Structure-reactivity relationships of amido-pyridine-supported rare-earth-metal alkyl complexes

Article abstract of DOI:10.1021/om701195x

Treatment of rare-earth-metal dialkyl complexes with group 13 cocatalysts is a prominent approach to generate homogeneous catalysts active in olefin polymerization. Reaction of Ln(CH₂SiMe₃) ₃(THF)₂ with monovalent imino-amido-pyridine [2-{(2,6-iPr₂C₆H₃)N=CMe}-6-{(2,6-iPr ₂C₆H₃)NHCMe₂}C₅H ₃N] (HL₂) gives donor solvent-free discrete dialkyl compounds [L₂]Ln(CH₂SiMe₃)₃ (Ln = Sc, Y, Lu). In the solid state the scandium derivative is isostructural to the previously reported lutetium complex (Gordon et al.). Activation by borate cocatalysts [Ph₃C][B(C₆F₅)₄] and [PhNMe₂H][B(C₆F₅)₄] produces ion pairs that polymerize ethylene in moderate yields (activity: Sc > Lu). Cationization with N-[tris(pentafluorophenyl)borane]-3H-indole gives inactive species. ¹H/¹³C/¹¹B/₁₉F NMR spectroscopy is applied to examine the interaction of the rare-earth-metal dialkyl complexes with the boron cocatalysts. In contrast to the monoalkyl diamido-pyridine compounds [L₁]Ln(CH₂SiMe ₃)(THF)_x (HL₁ = [2,6-((2,6-iPr ₂C₆H₃)NH-CH₂]C₅H ₃N], the dialkyl imino-amido-pyridine complexes do not polymerize methyl methacrylate.

Full text of DOI:10.1021/om701195x

4310
Organometallics 2008, 27, 4310–4317
Structure-Reactivity Relationships of Amido-Pyridine-Supported
Rare-Earth-Metal Alkyl Complexes
Melanie Zimmermann,† Karl W. To¨rnroos,† Robert M. Waymouth,*,‡ and
Reiner Anwander*,†
Department of Chemistry, UniVersity of Bergen, Alle´gaten 41, 5007 Bergen, Norway, and Chemistry
Department, Stanford UniVersity, Stanford, California 94305
ReceiVed NoVember 28, 2007
Treatment of rare-earth-metal dialkyl complexes with group 13 cocatalysts is a prominent approach to
generate homogeneous catalysts active in olefin polymerization. Reaction of Ln(CH2SiMe3)3(THF)2 with
monovalent imino-amido-pyridine [2-{(2,6-iPr2C6H3)NdCMe}-6-{(2,6-iPr2C6H3)NHCMe2}C5H3N] (HL2)
gives donor solvent-free discrete dialkyl compounds [L2]Ln(CH2SiMe3)2 (Ln ) Sc, Y, Lu). In the solid
state the scandium derivative is isostructural to the previously reported lutetium complex (Gordon et al.).
Activation by borate cocatalysts [Ph3C][B(C6F5)4] and [PhNMe2H][B(C6F5)4] produces ion pairs that
polymerize ethylene in moderate yields (activity: Sc > Lu). Cationization with N-[tris(pentafluorophe-
1
nyl)borane]-3H-indole gives inactive species. H/13C/11B/19F NMR spectroscopy is applied to examine
the interaction of the rare-earth-metal dialkyl complexes with the boron cocatalysts. In contrast to the
monoalkyl diamido-pyridine compounds [L1]Ln(CH2SiMe3)(THF)x (HL1 ) [2,6-{(2,6-iPr2C6H3)NH-
CH2}C5H3N], the dialkyl imino-amido-pyridine complexes do not polymerize methyl methacrylate.
Chart 1. Rare-Earth-Metal Bis(alkyl) Complexes with
N-Type Ancillary Ligands, Active in Ethylene Polymeriza-
tion upon Addition of Activators (cf., Table 2)
Much of the recent interest in organolanthanide chemistry is
linked to the academic and industrial quest for novel types of
olefin polymerization catalysts.1 Improvement of the overall
catalytic performance is by its very nature related to ancillary
ligand design and the generation of highly electron deficient
metal centers (metal cationization). While cyclopentadienyl and
related carbocyclic ligand environments (e.g., indenyl) have
yielded a number of isolable and active catalysts, the rich
coordination chemistry of the lanthanides provides considerable
opportunities for further ligand design and optimization.2
Nitrogen (imines, amides) and oxygen donor ligands (alkoxides)
have proven to be versatile components of polydentate ligands
for lanthanide polymerization catalysts. N-type (amide, imine)
ligands have been successfully employed for the synthesis of
discrete organorare-earth-metal complexes; nevertheless the
number of reported active catalyst systems remains limited.1b
Chart 1 depicts representative N-type (amide, imine) catalyst
precursors for ethylene polymerization (Table 2).3-8 Typically,
these complexes contain at least two alkyl ligands and only
* To whom correspondence should be addressed. Fax: (+47) 5558-9490.
E-mail: reiner.anwander@kj.uib.no.
become active for polymerization upon activation by organo-
boron and/or organoaluminum cocatalysts.
† University of Bergen.
‡ Stanford University.
Due to their successful application as ligands for group 4
chemistry,9 we investigated the coordination chemistry of the
diamido-pyridine ligands of the [NNN]2- type (L1, Chart 2)
for organorare-earth-metal chemistry.10 The influence of ligand
modifications (aryl substituents, donor atoms) and the effect of
(1) For reviews see: (a) Hou, Z.; Wakatsuki, Y. Coord. Chem. ReV. 2002,
231, 1. (b) Gromada, J.; Carpentier, J. F.; Mortreux, A. Coord. Chem. ReV.
2004, 248, 397. (c) Hyeon, J. Y.; Gottfriendsen, J.; Edelmann, F. T. Coord.
Chem. ReV. 2005, 249, 2787. (d) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.;
Okuda, J. Chem. ReV 2006, 106, 2404, and references therein.
(2) For recent reviews see: (a) Piers, W. E.; Emslie, D. J. H. Coord.
Chem. ReV. 2002, 233-234, 131. (b) Gibson, V. C.; Spitzmesser, S. K.
Chem. ReV. 2003, 103, 283.
(3) (a) Bambirra, S.; Bouwkamp, M. W.; Meetsma, A.; Hessen, B. J. Am.
Chem. Soc. 2004, 126, 9182. (b) Bambirra, S.; van Leusen, D.; Meetsma,
A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2003, 522. (c) Bambirra,
S.; Otten, E.; van Leusen, D.; Meetsma, A.; Hessen, B. Z. Anorg. Allg.
Chem. 2006, 632, 1950. (d) Bambirra, S.; Meetsma, A.; Hessen, B.
Organometallics 2006, 25, 3454.
(6) Bambirra, S.; van Leusen, D.; Tazelaar, C. G. J.; Meetsma, A.;
Hessen, B. Organometallics 2007, 26, 1014.
(7) Bambirra, S.; Boot, S. T.; van Leusen, D.; Meetsma, A.; Hessen, B.
Organometallics 2004, 23, 1891.
(8) Kretschmer, W. P.; Meetsma, A.; Hessen, B.; Schmalz, T.; Qayyum,
S.; Kempe, R. Chem.-Eur. J. 2006, 12, 8969.
(9) (a) Gue´rin, F.; McConville, D. H.; Payne, N. C. Organometallics
1996, 15, 5085. (b) Gue´rin, F.; McConville, D. H.; Vittal, J. J. Organo-
metallics 1996, 15, 5586.
(4) Hayes, P. G.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc. 2002,
124, 2132.
(5) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben,
J. H. Chem. Commun. 2001, 637.
(10) Estler, F.; Eickerling, G.; Herdtweck, E.; Anwander, R. Organo-
metallics 2003, 22, 1212.
10.1021/om701195x CCC: $40.75
2008 American Chemical Society
Publication on Web 08/16/2008

Amido-Pyridine-Supported Rare-Earth-Metal Complexes
Organometallics, Vol. 27, No. 17, 2008 4311
Chart 2. Dianionic [NNN]2- and Monoanionic [NNN]-
Ligand Precursors
Scheme 1. Synthesis of [L1]Ln(CH2SiMe3)(THF)x (2) and
[L2]Ln(CH2SiMe3)2 (3) by Alkane Elimination
Figure 1. Molecular structure of 3a (atomic displacement param-
eters set at the 50% level). Hydrogen atoms and solvent are omitted
for clarity. Selected bond distances [Å] and angles [deg]: Sc-N1
2.245(9), Sc-N2 2.103(9), Sc-N3 2.436(9), Sc-C35 2.23(1),
Sc-C39 2.25(1), N2-C2 1.48(2), N3-C21 1.31(2), C2-C3
1.52(2), C2-C4 1.56(2), C1-C2 1.51(2), C20-C21 1.49(2);
N1-Sc-N2 72.3(3), N1-Sc-N3 67.6(3), N2-Sc-N3 134.1(3),
N1-Sc-C35 103.4(3), N1-Sc-C39 145.3(4), C35-Sc-C39
107.6(5),N2-Sc-C35111.5(4),N2-Sc-C39109.4(5),N3-Sc-C35
99.0(4), N3-Sc-C39 92.1(4), C1-C2-N2 108.1(9), C20-C21-N3
116.1(10), C20-C21-C22 119.9(11), Sc-N2-C5 121.0(7),
Sc-N3-C23 124.2(7).
the lanthanide metal size revealed that the catalytic activity is
sensitively balanced by steric and electronic factors.10,11 Monoan-
ionic imino-amido-pyridine ligands (L2, Chart 1) yield late
transition metal catalysts active for ethylene polymerization12
but also enabled the synthesis of discrete conformationally rigid
lanthanide complexes.13,14 The [NNN]- ligand L2, a monoan-
ionic analogue of its dianionic congener L1, retains the
characteristic features of the pyridine ligand backbone and the
(aryl)substitution pattern at the amido/imino functionality,
enabling a direct comparison of steric and electronic properties
of lanthanide complexes derived from sterically similar monoan-
ionic or dianionic ligand environments.
Herein, we describe structure-reactivity relationships of rare-
earth-metal (Ln) alkyl complexes bearing diamido-pyridine (L1)
and imino-amido-pyridine ligands (L2) and their performance
as catalyst precursors for ethylene polymerization, giving special
consideration to the impact of the Ln3+ size and the type of
cocatalyst.
6-{(2,6-iPr2C6H3)NHCMe2}-C5H3N] (HL2) with release of
SiMe4 and THF to form donor solvent-free compounds
[L2]Ln(CH2SiMe3)2 (3) (Scheme 1, procedure described by
Gordon).13 An instantaneous color change of the reaction
mixture to dark red evidenced the coordination of the monoan-
ionic imino-amido ligand to the lanthanide metal center. Upon
removal of the solvent and the volatile reaction byproducts, dark
red powdery complexes 3 were obtained with yields decreasing
with increasing Ln3+ size (Ln ) Sc, 92%; Lu, 52%; Y, 32%).
The IR spectra of complexes 3 show a strong absorption at
1582 cm-1 attributed to the stretching vibration of a metal-
coordinated imino group (HL2: 1644 cm-1). Similar shifts were
observed in imino-amido pyridine complexes [L2]Ln(AlMe4)2.14
Due to the insolubility in aliphatic solvents and low solubility
in benzene, NMR spectroscopic investigations of compounds
3 were performed in chlorinated solvents. The 1H NMR spectra
of complexes 3 in CD2Cl2 at ambient temperature show a highly
fluxional behavior even for the smallest metal center, scandium.
Cooling to -50 °C, however, revealed 1H and 13C NMR spectra
in accordance with the solid state structure. Three singlets at
2.35 ppm (3 H), 1.64 ppm (3 H), and 1.10 ppm (3 H) (3a) are
characteristic of the imino and amido functionalities of the
pyridine ligand backbone (3c: 2.36, 1.71, and 1.33 ppm). The
presence of four multiplets for the methine groups (ArCHMe2)
indicates a large rotational barrier for the aryl groups around
the N-Cipso bond at low temperature. As reported by Gordon13
Results and Discussion
Synthesis and Characterization of [L1]Ln(CH2SiMe3)-
(THF)x and [L2]Ln(CH2SiMe3)2. Mono(alkyl)diamidopyridine
complexes [L1]Ln(CH2SiMe3)(THF)x (Ln ) Sc, x ) 1 (2a);
Lu, x ) 2 (2b)) were prepared according to an alkane
elimination reaction from H2L1 and Ln(CH2SiMe3)3(THF)2 in
hexane as described previously (Scheme 1).10 The trialkyl
Ln(CH2SiMe3)3(THF)2 (Ln ) Sc (1a), Lu (1b), and Y (1c))
reacts similarly with light yellow [2-{(2,6-iPr2C6H3)NdCMe}-
1
for the lutetium derivative, the H NMR spectrum of yttrium
(11) Zimmermann, M.; Estler, F.; Herdtweck, E.; To¨rnroos, K. W.;
Anwander, R. Organometallics 2007, 26, 6029.
(12) Britovsek, G. J. P.; Gibson, V. C.; Mastroianni, S.; Oakes, D. C. H.;
Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. Eur. J. Inorg.
Chem. 2001, 431.
(13) Cameron, T. M.; Gordon, J. C.; Michalczyk, R.; Scott, B. L. Chem.
Commun. 2003, 2282.
(14) Zimmermann, M.; To¨rnroos, K. W.; Anwander, R. Angew. Chem.,
Int. Ed. 2007, 46, 3126; Angew. Chem. 2007, 119, 3187.
complex 3c shows four distinct resonances for the R-CH2 of
the neosilylalkyl ligands. Surprisingly, the scandium complex
3a revealed only two R-CH2 resonances at low temperature.
However, an X-ray structure analysis of the latter Sc compound
3a (dark red single crystals were obtained from a saturated
benzene solution at -30 °C) proved it to be isostructural to the
previously reported lutetium derivative 3b (Figure 1).13

4312 Organometallics, Vol. 27, No. 17, 2008
Zimmermann et al.
Scheme 2. Cationization of [L2]Lu(CH2SiMe3)2 with B(C6F5)3
(the product was characterized by multinuclear NMR
spectroscopy)13
The geometry about the five-coordinate rare-earth-metal
center is best described as distorted square pyramidal. The Sc
atom is located 0.624(6) Å above the least-squares plane defined
by the coordinating atoms N1, N2, N3, and C39, which is
slightly less than in the corresponding lutetium compound 3b
(0.663 Å).13 In accordance with the smaller size of the scandium
cation, all Sc-N bonds and the Sc-C35/C39 bonds are
shortened compared to the lutetium derivative.10,13 In contrast,
the geometry about the scandium metal center in
[L1]Sc(CH2SiMe3)(THF) (2a) was described as distorted trigonal
bipyramidal with the pyridine nitrogen and the THF occupying
the apical positions (N-Sc-O ) 156.01(5)°).10 The N1-Sc-C39
angle as the widest angle in 3a, however, measures only
145.3(5)°. Further, the ligand bite angle in bis(alkyl) 3a is
slightly smaller than the one found in the solid state structure
of 2a (134.1(3)° vs 137.04(6)°). The Sc-N(amido) (2.102(9)
Å (3a); av 2.097 Å (2a)) and the Sc-C(alkyl) bond lengths
(av 2.24(1) Å (3a); 2.248(2) Å (2a)) are comparable, while the
Sc-N(pyridine) distance of 2.245(9) Å in 3a appears slightly
longer than that in 2a (2.219(1) Å).
Gordon et al. proved that the [NNN]- ligand (L2) is suitable
to stabilize electron-deficient cationic lanthanide metal centers
formed upon B(C6F5)3 activation of [L2]Lu(CH2SiMe3)2 (Scheme
2).13
As Gordon et al. had prepared stable cationic Lu derivatives
of the [NNN]- ligand [L2]Lu(CH2SiMe3)2 (Scheme 2), we
13
investigated the polymerization behavior of binary catalyst
mixtures consisting of lanthanide bis(alkyl) complexes [L2]Ln-
(CH2SiMe3)2 and [Ph3C][B(C6F5)4] (A), [PhNMe2H][B(C6F5)4]
(B), or N-[tris(pentafluorophenyl)borane]-3H-indole (C), re-
spectively. Each experiment was performed twice, and
representative results are summarized in Table 1 (runs 1-4).
Under similar polymerization conditions, the highest activities
were observed for the Sc-based initiators (runs 1 and 3), while
the lutetium catalysts exhibited slightly lower activity (runs
2 and 4). A similar impact of the lanthanide cation size on
the catalytic performance has previously been reported for
lanthanide catalysts based on neutral fac-κ3-coordinated
[NNN]0-type donor ligands {(Me3[9]aneN3)Ln(CH2SiMe3)3}
and {[HC(Me2pz)3]Ln(CH2SiMe3)3} (Sc > Y) as well as the
recently reported [(6-amino-6-methyl-1,4-diazepine)Ln-
(CH2SiMe3)3] (Sc > Y).18,19
For further comparison, the ethylene polymerization behavior
of the most active rare-earth-metal catalysts based on amido/
imino ancillary ligands (Chart 1) are listed in Table 2. The
polymerization activities strongly depend on the ancillary ligand,
the size of the rare-earth-metal center (Table 2, entries 1-3 and
8-11), polymerization temperatures (Table 2, entries 6, 7, and
14-16), and the cocatalyst/scavenger applied (Table 2, entries
4, 5, and 8-13).
We also observed a dependence of the polymerization
activities of precatalysts 3 on the nature of the organoboron
cocatalyst. The cocatalyst effect, A vs B, is more pronounced
for initiators 3a, featuring the smaller scandium center (Table
1, runs 1 and 3). Accordingly, catalyst mixtures containing
[PhNMe2H][B(C6F5)4] produced species with higher activity
(Table 1, run 3). The coordinating ability of the side-product
PhNMe2 has proven to influence the catalytic performance in
several cases20 and might as well interact with the active species
formed by reaction of [L2]Ln(CH2SiMe3)2 (3) and [PhNMe2H]-
[B(C6F5)4].
At ambient temperature complexes 3 undergo slow thermal
decomposition. Monitoring the complex degradation by 1H
NMR spectroscopy revealed the protonated ligand precursor HL2
and SiMe4 as the only soluble decomposition products (Sup-
porting Information Figure S1). Additionally the formation of
a white rare-earth-metal-containing insoluble solid was observed.
Pronounced thermal instability was found for the scandium (3a)
(total decomposition after 24 h at 40 °C) and yttrium (3c)
compounds (total decomposition after 4 days at 40 °C), while
the lutetium derivative (3b) appeared to be more stable
(decomposition after several weeks). Solids and solutions of 3
in toluene can be stored at -30 °C under argon for several weeks
with only traces of decomposition. Decreasing thermal stability
with increasing effective size of the metal cation had been found
for complexes 2 (Sc > Lu > Y) and was assumed to reflect the
“fit” of the ligand to the rare-earth-metal cation.10
Mechanistic details of the decomposition pathway, however,
remain elusive. Further investigation of the white rare-earth-
metal-containing solid was hampered by the insolubility in
aliphatic, aromatic, and etheral solvents. Reasonable degradation
pathways might include R-H or γ-H elimination from [Ln-
CH2SiMe3] moieties, as previously proposed for the thermal
decomposition of Ln(CH2SiMe3)3(THF)x.15 Alkyl migration to
the ligand imino carbon atomsearlier found for the donor-
14
induced cleavage of [L2]La(AlMe4)2 and for related salicyl-
aldimine complexes16swas not observed.
Polymerization of Ethylene. The ethylene polymerization
behavior of the mono(alkyl) diamido-pyridine complexes
[L1]Ln(CH2SiMe3)(THF)x (Ln ) Sc, x ) 1 (2a); Lu, x ) 2
(2b)) and the bis(alkyl) imino-amido-pyridine complexes
[L2]Ln(CH2SiMe3)2 (Ln ) Sc (3a), Lu (3b)) was investigated
to assess the effect of the ancillary ligands (L1 vs L2), metal
size, and the cocatalyst on the catalytic performance. In the
absence of a cocatalyst neither mono(alkyl)s 2 nor bis(alkyl)s
3 displayed any activity.17 Interestingly, neutral complexes 2
had previously been found to initiate the polymerization of
methyl methacrylate (MMA), but are inactive toward R-olefins.10
Resconi et al. developed the soluble N-[tris(pentafluorophe-
nyl)borane]-3H-indole (C) as an activator for the polymerization
(17) (a) Fryzuk, M. D.; Giesbrecht, G. R.; Rettig, S. J. Organometallics
1996, 15, 3329. (b) Fryzuk, M. D.; Giesbrecht, G. R.; Rettig, S. J. Can.
J. Chem. 2000, 78, 1003.
(18) Lawrence, S. C.; Ward, B. D.; Dubberley, S. R.; Kozak, C. M.;
Mountford, P. Chem. Commun. 2003, 2880.
(19) Ge, S.; Bambirra, S.; Meetsma, A.; Hessen, B. Chem. Commun.
2006, 3320.
(20) Pe´deutour, J.-N.; Radhakrishnan, K.; Cramail, H.; Deffieux, A.
Macromol. Rapid Commun. 2001, 22, 1095.
(15) (a) Schumann, H.; Mu¨ller, J. J. Organomet. Chem. 1978, 146, C5.
(b) Schumann, H.; Freckmann, D. M. M.; Dechert, S. Z. Anorg. Allg. Chem.
2002, 682, 2422. (c) Rufanov, K. A.; Freckmann, D. M. M.; Kroth, H.-J.;
Schutte, S.; Schumann, H. Z. Naturforsch. B: Chem. Sci. 2005, 60, 533.
(16) (a) Emslie, D. J. H.; Piers, W. E.; Parvez, M.; McDonald, R.
Organometallics 2002, 21, 4226. (b) Emslie, D. J. H.; Piers, W. E.; Parvez,
M. Dalton Trans. 2003, 2615.

Amido-Pyridine-Supported Rare-Earth-Metal Complexes
Organometallics, Vol. 27, No. 17, 2008 4313
Table 1. Catalytic Ethylene Polymerization at 25 °C
d
d
runa
precatalyst
cocatalystb
polymer yield [g]
activity [kg/mol bar h]c
Mn
Mw
Mw/Mn
1
2
3
4
5
6
3a
3b
3a
3b
3a
3b
A
A
B
B
C
C
2.60
1.58
3.43
1.39
25
15
33
13
195 800
213 300
222 700
165 200
627 900
434 800
822 600
325 200
3.21
2.04
3.69
1.97
a General polymerization procedure: 0.01 mmol of precatalyst, 50 mL of toluene, [cat]/[cocat] ) 1:1 (mol/mol), ethylene 150 psi; 1 h, 25 °C.
b Cocatalyst: A ) [Ph3C][B(C6F5)4], B ) [PhNMe2H][B(C6F5)4], C ) N-[tris(pentafluorophenyl)borane]-3H-indole. c Given in kg polymer/(mol Ln atm
h). d Determined by high-temperature gel permeation chromatography using polyethylene standards.
Table 2. Catalytic Ethylene Polymerization with Complexes Depicted in Chart 1
entry
precatalysta
cocatalyst (equiv)b
T [°C]
activity [kg/mol bar h]
Mw (× 103)
Mw/Mn
ref
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
I (Ln ) Sc)
B/TiBAOc (1/20)
30
30
30
50
50
30
80
50
50
50
50
50
50
30
80
100
24
3006
14
1200
300
700
1790
75
145
1343
1280
20
93
1666
470
1866
1051
471
98
690
939
127
139
55
1.6
2.0
2.5
2.0
1.7
4.0
6.0
2.2
1.7
6.6
10.5
2.2
3a
3a
3a
4
4
5
5
6
6
6
6
7
7
8
8
8
I (Ln ) Y)
B/TiBAOc (1/20)
I (Ln ) La)
B/TiBAOc (1/20)
II
II
PMAO-IPd (20)
B(C6F5)3/PMAO-IPd(1.05/3.33)
III (Ln ) Y)
B (1)
B (1)
A (1)
B (1)
A (1)
B (1)
A (1)
B (1)
III (Ln ) Y)
IV (Ln ) Sc)
IV (Ln ) Sc)
IV (Ln ) Y)
IV (Ln ) Y)
V
V
VI
VI
VI
[R2N(CH3)H][B(C6F5)4]/TiBAOc (1/20)
[R2N(CH3)H][B(C6F5)4]/TiBAOc (1/20)
[R2N(CH3)H][B(C6F5)4]/TiBAOc (1/20)
40
1072
808
68
67
16
43.0
3.2
1.4
a Precatalysts depicted in Chart1. b Cocatalyst: A ) [Ph3C][B(C6F5)4], B ) [PhNMe2H][B(C6F5)4]. c TiBAO ) tetraisobutylalumoxane. d PMAO-IP )
AlMe3-free methylalumoxane.
Scheme 3. Reaction of [L2]Lu(CH2SiMe3)2 (3b) with A, B,
and C
flourophenyl)borane]-3H-indole (C) did not yield a catalytically
active species (Table 1, runs 5 and 6). This distinct polymeri-
zation protocol implies a marked influence of the cocatalyst
properties, especially the counterion’s ability to stabilize and
interact with the cationic lanthanide species.
In order to better understand the catalytic activity/inactivity
of the catalyst-activator mixtures, we studied equimolar reac-
tions of [L2]Lu(CH2SiMe3)2 (3b) with the borate activators
[Ph3C][B(C6F5)4] (A), [PhNMe2H][B(C6F5)4] (B), and N-[tris(pen-
tafluorophenyl)borane]-3H-indole (C) in more detail. Treatment
of complex 3b with 1 equiv of A in chlorobenzene-d5 at 25 °C
led to instant formation of a cationic lutetium alkyl species
assignable to {[L2]Lu(CH2SiMe3)}{B(C6F5)4} (4a) as monitored
by 1H, 11B, and 19F NMR spectroscopy (Scheme 3, Figure 2B).
The cation formation was accompanied by three organic side-
products. While one species could clearly by identified as Ph3CH
1
(Ph3CH: δ ) 5.56 ppm), the H NMR spectrum features two
SiMe3 resonances (0.01 and -0.30 ppm) and two methylene
resonances (2.19 and 2.10 ppm) tentatively attributed to
“Ph3CCH2SiMe3” species. Similar organic byproducts have
previously been observed by Mountford et al. when reacting
[Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2] with [Ph3C][B(C6F5)4].23
For comparison, the equimolar reaction of LiCH2SiMe3 and
Ph3CCl was monitored by 1H NMR spectroscopy in chloroben-
zene-d5, revealing the formation of comparable organic products
(Figure 2A).
of ethylene.21 Equimolar mixtures of dimethyl zirconocenes and
N-[tris(pentafluorophenyl)borane]-3H-indole provided signifi-
cantly higher catalytic activities than systems activated by
methylalumoxane (MAO) or B(C6F5)3/AliBu3. N-[Tris(pen-
tafluorophenyl)borane]-3H-indole, derived from the reaction of
indole with B(C6F5)3, contains a highly acidic sp3 carbon
(indicated in Scheme 3), generated by a formal NfC hydrogen
shift.22 This soluble proton source provides a convenient method
for generating cationic alkyl metallocene precatalysts.21 How-
ever, treatment of [L2]Ln(CH2SiMe3)2 (3) with N-[tris(penta-
Despite a detailed investigation of the organic side-products,
the actual nature of the two “Ph3CCH2SiMe3” species as well
as mechanistic details leading to the formation of Ph3CH remain
unknown.23 The analogous reaction of complex 3b with 1 equiv
of A in CD2Cl2 at 25 °C produced a complicated mixture of
(21) Guidotti, S.; Camurati, I.; Focante, F.; Angellini, L.; Moscardi, G.;
Resconi, L.; Laerdini, R.; Nanni, D.; Mercandelli, P.; Sironi, A.; Beringhelli,
T.; Maggioni, D. J. Org. Chem. 2003, 68, 5445.
(22) Bonazza, A.; Camurati, I.; Guidotti, S.; Mascellari, N.; Resconi,
L. Macromol. Chem. Phys. 2004, 205, 319.
(23) Bolton, P. D.; Clot, E.; Adams, N.; Dubberley, S. R.; Cowley, A. R.;
Mountford, P. Organometallics 2006, 25, 2806.

4314 Organometallics, Vol. 27, No. 17, 2008
Zimmermann et al.
Figure 2. 1H NMR spectra (400.13 MHz) of (A) the equimolar reaction of Ph3CCl and LiCH2SiMe3 and (B) 3b/[Ph3C][B(C6F5)4] in
chorobenzene-d5 at 298 K.
1
Figure 3. H NMR spectrum (400.13 MHz) of 3b/N-[tris(pentafluorophenyl)borane]-3H-indole (C) in chlorobenzene-d8 at 298 K (* )
toluene residue).
Ph3CH, “Ph3CCH2SiMe3”, and other silylated (aliphatic and
olefinic) byproducts [RxSiMey]n (Supporting Information; Figure
S2).
3). These signals show a significant upfield shift compared to
the ones found for the separated ion pair [Ind2ZrMe][B-
(indolyl)(C6F5)3] (6.37-7.14 ppm)21 and are in the range of
π-coordinated indenyl moieties. These findings suggest a strong
interaction of the indolyl π-system with the electron-deficient
lutetium metal center. Few previous investigations document
the coordination flexibility of indolyl ligands with respect to
η6fη5(η3, η1) shifts.24 Further evidence of extensive steric
constraint due to interaction with the counterion is given by
the appearance of four multiplets for the methine groups
(ArCHMe2: δ ) 3.65, 3.14, 2.66, and 2.53 ppm). This indicates
a large rotational barrier for the aryl groups around the N-Cipso
bond already at 25 °C, while resolution of these signals in
[L2]Lu(CH2SiMe3)2 (3b) occurred only at low temperatures
(Vide supra). One single signal in the 11B NMR spectrum
corroborates the presence of only one boron-containing species,
while the 19F NMR spectrum shows a complicated pattern of
10 resonances, indicating conformational rigidity on the NMR
1H NMR investigations of the reaction of equimolar amounts
of [L2]Lu(CH2SiMe3)2 (3b) and B in chlorobenzene-d5 revealed
the formation of an ion pair {[L2]Lu(CH2SiMe3)}{B(C6F5)4}
(4b), SiMe4, and PhNMe2 (Figure S3, Supporting Information).
11B and 19F NMR spectra substantiate the presence of only one
anionic species, the chemical shifts being similar to the ones
1
observed for 4a. The H NMR spectrum, however, shows a
highly fluxional behavior of the imino-amido-pyridine ancillary
ligand at ambient temperature (Figure S3).
1H NMR spectroscopic investigation of an equimolar 3b/N-
[tris(pentafluorophenyl)borane]-3H-indole (C) mixture in chlo-
robenzene-d5 at 25 °C showed the formation of a new species,
which we tentatively assigned as {[L2]Lu(CH2SiMe3)}-
{[B(indolyl)(C6F5)3]} (4c, Scheme 3). The complete disappear-
ance of the diagnostic indole H3/H3′ signals at 2.48 ppm and
the formation of SiMe4 indicated the anticipated protonolysis
of one [CH2SiMe3] ligand by N-[tris(pentafluorophenyl)borane]-
(24) (a) Evans, W. J.; Brady, J. C.; Ziller, J. W. Inorg. Chem. 2002, 41,
3340. (b) White, C.; Thompson, S. J.; Maitlis, P. M. J. Chem. Soc., Dalton
Trans. 1977, 1654. (c) Chen, S.; Carperos, V.; Noll, B.; Swope, R. J.;
DuBois, M. R. Organometallics 1995, 14, 1221. (d) Chen, S.; Noll, B. C.;
Peslherbe, L.; DuBois, M. R. Organometallics 1997, 16, 1089.
1
3H-indole. Strikingly, the H NMR spectrum features a set of
relatively broad resonances between 5.63 and 6.43 ppm assign-
able to H3, H4, H5, and H6 of the indolyl counterion (Figure

Amido-Pyridine-Supported Rare-Earth-Metal Complexes
Organometallics, Vol. 27, No. 17, 2008 4315
time scale. Each signal shows coupling with several other nuclei,
suggesting additional intramolecular C-H · · · F “through-space”
coupling.25 Indeed, upon cooling to 258 K the indolyl signals
in the H NMR spectrum of 4c shifted to higher field and the
signal shape indicated coupling with fluorine (Figure 3).
sensitivity of closely related compounds 2 and 3 to steric and
electronic modifications.
1
Conclusions
A series of structurally related mono(alkyl) diamido-pyridine
and bis(alkyl) imino-amido-pyridine lanthanide complexes have
been synthesized, and their initiating performance in the
polymerization of ethylene has been studied. While neutral alkyl
complexes were inactive, cationic compounds bearing the imino-
amido-pyridine ligand polymerized ethylene with moderate
activities. The initiating performance is governed by the
lanthanide metal size (Sc > Lu) and the nature of the cocatalyst.
Routinely used borate cocatalysts [Ph3C][B(C6F5)4] and
[PhNMe2H][B(C6F5)4] yielded polyethylene, while cationization
with N-[tris(pentafluorophenyl)borane]-3H-indole gave inactive
species, most likely due to π-coordination of the [B(indolyl)-
(C6F5)3] anion to the cationic lanthanide metal center. Generally,
the activity/inactivity of the investigated catalysts in ethylene
polymerization is sensitively influenced by the presence of
species strongly coordinating to the electron-deficient cationic
lanthanide metal center. The availability of an initiating alkyl
group is essential to provide catalytic performance, as sup-
ported by the complete inactivity of cationic species derived
from the dianionic diamido-pyridine ligand. In contrast, the
homopolymerization of MMA is only initiated by the neutral
mono(alkyl) diamido-pyridine complexes. Neither the neutral
bis(alkyl) imino-amido-pyridine complexes nor their cationic
variants gave positive polymerization protocols.
Strong interaction with the counterion often results in a
decreased catalytical activity and reduced molar mass of the
polymer.20,25,26 These findings are in agreement with the
observed inactivity of mixtures composed of [L2]Ln(CH2SiMe3)2
and N-[tris(pentafluorophenyl)borane]-3H-indole (C). Strong
coordination of the anion competes with the coordination of
ethylene at the active site and deactivates the “catalyst”.
All of the active catalyst mixtures produced linear polyeth-
ylene with molecular weights (Mw) ranging from 3.3 × 105 to
8.2 × 105. Significantly higher molecular weights were obtained
for the Sc-based catalysts (Table 1, runs 1 and 3), while lower
polydispersities (Mw/Mn ) 1.97-2.04) could be achieved with
the less active lutetium catalysts (Table 1, runs 2 and 4).
Monomodal molecular weight distributions indicate the presence
of a single active species.
In contrast to the bis(alkyl) imino-amido-pyridine precursors
[L2]Ln(CH2SiMe3)2 (3), complexes [L1]Ln(CH2SiMe3)(THF)x
(2) were inactive in the polymerization of ethylene. The
dianionic nature of the diamido pyridine ancillary ligand (L1)
allows for only one further alkyl ligand being removed when
adding the alkyl-abstracting borate/borane compounds. Most
likely, the lack of an initiating alkyl group combined with high
instability of the produced species (NMR experiments showed
immediatedecomposition)preventstheinitiationofpolymerization.
Polymerization Studies with Styrene and Methyl Meth-
acrylate. Catalyst mixtures 3/[Ph3C][B(C6F5)4] were further
investigated in the homopolymerization of styrene as well as
copolymerization of ethylene and styrene. Attempted homopo-
lymerization of styrene was carried out at 25 °C in 12 mL of
toluene (21 µmol cat./21 µmol cocat./10.5 mmol styrene). No
polymeric material could be obtained after 1.5 h. The copo-
lymerization experiments were carried out in a 300 mL stainless
steel reactor with a styrene solution in toluene at 25 °C. None
of the cationic lanthanide complexes under investigation initiated
the copolymerization of ethylene and styrene. Moreover, no
homopolymerization of ethylene was observed even though
these catalyst mixtures had shown catalytic activity in the
absence of styrene. Monitoring the reaction of in situ formed
cationic species 4a with 1 equiv of styrene by 1H and 13C NMR
spectroscopy showed no evidence for an interaction between
the cationic rare-earth-metal center and the olefinic bond. Due
to extensive overlap of the aromatic signals, π-coordination of
styrene to the electron-deficient lanthanide cation cannot be
precluded and might inhibit further monomer coordination and
catalytic activity. (See Supporting Information Figure S4.)
Experimental Section
General Considerations. All operations were performed with
rigorous exclusion of air and water, using standard Schlenk, high-
vacuum, and glovebox techniques (MBraun MBLab; <1 ppm O2,
<1 ppm H2O). Hexane and toluene were purified by using Grubbs
columns (MBraun SPS, solvent purification system) and stored in
a glovebox. CD2Cl2 was obtained from Aldrich, vacuum transferred
from calcium hydride, and degassed. [PhNMe2H][B(C6F5)4] and
[Ph3C][B(C6F5)4] were purchased from Boulder Scientific Company
and used without further purification. LnCl3(THF)x,27 LiCH2-
SiMe3,28 Ln(CH2SiMe3)3(THF)2,29 2-{(2,6-iPr2C6H3)NdCMe}-6-
{(2,6-iPr2C6H3)NHCMe2}C5H3N] (HL2),30 [L1]Ln(CH2SiMe3)-
(THF)x (2),10 [2-{2,6-iPr2C6H3)NdCMe}-6-{(2,6-iPr2C6H3)NC-
Me2}C5H3N]Lu(CH2SiMe3)2 (3b),13 and N-[tris(pentaflourophe-
nyl)borane]-3H-indole21 were prepared according to literature
procedures. The NMR spectra of air- and moisture-sensitive
compounds were recorded by using J. Young valve NMR tubes at
25 °C on a Varian UI 300 MHz, a Bruker-AVANCE-DMX400 (5
mm BB, 1H: 400.13 MHz; 13C: 100.62 MHz), and a Bruker-
BIOSPIN-AV500 (5 mm BBO, 1H: 500.13 MHz; 13C: 125.77
MHz). 1H and 13C shifts are referenced to internal solvent
resonances and reported in parts per million relative to TMS. 11B
NMR (161 MHz) spectra were referenced to an external standard
of boron trifluoride diethyl etherate (0.0 ppm, C6D6). 19F NMR
spectra (471 MHz) are referenced to external CFCl3. IR spectra
were recorded on a Nicolet Impact 410 FTIR spectrometer as Nujol
mulls sandwiched between CsI plates. Elemental analyses were
performed on an Elementar Vario EL III.
Motivated by the promising catalytic behavior of [L1]Sc-
(CH2SiMe3)(THF) (2a) in the polymerization of methyl meth-
acrylate (MMA)10 the initiating performance of corresponding
neutral complexes [L2]Ln(CH2SiMe3)2 (3) as well as binary
catalyst mixtures 3/A and 3/B has been investigated. However,
under the same polymerization conditions only traces of
polymeric product (PMMA) could be isolated from the reaction
mixtures. Once again, these findings underline the pronounced
(27) Anwander, R. Top. Organomet. Chem. 1999, 2, 1.
(28) Hultzsch, K. C. Ph.D. Thesis, Johannes Gutenberg-Universita¨t
Mainz, 1999.
(29) Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973,
126.
(25) Focante, F.; Camurati, I.; Resconi, L.; Guidotti, S.; Beringhelli,
T.; D’Alfonso, G.; Donghi, D.; Maggioni, D.; Mercandelli, P.; Sironi, A.
Inorg. Chem. 2006, 45, 1683.
(26) Hayes, P. G.; Piers, W. E.; Parvez, M. J. Am. Chem. Soc. 2003,
125, 5622.
(30) Bruce, M.; Gibson, V. C.; Redshaw, C.; Solan, G. A.; White,
A. J. P.; Williams, D. J. Chem. Commun. 1998, 2523.

4316 Organometallics, Vol. 27, No. 17, 2008
Zimmermann et al.
[2-{(2,6-iPr2C6H3)NdCMe}-6-{(2,6-iPr2C6H3)NCMe2}C5H3N]-
Sc(CH2SiMe3)2 (3a). To a stirred solution of Sc(CH2SiMe3)3(THF)2
(517 mg, 1.15 mmol) (1a) in 8 mL of toluene was added a solution
of yellow HL2 (571 mg, 1.15 mmol) in 15 mL of toluene, affording
an immediate red color change. The resulting mixture was stirred
for 3 h and then concentrated to approximately 15 mL. Cooling
the red solution to -30 °C overnight gave red microcrystals of 3a,
which were isolated by filtration, washed with hexane, and dried
under vacuum (758 mg, 1.06 mmol, 92% isolated yield). IR (Nujol):
1582 s (CdN), 1458 vs (Nujol), 1385 vs (Nujol), 1303 s, 1251 m,
1240 w, 1204 w, 1158 m, 1137 w, 1111 w, 1090 w, 1059 w,
1013 w, 1002 w, 976 w, 940 w, 857 m, 826 w, 764 m, 733 s,
-0.15 (s, 9 H, Si-CH3), -0.30 (Si-CH3), -0.44 (s br, 2 H, Lu-
1
3
CH2) ppm. H NMR (500 MHz, CD2Cl2, 25 °C): δ 8.21 (t, J )
8.0 Hz, 1 H, C5H3N-p-proton), 7.96 (d, 3J ) 8.0 Hz, 1 H, C5H3N-
m-proton), 7.89 (d, 3J ) 8.0 Hz, 1 H, C5H3N-m-proton), 7.33-7.08
(m, 6 H, ar), 3.63 (m, 2 H, ar-CH), 2.85 (m, 2 H, ar-CH), 2.41 (s,
3 H, NdCCH3), 1.47 (s, 6 H, NCCH3), 1.27 (d, 3J ) 6.5 Hz, 6 H,
CH3), 1.20 (d, 3J ) 6.5 Hz, 6 H, CH3), 1.17 (d, 3J ) 6.5 Hz, 6 H,
3
CH3), 1.11 (d, J ) 6.5 Hz, 6 H, CH3), -0.02 (s, 9 H, Si-CH3),
-0.32 (s br, 2 H, Lu-CH2) ppm. 13C{1H} NMR (126 MHz, C6D6,
25 °C): δ 179.0, 149.5, 141.7, 141.4, 140.0, 129.9, 129.6, 129.5,
128.9, 128.7, 128.2, 126.5, 125.8, 125.0, 124.6, 123.9, 123.6, 68.9,
54.5, 31.0, 29.6, 28.5, 27.4, 24.9, 23.9, 19.6, 3.5, 0.2, -2.0 ppm.
11B{1H} NMR (161 MHz, C6D5Cl, 25 °C): δ -16.2 (s) ppm. 19F
NMR (471 MHz, C6D5Cl, 25 °C): δ -131.6 (d, o-F), -162.4 (t,
p-F), -166.4 (t, m-F) ppm.
1
676 w, 572 w, 536 w cm-1. H NMR (500 MHz, CD2Cl2, -50
3
3
°C): δ 8.12 (t, J ) 8.0 Hz, 1 H, C5H3N-p-proton), 7.87 (d, J )
7.5 Hz, 1 H, C5H3N-m-proton), 7.81 (d, 3J ) 8.4 Hz, 1 H, C5H3N-
m-proton), 7.28-7.02 (m, 6 H, ar), 4.22 (m, 1 H, ar-CH), 3.12 (m,
1 H, ar-CH), 2.86 (m, 1 H, ar-CH), 2.64 (m, 1 H, ar-CH), 2.35 (s,
3 H, NdCCH3), 1.64 (s, 3 H, NCCH3), 1.30 (d, 3J ) 6.3 Hz, 3 H,
Reaction of LiCH2SiMe3 and Ph3CCl. In a glovebox,
LiCH2SiMe3 (3 mg, 0.03 mmol) and Ph3CCl (8 mg, 0.03 mmol)
were placed in a J. Young valve NMR tube, and 0.5 mL of C6D5Cl
was added. 1H NMR (400 MHz, C6D5Cl, 25 °C): δ 7.44-7.09
(overlapping m, Ph), 5.56 (s, Ph3CH), 2.19 (s, Si-CH2), 2.10 (s,
Si-CH2), 0.01 (Si-CH3), -0.30 (Si-CH3) ppm.
3
CH3), 1.21 (m, 12 H, CH3), 1.10 (s, 3 H, NCCH3), 1.03 (d, J )
6.3 Hz, 3 H, CH3), 1.01 (d, 3J ) 6.3 Hz, 3 H, CH3), 0.90 (d, 3J )
6.3 Hz, 3 H, CH3), 0.04 (s, 2 H, Sc-CH2), -0.51 (s, 9 H, Si-CH3),
-0.77 (s, 9 H, Si-CH3), -1.02 (s, 2 H, Sc-CH2) ppm. 13C{1H}
NMR (125 MHz, CD2Cl2, 25 °C): δ 177.3, 175.3, 150.2, 148.7,
147.8, 143.0, 140.7, 139.7, 129.5, 128.7, 127.5, 126.1, 125.8, 125.2,
123.8, 123.3, 122.3, 68.7, 43.5, 29.4, 28.2, 27.6, 25.2, 24.3, 20.5,
3.4 ppm. Anal. Calcd for C42H68N3Si2Sc: C, 70.44; H, 9.57; N,
5.87. Found: C, 70.83; H, 9.28; N, 5.82.
Synthesis of {[L2]Lu(CH2SiMe3)}+{B(C6F5)4}- (4b) from
[L2]Lu(CH2SiMe3)2 (3b) and [PhNMe2H][B(C6F5)4] (B). In a
glovebox, 3b (15 mg, 0.02 mmol) and B (13 mg, 0.02 mmol) were
placed in a J. Young valve NMR tube, and 0.5 mL of C6D5Cl was
1
3
added. H NMR (400 MHz, C6D5Cl, 25 °C): δ 7.83 (t, J ) 7.5
3
Hz, 1 H, C5H3N-p-proton), 7.66 (d, J ) 7.5 Hz, 1 H, C5H3N-m-
3
[2-{(2,6-iPr2C6H3)NdCMe}-6-{(2,6-iPr2C6H3)NCMe2}C5H3N]-
Y(CH2SiMe3)2 (3c). To a stirred solution of Y(CH2SiMe3)3(THF)2
(287 mg, 0.58 mmol) (1c) in 5 mL of toluene was added a solution
of yellow HL2 (289 mg, 0.58 mmol) in 5 mL of toluene, affording
an immediate red color change. The resulting mixture was stirred
for 4 h and then concentrated to approximately 5 mL. Cooling the
red solution to -30 °C overnight gave red microcrystals of 3c,
which were isolated by filtration, washed with hexanes, and dried
under vacuum (140 mg, 0.18 mmol, 32% isolated yield). IR (Nujol):
1582 s (CdN), 1468 vs (Nujol), 1375 vs (Nujol), 1308 s, 1282 m,
1251 m, 1235 w, 1204 w, 1095 w, 1049 w, 1013 w, 982 w, 935 w,
proton), 7.41 (d, J ) 7.5 Hz, 1 H, C5H3N-m-proton), 7.36-7.12
(m, 11 H, ar, Ph), 2.70 (s br, 6 H, N(CH3)2, 2.66 (m, 4 H, ar-CH),
3
2.24 (s, 3 H, NdCCH3), 1.46 (s, 6 H, NCCH3), 1.41 (d, J ) 6.5
Hz, 6 H, CH3), 1.29 (d, 3J ) 6.5 Hz, 6 H, CH3), 1.23 (d, 3J ) 6.5
Hz, 6 H, CH3), 1.10 (d, 3J ) 6.5 Hz, 6 H, CH3), 0.00 (s, Si(CH3)4),
-0.08 (s, 9 H, Si-CH3), -0.47 (s br, 2 H, Lu-CH2) ppm. 13C{1H}
NMR (126 MHz, C6D5Cl, 25 °C): δ 180.0, 150.0, 148.1, 142.1,
139.8, 138.0, 136.0, 129.9, 125.3, 117.1, 112.7, 72.5, 40.4, 32.1,
30.4, 28.5, 27.5, 24.7, 24.4, 23.2, 19.7, 3.6, 0.2, -1.4, ppm. 11B{1H}
NMR (161 MHz, C6D5Cl, 25 °C): δ -16.3 (s) ppm. 19F NMR
(471 MHz, C6D5Cl, 25 °C): δ -131.4 (d, o-F), -162.4 (t, p-F),
-166.2 (t, m-F) ppm.
857 s, 821 w, 795 m, 769 m, 728 s, 671 w, 567 w, 531 w cm-1
.
3
1H NMR (400 MHz, CD2Cl2, -50 °C): δ 8.12 (t, J ) 7.6 Hz, 1
Synthesis of {[L2]Lu(CH2SiMe3)}+{B(indolyl)(C6F5)3}- (4c)
from [L2]Lu(CH2SiMe3)2 (3b) and N-[tris(pentafluoro-
phenyl)borane]-3H-indole (C). In a glovebox, 3b (13 mg, 0.01
mmol) and C (9 mg, 0.01 mmol) were placed in a J. Young valve
NMR tube, and 0.5 mL of C6D5Cl was added. 1H NMR (400 MHz,
H, C5H3N-p-proton), 7.89 (d, 3J ) 7.6 Hz, 1 H, C5H3N-m-proton),
3
7.81 (d, J ) 7.6 Hz, 1 H, C5H3N-m-proton), 7.31-7.03 (m, 6 H,
ar), 4.27 (m, 1 H, ar-CH), 3.00 (m, 1 H, ar-CH), 2.88 (m, 1 H,
ar-CH), 2.58 (m, 1 H, ar-CH), 2.36 (s, 3 H, NdCCH3), 1.71 (s, 3
H, NCCH3), 1.33 (s, 3 H, NCCH3), 1.23 (s br, 6 H, CH3), 1.18 (s
br, 6 H, CH3), 1.11 (s br, 3 H, CH3), 1.02 (s br, 3 H, CH3), 0.93 (s
3
C6D5Cl, 25 °C): δ 7.80 (d, J ) 7.6 Hz, 1 H, C5H3N-m-proton),
7.71 (s br, 1 H, H2), 7.38-6.97 (m, 9 H, ar, C5H3N-p-proton,
C5H3N-m-proton, H7), 6.50 (s br, 1 H, H4), 6.35 (s br, 1 H, H6),
6.06 (s br, 1 H, H5), 5.73 (s br, 1 H, H3), 3.76 (m, 1 H, ar-CH),
3.07 (m, 1 H, ar-CH), 2.65 (m, 1 H, ar-CH), 2.43 (m, 1 H, ar-CH),
1.61 (s, 3 H, NdCCH3), 1.59 (s, 6 H, NCCH3), 1.26 (m, 6 H, CH3),
1.09 (d, 3J ) 5.4 Hz, 3 H, CH3), 0.99 (m, 12 H, CH3), 0.69 (d, 3J
) 4.7 Hz, 3 H, CH3), 0.01 (s, Si(CH3)4), -0.04 (s br, 2 H, Lu-
CH2), -0.28 (s, 9 H, Si-CH3) ppm. 13C{1H} NMR (126 MHz,
C6D5Cl, 25 °C): δ 181.1, 178.2, 149.7, 148.8, 139.9, 139.2, 137.9,
135.9, 127.0, 125.7, 125.0, 123.9, 122.1, 119.3, 72.4, 69.6, 69.2,
68.2, 32.1, 30.4, 28.5, 27.4, 25.1, 24.8, 23.2, 19.8, 3.6, 3.3, 0.2
ppm. 11B{1H} NMR (161 MHz, C6D5Cl, 25 °C): δ -8.4 (s br)
ppm. 19F NMR (471 MHz, C6D5Cl, 25 °C): δ -126.4 (m, o-F),
-129.4 (m, o-F), -131.6 (m, o-F), -134.4 (m, o-F),-159.1 (m,
p-F), -160.3 (m, p-F), -163.7 (m, m-F), -164.2 (m, m-F), -164.9
(m, m-F), -166.0 (m, m-F) ppm.
2
br, 6 H, CH3), -0.40 (s, 9 H, Si-CH3), -0.58 (d, J ) 9.2 Hz, 1
H, Y-CH2), -0.71 (s, 9 H, Si-CH3), -0.99 (d, 2J ) 11.2 Hz, 1 H,
Y-CH2), -1.47 (d, 2J ) 11.2 Hz, 1 H, Y-CH2), -1.68 (d, 2J ) 9.2
Hz, 1 H, Y-CH2) ppm. 13C{1H} NMR (101 MHz, CD2Cl2, 25 °C):
δ 178.8, 177.0, 150.5, 149.2, 146.8, 140.8, 139.5, 129.5, 128.7,
127.9, 125.7, 125.2, 123.6, 123.4, 122.9, 70.9, 67.8, 36.2, 29.4,
28.8, 28.3, 27.4, 25.2, 24.3, 20.5, 3.8, 1.4, 0.2 ppm. Anal. Calcd
for C42H68N3Si2Y: C, 66.37; H, 9.02; N, 5.53. Found: C, 66.04; H,
9.12, N, 5.09.
Synthesis of {[L2]Lu(CH2SiMe3)}+{B(C6F5)4}- (4a) from
[L2]Lu(CH2SiMe3)2 (3b) and [Ph3C][B(C6F5)4] (A). In a glovebox,
3b (11 mg, 0.01 mmol) and A (11 mg, 0.01 mmol) were placed in
a J. Young valve NMR tube, and 0.5 mL of C6D5Cl or CD2Cl2,
1
respectively, was added. H NMR (500 MHz, C6D5Cl, 25 °C): δ
7.83 (t, 3J ) 6.0 Hz, 1 H, C5H3N-p-proton), 7.63 (d, 3J ) 6.0 Hz,
1 H, C5H3N-m-proton), 7.40 (d, 3J ) 6.0 Hz, 1 H, C5H3N-m-proton),
7.33-6.97 (m, 21 H, ar, Ph), 5.56 (s, Ph3CH), 3.60 (m, 2 H, ar-
CH), 2.63 (m, 2 H, ar-CH), 2.20 (s, 3 H, NdCCH3), 2.19 (s,
Ethylene Polymerization. The Parr reactor was flushed 3-4
times with ethylene. In a nitrogen-filled glovebox an injector was
charged with a solution of the borate activator (0.01 mmol) in 30
mL of toluene. This was injected into the reactor under ethylene
pressure. The solution was heated to 25 °C and overpressurized
with ethylene to a total pressure of 150 psi. The solution was
3
Si-CH2), 2.10 (s, Si-CH2), 1.49 (s, 6 H, NCCH3), 1.30 (d, J )
5.2 Hz, 6 H, CH3), 1.23 (d, 3J ) 5.2 Hz, 6 H, CH3), 1.10 (d, 3J )
5.2 Hz, 6 H, CH3), 1.03 (d, 3J ) 5.2 Hz, 6 H, CH3), 0.01 (Si-CH3),

Amido-Pyridine-Supported Rare-Earth-Metal Complexes
Organometallics, Vol. 27, No. 17, 2008 4317
equilibrated at 25 °C under constant ethylene pressure for at least
20 min. The catalyst (0.01 mmol) was dissolved in 20 mL of
toluene, added into an injector, and injected into the reactor under
ethylene pressure. Immediately prior to catalyst injection the
ethylene line was disconnected and the pressure in the reactor was
reduced by 60 psi to provide the pressure differential and allow
the catalyst solution to flow into the reactor. The ethylene hose
was reconnected immediately after catalyst injection. The reaction
was run for 1 h at constant pressure and temperature; it was then
quenched by injection of methanol (10 mL), and the reactor was slowly
vented and opened. The polymer was precipitated in 400 mL of
acidified methanol (5% HCl), filtered, washed with methanol, and dried
under vacuum at 40 °C to a constant weight. Polymer molecular
weights and molecular weight distributions were determined by the
high-temperature gel permeation chromatography using polyethylene
for GPC calibration. A Varian UI 300 spectrometer was used to
perform 13C NMR measurements. The polymer samples were
prepared by dissolving 100-200 mg of polymer in 3 mL of
o-dichlorobenzene/10 vol % benzene-d6 in a 10 mm NMR tube.
The spectra were measured at 100 °C using acquisition times )
1 s, additional delays ) 5 s, and gated proton decoupling.
Acknowledgment. Financial support from the Bayerische
Forschungsstiftung, the Norwegian Research Council, the
Deutsche Forschungsgemeinschaft (SPP 1166), and the NSF
(CHE-0611563) is gratefully acknowledged. We thank Lutz
H. Gade and Rich Jordan for stimulating discussions.
Supporting Information Available: 1H NMR spectra of the
soluble decomposition products of 3a, 3b/[Ph3C][B(C6F5)4] in
CD2Cl2, 3b/[PhNMe2H][B(C6F5)4] in chlorobenzene-d5, and 3b/
[Ph3C][B(C6F5)4] with 1 equiv of styrene, and a CIF file giving
full crystallographic data for 3a. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM701195X