Di- and trinuclear iron/titanium and iron/zirconium complexes with heterocyclic ligands as catalysts for ethylene polymerization

Article abstract of DOI:10.1016/j.poly.2016.07.033

The properties of polyolefin resins depend very much on their molecular weights, the amount of side chain branchings and molecular weight distributions. One way to obtain such tailored products in only one reaction step consists in the application of dissymmetric multi nuclear catalysts with different active sites. Since every active site is producing its own polymer, a “molecular blending” is the result. In order to reach this goal, a variety of mono, di- and trinuclear complexes of iron, titanium and zirconium, containing 2,6-bis(aryliminoethyl)pyridine and phenoxyimine building blocks have been synthesized and characterized. The reaction of iodo functionalized 2,6-bis(arylimino-ethyl)pyridine derivatives with alkyne functionalized phenoxyimine compounds via Sonogashira cross-coupling reactions results in ligand precursors that can provide coordination sites for two different metals. Trinuclear complexes with the combinations Ti/Fe and Zr/Fe, each molecule containing two iron atoms in two 2,6-bis(aryliminoethyl)pyridine units, gave the best ethylene polymerization results. Due to fast ligand exchange reactions, dinuclear iron/titanium complexes could not be isolated from reactions of mono(phenoxyimine) titanium complexes and the coupled bis(chelate) ligand precursor. Since the metal centers show their best performances at different polymerization temperatures, the compositions (and, therefore, the molecular weight distributions) of the desired polyethylenes may be adjusted by a simple change of the reaction temperature.

Full text of DOI:10.1016/j.poly.2016.07.033

Accepted Manuscript
Di- and trinuclear iron/titanium and iron/zirconium complexes with heterocyclic
ligands as catalysts for ethylene polymerization
Christian Görl, Eva Betthausen, Helmut G. Alt
PII:
S0277-5387(16)30330-8
DOI:
http://dx.doi.org/10.1016/j.poly.2016.07.033
POLY 12127
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
20 June 2016
22 July 2016
25 July 2016
Please cite this article as: C. Görl, E. Betthausen, H.G. Alt, Di- and trinuclear iron/titanium and iron/zirconium
complexes with heterocyclic ligands as catalysts for ethylene polymerization, Polyhedron (2016), doi: http://
dx.doi.org/10.1016/j.poly.2016.07.033
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REVISED MANUSCIPT
Di- and trinuclear iron/titanium and iron/zirconium complexes
with heterocyclic ligands as catalysts for ethylene polymerization
Dedicated to Professor Dr. Max Herberhold on the occasion of his 80th birthday (August 02,
2016)
Christian Görl, Eva Betthausen, Helmut G. Alt1
Laboratorium für Makromolekulare Chemie, Universität Bayreuth,
Postfach 10 12 51, Bayreuth D-95440, Germany
Keywords: 2,6-Bis(arylimino)ethyl pyridine iron complexes; Phenoxyimine complexes;
Multinuclear complexes; Ethylene polymerization; Polyethylene
The properties of polyolefin resins depend very much on their molecular weights, the amount
of side chain branchings and molecular weight distributions. One way to obtain such tailored
products in only one reaction step consists in the application of dissymmetric multi nuclear
catalysts with different active sites. Since every active site is producing its own polymer, a
“molecular blending” is the result. In order to reach this goal, a variety of mono, di- and
trinuclear
bis(aryliminoethyl)pyridine and phenoxyimine building blocks have been synthesized and
characterized. The reaction of iodo functionalized 2,6-bis(arylimino-ethyl)pyridine
complexes
of
iron,
titanium and
zirconium,
containing 2,6-
derivatives with alkyne functionalized phenoxyimine compounds via Sonogashira cross-
coupling reactions results in ligand precursors that can provide coordination sites for two
different metals. Trinuclear complexes with the combinations Ti/Fe and Zr/Fe, each molecule
containing two iron atoms in two 2,6-bis(aryliminoethyl)pyridine units, gave the best ethylene
polymerization results. Due to fast ligand exchange reactions, dinuclear iron/titanium
complexes could not be isolated from reactions of mono(phenoxyimine) titanium
complexes and the coupled bis(chelate) ligand precursor. Since the metal centers show
their best performances at different polymerization temperatures, the compositions (and,
therefore, the molecular weight distributions) of the desired polyethylenes may be
adjusted by a simple change of the reaction temperature.
_______________________
1 Corresponding author: Tel.: +49-921-43864
E-mail-address: helmut.alt@uni-bayreuth.de (H. G. Alt)
1

Introduction
Even after 60 years of its beginning, the field of catalytic olefin polymerization did not lose its
attraction. A series of reviews describes the situation [1-5] and it is fascinating to see the
catalytic potential of a variety of transition metal complexes. In the 1990s metallocene
complexes with group IV metals proved as very efficient homogeneous catalysts for
ethylene and propylene polymerization [6-15] and references therein]. Ziegler et al.
[16,17] reported already in 1955 that traces of nickel inhibited ethylene insertion into
aluminium alkyl bonds. In spite of this negative “nickel effect” Ostoja Starzewski showed in
the 1980s that nickel ylide complexes can polymerize ethylene very efficiently without any
cocatalysts [18] to give polyethylenes with high molecular weights. The breakthrough for
late transition metal complexes as catalysts for olefin polymerization came later: In 1995,
Brookhart et al. [19-21] described nickel complexes with α,α'-diimine ligands as highly
reactive ethylene polymerization catalysts. Depending on the substitution pattern at the
imino moieties, these complexes either oligomerized ethylene to give higher olefins
(terminal, internal, and branched) or produced high molecular weight polyethylenes. In
1998, Gibson [22-25] and Brookhart [26-28] independently reported the application of
2,6-bis(aryliminoethyl) pyridine iron complexes as efficient catalysts for the
polymerization and oligomerization of ethylene with a compareable potential. Structure-
property-relationship studies allowed the tailoring of polyolefin resins [22-45]. In the course
of designing and improving new types of transition metal catalysts, the research group
of Fujita presented bis(phenoxyimine) complexes of group IV and group V metals in
1998 [46-63]. Due to their simple preparation and a wide variety of possible ligand
structures, these complexes have gained a lot of attraction. The fast growth of the
polyolefin industry was possible because the properties of the produced polyolefins could be
modified by the molecular weight, the density and the branching of the resins to give high
density polyethylene (HDPE), "linear low density polyethylene" (LLDPE)) [64] and
other “new materials”. In addition, copolymerization of two or more olefinic monomers
allowed to modify the properties of polyolefins [65-70]. Catalyst compositions usually
produce unimodal polyethylenes while mixtures of two different polymerization
catalysts (for instance, a bis(aryliminoethyl)pyridine iron complex and a zirconium based
metallocene complex) may also produce bimodal molecular weight distributions [71]. In
order to avoid disadvantages of heterogeneous catalyst mixtures, like non-uniform
distribution of the different catalyst molecules on the support surface or leaching
tendencies to give reactor fouling, multinuclear complexes containing differently
2

coordinated metal centers as catalyst precursors [72-80] can solve the problem. Each
metal center of such complexes is supposed to produce its own type of polymer but
additional blending becomes unnecessary due to the immediate vicinity of the active
centers (molecular blending). Covalently bridged, combined ligand systems are required
assuring an equal distribution of the different active sites in both homogeneous and
heterogeneous polymerization reactions. Dinuclear zirconocene complexes as well as
zirconium complexes containing a metallocene moiety and an indenylsilylamido
function (based on the "constrained geometry catalysts") have been described by our
group [76-84]. Combinations of bis(aryliminoethyl)pyridine iron and zirconium based
metallocene complexes have been described by Pronko in 2004 [85]. Metallocene type
ligand frameworks have also been coupled with α,α'-diimines yielding dinuclear
nickel/zirconium complexes [86], or Fujita's phenoxyimine compounds yielding
trinuclear zirconium complexes [87-90]. Another type of early/late heterobinuclear
complexes was described by Bianchini et al. [91]. It consists of a palladium, cobalt,
or nickel pyridyl imine moiety which is linked to
a
bridged, substituted
bis(cyclopentadienyl) zirconium complex. More recent papers depict the synthesis of
dinuclear α,α'-diimine nickel/bis(aryliminoethyl)pyridine iron complexes [92] or α,α'-
diimine nickel/bis(aryliminoethyl)pyridine cobalt complexes [93].
Due to the simple synthesis of phenoxyimine compounds, we first laid our focus on
coupling reactions of phenoxyimines with metallocene type ligand precursors and
obtained trinuclear zirconium complexes [82] which gave polyethylenes with broad or
bimodal molecular weight distributions (see Figure 1).
"phenoxy-
imine part"
"metallocene
part"
Figure 1. Bimodal molecular weight distribution of a polyethylene sample obtained
with a trinuclear zirconium complex [82].
3

In this paper, we present
a
strategy to connect phenoxyimine and
bis(aryliminoethyl)pyridine compounds. The behavior of the resulting trinuclear
iron/titanium and iron/zirconium complexes in ethylene polymerization reactions is
described, and the results are compared with the data obtained for the corresponding
mononuclear complexes.
Experimental
General remarks
All experimental work was routinely carried out using Schlenk technique. Anhydrous
and purified argon was used as inert gas. The solvents n-pentane, diethyl ether,
toluene und tetrahydrofuran were purified by distillation over Na/K alloy. Diethyl ether
was additionally distilled over lithium aluminum hydride, toluene was additionally
distilled over phosphorus pentoxide. Methanol was distilled over magnesium filings,
ethanol over pieces of sodium sand. 1-Butanol (p. a.) was purchased from Merck and
used without prior distillation. Methylaluminoxane was purchased from Crompton
(Bergkamen) as a 10 wt % solution in toluene. Ethylene (3.0) and argon (4.8/5.0) were
supplied by Rießner Company (Lichtenfels). All other starting materials were
commercially available and were used without further purification.
NMR spectra were recorded at 25 °C on a Varian Inova 400 spectrometer. The
1
chemical shifts in the H NMR spectra are referred to the residual proton signal of
the solvent (δ = 7.24 ppm for CDCl3) and in 13C NMR spectra to the solvent signal (δ
= 77.0 ppm for CDCl3). EI mass spectra were routinely recorded with a VARIAN
MAT CH-7 instrument (direct inlet, E = 70 eV) and a VARIAN MAT 8500
spectrometer. MALDI-TOF MS measurements were performed on a Bruker Daltonic
Reflex TOF using graphite as the matrix. The laser intensity was set to 60-70 %.
GC/MS spectra were recorded with
a
Thermo Focus gas chromatograph in
combination with a Thermo DSQ mass detector (EI, 70 eV) using a HP-5MS GC
column (length: 30 m, film thickness: 0.25 µm, flow: 1.5 ml/min, split ratio: 1:50) and
helium as the carrier gas. The routinely used temperature program contained a starting
phase (2 min at 50 °C), a heating period (10K/min for 24 minutes) and a plateau
phase (15 min at 290 °C) resulting in a run length of 41 minutes. GC/MS spectra
4

were recorded with a HP5890 gas chromatograph in combination with a MAT 95
mass detector. GPC measurements were performed on a HT-GPC PL-220 device (RI
detector; T = 150°C). Elemental analyses were conducted with a VarioEl III CHN
instrument using acetanilide for calibration.
Synthesis of 2-acetyl-6-(arylimino)pyridine compounds ("mono-imino compounds")
At 0 °C, formic acid (50 µl) was added dropwise to a solution of 2,6-diacetylpyridine
(1.63 g; 10 mmol) and the appropriate aniline derivative (9 mmol) in methanol (15 ml).
The mixture was kept at 0 °C for 24 hours without stirring. The desired mono-imino
compounds precipitated as bright yellow crystals which were separated by filtration,
washed with cold methanol (0 °C), and finally dried in vacuo. Second crops of
crystals could be obtained after prolonged storage of the mother liquor at -20 °C.
2-Acetyl-6-[1-(2,6-diisopropylphenyl)iminoethyl]pyridine (2)
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.35 (d, 1H, Py-H), 7.93 (d, 1H, Py-H), 7.73 (t, 1H,
i
Py-H), 6.97 (d, 2H, Ar-H), 6.90 (t, 1H, Ar-H), 2.58 (s, 3H, O=C-CH3), 2.52 (sept, 2H, Pr-
CH), 2.06 (s, 3H, N=C-CH3), 0.95 (s, 6H, iPr-CH3), 0.94 (s, 6H, iPr-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 200.1 (1C, Cq, O=C-CH3), 166.4 (1C, Cq,
(ArN)=C-CH3), 155.5 (1C, Cq, Py), 152.5 (1C, Cq, Py), 146.2 (1C, Cq, Ar-C-N), 137.3 (1C,
Py-CH), 135.7 (2C, Ar-Cq), 124.5 (1C, Ar-CH), 123.7 (1C, Py-CH), 123.0 (2C, Ar-CH),
i
i
122.6 (1C, Py-CH), 28.3 (2C, Pr-CH3), 25.6 (1C, O=C-CH3), 23.2 (1C, Pr-CH3), 22.9 (1C,
iPr-CH3), 17.0 (1C, (ArN)=C-CH3).
MS [m/z] (rel. intensity in brackets): 322 M·+ (38), 307 M-Me (100). Yield: 91 %.
2-Acetyl-6-[1-(2,6-dimethylphenyl)iminoethyl]pyridine (3)
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.57 (d, 1H, Py-H), 8.12 (d, 1H, Py-H), 7.92 (t, 1H,
Py-H), 7.07 (d, 2H, Ar-H), 6.94 (t, 1H, Ar-H), 2.78 (s, 3H, O=C-CH3), 2.23 (s, 3H, N=C-
CH3), 2.03 (s, 6H, Ar-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 200.1 (1C, Cq, O=C-CH3), 166.6 (1C, Cq,
(ArN)=C-CH3), 155.5 (1C, Cq, Py), 152.4 (1C, Cq, Py), 148.5 (1C, Cq, Ar-C-N), 137.3 (1C,
Py-CH), 127.9 (2C, Ar-CH), 125.3 (2C, Ar-Cq), 124.5 (1C, Ar-CH), 123.2 (1C, Py-CH),
122.6 (1C, Py-CH), 25.6 (1C, O=C-CH3), 17.9 (2C, Ar-CH3), 16.3 (1C, (ArN)=C-CH3).
MS [m/z] (rel. intensity in brackets): 266 M·+ (21), 251 M-Me (100). Yield: 85 %.
5

2-Acetyl-6-[1-(4-bromo-2,6-dimethylphenyl)iminoethyl]pyridine (4)
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.57 (d, 1H, Py-H), 8.12 (d, 1H, Py-H), 7.92 (t, 1H,
Py-H), 7.07 (d, 2H, Ar-H), 6.94 (t, 1H, Ar-H), 2.78 (s, 3H, O=C-CH3), 2.23 (s, 3H, N=C-
CH3), 2.03 (s, 6H, Ar-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 199.9 (1C, Cq, O=C-CH3), 167.4 (1C, Cq,
(ArN)=C-CH3), 155.2 (1C, Cq, Py), 152.5 (1C, Cq, Py), 147.6 (1C, Cq, Ar-C-N), 137.4 (1C,
Py-CH), 130.5 (2C, Ar-CH), 127.5 (2C, Ar-Cq), 124.5 (1C, Py-CH), 122.7 (1C, Py-CH),
115.7 (1C, Ar-Cq, C-Br), 25.6 (1C, O=C-CH3), 17.7 (2C, Ar-CH3), 16.5 (1C, (ArN)=C-CH3).
MS [m/z] (rel. intensity in brackets): 344/346 M·+ (42), 329/331 M-Me (100). Yield: 93
%.
Synthesis of unsymmetrical bis(aryliminoethyl)pyridine compounds
The desired mono(aryliminoethyl)pyridine compound (3.14 mmol) was dissolved in
toluene (40ml) and molecular sieves (4 Å or 3 Å; 15 g) were added. The
corresponding aniline derivative (3.14 mmol) and, finally, the silica/alumina catalyst
(0.5 g) were added. The reaction mixture was heated under argon to 45-50 °C for 24
hours. If the reactions were not completed (according to GC/MS analyses), heating
was continued till completion. After cooling to room temperature, the mixture was
filtered over sodium sulfate, and the residue was washed several times with toluene.
After removal of the solvent, the residue was extracted with hot isopropanol and the
remaining solid was discarded. After removal of isopropanol in vacuo and subsequent
addition of methanol, the bis(imino)pyridine compounds precipitated on storage at -20
°C. They were isolated by filtration, washed twice with cold methanol (0 °C) and
dried in vacuo.
2-[1-(4-Iodo-2,6-dimethylphenyl)iminoethyl]-6-[1-(2,6-diisopropylphenyl)iminoethyl]
pyridine (5)
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.44 (d, 1H, Py-H), 8.40 (d, 1H, Py-H), 7.87 (d, 1H,
i
Py-H), 7.37 (s, 2H, Ar-H), 7.12 (t, 1H, Ar-H), 7.10 (d, 2H, Ar-H), 2.72 (sept, 2H, Pr-CH),
i
2.22 (s, 3H, N=C-CH3), 2.20 (s, 3H, N=C-CH3), 1.96 (s, 6H, Ar-CH3), 1.12 (s, 6H, Pr-CH3),
1.10 (s, 6H, iPr-CH3).
6

13C{1H}3 NMR (100 MHz, CDCl3): ä [ppm] = 167.8 (1C, Cq, (ArN)=C-CH3), 166.8 (1C, Cq,
(ArN)=C-CH3), 155.2 (1C, Cq, Py), 154.8 (1C, Cq, Py), 148.6 (1C, Cq, Ar-C-N), 146.4 (1C,
Cq, Ar-C-N), 136.9 (1C, Py-CH), 136.5 (2C, Ar-CH), 135.7 (2C, Ar-Cq), 128.0 (2C, Ar-Cq),
123.6 (1C, Ar-CH), 123.0 (2C, Ar-CH), 122.4 (1C, Py-CH), 122.2 (1C, Py-CH), 86.4 (1C, Cq,
C-I), 28.3 (2C, iPr-CH3), 23.2 (1C, iPr-CH3), 22.9 (1C, iPr-CH3), 17.6 (2C, Ar-CH3), 17.1 (1C,
(ArN)=C-CH3), 16.6 (1C, (ArN)=C-CH3).
MS [m/z] (rel. intensity in brackets): 551 M·+ (67), 536 M-Me (100), 508 M-iPr (8).
Yield: 78 %.
2-[1-(4-Iodo-2,6-dimethylphenyl)iminoethyl]-6-[1-(2,6-dimethylphenyl)iminoethyl]-
pyridine (6)
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.52 (dd, 1H, Py-H), 8.44 (dd, 1H, Py-H), 7.91 (t,
1H, Py-H), 7.40 (s, 2H, Ar-H), 7.08 (d, 2H, Ar-H), 6.95 (t, 1H, Ar-H), 2.24 (s, 3H, N=C-
CH3), 2.23 (s, 3H, N=C-CH3), 2.05 (s, 6H, Ar-CH3), 1.99 (s, 6H, Ar-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 167.8 (1C, Cq, (ArN)=C-CH3), 167.1 (1C, Cq,
(ArN)=C-CH3), 155.2 (1C, Cq, Py), 154.8 (1C, Cq, Py), 148.7 (1C, Cq, Ar-C-N), 148.6 (1C,
Cq, Ar-C-N), 136.9 (1C, Py-CH), 136.5 (2C, Ar-CH), 128.1 (2C, Ar-Cq), 127.9 (2C, Ar-CH),
125.4 (2C, Ar-Cq), 123.1 (1C, Ar-CH), 122.5 (1C, Py-CH), 122.3 (1C, Py-CH), 86.5 (1C, Cq,
C-I), 17.9 (2C, Ar-CH3), 17.6 (2C, Ar-CH3), 16.6 (1C, (ArN)=C-CH3), 16.4 (1C, (ArN)=C-
CH3).
MS [m/z] (rel. intensity in brackets): 495 M·+ (47), 480 M-Me (100). Yield: 56 %.
2-[1-(4-Iodo-2,6-dimethylphenyl)iminoethyl]-6-[1-(4-bromo-2,6-dimethylphenyl)imino-
ethyl]pyridine (7)
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.44 (d, 2H, Py-H), 7.89 (t, 1H, Py-H), 7.39 (s, 2H,
Ar-H), 7.20 (s, 2H, Ar-H), 2.21 (s, 3H, N=C-CH3), 2.00 (s, 6H, Ar-CH3), 1.98 (s, 6H, Ar-
CH3).
13C{1H NMR (100 MHz, CDCl3): ä [ppm] = 167.8 (1C, Cq, (ArN)=C-CH3), 167.7 (1C, Cq,
(ArN)=C-CH3), 154.8 (2C, Cq, Py), 148.5 (1C, Cq, Ar-C-N), 147.7 (1C, Cq, Ar-C-N), 136.9
(1C, Py-CH), 136.5 (2C, Ar-CH), 130.5 (2C, Ar-CH), 128.0 (2C, Ar-Cq), 127.6 (2C, Ar-Cq),
122.4 (2C, Py-CH), 115.5 (1C, Ar-Cq, C-Br), 86.5 (1C, Cq, C-I), 17.7 (2C, Ar-CH3), 17.6 (2C,
Ar-CH3), 16.6 (1C, (ArN)=C-CH3), 16.5 (1C, (ArN)=C-CH3).
MS [m/z] (rel. intensity in brackets): 573/575 M·+ (60), 558/560 M-Me (100). Yield: 58
%.
7

Synthesis of the 2,6-bis(aryliminoethyl)pyridine iron(II) complexes
The 2,6-bis(arylimino)pyridine compound (1 mmol) was dissolved in 1-butanol (20 ml;
alternatively, THF or a 1:1 mixture of THF and diethylether were used) and reacted
with anhydrous iron(II) chloride (1 mmol) resulting in a colour change to intense blue.
The mixture was stirred for three hours at room temperature, whereby the complexes
precipitated. n-Pentane (20 ml) was added for complete precipitation, and the mixture
was stirred for another 15 minutes. The iron complex was separated by filtration over
a glass frit, washed three times with 15 ml n-pentane, and dried in vacuo.
2-[1-(2,6-Diisopropylphenyl)iminoethyl]-6-[1-(4-iodo-2,6-dimethylphenyl)iminoethyl]-
pyridine iron dichloride (8)
1H NMR (400 MHz, CD2Cl2) Due to the paramagnetism of the complex all signals appear as
broad singlets): δ [ppm] = 85.60 (1H, Py-H), 81.24 (1H, Py-H), 57.26 (1H, Py-H), 17.33 (2H,
i
Ar-H), 14.40 (2H, Ar-H), 10.05 (6H, Ar-CH3), 0.08 (s, 6H, Pr-CH3), -1.26 (1H, Ar-H), -3.82
(6H, iPr-CH3), -15.93 (2H, iPr-CH), -18.14 (3H, N=C-CH3), -39.22 (3H, N=C-CH3).
MS [m/z] (rel. intensity in brackets): 677 M•+ (3), 642 M-Cl (4), 551 M-FeCl2 (32), 550
M-H-FeCl2 (100), 535 M-H-FeCl2-Me (94).
Elemental analysis [%]: calculated: C 51.4, H 5.05, N 6.20; found: C 52.0, H 5.06, N 6.05.
Yield: 75 %.
2-[1-(4-Iodo-2,6-dimethylphenyl)iminoethyl]-6-[1-(2,6-dimethylphenyl)iminoethyl]-
pyridine iron dichloride (9)
1H NMR (400 MHz, CD2Cl2) Due to the paramagnetism of the complex all signals appear as
broad singlets): δ [ppm] = 84.11 (1H, Py-H), 82.95 (1H, Py-H), 31.54 (1H, Py-H), 16.06 (2H,
Ar-H), 15.39 (2H, Ar-H), 12.73 (6H, Ar-CH3), 12.65 (Ar-CH3), -12.04 (3H, N=C-CH3), 19.80
(3H, N=C-CH3), -26.18 (1H, A-H).
MS [m/z] (rel. intensity in brackets): 621 M•+ (11), 606 M-Me (5), 586 M-Cl (8), 495 M-
FeCl2 (88), 480 M-FeCl2-Me (100).
Elemental analysis [%]: calculated: C 48.3, H 4.21, N 6.75; found: C 48.2, H 4.46, N 6.67.
Yield: 46 %.
8

2-[1-(4-Iodo-2,6-dimethylphenyl)iminoethyl]-6-[1-(4-bromo-2,6-dimethylphenyl)imino-
ethyl]pyridine iron dichloride (10)
1H NMR (400 MHz, CD2Cl2) Due to the paramagnetism of the complex all signals appear as
broad singlets): δ [ppm] = 90.61 (2H, Py-H), 35.17 (1H, Py-H), 17.16 (2H, Ar-H), 16.80 (2H,
Ar-H), 13.82 (12H, Ar-CH3), -12.81 (6H, N=C-CH3).
MS [m/z] (rel. intensity in brackets): 699/701 M•+ (4) 664/666 M-Cl (6), 572/574 M-H-
FeCl2 (41), 557/559 M-H-FeCl2-Me (60).
Elemental analysis [%]: calculated: C 42.8, H 3.59, N 5.99; found: C 43.3, H 3.46, N 5.73.
Yield: 71 %.
Synthesis of 3-tert-butyl-5-iodosalicylaldehyde (11)
3-tert-Butyl salicylaldehyde (1.5 g; 8.4 mmol) was dissolved in a mixture of methanol
(30 ml) and methylene chloride (70 ml). Benzyltrimethylammonium dichloroiodate (3.23
g; 9.2 mmol) and anhydrous calcium carbonate (1.1 g; 11 mmol) were added. After
two hours, the excess calcium carbonate was filtered off. After removal of about 80 %
of the solvent, an aqueous sodium hydrogensulfite solution (5%; 20 ml) was added
decolorizing the mixture. Extraction with diethyl ether (4 x 20 ml), drying over sodium
sulfate and removal of the solvent yielded the aldehyde as raw product. Purification
by recrystallization from n-pentane furnished 3-tert-butyl-5-iodosalicylaldehyde in a
48% yield as bright yellow crystals which are slightly light sensitive and should be
stored in the dark.
1H NMR (400 MHz, CDCl3): δ [ppm] = 11.82 s (1H, OH), 9.85 s (1H, O=C-H), 7.52 d (1H, Ar-
H), 7.38 d (1H, Ar-H), 1.42 s (9H, tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 197.1 (O=C-H), 161.2 (Cq, C-OH), 138.2, 120.6
(Cq), 134.1, 132.0 (Ar-CH), 74.7 (Cq, C-I), 34.8 (tBu-Cq), 29.2 (tBu-CH3).
MS [m/z] (rel. intensity in brackets): 304 M•+ (65), 289 M-Me (100), 261 M-C3H7 (40).
Synthesis of phenoxyimine compounds
An amount of 15 mmol of the appropriate salicylaldehyde derivative was dissolved in
toluene (150 ml). After addition of a substituted amine or aniline (1,2 equivalents) and
a few crystals of para-toluenesulfonic acid, the reaction mixture was stirred under
9

reflux for three hours applying a Dean-Stark-trap. After cooling to room temperature,
a saturated sodium hydrogencarbonate solution (150 ml) was added for neutralization.
The organic phase was separated, extracted twice with toluene (20 ml) and filtered
over sodium sulfate and silica. After removal of the solvent, crystallization of the
phenoxyimine compounds was achieved from ethanol or methanol at -20 °C.
Subsequent filtration, washing with cold ethanol or methanol (15 ml) and drying in
vacuo yielded the phenoxyimine compounds as yellow solids.
2-Cyclopentyliminomethyl-6-tert-butylphenol (12)
1H NMR (400 MHz, CDCl3): δ [ppm] = 14.20 (s br, 1H, OH), 8.36 (s, 1H, N=C-H), 7.36 (dd,
1H, Ar-H), 7.13 (dd, 1H, Ar-H), 6.85 (t, 1H, Ar-H), 3.75-3.80 (m, 1H, N-CH), 1.72-1.94 (m,
8H, CH2), 1.49 (s, 9H, tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 163.1 (N=C-H), 160.5 (Cq, C-OH), 137.3,
118.8 (Cq), 129.5, 129.1, 117.7 (Ar-CH), 70.1 (N-CH), 34.9 (tBu-Cq), 34.8, 24.5 (CH2), 29.3
(tBu-CH3).
MS [m/z] (rel. intensity in brackets): 245 M•+ (62), 230 M-Me (100), 202 M-C3H7 (97).
2-Cyclohexyliminomethyl-6-tert-butylphenol (13)
1H NMR (400 MHz, CDCl3): δ [ppm] = 14.28 (s br, 1H, OH), 8.37 (s, 1H, N=C-H), 7.32 (dd,
1H, Ar-H), 7.11 (dd, 1H, Ar-H), 6.81 (t, 1H, Ar-H), 3.18-3.23 (m, 1H, N-CH), 1.36-1.86 (m,
10H, CH2), 1.47 (s, 9H, tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 163.0 (N=C-H), 160.7 (Cq, C-OH), 137.4,
118.8 (Cq), 129.4, 129.1, 117.6 (Ar-CH), 67.5 (N-CH), 34.8 (tBu-Cq), 34.3, 25.5, 24.5 (CH2),
29.4 (tBu-CH3).
MS [m/z] (rel. intensity in brackets): 259 M•+ (66), 244 M-Me (100), 216 M-C3H7 (79).
4-Iodo-2-cyclohexyliminomethyl-6-tert-butylphenol (14)
1H NMR (400 MHz, CDCl3): δ [ppm] = 14.36 (s br, 1H, OH), 8.24 (s, 1H, N=C-H), 7.48 (d,
1H, Ar-H), 7.37 (d, 1H, Ar-H), 3.17-3.21 (m, 1H, N-CH), 1.24-1.82 (m, 10H, CH2), 1.39 (s,
9H, tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 161.6 (N=C-H), 160.7 (Cq, C-OH), 140.5,
120.8 (Cq), 137.7, 137.6 (Ar-CH), 78.9 (Cq, C-I), 67.4 (N-CH), 34.9 (tBu-Cq), 34.2, 24.4, 22.7
(CH2), 29.1 (tBu-CH3).
MS [m/z] (rel. intensity in brackets): 385 M•+ (100), 370 M-Me (64), 342 M-C3H7 (73).
10

2-Phenyliminomethyl-6-tert-butylphenol (15)
1H NMR (400 MHz, CDCl3): δ [ppm] = 13.97 (s br, 1H, OH), 8.64 (s, 1H, N=C-H), 7.42-
7.46 (m, 3H, Ar-H), 7.26-7.33 m (4H, Ar-H), 6.91 (t, 1H, Ar-H), 1.54 (s, 9H, tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 163.4 (N=C-H), 160.6 (Cq, C-OH), 148.4,
137.7, 119.1 (Cq), 130.7, 130.7, 130.4, 129.4, 126.8, 121.2, 118.4, 118.3 (Ar-CH), 35.0 (tBu-
Cq), 29.4 (tBu-CH3).
MS [m/z] (rel. intensity in brackets): 253 M•+ (57), 238 M-Me (100), 210 M-C3H7 (91).
Alternative route for the preparation of 14
The phenoxyimine compound 13 was subjected to iodination according to Kajigaeshi
[86] with little modifications. Compound 13 (6.16 g; 23.78 mmol) was dissolved in a
mixture
of
methanol
(40 ml)
and
methylene
chloride
(100 ml).
Benzyltrimethylammonium dichloroiodate (8.25 g; 23.78 mmol) and anhydrous calcium
carbonate (3.09 g; 30.92 mmol; 1.3 equivs.) were added, and the mixture was stirred at
room temperature in the dark for 24 hours. The mixture was filtered, and the residue
was washed twice with diethylether. After removal of the solvents, the residue was
dissolved in toluene and decolorized by adding a sodium hydrogensulfite (5%) solution
followed by repeated extraction with toluene. The combined organic phases were dried
over sodium sulfate and the solvent was removed in vacuo. The residue was dissolved
in n-pentane, and compound 14 was obtained as a yellow solid by slow evaporation
of the n-pentane. Yield: 96 %.
Introduction of alkynyl groups into phenoxyimine compounds
The iodinated phenoxyimine compound 14 (0.52 g; 1.34 mmol) was dissolved in
triethylamine. Bis(triphenylphosphine)palladium dichloride (12 mg, 0.0536 mmol) and
copper(I) iodide (20 mg; 0.0268 mmol) were added. 2-Methylbut-3-yn-2-ol (0.12 g; 1.34
mmol; method A) or, preferably, trimethylsilylacetylene (0.13 g; 1.34 mmol; method B)
was added slowly by syringe, and the reaction mixture was stirred for 20 hours at
room temperature. After removal of the solvent in vacuo the residue was suspended
with n-pentane and filtered to separate the precipitated triethylammonium iodide. n-
Pentane was removed in vacuo, and the residue was subjected to chromatography ( n-
pentane/toluene 1:1) yielding a white solid (16, method A), respectively, a yellow
solid (18, method B). Yields: 69 % (method A), 82 % (method B).
11

Deprotection failed for 16, instead an "ene-yne" moiety was formed (compound 17).
In contrast, 18 (0.47 g; 1.32 mmol) reacted smoothly with K2CO3 (0.27 g; 2.00 mmol) in
a mixture of methanol (80 ml) and methylene chloride (20 ml). Completion of the
reaction was checked by GC. The mixture was filtered, and the solvents were
removed in vacuo. The crude product was purified by column chromatography (n-
pentane/ethyl acetate 7:3) to give compound 19 as a brown oil in a 88 % yield.
2-Cyclohexyliminomethyl-4-(3-hydroxy-3-methylbut-1-ynyl)-6-tert-butylphenol (16)
1H NMR (400 MHz, CDCl3): δ [ppm] = 14.45 (s br, 1H, OH), 8.17 (s, 1H, N=C-H), 7.25 (d,
1H, Ar-H), 7.11 (d, 1H, Ar-H), 3.13-3.19 (m, 1H, N-CH), 1.27-1.70 (m, 10H, CH2), 1.50 (s,
6H, CH3), 1.33 (s, 9H, tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 162.2 (N=C-H), 161.6 (Cq, C-OH), 137.8,
118.3, 111.3 (Ar-Cq), 132.8, 132.4 (Ar-CH), 91.7, 82.2 (Cq, C≡C), 67.1 (N-CH), 65.4 (Cq, C-
OH), 34.8 (tBu-Cq), 34.2 (2C, CH2), 31.6 (2C, CH3), 29.1 (tBu-CH3), 25.4 (CH2), 24.3 (2C,
CH2).
MS [m/z] (rel. intensity in brackets): 341 M•+ (100), 326 M-Me (78).
2-Cyclohexyliminomethyl-4-(3-methylbut-3-en-1-ynyl)-6-tert-butylphenol (17)
MS [m/z] (rel. intensity in brackets): 323 M•+ (100), 308 M-Me (51).
2-Cyclohexyliminomethyl-4-(2-trimethylsilylethyn1-yl)-6-tert-butylphenol (18)
1H NMR (400 MHz, CDCl3): δ [ppm] = 14.41 (s br, 1H, OH), 8.03 (s, 1H, N=C-H), 7.15 (d,
1H, Ar-H), 7.00 (d, 1H, Ar-H), 3.15-3.19 (m, 1H, N-CH), 1.09-1.60 (m, 10H, CH2), 1.17 (s,
9H, tBu-CH3), 0.00 (9H, Si-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 162.3 (N=C-H), 162.1 (Cq, C-OH), 138.0,
118.3, 111.7 (Ar-Cq), 133.4, 132.9 (Ar-CH), 105.7, 91.4 (Cq, C≡C), 67.2 (N-CH), 34.9 (tBu-
Cq), 34.3 (2C, CH2), 29.2 (tBu-CH3), 25.5 (CH2), 24.4 (2C, CH2), 0.1 (Si-CH3).
29Si NMR (79.4 MHz, CDCl3): ä [ppm] = -18.3.
MS [m/z] (rel. intensity in brackets): 355 M•+ (100), 340 M-Me (58).
2-Cyclohexyliminomethyl-4-ethynyl-6-tert-butylphenol (19)
1H NMR (400 MHz, CDCl3): δ [ppm] = 14.62 (s br, 1H, OH), 8.22 (s, 1H, N=C-H), 7.35 (d,
1H, Ar-H), 7.19 (d, 1H, Ar-H), 3.15-3.19 (m, 1H, N-CH), 2.90 (s, 1H, ≡CH), 1.19-1.78 (m,
10H, CH2), 1.35 (s, 9H, tBu-CH3).
12

13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 162.2 (N=C-H), 162.1 (Cq, C-OH), 138.1,
118.4 (Ar-Cq), 133.5, 132.9 (Ar-CH), 110.6 (Cq, C≡C), 74.9 (≡CH), 67.2 (N-CH), 34.9 (tBu-
Cq), 34.2 (2C, CH2), 25.5 (CH2), 24.4 (2C, CH2), 29.2 (tBu-CH3).
MS [m/z] (rel. intensity in brackets): 283 M•+ (100), 268 M-Me (83), 240 M-C3H7 (86).
Synthesis of the alkynyl substituted bis(phenoxyimine)zirconium complex 20
The alkynyl substituted phenoxyimine compound 19 (0.16 g; 0.56 mmol) was dissolved
in THF (20 ml), and potassium hydride (23 mg; 0.56 mmol) was added. After hydrogen
evolution had ceased, ZrCl4(THF)2 (0.106 g; 0.28 mmol) was added and the resulting
yellow suspension was stirred at room temperature for 20 hours. THF was removed in
vacuo and replaced by methylene chloride (25 ml). Subsequently, the mixture was
filtered over sodium sulfate and its volume was reduced to about 5 ml. Addition of n-
pentane (25 ml) caused precipitation of the zirconium complex. After storage at -20 °C
for 20 hours, the precipitate was separated, washed with n-pentane (3x 20 ml) and
dried in vacuo. Yield: 0.09 g (45 %).
Analytical data for 20:
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.18, 8.21 (s,s 2H, N=C-H), 7.41 (d, 2H, Ar-H), 7.08
(d, 2H, Ar-H), 3.04-3.18 (m, 2H, N-CH), 3.48 (s, 1H, ≡CH), 1.99-2.31 (m, 10H, CH2), 1.37-
1.43 (m, 8H, CH2), 1.25, 1.22, 1.20 (s,s,s, 18H, tBu-CH3). The presence of different chemical
shifts for the N=CH protons and the tert-butyl groups speaks for the existence of different
isomers.
13C{1H} NMR (100 MHz, CDCl3): no signals visible.
MS [m/z] (rel. intensity in brackets): 724/726 M•+ (6), 689 M-Cl (2), 446 M-ligand (3),
278 [ligand] (49).
Elemental analysis [%]: calculated: C 62.8, H 6.66, N 3.85; found: C 63.4, H 6.94, N 3.89.
O-silylation of phenoxyimine compounds
The phenoxyimine compounds (6.37 mmol) were dissolved in diethylether, and
potassium hydride (0,26 g; 6.37 mmol) was added. The reaction mixture was stirred at
room temperature for two hours. After the evolution of hydrogen had ceased,
chlorotrimethylsilane (0.69 g; 6.40 mmol) was added by syringe and the mixture was
stirred for 20 hours at room temperature. The solvent and excess of the silane were
removed in vacuo, and the residue was extracted with n-pentane. Subsequent filtration
13

and removal of the solvent gave the O-silylated phenoxyimine compounds in nearly
quantitative yields as viscous yellow oils.
N-[(3-tert-butyl-2-trimethylsilyloxy)phenyl]methylene cyclopentylamine (21)
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.47 (s, 1H, N=C-H), 7.59 (dd, 1H, Ar-H), 7.27 (dd,
1H, Ar-H), 6.85 (t, 1H, Ar-H), 3.66-3.74 (m, 1H, N-CH), 1.59-1.81 (m, 8H, CH2), 1.32 (s,
9H, tBu-CH3), 0.23 (s, 9H, Si-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 157.3 (N=C-H), 154.0 (Cq, C-OSi), 140.6,
129.0 (Ar-Cq), 129.1, 126.5, 121.5 (Ar-CH), 71.9 (N-CH), 34.7 (tBu-Cq), 34.4 (2C, CH2), 30.4
(tBu-CH3), 24.9 (2C, CH2), 1.9 (Si-CH3).
29Si NMR (79.4 MHz, CDCl3): ä [ppm] = 19.9.
MS [m/z] (rel. intensity in brackets): 317 M•+ (4), 302 M-Me (100).
N-[(3-tert-butyl-2-trimethylsilyloxy)phenyl]methylene aniline (22)
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.50 (s, 1H, N=C-H), 7.65 (dd, 1H, Ar-H), 7.22 (dd,
1H, Ar-H), 7.14-7.18 (m, 2H, Ar-H), 6.96-7.02 m (3H, Ar-H), 6.78 (t, 1H, Ar-H), 1.19 (s, 9H,
tBu-CH3), 0.00 (s, 9H, Si-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 159.0 (N=C-H), 155.5 (Cq, C-OSi), 148.4 (Cq,
C-N), 141.1, 128.7 (Cq), 130.6, 129.1 (2C), 126.2, 125.8, 121.7, 121.0 (2C) (Ar-CH), 34.8
(tBu-Cq), 30.5 (tBu-CH3), 1.8 (Si-CH3).
29Si NMR (79.4 MHz, CDCl3): ä [ppm] = 20.7.
MS [m/z] (rel. intensity in brackets): 326 M•+ (100).
Synthesis of THF adducts of transition metal salts
Titanium tetrachloride (5 g; 2.9 ml; 26.3 mmol) was added to methylene chloride (50 ml)
in a 250 ml Schlenk tube. THF (8.2 ml; 100 mmol) was added dropwise and slowly to
avoid a strong exothermic reaction. The mixture was stirred at room temperature for
15 minutes, and n-pentane (50 ml) was added. After cooling to -25 °C for one hour,
the resulting yellow precipitate was filtered, washed with n-pentane (2x 20 ml), and
dried in vacuo. The combined liquid fractions were stored at -25 °C for another hour
yielding a second crop of yellow crystals. The combined yield of TiCl4(THF)2 (23) was
98 %. The synthesis of ZrCl4(THF)2 (24) was conducted analogously, except that a
stoichiometric amount of THF was used (Zr:THF = 1:2). ZrCl4(THF)2 (24) was isolated
as a white powder in a 61 % yield.
14

TiCl4(THF)2 (23):
1H NMR (400 MHz, CDCl3): δ [ppm] = 4.33 (t, 4H, O-CH2), 1.91 (t, 4H, CH2).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 84.0 (O-CH2), 25.6 (CH2).
Elemental analysis [%]: calculated: C 28.8, H 4.83; found: C 28.7, H 4.68.
ZrCl4(THF)2 (24):
1H NMR (400 MHz, CDCl3): δ [ppm] = 4.55 (br, 4H, O-CH2), 2.10 (t, 4H, CH2).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 69.9 (br, O-CH2), 25.6 (CH2).
Elemental analysis [%]: calculated: C 25.4, H 4.27; found: C 25.2, H 4.23.
Preparation of mono(phenoxyimine) titanium complexes
The desired O-silylated phenoxyimine compound (3.08 mmol) was dissolved in
methylene chloride and cooled to -78 °C using an isopropanol/dry ice bath. With
vigorous stirring, a cooled (0 °C) solution of TiCl4(THF)2 (23; 1.03 g; 3.08 mmol) in
methylene chloride (20 ml) was added via syringe through a rubber septum. The
solution was allowed to come to room temperature and was stirred for 16 hours. The
volatile components (Me3SiCl and methylene chloride) were removed in vacuo. The
residue was dissolved in methylene chloride (10 ml) again, and n-pentane (50 ml) was
added causing the precipitation of the titanium complex. The red complex was filtered,
washed with n-pentane (2x 20 ml), and dried in vacuo.
Trichloro-[(2-cyclopentyliminomethyl-6-tert-butyl)phenolato](tetrahydrofurane)
titanium (25)
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.25 (s, 1H, N=C-H), 7.38 (dd, 1H, Ar-H), 7.19 (dd,
1H, Ar-H), 6.91 (t, 1H, Ar-H), 5.00 (s, br, 1H, N-CH), 3.95 (s, br, 4H, O-CH2), 1.77 (s, br,
4H, CH2), 1.09-1.46 (m, 8H, CH2), 1.35 (s, 9H, tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 164.0 (N=C-H), 162.4 (Cq, C-OH), 138.8,
123.4 (Cq), 134.8, 128.8, 121.9 (Ar-CH), 53.3 (N-CH), 35.0 (tBu-Cq), 31.1, 23.8 (CH2), 29.4
(tBu-CH3).
Elemental analysis [%]: calculated: C 51.0, H 6.42, N 2.98; found: C 51.4, H 6.59, N 2.89.
MS [m/z] (rel. intensity in brackets): 469 M•+ (not detected; decomposition observed
during sample preparation).
15

Yield: 79 %.
Trichloro-[(2-phenyliminomethyl-6-tert-butyl)phenolato](tetrahydrofurane)
(26)
titanium
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.14 (s, 1H, N=C-H), 7.63 (dd, 1H, Ar-H), 7.29-7.40
(m, 6H, Ar-H), 7.13 (t, 1H, Ar-H), 3.99 (s, br, 4H, O-CH2), 1.75 (s, br, 4H, CH2), 1.58 (s, 9H,
tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 166.1 (N=C-H), 164.6 (Cq, C-O), 152.4 (Cq, br,
C-N), 138.8, 128.1 (Cq), 134.0, 133.4, 128.7 (2C), 127.4, 124.7, 124.0 (2C) (Ar-CH), 91.5
(2C, br, O-CH2), 35.3 (tBu-Cq), 29.7 (tBu-CH3), 25.4 (2C, CH2).
MS [m/z] (rel. intensity in brackets): 479 M•+ (not detected; decomposition observed
during sample preparation).
Elemental analysis [%]: calculated: C 52.7, H 5.47, N 2.93; found: C 53.2, H 5.42, N 2.89.
Yield: 82 %.
Sonogashira coupling of phenoxyimine and bis(aryliminoethyl)pyridine compounds
The unsymmetrical bis(imino) compound 6 (0.57 g; 1.15 mmol) was dissolved in
triethylamine (30 ml). Bis(triphenylphosphine)palladium dichloride (5 mg, 0.0230 mmol)
and copper(I) iodide (9 mg; 0.0115 mmol) were added with vigorous stirring. A solution
of 2-(cyclohexyliminomethyl)-6-tert-butyl-4-ethynylphenol (19; 0.39 g; 1.15 mmol) in
triethylamine (5ml) was added slowly by syringe, and the reaction mixture was stirred
for 24 hours at room temperature. After removal of the solvent in vacuo the residue
was suspended in n-pentane and filtered to separate the precipitated triethylammonium
iodide. n-Pentane was removed in vacuo, methanol was added, and the desired product
27 was crystallized at -20 °C. The yellow precipitate was washed with cold methanol
(-20 °C) and dried in vacuo. From the mother liquor, a secrond crop of micro-
crystalline product was obtained. Yield: 71 %.
2-Cyclohexyliminomethyl-4-{2-{1-[4-(ethynyl-1-yl)-κC-2,6-dimethylphenyl]iminoethyl}-
6-[1-(2,6-dimethylphenyl)iminoethyl]-pyridine}-6-tert-butylphenol (27)
1H NMR (400 MHz, CDCl3): δ [ppm] = 14.59 (s, br, OH), 8.46 (dd, 1H, Py-H), 8.45 (dd, 1H,
Py-H), 8.29 (s, 1H, N=C-H), 7.89 (dd, 1H, Py-H), 7.44 (d, 1H, Ar-H), 7.39 (d, 1H, Ar-H),
7.26 (d, 2H, Ar-H), 7.05 (d, 2H, Ar-H), 6.91 (t, 1H, Ar-H), 3.18-3.28 (m, 1H, N-CH), 2.23 (s,
16

3H, Ar-CH3), 2.21 (s, 3H, N=C-CH3), 2.20 (s, 3H, Ar-CH3), 2.13 (s, 3H, N=C-CH3), 2.02 (s,
6H, Ar-CH3), 1.22-1.82 (m, 10H, CH2), 1.42 (s, 9H, tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): ä [ppm] = 167.5 (1C, Cq, (ArN)=C-CH3), 167.1 (1C, Cq,
(ArN)=C-CH3), 162.4 (N=C-H), 161.5 (Cq, C-OH), 155.2 (1C, Cq, Py), 154.8 (1C, Cq, Py),
148.8 (1C, Cq, Ar-C-N), 148.7 (1C, Cq, Ar-C-N), 138.0 (Ar-Cq), 136.9 (1C, Py-CH), 132.7,
132.5 (each 1C, phenoxy ring), 131.1 (2C, Ar-CH), 127.9 (2C, Ar-CH), 125.7 (2C, Ar-Cq),
125.4 (2C, Ar-Cq), 123.0 (1C, Py-CH), 122.4 (1C, Ar-CH), 122.3 (1C, Py-CH), 118.5, 117.9,
112.3 (Ar-Cq), 88.2, 87.6 (Cq, C≡C), 67.3 (N-CH), 34.9 (tBu-Cq), 34.4 (2C, CH2), 29.3 (tBu-
CH3), 25.5 (CH2), 24.4 (2C, CH2), 17.9 (2C, Ar-CH3), 17.8 (2C, Ar-CH3), 17.6 (2C, Ar-CH3),
16.7 (1C, (ArN)=C-CH3), 16.4 (1C, (ArN)=C-CH3).
MS [m/z] (rel. intensity in brackets): 650 M•+ (100), 635 M-Me (19)
Yield: 71 %.
Attempted synthesis of a dissymmetric bis(phenoxyimine) titanium complex: isolation
of the symmetric complex 28
The coupled bis(aryliminoethyl)pyridine/phenoxyimine compound 27 (0.53 g; 0.82 mmol)
was dissolved in THF (20 ml), and potassium hydride (33 mg; 0.82 mmol) was added.
When hydrogen evolution had ceased, trimethylchlorosilane (0.10 ml; 0.82 mmol) was
added with a syringe, and the reaction mixture was stirred for 20 hours at room
temperature. After removal of the volatiles, the residue was dissolved in methylene
chloride (25 ml) and filtered over sodium sulfate. The resulting clear solution was
cooled to -78 °C and added dropwise to
a
cold solution (-78°C) of the
mono(phenoxyimine) titanium complex 26 (0.39 g; 0.82 mmol) in methylene chloride
(20 ml). The resulting yellow solution was allowed to come to room temperature and
was stirred for 16 hours. The volatiles were again removed in vacuo and the residue
was treated with n-pentane providing a yellow powder which was washed twice with
n-pentane (20 ml) and dried in vacuo. NMR analyses gave proof that a symmetrical
bis(phenoxyimine) complex (28) had been obtained (yield: 8 %). Further NMR
analyses of the pentane washing fractions revealed that ligand displacement reactions
had lead to a mixture of symmetrical and unsymmetrical bis(phenoxyimine) titanium
complexes as indicated by the appearance of three different tert-butyl signals in the 1H NMR
spectrum.
17

Analytical data for 28:
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.33 (dd, 2H, Py-H), 8.30 (dd, 2H, Py-H), 8.16 (s,
2H, N=C-H), 7.76 (dd, 2H, Py-H), 7.30 (d, 2H, Ar-H), 7.25 (d, 2H; Ar-H), 7.12 (d, 2H, Ar-
H), 7.10 (d, 2H, Ar-H), 6.92 (d, 4H, Ar-H), 6.78 (t, 2H, Ar-H), 3.00-3.14 (m, 2H, N-CH), 2.09
(s, 6H, N=C-CH3), 2.07 (s, 6H, N=C-CH3), 1.89 (s, 2x12H, Ar-CH3), 0.98-1.73 (m, 20H,
CH2), 1.09, 1.25, 1.28 (3x s, 18H, tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): no signals visible.
MALDI-TOF MS [m/z] (rel. intensity in brackets): 1416 M•+ (2), 1381 M-Cl (5), 767 M-
ligand (31).
Elemental analysis [%]: calculated: C 74.5, H 6.96, N 7.90; found: C 75.3, H 7.28, N 7.78.
Synthesis of the symmetrical bis(phenoxyimine) zirconium complex 29
The coupled bis(aryliminoethyl)pyridine/phenoxyimine compound 26 (0.23 g; 0.35 mmol)
was dissolved in THF (20 ml), and potassium hydride (15 mg; 0.35 mmol) was added.
After hydrogen evolution had ceased, ZrCl4(THF)2 (24; 67 mg; 0.18 mmol) was added
and the resulting yellow suspension was stirred at room temperature for 20 hours.
THF was removed in vacuo and replaced by methylene chloride (25 ml). Subsequently,
the mixture was filtered over sodium sulfate and its volume was reduced to about 5
ml. Addition of n-pentane (25 ml) caused precipitation of the zirconium complex.
After storage at -20 °C for 20 hours, the precipitate was separated, washed with n-
pentane (3x 20 ml) and dried in vacuo. The appearance of three different tert-butyl signals
in the 1H NMR spectrum speaks for the existence of different isomers.
Analytical data for 29:
1H NMR (400 MHz, CDCl3): δ [ppm] = 8.35 (dd, 2H, Py-H), 8.27 (dd, 2H, Py-H), 8.19 (s,
2H, N=C-H), 7.89-7.91 (m, 2H, Py-H), 7.66 (d, 2H, Ar-H), 7.41 (d, 2H; Ar-H), 7.00-7.09 (m,
8H, Ar-H), 6.80-6.82 (m, 2H, Ar-H), 3.05-3.17 (m, 2H, N-CH), 2.15, 2.10, 2.07, 1.99 (4x s,
12H, N=C-CH3), 1.38, 1.43 (s, 2x12H, Ar-CH3), 1.34-1.70 (m, 20H, CH2), 1.25, 1.23, 1.20
(3x s, 18H, tBu-CH3).
13C{1H} NMR (100 MHz, CDCl3): no signals visible.
MALDI-TOF MS [m/z] (rel. intensity in brackets): 1460/1462 M•+ (2), 1445 M-Me (2),
1425/1427 M-Cl (9), 1304 M-2HCl-C6H12 (15), 1215 M-[C6H11-NC(H)-(tBu-phenoxy)] (30),
923 M-[bis(imino)pyridine-C≡C-(tBu-phenoxy)] (11), 650 [ligand+H] (100).
18

Elemental analysis [%]: calculated: C 72.3, H 6.76, N 7.66; found: C 71.8, H 6.94, N 7.53.
Synthesis of the trinuclear bis(aryliminoethyl)pyridine iron/bis(phenoxyimine) Ti/Zr
complexes 30 and 31
The bis(phenoxyimine) complex (28 or 29; 0.12 mmol) was dissolved in diethylether/
THF (20ml; v/v 4:1) and anhydrous ferric chloride (30 mg; 0.24 mmol) was added
causing an immediate color change from yellow to blue/green. The mixture was stirred
for two hours at room temperature, and n-pentane (15 ml) was added for complete
precipitation. The resulting suspension was filtered, and the residue was washed twice
with n-pentane (20 ml) and dried in vacuo.
Analytical data for 30:
1H NMR (400 MHz, CD2Cl2). Because of the paramagnetic Fe(II) component, all signals
appear as broad singlets unless otherwise stated): δ [ppm] = 84.29 (2H, Py-H), 82.63 (2H, Py-
H), 34.22 (2H, Py-H), 17.51 (4H, Ar-H), 15.45 (2H, Ar-H), 14.80 (2H, Ar-H), 12.01 (12H,
Ar-CH3), 8.56 (2H, N=C-H), 7.45 (12H, Ar-CH3), 6.91 (2H, Ar-H), 6.48 (2H, Ar-H), 3.67
t
(2H, N-CH), 1.26-2.11 (m, 38H, CH2 + Bu-CH3), -11.78 (2H, Ar-CH), -16.90 (6H, N=C-
CH3), -25.35 (6H, N=C-CH3).
13C{1H} NMR (100 MHz, CDCl3): no signals visible.
MALDI-TOF MS [m/z] (rel. intensity in brackets): 1672/1674 M•+ (6), 1639 M-Cl (3),
1348 M-2Cl-2x(FeCl2) (2), 923 M-3Cl-ligand (27), 650 ligand (100).
Elemental analysis [%]: calculated: C 63.2, H 5.91, N 6.70; found: C 62.7, H 5.82, N 6.56.
Analytical data for 31:
1H NMR (400 MHz, CD2Cl2). Because of the paramagnetic Fe(II) component, all signals
appear as broad singlets unless otherwise stated): δ [ppm] = 98.16 (2H, Py-H), 96.76 (2H, Py-
H), 47.98 (2H, Py-H), 19.83 (4H, Ar-H), 18.78 (12H, Ar-CH3), 17.75 (4H, Ar-H), 17.43
(12H, Ar-CH3), 13.60 (2H, Ar-H), 8.02 (2H, N=C-H), 7.48 (2H, Ar-H), 6.81 (2H, Ar-H), 3.43
(2H, N-CH), -1.10-3.30 (m, 38H, CH2 + tBu-CH3), -12.50 (2H, Ar-CH), -13.29 (6H, N=C-
CH3), -14.61 (6H, N=C-CH3).
13C{1H} NMR (100 MHz, CDCl3): no signals visible.
MALDI-TOF MS [m/z] (rel. intensity in brackets): 1712 M•+ (3), 1675 M-Cl (3), 1640 M-
2Cl (3), 1586 M-FeCl2 (4), 1572 M-4Cl (4), 1460 M-2x(FeCl2) (7), 1304 M-(2x FeCl2)-2HCl-
C6H12 (15), 1215 M-(2x FeCl2)-[C6H11-NC(H)-(tBu-phenoxy)] (30), 923 M-
19

[bis(imino)pyridine-C≡C-(tBu-phenoxy)] (11),847 M-(2x FeCl2)-ligand (18), 650 ligand
(100).
Elemental analysis [%]: calculated: C 61.6, H 5.76, N 6.53; found: C 60.8, H 5.53, N 6.28.
Polymerization of ethylene
The corresponding iron complex (n = 3·10-6 mol) was suspended in toluene (5 ml).
Methylaluminoxane (10% in toluene) was added to maintain a ratio Fe : Al = 1 : 2500
resulting in an immediate colour change to orange/brown. The mixture was added to a
1 l Schlenk flask filled with 250 ml n-pentane. This mixture was transferred to a 1 l
Büchi laboratory autoclave under inert atmosphere and the temperature of the
autoclave was set to 60 °C. A permanent ethylene pressure of 10 bar was applied for
one hour. After cooling down to 15 °C, the ethylene pressure was carefully released.
To the polymer suspensions was added isopropanol and diluted hydrochloric acid
resulting in biphasic systems. The polymer was filtered off using a glass frit, washed
with water and acetone, and finally dried in vacuo.
Results and Discussion
Our strategy for the synthesis of dinuclear or trinuclear transition metal complexes
based on covalently bridged bis(aryliminoethyl)pyridine/phenoxyimine ligand precursors
included Sonogashira coupling reactions of para-iodo substituted 2,6-bis(arylimino-
ethyl)pyridine compounds with alkynyl substituted phenoxyimine derivatives. The
opposite route starting with iodo containing phenoxyimine compounds and alkynyl
substituted bis(aryliminoethyl)pyridines appeared less attractive since the latter are
based on alkynyl anilines which were found to be prone to self condensation reactions
[39] and therefore require much more synthetic efforts.
1. Synthesis of 4-iodo-2,6-dimethylaniline
According to Kajigaeshi et al., the introduction of iodo substituents into the ortho and
para-positions of aniline [89] or phenol [90] derivatives proceeds at room temperature
when using benzyltrimethylammonium dichloroiodate as the iodinating reagent. Starting
20

from 2,6-dimethylaniline, 4-iodo-2,6-dimethylaniline (1) [89] was prepared (see Scheme
1) in a 78 % yield.
NH
NH
-
2
BzNMe3+ ICl2
2
CH2Cl2, MeOH
- HCl +
- BzNMe3 Cl-
I
1
Scheme 1. Synthesis of 4-iodo-2,6-dimethylaniline (1) [89]
2. Preparation of 2-acetyl-6-(aryliminoethyl)pyridine compounds ("mono-imino
compounds")
Dissymmetric bis(aryliminoethyl)pyridine compounds can be prepared from two subsequent
condensation reactions. In the first step, 2,6-diacetylpyridine was reacted with
substoichiometric amounts of either 2,6-diisopropylaniline, 2,6-dimethylaniline, or 4-
bromo-2,6-dimethylaniline yielding the 2-acetyl-6-(aryliminoethyl)pyridine compounds 2-
4 ("mono-imino compounds", see Scheme 2) [91,92].
R2
R3
N
O
O
NH2
HCOOH
MeOH
R3
R1
N
O
R1
N
0 °C, 24 h
- H2O
R2
R1 = R3 = iPr, R2 = H: 2 [91]
R1 = R3 = Me, R2 = H: 3 [91]
R1 = R3 = Me, R2 = Br: 4 [35]
Scheme 2. Synthesis of 2-acetyl-6-(aryliminoethyl)pyridine compounds.
Small amounts of the corresponding symmetric bis(imino) compounds were detected by
GC/MS analyses. Purification of the 2-acetyl-6-(aryliminoethyl)pyridine derivatives was
accomplished by extraction of the crude products with methanol or isopropanol which
dissolves the bis(imino) compounds [91].
3. Synthesis of unsymmetrically substituted 2,6-bis(aryliminoethyl)pyridine ligands and
their iron(II) complexes
21

Bis(aryliminoethyl)pyridine compounds with differently substituted imino arms were
prepared through condensation reactions of 2-acetyl-6-(aryliminoethyl)pyridines (2-4)
with 4-iodo-2,6-dimethylaniline (1) according to Qian [29,30] et al. using a Lewis acidic
SiO2/Al2O3 catalyst and molecular sieves (4 Å) for water absorption (see Scheme 3).
The addition of anhydrous iron(II) chloride to solutions of the unsymmetrical
bis(aryliminoethyl)pyridine compounds 5-7 gave the corresponding C1-symmetrical
tridentate iron complexes 8-10 (Scheme 3) [92-111]. These unsymmetrical mononuclear
complexes serve as objects for comparison in the discussion of ethylene
polymerization results of multinuclear complexes.
R2
R1
R2
R2
R3
N
R1
R1
N
Si/Al catalyst,
molecular sieves,
toluene
R3
R3
N
N
N
N
FeCl2
Cl
Cl
O
+
N
Fe
N
n-BuOH
or THF/Et2O,
r.t., 3h
45°C, 24 h
- H2O
NH2
I
I
I
unsymmetrical
bis(aryliminoethyl)
pyridine compound
Fe(II)
complex
R1
R2
R3
iPr
Me
Me
H
H
iPr
Me
Me
5
6
7
8
9
Br
10
Scheme 3. Synthesis of dissymmetric 2,6-bis(aryliminoethyl)pyridine compounds and
their iron(II) chloride complexes.
The iron complexes 8-10 were characterized by 1H NMR spectroscopy (solvent:
CD2Cl2), mass spectrometry and elemental analyses. Due to their paramagnetism, all
22

signals in the 1H NMR spectra appear as broad singlets [23,40] in an extended
measuring range between δ = -50 ppm and +100 ppm. Small changes in the ligand
frameworks extremely affect the chemical shifts, therefore, assignment of the signals
requires a comparison with already known symmetrical iron complexes[23,39,40].
4. Synthesis of phenoxyimine compounds
Alkynyl substituted phenoxyimine compounds suitable for Sonogashira coupling
reactions were prepared in a multistep synthetic approach starting from 3-tert-butyl
salicylaldehyde or 3-tert-butyl-5-iodosalicylaldehyde. 3-tert-Butylsalicylaldehyde was
obtained by deprotonation of 2-tert-butylphenol with methylmagnesium bromide and
subsequent reaction with paraformaldehyde [49,82,111]. Similarly to phenol derivatives,
3-tert-butyl-salicylaldehyde underwent iodination in para-position to the phenolic OH
group[112] when applying the conditions of Kajigaeshi et al. [89], however, a
prolonged reaction time was required due to the decreased electron density in the
aromatic ring [113].
O
OH
O
OH
OH
1. EtMgBr, THF, 0 °C, 1h
2. (CH2O)n, toluene, NEt3,
88 °C, 2h
-
BzNMe3+ ICl2
CH2Cl2, MeOH
H
H
3. HCl, H2O
20 h
- BzNMe3+ Cl-
- HCl
I
11
Scheme 4. Synthesis of substituted salicylaldehydes. [113]
Subsequent condensation reactions of the substituted salicylaldehydes with amine or
aniline derivatives yielded the phenoxyimine compounds 12-15 (see Scheme 5).
R3
O
OH
N
OH
R1
R1
toluene
H
H
+
R3 - NH2
p-TosOH
- H2O
R2
R2
phenoxyimine
compound
R1
R2
R3
tBu
tBu
H
H
cyclopentyl
cyclohexyl
12
13
23

phenoxyimine
compound
R1
R2
R3
tBu
tBu
I
cyclohexyl
phenyl
14
15
H
Scheme 5. Synthesis of phenoxyimine compounds. [46,49,82]
Phenoxyimine compound 14 could be obtained alternatively from iodination of 13 with
benzyltrimethylammonium dichloroiodate [89]. With regard to the synthesis of ligand
precursors for multinuclear bis(aryliminoethyl)pyridine/phenoxyimine transition metal
complexes, the iodo substituted phenoxyimine compound 14 was subjected to
palladium catalyzed Sonogashira coupling reactions introducing either a 3-hydroxy-3-
methylbut-1-ynyl group (Scheme 6) or a trimethylsilylethynyl group (Schemes 7). An
attempt to deprotect the methyl-hydroxybutynyl group of precursor 16 using KOH in
toluene failed. Instead of the desired terminal ethynyl group, the main reaction product
17 contained an "ene-yne" moiety resulting from the loss of a water molecule
(Scheme 6).
N
OH
N
OH
N
OH
(Ph3P)2PdCl2
CuI, NEt3
H
H
H
KOH
rt, 20 h
- HNEt3I
toluene,
110 °C, 3h
I
14
+
HO
17
16
HO
Scheme 6. Synthesis and unsuccessful deprotection of the alkynyl group of
phenoxyimine compound 16 providing the "ene-yne" derivative 17.
The palladium catalyzed alkynylation of 14 with trimethylsilylacetylene proceeded
smoothly, and the trimethylsilyl capped phenoxyimine compound 18 was obtained. In
contrast to the hydroxyalkyl group of 16, the trimethylsilyl substituent could be
removed cleanly using K2CO3 in methanol/methylene chloride (4:1) providing the
ethynyl substituted phenoxyimine compound 19 [82].
24

OH
N
OH
N
OH
N
(Ph3P)2PdCl2
CuI, NEt3
K2CO3
H
H
H
rt, 20 h
- HNEt3I
MeOH,
CH2Cl2
I
SiMe3
14
18
SiMe3
19
+
Scheme 7. Successful synthesis of phenoxyimine compound 19 containing a terminal
alkynyl group.
Compound 19 was found sensitive towards air and light resulting in considerable
darkening even when stored under argon at -20 °C. The bis(phenoxyimine)zirconium
complex 20 could be prepared from 19 in good yield using potassium hydride and
ZrCl4(THF)2 (Scheme 8). Complex 20 represents another example for catalytically
active bis(phenoxyimine)zirconium complexes containing terminal alkynyl groups[111].
tBu
N
OH
1. 2 eq. KH, THF
r.t., 1h
- H2
O
Zr
O
H
tBu
N
N
H
H
2. ZrCl4, THF
r.t., 20h
- 2 KCl
Cl
Cl
2 equiv.
tBu
19
20
Scheme 8. Preparation of the alkynyl functionalized bis(phenoxyimine)zirconium
complex 20.
5. Synthesis of mono(phenoxyimine)titanium complexes
Bis(phenoxyimine)titanium or -zirconium complexes containing different phenoxyimine
ligands have been rarely described in the literature[114]. Some mono(phenoxyimine)
25

titanium
and
zirconium
complexes
were
reported[115-117],
however,
mono(phenoxyimine) zirconium complexes are only stable when they contain a
voluminous imino moiety [116].
For the synthesis of mono(phenoxyimine)titanium complexes, the required O-silylated
ligand precursors could be prepared in high yields (Scheme 9) [114,115]. These
trimethylsilyl protected phenoxyimine compounds were then reacted with TiCl4(THF)2
(23) providing the octahedrally coordinated mono(phenoxyimine) titanium complexes
which still contain one tetrahydrofurane molecule. TiCl4(THF)2 (23) as well as
ZrCl4(THF)2 (24) were obtained from controlled addition of tetrahydrofurane to
suspensions of the anhydrous transition metal salts in methylene chloride[118].
H
Cl
Ti
R
H
R
H
SiMe3
tBu
R
N
OH
TiCl4(THF)2
CH2Cl2
N
O
1. KH, Et2O,
6 h, rt, - H2
N
tBu
O
O
tBu
2. Me3SiCl,
24 h, rt,
- KCl
- Me3SiCl
- THF
Cl
Cl
R = cyclopentyl: 21
R = phenyl: 22
R = cyclopentyl: 25
R = phenyl: 26
Scheme 9. Synthesis of mono(phenoxyimine) titanium complexes. [115]
The silylated phenoxyimine compounds 21 and 22 were also reacted with ZrCl4(THF)2
(24), however, ligand transfer reactions at temperatures higher than -50 °C occurred
providing the bis(phenoxyimine) zirconium complexes exclusively (Scheme 10). At that
temperature, a color change of the reaction mixture (from orange to yellow/green) was
observed indicating the thermal instability of mono(phenoxyimine)zirconium complexes.
The N-cyclopentyl-salicylaldiminato ligand of 25 seems to be quite labile as indicated
1
1
by the H NMR data. Compared with the H NMR data for 26, most of the signals
showed broader half widths corresponding to an increased fluctuation due to ligand
exchange reactions. DFT studies of Flisak [119] on the relative stabilities of the
possible isomers in a number of bis(phenoxyimine) complexes revealed a dependence
on the nature of the substituent at the imino nitrogen atom. Confirming our
experimental results, complexes containing unsubstituted N-cycloalkyl groups showed
lower energy barriers between the isomeric coordination modes compared with
complexes having N-aromatic substituted phenoxyimine ligands.
26

H
Cl
Zr
R
N
O
O
tBu
Cl
R
H
SiMe3
tBu
Cl
N
O
ZrCl4(THF)2
CH2Cl2
T > - 50 °C
- ZrCl4(THF)2
x2
- Me3SiCl
- THF
tBu
O
R
H
N
N
H
R
Zr
O
Cl
Cl
R = cyclopentyl,
phenyl
tBu
Scheme 10. Instability of mono(phenoxyimine) zirconium complexes: rearrangement of
ligands leading to bis(phenoxyimine) zirconium complexes.
6. Sonogashira coupling of phenoxyimine and bis(aryliminoethyl)pyridine compounds
As demonstrated by Ionkin et al. [35], bromo substituents at the iminophenyl rings of
bis(arylimino)pyridine compounds can be easily exchanged with aryl groups applying
Suzuki
coupling
reactions.
For
Sonogashira
coupling
reactions
with
bis(aryliminoethyl)pyridine compounds, para-iodo substitution at the iminophenyl
moieties is preferred against ortho and meta substitution due to less steric bulk around
the iron center [39]. Bromo substituents in bis(aryliminoethyl)pyridine compounds could
not be replaced under analogous Sonogashira reaction conditions since the imino
functions are not electrophilic enough to activate the carbon-bromo bonds at the
iminophenyl rings.
Since complex 9 exhibited the highest polymerization activity among the dissymmetric
bis(aryliminoethyl)pyridine iron complexes 8-10 (see chapter 8), its ligand (6) was
chosen for the Sonogashira cross-coupling reaction with the alkynyl functionalized
phenoxyimine compound 19 providing the ligand precursor 27 in a 71 % yield
(Scheme 11).
27

H
N
N
N
N
I
OH
+
19
6
(Ph3P)2PdCl2
CuI, NEt3
rt, 20 h
- HNEt3I
H
N
N
N
N
OH
27
Scheme 11. Synthesis of the ligand precursor 27 via Sonogashira cross-coupling.
The air stable bis(chelate) ligand precursor 27 was characterized by mass spectrometry,
1H NMR, and 13C NMR spectroscopy.
7. Preparation of dinuclear and trinuclear bis(aryliminoethyl)pyridine iron /
phenoxyimine titanium/zirconium complexes
At -78 °C, the mono(phenoxyimine) titanium complexes 25 and 26 were reacted with
the bis(chelate) ligand precursor 27 using methylene chloride as the solvent. In both
cases, ligand transfer reactions occurred rapidly as could be seen from color changes
of the reaction mixtures from orange/red (mono(phenoxyimine) titanium complexes) to
dark red (bis(phenoxyimine) titanium complexes). However, instead of the desired pure
titanium complexes bearing two different phenoxyimine ligands, mixtures of complexes
were obtained which contained the symmetric bis(phenoxyimine) titanium complexes
along with small amounts of the unsymmetric complex. For the reaction of 25 and
27, separation of the products was not possible. From the reaction of the N-phenyl-
salicylaldiminato derivative 26 and ligand precursor 27, a small amount of the
symmetrical bis(phenoxyimine) titanium complex 28 (ligand derived from 27) could be
isolated (Scheme 12).
28

H
Cl
Ti
Cl
H
R
N
N
N
O
O
tBu
N
N
OH
+
Cl
27
R = cyclopentyl: 25
R = phenyl: 26
1. KH, THF
2. Me3SiCl
2. CH2Cl2
- 78 °C
- H2
- KCl
- Me3SiCl
H
O
N
R
TiCl2
Cl
Ti
Cl
N
N
O
H
O
H
R
N
H
TiCl2
not isolable
28
O
+
+
tBu
not isolable
2
N
N
N
N
N
N
2
isolated in low yield (8%)
Scheme 12. Attempts to prepare dissymmetric bis(phenoxyimine) titanium complexes
lead to isolation of the homoleptic bis(phenoxyimine) titanium complex 28.
The high tendencies of unsymmetric bis(phenoxyimine) titanium and zirconium
complexes towards ligand transfer reactions as well as the successful isolation of
complex 28 prompted us to investigate whether the straightforward synthetic route
usually used for the synthesis of simple bis(phenoxyimine) complexes is also
applicable for coupled bis(aryliminoethyl)pyridine / phenoxyimine ligand precursors like
27. Indeed, simple deprotonation of 27 with one equivalent of potassium hydride and
subsequent reaction with the THF complexes of titanium tetrachloride (23) or
zirconium tetrachloride (24) furnished the complexes 28 and 29. Due to the (slightly
distorted) octahedral coordination of the metal centers, the pendant arylimino moieties
29