Alternative coordination modes in palladium(II)-diimino-bispyridine complexes with an axially chiral biphenyl backbone

Article abstract of DOI:10.1002/ejic.200400913

The chiral biphenyl-bridged diimino-bispyridine ligands N,N′-(6,6′-dimethylbiphenyl-2,2′-diyl)bis(2-pyridylmethyl) -diimine(1)and N,N′-(6,6′-dimethylbiphenyl-2,2′-diyl)bis[(6- methyl-2-pyridyl)methyl]diimine (2) react with Pd(COD)Cl₂ to give, depending on the reaction conditions, either mono- or binuclear PdCl₂ complexes. In the binuclear complex 1-(PdCl₂)₂, the Pd nuclei are held at a distance of 3.37 A by the ligand backbone. N,N′-(6,6′-dimethylbiphenyl-2,2′-diyl) bis[(5-methyl-2-furyl) methyl]diimine (3), with furyl instead of pyridyl rings, gives mononuclear, C₂-symmetric complexes only. Reactions of [Pd(NCCH₃) ₄]₂₊(BF₄^-)₂ with ligand 1 or 3 give the C₂-symmetric cations [1-Pd]²⁺or [3-Pd(NCCH₃)₂]²⁺, respectively, as their BF₄^- salts, Solid-state structures of the chloride complexes 1-PdCl₂, 1-(PdCl₂)₂ and 3-PdCl ₂, and of the complex cations [1-Pd]²⁺ and [3-Pd(NCCCH₃)₂]²⁺ with tetradentate and bidentate ligand coordination, respectively, all show square-planar coordination, with some distortion toward tedrahedral geometry due to the twisted biaryl-backbone. Preliminary observations on norbornene polymerization with the catalysts 1-PdCl₂/MAO, 2-PdCl₂/MAO and [(3-Pd(NCCH₃)₂]²⁺ suggest that a certain degree of stereoregularity of the polymers is induced by these chiral catalysts. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejic.200400913

FULL PAPER
Alternative Coordination Modes in Palladium(II)-Diimino-Bispyridine
Complexes with an Axially Chiral Biphenyl Backbone
Mika Kettunen,[a] Christoph Vedder,[b] Hans-Herbert Brintzinger,[b] Ilpo Mutikainen,[a]
Markku Leskelä,[a] and Timo Repo*[a]
Keywords: Chiral biaryl ligands / Palladium imino complexes / Binuclear complexes
–
The chiral biphenyl-bridged diimino-bispyridine ligands
respectively, as their BF4 salts. Solid-state structures of the
N,NЈ-(6,6Ј-dimethylbiphenyl-2,2Ј-diyl)bis(2-pyridylmethyl)- chloride complexes 1-PdCl2, 1-(PdCl2)2 and 3-PdCl2, and of
diimine(1)and N,NЈ-(6,6Ј-dimethylbiphenyl-2,2Ј-diyl)bis[(6-
methyl-2-pyridyl)methyl]diimine (2) react with Pd(COD)Cl2
to give, depending on the reaction conditions, either mono-
or binuclear PdCl2 complexes. In the binuclear complex 1-
(PdCl2)2, the Pd nuclei are held at a distance of 3.37 Å by
the ligand backbone. N,NЈ-(6,6Ј-dimethylbiphenyl-2,2Ј-diyl)
bis[(5-methyl-2-furyl)methyl]diimine (3), with furyl instead of
the complex cations [1-Pd]2+ and [3-Pd(NCCCH3)2]2+ with
tetradentate and bidentate ligand coordination, respectively,
all show square-planar coordination, with some distortion to-
ward tedrahedral geometry due to the twisted biaryl-back-
bone. Preliminary observations on norbornene polymeriza-
tion with the catalysts 1-PdCl2/MAO, 2-PdCl2/MAO and [(3-
Pd(NCCH3)2]2+ suggest that a certain degree of stereoregu-
larity of the polymers is induced by these chiral catalysts.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
pyridyl rings, gives mononuclear, C2-symmetric complexes
–
only. Reactions of [Pd(NCCH3)4]2+ (BF4
) with ligand 1 or 3
2
give the C2-symmetric cations [1-Pd]2+or [3-Pd(NCCH3)2]2+
,
scribed as effective catalyst precursors for Heck coupling[7]
and for ethene polymerization,[8] respectively, as well as
with shorter chiral spacers to produce optically active poly-
ketones.[9] Palladium complexes with chiral bidentate bis-
(oxazoline) ligands have been shown to be efficient in asym-
metric allylic alkylation,[10] while biaryl Schiff base Cu com-
plexes catalyze the aziridination of alkenes.[11]
Introduction
Considerable attention has lately been focused on binu-
clear organometallic compounds, based on expectations
that their reactivity in synthesis and catalysis may differ sig-
nificantly from that of analogous mononuclear species.[1]
Interactions between closely adjacent metal centers might
cause increased reaction rates or transformations not occur-
With a structurally rigid 6,6Ј-disubstituted biaryl ligand
ring with monometallic species, as was recently shown for backbone, the configuration of the ligand is fixed and its
copolymerization of styrene and ethene by binuclear titano- axial chirality can efficiently be transmitted to the stereo-
cene complexes.[2] The distance between two metal centers topicity of the active site.[12] Biphenyl-bridged ligands form,
and their orientation to each other can be important for in general, mononuclear complexes,[13] but binuclear com-
catalytic performance, as had been noted for binuclear rho- plexes, e. g. with CuII, have also been reported.[14] Tetraden-
dium hydroformylation catalysts[3] and for palladium com- tate N4, N2O2 and N2P2 ligands are known to form both
plexes that catalyze hydration reactions.[4] Additional oxi- mono- and binuclear PdII complexes,[15,16,17] but only few
dation states might also be accessible in binuclear com- of these have chiral biaryl backbones.[16a,17c]
plexes as a result of stabilizing metal–metal interactions.[5]
Late transition metal complexes with nitrogen-based li-
gands have found a wide range of applications in homogen-
eous catalysis including polymerization of olefins or acry-
lates as well as hydrogenation reactions.[6] Pyridylimine-PdII
chelates as dendrimeric complexes and binuclear PdII com-
plexes with long aliphatic spacers have recently been de-
Since cationic PdII complexes bearing diimine ligands
with bulky substituents have been discovered to catalyze co-
polymerizations of α-olefins with functional vinyl mono-
mers,[18] significant amounts of research have been aimed at
tuning the electronic and steric properties of these ligands.
Bulky aryls disfavor associative displacement and chain
transfer reactions by steric protection of the electrophilic
metal center; ligands with labile donor atoms like oxygen
or sulfur in their side arms might likewise hinder β-H elimi-
nation by temporarily occupying a vacant site on the metal
center.[19] Interesting featuresmight thus be expected for C2-
symmetric PdII diimine complexes with side-arm donors
bridged by a chiral ligand backbone.
[a] Laboratory of Inorganic Chemistry, University of Helsinki,
00014 Helsinki, Finland
Fax: +358-9-1915-0198
E-mail: timo.repo@helsinki.fi
[b] Fachbereich Chemie, Universität Konstanz,
78457 Konstanz, Germany
Eur. J. Inorg. Chem. 2005, 1081–1089
DOI: 10.1002/ejic.200400913
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M. Kettunen, C. Vedder, H.-H. Brintzinger, I. Mutikainen, M. Leskelä, T. Repo
FULL PAPER
In previous contributions, we have studied complexes of
tetradentate 6,6Ј-dimethylbianiline-based ligands with met-
als such as Zr, Fe, Co or Cr in regard to their structures
and catalytic activities.[20] In this work, we extend these
studies to mono- and bimetallic PdII complexes bearing chi-
ral diimino ligands with a biphenyl backbone.
Results and Discussion
Ligands 1, 2 and 3 were prepared, as described earlier,[20]
by imine condensation of N,NЈ-(6,6Ј-dimethylbiphenyl-2,2Ј-
diyl)diamine with the required aldehydes. Reaction of N,NЈ-
(6,6Ј-dimethylbiphenyl-2,2Ј-diyl)bis(2-pyridylmethyl)di-im-
ine (1) with one equivalent of Pd(COD)Cl2 at 0 °C gave 1-
PdCl2, which precipitated from the reaction mixture in al-
most quantitative yield [Equation (1)]. When the reaction
was repeated in an NMR tube, starting at 0 °C and continu-
ing at room temperature, the rate of the reaction was found
to be quite fast; 95% of the Pd(COD)Cl2 was consumed
after 30 minutes. Ligand 2 likewise reacted readily with
Pd(COD)Cl2 under similar reaction conditions, but 2-PdCl2
was isolated with lower yield due to its higher solubility.
Figure 1. Crystal structure of 1-PdCl2 (ORTEP plot, thermal ellip-
soids drawn at 50% probability, H atoms and CH2Cl2 solvent mole-
cules omitted for clarity).
Table 1. Selected bond lengths (Å) and angles [°] for 1-PdCl2 (c.f.
Figure 1).
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–Cl(2)
Pd(1)–Cl(1)
2.022(3)
2.037(3)
2.2893(11)
2.2916(11)
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–Cl(2)
N(2)–Pd(1)–Cl(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
Cl(2)–Pd(1)–Cl(1)
80.38(12
175.56(9)
95.26(9)
93.28(9)
173.61(9)
91.06(4)
Pd-coordinated and an uncoordinated ligand moiety, for
the methyl groups at the biphenyl bridge (1.96 and
2.05 ppm), for the methyl groups in 6-position of each pyri-
dyl ring (2.47 and 2.80 ppm) and for the imine protons (8.21
and 8.69 ppm).
(1)
A single-crystal X-ray structure analysis of 1-PdCl2 con-
firms an approximately square-planar coordination of the
PdIIcis-dichloro unit to one of the pyridylimine moieties of
ligand 1 (Figure 1), which thus forms a five-membered pyri-
dylimine chelate, with Pd–N and Pd–Cl distances (Table 1)
close to values reported for similar complexes.[15Ϫ17] In the
solid state, the non-coordinated pyridylimine moiety lies on
the backside of the biphenyl bridge, pointing away from the
PdCl2 unit.
1
(2)
The H NMR spectrum of 1-PdCl2 in [D6]DMSO solu-
tion reveals, instead of two singlets expected for the non-
equivalent methyl groups in 6- and 6Ј-positions of the biaryl
With ligand 3, where the side-arm pyridyl groups are re-
backbone, three sharp CH3 signals at δ = 1.82, 2.02 and placed by furyl rings, a significantly longer reaction time
2.23 ppm with an integral ratio of 1:2:1.[21] The occurrence (20 h) was required for complex formation with Pd(COD)-
of these three CH3 signals, as well as non-integer ratios for Cl2 [Equation (2)]. As shown by the crystal structure of 3-
the aromatic proton signal integrals (see Experimental sec- PdCl2 (Figure 2, Table 2), ligand 3 is bound in a bidentate
tion), indicate the presence of two isomers in [D6]DMSO manner again. Here, however, the two imino nitrogens form
solution of 1-PdCl2, each with one Pd-coordinated and one a seven-membered chelate with the cis-dichloro Pd unit to
non-coordinated ligand moiety. Related phenomena in con- give an approximately square-planar and C2-symmetric ge-
nection with possible isomers of 1-(PdCl2)2 will be dis- ometry. Due to the dihedral angle of 67° between the phenyl
cussed below.
rings of the biphenyl bridge, the ligand plane at the Pd cen-
For 2-PdCl2 in [D6]DMSO solution, however, only two ter is somewhat distorted, with an angle of 5.9(2)° spanned
singlets are observed, in agreement with the presence of a by the planes Cl1–Pd–N1 and Cl2–Pd–N2. The furyl oxy-
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Coordination Modes in Palladium(ii)-Diimino-Bispyridine Complexes
FULL PAPER
gen atoms are located at non-bonding distances of 5.0 and
5.1 Å from the Pd center, from which the side arms are
pointing away.[22] The preference of the Pd center for N over
O ligand atoms obviously overrides its preference for five-
membered over seven-membered chelate rings to such an
extent that a C2-symmetric geometry becomes favored for
3-PdCl2 over the C1-symmetric structures of 1-PdCl2 and
2-PdCl2.
(3)
In 1-PdCl2 one halve of ligand 1 remains available for
further coordination and provides a possibility for the prep-
aration of bimetallic complexes. The dipalladium complex
1-(PdCl2)2 was indeed isolated in 97% yield when ligand 1
was treated with two equivalents of Pd(COD)Cl2 at room
temperature [Equation (3)].[23] In the solid-state structure
of binuclear 1-(PdCl2)2, one PdCl2 unit is coordinated, as
expected, to each of the biphenyl-bridged pyridylimine moi-
eties (Figure 3, Table 3). The two square-planar N2PdCl2
units are almost parallel to each other, stacking under an
angle of 7.40(2)°. Viewed along the Pd–Pd axis, the two
PdCl2 units are rotated by an angle of 104.9° relative to
each other. The Pd(1)–Pd(2) distance of 3.37 Å is in the
range of quite a number of binuclear PdII complexes with
relatively short (2Ϫ4 atom) bridging ligands.[24] Apparently
a similarly favorable situation for a close PdII···PdII contact
is created by the preference of the biaryl bridge for a twist
angle of ca. 70°. In addition, some attractive interaction
between Pd–Cl dipoles might contribute to keep the Pd cen-
ters at a distance close to the sum of their van-der-Waals
radii.
Figure 2. Crystal structure of 3-PdCl2 (ORTEP plot, thermal ellip-
soids drawn at 50% probability, H atoms and CH2Cl2 solvent mole-
cule omitted for clarity).
Table 2. Selected bond lengths (Å) and angles [°] for 3-
PdCl2·CH2Cl2 (c.f. Figure 2).
Pd(1)–N(1) 2.029(3)
Pd(1)–N(2) 2.057(3)
Pd(1)–Cl(1) 2.2944(9)
Pd(1)–Cl(2) 2.2973(9)
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(2)
N(2)–Pd(1)–Cl(2)
Cl(1)–Pd(1)–Cl(2)
90.26(11)
89.26(8)
174.45(9)
177.96(9)
90.17(8)
90.51(4)
CDCl3 solutions of 3-PdCl2 give 1H NMR spectra in
agreement with an apparent C2 symmetry, with a singlet at
δ = 1.88 ppm due to the two methyl groups in the biphenyl
backbone, another singlet at δ = 2.18 ppm due to the methyl
groups at the furyl rings, and a singlet at δ = 8.32 ppm as-
signed to the imine protons. These signals are accompanied,
however, by a set of smaller signals located slightly up-field,
at δ = 1.82, 2.12 and 8.29 ppm, which integrate to ratios of
ca. 1:10 relative to the respective main peaks. The observa-
tion of this additional signal set in solutions of 3-PdCl2
would indicate that some minor isomer is present, in ad-
dition to the structure represented in Figure 2. From our
Figure 3. Crystal structure of 1-(PdCl2)2 (ORTEP plot, thermal el-
lipsoids drawn at 50% probability, H atoms and CH2Cl2 solvent
molecules omitted for clarity).
In the 1H NMR spectra of 1-(PdCl2)2 in [D6]DMSO
data it is not clear, which alternative geometry prevails in solution, the methyl groups at the biphenyl bridge give rise
this isomer, whether (and how) e. g. furyl oxygen atoms to a sharp signal at δ = 2.02 ppm and a broader one at δ =
might be coordinated to the PdII center.[19]
2.12 ppm, each corresponding to 3 protons; the 6-posi-
Eur. J. Inorg. Chem. 2005, 1081–1089
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M. Kettunen, C. Vedder, H.-H. Brintzinger, I. Mutikainen, M. Leskelä, T. Repo
FULL PAPER
Table 3. Selected bond lengths (Å) and angles [°] for 1-(PdCl2)2· late ring with each of the pyridylimine moieties, with Pd–N
2CH2Cl2 (c.f. Figure 3).
distances (Table 4) in the range reported for other Pd-imino
complexes.[15Ϫ17] Due to the dihedral angle of 71° in the
Pd(1)–N(1) 2.034(6)
Pd(1)–N(2) 2.048(6)
Pd(1)–Cl(1) 2.292(2)
Pd(1)–Cl(2) 2.2930(19) N(2)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(2)
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–Cl(1)
Cl(1)–Pd(1)–Cl(2)
79.8(3)
94.4(2)
2,2Ј-dimethyl-substituted biphenyl backbone, the square-
planar coordination at the Pd atom shows some tetrahedral
distortion, so that the planes N1–Pd–N2 and N3–Pd–N4
span an angle of 12.9(5)°.[26]
88.56(7)
173.42(19)
176.94(19)
97.31(18)
127.1(6)
113.7(5)
80.3(2)
173.60(18)
97.19(18)
93.44(19)
89.04(8)
N(2)–Pd(1)–Cl(2)
C(1)–N(1)–Pd(1)
C(5)–N(1)–Pd(1)
N(3)–Pd(2)–N(4)
N(3)–Pd(2)–Cl(4)
N(3)–Pd(2)–Cl(3)
N(4)–Pd(2)–Cl(4)
Cl(4)–Pd(2)–Cl(3)
Pd(2)–N(3) 2.044(6)
Pd(2)–N(4) 2.056(6)
Pd(2)–Cl(3) 2.300(2)
Pd(2)–Cl(4) 2.281(2)
tioned protons of the pyridyl rings likewise appear as two
doublets at 8.83 and at δ = 9.04 ppm representing one pro-
ton each and the other aromatic and imine signals are also
grouped in a manner incompatible with a C2-symmetric
complex. These observations can be explained either by the
occurrence of two diastereomers, e.g. meso- and rac-like
conformers of the two complex moieties, in a ratio of ca.
1:1 or by some nonequivalence of the two complex moieties
in solution, caused e.g. by co-ordination of a solvent mole-
cule to one of the Pd centers. Our data do not allow us to
estimate the lifetimes of isomers of this kind.
Figure 4. Crystal structure of [1-Pd]2+ (BF4Ϫ)2 (ORTEP plot, ther-
mal ellipsoids drawn at 50% probability, H atoms, 0.5 H2O and
Ϫ
BF4 omitted for clarity).
The cis-PdCl2 unit considered so far obviously favors for-
mation of a five-membered pyridyl-imine chelate over that
of a seven-membered diimine chelate; complexes such as
1-PdCl2 or 2-PdCl2 are thus of C1 symmetry. In order to
synthesize complexes which fully exploit the axialsymmetry
inherent in the biaryl backbone to generate C2-symmetric
complexes suitable for asymmetric catalysis,[25] we have
sought to induce tetradentate coordination of ligands 1 and
2 with formation of cationic complexes by use of the more
Table 4. Selected bond lengths (Å) and angles [°] for [1-Pd]2+
-
–
(BF4 )2 (c.f. Figure 4).
Pd(1)–N(3) 2.012(7)
Pd(1)–N(2) 2.017(6)
Pd(1)–N(4) 2.021(7)
Pd(1)–N(1) 2.044(7)
N(3)–Pd(1)–N(2)
N(3)–Pd(1)–N(4)
N(2)–Pd(1)–N(4)
N(3)–Pd(1)–N(1)
N(2)–Pd(1)–N(1)
N(4)–Pd(1)–N(1)
99.0(3)
80.4(3)
161.7(3)
164.5(3)
79.7(3)
105.6(3)
–
electron-deficient Pd precursor [Pd(NCCH3)4]2+ (BF4 )2
[Equation (4)].
1H NMR spectra in CD3CN solution indicate, again,
some deviations of the cation [1-Pd]2+ from the approxi-
mate C2 symmetry found in the solid state. The 6,6Ј-posi-
tioned methyl groups of the ligand backbone give rise to a
multiplet with two maxima at δ = 1.72 and 1.76 ppm, and
the aromatic protons are likewise grouped in multiplets
which do not appear to be compatible with an overall C2
symmetry. Even though we do not have any direct evidence
in this regard, we would assume that the equivalence of
both halves of the complex molecule might be destroyed, as
in the cases discussed above, by coordination of a solvent
molecule.
(4)
Reaction of ligand 1 with one equivalent of [Pd-
In order to test whether a tetradentate coordination sim-
–
(NCCH3)4]2+ (BF4 )2 in acetonitrile at room temperature ilar to that achieved for ligand 1 might also be accessible
–
gave the ion pair [1-Pd]2+ (BF4 )2 in high yield. The ex- for the furyl-substituted ligand 3,[27] the latter was likewise
–
pected tetradentate coordination of ligand 1 in [1-Pd]2+
(BF4 )2 was verified by single-crystal structure determi- tion. The reaction proceeded fast and with high yield, but
-
reacted with [Pd(NCCH3)4]2+ (BF4 )2 in acetonitrile solu-
–
nation (Figure 4). The Pd center forms an approximately gave, instead of a product with tetracoordinate ligand 3, [3-
–
C2-symmetric seven-membered chelate ring with the bi- Pd]2+ (BF4 )2, the bis(acetonitrile) adduct [3-Pd-(NCCH3)2]
–
phenyl-bridged imine nitrogens and one five-membered che- 2+ (BF4 )2 [Equation (5)].
1084
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Coordination Modes in Palladium(ii)-Diimino-Bispyridine Complexes
FULL PAPER
and furyl methyl substituents give rise to only one singlet
signal each, at δ = 2.08, 2.20 and 2.63 ppm, respectively.
Apparently, the binding of the furyl groups to the cationic
PdII center, however weak, protects the latter from interac-
tion with a solvent donor, which might otherwise destroy
the overall C2 symmetry of the complex molecule in solu-
tion.
Since two nitrogen ligand atoms are sufficient for the for-
mation of a cationic di-acetonitrile complex, ligand 1 was
also treated with two equivalents of [Pd(NCCH3)4](BF4)2
to prepare the binuclear cationic complex 1-([Pd-
(5)
–
(NCCH3)2]2+)2(BF4 )4 [Equation (6)]. The reaction yielded
–
In the crystal structure of [3-Pd(NCCH3)2]2+ (BF4 )2
1
an oily product, the elemental analysis and H NMR spec-
(Figure 5, Table 5), square-planar coordination at the cat-
ionic Pd center is found to involve two cis-positioned aceto-
nitrile ligands and the two imino nitrogen atoms of ligand
3; as in 3-PdCl2, the ligand 3 forms again a seven-membered
chelate ring with the Pd center. In distinction to 3-PdCl2,
however, where the furyl oxygen atoms point away from the
Pd center, they are now turned towards the latter and lie
rather close to it, in pseudo-axial positions at Pd–O dis-
tances of 3.0(1) Å. Some (presumably weak) coordination
or dipolar attraction of the furyl oxygen atoms to the PdII
center thus appears to be stabilized by the cationic nature
of the metal.[27,28]
tra of which indicated formation of the expected complex.
As no crystals suitable for X-ray diffraction were obtained,
it was not possible to study the effect of the increased
charges on the mutual arrangement of the metal centers in
this binuclear complex.
(6)
Preliminary data concerning catalytic activities of the
new PdII complexes described above were obtained with re-
gard to polymerization of norbornene at room tempera-
ture.[29] When activated by addition of methylaluminoxane
(MAO), the dichloro complexes 1-PdCl2, 2-PdCl2 and 3-
PdCl2 gave polymers which were insoluble in organic sol-
vents such as trichlorobenzene even at elevated tempera-
–
tures. The cationic complex [3-Pd(NCCH3)2]2+ (BF4 )2 gave,
Figure 5. Crystal structure of [3-Pd(NCCH3)2]2+ (BF4Ϫ)2 (ORTEP
without activation by MAO,[29] polymers with good solubil-
ity, e.g. in toluene or chloroform, in moderate yield. For
these polynorbornenes, a molar mass of 33800 g/mol and a
polydispersity index of 1.26 were determined. Complex [1-
plot, thermal ellipsoids drawn at 50% probability, H atoms,
Ϫ
CH3CN solvent molecule and BF4 omitted for clarity).
–
Pd]2+ (BF4 )2, in which the Pd center is bound to all four N
Table 5. Selected bond lengths (Å) and angles [°] for [3-Pd-
atoms of the tetradentate ligand, was found to be inactive
for polymerization of norbornene at room temperature.
Decomposition temperatures, determined by thermo-
gravimetric analysis, of the polymers obtained with MAO-
activated 1-PdCl2, 2-PdCl2 and 3-PdCl2 as well as of those
–
(NCCH3)2]2+ (BF4 )2 (c.f. Figure 5).
Pd(1)–N(1)
Pd(1)–N(4)
Pd(1)–N(2)
Pd(1)–N(3)
2.006(2)
2.009(2)
2.016(2)
2.022(2)
N(1)–Pd(1)–N(4)
N(1)–Pd(1)–N(2)
N(4)–Pd(1)–N(2)
N(1)–Pd(1)–N(3)
N(4)–Pd(1)–N(3)
N(2)–Pd(1)–N(3)
171.03(8)
86.35(9)
93.37(9)
91.97(9)
89.15(9)
174.21(8)
–
obtained with [(3-Pd(NCCH3)2]2+ (BF4 )2, were found to be
exceptionally high (ca. 450 °C), i.e. more than 100 °C higher
than that (335 °C) determined for the polymer obtained
with [Pd(NCCH3)4](BF4)2.[29] This might suggest that a cer-
The H NMR spectrum of [3-Pd(NCCH3)2]2+ is entirely tain degree of stereoregularity is induced in the polymer by
1
in agreement with the overall C2 symmetry expected from the chiral ligands of the catalysts 1-PdCl2/MAO, 2-PdCl2/
its solid-state structure. Its NCCH3 ligands and its biphenyl MAO, 3-PdCl2/MAO and [(3-Pd(NCCH3)2]2+ [30]
.
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M. Kettunen, C. Vedder, H.-H. Brintzinger, I. Mutikainen, M. Leskelä, T. Repo
FULL PAPER
for 20 h. Diethyl ether (20 mL) was added to reaction mixture,
which was then filtered and kept at –20 °C. The product was col-
Conclusions
Axially symmetric, biphenyl-bridged diimino ligands
lected as orange crystals by filtration after 24 h. Yield 0.36 g, 50%.
with additional pyridyl or furyl side arms are highly versa- 1H NMR (200 MHz, CDCl3): δ = 1.88 (s, 6 H, furyl-CH3), 2.18 (s,
tile with respect to PdII complex formation. Depending on
the Pd precursors and the reaction conditions used, mono-
6 H, biaryl-CH3), 6.01 (d, J = 3.6 Hz, 2 H, furyl-CH), 6.16 (d, J =
3.2 Hz, 2 H, furyl-CH), 7.09 (d, J = 7.8 Hz, 2 H, biaryl-CH), 7.22
(d, J = 7.0 Hz, 2 H, biaryl-CH), 7.29 (pt, J = 7.6 Hz, 2 H, biaryl-
nuclear-bidentate complexes of C1 or C2 symmetry, as well
CH), 8.32 ppm (s, 2H imine-CH). Minor isomer: 1.82 (s, biaryl-
as binuclear and mononuclear-tetradentale PdII complexes
can be obtained in a controlled manner and with high
yields. Preliminary observations indicate distinctly different
properties of cationic species derived from them as norbor-
CH3), 2.12 (s, furyl-CH3), 8.29 ppm (s, imine-CH). 13C NMR
(50 MHz, CDCl3): δ = 13.9, 18.7, 109.9, 120.3, 124.5, 127.7 129.3,
129.7, 138.5, 145.9, 146.4, 156.3, 159.5 ppm; elemental analysis (%)
calcd. for C26H24Cl2N2O2Pd·CH2Cl2 (658.75): C 49.23, H 3.98, N
4.25; found: C 48.26, H 4.57, N 4.06.
nene polymerization catalysts.
N,NЈ-(6,6Ј-Dimethylbiphenyl-2,2Ј-diyl)bis(2-pyridylmethyl)diimine-
(PdCl2)2 [1-(PdCl2)2]: A solution of ligand 1 (0.43 g, 1.10 mmol)
and Pd(COD)Cl2 (0.63g, 2.20 mmol) in CH2Cl2 (35 mL) was
stirred at room temperature for 20 h. The product precipitated as
a yellow powder, which was collected by filtration, washed with
diethyl ether and dried in vacuo. Yield 0.80 g, 97%. 1H NMR
(200 MHz, [D6]DMSO): δ = 2.02 (s, 3 H, CH3), 2.12 (s, 3 H, CH3),
7.31Ϫ7.38 (m, 3.5 H, Ar-H), 7.48Ϫ7.51 (m, 2.5 H, Ar-H), 7.80 (br.,
3.5 H, Ar-H), 8.21 (m, 3.5 H, CH), 8.83 (d, J = 5.2 Hz, 1 H, CH),
8.88 (s, 1 H, imine-CH), 9.04 ppm (br., 1 H, pyridine-CH). 13C
NMR (50 MHz, CDCl3): δ = 19.30, 120.23, 128.90Ϫ130.16 (m),
131.39, 144.01, 150.91, 171.36 ppm; elemental analysis (%) calcd.
for C26H22N4Pd2Cl4 (745.14): C 41.91, H 2.97, N 7.51; found: C
41.25, H 2.78, N 7.67.
Experimental Section
All complex preparation and polymerization reactions were per-
formed under argon atmosphere using standard Schlenk tech-
niques. N,NЈ-(6,6Ј-Dimethylbiphenyl-2,2Ј-diyl)diamine,[31] the li-
gands 1–3[20] and dichloro(1,5-cyclooctadiene)palladium(ii)
[Pd(COD)Cl2],[32] were prepared as reported earlier. Solvents were
dried prior to use by refluxing over and distillation from sodium
(hydrocarbons), magnesium (alcohols), P2O5 (acetonitrile) or cal-
cium hydride (dichloromethane). Deuterated solvents were dried
over 4-Å molecular sieves. All other chemicals were purchased from
commercial suppliers and used without further purification. Ele-
mental analyses were performed with an EA 1110 CHNS-O CE
instrument. NMR spectra were collected with a Varian Gemini 200
spectrometer. Polymer molar mass and molar mass distributions
were measured by gel permeation chromatography (GPC) relative
to polystyrene standards.
[N,NЈ-(6,6Ј-Dimethylbiphenyl-2,2Ј-diyl)bis(2-pyridylmethyl)diimine-
Pd]2+ (BF4 )2 {[1-Pd]2+ (BF4 )2}: A filtered solution of ligand 1
–
–
(0.29 g, 0.74 mmol) in acetonitrile (15 mL) was added to a solution
–
of [Pd(NCCH3)4]2+ (BF4 )2 (0.33 g, 0.74 mmol) in acetonitrile
(15 mL) and the reaction mixture stirred at room temperature for
5 h. Reaction was then evaporated and dried in vacuo. Yield 0.49 g,
98%. 1H NMR (200 MHz, CD3CN): δ = 1.67Ϫ1.81 (m, 6 H, CH3),
7.16Ϫ7.45 (m, 7 H, Ar-H), 7.65Ϫ7.82 (m, 2 H, Ar-H), 7.93Ϫ7.97
(m, 2 H, Ar-H), 8.09Ϫ8.16 (m, 3 H, Ar-H), 8.37Ϫ8.39 ppm (m, 2
N,NЈ-(6,6Ј-Dimethylbiphenyl-2,2Ј-diyl)bis(2-pyridylmethyl)-diimine-
PdCl2 (1-PdCl2): A solution of ligand 1 (0.59 g, 1.52 mmol) and
Pd(COD)Cl2 (0.39 g, 1.38 mmol) in CH2Cl2 (25 mL) was stirred at
0 °C. The product started to precipitate as a light yellow powder
after 1 h. After stirring for another 20 h at room temperature, the
product was filtered, washed with diethyl ether and dried in vacuo.
Yield 658 mg, 84%. 1H NMR (200 MHz, [D6]DMSO): δ = 1.82,
2.02 and 2.23 (3 lines, 6 H, CH3), 7.02 (d, J = 8.0 Hz, 0.5 H, Ar-
H), 7.25Ϫ7.39 (m, 3.5 H, Ar-H), 7.5 (m, 2 H, Ar-H), 7.71Ϫ7.94
(m, 3.5 H, Ar-H), 8.21Ϫ8.27 (m, 2.5 H, CH), 8.5 (s, 0.5 H, imine-
CH), 8.64Ϫ8.71 (m, 1 H, CH), 8.83Ϫ8.97 (m, 1.5 H, CH),
8.88 ppm (s, 1 H, imine-CH); elemental analysis (%) calcd. for
C26H22Cl2N4Pd (567.81): C 55.00, H 3.91, N 9.87; found: C 54.70,
H 3.71, N 10.25.
H,
imine-CH);
elemental
analysis
(%)
calcd.
for
C26H22B2F8N4Pd·CH3CN (711.57): C 47.26, H 3.54, N 9.84;
found: C 47.44, H 3.31, N 9.92.
[N,NЈ-(6,6Ј-Dimethylbiphenyl-2,2Ј-diyl)bis[(5-methyl-2-furyl)methyl-
–
–
]diimine-Pd(NCCH3)2]2+ (BF4 )2 {[(3-Pd(NCCH3)2]2+ (BF4 )2}: This
complex was prepared in the same manner as described above for
–
1
complex [(1-Pd]2+ (BF4 )2. Yield 0.53 g, 94%. H NMR (200 MHz,
CD3CN): δ = 2.08 (s, 6 H, NCCH3), 2.20 (s, 6 H, biaryl-CH3), 2.63
(s, 6 H, furyl-CH3), 6.52Ϫ6.55 (m, 2 H, furyl-CH), 7.30Ϫ7.39 and
7.48Ϫ7.50 ppm (m, 10 H, Ar-H); elemental analysis (%) calcd. for
C28H30B2F8N4O2Pd (734.60): C 45.78, H 4.11, N 7.62; found: C
45.62, H 3.97, N 7.66.
N,NЈ-(6,6Ј-Dimethylbiphenyl-2,2Ј-diyl)bis[(6-methyl-2-pyridyl)meth-
yldiimine-PdCl2 (2-PdCl2): This complex was prepared in the same
manner as described above for complex 1-PdCl2. Yield 0.16 g, 50%.
1H NMR (200 MHz, [D6]DMSO): δ = 1.96 (s, 3 H, biaryl-CH3),
2.05 (s, 3 H, biaryl-CH3 on Pd-coordinated side), 2.47 (s, 3 H, pyri-
dine-CH3), 2.80 (s, 3 H, pyridine-CH3 on Pd-side), 6.96 (d, J =
8 Hz, 1 H, pyridine-CH), 7.16 (d, J = 8 Hz, 1 H, pyridine-CH),
7.24Ϫ7.48 (m, 6 H, 1 pyridine-CH and 2 biaryl-CH on non-coordi-
nated side, and 3 Ar-CH on Pd-coordinated side), 7.65Ϫ7.73 (m,
2 H, 1 pyridine-CH from Pd-free side and 1 Ar-H from Pd-coordi-
nated side), 7.97Ϫ8.11 (br., 2 H, Ar-H on Pd-side), 8.21 (s, 1 H,
imine-CH), 8.69 ppm (br., 1 H, Pd-coordinated imine-CH); elemen-
tal analysis (%) calcd. for C28H26Cl2N4Pd (595.86): C 56.44, H
4.40, N 9.40; found: C 55.85, H 4.34, N 9.21.
[N,NЈ-(6,6Ј-Dimethylbiphenyl-2,2Ј-diyl)bis(2-pyridylmethyl)diimine-
–
–
{Pd(NCCH3)2}2]4+ (BF4 )4 {[1-{Pd(NCCH3)2}2]4+ (BF4 )4}: This
complex was prepared in the same manner as described for com-
–
plex [1-Pd]2+ (BF4 )2 above except for the use of only 0.15 g
(0.37 mmol) of ligand 1 for reaction with 0.33 g (0.74 mmol) of
[Pd(NCCH3)4]2+ (BF4 )2. Yield 0.41 g, 95%. 1H NMR (200 MHz,
–
CD3CN): δ = 1.72 (s, 6 H, biaryl-CH3), 2.05 (br., 12 H, NCCH3),
7.35Ϫ7.37 (m, 8 H, Ar-H), 7.77 (t, 2 H, Ar-H), 7.97 (d, 2 H, Ar-
H), 8.21 (t, 2 H, Ar-H), 8.58 ppm (d, 2 H, Ar-H); elemental analysis
(%) calcd. for C34H34B4F16N8Pd2, (1114.75): C 36.63, H 3.07, N
10.05; found: C 36.00, H 3.16, N 10.74%.
N,NЈ-(6,6Ј-Dimethylbiphenyl-2,2Ј-diyl)bis[(5-methyl-2-furyl)methyl]-
Crystal Structure Determinations: Single crystals of complexes 1-
PdCl2, 1-(PdCl2)2,[(1-Pd]2+ (BF4 )2 and [(3-Pd(NCCH3)2]2+ (BF4 )2
–
–
diimine-PdCl2 (3-PdCl2): Ligand
3
(0.49 g, 1.25 mmol) and
Pd(COD)Cl2 (0.36 g, 1.25 mmol) were refluxed in CH2Cl2 (20 mL)
were obtained as yellow-orange blocks upon layering a filtered re-
1086
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 1081–1089

Coordination Modes in Palladium(ii)-Diimino-Bispyridine Complexes
FULL PAPER
Table 6. Details for the crystal structure determinations
1-PdCl2·
2CH2Cl2
3-PdCl2·
CH2Cl2
1-(PdCl2)2·
2CH2Cl2
[1-Pd]2+(BF4–)2·
(H2O)0.5
[3-Pd(NCCH3)2]2+
3-PdCl2
–
(BF4
)
2
CCDC number
Formula
243264
243267
C26H25Cl2N2O2Pd
243268
243265
243266
C26H24N4Pd(BF4)2·
(H2O)0.5
680.51
173(2)K
monoclinic
P21/c
12.593(4)
14.363(5)
19.361(4)
90
243269
C30H30N4O2Pd(BF4)2·
(C2H3N)
799.65
173(2)K
triclinic
¯
P1
12.023(2)
12.9240(7)
14.341(3)
104.178(8)
C
26H22Cl2N4Pd·
C26H24Cl2N2O2Pd· C25H20Cl4N4Pd2·
(CH2Cl2)
658.70
173(2)K
monoclinic
P21/c
10.7960(7)
17.573(2)
17.484(2)
90
(CH2Cl2)2
737.63
173(2)K
monoclinic
P21/c
14.003(2)
14.360(1)
17.917(2)
90
121.844(14)
90
(CH2 Cl2)2
999.85
173(2)K
triclinic
Formula mass
Temperature
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
574.78
173(2)K
monoclinic
P21/c
8.4180(8)
15.2480(17)
18.679(3)
90
¯
P1
9.0280(12)
14.6330(17)
15.5050(19)
113.074(11)
98.359(13)
90.177(9)
99.244(8)
90
122.895(5)
90
128.47(3)
90
99.756(11)
117.483(6)
γ (°)
V (Å3); Z
dcalcd. [g/cm3]
μ [mm–1], F(000)
3060.5(6); 4
1.601
1.156; 1480
2366.5(5); 2
1.613
2785.2(5); 4
1.571
1.078; 1328
0.25 × 0.18 × 0.12 0.20 × 0.05 × 0.05
5.01 to 27.53
29085 / 6210
1860.4(4); 2
1.785
1.713; 984
2741.6(14); 4
1.649
1810.4(5); 2
1.467
0.590; 808
0.20 × 0.20 × 0.20
3.10 to 27.50
26221 / 8243
[R(int) = 0.0459]
0.9127, 0.8932
1.037; 1164
0.30 × 0.25 × 0.20
5.03 to 27.51
16675 / 5352
[R(int) = 0.1057]
0.8194, 0.7461
0.758; 1360
0.18 × 0.04 × 0.02
3.04 to 25.25
39662 / 4875
[R(int) = 0.1233]
0.9850, 0.8757
Crystal size (mm) 0.25 × 0.15 × 0.12
Theta range (°)
Reflections col-
lected/unique
Tmax, Tmin
5.03 to 27.51
24160 / 6960
[R(int) = 0.0714]
0.8737, 0.7609
2.66 to 27.57
28531 / 8435
[R(int) = 0.0572]
0.9193, 0.7258
[R(int) = 0.0456]
0.8816, 0.7744
Data/restraints/
parameters
GoF(F2)
6960 / 0 / 352
5352 / 0 / 302
6210 / 0 / 325
8435 / 80 / 462
4875 / 74 / 416
8243 / 0 / 463
0.989
0.963
0.628
1.050
1.033
1.030
Final R indices
[I Ͼ 2σ(I)]
R indices
(all data)
Largest diff. peak 0.671 eAϪ3
R1 = 0.0471,
wR2 = 0.0883
R1 = 0.0993,
wR2 = 0.1025
R1 = 0.0649,
wR2 = 0.1009
R1 = 0.1561,
wR2 = 0.1236
0.539 eAϪ3
R1 = 0.0344,
wR2 = 0.1232
R1 = 0.0537,
wR2 = 0.1545
0.997 eAϪ3
R1 = 0.0597,
wR2 = 0.1530
R1 = 0.0863,
wR2 = 0.1698
1.136 eAϪ3
R1 = 0.0726,
wR2 = 0.1781
R1 = 0.1163,
wR2 = 0.1990
1.047 eAϪ3
R1 = 0.0381,
wR2 = 0.0823
R1 = 0.0584,
wR2 = 0.0887
0.572 eAϪ3
action solution with diethyl ether at ambient temperature. Crystals
of 3-PdCl2 were obtained at 4 °C; at room temperature, 3-PdCl2
gave crystals with a different unit cell. Crystals selected for X-ray
measurements were mounted on a glass fiber using the oil-drop
method. Data were collected on a Nonius–Kappa CCD dif-
fractometer using Mo-Kα radiation (71.073 pm) and a graphite
monochromator. Structures were solved by direct methods. All
non-hydrogen atoms were refined anisotropically.[33] Hydrogen
atoms were introduced at calculated positions and refined with
fixed geometry with respect to their carrier atoms. Cell parameters
and data collection parameters are summarized in Table 6. CCDC-
243264 (for 1-PdCl2), CCDC-243267 and CCDC-243268 (for 3-
PdCl2, two crystals with different structures), CCDC-243265 (for
ture for 1 h. Conversions were 0 and 44%, respectively. After
quenching the reaction by addition of methanol (200 mL), acidified
with HCl (1 mL), the precipitate was collected by filtration, washed
with methanol and dried at 60 °C. Decomposition points were de-
termined with thermogravimetric balance under N2 flow. 1H NMR
(200 MHz, CDCl3): δ = 0.87Ϫ2.23 (br. m, 10 H) ppm. 13C NMR
(50 MHz, CDCl3): δ = 28Ϫ44 (br. m), 48Ϫ55 ppm (br. m).
Acknowledgments
M.K. thanks the foundation of Alfred Kordelin for support. The
Academy of Finland is acknowledged for financial support via
Centre of Excellence (Bio- and Nanopolymer Research Group, pro-
ject 77317).
–
1-(PdCl2)2), CCDC-243266 (for [1-Pd]2+ (BF4 )2) and CCDC-
243269 (for [3-Pd(NCCH3)2]2+ (BF4 )2) contain the supplementary
–
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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M. Kettunen, C. Vedder, H.-H. Brintzinger, I. Mutikainen, M. Leskelä, T. Repo
FULL PAPER
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The ratio of the integrals of the methyl proton signals changed
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When grown from CH2Cl2/Et2O solution at room temperature,
3-PdCl2 crystallized in another modification without a solvent
molecule in the unit cell. The coordination geometry of this
modification is practically superimposable to that of 3-PdCl2
described above, but it contains one of the uncoordinated furyl
side arms in a different orientation.
When ligand 1 was reacted with one equivalent of Pd(COD)
Cl2 at room temperature, complex 1-[PdCl2]2didprecipitate first
under partial consumption of the ligand, while mononuclear
1-PdCl2 was isolated later by recrystallization.
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[27]
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To the best of our knowledge, no structurally characterized
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been reported so far.
II
Pentacoordinate Pd centers have been reported to occur in
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II
Use of an enantiomerically pure Pd complex with a (1R,2R)-
(Ϫ)-N,NЈ-bis(quinoline-2-methylene)diiminocyclohexane back-
bone for MAO-activated norbornene polymerization has been
1088
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2005, 1081–1089

Coordination Modes in Palladium(ii)-Diimino-Bispyridine Complexes
FULL PAPER
reported to give, under similar conditions, polynorbornene
with an elevated decomposition temperature of 415 °C (see
ref.[15b]).
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University of Göttingen, Germany. G. M. Sheldrick, SADABS,
1996, University of Göttingen, Germany. G. M. Sheldrick,
SHELX97, 1997, University of Göttingen, Germany.
Received: October 28, 2004
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Eur. J. Inorg. Chem. 2005, 1081–1089
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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