A. de Souza Maia et al. / Inorganic Chemistry Communications 6 (2003) 304–307
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described by Maggin et al. [7] for cyclopentadienyllanth-
anide dichlorides. NaCp (Aldrich) and MAO, 10 wt% in
toluene suspension (Akzo), were used as received.
solvent, 3.5–4.5 mg of organolanthanide compound,
MAO (10% in toluene) in the molar ratio Al/Ln of 2000
and ethylene (3 bar). Polymerization was interrupted
after 2 h by ethanol addition. The polymers formed were
washed with ethanol and dried at 50 °C for 6 h.
Microanalysis (%C, %H, %N) were performed in a
Perkin–Elmer CHN 2400 equipment. Percentage of Ln
was determined by complexometric titration with EDTA
[8]. Percentage of Br was determined by argentimetric
titration [9]. Thermogravimetric (TG) and derived ther-
mogravimetric (DTG) curves were recorded on a Shi-
madzu Thermogravimetric Analyzer-TGA-50, heating
2–5 mg samples in a platinum crucible from 25 to 850 °C at
20 °C/min in air (50.0 ml/min) using 2–5 mg samples in a
platinum crucible. Infrared spectra were recorded on
FTIR-BOMEM MB-102, from 4000 to 200 cmÀ1, using
Nujol or Fluorolube mulls between cesium iodide win-
dows. 1H NMR spectra were recorded on a Bruker-DPX
300 MHz spectrometer, using acetone-d6 or chloroform-d
as solvents and TMS as internal reference. Differential
Scanning Calorimetry (DSC) measurements were per-
formedon a DSC 2910 TA Instruments. The samples were
heated from 25 to 200 °C at a heating rate of 10 °C/min.
The melting temperature values (Tm) and the heat of fu-
sion (DHf ) were taken from the second heating curve. The
degree of crystallinity was calculated from DHf , using the
equation wCH ¼ DHf  100=288 [10].
3. Results and discussion
Reaction of TbBr2Cp with pyrazole or triphenyl-
phosphine in toluene at room temperature yielded
amorphous solids, formulated TbBr2CpHPz and
TbBr2CpPPh3 according to elemental analysis. Removal
of THF from the starting compound was undertaken to
facilitate subsequent coordination of the softer N- or
P-donor ligands to Tb(III).
The monocyclopentadienyl derivatives are insoluble
in THF and present low solubility in acetone, toluene
and chloroform. Attempts to grow single crystals from
acetone or toluene solutions failed.
Thermal analysis showed that the compounds lose
weight gradually with increasing temperature from 25
°C, forming TbOBr at ca. 650 °C under air atmospheres
(Table 1). The molar weight of compounds were calcu-
lated from TG weight losses, and are in agreement with
the expected values based on analytical data presented
in experimental section.
2.1. Synthesis and characterization of compounds
Infrared spectra of the compounds (Table 2) exhibit
characteristic frequencies of cyclopentadienyl and pyr-
azole or triphenylphosphine ligands. Assignment of cy-
clopentadienyl vibrational modes indicated a r-centered
coordination to the lanthanide(III) ions under C5V local
symmetry with ionic character [11]. The characteristic
frequencies of pyrazole were assigned according to Orza
et al. [12] and King [13] indicating the coordination of
the neutral ligand. Triphenylphosphine ligand frequen-
cies were assigned according to Whiffen [14], Jensen and
Nielsen [15], and Deacon et al. [16]. Some vibrational
modes of triphenylphosphine are shifted by coordina-
tion of this ligand to metallic ions [14]. In the spectrum
of TbBr2CpPPh3, only one of these X-sensitive modes,
2.1.1. TbBr2Cp
THF was removed from the compound TbBr2Cp
ðTHFÞ3 (4 mmol) by evaporation under high vacuum at
40 °C for 24 h, yielding an amorphous orange solid (3.6
mmol). Yield: 90%. Calc. Anal. for: TbBr2Cp: C, 15.64;
H, 1.31; Tb, 41.40; BrÀ, 41.63. Found: C, 15.70; H, 1.27;
Tb, 41.78; BrÀ, 41.81.
2.1.2. TbBr2CpHPz and TbBr2CpPPh3
A solution of pyrazole (6 mmol) or triphenylphos-
phine (1 mmol) in 30 ml of toluene was added to a
suspension of cyclopentadienylterbium dibromide (1
mmol) in 50 ml of toluene. The resulting mixture was
stirred for 24 h at room temperature followed by evap-
oration under vacuum for 16 h at 30 °C to give the or-
ganolanthanide compounds TbBr2CpHPz (0:75 mmol)
and TbBr2CpPPh3 (0.8 mmol) as amorphous orange
solids. Yields: 75% for TbBr2CpHPz and 80% for TbBr2
CpPPh3. Calc. Anal. for: TbBr2CpHPz: C, 21.26; H,
2.01; N, 6.20; Tb, 35.16; BrÀ, 35.36. Found: C, 20.92; H,
2.14; N, 6.39; Tb, 35.34; BrÀ, 35.62; For: TbBr2CpPPh3:
C, 42.75; H, 3.12; Tb, 24.59; BrÀ, 24.73. Found: C,
42.37; H, 3.18; Tb, 24.21; BrÀ, 24.47.
mode t, was shifted to higher wave number (445 cmÀ1
)
when compared to free triphenylphosphine (432 cmÀ1),
indicating a probable coordination of PPh3 to Tb(III).
In the NMR spectra of these compounds, broad
signals were observed for Cp protons at 10.4 ppm
(TbBr2Cp), 7.0 ppm (TbBr2CpHPz) and 16.4 ppm
(TbBr2CpPPh3). Broadening of Cp signals may be re-
lated to the paramagnetic nature of Tb(III) [17]. Pyr-
azole protons of TbBr2CpHPz yielded sharp signals at
7.0 ppm (doublet, 2H) and 6.3 ppm (triplet, 1H), and a
broad signal at 12.0 ppm (N–H). Triphenylphosphine
protons in TbBr2CpPPh3 originated a multiplet of sharp
signals centered at 7.3 ppm.
2.2. Catalytic polymerization of ethylene
The polymerization experiments were carried out in a
The organolanthanide compounds TbBr2Cp,
TbBr2CpHPz and TbBr2CpPPh3 presented catalytic
€
Buchi autoclave at 70 °C, using 50 ml of toluene as
De Souza Maia, Alessandra
