Complexes of hydrophilic triphenylphosphines modified with gem-bis(phosphonate) moiety. An unusual simultaneous cis and trans arrangements in the Pt(ii) dinuclear complex

Article abstract of DOI:10.1039/b818259k

New triphenylphosphines substituted with the gem-bis(phosphonate) moiety in the form of ethyl esters, tetraethyl [4-(diphenylphosphanyl)benzyl]methylene- bis(phosphonate) (2a) and octaethyl bis[4-(diphenylphosphanyl)benzyl]methylene- bis(phosphonate) (2b), and the corresponding free acids 3a and 3b were prepared by a multi-step synthesis and characterized by multinuclear NMR spectroscopy and mass spectrometry. The ester ligands 2a and 2b were conveniently purified through their borane adducts. The X-ray structure of 2b·2BH ₃·H₂O was determined. Coordination properties of new ligands towards Rh(i), Pd(ii) and Pt(ii) ions were studied. ¹H, ³¹P and ¹⁹⁵Pt NMR spectroscopy showed that ligands 2a and 3a form the expected [RhCl(η²:η²-cod)(L)] (cod = cycloocta-1,5-diene) and [MCl₂(L)₂] (M = Pd, Pt) complexes. The compounds 2b and 3b behave as bridging bidentate ligands forming dinuclear complexes of the {[RhCl(η²:η²-cod)] ₂(μ-L-κ²P,P′)} and [M₂Cl ₄(μ-L-κ²P,P′)₂] (M = Pd, Pt) type. These findings are consistent with mass spectrometry and far-IR and Raman spectroscopy results. X-Ray structures of trans-[PdCl₂(2a-κP) ₂] and cis,trans-[Pt₂Cl₄(μ-2b- κ²P,P′)₂] were determined; the dinuclear complex exhibits a different arrangement on the Pt(ii) centres which was observed for the first time in the solid state. Salts of complexes of the free acid 3a are highly soluble in water. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b818259k

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Complexes of hydrophilic triphenylphosphines modified with
gem-bis(phosphonate) moiety. An unusual simultaneous cis and
trans arrangements in the Pt(II) dinuclear complex†
Bohuslav Drahosˇ, Zbyneˇk Rohl´ık, Jan Kotek, Ivana C´ısarˇova´ and Petr Hermann*
Received 15th October 2008, Accepted 7th April 2009
First published as an Advance Article on the web 14th May 2009
DOI: 10.1039/b818259k
New triphenylphosphines substituted with the gem-bis(phosphonate) moiety in the form of ethyl esters,
tetraethyl [4-(diphenylphosphanyl)benzyl]methylene-bis(phosphonate) (2a) and octaethyl
bis[4-(diphenylphosphanyl)benzyl]methylene-bis(phosphonate) (2b), and the corresponding free acids
3a and 3b were prepared by a multi-step synthesis and characterized by multinuclear NMR
spectroscopy and mass spectrometry. The ester ligands 2a and 2b were conveniently purified through
their borane adducts. The X-ray structure of 2b·2BH3·H2O was determined. Coordination properties of
new ligands towards Rh(I), Pd(II) and Pt(II) ions were studied. 1H, 31P and 195Pt NMR spectroscopy
2
2
showed that ligands 2a and 3a form the expected [RhCl(h :h -cod)(L)] (cod = cycloocta-1,5-diene) and
[MCl2(L)2] (M = Pd, Pt) complexes. The compounds 2b and 3b behave as bridging bidentate ligands
2
2
2
2
forming dinuclear complexes of the {[RhCl(h :h -cod)]2(m-L-k P, P ¢)} and [M2Cl4(m-L-k P, P ¢)2] (M =
Pd, Pt) type. These findings are consistent with mass spectrometry and far-IR and Raman spectroscopy
results. X-Ray structures of trans-[PdCl2(2a-kP)2] and cis,trans-[Pt2Cl4(m-2b-k P, P ¢)2] were determined;
2
the dinuclear complex exhibits a different arrangement on the Pt(II) centres which was observed for the
first time in the solid state. Salts of complexes of the free acid 3a are highly soluble in water.
Thus, to continue our previous work,9 we have de-
Introduction
cided to synthesize gem-bis(phosphonate)-modified triphenyl-
phosphine-based ligands and study their coordination prop-
erties. In the literature, only one phosphine type substi-
tuted with a gem-bis(phosphonate) group, a derivative of
diphenylalkylphosphine,4,10,11 has been described so far despite
the availability of many synthetic routes for the introduction of
the bis(phosphonate) moiety due to the enormous interest in
bis(phosphonates) for medical utilization.12 The bis(phoshonate)
moiety offers a more polar character and a higher solubility of
complexes in aqueous solution as well as stronger interaction with
oxide supports compared with other polar groups which have been
used for phosphine modification until now.
Platinum group metal complexes, especially those with phosphine
ligands, are often used as catalysts in various industrial and
laboratory-scale processes. For the application of these catalysts
in more sophisticated set-ups (e.g. heterogeneous or biphasic
catalysis), it is necessary to make the complex soluble in polar
solvents or attachable to a solid support. This problem can be
solved, more or less easily, by the modification of the phosphine
scaffold with an appropriate moiety. There is a number of various
suitable functionalities1 but obviously each such moiety has
its advantages and disadvantages. When synthetic availability,
acid–base properties and/or hydrophilicity of these moieties are
compared, the phosphonate moiety seems to be very suitable.2 It
not only makes the ligands (and its complexes) very water-soluble
in a wide pH-range but it can also be used to anchor the molecules
to oxide solid supports such as TiO2, SiO2, Al2O3 or ZrO2.3
It can also be bound in a zirconium phosphonate/phosphate
three-dimensional framework4–6 or used for stabilization of metal
clusters in aqueous solution.7,8 The number of phosphonate groups
and their mutual position affects strongly all the properties
mentioned above, as well as the coordination behaviour.
Results and discussion
Ligand syntheses
The synthesis of ligands is shown in Scheme 1. 4-Bromomethyl-
1-iodobenzene (IBnBr) was reacted with tetraethyl methylene-
bis(phosphonate) sodium salt (Na+TMBP-) in THF.13 The reac-
tion resulted in a mixture of mono- and disubstituted products 1a
and 1b, in a ratio dependent on the relative amount of TMBP, NaH
and IBnBr in the reaction mixture. The C–H acidity of 1a is higher
than that of the parent TMBP and, therefore, 1a formed during
the reaction reacts with Na+TMBP- forming free TMBP and the
sodium salt of 1a. This salt further reacts with IBnBr leading to the
compound 1b which was always present in the product mixture.
The best results for production of 1a were obtained employing
the NaH:TMBP:IBnBr ratio of 1.2:1:1. Higher excesses of NaH
and IBnBr (typically 3.5:1:2) led to pure 1b. The reactions were
Department of Inorganic Chemistry, Universita Karlova (Charles Uni-
versity), Hlavova 2030, 128 43, Prague 2, Czech Republic. E-mail:
petrh@natur.cuni.cz; Fax: +420-22195-1253; Tel: +420-22195-1263
† Electronic supplementary information (ESI) available: dP of prepared
organic phosphorus-containing compounds, characterization of the 2a
and 2b complexes, coordination shift of 31P NMR resonances, selected ge-
ometric parameters found in the structure of 2b·2BH3·H2O, experimental
1
X-ray data and figures of 31P{ H} NMR spectra of the complexes. CCDC
reference numbers 705469–705471. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b818259k
4942 | Dalton Trans., 2009, 4942–4953
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Scheme 1 Synthesis of the ligands. (i) NaH:TMBP:IBnBr 1.2:1:1, THF; (ii) NaH:TMBP:IBnBr 3.5:1:2, THF; (iii) HPPh2, KOAc, Pd(OAc)2, toluene;
(iv) 1.1 eq. BH3·THF, THF; (v) a) HBF4·Me2O, b) sat. aq. NaHCO3; (vi) HCl (6M aq.), 90 ◦C.
monitored by 31P NMR spectroscopy, as the signals of TMBP, 1a
and 1b were well separated (19.6, 22.7 and 23.7 ppm, respectively).
The products were separated by column chromatography (silica,
CH2Cl2:THF 2:1).
The Rh(I) complexes of 2a and 2b (Schemes 2 and 3)
were prepared in dichloromethane solution at slightly elevated
2
2
temperature, using [Rh(m-Cl)(h :h -cod)]2 as the source of the
metal ion. The (metal atom):(phosphine atom) ratio was 1:1,
because the phosphine only breaks the dimeric precursor with-
out substitution of the olefin. The Pd(II) and Pt(II) complexes
of 2a and 2b (Schemes 2 and 3) were prepared similarly
Introduction of the diphenylphosphanyl moiety was achieved
by the palladium-catalyzed P–C coupling analogously as de-
◦
scribed elsewhere.9,14 The reaction mixtures were kept at ~70 C;
2
2
at higher temperatures some degradation occurred. The crude
products were contaminated mainly by the unreacted HPPh2
and, in order to remove the impurity, the products were
purified through borane adducts by the standard borane-
protection/purification/deprotection procedure.15 This procedure
completely removed any trivalent phosphorus impurities; impu-
rities still present (according to the 31P NMR data) contained
only pentavalent phosphorus and not one exceeded <1.5%. Single
crystals of bis(borane)adduct of 2b suitable for X-ray diffraction
analysis were obtained (vide infra).
with the ligands, metal precursors [MCl2(h :h -cod)] and prod-
ucts being well soluble in dichloromethane; the used (metal
atom):(phosphine atom) ratio was 1:2. After work-up, the com-
plexes of 2a were further purified by column chromatography,
but the final product still contained trace amounts of the
starting 1,5-cod complex. All resulting complexes of ester ligands
2a and 2b are well soluble in polar solvents (THF, CHCl3,
CH2Cl2), slightly soluble in toluene and insoluble in other hydro-
carbons.
When impure ligands obtained directly from the coupling
reaction were used for preparation of the Pt(II) complexes, the
31P NMR spectrum of the product contained additional signals
with a rather complex coupling pattern. It suggested that these
signals belong to the mixed diphenylphosphine-L complexes, cis-
Free acids 3a and 3b were prepared by hydrolysis of the esters
◦
2a and 2b in 6M aq. HCl (90 C, 2 d).9 A higher purity of the
prepared acids, if compared to the initial esters, was caused by a
precipitation of impurities during the hydrolytic procedure.
2
[PtCl2(2a-kP)(HPPh2)] and cis,cis-[Pt2Cl4(m-2b-k P, P ¢)(HPPh2)2]
formed because of the presence of a small amount of the unreacted
HPPh2. A literature search showed, surprisingly, that only a very
limited number of platinum(II) complexes containing the intact
diphenylphosphine (i.e. not in the form of a phosphide anion)
and another phosphine have been described.16,17 To confirm the
Synthesis of complexes
In order to characterize the coordination behaviour of 2a, 2b, 3a
and 3b, we have prepared and studied their Rh(I), Pd(II) and Pt(II)
complexes.
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Scheme 2 Synthesis of complexes of the monophosphine ligands 2a and 3a.
Scheme 3 Synthesis of complexes of the bis(phosphine) ligands 2b and 3b.
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nature of these by-products and to gain more data on such
mixed HPPh2–phosphine complexes we decided to synthesize
them by targeted preparation from the equimolar mixture
of HPPh2, the appropriate phosphine ligand and the metal
precursor in the same way as described above for the other
phosphine complexes (Schemes 2 and 3). The cis,cis-[Pt2Cl4(m-2b-
k P, P ¢)(HPPh2)2] complex is the only known dinuclear complex
containing HPPh2 where diphenylphosphine is present as a
non-bridging ligand.
of the gem-bis(phosphonate) moiety were always close to those
of the corresponding free ligands with no sign of phosphoryl–
metal interaction. Therefore, mostly 31P (phosphine signals) and
195Pt (measured where possible) NMR spectra are discussed
below.
The 1H NMR spectra of the Rh(I) complexes contained signals
of the phosphine ligands (virtually unaffected by the coordination)
and the coordinated cod (its dH coordination shift confirms the
presence of chloride and phosphine ligands in the complexes20). In
31P NMR spectra, the phosphine signals (~30 ppm) were split into
2
Rh(I) complexes of 3a and 3b were obtained by mixing an
2
2
1
ethanolic suspension of [Rh(m-Cl)(h :h -cod)]2 with the appro-
priate phosphine ligand in ethanol and heating overnight at
70 ◦C. The Pd(II) complexes of 3a and 3b were prepared by treating
the suspension of PdCl2 in 6M aq. HCl with the phosphine ligand
dissolved in the same solvent; the yellow product precipitated
immediately. The Pt(II) complexes of 3a and 3b were prepared by
a doublet with JRhP ~150 Hz. A very minor signal of the ligand
phosphinoxide was often present due to the oxidation of the ligand
excess during work-up. There were no signs of P, O-hemilabile
behaviour of the ligands. The NMR spectra fully support the
2
2
suggested structure of the complexes as [RhCl(h :h -cod)(L-kP)]
2
2
2
(ligands 2a and 3a) and {[RhCl(h :h -cod)]2(m-L-k P, P ¢)} (ligands
2b and 3b).
2
2
vigorous stirring of [PtCl2(h :h -cod)] dichloromethane solution
with the phosphine ligand dissolved in aq. 6M HCl. The products
precipitated in the dichloromethane phase. The complex syntheses
are compiled in Schemes 2 and 3.
In the 31P NMR spectra of palladium(II) complexes of 2a
and 2b, the phosphine signal is slightly overlapping with the
phosphonate signal. Stereochemical information was obtained
from the 31P-coordination chemical shift (DdP = dP(coord.) -
dP(free))21 and confirmed by the analysis of cis/trans isomerisation
of the complexes in three solvents with different polarity (chloro-
form, toluene, methanol). Cis/trans isomerism of many similar
Pd(II) complexes in different solvents has been well documented21
and our data correlate well with those for known complexes
(Table S2†). D2O solutions of Pd(II) complexes with 3a and 3b
were prepared by careful addition of ~0.2M NaOD/D2O until
complete dissolution. These solutions were moderately stable
up to pH 9; a long standing or higher pH value led to their
degradation. From the comparison of the calculated and observed
values of DdP (Table S3†), it can be concluded that the complexes
have predominantly the cis-arrangement; the cis arrangement
is expected to be preferred with increasing polarity of solvent.
Despite a number of attempts to obtain single crystals suitable
for X-ray diffraction analysis and to confirm the geometry,
only crystals of trans-[PdCl2(2a-kP)2] were successfully obtained
(vide infra).
NMR spectroscopy
NMR spectroscopy of ligands. For 1a–3a, the 1H NMR spectra
contain a characteristic pattern of the ethylidene group (a and
b hydrogen atoms) due to phosphorus–hydrogen and hydrogen–
hydrogen coupling (a: triplet of triplets, 2JPH ~24 Hz, 3JHH ~6.5 Hz;
3
3
b: triplet of doublets, JPH ~16.5 Hz, JHH ~6.5 Hz). On the
3
contrary, 1b–3b have the b hydrogen atoms only (triplet, JPH
~16.5 Hz). However, the aromatic region of the 1H NMR spectra
is unresolved.
1
In the 13C{ H} NMR spectra, the phosphorus–carbon coupling
was well resolved in both bis(phosphonate) and phosphine parts
of the ligand molecule. In the phosphonate part, the ethylidene
1
carbon atoms signals were found at dC ~40 ppm (a: triplet, JPC
~132 Hz) and dC ~30 ppm (b: multiplet). In addition, the signal
of quarternary aromatic carbon atom was found at dC ~138 ppm
(multiplet). In the phosphine part of the molecule, the doublets
with 1JPC ~10 Hz, 2JPC ~20 Hz and 3JPC ~7 Hz were found for the
aromatic carbon signals. However, the interpretation of aromatic
region is difficult because of a long-range coupling of the aromatic
carbon atoms with both sets of non-equivalent phosphorus atoms.
Analysis of 31P-coordination chemical shift (DdP),21 and 195Pt–
31P coupling interaction (1JPtP)9 in both 195Pt (a triplet) and 31P
NMR (a quasi-triplet; a central line with satellites in the ratio
1:4:1) spectra confirmed the expected22 stoichiometry (generally
[PtCl2(P(III))2]) and cis-stereochemistry (1JPtP ~3700 Hz) of the pre-
pared Pt(II) complexes (Tables S2 and S3†). To have a complete set
of data, the trans-isomers were prepared in situ by photochemical
isomerisation.23 After irradiation, a new set of signals appeared in
the 31P and 195Pt NMR spectra, which apparently belongs to the
trans-complex (1JPtP about ~2600 Hz, DdP close to the expected
values; Table S2†). All attempts at preparation of single crystals for
X-ray diffraction analysis failed except one. A few single crystals of
III
The significantly higher values of P –C coupling constants on the
benzene ring bridging the phosphine and bis(phosphonate) parts
than on the other rings were observed. The detailed assessment of
the 13C spectra was based on the results reported for analogous
compounds.9
The 31P NMR spectra contain the signals of the phosphine
moiety at dP ~(-6) ppm (similar to the value for triphenylphos-
phine itself, -4.7 ppm)18 and bis(phosphonate) with dP in range
of 20.2–22.8 for 1a–3a and 23.7–24.8 for 1b–3b. The chemical
shifts are pH- and solvent-dependent, but in general follow the
trend d(tetraethyl ester) ≥ d(acid) > d(salt).19 Further chemical
modifications of the phosphine phosphorus atom (protonation to
phosphonium, adduct formation with borane) affect the chemical
shifts as indicated in Table S1.†
2
the cis,trans-[Pt2Cl4(m-2b-k P, P ¢)2] complex crystallized from the
mother liquor after removal of the precipitated cis,cis-[Pt2Cl4(m-
2
2b-k P, P ¢)2] complex. The very unusual arrangement was definitely
confirmed by X-ray diffraction study. The 31P NMR spectrum of
this compound showing two different phosphine signals (13.8 and
20.0ppm) withdifferent 1JPtP (3679 and 2639 Hz)as well as infrared
spectra (see below) are in accord with the presence of the cis- and
trans-arrangements on the metal centres. Spectra of the mixed
HPPh2-L complexes are more complex. Both phosphine signals in
1
NMR spectroscopy of complexes. The H NMR spectra of
Rh(I), Pd(II) and Pt(II) complexes of 2a, 2b, 3a and 3b were
similar to those of the free ligands. The 31P chemical shifts
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1
the 31P{ H} NMR spectrum are shifted downfield unequally and
Crystal structures
split into a doublet of 1:4:1-quasi-triplets due to the mutual P–P
interaction (2JPP ~15 Hz) and the interaction with platinum (with
a similar JPtP for HPPh2 and 2a or 2b, ~3580 Hz) (Fig. 1A). It
Crystal structure of 2b·2BH3·H2O‡. Crystals suitable for
X-ray diffraction study were prepared by vapour diffusion of hex-
ane into THF solution of 2b·2BH3 at +5 ◦C. The independent unit
contains one molecule of the phosphine–BH3 adduct together
with the water solvate. The geometries around the phosphine
phosphorus atoms are roughly tetrahedral (angles 105–113◦), with
1
points to the cis-arrangement of the phosphines and to the stoi-
chiometry [PtCl2(L)(L¢)]. In proton-coupled 31P NMR spectrum,
the diphenylphosphine signal is further split into a doublet due to
the P–H bond (1JPH ~400 Hz, Fig. 1B). The 195Pt NMR confirms
the structural motif obtained from the 31P NMR measurement
(triplet with 1JPtP ~3580 Hz; the coupling constants of 2a or 2b and
HPPh2 had the same value). It should be noted that, surprisingly,
these data are the only published NMR data for mixed HPPh2-
phosphine platinum(II) complexes except for a complex of the
˚
P–C distances around 1.81–1.82 A and a P–B coordination bond
˚
of 1.91 A. Geometry of the phosphonate groups is also tetrahedral
◦
˚
˚
(101–116 ), with a phosphoryl bond length of 1.47 A, P–O(ester)
˚
distances of 1.57 A, and a P–C bond length of 1.84 A. The P1A–
C1–P1B angle is 110◦. All other bond lengths and angles also fall
into the expected ranges.24 Crystal solvated water forms medium-
HPPh2-nBu3P17a and the HP(Mes)2-PPh3 pairs. In the case of
17b
˚
to-strong (2.8–2.9 A) hydrogen bonds to phosphoryl oxygen atoms
complexes with 3a and 3b, the coordination chemical shift is lower
than expected. The dP of bis(phosphonate) is shifted to ~20 ppm
as an effect of pH (see Experimental). Data for trans-isomers were
not accessible, because the photochemical isomerization did not
proceed in polar (aqueous) solutions.9,23 No crystals suitable for
X-ray diffraction study were prepared in the case of the 3a and
3b complexes.
of the bis(phosphonate) unit. The molecular structure of 2b·2BH3
is depicted in Fig. 2 and selected structural parameters are given
in Table S4.†
Fig. 2 The molecular structure of the 2b·2BH3 adduct found in the
structure of 2b·2BH3·H2O. Hydrogen atoms (except the boran bound)
were omitted for clarity; the thermal ellipsoids are drawn with 50%
probability.
Crystal structure of trans-[PdCl2(2a-jP)2]·2CHCl3‡. The
Pd(II) coordination sphere is planar and centrosymmetric, with a
small distortion of the bond angles P–Pd–Cl 87.0◦ and 93.0◦. The
Pd(II) ion is located on the crystallographic centre of symmetry
‡ Selected experimental crystallographic data: Crystal data for
2b·2BH3·H2O. C47H60B2O7P4, M = 882.45, mono◦clinic, a = 23.2795(2),
3
˚
˚
b = 14.6939(1), c = 14.2210(3) A, b = 105.9901(6) , U = 4676.32(10) A ,
T = 150 K, space group P21/c (no. 14), Z = 4, 69 921 reflections
measured, 10 721 unique (Rint = 0.040) which were used in all calculations.
The final wR(F2) was 0.1190 (all data).Crystal data for trans-[PdCl2(2a-
kP)2]·2CHCl3. C58H76Cl8O12P6Pd, M = 1541.01, triclinic, a = 8.2868(3),
˚
b = 10.5786(3), c = 21.4686(7) A, a = 103.009(2), b = 92.235(2), g =
◦
3
˚
107.821(2) , U = 1733.86(10) A , T = 150 K, space group P-1 (no. 2), Z =
1, 31622 reflections measured, 7631 unique (Rint = 0.077) which were used
in all calculations. The final wR(F2) was 0.1202 (all data).Crystal data
2
for cis,trans-[Pt2Cl4(m-2b-k P, P ¢)2]·7CH2Cl2. C101H118Cl18O12P8Pt2, M =
˚
2799.98, triclinic, a = 17.5897(2), b = 18.3345(3), c = 20.9857(3) A, a =
◦
3
˚
84.3179(7), b = 68.7386(9), g = 69.7078(9) , U = 5913.0(2) A , T = 150 K,
space group P-1 (no. 2), Z = 2, 109563 reflections measured, 26 966 unique
(Rint = 0.040) which were used in all calculations. The final wR(F2) was
0.1515 (all data).
1
Fig. 1 31P{ H} (A) and 31P NMR (B) spectra of the cis-[PtCl2(2a-
kP)(HPPh2)] complex.
4946 | Dalton Trans., 2009, 4942–4953
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˚
(Fig. 3). The lengths of coordination bonds are 2.33 A for Pd–
˚
P and 2.30 A for Pd–Cl that is in the typical range of atom
distances for such types of Pd(II) complexes.24 Selected geometrical
parameters are compiled in Table 1.
Fig. 3 The molecular structure of the trans-[PdCl2(2a-kP)2] complex
found in the structure of trans-[PdCl2(2a-kP)2]·2CHCl3. Hydrogen atoms
were omitted for clarity; the thermal ellipsoids are drawn with 30%
probability.
2
Fig. 4 The molecular structure of the cis,trans-[Pt2Cl4(m-2b-k P, P ¢)2]
2
complex found in the structure of cis,trans-[Pt2Cl4(m-2b-k P, P ¢)2]·7CH2Cl2.
Crystal structure of cis,trans-[Pt2Cl4(l-2b-j2P,P¢)2]·7CH2Cl2‡.
The crystals appeared as a very minor product from the mother
solution after precipitation of the cis,cis isomer; the compound
was hardly detectable by NMR spectroscopy even in this mother
solution (see also above). In the structure of this Pt(II) complex,
a very unusual feature appeared—one of the platinum atoms
(Pt1) has a cis- and the other one (Pt2) a trans-arrangement
of the coordination sphere (Fig. 4). This coordination mode
in dinuclear complexes has been observed for the first time.
Surroundings of both metal centres are slightly distorted from the
ideal square planar arrangement. The sphere of Pt1 is tetrahedrally
distorted and that of Pt2 has tetragonal-pyramidal distortion.
The large distortion from the regular square-planar geometry
caused by the sterically demanding ligand 2b can be seen from
the bond angle P1A–Pt1–P2C 97.0◦ in the cis-Pt1 unit. The
Hydrogen atoms are omitted and only pivot atoms of phenyl groups are
shown for clarity. The methyl groups of ethyl esters were omitted as well.
The thermal ellipsoids are drawn with 40% probability.
value is significantly higher than the Cl1–Pt1–Cl2 angle (86.1◦).
The Pt1–P bonds (2.25 and 2.27 A, respectively) are noticably
shorter than the Pt1–Cl bonds (2.34 and 2.37 A, respectively).
Contrary to the coordination sphere of Pt1, parameters of the
coordination sphere of the trans-Pt2 centre are more regular,
with P–Pt2–Cl angles in the range of 87.2–93.2◦, and Pt2–Cl
˚
˚
˚
and Pt2–P bond distances in the range of 2.31–2.33 A. Selected
geometrical parameters are compiled in Table 1. This structure
suggests that the ligand 2b is prone to serve as a bridge in the
binuclear complexes. The presence of the cis- and trans-isomers
in one molecule is enabled by a flexible (and rather long)
◦
˚
Table 1 Selected interatomic distances (A) and bond angles ( ) found in the crystal structures of the trans-[PdCl2(2a-kP)2]·2CHCl3 and cis,trans-
2
[Pt2Cl4(m-2b-k P, P ¢)2]·7CH2Cl2 complexes
2
trans-[PdCl2(2a-kP)2]
cis,trans-[Pt2Cl4(m-2b-k P, P ¢)2]
cis
trans
˚
Distances (A)
Pd1–P1
Pd1–Cl1
2.3276(8)
2.3023(8)
Pt1–P2A
Pt1–P2C
Pt1–Cl1
Pt1–Cl2
2.247(1)
Pt2–P2B
Pt2–P2D
Pt2–Cl3
Pt2–Cl4
2.309(2)
2.307(2)
2.329(2)
2.315(2)
2.266(2)
2.365(1)
2.340(2)
Angles (◦)
P1–Pd1–P1a
P1–Pd1–Cl1
P1–Pd1–Cl1a
Cl1–Pd1–Cl1a
180
P2A–Pt1–P2C
P2A–Pt1–Cl1
P2A–Pt1–Cl2
P2C–Pt1–Cl1
P2C–Pt1–Cl2
Cl1–Pt1–Cl2
96.95(5)
176.12(6)
91.23(5)
85.97(5)
170.55(6)
86.07(6)
P2B–Pt2–P2D
P2B–Pt2–Cl3
P2B–Pt2–Cl4
P2D–Pt2–Cl3
P2D–Pt2–Cl4
Cl3–Pt2–Cl4
168.65(5)
93.21(5)
88.08(5)
87.16(5)
90.69(5)
175.27(6)
92.99(3)
87.01(3)
180
a Centrosymmetrically related atom.
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Table 2 Values of valence vibrations nM–Cl of the Pd(II) and Pt(II) complexes in Raman and Far-IR spectra and the corresponding stereochemistry of the
complexes
Complex
IR nM–Cl (cm-1)a
Raman nM–Cl (cm-1)a
Geometry
[PdCl2(2a-kP)2]
361s
357s
307s
303s
trans
trans
cis,transc
cis,transc
cis
2
[Pd2Cl4(m-2b-k P, P ¢)2]
[PdCl2(3a-kP)2]
284m, 305m
(290, 314)m, 355m
296s, 320s
296s, 320s
298s, 319s, 343s
287s, 316s
293s, 319s
293s, 317s
294s, 319s
306br m
2
b
[Pd2Cl4(m-3b-k P, P ¢)2]
–
[PtCl2(2a-kP)2]
298s, 320s
297s, 321s
—
2
[Pt2Cl4(m-2b-k P, P ¢)2]
cis
2
[Pt2Cl4(m-2b-k P, P ¢)2]d
cis,trans
cis
[PtCl2(3a-kP)2]
287m, 316s
294m, 319s
2
[Pt2Cl4(m-3b-k P, P ¢)2]
cis
b
[PtCl2(2a-kP)(HPPh2)]
–
–
cis
2
b
[Pt2Cl4(m-2b-k P, P ¢)(HPPh2)2]
cis
a s = strong, m = medium, br = broad. b Decomposed under laser irradiation. c Obtained as a mixture of isomers. d Minor by-product characterized by
2
X-ray diffraction as the cis,trans-[Pt2Cl4(m-2b-k P, P ¢)2] complex (vide supra).
C3-chain connecting the two triphenylphosphine units in the para
position.
mode, mostly the ions formed by the ethyl group elimination were
found. The m/z values of the molecular ions correspond well
to the theoretical Mr for mononuclear [MCl2(2a)2] and binuclear
[M2Cl4(2b)2] complexes (see Experimental part).
This simultaneous cis/trans coordination arrangement has been
only very recently observed in dinuclear Pd(II) complexes with
ligands derived from [2-(pyridin-2-yl)ethyl]diphenylphosphine.25
Depending on the steric demands of other substituents on the lig-
and skeleton, cis/trans or trans/trans configurations were found. It
was explained by the presence of a rather flexible three-atom chain
between pyridine nitrogen and phoshine phosphorus donor atoms.
Two cis and one trans configuration was also observed in a trinu-
clear Pd(II) complex with 2,6-bis(diphenylphosphanyl)pyridine.26
Experimental
General
All manipulations involving air-sensitive compounds were per-
formed under an atmosphere of argon (5.6, Linde) using standard
Schlenk techniques. Dry solvents were prepared by standard
purification procedures,29 distilled under argon and stored over
Far-infrared and Raman spectroscopy
˚
4 A molecular sieves in an argon atmosphere: Et2O (Lachema,
distilled from Na), CH2Cl2 (Lachema, distilled from P2O5),
N,N-dimethylacetamide (Fluka, vacuum-distilled from BaO),
THF (Lachema, distilled from Na,K/benzophenone), toluene
(Lachema, distilled from Na,K/benzophenone), ethyl acetate,
hexane, chloroform and methanol (Lachema, used as received),
35% aq. HCl (Lachema, distilled under Ar). Anhydrous KOAc
(Acro¯s) and Pd(OAc)2 (Strem) were dried by prolonged heating at
90 ◦C in vacuo.
Stereochemistry of the prepared complexes in the solid phase was
studied by Far-IR and Raman spectroscopies. The number of
valence vibration bands (~300 cm-1) is determined by the coordina-
tion polyhedron symmetry and, in the case of square-planar com-
plexes [MX2(L)2], it can be used to distinguish between the more
symmetrical trans (one band) and less symmetrical cis isomers
(two bands).27 The wave numbers of the M–Cl valence vibrations
observed for the prepared complexes are compiled in Table 2.
From the data in Table 2, it can be assumed that all isolated
Pt(II) complexes (except one) have cis configuration and the
Diphenylphosphine, 4-iodotoluene and 4-bromomethyl-1-
iodobenzene,9 tetraethyl methylene-bis(phosphonate),30 [PdCl2-
2
2
2
2
2
2
33
(h :h -cod)],31 [PtCl2(h :h -cod)]32 and [Rh(m-Cl)(h :h -cod)]2
2
[PdCl2(2a-kP)2] and [Pd2Cl4(m-2b-k P, P ¢)2] complexes have trans
were prepared by literature procedures. Other chemicals were
obtained from commercial sources and used without further
purification.
configuration in the solid state. For the [PdCl2(2a-kP)2] complex,
the trans-configuration was also confirmed by the single crystal
diffraction. In the case of the [PdCl2(3a-kP)2] and [Pd2Cl4(m-3b-
NMR spectra: 1H [399.95 MHz, TMS (internal) d = 0.00 ppm;
CHD2OD (internal) d = 3.31 ppm], 11B [128.32 MHz, BF3·OEt2
(external) d = 0.00 ppm], 13C [100.6 MHz, TMS (internal) d =
0.00 ppm; CHCl3 (internal) d = 77.00 ppm], 31P [161.9 MHz, 85%
H3PO4 (external) d = 0.00 ppm] and 195Pt [85.6 MHz, K2PtCl4,
saturated solution in D2O (external) d = 1620 ppm] were recorded
on a Varian UNITYINOVA 400 spectrometer at 25 ◦C. Multiplic-
ity of the signals is indicated as follows: s–singlet, d–doublet,
t–triplet, q–quartet, m–multiplet, br–broad. Deuterated solvents,
D2O (99.9% D), CDCl3 (99.8% D) and CD3OD (99.8% D) from
Chemtrade, were used as received. The atom numbering scheme
of the compounds is given in Fig. 5. The NMR spectra presented
in Fig. 1 were obtained by deconvolution of the experimental data
in program Mestre-C 4.9.9.6.34
2
k P, P ¢)2] complexes, two or three bands appeared, probably due
to the presence of both cis- and trans-species. The results are in
good agreement with data obtained previously for complexes with
similar ligands; the cis configuration of Pd(II) complexes with 3a
and 3b can be caused by the inter- or intramolecular hydrogen
bond system involving the gem-bis(phosphonic) moiety.9,28
Mass spectrometry
The mass spectra of the complexes with 2a and 2b were recorded
(complexes with the acid ligands 3a and 3b could not be measured
due to their large charge). The ions formed by an addition of
H+ or Na+ or by an elimination of Cl- to form [MCl(2a)2]+ or
[M2Cl3(2b)2]+ were observed in the positive mode. In the negative
4948 | Dalton Trans., 2009, 4942–4953
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29.3 mmol, 3.5 eq., 55% in mineral oil), TMBP (2.42 g, 8.4 mmol)
and IBnBr (5.00 g, 16.8 mmol). Crude product was recrystallized
from hexane, filtered and dried in vacuo at 60 ◦C. Pure 1b was
obtained as a white solid (4.33 g, 71% based on IBnBz; purity
99+% according to 31P NMR).
1
3
NMR (CDCl3): H d 1.16 (CH3, 12H, t, JHH = 7.0 Hz); 3.22
3
(CH2, 4H, t, JPH = 16.4 Hz); 4.02 (O–CH2, 8H, m); 7.36 (CH,
1
8H, AA¢BB¢); 13C{ H} d 16.0 (CH3, 4C, m); 37.5 (CH2, 2C, t,
Fig. 5 Structures and numbering scheme of the prepared ligands: 2a (R1 =
Et, R3 = H), 2b (R1 = Et, R3 = R2), 3a (R1 = R3 = H) and 3b (R1 = H,
R3 = R2).
2JPC = 4.6 Hz); 48.2 (C–P, 1C, t,1JPC = 131.4 Hz); 62.3 (O–CH2,
4C, m); 92.1 (C–I, 2C, s); 133.6 (CH, 4C, s); 136.0 (C–CH2, 2C, t,
3JPC = 6.3 Hz); 136.3 (CH, 4C, s); 31P{ H} d 23.7 (s); 31P d 23.7
1
(m); MS: m/z (+) 743.0 (M + Na)+; (-) 690.7 (M - Et)-; TLC
(SiO2; CH2Cl2:THF 2:1; UV) Rf = 0.7; elemental analysis for
C23H32O6P2I2, Mr = 720.26; found (calculated) C 38.57 (38.35); H
4.31 (4.48); I 35.24 (34.53).
Mass spectra were measured on a Bruker spectrometer ES-
QUIRE 3000 equipped with an electrospray ion source and ion
trap in positive/negative mode. Far-IR spectra (50–600 cm-1) were
obtained on the MAGNA 760 (Nicolet). Samples were measured
at 25 ◦C in polyethylene pellets under dry air. Raman spectra (100–
600 cm-1) were recorded on the same device with the NEXUS
NICOLET Raman module (Nd-YVO4 laser, l = 1064 nm). For
thin layer chromatography, Merck aluminium foils with silica gel
60 F254 or aluminium oxide 60 F254 impregnated with fluorescent
dye were used. Elemental analyses were performed at the Institute
of Macromolecular Chemistry (Prague). However, analyses of
phosphonic acid metal complexes are generally incorrect due to
an incomplete combustion of the samples as a consequence of
formation of metal phosphates (holding undecomposed organic
matter) as a final product; so, elemental analyses of the metal
complexes were not recorded.
Tetraethyl [4-(diphenylphosphanyl)benzyl]methylene-bis(phos-
phonate) (2a). The compound was prepared analogously to
the reported procedure.9,14 Compound 1a (2.98 g, 5.8 mmol),
anhydrous potassium acetate (1.02 g, 6.5 mmol) and diphenyl-
phosphine (1.0 ml, 5.9 mmol) in dry toluene (20 ml) in a 100-ml
Schlenk flask fitted with a rubber septum were treated with a
solution of Pd(OAc)2 (2.6 mg, 12 mmol, 2 molꢀ) in dry N,N -
dimethylacetamide (1.5 ml). The reaction mixture was heated at
◦
70 C for 24 h. The progress of the reaction was followed by 31P
NMR. After cooling to RT, the mixture was stirred vigorously
with deoxygenated water (25 ml) for 2 h. The emulsion was left
standing to separate. The organic layer was separated and dried
with anhydrous Na2SO4. The solvents were removed in vacuo to
give a red oil (1.91 g, 59% based on 1a; 89% 2a and 11% HPPh2
according to 31P NMR).
Tetraethyl (4-iodobenzyl)methylene-bis(phosphonate) (1a).
The compound was prepared analogously to the reported
procedure.13a,c To a stirred suspension of NaH (0.88 g, 20.2 mmol,
1.2 eq.; 55% in mineral oil) in THF (10 mg) in a 100-ml Schlenk
flask with a rubber septum, the solution of TMBP (4.85 g,
16.8 mmol) in THF (10 ml) was added dropwise by means of a
syringe under ice-cooling. The resulting mixture was stirred for
2 h at room temperature. Then, the solution of IBnBr (5.00 g,
16.8 mmol) in THF (10 ml) was added in one portion by means
of a syringe. The resulting white slurry was stirred overnight at
RT and checked by TLC (SiO2; CH2Cl2:THF 2:1; UV detection;
Rf = 0.5). The following manipulations were performed in air.
The reaction was carefully quenched by water (20 ml), stirred for
5 min and the mixture was extracted with dichloromethane (4 ¥
25 ml). Combined organic extracts were dried over anhydrous
Na2SO4 and concentrated. The product was purified by column
chromatography (SiO2, CH2Cl2:THF 2:1, Rf = 0.5) and dried
in vacuo by 60 ◦C to obtain a yellowish oil (3.96 g, 46% based on
IBnBz; purity 98+% according to 31P NMR).
1
NMR (CDCl3): H d 1.18 (CH3, 12C, m); 2.57 (CH–P, 1H, tt,
2JPH = 23.8 Hz, 3JHH = 6.4 Hz); 3.17 (CH2, 2H, td, 3JPH = 16.4 Hz,
3JHH = 6.4 Hz); 4.02 (O–CH2, 8H, m); 7.14–7.26 (CH, 14H, m);
1
13C{ H} d 16.2 (CH3, 4C, m); 31.0 (CH2, 1C, m); 38.8 (CH–P, 1C,
t, 1JPC = 132.8 Hz); 62.5 (O–CH2, 4C, m); 128.4 (C2, 4C, d, 3JPC
=
6.8 Hz); 128.6 (C1, 2C, s); 129.1 (C7, 2C, d, 3JPC = 7.3 Hz); 133.5
2
2
(C3, 4C, d, JPC = 18.3 Hz); 133.7 (C6, 2C, d, JPC = 20.2 Hz);
135.0 (C5, 1C, d, 1JPC = 10.3 Hz); 137.2 (C4, 2C, d, 1JPC = 10.8 Hz);
140.4 (C8, 1C, m); 31P{ H} d -6.1 (P–C, 1P, s); 22.8 (P–O, 2P, s);
1
31P d -6.1 (P–C, 1P, s); 22.8 (P–O, 2P, m); MS: m/z (+) 585.2 (M +
Na)+; 601.2 (MOX + Na)+; (-) 533.1 (M - Et)-; 561.1 (M - H)-.
Octaethyl bis[4-(diphenylphosphanyl)benzyl]methylene-bis(phos-
phonate) (2b). The synthetic procedure as for 2a was repeated
using 1b (4.33 g, 6.0 mmol), KOAc (2.1 g, 13.2 mmol), HPPh2
(2.1 ml, 12.3 mmol, 1.02 eq.) and Pd(OAc)2 (6.0 mg, 24 mmol,
2 mol ꢀ) in DMAA (3.4 ml). The product was obtained as a
reddish oil (3.76 g, 73% based on 1b; 88% 2b and 12% HPPh2
according to 31P NMR).
NMR (CDCl3): 1H d 1.21 (CH3, 12H, td, 3JHH = 7.1 Hz, 4JPH
=
3.8 Hz); 2.50 (CH–P, 1H, tt, 2JPH = 23.8 Hz, 3JHH = 6.4 Hz); 3.11
(CH2, 2H, td, 3JPH = 16.4 Hz, 3JHH = 6.4 Hz); 4.03 (O–CH2, 8H,
1
m); 7.25 (CH, 4H, AA¢BB¢); 13C{ H} d 16.1 (CH3, 4C, m); 30.6
1
3
NMR (CDCl3): H d 1.03 (CH3, 12H, t, JHH = 7.1 Hz); 3.24
(CH2, 1C, t, 2JPC = 4.8 Hz); 38.7 (CH–P, 1C, t, 1JPC = 132.8 Hz);
3
(CH2, 4H, t, JPH = 16.2 Hz); 3.90 (O–CH2, 8H, m); 7.11–7.33
62.4 (O–CH2, 4C, m); 91.4 (C–I, 1C, s); 130.8 (CH, 2C, s); 137.0
(CH, 28H, m); 13C{ H} d 16.1 (CH3, 4C, m); 37.8 (CH2, 2C, m);
1
3
1
(CH, 2C, s); 139.1 (C–CH2, 1C, t, JPC = 7.6 Hz); 31P{ H} d
22.7 (s); 31P d 22.7 (m); MS: m/z (+) 527.0 (M + Na)+; (-) 502.8
(M - H)-; elemental analysis for C16H27O6P2I, Mr = 504.24; found
(calculated) C 39.00 (38.11); H 5.20 (5.40); I 27.42 (25.17).
48.6 (C–P(O), 1C, t, 1JPC = 131.6 Hz); 62.3 (O–CH2, 4C, m); 128.4
3
(C2, 8C, d, JPC = 6.8 Hz); 128.5 (C1, 4C, s); 131.8 (C7, 4C, d,
3JPC = 7.2 Hz); 132.9 (C6, 4C, d, 2JPC = 19.7 Hz); 133.5 (C3, 8C,
d, 2JPC = 19.3 Hz); 135.1 (C5, 2C, d, 1JPC = 10.3 Hz); 137.3 (C4,
1
1
Octaethyl bis(4-iodobenzyl)methylene-bis(phosphonate) (1b).
The synthetic procedure for 1a was repeated using NaH (1.28 g,
4C, d, JPC = 10.5 Hz); 137.4 (C8, 2C, m); 31P{ H} d -6.1 (P–C,
2P, s); 24.0 (P–O, 2P, s); 31P d -6.1 (P–C, 2P, bs); 24.0 (P–O, 2P,
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m); MS: m/z (+) 859.4 (M + Na)+; 875.3 (MOX + Na)+; (-) 807.2
(M - Et)-.
for 24–36 h. The solution was diluted with CH2Cl2 (10 ml) and
deoxygenated saturated aq. NaHCO3 (20 ml) was carefully added.
The emulsion was stirred vigorously for 10 min. Et2O (10 ml) was
added, the organic layer was separated and washed with water
(10 ml) and dried over anhydrous Na2SO4. Volatiles were removed
in vacuo to give the desired foamy product (1.02 or 0.77 g, 89%
or 88%; purity 95+% and 93+% according to 31P NMR; for 2a
and 2b, respectively). 2a elemental analysis for C28H37O6P3·2H2O,
found (calculated) C 56.23 (56.19); H 6.66 (6.90). 2b elemental
analysis for C47H56O7P4·H2O, found (calculated) C 65.82 (66.04);
H 6.26 (6.37).
Borane adduct of tetraethyl [4-(diphenylphosphanyl)benzyl]-
methylene-bis(phosphonate) (2a·BH3). The compound was pre-
pared analogously to the reported procedure.15 The crude red oil
containing 2a (1.91 g, 3.26 mmol of 2a + 0.4 mmol of HPPh2)
was dissolved in dry THF (10 ml) in a 100-ml Schlenk flask. The
1M solution of BH3·THF in THF (3.7 ml, 3.7 mmol) was added
dropwise under ice-cooling. The mixture was stirred for about 5 h
at RT. After removal of the solvents, the residue was purified by
SiO2 chromatography with CH2Cl2:THF 2:1 as eluent (TLC: SiO2,
CH2Cl2:THF 2:1, UV detection, Rf = 0.6). The desired borane
adduct was obtained as a light yellow oil (1.30 g, 39% based on
1a; purity 100% according to 31P NMR).
[4-(diphenylphosphanyl)benzyl]methylene-bis(phosphonic acid)
(3a). The compound was prepared analogously to the reported
procedure.9 Compound 2a (0.76 g, 1.69 mmol) was dissolved in
6M aq. HCl (25 ml) and heated to 90 ◦C for 2 d in a sealed Schlenk
vessel. The reaction mixture was left to cool in a refrigerator
overnight and the precipitated impurities were filtered off on a
0.2 mm Teflon syringe filter (Whatman). Volatiles were removed
in vacuum and the residue was dissolved in ethanol (5 ml) and
evaporated (three times). Free acid 3a was obtained as a white
foam (0.57 g, 95%; purity 100% according to 31P NMR).
1
NMR (CDCl3): H d 1.26 (CH3, 12H, m); 2.64 (CH–P, 1H,
2
3
3
tt, JPH = 24.0 Hz, JHH = 6.4 Hz); 3.28 (CH2, 2H, td, JPH
=
3
16.4 Hz, JHH = 6.4 Hz); 4.10 (O–CH2, 8H, m); 7.28–7.59 (CH,
14H, m); 13C{ H} d 16.2 (CH3, 4C, m); 31.1 (CH2, 1C, m); 38.7
1
(CH–P, 1C, t, 1JPC = 133.0 Hz); 62.6 (O–CH2, 4C, m); 127.1 (C5,
1
3
1C, d, JPC = 58.7 Hz); 128.7 (C2, 4C, d, JPC = 10.3 Hz); 129.2
1
3
(C4, 2C, d, JPC = 57.9 Hz); 129.4 (C7, 2C, d, JPC = 10.7 Hz);
131.2 (C1, 2C, d, 4JPC = 2.2 Hz); 133.0 (C3, 4C, d, 2JPC = 9.6 Hz);
133.1 (C6, 2C, d, 2JPC = 9.3 Hz); 143.2 (C8, 1C, td, 3JPC = 7.6 Hz,
NMR (D2O + NaOD): 1H d 2.13 (CH–P, 1H, tt, 2JPH = 22.0 Hz,
3JHH = 5.6 Hz); 3.14 (CH2, 2H, td, 3JPH = 15.6 Hz, 3JHH = 5.6 Hz);
1
7.32–7.78 (CH, 14H, m); 31P{ H} d -7.8 (P–C, 1P, s); 20.2 (P–O,
4JPC = 2.3 Hz); 31P{ H} d 20.1 (P–B, 1P, bs); 22.5 (P–O, 2P, s);
1
2P, s); 31P d -7.8 (P–C, 1P, bs); 20.2 (P–O, 2P, m); NMR (CD3OD):
31P d 20.1 (P–B, 1P, bs); 22.5 (P–O, 2P, bs); MS: m/z (+) 599.2
(M + Na)+; 563.2 (M + H)+ Mr = 576.36; elemental analysis for
C28H40O6P3B·1.5H2O, found (calculated) C 55.64 (55.69); H 6.72
(7.13).
1
13C{ H} d 31.0 (CH2, 1C, m); 40.5 (CH–P, 1C, t, 1JPC = 127.0 Hz);
128.5 (C2, 4C, d, 3JPC = 6.7 Hz); 128.9 (C1, 2C, s); 129.2 (C7, 2C,
d, 3JPC = 7.3 Hz); 133.6 (C3, 4C, d, 2JPC = 18.3 Hz); 133.8 (C6, 2C,
d, 2JPC = 20.2 Hz); 135.0 (C5, 1C, d, 1JPC = 10.3 Hz); 137.2 (C4,
2C, d, 1JPC = 10.8 Hz); 140.4 (C8, 1C, m); MS: m/z (-) 464.9 (M +
O–H)-, Mr = 450.31; elemental analysis for C20H21O6P3·EtOH,
found (calculated) C 53.65 (53.29); H 5.17 (5.44); P 17.47 (18.73).
Bis(borane) adduct of octaethyl bis[4-(diphenylphosphanyl)ben-
zyl]methylene-bis(phosphonate) monohydrate (2b·2BH3·H2O).
The synthetic procedure for 2a·BH3 was repeated using crude
2b (3.24 g, 3.65 mmol of 2b + 1.0 mmol of HPPh2) and 1M
BH3·THF in THF (8.5 ml, 8.5 mmol, 1.1 eq.). The residue after
silica gel column chromatography with CH2Cl2/THF 2:1 (TLC:
SiO2, CH2Cl2:THF 2:1, UV detection, Rf = 0.7) was dissolved in
THF (20 ml) and the crystalline product was obtained by vapour
diffusion of hexane at 5 ◦C (1.04 g, 23% based on 1b; purity 100%
according to 31P NMR).
Bis[4-(diphenylphosphanyl)benzyl]methylene-bis(phosphonic acid)
(3b). The procedure for 3a was repeated using 2b (0.95 g,
1.31 mmol) and 6M aq. HCl (50 ml). Free acid 3b was obtained as
a white foam (0.80 g, 97%; purity 100% according to 31P NMR).
NMR (D2O + NaOD): 1H d 3.24 (CH2, 4H, m); 7.12–7.88 (CH,
1
28H, m); 31P{ H} d -5.6 (P–C, 2P, s); 24.8 (P–O, 2P, s); 31P d -5.6
1
(P–C, 2P, bs); 24.8 (P–O, 2P, bs); NMR (CD3OD): 13C{ H} d 39.2
1
3
NMR (CDCl3): H d 1.11 (CH3, 12H, t, JHH = 7.0 Hz); 3.34
3
3
(CH2, 2C, m); 129.6 (C2, 8C, d, JPC = 7.2 Hz); 130.1 (C1, 4C,
(CH2, 4H, t, JPH = 16.4 Hz); 4.00 (O–CH2, 8H, m); 7.40–7.60
2
(CH, 28H, m); 13C{ H} d 16.0 (CH3, 4C, m); 38.2 (CH2, 2C, m);
1
s); 133.1 (C7, 4C, m); 133.9 (C6, 4C, d, JPC = 19.4 Hz); 134.7
2
1
48.5 (C–P(O), 1C, t, 1JPC = 131.8 Hz); 62.5 (O–CH2, 4C, m); 127.3
(C5, 2C, d, 1JPC = 58.7 Hz); 128.7 (C2, 8C, d, 3JPC = 9.9 Hz); 129.2
(C4, 4C, d, 1JPC = 57.9 Hz); 131.1 (C1, 4C, d, 4JPC = 2.3 Hz); 132.0
(C6, 4C, d, 2JPC = 10.7 Hz); 132.2 (C7, 4C, d, 3JPC = 9.9 Hz); 133.0
(C3, 8C, d, JPC = 19.1 Hz); 135.4 (C5, 2C, d, JPC = 6.2 Hz);
137.9 (C4, 4C, d, 1JPC = 6.4 Hz); 139.2 (C8, 2C, t, 3JPC = 5.3 Hz).
Triplet corresponding to the signal of C–P(O) was overlapped with
the solvent peak; MS: m/z (+) 725.1 (M + H)+, (-) 723.1 (M -
H)-, Mr = 724.61; elemental analysis for C39H36O6P4·EtOH·H2O,
found (calculated) C 62.00 (62.39); H 5.13 (5.58); P 15.19 (15.72).
(C3, 8C, d, 2JPC = 9.5 Hz); 140.1 (C8, 2C, m); 31P{ H} d 20.0 (P–B,
1
2P, bs); 23.4 (P–O, 2P, s); 31P d 20.0 (P–B, 2P, bs); 23.4 (P–O, 2P, bs);
MS: m/z (+) 888.2 (M + Na)+; (-) 835.2 (M - Et)-, Mr = 864.50;
elemental analysis for C47H60O7P4B2·H2O·THF, found (calculated)
C 63.94 (64.11); H 6.84 (7.12); P 12.14 (12.99).
Synthesis of complexes
General procedure for preparation of 2a and 2b complexes. The
compounds were prepared analogously to a reported procedure.9
The solution of 2a or 2b (~100 mg) in CH2Cl2 (2.5 ml) was treated
with a solution of the metal precursor (0.9 eq.) in CH2Cl2 (2.5 ml).
The flask was sealed and heated to 40 ◦C overnight. The following
manipulations were performed in air. Volatiles were removed
in vacuo. Rh(I) complexes were dissolved in CH2Cl2 (1.0 ml), the
same volume of hexane was added to the dichloromethane solution
Deprotection of borane adducts 2a·BH3 and 2b·2BH3·H2O.
The deprotection was performed according to the reported
procedure.15 The borane adduct 2a·BH3 (1.18 g, 2.05 mmol) or
2b·2BH3·H2O (0.90 g, 1.04 mmol) was dissolved in dry CH2Cl2
(20 ml) in a 100-ml Schlenk flask and cooled to -5 ◦C. HBF4·Me2O
(2.11 ml, 20.5 mmol, 10 eq. for 2a or 2.15 ml, 20.8 mmol, 10 eq.
for 2b) was added dropwise and the mixture was stirred at RT
4950 | Dalton Trans., 2009, 4942–4953
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and volatiles were removed in vacuo. Pt(II) and Pd(II) complexes
were dissolved in CH2Cl2 (1.0 ml), precipitated by addition of an
excess of hexane and separated by centrifugation. The procedure
was repeated (removal of 1,5-cod). All desired products were dried
in vacuo (0.02 Torr, RT, overnight). All yields are based on the
dissolved in MeOH (5 ml) and evaporated to dryness (three times).
The product was washed with hexane (3 ¥ 5 ml) and CH2Cl2 (3 ¥
5 ml). The yellowish oily product was dried in vacuo (39.2 mg,
68%).
NMR (D2O + NaOD): 1H d 2.11 (CH–P, 1H, tt, 2JPH = 22.0 Hz,
2
2
2
2
amount of the precursors, [Rh2(m-Cl)2(h :h -cod)2], [PdCl2(h :h -
3JHH = 6.0 Hz); 3.14 (CH2, 2H, td, 3JPH = 15.6 Hz, 3JHH = 6.0 Hz);
2
2
1
1
cod)] or [PtCl2(h :h -cod)]. All characterizations of the complexes
7.26–7.53 (CH, 14H, m); 31P{ H} d 7.8 (Pt–P, 1P, s + d, JPtP
=
=
1
can be found in the ESI.†
3554 Hz); 20.2 (P–O, 2P, s); 31P d 7.8 (Pt–P, 1P, s + d, JPtP
3590 Hz); 20.2 (P–O, 2P, m); Far-IR: 287s, 316s; Raman: 287m,
2
2
[RhCl(h :h -cod)(3a-kP)]. Yellow suspension of [Rh2(m-
316s.
2
2
Cl)2(h :h -cod)2] (16.4 mg, 33 mmol) in EtOH (3 ml) in a 25-ml
Schlenk flask was treated with a solution of 3a (30.0 mg, 67 mm◦ol)
in the same solvent (3 ml) and the mixture was heated at 70 C
overnight. The following manipulations were performed in air.
After cooling down to RT, the solvent was evaporated and the
desired orange product was dried in vacuo (41.1 mg, 89%).
2
cis,cis-[Pt2Cl4(m-3b-k P,P¢)2]. The procedure for cis-[PtCl2(3a-
2
2
kP)2] was repeated using 3b (76.3 mg, 105 mmol) and [PtCl2(h :h -
cod)] (39.4 mg; 105 mmol). The product was obtained as a white
powder (79.9 mg, 92%).
NMR (D2O + NaOD): 1H d 3.14 (CH2, 4H, m); 6.89–7.82 (CH,
1
28H, m); 31P{ H} d 7.2 (Pt–P, 2P, br s); 21.4 (P–O, 2P, br m); 31
P
1
NMR (CD3OD + CDCl3): H d 2.02 (CH2–1,5-cod, 4H, m);
d 7.2 (Pt–P, 2P, br m); 21.4 (P–O, 2P, br m; Far-IR: 293s, 319s;
Raman: 294m, 319s.
2.40 (CH2–1,5-cod, 4H, m); 2.53 (CH–P, 1H, m); 3.20 (CH-1,5-
cod trans to Cl, 2H, bs); 3.27 (CH2, 4H, m); 5.44 (CH-1,5-cod
1
trans to P, 2H, bs); 7.35–7.79 (CH, 14H, m); 31P{ H} d 22.1 (P–O,
cis-[PtCl2(2a-kP)(HPPh2)]. Diphenylphosphine (33 ml, 192
mmol) was added via a Hamilton syringe to a solution of 2a
(108 mg, 192 mmol) in CH2Cl2 (5 ml) in a 25-ml Schlenk flask.
1
2P, s); 30.4 (Rh–P, 1P, d, JPRh = 149.6 Hz); 31P d 22.1 (P–O, 2P,
s); 30.4 (Rh–P, 1P, d, 1JPRh = 149.6 Hz).
2
2
2
2
2
The resulting mixture was treated with a solution of [PtCl2(h :h -
cod)] (71.8 mg, 192 mmol) in CH2Cl2 (10 ml) and heated at 40 ◦C
overnight. The following manipulations were performed in air.
After cooling to RT, volatiles were removed in vacuo, the residue
was dissolved in CH2Cl2/hexane and evaporated (three times).
The light yellow product was dried in vacuo (167 mg, 86%).
{[RhCl(h :h -cod)]2(m-3b-k P,P¢)}. The
procedure
for
2
2
[Rh(Cl)(h :h -cod)(3a-kP)] was repeated using 3b (45.4 mg, 63
2
2
mmol) and [Rh2(m-Cl)2(h :h -cod)2] (30.9 mg, 63 mmol). A yellow
powder was obtained (61.8 mg, 81%).
NMR (MeOD + NaOH): 1H d 2.38 (CH2–1,5-cod, 8H, m); 3.14
(CH-1,5-cod trans to Cl, 2H, bs); 3.65 (CH2, 4H, m); 5.67 (CH-
1
3
1,5-cod trans to P, 2H, bs); 7.36–7.78 (CH, 28H, m); 31P{ H} d
1
NMR (CDCl3): H d 1.19 (CH3, 12H, t, JHH = 7.2 Hz); 2.55
2
3
23.1 (P–O, 2P, br s); 30.4 (Rh–P, 2P, br s) 31P d 23.1 (P–O, 2P, br
(CH–P, 1H, tt, JPH = 24.0 Hz, JHH = 6.4 Hz); 3.20 (CH2, 2H,
3
3
td, JPH = 16.4 Hz, JHH = 6.4 Hz); 4.02 (O–CH2, 8H, m); 4.73
(P–H, 1H, dd, 1JPH = 400.0 Hz, 3JPH = 12.8 Hz); 7.27–7.66 (CH,
s); 30.4 (Rh–P, 2P, br s).
[PdCl2(3a-kP)2]. Compound 3a (52.4 mg, 116 mmol) in 6M
aq. HCl (2,5 ml) in a 25-ml Schlenk flask was treated with a fresh
suspension of PdCl2 (10.3 mg, 58 mmol) in 6M aq. HCl (2.5 ml). The
yellow suspension was stirred at RT overnight. The precipitate was
separated by centrifugation, washed with 6M aq. HCl (2 ml) and
centrifuged again. The orange product was dried in a desiccator
over KOH (39.0 mg, 62%).
24H, m); 31P{ H} d -3.1 (Pt–P–H, 1P, d + dd, JPtP = 3567 Hz,
1
1
2JPP = 15.2 Hz); 14.9 (Pt–P, 1P, d + dd, JPtP = 3580 Hz, JPP
=
1
2
15.2 Hz); 22.5 (P–O, 2P, s); 31P d -3.1 (Pt–P–H, 1P, dm + ddm,
1JPtP = 3558 Hz, 1JPH = 400.0 Hz); 14.9 (Pt–P, 1P, bs + dm, 1JPtP
=
3591 Hz); 22.5 (P–O, 2P, m); 195Pt d -1278 (t, JPtP = 3572 Hz);
MS: m/z (+) 1036.2 (M + Na)+; (-) 1013.2 (M - H)-; Far-IR: 293s,
317s.
1
1
NMR (D2O + NaOD): H d 2.11 (CH–P, 1H, m); 3.07 (CH2,
1
2H, m); 7.23–7.72 (CH, 14H, m); 31P{ H} d 20.0 (P–O, 2P, s); 22.4
cis,cis-[Pt2Cl4(l-2b-j2P,P¢)(HPPh2)2]. The procedure for the
cis-[PtCl2(2a-kP)(HPPh2)] complex was repeated using 2b
(Pd–Ptrans, 1P, br s); 34.8 (Pd–Pcis, 1P, m); 31P d 20.0 (P–O, 2P,
m); 22.4 (Pd–Ptrans, 1P, m); 34.8 (Pd–Pcis, 1P, m); Far-IR: 284m,
305m; Raman: 306 br m.
2
2
(182 mg, 217 mmol), HPPh2 (76 ml, 434 mmol) and [PtCl2(h :h -
cod)] (162 mg, 434 mmol). Light yellow powder was obtained
(345 mg, 92%).
2
[Pd2Cl4(m-3b-k P,P¢)2]. The procedure for the [PdCl2(3a-kP)2]
1
3
complex was repeated using 3b (43.4 mg, 60 mmol) and PdCl2
(10.6 mg, 60 mmol). A yellow powder was obtained (38.9 mg,
72%).
NMR (CDCl3): H d 1.04 (CH3, 12H, t, JHH = 7.2 Hz); 3.23
3
(CH2, 4H, t, JPH = 16.4 Hz); 3.91 (O–CH2, 8H, m); 4.73 (P–H,
2H, dd, 1JPH = 400.3 Hz, J = 12.8 Hz); 7.19–7.62 (CH, 38H, m);
NMR (D2O + NaOD): 1H d 3.20 (CH2, 4H, t, 3JPH = 15.6 Hz);
31P{ H} d -3.0 (Pt–P–H, 2P, d + dm, JPtP = 3572 Hz, JPP
=
1
1
2
1
7.41–7.71 (CH, 28H, m); 31P{ H} d 20.6 (P–O, 2P, s); 24.7 (Pd–
15.2 Hz); 14.9 (Pt–P, 2P, d + dm, 1JPtP = 3587 Hz, 2JPP = 15.2 Hz);
Ptrans, 2P, s); 37.9 (Pd–Pcis, 2P, s); 31P d 20.6 (P–O, 2P, m); 24.7
(Pd–Ptrans, 2P, s); 37.9 (Pd–Pcis, 2P, m); Far-IR (290, 314)m,
355m.
23.4 (P–O, 2P, s); 31P d -3.0 (Pt–P–H, 1P, dm + ddm, JPtP
=
1
3565 Hz, 1JPH = 401.4 Hz); 14.9 (Pt–P, 1P, bs + d, 1JPtP = 3587 Hz);
23.4 (P–O, 2P, m); 195Pt d -1278 (t, 1JPtP = 3571 Hz); Far-IR: 294s,
319s.
cis-[PtCl2(3a-kP)2]. Compound 3a (44.9 mg, 100 mmol) in
azeotropic aq. HCl (2.5 ml) in a 25-ml Schlenk flask was treated
Photochemical isomerisation of cis-[PtCl2(2a-kP)2] and cis,cis-
2
2
2
with a solution of [PtCl2(h :h -cod)] (18.6 mg, 50 mmol) in CH2Cl2
(2.5 ml). The suspension was stirred at RT overnight. The following
manipulations were performed in air. The organic phase with
the precipitate was separated and concentrated. The residue was
[Pt2Cl4(m-2b-k P,P¢)2]. Photochemical isomerisation was per-
formed as described previously.23 cis-[PtCl2(2a-kP)2] (77.2 mg) or
2
cis,cis-[Pt2Cl4(m-2b-k P, P ¢)2] (133 mg) were dissolved in CDCl3
(1 ml) in a quartz NMR tube. Samples were irradiated by a
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UV lamp (366 nm, 8 W) for 24 h. 31P and 195Pt NMR spectra
were recorded. Conversion to trans isomers was 62% or 55%,
respectively.
other; therefore, the DFIX command was applied to fix the
appropriate C–C bond lengths.
The asymmetric unit in the crystal structure of cis,trans-
1
2
NMR (CDCl3) after irradiation of cis-[PtCl2(2a-kP)2]: 31P{ H}
[Pt2Cl4(m-2b-k P, P ¢)2]·7CH2Cl2 contains a whole molecule of the
1
d 13.6 (Pt–Pcis, s + d, JPtP = 3687 Hz); 19.8 (Pt–Ptrans, s + d,
complex and seven solvate molecules of dichloromethane. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
were treated in theoretical positions. Some of the ethyl ester
groups and dichloromethane chlorine atoms have large thermal
parameters; however, trials to refine the atom split into two
positions led to large uncertainties in the atom positions (due to the
increase in the number of the parameters) and some nonrealistic
bond distances. Therefore, the final refinement was performed
without modulation of the disorder. Similarly as in the previous
case, the DFIX command was applied to fix the appropriate C–C
bond lengths in several ethyl ester groups as the free refinement
led to unrealistically close contacts.
1JPtP = 2636 Hz); 22.6 (P–O, s); 195Pt d -817 (Pt–Ptrans, t, 1JPtP
=
2625 Hz); -1199 (Pt–Pcis, t, 1JPtP = 3666 Hz).
2
NMR (CDCl3) after irradiation of cis,cis-[Pt2Cl4(m-2b-k P, P ¢)2]
1
31P{ H} d 13.5 (Pt–Pcis, s + d, 1JPtP = 3680 Hz); 19.8 (Pt–Ptrans, s +
d, 1JPtP = 2629 Hz); 23.6 (P–O, s); 195Pt d -815 (Pt–Ptrans, t, 1JPtP
2625 Hz); -1199 (Pt–Pcis, t, 1JPt = 3664 Hz).
=
X-Ray crystallography
Single crystals of 2b·2BH3·H2O suitable for X-ray analysis were
prepared by slow diffusion of hexane vapour into a THF solution
of the compound at 5 ◦C. The crystals of trans-[PdCl2(2a-
kP)2]·2CHCl3 were prepared by slow diffusion of hexane vapour
into a chloroform solution of the complex at 5 ◦C. The cis,trans-
The experimental and refinement data are listed in the ESI†
(Table S5).
2
[Pt2Cl4(m-2b-k P, P ¢)2]·7CH2Cl2 complex crystallized by slow evap-
Conclusions
oration (at 5 ◦C) of the hexane/CH2Cl2 mother solution after
2
removal of the precipitate of the cis,cis-[Pt2Cl4(m-2b-k P, P ¢)2]
New bis(phosphonate)-substituted triphenylphosphines were syn-
thesized in the form of ethyl esters 2a and 2b and corresponding
free acids 3a and 3b. The complexation with the most impor-
tant platinum group metal ions, Rh(I), Pd(II) and Pt(II), was
complex.
The selected crystals were mounted in random orientations
onto a glass fibre using an epoxy glue. The diffraction data were
collected using a Nonius Kappa CCD diffractometer (Enraf-
2
2
studied. The expected complexes of [RhCl(h :h -cod)(L)] and
[MCl2(L)2] (M = Pd, Pt) stoichiometry were prepared for the
monodentate ligands, 2a and 3a. The bidentate ligands 2b and
˚
Nonius) at 150(1) K using Mo-Ka radiation (l = 0.71073 A)
and analysed using the HKL program package.35 The structures
were solved using direct methods and refined by full-matrix least-
squares techniques (SIR9236 and SHELXL9737). Scattering factors
for neutral atoms were included in the SHELXL97 program.
Positions of heavy metal, phosphorus, oxygen and some carbon
atoms were determined from direct solution, other non-hydrogen
atoms were found as maxima in the difference map of the electron
density. In general, the hydrogen atoms of the phosphine moieties
were fixed in theoretical positions using a riding model, with their
isotropic thermal factors restrained to 1.2 multiples of a U-value of
the corresponding carbon atoms. The hydrogen atoms of the ester
groups were restrained in the same way, using isotropic thermal
factors of 1.2 for methylene and 1.5 for methyl groups.
2
2
3b serve as bridging ligands forming the {[RhCl(h :h -cod)]2(m-
2
2
L-k P, P ¢)} and [M2Cl4(m-L-k P, P ¢)2] (M = Pd, Pt) complexes.
Bis(triphenylphosphines) 2b and 3b, having a flexible propylene
spacer in the para-positions not sterically suitable for chelation to
the same metal ion, were prepared and studied for the first time.
The Pt(II) complexes show a preference for the cis-arrangement
and they can be rearranged to the trans complexes by UV-
irradiation. As a consequence of the steric possibilities of ligand
2b, the dinuclear complex showing both cis and trans arrangements
around the central Pt(II) ions was observed for the first time. In
the case of the Pd(II) complexes, a different ratio of cis- and trans-
isomers depending on the solvent was observed. In general, the
solubility of 2a and 3a (in organic polar solvents and NaOH/H2O,
respectively) and their complexes is higher than that of 2b and 3b
and their complexes. So, the systems containing 2a or 3a are more
convenient for use in biphasic or solid-supported catalysis and a
supported catalyst with the Rh(I)–3a complex anchored on TiO2
is under investigation in our laboratory.
In the crystal structure of 2b·2BH3·H2O, one ligand molecule
and one water solvated molecule form the independent (asym-
metric) unit. However, the phosphine molecule adopts a roughly
(non-crystallographic) C2 symmetry. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms attached to carbon atoms
were treated using the riding model, but those attached to boron
atoms were refined freely.
In the crystal structure of trans-[PdCl2(2a-kP)2]·2CHCl3, one
half of the complex molecule forms the asymmetric unit. The
solvate molecules were extremely disordered and form rather a
mass of diffraction maxima and, therefore, the disordered electron
density was squeezed using PLATON98.38 It corresponds to
61 electrons per independent unit, i.e. roughly to one molecule
of the chloroform solvate. All non-hydrogen atoms were re-
fined anisotropically. Hydrogen atoms were treated in theoretical
positions. Some of the ethyl ester groups have large thermal
parameters; however, trials to refine them disordered in to two
positions brought no improvement to the fit. Carbon atoms of
several ethyl ester groups were found unrealistically close to each
Acknowledgements
This work was supported by the Ministry of Education and Youth
of Czech Republic (MSM0021620857).
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