Synthesis and ethylene polymerization capability of metallocene-like imido titanium dialkyl compounds and their reactions with AliBu3

Organometallics 2006, 25, 5549-5565

5549

Synthesis and Ethylene Polymerization Capability of

Metallocene-like Imido Titanium Dialkyl Compounds and

Their Reactions with AlⁱBu₃

Paul D. Bolton,^†Nico Adams,^†Eric Clot,^‡Andrew R. Cowley,^†Paul J. Wilson,^§

Martin Schro¨der,^§and Philip Mountford*^,†

Chemistry Research Laboratory, UniVersity of Oxford, Mansfield Road, Oxford OX1 3TA, U.K.,

Laboratoire de Structure et Dynamique des Syste`mes Mole´culaires et Solides (UMR 5636 CNRS-UM2),

Institut Charles Gerhardt, cc 14, UniVersite´ Montpellier 2, 34095 Montpellier Cedex 5, France, and

School of Chemistry, UniVersity of Nottingham, UniVersity Park, Nottingham NG7 2RD, U.K.

ReceiVed July 7, 2006

A series of alkyl- and aryl-imido titanium dialkyl compounds Ti(N^tBu)(Me₃[9]aneN₃)R₂(R ) Me (1),

t

i

CH₂SiMe₃(3), CH₂Bu (4), CH₂Ph (5)), Ti(NR)(Me₃[9]aneN₃)Me₂(R ) Pr (6), Ph (7), 3,5-C₆H₃(CF₃)₂

i

t

(8), 2,6-C₆H₃Pr₂(9), 2-C₆H₄CF₃(10), 2-C₆H₄Bu (11)), and Ti(NR)(Me₃[9]aneN₃)(CH₂SiMe₃)₂(R ) ⁱPr

(12), Ar^F(13)) were prepared and crystallographically characterized in the case of 1, 6-9, and 11 (Me₃-

[9]aneN₃) 1,4,7-trimethyl triazacyclononane; Ar^F) C₆F₅). These compounds, isolobal with the titanocenes

Cp₂TiR₂, were thermally stable at elevated temperatures except for 4. Reaction of 7 with [Ph₃C][BAr^F]

4

(TB) and diisopropylcarbodiimide in CH₂Cl₂gave the Ti-Me insertion product [Ti(NPh)(Me₃[9]-

aneN₃){MeC(NⁱPr)₂}][BAr^F] (15-BAr^F). The corresponding reaction of 7 in the absence of organic

4

substrate gave [Ti₂(µ-NPh)₂(Me₃[9]aneN₃)₂Cl₂][BAr^F] via a solvent activation reaction. The room-

4 2

temperature ethylene polymerization capabilities of the dialkyl compounds were evaluated using TB

cocatalyst in the presence of AlⁱBu₃(TIBA). Among the dimethyl precatalysts, only the systems 1 and

11, with the bulkiest imido groups, showed high productivities (6230 and 1210 kg mol^-1h^-1bar^-1,

respectively). The productivites of the other tert-butyl imido precatalysts 3 and 4 (130 and 120 kg mol^-1

h^-1bar^-1, respectively) were substantially lower than that of 1. The catalyst system 1/TIBA (2500 equiv,

no added TB) was also active for ethylene polymerization (225 kg mol^-1h^-1bar^-1). The less productive

imido dialkyl precatalysts all formed complex mixtures on exposure to TIBA. The polyethylenes produced

with 1, 3, and 5-11 generally had M_w/M_nvalues in the range 2.6-3.0. The PE formed with 1/TB/TIBA

was terminated only by methyl end groups, consistent with chain transfer to TIBA followed by subsequent

â-H transfer by the resultant titanium isobutyl cation. The alkyl cations [Ti(N^tBu)(Me₃[9]aneN₃)R]⁺(R

) Me or CH₂SiMe₃) reacted rapidly with TIBA in C₆D₅Br at -30 °C, forming isobutene. DFT calculations

found that TIBA adducts of the model methyl cation [Ti(NMe)(H₃[9]aneN₃)Me]⁺were energetically

favorable by ca. -80 to -110 kJ mol^-1. Whereas 1 alone or with AlMe₃present has been shown to form

only Ph₃CMe on reaction with [Ph₃C]⁺, 1:1 mixtures of 1 and TIBA gave Ph₃CH as the only trityl-

containing product, suggesting a key role for transient [AlⁱBu₂]⁺in the activation process for these catalysts.

Overall, the imido group in the Ti(NR)(Me₃[9]aneN₃)Me₂/TB/TIBA catalysts systems appears to have

two roles: to stabilize the dialkyl precatalyst toward degradation by the TIBA itself prior to activation,

and to inhibit the formation of catalytically inactive hetero- or homo-bimetallic complexes.

assessed, including transition metal imido compounds, L_nM-

(NR)_mX₂(L_n) additional ligand or ligand set; X ) alkyl or

halide typically).⁸The formally dianionic imido ligand [NR]^2-

is isolobal with cyclopentadienide,^9-12a conceptual feature that

has been used in the design of catalysts containing these N-donor

groups. Group 6 bis(imido) and group 5 cyclopentadienyl-imido

catalysts of the type M(NR)₂X₂and CpM(NR)X₂, respectively,

Introduction

The development of nonmetallocene, transition metal olefin

polymerization catalysts continues to be an area of considerable

academic and industrial activity.^1-8Complexes of a wide range

of heteroatom-donor supporting ligands have been prepared and

* Corresponding author. E-mail: philip.mountford@chem.ox.ac.uk.

^†University of Oxford.

(6) Mitani, M.; Saito, J.; Ishii, S.; Nakayama, Y.; Makio, H.; Matsukawa,

N.; Matsui, S.; Mohri, J.; Furuyama, R.; Terao, H.; Bando, H.; H., T.; Fujita,

T. Chem. Rec. 2004, 4, 137.

^‡Universite´ Montpellier 2.

^§University of Nottingham.

(1) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.

Ed. 1999, 38, 429.

(2) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,

1169.

(7) Stephan, D. W. Organometallics 2005, 24, 2548.

(8) Bolton, P. D.; Mountford, P. AdV. Synth. Catal. 2005, 347, 355.

(9) Williams, D. S.; Schofield, M. H.; Anhaus, J. T.; Schrock, R. R. J.

Am. Chem. Soc. 1990, 112, 6728.

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131.

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Organometallics 1992, 11, 4221.

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(5) Suzuki, Y.; Terao, H.; Fujita, T. Bull. Chem. Soc. Jpn. 2003, 76,

1493.

(11) Williams, D. S.; Schofield, M. H.; Schrock, R. R. Organometallics

1993, 12, 4560.

(12) Gibson, V. C. J. Chem. Soc., Dalton Trans. 1994, 1607.

Publication on Web 10/17/2006

5550 Organometallics, Vol. 25, No. 23, 2006

Bolton et al.

have been assessed as isolobal analogues of the ubiquitious

group 4 metallocene family.^13-16We have extended this

approach by combining imido titanium¹⁷fragments with neutral,

six-electron donor ligands such as Me₃[9]aneN₃(1,4,7-

trimethyltriazacyclononane),^18-23tris(pyrazolyl)methanes,^24,25

triazacyclohexanes,^23,26and others.^18,27Since both the dianionic

NR^2-and conical fac-N₃ligands²⁸are isolobal with C₅H₅^-, the

compounds Ti(NR)(fac-N₃)X₂(X ) halide or alkyl) are also

isolobal analogues of the group 4 metallocenes Cp₂MCl₂. We

have also described detailed studies of the electronic structures

of Ti(NR)(Me₃[9]aneN₃)X₂, certain well-defined monoalkyl

cations [Ti(N^tBu)(Me₃[9]aneN₃)R]⁺(R ) Me or CH₂SiMe₃),

and their relationships to the isolobal bis(cyclopentadienyl)-

titanium systems.²²The alkyl cations were prepared by reaction

It fulfills a dual role as both a precatalyst activator and impurity

scavenger, and is typically used in a large Al:M ratio. The active

species in Zieger-Natta systems are cationic alkyl complexes

of the type “[L_nM-R]⁺”.^4,32-34Typically, however, the MAOs

used in these studies contain up to 20-30 wt % AlMe₃(TMA),

and the catalyst resting state in these instances is probably a

bimetallic species of the type [L_nM(µ-R)₂AlR₂]⁺.^35-44Even this

can be a simplistic view, with a range of homo- and hetero-

bimetallic alkyl and alkyl-chloride species potentially being

formed when dichloride precatalysts are activated with an excess

of MAO.^37,40,45For example, the titanium species formed in

the reactions of Cp₂TiCl₂with an excess of MAO included Cp₂-

TiMe₂, Cp₂TiMeCl, [Cp₂TiMe(µ-Cl)Cp₂TiCl]⁺, [Cp₂TiMe(µ-

Cl)Cp₂TiMe]⁺, [Cp₂TiMe(µ-Me)Cp₂TiMe]⁺, and [Cp₂Ti(µ-

Me)₂AlMe₂]⁺.⁴⁰

of [Ph₃C][BAr^F] (TB, Ar^F) C₆F₅) with the corresponding

4

dialkyls, the syntheses of which are reported for the first time

here.

As mentioned, we have recently reported the well-defined

monoalkyl cations [Ti(N^tBu)(Me₃[9]aneN₃)R]⁺(R ) Me or

CH₂SiMe₃) and some preliminary accounts of their reactions,

including stoichiometric Ti-R bond insertion, Lewis base

addition, and C-H bond and solvent activation processes.^20-22

However, the methyl cation [Ti(N^tBu)(Me₃[9]aneN₃)Me]⁺also

formed the mono(µ-methyl)-bridged homobimetallic species

[Ti₂(N^tBu)₂(Me₃[9]aneN₃)₂Me₂(µ-Me)]⁺with excess Ti(N^tBu)-

(Me₃[9]aneN₃)Me₂(1)²²and the stable bis(µ-methyl)-bridged

heterobimetallic [Ti(N^tBu)(Me₃[9]aneN₃)(µ-Me)₂AlMe₂]⁺with

TMA.²¹The chloride cation [Ti(N^tBu)(Me₃[9]aneN₃)Cl]⁺formed

the homobimetallic species [Ti₂(N^tBu)₂(Me₃[9]aneN₃)₂Me₂(µ-

Cl)]⁺on reaction with 1.²²These rather stable bimetallic

complexes are analogues of the titanocenium and zirconocenium

species identified in MAO-activated metallocene catalyst sys-

tems.^40,45Although we have no direct evidence for the presence

of such species in the Ti(NR)(fac-N₃)Cl₂/MAO catalyst systems,

it is not unlikely they could represent catalyst trapping and/or

deactivation routes. The extent to which each species might form

would likely depend on the imido substituents, which would in

turn influence the overall structure-productivity relationships

in these catalysts.

Of the Ti(NR)(fac-N₃)Cl₂/MAO catalyst systems studied

(MAO ) methylaluminoxane), those with Me₃[9]aneN₃and tris-

(3,5-dimethylpyrazolyl)methane co-ligands gave the best pro-

ductivites and molecular weight distributions. Furthermore, only

t

compounds with bulky imido R-substituents (e.g., R ) Bu,

t

adamantyl, 2-C₆H₄Bu) afforded highly productive catalysts,

especially under more commercially relevant conditions.^20,23,25

We recently found analogous structure-productivity trends in

an isostructural series of vanadium(IV) catalyst systems V(NR)-

{HC(Me₂pz)₃}Cl₂/MAO, implying that adequate steric protec-

tion of the TidNR bond is a prerequisite for highly active

systems.²⁹

MAO is one of the most widely used activators in Zieger-

Natta catalysis, especially with regard to metallocene systems.^30-34

(13) Chan, M. C. W.; Chew, K. C.; Dalby, C. I.; Gibson, V. C.;

Kohlmann, A.; Little, I. R.; Reed, W. Chem. Commun. 1998, 1673.

(14) Coles, M. P.; Dalby, C. I.; Gibson, V. C.; Little, I. R.; Marshall, E.

L.; Ribeiro, da Costa, M. H.; Mastroianni, S. J. Organomet. Chem. 1999,

591, 78.

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R. J. J. Chem. Soc., Chem. Commun. 1995, 1709.

(17) Hazari, N.; Mountford, P. Acc. Chem. Res. 2005, 38, 839.

(18) Wilson, P. J.; Blake, A. J.; Mountford, P.; Schro¨der, M. Chem.

Commun. 1998, 1007.

(19) Male, N. A. H.; Skinner, M. E. G.; Wilson, P. J.; Mountford, P.;

Schro¨der, M. New J. Chem. 2000, 24, 575.

(20) Adams, N.; Arts, H. J.; Bolton, P. D.; Cowell, D.; Dubberley, S.

R.; Friederichs, N.; Grant, C.; Kranenburg, M.; Sealey, A. J.; Wang, B.;

Wilson, P. J.; Cowley, A. R.; Mountford, P.; Schro¨der, M. Chem. Commun.

2004, 434.

(21) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. Chem.

Commun. 2005, 3313.

(22) Bolton, P. D.; Clot, E.; Adams, N.; Dubberley, S. R.; Cowley, A.

R.; Mountford, P. Organometallics 2006, 25, 2806.

(23) Adams, N.; Arts, H. J.; Bolton, P. D.; Cowell, D.; Dubberley, S.

R.; Friederichs, N.; Grant, C. M.; Kranenburg, M.; Sealey, A. J.; Wang,

B.; Wilson, P. J.; Zuideveld, M. A.; Blake, A. J.; Schro¨der, M.; Mountford,

P. Organometallics 2006, 25, 3888.

Preliminary experiments on the dialkyl compounds Ti(N^tBu)-

(Me₃[9]aneN₃)R₂(R ) Me (1) or CH₂SiMe₃(3)) as polymer-

ization precatalysts were promising and suggested that they

would offer a way to avoid MAO as an activator-scavenger.²⁰

Reaction of 3 with TB on the NMR tube scale followed by

addition of C₂H₄afforded a copious white precipitate of poly-

ethylene (PE). Polymerization of ethylene with 1 using TB

(32) Bochmann, M. J. Organomet. Chem. 2004, 689, 3982.

(33) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth,

R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.

(34) Kaminsky, W. J. Chem. Soc., Dalton Trans. 1998, 1413.

(35) Bochmann, M.; Lancaster, S. J. Angew. Chem., Int. Ed. Engl. 1994,

33, 1634.

(36) Bochmann, M.; Lancaster, S. J. J. Organomet. Chem. 1995, 497,

55.

(37) Tritto, I.; Donetti, R.; Sacchi, M. C.; Locatelli, P.; Zannoni, G.

Macromolecules 1997, 30, 1247.

(24) Lawrence, S. C.; Skinner, M. E. G.; Green, J. C.; Mountford, P.

Chem. Commun. 2001, 705.

(25) Bigmore, H. R.; Dubberley, S. R.; Kranenburg, M.; Lawrence, S.

C.; Sealey, A. J.; Selby, J. D.; Zuideveld, M.; Cowley, A. R.; Mountford,

P. Chem.Commun. 2006, 436.

(26) Wilson, P. J.; Blake, A. J.; Mountford, P.; Schro¨der, M. J.

Organomet. Chem. 2000, 600, 71.

(27) Wilson, P. J.; Blake, A. J.; Mountford, P.; Schro¨der, M. Inorg. Chim.

Acta 2003, 345, 44.

(28) Elian, M.; Chen, M. M. L.; Mingos, D. M. P.; Hoffmann, R. Inorg.

Chem. 1976, 15, 1148.

(29) Bigmore, H. R.; Zuideveld, M.; Kowalczyk, R. M.; Cowley, A. R.;

Kranenbrug, M.; McInnes, E. J. L.; Mountford, P. Inorg. Chem. 2006, 45,

6411.

(38) Vollmerhaus, R.; Rahim, M.; Tomaszewski, R.; Xin, S.; Taylor, N.

J.; Collins, S. Organometallics 2000, 19, 2161.

(39) Zakharov, I. I.; Zakharov, V. A. Macromol. Theory Simul. 2002,

11, 352.

(40) Bryliakov, K. P.; Talsi, E. P.; Bochmann, M. Organometallics 2004,

23, 149.

(41) Schro¨der, L.; Brintzinger, H. H.; Babushkin, D. E.; Fischer, D.;

Mu¨lhaupt, R. Organometallics 2005, 24, 867.

(42) Bryliakov, K. P.; Babushkin, D. E.; Talsi, E. P.; Voskobynikov, A.

Z.; Gritzo, H.; Schro¨der, L.; Damrau, H.-R. H.; Wieser, U.; Schaper, F.;

Brintzinger, H. H. Organometallics 2005, 24, 894.

(43) Petros, R. A.; Norton, J. R. Organometallics 2005, 23, 5105.

(44) Eilertsen, J. L.; Støvneng, J. A.; Ystenes, M.; Rytter, E. Inorg. Chem.

2005, 44, 4843.

(30) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391.

(31) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255.

(45) Babushkin, D. E.; Semikolenova, N. V.; Zakharov, V. A.; Talsi, E.

P. Macromol. Chem. Phys. 2000, 201, 558.

Metallocene-like Imido Titanium Dialkyl Compounds

Organometallics, Vol. 25, No. 23, 2006 5551

Scheme 1. Synthesis of tert-Butyl Imido Titanium Alkyl

of the reaction mixture for 4 showed incomplete conversion to

the desired product. An additional quantity of LiCH₂Bu was

t

Compounds

required to drive the reaction to completion, and compound 4

was eventually obtained in 20% yield. The analytical data for

3-5 are consistent with the proposed structures. The ¹H NMR

spectra are analogous to those of 1 and show pairs of mutually

coupled doublets for the diastereotopic alkyl group methylene

resonance. Attempts to synthesize analogues of 3-5 using

2 equiv of LiCH(SiMe₃)₂or LiCH₂CMe₂Ph were unsuccessful,

resulting in either no reaction or a complex mixture of products,

respectively.

The syntheses of 1-5 were typically conducted in the absence

of light, but where they have been repeated without this

precaution, there were no obvious detrimental effects. This is

in contrast to the behavior of the isolobal titanocene systems.⁴⁶

In addition to their light-sensitivity, titanocene dialkyls are

typically thermally sensitive. Hessen and co-workers reported

t

that Cp₂Ti(CH₂Bu)₂decomposes at ambient temperature in

C₆D₆to form Cp₂Ti(CHD^tBu)(C₆D₅), the reaction proceeding

by an R-hydrogen elimination and the alkylidene intermediate

Cp₂TidCH^tBu.⁴⁷Furthermore, Cp₂Ti(CH₂SiMe₃)₂affords the

transient alkylidene Cp₂TidCHSiMe₃when heated to 80 °C.^48,49

In contrast, samples of Ti(N^tBu)(Me₃[9]aneN₃)R₂(R ) CH₂-

SiMe₃(3), CH₂Ph (5)) could be heated in C₆D₆at 70 °C for

weeks without significant change. However, while solutions of

activator in the presence of AlⁱBu₃(TIBA) scavenger proceeded

with a productivity in excess of 10³kg mol^-1h^-1bar^-1, twice

that of the Ti(N^tBu)(Me₃[9]aneN₃)Cl₂/MAO system under

otherwise identical experimental conditions.²⁰Encouraged by

these results, we decided to extend the range of Ti(NR)(Me₃-

[9]aneN₃)R′₂(R ) alkyl or aryl; R′ ) Me or other alkyl) dialkyl

compounds and evaluate their ethylene polymerization characteris-

tics, with the aim of gaining a better insight into the structure-

productivity relationships for imido-based catalyst systems. Part

of this work has been communicated.²⁰

Ti(N^tBu)(Me₃[9]aneN₃)(CH₂Bu)₂(4) in C₆D₆are stable at

t

ambient temperature for at least 16 h, heating to 70 °C for 4 h

resulted in decomposition to free macrocycle and a complex

mixture of other unidentified products. The macrocycle-imido

compounds are therefore significantly more thermally stable than

their metallocene counterparts, but the order of stability remains

the same, with the bis(neo-pentyl) 4 being considerably less

stable than the bis(trimethylsilyl) derivative 3.

Results and Discussion

Synthesis of Imido Titanium Dialkyl Compounds Ti(NR)-

(Me₃[9]aneN₃)R′₂. Initial studies focused on alkyl derivatives

of the tert-butyl imido dichloride Ti(N^tBu)(Me₃[9]aneN₃)Cl₂.

These are summarized in Scheme 1. The syntheses of all the

starting dichlorides used herein have been described elsewhere.²³

Addition of a small excess (2.2 equiv) of LiMe to Ti(N^tBu)-

(Me₃[9]aneN₃)Cl₂in THF at -78 °C followed by extraction

and crystallization from a cold hexane/benzene (2:1 v/v) mixture

afforded Ti(N^tBu)(Me₃[9]aneN₃)Me₂(1) as a yellow solid in

70% yield. Compound 1 has been crystallographically charac-

terized, and the structure, which confirms that illustrated in

Scheme 1, is discussed below together with those of a number

Equation 1 summarizes the range of other imido titanium

i

dimethyl compounds Ti(NR)(Me₃[9]aneN₃)Me₂(R ) Pr (6),

i

Ph (7), 3,5-C₆H₃(CF₃)₂(8), 2,6-C₆H₃Pr₂(9), 2-C₆H₄CF₃(10),

t

2-C₆H₄Bu (11)) that have been prepared in an analogous way

to that for 1. The preparations of 6, 7, and 11 were relatively

straightforward. Compounds 8 and 10 (containing CF₃groups)

required a significant excess of LiMe to achieve quantitative

dialkylation and were obtained in comparatively low yields (31%

and 19%). This, and the dark brown colors of the reaction

mixtures, suggests that competing side-reactions occur (the

reaction mixtures for the other dialkyl compounds were typically

bright yellow). Attempts to prepare Ti(NAr^F)(Me₃[9]aneN₃)-

Me₂(Ar^F) C₆F₅) from the corresponding dichloride and MeLi

were unsuccessful. The X-ray structures of 6-9 are discussed

below. As for Ti(N^tBu)(Me₃[9]aneN₃)(CH₂SiMe₃)₂(3), reaction

of Ti(NⁱPr)(Me₃[9]aneN₃)Cl₂with 2 equiv of LiCH₂SiMe₃

1

of alkyl and aryl imido homologues. The H and ¹³C NMR

spectra of 1 are consistent with the molecular C_ssymmetry.

These data and those of all the other new compounds are listed

in the Experimental Section. Reaction of Ti(N^tBu)(Me₃[9]-

aneN₃)Cl₂with 1 equiv of LiMe in cold THF afforded the yellow

monomethyl derivative Ti(N^tBu)(Me₃[9]aneN₃)(Cl)Me (2) in

55% yield. The FI high-resolution mass spectrum showed the

expected parent ion with the correct isotope distribution, and

the NMR spectra were consistent with a lack of molecular

1

symmetry (e.g., three macrocycle methyl group H and ¹³C

resonances and six methylene group ¹³C resonances (two

overlapping)).

Reaction of Ti(N^tBu)(Me₃[9]aneN₃)Cl₂with 2 equiv of

(46) Erskine, G. J.; Hartgerink, J.; Weinberg, E. L.; McCowan, J. D. J.

Organomet. Chem. 1979, 170, 51.

(47) van der Heijden, H.; Hessen, B. J. Chem. Soc., Chem. Commun.

1995, 145.

(48) Petasis, N. A.; Akritopoulou, I. Synlett 1992, 665.

(49) Petasis, N. A.; Fu, D. K. J. Am. Chem. Soc. 1993, 115, 7208.

t

LiCH₂SiMe₃, LiCH₂Bu, or PhCH₂MgCl gave the correspond-

ing derivatives Ti(N^tBu)(Me₃[9]aneN₃)R₂(R ) CH₂SiMe₃(3),

t

CH₂Bu (4), CH₂Ph (5)). Compounds 3 and 5 were straightfor-

wardly obtained in 72% and 86% yield, respectively. An aliquot

5552 Organometallics, Vol. 25, No. 23, 2006

Bolton et al.

t

i

Figure 1. Displacement ellipsoid plots (20% probability) of alkyl imido compounds Ti(NR)(Me₃[9]aneN₃)Me₂(R ) Bu (1), Pr (6)).

H atoms are omitted.

Figure 2. Displacement ellipsoid plots (20-25% probability) of the aryl imido compounds Ti(NAr)(Me₃[9]aneN₃)Me₂(Ar ) Ph (7),

i

t

C₆H₃(CF₃)₂(8), 2,6-C₆H₃Pr₂(9), 2-C₆H₄Bu (11)). H atoms are omitted.

straightforwardly gave pale yellow Ti(NⁱPr)(Me₃[9]aneN₃)(CH₂-

7-9 and 11). The crystals of 1 and 6 contained benzene of

crystallization. Minor disorder of some of the macrocycle

methylene groups was satisfactorily resolved (see Supporting

Information). All of the complexes adopt approximately octa-

hedral structures. The parent dichloride complexes Ti(NR)(Me₃-

SiMe₃)₂(12). However, the corresponding reactions with Ti-

i

(NR)(Me₃[9]aneN₃)Cl₂(R ) Ph or 2,6-C₆H₃Pr₂) were unsuc-

cessful, while that with Ti(NAr^F)(Me₃[9]aneN₃)Cl₂gave

Ti(NAr^F)(Me₃[9]aneN₃)(CH₂SiMe₃)₂(13) in only 8% yield.

The X-ray structures of Ti(NR)(Me₃[9]aneN₃)Me₂(R ) ^tBu (1),

i

[9]aneN₃)Cl₂(R ) ^tBu, Ph, 2,6-C₆H₃Pr₂)²³have been crystallo-

i

ⁱPr (6), Ph (7), 3,5-C₆H₃(CF₃)₂(8), 2,6-C₆H₃Pr₂(9), and

graphically characterized previously. The dimethyls have features

similar to the dichlorides, but the Ti-N distances for the

macrocycle and the imido groups are slightly longer in each

case as a result of the electron-releasing methyl ligands.

t

2-C₆H₄Bu (11)) have been determined. Selected bond lengths

and angles are listed in Table 1, and the molecular structures

are shown in Figures 1 (compounds 1 and 6) and 2 (compounds

Metallocene-like Imido Titanium Dialkyl Compounds

Organometallics, Vol. 25, No. 23, 2006 5553

t

i

Table 1. Selected Bond Lengths (Å) and Angles (deg) for Ti(NR)(Me₃[9]aneN₃)Me₂(R ) Bu (1), Pr (6), Ph (7), 3,5-C₆H₃(CF₃)₂

i

t

(8), 2,6-C₆H₃Pr₂(9), and 2-C₆H₄Bu (11))

parameter

Ti(1)-N(1)

1

6

7

8

9

11

1.7180(18)

2.463(2)

2.335(2)

2.334(2)

2.205(3)

2.221(3)

1.438(3)

0.128(3)

0.129(3)

1.7190(18)

2.4784(18)

2.3594(17)

2.3259(17)

2.206(2)

2.211(2)

1.437(3)

0.119(3)

0.153(3)

1.746(3)

2.435(3)

2.337(2)

2.334(2)

2.186(4)

2.186(3)

1.377(4)

0.098(4)

0.101(4)

1.751(2)

2.409(2)

2.316(2)

2.312(2)

2.176(3)

2.172(3)

1.362(3)

0.093(3)

0.097(3)

1.755(2)

2.452(2)

2.328(2)

2.338(2)

2.240(2)

2.226(2)

1.380(3)

0.124(3)

0.114(3)

1.7644(16)

2.4703(18)

2.3328(17)

2.3440(17)

2.2118(18)

2.2008(19)

1.388(2)

Ti(1)-N(2)

Ti(1)-N(3)

Ti(1)-N(4)

Ti(1)-C(1)

Ti(1)-C(2)

N(1)-C(3)

trans

0.138(3)

0.126(3)

influence (Å)^a

N(1)-Ti(1)-N(2)

N(1)-Ti(1)-N(3)

N(1)-Ti(1)-N(4)

N(1)-Ti(1)-Cl(1)

N(1)-Ti(1)-Cl(2)

Cl(1)-Ti(1)-Cl(2)

Ti(1)-N(1)-C(3)

167.30(8)

97.90(8)

96.91(8)

99.02(11)

98.59(11)

98.13(15)

171.52(16)

168.41(7)

99.38(8)

96.99(7)

97.85(9)

100.25(8)

96.24(9)

172.32(17)

165.94(10)

97.56(10)

93.97(11)

97.76(16)

98.10(14)

101.23(13)

169.3(2)

168.81(9)

95.87(10)

98.68(9)

98.22(18)

98.97(12)

95.89(13)

166.8(2)

172.50(8)

100.37(9)

101.50(8)

97.78(10)

98.34(10)

97.35(10)

168.97(17)

169.89(7)

97.73(7)

102.19(7)

94.63(8)

100.72(7)

97.03(8)

158.70(13)

^aDefined as the difference between the Ti(1)-N(2) distance (i.e., trans to TidNR) and Ti(1)-N(3) and Ti(1)-N(4) distances.

The bonds to the imido ligands (Ti(1)-N(1)) are shorter for

the alkyl imides 1 and 6 than for the aryl imides and slightly

longer for the bulkier homologues among the latter group. These

are common features of the structural chemistry of imido

compounds.^50,51The significantly shorter Ti-N_macrocycleand

Ti-Me distances in 8 are attributed to the electron-withdrawing

CH₂Cl₂. To underpin the further studies described below, we

briefly investigated the reactivity and properties of alkyl cations

derived from some of the other new dialkyls.

meta-CF₃groups. This is also reflected in the shorter N_imide

-

C_ipsodistance in 8 (N(1)-C(3) ) 1.362(3) Å) compared to those

in the other aryl imides (range 1.377(4)-1.388(2) Å). All of

the compounds show a lengthening of the Ti-N_macrocyclebond

trans to the imide (Ti(1)-N(2)) relative to those in the cis

positions (Ti(1)-N(3) and Ti(1)-N(4)). This trans labilizing

influence of imido ligands is also well known.⁵²The largest

trans influences (Table 1) are found for the alkyl imides 1 and

6 and for the more electron-donating aryl imides 9 and 11.

Figure 2 shows that the N-aryl substituents in 7-9 and 11

adopt two types of orientation. The C₆H_xR_y(x + y ) 5) ring

carbons lie approximately within the molecular mirror planes

in 8 and 9, whereas in 7 and 11 the aryl rings are orientated

perpendicular to this plane. In the case of 9, analogous orien-

tations of the aryl rings were found in the di-ortho-substituted

chlorides Ti(N-2,6-C₆H₃R₂)(Me₃[9]aneN₃)Cl₂(R ) Me, ⁱPr);²³

for 11, analogous orientations of the mono-ortho-substituted aryl

rings were found in the vanadium chlorides V(N-2-C₆H₄R)-

(Me₃[9]aneN₃)Cl₂(R ) ^tBu, CF₃);²⁹for 7, an analogous orien-

tation of the phenyl ring in Ti(NPh)(Me₃[9]aneN₃)Cl₂was

observed.²³It appears that there is a common trend in the

orientations of the aryl rings in complexes of the type M(NAr)-

(Me₃[9]aneN₃)X₂(M ) Ti, V; X ) Cl, Me), which probably

results from the minimization of intramolecular repulsions

between the N-Ar and macrocycle N-Me groups.

We previously studied the different nonclassical interactions

in the formally 14-valence-electron cations [Ti(N^tBu)(Me₃[9]-

aneN₃)R]⁺(R ) Me or CH₂SiMe₃) and the corresponding DFT

model systems [Ti(NMe)(H₃[9]aneN₃)R]⁺(I-Me or I-CH₂Si-

Me₃).²²For R ) Me only a very weak R-C-H‚‚‚Ti agostic

interaction was found, whereas for R ) CH₂SiMe₃a significant

â-Si-C‚‚‚Ti agostic interaction was present. Since benzyl

ligands are known to stabilize electron-deficient centers through

M‚‚‚C_ipsointeractions,^53-56we attempted to observe spectroscop-

ically a monoalkyl cation derived from Ti(N^tBu)(Me₃[9]aneN₃)-

(CH₂Ph)₂(5). Reaction of 5 with TB in C₆D₅Br yielded the

expected organic side-product Ph₃CCH₂Ph and an insoluble

orange-brown oil, which could not be further characterized. This

is in contrast to the analogous reactions of 1 and 3 forming

C₆D₅Br-soluble [Ti(N^tBu)(Me₃[9]aneN₃)R][BAr^F].²²The cor-

4

responding reaction of 5 with TB in CD₂Cl₂quantitatively

formed the chloride cation [Ti(N^tBu)(Me₃[9]aneN₃)Cl]⁺.²²This

reactivity is analogous to that of 1 but contrasts that of 3 since

[Ti(N^tBu)(Me₃[9]aneN₃)CH₂SiMe₃]⁺was stable in CD₂Cl₂. We

previously found that reaction of 1 with neutral BAr^F₃gave the

C₆D₅Br-soluble solvent-separated ion pair [Ti(N^tBu)(Me₃[9]-

Cationic Derivatives of Selected M(NR)(Me₃[9]aneN₃)R′₂

Complexes. In previous contributions we described the syn-

thesis, electronic structures (using DFT),²²and, briefly, selected

reactions²¹of the tert-butyl imido alkyl cations [Ti(N^tBu)(Me₃-

[9]aneN₃)R]⁺(R ) Me or CH₂SiMe₃). While stable in C₆D₅Br

or C₆D₅Cl, the methyl species immediately underwent solvent

activation in CH₂Cl₂to form the highly fluxional, monomeric

chloride cation [Ti(N^tBu)(Me₃[9]aneN₃)Cl]⁺.²²In contrast,

[Ti(N^tBu)(Me₃[9]aneN₃)CH₂SiMe₃]⁺was stable for days in

aneN₃)Me][MeBAr^F], although reaction of 3 with this reagent

3

gave unidentified mixtures.²²Unfortunately, reaction of 5 with

BAr^F₃in C₆D₅Br again gave an insoluble oil. The soluble portion

of the reaction product was a complex mixture of unidentified

species.

Although the real benzyl cation [Ti(N^tBu)(Me₃[9]aneN₃)-

CH₂Ph]⁺could not be observed experimentally, we have used

(50) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf. Comput.

Sci. 1996, 36, 746 (The United Kingdom Chemical Database Service).

(51) Allen, F. H.; Kennard, O. Chem. Des. Automation News 1993, 8,

1&31.

(52) Kaltsoyannis, N.; Mountford, P. J. Chem. Soc., Dalton Trans. 1999,

781.

(53) Bei, X.; Swenson, D. C.; Jordan, R. F. Organometallics 1997, 16,

3282.

(54) Wu, F.; Dash, A. K.; Jordan, R. F. J. Am. Chem. Soc. 2004, 126,

15360.

(55) Chen, Y.-X.; Marks, T. J. Organometallics 1997, 16, 3649.

(56) Bochmann, M.; Lancaster, S. J. Organometallics 1993, 12, 633.

5554 Organometallics, Vol. 25, No. 23, 2006

Bolton et al.

derivative [Ti₂(µ-NPh)₂(Me₃[9]aneN₃)₂Cl₂][BAr^F] , 14-BAr^F,

4 2

4

in 74% yield. Thus, just as for the tert-butyl imido cations [Ti-

(N^tBu)(Me₃[9]aneN₃)R]⁺(R ) Me, CH₂Ph), the Ti-Me bond

of the putative transient methyl cation [Ti(NPh)(Me₃[9]aneN₃)-

Me]⁺readily underwent solvent activation.

Figure 3. DFT structure of [Ti(NMe)(H₃[9]aneN₃)CH₂Ph]⁺(I-

CH₂Ph).

The ¹H and ¹³C NMR spectra of 14-BAr^F₄were sharp at room

temperature and consistent with a C_2V- or C_2h-symmetric titanium

species. In contrast, those of [Ti(N^tBu)(Me₃[9]aneN₃)Cl]⁺and

also [Ti(N^tBu)(Me₃[9]aneN₃)R]⁺(R ) Me or CH₂SiMe₃) were

very broad and consistent with the complexes being five-

coordinate fluxional monomers.²²On the basis of these observa-

tions and our experience of these macrocycle-imido systems in

general, the sharp spectra for 14-BAr^F₄indicate that the titanium

centers are six-coordinate and that the product contains a dimeric

dication. The most likely structure is [Ti₂(µ-NPh)₂(Me₃[9]aneN₃)₂-

Cl₂]²⁺(14²⁺), with bridging phenyl imido ligands, although a

chloride-bridged dimer [Ti₂(NPh)₂(Me₃[9]aneN₃)₂(µ-Cl)₂]²⁺

(14a²⁺) is in principle also feasible. Isomer 14²⁺is favored over

14a²⁺since Teuben et al. have reported dimeric imido-bridged

species Cp₂Ti₂(µ-NR)₂Cl₂(R ) Et, ⁱPr, ^tBu, Ph), which are the

a DFT calculation of the model species [Ti(NMe)(H₃[9]aneN₃)-

CH₂Ph]⁺(I-CH₂Ph) to gain insights into its structure. The

computed geometry of I-CH₂Ph is shown in Figure 3 and

exhibits a pronounced η²-coordination of the benzyl ligand.^53-56

This is manifested in an acute Ti-CH₂-C_ipsoangle of 85.6°

and a Ti‚‚‚C_ipsocontact of only 2.513 Å. The geometry of

I-CH₂Ph is reminiscent of that for I-CH₂SiMe₃, where a Ti-

CH₂-Si angle of 90.7° and Ti‚‚‚Si and Ti‚‚‚C_âdistances of

2.841 and 2.534 Å were calculated. To estimate the strength of

the Ti‚‚‚C_ipsointeraction in I-CH₂Ph, a DFT calculation was

carried out on a model species with all the angles subtended at

the Ti-CH₂-Ph methylene carbon fixed at 109.5°. This

constrained structure was 25.5 kJ mol^-1less stable than

I-CH₂Ph. A similar calculation has been carried out on

I-CH₂SiMe₃,²²and in this case the constrained geometry was

only 14.8 kJ mol^-1less stable than the optimized one. Analogous

calculations on [Ti(NMe)(H₃[9]aneN₃)Me]⁺(I-Me) estimated

the R-C-H‚‚‚Ti agostic interaction as providing less than 2 kJ

mol^-1stabilization. Therefore, the presence of nonclassical

interactions in the imido titanium alkyl cations [Ti(N^tBu)(Me₃-

[9]aneN₃)R]⁺(R ) CH₂SiMe₃, CH₂Ph) can provide significant

additional stabilization. Interestingly, although the extra stabi-

lization present in the real system [Ti(N^tBu)(Me₃[9]aneN₃)CH₂-

Ph]⁺is probably greater than in [Ti(N^tBu)(Me₃[9]aneN₃)CH₂-

SiMe₃]⁺, it is the latter species that has the better stability in

CH₂Cl₂. The tendency for solvent activation (R ) Me, CH₂Ph

or CH₂SiMe₃) in the three types of cation [Ti(N^tBu)(Me₃[9]-

aneN₃)R]⁺is therefore not correlated with these nonclassical

ground-state stabilization effects, at least according to these gas-

phase model systems.

isolobal analogues of 14²⁺/14a^{2+ 58}

. The homologue Cp*₂Ti₂(µ-

NTol)₂Cl₂is also dimeric.⁵⁹The differing behavior of five-

coordinate [Ti(N^tBu)(Me₃[9]aneN₃)Cl]⁺versus dimeric 14²⁺

reflects the reduced steric protection at the imido nitrogen atoms

in the latter. A related pair of complexes from the recent imido

titanium literature are the crystallographically characterized Ti-

(η-C₈H₈)(N^tBu) and Ti₂(η-C₈H₈)₂(µ-NPh)₂.⁶⁰Unfortunately, we

were not able to obtain diffraction-quality crystals of 14-BAr^F

4

or to obtain a useful mass spectrum to support our conclusions.

We have built up a good understanding of the properties and

reactivity of the tert-butyl imido cations [Ti(N^tBu)(Me₃[9]-

aneN₃)R]⁺.^21,22However, a number of the polymerization

experiments described below are based on aryl imido precursors,

and it is well established that these can sometimes have different

reactivity from that of their alkyl imido analogues.^17,57Selected

reactivity studies were therefore carried out on the phenyl imide

7 as the parent member of the aryl-substituted series 7-11.

Addition of TB (1 equiv) to a solution of Ti(NPh)(Me₃[9]-

aneN₃)Me₂(7) in C₆D₅Br again gave an insoluble oil (cf. the

dibenzyl 5). Other aryl imides studied and also the isopropyl

imide 6 showed similar behavior. Reaction of 7 with TB in

CD₂Cl₂formed the expected side-product Ph₃CMe and a mixture

of species. After 2 days a single phenyl imido product was

Further experiments were carried out to gain evidence for

the transient methyl cation [Ti(NPh)(Me₃[9]aneN₃)Me]⁺. We

recently reported that [Ti(N^tBu)(Me₃[9]aneN₃)CH₂SiMe₃]⁺re-

acts with diisopropylcarbodiimide to form the insertion product

[Ti(N^tBu)(Me₃[9]aneN₃){Me₃SiCH₂C(NⁱPr)₂}]⁺. Furthermore,

generating the methyl cation [Ti(N^tBu)(Me₃[9]aneN₃)Me]⁺in

CH₂Cl₂in the presence of TMA quantitatively yielded the adduct

[Ti(N^tBu)(Me₃[9]aneN₃)(µ-Me)₂AlMe₂]⁺.²¹

As shown in eq 2, reaction of Ti(NPh)(Me₃[9]aneN₃)Me₂(7)

with TB in CH₂Cl₂in the presence of diisopropylcarbodiimide

successfully gave the acetamidinate derivative [Ti(NPh)(Me₃-

[9]aneN₃){MeC(NⁱPr)₂}][BAr^F] (15-BAr^F) as a yellow powder

4

in 44% isolated yield. When the reaction was carried out on

1

present according to the H NMR spectrum. The reaction was

successfully scaled up in CH₂Cl₂, affording the dimeric chloride

(58) Vroegop, C. T.; Teuben, J. H.; van Bolhuis, F.; van der Linden, J.

G. M. J. Chem. Soc., Chem. Commun. 1983, 550.

(59) Guiducci, A. E. D.Phil. Thesis, University of Oxford, 2002.

(60) Dunn, S. C.; Hazari, N.; Jones, N. M.; Moody, A. G.; Blake, A. J.;

Cowley, A. R.; Green, J. C.; Mountford, P. Chem. Eur. J. 2005, 11, 2111.

(57) Gade, L. H.; Mountford, P. Coord. Chem. ReV. 2001, 216-217,

65.

Metallocene-like Imido Titanium Dialkyl Compounds

Organometallics, Vol. 25, No. 23, 2006 5555

i

(3), Pr (12), and Ar^F(13, very low yield), it was not possible

to obtain other members of this family. Therefore we focused

on the series of dimethyl compounds Ti(NR)(Me₃[9]aneN₃)Me₂

t

i

(R ) Bu (1), Pr (6), Ph (7), 3,5-C₆H₃(CF₃)₂(8), 2,6-C₆H₃Pr₂

t

(9), 2-C₆H₄CF₃(10), 2-C₆H₄Bu (11)). In addition to these

precatalysts, the other tert-butyl imides Ti(N^tBu)(Me₃[9]-

aneN₃)R₂(R ) CH₂SiMe₃(3) and CH₂Ph (5)) were also studied

to probe for potential initiator effects⁶¹arising from the different

precatalyst alkyl groups.

TB was chosen as a methide ion abstraction reagent, as this

has proved successful in a range of previous systems^4,30,32and

in the stoichiometric cation chemistry derived from Ti(NR)-

(Me₃[9]aneN₃)R′₂as described above and elsewhere.^20-23Ethyl-

ene polymerization experiments are typically conducted in the

presence of a scavenger to reduce the background level of trace

impurities (typically H₂O) in the system since the highly elec-

trophilic and electron-deficient alkyl cations are very reactive.

TIBA is routinely used as a scavenger in dialkyl catalyst systems

using borane or borate activators.^30,32It is generally thought

that the bulky nature of the isobutyl groups disfavors the

formation of adducts of the kind [L_nM(µ-R)₂AlR₂]⁺, making

these systems more highly active than the related MAO-activated

systems (typically containing 20-30% TMA, which coordinates

well to alkyl cations^35-44). However, it is also recognized that

the chemistry of TIBA-based activator systems is complex, and

we address the reactions of neutral and cationic imido titanium

alkyl compounds with TIBA later in this paper.^30,32,62-65

Polymerization experiments were performed in toluene under

6 bar ethylene pressure with room-temperature initiation in order

to make as close a comparison as possible with the recently

reported results for the Ti(NR)(Me₃[9]aneN₃)Cl₂/MAO catalysts

Figure 4. Displacement ellipsoid plot (20% probability) of the

cation [Ti(NPh)(Me₃[9]aneN₃){MeC(NⁱPr)₂}]⁺(15⁺). H atoms are

omitted.

Table 2. Selected Bond Lengths (Å) and Angles (deg) for

[Ti(NPh)(Me₃[9]aneN₃){MeC(NⁱPr)₂}]⁺(15⁺)

Ti(1)-N(1)

Ti(1)-N(2)

Ti(1)-N(3)

Ti(1)-N(4)

Ti(1)-N(5)

2.4157(16)

2.2750(16)

2.2515(15)

1.7248(16)

2.1275(15)

Ti(1)-N(6)

N(4)-C(10)

C(16)-N(5)

C(16)-N(6)

2.1010(15)

1.386(2)

1.339(2)

1.342(2)

1.508(3)

N(1)-Ti(1)-N(2)

N(1)-Ti(1)-N(3)

N(2)-Ti(1)-N(3)

N(1)-Ti(1)-N(4)

N(2)-Ti(1)-N(4)

N(3)-Ti(1)-N(4)

N(1)-Ti(1)-N(5)

N(2)-Ti(1)-N(5)

N(3)-Ti(1)-N(5)

75.47(6)

74.93(6)

78.17(6)

167.26(7)

93.77(7)

96.44(7)

88.94(6)

163.39(6)

103.60(6)

N(4)-Ti(1)-N(5)

N(1)-Ti(1)-N(6)

N(2)-Ti(1)-N(6)

N(3)-Ti(1)-N(6)

N(4)-Ti(1)-N(6)

N(5)-Ti(1)-N(6)

Ti(1)-N(4)-C(10)

N(5)-C(16)-N(6)

102.36(7)

86.26(6)

108.26(6)

158.09(6)

103.85(7)

64.24(6)

t

i

systems where available (R ) Bu, Ph, 2,6-C₆H₃Pr₂, 2-C₆H₄-

176.67(14)

114.05(16)

t

CF₃, 2-C₆H₄Bu).²³Catalysis runs were typically carried out in

duplicate and were generally reproducible with (10% of the

mean values reported. Full details are given in the Experimental

Section.

the NMR tube scale in CD₂Cl₂, 15-BAr^F₄was formed in quanti-

tative yield, with no evidence for a competing [2+2] cycload-

dition reaction at the TidNPh bond. The X-ray structure of the

cation 15⁺is shown in Figure 4, and selected bond lengths and

Productivities. Table 3 summarizes the results of the

polymerization experiments. We consider first the dimethyl

systems (entries 1-10). The tert-butyl imide 1 provides the most

productive system of all (6230 kg mol^-1h^-1bar^-1), and among

the aryl imides the bulkiest precatalyst 11 is the most productive

(1210 kg mol^-1h^-1bar^-1). The other systems showing non-

negligible productivity are 9 and 10 (200 and 105 kg mol^-1

h^-1bar^-1, respectively). Precatalysts 6-8 were effectively

inactive. There is therefore a strong correlation between the

steric bulk of the imido substituents and catalyst productivity,

and we discuss this in further detail below.

The catalyst system 1/TB/TIBA gave a 75 °C temperature

rise over the 20 min polymerization run time and produced 24.9

g of PE. The productivity is therefore probably mass transport

limited, and the changing reaction conditions may impact on

the PE molecular weights and their distribution.³²However,

attempts to reduce the catalyst loading below 2 µmol of 1 in

250 mL of toluene gave substantial decreases in productivity.

For example, at 1 µmol loading of 1 (with the same quantity of

TIBA as in entry 1) the PE yield was 1.81 g (905 kg mol^-1h^-1

bar^-1). Therefore the excellent productivity listed for 1 should

1

angles are given in Table 2. Consistent with this, the H and

¹³C NMR spectra for 15⁺were indicative of C_smolecular sym-

metry, and the high-resolution electrospray mass spectrum of

15-BAr^Fin MeCN (positive ion mode) showed the expected

4

pattern for the molecular ion 15⁺. Attempts were also made to

generate a bimetallic TMA adduct [Ti(NPh)(Me₃[9]aneN₃)(µ-

Me)₂AlMe₂]⁺, but only complex mixtures were formed.

Cation 15⁺contains an approximately octahedral titanium

center with a fac-coordinated macrocycle, a terminal phenyl

imido group, and a diisopropyl acetamidinate ligand. All of the

Ti-N_macrocycledistances and the Ti-N_imidedistance are slightly

shorter than in the dimethyl precursor Ti(NPh)(Me₃[9]aneN₃)-

Me₂(7), which can be attributed to the cationic nature of 15⁺.

The trans influence of the imido ligand is apparent from the

elongation of the Ti(1)-N(1) bond relative to Ti(1)-N(2) and

Ti(1)-N(3). The bond lengths within the acetamidinate ligand

are the same within error as those in the analogue [Ti(N^tBu)-

(Me₃[9]aneN₃){Me₃SiCH₂C(NⁱPr)₂}]⁺.²¹The formation of 15⁺

shows clearly that a monomethyl cation was successfully

generated from 7.

(61) Mehrkhodavandi, P.; Schrock, R. R.; Pryor, L. L. Organometallics

2003, 22, 4569.

(62) Song, F.; Cannon, R. D.; Lancaster, S. J.; Bochmann, M. J. Mol.

Catal. A: Chem. 2004, 218, 21.

(63) Go¨tz, C.; Rau, A.; Luft, G. J. Mol. Catal. A: Chem. 2002, 184, 95.

(64) Bochmann, M.; Sarsfield, M. J. Organometallics 1998, 17, 5908.

(65) Carr, A. G.; Dawson, D. M.; Thornton-Pett, M.; Bochmann, M.

Organometallics 1999, 18, 2933.

Ethylene Polymerization Studies. A principal aim of this

work was to determine the structure-productivity relationships

for ethylene polymerization by a homologous series of well-

defined imido titanium dialkyl precatalysts in the absence of

MAO. Although bis(trimethylsilylmethyl) derivatives Ti(NR)-

t

(Me₃[9]aneN₃)(CH₂SiMe₃)₂have been prepared for R ) Bu

5556 Organometallics, Vol. 25, No. 23, 2006

Bolton et al.

Table 3. Ethylene Polymerization Data for Ti(N^tBu)(Me₃[9]aneN₃)R₂(R ) Me (1), CH₂SiMe₃(3), CH₂Ph (5)) and

i

t

Ti(NR)(Me₃[9]aneN₃)Me₂(R ) Pr (6), Ph (7), 3,5-C₆H₃(CF₃)₂(8), 2,6-C₆H₃Pr₂(9), 2-C₆H₄CF₃(10), and 2-C₆H₄Bu (11))^a

additional

comment

yield of

PE (g)

productivity

M_w

M_n

entry

precatalyst

(kg mol^-1h^-1bar^-1

)

(g mol^-1

)

(g mol^-1

)

M_w/M_n

1

2

3

Ti(N^tBu)(Me₃[9]aneN₃)Me₂(1)

24.9

0.04

0

6230

10

19 700

7130

2.8

b

Ti(NⁱPr)(Me₃[9]aneN₃)Me₂(6)

b

Ti(NPh)(Me₃[9]aneN₃)Me₂(7)

0

4

5

6

7

8

9

10

11

12

13

14

15

Ti(N-3,5-C₆H₃(CF₃)₂)(Me₃[9]aneN₃)Me₂(8)

Ti(N-2,6-C₆H₃Pr₂)(Me₃[9]aneN₃)Me₂(9)

0.02

0.80

0.41

4.8

8.7

0

0.43

0.53

0.48

0.29

0.45

0.90

5

b

342 000

380 000

474 000

245 000

b

54 600

137 000

158 000

92 400

b

i

200

105

1210

2180

0

110

130

120

75

6.3

2.8

3.0

2.7

Ti(N-2-C₆H₄CF₃)(Me₃[9]aneN₃)Me₂(10)

t

Ti(N-2-C₆H₄Bu)(Me₃[9]aneN₃)Me₂(11)

t

Ti(N-2-C₆H₄Bu)(Me₃[9]aneN₃)Me₂(11)

c

Ti(NPh)(Me₃[9]aneN₃)Me₂(7)

Ti(N-2-C₆H₄CF₃)(Me₃[9]aneN₃)Me₂(10)

Ti(N^tBu)(Me₃[9]aneN₃)(CH₂SiMe₃)₂(3)

Ti(N^tBu)(Me₃[9]aneN₃)(CH₂Ph)₂(5)

Ti(N^tBu)(Me₃[9]aneN₃)(CH₂SiMe₃)₂(3)

Ti(N^tBu)(Me₃[9]aneN₃)(CH₂Ph)₂(5)

Ti(N^tBu)(Me₃[9]aneN₃)Me₂(1)

244 000

118 600

83 800

b

82 800

39 500

29 100

b

3.0

2.9

b

4.4

c

d

115

225

b

134 500^e

30 400^e

^aConditions unless stated otherwise: 6 bar of C₂H₄on demand, 2 µmol of precatalyst, 1 equiv of TB, 5 mmol of TIBA, 250 mL of toluene, 1 L reactor,

b

c

d

e

20 min, initiated at 22-24 °C. Not recorded. Initiated at 35 °C. No added TB. Bimodal polymer with M_p) 51 100 and 165 500 g mol^-1. See Experimental

Section for other details.

in fact be viewed as a lower limit, and the polydispersity index

(PDI, M_w/M_n) as the least favorable. These limitations for 1 do

not detract from our overall ability to establish qualitative

structure-productivity correlations within the family of imides

evaluated.

The catalyst system 11/TB/TIBA appeared to show an

induction period. Monitoring of the ethylene uptake rate (flow

rate into the reactor) showed a significant increase after ca. 10

min, which was accompanied by a ca. 10 °C rise in temperature.

This polymerization experiment was repeated with an initiation

temperature of 35 °C (entry 8, Table 3), which gave an increase

in polymer yield from 4.8 g (1210 kg mol^-1h^-1bar^-1) to 8.7 g

(2180 kg mol^-1h^-1bar^-1) and an ethylene uptake at the higher

flow rate from the beginning of the experiment. For comparison,

the catalyst systems 7/TB/TIBA and 10/TB/TIBA were also

evaluated at the 35 °C initiation temperature (entries 9 and 10).

In these cases no productivity gain was observed.

Somewhat surprisingly, the productivities for the other tert-

butyl imides Ti(N^tBu)(Me₃[9]aneN₃)R₂(R ) CH₂SiMe₃(3),

CH₂Ph (5)) were very disappointing, both at 22-24 °C initiation

(130 and 120 kg mol^-1h^-1bar^-1, entries 11 and 12) and at

35 °C (75 and 115 kg mol^-1h^-1bar^-1, entries 13 and 14). Likely

origins of this behavior will be discussed later. We also

evaluated the ethylene polymerization capability of 1/TIBA in

the absence of TB activator (entry 15, Table 3).⁶⁶This run

resulted in 0.90 g of PE in 20 min, corresponding to a pro-

ductivity of 225 kg mol^-1h^-1bar^-1, demonstrating that the

reaction between 1 and TIBA produces a reasonably active

catalyst, but that this productivity is negligible compared to that

with TB present. TIBA alone has also been used as an activator

in other catalyst systems.^67,68

polymer having a PDI of 2.0, the values of 2.7-3.0 are still

consistent with single-site type catalysts. PDIs greater than 2.0

can be attributed to the presence of more than one active species,

or polymerization conditions changing over time, due for

example to a large exotherm or polymer precipitation during

the experiment. For the 9/TB/TIBA catalyst system the GPC

analysis showed a single broad fraction, whereas for 1/TIBA

the sample was clearly bimodal with M_pvalues of 51 100 and

165 500 (overall M_w) 134 500, PDI ) 4.4).

The molecular weight of the PE formed with 1/TB/TIBA was

much lower than those of the other samples. This is attributed

to the larger exotherm during the polymerization process since

chain transfer has a higher activation energy than propagation.⁷⁰

The same effect can be seen when comparing the PEs formed

with 10 and 11 at ambient temperature (entries 6 and 7 in Table

3) and 35 °C (entries 8 and 10).

The M_nvalues for the PE produced with 1/TB/TIBA suggest

that ca. 1750 PE chains are formed per metal center, assuming

that all are productive. In contrast, with the exception of 11/

TB/TIBA at 35 °C initiating temperature (ca. 50 chains per

metal), the other catalyst systems produce only ca. 10-15 chains

per titanium present. This may indicate that fewer precatalyst

centers are actually activated/active and/or that efficient chain

transfer is more energetically accessible at higher temperatures.⁷⁰

It has been suggested that chain transfer to TIBA is disfavored

in zirconocene systems due to unfavorable steric interactions

in forming the necessary isobutyl-bridged heteronuclear bimetal-

lic intermediate.^71,72Diiminopyridyl iron catalysts, on the other

hand, have been shown to readily undergo chain transfer with

TIBA and also the Al-ⁱBu groups of MMAO, giving isopropyl-

terminated polymer chains.⁷³

Polymer Properties. The PEs produced by the more active

catalyst systems were analyzed by GPC (Table 3). The M_w

values are typically in the range 10⁵-10⁶g mol^-1. With the

exception of the PEs from 9/TB/TIBA and 1/TIBA, the polymers

were unimodal with PDIs between 2.7 and 3.0. Although the

Schultz-Flory distribution⁶⁹predicts that a single-site catalyst

undergoing chain transfer processes should give rise to a

We also note Brintzinger’s proposal that, at elevated tem-

peratures, aluminum hydride species may be formed from TIBA

by loss of isobutene and that chain transfer to these hydride

species would be more favored relative to chain transfer to TIBA

itself.⁷²However, the ¹H NMR spectrum of our TIBA in C₆D₆

showed no evidence for aluminum hydrides present in greater

(69) Flory, P. J. Principles of Polymer Chemistry; Cornell University

Press: Ithaca, NY, 1992.

(70) D’Agnillo, L.; Soares, J. B. P.; Penlidis, A. Macromol. Chem. Phys.

1998, 199, 955.

(71) Lieber, S.; Brintzinger, H. H. Macromolecules 2000, 33, 9192.

(72) Bhriain, N. N.; Brintzinger, H. H.; Ruchatz, D.; Fink, G. Macro-

molecules 2005, 38, 2056.

(66) The TB/TIBA mixture alone does not act as a catalyst system under

the conditions used in this study.

(67) Franceschini, F. C.; Tavares, T. T. d. R.; Greco, P. P.; Galland, G.

B.; dos Santos, J. H. Z.; Soares, J. B. P. J. Appl. Polym. Sci. 2005, 95,

1050.

(68) Bryliakov, K. P.; Semikolenova, N. V.; Zakharov, V. A.; Talsi, E.

P. Organometallics 2004, 23, 5375.

(73) Small, B. L.; Brookhart, M. Macromolecules 1999, 32, 2120.

Metallocene-like Imido Titanium Dialkyl Compounds

Organometallics, Vol. 25, No. 23, 2006 5557

Scheme 2. Reaction of [Ti(N^tBu)(Me₃[9]aneN₃)R]⁺with

TIBA in C₆D₅Br at -30 °C (R ) Me or CH₂SiMe₃)

than 1% quantities. Furthermore, heating this solution in a sealed

NMR tube at 80 °C for 20 min (the run-times used in the

polymerization experiments) gave no change in the appearance

of the spectrum or decay of the TIBA resonances as judged by

integration against an internal toluene standard. Nonetheless, it

may still be possible that aluminum-hydride species play a role

under the experimental polymerization conditions.

Experiments on the Ti(N^tBu)(Me₃[9]aneN₃)Cl₂/MAO catalyst

system identified two chain transfer mechanisms,²³namely,

chain transfer to TMA, which results in methyl end groups, and

â-H transfer (either to metal or direct to monomer), resulting

in vinyl-terminated PE. A series of experiments in which the

amount of free TMA was varied showed that as the TMA:Ti

ratio increased, the amount of chain transfer to TMA also

increased, resulting in fewer vinyl-terminated PE chains and

lower molecular weights.

The PE sample from the 1/TB/TIBA catalyst system was

analyzed by NMR spectroscopy in 1,2-C₆D₄Cl₂at 100 °C. The

PE contained no detectable vinyl end groups, therefore indicating

that chain termination by â-H transfer is not significant in this

system. However, no isopropyl end groups were observed either,

which at first sight would have been the expectation for a

mechanism involving chain transfer to TIBA followed by

renewed chain growth at a Ti-CH₂Pr group.⁷³This aspect is

i

discussed further below. By assuming two methyl end groups

Reaction of [Ti(N^tBu)(Me₃[9]aneN₃)R]⁺(R ) Me or

CH₂SiMe₃) with TIBA. We previously showed that reaction

of the methyl cation [Ti(N^tBu)(Me₃[9]aneN₃)Me]⁺with TMA

in C₆D₅Br cleanly and quantitatively formed [Ti(N^tBu)(Me₃[9]-

aneN₃)(µ-Me)₂AlMe₂]⁺.²¹Analogous reactions were therefore

performed between [Ti(N^tBu)(Me₃[9]aneN₃)R]⁺(R ) Me or

CH₂SiMe₃) and TIBA. As mentioned above, attempts to generate

other imido titanium alkyl cations in C₆D₅Br gave oily pre-

cipitates, and so the corresponding reactions with TIBA were

not carried out for these. Addition of TIBA (1 equiv) to pre-

formed [Ti(N^tBu)(Me₃[9]aneN₃)Me]⁺in C₆D₅Br at -30 °C

immediately formed a mixture of macrocycle- and isobutyl-

containing species and isobutene. None of the original reactants

remained. No further change took place place after 20 min,

and the sample was allowed to warm up. After 30 min at

1

per chain, analysis of the PE H integrals gave M_n) 7300 g

mol^-1, a value very close to the M_n) 7130 g mol^-1determined

by GPC. We also attempted to analyze the PE from the 11/TB/

TIBA (35 °C initiation) catalyst system by ¹H NMR. Unfortu-

nately the PE was too insoluble for any end group analysis to

be carried out.

Comparison with the Ti(NR)(Me₃[9]aneN₃)Cl₂/MAO Cata-

lyst Systems. It is interesting to compare the reported ethylene

polymerization capability of the dichloride precatalysts Ti(NR)-

t

i

(Me₃[9]aneN₃)Cl₂(R ) Bu, Ph, 2,6-C₆H₃Pr₂, 2-C₆H₄CF₃,

t

2-C₆H₄Bu). These were activated with MAO (Al:Ti ratio )

1500:1) at ambient temperature under conditions otherwise

comparable to those used here.²³The aryl imido systems showed

structure-productivity and PDI trends broadly comparable to

those for the TB/TIBA-activated dimethyl systems: for R ) Ph,

1

room temperature the H NMR spectrum showed two major

productivity < 1 kg mol^-1h^-1bar^-1; for R ) 2,6-C₆H₃Pr₂,

i

macrocycle-containing species in a ca. 2:1 ratio by integra-

tion. The same mixture was formed when the reaction was

repeated entirely at room temperature. In an analogous reaction,

[Ti(N^tBu)(Me₃[9]aneN₃)CH₂SiMe₃]⁺was generated in situ in

C₆D₅Br, cooled to -30 °C, and TIBA was added. Again iso-

butene was formed immediately, along with complete conver-

sion to a mixture of new organometallic species. On warming

to room temperature, further changes took place, and ultimately

the major macrocycle-containing product was the same as

the dominant species formed in the reaction with [Ti(N^tBu)-

(Me₃[9]aneN₃)Me]⁺. This species appears to possess molecular

C_ssymmetry and two aluminum-bound isobutyl groups. The

¹⁹F NMR spectrum of the mixtures showed only the expected

productivity ) 120 kg mol^-1h^-1bar^-1(PDI ) 7.9); for R )

2-C₆H₄CF₃, productivity ) 220 kg mol^-1h^-1bar^-1(PDI )

2.4); for R ) 2-C₆H₄Bu, productivity ) 580 kg mol^-1h^-1bar^-1

t

(PDI ) 3.3). Interestingly, whereas Ti(N^tBu)(Me₃[9]aneN₃)-

t

Me₂(1) is 5 times as productive as Ti(N-2-C₆H₄Bu)(Me₃[9]-

aneN₃)Me₂(11) in the dimethyl/TB/TIBA systems, it was found

that Ti(N^tBu)(Me₃[9]aneN₃)Cl₂/MAO had a comparable activity

(630 kg mol^-1h^-1bar, PDI ) 4.3) to that of Ti(N-2-C₆H₄Bu)-

t

(Me₃[9]aneN₃)Cl₂/MAO. Nonetheless, despite these differences

between the two catalyst systems, it is clear that both the

dimethyl/TB/TIBA and dichloride/MAO catalyst families require

a bulky imido substituent to achieve high productivities.

Reactions of [Ti(NR)(Me₃[9]aneN₃)R′]⁺and Ti(NR)(Me₃-

[9]aneN₃)R′₂with TIBA: NMR and DFT Studies. A focused

series of NMR tube scale experiments and selected DFT

calculations was carried out. While the chemistry of the imido

titanium alkyl systems with TIBA is likely to be very com-

plex,^30,32,71,72it was hoped that additional insights could be

gained regarding certain aspects of this work, namely, the

dependence of productivity on steric bulk at the imido nitrogen,

the formation of saturated PE chains in the 1/TB/TIBA catalyst

system, and the apparent chain transfer to aluminum within the

systems studied.

resonances for [BAr^F]^-, ruling out anion activation, although

4

solvent activation pathways cannot be discounted.⁷⁴

As shown in Scheme 2, the appearance of isobutene in these

reactions suggests that the first step (rapid even at -30 °C) is

exchange of the Ti-bound alkyl group with one of the isobutyl

groups of TIBA to form II (Scheme 2), which is followed by

rapid â-H elimination. The presence of a mixture of species at

-30 °C suggests that this putative first-formed hydride cation⁷⁴

(74) Ma, K.; Piers, W. E.; Gao, Y.; Parvez, M. J. Am. Chem. Soc. 2004,

126, 5668.

5558 Organometallics, Vol. 25, No. 23, 2006

Bolton et al.

Figure 5. DFT structures of three isomers of the adduct formed between [Ti(NMe)(H₃[9]aneN₃)Me]⁺and TIBA. Relative energies are

given in kJ mol^-1. The values in parentheses are formation energies with respect to separated [Ti(NMe)(H₃[9]aneN₃)Me]⁺and TIBA (for

IV-TIBA and V-TIBA) or [Ti(NMe)(H₃[9]aneN₃)ⁱBu]⁺and MeAlⁱBu₂(for VI). Ti, Al, and N atoms are shown in red, green, and blue,

respectively.

III and the new alkyl aluminum species RAlⁱBu₂give rise to

further reactions. The precise identity of the final dominant

product(s) formed on warming to room temperature is unknown,

and it was not possible to isolate a pure compound on the

preparative scale.

catalyst systems, we carried out DFT calculations on three

potential products (IV-TIBA, V-TIBA, and VI) formed between

the model methyl cation [Ti(NMe)(H₃[9]aneN₃)Me]⁺and TIBA.

Line drawing representations are shown below, and the DFT

structures themselves are presented in Figure 5.

The rapid reaction of [Ti(N^tBu)(Me₃[9]aneN₃)R]⁺with TIBA

for both R ) Me or CH₂SiMe₃supports the view that chain

transfer to TIBA could in principle be facile in these catalyst

systems. To account for the absence of isopropyl end groups in

the PE formed by 1/TB/TIBA, renewed chain growth following

i

formation of [Ti(N^tBu)(Me₃[9]aneN₃)CH₂Pr]⁺(II) presumably

occurs either after â-H elimination to form III (which may then

insert C₂H₄, forming an ethyl cation [Ti(N^tBu)(Me₃[9]aneN₃)-

Et]⁺) or after â-H transfer to monomer, directly forming an ethyl

cation and isobutene.³²In other words, the isobutyl cation II is

not a competitive chain growth initiating species in these catalyst

systems.

The bis(µ-alkyl) adduct [Ti(NMe)(H₃[9]aneN₃)(µ-Me)(µ-ⁱBu)-

AlⁱBu₂]⁺(IV-TIBA) was calculated to have a formation energy

of -80.2 kJ mol^-1relative to separated [Ti(NMe)(H₃[9]aneN₃)-

Me]⁺and TIBA. The corresponding model with TMA (IV-

DFT-Computed TIBA Adducts of [Ti(NMe)(H₃[9]aneN₃)-

Me]⁺. In the catalyst system Ti(N^tBu)(Me₃[9]aneN₃)Cl₂/MAO,

it was found that increasing the amount of TMA present resulted

not only in a decrease in M_wand the number of PE vinyl end

groups (see above) but also in a decrease of productivity.^20,23

This was attributed to a higher fraction of the titanium present

being trapped as nonproductive resting-state adducts^35-44of

the type [Ti(N^tBu)(Me₃[9]aneN₃)(µ-Me)(µ-R)AlMe₂]⁺(R )

polymeryl or Me²¹). The poor productivities of precatalysts

Ti(NR)(Me₃[9]aneN₃)Cl₂with smaller imido R-groups were

attributed to a lack of steric protection of the TidNR linkage

toward attack by TMA or other species present. Very recently,

we performed DFT calculations on the energies of the potential

adducts formed between TMA and the model species [Ti(NMe)-

(H₃[9]aneN₃)Me]⁺(IV-TMA, V-TMA; see below).⁷⁵It is ex-

pected that TIBA would be less likely than TMA to form such

adducts because of the associated adverse steric effects.^30,72,76

Nonetheless, the polymerization results and NMR tube scale

experiments for [Ti(N^tBu)(Me₃[9]aneN₃)R]⁺with TIBA suggest

that such interactions are possible in these cases. To better

quantify the situation, and to evaluate the types of adducts that

might be formed in the Ti(NR)(Me₃[9]aneN₃)Me₂/TB/TIBA

TMA) had a formation energy of -98.4 kJ mol^{-1 75}

. The lower

stability of IV-TIBA relative to IV-TMA is attributable to the

bulky isobutyl groups. These results are supported by recent

experimental studies by Anwander on neutral yttrocene tet-

raalkylaluminates rac-{Me₂Si(2-C₉H₅Me)₂}Y(µ-R)(µ-R′)AlR′₂

(R ) Me, Et; R′ ) Me, Et, ⁱBu).⁷⁶The presence of imido nitro-

gen lone pairs in the cations [Ti(NR)(Me₃[9]aneN₃)R′]⁺suggests

the possibility of forming a dative NfAl bond. as has been

found for the labile adduct Ti(η-C₈H₈)(µ-N^tBu)(µ-Me)AlMe₂

(formed by reaction of Ti(η-C₈H₈)(N^tBu) with TMA).⁷⁷The

relevant model species is V-TIBA, which had a formation

energy of -103.8 kJ mol^-1. The analogous TMA adduct (V-

TMA) had a formation energy of -136.1 kJ mol^{-1 75}

Model

.

VI, which is an isomer of V-TIBA but with the smaller methyl

group in the Ti(µ-CH₂R)Al linkage, was 11.1 kJ mol^-1more

stable than V-TIBA, consistent with a reduction in steric pres-

sure in the bridging unit.

In terms of electronic preferences, the calculations shown that

simultaneous bonding of TIBA to the Ti-R′ and TidNR groups

of [Ti(NR)(Me₃[9]aneN₃)R′]⁺(cf. V-TIBA) would provide a

greater stabilizing effect than forming two µ-alkyl bridges (cf.

(75) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. J. Am. Chem.

Soc., accepted for publication.

(76) Klimpel, M. G.; Eppinger, J.; Sirsch, P.; Scherer, W.; Anwander,

R. Organometallics 2002, 21, 4021.

(77) Dunn, S. C.; Hazari, N.; Cowley, A. R.; Green, J. C.; Mountford,

P. Organometallics 2006, 25, 1755.

Metallocene-like Imido Titanium Dialkyl Compounds

Organometallics, Vol. 25, No. 23, 2006 5559

IV-TIBA). This in turn would lead to a lower fraction of the

metal centers being active for olefin polymerization. Such

N-adducts would be very sensitive to the steric bulk at the imido

nitrogen. Note also that while both model NfAl adducts V are

more stable than their bis(µ-alkyl) counterparts IV, the stability

gain in V-TIBA (-23.6 kJ mol^-1) is significantly less than in

V-TMA (-37.7 kJ mol^-1). Since the real TMA adduct [Ti(N^t-

Bu)(Me₃[9]aneN₃)(µ-Me)₂AlMe₂]⁺does not contain a N_imidefAl

interaction, it is unlikely that adducts of the type V-TIBA would

form for sterically encumbered imido ligands. Moreover, bis-

(µ-alkyl) adducts of the type IV with TIBA should also be at

least ca. 20 kJ mol^-1enthalpically less stable than their TMA

counterparts.⁷⁶

Overall, the DFT calculations find that both types of TIBA

adduct may be accessible to varying degrees (depending on

steric factors) in the experimental catalyst systems Ti(NR)(Me₃-

[9]aneN₃)R′₂/TB/TIBA. Bis(µ-alkyl) species would provide

catalytically inactive resting states and/or intermediates on the

pathway to chain transfer to TIBA, while NfAl adducts (for

small imido R-groups) would also represent inactive/dormant

species.

Reactions of Ti(NR)(Me₃[9]aneN₃)R′₂with TIBA. At first

sight, the structure-productivity trends for the dimethyl catalyst

systems Ti(NR)(Me₃[9]aneN₃)Me₂/TB/TIBA could be ad-

equately explained in terms of steric protection of the active

species “[Ti(NR)(Me₃[9]aneN₃)R′]⁺” (R′ ) polymeryl) toward

the formation of heterobimetallic TIBA adducts (cf. Figure 5)

and/or imido-bridged homobimetallic species [Ti₂(µ-NR)₂(Me₃-

[9]aneN₃)₂(R′)₂]²⁺(cf. dimeric 14²⁺vs monomeric²²[Ti(N^tBu)-

(Me₃[9]aneN₃)R′]⁺). Similar explanations could be advanced

for the Ti(NR)(Me₃[9]aneN₃)Cl₂/MAO²³and related²⁵catalyst

systems.

resonances for a single C_ssymmetric titanium species containing

a macrocycle, tert-butyl imido, and titanium-bound methyl

ligands and a single isobutyl environment. The spectrum was

reminiscent of the separated 1 and TIBA in the respective

solvents, but the shifts clearly differed, indicative of an inter-

action between the two compounds. Cooling the C₆D₅Br solution

to -30 °C resulted in broadening of the resonances. The NMR

spectra are consistent with a “cation-like”⁷⁸weak adduct of the

type Ti(N^tBu)(Me₃[9]aneN₃)Me(µ-Me)AlⁱBu₃(1‚TIBA), which

is still in the fast-exchange regime at -30 °C (eq 3). As drawn,

1‚TIBA is an analogue of the well-established zwitterions

L_nMMe(µ-Me)BAr^F, which are sometimes formed when di-

3

methyl complexes are activated with BAr^F.^30,78,79Compound

3

1‚TIBA may be considered as a “masked” form of [Ti(N^tBu)-

(Me₃[9]aneN₃)Me]⁺stabilized by a polarizable and coordinating

[AlⁱBu₃Me]^-anion. Strong anion coordination quenches the

polymerization capability of Ziegler catalysts.^30,32Therefore,

although the catalyst system 1/TIBA has some productivity, it

is only in the presence of TB that a very good catalyst system

is formed. The origin of the bimodal molecular weight distribu-

tion in this case is not clear. The reaction of 1‚TIBA with TB

is described below.

NMR tube scale reactions were also carried out between Ti-

(N^tBu)(Me₃[9]aneN₃)R₂(R ) CH₂SiMe₃(3) or CH₂Ph (5)) and

TIBA (1 equiv) in C₆D₆. Each immediately formed ill-defined

and complex mixtures, with sets of resonances for several

macrocycle, tert-butyl, and isobutyl environments. This behavior

of 3 and 5 is in stark contrast to the clean formation of 1‚TIBA

in the case of the dimethyl homologue 1. Further reactions were

carried out between TIBA (1 equiv) and Ti(NPh)(Me₃[9]aneN₃)-

i

Me₂(7) or Ti(N-2,6-C₆H₃Pr₂)(Me₃[9]aneN₃)Me₂(9), both

t

poorly or unproductive precatalysts, and also Ti(N-2-C₆H₄Bu)-

However, the very contrasting productivities for the equally

sterically protected tert-butyl imides Ti(N^tBu)(Me₃[9]aneN₃)-

R₂(R ) Me (1) . CH₂SiMe₃(3) ≈ CH₂Ph (5)), which differ

only in the identity of the precatalyst Ti-R groups, show that

this is not the only factor to consider. In these three systems,

the catalytically active species ultimately formed should be

effectively the same in each case after the first ethene insertions

and/or chain transfer event. Furthermore, although the first-

formed cations [Ti(N^tBu)(Me₃[9]aneN₃)R]⁺(all instantly pro-

duced with TB) have nonclassical interactions that provide

differing degrees of stabilization (modeled by I-Me, I-CH₂SiMe₃,

and I-CH₂Ph), the NMR tube experiments between TIBA and

[Ti(N^tBu)(Me₃[9]aneN₃)Me]⁺and [Ti(N^tBu)(Me₃[9]aneN₃)-

CH₂SiMe₃]⁺showed both these cations react rapidly to exchange

the precatalyst Ti-R groups. Therefore an “initiator effect”

based on the ease of formation or stability of the first-formed

[Ti(N^tBu)(Me₃[9]aneN₃)R]⁺cations also appears to be ruled out.

These questions, and the observation that 1/TIBA alone (Table

3, entry 15) also forms a productive catalyst system, prompted

us to examine the reactions of representative dialkyls Ti(NR)-

(Me₃[9]aneN₃)Me₂with TIBA.

(Me₃[9]aneN₃)Me₂(11), the only other highly productive com-

pound in Table 3. Like 3 and 5, compounds 7 and 9 gave

complex mixtures with TIBA in C₆D₆. In contrast, the ¹H NMR

spectrum of the 1:1 mixture of 11 and TIBA was well-defined,

showing resonances for the two components that were somewhat

shifted from their positions prior to reaction. For completeness

we also examined the reaction between the phenyl imido

dichloride Ti(NPh)(Me₃[9]aneN₃)Cl₂²³and TIBA (1 equiv), in

order to confirm that it is the Ti-Me bonds of 7 (rather than

the imido or macrocyclic ligands) that react. In contrast to the

complex mixture formed between 7 and TIBA, no reaction

occurred in the case of Ti(NPh)(Me₃[9]aneN₃)Cl₂. Overall these

results suggest that the low polymerization productivity of many

of the compounds in Table 1 might in part be attributable to

unfavorable reactions between the precatalyst Ti-alkyl bonds

and the TIBA.

Role of TIBA in the Catalyst Activation Process for 1.

Transition metal isobutyl compounds undergo hydride abstraction

with [Ph₃C]⁺, forming Ph₃CH, isobutene, and polymerization-

active cations.^61,65However, this is not a likely activation process

for 1/TIBA since 1 did not undergo any detectable Ti-Me/

Al-ⁱBu group exchange on the NMR tube scale even after

extended periods.⁸⁰However, it is known that TB rapidly reacts

with TIBA at ambient remperature via hydride abstraction to

form Ph₃CH, isobutene, and “[AlⁱBu₂]⁺”.⁶⁴The aluminum cation

subsequently reacts with [BAr^F]^-, giving mixtures of Al(ⁱBu)_x-

4

(78) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991, 113,

3623.

(79) Piers, W. E. AdV. Organomet. Chem. 2005, 52, 1.

(80) We cannot rule out the possibility of a small degree of alkyl group

exchange between Ti and Al at the high ratios used in the polymerization

experiments.

1

The H NMR spectrum of a mixture of Ti(N^tBu)(Me₃[9]-

aneN₃)Me₂(1) with TIBA (1 equiv) in C₆D₆or C₆D₅Br showed

5560 Organometallics, Vol. 25, No. 23, 2006

Bolton et al.

(Ar^F)_yand B(ⁱBu)_x(Ar^F)_y(x + y ) 3). Similar chemistry has

giving poor polymerization productivity also form a number of

different and unknown products on exposure to TIBA. Since

TB reacts preferentially with TIBA to 1, forming Ph₃CH, it

appears that a transient “[AlⁱBu₂]⁺” cation plays an important

role in the activation of the titanium dialkyl species.

The adverse effects of aluminum alkyls on group 4 catalyst

systems and their precursors are well known and involve the

trapping of active species as well as (pre)catalyst decomposition

and other detrimental pathways.^{30,35-44,81-90}Therefore, in the

catalyst systems reported here, the imido group appears to have

two roles: (i) to stabilize the dialkyl precatalyst to degradation

by the TIBA itself and (ii) to inhibit the formation of catalyti-

cally inactive heterobimetallic or homobimetallic complexes.

been reported for the anilinium borate [PhNMe₂H][BAr^F].⁶³

4

As we have shown, reaction of Ti(N^tBu)(Me₃[9]aneN₃)Me₂

(1) with TB quantitatively gives the methyl cation [Ti(N^tBu)-

(Me₃[9]aneN₃)Me]⁺and the trityl derivative Ph₃CMe.^20,22In

the presence of TMA (1 equiv), methide abstraction also occurs,

forming Ph₃CMe and [Ti(N^tBu)(Me₃[9]aneN₃)(µ-Me)₂AlMe₂]⁺.²¹

However, it was not apparent what the equivalent activation

reaction of 1 with TB would be in the presence of TIBA, and

so a further NMR tube scale experiment was carried out.

Reaction of TB (1 equiv) with a 1:1 mixture of 1 and TIBA in

C₆D₅Br immediately gave complete consumption of all of the

1

starting materials. The H spectrum in the δ 3.5 to -0.5 ppm

region was reminiscent of the mixture formed in the reaction

between [Ti(N^tBu)(Me₃[9]aneN₃)Me]⁺and TIBA (Scheme 2)

with some sets of resonances apparently in common. Most

importantly, the only trityl-derived product observed was Ph₃-

CH. This was formed in essentially quantitative yield, as judged

against an internal toluene standard (comparing Ph₃CH and

PhMe) resonances. There was no detectable Ph₃CMe, which

would have arisen from methide abstraction from 1. The ¹⁹F

NMR spectrum of the mixture showed a single set of resonances

Experimental Section

General Methods and Instrumentation. All manipulations were

carried out using standard Schlenk line or drybox techniques under

an atmosphere of argon or of dinitrogen. Protio- and deuterosolvents

were predried over activated 4 Å molecular sieves and were refluxed

over the appropriate drying agent, distilled, and stored under

dinitrogen in Teflon valve ampules. NMR samples were prepared

under dinitrogen in 5 mm Wilmad 507-PP tubes fitted with J. Young

Teflon valves. ¹H, ¹³C{¹H}, ¹⁹F, and ²⁹Si NMR spectra were

recorded on Varian Mercury-VX 300 and Varian Unity Plus 500

spectrometers. ¹H and ¹³C assignments were confirmed when

necessary with the use of DEPT-135, DEPT-90, and two-

for the [BAr^F]^-anion and none for the redistribution products

4

Al(ⁱBu)_x(Ar^F)_yor B(ⁱBu)_x(Ar^F)_y.^63,64

These results are interesting since they suggest that â-hydride

abstraction from TIBA (free or weekly coordinated as 1‚TIBA

(eq 3)) is considerably more favored that methide abstraction,

even at a 1:1 Al:Ti molar ratio (in the polymerization experi-

ments a 2500:1 ratio was used). The implication is that the first-

formed cation in the 1/TB/TIBA catalyst system is of the type

[Ti(N^tBu)(Me₃[9]aneN₃)(µ-Me)₂AlⁱBu₂]⁺, formally derived from

addition of “[AlⁱBu₂]⁺” to 1. Further equilibria arising from this

species (e.g., via alkyl group redistribution and/or â-H elimina-

tion from monomeric species of the type II in Scheme 2) would

dimensional H-¹H and ¹³C-¹H NMR experiments. H and ¹³C

spectra were referenced internally to residual protiosolvent (¹H) or

solvent (¹³C) resonances and are reported relative to tetramethyl-

silane (δ ) 0 ppm). ¹⁹F and ²⁹Si spectra were referenced externally

to CFCl₃and tetramethylsilane, respectively. Chemical shifts are

quoted in δ (ppm) and coupling constants in Hertz. Infrared spectra

were prepared as Nujol mulls between KBr or NaCl plates and

were recorded on Perkin-Elmer 1600 and 1710 series FTIR

spectrometers. Infrared data are quoted in wavenumbers (cm^-1).

Mass spectra were recorded by the mass spectrometry service of

Oxford University’s Department of Chemistry. Elemental analyses

were carried out by the analytical laboratory of the School of

Chemistry, University of Nottingham, Inorganic Chemistry Labora-

tory, University of Oxford, or Elemental Analysis Service at the

London Metropolitan University. GPC analyses were carried out

by Rapra Technology Ltd. in 1,2,4-trichlorobenzene solvent at

160 °C relative to polystyrene calibrants and using the appropriate

Mark Houwink parameters for polyethylene.

1

help explain the appearance of the H NMR spectra of the

reaction mixture. Unsurprisingly, admisison of ethylene (1.1 bar)

to the NMR tube containing the 1/TB/TIBA mixture produced

a precipitate of polyethylene. We note that Go¨tz and co-workers

have proposed a role for “[AlⁱBu₂]⁺” in TIBA/anilinium borate-

activated zirconocene catalyst systems, although this case

involved hydride abstraction from an isobutyl ligand.⁶³

Conclusions

Starting Materials. The compounds Ti(NR)(Me₃[9]aneN₃)Cl₂,²³

We have developed synthetic routes to a range of macrocycle-

supported imido titanium dialkyl compounds and determined a

number of their X-ray structures. These compounds are generally

less thermally and light sensitive than their isolobal titanocene

analogues. A number of them form single site-type ethylene

polymerization catalysts on activation with TB in the presence

of TIBA. The structure-productivity trends for the dimethyl

precatalysts vary as a function of imido substituent and parallel

those of the dichloride-based Ti(NR)(Me₃[9]aneN₃)Cl₂/MAO

family reported before.²³

In the Ti(NR)(Me₃[9]aneN₃)Me₂/TB/TIBA catalysts the TIBA

acts both as a scavenger and as a chain transfer reagent, forming

isobutyl cations, which readily undergo â-H transfer in either

stoichiometric or catalytic contexts. DFT calculations indicated

that TIBA, although it is a rather bulky aluminum alkyl, is able

to form adducts with imido titanium alkyl cations and that the

stability and type of adduct formed will depend on the steric

properties of the imido substituent. The outcomes of the reac-

tions between the various Ti(NR)(Me₃[9]aneN₃)R′₂species and

TIBA appeared to broadly parallel the polymerization capabili-

ties of the associated catalyst systems. Thus the precatalysts

t

LiCH₂SiMe₃,⁹¹and LiCH₂Bu,⁹²were prepared according to the

(81) Zhu, F.; Huang, Q.; Lin, S. J. Polym. Sci., Part A: Polym. Chem.

1999, 37, 4497.

(82) Chien, J. C. W.; Salajka, Z.; Dong, S. Macromolecules 1992, 25,

3199.

(83) Zhu, F.; Huang, Y.; Yang, Y.; Lin, S. J. Polym. Sci., Part A: Polym.

Chem. 2000, 38, 4258.

(84) Kickham, J. E.; Guerin, F.; Stephan, D. W. J. Am. Chem. Soc. 2002,

124, 11486.

(85) Kickham, J. E.; Guerin, F.; Stewart, J. C.; Stephan, D. W. Angew.

Chem., Int. Ed. 2000, 39, 3263.

(86) Kickham, J. E.; Guerin, F.; Stewart, J. C.; Urbanska, E.; Ong, C.

M.; Stephan, D. W. Organometallics 2001, 20, 1175.

(87) Kickham, J. E.; Guerin, F.; Stewart, J. C.; Urbanska, E.; Ong, C.

M.; Stephan, D. W. Organometallics 2001, 20, 3209.

(88) Kretschmer, W. P.; Dijkhuis, C.; Meetsma, A.; Hessen, B.; Teuben,

J. H. Chem. Comm. 2002, 608.

(89) Stapleton, R. A.; Galan, B. R.; Collins, S.; Simons, R. S.; Garrison,

J. C.; Youngs, W. J. J. Am. Chem. Soc. 2003, 125, 9246.

(90) Busico, V.; Cipullo, R.; Cutillo, F.; Friederichs, N.; Ronca, S.; Wang,

B. J. Am. Chem. Soc. 2003, 125, 12402.

(91) Tessier-Youngs, C.; Beachley, O. T. Inorg. Synth. 1986, 24, 95.

(92) Davidson, P. J.; Lappert, M. F.; Pearce, R. J. Organomet. Chem.

1973, 57, 269.

Metallocene-like Imido Titanium Dialkyl Compounds

Organometallics, Vol. 25, No. 23, 2006 5561

literature methods. Other reagents were purchased and used without

further purification.

1.65 (2H, m, NCH₂), 1.62 (2H, m, NCH₂), 1.58 (2H, m, NCH₂),

1.51 (9H, s, NCMe₃), 0.49 (18H, s, CH₂SiMe₃), 0.42 (2H, d, ²J 10.4

2

Hz, CH_aH_bSiMe₃), -0.19 (2H, d, J 10.4 Hz, CH_aH_bSiMe₃). ¹³C-

Ti(N^tBu)(Me₃[9]aneN₃)Me₂(1). Methyl lithium (3.05 mL, 1.6 M

in Et₂O, 4.87 mmol) was added to a vigorously stirred suspension

of Ti(N^tBu)(Me₃[9]aneN₃)Cl₂(0.800 g, 2.21 mmol) in THF (30

mL) at -78 °C. The reaction mixture was allowed to warm very

slowly to room temperature and then stirred for 16 h. The volatiles

were removed under reduced pressure to give a yellow solid. The

solid was extracted into benzene (20 mL) and filtered, and the

volatiles were removed under reduced pressure. The resulting yellow

solid was dissolved in a mixture of hexane and benzene (20 mL:

10 mL), filtered to remove undissolved material, and cooled to -30

°C for 1 day to give 1 as yellow crystals. Yield: 0.500 g (70%).

Diffraction-quality crystals were grown from a saturated benzene/

{¹H} NMR (C₆D₆, 75.5 MHz, 298 K): 66.1 (NCMe₃), 56.0 (NCH₂),

55.3 (NCH₂), 55.1 (NCH₂), 52.6 (NMe cis), 49.4 (NMe trans), 41.6

(CH₂SiMe₃), 33.8 (NCMe₃), 4.7 (CH₂SiMe₃). ²⁹Si NMR (HMQC

¹H-observed, CD₂Cl₂, 299.9 MHz, 293 K): -1.8 (CH₂SiMe₃).

1

²⁹Si NMR (HMQC H-observed, C₆D₅Br, 299.9 MHz, 293 K):

-3.1 (CH₂SiMe₃). IR (KBr pellet, cm^-1): 2816 (br s), 1494 (m),

1464 (s), 1366 (w), 1346 (m), 1300 (m), 1236 (s), 1202 (m), 1152

(m), 1112 (m), 1082 (s), 1070 (s), 1010 (s), 884 (s), 850 (s), 816

(s), 776 (m), 748 (s), 730 (s), 666 (m), 588 (m), 528 (m), 410 (m).

Anal. Found (calcd for C₂₁H₅₂N₄Si₂Ti): C 52.6 (54.3), H 11.4

(11.3), N 11.8 (12.1). The low %C is attributed to titanium carbide

formation.

1

hexane solution at -30 °C. H NMR (C₆D₆, 300.1 MHz, 298 K):

t

Ti(N^tBu)(Me₃[9]aneN₃)(CH₂Bu)₂(4). Cold benzene (60 mL)

2.65 (6H, s, NMe cis), 2.52 (2H, m, CH₂), 2.43 (3H, s, NMe trans),

2.35 (2H, m, CH₂), 2.19 (2H, m, CH₂), 1.69 (2H, m, CH₂), 1.66

(2H, m, CH₂), 1.65 (9H, s, NCMe₃), 1.61 (2H, m, CH₂), 0.36 (6H,

s, TiMe). ¹³C{¹H} NMR (C₆D₆, 75.5 MHz, 298 K): 64.7 (NCMe₃),

55.5 (CH₂), 55.1 (CH₂), 54.8 (CH₂), 51.8 (NMe cis), 48.5 (NMe

trans), 33.5 (NCMe₃), 26.4 (TiMe). IR (NaCl plates, Nujol mull,

cm^-1): 2920 (s), 2853 (s), 1495 (m), 1364 (m), 1343 (m), 1299

(m), 1245 (s), 1204 (s), 1151 (m), 1117 (m), 1099 (m), 1008 (s),

993 (m), 891 (m), 777 (s), 747 (m). FI-MS: m/z 320.3 (12%) [M]⁺,

305.3 (100%) [M - Me]⁺. Anal. Found (calcd for C₁₅H₃₆N₄Ti):

C 56.2 (56.2), H 11.2 (11.3), N 17.4 (17.5).

was added to a mixture of Ti(N^tBu)(Me₃[9]aneN₃)Cl₂(0.361 g, 1.00

t

mmol) and LiCH₂Bu (0.156 g, 2.00 mmol) at 5 °C with vigorous

stirring and in the absence of light. The orange suspension was

allowed to warm to room temperature and then stirred for 17 h.

An aliquot was taken, and the ¹H NMR spectrum showed that the

reaction mixture contained a 1:3 mixture of the desired product to

a monoalkylated species. Therefore a further 0.10 g (1.3 mmol) of

t

LiCH₂Bu was added to the reaction mixture. The reaction mixture

was stirred for a further 17 h. The resulting deep yellow, cloudy

solution was filtered to remove suspended material, and then the

volatiles were removed under reduced pressure to give a yellow-

brown solid. The product was extracted into hexane (60 mL), and

the volatiles were removed under reduced pressure to give 4 as a

yellow powder. Yield: 0.086 g (20%). ¹H NMR (C₆D₆, 300.1 MHz,

293 K): 2.67 (6H, s, NMe cis), 2.42 (2H, m, NCH₂), 2.31 (3H, s,

NMe trans), 2.31-2.18 (4H, overlapping m, NCH₂), 1.71 (18H, s,

CH₂CMe₃), 1.63 (9H, s, NCMe₃), 1.63-1.48 (6H, overlapping m,

NCH₂), 0.80 (2H, d, ²J 11.7 Hz, CH_aH_bCMe₃), 0.58 (2H, d, ²J 11.7

Hz, CH_aH_bCMe₃). ¹³C{¹H} NMR (C₆D₆, 75.4 MHz, 293 K): 78.0

(CH₂CMe₃), 67.0 (CH₂CMe₃), 57.7 (NCMe₃), 55.9 (NCH₂), 55.7

(NCH₂), 55.5 (NCH₂), 52.7 (NMe cis), 49.6 (NMe trans), 37.0

(CH₂CMe₃), 35.2 (NCMe₃). IR (NaCl plates, Nujol mull, cm^-1):

2924 (s), 2854 (s), 1492 (m), 1346 (s), 1301 (m), 1260 (w), 1237

(s), 1219 (s), 1201 (s), 1152 (m), 1126 (w), 1100 (m), 1083 (m),

1073 (m), 1011 (s), 889 (w), 797 (w), 773 (m), 749 (m). Anal.

Found (calcd for C₂₃H₅₂N₄Ti): C 63.7 (63.9), H 12.2 (12.1), N

12.8 (13.0).

Ti(N^tBu)(Me₃[9]aneN₃)(Cl)Me (2). Methyl lithium (0.62 mL,

1.6 M in Et₂O, 1.00 mmol) was added to a stirred suspension of

Ti(N^tBu)(Me₃[9]aneN₃)Cl₂(0.361 g, 1.00 mmol) in tetrahydrofuran

(20 mL) at -78 °C and in the absence of light. The reaction mixture

was allowed to warm slowly to room temperature and then stirred

for a further 16 h. The volatiles were removed under reduced

pressure to give a yellow solid. The solid was extracted into benzene

(20 mL) and filtered, and the solution concentrated to approximately

5 mL. The product was then cautiously precipitated by the slow

addition of pentane (25 mL) with vigorous stirring. The resulting

yellow precipitate was filtered off, washed with pentane (3 × 5

mL), and dried in vacuo to give 2 as a pale yellow powder. Yield:

0.186 g (55%). ¹H NMR (C₆D₆, 300.1 MHz, 298 K): 2.92 (3H, s,

NMe cis), 2.73 (3H, m, CH₂), 2.71 (3H, s, NMe cis), 2.59 (3H, s,

NMe trans), 2.27 (3H, m, CH₂), 2.03 (2H, m, CH₂), 1.89 (4H,

overlapping m, CH₂), 1.50 (9H, s, NCMe₃), 0.75 (3H, s, TiMe).

¹³C{¹H} NMR (C₆D₆, 75.5 MHz, 298 K): 66.9 (NCMe₃), 56.7

(CH₂), 55.8 (CH₂), 55.5 (CH₂), 55.3 (2 × CH₂), 54.6 (CH₂), 53.0

(NMe cis), 52.8 (NMe cis), 49.2 (NMe trans), 33.4 (TiMe), 32.5

(NCMe₃). IR (NaCl plates, Nujol mull, cm^-1): 2920 (s), 2854 (s),

1497 (m), 1347 (m), 1298 (m), 1249 (s), 1205 (m), 1155 (m), 1121

(w), 1008 (s), 993 (m), 893 (w), 780 (m), 747 (m). FI-MS: m/z

340.2 (70%) [M]⁺, 325.2 (100%) [M - Me]⁺, 171.2 (15%) [Me₃-

[9]aneN₃]⁺. FI-HRMS: m/z found (calcd for C₁₄H₃₃ClN₄Ti, [M]⁺)

340.1857 (340.1873). Anal. Found (calcd for C₁₄H₃₃ClN₄Ti): C

48.6 (49.4), H 9.6 (9.8), N 16.3 (16.4). The low %C may be

attributed to the presence of trace amounts of the Ti(N^tBu)(Me₃-

[9]aneN₃)Cl₂starting material.

Ti(N^tBu)(Me₃[9]aneN₃)(CH₂SiMe₃)₂(3). Cold benzene (60 mL)

was added to a mixture of Ti(N^tBu)(Me₃[9]aneN₃)Cl₂(0.361 g, 1.00

mmol) and LiCH₂SiMe₃(0.188 g, 2.00 mmol) at 5 °C with vigorous

stirring and in the absence of light. The orange suspension was

allowed to warm to room temperature and then stirred for 17 h.

The resulting deep yellow, cloudy solution was filtered to remove

suspended material, and then the volatiles were removed under

reduced pressure to give a yellow-brown semisolid. The product

was extracted into the minimum pentane (35 mL) and cooled first

to -25 °C for 24 h and then to -80 °C for 2 days to give 3 as

bright yellow crystals. Yield: 0.336 g (72%). ¹H NMR (C₆D₆, 300.1

MHz, 298 K): 2.65 (6H, s, NMe cis), 2.51 (2H, m, NCH₂), 2.28

(3H, s, NMe trans), 2.27 (2H, m, NCH₂), 2.24 (2H, m, NCH₂),

Ti(N^tBu)(Me₃[9]aneN₃)(CH₂Ph)₂(5). Benzylmagnesium chlo-

ride (2.00 mL, 1.0 M in Et₂O, 2.00 mmol) was added to a stirred

solution of Ti(N^tBu)(Me₃[9]aneN₃)Cl₂(0.361 g, 1.00 mmol) in THF

(50 mL) at -45 °C and in the absence of light. The resulting bright

yellow solution was allowed to slowly warm to room temperature

and then stirred for a further 20 h. 1,4-Dioxane (0.5 mL, 5.9 mmol)

was added to the solution with stirring, resulting in a slight cloudi-

ness. The volatiles were removed under reduced pressure to give a

pale yellow solid. The product was extracted into toluene (120 mL)

and the solution then filtered and the volume reduced to approx-

imately 50 mL. The product was then cautiously precipitated by

the slow addition of hexane (100 mL) with vigorous stirring. The

resulting yellow precipitate was filtered off and dried under reduced

pressure to give 5 as a bright yellow powder. Yield: 0.406 g (86%).

3

¹H NMR (C₆D₆, 300.1 MHz, 298 K): 7.41 (4H, d, J 7.3 Hz,

3

2-C₆H₅), 7.32 (4H, app. t, app. J 7.6 Hz, 3-C₆H₅), 6.91 (2H, t,

³J 7.2 Hz, 4-C₆H₅), 2.89 (2H, d, ²J 9.2 Hz, CH_aH_bPh), 2.46 (6H, s,

NMe cis), 2.43 (2H, d, ²J 9.2 Hz, CH_aH_bPh), 2.38 (2H, m, NCH₂),

2.09 (2H, m, NCH₂), 2.08 (2H, m, NCH₂), 2.02 (3H, s, NMe trans),

1.51 (2H, m, NCH₂), 1.50 (2H, m, NCH₂), 1.48 (2H, m, NCH₂),

1.29 (9H, s, NCMe₃). ¹³C{¹H} NMR (C₆D₆, 75.5 MHz, 298 K):

158.0 (1-CH₂Ph), 127.7 (3-CH₂Ph), 125.8 (2-CH₂Ph), 118.2 (4-

CH₂Ph), 67.7 (NCMe₃), 61.1 (CH₂Ph), 55.9 (NCH₂), 55.2 (NCH₂),

55.0 (NCH₂), 52.0 (NMe cis), 49.0 (NMe trans), 33.0 (NCMe₃).

5562 Organometallics, Vol. 25, No. 23, 2006

Bolton et al.

IR (NaCl plates, Nujol mull, cm^-1): 3060 (w), 2932 (s), 2853 (s),

1591 (s), 1346 (w), 1299 (m), 1241 (s), 1217 (s), 1174 (w), 1153

(w), 1114 (w), 1008 (s), 948 (s), 929 (m), 871 (w), 777 (m), 743

(s), 697 (s). Anal. Found (calcd for C₂₇H₄₄N₄Ti): C 67.4 (68.6), H

9.3 (9.4), N 11.7 (11.9). The low %C is attributed to incomplete

combustion (TiC formation).

concentrated to approximately 5 mL, and then the product was

cautiously precipitated by the slow addition of pentane (20 mL)

with vigorous stirring. The resulting orange precipitate was filtered

off, washed with pentane (3 × 5 mL), and dried in vacuo to give

8 as an orange powder. Yield: 173 mg (31%). Diffraction-quality

single crystals were grown by slow evaporation of a diethyl ether

1

Ti(NⁱPr)(Me₃[9]aneN₃)Me₂(6). Methyl lithium (1.80 mL, 1.6

M in Et₂O, 2.88 mmol) was added slowly to a stirred suspension

of Ti(NⁱPr)(Me₃[9]aneN₃)Cl₂(500 mg, 1.44 mmol) in THF (60 mL)

at -78 °C. The reaction mixture was allowed to warm slowly to

room temperature and stirred for 16 h. The volatiles were removed

under reduced pressure and the resulting yellow-brown solid

extracted into benzene (20 mL). Hexanes were added to induce

crystallization, and the mixture was cooled to -30 °C for 3 days.

The solids were filtered off, washed with pentane (3 × 10 mL),

and dried in vacuo to give a yellow-brown solid. Yield: 230 mg

(52%). Diffraction-quality crystals were grown by cooling a

solution of 7. H NMR (C₆D₆, 499.9 MHz, 293 K): 7.70 (2H, s,

2-C₆H₃(CF₃)₂), 7.34 (1H, s, 4-C₆H₃(CF₃)₂), 2.41 (3H, s, NMe trans),

2.23 (2H, m, CH₂), 2.19 (6H, s, NMe cis), 2.05 (2H, m, CH₂),

1.90 (2H, m, CH₂), 1.61 (2H, m, CH₂), 1.42-1.35 (4H, overlapping

m, CH₂), 0.45 (6H, s, TiMe). ¹³C{¹H} NMR (C₆D₆, 125.8 MHz,

2

293 K): 159.4 (1-C₆H₃(CF₃)₂), 131.9 (q, J_C-F31.5 Hz, 3-C₆H₃-

(CF₃)₂), 125.0 (q, ¹J_C-F273.0 Hz, CF₃), 123.0 (2-C₆H₃(CF₃)₂), 108.4

(4-C₆H₃(CF₃)₂), 57.5 (CH₂), 55.6 (CH₂), 55.2 (CH₂), 50.7 (NMe

cis), 49.1 (NMe trans), 36.2 (TiMe). ¹⁹F NMR (C₆D₆, 282.2 MHz,

293 K): -67.7 (CF₃). IR (NaCl plates, Nujol mull, cm^-1): 1585

(m), 1397 (s), 1275 (s), 1166 (s), 1131 (s), 1115 (s), 1080 (w),

1062 (w), 1017 (s), 892 (w), 871 (w), 842 (w), 774 (m), 745 (w),

704 (w), 681 (m). FI-MS: m/z 460.9 (100%) [M - Me]⁺, 445.8

(18%) [M - 2Me]⁺, 229.0 (50%) [H₂N-3,5-(CF₃)₂C₆H₃]⁺, 171.2

(20%) [Me₃[9]aneN₃]⁺. Anal. Found (calcd for C₁₉H₃₀F₆N₄Ti): C

48.0 (47.9), H 6.4 (6.3), N 11.8 (11.8).

1

subsaturated solution of 6 in benzene to 5 °C. H NMR (C₆D₆,

3

500.0 MHz, 293 K): 4.13 (1H, sept., J ) 6.4 Hz, CHMe₂), 2.59

(6H, s, NMe cis), 2.41 (3H, s, NMe trans), 2.32 (2H, m, CH₂),

2.16 (2H, m, CH₂), 1.67 (4H, overlapping m, CH₂), 1.59 (4H,

overlapping m, CH₂), 1.54 (6H, d, ³J ) 6.4 Hz, CHMe₂), 0.34 (6H,

s, TiMe). ¹³C{¹H} NMR (C₆D₆, 125.7 MHz, 293 K): 61.9

(CHMe₂), 55.4 (CH₂), 55.2 (CH₂), 54.7 (CH₂), 51.4 (NMe cis),

48.5 (NMe trans), 27.4 (CHMe₂), 26.1 (TiMe). IR (KBr plates,

Nujol mull, cm^-1): 1496 (w), 1344 (w), 1298 (m), 1286 (m), 1260

(w), 1238 (s), 1208 (w), 1150 (w), 1130 (w), 1096 (m), 1078 (m),

1064 (m), 1008 (s), 990 (w), 892 (m), 778 (m), 746 (m), 722 (m),

642 (m), 580 (m), 512 (m), 444 (m). FI-MS: m/z 306.2 (68%)

[M]⁺, 291.2 (100%) [M - Me]⁺, 171.2 (10%) [Me₃[9]aneN₃]⁺.

FI-HRMS: m/z found (calcd for C₁₄H₃₄N₄Ti, [M]⁺) 306.2251

(306.2263). Surprisingly, a satisfactory combustional analysis could

not be obtained.

i

Ti(N-2,6-C₆H₃Pr₂)(Me₃[9]aneN₃)Me₂(9). Methyl lithium (1.61

mL, 1.6 M in Et₂O, 2.58 mmol) was added slowly to a stirred

i

suspension of Ti(N-2,6-C₆H₃Pr₂)(Me₃[9]aneN₃)Cl₂(600 mg, 1.29

mmol) in THF (30 mL) at -78 °C. The reaction mixture was

allowed to warm slowly to room temperature and stirred for 16 h.

The volatiles were removed under reduced pressure, and the

resulting yellow solid was extracted into chlorobenzene (20 mL).

The chlorobenzene solution was concentrated to approximately

5 mL and layered with pentane (10 mL). After 2 days at -30 °C

a yellow-brown precipitate had formed. This was filtered off and

dissolved in THF (10 mL). The solution was concentrated to

approximately 5 mL and cooled to -80 °C for 5 days to give 9 as

orange crystals. Yield: 206 mg (38%). Diffraction-quality single

crystals were grown by slow diffusion of pentane into a toluene

Ti(NPh)(Me₃[9]aneN₃)Me₂(7). Methyl lithium (1.97 mL, 1.6

M in Et₂O, 3.15 mmol) was added slowly to a stirred suspension

of Ti(NPh)(Me₃[9]aneN₃)Cl₂(600 mg, 1.57 mmol) in THF (70 mL)

at -78 °C. The reaction mixture was allowed to warm slowly to

room temperature and stirred for 16 h. The volatiles were removed

under reduced pressure, and the resulting yellow solid was extracted

into toluene (200 mL). After 3 days at 4 °C orange crystals of 7

had formed, which were filtered off and dried in vacuo. The mother

liquor was concentrated to approximately 40 mL and cooled to 4 °C

for a further 3 days resulting in a second crop of crystals. Yield:

282 mg (53%). Diffraction-quality single crystals were grown by

slow evaporation of a diethyl ether solution of 6. ¹H NMR (C₆D₆,

1

solution of 9. H NMR (C₆D₆, 499.9 MHz, 293 K): 7.28 (2H, d,

i

3

i

³J 7.6 Hz, 3-C₆H₃Pr₂), 7.00 (1H, t, J 7.6 Hz, 4-C₆H₃Pr₂), 4.84

3

(2H, sept., J 7.0 Hz, CHMe₂), 2.50 (2H, m, CH₂), 2.43 (6H, s,

NMe cis), 2.42 (3H, s, NMe trans), 2.38 (2H, m, CH₂), 2.13 (2H,

m, CH₂), 1.70-1.59 (4H, overlapping m, CH₂), 1.52 (2H, m, CH₂),

3

1.48 (12H, d, J 7.0 Hz, CHMe₂), 0.51 (6H, s, TiMe). ¹³C{¹H}

i

NMR (C₆D₆, 125.7 MHz, 293 K): 156.5 (1-C₆H₃Pr₂), 143.4 (2-

i

C₆H₃Pr₂), 123.2 (3-C₆H₃Pr₂), 118.0 (4-C₆H₃Pr₂), 56.2 (CH₂), 55.9

(CH₂), 55.5 (CH₂), 51.6 (NMe cis), 49.0 (NMe trans), 34.1 (TiMe),

27.5 (CHMe₂), 25.9 (CHMe₂). IR (NaCl plates, Nujol mull, cm^-1):

1582 (m), 1490 (w), 1415 (s), 1364 (m), 1355 (m), 1335 (s), 1273

(s), 1205 (w), 1153 (m), 1116 (m), 1101 (m), 1078 (m), 1067 (s),

1024 (m), 1007 (s), 954 (s), 891 (m), 778 (s), 754 (s). FI-MS: m/z

424.1 (4%) [M]⁺, 177.2 (21%) [H₂N-2,6-ⁱPr₂C₆H₃]⁺, 171.2 (100%)

[Me₃[9]aneN₃]⁺. Anal. Found (calcd for C₂₃H₄₄N₄Ti): C 65.1

(65.1), H 10.4 (10.4), N 13.3 (13.2).

3

4

499.9 MHz, 293 K): 7.35 (2H, dt, J 8.5 Hz, J 1.4 Hz, 2-C₆H₅),

3

7.31 (2H, app. t, app. J 7.7 Hz, 3-C₆H₅), 6.84 (1H, tt, J 7.2 Hz,

⁴J 1.5 Hz, 4-C₆H₅), 2.48 (3H, s, NMe trans), 2.45 (6H, s, NMe

cis), 2.36-2.25 (4H, overlapping m, CH₂), 2.06 (2H, m, CH₂), 1.69

(2H, m, CH₂), 1.55-1.47 (4H, overlapping m, CH₂), 0.51 (6H, s,

TiMe). ¹³C{¹H} NMR (C₆D₆, 125.7 MHz, 293 K): 160.8 (1-C₆H₅),

128.7 (2-C₆H₅), 124.0 (3-C₆H₅), 117.2 (4-C₆H₅), 55.7 (CH₂), 55.5

(CH₂), 54.7 (CH₂), 51.1 (NMe cis), 49.1 (NMe trans), 32.7 (TiMe).

IR (NaCl plates, Nujol mull, cm^-1): 1575 (m), 1331 (s), 1159 (w),

1107 (w), 1063 (m), 1008 (m), 991 (m), 952 (w), 779 (w), 761

(m), 693 (w), 681 (w). FI-MS: m/z 340.2 (100%) [M]⁺, 325.2

(58%) [M - Me]⁺, 171.2 (40%) [Me₃[9]aneN₃]⁺. Anal. Found

(calcd for C₁₇H₃₂N₄Ti): C 60.2 (60.0), H 9.4 (9.5), N 16.4 (16.5).

Ti(N-2-C₆H₄CF₃)(Me₃[9]aneN₃)Me₂(10). Methyl lithium (1.72

mL, 1.6 M in Et₂O, 2.75 mmol) was added slowly to a stirred

suspension of Ti(N-2-C₆H₄CF₃)(Me₃[9]aneN₃)Cl₂(449 mg, 1.00

mmol) in THF (20 mL) at -78 °C. The reaction mixture was

allowed to warm slowly to room temperature and stirred for 16 h.

The volatiles were removed under reduced pressure, and the result-

ing black semisolid was extracted into chlorobenzene (20 mL). The

volatiles were removed, and the resulting yellow-brown solid was

extracted into diethyl ether (140 mL), resulting in a bright yellow

solution. The solution was concentrated to approximately 5 mL,

and the resulting yellow precipitate was filtered off, washed with

pentane (3 × 5 mL), and dried in vacuo to give 10 as a yellow

Ti(N-3,5-C₆H₃(CF₃)₂)(Me₃[9]aneN₃)Me₂(8). Methyl lithium

(1.81 mL, 1.6 M in Et₂O, 2.90 mmol) was added slowly to a stirred

suspension of Ti(N-3,5-C₆H₃(CF₃)₂)(Me₃[9]aneN₃)Cl₂(600 mg, 1.16

mmol) in THF (40 mL) at -78 °C. The reaction mixture was

allowed to warm slowly to room temperature and stirred for 16 h.

The volatiles were removed under reduced pressure, and the result-

ing orange-brown solid was extracted into benzene (40 mL). The

benzene solution was concentrated to approximately 30 mL and

filtered away from some brown precipitate. The solution was further

1

powder. Yield: 79 mg (19%). H NMR (C₆D₆, 499.9 MHz, 293

K): 8.14 (1H, d, ³J 8.3 Hz, 6-C₆H₄(CF₃)), 7.61 (1H, d, ³J 7.8 Hz,

3-C₆H₄(CF₃)), 7.28 (1H, app. t, app. ³J 7.7 Hz, 5-C₆H₄(CF₃)), 6.56

Metallocene-like Imido Titanium Dialkyl Compounds

Organometallics, Vol. 25, No. 23, 2006 5563

(1H, app. t, app. ³J 7.6 Hz, 4-C₆H₄(CF₃)), 2.54 (2H, m, CH₂), 2.44

(3H, s, NMe trans), 2.41 (6H, s, NMe cis), 2.31 (2H, m, CH₂),

2.02 (2H, m, CH₂), 1.69 (2H, m, CH₂), 1.57 (2H, m, CH₂), 1.52

(2H, m, CH₂), 0.53 (6H, s, TiMe). ¹³C{¹H} NMR (C₆D₆, 125.7

MHz, 293 K): 158.7 (1-C₆H₄(CF₃)), 133.5 (q, ¹J_C-F307.8 Hz, CF₃),

133.4 (6-C₆H₄(CF₃)), 132.1 (5-C₆H₄(CF₃)), 125.6 (q, ³J_C-F6.1 Hz,

Ti(NAr^F)(Me₃[9]aneN₃)(CH₂SiMe₃)₂(13). To an ice-cooled

mixture of Ti(NAr^F)(Me₃[9]aneN₃)Cl₂(500 mg, 1.28 mmol) and

LiCH₂SiMe₃(240 mg, 2.56 mmol) was added partially frozen

benzene (50 mL) in the absence of light. The mixture was allowed

to warm to room temperature and left to stir for a further 16 h in

the dark. Removal of the volatiles under reduced pressure afforded

a brown oil, which was extracted into hot hexanes (5 × 10 mL) to

give a yellow solution. The volatiles were removed under reduced

pressure from the combined extracts to afford 13 as a yellow

powder. Yield: 60 mg (8%). ¹H NMR (C₆D₆, 300.1 MHz, 293 K):

2.41 (6H, s, NMe cis), 2.39 (3H, s, NMe trans), 2.26 (4H,

overlapping m, NCH₂), 2.06 (2H, m, NCH₂), 1.61 (6H, overlapping

2

3-C₆H₄(CF₃)), 116.0 (q, J_C-F25.9 Hz, 2-C₆H₄(CF₃)), 115.4 (4-

C₆H₄(CF₃)), 55.6 (CH₂), 55.2 (CH₂), 55.2 (CH₂), 50.7 (NMe cis),

49.2 (NMe trans), 37.3 (TiMe). ¹⁹F NMR (C₆D₆, 282.2 MHz, 293

K): -64.4 (CF₃). IR (NaCl plates, Nujol mull, cm^-1): 1590 (m),

1542 (w), 1445 (s), 1344 (s), 1317 (m), 1281 (w), 1219 (w), 1159

(w), 1107 (m), 1091 (m), 1048 (w), 1025 (m), 1007 (m), 951 (w),

779 (w). Anal. Found (calcd for C₁₈H₃₁F₃N₄Ti): C 53.1 (52.9), H

7.7 (7.7), N 13.0 (13.7).

2

m, NCH₂), 0.77 (2H, d, J 11.0 Hz, CH_aH_bSiMe₃), 0.46 (18H, s,

CH₂SiMe₃), 0.04 (2H, d, ²J 10.5 Hz, CH_aH_bSiMe₃). ¹³C{¹H} NMR

(C₆D₆, 75.5 MHz, 293 K): 56.1 (NCH₂), 55.8 (NCH₂), 55.1

(NCH₂), 51.6 (NMe cis), 50.3 (NMe trans), 3.9 (CH₂SiMe₃). The

C₆F₅and CH₂SiMe₃resonances were not observed. ¹⁹F NMR (C₆D₆,

282.4 MHz, 293 K): -153.6 (2F, dd, ³J 19.2 Hz, ⁴J 5.5 Hz, 2-C₆F₅),

-168.5 (2F, app. t, app. ³J 21.9 Hz, 3-C₆F₅), -176.3 (1F, m,

4-C₆F₅). IR (KBr plates, Nujol mull, cm^-1): 1313 (m), 1235 (m),

1205 (m), 1155 (w), 1068 (w), 1035 (m), 1007 (m), 975 (w), 892

(m), 849 (m), 817 (m), 777 (m), 723 (m), 668 (w), 522 (w), 433

(w). EI-MS: m/z 487 (46%) [M - CH₂SiMe₃]⁺, 400 (65%) [M -

2CH₂SiMe₃]⁺. Anal. Found (calcd for C₂₃H₄₃F₅N₄Si₂Ti): C 48.1

(48.1), H 7.6 (7.6), N 9.6 (9.8).

t

Ti(N-2-C₆H₄Bu)(Me₃[9]aneN₃)Me₂(11). Methyl lithium (1.03

mL, 1.6 M in Et₂O, 1.65 mmol) was added slowly to a stirred

t

suspension of Ti(N-2-C₆H₄Bu)(Me₃[9]aneN₃)Cl₂(360 mg, 0.82

mmol) in THF (30 mL) at -78 °C. The reaction mixture was

allowed to warm slowly to room temperature and stirred for 16 h.

The volatiles were removed under reduced pressure, and the result-

ing yellow solid was extracted into chlorobenzene (30 mL). The

chlorobenzene solution was concentrated to approximately 5 mL,

and then the product was cautiously precipitated by the slow

addition of pentane (20 mL) with vigorous stirring. The resulting

yellow precipitate was filtered off, washed with pentane (3 × 5

mL), and dried in vacuo to give 11 as a yellow powder. Yield:

188 mg (58%). Diffraction-quality single crystals were grown by

[Ti₂(µ-NPh)₂(Me₃[9]aneN₃)₂Cl₂][BAr^F] (14-BAr^F). To a solu-

4 2

4

tion of Ti(NPh)(Me₃[9]aneN₃)Me₂(7, 50 mg, 0.147 mmol) in CH₂-

1

slow diffusion of pentane into a benzene solution of 10. H NMR

Cl₂(1 mL) was added [Ph₃C][BAr^F] (136 mg, 0.147 mmol) in

4

3

4

(C₆D₆, 499.9 MHz, 293 K): 7.58 (1H, dd, J 7.8 Hz, J 1.6 Hz,

CH₂Cl₂(1 mL) to give a deep red solution. The solution was left

to stand for 2 days, after which time some deep red-brown solid

had formed. Pentane (2 mL) was added with stirring to precipitate

more product, then the resulting dark red solid was filtered off,

washed with pentane (3 × 1 mL), and dried in vacuo. Yield: 111

mg (74%). ¹H NMR (CD₂Cl₂, 499.9 MHz, 293 K): 7.15 (4H, app.

t

3

4

t

3-C₆H₄Bu), 7.25 (1H, app. td, J 7.6 Hz, J 1.6 Hz, 5-C₆H₄Bu),

7.19 (1H, dd, ³J 8.1 Hz, ⁴J 1.5 Hz, 6-C₆H₄Bu), 6.91 (1H, app. td,

t

³J 7.5 Hz, ⁴J 1.5 Hz, 4-C₆H₄Bu), 2.53 (2H, m, CH₂), 2.45 (3H, s,

NMe trans), 2.45 (6H, s, NMe cis), 2.30 (2H, m, CH₂), 2.16 (9H,

s, CMe₃), 2.08 (2H, m, CH₂), 1.67 (2H, m, CH₂), 1.56 (2H, m,

CH₂), 1.51 (2H, m, CH₂), 0.49 (6H, s, TiMe). ¹³C{¹H} NMR (C₆D₆,

3

t, app. J ) 7.8 Hz, 3-C₆H₅), 7.00 (2H, t, J ) 7.3 Hz, 4-C₆H₅),

6.81 (4H, d, ³J ) 8.8 Hz, 2-C₆H₅), 3.78 (4H, m, CH₂), 3.42 (12H,

s, NMe cis), 3.34 (4H, m, CH₂), 3.21 (4H, m, CH₂), 3.13 (4H, m,

CH₂), 2.77-2.74 (8H, overlapping m, CH₂), 2.30 (6H, s, NMe

trans). ¹³C{¹H} NMR (CD₂Cl₂, 75.5 MHz, 293 K): 158.0 (1-C₆H₅),

t

125.7 MHz, 293 K): 160.1 (1-C₆H₄Bu), 142.8 (2-C₆H₄Bu), 129.1

t

(6-C₆H₄Bu), 126.7 (3-C₆H₄Bu), 125.7 (5-C₆H₄Bu), 117.2 (4-C₆H₄-

Bu), 55.9 (CH₂), 55.8 (CH₂), 55.3 (CH₂), 51.3 (NMe cis), 49.3

(NMe trans), 37.4 (TiMe), 36.6 (CMe₃), 31.2 (CMe₃). IR (NaCl

plates, Nujol mull, cm^-1): 1578 (w), 1423 (m), 1297 (s), 1003

(m), 951 (m), 776 (w), 745 (m). FI-MS: m/z 396.5 (23%) [M]⁺,

171.2 (40%) [Me₃[9]aneN₃]⁺, 149.1 (100%) [H₂N-2-^tBuC₆H₄]⁺.

Anal. Found (calcd for C₂₁H₄₀N₄Ti): C 63.5 (63.6), H 10.1 (10.2),

N 14.0 (14.1).

1

148.5 (br. d, J_C-F) 238 Hz, 2-C₆F₅), 138.6 (br d, J_C-F) 247

Hz, 4-C₆F₅), 136.7 (br d, ¹J_C-F) 250 Hz, 3-C₆F₅), 128.6 (3-C₆H₅),

126.0 (4-C₆H₅), 125.2 (2-C₆H₅), 57.5 (CH₂), 57.2 (CH₂), 54.5 (CH₂),

52.1 (NMe cis), 50.9 (NMe trans). ¹⁹F NMR (CD₂Cl₂, 282.1 MHz,

3

293 K): -133.5 (d, J ) 10.6 Hz, 2-C₆F₅), -164.0 (t, J ) 20.4

Hz, 4-C₆F₅), -167.9 (app. t, app. ³J ) 18.1 Hz, 3-C₆F₅). IR (KBr

plates, Nujol mull, cm^-1): 1643 (m), 1582 (w), 1514 (s), 1411

(w), 1295 (w), 1274 (m), 1222 (w), 1088 (s), 997 (m), 978 (s), 887

(w), 774 (m), 757 (m), 684 (m), 662 (m). Anal. Found (calcd for

C₇₈H₅₂B₂Cl₂F₄₀N₈Ti₂): C 45.8 (45.7), H 2.7 (2.6), N 5.6 (5.5).

Ti(NⁱPr)(Me₃[9]aneN₃)(CH₂SiMe₃)₂(12). To an ice-cooled mix-

ture of Ti(NⁱPr)(Me₃[9]aneN₃)Cl₂(81 mg, 0.23 mmol) and LiCH₂-

SiMe₃(44 mg, 0.46 mmol) was added partially frozen benzene (20

mL) in the absence of light. The mixture was allowed to warm to

room temperature and left to stir for a further 16 h in the dark.

Subsequently the solids were filtered off to give a yellow solution.

Removal of the volatiles under reduced pressure afforded 12 as a

yellow powder. Yield: 40 mg (39%). ¹H NMR (C₆D₆, 499.9 MHz,

[Ti(NPh)(Me₃[9]aneN₃){MeC(NⁱPr)₂}][BAr^F] (15-BAr^F). To

4

a solution of Ti(NPh)(Me₃[9]aneN₃)Me₂(7, 50 mg, 0.147 mmol)

and ⁱPrNCNⁱPr (23 µL, 0.147 mmol) in CH₂Cl₂(1 mL) at -35 °C

3

293 K): 4.25 (1H, sept, J 6.3 Hz, CHMe₂), 2.56 (6H, s, NMe

was added [Ph₃C][BAr^F] (136 mg, 0.147 mmol) in CH₂Cl₂(1 mL)

4

cis), 2.38 (2H, m, NCH₂), 2.21 (3H, s, NMe trans), 2.17 (4H,

overlapping m, NCH₂), 1.54 (6H, overlapping m, NCH₂), 1.33 (6H,

d, ³J 6.3 Hz, CHMe₂), 0.53 (18H, s, CH₂SiMe₃), 0.03 (2H, d,

²J 11.2 Hz, CH_aH_bSiMe₃), -0.48 (2H, d, ²J 11.2 Hz, CH_aH_bSiMe₃).

¹³C{¹H} NMR (C₆D₆, 125.7 MHz, 293 K): 63.2 (CHMe₂), 55.8

(NCH₂), 55.2 (NCH₂), 55.1 (NCH₂), 52.3 (NMe cis), 49.3 (NMe

trans), 41.0 (CH₂SiMe₃), 27.4 (CHMe₂), 4.7 (CH₂SiMe₃). IR (KBr

plates, Nujol mull, cm^-1): 1492 (m), 1366 (m), 1297 (s), 1240

(w), 1221 (s), 1153 (m), 1126 (w), 1094 (w), 1087 (m), 1071 (m),

1059 (m), 1040 (m), 1008 (s), 966 (w), 913 (s), 888 (s), 879 (s),

853 (s), 810 (s), 774 (m), 745 (m), 724 (s), 679 (m), 662 (m), 618

(m), 574 (m), 511 (m), 495 (m), 450 (w), 411 (m). EI-MS: m/z

363 (35%) [M - CH₂SiMe₃]⁺. Anal. Found (calcd for C₂₀H₅₀N₄-

Si₂Ti): C 53.1 (53.3), H 11.3 (11.2), N 12.2 (12.4).

to give a brown-yellow solution. The solution was concentrated to

approximately 1 mL, then pentane (4 mL) was added with stirring,

resulting in a brown-yellow oil. The supernatant was decanted and

the oil triturated in pentane for 10 min to give 15-BAr^F₄as a yellow

powder, which was washed with pentane (3 × 1 mL) and dried in

1

vacuo. Yield: 73 mg (44%). H NMR (CD₂Cl₂, 299.9 MHz, 293

K): 7.04 (2H, app. t, app. ³J ) 7.7 Hz, 3-C₆H₅), 6.76 (1H, t, ³J )

7.5 Hz, 4-C₆H₅), 6.72 (2H, d, ³J ) 7.5 Hz, 2-C₆H₅), 4.10 (2H, app.

sept., app. ³J ) 6.8 Hz, CHMe₂), 3.82 (2H, m, CH₂), 3.26 (2H, m,

CH₂), 3.19 (6H, s, NMe cis), 3.01-2.95 (4H, overlapping m, CH₂),

2.76 (2H, m, CH₂), 2.65 (2H, m, CH₂), 2.32 (3H, s, CMe), 2.29

(3H, s, NMe trans), 1.37 (6H, d, ³J ) 6.8 Hz, CHMe₂), 1.33 (6H,

3

d, J ) 6.8 Hz, CHMe₂). ¹³C{¹H} NMR (CD₂Cl₂, 75.4 MHz, 293

1

K): 167.5 (CMe), 159.0 (1-C₆H₅), 148.5 (br d, J_C-F) 238 Hz,

5564 Organometallics, Vol. 25, No. 23, 2006

Bolton et al.

t

i

Table 4. X-ray Data Collection and Processing Parameters for Ti(NR)(Me₃[9]aneN₃)Me₂‚xC₆H₆(R ) Bu (1‚C₆H₆), Pr

(6‚0.5C₆H₆), Ph (7), 3,5-C₆H₃(CF₃)₂(8))

parameter

1‚C₆H₆

6‚0.5C₆H₆

7

8

empirical formula

fw

C₁₅H₃₆N₄Ti‚C₆H₆

398.49

C₁₄H₃₄N₄Ti‚0.5(C₆H₆)

345.41

C₁₇H₃₂N₄Ti

340.37

C₁₉H₃₀F₆N₄Ti

476.36

temp/K

150

wavelength/Å

space group

a/Å

b/Å

c/Å

0.71073

P2₁/c

16.6168(3)

9.0660(2)

17.3742(4)

90

114.96(1)

90

2373.0(2)

4

1.115

0.372

R₁) 0.0506

R_w) 0.0617

0.71073

C2/c

35.1006(8)

8.3540(2)

13.6754(4)

90

95.7541(8)

90

3989.8(2)

8

1.150

0.430

R₁) 0.0417

R_w) 0.0238

0.71073

P2₁/n

11.6320(4)

13.6112(6)

12.2864(6)

90

103.7200(15)

90

1889.75(14)

4

1.196

0.456

R₁) 0.0449

R_w) 0.0544

0.71073

P2₁2₁2₁

8.5573(2)

14.1080(2)

18.5066(2)

90

R/deg

â/deg

90

γ/deg

V/Å³

2234.23(7)

4

1.416

0.445

R₁) 0.0414

R_w) 0.0487

Z

d(calcd)/ Mg m^-1

abs coeff/mm^-1

R indices^a

[I > 3σ(I)]

2

^aR₁) ∑||F_o| - |F_c||/∑|F_o|; R_w) x{∑w(|F_o| - |F_c|)²/∑w|F_o| }. wR₂) x{∑w(F_o- F_c)²/∑w(F_o)²}.

i

Table 5. X-ray Data Collection and Processing Parameters for Ti(NR)(Me₃[9]aneN₃)Me₂‚xC₆H₆(R ) 2,6-C₆H₃Pr₂(9),

t

2-C₆H₄Bu (11)) and [Ti(NPh)(Me₃[9]aneN₃){MeC(NⁱPr)₂}][BAr^F]‚CH₂Cl₂(15-BAr^F‚CH₂Cl₂)

4

parameter

9

11

15-BAr^F₄‚CH₂Cl₂

empirical formula

C₂₃H₄₄N₄Ti

C₂₁H₄₀N₄Ti

C₄₇H₄₃BF₂₀N₆Ti‚

CH₂Cl₂

fw

424.53

150

396.48

150

1215.50

150

0.71073

P2₁/c

9.2576(2)

15.0649(3)

16.0266(3)

90

107.6272(10)

90

5095.86(16)

4

1.584

0.389

R₁) 0.0332

R_w) 0.0387

temp/K

wavelength/Å

space group

a/Å

b/Å

c/Å

0.71073

P2₁/c

9.1367(3)

16.2609(5)

16.4873(5)

90

93.5206(16)

90

2444.91(13)

4

1.153

0.365

R₁) 0.0461

R_w) 0.0532

0.71073

monoclinic

9.1367(3)

16.2609(5)

16.4873(5)

90

98.1573(11)

90

2212.53(8)

4

1.190

0.399

R₁) 0.0469

R_w) 0.0603

R/deg

â/deg

γ/deg

V/Å³

Z

d(calcd)/ Mg m^-1

abs coeff/mm^-1

R indices^a

[I > 3σ(I)]

2

^aR₁) ∑||F_o| - |F_c||/∑|F_o|; R_w) x{∑w(|F_o| - |F_c|)²/∑w|F_o| }. wR₂) x{∑w(F_o- F_c)²/∑w(F_o)²}.

1

2-C₆F₅), 138.6 (br d, J_C-F) 247 Hz, 4-C₆F₅), 136.7 (br d, J_C-F

) 250 Hz, 3-C₆F₅), 128.7 (3-C₆H₅), 124.6 (2-C₆H₅), 121.9 (4-C₆H₅),

57.4 (CH₂), 56.1 (CH₂), 54.9 (CH₂), 51.3 (NMe cis), 50.6 (CHMe₂),

47.5 (NMe trans), 25.2 (CHMe₂), 24.6 (CHMe₂), 14.0 (CMe). ¹⁹F

carefully released. The reactor was opened and the reaction mixture

“quenched” by careful dropwise addition of MeOH (ca. 10 mL).

Distilled water (50 mL) was then added and the mixture acidified

to pH 1 (10% HCl in MeOH) (ca. 25 cm³). The reaction mixture

was stirred for 16 h and then filtered. The solid PE was washed

with distilled water (1000 mL) and dried at ca. 100 °C to constant

weight.

3

NMR (CD₂Cl₂, 282.1 MHz, 293 K): -133.5 (d, J ) 10.6 Hz,

2-C₆F₅), -164.0 (t, J ) 20.4 Hz, 4-C₆F₅), -167.9 (app. t, app.

3

³J ) 18.1 Hz, 3-C₆F₅). IR (NaCl plates, Nujol mull, cm^-1): 1643

(m), 1581 (w), 1513 (s), 1413 (m), 1312 (m), 1275 (m), 1204 (m),

1177 (w), 1086 (s), 1002 (m), 979 (s), 775 (m), 757 (m), 684 (m),

662 (m). ES⁺MS (MeCN): m/z 451.3 (100%) [M]⁺, 143.1 (80%)

[ⁱPrNHCMeNHⁱPr]⁺. ES⁺HRMS (MeCN): m/z found (calcd for

C₂₃H₄₃N₆Ti, [M]⁺) 451.3018 (451.3029). Anal. Found (calcd for

C₄₇H₄₃BF₂₀N₆Ti): C 49.8 (49.9), H 3.9 (3.8), N 7.6 (7.4).

Ti(N^tBu)(Me₃[9]aneN₃)Me(µ-Me)AlⁱBu₃(1‚TIBA). To a solu-

tion of Ti(N^tBu)(Me₃[9]aneN₃)Me₂(1, 7.0 mg, 0.022 mmol) in

either C₆D₆or C₆D₅Br (0.75 mL) was added a solution of AlⁱBu₃

1

(1.0 M in toluene, 21.9 µL, 0.022 mmol). A H NMR spectrum

recorded after 10 min contained resonances attributed to Ti(N^tBu)-

(Me₃[9]aneN₃)Me(µ-Me)AlⁱBu₃(1‚TIBA). All other NMR tube

reactions of metal dialkyl or monoalkyl cations were perfomed in

an analogous way. ¹H NMR (C₆D₅Br, 499.9 MHz, 293 K): 2.76-

2.59 (4H, overlapping m, NCH₂), 2.46 (6H, s, NMe cis), 2.25-

1.82 (11H, overlapping m, NCH₂and CHMe₂), 2.09 (3H, s, NMe

Typical Procedure for Ethylene Polymerization Using TB and

TIBA. All manipulations were carried out under ethylene (∼1.1

bar) working gas. Stock solutions of Ti(N^tBu)(Me₃[9]aneN₃)Me₂

(1, 6.4 mg, 20 µmol in 100 mL of toluene) and [Ph₃C][BAr^F] (9.2

4

3

trans), 1.09 (18H, d, J 6.5 Hz, CHMe₂), 1.07 (9H, s, NCMe₃),

mg, 10 µmol in 50 mL of toluene) were made up. Toluene (225

mL) was added to AlⁱBu₃(1 M toluene solution, 5 mL, 5 mmol)

and transferred to the reactor. The mixture was stirred for 5 min

(1000 rpm) to “scrub” the apparatus. Ti(N^tBu)(Me₃[9]aneN₃)Me₂

(1, 10 mL of stock solution, 2 µmol) was added to the reactor,

3

0.14 (6H, d, J 7.0 Hz, CH₂CHMe₂), 0.06 (6H, br s, TiMe).

Crystal Structure Determinations of Ti(NR)(Me₃[9]aneN₃)-

t

i

Me₂‚xC₆H₆(R ) Bu (1‚C₆H₆), Pr (6‚0.5C₆H₆), Ph (7), C₆H₃-

i

t

(CF₃)₂(8), 2,6-C₆H₃Pr₂(9), 2-C₆H₄Bu (11)) and [Ti(NPh)(Me₃-

[9]aneN₃){MeC(NⁱPr)₂}][BAr^F]‚CH₂Cl₂(15-BAr^F‚CH₂Cl₂).

followed by [Ph₃C][BAr^F] (10 mL of stock solution, 2 µmol). A

4

dynamic ethylene pressure of 6 bar was applied. The temperature

and ethylene uptake were monitored, and the reaction was run for

20 min, after which the ethylene flow was stopped and the pressure

Crystal data collection and processing parameters are given in

Tables 4 and 5. Crystals were mounted on glass fibers using

perfluoropolyether oil and cooled rapidly in a stream of cold N₂

Metallocene-like Imido Titanium Dialkyl Compounds

Organometallics, Vol. 25, No. 23, 2006 5565

using an Oxford Cryosystems Cryostream unit. Diffraction data

were measured using either an Enraf-Nonius KappaCCD diffrac-

tometer. As appropriate, absorption and decay corrections were

applied to the data and equivalent reflections merged.⁹³The

structures were solved by direct methods (SIR92⁹⁴), and further

refinements and all other crystallographic calculations were per-

formed using the CRYSTALS program suite.⁹⁵Details of the

structure solution and refinements are given in the Supporting

Information (CIF data). A full listing of atomic coordinates, bond

lengths and angles, and displacement parameters for all the

structures have been deposited at the Cambridge Crystallographic

Data Centre. See Notice to Authors, Issue No. 1.

Computational Details. All the calculations have been per-

formed with the Gaussian03 package⁹⁶at the B3PW91 level.^97,98

The titanium atom was represented by the relativistic effective core

potential (RECP) from the Stuttgart group (12 valence electrons)

and its associated basis set,⁹⁹augmented by an f polarization

function (R ) 0.869).¹⁰⁰The remaining atoms (C, H, N, Al) were

represented by a 6-31G(d,p) basis set.¹⁰¹Full optimizations of

geometry without any constraint were performed, followed by

analytical computation of the Hessian matrix to confirm the nature

of the located extrema as minima on the potential energy surface.

the X-ray data for 6‚0.5C₆H₆, and DSM Research for generous

gifts of [Ph₃C][BAr^F].

4

Supporting Information Available: X-ray crystallographic data

in CIF format for the structure determinations of 1‚C₆H₆, 6‚

0.5C₆H₆, 7, 8, 9, 11, and 15-BAr^F‚CH₂Cl₂. This information is

4

available free of charge via the Internet at http://pubs.acs.org.

OM0606136

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Article Doi

Synthesis and ethylene polymerization capability of metallocene-like imido titanium dialkyl compounds and their reactions with AliBu3

DOI: 10.1021/om0606136

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Full text of DOI:10.1021/om0606136

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