Group 4 post-metallocene complexes incorporating tridentate silyl-substituted bis(naphthoxy)pyridine and bis(naphthoxy)thiophene Ligands: Probing systems for "oscillating" olefin polymerization catalysis

5036 Organometallics 2009, 28, 5036–5051

DOI: 10.1021/om900550s

Group 4 Post-metallocene Complexes Incorporating Tridentate Silyl-

Substituted Bis(naphthoxy)pyridine and Bis(naphthoxy)thiophene Ligands:

Probing Systems for “Oscillating” Olefin Polymerization Catalysis

Evgueni Kirillov,*^,†Thierry Roisnel,^†Abbas Razavi,^‡and Jean-Franc-ois Carpentier*^,†

^†Catalysis and Organometallics, UMR 6226 Sciences Chimiques de Rennes, CNRS-University of Rennes 1,

35042 Rennes Cedex, France, and ^‡Total Petrochemicals Research, Zone Industrielle C, 7181 Feluy, Belgium

Received June 25, 2009

New bulky silyl ortho-substituted tridentate 2,6-bis(naphthol)pyridine ({ONO^SiR3}H₂, SiR₃=SiPh₃,

SiMe₂tBu) and 2,5-bis(naphthol)thiophene ({OSO^SiPh3}H₂) pro-ligands were synthesized via a four-

step approach. The solid-state structures of pro-ligands {ONO^SiPh3}H₂(3a) and {OSO^SiPh3}H₂(3b)

were established by X-ray diffraction analysis. Both types of ligands were introduced onto group 4

metal centers (M = Ti, Zr, Hf) using straightforward one-step alkane, amine, or alcohol elimination

protocols. Dibenzyl {ONO^SiPh3}M(CH₂Ph)₂(M = Ti, 4a; Zr, 5a; Hf, 6a) and {ONO^SiMe2tBu}M(CH₂Ph)₂

(M = Ti, 4b; Zr, 5b), diamido {ONO^SiPh3}Hf(NMe₂)₂(7a and 7a (NHMe₂)), and di(isopropoxy)

3

{ONO^SiPh3}Ti(OiPr)₂(8a) complexes were authenticated using NMR spectroscopy and X-ray crystal-

lography methods for some of them. In the solid state, complexes 4a, 4b, and 6a feature rac-like

binding of the ligand, while ligands in complexes 5b and 7a (NHMe₂) are meso-like coordinated.

3

The solution structures of 4b and 5b were investigated by VT NMR spectroscopy, which revealed

that both complexes exist as rac and meso stereoisomers, which interconvert (activation para-

meters: 4b, ΔH^q= 12.9(7) kcal mol^-1and ΔS^q= -3(1) cal mol^-1K^-1; 5b, ΔH^q= 13.4(8)

3

kcal mol^-1and ΔS^q=-7(1) cal mol^-1K^-1). A mechanism for this interconversion process, implying

3

straightforward racemization, was proposed on the basis of DFT computations at the B3LYP (BP86)

level, with computed activation barriers for Ti, Zr, and Hf complexes of 11.4 (10.1), 12.5 (11.2), and

12.2 (11.1) kcal mol^-1, respectively. The catalytic activity of dibenzyl and diamido precursors

in homopolymerization of propylene and ethylene, upon activation with MAO, “dried-MAO”, and

[Ph₃C](B(C₆F₅)₄]/Al(iBu)₃, has been explored as well.

3

Introduction

problem can be tackled by engineering of a single-site

catalyst component that would alternate geometry of its

active site through a reversible interconversion between

several stable stereodictating forms. A conceptual advance

along this line came from Waymouth³and others,⁴who

proposed that the atropisomeric metallocenium cation

[(2-phenylindenyl)₂ZrMe]⁺may exist under two conforma-

tional states, namely rac and meso, in “quasi-controlled”

equilibrium (Scheme 1); this would provide enchainment of

propylene in a given growing polymer chain, under different

The production of thermoplastic elastomeric materials

composed of polyolefins stereoblocks has constituted a

challenge of both fundamental and industrial relevance over

the past decades.¹Successful manufacturing of such valuable

materials requires the development of nonconventional cat-

alytic processes and/or advanced catalyst systems.²If tradi-

tional Ziegler-Natta polymerization catalysis (including its

single-site developments), with its Cossee-Arlman coordi-

native/insertive mechanism, is reasonably considered for this

application, its main drawback lies in the fact that the

geometry of an active site normally remains unchanged

and, as a consequence, the growing polymer chain features

a constant distribution of imposed stereosequences. Such a

(3) (a) Coates, G. W.; Waymouth, R. M. Science 1995, 267, 217.

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*Corresponding authors. Fax: (+33)(0)223-236-939. E-mail: evgueni.

kirillov@univ-rennes1.fr; jean-francois.carpentier@univ-rennes1.fr.

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r

pubs.acs.org/Organometallics

Published on Web 08/14/2009

2009 American Chemical Society

Article

Organometallics, Vol. 28, No. 17, 2009 5037

Scheme 1

stereoenvironments, giving rise to multiblock isotactic-

atactic polypropylene. Yet, as argued by Busico et al.,⁵the

reality of this effective process appeared even more sophis-

ticated, incorporation of propylene proceeding into confor-

mationally “locked” rac-like species with restricted ring

mobility and probable important contribution of the coun-

teranion.

polymerization catalysis.⁷Group 4 metal complexes sup-

ported by tridentate bis(phenolate) ligand systems bridged

by a fused ring L-type donor (pyridine, thiophene, furan)

were shown to adopt either C₂(in Ti complexes) or C₁/C_s(in

Zr complexes) symmetry in the solid state (Scheme 2).^7,8

However, the sole species observed in solution by NMR over

a broad range of temperatures featured an average sym-

metric binding of the tridentate ligands. This result was

accounted for by a fast exchange between species of different

symmetry. As a consequence, propylene polymerization

reactions mediated by these complexes yielded atactic poly-

mers.⁷

Also encouraged by the outstanding catalytic perfor-

mances of phenoxy-based catalysts,^9-12we independently

investigated systems that incorporate sterically demanding

ligands related to those of Bercaw (Scheme 3).¹³The antici-

pated key feature of these ligands is the possibility for firm

stereoselective coordination to the metal center provided by

the non-coplanar orientation of the bridging heterocyclic

In a general fashion, viability of the production of stereo-

block polyolefin chains via “oscillating” polymerization cat-

alysis is ensured by the following main requirements: (i)

activation of a given catalyst precursor must give rise to the

formation of a catalytically active species that undergoes

a reasonably easy dynamic interconversion between geome-

trically stable isomers, e.g., rac (stereospecific) and meso

(nonstereospecific); that is, in terms of thermodynamics, these

species must be ground states with close energies and con-

nected through an attainable transition state. (ii) The “oscilla-

tion”/interconversion rate must be somewhat lower than the

propagation rates. (iii) The latter propagation rates for iso-

mers of the active species must be significantly higher than

rates of termination/transfer processes, to allow building up/

chain growth of blocks. It must be noted that the system may

be sensitive to the polymerization conditions and to the nature

of the activator as well. Indeed, activators possessing an

appropriate hydrodynamic volume and/or coordinating pro-

pensity can interact not necessarily with the metal center, but

rather with the ligand backbone of a catalytic species,^5d,6thus

interfering in the interconversion process.

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5038 Organometallics, Vol. 28, No. 17, 2009

Kirillov et al.

and adjacent naphthoxy groups, due to steric repulsion

between protons at meta and 8-positions¹⁴of these moieties,

respectively.

Scheme 2

In this contribution we report the synthesis of tridentate

pyridine- and thiophene-bridged bis(naphthoxy) pro-ligands

having bulky silyl ortho-substituents and group 4 metal

complexes derived thereof. The solid-state and solution

structures, as well as the interconversion/racemization pro-

cess taking place in those species, have been investigated by

experimental (X-ray crystallography, NMR spectroscopy)

and theoretical (DFT) methods. The performance of those

catalyst precursors in propylene and ethylene polymeriza-

tion reactions is reported.

Scheme 3

Results and Discussion

Synthesis of Pro-ligands. Preparation of the diprotio pro-

ligand {ONO^SiPh3}H₂was initially attempted starting from

commercially available and inexpensive 2-methoxynaphtha-

lene (Scheme 4, protecting group, Pg=Me). The four-step

procedure, followed by Negishi cross-coupling reaction

using extended S-Phos Buchwald’s phosphine ligand,¹⁵

ended up with the formation of Ph₃Si-substituted 2,6-bis-

(methoxynaphthyl)pyridine, 1a-Me, in good yield. However,

further deprotection of the methoxy groups in 1a-Me to

release the desired bis(naphthol) 3a under standard condi-

tions (HBr/CH₃COOH, 140 ꢀC, reflux,¹⁶or melted pyridi-

ne HCl, 220 ꢀC¹⁷) failed, as the compound was found to be

3

18

stable. Effective demethylation using BBr₃

yielded

straightforwardly boron complex {ONO^SiPh3}B(OH) (2) in

reasonable yield. The identity of this compound was estab-

lished by ESI-MS, NMR spectroscopy, and an X-ray dif-

fraction study (vide infra). Surprisingly, borate ester 2

appeared to be remarkably robust toward hydrolysis under

both acidic and basic conditions, and recovery of the desired

bis(naphthol) 3a could not be achieved.

(11) (a) Yeori, A.; Goldberg, I.; Shuster, M.; Kol, M. J. Am. Chem.

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Since the above approach turned out to be problematic, an

alternative pathway was investigated. The preparation of

2,6-bis(naphthol)pyridine pro-ligands 3a and 3b was success-

fully achieved starting from methoxymethyl-protected

β-napthol (Pg = MOM), following a similar three-step

synthetic protocol as depicted in Scheme 3.¹⁹The same

synthetic strategy was applied to the preparation of a con-

gener thiophene-bridged pro-ligand ({OSO^SiPh3}H₂, 3c),

although it resulted in somehow lower isolated yield (see

the Experimental Section). Despite the fact that 2,6-dichlor-

opyridine is quite active toward cross-coupling under the

conditions used, we observed that no reaction took place

when 1,4-dichlorophthalazine was used (Scheme 4). Presum-

ably, the latter observation may stem from a larger steric

hindrance imposed by the adjacent phenyl ring of the

phthalazine fragment.

Pro-ligands 3a-c are stable compounds at room tempera-

ture and are all readily soluble in aromatic hydrocarbons and

other common solvents (CHCl₃, CH₂Cl₂, THF). These

1

compounds were fully characterized in solution by H and

¹³C NMR spectroscopy and by elemental analysis. The

NMR spectra at 25 ꢀC (in CDCl₃or CD₂Cl₂) show a single

(16) Sweetman, B. A.; Mueller-Bunz, H.; Guiry, P. J. Tetrahedron

Lett. 2005, 46, 4643.

(17) Zhang, H.; Kwong, F. Y.; Tian, Y.; Chan, K. S. J. Org. Chem.

(13) Kirillov, E.; Carpentier, J.-F.; Razavi, A. Eur. Pat. Appl. 290

410.3, 2008.

(14) The following atom numbering of the naphtholate unit is used:

1998, 63, 6886.

(18) Luening, U.; Baumstark, R.; Schyja, W. Tetrahedron Lett. 1993,

34, 5063.

(19) (a) Interestingly, the cross-coupling reaction using the S-Phos

ligand did not proceed in more than 50% yield (in the best case, with 2,6-

dibromopyridine), regardless of the reaction time and temperature.

The main byproduct isolated after workup turned out to be

[3-(methoxymethoxy)-2-naphthyl](R-)silane. The yield in the desired

cross-coupling product could be fairly increased when the bulkier

X-Phos phosphine ligand was used. (b) Formation of unidentified

heavy aromatic side products that contain no SiMe₂tBu groups was also

detected when synthesizing 1b-MOM by cross-coupling reaction.

(15) Milne, J. E.; Buchwald, S. L. J. Am. Chem. Soc. 2004, 126, 13028.

Article

Organometallics, Vol. 28, No. 17, 2009 5039

Scheme 4

Scheme 5

set of resonances, consistent with a single, time-averaged

species and low rotation barriers of the substituted naphthol

fragments with respect to the central heterocycle plane.²⁰In

addition, the solid-state structures of 3a and 3b were deter-

mined by X-ray diffraction studies (vide infra).

Synthesis of Group 4 Metal Complexes {OZO^SiR3}MX₂. σ-

Bond metathesis reactions between group 4 metal precursors

MX₄(X = CH₂Ph, NMe₂, OiPr; M = Ti, Zr, and Hf) and

pro-ligands {OZO^SiR3}H₂(Z = N, S) were investigated. For

instance, the reaction between Ti(CH₂Ph)₄or Hf(NMe₂)₄

and 1 equiv of {ONO^SiPh3}H₂in benzene-d₆or toluene-d₈

solution was monitored by ¹H NMR spectroscopy and

found to proceed readily at room temperature within a few

minutes to yield quantitatively the desired dibenzyl or dia-

mido complexes, with concomitant release of 2 equiv of

alkane or amine, respectively. The target compounds were

readily resynthesized on a preparative scale using this pro-

cedure (Scheme 5). Freshly prepared hafnium amido com-

{ONO^SiPh3}Hf(CH₂Ph)₂(6a), and {ONO^SiPh3}Hf(NMe₂)₂

(7a and 7a (NHMe₂)): bright yellow; {ONO^SiPh3}Ti(OiPr)₂

3

plex 7a (NHMe₂) appeared to be rather unstable, as it

3

(8a): pale yellow). These compounds are moderately (SiPh₃-

substitued) to readily (SiMe₂tBu-substituted) soluble in aro-

matic hydrocarbons (benzene, toluene) and in methylene

chloride as well. Dibenzyl complexes 4a,b,c, 5a, 6a, and 8a

were found to be thermally robust and do not undergo

decomposition in solution (benzene, toluene) up to 100 ꢀC

readily loses the coordinated NHMe₂molecule upon stan-

dard workup (recrystallization, drying under vacuum), to

afford base-free complex 7a. Alternatively, the latter com-

pound 7a can be prepared in a more straightforward manner,

by performing the amine elimination reaction in diethyl

ether. Note, however, that similar alkane elimination reac-

tions between pro-ligand 3a and M(CH₂Ph)₄(M=Zr and

Hf) and between 3c and Ti(CH₂Ph)₄appeared to be less

facile when conducted in diethyl ether (in contrast to those

performed in toluene), giving rise to unidentified byproducts,

which were only difficultly removed by recrystallization. The

preparative-scale reaction of 3a and Ti(OiPr)₄in benzene

enabled the synthesis of diisopropoxide complex 8a in

good yield.

1

(hours, H NMR monitoring). Also, no significant decay

was observed upon aging toluene solutions of these com-

plexes at room temperature over 3 months. On the other

hand, dibenzyl zirconium complex 5b, which is stable in the

solid state, slowly (τ_1/2≈ 40 h) decomposes in solution

(benzene, toluene) at room temperature, giving mixtures of

yet unidentified products.

Solid-State Structures of Pro-ligands 3a and 3c and Com-

plexes 4a,b, 5b, 6a, and 7a (NHMe₂). Single crystals suitable

3

The isolated complexes are air-sensitive, colored materials

({ONO^SiPh3}Ti(CH₂Ph)₂(4a), {ONO^SiMe2tBu}Ti(CH₂Ph)₂

(4b), and {OSO^SiPh3}Ti(CH₂Ph)₂(4c): brownish-red; {ON-

for X-ray diffraction studies were successfully prepared by

recrystallization for the following compounds: 2 and 3c from

chloroform, 4a from toluene, 3a and 7a (NHMe₂) from

3

O

^SiPh3}Zr(CH₂Ph)₂(5a), {ONO^SiMe2tBu}Zr(CH₂Ph)₂(5b),

benzene, 4b from hexane, 5b from hexane/toluene, and 6a

from benzene/toluene.

(20) The racemization barrier for 1,1⁰-binaphthalene-2,2⁰-diol

The molecule of pro-ligand 3a adopts in the solid state an

approximate (noncrystallographic) C₂symmetry, in which

(“Binol”) was measured to be ΔG^q_{493 K}= 37.7 kcal mol^-1: Meca, L.;

3

Reha, D.; Havlas, Z. J. Org. Chem. 2003, 68, 5677.

5040 Organometallics, Vol. 28, No. 17, 2009

Kirillov et al.

the naphthol groups are twisted from the pyridine plane in

the opposite directions (Figure 1). The resulting rac-confor-

mation features large torsion angles of 44.57ꢀ and 47.79ꢀ

between the planes of the pyridine unit and the naphthol

ꢀ

˚

fragments. The relatively short distance of 4.224 A between

the oxygen atoms in 3a apparently results from intramole-

cular hydrogen bonding²¹between the nitrogen atom N(1)

and the HO(1) and HO(2) groups (N H distances of 1.885

3 3 3

ꢀ

˚

and 1.980 A, respectively). In the C₂-symmetric molecule of

3c (Figure 2), the nearly coplanar naphthol fragments

(torsion angle of 4.49ꢀ) are bent off the thiophene plane

by 68.45ꢀ and 68.13ꢀ. No short intramolecular hydrogen

bonding between the sulfur atom and hydroxy groups is

observed.

Figure 1. Molecular structure of pro-ligand {ONO^SiPh3}H₂(3a)

(all hydrogen atoms, except of hydroxyl groups, are omitted

for clarity; thermal ellipsoids drawn at 50% probability). Se-

The borate ester 2 features in the solid state a monome-

ric structure with a tetrahedral geometry typical of

boron compounds bearing tridentate {ONO}-type ligands

(Figure 3).²²The B(1)-N(1) and B(1)-O(1,2) bond lengths,

as well as the N(1)-B(1)-O angles (105.68(2)ꢀ, 106.65(2)ꢀ,

and 107.33(3)ꢀ) in 2 compare well with those observed in

related boron compounds of bis(phenolate)pyridine ligands

(104.9(2)-109.1(2)ꢀ).²²Both naphthoxy moieties take posi-

tion on the same side of the pyridine unit. An interesting

feature of 2 lies in the intramolecular hydrogen bonding

involving the HO(3) group and one of phenyl rings of the

˚

lected bond distances (A) and angles (deg): H(O(1))-N(1),

1.885; H(O(2))-N(1), 1.980; —Py-Np(1), 44.57; —Py-Np(2),

47.79.

ꢀ

˚

Ph₃Si(2) group (shortest distance of 2.935 A between hydro-

gen and ortho carbon atoms). A similar type of OH

π

3 3 3

interaction was previously observed in [(2,6-tBu₂PhO)-

(Ph)B(OH)]₂dimer.²³

The solid-state structures of base-free complexes

{OZO^SiR3}MX₂4a,b, 5b, and 6a reveal five-coordinate

mononuclear species (Figures 4-7). The metal centers

(Ti, Zr, and Hf, respectively) are in a distorted trigonal-

bipyramidal geometry, similar to that observed recently for

related CR₃(R = Me, Et) ortho-substituted pyridine-bis-

(phenolate) group 4 metal complexes.⁷Complexes of tita-

nium 4a,b and hafnium 6a revealed one common feature in

Figure 2. Molecular structure of pro-ligand {OSO^SiPh3}H₂

(3c 2CHCl₃) (disordered atoms of the thiophene, solvent mo-

lecules, and all hydrogen atoms, except of hydroxyl groups,

are omitted for clarity; thermal ellipsoids drawn at 50%

˚

probability). Selected bond distances (A) and angles (deg):

H(O(1))-S(1), 2.800; H(O(2))-S(1), 3.514; —Thioph-Np(1),

68.45; —Thioph-Np(2), 68.13.

3

the solid state, that is, rac-coordination of the {ONO^SiR3

}

ligand, leading to an approximate (noncrystallographic) C₂

symmetry in these molecules (Figures 4, 5, and 7).^24,25The

twist angles between the naphthoxy and pyridine fragment

planes in 4a,b are, on average, ca. 3-8ꢀ larger than the

(21) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48.

(22) (a) Zhang, H.; Huo, C.; Zhang, J.; Zhang, P.; Tian, W.; Wang, Y.

Chem. Commun. 2006, 281. (b) Zhang, H.; Huo, C.; Ye, K.; Zhang, P.; Tian,

W.; Wang, Y. Inorg. Chem. 2006, 45, 2788.

(23) Galbraith, E.; Fyles, T. M.; Marken, F.; Davidson, M. G.;

James, T. D. Inorg. Chem. 2008, 47, 6236.

corresponding angles in the C₂-symmetric dibenzyltitanium

pyridine-bis(phenolate) complexes described by Bercaw et al.⁷

(Table 1). This slight but noticeable difference apparently

stems from a larger constraint imposed by bulkier SiR₃

groups, as compared to CR₃groups. At the same time,

(24) The molecular structure of complex 4b possesses a crystallo-

graphic C₂axis.

(25) Titanium bis(isopropoxy) complex 8a also displays rac coordi-

however, the distances between the phenolate oxygens (d_OO)

in 4a,b are identical (3.79 A) and only slightly larger than

˚

nation of the {ONO^{SiPh3 2-}ligand in the solid state; however, due to the

}

that observed in {ONO^CMe3}Ti(CH₂Ph)₂(3.70 A). Interest-

7

˚

poor final R value (ca. 20%), the structural parameters are not reported.

(26) η²-Binding of benzyl groups onto zirconium is documented in

ingly, in C₂-symmetric complexes 4a,b and 6a, the two

benzyl groups are clearly η¹-bound to the metal center, as

ꢀ

˚

the literature by short Zr-C_ipsodistances (typically, 2.57-2.65 A) and

acute Zr-C-C_ipsoangles (typically, 82.7-84.9ꢀ): (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) Jordan,

R. F.; LaPointe, R. E.; Baenziger, N.; Hinch, G. D. Organometallics 1990, 9,

1539. (d) Growther, D. J.; Borkowsky, S. L.; Swenson, D.; Meyer, T. Y.;

Jordan, R. F. Organometallics 1993, 12, 2897. (e) Pellecchia, C.; Grassi, A.;

Immirzi, A. J. Am. Chem. Soc. 1993, 115, 1160. (f) Cloke, F. G. N.;

Geldbach, T. J.; Hitchcock, P. B.; Love, J. B. J. Organomet. Chem. 1996,

506, 343. (g) Bochmann, M.; Lancaster, S. J.; Hursthouse, M. B.; Abdul

Malik, K. M. Organometallics 1994, 13, 2235. (h) Gauvin, R. M.; Osborn, J.

A.; Kress, J. Organometallics 2000, 19, 2944. (i) Kirillov, E.; Lavanant, L.;

Thomas, C. M.; Roisnel, T.; Chi, Y.; Carpentier, J.-F. Chem-Eur. J. 2007,

13, 923.

˚

revealed by long M C_ipsocontacts (>2.97 A) and obtuse

3 3 3

M-C-C_ipsoangles (>108ꢀ).^26,27This leads to formally

(27) Due to the large number of aromatic carbons in those complexes,

the ¹³C NMR resonances for the C_ipsoatoms of benzylic groups in 4a,b

and 6a could not be unambiguously assigned and could not therefore be

used to probe the coordination mode of benzyl groups in solution.

Usually, low-field chemical shifts (δ ca. 144-146 ppm) indicate that

benzyl groups are η¹-coordinated onto the metal center, while η²-

coordinated benzyl groups appear at high-field (δ ca. 140-141 ppm);

see ref 26.

Article

Organometallics, Vol. 28, No. 17, 2009 5041

Figure 3. Molecular structure of {ONO^SiPh3}B(OH) (2 2CH-

3

Cl₃) (all solvent molecules and hydrogen atoms, except that of

the hydroxyl group, are omitted for clarity; in the bottom view,

the SiPh₃phenyl rings are also omitted; thermal ellipsoids drawn

Figure 4. Molecular structure of {ONO^SiPh3}Ti(CH₂Ph)₂

(4a 2C₇H₈) (all solvent molecules and hydrogen atoms are

˚

at 50% probability). Selected bond distances (A) and angles

3

(deg): B(1)-O(1), 1.475(3); B(1)-O(2), 1.469(3); B(1)-O(3),

1.414(3); B(1)-N(1), 1.604(3); N(1)-B(1)-O(1), 105.68(2),

N(1)-B(1)-O(2), 106.65(2); N(1)-B(1)-O(3), 107.33(3); O(1)-

B(1)-O(3), 114.74(3).

omitted for clarity; in the bottom view, the SiPh₃phenyl rings

are also omitted; thermal ellipsoids drawn at 50% probability).

˚

Selected bond distances (A) and angles (deg): Ti-O(1), 1.905(1);

Ti-O(2), 1.918(1); Ti-N(1), 2.174(2); Ti-C(1), 2.099(2); Ti-

C(2), 2.094(2); N(1)-Ti-O(1), 82.25(9); C(1)-Ti-C(2),

107.78(9); O(1)-Ti-O(2), 164.62(6).

{ONO^{SiR3 2-}

} ligands in complexes 5b (C_s) and 6a (C₂) [at

14-electron species, counting the phenoxides as four-electron

(σ, π) donors.²⁸

On the other hand, in the five-coordinate base-free com-

plex 5b and six-coordinate octahedral NHMe₂adduct 7a

least in the solid state] is somewhat surprising considering the

close similarity of ionic radii of Zr and Hf;^29,7however, too

few data are available to establish what parameter(s) actually

dictate(s) the coordination mode in this series of complexes.

Actually, the same factors may govern the formation of

3

(NHMe₂), the pyridine-bis(naphthoxy) ligands are coordi-

nated in a C_s-symmetric fashion. In both molecules, the

pyridine planes are deviated from the M-N vector in the

same direction, as observed also for pyridine-bis(phenolate)

complexes of group 4 and 5 metals.⁷The twist angles between

7a (NHMe₂) (Figure 8). The coordination of the pyridine

3

the pyridine unit and naphthoxy planes in 5b and 7a

moiety in this compound is rather weak, as revealed by the

3

relatively long Hf-N(1) distance of 2.480(2) A.³⁰Coordina-

ꢀ

˚

(NHMe₂) are, at least, 5ꢀ more tilted than those in C₂-

symmetric analogues. Also, in striking contrast to C₂-sym-

metric dibenzyl complexes 4a,b and 6a, zirconium complex

5b features noticeable η²binding of both benzyl groups with

the metal center. This is evidenced by short M-C_ipsodis-

tion of an additional molecule of the relatively weak donor

NHMe₂to the hafnium center obviously compensates its elec-

tronic demand. Such coordination is also not strong, as

31

˚

judged from the relatively long Hf-N(2) distance (2.461(2) A).

ꢀ

˚

tances (2.632 and 2.716 A) and relatively acute M-C-C_ipso

angles (89.55ꢀ and 85.59ꢀ).^26,27This situation can result from

two either independent or synergetic effects: (i) following the

hypothesis proposed by Bercaw et al.,⁷the less donating

character of the tilted pyridine moiety (vide supra), as

compared to that of the “in-line” (vs the M-N vector)

pyridine moiety in C₂-symmetric compounds, generates a

more electrophilic metal center in C_s-symmetric compounds

(e.g., 5b); (ii) C_scoordination of the pyridine-bis(phenolate)

or pyridine-bis(naphthoxy) ligands provokes steric unload-

ing of the metal center. The different coordination mode of

This is consistent with the observation that 7a (NHMe₂)

rapidly loses the coordinated NHMe₂molecule under

vacuum to eventually yield 7a (vide supra). Attempts to grow

3

(29) Effective ionic radii for six-coordinate metal centers: Ti⁴⁺, 0.605 A;

˚

Zr⁴⁺, 0.72 A; Hf , 0.71 A. Shannon, R. D. Acta Crystallogr., Sect. A

4+

˚

1976, A32, 751–767.

(30) Hf-N(pyridine) distances are typically in the range 2.292-2.472

ꢀ

˚

A: (a) Boussie, T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe,

A. M.; Leclerc, M. C.; Murphy, V.; Shoemaker, J. A. W.; Turner, H.;

Rosen, R. K.; Stevens, J. C.; Alfano, F.; Busico, V.; Cipullo, R. Angew.

Chem., Int. Ed. 2006, 45, 3278. (b) Domski, G. J.; Edson, J. B.; Keresztes, I.;

Lobkovsky, E. B.; Coates, G. W. Chem. Commun. 2008, 6137.

ꢀ

˚

(31) Hf-NHR₂distances are typically in the range 2.458-2.462 A:

(a) Gao, M.; Tang, Y.; Xie, M.; Qian, C.; Xie, Z. Organometallics 2006,

25, 2578. (b) Roberts, J. L.; Marshall, P. A.; Jones, A. C.; Chalker, P. A.;

Bickley, J. F.; Williams, P. A.; Taylor, S.; Smith, L. M.; Critchlow, G. W.;

Schumacher, M.; Lindner, J. J. Mater. Chem. 2004, 14, 391.

(28) (a) Tsukahara, T.; Swenson, D. C.; Jordan, R. F. Organometal-

lics 1997, 16, 3303. (b) Lavanant, L.; Chou, T.-Y.; Chi, Y.; Lehmann, C. W.;

Toupet, L.; Carpentier, J.-F. Organometallics 2004, 23, 5450.

5042 Organometallics, Vol. 28, No. 17, 2009

Kirillov et al.

Figure 7. Molecular structure of complex {ONO^SiPh3}Hf-

(CH₂Ph)₂(6a) (thermal ellipsoids drawn at 50% probability).

Selected bond distances (A) and angles (deg): Hf-O(1),

2.017(3); Hf-O(2), 2.017(3); Hf-N(1), 2.280(4); Hf-C(1),

Figure 5. Molecular structure of {ONO^SitBuMe2}Ti(CH₂Ph)₂(4b)

(all hydrogen atoms are omitted for clarity; thermal ellipsoids

˚

drawn at 50% probability). Selected bond distances (A) and angles

(deg): Ti-O(1), Ti(1)-O(2), 1.9234(12); Ti-N(1), 2.155(2); Ti-

C(1), Ti-C(2), 2.110(2); N(1)-Ti-O(1), 80.91(4); C(1)-Ti-

C(2), 102.82(17); O(1)-Ti-O(2), 161.82(7).

˚

2.207(5); Hf-C(2), 2.211(5); Hf-C_ipso(1), 2.971(5); Hf-C_ipso

-

(2), 3.068(5); N(1)-Hf-O(1), 79.05(13); C(1)-Hf-C(2),

110.8(3); O(1)-Hf-O(2), 158.00(13).

CD₂Cl₂solutions upon lowering the temperature. Therefore,

detailed low-temperature NMR studies were performed only

for {ONO^SiMe2tBu}Ti(CH₂Ph)₂(4b) and {ONO^SiMe2tBu}-

Zr(CH₂Ph)₂(5b). Upon cooling a toluene solution of 4b,

the signals in the ¹H NMR spectrum decoalesced (T_coal= ca.

10 ꢀC for TiCH₂Ph at 500 MHz) and, finally, split and

1

sharpened at -50 ꢀC. At this temperature, the H NMR

spectrum of 4b contains two sets of signals attributed to two

species found in a 5:1 molar ratio (Figure 9). The major

compound is represented by a singlet at δ 8.23 ppm for the

naphthoxy H⁴hydrogens, two doublets at δ 3.98 and 3.69

ppm (²J_H-H= 8.1 Hz) characteristic of an AB system for

diastereotopic TiCHHPh hydrogens, a singlet resonance at δ

1.26 ppm for the tBu groups, and two singlets at δ 1.16 and

0.70 ppm for nonequivalent SiMeMe groups. Some of the

resonances of the minor compound overlap with those of the

major compound; however, some key resonances were iden-

tified and typically found shifted downfield from those of the

major compound: the resonance for the naphthoxy H⁴

hydrogens is found at δ 8.35 ppm, two singlets of equal

intensity for the Ti(CH₂Ph)₂groups appear at δ 4.43 and

4.02 ppm, while resonances for the tBu and nonequivalent

SiMeMe groups are found at δ 1.34 and δ 1.30 and 0.86 ppm,

respectively. These observations are consistent with 4b ex-

isting as a mixture of two isomers of different symmetry,

namely, C₂or rac-4b (major; as observed in the solid state)

and C_sor meso-4b (minor), which dynamically interconvert

via an equilibrium, fast on the NMR time scale. At -50 ꢀC,

when the interconversion is frozen, the molar ratio between

these species³²allowed calculating the energy difference (0.71

Figure 6. Molecular structure of {ONO^SitBuMe2}Zr(CH₂Ph)₂(5b)

(all hydrogen atoms are omitted for clarity; thermal ellipsoids

˚

drawn at 50% probability). Selected bond distances (A) and

angles (deg): Zr(1)-O(1), 1.999(5), Zr(1)-O(2), 2.018(5); Zr(1)-

N(1), 2.449(6); Zr(1)-C(1), 2.282(6); Zr(1)-C(2), 2.277(6); Zr-

(1)-C_ipso(1), 2.716(6); Zr(1)-C_ipso(2), 2.632(6); N(1)-Zr(1)-

O(1), 80.25(2); C(1)-Zr(1)-C(2), 97.18(2); O(1)-Zr(1)-O(2),

158.45(19).

crystals of the latter compound suitable for X-ray diffraction

study failed so far.

Dynamic Properties of Dibenzyl Complexes in Solution. All

the compounds within the series of dibenzyl complexes of

{ONO^{SiR3 2-}

ligands (i.e., 4a-c, 5a,b, and 6a) feature

}

fluxional dynamics in toluene or dichloromethane solution,

as revealed by VT NMR studies. The room-temperature ¹H

NMR spectra of these compounds display broadened reso-

nances (Figures S4-S6; see the Supporting Information).

Upon raising the temperature to 80 ꢀC (70 ꢀC for 4a and 60 ꢀC

for 4b), the resonances collapse to a set of sharp signals,

affording a pattern consistent with a single average C₂- or C_s-

symmetric structure on the NMR time scale. Key resonances

include (a) one sharp singlet for H⁴hydrogens of the naphthoxy

groups,¹⁴(b) one sharp triplet for H_paraof the pyridine group,

(c) one (still broadened) singlet resonance for the CH₂benzyl

groups, (d) optionally, for 4b and 5b, singlet resonances for

both SiMe₂and tBu groups.

kcal mol^-1) between the ground states using Maxwell-

3

Boltzmann statistics.³³

(32) The fact that the ratio between the two isomers is thermodyna-

mically controlled was confirmed by the following experiment: an NMR

tube with the desired sample was reheated at 90 ꢀC over 3 h, and ¹H

NMR spectroscopy was recorded again at low temperature (-50 ꢀC for

4b,-40 ꢀC for 5b). The same ratio between the two isomers was

observed, whatever was the cooling rate.

(33) The Maxwell-Boltzmann statistical equation was used: N₁/

N₂= (g₁/g₂)e^-ΔE/RT, where N₁/N₂is the molar isomeric ratio, g₁= g₂=

degeneracy. (a) Goodman, J. M.; Kirby, P. D.; Hausted, L. O.

Tetrahedron Lett. 2000, 41, 9879. (b) McQuarrie, D. A.; Simon, J. D.

Molecular Thermodynamics; University Science Books: Sausalito, CA,

1999.

Complexes incorporating o-SiPh₃groups (4a-6a) are

poorly soluble and precipitated out from toluene-d₈or

Article

Organometallics, Vol. 28, No. 17, 2009 5043

Table 1. Selected Bond Distances (A) and Angles (deg) for Complexes 4a,b, 5b, 6a, and 7a (NHMe₂)

˚

3

˚

d_OO(A)

˚

complex

twist angle (deg)

M-C (A)

M-C_ipso(A)

M-C-C_ipso(deg)

{ONO^SiPh3}Ti(CH₂Ph)₂(4a)

38.7

40.8

44.3

50.96

62.68

40.5

45.9

64.4

27.6

28.2

35.3

36.1

3.79

2.094(2)

2.099(2)

2.110(2)

2.282(6)

2.277(6)

2.207(5)

2.211(5)

2.924(2)

2.998(2)

3.120(2)

2.716(6)

2.632(6)

2.971(5)

3.068(5)

108.59(9)

112.70(9)

119.34(7)

89.55(2)

85.59(2)

110.87(15)

105.79(17)

{ONO^SitBuMe2}Ti(CH₂Ph)₂(4b)

{ONO^SitBuMe2}Zr(CH₂Ph)₂(5b)

3.79

3.95

{ONO^SiPh3}Hf(CH₂Ph)₂(6a)

3.96

3.70

3.74

{ONO^SiPh3}Hf(NMe₂)₂(NHMe₂) (7a)

3

{ONO^CMe3}Ti(CH₂Ph)₂(from ref 7)

{ONO^CEt3}Ti(CH₂Ph)₂(from ref 7)

2.1207(17)

2.1222(17)

2.1022(10)

2.1167(10)

2.74

2.73

3.03

2.93

96.92(10)

97.43(10)

114.04(7)

107.67(7)

The kinetics of rac/meso interconversion/racemization for

4b and 5b were probed by line-shape analysis of the benzyl

region of the ¹H NMR spectra (-50 to 60 ꢀC for 4b,

Figure 11; -40 to 80 ꢀC for 5b; Figure S13, see the Support-

ing Information). In each case, the spectra were simulated for

a two-site system with the populations corresponding to the

isomeric ratio found experimentally, i.e., 5:1 for 4b and 10:1

for 5b. The activation parameters for the interconversion/

racemization process were extracted by a standard Eyring

analysis (Figure S14, Supporting Information): 4b, ΔH^q=

12.9(7) kcal mol^-1and ΔS^q= -3(1) cal mol^-1K^-1; 5b,

3

ΔH^q=13.4(8) kcal mol^-1and ΔS^q=-7(1) cal mol^-1K^-1

.

3

The interconversion/racemization thus appeared to be some-

what more facile for 4b, as evaluated from the rate cons-

tant ratios k^4b/k^5bof 7.8 at 313 K and the difference between

the experimentally determined free energies for these com-

Figure 8. Molecular structure of {ONO^SiPh3}Hf(NMe₂)₂

(NHMe₂) (7a (NHMe₂) 4(C₆H₆)) (all solvent molecules and

hydrogen atoms are omitted for clarity; thermal ellipsoids

plexes, ΔG^q₃₁₃(4b) = 13.8(7) kcal mol^-1and ΔG^q₃₁₃(5b) =

3

15.6(8) kcal mol^-1, respectively.

In sharp contrast with the aforementioned pyridine-bis-

3

˚

drawn at 50% probability). Selected bond distances (A) and

(naphthoxy) complexes, compound 4c, bearing thiophene-

based ligand {OSO }

^{SiPh3 2-}, showed no fluxional dynamics

angles (deg): Hf-O(1), 2.040(2); Hf-O(2), 2.068(2); Hf-N(1),

2.480(2); Hf-N(2), 2.461(2); Hf-N(3), 2.054(2); Hf-N(4),

2.043(2); N(1)-Hf-N(4), 173.72(8); N(2)-Hf-N(3), 175.22-

(9); O(1)-Hf-O(2), 148.95(7).

phenomena (i.e., no broadening) in toluene-d₈in the tem-

perature range 0 to 80 ꢀC.³⁴The room-temperature ¹H NMR

spectrum of 4c showed a series of sharp signals consistent

with the presence of only one species. Key resonances include

(a) a singlet for naphthoxy H⁴hydrogens at δ 8.37 ppm, (b) a

singlet for the thiophene hydrogens at δ 6.45 ppm, and (c)

two singlets for the nonequivalent Ti(CH₂Ph)₂groups at δ

2.51 and 2.15 ppm. In the ¹³C NMR spectrum (25 ꢀC, 125

MHz), benzylic carbons appear as two resonances at δ 94.7

and 93.7 ppm. These data indicate that 4c features an average

C_ssymmetry in toluene.³⁵

Theoretical Investigation on the Interconversion Mechan-

ism. To get a better insight in the mechanism of interconver-

sion that operates in these neutral group 4 metal pyridine-

bis(naphthoxy) systems, DFT calculations were carried out at

both B3LYP and BP86 levels (see the Experimental Section,

Computational Details). In order to evaluate the “net” impact

of the coordination mode of the pyridine-bis(naphthoxy)

ligand backbone on the thermodynamic distribution of iso-

mers and nature of the transition state, a few simplifications

were imposed on the model system: the bulky SiR₃groups and

benzyl groups at the metal center were replaced by hydrogen

and methyl groups, respectively. The main relevant computed

data are summarized in Table 2.

Similar low-temperature NMR investigations were per-

formed for 5b. The decoalescence of the ZrCH₂Ph benzylic

signals was observed at higher temperature (T_coal= ca. 40 ꢀC

at 500 MHz), as compared to that determined for its Ti

analogue 4b, and the exchange was entirely frozen at -40 ꢀC

(Figure 10). Similarly to 4b, the low-temperature (-40 ꢀC)

¹H NMR spectrum of 5b displays two sets of resonances that

are consistent with coexistence of two isomers in a 10:1 ratio.

The major isomer of 5b features a C_s-symmetric structure in

solution, in agreement with the solid-state structure

(Figure 6). The most characteristic NMR feature, diagnostic

of the meso-like coordination of the ligand, is the pattern of

two singlets of equal intensity at δ 3.76 and 3.39 ppm for two

nonequivalent Zr(CH₂Ph)₂groups. This assignment was

confirmed in the ¹³C NMR spectrum (-40 ꢀC, 125 MHz),

where the ZrCH₂Ph benzylic carbons appear as two reso-

nances at δ 64.7 and 63.9 ppm.²⁷The minor isomer of 5b is

evidently C₂-symmetric and, accordingly, shows the same pat-

tern of ¹H NMR resonances as established for rac-4b, in

particular a diagnostic AB system for the ZrCHHPh groups

with two doublets (²J_H-H= 10.1 Hz) at δ 2.68 and 2.49 ppm.

Also, the ¹³C NMR spectrum of rac-5b at -40 ꢀC contains only

one resonance for the benzyl groups at δ 69.4 ppm (as estab-

lished from 2D ¹H-¹³C HMBC and HMQC experiments). An

(34) Below 0 ꢀC, significant precipitation is observed due to the poor

solubility of this complex.

(35) If any putative C₁stereoisomer would be considered, this would

indicate very low interconversion barrier.

energy preference of 1.01 kcal mol^-1for meso-5b over rac-5b

3

was calculated on the basis of NMR data at -40 ꢀC.³³

5044 Organometallics, Vol. 28, No. 17, 2009

Kirillov et al.

Figure 9. ¹H NMR (500 MHz, toluene-d₈, 223 K) spectrum of {ONO^SitBuMe2}Ti(CH₂Ph)₂(4b); 9 = rac-4b, 2 = meso-4b (* stands for

residual solvent resonances).

Figure 10. ¹H NMR (500 MHz, toluene-d₈, 233 K) spectrum of {ONO^SitBuMe2}Zr(CH₂Ph)₂(5b); 9 = rac-5b, 2 = meso-5b (* stands

for residual solvent resonances).

First, the structures of the two stationary points (i.e., C₂

and C_sisomers) for each of the Ti, Z,r and Hf {ONO^H}-

MMe₂complexes were optimized to assess the degree of

agreement between the experimental and calculated geome-

trical parameters on both levels of theory. Regardless the

nature (or ionic radius) of the metal center or DFT functional

used, the meso-like conformation was found to be system-

atically favored over the rac-like conformation. This is in

agreement only for Zr complex 5b, as solid-state and solution

structures of 4a,b, 6a, and 8a²⁵indicate that the rac conforma-

tion is more stable. However, it must be noted that the energy

differences between the computed meso and rac conforma-

In every case, the transition state connecting directly the two

minima of the C₂and C_sisomers was located. The nature of the

TS was probed by a full vibrational analysis, which resulted in a

single imaginary frequency. The transition-state geometries

found for the three metal systems (Ti, Zr, and Hf) are very

similar. The general optimized structure (Figure 12) clearly

features an asymmetric coordination of the {ONO} ligand,

which is intermediary between those represented in C₂and C_s

isomers; that is, one naphthoxy moiety becomes substantially

twisted with respect to the bridging pyridine unit (—(pyridine-

˚

naphthoxy)[1] =52.25-55.21ꢀ and d_HH[1]=2.454-2.521 A),

while the second naphthoxy moiety approaches the plane of the

pyridine unit with its proximal edge (—(pyridine-naphthoxy)[2]

tions were quite low (0.5-1.8 kcal mol^-1at the BP86 level;

3

2.1-3.6 kcal mol^-1at the B3LYP level), which remain within

= 35.34-40.37ꢀ and d_HH[2] = 1.563-1.591 A).

˚

3

the uncertainty of these DFT calculations.³⁶Apart from the

two ground states (C₂and C_sisomers), no other stable

stationary points (species featuring geometries other than

those of the C₂and C_sisomers) or intermediates (for example,

species with unbound pyridine group) were located.³⁷

The activation barriers calculated for this process (Ti,

11.4(10.1) kcal mol^-1; Zr, 12.5(11.2) kcal mol^-1; Hf,

3

12.2(11.1) kcal mol^-1) turned out to be very close to those

determined experimentally for Ti (4b) and Zr (5b) complexes

3

(12.9(7) and 13.4(8) kcal mol^-1, respectively).

3

Studies on the Polymerization Activity. The catalytic po-

tential of the prepared compounds was preliminarily inves-

tigated in the polymerization of propylene using different

conditions (Table 3). The results obtained appeared to

be somewhat disappointing and not easy to rationalize.

Surprisingly enough, no activity was observed with all

(36) It must be emphasized that a simplified model was used for

calculations, with the assumption that the contribution of benzyl groups

at the metal and SiR₃groups at the ortho positions of the naphthoxy

moieties to the final geometry of the ligand framework is insignificant.

(37) Attempts to optimize each of these geometries as starting points

led to the ground states of either C₂or C_sisomers.

Article

Organometallics, Vol. 28, No. 17, 2009 5045

Table 2. Main Computed Data for C₂/C_sInterconversion Process in {ONO}MMe₂Complexes^a

Ti

Zr

Hf

C₂

C_s

TS

11.41

(10.06)

C₂

C_s

TS

12.48

(11.16)

C₂

C_s

TS

12.19

(11.08)

relative energy 2.13

(kcal mol^-1

0

3.53

0

3.56

0

)

3

(0.48)

(0)

(5.84)

(0)

(1.76)

(0)

M-O

1.878, 1.878 1.827, 1.827 1.831, 1.850 2.034, 2.035 1.985, 1.985 1.982, 1.999 2.001, 2.001 1.955, 1.955 1.952, 1.967

(1.889, 1.889) (1.844, 1.844) (1.845, 1.865) (2.044, 2.044) (1.995, 1.996) (1.994, 2.012) (2.010, 2.010) (1.964, 1.964) (1.962, 1.978)

[1.905, 1.918]

2.201

(2.178)

[1.999, 2.018]

2.590

(2.516)

[2.016, 2.017]

2.338

(2.312)

M-N(1)

M-C

d_OO

2.512

(2.379)

2.339

(2.269)

2.358

(2.335)

2.491

(2.437)

2.566

(2.496)

2.472

(2.419)

[2.174]

[2.449]

[2.279]

2.063, 2.064 2.062, 2.068 2.061, 2.075 2.227, 2.228 2.230, 2.231 2.229, 2.234 2.203, 2.203 2.203, 2.206 2.203, 2.210

(2.074, 2.074) (2.074, 2.084) (2.072, 2.090) (2.227, 2.227) (2.231, 2.235) (2.229, 2.238) (2.201, 2.201) (2.203, 2.207) (2.201, 2.211)

[2.100, 2.094]

3.711

(3.739)

[2.277, 2.282]

3.845

(3.892)

[2.207, 2.211]

3.910

(3.939)

3.566

(3.634)

3.605

(3.650)

3.969

(3.997)

3.838

(3.884)

3.788

(3.832)

3.374

(3.819)

[3.788]

[3.947]

[ 3.959]

d_HH

2.241, 2.242 2.353, 2.355 1.574, 2.454 2.293, 2.293 2.405, 2.406 1.587, 2.517 2.281, 2.281 2.386, 2.387 1.591, 2.488

(2.259, 2.259) (2.333, 2.334) (1.563, 2.455) (2.309, 2.310) (2.391, 2.391) (1.584, 2.521) (2.297, 2.297) (2.374, 2.377) (1.581, 2.492)

[2.225, 2.272]

[2.370, 2.579]

75.91

(77.59)

[79.01, 80.25] (74.17, 80.70) [78.98, 79.05]

106.50

(107.88)

[97.18]

151.17

(154.39)

[158.43]

[2.243, 2.279]

77.76

(78.44)

N(1)-M- O(1) 81.09

(81.75)

[82.25]

C(1)-M-C(2) 110.96

(112.19)

[107.78]

O(1)-M- O(2) 162.18

(163.50)

[164.62]

77.81

(80.63)

76.86,

82.39

(78.30, 83.66)

107.16

(109.89)

77.25

(77.89)

72.90,

79.40

76.12

(77.80)

73.41,

79.50

(74.65, 80.74)

105.78

(106.74)

104.22

(107.94)

110.94

(111.60)

108.06

(109.37)

109.19

104.94

(105.55)

(109.56)

[110.32]

155.53

(156.87)

[158.02]

154.85

(160.45)

156.75

(159.50)

154.53

(155.77)

149.11

(151.69)

151.37

(154.69)

148.73

(151.59)

twist angle

38.53, 38.54 47.61, 47.62 35.34, 52.25 40.44, 40.45 49.83, 49.95 38.42, 54.65 39.83, 39.84 48.85, 48.93 37.92, 53.16

(39.16, 39.19) (45.70, 45.71) (36.24, 52.85) (40.99, 40.99) (48.45, 48.47) (40.37, 55.21) (40.47, 40.48) (47.51, 47.69) (39.52, 53.80)

[38.67, 40.79]

[50.96, 49.33]

[40.47, 40.50]

^aThe first values correspond to the B3LYP level, the values in parentheses correspond to the BP86 level; in the square brackets are the average

experimental values for complexes 4a (Ti), 5b (Zr), and 6a (Hf).

dibenzyl complexes when [Ph₃C][B(C₆F₅)₄] was used as the

activator (entries 1, 3, 5, 10).³⁸In the series of benzyl

complexes, only zirconium precursor 5b was found to be

active when activated with MAO (1000 equiv vs Zr). How-

ever, the activity of the 5b/MAO system (320-490 kg

3

mol^-1

h

^-1) was at least 1 order of magnitude inferior to

3

that of related systems based on pyridine-bis(phenoxy)

zirconium dibenzyl complexes.⁷The polymers recovered

were oily products and readily soluble in toluene and hardly

precipitated by addition of methanol. These products were

analyzed by GPC and ¹H and ¹³C NMR spectroscopy. In line

with the observations made by Bercaw et al. on similar

catalytic systems,⁷the polypropylenes obtained with 5b/

MAO featured bimodal distributions, that is, a minor high

(M_n=120 000-140 000 g mol^-1, PDI=1.25-1.37) and a

3

major low (M_n= 720-800 g mol^-1, PDI = 1.24-1.53)

3

molecular weight fraction (Figure 13b) (entries 6-8). The

observation of two relatively narrow distributions

could be explained by the presence of two types of “single-

site” catalysts, possibly resulting from different activation

pathways of the neutral precursor with commercial MAO.⁷

The latter reagent is actually well known to contain signifi-

cant amounts of AlMe₃(TMA). To assess this hypothesis, an

experiment with activation of 5b by a TMA-free, so-called

“dried” MAO (“DMAO”) was attempted (entry 9). In this

case, the catalytic system produced selectively the lower

molecular weight fraction (Figure 13a).

1

Figure 11. Experimental (left) and simulated (right) H NMR

(38) All attempts to isolate the cationic species resulting from neutral

benzyl complexes failed. This hampered us also from investigating

interconversion processes in these species, which are more relevant to

polymerization than their neutral precursors.

spectra (region of benzylic protons) of {ONO^SitBuMe2}-

Ti(CH₂Ph)₂(4b). Best fit first-order rate constants are given

above the spectra.

5046 Organometallics, Vol. 28, No. 17, 2009

Kirillov et al.

Figure 13. GPC traces for propylene oligo/polymers obtained

with 5b: (a) activated with “DMAO” (entry 9, Table 3), (b)

activated with MAO (entry 7, Table 3).

Figure 12. DFT-optimized structure of the transition state for

the C₂/C_sinterconversion process in {ONO}MMe₂complexes.

Table 3. Propylene Polymerization Data^a

entry

cat. (μmol)

cocat. (equiv vs M)

T_polym(ꢀC)

time (min)

m (g)

activity, (kg mol^-1h^-1

)

M_n(g mol^-1

)

M_w/M_n

3

1

2

3

4

5

6

4a (9.0)

4b (9.0)

5a (9.0)

5b (25.0)

Trityl/TIBAL (3:200)

“DMAO” (1000)

Trityl/TIBAL (3:200)

“DMAO” (1000)

Trityl/TIBAL (3:200)

MAO (1000)

50

25

50

25

50

25

30

15

30

15

30

15

0

3.00

0

480

120 100

800

116 300

760

140 800

720

1100

1.3

1.5

1.4

1.5

1.2

1.4

7

8

5b (9.0)

MAO (1000)

25

50

15

1.11

0.71

490

320

9

10

5b (9.0)

“DMAO” (1000)

Trityl/ TIBAL (3:200)

25

50

15

0.93

0

413

0

^aGeneral conditions, unless otherwise stated: toluene (80 mL), P = 5 bar.

The ¹³C{¹H} NMR spectra of the oligo/polypropylenes

obtained with 5b/MAO and 5b/“DMAO” were overall very

similar to those recorded for materials obtained with pyr-

idine-bis(phenolate) systems.⁷As evidenced by the complex

pattern of signals in the CH region at δ 27.0-27.8 ppm, these

materials feature an irregular microstructure (Figure 14).³⁹

Although the overall pattern of resonances is similar when

“DMAO” was used instead of MAO, the intensity ratio of

some signals was affected. For instance, the intensities of the

resonances for isobutyl end-groups at δ 22-24 ppm were

substantially decreased when “DMAO” was used.⁴⁰With

both MAO and “DMAO”, the presence of intense olefinic

resonances was observed in the downfield region of both the

¹H and ¹³C NMR spectra at δ 4.73 and 4.66 (δ 144.9 and

111.5) (CH₂dCH(CH₃)-), 5.48 and 5.40 (δ 139.5 and 120.4)

(CH₃CHdCH-), and 5.81, 5.00, and 4.93 (δ 145.0 and

114.2) (CH₂dCHCH(CH₃)-) ppm.⁴¹These observations

indicate that enchainment of propylene is not regioselective

and proceeds both in 1,2- and 2,1-fashions and that chain

termination proceeds via β-H and β-Me elimination.

The performance of Ti (4a,b,c), Zr (5a), and Hf (7a)

precursors was also briefly assessed in ethylene polymeriza-

tion (Table 4). When activated with MAO (1000 equiv vs

metal), M{ONO^SiR3}-type complexes 4a and 7a showed a

low catalytic activity (entries 1 and 7, respectively) and

yielded polyethylenes with bimodal distributions, as ob-

served with 5b/MAO in propylene polymerization (vide

supra). When activated with [Ph₃C](B(C₆F₅)₄]/Al(iBu)₃

(3:200),⁴²dibenzyl complexes 4a,b and 5a provided higher

activities (2090-3010 kg mol^-1h^-1at 50 ꢀC, 5 atm), which

3

are comparable to those of Chan’s pyridine-bis(phenolate)

systems.⁸The isolated polymers all featured monomodal

distributions, even when [Ph₃C](B(C₆F₅)₄]/Al(iBu)₃was

used, which calls for the absence of any chain transfer to

Al. The melting temperatures were in the range 134-140 ꢀC,

indicative of the linear microstructure of these polyethylenes.

Surprisingly enough, dibenzyl-titanium complex 4c derived

from the sulfur-based {OSO }

^{SiPh3 2-}ligand was found com-

pletely inactive (entries 4, 5). This observation highlights the

key influence of the bridging heteroatom. We have pre-

viously reported that some Ti-{OSO} complexes based on

thio-bridged dialkoxide ligands are poorly active for ethy-

lene polymerization when activated with MAO, while ana-

logous Zr-{OSO}/MAO systems are quite active but

(39) Schilling, F. C.; Tonelli, A. E. Macromolecules 1980, 13, 270.

(40) This fact is in agreement with one of the hypotheses by Bercaw et

al. (ref 7) that isobutyl groups are formed not only by primary insertion

of a propylene molecule in the [Zr-Me] bond but also by chain transfer

to Al of TMA followed by hydrolysis upon quenching.

(41) (a) Shiono, T.; Kang, K. K.; Hagihara, H.; Ikeda, T. Macro-

molecules 1997, 30, 5997. (b) Kawahara, N.; Kojoh, S.; Toda, Y.; Mizuno, A.;

Kashiwa, N. Polymer 2004, 45, 355. (c) Lu, C.; Zhang, Y.; Mu, Y. J. Mol.

Catal. A: Chem. 2006, 258, 146.

(42) (a) Song, F.; Cannon, R. D; Lancaster, S. J.; Bochmann, M.

J. Mol. Catal. A: Chem. 2004, 218, 21. (b) Bochmann, M.; Srasrfield, M. J.

Organometallics 1998, 17, 5908.

(43) Lavanant, L.; Silvestru, A.; Faucheux, A.; Toupet, L.; Jordan,

R. F.; Carpentier, J.-F. Organometallics 2005, 24, 5604.

Article

Organometallics, Vol. 28, No. 17, 2009 5047

Figure 14. Selected region of ¹³C NMR spectra of propylene oligo/polymers obtained with 5b: (up) activated with “DMAO” (entry 9,

Table 3), (bottom) activated with MAO (entry 7, Table 3).

Table 4. Ethylene Polymerization Data^a

entry cat. (μmol)

cocat. (equiv vs M)

MAO (1000)

T_polym(ꢀC) time (min) m (g) activity, (kg mol^-1h^-1

)

M_n(g mol^-1

)

M_w/M_nT_m(ꢀC)

3

1

4a (4.5)

50

30

0.55

244

7 200

752 000

15 700

12 230

2.8

2.0

4.2

2.5

136

2

3

4

5

6

7

8

4a (9.0)

4b (9.0)

4c (9.0)

5a (9.0)

7a (9.0)

Trityl/TIBAL (3:200) 50

MAO (1000)

Trityl/TIBAL (3:200) 50

10

5

10

5

3.14

1.97

0

2090

2360

0

3010

48

134

132

50

0

Trityl/TIBAL (3:200) 50 (∼60)

2.26

0.11

0

135 500

7 920

4.1

58

140

131

MAO (1000) 50

Trityl/TIBAL (3:200) 50

15

0

^aGeneral conditions, unless otherwise stated: 300 mL glass reactor, toluene (80 mL), P = 5 bar.

deactivate extremely rapidly (within seconds).⁴³The polym-

erization performance and overall behavior of this family of

catalysts was also quite different from those of related

catalysts based on amino-dialkoxide ligands.⁴⁴

nium the ligand coordination is meso-like. Possible inter-

conversion between these two stereoisomeric neutral

compounds has been demonstrated using both experimental

and computational methods.³⁸

Among the different complexes prepared, only zirconium

complex 5b supported by a {ONO^{SiMe2tBu 2-}

} ligand, upon

Conclusions and Perspectives

activation with MAO, was found to oligomerize pro-

pylene. The surprising inactivity of dibenzyl precursors 4a,

b and 5a may stem from significant sterical hindrance

imposed by SiR₃groups. Further modification of these

systems by tuning of ligand platforms to enhance their

catalytic performance is underway and will be reported in

due course.

We have elaborated a simple and effective synthetic strat-

egy toward a new type of silyl-substituted bis(naphthoxy)-

based ligand system incorporating both pyridine and

thiophene donors. A variety of pro-ligands have been synthe-

sized and used in the preparation of discrete mononuclear

group 4 metal complexes. As anticipated, the {ONO^{SiR3 2-}

}

ligands provide two different coordination modes, giving rise

to two stable stereoisomers in neutral compounds, namely,

C₂(rac-like)- and C_s(meso-like)-symmetric forms; on the

Experimental Section

other hand, the {OSO }

^{SiPh3 2-}ligand apparently leads only to

C_s-symmetric compounds. No notable effect of the metal

General Considerations. All manipulations were performed

under a purified argon atmosphere using standard Schlenk

techniques or in a glovebox. Solvents were distilled from Na/

benzophenone (THF, Et₂O) and Na/K alloy (toluene, pentane)

under nitrogen, degassed thoroughly, and stored under nitro-

gen prior to use. Deuterated solvents (benzene-d₆, toluene-d₈,

THF-d₈; >99.5% D, Eurisotop) were vacuum-transferred

from Na/K alloy into storage tubes. Tetrabenzyl M(CH₂Ph)₄

ionic radius on the coordination mode was revealed. In

}

titanium and hafnium neutral complexes, the {ONO^{SiR3 2-}

framework chelates in a rac-like fashion, while with zirco-

(44) Lavanant, L.; Toupet, L.; Lehmann, C. W.; Carpentier, J.-F.

Organometallics 2005, 24, 5620, and references therein.

5048 Organometallics, Vol. 28, No. 17, 2009

Kirillov et al.

(M = Ti, Zr, Hf), Hf(NMe₂)₄precursors, S-Phos (dicyclohexyl-

(2⁰,6⁰-dimethoxy-1,1⁰-biphenyl-2-yl)phosphine), and RuPhos (dicyclo-

hexyl(2⁰,6⁰-diisopropoxy-1,1⁰-biphenyl-2-yl)phosphine) were pre-

pared using reported procedures.¹⁵Other starting materials

were purchased from Acros, Strem, and Aldrich and used as

received. NMR spectra of complexes were recorded on Bruker

AC-200, AC-300, and AM-500 spectrometers in Teflon-valved

NMR tubes at 25 ꢀC unless otherwise indicated. ¹H and ¹³C

chemical shifts are reported in ppm vs SiMe₄and were deter-

mined by reference to the residual solvent peaks. Assignment of

resonances for organometallic complexes was made from 2D

¹H-¹³C HMQC and HMBC NMR experiments. Coupling

constants are given in hertz. Elemental analyses (C, H, N) were

performed using a Flash EA1112 CHNS Thermo Electron

apparatus and are the average of two independent determina-

tions.

over Na₂SO₄. Solvent was removed under vacuum, and the

residue was purified by column chromatography (silica, hep-

tane/CH₂Cl₂, 1:1, R_f= 0.12) to give 2 as a pale yellow micro-

1

crystalline material (0.57 g, 0.63 mmol, 43%). H NMR (500

MHz, CD₂Cl₂, 25 ꢀC): δ (resonance for OH was not observed)

8.29 (d, J = 8.5 Hz, 2H), 8.10 (d, J = 7.9 Hz, 2H), 8.02 (t, J =

7.9 Hz, 1H), 7.78 (s, 2H), 7.60 (d, J = 7.9 Hz, 2H), 7.54 (t, J =

8.0 Hz, 2H), 7.48 (d, J = 7.2 Hz, 12H), 7.32 (t, J = 7.9 Hz, 2H),

7.27 (t, J = 7.2 Hz, 6H), 7.14 (t, J = 7.2 Hz, 12H). ¹³C{¹H}

NMR (125 MHz, CD₂Cl₂, 25 ꢀC): δ 139.3, 136.7, 136.5, 136.3,

134.6, 132.1, 129.7, 129.3, 129.1, 129.1, 128.3, 127.6, 126.7,

123.6, 122.9, 122.4, 111.9. MS-FAB (m/z): 905.3 (M⁺). Anal.

Calcd for C₆₁H₄₄BNO₃Si₂: C, 80.87; H, 4.90. Found: C, 80.7;

H, 4.34.

2-(Methoxymethoxy)naphthalene. To a suspension of NaH

(5.00 g, 208 mmol) in DMF (150 mL), under argon flow, was

added solid 2-hydroxynaphthalene (20.0 g, 138.7 mmol) at 0 ꢀC

by small portions. After stirring for 4 h at room temperature,

methoxymethyl chloride (17.8 g, 221 mmol) was added slowly,

and the reaction mixture was stirred for 10 h. The reaction

mixture was carefully diluted with water (ca. 1 L), and organic

materials were extracted with CH₂Cl₂(3 ꢀ 50mL). The combined

organic extracts were washed with water (2 ꢀ 500 mL) and brine

and dried over MgSO₄. The solution was evaporated todryness at

80 ꢀC to give a colorless oily product (25.1 g, 133.3 mmol), which

was used without further purification. ¹H NMR (200 MHz,

CDCl₃, 25 ꢀC): δ 7.80 (m, 3H), 7.55-7.37 (m, 3H), 7.26 (m,

1H), 5.34 (s, 2H, OCH₂O), 3.57 (s, 3H, OCH₃). Anal. Calcd for

C₁₂H₁₂O₂: C, 76.57; H, 6.43. Found: C, 76.59; H, 6.55.

(3-Methoxy-2-naphthyl)(triphenyl)silane. A solution of sec-

BuLi (15.3 mL of a 1.3 M solution in hexane/cyclohexane,

19.9 mmol) was added dropwise to a stirred solution of

2-methoxynaphthalene (3.00 g, 19.0 mmol) in THF (70 mL) at

-30 ꢀC over 15 min. After stirring overnight at room tempera-

ture, a dark solution was obtained, to which was added a

solution of Ph₃SiCl (5.87 g; 19.9 mmol) and HMPA (3.46 mL,

19.9 mmol) in THF (50 mL). The reaction mixture was refluxed

for 20 h, cooled, and diluted with water (500 mL). The organic

part was extracted with Et₂O (3 ꢀ 50 mL). The combined

organic extracts were dried over MgSO₄and evaporated. The

crude residue was recrystallized from heptane and dried under

vacuum to give (3-methoxy-2-naphthyl)(triphenyl)silane (7.11 g,

1

17.1 mmol, 90%). H NMR (200 MHz, CDCl₃, 25 ꢀC): δ 7.80

[3-(Methoxymethoxy)-2-naphthyl](triphenyl)silane.

A solu-

(m, 2H), 7.67 (m, 7H), 7.55-7.23 (m, 12 H), 3.69 (s, 3H, OCH₃).

Anal. Calcd for C₂₉H₂₄OSi: C, 83.61; H, 5.81. Found: C, 83.5; H,

5.73.

tion of sec-BuLi (19.0 mL of a 1.3 M solution in hexane/

cyclohexane, 24.7 mmol) was added dropwise to a stirred

solution of 2-(methoxymethoxy)naphthalene (4.64 g, 24.7

mmol) in THF (150 mL) at -78 ꢀC over 15 min. After stirring

overnight at room temperature, a dark solution was obtained, to

which was added a solution of Ph₃SiCl (7.27 g, 24.7 mmol) and

HMPA (4.3 mL, 24.7 mmol) in THF (100 mL). The reaction

mixture was refluxed for 40 h, cooled to room temperature, and

diluted with water (1 L). The organic materials were extracted

with Et₂O (3 ꢀ 100 mL), and the combined organic extracts were

dried over MgSO₄and evaporated to dryness. The crude residue

was recrystallized from heptane and dried under vacuum to give

[3-(methoxymethoxy)-2-naphthyl](triphenyl)silane (8.25 g, 18.5

mmol, 75%). ¹H NMR (200 MHz, CDCl₃, 25 ꢀC): δ 7.83-7.75

(m, 2H), 7.72-7.58 (m, 7H), 7.55-7.25 (m, 12 H), 4.96 (s, 2H,

OCH₂O), 3.00 (s, 3H, OCH₃). Anal. Calcd for C₃₀H₂₆O₂Si: C,

80.68; H, 5.87. Found: C, 80.4; H, 5.41.

(4-Bromo-3-methoxy-2-naphthyl)(triphenyl)silane. A 150 mL

Schlenk flask was charged with (3-methoxy-2-naphthyl)-

(triphenyl)silane (4.68 g, 11.23 mmol) and NBS (2.20 g, 12.36

mmol) under argon, followed by addition of DMF (10 mL). The

resultant mixture was stirred overnight at room temperature,

then diluted with water (500 mL) and extracted with CH₂Cl₂

(3ꢀ50 mL). The combined organic extracts were washed with

water (200 mL) and brine and dried over Na₂SO₄. The product

was purified by passing through a short silica column using

heptane/EtOAc (15:1) as eluent, to afford the product as an off-

1

white solid (5.28 g, 10.66; 96%). H NMR (200 MHz, CDCl₃,

25 ꢀC): δ 8.29 (d, J = 8.4 Hz, 1H), 7.80 (s, 1H), 7.66 (m, 8H),

7.52-7.27 (m, 10H), 3.18 (s, 3H, OCH₃). Anal. Calcd for

C₂₉H₂₃BrOSi: C, 70.30; H, 4.68. Found: C, 70.0; H, 4.56.

One-Pot Synthesis of {ONO^SiPh3}B(OH) (2). (i) To a solution

of (4-bromo-3-methoxy-2-naphthyl)(triphenyl)silane (1.44 g,

[3-(Methoxymethoxy)-2-naphthyl](tert-butyldimethyl)silane. A

solution of sec-BuLi (25.3 mL of a1.3 M solution in hexane/

cyclohexane; 32.9 mmol) was added dropwise to a stirred solution

of 2-(methoxymethoxy)naphthalene (6.20 g, 32.9 mmol) in THF

(180 mL) at -78 ꢀC over 15 min. After stirring overnight at room

temperature, a dark solution was obtained, to which was added a

solution of tBuMe₂SiCl (5.00 g, 33.2 mmol) and HMPA (5.7 mL,

32.8 mmol) in THF (50 mL). The reaction mixture was refluxed

for 40 h, cooled at room temperature, and diluted with water

(1 L). The organic materials were extracted with Et₂O(3 ꢀ 100 mL),

and the combined organic extracts were dried over MgSO₄and

evaporated to dryness. The residue was redissolved in heptane

(100 mL), passed through a short pad of silica, and evaporated.

The resultant pale yellow oil was dried under vacuum to give

[3-(methoxymethoxy)-2-naphthyl](tert-butyldimethyl)silane (8.97 g,

2.91 mmol) in THF (20 mL) was added iPrMgCl LiCl (3.7 mL

3

of a 0.82 M solution in THF, 3.06 mmol). The reaction mix-

ture was stirred at 60 ꢀC for 2 h; then volatiles were removed

under vacuum. (ii) Anhydrous ZnCl₂(0.41 g, 3.01 mmol) was

charged in a Schlenk flask, THF (30 mL) was vacuum trans-

ferred, and the resultant solution was stirred for 30 min at room

temperature. (iii) The previous solution was transferred to a

Teflon-valved Schlenk followed by addition of Pd₂(dba)₃(0.053 g,

57.9 μmol), S-Phos (0.095 g, 231 μmol), and 2,6-dibromopyr-

idine (0.34 g, 1.45 mmol). The reaction mixture was stirred for

30 h at 105 ꢀC, cooled to room temperature, diluted with water

(200 mL), and extracted with CH₂Cl₂(3ꢀ20 mL). The combined

organic extracts were dried over MgSO₄and evaporated to

dryness. The crude material was composed of ca. 80% of desired

product, 2,6-bis[2-methoxy-3-(triphenylsilyl)-1-naphthyl]pyri-

dine, as judged by ¹H NMR spectroscopy. (iv) The crude

material was redissolved in dry CH₂Cl₂(40 mL) under argon

and treated with BBr₃(4.36 mL of a 1.0 M solution in CH₂Cl₂,

4.36 mmol) at -30 ꢀC. The resultant solution was stirred over-

night at room temperature, cooled to 0 ꢀC, and then quenched

with water (50 mL). The organic layer was separated and dried

1

29.7 mmol, 90%). H NMR (200 MHz, CDCl₃, 25 ꢀC): δ 7.91

(s, 1H), 7.78 (m, 2H), 7.41 (m, 3H), 5.31 (s, 2H, OCH₂O), 3.54 (s,

3H, OCH₃), 0.97 (s, 9H, tBu), 0.41 (s, 6H, Me). Anal. Calcd for

C₁₈H₂₆O₂Si: C, 71.47; H, 8.66. Found: C, 71.1; H, 8.76.

One-Pot Synthesis of {ONO^SiPh3}H₂(3a). (i) To a solution of

[3-(methoxymethoxy)-2-naphthyl](triphenyl)silane (2.30 g, 5.15

mmol) in THF (40 mL) was added TMEDA (0.78 mL, 5.16

mmol) followed by addition of sec-BuLi (4.2 mL of a 1.3 M

Article

Organometallics, Vol. 28, No. 17, 2009 5049

solution in hexane/cyclohexane, 5.46 mmol) at -78 ꢀC. The

reaction mixture was stirred at room temperature overnight;

afterward volatiles were evaporated and the residue was dried

for 1 h under vacuum. (ii) Anhydrous ZnCl₂(0.70 g, 5.15 mmol)

was charged in a Schlenk flask, THF (30 mL) was vacuum

transferred in, and the resultant solution was stirred for 30 min

at room temperature. (iii) The previous solution was transferred

to a Teflon-valved Schlenk followed by addition of Pd₂(dba)₃

(0.094 g, 103 μmol), S-Phos (0.168 g, 409 μmol), and 2,6-

dibromopyridine (0.61 g, 2.57 mmol). The reaction mixture

was stirred for 40 h at 105 ꢀC, cooled to room temperature,

diluted with water (200 mL), and extracted with CH₂Cl₂(3 ꢀ

20 mL). The combined organic extracts were dried over MgSO₄

and evaporated to dryness. The crude material contained

ca. 50% of desired product, 2,6-bis[2-(methoxymethoxy)-

enylsilyl)-1-naphthyl]thien-2-yl}-2-naphthyl)(triphenyl)silane

after Pd-catalyzed coupling reached ca. 30% over 100 h. After the

deprotection step and further workup, crude 3c was recovered as a

deep blue powder, which was purified by passing through a short

silica pad (heptane/CH₂Cl₂, 1:1) to afford 3c as a colorless solid

1

(1.01 g, 1.14 mmol, 98%). H NMR (500 MHz, CDCl₃, 25 ꢀC):

δ 7.89 (s, 2H), 7.76 (d, J = 8.6 Hz, 2H), 7.73-7.69 (m, 14H), 7.54-

7.46 (m, 8H), 7.46-7.41 (m, 12H), 7.38-7.33 (m, 4H), 5.85 (s, 2H,

OH). ¹³C{¹H} NMR (125 MHz, CDCl₃, 25 ꢀC): δ 155.7 (C-O),

141.9, 137.6, 136.4, 135.4, 134.3, 130.9, 129.6, 128.7, 128.6, 128.0,

127.9, 124.2, 123.6, 122.9, 112.1. Anal. Calcd for C₆₀H₄₄O₂SSi₂:

C, 81.41; H, 5.01. Found: C, 80.9; H, 4.87.

{ONO^SiPh3}Ti(CH₂Ph)₂(4a). A Schlenk flask was charged

with {ONO^SiPh3}H₂(0.20 g, 0.23 mmol) and Ti(CH₂Ph)₄(0.094

g, 0.23 mmol), and toluene (5 mL) was vacuum transferred in.

The reaction mixture was stirred overnight at room tempera-

ture, filtered, evaporated, and dried in vacuo to give 4a as a

brownish-red microcrystalline material (0.24 g, 0.22 mmol,

1

3-(triphenylsilyl)-1-naphthyl]pyridine, as judged by H NMR

spectroscopy. This crude material was purified by column

chromatography (silica, heptane/EtOAc (15:1), R_f= 0.12).

(iv) The resultant solid was dissolved in a mixture of concen-

trated HCl (20 mL), CHCl₃(30 mL), and EtOH (40 mL), and the

solution was refluxed for 24 h. The reaction mixture was cooled

to 0 ꢀC and then carefully diluted with a concentrated solution of

NaOH (50 mL). Then, a concentrated solution of NH₄Cl was

added to adjust the pH value to 7-8. The product was extracted

with CH₂Cl₂(3 ꢀ 20 mL), and the combined organic extracts

were dried over MgSO₄and evaporated to afford 3a as an off-

white solid (1.11 g, 1.26 mmol, 98%). ¹H NMR (500 MHz,

CD₂Cl₂, 25 ꢀC): δ 9.88 (br s, 2H, OH), 8.12 (t, J = 7.9 Hz, 1H),

8.06 (m, 2H), 7.83 (m, 4H), 7.71-7.63 (m, 14H), 7.52-7.43

(m, 9H), 7.38-7.33 (m, 13H). ¹³C{¹H} NMR (125 MHz,

CD₂Cl₂, 25 ꢀC): δ 157.5 (C-O), 155.8, 142.6, 138.3, 136.3,

134.4, 133.3, 129.5, 129.0, 128.9, 127.9, 127.8, 125.4, 124.1,

123.7, 123.4, 115.7. MS-FAB (m/z): 880.3 (M⁺). Anal. Calcd

for C₆₁H₄₄NO₂Si₂: C, 83.24; H, 5.15. Found: C, 82.8; H, 5.01.

One-Pot Synthesis of {ONO^SiMe2tBu}H₂(3b). Using a similar

synthetic approach to that described above for {ONO^SiPh3}H₂,

pro-ligand {ONO^SiMe2tBu}H₂was prepared from [3-(methoxy-

methoxy)-2-naphthyl](tert-butyldimethyl)silane (2.75 g, 9.09

mmol), TMEDA (1.40 mL, 9.09 mmol), sec-BuLi (7.3 mL of a

1.3 M solution in hexane/cyclohexane, 9.10 mmol), ZnCl₂(1.24 g,

9.09 mmol), Pd₂(dba)₃(0.083 g, 90.0 μmol), S-Phos (0.147 g,

358 μmol), and 2,6-dibromopyridine (1.08 g, 4.56 mmol). The

reaction mixture was stirred for 40 h at 105 ꢀC, cooled to room

temperature, diluted with water (200 mL), and extracted with

CH₂Cl₂(3 ꢀ 20 mL). The combined organic extracts were dried

over MgSO₄and evaporated to dryness. The crude material

contained ca. 20% of desired product, 2,6-bis[3-[tert-butyl-

(dimethyl)silyl]-2-(methoxymethoxy)-1-naphthyl]pyridine, as

judged by ¹H NMR spectroscopy. This crude material was

passed through a silica column (heptane/EtOAc (15:1), R_f=

0.42) and used further without complete characterization. After

the deprotection step and purification by column chromato-

graphy (silica, heptane/CH₂Cl₂(3:1), R_f= 0.38), pure 3b was

recovered as an off-white powder (0.53 g, 0.89 mmol). ¹H NMR

(500 MHz, CDCl₃, 25 ꢀC): δ 10.39 (s, 2H, OH), 8.11 (m, 3H),

8.00 (s, 2H), 7.85 (m, 4H), 7.50 (m, 2H), 7.39 (m, 2H), 0.95 (s,

18H, tBu), 0.40 (s, 12H, Me). ¹³C{¹H} NMR (125 MHz, CDCl₃,

25 ꢀC): δ 158.4 (C-O), 156.0, 140.1, 138.4, 138.2, 132.4, 129.1,

128.4, 127.4, 124.8, 123.3, 114.5, 72.3, 27.3 (CCH₃), 17.7

(CCH₃), -4.6 (SiMe₂). Anal. Calcd for C₃₇H₄₅NO₂Si₂: C,

75.08; H, 7.66. Found: C, 74.7; H, 7.59.

1

95%). H NMR (500 MHz, toluene-d₈, 70 ꢀC): δ 8.29 (s, 2H),

8.02 (m, 12 H), 7.48 (d, J = 8.2 Hz, 2H), 7.34 (d, J = 8.2 Hz, 2H),

7.32 (d, J = 8.2 Hz, 2H), 7.23 (m, 12H), 7.13 (t, J = 6.8 Hz, 2H),

7.06 (m, 2H), 6.99 (m, 6H), 6.81 (t, J = 8.2 Hz, 1H), 6.05 (t, J =

7.5 Hz, 2H, CH₂Ph), 5.94 (t, J = 7.5 Hz, 4H, CH₂Ph), 5.75 (d,

J = 7.5 Hz, 4H, CH₂Ph), 2.36 (br s, 4H, CH₂Ph). ¹³C{¹H} NMR

(125 MHz, benzene-d₆, 70 ꢀC) (three signals from quaternary

aromatic carbons and one from CH₂of the benzylic groups were

not observed): δ 161.3 (C-O), 151.0, 144.1, 142.3, 137.1, 137.0,

134.6, 133.1, 129.6, 128.3, 128.1, 125.7, 125.2, 123.0, 122.9,

122.0, 121.9, 116.9. Anal. Calcd for C₇₅H₅₇NO₂Si₂Ti: C,

81.28; H, 5.18. Found: C, 80.9; H, 4.97.

{ONO^SiPh3}Zr(CH₂Ph)₂(5a). In a similar manner to that

described above for 4a, complex 5a was prepared from

{ONO^SiPh3}H₂(0.350 g; 0.397 mmol) and Zr(CH₂Ph)₄(0.181 g;

1

0.397 mmol) and isolated as a yellow solid (0.412 g, 90%). H

NMR (500 MHz, C₆D₆, 80 ꢀC): δ 8.29 (s, 2H), 8.05 (m, 12 H),

7.56 (d, ³J = 7.9 Hz, 2H), 7.49 (d, ³J = 8.6 Hz, 2H), 7.40-7.15

3

(m, 24H), 6.99 (t, J = 7.9 Hz, 1H), 6.40 (t, J = 7.3 Hz, 2H,

CH₂Ph), 6.30 (t, ³J = 7.3 Hz, 4H, CH₂Ph), 6.25 (d, ³J = 7.3 Hz,

4H, CH₂Ph), 1.66 (m, 4H, CH₂Ph). ¹³C{¹H} NMR (125 MHz,

benzene-d₆, 80 ꢀC) (several signals overlapped): δ 160.3 (C-O),

157.3, 143.9, 138.8, 136.9, 135.4, 129.5, 128.8, 128.2, 127.2,

125.5, 123.8, 123.7, 122.7, 121.6, 118.7, 65.7 (CH₂Ph). Anal.

Calcd for C₇₅H₅₇NO₂Si₂Zr: C, 78.22; H, 4.99. Found: C, 78.0;

H, 4.59.

{ONO^SiPh3}Hf(CH₂Ph)₂(6a). Complex 6a was prepared in a

similar manner to that described above for 4a, starting from

{ONO^SiPh3}H₂(0.350 g, 0.398 mmol) and Hf(CH₂Ph)₄(0.216 g,

0.398 mmol). 6a was recovered as a bright yellow crystalline

solid (0.424 g, 86%). Crystals suitable for X-ray diffraction

1

analysis were obtained from this batch. H NMR (500 MHz,

C₆D₆, 80 ꢀC): δ 8.43 (s, 2H), 8.11 (m, 12 H), 7.58 (d, ³J = 8.4 Hz,

2H), 7.46 (d, ³J = 8.0 Hz, 2H), 7.40-6.95 (m, 24H), 6.83 (t, ³J =

8.0 Hz, 2H), 6.38-6.05 (m, 10H, CH₂Ph), 1.49 (m, 4H, CH₂Ph).

¹³C{¹H} NMR (75 MHz, benzene-d₆, 80 ꢀC) (two signals from

quaternary aromatic carbons and one from CH₂of the benzylic

groups were not observed): δ 160.6 (C-O), 153.7, 144.3, 144.1,

140.0, 138.0, 136.7, 135.0, 133.6, 131.7, 130.2, 128.8, 129.6,

128.1, 128.0, 124.5, 122.8, 121.5, 117.4. Anal. Calcd for

C₇₅H₅₇NO₂Si₂Hf: C, 72.71; H, 4.64. Found: C, 72.4; H, 4.07.

{ONO^SiPh3}Hf(NMe₂)₂(NHMe₂) (7a (NHMe₂)). (A)

A

3

Schlenk flask was charged with {ONO^SiPh3}H₂(0.11 g, 0.12

mmol) and Hf(NMe₂)₄(0.044 g, 0.12 mmol), and benzene

(5 mL) was vacuum transferred in. The reaction mixture was

stirred overnight at room temperature. Yellow crystals of

{ONO^SiPh3}Hf(NMe₂)₂(NHMe₂) suitable for X-ray analysis

were obtained from this solution at room temperature. The

solution was evaporated and dried in vacuo to give 7a as a yellow

microcrystalline material (0.12 g, 0.10 mmol, 84%). (B) Alter-

natively, complex 7a was prepared from {ONO^SiPh3}H₂(0.255 g,

0.290 mmol) and Hf(NMe₂)₄(0.103 g, 0.290 mmol) in Et₂O

One-Pot Synthesis of {OSO^SiPh3}H₂(3c). Using a similar

synthetic approach to that described above for {ONO^SiPh3}H₂,

pro-ligand {OSO^SiPh3}H₂was prepared from [3-(methoxy-

methoxy)-2-naphthyl](triphenyl)silane (3.48 g, 7.79 mmol),

TMEDA (1.18 mL, 7.82 mmol), sec-BuLi (6.3 mL of a 1.3 M

solution in hexane/cyclohexane, 8.18 mmol), ZnCl₂(1.06 g, 7.78

mmol), Pd₂(dba)₃(0.142 g, 155 μmol), S-Phos (0.255 g, 621

μmol), and 2,5-dibromothiophene (0.94 g, 3.89 mmol). The yield

of (3-(methoxymethoxy)-4-{5-[2-(methoxymethoxy)-3-(triph-

5050 Organometallics, Vol. 28, No. 17, 2009

Kirillov et al.

(8 mL) at room temperature and then recrystallized from a

hexane/toluene (1:5) mixture to yield 7a as a yellow microcrys-

talline material (0.295 g, 89%). ¹H NMR (500 MHz, toluene-d₈,

80 ꢀC): δ 8.10 (s, 2H), 7.83 (m, 12 H), 7.68 (br m, 6H), 7.42 (m,

4H), 7.35-6.95 (18H overlapped with solvent signals), 6.87 (br s,

1H), 2.48 (s, 6H, NMe₂). ¹³C{¹H} NMR (75 MHz, toluene-d₈,

80 ꢀC): 165.6 (C-O), 156.5, 144.2, 143.9, 142.9, 136.1, 135.8,

135.1, 129.9, 128.8, 128.4, 128.2, 127.3, 126.4, 123.2, 119.5, 38.2

(NMe₂). Anal. Calcd for C₆₅H₅₅HfN₃O₂Si₂: C, 68.19; H, 4.84.

Found: C, 67.9; H, 4.64.

brown-red microcrystalline powder (0.080 g, 0.073 mmol, 65%).

¹H NMR (500 MHz, toluene-d₈, 25 ꢀC): δ 8.37 (s, 2H), 8.14 (d,

³J = 8.3 Hz, 2H), 8.06 (m, 12H), 7.42 (d, ³J = 7.9 Hz, 2H), 7.33

(m, 2H), 7.28-7.20 (m, 18H), 7.11 (m, 2H), 6.49-6.36 (m, 8H,

CH₂Ph (6H)+thiophene (CHd, 2H)), 6.28-6.22 (m, 4H,

CH₂Ph), 2.51 (s, 2H, CH₂Ph), 2.15 (s, 2H, CH₂Ph). ¹³C{¹H}

NMR (125 MHz, toluene-d₈, 25 ꢀC): δ 165.9 (C-O), 142.4, 138.1,

137.1, 136.9, 136.8, 135.7, 134.9, 133.7, 130.7, 130.4, 129.6, 129.2,

128.9, 128.8, 128.0, 127.9, 125.2, 125.0, 124.4, 124.1, 123.5, 121.9,

118.9, 94.7 (CH₂Ph), 93.7 (CH₂Ph). Anal. Calcd for C₇₄H₅₆O₂S-

Si₂Ti: C, 79.83; H, 5.07. Found: C, 79.4; H, 4.87.

{ONO^SiPh3}Ti(OiPr)₂(8a). Similarly, complex 8a was pre-

pared from {ONO^SiPh3}H₂(0.100 g; 0.11 mmol) and Ti(OiPr)₄

(0.032 g; 0.11 mmol) in toluene (10 mL). The reaction mixture

was evaporated under vacuum, and the residue was recrystal-

lized from hexane to give pale yellow crystals (0.085 g, 0.08

mmol, 72%). ¹H NMR (500 MHz, C₆D₆, 25 ꢀC): δ 8.30 (s, 2H),

8.08 (m, 12H), 7.78 (d, ³J = 8.3 Hz, 2H), 7.49 (d, ³J = 7.9 Hz,

2H), 7.46 (d, ³J = 8.3 Hz, 2H), 7.32 (m, 20H), 7.14 (m, 2H), 6.92

(t, ³J = 7.9 Hz, 1H), 4.24 (m, ³J = 5.8 Hz, 2H, CH(CH₃)₂), 0.51

Crystal Structure Determination of 3a, 3c, 4a, 4b, 5b, 6a, and

7a (NHMe₂). Crystals of 3a, 3c, 4a, 4b, 5b, 6a, and 7a (NHMe₂)

3

suitable for X-ray diffraction analysis were obtained by recrys-

tallization of purified products (see Experimental Section).

Diffraction data were collected at 100 K using a Bruker APEX

CCD diffractometer with graphite-monochromatized Mo KR

˚

radiation (λ = 0.71073 A). A combination of ω and φ scans was

carried out to obtain at least a unique data set. The crystal

structures were solved by direct methods, and remaining atoms

were located from difference Fourier synthesis followed by full-

matrix least-squares refinement based on F²(programs SIR97

and SHELXL-97).⁴⁵Many hydrogen atoms could be found

from the Fourier difference analysis. Carbon- and nitrogen-

bound hydrogen atoms were placed at calculated positions and

forced to ride on the attached atom. The hydrogen atom

contributions were calculated but not refined. All non-hydrogen

atoms were refined with anisotropic displacement parameters.

Crystals of 4a and 6a were found to contain lattice disordered

solvent molecules, which could not be sufficiently modeled in

the refinement cycles. These molecules were removed using the

SQUEEZE procedure⁴⁶implemented in the PLATON pack-

age.⁴⁷The locations of the largest peaks in the final difference

Fourier map calculation as well as the magnitude of the residual

electron densities were of no chemical significance. Crystal data

and details of data collection and structure refinement for the

different compounds are given in the Supporting Information.

Main crystallographic data (excluding structure factors) are

available as Supporting Information, as cif files.

3

(d, J = 5.8 Hz, 12H, CH(CH₃)₂). ¹³C{¹H} NMR (125 MHz,

C₆D₆, 25 ꢀC): δ 165.0 (C-O), 144.6, 136.9, 135.7, 133.9, 129.4,

129.2, 129.1, 128.9, 127.7, 127.6, 127.3, 125.9, 124.4, 123.7,

122.7, 116.3, 80.9 (CH(CH₃)₂), 25.0 (CH(CH₃)₂). Anal. Calcd

for C₆₇H₅₇NO₄Si₂Ti: C, 77.06; H, 5.50. Found: C, 76.7; H, 5.34.

{ONO^SiMe2tBu}Ti(CH₂Ph)₂(4b). Similarly, complex 4b was

prepared from {ONO^SiMe2tBu}H₂(0.080 g, 0.14 mmol) and

Ti(CH₂Ph)₄(0.056 g, 0.14 mmol) and recrystallized from hexane

1

to give brownish-red crystals (0.098 g, 0.12 mmol, 88%). H

NMR (500 MHz, toluene-d₈, 60 ꢀC): δ 8.20 (s, 2H), 7.79 (m, 2H),

3

7.41 (m, 2H), 7.24 (d, J = 7.7 Hz, 2H), 7.18 (m, 4H), 6.83 (t,

³J = 8.1 Hz, 1H), 6.47 (d, ³J = 7.7 Hz, 4H, CH₂Ph), 6.23 (t, ³J =

7.7 Hz, 4H, CH₂Ph), 6.11 (t, ³J = 7.7 Hz, 2H, CH₂Ph), 3.74 (br

s, 4H, CH₂Ph), 1.22 (s, 18H, tBu), 0.95 (br s, 6H, Me). ¹³C{¹H}

NMR (125 MHz, toluene-d₈, 60 ꢀC): δ 161.5 (C-O), 141.2,

137.1, 136.8, 135.5, 133.8, 129.4, 128.7, 127.8, 127.0, 126.5,

125.2, 125.0, 124.9, 124.5, 122.7, 122.5, 27.2 (CCH₃), 17.7

(CCH₃), -3.4 (SiMe₂) (the signal from the methylene unit of

the benzyl group was not observed, due to long relaxation

1

times). H NMR (500 MHz, toluene-d₈, -50 ꢀC) (only reso-

Variable-Temperature ¹H NMR Study. ¹H NMR spectra were

recorded on a Bruker AM-500 spectrometer using the following

parameters: relaxation delay D1, 1.5 s; number of scans, 24.

Simulation of ¹H NMR spectra was carried out using the gNMR

Simulation Package of Budzelaar.⁴⁸First, the chemical shifts

observed for benzylic protons in the slow exchange limit at

-50 ꢀC (for 4b) and at -40 ꢀC (for 5b) were used to set up the

exchange system. The relative populations were fixed at molar

fraction ratios of 1:0.2 for 4b and 1:0.1 for 5b. The natural line

width in the absence of exchange (3.0 Hz) was measured at given

temperatures and confirmed by observation of the same line

width at -60 ꢀC for both species. A linear extrapolation was

used to estimate the chemical shifts of benzylic protons in the

explored temperature range. For the two species in equilibrium,

1 and 2, incorporating nuclei 1-1, 1-2 and 2-1, 2-2, respec-

tively, the exchange matrix was set as follows:

nances for the major species are reported): δ 8.23 (s, 2H), 7.67 (d,

³J = 7.7 Hz, 2H), 7.37 (d, ³J = 8.3 Hz, 2H), 7.23 (m, 5H), 7.13

(m, 2H), 6.55 (d, ³J = 7.5 Hz, 4H, CH₂Ph), 6.38 (t, ³J = 7.5 Hz,

4H, CH₂Ph), 6.23 (t, ³J = 7.5 Hz, 2H, CH₂Ph), 3.98 (d, ²J = 8.1

Hz, 2H, CHHPh), 3.69 (d, ²J = 8.1 Hz, 2H, CHHPh), 1.26 (s,

18H, tBu), 1.16 (s, 6H, Me), 0.70 (3, 6H, Me). Anal. Calcd for

C₅₁H₅₇NO₂Si₂Ti: C, 74.70; H, 7.01. Found: C, 74.3; H, 6.91.

{ONO^SiMe2tBu}Zr(CH₂Ph)₂(5b). Similarly, complex 5b was

prepared from {ONO^SiMe2tBu}H₂(0.342 g, 0.578 mmol) and

Zr(CH₂Ph)₄(0.263 g, 0.578 mmol) and recrystallized from a

hexane/toluene (1:1) mixture to give a bright yellow microcrys-

talline powder (0.300 g, 60%). ¹H NMR (500 MHz, toluene-d₈,

-40 ꢀC) (only resonances for the major species are reported): δ

8.21 (s, 2H), 7.67 (m, 2H), 7.27 (m, 2H), 7.23-7.15 (m, 6H), 6.67

(m, 4H, Ar(1H) + CH₂Ph¹(3H)), 6.55 (m, 3H, CH₂Ph¹(1H) +

CH₂Ph²(2H)), 6.43 (t, ³J = 7.3 Hz, CH₂Ph¹(1H))), 5.76 (t, ³J =

7.4 Hz, CH₂Ph²(1H))), 5.69 (t, ³J = 7.4 Hz, CH₂Ph¹(2H))), 3.76

(s, 2H, CHHPh), 3.39 (s, 2H, CHHPh), 1.25 (s, 18H, tBu), 1.16

(s, 6H, Me), 0.65 (3, 6H, Me). ¹³C{¹H} NMR (125 MHz,

toluene-d₈, -40 ꢀC): δ 159.3 (C-O), 158.1, 140.4, 137.3, 134.6,

133.9, 132.4, 130.3, 129.5, 129.2, 129.1, 128.6, 128.5, 128.0,

127.4, 125.3, 123.2, 122.7, 122.5, 121.6, 119.4, 64.6 (CH₂Ph),

63.9 (CH₂Ph), 27.3 (CCH₃), 17.9 (CCH₃), -1.9 (SiMeMe), -4.1

(SiMeMe). Anal. Calcd for C₅₁H₅₇NO₂Si₂Zr: C, 70.95; H, 6.65.

Found: C, 70.4; H, 6.45.

k⁰

k⁰⁰

1-1

1-2

2-1

2-2

1-2

1-1

2-2

2-1

2-2

1-1

1-2

(45) (a) Sheldrick, G. M. SHELXS-97, Program for the Determination

of Crystal Structures; University of Goettingen: Germany, 1997. (b) Shel-

drick, G. M. SHELXL-97, Program for the Refinement of Crystal Structures;

University of Goettingen: Germany, 1997.

(46) Van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.

(47) Spek, A. L. Acta Crystallogr. 1990, A46, C-34.

{OSO^SiPh3}Ti(CH₂Ph)₂(4c). A Schlenk flask was charged

with {OSO^SiPh3}H₂(0.100 g, 0.11 mmol) and Ti(CH₂Ph)₄(0.050 g,

0.12 mmol), and benzene (5 mL) was vacuum transferred in.

The reaction mixture was stirred overnight at room temperature

and evaporated to dryness. The brownish residue was twice

recrystallized from benzene and dried in vacuo to give 4c as a

(48) Budzelaar, P. H. M. gNMR, NMR Simulation Program, version

5.0.6.0; IvorySoft, 2006.

Article

Organometallics, Vol. 28, No. 17, 2009 5051

where the exchange rate was set k=k⁰=k⁰⁰. For 10 tem-

peratures in the range 50 to 60 ꢀC for 4b and 12 temperatures

in the range 40 to 80 ꢀC for 5b, the exchange rate k was varied

to get the best fit between experimental and simulated data.

The activation parameters for the isomerization process were

obtained from a standard least-squares Eyring analysis

according to the equation

two minima.⁵³Zero-point vibrational energy corrections

(ZPVE) were estimated by a frequency calculation at the same

level of theory, to be considered for the calculation of the total

energy values. Pictures of the optimized structures were gener-

ated using the program MOLEKEL 5.3.0.⁵⁴

Typical Procedure for (Co)polymerization. A 300 mL high-

pressure glass reactor was charged with 80 mL of freshly distilled

toluene under argon flash. Mechanical stirring (Pelton turbine,

1000 rpm) was started. The reactor was then purged with the

appropriate gas (ethylene or propylene), loaded with a solution

of MAO, “DMAO”, or TIBAL at atmospheric pressure, and

then kept at the desired temperature by circulating water in the

double wall. A solution of [Ph₃C][B(C₆F₅)₄] (when used) in 2 mL

of toluene was injected in by syringe, followed by injection of a

solution of the precatalyst in 2 mL of toluene. The gas pressure

in the reactor was maintained immediately and kept constant

with a back regulator throughout the experiment. The ethylene

consumption was monitored via an Aalborg flow meter. After a

given time period, the reactor was depressurized and the reac-

tion was quenched by adding ca. 5 mL of a 10% solution of HCl

in methanol. The polymer was further precipitated by adding

500 mL of methanol, washed, and dried in vacuo overnight at

room temperature.

ꢀ ꢁ

k

ΔE ΔS

RT

k_B

h

ln

¼ -

þ

þ ln

R

T

where k is the first-order rate constant and k_Bis the Boltz-

mann constant. The standard deviations from the least-

squares fit were used to estimate the uncertainties in ΔE^q

and ΔS^q.⁴⁹

Computational Details. DFT calculations were carried out

using the Gaussian 03 package,⁵⁰employing B3LYP⁵¹and

BP86⁵²functionals, and using a standard double-ξ polarized

basis set, namely, the LANL2DZ set, augmented with a single

polarization f function on titanium, zirconium, and hafnium

(1.506, 0.875, and 0.784, respectively). All stationary points were

fully characterized via analytical frequency calculations as

either true minima (all positive eigenvalues) or transition states

(one imaginary eigenvalue). The IRC procedure was used

to confirm the nature of each transition state connecting

When oligomers of propylene were formed, the toluene

solution was washed twice with a water/HCl solution and, then,

with water. An aliquot of the toluene solution (1 mL) was then

analyzed by GLC to probe the presence of light oligomers. The

rest was evaporated and dried under vacuum to afford oily

materials.

(49) (a) Bevington, P. R. Data Reduction and Error Analysis for the

Physical Sciences; McGraw-Hill: New York, 1969. (b) Skoog, D. A.; Leary,

J. J. Principles of Instrumental Analysis, 4th ed.; Saunders College: Fort

Worth, TX, 1992; pp 13-14.

Acknowledgment. This work was financially supported

by Total Petrochemicals (grant to E.K.). We are grateful

to the Rennes theoretical group computational facilities.

We gratefully thank Prof. Richard F. Jordan (The Uni-

versity of Chicago) for HT-GPC analyses. J.F.C. thanks

the Institut Universitaire de France for a Junior IUF

fellowship (2005-2009).

(50) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;

Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;

Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;

Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,

G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;

Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,

H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo,

C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin,

A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Moroku-

ma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.;

Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.;

Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.;

Baboul, A. G.; Clifford, S.; Cioslowski, J.;Stefanov, B. B.; Liu, G.;

Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D.

J.;Keith, T.; Al-Laham, M. A.;Peng, C. Y.; Nanayakkara, A.;

Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M.

W.; Gonzalez, C.;Pople, J. A. Gaussian 03, Revision B.04; Gaussian, Inc.:

Pittsburgh, PA, 2003.

Supporting Information Available: Crystallographic data for

3a, 3c, 4a, 4b, 5b, 6a, and 7a (NHMe₂) as CIF files and a table

3

summarizing crystal and refinement data; NMR spectra of

ligands 3a-3c and complexes 4a-4c, 5a, 5b, 7a, and 8a. This

material is available free of charge via the Internet at http://

pubs.acs.org.

(53) Gonzales, C.; Schlegel, H. B. J. Chem. Phys. 1989, 90, 2154.

(54) Flukiger, P.; Luthi, H. P.; Portmann, S.; Weber, J. MOLEKEL

5.3.0; Swiss Center for Scientific Computing: Manno, Switzerland, 2008;

http://www.cscs.ch.

(51) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (b) Becke, A. D. J.

Chem. Phys. 1993, 98, 5648. (c) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B

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(52) Perdew, J. P. Phys. Rev. B 1986, 33, 8822.

Article Doi

Group 4 post-metallocene complexes incorporating tridentate silyl-substituted bis(naphthoxy)pyridine and bis(naphthoxy)thiophene Ligands: Probing systems for "oscillating" olefin polymerization catalysis

DOI: 10.1021/om900550s

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