university of groningen · 67 generation and stability of cationic...

University of Groningen

Non Flory-Schulz ethene oligomerization with titanium-based catalystsDeckers, Patrick Jozef Wilhelmus

IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.

Document VersionPublisher's PDF, also known as Version of record

Publication date:2002

Link to publication in University of Groningen/UMCG research database

Citation for published version (APA):Deckers, P. J. W. (2002). Non Flory-Schulz ethene oligomerization with titanium-based catalysts. s.n.

CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).

Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.

Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.

Download date: 26-03-2021

https://research.rug.nl/en/publications/non-floryschulz-ethene-oligomerization-with-titaniumbased-catalysts(8907b0e5-77ee-4451-911a-95d3fd02c49d).html

67

Generation and stability of cationic (ηηηη5-

cyclopentadienyl)(ηηηη6-arene) half-sandwichcomplexes of titanium*

3.1 Introduction

Cationic titanium half-sandwich (monocyclopentadienyl) species show interestingcatalytic activity (Scheme 1), most notably in the syndiotactic polymerization ofstyrene1. Recently, it has been shown that the representative species[Cp*TiMe2][MeB(C6F5)3] effects the ‘living’ polymerization of propene to affordhigh molecular weight atactic polypropene2, which has interesting elastomericproperties3. Pellecchia and coworkers showed that the same catalyst system intoluene solvent polymerizes ethene to branched polyethene with n-butyl side chains4.

TiMe B(C6F5)3

MeMe

n

Ph PhPh Ph

n

n

. .

atacticpolypropene

syndiotacticpolystyrene

polyethene withn-butyl side chains

propene styrene

ethene

Scheme 1: Olefin polymerization by the [Cp*TiMe2][MeB(C6F5)3] species

There has been considerable debate in the literature about the nature of the actualactive species in these catalyst systems, e.g. whether in the catalytic polymerizationof styrene a Ti(IV) or Ti(III) active species is involved (or both)5, and which speciesis involved in the in situ formation of 1-hexene6, believed to be the source of the n-butyl side chains found in the ethene homopolymer (a feature which is unusual forpolyethene produced by early transition metal Ziegler-Natta catalysts7).

* Parts of this work have been published:

Deckers, P.J.W., Van der Linden, A.J., Meetsma, A., Hessen, B., Eur. J. Inorg. Chem. 2000, 929

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

68

As the cationic species [(η5-C5R5)TiMe2]+ are highly electron-deficient, we soughtways of stabilizing these by an intramolecular interaction without resorting to strongheteroatom-based Lewis basic moieties, which coordinate strongly to the titaniumcenter8 and substantially alter the reactivity towards olefins. We set out to preparemonocyclopentadienyl titanium complexes with hemilabile ancillary ligandscontaining a labile aromatic moiety (vide infra), in the hope that this group willquench the reactivity of the metal center when coordinated, but restore its originalreactivity upon dissociation. This should then allow us to study both the reactiveintermediates and their properties in olefin polymerization.

The substituted cyclopentadienyl ligand [C5H4CMe2Ar]- should be able to stabilizethe cationic species, in the absence of substrates, via coordination of the aromaticgroup, which is suitably labile (see section 3.2) to give way in the presence ofolefins. During our studies on cationic (C5H4CMe2Ar)Ti-systems, Sassmannshausenand Bochmann and coworkers prepared similar cationic half-sandwich titanium andzirconium species for which arene coordination was observed as well9. The catalyticproperties of these species, obtained via activation with MAO or B(C6F5)3, inpropene and styrene polymerization have also recently been reported9a,10.

3.2 Interactions of arenes with cationic half-sandwich group 4 metal dialkyls

Baird and coworkers studied species generated by the reaction of Cp*MMe3 (M =Ti, Zr, Hf) with B(C6F5)3 in aromatic solvents (Scheme 2)11. For Zr and Hf, π-arenesolvent complexes are formed that could in some cases be isolated, and a crystalstructure of {[C5H3(SiMe3)2]HfMe2(η6-toluene)}[MeB(C6F5)3] has been reported12.In the case of Ti, the metal arene interaction appeared to be much weaker, as thecorresponding solvent adducts could only be characterized spectroscopically at lowtemperature.

..

M = Ti

tolueneM = Zr, Hf

B(C6F5)3

MMeMe

MeB(C6F5)3

TiMe

MeMe B(C6F5)3

MMe

Me Me

TiMeMe

MeB(C6F5)3

Scheme 2: Reaction of Cp*MMe3 and B(C6F5)3 in toluene solvent

Cationic [(η5,η6-C5H4CMe2Ar)TiR2]+ Species; Generation and Stability▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

69

The formation of toluene adducts reflects the propensity of half-sandwich group 4cationic species to associate relatively strongly with neutral aromatic groups. Group4 benzyl complexes can be stabilized by intramolecular interactions with thearomatic moiety that are not available for the corresponding methyl compounds. Oneor both benzyl ligands in the cationic species may be coordinated in a multihaptofashion. In [Cp*Zr(CH2Ph)2]+ both η3- and η7-coordination has been observed(Scheme 3, top left)13, while for {[C5H3(CMe3)2]Zr(CH2Ph)2}+ η1- and η3-bondinghas been suggested14. If the cation is generated by benzyl abstraction with B(C6F5)3,π-coordination of the benzyl group of the [PhCH2B(C6F5)3]- anion is reinforced byelectrostatics and can become prevalent15, as for example in [CpZr(CH2Ph)2][η6-PhCH2B(C6F5)3] (Scheme 3, top right). In the closely related Cp-amido species{[η5,η1-C5H4(CH2)2N(t-Bu)]Zr(CH2Ph)}[PhCH2B(C6F5)3], a similar contact ion pairis in equilibrium with a solvent-separated ion pair, in which the Zr-bound benzylgroup shows η2-coordination (Scheme 3, bottom)16.

.. ZrPhCH2B(C6F5)3 ZrPh

Ph

B(C6F5)3

ZrN

Ph

B(C6F5)3

ZrN PhCH2B(C6F5)3

Scheme 3: Arene coordination in half-sandwich Zr-benzyl cationic species

The preparation of half-sandwich titanium complexes with cyclopentadienylligands substituted with a pendant arene group provides a different opportunity touse arene coordination in an intramolecular fashion, to generate ansa-cyclopentadienyl-arene cationic titanium species (Scheme 4, bottom). The feasibilityof this approach was suggested by low temperature NMR observations of Chien andRausch on the [(η5,η6-C5Me4CH2CH2Ph)TiMe2][B(C6F5)4] species17. Their idea wasto study the influence of intramolecular arene coordination on styrenepolymerization with (η5-C5H5-nRn)Ti-species, for which arene coordination of thephenyl group of the last inserted monomer is proposed (Scheme 4, top)5d,18.

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

70

Ph

[Ti]

Pn

[Ti]

Pn

[Ti]Pn[Ti] Pn[Ti] Pn

. .

Scheme 4: Proposed arene coordination during styrene polymerization (top) andansa-cyclopentadienyl-arene coordination (bottom)

Comparison of the phenyl-substituted Cp* ligand, [C5Me4CH2CH2Ph]-, withregular Cp* in styrene polymerization showed that the half-sandwich titaniumcompound with the substituted cyclopentadienyl ligand is 2-3 times less active,depending on reaction conditions. The ansa-cyclopentadienyl-arene structuresupposedly represents an inactive species, and the species thus formed competes fortitanium-arene interaction with the arene stabilized styrene and growing chain, theproposed prerequisites for chain growth.

In this chapter the generation of cationic species from the trimethyl and tribenzylderivatives (η5-C5H4CMe2Ar)TiR3 (Ar = Ph, 3,5-Me2C6H3; R = Me, CH2Ph) byreaction with B(C6F5)3 and [Ph3C][B(C6F5)4] is presented. The stability of theinitially generated cationic [(η5,η6-C5H4CMe2Ar)TiR2]+ species will be discussed,including the decomposition of [(η5,η6-C5H4CMe2-3,5-Me2C6H3)TiMe2][MeB(C6F5)3] (16) to give the first structurally characterized ansa-cyclopentadienyl-arene (titanium) species, and the instantaneous ortho cyclometalation of the ancillaryligand in the transient [(η5,η6-C5H4CMe2Ph)Ti(CH2Ph)2][RB(C6F5)3] (R = CH2Ph,C6F5) species.

3.3 Generation of [(ηηηη5,ηηηη6-C5H4CMe2Ar)TiMe2]+ cationic species

The reaction of the complexes (η5-C5H4CMe2Ar)TiMe3 (Ar = Ph, 3, and 3,5-Me2C6H3, 4), the synthesis of which was described in Chapter 2, with the Lewis acidB(C6F5)3 was studied by NMR spectroscopy. Reaction of 3 and 4 with 1 equiv ofB(C6F5)3 at -30 °C in bromobenzene-d5 or d2-1,1,2,2-tetrachloroethane yields darkred solutions of a species that were identified by 1D and 2D NMR techniques as theionic ansa-cyclopentadienyl-arene species [(η5,η6-C5H4CMe2Ar)TiMe2][MeB(C6F5)3] (Ar = Ph, 15, and 3,5-Me2C6H3, 16, Scheme 5).


71

R

R

Ti

MeMe Me

R

R

Ti MeMe

MeB(C6F5)3

B(C6F5)3

3 R = H4 R = Me

15 R = H16 R = Me

. .

Scheme 5: Generation of the cationic species [(η5,η6-C5H4CMe2Ar)TiMe2]+

The ansa-cyclopentadienyl-arene character of the cation 16 is indicated by theresonances for the arene moiety that show substantial coordination chemical shifts(downfield for o-C and p-C, upfield for m-C; the o-H proton resonances are foundupfield shifted at δ 5.91 ppm compared to δ 6.94 ppm in 4), and by the increase inthe separation of the two CH 1H NMR signals of the monosubstitutedcyclopentadienyl ring (∆δ 1.59 ppm in 16, 0.14 ppm in 4). This increase of ∆δ isrelated to the constrained geometry associated with the simultaneous bonding of bothcyclopentadienyl and arene moieties to the metal. This effect was also observed foransa-metallocenes of the type [X(η5-C5H4)2]TiCl2 (X = (CH2)3, GeMe2, SiMe2,CH2), where the separation of the two sets of Cp protons increases with decreasingCp(centroid)-Ti-Cp(centroid) angle19. Addition of a drop of d8-THF to a C6D5Brsolution of 16 shows a shift of the Cp (δ 6.14, 6.04 ppm; ∆δ = 0.10 ppm) and arylproton (o-H at δ 6.72 ppm) resonances back to ‘normal’ chemical shift ranges,indicating release of the arene moiety in the presence of a hard Lewis base to give a[(η5-C5H4CMe2Ar)TiMe2(d8-THF)x][MeB(C6F5)3] species.

The resonances for the [MeB(C6F5)3]- anion in the ionic species 16 are consistentwith those for a non-coordinated anion20. Horton and coworkers found that the ∆(δm-

F-δp-F) shift difference (19F NMR) is a good probe of coordination of [RB(C6F5)3]- (R= Me, CH2Ph) to cationic d0 metals (values of 3-6 ppm indicate coordination; <3ppm indicates non-coordination). The observed ∆(δm-F-δp-F) shift difference of 2.6ppm in the 19F NMR thus is consistent with those for a non-coordinated anion.

The thermally more labile ionic species [(η5,η6-C5H4CMe2Ph)TiMe2][MeB(C6F5)3](15) displays a similar pattern in the chemical shifts as 16. The ∆δ for the two CH 1HNMR signals of the cyclopentadienyl ring is 1.42 ppm (∆δ = 0.28 ppm in 3), the o-Hresonance is found at δ 6.18 ppm (δ 6.82 ppm for 3), and the ∆(δm-F-δp-F) shiftdifference of 2.8 ppm in the 19F NMR indicates non-coordination of the anion.Bochmann and coworkers observed similar NMR characteristics for the [(η5,η6-C5H4CMe2Ph)TiMe2][B(C6F5)4] species in CD2Cl2

9a. The cation 15 decomposesrapidly (t1/2 ≈ 10 min) at ambient temperature to liberate methane and to formparamagnetic titanium species, as seen by NMR spectroscopy.

The cations 15 and 16 can also be prepared from the reaction of the trimethylderivatives (η5-C5H4CMe2Ar)TiMe3 (Ar = Ph, 3, and 3,5-Me2C6H3, 4) with

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

72

[Ph3C][B(C6F5)4]. Compound 4 reacts with [Ph3C][B(C6F5)4] in bromobenzene-d5 togive release of 1 equiv of 1,1,1-triphenylethane and the dark red ansa-Cp-arenespecies [(η5,η6-C5H4CMe2-3,5-Me2C6H3)TiMe2][B(C6F5)4] (16a). The 1H NMRresonances observed for the cation of 16a (see Experimental Section) are the same asthose of 16 (with [MeB(C6F5)3]- anion).

3.4 Decomposition of [(ηηηη5,ηηηη6-C5H4CMe2-3,5-Me2C6H3)TiMe2][MeB(C6F5)3]

Compound 16 is reasonably stable in C2D2Cl4 or C6D5Br solvent and only verygradually decomposes at ambient temperature. Solutions of 16, prepared in situ in d5-bromobenzene, produce a few deep brown-green crystals upon standing at ambienttemperatures for several days (vide infra).

The presence of 1 equiv of excess B(C6F5)3 in bromobenzene solutions of 16resulted in a reaction (complete in about 20-24 h at ambient temperature) formingMeB(C6F5)2

21 and an organometallic species that, based on NMR spectroscopy, wasidentified as the mixed methyl/perfluorophenyl species [(η5,η6-C5H4CMe2-3,5-Me2C6H3)Ti(C6F5)Me][MeB(C6F5)3] (17, Scheme 6).

..

faster< 4 days

slower> 4 days

18

TiTi BrBr

2 B(C6F5)4

Ti MeMe

MeB(C6F5)3

Ti MeC6F5

MeB(C6F5)3

16 17

B(C6F5)3

- MeB(C6F5)2

C6D5Br C6D5Br

Scheme 6: Formation of the cationic species 17 and 18

The 19F NMR spectrum shows a C6F5 group with an o-F resonance (δ -114.3 ppm)that is downfield shifted relative to that of the [MeB(C6F5)3]- anion (δ -132.9 ppm),and the 13C NMR spectrum a triplet with 3JCF of 7.3 Hz at δ 102.7 ppm for the Ti-Megroup. These features are consistent with a Ti(Me)(C6F5)-species22. The 1H NMR


73

resonances of 17 are broad at ambient temperature, but at -30 °C they reveal anasymmetric structure, and the retention of the η5,η6-coordination mode of theancillary ligand. Thus the addition of an extra equivalent of the Lewis acid B(C6F5)3induces a scrambling of Ti-bound and B-bound hydrocarbyl groups23.

Upon standing at ambient temperature the solution produces brown-green crystalsthat (based on lattice parameters) are identical to those that are (more slowly) formedin solutions of 16. An X-ray structure determination showed that these crystals are ofthe salt {[(η5,η6-C5H4CMe2-3,5-Me2C6H3)Ti(µ-Br)]2}[B(C6F5)4]2 (18, Figure 1) Inthis compound a dicationic dimeric Ti(III) ansa-cyclopentadienyl-arene bromidecomplex is complemented by two tetrakis(pentafluorophenyl)borate anions (Scheme6). The dication is centrosymmetric, with nearly equivalent Ti-Br bond lengths in theTi(µ-Br)2Ti-bridge (Table 1). The Ti-Br distances are on average 0.085 Å shorterthan in the isoelectronic neutral [(C5H4Me)2Ti(µ-Br)]2 complex24 and this, combinedwith the wider Br-Ti-Br' angle, results in a Ti⋅⋅⋅Ti distance of 3.7858(9) Å in 18 thatis 0.34 Å shorter than in the latter compound (Table 1). The bend-angle of the Cp-arene ligand backbone, C(5)-C(6)-C(7), is quite acute at 95.8(3)°, and theCp(centroid)-Ti-Ar(centroid) angle is 125.0°. The arene ring does not deviatesignificantly from planarity, but the bonding to the Ti atom is highly asymmetric,with Ti-C(7), Ti-C(8) and Ti-C(12) being much shorter than the Ti to C(9), C(10)and C(11) distances. This results in a slight lengthening of the C(7)-C(8) and C(7)-C(12) bonds relative to the other arene C-C bonds.

C3

C4

C2

C3

C1

C5

C6

C15

C16

C7

C12

C11

C14

C10

C13C9

C8 Ti

Br

Figure 1: ORTEP diagram of the molecular structure of the cationic part of 18

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

74

Table 1: Selected interatomic distances and angles for the cationic part of 18Distances (Å) Angles (°)

Ti-C(1) 2.341(4) C(7)-C(8) 1.419(6) Br-Ti-Br’ 87.90(2)Ti-C(2) 2.410(5) C(8)-C(9) 1.393(5) Ti-Br-Ti’ 92.10(2)Ti-C(3) 2.383(5) C(9)-C(10) 1.393(6) C(5)-C(6)-C(7) 95.8(3)Ti-C(4) 2.313(4) C(10)-C(11) 1.394(6) C(15)-C(6)-C(16) 107.6(3)Ti-C(5) 2.323(3) C(11)-C(12) 1.395(5)Ti-C(7) 2.379(3) C(7)-C(12) 1.410(6)Ti-C(8) 2.473(4)Ti-C(9) 2.674(4) Ti-Br 2.6250(7)Ti-C(10) 2.725(3) Ti-Br' 2.6334(7)Ti-C(11) 2.713(4)Ti-C(12) 2.470(4) Ti···Ti' 3.7858(9)

The formation of compound 18 is remarkable for at least two reasons: a) thereaction of a Ti(IV) cation with a Lewis acid in a halogenated solvent yields aTi(III)-halide species, and b) starting from a cation with the [MeB(C6F5)3]-

counterion, a product is formed with [B(C6F5)4]- counterions. This indicates that thereaction involves a reduction of the metal center, cleavage of the solvent C-Br bond,and a scrambling of the substituents on the borane/borate species. In C6D5Br solvent,formation of CH3C6D5 is seen (GC/MS). The isolated yield of 18 is rather low (18%)and precise reactive pathways in this transformation are as yet unclear, but theobservations made so far are of interest. For instance, they may shed some light onthe way in which Ti(III) centers can be generated by the reaction of Ti(IV) alkylhalf-sandwich titanium compounds with an excess of Lewis acid activator, a similarreduction as suggested in styrene polymerization catalysts. It may be noted thatGrassi and coworkers used chlorobenzene as solvent for their ESR experiments withCp*TiMe3 and Lewis acids5c, in which Ti(III) species were detected. It alsodemonstrates the dynamic nature of perfluoroarylborate ‘weakly coordinating’anions, in which tetra-arylborates may be formed from alkyl-triarylborates (aninteresting contrast to the aryl abstraction from the [B(C6F5)4]- anion by transient[AlMe2]+ to give mixtures of BMen(C6F5)3-n and AlMe2-n(C6F5)n+1 (n = 0-2), recentlyreported by Bochmann and coworkers25).


75

3.5 Cationic species from (ηηηη5-C5H4CMe2-3,5-Me2C6H3)Ti(CH2Ph)3 (6)

The reaction of the tribenzyl compound 6 with the Lewis acid B(C6F5)3 in d5-bromobenzene was studied by NMR spectroscopy. At -30 °C this results in the rapidformation of the brown ionic ansa-cyclopentadienyl-arene complex [(η5,ηn-C5H4CMe2-3,5-Me2C6H3)Ti(ηn-CH2Ph)2][PhCH2B(C6F5)3] (19, Scheme 7).

Ti

PhPh

Ph

..

Ti

Ph

Ph

PhCH2B(C6F5)3

B(C6F5)3

6 19

. .

Scheme 7: Generation of 19

1H and 19F NMR data are consistent with the abstraction of one benzyl group togive the [PhCH2B(C6F5)3]- anion13,15,26. The chemical shift difference between thetwo sets of Cp protons increases strongly (∆δ 1.62 ppm in 19, as compared to ∆δ0.29 ppm in the neutral tribenzyl 6) indicating ansa-Cp-arene coordination (videsupra). In contrast with this observation, the benzyl CH2 protons do not show theexpected AB pattern, but one broad singlet resonance, and the rather large 1JCHcoupling constant of 148 Hz (compared to 125 Hz in 6) suggests some dihapto-character of these groups27. For the related species [(η5,η6-C5H4CMe2-4-MeC6H4)Zr(CH2Ph)2][B(C6F5)4]9b, the two sets of diastereotopic methylene protonsare marginally separated (∆δ = 0.01 ppm), but the observed 1JCH coupling constant of127 Hz unequivocally indicates η1-coordination28. The NMR spectroscopic datapossibly indicate highly fluxional character for the coordination mode of thearomatic moieties in 19 (i.e. the hapticity of the two benzyl groups and the arenefunctionality, Scheme 8) on NMR time scale, yielding an average NMR spectrum ofan ansa-complex with η1-benzyl ligands, and an η2-benzyl isomer where the π-arenecoordination is weakened (or lost). Bochmann and coworkers recently demonstratedsimilar behavior for the closely related species [(η5,ηn-C5H4CHPh2)Ti(ηn-CH2Ph)2][B(C6F5)4] in CD2Cl2, for which the two different structures could beobserved separately by NMR spectroscopy at -90 °C9a.

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

76

TiTi

THFxPhPh

Ti

Ph

PhTHF-d8

Scheme 8: Fluxional behavior of the aromatic moieties of the cationic part of 19

Addition of a drop of THF-d8 to a C6D5Br solution of 19 shows a shift of thecyclopentadienyl proton resonances back to the ‘normal’ chemical shift ranges (δ6.11 and 5.90 ppm), indicating release of the arene moiety in the presence of a hardLewis base to give a [(η5-C5H4CMe2-3,5-Me2C6H3)Ti(CH2Ph)2(THF-d8)x][PhCH2B(C6F5)3] species (Scheme 8). The Ti-benzyl methylene protonresonances form an AB system (δ 3.19 and 2.18 ppm) with 2JHH of 9.2 Hz, and thecorresponding methylene carbon resonance is a triplet at δ 107.0 ppm (1JCH 129 Hz),indicative for η1-coordination of the benzyl ligands in the presence of THF28.

Compound 19 is reasonably stable at -30 °C in bromobenzene-d5, but rapidlydecomposes at ambient temperature (t1/2 ≈ 10 min) to give paramagnetic species andliberation of toluene, as seen by NMR spectroscopy. After 20 h deep brown-greencrystals had formed which, from a unit cell determination by X-ray diffraction, wereidentified as {[(η5,η6-C5H4CMe2-3,5-Me2C6H3]Ti(µ-Br)]2}{B(C6F5)4}, the sameproduct as formed in the decomposition of [(η5,η6-C5H4CMe2-3,5-Me2C6H3)TiMe2][MeB(C6F5)3] (16) in C6D5Br solution (vide supra).

Reaction of (η5-C5H4CMe2-3,5-Me2C6H3)Ti(CH2Ph)3 (6) with [Ph3C][B(C6F5)4] inC6D5Br resulted in the release of 1 equiv of 1,1,1,2-tetraphenylethane and theformation of the ansa-cyclopentadienyl-arene species [(η5,ηn-C5H4CMe2-3,5-Me2C6H3)Ti(ηn-CH2Ph)2][B(C6F5)4] (20). The NMR data for the cation are identicalto those of 19. This suggests that the rapid equilibrium between the differentcoordination modes of the aromatic moieties in the cations is apparently notinfluenced by the counterion.

3.6 Generation of cationic species from (ηηηη5-C5H4CMe2Ph)Ti(CH2Ph)3 (5)

The reaction of the tribenzyl complex 5 with B(C6F5)3 in bromobenzene-d5 resultsin release of 1 equiv of toluene, and the formation of an ionic species that wascharacterized as the contact ion pair [(η5,η1-C5H4CMe2C6H4)Ti(CH2Ph)][η6-PhCH2B(C6F5)3] (21, Scheme 9), in which the pendant aromatic group has beenortho cyclometalated. In contrast to the ionic compounds [(η5,η6-C5H4CMe2Ar)TiMe2][MeB(C6F5)3] (15, 16) and 19, compound 21 is also soluble in


77

benzene and toluene, and was obtained analytically pure as a green microcrystallinesolid from the reaction of 5 with B(C6F5)3 in pentane.

..

B(C6F5)3

- tolueneRT

215

Ti

Ph

B(C6F5)3

Ti

PhPh Ph

Scheme 9: Reaction of 5 with B(C6F5)3 involving rapid ligand cyclometalation

The Ti-C 13C NMR resonance of the cyclometalated pendant arene group is foundat δ 199.7 ppm, which is comparable to the chemical shift found for the ipso carbonof the Ti-Ph group in the neutral metallocenes [Me2Si(η5-C5Me4)2]TiPh2 (δ 199.6ppm, CDCl3, 25 °C) and (η5-C5H4CMe3)2TiPh2 (δ 191.9 ppm, C6D6, 25 °C)29. Thecomplex 21 has an asymmetric structure in solution (toluene-d8, -30 °C), due to theη6-coordination of the [PhCH2B(C6F5)3]- anion to the metal center. This can be seenby 19F NMR, where the ∆(δm-F-δp-F) shift difference is 4.2 ppm, indicative of acontact-ion pair20, and by 1H NMR, where separate resonances are seen for allaromatic and benzylic protons of the anion. The Ti-benzyl group is η1-bound, as canbe seen from the 2JHH coupling constant of 10 Hz, and the 1JCH coupling constant of126 Hz of the benzyl methylene group, both of which are characteristic of η1-benzylcoordination28.

..

13

12

11

23

1

4

5

67

89

10

Ti PhH

H

B(C6F5)3

HH

Figure 2: Solution structure of 21 in toluene-d8 at -30 °C

From its low-temperature (-30 °C) 1H,1H NOESY spectrum the solution structureof 21 can be determined (Figure 2). The methylene protons of the benzyl of the[PhCH2B(C6F5)3]- anion (H12,H13) show a correlation with the two β-protons of thecyclopentadienyl ring (H2,H3). Methylene proton H13 (δ 3.39 ppm) interacts with

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

78

both H2 and H3, while H12 (δ 2.8 ppm) only correlates with H3. The methyleneproton of the titanium-benzyl ligand (H9, δ 2.80 ppm) displays NOE interactionswith the Ph m-H (H8), adjacent to the Ph o-C ipso. Additionally, the other methyleneproton (H10, δ 0.81 ppm) correlates with the para-H (H11) of the benzyl ligand of theanion. From the NOE interactions, it can be concluded that in solution at lowtemperature complex 21 adapts a structure in which the benzyl methylene group ofthe coordinated anion is directed towards the cyclopentadienyl ligand, and themethylene protons of the metal-bound benzyl group are pointing away from thecyclopentadienyl moiety. At ambient temperature considerable line broadening isobserved, suggesting fluxional behavior of the remaining benzyl ligand and thecoordinated anion. The thermal lability of 21 precludes a detailed study of thesolution structure at ambient temperature.

In the closely related cyclopentadienyl-amido ‘constrained geometry’ type catalysts[(η5,η1-C5H4CH2CH2NR)Ti(CH2Ph)][PhCH2B(C6F5)3] (R = Me, i-Pr, t-Bu) the anionis either not coordinated to the titanium center (R = i-Pr, t-Bu) or participates in anequilibrium between a coordinated and a non-coordinated state (R = Me, similar asobserved for the Zr analogs)16,30. The different degrees of coordination of the[PhCH2B(C6F5)3]- anion in the Cp-amido systems and 21 may be due to both stericand electronic factors. In metal-(σ-aryl) complexes, such as 21, π-donation of thearyl π-system is of relatively little importance31. For example, both [ZrMe6]2- and[ZrPh6]2- show trigonal-prismatic rather than octahedral geometries, which isattributed to the lack of ligand-to-metal π-donation from the σ-Ph ligand32. Incontrast, the lone pair on the nitrogen atom in the cyclopentadienyl-amido systemcan serve as an additional 2-electron donor, thus affording a 12-electron cationicspecies, as opposed to the formally 10-electron species 21. The importance of stericeffects is clear from the different degrees of anion coordination in the Cp-amidotitanium species, but it can be expected, from electronic considerations, that forsterically comparable Cp-amido and Cp-aryl systems, cation-anion interactions willbe stronger in the Cp-aryl species. Hence, in compound 21, the highly electron-deficient cation [(η5,η1-C5H4CMe2C6H4)Ti(CH2Ph)]+ is stabilized by coordinativearomatic contacts of the anion (to give a 16-electron species), whereas for the leaststerically demanding Cp-amido system, [(η5,η1-C5H4CH2CH2NMe)Ti(CH2Ph)]+, anequilibrium between solvent-separated and contact ion pairs is observed.

Upon reaction of [Ph3C][B(C6F5)4] with the tribenzyl complex 5 in bromobenzene-d5 at -30 °C, 1 equiv of 1,1,1,2-tetraphenylethane and 1 equiv of toluene areliberated, and an ionic species with an ortho cyclometalated pendant arene group anda η2-coordinated benzyl ligand, [(η5,η1-C5H4CMe2C6H4)Ti(η2-CH2Ph)][B(C6F5)4](22, Scheme 10), is formed.


79

.

.[Ph3C][B(C6F5)4]

C6D5Br, -30 °C

- Ph3CCH2Ph- toluene

(22)

5

Ti

PhPh Ph

B(C6F5)4Ti

Ph

Ti

B(C6F5)4 B(C6F5)4

Ti

Scheme 10: Generation of 22; interconversion of stereoisomers

The 13C NMR resonance of the Ti-bound aryl carbon is observed at δ 215.8 ppm,16 ppm downfield from that in 21. The methylene 13C NMR resonance of the benzylligand in 22 is found at δ 88.1 ppm with a 1JCH coupling constant of 154 Hz,indicative of η2-benzyl coordination27. The corresponding benzyl methylene protonsare observed as two broadened singlets (W1/2 = 37 Hz), indicating fluxional behaviorof 22, as is also suggested by the broadened singlets (W1/2 = 33 Hz) for theinequivalent cyclopentadienyl protons. Upon warming to room temperature the Cpand the methylene protons each coalesce into broad signals with linewidths at half-height of 56 and 160 Hz, respectively. It appears that at low temperature compound22 has an asymmetric solution structure due to the multihapto coordination of thebenzyl ligand bound in the cleft between the cyclopentadienyl and arene moiety(Scheme 10). At higher temperatures, rapid fluxionality of the benzyl ligand leads toa Cs symmetrically averaged structure.

3.7 Deuterium labeling experiments

To establish the cyclometalation mechanism in the reaction of the tribenzylcompound 5 with B(C6F5)3 to give 21, isotopic labeling experiments were carried outwith (η5-C5H4CMe2C6D5)Ti(CH2Ph)3 (9), the synthesis of which was described inChapter 2. The reaction of 9 with B(C6F5)3 in C6D6 results in the selective formationof α-d1-toluene, and the contact ion pair [(η5,η1-C5H4CMe2C6D4)Ti(CH2Ph)][η6-PhCH2B(C6F5)3] (23). The 1H NMR resonance of the CH2D group in α-d1-toluene isobserved as a triplet at δ 2.08 ppm with a 2JHD coupling constant of 2.2 Hz, and thecorresponding methyl 13C NMR resonance is a triplet at δ 21.2 ppm with a 1JCDcoupling constant of 19 Hz. Compound 23 has the same NMR characteristics as itsnon-deuterated analog 21, except for the resonances of the perdeutero-phenyl ring.

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

80

B(C6F5)3

..

B(C6F5)3

217

5

- toluene - toluene

PhCH2B(C6F5)3PhCH2B(C6F5)3

Ti

Ph

B(C6F5)3

HTi

Ph

Ph Ti

HPh Ph

H Ti

PhPh Ph

Ti

Ph

Ph

Scheme 11: Formation of the ionic species 21 from 5 and 7 with B(C6F5)3

The formation of α-d1-toluene indicates that the ortho cyclometalation of thependant arene group in the cationic species proceeds via σ-bond metathesis, incontrast to the benzylidene pathway identified for the ligand cyclometalation in thethermolysis of the neutral compounds (η5-C5H4CMe2Ar)Ti(CH2Ph)3 (Ar = Ph, 5, and3,5-Me2C6H3, 6, Chapter 2). Apparently, B(C6F5)3 initially abstracts a benzyl groupfrom the titanium tribenzyl species to form the ansa-cyclopentadienyl-phenyltitanium dibenzyl cation, which subsequently gives ortho C-H/D bond activation toafford the cyclometalated cationic species [(η5,η1-C5H4CMe2C6(H/D)4)Ti(CH2Ph)]+

(Scheme 11, top). The reaction is accompanied by a distinctive color change frombrown to green. Although the reaction is too fast to determine the rate constants forthe process, this color change allows a qualitative assessment of the isotope effect atambient temperature. Solutions of 5 turn green within 10 seconds of the addition ofB(C6F5)3, whereas solutions of 9/B(C6F5)3 take about 3 min after mixing for a fullcolor change. These observations suggest ortho C-H/D bond activation in the rate-determining step, confirming the proposed σ-bond metathesis pathway.

Reaction of 7, prepared in situ (see Chapter 2), with 1 equiv of B(C6F5)3 in d6-benzene affords the expected ionic species 21 (Scheme 11, bottom).Correspondingly, 7 reacts with [Ph3C][B(C6F5)4] in d5-bromobenzene to give[(η5,η1-C5H4CMe2C6H4)Ti(η2-CH2Ph)][B(C6F5)4] (22).

Treatment of (η5,η1-C5H4CMe2-3,5-Me2C6H2)Ti(CH2Ph)2 (8, see Chapter 2) with[Ph3C][B(C6F5)4] or B(C6F5)3 in C6D5Br yields extremely thermally labilecompounds that decompose with a t1/2 of seconds even at -30 °C. Monitoring thereactions with 1H NMR shows that additional toluene is liberated upon degradationto give unidentified paramagnetic titanium species. The 19F NMR indicates that thedecomposition pathway of 8 with B(C6F5)3 is different from that of [(η5,ηn-C5H4CMe2-3,5-Me2C6H3)Ti(ηn-CH2Ph)2][PhCH2B(C6F5)3] (19). In contrast to the


81

decomposition of 19, resonances for the [B(C6F5)4]- anion are not observed in thedecomposition of the system 8/B(C6F5)3. In benzene solvent, a brown oil separatesfrom the solution on reaction of 8 with B(C6F5)3, indicating the formation of asolvent-separated ion pair, in contrast to contact ion pairs, like [(η5,η1-C5H4CMe2C6H4)Ti(CH2Ph)][η6-PhCH2B(C6F5)3] (21), that are usually quite solublein benzene.

3.8 Conclusions

Reactions of (η5-C5H4CMe2Ar)TiR3 (Ar = Ph, 3,5-Me2C6H3; R = Me, CH2Ph) withB(C6F5)3 or [Ph3C][B(C6F5)4] initially generate cationic ansa-cyclopentadienyl-arenetitanium dialkyl species. For the dibenzyl cations, competetive complexation of thebenzyl ligands with the coordinated arene has been observed, indicating thepropensity of half-sandwich group 4 compounds to form metal-arene coordinativecontacts. For the tribenzyl compound (η5-C5H4CMe2Ph)Ti(CH2Ph)3 (5), with anunsubstituted pendant arene group, activation with B(C6F5)3 or [Ph3C][B(C6F5)4]leads to ortho cyclometalation of the ancillary ligand via direct σ-bond metathesis inthe initially formed cationic [(η5,η6-C5H4CMe2Ph)Ti(CH2Ph)2]+ species, in contrastto metalation via an intermediate benzylidene species observed for the neutraltribenzyl complex. The observation that the cationic species [(η5,η6-C5H4CMe2Ph)TiMe2]+ is more stable towards cyclometalation than the [(η5,η6-C5H4CMe2Ph)Ti(CH2Ph)2]+ cation suggests that initial displacement of thecoordinated arene is required for cyclometalation. In the [(η5,η6-C5H4CMe2Ph)Ti(CH2Ph)2]+ cation this is likely to be compensated for or assisted bydihapto bonding of the benzyl group(s), something which is not possible for theanalogous dimethyl cationic species.

The [(η5,η6-C5H4CMe2-3,5-Me2C6H3)TiR2][RB(C6F5)3] (R = Me, CH2Ph) ionicspecies decompose gradually in bromobenzene to produce a dimeric Ti(III) complex,the first structurally characterized ansa-Cp-arene early transition metal derivative.For the methyl species, the decomposition is accelerated by the presence of excessLewis acid, and proceeds via an unusual reduction of Ti(IV) to Ti(III) inbromobenzene, involving hydrocarbyl ligand scrambling and bromobenzene solventactivation. These observations provide an interesting insight into the possibleactivation and degradation processes in titanium-based half-sandwich olefinpolymerization catalysts. The results show that reduction of Ti(IV) to Ti(III) inmonocyclopentadienyl titanium species can occur readily in the presence of excessLewis acid, such as B(C6F5)3, without the participation of an olefinic substrate, e.g.styrene. The experimental evidence for the involvement of Ti(III) species insyndiotactic styrene polymerization has been obtained under similar conditions(C6D5Cl solvent, B(C6F5)3 or [Ph3C]][B(C6F5)4] activator), and might be an intrinsicfeature of the catalyst system as such33, and not necessarily a result of thepolymerization process.

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

82

3.9 Experimental Section

General considerations - All experiments were carried out under purified nitrogenatmosphere using standard Schlenk and glovebox techniques. Deuterated solvents (Aldrich,Acros) were either degassed and dried over molecular sieves (Aldrich, 4Å) or dried overNa/K alloy and vacuum transferred before use (C6D6, toluene-d8, THF-d8). Bromobenzenewas distilled from Ca chips and pentane was distilled from Na/K alloy prior to use. - NMRspectra were recorded on Varian Gemini 200/300 and Unity 500 spectrometers in NMRtubes equipped with a Teflon (Young) valve. The 1H NMR spectra were referenced toresonances of residual protons in the deuterated solvents (δ = 7.15 ppm for C6D6, δ = 2.15ppm for methyl resonance of toluene-d8, δ = 7.28 ppm for downfield signal of C6D5Br). The13C NMR spectra were referenced to the carbon resonances of the deuterated solvent (δ =128 ppm for C6D6, δ = 137.5 ppm for C ipso for toluene-d8, δ =122.4 ppm for C ipso forC6D5Br). Chemical shifts (δ) are given relative to tetramethylsilane (downfield shifts arepositive). GC/MS analyses were conducted using a HP 5973 mass-selective detectorattached to a HP 6890 GC instrument. Elemental analyses were performed at theMicroanalytical Department of the University of Groningen. Given values are the averageof at least two independent determinations. - B(C6F5)3

34 and [Ph3C][B(C6F5)4]35 wereprepared according to published procedures.

Generation of [(ηηηη5,ηηηη6-C5H4CMe2Ph)TiMe2][MeB(C6F5)3] (15) - A solution of (η5-C5H4CMe2Ph)TiMe3 (3, 8.7 mg, 32 µmol) in 0.25 ml C6D5Br was added to a solution ofB(C6F5)3 (16 mg, 32 µmol) in 0.25 ml of C6D5Br to give a dark red solution of the cationicspecies 15. Compound 15 is thermally labile, and decomposes (at room temperature in 15min), liberating methane. - 1H NMR (300 MHz, C6D5Br, -10 °C): δ 7.56 (m, 2H, Ph m-H),Ph p-H overlapped by solvent, 6.60 (ps. t, 3JHH = 2.6 Hz, 2H, Cp), 6.18 (m, 2H, Ph o-H),5.18 (ps. t, 3JHH = 2.6 Hz, 2H, Cp), 1.2 (br, 3H, BMe), 0.99 (s, 6H, CMe2), 0.59 (s, 6H,TiMe) - 19F NMR (188.15 MHz, C6D5Br): δ -131.6 (o-F), -162.0 (p-F), -164.8 (m-F)

Generation of [(ηηηη5,ηηηη6-C5H4CMe2-3,5-Me2C6H3)TiMe2][MeB(C6F5)3] (16) - A solution of(η5-C5H4CMe2-3,5-Me2C6H3)TiMe3 (4, 13.5 mg, 44.3 µmol) in 0.25 ml of C2D2Cl4 wasadded to a solution of B(C6F5)3 (22.7 mg, 44.3 µmol) in 0.25 ml of C2D2Cl4 to give a deepred solution of 16. The reaction proceeds in similar fashion in C6D5Br solvent. - 1H NMR(300 MHz, C6D5Br): δ 7.02 (s, 1H, Ar p-H), 6.74 (ps. t, 3JHH = 2.7 Hz, 2H, Cp), 5.91 (s, 2H,Ar o-H), 5.15 (ps. t, 3JHH = 2.6 Hz, 2H, Cp), 2.10 (s, 6H, ArMe), 1.07 (s, 6H, CMe2 and s,3H, BMe), 0.34 (s, 6H, TiMe) - 13C NMR (75.4 MHz, C2D2Cl4, -40oC): δ 155.2 (s, Ar Cipso), 151.2 (d, 1JCF = 236 Hz, o-CF), 140.3 (d, 1JCF = 236 Hz, p-CF), 139.2 (d, 1JCF = 236Hz, m-CF), 138.0 (s, Cp C ipso), 135.3 (d, 1JCH = 166 Hz, Ar p-CH), 131.4 (br, C6F5 Cipso), 128.2 (d, 1JCH = 186 Hz, Ar o-CH), 125.3 (d, 1JCH = 166 Hz, Cp CH), 123.4 (s, Ar m-C ipso), 115.9 (d, 1JCH = 172 Hz, Cp CH), 74.4 (q, 1JCH = 126 Hz, TiMe), 43.9 (s, CMe2 Cipso), 25.8 (q, 1JCH = 130 Hz, CMe2), 21.6 (q, 1JCH = 126 Hz, ArMe), 13.5 (br, BMe) - 19FNMR (188.15 MHz, C2D2Cl4): δ -132.8 (o-F), -164.1 (p-F), -166.7 (m-F)

Reaction of 16 with THF-d8 - To a deep red solution of 16 in C6D5Br, prepared asdescribed above, a drop of THF-d8 was added, resulting in a red solution of [(η5-C5H4CMe2-3,5-Me2C6H3)TiMe2(THF-d8)x][MeB(C6F5)3]. - 1H NMR (500 MHz,


83

C6D5Br/THF-d8): δ 6.72 (s, 2H, Ar o-H), 6.66 (s, 1H, Ar p-H), 6.14 (ps. t, 3JHH = 2.8 Hz,2H, Cp), 6.04 (ps. t, 3JHH = 2.7 Hz, 2H, Cp), 2.14 (s, 6H, ArMe), 1.37 (s, 6H, CMe2 and s,6H, TiMe), 1.04 (br, 3H, BMe)

Generation of [(ηηηη5,ηηηη6-C5H4CMe2-3,5-Me2C6H3)TiMe2][B(C6F5)4] (16a) - A solution of 4(10.1 mg, 33 µmol) in 0.25 ml C6D5Br was mixed with a solution of [Ph3C][B(C6F5)4] (30.6mg, 33 µmol) in 0.25 ml C6D5Br. This resulted in a dark red solution containing Ph3CMeand the ionic species 16a. - 1H NMR (300 MHz, C6D5Br): δ 7.4-6.8 (16H, aromatic protons,poorly resolved), 6.77 (ps. t, 3JHH = 2.6 Hz, 2H, Cp), 5.93 (s, 2H, Ar o-H), 5.16 (ps. t, 3JHH =2.6 Hz, 2H, Cp), 2.12 (s, 6H, ArMe), 2.04 (s, 3H, Ph3CMe), 1.08 (s, 6H, CMe2), 0.36 (s,6H, TiMe) - 13C NMR (75.4 MHz, C6D5Br): δ 151.9 (Ar C ipso), 134.7 (Cp C ipso),aromatic CH resonances poorly resolved, 125.0 (Cp CH), 120.4 (Ar m-C ipso), 112.6 (CpCH), 71.9 (TiMe), 40.4 (CMe2 C ipso), 22.2 (CMe2), 21.0 (ArMe) - 19F NMR (188.15 MHz,C6D5Br): δ -132.8 (o-F), -162.5 (p-F), -166.4 (m-F)

Reaction of 16 with B(C6F5)3 - In an NMR tube with Teflon (Young) valve, a solution of16 was prepared as described above, but using two equivalents of B(C6F5)3 per Ti. The tubewas allowed to stand at ambient temperature, and was monitored at regular intervals by 1Hand 19F NMR. After 24 h all of 16 had disappeared, giving 17 and MeB(C6F5)2. - 17: 1HNMR (500 MHz, C6D5Br, -30 oC): δ 6.85, 6.80 (br, 1H, Cp), 6.71 (s, 1H, Ar p-H), 5.96,5.74 (s, 1H, Ar o-H), 5.66, 5.53 (br, 1H, Cp), 2.11, 1.38 (s, 3H, ArMe), 1.13-1.09 (total 9H,CMe2 and TiMe) - 13C NMR (125.7 MHz, C6D5Br, -30 oC): δ 102.7 (t, 3JCF = 7.3 Hz,TiMe), 40.5 (CMe2 C ipso), 22.2 (CMe2), 20.2, 21.0 (ArMe), aromatic resonances poorlyresolved - 19F NMR (470 MHz, C6D5Br, -30 oC): δ -114.3 (o-F Ti-Ar), -132.9 (o-F B-Ar), -149.9 (p-F Ti-Ar), -159.5 (m-F Ti-Ar), -164.7 (p-F B-Ar), -167.3 (m-F B-Ar) - MeB(C6F5)2:1H NMR (500 MHz, C6D5Br, 20 oC): δ 1.52 (qui, 5JHF = 2 Hz, BMe) - 19F NMR (470 MHz,C6D5Br, -30 oC): δ -129.9 (o-F), -147.5 (p-F), -161.5 (m-F)

Formation of {[(ηηηη5,ηηηη6-C5H4CMe2-3,5-Me2C6H3)Ti(µµµµ-Br)]2}[B(C6F5)4]2 (18) - A solutionof 4 (0.120 g, 0.39 mmol) in 5 ml of bromobenzene was added to B(C6F5)3 (0.40 g, 0.78mmol). Over a period of 3 weeks at ambient temperature green-brown crystals separatedfrom the solution. The supernatant was decanted and the crystals rinsed twice with 10 ml ofpentane. Yield: 0.070 g (34 µmol, 18%) of analytically pure 18. - Anal. Calcd. ForC80H38F40Ti2Br2B2: C, 47.19; H, 1.88; Ti, 4.70. Found: C, 47.03; H, 2.22; Ti, 4.58.

Crystal structure analysis of 18 - Enraf-Nonius CAD4-F diffractometer, Mo-Kα radiation(λ = 0.71073 Å) , T = 130 K; monoclinic, P21/n, a = 13.616(2), b = 16.014(1), c = 17.702(2)Å, β = 109.01(1), V = 3649.4(7) Å3, Z = 2, Dx = 1.853 g cm-3, µ = 14.7 cm-1. The structurewas solved by direct methods. A final refinement on F2 converged at wR(F2) = 0.1143 for7118 reflections with Fo

2 ≥ 0 and R(F) = 0.0415 for 5390 reflections with Fo ≥ 4.0 σ(Fo)and 644 parameters. Crystallographic data (excluding structure factors) for the structurereported in this chapter have been deposited with the Cambridge Crystallographic DataCentre as supplementary publication no. CCDC-135683.

Generation of [(ηηηη5,ηηηηn-C5H4CMe2-3,5-Me2C6H3)Ti(ηηηηn-CH2Ph)2][PhCH2B(C6F5)3] (19) -A solution of 37 mg (69 µmol) of (η5-C5H4CMe2-3,5-Me2C6H3)Ti(CH2Ph)3 (6) in 0.25 ml

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

84

of C6D5Br (-30 °C) was added to a solution of 36 mg (70 µmol) B(C6F5)3 in 0.25 ml ofC6D5Br (- 30 °C) to obtain a deep red solution of the cationic complex 19. - 1H NMR (500MHz, C6D5Br, -30 °C): δ 7.18 (br, 2H, B-Bz m-H), 7.04 (br, 2H, B-Bz o-H, partial overlapwith solvent), 6.99 (s, 6H, Ti-Bz m- and p-H), 6.62 (s, 1H, Ar p-H), 6.58 (s, 2H, Ar o-H),6.46 (s, 2H, Cp), 6.14 (s, 4H, Ti-Bz o-H), 4.84 (s, 2H, Cp), 3.36 (br, 2H, B-CH2), 2.88 (s,4H, Ti-CH2), 2.21 (s, 6H, ArMe), 1.03 (s, 6H, CMe2) - 13C NMR (125.7 MHz, C6D5Br, -30°C): δ 148.8 (d, 1JCF = 240 Hz, o-CF), 146.0 (s, Ar C ipso), 144.8 (s, Cp C ipso), 142.0 (s,Ar m-C ipso or Ti-Bz C ipso), 140.2 (s, Ar m-C ipso or Ti-Bz C ipso), 138.0 (d, 1JCF = 240Hz, p-CF and s, B-Bz C ipso), 137.0 (d, 1JCF = 240 Hz, m-CF), 136.8 (d, 1JCH = 164 Hz, Ti-Bz m-CH), 129.6-128.8 (Ti-Bz p-CH, Ar p-CH, B-Bz o-CH, B-Bz p-CH, B-Bz m-CH,overlap with solvent), 127.0 (d, 1JCH = 161 Hz, Ti-Bz o-CH,), 123.1 (d, 1JCH = 180 Hz, CpCH), 123.0 (d, 1JCH = 154 Hz, Ar o-CH), 119.7 (d, 1JCH = 174 Hz, Cp CH), 101.5 (t, 1JCH =148 Hz, Ti-CH2), 40.3 (s, CMe2 C ipso), 32.4 (br, B-CH2), 28.7 (q, 1JCH = 127 Hz, CMe2),22.1 (q, 1JCH = 128 Hz, ArMe) - 19F NMR (188.2 MHz, C6D5Br, -30 °C): δ -128.4 (o-F), -160.5 (p-F), -163.5 (m-F)

Reaction of 19 with THF-d8 - To a deep brown solution of 19 in C6D5Br, prepared asdescribed above, was added a drop of THF-d8, resulting in a red solution of [(η5-C5H4CMe2-3,5-Me2C6H3)Ti(CH2Ph)2(THF-d8)x][PhCH2B(C6F5)3]. - 1H NMR (500 MHz,C6D5Br/THF-d8, -30 °C): δ 7.25-6.5 (18H, aromatic protons), 6.11 (s, 2H, Cp), 5.90 (s, 2H,Cp), 3.28 (br, 2H, B-CH2), 3.19 (d, 2JHH = 9.2 Hz, 2H, Ti-CH2), 2.19 (s, 6H, ArMe), 2.18(2H, Ti-CH2, overlapped by ArMe), 1.32 (s, 6H, CMe2) - 13C NMR (125.7 MHz,C6D5Br/THF-d8, -30 °C): δ 151.1, 148.7, 146.1, 142.1, 138.3 (s, Ar, Cp, Ti-Bz and B-Bz Cipso), 148.6 (d, 1JCF = 237 Hz, o-CF), 137.8 (d, 1JCF = 246 Hz, p-CF), 136.8 (d, 1JCF = 249Hz, m-CF), 132-122 (aromatic CH, overlapped by solvent), 121.2 (d, 1JCH = 174 Hz, CpCH), 117.4 (d, 1JCH = 169 Hz, Cp CH), 107.0 (t, 1JCH = 129 Hz, Ti-CH2), 40.4 (s, CMe2 Cipso), 32.5 (br, B-CH2), 30.2 (q, 1JCH = 126 Hz, CMe2), 22.7 (q, 1JCH = 127 Hz, ArMe)

Generation of [(ηηηη5,ηηηηn-C5H4CMe2-3,5-Me2C6H3)Ti(ηηηηn-CH2Ph)2][B(C6F5)4] (20) - Asolution of 25 mg (47 µmol) of 6 in 0.25 ml of C6D5Br (-30 °C) was added to a solution of43 mg (48 µmol) B(C6F5)3 in 0.25 ml of C6D5Br (- 30 °C) to obtain a deep brown solutioncontaining the cationic complex 20 and Ph3CCH2Ph. - 1H NMR (500 MHz, C6D5Br, -30°C): δ 7.2-6.1 (33H, aromatic protons, ill-resolved), 6.33 (s, 2H, Cp), 4.85 (s, 2H, Cp), 3.78(s, 2H, Ph3CCH2Ph), 2.90 (s, 4H, Ti-CH2), 2.21 (s, 6H, ArMe), 1.04 (s, 6H, CMe2) - 13CNMR (125.7 MHz, C6D5Br, -30 °C): δ 148.6 (d, 1JCF = 240 Hz, o-CF), 146.7, 146.0, 144.5,144.0, 143.0, 141.7, 139.9, 138.4, 136.5 (s, Ar, Cp, Ti-Bz, B-Bz, and Ph3CCH2Ph C ipso),138.5 (d, 1JCF = 235 Hz, p-CF), 136.6 (d, 1JCF = 241 Hz, m-CF), 132-122 (aromatic CH andCp CH, overlapped by solvent), 119.4 (d, 1JCH = 169 Hz, Cp CH), 101.2 (t, 1JCH = 147 Hz,Ti-CH2), 58.6 (s, Ph3C C ipso), 45.9 (t, 1JCH = 128 Hz, Ph3CCH2Ph), 40.1 (s, CMe2 C ipso),28.4 (q, 1JCH = 126 Hz, CMe2), 21.8 (q, 1JCH = 128 Hz, ArMe)


85

Preparation of [(ηηηη5,ηηηη1-C5H4CMe2C6H4)Ti(CH2Ph)][ηηηη6-PhCH2B(C6F5)3] (21) - At -40°C, a solution of (η5-C5H4CMe2Ph)Ti(CH2Ph)3 (5, 430 mg, 0.85mmol) in 20 ml of pentane was added to a solution of 440 mg(0.86 mmol) B(C6F5)3 in 20 ml of pentane. A green precipitatewas instantaneously formed. The supernatant was decanted. Thegreen residue was brought on a glass frit and was thoroughlyrinsed with pentane to yield 520 mg (0.56 mmol, 66%) ofanalytically pure 21. - 1H NMR (500 MHz, toluene-d8, -30 °C): δ

6.88 (t, 3JHH = 7.7 Hz, 2H, Ti-Bz m-H), 6.73 (m, 3H, Ti-Bz p-H and H6, H8), 6.65 (t, 3JHH =7.5 Hz, 1H, H7), 6.46 (d, 3JHH = 8.1 Hz, 1H, H5), 6.44 (d, 3JHH = 8.1 Hz, 1H, B-Bz o-H),6.28 (d, 3JHH = 7.7 Hz, 1H, B-Bz o-H’), 6.20 (t, 3JHH = 7.3 Hz, 1H, B-Bz m-H), 5.91 (d, 3JHH

= 7.3 Hz, 2H, Ti-Bz o-H), 5.88 (s, 1H, H1), 5.86 (t, 1H, H11, partial overlap), 5.84 (s, 1H,H4), 5.62 (t, 3JHH = 7 Hz, B-Bz m-H’), 5.11 (s, 1H, H3), 4.82 (s, 1H, H2), 3.39 (br, 1H, H13),2.80 (d, 2JHH = 10 Hz, 1H, H9), 2.8 (br, 1H, H12, overlap with H9), 1.15 (s, 3H, CMe2), 0.81(d, 2JHH = 10 Hz, 1H, H10), 0.73 (s, 3H, CMe2) - 13C NMR (125.7 MHz, toluene-d8, -30 °C):δ 199.7 (Ph o-C ipso), 170.9 (Cp C ipso), 160.5, 157.3, 150.4 (Ph, Ti-Bz, B-Bz C ipso),148.5 (d, 1JCF = 238 Hz, o-CF), 139.0 (d, 1JCF = 238 Hz, p-CF), 137.4 (d, 1JCF = 238 Hz, m-CF), 134.7 (B-Bz m-CH), 132.0 (CH6 or CH8), 131.2 (B-Bz o-CH), 130.9 (B-Bz m-CH’),128.5 (Ti-Bz p-CH, overlap with solvent), 127.7 (Ti-Bz m-CH, overlap with solvent), 126.5(Ti-Bz o-CH), 125.5-124.5 (B-Bz o-CH’, CH1, CH5, CH11, overlap with solvent), 124.0(CH6 or CH8), 123.9 (CH4), 122.6 (CH7), 116.1 (CH3), 111.2 (CH2), 93.3 (Ti-CH2, 1JCH =126 Hz), 43.6 (CMe2 C ipso), 35.3 (br, B-CH2), 29.7, 28.9 (CMe2) - 19F NMR (188.2 MHz,C6D6): δ -132.8 (d, 3JFF = 22.8 Hz, 2F, o-F), -162.3 (t, 3JFF = 21.6 Hz, 1F, p-F), -166.5 (m,2F, m-F) - Anal. Calcd. for C46H28TiBF15: C, 59.77; H, 3.05; Ti, 5.18. Found: C, 59.61; H,3.11; Ti, 5.08.

Generation of [(ηηηη5,ηηηη1-C5H4CMe2C6H4)Ti(ηηηη2-CH2Ph)][B(C6F5)4] (22) - A solution of 10.2mg (20 µmol) of 5 in 0.6 ml bromobenzene-d5 was added to 18.5 mg (20 µmol) of[Ph3C][B(C6F5)4] in an NMR tube equipped with a Teflon (Young) valve. This resulted in abrown solution containing Ph3CCH2Ph, toluene, and the thermally labile species 22. - 1HNMR (500 MHz, C6D5Br, -30 °C): δ 7.8-6.6 (34H, aromatic protons, ill-resolved), 5.91 (br,W1/2 = 33 Hz, 1H, Cp), 5.52 (br, W1/2 = 33 Hz, 1H, Cp), 5.38 (br, W1/2 = 33 Hz, 1H, Cp),4.79 (br, W1/2 = 33 Hz, 1H, Cp), 3.88 (br, W1/2 = 37 Hz, 1H, Ti-CH2), 3.77 (s, 2H,Ph3CCH2Ph), 2.16 (s, 4H, PhCH3 and Ti-CH2), 1.24 (br, 3H, CMe2), 1.07 (br, 3H, CMe2) -13C NMR (125.7 MHz, C6D5Br, -30 °C): δ 215.8 (s, Ph o-C ipso), 169.9, 158.2, 146.7,142.2, 138.4 (s, Cp and aromatic C ipso), 148.6 (d, 1JCF = 239 Hz, o-CF), 138.6 (d, 1JCF =232 Hz, p-CF), 136.7 (d, 1JCF = 248 Hz, m-CF), 133.5-120.5 (aromatic CH, overlapped bysolvent), 119.9, 118.6, 117.1, 115.5 (br, Cp CH), 88.0 (t, 1JCH = 154 Hz, Ti-CH2), 58.6 (s,Ph3C C ipso), 45.9 (t, 1JCH = 128 Hz, Ph3CCH2Ph), 44.7 (s, CMe2 C ipso), 28.2, 27.9 (br,CMe2) - 1H NMR (500 MHz, C6D5Br, 25 °C): δ 7.8-6.6 (36H, aromatic protons and Cp, ill-resolved), 5.43 (br, W1/2 = 56 Hz, 2H, Cp), 3.82 (s, 2H, Ph3CCH2Ph), 3.76 (br, W1/2 = 160Hz, 2H, Ti-CH2), 2.16 (s, 3H, PhCH3), 1.18 (s, 6H, CMe2) - 19F NMR (188.2 MHz, C6D5Br,25 °C): δ -132.8 (s, 2F, o-F), -162.9 (t, 3JFF = 21 Hz, 1F, p-F), -168.7 (s, 2F, m-F)

Generation of [(ηηηη5,ηηηη1-C5H4CMe2C6D4)Ti(CH2Ph)][ηηηη6-PhCH2B(C6F5)3] (23) - A solutionof 16.5 (32 µmol) of 9 in 0.6 ml of benzene-d6 was added to 16.7 mg (33 µmol) B(C6F5)3.

..

13

12

11

23

1

4

5

67

89

10

Ti PhH

H

B(C6F5)3HH

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

86

The solution was transferred to an NMR tube equipped with a Teflon (Young) valve andinvestigated by NMR spectroscopy at 6 °C. - 1H NMR (500 MHz, C6D6, 6 °C): δ 6.90 (t,3JHH = 7.7 Hz, 2H, Ti-Bz m-H), 6.73 (t, 3JHH = 7.3 Hz, 1H, Ti-Bz p-H), 6.51 (d, 3JHH = 7.7Hz, 1H, B-Bz o-H), 6.33 (d, 3JHH = 7.7 Hz, 1H, B-Bz o-H’), 6.23 (t, 3JHH = 7.3 Hz, 1H, B-Bz m-H), 6.06 (t, 3JHH = 7.1 Hz, 1H, B-Bz m-H’), 5.95 (d, 3JHH = 7.3 Hz, 2H, Ti-Bz o-H),5.89 (br, 1H, Cp), 5.86 (br, 2H, B-Bz p-H and Cp), 5.13 (d, 3JHH = 2.2 Hz, 1H, Cp), 4.83 (m,1H, Cp), 3.28 (br, 1H, B-CH2), 2.93 (br, 1H, B-CH2), 2.83 (d, 2JHH = 9.9 Hz, 1H, Ti-CH2),2.08 (t, 2JHD = 2.2 Hz, 2H, toluene-α-d1) 1.15 (s, 3H, CMe2), 0.93 (d, 2JHH = 9.9 Hz, 1H, Ti-CH2), 0.76 (s, 3H, CMe2) - 13C NMR (125.7 MHz, C6D6, 6 °C): δ 200.0 (Ph o-C ipso),171.0, 160.6, 157.8, 150.4 (Cp, Ph, Ti-Bz and B-Bz C ipso), 148.5 (d, 1JCF = 235 Hz, o-CF),138.9 (d, 1JCF = 250 Hz, p-CF), 137.4 (d, 1JCF = 239 Hz, m-CF), 133.9 (B-Bz m-CH), 131.2(B-Bz o-CH), 130.8 (B-Bz m-CH’), 128.3 (Ti-Bz m-CH), 127.9 (Ti-Bz p-CH, overlap withsolvent), 126.5 (Ti-Bz o-CH), 124.7, 124.1 (B-Bz o-CH’, B-Bz p-CH), 124.5, 124.1, 115.9,111.4 (Cp CH), 94.2 (Ti-CH2), 43.6 (CMe2 C ipso), 35.6 (br, B-CH2), 29.6, 28.9 (CMe2),21.2 (t, 1JCD = 19 Hz, toluene-α-d1)

3.10 References and notes

(1) (a) Quyuom, R., Wang, Q., Tudoret, M.-J., Baird, M.C., J. Am. Chem. Soc. 1994, 116, 6435,(b) Pellecchia, C., Pappalardo, D., Oliva, L., Zambelli, A., J. Am. Chem. Soc. 1995, 117,6593, (c) Pellecchia, C., Proto, A., Longo, P., Zambelli, A., Makromol. Chem. RapidCommun. 1992, 13, 265, (d) Pellecchia, C., Longo, P., Grassi, A., Humendola, P., Zambelli,A., Makromol. Chem. Rapid Commun. 1987, 8, 277, (e) Flores, J.C., Ready, T.E., Chien,J.C.W., Rausch, M.D., J. Organomet. Chem. 1998, 562, 11, (f) Minieri, G., Corradini, P.,Zambelli, A., Guerra, G., Cavallo, L., Macromolecules 2001, 34, 2459, (g) Kucht, A., Kucht,H., Barry, S., Chien, J.C.W., Rausch, M.D., Organometallics 1993, 12, 3075, (h) Ready,T.E., Day, R.O., Chien, J.C.W., Rausch, M.D., Macromolecules 1993, 26, 5822, (i) Foster,P., Chien, J.C.W., Rausch, M.D., Organometallics 1996, 15, 2404, (j) Ready, T.E., Chien,J.C.W., Rausch, M.D., J. Organomet. Chem. 1999, 583, 11

(2) Sassmannshausen, J., Bochmann, M., Rosch, J., Lilge, D., J. Organomet. Chem. 1997, 548,23

(3) (a) Resconi, L., Jones, R.L., Rheingold, A.L., Yap, G.P.A., Organometallics 1996, 15, 998,(b) Xie, M., Wu, Q., Lin, S., Macromol. Rapid Commun. 1999, 20, 167

(4) Pellecchia, C., Pappalardo, D., Gruter, G.J., Macromolecules 1999, 32, 4491(5) (a) Ready, T.E., Gurge, R., Chien, J.C.W., Rausch, M.D., Organometallics 1998, 17, 5236,

(b) Ewart, S.W., Sarsfield, M.J, Jeremic, D., Tremblay, T.L., Williams, E.F., Baird, M.C.,Organometallics 1998, 17, 1502, (c) Grassi, A., Saccheo, S., Zambelli, A., Laschi, F.,Macromolecules 1998, 31, 5588, (d) Grassi, A., Zambelli, A., Laschi, F., Organometallics1996, 15, 480, (e) Williams, E.F., Murray, M.C., Baird, M.C., Macromolecules 2000, 33,261, (f) Huang, Y.H., Wang, W.-J., Zhu, S., Rempel, G.L., J. Polym. Sci. A Polym. Chem.1999, 37, 3385

(6) Pellecchia and coworkers propose the in situ trimerization of ethene to 1-hexene by asecondary Ti(II) species and subsequent copolymerization of the 1-hexene formed.

(7) Branched polyethene structures have been reported for late transition metal catalysts, see: (a)Johnson, L.K., Killian, C.M., Brookhart, M., J. Am. Chem. Soc. 1995, 117, 6414, (b) Svejda,S.A., Johnson, L.K., Brookhart, M., J. Am. Chem. Soc. 1999, 121, 10634, (c) Shultz, L.H.,Brookhart, M., Organometallics 2001, 20, 3975


87

(8) (a) Qichen, H., Yanlong, Q., Guisheng, L., Youqi, T., Transition Met. Chem. 1990, 15, 483,(b) Flores, J.C., Chien, J.C.W., Rausch, M.D., Organometallics 1994, 13, 4140, (c) Flores,J.C., Chien, J.C.W., Rausch, M.D., Macromolecules 1996, 29, 8030, (d) Herrmann, W.A.,Morawietz, M.J.A., Priermeier, T.S., Mashima, K., J. Organomet. Chem. 1995, 486, 291, (e)Okuda, J., Du Plooy, K.E., Toscano, P.J., J. Organomet. Chem. 1995, 495, 195, (f) Van derZeijden, A.A.H., J. Organomet. Chem. 1996, 518, 147, (g) Blais, M.S., Chien, J.C.W.,Rausch, M.D., Organometallics 1998, 17, 3775, (h) Eshuis, J.J.W., Dissertation, Universityof Groningen, 1991

(9) (a) Sassmannshausen, J., Powell, A.K., Anson, C.E., Wocadlo, S., Bochmann, M., J.Organomet. Chem. 1999, 592, 84, (b) Sassmannshausen, J., Organometallics 2000, 19, 482

(10) (a) Schwecke, C., Kaminsky, W., J. Polym. Sci. A Polym. Chem. 2001, 39, 2805, (b) Longo,P., Amendola, A.G., Fortunato, E., Boccia, A.C., Zambelli, A., Macromol. Rapid Commun.2001, 22, 339

(11) (a) Gillis, D.J., Tudoret, M.-J., Baird, M.C., J. Am. Chem. Soc. 1993, 115, 2543, (b) Gillis,D.J., Quyoum, R., Tudoret, M.-J., Wang, Q., Jeremic, D., Roszak, A.W., Baird, M.C.,Organometallics 1996, 15, 3600, (c) Wang, Q., Gillis, D.J., Quyoum, R., Jeremic, D.,Tudoret, M.-J., Baird, M.C., J. Organomet. Chem. 1997, 527, 7

(12) Lancaster, S.J., Robinson, O.B., Bochmann, M., Coles, S.J., Hursthouse, M.B.,Organometallics 1995, 14, 2456

(13) Pellecchia, C., Immirzi, A., Pappalardo, D., Peluso, A., Organometallics 1994, 13, 3773(14) Amor, J.I., Cuenca, T., Galakhov, M., Royo, P., J. Organomet. Chem. 1995, 497, 127(15) (a) Pellecchia, C., Immirzi, A., Zambelli, A., J. Organomet. Chem. 1994, 479, C9, (b)

Pellecchia, C., Grassi, A., Immirzi, A., J. Am. Chem. Soc. 1993, 115, 1160, (c) Pellecchia, C.,Immirzi, A., Grassi, A., Zambelli, A., Organometallics 1993, 12, 4473

(16) Sinnema, P.-J., Dissertation, University of Groningen, 1999(17) Flores, J.C., Wood, J.S., Chien, J.C.W., Rausch, M.D., Organometallics 1996, 15, 4944(18) (a) Zambelli, A., Pellecchia, C., Oliva, L., Longo, P., Grassi, A., Makromol. Chem. 1991,

192, 223, (b) Longo, P., Proto, A., Zambelli, A., Macromol. Chem. Phys. 1995, 196, 3015(19) Köpf, H., Klouras, N., Z. Naturforsch. Teil B 1983, 38, 321(20) Horton, A.D., De With, J., Van der Linden, A.J., Van de Weg, H., Organometallics 1996, 15,

2672(21) (a) Biagini, P., Lugli, G., Garbassi, F., Andreussi, P., EP 667 357 (1995) to Enichem, (b)

Qian, B., Ward, D.L., Smith III, M.R., Organometallics 1998, 17, 3070(22) Sarsfield, M.J., Ewart, S.W., Tremblay, T.L., Roszak, A.W., Baird, M.C., J. Chem. Soc.

Dalton Trans. 1997, 3097(23) For other recent examples of B/M-alkyl scrambling, see: (a) Thorn, M.G., Etheridge, Z.C.,

Fanwick, P.E., Rothwell, I.P., Organometallics 1998, 17, 3636, (b) Pindado, G.J., Thornton-Pett, M., Hursthouse, M.B., Coles, S.J., Bochmann, M., J. Chem. Soc. Dalton Trans. 1999,1663

(24) Jungst, R., Sekutowski, D., Davis, J., Luly, M., Stucky, G., Inorg. Chem. 1977, 16, 1645(25) Bochmann, M., Sarsfield, M.J., Organometallics 1998, 17, 5908(26) Horton, A.D., De With, J., Chem. Commun. 1996, 1375(27) (a) Latesky, S.L., McMullen, A.K., Niccolai, G.P., Rothwell, I.P., Huffman, J.C.,

Organometallics 1985, 4, 902, (b) Jordan, R.F., LaPointe, R.E., Bajgur, C.S., Echols, S.F.,Willett, R., J. Am. Chem. Soc. 1987, 109, 4111, (c) Bochmann, M., Lancaster, S.J.,Hursthouse, M.B., Abdul Malik, K.M., Organometallics 1994, 13, 2235, (d) Bochmann, M.,Lancaster, S.J., Organometallics 1993, 12, 633, (e) Jordan, R.F., LaPointe, R.E., Baenzinger,N., Hinch, G.D., Organometallics 1990, 9, 1539

Chapter 3▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬

88

(28) (a) Ciruelo, G., Cuenca, T., Gómez, R., Gómez-Sal, P., Martín, A., Rodríguez, G., Royo, P.,J. Organomet. Chem. 1997, 547, 287, (b) Shao, P., Gendron, R.A.L., Berg, D.J., Bushnell,G.W., Organometallics 2000, 19, 509, (c) Horton, A.D., De With, J., Organometallics 1997,16, 5424, (d) Thorn, M.G., Etheridge, Z.C., Fanwick, P.E., Rothwell, I.P., Organometallics1998, 17, 3636, (e) Cloke, F.G.N., Hitchcock, P.B., Love, J.B., J. Chem. Soc. Dalton Trans.1995, 25

(29) (a) Erker, G., Korek, U., Petrenz, R., Rheingold, A.L., J. Organomet. Chem. 1991, 421, 215,(b) Lee, H., Bonanno, J.B., Hascall, T., Cordaro, J., Hahn, J.M., Parkin, G., J. Chem. Soc.Dalton Trans. 1999, 1365

(30) (a) Sinnema, P.-J., Van der Veen, L., Spek, A.L., Veldman, N., Teuben, J.H.,Organometallics 1997, 16, 4245, (b) Sinnema, P.-J., Hessen, B., Teuben, J.H., Macromol.Rapid Commun. 2000, 21, 562, (c) Sinnema, P.-J., Lielkelema, K., Staal, O.K.B., Hessen, B.,Teuben, J.H., J. Mol. Catal. 1998, 128, 143

(31) Bouwkamp, M., Van Leusen, D., Meetsma, A., Hessen, B., Organometallics 1998, 17, 3645(32) (a) Morse, P.M., Girolami, G.S., J. Am. Chem. Soc. 1989, 111, 4114, (b) Girolami, G.S.,

Nelsen, M.J., Abstracts of Papers, 213th National Meeting of the American ChemicalSociety, San Francisco, April 1997; American Chemical Society: Washington, DC, 1997;INOR 710

(33) Very recently, polarographic studies showed that mixtures of CpTiCl2(OAr)/MAO in toluenesolvent contain considerable amounts of Ti(III) and Ti(II): Skupínski, W., Nicínski, K.,Maksimowski, P., Wasek, M., J. Mol. Catal. A Chem. 2002, 178, 73

(34) Massey, A.G., Park, A.J., J. Organomet. Chem. 1964, 2, 245. Also see: (a) Massey, A.G.,Park, A.J., J. Organomet. Chem. 1966, 5, 218, (b) Yang, X., Stern, C.L., Marks, T.J., J. Am.Chem. Soc. 1991, 113, 3623, (c) Yang, X., Stern, C.L., Marks, T.J., J. Am. Chem. Soc. 1994,116, 10015

(35) Chien, J.C.W., Tsai, W.-M., Rausch, M.D., J. Am. Chem. Soc. 1991, 113, 8570

university of groningen · 67 generation and stability of cationic...

Documents