Synthesis and structure of the first boron-bridged constrained geometry complexes

Article abstract of DOI:10.1039/b000380h

In the course of investigations on new Ziegler-Natta-analogous catalyst systems, the first 'constrained geometry' complexes of titanium with a bridging boron atom have been conveniently obtained by a high yield synthesis and were structurally characterized.

Full text of DOI:10.1039/b000380h

Synthesis and structure of the first boron-bridged constrained geometry
complexes†
Holger Braunschweig,* Carsten von Koblinski and Ulli Englert
Institut fu¨r Anorganische Chemie der Technischen Hochschule, RWTH Aachen, Templergraben 55, D-52056 Aachen,
Germany. E-mail: holger.braunschweig@ac.rwth.aachen.de
Received (in Basel, Switzerland) 21st December 1999, Accepted 3rd May 2000
Published on the Web 25th May 2000
In the course of investigations on new Ziegler–Natta-
analogous catalyst systems, the first ‘constrained geometry’
complexes of titanium with a bridging boron atom have been
conveniently obtained by a high yield synthesis and were
structurally characterized.
Since 19901 ‘constrained geometry’ complexes as catalysts for
olefin polymerization have attracted considerable interest, since
they show some distinct advantages in comparison to metal-
locene-based Ziegler–Natta type catalysts,2 such as formation
of copolymers and an increased stability towards MAO even
under thermally harsh reaction conditions.1d‡ Very recently it
4
was shown by us3 and others that [1]borametallocenophanes
of group 4 elements are easily accessible, highly active catalysts
for the polymerization of ethene and propene.
In order to combine the properties of the small and Lewis
acidic bridging boron atom with the advantages of constrained
5
1
geometry catalysts we prepared the compounds [{h +h -
C5H4B(NPri2)NPh}TiX2] (X = NMe2, 1; X = Cl, 2).
Similarly to the synthesis of the corresponding [1]bora-
Fig. 1 Molecular structure of 1. Selected distances (Å) and angles (°): B–
N(1) 1.428(3), B–N(2) 1.409(3), Ti–N(1) 2.020(2), Ti–N(3) 1.9045(19),
Ti–N(4) 1.913(2), N(3)–Ti–N(4) 103.44(9), N(1)–B–N(2) 131.0(2), C(1)–
B–N(1) 103.57(18). Thermal ellipsoids are drawn at the 30% probability
level.
5
titanocenophanes [{(h -C5H4)2BNR2}Ti(NMe2)2],3a complex
1 is obtained in a convenient three-step synthesis according to
Scheme 1 as an orange, crystalline material in 80% yield.
Subsequent treatment of 1 with an excess of Me3SiCl gave the
corresponding dichloro complex 2 in almost quantitative yield
as a yellow solid. The structures of 1 and 2 in solution were
respectively, while the Ti–N1 distance is markedly longer at
2.020(2) Å.
1
derived from the multinuclear NMR data.§ In the H NMR
Preliminary polymerisation experiments showed compound
2 to be an effective catalyst for the polymerisation of ethene in
the presence of MAO. In a typical experiment polyethylene with
a molecular weight of ca. 470 000 was obtained with an activity
of 500 kg polymer (mol cat h)21. As to be expected,5 complex
1 showed a considerably lower activity towards the polymer-
isation of olefins. Further investigations of the catalytic
properties of compound 2 and related complexes for ethene/
styrene-copolymerisation are in progress.
spectra both compounds show the expected two pseudo-triplets
for the cyclopentadienlyl protons forming an AAABBA spin
system. Double sets of signals for the isopropyl groups in the 1H
and 13C NMR spectra indicate a hindered rotation with respect
to the boron–nitrogen double bond in 1 and 2. The 11B NMR
spectra show signals at d 27.8 (1) and 28.4 (2), in the expected
range for aryl(diamino)boranes.
Suitable single crystals of 1 (Fig. 1) for an X-ray structural
analysis¶ were obtained from hexane at 230 °C. The compound
This work was supported by the Deutsche Forschungsge-
meinschaft, the Fonds der Chemischen Industrie, and the BASF
AG Ludwigshafen.
¯
crystallises in the triclinic space group P1 and the molecule
adopts C1 symmetry in the crystal. Both atoms B and N2 are
trigonal planar, and the planes C20–N2–C23 and N1–B–C1 are
almost coplanar with a dihedral angle of 2.2(3)°. The B–N
distances of 1.428(3) Å (B–N1) and 1.409(3) Å (B–N2) are in
the expected range for B–N double bonds, and the Ti–N
distances were found to be ca. 1.91 Å for N3 and N4,
Notes and references
‡ For a recent review on non-metallocene catalysts see ref. 1(f).
§ Spectroscopic data: 1: 1H NMR (499.658 MHz, CD2Cl2): d 0.90 (br, 6H,
CHCH3), 1.45 (br, 6H, CHCH3), 2.97 (s, 12H, NMe2), 3.31 (br, 2H,
CHCH3), 5.94 (m, 2H, C5H4), 6.44 (m, 2H, C5H4), 6.73 (m, 2H, C6H5), 6.83
(m, 1H, C6H5), 7.14 (m, 2H, C6H5). 11B NMR (160.310 MHz, CD2Cl2): d
27.76. 13C NMR (125.639 MHz, CD2Cl2): d 21.36 (br), 27.01 (br), 44.62
(br), 46.11 (br), 47.90 (NMe2), 120.95 (C5H4), 124.00 (C5H4), 115.81,
119.99, 128.16, 155.48. MS (EI) (m/z, %): 402 (M+, 45), 387 (M+ 2 Me, 5),
358 (M+ 2 NMe2, 65), 314 (M+ 2 2NMe2, 100), 93 (C6H5NH2+, 95), 64
(C5H4+, 45). Correct elemental analysis.
2: 1H NMR (499.658 MHz. CD2Cl2): d 0.90 (d, 6H, 3J 6.71 Hz, CHCH3),
1.54 (d, 6H, 3J 6.71 Hz, CHCH3), 3.14 (m, 1H, 3J 6.71 Hz, CHCH3), 3.41
(m, 1H, 3J 6.71 Hz, CHCH3), 6.44 (m, 2H, C5H4), 7.08 (m, 2H, C5H4), 6.91
(m, 2H, C6H5), 7.14 (m, 1H, C6H5), 7.38 (m 2H, C6H5). 11B NMR (160.310
MHz, CD2Cl2): d 28.29. 13C NMR (125.639 MHz, CD2Cl2): d 21.40, 27.72,
45.20, 47.28, 122.52 (C5H4), 125.71 (C5H4), 124.32, 127.21, 129.62,
Scheme 1 Reagents and conditions: i, hexane, 0 °C, Na(C5H5); ii, toluene,
0 to 25 °C, Li(NPhH); iii, toluene, 278 to 40 °C, [Ti(NMe2)4], 78%; iv,
hexane, 0 °C, Me3SiCl, 98%.
† Electronic supplementary information (ESI) available: experimental and
polymerisation studies. See http://www.rsc.org/suppdata/cc/b0/b000380h/
152.39. MS (EI) (m/z, %): 384 (M+, 15), 369 (M+ 2 Me, 30), 348 (M+
2
DOI: 10.1039/b000380h
Chem. Commun., 2000, 1049–1050
This journal is © The Royal Society of Chemistry 2000
1049

Cl, 50), 333 (M+ 2 Cl 2 Me, 20), 318 (M+ 2 Cl 2 2Me, 20], 93
(C6H5NH2+, 70), 64 (C5H4+, 25). Correct elemental analysis.
1649; (c) T. Eberle, T. P. Spaniol and J. Okuda, Eur. J. Inorg. Chem.,
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¶ X-Ray structure determination of 1: ENRAF-Nonius CAD4 diffract-
ometer, Mo-Ka radiation, incident beam graphite monochromator (l =
0.71073 Å), T = 213 K, orange platelet of approximate dimensions 0.70 3
0.60 3 0.15 mm directly mounted in dry air flux (Whatman 75-52).
¯
2 W. Kaminski, J. Chem. Soc., Dalton Trans., 1998, 1413 and references
therein.
Crystal data: triclinic, space group P1, a = 9.464(6), b = 9.754(4), c =
13.596 Å, a = 101.94(2), b = 102.32(4), g = 103.37(4)°, V = 1149 Å3,
= 2, Dc = =
1.17 g cm23, m 3.8 cm21. 4351 reflections, 4068
3 (a) H. Braunschweig, C. von Koblinski and R. Wang, Eur. J. Inorg.
Chem., 1999, 69; (b) H. Braunschweig, C. von Koblinski and M. O.
Kristen, Patentschrift, O.Z.0050/49643, 1998, submitted; H. Braunsch-
weig, C. von Koblinski, M. Mamuti, U. Englert and R. Wang, Eur. J.
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4 A. J. Ashe, III, X. Fang and J. W. Kampf, Organometallics, 1999, 18,
2288; M. T. Reetz, M. Willuhn, C. Psiorz and R. Goddard, Chem.
Commun., 1999, 1105.
Z
independent, qmax = 26°, solution with direct methods (SHELXS97),6
refinement on F2 (SHELXL97),8 252 variables, wR2 (all data) = 0.1162, R1
[for 3347 data with I > 2s(I)] = 0.0444, max./min. electron density from
final difference Fourier map, 0.437 and 20.200 e Å23
.
CCDC 182/1628. See http://www.rsc.org/suppdata/cc/b0/b000380h/ for
crystallographic files in .cif format.
5 Y. Chen and T. J. Marks, Organometallics, 1997, 16, 3649.
6 G. M. Sheldrick, SHELXL97: Program for Crystal Structure Determina-
tion, University of Go¨ttingen, Germany, 1997.
1 (a) P. J. Shapiro, E. E. Bunel, W. P. Schaefer and J. E. Bercaw,
Organometallics, 1990, 9, 867; (b) J. Okuda, Chem. Ber., 1990, 123,
1050
Chem. Commun., 2000, 1049–1050