The synthesis, structure and catalytic activity of mono(salicylaldiminato) titanium complexes

Article abstract of DOI:10.1039/b307793b

The synthesis of mono(salicylaldiminato) complexes of titanium was reported. The catalytic activity of the compounds to the polymerization of ethene was studied. The complexes were shown to give good productivities for ethene polymerization when activated by methylaluminoxane. The results were found to comparable with those obtained for cyclopentadienyl salicylaldiminato titanium complexes.

Full text of DOI:10.1039/b307793b

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The synthesis, structure and catalytic activity of
mono(salicylaldiminato) titanium complexes
Dale A. Pennington, David L. Hughes, Manfred Bochmann* and Simon J. Lancaster*
Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy,
University of East Anglia, Norwich, UK NR4 7TJ. E-mail: S.Lancaster@uea.ac.uk;
Fax: 44 1603 592009; Tel: 44 1603 592009
Received 9th July 2003, Accepted 8th August 2003
First published as an Advance Article on the web 18th August 2003
Reaction between 3-But-2-(OSiMe )C H CH᎐N(2,6-R C -
The X-ray crystal structure of 2a (Fig. 1) confirmed the
᎐
3
6
3
2
6
H3) (where R ؍ H (1a) or Pri (1b)) and TiCl4(THF)2 affords
expected essentially octahedral coordination geometry.‡ The
three chloride ligands are meridonally arranged. The two O
ligating atoms are mutually trans; in this respect the geometry is
similar to the bis(salicylaldiminato) titanium complex {3-But-
the octahedral complexes Ti{3-But-2-(O)C H CH᎐N(2,6-
᎐
6
3
R2C6H3)}Cl3(THF) while in the absence of THF 1b reacts
with TiCl4 to give the binuclear complex [Ti{3-But-2-(O)-
C H CH᎐N(2,6-Pri C H )}Cl(ꢀ–Cl) TiCl ]; the complexes
2-(O)C H CH᎐NPh} TiCl (O–Ti–O = 171.6Њ).5 The bond
᎐
᎐
6
3
2
6
3
3
3
6
3
2
2
give good productivities for ethene polymerisation when
activated with MAO.
lengths in the salicylaldiminato ligand and to the chloride
ligands are similar to those observed in {3-But-2-(O)C H CH᎐
᎐
6
3
NPh}2TiCl2 5andCp{3-But-2-(O)C H CH᎐N(2,4,6-Me C H )}-
᎐
6
3
3
6
2
TiCl2.4
Transition metal complexes of the monoanionic bidentate N, O
chelate salicylaldiminato (iminophenolato) ligands have
attracted considerable attention since the discovery of highly
active,1 and living2 bis(salicylaldiminato) group 4 and neutral
mono(salicylaldiminato) nickel3 catalysts for the polymeris-
ation of ethene. Following our recent report on the synthesis of
salicylaldiminato cyclopentadienyl complexes of titanium and
zirconium,4 we report here the synthesis of mono(salicyl-
aldiminato) complexes of titanium and preliminary results for
their application in the polymerisation of ethene.
Bis(salicylaldiminato) complexes of titanium are normally
prepared through reaction of two equivalents of the depro-
tonated iminophenol with TiCl4 in tetrahydrofuran.1,2 This
approach is not suitable for the preparation of mono(salicyl-
aldiminato) complexes; for example the reaction between equi-
molar quantities of even the bulky Li{3-But-2-(O)C H CH᎐
᎐
6
3
Fig. 1 Structure of 2a with thermal ellipsoids at 50% probability. H
atoms are omitted for clarity. Selected bond lengths (Å) and angles (Њ):
Ti–Cl(4) 2.281(2), Ti–Cl(5) 2.342(2), Ti–Cl(6) 2.327(2), Ti–N(2)
2.240(6), Ti–O(1) 1.791(5), Ti–O(3) 2.146(5), C(20)–N(2) 1.296(8),
C(11)–O(1) 1.371(7); C(11)–O(1)–Ti 146.1(5), C(20)–N(2)–Ti 123.0(5),
N(2)–Ti–Cl(4) 176.72(18), O(1)–Ti–O(3) 171.76(19), Cl(5)–Ti–Cl(6)
167.17(9).
N(2,6-Pri2C6H3)} and TiCl4 led only to an intractable mixture
of products.
The deprotonation and subsequent reaction with Me3SiCl of
the imino-phenols gave the silylated ligands 3-But-2-(OSi-
Me )C H CH᎐NR (where R = C H (1a) or 2,6-Pri C H (1b)).
᎐
3
6
3
6
5
2
6
3
These react selectively with TiCl4(THF)2 in dichloromethane
to give the six-coordinate mono(salicylaldiminato) titanium
The tetrahydrofuran-free reaction between 1b and TiCl4 in
hexanes led to the slow precipitation of a dark red solid (3b).
The same product was obtained in good yield after an overnight
reflux in toluene (Scheme 1). 3b was identified as a salicyl-
aldiminato complex by 1H NMR. However, the elemental
analysis afforded a N:Cl ratio of 1:7 and was consistent with the
composition LTi2Cl7. 3b does not react with a second equiv-
alent of 1b even after refluxing for two days in toluene solution.
3b reacts readily with THF to give 2b and TiCl4(THF)2. The
elemental analysis of the reaction product between 1a and
TiCl4 suggests a dinuclear complex analogous to 3b.
complexes Ti{3-But-2-(O)C H CH᎐NR}Cl (THF) (2a and 2b)
᎐
6
3
3
(Scheme 1).†
The crystal structure of 3b (Fig. 2) establishes that the com-
plex is binuclear, with three bridging Cl ligands.‡ The two
titanium atoms are six-coordinate with octahedral geometries.
One metal centre is bonded to six chloride ligands, the other to
four chlorides and the bidentate salicylaldiminato ligand. The
bonding of the salicylaldiminato ligand is unremarkable, and
the bond lengths are very similar to those observed for 2a.
There are few structurally characterised precedents for com-
pounds of type 3b with a titanium centre surrounded only by an
octahedron of chloride ligands. The neutral tetranuclear com-
plex {Cl3Ti(µ-Cl)3Ti(NPPh3)}2(µ-Cl)2 contains titanium with a
similar octahedral chloride ligand coordination environment to
3b, the terminal Ti–Cl bond lengths are similar (2.189–2.213)
but the bridging Ti–Cl bond lengths cover a greater range
Scheme 1 Reagents and conditions: i, dichloromethane, TiCl4(THF)2,
room temperature; ii, toluene, TiCl4, overnight reflux; iii, THF
D a l t o n T r a n s . , 2 0 0 3 , 3 4 8 0 – 3 4 8 2
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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Table 1 Ethene polymerisation resultsa
Run
Complex/µmol
MAO/mmol
T/ЊC
t/min
Polymer yield/g
Productivityb
1
2
3
4
5
6
7
8
9
10
11
12
13
2a (6.3)
2a (6.3)
2a (6.3)
2b (6.0)
2b (6.0)
2b (6.0)
3b (6.0)
3b (6.0)
3b (6.0)
TiCl4 (6.0)
3b (6.0)c
3b (6.0)c
3b (6.0)c
6.3
6.3
6.3
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
0
20
60
0
20
60
0
20
60
20
0
20
60
5
5
5
0.121
0.158
0.233
0.107
0.168
0.074
0.163
0.366
0.179
0.119
0.265
0.412
0.184
2.3
3.0
4.4
0.3
0.5
0.2
1.6
3.7
1.8
0.3
2.6
4.1
1.8
35
35
35
10
10
10
35
10
10
10
a In 50 cm3 toluene, 1 bar ethene pressure. b In 105 g PE {(mol complex) h bar}Ϫ1 c 12.0 µmol THF.
.
Notes and references
† Synthesis and spectroscopic data: 2a: A solution of 3-But-2-(OSi-
Me3)C6H3CH᎐NC6H5 (1.12 g, 3.45 mmol) in dichloromethane (20 cm3)
᎐
was added to TiCl4(THF)2 (1.095 g, 3.44 mmol) in dichloromethane
(20 cm3) at Ϫ78 ЊC. The reaction was stirred for 4 h while being allowed
to warm slowly to room temperature, giving a dark red solution. Purifi-
cation by recrystallisation from dichloromethane/light petroleum at
room temperature gave the title compound as fine red needles. δ 1H (300
MHz, CDCl3, 20 ЊC) 8.17 (s, 1H, CH᎐N), 7.15–7.69 (m, 8H, Ar), 4.24
᎐
(m, 4H, THF), 1.72, (m, 4H, THF), 1.62 (s, 9H, t-Bu). δ 13C (75 MHz,
CDCl3, 20 ЊC) 134.5, 133.9, 129.2, 128.3, 128.0, 125.1, 124.4, 30.1, 25.7.
Anal. found: C, 51.49; H, 5.38; N, 2.77; Cl, 22.60. Requires: C, 52.69; H,
5.47; N, 2.93; Cl, 22.22.
2b: Following a similar procedure to 2a 3-But-2-(OSiMe3)C6H3-
CH᎐N(2,6-Pri2C6H3) (1b) (1.36 g, 3.44 mmol) reacted with TiCl4 (0.38
᎐
cm3, 3.44 mmol) in dichloromethane (40 cm3) to give a dark red solu-
tion. The solvent was concentrated and cooled to Ϫ25 ЊC to precipitate
a red/brown powder. δ 1H (300 MHz, CDCl3, 20 ЊC) 8.25 (s, 1H,
CH=N), 6.75–7.47 (m, 6H, Ar), 4.20 (m, 4H, THF), 3.70–3.75 (m, 2H,
CH(Me)2), 1.69 (s, 9H, t-Bu), 1.45 (d, 6H, J 6.68, CH(Me)2), 1.35 (m,
4H, THF), 0.99 (d, 6H, J 6.82, CH(Me)2). δ 13C (75 MHz, CDCl3,
20 ЊC) 169.9, 142.0, 138.4, 135.1, 133.9, 128.2, 124.4, 124.3, 35.7, 30.3,
28.5, 26.4, 25.8, 23.4. Anal. found: C, 57.03; H, 6.79; N, 2.26; Cl, 19.17.
Requires: C, 57.62; H, 6.81; N, 2.49; Cl, 18.90.
Fig. 2 Structure of 3b with thermal ellipsoids at 50% probability. H
atoms are omitted for clarity. Selected bond lengths (Å) and angles (Њ):
Ti(1)–O(1) 1.784(2), Ti(1)–N(2) 2.138(2), Ti(1)–Cl(3) 2.1987(10), Ti(1)–
Cl(4) 2.4907(10), Ti(1)–Cl(5) 2.4336(7), Ti(1)–Cl(6) 2.4091(7), C(20)–
N(2) 1.285(3), C(1)–O(1) 1.352(3), Ti(2)–Cl(4) 2.4618(9), Ti(2)–Cl(5)
2.5417(7), Ti(2)–Cl(6) 2.5381(9), Ti(2)–Cl(7) 2.2106(10), Ti(2)–Cl(8)
2.1845(9), Ti(2)–Cl(9) 2.1971(7); C(1)–O(1)–Ti(1) 135.86(14), Ti(1)–
Cl(4)–Ti(2) 85.38(3), Ti(1)–Cl(5)–Ti(2) 84.86(2), Ti(1)–Cl(6)–Ti(2)
85.45(3).
3b: A solution of 1b (2.79 g, 7 mmol) in toluene (30 cm3) was
added to TiCl4 (1.54 cm3, 14 mmol) in toluene (50 cm3) at Ϫ78 ЊC.
The reaction was warmed slowly and refluxed overnight. The solvent
was removed under reduced pressure yielding a crude red solid. Purifi-
cation by recrystallisation in dichloromethane/light petroleum at 0 ЊC
gave 3b as small dark red crystals. δ 1H (300 MHz, CDCl3, 20 ЊC)
8.54 (s, 1H, CH=N), 7.24–7.89 (m, 6H, Ar), 2.75–2.89 (m, 2H,
CH(Me)2), 1.65 (s, 9H, t-Bu), 1.35 (d, 6H, J 6.73, CH(Me)2), 1.10 (d,
6H, J 6.80, CH(Me)2). δ 13C (75 MHz, CDCl3, 20 ЊC) 136.8, 133.8,
128.8, 125.0, 124.5, 124.4, 30.4, 29.5, 25.6, 23.1. Anal. found: C, 40.36;
H, 4.33; N, 1.82; Cl, 37.33. Requires: C, 40.60; H, 4.44; N, 2.06; Cl,
36.47.
‡ X-ray analyses: intensity data from Rigaku R-Axis IIc image-plate
diffractometer, processed in DENZO/SCALEPACK.8 Structure deter-
mination and refinement with SHELX-97 programs.9 Crystal data for
2a: C21H26Cl3NO2Ti, M = 478.7, monoclinic, space group P21/c (no. 14),
a = 7.385(2), b = 31.797(6), c = 9.815(2) Å, β = 102.50(3)Њ, V = 2250.1(8)
Å3, Z = 4, Dc = 1.413 Mg mϪ3, F(000) = 992, T = 140(1), µ(Mo Kα) =
0.75 mmϪ1, λ(Mo Kα) = 0.71073 Å, reflections measured 7928, unique
3383 (Rint = 0.268), F 2 refinement, R1 = 0.088 (1907 reflections with
I>2σI), wR2 = 0.237 (all data).
Crystal data for 3b: C23H30Cl7NOTi2, M = 680.4, monoclinic, space
group P21/n (equiv. to no. 14), a = 9.880(1), b = 19.315(1), c = 15.511(6)
Å, β = 102.80(1)Њ, V = 2886.4(12) Å3, Z = 4, Dc = 1.566 Mg mϪ3, F(000) =
1384, T = 140(1) K, µ(Mo Kα) = 1.22 mmϪ1, λ(Mo Kα) = 0.71073 Å,
reflections measured 15791, unique 5091 (Rint = 0.043), F 2 refinement,
R1 = 0.034 (4308 reflections with I>2σI), wR2 = 0.094 (all data).
CCDC reference numbers 214921 and 214922. See http://
www.rsc.org/suppdata/dt/b3/b307793b/ for crystallographic data in
CIF or other electronic format.
(2.399–2.614).6 The crystal structure of the [Ti2Cl9]Ϫ anion, in
which both titanium centres have an octahedral face-sharing
geometry, has been reported and both the terminal (2.197–
2.225 Å) and bridging Ti–Cl (2.480–2.556Å) bond lengths are
very similar to those observed for 3b.7
Complexes 2a, 2b and 3b catalyse the polymerisation of eth-
ene when activated with methylaluminoxane (Table 1). The
productivities for 2a compare favourably to the best results
obtained for cyclopentadienyl salicylaldiminato titanium com-
plexes.4 The greater productivity of the dinuclear 3b versus
mononuclear 2b is intriguing, since we expected the same active
species to be formed in the presence of MAO. TiCl4 does form
an active polymerisation catalyst when combined with MAO
but its productivity is insufficient to explain the difference
between the mono- and dinuclear pre-catalysts (run 10). The
difference is probably not due to the THF in 2b competing for
the coordination site during polymerisation since addition of
two equivalents of THF to catalysts prepared from 3b did not
significantly affect the productivity (runs 11–13). The nature of
the active species derived from the reactions of 2b and 3b with
MAO will be the subject of further investigations. Attempts to
determine the polyethylene molecular weights by GPC were
frustrated by low solubility.
Studies to determine whether the more open geometry of
these mono(salicylaldiminato)metal catalysts favour comono-
mer incorporation when compared to bis(ligand) systems are
underway.
We thank the Engineering and Physical Science Research
Council for support.
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D a l t o n T r a n s . , 2 0 0 3 , 3 4 8 0 – 3 4 8 2
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D a l t o n T r a n s . , 2 0 0 3 , 3 4 8 0 – 3 4 8 2
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