Synthesis, characterization, and ethylene polymerization behavior of [(RR′-admpzp)2Ti(OPri)2] complexes (RR′-admpzp = 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-olate)

Article abstract of DOI:10.1016/j.jorganchem.2007.08.040

[(RR′-admpzp)₂Ti(OPrⁱ)₂] complexes (2a-c), synthesized from reaction of Ti(OPrⁱ)₃Cl (0.5 equiv) with 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-ol compounds in the presence of triethylamine

Full text of DOI:10.1016/j.jorganchem.2007.08.040

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 692 (2007) 5375–5382
www.elsevier.com/locate/jorganchem
Synthesis, characterization, and ethylene polymerization behavior
of [(RR0-admpzp)2Ti(OPri)2] complexes (RR0-admpzp =
1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-olate)
1
*
Alexey Zazybin , Sean Parkin, Folami T. Ladipo
Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, United States
Received 19 March 2007; received in revised form 23 August 2007; accepted 23 August 2007
Available online 11 September 2007
Abstract
[(RR0-admpzp)2Ti(OPri)2] complexes (2a–c), synthesized from reaction of Ti(OPri)3Cl (0.5 equiv) with 1-dialkylamino-3-(3,5-
dimethyl-pyrazol-1-yl)-propan-2-ol compounds in the presence of triethylamine (0.5 equiv), are pseudo-octahedral with each RR0-
admpzp ligand j2-O,N(pyrazolyl) coordinated to the titanium center. In solution, 2a–c adopt isomeric structures that are in dynamic
equilibrium. At 23 ꢀC, 2a–c/1000 MAO catalyst systems furnished high molecular weight polymers with narrow molecular weight dis-
tributions (Mw/Mn = 2.7–2.8). At 100 ꢀC, 2a–c/MAO catalyst systems exhibited increased polymerization activity and 2c/1000 MAO
system furnished high molecular weight polyethylene with a molecular weight distribution (Mw/Mn = 2.1) that is close to that found
for single-site catalysts.
ꢁ 2007 Elsevier B.V. All rights reserved.
Keywords: Olefin polymerization; Titanium(IV) catalysts; 1-Dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-olate ligands
1. Introduction
at further developing the potential of non-cyclopentadienyl
ligand arrays in early transition metal chemistry, we
recently initiated a study of titanium(IV) complexes sup-
ported by 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-
propan-2-olate ligands (RR0-admpzp). The modular nature
of this ligand framework is especially attractive since it
should facilitate easy modification of ligand properties.
Also, while RR0-admpzp ligands are potentially multiden-
tate, dissimilar steric and electronic properties of the
amine- and pyrazol-1-yl donor groups may facilitate flexi-
ble ligation behavior and thereby allow different molecular
geometries to be realized. In this regard, both j2-O,N
coordination of RR0-admpzp ligands (analogous to phen-
oxy-imines in Ti–FI catalysts, Fig. 1) [5] and j3-O,N,N
coordination (analogous to heteroscorpionate ligands in
which a pyrazolyl group of a tris(pyrazol-1-yl)methane sys-
tem has been replaced with an oxygen donor group, Fig. 1)
[7,8] are possible. Herein we describe the synthesis and
structural characterization of [(RR0-admpzp)2Ti(OPri)2]
complexes (2a, R = R0 = Pri; 2b, R = R0 = Bn; 2c,
The discovery of single-site ethylene and a-olefin poly-
merization catalyst systems based on Cp2MX2 [1] and
(CpSiR2NR)MX2 [2] complexes of the group 4 metals
has stimulated investigation of the potential of a diverse
array of non-cyclopentadienyl ligand environments in early
transition metal chemistry. These studies have established
that steric and electronic properties of ancillary ligands
greatly influence reactivity of transition metal complexes,
and some highly active (and sometimes living) olefin poly-
merization catalysts have been generated via activation of
group 4 metal complexes supported by chelating di(amide)-
[3], amine-bis(phenolate)- [4], bis(phenoxy-imine)- [5], or
phosphinimide [6] ligation. As part of our program aimed
*
Corresponding author. Fax: +1 859 323 1069.
E-mail address: fladip0@uky.edu (F.T. Ladipo).
Present address: Department of Chemistry, Kazan State University,
1
420045 Kazan, Kremlyovskaya 18, Russia.
0022-328X/$ - see front matter ꢁ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.08.040

5376
A. Zazybin et al. / Journal of Organometallic Chemistry 692 (2007) 5375–5382
But
R1
Y
N
N
But
O
Ti
N
Cl
Cl
TiCl2
N
O
Ti
O
N
N
Cl
Cl
N
N
Cl
N
R2
2
Cl
Y = CO, bdmpza
Y = CH2, bdmpze
R1 and/or R2 = alkyl, aryl, F. fluoroaryl, etc.
(bpzmp)TiCl3
Ti-FI catalysts
Fig. 1. Ti–Fl catalysts.
R = Bn, R0 = But), as well as results from a preliminary
study of the ethylene polymerization behavior of catalysts
generated upon MAO-activation of the complexes
(MAO = methylalumoxane).
Me
i
0.5 Ti(OPr ) Cl,
3
0.5 NEt
3
OH
N
i
[(RR'-admpzp) Ti(OPr ) ] (2a-c)
2
2
R'RN
N
pentane, 25 ÞC
74-96%
t
Me
1a-c
i
a, R = R' = Pr ; b, R= R' =C H Ph;c ,R=C H Ph, R' =B u
2
2
ð1Þ
2. Results and discussion
The formulation and molecular structure of [(RR0-ad-
mpzp)2Ti(OPri)2] complexes (2a–c) were characterized by
means of microanalysis and spectroscopic (IR, 1H and
13C NMR, along with 2D 13C–1H HSQC) experiments,
as well as by single crystal X-ray diffraction study of
[(ButBn-admpzp)2Ti(OPri)2] (2c). The molecular structure
of 2c is shown in Fig. 2, and crystallographic data and se-
lected metrical parameters are collected in Tables 1 and 2.
Each ButBn-admpzp ligand is coordinated via the alkoxide
group and the pyrazolyl nitrogen. The compound adopts a
distorted octahedral structure with two mutually cis iso-
propoxide ligands and two mutually cis pyrazolyl ligands
coordinated in the equatorial plane. The distortion from
idealized octahedral geometry results from acute bite
angles of chelating ButBn-admpzp ligands {ca. 79.2ꢀ for
O(1)–Ti(1)–N(1) and ca. 79.6ꢀ for O(2)–Ti(1)–N(4)}, as
well as steric constraints imposed by cis-orientation of
bulky isopropoxide ligands {O(4)–Ti(1)–O(3) ca. 101ꢀ}.
2.1. Synthesis and characterization of [(RR0-admpzp)2-
Ti(OPri)2] complexes (2a–c)
The new 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-
propan-2-ol compounds {(RR0-admpzp)H, 1a–c, Scheme
1} were prepared by modification of the method reported
by Darbinyan et al. [9] (see Section 4). Reaction of
Ti(OPri)3Cl (0.5 equiv) with 1a–c in the presence of trieth-
ylamine (0.5 equiv) produced 2a–c in good to excellent
yield (Eq. 1). Both [(Pri2-admpzp)2Ti(OPri)2] (2a) and
[(Bn2-admpzp)2Ti(OPri)2] (2b) were isolated as colorless
oils while [(ButBn-admpzp)2Ti(OPri)2] (2c) was obtained
as a white crystalline solid. All of the compounds are highly
sensitive to hydrolysis and oxidation (even in the solid-
state) hence they are best stored for extended periods of
time under N2 atmosphere. The compounds are highly sol-
uble in diethyl ether, THF, and most aliphatic and aro-
matic hydrocarbon solvents, including hexane, benzene,
and toluene. However, while 2a and 2b are highly soluble
in pentane, 2c is moderately soluble in pentane and could
be recrystallized from pentane at low temperatures.
˚
The Ti–O bond distances {average = 1.864(2) A} [10] are
shorter than the Ti–O sigma-bond distance predicted on
˚
the basis of covalent radii (ca. 1.99–2.05 A) [11] but longer
than Ti–O bond lengths reported for more highly
Me
N
H
O
N
Me
+
+ KOH
N
Cl
N
25 ÞC
O
Me
Me
neat RR'NH
Me
², 3h
OH
N
N
i
1a, R = R' = Pr
1b, R = R' = CH Ph
R'RN
2
t
1c, R = CH Ph, R' = Bu
2
Me
(RR'-admpzp)H
Scheme 1.

A. Zazybin et al. / Journal of Organometallic Chemistry 692 (2007) 5375–5382
5377
electron-deficient Ti(IV) alkoxides, such as [(2,6-Ph2-
C6H3O)2TiCl2] (1.73 A) [12] and [(2-But-C6H4O)4Ti]
˚
˚
(1.78 A) [13]. The short Ti–O bond distances observed for
2c likely reflect partial Ti–O p-bonding. Also consistent
with existence of partial Ti–O double bond character, the
Ti–O–C units in 2c are bent (Ti–O–C range from ca.
133–143ꢀ) hence the oxygens are sp2-hybridized and each
oxygen has one p orbital available for O–Ti p bonding;
similar observations and interpretation have been
reported for related [(pyCAr2O)2M(NMe2)2] complexes
(pyCAr2O = chelating pyridne-alkoxide ligand; M = Ti,
Zr, or Hf) [11]. The Ti–N bond distances in 2c are long
˚
{average = 2.358(2) A} due to strong trans influence of
Fig. 2. Molecular structure of [(ButBn-admpzp)2Ti(OPri)2] (2c) (50%
probability ellipsoids).
the isopropoxide ligands; comparable Ti–N bond distances
have been observed for a Ti(IV) heteroscorpionate complex
that has a strong trans-influence ligand bound opposite a
pyrazolyl donor [(bpzmp)Ti(NMe2)3] (average Ti–N(pyraz-
Table 1
˚
Summary of crystallographic data for 2c
olyl) = 2.392(2) A) [8e].
It is important to note that five idealized octahedral
structures (A–E, Chart 1) are possible for j2-O,N(pyrazolyl)
coordinated [(RR0-admpzp)2Ti(OPri)2] complexes, based
on consideration of first coordination sphere atoms only;
the number of possible idealized octahedral structures
increases to 15 when the orientation (axial/equatorial) of
pendant CH2NRR0 groups is also considered. Even though
X-ray crystallography clearly established j2-O,N(pyrazolyl)
coordination of the ButBn-admpzp ligands and the pseudo-
octahedral solid-state structure (Fig. 2) corresponding to
structure A (Chart 1) for [(ButBn-admpzp)2Ti(OPri)2] (2c),
structures A–C are expected to be comparable in energy
because in each structure, two short Ti–O bonds are trans
to each other, two strong trans-influence alkoxide groups
are trans to weak pyrazolyl donors, and the alkoxide oxy-
gens can participate in O–Ti–p bonding with different metal
d orbitals [11,14]. However, structures D and E should be
disfavored by trans arrangement of all of the alkoxide
ligands and because the alkoxides must share a single metal
d orbital for O–Ti p donation. In solution, [(RR0-
admpzp)2Ti(OPri)2] complexes (2a–c) show multiple sets
Empirical formula
Formula weight
T (K)
Crystal system
Space group
Z
C44H70N6O4Ti
794.96
90.0(2) K
Triclinic
ꢀ
P1
2
˚
a (A)
12.7297(7)
12.8371(6)
14.2719(7)
90.494(2)
96.845(2)
108.088(2)
2198.57(19)
1.201
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
3
˚
V (A )
Dcalc (g/cm3)
Final R indices [I > 2r(I)]: R1, wR2
wR2, R1 (all data)
0.0592, 0.1553
0.0631, 0.1578
Table 2
˚
Selected bond distances (A) and angles (ꢀ) for 2c
Ti(1)–O(4)
Ti(1)–O(1)
Ti(1)–O(2)
Ti(1)–O(3)
Ti(1)–N(4)
Ti(1)–N(1)
1.850(2)
1.8511(18)
1.8523(18)
1.904(2)
2.348(2)
2.368(2)
91.36(9)
99.23(9)
163.60(9)
100.95(9)
98.76(9)
91.53(9)
89.74(9)
88.05(8)
79.56(8)
167.12(9)
167.81(8)
79.19(8)
88.47(8)
88.19(8)
82.33(7)
143.20(17)
143.24(16)
137.7(2)
133.39(18)
1
13
of H and C NMR resonances for the RR0-admpzp and
isopropoxide ligands; when dissolved in solution, single-
crystals of [(ButBn-admpzp)2Ti(OPri)2] (2c) produced iden-
O(4)–Ti(1)–O(1)
O(4)–Ti(1)–O(2)
O(1)–Ti(1)–O(2)
O(4)–Ti(1)–O(3)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(4)–Ti(1)–N(4)
O(1)–Ti(1)–N(4)
O(2)–Ti(1)–N(4)
O(3)–Ti(1)–N(4)
O(4)–Ti(1)–N(1)
O(1)–Ti(1)–N(1)
O(2)–Ti(1)–N(1)
O(3)–Ti(1)–N(1)
N(4)–Ti(1)–N(1)
C(7)–O(1)–Ti(1)
C(26)–O(2)–Ti(1)
C(39)–O(3)–Ti(1)
C(42)–O(4)–Ti(1)
1
tical H and 13C NMR spectra as the bulk material. The
intensities of the observed resonances are temperature
dependent and a single isomer does not prevail in solution
(for 2a–c) in the 213–373 K temperature range. The data
suggests low coordination energy of the pyrazolyl nitrogen
to the titanium center and the existence of a dynamic equi-
librium between at least two isomeric structures [15,16].
Thus, the room temperature 1H NMR spectrum of
[(ButBn-admpzp)2Ti(OPri)2] (2c) showed a broad multiplet
(ostensibly composed of overlapping broad singlet reso-
nances and integrating as two protons) between d 5.70
and 5.50 for protons at the pyrazolyl 4-position (pyz-4). A
multiplet resonance (composed of broad singlets and
integrating as six protons) was observed in the d 2.65–2.15
range for methyl groups at the pyrazolyl 3-position

5378
A. Zazybin et al. / Journal of Organometallic Chemistry 692 (2007) 5375–5382
NRR'
N
N
R'RN
i
i
OPr
Ti
N
N
O
N
N
O
O
Ti
i
i
R'RN
i
i
OPr
OPr
OPr
O
N
N
Ti
O
OPr
OPr
N
N
O
C
N
N
NRR'
NRR'
NRR'
B
A
N
R'RN
R'RN
N
Ti
N
i
i
OPr
O
N
i
i
OPr
Ti
NRR'
OPr
O
N
O
N
O
R'RN
N
OPr
N
D
E
Chart 1.
(pyz-3) while methyl groups at the pyrazolyl 5-position
(pyz-5) showed as a multiplet (integrating as six protons)
in the d 2.14–1.68 range. The Ti–OCHMe2 methyl protons
were observed as a multiplet in the d 1.51–1.17 range (inte-
grating as 12 protons). In the 13C NMR spectrum, each car-
bon atom is observed as a set of closely spaced singlet
resonances (only the most intense peak is reported in Sec-
tion 4). The pyz-3 carbon showed in the d 148.0–147.4 range
with the most intense peak at d 148.0 while the pyz-5 carbon
showed in the d 139.5–138.8 range with the most intense
peak at d 139.1. The pyz-4 carbon is observed in the d
105.5–104.6 range with the most intense peak at d 105.0.
The methyl substituent at the pyrazolyl 3-position is
observed in the d 14.4–13.8 range with the most intense peak
at d 14.3 while the methyl substituent at the pyrazolyl 5-
position is observed in the d 11.3–10.8 range with the most
intense peak at d 11.1. While RR0-admpzp ligands possess
amine- and pyrazol-1-yl donor groups with dissimilar steric
and electronic properties, and hence can possibly bind tita-
nium through either amine or pyrazoyl donor, we believe
that [(Pri2-admpzp)2Ti(OPri)2] (2a) and [(Bn2-admpzp)2-
Ti(OPri)2] (2b) adopt pseudo-octahedral geometry with
each RR0-admpzp ligand j2-O,N(pyrazolyl) coordinated
to the titanium center, similar to 2c. This belief finds strong
conducted at 23 ꢀC and 100 ꢀC for 30 min, using different
Al/Ti ratios under 10 bar ethylene pressure. The data from
the studies are collected in Table 3. At 23 ꢀC and Al/Ti
ratio of 500 or 1000, all of the catalyst systems (2a–c/
MAO) furnished high molecular weight polyethylenes
(Mw P 1.1 · 106 g/mol) that showed narrow molecular
weight distributions (Mw/Mn = 2.7–3.3; Table 3, entries
1–6) although the polydispersities are broader than those
(Mw/Mn 6 2.0) typical of single-site catalysts. In contrast
to related group 4 metal heteroscorpionate complexes
which typically achieve maximum polymerization activity
at low temperatures (635 ꢀC) [8], 2a–c/1000 MAO catalyst
systems exhibited increased polymerization activity at
100 ꢀC (Table 3) although polyethylenes obtained showed
lower molecular weights (up to Mw = 2.8 · 106 g/mol,
Table 3, entries 10–12) than those obtained at 23 ꢀC and
generally possessed broader multimodal molecular weight
distributions (Mw/Mn = 3.5–5.9); the exception being the
polyethylene produced by using the 2c/1000 MAO at
Table 3
Summary of ethylene polymerization results
Entry Precatalysta Temperature Al/ Activity [kg PE/ Mwc
Mw/
Mn
(ꢀC)
Ti
(mol Ti h bar)]b (g molꢀ1
)
1
support in the observation of parallel H and 13C NMR
1
2
3
4
5
6
7
8
2a
2b
2c
2a
2b
2c
2a
2b
2c
2a
2b
2c
23
23
23
23
23
500 7.1
1.11 · 106 3.3
1.38 · 106 2.7
1.34 · 106 3.0
1.36 · 106 2.7
1.50 · 106 2.8
1.50 · 106 2.7
5.9 · 104 6.3
1.07 · 105 4.1
2.63 · 105 4.0
2.84 · 105 5.9
2.76 · 105 3.6
1.46 · 105 2.1
data for 2a–c (see Section 4) and in the fact that coordina-
tion of amine nitrogen will produce a 5-membered chelate
ring that is more strained than the 6-membered chelate ring
formed on pyrazolyl nitrogen coordination; and acute bite
angles are present in 6-membered chelate rings of 2c (vide
supra). In addition, although the –NRR0 group is more
basic than the pyrazolyl group, its coordination at the
crowded titanium center should be disfavored (relative to
pyrazolyl) because of its substantially greater steric demand.
500 6.4
500 7.1
1000 8.6
1000 13.5
1000 6.8
500 18.4
500 12.1
500 13.8
1000 28.6
1000 22.3
1000 19.0
23
100
100
100
100
100
100
9
10
11
12
a
2.2. Ethylene polymerization behavior of [(RR0-
admpzp)2Ti(OPri)2] complexes (2a–c)
Polymerizations conditions (unless stated otherwise): glass reactor; in
toluene; 10 bar pressure of ethylene; 10 lmol of precatalyst; (MAO solu-
tion in toluene, 10% wt% total Al); reaction time = 30 min.
b
Average activity from three experiments.
Molecular weight data were determined by GPC and measured relative
c
Studies of ethylene polymerization catalyzed by MAO-
activated [(RR0-admpzp)2Ti(OPri)2] complexes (2a–c) were
to linear polystyrene standards.

A. Zazybin et al. / Journal of Organometallic Chemistry 692 (2007) 5375–5382
5379
100 ꢀC, its molecular weight distribution (Mw/Mn = 2.1) is
close to that found for single-site catalysts. The close par-
allel in ethylene polymerization behavior of 2a–c/MAO
catalyst systems suggests that similar Ti4+ active species
are generated from these precatalysts. Hence pyrazolyl
coordination to titanium is likely maintained in the puta-
tive active cationic titanium species [17], and slight differ-
ences observed in ethylene polymerization behavior of the
catalysts likely reflect differences in inductive and steric
effects of amine moieties of the RR0-admpzp ligands.
MS analyses were performed on a Hewlett Packard 5890
series II gas chromatograph with a Hewlett Packard 5972
series mass selective detector at an ionizing potential of
70 eV. Gel permeation chromatography experiments were
performed at Cornell Center for Materials Research, Ith-
aca, NY. All molecular weights were measured relative
to linear polystyrene standards. Elemental analyses were
performed by Complete Analysis Laboratories Inc., Par-
sippany, NJ.
4.2. General synthesis of 1-dialkylamino-3-(3,5-dimethyl-
pyrazol-1-yl)-propan-2-ols (1a–c)
3. Conclusions
Preliminary studies of the ethylene polymerization
behavior of catalysts generated via MAO activation of
[(RR0-admpzp)2Ti(OPri)2] complexes (2a–c) indicate that
they exhibit modest ethylene polymerization activity and
provide inferior control of ethylene polymerization in com-
parison to extensively developed Ti–FI catalysts (Fig. 1) [5].
However, 2a–c/MAO catalysts display good thermal stabil-
ity and given that [(RR0-admpzp)2Ti(OPri)2] complexes are
structurally related to Ti–FI catalysts and that the modular
nature of 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-
propan-2-olate ligands (RR0-admpzp) should facilitate fac-
ile modification of the electronic and geometric structure of
[(RR0-admpzp)2Ti(OPri)2] complexes, further investigation
of the ligation properties of RR0-admpzp and related
ligands in titanium chemistry is of interest. Hence studies
aimed at determining the nature of the active catalyst spe-
cies generated in 2a–c/MAO systems and tailoring catalyst
properties through systematic modification of the ligand
framework are currently underway in our laboratory in
hopes of developing more active and thermally stable cata-
lysts that provide excellent control of polymer properties.
NaOH pellets (7.50 g, 0.188 mol) were added into a
slightly heterogeneous mixture of 3,5-dimethylpyrazole
(15.0 g, 0.156 mol) and epichlorohydrin (250 ml, 3.19 mol).
After stirring for several minutes, NaCl began to precipitate
and the reaction mixture was stirred at room temperature
for 24 h. The resulting suspension was then filtered and the
filtrate was evaporated under reduced pressure to give 3,5-
dimethyl-1-oxiranylmethyl-1H-pyrazole as a viscous oil.
This crude product, which contained 5–10% (by GC–MS)
of 1,3-bis(3,5-dimethyl-1H-pyrazol-1-yl)propan-2-ol, was
used in the preparation of 1a–c without purification.
4.2.1. 1-Diisopropylamino-3-(3,5-dimethyl-pyrazol-1-yl)-
propan-2-ol (1a)
Distilled water (2.00 mL, 0.156 mol) and Pri2NH
(65.6 mL, 0.468 mol) were added to the viscous oil of
3,5-dimethyl-1-oxiranylmethyl-1H-pyrazole and the result-
ing solution was stirred at reflux for 3 h. After cooling to
room temperature, the solution was concentrated under
reduced pressure to give a brown-yellow viscous oil. This
crude product was purified by column chromatography
using a 35:4:1 ethyl acetate–hexane–triethylamine mixture
as eluent. The solution was evaporated under reduced pres-
4. Experimental
1
sure to give 1a as a white powder. Yield: 21.7 g, 55%. H
4.1. General
NMR (C6D6): d 5.71 (s, 1H, pyz-4), 4.39 (s, 1H, CH–
OH), 4.03 (dd, 2J = 13.8 Hz, 3J = 4 Hz, 1H, HA of
2
All experiments were performed under dry nitrogen
atmosphere using standard Schlenk techniques or in a Vac-
uum Atmospheres, Inc. glovebox. Solvents were dried and
distilled by standard methods before use [18]. All solvents
were stored in the glovebox over 4A molecular sieves that
were dried in a vacuum oven at 150 ꢀC for at least 48 h
prior to use. Unless otherwise stated, all reagents were pur-
chased from Aldrich Chemical Company. 3,5-Dimethylpy-
razole was purchased from Alfa Aesar and dried under
vacuum at 60 ꢀC for 3 h prior to use. Epichlorohydrin
was dried overnight over anhydrous Na2SO4 prior to
use. Ethylene (99.9% purity) was purchased from Scott-
–CH2pyz), 3.91 (m, 1H, HO–CH), 3.73 (dd, J = 13.8 Hz,
3
3J = 8.5 Hz, 1H, HB of –CH2pyz), 2.72 (sept, J = 8.5 Hz,
2H, N{CHMe2}2), 2.44 (dd, 2J = 17 Hz, 1H, HA of
–CH2NPri2), 2.42 (dd, J = 17 Hz, 1H, HB of –CH2NPri2),
2.25 (s, 3H, CH3 at pyz-3), 2.07 (s 3H, CH3 at pyz-5),
0.81 (d, 3J = 8.5 Hz, 6H, N–CHMe2), 0.77 (d, 6H,
3J = 8.5 Hz, N–CHMe2). 13C NMR (C6D6): d 147.0 (pyz-
3), 139.7 (pyz-5), 104.8 (pyz-4), 68.6 (CH–OH), 52.6
(CH2pyz), 48.4 (N{CHMe2}2), 48.3 (CH2NPri2), 21.4 (N–
CHMe2), 20.3 (N–CHMe2), 13.8 (CH3 at pyz-3), 11.1
(CH3 at pyz-5). IR (Nujol, cmꢀ1): 3136, 1552, 1465, 1384,
1360, 1333, 1296, 1191, 1176, 1128, 1096, 974, 885, 787.
GC–MS(EI): M+ (253).
Gross Co. or Matheson Tri-Gas Inc. H and 13C NMR
1
spectra were recorded on a Varian Gemini-200 spectrome-
ter or a Varian VXR-400 spectrometer at room tempera-
4.2.2. 1-Dibenzylamino-3-(3,5-dimethyl-pyrazol-1-yl)-
propan-2-ol (1b)
1
ture unless otherwise stated. H and 13C chemical shifts
were referenced to residual solvent peaks. Infrared spectra
were recorded on a Nicolet Magna 560 spectrometer. GC–
Prepared as described for 1a except using dibenzylamine
(30 mL, 0.156 mol) and heating the reaction mixture at

5380
A. Zazybin et al. / Journal of Organometallic Chemistry 692 (2007) 5375–5382
80 ꢀC for 3 h. Compound 1b was isolated as a white
–CH2pyz), 3.82–3.54, (m, 2H, HB of –CH2pyz), 3.07–2.78
(br m, 4H, N(CHMe2)2) 2.93–2.70 {m, 2H, HA of
–CH2NPri2}, 2.63–2.38 (m, 6H, CH3 at pyz-3), 2.38–2.25
(m, 2H, HB of –CH2NPr2i ), 2.20–1.87 {m, 6H, (CH3 at
pyz-5)}, 1.45–1.24 (m, 12H, Ti–OCHMe2), 1.07–0.72
(br m, 24 H, {N(CHMe2)2}. 13C (C6D6) d: 147.8 (pyz-3),
147.3 (pyz-3), 139.2 (pyz-5), 105.0 (pyz-4), 81.7
(Ti–OCH–), 80.8 (Ti–OCH–), 77.0 (Ti–OCH–), 52.7
(–CH2pyz), 50.5 (CH2NPri2), 48.6 (CH2NPr2i ), 26.7 (Ti–
OCHMe2), 22.3 {N(CHMe2)2}, 19.9 {N(CHMe2)2}, 14.2
(CH3 at pyz-3), 11.0 (CH3 at pyz-5). IR (neat, cmꢀ1):
2965, 2928, 2867, 2617, 1553, 1464, 1425, 1385, 1362,
1324, 1260, 1207, 1123, 1045, 987, 930, 886, 809, 775,
738, 696, 632. Anal. Calc. for C34H66N6O4Ti: C, 60.88;
H, 9.92; N, 12.53. Found: C, 61.11; H, 9.81; N, 12.63%.
1
powder. Yield: 30.5 g, 56%. H NMR (C6D6): d 7.22–7.04
3
(m, 10H, N(CH2Ph)2), 5.64 (s, 1H, pyz-4), 4.61 (d, J =
2.5 Hz, 1H, CH–OH), 4.12 (m, 1H, HO–CH), 3.82 (dd,
2J = 17 Hz, 3J = 3.5 Hz, 1H, HA of –CH2pyz), 3.56
2
3
(dd, J = 17 Hz, J = 9.5 Hz, 1H, HB of –CH2pyz), 3.43
2
2
(d, J = 17 Hz, 2H, HA of CH2Ph), 3.39 (d, J = 17 Hz,
2H, HB of CH2Ph), 2.54 (dd, 2J = 16.5 Hz, 1H, HA of
–CH2NPri2), 2.52 (dd, 2J = 16.5 Hz, 1H, HB of –CH2NPri2),
2.20 (s, 3H, CH3 at pyz-3), 1.82 (s, 3H, CH3 at pyz-5). 13C
NMR (C6D6): d 147.4 (pyz-3), 139.5 (pyz-5), 139.3, 129.3,
128.5, 127.3, 104.8 (pyz-4), 69.1 (CH–OH), 59.1 (CH2Ph),
57.0 (CH2N(CH2Ph)2), 52.1 (CH2pyz), 13.7 (CH3 at pyz-
3), 10.5 (CH3 at pyz-5). IR (Nujol, cmꢀ1): 3174, 1548,
1461, 1377, 1359, 1123, 1092, 1077, 1047, 1032, 910, 860,
782, 751, 736, 699. GC–MS(EI): M+ (349).
4.4. Synthesis of [(Bn2-admpzp)2Ti(OPri)2] (2b)
4.2.3. 1-(Benzyl-tert-butyl-amino)-3-(3,5-dimethyl-pyrazol-
1-yl)-propan-2-ol (1c)
Into a pentane (20 mL) solution of Ti(OPri)3Cl (0.500 g,
1.92 mmol) was slowly added (dropwise) a pentane (40 mL)
solution of 1-dibenzylamino-3-(3,5-dimethyl-pyrazol-1-yl)-
propan-2-ol (1b, 0.670 g, 1.92 mmol) and NEt3 (0.194 g,
1.92 mmol). Next, another equivalent of 1b (0.670 g,
1.92 mmol) in pentane (40 mL) was slowly added. The
reaction mixture was let stir for 2 h at room temperature,
during which time [HNEt3]Cl precipitated. After the pre-
cipitate was filtered off, the yellow filtrate was cooled at
ꢀ30 ꢀC overnight. The bottom layer of the resulting bipha-
sic mixture was collected and dried under vacuum for 4 h
to give 2b as a viscous yellow liquid. A colorless oil could
be obtained via dissolution in pentane, filtration through
a plug of dry activated carbon, and evaporation of the
solvent. Yield: 1.56 g. 94%. 1H (C6D6) d: 7.50–6.98 (m,
20H, {PhCH2)2N}, 5.55 (br s, 2H, pyz-4), 4.95–4.60 (br
m, 4H, Ti–OCH–), 4.22–4.00 (m, 2H, HA of CH2pyz),
3.93–3.67 (m, 4H, HA of (PhCH2)2N), 3.67–3.26 (m, 2H,
HB of CH2pyz), 3.47–3.26 (m, 4H, HB of (PhCH2)2N),
2.81–2.50 (br m, 4H, –CH2NBn2), 2.47–2.08 (m, 6H, CH3
at pyz-3), 2.06–1.67 (m, 6H, (CH3 at pyz-5), 1.45–0.80 (br
m, 12H, Ti–OCHMe2). 13C (C6D6) d: 147.8 (pyz-3), 140.1
(pyz-5), 139.2, 129.4, 128.4, 127.1 {(PhCH2)2N}, 105.0
(pyz-4), 79.4 (Ti–OCH–), 77.4 (Ti–OCH–), 59.4
{(PhCH2)2N}, 59.0 (–CH2NBn2), 52.8 (CH2pyz), 26.5
(Ti–OCHMe2), 14.2 (CH3 at pyz-3), 11.1 (CH3 at pyz-5).
IR (neat, cmꢀ1): 3084, 3061, 3027, 2963, 2853, 2792,
2714, 2617, 1948, 1877, 1809, 1754, 1602, 1585, 1553,
1494, 1454, 1373, 1240, 1097, 1018, 933, 847, 780, 747,
698. Anal. Calc. for C50H66N6O4Ti: C, 69.59; H, 7.71; N,
9.74. Found: C, 69.65; H, 7.91; N, 9.80%.
Prepared as described for 1b using benzyl-tert-butyl-
amine (28.3 mL, 0.156 mol). Compound 1c was isolated
1
as a yellow liquid. Yield: 18.7 g, 38%. H NMR (C6D6):
d 7.20–6.98 (m, 5H, CH2Ph) 5.60 (s, 1H, pyz-4), 4.24 (br
2
3
s, 1H, CH–OH), 3.83 (dd, J = 17 Hz, J = 4 Hz, 1H, HA
of –CH2pyz), 3.64 (m, 1H, HO–CH), 3.41 (dd, 2J =
17 Hz, 3J = 8.5 Hz, 1H, HB of –CH2pyz), 3.46 (d, 2J =
2
18.5 Hz, 1H, HA of CH2Ph), 3.35 (d, J = 18.5 Hz, 1H,
2
3
HB of CH2Ph), 2.74 (dd, J = 17 Hz, J = 9 Hz, 1H, HA
of CH2NButBn), 2.52 (dd, 2J = 17 Hz, 3J = 8.5 Hz, 1H,
HB of CH2NButBn), 2.13 (s, 3H, CH3 at pyz-3), 1.85 (s,
3H, CH3 at pyz-5), 0.89 (s, 9H, But). 13C NMR (C6D6): d
147.0 (pyz-3), 139.5 (pyz-5), 142.9, 128.5, 128.1, 126.8,
104.7 (pyz-4), 70.0 (CH–OH), 55.9 (CH2Ph), 55.5
(N–CMe3), 55.1 (CH2NButBn), 52.0 (CH2pyz), 27.2
(N–CMe3), 13.7 (CH3 at pyz-3), 11.0 (CH3 at pyz-5). IR
(Neat, cmꢀ1): 3381, 3027, 2970, 2870, 1553, 1493, 1467,
1425, 1391, 1364, 1258, 1245, 1199, 1123, 1055, 1026,
948, 900, 842, 774, 750, 735, 715, 699. GC–MS(EI): M+
(315).
4.3. Synthesis of [(Pri2-admpzp)2Ti(OPri)2] (2a)
Into a pentane (20 mL) solution of Ti(OPri)3Cl (0.500 g,
1.92 mmol) was added dropwise a pentane (20 mL) solu-
tion of 1-diisopropylamino-3-(3,5-dimethyl-pyrazol-1-yl)-
propan-2-ol (1a, 0.490 g, 1.92 mmol) and NEt3 (0.194 g,
1.92 mmol). Next, another equivalent of 1a (0.490 g,
1.92 mmol) in pentane (20 mL) was slowly added. The
reaction mixture was let stir for 2 h at room temperature,
during which time [HNEt3]Cl precipitated. After filtering
off the precipitate, the yellow filtrate was evaporated under
reduced pressure to give 2a as a yellow oily liquid. This
product could be obtained as a colorless oil following
dissolution in pentane, filtration through a plug of dry
activated carbon, and evaporation of the solvent. Yield
4.5. Synthesis of [(ButBn-admpzp)2Ti(OPri)2] (2c)
Into a pentane (20 mL) solution of Ti(OPri)3Cl (0.500 g,
1.92 mmol) was slowly added (dropwise) a pentane (20 mL)
solution of 1-(benzyl-tert-butyl-amino)-3-(3,5-dimethyl-
pyrazol-1-yl)-propan-2-ol (1c, 0.610 g, 1.92 mmol) and
NEt3 (0.194 g, 1.92 mmol). Next, another equivalent of 1c
1
1.24 g, 96%. H (C6D6) d: 5.68 (br s, 2H, pyz-4), 5.12–
4.46 (br m, 4H, Ti–OCH–), 4.44–4.10 (m, 2H, HA of

A. Zazybin et al. / Journal of Organometallic Chemistry 692 (2007) 5375–5382
5381
(0.610 g, 1.92 mmol) in pentane (20 mL) was slowly added.
Acknowledgements
The reaction mixture was let stir for 2 h at room tempera-
ture, during which time [HNEt3]Cl precipitated. After the
precipitate was filtered off, the filtrate was concentrated
under reduced pressure to ꢁ20 mL and cooled at ꢀ30 ꢀC
overnight. The resulting yellowish-white crystals were col-
lected, recrystallized from hot pentane by cooling a
saturated solution at ꢀ30 ꢀC for several days, and then
dried under vacuum to give 2c. Yield: 1.13 g. 74%. 1H
(C6D6) d: 7.62–6.99 (m, 10H, But(PhCH2)N), 5.60 (br m,
2H, pyz-4), 5.16–4.32 (br m, 4H, Ti–OCH–), 4.12–3.82
(m, 2H, HA of CH2pyz), 3.83–3.50, (m, 4H, But(PhCH2)N),
3.50–3.31 (m, 2H, HB of CH2pyz), 3.05–2.64 (br m,
4H, –CH2NBnBut), 2.65–2.15 (m, 6H, CH3 at pyz-3),
2.14–1.68 (m, 6H, CH3 at pyz-5), 1.51–1.17 (m, 12H,
Ti–OCHMe2), 1.15–0.85 (m, 18H, But). 13C (C6D6) d:
148.0 (pyz-3), 144.1 (But(PhCH2)N), 139.0 (pyz-5),
128.4 (But(PhCH2)N), 127.1 (But(PhCH2)N), 126.5
(But(PhCH2)N), 105.0 (pyz-4), 80.7 (Ti–OCH–), 76.9 (Ti–
OCH–), 57.0 (Bn(Me3C)N), 56.1 (–CH2NBnBut), 55.5
(But(PhCH2)N), 52.3 (CH2pyz), 27.3 (Ti–OCHMe2), 26,5
(Bn(CH3)3CN), 14.3 (CH3 at pyz-3), 11.1 (CH3 at pyz-5).
IR (Nujol, cmꢀ1): 1551, 1465, 1367, 1323, 1296, 1201,
1160, 1135, 1092, 989, 931, 843, 734, 699. Anal. Calc. for
C44H70N6O4Ti: C, 66.48; H, 8.88; N, 10.57. Found: C,
66.33; H, 8.75; N, 10.69%.
Thanks are expressed to the US National Science Foun-
dation (Grant No. CHE-0416098) for financial support of
this work. NMR instruments utilized in this research were
funded in part by the CRIF program of the US National
Science Foundation (Grant No. CHE-9974810). This work
made use of the materials characterization facility of the
Cornell Center for Materials Research (CCMR) with sup-
port from the National Science Foundation Materials Re-
search Science and Engineering Centers (MRSEC)
Program (DMR 0520404).
Appendix A. Supplementary material
Full crystallographic data for compound 2c, as well as
1H, 13C, and 2D 13C–1H HSQC NMR spectra for com-
pounds 1a–c and 2a–c (34 pages). Crystallographic data
for 2c has been deposited with the Cambridge Crystallo-
graphic Data Centre. CCDC 662008 contains the supple-
mentary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crys-
tallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this
article can be found, in the online version, at
doi:10.1016/j.jorganchem.2007.08.040.
4.6. General procedure for ethylene polymerization reactions
References
[1] See for example (a) H. Sinn, W. Kaminsky, H.J. Vollmer, R. Woldt,
Angew. Chem., Int. Ed. Engl. 19 (1980) 390;
(b) H.H. Brintzinger, D. Fischer, R. Mullhaupt, B. Rieger, R.
Waymouth, Angew. Chem., Int. Ed. Engl. 34 (1995) 1143;
(c) G.J.P. Britovsek, V.C. Gibson, D.F. Wass, Angew. Chem., Int.
Ed. 38 (1999) 428;
Toluene (35 ml) was charged into a 90 ml Swagelok
glass-tube reactor under N2 atmosphere in a glovebox.
The reactor was maintained at the desired temperature
for 20 min. Next, 10 lmol of catalyst precursor (2.5 mL
of 0.004 M solution in toluene) was added followed by an
excess of MAO (Al/Ti ratio = 500/1 or 1000/1) and the
solution was stirred for 5 min. The N2 atmosphere was
replaced with ethylene and the reactor was maintained at
the pressure of 145 psi (10 bar). The polymerization was
carried out for 30 min. The reactor was vented and the
polymerizations were quenched with ethanol (25 mL) and
then 1 M HCl solution (25 mL). The resulting suspension
was vigorously stirred until both layers were colorless
and clearly separated (ꢁ1 h). Polyethylene was filtered
off, washed with 1 M HCl, and repeatedly rinsed twice with
ethanol on a glass frit. The polymer was then dried at 70 ꢀC
for 72 h.
(d) S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000)
1169;
(e) X. Yang, C.L. Stern, T.J. Marks, J. Am. Chem. Soc. 113 (1991)
3623;
(f) Z. Wu, R.F. Jordan, J.L. Petersen, J. Am. Chem. Soc. 117 (1995)
5867;
(g) X. Yang, C.L. Stern, T.J. Marks, J. Am. Chem. Soc. 116 (1994)
10015.
[2] See, for example, (a) P.J. Sharpiro, E. Bunel, W.P. Schaefer, J.E.
Bercaw, Organometallics 9 (1990) 867;
(b) D.D. Devore, F.J. Timmers, D.L. Hasha, R.K. Rosen, T.J.
Marks, P.A. Deck, C.L. Stern, Organometallics 14 (1995) 3132;
(c) A.C. McKnight, R.M. Waymouth, Chem. Rev. 98 (1998) 2578;
(d) J.A.M. Canich, H.W. Turner, PCT Appl. WO 9212162, 1992;
(e) J.C. Stevens, F.J. Timmers, D.R. Wilson, G.F. Schmidt, P.N.
Nickias, R.K. Rosen, G.W. Knight, S.-Y. Lai, Eur. Pat Appl.
0416815, 1990.
4.7. Crystallographic study
[3] (a) J.D. Scollard, D.H. McConville, J. Am. Chem. Soc. 118 (1996)
10008;
Single crystals of [(ButBn-admpzp)2Ti(OPri)2] (2c) suit-
able for X-ray crystallographic analysis were obtained by
low temperature (ꢀ30 ꢀC) crystallization of a saturated
pentane solution of 2c (obtained by dissolution of 2c in
hot pentane). The crystal data for 2c are collected in Table
1. Further details of the crystallographic study are given in
the Supplementary material.
(b) J.D. Scollard, D.H. McConville, N.C. Payne, J.J. Vittal, Macro-
molecules 29 (1996) 5241;
(c) J.D. Scollard, D.H. McConville, J.J. Vittal, N.C. Payne, J. Mol.
Catal. A 128 (1998) 201.
[4] (a) E.Y. Tshuva, I. Goldberg, M. Kol, H. Weitman, Z. Goldschmidt,
Chem. Commun. (2000) 379;
(b) E.Y. Tshuva, I. Goldberg, M. Kol, Z. Goldschmidt, Inorg. Chem.
Commun. 3 (2000) 611;

5382
A. Zazybin et al. / Journal of Organometallic Chemistry 692 (2007) 5375–5382
(c) M. Kol, M. Shamis, I. Goldberg, Z. Goldschmidt, S. Alfi, E.
Hayut-Salant, Inorg. Chem. Commun. 4 (2001) 177.
(f) S. Milione, C. Montefusco, T. Cuenca, A. Grassi, Chem.
Commun. (2003) 1176;
[5] (a) T. Matsugi, S. Matsui, S. Kojoh, Y. Takagi, Y. Inoue, T. Fujita,
N. Kashiwa, Chem. Lett. (2001) 566;
(g) T.C. Higgs, D. Ji, R.S. Czernuszewicz, B.F. Matzanke, V.
Schunemann, A.X. Trautwein, M. Helliwell, W. Ramirez, C.J.
Carrano, Inorg. Chem. 37 (1998) 2383.
(b) M. Mitani, J. Mohri, Y. Yoshida, J. Saito, S. Ishii, K. Tsuru, S.
Matsui, R. Furuyama, T. Nakano, H. Tanaka, S.-I. Kojoh, T.
Matsugi, N. Kashiwa, T. Fujita, J. Am. Chem. Soc. 124 (2002)
3327;
(c) R. Furuyama, J. Saito, S.-I. Ishii, M. Mitani, S. Matsui, Y. Tohi,
H. Makio, N. Matsukawa, H. Tanaka, T. Fujita, J. Mol. Catal. A
200 (2003) 31;
[9] E.G. Darbinyan, M.S. Matsoyan, D. Joel, A.A. Saakyan, Arm.
Khim. Zh. 33 (1980) 584.
˚
[10] Average Ti–O bond distances of ꢁ1.910(4) A were reported for
related octahedral Ti(IV) complexes, [{j2-OCAr2C5H4N}2Ti(NMe2)2]
(CAr2 = 9-fluorenyl and Ar = 4-NEt2-C6H4) [11].
[11] I. Kim, Y. Nishihara, R.F. Jordan, R.D. Rogers, A.L. Rheingold,
G.P.A. Yap, Organometallics 16 (1997) 3314.
[12] J.R. Dilworth, J. Hanich, M. Krestel, J. Beck, J. Strahle, J.
Organomet. Chem. 315 (1986) C9.
[13] R.T. Toth, D.W. Stephan, Can. J. Chem. 69 (1991) 172.
[14] D.L. Keppert, in: S.L. Lippard (Ed.), Progress in Inorganic Chem-
istry, Vol. 23, John Wiley & Sons, New York, 1977, Chapter 1.
[15] Two isomeric structures A and B, which differ in the positioning of
one of the ligands, are dominant in solution for related titanium(IV)
phenoxyimine complexes (below) [16].
(d) Y. Yoshida, S. Matsui, Y. Takagi, M. Mitani, T. Nakano, H.
Tanaka, N. Kashiwa, T. Fujita, Organometallics 20 (2001) 4793;
(e) A. Sakuma, M.-S. Weiser, T. Fujita, Polym. J. 39 (2007) 193.
[6] D.W. Stephan, F. Guerin, R.E.v.H. Spence, L. Koch, X. Gao, S.J.
Brown, J.W. Swabey, Q. Wang, W. Xu, P. Zoricak, D.G. Harrison,
Organometallics 18 (1999) 2046.
´
[7] (a) J. Fernandez-Baeza, F.A. Jalon, A. Otero, M.E. Rodrigo, J.
Chem. Soc., Dalton Trans. (1995) 1015;
´
(b) A. Antinolo, F. Carrillo-Hermosilla, E. Diez-Barra, J. Fernan-
˜
´
dez-Baeza, M. Fernandez-Lopez, A. Lara-Sanchez, A. Moreno, A.
Otero, A.M. Rodriguez, J. Tejeda, J. Chem. Soc., Dalton Trans.
(1998) 3737.
R
O
O
O
I
N
N
O
Cl
Cl
N
Cl
N
I
´
[8] See for example: (a) A. Otero, J. Fernandez-Baeza, A. Antinolo, J.
˜
=
Ti
N
Ti
O
O
Cl
A
´
Tejeda, A. Lara-Sanchez, Dalton Trans. (2004) 1499;
N
R = 2,6-F C H
2 6 3
B
´
(b) A. Otero, J. Fernandez-Baeza, A. Antinolo, F. Carrillo-Hermo-
˜
´
silla, J. Tejeda, A. Lara-Sanchez, L. Sanchez-Barba, M. Fernandez-
Lopez, A.M. Rodriguez, I. Lopez-Solera, Inorg. Chem. 41 (2002)
5193;
[16] M.-S. Weiser, M. Wesolek, R. Mulhaupt, J. Organomet. Chem. 691
¨
(2006) 2945.
´
(c) A. Otero, J. Fernandez-Baeza, A. Antinolo, J. Tejeda, A. Lara-
˜
[17] The putative active catalyst generated upon MAO activation of
LnMX2 compounds is a cationic LnMR+ species. See for example:
A.S. Guram, R.F. Jordan, in: M.F. Lappert (Ed.), Comprehensive
Organometallic Chemistry II, Vol. 4, Pergamon Press, Oxford, UK,
1995, p. 589, and references cited therein.
´
Sanchez, L. Sanchez-Barba, M. Fernandez-Lopez, I. Lopez-Solera,
Inorg. Chem. 43 (2004) 1350;
´
(d) A. Otero, J. Fernandez-Baeza, A. Antinolo, F. Carrillo-Hermo-
˜
silla, J. Tejeda, E. Diez-Barra, A. Lara-Sa´nchez, L. Sanchez-Barba,
I. Lopez-Solera, Organometallics 20 (2001) 2428;
(e) S. Milione, V. Bertolasi, T. Cuenca, A. Grassi, Organometallics
24 (2005) 4915;
[18] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory Chemi-
cals, Butterworth-Heinemann, Oxford, 1988.