Phosphite ligands derived from distally and proximally substituted dipropyloxy calix[4]arenes and their palladium complexes: Solution dynamics, solid-state structures and catalysis

Article abstract of DOI:10.1016/j.jorganchem.2008.03.008

Two bisphosphite ligands, 25,27-bis-(2,2′-biphenyldioxyphosphinoxy)-26,28-dipropyloxy-p-tert-butyl calix[4]arene (3) and 25,26-bis-(2,2′-biphenyldioxyphosphinoxy)-27,28-dipropyloxy-p-tert-butyl calix[4]arene (4) and two monophosphite ligands, 25-hydroxy-27-(2,2′-biphenyldioxyphosphinoxy)-26,28-dipropyloxy-p-tert-butyl calix[4]arene (5) and 25-hydroxy-26-(2,2′-biphenyldioxyphosphinoxy)-27,28-dipropyloxy- p-tert-butyl calix[4]arene (6) have been synthesized. Treatment of (allyl) palladium precursors [(η³-1,3-R,R′-C₃H₄)Pd(Cl)]₂ with ligand 3 in the presence of NH₄PF₆ gives a series of cationic allyl palladium complexes (3a-3d). Neutral allyl complexes (3e-3g) are obtained by the treatment of the allyl palladium precursors with ligand 3 in the absence of NH₄PF₆. The cationic allyl complexes [(η³-C₃H₅)Pd(4)]PF₆ (4a) and [(η³-Ph₂C₃H₃)Pd(4)]PF₆ (4b) have been synthesized from the proximally (1,2-) substituted bisphosphite ligand 4. Treatment of ligand 4 with [Pd(COD)Cl₂] gives the palladium dichloride complex, [PdCl₂(4)] (4c). The solid-state structures of [{(η³-1-CH₃-C₃H₄)Pd(Cl)}₂(3)] (3f) and [PdCl₂(4)] (4c) have been determined by X-ray crystallography; the calixarene framework in 3f adopts the pinched cone conformation whereas in 4c, the conformation is in between that of cone and pinched cone. Solution dynamics of 3f has been studied in detail with the help of two-dimensional NMR spectroscopy. The solid-state structures of the monophosphite ligands 5 and 6 have also been determined; the calix[4]arene framework in both molecules adopts the cone conformation. Reaction of the monophosphite ligands (5, 6) with (allyl) palladium precursors, in the absence of NH₄PF₆, yield a series of neutral allyl palladium complexes (5a-5c; 6a-6d). Allyl palladium complexes of proximally substituted ligand 6 showed two diastereomers in solution owing to the inherently chiral calix[4]arene framework. Ligands 3, 6 and the allyl palladium complex 3f have been tested for catalytic activity in allylic alkylation reactions.

Full text of DOI:10.1016/j.jorganchem.2008.03.008

Journal of Organometallic Chemistry 693 (2008) 2097–2110
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Phosphite ligands derived from distally and proximally substituted dipropyloxy
calix[4]arenes and their palladium complexes: Solution dynamics, solid-state
structures and catalysis
*
Arindam Sarkar, Munirathinam Nethaji, Setharampattu S. Krishnamurthy
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
a r t i c l e i n f o
a b s t r a c t
Two bisphosphite ligands, 25,27-bis-(2,20-biphenyldioxyphosphinoxy)-26,28-dipropyloxy-p-tert-butyl
calix[4]arene (3) and 25,26-bis-(2,20-biphenyldioxyphosphinoxy)-27,28-dipropyloxy-p-tert-butyl
calix[4]arene (4) and two monophosphite ligands, 25-hydroxy-27-(2,20-biphenyldioxyphosphinoxy)-
26,28-dipropyloxy-p-tert-butyl calix[4]arene (5) and 25-hydroxy-26-(2,20-biphenyldioxyphosphinoxy)-
27,28-dipropyloxy- p-tert-butyl calix[4]arene (6) have been synthesized. Treatment of (allyl) palladium
precursors [(g3-1,3-R,R0-C3H4)Pd(Cl)]2 with ligand 3 in the presence of NH4PF6 gives a series of cationic
allyl palladium complexes (3a–3d). Neutral allyl complexes (3e–3g) are obtained by the treatment of
the allyl palladium precursors with ligand 3 in the absence of NH4PF6. The cationic allyl complexes
[(g3-C3H5)Pd(4)]PF6 (4a) and [(g3-Ph2C3H3)Pd(4)]PF6 (4b) have been synthesized from the proximally
(1,2-) substituted bisphosphite ligand 4. Treatment of ligand 4 with [Pd(COD)Cl2] gives the palladium
dichloride complex, [PdCl2(4)] (4c). The solid-state structures of [{(g3-1-CH3-C3H4)Pd(Cl)}2(3)] (3f) and
[PdCl2(4)] (4c) have been determined by X-ray crystallography; the calixarene framework in 3f adopts
the pinched cone conformation whereas in 4c, the conformation is in between that of cone and pinched
cone. Solution dynamics of 3f has been studied in detail with the help of two-dimensional NMR spectros-
copy.
Article history:
Received 27 November 2007
Received in revised form 19 February 2008
Accepted 5 March 2008
Available online 18 March 2008
Keywords:
Allyl complexes
Calix[4]arene
Conformational analysis
NMR spectroscopy
Palladium
P-ligands
The solid-state structures of the monophosphite ligands 5 and 6 have also been determined; the calix[4]-
arene framework in both molecules adopts the cone conformation. Reaction of the monophosphite
ligands (5, 6) with (allyl) palladium precursors, in the absence of NH4PF6, yield a series of neutral allyl
palladium complexes (5a–5c; 6a–6d). Allyl palladium complexes of proximally substituted ligand 6
showed two diastereomers in solution owing to the inherently chiral calix[4]arene framework. Ligands
3, 6 and the allyl palladium complex 3f have been tested for catalytic activity in allylic alkylation
reactions.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
only a few examples of calixarene monophosphites known in the
literature [3]. Moreover, to the best of our knowledge, proximally
Interest in synthetic receptors containing pendent phosphorus
atoms stems from the perception that such systems will facilitate
both molecular recognition and catalysis involving transition met-
als. In this context, the chemistry of calixarenes incorporating tri-
valent phosphorus donor atoms [1] has been investigated by
several research groups. In recent years, there is a surge of interest
on the solution dynamics, solid-state structure and catalytic activ-
ity of calixarene phosphites in which the phosphorus atoms are
closely appended to the macrocyclic cavity [2]. Most of theses
studies are concerned with calix[4]arene bisphosphites. There are
substituted bisphosphites (phosphorus atoms attached to the adja-
cent oxygen atoms of the lower rim of calix[4]arene) have not been
reported. In this paper, we report the synthesis of mono and bis-
phosphites derived from proximally and distally substituted
(dipropyloxy)calix[4]arenes and their (allyl) palladium complexes.
While (allyl) palladium complexes of phosphorus containing
bidentate ligands have engendered a lot of interest owing to their
dynamic behavior in solution and catalytic applications [4], there
are only a few reports on the allyl(palladium) complexes of phos-
phorus functionalized calixarenes [2c,2d,5] and neutral allyl(palla-
dium) complexes of monodentate phosphites [6]. Our aim is to
design a series of calix[4]arene phosphite ligands in such a way
that the coordination of the ligands to the palladium center can
* Corresponding author. Tel.: +91 80 2293 2401; fax: +91 80 2360 0683.
E-mail address: sskrish@ipc.iisc.ernet.in (S.S. Krishnamurthy).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.03.008

2098
A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
be easily tuned. We have chosen sterically bulky propyl groups as
lower-rim substituents for two reasons. The presence of two bulky
propyl groups in the lower rim of the mono or bisphosphite ligand
increases the steric interaction between the adjacent bulky group/s
and the tert-butyl group/s of the inverted aryl ring. As a result,
‘‘cone” conformation of the calixarene framework becomes highly
stable. The presence of bulky substituents in the lower rim of the
calix-matrix may also affect the mode of binding of a transition
metal to the phosphorus donor sites of the ligand. Fig. 1 shows
the probable coordination modes and bite angles of the 1,3- and
1,2-dipropyloxy calix[4]arene bisphosphite ligands.
The 1H NMR spectrum of ligand 3 shows two singlets at 1.02
and 1.17 ppm for the tert-butyl protons in the ratio of 1:1 and
two doublets for the methylene bridge protons (Fig. S1, Support-
ing Information). There is a large difference in the chemical
shifts (Dd > 0.9) of the two sets of geminal methylene protons.
A single triplet for the terminal methyl groups of the propyl sub-
stituents indicates that the two propyl groups are magnetically
equivalent. The 31P NMR spectrum displays a singlet indicating
that the two phosphorus nuclei are equivalent. From these
observations, it can be concluded that the calix[4]arene frame-
work in the ligand (3) adopts the cone conformation character-
ized by the presence of two planes of symmetry in the
molecule [7]. These mirror-planes pass through the pair of aryl
rings facing each other and perpendicular to the plane passing
through the methylene bridge carbon atoms. Because of the
complicated nature of the 1H NMR spectrum of the reaction mix-
ture containing ligand 4, the conformation of the major compo-
nent in solution could not be determined. A cone conformation
would be expected on steric grounds. The observation of a single
resonance in the 31P NMR spectrum of 4 is consistent with cone
conformation (Fig. S2).
2. Results and discussion
2.1. Synthesis and conformational aspects of ligands 3–6
Reaction of dipropyloxy calix[4]arenes (1 or 2) with [1,10-biphe-
nyl]-2,20-phosphorochloridite in the presence of sodium hydride
yields the phosphite ligands 3–6 (Scheme 1). Even when the stoi-
chiometry of the reactants is carefully controlled, both mono-
and bis-phosphites along with some minor conformational isomers
are formed in each reaction. The 31P–31P NOESY measurements
show that the conformers do not exchange among themselves.
The ligands 3, 5 and 6 could be isolated in a pure form by column
chromatography followed by fractional crystallization. Efforts to
isolate ligand 4 in a pure form were unsuccessful (see Section 4
and supporting information).
The 1H NMR spectrum of ligand 5 shows three singlets at 0.86,
1.25, and 1.31 ppm for the tert-butyl protons (relative intensities
2:1:1, respectively) and four doublets for the methylene protons
of the calixarene framework. A single triplet for the terminal
methyl groups of the propyl substituents indicates that the two
propyl groups are magnetically equivalent (Fig. S3). These data
Fig. 1. Effect of propyl group substitution in the lower rim of calix[4]arene bisphosphites on the coordination of pendent phosphorus atoms to a transition metal.
Scheme 1. Synthesis of phosphite ligands 3, 4, 5 and 6.

A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
2099
Fig. 2. Molecular structure of 5.
suggest the presence of a plane of symmetry in the molecule as
would be expected for cone or partial cone conformation. Two-
dimensional 1H–1H COSY measurement shows that the chemical
shift difference (Dd > 0.9) for the geminal methylene protons is in
the characteristic range for cone conformation of the calix[4]arene
framework [7]. The 31P NMR spectrum of 6 shows a singlet indicat-
ing the presence of a single conformer (Fig. S4). The 1H NMR spec-
trum shows eight doublets for the methylene protons signifying
the absence of any symmetry element in the molecule. Hence, li-
gand 6 can be considered as inherently chiral [8]. The geminal
methylene protons of the calix[4]arene framework are identified
by carrying out a 1H–1H COSY experiment; the characteristic dif-
ference in their chemical shifts (Dd > 0.9) supports the cone confor-
mation. The solid-state structures of ligands 5 and 6 (Figs. 2 and 3)
show cone conformation of the calixarene framework (see Tables 1
and 2 and SI for details).
A single resonance in the 31P NMR spectra and two singlets for
the tert-butyl protons in the 1H NMR spectra of the neutral allyl
complexes (3e and 3g) point to the presence of a single species
in solution. The room temperature 31P NMR spectrum of complex
3f shows two closely spaced singlets at 152.4 and 152.5 ppm; this
result is in accord with two different orientations of the allyl li-
gands (exo and endo) at the two palladium centers as observed in
the solid state (see later). The exo isomer is one in which central al-
lyl proton is oriented away from the calixarene core whereas the
endo isomer is defined as one in which the central allyl proton is
oriented towards the calixarene core (see Section 2.6). The
difference in the orientation of the two allyl moieties in the solu-
tion state could not be confirmed by 1H NMR measurements be-
cause of the overlapping of the resonances of the protons of the
two different allyl ligands. (Fig. S6a). The 1H–1H NOESY spectrum
shows strong exchange cross peaks between the meta aryl protons
0
0
0
0
A variable temperature NMR study (CD3COCD3, 400 MHz), car-
ried out between 190 and 321 K reveals that the ligands 3, 5 and
6 do not undergo any significant structural changes in solution in
this temperature range.
Ha—Ha and Hb—Hb (Fig. S8). Protons Ha, Hb, Ha , Hb were identified
by the through space contacts with the nearest tert-butyl groups,
(see Fig. S7). This observation clearly shows exchange between
0
0
Ha and Hb as well as Ha and Hb protons. The exchange among
these protons is only possible through exo–endo exchange of the al-
lyl ligands. Three isomers (I, II and III) are possible for complex 3f
as shown in Fig. 4. It may be noted that only for the exo–endo iso-
mer (I), the allyl moiety would undergo exchange between two
indistinguishable forms (I and I0). In all the isomers, the substituted
terminal allyl carbon is oriented trans to the phosphorus atom. The
31P NMR spectrum of complex 3f at ꢁ80 °C shows three signals of
different intensities. This result suggests that the complex exists as
a mixture of three isomers exchanging among themselves in solu-
tion. At a higher temperature (>30 °C), fast exchange among the
isomers gives rise to a single signal.
2.2. Allyl palladium complexes of ligand 3
The complexation reactions were carried out under two differ-
ent reaction conditions (Scheme 2). A series of cationic allyl palla-
dium complexes (3a–d) were synthesized by using NH4PF6 as the
anion scavenger and acetone as the solvent. A series of neutral allyl
palladium complexes (3e–3g) were obtained when the (allyl) pal-
ladium chloro dimers were treated with ligand 3 in dichlorometh-
ane in the absence of NH4PF6. Complexes 3b and 3f have been
isolated in pure form and characterized by 1H and 31P NMR spec-
troscopy and elemental analysis. All other complexes were charac-
terized only in solution by 31P NMR spectra of the reaction
mixtures (Fig. S5). The 31P chemical shifts for the neutral com-
plexes (ꢀ150 ppm) lie downfield from those for the cationic com-
plexes (120–130 ppm).
2.3. Reactions of 4 with (allyl) palladium dimers [(g3-C3H3R2)PdCl]2
The reaction of ligand 4 with (allyl) palladium chloro dimers,
[(g3-C3H3R2)PdCl]2(R@H or Ph) in the presence of ammonium

2100
A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
Fig. 3. Molecular structure 6.
Table 1
Crystallographic data for 5, 6, 3f and 4c
Identification code
Empirical formula
Formula weight
Temperature (K)
Wavelength
5
6
3f
4c
C66 H85O6P
1005.31
293(2)
0.71073
Triclinic
C73 H99O6P
1103.49
293(2)
0.71073
Triclinic
C86 H100Cl14O8P2Pd2
2032.70
293(2)
C82.25H102Cl2O8P2Pd
1457.88
293(2)
0.71073
Monoclinic
C2/c
0.71073
Triclinic
Crystal system
Space group
ꢀ
ꢀ
ꢀ
P1
P1
P1
Unit cell dimensions
a (Å)
b (Å)
c (Å)
a (°)
10.431(3)
14.643(5)
21.153(7)
88.450(5)
82.521(5)
84.826(5)
3190.2(17)
2
1.047
0.089
1088
0.78 ꢂ 0.47 ꢂ 0.02
0.97–24.00
ꢁ11 6 h 6 11,
ꢁ16 6 k 6 15,
ꢁ24 6 l 6 24
20888
11.162(4)
13.305(5)
23.191(9)
86.067(8)
80.510(7)
88.467(8)
3389(2)
14.698(4)
15.864(4)
22.708(6)
79.789(5)
83.130(4)
70.934(4)
4914(2)
39.805(2)
23.308(6)
18.167(5)
90
98.893(5)
70.934(4)
16653(7)
8
1.163
0.375
6156
0.42 ꢂ 0.30 ꢂ 0.10
1.02–26.07
ꢁ48 6 h 6 48,
ꢁ28 6 k 6 28,
ꢁ22 6 l 6 22
63935
b (°)
c (°)
Volume (Å3)
Z
2
2
dcalc (Mg/m3)
1.082
0.089
1200
0.14 ꢂ 0.10 ꢂ 0.09
0.89–26.37
ꢁ13 6 h 6 13,
ꢁ16 6 k 6 16,
ꢁ28 6 l 6 28
35762
1.374
0.828
2080
0.44 ꢂ 0.30 ꢂ 0.10
0.91–24.96
ꢁ17 6 h 6 17,
ꢁ18 6 k 6 18,
ꢁ26 6 l 6 26
35267
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm3)
h Range for data collection (°)
Index ranges
Reflections collected
Independent reflections [R(int)
Completeness to h (%)
]
9976 [0.0473]
99.7
13582 [0.1081]
98.2
17046 [0.0675]
98.9
16358 [0.1519]
99.3
Maximum and minimum transmission
Data/restraints/parameters
Goodness-of-fit on F2
0.9980, 0.9339
9976/0/624
1.517
0.9925, 0.9872
13582/0/650
0.942
0.9233, 0.7111
17046/0/1009
1.077
0.9642, 0.8578
16358/0/804
1.016
Final R indices [I > 2r(I)]
R1 = 0.1619,
R1 = 0.0995
R1 = 0.1116
R1 = 0.1156
wR2 = 0.3756
wR2 = 0.2539
wR2 = 0.2395
wR2 = 0.2607
R indices (all data)
R1 = 0.2073,
R1 = 0.2746,
R1 = 0.2033
R1 = 0.2429
wR2 = 0.3980
wR2 = 0.3369
wR2 = 0.2887
wR2 = 0.3317
Largest difference in peak and hole (e Åꢁ3
)
0.932, ꢁ0.623
0.651, ꢁ0.245
0.983, ꢁ0.672
1.064, ꢁ1.016

A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
2101
Table 2
Dihedral angles (°) between the planes of the aryl rings of the calixarene framework and the mean plane (X) defined by methylene carbon atomsa
Planes
Dihedral angles [ligand (5)]
Dihedral angles [ligand (6)]
Dihedral angles [complex (3f)]
Dihedral angles [complex (4c)]
A–X
B–X
C–X
D–X
85.1
49.2
75.8
40.5
80.3
38.2
84.3
42.4
43.7
89.9
43.9
89.3
75.7
49.1
84.9
44.9
a
A B, C and D are the plane of aromatic rings defined by C26–C32, C34–C39, C13–C18 and C20–C25, respectively for 6; C33–C38, C13–C18, C20–C24 and C26–C30 for 5;
C40–C45, C33–C38, C54–C59 and C47–C52 for 3f; C46–C51, C39–C44, C32–C37 and C25–C30 for 4c.
Scheme 2. Reactions of ligands 3 and 4 with palladium precursors.
hexafluorophosphate gives the expected complexes (4a and 4b)
(Scheme 2). Both the complexes have been characterized in solu-
tion by 1H and 31P NMR spectroscopy (Figs. S9 and S10). Attempts
to synthesize (allyl) palladium complexes in which ligand 4 would
bridge two palladium centers were unsuccessful. Complex 4b
could be isolated in a pure form and characterized by elemental
analysis. The structures of the allyl complexes 4a and 4b in solu-
tion, as deduced from NMR data, are shown in Fig. 5. The 31P
NMR spectrum of complex 4a shows two closely spaced singlets
at d 128.3 and 128.8 in the ratio of 1:1.5, indicating the presence
of two isomers. The resonances arising from the protons of the
methylene bridge as well as allyl carbon atoms were not resolved
and as a result, unambiguous assignment of the structures of the
two isomers could not be made. However, the cone conformation
of the major isomer can be predicted from a pair of singlets
(d 0.95 and 1.25) for the four tert-butyl groups. The minor isomer
also shows a pair of singlets (d 0.96 and 1.23) for the four tert-butyl
groups. This observation signifies the presence of a symmetry
plane bisecting the plane formed by methylene bridge carbon
atoms and passing through two of these carbon atoms and would
be consistent with the presence of the 1,2-alternate conformer.
However, the formation of this high-energy conformer can be ruled
out on steric grounds. Two isomers can arise because of the exo and
endo configuration of the allyl ligand with respect to the calixarene
framework. A similar kind of exo–endo isomerism was observed by
Matt and coworkers for the palladium methyl allyl complex of a
pendent calix[4]arene-1,3-bisphosphinite ligand [2c]. Assignment
of the exo and endo isomers by 2D NMR experiments was not pos-
sible because of the overlapping of the resonances arising from the
protons of the propyl, methylene and terminal allyl groups. Tenta-
tively the major isomer (4a0) is assigned the exo configuration and
the minor isomer (4a) the endo configuration. The 1H–1H NOESY
experiment shows the absence of exchange between the isomers.
The 31P NMR spectrum of the diphenyl allyl complex 4b shows a
single resonance at d 125.6. The 1H–1H NOESY experiment shows
the absence of any cross peak between the central allyl proton
(d 6.36) and the protons of the propyl groups (Fig. S11). This obser-
vation suggests that the central allyl proton is oriented away from
the calixarene core i.e exo arrangement of the allyl ligand. The cone
conformation of the calix-matrix can be deduced from the pres-
ence of only two singlets (d 0.91 and 1.22) for the four tert-butyl
groups and also by the characteristic difference Dd (>0.9) in the
chemical shifts of the adjacent methylene protons. All the methy-
lene protons of the calixarene framework have been assigned by
1H–1H COSY measurement.
2.4. Reactions of ligand 5 with (allyl) palladium precursors
The reactions of (allyl) palladium precursors with the mono-
phosphite ligand (5) in dichloromethane give the neutral allyl com-
plexes 5a–c as shown in Scheme 3. The 31P NMR spectra of 5a–c
display a singlet in each case (Fig. S13); the chemical shifts
(d ꢀ 150) lie in the region observed for neutral allyl complexes of
phosphite ligands (e.g complex 3f). The 1H NMR spectra of

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A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
Fig. 4. Schematic representation of exchange among three isomers of complex 3f. Arrows indicate exchanging protons.
Fig. 5. Probable solution structures of (a) (allyl) palladium (4a, 4a0) and (b) (diphenyl-allyl) palladium (4b) complexes.
Scheme 3. Reactions of ligands 5 and 6 with chloro-bridged allyl palladium dimers.

A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
2103
complexes 5b and 5c are broad and could not be analyzed. The 1
H
NMR spectrum of 5a is more informative (Fig. S14). Three singlets
for the tert-butyl protons in the ratio of 1:2:1 and one triplet for the
six methyl protons of the two propyl groups indicate the retention
of the plane of symmetry in the molecule. The only difference ob-
served from the 1H NMR spectrum of the ligand is the further split-
ting of methylene proton resonances to give rise to six doublets at
d 3.18, 3.35, 3.43, 4.35, 4.69 and 4.77 in the ratio of 2:1:1:2:1:1,
respectively. The two ‘higher-intensity’ doublets are due to the res-
onances of the protons (He, Hf) attached to two methylene bridge
carbons located far from the palladium center. Four protons of
the methylene bridge carbons near the palladium center are all
magnetically nonequivalent and give rise to four doublets. This
nonequivalence of methylene bridge protons arises because of
the coordination of two different atoms (P and Cl) to palladium.
2.5. Allyl palladium complexes of ligand 6
The reactions of the monophosphite ligand (6) with (allyl) pal-
ladium precursors [(g3-C3H5)PdCl]2, [(g3-1-Me-C3H4)PdCl]2, [(g3-
1-Ph-C3H4)PdCl]2 and [(g3-1,3-Ph2-C3H3)PdCl]2 give the expected
neutral allyl palladium complexes 6a–d (Scheme 3). The com-
plexes have been characterized in solution by 31P and 1H NMR
spectra. Formation of the neutral complexes is confirmed by
observing the 31P resonances in the 150 ppm region (Fig. S15),
characteristic of neutral allyl complexes such as 3e–g (See Section
2.2 ). The spectra of the complexes 6a and 6c show two resonances
with almost equal intensities. These allyl palladium complexes,
formed by an inherently chiral calixarene, exist in two diastereo-
meric forms. The spectra of 6b and 6d show two additional singlets
due to the presence of two other minor isomers [(III) and (IV)]
(Fig. 6). Room temperature 31P–31P NOESY measurements on 6a
and 6d reveal that the diastereomers undergo exchange in solu-
tion. Complex 6d also undergoes exchange among major and min-
or isomers. Although two distinct peaks appeared in the 31P NMR
spectra of the complexes, the 1H NMR spectra of the complexes
were not clearly resolved at room temperature. The NMR data
are consistent with cone conformation of the calixarene framework
as found in the ligand 6.
Fig. 6. Probable isomers of complex 6b in solution. [In the present study ‘cis–trans’
configurations are defined by the relative orientation of phosphorus (bonded to
calix[4]arene unit) and terminal methyl group of the allyl moiety. When both are on
the same side of the palladium square plane, the arrangement is named as ‘cis’].
ligands 2–6 and their palladium complexes. There are only a few
metal complexes of unsubstituted (biphenyldioxy)phosphorus li-
gands known for which different 31P and 1H NMR peaks have been
observed at low temperatures for isomers arising from the re-
The 1H resonances of the allyl protons of diastereomers I and II
were assigned by comparison with literature data [6d] and also
from the ‘‘through-bond” coupled allyl protons identified from
the 1H–1H COSY spectrum (Fig. S16). High field shifts of Hf and
stricted rotation around C1—C0 bond. Piarulli and coworkers have
1
observed that biphenolic phosphorus ligands (both phosphite
and phosphoramidite types) exhibit tropos behavior even at
190 K. The Rh complexes of biphenolic phosphites show tropos
nature of the ligand upto 230 K, the lowest temperature at which
measurements could be made[10]. Similarly, Hartwig and cowork-
ers have noted that the iridium complex of a phosphoramidite li-
gand with a biphenol backbone shows atropoisomerism only
below 230 K [11]. In the present investigation, variable tempera-
ture 31P and 1H NMR spectra of the ligands 3, 5, 6 and complexes
3b, 4a, 4b, 5a, 6a, 4c did not show any significant changes upto
193 K showing the tropos (free-to-rotate) nature of biphenyldioxy
units throughout this temperature range. The tropos nature of the
biphenyldioxy units has also been supported by high thermal
parameters of biphenyldioxy carbon atoms in the solid-state struc-
tures of 3f and 4c. Moreover, the solid-state structures of these
complexes clearly show that the biphenyldioxy units are away
from the calixarene backbone. As a result, any steric interaction
which might be responsible for atropos nature of biphenyldioxy
unit can be ruled out. In the case of complex 3f and 6b, broadening
of the 31P NMR signals has been observed at 193 K (see Fig. S22 and
S23). Although, the origin of three 31P resonances at low tempera-
ture for complex 3f and four 31P resonances (two major and two
minor) at room temperature for complex 6b have been already de-
scribed in Figs. 4 and 6, respectively (see also Fig. S22), the pres-
ence of other isomers due to restricted rotation of biphenyldioxy
0
Ha points to the close proximity of these protons to aromatic rings
of calix[4]arene framework. Fig. S17 shows the phase sensitive
1H–1H NOESY spectrum of complex 6b. Fig. 6 shows possible iso-
mers (I–IV) of complex 6b in solution and the observed exchange
pattern among the protons of the allyl moiety. Clearly there is ex-
change between analogous protons of the two diastereomers (I and
II) as well as between protons of the same diastereomer. Cross
peaks between the syn (Ha) and the anti (Hf) protons as well as
0
0
those between Ha and Hf protons indicate the presence of syn-anti
0
isomerization. Cross peaks between Hf and Hf as well as between
0
Hb and Hb protons indicate the presence of syn–syn/anti–anti isom-
erization processes [4e,4f,9]. Cis arrangement of the terminal
methyl group with respect to the central allyl proton in both the
isomers I and II can be inferred by the presence of NOE cross peaks
between the protons of methyl group and that of the central allyl
carbon (Fig. S18). Fig. S19 shows the exchange cross peaks between
the allyl protons of two major isomers I and II and those of the
minor isomers (III and IV).
2.6. Chirality of Pd(allyl) complexes
We have considered the possibility of restricted rotation of
phenyl groups of biphenyldioxy units around C1—C0 bond in the
C1—C0 bond at temperatures below 193 K cannot be discounted.
1
1

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A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
R''
a
b
R'
R''
R'
Pd
Pd
P
Cl
P
Cl
Calix
Calix
R
endo
exo
R' = R'' = H (3e, 5a)
R
R
R
*
*
Pd
*
*
Pd
Pd
Pd
P
Cl
P
Cl
P
Cl
P
Cl
Calix
Calix
Calix
Calix
endo-cis (R Pd
)
exo-cis (S Pd
)
endo-trans (R Pd
)
exo-trans (S Pd)
R = Me (5b, 3f)
R = Ph (5c, 3g)
Fig. 7. Different diastereomers produced by the combinations of (a) symmetric allyl or (b) unsymmetrical allyl moiety with calixarene backbone.
Neutral (allyl) palladium complexes with a symmetric allyl
detachment of the Pd(allyl)(Cl) moiety from the calixarene back-
bone. Diastereomers (I–IV) of complex 6b shows exchange among
each other (see Fig. S17 and S19). Thus, the possibility of genera-
tion of these diastereomers from the chiral calixarene backbone
can be ruled out. In essence, the relative arrangement of the Pd
substituents with respect to the calixarene backbone remains same
in all the complexes (either V or VI) and as a result, instead of eight
probable diastereomers of complex 6b, only four have been
observed.
moiety can show exo or endo diastereomers (Fig. 7a) whereas the
Pd center itself is chiral for nonsymmetric allyl complexes, for
which the possible diastereomers are shown in Fig. 7b. The situa-
tion becomes more complicated when a chiral calixarene ligand
(6) is used to generate neutral allyl complexes. Possible diastereo-
mers with different combinations of allyl and calixarene backbone
can be described as follows: (1) symmetric allyl (where R0@R00) Pd
complexes can form only exo and endo isomers; (2) coordination of
an unsymmetrical allyl (where R0 # R00) moiety with Pd will gener-
ate a chiral Pd center and such a complex can exist as four diaste-
reomers, viz. exo-cis, endo-cis, exo-trans, endo-trans; (3) symmetric
allyl complex with a chiral calixarene backbone can exist as four
diastereomers, viz. R(calix)-exo, R(calix)-endo, S(calix)-exo, S(ca-
lix)-endo; (4) unsymmetrical allyl complex with a chiral calixarene
backbone can produce eight diastereomers, viz. R(calix)-exo-cis,
R(calix)-endo-cis, R(calix)-exo-trans, R(calix)-endo-trans, S(calix)-
exo-cis, S(calix)-endo-cis, S(calix)-exo-trans and S(calix)-endo-trans.
The spatial arrangement of the substituents at the Pd coordination
center attached to an asymmetric calixarene ligand is shown in
Fig. 8. The exchange between the diastereomers V and VI is a for-
bidden process as it involves the breaking of Pd–P bond and the
2.7. Molecular structure of the allyl(palladium) complex 3f
The molecular structure of the palladium methyl allyl complex
(3f) is shown in Fig. 9. The steric interaction of the two bulky
bisphenol units with the pendent propyl arms causes the two
bisphenol substituted aryl rings to be oriented perpendicular to
the plane (X) of the methylene bridge carbon atoms (Table 2).
The other two aryl rings are inclined at an angle of ꢀ45° with
respect to the same plane (X) leading to an ideal pinched cone con-
formation of the calix[4]arene framework with a C2v symmetry axis
passing through the center of calixarene cavity [12]. The sequence
of signs i.e. + ꢁ, + ꢁ, + ꢁ, + ꢁ of the torsional angles (see Table S3)
Cl-Pd bond towards OH of
chiral calix backbone
allyl-Pd bond towards OH of
R'
chiral calix backbone
R'
OH
OH
Cl
O
O
O
O
Pd
Pd
O
Pr
O
P
Pr
R''
P
Pr
Cl
R''
Pr
O
O
O
O
VI
6a, R' = R'' = H
V
6b, R' = Me, R" = H
6c, R' = H, R'' = Ph
6d, R' = R'' = Ph
Fig. 8. Diastereomers produced due to the asymmetry of calixarene backbone. One of the forms V or VI has been observed for each complex of ligand 6a–6d.

A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
2105
Fig. 9. Molecular structure of 3f.
confirms the cone conformation of the calix[4]arene framework.
Selected bond lengths, bond angles and dihedral angles around
palladium coordination plane are listed in Table 3 and Table S4,
respectively. The geometry around both the palladium is almost
planar as can be seen from the low value of the dihedral angles be-
tween the planes of the terminal allyl carbon atoms passing
through palladium (C–Pd–C) and that of coordinated phosphorus
and chlorine atoms passing through corresponding palladium cen-
ter (P–Pd–Cl). The angles made by the two terminal allyl carbons to
the palladium and also by the chlorine and phosphorus atoms to
the palladium deviate considerably from 90°. This observation sug-
gests that the coordination of the ligands to palladium differ to an
appreciable extent from the square geometry. A considerable dif-
ference in the bending of the terminal methyl groups can be ob-
served for the two allyl ligands coordinated to the two palladium
centers. This bending of terminal methyl groups is indicated by
the dihedral angles (4° and 16°) between the planes passing
through the terminal carbon atom attached to the methyl group,
methyl group itself and the palladium atom and the plane passing
through two terminal allyl carbon atoms and the palladium center
(Table S4). An expanded view of the palladium coordination plane
is shown in Fig. S21, which clearly shows that the hydrogen at-
tached to the central allyl carbon C3 is oriented away from calixa-
rene framework whereas the hydrogen attached to the central allyl
carbon C7 is directed towards the calixarene framework. The Pd–Cl
and Pd–P bond lengths are similar to those observed in other pal-
ladium complexes. Greater trans influence of the phosphorus
atoms is reflected in the higher (0.16 and 0.09 Å) bond distances
of the terminal allyl carbons (C6, C2) bonded trans to the phospho-
rus atoms with respect to the terminal allyl carbons (C4, C8)
bonded trans to the chlorine atoms. Both the biphenol units are
in R/S configuration in the solid-state structure of complex 3f.
2.8. Molecular structure of PdCl2 complex (4c)
The molecular structure of the palladium dichloride complex
(4c) has been established by the single crystal X-ray diffraction
analysis and is shown in Fig. 10. This complex is the first of its kind
arising from the chelation of phosphorus atoms, appended to the
lower rim of two adjacent aryl rings of the calix-matrix, to a single
palladium center. The conformation of the calix[4]arene frame-
work in the complex (4c) can be described in terms of torsion an-
gles (Table S5) and dihedral angles (Table 2). Opposite signs of the
consecutive torsion angles (ꢁ +, ꢁ +, ꢁ +, ꢁ +) showed that the ca-
lix[4]arene matrix adopts a cone conformation. However, the dihe-
dral angles between the aryl rings of calix-matrix and the plane of
the methylene bridge carbons show a considerable deviation from
the values expected for a cone or a pinched cone conformation.
Chelation of the phosphorus atoms, attached to the lower rim of
two adjacent aryl rings of the calix-matrix to the palladium center
is probably responsible for this intermediate conformation. One of
the aryl rings, attached to the coordinated phosphorus, makes an
angle of 75° with the methylene bridge plane and consequently
the dihedral angles of the other aryl rings also show values be-
tween 45° and 90°. These values lie in between the dihedral angles
for an ideal cone (all 45°) and pinched cone (two 45° and two 90°)
conformations [12]. Selected bond lengths, bond angles around
palladium coordination center are listed in Table 4. The deviation
of P1–Pd1–P2 and Cl1–Pd1–Cl2 angles, from the ideal value (90°)
expected for a square geometry, is small. The dihedral angles be-
tween the planes passing through the atoms (P1–Pd1–P2) and
(CL1–Pd1–CL2) is low (3.1°). The P–Pd–P bite angle is 5–8° lower
than any other chelated allyl palladium complexes of calix[4]arene
reported in literature [2d]. The Pd–P and Pd–Cl bond lengths are
within the range reported for palladium dichloride complexes of
calix[4]arene bisphosphite ligands [2a,13]. One of the biphenol
Table 3
Selected bond distances (A°) and bond angles for complex 3f
Atoms
Distance (A°)
Atoms
Angle (°)
P(1)–PD(1)
CL(1)–PD(1)
C(2)–PD(1)
C(3)–PD(1)
C(4)–PD(1)
P(2)–PD(2)
CL(2)–PD(2)
C(6)–PD(2)
C(7)–PD(2)
C(8)–PD(2)
2.238(3)
2.356(2)
2.21(2)
2.13(2)
2.12(1)
2.237(2)
2.361(3)
2.25(1)
2.11(1)
2.09(1)
C(2)–PD(1)–C(4)
C(6)–PD(2)–C(8)
C(2)–C(3)–C(4)
C(6)–C(7)–C(8)
CL(1)–PD(1)–P(1)
CL(2)–PD(2)–P(2)
67.0(6)
68.1(6)
149.2(4)
146.4(2)
102.4(1)
101.9(1)

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A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
Fig. 10. Molecular structure of 4c.
metric carbon atoms of substituents attached to phosphorus [14].
Table 4
They have also shown that calixarene bisphosphites bearing chiral
binaphthol backbone gave linear products with 98% selectivity
[2d]. These results prompted us to study the catalytic activity of
conformationally rigid bisphosphite ligand 3 and its palladium
methyl allyl complex 3f in allylic alkylation reactions of crotyl ace-
tate using dimethyl malonate as the nucleophile. The relative
amounts of the products were determined by the integrated inten-
sities of the respective signals in the 1H NMR spectrum. The results
are shown in Table 5. The relative yield of the branched product is
considerably high. This increase is probably due to the involve-
ment of neutral allyl complex in the catalytic cycle as shown in
Fig. S24. As can be seen from the solid-state structure of the allyl
complex 3f, the methyl group substituted terminal allyl carbon is
oriented trans to the phosphorus atom. The trans directing effect
of phosphorus is higher than that of chloride and as a result, the
substituted allyl terminus is more susceptible to nucleophilic at-
tack than the unsubstituted allyl terminus, leading to higher yield
of the branched isomer [15]. The relative yield of the branched
product is higher (51%) with complex 3f than that observed
Selected bond distances (Å) and bond angles (°) at the palladium coordination center
for the complex 4c
Atoms
Distance and angles
PD1–P1
PD1–P2
PD1–CL1
PD1–CL2
P(1)–PD(1)–P(2)
CL(1)–PD(1)–CL(2)
2.215(2)
2.242(2)
2.316(2)
2.331(2)
98.7
91.4
units adopts R/S and the other S/R configuration in the solid-state
structure of complex 4c.
2.9. Catalytic studies
Matt and cowokers have reported that inherently chiral ca-
lix[4]arene phosphines gave superior enatioselectivities in Pd-cat-
alyzed allylic alkylations compared to those induced by related
diphosphines in which the only sources of chirality are the asym-
Table 5
Relative yields (%) of products in the palladium catalyzed nucleophilic substitution of (E) crotyl acetate using dimethyl malonate (DMM) as nucleophilea
Catalyst
Reagents
Yield
Me
CH(COOMe)2
CH(COOMe)2
Me
Me
Linear trans
CH(COOMe)2
Branched
Linear cis
3 + Pd-precursor
Complex 3f
BSA/KOAc/DMM
Sodium salt of DMM
Sodium salt of DMM
55
49
45
7
0
0
38
51
55
60
30
82
Complex 3fb
a
Reaction conditions: 25 °C, 0.05 mol% of catalyst; time taken for the completion of reaction (as monitored by TLC): 24 h.
Stoichiometric.
b

A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
2107
(38%) with ligand 3. Presumably, the neutral allyl complex is more
active than the chelated cationic complex formed in the latter case
(see SI for the 31P NMR evidence of the formation of cationic com-
plex during the reactions of ligand 3 with allyl palladium dimers).
The monophosphite ligand 6 is also able to catalyze the reaction
but there is no significant amount of branched product formed
during the catalytic reaction. Our effort to apply the proximally
substituted ligand 4 in catalytic allylic alkylation reaction to verify
the effect of smaller bite angle on the relative amount of branched
product was not successful because of the difficulty in isolating
ligand 4 in a pure form.
6.69, 6.90 (2s, 8m-ArH, calixarene); 7.1–7.5 (m, 8H, biphenol
ArH). MS (MALDI, M = 1161.2): m/z = 1162.2 (MH+).
4.2. Synthesis of 25,26-bis-(2,20-biphenyldioxyphosphinoxy)-27,28-
dipropyloxy-p-tert-butyl calix[4]arene (4)
A suspension of 25,26-dihydroxy-27,28-dipropyloxy-p-tert-bu-
tyl calix[4]arene (2) (1.61 g, 2.2 ꢂ 10ꢁ3 mol) and NaH (60% disper-
sion in oil) (0.185 g, 4.6 ꢂ 10ꢁ3 mol) in toluene (60 mL) was heated
under reflux for 12 h at 110 °C. The solution was cooled to 0 °C and
[1,10-biphenyl]-2, 20-phosphorochlororidite (4.6 ꢂ 10ꢁ3 mol) in tol-
uene (30 mL) was added. The reaction mixture was stirred for 2 h
at room temperature. The reaction was followed by TLC [Rf = 0.8
(ligand 4); silicagel; EtOAc/petrol (1/99-v/v)]. Solvent was evapo-
rated under reduced pressure and the residue was subjected to col-
umn chromatography to obtain a colorless solid which consisted of
the desired bisphosphite ligand (4) as the major component with
the corresponding monophosphite (6) as the minor component.
The 31P NMR spectrum showed several other resonances of low
intensity indicating the presence of other conformational isomers
of both mono and bisphosphites. The ligand (4) could not be sepa-
rated in a pure form. This mixture of compounds was used as such
for further complexation reactions. 31P{1H} NMR (CDCl3,
162 MHz): d = 113.7 (s), 128.1 (s), 129.2 (s, major product, bis-
phosphite, 4), 133.1(s), 137.5 (s), 145.1 (s), 147.1 (s, monophosph-
ite 6). 1H NMR (CDCl3, 400 MHz): Not resolved.
3. Conclusions
In conclusion, we have synthesized four conformationally rigid
calix[4]arene phosphite ligands and their palladium complexes.
Relative positioning of the phosphorus atoms in the lower rim of
the calixarene unit plays an important role in determining the nat-
ure of coordination to the palladium center: 1,3-Substituted bis-
phosphites give neutral as well as cationic (allyl) palladium
complexes whereas 1,2-substituted bisphosphite forms only cat-
ionic (allyl) palladium complexes. The P–Pd–P bite angle shows
significant difference between palladium complexes of 1,2-substi-
tuted bisphosphite (complex 4c) and those of the analogous 1,3-
substituted bisphosphite [16]. Neutral allyl complex (involving
coordination of single phosphorus to palladium) appears to be
more effective in forming the branched product during the cata-
lytic allylic alkylation reactions than the chelated cationic complex.
4.3. Synthesis of 25-hydroxy-27-(2,20-biphenyldioxyphosphinoxy)-
26,28-dipropyloxy-p-tert-butyl calix[4]arene (5)
4. Experimental
A suspension of 25,27-dihydroxy-26,28-dipropyloxy-p-tert-bu-
tyl calix[4]arene (1) (1.61 g, 2.2 ꢂ 10ꢁ3 mol) and NaH (60% disper-
sion in oil) (0.14 g, 3.5 ꢂ 10ꢁ3 mol) in toluene (60 mL) was heated
for 12 h at 80 °C. [1,10-Biphenyl]-2,20-phosphorochlororidite
(3.5 ꢂ 10ꢁ3 mol) in toluene (30 mL) was added at 0 °C and the reac-
tion mixture stirred for 2 h at room temperature. The reaction was
followed by TLC [Rf = 0.65 (ligand 5); SiO2; EtOAc/petrol (1/99-v/
v)]. Solvent was evaporated under reduced pressure and the resi-
due was subjected to column chromatography to obtain the title
compound as a colorless solid which consisted of the desired
monophosphite ligand (5) as the major component along with
the corresponding bisphosphite (3) as the minor component. The
product was purified further by subjecting it to column chroma-
tography for a second time to obtain a pure sample of ligand 5
(yield = 0.6 g, 28.8%). 31P{1H} NMR (CDCl3, 162 MHz): d = 128.1
(s); 1H NMR (CDCl3, 400 MHz): d = 0.86 (s, 18H, –C(CH3)3), 0.94
(t, 3H, –C2H5CH3), 1.25 (s, 9H, –C(CH3)3), 1.31 (s, 9H, –C(CH3)3);
1.93 (m, 2H, –C2H5CH3), 3.24 (2d, 4H, ArCH2Ar), 3.74 and 3.91
(2m, 4H, –C2H5CH3), 4.35 (d, 2J(H,H) = 13.2 Hz, 2H, ArCH2Ar), 4.87
(d, 2J(H,H) = 12.8 Hz, 2H, ArCH2Ar); 6.59, 6.62, 7.03, 7.05 (4s, 8m-
ArH, calixarene). 7.20–7.43 (m, 8H, biphenol ArH). MS (MALDI,
M = 947.2): m/z = 985.8 (M + K+, from matrix).
The general experimental procedures and details of spectro-
scopic and other physical measurements were as described in
our previous publications [17,18]. Phosphorochloridite (C12H8O2)-
PCl [19], 1,3-dipropyloxy calix[4]arene [20], 1,2-dipropyloxy ca-
lix[4]arene [21] and the organometallic precursor complexes,
[Pd(COD)Cl2] [22], [(g3-C3H5)PdCl]2 [23], [(g3-1-Me-C3H4)PdCl]2
[24], [(g3-1-Ph-C3H4)PdCl]2 [24], and [(g3-1,3-Ph2-C3H3)PdCl]2
[25] were prepared by published procedures. Modified literature
procedures were followed for catalytic allylic alkylation reactions
of crotyl acetate (see Supporting Information) [26]. Isomer distri-
bution was determined from the 1H NMR intensities [26,27].
4.1. Synthesis of 25,27-bis-(2,20-biphenyldioxyphosphinoxy)-26,28-
dipropyloxy-p-tert-butyl calix[4]arene (3)
A suspension of 25,27-dihydroxy-26,28-dipropyloxy-p-tert-bu-
tyl calix[4]arene (1) (1.61 g, 2.2 ꢂ 10ꢁ3 mol) and NaH (60% disper-
sion in oil) (0.185 g, 4.6 ꢂ 10ꢁ3 mol) in toluene (60 mL) was heated
under reflux for 12 h at 110 °C. [1,10-Biphenyl]-2,20-phosphoro-
chlororidite (4.6 ꢂ 10ꢁ3 mol) in toluene (30 mL) was added at
0 °C and the reaction mixture stirred for 2 h at room temperature.
The reaction was followed by TLC [Rf = 0.8 (ligand 3); SiO2; EtOAc/
petrol (1/99-v/v)]. Solvent was evaporated under reduced pressure
and the residue was subjected to column chromatography to ob-
tain the title compound as a colorless solid which consisted of
the desired bisphosphite ligand as the major product with the cor-
responding monophosphite as the minor product. The sample was
dissolved in minimum volume of petrol and the solution kept over
night to give a precipitate of the pure bisphosphite ligand (3)
(yield = 0.8 g, 31%); m.p = 205–210 °C; 31P{1H} NMR (CDCl3,
162 MHz): d = 136.1 (s); 1H NMR (CDCl3, 400 MHz): d = 0.52 (t,
6H, –C2H5CH3), 1.02 (s, 18H, –C(CH3)3), 1.17 (s, 18H, –C(CH3)3);
1.85(m, 4H, –C2H5CH3), 3.21 (d, 2J(H,H) = 12 Hz, 4H, ArCH2Ar),
3.75 (t, 4H, –OCH2C2H5), 4.69 (d, 2J(H,H) = 12 Hz, 4H, ArCH2Ar),
4.4. Synthesis of 25-hydroxy-26-(2,20-biphenyldioxyphosphinoxy)-
27,28-dipropyloxy-p-tert-butyl calix[4]arene (6)
A suspension of 25,26-dihydroxy-27,28-dipropyloxy-p-tert-bu-
tyl calix[4]arene (2) (1.61 g, 2.2 ꢂ 10ꢁ3 mol) and NaH (60% disper-
sion in oil) (0.14 g, 3.5 ꢂ 10ꢁ3 mol) in toluene (60 mL) was heated
for 12 h at 80 °C. [1,10-Biphenyl]-2,20-phosphorochlororidite
(3.5 ꢂ 10ꢁ3 mol) in toluene (30 mL) was added at 0 °C and the reac-
tion mixture stirred for 2 h at room temperature. The reaction was
followed by TLC [Rf = 0.7 (ligand 6); SiO2; EtOAc/petrol (1/99-v/v)].
Solvent was evaporated under reduced pressure and the residue
subjected to column chromatography to obtain a colorless solid
which consisted of the desired monophosphite ligand (6) as the

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A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
major component and the corresponding bisphosphite (4) as the
minor component. The mixture was dissolved in petrol and the
stirred for 1 h at 25 °C and the solution was evaporated under vac-
uum to obtain the title complex 3e as a colorless solid. 31P{1H}
NMR (CDCl3, 162 MHz): d = 149.7 (s).
solution kept overnight to obtain colorless crystals of
6
(yield = 0.75 g, 36%); m.p = 100–105 °C; 31P{1H} NMR (CDCl3,
162 MHz): d = 147.1 (s); 1H NMR (CDCl3, 400 MHz): d = 0.33 (t,
3H, –C2H5CH3), 0.73 (s, 9H, –C(CH3)3), 0.90 (s, 9H, –C(CH3)3),
1.09 (t, 3H, –C2H5CH3), 1.34 (s, 18H, –C(CH3)3); 1.83(m, 2H,
–C2H5CH3), 1.91 (m, 2H, –C2H5CH3), 3.129 (d, 2J(H,H) = 12.4 Hz,
1H, ArCH2Ar), 3.253 (d, 2J(H,H) = 12.8 Hz, 1 H, ArCH2Ar), 3.321 (d,
2J(H,H) = 10.0 Hz, 1H, ArCH2Ar), 3.354 (d, 2J(H,H) = 9.6 Hz, 1H,
ArCH2Ar), 3.585 (t, 2H, –OCH2C2H5), 3.721 (m, 1H, –OCH2C2H5),
3.85 (m, 1H, –OCH2C2H5), 4.155 (d, 2J(H,H) = 13.6 Hz, 1H, ArCH2Ar),
4.268 (d, 2J(H,H) = 12.4 Hz, 1H, ArCH2Ar), 4.566 (d, 2J(H,H) =
13.2 Hz, 1H, ArCH2Ar), 4.741 (d, 2J(H,H) = 12.8 Hz, 1H, ArCH2Ar),
6.43, 6.45, 6.62, 6.65, 7.05, 7.15 (6s, 8m-ArH, calixarene), 7.28–
7.6 (m, 8H, biphenol ArH). MS (MALDI, M = 947.2): m/z = 985.8
(M + K+, from matrix).
Complexes 3f, 3g, 5a–5c, 6a–6d were synthesized by a proce-
dure similar to that used for the preparation of complex 3e.
4.10. Synthesis of [{(g3-1-Me-C3H4)Pd(Cl)}2(3)] (3f)
Starting materials: [(g3-1-Me-C3H4)PdCl]2 (15 mg, 4 ꢂ 10ꢁ5
mol) and ligand (3) (47 mg, 4 ꢂ 10ꢁ5 mol). Yellow micro-crystals
of 3f were grown from chloroform solution by layering with hex-
ane. (yield = 0.020 g, 62.5%); m.p. = 225–230 °C (dec.); 31P{1H}
NMR (CDCl3, 162 MHz): d = 152.4 (s), 152.5 (s); 1H NMR (CDCl3,
400 MHz): d = 0.04(t, 6H, –C2H5CH3), 0.03 and 0.12 (2t, –C2H5CH3,
other isomers), 0.79, 0.80 (2s, 18H, –C(CH3)3), 1.36 (s, 18H,
–C(CH3)3); 1.54 (m, 4H, –C2H5CH3), 1.62 (2d, 6H, –CH3, CH3C3H4)
3.30–3.64 (m, 4H, –OCH2C2H5, 4H, ArCH2Ar), 3.91 (m, 4H, termi-
nal-CH3C3H4), 4.50–4.58 (m, 4H, ArCH2Ar), 4.62 (m, 2H, terminal-
CH3C3H4), 4.73 (m, 2H, central-CH3C3H4), 6.46, 6.52 (2s, 4H, m-ArH,
calixarene); 7.21, 7.22 (2s, 4H, m-ArH, calixarene), 7.25–7.80 (m,
16H, biphenol ArH). Elemental Anal. Calc. for C82H96O8P2Pd2Cl2: C,
63.3; H, 6.2. Found: C, 63.6; H, 6.2%.
4.5. Synthesis of [(g3-C3H5)Pd(j2-P,P0-3)](PF6) (3a)
Calix[4]arene phosphite (3) (94 mg, 8 ꢂ 10ꢁ5 mol) in acetone
(30 mL) was added drop-wise to a suspension of [(g3-C3H5)PdCl]2
(14 mg, 4 ꢂ 10ꢁ5 mol) and NH4PF6 (15 mg, 8.8 ꢂ 10ꢁ5 mol) in ace-
tone (30 mL) at 0 °C. The reaction mixture was stirred for 1 h at
0 °C and filtered through celite. Solvent was evaporated from the
filtrate. The residue was dissolved in chloroform (3 mL) and hexane
was added slowly until the solution became hazy. The solution was
kept aside for 12 h to obtain colorless precipitate of the title com-
pound (3a). 31P{1H} NMR (CDCl3, 162 MHz): d = 127.2 (s).
4.11. Synthesis of [{(g3-1-Ph-C3H4)Pd(Cl)}2(3)] (3g)
Starting materials: [(g3-1-Ph-C3H4)PdCl]2 (20 mg, 4 ꢂ 10ꢁ5 mol)
and ligand (3) (47 mg, 4 ꢂ 10ꢁ5 mol). 31P{1H} NMR (CDCl3,
162 MHz): d = 152.2 (s).
Complexes 3b–3d, 4a, 4b were synthesized by a procedure sim-
ilar to that used for the preparation of complex 3a.
4.12. Synthesis of [(g3-C3H5)Pd(j2-P,P0-4)](PF6) (4a)
Starting materials: [(g3-C3H5)PdCl]2 (14 mg, 4 ꢂ 10ꢁ5 mol);
NH4PF6 (15 mg, 8.8 ꢂ 10ꢁ5 mol) and ligand (4) (94 mg, 8 ꢂ
10ꢁ5 mol). (yield = 0.005 g, 30%); m.p. = 210–220 °C (dec.), 31P{1H}
NMR (CDCl3, 162 MHz): d = 128.3 (s, minor), 128.8 (s, major)
1H NMR (CDCl3, 400 MHz): d = 0.95 and 1.25 (2s, 18H + 18H,
–C(CH3)3, major); 0.96 and 1.23(2s, 18H + 18H, –C(CH3)3, minor);
1.01(t, 6H, –C2H5CH3, major); 1.07 (t, 6H, –C2H5CH3, minor); 1.97
and 2.1 (2m, 4H, major and 4H minor –C2H5CH3); 2.61, (m, 2H, ter-
minal allyl –C3H5, major); 2.72 (m, 2H, terminal allyl –C3H5,minor)
5.26 (m, 1H, central allyl, minor); 5.51 (m, 1H, central allyl, major);
other peaks were not resolved.
4.6. Synthesis of [(g3-1-Me-C3H4)Pd(j2-P,P0-3)](PF6) (3b)
Starting materials: [(g3-1-Me-C3H4)PdCl]2 (15 mg, 4 ꢂ 10ꢁ5
mol); NH4PF6 (15 mg, 8.8 ꢂ 10ꢁ5 mol) and ligand (3) (94 mg,
8 ꢂ 10ꢁ5 mol). (yield = 0.060 g, 50.5%); m.p. = 215–220 °C (dec.);
31P NMR: (162 MHz, CDCl3): d 126.0 and 129.5; AB pattern, JPP
128.0 Hz [major isomer] 126.8 and 128.3 (broad) [minor isomer].
1H NMR (CDCl3, 400 MHz): d 0.77 (t, 6H, –C2H5CH3), 0.80, 0.83
(2s, 9H each, –C(CH3)3), 1.09 (m, 3H, CH3-allyl), 1.29 (s, 18H,
–C(CH3)3); 1.7 (m, 4H, –C2H5CH3), 3.30 (2d, 2H, ArCH2Ar), 3.55
(m, 2H, terminal allyl), 3.83 and 4.05 (2m, 4H, –C2H5CH3), 4.8–
5.0 (4d, 4H, ArCH2Ar), 5.05 (m, H, central allyl), 6.42 and 6.48
(2s, 4H, m-ArH, calixarene); 6.9–7.6 (m, 16H, biphenol ArH, 4H
m-ArH-calixarene). Elemental Anal. Calc. for C70H89O8P3PdF6: C,
61.3; H, 6.5. Found: C, 62.2; H, 6.3%.
4.13. Synthesis of [(g3-1,3-Ph2-C3H3)Pd(j2-P,P0-4)](PF6) (4b)
Starting materials: [(g3-1,3-Ph2-C3H3)PdCl]2 (26 mg, 4 ꢂ
10ꢁ5 mol); NH4PF6 (15 mg, 8.8 ꢂ 10ꢁ5 mol) and ligand (4) (94 mg,
8 ꢂ 10ꢁ5 mol). (yield = 0.052 g, 40%). m.p. = 192–200 °C (dec.);
31P{1H} NMR (CDCl3, 162 MHz): d = 125.6(s); 1H NMR (CDCl3,
400 MHz): d = 0.81 (t, 6H, –C2H5CH3); 0.91 and 1.22 (2s,
18H + 18H, –C(CH3)3); 1.82 (m, 4H, –C2H5CH3); 2.98, 3.84, 4.26,
4.67 (4d, 1H each, ArCH2Ar), 3.97 and 5.47 (2d, 2H each, ArCH2Ar);
3.51 and 3.60 (2m, 4H, C2H5CH3); 5.22 (m, 2H, terminal allyl), 6.36
(m, 1H, central allyl); 6.5–8.0 (ArH). Elemental Anal. Calc. for
4.7. Synthesis of [(g3-1-Ph-C3H4)Pd(j2-P,P0-3)](PF6) (3c)
Starting materials: [(g3-1-Ph-C3H4)PdCl]2 (20 mg, 4 ꢂ 10ꢁ5
mol); NH4PF6 (15 mg, 8.8 ꢂ 10ꢁ5 mol) and ligand (3) (94 mg,
8 ꢂ 10ꢁ5 mol). 31P{1H} NMR (CDCl3, 162 MHz):
129.6; JP,P = 147.4 Hz.
d 122.7 and
C
89H95O8P3PdF6: C, 66.6; H, 6.0. Found: C, 66.8; H, 5.5%.
4.8. Synthesis of [(g3-1,3-Ph2-C3H3)Pd(j2-P,P0-3)](PF6) (3d)
4.14. Synthesis of [{(g3-C3H5)Pd(Cl)}(5)] (5a)
Starting materials: [(g3-1,3-Ph2-C3H3)PdCl]2 (26 mg, 4 ꢂ 10ꢁ5
mol); NH4PF6 (15 mg, 8.8 ꢂ 10ꢁ5 mol) and ligand (3) (94 mg,
8 ꢂ 10ꢁ5 mol). 31P{1H} NMR (CDCl3, 162 MHz): d 122.7 (s).
Starting materials: [(g3-C3H5)PdCl]2 (3.5 mg, 1 ꢂ 10ꢁ5 mol); li-
gand 5 (19 mg, 2 ꢂ 10ꢁ5 mol) (yield = 0.010 g, 44.1%); m.p. = 217–
225 °C (dec); 31P{1H} NMR (CDCl3, 162 MHz): d = 148.4 (s) (major
isomer); 126.9 (s) (minor isomer); 1H NMR (CDCl3, 400 MHz):
0.65 (t, 6H, –C2H5CH3), 0.95 (s, 9H, –C(CH3)3), 1.12 (s, 18H,
–C(CH3)3); 1.14 (s, 9H, –C(CH3)3), 1.75 (m, 4H, –C2H5CH3), 1.96
(d, 1H, terminal allyl), 3.18 (d, 2J(H,H) = 13.2 Hz, 2H, ArCH2Ar),
3.35 (d, 2J(H,H) = 15.6 Hz, 1H, ArCH2Ar), 3.43(d, 2J(H,H) = 12.7 Hz,
4.9. Synthesis of [{(g3-C3H5)Pd(Cl)}2(3)] (3e)
To a solution of [(g3-C3H5)PdCl]2 (14 mg, 4 ꢂ 10ꢁ5 mol) in
CH2Cl2 (10 ml) was added
a solution of ligand 3 (47 mg,
4 ꢂ 10ꢁ5 mol) in CH2Cl2 (10 ml) at 0 °C. The reaction mixture was

A. Sarkar et al. / Journal of Organometallic Chemistry 693 (2008) 2097–2110
2109
1H, ArCH2Ar), 3.53 (m, 2H, terminal allyl), 3.6 (m, 2H, –C2H5CH3),
3.8 (m, 2H, –C2H5CH3), 4.35 (d, 2J(H,H) = 12.8 Hz, 2H, ArCH2Ar),
4.57 (m, 1H, terminal allyl), 4.69 (d, 2J(H,H) = 13.7 Hz, 1H, ArCH2-
Ar), 4.77 (d, 2J(H,H) = 12.7 Hz, 1H, ArCH2Ar), 4.98 (m, 1H, central al-
lyl), 6.76, 6.80, 6.86, 6.88, 6.97, 6.98 (6s, 8m-ArH, calixarene), 7.35–
7.82 (m, 8H, biphenol ArH). Elemental Anal. Calc. for
(CDCl3, 162 MHz): d = 145.5 (s) and 144.4 (s) (major isomer);
144.9 (s) and 143.5 (s) (minor isomer).
4.21. Synthesis of [Cl2Pd(4)] (4c)
A
mixture of ligand
4
(50 mg, 4.33 ꢂ 10ꢁ5 mol) and
C65H80O6PPdCl: C, 67.2; H, 6.9. Found: C, 68.0; H, 6.7%.
[Pd(COD)Cl2] 13 mg (4.33 ꢂ 10ꢁ5 mol) was dissolved in 20 mL of
benzene. The solution was stirred for 1 hr at 25 °C. Reaction mix-
ture was washed with hot petrol and the residue was dissolved
in chloroform. Addition of petrol to the chloroform solution in
5:1 ratio gave the title compound 4c as pale green crystals. (yield
10 mg, 17.3%); m.p. = 198–205 °C (dec); 31P{1H} NMR (CDCl3, 162
MHz): d = 94.1 (s); 1H NMR (CDCl3, 400 MHz): d = 0.91 and 1.20
(2s, 18H + 18H, –C(CH3)3); 0.97 (t, 6H, –C2H5CH3); 1.97 and 2.09
(2m, 4H, –C2H5CH3); 3.07, 3.98, 4.34, 4.87 (4d, 4H, ArCH2Ar);
2.38 and 4.23 (2d, 2H each, ArCH2Ar); 5.94, 6.53, 6.65, 6.72 (4s,
2H each, calix m-ArH); 8.84–7.63 (m, ArH).
4.15. Synthesis of [{(g3-1-Me-C3H4)Pd(Cl)}(5)] (5b)
Starting materials: [(g3-1-Me-C3H4)PdCl]2 (4 mg, 1 ꢂ 10ꢁ5 mol)
and ligand (5) (19 mg, 2 ꢂ 10ꢁ5 mol). 31P{1H} NMR (CDCl3,
162 MHz): d = 151.3 (s).
4.16. Synthesis of [{(g3-1-Ph-C3H4)Pd(Cl)}(5)] (5c)
Starting materials: [(g3-1-Ph-C3H4)PdCl]2 (5 mg, 1 ꢂ 10ꢁ5 mol)
and ligand (5) (19 mg, 2 ꢂ 10ꢁ5 mol). 31P{1H} NMR (CDCl3, 162
MHz): d = 152.2 (s).
4.22. X-ray crystallography
4.17. Synthesis of [{(g3-C3H5)Pd(Cl)}(6)] (6a)
X-ray diffraction data were collected in frames with increasing
x (width of 0.3°/frame) on a Bruker SMART APEX CCD diffractom-
eter, equipped with a fine focus 1.75 kW sealed tube X-ray source.
The SMART software was used for cell refinement and data acquisi-
tion [28] and the SAINT software was used for data reduction [29].
An absorbtion correction was made on the intensity data using
the SADABS programme [30]. All the structures were solved using
SHELXTL [31] and the WinGX graphical user interface [32]. Least-
square refinements were performed by the full-matrix method
with SHELXL-97 [33]. All non-hydrogen atoms were refined aniso-
tropically and hydrogen atoms were refined isotropically. The
crystal data and details of structure refinement are summarized
in Table 1.
Starting materials: [(g3-C3H5)PdCl]2 (3.5 mg, 1 ꢂ 10ꢁ5 mol); li-
gand 6 (19 mg, 2 ꢂ 10ꢁ5 mol). 31P{1H} NMR (CDCl3, 162 MHz):
d = 149.8 (s) and 150.2 (s); 1H NMR (CDCl3, 400 MHz): 1H NMR
(CDCl3, 400 MHz): 0.20 (t, 3H, –C2H5CH3), 0.73 (s, 9H, –C(CH3)3),
0.88 (s, 9H, –C(CH3)3), 1.05 (t, 3H, –C2H5CH3), 1.33 (s, 9H,
–C(CH3)3), 1.35 (s, 9H, –C(CH3)3), 1.74 (m, 2H, –C2H5CH3), 1.88
(m, 2H, –C2H5CH3), 2.15, 2.23 (2d, 2H, terminal allyl), 3.12 (d, 1H,
ArCH2Ar), 3.33 (d, 1H, ArCH2Ar), 3.43 (d, 1H, ArCH2Ar), 3.46–
3.82 (m, 1H, ArCH2Ar, 4H, –C2H5CH3); 4.11 (d, 1H, ArCH2Ar);
4.23 (d, 1H, ArCH2Ar), 4.49 (m, 1H, ArCH2Ar, 1H, terminal allyl);
4.78 (d, 1H, ArCH2Ar, 1H, central allyl); 4.98 (m, 1H, central allyl);
6.4–6.7 (6 br s, 8H, m-ArH); 7.05–7.9 (m, 8H, ArH-calix, 8H, ArH-
biphenol).
Acknowledgements
4.18. Synthesis of [{(g3-1-Me-C3H4)Pd(Cl)}(6)] (6b)
We thank the Department of Science and Technology (DST),
New Delhi, India for financial support. SSK thanks the Indian
national Science Academy, New Delhi for the position of a Senior
Scientist.
Starting materials: [(g3-1-Me-C3H4)PdCl]2 (8 mg, 2 ꢂ 10ꢁ5 mol)
and ligand (6) (38 mg, 2 ꢂ 10ꢁ5 mol). (yield = 0.030 g, 66.2%);
m.p. = 210–215 °C (dec.); 31P{1H} NMR (CDCl3, 162 MHz):
d = 153.0 (s) and 152.4 (s) (major isomer); 153.7 (s) (minor isomer).
1H NMR (CDCl3, 400 MHz): 0.19 (t, 6H, –C2H5CH3), 0.74 (br, s, 18H,
–C(CH3)3), 0.88(br, s, 18H, –C(CH3)3), 1.06 (t, 6H, –C2H5CH3), 1.34
(s, 18H, –C(CH3)3), 1.36(s, 18H, –C(CH3)3), 1.54-1.64 (m, 6H, allyl-
CH3), 1.73 (m, 4H, –C2H5CH3), 1.87 (m, 4H, –C2H5CH3), 2.03 (d,
2H, terminal allyl), 3.12 (d, 2H, ArCH2Ar), 3.33 (d, 2H, ArCH2Ar),
3.4–3.7 (m, 4H, ArCH2Ar, 4H, –C2H5CH3, 2H, terminal allyl); 3.8
(m, 2H, –C2H5CH3,1H, terminal allyl), 4.00 (m, 1H, terminal allyl);
4.13 (d, 2H, ArCH2Ar), 4.22 (d, 2H, ArCH2Ar), 4.46 (2d, 1H, ArCH2-
Ar), 4.53 (d, 1H, ArCH2Ar), 4.60 (m, 1H, central allyl); 4.80 (d, 2H,
ArCH2Ar); 4.85 (m, 1H, central allyl); 6.4–6.6 (5 br s, 8H, m-
ArH); 7.1–7.6 (m, 8H, ArH-calix, 8H, ArH-biphenol). Elemental
Anal. Calc. for C66H82O6PPdCl: C, 69.3; H, 7.2. Found: C, 68.9; H,
7.2%.
Appendix A. Supplementary material
CCDC 663232, 663233, 663234 and 663235 contain the supple-
mentary crystallographic data for compounds 5, 6, 3f and 4c. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2008.03.008.
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