cis, trans - Or both: Steric bulk determines coordination mode of dimeric palladium complexes with bridging pyridine-phosphane ligands

Article abstract of DOI:10.1002/ejic.200800804

The coordination mode in a metal complex is critically dependent on the ligands surrounding the metal, on the precursors used, and on the conditions during synthesis. Our goal was to obtain palladium compounds with pyridine-phosphane ligands for catalysis. Therefore, we synthesized ligands 1a-d, which differ in the bulky aryl substituent at the pyridyl moiety. The palladium complexes 6a-d of these ligands are insoluble and have been characterized by various techniques, including solid-state NMR and (for 6a, b, and d) single-crystal X-ray diffraction, showing that bimetallic complexes are formed in which two ligands span two palladium centers. The configuration around these centers is determined by the steric bulk of the ligand. In complexes 6c,d, with the ligands bearing the largest steric groups, both centers have a trans configuration of the methyl and chloride anions. With intermediately sized pyridyl substituents, complex 6b is formed, having one cis surrounded and one trans-surrounded palladium center in the molecule. This kind of complexation has not been observed before. With the least bulky ligand, complex 6a is formed. Depending on the synthetic conditions employed, the methyl and the chloride in this complex can be in a cis configuration at both palladium atoms, or show the unique cis-trans coordination. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800804

FULL PAPER
DOI: 10.1002/ejic.200800804
cis, trans – or Both: Steric Bulk Determines Coordination Mode of Dimeric
Palladium Complexes with Bridging Pyridine-Phosphane Ligands
Jitte Flapper,[a,b] Philip Wormald,[c] Martin Lutz,[d] Anthony L. Spek,[d]
Piet W. N. M. van Leeuwen,[a] Cornelis J. Elsevier,[a] and Paul C. J. Kamer*[a,c]
Keywords: Bimetallic complexes / Coordination modes / N,P ligands / Palladium / Solid-state NMR
The coordination mode in a metal complex is critically de-
with the ligands bearing the largest steric groups, both cen-
pendent on the ligands surrounding the metal, on the precur- ters have a trans configuration of the methyl and chloride
sors used, and on the conditions during synthesis. Our goal
was to obtain palladium compounds with pyridine-phos-
phane ligands for catalysis. Therefore, we synthesized li-
gands 1a–d, which differ in the bulky aryl substituent at the
pyridyl moiety. The palladium complexes 6a–d of these li-
gands are insoluble and have been characterized by various
techniques, including solid-state NMR and (for 6a, b, and d)
single-crystal X-ray diffraction, showing that bimetallic com-
plexes are formed in which two ligands span two palladium
centers. The configuration around these centers is deter-
mined by the steric bulk of the ligand. In complexes 6c,d,
anions. With intermediately sized pyridyl substituents, com-
plex 6b is formed, having one cis surrounded and one trans-
surrounded palladium center in the molecule. This kind of
complexation has not been observed before. With the least
bulky ligand, complex 6a is formed. Depending on the syn-
thetic conditions employed, the methyl and the chloride in
this complex can be in a cis configuration at both palladium
atoms, or show the unique cis-trans coordination.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Different donor atoms of a chelating ligand induce asym-
metry and invoke different trans-influence and -effect on
Introduction
The catalytic performance of palladium complexes is their responsive trans-ligands. By choosing these features
strongly dependent on the ligands coordinated to the metal. of the ligating groups, selective binding and reactivity of
Properties such as activity and selectivity can be steered by coordinated substrates can be achieved. This is one of the
electronic and steric factors of the ligand. The way in which reasons why P,N ligands (chelating ligands with one nitro-
a ligand coordinates is important as well. Subtle changes in gen and one phosphorus donor atom) are extensively
coordination mode, like chelate bite angles, can have large studied in catalysis.[3,4] In our previous work concerning
effects on catalysis.[1] Likewise, a change of coordination palladium complexes of these bidentates, we have studied
geometry can induce a significant effect in catalysis; palla- the effects on carbonylation[5] and allylic alkylation.[6] In
dium complexes that contain chelating ligands in a cis con- our current research, we were particularly interested in pal-
figuration can show totally different behavior from that of ladium complexes of pyridine-phosphane ligands.[4] Recent
trans-coordinated species. For example, the competition be- applications in catalysis of this class of complexes include
tween alkoxycarbonylation or CO/ethene copolymerization ethene oligomerization and polymerization,[7] alkene/CO
activity of palladium catalysts seems to be dependent on copolymerization,[8] allylic substitution,[9] carbonylation,[10]
the coordination modes of the ligand.[2]
and Suzuki coupling.[11a]
Usually, the 1:1 complexes of pyridine-phosphane li-
gands with palladium are monometallic with a cis configu-
ration around the metal, but trans-coordinated monometal-
lic species[11] and bimetallic complexes in which two ligands
span two palladium centers[11a,11c,12] have been reported.
The latter type of coordination can be of particular interest
for bimetallic catalysis. In this type of catalysis, ideally the
two metal centers have a cooperative effect, thus enhancing
activity and selectivity.[13] This phenomenon is the reason
behind the extreme efficiency of many enzymatic systems[14]
and it’s value has also been shown in chemical catalysis.[15]
[a] van ’t Hoff Institute for Molecular Sciences, University of Am-
sterdam,
Nieuwe Achtergracht 166, 1018WV Amsterdam, The Nether-
lands
[b] Dutch Polymer Institute
P. O. Box 902, 5600 AX Eindhoven, The Netherlands
[c] School of Chemistry, University of St. Andrews,
St. Andrews, Fife, Scotland KY16 9ST, UK
Fax: +44-1334-463-808
E-mail: pcjk@st-andrews.ac.uk
[d] Bijvoet Center for Biomolecular Research, Crystal and Struc-
tural Chemistry, Utrecht Univerity,
Padualaan 8, 3584 CH Utrecht, The Netherlands
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Coordination Mode of Dimeric Palladium Complexes
In this article, we present the synthesis and characteriza- phinated with diphenylphosphane using a catalytic amount
tion of new pyridine-phosphane bidentate ligands (1) and of KOtBu. Subsequent oxidation with household bleach
their dimeric methylpalladium chloride complexes (6). The gave 2-bromo-6-[2-(diphenylphosphinoyl)ethyl]pyridine (4)
ligands differ in the bulky aryl substituents at the pyridine. in 91%. The oxidation of this compound was required be-
Recently, Grubbs showed that the introduction of such cause test reactions with the non-oxidized 2-bromo-6-[2-(di-
groups on salicylaldiminato ligands improved their per- phenylphosphanyl)ethyl]pyridine did not show any conver-
formance in nickel catalyzed ethene polymerization and sion in the palladium-catalyzed cross-coupling. We assume
also suppresses bis-ligation of the metal.[16]
a stable palladium complex is formed, with the phosphorus
The palladium complexes 6 of the ligands 1 appear as of the substrate coordinating to the metal. This coordina-
bimetallic compounds, in which two ligands span two metal tion is prevented by oxidation of the phosphane and conse-
centers. The complexes differ in the coordination mode quently the cross-coupling did proceed. This reaction be-
around palladium (cis or trans), and this depends on the tween 4 and phenyl-, 1-naphthyl-, or 9-phenanthrylboronic
ligands used. By variation of the steric bulk at the ligand, acid yielded 5a, 5b and 5c in good yields. Unfortunately,
all possible coordination geometries of the bimetallic com- when this reaction was carried out with 9-anthracylboronic
plex can be obtained. Remarkably, both cis and trans coor- acid, product 5d could not be obtained in pure form. There-
dination in one bimetallic complex is observed. A binuclear fore, a Negishi–Takahashi coupling was tried between 9-
complex showing different coordination modes for the two anthracylzinc chloride and 4. Using this method, pure 5d
metal centers that have the same ligand, has not been ob- was obtained in almost quantitative yield. Phosphinoyls 5
served previously.
were reduced using phenylsilane to give ligands 1 in good
to excellent yields. Under aerobic conditions in solution,
they are oxidized back slowly to compounds 5. In the solid
state, however, they are stable in air. All new compounds
were fully characterized.
Results and Discussion
Ligand Synthesis
The 2-aryl-6-[2-(diphenylphosphanyl)ethyl]pyridine li-
gands of type 1 which we used in this study have different
aryl substituents at C-2 of the pyridine ring, being phenyl
(for 1a), 1-naphthyl (for 1b), 9-phenanthryl (for 1c), or 9-
anthracyl (for 1d). They were synthesized as depicted in
Scheme 1.
Complex Synthesis and Characterization
Palladium complexes were obtained by reaction of the
ligands with (COD)Pd(CH3)Cl [COD
= 1,5-cyclooc-
tadiene], see Scheme 2. To our surprise, all compounds
turned out to be insoluble. Solvents like chloroform, THF,
acetone, DMSO and toluene were tried, but in none of
them the complexes dissolved. We are unable to explain this
phenomenon, but it has been observed before for palladium
complexes with pyridine-phosphane ligands.[12a,12e] As a
consequence of the insolubility, solution phase analysis
could not be performed and the complexes were charac-
terized by elemental analysis, high resolution mass spec-
trometry, solid-state NMR and, for 6a, 6b, and 6d, single-
crystal X-ray diffraction. As the products are insoluble,
crystals of 6 suitable for X-ray diffraction had to be ob-
tained directly from the synthesis. This was accomplished
by layering a solution of (COD)Pd(CH3)Cl in dichloro-
methane in a small glass tube, with a solution of the appro-
priate ligand in a mixture of dichloromethane and ether.
Because of diffusion, the reactants slowly mixed and crys-
tals of the product formed at the interface of the two layers.
When the mixing of the reactants was too fast (for example,
when too concentrated solutions were used), only amorph-
ous products formed.
Scheme 1. Synthesis of ligands 1. i: H2SO4, 90 °C, 90 h; ii: 1)
HPPh2, KOtBu, THF, 60 °C, 16 h. 2) NaClO4, room temp., 1 h; iii
(for a, b, and c): RB(OH)2, Pd(PPh3)4, K2CO3, toluene, water, re-
flux, 16 h; iv (for d): RZnCl, Pd(PPh3)4, THF, 60 °C, 24 h; v:
PhSiH3, reflux, 16 h.
The crystal structures of complexes 6a, 6b, and 6d re-
Dehydration of 2-bromo-6-(1-hydroxyethyl)pyridine (2)[17] vealed dimeric species with two ligands spanning two palla-
yielded 2-bromo-6-vinylpyridine (3) in good yield after dium centers in a head-to-tail fashion forming a 12 mem-
heating it in sulfuric acid for almost 4 d. When 3 was stored bered ring, as shown in Figure 1. The structures are dis-
at room temperature for a few days, it decomposed to give cussed in detail below. The high resolution mass spectra
a sticky substance, most likely due to polymerization of the [fast atom bombardment (FAB) ionization] showed the
compound. It is therefore best stored at low temperatures peak for the [(ligand)2Pd2(CH3)2Cl]+ ion for all complexes
in the dark or used immediately. Alkene 3 was hydrophos- (loss of one chlorine atom is a consequence of the ioniza-
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Scheme 2. Synthesis of complexes 6. i: (COD)Pd(CH3)Cl, CH2Cl2,
room temp., 16 h.
tion technique employed: the ionization of the complex by
proton addition is immediately followed by loss of HCl).
Thus, the dimeric nature of the complexes was also demon-
strated for 6c. Elemental analyses were in agreement with
the proposed structures. The most striking difference be-
tween structures 6a and 6b and the structure of 6d concerns
the surrounding of the individual palladium centers. In
compound 6d, having the bulky anthracene substituent on
the pyridyl units, both palladium centers have the methyl
and chloride anions in mutual trans positions. In 6a and 6b,
one of the two palladium centers exhibits the cis configura-
tion (again, with respect to methyl and chloride), while the
other center has these anions trans to one another.
This is a peculiar and unexpected finding, as the binding
mode is usually determined by the ligands coordinating to
the metal, the precursors used for the synthesis, and the
reaction conditions employed. These are all identical in our
case. To the best of our knowledge, these are the first re-
ported examples of a homonuclear, bimetallic complex that
has both cis and trans surrounded metal centers in one
complex in which both centers coordinate to identical li-
gands. Known palladium complexes with the ligand 2-[2-
(diphenylphosphanyl)ethyl]pyridine (1 with R = H) all exist
as monomeric, cis-coordinated species.[10a,18] Bridging
structures containing the related ligands N-[(diphenylphos-
phanyl)methyl]-2-pyridinamine[12b,12c] and N-[(diphenyl-
phosphanyl)methyl]-2-pyrimidinamine[12d] are known, but
in those cases both palladium centers show the trans config-
uration.
The solids were further characterized with 31P direct po-
larization magic-angle spinning (DPMAS) NMR spec-
troscopy. Spectra are shown in Figure 2. The spectrum of
6d, bearing the 9-anthracyl-substituted ligand, shows one
signal at δ = 23.8 ppm, consistent with the presence of one
unique phosphorus nucleus in the crystal structure. For 6b,
which has the 1-naphthyl substituent at the pyridyl-6 posi-
tion, signals at δ = 38.1 and 21.1 ppm are observed. Again,
this is in agreement with the X-ray crystal structure, which
shows two inequivalent phosphanes. We attribute the for-
Figure 1. Displacement ellipsoid plots of 6a (top), 6b (middle), and
6d (bottom) in the crystal, drawn at the 50% probability level. Hy-
drogen atoms and disordered solvent molecules are omitted for
clarity. Symmetry operation a (compound 6d): 1 – x, 1 – y, 1 – z.
mer signal to the phosphorus cis to the pyridine, and the signal for 6d and the trans signal for 6b. On the basis of the
latter to the trans-coordinating phosphorus on basis of the NMR spectrum and the characterization mentioned above,
chemical shift observed for trans-coordinated complex 6d. we propose a structure for 6c in which two ligands span
The appearance of the cis-coordinating phosphorus signal two trans-coordinated Pd(CH3)Cl centers in a head-to-tail
at high ppm value compared to the trans signal has been fashion, similar to the structure of 6d. The spectrum of 6a
observed for palladium complexes with bridging P,N li- (having the phenyl-substituted ligand) shows one peak at δ
gands[19] and with chelating diphosphanes.[20] Complex 6c, = 36.3 ppm. This is in contrast to the X-ray crystal struc-
with the 9-phenanthryl group at the ligand, gives rise to one ture, in which two inequivalent phosphorus nuclei are pres-
signal, at δ = 26.9 ppm. This is in the same region as the ent. Apparently, the conformation of the amorphous solid
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Coordination Mode of Dimeric Palladium Complexes
formed from the reaction when stirring is employed is dif- X-ray Crystal Structures
ferent from that of the single crystals formed after slow dif-
The crystal structures of compounds 6a, 6b, and 6d con-
fusion of the reactants. This again emphasizes that subtle
changes can give rise to different coordination behavior in
these complexes. The mass spectrum proved the dimeric na-
ture of the complex prepared while stirring. We assign a
structure to complex 6a in which both palladium centers
have the methyl and chloride anions in a cis configuration.
tain co-crystallized solvent molecules, which are severely
disordered. In 6d the solvent accessible voids are arranged
in channels in the crystallographic a,b-plane, which occupy
31% of the unit cell volume (see Figure 3). Complexes 6a
and 6b have no molecular symmetry, while 6d is located on
an inversion center. Details of the crystal structure determi-
nations are summarized in the experimental section. Both
metal centers in the crystal structure of 6a have a slightly
distorted square planar surrounding, but with opposite ori-
entations of the ligands. Selected bond lengths and dis-
tances are shown in Table 1. The coordination environ-
ments of the two Pd centers are significantly different. This
might be a consequence of different trans-effects of the li-
gands. Minor substitutional disorder between methyl and
chloride fragments, which is rather common in such mixed
ligand systems and influences the geometries, cannot be ex-
cluded either.[21] The intermetallic distance confirms the ab-
sence of Pd···Pd interactions. The structure of 6b is similar
to that of 6a. Selected bond lengths and distances are sum-
marized in Table 2. Both metal centers have a distorted
square planar surrounding and the palladium atoms have a
Figure 3. Packing of 6d in the crystal. View along the crystallo-
graphic c axis. The Pd complex is shown as a black wire model.
The solvent accessible voids are shown in gray. For the treatment
of the disordered solvent see Exp. Section.
Figure 2. The 31P MAS solid-state NMR spectra of compound 6a–
d. The asterisk * denotes spinning sidebands.
Table 1. Selected bond lengths [Å], angles [°], and dihedral angles
[°] in complex 6a.
Thus, different geometric configurations around each of
the palladium centers in the dimeric complex are possible.
The influence of the substituent in position 2 of the pyr-
idine ring of the ligand on the outcome is noteworthy. Start-
ing from complex 4 (Scheme 1), different groups can be in-
troduced. Clearly, the steric bulk of the substituent deter-
mines the coordination chemistry in the complex: de-
pending on the ligand (and synthetic conditions) a cis-cis,
cis-trans, or trans-trans bimetallic complex can be obtained.
Therefore, dimeric species with identical or different (but
homonuclear) metal centers can be obtained from bidentate
ligands and the coordination mode can be varied by choice
of the ligand substituent.
Pd1–Cl1
Pd1–C26
Pd1–P1A
Pd1–N1
2.4116(6)
2.058(2)
2.2137(6)
Pd1A–Cl1A
Pd1A–C26A
Pd1A–P1
2.4248(6)
2.097(2)
2.2320(6)
2.1652(18)
2.1953(18) Pd1A–N1A
Pd1···Pd1A
Cl1–Pd1–C26
Cl1–Pd1–P1A
Cl1–Pd1–N1
P1A–Pd1–N1
P1A–Pd1–C26
N1–Pd1–C26
Pd1-coordination plane Є N1-pyridyl ring
Pd1A-coordination plane Є N1A-pyridyl ring
Pd1- Є Pd1A-coordination planes
5.3353(3)
87.42(7)
167.52(2)
92.88(5)
95.19(5)
85.30(7)
175.30(8)
Cl1A–Pd1A–C26A 176.10(7)
Cl1A–Pd1A–P1 88.89(2)
Cl1A–Pd1A–N1A 90.42(5)
P1–Pd1A–N1A
P1–Pd1A–C26A
173.23(5)
93.38(6)
N1A–Pd1A–C26A 87.70(8)
82.76(8)°
78.58(9)
8.67(6)°
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FULL PAPER
nonbonding distance. In Table 3, selected bond lengths and
distances are collected for 6d. The structure of 6d is centro-
symmetric; consequently there is only one independent pal-
ladium center. The angles around palladium show a slight
distortion from exact square-planar geometry. As a conse-
quence of symmetry, the coordination planes around Pd1
and Pd1a are parallel.
Experimental Section
General Information: All reactions involving sensitive compounds
were carried out under an atmosphere of purified dinitrogen using
standard Schlenk techniques. Solvents were dried and distilled un-
der dinitrogen; CH2Cl2 from CaH2, toluene from sodium, Et2O and
THF from sodium/benzophenone, and hexanes from sodium/
benzophenone/triglyme. 2-Bromo-6-(1-hydroxyethyl)pyridine (2),[17]
9-phenanthrylboronic acid,[22] and (COD)Pd(CH3)Cl[23] were pre-
pared according to literature procedures. Zincchloride was dried by
refluxing in freshly distilled thionyl chloride for 16 h, removal of
the solvent under reduced pressure and drying in vacuo for 24 h.
Phenylsilane was distilled under dinitrogen. All other chemicals
were purchased from commercial suppliers and used as received.
Silica 60 was used for column chromatography. Elemental analyses
were carried out by Kolbe Mikroanalytisches Laboratorium,
Mülheim an der Ruhr (Germany). Electron ionization (EI) mass
spectrometry (MS) was carried out on an Agilent Technologies
6890N/5973N GC-MS using an ionizing energy of 70 eV. Samples
were dissolved in Et2O or CH2Cl2. Fast Atom Bombardment
(FAB) high resolution mass spectrometry (HRMS) was carried out
at the Department of Mass Spectrometry at the University of Am-
sterdam using a JEOL JMS SX/SX102A four-sector mass spec-
trometer, coupled to a JEOL MS-MP9021D/UPD system program.
Samples were loaded in a matrix solution (3-nitrobenzyl alcohol)
on to a stainless steel probe and bombarded with xenon atoms with
an energy of 3 keV. During the high resolution FAB-MS measure-
ments a resolving power of 10000 (10% valley definition) was used.
Solution phase NMR spectra were recorded on a Varian Mercury
300 operating at 300.1 (1H), 75.5 (13C), and 121.5 (31P) MHz or a
Varian Inova 500 operating at 499.8 (1H) and 125.7 (13C) MHz at
ambient temperature. Signals are referenced to TMS (1H and 13C)
or 85% H3PO4 (31P) as external standards. The following abbrevi-
ations are used: py = pyridyl, naph = naphthyl, phen = phenan-
thryl, anth = anthracyl.
Table 2. Selected bond lengths [Å], angles [°], and dihedral angles
[°] in complex 6b..
Pd1–Cl1
Pd1–C301
Pd1–P2
Pd1–N1
2.4451(8)
2.055(3)
2.2303(8)
2.152(2)
5.1004(3)
178.85(9)
87.41(3)
92.13(7)
177.05(7)
93.34(9)
87.16(11)
Pd2–Cl2
Pd2–C302
Pd2–P1
2.3945(8)
2.050(3)
2.2409(8)
2.209(2)
Pd2–N2
Pd1···Pd2
Cl1–Pd1–C301
Cl1–Pd1–P2
Cl1–Pd1–N1
P2–Pd1–N1
P2–Pd1–C301
N1–Pd1–C301
Cl2–Pd2–C302 86.65(9)
Cl2–Pd2–P1
Cl2–Pd2–N2
P1–Pd2–N2
P1–Pd2–C302
170.42(3)
91.31(6)
98.26(6)
83.80(9)
N2–Pd2–C302 175.83(11)
Pd1-coordination plane Є N1-pyridyl ring
Pd2-coordination plane Є N2-pyridyl ring
Pd1- Є Pd2-coordination planes
76.38(12)
75.53(11)
2.63(7)
Table 3. Selected bond lengths [in Å], angles [in °], and dihedral
angles [in °] in complex 6d.[a]
Pd1–Cl1
Pd1–C34
Pd1–P1a
Cl1–Pd1–C34
Cl1–Pd1–P1a
Cl1–Pd1–N1
2.4229(6)
2.084(2)
2.2273(6)
167.49(7)
97.18(2)
89.17(5)
Pd1–N1
Pd1···Pd1a
2.1431(18)
4.7131(2)
P1a–Pd1–N1 172.01(5)
P1a–Pd1–C34 86.64(6)
N1–Pd1–C34
88.16(8)
88.33(9)
Pd1-coordination plane Є N1-pyridyl ring
Solid State NMR: The 31P direct polarisation magic-angle spinning
solid-state nuclear magnetic resonance (31P-DPMAS SSNMR)
spectra were recorded on a triple channel 500 MHz Varian Infin-
ityplus spectrometer operating at a frequency of 202.460 MHz for
31P. A 4 mm Chemagnetics T3 triple channel MAS probe was used
at ambient temperature. The spectrum 6b Figure 2 was recorded
on a Bruker 400 MHz Avance III operating at a frequency of
161.976 MHz for 31P with a 4-mm triple-channel MAS probe. The
rotors in were zirconium oxide fitted with vespel end caps. Spinning
speeds were 12 kHz (MAS) with a 90° pulse length of 4 µs (Varian)
and 3.5 (Bruker) and a 120 s recycle time in both cases. The number
[a] Symmetry operation a: 1 – x, 1 – y, 1 – z.
Conclusions
We have prepared new pyridine-phosphane bidentate li-
gands 1a–d, having substituents with different, tunable ste-
ric bulk at C-2 of the pyridine ring. The insoluble methyl-
palladium chloride complexes 6 of these ligands are dimeric of transients varied between 24 and 400 and spectra were refer-
enced to Brushite at δ = –1.6 ppm. The pulse program used is a
standard direct-polarization sequence with a spectra width of
100 kHz.
structures, in which two ligands span two palladium centers
in a head-to-tail fashion forming a 12-membered ring. In
6c and 6d, bearing the largest substituents at the pyridyl
unit, both palladium centers exhibit trans orientation of the
X-ray Crystal Structure Determinations: Crystals of 6a, 6b, and 6d
chloride and methyl ligands. Complex 6b, containing an in- suitable for X-ray diffraction were obtained by layering a solution
of (COD)Pd(CH3)Cl (≈ 10 mg) in CH2Cl2 (≈ 1 mL) in a small glass
tube with a solution of the appropriate ligand (1.0 equiv.) in a 2:1
mixture of Et2O and CH2Cl2 (≈ 2 mL). Reflections were measured
on a Nonius Kappa CCD diffractometer with rotating anode
(graphite monochromator, λ = 0.71073 Å) at a temperature of
150 K up to a resolution of (sin θ/λ)max = 0.65 Å–1. The structures
were solved with Direct Methods (SHELXS-97[24]) and refined with
SHELXL-97[24] against F2 of all reflections. Non hydrogen atoms
were refined with anisotropic displacement parameters. All hydro-
gen atoms were introduced in calculated positions and refined with
a riding model. Geometry calculations and checking for higher
termediately sized pyridyl-substituent, consists of one cis-
and one trans-surrounded metal center. Complex 6a, con-
taining the smallest pyridyl-substituent, can orient the
anions at one palladium center cis and at the other trans
(like in 6b), or have both centers in cis configuration, de-
pending on the conditions during synthesis. The unique and
tunable coordination behavior of the ligands enables con-
trolled interaction of the metal centers with bifunctional
substrates which has great potential in the fields of catalysis
and transition metal chemistry.
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Coordination Mode of Dimeric Palladium Complexes
Table 4. Details of the X-ray crystal structure determinations.
Complex
Formula
6a
6b
6d
C52H50Cl2N2P2Pd2·disordered
C60H54Cl2N2P2Pd2·disordered
solvent
C68H58Cl2N2P2Pd2·disordered
solvent
solvent
Fw
1048.58[a]
yellow
1148.69[a]
1248.80[a]
yellow
Crystal colour
Crystal size [mm3]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
yellowish
0.40ϫ0.18ϫ0.09
triclinic
0.42ϫ0.24ϫ0.06
triclinic
0.36ϫ0.15ϫ0.15
tetragonal
I41/a (no. 88)
31.5532(1)
31.5532(1)
14.8255(1)
90
¯
¯
P1 (no. 2)
P1 (no. 2)
11.2408(3)
13.0342(4)
16.4293(3)
83.947(1)
77.022(2)
80.589(2)
2308.16(10)
2
11.2735(2)
15.1764(2)
17.9279(3)
66.1520(7)
80.9984(8)
81.8334(8)
2760.31(8)
2
α [°]
β [°]
90
90
γ [°]
V [Å3]
14760.33(12)
8
1.124
Z
Dx [g/cm3]
1.509
1.002
1.382
0.845
[a]
[a]
[a]
µ [mm–1]
0.637
[a]
[a]
[a]
Absorption correction method multi-scan
Absorption correction range 0.55–0.92
Reflections (measured/unique) 47280/10588
multi-scan
0.76–0.95
36936/12491
615/0
0.0386/0.0851
0.0576/0.0930
1.055
multi-scan
0.81–0.91
78094/8442
344/0
0.0349/0.0934
0.0451/0.0974
1.086
Parameters/restraints
R1/wR2 [IϾ2σ(I)]
R1/wR2 (all reflections)
S
543/0
0.0261/0.0598
0.0356/0.0624
1.107
ρmin/max [e/Å3]
–0.42/0.63
–0.93/1.53
–0.51/0.68
[a] Derived parameters do not contain the contribution of the disordered solvent.
symmetry was performed with the PLATON program.[25] Further
details are given in Table 4.
C7H6BrN (184.03): calcd. C 45.68, H 3.29, N 7.61; found C 45.63,
H 3.22, N 7.49.
6a: The crystal structure contains voids (93 Å3/unit cell) filled with
disordered solvent molecules. Their contribution to the structure
factors was secured by back-Fourier transformation using the
SQUEEZE routine of the program PLATON,[25] resulting in 31
electrons/unit cell. by back-Fourier transformation using the
SQUEEZE routine of the program PLATON,[25] resulting in 93
electrons/unit cell.
6d: The crystal structure contains large voids (4647 Å3/unit cell)
filled with disordered solvent molecules. Their contribution to the
structure factors was secured by back-Fourier transformation using
the SQUEEZE routine of the program PLATON,[25] resulting in
852 electrons/unit cell.
Note: When 3 was kept at room temperature for a few days, it
decomposed to give a sticky substance, most likely due to polymeri-
zation of the compound. It is therefore best stored at low tempera-
tures in the dark or used immediately.
2-Bromo-2-[2-(diphenylphosphinoyl)ethyl]pyridine (4): 2-Bromo-6-
vinylpyridine (3) (2.27 g, 12.4 mmol, 1.0 equiv.) and diphenylphos-
phane (2.15 mL, 12.4 mmol, 1.0 equiv.) were dissolved in THF
(60 mL). KOtBu (139 mg, 1.24 mmol, 0.1 equiv.) was added and
the deep blue mixture was stirred at 60 °C for 20 h, after which it
turned brown and 31P NMR showed full conversion. Water (5 mL)
was added and the mixture was concentrated in vacuo. The remain-
der was redissolved in CH2Cl2 and 50 mL of household bleach (4 g
active chlorine/100 mL) was added. The mixture was stirred vigor-
ously for 1 h. Water was added, the aqueous phase was extracted
twice with CH2Cl2 and the combined organic phases were dried
and concentrated to yield an off-white solid. This was purified by
column chromatography (5% MeOH in CH2H2 as the eluent) to
yield the product as a white solid (4.32 g, 11.1 mmol, 91%); m.p.
CCDC-689397 (for 6a), -689398 (for 6b), and -689399 (for 6d) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
2-Bromo-6-vinylpyridine (3): 2-Bromo-6-(1-hydroxyethyl)pyridine
(2) (10.7 g, 52.8 mmol, 1 equiv.) was dissolved in sulfuric acid
(50 mL, 938 mmol, 18 equiv.) and stirred at 90 °C using a CaCl2
tube. After 90 h, the mixture was poured on ice, made basic with
sodium carbonate and extracted with Et2O. The organic layer was
washed with water (2ϫ) and brine, dried with MgSO4 and concen-
trated in vacuo to yield the product as a yellowish oil (8.52 g,
46.3 mmol, 88%). 1H NMR (300 MHz, CDCl3): δ = 7.47 (t, J =
7.7 Hz, 1 H, py-H4), 7.30 (dd, J = 7.9, 0.7 Hz, 1 H, py-H3), 7.24
(dd, J = 7.6, 0.7 Hz, 1 H, py-H5), 6.70 (dd, J = 17.4, 10.7 Hz, 1
H, vinyl-CH), 6.21 (dd, J = 17.4, 1.1, 1 H, vinyl-CHH), 5.49 (dd,
J = 10.7, 1.1 Hz, 1 H, vinyl-CHH) ppm. 13C{1H} NMR (75 MHz,
CDCl3): δ = 157.2 (py-C6), 142.2 (py-C2), 139.0, 135.6, 126.9,
120.2, 120.1 ppm. MS (EI): m/z (%) = 185 (88) [M (81Br)]+, 183
1
160 °C. H NMR (300 MHz, CDCl3): δ = 7.80–7.70 (m, 4 H, o-H,
Ph), 7.53–7.41 (m, 6 H, m- and p-H, Ph), 7.35 (t, J = 7.7 Hz, 1 H,
py-H4), 7.24 (dd, J = 7.7, 0.6 Hz, 1 H, py-H3), 7.07 (dd, J = 7.7,
0.6 Hz, 1 H, py-H5), 3.15–3.05 (m, 2 H, PCH2CH2), 2.81–2.71 (m,
2 H, PCH2). 13C{1H} NMR (125 MHz, CDCl3): δ = 161.9 (d, J =
13.3 Hz, py-C6), 141.8 (s, py-C2), 138.9 (s, CH), 132.8 (d, J =
98.9 Hz, i-C, Ph), 132.0 (s, CH), 131.0 (d, J = 9.4 Hz, CH), 128.8
(d, J = 11.6 Hz, CH), 126.0 (s, CH), 122.1 (s, CH), 29.6 (s,
PCH2CH2), 29.1 (d, J = 71.4 Hz, PCH2) ppm. 31P{1H} NMR
(121 MHz, CDCl3): δ = 33.4 ppm. HRMS (FAB) m/z calcd. for
C19H18BrNOP [M
+
H]+: 386.0309; found 386.0303.
C19H17BrNOP (386.22): calcd. C 59.09, H 4.44, N 3.63; found C
59.15, H 4.48, N 3.55.
(91) [M (79Br)]+, 159 (15) [M (81Br) – C2H2]+, 157 (15) [M (79Br) – 2-[2-(Diphenylphosphinoyl)ethyl]-6-phenylpyridine (5a): A mixture
C2H2]+, 104 (100) [M – Br]+, 77 (13) [M – Br – (CH2CH)]+.
of 2-bromo-6-[2-(diphenylphosphinoyl)ethyl]pyridine (4) (1.50 g,
Eur. J. Inorg. Chem. 2008, 4968–4976
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4973

P. C. J. Kamer et al.
FULL PAPER
3.88 mmol, 1.0 equiv.), phenylboronic acid (710 mg, 5.83 mmol,
1.5 equiv.), Pd(PPh3)4 (9.0 mg, 7.7 µmol, 0.002 equiv.), K2CO3
(22.8 g, 165 mmol, 43 equiv.), water (20 mL) and toluene (40 mL)
was refluxed for 16 h. EtOAc was added, and the organic phase
was washed with water (3 times) and brine, dried, and concentrated
in vacuo. The product was purified using column chromatography
(eluent: 5% MeOH in CH2Cl2) to yield the product as an off-white
-H6), 7.63–7.59 (m, 1 H, phen-H2), 7.56–7.52 (m, 1 H, phen-H7),
7.48–7.44 (m, 2 H, p-H, Ph), 7.43–7.38 (m, 5 H, py-H5 + m-H,
Ph), 7.21 (d, J = 7.7 Hz, 1 H, py-H3), 3.32–3.21 (m, 2 H,
PCH2CH2), 2.95–2.83 ppm (m, 2 H, PCH2) ppm. 13C{1H} NMR
(125 MHz, CDCl3): δ = 160.0 (d, J = 13.9 Hz, py-C2), 158.9 (s, py-
C6), 137.3 (s, Cq), 137.0 (s, CH), 133.0 (d, J = 98.4 Hz, i-C, Ph),
131.8 (d, J = 2.7 Hz, CH), 131.4 (s, Cq), 130.9 (d, J = 9.3 Hz, CH),
130.9 (s, Cq), 130.5 (s, Cq), 130.4 (s, Cq), 129.0 (s, CH), 128.7 (d, J
1
solid (1.41 g, 3.67 mmol, 95%); m.p. 145 °C. H NMR (500 MHz,
CDCl3): δ = 8.01–7.98 [m, 2 H, o-H, Ph(py)], 7.82–7.77 [m, 4 H, = 11.6 Hz, CH), 128.5 (s, CH), 127.1 (s, CH), 126.9 (s, CH), 126.8
o-H, Ph(P)], 7.60 (t, J = 7.7 Hz, 1 H, py-H4), 7.52 (d, J = 7.7 Hz, (s, CH), 126.7 (s, CH), 126.6 (s, CH), 123.0 (s, CH), 122.9 (s, CH),
1 H, py-H5), 7.51–7.40 [m, 9 H, o- + p-H, Ph(P) + o- + p-H, 122.6 (s, CH), 121.5 (s, CH), 30.0 (d, J = 2.6 Hz, PCH2CH2),
Ph(py)], 7.07 (d, J = 7.7 Hz, 1 H, py-H3), 3.25–3.18 (m, 2 H,
29.2 ppm (d, J = 71.5 Hz, PCH2) ppm. 31P{1H} NMR (121 MHz,
PCH2CH2), 2.95–2.89 ppm (m, 2 H, PCH2) ppm. 13C{1H} NMR CDCl3): δ = 33.4 ppm. HRMS (FAB): m/z calcd. for C33H27NOP
(125 MHz, CDCl3): δ = 160.0 (d, J = 13.9 Hz, py-C2), 156.8 (s, py- [M + H]+: 484.1830; found 484.1841. C33H26NOP (483.54): calcd.
C6), 139.5 [s, i-C, Ph(py)], 137.3 (s, CH), 133.2 [d, J = 98.3 Hz, i-
C, Ph(P)], 131.8 (d, J = 2.7 Hz, CH), 131.0 (d, J = 9.3 Hz, CH),
129.1 (s, CH), 128.8 (s, CH), 128.7 (s, CH), 127.1 (s, CH), 121.5 (s,
CH), 118.3 (s, CH), 30.0 (d, J = 2.5 Hz, PCH2CH2), 29.2 ppm (d,
J = 71.7 Hz, PCH2) ppm. 31P{1H} NMR (121 MHz, CDCl3): δ =
33.1 ppm. HRMS (FAB): m/z calcd. for C25H23NOP [M + H]+:
384.1517; found 384.1512. C25H22NOP (383.42): calcd. C 78.31, H
5.78, N 3.65; found C 78.24, H 5.79, N 3.57.
C 81.97, H 5.42, N 2.90; found C 81.90, H 5.37, N 2.79.
2-(9-Anthracyl)-6-[2-(diphenylphosphinoyl)ethyl]pyridine (5d): To a
solution of 9-bromoanthracene (3.21 g, 12.5 mmol, 5.0 equiv.) in
THF (20 mL) was slowly dropped a 2.5  solution of n-butyllith-
ium (5.0 mL, 12.5 mmol, 5.0 equiv.) in hexanes at –78 °C. The mix-
ture was stirred at that temperature for 30 min, after which a solu-
tion of ZnCl2 (1.70 g, 12.5 mmol, 5.0 equiv.) in THF (15 mL) was
added. The mixture was stirred for 1 h at room temperature, after
which a solution of Pd(PPh3)4 (144 mg, 0.125 mmol, 5%) in THF
(5 mL) was added. The mixture was cooled to 0 °C, a solution of
2-[2-(Diphenylphosphinoyl)ethyl]-6-(1-naphthyl)pyridine (5b): A mix-
ture of 2-bromo-6-[2-(diphenylphosphinoyl)ethyl]pyridine (4)
(2.51 g, 6.49 mmol, 1.0 equiv.), 1-naphthylboronic acid (1.68 mg, 2-bromo-6-[2-(diphenylphosphinoyl)ethyl]pyridine (4) (966 mg,
9.74 mmol, 1.5 equiv.), Pd(PPh3)4 (15 mg, 13 µmol, 0.002 equiv.),
K2CO3 (38.1 g, 276 mmol, 43 equiv.), water (30 mL) and toluene
(60 mL) was refluxed for 16 h. EtOAc was added, and the organic
phase was washed with water (3 times) and brine, dried and concen-
trated in vacuo. The product was purified by column chromatog-
raphy (eluent: 5% MeOH in CH2Cl2) to yield the product as a
white solid (2.46 mg, 5.69 mmol, 88%); m.p. 153 °C. 1H NMR
2.50 mmol, 1.0 equiv.) in THF (40 mL) was added and the mixture
was stirred at 60 °C for 24 h. After that, water was added, the mix-
ture was concentrated in vacuo and EtOAc was added. The organic
layer was washed with water, a solution of potassium oxalate
(4.00 g, 22.0 mmol) in water, water again, and finally brine, then
dried and concentrated in vacuo. Column chromatography (eluent:
CH2Cl2 to 5% MeOH in CH2Cl2) yielded the product as a yellow
1
(500 MHz, CDCl3): δ = 8.07 (d, J = 8.4 Hz, 1 H, naph-H4), 7.92– solid (1.19 g, 2.46 mmol, 99%); m.p. 188 °C. H NMR (500 MHz,
7.89 (m, 2 H, naph-H6 + -H7), 7.80–7.73 (m, 4 H, o-H, Ph), 7.66 CDCl3): δ = 8.51 (s, 1 H, anth-H10), 8.03 (d, J = 8.4 Hz, 2 H, anth-
(t, J = 7.7 Hz, 1 H, py-H4), 7.59–7.53 (m, 2 H, naph-H8 + -H5),
7.52–7.45 (m, 4 H, p-H, Ph + naph-H2 + -H3), 7.44–7.39 (m, 4 H,
m-H, Ph), 7.37 (d, J = 7.7 Hz, 1 H, py-H5), 7.19 (d, J = 7.7 Hz, 1
H, py-H3), 3.30–3.18 (m, 2 H, PCH2CH2), 2.93–2.82 (m, 2 H,
PCH2) ppm. 13C NMR (125 MHz, CDCl3): δ = 160.0 (d, J =
H1), 7.77–7.71 (m, 4 H, o-H, Ph), 7.55 (d, J = 8.8 Hz, 2 H, anth-
H4), 7.48–7.43 (m, 5 H, py-H4 + p-H, Ph + anth-H2), 7.42–7.38
(m, 4 H, m-H, Ph), 7.37–7.29 (m, 4 H, py-H3 + -H5 + anth-H3),
3.34–3.26, (m, 2 H, PCH2CH2), 2.87–2.80 ppm (m, 2 H, PCH2).
13C{1H} NMR (125 MHz, CDCl3): δ = 160.7 (d, J = 13.7 Hz, py-
13.9 Hz, py-C2), 158.7 (s, py-C6), 137.0 (s, Cq), 138.5 (s, Cq), 134.1 C6), 157.8 (s, py-C2), 136.8 (s, CH) 135.4 (s, Cq), 133.0 (d, J =
(s, Cq), 133.0 (d, J = 98.5 Hz, i-C, Ph), 131.8 (d, J = 2.7 Hz, CH), 98.5 Hz, i-C, Ph), 131.8 (d, J = 2.5 Hz, CH), 131.6 (s, Cq), 131.0
131.3 (s, Cq), 131.0 (d, J = 9.3 Hz, CH), 129.0 (s, CH), 128.8 (d, J (d, J = 9.3 Hz, CH), 130.2 (s, Cq), 128.8 (d, J = 11.6 Hz, CH),
= 11.6 Hz, CH), 128.5 (s, CH), 127.7 (s, CH), 126.4 (s, CH), 126.0 128.6 (s, CH), 127.7 (s, CH), 126.3 (s, CH), 125.9 (s, CH), 125.3 (s,
(s, CH), 125.9 (s, CH), 125.5 (s, CH), 123.0 (s, CH), 121.5 (s, CH), CH), 124.8 (s, CH), 121.7 (s, CH), 30.1 (s, PCH2CH2), 29.4 ppm
30.0 (d, J = 1.9 Hz, PCH2CH2), 29.3 (d, J = 71.5 Hz, PCH2) ppm. (d, J = 71.4 Hz, PCH2). 31P{1H} NMR (121 MHz, CDCl3): δ =
31P{1H} NMR (121 MHz, CDCl3): δ = 32.9 ppm. HRMS (FAB):
m/z calcd. for C29H25NOP [M + H]+: 434.1674; found 434.1673.
C29H24NOP (433.48): calcd. C 80.35, H 5.58, N 3.23; found C
80.23, H 5.62, N 3.28.
33.4 ppm. HRMS (FAB): m/z calcd. for C33H27NOP [M + H]+:
484.1830; found 484.1843; C33H26NOP (483.54): calcd. C 81.97, H
5.42, N 2.90; found C 81.85, H 5.47, N 2.82.
2-[2-(Diphenylphosphanyl)ethyl]-6-phenylpyridine (1a): 2-[2-(Di-
phenylphosphinoyl)ethyl]-6-phenylpyridine (5a) (1.00 g, 2.61 mmol,
1.0 equiv.) was dissolved in phenylsilane (5.0 mL, 40 mmol,
15 equiv.) and the mixture was refluxed overnight, after which 31P
NMR showed full conversion. The mixture was concentrated in
vacuo and co-evaporated with 3 times 5 mL toluene. The product
was purified using column chromatography with Et2O as the eluent
and a second column with CH2Cl2 as the eluent to yield the prod-
uct as a white solid (960 mg, 2.61 mmol, 100%); m.p. 94 °C; 1H
NMR (500 MHz, CDCl3): δ = 8.04 [dd, J = 8.6, 1.4 Hz, 2 H, o-H,
Ph(py)], 7.64 (t, J = 7.7 Hz, 1 H, py-H4), 7.56 (d, J = 7.7 Hz, 1 H,
2-[2-(Diphenylphosphinoyl)ethyl]-6-(9-phenanthryl)pyridine (5c): A
mixture of 2-bromo-6-[2-(diphenylphosphinoyl)ethyl]pyridine (4)
(1.36 g, 3.52 mmol, 1.0 equiv.), 9-phenanthrylboronic acid (1.17 g,
5.27 mmol, 1.5 equiv.), Pd(PPh3)4 (8 mg, 10 µmol, 0.002 equiv.),
K2CO3 (20.6 g, 149 mmol, 43 equiv.), water (20 mL) and toluene
(40 mL) was refluxed for 16 h. Then EtOAc was added, and the
organic phase was washed with water (4 times) and brine, dried
and concentrated in vacuo. The product was purified by column
chromatography (5% MeOH/CH2Cl2) to yield the product as a
white solid (1.64 g, 3.39 mmol, 96%); m.p. 178 °C. 1H NMR
(500 MHz, CDCl3): δ = 8.76 (d, J = 8.3 Hz, 1 H, phen-H4), 8.71 py-H5), 7.54–7.47 [m, 6 H, o-H, Ph(P) + m-H, Ph(py)], 7.45–7.41
(d, J = 8.3 Hz, 1 H, phen-H5), 8.07 (d, J = 8.2 Hz, 1 H, phen-H8),
7.92 (d, J = 7.5 Hz, 1 H, phen-H1), 7.81 (s, 1 H, phen-H10), 7.79–
7.74 (m, 4 H, o-H, Ph), 7.69–7.65 (m, 3 H, py-H4 + phen-H3 +
[m, 1 H, p-H, Ph(py)], 7.39–7.33 [m, 6 H, m- + p-H, Ph(P)], 7.07
(d, J = 7.7 Hz, 1 H, py-H3), 2.99–3.06 (m, 2 H, CH2CH2), 2.66–
2.61 ppm (m, 2 H, PCH2). 13C{1H} NMR (125 MHz, CDCl3): δ =
4974
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4968–4976

Coordination Mode of Dimeric Palladium Complexes
161.9 (d, J = 13.1 Hz, py-C2), 157.0 (s, py-C6), 140.1 [s, i-C, 6-(9-Anthracyl)-2-[2-(diphenylphosphanyl)ethyl]pyridine (1d): 6-(9-
Ph(py)], 139.5 [d, J = 14.7 Hz, i-C, Ph(P)], 136.9 (s, CH), 133.2 (d,
J = 18.7 Hz, CH), 129.0 (s, CH), 128.8 (d, J = 17.4 Hz, CH), 128.7
(d, J = 12.4, CH), 128.4 (s, CH), 127.4 (s, CH), 121.1 (s, CH), 117.7
(s, CH), 35.2 (d, J = 17.9 Hz, PCH2CH2), 28.5 ppm (d, J = 13.3 Hz,
Anthracyl)-2-[2-(diphenylphosphinoyl)ethyl]pyridine (5d) (853 mg,
1.76 mmol, 1.0 equiv.) was dissolved in phenylsilane (10 mL,
81 mmol, 46 equiv.) and the mixture was refluxed overnight, after
which 31P NMR showed full conversion. The mixture was concen-
PCH2). 31P{1H} NMR (121 MHz, CDCl3): δ = –14.3 ppm. MS trated in vacuo and purified by column chromatography using
(EI): m/z (%) = 367 (6) [M]+, 290 (100) [M – Ph]+, 182 (18) [M – CH2Cl2 as the eluent. Co-evaporation with hexanes yielded the
PPh2]+. C25H22NP (367.42): calcd. C 81.72, H 6.04, N 3.81; found
C 81.63, H 5.96, N 3.72.
product as a yellow solid (656 mg, 1.40 mmol, 80%); m.p. 145 °C.
1H NMR (500 MHz, CDCl3): δ = 8.52 (s, 1 H, anth-H10), 8.04 (d,
J = 8.5 Hz, 2 H, anth-H1), 7.79 (t, J = 7.7 Hz, 1 H, py-H4), 7.62
(d, J = 8.8 Hz, 2 H, anth-H4), 7.48–7.42 (m, 6 H, o-H, Ph + anth-
H2), 7.34 (d, J = 7.7 Hz, 1 H, py-H3), 7.34–7.30 (m, 8 H, m- + p-
H, Ph + anth-H3), 7.27 (d, J = 7.7 Hz, 1 H, py-H5), 3.10–3.04 (m,
2 H, PCH2CH2), 2.62–2.58 ppm (m, 2 H, PCH2). 13C{1H} NMR
(125 MHz, CDCl3): δ = 162.3 (d, J = 12.1 Hz, py-C6), 157.9 (s, py-
C2), 138.6 (d, J = 13.1 Hz, i-C, Ph), 136.7 (s, CH), 135.5 (s, anth-
C9), 133.0 (d, J = 18.5 Hz, CH), 131.7 (s, Cq), 130.3 (s, Cq), 128.7
(d, J = 12.0 Hz, CH), 128.6 (s, CH), 127.7 (s, CH), 126.4 (s, CH),
125.9 (s, CH), 125.3 (s, CH), 124.6 (s, CH), 121.5 (s, CH), 34.9 (d,
J = 17.8 Hz, PCH2CH2), 28.6 ppm (d, J = 12.6 Hz, PCH2).
31P{1H} NMR (121 MHz, CDCl3): δ = –14.8 ppm. MS (EI): m/z
(%) = 467 (10) [M]+, 390 (100) [M – Ph]+, 280 (25) [M – PPh2]+.
C33H26NP (467.54): calcd. C 84.77, H 5.61, N 3.00; found C 84.68,
H 5.65, N 2.93.
2-[2-(Diphenylphosphanyl)ethyl]-6-(1-naphthyl)pyridine (1b): 2-[2-
(Diphenylphosphinoyl)ethyl]-6-(1-naphthyl)pyridine (5b) (1.06 g,
2.45 mmol, 1.0 equiv.) was dissolved in phenylsilane (12 mL,
97 mmol, 40 equiv.) and the mixture was refluxed overnight, after
which 31P NMR showed full conversion. The mixture was concen-
trated in vacuo and purified by column chromatography using
CH2Cl2 as the eluent. Co-evaporation with hexanes yielded the
product as a white solid (875 mg, 2.10 mmol, 86%); m.p. 64 °C. 1H
NMR (500 MHz, CDCl3): δ = 8.13 (d, J = 8.4 Hz, 1 H, naph-H4),
7.90 (d, J = 8.2 Hz, naph-H6 + -H7), 7.70 (t, J = 7.7 Hz, 1 H, py-
H4), 7.59 (d, J = 6.4 Hz, 1 H, naph-H2), 7.56–7.52 (m, 1 H, naph-
H5), 7.50–7.45 (m, 5 H, o-H, Ph + naph-H8), 7.44–7.40 (m, 1 H,
naph-H3), 7.38 (d, J = 7.7 Hz, 1 H, py-H5), 7.35–7.30 (m, 6 H, m-
+ p-H, Ph), 7.15 (d, J = 7.7 Hz, 1 H, py-H3), 3.08–3.00 (m, 2 H,
PCH2CH2), 2.65–2.59 ppm (m, 2 H, PCH2). 13C{1H} NMR
(125 MHz, CDCl3): δ = 161.7 (d, J = 12.5 Hz, py-C2), 159.0 (s, py-
C6), 138.9 (s, Cq), 138.7 (d, J = 13.1 Hz, i-C, Ph), 136.9 (s, CH),
134.2 (s, Cq), 133.0 (d, J = 18.5 Hz, CH), 131.5 (s, Cq), 129.0 (s,
CH), 128.8 (s, CH), 128.6 (d, J = 6.6 Hz, CH), 128.5 (s, CH), 127.7
(s, CH), 126.5 (s, CH), 126.1 (s, CH), 126.0 (s, CH), 125.5 (s, CH),
122.7 (s, CH), 121.1 (s, CH), 34.9 (d, J = 17.5 Hz, PCH2CH2), 28.3
(d, J = 12.6 Hz, PCH2). 31P{1H} NMR (121 MHz, CDCl3): δ =
–14.7 ppm. MS (EI): m/z (%) = 417 (6) [M]+, 340 (100) [M – Ph]+,
232 (13) [M – PPh2]+. C29H24NP (417.48): calcd. C 83.43, H 5.79,
N 3.36; found C 83.56, H 5.83, N 3.28.
Dichloro-µ-{2-[2-(diphenylphosphanyl-1κP)ethyl]-6-phenylpyridine-
2κN}-µ-{2-[2-(diphenylphosphanyl-2κP)ethyl]-6-phenylpyridine-
1κN}(dimethyl)dipalladium (6a): 2-[2-(Diphenylphosphanyl)ethyl]-
6-phenylpyridine (1a) (141 mg, 0.38 mmol, 1.0 equiv.) and (COD)
Pd(CH3)Cl (102 mg, 0.38 mmol, 1.0 equiv.) were dissolved in
CH2Cl2 (10 mL) and the mixture was stirred for 16 h. Then, it was
filtered and washed with CH2Cl2 and Et2O. Drying in vacuo
yielded the product as an off-white solid (131 mg, 0.25 mmol,
65%). 31P-DPMAS NMR: δ = 36.3 ppm. HRMS (FAB): m/z calcd.
for C52H50ClN2P2Pd2 [M – Cl]+: 1013.1228; found 1013.1238.
C52H50Cl2N2P2Pd2 (1048.66): calcd. C 59.56, H 4.81, N 2.67; found
C 59.65, H 4.77, N 2.56.
2-[2-(Diphenylphosphanyl)ethyl]-6-(9-phenanthryl)pyridine (1c): 2-[2-
(Diphenylphosphinoyl)ethyl]-6-(9-phenanthryl)pyridine (5c) (500
mg, 1.03 mmol, 1.0 equiv.) was dissolved in phenylsilane (5.0 mL,
40 mmol, 39 equiv.) and the mixture was refluxed overnight, after
which 31P NMR showed full conversion. The mixture was concen-
trated in vacuo and co-evaporated with 3 times 5 mL toluene. The
product was purified using column chromatography with Et2O as
the eluent and a second column with CH2Cl2 as the eluent to yield
the product as a white solid (371 mg, 0.79 mmol, 77%); m.p. 74 °C.
1H NMR (500 MHz, CDCl3): δ = 8.77 (d, J = 8.3 Hz, 1 H, phen-
H4), 8.72 (d, J = 8.3 Hz, 1 H, phen-H5), 8.10 (d, J = 8.1 Hz, 1 H,
naph-H8), 7.92 (d, J = 7.8 Hz, 1 H, naph-H1), 7.84 (s, 1 H, naph-
H10), 7.73 (t, J = 7.6 Hz, 1 H, py-H4), 7.69–7.64 (m, 2 H, naph-
H3 + -H6), 7.63–7.59 (m, 1 H, naph-H2), 7.53–7.50 (m, 1 H, naph-
H7), 7.50–7.45 (m, 4 H, o-H, Ph), 7.44 (d, J = 7.6 Hz, 1 H, py-
H5), 7.35–7.30 (m, 6 H, m- + p-H, Ph), 7.19 (d, J = 7.6 Hz, 1 H,
py-H3), 3.09–3.02 (m, 2 H, PCH2CH2), 2.66–2.60 ppm (m, 2 H,
PCH2). 13C{1H} NMR (125 MHz, CDCl3): δ = 161.7 (d, J =
6.3 Hz, py-C2), 159.1 (s, py-C6), 138.7 (d, J = 13.0 Hz, i-C, Ph),
137.6 (s, Cq), 137.0 (s, CH), 133.1(s, CH), 133.0 (s, CH), 131.6 (s,
Cq), 131.1 (s, Cq), 130.7 (s, Cq), 130.6 (s, Cq), 129.2 (s, CH), 128.8
(s, CH), 128.6 (d, J = 6.5 Hz, CH), 128.5 (s, CH), 127.5 (s, CH),
127.0 (s, CH), 126.9 (s, CH), 126.7 (d, J = 4.1 Hz, CH), 123.1 (s,
CH), 122.8 (s, CH), 122.7 (s, CH) 121.3 (s, CH), 34.9 (d, J =
17.5 Hz, PCH2CH2), 28.3 ppm (d, J = 12.6 Hz, PCH2). 31P{1H}
NMR (121 MHz, CDCl3): δ = –14.8 ppm. MS (EI): m/z (%) = 467
(9) [M]+, 390 (100) [M–Ph]+, 280 (14) [M – PPh2]+. C33H26NP
(467.54): calcd. C 84.77, H 5.61, N 3.00; found C 84.70, H 5.68, N
2.94.
Dipalladium Complex 6b: 2-[2-(Diphenylphosphanyl)ethyl]-6-(1-
naphthyl)pyridine (1b) (148 mg, 0.355 mmol, 1.0 equiv.) and
(COD)Pd(CH3)Cl (94 mg, 0.355 mmol, 1.0 equiv.) were dissolved
in CH2Cl2 (10 mL) and the mixture was stirred for 16 h. Then, it
was filtered off and washed with CH2Cl2 and Et2O. Drying in
vacuo yielded the product as a white solid (146 mg, 0.254 mmol,
72%); m.p. 184 °C (dec.); 31P-DPMAS NMR: δ = 38.1, 21.1 ppm.
HRMS (FAB): m/z calcd. for C60H54ClN2P2Pd2 [M – Cl]+:
1113.1544; found 1113.1531. C60H54Cl2N2P2Pd2 (1148.78): calcd.
C 62.73, H 4.74, N 2.44; found C 62.58, H 4.66, N 2.32.
Dipalladium Complex 6c: 2-[2-(Diphenylphosphanyl)ethyl]-6-(9-
phenanthryl)pyridine (1c) (200 mg, 0.43 mmol, 1.0 equiv.) and
(COD)Pd(CH3)Cl (113 mg, 0.43 mmol, 1.0 equiv.) were dissolved
in CH2Cl2 (10 mL) and the mixture was stirred for 16 h. Then, it
was concentrated in vacuo to approximately 1 mL, after which
10 mL Et2O was added under vigorous stirring. The white precipi-
tate was filtered off and washed with Et2O. Drying in vacuo yielded
the product as a white solid (219 mg, 0.35 mmol, 82%); m.p. 182 °C
(dec.). 31P-DPMAS NMR: δ = 26.9 ppm. HRMS (FAB): m/z calcd.
for C68H58ClN2P2Pd2 [M – Cl]+: 1213.1860; found 1213.1869.
C68H58Cl2N2P2Pd2 (1248.90): calcd. C 65.40, H 4.68, N 2.24; found
C 65.28, H 4.62, N 2.15.
Dipalladium Complex 6d: 6-(9-Anthracyl)-2-[2-(diphenylphos-
phanyl)ethyl]pyridine (1d) (386 mg, 0.83 mmol, 1.0 equiv.) and
(COD)Pd(CH3)Cl (219 mg, 0.83 mmol, 1.0 equiv.) were dissolved
in CH2Cl2 (20 mL) and the mixture was stirred for 16 h. Then, it
Eur. J. Inorg. Chem. 2008, 4968–4976
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4975

P. C. J. Kamer et al.
FULL PAPER
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Acknowledgments
This work is part of the research program of the Dutch Polymer
Institute (project 106). It was financially supported (M. L., A. L.
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Received: August 12, 2008
Published Online: September 16, 2008
4976
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Eur. J. Inorg. Chem. 2008, 4968–4976