η5-Cyclopentadienylpalladium(II) complexes: Synthesis, characterization and use for the vinyl addition polymerization of norbornene and the copolymerization with 5-vinyl-2-norbornene or 5-ethylidene-2-norbornene

Article abstract of DOI:10.1016/j.jorganchem.2010.08.050

Dinuclear complexes of palladium(II), containing two bridging halogen (Cl or Br) ligands, [NⁿBu₄]₂[(X₅C ₆)₂Pd(μ-Cl)₂Pd(C₆X ₅)₂] and [(X₅C₆)(L)Pd(μ-Y) ₂Pd(C₆X₅)(L)] (X = F, Cl; Y = Cl, Br), readily react with cyclopentadienylthallium, C₅H₅Tl, to give the corresponding air stable half-sandwich, pseudo-trigonal η⁵- cyclopentadienylpalladium complexes, [NⁿBu₄] [(η⁵-C₅H₅)Pd(C₆X ₅)₂] (X = F 1, Cl 2) and (η⁵-C ₅H₅)Pd(C₆X₅)(L) (X = F, L = CNBu^t 3, PPh₃ 4, PMe₂Ph 5, PEt₃ 6, AsPh₃ 7, SbPh₃ 8; X = Cl, L = PMe₂Ph 9, PEt₃ 10), respectively. With tetraphenylcyclopentadienylthallium, C₅Ph₄HTl or pentabenzylcyclopentadienylthallium, C ₅Bn₅Tl (Bn = CH₂Ph) the air stable half-sandwich complexes (η⁵-C₅Ph₄H) Pd(C₆F₅)(AsPh₃), 12 and (η⁵- C₅Bn₅)Pd(C₆F₅)(AsPh₃), 13 are synthesized accordingly. The molecular structures were verified by NMR-spectroscopy, X-ray crystallography (7, 12, 13) and electron impact-mass spectrometry (EI-MS). The precatalysts 4 and 7 can be activated with methylalumoxane (MAO) for the homopolymerization of norbornene (NB) and 5-ethylidene-2-norbornene (ENB) and for the copolymerization of NB with 5-vinyl-2-norbornene (VNB) or ENB with activities of more than 10⁶ g_PNB/(mol_Pd·h). The higher activity of 7/MAO over 4/MAO towards NB homopolymerization was reversed when the olefin-substituted VNB or ENB were added. Then, the more strongly bound PPh₃ ligand of 4 (versus AsPh₃ of 7) can compete with the olefin functionality of VNB or ENB and assume a directing role for the insertion of the ring double bond. As a consequence 4/MAO shows almost the same activity in NB and ENB homopolymerization.

Full text of DOI:10.1016/j.jorganchem.2010.08.050

Journal of Organometallic Chemistry 696 (2011) 473e487
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
h
5-Cyclopentadienylpalladium(II) complexes: Synthesis, characterization and use
for the vinyl addition polymerization of norbornene and the copolymerization
with 5-vinyl-2-norbornene or 5-ethylidene-2-norbornene
,
b
a,
Frederik Blank a, Jana K. Vieth a, José Ruiz b , Venancio Rodríguez , Christoph Janiak
*
*
a Institut für Anorganische und Analytische Chemie, Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany
b Departamento de Química Inorgánica, Facultad de Química, Universidad de Murcia, 30071 Murcia, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Dinuclear complexes of palladium(II), containing two bridging halogen (Cl or Br) ligands,
[NnBu4]2[(X5C6)2Pd(
-Cl)2Pd(C6X5)2] and [(X5C6)(L)Pd(
-Y)2Pd(C6X5)(L)] (X ¼ F, Cl; Y ¼ Cl, Br), readily react
Received 18 May 2010
Received in revised form
8 August 2010
m
m
with cyclopentadienylthallium, C5H5Tl, to give the corresponding air stable half-sandwich, pseudo-trigonal
h
5-cyclopentadienylpalladium complexes, [NnBu4][(
h
5-C5H5)Pd(C6X5)2] (X ¼ F 1, Cl 2) and (
h
5-C5H5)Pd
Accepted 12 August 2010
(C6X5)(L) (X ¼ F, L ¼ CNBut 3, PPh3 4, PMe2Ph 5, PEt3 6, AsPh3 7, SbPh3 8; X ¼ Cl, L ¼ PMe2Ph 9, PEt3 10),
respectively. With tetraphenylcyclopentadienylthallium, C5Ph4HTl or pentabenzylcyclopentadienylth-
allium, C5Bn5Tl (Bn ¼ CH2Ph) the air stable half-sandwich complexes (
h
5-C5Ph4H)Pd(C6F5)(AsPh3), 12 and
In memoriam to Prof. Herbert Schumann
and his seminal contributions, among others,
to the chemistry of cyclopentadienylemetal
complexes.
(
h
5-C5Bn5)Pd(C6F5)(AsPh3), 13 are synthesized accordingly. The molecular structures were verified by
NMR-spectroscopy, X-ray crystallography (7, 12, 13) and electron impact-mass spectrometry (EI-MS). The
precatalysts 4 and 7 can be activated with methylalumoxane (MAO) for the homopolymerization of nor-
bornene (NB) and 5-ethylidene-2-norbornene (ENB) and for the copolymerization of NB with 5-vinyl-
2-norbornene (VNB) or ENB with activities of more than 106 gPNB/(molPd$h). The higher activity of 7/MAO
over 4/MAO towards NB homopolymerization was reversed when the olefin-substituted VNB or ENB were
added. Then, the more strongly bound PPh3 ligand of 4 (versus AsPh3 of 7) can compete with the olefin
functionality of VNB or ENB and assume a directing role for the insertion of the ring double bond. As
a consequence 4/MAO shows almost the same activity in NB and ENB homopolymerization.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Palladium, cyclopentadienyl complexes
Half-sandwich complexes
Norbornene
Polymerization, vinyl e addition
Methylalumoxane, MAO
1. Introduction
Norbornene (NB, bicyclo[2.2.1]hept-2-ene) can be polymerized
by three different ways, each leading to its own polymer type
(Scheme 1) [1e3]. Of special interest is the vinyl or addition poly-
merization of NB. In this case, the bicyclic structure of the monomer
remains intact, and only the double bond of the
opened [4].
p component is
Vinyl PNB is of interest due to its good mechanical strength, heat
resistivity, and optical transparency for deep ultraviolet (193 nm)
photoresist binder resins in lithographic processes [5], interlevel
dielectrics in microelectronics applications, or as a cover layer for
liquid-crystal displays [6,7]. Films made from norbornene vinyl
polymer are excellent in transparency and heat resistance and have
unchanged viscoelastic and electric characteristics to markedly
high temperatures. Such a film is suitable for a condensor or an
Scheme 1. Schematic representation of the three different types of polymerization of
norbornene.
insulator [8]. Furthermore, it shows a low water uptake, a small
optical birefringence and dielectric loss [9] The vinyl polymeriza-
tion of NB uses catalytic systems based on titanium, chromium,
iron, cobalt, copper, with recent emphasis on highly active nickel
and palladium complexes [1,2,3,10].
* Corresponding authors. Tel.: þ34 976761185 (J. Ruiz), þ49 7612036127 (C. Janiak).
E-mail addresses: jruiz@um.es (J. Ruiz), janiak@uni-freiburg.de (C. Janiak).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.08.050

474
F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
However, the poor solubility of vinyl polynorbornene (PNB) in
common organic solvents and the poor adhesion are disadvantages
of the homopolymer. The adhesion can be improved by attaching
triethoxysilyl groups on the backbone to lower the rigidity of the
system and result in higher elongation-to-break values and
a decrease in residual stress [7]. A possibility to improve the solu-
bility is to incorporate functional groups in the PNB chain. Hence,
the copolymerization of norbornene with ethene [11], propene [1]
or substituted NB-derivatives and the (co- and ter)polymerization
of functionalized NB monomers are of current interest [12,13],
because the resulting polymers can exhibit improved properties,
e.g. transparency, for the above applications. Palladium and nickel
catalysts in particular allow the polymerization of functionalized
norbornene monomers [1,5,14].
Very few cyclopentadienyl metal complexes were reported for the
application in the norbornene polymerization. Complex (h
5-C5H5)Pd
(CH3)(PPh3) did not afford remarkable polymerization results for the
homopolymerization of norbornene with the cocatalysts B(C6F5)3,
[Ph3C][B(C6F5)4] and MMAO, whereas the catalytic system (
h
5-C5H5)
Pd(
h
3-allyl)/[Ph3C][B(C6F5)4] provided an activity of more than 105
gPNB/(molPd$h) [15]. Recently, the complexes [(
h
5-C5Me5)Ir(M/E-bi-t/
s)Cl]Cl {M/E-bi-t/s ¼ 1,10-methylene/(1,2-ethanediyl)-bis(3-methyl)-
imidazole-2-thione/selone}
exhibited
moderate
activities
[4e56 ꢀ 103 gPNB/(molIr$h)] for the vinyl polymerization of norbor-
nene [16]. The half-sandwich iridium complexes [(h
5-C5Me5)Ir(Cl)
Scheme 2. Synthetic routes to h
5-cyclopentadienylpalladium(II) complexes 1e13.
{(C6H3-i-(R1)2-2,6)N ¼ CC2H3(CH3)C6H(CH3)(R2)O-
kN,O}], containing
hydroxyindanimine ligands produced the NB-ROMP polymer as
a low-MAO catalyst, while the high-MAO catalyst initiates the vinyl-
type NB polymerization according to IR,1H NMR and 13C NMR studies
atmosphere. Chemical ionization mass spectra (CI-MS, with NH3 as
ionizing gas) were obtained on a Thermo TSQ 700. Electron-spray
ionization mass spectra (ESI-MS) were measured on a Thermo LCQ
Advantage as a CH2Cl2/methanol solution (1:1). Palladium con-
taining signals were assigned upon the presence of the clearly
visible metal isotope pattern, arising from the distribution: 102Pd
(1.02%), 104Pd (11.14%), 105Pd (22.33%), 106Pd (27.33%), 108Pd
(26.46%), 110Pd (11.72%) [20]. Fluorine, phosphorus and arsenic are
isotope-pure elements. Most intense Pd-containing mass peaks
correspond to the 106Pd isotope. UV/Vis-spectra were recorded on
a JASCO V-570 UV/VIS spectrometer.
of the polymers. Still the activity remained modest with 104 gPNB
/
-
(molIr$h) even at 2000 equivalents of MAO [17]. Also the system (h5
C5H5)Ni(CH3)(PPh3)/B(C6F5)3 yields polynorbornene [18].
In this work,
a series of h
5-cyclopentadienylpalladium(II)
complexes of the general type [NnBu4][( 5-C5H5)Pd(C6X5)2] (1, 2) and
h
(h
5-Cp)Pd(C6X5)(L) (X ¼ F, Cl; Cp ¼ (substituted) cyclopentadienyl,
L ¼ C [isonitrile], P, As or Sb two-electron donor ligand) (3e12) were
synthesized and fully characterized (Scheme 2). The precatalysts 4
and 7 were tested for the homopolymerization of NB, 5-vinyl-2-
norbornene (VNB) and 5-ethylidene-2-norbornene (ENB) as well for
the copolymerization of NB with VNB and ENB, respectively. Meth-
ylalumoxane, MAO was used as cocatalyst and 4/MAO was selected
for activation studies with the 19F nucleus of the pentafluorophenyl
group C6F5 as a potential probe for molecular dynamics and for pre-
catalyst activation mechanism by 19F NMR spectroscopy [19].
Toluene and dichloromethane were dried under argon with an
MBraun SPS-800 system. The drying agent for toluene was acti-
vated Al2O3 in addition to a copper-catalyst used as an oxygen
scavenger. Al2O3 alone was used as the drying agent for dichloro-
methane. Diethyl ether and acetone were dried over and distilled
ꢀ
from molar sieve (3 A). After the drying process the water content
was determined by a Karl-Fischer titration, which showed a water
mass percentage of 0.0008% for toluene, 0.0004% for dichloro-
methane, 0.0005% for diethyl ether. Subsequently, the solvents
were stored under argon prior to use.
2. Experimental part
2.1. General and materials
PdCl2 (Applichem), PPh3 (Acros), AsPh3 (Aldrich), C6F5Br
(Chempur), Mg turnings (Aldrich), thallium(I) ethoxide
(Aldrich), thallium(I) sulfate (Fluka) and MAO (10% solution in
toluene, Witco) were used as received. Norbornene (Acros), 5-
vinyl-2-norbornene (Acros) and 5-ethylidene-2-norbornene
(Acros) were purified by distillation under argon and used as
a 7.07 mol/l solution in toluene. Cyclopentadienylthallium(I)
All work involving air- and/or moisture-sensitive compounds
was carried out with standard vacuum, Schlenk, or drybox tech-
niques. Flasks were conditioned by heating in high vacuum three
times and filling with argon. CHN analyses were performed with
a
Carlo Erba model EA 1108 microanalyzer. Decomposition
temperatures were determined with a Mettler TG‑50 thermoba-
lance at a heating rate of 5 ꢁC minꢂ1. Conductance measurements
were performed in acetone solution (c z 5 ꢀ10ꢂ4 mol Lꢂ1) with
a Crison 525 conductimeter. Infrared spectra were recorded on
a PerkineElmer 16F PC FT-IR spectrophotometer using Nujol mulls
between polyethylene sheets. The 1H, 13C, 19F and 31P NMR spectra
were recorded on a Bruker AC 200E, a Varian Unity 300 spec-
trometer or a Bruker Avance II 400 WB spectrometer using SiMe4,
CFCl3 or H3PO4 as standards respectively. The NMR spectra were
measured in NMR tubes with a screw cap to ensure an inert
atmosphere. The NMR tube was filled in a Schlenk tube under argon
C5H5Tl
[21],
1,2,3,4-tetraphenylcyclopentadienylthallium(I)
C5Ph4HTl [22], and 1,2,3,4,5-pentabenzylcyclopentadienylth-
allium(I) C5Bn5Tl [22,23] were synthesized according to litera-
ture procedures.
The starting compounds [NnBu4]2[{Pd(C6X5)2}2(
m
-Cl)2] (X ¼ F
[24], Cl [25]), [{(Pd(C6F5)L}2(
m
-Y)2] (L ¼ CNBut [26], PPh3, AsPh3 or
SbPh3 [27], Y ¼ Cl; L ¼ PMe2Ph or PEt3, Y ¼ Br [28]) and [{(Pd(C6Cl5))
L}2(
described in the indicated references. The synthesis of [{(Pd(C6F5)
(AsPh3)}2( -Cl)2] is described in the literature starting from
PdCl2(AsPh3)2 which is reacted with C6F5Li [27]. The PPh3
m
-Br)2] (L ¼ PMe2Ph or PEt3) [28] were prepared by procedures
m

F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
475
compound [{(Pd(C6F5)(PPh3)}2(
m
-Cl)2] is then obtained by reacting
and then TlCl was removed by filtration through celite and the
solution was concentrated to dryness under reduced pressure. The
residue was treated with PriOH-hexane yielding a redish-pink (1)
or brown (2) solid, which was filtered-off and air dried.
the As-derivative with an excess of PPh3 [27]. Because of the
potentially explosive nature of C6F5Li above wꢂ70 ꢁC we have
introduced the C6F5 ligand with the Grignard reagent C6F5MgBr as
described below.
Complex 1: Yield 80%; m.p. 210 ꢁC (dec.). Calcd. for
C33H41F10NPd: C 53.0, H 5.5, N 1.9; found C 53.3, H, 5.3, N 2.1%. L
M
105 S cm2 molꢂ1. IR (Nujol, cmꢂ1): 784, 772 (PdeC6F5). 1H-NMR
2.2. Syntheses
((CD3)2CO): d/ppm 5.62 (s, 5H, Cp), 3.43 (m, 8 H, NCH2),1.80 (m, 8 H,
NCH2CH2), 1.40 (m, 8 H, NCH2CH2CH2), 0.95 (t, 12 H, CH3,
2.2.1. [{(Pd(C6F5)(EPh3))}2(m-Cl)2] (E ¼ P, As) (see Eq. (1))
JHH ¼ 19.8 Hz). 13C{1H}-NMR ((CD3)2CO):
d
/ppm 95.1 (s, Cp). 19F-
NMR ((CD3)2CO):
ꢂ167.2 (m, 4Fm).
d/ppm ꢂ106.5 (m, 4Fo), ꢂ166.5 (t, 2Fp, Jmp ¼ 19.8),
Complex 2: Yield 78%; m.p. 216 ꢁC (dec.). Calcd. for
C33H41Cl10NPd: C 43.4, H 4.5, N 1.5; found C 43.3, H 4.3, N 1.5%. L
M
100 S cm2 molꢂ1. IR (Nujol, cmꢂ1): 830, 810 (PdeC6Cl5). 1H-NMR
(1)
((CD3)2CO): d/ppm 5.65 (s, 5H, Cp), 3.43 (m, 8 H, NCH2),1.80 (m, 8 H,
NCH2CH2), 1.40 (m, 8 H, NCH2CH2CH2), 0.95 (t, 12 H, CH3,
JHH ¼ 19.8 Hz). 13C{1H}-NMR ((CD3)2CO):
d/ppm 97.9 (s, Cp).
2.2.3. Cyclopentadienyl-pentafluorophenyl-(ligand L)-palladium
(II), (C5H5)Pd(C6F5)(L), 3e8
To a solution of [{(Pd(C6F5))(L)}2(
m
-Y)2] (L ¼ CNBut, PPh3, AsPh3
Magnesium turnings (525 mg, 21.6 mmol) were placed in
a 100 ml Schlenk flask together with a magnetic stir bar and diethyl
ether (10 ml). A solution of C6F5Br (5.3 g, 2.7 ml, 21.5 mmol) in
diethylether (40 ml) was added dropwise overa period of30 minvia
a syringe at room temperature. An ice bath was not necessary. The
suspension was stirred for 5 h, until the Mg was completely
consumed. PdCl2(EPh3)2 (4.26 g (E ¼ As) g, 3.79 g (E ¼ P) 5.4 mmol),
which has been prepared by the reaction of PdCl2 and 2 equivalents
of EPh3, was added in an Ar counter flow and the resulting yellow
suspension was heated to reflux, until it had turned into a colorless
suspension of MgBrCl (10 h for AsPh3 to 36 h for PPh3). The reaction
mixture was quenched with Et2O (30 ml) and the suspension was
allowed to stir in air for 2 h. After filtration, the ether was removed
and the residue was extracted with toluene (3 ꢀ 30 ml), filtrated
again and the organic phases were combined. After removal of the
toluene, the almost colorless solids of Pd(C6F5)2(EPh3)2 were dried in
vacuo for 12 hand then dissolved in dryacetone. After theaddition of
1 equivalent PdCl2 the reddish suspensions were heated to reflux,
until the PdCl2 had completely reacted. The reactions mixtures were
filtered and then reduced almost to a volume of 15 ml. The precipi-
or SbPh3, Y ¼ Cl; L ¼ PMe2Ph or PEt3, Y ¼ Br) (0.26 mmol) in acetone
(20 ml) was added C5H5Tl (140 mg, 0.52 mmol). The mixture was
stirred for 1 h at room temperature and then TlCl was removed by
filtration through celite and the solution was concentrated to
dryness under reduced pressure. The residue was treated with
diethyl ether-hexane (3, 6, 7, 8) or PriOHeH2O (1:1 v:v) (4, 5, also 7)
yielding a redish-pink solid, which was collected by filtration and
air-dried. For complex 4 the synthesis was upscaled to 1.59 g
(1.39 mmol) of [{(Pd(C6F5)(PPh3)}2(m-Cl)2] and 0.75 g, 2.78 mmol of
C5H5Tl which were dissolved in 50 ml of acetone. For complex 7 an
upscaled synthesis was carried out with 0.78 g (0.63 mmol) of [{(Pd
(C6F5)(AsPh3)}2(m-Cl)2]. Crystals of 4 and 7 were obtained by slow
diffusion of overlayered hexane into a solution of 4 and 7, respec-
tively, in CHCl3.
Complex 3 (L ¼ CNBut): Yield 75%; m.p. 185 ꢁC (dec.). Calcd. for
C16H14F5NPd: C 45.6, H 3.4, N 3.3; found C 45.6, H 3.3, N 3.2%. IR
(Nujol, cmꢂ1): 2198
n
(CN), 770 (PdeC6F5). 1H-NMR (CDCl3):
d
d
/ppm
/ppm
5.77 (s, 5H, Cp), 1.36 (s, 9H, CNBut). 13C{1H}-NMR (CDCl3):
96.7 (s, Cp), 30.1 (s, CNBut). 19F-NMR (CDCl3):
d/ppm ꢂ108.1 (m,
2Fo), ꢂ160.6 (t, 1Fp, Jmp ¼ 19.8), ꢂ163.6 (m, 2Fm).
tation of [{(Pd(C6F5))(EPh3)}2(m-Cl)2] succeeded by the addition of
Complex 4 (L ¼ PPh3): Yield 83% (upscaled 1.2 g, 72%); m.p.
209 ꢁC (dec.). Calcd. for C29H20F5PPd: C 58.0, H 3.4; found C 57.6,
H, 3.4%. IR (Nujol, cmꢂ1): 770 (PdeC6F5). UV (CH2Cl2,
c ¼ 2.5$10ꢂ5 mol/l): lmax 510 nm (emax 138 l molꢂ1 cmꢂ1). 1H-NMR
hexane (E ¼ As) and diethyl ether (E ¼ P), respectively.
The Cl to C6F5 ligand substitution reaction could only be
accomplished with a twofold stoichiometric excess (molar Mg:Pd
ratio 4:1) of the Grignard reagent, but then delivered the dinuclear
(CDCl3):
d/ppm 7.25e7.53 (m, 15H, PPh3), 5.75 (d, 5H, Cp,
complexes [(F5C6)(Ph3E)Pd(m-Cl)2Pd(C6F5)(EPh3)] in almost quan-
JHP ¼ 2.0 Hz), 13C{1H}-NMR (CDCl3):
d/ppm 133.6 (d, Co of PPh3,
titative yield. The synthesis of the analoguous complexes bearing
a triphenylantimony ligand failed due to the in situ reduction of Pd
(II) to metallic palladium during the ligand substitution reaction
with the C6F5MgBr Grignard reagent (Eq. (2)).
JCP ¼ 12.7 Hz), 132.6 (d, Cipso of PPh3, JCP ¼ 48.2), 130.4 (d, Cp of
PPh3, JCP ¼ 2.6), 128.0 (d, Cm of PPh3, JCP ¼ 10.8), 97.9 (d, Cp, JCP
2.6). 19F-NMR (CDCl3):
d
/ppm ꢂ108.1 (m, 2Fo), ꢂ161.8 (t, 1Fp, Jmp
20.0), ꢂ163.8 (m, 2Fm). 31P{1H}-NMR (CDCl3):
d
/ppm 41.1 (s). CI-
MS:
m/z
(abundance,
%) ¼ 600.1
(100) [C5H5Pd(C6F5)
(PPh3)]þ ¼ [M]þ, 552.0 (7.3) [Pd(C6F5)(PPh3)(NH3)]þ, 535.0 (8.6)
[Pd(C6F5)(PPh3)]þ, 476.9 (very low intensity) [C5H5Pd(PPh3)
(NH3)2]þ, 450.0 (22.0) [C5H5Pd(PPh3)(NH3)]þ, 433.0 (87.8)
[C5H5Pd(PPh3)]þ, 385.0 (8.3) [Pd(PPh3)(NH3)]þ, 368.0 (10.8) [Pd
(PPh3)]þ, 262.1 (11.5) [PPh3]þ, 232.0 (very low intensity)
[C11H5F5]þ, 185.1 (very low intensity) [PPh2]þ, 168.0 (8.13)
[C6F5H]þ.
(2)
2.2.2. Tetra-n-butylammonium cyclopentadienyl-bis
(pentahalophenyl)-palladium(II), [NnBu4][(C5H5)Pd(C6X5)2], 1 (halo,
X ¼ fluoro) and 2 (halo, X ¼ chloro)
Complex 5 (L ¼ PMe2Ph): Yield 87%; m.p. 173 ꢁC (dec.). Calcd. for
C19H16F5PPd: C 47.9, H 3.4; found C 47.9, H 3.5%. IR (Nujol, cmꢂ1):
To
a
solution of [NnBu4]2[{Pd(C6X5)2}2(
m
-Cl)2] (X ¼ F, Cl)
770 (PdeC6F5). 1H-NMR (CDCl3):
d/ppm 7.59 (m, 2Ho, PPh), 7.39 (m,
(0.14 mmol) in acetone (20 ml) was added C5H5Tl (75.5 mg,
0.28 mmol). The mixture was stirred for 1 h at room temperature
2Hm þ 1Hp, PPh), 5.64 (d, 5H, Cp, JHP ¼ 1.8 Hz), 1.53 (d, 6H, PMe2,
JHP ¼ 10.6). 13C{1H}-NMR (CDCl3):
d/ppm 130.4 (d, Cp of PMe2Ph,

476
F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
JCP ¼ 2.6), 130.3 (d, Co of PMe2Ph, JCP ¼ 12.3), 128.5 (d, Cm of PMe2Ph,
JCP ¼ 10.6), 96.8 (d, Cp, JCP 2.7), 19.1 (d, PMe2, JCP ¼ 31.9). 19F-NMR
additional 6 h at room temperature. The dark suspensionwas filtered
overCeliteÒ toremovetheprecipitatedTlClandwashedwithacetone,
until the filtrate was colorless. The greenish filtrate was concentrated
under reduced pressure to a volume of 20 ml. Under stirring a H2O/i-
PrOH mixture (1:1 v:v, 50 ml) was added slowly and dropwise via
syringe to precipitate the desired compound, which was filtered,
washed with H2O (10 ml) and iPrOH (ꢂ20 ꢁC, 20 ml). The olive-green
product was then dried in high vacuum for 6 h. The obtained air-
stable complex is soluble as an olive-green solution in acetone,
CH2Cl2, CHCl3 and toluene and insoluble in unpolar solvents like
n-alkanes and polar protic solvents like iPrOH or EtOH. Yield 0.24 g,
(CDCl3):
d
/ppm ꢂ108.4 (d, 2Fo, Jom ¼ 29.1 Hz), ꢂ160.6 (t, 1Fp,
Jmp ¼ 20.0), ꢂ163.3 (m, 2Fm). 31P{1H}-NMR (CDCl3):
d/ppm 8.0 (s).
Complex 6 (L ¼ PEt3): Yield 85%; m.p. 202 ꢁC (dec.). Calcd. for
C17H20F5PPd: C 44.7, H 4.4; found C 44.7, H 4.5%. IR (Nujol, cmꢂ1):
770 (PdeC6F5). 1H-NMR (CDCl3):
d/ppm 5.68 (d, 5H, Cp,
JHP ¼ 1.9 Hz), 1.44 (m, 6H, PCH2), 1.01 (m, 9H, PCH2CH3). 13C{1H}-
NMR (CDCl3):
d
/ppm 96.1 (d, Cp, JCP ¼ 2.5 Hz), 19.5 (d, PCH2,
JCP ¼ 28.2), 7.8 (s, PCH2CH3). 19F-NMR (CDCl3):
/ppm ꢂ107.9 (d, 2Fo,
d
Jom ¼ 26.0 Hz), ꢂ160.8 (t, 1Fp, Jmp ¼ 19.8), ꢂ163.4 (m, 2Fm). 31P{1H}-
NMR (CDCl3):
d/ppm 37.7 (s).
60%.1H-NMR (CDCl3):
d
/ppm ¼ 6.40e7.70 (m, 35H, PPh3 and C5Ph4H),
Complex 7 (L ¼ AsPh3): Yield 90% (upscaled 0.61 g, 75%); m.p.
177 ꢁC (dec.). Calcd. for C29H20AsF5Pd: C 54.0, H 3.1; found C 53.7, H
3.1%. IR (Nujol, cmꢂ1): 770 (PdeC6F5). UV (CH2Cl2, c ¼ 7.4$10ꢂ5 mol/
6.09 (s, 1H, C5Ph4H). 19F-NMR (CDCl3):
d
/ppm ¼ ꢂ108.5 (2Fo), ꢂ160.3
(1Fp), ꢂ162.5 (2Fm). ESI-MS: m/z (abundance, %) ¼ 905.9 (15.6)
[C5Ph4HPd(C6F5)(PPh3)]þ ¼ [M]þ, 738.2 (100) [C5Ph4HPd(PPh3)]þ.
l): lmax 501 nm (emax 142 l molꢂ1 cmꢂ1). 1H-NMR (CDCl3):
d/ppm
7.24e7.45 (m, 15H, AsPh3), 5.85 (s, 5H, Cp). 13C{1H}-NMR (CDCl3):
ppm 134.2 (s, Cipso of AsPh3), 132.7 (s, Co of AsPh3), 130.1 (s, Cp of
AsPh3), 128.6 (s, Cm of AsPh3), 96.9 (s, Cp). 19F-NMR (CDCl3):
/ppm
d/
2.2.6. Tetraphenylcyclopentadienyl-pentafluorophenyl-
triphenylarsane-palladium(II), (C5Ph4H)Pd(C6F5)(AsPh3), 12
Complex 12 was obtained by the same procedure as for 11 using
d
ꢂ107.3 (d, 2Fo, Jom ¼ 25.9 Hz), ꢂ161.6 (t, 1Fp, Jmp ¼ 19.8), ꢂ163.9 (m,
2Fm). CI-MS: m/z (abundance, %) ¼ 644.0 (16.9) [C5H5Pd(C6F5)
(AsPh3)]þ ¼ [M]þ, 494.0 (9.4) [C5H5Pd(AsPh3)(NH3)]þ, 476.9 (12.5)
[C5H5Pd(AsPh3)]þ, 333.9 (2.0) [C6F5eC6F5]þ, 307.0 (100) [HAsPh3]þ,
305.9 (24.7) [AsPh3]þ, 244.0 (8.6) [C6F5eC6H5]þ, 168.0 (6.8)
[C6F5H]þ, 77.1 (0.9) [C6H5]þ.
[{(Pd(C6F5)(AsPh3))}2(m-Cl)2] (0.29 g, 0.23 mmol) and C5Ph4HTl
(0.27 g, 0.47 mmol), instead and stirring the reaction mixturefor 3 h.
Crystals were obtained by slow diffusion of overlayered hexane into
a solution of 12 in CHCl3. Complex 12 is an air stable silver-grey solid.
Yield 0.29 g, 66%. UV (CH2Cl2, c ¼ 4.3$10ꢂ5 mol/l): lmax 589 nm (emax
202 l molꢂ1 cmꢂ1). 1H-NMR (CDCl3):
d
/ppm ¼ 6.94e7.44 (m, 35H,
Complex 8 (L ¼ SbPh3): Yield 86%; m.p. 143 ꢁC (dec.). Calcd. for
AsPh3 and C5Ph4H), 6.13 (s, 1H, C5Ph4H). 19F-NMR (CDCl3):
d/
C29H20F5PdSb: C 50.4, H 2.9; found: C 50.1, H 2.8%. IR (Nujol, cmꢂ1):
ppm ¼ ꢂ108.5 (2Fo), ꢂ160.3 (1Fp), ꢂ162.6 (2Fm). ESI-MS: m/z
(abundance, %) ¼ 947.8 (100) [C5Ph4HPd(C6F5)(AsPh3)]þ ¼ [M]þ,
769.8 (91.2) [C5Ph4HeOeOeC5Ph4H]þ, 738.2 (68.5) [(C5Ph4H)2]þ,
642.1 (54.1) [C5Ph4HPd(C6F5)]þ, 323.2 [HOAsPh3]þ.
770 (PdeC6F5). 1H-NMR (CDCl3):
d
/ppm 7.33 (m, 15H, SbPh3), 5.91
(s, 5H, Cp). 13C{1H}-NMR (CDCl3):
d/ppm 134.9 (s, Co of SbPh3), 131.1
(s, Cipso of SbPh3), 130.2 (s, Cp of SbPh3), 129.1 (s, Cm of SbPh3), 96.3
(s, Cp). 19F-NMR (CDCl3):
ꢂ161.0 (t, 1Fp, Jmp ¼ 20.0), ꢂ163.6 (m, 2Fm).
d
/ppm ꢂ105.3 (d, 2Fo, Jom ¼ 30.5 Hz),
2.2.7. Pentabenzylcyclopentadienyl-pentafluorophenyl-
triphenylarsane-palladium(II), (C5Bn5)Pd(C6F5)(AsPh3), 13
2.2.4. Cyclopentadienyl-pentachlorophenyl-(ligand L)-palladium
(II), (C5H5)Pd(C6F5)(L), 9 and 10
Complex 13 was obtained by the same procedure as for 11 using
C5Bn5Tl (0.32 g, 0.44 mmol), instead. Crystals were obtained by
slow diffusion of overlayered into a solution of 13 in CHCl3.
Complex 13 is an air stable silver-grey solid. Yield 0.29 g, 61%. UV
(CH2Cl2, c ¼ 1.1$10ꢂ4 mol/l): lmax 576 nm (emax 109 l molꢂ1 cmꢂ1).
To a solution of [{(Pd(C6Cl5))(L)}2(
m
-Br)2] (L ¼ PMe2Ph or PEt3)
(0.18 mmol) in acetone (20 ml) was added C5H5Tl (97 mg,
0.36 mmol). The mixture was stirred for 1 h at room temperature
and then TlCl was removed by filtration through celite and the
solution was concentrated to dryness under reduced pressure. The
residue was treated with MeOH yielding a brown solid, which was
filtered-off and air dried.
1H-NMR (CDCl3):
d
/ppm ¼ 6.67e7.53 (m, 40H, AsPh3, C5(CH2Ph)5),
3.52 (s, 10H, C5(CH2Ph)5). 19F-NMR (CDCl3):
ꢂ160.3 (1Fp), ꢂ162.5 (2Fm). ESI-MS: m/z (abundance, %) ¼ 1093.8
(100) [C5Bn5Pd(C6F5)(AsPh3)]þ ¼ [M]þ, 925.6 (34.5) [C5Bn5Pd
(AsPh3)]þ, 788.0 (7.4) [C5Bn5Pd(C6F5)]þ, 621.1 (12.6) [C5Bn5Pd]þ.
d
/ppm ¼ ꢂ108.8 (2Fo),
Complex 9 (L ¼ PMe2Ph): Yield 78%; m.p. 179 ꢁC (dec.). Calcd. for
C19H16Cl5PPd: C 40.8, H 2.9; found C 40.5, H 2.8%. IR (Nujol, cmꢂ1):
832 (PdeC6Cl5). 1H-NMR (CDCl3):
d
/ppm 7.58 (m, 2Ho, PPh), 7.37 (m,
2.2.8. (Bromo/chloro)-pentafluorophenyl-bis(triphenylarsane)-
palladium(II), Pd(Br/Cl)(C6F5)(AsPh3)2, 14
2Hm þ 1Hp, PPh), 5.62 (d, 5H, Cp, JHP ¼ 1.7 Hz), 1.49 (d, 6H, PMe2,
JHP ¼ 10.6). 13C{1H}-NMR (CDCl3):
d
/ppm 130.1 (d, Cp of PMe2Ph,
Compound 14 was obtained by slow diffusion of hexane into
a solution of 13 in CHCl3. Due to the instability of 13, crystals of 14
were obtained as a decomposition product. The bromine impurity
in the investigated crystal probably was carried over from the
magnesium Grignard reagent.
JCP ¼ 2.0), 130.0 (d, Co of PMe2Ph, JCP ¼ 12.1), 128.3 (d, Cm of PMe2Ph,
JCP ¼ 10.1), 97.6 (d, Cp, JCP 2.5), 18.1 (d, PMe2, JCP ¼ 31.9). 31P{1H}-
NMR (CDCl3): d/ppm 5.1 (s).
Complex 10 (L ¼ PEt3): Yield 80%; m.p. 180 ꢁC (dec.). Calcd. for
C17H20Cl5PPd: C 37.9, H 3.7; found C 37.7, H 3.5%. IR (Nujol, cmꢂ1):
834 (PdeC6Cl5). 1H-NMR (CDCl3):
d
/ppm 5.68 (d, 5H, Cp,
2.3. X-ray structure determination
JHP ¼ 1.5 Hz), 1.45 (m, 6H, PCH2), 1.05 (m, 9H, PCH2CH3). 13C{1H}-
NMR (CDCl3):
d
/ppm 97.2 (d, Cp, JCP ¼ 2.0 Hz), 19.0 (d, PCH2,
Suitable single crystals were carefully selected under a polar-
izing microscope. Data Collection: Rigaku R-axis Spider image plate
JCP ¼ 27.2), 7.9 (s, PCH2CH3). 31P{1H}-NMR (CDCl3):
d
/ppm 32.1 (s).
detector diffractometer, temperature 173(2) K, Mo-K
a radiation
ꢀ
2.2.5. Tetraphenylcyclopentadienyl-pentafluorophenyl-
triphenylphosphane-palladium(II), (C5Ph4H)Pd(C6F5)(PPh3), 11
(l
¼ 0.71073 A), graphite monochromator, double-pass method
u-
scan. Data collection, cell refinement and data reduction with
CrystalClear [29], empirical (multi-scan) absorption correction with
ABSCOR [30].
[{(Pd(C6F5)(PPh3))}2(m-Cl)2] (0.50 g, 0.44 mmol) was dissolved in
dry acetone (40 ml) by gentle warming to 40 ꢁC. The resulting yellow
solution was cooled to room temperature and thalliumte-
traphenylcyclopentadienide, C5Ph4HTl (0.50 g, 0.88 mmol) was
added with caution in an Ar counter flow. The yellow solution turned
into a black suspension within seconds and was stirred for an
Structure analysis and refinement: the structure was solved by
direct methods (SHELXS-97) [31]; refinement was done by full-
matrix least squares onF2 using the SHELXL-97 programsuite [31]. All
non-hydrogen positions were refined with anisotropic temperature

F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
477
factors. Hydrogen atoms for aromatic CH, were positioned geomet-
to ensure reproducibility of the polymerization results. The molar
Pd:Al ratio was kept constant at a value of 1:100 for all polymeri-
zation reactions. The vinyl type polymerization of norbornene was
ensured by infrared spectroscopy of the PNB homopolymers which
showed no absorption bands in the region of 1640 cmꢂ1, which
otherwise would indicate the presence of double bonds.
ꢀ
rically(CeH ¼ 0.94 A) and refinedusingaridingmodel (AFIX43)with
Uiso(H) ¼ 1.2Ueq(CH). Two phenyl rings in 12 and one benzyl group in
13 is disordered (see Fig. S7 and S8 in Supplementary Material). In
3
ꢀ
compound 14 a large residual electron density of 2.4 e/A was origi-
ꢀ
nally found within 0.3 A from the Cl atom. Initially this residual
electron density was unsuccessfully tried to refine as a disordered Cl
atom position. When the occupation factor of the one Cl atom was
allowed to refine, however, a value of 1.3 was obtained that indicated
a heavier atom in place of the chlorine atom. Hence, in 14 a possible
contamination of bromine instead of chlorine positions was consid-
ered. Allowing a partial occupancy of Br (23.3%) near the Cl atomwith
refinementofbothoccupationfactors (addingupto1)improvedtheR
values, goodness-of-fit and weighting parameters considerably and
lowered the otherwise large residual electron density near the chlo-
rine atom (to 0.53 e/A within 0.8 A from As2). Both the chlorine and
bromine atom in 14 can be refined anisotropically (using the PART
command). Two AsPh3 phenyl rings on As2 in 14 are disordered
(see Fig. S12 in Supplementary material). Crystal data and details on
the structure refinement are given in Table 1. Graphics were drawn
with DIAMOND [32], analyses of the PdeCp(centroid, ring) and on
2.4.1. Homopolymerization of norbornene (NB)
A
solution of norbornene in toluene (7.07 mol/l, 1.5 ml,
10.6 mmol) was placed in a 50 ml Schlenk flask under inert Ar
atmosphere at the chosen temperature. Toluene (3.8 ml) was added
to ensure a total reaction volume of 10.0 ml. Then, a solution of MAO
in toluene (0.7 ml, 1.06 mmol) was added via syringe to the nor-
bornene solution in toluene. After 1 min the polymerization was
started by addition of a solution of the precatalyst (4 or 7) in
dichloromethane (4 ml) via syringe and the reaction mixture was
stirred rapidly for the chosen time. The resulting polymer
precipitated as a colorless solid and the reaction was stopped by
addition of a mixture of concentrated HCl and methanol (1:1, 30 ml).
The polynorbornene was filtered and washed several times with
methanol and then dried in high vacuum for 6 h. Different temper-
atures (22 ꢁC, 40 ꢁC), polymerization times (0.5 min, 1 min, 2 min,
5 min) and amounts of the precatalysts 4 and 7 (1.06$10ꢂ2 mmol and
2.12 ꢀ 10ꢂ2 mmol) were used for the homopolymerization of nor-
bornene. The constant amount of NB (10.6 mmol) then gave the two
different molar NB:Pd ratios of 1000:1 and 500:1.
3
ꢀ
ꢀ
the supramolecular
pe, CeH/F and CeF/p-interactions with
PLATON for Windows [33]. The structural data have been deposited
with the Cambridge Crystallographic Data Center (CCDC-No.
787885e787888).
2.4. Polymerizations
2.4.2. Copolymerization of norbornene and 5-vinyl-2-norbornene
(VNB)
A solution of norbornene in toluene (7.07 mol/l, 1.5$x ml,
10.6$x mmol) and a solution of 5-vinyl-2-norbornene in toluene
The polymerizations were carried out in 50 ml Schlenk flasks,
which were conditioned three times by heating in high vacuum and
filling with argon. All polymerization reactions were run three times
Table 1
Crystal data and structure refinement for 7, 12, 13, 14.
Compound
7
12
13e
14
Empirical formula
M/g molꢂ1
C
29H20AsF5Pd
C53H36AsF5Pd
949.14
C64H50AsF5Pd
1095.36
C42H30As2Br0.23Cl0.77F5Pd
931.69
644.77
Crystal size/mm
Crystal appearance
0.47 ꢀ 0.28 ꢀ 0.25
Block, dark-red
6.10e54.96
99.8
ꢃ22; ꢃ20; ꢃ23
Orthorhombic
Pbca
17.279(4)
15.814(3)
18.096(4)
90
0.51 ꢀ 0.36 ꢀ 0.26
Isometric, grey
6.00e54.92
99.8
ꢃ14; ꢃ27; ꢃ26
Monoclinic
P21/c
11.218(2)
21.162(4)
20.537(6)
90
120.35(2)
90
0.16 ꢀ 0.13 ꢀ 0.05
Plate, grey
6.06e54.96
99.7
ꢃ44; ꢃ19; ꢂ26,24
Monoclinic
C2/c
33.936(7)
15.213(3)
20.102(4)
90
103.90(3)
90
0.27 ꢀ 0.12 ꢀ 0.12
Isometric, red
6.02e50.30
99.9
ꢃ14; ꢂ29,25; ꢃ31
Orthorhombic
Pbca
11.709(2)
24.260(5)
26.373(5)
90
90
90
7492(3)
8
1.652
3681
2.606
2q
range/ꢁ
completeness to 2
h; k; l range
q/%
Crystal system
Space group
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
ꢁ
ꢁ
a
/
b
/
90
90
ꢁ
g
/
3
ꢀ
V/A
4944.6(17)
8
2.133
2544
1.732
4207.2(16)
4
1.498
1912
1.281
10074(3)
8
1.444
4464
1.080
Z
Dcalc/g cmꢂ3
F(000)
m
/mmꢂ1
Max/min transmission
Reflections collected
0.6176/0.4338
129727
0.7319/0.5612
248319
0.9480/0.8461
127142
0.7450/0.5396
108733
Indep. reflections (Rint
Obs. reflect [I > 2 (I)]
Parameters refined
ꢀꢂ3
)
5677 (0.0398)
5028
325
0.424/ꢂ0.381
0.0230/0.0556
0.0277/0.0573
1.026
9613 (0.0301)
8939
633
0.414/ꢂ0.354
0.0212/0.0523
0.0234/0.0535
1.041
11518 (0.0892)
9017
704
0.545/ꢂ0.597
0.0397/0.0804
0.0578/0.0867
1.054
6681 (0.0340)
5760
580
0.527/ꢂ0.502
0.0207/0.0474
0.0263/0.0494
1.027
s
Max./min. Dra/e A
R1/wR2 [I > 2s
(I)]b
R1/wR2 (all reflect.)b
Goodness-of-fit on F2c
Weight. scheme w; a/bd
0.0266/3.9284
0.0245/2.6066
0.0313/17.9567
0.0193/5.8388
a
Largest difference peak and hole.
P
P
P
P
b
c
R1 ¼ [ (kFoj ꢂ jFck)/ jFoj]; wR2 ¼ [ [w(F2o ꢂ Fc2)2]/ [w(Fo2)2]]1/2
.
P
Goodness-of-fit ¼ [ [w(F2o ꢂ F2c)2]/(n ꢂ p)]1/2
.
d
e
w ¼ 1/[
s
2(Fo2) þ (aP)2 þ bP] where P ¼ (max(Fo2 or 0) þ 2Fc2)/3.
The data set quality of 13 was lowered by the necessary fast crystallization in view of the instability of 13 in CHCl3 solution.

478
F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
(7.07 mol/l, 1.5$(1 ꢂ x) ml, 10.6$(1 ꢂ x) mmol) (with x set to the
values of 0.8, 0.6, 0.5, 0.4, 0.2 to vary the NB:VNB ratio) were placed
in a 50 ml Schlenk flask under inert Ar atmosphere. Toluene
(3.8 ml) was added to ensure a total reaction volume of 10.0 ml.
Then, a solution of MAO in toluene (0.7 ml, 1.06 mmol) was added
via syringe to the norbornene solution in toluene. After 1 min the
polymerization was started by addition of a solution of the pre-
catalyst (4 or 7) in dichloromethane (4.0 ml) via syringe and the
reaction mixture was stirred rapidly for 1 h. The resulting polymer
precipitated as a colorless solid and the reaction was stopped by
addition of a mixture of concentrated HCl and methanol (1:1,
30 ml). The copolymer was filtered and washed several times with
methanol and then dried in high vacuum for 6 h. All copolymeri-
zations were performed at 22 ꢁC. The amount of the precatalysts 4
and 7 was varied (1.06 ꢀ 10ꢂ2 mmol and 2.12 ꢀ 10ꢂ2 mmol), the
amount of (NB þ VNB) was kept constant at 10.6 mmol leading to
the different molar (NB þ VNB):Pd ratios of 1000 and 500:1. The
polymerization time of 1 h was fixed.
AsPh3, SbPh3) can easily be prepared in excellent yields by reacting
the chloro- or bromo bridged organopalladium dimers
[NnBu4]2[(X5C6)2Pd(
m
-Cl)2Pd(C6X5)2] and [(X5C6)(L)Pd(
(C6X5)(L)] (Y ¼Cl, Br) with cyclopentadienylthalium (Scheme 2).
The half-sandwich
5-cyclopentadienyl complexes are air-stable,
m-Y)2Pd
h
both in the solid state and in solution. They are all soluble in polar
organic solvents like acetone, dichloromethane and chloroform.
Good solubilities are also obtained in the aromatic solvents toluene
or benzene, whereas insolubility exists in the aprotic and non-polar
aliphatic solvents n-pentane or n-hexane. The new complexes have
been characterized by partial elemental analyses and spectroscopic
(IR and 1H, 19F, 13C and 31P NMR) methods. In acetone solution,
complexes 1 and 2 behave as 1:1 electrolytes [34]. The IR spectra
show the bands attributed to the C6F5 (1630, 1490, 1460, 1050, and
950 cmꢂ1) [35] or the C6Cl5 (1315, 1285, 1220 and 670 cmꢂ1) [36]
groups. Morever, a split absorption located at ca. 800 cmꢂ1 in the
spectra of the bis(pentafluorophenyl) derivative
1 or at ca.
830 cmꢂ1 for the bis(pentachlorophenyl)derivative 2 has been
previously used for structural elucidation [37]. It is derived from the
so-called halogen-sensitive mode in C6F5 and C6Cl5 halogen mole-
cules and in square-planar MR2L2 (R ¼ C6F5, C6Cl5) complexes is
related to the skeletal symmetry of the entire molecule [37] and
2.4.3. Copolymerization of norbornene and 5-ethylidene-2-
norbornene (ENB)
A
solution of norbornene in toluene (7.07 mol/l, 1.5$x ml,
10.6$x mmol)andasolutionof5-ethylidene-2-norborneneintoluene
(7.07 mol/l,1.5$(1 ꢂ x) ml,10.6$(1 ꢂ x) mmol) (with x set to the values
of0.8, 0.6, 0.5, 0.4, 0.2 tovarytheNB:VNBratio) were placedina 50 ml
Schlenk flask under inert Ar atmosphere. Toluene (3.8 ml) was added
to ensure a total reaction volume of 10.0 ml. Then, a solution of MAO
in toluene (0.7 ml, 1.06 mmol) was added via syringe to the norbor-
nene solution in toluene. After 1 min the polymerization was started
by addition of a solution of the appropriate precatalyst (4 or 7) in
dichloromethane (4.0 ml) via syringe and the reaction mixture was
stirred rapidly for 1 h. The resulting polymer precipitated as a color-
less solid and the reaction was stopped by addition of a mixture of
concentrated HCl and methanol (1:1, 30 ml). The copolymer was
filtered and washed several times with methanol and then dried in
high vacuum for 6 h. All copolymerizations were performed at 22 ꢁC.
The amount of the precatalysts 4 and 7 was varied (1.06 ꢀ 10ꢂ2 mmol
and 2.12 ꢀ 10ꢂ2 mmol), the amount of (Nb þ ENB) was kept constant
at 10.6 mmol leading to the different molar (NB þ ENB):Pd ratios of
1000 and 500:1. A polymerization time of 1 h was chosen.
behaves like a
n(MeC) which is characteristic of the cis-MR2 frag-
ment (C2v symmetry). The IR spectrum of complex 3 shows also an
absorption assigned to
[38e40].
n
(CN) of the CNBut group at ca. 2235 cmꢂ1
5-Cp)Pd(C6F5)
The substituted cyclopentadienyl complexes (
(EPh3) (11e13) were obtained by reacting the chlorine bridged
dinuclear palladium(II) complexes [{(Pd(C6F5)(EPh3))}2( -Cl)2] [27]
in acetone with two equivalents of the appropriate CpTl compound
1,2,3,4-tetraphenylcyclopentadienylthallium(I), C5Ph4HTl [22] for
11 (E ¼ P), 12 (E ¼ As) and 1,2,3,4,5-pentabenzylcyclopentadie-
nylthallium(I), C5Bn5Tl [22,23] for 13 (E ¼ As) as Cp-transfer agents
[41].
h
m
The cyclopentadienyl complexes are air- and moisture-stable in
the solid state. In solution complexes 1 and 10 proved to be stable
over a long period of time (several weeks) in the presence of air.
Complex 12 was also quite stable in solution, but decomposition
occurred after several weeks, whereas complex 13 was only stable
in solution for approximately 2 days even under argon. The 19F NMR
spectrum in CDCl3 solution reveals the presence of a freely rotating
pentafluorophenyl ring which gives three resonances (in the ratio
2:1:2) for the o-, p-, and m-fluorine atoms. CI and ESI mass spec-
trometric investigations show the molecular ion as the base peak
for 4, 12 and 13. Also observed are peaks for [CpPd(C6F5)]þ and
[CpPd(EPh3)]þ (see Figs. S1eS4 in Supplementary material). The ESI
mass spectra of 12 and to a lesser extent of 13 also exhibit the
oxygenated Cp-ligand peaks [CpeOeOeCp]þ (Cp ¼ C5Ph4H and
C5Bn5) and [C5Bn5OH]þ (Figs. S3 and S4) which may help to explain
part of the instability of these two compounds in solution.
For reactive CpeM bonds an increased inertness is typically seen
in a comparison between the C5H5 and bulkier-Cp derivative
[22,23,42e46]. However, bulky-Cp complexes can be more reactive
than their less bulky analogs if a dissociative mechanism is oper-
ating for the other ligands. For example, the activation parameters
2.4.4. Homopolymerization of 5-ethylidene-2-norbornene (ENB)
A solution of 5-ethylidene-2-norbornene in toluene (7.07 mol/l,
1.5 ml, 10.6 mmol) was placed in a 50 ml schlenk flask under inert Ar
atmosphere. Toluene (3.1 ml) was added to ensure a total reaction
volume of 10.0 ml. Then, a solution of MAO in toluene (1.4 ml,
2.12 mmol) was added via syringe to the norbornene solution in
toluene. After 1 min the polymerization was started by addition of
a solution of the appropriate precatalyst (4 or 7, 2.12 ꢀ 10ꢂ2 mmol) in
dichloromethane (4.0 ml) via syringe and the reaction mixture was
stirred rapidly for the chosen time. The resulting polymer precipitated
as a colorless solid and the reaction was stopped by addition of
a mixture of concentrated HCland methanol (1:1, 30 ml). The polymer
was filtered and washed several times with methanol and then dried
inhighvacuumfor6 h. Differentpolymerizationtimesforthecatalytic
system4/MAO (1 min, 2 min, 5 min,10 min30 min and 60 min) and 7/
MAO (1 h, 2 h, 6 h,12 h, 24 h) were chosen. All homopolymerizations
were performed at 22 ꢁC and a molar ENB:Pd ratio of 500:1.
(D D
Hz and Sz) for the carbonyl displacement in CpRu(CO)2Br with
phosphorus donor ligands increase from Cp ¼ C5Ph5 over C5Me4Et
to C5H5 with relative reaction rates of about 20:14:1, respectively.
There is an enhanced lability of CO in the pentaphenyl derivative
[47].
3. Results and discussion
The synthesis of
h
5-CpPd(C6F5)(EPh3) (E ¼ P, As) with the pen-
3.1. Syntheses and molecular structures
taphenylcyclopentadienyl ligand has been unsuccessfully attemp-
ted a couple of times using the available C5Ph5Tl compound [22]. No
(C5Ph5)Pd fragment was found by NMR in the reaction mixture,
The complexes [NnBu4][( 5-C5H5)Pd(C6X5)2] (1, 2) or [( 5-C5H5)
h h
Pd(C6X5)(L)] (3e10) (X ¼ F or Cl, L ¼ CNBut, PPh3, PMe2Ph, PEt3,
although complexes with the (h
5-C5Ph5)Pd moiety are known [48].

F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
479
The
neutral
half-sandwich
cyclopentadienylpalladium
5-C5H5 ligand are
palladium and platinum cyclopentadienyl complexes [49,54]. Such
compounds 3e10 with the unsubstituted
h
MeC(Cp) (M ¼ Ni, Pd, Pt) bond length differences have been
redish-pink solids and also give a pink to violet solution in chlo-
roform. Complexes 11e13 with the substituted tetraphenyl- or
pentabenzylcyclopentadienyl ligands are olive-green (11) or silver-
grey (12, 13) in the solid state and give green to blue solutions in
CHCl3 (Fig. S5). The UV-spectra of the (C5H5)Pd complexes 4 and 7
are shown in Fig. 1. Their metal-centered ded absorption peak
appears at lmax of 501 and 510 nm. The slightly stronger PPh3
versus the AsPh3 ligand yields the shorter wavelength absorption in
4 versus 7. The ded absorption of the (C5Ph4H)Pd and (C5Bn5)Pd
complexes 12 and 13, respectively, have a lmax of 589 nm (12) and
576 nm (13), which indicates a Cp ligand field strength of the order
CpPh4H < C5Bn5 < C5H5.
Crystals of 4, 7, 12 and 13 suitable for X-ray diffraction studies
were obtained by slow diffusion of overlayered hexane into
a solution of the complex in CHCl3. Due to the instability of 13 in
solution, it was neccessary to enforce a fast crystallization within 2
days. Compounds 4, 7, 12 and 13 are molecular palladium(II)
rationalized in terms of the trans influence of the s-aryl ligand. Also
the variation in CeC bond lengths in the Cp rings of 7 is similar to
other cyclopentadienyl complexes of nickel, platinum and espe-
cially palladium [54] and could again be attributed to the different
trans influence of the s-C6F5 and AsPh3 ligands. The PdeC6F5 bond
lengths are in the range found in the literature for penta-
fluorophenylepalladium complexes [55].
Compound 13 has four phenyl rings of the benzyl group situ-
ated “above” the Cp ring or away from the metal atom and one
phenyl ring “below” the Cp plane approaching the other two
ligands. This four versus one ratio was also seen in the deca-
benzylmetallocenes, (C5Bn5)2M of germanium, tin and lead [42]
and the half-sandwich transition metal complexes (C5Bn5)Co
(CO)2 [56] and (C5Bn5)Mn(CO)3 [57]. In the pentabenzylcyclo-
pentadienyl-thallium, pentabenzylcyclopentadienyl-indium and
pentabenzylcyclopentadienyl-potassium compound the ratio is
two versus three or three versus two [23,43]. Having all five
benzyl groups lying on the same side of the Cp ring is an unfa-
vorable situation and was only observed in the structure of dec-
abenzylferrocene, (C5Bn5)2Fe with all 10 phenyl rings being
directed away from the metal atom. This benzyl orientation in the
ferrocene derivative results from the small size of the iron atom
complexes with
a
pentahapto-bound (substituted) cyclo-
pentadienyl ring, a pentafluorophenyl and a triphenylphosphine or
-arsine ligand. The structure of 4 has been communicated earlier by
us and shows the expected pseudo-trigonal coordination of the h5
-
C5H5, C6F5 and PPh3 ligands around the palladium atom [49]. The
solid-state molecular structures of 7, 12 and 13 with their pseudo-
trigonal palladium coordination are depicted in Figs. 2e4, respec-
tively. CpePd distances (Table 2) are as expected from a comparison
ꢀ
and the close approach of the Cp ring planes (3.3 A apart) [44].
Despite the presence of ligand
are no intermolecular interactions [58] evident (vide infra). In
terms of -contacts the packing in 7, 12 and 13 seems to be
controlled by CeH/ interactions (see Supplementary material)
[59]. The intermolecular CeH/
(Ce)H/ring centroid distances. These CeH/
p-systems in 7, 12 and 13 there
pep
to related (
h
5-C5H5)Pd-phosphine [49,50] and estibine [51], (h5
-
p
indenyl)Pd-phosphine [52] and eamine [53] complexes. The only
other CpPd(C6F5) derivative available is (
[49].
In 7, 12 and 13 the PdeC(Cp) bond length trans to the
tafluorophenyl ligand is one of the shortest. A similar pattern has
p
5-C5H5)Pd(C6F5)(PPh3)
-pen-
p
contacts start around 2.7 A for the
contacts lie at the
ꢀ
h
p
s
short end of the accepted distance range for this type of contact
[59,60]. In addition, a few CeH/FeC contacts can be found in 7, 12
and 13 (see Supplementary material) [49,61].
already been observed in a number of other structures of nickel,
Fig. 1. UV-spectra of the CpPd(C6F5)(L) complexes in CH2Cl2 (a) Cp ¼ C5H5, L ¼ PPh3 (4), (b) Cp ¼ C5H5, L ¼ AsPh3 (7), (c) Cp ¼ C5Ph4H, L ¼ AsPh3 (12), (d) Cp ¼ C5Bn5, L ¼ AsPh3 (13).

480
F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
Fig. 2. Thermal ellipsoid plot (50% probability) of complex 7; selected distances and
angles in Table 2. For the intramolecular
Fig. S6 in Supplementary material.
p-contact between C6F5 and C7eC12 see
In 7 two neighboring molecules form pairs through the six-fold
phenyl embrace by CeH/ contacts between the AsPh3 ligands
Fig. 4. Thermal ellipsoid plot (50% probability) of complex 13; selected distances and
angles in Table 2.
p
(Fig. 5) [62]. The sextuple phenyl embrace is a supramolecular
attraction between Ph3P moieties due to a concert of six attractive
edge-to-face interactions between phenyl groups and has frequent
occurrence in crystals, is usually centrosymmetric, and contributes
an attraction of 60e85 kJ molꢂ1 [62]. Noteworthy in the structure of
4, the PPh3 analog to 7, the phenyl embrace was not present (Fig. S9
From the decomposition of compound 13 in CHCl3 solution
a
square-planar, Cp-free halo-pentafluorophenyl-bis(triphenyl-
arsane)palladium(II) complex could be isolated (Fig. 6). In the
structure of compound 14 a possible contamination of bromine
instead of chlorine positions had to be considered. Contamination of
14 with PdBr(C6F5)(AsPh3)2 may originate from the starting material
C6F5Br, respectively the Grignard reagent C6F5MgBr which is reacted
with PdCl2(AsPh3)2 (Eq. (1)). Allowing a partial occupancy of Br
(23.3%) near the Cl atom (76.7%) improves the R values and lowers
the otherwise large residual electron density near the chlorine atom.
in Supplementary material). Instead, in [(h
5-C5H5)Pd(C6F5)(PPh3)],
4 there are two symmetry-independent molecules in the unit cell
(also proven by solid state 19F NMR) due to an intermolecular
CeH/FeC contact [49]. Both 4 and 7 crystallize in the same
orthorhombic space group Pbca with very similar a and b cell
ꢀ
constants, but the c axis is doubled (35.5 A) for 4. Also in 12 and 13
the phenyl embrace is no longer present for the packing (Figs. S10
and S11) which indicates a dominance of CeH/phenyl(Cp) and
CeH/C6F5
p contacts in 12 and simple van der Waals contacts in
13 besides an CeH/FeC contact in both (see supramolecular
interactions in Supplementary material).
Table 2
ꢁ
ꢀ
Selected bond lengths (A) and angles ( ) for 7, 12, 13.
Compound
7
12
13
PdeC1
PdeAs
2.031(2)
2.3560(4)
2.281(2)d
2.324(2)
2.254(2)
2.340(2)
2.377(2)
1.9795(12)
1.9778(2)
0.081
2.0355(15)
2.3678(5)
2.2470(15)d
2.3704(14)
2.3641(15)
2.3851(16)
2.4146(16)
2.0163(9)
2.0141(1)
0.095
2.057(3)
2.3840(9)
2.363(3)
2.240(3)
2.325(3)
2.308(3)d
2.405(3)
1.9829(13)
1.9791(2)
0.123
PdeC25
PdeC26
PdeC27
PdeC28
PdeC29
PdeCta
PdeCp(plane)
Ring slippagec
AseC7
b
1.947(2)
1.945(2)
1.939(2)
1.9376(17)
1.9396(16)
1.9491(16)
1.946(3)
1.943(3)
1.952(3)
AseC13
AseC19
C1ePdeAs
C1ePdeCta
AsePdeCta
C7eAseC13
C7eAseC19
C13eAseC19
90.44(6)
89.02(5)
99.87(7)
132.89(6)
136.08(2)
103.98(9)
101.95(8)
105.20(9)
136.94(6)
134.05(3)
103.61(7)
102.75(7)
101.23(7)
125.37(8)
134.00(2)
102.17(11)
101.67(11)
103.45(11)
Dihedral angle
86.25(12)
88.32(8)
85.68(14)
plane(C1ePdeAs)eCp(plane)
a
Ct, ring centroid.
b
Normal or perpendicular projection from the Pd atom onto the Cp ring plane.
Distance between perpendicular projection of Pd atom on Cp ring plane and ring
c
Fig. 3. Thermal ellipsoid plot (50% probability) of complex 12; H atoms on the phenyl
rings are not shown for clarity; selected distances and angles in Table 2.
centroid.
d
Carbon atom trans to the s-C6F5 ligand.

F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
481
ꢀ
ꢀ
the longer PdeAs (w2.36 A) over the shorter PdeP bond (2.23 A)
[49]. Previous work has shown that upon borane or MAO activation
ligands will be lost to give a coordinatively unsaturated or even
a “naked” Pd2þ as the active species [74,75]. Hence, more weakly
bound ligands which will be removed faster will lead more quickly
to the active palladium catalyst. In addition, the still present and
stronger coordinating PPh3 ligand can compete in equilibrium with
the NB monomer for the free metal coordination site (Eq. (3))
which, as a consequence, slows the chain growth rate [77,69]. Such
a PPh3/ethene competition is used in the Shell higher olefin process
(SHOP) to control the oligomer chain length [70].
Fig. 5. Pair formation of complex 7 through the six-fold phenyl-embrace of two AsPh3
ligands in space-filling mode.
Both the chlorine and bromine atom can be refined anisotropically.
Such a contamination or a solid solution of two complexes would be
reminiscent to the mixture of [MoCl2(O)(PR3)3] and [MoCl3(PR3)3]
that was responsible for the notorious “bond-stretch isomer”
problem [63]. The syntheses of PdCl(C6F5)(AsPh3)2 [64] and PdBr
(C6F5)(AsPh3)2 have been described [65]. Related, structurally
authenticated complexes with a trans ClePdeC6F5 moiety are [PdCl
(C6F5)(N10-9-aminoacridine)(PPh3)] [66] and [PdCl(C6F5)(PPh3)2]
[67]; also related are complexes [Pd(C6F5)(AsR2R0)2(NCMe)]þ [77]
and [PdCl(C6H2-2,4,6-(NO2)3)(AsPh3)2] [68].
(3)
The insolubility of the obtained polynorbornenes (PNBs) as is
often encountered with Pd catalysts, except for vinyl poly-
norbornenes from dicationic, single-component Pd complexes of
the type [Pd(NCCH3)4]2þ [10a], made a further characterization of
the polymer molar mass and mass distribution by gel permeation
chromatography (GPC) impossible. The origin of this insolubility is
still not quite clear. One possibility may be chain cross-linking due
to partial cationic polymerization or tacticity [1e3].
We opted to primarily compare conversions rather than activi-
ties. A comparison of activities for different reaction times can be
misleading as highly reactive and sensitive catalysts with a high
intrinsic activity will show a lower over-time activity at longer
reaction times due to faster deactivation. Norbornene conversions
increase with polymerization time and are higher for an NB:Pd
ratio of 500 than for a ratio of 1000:1 for both catalysts 4/MAO and
7/MAO (Fig. 7 and Fig. S13).
3.2. Norbornene homopolymerization
The homopolymerization of norbornene (NB) with 4/MAO and
7/MAO was performed under different molar norbornene:Pd ratios
(1000:1 and 500:1), polymerization times (0.5 min, 1 min, 2 min,
5 min) and temperatures (22 and 40 ꢁC). The polymerization
activities cover a range from 3.17 ꢀ 105 gPNB/(molPd$h) (Table S1,
entry 1) to 2.07 ꢀ 106 gPNB/(molPd$h) (Table S1, entry 21) which
can be classified as good to high [1,2]. The system 7/MAO generally
yielded higher activities than 4/MAO. This is reasoned with
a kinetic activation effect through a faster removal of the more
weakly bound AsPh3 ligand in 7 over the PPh3 ligand in 4 upon
reaction with MAO together with the C6F5 ligand to give the active
Pd species (see below) [77]. The weaker AsPh3 bonding is based on
Fig. 6. Thermal ellipsoid plot (50% probability) of complex 14. The Cl and Br atom are
almost superimposed. Selected distances (A) and angles (ꢁ): PdeAs1 2.4022(5),
ꢀ
PdeAs2 2.4027(6), PdeC-1 2.011(2), PdeCl ¼ 2.390(4), PdeBr 2.388(6), C-1ePdeAs1
91.73(5), C-1ePdeAs2 91.71(5), C-1ePdeCl 178.4(2), C-1ePdeBr 178.1(2), ClePdeAs1
86.7(2), ClePdeAs2 89.8(2), BrePdeAs1 88.0(2), BrePdeAs2 88.6(2), As1ePdeAs2
176.32(1).
Fig. 7. Norbornene conversion-time plot for the catalytic system 4/MAO at two
different molar NB:Pd ratios; conditions: NB 10.6 mmol, molar ratio Al:Pd ¼ 100:1,
total reaction volume 10.0 ml. temperature 22 ꢁC, see Table S1, entries 1e8.

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F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
3.3. Copolymerization of norbornene and 5-vinyl-2-norbornene
(VNB)
Both catalytic systems 4/MAO and 7/MAO gave noticeable lower
conversions in NB-VNB copolymerization than in the NB homo-
polymerization (Table S2). It is well established for the polymeri-
zation of norbornene derivatives that donor atoms or a donor
functionality like a C]C double bond slow down the chain prop-
agation through metal coordination [12,13]. Work on the vinyl
polymerization of functionally substituted norbornenes shows that
generally the endo-functionalized norbornenes are polymerized
more slowly compared to the exo-analogs because of the possible
coordination of the donor-containing substituent to the metal atom
(Scheme 3) [12,71], which attenuates the polymerization activity.
Since the synthesis of substituted norbornenes is accomplished in
a Diels-Alder reaction, always a mixture of endo- and exo-isomers is
obtained.
The NB/VNB copolymerization activities range from
Fig. 8. Total conversion in the copolymerization of norbornene (NB) and 5-vinyl-2-
norbornene (VNB) with 4/MAO and 7/MAO as a function of the molar NB:VNB ratio.
Conditions: NB þ VNB 10.6 mmol, molar ratio Al:Pd ¼ 100:1, temperature 22 ꢁC, reac-
tion time 1 h, total volume 10.0 ml; see Table S2, entries 1e10 and 11e20, respectively.
4.64 ꢀ103 gpolymer/(molPd h)
(7/MAO,
NB:VNB ¼ 20:80)
to
3.98 ꢀ 104 gpolymer/(molPd h) (4/MAO, NB:VNB ¼ 80:20, Table S2).
Activities between 103 and 105 are in same the range as found with
PdCl2(bisphosphane)/MAO [75]. Again, conversions are higher for an
(NB þ VNB):Pd ratio of 500:1 than for a ratio of 1000:1 for both
catalysts 4/MAO and 7/MAO (Fig. 8). Different from the homo-
polymerization of NB, the catalytic system 4/MAO yields higher
conversions and activities in the copolymerization of NB and VNB
than 7/MAO (see below). The conversions and subsequent activities
depend highly on the molar NB:VNB ratio. The activity decreases with
the increase in VNB content. The highest activities are obtained for an
NB:VNBratioof 80:20, the lowestforanNB:VNBratioof20:80 (Fig. 8).
From 1H NMR the endo:exo ratio for VNB is about 2:1 (Fig. S16). As the
minor exo isomer is polymerized faster this contributes to the drop in
overall conversion with increasing VNB content.
NB-VNP copolymer is still insoluble, precluding
characterization.
a
GPC
3.4. Copolymerization of norbornene and 5-ethylidene-2-
norbornene (ENB)
Conversions and activities for the copolymerization of NB and
ENB (Table S3) are lower than for the homopolymerization of
norbornene but can be higher than for the copolymerization of NB
and VNB under otherwise identical conditions (cf. Table S2). The
NB/ENB copolymerization activities range from 2.17 ꢀ 103 gpolymer
/
(molPd h) (7/MAO, NB:ENB ¼ 20:80) to 5.76 ꢀ 104 gpolymer/(molPd h)
(4/MAO, NB:VNB ¼ 40:60, Table S3). This supports the formation of
a less active diolefin complex with VNB (Scheme 4) since the
relative and rigid spatial disposition of the two olefin bonds in ENB
(Scheme 5) renders an ENB-diolefin complex unlikely.
The lower activities in the presence of VNB are due to its
terminal a-olefin functionality. Coordination of both olefin func-
tions of VNB can give a stable diolefin palladium complex from
which the insertion polymerization is unlikely to proceed (Scheme
4; see below for support of this interpretation). The higher activity
of 4/MAO in the NB-VNB copolymerization is traced to the presence
of the PPh3 ligand in the reaction mixture. The competition of the
PPh3 and olefin coordination [69] which was disadvantageous in
the NB homopolymerization (cf. Eq. (3)) now raises the activity of 4/
MAO over 7/MAO by making the diolefin coordination more diffi-
cult (Scheme 4). The steric demand of the PPh3 group may also play
a directing role for the suggested exoeexo enchainment with the
insertion of the ring double bond in the polymerization [72]. The
Also, the ethylidene group in ENB is a trisubstituted internal
olefin whose insertion into the PdeC bond is less likely. Still, the
ethylidene group can form an inactive Pd-olefin complex so that
the presence of ENB lowers the activity compared to the NB
homopolymerization. Again the system 4/MAO was more active
and much less affected by an increasing molar NB:ENB ratio than
Scheme 4. Competition in the VNB-olefin and PPh3 coordination of 4/MAO; the
formulation [Pd] indicates that additional ligands can be present. The VNB-diolefin
complex may be a resting state.
Scheme 3. Structure of VNB and ENB and bonding modes for functionalized norbor-
nene derivatives (X ¼ coordinating functionality).

F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
483
poly-ENB within 5 min of reaction time (Table S4, entry 3), 7/MAO
required 24 h for a conversion of 44% (Table S4, entry 11). This
difference in catalyst activity is further evidence for the structure
directing role of the PPh3 ligand (in 4) according to Scheme 5. The
ENB homopolymer (as the above copolymers) is still insoluble in
1,2,4-trichlorobenzene even at elevated temperatures, so that a gel
permeation chromatography (GPC) could not be done in order to
obtain a polymer molar mass and mass distribution.
The activity of 4/MAO in the homopolymerization of ENB was
only slightly lower than in the homopolymerization of NB under
identical reaction conditions (compare entries 1e3 in Table S4 with
entries 6e8 in Table S1, Fig. 10). Thus, the ethylidene functionality
has little effect on the polymerization activity with 4/MAO or in the
presence of PPh3, thereby supporting the notions of Scheme 5. On
the other hand, when 7/MAO is used as the catalyst, there is
a dramatic decrease in activity. Apparently in the absence of PPh3 the
ENB-ethylideneePd olefin complex may be an effective resting state.
4. Pre-catalyst activation
Scheme 5. Competition in the ENB-olefin and PPh3 coordination of 4/MAO; the
formulation [Pd] indicates that additional ligands can be present. The ENB-diolefin
complex is less likely because of the rigid disposition of the two olefin groups. The
ethylidene-Pd olefin complex may be a resting state.
Generally, the species in MAO-activated Ni- or Pd-complexes and
initiation steps for norbornene polymerization are not well
known [1,2,3,73]. For the better defined co-catalytic system
B(C6F5)3 or B(C6F5)3/AlEt3 the activation process of the pre-catalyst
[Ph3PCH2C(O)CH3]2[Pd2Cl6] was followed by multinuclear (1H-,13C-,
19F-, and 31P-)NMR investigations and points to the formation of
molecular PdCl2 which may represent the active species in the
polymerization process [74]. Multinuclear (31P and 19F) NMR
investigations on [PdCl2(dppe)] and [PdCl2(dppp)] in combination
with B(C6F5)3 and B(C6F5)3/AlEt3 suggest the formation of [Pd(L)]2þ
cations (L ¼ dppe, 1,2-bis(diphenylphosphino)ethane; dppp, 1,3-bis
(diphenylphosphino)propane) in the activation process. E(C6F5)3
(E ¼ B, Al) reacts with the pre-catalysts [MCl2(L)] under abstraction
of the two chloride atoms followed by the formation of highly active
“naked” Pd2þ through a ligand redistribution of the unstable [Pd
(dppe)]2þ cation to yield [Pd(dppe)2]2þ and Pd2þ [75].
7/MAO (Table S3, Fig. 9). This is again reasoned by the competition
of the PPh3 and olefin coordination (Scheme 5) [69].
The significant decrease in the conversion for the NB-ENB
copolymerization with 7/MAO compared to 4/MAO (Fig. 9) further
underscores the role of the PPh3 ligand, as this is the only difference
between 4 and 7. The PPh3 group can more effectively exert
a structure directing role towards the exo-ENB-monoolefin-Pd
coordination which is suggested for the vinyl enchainment as ENB
apparently lacks the possibility for diolefin-chelate formation. In
the absence of PPh3 (AsPh3 is a weaker coordinating ligand) the
ENB-ethylidene-Pd olefin complex may be an effective resting state
(see below for further support of this interpretation). Irrespective of
the role of the phosphane it should be remembered that
substituted norbornes are always less effectively incorporated into
the growing polymer chain [12,13].
1H-NMR and 19F-NMR showed that the polynorbornene
obtained in the presence of ethylene with activator-free (h6
-
C6H5CH3)Ni(C6F5)2 had the end-groups eCH]CH2 and eC6F5 [76].
The reaction of trans-[Pd(C6F5)Br(AsRfPh2)2] (Rf ¼ 3,5-dichloro-
2,4,6-trifluorophenyl,C6Cl2F3) and [Pd(C6F5)(NCMe)(bipy)]BF4 with
an excess of norbornene but no cocatalyst was monitored by 19F-
NMR and signals from (NB)CeC6F5 indicated that the polymeriza-
tion process starts with the insertion of NB into the PdeC6F5 bond
3.4.1. Ethylidene-2-norbornene (ENB) e homopolymerization
The ENB conversion is dramatically affected by the choice of the
catalyst. While the catalytic system 4/MAO gave 46% conversion to
[77,78].
From
the
cationic
complex
trans-[Pd(C6F5)
(AsRfPh2)2(NCMe)]BF4 and norbornene (NB:Pd ¼ 10:1), the poly-
merization starts with the substitution of an AsRfPh2 ligand cis to
Fig. 9. Total conversion in the copolymerization of norbornene (NB) and 5-ethylidene-
2-norbornene (ENB) with 4/MAO and 7/MAO as a function of the molar NB:ENB ratio.
Conditions: NB þ ENB 10.6 mmol, molar ratio Al:Pd ¼ 100:1, temperature 22 ꢁC, reac-
tion time 1 h, total volume 10.0 ml; see Table S3, entries 1e10 and 11e20, respectively.
Fig. 10. Activity comparison for the different polymerization types and the catalytic
systems 4/MAO and 7/MAO (NB:Pd ratios are 500:1); given are the maximal observed
activities from Tables S1eS4. Note that some of the activity differences are due to the
different polymerization times ranging from 0.5 min to 1 h.

484
F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
Fig. 11. 1H-NMR spectrum of NB-MAO-4 reaction mixtures with (a) the molar NB:Al:Pd
ratio of 10:10:1 (*toluene-d8), (b) the molar NB:Al:Pd ratio of 10:100:1 (toluene-d8/
CD2Cl2, */**). NB signals are numbered according to Scheme 6.
Fig. 12. 19F-NMR spectrum of (a) complex 4 (CDCl3), and NB-MAO-4 reaction mixtures
with (b) the molar NB:Al:Pd ratio of 10:10:1 (toluene-d8), (c) the molar NB:Al:Pd ratio
of 10:100:1 (CD2Cl2/toluene-d8). Boxes mark signals assigned to C6F5 attached to an NB
polymer chain.
the C6F5 group followed by insertion of norbornene into the
PdeC6F5 bond and the chain growth (by 1H-NMR and 19F-NMR)
[77].
pentafluorophenyl ligand remains bound to the palladium atom.
There are no significant shifts of the resonances for the ortho-,
meta- and para-fluorine atoms of 4 upon MAO activation. In addi-
tion, hardly any new sets of resonances appear. A set of very small
signals at the NB:Al:Pd ratio of 10:100:1 (Fig. 12c) at ꢂ139, ꢂ160
and ꢂ164 ppm can be assigned to signals for C6F5 attached to an NB
polymer chain (cf. Fig. 14b) [77,78]. The almost unchanged 19F NMR
of 4 upon activation indicates that either only a very small fraction
of complex molecules is activated and takes part in the polymeri-
zation with a monomer insertion into the PdeC6F5 bond or that the
starting monomer does not insert into the PdeC6F5 bond in 4.
Activation experiments of complex 4 and MAO at the molar
Al:Pd ratios of 10:1 and 100:1, with no NB monomer present,
showed a dark precipitate within a short time after MAO was added
to a solution of 4. This fine precipitate did not settle so that no NMR
spectrum of this suspension could be obtained. This dark precipi-
tate was insoluble even in DMSO-d6 and after filtration the violet
solution still gave the 1H NMR of 4.
Complex 12 was found unstable in solution after several weeks.
Hence, the possibility of a norbornene polymerization without
MAO as cocatalyst was investigated. At an NB:Pd ratio of 11:1, NB
(32.7 mg, 3.48 ꢀ 10ꢂ1 mmol) and 12 (30 mg, 3.16 ꢀ 10ꢂ2 mmol)
were irradiated with ultrasound at 50 ꢁC in 0.8 ml of a 1:1 mixture
of toluene-d8 and CD2Cl2 in an NMR tube. After 6 h of ultrasonic
radiation 1H-NMR spectra showed still the signals of unreacted 12
and NB (Fig. 13a). The signal intensities of C5Ph4H and the two
The complex (
a structurally characterized, albeit NB-polymerization inactive,
contact ion pair [(
5-C5H5)Ni(PPh3)2][CH3-B(C6F5)3] and a 19F NMR
study shows the polynorbornene obtained with (
5-C5H5)Ni(CH3)
h
5-C5H5)Ni(CH3)(PPh3) reacts with B(C6F5)3 to
h
h
(PPh3)/B(C6F5)3 to have the C6F5 end group [18]. From cationic
[(tmeda)Pd(OEt2)(CH3)][B(ArF)4] (tmeda ¼ N,N,N0,N0-tetramethyl-
ethylenediamine, ArF ¼ C6H3-3,5-(CF3)2) the propagating species
and resting state [(tmeda)Pd(CH3-(NB)2)][B(ArF)4] was identified
by extensive NMR studies and single X-ray diffraction analysis [79].
Complex 4 was chosen for an investigation of the polymeriza-
tion mechanism. Polymerization reactions were set up in 5 ml
Schlenk flasks with the two different molar NB:Al:Pd ratios of
10:10:1 and 10:100:1. To a solution of 4 and NB in toluene-d8 (for
a ratio of 10:10:1) or a 1:1 mixture of CD2Cl2 and toluene-d8 (for
a ratio of 10:100:1) the appropriate amount of MAO (dried in high
vacuum and re-dissolved in toluene-d8) was added. After stirring
for 5 min at 22 ꢁC the reaction mixtures were transferred into NMR
tubes under argon and the NMR-spectra were measured. An Al:Pd
ratio of 10:1 was sufficient to create an active palladium center for
norbornene polymerization. However, no quantitative monomer
conversion was reached as the still present NB-olefin resonance
shows (Fig. 11a, 2,3-label). The broad NB resonances in Fig. 11a are
suggested due to formation of a complex [(C5H5)Pd(C6F5)(p-NB)]
where NB replaces the phosphane at the palladium center in an NB-
PPh3 equilibrium according to Eq. (3). PdeNB complexes are known
[80]. Even when NB coordinates to Pd the subsequent insertion
reaction into the PdeC6F5 bond is known to be slow on neutral
complexes [77]. For an Al:Pd ratio of 100:1 complete norbornene
conversion within 5 min was achieved (Fig. 11b). Because of poly-
mer precipitation at this ratio no broad PNB signals are observed
anymore in the aliphatic region (compare Fig. 11a and b).
A comparison of the 19F-NMR spectra of complex 4 (Fig. 12a)
with those of an NB-MAO-4 reaction mixture at the molar NB:Al:Pd
ratios of 10:10:1 (Fig. 12b) and 10:100:1 (Fig. 12c) shows that the
Fig. 13. 1H-NMR spectrum of the reaction mixture of 12 and NB (NB:Pd 11:1) after (a)
6 h, (b) 24 h treatment with ultrasonic radiation in toluene-d8/CD2Cl2 (*/**) at 50 ꢁC.
NB signals are numbered according to Scheme 6.
Scheme 6. NMR numbering for norbornene.

F. Blank et al. / Journal of Organometallic Chemistry 696 (2011) 473e487
485
insertion directing role of PPh3 leads to almost the same activity of
4/MAO in NB and ENB homopolymerization.
Acknowledgment
This work was supported by the Ministerio de Ciencia e Inno-
vación of Spain and FEDER (Project CTQ2008-02178/BQU) and
Fundación Seneca-CARM (Project 08666/PI/08).
Appendix. Supplementary material
Supplementary material associated with this article can be found
in the online version, at doi:10.1016/j.jorganchem.2010.08.050.
References
Fig. 14. 19F-NMR spectrum of (a) complex 12, (b) 12/NB after 24 h treatment with
ultrasonic radiation in toluene-d8/CD2Cl2 at 50 ꢁC. Boxes mark the resonances assigned
to C6F5 attached to a growing polymer chain; arrows mark the resonances assigned to
[PdCl(C6F5)(AsPh3)2]. The rising base line in (b) does not allow for a reasonable inte-
gration upfield from ꢂ150 ppm. Hence, the position of the third signal to the arrow set
(below p-F or m-F of Pd-C6F5) could not be determined.
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5. Conclusions
The half-sandwich
5-C5H5)Pd(C6X5)2]ꢂ, [(
electron donor ligand), (
h
5-cyclopentadienylpalladium complexes
[(
h
h
5-C5H5)Pd(C6X5)(L)] (X ¼ F, Cl, L ¼ 2-
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h
5-C5Ph4H)Pd(C6F5)(AsPh3) and ( 5-C5Bn5)
h
Pd(C6F5)(AsPh3) are air stable pseudo-trigonal compounds. [(h5
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C5H5)Pd(C6F5)(L)] (L ¼ PPh3, 4 and AsPh3, 7) in the presence of MAO
polymerize norbornene (NB), 5-vinyl-2-norbornene (VNB) and 5-
ethylidene-2-norbornene (ENB) in a vinyl addition polymerization.
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