Notes
Organometallics, Vol. 26, No. 4, 2007 1115
recrystallization from toluene. Yield: 2.47 g (74%). NMR
spectroscopic data were identical to those of an authentic sample.3a
tion of HNMe2 is not observed in the case of the analogous
reaction of 1b most likely reflects a stereoelectronic effect due
to the bulky arylamido ligands present in the product. Owing
to the perpendicular orientation of the aryl ring planes with
respect to the bonding plane of the N atoms of the chelate ring
(vide supra), each aryl π-system is decoupled from the respective
p-type nitrogen lone pair. Just the opposite is the case for the
less bulky phenylamido chelate 4, whose phenyl rings are
positioned in the bonding plane of the N atoms of the chelate
ring, leading to perfect conjugation of each phenyl π-system
with the respective nitrogen lone pair.3b Consequently, the
zirconium atom of 4 competes with the phenyl rings for nitrogen
lone pair electron density. This competition is absent in 3,
leading to a higher π-loading of its zirconium atom.
We have utilized 2-4 as precatalysts in the polymerization
of ethylene. According to results of a computational study by
Ziegler and co-workers, the π-loading of the metal center
described above is expected to be beneficial for R-olefin
polymerization.17 The activity was poor when MAO was used
as activator for the tetraamides (Zr/Al 1:500, 10 bar ethylene,
70 °C; 3 0.8 g/mmol‚h‚bar, 4 3.3 g/mmol‚h‚bar). In the case of
the dibenzyl derivative 2, the use of B(C6F5)3 as cocatalyst did
not lead to any noticeable activity. This is compatible with
results reported by Shafir and Arnold with B(C6F5)3-activated
[(PhCH2)2Zr{Fe[C5H4(N-2,4,6-Me3-C6H2)]2}].4 With [Ph3C]-
[B(C6F5)4] as cocatalyst a rather low activity was observed for
2 in chlorobenzene solvent (1 bar ethylene, 40 °C; 4.0 g/mmol‚
h‚bar). Shafir and Arnold have reported an ethylene polymer-
ization activity of 102 g/mmol‚h‚bar for [Ph3C][B(C6F5)4]-
activated [(PhCH2)2Zr{Fe[C5H4(NSiMe3)]2}] under very similar
reaction conditions.18 The reasons for this large difference in
polymerization activity remain unclear and are unexpected,
especially in view of the work performed by Ziegler’s
group.
2. 1b (766 mg, 1.24 mmol), Zr(CH2Ph)4 (630 mg, 1.39 mmol),
and a small amount of sodium tert-butoxide4 (ca. 5 mg, ca. 0.05
mmol) were placed in a thick-walled Rotaflo ampule. Toluene (15
mL) was added and the mixture stirred for 14 days. Volatile
components were removed in vacuo, and n-hexane (5 mL) was
added. Storing of the mixture at -40 °C afforded the product as a
yellow, microcrystalline solid, which was isolated by cannula
filtration. Yield: 604 mg (55%). 1H NMR (C6D6): δ 1.28 (d, J )
6.8 Hz, 24 H, CHMe2); 1.48 (d, J ) 6.4 Hz, 12 H, CHMe2); 2.43
(s, 4 H, CH2); 2.84 (sept, J ) 6.4 Hz, 2 H, CHMe2); 3.75 (s, 4 H,
cyclopentadienyl); 3.84 (sept, J ) 6.8 Hz, 4 H, CHMe2); 4.00 (s,
4 H, cyclopentadienyl); 6.79 (d, J ) 7.3 Hz, 4 H, Ph); 6.88 (t, J )
6.8 Hz, 2 H, Ph); 7.10 (“t”, apparent J ) 7.3 Hz, 4 H, Ph); 7.21 (s,
4 H, 2,4,6-iPr-C6H2). 13C{1H} NMR (C6D6): δ 25.0, 26.0, 27.5
(CHMe2); 29.8, 35.5 (CHMe2); 70.0, 70.1 (cyclopentadienyl); 73.0
(CH2); 94.0 (cyclopentadienyl); 123.0, 126.5, 127.9, 129.9, 145.2,
146.8, 147.1, 147.8 (Ph and 2,4,6-iPr-C6H2). Anal. Calcd for
C54H68N2FeZr (892.2): C, 72.69; H, 7.68; N, 3.14. Found: C, 72.30;
H, 7.67; N, 3.09.
3. 1b (621 mg, 1.00 mmol) and Zr(NMe2)4 (268 mg, 1.00 mmol)
were placed in a thick-walled Rotaflo ampule. Toluene (15 mL)
was added and the mixture stirred for 21 days. The volume of the
solution was reduced to ca. 5 mL in vacuo. Crystallization at -40
°C afforded the product as a yellow, microcrystalline solid, which
was isolated by cannula filtration. Yield: 679 mg (85%). 1H NMR
(C6D6): δ 1.23, 1.37 (2 d, J ) 6.8 Hz, 2 × 12 H, CHMe2); 1.43
(d, J ) 6.6 Hz, 12 H, CHMe2); 2.83 (sept, J ) 6.6 Hz, 2 H,
CHMe2); 2.84 (s, 12 H, NMe2); 3.91 (s, 4 H, cyclopentadienyl);
3.96 (sept, J ) 6.8 Hz, 4 H, CHMe2); 4.29 (s, 4 H, cyclopentadi-
enyl); 7.18 (s, 4 H, aryl). 13C{1H} NMR (C6D6): δ 25.1, 26.0, 26.6
(CHMe2); 29.1, 35.1 (CHMe2); 43.9 (NMe2); 68.8, 70.0, 99.8
(cyclopentadienyl); 122.6, 146.0, 146.3, 147.2 (aryl). Anal. Calcd
for C44H66N4FeZr (798.1): C, 66.22; H, 8.34; N, 7.02. Found: C,
66.07; H, 8.30; N, 6.88.
Experimental Section
All reactions were performed in an inert atmosphere (dinitrogen)
by using standard Schlenk techniques or a conventional glovebox.
1,1′-Diaminoferrocene was prepared according to a published
procedure.15 Solvents and reagents were procured from standard
commercial sources. NMR spectra were recorded with a Varian
Polymerization of Ethene with 3 and 4 as Precatalyst. An
autoclave was charged with n-heptane (400 mL) and heated to 70
°C. The precatalyst (3 20 mg; 4 15 mg) was added, followed by
MAO (30% in toluene, 2.5 mL). The autoclave was pressurized
with ethene (10 bar). After 60 min the reaction was quenched and
the polymer precipitated by addition of a mixture of methanol (300
mL) and concentrated hydrochloric acid (10 mL). The polymer was
filtered off, washed with methanol (3 × 50 mL), and dried in vacuo
at 80 °C.
1
Unity INOVA 500 spectrometer operating at 500.13 MHz for H.
Elemental analyses were performed by the microanalytical labora-
tory of the University of Halle and by Mikroanalytisches Labora-
torium H. Kolbe (Mu¨lheim an der Ruhr).
Improved Synthesis of 1a. This compound was prepared in
analogy with 1b.3a Pd2(dba)3 (0.42 g, 0.45 mmol) and dppf (0.42
g, 0.75 mmol) were placed in a thick-walled Rotaflo ampule.
Toluene (50 mL) was added and the resulting red solution stirred
for 5 min. Sodium tert-butoxide (1.76 g, 18.3 mmol) and bro-
mobenzene (2.87 g, 18.3 mmol) were added, followed after 10 min
by 1,1′-diaminoferrocene (1.95 g, 9.15 mmol) in THF (100 mL).
The mixture was stirred at 90 °C for 70 h. It was subsequently
allowed to cool to room temperature, poured into degassed water
(300 mL), and extracted with diethyl ether (5 × 100 mL). The
combined organic layers were dried with sodium sulfate. Volatile
components were removed in vacuo. The solid residue was extracted
with a mixture of diethyl ether and n-hexane (2:3, 100 mL) and
the extract filtered through a pad of Florisil (ca. 5 cm). The volume
of the filtrate was reduced to ca. 20 mL, affording the crude product
as a light orange, microcrystalline solid, which was purified by
Polymerization of Ethene with 2 as Precatalyst. A two-necked
flask was charged with 2 (40 mg, 50 µmol) and [Ph3C][B(C6F5)4]
(46 mg, 50 µmol). Chlorobenzene (5 mL) was added and the
mixture stirred for 5 min. A stream of ethene was passed through
the stirred solution for 60 min. The mixture was subsequently
purged with argon. The polymer was precipitated by addition of a
mixture of methanol (30 mL) and concentrated hydrochloric acid
(1 mL). The polymer was filtered off, washed with methanol (3 ×
20 mL), and dried in vacuo at 80 °C.
Acknowledgment. This work was supported in part by the
Fonds der Chemischen Industrie. We thank Umicore AG & Co.
KG (Hanau, Germany) for a generous gift of palladium
compounds.
(16) Lee, C. H.; La, Y.-H.; Park, J. W. Organometallics 2000, 19, 344-
351.
Supporting Information Available: CIF files for the structures
of 1a, 1b, 2, and 3. This material is available free of charge via the
(17) (a) Margl, P.; Deng, L.; Ziegler, T. J. Am. Chem. Soc. 1999, 121,
154-162. (b) Margl, P.; Deng, L.; Ziegler, T. J. Am. Chem. Soc. 1998,
120, 5517-5525. (c) Margl, P.; Deng, L.; Ziegler, T. Organometallics 1998,
17, 933-946.
(18) Shafir, A.; Arnold, J. Organometallics 2003, 22, 567-575.
OM061063E
Siemeling, Ulrich
