the channel with discrete gaps. This difference may be due to the
orientation of the iso-menthyl and menthyl subunits in the two
complexes.
Fig. 3. A view of a crystal segment of palladium dichloride complex (4) showing the
bifurcated intermolecular and intramolecular hydrogen bonding interactions.

P. Maji et al. / Polyhedron 27 (2008) 3519–3527
3525
calix[4]arene framework [Cl(1)ꢀ ꢀ ꢀH(19) menthyl proton dis-
tance = 2.833 Å, O(1)ꢀ ꢀ ꢀH(13B) distance = 2.322 Å] are observed
(Fig. 3).
The PdCl2 and PtCl2 complexes (7) and (8) crystallize in the
monoclinic C2/c space group and are isostructural. The ORTEP plots
of the molecular structures of complexes (7) and (8) are shown in
Figs. 4 and 5, respectively. The structural features are similar to
those of the chiral p-tert-butyl-calix[4]arene iso-menthyl and men-
thyl palladium dichloride complexes (1) and (4) described above.
The packing of molecules of complex (7) in the crystal lattice
shows a layer-like arrangement along the b-axis; the orientations
of the two adjacent molecules are different from each other. Each
molecule is surrounded by two other molecules connected by
intermolecular hydrogen bonds formed between the chlorine atom
and a methylene proton [Cl(1)ꢀ ꢀ ꢀH(2A) distance = 2.867 Å], and
also between the oxygen atom and alkyl proton of the tert-butyl
group [O(3)ꢀ ꢀ ꢀH(51A) distance = 2.694 Å]. There is also an intramo-
lecular hydrogen bond formed between the oxygen atom and a
Fig. 6. A view of a crystal segment of palladium dichloride complex (7) showing the
intra and intermolecular hydrogen bonding interactions.
methylene proton [O(6)ꢀ ꢀ ꢀH(14B) distance = 2.311 Å] (see Fig. 6).
In the crystal lattice of complex (8), each discrete molecule is sur-
rounded by two other molecules and one solvent molecule. The ob-
served intra- and intermolecular hydrogen bonds are shown in
Fig. S3 (see Supplementary information). The relevant data are gi-
ven in Table 5.
The calix[4]arene framework in all these compounds (1), (4), (7)
and (8) adopts a cone conformation. The conformation of the ca-
lix[4]arene backbone can be discussed in terms of either torsion
angles or dihedral angles. The dihedral angles of the calix[4]arene
aryl rings (A = A0 and B = B0) with the plane X of the four methylene
carbon atoms{C17, C22, C170 and C220 for the complex (1) and C13,
C24, C130 and C240 for complex (4)} are listed in Table S-1 (see Sup-
plementary information). These data show that there is a distortion
of the cone conformation in the two complexes. The torsion angles
involving the bridging methylene carbon atoms and aryl ring car-
bon atoms for the complexes (1) and (4) are listed in Table S-2
(see Supplementary information). The sequence of signs for the
Fig. 4. ORTEP plot of calix[4]arene 4-tert-butyl-phenyl bisphosphite-palladium
dichloride complex (7). Selected atoms are labelled and hydrogen atoms and
solvent molecules are omitted for clarity.
two torsion angles / and
firms the cone conformation for both the complexes. A comparison
of the observed torsion angles / and for the two palladium com-
v
is found to be +ꢁ, +ꢁ, +ꢁ, +ꢁ and con-
v
plexes (1) and (4) with those expected for an ideal cone conforma-
tion [90° and 90°, respectively] shows that there is a larger
deviation for two aryl rings (larger torsion angles) and a smaller
deviation for the other two aryl rings (smaller torsion angles).
The two aryl rings with larger torsion angles are parallel with re-
spect to each other; the other two aryl rings with smaller torsion
angles are tilted from the mean plane X of the methylene carbon
atoms. This type of conformation is known as a ‘‘flattened cone
conformation” [32]. Similar results are observed for the palladium
and platinum dichloride complexes, (7) and (8). The relevant dihe-
dral angles and torsion angles are listed in Tables S-3 and S-4,
respectively (see Supplementary information). These values indi-
cate that the cone conformation is more flattened in complexes
(1), (4), (7) and (8) than in the free calix[4]arene bisphosphites
[19a,33].
Fig. 5. ORTEP plot of calix[4]arene 4-tert-butyl-phenyl bisphosphite–platinum
dichloride complex (8). Selected atoms are labelled and hydrogen atoms and
solvent molecules are omitted for clarity.

3526
P. Maji et al. / Polyhedron 27 (2008) 3519–3527
Table 5
Hydrogen bonding parameters for complexes (1), (4), (7) and (8)
D–Hꢀ ꢀ ꢀA
r(Hꢀ ꢀ ꢀA) (Å)
r(Dꢀ ꢀ ꢀA) (Å)
Angle (D–Hꢀ ꢀ ꢀA) (°)
A: Hydrogen bonding (C–Hꢀ ꢀ ꢀCl and C–Hꢀ ꢀ ꢀO) parameters for [PdCl2(L1)] (1)
C(22)–H(22B) ꢀ ꢀ ꢀO(1)
C(13)–H(13) ꢀ ꢀ ꢀCl(1)
C(24)–H(24) ꢀ ꢀ ꢀCl(1)
2.343[0]
2.954[i]
2.936[i]
3.069[0]
3.695[i]
3.838[i]
131.0[0]
137.6[i]
163.8[i]
Symmetry codes: [0] x, y, z; [i] y + 1, +x, ꢁz + 1/3 + 1.
B: Hydrogen bonding (C–H. . .Cl and C–H. . .O) parameters for [PdCl2(L2)] (4)
C(1)–H(1)ꢀ ꢀ ꢀCl(1)
2.576[0]
2.322[0]
2.833[i]
3.222[0]
3.051[0]
3.748[i]
133.0[0]
132.2[0]
167.9[i]
C(13)–H(13B)ꢀ ꢀ ꢀO(1)
C(19)–H(19)ꢀ ꢀ ꢀCl(1)
Symmetry codes: [0] x, y, z; [i] y + 1, +x, ꢁz + 1/3.
C: Intra and intermolecular hydrogen bonding (C–Hꢀ ꢀ ꢀCl and C–Hꢀ ꢀ ꢀO) parameters for complex (7)
[i]
C(2)ꢀ ꢀ ꢀH(2A)ꢀ ꢀ ꢀCl(1)
C(51)ꢀ ꢀ ꢀH(51A)ꢀ ꢀ ꢀO(3)
C(14)ꢀ ꢀ ꢀH(14B)ꢀ ꢀ ꢀO(6)
2.867
3.795[i]
3.619[ii]
3.043[0]
160.6[i]
162.1[ii]
131.6[0]
2.694[ii]
2.311[0]
Symmetry codes: [0] x, y, z; [i] x + 1/2, +y ꢁ 1/2, z + 1/2 + 1; [ii] x, y, +z ꢁ 1/2.
D: Intra and intermolecular hydrogen bonding (C–Hꢀ ꢀ ꢀCl and C–Hꢀ ꢀ ꢀO) parameters for complex (8)
C(2)ꢀ ꢀ ꢀH(2A)ꢀ ꢀ ꢀO(3)
2.299[0]
2.353[0]
2.881[iii]
2.810[i]
2.888[i]
2.823[ii]
2.958[ii]
2.967[0]
3.034[0]
3.078[0]
3.804[iii]
3.754[i]
3.756[i]
3.749[ii]
3.698[ii]
3.771[0]
131.9[0]
131.1[0]
161.6[iii]
164.6[i]
155.9[i]
162.6[ii]
134.8[ii]
142.1[0]
C(14)ꢀ ꢀ ꢀH(14B)ꢀ ꢀ ꢀO(6)
C(42)ꢀ ꢀ ꢀH(42B)ꢀ ꢀ ꢀO(1)
C(14)ꢀ ꢀ ꢀH(14A)ꢀ ꢀ ꢀCl(2)
C(40)ꢀ ꢀ ꢀH(40)ꢀ ꢀ ꢀCl(1)
C(43)ꢀ ꢀ ꢀH(43C)ꢀ ꢀ ꢀO(6)
C(43)ꢀ ꢀ ꢀH(43C)ꢀ ꢀ ꢀO(4)
C(52)ꢀ ꢀ ꢀH(52B)ꢀ ꢀ ꢀCl(4)
Symmetry codes: [0] x, y, z; [i] ꢁx + 1/2, y + 1/2, z + 1/2, [ii] x, y + 1, +z ꢁ 1/2; [iii] ꢁx + 1/2, y + 1/2, z.
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We have described the synthesis of new chiral and achiral bis-
phosphites anchored to a p-tert-butyl-calix[4]arene framework.
These bisphosphites behave as chelating ligands in palladium(II)
and platinum(II) complexes. These complexes provide examples
of the presence of non-covalent interactions such as intermolecular
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We thank the Department of Science and Technology, New Del-
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CCD X-ray facility at IISc, Bangalore set up under the IRHPA pro-
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Appendix A. Supplementary data
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CCDC 692825, 692826, 692827 and 692828 contain the supple-
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obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
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033; e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associ-
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