Coordination chemistry and X-ray studies with novel sterically constrained diphosphonite ligands

Article abstract of DOI:10.1039/b311328k

The coordination of two novel, sterically constrained diphosphonite ligands towards different palladium, platinum and rhodium precursors has been studied. Complexes of this hitherto unexplored class of diphosphonites, based on rigid xanthene backbones, ha

Full text of DOI:10.1039/b311328k

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Coordination chemistry and X-ray studies with novel sterically
constrained diphosphonite ligands
Jarl Ivar van der Vlugt,a Rafael Sablong,a Allison M. Mills,b Huub Kooijman,b
Anthony L. Spek,b Auke Meetsmac and Dieter Vogt*a
a Laboratory for Homogeneous Catalysis, Schuit Institute for Catalysis,
Eindhoven University of Technology, Den Dolech 2, 5600 MB Eindhoven, The Netherlands
b Department for Crystal and Structural Chemistry, Utrecht University, Padualaan 2, Utrecht,
The Netherlands
c Crystal Structure Center, Chemical Physics, Materials Science Center,
University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
E-mail: d.vogt@tue.nl; Fax: ϩϩ31 (0)40 2455054
Received 17th September 2003, Accepted 27th October 2003
First published as an Advance Article on the web 11th November 2003
The coordination of two novel, sterically constrained diphosphonite ligands towards different palladium, platinum
and rhodium precursors has been studied. Complexes of this hitherto unexplored class of diphosphonites, based on
rigid xanthene backbones, have been characterized by X-ray crystallography as well as by NMR and IR spectroscopy.
A short and concise overview is given on the scarce literature on phosphonite related chemistry. Structural differences
in the complexes obtained due to steric influences of the ligands are discussed. Ligand 1, bearing 2-tert-butyl-
phenolate groups, led to orthometallated complexes cis-[MCl{1-κ3C,P,P}] (M = Pd, Pt) and to trans-[RhCl(CO)(1)].
These complexes were compared with those formed with ligand 2, bearing 2,2Ј-dioxo-3,3Ј-di-tert-butyl-5,5Ј-
dimethoxy-1,1Ј-biphenyl groups, preventing orthometallation. The complexes trans-{PdCl2(2)], cis-[PtCl2(2)] and
trans-[RhCl(CO)(2)] were structurally characterized. Valuable data were collected on chemical shifts, Pt–P coupling
constants, as well as CO stretch frequencies of Rh–CO complexes as important tools for structural characterization
of such complexes.
such a xanthene backbone, in the asymmetric hydrocyanation
Introduction
of styrene.14a We have recently also studied the asymmetric
Progress and development of homogeneous catalysis is very
hydroformylation of styrene, with either rhodium14b or plat-
much related and dependent on the synthesis and availability of
inum/tin14c as the transition metal system of choice.
ligands. In recent years a number of powerful new ligand
We report here on the coordination behavior of a new class
classes have emerged, most of which are chelating phosphorus-
of diphosphonite ligands based on such xanthene backbones,
combining large bite-angle and π-acceptor properties. Those
ligands have recently been developed in our group. Some of
based compounds1 such as phosphines2 or phosphites.3 Phos-
phonites however have been widely neglected and only very
recently a few examples were reported. Reetz et al. used several
those new ligands have turned out to give very active rhodium
backbones, amongst others ferrocene, to prepare chelating
catalysts for the hydroformylation of both terminal as well as
diphosphonites and used them in asymmetric Rh-catalyzed
internal alkenes.15 Focussing on two typical representatives of
hydrogenations of the typical benchmark substrates4 as well
these new diphosphonites based on 9,9-dimethylxanthene
and 2-tert-butylphenol (1) as well as 2,2Ј-dihydroxy-3,3Ј-
as in conjugate addition of aryl boronic acids.5 Zanotti-
Gerosa et al. also described diphosphonites but they used the
bis(tert-butyl)-5,5Ј-dimethoxy-1,1Ј-biphenyl (2), respectively
para-cyclophane backbone and performed hydrogenation
(see Fig. 1), we studied the complexation behavior with the
reactions.6 Pringle andco-workers used binaphthol-derived
platinum group metals.
mono- and bidentate phosphonites for conjugate additions of
diethyl zinc to enones.7 The same monophosphonites were used
by Claver and Pringle in asymmetric hydrogenations.8 Scharf
and co-workers used the monodentate phosphonites based on
TADDOL as the chiral auxiliary for the rhodum-catalyzed
hydrosilylation of ketones.9 Börner and co-workers have
published on the use of both monodentate and bidentate
phosphonite ligands in the hydroformylation of alkenes, with
varying results.10 Finally the Reetz group, in line with their
earlier work, prepared phosphite–phosphonite bidentate
ligands but no applications in catalysis were reported so
far.11
Results and discussion
Synthesis of ligands and determination of the molecular structure
of compound 1
The diphosphonite ligands were prepared using a straight-
forward synthetic route.14–16 Starting from the commercially
available compound 9,9-dimethylxanthene and the appropriate
phenols two ligands were prepared (Scheme 1). As an inter-
mediate product the bis-diethylamidophosphonitoxanthene is
prepared, via a known procedure.16 By substitution using two
equivalents of the appropriate phenol the phosphonite-group is
formed under evolution of diethylamine. Tetrazole is used as a
catalyst for this reaction, that was carried out in a high-boiling
polar, aprotic solvent. Work up to obtain the ligands mainly
comprized of removing solvents in vacuo and crystallization of
the product using layering techniques.
During recent years xanthene-based chelating ligands have
been introduced and extensively used in transition metal
catalyzed C–C bond forming reactions.12 These backbones pro-
vide a unique combination of rigidity and P–P distance in such
a way, that specific, large bite-angle coordination modes are
supported. Additionally interaction of the central oxygen atom
in the backbone with a metal atom coordinated is possible
under certain conditions.13 We have already shown the first
catalytic applicability of a chiral diphosphonite derived from
From a crystallization mixture meant to obtain a new metal
complex, we obtained single crystals, suitable for X-ray analysis
and the molecular structure, displayed in Fig. 2, turned out to
D a l t o n T r a n s . , 2 0 0 3 , 4 6 9 0 – 4 6 9 9
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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Scheme 1 Synthetic methodology for ligands 1 and 2: (i) n-BuLi, TMEDA, Et2O, Ϫ40 ЊC, 16 h; (ii) ClP(NEt2)2, pentane, Ϫ60 ЊC, 16 h; (iii) 2-tert-
butylphenol (6 mol eq.), diglyme, tetrazole, 4 days reflux; (iv) 2,2Ј-dihydroxy-3,3Ј-bis(tert-butyl)-5,5Ј-dimethoxy-1,1Ј-biphenyl (6 mol eq.), diglyme,
tetrazole, 5 days reflux.
Fig. 2 Displacement ellipsoid plot of the triclinic polymorph of
compound 1, top view. Displacement ellipsoids are drawn at the 50%
probability level. All hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and angles (Њ): P1–O1 1.6531(9), P1–O2 1.6516(10), P2–
O3 1.6616(9), P2–O4 1.6454(10), P1–C21 1.8140(12), P2–C34 1.8268(12),
O5–C26 1.3818(14), O5–C35 1.3828(14), P1–P2 3.9261(5); O1–P1–O2
99.31(5), O3–P2–O4 100.04(5), O1–P1–C21 95.97(5), O2–P1–C21 97.76(5),
O3–P2–C34 97.13(5), O4–P2–C34 93.17(5), C26–O5–C35 116.77(9), C25–
C27–C30 107.89(9).
Fig. 1
and P2–O4 1.6454(10) Å), comparable to bond lengths in known
phosphite crystal structures.
To the best of our knowledge, only four papers have
be that of compound 1. We have also obtained a monoclinic
appeared on the X-ray structure determination of palladium
polymorph of the same compound, which will be reported
phosphonite species. Agbossou et al., have characterized a
elsewhere.16 From the structure discussed here, it is evident that
cis-dichloro(dioxazaphosphocine)palladium complex as well as
due to the steric bulk there is no π-stacking as in the case of the
a Pd-allyl complex with an aminophosphonite.17 Braunstein
diphenylphosphine derivatives,12 but that the phenol groups are
and co-workers synthesized monophosphonite-bis-oxazoline
oriented anti-parallel. Comparing both polymorphs of the
compounds that acted as tridentate ligands in Pd-complexes.18
same compound there are only minute deviations in most bond
The group of Schmutzler reported on the preparation of the
angles and lengths. However, in the structure depicted in Fig. 2,
diphosphonite 1,8-bis[(dimethoxy)phosphino]naphthalene and
the xanthene backbone is bent, so that the dihedral angle
its corresponding Pd-complex.19
between the two aromatic rings is 144Њ. This leads to an intra-
molecular P1–P2 distance of 3.9261(5) Å. This behavior is
believed to originate solely in the solid state, while in solution
the flat backbone is most likely the energetically favored con-
formation. The phosphorus-oxygen bonds are all around 1.65
Å (P1–O1 1.6531(9) Å, P1–O2 1.6516(10) Å, P2–O3 1.6616(9) Å
Coordination of ligands 1 and 2 to palladium
We have performed in situ 31P{1H} and 1H NMR measure-
ments in order to understand the behavior of ligands 1 and 2
towards palladium using various precursors. It turns out that
D a l t o n T r a n s . , 2 0 0 3 , 4 6 9 0 – 4 6 9 9
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the difference in steric bulk between these ligands has a big
influence on their coordination behavior and on the rate of
complexation. With ligand 1 and PdCl2(cod) as a precursor,
conversion was only 40% after stirring overnight at room tem-
perature. When the same reaction is carried out at 75 ЊC, a
singlet is observed at δ 109.7 ppm in the 31P NMR spectrum for
complex 3. Attempts to obtain single crystals, suitable for X-ray
analysis failed, so in order to be able to determine whether
cis- or trans-coordination was preferred, [PdCl(CH3)(cod)] was
used as the precursor. The complexation was very slow at room
temperature, but proceeded readily at 60 ЊC. For this complex 4
a singlet was found at δ 123.1 ppm in the 31P NMR, while the 1H
NMR spectrum showed a clear triplet, at δ 0.80 ppm, for the
methyl-ligand (Fig. 3). Both findings indicate that the desired
complex [PdCl(CH3)(1)] is formed, with a preferred trans
coordination of the ligand. This might imply that in complex 3
the ligand will also adopt the trans-configuration.
Fig. 4 Displacement ellipsoid plot of complex 4A, [PdCl{1-κ3C,P,P}].
The ellipsoids are drawn at the 50% probability level. All hydrogens
atoms are omitted for clarity. Selected bond lengths (Å) and angles (Њ):
Pd–P1 2.4416(8), Pd–P2 2.2131(7), Pd–Cl,2.3416(7), Pd–C41 2.073(3),
P1–O1 1.6208(19), P1–O2 1.6119(17), P1–C1 1.826(3), P2–O3 1.6126(18),
P2–O4 1.6106(17) P2–C7 1.809(2), O5–C2 1.387(3), O5–C8 1.395(3),
Pd–O1 3.5308(16), P1–P2 3.6685(11); Cl1–Pd–C41 91.11(7); P1–Pd–P2
103.91(3), Cl–Pd–P1 85.93(2), Cl1–Pd–P2 169.06(3), P1–Pd–C41
176.82(7), P2–Pd–C41 78.94(7), O1–P1–O2 97.54(9), O3–P2–O4 101.82(9),
Pd–P1–O1 117.08(7), Pd–P1–O2 114.94(8), Pd–P2–O3,108.79(7), Pd–P2–
O4 121.02(7), Pd–P1–C1 123.85(8), Pd–P2–C7 121.84(8), C2–O5–C8
112.49(17), C3–C13–C9 106.1(2), O1–P1–C1 100.61(11), O2–P1–C1
98.22(10), O3–P2–C7 102.67(10), O4–P2–C7 97.68(9).
Fig.
3
1H NMR spectrum of complex 4, trans-[PdCl(CH3)(1)],
showing both the methyl groups of the xanthene backbone (1), the
tert-butyl groups of the phosphonite units (2) and the triplet of the
methyl ligand (3).
1
In the H NMR spectrum of complex 4 both the methyl-
groups in the xanthene backbone as well as the tert-butyl
groups on the phenol rings of the phosphonite moieties appear
as two singlets, since they are chemically inequivalent. This is
due to the conformation of the xanthene backbone, which
is bent.16 Single crystals, suitable for X-ray analysis, were
obtained, albeit in low yield, by layering with CH2Cl2–CH3CN.
The molecular structure is depicted in Fig. 4.
Much to our surprise the structure corresponds to an ortho-
metallated species, with one chlorine atom still bound to the
palladium. The methyl group has been replaced by an aryl
group, coordinated to the palladium center, leading to [PdCl-
{1-κ3C,P,P}], complex 4A. The spectroscopic data of the com-
plex originally formed in solution, however, do not fit with the
presence of this complex. Its formation is therefore most likely
due to slow activation of the Pd–CH3 bond in the aprotic
crystallization solvent CH2Cl2, leading to the formation of
methane. To confirm this, degradation of the initial complex in
CDCl3 was followed with time. After one week, two doublets
were clearly present in the 31P NMR spectrum, thereby confirm-
ing the slow conversion of the [PdCl(CH3)(1)], complex 4, in the
mother-liquor, into complex 4A, identified by X-ray analysis
(Fig. 4)
The geometry around the palladium atom in complex 4A is
distorted square planar, with the two phosphorus atoms co-
ordinating in a cis-fashion to the palladium center. The bite
angle of the ligand, in this conformation, P1–Pd–P2, is found to
be only 103.91(3)Њ, while the Cl–Pd–C41 angle is 91.11(7)Њ. The
Cl–Pd–P2 angle is small at only 169.06(3)Њ instead of the 180Њ in
case of a true trans-configuration. The two Pd–P bond lengths
differ quite a lot as Pd–P1 is 2.4416(8) Å while Pd–P2 is only
2.2131(7) Å. This stems from the orthometallation of one of
the substituents on the P2 moiety, leading to elongation of the
Pd–P1 bond. The carbon–palladium bond length Pd–C41 is
2.073(3) Å. This agrees well with other (orthometallated) Pd-
aryl complexes.20,21 Remarkably, the metal atom is positioned
relatively far outside of the ligand plane, creating a dihedral
angle between the P1–O5–P2 plane and the Cl1–Pd–C41 plane of
155Њ. Alternatively, the dihedral angle between the plane P1–P2–
C1 and the plane Cl1–Pd–C41 is calculated to be 115.6Њ (Fig. 5).
The dihedral angle of the aromatic rings in the backbone was
calculated to be 100.34Њ, meaning a large deformation from the
situation in the free ligand in order to accompany this atypical
conformation. The constrained cis-position of the two phos-
phorus atoms is also reflected in a decrease of the P–P distance
from 3.9261(5) Å in the free ligand, to 3.6685(11) Å in complex
4A.
With ligand 2, no unwanted side-reaction to any ortho-
palladated complex can occur, since all orthopositions are
occupied by tert-butyl groups. The reaction of 2 with PdCl2-
(cod) proceeded smoothly at room temperature overnight
(Scheme 2).
A singlet was found at δ 136.5 ppm in the 31P NMR spec-
trum. This chemical shift indicates a trans-coordination of
the diphosphonite ligand, since the chemical shift difference to
the free ligand is in the same range as that seen with ligand 1.
We were able to grow single crystals suitable for a crystallo-
graphic study from a CH2Cl2–CH3CN solution of complex 5.
The molecular structure is depicted in Fig. 6.
Clearly, the trans configuration is preserved in solid state as
well, with a square-planar geometry around the palladium
atom of complex 5. There is significant distortion, possibly
towards
a square-pyrimidal configuation. The molecule
possesses a plane of symmetry. The P1–Pd–P2 angle is only
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Fig. 6 Displacement ellipsoid plot of complex 5, trans-[PdCl2(2)]. The
ellipsoids are drawn at the 50% probability level. All hydrogens atoms
and solvent molecules are omitted for clarity. Selected bond lengths (Å)
and angles (Њ): Pd–P1 2.2767(6), Pd–Cl1 2.2823(8), Pd–Cl2 2.3262(10),
P1–O2 1.6048(18), P1–O3 1.6114(19), P1–C2 1.823(2), Pd–O4 2.694(2),
P1–P2 4.3995(9); P1–Pd–P1a 150.12(3), Cl1–Pd–Cl2 174.79(4), Cl1–Pd–P1
93.78(2), Cl2–Pd–P1 87.53(2) Pd–P1–O2 113.34(7), Pd–P1–O3 124.30(7),
Pd–P1–C2 107.21(9), O2–P1–O3 104.80(9), O2–P1–C2 108.42(11), O3–P1–
C2 96.86(11), C3–O4–C3a 118.4(2), C4–C8–C4a 109.5(3).
complex 4A and the cis-complexes reported in literature, while
the Pd–P bond length is slightly longer in comparison with
these cis-complexes. The palladium–chloride bonds have
dimensions close to the values found in (di)phosphite-based
structures.22,23
The trans coordination in square-planar palladium
complexes with xanthene-based diphosphine ligands has been
reported before by van Leeuwen and co-workers13 and
independently by Yin and Buchwald.24 In both cases, bite
angles of around 150Њ were found in the solid state structures
with Pd–Obackbone distances of around 2.6 Å, which might point
to a weak bonding interaction, and consequently to a square
pyrimidal coordination around the palladium atom. Normal
palladium–ether bonds are in the order of 2.04–2.15 Å.25 In our
structure the Pd–O5 intramolecular distance is 2.694(2) Å.
Fig. 5 Side view on the metallacycle of complex 4A, showing the non-
planarity between the P1–Pd–P2 plane and the P1–C1–C5–P2 ligand
plane.
Coordination of ligands 1 and 2 to platinum
Upon changing to PtCl2(cod) as the metal precursor we found a
remarkable difference in reactivity for ligand 1 and 2. With
ligand 1, a complex spectrum was always obtained. Two broad
singlets appeared in a 1 : 1 ratio, one at δ 118.9 ppm flanked by
195Pt satellites, and a 1JPt–P of 5270 Hz, the other at δ 128.0 ppm
2
with 195Pt-satellites and a coupling constant JPt–P of only
2517 Hz. To date, only six papers dealing with platinum
diphosphonite complexes have appeared. Two reports are
based on diphosphonites with 1,2-substituted cyclopentyl
backbones, giving typical coupling constants JPt–P of ∼4700
Hz,26 while the third paper deals with various other alkyl-
derived backbones and with one alkyl ligand instead of a chlor-
ine.27 Due to these differences, those results are not comparible
with our present work. A combined effort from the groups of
Claver and Pringle has resulted in a study on the use of mono-
phosphonites in asymmetric hydrogenation.8 Herein, also the
X-ray analysis of a PtCl2 complex with a chelating diphos-
phonite is reported, but without any spectroscopic identifi-
cation of this complex in solution. Puddephatt and co-workers
have reported on a dimeric species, made possible by the use of
diethoxyphosphonitomethane as the ligand.28 The groups of
Schmutzler and Börner have prepared a new calix[4]arene-
based diphosphonite, starting from 6-chlorodibenzo-1-oxa-
σ3λ3-phosphorine as the P-building block. They have made
notice of the related PtCl2 complex, for which the 31P NMR
spectrum showed two doublets (due to stereogenic P-atoms)
and coupling constants JPt–P of around 5060 Hz.10b Puddephatt
Scheme 2
150.12(3)Њ, while the Cl1–Pd–Cl2 angle is nearly straight at
174.79(4)Њ. The backbone deformation is only moderate com-
pared to the previous complex, with a dihedral angle between
the two aromatic planes of 155.8Њ. The Pd–P bond length is
2.2767(6) Å, which is in the same range as the distances found
in complex 4 and in literature.17,19 However, due to the trans-
effect, the Pd–Cl bond is slightly shortened to 2.30 Å on average
(Pd–Cl1 is 2.2823(8) Å and Pd–Cl2 is 2.3262(10) Å) compared to
D a l t o n T r a n s . , 2 0 0 3 , 4 6 9 0 – 4 6 9 9
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and co-workers have described a platinum complex containing
a monophosphonite, which showed a coupling constant of 4966
Hz.29 Atherton et al. have published several [PtCl2(PEt)3L]
complexes (L = a monophosphonite), all with coupling
constants around 5200 Hz.30
trans to a chlorine.8,26 The carbon–platinum bond length C41–Pt
is normal at 2.073(4) Å33 Comparing the Pt–Cl bond length
with the work by Dahlenburg and Mertel we find a similar
distance of 2.3408 Å.26 The Pt–Cl bond length of 2.3408 Å is
comparable with the few values reported in literature for other
Pt-phosphonite complexes.8,26 The platinum atom is located
outside of the ligand plane, with the angles Pt–P1–C1 of 124.01Њ
and Pt–P2–C7 of 122.19Њ. Due to the large degree of similarity
between complex 4A and 6, the dihedral angle between the Cl1–
Pd–C41 plane and the P2–P1–C1-plane is also 115.6Њ. This has
to be a result of the bulky phosphonite groups and it is in
accordance with the same findings in another cis-platinum–
diphosphonite complex recently obtained in our group.14c The
xanthene backbone is bent strongly to accompany the cis-
conformation in the solid state, leading to a dihedral angle of
106.5Њ, leaving a P1–P2 distance of 3.5828(15) Å, shorter than
commonly found for xantphos-derived structures. The distance
Pt–O5 is found to 3.533(2) Å, too long to allow for any plat-
inum–oxygen interaction. We are curently investigating the
mechanism for the formation of this unique orthoplatinated
species, as well as its reactivity. Balakrishna has claimed the
formation of an orthometallated platinum complex with the
We were able to grow single crystals suitable for X-ray struc-
ture determination from a CH2Cl2 solution of complex 5 by layer-
ing with CH3CN. The molecular structure obtained for complex
5, as depicted in Fig. 7, is again the orthometallated species, with
one chlorine atom still coordinated to the platinum, making the
structure isomorphous to complex 4A. This also explains the
complicated 31P NMR spectrum. The broad singlets are due to
fluxional behavior of the P-atoms in the ligand while complexed
to this orthometallated species. The difference in coupling con-
stants arises from the fact that there is one phosphorus atom
trans to the chlorine (1JPt–P 5240 Hz) and the other phosphorus
atom is trans to a carbon fragment (1JPt–P 2517 Hz). The groups
of Pidcock31 and later Pringle32 have reported on related
[PtCl(CH3)(P)2] complexes but unfortunately no P–P coupling
constants were reported in either case.
ligand (PhCH2O)2P–N(Ph)–P(OCH2Ph)2 coordinated as
a
κ3P,P,C chelating ligand, next to the expected cis-PtCl2(PP)
complex.34a This intramolecular rearrangement to the ortho-
metallated species is suggested solely on the basis of the 31P
NMR spectrum, which showed two doublets with coupling
constants JPt–P of 5381 Hz and 5363 Hz, respectively, for both
inequivalent phosphorus atoms, coordinated in a cis-fashion.
This implies that the trans-effect of a chlorine atom is virtually
the same as that of a phenyl ligand, which seems highly unlikely
and is also clearly contradictory to the spectroscopic and struc-
tural data presented in our work. Bennet et al. have reported on
complexes containing orthoplatinated triphenylphosphine.34b
Recently, Bedford et al. have shown the application of ortho-
platinated triaryl phosphite and phosphinite complexes in
Suzuki biaryl coupling reactions.34c
To prevent the undesired orthometallation and to draw an
analogy with the palladium complexes described before, the
reaction of PtCl2(cod) with ligand 2 was investigated. The reac-
tion proceeded at room temperature, with 43% conversion after
3 hours but complete disappearance of free ligand after reac-
tion overnight (Scheme 3). The 31P NMR spectrum showed a
Fig. 7 Displacement ellipsoid plot of complex 6, [PtCl{1-κ3C,P,P}].
The ellipsoids are drawn at the 50% probability level. All hydrogens
atoms are omitted for clarity. Selected bond lengths (Å) and angles (Њ):
Pt–P1 2.3680(11), Pt–P2 2.1922(9), Pt–Cl,2.3408(9), Pt–C41 2.073(4),
P1–O1 1.613(3), P1–O2 1.606(3), P1–C1 1.826(4), P2–O3 1.613(3), P2–O4
1.602(3), P2–C7 1.803(4), O5–C2 1.372(4), O5–C8 1.387(4), Pt–O5
3.533(2), P1–P2 3.5828(15); Cl1–Pt–C41 89.87(10), P1–Pt–P2 103.50(3),
Cl–Pt–P1 86.64(3), Cl–Pt–P2 168.87(4), P1–Pt–C41 176.12(10), P2–Pt–
C41 79.86(10), O1–P1–O2 97.64(14), O3–P2–O4 101.68(14), Pt–P1–O1
116.34(10), Pt–P1–O2 115.79(10), Pt–P2–O3 108.04(9), Pt–P2–O4
121.35(10), Pt–P1–C1 124.01(13), Pt–P2–C7 122.19(13), C2–O5–C8
112.2(3), C3–C13–C9 105.4(3), O1–P1–C1 100.35(15), O2–P1–C1
98.13(16), O3–P2–C7 102.66(16), O4–P2–C7 97.84(15).
The formation of this complex can be explained by the
relatively high temperature applied during the complexation
reaction (70 ЊC). The ligand coordinates in a cis-fashion to the
platinum center in order to accommodate the phosphonite ring
as well. The bite angle, P1–Pt–P2, is found to be only 103.50(3)Њ
while the Cl–Pt–C41 angle is 89.87(10)Њ. The P–Pt bond lengths
are found to be 2.3680(11) Å for P1–Pt and 2.1922(9) Å for P2–
Pt, the latter being close to the value reported for a phosphonite
Scheme 3
D a l t o n T r a n s . , 2 0 0 3 , 4 6 9 0 – 4 6 9 9
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singlet at δ 86.8 ppm, flanked by two 195Pt-satellites and a coup-
ling constant JPt–P of 5188 Hz. This clearly indicates that with
this rigid and sterically constrained ligand the cis-coordination
is the only occurring mode with ligand 2.
Yet, since orthometallation is impossible in this case, a true
cis-coordination for the diphosphonite ligand is anticipated.
The 1H NMR spectrum contained the same features as for
trans-[PdCl2(2)]. There are two signals for both the tert-butyl
and the methoxy-groups of the dioxaphosphepin units, show-
ing that there are two chemically inequivalent sets. By layering a
dichloromethane solution of complex 7 with acetonitrile, we
were able to grow single crystals suitable for an X-ray crystallo-
graphic study (Fig. 8).
Coordination of ligands 1 and 2 to rhodium
Starting from the dimeric rhodium precursor [Rh(µ-Cl)(CO)2]2
and either ligand 1 or 2, a yellow–brown powder was obtained
(see example for ligand 1 in Scheme 4). The 31P NMR spectrum
in both cases showed only one doublet, indicating the form-
ation of trans-[RhCl(CO)(P–P)] complexes, with a coupling
constant JRh–P of 184 Hz (1) and 192 Hz (2), respectively.
Fig. 8 Displacement ellipsoid plot of complex 7, cis-[PtCl2(2)]. The
ellipsoids are drawn at the 50% probability level. All hydrogens atoms
are omitted for clarity. Selected bond lengths (Å) and angles (Њ): Pt–P1
2.2725(16), Pt–P2 2.2660(16), Pt–Cl1 2.3216(13), Pt–Cl2 2.3334(16), P1–
O2 1.612(5), P1–O3 1.620(4), P1–C2 1.826(6), Pt–O4 3.466(4), P1–P2
3.794(2); P1–Pt–P2 113.43(6), Cl1–Pt–Cl2 84.74(5), Cl1–Pt–P1 80.61(5),
Cl2–Pt–P1 165.32(5), Cl1–Pt–P2 165.58(5), Cl2–Pt–P2 81.14(6), Pt–P1–C2
131.3(2), Pt–P1–O2 114.24(15), Pt–P1–O3 104.66(15), O2–P1–O3
107.1(2), O2–P1–C2 93.9(2), O3–P1–C2 103.6(2).
Scheme 4
In the IR spectrum (ATR mode) the CO-stretch vibration is
visible at νCO = 1996 cmϪ1 (1) and 1998 cmϪ1 (2) respectively.
This indicates that the ligands are virtually the same regarding
σ-donor and π-acceptor properties, since the νCO for these com-
plexes can be related to the electronic χ-factor as introduced by
Tolman for Ni(CO)3L compounds.35 The νCO values found for
these Rh-complexes fall between those of typical phosphites
The solid state structure is in good agreement with the
spectroscopic data, since the diphosphonite ligand is clearly co-
ordinated in a cis-fashion to the platinum atom. The geometry
around the platinum atoms is square planar, albeit heavily dis-
torted due to the relatively large bite angle P1–Pt–P2 of 113.43Њ.
This leads to an angle Cl1–Pt–Cl2 of only 84.74(5)Њ, while the
angle P1–Pt–Cl1 is even smaller at 80.61(5)Њ. The platinum–
phosphorus bond lengths of 2.2725(16) and 2.2660(16) Å are
longer in comparison with the literature.8,24,29
From the side view on the metal core of complex 7 it is clear
that the coordination around the platinum atom is square
planar (Fig. 9). In contrast to the structure found for complex 6
and in contrast to our other work on Pt-diphosphonite com-
plexes2c however, the angle of the P1–Pt–P2 plane with the P1–
P2–C9 plane is negligible at 5.1Њ. Also in complex 7 the xanthene
backbone is bent significantly, leading to a dihedral angle
between the two aromatic rings of 101.4Њ (Fig. 9).
36
(∼2015 cmϪ1
)
and phosphinites (1990 cmϪ1),37 thereby con-
firming the findings for the 195Pt coupling constants, where a
similar trend could be observed (vide supra). The group of
Broussier has made notice of a mixed phosphonite–phosphine
ligand with a ferrocenyl backbone. In the corresponding
RhCl(CO)-complex, the carbonyl is believed to be positioned
trans to the phosphonite moiety. This is supported by the
observation that the CO stretch vibration appears as high as
2041 cmϪ1 38
. Unfortunately no solid state confirmation of the
spectroscopic observations was reported.
For our system, a trans-relationship is expected to exist
between both P-atoms, since only one doublet without any
splitting, that would indicate an inequivalence of both phos-
phonite moieties, is observed. Both complexes, trans-[RhCl-
(CO)(1)] 8 and trans-[RhCl(CO)(2)] 9 readily crystallized from
CH2Cl2–CH3CN as yellow blocks. The complexes turned out to
have the anticipated coordination of the chlorine trans to the
carbonyl ligand and both phosphorus atoms also trans to each
other, as depicted in Figs. 10 and 11.
For complex 8, the geometry around the rhodium atom is
clearly distorted square planar, possibly towards a square
pyrimidal configuration. This is reflected by all angles around
the rhodium atom. The P1–Rh–P2 bite angle is 147.19(3)Њ; the
Cl1–Rh–C1 angle is 166.11(8)Њ. The Rh–O4 distance of only
2.7193(16) Å indicates that there might be a weak interaction.
The intramolecular P1–P2 distance is 4.3408(10) Å. The struc-
tural differences to complex 9 are mainly found in the orien-
tation of the tert-butyl groups, leading to a different steric
environment for the phosphorus atoms. Also, the latter complex
has crystallographically imposed mirror symmetry. In complex
Fig. 9 Side view on the metallic core of complex 7, showing the square
planarity around the platinum atom and the alignment of the P1–Pt–P2
plane and the P1–P2–C2 plane.
D a l t o n T r a n s . , 2 0 0 3 , 4 6 9 0 – 4 6 9 9
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for a good comparison with complexes 8 and 9 are similar
structures with (di)phosphite ligands. In such complexes with
either mono- or bidentate ligands, normal Rh–P distances
are around 2.15 Å and the Rh–Cl distances are on average
2.36–2.37 Å.
Fernandez et al. described the first X-ray structure of the
type trans-[RhCl(CO){P(OR)3}2] with tert-butylphenyl groups
on the phosphite ligands.42 Paciello and co-workers published
two crystal structures based on ligands known from the patent
literature, where the two phosphite groups are clearly co-
ordinated in a cis-fashion to the rhodium. No spectroscopic or
crystallographic data were given for these complexes.43 Van der
Beuken et al. also concluded from spectroscopic studies, that a
cis-[RhCl(CO)(ligand)] complex was present in solution, with
the elegant tetraphosphite ligand 1,4-bis{bis[2-(diphenoxy-
phosphinoxy)-1-naphthyl]methyl}benzene.44 With
a mixed
phosphine–phosphite ligand based on a benzene backbone, the
group of Pizzano described a cis-[RhCl(CO)(P1–P2)] complex,
the phosphite sitting trans to the chlorine ligand.45 Cobley et al.
recently reported a chloro-bridged dinuclear rhodium com-
plex with only one, calixarene-based monodentate phosphite
coordinated per rhodium atom, leading to a phosphite trans of
a bridging chlorine atom.46
Fig. 10 Displacement ellipsoid plot of complex 8, trans-[RhCl-
(CO)(1)]. The ellipsoids are drawn at the 50% probability level. All
hydrogens atoms and solvent molecules are omitted for clarity. Selected
bond lengths (Å) and angles (Њ): Rh–P1 2.2583(7), Rh–P2,2.2668(7),
Rh–Cl 2.3504(8), Rh–C1 1.818(3), C1–O1 1.149(3), P1–O2 1.6300(17),
P1–O3 1.6141(17), P1–C2 1.826(3), Rh–O4 2.7193(16), P1–P2 4.3408(10);
P1–Rh–P2 147.19(3), Cl1–Rh–C1 166.11(8), P1–Rh–Cl1 88.49(3), P1–
Rh–C1 95.52(8), Rh–C1–O1 174.1(2), Rh–P1–O2 120.30(7), Rh–P1–O3
124.61(7), Rh–P1–C2 109.74(9), O2–P1–O3 97.80(9), O2–P1–C2
103.26(10), O3–P1–C2 97.13(10).
Conclusions
We have carefully investigated the coordination chemistry of
two novel sterically demanding diphosphonite ligands based on
the xanthene backbone with palladium, platinum and rhodium.
Eight complexes have been characterized by full X-ray crystal
analysis, two of which represent interesting orthometallated
species. Extensive new 31P NMR data have been obtained allow-
ing for future comparisons and structure assignments. We
believe that the comparably easy synthesis combined with inter-
esting coordination properties give those diphosphonite ligands
great potential for applications in catalytic processes such as e.g.
hydroformylation or hydrocyanation. Research is in progress
towards this end.
Experimental
General information
All chemicals were purchased from Aldrich, Acros or Merck.
Synthesis gas (1 : 1) with a purity of 5.0 was purchased from
Hoekloos. All preparations were carried out under an argon
atmosphere using standard Schlenk techniques. Solvents were
distilled from sodium/benzophenone (diethyl ether, toluene and
hexanes) or calcium hydride (CH2Cl2, CH3CN and CDCl3)
prior to use. All glassware was dried by heating under vacuum.
The NMR spectra were recorded on a Varian Mercury 400
MHz spectrometer with both the 31P and 13C spectra measured
1H decoupled. Chemical shifts are given in ppm referenced to
solvent (1H, 13C{1H}) or a 85% solution of H3PO4 (31P{1H}).
PdCl2(cod),47 PdClMe(cod),48 and PtCl2(cod)49 were prepared
according to literature procedures. Ligands 1 and 2 were
prepared according to a literature procedure.16
Fig. 11 Displacement ellipsoid plot of complex 9, trans-[RhCl-
(CO)(2)]. The ellipsoids are drawn at the 50% probability level. All
hydrogens atoms and solvent molecules are omitted for clarity. Selected
bond lengths (Å) and angles (Њ): Rh–P1 2.2554(9), Rh–P2 2.2554(9),
Rh–Cl 2.3840(3), Rh–C1 1.818(5), C1–O1 1.154(6), P1–O2 1.621(2), P1–
O3 1.626(2), P1–C2 1.830(3), Rh–O4 2.664(3), P1–P2 4.3526(13); P1–Rh–
P2 149.56(3), Cl1–Rh–C1 172.84(15), P1–Rh–Cl1 87.89(2), P1–Rh–C1
93.95(4), Rh–C1–O1 179.1(4), Rh–P1–O2 113.26(8), Rh–P1–O3
125.74(8), Rh–P1–C2 108.34(11), O2–P1–O3 103.70(11), O2–P1–C2
107.25(13), O3–P1–C2 96.25(13).
9, the rhodium atom is also distorted square planar, with the
P1–Rh–P2 bite angle at 149.56(3)Њ and the Cl1–Rh–C1 angle at
172.84(15)Њ, significantly less deviated from the ideal 180Њ com-
pared to complex 7. The intramolecular P–P distance is
4.3526(13) Å and in this case the distance Rh–O4 is 2.664(3) Å.
So far, no examples of X-ray analysis of RhCl(CO)-com-
plexes with diphosphonites exist in literature. That makes it
hard to compare bond lengths found for this particular system.
The group of Pastor reported a Rh(acac)(diphosphonite)
complex,39 while Nifant’ev et al. prepared the [RhCl(CO)(PP)]
complex with a ferrocenyl based alkylphosphonite system,
however without any mention of crystallographic data.40 Also
their depiction of this structure as an ionic complex seems ques-
tionable. Selent and Börner have recently published some inter-
esting (coordination) chemistry of a hydroxyphosphonite,
involving transformation to a phosphite.41 The best alternatives
[PdCl2(1)] (complex 3). PdCl2(cod) (28.2 mg, 9.88 µmol) and
ligand 1 (87.4 mg, 10.08 µmol) were dissolved in 5 mL of tolu-
ene and the solution stirred at 70 ЊC overnight. The solvent was
removed in vacuo to leave a yellow solid. Yield 97% (100.1 mg,
9.58 µmol).
1
1H NMR (CDCl3): δ 7.75 (d, 4H, J = 8.0 Hz), 7.63 (d, 4H,
1J = 8.0 Hz), 7.33 (dd, 4H, 1J = 8.0 Hz, 2J = 1.6 Hz), 7.22 (dt, 4H,
1J = 8.0 Hz, 2J = 1.6 Hz), 7.15 (t, 2H, 1J = 8.0 Hz), 7.09 (dt, 1J =
8.0 Hz, 2J = 1.6 Hz), 1.64 (s, 6H, CH3), 1.36 (s, 36H, C(CH3)3).
31P{1H} NMR (CDCl3): δ 109.7 (s).
Anal. Calc. for C55H64Cl2O5P2Pd: C, 63.25; H, 6.18. Found:
C, 63.18; H, 6.26%.
D a l t o n T r a n s . , 2 0 0 3 , 4 6 9 0 – 4 6 9 9
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trans-[PdCl(CH3)(1)] (complex 4). PdCl(CH3)(cod) (46.6 mg,
175.8 µmol) and ligand 1 (162.1 mg, 187.0 µmol) were dissolved
in 5 mL of toluene and the solution stirred at 75 ЊC overnight.
The solvent was removed in vacuo to leave 3 as a light-yellowish
solid. Yield 95% (171.0 mg, 167.0 µmol). Single crystals, suit-
able for X-ray analysis, were grown by slow diffusion of
CH3CN into a CH2Cl2 solution, for complex 4A, cis-[Pd(Cl-
{1-κ3P,P,C}].
solid. Yield 85% (182.5 mg, 176.6 µmol). An analytically pure
sample was obtained by layering with CH2Cl2–CH3CN.
1H NMR (CDCl3): δ 8.37 (dd, 2H, 1J = 8.0 Hz, 2J = 1.2 Hz),
1
2
3
7.81 (ddt, 2H, J = 7.6 Hz, J = 4.4 Hz, J unresolved), 7.62
1
2
1
(dd, 2H, J = 7.6 Hz, J = 1.2 Hz), 7.41 (dd, 2H, J = 7.6 Hz,
2J = 1.2 Hz), 7.35 (dd, 1H, J = 7.6 Hz, J = 1.6 Hz), 7.33
1
2
1
2
(dd, 1H, J = 7.6 Hz, J = 1.6 Hz), 7.27 (m, 2H), 7.19 (t, 2H,
1J = 7.6 Hz), 7.16 (dt, J = 8.0 Hz, J = 1.2 Hz), 7.01 (m, 4H),
1.90 (s, 3H, CCH3), 1.42 (s, 18H, C(CH3)3), 1.37 (s, 3H, CCH3),
1.25 (s, 18H, C(CH3)3).
1
2
1H NMR (CDCl3): δ 7.69 (dt, 4H, 1J = 7.6 Hz), 7.64 (dq, 2H,
1J = 4.0 Hz), 7.57 (dd, 2H, 1J = 7.6 Hz, 2J = 1.2 Hz), 7.3 (dd, 4H,
1J = 7.6 Hz, 2J = 1.2 Hz), 7.20 (dt, 4H, 1J = 7.6 Hz), 7.10 (t, 2H,
1J = 7.6 Hz), 7.07 (m, 2H), 1.63 (s, 3H, CCH3), 1.57 (s, 3H,
CCH3), 1.39 (s, 36H, C(CH3)3), 1.32 (s, 36H, C(CH3)3), 0.79 (dt,
3H, PdCH3).
13C NMR (CDCl3): δ 152.2, 140.5, 139.5, 133.5, 129.4, 128.8,
1
1
127.5, 127.0 (d, JP–C = 25.5 Hz), 124.0 (d, JP–C = 12.8 Hz),
123.5, 121.5, 119.2, 35.5, 34.8, 34.6, 34.3, 30.2, 23.7.
31P{1H} NMR (CDCl3): δ 138.4 (s, JRh–P = 184.4 Hz).
FTIR (ATR mode, solid, cmϪ1): ν 1996 (Rh(CO)).
Anal. Calc. for C56H64ClO6P2Rh: C, 65.09; H, 6.24. Found:
C, 64.86; H, 6.31%.
13C NMR (CDCl3): δ 153.8, 152.2, 152.0, 140.0, 139.5, 134.0,
1
129.8, 128.8, 127.6, 127.5, 126.9, 124.0 (d, JP–C = 20.6 Hz),
123.5, 120.6, 119.9, 35.6, 34.8, 30.4, 30.3, 29.1, 27.4.
31P{1H} NMR (CDCl3): δ 123.1 (s).
Anal. Calc. for C56H67ClO5P2Pd: C, 65.69; H, 6.60. Found: C,
65.78; H, 6.67%.
trans-[RhCl(CO)(2)] (complex 9). [Rh(µ-Cl)(CO)2]2 (18.3 mg,
47.1 µmol) and ligand 2 (92.7 mg, 94.2 µmol) were dissolved in
5 mL of dichloromethane and the solution stirred for 2 h at
r.t.The solvent was then removed in vacuo to leave a yellow/red
solid. Yield 91% (107.5 mg, 85.7 µmol). Crystals suitable for
X-ray analysis were obtained by layering with CH2Cl2–CH3CN.
1H NMR (CDCl3): δ 7.54 (dd, 1H, 1J = 3.6 Hz, 2J = 1.2 Hz),
7.16 (m, 2H), 7.12 (d, 1H, 1J = 3.2 Hz), 7.00 (d, 3H, 1J = 3.2 Hz),
6.94 (t, 2H, 1J = 7.6 Hz), 6.86 (d, 2H, 1J = 1.2 Hz), 6.86 (d, 1H,
1J = 7.6 Hz), 6.75 (d, 2H, 1J = 3.2 Hz), 6.67 (d, 3H, 1J = 2.8 Hz),
3.90 (s, 3H, OMe), 3.89 (s, 3H, OMe), 3.81 (s, 6H, OMe), 1.81
(s, 3H, CCH3), 1.62 (s, 18H, C(CH3)3), 1.47 (s, 36H, C(CH3)3),
1.30 (s, 3H, CCH3), 1.20 (s, 18H, C(CH3)3).
trans-[PdCl2(2)] (complex 5). PdCl2(cod) (16.1 mg, 56.4 µmol)
and ligand 2 (56.1 mg, 57.0 µmol) were dissolved in 5 mL of
dichloromethane and the solution stirred overnight at r.t. The
solvent was then removed in vacuo to leave a yellow solid. Yield
92% (65.4 mg, 51.9 µmol). Orange rectangles, suitable for X-ray
crystallographic analysis were obtained by layering with
CH2Cl2–CH3CN.
1
1
2
1H NMR (CDCl3): δ 7.59 (d, H, J = 7.6 Hz, J = 1.2 Hz),
1
1
7.22 (m, 2H), 7.10 (dq, 2H, J = 3.6 Hz, J = 1.2 Hz), 7.00 (d,
2H, 1J = 3.6 Hz), 6.952 (t, 3H, 1J = 7.6 Hz), 6.78 (m, 3H), 6.67
1
(d, 1H, J = 2.8 Hz), 3.88 (s, 6H, OCH3), 3.81 (s, 6H, OCH3),
31P{1H} NMR (CDCl3): δ 163.6 (s, JRh–P = 191.8 Hz).
1.71 (s, 3H, CCH3), 1.47 (s, 36H, C(CH3)3), 1.27 (s, 3H, CCH3).
FTIR (ATR mode, solid, cmϪ1): ν 1998 (Rh(CO)).
Anal. Calc. for C60H68ClO10P2Rh: C, 62.69; H, 5.96. Found:
C, 62.78; H, 6.10%.
31P{1H} NMR (CDCl3): δ 136.5 (s).
Anal. Calc. for C59H68ClO9P2Pd: C, 61.07; H, 5.91. Found: C,
61.11; H, 5.84%.
Crystal structure determination of 1
cis-[PtCl{1-ꢀ3P,P,C}] (complex 6). (PtCl2(cod) (155.1 mg,
414.5 µmol) and 1 (366.3 mg, 422.4 µmol) were stirred in 10 mL
toluene at 75 ЊC overnight. During this period a white turbid
mixture was formed. After removal of the solvent, a white solid
remained. Yield 94% (427.3 mg, 389.6 µmol). Single crystals,
suitable for X-ray analysis, were grown from CH2Cl2–CH3CN.
31P{1H} NMR (CDCl3): δ 118.9 (br s, JPt–P = 5270 Hz), 128.0
(br s, JPt–P = 2517 Hz).
The data was collected on a Bruker SMART APEX CCD. Data
integration and global cell refinement was performed with the
program SAINT. Intensity data were corrected for Lorentz and
polarization effects. The structure was solved by Patterson
methods and extension of the model was accomplished by
direct methods applied to difference structure factors using the
program DIRDIF.50 The positional and anisotropic displace-
ment parameters for the non-hydrogen atoms were refined. The
hydrogen atoms were included in the final refinement riding on
the C-atom as appropriate with Uiso = c × Uequiv. Final refine-
ment on F 2 carried out by full-matrix least-squares techniques
converged at wR(F 2) = 0.1133 for 12282 reflections and R(F) =
0.0410 for 10321 reflections with Fo ≥ 4.0σ(Fo) and 815 param-
eters. Crystal data are given in Table 1.
Anal. Calc. for C55H63ClO5P2Pt: C, 60.24; H, 5.79. Found: C,
60.18; H, 5.76%.
cis-[PtCl2(2)] (complex 7). PtCl2(cod) (23.4 mg, 62.5 µmol)
and ligand 2 (62.9 mg, 64.0 µmol) were dissolved in 5 mL of
dichloromethane and the solution stirred overnight at r.t. The
solution was filtered by cannula to remove insolubles and the
solvent was then removed in vacuo to leave a yellow solid. Yield
88% (68.7 mg, 55.0 µmol). Analytically pure cubic shaped
crystals 6 were obtained by layering with CH2Cl2–CH3CN.
1H NMR (CDCl3): δ 7.49 (dd, 1H, 1J = 7.2 Hz, 2J = 1.2 Hz),
7.18 (m, 1H), 6.97 (d, 3H, 1J = 7.2 Hz), 6.94 (t, 1H, 1J = 7.2 Hz),
6.85 (d, 2H, 1J = 2.4 Hz), 6.67 (d, 3H, 1J = 2.8 Hz), 6.32 (d, 3H,
1J = 2.8 Hz), 3.81 (s, 6H, OMe), 3.78 (s, 6H, OMe), 1.67 (s, 3H,
CCH3), 1.43 (s, 18H, C(CH3)3), 1.38 (s, 18H, C(CH3)3), 1.21
(s, 3H, CCH3).
Crystal structure determinations of 4A–9
Intensity data were collected using graphite-monochromated
Mo-Kα radiation, λ = 0.71073 Å, on a Nonius Kappa CCD
diffractometer at 150 K. Corrections for absorption were
applied with PLATON/MULABS51 (complexes 4A and 6) or
PLATON.DELABS51 (complex 5). The structures were solved
by direct methods using SHELXS8652 (complexes 4A, 7 and 9)
or by Patterson techniques using DIRDIF9950 (complexes. 5, 6
and 8). Refinement on F 2 was done by SHELXL97.52 Hydrogen
atoms were introduced at calculated positions and refined
riding on their carrier atoms. Structures 4A, 6 and 9 contain
small voids of about 50 Å3. No residual electron density was
found in those voids. One molecule of acetonitrile is present in
the asymmetric unit cell of complexes 5 and 9. The unit cell of
complex 7 contained four solvent accessible voids filled with
disordered solvent, two of 448 Å3, incorporating 47 electrons,
and two of 198 Å3, with 34 electrons each. Their contributions
31P{1H} NMR (CDCl3): δ 86.8 (s, JPt–P = 5188 Hz).
Anal. Calc. for C59H68Cl2O9P2Pt: C, 56.73; H, 5.49. Found:
C, 56.83; H, 5.55%.
trans-[RhCl(CO)(1)] (complex 8). [Rh(µ-Cl)(CO)2]2 (28.2 mg,
103.9 µmol) and ligand 1 (181.0 mg, 208.8 µmol) were dissolved
in 5 mL of dichloromethane and the solution stirred overnight
at r.t. The solution was filtered by cannula to remove insolubles
and the solvent was then removed in vacuo to leave a yellow
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to the structure factor calculation in the refinement was taken
into account using the PLATON/SQUEEZE procedure.53
Structure validation and molecular graphics preparation were
performed with the PLATON package.53 Crystal data are given
in Table 1.
CCDC reference numbers 220609–220615.
See http://www.rsc.org/suppdata/dt/b3/b311328k/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
This work has been financially supported by the National
Research School Combination on Catalysis (NRSCC) and in
part (A.M.M. and A.L.S.) by the Netherlands Foundation of
Chemical Research (SON) with financial aid from the Nether-
lands Organisation for Scientific Research (CW-NWO). OMG
is thanked for a generous loan of transition metal precursors.
Dr Rob Hanssen and Dr Christian Müller are appreciated for
scientific discussions.
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