A new type of doubly silylamido-bridged cyclopentadienyl group 4 metal complexes

Article abstract of DOI:10.1002/1521-3773(20010702)40:13<2495::AID-ANIE2495>3.0.CO;2-R

Doubly bridged di(silyl-η-amido)cyclopentadienyltitanium and -zirconium complexes and their related cations as the [(PhCH₂)B(C₆F₅)₃]^- salts have been isolated (see structure of the Ti derivative). The neutral benzylzirconium complex was a very efficient catalyst in the presence of methylaluminoxane for producing high molecular weight polyethylene and ethylene-1-hexene copolymers.

Full text of DOI:10.1002/1521-3773(20010702)40:13<2495::AID-ANIE2495>3.0.CO;2-R

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A New Type of Doubly Silylamido-Bridged
Cyclopentadienyl Group 4 Metal Complexes**
Â
Jesus Cano, Pascual Royo,* Maurizio Lanfranchi,
Maria Angela Pellinghelli, and Antonio Tiripicchio
Â
Dedicated to Professor Rafael Uson
on the occasion of his 75th birthday
The isolation of metal complexes containing the h1-amido-
silyl-h5-cyclopentadienyl ligand, which provides more acidic
metal centers with a more open coordination site than the
ansa-dicyclopentadienyl compounds, has proved particularly
useful.[1] These structural features are responsible for their
catalytic ability to copolymerize long-chain a-olefins.[2] Nu-
merous contributions in this field have benefited from the
research into the use of variously substituted ligands,[3] the
characterization of the active cationic species,[4] the develop-
ment of new industrial applications,[5] and the reactivity of the
metal-coordinated amidosilyl moiety.[6]
Scheme 1. Synthesis of neutral bridged h5-cyclopentadienyl mono- and
di(h-amidosilyl)titanium and -zirconium complexes and their cationic
species.
Few examples of doubly bridged h5-cyclopentadienyl-di(h1-
ligand) metal compounds have been reported.[7] We have now
extended our studies in this field by synthesizing new
substituted cyclopentadienyl ligands that can form more than
one amidosilyl bridge, that is di(h-amidosilyl)-h5-cyclopenta-
dienyl ligands, and characterizing and studying the reactivity
of their Group 4 metal complexes.
temperatures higher than 658C. The deprotonating capacity
of complex 5 facilitated the irreversible transformation of 2
into 3 by elimination of the NHMe2 resulting from that
transformation. A similar reaction of 1 with [Ti(CH2Ph)4]
gave the monosilylamido complex 6 as a red solid, which could
only be transformed into the disilylamido derivative 7 by
refluxing a solution of the compound in toluene.
The di(amidosilyl)cyclopentadiene C5H4[SiMe2(NHtBu)]2
[8]
All the new compounds were characterized by elemental
(1) was synthesized as a yellow oil from 1,1-(SiMe2Cl)2C5H4
1
analyses, and the H and 13C NMR spectra were consistent
and LiNHtBu in 12 h at room temperature using THF as
solvent. Selective deprotonation of the more acidic cyclo-
pentadiene proton and only one of the amino protons of 1 by
using [Zr(NMe2)4] afforded the monosilylamido derivative 2
as a light-brown oil (Scheme 1). A C6D6 solution of 2 was
heated to 1108C to give the disilylamido compound 3 with
evolution of NHMe2. However this reaction was reversed
when the mixture was cooled to room temperature, prevent-
ing the isolation of 3. Similar deprotonation of 1 by using the
tetrabenzyl compound [Zr(CH2Ph)4], gave a mixture of the
brown monosilylamido 4, identified by 1H NMR spectroscopy,
and the disilylamido derivative 5 at room temperature
(Scheme 1), while 5 was the unique reaction product at
(see Supporting Information) with the asymmetry of the
monosilylamido compounds 2, 4, and 6, and with the presence
of a plane of symmetry in the disilylamido compounds 3, 5,
and 7 (Scheme 1). The chemical shifts of the tBu tertiary
carbon atoms were observed between d ˆ 55.8 (3) and d ˆ 61.5
(6) for bridged, and between d ˆ 49.6 (2) and d ˆ 49.8 (6) for
unbridged amidosilyl groups; the Dd values[9] were between
20.2 and 27.2 for bridged and between 15.7 and 16.0 for
unbridged amidosilyl groups, respectively. Treatment of
solutions of 5 and 7 in toluene with one equivalent of
B(C6F5)3 gave the complexes 8 and 9, respectively (Scheme 1).
1
The H, 13C, and 19F NMR spectra of 8 and 9 in C6D6 were
consistent with their formulation as the salts of Cs-symmetric
base-free cations and the [(CH2Ph)B(C6F5)3] ion.[10, 11]
[*] Prof. Dr. P. Royo, J. Cano
Crystals of 9 suitable for a single-crystal X-ray structure
determination were grown by cooling a saturated solution of 9
in benzene. The structure of 9 (Figure 1) shows a titanium
cation with the centroid of the cyclopentadienyl ring and the
two amido-N atoms occupying three positions in a pseudo-
tetrahedral ligand arrangement, the fourth position being
occupied by the ªmeta-C H bondº or alternatively by a
ªmeta-C atomº of the phenyl ring of the benzylborate anion.
The h5-cyclopentadienyl di(h-amidosilyl) ligand shows a
strongly constrained geometry, which allows it to interact
with the metal as a tridentate ligand; the C1 and C3 atoms that
bear the amidosilyl arms are pyramidally distorted, as shown
by the sums of the bond angles (348.08 and 348.18, respec-
tively). The Ti N and the Ti CE1 (CE1 is the Cp centroid)
distances are similar to those observed in related neutral
amidosilylcyclopentadienyl compounds.[3d] The Ti C21 dis-
Â
Departamento de Química Inorganica
Â
Facultad de Ciencias, Universidad de Alcala
Campus Universitario, 28871 Alcala de Henares (Spain)
Â
Fax : (‡34)91-8854683
E-mail: pascual.royo@uah.es
Prof. Dr. M. Lanfranchi, Prof. Dr. M. A. Pellinghelli,
Prof. Dr. A. Tiripicchio
Dipartimento di Chimica Generale ed Inorganica
Chimica Analitica, Chimica Fisica
Á
Universita di Parma, Centro di Studio per la Strutturistica Diffratto-
metrica del CNR
Parco Area delle Scienze 17A, 43100 Parma (Italy)
Â
Ä
[**] We thank the Direccion General de Ensenanza Superior e Inves-
Â
tigacion Científica (DGESEIC) for financial support of this work
(Project PB97-0776). J.C. thanks the CAM for
Fellowship.
a Postgraduate
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
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added by syringe. The resulting yellow solution was warmed for 5 h to
658C. The solvent was removed under vacuum and the residue was
extracted into pentane (70 mL). After filtration and removal of the solvent,
complex 6 was isolated as a red solid (2.87 g, 5.2 mmol, 100%).
A similar reaction carried out under reflux gave complex 7 (5.93 g,
12.9 mmol, 100%) as a dark red solid.
A solution of the monobenzyl complex 7 (0.116 g, 0.25 mmol) in toluene
(20 mL) was treated with B(C6F5)3 (0.126 g, 0.25 mmol) at room temper-
ature and the mixture was stirred for 30 min and then cooled to 358C. The
solvent was filtered off from the resulting insoluble residues, which were
then dried under vacuum to give 9 (0.13 g, 60% yield) as an orange
crystalline solid. An appropriate monocrystal of 9 was separated for study
using X-ray diffraction methods.
1H NMR (300 MHz, C6D6, 208C, TMS) for 6: d ˆ 0.21, 0.27 (2s, 2  3H;
SiMe2NHtBu), 0.37, 0.38 (2s, 2 Â 3H; SiMe2NtBu), 0.72 (s, 1H; NHtBu) 1.07
(s, 9H; NHtBu), 1.44 (s, 9H; NtBu), 2.47, 2.55, 2.81, 2.97 (4d, J ˆ 10.5 Hz,
4 Â 1H; CH2Ph), 5.83, 6.14, 6.83 (3m, 3 Â 1H; C5H3), 6.87 ± 7.20 (m, 10H;
CH2Ph); 13C NMR (300 MHz, C6D6, 208C, TMS): d ˆ 0.6, 1.5 (SiMe2NH-
tBu), 2.4, 2.9 (SiMe2NtBu), 33.8(NHtBu), 34.3 (NtBu), 49.8(NHtBuipso), 61.5
(NtBuipso), 79.6, 83.7 (CH2Ph), 110.2, 122.8 (C5H3ipso), 122.1, 122.5, 123.0
(C5H3), 125.9 126.8, 126.8, 127.4, 128.5, 128.6, 128.7, 128.9, 129.8, 132.6
(C6H5), 149.6, 150.1 (C6H5ipso); elemental analysis for 6: calcd: C 62.68, H
8.68, N 5.76; found: C 62.58, H 8.75, N 6.08.
Figure 1. Molecular structure of 9 (the ellipsoids for the atoms are drawn
at 30% probability level). Selected interatomic distances [Š] and angles [8]:
Ti-CE1 1.997(5), Ti-N1 1.959(4), Ti-N2 1.946(5), Ti-C21 2.447(6), Ti-M1
2.33, Ti-H21 2.30; N1-Ti-N2 126.3(2), CE1-Ti-N1 106.7(2), CE1-Ti-N2
106.6(2), CE1-Ti-M1 129.5(3), N1-Ti-M1 95.0(3), N2-Ti-M1 95.0(3); CE1
and M1 are the centroid of the Cp ring and the midpoint of the C21-H
bond, respectively.
1H NMR (300 MHz, C6D6, 208C, TMS) for 7: d ˆ 0.39, 0.40 (2s, 2  6H;
SiMe2), 1.42 (s, 18H; NtBu), 2.61 (s, 2H; CH2Ph), 6.14 (d, 2H; C5H3), 6.40
(t, 1H; C5H3), 6.89 (m, 1H; C6H5), 7.00 (m, 2H; C6H5), 7.22 (m, 2H; C6H5);
13C NMR (300 MHz, C6D6, 208C, TMS):d ˆ 2.1, 2.2 (SiMe2), 35.6 (NtBu),
59.3 (NtBuipso), 69.6 (CH2Ph), 117.7 (C5H3ipso), 121.5, 126.3 (C5H3), 128.5,
130.3, 132.6 (C6H5), 152.4 (C6H5ipso); elemental analysis for 7: calcd: C 67.82,
H 8.71, N 4.81; found: C 67.36, H 8.75, N 5.07.
1H NMR (300 MHz, C6D6, 208C, TMS) for 9: d ˆ 0.19, 0.38 (2s, 2  6H;
SiMe2), 1.12 (s, 18H; NtBu), 3.49 (s, 2H; BCH2), 5.03 (m, 1H; C5H3), 5.86
(m, 2H; C5H3), 6.21 ± 7.10 (m, 5H; C6H5); 13C NMR (300 MHz, C6D6, 208C,
TMS): d ˆ 0.6, 1.4 (SiMe2), 34.6 (NtBu), 59.3 (NtBuipso), 122.1, 126.2 (C5H3),
126.1 (C5H3ipso), 128.3, 128.7, 132.9 (C6H5), 135.1, 140.1, 145.8, 150.9 (C6F5);
19F NMR (300 MHz, C6D6, 208C, CCl3F): d ˆ 132.1 (m, 2F; o-C6F5), 163.6
(m, 1F; p-C6F5), 167.2 (m, 2F; m-C6F5).
tance (Ti C21 2.447(6) Š) is about 0.3 Š longer than that
normally expected for covalent Ti C s bonds. The interaction
with the electron pair in the C H bond is consistent with the
distances observed from Ti to H21 and to the middle of the
C H bond (M1) (Ti H21 2.30, Ti M1 2.33 Š). Metal ± h6-
phenyl,[11, 12] metal ± h5-phenyl,[13] and metal ± h3-phenyl[14] in-
teractions for related benzylborate anions have been reported
but, as far as we are aware, there have been no reports of this
type of interaction in which a single meta-Cphenyl H bond of
the benzylborate anion interacts with the empty hybrid metal
orbital of a typical ªthree leg piano stoolº coordination.
Furthermore, the alternative interaction with the p orbital of
the meta-Cphenyl atom similar to that found for h1-benzene-
coordinated silver compounds[15] cannot be ignored.
Crystal data of 9 (C42H40BF15N2Si2Ti, Mr ˆ 972.65): Tˆ 173(2) K, l ˆ
Å
1.54184 Š; triclinic, space group P1, unit cell dimensions, a ˆ 11.564(6),
b ˆ 13.531(6), c ˆ 14.020(7) Š, a ˆ 78.32(2), b ˆ 87.64(2), g ˆ 87.01(2)8, Vˆ
2144.3(18) Š3; Z ˆ 2; 1calcd ˆ 1.506 gcm 3; m ˆ 3.124 mm 1, F(000) ˆ 992,
crystal size 0.42 Â 0.38 Â 0.25 mm, q range 3.22 ± 69.998. Reflections col-
lected and unique 8113, observed 4019 [I > 2s(I)]. Full-matrix least-
squares refinement on F 2,[17] 578 parameters, hydrogen atoms introduced in
the geometrically calculated positions and refined riding on the parent
atoms, goodness-of-fit on F 2 0.877. Final R indices [I > 2s(I)], R1 ˆ 0.0665,
wR2 ˆ 0.1634, R indices (all data) R1 ˆ 0.1349, wR2 ˆ 0.2051. Crystallo-
graphic data (excluding structure factors) for the structure reported in this
paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-152472. Copies of the data
can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB21EZ, UK (fax: (‡44)1223-336-033; e-mail: deposit@ccdc.
cam.ac.uk).
Compound 8 polymerizes ethylene at room temperature
and pressure[16] despite being free of alkyl ligands. Immediate
polymerization was observed when a teflon-valved Schlenk
tube containing 8 was evacuated and filled with ethylene. The
polymerization activity of compound 5 was measured by using
a solution containing methylaluminoxane (MAO; 19.3 mmol)
and 5 (4.2 mmol) in n-hexane (600 mL) at 4 atm ethylene and
708C. The observed activity after 15 min was 7.4 Â
1
105 gPE(molZr) 1 h 1 atm . The polyethylene (PE) pro-
duced showed a very high molecular weight (Mw ˆ 5.4  105)
with a polydispersity index Mw/Mn of 1.9. It was insoluble in
1,2,4-trichlorobenzene preventing its characterization by
NMR spectroscopy. Compound 5 was also an active catalyst
for the copolymerization of ethylene and 1-hexene. When the
same experiment was carried out under the same conditions
but with the prior addition of 1-hexene (10 mL), the resulting
polymer (Mw ˆ 4.1  105 and Mw/Mn ˆ 2.2) after 30 min con-
tained 0.7 mol% of 1-hexene and the catalytic activity was
Received: January 22, 2001 [Z16465]
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3.5 Â 105 gpolymer(molZr) 1 h 1 atm .
Experimental Section
Full experimental details, analytical data and NMR assignments for all
compounds are provided as Supporting Information.
Representative procedure: A solution of [Ti(CH2Ph)4] (2.14 g, 5.2 mmol) in
toluene (70 mL) was cooled to 08C, and an equimolar amount of 1 was
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Dedicated to Professor Michael P. Cava
on the occasion of his 75th birthday
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‡
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[*] Prof. J. Becher, Dr. T. Brimert, M. Sc. J. O. Jeppesen,
Dr. J. Z. Pedersen, Prof. R. Zubarev
Department of Chemistry
Odense University (University of Southern Denmark)
Campusvej 55, 5230, Odense M (Denmark)
Fax : (‡45)66-15-87-80
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E-mail: jbe@chem.sdu.dk
Â
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Nano-Science Center, Department of Chemistry
University of Copenhagen
Universitetsparken 5, 2100, Copenhagen é (Denmark)
Dr. T. R. Jensen, Dr. K. Kjaer
Condensed Matter Physics and Chemistry Department
Risù National Laboratory
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Building 108, Post Office Box 49, 4000 Roskilde (Denmark)
Dr. E. Levillain
Â
Â
Â
Ingenierie Moleculaire et Materiaux Organiques
Â
CNRS UMR 6501, Universite d'Angers, 49045 Angers (France)
[**] We gratefully acknowledge financial support from Carlsbergfondet
and Bengt Lundquists Minnesfond for a post-doctoral position to
T. B., the University of Odense for a Ph.D. scholarship to J. O. J. and
the French Embassy Copenhagen for a travel grant to J. B. We thank
HASYLAB at DESY, Hamburg for beam time at beam line BW1 and
DANSYNC for financial support. The gift of Jan Skov Petersonꢁs
FORTRAN program LSQREFL is gratefully acknowledged. Finally,
we thank Prof. K. S. Murray, University of Monash, Australia for
helpful discussions.
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
Angew. Chem. Int. Ed. 2001, 40, No. 13
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