A novel hemilabile calix[4],quinoline-based P,N-ligand: Coordination chemistry and complex characterisation

Article abstract of DOI:10.1039/b814469a

The synthesis of the calix[4]arene-based P,N-ligand 3 (5,11,17,23-tetra- tert-butyl-25-[(2-quinolylmethyl)oxy]-26,27,28-(μ₃- phosphorustrioxy)calix[4]arene), in which the nitrogen atom-containing moiety has been introduced at the lower rim of t

Full text of DOI:10.1039/b814469a

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www.rsc.org/dalton | Dalton Transactions
A novel hemilabile calix[4],quinoline-based P,N-ligand: coordination
chemistry and complex characterisation†
Angelica Marson,a Johanneke E. Ernsting,a Martin Lutz,b Anthony L. Spek,b Piet W. N. M. van Leeuwen‡a and
Paul C. J. Kamer*§a
Received 20th August 2008, Accepted 30th September 2008
First published as an Advance Article on the web 18th November 2008
DOI: 10.1039/b814469a
The synthesis of the calix[4]arene-based P,N-ligand 3 (5,11,17,23-tetra-tert-butyl-25-
[(2-quinolylmethyl)oxy]-26,27,28-(m3-phosphorustrioxy)calix[4]arene), in which the nitrogen
atom-containing moiety has been introduced at the lower rim of the cavity prior to P-functionalisation,
is described and its coordination properties investigated. In the crystal structure, the calix[4]-cavity
adopts a cone conformation with an exo orientation of the phosphorus lone pair enabling P-N
15
chelation. 1H, 13C, 31P and 1H{ N} HMQC NMR spectra indicated that, in complexes [PdCl(CH3)(3)]
(4) and [Rh(CO)Cl(3)] (5), ligand 3 coordinates in a chelating fashion, while in cis-[PtCl2(3)2] (6) and
[Rh(acac)(CO)(3)] (7) it behaves as a monodentate ligand, coordinating via the phosphorus atom only.
X-Ray crystal structure determinations were performed for [PdCl(CH3)(3)] (4) and cis-[PtCl2(3)2] (6).
The cationic Pd complex [Pd(CH3)(CH3CN)(3)][PF6] (8) was found to be active in a CO/ethylene
copolymerisation reaction. Good selectivities were observed for the Pd-catalysed allylic alkylation of
cinnamyl acetate with in situ prepared catalysts. [Rh(acac)(CO)2] modified with ligand 3 catalyses the
hydroformylation of 1-octene with low selectivities towards linear aldehydes. High-pressure NMR
experiments on the hydrido carbonyl rhodium(3) were inconclusive, different species were formed.
palladium catalysts the symmetrical diphosphines and dipyridyl
ligands both afford more active catalysts than the mixed pyridyl
phosphine ligands.7
Introduction
In organometallic chemistry, the use of a heteroditopic type ligand
provides several advantages. Such heterofunctionalised systems
are characterised by an intrinsic and electronic dissymmetry. Their
versatility lies mainly in the wide range of catalytic transformations
that can be optimised by varying, for example, the steric and
electronic properties of the two donor atoms and the structure of
the bridge between them. In particular, unsymmetrical bidentates,
which combine nitrogen and phosphorus donor atoms, have
been investigated extensively. When they behave as hemilabile
ligands by reversible dissociation of one arm of the ligand, they
can selectively liberate a coordination site at the metal centre
and thus, favour the formation and stabilisation of intermediate
species. Mixed P,N-chelates have found to be efficient ligands for
important catalytic reactions,1 including hydrogenation,2 allylic
alkylation,3 CO/olefin copolymerisation,4 and the Heck reaction.5
In several cases, due to their specific properties, catalytic activities
and selectivities higher than those observed with diphosphines
or dinitrogen donor ligands have been achieved.6 This cannot
be generalized, as for instance in polyketone formation using
Although many sp2-N donors have been used for the design
of P,N-ligands, less attention has been paid to the variation of
the phosphorus moiety, the great majority of P,N-ligands bearing
diphenylphosphino fragments. This, together with our current
investigations on bulky calixarene-based phosphite ligands,8
prompted us to incorporate calixarene moieties in multifunctional
structures, thus leading to a unique type of P,N-chelate. Pyridine
phosphite ligands9 have been used before in asymmetric allylic
alkylation10 and 1,4-conjugate addition reactions.11
It is well-established that the presence of transition metal
centres bound to calixarene scaffolds may perturb the shape
and the structural properties of such macrocycles leading to
potential shape-selective catalysts.12 Nevertheless, many aspects
of the coordination chemistry of calixarenes still remain to be
explored and, only recently, their potential, especially for transi-
tion metal catalysed reactions, has been recognised. In the last
decade numerous publications appeared dealing with mono- and
bidentate phosphite ligands based on calix[4]- and calix[6]arene
building blocks,8,13 but only in few cases unsymmetrical chelates
have been discussed.9,14
Attracted by such systems we developed the synthesis of the
first heteroditopic P,N-calix[4]arene-modified ligand in which the
properties of a hard and soft donor atom are associated with the
unique structure of the calix[4]arene matrix.
This paper deals with a new P,N-ligand 3 in which the
N-containing moiety has been introduced at the lower rim of
the calix[4]-cavity prior to P-functionalisation and the p-acceptor
aVan ‘t Hoff Institute for Molecular Sciences, University of Amsterdam,
Nieuwe Achtergracht 166, 1018 WV, Amsterdam, The Netherlands
bCrystal and Structural Chemistry, Bijvoet Center for Biomolecular Re-
search, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands
† CCDC reference numbers 699253–699255. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b814469a
‡ Present address: Institute of Chemical Research of Catalonia (ICIQ), Av.
Pa¨ısos Catalans 16, 43007 Tarragona, Spain.
§ Present address: School of Chemistry, University of St Andrews, St.
Andrews, Fife, UK KY16 9ST.
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character of the phosphorus donor centre has been increased by
using a m3-bridging phosphite unit. Note that the latter, when
linked to three proximal phenolic oxygen atoms at the lower
rim of a calix[4]arene cavity, displays the unique air-robustness
and stability previously reported for other calix[4]arene-based
phosphites, thus representing a suitable ligand to be applied in
homogeneous catalysis.6,15 The coordination properties of the P,N-
ligand 3 towards Pd(II), Pt(II) and Rh(I) metal precursors have been
investigated and the resulting complexes structurally characterised
structures in a cone conformation and thus, bidentate ligands with
chelating properties.17 The presence of the quinoline moiety at the
lower rim of the cavity prevents trans annulus inversion and hence
leads, once the product has been formed, to the selective formation
of a potential P,N-chelating system in which the phosphorus atom
and the N-heterocyclic fragment are oriented towards the same
side of the calix[4]arene main plane (defined by the bridging
methylene units ArCH2Ar).
The phosphito, quinoline-based ligand 3 is characterised by
one singlet in the 31P NMR at d = 103.9 ppm (see Table 1).
This value is in accordance with other reported monoalkylated
calix[4]arene monophosphites adopting a so-called up-up-out-
up conformation and characterised by an exo orientation of
the phosphorus lone pair.8a It has been established before that
the phosphorylation reaction performed with PCl3/NEt3 on a
lower rim monofunctionalised calix[4]arene affords quantitatively
and exclusively phosphites in which the phosphorus lone pair is
pointing outwards to the cavity and this can be deduced also from
13C NMR chemical shifts of the methylene groups connecting
each pair of aromatic rings of the cavity (ArCH2Ar). Studies
showed that for syn-arranged ArCH2Ar moieties the 13C NMR
chemical shift of the methylene bridge lies between ca. 29 and
33 ppm, while for an anti arrangement a shift to 37–39 ppm is
observed. Steric effects are believed to be the main cause of such
a large difference.18 For ligand 3, one of these signals appears
in the expected range for syn-oriented phenolic neighbours (at
34.52 ppm), while the other one falls in an intermediate range of
values (at 36.86 ppm). It should be noted that the up-up-out-up
conformation adopted by the calix[4]arene-based phosphite 3 is
the result of the strain imposed by the very short m3-phosphite unit
and thus, the observation of a signal with an intermediate chemical
shift might be interpreted in terms of partial flattening of the
calixarene core.
15
by means of 1H, 13C, 31P and 1H{ N} HMQC NMR spectroscopy
and X-ray diffraction studies. The new hemilabile P,N-chelate
has been evaluated as ligand in the Pd-catalysed CO/ethylene
copolymerisation, in the Pd-catalysed allylic alkylation and in the
Rh-catalysed hydroformylation of 1-octene.
Results and discussion
Synthesis
The calix[4]arene-based P,N-ligand 3 was obtained through a two-
step synthesis starting from p-tert-butylcalix[4]arene 1 (Scheme 1).
The latter was first monofunctionalised at the lower rim by
reaction with 2-(chloromethyl)-quinoline hydrochloride in the
presence of tBuOK as a base. Unfortunately this reaction is
non-selective towards monofunctionalisation and gives rise to the
formation of a distal 1,3-disubstituted calix[4]arene as by-product,
yielding only 15% of product 2. Subsequently, the monoprotected
cone-calix[4]arene 2 was reacted with PCl3 in the presence of NEt3
to give selectively the phosphito,quinoline-based ligand 3 in which
the m3-bridging phosphorus atom is tethered to three neighbouring
phenolic oxygen atoms of the calixarene scaffold.
Both steps are accessible from well-established calixarene alky-
lation and phosphorylation procedures.14,16 The sequence in which
the two steps are conducted is crucial in order to obtain calixarene
Scheme 1 Synthetic route to calix[4],quinoline-based P,N-ligand (3).
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a
Table 1 Selected 31P, 1H and 15N NMR data for transition metal complexes obtained with ligand 3 in CD2Cl2
Compound
d (31P)b
CIS (Dd)c
d (H8)d
CIS (Dd)c
d (15N)e
CIS (Dd)c
Free 3
103.9
85.7
102.6
33.2
105.8
81.4
—
8.03
9.75
10.09
8.23
8.12
9.76
—
–75.3
-110.6
n.d.f
-70.8
-69.8
n.d.f
—
-35.3
—
4.5
5.5
—
[PdCl(CH3)(3)] (4)
[Rh(CO)Cl(3)] (5)
[PtCl2(3)2] (6)
-18.2
-1.3
-70.7
1.9
1.72
2.06
0.20
0.09
1.73
[Rh(acac)(CO)(3)] (7)
[Pd(CH3)(CH3CN)(3)][PF6] (8)
-22.5
a T = 20 ◦C. d in ppm. b Measured at 121.5 MHz. c Coordination Induced Shift = d(complex)–d(ligand). d Measured at 300.1 MHz. e Measured at
30.42 MHz. f Not determined.
The 1H NMR spectrum shows three signals for the But groups
in a 1 : 1 : 2 ratio and two AB patterns for the methylene units
of the calix[4]-scaffold, indicating that in solution the ligand is
Cs symmetric with a mirror plane containing the phosphorus
atom and the quinoline moiety. This is in accordance with the
facile dynamics (up-up-out ↔ out-up-up interconversion) already
evidenced for m3-bridging phosphite moieties, which exchange the
two distal aryl units between an up and an out position.8
cavity determines an up-up-out-up conformation of the calixarene
scaffold with one aryl-OP ring strongly tilted with respect to the
reference plane of the molecule (out refers to the phenol unit
containing O(13); dihedral angle 10.07(5)◦).
Although ligand 3 appears to be C1-symmetric in the solid
state, the structural up-up-out ↔ out-up-up rearrangement dis-
cussed above and previously evidenced by Parlevliet et al. for
m3-bridging phosphite moieties,8a renders the O(11) and O(13)
phenol rings equivalent on the NMR time scale. Furthermore,
the phosphorus and the nitrogen donor atoms are oriented in a
distant conformation in the solid state and hence, rotation of the
quinoline moiety around the Cipso-CH2Ar bond is required to
form chelating complexes.
The resonances for the protons of the quinoline unit were
assigned using HH COSY experiments, while the 15N NMR
15
chemical shift (see Table 1) was obtained via PFG HMQC 1H{ N}
measurements at natural abundance of the 15N isotope (see
Experimental). For ligand 3, a correlation between the 15N nucleus
and the protons of the methylene bridge (ArOCH2-quinoline) was
observed at d = -75.3 ppm. This value is in good agreement with
15N NMR chemical shifts reported in literature for nitrogen donor
ligands based on a phenanthroline skeleton.19
Coordination chemistry
Single crystals of ligand 3 as a CH2Cl2 solvate were grown
from a CH2Cl2/hexane solution. The X-ray crystal structure
(Fig. 1) further corroborates the spectroscopic data reported
above, showing the overall cone conformation of the calix[4]-
scaffold and the exo orientation of the phosphorus lone pair.
Several transition metal precursors have been chosen in order to
study the coordination modes of ligand 3, which may coordinate
in a monodentate fashion, most likely via the phosphorus atom,
or act as an N–P bidentate ligand.20 Because of their many
applications in metal-catalysed transformations, Rh(I) precursors
such as [Rh(CO)2Cl]2 and [Rh(acac)(CO)2], as well as Pd(II)
complexes such as [PdCl2(cod)] and [PdCl(CH3)(cod)],21 and
1
As already deduced from the H, 13C and 31P NMR spectra, the
presence of a short m3-P capping unit at the lower rim of the
Fig. 1 Different views of calix[4]-based P,N-ligand 3 in the crystal. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms and
solvent molecules are omitted for clarity. Only the major conformations of the disordered tbutyl groups are shown.
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[PtCl2(cod)] (acac = acetylacetonato, cod = 1,5-cyclooctadiene)
were chosen as models for the coordination chemistry studies.
All complexes have been isolated and structurally characterised
by NMR spectroscopy, elemental analysis and two of them by
X-ray diffraction analysis.
H8 of the heterocyclic aromatic ring and it is remarkably downfield
shifted with respect to the same signal in the free ligand (CIS =
1.72 ppm; Table 1).
In order to substantiate the coordination of the nitrogen
donor atom to the palladium centre, we carried out 15N NMR
15
Ligand 3 reacts with an equimolar amount of [PdCl(CH3)(cod)]
to form selectively the chelate complex [PdCl(CH3)(3)] (4). The
31P NMR spectrum shows one singlet at d = 85.7 ppm (CIS¶ =
measurements performed by recording PFG HMQC 1H{ N}
spectra at natural abundance of the 15N isotope.
Together with a cross peak between the 15N nucleus and proton
H4 of the quinoline, the correlation with the protons of the methyl
group trans to the N atom (Fig. 4) was also observed, further
corroborating the chelating nature of the P,N-ligand in complex
4. The 15N NMR chemical shift of -110.6 ppm (Table 1) found for
the quinoline fragment falls within the expected range, with a CIS
value of -35.3 ppm similar to previously reported N trans to C
in parent palladium complexes with coordinated nitrogen donor
ligands.19
1
-18.2 ppm) and in the H NMR the methyl group Pd-CH3 is
3
characterised by one doublet at d = 0.90 ppm with J(P,H) =
3.0 Hz, in keeping with the presence of only one phosphorus
ligand in cis position. The resonances for the methylene bridges
of the calix[4]arene cavity (ArCH2Ar) appear as two broad signals
at room temperature. This indicates that the activation energy for
the fluxional process involving the aryl fragments increases upon
complexation, due to the loss of mobility of the calix[4]-moiety.
Cooling a sample of palladium complex 4 to T = -20 ◦C resulted
in a resolved 1H NMR spectrum which allowed a clear attribution
of four distinct AB patterns for the ArCH2Ar of the cavity and
one AB pattern for the ArOCH2-quinoline bridge (Fig. 2).
The crystal structure depicted in Fig. 5 proves the mononuclear
structure of 4 and shows that the calixarene core adopts an up-up-
out-up cone conformation [‘out’ refers to the phenol ring bearing
O(3); dihedral angle ca. 12.42(7)◦].
COSY experiments were performed in order to assign the
resonances of the quinoline unit, which are well separated at
20 C. Fig. 3 shows for comparison the aromatic regions of the
1H NMR spectra for the free 3 and the coordinated P,N-ligand
in the palladium complex 4. It should be noted that the low-field
resonance (d = 9.75 ppm) corresponds to the doublet assigned to
All metal–ligand bond distances fall in the expected range of
values (Table 2) but, as frequently observed in chelate complexes,
the palladium geometry deviates somewhat from an ideal square
plane. Thus, the larger P(1)–Pd(1)–N(1) angle (97.88(5)◦) reflects
the strain imposed on the rigid 12-membered P,N-chelate ring by
the coordination of the quinoline fragment to the metal centre. In
fact, the Pd–N bond formation forces the quinoline plane to be
perpendicular to the coordination plane, inducing an increased
◦
¶ Coordination Induced Shift = d(complex) - d(ligand)
Fig. 2 Low temperature 1H NMR experiments performed with [PdCl(CH3)(3)] (4) (CD2Cl2; * = CH2 groups of the calix[4]-cavity (ArCH2Ar), D = CH2
groups of the bridging unit (ArOCH2-quinoline)).
Fig. 3 Quinoline region of the 1H NMR spectrum for the free ligand (3) (above) and complex [PdCl(CH3)(3)] (4) (below) (CD2Cl2, T = 20 ◦C).
624 | Dalton Trans., 2009, 621–633
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22
Table 2 Selected bond lengths and angles for [PdCl(CH3)(3)] (4)
˚
structures) of ca. 1.8–2.2 A, Albinati et al. have suggested a
much weaker variation of this interaction for a series of trans-
˚
Bond lengths (A)
Bond angles (◦)
=
[PtCl2R(L)] complexes (R = PR3, AsR3, C2H4, PhCH CH2;
L = nitrogen donor ligand) containing coordinated nitrogen donor
Pd(1)–P(1)
Pd(1)–N(1)
Pd(1)–Cl(1)
Pd(1)–C(55)
P(1)–O(1)
P(1)–O(2)
P(1)–O(3)
2.1892(6)
2.2237(19)
2.3534(6)
2.075(2)
1.5819(16)
1.6049(17)
1.6185(17)
P(1)–Pd(1)–N(1)
Cl(1)–Pd(1)–N(1)
C(55)–Pd(1)–P(1)
C(55)–Pd(1)–Cl(1)
Pd(1)–P(1)–O(1)
Pd(1)–P(1)–O(2)
Pd(1)–P(1)–O(3)
O(1)–P(1)–O(2)
O(1)–P(1)–O(3)
O(2)–P(1)–O(3)
96.88(5)
89.08(5)
86.08(6)
ligands.23 These molecules revealed downfield 1H NMR shifts24 but
˚
larger H ◊ ◊ ◊ Pt separations of ca. 2.3–2.9 A, as typical values for
88.01(6)
this type of interaction. The ligands were specifically chosen so that
one or more C–H bonds would be situated above the coordination
plane defined by the Pt atom, the P atom and the two Cl atoms, and
have restricted motional freedom due to built-in rigidity and/or
bulky substituents on the nitrogen donor ligand, which increase
the energy barrier for rotation about the Pt–N bond.
110.97(6)
111.63(6)
121.62(6)
105.77(9)
103.02(9)
102.38(8)
Addition of ligand 3 to 0.5 equivalents of [Rh(CO)2Cl]2 resulted
in the formation of the mononuclear chelate species [Rh(CO)Cl(3)]
(5), as suggested by the spectroscopic data similar to those
observed for [PdCl(CH3)(3)] (4). The structure of complex 5 is
supported both by the 31P NMR spectrum, showing a doublet
1
at d = 102.6 ppm with J(P,Rh) = 307 Hz and by the n(CO)
frequency in the IR spectrum at 2012 cm-1. These values are
in good agreement with other reported square planar chelate
Rh(I) complexes [Rh(CO)Cl(PŸN)] containing cis coordinated
P,N-ligands.25 Analogous to the Pd(II) complex 4, a large downfield
shift for the resonance of H8 of the quinoline is observed in
the 1H NMR spectrum (CIS = 2.06 ppm; Table 1). Again,
this NMR evidence may be attributed to the presence of a
weak interaction M←H–C as a result of proton H8 approaching
the metal centre in a pseudoaxial position. Furthermore, the
broadening of the ArCH2Ar and the ArOCH2-quinoline signals,
observed also for 4, indicates that the P,N-ligand acts as a bidentate
ligand and upon coordination, through both the phosphorus
and the nitrogen atoms, generates a rigid structure with limited
flexibility. Similarly, the singlet found for the free ligand at d =
5.51 ppm, which was assigned to the methylene bridge (ArOCH2-
quinoline), splits into two broad signals of two non-equivalent
protons, further corroborating the increased rigidity of the P,N-
ligand induced by the coordination of the quinoline fragment to
the metal centre.
Fig. 4 1H,15N PFG HMQC spectrum of complex [PdCl(CH3)(3)] (4)
recorded at natural abundance of 15N (CD2Cl2, T = 20 ◦C).
distortion of the calixarene shape as revealed by the strong
inclination of the O(4) phenol plane with respect to the calixarene
reference plane, defined by the bridging methylene units (dihedral
angle ca. 74.70(8)◦ for O(4) vs. 61.58(8)◦ for the O(2) phenol plane).
Furthermore, the particular orientation of the quinoline moiety
favours the approach of proton H8 to the palladium centre, with
8
˚
a resulting H ◊ ◊ ◊ Pd distance of 2.66 A. This evidence, together
with the large downfield 1H NMR shift of 1.72 ppm observed for
this proton (vide supra), suggests the presence in complex 4 of a
weak M←H–C interaction.
Low temperature NMR experiments performed for
[Rh(CO)Cl(3)] (5) showed that the fluxional process in which the
aryl rings of the cavity are involved can be halted at T = 0 ◦C. At
this temperature de-coalescence is reached and the 1H NMR
spectrum again shows five AB patterns, which can be assigned to
In addition to the so-called ‘agostic interaction’, which shows
high-field 1H NMR shifts and H ◊ ◊ ◊ M separations (X-ray crystal
Fig. 5 Different views of the chelate complex [PdCl(CH3)(3)] 4 in the crystal. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen
atoms and solvent molecules are omitted for clarity. Only the major conformation of the disordered tbutyl group is shown.
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Table 3 Selected bond lengths and angles for [PtCl2(3)2] (6)
the bridging ArCH2Ar and the ArOCH2-quinoline protons (see
Experimental).
˚
Bond lengths (A)
Bond angles (◦)
Mixing the Pt(II) precursor with two equivalents of 3 leads to
the formation of complex [PtCl2(3)2] (6). The 31P NMR spectrum
Pt(1)–P(1)
Pt(1)–P(2)
Pt(1)–Cl(1)
Pt(1)–Cl(2)
P(1)–O(11)
P(1)–O(12)
P(1)–O(13)
P(2)–O(21)
P(2)–O(22)
P(2)–O(23)
2.210(2)
2.215(2)
2.3387(19)
2.3420(19)
1.577(6)
1.599(6)
1.569(5)
1.596(5)
1.601(6)
1.580(6)
P(1)–Pt(1)–P(2)
95.25(7)
89.92(7)
87.34(7)
87.79(7)
119.6(2)
108.1(2)
113.0(2)
105.1(3)
107.2(3)
103.1(3)
120.1(2)
108.8(2)
112.3(2)
105.0(3)
106.9(3)
102.9(3)
1
shows one singlet with Pt satellites (d = 33.2 ppm, J(Pt, P) =
P(2)–Pt(1)–Cl(2)
Cl(2)–Pt(1)–Cl(1)
Cl(1)–Pt(1)–P(1)
Pt(1)–P(1)–O(11)
Pt(1)–P(1)–O(12)
Pt(1)–P(1)–O(13)
O(11)–P(1)–O(12)
O(12)–P(1)–O(13)
O(11)–P(1)–O(13)
Pt(1)–P(2)–O(21)
Pt(1)–P(2)–O(22)
Pt(1)–P(2)–O(23)
O(21)–P(2)–O(22)
O(22)–P(2)–O(23)
O(21)–P(2)–O(23)
6833 Hz) indicating coordination of the phosphite moiety to
the metal centre. The magnitude of the Pt–P coupling constant,
nearly identical to values reported for other cis-[PtCl2(phosphite)2]
complexes containing calix[4]-based phosphites, suggests the for-
mation of a species with two phosphorus atoms coordinated in a
cis-position.14,15 In contrast to the previous examples, the signal
of H8 in the quinoline unit is only slightly shifted compared to
the free ligand (Table 1) and no broadening of the signals for the
methylene bridges of the calix[4]arene cavity is observed and most
likely 3 is acting as a monodentate ligand.
15
The PFG 1H{ N}-HMQC NMR spectrum recorded for com-
plex 6 evidenced a 15N chemical shift of d = -70.8 ppm as a result
of two correlations: one between the 15N nucleus and the bridging
ArOCH2-quinoline and a second one between the 15N nucleus
and proton H3 of the quinoline unit. The observed 15N chemical
shift of complex 6 is almost identical to the one reported for the
free ligand, thus a negligible CIS value was obtained in this case
upon coordination (Table 1). This, together with the other NMR
data, supports the fact that in complex 6 the N-containing unit
behaves as non-coordinating pendant arm. Furthermore, the two
AB patterns typical of the ArCH2Ar in the free ligand, split
into four AB patterns once 6 is formed, indicating that upon
complexation the calix[4]arene fragment is no longer Cs-symmetric
on the NMR time scale. The high steric crowding resulting from
the cis coordination of the two calix[4]-based phosphite moieties
prevents the rotation of the backbone through the Pt–P bond.
The equivalence of the two phosphorus atoms, indicated by the
31P NMR, may be due to the presence of a two-fold axis, as found
in the X-ray structure (vide infra).
The nature of complex [PtCl2(3)2] was further corroborated
by X-ray crystal structure determination carried out on single
crystals obtained from a CH2Cl2/CH3CN solution of 6 (Fig. 6).
The platinum centre has, as expected, a planar coordination
environment and the Pt–P bond lengths (Table 3) are compa-
rable to those found in other [PtCl2(phosphite)2] complexes.14,26
Analogous to complex 4 reported above, in complex 6 both
calix[4]arene cores adopt an up-up-out-up cone conformation [‘out’
refers to the phenol rings bearing O(11) and O(21); dihedral angles
23.6(3)◦ and 16.6(3)◦, respectively] with an out phenol ring whose
orientation approaches that of the calixarene reference plane. The
large P(1)–Pt(1)–P(2) angle of 95.25(7)◦ clearly reflects the high
steric crowding generated by the two calix[4]arene frameworks
when cis-coordinated. Due to the spatial expansion of each ligand,
particularly important when considering the region containing the
quinoline pendent arm, the rotation of one particular phosphite
around its Pt–P axis is hindered by the neighbouring phosphite
ligand.
Fig. 6 Complex cis-[PtCl2(3)2] 6 in the crystal. Displacement ellipsoids
are drawn at the 50% probability level. tButyl groups, hydrogen atoms and
solvent molecules are omitted for clarity.
(ArCH2Ar) indicates that, upon complexation, ligand 3 retains its
Cs symmetry. This suggests that only one P,N-ligand is coordinated
to the rhodium centre giving rise to the formation of complex
[Rh(acac)(CO)(3)] (7), in which the steric congestion derived from
the presence of only one bulky calixarene scaffold still allows free
rotation of the phosphite moiety around the Rh–P bond. The
monodentate coordination of ligand 3 in complex 7 was inferred
by the presence of the n(CO) frequency in the IR spectrum at
2002 cm-1 and the slight shift of the signal of proton H8 of the
quinoline compared to the signal in the free ligand (Table 1). This
When [Rh(acac)(CO)2] is treated with one equivalent of P,N-
ligand 3 in dichloromethane, the 31P NMR spectrum of the reac-
tion mixture shows a doublet at d = 105.8 ppm with a rhodium–
phosphorus coupling constant 1J(P,Rh) of 311 Hz, which is
similar to values reported for analogous rhodium complexes
with coordinated phosphites.14 The presence, in the 1H NMR
spectrum, of two AB patterns for the methylene bridging units
1
15
was further corroborated by the PFG H{ N}-HMQC NMR
spectrum, which showed a 15N NMR chemical shift of -69.8 ppm
with negligible CIS value (Table 1), resulting from one correlation
of the 15N nucleus with the methylene bridge ArOCH2-quinoline
and a second correlation with proton H3 of the quinoline moiety.
626 | Dalton Trans., 2009, 621–633
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Catalytic investigations
neither case formation of palladium metal, resulting from catalyst
decomposition, was observed.
The calix[4]-based P,N-ligand 3 was employed in three dif-
ferent metal-catalysed transformations: the palladium-catalysed
CO/olefin co- and terpolymerisation, the palladium-catalysed
allylic alkylation of cinnamyl ester and the rhodium-catalysed
hydroformylation of 1-octene.
CO/styrene copolymerisation experiments performed with
complex 8 did not lead to product formation. This corrobo-
rates the general observation that, apart from a few exceptions,
nitrogen-donor ligands are the ligands of choice for obtaining
CO/vinylarene copolymers in high yields and with high molecular
weight values.30 Attempts were also undertaken to perform
CO/ethylene/styrene terpolymerisation reactions, but no product
was obtained.
CO/ethylene copolymerisation
In the early 1990s several groups and chemical companies
reported on the palladium-catalysed alternating copolymerisation
of olefins with carbon monoxide to yield copolymers with very
attractive physical properties.27 Catalysts are usually of the type
[Pd(solvent)2(L)]2+ or [Pd(CH3)(solvent)(L)]+ where L is a diphos-
phine, a bipyridine or diimine ligand, but interest in searching for
new catalysts with unsymmetrical bidentate ligands has also been
To the best of our knowledge, ligand 3 is the first phosphito-
based P,N-ligand to find successful application in the copoly-
merisation of CO/ethylene under mild conditions, albeit with low
activity.
Allylic alkylation of cinnamyl ester
increasing, particularly with P,N-ligands.[4,7
Transition metal-catalysed allylic alkylation is a useful tool in
synthetic organic chemistry. In many cases, palladium-based
catalysts are the systems of choice and thus, the most widely
studied. When substrates giving symmetrical substituted Pd(allyl)
complexes are used (cyclopent-2-enyl acetate or 1,3-diphenylprop-
2-enyl 1-acetate), high enantioselectivities can be obtained. When
other types of allylic substrates are used, such as crotyl acetate
or cinnamyl acetate, non–symmetrical substituted Pd(allyl) com-
plexes are formed and regiocontrol becomes an issue prior to
enantiocontrol. Three products can be formed: the achiral (E)
and (Z) linear products and the chiral branched product, which
is the product of interest for applications in asymmetric synthesis
(Scheme 2).
]
Phosphite ligands have not found wide application in the
CO/olefin copolymerisation reaction, the limitation of their
use being mainly due to two reasons: (i) phosphites promote
side reactions to palladium(0) complexes and thus, decrease
the concentration of the active catalyst in the reaction mixture,
(ii) phosphites are sensitive to alcoholysis, and the use of methanol,
the solvent in industrial CO/ethylene copolymerisation, leads
to decomposition. To avoid this problem, the catalysis can be
performed in dichloromethane or other non-protic solvents.28
Nozaki et al. have studied the use of a bisnaphthol-based
diphosphite in CO/propene copolymerisation, but no polymer
was obtained.28b Only when the calix[6]arene-based diphosphite
reported by Parlevliet et al. was employed, was the corresponding
cationic palladium complex found to be active in the palladium-
catalysed CO/ethylene copolymerisation reaction.8b
As higher activities are obtained when weakly coordi-
nating anions29 are used, the catalyst precursor [Pd(CH3)-
(CH3CN)(3)][PF6] (8) was chosen as the catalyst. It was syn-
thesized by chloride abstraction using AgPF6 in a coordinating
solvent such as acetonitrile. Complex 8 was isolated prior to
use and characterised by NMR spectroscopy. The broad signals
Scheme 2 Regioselectivity in the palladium-catalysed allylic alkylation of
cinnamyl acetate.
1
displayed in the H NMR spectrum for the bridging methylene
groups ArCH2Ar and ArOCH2-quinoline, and the low-field shift
(CIS = 1.73 ppm; Table 1) observed for proton H8 of the
quinoline unit, are indicative of the chelating nature of complex
8, in which the P,N-ligand is coordinated via both the phosphorus
and the nitrogen atoms (see Experimental). Furthermore, the
Although palladium complexes have a preference for the
formation of the linear achiral product, it was recently shown
that, in combination with P,N-ligands, they can also direct the
regioselectivity towards the preferential formation of the branched
product with excellent enantioselectivities.31
Ligand 3 was used in the palladium-catalysed allylic alkyla-
tion of cinnamyl acetate using diethyl 2-methylmalonate as a
nucleophile. The catalyst precursor was formed in situ by mixing
[Pd(allyl)Cl]2 with two equivalents of ligand 3 in THF solution
under an inert atmosphere. Subsequently, the substrate and the
internal standard (decane) were added and the reaction started
upon addition of the nucleophile to the mixture.
Quantitative conversion was reached after 20 h reaction time
providing only two products: the linear (E) and the branched
product. The linear cis product was not observed under the
employed reaction conditions. Similarly to other P,N-ligands
reported in literature, ligand 3 shows a preference for the trans
species, affording a product distribution of 44% for the branched
1
singlet found in the H NMR at d = 2.02 ppm corroborates the
presence of acetonitrile in the coordination sphere of the palladium
centre.4a
Complex [Pd(CH3)(CH3CN)(3)][PF6] (8) was tested in the
CO/ethylene copolymerisation reaction that was performed in
dichloromethane, in the presence of 1,4-benzoquinone and at
the pressure of 30 bar (p(CO)/p(ethylene) = 1). An appreciable
amount of copolymer, corresponding to a productivity of 17 g of
copolymer per gram of palladium, could be isolated. The polymer
structure was confirmed by the 13C NMR spectrum, which showed
the characteristic signals for the carbonyl and methylene groups.
Catalytic runs performed with varying CO/ethylene pressure,
indicated that a minimum pressure of 30 bar is required to obtain
copolymer in isolable amounts. It is important to mention that in
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and 56% for linear (E) product. The observed regioselectivity is
in the range of values reported for chiral P,N-ligands used in
asymmetric allylic alkylation but superior to achiral P,N-ligands.30c
with the characteristic multiplicity displayed by the hydride signal,
suggests that two calix[4]-based P,N-ligands are coordinated to the
rhodium centre through the phosphorus atoms, both equatorially
positioned, generating [HRh(3)2(CO)2] (9). A second doublet,
found at higher fields (d = 97.9 ppm), showed a rhodium–
phosphorus coupling constant 1J(Rh,P) = 225 Hz, which could be
attributed to monohydrido species [HRh(3)(CO)3] (10), in which
only one P,N-ligand is coordinated to the rhodium centre. The
hydride region of the 1H NMR spectrum showed for this complex
a weak broad singlet at d = -9.87 ppm, as a result of small
phosphorus–hydride 2J(H,P) and rhodium–hydride 1J(H,Rh)
coupling constants, which could not be resolved completely.
This indicates that, in the trigonal bipyramidal structure, the
rhodium centre has an apical hydride with a phosphite moiety
cis-positioned, thus suggesting the equatorial coordination of
ligand 3. In this species, 3 is considered to behave most likely
as a monodentate ligand, coordinating exclusively through the
phosphorus atom, but at this stage of investigation the formation
of chelates, in which 3 acts as a bidentate ligand, cannot be
discarded a priori.
Species 9 and 10 are the only hydrides present in solution since
no additional hydrides are visible in the 1H NMR spectrum.
The third signal at d = 117.5 ppm, which is characterised by a
second-order multiplicity, could be resolved at 0 ◦C. The pattern
of signals obtained, consistent with an AA’XX’ spin system,
could be satisfactorily simulated leading to the coupling constants:
1J(Rh,P) = 277 Hz, 2J(Rh,P) = 15 Hz and 3J(P,P) = 18 Hz (Fig. 7).
The values found for 1J(Rh,P) are similar to those reported
for rhodium(0) dimers containing diphosphite ligands.34,35 Hence,
we assume that the compound at d = 117.5 ppm corresponds
to a Rh(0) dimeric species which can be formulated as [Rh(m-
CO)(CO)2(3)]2 (11a) or [Rh(m-CO)(CO)(3)2]2 (11b).
Hydroformylation of 1-octene
The catalyst precursor was formed in situ by mixing three
equivalents of ligand 3 with [Rh(acac)(CO)2] in toluene solution
under an inert atmosphere. Experiments were run by means of
a semiautomated autoclave (AMTEC SPR16, see Experimental)
equipped with sixteen independent reactors and an automated
sampling under reaction conditions. After 2 h reaction time, full
conversion of 1-octene was reached, affording a linear/branched
ratio of 1.432 and isomerisation of about 13%. The correspond-
ing activity (turnover frequency (TOF) = (mol aldehyde) · (mol
Rh)-1 · h-1), determined at ca. 30% conversion, was 650 which
is much lower than the activities reported for calix[4]arene-
based monophosphite ligands.8a It should be recalled that the
heterofunctionalised P,O-ligands reported by Steyer et al. have
also found to be less active than the parent monoalkylated calix[4]-
monophosphites reported by Parlevliet et al.14
In the present work, bidentate coordination of ligand 3 and
formation of chelate complexes have been observed and unam-
biguously demonstrated for Pd(II) and Rh(I) metal precursors and
thus, cannot be discarded even when discussing the coordination
mode of 3 under catalytic conditions. Additionally, the low
selectivity obtained in the catalytic experiment might be attributed
to the hemilabile nature of the P,N-ligand 3 and to the possible
formation of different rhodium species in solution in which 3
coordinates in a monodentate fashion or acts as a chelating system.
High-pressure (HP) NMR studies
High-pressure NMR experiments have been carried out to inves-
tigate the composition of the catalyst solution in the rhodium-
catalysed hydroformylation of olefins and elucidate the coordina-
tion mode of the P,N-ligand 3 under syngas pressure. The complex-
ation reaction was studied in situ upon addition of two equivalents
of ligand 3 to a toluene solution of the [Rh(acac)(CO)2] precursor
and then by pressurising the NMR tube with 20 bar of syngas
(CO/H2 1:1). The 31P NMR of the mixture, recorded at room
temperature under argon, displayed one singlet corresponding to
the free ligand (d = 104.3 ppm) and one doublet at d = 104.7 ppm
1
with J(Rh,P) = 217 Hz in a 1:1 ratio. This, together with the
spectroscopic data previously discussed, indicates the formation
of the species [Rh(acac)(CO)(3)] (7), in which the P,N-ligand 3 is
coordinated to the rhodium centre exclusively via the phosphorus
atom. The solution was then pressurised with 20 bar of syngas and
subjected to 5 h activation period at 40 ◦C. The reaction was found
to proceed unselectively. Thus, the resulting 31P NMR spectrum
showed several signals corresponding to the presence of at least
four different rhodium complexes in solution.
1
The doublet at d = 127.8 ppm with J(Rh,P) = 240 Hz and
1
Fig. 7 31P{ H} NMR spectra of species 11: (A) experimental (toluene-d8,
the broad double triplet in the hydride region (d = -9.58 ppm) of
1
T = 0 ◦C); (B) simulated for a AA‘XX’ system.
the H NMR proved the formation of a rhodium hydride com-
plex with two equivalent phosphorus atoms. Hydride complexes
[HRh(diphosphite)(CO)2] generated in the presence of chelating
diphosphites, bisequatorially coordinated to the rhodium centre,
have been found to display similar 1J(Rh,P) values.33 This, together
Analysis of chemical shifts and coupling constants allowed
the attribution of all the resonances displayed in the 31P NMR
spectrum, with the exception of a complex pattern of signals
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found at d = 111 ppm, which could not be resolved even at low
temperature. Due to the spectroscopic similarities displayed in
HP NMR experiments performed with DIOP-based P,N-ligands
reported by Aghmiz et al.,36 we might attribute these signals
to dimeric rhodium species formulated as [(PŸN)2(CO)Rh(m-
CO)2Rh(CO)(PŸN)].
calix[4]arene backbone. The 15N NMR spectra were recorded
using the PFG HMQC (Pulse Field Gradient Heteronuclear
Multiple-Quantum Correlation) sequence in a Bruker DRX-
300 equipped with a 5 mm triple resonance inverse probe with
z-gradient, operating at 30.42 MHz 15N frequency and a second
300 W X decoupler giving a 90◦ 15N pulse of 10 ms.19c Chemical
shifts were referenced to external nitromethane = 0 ppm, nega-
tive chemical shifts are reported for lower frequencies. Gas chro-
matographic analysis were performed on a Shimadzu GC-17A
apparatus (split/splitless, equipped with a FID detector and a
DB-1 column, internal diameter of 0.32 mm, film thickness 3 mm,
carrier gas 80 kPa He). Elemental analyses data were performed
at the H. Kolbe Mikroanalytisches Laboratorium in Mu¨lheim
(Germany).
Conclusions
We have described the synthesis of the first hybrid P,N-
ligand based on a calix[4]arene platform. Due to the cone
conformation of the calixarene cavity, the bidentate P,N-ligand
becomes a potential chelating system. In the presence of
[PdCl(CH3)(cod)] and [Rh(CO)2Cl]2 metal precursors, it readily
forms 12-membered chelate P,N-rings, while with [PtCl2(cod)]
and with [Rh(acac)(CO)2] shows monodentate coordination ex-
clusively via the phosphorus atom, affording a 2:1 and a 1:1
complex, respectively. The nature of these species was confirmed
by 1H, 31P and 15N NMR spectroscopy and X-ray crystal structure
determination. Interestingly, due to the particular orientation
of the quinoline moiety in the chelate complexes, a detectable
weak M←H–C interaction was observed, which was supported
by downfield 1H shifts and crystallographic H ◊ ◊ ◊ M separation.
P,N-ligands have not been widely studied in the hydroformy-
lation of olefins and not many investigations have been carried
out to elucidate their coordination mode under syngas pressure.
Coordination of a pyridyl group to a rhodium hydrido carbonyl
may be interesting for photochemical activation of the catalyst, but
so far no indications have been found that such species form. We
tested the new P,N-ligand in three metal catalysed transformations.
Under the employed reaction conditions, poor activities were
obtained in the palladium-catalysed CO/ethylene copolymerisa-
tion, while good regioselectivities towards the branched product
were observed in the palladium-catalysed allylic alkylation of
cinnamyl acetate. When employed in the rhodium-catalysed
hydroformylation of 1-octene, ligand 3 showed low activities and
very poor selectivities towards linear aldehydes. Most likely, if P–
N coordinated species are formed, they are not carbonyl hydrides
and inactive as hydroformylation catalysts.
Catalytic experiments
CO/ethylene copolymerisation experiments. CO/olefins
copolymerisation reactions were performed in
a stainless
steel autoclave equipped with a temperature controller and
a mechanical stirrer. In a typical CO/ethylene copolymeri-
sation experiment, dichloromethane (50 ml), 1,4-benzoquinone
([BQ]/[Pd] = 40) and the catalyst (12.7 mmol of [Pd(CH3)-
(CH3CN)(3)][PF6] (8)) were introduced in an autoclave that was
purged with 30 bar of CO/ethylene (p(CO)/p(ethylene) = 1)
for 10 min. The autoclave was then closed, charged with 30 bar
of CO/ethylene and heated to 50 ◦C. After 24 h, the autoclave
was cooled to room temperature, the pressure was released and
the reaction mixture was poured into methanol, affording the
precipitation of a white solid that was filtered, washed with
methanol and dried under vacuum.
Allylic alkylation reaction. The alkylation experiments were
performed at room temperature (20 ◦C) in THF (10 ml), using
0.1 mol% of catalyst prepared in situ (0.5 mmol of [Pd(allyl)Cl]2 and
1 mmol of P,N-ligand 3 in THF under stirring for 30 min), 1 mmol
of cinnamyl acetate as substrate and 2 mmol of sodium diethyl
2-methymalonate as nucleophile. The reaction was monitored by
taking samples which, after aqueous work up, were analysed by
GC using decane as the internal standard.
Hydroformylation reaction. The hydroformylation experi-
ments were performed in a semiautomated autoclave (AMTEC –
Slurry Phase Reactor – SPR16) equipped with sixteen stainless
steel 15 ml reactors and an automated sampling under reaction
conditions. All reactors are connected via a valve system with
gas and liquid supply and equipped with individually adjustable
stirring (magnetic stirrer bars – 500 to 2000 rpm) and heating
(external electrical heating jacket, up to 220 ◦C).
In a typical run, the autoclave was charged with 5 ml of a
1.8 mM toluene solution of [Rh(acac)(CO)2] and 3 eq of ligand
(0.043 mmol). Once closed, the autoclaves were purged with 30 bar
of syngas (CO/H2 1:1 v/v) five times at 90 ◦C and five times
at 30 ◦C, then pressurised with 10 bar of syngas and heated
for 3 h at 80 ◦C to preform the catalysts. After releasing the
pressure, 3 ml of a stock solution (internal standard (decane,
1.5 ml, 7.75 mmol), substrate (1-octene, 7.5 ml, 0.048 mol) and
toluene (6.0 ml)) were added to the catalyst mixtures and the total
pressure raised to 20 bar (stirring rate 1000 rpm). Progress of the
reaction was checked by monitoring the pressure decrease. During
Experimental
General considerations
Unless otherwise stated, all preparations were carried out under
an inert atmosphere of argon using standard Schlenk techniques.
Materials were obtained from commercial suppliers and used with-
out further purification. Solvents were dried over suitable reagents
and freshly distilled under nitrogen prior to use. Calix[4]arene-
based P,N-ligand (3) was obtained in pure form by prepara-
tive, centrifugally accelerated, radial, thin layer chromatography
R
(Chromatotronꢀ, Harrison Research, model 7924T). Routine 1H,
1
1
13C{ H} and 31P{ H} NMR spectra were recorded on Varian
Mercury 300 and Bruker DRX-300 spectrometers (300.1 MHz
for 1H NMR, 75.5 MHz for 13C{ H} NMR and 121.5 MHz
1
1
for 31P{ H}). The deuterated solvents used are indicated in the
experimental part; shifts are given, relative to TMS (1H, 13C)
and 85% H3PO4 (31P). The nomenclature ‘m-H’ specifically refers
to aromatic protons in meta position on phenolic rings of the
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the experiments, several samples were taken, which were diluted
with toluene and analysed by GC.
(s, C(CH3)), 31.64 (s, C(CH3)), 34.34 (s, C(CH3)), 34.52 (s,
ArCH2Ar), 34.62 (s, C(CH3)), 34.72 (s, C(CH3)), 36.86 (s,
ArCH2Ar), 78.95 (s, ArOCH2-quinoline), 120.59–137.13 and
High-pressure NMR experiments. High-pressure NMR ex-
periments were performed in a 10 mm outer diameter/8 mm
inner diameter sapphire tube glued into a Ti (6A1–4V) alloy
pressure head, which allows measurements up to 140 bar.37 In
a typical experiment, 10 mg (0.039 mmol) of [Rh(acac)(CO)2]
and 63.41 mg (0.077 mmol) of P,N-ligand 3 were dissolved in
2.0 ml of toluene-d8 under argon atmosphere. The solution was
then transferred, via cannula, to the NMR tube which was purged
three times with 10 bar syngas (CO/H2 1:1), pressurised to 20 bar
and incubate at 40 ◦C. Spectroscopic measurements were then
performed at variable temperature on a Bruker Avance DRX-
300 MHz. Samples in the high-pressure NMR tube could not be
spun during measurements as a consequence of technical set-up
of the NMR spectrometer.
1
145.29–158.80 (aryl C). 31P{ H} NMR (121.5 MHz, CD2Cl2,
293 K): d = 103.9 (s, P(OAr)3).
cis-Chloromethyl-{5,11,17,23-tetra-tert-butyl-25-[(2-quinolyl-
methyl)oxy]-26,27,28-(l3 -phosphorustrioxy)calix[4]arene}-palla-
dium(II) (4). Ligand 3 (200 mg, 0.24 mmol) was added to a
solution of [PdCl(CH3)(cod)]21b (64.8 mg, 0.24 mmol) in dry
CH2Cl2 (3 ml). After stirring for 30 min at room temperature,
the solution was concentrated under vacuum and the product
precipitated as a white solid by addition of diethyl ether and
◦
1
cooling to -20 C. Yield: 181 mg, 0.19 mmol (76%). H NMR
3
(300 MHz, CD2Cl2, 253 K): d = 0.79 (d, J = 1.59 Hz, 3H; Pd-
CH3), 1.09 (s, 9H; C(CH3)3), 1.11 (s, 9H; C(CH3)3), 1.16 (s, 9H;
C(CH3)3), 1.32 (s, 9H; C(CH3)3), 3.09 and 3.38 (AB q, 2J = 12.5 Hz,
2H; ArCH2Ar), 3.31 and 4.26 (AB q, 2J = 13.3 Hz, 2H; ArCH2Ar),
3.64 and 4.56 (AB q, 2J = 15.1 Hz, 2H; ArCH2Ar), 3.77 and 5.18
Syntheses
2
2
(AB q, J = 14.2 Hz, 2H; ArCH2Ar), 4.86 and 6.18 (AB q, J =
13.8 Hz, 2H; ArOCH2-quinoline), 6.86 (bd, 1H; m-ArH), 6.93 (bd,
1H; m-ArH), 7.03 (bd, 2H; m-ArH), 7.10 (bd, 1H; m-ArH), 7.12
(s, 2H; m-ArH), 7.28 (bd, 1H; m-ArH), 7.42 (d, 2J = 8.3 Hz, 1H;
quinoline-H3), 7.61 (t, 2J = 7.4 Hz, 1H; quinoline-H6), 7.88 (d, 2J =
7.9 Hz, 1H; quinoline-H5), 7.92 (t,2J = 8.4 Hz, 1H; quinoline-H7),
8.29 (d, 2J = 8.3 Hz, 1H; quinoline-H4), 9.75 (d, 2J = 8.6 Hz, 1H;
5,11,17,23-tetra-tert-butyl-25-[(2-quinolylmethyl)oxy]-26,27,28-
trihydroxycalix[4]arene (2). p-tert-butyl-calix[4]arene (1) (5.00 g,
7.7 mmol) and 2-(chloromethyl)-quinoline hydrochloride (3.30 g,
15.4 mmol) were refluxed in dry toluene (250 ml) for about 20 h in
the presence of tBuOK (3.46 g, 30.8 mmol) as a base. The reaction
mixture was then partitioned between water and CHCl3 and the
organic layer washed twice with water and dried over Na2SO4.
After evaporation of the solvent to dryness the crude product was
purified by column chromatography (CH2Cl2/pentane/AcOEt
eluent).Yield: 0.91 g, 1.15 mmol (15%). 1H NMR (300 MHz,
CDCl3, 293 K): d = 1.23 (s, 36H; C(CH3)3), 3.45 and 4.30 (AB
q, 2J = 13.7 Hz, 4H; ArCH2Ar), 3.45 and 4.65 (AB q, 2J =
13.2 Hz, 4H; ArCH2Ar), 5.54 (s, 2H; ArOCH2quinoline), 7.0 (s,
2H; m-ArH), 7.07 (s, 2H; m-ArH), 7.10 (s, 2H; m-ArH), 7.14 (s,
2H; m-ArH), 7.60 (t, 2J = 7.8 Hz, 1H; quinoline-H), 7.77 (t, 2J =
7.8 Hz, 1H; quinoline-H), 7.91 (d, 2J = 7.2 Hz, 1H; quinoline-H),
8.26 (d, 2J = 8.4 Hz, 1H; quinoline-H), 8.36 (d, 2J = 9.0 Hz, 1H;
quinoline-H), 9.94 (bs, 3H; OH).
quinoline-H8). 31P{ H} NMR (121.5 MHz, CD2Cl2, 293 K): d =
1
85.7 (s, P(OAr)3). Anal. Calcd. for C55H63ClNO4PPd: C, 67.76; H,
6.51. Found: C, 67.83; H, 7.02%.
cis-Chlorocarbonyl-{5,11,17,23-tetra-tert-butyl-25-[(2-quinolyl-
methyl)oxy] - 26,27,28 - (l3 - phosphorustrioxy)calix[4]arene} - rho -
dium(I) (5). Ligand 3 (203 mg, 0.25 mmol) was added to a
solution of [Rh(CO)2Cl]2 (52.2 mg, 0.12 mmol) in dry CH2Cl2
(3 ml). After stirring for 30 min at room temperature, dry Et2O
was added to precipitate the product as a yellow solid. Yield:
0.17 mmol (72%). 1H NMR (300 MHz, CD2Cl2, 273 K): d = 1.10
(s, 9H; C(CH3)3), 1.12 (s, 9H; C(CH3)3), 1.16 (s, 9H; C(CH3)3),
2
1.33 (s, 9H; C(CH3)3), 3.16 and 3.42 (AB q, J = 12.5 Hz, 2H;
5,11,17,23-tetra-tert-butyl-25-[(2-quinolylmethyl)oxy]-26,27,28-
(l3-phosphorustrioxy)calix[4]arene (3). Monoalkylated calix[4]-
arene 2 (0.91 g, 1.15 mmol) was azeotropically dried twice with
dry toluene and then dissolved in 60 ml of dry toluene. Distilled
NEt3 (2.4 ml, 17.3 mmol) was added and the solution was cooled
2
ArCH2Ar), 3.28 and 4.21 (AB q, J = 11.5 Hz, 2H; ArCH2Ar),
3.63 and 4.38 (AB q, 2J = 15.3 Hz, 2H; ArCH2Ar), 3.83 and 5.22
2
2
(AB q, J = 14.5 Hz, 2H; ArCH2Ar), 4.86 and 6.05 (AB q, J =
13.6 Hz, 2H; ArOCH2-quinoline), 6.90 (bs, 1H; m-ArH), 6.94 (bs,
1H; m-ArH), 7.06 (bs, 2H; m-ArH), 7.12 (bs, 1H; m-ArH), 7.14
(bs, 2H; m-ArH), 7.32 (bs, 1H; m-ArH), 7.43 (d, 2J = 8.3 Hz, 1H;
quinoline-H3), 7.64 (t, 2J = 7.5 Hz, 1H; quinoline-H6), 7.87 (d, 2J =
8.0 Hz, 1H; quinoline-H5), 7.94 (t,2J = 7.8 Hz, 1H; quinoline-H7),
8.32 (d, 2J = 8.3 Hz, 1H; quinoline-H4), 10.09 (d, 2J = 8.7 Hz, 1H;
◦
to -78 C. PCl3 (0.1 ml, 1.15 mmol) in toluene (10 ml) was then
added dropwise and the solution was allowed to come to room
temperature whilst stirring under argon atmosphere. After 20 h
at 80 ◦C, the salts formed were removed by filtration through a
layer of SiO2 and washed with toluene. The filtrate and washing
solutions were then evaporated under vacuum giving 3 in a pure
form.Yield: 1.03 mmol (90%). 1H NMR (300 MHz, CD2Cl2,
293 K): d = 1.17 (s, 9H; C(CH3)3), 1.26 (s, 9H; C(CH3)3), 1.32
(s, 18H; C(CH3)3), 3.50 and 4.43 (AB q, 2J = 13.8 Hz, 4H;
1
quinoline-H8). 31P{ H} NMR (121.5 MHz, CD2Cl2): d = 102.6 (d,
1JPRh = 307 Hz, P(OAr)3). IR(CH2Cl2): n(cm-1) 2012 (CO). Anal.
Calcd. for C55H60ClNO5PRh: C, 67.11; H, 6.14. Found: C, 67.18;
H, 6.52%.
2
ArCH2Ar), 3.57 and 4.67 (AB q, J = 13.8 Hz, 4H; ArCH2Ar),
cis-Dichlorobis-{5,11,17,23-tetra-tert-butyl-25-[(2-quinolylme-
thyl)oxy]-26,27,28-(l3 -phosphorustrioxy)calix[4]arene}-platinum-
(II) (6). Ligand 3 (98.7 mg, 0.12 mmol) was added to a solution
of [PtCl2(cod)] (22.5 mg, 0.06 mmol) in dry CH2Cl2 (2 ml).
After stirring for 30 min at room temperature, the solution was
concentrated under vacuum and the product precipitated as a
white solid by addition of CH3CN and cooling to -20 ◦C. Yield:
5.51 (s, 2H; ArOCH2-quinoline), 7.06 (s, 2H; m-ArH), 7.13 and
4
7.19 (AB q, J = 2.3 Hz, 4H, m-ArH), 7.19 (s, 2H; m-ArH),
2
2
7.57 (t, J = 7.4 Hz, 1H; quinoline-H6), 7.74 (t, J = 7.4 Hz, 1H;
quinoline-H7), 7.90 (d, 2J = 8.0 Hz, 1H; quinoline-H5), 8.03 (d, 2J =
8.4 Hz, 1H; quinoline-H8), 8.30 (m, 2H; quinoline-H3,H4).13C{ H}
1
NMR (75 MHz, CD2Cl2, 293 K): d = 31.52 (s, C(CH3)), 31.60
630 | Dalton Trans., 2009, 621–633
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0.052 mmol (87%). 1H NMR (300 MHz, CD2Cl2, 293 K): d = 1.04
(s, 9H; C(CH3)3), 1.15 (s, 18H; C(CH3)3), 1.21 (s, 9H; C(CH3)3),
2.54 and 3.95 (AB q, 2J = 13.0 Hz, 2H; ArCH2Ar), 2.65 and 4.47
Absorption correction was based on multiple measured reflections
(3 and 4). The structures were solved with Direct Methods (SIR-
9738 for 3; SHELXS-9739 for 6) or automated Patterson methods
(DIRDIF-9740 for 4) and refined with SHELXL-9741 against F2 of
all reflections. Non hydrogen atoms were refined with anisotropic
displacement parameters (3 and 4). All hydrogen atoms were
introduced in geometrically idealized positions and refined with
a riding model. Geometry calculations and checking for higher
symmetry was performed with the PLATON program.42
2
2
(AB q, J = 13.0 Hz, 2H; ArCH2Ar), 3.48 and 4.57 (AB q, J =
13.5 Hz, 2H; ArCH2Ar), 3.56 and 4.79 (AB q, 2J = 12.0 Hz, 2H;
2
ArCH2Ar), 4.98 and 6.41 (AB q, J = 11.9 Hz, 2H; ArOCH2-
quinoline), 6.61 (bs, 1H; m-ArH), 6.69 (bs, 1H; m-ArH), 6.87 (bs,
1H; m-ArH), 6.98 (bs, 1H; m-ArH), 7.05 (bs, 2H; m-ArH), 7.18
2
(bs, 2H; m-ArH),7.51 (t, J = 7.2 Hz, 1H; quinoline-H6), 7.62 (t,
2J = 7.2 Hz, 1H; quinoline-H7), 7.82 (m, 2H; quinoline-H4,H5),
8.23 (d, 2J = 8.3 Hz, 1H; quinoline-H8), 8.77 (d, 2J = 8.3 Hz, 1H;
X-Ray crystal structure determination of 3. C54H60NO4P·
CH2Cl2 + disordered solvent, Fw = 902.93 [*], colourless plate,
1
quinoline-H3). 31P{ H} NMR (121.5 MHz, CD2Cl2, 293 K): d =
3
¯
0.60 ¥ 0.60 ¥ 0.15 mm , triclinic, P1 (no. 2), a = 13.2138(1), b =
33.2 (s with Pt satellites, 1JPtP = 6833 Hz, P(OAr)3). Anal. Calcd.
for C108H120Cl2N2O8P2Pt: C, 68.20; H, 6.36. Found: C, 68.31; H,
6.57%.
˚
19.6378(1), c = 22.6813(2) A, a = 65.8298(3), b = 77.0409(3), g =
◦
3
3
˚
76.6873(3) , V = 5169.01(7) A , Z = 4, Dx = 1.160 g/cm [*],
m = 0.20 mm-1[*]. 102943 Reflections were measured up to a
-1
˚
Acetylacetonato(carbonyl)-{5,11,17,23-tetra-tert-butyl-25-[(2-
quinolylmethyl)oxy]-26,27,28-(l3-phosphorustrioxy)calix[4]arene}-
rhodium(I) (7). Ligand 3 (0.24 mmol) was added to a solution of
[Rh(acac)(CO)2] (0.24 mmol) in 3 ml of dichloromethane. After
stirring for 30 min, the volatiles were evaporated under vacuum
to give 7 as a yellow solid. Owing to its high solubility in all
common organic solvents, complex 7 was not purified further.
resolution of (sin q/l)max = 0.65 A at a temperature of 110 K.
23594 reflections were unique (Rint = 0.0416). The crystal structure
3
˚
contains large voids (603.0 A /unit cell) filled with disordered
solvent molecules. Their contribution to the structure factors was
secured by back-Fourier transformation using the SQUEEZE rou-
tine of the PLATON program42 resulting in 168 electrons/unit cell.
Two tbutyl groups were rotationally disordered. 1207 parameters
were refined with 204 restraints concerning the disordered tbutyl
groups. R1/wR2 [I > 2s(I)]: 0.0415/0.1049. R1/wR2 [all refl.]:
0.0511/0.1090. S = 1.072. Residual electron density between -0.59
1
Yield: 0.23 mmol (95%). H NMR (300 MHz, CD2Cl2, 293 K):
d = 0.73 (s, 9H; C(CH3)3), 0.98 (s, 9H; C(CH3)3), 1.28 (s, 18H;
C(CH3)3), 1.31 (s, 3H; acac-CH3), 1.74 (s, 3H; acac-CH3), 3.27
2
3
˚
and 4.64 (AB q, J = 14.2 Hz, 4H; ArCH2Ar), 3.43 and 5.19
and 0.42 e/A .
2
(AB q, J = 14.2 Hz, 4H; ArCH2Ar), 4.97 (s, 1H; acac-CH),
[*] Derived values do not contain the contribution of the
disordered solvent molecules.
5.37 (s, 2H; ArOCH2-quinoline), 6.80 (s, 2H; m-ArH), 6.96 (s,
4
2H; m-ArH), 7.04 and 7.14 (AB q, J = 2.4 Hz, 4H, m-ArH),
X-ray crystal structure determination of 4. C55H63ClNO4PPd·
2C4H10O + disordered solvent, Fw = 1123.12 [*], colourless
plate, 0.30 ¥ 0.24 ¥ 0.06 mm3, monoclinic, P21/c (no. 14), a =
7.13 (t, 2J = 7.0 Hz, 1H; quinoline-H6), 7.33 (t, 2J = 7.0 Hz,
2
1H; quinoline-H7), 7.46 (d, J = 8.1 Hz, 1H; quinoline-H5), 7.91
2
2
(d, J = 8.5 Hz, 1H; quinoline-H4), 8.12 (d, J = 8.3 Hz, 2H;
◦
˚
26.1478(2), b = 12.9326(1), c = 18.9151(1) A, b = 94.6368(3) , V =
quinoline-H8), 8.67 (d, J = 8.5 Hz, 2H; quinoline-H3). 31P{ H}
NMR (121.5 MHz, CD2Cl2, 293 K): d = 105.8 (d, 1JPRh = 311 Hz,
P(OAr)3). IR(CH2Cl2): n(cm-1) 2002 (CO).
2
1
3
3
-1
˚
6375.38(8) A , Z = 4, Dx = 1.170 g/cm [*], m = 0.40 mm [*].
99310 Reflections were measured up to a resolution of (sin
-1
˚
q/l)max = 0.65 A at a temperature of 110 K. 14575 reflections
cis-Acetonitrile(methyl)-{5,11,17,23-tetra-tert-butyl-25-[(2-qui-
nolylmethyl)oxy] - 26,27,28 - (l3 - phosphorustrioxy)calix[4]arene} -
palladium(II) hexafluorophosphate (8). To a solution of complex
[PdCl(CH3)(3)] (4) (100 mg, 0.103 mmol) in a CH2Cl2/CH3CN
(10:1) mixture, a solution of NH4PF6 (16.7 mg, 0.103 mmol) in
1 ml of CH3CN was added dropwise. The precipitated NH4Cl
was filtered off, and the filtrate was evaporated to dryness.
The compound, obtained as a white solid, was spectroscopically
pure and was used without further purification. Yield: 100 mg,
0.094 mmol (92%). 1H NMR (300 MHz, CD2Cl2, 293 K): d = 0.98
(s, 3H; Pd-CH3), 1.15 (s, 9H; C(CH3)3), 1.20 (s, 9H; C(CH3)3), 1.25
(s, 18H; C(CH3)3), 2.02 (s, 3H; CH3CN), 3.52 (bd, 2J = 13.8 Hz,
4H; ArCH2Ar), 4.42 (bd, 2J = 13.8 Hz, 4H; ArCH2Ar), 5.62 (bs,
2H; ArOCH2-quinoline), 7.06–7.16 (m, 8H; m-ArH), 7.46 (d, 2J =
8.4 Hz, 1H; quinoline-H3), 7.66 (t, 2J = 7.4 Hz, 1H; quinoline-H6),
were unique (Rint = 0.0560). The crystal structure contains large
3
˚
voids (740.4 A /unit cell) filled with disordered solvent molecules.
Their contribution to the structure factors was secured by back-
Fourier transformation using the SQUEEZE routine of the
PLATON program42 resulting in 97 electrons/unit cell. One tbutyl
group was rotationally disordered. 706 parameters were refined
t
with 105 restraints concerning the disordered butyl group and
the diethylether molecules. R1/wR2 [I > 2s(I)]: 0.0401/0.1027.
R1/wR2 [all refl.]: 0.0596/0.1105. S = 1.101. Residual electron
3
˚
density between -1.05 and 1.25 e/A .
[*] Derived values do not contain the contribution of the
disordered solvent molecules.
X-ray crystal structure determination of 6. C108H120Cl2N2O8-
P2Pt·5CH3CN + disordered solvent, Fw = 2107.26 [*], colourless
3
¯
2
block, 0.20 ¥ 0.20 ¥ 0.20 mm , triclinic, P1 (no. 2), a = 16.7427(6),
7.88 (m, J = 7.9 Hz, 2H; quinoline-H5,H7), 8.35 (d,2J = 8.1 Hz,
˚
1
b = 20.2761(8), c = 22.7693(10) A, a = 67.813(2), b = 83.508(2),
1H; quinoline-H4), 9.76 (d, 2J = 8.4 Hz, 1H; quinoline-H8). 31P{ H}
◦
3
3
˚
g = 75.362(1) , V = 6923.7(5) A , Z = 2, Dx = 1.011 g/cm [*], m =
NMR (121.5 MHz, CD2Cl2, 293 K): d = 81.4 (s, P(OAr)3).
1.12 mm-1[*]. X-ray intensities were measured up to a resolution
-1
˚
of (sin q/l)max = 0.61 A at a temperature of 150 K. The crystal
X-Ray crystal structure determinations
appeared to be cracked into two fragments. Only 61712 non-
overlapping reflections of the major fragment were integrated.
An absorption correction was not considered necessary. 22534
Reflections were measured on a Nonius KappaCCD diffractome-
˚
ter with rotating anode (graphite monochromator, l = 0.71073 A).
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reflections were unique (Rint = 0.0871). Pt, P, Cl, and O atoms
Tetrahedron: Asymmetry, 2000, 11, 2765; (c) F. Rahm, A. Fischer and
C. Moberg, Eur. J. Org. Chem., 2003, 4205.
were refined with anisotropic displacement parameters; C and N
11 (a) X. Luo, Y. Hu and X. Hu, Tetrahedron: Asymmetry, 2005, 16,
1227; (b) Y. Hu, X. Liang, J. Wang, Z. Zheng and X. Hu, Tetrahedron:
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7144.
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Reviews, 1997, 165, 93; (b) C. J. Cobley, D. D. Ellis, A. G. Orpen and
P. G. Pringle, J. Chem. Soc., Dalton Trans., 2000, 1109; (c) S. Steyer, C.
Jeunesse, J. Harrowfield and D. Matt, Dalton Trans., 2005, 1301; (d) R.
Paciello, L. Siggel and M. Ro¨per, Angew. Chem., Int. Ed., 1999, 38,
1920; (e) C. Kunze, D. Selent, I. Neda, R. Schmutzler, A. Spannenberg
and A. Bo¨rner, Heteroat. Chem., 2001, 12, 577; (f) C. Kunze, D. Selent,
I. Neda, M. Freytag, P. G. Jones, R. Schmutzler, W. Baumann and A.
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atoms were refined isotropically. The crystal structure contains
3
˚
large voids (2009.7 A /unit cell) filled with disordered solvent
molecules. Their contribution to the structure factors was secured
by back-Fourier transformation using the SQUEEZE routine
of the PLATON program42 resulting in 387 electrons/unit cell.
Three tbutyl groups were rotationally disordered. 661 parameters
were refined with 1008 restraints concerning the disordered
tbutyl groups, the acetonitrile molecules. Additionally, chemically
equivalent parts of the molecule were restrained to obtain similar
bond distances and angles. R1/wR2 [I > 2s(I)]: 0.0832/0.1987.
R1/wR2 [all refl.]: 0.0978/0.2063. S = 1.052. Residual electron
3
˚
density between -1.52 and 3.83 e/A .
[*] Derived values do not contain the contribution of the
disordered solvent molecules.
Acknowledgements
14 S. Steyer, C. Jeunesse, D. Matt, R. Welter and M. Wesolek, J. Chem.
Soc., Dalton Trans., 2002, 4264.
This research was financed by the Division of Chemical Sciences
of the Netherlands Organization for Scientific Research (NWO-
CW). Dr Barbara Milani and Dr Jerome Durand (University of
Trieste) are kindly acknowledged for fruitful discussions and for
investigating the CO/olefin co- and terpolymerisation reactions.
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632 | Dalton Trans., 2009, 621–633
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